Energy from Biological Processes: Volume …Library of Congress Catalog Card Number 80-600118 For...

Energy from Biological Processes: VolumeII—Technical and Environmental Analyses

September 1980

NTIS order #PB81-134769

Library of Congress Catalog Card Number 80-600118

For sale by the Superintendent of Documents, U.S. Government Printing OfficeWashington, D.C. 20402 Stock No. 052-003-00782-7

ForewordIn this volume of Energy From Biological Processes, OTA presents the technical

and environmental analyses on which the conclusions in volume I are based. The“Part 1: Biomass Resource Base” includes forestry, agriculture, processing wastes,and various unconventional sources including oil-bearing and aquatic plants. “Part11: Conversion Technologies and End Uses” considers thermochemical conversions,fermentation for ethanol production, anaerobic digestion, use of alcohol fuels,select energy balances, and a brief description of chemicals from biomass. In eachcase, appropriate technical, economic, and environmental details are presented andanalyzed.

JOHN H. GIBBONSDirector

Energy From Biological Processes Advisory Panel

Thomas Ratchford, ChairmanAssociate Executive Director, American Association for the Advancement of Science

Henry ArtCenter for Environmental StudiesWilliams College

Stanley BarberDepartment of AgronomyPurdue University

John BenemannSanitary Engineering LaboratoryUniversity of California, Richmond

Paul F. Bente, Jr.Executive DirectorThe Bio-Energy Council

Calvin BurwellOak Ridge National Laboratory

Robert HodamCalifornia Energy Commission

Kip HewlettGeorgia Pacific Corp.

Ralph KienkerMonsanto Co.

Dean KlecknerPresidentIowa Farm Bureau Federation

Kevin MarkeyFriends of the Earth

Jacques MaroniEnergy Planning ManagerFord Motor Co.

Michael NeushulMarine Science InstituteUniversity of California, Santa Barbara

William SchellerDepartment of Chemical EngineeringUniversity of Nebraska

Kenneth SmithOff ice of Appropriate TechnologyState of California

Wallace TynerDepartment of Agricultural EconomicsPurdue University

Robert HirschEXXON Research and Engineering Co.

- NOTE. The Advisory Panel provided advice and comment throughout the assessment, but the members do not necessarily approve,disapprove, or endorse the report for which OTA assumes full responsibility

Working Group on Photosynthetic Efficiencyand Plant Growth

One BjorkmanCarnegie InstitutionStanford University

G l e n n B u r t o nSouthern RegionU.S. Department of Agriculture

G a r y H e i c h e lNorth Central RegionU.S. Department of AgricultureUniversity of Minnesota

Edgar LemonNortheastern RegionU S. Department of AgricultureCornell University

Contractors and Consultants

The Baham Corp.Charles BergCalifornia Energy CommissionOtto Doering IllDouglas FrederickCharles Hewett1 E AssociatesLarry JahnRobert KellisonNeushul Mariculture, Inc.Participation PublishersPrinceton University, Department of

Aerospace and Mechanical Sciences

Purdue University, Departments ofAgricultural Economics, AgriculturalEngineering, and Agronomy

Santa Clara University, Department ofMechanical Engineering

State of California, Office of AppropriateTechnology

T B Taylor, AssociatesTexas A&M University, Departments of

Agricultural Economics and AgriculturalEngineering

Texas Tech University, Department ofChemical Engineering

R i c h a r d R a d m e rMartin-Marietta Laboratory

University of California at Davis, College ofAgricultural and Environmental Sciences

University of California, Richmond FieldStation

University of Pennsylvania, Department ofChemical and Biochemical Engineering

University of Texas at Austin, Center forEnergy Studies

University of Washington, College ofForest Resources

RonaId Zweig

iv

Energy From Biological Processes Project Staff

Lionel S. Johns, Assistant Director, OTAEnergy, Materials, and International Security Division

Richard E. Rowberg, Energy Program Manager

Thomas E. Bull, Project Director

A. Jenifer Robison, Assistant Project Director

Audrey Buyrn*

Steven Plotkin, Environmental Effects

Richard Thoreson, Economics

Franklin Tugwell, Policy Analysis

Peter Johnson, Ocean Kelp Farms

Mark Gibson, Federal Programs

Administrative Staff

Marian Growchowski Lisa Jacobson

Lillian Quigg Yvonne White

Supplements to Staff

David Sheridan, Editor

Stanley Clark

OTA Publishing Staff

John C. Holmes, Publishing Officer

Kathie S. Boss Debra M. Datcher Joanne Mattingly

*Project director from April 1978 to December 1978

Acknowledgments

OTA thanks the fo l lowing people who took t ime to prov ide in format ion or rev iew par t or a l l o f the s tudy

Don Augenstein, Flow LaboratoriesEdgar E. Bailey, Davy McKee Corp.Richard Bailie, Environmental Energy

Engineering, Inc.Weldon Barton, U.S. Department of

AgricultureCharles Bendersky, Pyres, Inc.Edward Bentz, National Alcohol Fuels

CommissionBeverly Berger, U.S. Department of EnergyBrian Blythe, Davy McKee Corp.Hugh Bollinger, Plant Resources InstituteDiane Bonnert, Soil Conservation ServiceCarroll Bottum, Purdue UniversityRobert Buckman, U.S. Forest ServiceFred Buttel, Cornell UniversityJames Childress, National Alcohol Fuels

CommissionRaymond Costello, Mittlehauser Corp.Gregory D’Allessio, U S Department of

EnergyRay Dideriksen, Soil Conservation ServiceRichard Doctor, Argonne National

LaboratoryJames Dollard, U.S. Department of EnergyWarren Doolittle, U.S. Forest ServiceErnest Dunwoody, Mittlehauser Corp.Ed Edelson, Pacific Northwest LaboratoryEugene Eklund, U.S. Department of EnergyGeorge Emert, University of ArkansasJohn Erickson, U.S. Forest ServiceWilliam Farrell, EXXON Research and

Engineering CoWinston C. Ferguson, Conservation Con-

sultants of New EnglandKenneth Foster, University of ArizonaDouglas Frederick, North Carolina State

UniversityRalph E C. Fredrickson, Raphael Katzen

Associates

Tim Clidden, Dartmouth CollegeIrving Goldstein, North Carolina State

UniversityJohn Goss, University of CaliforniaRoy Gray, Soil Conservation ServiceLoren Habegger, Argonne National

LaboratoryJohn Harkness, Argonne National

LaboratorySanford Harris, U.S. Department of EnergyMarilyn Herman, National Alcohol Fuels

CommissionEdward Hiler, Texas A&M UniversityDexter Hinckley, Flow Resources Corp.Wally Hopp, Pacific Northwest LaboratoryJohn Hornick, U.S. Forest ServiceWilliam Jewell, Cornell (UniversityFred Kant, EXXON Research and Engineer-

ing Co,J L. Keller, Union Oil of CaliforniaDon Klass, Institute of Gas TechnologyJ. A. Klein, Oak Ridge National LaboratoryAl Kozinski, Amoco Oil CoSuk Moon Ko, Mitre Corp.Kit Krickensberger, Mitre Corp.Barbara Levi, Georgia Institute of

TechnologyLes Levine, U.S. Department of EnergyEdward Lipinsky, Battelle Columbus

LaboratoryWilliam Lockeretz, Northeast Solar Energy

CenterDwight Miller, U.S. Department of

AgricultureJohn Milliken, U.S. Environmental Protec-

tion AgencyLarry Newman, Mitre Corp.

Edward Nolan, General Electric CoJohn Nystrom, Arthur D. Little, Inc.Ralph Overend, National Research Council

of CanadaBilly Page, U.S. Forest ServiceR. Max Peterson, U S. Forest ServiceDavid Pimentel, Cornell UniversityL. H. Pincen, U.S. Department of

AgricultureHarry Potter, Purdue UniversityT. B. Reed, Solar Energy Research InstituteMark Rey, National Forest Products

AssociationRobert San Martin, U.S. Department of

EnergyKyosti Sarkanen, University of WashingtonJohn Schaeffer, Schaeffer and Roland, Inc.Rolf Skrinde, Olympic AssociatesThomas Sladek, Colorado School of Mines

Research InstituteFrank Sprow, EXXON Research and

Engineering Co.George Staebler, Weyerhauser Corp.Terry Surles, Argonne National LaboratoryRobert Tracy, U.S. Forest ServiceR Thomas Van Arsdall, U.S. Department

of AgricultureR. I Van Hook, Oak Ridge National

LaboratoryThomas Weil, Amoco ChemicalsDonald Wise, Dynatech R&DRobert Wolf, Congressional Research

ServiceRobert Yeck, U S Department of

AgricultureJohn Zerbe, U S. Department of

Agriculture

vi

Contents

Chapter PagePart 1: Biomass Resource Base

1.2.3.4.5.

Introduction and Summary . . . . . . . . . 5Forestry . . . . . .Agriculture. . . .UnconventionalBiomass Wastes

9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Biomass Production. . . . . . . . . . . . . . . .111. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

91

Part II: Conversion Technologies and End Use

6.7.8.9.

10.11.12.

Introduction and Summary . . . . . . . . . . . . . . . . . . . . . ..................119Thermochemical Conversion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 123Fermentation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .159Anaerobic Digester . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .181Use of Alcohol Fuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....201Energy BaIances for Alcohol Fuels. . . . . . . . . . . . . . . . . . . . . . . . ..........219Chemicals From Biomass. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227

vii

Part I.

Biomass Resource Base

Chapter 1

INTRODUCTION AND SUMMARY

Chapter 1


The biomass resource base potentially in-cludes hundreds of thousands of differentpIant species and various animal wastes. Inprinciple, plants can be cultivated anywherethere is a favorable climate with sufficientwater, sunlight, and nutrients. In practice,there are numerous limitations, and the mostimportant of these appears to be the soil typefor land-based plants and cultivation and har-vesting techniques for aquatic plants.

The largest area of underutilized land that iswelI suited to plant growth is the Nation’s for-estland. Through more intensive forest man-agement— particularly on privately ownedlands–the supply of wood for energy, as wellas for traditional wood products, could be sub-stantially increased. However, haphazardwood harvest could cause severe environmen-tal damage and reduce the available supply ofwood.

The highest quality land suitable for inten-sive cultivation of plants is the Nation’s crop-Iand. The best cropland is dedicated to foodproduct ion, but there is some underutilizedhayland and pastureland as well as land thatcan be converted to cropland. To a certain ex-tent, grains—especially corn — can be grownfor ethanol production and the distillery by-product used as an animal feed to displacesoybean production. More grain can then begrown on the former soybean land. As the etha-nol production level grows, however, the ani-mal feed market for the distillery byproductwill become saturated and grass productionquickly will become a more effective energyoption for the cropland. To a certain extent,environmental damage appears to be practi-cally unavoidable with grain production, butgrass cultivation is more environmentallybenign.

The candidates for bioenergy crops are nu-merous, but crop development directed to-

ward energy production is needed to comparethe options and to establish cultivation re-quirements and yields.

In addition to energy crops, substantialquantities of crop residues can be collectedand used for energy without exceeding crop-Iand erosion standards.

The third major land category is rangeland,which vary from highly productive wetlands todeserts. Cultivation and harvesting techniquesand plant growth are uncertain, and in drierregions the lack of water will Iimit yields unlessthe crops are irrigated. However, irrigationgreatly increases the energy needed for farm-ing and it is uncertain whether it will be social-ly acceptable to use the available water forenergy production.

Aside from natural wetlands, there are otherareas where freshwater plants might be grownand there are vast areas of ocean in whichocean farms might be built. Cultivation andharvesting techniques and crop yields arehighly uncertain.

In addition to crop cultivation and residuesthere is biomass potential from processing andanimal wastes. * Most processing wastes cur-rently are used for energy, animal feed, orchemical production, but much of the remain-der could be used for energy. Moreover, mostof the manure from animals in confined live-stock operations could be used for energy.

These biomass sources and various otheraspects of the resource base are considered inthe following chapters.

*Wastes are defined as byproducts of biomass processing thatare not dispersed over a wide area and therefore need not be col-lected Residues must be collected

5

Chapter 2

FORESTRY

Chapter 2.- FORESTRY

PageIntroduction ● 9Present Forestland. . . . . . . . . . . . . . . . . . . . . . . . 10Present Cutting of Wood. . . . . . . . . . . . . . . . . . . 10

Forest Products Industry RoundwoodHarvesting . . . . . . . . . . . . . . . . . . . . . . . . . 11

household Fuelwood. . . . . . . . . . . . . . . . . . . 13Stand improvements . . . . . . . . . . . . . . . . . . . 13Clearing of Forestland . . . . . . . . . . . . . . . . . . 14Summary of Current Cutting of Wood . . . . . . 14

Present lnventory of Forest Biomass. . . . . . . . . . . 14Noncommercial Forestland . . . . . . . . . . . . . . 14Commercial Forestland. . . . . . . . . . . . . . . . . 15Quantity Suitable for Stand Improvement. . . 15

Present and Potential Growth of Biomass inU.S. Commercial Forestso . . . . . . . . . . . . . . . . . 16

Forest Biomass Harvesting. . . . . . . . . . . . . . . . . . 18Factors Affecting Wood Availability . . . . . . . . . . . 21

Landownership . . . . . . . . . . . . . . . . . . . . . . . . 21Alternate Uses for the Land . . . . . . . . . . . . . . 22Public Opinion . . . . . . . . . . . . . . . . . . . . . . . . 22Alternate Uses for Wood . . . . . . . . . . . . . . . . 22Other Factors and Constraints . . . . . . . . . . . . 23

Net Resource Potential . . . . . . . . . . . . . . . . . . . . 23Enviromental Impacts. . . . . . . . . . . . . . . . . . . . . 25

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . 25Environmental Effects of Conventional

Silviculture . . . . . . . . . . . . . . . . . . . . . . . . . 27Potential Environmental Effects of

Harvesting Wood for Energy . . . . . . . . . . . 32Controlling Negative Impacts . . . . . . . . . . . . 41Potential Environmental Effects–Summary. 45

R&D Needs ● **,.**. . . . . . . . . . ...***,., 46

TABLESPage

l. Logging Residues Estimate—summary . . . . 122. Logging Residue Estimates. . . . . . . . . . . . . . 13

Page3. Fuelwood Harvests in 1976. . . . . . . . . . . . . . 134. Current and Expected Annual Stand

Improvements . . . . . . . . . . . . . . . . . . . . . . . 145. Estimated Above ground Standing Biomass of

Timber in U.S. Commercial Forestland. . . . . 156. Assumptions for Whole-Tree Harvesting

Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . 197 Annual Whole-Tree Chipping System Costs. 198. Assumptions for Cable Yarding Equipment . 209. Cable Logging System Costs. . . . . . . . . . . . . 20

10. Factors Affecting Logging Productivity . . . . 2111 . Potential Environmental Effects of Logging

and Forestry . . . . . . . . . . . . . . . . . . . . . . . . . 2812. Environmental impacts of Harvesting

Forest Residues . . . . . . . . . . . . . . . . . . . . . . 3413, Control Methods . . . . . . . . . . . . . . . . . . . . . 43

FIGURES

Pagel. Forestland as a Percentage of Total Land

Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112. Area of Commercial Timberland by Region

and Commercial Growth Capability as ofJanuary 1,1977. . . . . . . . . . . . . . . . . . . . . . . 12

3. Forest Biomass inventory, Growth, and Use. 174. Supply Curve for Forest Chip Residues for

Northern Wisconsin and Upper Michigan . . 21S. Materials Flow Diagram for Felled Timber

During Late 1970’s . . . . . . . . . . . . . . . . . . . . 246. Environmental Characteristics of Forest

Regions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Chapter 2

FORESTRY

Introduction

The use of wood for fuel is at least as old ascivilization. Worldwide, wood is still a very im-portant source of energy. The U.N. Food andAgricultural Organization estimates that thetotal annual world harvest of wood in 1975 was90 billion ft3 (about 25 Quads) of which nearlyone-half was used directly for fuel. ’ Much ofthe wood that is processed into other productsis available for fuel when the product is dis-carded from its original use, and indeed largebut unknown quantities are used in this man-ner.

Wood has been a very important fuel in theUnited States, having been used for homeheating and cooking, locomotive fuel, the gen-eration of electricity for home, business, andindustrial use, and for the generation of steamfor industry. According to Reynolds and Pier-son, more than half of the wood harvestedfrom U.S. forests for the 300 years of Americanhistory preceding 1940 was used as fuel. z Con-sumption of wood fuel reached its peak in theUnited States in 1880 when 146 million cords(2.3 Quads) were used according to Panshin, etal.3 The same authors report that per capitaconsumption of wood fuel peaked in 1860 at4.5 cords/yr. During the past 100 years, thedirect use of wood for fuel declined in theUnited States to about 30 million cords/yr (0.5Quad/yr). It was used primarily as a fuel by theforest products industries, which used manu-facturing residues, and for home fireplacesand outdoor cooking, which created demandfor charcoal and hardwood roundwood.

There have, however, been periodic revivalsof fuelwood use to replace conventional fuelsin the United States. They have usually oc-curred during times of crises, such as World

1 Yearbook of Forest Products 1%4-1975 (Rome: Food and Agri-culture Organization of the United Nations, 1977)

‘R V Reynolds and A. H. Pierson, “Fuelwood Used In the U.S.16301930, ” USDA Clr. 641, 1942

3A J Panshin, E. S H arrar, J S Bethel, and W. J. Baker, ForestProducts (New York: McGraw-Hill, 1962)

Wars I and 11, when conventional fuels becamescarce. After the crises abated fuelwood usedwindled rapidly, even though the reemerg-ence of the same conditions in the near futuremay have been expected.

During 1917-18, for example, the EasternUnited States suffered a shortage of coal. FueI-wood was used whenever possible to replacecoal, as were sawdust briquettes and othercombustible biomass. Individual towns in NewEngland organized “cutting bees” and “cut acord” clubs for gathering wood fuel to offsetthe shortage of coal. Between 1916 and 1917the price of fuelwood increased by about 20 to30 percent.

The U.S. Forest Service prepared a publica-tion explaining, among other things, how woodcould be used as fuel to conserve coal.4 It wasthought at the time that coal reserves in theUnited States were dangerously low and thatthe war-induced shortage of 1917-18 had mere-ly emphasized the inevitable need to conservethem. This publication advocated a broadGovernment policy for development of a fuel-wood industry. The role that cutting fuelwoodcould play in forest management was consid-ered, and an analysis of the economics of cut-ting and gathering, etc., was given. The reportconcluded that a fuelwood industry could beprofitable and could benefit the forest in otherways as well. The document was publishedMarch 10, 1919, by which time the war hadended, and the Nation’s fuel situation was al-ready beginning to return to prewar condi-tions. There is no evidence that any of the rec-ommendations were folIowed.

Since World War 11, the major emphasis onwood use has been for lumber and paper pulp.The annual harvest of commercial wood (woodappropriate for the forest products industry)grew by 22 percent between 1952 and 1976.During this same period, the net growth of

‘USDA Bulletin 753, Forest Service, Mar 10,1919

9

10 ● VOI. II—Energy From Biological Processes

commercial wood (total growth of commercialtimber less mortality of commercial timber) in-creased by 56 percent. In only one region inthe country, the Pacific Coast, did the inven-tory of live commercial wood on commercialforestlands decline. In the Pacific Coast re-gion, however, the growth, as a percentage ofthe standing inventory, is the lowest in thecountry due to the old age of the timber. Na-tionwide the inventory of commercial timber

Present

Forestland is defined as land that is at least10-percent stocked with forest trees or hasbeen in the recent past and is not permanentlyconverted to other uses. The forestlands aredivided into two categories: commercial andnoncommercial. Commercial forestland is de-fined as forestland that is capable of produc-ing at least 20 ft3/acre-yr (0.3 dry ton/acre-yr) ofcommercial timber in naturally stocked standsand is not withheld from timber production(e.g., parks or wilderness areas). The rest istermed noncommercial.

The forest regions of the United States andthe percentage of the total land area of eachState that is forestland are shown in figure 1.Currently, there are 740 million acres of forest-Iand in the United States, with about half inthe East (i.e., North plus South) and half in theWest. About 490 million acres are classified ascommercial forestland and nearly three-quar-ters of this are in the East. The productivepotential of commercial forestlands is shownin figure 2.

In addition, there are 205 million acres ofnoncommercial forestland, which are classi-fied this way because of their low productivepotential (i. e., less than 20 ft3/acre-yr). Prac-tically all of the noncommercial forestland is

increased by 20 percent from 1952 to 1976.Thus, increased harvests of wood do not neces-sarily imply that the forests are being depleted.

The growth of wood depends not only on theclimate and soil type, but also on the type andage of trees and the way the forest is managed.In this chapter, the potential for fuelwood pro-duction from the Nation’s forests is examined.

Forestland

in the West. Despite the low-productivity clas-sification, however, timber is harvested frommany areas of land in this category.

Most of the forestland in the East is privatelyowned, while about 70 percent of the westernforestland is publicly owned and managed bythe Federal Government or State and localauthorities.

The U.S. Department of Agriculture (USDA)projects that the forestland area will decreaseby 3 percent by the year 2030 (about 0.4 mil-lion acres/yr or a total of 20 million acres). s Inthe 1980’s, a significant portion of the declinewill result from conversion to cropland, par-ticularly in the Southeast. USDA projects thatin the 1990’s, most of the conversion will be toreservoirs, urban areas, highway and airportconstruction, and surface mining sites.

However, about 32 million acres of potentialcropland are now classified as forestland (seech. 3). Consequently, if a strong demand de-velops for cropland, then the decrease in forestarea will be somewhat larger than USDA’s pro-jection.

‘An Assessment of the Forest and Range Land Situation in theUnited States, review draft, USDA Forest Service, 1979.

Present Cutting of Wood

Forest wood is currently being cut for four dustry roundwood, 2) production of householdpurposes: 1) production of forest products in- fuelwood, 3) timber stand improvements, and

Ch. 2—Fores t ry ● 1 1

Figure 1.— Forestland as a Percentage of Total Land Area

SOURCE Forest Service u S Department of Agriculture

4) clearing of timberland for other uses. Eachof these produces wood that can be or is usedfor energy.

Forest Products IndustryRoundwood Harvesting

Currently, the forest products industry is har-vesting 200 million dry ton/yr (3.1 Quads/yr) forlumber, plywood, pulp, round mine timber,etc.). During the processing of this wood, 90million ton/yr of primary and secondary manu-facturing wastes are produced. These wastesare discussed later under “Biomass ProcessingWastes” in chapter 5.

In addition, the process of harvesting thewood generates considerable logging residue.The logging residue consists of the material

left at the logging site after the commercialroundwood is removed. These residues arebranches, small trees, rough and rotten wood,tops of harvested trees, etc.

The statistics on logging residues reportedfor 1970 and 1976 by the Forest Service under-estimate the total quantity of residues gener-ated by harvesting activities. The Forest Serv-ice data only include wood logging residuesfrom growing stock trees. *

Not reported are:

1. bark — most studies of logging residue pre-sent volumes without bark;

2. residues from:● nongrowing stock trees on logged-over

areas,‘Commercial stock trees that are 1 ) at least 5-inch diameter at

breast height (dbh) and 2) not classified as rough or rotten

12 ● Vol. I I-Energy From Biological Processes

Figure 2.—Area of Commercial Timberland byRegion and Commercial Growth Capability

as of January 1, 1977

No. of acres(millions) s

180

170

160

150

140

130

120

110

100

90

80

70

60

50

40

30

20

10

N = NorthS = SouthPC = Pacific Coast. Alaska, HawaiiR M = R o c k y M o u n t a i n a n d G r e a t P l a i n s

From various sources’ 78 and OTA estimates,the ratios of growing stock residues to totalbiomass residues were derived. ’ Using theseratios and the Forest Service data for growingstock residues, the quantity of logging residueswas estimated to be about 84 million dry tons(1.3 Quads) in 1976. The regional breakdown isshown in table 1, and a more detailed break-down is shown in table 2.

Table 1.–Logging Residues Estimatea–Summary(in million dry tons)

Region Softwood Hardwood Total b

North . . . . . . . . . . . . . . . . . 2.9 13.2 “ 16.0South . . . . . . . . . . . . . . . . 17.6 15.2 32.8

2050 50-85 85120 120 + T o t a l

Growth capability(ft3 commercial timber/acre-yr)

SOURCE Data from Forest Statistics, 1977, Forest Service, U S Department o fAgriculture, 1978

trees of growing stock species and qual-ity, but less than 5-inch diameter atbreast height,trees that would be growing stock treesexcept that they are classified as roughor rotten, andtrees of noncommercial species;

3. tops and branches; and4. stumps.

All of these logging residue components, aswell as the residue presented in the aforemen-tioned reports, are potentially usable as fuel. *

*In this report, the stumpwood component IS not considered

Total b . . . . . . . . . . . . . . . 54.5 29.5 84.1

aFrom a Ig76 harvest of 130 mllllon dry tons of softwood and 54 mllllon dry tom Of hardwoodbsurns may not agree due to round off error

SOURCE J S 8ethel, et al,, “Energy From Wood, ” College of Forest Resources, University ofWashington, Seattle, contractor report to OTA, April 1979.

There is some uncertainty as to whether var-ious logging residue studies are in agreementas to what constitutes nongrowing stock log-ging residue. Loggers may avoid cutting non-growing stock trees that hold little or no eco-nomic value. This practice would be commonin selective logging. In many logging residuestudies, it is unclear whether or not such uncuttrees were considered residue. Some of the dif-ferences observed in logging residue factors re-ported by various authors in the same regionmay be due largely to these methodologicaldifferences. There is a danger that if uncutnongrowing stock is counted as a logging resi-due, it might again be counted as part of thebiomass that should be removed by various sil-vicultural stand improvements. Every effortwas made to avoid this type of double count-ing.

‘J O Howard, “Forest Residues– Their Voiume, Vaiue andUse, ” Part 2: Volume of Residues From Logging Forest Industries,98(1 2), 1971

‘R L Weich, “Predicting Logging Residues for the Southeast, ”USDA Forest Service Research Note SE-263, 1978

“J. T Bones, “Residues for Energy in New Engiand,” NorthernLogger and Timer Processor 25(1 2), 1977

‘j S Bethei, et al , “Energy From Wood, ” Coiiege of Forest Re-sources, University of Washington, Seattle, contractor report toOTA, Apni 1979

Ch. 2—Forestry . 1 3

Table 2.–Logging Residue Estimates (thousand dry tons)

From growing stock From nongrowing stock

Tops andHarvest branchesin 1976 Wood Bark Total Wood Bark Total incl. bark Total

SoftwoodsNorth. . . . . . . . . . .South. . . . . . . . . . . .W.Pine . . . . . . . . .Coast . . . . . . . . . . . .

7,4486303116,50043,190

8233,7561,5487,496

393181876

9084,1491,7298,372

15,158

5972,6972,0228.117

64314236949

1,563

6612,9932,2589,066

1,32310,4153,0009,668

24,406

2,892’17,5576,987

27,106

54,5421,535 13,433Total. . . . . . . . . . .HardwoodsN o r t h . . . . . . . . . . . .South. . . . . . . . . . . .W.Pine . . . . . . . . . .Coast . . . . . . . . . . . .

130,169 13.623 14,978

24,54627,974

341,094

53,648

4,2144,984

3345

313381—

36

4,5275,275

3381

10,186

1,4101,637

2255

100123—

27

250

1,5101,760

2282

7,1478,185

11458

15,801

13,18415,220

161,121

29,541Total . . . . . . . . . . . 9,456 730 3,304 3,554

SOURCE J S Bethel, et al, ’’Energy From Wood, “College of Forest Resources, University of Washington, Seattle, contract or reporf to OTA, April 1979

space for the higher quality trees. These cut-ting activities are generally referred to as standimprovements, and include stand conversions*and thinning operations. Wood from these ac-tivities or sources is suitable for fuel.

The data on the amount of current stand im-provement activity are very limited and do notallow a detailed analysis. During the 1968-71period, various practices, such as precommer-cial and commercial thinning, species conver-sion, weed control, and other stand improve-ments were carried out on a total of 1.4 millionacres. This represents only 0.3 percent of thecommercial timberland. Generally these prac-tices are carried out irregularly, or on a when-and where-needed basis. Undoubtedly most ofthe activity is carried out on industry landswhere intensive forest management is most ad-vanced. A recent survey of forest industryfirms that manage their own lands revealed thecurrent level of these practices. ’ These aresummarized in table 4.

In addition, there are timber stand improve-ments (excluding thinnings), species conver-sion, and weed control items, on about 1.7 mil-lion acres of low-quality stands per year. Yieldswould vary tremendously among these prac-

*Stand conversion is the practice of eliminating tree speciescurrently occupying a stand and replacing them with otherspecies.

‘ID S DeBell, A P Brunette, and D C Schweitzer, “Expecta-tions From Intensive Culture on Industrial Forest Lands,” ). For.,January 1977

Household Fuelwood

The harvest of roundwood for use as house-hold fuel was estimated in 1976 to be 657 mil-lion ft3, or approximately 10 million dry tons(0.16 Quad). These figures are similar to theresults reported by EIlis, who found that 600mill ion ft3 of roundwood, excluding bark, wereharvested for fuelwood. ’” Allowing a IO-per-cent increase for bark, this becomes 660 mil-lion ft3. The regional breakdown is shown intable 3. The quantity harvested in more recentyears is considerably larger, however,

Table 3.–Fuelwood Harvests in 1976 (in million dry tons)

Region Softwood Hardwood Total a

North, ., ... . . . . . . 0.05 3.7 3.8South . . . . . . 1.3 4.2 5.7R o c k y M o u n t a i n s 0.43 0.01 0.44Pacific Coast. . . . . . . 0.33 0.11 0.39

Total . . . . . . . . . 2.3 8.2 10.2

asums may not agree due to round off errors

SOURCE J S Bethel et al Energy From Wood, ‘ College of Forest Resources, Umverslty ofWashmgtorr Seattle contractor report toOTA Aprd f979

Stand Improvements

In normal forestry operations, there may beseveral times during the growth of a stand oftrees that malformed, rough, or otherwise un-desirable trees are cut to make more growing

‘OT H EIIIs, “FuelwoOd,” unpublished manuscript, 1978

14 ● Vol. II—Energy From Biological Processes

Table 4.–Current and Expected AnnualStand Improvements

Percent ofPercent of firms expectingIndustry Estimated to maintain or

lands acres increase levelTreatment treated treateda of treatment

Precommercial thinning ., 0.2 135,000 53Timber stand

Improvement, . 1 8 1,212,000 69Commerc ia l thron ing . . . 25 1,684,000 92Species conversion 04 269,000 65Weed control . . ., 0.3 202,000 50

aPercenl 01 lands treated hmes toial acreage owned by industry

S O U R C E O S OeBell A P Brunel[e a n d O C S c h w e i t z e r Expectations From IntensweCulture on Induslnal Forest Lands J For January 1977

tices, but assuming 17 dry ton/acre (as derivedby Bethel for rough, rotten, and salvageabletrees in the South), this amounts to 29 milliondry ton/yr.

Thinnings were also carried out on 1.8 mil-lion acres, but there is little information re-garding the amounts of residue produced.Yields have been reported of 2.2 dry ton/acrein 4-year-old Ioblolly pine thinning, 12 and 17 to28 dry ton/acre in pole timber hardwoods inthe North. ” If a national average of 10 ton/acre is assumed, thinning would provide 18milIion dry ton/yr of residue.

‘‘Si/vicu/ture Biomass Farms (McLean, Va The MITRE Corp ,1977)

‘‘F E Blltoner, W A Hlllstrom, H M Stelnhlll, and R M Gad-mar, USDA Fore$t Service Research Paper NC-1 37, 1976

Combining these two sources results in 47million ton/yr (0.7 Quad/yr) of residues fromstand improvements.

Clearing of Forestland

Clearing of forest land for other uses can pro-vide a temporary, but potentially significant,local supply of wood. The yield per acre har-vested varies widely with the locality. Assum-ing 30 ton/acre cleared, then USDA projectionsfor forestland clearing would provide about0.2 Quad/yr to 2030. If the forestland with ahigh and medium potential for conversion tocropland is all cleared over the next 15 years,then this would provide 1 Quad/yr of wood forthese 15 years. Most of this would occur in theSoutheast (see ch. 3).

Summary of Current Cutting of Wood

The forest products industry currently har-vests about 200 million dry ton/yr (3.1 Quads/yr) of wood for lumber, plywood, paper pulp,and other products. The process generates anadditional 84 million ton/yr (1.3 Quads/yr) oflogging residues. Another 10 million dry tons(0.2 Quad/yr) are harvested for fuelwood, andabout 47 dry ton/yr (0.7 Quad/yr) are cut duringstand improvements. This results in a total har-vest of about 340 million dry ton/yr or the eqiv-a lent of 5.3 Quads/yr. Another 0.2 Quad/yr isobtained from clearing and converting forest-Iands to other uses.

Present Inventory of Forest Biomass

It is not a simple matter to derive the total base, the present inventory of forest biomassforest biomass inventory from the Forest Serv- can only be estimated.ice surveys. As noted earlier, this lack of anadequate” census base stems from the tradi-tional practice of evaluating the wood in a for-

Noncommercial Forestland

est only in terms of what is assumed to be mer- As mentioned above, of the one-quarter bil-chantable, rather than on a whole-tree or lion acres of noncommercial land, 24 millionwhole-biomass basis. Furthermore, the Forest acres (about 10 percent) are so classified be-Service does not survey noncommercial forest- cause they are recreation or wilderness areas,lands (about one-third of the total forest area). or are being studied for these uses. These landsAs a result of this inadequate information are not included in the inventory of standing

Ch. 2—Forestry ● 1 5

timber. Approximately 205 million acres areclassified as noncommercial because they areconsidered incapable of producing as much as20 ft3 of commercial wood per acre-year. Thiscriterion, is an arbitrary one, however, andtimber is, in fact, harvested from many areasof land in this category. For this reason, the lat-ter category of noncommercial forestlands isincluded in the inventory of standing timber.

Assuming that these 205 million acres pro-duce an average of 10 ft3/acre-yr of commer-cial wood, that they are mature stands (80years old or more), and that the abovegroundbiomass is 1.5 times the amount of commercialtimber, the inventory of these noncommerciallands is 3.7 billion dry tons (57 Quads).

In addition, 23 million acres, mostly inAlaska, were classified in 1978 as noncommer-cial because they were considered inaccessi-ble. Assuming a production capability of 35ft3/acre-yr and the same assumptions as above,the inventory from these lands is 1.4 billion drytons (22 Quads).

These two categories result in an inventoryon 1978 noncommercial lands of about 5 bil-lion dry tons (80 Quads).

Commercial Forestland

Approximately 488 million acres of forest-land are classified by the Forest Service ascommercial forestland for purposes of report-ing a national forest survey. It is possible toestimate a fuel inventory from commercial for-estland, using national forest survey data, withmuch more precision than was the case fornoncommercial lands.

Two options were considered for developingestimates of total biomass on commercial for-estland based on the national forest survey.One procedure involved the assumption ofmultipliers that would convert the basic prod-uct inventory data to whole-stem biomass esti-mates. A second method involved the use ofstand tables from the national forest surveyand allometric regression equations for esti-mating biomass for various tree components. 4

“llethel, op clt

For the purposes of this study, an estimateof total whole-stem biomass for the UnitedStates was developed, based on Forest Statis-tics for the United States, 1977.5 Table 5 showsthe result of this analysis for commercial for-estland. The details of these computations andmore extensive tables are given in OTA’stractor report “Energy From Wood. ”16

Table 5.-Estimated Above-ground StandingBiomass of Timber in U.S. Commercial Forestland

(excluding foliage and stumps, in billion dry tonsa)

con-

Region Hardwood Softwood TotalN o r t h . 5.2 1,3 6.5South . . . : : : : : ., 4.6 2,3 6.9R o c k y M o u n t a i n s . , 0.2 2 4 2.6Pacific Coast, ., 06 4 2 4 8Alaska, ., ., 0.08 1,3 1 4

Total ., . . 10.6 11 5 221

asum~ may noI agree due to round off errors

SOURCE J S Bethel, et al Energy From Wood College of Forest Resources Umverslty ofWashmgfon Seaftle contractor reporl to OTA April 1979

Adding commercial and noncommercialland inventories gives 27 billion tons (430Quads), which is estimated to be the inventoryof biomass in U.S. forests, excluding stumps,foliage, and roots and the biomass in parks andwilderness areas, or areas being consideredfor these uses. *

Quantity Suitable forStand Improvement

Of the 27 billion tons of standing biomass,some of the wood is of the type that would beremoved in stand improvements. This wouldinclude brush, rough, rotten, salvageable deadwood, and Iow-quality hardwood stands occu-pying former conifer sites. In Alaska, there areroughly 330 miIIion tons of this type of wood. 7

In the rest of the Pacific Coast region, there are565 million tons, and in the Rocky Mountainregion, 324 million tons. The North and Southhave 822 million and 978 million tons, respec-

1‘Forest Statfstlcs of the U S . J 977, USDA Iorest Service, re-view draft

‘013ethel, Of) clt* For the purpose> of this report, ~turnps, root$, and follage are

exc I uded from who le-~tenl b Iom as~‘‘1 bld

16 ● VOI. Il—Energy From Biological processes

tively.18 The total is 3.1 billion tons (49 Quads) or all of the cuttings that could be used to con-of wood that would be appropriate for remov- vert stands of one kind of trees to a more pro-al in stand improvements on commercial for- ductive type. Consequently, this is a conserva-estlands. This figure does not include foliage tive estimate of the biomass available from

‘“lbd stand improvements.

Present and Potential Growth of Biomass in U.S. Commercial Forests

Current gross annual biomass growth incommercial U.S. forests has been estimatedfrom Forest Service data to be 570 million dryton/yr, of which 120 million ton/yr are mortali-ty, and 450 million ton/yr net growth. * Theusual method of determining the productivityof a particular stand occupying a site is by ref-erence to normal yield tables. These tables aremodels used to predict growth of active nat-ural stands, and are based on stands of “full”or “normal “ stock.

Because of the utilization assumptions builtinto normal yield tables, however, productivitymay consistently be assigned a low, and mis-leading rating. For example, when the actualgrowth in 131 Douglas-fir plots scatteredthroughout western Washington and Oregonwas compared with Forest Service BuIIetin nor-mal yield tables for Douglas fir, it was foundthat the yield tables consistently underesti-mated the actual growth. Actual growth insome age-site combinations was more thandouble the normal yield table value, and theoverall average growth exceeded the yieldtable by nearly 40 percent.20 Furthermore, inparts of the Rocky Mountains where ForestService and industry lands are co-mingled, in-dustry representatives report that measure-ments of actual growth are two to three timesthe productivity assigned by normal yieldtables” Because of the errors associated withestimating tree types, their number, and theirsize from normal yield tables, OTA estimates

‘“H Wahlgren a n d T EIIIs, “Potential Resource AvallabllttyWith Whole Tree Uttllzatlon, ” TAPPI, VOI 61, No 11, 1978

● The 120 million tons of annual mortallty are from growingstock trees only Mortallty from nongrowtng stock trees IS notknown Under Intensive management, much of the mortality losscou Id potentla I Iy be captured for product Ive use

“)Bethel , Or) CltJ ‘ I bld

that the actual current biomass growth oncommercial forestland is one to two times thevalues derived from normal yield tables, or 570million to 1,140 million dry ton/yr (9 to 18Quads/y r). (See figure 3.)

These estimates do not take into accountthe productive potential of the forestland. For-est site productivity is estimated on the basisof the vegetation currently occupying the areaat the time of the survey. But over 20 millionacres of commercial forestland are unstocked,and much more land is stocked with speciesthat are growing more slowly than could beachieved with species better suited to the site.The forest survey indicates that, due to thesefactors, current growth is about half thegrowth that could be achieved with full stock-ing of highly productive tree types (i. e., currentgrowth is estimated by the Forest Service at 38ft3/acre-yr while the land capability is esti-mated by USDA at 74 ft3/acre-yr). OTA there-fore estimates the potential growth to beabout two to four times that derived from nor-mal yield tables, or 1.1 billion to 2.3 billion dryton/yr (18 to 36 Quads/yr) with full stocking ofproductive tree species on commercial forest-Iand. This corresponds to slightly more than 2to 4 ton/acre-yr on the average.

Beyond the potential growth with unfertil-ized timber, studies in the Southeast indicatethat fertilizers and genetic hybrids could in-crease the ‘biomass growth by 30 percent.22

However, not all of the potential growth isphysically accessible or economically attrac-tive as discussed below.


Figure 3.—Forest Biomass Inventory, Growth, and Use (billion dry tons with equivalent values in Quads)

land/

trees4 b i l l i on d ry t ons / —

64 Quads /

/ ’

O 01 billion dry tons

I mortalitybillion dry tons \

0.45-0.90 billion dry tonsCommercial 7.0-14.0 Quads

f o r e s t l a n d

I n d u s t r i a l

w o o d c u t t i n g

/

/

SOURCE Office of Technology Assessment

18 ● VOI. II—Energy From Biological Processes

Forest Biomass Harvesting

Variations on the current harvesting tech-niques (described below) are likely to be com-mon with fuelwood harvests and stand im-provement activities that produce residuessuitable for fuel. Nevertheless development ofnew techniques and equipment designed forfuelwood harvests and stand improvementscould lower the cost.

Intensive forest management might typical-ly consist of the following: The stand would beclearcut, and the slash (or logging residue) re-moved. The stand would then be replantedwith the desired trees. After 5 to 20 years thestand would be thinned so as to provide morespace for the remaining trees. The stand wouldthen continue to be thinned at about 10-yearintervals, by removing diseased, rough, rotten,and otherwise undesirable trees and brush. Invery intensively managed stands, the treesmight also be pruned to avoid the formation oflarge knots in the stem of the tree (e.g., forveneer). These periodic thinnings and (possi-ble) prunings would continue until the stand isagain clearcut and the entire cycle repeated.

For each operation mentioned above (exceptthe replanting), some woodchips suitable forenergy could be made available. The methodchosen for harvesting the fuelwood would de-pend on a number of site-specific factors. Theprimary objective would be to fell and trans-port the selected trees or to transport the slashin the most cost-effective manner, while doinga minimum of damage to the remaining stand.

Currently there are four basic methods oflogging, each of which is designed to accom-modate a number of physical and economicfactors peculiar to the logging site. Once thetree is felled: 1 ) it can be skidded (dragged) to aroadside as a who/e tree, 2) it can be delimbedand the top cut off, and the entire stem or treelength skidded to the roadside, 3) it can be de-Iimbed, topped, and cut (bucked) into longlogs which are skidded, or 4) it can be cut intoshorter logs or short wood which are skidded.The whole-tree skidding brings out the mostbiomass. However, if the limbs cannot be used

they represent a disposal problem. Also thewhole-tree and tree length methods tend to domore damage to the timber being skidded andto the residual stand. If there is thick under-brush, the who/e-tree method may be difficultor impossible. A weighing of the various fac-tors appropriate to the site being logged resultsin the method used. If markets for the limbsdevelop, however, then more who/e-tree skid-ding may be used than is now the case.

Once the wood is at the roadside, it can becut and loaded or loaded directly into trucksfor transport to the mill or conversion site.Alternatively, the wood can be chipped at theroadside with the chips being blown into a vanfor transport.

Two large-scale harvesting systems consid-ered here are whole-tree harvesting and cablelogging. In the whole-tree chip system, thetrees are felled by a vehicle called a feller-buncher, which grabs the tree and uses a hy-draulic shear to cut the tree at its base. Thetree is then lowered to the ground for skidding.This method is most appropriate for relativelyflat land and smaller trees (i.e., less than 20-inch diameter).

In the cable logging method, cables are ex-tended from a central tower and the felledtrees are dragged to a central point, where theyare sorted and skidded to the roadside. Thismethod is used primarily on terrain with steepslopes and large trees. Estimates for the equip-ment and annual operating costs of these twosystems are shown in tables 6 to 9. There areother logging systems, but these two methodsare fairly representative of the range of exist-ing systems.

The major difference between the harvest-ing of various categories of wood (e. g., resi-dues from logging, stand improvements, or pri-mary logging) is the quantity of wood that canbe removed from a site per unit of time, i.e.,the logging productivity. Several factors affectthe logging productivity, and the most impor-tant of these are shown in table 10. The pro-duction of the logging operations discussed


above might range from 15,000 to 75,000 greenton/yr, leading to harvesting costs from about$5 to $30/green ton. In addition, transporta-tion, possible roadbuilding, and stumpage fees(fees paid to the landowner for the right to har-vest the wood) must be included. Transporta-tion ranges from $0.06 to $0.20/ton-mile, andwhere road building is necessary, the costs willbe considerably higher. Stumpage fees forfuelwood have been estimated at $0.40 to$1 .00/green ton in New England, *J but thesewill change with the market.

The costs of whole-tree chipping 33 stands innorthern Wisconsin and the Michigan penin-sula have been modeled by computer simula-tion.24 In each case, the center of the country

was assumed to be the destination for thewood. The supply curve for these stands isshown in figure 4, exclusive of stumpage fees.The cost average varies from $6 to $1 5/greenton ($1 2 to $30/dry ton) in 1978 dollars. Therange of delivered costs included relogging oflogging residues ($16.50 to $20.30/green ton),thinning ($10.00 to $1 3.80/green ton), and inte-grated logging for lumber and residue chipping($9.75 to $12.30/green ton). An equalizing fac-tor in the delivered cost is the stumpage fee.

I K Hewett, school of Forestry, Ya Ie Unlversltv, Private com-munication

14j A Mattson, D P Bradley, and E M Carpenter,“Harvesting Forest Residues for E r-serrgy,” Proceedings of the Sec-ond Annual Fue/s From B/ornas$ S yrnposiurn (Troy, N Y Rensse-laer Polytechnic Institute, June 20-22, 1978)

Table 6.–Assumptions for Whole-TreeHarvesting Equipment

Initial Salvagecost value Life Labora

Equipment (dol lars) (percent) years $/hour

Whole-tree chipper380 hp . . . . . . . . . . . . $115,000600 hp . . . . . . . . . . . 132,000

Feller-buncher . . . . . . 100,000Skidder (each) . . . . . . . 55,000Used skidder . . . . . . . . . 10,000Lowboy trailer. . . . . . . . . 10,000Used crawler . . . . . . . . 30,000Equipment moving

truck . . . . . . . . . . . . . 1,680/yr3/4-ton crew cab pickup . . 8,400/yr1 / 2 .ton pickup . 7,862/yrChain saws (3) . . . . . . . . 3,024/yrOther labor

deck hands (2) . . . . .foreman ... ... . . .supervisor . . . . .

20 5 $4.6220 5 4.6220 5 4.6220 4 4.2010 310 1020 5

7.208.402.81

aSouth, includes payroll benefits

SOURCE J S Bethel et al , Energy From Wood College of Forest Resources Umverslty ofWashington, Seattle, contractor report to OTA April 1979

Where logging, transportation, and other costsare low, stumpage fees will be high and viceversa. The market will determine these fees, aswell as the quantity and types of wood thatcan be economically harvested.

The 1979 delivered cost of fuel chips wasabout $12 to $18/green ton in New England. 25 Adetailed national cost curve, however, wouldrequire a survey of all potential logging sites,

1’Connectl~ ut Valley Chipping, P l y m o u t h , N H , L WHawhensen, president, letter to Conservation Consultants ofNew Eng[dnci, Dec 20, 1979

Table 7.–Annual Whole-Tree Chipping System Costs

Annual costs to pay all expenses and earn 15% aftertax ROI, shown in thousands of dollars (values in columns are shown only when a change occurs).

Annual Fuel, Local taxes MiscellaneousRegion capital cost Maintenance lube, etc. and insurance Labora equipment b Total

System based on 380-hp chipperInitial investment: $375,000

North. ., . . . . $221 $35 $44 $7 $ 8 3 $21 $442S o u t h 221 — — — 62 — 390West ... . . . . . . . 221 — — — 104 — 432

System based on 600-hp chipperInitial investment $447,000

North. . . . . . . . 264 40 50 9 94 21 478South . . . . . . . ., . 264 — — — 70 — 454West ., ... . . . 264 — — — 118 — 502

alncludes foreman and superwsorbplckup trucks chamsaws elc

SOURCE J S Bethel et al Energy From Wood College of Forest Resources Unwersl!y of Washington Seattle contractor report to OTA April 1979

20 . VoI. II-Energy From Biological Processes

Table 8.–Assumptions for Cable Yarding Equipment which is not available. Nevertheless, somefuelwood can be had for as little as $10/green

Initial Salvagecost value Life Labora ton ($20/dry ton) plus stumpage fees.26 In un-

foreman . . ... ...supervisor (1/3 time).

200

20202020101020

84

55463

105

10.29—

7.767.767.06

10,64

47,84(5 men)

14, 114.72

Equipment (dol lars) (percent) years $/hour f a v o r a b l e c i r c u m s t a n c e s , t h e w o o d c o u l d c o s tYarder wi th 50- f t tower $180,000 20 8 $10.29 as much as $30/green ton ($60/dry ton for relog-Yarder with 90-ft tower 228,000Radio and accessories . . . 11,386Whole-tree chipper

380 hp . . . . . . . . . 115,000600 hp . ., ., . . . 132,000

Skidder (each) . . . ., 55,000Hydraulic loader . . . . 207,000Used skidder ... . . . 10,000L o w b o y t r a i l e r , . , . , 10,000Used crawler . , . , . , 30,000Equipment moving

truck ., ., . . . . . . . 1,680/yr3/4-ton crew cab pickup 8,400/Yr

7,862/yr1/2-ton pickup

Chain saws (3) . . . . . 3,024/yrOther labor

yard ing crew. . . .

ging of loggingresidues in the Northwest).27

Thus, fuelwood chips may vary in price fromabout $20 to $60/dry ton which is in substantialagreement with the cost estimates based onharvesting costs.

In each category of wood there will be smallbusinesses or individuals who are willing towork at lower rates, who are figuring onlymarginal costs, and/or who own the land andassign a zero stumpage fee. In other words,there will always be limited supplies of woodbelow the average market price.

‘(’C Hewett, The A val/abi/lty of LVood for a 50 MW Wood F/redPower P/ant In Northern Vermont, report to Vermont State Fn-erg~ Off Ice under grant No 01-6-01659

‘i IK ,P Hewlett, ‘~eorgla Paclf IC Corp , At Ianta, (;a , Prlvat@awest, includes payroll benehts

SOURCE Off Ice of Technology Assessmentcommunlcat ion, 1979

Table 9.-Cable Logging System Costs

Annual requirement to pay all expenses and earn 15% aftertax ROI (thousands of dollars)

Annual Localcapital Fuel, taxes and Miscellaneous

Equipment cost Maintenance lube, etc. insurance Labora equipment Total

50-ft tower/ 380-hp chipperinvestment: $466,000 ., . . . . $200 $43 $44 $ 9 $158 $21 $475

90-ft tower/600-hp chipper$531,000 . . . . . . . . . . . . 228 61 47 11 158 21 526

alnlcudes foreman and SupervisorbplCkup trucks chamsaws e[c

SOURCE Olflce of Technology Assessment

Ch. 2—Fores t ry ● 2 1

Table 10.–Factors Affecting Logging Productivity

Road space.Slope and slope changes-slope steepness and whether logging is uphill

or downhill.Size and shape of landing.Skidding distances–both loaded and return if different, affected by the

tract shape and its relation to the road systemSkid trail preparation.Timber character–

Species–Especially hardwood v. softwood.Volume and number of trees per acre to be removed–The size of trees

and logs IS a very Important consideration.Quality– More defective timber IS likely to result in more breakage, in-

creasing materials handling problemsResidual stand, if any, m terms of number of trees and volume per

acre This IS prescribed by the silvicultural method.Cutting policy–appropriate for the standFelling and logging methods–whole tree, shortwood, tree length, etc.Brush height and density.Condition and number of windfalls,Drainage and stream crossings.Season.Crew size and aggressiveness.Wage plan.

old stumps, and slash per acre.

Figure 4.—Supply Curve for Forest Chip Residuesfor Northern Wisconsin and Upper Michigan

20

15

10

5

1 I I I I I5 10 15 20 25 30

SOURCE:

Cumulat ive vo lume—mi l l ions o f tons

J. A. Mattson, D. P Bradley, and E M. Carpenter, “Harvesting ForestRestdues for Energy, ” Proceedings of the Second Annual 13!omassSympos/um ( T r o y , N . Y . : R e n s s e l a e r P o l y t e c h n i c I n s t i t u t e ) ,

June 20-22, 1978.

Equipment types, functions, and balance–especially the number ofplaces handled per cycle,

Maintenance policy.Environmental regulations–may prescribe certain practices or preclude

certain equipment from areas with sensitive mixes of soils, slopes,and/or drainage thereby reducing production or Increasing costs Inthe West these regulations have caused a shift in the mix of tractor v.cable Iogging as well as shifts within each of these general categories

S O U R C E J S Bethel et al Energy From Wood College of Fores! Resources Un[verslty ofWasmngton Seatlle conlracfor report 10 OTA April 1979

Factors Affecting Wood Availability

The presence of nearby roads, the concen-tration of wood on the logging site, and the ter-rain (steepness of the slope) are the most im-portant physical factors affecting the econom-ics, and thus the availability, of harvestedwood, Nevertheless, landownership, alternateuses for the land, taxation, and some sub-sidiary benefits and constraints also play animportant role in wood availability. Theseother factors are discussed below.

Landownership

One of the more important features distin-guishing the various forest regions in the coun-try is landownership. In New England 2 percentof the commercial forestland is federallyowned, and public ownership accounts for

only 6 percent. In the East as a whole, 14 per-cent of the commercial forestland is publiclyowned, while 7 percent is federally owned.Ownership patterns in the West are reversed,with 68 percent of the commercial forestlandbeing publicly owned (96 percent in Arizona)and 58 percent in Federal ownership.

Although patterns in the West permit log-ging firms to deal with a limited number oflarge landowners, other restrictions may beplaced on the logging operations. One exam-ple is the Federal requirement that loggingresidues be removed from or otherwise dis-posed of on national forests in the West, tominimize the risks of forest fires.

Logging firms in the East must deal with alarger number of landowners, and in the North-

22 . VOI. II-Energy From Biological Processes

east, forestlands are often owned for recrea-tional or investment purposes. It may be dif-ficult to determine who owns the land, to con-tact the owner, or to interest the owner in usingthe land for logging. In the South this is less ofa problem. Large areas of forestland owned byrelatively small landowners are managed bythe forest products industry and are availablefor logging.

Alternate Uses for the Land

The fact that a tract of land is forested anddesignated commercial does not necessarilymean that it can be logged. The owner mayhave esthetic objections to logging, may usethe land for recreational purposes, or, in thecase of an investor, may feel that it would bemore difficult to sell the land after logging. inNew Hampshire and Vermont, for example, arecent study concluded that only 6 percent ofthe owners of commercial forestland consid-ered timber production as a reason for owningforestland, and only 1.3 percent listed it as themost important reason. 28 (This 6 percent owns21 percent of the commercial forestland in thetwo States). Nevertheless, 10 percent of theprivate owners (representing 53 percent of theforestland) intended to harvest their timberwithin 10 years and over one-third of theowners (representing 87 percent of the land) in-tended to harvest “some day. ” About half ofthe landowners (owning 9 percent of the land)indicated that they would not harvest the landbecause of its scenic value or because theirtracts were too small.

Public Opinion

While proper management of a forest canimprove the health and vitality of the trees, im-proper management can have severe environ-mental consequences. (See “EnvironmentalImpacts”. ) In any event, an intensively man-aged forest will look like it is being managed.

IJN p Klng+y and T W Birch, “The Forest-Land Owners of

New Hampshire and Vermont, ” USDA Forest Service ResourceBulletln NE-51, 1977

There will be fewer overmature trees, the treeswill be more uniform in appearance and spac-ing, and the forest floor will have less debrisand “extraneous” vegetation. The managedforest will not look like a natural forest, andthe difference in appearance can be quitelarge.

This change in appearance, together withvarious environmental uncertainties (see “En-vironmental Impacts”), leads to widely varyingopinions about the benefits of forest manage-ment. If the citizenry affected by increasedmanagement cannot effectively participate inthe process of deciding where and how inten-sively the forests will be managed, and if busi-ness and Government officials are not sensi-tive to the concerns of the citizenry, then thepolitical atmosphere surrounding forest man-agement for energy could become polarized.Public opposition could then seriously restrictthe use of forests for energy.

Forest management, however, is not an ab-solute. There are many ways to manage forest-Iands, from wood plantations to the occasion-al gathering of fallen trees and branches. Theability of political leaders to convey this factto the public, and the ability of Government toaid in striking an equitable balance betweenenvironmental and esthetic concerns and theeconomics of wood harvesting, may prove tobe one of the most significant factors affectingan increased availability of wood for energyoutside of the forest products industry.

Alternate Uses for Wood

Much of the wood that will be used for en-ergy in the near future is less suitable for ma-terials (e. g., particle board or paper) than thewood currently used for these products. Ifthere is a strong demand for wood products,however, some of this lower quality wood willbe drawn into the materials market. Similarly,technical advances in wood chemistry maycreate an additional demand for wood to beprocessed into chemicals.

It must be remembered that a strong woodenergy market would provide an incentive to


increase the number of stand improvements.This will result in an increased supply of whatis considered commercial-grade timber. Fur-thermore, some stands that cannot now be har-vested economically for only lumber or pulp-wood will become economically attractive fora combined harvest of lumber, pulpwood, andwood chips for energy.

In the very long term, competition for woodmay develop between the energy and materi-als/chemicals markets. For the next 20 years,however, a wood energy market–properlymanaged—will increase the supply of woodfor other uses over what would occur in itsabsence, and indeed this situation is likely toprevail for at least 50 to 60 years.

Other Factors and Constraints

As noted previously, the Forest Service re-quires that logging residues on national forests

be disposed of to minimize the risks of forestfires. Stumpage fees for logging national for-estlands are therefore lower than for compara-ble private lands in the region, in order tocover the cost of disposing of the residues. Inthe early 1970’s, as a result of a strong demandfor paper, some of these residues were col-lected and chipped for paper pulp. Currently,however, the residues (about 0.2 Quad/yr) aredisposed of onsite by burning and other tech-niques. If a strong energy market existed, muchof this could be chipped and used for energy.

It has been common practice in site prepara-tion to use herbicides to kill unwanted plantsso that preferred trees could regenerate eithernaturally or artificially. Increasingly, however,the use of herbicides for this purpose is beingrestricted and in some cases banned (e. g., 2, 4,5-T). A strong energy market would provide anadditional incentive to harvest the brush andother low-quality wood and thereby minimizethe use of these controversial chemicals.

Net Resource Potential

There is no simple way to assess accuratelythe impacts of the various and sometimes con-tradictory factors affecting the availability ofwood for energy. Many of the important fac-tors, such as public opinion, the way the for-ests are managed, and the presence of roads,will depend on actions taken in the future. As-suming, however, that 40 percent of the growthpotential of the U.S. commercial forestland iseventually accessible, 450 million to 900 mil-lion dry ton/yr (7.3 to 14.6 Quads/yr) could beavailable for harvest.

In terms of energy, the forest products in-dustry currently cuts 5.1 Quads/yr of wood, in-cluding logging residues (1.3 Quads/yr) andstand improvement cutting (0.7 Quad/y r). Ofthis total, 1.7 Quads/yr are converted intoproducts sold by primary or secondary manu-facturers, and 1.2 Quads/yr, supplied by woodwastes, satisfies over 45 percent of the in-dustries direct energy needs. This leaves about2.2 Quads/yr of wood that are currently being

cut but not used (see figure 5), and there is atleast 40 Quads (total) of unmerchantablestanding timber.

Assuming that the demand for traditionalforest products doubles by 2000, then 3.4Quads/yr will be needed for finished woodproducts, and 3.9 to 11.2 Quads/yr could beused for energy, provided increased forestmanagement occurs. If, however, the forestproducts industry becomes energy self-suffi-cient by 2000, it could require as much energyas the lower limit of available wood energy,but three factors will probably alter this simpleprojection. First, the increased demand forwood products is likely to increase the numberof stand improvements. Second, the energy ef-ficiency of the forest products industry willprobably increase as a result of higher energyprices and new processes (such as anthraqui-none catalyzed paper pulping). Third, if theforest products industry requires most of theavailable output of 40 percent of the commer-

24 . Vol. Il—Energy From Biological Processes

cial forestlands to supply its needs, then addi- These estimates are admittedly approxi-tional roads would be built to access more tim- mate, but a more precise estimate would re-berland. Additional wood that is not of high quire a survey of potential logging sites, landenough quality for lumber, veneer, paper pulp, capability, road availability, and the costs ofetc., would therefore become available. In harvesting.light of these factors, it is likely that significantquantities of wood will become available for The results of such a survey could changeenergy uses outside of the forest products inthese estimates, but 5 to 10 Quads/yr is OTA’sdustry, but this industry could be the major best estimate of the energy potential from ex-user isting commercial forestland

Figure 5.—Materials Flow Diagram for Felled TimberDuring Late 1970’s (Quads/yr)

F e l l e d t i m b e r

F o r e s t p r o d u c t si n d u s t r y h a r v e s t

3.1

R e t u r n e d t o s o i lb y b a c t e r i a l

d e c o m p o s i t i o n o rb u r n e d i n f o r e s t

2.0

P u l p w o o d h a r v e s t s

Primary andsecondary

manufacturing 0.7 Paper and pulp

, Residues of primarya n d s e c o n d a r ym a n u f a c t u r i n g

Total left in forest 2.0 Quads/yrTotal used as energy 1.5 Quads/yr

U n u s e d r e s i d u e s 0 . 1 4 Q u a d / y r

T o t a l p r o d u c t s 1 . 7 Q u a d s / y r


Ch. 2—Forestry . 2 5

Environmental Impacts

Introduction

A forest may be perceived as:

●

●

●

●

●

●

●

●

●

a natural ecosystem deserving protection;a source of materials — renewable or oth-erwise;a physical buffer to protect adjacentareas from erosion, flood, pollution, etc.;a source of esthetic beauty;a wiIdlife preserve;a source of recreation — hiking, hunting,etc.;a temporary land use;a place to retreat from civiIization; oran obstacle to another desired land usesuch as mining or agriculture.

This range of perceptions is complicated bythe fact that individuals do not perceive allforests to be alike, and few would attach thesame perspective—or value— to all forests.Thus, the keenest environmentalist may com-fortably accept a managed, single-aged pineforest in the same terms as he accepts a wheat-field, while a lumber company president mayview a preserve of giant Sequoias with as muchreverence as a Sierra Club conservationist.

These perceptual differences make an eval-uation of the environmental effects of a wood-for-energy strategy difficult, because many ofthe effects may be valued by some groups aspositive and by others as negative. In otherwords, although some potential effects ofgrowing and harvesting operations (e.g., ef-fects such as impaired future forest productivi-ty or extensive soil erosion) are clearly nega-tive or (in the case of restoration of landsdamaged by mining) positive, other effects aremore ambiguous. Changes in such forest char-acteristics as wildlife mix, physical appear-ance, accessibility to hikers, and water storagecapabilities may be viewed as detrimental orbeneficial depending on one’s objectives oresthetic sense. For instance, measures that in-crease forest productivity by substituting soft-wood for hardwood production would be con-sidered as strongly beneficial by those whovalue the forest mainly for its product output,

but may be perceived as detrimental by thosewho cherish the same forest in its originalstate. Hence, it is likely that a wood-for-energystrategy that increases the areal extent or in-tensity of forestry management will promote awide range of reactions . . . even if the physicalimpacts are fully predictable and if forecasts ofthese physical changes are believed by all par-ties.

Environmental evaluation is further compli-cated both by difficulties in predicting thephysical impacts and by the strong possibilitythat even those predictions that can be accu-rately made will not be accepted as credibleby all major interest groups.

The problem of credibility stems largelyfrom the history of logging activities in theUnited States and the negative impact it hashad on public perceptions of logging. Theadaptation of the steam engine to loggingaround 1870 began an era (lasting into the 20thcentury) when America’s forest resource wasmined and devastated .29 The dependence oflogging on the railroads and on cumbersomesteam engines— capital-intensive equipmentthat could not easily be moved from site tosite–led to the cutting of vast contiguousareas. There was virtualIy no attention to refor-estation. In fact, it was then thought that mostof this land would be used for agriculture, andthat clearcutting enhanced the value of theland. It also was thought that the timber re-source was essentially unlimited and that itwas unnecessary to worry about regeneration.

Massive cutting followed by repeated firesled to the destruction of tens of millions ofacres of hardwood (in the South and East) andsoftwood (in the Lake States, Rockies, and partof the Northwest) forest and their replacementby far less valuable tree types or by grassland.This massive destruction led to a considerablepublic revulsion towards logging, much ofwhich still survives. It also led to a revulsion

29M Smith, “Appendix L, Maintaining Timber Supply in aSound Environment” In Report of the Presidents Advisory Pane/orI Timber and the .Environment (Washington, D C Forest Serv-ice, U S Department of Agriculture, 1973)

67-968 0 - 80 - 3

26 . Vol. II-Energy From Biological Processes

against clearcutting and even-aged manage-ment within the forestry profession whichlasted for 20 years; 30 although clearcutting (at

least the very limited version used today,which involves very much smaller areas thanwere routinely cut in the past) is now an ac-cepted and even popular practice in the pro-fession, the attitudes formed by attempts atpublic education about forest values in the1930’s and 1940’s linger on. Furthermore, therehave been enough reports of unsound forestmanagement and widely publicized environ-mental fights over such management in the in-tervening decades to create a sizable constitu-ency that is generally very skeptical about log-ging practices. As a result, assessments thatfocus on the potential positive effects of in-creased forest management may be greetedwith skepticism by large segments of the pub-lic.

The prediction of environmental changesthat might occur in American forest areas if de-mand for wood energy grows is extremely diffi-cult. The potential for wood energy identifiedpreviously is based on a “scenario”-a visionof a possible future—that assumes an in-creased collection of wood residues that arenow left to rot in the forest as well as an as-sumed intensification of silvicultural manage-ment on suitable land that would increasegrowth rates and timber quality, increasing thesupply of nonenergy wood products while pro-viding a steady supply of wood fuel. This typeof strategy could lessen harvesting pressureson wilderness areas and other vulnerable for-estlands. It probably would be perceived bymany groups as environmentally beneficial, al-though it would lead to esthetic and ecosys-tem changes on those lands where manage-ment was intensified. Given the present institu-tional arrangements, however, there is no guar-antee that this assumed “scenario” will unfoldas outlined. Instead, a combination of Federal,State, business, and other private interests willrespond to a complex market amid a variety ofinstitutional constraints. In order to predict theenvironmental outcome of such a response,the following factors must be understood:

‘“I bid

1.

2

3

The environmental effects that occurwhen different kinds of silvicultural oper-ations (including different kinds and in-tensities of cuts, regeneration practices,roadbuilding methods, basic managementpractices, etc.) are practiced on differentforest types and land conditions.The kinds and amounts of Iand likely tobe harvested and their physical-environ-mental condition.The types of practices, controls, etc., like-ly to be adopted by those harvesting thisland.

There is an extensive literature describingfactor #1. However, the range of forest ecosys-tems and possible silvicultural practices is fargreater than the range of existing research, andthere are as well substantial gaps in the knowl-edge of some important cause-effect relation-ships such as the effect of whole-tree removaland short rotations on nutrient cycling, or,more generally, the ecosystem response tophysical pollutants such as sediments and pes-ticides.

Identification and characterization of theland base most likely to be affected by in-creased wood demand (#2) are complicated bya lack of good land resource data, the lack ofinformation on the precise nature of the futurewood market, and the complexity of incentivesthat affect the decisionmaking of small wood-land owners.

Predicting the types of practices and envi-ronmental controls likely to be adopted (#3) isdifficult because State and local regulatorycontrols generally do not specify or effectivelyenforce “best management practices. ” Thus,existing regulations cannot be used as a guideto actual practices. Also, although knowledgeabout the present environmental performanceof the forest industry might provide a startingpoint for gaining an understanding of what toexpect in the future (because most wood-for-energy operations are more intensive exten-sions of conventional forestry), it is surprising-ly difficult to produce a clear picture of howwell the forestry industry is performing. Withthe exception of a few isolated State surveysand a detailed survey of erosion parameters


(percentage of bare ground, compaction, etc.)in the Southeast,31

there appears to be a severelack of surveys or credible assessments of ac-tual forestry operations and their environmen-tal impacts. As a result, a critical part of thebasis for an adequate environmental assess-ment is unavailable.

Because of these limitations, this discussiongenerally is limited to a description of poten-tial impacts, although a few of the impactsdescribed are inevitable. The economic andother incentives that influence the behavior ofthose engaging in forestry are examined todetermine how probable some of these im-pacts are. The types of controls and practicesavailable to moderate or eliminate the nega-tive impacts also are described.

As discussed above, wood for energy may beobtained from several sources. With thegrowth of a wood-for-fuel market, the residueof slash from logging may be removed andchipped. Thinning operations may becomemore widespread because the wood obtainedwill have considerable value as fuel. Standconversions— clearing of low-quality trees fol-lowed by controlled regeneration–as well asharvesting of low-quality wood on marginallands may increase, also because of the in-creased value of the fuelwood gained. Newharvesting practices such as whole-tree remov-al may become more common. Waste woodfrom milling and other wood-processing opera-tions will certainly be more fully utilized.Finally, wood “crops” may be grown on largeenergy farms.

Many of these activities are similar to(though usually more intensive than) conven-tional logging. In addition, other activities as-sociated with using wood as a long-term ener-gy supply — including tree planting, pesticideand fertilizer application, etc. — are similar oreven identical to “ordinary” silvicultural activ-ities. This section, therefore, first discusses thegeneral impacts of silviculture and then de-scribes any changes or added effects associ-

“C Dlssmeyer and K Stump, “Predicted Erosion Rates forForest Management Actlvltles and Conditions Sampled In theSoutheast,” USDA Forest Service, April 1978

ated with alternative wood-for-energy systems.In each case, the discussion will attempt todraw a distinction between clearly positive ornegative pollution and land degradation andrestoration impacts and the more ambiguousecosystem and esthetic impacts. Because theenvironmental effects of silviculture are ex-ceedingly varied and complex and because anumber of good reviews are available, the dis-cussion highlights only the major and mostwidespread impacts. It is stressed that few ifany of the environmental relationships de-scribed in the discussion are applicable to allsituations.

Environmental Effects ofConventional Silviculture

The practice of silviculture can have bothpositive and negative effects on the soils,wildlife, water quality, and other componentsof both the forest ecosystem and adjacentlands. Table 11 provides a partial list of thepotential environmental effects of convention-al silviculture. The magnitude of these impactsin any situation, however, depends almost en-tirely on management practices and on thephysical characteristics of the site, i.e., type oftrees and other vegetation, age of the forest,soil quality, rainfall, slope, etc. It is also impor-tant to remember that most of the negative im-pacts generally are short term and last only afew years (or less) over each rotational cycle.

Erosion has always been a concern in silvi-culture, especially in logging operations (andparticularly in road construction). Undisturbedforests generally have extremely small erosionrates — often less than 75 lb of soil per acre peryear32 — and in fact tree planting is often usedto protect erosion-prone land. * Increased ero-sion caused by logging, however, varies fromnegligible (light thinning and favorable condi-

‘zEnvironmenta/ Implications of Trends in Agriculture and $Ilvi-cu/ture, Vo/ume 1 Trend Identification and Evacuation (Washing-ton, D C Environmental ProtectIon Agency, December 1978),E PA-600/3 -77-l 21

*However, from a historical perspective, all land forms gothrough natural erosional cycles that produce much htgher ratesof soil loss These rates are often drwen by natural catastrophicevents Including wildfire and storms

i--

28 . Vol. II—Energy From Biological Processes

Table 11.-Potential Environmental Effects ofLogging and Forestry

Water●

●

●

●

●

●

Air.●

●

●

Land●

●

●

●

●

●

●

●

●

increased flow of sediments into surface waters from logging ero-sion (especially from roads and skid trails)clogging of sfreams from logging residueleaching of nutrients into surface and ground waterspotential improvement of water quality and more even flow from for-estation of depleted or mined landsherbicide-pesticide pollution from runoff and aerial application (froma small percentage of forested acreage)warming of streams from loss of shading when vegetation adjacentto streams is removed

fugitive dust, primarily from roads and skid trailsemissions from harvesting and transport equipmenteffects on atmospheric CO2 concentrations, especially if forestedland is permanently converted to cropland or other (lower biomass)use or vice-versaairpollution from prescribed burning

compaction of soils from roads and heavy equipment (leading to fol-lowing two impacts)surface erosion of forest soils from roads, skid trails, other disturb-ancesloss of some long-term water storage capacity of forest, increasedflooding potential (or increased water availability downstream) untilrevegetation occurschanges in fire hazard, especially from debrispossible loss of forest to alternative use or to regenerative failurepossible reduction in soil quality/nutrient and organic level fromshort rotations and/or residue removal (inadequately understood)positive effects of reforestation–reduced erosion, increase in waterretention, rehabilitation of strip-mined land, drastically improvedesthetic quality, etc.slumps and landslides from loss of root support or improper roaddesigntemporary degrading of esthetic quality

Ecological● changes in wildlife from transient effect of cutting and changes in

forest type● temporary degradation of aquatic ecosystems● change in forest type or improved forest from stand conversion


tions) to hundreds of tons per acre per year(poorly managed clearcuts on steep slopes inhigh rainfall areas) .33

A recent Environmental Protection Agency(EPA) report suggests the loss of 7 or 8 tons ofsediment per acre per year as a mean value forrecently harvested forests, although the varia-tion around this mean is very large. ” To placethis rate in perspective, the continuous sheet

“Environmental Readiness Document, Wood Commercializa-tion, draft (Washington, D.C : Department of Energy, 1979).

J4Envlronmenta/ /mp/;ca(/on5 of T rends in Agriculture and SIIVI-cuhure, vol. 1, op cit

and rill erosion rate on intensively managedagricultural land averages 6.3 ton/acre-yr.

Most forestland is harvested at most onceevery several decades and the increased ero-sion generally lasts only a year or two on themajority of the affected acreage. Increasederosion from poorly constructed roads, how-ever, may last longer.

The processes involved in erosion of forest-Iand are stream cutting, sheet and gully ero-sion, and mass movement of soil. Erosion dan-ger increases sharply with the steepness of thelandscape, and the most common form of thiserosion is mass movement. Mass movement“includes abrupt or violent events such aslandslides, slumps, flows and debris ava-lanches, as well as continuous, almost imper-ceptible creep phenomena."35 Occurrence ofmass movements is most often associated withsteep slope conditions where the forest soil isunderlaid with impermeable rock. 36 Thesemovements are natural processes associatedwith the downwearing of these steep slopes,but they can be triggered by man’s activities.In contrast, sheet and gully erosion are rare inundisturbed forests, but they can be triggeredby soil disturbances caused by careless roadconstruction or logging practices.

The major causes of erosion problems inforestry operations are the construction anduse of roads and other activities that may com-pact or expose soil or concentrate water.37 Thecompaction caused by the operation of heavymachinery can reduce the porosity and water-holding capacity of the soil, encouraging ero-sion and restricting vegetation that eventuallywould reduce erosion. Roads and skid trailscomprise up to 20 percent of the harvestarea, 38 and the total area that may be com-pacted at a site may range up to 29 percent in

“Earl Stone, “The Impact of Timber Harvest on Soils andWater, ” Report of the President’s Advisory Panel on Timber andthe Environment (app M, Washington, D C Forest Service, U SDepartment of Agriculture, April 1973)

“Environmental Implications of Trends in Agriculture and Si/vi-cu/ture, vo/. 1., op cit

“Stone, op cit“Draft 208 Preliminary Non-Point Source Assessment Report

(Augusta, Maine Land Use Regulatory Commission, State ofMaine, 1978


some instances. 39 Although in most areas thethawing and freezing cycle allows compactedsoil to recover in 3 to 10 years, recovery takesfar longer when, as in parts of the Southeast,this cycle does not occur.40 Also, when com-paction is very severe, recovery may take con-siderably longer than 10 years; old loggingroads are still visible in the Northeast, evenwith the frost cycle.

The vulnerability of logging roads to erosionis related to topography and soil type as wellas to road design. Roads developed on gentleto moderate slopes in stable topography posefew problems with the exception of carelessmovements of soil during construction. Largeareas of forestland served by such roads drawlittle attention or criticism.41

The great majority of difficulties and haz-ards arise, however, when roads are con-structed on steep terrain, cut into erosive soilsor unstable slopes, or encroach on streamchannels. Steep land conditions present adilemma for road development, and criteriafor location, design, and construction that aresatisfactory on even moderate slopes may leadto intolerable levels of disturbance on steeplands. Building a road on a slope involves cut-ting into the slope to provide a level surface.The soil removed from the cut is used as fill ordumped. The steeper the slope, the more soilthat must be disposed of and the more difficultis the job of stabilizing this soil. In the absenceof proper attention to soil and geology, roaddesign (especially alinement and drainage),and other factors, surface erosion from roadand fill surfaces can continue for years. Road-building on steep slopes may also removeenough support from the higher elevations tocause mass failures; problems created by theroad cut may be aggravated by inadequatedrainage allowing further cutting away of sup-porting soil.

Aside from roads, the movement of logsfrom the harvest site to loading points maypresent considerable erosion potential. “Skid-

“fnvlronmental Implications of Trends in Agriculture and Silvi-

cu//ure, vo/ 1 , o p clt‘“lbd“Stone, OP clt

ding” logs may expose the subsoil, or compactthe soil. Exposing the surface is a problemwhen the soil is highly erosive or when waterconcentrates, but is usually not a major ero-sion problem. The deeper disturbances of com-paction and of cutting into the soil createmore significant erosion problems, especiallywhen they occur parallel to the flow of water.Most surveys of logging have concluded thatthe hauling or skidding of logs “generally doesnot lead to appreciable soil erosion or im-paired stream quality;”42 however, the samesurveys conclude that “exceptions are com-men, ” and logging in vulnerable areas, underwet weather conditions, or with inappropriateequipment are thought to be important prob-lems in the industry.

Erosion caused by the actual cutting of thetrees generally is considered to be relativelyunimportant. Vegetation usually regeneratesquickly and reestablishes a protective cover onthe land, preventing surface erosion except inareas where other components of the loggingoperation have damaged the soil. “Many ob-servations and several studies on experimentalwatersheds demonstrate that sheet and gullyerosion simply do not occur as a result of treecutting alone, even on slopes as steep as 70percent. ”43

However, land that is vulnerable to massmovements may be damaged by tree cutting.The decay of the old root systems will removecrucial support from a vulnerable slope fasterthan it can be replaced by the root systems ofnew growth; within 4 to 5 years after tree cut-ting (or fire), mass movement potential may in-crease dramatically. Forests in the NorthwestUnited States and coastal Alaska are the mainareas for this type of damage potential .44

The method of clearing for forest regenera-tion may also affect erosion potential. Inten-sive mechanical preparation of land beforetree planting (i.e., use of rakes, blades, andother devices to reduce a forest to bare groundto favor reproduction of pine) can cause very

“lbld‘Jlbld“’lbld

30 . VOI. II—Energy From Biological Processes

serious erosion problems. This practice is oc-curring on hilly sites in the South that havebeen depleted by intensive cotton productionin the past; it “may foster a dangerous cycle oftopsoil and nutrient loss and increased sedi-ment loading in streams. ”45 Poorly managedraking may have adverse effects on forest pro-ductility. ” Area burning can also badly dam-age forest soils if managed improperly or ifused on improper soils. Although suitable forhighly porous, moist soils (where much of thesurface cover is not consumed), poorly man-aged burning may consume most of the coverand leave the soil exposed to surface erosion.(However, area burning is considered to have alesser potential to degrade productivity thanraking.”) Burning may also represent a signifi-cant local source of air pollution. On the otherhand, “controlled” burning may reduce futurefire hazard by reducing slash buildup and mayfavor regeneration on the site of fire-resistanttrees.

The sediment resulting from the erosion de-scribed in this section is “the major cause ofimpaired water quality associated with log-ging.” 48 These sediments are directly responsi-ble for water turbidity, destruction of streambottom organisms by scouring and suffoca-tion, and the destruction of fish reproductivehabitat. Sediments also carry nutrients fromthe soil. Nutrient pollution is further increasedby increased leaching and runoff as increasedsolar radiation reaches the forest floor andwarms it, microbial activity (which transformsnutrients to soluble forms) accelerates and nu-trient availability increases (this soil heating ef-fect also has been known to retard regenera-tion, especially on south-facing slopes, by kill-ing off seedlings). The increased nutrient load-ing of streams may have a variety of effects, in-cluding accelerated eutrophication and oxy-gen depletion. Fortunately, the increased nutri-

45 Environrrrenta/ Effects of Trends, vo/. 2 (Washington, D C En-vironmental Protection Agency, December 1978), E PA-600/3-77-121

“Stone, op clt“lbld4“Silviculture Act iv i t ies and Non-Po in t Pollution Abatement : A

Cost-Effectiveness Ana/ysis Procedure (Washington, D C ForestService, US Department of Agriculture, November 1977),E PA-600/8-77-Ol 8

ent loading is usually short-lived, because re-vegetation of the site slows runoff and leach-ing, increases nutrient uptake, and, by shadingand cooling the soil, slows the decompositionof organic material and consequent nutrientrelease.

The effects of nutrient enrichment are ag-gravated by the decomposition of organic mat-ter from slash that is swept into streams, andby any water temperature increases caused byloss of streambank shading* (the temperatureincreases speed up eutrophication and furtherreduce oxygen content of the water). Tempera-ture increases may also directly harm somefreshwater ecosystems by affecting feedingbehavior and disease incidence of cold waterfish.

Logging operations affect water supply andmay decrease a watershed’s ability to absorbhigh-intensity storm waters without flooding(although this problem may have been exag-gerated somewhat in the past).

The possibility of increased flooding stemsfrom two causes. First, cutting the forest re-duces the very substantial removal by trans-piration of water from underground storage.During the period before substantial revegeta-tion has taken place, the amount of this long-term “retention storage” capacity available toabsorb floodwaters will be lessened and peakstream flows may rise. For example, increasesin peak flows of 9 to 21 percent in the East and30 percent in Oregon following clearcuttinghave been reported. These increases are usual-ly observed only during or right after the grow-ing season, where continual drawdown of stor-age would be occurring had the trees not beencut (floods occurring during the winter, as inthe Northwest, may be unaffected or less af-fected because drawdown would not normallybe occurring). This decrease in storage capaci-ty apparently is not significant unless at least20 percent of the canopy is removed.49 Second,

*The extent of any Increases depends on stream volume,degree of removal of understory vegetation, and several otherfactors In many cases, no significant effects occur

“An Assessment of the Forest and Range Land Situation in theUnited States (Washington, D C Forest Service, U S Depart-ment of Agriculture, 1979), review draft


damage to forest soil increases runoff and in-hibits the action of even the temporary “deten-tion storage” potential wherein water is tem-porarily stored in pores in the upper soil layersand can be delayed from reaching streams foranywhere from several minutes to severaldays. Although treecutting, even clearcutting,is not likely to affect this temporary storagecapacity, compaction of the soil by roadbuild-ing, log skidding, and operation of heavy ma-chinery may reduce the infiltration of waterinto the soil if the compaction occurs over awide area50 and thus drastically reduce stor-age. Area burning on coarse-textured soils cancreate a water-repellant layer that would alsodecrease this infiltration and thus reduce thesoils’ capacity for detention storage. 51

The reduction of transpiration that is causedby timber harvest may be beneficial by in-creasing stream flow and groundwater suppliesin water short areas. Also, carefully structuredcuts can be used to trap and maintain snowaccumulation, greatly reducing evaporationlosses, It is claimed that by using such tech-niques, water yield from commercial forest-Iand in the West could be increased, supplyingmillions of additional acre feet at a cost of afew dollars per acre foot. 52

Large-scale forestry operations often dras-tically alter local ecosystems, even for the longterm. Wetlands in the South are being drainedand pine forests are being created with the aidof substantial applications of phosphate fertil-izers. In the process, aquatic ecosystems arebeing replaced by terrestrial ones and somecritical wildlife habitats, especially for water-fowl, are being destroyed.53 In the PacificNorthwest, old stands of Douglas fir are beingreplaced by single-aged plantings of the samespecies. EIsewhere, mixed hardwood forestsare being replaced by plantations of conifers.In many cases, however, the ecosystems beingreplaced are themselves the result of past log-

“’Stone, op clt“R M Rice, et al , “Erosional Consequences of Timber Har-

vesting An Appraisal, ” W a t e r s h e d jr-i Trarrs/t/on, (Urbana, I l lAmerican Water Res Assoc Proc Ser 14, 1972)

“An As~essment of the Fore$t and Range Land S/ fuat/on In theUn/ted State\, o p cit

5‘Vo/ //, fnv(ronmenta/ Effects of Trend\, op clt

ging and agriculture as well as “unnatural” for-est fire suppression that gradually replacedconifer forests with mixed hardwoods.

All types of replanting are accompanied bymajor changes in habitats available for wild-life. In the short term, any wood-harvestingoperation, other than large area clearcutting,usually increases wildlife populations becausemature forests normally do not support asgreat a total population of wildlife as do younggrowing forests. Many species require bothcleared and forested area to survive, and thus,the “edges” created by logging operations areparticularly attractive to deer and other spe-cies. Other species dependent on subclimaxhabitats (such as eastern cottontails) will alsoincrease following logging, while species de-pendent on mature climax forests (e. g., wolver-ine, pileated woodpecker) will decline.54

Although the desirability of the ecosystemchanges caused by logging may always be sub-ject to one’s point of view, different forestrypractices tend to have varying effects that maybe judged unambiguously from the standpointof wildlife diversity and abundance:

F o r e s t m a n a g e m e n t p r a c t i c e s t h a t r e d u c es t r u c t u r a l d i v e r s i t y o f h a b i t a t , s u c h a s e x t e n -s i v e o l d g r o w t h c l e a r c u t t i n g , t h e r e m o v a l o fs n a g s t h a t p r o v i d e w i l d l i f e f o o d a n d n e s t i n gs i t e s , a n d c o n v e r s i o n t o p l a n t a t i o n m a n a g e -ment w i l l genera l Iy reduce wi ld l i fe a b u n d a n c eand diversity by reducing habitat essential tomany species. Conversely, animal diversityand wildlife abundance generally will be in-creased by opening up dense stands, makingsmall patch cuts, or by conducting other tim-ber management activities that increase struc-tural diversity and provide a wide mix of hab-itat types. 55

Current pesticide and fertilizer use in U.S.forests is low, In 1972, insecticides were usedon only 0.002 percent of commercial forest-Iands, and fertilizers were used on less than500,000 acres. 5’ Because long-rotation loggingand removal of only boles generally do not

“An Assessment of the Forest and Range Land Sltuatlon In f~eUnited States, op clt

“lblci‘6Vo/ 1 Errvironmenta/ lrnpllcatlon~ o f Trends In Agrlcu/ture

and S\lv/cu/ture, op c(t


deplete nutrients from forest soils, the mostimportant use of fertilizers is on soils that arenaturally deficient in nutrients or that havebeen depleted by past farming practices. Forexample, intensive cotton production in theSoutheast seriously depleted soils and much ofthis land was abandoned long ago. Phosphatefertilization has allowed this land to becomeproductive in the growth of softwood forests.Pesticides generally are used in forest manage-ment to control weed vegetation during refor-estation or to combat serious outbreaks of in-sect pests. There is considerable controversyover aerial spraying of insecticides to controlthe gypsy moth and other damaging insects.Also, circumstantial evidence exists that cer-tain herbicides in recent use may have causedoutbreaks of birth defects and other damagewhen inadvertently sprayed over populatedareas. Although the existence of these effectshas been vigorously denied by the manufactur-ers, and although pesticide use in forests is atiny fraction of the use in food production andis likely to remain so,57 this use is likely to con-tinue to be a source of disquiet accompanyingintensive management of forests.

Silvicultural activities, and especially inten-sive harvesting operations, strongly affect theesthetic appeal of forests. The immediate af-termath of intensive logging is universally con-sidered to be visually unattractive, especiallywhere large amounts of slash are left on thesite. Therefore, wood harvesting has a strongpotential to conflict with other forest usessuch as recreation or wiIderness.

The significance of any negative effects de-pends on the nearness of logging sites to activi-ty areas or to scenic vistas, the rapidity of re-vegetation, and the extensiveness of the oper-ation. Therefore, the Forest Service seeks toroute trails away from active harvesting sites,to avoid interrupting vistas, and to plan the ex-tent and shape of the areas to minimize visualimpacts.

The negative effect on the esthetic and rec-reational quality of forests caused by loggingmay be aggravated by a negative public per-

“lbld

ception of the environmental effects of clear-cutting in particular and logging in general. Asnoted earlier, this perception has been exag-gerated by a number of factors including thegrim history (1870-1930) of forest exploitationin the United States, the former revulsionagainst clearcutting practices within the for-estry profession itself during the 1930’s and1940’s, and continued attacks against loggingby the environmental community. Although alogged-over area may be no uglier, objectivelyspeaking, than a harvested field, the publicperception of the two vistas is vastly different.

All reviews of logging and general forestryimpacts stress the importance of regional dif-ferences –as well as extensive site-specific dif-ferences – in determining the existence andmagnitude of environmental effects. Figure 6presents a summary of those characteristics ofU.S. forest regions that are most relevant topotential silvicultural impacts. Because thedescriptions in figure 6 are, of necessity, muchoversimplified, they are meant to give someperspective of the general range of environ-mental conditions and problems in Americanforestlands and should not be considered asfully representing all of the major conditionsand problems in these lands.

Potential Environmental Effects ofHarvesting Wood for Energy

This section discusses the activities— har-vesting logging residues, whole-tree removal,intensifying and expanding silvicultural man-agement, and harvesting for the residentialspace-heating market — which are characteris-tic of an expansion in the use of wood as anenergy source.

Harvesting Logging Residuesand Whole-Tree Removal

The harvesting of logging residues for an en-ergy feedstock has potential for both positiveand negative environmental impacts depend-ing on the nature of the forest ecosystem andthe previous manner of handling these resi-dues.

Ch.2-Forestry • 33

Figure 6.-Envlronmental Characteristics 01 Forest Regions

SOURCE: Silviculture Activities and Nonpoint Pollution Abatement: A Cost·Effectiveness Analysis Procedure (Washington, D.C.: Forest Service, U.S. Department of

Agriculture, November 1977).


In forests where wood residues–tops, limbs,and possibly leaves and understory — are rou-tinely gathered into piles for open burning (thisis required in forest fire prone areas of theWest), residue use for energy production is en-vironmentally beneficial. It eliminates the airpollution caused by this burning and has essen-tially no additional adverse impacts exceptthose incurred in physically moving the residueout of the forest (and burning it, with controls,in a boiler). In forests where residues wouldotherwise be broadcast burned, physical re-moval prevents some of the potential adverseeffects of burning — especially destruction of aportion of the organic soil layer. The removaldoes, however, subject the soil to compactionor scraping damage by the mechanical remov-al process that would otherwise be avoided.Also, broadcast burning is, at times, used tocontrol weed vegetation, and in some circum-stances herbicide use may be substituted ifburning cannot be practiced.

Where logging residues are normally left inthe forest, institution of a residue removal pro-gram will have mixed environmental effectswhich are summarized in table 12.

A worrisome effect of residue removal is theincreased potential for long-term depletion ofnutrients from the forest soils and consequentdeclines in forest productivity. These effectsare not well understood and although nutrientcycling in natural and managed forests hasbeen extensively studied, few of these studieshave included the effects of residue removal.58

The existing studies indicate that short-rota-tion Southern forests may be more susceptibleto depletion than longer rotation Northernforests, and that marginal sites suffer far moreheavily than forests with fertile soils. 59 60 61 62

“C. J. High and S E. Knight, “Environmental Impact of Har-vesting Noncommercial Wood for Energy Research Problems, ”Thayer School of Engineering, Dartmouth College paper DSDNo. 101, October 1977.

“E H White, “Whole-Tree Harvesting Depletes SOII Nutri-ents, ” Can 1. Forest. Res. 4.530-535,1974

‘“J R Jorgensen, et al., “The Nutr ient Cycle Key to Con-tinuous Forest Production, ” /. Forestry 73.400-403, 1975.

“J R Boyle, et al , “Whole-Tree Harvesting. Nutrient BudgetEvaluation, ” ). Forestry 71 760-762

“C F Weetman and B Webber, “The Influence of Wood Har-vesting on the Nutrient Status of Two Spruce Stands, ” Can. /. For-est. Res. 2 351-69, 1972

Table 12.-Environmental Impacts ofHarvesting Forest Residues

Waterdecrease in clogging of streams caused by entry of slashincreased short-term flow of sediments into streams because of loss oferosion control provided by residues, soil damage caused by removaloperations; somewhat counteracted by decline in broadcast burning,which at times destroys surface cover and causes erosion potential toincreasepossible changes in long-term flow of sediments where residueremoval affects revegetation; this effect is mixedchanges in herbicide usage–on the one hand, chemical destruction ofgrowing residues (valueless trees) will cease; on the other, broadcastburning no longer effective in retarding vegetative competition to newtree growth, herbicide use may increaseincreased short-term nutrient leaching because of increased soil tem-peratures, accelerated decomposition

Air● reduction in air pollution from forest fires● reduction in air pollution from open burning of residues (if the residues

normally are broadcast burned or burned after collection)● dust from decreased land cover, harvesting operationsLand● potential depletion of nutrients and organic matter from forest soils and

possible long-term loss of productivity (inadequately understood)● short-term increase in erosion and loss of topsoil, possible long-term

decrease or increase● reduction in forest fire hazard● short-term decreased water retention, increased runoff (and flooding

hazard) until revegetation takes place; aggravated by any soil compac-tion caused by removal operation

Other● change in wildlife habitat—bad for small animals and birds, good for

large animals unless serious erosion results● changes in tree species that can regrow● esthetic change, usually considered beneficial when slash is heavy● reduction in bark beef/es and other pathogens that are harbored by

residues

SOURCE Office of Technology Assessment.

Further study and careful soil monitoringwould allow the use of fertilizers to compen-sate for nutrient depletion, but fertilizer ap-plication is energy intensive; it may increasethe flow of nutrients to neighboring streams,and its correct use may be difficult to ad-minister for smaller stands. Also, successfulapplication may be difficult unless the nutri-ent depletion is a simple one involving onlyone or a few nutrient types<

Residues serve a number of ecological func-tions in addition to nutrient replenishment,and their removal will eliminate or alter thesefunctions. They provide shelter and food tosmall mammals and birds, provide a temporaryfood supply for deer and other larger mam-mals, moderate soil temperature increases that


normally occur after logging, provide someprotection to the forest floor against erosion,and are a source of organic matter for forestsoils. Thus, removal of residues will reduce cer-tain wildlife habitats and may expose the for-est floor to some additional erosion above andbeyond that caused by conventional logging.Higher soil temperatures resulting from loss ofthe shade provided by residue cover will accel-erate organic decomposition activity and maylead to a period of increased nutrient leachingbefore revegetation commences. Also, the in-creased rate of organic decomposition cou-pled with the removal of a primary source oforganic matter may lower the organic contentof forest soils. Declines in soil organic matterare expected to be accompanied by declines innitrogen-fixing capacity, soil microbial activityrates, and cation exchange capacity, all con-sidered to be important determinants of long-term forest health. 63 64 The present scientificunderstanding of organic matter removal is,however, insufficient to allow a determinationof the significance of these possible effects.

The extensive residue left on the forest floorafter cutting dense stands can inhibit revegeta-tion, especially in softwood forests. To the ex-tent that residue removal may promote newvegetation, this will counteract the removal’sshort-term negative erosion and nutrient-leach-ing effect (as long as removal is not so com-plete as to eliminate the light mulch necessaryto shade the surface and maintain soil mois-ture).

Residues also provide a habitat for diseaseand pest organisms such as the bark beetleand, when washed into neighboring streams,may clog their channels and degrade waterquality. They add considerably to the inci-dence and intensity of forest fires, especially inthe West. Also, the esthetic impact of residues

*‘E L Stone, “Nutrient Removals by Intensive Harvest— SomeResearch Gaps and Opportunttles, ” Proceedings Impact of Har-vesting on Forest Nutr\ent Cycle (Syracuse, N Y State Unlversltyof New York, College of Environmental Science and Forestry,1 979)

“E H Wh/te and A E Harvey, “Modlficatlon of IntensiveManagement Practices to Protect Forest Nutrient Cycles, ” Pro

ceedlngs /rnpact of Har\,e$t/ng on Forest Nutr/ent Cyc/e [ S y r a -cuse, N Y State Untverslty of New York, College of Environ-mental Science and Forestrv, 1979)

is generally considered to be negative whenthey are left at the logging site; when denselyforested areas are cut, residues will completelycover the ground with several feet of unsightlyslash. Therefore, removal of residue will, in apositive sense, reduce the number and severityof forest fires and pest infestations, improveesthetics, and reduce the potential for streamclogging.

“Whole-tree harvesting” is really a variationof residue removal with the bole and “resi-d u e ” - branches, leaves, twigs– removed inone integrated operation. It is most likely tooccur when the entire tree is to be chipped forfuel or some other use.

The problems of long-term nutrient and or-ganic matter depletion from whole-tree har-vesting are basically the same as those ofresidue removal, and whole-tree logging simi-larly removes far greater nutrients and organicmatter from forest soils than do other conven-tional methods. Whole-tree removal of Nor-way spruce, for example, results in a loss of 2to 4 times more nitrogen, 2 to 5 times morephosphorus, 1.5 to 3.5 times more potassium,and 1.5 to 2.5 times more calcium than conven-tional Iogging. 65 In addition, ground disturb-ance from the actual tree removal is likely tobe worse with whole-tree harvesting when thefully branched trees are dragged off the log-ging site, eradicating understory vegetation inthe process. This disturbance, besides promot-ing erosion, will accelerate organic matter de-composition. As noted previously, however,the effects of these organic matter and nutri-ent removals on long-term forest productivityare poorly understood.

Intensifying and ExpandingSilvicultural Activities

The creation of new energy markets forwood will have a significant effect on the eco-nomics of managing forested land, includingland not currently considered to be high-grade

“E Malkonen, “The Effects of Fuller Biomass Harvesting onSOI1 Fertlllty, ” SyrnposIurn on the Harvest~ng of a Larger Parf ofthe Forest Biomass (Hyvlnkaa, Finland E conomlc Commlsslonfor Europe, Food and Agriculture Organlzatlon, 1976)


forest. New lands will be harvested and silvi-cultural practices will intensify.

One effect will be the expansion of loggingonto lands that are not now in the wood mar-ketplace. The operational costs of loggingsome of these lands cannot, at present, be re-couped through increased property values, thesale of the harvested wood, or the value of fu-ture growth of a regenerated forest. Additionallands that currently are economically attrac-tive targets for logging activities (stand conver-sion, clearing for nonforest use, etc.) are with-held by their owners for a variety of reasons(their higher valuation of the land’s recre-ational potential, fear of environmental dam-age, etc.). As an energy market for wood devel-ops, however, harvesting part or all of thewood resource on these lands will become in-creasingly attractive.

The logging of some forests that wouldotherwise be untouched (or, perhaps morerealistically, that would only be logged atsome later time) may be viewed as beneficialby some groups. Most reviews depict Americanforests as being characterized by “overmaturestands of old-growth timber, especially in theWest, and . . . many stands, mainly in the Eastand South, that were repeatedly mined of goodtrees in earlier, more reckless times. ”66 Conver-sion of such stands is often characterized as astep towards a healthier forest, because treegrowth generally is enhanced and more “desir-able” tree species are introduced. Wherewhole-tree harvesting or residue removal ispracticed, the forest may become more acces-sible to hikers and may be more estheticallyappealing. The extent to which all this is con-sidered a benefit depends heavily on one’s per-spective, however, and optimizing commercialvalue is not necessarily synonymous with opti-mizing other values such as ecosystem mainte-nance or wildlife diversity.

As discussed later, expansion of silviculturalmanagement onto suitable lands, combinedwith an increase in the intensity of manage-ment on existing commercially managed lands,

“Smith, op. cit

may provide important environmental benefitsin the form of decreasing logging pressures onlands that combine high-quality timber withcompeting values that would be compromisedby logging. Unfortunately, a decrease in log-ging pressures on one segment of America’sforests may be coupled with an undesirable in-creased pressure on another segment.

A particular fear associated with the rise indemand for “low quality” wood is that mar-ginal, environmentally vulnerable lands withstands of such wood may become targets forlogging. Much of this land that may be vulner-able to logging for energy, although “poor”from the standpoint of commercial productivi-ty, is valuable for esthetic, recreational, water-shed protection, and other alternative forestuses. These forest values may be lost or com-promised by permanent clearing or by harvest-ing on sites where regeneration may be a prob-lem. For example, forests in areas with margi-nal rainfall —e. g., in the Southwest— may beparticularly vulnerable to regeneration failuresand thus may be endangered by a growth inwood demand. On lands with poor soils andsteep slopes, clearcutting and other intensiveforms of harvesting create a high potential fornutrient depletion, mass movement, and otherproblems as described earlier. Because, as dis-cussed later, the Federal Government main-tains supervisory control over forest opera-tions on federally owned lands, this potentialproblem is likely to be concentrated on privatelands. The overall danger is somewhat miti-gated, therefore, by the Federal Government’sownership of a significant percentage of themost vulnerable land.

It is difficult to predict whether wood-for-energy operations will tend to gravitate to thepoorer quality and more vulnerable lands. Theseveral factors that will determine the tenden-cy of wood-for-energy harvesting to gravitateto vulnerable lands include:

1. The direct cost of wood harvesting, – De-velopment of more versatile harvestingequipment can lower the cost of operat-ing on steep slopes and promote harvest-ing on vulnerable lands.

Ch. 2—Forestry ● 37

2.

3.

4.

5.

6.

7.

The stringency and enforcement of envi-ronmental standards. –The stronger thecontrols, the more likely it is that loggerswill avoid the more vulnerable stands.The price of woodchips for energy. –At ahigh enough price, the “value-added” tothe land by clearing will become less im-portant, and poorer quality lands will be-come more attractive targets for harvest-ing.The price of agricultural land and “highvalue” forestland. –At high prices, woodharvesting for energy would tend to gravi-tate to higher quality, less erosion-prone/depletion-prone lands because clearingfor agriculture or stand conversion will bemore profitable.The distribution of different soil/slope/rainfall conditions in forestland potential-ly available for cutting.The attitude of private landowners, w h ocurrently own much of the land availablefor clearing but who often are reluctant toallow harvesting.The cost of transporting wood. – Becausethe higher this cost, the more likely it isthat local shortages could force harvest-ing onto vulnerable lands.

Except for (1) and (5), these factors may be ex-tremely volatile and will themselves depend onthe availability of alternate fuels, the state ofthe economy, etc. Except for forestland in theSoutheast, the data necessary to define (5) arenot available.

The Department of Energy, in its draft“Wood Commercialization EnvironmentalReadiness Document,’’67 asserts that the siteswith “nutrient deficiencies and delicate nutri-ent balances, and subsequently low productiv-ity . . . are the non-commercial forests thatoften are considered available for whole-treeharvest for energy.” And a recent EPA reportasserts that “areas previously left unlogged. . . are most often increasingly steep with dif-ficult terrain.’’” Both of these statements im-ply that an areal expansion of logging to satis-

‘7 E n v i r o n m e n t a l Read/ness Document , W o o d Commercializa-tion, op clt

bOVo/ II, En vjronmenta/ Effects of Trends, OP c It

fy energy demands could be expected to leadto exploitation of lands particularly vulnerableto environmental damage.

These references may have overlooked sev-eral

1.

2.

3.

4.

factors, however:

As noted previously, there is considerableforest acreage of high quality— lowslopes, rich and nonerosive soils, ade-quate rainfall —with low-quality timbergrowing on it. This is especially true in theEast.The cost of harvesting timber on flatter—and thus less erosive —slopes is consid-erably less than on steep-sloped lands.These flatter lands presumably would bethe first choice for harvesting.The higher quality, less vulnerable sitesoffer the landowner the economic incen-tive of an added return from regrowth ofhigh-quality timber or else alternativeland uses such as farming.Increases in land prices for rural acreagewith high recreational and esthetic valuehave increased the economic incentive toguard against environmental damage thatwould compromise these values.

On balance, it would appear that marketpressures would tend to favor the harvesting ofthe less environmentally vulnerable lands.However, variations of land availability fromregion to region, landowner decisions based onother than land suitability grounds, and otherfactors are likely to lead to some level of inap-propriate harvesting — especially if the currentstate of regulatory “laissez-faire” continues(see discussion on “The Institutional Climatefor Environmental Control”).

A second effect of new energy markets forwood will be an intensification of forest man-agement—especially of thinning— becausepart or all of its cost will be recouped throughuse or sale of the collected wood. Residueremoval or whole-tree harvesting, discussedpreviously, are likely to be another facet ofthis management intensification.

The process of removing trees that are deador diseased, stunted, poorly shaped, or of “un-desirable” species is considered by foresters to

38 . VOl. II-Energy From Biological Processes

be beneficial to the forest. Thinning allows in-creased growth in the remaining trees, esthetic-ally and physically “opens up” the forest, andmay allow some additional growth of under-story vegetation if the thinning is extensiveenough. If heavy machinery is used, however,resulting soil compaction can cause adverseimpacts, and care must be taken during thethinning operation to avoid damaging the treesthat remain.

A critical argument in favor of thinning andother logging operations is that these activitiesresult in increased wildlife populations and di-versity. The definition of “diversity” is criticalto this argument. There is a substantial differ-ence between maximizing diversity in a singleforest stand and maximizing it in the forestsystem composed of many forest stands in aregion. The first definition may be well servedby more intensive management because suchmanagement provides more “edges” and un-derstory vegetation for browse. On the otherhand, many species will suffer from such man-agement. A great many species depend fortheir food and shelter on “unhealthy” –dead,dying, rotten —trees that would be removed ina managed forest, and other species cannottolerate the level of disturbance that would becaused by thinning operations. Maintaining di-versity in a forest system must include protect-ing these species by deliberately leaving un-managed substantial portions of the forest or apercentage of the individual stands within theentire system. in regions where officially desig-nated wilderness areas or other protectivemeasures are adequate, intensive managementon the remaining stands may be considered(even by environmental groups) as benign orbeneficial if good management practices arecarefully followed. In other regions, especiallyin the East, intensive management may con-ceivably work to the detriment of species di-versity although it may increase the total wild-life population. Even in these regions, how-ever, there is a possibility that large numbersof property owners may choose to leave theirlands unmanaged because of personal prefer-ences. This would serve to protect diversity.

The potential for added growth of high-quality timber from stand conversions of low-

quality forest and the increased use of thinningon commercial forestlands may have, as itsmost important effect, a decrease in the pres-sures to log forests that have both high-valuetimber and strong nontimber values —recrea-tion, esthetic, watershed protection, etc. — andthat may be quite vulnerable to environmentaldamage. Analysts such as Marion Clawson ofResources for the Future have long argued thatthe management of American forestland is ex-tremely inefficient, that by concentrating in-tensive management practices on the most ,productive lands we could increase harvestyields while withdrawing from silviculture lessproductive or more environmentally vulner-able lands. 69 70 An expansion of wood use forenergy and the consequent creation of a strongmarket for “low quality” wood may have thisbeneficial effect.

OTA estimates that placing 200 millionacres of commercial forestland into intensivemanagement (full stocking, thinnings every 10years, 30- to 40-year rotations) could allowwood energy use to reach 10 Quads annuallywhile the availability of wood for nonenergyproducts might double its 1979 value. Alter-natively, the same result might be achieved byusing less intensive management on a largeracreage. The nature of any actual benefits,however, are dependent on the following con-siderations:

● Major effects on the availability of high-quality timber probably would not occurfor a number of years. Some additionalhigh-quality wood might be available im-mediately from stand conversions andharvest of noncommercial timber, andsome in about 20 years from timbergrowth in stands that required only thin-ning for stand improvement. The quan-tities would not peak, however, beforeabout 30 to 40 years as stands that hadbeen cleared and replanted began toreach harvesting age, By this time, most ofthe old-growth stands accessible to log-ging already may have been harvested, al-

“M. Clawson, “The National Forests, ” Science, VOI 20, Febru-ary 1976

‘“M Clawson, “Forests in the Long Sweep of American His-tory, ” Science, VOI 204, June 15, 1979


though significant benefits from reducinglogging pressures on other valuable orfragile lands would still be available.

● Although the increased availability ofhigh-quality timber might negate argu-ments that these valuable or fragiIe standsmust be cut to provide sufficient wood tomeet demand, there is no guarantee thatthe wood made available from intensifiedmanagement will be less expensive thanthat obtainable from these stands, andeconomic pressure to harvest them mightcontinue.

Although the long-range economic goals ofintensive management provide an incentiveagainst poor environmental practices, carelesslogging and regeneration practices will still oc-cur on a portion of the managed sites. Poormanagement may be practiced on a smallerproportion of sites than would have been thecase without an expansion of wood for energy,but the effects of such management may beaggravated with such an expansion because:

● more acreage wilI be logged each year,● most affected sites will have fewer years

to recover before they are logged again,and

● the removal of maximum biomass andsubsequent soil depletion may reduce thesites’ ability to recover.

Thus, the impacts associated with conven-tional logging— including erosion and soil deg-radation, damage to water quality, estheticdamage, and other impacts–are likely to oc-cur with even greater severity on a portion ofthose lands devoted to wood production forenergy. Unfortunately, because of the lack ofdata on logging practices and the very mixednature of the incentives for good management,it is impossible to make a good quantitativeprediction of the size of this portion.

A basic— and difficult to resolve— issueconcerning the wisdom of moving to a veryhigh level of intensive management of U.S. for-estland is the possibility that the long-termviability of these forests may be harmed. Thepossibility of soil depletion is only one aspectof this. The cycles of natural succession oc-

curring in an unmanaged forest give that forestsubstantial resilience, because the diversity ofvegetation and wildlife of the more maturestates of the forest cycle as well as the diversi-ty created by the heterogeneous mix of stagestend “to buffer the system against drasticchange as by diluting the effects of pests onsingle species.’’” Ecologists often have arguedthat man pays a significant price in moving toofar from this natural state:

The whole history of agriculture, and later,forestry, is basically a continuous effort tocreate simplifed ecosystems in which special-ized crops are kept free of other species whichinterfere with the harvest through competi-tion . . . diversified systems have built-in insur-ances against major failures, while the simpli-fied systems need constant care. ’z

In relation to human needs, the human strat-egy can be viewed as a reversal of the succes-sional sequence, creating and maintainingearly successional types of ecosystem wheregross production exceeds community respira-tion. Such . . . ecosystems, despite their highyield to mankind, carry with them the disad-vantages of all immature ecosystems, in par-ticular they lack the ability to perform essen-tially protective functions in terms of nutrientcycling, soil conservation and population reg-ulation. The functioning of the system is thusdependent upon continued human interven-tion. 73

There are, of course, counterarguments tothe thesis that this simplification of ecosys-tems places these systems under significantrisk. One argument is that much of silvicultureduplicates natural events, and purposely so;for example, clearcutting, sometimes followedby broadcast burning, is said to duplicate theeffects of severe storms or catastrophic fires. 74Another is that professional silviculturalistscan compensate for any tendency towards a

“Smith, op cit“A H Hoffman, “Comprehensive Planning and Management

of the CountrVslde A Step Towards Perpetuation of an Ecologi-cal Balance, ” C/oba/ Perspectives on Eco/ogy, Thomas C Em-mel, ed (May field Publlshlng Co , 1977)

‘‘R Manners, “The Environmental Impacts of Modern Agricul-tural Technologies, ” Perspectives orI Environment, I R Mannersand M W Mlkesell, eds (Association of American Geographers,1974), publication No 13

74 Smith, op clt

40 . VOI. II-Energy From Biological Processes

decline in resiliency. In its extreme, this argu-ment is particularly unacceptable to thosewho are skeptical of placing too great a faithin science:

We ought to believe that we can excel overnature; and if we do, we should not be re-stricted to blind imitation of her methods. . . we have the chance to sift nature’s truths,and recombine them into a new order in whichnot only survival, but enhanced productivityare the ruling criteria . . . (we) must look tonear-domestication of our forests . . . we mustmove forestry close to agriculture. 75

The strongest argument that can be made,however, is that past forestry experience hasdemonstrated that temperate forests can ab-sorb an unusual amount of stress without suf-fering long-term damage. For example, largeacreages in Europe as well as the United Statesthat today are densely forested were intenselyexploited as agricultural land in the past. Inmany instances, foresters can point to inten-sive management practices in European for-ests that have continued to provide high pro-ductivity of lumber for a hundred or moreyears. In counterpoint to these arguments,some environmentalists are worried about thefuture of Europe’s forests and point to increas-ingly high external costs in terms of pollutedwater and increasing incidence of disease epi-demics. 76 Also, insufficient data is available toindicate whether or not small but significantdrops in long-term productivity may have oc-curred because of such past practices.

A similar argument rages about high-yieldagriculture: yield levels in the Western coun-tries have climbed steadily over the past cen-tury, with temporary setbacks that have thusfar been dealt with by further adjusting the sys-tem, but environmentalists as well as manyagronomists are worried about increasing num-bers of pesticide-resistant insects and rising en-vironmental costs.

Pursuit of the evidence on both sides of thisargument may be worthwhile, but it is beyond

‘% Staebler, “The Forest and the Railroad, ” brochure pubIlshed by Weyerhaeuser Co , December 1975

“Goldsmith, “The Future of Tree Diseases, ” The Eco/ogist, No4[5, July-August 1979

the resources of this assessment. Also, the highlevel of emotional commitment that is at-tached to the alternative views of how farnature can be safely manipulated makes it un-likely that such a gathering of evidence willchange many minds. However, it is at /eastclear that a substantial increase in intensivemanagement must be accompanied by a thor-ough research program stressing examinationof such critical factors as nutrient cycling, therole of soil organic material vis-a-vis resistanceto tree disease, and other factors affecting sys-tem resiliency. The possibility that forest via-bility might be at excessive risk if hundreds ofmillions of acres in the United States wereplaced in intensive management should not beautomatically rejected, even though some de-gree of success in such management appar-ently has been achieved elsewhere.

Harvesting for the Residential Market

The rapidly expanding demand for woodfuel for residential use currently is satisfiedlargely by harvesting of wood by homeownersand by local entrepreneurs. The high price ofwood for residential use is an incentive forlarger scale loggers to enter the market, and atrend in this direction probably should be ex-pected in the future. The identity of the sup-plier may be an important component in deter-mining the environmental effects of satisfyinga high residential demand for wood fuel.

An expansion of the residential wood marketrepresents an opportunity for improved forestmanagement because of the value it places onlower quality wood, which in turn should stim-ulate an increase in thinning activities. Thepotential benefits are the same as those de-scribed for the increase in intensive manage-ment: an increase in productivity and timbervalue on the affected lands. This opportunityexists on woodlands ranging from smalI privatewoodlots to federally- and State-managed for-ests. The latter could use homeowners as a“free” work force to harvest selected trees, apractice that is already in operation in manyareas.

Unfortunately, a rising demand for woodwill bring with it a potential for significant


negative effects on woodlands. High prices forwood fuels are likely to stimulate an increasedincidence of illegal cutting of wood. “Timberrustling” apparently is frequently encounteredin stands of very high-quality timber such asredwood and walnut. More substantial cuttinginvolving multiple acres at a time must be ex-pected as wood demand grows and prices in-crease; remote areas, or areas where propertyboundaries are not well marked should be par-ticularly vulnerable. (Illegal mining of coalmay be an analogous and somewhat propheticexample. Although it takes considerable timeand effort to expose and mine a coal seam,coal poaching is not at all unusual in Appa-lachia, and some examples involving millionsof dollars worth of coal have been reported re-cently. Poaching timber is going to be a loteasier than poaching coal. ) In areas wherewood stoves are oversold or where forest prod-ucts companies occasionally enter the (lowerquality) wood market, temporary fuelwoodshortages or price escalation may further stim-ulate illegal cutting, especially among poorerhomeowners or those who cannot shift to analternative fuel for space heating.

The same forces that stimulate illegal cut-ting, especially where coupled with ignoranceof forest management, are likely to result in avariety of poor practices: improper harvestingtechniques leading to damage to adjacenttrees or to forest soils, incorrect tree selection,overcutting, etc.

The balance between beneficial and adverseeffects of a rising demand for wood as a resi-dential fuel is uncertain. Positive measuressuch as an increased availability of trainedforesters to provide assistance to small wood-Jot owners, better dissemination of informa-tion on woodlot management, and the organi-zation of efficent and competitive retail sup-pliers would help to limit adverse impacts. Onthe other hand, the combination of a sharplyincreased demand for wood coupled with a re-source base that is accessible and vulnerableto illegal or poorly managed cutting appears tobe virtually a guaranteed source of trouble.

Tree Plantations

The concept of an energy farm or plantationwhere trees are grown and harvested on shortrotations like agricultural crops is a logical ex-tension of current intensive single-aged man-agement of forests. In fact, the growing ofChristmas trees on plantations is a more inten-sively managed activity than an energy farm islikely to be, because the level of “manage-ment” — including pesticide and fertilizer use—will tend to increase with the unit value ofthe crop. In addition, a Christmas tree farmercannot tolerate relatively minor levels of pestor drought damage because his crop value isstrongly dependent on appearance, and thushe must apply pesticides or irrigation waterduring episodes that the energy “farmer” maybe able to ignore.

The land requirements, growing needs andharvesting techniques associated with energyfarms appear to be very similar to those of alarge agricultural enterprise growing perennialfood crops. Because of this resemblance, theenvironmental impacts are not treated in thissection. The chapter on agricultural biomassproduction should provide sufficient informa-tion about these impacts.

Controlling Negative Impacts

A common theme running through reviewsof silvicultural practices by the forestry es-tablishment—the wood products industry,schools of forestry, and the Forest Service— isthat these practices may have negative envi-ronmental consequences but that the conse-quences are readily controlled, that significantenvironmental damages today are the excep-tion rather than the rule, and that in thosecases where damages occur they are almost al-ways short lived, i.e., the forest quickly recov-ers and normal forest dynamics are restored.

The President’s Advisory Panel on Timberand the Environment reported that: 77

“Fred A Seaton, et al , Report of the Presjdenr’s AdvisoryPane/ on Timber and the Environment (Washington, D C Presi-dent’s Advisory Panel, April 1973)

67-968 0 - 80 - 4

42 . VOl.II-Energy From Biological Processes

A careful review . . . revealed that most of. . . (the environmental) damage caused by log-ging can be avoided or minimized. Many ofthe fears that have been expressed are un-founded, misleading, or exaggerated, oftendue to extrapolation from an isolated case toforest lands in general.

Properly executed timber harvesting andother silvicultural procedures need not resultin important long-term losses of soil nutrients,deterioration of the soil, nor cause other phys-ical environmental damage. Damage that hasoccurred resulted primarily from erosion asso-ciated with logging road construction and use,skidding of logs downhilI or across streams, orharvesting on steep slopes where removal ofvegetative cover caused slides. With updatedm e t h o d s , s u c h d i f f i c u l t i e s w i l l b e c o m e r a r e e x -ceptions. Such damage as has occurred will becorrected through natural processes as theforest grows back. (Emphasis added.)

The problem with statements such as theseis that they do not acknowledge the currentpaucity of information on actual logging prac-tices and effects. As noted in the introductionto this section, there are few credible as-sessments of forestry operations on a state-wide or regional basis, The few that have beenattempted are limited in scope; for instance, asurvey of practices in Maine in support of the208 program (sec. 208, Public Law 92-500/Federal Clean Water Act) is limited to record-ing the occurrence of gullying and the use ornonuse of simple erosion controls. 78

The limited information that is available seemsto indicate that the generally optimistic tone ofmost reviews of forestry impacts should beviewed with caution. An interesting conclusionof the Maine study was that “the area widemagnitude of the (erosion and sedimentation)problem is somewhere between the positionsespoused by the industry representatives onthe one hand, and groups and agencies con-cerned with maintaining environmental quali-ty on the other hand. 79 The survey found thatsimple — and supposedly standard — erosion

““A Survey of Erosion and Sedlmentatlon Problems Associ-ated With Logging In Maine, ” Land Use Regulation Commission,State of Maine, for the Maine Department of Environmental Pro-tection, May 1979

‘q I bid

control techniques such as using water barsand artificially seeding erodible areas “are(done) so infrequently that the role of theseconvenient erosion control devices in prevent-ing postlogging degradation of water quality isminimal at present. ” 80

Given the lack of knowledge of current for-est practices and the hints of environmentalproblems provided by the limited data, Con-gress should consider both the availability ofcontrol measures and the institutional climatefor putting these measures into practice beforeattempting to stimulate the increased use ofwood for energy.

Control Capability

The technical capability exists to control orreduce the negative effects of logging and,more generally, of all silvicultural activities.Table 13 presents a partial list of the controlmethods available to the forester. Some of themore critical are:

● Site selection/identification and possiblyavoidance of problem areas. — Becausemany of the environmental problems oflogging are strongly site-dependent, iden-tification of problem areas followed byrevision or abandonment of logging plansis a critical environmental control strat-egy. Avoidance of steeply sloped siteswith unstable soils is important for mini-mizing erosion. This often coincides witheconomic incentives, because the moreefficient heavy equipment cannot operateon steep slopes. Geologic surveying of thesite can often detect vulnerable soil/rock/slope formations, although this capabilityis not fully developed. Temporary avoid-ance of some areas, for example, duringrainy conditions, can avoid major prob-lems of soil compaction and destructionof soil structure. Other site conditionsthat must be treated with special care oravoided include nutrient-deficient andthin soils, and sites in immediate proximi-ty to lakes and streams. In the latter case,a buffer strip of smaller trees and shrubs

‘[)lbld


Table 13.–Control Methods

Mitiaative a Preventive

Surface protection:● Access: seeding, mulching, riprap, or mat on cut-and-fill slopes● Timber harvest: maintenance of vegetative cover; distribution of slash● Cultural treatments: seeding; planting; fertilizationFlow diversion and energy:● Access: berms above cut slopes; benches on cut slopes; checkdams

in ditches; drop structure at culvert ends; water bars on road surface;flow diversion from potential mass failures or at mid-slope

● Timber harvest: buffer strips; water bars on skid trails● Cultural practices: plowing, furrowing, beddingAccess design modification

System design and maintenance:● Access: minimize cuts and fills, roadway widths and slopes; control

road density● Timber harvest: minimize soil compaction from equipment operation;

use site-compatible log removal system; control harvested volumewithin a watershed; limit harvest on unstable slopes; shape openingsfor minimum esthetic impact, avoid cutting next to recreational activityareas

● Cultural treatments: minimize reentry disturbances; fire controlTiming:● Access: closure of temporary roads; limited access; closure during

adverse conditions● Timber harvest: limit operation during adverse climatic conditions; site

preparations during favorable conditions● Cultural treatments: intensity and number of thinnings

acontrol~ can be described as preventive’ or ‘‘mltlgal[ve” according to the mode of applications Preverrwe COfIfrO/S apply to the prelmplementatlon Phase Of an oPeratlon These controls involve stopping

or changing the actwlty before the sod-dlsturbmg actlwty has a chance fo occur Mmgalwe corwok include vegetatwe or chemical measures or physmal structures which alter the response of the soIl dls-turbmg achwty after it has occurred

SOURCE S/lvlcullureAcl/vll/es and NonpovMPo//ul/onAb aternent A Cost-E/(ecOvenes sAna/ys/s Procedure (Washington, D C Forest Serwce, USDA, November 1977)

along the shoreline may be sufficient toprovide shading and some sediment pro-tection to the body of water.

● Selection of harvesting system. — Controlof erosion, esthetic, and other impactscan be achieved by matching the harvest-ing system to the site conditions. For ex-ample, the type of forest regenerated atthe site can be controlled by the harvestsystem, because different degrees of dis-turbance favor different tree species.Clearcutting and residue removal favorspecies that need maximum disturbanceto grow (e. g., Douglas fir, jack and lodge-pole pine, paper birch, red alder, and cot-tonwood 81) and shelterwood cutting(which leaves residual trees in sufficientnumbers to shade new seedlings) favorsspecies (such as true firs, spruces, andmaples) that require light shade to thrive.The harvesting system may also be used toavoid some of the negative effects towhich the site is particularly vulnerable.Clearcutting, for example, would be in-dicated for old, decrepit stands in whichresidual trees would be likely to blowdown in the first severe storm followingharvest. Shelterwood cutting would be ap-propriate for stands important to scenicviews. A light selection cut may be the

“Smith, op clt

●

The

only harvesting allowed on soils subject tomass movement.Erosion/sediment control measures. — Al-though a certain amount of erosion fromsoil compaction and mineral soil exposureis inevitable in logging operations, it canbe reduced by using lighter equipment toavoid compaction, by using overhead oreven aerial (balloon or helicopter) log col-lection methods (although these methodsare economically feasible only for veryhigh-quality timber), by properly design-ing roads and minimizing their overalllength, by mulching the site, and by avariety of other methods. Furthermore,the erosion that cannot be controlled canbe prevented from damaging water quali-ty by using buffer strips, sediment traps,and other means.

Institutional Climate forEnvironmental Control

Despite the generally resilient nature of theforests and considerable scientific knowledgeof forest ecology and regeneration, forest en-vironments may be threatened in the future be-cause certain market forces or institutionalconstraints discourage adequate environmen-tal protection. These problems include a lackof expertise in the logging community, a vola-tile market that hinders adequate planning in

i—

44 . VOI. //—Energy From Biological Processes

certain segments of the industry, and a lack ofsufficient incentives to practice environmen-tally sound management.

1.

I

2.

Lack of expertise. –Although the majority ofnegative impacts may occur because offailure to follow well-recognized guidelines,others occur because of failures of judg-ment; forest environments are extremelycomplex and often require expert judgmentabout site conditions to select correctharvesting strategies. Some important im-pacts can be avoided only if the logger canrecognize subtle clues to the existence ofvulnerable conditions. For example, manyunstable soil conditions may be recogniz-able only to a soils expert. This type of ex-pertise usually is not available to the smalloperator, except possibly where local andState governments offer preoperation in-spections and guidance (e. g., in Oregon].This poses a special problem if the residen-tial market for wood expands considerably,because small operators may be expected tosatisfy much of this new demand.Insufficient time for proper planning. – I ncurrent mill operations in Maine, many “millmanagers commonly call on short notice fora certain volume of a given type of productfrom the firms’ logging division . . . A com-mon result is that a considerable amount ofthe haul road construction is done on shortnotice . . . (without) . . . proper planning andcorrectly installed and maintained drainagestructures. ”82 It is not clear that problems ofthis nature will be as severe for wood har-vesting for energy, because demand for thewood as a feedstock may be more uniformand predictable than the demand for tradi-tional forest products (it also is not certainthat the Maine experience is widely ap-plicable). Nonetheless, most operations willcombine lumber and energy feedstock oper-ations— removing the high-quality wood,and then clearing to harvest the remainderof the biomass for energy users. To the ex-tent that the timing of these operations de-pends on the demand for the (higher value)lumber, this problem may remain.

‘*”A Survey of Erosion and Sedimentation Problems Associ-ated With Logging in Maine, ” op cit

3. Lack of incentive. —These are four reasonswhy a logger would pay strict attention tominimizing environmental damages:● personal environmental or esthetic ideal-

ism,● economic incentive,● regulatory controls, or● public relations

Idealism–and the role of education in fos-tering it—should not be ignored in predictingimpacts and attempting to mitigate them. Thestrengthening of existing programs to educatepotential wood harvesters about the adverseenvironmental effects of careless harvestingmay be useful in tapping the vein of environ-mental idealism in the United States. Idealismis clearly insufficient to assure environmentalprotection, however, and more selfish incen-tives are needed.

The long time period needed to recoup thebenefits of protective measures and the tend-ency of many of the benefits to accrue to adja-cent landowners or the general public reducethe economic incentive of environmental pro-tection. The shorter rotation periods that maybe used for obtaining wood for energy may en-hance the economic incentive, especially forowners of large tracts of land (because they arethe “adjacent landowners”). Also, some “bestmanagement” measures do yield immediatereturns to loggers, for example, measures thatminimize road length or that prevent roadbedsfrom washing away.

Finally, to the extent that poor managementof logging does long-term physical and estheticdamage to the forest, the value of forestedland as a recreational and esthetic asset offersa strong incentive to the landowner to insist onsound practices. This incentive will be partic-ularly strong in areas that have seen recent in-creases in market value because of their envi-ronmental value. This incentive will be effec-tive, however, only where the landowner main-tains close supervisory control over the logger.

Regulatory control of wood harvesting oper-ations in the United States is very uneven. Al-though the Forest Service can exert considera-ble control of logging operations on Federal


lands, logging on private lands is largely un-controlled or very loosely controlled.

The 1976 National Forest Management Actincludes requirements that federally ownedtimber “be harvested only where soil or . . .water conditions will not be irreversibly dam-aged, that harvests be on a sustained yield ba-sis, that silvicultural prescriptions be written toensure that stands of trees will generally not beharvested until they are mature (although thin-ning and other stand improvement work is per-mitted), that clearcutting meet certain stand-ards, and that land management plans be writ-ten with public participation. ”83 The MultipleUse Act of 1960, by defining environmentallyoriented uses (such as wildlife protection) aslegislated uses of the national forests, requiresmanagement practices in these forests to con-sider environmental protection as a direct re-quirement. In response to these mandates, theForest Service enforces strict standards forharvesting lumber on Federal lands.

The degree of control exerted on non-Fed-eral forests — especially privately owned for-ests — is noticeably weaker. Water quality im-pacts from wood harvesting theoreticallyshould be regulated through the developmentof nonpoint source control plans under section208 of the Federal Water Pollution ControlAct. As discussed in volume 1, however, im-plementation of section 208 generally hasbeen disappointingly slow, and the eventualeffectiveness of the 208 plans is highly uncer-tain. Also, few States have comprehensive for-est practices legislation or the manpower toenforce such legislation. A major problem fac-ing States wishing to control forest practices isthe complexity and site-specific nature of theenvironmental impacts, forcing the difficultchoice of using either a substantial force ofhighly trained foresters enforcing loosely writ-ten performance guidelines or else a more(economically) manageable agency enforcingrigid — and perhaps impractical — rules. This

n IE ~ “lronmenta/ Readjne55 D o c u m e n t , wood CommerC/a /;~a-

tlon, op clt “

problem is discussed with insight in Brown1976: 84

The difficulty is that rules specific to thewide variety of situations encountered wouldoften be difficult to write and cumbersome toenforce for a great many problem areas, par-ticularly within the context of our presentstate of technology. Field personnel recognizethe dilemma of rules so vaguely written thatthey provide no control versus rules so spe-cific that they prohibit flexibility and preventforest practice officers and operators from ad-justing methods to meet complex or highlyvarying situations. Given the option, most fieldpeople prefer to have flexibility at the risk oflosing some control.

Finally, many State forestry agencies haveconcentrated their attention on forest fireprevention and control and not on forest man-agement. Hence, the experience, interest, andexpertise of present State forestry personnelmay not provide a good base on which to builda strong management-oriented program.

The public’s increasing awareness of envi-ronmental problems and willingness to actmay serve as a strong incentive for the largerforest products companies to consider thepublic relations implications of their decisions.Companies like Weyerhaeuser spend largesums of money explaining their activities insophisticated advertisements; presumably, thisawareness of the importance of public approval affects their decision making and operations.

Environmental Effects—Summary

wood as an energy feedstock

Potential

The use ofholds considerable potential for reducing theadverse impacts associated with fossil fueluse. It also offers the potential for some impor-tant environmental benefits to forests, includ-ing:

● decreased logging pressures on some envi-ronmentalIy valuable forests;

‘“Brown, et al , Meet/rig Water Qua//ty Objecr/~es Through the

Oregon Fores t Pract/ces Act, (O regon S ta te Depa r tmen t o fForestry, 1976)


●

●

improved management of forests thathave been mismanaged in the past, withconsequent improvements in productivi-ty, esthetics, and other values; andreduced incidence of forest fires.

There is considerable uncertainty, however,about the extent to which a significant in-crease in the use of wood for energy will ac-tually result in these benefits and avoid thenegative impacts that could also accompanysuch an increase. There are important econom-ic incentives for good management, includingincreased production of high-value timber andavoidance of losses in land values. There are anumber of factors, on the other hand, thatmust be interpreted as warning signals:

1.

2.

3.

4.

Environmental regulation of forestry oper-ations, especially on private lands, gen-eralIy is weak or nonexistent.Some of the existing economic incentivesmay induce cutting of vulnerable lands orneglect of best management practices.Important gaps in the knowledge of theeffects of intensive silvicultural activity—for example, of the nutrient and organicmatter changes in the soil caused bywhole-tree logging — may deter environ-mentally sound choices from being made.The complexity and site-specificity of theharvesting choices that “must be mademay complicate adoption of environ men-

R&D

The primary R&D needs in the area of woodsupplies from forests fall into the categories ofharvesting technology, growth potential, en-vironmental impacts, and surveys. Traditionalharvesting technologies are geared toward re-moving large pieces of wood in a way that isappropriate for lumber or paper pulp produc-tion. The wood that can be harvested for fuel,however, is considerably more varied, involv-ing brush, rough and rotten timber, and thesmaller pieces associated with logging resi-dues. Although the whole-tree chip methodseems to work well on relatively flat land,

tally sound harvesting plans, especially bysmalI operators.

If careful environmental management is notpracticed, the result might be:

●

●

●

●

●

increased erosion of forest soils and con-sequent degradation of water quality,significant losses in esthetic and recrea-tional values in forested areas,possible long-term drop in forest produc-tivity,decline in forested area, andreduction of forest ecosystem diversityand loss of valued ecosystems and theirwiIdlife.

Because the quality of forest managementand the capacity for environmental regulationcurrently span the entire range from very low(or nonexistent) to high, the expected result ofa “business as usual” approach to wood-for-energy environmental management would un-doubtedly be a complex mix of the above im-pacts and benefits —with the marketplace de-termining the balance between positive andnegative effects. Government action — includ-ing improved programs for local managementassistance, increased research on the effects ofintensive management, and increased incen-tives (economic or regulatory) for good man-agement — may be capable of shifting this bal-ance more towards the positive.

Needs

there is a need to develop low-cost techniquesand equipment for harvesting smaller pieces ofwood and brush on more varied terrains and atgreater distances from roads.

Most research into forest growth potential isaimed at producing large straight trees suit-able for the traditional forest products in-dustry. Although some of this is research ap-plicable to the production of wood for energy,the conditions and techniques for enhancingcommercial timber growth are not the same asthose for enhancing total biomass growth. As

Ch. 2—Forestry . 47

an example, thinning of tree stands reduces thetotal leaf surface and, with it, the amount ofsunlight that is being captured by plants. Thisreduces the total biomass growth on the stand,although it tends to increase the growth ofcommercial timber. If a strong wood energymarket develops, the ideal forest compositioncould involve a mix of tree types, sizes, andqualities. Various strategies for achieving in-tegrated and economical energy-commercialtimber operations need to be investigated.Tree hybrids, for example, should be devel-oped with both commercial timber productionand biomass production as dual goals.

There are a number of uncertainties regard-ing the environmental impacts of increasedlogging for energy. The nutrient balance inforests, as noted, needs to be better under-stood in order to better define the types andquantities of wood that can be removed with-out depleting the soil’s nutrients. The effectsof high biomass removal on soil carbon con-tent and any subsequent long-term impacts onproductivity or on forest viability require con-siderable research. The relationship betweenthe diversity of tree and understory species in aforest and the forest’s resilience to environ-mental stresses must be better understood be-fore highly intensive management is allowedto expand to a majority of the commercial for-est acreage. Alternative harvesting techniquessuch as strip cutting (or the cutting of strips oftrees through the forest rather than clearcut-ting a large area) should be pursued in order to

provide a repertoire of techniques that can beused where soil erosion may be a problem,such as in steeper slope terrains. Harvestingtechniques that decrease the degree of soilcompaction should also be developed. Further-more, the entire forest ecosystem needs to bebetter understood if the environmental im-pacts of various types of forest activities are tobe appropriately managed.

The national forest survey is primarily in-tended as a survey of commercial timber. Theassumptions as to what is commercial shouldbe separated from the survey of the biomassinventory and growth potential, in order tohave an accurate assessment of the quantitiesavailable for all uses. The survey should in-corporate noncommercial forest lands whichare classified that way because of low growthpotential.

A thorough assessment of the energy poten-tial of the forests should also include a qualita-tive assessment of the conditions of the stock-ing on forestlands and the silvicultural activ-ities (e. g., stand improvements) that could becarried out to increase the yield. The surveydata should include environmental conditionssuch as soil types, rainfall, and other parame-ters. Finally, the size of tract is an importantfactor affecting the availability of the wood.Consequently, the farm and miscellaneous for-est landowner classifications in forest surveysshould be subdivided according to tract sizeand ownership.

Chapter 3

AGRICULTURE

Chapter 3.—AGRICULTURE

PageIntroduction . . * . . * * . . . * * * . . . . . . . . . . . . . . . 51Plant Growth, Crop Yields, and Crop

Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51Theoretical Maximum Yield. . . . . . . . . . . . . . 51Historical Yield Trends. ., ., . . . . . . . . . . . . . 53Record Yields . . . . . . . . . . . . . . . . . . . . . . . . . 54Future Yields . . . . . . . . . . . . . . . . . . . . . . . . . 54

land Availability . . . . . . . . . . . . . . . . . . . . . . . . . 54Types of Crops . . . . . . . . . . . . . . . . . . . . . . . . . . 60Current Agricultural Practices and Energy and

Economic Costs. . . . . . . . . . . . . . . . . . . . . . . . . 61Energy Potential From Conventional Crops . . . . . . 64Energy Potential From Crop Residues . . . . . . . . . . 67Environmental impacts of Agricultural Biomass

Production .0.,... . . . . . . . . ● . . . . . . . ..*** 70Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 70The Environmental lmpacts of American

Agriculture. .,...... . . . . . . . . . . . . . . . . 701973-74: A Case Study in Increased

Cropland Use . . . . . . . . . . . . . . . . . . . . . . . 75Potential impacts of Production of Biomass

for Energy Feedstocks . . . . . . . . . . . . . . . . 76Environmental lmpacts of Harvesting Agricultural

Residues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86R&D Needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

TABLESPage

14. Photosynthetic Efficiency Summary . . . . . . 5215. Factors Limiting Plant Growth . . . . . . . . . . . 5216. Cropland Use in 1977 . . . . . . . . . . . . . . . . . . 5617. Potential Cropland. . . . . . . . . . . . . . . . . . . . 5818. Cropland Balance Sheet . . . . . . . . . . . . . . . . 5819. Cropland Available for Biomass Production 5920. Annual Production and Disposition of

Corn for Grain in the United States, 1966-75. 6021. Annual Production and Disposition of

Wheat in the United States, 1966-75. . . . . . . 6022. Estimated per Acre Production Costs in

lndiana, 1979 . . . . . . . . . . . . . . . . . . . . . . . . 62

23. Energy lnputs for Various Crops . . . . . . . . . . 6224. Energy inputs and Outputs for Corn in U.S.

Corn Belt . . . . . . . . . . . . . . . . . . . . . . . . . . . 6225. Estimated Costs of Producing Grass

Herbage at Three Yield Levels . . . . . . . . . . . 6326. Total Crop Residues in the United States

for 10 Major Crops. . . . . . . . . . . . . . . . . . . 6527. Total Usable Crop Residue by Crop . . . . . . . 6828. State Average Estimated Usable Group

Residue Quantities and Costs. . . . . . . . . . . . 6929. Environmental impacts of Agriculture, . . . . 7030. 1977 Cropland and Potential Cropland

Erosion Potential . . . . . . . . . . . . . . . . . . . . . 7731. Mean National Erosion Rates by

Capability Class and Subclass . . . . . . . . . . . 7732. Agricultural Production Practices That

Reduce Environmental Impacts . . . . . . . . . . 7933. Enviromental Pollution Effects of

Agricultural Conservation Practices . . . . . . . 8134. Ecological Effects of Agricultural

Conservation Practices. . . . . . . . . . . . . . . . . 8335. Environmental impacts of Plant Residue

Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

FIGURES

Page7. U.S. Average Corn Yield . . . . . . . . . . . . . . . . 538. U.S. Average Crop Output . . . . . . . . . . . . . . 549. Farm Production Regions of the

United States . . . . . . . . . . . . . . . . . . . . . . . . 5510. Cropland as a Percentage of Total Land

Area by Farm Production Region ..,...... 5611. Present Use of Land With High and

Medium Potential for Conversion toCropland by Farm Production Region . . . . . 57

12, Net Displacement of Premium Fuel perAcre of New Cropland Brought IntoProduction . . . . . . . . . . . . . . . . . . . . . . . . . . 66

Chapter 3

AGRICULTURE

Introduction

Agriculture was originally developed to pro-vide a reliable source of food. Later feed wasincluded in farm production and animals pro-vided large parts of the population’s energyneeds. Although animals are rarely used for en-ergy on U.S. farms today, agriculture has ex-panded to include the production of nonfoodcommodities, including cotton, tobacco, paintsolvents, specialty chemicals, and various in-dustrial oils. In 1977, these nonfood products

accounted for over 13 percent of total farmproduction.

Many of the food and feed crops as well asfarming byproducts can also be used to pro-duce fuels or be combusted directly. In thischapter, the technical aspects of conventionalagriculture are considered, leading to esti-mates of its potential for supplying energy.

Plant Growth, Crop Yields, and Crop Production

Harvested yields of many crops have in-creased dramatically over the past 30 years asa result of the development of genetically im-proved crop strains, as well as increased use offertilizers and irrigation. Also, increased ap-plication of chemicals for control of insects,diseases, and weeds; further mechanization sothat operations can be timely; improved tillageand harvesting operations; and other forms ofimproved management have also helped toraise yields.

Photosynthesis is the basic process provid-ing energy for plant growth. Solar energy is ab-sorbed by the green chlorophyll in the leaf andused to combine carbon dioxide (CO2) from theair with water from the soil into stored chemi-cal energy in the form of glucose. Glucose isused in the formation of compounds like aden-osine triphosphate which provides energy forthe synthesis of the various materials neededin the plant such as cellulose and Iignins forcell walls and the structural parts of the plantand various amino acids (protein components).Glucose is respired to provide energy for pro-duction of other compounds, plant growth,and absorption of nutrients from the soil. Asthe plant matures, carbohydrates are stored inthe seed to provide energy for the growth ofnew plants.

Sixteen nutrients are essential for plantgrowth and two or three more may increaseyields but are not essential for the plant tocomplete its growth cycle. Of the 16, nitrogen,phosphorus, and potassium are the 3 main nu-trients needed in large quantities to supple-ment the soil supply in order to obtain highcrop yields. Calcium and magnesium are ap-plied where needed as finely ground lime-stone. Sulfur is added as elemental sulfur or assulfates when needed. Carbon, hydrogen, andoxygen come from the air and water and the re-maining seven are used in extremely smallamounts and are absorbed from the soil. All ofthese nutrients play essential roles in thegrowth processes within the plant.

Theoretical Maximum Yield

The theoretical maximum photosynthetic ef-ficiency can be estimated as follows:

Ten percent of the light striking a leaf isreflected. Only 43 percent of the light thatpenetrates the leaf is of a proper energy tostimulate the chlorophyll. The basic chemicalreactions (10 photon process) which use stimu-lated (“excited”) chlorophyll to convert CO2

and water to glucose have an overall efficien-

51

52 ● Vol. I/—Energy From Biological Processes

cy of 22.6 percent. The net result of these fac-tors is, in theory, a maximum photosyntheticefficiency of about 9 percent. A summary ofthe various cases of photosynthetic efficiencyis presented in table 14.

Table 14.–Photosynthotic Efficiency Summary

Average PSEa duringgrowth cycle

(percent)

Maximum theoretical . . . . . . . . . . . . . . . . . . .Highest laboratory short-term PSEa . . . . . . . .Laboratory single leaves, high CO2 or

low O2, C-3 plants, c 7% full sunlight. . . . .Same as above, for C-4 plants. . . . . . . . . . . . .Corn canopy, single day, no respiration . . . . .Record U.S. corn (345 bu of grain/acre,

120-day crop) . . . . . . . . . . . . . . . . . . . . .Record sugar cane (Texas) . . . . . . . . . . .Record Napier grass (El Salvador) ... . . . . . .Record U.S. State average for corn (128

bu/acre, Illinois, 1979). . . . . . . . . . . . . . . .Record U.S. average for corn (108

bu/acre, 1979 . . . . . . . . . . . . . . . . . . . . .

8.7- 9

6.34.45,0

3.03.02.5

1.1

0.9

apSE.pholo5ynthetlc efficiency

SOURCE OftIce of Technology Assessment

An efficiency approaching the theoreticalmaximum appears to have been achieved for ashort time under laboratory conditions usingan alga or single-celled water plant. Theseresults are controversial, however, and in prac-tice there are always several other factors thatlimit the efficiency of photosynthesis, and thetransformation of glucose into plant material.The most important of these factors, many ofwhich are interdependent, are listed in table15. For example, light saturation can be influ-enced by the CO2 concentration, which is af-fected by other things. The key factors arelight saturation, soil productivity (its ability tohold water, supply oxygen, release nutrients,and allow easy root development), weather(amount and timing of rainfall, absence of se-vere storms, length of growing season, temper-ature and insolation during the growing sea-son), and plant type (leaf canopy structure,longevity of the photosynthetic system, sensi-tivity to various environmental stresses, etc.).

‘V C Coedheer and J W Klelnen Hammans, Nature, VOI 256,p 333, 1975

Table 15.–Factors Limiting Plant Growth

●

●

●

●

●

●

●

●

●

●

●

●

●

●

●

●

●

●

●

●

�

Water availability,Light saturation–a tendency for the photosynthetic efficiency to dropas the incident light intensity increases above values as low as about10% of peak solar radiation intensity.Ambient temperature, especially wide fluctuations from ideal.Mismatch between plant growth cycle and annual weather cycle.Length of photoperiod (hours of significant illumination per day).Plant respiration,Leaf area index–completeness of coverage of illuminated area byleaves or other photosensitive surfaces.Availability of primary nutrients–especially nitrogen, phosphorus, andpotassium,Availability of trace chemicals necessary for growth.Physical characteristics of growth medium.Acidity of growth medium.Aging of photosynthetically active parts of plants.Wind speed.Exposure to heavy rain or hail or icing conditions.Plant diseases and plant pests.Changes in light, absorption by leaves due to accumulations of waterfilm, dirt, or other absorbers or reflectors on surfaces of leaves or anyglazing cover.Nonuniformity of maturity of plants in crop.Toxic chemicals in growth medium, air, or water, such as pollutantsreleased by human activity.Availability of CO2.Adjustment to rapid fluctuations in insolation or other environmentalvariables —i. e., ‘‘inertia’ of plant response to changing conditions.

SOURCE. Off Ice of Technology Assessment

In an untended system, the environmentalfactors are left to chance. Consequently, inany given year, some areas of the country willexperience a favorable combination of factors,resulting in more plant growth, while in otherareas environmental factors will be unfavor-able, resulting in less plant growth. The exactplaces where the growth is favorable or unfa-vorable will also change from year to year, aswill the exact growth at the most favorablearea in each year. In the absence of long-rangeenvironmental changes, however, such asweather changes or soil deterioration, the aver-age growth over a very large area and for manyyears will remain relatively constant.

Some of the environmental factors can becontrolled, while others cannot within thepresent state of knowledge. Managing a plantand soil system consists of artificially main-taining some of the environmental factors,such as nutrients or water, at a more favorablelevel than would occur naturally. The many re-maining factors, however, are still left tochance. Furthermore, there is a limit to how

Ch. 3—Agriculture . 53

much plant growth (or other characteristicssuch as grain yield) can be influenced bychanges in given environmental factors. Oncesome of the factors have been optimized forplant growth (or, e.g., grain yield) the plant’sperformance will not be improved by furtherchanges of these factors. Too much water orfertilizer, for example, could actually inhibitgrowth rather than increase it.

Because plants vary in their sensitivity togrowth-limiting factors yields can be improvedby selecting or breeding for plants that arerelatively insensitive to environmental factorsthat cannot be controlled and/or that respondwell to factors that can.

A dramatic example of the success of breed-ing and management is corn. The history ofU.S. average corn yields from 1948-78 is shownin figure 7. While the national average yieldshave not been analyzed in detail, Duvick hasanalyzed the changes in yields from hybridsgrown in various Midwestern locations.2 H e

Figure 7.—U.S. Average Corn Yield

A. .

1940 1950 1960 1970 1980 1990 2000

YearS O U R C E . ~gr~cultura~ S~at~stKs (Washington, D C: U S Department of Agri-

culture. 1978)

‘D N Duvick, Mayd~ca XXII, p 187,1977

concluded that 60 percent of the increase onthese plots was due to genetic improvementswhile 40 percent was attributed to improvedmanagement. The management tends to re-duce the environmental stresses, while hybridswere developed that are less sensitive to ad-verse environmental factors and more respon-sive to the factors that can be controlled (e. g.,fertilizers, weed control, insect control, etc.).

Historical Yield Trends

Past yield trends can be used as a guide forprojection of future yields. A period of at least15 years should be considered because ofweather fluctuations since the desired value isthe yield trend if weather remained constant. Aperiod of dry years from 1973 to 1976 tendedto exert some influence on data variability.During the 1948-78 period, corn yields in-creased an average of 2 bu/acre-yr giving a1978 yield just over 100 bu/acre. Similarlysoybean yields showed an increase of about0.4 bu/acre-yr and a 1978 yield of 29.2 bu/acre.National wheat yields are somewhat morevariable since wheat is grown primarily inareas that are more affected by drought thanis corn. Nonetheless, the yield trend indicatesan increase of 0.5 bu/acre-yr and a 1978 aver-age yield of 31.6 bu/acre. The U.S. Departmentof Agriculture (USDA) has calculated a sum-mary of all crop yields per acre using a relativevalue of 100 for the 1967 yield. The trend forincrease over this period was 1.4 units per year,but the uncertainty in this number is large (seefigure 8).

Yield increases in the future as in the pastwill come from a combination of improvedcrop varieties and improved cultural practices.Since current fertilization practices havereached near optimum rates, increases in yielddue to increases in fertilization rates will beless than for the past 20 years. As yield poten-tials of varieties are increased, however, in-creased rates of fertilization will be needed tokeep pace with the increased yields. Sinceyield increases result from a combination ofpractices, it is difficult to attribute yield in-creases to any one practice.

54 . Vol. II—Energy From Biological processes

II

Figure 8.—U.S. Average Crop Output

120

110

100

90

o 1965 1970 1975 1980

Year

SOURCE: Agricultural Statistics (Washington, D. C.: U.S. Department of Agri-culture, 1978).

Record Yields

Projection of yields and determination ofwhere yield increases will diminish may bejudged on the basis of yields that have beenobtained. For example, the average U.S. cornyield has reached over 100 bu/acre, but the

average yield in Illinois in 1979 was 128bu/acre and in Iowa in 1979 it was 127 bu/acre. * If county averages within a State are ex-amined, average yields are found to approach140 bu/acre. If individual farms of 500 acres ofcorn are considered, yields of 175 bu/acre haveoccurred. And on selected areas of 2 or 3 acresyields of 345 bu/acre have been noted.

Future Yields

Over the past 30 years corn yields have in-creased at an average rate of about 2 bu/acre-yr. One would not expect this rate of increaseto rise, and it may decline. Therefore, in pro-jecting corn yields in the year 2000, 140 bu/acre would be optimistic. A less optimistic pro-jection, based on annual average yields in-creasing at one-half the rate that they have inthe recent past, is 120 bu/acre in 2000. A studyby the National Defense University in 1978gave a projected corn yield for 2000 of 132bu/acre.

Future increases in the yields of other cropsare also expected, but each crop together withthe cropland on which it will be grown must beconsidered separately. Dramatic increases,such as a doubling in crop yields by 2000, how-ever, are not expected for conventional crops.

*The weather in 1979 was ideal for corn growing

Land Availability

Cropland is land used for the production ofadapted crops for harvest, alone or in a rota-tion with grasses and legumes, and includesrow crops (e. g., corn), small grain crops (e. g.,wheat), hay crops, nursery crops, orchardcrops, and other similar specialty crops. Crop-Iand is generally categorized into the agricul-tural production regions shown in figure 9.

Of the U.S. total land area of 2.3 billionacres, 413 million or 467 million acres are cur-rently classified as cropland depending onwhether one uses the Soil Conservation Service(SCS) or the other USDA classification system.

The second is a broader classification that in-cludes some land not currently cropped that isrotated into cropland but may now be in pas-ture or other use. The percentage of the totalland area of each State that is cropland isshown in figure 10 and the cropland used in1977 is shown in table 16. Both of these arebased on the more restrictive SCS classifica-tion of cropland.

Cropland, however, is not a static category.The location of cropland may shift eventhough the quantity of cropland remains rela-

Ch. 3—Agriculture . 55

Figure 9.— Farm Production Regions of the United States

S O U R C E S O i I Conservation Service, U S Department of Agriculture

tively constant. Over time there are both addi-tions and deletions to the cropland inventory.

The quality of land and cropping systemsmay shift as well. One such change has beenthe increase in irrigation, in areas like theTexas high plains, from 1.2 million acres in1948 to 6.4 million acres in 1976. This repre-sents both a trend in improving the productivi-ty of existing cropland and a trend towardsopening new, marginal land that is only pro-ductive and economic with irrigation. To someextent, the United States has been replacingrainfed arable land that is lost to agriculturewith irrigated land in dry areas. This trend,however, is likely to change due to increasingenergy costs and depletion of some Westernground water.

Over time, the content of a land inventorycan be influenced by the way that a given sta-

tistic is enumerated. For example, up to 1964the agricultural census was personally enu-merated and in 1969 it was done by mail. Ac-cording to the broader USDA classification,cropland pasture increased by over 30 millionacres between these surveys, and the suspicionis that the farmer applied a less strict defini-tion to cropland pasture which resulted in theinclusion of 30 million acres of pasturelandand grassland into the cropland pasture cate-gory even though the actual usage had notchanged.

One strong influence on the land inventoryhas been the Government’s agricultural pro-grams. The land retirement programs of the1960’s reduced planted cropland and had thenet effect of moving less productive land outof crop production temporarily or even perma-nently in the case of very low-quality land. As


Figure 10.—Cropland as a Percentage of Total Land Area by Farm Production Region

Table 16.-Cropland Use in 1977 (thousand acres)

OccasionallyRow crops Close-grown crops Rotation hay improved hayland

Region Irrigated Nonirrigated Irrigated Nonirrigated Irrigated Nonirrigated Irrigated Non irrigatedNortheast ., . . . . . . . . . . . . 254 6,771 1,033 9 3,339 5 3,286Appalachian. ... ... . . . . 349 14,445 33 543 7 1,248 10 3,151Southeast . . . . . . . . . . . . . . 1,681 12,108 23 342 24 74 8 604Delta States. . . . . . . . . . . . . 2,294 15,358 1,489 285 170 299 0 397Corn Belt. . . . . . . . . . . . . . 1,035 70,291 31 7,228 8 5,987 4 4,116Lake States. . . . . . . . . . . . . 799 20,930 80 9,140 36 7,753 2,802Northern Plains ... . . . . . . 8,641 18,062 920 40,007 690 5,387 325 3,885Southern Plains . . . . . . . . . . 5,935 13,908 2,354 15,784 33 802 286 725Mountain. ... . . . . 4,117 962 3,316 14,021 2,269 380 3,821 1,276Pacific. . . . . . . ., ., . . . . . 4,477 132 2,757 5,556 1,124 502 1,092 295

Total a . ... . . 29,750 173,493 11,025 93,865 4,398 25,818 5,559 20,839

Native hay Orchards, etc. All cropland

Region Irrigated Nonirrigated Summer fallow Irrigated Nonirrigated Other Irrigated Nonirrigated

Northeast . . . . . . . . . . . . . 0 789 24 84 508 493 372 16,534A p p a l a c h i a n , . . . . . . 0 86 112 0 149 690 406 20,339Southeast . . . . . . . . . . . . . . 0 0 54 699 661 1,324 2,449 15,053Delta States. . . . . . . . . ., 0 84 179 6 136 489 3,979 17,207Corn Belt. . . . . . . . . . . . . . . 0 117 749 22 72 876 1,115 88,739Lake States. . . . . . . . . . . . 0 719 466 42 291 1,073 972 43,167Northern Plains . . . . . . . . . . 33 2,493 13,825 0 15 268 10,790 83,733Southern Plains . . . . . . . . . . 0 405 1,061 33 153 755 9,011 33,223Mountain. . . . . . . . . . . . . . . 1,460 320 9,449 0 641 17,208 26,111Pacific. . . . . . . . . . . . . . . . . 261 208 4,082 2,242 183 277 12,261 10,927

Total a. . . . . . . . . . . . . . . . 1,754 5,221 28,319 3,295 2,225 6,806 57,647 355,520

aAlsO Includm Canbbe.an and Hawall

SOURCE SoIl Conservation Serwce, U S Oeparlment of Agriculture

Ch. 3—Agr icul ture ● 5 7

programs were terminated in the early 1970’s,some of these acres came back into crop pro-duction.

USDA’S SCS surveyed non-Federal lands in1977 and identified the land that potentiallycould become cropland. 3 The survey classifiedpotential croplands according to whether theland was judged to have a high, medium, low,or zero potential for conversion. Figure 11summarizes the quantities of land that have a

Figure 11 .—Present Use of Land With High andMedium

N o r t h e a s t

L a k e

S t a t e s

C o r n B e l t

N o r t h e r n

P l a i n s

A p p a l a c h i a n

S o u t h e a s t

D e l t a S t a t e s

S o u t h e r n

P l a i n s

M o u n t a i n

P a c i f i c

Potential for Conversion to Croplandby Farm Production Region

Q 5 10 15 20( m i l l i o n s o f a c r e s )

F o r e s t

P a s t u r e a n d n a t i v e l a n d s

R a n g e l a n d

O t h e r

SOURCE: 1977 National ErosIon Inventory Preliminary Estimates, Soil Conser.vation Service, U.S. Department of Agriculture, Apr!l 1979.

319775011 Conservation Service National Erosion Inventory Es-timate (Washington, D C SoIl Conservation Service, U S De-partment of Agriculture, December 1978)

high or medium potential for conversion tocropland. Of the total potential cropland in1977, 40 million acres have a high probabilityto be converted and another 95 million acresare classified as having medium probability. *

The breakdown of the potential croplandinto high and medium potential for conversionis an attempt to define a crude cost curve forthe availability of new cropland. It was judgedby SCS that the land with a high potential willenter agriculture as a matter of course, if pricerelationships are somewhat more favorable tothe farmer than the 1976 prices on which thesurvey was based. The medium potential, how-ever, is a category involving lands with a widevariety of problems but which cannot be cate-gorically excluded from conversion if farm-land prices increase sufficiently.

The SCS survey, however, does not include aquantitative measure of the price increasesnecessary to bring potential cropland undercultivation. A conservative approach would beto assume that only land with high potentialcan be included in the cropland base withoutexcessive inflation in food prices above thatwhich would occur normally due to increaseddemand for food. A more optimistic approachwould be to include those types of medium-po-tential land that probably will be consideredhigh potential in the future, as increased de-mand for food raises cropland prices. This isthe approach that was taken.

Two major factors, mentioned above, thataffect crop productivity are water availabilityand soil quality. Therefore, land was includedfrom the medium-potential category that hasgreater than 28 inches of annual rainfall andpotentially has good productivity (capabilityclasses 1 and 2 of the eight agricultural landcapability classes). These land types are themost Iikely to be brought into cultivation if de-mand exceeds the high-potential category.

With these assumptions, the potential crop-I and is shown in table 17. This together with ex-isting cropland provides the cropland base, to-

*As of November 1979, these numbers were 36 million and 91million acres, respectively

67-968 o - 80 - 5

58 ● Vol. n-Energy From Biological Processes

Table 17.-Potential Cropland (thousand acres)

Source

Region Forest Pasture Rangeland Other

High potential with over 28 inches rainfallLake States. , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 868 1,206 22 443Delta . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1,482 1,781 0 129Corn Belt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 664 4,451 23 368Northeast ..,..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268 562 0 371Southeast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2,111 2,926 133 151Appalachian . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1,981 2,974 0 183

7,374 13,900 178 1,645Total of forest pasture, and rangeland: 21,452

Medium potential, class l&2 land only with over 28 inches rainfallLake States. .... . ., . . . . .. . . . . . . . . . . . . . 1,463 723 0 315Delta . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 986 1,423 0Corn Belt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 974 2,590 0 356Northeast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 656 433 0 306Southeast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2,082 1,256 0 17Appalachian . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2,012 1,157 0 119

8,137 7,582 0 1,113Total of forest, pasture, and rangeland: 15,755

High potential with less than 28 inches rainfallArid regions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312 5,503 9,549

Total of forest, pasture, and rangeland: 15,364—

SOURCE: Otto C. Doermg lll, “Cropland Availability for Biomass Production,” contractor report to OTA, August 1979.

taling 520 million acres. (This is based on thebroader cropland classification as used inUSDA’s Agricultural Statistics and all Econom-ics, Statistics, and Cooperatives Service pub-libations) Although it is impossible to predictexactly how the cropland base will develop inthe future, one plausible scenario is shown intable 18 based on continuation of past trendsto 1984 and on USDA’s National InterregionalAgricultural Projections System (NIRAP) for1990 and 2000.4

‘L Quance, A Smith, K. Liu, and L. Yao-Ch~ “AdjustmentPo-tentials m US Agriculture,” Vol. I–hiational lnterregional Pro-jections System (Washington, DC,: Economics, Statistics, andCooperatives Service, US Department of Agriculture, May1979)

By examining the detailed demand forvari-ous crops from NIRAP and the land available,Doering has derived baseline estimates for thequantity of cropland that could be availablefor bioenergy production, which are shown intable 19.5 Doering, also derived high and lowfood demand scenarios for 1984 based on ex-trapolation of trends in the recent past and in-creased this demand range proportionately tothe increase in baseline crop demand from theNIRAP projections for 1990 and 2000. Finallythese demand ranges were combined with

50ttoC Doering Ill, “CroplandA vailability for Biomass Pro-diction;’ contractor reportto OTA, August1979,

Table 18.-Cropland Balance Sheet (million acres)

Year 1977a 1979 1984 1990 2000

Cropland (except cropland pasture and hayland) .... 393 395 404 407 439Cropland pasture and hayland . . . . . . . . . . . . . . . . . . . 74 72 65 80 60Noncropland pasture . . . . . . . . . . . . . . . . . . . . . . . . . 27 27 22 10 2Other potential cropland . . . . . . . . . . . . . . . . . . . . . . . 26 24 22 13 4

Total . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 520 518 514 510 505Total land lost to other uses to date . . . . . . . . . . . . . . 0 2 6 10 15

Total . . . . . . . ... , . . . . . . . . . . . . . ... , . . . . . 520 520 520 520 520

With scs acreage Courltmg system, the 1977 acreages (in miltions of acres) would be as follows, cropland except cropland pasture and hayland, 343; cropland pastaure and hayland, 63, noncroplandpasture which is potential cropland or IS pemdically rotated into cropland, 88; and other potential cropland, 26 The malor differences are that the cropland categories total 406 million acres with the SCSClassiflcatlon rather than 467 million acres and the noncropland categories are increased accordingly. In both classification schemes there are additional noncropland pature categories which are neitherptential cropland nor periodically rotated into cropland, primarily because the terrain is too rocky or rough to allow mechamzed harvests

SOURCE. Oeduced from Otto C Ooermg Ill, “Cropland Availability for Biomass Production, “ contractor report to OTA, August 1979

Ch. 3—Agriculture ● 5 9

NIRAP high and low productivity (yield/acre)estimates to determine plausible ranges of de-mand for cropland for food and feed produc-tion and thus the ranges of land available forbioenergy production. These estimates areshown in table 19.

Table 19.–Cropland Available for Biomass Production

Million acres

1984From cropland pasture . . . . . . . . . . . . . . . .From high potential . . . . . . . . . . . . . . . . . .From medium potential . . . . . . . . . . . . . . . .

101010

Range of uncertainty, . . . . . . . . . . . . . . .1990From cropland pasture . . . . . . . . . . . . . . . .From high potential . . . . . . . . . . . . . . . . . .From medium potential . . . . . . . . . . . . . . . .

Range of uncertainty . . . . . . . . . . . . . . . .2000From cropland pasture . . . . . . . . . . . . . . . .From high potential . . . . . . . . . . . . . . . . . .From medium potential . . . . . . . . . . . . . . . .

3030-70

2555

359-69

10NANA

Range of uncertainty. . . . . . . . . . . . . . . .10

0-65

NA=none available

SOURCE” Otfo C Ooerlng Ill, “Cropland AvallabMy for Biomass Production, ” contractor report toOTA, August 1979

It should be emphasized that these are notpredictions, but rather plausible estimatesgiven the current state of knowledge. Theranges are less than &10 percent of the crop-Iand base, so it is unlikely that more accurateestimates can be made. Furthermore, unex-pected increases in crop productivity, in worldfood demand, or in demand for cropland fornonagricultural uses could increase or de-crease the quantity of cropland available forbioenergy production beyond the rangesshown. Also, since this only refers to croplandcapable of producing more or less convention-al crops, the development of unconventionalcrops could open new land categories not con-sidered here.

In addition to the physical availability ofcropland, one must consider the cost of bring-ing it into production. Four major factors in-fluence this cost. First the land is currently be-ing used for some purpose that the owner con-siders to be more valuable. than crop produc-

tion. Second an investment is sometimes nec-essary to convert the land to crop production,such as installation of drainage tiles or remov-ing trees occupying the site. These costs canvary from virtually nothing to as much as$600/acre.’ Third, the land that can be broughtinto production is generally less productive, onthe average, than cropland currently in pro-duction. Finally, this land also typically suffersfrom problems of drought or flooding thatmake crop yields extremely sensitive to weath-er (particularly the rainfall pattern). Conse-quently, farming this land involves a largercost and risk than with average cropland; and,from the national perspective, using it will in-crease the year-to-year fluctuations in foodsupplies and prices.

As a result of these added costs and risks,farm commodity prices will have to rise beforeit will be profitable to bring new land into cropproduction. Eventually this raises the cost ofall farmland, the cost of farming, and foodprices. The exact price rise needed to increasethe cropland in production by a given amountis unknown, but some things can be deducedfrom this analysis. During the next few years,bioenergy production from cropland is notlikely to be constrained by the availability ofcropland. However, the quantity of land thatcan be devoted to energy production withoutreducing food production is likely to decreasein the future. Furthermore, since the marginalcost of bringing new cropland into productionincreases as the quantity of cropland in pro-duction expands, the added cost in terms ofhigher food prices needed to keep a givenamount of cropland in energy production islikely to increase with time. In other words, it islikely to be increasingly expensive to produceenergy crops, even if the energy output re-mains constant.

The above comments are particularly appli-cable to grains and sugar crops. Considerablequantities of land, however, already are de-voted to forage grass production and the yieldscan be raised through increased fertilization(see below). Furthermore, grass yields tend tobe less sensitive to poor soil quality than grains

Cl bid


and sugar crops. Consequently, the economic Nevertheless, in the long term, there may bebarriers to increased grass production are con- Iittle cropland suitable for food/feed produc-siderably lower than for increased grain or tion that can be devoted to energy, and anysugar production, and one would expect the in- energy crops would have to be grown on landdirect costs of grass production to be less than totally unsuited to food and feed production.those of grains and sugar crops.

Types of Crops

There are over 300,000 plant species in theworld, but less than 100 are grown as crops inthe United States. Of the various crops, threebasic types are currently of interest for imme-diate energy production: starch, sugar, and for-age.

The major starch crops are corn (for grain)and wheat, accounting for 21 percent each ofthe total acreage of harvested crops, or about70 million acres each. The annual productionand disposition of corn and wheat are shown intables 20 and 21. In addition, oats, barley,grain sorghum, and rice are other importantstarch crops.

The main sugar crops currently grown in theUnited States are sugarcane and sugar beets.About 760,000 acres are devoted to sugarcane(in Florida, Louisiana, Texas, and Hawaii) andsugar beets were grown on 1.2 million acres in1977. Also, a smaller acreage is devoted tosweet sorghum production, primarily for sor-ghum syrup. The sugar yields averaged about3.7 ton/acre for sugarcane (some growing sea-sons were 18 to 24 months) and 2.6 ton/acre forsugar beets. The very limited commercial acre-age of sweet sorghum has yielded about 1.9ton/acre of sugar, however, the acreage is toosmall to accurately reflect the yields thatwould occur from large-scale production ofthis crop.

Forage crops are grown for feed and bed-ding. Including alfalfa, the area under foragecrop production is about 60 miIIion acres. 7 For-age crops include orchard grass, brome grass,tall fescue, alfalfa, clover, and reed canary-

7Agricu/tura/ Statistics (Washington, D C.: U S Department ofAgriculture, 1978).

Table 20.–Annual Production and Disposition of Corn for Grainin the United States, 1966-75 (million bushels)

DomesticYear Production consumption ExPorts Stocks

1966 . . . . 4,167 3,697 487 8261967 . . . . 4,860 3,885 633 1,1691968 . . . . 4,450 3,966 536 1,1181969 . . . . 4,687 4,189 612 1,0051970 . . . . 4,152 3,977 517 6671971 . . . . 5,641 4,387 796 1,1261972 . . . . 5,573 4,733 1,258 7061973 . . . . 5,647 4,631 1,243 4831974 . . . . 4,664 3,641 1,149 3591975 . . . . 5,797 4,049 1,711 398

SOURCE Agr~cullural Stafrstlcs 1977( WashmgIon, D C U S Department of Agriculture, 1977)

Table 21.-Annual Production and Disposition of Wheatin the United States, 1966-75 (million bushels)

DomesticYear Production consumption Exports Stocks

1966 . . . . 1,967 683 771 5131967 . . . . 2,202 626 765 6301968 . . . . 2,188 740 544 9041969 . . . . 2,350 764 603 9831970 . . . . 2,336 772 741 8231971 .., . 2,442 848 610 9831972, . . . 2,530 798 1,135 5971973, . . . 2,305 748 1,217 3401974 . . . . 2,140 686 1,019 4351975 . . . . 2,572 735 1,173 664

SOURCE Agr/cu/tura/Stat/sl(cs 1977( Washington, D C U S Department of Agriculture, 1977)

grass. Yields average about 1.5 to 2.5 ton/acrebut could be increased to 4 to 5 ton/acre by rel-atively straightforward changes in manage-ment practices.

Most crops can be grown in several differentareas of the country. However, each crop hasunique characteristics that enable it to do wellunder certain combinations of soil type, grow-ing season, rainfall, etc. Since these parame-ters vary widely throughout the United States,it is unlikely that any one crop could prove to


be the correct energy crop for a given product. The crops mentioned here do not exhaustRather, the available cropland can best be uti- the possibilities, even for starch, sugar, andlized for energy by growing various different cellulosic products. Other crops may be supe-crops suited to the various soil types, climates, rior to these under certain circumstances. Butand other conditions. Nevertheless, there are these crops do serve to illustrate U.S. agricul-some striking differences when national aver- ture’s energy potential, costs, and impacts.age yields are compared. (See “Energy Poten-tial From Conventional Crops” below.)

Current Agricultural Practices and Energy and Economic Costs

As mentioned above, the purpose of manag-ing a plant system is to provide an artificiallyfavorable environment for plant growth. Sinceincreasing the intensity of management costsmoney, there is always a tradeoff between theincreased cost and the expected increase inyields. As price relationships change, the inten-sity of management will also change. A sum-mary of some current agricultural practicesand their costs and energy usage is given be-low.

Aside from weather and soil type, the plant-ing date, planting density, weed, disease, andinsect control, and tillage practices can all af-fect crop yield. Different plants have differentsensitivities to these various factors. Practicesalso have to be suited to the climate and soiltype that is being farmed. Consequently, thedirect costs of farming will vary depending onthe crop and region. There can even be signifi-cant differences for the same crop within agiven region (e. g., erosion control measures,irrigation, etc.).

A “typical” farming operation for annualcrops such as corn and soybeans, however,might be as follows: After harvest of the cropin the fall the residues are chopped or the soilis disked to reduce the size of the residues andto level the soil. Phosphate and potassium fer-tilizer are broadcast and the residues and fer-tilizer are plowed under. In the spring, surfacetillage to level the soil is done soon after thesoil becomes suitable for tillage. Nitrogen fer-tilizer — anhydrous (dry) ammonia, etc. — ifneeded, is applied to the soil. Five to ten dayslater the soil is surface tilled with a cultivator

or disk and the crop planted. During plantingsome additional fertilizer may be added, an in-secticide may be applied, and herbicides maybe broadcast on the soil surface. The crop maybe cultivated for weed control once or twicewithin the first month of growth. No additionaloperations occur until the crop is harvestedwith a harvestor that separates the grain andleaves the residue on the field. If the grain hasa moisture content above that needed for stor-age without spoilage, it is dried. The grain maybe fed on the farm, stored and sold later, orsold directly to a grain company at harvest.

Minimum or reduced tillage operations areused to reduce soil erosion. With their use thesoil may be chisel-plowed rather than mold-board-plowed so that much of the residue re-mains in the surface. Herbicides may be usedto give complete weed control so that no fur-ther cultivation is needed.

Forage crop management is considerablysimpler. Since forage crops are usually peren-nials, crop planting is done only once every 4to 5 years, or longer. Aside from planting, theonly management is the application of fer-tilizers and the harvesting of the forage crop.

The estimated costs for producing corn (arow crop) and wheat (a close-grown crop) areshown in table 22. These costs are fairly repre-sentative of what can be expected for the pro-duction costs per acre for annual crop produc-tion, with intensive agriculture. Costs will varyfrom place to place, but where costs otherthan land costs are higher and/or yields arelower, the land will be worth less and landcosts will be lower.

62 ● VOl. II—Energy From Biological Processes

Table 22.-Estimated per Acre Production Costsin Indiana, 1979

Production cost item Corn WheatYield per acre. . . . . . . . . . . . . . . . . . . . 110 bu 50 buDirect cost per acreFertilizer and limea . . . . . . . . . . . . . . . . $ 3 2 . 0 0 $ 2 2 . 5 0Seed and chemicals . . . . . . . . . . . . . . . 20.00 10.00Machine operating and drying ., . . . . . . 25.50 11.25Interest on operating capital. . . . . . . . . . 9.00 7,00

Total direct costs. ., , ., . . . . . . . . . . $ 8 6 . 5 0 $ 5 0 . 7 5Indirect costs per acreMachinery and equipment . . . . . . . . . . . $ 4 3 . 0 0 $ 1 8 . 0 0Labor and management. . . . . . . . . . . . . 31.00 20.00Grain storage (bin only). . . . . . . . . . . . . 11.00 –Land costb. . . . . . . . . . . . . . . . . . . . . . 92.00 92.00

Total indirect costs . . . . . . . . . . . . . . $ 1 7 7 . 0 0 —$130.00Total costs per acre . . . . . . . . . . . . $263.50 $180.75

Cost per bushel . . . . . . . . . . . . . . . . . . 2.40 3.62

aNitrWen prices at $0, IZ/IfI for corn and $020 for wheat Phosphorus pentoxide Priced atSO.18/lb; potassium monoxide priced at $009 for all crops A corn-soybean rotation is as-sumed Thus soybeans produce a rutrogen credit for corn production and no msectide IS used

b~nd COSIS approximate current cash rental rates

SOURCE Barber, et al , “The Potenllal of Producing Energy From Agriculture, ” Purdue Universi-ty, contractor report to OTA, May 1979

The energy used for farming varies consider-ably. Typical energy inputs per acre for variouscrops are shown in table 23. These energies arefor cultivation without pumped irrigation. Acomparison of the energy inputs for irrigatedand nonirrigated corn is shown in table 24.Overall, the energy per ton of grain can vary at

Table 24.-Energy Inputs and Outputs for Corn in U.S. Corn Belt

Energy units

Nonirrigated a Sprinkler(10’ Btu) (10 5 Btu)

outputGrain . . . . . . . . . . . . . . . . . . . . 543.7 666.4Residue . . . . . . . . . . . . . . . . . . 543.7 666.4

Total output. , . . . , . . . . . . . . 1087.4 1332.8InputIrrigation pumping. , ., . . . . . . . – 60.0Fertilizer. ... , . . . . . . . . . . . . . 47.0 57.6Drying fuel . . . . . . . . . . . . . . . . 19.4 23.8Equipment fuel . . . . . . . . . . . . . 10.0 10.5Pesticides. . . . . . . . . . . . . . . . . 6.0 6.0

Total input. ... , . . . . . . . . . . 82.4 157.9

a&atfl yield, tsg bu/acre; residue yield: 7,770 ib/acre.bpump Irrigated ts inches water, 100 ft depth Grain yield and residue yield are 170 bulacre and

9,520 lb/acre, respectively.

SOURCE Barber, et al , ‘ ‘The Potential ot Producing Energy From Agriculture, ’ Purdue Universi-ty, contractor report to OTA, May 1979.

least from 1.2 million Btu/ton for oats in lowato 6.5 million Btu/ton for grain sorghum inTexas. For corn the variation is at least from2.6 million Btu/ton of grain (Illinois average) to4.6 million Btu/ton (Nebraska). The U.S. aver-age for corn is 3.1 million Btu/ton of corngrain.

These differences reflect not only differ-ences in cultivation practices and, yields, butalso the presence or absence of pumped irriga-

Table 23.-Energy Inputs for Various Crops (105 Btu per acre)

Corn

Conventional Minimum Notillage tillage tillage Soybeans Wheat Alfalfa

Nitrogen a. . . . . . . . . . . . . . . 43.75 43.75 43,75 — 20,00 1.25Phosphorus pentoxide +

potassium monoxideb. . . . . 3.20Drying c . . . . . . . . . . . . . . . .

3.20 3.20 2.70 3.00 6.5619.35 19,35 19.35 — —

Diesel d

Ground preparation . . . . . . 7.36 e 5.13 f 2.21 g 5.67 h 3.15 i —Planting. . . . . . . . . . . . . . 1.34 1.34 1.34 1.34 1.34 –Cultivation . . . . . . . . . . . . 1.34 1.34 — 1.34 – 21.07Harvest . . . . . . . . . . . . . . 2.15 2.15 2.15 1,69 1.54 –

Herbicides . . . . . . . . . . . . . 4.20 4.65 6.00 4.80 – –Insecticide. . . . . . . . . ... , 1.80 1.80 1.80 — — 5.60

Total . . . . . . . . . . . . . . . . 84.49 82.71 79.80 17.54 29.03 34.48

a25,000 Btu/lb nitrogen. fspread feflilizer, chisel plow, apply anhydrous ammOnla, field cultivateb3,000 Btu/lb phosphorus pentoxide and 2,000 Btu/lb potassium rnonoxlde gSpread fertilizer, spray, apply anhydrous ammonia.c93,500 Btu/gal LP-gas, 3,414 Btu/kW-hr electricity. hspread fedllizer, PIOW, disk, disk’132 250 Btu/gal diesel fuel ioisk, disk, spread ferhlizer in sprin9espr~d fe~llizer, pIOW, disk, apply anhydrous ammonia, disk 11211,000 Btu/lb actwe ingredient

SOURCE: Barber, et al , “The Potential of Producing Energy From Agricuffure, ” Purdue University, contractor repotl to OTA, May 1979,

Ch. 3—Agricul ture . 63

tion and the fuel used for irrigation. Examplesof energy-intensive crops range from corngrown in Nebraska which is irrigated withground water brought to the surface by elec-tric pumps and is dried with liquefied petro-leum, to grain sorghum which has relativelylow yields compared to energy inputs through-out the United States. Other crops, such asrice, can be even more energy intensive (7.8million Btu/ton, U.S. average).

For most corn cultivation, over half of theenergy input comes from fertilizer, principallynitrogen. However, without nitrogen fertil-izers, average corn yields would drop fromabout 100 bu/acre to less than 30 bu/acre. Inthe example in table 23, the energy used wouldincrease from 3.0 million to 4.9 million Btu/tonif nitrogen fertilizers were not used, assumingthe above yield change.

The other big energy input for some areas—irrigation —can have the opposite effect. Inthe example given in table 24, the use of irriga-tion raises the energy input from 2.2 million to3.4 million Btu/ton. And in some areas (e.g.,west Texas and southern Arizona), the energy

required for pumped irrigation is more thantwice that shown in table 24.8 In all, 85 percentof the 58 million acres of irrigated croplandare in the West (Northern Plains, SouthernPlains, Mountain, and Pacific farm productionregions) and 94 percent of the 0.26 Quad/yrused for pumped irrigation in the United Statesin 1974 was in the West.9 On the average, theenergy needed to pump the equivalent of 22inches of rainfall in the West is 6 millionBtu/acre. Consequently, this is a reasonableaverage figure for the energy input due to irri-gation.

Another possible type of energy crop is for-age grass. Currently, little or no fertilizer isused to cultivate forage grass; and yields areabout 2 ton/acre. However, if fertilizers wereused and the crops harvested more times peryear, additional biomass could be obtained.Table 25 shows the costs of producing grass

“D, Dvoskin, K, Nicol, and E. O. Heady, “ Irrigation Energy Re-quirements in the 17 Western States,” Agrku/ture and Energy, W,Locheretz, ed. (Academic Press, 1977)

%. Sloggett, “Energy Used for Pumping Irrigation Water in theUnited States, 1974,” Agrku/ture and Energy, W. Locheretz, ed(Academic Press, 1977).

Table 25.–Estimated Costs of Producing Grass Horbage at Three Yield Levels

Yield level (ton/acre)

2 3 4

Growing costs ($/acre)Fertilizer . . . . . . . . . . . . . . . . . — 1 9 . 4 5 b - 24.42C 41.59 d - 50.70e

Seed and seeding . . . . . . . . . . . 2.30 2.30 2.30Interest and miscellaneous. . . . . 0.22 2.07 - 2.54 4.17 - 5.04

Total. . . . . . . . . . . . . . . . . . . 2.52 23.92 - 29.26 48.06 - 58.04Harvest costs ($/acre)Machine operating. . . . . . . . . . . 8.00 12.00 16.00Interest and miscellaneous . . . . . 0.76 1.14 1.52Machine investment. . . . . . . . . . 34.06 34.06 34.06Hay storageg. . . . . . . . . . . . . . . 0 - 8.72 0 - 13.08 0 - 17.44Labor @ $4/hrh. . . . . . . . . . . . . 3.68 -11.04 5.52 - 16.56 7.36 - 22.08

Total. . . . . . . . . . . . . . . . . . . 46.50 -62.58 52.72 - 76.84 58.94 - 91.10Total non-land costs$/acre . . . . . . . . . . . . . . . . . . . 49.02 -65,10 76.54 -106.10 107.00 -149.14$/ton i. . . . . . . . . . . . . . . . . . . . 27.23 -32.55 28.35 - 35.37 29.72 - 37.29

alncludes cost of apphcatlonb60 lb nitrogen< 20 lb phosphorous pentoxide, 50 lb potassium monoxide/acre.c&I lb nitrogen, 30 lb phosphorous pentoxlde, 90 lb potassium rnonoxideiacredlso lb nitrogen, 30 It) phosphorous perrtoxtde, 60 lb potassium monoxidelacree150 lb nitrogen, 50 lb phosphorous pentoxide, 150 lb potassium rnmoxldejacre.‘9-percent interest = O 5% miscellaneous costsgRange from no cost If iarge hay package stored outside to new barn costs for rectangular baleshHlgh labor values for rectangular bale handled by hand, low labor bales for lar9e hay Pa*a9esIAssumes 10% additional storage loss If hay stored outside (average st0ra9e period).

SOURCE. Barber, et al , “The Potential of Producing Energy From Agriculture, “ Purdue University, contractor report to OTA, May 1979


herbage at various levels of fertilization andgrass production. The additional production isestimated to cost $28 to $37/dry ton. Noteparticularly that no land charges are includedin these cost calculations, because the use ofthe land has not changed. Only the output hasbeen increased. Nevertheless, some farmerprofit in addition to the labor charge may beneeded to induce farmers to increase produc-tion. Furthermore, obtaining the full potential

1OS. Barber, et al., “The Potential of Producing Energy FromAgriculture,” Purdue University, contractor report to OTA, May1979.

from this resource would require a 50- to 100-percent increase in fertilizer use in agriculture.

With no fertilization the energy used to pro-duce the grass is about 0.1 million Btu/ton ofgrass at the present estimated level of 2 ton/acre. At 3 and 4 ton/acre, the additional energyuse is about 1.9 million Btu for the third and2.4 million Btu for the fourth ton. About 0.1million to 0.2 million Btu/ton should be addedto these energy inputs for a 15-mile transportof the grass.

‘}Ibid

Energy Potential From Conventional Crops

Aside from crop residues, the two majornear- to mid-term sources of bioenergy fromconventional crops are grains and sugar cropsfor liquid fuels production and increasedforage grass production, On the land capableof supporting grain and sugar crop production,grasses could also be grown; and a comparisonof these choices is considered first.

The mechanism through which food andfuel production compete is the increase infarm commodity prices. Since farm commodi-ty prices must rise in order to make it profit-able for farmers to increase the quantity ofland under intensive production, it is impor-tant to examine the net quantities of premiumfuels that can be displaced, through liquidfuels production, by each of the alternativeswhen new cropland is brought into production.(For details of the energy balances, see ch. 11.)

The calculations for sugar crops and grassesare relatively straightforward, since these feed-stocks have very little protein in them and,consequently, the byproduct probably has lit-tle value as an animal feed (see “Byproducts”in ch. 8). The distillation of grains, in contrast,produces a protein concentrate byproduct thatcan displace significant quantities of soybeanmeal and thus soybean production. Additionalgrains could then be grown on the land former-ly devoted to soybean production. Estimatesof the effect of this substitution are calculatedbelow.

First, let X represent the number of acres ofaverage soybean production that can be dis-placed by growing 1 acre of average corn pro-duction, converting the corn to ethanol, andfeeding the byproduct to livestock. Assumingthat the corn yield on marginal cropland (i.e.,the new cropland that can be brought into pro-duction) is y times as great as on average crop-Iand, then 1 acre of marginal cropland grownwith corn for ethanol production results in abyproduct that can displace yX acres of soy-bean production. Planting this yX acres withcorn for ethanol and using the distillery by-product for animal feed displace an additionalyX2 acres of soybeans, etc. In all, the total acre-age of average soybean production displacedby this marginal acre of corn is:

yx + yx2 + yx3 . . . . = YX (1)1 - x

If Nm and Na are the net premium fuels dis-placement per acre of marginal and averagecorn production, then the total net premiumfuels displacement attributable to bringing 1marginal acre into corn production is:

N = N m + N a

( )

y X (2)1 - x

The ideal crop switching technique wouldbe where X =1, i.e., where one can simplyswitch to another crop which produces all ofthe products of the first crop and liquid fuelsas well, without expanding the acreage under


intensive cultivation. Several imaginative sug-gestions for crop switching have achieved thisideal but none are proven. 2 The closest to thisideal that has been demonstrated is the corn-soybean switch, in which X = 0.77, based onnational average yields of the respectivecrops. * 1 3 Nevertheless, even this switch islimited by the quantity of land suitable forcorn production and the fact that the corn dis-tillery byproduct is not a perfect substitute forsoybeans in all of its uses. As a fuel ethanol in-dustry is first developing, however, these limi-tations are probably of minimal importance.

Assuming, then, that the distillery byproductis fully utilized and that marginal croplandproduces 75 percent of the yield of averagecropland, OTA has calculated the net premiumfuels displacement per acre of marginal (new)cropland brought into production for variousliquid fuels options. These include ethanolfrom various grains and sugarcane and bothmethanol and ethanol from grass. The energyinputs were assumed to be national averageenergy inputs for the various grains and sugar-cane and 1 million Btu/dry ton for grass** andthe alcohols are assumed to be used as octane-boosting additives to gasoline. The results areshown in figure 12. Although the exact num-bers cannot be taken too literally because ofthe various assumptions required to derivethem, the relative values are fairly insensitiveto the assumptions chosen, provided the alco-hols are used as octane-boosting additives. *Also, utilization of crop residues does not sub-stantially change the results.

Among the grain and sugar crops, corn ap-pears to be the best choice, as long as the dis-

‘2R Carlson, B Commoner, D Freedman, and R Scott, “inter-im Report on Possible Energy Production Alternatives in Crop-Llvestock Agriculture, ” Center for the Biology of Natural Sys-tems, Washington University, St. LouIs, Mo , Jan 4, 1979

● The byproduct of 1 bu of corn can displace the meal fromabout O 25 bu of soybean. See “Byproducts” under “Fermenta-tion “

‘ ‘Improving SoI/s With Organic Wastes, op. cit* *One-half that denved above for Increased grass production,

because here it is assumed that the entire grass production goesto energy

*If the alcohols are used as standalone fuels, the relative val-ues are similar, but the net displacement is about half that shownIn figure 12

tillery byproduct is fully utilized to displacesoybeans. 1 n this calculation, 2.5 acres of aver-age soybean land plus 1 acre of marginal land,all grown in corn for ethanol production, canproduce an equivalent amount of animal feedprotein concentrate as 2.5 average acres grownwith soybeans, and provide the ethanol aswell. However, as the utilization (i. e., X inequation 2) drops, then grass quickly becomesa superior alternative. If, for example, 1 lb ofdistillery byproduct displaces 0.5 lb of soybeanmeal instead of the maximum of 0.67 lb (seech. 8), then grass and corn would be roughlyequivalent. Similarly if grass yields increase to8 dry ton/acre-yr, then grass would be as goodor better than corn regardless of the byproductutilization. (It should be noted, however, thatthese calculations do not take the economicsof producing ethanol from grass or the diffi-culties of using methanol as an octane-boost-ing additive into consideration. )

Sugarcane appears to be roughly equivalentto grass, but sugarcane can be grown on only alimited amount of U.S. cropland and the etha-nol produced from it would be considerablymore expensive than corn-derived ethanol.Other sugar crops have considerably loweryields than sugarcane.

The exact point where the byproduct utiliza-tion will drop is unknown. Some analyses haveput it at 2 billion to 3 billion gal/yr of ethanolwhen distillers’ grain is the distillery byprod-uct. ‘4 Producing corn gluten meal could, how-ever, increase this to as much as 7 billiongal/yr, based on the total domestic use of soy-bean meal for animal feed. ’s As mentionedabove, however, the byproduct is not equiva-lent to the soybean products, so it is unlikelythat one can reach this level with full byprod-uct utilization to displace other crops. For thepurposes of these estimates, it is assumed that2 billion to 4 billion gal/yr of ethanol from corn

“R C. Meekhof, W E. Tyner, and F. D Holland, “AgriculturalPolicy and Gasohol,” Purdue University, May 1979. This refer-ence reports a 3-billion-gal limit based on a 2-lb substitution ofdistillers’ grain for 1 lb of soybean meal. Other studies, however,have put the feed ratio at 1 5:1, which would reduce the limit to2.25 billion gal/yr

“improving Soi/s With Organic Wastes, op cit.


Crop

Figure 12.—Net Displacement of Premium Fuel(oiland naturalgas) per Acre ofNew Croplnd Brought into Production

Alcohol Net premium fuel displacement per acre of marginal croplandbrought into production (energy equivalent of barrelaof oil/acre-yr)

Grains and sugar cropsb o 5 10 15 20

Corn EthanolGrain sorghum E t h a n o l Spring wheat EthanolOats EthanolBarley EthanolSugarcane Ethanol by displacement of other

crops with byproductOther d

Grass or other crops with high dry-matter yields.

(4 ton/acre-y r’) Ethanol(10 ton/acre-yr) Ethanol

(4 ton/acre-yr e) M e t h a n o l (10 ton/acre-yr) MethanolaBased on 5 9 mllllon Btu/bbl a l c o h o l u s e d a s octaneboostlng addltlve to 9asOllneb A s su m e s national average energy ,nput~ per acre cult ivated and ~lelds (On the nl’rgln’l cropland) Of 750/0 of the national a v e r a g e y i e l d s b e t w e e n 1 9 7 4 . 7 7 Y i e l d s o n

average cropland are assumed to be the average of 1974.77 national averages This methodology IS Internally consistent, ralstng the average cropland yield to 1979yields would not slgnlf!cantly change the relative results ff usable crop residues are converted to ethanol. the lower value (no distillery byproduct utlllzat[on) would beIncreased by about 1 2 bbl/acre.yr or less for the grains and 26 bbl/acre.yr or less for sugarcane

c&onoml~ and physical Opportunltles for full byproduct utlllzatlon dlmlrrlsh with greater quantities of by Product productionduncerta(nty of ~ 3000 for methanol and more for ethanol from grass, since the ethanol processes are not well defined at present Assumes 1 mllllon 13tu/dry ton of

grass needed for cultivation harvest and transport of the grass and conversion process yields (after all process steam requirements are satlsffed with waste heat orpart of the feeds tock} of 84 gal/dry ton of grass for ethanol and 100 gal/dry ton of grass of methanol

‘Four to n/ ac r e. yr can be ac hleved with current grass varletleS grown On mar91nal crodand

SOURCE Off Ice of Technology Assessment yields from USDA Agricultural Statistics. 1978

Data Used in Figure 12

Net premium fuels displacement a(bbl of oil equivalent/acre)

National average farming Land that is 75 percent as

Average 1974-77 national energy (10 3 Btu/gal of ethanol) Average land productive as average land

average yields (gal of Land that is 75 percent as With byproduct Without byproduct With byproduct Without byproductCrop ethanol/acre) Average land productive as average credit credit credit credit

Corn . . . . . . . . 220 33.3 44.4 4.4 4.0 3.0 2.7G r a i n s o r g h u m . 130 54.5 72.7 2.1 1.9 1.3S p r i n g w h e a t . . .

1.173 23.8 31.7 1.6 1.5 1.1 1.0

Oats . . . . . . . . . . 74 24.2 32.3 1.6 1.5 1.1 1,0Barley . . . . . . . . . . . 79 29.4 39.2 4.6 1.5 1.1 1.0S u g a r c a n e . 504 30.3 40.4 N A 9.7 N A 6.4Grass ... 4 0 0b N A 10 N A N A N A

A =-none available.

7.3— . — — — . — . — .

aA~sumes gross displacement of 140,000 BtU/g’l of ethanol, byproduct credit of 10,500 Btulgal, and 5.9 million Btulbbl of Oil. For methanol, 117,000 Btulgal 9ross dis-placement.

bASSumeS 4 tonlacre on marginat land and 100 gal methanol Per tOn.

0.75X Net premium fuels displacement from 1 acre of marginal landDisplacement of soybean productionc1-x (total acres of soybeans displaced by 1 0.75X(average acres of soybeans displaced marginal acre of grain and additional cultivation plus 1-x acres displaced soybean land (bbl oil

Crop per average acre of grain = x) of grain on former soybean land equivalent/acre of marginal land)

Corn. . . . . . . . . 0.77 2.5Grain sorghum

13.90.46

Spring wheat.0.64 2.7

0.26Oats. . . . . . . . .

0.26 1.50.26 0.26

Barley . . . . . . . .1.5

0.28 0.29 1.6Sugarcane, 0 0 6.4Grass. . . . . . . . . 0 0 7.3‘Assumes average soybean yield of 27.1 bulacre, a displacement of 1 lb of soybean meal per 1.5 lb of distillers’ grain, and 48 fb of soybean meal per bushel of soybeans.

—

SOURCE: S. Barber, et al., “The Potential of Producing Energy From Agriculture,” Purdue University, contractor report to OTA; and Agricultural Statwtics, 1978 (Wash-ington, D. C.: U.S. Department of Agriculture, 1978).


(about 0.2 to 0.4 Quad/yr) can be producedwhile utilizing the byproducts fully. This wouldrequire about 2 million to 5 million additionalacres in intensive crop production and expan-sion of corn production by over three timesthis acreage. It is not certain that cropland willbe available for energy production by 2000;but if it is, it is assumed that any further pro-duction above this level will use grass as theenergy crop.

In the near to mid-term, increased produc-tion of forage grass can be obtained on about100 million acres of hayland, cropland pasture,and noncropland pasture. Assuming a 1- to 2-ton/acre-yr increase in yields, this would resultin 100 million to 200 million tons of grass orabout 1.3 to 2.7 Quads/yr. Deducting the ener-gy needed to cultivate and transport the grassreduces the output to about 1.1 to 2.2 Quads/yr.

By 2000 anywhere from zero to 65 millionacres could be used for energy crops. Assum-ing that grasses with average yields of 6 dryton/acre-yr on this cropland have been devel-oped, then the energy potential would be zeroto 5 Quads/yr.

Although adding this to the ethanol yieldfrom corn involves a small amount of doublecounting, the uncertainty in the actual crop-Iand availability and future grass yields is toogreat to warrant a detailed separation. Conse-quently, OTA estimates that 1 to 3 Quads/yrcan be obtained in the near to mid-term andzero to 5 Quads/yr in the long term from theproduction of conventional crops for energy.

The above mix of corn and grass was chosenas the one that appears to be the least infla-

tionary to food prices in the long term per unitof liquid fuel produced. However, if 65 millionacres are available for energy production in2000, one could conceivably produce over 15billion gal of ethanol from corn* or about 1.3Quads/yr of liquid fuel. Grass production, onthe other hand, would yield about 2.5 Quads/yr** of liquid fuel from this same cropland andwith the same or lower inflationary impact.

Judging when the emphasis should shiftfrom corn to grass is likely to be difficult. As afallible rule of thumb, however, any significantincrease in corn prices relative to the othergrains would be an economic signal to distil-lers and/or animal feeders to use grains otherthan corn, which would make grass a superioroption for energy production. Similarly a sig-nificant drop in the price of distillery byprod-uct, relative to the alternatives, would be aneconomic signal that the distillery byproductsare not being fully utilized and, again, grasswould be superior. Consequently, if there is asignificant rise in corn prices or drop in distil-lery byproduct prices, relative to the alterna-tives, then these could be indications that thecropland could better be utilized by producinggrass.

*Seven billion gal with complete substitution of soybean mealand requiring about 10 million of the 65 million acres. The re-maining 55 million acres, with yields of 65 bu/acre, could pro-duce an additional 9 billion gal/yr of ethanol.

**5 Quads/yr of grass could yield slightly less than 25Quads/yr of methanol

Energy Potential From Crop Residues

Crop residues are the plant material left in of soil organic matter. (See also “Environmen-the field after a crop harvest. Their major func- tal Impacts.”)tion is to protect the soil against wind and wa-ter erosion by providing a protective cover,and they have a modest fertilizer value16 and a Barber, et al., have calculated the totalsoil-conditioning value through maintenance quantities of residues by multiplying the crop

“Residues are about O 7 percent nitrogen, O 2 percent phos- yields reported by USDA by residue factors,phorus, and 4 percent potash See Barber, et al., op cit. i . e . , t h e r a t i o o f r e s i d u e t o t h e y i e l d o f t r a d i -

68 . Vol. Ii—Energy From Biological Processes

tional crop for the various types of crops. ’7The results of these calculations are shown intable 26. The total quantity of residues gener-ated is about 400 million ton/yr or about 5Quads/yr.

Table 26.-Total Crop Residues in the United States for10 Major Crops (based on 1975-77 average production)

Acres Total residuek acres k tons

Corn. . . . . . . . . . . . . . . . . . . . . 69,530 171,084Wheat . . . . . . . . . . . . . . . . . . . 68,789 99,890Soybeans . . . . . . . . . . . . . . . . . 53,616 67,556Sorghum . . . . . . . . . . . . . . . . . 14,714 21,123Oats. ., . . . . . . . . . . . . . . . . . . 12,831 20,677Barley . . . . . . . . . . . . . . . . . . . 8,772 13,341Rice. . . . . . . . . . . . . . . . . . . . . 2,515 8,584Cotton . . . . . . . . . . . . . . . . . . . 10,990 3,578Sugarcane . . . . . . . . . . . . . . . . 660 4,700Rye . . . . . . . . . . . . . . . . . . . . . 715 708

U.S. Total . . . . . . . . . . . . . . . 243,132 411,240

SOURCE. Barber, etal , “ThePotentialofProducingEnergy From Agriculture,’’ Purdue lJnwershIy, contractorreporttoOTA, May1979

During fall plowing many farmers turn underthe residues, rendering them useless as a pro-tection against erosion. These residues couldbe collected and used for energy without wor-sening the erosion on these lands. However,current agriculture policy is to encouragefarming practices that Iimit soil erosion to thesoil-loss tolerance levels, or the levels of ero-sion that are believed not to impair the long-term productivity of the land (see “Environ-mental Impacts”). Consequently, a more de-tailed consideration of crop residues is ap-propriate.

Using data supplied by Dr W. Larson,’* thetotal crop residues were calculated for each ofthe major land resource areas or subregions ofStates. Using standard equations for soil ero-sion,’ the quantities of residues that could beremoved without exceeding standard soil-losstolerance values were calculated. These werethen modified to take into consideration thequantities that can be physically collectedwith current harvesting equipment (about 60percent in field trials at Purdue University). In

171 bid“W. E. Larson, “Plant Residues–How Can They Be Used

Best,” paper No. 10585, Science Journal Series, SEA-AR/USDA,1979

● Universal soil-loss equation and wind erosion equation.

addition, a 15-percent storage loss was as-sumed. The results of these calculations areshown in table 27 as the usable crop residues,which are about 20 percent of the total cropresidues.

Table 27.–Total Usable Crop Residue by Crop

Amount Harvestable acres Average yieldCrops (k tons) (k acres) (ton/acre)Corn. . . . . . . . . . 37,098 39,122 0.95Small grains . . . . 33,623 36,324 0.93Sorghum. . . . . . . 1,452 4,100 0,35Rice . . . . . . . . . . 5,457 2,516 2.17Sugarcane. . . . . . 590 331 1.78

Total ... , . . . . 78,220 82,393 0.95

SOURCE Barber, et al., “The Potential of Producing Energy From Agriculture, ” Purdue IJnlversl-ty, contractor reporl to OTA, May 1979

H a r v e s t i n g c r o p r e s i d u e s w o u l d t y p i c a l l y

c o n s i s t o f m o v i n g t h e r e s i d u e s i n t o w i n d r o w s ,

or long thin piles of residues. The windrowswould then be collected with baling machineryand the bales dumped at the roadside. Thewindrows would be collected and transportedto a place where they would be stored or used.

Crop residues typically contain 40- to 60-per-cent moisture 2 days after the grain harvests.In favorable weather conditions, the residuesdry to about 20-percent moisture in 18 days. ”With these moisture contents, bacteria willgradually consume the residues. If the residuebales are compacted too tightly, the heat gen-erated from the bacterial action can cause thematerial to spontaneously combust. However,with relatively loose bales, the bacterial heat-ing will dry the material to a moisture contentat which the bacteria do not consume the ma-terial. Some loss, however, is inevitable (15-percent loss has been assumed in table 27).

The extra fertilizers necessary to replace thenutrients in the residues removed cost about$7.70/ton of residue removed.

In addition, one of the main problems withharvesting residues is that it delays the fallground preparation. If winter rains come toosoon, there may not be sufficient time to col-lect the residues and prepare the ground forthe spring planting. The spring planting is then

“Barber, et al., op. cit.


delayed and yields for the following year maysuffer. Using computer simulations of farmingoperations and the actual weather conditionsin central Indiana between 1968 and 1974, itwas found that residue harvests reduced cornyields by an average of 1.6 bu/acre-yr.20 If thiscost is attributed to the residues, then it raisesthe residue costs by $2.70/ton. This factor isless of a problem with most other grains, how-ever, since they are less sensitive to the exactplanting time.

Adding these various costs and assuming amarkup of 20 percent above costs gives theState average costs for various residues (table28). Care should be exercised when using thistable, however, since the costs within a Statecan vary considerably. In favorable cases the

’01 bid

Table 28.–State Average Estimated Usable GroupResidue Quantities and Costs

Total usable crop Delivered costa

residues (million ($/ton) (estimatedState tons/yr) uncertainty: 20%))

CornIllionois . . . . . . . . . . .Indiana . . . . . . . . .lowa ., . . . . . . . . . . .Minnesota . . . . . . . . . .Nebraska. ., . . . . . . . .Ohio ., . . . . . . . . . . .

Small grainsCalifornia. . . . . . . . . .Illinois. . . . . ...Minnesota ., . . . . . . . .South Dakota . . . . . .W a s h i n g t o n . . . . .Wisconsin . . . . . . . .

Sorghum grainColorado . . . . . . . . . .Kansas . . ., . . . . . . .Missouri . . . . . . . .

RiceArkansas, . . . . . . . . .California. ., . . . . . . . . .Texas . . . . . . . . . . . . . .

SugarcaneFlorida. . . . . . . . . . . . . .

8.04.66.94.21.82.6

1.81.06.11.83.02.0

0.120.720.28

1.91.11.2

0.53

32.1632.4232.7738.6741.6835.18

28.2931.5330.5433.0531.0126.93

35.6057.6236.87

36.3234.8236.08

30.93

costs might be as low as $20/dry ton and, in un-favorable cases, as high as $60/dry ton or more.

Crop residues contain about 13 million Btu/ton. The energy costs for harvesting and trans-porting the residues are about 0.9 millionBtu/ton for a 15-mile transport and 1.8 millionBtu/ton for a 50-mile transport. (With inte-grated residue and crop harvests the energycosts would be slightly less, but this may notbe a practical alternative because it delays theharvest.) In addition, the energy content of theadditional fertilizer needed to replace the nu-trients lost in the residues is about 0.6 millionBtu/ton. Thus, the total energy use associatedwith collecting and transporting the residues isabout 1.5 million to 2.5 million Btu/ton of resi-due.

National average crop yields can fluctuateby ± ± 5 percent or more from year to year and

the usable crop residues will fluctuate byabout ± 10 percent, since an absolute quantityof residue should be left regardless of the cropyield. On a local basis, usable crop residuescan vary considerably. Within a county lo-cated in a humid region of the country, thefluctuation may be ± 20 percent and for cropsthat are not irrigated in dry regions, the year-to-year variations can reach ± 100 percent.The areas with the largest fluctuations, how-ever, also have the lowest quantities of usableresidues.

In summary, the total crop residue produc-tion in the United States is about 5 Quads/yr,of which about 3 Quads/yr can be collectedwith current harvesting equipment. The quanti-ty that can be collected while maintaining cur-rent soil erosion standards is about 1 Quad/yr.Considerations of a reliable supply, however,would reduce this to roughly 0.7 Quad/yr* ofreliable feedstock, if soil erosion standards arestrictly adhered to. By 2000, increases in cropproduction could raise this by 20 percent to 0.8to 1.2 Quads/yr.

alncludmg 15-rnlle transport, labor at $5/hr, $0 80/gal diesel fuel, y!eld Penalty of $2 70/lon ofresidues for corn, adctmonal ferlhzers for $7 70/ton of residues, and profit of 20 percent otcosts

SOURCE Barber, et al , < ‘The Potential of Producing Energy From Agriculture, Purdue Unlversl-ly, contractor report to OTA, May 1979

● Calculated by assuming that the total quantity of residue canfluctuate by ± 20 percent at the local level; i.e , by subtracting20 percent of the total residues from the usable residues on aState-by-State basis


Environmental Impacts of Agricultural Biomass Production

Introduction Table 29.-Environmental Impacts of Agriculture

American agriculture, with its astonishingproductivity and reliability, bestows criticallyimportant benefits on the economy and gener-al well being of the United States. Unfortu-nately, it also has serious negative environ-mental impacts. Any substantial increase inland cultivation or intensification of presentcrop production to produce energy crops—biomass–will cause an extension and intensi-fication of many of the impacts of the presentsystem.

There are substantial uncertainties in theunderstanding of the consequences of relyingon agricultural feedstocks for energy produc-tion. These uncertainties stem from a lack ofcomplete understanding of present impacts,the potential for changes in crop productionmethods in the future, and uncertainty as tothe pace of development. This section at-tempts to place the potential impacts of large-scale biomass production from agriculture intoperspective by briefly describing what isknown of the impacts of food crop production(the energy feedstock production systemshould resemble the food production system),describing how the pace of development mayintensify impacts, and finally identifying thosedifferences between food and energy feed-stock production that are most critical indetermining impacts.

The Environmental Impacts ofAmerican Agriculture

Agriculture is a major source of pollutionand causes serious environmental impacts.Table 29 lists the major environmental impactsassociated with present forms of large-scalemechanized agricultural production. Most ofthe impacts apply to the majority of farmingsituations (although with varying magnitude),but some impacts are negligible or nonexistentin certain situations. Also, most of the impactsare more or less controllable, but for a varietyof reasons (a high perceived cost or negative

Water use (irrigated only) that can conflict with other uses or causeground water mining.Leaching of salts and nutrients into surface and ground waters, (andrunoff into surface waters) which can cause pollution of drinking watersupplies for animals and humans, excessive algae growth in streamsand ponds, damage to aquatic habitats, and odors.Flow of sediments into surface waters, causing increased turbidity,obstruction of streams, filling of reservoirs, destruction of aquatic hab-itat, increase of flood potential.Flow of pesticides into surface and ground waters, potential buildup infood chain causing both aquatic and terrestrial effects such as thinningof egg shells of birds.Thermal pollution of streams caused by land clearing on stream banks,loss of shade, and thus greater solar heating. -

Air• Dust from decreased cover on land, operation of heavy farm machin-

ery.● Pesticides from aerial spraying or as a component of dust.● Changed pollen count, human health effects.● Exhaust emissions from farm machinery.Land●

●

●

●

●

●

Erosion and loss of topsoil from decreased cover, plowing, increasedwater flow because of lower retention; degrading of productivity.Displacement of alternative land uses–wilderness, wildlife, esthetics,etc.Change in water retention capabilities of land, increased flooding po-tential.Buildup of pesticide residues in soil, potential damage to soil microbialpopulations.Increase in soil salinity (especially from irrigated agriculture), degrad-ing of soil productivity.Depletion of nutrients and organic matter from soil.

Other● Promotion of plant diseases by monoculture cropping practices.● Occupational health and safety problems associated with operation of

heavy machinery, close contact with pesticide residues and involve-ment in spraying operations.


effect on crop yields are almost certainly themost important) many control techniques arerarely used.

Water pollution and land degradation dueto erosion are American agriculture’s primaryproblems, and the two impacts are intimatelylinked. The action of wind and water stripsfarmland of its productive topsoil cover, andmuch of this soil ends up in the Nation’s water-ways. Thus, estimates of soil erosion are criti-cal to understanding the effects of agricultureon both soil productivity and on water ecosys-tems.


SCS has recently revised downward its esti-mates of cropland erosion. Its 1977 NationalErosion Inventory estimates average annualsheet and rill erosion from all cropland to be4.77 ton/acre-yr (or a total of about 2 billionton/y. 21 Previously, it had estimated croplandsheet and rill erosion at about 9 ton/acre-yr,22

and other sources had estimated total erosion(including wind erosion) from croplands to beas high as 12 ton/acre-yr.23 SCS attributes thedecrease to the greatly improved data base re-cently made available by the 1977 Inventory.Also, the original 9-ton/acre-yr estimate appar-ently referred only to land in row crops, close-grown crops, and summer fallow, whereas themore recent estimate includes lands that are inless intensive (and less erosive) uses such asrotation hay and pasture, or native hay.

Data from the 1977 Inventory has only re-cently begun to be released to the general pub-lic, and it seems likely to generate contro-versy — especialIy because its estimate of aver-age erosion is under the 5 ton/acre-yr that SCSgenerally considers to be a tolerable level (i. e.,a level that wilI not affect long-term produc-tivity) for much U.S. cropland. However, thelower estimate is not especially comforting fora number of reasons:

● National (sheet and rill) erosion rates forcropland in intensive production are esti-mated by SCS to be 6.26 ton/acre-yr.

● The national estimate tends to hide sever-al important food-producing areas withuncomfortably high erosion rates (e. g.,Missouri averages 11.38 ton/acre-yr; Iowaaverages 9.91 ton/acre-y r).

● The estimates do not include wind erosionand alternative forms of water erosion.Cropland wind erosion in 10 westernStates averages 5.29 ton/acre-yr. Thus, al-though Texas cropland has a sheet and rillerosion rate of only 3.47 ton/acre-yr, its to-tal erosion rate is greater than 18 ton/acre-yr because of wind erosion.

“1977 SCS Natfona/ Erosion Inventory Estimate, op. cit.’21 bld“D Plmentel, et al , “Land Degradation, Effects on Food and

Energy Resources, ” Science, VOI 194, Oct 8, 1976

●

●

●

Although SCS generally considers 5 ton/acre-yr as an (average) annual erosion atwhich long-term productivity on goodsoils will not suffer, it is not certain thatsoil is actually replaced this fast. Authori-tative estimates of soil replacement ratesdo not exist, but average rates of as low as1.5 ton/acre-yr have been claimed. z’ How-ever, the SCS rates do represent the gener-al consensus of the agronomy community.Even the new lower erosion rate impliesthat about a billion or more tons of sedi-ment from croplands are entering the Na-tion’s waterways each year.25

Erosion rates from croplands are manytimes higher than those of natural ecosys-tems. Forests typically erode at a rate ofless than one-tenth of a ton/acre-yr, andgrassland at less than half a ton/acre/yr.26

As a result of the mismatch between erosionand soil replacement, the United States haslost a considerable portion of its topsoil and,some have claimed, its production potential.Pimentel estimates that U.S. cropland has lostabout one-third of its topsoil and 10 to 15 per-cent of its production potential over the last200 years. z’ Bennett estimates that, during theperiod prior to 1935, 100 million acres of crop-I and were lost to erosion and an additional 100million acres were stripped of more than halfof their topsoil .28 At best, however, these val-ues represent extremely rough estimates, andthe new SCS erosion inventory may cause theirdownward revision.

It appears likely that the process of landdegradation will continue for the immediatefuture. Although USDA has spent nearly $15billion in its soil conservation programs sincetheir inception in 1935,29 only 36 percent of the

“Ibid“Environmental Implications of Trends in Agriculture and Silvi-

cu/ture– Vo/ume 1: Trend Identification and Evo/ution (Washing-ton, D C Environmental Protection Agency, October 1977),EPA-60013-77-I 21

‘61 bid*7D Pimentel, op cit“H H Bennett, So;l Conservat ion (New York . McGraw-Hi l l ,

1939),“TO Protect Tomorrow’s Food Supp/y, Soi/ Conservation Needs

Priority Attention (Washington, D C : General Accounting Of-fice, Feb 4, 1977), CED-77-30


472 million acres of cropland in 1967 werejudged to have adequate conservation treat-ment30 and the programs have been criticizedas inadequate by the General Accounting Of-fice.31

A reason for the inability of USDA conserva-tion programs to satisfy their critics may be thedifficulty of demonstrating to the farmer (in allbut the more severe cases) the benefits of addi-tional conservation measures. Because an inchof topsoil weighs about 150 ton/acre, a net lossof 5 ton/acre-yr would result in a loss of 1 inchof soil every 30 years. During that time, farm-ing procedures would be gradually changing,obscuring the effects of any soil loss. For exam-ple, during the past 30 years, more intensiveuse of fertilizers, pesticides, and other inputs,better information on future weather andother critical factors, and improved crop varie-ties more than compensated for erosion-caused losses on most lands. Also, the actualeffect on productivity may not be large insome circumstances because the effect of soilloss is very sensitive to soil conditions: whileloss of soil from a very shallow soil over rock inKentucky may cause the land to be withdrawnfrom production, on some deep Ioess soils oflowa, the loss of several inches of topsoil mayhave little effect on productivity. Few if anyagricultural scientists would argue that net soilloss can continue indefinitely without majorlosses in productivity. However, on many landsthe damages of erosion may never become vis-ible to the farmer; rather they will be perceivedby his children or grandchildren. Moreover,short-term economic constraints may compel afarmer to discount the future benefits of con-servation by much more than he would person-ally prefer.

Aside from the long-term consequences inland degradation, soil erosion represents asevere water pollution problem. Not only issoil itself a serious pollutant, it also acts as acarrier of other pollutants: phosphorus, pesti-cides, heavy metals, and bacteria.32 The soil

‘“’’Potential Cropland Study, ” Statistical Bulletin No. 578, SoilConservation Service, U.S. Department of Agriculture, 1977.

31 T. protect Tomorrow’s Food SUPp/Y, OP. cit.Jl~nvjronmental /mp/ications of Trends, OP. cit.

lost to agricultural erosion represents morethan half of the sediment entering the Nation’ssurface waters. 33 34 Sediment causes turbidity,fills reservoirs and lakes, obstructs irrigationcanals, and destroys aquatic habitats. Yearlymaterial damages have been estimated at over$360 million,35 not including damage to aqua-tic habitats and other noneconomic costs.Adding the flooding damage caused by the de-crease in storage capacity of reservoirs andstreams would increase annual costs to over $1billion. 36

The effects on aquatic ecosystems of theenormous flow of sediments into the Nation’swaterways have never been satisfactorily esti-mated. Research on the impacts of “nonpoint”sources of water pollution—agriculture, con-struction, etc. –has not been given a high pri-ority within the Environmental ProtectionAgency (EPA) or USDA, and the result is a scar-city of information from which to draw conclu-sions about either present impacts or futureimpacts associated with the devotion of mil-lions of additional cropland acres to biomassproduction.

The other major water pollution problems ofagriculture involve the toxic effects of pesti-cides and inorganic salts and the nutrient in-flux into the Nation’s waterways associatedwith American agriculture’s increasing use offertilizers.

Pesticide use in American agriculture hasgrown from 466 million lb in 197137 to 900million lb in 1977.38 By 1985, American farmersare expected to be using as much as 1.5 billionlb.39 Much of this increase can be traced to thegrowth in minimum tillage practices40 whichsubstitute increased herbicide use for tillage tocontrol weeds. These practices include leavingcrop residues on the soil surface, and theseresidues harbor plant pests and pathogens andgenerally increase pesticide requirements (al-

‘]Ibid.“Pimentel, op. cit.357977 SCS Nationa/ Erosion /nventOry f5t;mafe, 0p. cit.“Ibid.“Environmental /mp/ications of Trends, op. cit.‘S7977 SCS National Erosion Inventory Estimate, op cit.‘;l bid,40[nvironmenta/ Implications of Trends, op. cit.


though they offer substantial benefits in ero-sion control). Recent growth in the practice ofsingle- and double-cropping may also accountfor some of the increase. Although less than 5percent of the pesticides enter the surface andground water systems, ” pesticide use has beenassociated with fish kills and other damage toaquatic systems as well as reproductive fail-ures in birds and acute sickness and death inanimals. Under conditions of high exposure—in accidental spills, improper handling by ap-plicators, etc. —pesticides have been associ-ated with the sickness and death of humans.Recent research has implicated some widelyused pesticides as possible carcinogenicagents when ingested or inhaled, and EPA hasremoved certain of these— including Aldrin,Dieldrin, and Mirex–from the marketplaceunder the Federal Insecticide, Fungicide, andRodenticide Act (FIFRA). Amendments toFIFRA have considerably tightened the require-ments for testing and registering pesticides.However, the tremendous variety of pesticidecompounds [“1 ,800 biologically active com-pounds sold domestically in over 32,000 dif-ferent formulations”42 ) and the difficulty ofdetecting damages in human populations andin the environment will greatly complicate suc-cessful enforcement of the Act. At present, thelong-term impacts of pesticides on the environ-ment and on man are poorly understood.

The problems of pesticide use in agricultureare becoming particularly visible because ofa recent rash of instances where pesticidesthought to be safe have been accused of caus-ing severe injuries — including birth defects,miscarriages, and other acute physical disor-ders–and death to exposed populations, Thecontroversy surrounding the use of the her-bicide 2, 4, 5-T in Oregon and its suspension byEPA is a widely publicized– but by no meansunique —example of rising national concern.Resolution of the conflicting claims about thesafety (or lack of it) of these pesticides is wellbeyond the scope of this report. Based on cur-rent interest, however, it is likely that a majorpublic concern associated with any large in-

4’ I bid421977 SCS Nat;ona/ Erosion Inventory Estimate, op. cit.

crease in crop cultivation will be the concur-rent increase in pesticide use on the new lands.There is a distinct possibility that rising publicconcern over pesticide usage could put a se-vere constraint both on the continuing in-crease in this usage and on the expansion ofcrop production for energy feedstocks.

Salinity increases caused by irrigated agri-culture present another substantial impact. lr-rigated land produces one-fourth of the totalvalue of U.S. crops, mostly in the 17 westernStates. ’J Increased salinity in streams in theseareas is caused by the salts added to irrigationwater from upstream farms and by the concen-trating effect of the high evaporation rates inarid climates (evaporation leaves the salts be-hind). The same mechanisms can lead to in-creasing salt concentrations in the soils ofdownstream farms unless sufficient water canbe obtained to periodically flush excess saltsout of the soil profile. Damages associatedwith increased salinity of soils and irrigationwater include reduced crop yields, inability togrow salt-sensitive crops, increased industrialtreatment costs, and adverse effects on wild-life, domestic animals, and aquatic ecosys-tems. Trends in irrigated agriculture are lead-ing to improvements in irrigation efficiencyand decreased salt loadings in streams, butthese trends could be overwhelmed by sub-stantial increases in irrigated acreage either togrow crops for energy or to compensate forcompetition between food and biomass pro-duction in other areas.

Fertilizer use is of extreme importance incalculating the environmental impacts of agri-culture. Large amounts of energy— one-thirdof the energy consumed by the agriculturalsector and its suppliers— are needed to pro-duce fertilizer. The Haber-Bosche process forthe synthesis of anhydrous ammonia fertilizerrequires around 21 ft3 of natural gas to pro-duce 1 lb of nitrogen in fertilizer (and more forother forms of nitrogen);44 current U.S. nitro-gen fertilizer production is 10 million metric

4’1 bid“C. H. Davis and G M Blouin, “Energy Consumption In the

U.S. Chemical Fertilizer System From the Ground to theGround,” Agriculture and Energy, W. Lockeretz, ed. (New York:Academ~c Press, 1977), pp 315-371

67-968 0 - 80 - 6


tonnes per year consuming 3 percent of totalU.S. natural gas production. If current trendsof increased rates of fertilizer applicationscontinue and food demands increase by 3 per-cent per year, natural gas requirements for fer-tilizer production will triple by 2000.45

The application of large quantities of chemi-cal fertilizers also represents a water pollutionproblem because much of the nutrient valueends up in the Nation’s waterways. Wittwerestimates that only 50 percent of the nitrogenand less than 35 percent of the phosphorus andpotassium applied as fertilizer are actually re-covered by crops;46 other estimates for nitro-gen range from 46 to 85 percent.47 Although aportion of that which is lost is due to volatiliza-tion (and consequent loss to the atmosphere),much is lost to surface and ground waters viarunoff, leaching, and erosion processes. Theamount of nitrogen and phosphorus (potassi-um is not considered to have significant en-vironmental impacts48) entering the waterwaysfrom agricultural lands in the early 1970’s hasbeen estimated at 1,500 million to 15,000 mil-lion lb/yr and 120 million to 1,200 million lb/yr,respectively.49

This nutrient pollution from fertilizers maybe toxic to humans and wildlife in high concen-trations; nitrate poisoning of wells from con-taminated ground water is not unusual in someagricultural areas. The more common impact,however, is to speed up eutrophication ofstreams and the problems of oxygen demandand algae growth associated with eutrophica-tion.

The remaining major water-associated im-pact of agriculture is water use. The appropria-tion water rights system in the West offers lit-tle incentive to use water efficiently. * The

45S. H Wittwer, “The Shape of Things to Come, ” l?io/ogy ofCrop Productivity, P. Carlson, ed. (New York: Academic Press,1978),

*bIbid47Environmenta/ /mp/ications of Trends, op. cit.‘al bid,“Ibid.*For an excellent review of Western water law see E, Radose-

vitch, “Interface of Water Quantity and Quality Laws in theWest, in Proceedings of the Nationa/ Conference Irrigation Return F/ow Quantity Management, J. P. Law and G V. Skogerboe,eds. (Fort Collins, Colo.: Colorado State University, 1977).

combination of artificially low prices for waterand the requirement of the appropriation doc-trine that the holder of a water right mustmaintain that right through use (“use or lose”)has led to the cultivation of water-intensivecrops in arid climates. This has led to watershortages in many Western basins and to ag-gravation of salinity problems in several majorrivers.

Several water use trends will affect agricul-tural production capabilities in the near fu-ture. First, large-scale energy development—especially electrical generating stations and,possibly, synthetic fuel plants–will consumesubstantial quantities of water and, in somecases, compete directly with agricultural inter-ests for the limited supply. Second, expandedacreage for food production will occur, in-cluding projects on Indian land that may havepriority rights to the limited water supply. Onthe other hand, improvements in irrigation effi-ciency will have some conserving effect on wa-ter consumption even though this is not a pri-mary goal of efficiency increase (the primarygoal is to reduce water withdrawals and ‘returnflows and to improve water quality rather thanto reduce consumptive use). For example, SCSestimates that irrigated acreage in the criticalUpper Colorado River Basin could increasefrom 1,370,000 acres in 1975 to 1,442,000 acresin 2000 while water consumption declines by93,000 acre-ft with a concerted program to im-prove irrigation practices. so Further decreasesin water consumption are possible by “cropswitching” — shifting to less water-intensivecrops where markets are available—and re-moving marginal, low-productivity land fromcultivation.

51 Also, substantial potential forwater conservation exists in energy produc-tion.

Much of the agricultural land in the UnitedStates was’ obtained by forest clearing or plow-ing native grasslands, and the consequent re-placement of natural ecosystems with inten-sively managed monoculture must be consid-

50Conservation Needs Inventory (Washington, D. C.: Soil Con-servation Service, U.S. Department of Agriculture, 1976).

51S. E Plotkin, H. Gold, and 1. L. White, “Water and Energy inthe Western Coal Lands,” Water Resources Bu//etin, vol. 15, No.1, February 1979.


ered a major environmental impact of agricul-tural production. (This process is not a one-waystreet. A combination of changing crop pat-terns, alternative producing areas, increasingaverage productivity, and, especially in theSouth, depletion of soils has led during thiscentury to the abandonment of considerablefarmland acreage and, in many cases, rever-sion to second-growth forest. Principle areasinvolved in this transformation include thePiedmont areas of the Southeast, the hillierareas of the Northeast, and the upper lakeStates. However, farm abandonment no longerappears to be a significant force.52) Aside fromthe loss of esthetic and recreational values,this replacement represents a substantial de-cline in wildlife diversity, loss of watershedprotection, and the loss of the alternativewood (or other) resource. At present, this lossinvolves a bit over 400 million acres of desig-nated cropland53 and will probably increaseunless crop production efficiency can keeppace with the rising demand for food. Also, be-cause millions of acres of cropland are losteach year to roadbuilding and urban develop-ment, merely the maintenance of the statusquo demands continued clearing of unman-aged and lightly managed lands for crop pro-duction.

1973=74: A Case Study inIncreased Cropland Use54

In 1973, USDA told American farmers thatthey would be free to plant as many acres ofwheat, corn, and feed grains as they wishedduring the 1973-74 season. In response, 8.9million additional acres were planted andharvested during that season:

. 3.6 million acres from grassland,• 0.4 million acres from woodland, and● 4.9 million acres from idle cropland and

set-aside land.

The results of this new agricultural produc-tion may provide a basis on which to predict

‘2M Clawson, “Forests in the Long Sweep of American His-tory, ” Science, VOI 204, j une 15, 1979

5JPotentia/ Crop/and Study, op cit“Adapted from K E Grant, Erosion 1973-74: The Record and

the Cha//enge,

the potential impact of a surge in productioncaused by incentives to grow crops for biomassenergy production.

Of the 8.9 million acres, SCS estimated that5.1 million acres had inadequate conservationtreatment and water management, and 4 mil-lion acres had inadequate erosion control.These problems in land selection and environ-mental planning were soon translated intosevere erosion losses. Although poor weatherconditions (fall and winter drought in thesouthern high plains, spring floods in the north-ern Great Plains, torrential spring rains fol-lowed by drought in the Corn Belt) aggravatedthese losses, most observers appear willing toplace a major blame on the farmers’ land se-lection and inattention to erosion control prac-tices.

Soil losses on the additional acreage duringthe 1973-74 season averaged over 6 ton/acreover and above expected losses without pro-duction. Those lands designated as sufferingfrom inadequate conservation treatment lostan average of more than 12 ton/acre above ex-pected losses. First-year erosion losses are ex-pected to be lighter than subsequent years be-cause the root structures of the original covercrops are not totally destroyed by tilling andprovide some protection to the soil until theydecompose; thus, erosion rates would be ex-pected to rise still further unless conservationpractices were begun.

The hardest hit of the agricultural regionswere the Corn Belt (390,000 acres, 15 to 100ton/acre additional soil loss on the new land),western Great Plains— North Dakota, Mon-tana, Wyoming, eastern Colorado (325,000acres, 5 to 40 ton/acre), eastern Great Plains —Nebraska, Kansas, South Dakota (260,000acres, 5 to 55 ton/acre). Great Lakes (195,000acres, 5 to 55 ton/acre), and the southernCoastal Plains of Florida, Georgia, Louisiana,Alabama, and Mississippi (210,000 acres, 5 to70 ton/acre). In addition, a number of otherproducing regions experienced high soil losseson the additional acreage.

High as these soil losses were, however, theyare not unusual when compared to losses suf-


fered by land in continuous production. Asnoted previously, many areas that are criticallyimportant to U.S. grain production routinelylose soil at rates well above the 5-ton/acre-yrmaximum recommended by SCS. Assumingthat much of the converted land was taken outof relatively nonerosive uses (the 4 millionacres of grassland and woodland, nearly halfthe total, would have suffered virtually noerosive losses if left undisturbed), the erosionexperienced on the additional acreage wasonly slightly worse than the average erosionrates on all U.S. cropland. On the other hand,the lands designated as inadequately pro-tected did have much higher erosion than aver-age. The conclusion appears to be that a rapidincrease in land under production will not nec-essarily cause proportionately more erosionthan our current experience would lead us toexpect, but that conservation planning andtreatment will be required to keep erosionrates from escalating beyond current rates.

Potential Impacts of Production ofBiomass for Energy Feedstocks

Most proposals for using the agricultural sys-tem to produce energy feedstocks do not con-template growing and harvesting systems thatappear to be radically different from currentlarge-scale mechanized food-growing systemsfound in the Corn Belt and other centers ofAmerican agriculture. Proposals centeringaround gasohol, for example, assume that atleast the near-term feedstock (after foodwastes and spoiled grains are used up) will becorn and other conventional starch or sugarcrops. Even the more radical systems—for ex-ample, tree plantations — can be viewed as var-iations of common agricultural systems.

The key to identifying the impacts of imple-menting the various approaches to energyfeedstock production is to identify those dif-ferences from today’s systems that are mostcritical to causing differences in the impacts.These differences in impacts primarily dependon differences in:

• quality and previous use of the land,

● production practices, and● type of crop grown.

Land Quality and Previous Use

The land available for growing biomasscrops consists of cropland that is presently notin intensive use— for instance, land used togrow native hay— and land currently in range,forest, or other use that can be converted tocropland. Table 30 presents SCS estimates ofcropland not currently being utilized to itsmaximum production potential, and landavailable for conversion to cropland in 1977.(The acreage “not in intensive use” includesland where the current use meshes with thefarmers’ desired mix of livestock and crops andthus is unlikely to be converted to more inten-sive use; thus, the table may overestimate theacreage available for switching to biomass pro-duction.) Table 31 presents SCS estimates ofthe rates of erosion on these lands, by Iand useand capability class.

The data shows that there is a very substantialamount of land available for biomass productionthat could be cultivated with few environmentalproblems. For example, table 30 shows wellover 3 million acres of the highest quality(class I) land with high and medium conversionpotential. Over 10 million acres of high-qualityclass I I (for brief definitions, see table 30) landrequiring some drainage correction is avail-able. However, there currently is no guaranteethat land for biomass production will be selectedfor its environmental characteristics. Erosion po-tential, which is of critical environmental im-portance, is only one of several characteristicsused by farmers to decide whether to put landinto production. Characteristics such as con-tiguity of land, current ownership, and the costof conversion may be the deciding factors.

According to table 30, farmers currentlyhave biased their choice of land for row cropcultivation somewhat in favor of the lesserosive lands. Over 11 percent of land in rowcrops is prime class I land with both high pro-ductivity and minimal erosion. In contrast,other land uses typically have about 4 or 5 per-


Table 30.–1977 Cropland and Potential Cropland Erosion Potential (in thousand acres, % of total acreage)

Present croplandnot in intensive use

(rotation hay and

Present cropland in intensive usepasture, occasionally

improved/native Potential cropland

Class Row crops Close-grown crops hayland) High potential Medium potential1. Excellent capability, few restrictions. . . . . . . . . . . . . . . . 23,034

(11.3)Il. Some limitations, require moderate conservation practices

Erosive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45,954(22.6)

Other problems ... ... . . . . . . . . . . . . . . . . . . . . . 58,657(28.9)

Ill. Severe limitations, reduced crop choice and/or specialconservation practices required

Erosive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28,054(13.8)

Other . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27,676(13.6)

IV. Severe limitations, more restricted than aboveErosive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9,159

(4.5)Other . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5,436

(2.7)V-VIII. Generally not suited. . . . . . . . . . . . . . . . . . . . . . . . 5,728

(2.6)

Total, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203,243Percent of land that is erosive . . . . . . . . . . . . . . . . . . . . . . 40.9

4,471(3.4)

23,463(22.4)22,762(21 .7)

26,997(25.7)10,811(10.3)

9,324(8.9)2,933(2.8)

345(0.3)

104,89057.0

2,389(4.2)

11,718(20.8)9,855

(1 7.5)

12,561(22.3)6,557

(1 1.6)

5,701(10.1)3,154(5.6)4,479(7.9)

2,186(5.5)

10,543(26.3)8,278

(20,7)

7,893(19.7)4,797

(12.0)

1,896(4.7)1,601(4.0)2,888(7.2)

1,412(1 .5)

13,921(14.8)10,750(11 .3)

25,142(26.7)12,703(13.4)

11,531(12,3)7,210(7.6)

12,248(13.0)

56,414 40,08253.1 50.7

94,91753.4

SOURCE 1977S011 Corrsewahon Serwce Naflona/Eros~on /rrventory Eshrrale (Washington, D C SoIl Conservation Service, U S Department of Agriculture, DecemtNr 1978)

Table 31 .–Moan National Erosion Rates by Capability Class and Subclass (rates are in ton/acre-yr)

Potential

Class/subclass Row crop Close grown Nonintensive

Class 1. Excellent capability, few restrictions . . . . . . . . . 3.46” 1.75 0.66Class Il. Some limitations, require moderate conservation

practices/erosive . . . . . . . . . . . . . . . . . . . . . . . . . . 6.51 3.67 0.96Class n/other . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.46 2.55 0.43Class Ill. Severe limitations, reduced crop choice and/or

special conservation practices required/erosive . . . 12.39 6.62 1.51Class Ill/other. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.41 2.51 0.51Class IV. Severe limitations, more restricted than

Ill/erosive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17.88 12.20 2.93Class IV/other. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.52 1.85 0.45Classes V-VIII. Generally not suited/erosive . . . . . . . . . 46.82 19.61 5.42Classes V-Vlll/other. . . . . . . . . . . . . . . . . . . . . . . . . . 14.26 3.27 0.80

High Medium

0.31 0.35

0.67 0.710.30 0.31

1.08 1.280.21 0.28

2.01 2.280.46 0.432.38 4.151.51 0.38

SOURCE 1977 Sod Conservaflori Serwce Naf~ona/ Erosion Irwentory Estmate (Washington, DC SoIl Conservation Service, U S Oepaflment of Agriculture, December 1978)

cent of their land classified as class 1. In land towards use of less erosive land is not surpris-quality classes I through IV, 43 percent of the ing.row-cropped acreage is erosive, whereas over50 percent of every other land use category is Close-grown crop cultivation is considerablyerosive. Because row crop cultivation is gener- Iess erosive than row cropping. Apparently inally the most vulnerable to erosion, this bias response to this, farmers have placed close-

78 ● VOl. II—Energy From Biological Processes

grown crops on lands that are more vulnerableto erosion; 60 percent of close-grown croplandacreage is erosion-prone.

It is important to look beyond these overallpercentages and examine the percentage ofland in each land use capability class. Theerosivity of lands categorized as E (erosive] bySCS appears to be a strong function of thecapability class. For example, the average 1977annual sheet and rill erosion rates on erosivecroplands in intensive use were estimated tobe (from table 31 ):

Class I . . . . . . . . . . . . . . . . . . . 3.18 ton/acre-yrClass IIE. . . . . . . . . . . . . .....5.55Class IIIE . . . . . . . . . . . . .....9.56Class IVE . . . . . . . . . . . . ....15.02Class V-VIIIE . . . . . . . . . ....34.70

Thus, the erosion danger appears to increasemarkedly as land capability declines. If theerosive portions of the land with future bio-mass potential (present cropland not in inten-sive use and land with switching potential)were skewed towards the lower quality classes,then an examination of the overall erosivepotentials would underestimate the erosiondanger presented by massive shifts to intensivecultivation. An examination of table 30 in-dicates that the erosive portions of the presentcropland not in intensive use and the high-potential land are somewhat skewed towardsthe lower quality lands when compared withpresent cropland, but the differences do notappear to be substantial. For example, whereas53 percent of erodible land in intensive use isclass I I I E or below, 60 percent of erodible landwith high biomass potential is in this erosivityrange.

The surprising implication of the statisticspresented in table 30 is that the land availablefor agricultural biomass production is not radical-ly different in its erosion qualities from land cur-rently being utilized for intensive agricultural pro-duction. Although clearly some selection hasbeen made in utilizing the best lands and keep-ing idle the worst, this selection process ap-pears to have been skewed by other physicalattributes and economic and social factorsthat are as important or more important thanerosion potential. It appears that erosion prob-

Iems will be significant in adding new lands tointensive agricultural production, but it doesnot appear on a national basis that these prob-Iems will be very much worse than those thatcould be predicted by extrapolating from cur-rent erosion rates.

It is possible to estimate quantitatively thegeneral erosion danger from an expansion ofintensive production by utilizing the data intables 30 and 31 and by making the followingsimplifying assumptions:

●

●

●

The 1977 erosion rate for land under inten-sive production, for each land capabilitysubclass, is representative of the erosionthat would occur if additional land in thatsubclass were to be put into intensive pro-duction.Given a desire to place additional landinto intensive production, farmers will se-lect land mainly from cropland not now inintensive production and “high potential”land, and their selection will be random(this is probably a “worst case” assump-tion but may not be seriously in error judg-ing from the discussion above).A mix of row and close-grown biomasscrops will be grown, with the mix beingabout the same as the 1977 food crop mix.

Under these conditions, the average erosionrate on the new land put into intensive produc-tion will be about 7.5 ton/acre-yr. For compari-son, the 1977 erosion rate on intensively culti-vated lands was 6.26 ton/acre-yr. In otherwords, erosion from additional acres devotedto growing biomass crops may be about 20 per-cent worse than similar acreages of food cropsin production today (this assumes no Govern-ment action to improve land selection). Giventhe substantial uncertainties in this estimate,the 20-percent differential is well within therange of possible error. It is, however, consist-ent with what is known about agricultural landselection and the quality of available (but un-developed) farmland.

Because land quality is affected by net rath-er than gross erosion — i.e., by the differencebetween erosion and soil replacement–the ef-fect on the land of relatively small changes in


erosion rates may be greater than would be ap-parent at first glance. For example, if the aver-age topsoil replacement rate is 5 ton/acre-y r,*the 7.5 ton/acre-yr biomass erosion rate yieldsa 2.5 ton/acre-yr net soil loss, versus 1.26ton/acre-yr net loss from food production.Thus, while a large-scale expansion of acreagefor biomass production may have effects onwaterways that are similar in magnitude to theeffects of present intensive agriculture, thisacreage may lose its topsoil layer at twice therate of current agricultural land. However, itshould be noted that the rate of loss is (on theaverage) fairly low.

Aside from new biomass cropland’s capabili-ty to resist erosion and its productive poten-tial, an important factor determining the en-vironmental impact of the conversion to inten-sive production is the nature of the previousland use. For example, the conversion of landin rotation hay and pasture to intensive cropproduction would clearly be valued differentlyfrom a conversion from forest. Because differ-ent groups value alternative land uses differ-ently, it is difficult to place more or less weighton the conversion of one land use relative toanother. It seems likely, however, that most en-vironmentally oriented groups would prefer tosee the conversion of lands that are manmademonoculture (e. g., improved haylands) beforemore natural and diverse ecosystems wereconverted.

The cost of conversion will play an impor-tant role in determining which lands will bechosen. At the present time, conversion of pas-tureland and hayland is likely to be less expen-sive than conversion of forest, and land con-versions may be expected to be skewed awayfrom forests. Least expensive of all to convertare lands currently in set-aside, and these arelikely to be the first to be taken. The cost offorest conversion may, however, be loweredsignificantly if the demand for wood-for-ener-gy rises with the demand for energy crops (be-cause the value of the now-worthless cullwood and slash can be traded off against clear-ing and site preparation costs). Thus, there is

‘This IS almost certainly very optlmlstlc, but SCS guidelinesdef Ine 5 ton/acre-yr as an acceptable rate for many lands

no guarantee that forests—which make upabout one-quarter of the high- and medium-po-tential cropland55— will not be cleared in sig-nificant quantities if large-scale conversion tobiomass crop production occurs.

Production Practices

A variety of practices are available to con-trol the erosion and other impacts of farming.These range from crop rotation to conserva-tion tillage to scouting for pest infestations.Table 32 provides a partial list of these prac-

Table 32.–Agricultural Production PracticesThat Reduce Environmental Impacts

Runoff and erosion controlContour farming or contour stripcroppingTerraces and grass waterwaysMinimum tillage and no-tillCover cropsReducing fall plowing

Reducing chemical pollutionScouting (monitoring for pest problems)Disease- and insect-resistant cropsCrop rotationIntegrated pest managementSoil analysis for detecting nutrient deficienciesNitrogen-fixing cropsImproved fertilizer and pesticide placement, timing, and amountImproving irrigation efficiency-trickle irrigation, etc.Incorporating surface applications into soil


tices. Their future use will play a critical role indetermining the environmental impacts of bio-mass energy production.

The availability of these controls should notbe confused with the probability that impactswill not occur. in fact, it is unwise to assumethat the use of many of the practices listed intable 32 will be widespread. There are a num-ber of reasons for this.

First, the costs of the controls may consid-erably exceed the farmer’s perceived benefits.The effects of erosion on water quality arelargely “external” effects; although the farmermay benefit from the control efforts of others,he is unlikely to benefit from any water qualityimprovements caused by his own efforts. This

55 Natjona/ ~rosjon Inventory Estimate, op c It

80 ● Vol. 11—Energy From Biological Processes

problem of “external” benefits is endemic toAmerican agricultural practices. It is, in fact,merely one aspect of the “tragedy of the com-mons” that hinders voluntary environmentalcontrol in virtually all of man’s activities. Also,any success in delaying or preventing produc-tivity declines from erosion effects may bemasked by improvements in other productionpractices and in any case would be very longterm in nature. The farmer must balance thesebenefits against very high erosion controlcosts. SCS has examined the effects on farmproduction costs of requiring reductions incurrent erosion rates on croplands. For exam-ple, requiring a 10-percent reduction in each of105 producing areas would raise corn produc-tion costs by $0.07/bu in 1985. Requiring allacreage to conform to a maximum allowableerosion rate of 10 ton/acre-yr (twice the “noproductivity loss” rate) would cost $0.31/bu ora 16-percent increase over the projected 1985cost without controls. Further constraintscould raise costs astronomically (a 5-ton/acre-yr constraint leads to a $23.70/bu productioncost) because heroic efforts must be made onsome acreage in order to meet the con-straints. 56 Although these estimates are sharplydependent on a number of critical assump-tions (e.g., the role of Federal soil conservationassistance is ignored), they demonstrate thelarge potential cost (and price) increases thaterosion control requirements could cause.

Second, there are substantive scientific dis-agreements about the actual environmentalbenefits achieved by these controls. Some ofthe controls may reduce one environmentalimpact at the expense of increasing others. Aprimary example of this is the effect of someerosion controls— reductions in fall plowingand conservation tillage —on pesticide use.These controls leave crop residues on the sur-face, and the residues in turn act to break theforce of raindrops on the soil and drasticallydecrease erosion and runoff. Because the resi-dues harbor plant pathogens and insect pests,pesticide requirements will go up sharply.Also, increased applications of herbicides areused for weed control to compensate for the

’66. English, lowa State University, personal communication,June 15,1979.

reduced tillage. The net effect on the environ-ment is not entirely clear because a largesource of pesticide entry into surface waters —adsorption on soil particles and transport inrunoff — is considerably reduced by the con-trols, but EPA has identified increased pesti-cide use with conservation tillage as a signifi-cant problem .57 Tables 33 and 34 identify ingreater detail the environmental tradeoffs in-volved in erosion controls.

Third, some of these controls may appear tobe incompatible with the present agriculturalsystem and may not be accepted by farmers.For example, the use of nitrogen-fixing crops,cover crops, and crop rotations conflict withtoday’s large-scale, highly mechanized, chemi-cal-oriented farming although they were wide-ly practiced in the past. Although some scien-tists argue that the economic advantages ofpresent methods will evaporate (or have al-ready evaporated) in the face of rising pricesfor energy and energy-intensive agriculturalchemicals, and that the long-term environmen-tal viability of the methods is questionable, therelative advantages and disadvantages of thepresent system and its alternatives are a sub-ject of intense controversy in the agriculturalcommunity— with defense of the present sys-tem having the upper hand at present. It ap-pears virtually certain that in the absense ofGovernment intervention the provision offeedstocks for energy production will rely pri-marily on a mechanized, chemical-orientedphilosophy modified only by any economicpressures arising from increases in energyprices. Any substantive changes from this phi-losophy would represent essentially a revolu-tion from established practice and would beunlikely because the present system has clear-ly succeeded in providing a reliable supply offood at (comparatively) moderate prices.

Crop Types

The environmental impacts of growing andharvesting agricultural crops for energy willvary strongly with the type of crop grown,since different crops have different fertilizerand pesticide requirements, water needs, soil

57 Environmenta/ /mp/ications of Trends, op. cit.

Table 33.-Environmental Pollution Effects of Agricultural Conservation Practices

Pollutant changes m Pollutant changes mmedia: surface water media: ground water– Pollutant changes m Pollutant changes in

Extensiveness Resource use sediment Nutrients Pesticides nutrients–pesticides media: soil media: air

Contour farming/contour stripcroppingAcreage of crops farmed Fertizer and herbicideon the contour or strip- use remain constantcropped decreased 25% Insecticide use will re-between 1964 and main constant to very1969 and continued to slight increases.decrease slightly to1976, Contour farmingis more widely used innonirrigated crop pro-duction than m irrigatedcrop production.

Terraces and grass waterways

Sediment loss can be re-duced substantially onmoderate slopes, butmuch less on steepslopes, Reductions upto 50% are possible,but average reductionswill be about 35%.Contour stripcroppingcan reduce sedimentlosses more than con-tour alone. (Note: re-search shows substan-tial loss can occur withcontour watershedswith some soil types,with long slopes and/orwith steep slopes. )

Terraces and-grass wa- Fertilizer, herbicide, and Substantial reductions interways are not impor-tant in irrigated produc-tion, but are Importantfor nonirrigated crops.However, only 6% of allacres in 1969 had ter-races The acres withterraces in 1976 couldhave increased or de-creased slightly.

insecticide use is not sediment and runoffexpected to increase can usually be ex-(fertilizer could increase pected.if production percropped acre is ex-pected to increase tocompensate for landtaken out of produc-tion). However, terracepractices will not re-quire more fertilizers.Costs and maintenanceincrease for terraces,

Nutrients associated with Pesticlie reductions will Loss of nutrients and Erosion losses can be re- Pesticide losses throughsediment will be re- be less than that for pesticides through duced up to 50% with volatilization will de-duced, but reductions nutrients since a great- ground water will re- average reductions of crease if they are incor-may be proportional to er amount of pesticide main constant or de- 12Y0 (see conclusions porated into the soil bythe amount of sediment IS lost through surface crease slightly. How- on sediment). mechanical meanslost, water than bound to ever the amount of N

sediment. leached IS small com-pared to amount thatcan be lost in runoffand loss of pesticides toground water IS minorwith proper applicationrates.

Reductions in nitrates Reduction of pesticide N m ground water may Substantial reductions m No change.and phosphates are ex- residues in surface be reduced, based on erosion can result.pected with decreased water could be substan- limited research data.soil loss and surface tial with terrace sys- Leaching of pesticides IS

runoff. Reductions terns, since both sur- not likely to result incould be substantial face runoff and soil loss significant loss withwith some soils and are reduced. normal applicationscropping systems. rates

SOURCE U S Enwronmental Protection Agency, ErWlrOnmenfal /mPllCaf10/ts of Trencfslfr ~gricu/(ure and Si/v~cu/ture, Vo/urne // &wlronrnerrla/Ef feck of Trends, EPA-600/3-78-102, December 1978

Table 33.–Environmental Pollution Effects of Agricultural Conservation Practices-continued

Pollutant changes m Pollutant changes inmedia: surface water media: ground water— Pollutant changes m

Extensiveness Resource use sediment Nutrients Pesticides nutrients—pesticides media: soil

Conservation tillage; no-tillApproximately 2.6% of Fertilizer and herbicide Sediment reductions of While Iarqe soil loss re- Effect of no-till on pesti- Niall cropped land was use increases by 15%, 50 to 90% will result. ductions will tend to re-no-till in 1977. While insecticide use by 11 %. duce nutrient losses,this Practice is expected “An estimated 5 million fertilizer use will in-to increase to Iimiteduse in 2010, currentprojections (up to 55%of crops under no-till in2010) seem high. Ex-tensiveness may onlybe 10 to 20% in 2010.

acres of land could be crease by 15%. Thereshifted to crop produc- will probably still tendtion with no-till and re- to be reductions in totalduced-till methods. La- nutrient loss, but re-bor costs are reduced, duction will not be pro-More water will be con- portional to reductionsserved with no-till, asmuch as 2 inches peryear.

Conservation tillage; reduced tillageIn 1977, an estimated Fertilizer use will in-58.8 million acres (19%of total cropped acres)will be reduced tilled.An additional 40 millionacres will be classifiedas less tilled. Less tillincludes chisel plowing,disking once instead oftwice, and planting inrough ground.

In 2010, a total of 40%of all cropland may beclassified as reducedtilled.

crease slightly. Herbi-cide use is up (0.6%)and insecticide use in-creases by 8.6%. Anestimated 5 millionacres of land will beshifted to crop produc-tion with reduced andno-tillage methods. La-bor output will de-

in soil loss. N contentof soil may also in-crease from weatheringof crop residues.

cide losses is not welldocumented. Loss tosurface water is greaterwhen the compound issurface applied and notincorporated in the soil,and 11‘Yo more insecti-cides and 15% moreherbicides will be usedfor no-till. While reduc-tions of pesticides insurface water could oc-cur, current researchdoes not prove this. In-creased use and sur-face application, evenwith reduced soil losswith no-till, could evencause slight increasesin pesticide losses.

Sediment will be reduced There will probably be Effect of reduced tillagean average Of 14%. Re- reductions in total nutri- on pesticide loss IS notduced tillage is less ef - ent loss to surface wa- well documented. Lossfective than no-till in ter, but reduction will to surface water iscontrolling soil loss, not be proportional to greater when a pesti-

reductions in soil loss cide is surface applied(14%), and total pesticide use

IS 9% greater for re-duced till. While reduc-tions of pesticides insurface water could oc-

crease. Energy to plant cur, there is notcrops decreases, but enough research data toincreased energy will be support this.used in manufacture ofincreased fertilizers andinsecticides. Some soilmoisture will be con-served with reducedtillage.

titrates in ground water Erosion losses will be de-will show no change to creased 50 to 90%.slight increases. Pesti- Crop residues will in-cide loss to ground crease which may resultwater will not be signifi- in increased N loss tocantly changed with no- the soil or available fortill practices. runoff. Additionally,

residues may provide ahiding place for pestsand increase the in-cidence of pests.

Nitrates in ground water Erosion losses decreasewill show no change to an estimated 14%.slight increases. Pesti- Wind erosion losses willcide levels in ground also decrease slightly.water will not be signifi- Crop residues increase,cantly changed with re- which lead to increasedduced tillage. N available to the soil

for leaching and runoff.Residues on soil alsoincrease the incidenceof pests.

With some pesticides, in-increased volatilizationwill occur with surfaceapplications. The vaporpressure, molecularweight, and other prop-erties of a pesticide willdetermine the extent ofvaporization.

Surface applications ofsome pesticides typesleads to increased vola-tilization losses. Thevapor pressure, molecu-lar weight, and otherchemical properties of apesticide will determinethe extent of vaporiza-tion.

SOURCE U S. Enwronmental ProtectIon Agency, Envlmnmen?a/ /mp/icaf/onso( Trends lnAgncu/ture and Sl/vlcu/ture, Vo/urrre //: Environmenfa/ Eflecfsot Trends, EPA-600/3-78-102, Oecember 1978.


Table 34. -EcoIogical Effects of Agricultural Conservation Practices

Contour farming/contour stripcroppingExtensiveness of contouring in 1985 (over 1976 use) will be low, but will increase by 2010. Beneficial aquatic effects result from decreased turbidity and

pesticide residues in surface water. Species diversity will also increase in the aquatic ecosystem. Decreased erosion and retention of soil nutrient cycleswill have long-term beneficial terrestrial effects. Since pesticide residues at current levels in drinking water are not known to be a human health hazard,reduction of pesticide residues will have no significant human health effects. However, if pesticide residues are later determined to be dangerous at cur-rent levels, then human health effects would be beneficial.

Terraces and grass waterwaysTerraces are more effective than contouring in reducing pollutants, but extensiveness of use is tower for terraces. Aquatic effects are decreased turbidity,

increased species diversity, and decreased pesticide residues. Terrestrial effects are beneficial, resulting from increased vegetation on terraces andgrass waterways, increased diversity of wildlife, and more pathways for animal populations to travel. Valuable topsoil will also be retained. Based onpresent knowledge, there is no known human health effect. Decreased sediment in water might result in an unpleasant taste or odor in drinking water.

Reduced tillageReduced tillage (with crop residues remaining) is less effective than no-till in reducing soil loss, but extensiveness of reduced tillage will be greater. There-

fore, the intensity of ecological effects are comparable for the two practices. Sediment reductions will reduce turbidity and increase species diversity.However, the potential for increased pesticide residues in surface water could have adverse effects on the aquatic ecosystem. Crop residues remainingon the soil and decreased soil loss are beneficial to the terrestrial system, but increased pesticide use will have adverse effects on nontarget organisms.Human health effects will not be significant.

No-tillAquatic and terrestrial effects are both beneficial and adverse. Aquatic systems will benefit from reduced turbidity and increased species diversity. How-

ever, pesticide residues in surface water could potentially be increased with no-till and create adverse effects in the aquatic ecosystem. Increased pesti-cide use can also have adverse effects on nontarget terrestrial life. Retention of crop residues and reductions in erosion will have beneficial terrestrial ef-fects. Human health effects will not be significant since pesticide residue in surface water should still be within safety limits even if they increase slightlywith no-till.

SOURCE U S Enwronmental Protection Agency, Hrwromnerrfal lrnpllca(~orrs of Trerrds m Agrlcullwe arrd Sf/wmdLve, I/ohmre // Errvrorrrnerrta/ Hfeck of Trends, EPA-600/3-78-102, Oecember 1978

preparation methods, harvesting times, andother factors that may potentially affect im-pact. Some of the more important crop-deter-mined factors are:

● Annual or perennial, — Perennial crops(trees, sugarcane, perennial grasses, etc.)offer a substantive environmental advan-tage over annuals because their roots andunharvested top growth protect the soilfrom erosion year round, while annuals of-fer protection only during the growing

●

season and require seasonal tilling (unlessno-till is used) and planting.

● Row or close-grown crops. — Row crop cul-tivation is generally more erosive than cul-tivation of close-grown crops. For exam-ple, the average erosion rates of close-grown crops are significantly lower thanthose of row crops in every land capabili-ty class and subclass shown in table 34. Ingeneral, the rates of the close-grown cropsappear to be about half those of the rowcrops.

In the previous calculation of the ex-pected average erosion rates from newbiomass production, a mix of row andclose-grown biomass crops (in the same

tion) would be expected to have an aver-age (sheet and gully) erosion rate of about7.5 ton/acre-yr compared with about 6.3ton/acre-yr for food production. If the en-tire biomass crop were a row crop (e. g.,corn for large-scale alcohol production),the average erosion rate from the biomassacreage is estimated to be 9.3 ton/acre-yr— almost 50 percent higher than the ero-sion rate from food production.Water requirements. — High irrigation wa-ter use means greater competition for wa-ter among competing uses, greater draw-down of streams and consequent loss ofassimilative capacity, potential for entryof more salts into surface and ground wa-ters, depletion of aquifers (ground watermining), and energy use for pumping.There are substantial differences in waterconsumption among different crops. Forexample, irrigation requirements for cropsin Arizona during a dry year58 are:

Water use, acre-ft/ton of cropW h e a t . . . . . . . . . . . . . . 0 . 9O a t s . . . . . . . . . . . . . . . 1 . 6B a r l e y . . . . . . . . . . . . . . 1 . 3A l f a l f a . . . . . . . . . . . . . 0 . 7

proportion as existed in 1977 food produc- sacon~~rvat;on NeecjS Inventory, OP. Cit


●

●

●

Most discussions of biomass energyassume that irrigation generally will notbe used in growing feedstocks. However,an extension of the types of irrigationwater subsidies now available to Westernfarmers, however unlikely, could lead tosuch use.

Soil requirements. —The ability to utilizemarginal lands can avoid the problem ofcompetition with food production that isa major environmental and social/eco-nomic issue in evaluating biomass fuels.As discussed elsewhere in this chapter,however, the potential for high biomassyields under marginal soil, temperature,and water conditions has been exagger-ated.

Pesticide requirements. —The importanceof reducing pesticide applications is amatter of considerable controversy. How-ever, crops that have low pesticide re-quirements will be perceived as more en-vironmentally benign. In some instances,present pesticide use may be a poor in-dicator of future requirements for energycrops because cropping practices andland characteristics may be altered signifi-cantly in going to a crops-for-energy sys-tem. For example, regulatory restrictionson soil erosion could force virtually uni-versal use of conservation tillage and con-sequent increases in herbicide and (to alesser extent) insecticide applications. Thelack of esthetic requirements for biomassfeedstocks might also lead to some de-crease in pesticide requirements, but thiseffect may be small because minor insectdamage can lead to further damage byfungal and viral infections (especially dur-ing storage). Finally, although pesticide re-quirements for grasslands currently arevery low, pest problems conceivably mayaccelerate if productivity is pushed by ex-panded use of fertilizers.

Fertilizer requirements. – In general, highfertilizer requirements are an environmen-tal cost because of the energy used to pro-duce the fertilizer and the nutrient runoffthat results from applications. However,

●

crop requirements for very high levels ofnitrogen may be an environmental advan-tage; some high-nitrogen crops are com-patible with land disposal of sewagesludge and effluents and thus can be animportant component of urban sewagetreatment strategy.

Yield. — Because yield per acre determinesthe amount of land necessary to producea unit of energy, it is one of the most im-portant factors determining impact. Meas-urements of input requirements (water,fertilizer, pesticides, etc.) and measurabledamages (such as erosion) on a “per acre”basis are inadequate measures of relativeenvironmental impact because of thelarge variation in biomass yields fromcrop to crop. For example, corn is widelyperceived as an extremely energy- and wa-ter-intensive crop, but its very high yieldsessentially cancel its high “per acre” fer-tilizer, pesticide, and water needs; it is, infact, a relatively average crop on an “en-ergy per ton of product” basis.

The importance of these factors in determin-ing environmental impacts is extremely siteand region specific. For example, water re-quirements clearly are more important in thearid West than in the wet Southeast, while fac-tors affecting sheet and rill erosion potentialare more or less important in the reverse order.Much of the data needed to assess the differ-ent potential crops are not available, and thusit is premature to suggest which crops wouldbe the most environmentally benign in each re-gion or subregion. There are sufficient data,however, to draw some rough sketches of someof the possible advantages or disadvantages ofseveral of the suggested biomass crops.

Corn has been most often mentioned as theprimary candidate for an ethanol feedstock. Itis an annual row crop and thus a major contrib-utor to erosion, but much of the land on whichit is grown is relatively flat, a factor that limitsthe erosion rate. Corn’s high yield rate—cur-rently about 100 bu/acre, or about 260 gal/acreof ethanol —will minimize the land use impact


of additional production, although yields onnew lands will not be as high as the current av-erage, and the land displaced would be of highquality.

Because the protein-rich residue from thefermentation (ethanol producing) process is asubstitute (although not necessarily a perfectone) for soybean meal in cattle feed, switchingexisting cropland from soybean to corn pro-duction may allow large quantities of ethanolto be produced using far less acreage thanwould be needed if corn for ethanol produc-tion were planted only on new acreage. As dis-cussed in the section on “Energy PotentialFrom Conventional Crops,” corn’s effectiveyield per acre of new land could grow by over300 percent (i.e., about three-fourths of thecorn used for ethanol would be grown on landformerly planted in soybeans with no loss innational food and feed values) as long as thesoybean meal market remained unsaturated.Significant uncertainties concerning the cornresidue’s nutritive value, potential corn yieldson soybean land, soybean market response,and other factors must be overcome, however,before this crop-switching scenario can be ac-cepted as valid. In the absence of the neces-sary research, the higher estimate of new landrequired for each gallon of ethanol producedshould be used as a pessimistic measure of po-tential impact. At low levels of production, themore optimistic, lower acreage requirementsare likely to be accurate, but the requirementsmay increase as production increases. Above 2billion to 7 billion gal of ethanol produced an-nually, feed markets would be saturated evenunder the most optimistic assumptions and ad-ditional ethanol production would requirecropland conversion at the higher rate.

Sweet sorghum has been praised as a crop ofhigh biomass potential for fermentation andalcohol production. Although ethanol yields of260 to 530 gal/acre have been projected, theseprojections are based on minimal — and clearlyinadequate — experience. However, these highyields, if confirmed, would limit displacementof alternative land uses. Sweet sorghum maybe more tolerant of marginal growing condi-tions than corn, which could lead to a lower

level of displacement of the most productiveecosystems.

Sugarcane has been suggested as a biomasscrop for alcohol production in Hawaii and theGulf Coast. Because its cellulosic content ishigh enough to supply all of the heat energynecessary to ferment the sugar and distill alco-hol from it, no coal or other fossil fuel usewould be necessary to power the system.Sugarcane requires high-quality land and thusmay displace particularly valuable alternativeland uses.

Perennial grasses can be supplied in largequantities by increasing yields on present acre-age with more intensive harvesting and fertili-zation; the present average yield is 1½ to 2ton/acre, and this can be increased to 3 to 5tons. Because perennials provide excellent ero-sion control, and because no additional acre-age would have to be converted from alterna-tive uses, the environmental impact of a grass-based biomass strategy should be far less thanthat of a strategy based on annual crops. Envi-ronmental impacts of some significance couldoccur because of the expanded use of fertilizer(150 lb N, 30 to 50 lb P2O 5, 80 to 150 lb K2 foran incremental production of 78 gal of ethanolon each acre) and pesticides. Recovery ofadded fertilizer is very high for grasses, how-ever, so the potential for water pollution willbe less than for annual crops. Also, there isuncertainty about changes in susceptibility todisease and insect damage because of the in-tensification of production, and substantialnew use of pesticides conceivably could be re-quired. Finally, the frequent harvesting andgreater use of chemicals may disrupt the popu-lations of wildlife that now flourish in the lessintensively maintained grasslands.

Trees may be grown plantation-style and har-vested by coppicing to supply significant quan-tities of biomass. A carefully designed treeplantation should have few problems of ero-sion unless cultivation is practiced (which ap-pears unlikely); however, harvesting may con-ceivably create an erosion problem unless low-bearing-pressure machines are used to avoiddamaging the soil. Tree plantations present

86 . Vol. II—Energy From Biological P r o c e s e s

basically the same ecological problems as do from weeds– and consequently larger herbi-agricultural monocultures — higher potential cide requirements –but the sheltering effectfor disease attack and displacement of alterna- of the tree canopy and the greater ability oftive ecosystems. The spacing necessary for tree some tree species to compete for water maygrowth may also allow greater competition counterbalance this effect.

Environmental Impacts of Harvesting Agricultural Residues

The residues from agricultural productionhave a number of significant effects –benefi-cial or otherwise—when left on the land. Un-derstanding these effects is critical to under-standing the potential environmental impactsof the collection and use of these residues asan energy feedstock.

The effects of residues left on the land in-clude (table 35):

●

●

●

●

Control of wind and water erosion. –Retention of residues as a surface cover isa major erosion control mechanism onerosion-prone lands. For example, residueretention on land that is conventionallytilled (i.e., plow-disk-harrow) can cut ero-sion in half.59

Retention of plant nutrients. – Residuesfrom the nine leading crops in the UnitedStates contain about 40, 10, and 80 per-cent as much nitrogen, phosphorus, andpotassium, respectively, as in total fertil-izer use in U.S. agriculture.60

Enhanced retention of water by soils andmaintenance of ability of soil surfaces toallow water infiltration.Maintenance of organic matter levels (nec-essary to maintain soil structure, ion ex-change capacity, water retention proper-ties) in soils. –Croplands in the UnitedStates have lost major portions of their or-ganic content. Reductions (in North Cen-tral and Great Plains soils) of one-half totwo-thirds of what was present under na-tive grassland have been cited.61 Reten-tion of crop residues is a critical factor inmaintaining organic matter levels.

“W. E. Larson, et al., “Residues for Soil Conservation, ” paperNo. 9818, Science Journal Series, AR S-USDA, 1978.

‘“I bid.“Ibid.

Table 35.–Environmental impacts of Plant Residue Removal

Water●

●

●

Increased erosion and flow of sediments into surface waters if restric-tions on removal are not observed, causing increased turbidity,obstruction of streams, filling of reservoirs, destruction of aquatichabitat, increase of flood potential; under circumstances where con-servation tillage is encouraged by removal of a portion of the residues,erosion and its consequences will decrease,Increased use of herbicides and possible increased flow into surfaceand ground waters if conservation tillage is required for erosion con-trol; in some situations, removal of a portion of the residues would in-crease herbicide efficiency and greater use may not occur.Increased flow of nutrients if more runoff results from decreased waterretention of soil and greater erosivity of soil; if more fertilizer is appliedto compensate for nutrient loss, flow of nutrients will change but thenet affect is not certain.

Air● Dust from decreased cover on land, operation of residue harvesting

equipment (unless integrated operation).● Added herbicides from aerial spraying or as a component of dust.● Decreased insecticides, fungicides.● Reduction in pollution from open-burning of residues, where formerly

practiced.Land● Erosion and loss of topsoil, degrading of productivity if restrictions on

removal are not observed; the opposite, positive effect if conservationtillage is encouraged by residue removal.

● Decrease in water retention capabilities of land, increased floodingpotential if restrictions are not observed.

● Depletion of nutrients and organic matter from soil (nutrients may easi-ly be replaced),

Other• Reduction in plant diseases and pests (if lowering of soil organic mat-

ter does not adversely affect this factor) because residues can harborplant pathogens.

SOURCE: Office of Technology Assessment.

● A number of negative effects dependingon the type of crop and amount of resi-d u e – ” poor seed germination, stand re-duction, phytotoxic effects, nonuniformmoisture distribution, immobilization ofnitrogen in a form unavailable to plants,and increased insect and weed prob-lems."62 In all cases, the residues harborcrop pests; this can be a particularly sig-

6z/mprov;ng Soils With Organic Wastes, OP. cit.

Ch. 3—Agricul ture . 87

nificant problem if single cropping is prac-ticed (the same crop is grown in consecu-tive years). Because the residues shield thesoil, they may hinder soil warming and de-lay spring planting (causing reduced yieldsin corn).

When the problems associated with crop res-idues outweigh the benefits, farmers will phys-ically remove the residue (this practice is nec-essary in rice cultivation) or plow it under inthe fall (a common practice in the Corn Belt).The collected residues may be burned, al-though they have alternative uses such as live-stock bedding. Where removal is normallypracticed, use of the residues as an energyfeedstock is at worst environmentally benignand possibly beneficial (if air pollution fromopen burning is prevented). Because fall plow-ing negates much of the residues’ value as anerosion control, collection of a portion of theresidue is usually considered benign (fullremoval may affect soil organic content, theimportance of which is somewhat in debate).Because an excess of residue may inhibit theeffectiveness of herbicide treatments — espe-cially preemergence and preplant treatments— and also leave large numbers of weed seedsnear the soil surface, removal of a portion ofthe residues on land where they are in excessmay promote the use of reduced tillage byallowing more effective chemical weed con-trol, and thus be considered environmentallybeneficial.

When residues are normally left on the soilsurface as an erosion control, their removal po-tentially may be harmful. However, where sub-stantial quantities of residue are produced onflat, nonerosive soils, a portion of these resi-dues may be removed without significantly af-fecting erosion rates. SCS and the Science andEducation Administration –Agricultural Re-search have sponsored extensive research de-signed to compute the effects of residue re-moval practices and other practices on soilerosion. USDA believes that it can identify thequantity of residues that can be safely re-moved from agricultural lands in all parts ofthe United States. Although controversy existsover the rate of creation of new topsoil, and

thus the erosion rate that will maintain produc-tivity over the very long term, it seems likelythat errors in these computations will notcause significant harm as long as SCS main-tains its monitoring efforts at the current level.

The key to preventing significant environ-mental damage while harvesting large quanti-ties of residues is for the agricultural system toact in accordance with USDA’s knowledge.The discussion of the impacts of U.S. agricul-ture presented previously seems to indicate awillingness among farmers to ignore warningsabout using erosive practices or cultivatingfragile land, in order to gain short-term bene-fits. In the absense of additional constraints, asignificant number of farmers might be willingto remove their crop residues even when ad-verse erosion effects would occur. (interest-ingly enough, some farmers may ignore USDAwith the opposite effect—they may be reluc-tant to remove any residues because of theirfear of erosion and other negative conse-quences). Under these circumstances, the es-tablishment of a market for crop residuescould result in additional erosion from crop-Iands that cannot afford it and add to the al-ready significant sediment burden on surfacewaters caused by current farming practices.

Although the negative effects of any in-crease in erosion are straightforward, other ef-fects that have been associated with residueremoval are more ambiguous. For example, theremoval of pIant nutrients in the residues maybe compensated for by the return of the con-version process byproducts or by chemical fer-tilizers (both of which may have some adverseeffects on water quality). The removal of or-ganic content has been identified as a signifi-cant impact63 and soil scientists have longthought that soil organic content is a criticalvariable of the health of the agricultural eco-system (e. g., increasing the organic content ofsoils can stimulate the growth and activity ofsoil micro-organisms that compete with pIantpathogens). However, despite a variety of pa-pers in the agronomy literature that treat yield

‘) Pimentel, et al., op cit.


as a function of soil carbon level, there is insuf-ficient experimental evidence to establish thatany significant effects on crop yields would oc-cur. Also, the much higher yields of today’s ag-riculture means that removal of half of the res-

Considerable research has been and is di-rected at improving agriculture for food, feed,and materials production. While much of thisresearch is applicable to energy production,the specific goal of producing various types ofenergy crops has not been adequately ad-dressed. Changing the emphasis to energy orenergy and food production and the environ-mental concerns with agriculture suggest sev-eral R&D problems. Some examples are listedbelow.

●

●

●

A wide variety of crops that are not usedas food or feed crops could, potentially,be good bioenergy crops. The promisingvarieties should be developed. From a the-oretical point of view, grasses appear tobe promising candidates for high biomassproducers and on marginal cropland (seech. 4): and arid Iand and saline tolerantcrops may enable the economic use oflands and water supplies that are other-wise unsuited for agriculture.Food and feed crops are usually quite spe-cific as to their use. Corn, for example, isnot interchangeable with wheat. Many dif-ferent types of crops, however, can pro-duce the same or interchangeable bio-mass fuels. Consequently, extensive com-parative studies between various cropsare needed to determine the promisingbioenergy crops for the various soil typesand climates.If both the residues and the grain can besold, then the optimum plant may not bethe one that produces the most grain.Farming practices and hybrids that canchange the relative proportions of grain toresidue in the plant while maintaining ahigh overall yield should be investigated.

idue will leave the same amount of organicmaterial as would have occurred 25 years agoif all of the residue had been left on the land.This is an area that clearly deserves further re-search.

Needs

● Various crop-switching possibilities thatinvolve fuel production should be investi-gated further to determine the extent towhich they can provide fuels and the tra-ditional products from agriculture with-.out expanding the quantity of croplandcultivated. The extent to which the corn-soybean switch actually takes placeshould be studied, as should novel possi-bilities such as sugar beets used for ani-mal fodder. Included in this should be in-vestigations of the effect of substitutingcurrent feed rations with varying amountsof forage-distillers’ grain, forage-corn glu-ten mixtures, and other feeds that may beinvolved in the crop-switching schemes.

● Large-scale biomass development will re-quire the placement of millions of acresof land — now in low-intensity agriculture(e.g., pasture), forest, or other uses– intointensive production, coupled in manycases with very high rates of removal oforganic matter. Environmental R&D thatshould accompany, and preferably pre-cede, such development includes:–further investigation of long-term ef-

fects of reduction in soil organic mat-ter,

–determination of pesticide require-ments for high-yield grasses in intensiveproduction,

— intensification of breeding programsfor insect/disease-resistant strains ofcrops with high biomass potential,

–determination of economically opti-mum strategies for minimization of soilerosion, and

–development of effective/ programs toimprove farmer (environmental) behav-ior.

Chapter 4

UNCONVENTIONALBIOMASS PRODUCTION

Chapter 4.— UNCONVENTIONAL BIOMASS PRODUCTION

P a g eIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91Genetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91Crop Yields . * . . . . . . . . . . . . . . 92Unconventional land-Based Crops. . . . . . . . . . . . 95

Lignocellulose Crops . . . . . . . . . . . . . . . . . . . 95Vegetable Oil and Hydrocarbon Crops . . . . . 96Starch and Sugar Crops . . . . . . . . . . . . . . . . . 97General Aspects . . . . . . . . . . . . . . . . . . . . . . . 97

Aquiculture . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98Mariculture ● . . * * * * * * * * . . . . . . . . . . . * . * * * * * 101Other Unconventional Approaches . ..........105

Multiple Cropping . . . . . . . . . . . . . . . . . . . . .105Chemical Inoculation. . .................105Energy Farms . . . . . . . . . . . . . . . . . . . . .. ...105Biophotolysis. . . . . . . . . . . . . . . . . . . . . ....106Induc ing N i t rogen F ixa t ion in P lants . . . . . . . 107Greenhouses . . . . . . . . . . . . . . . . . . . . .. ...108

TABLESPage

36. Optimistic Future Average Crop Yields forPlants Under Large-Scale Production . . . . . . 94

37. incomplete List of CandidateUnconventional Bioenergy Crops . . . . . . . . . 95

38. Optimistic Cost Estimates forUnconventional Crops. . . . . . . . . . . . . . . . . 97

FIGURE

Page13. Macrocystis Pyrifera . .................102

Chapter 4

UNCONVENTIONAL BIOMASS PRODUCTION

Introduction

A number of unconventional approaches tobiomass energy production have been pro-posed. Several nontraditional crops that pro-duce vegetable oils, hydrocarbons, and otherchemicals or cellulosic material are under in-vestigation. Both freshwater and saltwaterplants are being considered, and various otherapproaches to biomass fuel production arebeing examined. A common feature to all ofthese approaches is that the full potential ofindividual plants proposed as fuel-producerscannot be fully assessed without further R&D.A description of some general plant character-

istics, however, can aid in comparing the vari-ous possible types of energy crops.

The general aspects of farming, plantgrowth, and the efficiency of photosynthesisare considered in chapter 3. Since future cropyields will depend on these factors and on thedevelopment of hybrids for energy production,the possibilities for genetic improvements areconsidered here. Following this, crop yieldsand various unconventional bioenergy cropsand approaches to farming them are discussed.

Genetics

There are two major areas of genetics. Thefirst, which plant breeders have used most ef-fectively to date is the classical Mendelian ap-proach (introduced by Gregor Mendel in the19th century). It involves selecting and cross-breeding those plants with desired characteris-tics (e.g., biomass yield, grain yield, pest re-sistance). The process is continued througheach succeeding generation until a hybrid, orparticularly favorable strain, is isolated.Strains with unique and desirable propertiesare often crossbred to produce hybrids thatoutperform the parents. Hybrid corn is an ex-ample. This technique is limited, however, bythe variability of characteristics that existnaturally in plants or mutations that occurspontaneously during breeding. One can iso-late the best, but one cannot produce betterthan nature provides.

The second approach to genetics, moleculargenetics, is a recent development that involvesmanipulating the genetic code more or less di-rectly. Three types of potential advances frommolecular genetics can be distinguished: 1 ) im-provements in the efficiency or rate of biologi-cal conversion processes (e.g., fermentation,anaerobic digestion), 2) introducing specific

characteristics into specialized cells such asthe ability to produce insulin,1 and 3) improve-ments in photosynthetic efficiency, plantgrowth, and crop yields. The complexity of thetasks increases greatly as one goes from 1) to3), as described below.

The first type involves subjecting single cellsto chemicals or radiation that cause mutationsin the celIs’ genes. The way these mutations oc-cur is not well understood and the effects aregenerally unpredictable. The result is to in-crease the diversity of cell types over what oc-curs naturally; and in favorable cases one mayproduce a cell that performs a particular func-tion “better” than naturally occurring cells.This method has been applied successfully tothe production of antibiotics, in biologicalconversion processes, 2 and in increasing thetolerance of plants to certain diseases; but it isgenerally a “hit and miss” proposition.

‘A Elrich, et al , Science, VOI 196, p, 1313, 1977‘ F o r e x a m p l e , s e e G H E i n e r t a n d R . K a t z e n , “ C h e m i c a l s

From B iomass by Improved Enzyme Techno logy , ” p resen ted a tthe Biomass as a Non-Fossi/ tue/ Source, ACS/CSJ Joint ChemicalCongress , Hono lu lu , Hawall, April 1979

91

92 ● Vol . n-Energy From Biological Processes

The second type involves identifying thegenes responsible for a particular function inone cell and transferring these genes to anoth-er cell. This transfer does not always require adetailed knowledge of how the gene producesthe desired characteristic. One can draw fromthe pool of naturally occurring characteristics,but the conceptual link between the gene andthe characteristic must be relatively direct.

The third type probably would involve alter-ing a complex set of interdependent processesin the plant. Although some plant physiologistsbelieve that some improvements in photosyn-thetic yield can be achieved by suppressingprocesses like photorespiration (a type of plantrespiration that occurs only in the presence oflight), this belief is highly controversial amongspecialists in the field. It is generally believedthat the processes involved in plant growthand photosynthesis and their relation to specif-ic genes are too subtle and poorly understoodat present to know what biochemical proc-esses should or can be altered to improve plantgrowth and crop yields.

Some additional near- to mid-term advancesare likely in the area of biological conversionprocesses and with gene transfers in the areaof synthesizing high-value chemicals, like in-sulin, that would be either impractical or im-possible to synthesize by other means. Thecomplexity of plant growth and photosynthet-ic efficiency, however, reduces the chances ofimproving ‘these characteristics in plantsthrough molecular genetics in the near future.Although the possibility cannot be precludedthat a scientist will alter a crucial process inplant growth despite the lack of knowledge,there are few grounds for predicting that thiswill occur before the fundamental biochemi-cal processes involved in plant growth andphotosynthesis and the way that environmen-tal factors limit them are better understood.There is a great deal of controversy surround-ing this subject, but most arguments— bothpro and con– are based on intuition ratherthan demonstrated fact.

Crop Yields

Current knowledge and theories of plantgrowth do not enable one to predict the cropyields that can be achieved with unconven-tional crops. Nevertheless, because of the im-portance of biomass yields in determining theeconomics of production, it is important tohave an idea of the approximate magnitude ofthe yields of various options that may be possi-ble.

To this end, corn – a highly successful exam-ple of crop development– is used as the basisfor these estimates. Corn has the highest pho-tosynthetic efficiency of any plant cultivatedover large areas of the United States. As dis-cussed in chapter 3, an optimistic estimate foraverage corn grain yields would be about 140bu/acre (3.9 tons of grain/acre) by 2000. Manyfarmers routinely exceed this yield, as do ex-perimental plot yields. This number, however,is quite optimistic for average yields from cul-tivation on millions of acres of average U.S.

cropland. Furthermore, since cropland thatcould be devoted to energy crops is generally ofpoorer quality than average cropland, using thisas a basis for estimates may be overstating thepotential.

A yield of 140 bu/acre for corn correspondsto a photosynthetic efficiency of about 1.2 per-cent over its 120-day growing season. Perennialcrops, however, probably will have somewhatlower efficiencies during the cold weather atthe beginning and end of their growing sea-sons. Consequently, it is assumed that peren-nials can achieve an average photosyntheticefficiency of 1.0 percent. With these assump-tions, and the others stated below, the follow-ing yields may be possible.

● Dry matter yield.— With an 8-month growingseason in the Midwest, biomass productioncould yield 15 ton/acre-yr of dry plant mat-ter. For the Gulf Coast (12-month growing

Ch. 4—Unconventional Biomass Production ● 9 3

●

●

●

●

●

season), the yields could reach 21 ton/acre-yr.Grain yields.– Based on corn yields, averagegrain production from some plants couldyield 3.9 ton/acre-yr.Sugar yields.– Good sugar crops are 40- to45-percent sugar on a dry weight basis (e.g.,sugarcane, sweet sorghum). In the Midwest,sugar crops will probably be annual cropsleading to poss ible y ields of 4 tons ofsugar/acre-yr. Along the Gulf Coast, there isa longer season. Current average sugaryields are 4 ton/acre-yr. As with corn, theyields could conceivably be increased by 40percent to 5.6 ton/acre-yr.Aquatic plant yields.– Estimates for water-based plants are more difficult to derive,since there is considerably less experienceand applicable information. Water plantshave a continuous supply of water and arenever water stressed. For maximum produc-tivity, nutrients and carbon dioxide (CO,)(for submerged plants) would be added tothe water and could be available continu-ously at near-optimum levels. The waterwould prevent rapid changes in tempera-ture. All of these factors favor plant growth,and i f other problems with cult ivat ingaquatic plants can be solved, yields may bequite high (see “Aquiculture” and “Maricul-ture”). Nevertheless the uncertainty is toogreat to make a meaningful comparisonwith the land-based plants. As with otherplants, experimental yields will probably notbe representative of commercially achiev-able yields.Y ie lds in greenhouses.– Y ie lds in green-houses are also very uncertain, due to a lackof sufficient data and potential problemssuch as fungal attacks on plants, root rot,and other problems with extremely humidenvironments. If these and other problemsare solved, then crop yields approachingthose estimated for the milder climates maybe achieved.Vegetable oil or hydrocarbon yields. – In addi-tion to solid material, plant biomass in-cludes oils. New seed oil crops typically con-tain 10-to 15-percent vegetable oil, and insunflowers the oil comprises up to 50 per-

●

●

✎

cent of the seed weight. 3 Assuming thatplants which are 50-percent seed containseeds that are 50-percent oil, the oil contentmay reach 25 percent of the total plantweight.

Assuming the biochemical reaction pro-ducing the oil is 75 percent as efficient asthat which produces cellulose, then for 1-percent photosynthetic efficiency the oilproduction would be 16 bbl/acre-yr for aplant that is 25-percent oil. For an oil-pro-ducing reaction that is 50 percent as effi-cient as the reaction that results in cellulose,the yield would be 12 bbl/acre-yr.

Plant material stored as hydrocarbons hasalso been proposed as a source of liquidfuels. Eucalyptus trees and milkweed, for ex-ample, contain up to 12-percent hydrocar-bons. Assuming that this content could bedoubled, the same yields as for oil cropswould apply.Arid land crop yields.– Another importantand sometimes l imiting factor in biomassproduction is water. Generally plants wil lgrow well without irrigation in areas of theUnited States where the rainfall is 20 to 30inches or more. For high biomass-producingcrops in relatively humid climates (like theMidwest), the minimum water necessary forplant growth in open fields is about 200weights of water for 1 weight of plantgrowth. There has been interest, however, inplants that can grow under more arid condi-tions. In desert regions with very low humidi-ties, requirements are more typically 1,000weights or more of water per 1 weight ofplant growth. (Some plants survive for longperiods of time without water, but they donot grow. ) Assuming the 1,000:1 figure, themaximum plant growth that could be ex-pected in a region with 5 inches of rain andno irrigation is 0.6 ton/acre-yr. Oil yieldswould be correspondingly low or less than 1bbl/acre-yr.Natural systems. — In addition to agriculture,there has also been interest in using biomassproduced by plants in their natural state. In

‘D. Gilpin, S Schwarzkopf, j. Norlyn, and R. M. Sachs, “Ener-gy From Agriculture– Unconventional Crops,” University of Cal-ifornia at Davis, contractor report to OTA, March 1979.

94 ● Vol. ii—Energy From Biological Processes

the natural state, most of the nutrients arereturned to the soil as the leaves drop offor the plant dies and decays. Harvesting ofsome of the biomass removes some of thenutrients, although animal excretions andthe natural breakdown of minerals in the soilprovide new nutrients. The rate of replenish-ment varies considerably from area to area,however, and this determines the rate thatbiomass could be removed from natural sys-tems without depleting the soil.

The potential growth of biomass in contin-uously harvested natural systems has appar-ently not been studied. (Forestlands are anexception, although the emphasis there hasbeen on the production of commercial tim-ber rather than on total biomass.) It has beenestimated, however, that some natural wet-lands produce more than 5 ton/acre-yr ofgrowth, and that 11.4 million acres of range-Iand produce more than 2.5 ton/acre-yr. 4

While no estimates for the production ofnatural systems can be given, they will cer-tainly permit less harvestable growth thanintensively managed systems on comparablesoil.

In evaluating the possible yields for biomassproduction, all of the yield estimates hereshould be treated with extreme caution. Noneof these yields has been achieved under large-scale cultivation (i. e., mill ions of acres) and theestimates for oil-producing plants are particu-larly uncertain. Experimental plot yields, onthe other hand, exceed these yields for manyplants.

Moreover, several factors operate to preventaverage yields from reaching these estimatesfor large-scale production of biomass. Themost important are the less than ideal soils ofmost potential cropland and the fundamentall imitat ions of plant genet ics with currentknowledge. On the other hand, managementpractices improve with time and increasedcosts for farm products may eventually justifymore extensive management practices, such asadditional fertilizers, extensive soil treatment,and expanded irrigation. *

*“An Assessment of the Forest and Range Land Situation in theUnited States, ” Forest Service, U S Department of Agriculture,review draft, 1979

● It is unclear whether Irrigation WIII be socially acceptable for

Each plant is, to a certain extent, a specialcase. The experience with large-scale cultiva-tion of crops is limited to a few food, animalfeed, fiber, and chemical crops. Many plantscientists argue that maximum food produc-tion implies maximum biomass production.However, few genetic and development pro-grams have been specifically aimed at max-imizing biomss output for crops suitable tolarge areas of the United States.

These contradictory factors mean that thepotential for biomass production is uncertain.And the uncertainty of the estimated yields isjudged to be at least 50 percent. Consequently,the yields could easily vary anywhere from 0.5to 1.5 times the numbers reported.

It is highly unlikely, however, that averageU.S. yields for corn will exceed 140 bu/acrebefore 2000, and perhaps not after then. Andcorn is one of the best biomass producers forthe U.S. climate known to man. Consequently,the numbers reported represent reasonablelimits in terms of what is known today. Anylarge-scale production of biomass that signifi-cantly exceeds these yields would represent amajor breakthrough. Estimates that are basedon projected yields significantly exceedingthose in table 36 either: 1) are limited to therelatively small acreage of the best U.S. soils,

Table 36.–Optimistic Future Average Crop Yields for PlantsUnder Large-Scale Productiona

Plausible average yieldb

Region Product (ton/acre-yr)

Midwest Dry plant matter 15Gulf Coast Dry plant matter 21Midwest Sugar 4Gulf Coast Sugar 5.6Midwest Grain 3.9Midwest Vegetable oil or 1.7- 2.2

hydrocarbons (12 -16 bbl)Area with 5 inches rainfall

per year and noirrigation. . . . . . . . . . . Dry plant matter 0.6

Area with 5 inches rainfallper year and noirrigation. . . . . . . . . Vegetable oil or 0.1

hydrocarbons (0.7 bbl)

aln thl~ ~Ont~xt, lar~~.~~al~ @UC(iOfl means cultivation On mllllotls 01 acres of average U S

croplandbEstlmaled Uricerfamly 250 percent

SOURCE Otflceot Technology Assessm@

energy production or whether the necessary water WIII be avail-able


2) rely on technologies that do notand are not anticipated in the near3) require extensive management

now existfuture, orpractices

Unconventional

A large number of plants not now growncommercially in the United States are poten-tially energy crop candidates. Some are rela-t ively h igh biomass producers and otherscould provide a source of a variety of chemi-cals that could be used as fuel or as chemicalfeedstocks. Unlike conventional crops, thesecrops could be considered primarily for theirvalue as fuel. (However, see also ch. 10.)

Assessing and comparing potential yields forthe unconventional crops from literature re-ports are extremely difficult, since these re-ports often do not give dry yields, the plantsoften are grown on unspecified soils and in dif-ferent climates, and the water and nutrient in-puts often are not given. Furthermore, it is awell-known fact that experimental plot yieldsare larger than those achieved with large-scalecommercial cultivation. For these reasons, theyields reported below should be treated withextreme skepticism. Comparative cultivationexperiments and crop development will beneeded in the various regions and soil types inorder to establish which crops are, in fact,suitable or superior for bioenergy production.In broad terms, the categories include: 1 ) ligno-cellulose, 2) vegetable oil and hydrocarbon,and 3) starch and sugar crops. Each group isconsidered briefly below, and an incompletelist of candidate bioenergy crops is shown intable 37.

Lignocellulose Crops

Various species of hardwood trees (e.g., redalder, hybrid poplar) and grasses (e. g., kenaf,Bermuda grass, Sudan grass, big bluestem) arecandidates for crops grown primarily for theirhigh dry matter yields (Iignocellulose crops).

Theoretically, one would expect perennialcrops (like trees and some grasses) to be su-perior biomass producers to annual crops,

that are not likely to be cost effective unlessthere are dramatic increases in the prices forfarm commodities,

Land= Based Crops

Table 37.–incomplete List of CandidateUnconventional Bioenergy Cropsa

Lignocellulose cropsAmerican sycamore Red alderBermuda grass Russian thistleBig bluestem Salt cedarGum tree (eucalyptus) Sudan grassKenaf SwitchgrassNapier grass TamarixPoplar Tall fescueReed canarygrass

Vegetable oil and hydrocarbon cropsCrambe MilkweedGuayule Mole plant (euphorbia)Gum tree (eucalyptus) SafflowerJojoba Turnip rape

Starch and sugar cropsBuffalo gourd Kudzu vineChicory Sweet potatoesFodderbeets Sweet sorghumJerusalem artichoke

asome of these crops are produced commercially today on a hmlted scale, but fIOt for their ener9Yvalue

SOURCE D Gdpm, S Schwarzkopf, J Norlyn, and R M Sachs, “Energy From Agrlculture–Unconventional Crops, ” Unwersity of Cahforrua at Davis, contractor report to OTA.March 1979, S Barber, et al , “The Potential of Producing Energy From Agriculture, ”Purdue Unwerslty, contractor report to OTA, and J S Bethel, et al , “Energy FromWood, ” UnwersNy of Washington, contractor report to OTA

since the perennials develop their leaf coversooner in the spring and do not need to gener-ate a complete root system each year. Onewould also expect grasses to be superior bio-mass producers to trees because of their largerleaf area per acre of ground, * but considerableattention has been focused on trees, since thetechnologies for using wood are more ad-vanced. Experimental plot yields for short-rota-tion trees are 5 to 20 ton/acre-yr.5 Yields of asmuch as 10 to 15 ton/acre-yr may be achievedfor large-scale cultivation of some of thesecrops in good soil (see “Crop Yields” section)but are likely to be 6 to 10 ton/acre-yr in poorersoils. Since farming costs could be similar tocorn, this could result in biomass for about $20to $50/ton.

“Thereby reducing Ilght saturation, which lowers photosyn-thetic efficiency

5Cllpin, et al , op clt


The trees would typically be grown for 6 to10 years before harvest, while the grasseswould be harvested several times a year. Withfewer harvests for the trees, each harvest couldbe considerably more expensive and consumemore energy than grass harvests without unfa-vorably affecting the economics or net energybalance. However, tree crops would requirethat the land be dedicated to the crop for sev-eral years and converting the land to otheruses would be more expensive, due to the de-veloped root system. Also, if a disease were tokill the crop, reestablishing a tree crop wouldbe more expensive. Both t rees and somegrasses are perennial crops and, consequently,would require fewer herbicides and would re-duce erosion on erosion-prone land as com-pared to annual crops. Grasses, having a morecomplete soil cover, would be more effectivein preventing soil erosion.

Vegetable Oil and Hydrocarbon Crops

Vegetable oils and hydrocarbons are chemi-cally quite different from petroleum oil. Nev-ertheless, most vegetable oils and hydrocar-bons can be burned and might prove to be asubstitute for fuel oils or, with refining, forother liquid fuels. However, appropriate meth-ods for extracting the oil from the plant andfor refining the oil are not well defined at pres-ent.

A number of edible and inedible vegetableoils are currently produced commercially.6 I naddition, unconventional crops such as gumtree (eucalyptus), mole pIant (euphorbias),guayule, milkweed, and others could be usedas vegetable oil and hydrocarbon crops (or fornatural rubber). The maximum current yieldsof commercial oil plants are in the range of100 to 200 gal/acre (2.5 to 5 bbl) of vegetableoil and/or hydrocarbon. Reports of 10 bbl/acre(420 gal) for euphorbia were apparently basedon measurements of plants on the edge of afield, which were 1.5 times larger than interiorplants. Also, in some cases, 16 months ofgrowth were used to obtain “annual” yields, ’

6Agricu/tura/ Statistics (Washington, D. C.: U.S. Department ofAgriculture, 1978).

‘Gilpin, et al., op. cit.

The theory of hydrocarbon and vegetable oilproduction in plants is not adequate to predictpossible yields. However, from other consid-erations (“Crop Yields” section) there may be asignificant potential for improvement. Further-more, some of these crops (e. g., guayule) maydo well on land where there is slightly less wa-ter available than would be needed for con-ventional crops. a Others, such as milkweed,can be grown with brackish water which wouldbe unusable for conventional food crops. ’Comparative tests under comparable condi-tions wil l be necessary to determine whichplants show the most promise for energy pro-duction.

Because of the higher prices that can bepaid for chemicals and natural rubber, the factthat these products are economic in somecases does not in any way imply that energyproduction from vegetable oil and hydrocar-bon plants will be economic. Some proponentsof hydrocarbon plant development have failedto distinguish between these end uses, a factthat has led to considerable confusion andmisunderstanding.

Critics of the development of vegetable oiland hydrocarbon plants for energy argue thatthe production of these products by plants isconsiderably less efficient than normal chemi-cal synthesis (e.g., to produce methanol or eth-anol from dry plant matter). They also pointout that the plant often must be subjected tostress (drought or cold) to produce hydrocar-bons, and this lowers the photosynthetic effi-ciency. Consequently, they contend that thehigh yields being predicted (e.g., 26 bbl/acre10),will not be achieved in the foreseeable future.

At present, however, the theory of and ex-perience with these types of plants is inade-quate to make a meaningful judgment.

‘K. E. Foster, et al., “A Sociotechnical Survey of Guayule Rub-ber Commercialization, ” Office of Arid Land Studies, Universityof Arizona, Tucson, Ariz., prepared for the National ScienceFoundation under grant PRA 78-11632, April 1979.

‘W. H, Bollinger, Plant Resources Institute, Salt Lake City,Utah, private communication, 198o.

‘“J D. Johnson and C. W Hinman, “Oils and Rubber From AridLand Plants,” Science, VOI 280, p. 460,1980.


Starch and Sugar Crops

Starch and sugar crops are of interest sincethey can be used to produce ethanol with com-mercial technology. Current corn grain yieldscan be processed into about 260 gal of ethanolper acre cultivated and sugar beets (usually ir-rigated) can produce about 350 gal/acre, onthe average. Irrigated corn, however, wouldmatch the sugar beet yield. Furthermore, ex-perimental plot yields for corn produce about430 gal/acre-yr and record yields exceed 850gal/acre. In addition to the conventional starchand sugar crops, several other plants havebeen proposed as ethanol feedstocks includingsweet sorghum and Jerusalem artichokes.

Experimental plot yields for sweet sorghumcould be processed into about 400 gal of etha-nol per acre year. Furthermore, this crop pro-duces large quantities of residues that are suit-able for use as a disti l lery boiler fuel. Theyields for large-scale cultivation, however, arestill unknown, and concern has been expressedthat droughts during parts of the growing sea-son could reduce sugar yields significantly.

Experimental plot yields for Jerusalem arti-chokes have produced about twice the sugaryields of sugar beets under the same growingconditions in Canada. Whether this result canbe applied to other regions is not known. Jeru-salem artichoke, like the sugar beet, is a rootcrop. Harvesting it, therefore, causes extensivesoil disturbance which increases the chancesof soiI erosion.

“Gllpln, et al , op clt

Other plants such as fodderbeets, sweet po-tatoes, and Kudzu vine are also potential etha-nol crops. Comparative studies are necessaryto determine which crops are best in each soiltype and region of the United States. As wasemphasized in chapter 3, this comparisonshould include the displacement of othercrops that can be achieved by the byproductsof ethanol production. This factor tends tofavor grains, but other possibilities do exist. ’2

General Aspects

Intens ive cult ivat ion of unconvent ionalcrops may cost about the same as corn, or $200to $400/acre-yr in the Midwest. These costs,together with the yield estimates given above,allow an approximate comparison of the costsfor various unconventional land crops, whichis shown in table 38. Since the exact cultiva-tion needs have not been established, a moredetailed comparison is not warranted at thistime. These costs estimates, however, showthat unconventional crops may be economicenergy sources. The ultimate costs will dependto a large extent on the yields that can actuallybe attained with intensive management andthe success of developing crops that can becultivated on land that is poorly suited to foodproduction.

The crops that are now grown in U.S. agricul-ture were selected for properties that are unre-

I IR Carl son, B commoner, D Freedman, and R Scott, “Inter-Im Report on Possible Energy Production Alternatives In Crop-Livestock Agriculture, ” Center for the Biology of Natural SVs-tems, Washington University, St Louis, Mo , Jan. 4, 1979

Table 38.-Optimistic Cost Estimates for Unconventional Cropsa

Product Ultimate fuel Yield of ultimate fuel per acre cultivated Contribution of feedstock to fuel costb

Dry plant matter Combustible dry matter 15 ton (195 106 Btu) $20/ton ($1 .53/ 106 Btu)Dry plant matter Methanol 1,500 gale (95 106 Btu) $0.20/gal ($3.15/10 6 Btu)Dry plant matter Ethanol 1,300 gald (107 106 Btu) $0.23/gal ($2.80/10’ Btu)Grain Ethanol 364 gal (31 106 Btu) $0.82/gale ($9.89/10’ Btu)Sugar (Midwest) Ethanol 540 gal (46 106 Btu) $0.56/gal ($6.50/10’ Btu)Vegetable oil or hydrocarbon crop Vegetable oil or hydrocarbon 504-670 gal (63-84 106 Btu) $0.45-$0.60/gal ($3.60-$4.70/10’ Btu)

aBased on yields m table 36bAssumlng $3i)o/acre cuttwatlon and harvest costs, does nOt include COnver510n costscAssumlng yw,lds of 100 gal/ton of btornassdAssumes yields of 85 galiton of biomasse~s not ,n~lude by Droduct credit for distillers’ grain H byproduct Credits Included, the Sltuatlon becomes more complex as described m ch 3, in the section on “Energy Potential From Conventlonai

Crops ‘‘ The bypro&ct credit would reduce the costs by roughly one-thtrd

SOURCE Otflce of Technology Assessment

98 ● Vol. Ii—Energy From Biological Processes

Iated to energy. It ‘is likely, therefore, thatother plants will prove to be superior to con-ventional crops for energy production. Beyondthe yields of these crops, properties like insen-sitivity to poor soils, multiple products (e.g.,vegetable oil, sugar, and/or starch plus dryplant herbage) displacement of other cropswith crop byproducts (e. g., corn distillery by-product), the energy requirements to cultivatethe crop, the energy needed to convert it into aform that can be stored (especially for sugarand starch crops), tolerance to adverse weath-er conditions, ease of harvesting and conver-sion to fuels, and the environmental impactsof growing the crop are all factors that shouldbe considered when choosing energy crops. Inshort , analyses of the net premium fuelsdisplacement per new acre cultivated (as wasdone for various conventional crops in ch. 3),the cost, and the environmental impacts areneeded to compare the options. Due to the di-versity of U.S. soils and climates, differentcrops will no doubt prove to be superior in dif-ferent regions. Many of the possible unconven-tional crops appear promising, but the ulti-mate decisions will have to come from experi-ment and experience. (Typically it requires 10to 20 years to develop a new crop.) Neverthe-less, some general aspects of plants can be ex-pected to hold for the unconventional crops.

Root plants (e.g., Jerusalem artichokes,sugar beets, potatoes, sweet potatoes) willcause the most soil erosion. Annual crops willbe next, and perennial grasses can virtuallyeliminate soil erosion.

Soil structure and climate are dominantfeatures controlling plant growth and thesecan be controlled by man only to a very lim-ited extent. Plants vary as to their sensitivity tothese factors and to the presence of nutrientsolubil izing mycorrhizae in the soil, ’3 butyields will decrease on going to poor soils andclimates. Crops grown in arid climates withoutirrigation or an underground supply of waterwill give low yields; and social resistance tousing water for energy production in the Westcould preclude irrigated energy crops, al-though some people maintain that this resist-ance will not extend to crops.

Finally, any crop that grows very well in anarea without inputs f rom man is l ike ly tospread and become a weed problem.

“J. M. Trappe and R. D. Fogel, “Ecosystematic Functions ofMycorrhizae,” reproduced from Range Sci. Dep Sci., series No,26, Colorado State University, Fort Collins, by U S. Departmentof Agriculture.

Aquiculture

Aquatic plants comprise a diversity of types, systems for energy production. ’4 The generalfrom the single-celled microalgae to the large conclusions were that the production of aqua-marsh plants such as cattails and even some tic biomass has near-term potential in conjunc-trees such as mangroves. Considerable interest tion with wastewater treatment and high-valueexists in the cultivation of many different chemicals production. However, the develop-aquatic plants as energy sources. Examples are ment of large-scale “energy farms” based onthe production of cattails in the extensive aquatic plants is less promising at present,marshes of Minnesota, the cultivation of water from both an economic or a resource potentialhyacinths on wastewaters in Mississippi or viewpoint. Nevertheless, aquatic plants haveFlorida, and the establishment in the South- certain unique attributes, the key one beingwest of large-scale brackish water ponds for high achievable biomass production ratesmicroalgal product ion of chemical feedstocks. -

OTA has prepared a detailed review of the po-“J. Benemann, “Energy From Aquiculture Biomass Systems:

Fresh and Brackish Water Aquatic Plants, ” Ecoenergetics, Inc ,tential of fresh and brackish water aquiculture Vacaville, Cal if , contractor report to OTA, April 1979


which justify continued research on a varietyof approaches to the development of aquacul-ture energy systems.

Higher aquatic plants growing in or onwater are not, as a rule, water limited — a com-mon and natural state of land plants. Thus,they are capable of higher rates of photosyn-thesis by keeping their stomata (plant pores)open longer than land plants* thereby, increas-ing C02 absorption. Thus, plants such as thewater hyacinth and cattails exhibit very highrates of biomass production, often exceeding20 ton/acre-yr . Th i s h igh p roduct iv i t y i sachieved, however, by evaporation of largeamounts of water, exceeding by a factor oftwo to four that transpired by land plants.Thus, cultivation of water plants can only beconsidered where ample supplies of water ex-ist or where the systems are covered, such as ingreenhouse structures.

Some aquatic plants, however, do not exhib-it very high biomass production rates. For ex-ample, the common duckweed (Lemna sp.)covers a water surface very rapidly; however,once this is achieved, further growth in the ver-tical direction is minimal. Thus, the productivi-ty of such plants is relatively low when com-pared to plants such as water hyacinths andmarsh plants which extend their shoots up toseveral feet into the air. Indeed, the high leafarea index (the ratio of the total leaf area tothe ground area), sometimes exceeding 10, ofthese plants, accounts, along with high trans-piration rates, for their high productivity.

Another type of aquatic plant that exhibitsrelatively low productivity is the salt marshplant Spartina, which does not produce asmuch biomass as its freshwater analogues suchas Typha (cattails) or Phragmites (bullrush). Thehigh salt concentration tolerated by Spartinaalso results in a decrease of transpiration andproductivity. Even among the f reshwatermarsh plants, biomass productivities are lim-ited by both the seasonal growth patterns ofthe plants in the temperate climate of the

‘Somata are closed to conserve water, but this also preventscarbon dioxide from entering the leaf

‘ ‘Ibid

United States and the large fraction of biomasspresent in the root system which may be diffi-cult to recover. The submerged aquatic plantssuch as the notorious weed Hydrilla, are alsonot remarkable for their biomass productivity.Adaptation to the light-poor environment fre-quently encountered below the water surfacehas made these plants poor performers at thehigh light intensities that would be the norm ina biomass production system.

Finally, the case of the microalgae must beconsidered. Being completely submerged theyalso are subject to significant light losses byreflection from the water surface (at low solarangles) and scattering of light. More important-ly, in a mixed algal pond, the cells near the sur-face tend to absorb more light than they canuse in photosynthesis, resulting in a significantwaste of solar energy. However, if a microalgalproduction system is designed to enhance mix-ing, then rapid adjustment by the algae occurs,thus overcoming, to some extent, the handicapinherent in inefficient sunlight absorption bymicroalgal cultures. Therefore, microalgal cul-tures could be considered in a biomass produc-tion system. A review of the rather sparse pro-ductivity data available, together with consid-eration of the basic photosynthetic processesinvolved, suggest that green algae and diatomsare promising candidates for mass cultivation,probably with achievable production rates ofat least 20 ton/acre-yr, with blue-green algae,particularly the nitrogen-fixing species, con-siderably less productive.

It must be noted that the available data onaquatic plant productivity are too limited toallow confident extrapolations to large-scalesystems. Most available data are based onnatural systems where nutrient limitations mayhave depressed productivity or small-scale,short-term experimental systems where edgeeffects and other errors may have increasedproductivity. Actual yearly biomass produc-tion rates in sufficiently large-scale managedsystems must be considered uncertain for anyaquatic plant, particularly if factors such asstand establishment, pest control, optimal fer-tilizer supply, and harvesting strategy are con-cerned. Thus, to a considerable extent, assess-


ing the potential of aquatic plants in energyf a r m i n g , l i k e t h a t o f o t h e r u n c o n v e n t i o n a lcrops, involves more uncertainty than specificdetailed knowledge.

Among the uncertainties are the economicsof the production system, including the har-vesting of the plants. Detailed economic anal-yses are not available; those that have beencarried out are based on too many optimisticassumptions to be credible or useful . Ofcourse each type of plant will require a dif-ferent cultivation and harvesting system. How-ever, in all cases, these appear to be signifi-cantly more expensive per acre in both capitaland operations than the costs of terrestrialplants. This increased cost per acre can only bejustified by an increased biomass productionrate or a specific, higher valued product. Be-cause the productivity and economics of aqua-tic plants are, to a large degree, unknown, thepotential for aquatic plant biomass energyfarming is in doubt.

One approach to improve the economics ofsuch systems is to combine the biomass energysystem with a wastewater treatment function.As aquatic plants are in intimate contact withwater, they can perform a number of very im-portant waste treatment functions—oxygenproduction (by microalgae) which allows bac-terial breakdown of wastes, settling and filtra-tion of suspended solids, uptake of organicsand heavy metals, and, perhaps most impor-tantly, uptake of the key nutrients that causepollution. The relatively high concentrationsof nitrogen and phosphorus in aquatic plants(e.g., about 10 percent nitrogen and 1 percentphosphorus in microalgae and 3 percent nitro-gen and 0.3 percent phosphorus in water hya-cinths), makes these plants particularly usefulin nutrient removal from wastewaters. Re-search in wastewater aquiculture is well ad-vanced, although some critical problems re-main to be elucidated, and several large dem-onstration projects are being initiated through-out the United States. For example, water hya-cinths are being used in wastewater treatmentplants in Coral Gables and Walt Disney World,Fla., in projects which involve fuel recovery byanaerobic digestion of the biomass. Microalgal

ponds have been used for several decades inmany wastewater treatment systems through-out the United States. More stringent waterquality standards are resulting in a need forbetter microalgal harvesting technology andpresenting an opportunity for fuel recoveryfrom the harvested microalgae. Several proj-ects throughout the United States have demon-strated the beneficial effects of marsh plantsin wastewater. treatment. In all cases, waste-water aquiculture appears more economicaland less energy intensive than conventionaltechnologies. 16 However, the total potentialimpact of wastewater aquiculture on U.S. en-ergy supplies, even when making favorablemarket penetration assumptions, is minimal —about 0.05 to 0.10 Quad/yr.17

For aquatic plants to make a more signifi-cant contribution to U.S. energy resources,other types of aquatic biomass energy systemsmust be developed. One alternative is the con-version to fuel of aquatic plants already har-vested from natural, unmanaged stands. Exam-ples are water hyacinth weeds removed by me-chanical harvesters from channels in Floridaand other southern States and cattails or bull-rushes cut periodically in natural marshes inMinnesota or South Carol ina to improvewildfowl habitats. However, the infrequentoccurrence of such harvests, the small bio-mass quantities involved, and transportationdifficulties make energy recovery from suchsources essentially impractical. The conver-sion, if practiced, of natural marsh systems tolarge-scale managed (planted, fertilized, har-vested) plantations will present significant eco-logical problems and, even if these are ameli-orated or overcome, opposition by environ-mental groups. Nonetheless, large areas ofmarshes do exist in the United States and they,in the long term, may become resources thatcould be exploited on a multipurpose and sus-tained yield basis like the national forests. Inthe near term, however, the technology foraquatic plant biomass energy systems must bedeveloped with presently unused or “margin-

“’Ibid“Ibid“Ibid.

Ch. 4—Unconventional Biomass Production ● 1 0 1

al” land and water resources. In addition,relatively high-value biomass energy products,specifically chemicals and liquid fuels, shouldbe produced by such systems. Examples ofsuch systems include the production of alco-hol fuels from cattails (either by hydrolysis ofthe areal parts or directly from the starchesstored in the roots) or the production of hydro-carbon fuels and specialty chemicals from mi-croalgae.

Microalgae are known to produce a varietyof useful chemicals. However, the develop-ment of such production technology is onlyjust now beginning, and the potential resourcebase (land, water, nutrients) available for suchsystems is not yet quantified. Thus, the futurecontribution to U.S. fuel supplies of aquaticplant biomass energy systems cannot be pre-dicted. However, sufficient possibil it ies andpromise exist to warrant further R&D efforts.

Mariculture

This section describes problems and oppor-tunities associated with developing futureocean farms which might use the giant kelp(macrocysts) as a future biomass energysource. Other macroalgae have also been pro-posed as potential marine biomass crops. Byexamining the possibil it ies of kelp and alsonoting other proposals, OTA hopes to illustratethe status of this technology in general, itsfuture potential, the problems involved, andthe Federal role in this segment of alternativeenergy research.

Macroalgae are harvested around the world.About 2 million wet metric tonnes are now cutannually, and estimates are that the total po-tential worldwide crop is 10 times this much—about 20 miIlion wet tonnes. 9

In recent decades seaweed cultivation hasrapidly become more successful and has sub-stantially added to annual harvest figures. Forexample, as of 1970 there were 130,000 acresof sea surface under cultivation in Japan,about 25,000 acres in The Peoples Republic ofChina, and additional acreage in Taiwan,Korea, the Philippines, and elsewhere. None ofthe current annual world harvest is being usedfor energy production.

In the United States, where wild seaweedbeds have been harvested for many years, thepossibil ity is beginning to be studied of in-creasing production through ocean farm cul-

‘9G Michanek, Seaweed Resources of the Ocean, U.N, Foodand Agriculture Organization, Rome, 1975,

tivation techniques. A small test farm has beeninstalled along the California coast. 20

Large ocean kelp farms could theoreticallysupply significant quantities of natural gas(methane). Linked to a methane productionsystem, for example, and assuming serioustechnical problems are solved, a l-million-acrekelp farm could produce enough gas to supply1 percent of current U.S. gas needs.

It would be no easy matter to farm such vasttracts of ocean. Much still needs to be learnedabout macroalgae cultivation. But serious research is reducing the areas of ignorance andseaweed may some day become a biomass pro-ducer.

Algae are among the simplest and mostprimitive of plants. The larger macroscopicalgae are commonly referred to as seaweeds ormacroalgae. Large seaweeds are the dominantplant in most shallow coastal waters includingthose off California and Mexico, where they at-tach themselves to rocks or some other hardsubstrate under water.

To date, the seaweeds apparently mostadaptable to human cultivation are the redand the brown algae. People have eaten redalgae varieties for thousands of years, espe-cially in countries such as Japan and China.

2“A. Flowers, statement before the House of RepresentativesCommittee on Merchant Marines and Fisheries, Subcommitteeon Oceanography, p. 18, committee report serial No, 95-4, June7,1978.

102 ● Vol. /l—Energy From Biological Processes

The brown algae group includes the giantkelp Macrocystis (figure 13), already harvested

Figure 13.—Macrocystis Pyrifera

(A: 1/64 natural size; B: 1/4 natural size.) The Giant Kelp isshown in the left part of the plate in a natural pose with thelong leafy stipes rising to the sea surface from the massiveholdfast. On the right is one of the leaf-like fronds showingthe gas-filled float bladder at its base and the distinctiveteeth along the margin (Anon. 1954).

SOURCE: Velco, Inc.

in the United States from wild and semiculti-vated beds and considered at present as thebest candidate for intensive cultivation offCalifornia and as a possible fuel producer. z’

z ‘Neushal, et al., “Biomass Production Through the Cultiva-tion of Macroalgae in the Sea, ” p 100, Neushul Mariculture,Inc , for OTA, Oct 6, 1978

Kelp may grow in length as much as 2 ft/dayor increase its weight by 5 percent per day un-der optimum conditions. The plants form natu-ral beds up to 3 miles wide and several mileslong in southern California. This kelp is nowharvested and put to a variety of uses, prin-cipally in the food-processing industry. Fuelshave never been produced from kelp except inminute quantities as part of research testing.22

Unfortunately, there is no consensus amongthe experts who have made projections as tothe potential of ocean energy farms. Theirestimated costs vary widely and are based onsuch very sparse data that they cannot be usedto either support or reject ocean farm propos-als. Estimates of production rates vary by fac-tors of as much as 100. Better experimentaldata and more complete biological engineer-ing tests will allow for better estimates in thefuture. The estimates used here lie approx-imately in the middle of responsible optimisticand pessimistic projections for a 400,000-hec-tare (1 million acre) ocean kelp farm:

● average productivity = 20 dry ash free(DAF) tons per acre per year, and

● average annual energy produced = 0.2Quad (1 percent of U.S. gas consumptionof 20 Quads/y r).

Such a system, if built, would provide theequivalent in energy supply of one large LNG-importing plant such as the one located atCove Point, Md. It would, of course, be a do-mestic rather than an imported fuel, however.

Experiments are underway into the bestlaboratory-reared seaweed farms. Eventually,some researchers hope to produce a “pedi-greed” kelp bred specifically for high methaneproduction, fast growth, and hardiness.

A key problem faced by potential oceankelp farmers is to deliver enough nutrients tothe plants to fertilize them. This is because,while the deep waters of the ocean containmany necessary nutrients, surface water isoften as devoid of nourishment as a desert is

ZZM. Neushal, “The C)cmnesticatlorl of the C iant Kelp, ~acrocystis as a Marine Plant Biomass Producer, ” presented at the Ma-rine Biomass of the Pacific Northwest Coast Symposium, OregonState University, Mar. 3,1977

Ch. 4—Unconventional Biomass Production ● 103

devoid of water. One fertilizing technique be-ing tried is artificial upwelling of seawater,which involves pumping nutrient-rich, deepocean water to the surface to benefit the kelpplants. 23

Current research on marine plants can be di-vided into two categories.

The first category, funded by several Federalagencies to a total of about $1 million in 1979,generally includes research projects aimed at abetter understanding of marine plants, theircultivation, and potential new uses of theplants.

The other “category” is actually just oneproject: the Marine Biomass Research Programjointly funded by the Gas Research Institute(GRI) and the Department of Energy (DOE),which has funded over $9 million of directedresearch as of 1979.

This ongoing marine biomass project in-cludes a test farm off California. The farmbegan artificial upwelling experiments late in1978, but was forced to suspend operations inearly 1979 due to storm damage. This proto-type is meant to provide biological informa-tion and research clues needed to operatemuch larger culture farms. It also aims at ex-perimental work into cultivation of giant kelpon moored structures in the open ocean. Thetest farm, may lead to the actual operation ofa full-scale ocean farm.

There is considerable difficulty at this timein evaluat ing the appropr iateness of theMarine Biomass Research Program because lit-tle has been produced. It is important thatresearch results on the cultivation of kelp onocean farms be reported in a comprehensiveway and subjected to critical review if a futurelarge program is to be justified.

Kelp and other seaweeds are potentially ahighly productive source of biomass for fuels.Estimates can vary drastically as to what maybe possible for future large ocean farms, butOTA’s evaluation of a hypothetical ocean kelpfarm indicates productiveness could rangefrom a low value of 6 DAF ton/acre-yr to a highvalue of 30. I n comparison, this country’s aver-

age corn harvest is 6 DAF ton/acre-yr and Ha-waiian sugarcane averages 14 DAF ton/acre-yr.

OTA estimates that if about 1 million acreswere ever farmed, the gross energy productioncould amount to 0.2 Quad. This is equal to ap-proximately 1 percent of current U.S. naturalgas consumption. These production estimatesshould be treated with caution since there areno ocean kelp energy farms and nobody hasever planted and harvested a macroalgaeenergy crop.

Actual gross energy production from such ahuge hypothetical ocean kelp plantation hasbeen projected by other researchers to rangefrom 10 times OTA’s estimate to only one-tenth that f igure. The entire project mightsimply prove impossible, others caution. Yearsof experiments will be necessary before anyprojections can be confirmed.

There is even less data to draw on in esti-mating net energy possibil it ies. In a reportprepared for DOE by the Dynatech R&D Corp.,net energy outputs were estimated to rangeanywhere from a negative number to about 70percent of crop energy .24

Much of the technology to construct pres-ent concepts of open ocean farms is alreadywell known. Similar platforms, structures, andmoorings have been built for the offshore oilindustry and the existing seaweed industry usesmechanical harvesting techniques.

Less certain areas of ocean farm engineeringat present include nutrient distribution, disper-sion characteristics of upwelled water, andspecif ic conf igurat ion of the st ructure towhich kelp plants will be attached. A majorproblem for cultivated kelp beds may be tosupply an ocean farm with proper nutrients incorrect quantities. The extreme difficulties ofnoting the delicate balance of nutrients foundin a natural environment and reproducing thisin a cultivated one are well known to research-ers.

24 Dynatech R&D Co , “Cost Analysis of Aquatic Biomass Sys-terns, ” prepared for the Department of Energy, contract NoHCP/ET-400-78/I

104 . Vol. II —Energy From Biological Processes

Test farms will upwell deep ocean water tosupply kelp with proper nutrients. Reservationsabout this procedure are twofold among skep-tics. They worry that deep water could becomestagnant under the farms, or that, once up-welled, the water would dilute too rapidly andsink again.

As previously mentioned, this country’s ma-jor ocean biomass project is jointly supportedby CR I and DOE. The project may become themost heavily funded biomass program of the1980’S, with grants projected to grow to over$50 million yearly by 1983. Plans for this proj-ect have been developed mainly by GRI, al-though regular DOE approval for phases of theproject is mandatory.25

GRI estimates imply that ocean kelp farmingcould be a commercially viable project for thiscountry. The Institute’s fuel production costestimates for methane generation from kelprange from $3 to $6/million Btu.

The previously mentioned Dynatech reporton fuels from marine biomass comes to a dif-ferent conclusion. Its estimates range from$7/million Btu up to several hundreds of dol-lars per million Btu, should productivity provelow and design costs high.

Some critics of the GRI marine biomass pro-gram contend that there is not enough dataavailable to justify the level of expendituresfor the biological test farm.

Critics have stated that the open ocean testfarm is an inappropriate and perhaps prema-ture step in a long, logical process of devel-oping future deep sea operations. Considera-tions which may be overlooked by this testfarm approach include:

the need for better information on kelpgrowth and productivity and limiting fac-tors in natural beds;the need for additional basic research intonutrients and productivity (much research

‘sGeneral Electric Co., briefing, “Energy From Marine BiomassProject, Program Review, ” for the Gas Research Institute, New-port Beach, Cal if., March 1978.

●

●

●

is also needed on plant diseases, preda-tors, and water movement and quality);the possibility of developing shallow wa-ter kelp farms either in areas of naturalupwelling or in conjunction with other fer-tilizing techniques (see ch. 10);hard data on net energy expectations islacking; andno plans are being readied at present asalternatives to fertilization by upwelling.

Since plans for future ocean biomass farmscall for the use of millions of acres of oceansurface, there will be conflicts with other tradi-tional users. The dedication of large areas ofopen ocean surface for a single commercialpurpose such as this is unprecedented. Itwould require complex, special regulationafter review of current local, national, and in-ternational laws.

Even though the ocean space within the 200-mile zone surrounding the United States is 1½billion acres, conflicts can be expected withsuch traditional ocean users as commercialshipping, the navy, commercial and sport fish-ing, offshore oil and gas operation, and recrea-tional boating. To date, no detailed investiga-tion of legal or institutional approaches to re-solving conflicts has been accomplished. Thisissue will need analysis prior to any large-scaleinitiative in ocean farming, and will have a ma-jor impact on feasibility, productivity, and costof marine biomass in the future. Analyses ofspecific sites and siting problems will be cru-cial to the ocean question.

OTA has found that Federal research pro-grams directed toward energy problems havenot been adequately coordinated with similarresearch directed toward production of food,chemicals, or other products.

Much research is needed to develop anysuitable marine pIant culture regardless ofwhether the end product is food or fuel. Suchbasic research could be better supported andcoordinated by all interested agencies. Pro-grams supported by Sea Grant and the Nation-al Science Foundation have tended to focus onbasic biological efforts or food productiongoals while DOE programs are focused on pri-

Ch. 4—Unconventional Biomass Production ● 1 0 5

mary fuel production. Since DOE now has the in deepwater, open ocean farms. This possibili-major funds available for seaweed research, ty would mean coordination of several existingthe tendency has been to create programs fo- research efforts; expanding some, developing

cused on fuel production. The encouragement some new ones, and generally integrating

of further diversity in existing seaweed re- many efforts focused on basic biological ques-search efforts is essential to a long-term im- tions and food production as well as energyprovement in the knowledge and capability of production.

developing future marine plant culture pro-grams.

One approach to conducting a systematicprogram for developing ocean farms would beto expand research in natural seaweed bedsand shallow water farms prior to experiments

Other Unconventional

There are several other unconventional ap-proaches to biomass production. Because ofthe complexity of plant growth, it is likely thatmany approaches will be tried and fail. How-ever, this complexity also gives rise to signifi-cant possibilities. While all unconventional ap-proaches cannot be covered here, a few arediscussed below.

Multiple Cropping

MultipIe cropping consists of growing two ormore crops on the same acreage in a year.Growing winter wheat on land that produced asummer crop is one example. The winter wheatcan delay spring planting, so its use is ap-plicable only for land where certain summercrops are to be grown. However, this is basical-ly a conventional approach.

The unconventional multiple cropping con-sists of growing more than one summer cropon an acreage by harvesting the first cropbefore it matures or developing species thatmature rapidly. Since starches, sugars, vegeta-ble oils, and hydrocarbons are generally pro-duced in the greatest quantities in matureplants, this approach would probably reducethe overall yields of these products. Also, thetime between the harvest of the first crop andthe development of a full leaf cover in the sec-ond crop will be a time when sunlight is not

Approaches

captured by the plants as effectively as itcould. Consequently, this approach would alsobe expected to reduce the total biomass yields.

Chemical Inoculation

By subjecting some plants to herbicides likeparaquat or 2,4-D, hydrocarbon or vegetableoil production can sometimes be increased.These chemicals block certain biochemicalpathways, thus promoting greater productionof other products. Prel iminary results withguayule, for example, indicate that 2,4-D maycause a doubling of the natural rubber contentof this plant. 26 While it is too soon to assessthis approach, it may prove to be an effectiveway of improving yields of these products.

Energy Farms

Energy farms have been proposed 27 as ameans of providing a reliable supply of largequantities of biomass for large conversionfacil it ies located on or near the farm. Thebasic idea is to have a large tract of land (tens

‘6Gilpin, et al,, op. cit.“See, e.g., G, Szego, “Design, Operation, and Economics of

the Energy Plantation, ” Proceedings Conference on Capturing theSun Through 6ioconversion (Washington Center for Metropoli-tan Studies, 1976); G C. Szego and C C Kemp, “Energy Forestsand Fuel Plantations,” Chemtech, p. 275, May 1973; and Si/vicu/-ture Biomass farms (McLean, Va.: MITRE Corp., 1977).

67-968 0 - 80 - 8

106 ● Vol. Il—Energy From Biological Processes

of thousands of acres) dedicated to growingthe biomass feedstock for a nearby conversionfacility. Although this is technically possible, anumber of practical and economic considera-tions probably will limit investment in energyfarms. Moreover, this approach ignores the ef-fect that bioenergy production has on relatedsectors. Some of the more important of thesepoints are:

●

●

●

●

Land. – The land avai lable for energyfarms has often been estimated to be sev-e ra l hundred mi l l ion acres .2829 O T A ’ sanalysis, however, indicates that consider-ably less land is available for biomass pro-duction (see ch. 3). Furthermore, therewould be practical difficulties with buy-ing large contiguous tracts of the sizeneeded for large conversion facilities (tensto hundreds of thousands of acres).

If cultivation on very poor or arid landproves to be feasible or if irrigation forenergy production is socially acceptableand the water is available, then these lim-itations could be somewhat less severethan they appear to be at present.Crop yields.– Estimates of future yieldsfrom short-rotation tree farms have beenas high as 30 ton/acre-yr, 30 wh ich OTAconsiders to be highly unrealistic. Yieldsof 6 to 10 ton/acre-yr are more realistic forthe poorer soil that could be available forenergy farms.Initial investment.– If short-rotation treesare used as the energy crop, there wouldbe a 6- to 10-year Ieadtime before the firstharvest could be made. This would beprohibit ively long for many investors .Grasses, however, would reduce the lead-time to a fraction of a year. In either case,the cost of acquiring the land would in-crease the initial investment substantially.Risk.— Using short-rotation trees as the en-ergy crop would give yields that are lesssensitive to weather than grass becausethe growth would be averaged over sev-

‘%zego, op. cit.29s;/v;cu/ture /3;c3fnass Farms, op. cit.

‘OJ. A Allich, Jr., and R E Inman, “Effective Utilization ofSolar Energy to Produce Clear Fuel, ” Stanford Research insti-tute, final report No NSF/RANN/SE/Cl 38723/FR/2 , 1974

●

●

eral years. A pest infestation, however,could destroy the entire crop in which anaverage of 3 to 5 years’ cultivation hadbeen invested, and this could be financial-ly disastrous. If grass is the energy crop,or the time between tree harvests is re-duced, the loss from a pest infestationwould be considerably less, but the yieldswould fluctuate more from year to year,making it necessary to rely on outsidesources of biomass in years with low har-vests or to se l l surpluses in years wi thbumper harvests.Competition with other uses for the land.– Because of the uncertainty about fu-ture cropland needs for food production,it would be unwise to assume that tens ofmillions of acres could be devoted to aconversion facility for 30 years without af-fecting the price of farmland and thusfood.Preclusion of nonenergy benefits. -OTA’sanalysis indicates that bioenergy harvests,if properly integrated into nonenergy sec-tors, can provide benefits beyond the en-ergy, such as increased growth of timbersuitable for paper and lumber. Attemptingto isolate bioenergy product ion f romthese other sectors would preclude someof the potential benefits.

Although none of these factors is insur-mountable, taken together they make energyfarms appear considerably less attractive thannumerous other bioenergy options. Particular-ly because of the risk and the initial invest-ment, it is more likely that bioenergy crops willbe grown as one of the many crop choicesavailable to farmers, rather than on largetracts dedicated solely to energy production.There is, however, no technical reason why en-ergy farms cannot be constructed.

Biophotolysis

Biophotolysis is generally defined as theprocess by which certain microscopic algaecan produce hydrogen (and oxygen) from wa-ter and sunlight. Two distinct mechanisms areknown by which microalgae can carry out bio-photolysis: 1) through a “hydrogenase” en-

Ch. 4—Unconventional Biomass Production . 107

zyme (biological catalyst) which is activated orinduced by keeping the microalgae in the darkwithout oxygen for a period of time; or 2)through the “nitrogenase” (nitrogen-fixing) en-zyme which normally allows some types of mi-croalgae (the “blue-green” algae) to fix atmos-pheric nitrogen to ammonia but which alsocan be used to produce hydrogen by keepingthe algae under an inert atmosphere such asargon gas.

In the case of biophotolysis with hydroge-nase the key problem is that when simultane-ous oxygen production occurs, the hydroge-nase enzyme reaction is strongly inhibited andthe enzyme itself inactivated. Although it wasrecently demonstrated that simultaneous pro-duction of oxygen and hydrogen does occur insuch algae,31 it is uncertain whether it will bepossible to sustain such a reaction in a prac-tical system. This difficulty has led to propos-als for separation of the reactions either by de-veloping an algal system which alternates oxy-gen and hydrogen production, (possibly on aday-night cycle) or by developing a two-stageprocess. Such systems are still at the concep-tual stage, although considerable knowledgeexists about the basic mechanisms involved.

Somewhat better developed is a biophotoly-sis process based on nitrogen-fixing blue-greenalgae. I n these algae the oxygen-evolving reac-tions of photosynthesis are separated from theoxygen-sensitive nitrogenase reaction by theirsegregation into two cell types — the photosyn-thetic vegetative cells and the nitrogen-fixingheterocysts. Heterocysts receive the chemicalsnecessary to produce hydrogen from vegeta-tive cells but are protected from oxygen bytheir heavy cell wall and active respiration.Using cultures of such algae from which nitro-gen gas was removed, a sustained biophotoly-sis reaction was demonstrated: about 0.2 to 0.5percent of incident solar energy was convertedto hydrogen gas over a l-month period. How-ever, significant problems stil exist in the de-velopment of a practical system —1 O timeshigher conversion efficiencies m u s t b eachieved, a goal which may not be reached

“ E Greenbaum, Bioengineering Biotechnology Symposium,VOI 9, In press

due to the high energy consumption of the ni-trogenase reaction. Also, the mixture of hydro-gen and oxygen generated by such a systemmay be expensive to separate.

Whichever biophotolys i s mechanisms orprocesses are eventually demonstrated to becapable of efficient and sustained solar energyconversion to hydrogen fuel from water, theymust take place in a very low-cost conversionsystem. The development of an engineeredbiophotolysis conversion unit must meet strin-gent capital and operational cost goals. As bio-photolysis will be limited by the basic proc-esses of photosynthesis— probably no morethan 3 to 4 percent of total solar energy con-version to hydrogen fuel —this sets an upperlimit to the allowable costs of the conversionunit. In principle, the algal culture—the cata-lyst which converts sunlight and water to hy-drogen and oxygen–can be produced verycheaply; however, the required “hardware” tocontain the algal culture and trap the hydro-gen produced may be relatively expensive.

Biophotolysis is still in the early stages ofdevelopment. No particular mechanism, con-verter design, or algal strain appears to be in-herently superior at this stage. Claims thatnear-term practical applications are possible,that genetic engineering or strain selection canresult in a “super” algae, or that biophotolysisis inherently more promising than other bio-mass energy options are presently not war-ranted. A relatively long-term (10 to 20 years)basic and applied research effort will be re-quired before the practical possibilities of bio-photolysis are established.

Inducing Nitrogen Fixation in Plants

The biological process of nitrogen fixation,the conversion of nitrogen gas (not a fertilizer)to ammonia (a fertilizer) has only been foundto occur in bacteria and the related blue-greenalgae. These primitive organisms maintain theecological nitrogen cycle by replacing nitrogenlost through various natural processes. Thecapability for nitrogen fixation expressed bymany pIants (soybeans, alfalfa, peas) is duesolely to their abil ity to I ive in a symbiotic

108 ● Vol. Ii—Energy From Biological Processes

association with certain bacteria (of the genusRhizobia), which form the characteristic “rootnodules.” A certain fraction of the photosyn-thetic products of these plants are transferredto the roots where they are used (as “fuel”) bythe bacteria to fix nitrogen to ammonia whichis then sent (in bound form) to the protein syn-thesizing parts of the plant.

This process is, in principle, energy inten-sive, with each nitrogen atom (fixed) reducingthe biomass production by several carbonatoms (about 2 to 3).32 In practice, significantinefficiencies in the process are often noted,most particularly the recent discovery thatsome Rhizobia bacteria in root nodules wastea large fraction of the “fuel” supplied by theplant in the form of hydrogen gas.33 By usingRhizobia strains that can effectively recyclethe hydrogen gas, this loss may be overcome.

Although biological nitrogen fixation cansubstitute, to a large extent, for the fossil-fuel-derived nitrogen fertilizers currently used inagriculture, the tradeoff may be an overallreduction in biomass yields. In an era of de-creasing fossil fuel availability, such a tradeoffmay be desirable, particularly as the price ofcommercial fertilizers is a limiting economicfactor in many biomass production proposals.However, nutrient recycling could be prefer-able to de novo production, as it probablywould be less costly and energy intensive.Alternatively to biological nitrogen fixation,thermochemical conversions of biomass tosynthesis gas and their catalytic conversion toammonia are feasible. Whether this is more fa-vorable both in terms of economics and energyefficiency is uncertain.

A number of scientists have proposed that,through genetic engineering, they could trans-fer the nitrogen-fixing genes directly to theplant. However, such proposals face technicalbarriers. For example, the nitrogen-fixing reac-tion is extremely oxygen sensitive and is unlike-ly to be able to take place in the highly oxygen-

rich environment of a plant leaf. In principle,there would only be a relatively minor advan-tage for a plant to directly fix nitrogen ratherthan do so symbiotically. Much more basicknowledge in many areas of plant physiology,genetics, biochemistry, etc., as well as devel-opments in genetic engineering and plant tis-sue culture will be required before the poten-tial for practical applications of such conceptscan be evaluated.

Greenhouses

It is well known that increasing the C02 con-centration in the air results in significantly im-proved plant growth for some plants. Depend-ing on the specific plant and the specific con-ditions of the experiments, a 50-to 200-percenti n c r e a s e i n b i o m a s s p r o d u c t i o n h a s b e e nnoted. Greenhouses have the addi t iona l ad-vantages of prov id ing a “contro l led env i ron-ment” where pest control, water supply, andfertilization can be better managed, resultingin potentially high yields. The higher tempera-ture in greenhouses allows extended growingseasons in temperate climates. Greenhouseagriculture is rapidly expanding thoughout theworld to meet the demands of affluent coun-tries for out-of-season vegetables and horticul-tural products. However, the high cost ofgreenhouse agriculture and its high energyconsumption make production of staple cropsunfeasible and proposals for biomass energyproduction unrealistic at present. Althoughsignificantly lower cost greenhouse technologyis feasible in principle, biomass productioncosts in Arizona, for example, would still be 10times as expensive as open-field biomass cropsgrown in the Midwest.34 A significant inflationin farm commodity, farmland, and waterprices could make greenhouse systems moreattractive. At present and in the foreseeablefuture, however, greenhouses do not appeareconomically feasible for bioenergy produc-tion.

‘2K. T Shanmugan, F. O’Gara, K. Andersen, and P C. Valen-tine, “Biological Nitrogen Fixation,” Ann. Rev. Plant Physio/. 29,p. 263,1978.

“Ibid.

“L. H. de Bivort, T. B. Taylor, and M, Fontes, “An Assessmentof Controlled Environment Agriculture Technology, ” report bythe International Research and Technology Corp. to the NationalScience Foundation, February 1978.

Chapter 5

BIOMASS PROCESSING WASTES

Chapter 5.— BIOMASS PROCESSING WASTES

PageIntroduction . . . . . . . . . . ... , . . . . . . . . . . . . .. 111Wood-Processing and Paper-Pulping Wastes .. ..111Agricultural Wastes . . . . . . . . . . . . . . . . . . . . .. .112A n i m a l M a n u r e . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 4

TABLESPage

39. The Ten Major Agricultural Wastes WithPotential to Produce Energy. . ...........113

Page40. Energy Potential From Animal Manure on

Confined Animal Operations . ...........114

FIGURES

Page14. Material Flow Diagram for Forest

P roducts Indus t ry . . . . . . . . . . . . . . . . . . . . . 11115. Total Energy Available From Manure by

Farm Size . . . . . . . . . ..................114

Chapter 5

BIOMASS PROCESSING WASTES

Introduction

There are a number of byproducts associ-ated with growing biomass and processing itinto finished products. The byproducts that arenot generally collected in one place, such aslogging or crop residues, are termed residuesand are dealt with in chapters 2 and 3. The by-products that are collected in one place aretermed processing wastes for the purposes ofthis report and are considered in this chapter.The three main types of wastes considered arethe primary and secondary manufacturing

wastes of the forest products industries, andthe wastes associated with the processing ofagricultural products and animal manures.Wastepaper, cardboard, and urban woodwastes are not considered in this report, sincethey fall into the category of municipal solidwastes, which is the subject of a previous OTAreport .

IMateria/s and Energy From Municipal Waste [Washington,D C.: Office of Technology Assessment, July 1979), OTA-M-93

Wood-Processing and Paper= Pulping Wastes

Based on published surveys and discussionswith people familiar with the forest productsindustries, the fraction of wood feedstock thatappears as residue was estimated for the vari-ous types of processes and regions of the coun-try. These fractions and the U.S. Departmentof Agriculture’s Forest Statistics* were used toestimate the quantities of residues generatedby wood-processing and paper-pulping indus-tries. There is, however, some uncertainty inthese figures, since published data usually arereported in board feet or cubic feet (ratherthan dry tons) and often the bark i s notcounted. Furthermore, moisture loss duringdrying must be accounted for, Every effort wasmade to avoid these potential problems andadjust for the shrinkage.

Current data on the use of the manufactur-ing residues are not complete. In some casesdata are available for only a few States or forsome of the industries. In other published data,regional surveys are extrapolated to the entirecountry. The estimates presented here arebased on several surveys,3 but are neverthelessbased on incomplete data.

‘Forest Statistics for the United 5tates, 1977 (Washington, D C :Forest Service, U.S. Department of Agriculture, 1978)

‘J S. Bethel, et al., “Energy From Wood,” contractor report toOTA, April 1979.

Figure 14 shows an approximate materialsflow diagram for the harvested wood proc-essed by the forest products industry. This is anational average diagram. There are, however,

Figure 14.—Material Flow Diagram for ForestProducts Industry (in energy units, Quads/yr)

Forest productsindustry harvest

3.1Pulpwood harvests

Primary andsecondary

manufacturing 0.7 Paper and pulp2.0 1.8

Residues of primaryand secondarymanufacturing

Unused Energy Energy0.14 0.3 1.0

Total wastes used as energy: 1.2 to 1.3 Quads/yrUnused waste 0.1 to 0.2 Quad/yrEnergy and unused 1.4 Quads/yr


111


significant variations between the regions,with the unused fraction being about twice aslarge in the East as in the West.

The largest user of biomass energy in theUnited States is the pulp and paper industry.This industry is currently 45- to 55 -percentenergy self-sufficient, up from 37 percent in1967. 4 A major reason for the use of wood en-ergy in the forest products industry is that theprocess used to recover the paper-pulpingchemicals in most of the pulping processes in-volves burning the spent pulping liquor. Thisaccounts for about 0.8 Quad/yr. The remaining0.2 Quad/yr of bioenergy used in the pulp andpaper industry comes from the bark of the har-vested wood and reject woodchips.

The primary manufacturing industry pro-duces lumber, plywood, poles, etc. The sec-ondary industry produces furniture, prefabri-cated housing, etc. These industries are 20- to40-percent energy self-sufficient. s About 50percent (40 million dry ton/yr) of the primary

‘E, P Gyftopoulos, L J Lazarides, and T. F Wldmer, PotentialEue/ Effectiveness in Industry (Cambridge, Mass : Balllnger Pub-lications).

5S. H Spurr, Renewable Resources for Energy and IndustrialMaterials (Austin, Tex LBJ School of Public Affairs, Universityof Texas, 1978)

manufacturing wastes and 40 percent (4 mil-lion dry ton/yr) of the secondary manufactur-ing wastes go to paper pulping. Another 20 per-cent of each of these industries’ residues goesto particle board and various other uses. About20 million dry ton/yr (0.3 Quad/yr) of wood areused for energy; 9 million dry ton/yr (about0.14 Quad/yr) are unused.

The main reasons that the unused portion isnot used appear to be the very low quality ofthese wastes and a geographical mismatch be-tween the source and potential users of thewaste. However, either a strong wood energymarket or cooperative agreements with elec-tric utilities for cogeneration could bring thesewastes into energy use.

There are alternative uses for some of thewastes other than for energy. If the demand forforest products increases and other fuels areavailable, then more of the primary and sec-ondary manufacturing byproduct may be di-verted from energy use to particle board andpaper and pulp production. In addition, asmal l f ract ion of the spent pulping l iquorcould be used to produce ethanol and Iigninproducts (as one Georgia Pacific Corp. plantdoes) instead of simply burning the spent liq-uor to recover the pulping chemicals.

Agricultural Wastes

With the exception of orchard prunings,agricultural waste byproducts are generallynot collected at the place where the crops aregrown. Rather, the wastes usually occur asbyproducts to the agricultural product-proc-essing industries. About 50 to 70 percent ofthese byproducts are sold as animal feed or forchemical production at prices that prohibittheir use for energy. ’ The waste byproducts notbeing used for other purposes are consideredin this section.

The various agricultural product-processingindustries were surveyed 7 to determine thequantities and types of waste byproducts that

‘R. Hodam, “Agricultural Wastes,” Hodam Associates, Sacra-mento, Calif., contractor report to OTA.

‘Ibid.

are produced. Table 39 shows the 10 majortypes of agricultural wastes and the energypotential of each. These 10 wastes representover 95 percent of all agricultural wastesavailable for energy. Of these 10, about 90 per-cent are materials relatively low in moisture,and suitable for thermal conversion (combus-tion or gasification). The remaining 10 percentappear to be acceptable for anaerobic diges-tion or possible fermentation to ethanol in thecase of fruit and vegetable wastes and cheesewhey.

In addition, there is an unknown quantity ofspoiled and substandard grain. One source8 es-

OM. T Danz iger, M, P, Steinberg, and A. I Nelson, “Storage ofHigh Moisture Field Corn,” Illinois Research, fall 1971

Ch. 5—Biomass Processing Wastes ● 1 1 3

Table 39.–The Ten Major Agricultural Wastes WithPotential to Produce Energy

Wastes Btu/yr x 1012

Orchard pruningsa . . . . . . . . . . . . . . . . .Cotton gin trasha . . . . . . . . . . . . . . . . . . . .Sugarcane bagassea. . . . . . . . . . . . . . . .Cheese wheyb . . . . . . . . . . . . . . . . . . . . . .Tobacco (burley)a. . . . . . . . . . . . . . . . . . . .Rice hullsa. . . . . . . . . . . . . . . . . . . . . .Tomato pumiceb. ., ., . . . . . . . . . .Potato peel and pulpb . . . . . . . . . . .Walnut shella. . . . . . . . . . ., . . . . . . .Citrus rag and peelb . . . . . .

Total . . . . . . ., . . . . . . . . . . . . .

30-6120-31

4-84-B c

2.32.2

1.3-1.81.0-1.1

0.90.3-1.0

66-117

asultable for combustion or gaslflcatlonbsultable for anaerobtc dtgestlon or fermentationc~sed on starch content of milk and the volume of cheese production frOrTl ~rJrlCUhJh3/ .%?tEflCS

(Washmgfon, D C U S Department of Agriculture, 1978)

SOURCE Off Ice of Technology Assessment, and R Hodam “Agricultural Wastes, ” HodamAssoclales, contractor report to OTA, 1979

timated corn spoilage from mold at 250 millionbu/yr, but this number should be viewed asspeculative. Furthermore, much of the spoiledgrain may be accessible only as a supplementto existing distillery feedstocks because its oc-currence is dispersed and unpredictable.

The four major sources of agr iculturalwastes are orchard prunings, cotton gin trash,sugarcane bagasse, and cheese whey. MostStates have fruit or nut orchards, with thelargest crops occurring in Arizona, California,Florida, Texas, New York, and Washington.Cotton gin trash is generally localized to thesouthern third of the United States and Califor-nia. Sugarcane is processed primarily along theGulf Coast, in Hawaii, and in New England.The majority of cheese whey is produced inWisconsin, Minnesota, New York, lowa, andCalifornia, but 30 States have some cheeseproduction.

Orchard prunings are generally collectedand burned onsite. A few growers disk wholeprunings into the soil, although this is not apreferred practice for growers. With a strongenergy market, much of this could be used forenergy. The major expense is transporting theprunings to the place they are used.

Cotton gin trash is another potential sourceof energy. Texas cotton gins produce aboutfive times as much energy in gin trash as theyconsume (mostly electricity). The major prob-lems with using the trash for energy seem to bethe difficulty of handling the trash, the season-al nature of the ginning operations, and the dif-ficulty in establishing cooperative ventureswith the electric utilities. In addition, in theareas where the cotton plants are killed witharsenic acid prior to harvest, such as in muchof Texas, special precautions will be necessaryto burn the trash in an environmentally accept-able way.

Sugarcane bagasse is widely used in Hawaiias a source of energy. The sugar refineries havelong-standing cooperative agreements with theelectric utilities. Cogeneration is used to gener-ate and export electricity to the utiIities and toproduce the process steam used by the sugarrefineries. The electric generating facil it iesrange in size from 1.5- to 33-MW electric. Mostof the Hawaiian sugar refineries are 99- to 100-percent energy self-sufficient.

The New England and Southern sugar refin-eries should be analyzed in detail for the po-tential to duplicate the Hawaii experience, in-cluding the potential to purchase orchardprunings or wood wastes which are found inthe same area in some cases.

OTA’s analysis indicates that cheese whey isthe largest source of food-processing wastesuitable for conversion to ethanol, althoughother studies have indicated that citrus wastesare a larger source.9 Based on total cheese pro-duction, 10 OTA estimates that 50 million to 100million gal/yr of ethanol could be producedfrom cheese whey. Current production fromthis source is about 5 million gal/yr.

‘The Report of the A/coho/ Fue/s Po/Icy Review (Washington,D C : Department of Energy, June 1979), GPO stock No 061-(XX3-OO31 3-4,

‘“The Out/ook for Timber in the U.S. (Washington, D C : ForestService, U S Department of Agriculture, 1974), report No. 24;and Agricu/tura/ Statistics (Washington, D C U S Department ofAgriculture, 1978)


Animal Manure

The major sources of animal manures suit-able for energy are from dairy cows, cattle onfeed, swine, chickens (broilers and layers), andturkeys. Only animals in confined animal oper-ations are considered. However, it has beenestimated that 48 percent of all manure voidedfrom livestock (primarily sheep and cattle), ison open range. ” This open range manurewould require collection and, therefore, willnot be economic in the foreseeable future.

The inventory of onfarm confined animalswas derived from inventory numbers for ani-mals that remain onfarm for more than a yearand from sales numbers and the average timethe animal spends on the farm for animals onfarm for less than a year. ’z These inventorynumbers were converted to the common basisof the number of animal units, or the equiv-alent of a 1,000-lb animal (defined in figure 15).The quantities of manure were calculated and,assuming that the manure is anaerobically di-gested to produce biogas (60 percent methane,40 percent carbon dioxide), the energy equiv-alent was derived.

Table 40 shows the energy potential fromeach type of animal operation, and figure 15shows the percent of this energy potential thatis present on confined animal operations ofvarious sizes (expressed in animal units). Cur-rently most of this manure is used as nitrogenfertilizer and soil conditioner or is unused.

The total energy potential from manure pro-duced in confined animal operations is about0.3 Quad/yr. From one-third to one-half of thismanure is currently allowed to wash away withrain or is allowed to dry which makes it unsuit-able for anaerobic digestion. However, if it be-comes economically attractive to digest themanure, then most of these operations canchange their manure-handling techniques toaccommodate anaerobic digestion.

Figure 15 shows that over 75 percent of theenergy potential occurs on farms with less than

1‘D. Van Dyne and C, C ilbertson, Estimating U.S. Livestock andPoultry Manure and Nutrient Production (Washington, DC.: U.S.Department of Agriculture, 1978), ESCS-12.

“1974 Census of Agriculture (Washington, D C : Bureau of theCensus, U S. Department of Commerce), vol. 1-50

1,000 animal units and that about 45 percentof the potential is on farms with less than 100animal units. Large feedlots (greater than10,000 animal units) only account for about 15percent of the total. Consequently, any tech-nology development that is aimed at fully uti-lizing the potential for energy from animal ma-nure will have to concentrate on relativelysmall-scale conversion units.

Figure 15.—Total Energy Available From Manure byFarm Size (confined animal operations)

16.2% I6.6%

30.9%

41.7%

4.6%

50 ”/0

10,000 + animal units I Percent of energy

100-999

10-99

0.1-9.0

4 0 %

3 0 %

2 0 %

10%

1 animal unit =

250 chickens250 broilers

50 turkeys1.25 cattle on feed

Farm size in animal units

0.83 dairy cow6.25 swine

SOURCE: K D, Smith, J. Philbin, L. Kulik, and D. Inman, “Energy From Agri-culture: Animal Wastes,” contractor report to OTA, March 1979.

Table 40.–Enorgy Potential From Animal Manureon Confined Animal Operations

Total energy potential PercentType animal Btu x 1012/ y r or total

Dairy cattle. . . . . . . . . . . . . . . . . . . . .Cattle on feed . . . . . . . . . . . . . . . . . . .Swine . . . . . . . . . . . . . . . . . . . . . . . .Chicken (broilers) . . . . . . . . . . . . . . . .Chicken (layers) . . . . . . . . . . . . . . . . .Turkeys. . . . . . . . . . . . . . . . . . . . . . .

Total energy potential from allmanures . . . . . . . . . . . . . . . . . . .

90 3380 3032 1230 1125 918 6

274 100

SOURCE K D. Smtth, J Phdbm, L Kuhk, and D. Innran, “Energy From Agriculture. AnimalWastes, contractor report to OTA, March 1979.

Part II.

Conversion Technologies andEnd Use

Chapter 6


Chapter 6


Most bioenergy currently comes from directcombustion of solid biomass for space heating,process steam, and a small amount of electricgeneration. As chemically stored solar energy,biomass can be converted to a number of gas-eous and liquid fuels, which can be used for avariety of energy purposes not suited to directcombustion.

Thermochemical conversion, or chemicalprocesses induced by heat, is currently themost suitable process for the major biomassfeedstocks–wood and plant herbage. Asidefrom direct combustion, these processes in-clude gasification and liquid fuels production.Various types of gasifiers are being developedwhich could be used for process heat and ret-rofits of oil- and natural-gas-fired boilers. Suit-able gasifiers may be commercially availablein less than 5 years with adequate develop-ment support. Methanol synthesis is the near-term option for liquid fuels production. Wood-to-methanol plants can be constructed imme-diately, while herbage-to-methanol processesneed to be demonstrated. Various other proc-esses are being developed, and thermochemi-cal conversion of biomass offers considerablepromise for improved processes and new appli-cations for fuel and chemical syntheses.

Fermentation is the biological process usedto convert grains and sugar crops to ethanol –currently the only l iquid fuel from biomassused in the United States. The byproduct ofdistillery grains can be used as an animal feed,thereby reducing the competition betweenfood and fuel uses for the grain. Some farmersare producing ethanol onfarm, but with cur-rent technology the processes are not eco-nomic unless they are heavily subsidized or theonfarm production leads to increased grainprices—thereby enabling the farmer to earnmore on the crops he/she sells for feed. How-ever, process development could decrease thecosts. Several processes for producing ethanolfrom wood and herbage are being developed,but the costs are highly uncertain.

Anaerobic digestion is a biological process,which produces a gas containing methane (theprincipal component of natural gas) and car-bon dioxide. Suitable feedstocks include manywet forms of biomass, such as animal manureand some aquatic plants. For the near to midterm, digesters for onfarm production of gasfrom animal manure appear to hold the great-est promise. Not only can this technology serveas a waste disposal process, but it also couldmake most confined animal operations energyself-sufficient. There is a need to demonstratea variety of digesters using different feed-stocks to gain operating experience. Becausethe major cost is the initial investment, pol-icies designed to lower capital charges will in-crease market penetration of the technology.

The alcohols most easily produced from bio-mass—ethanol and methanol —are not totallycompatible with the existing liquid fuels sys-tem and automobile fleet. These alcohols canbe used in gasoline blends or as standalonefuels, but methanol blends wil l have moreproblems than ethanol blends unless suitableadditives are included with the methanol. Allof the problems regarding the alcohols’ incom-patibility with the existing system have multi-ple solutions, but it is unclear which strategieswill prove to be the most cost effective.

The energy balance for ethanol from grainsand sugar crops has been the subject of consid-erable controversy, because the farming andprocessing energy consumption together areapproximately the same as the energy con-tained in the ethanol. A net displacement ofpremium fuels—oil and natural gas—can beassured with ethanol, however, if: 1 ) distilleriesdo not use premium fuel for their boilers and2) the ethanol is used as an octane-boosting ad-ditive to gasoline. Failure to fulfill either ofthese criteria could lead to ethanol productionand use increasing the U.S. consumption ofpremium fuels, although there would be asmall net displacement of premium fuels inmost cases. Failure to comply with both crite-

119

120 ● Vol. n-Energy From Biological processes

ria would almost certainly be counterproduc-tive in terms of premium fuels displacement.

Methanol and ethanol can be producedfrom wood and plant herbage, although etha-nol production is considerably more expensivewith current technology. In each case, how-ever, the biomass might be burned or gasifiedas a substitute for oil or natural gas. Liquidfuels production is considerably less efficientthan combustion or gasification if the liquid isused as a standalone fuel. Using the liquid asan octane-boosting additive to gasoline, how-ever, makes the options more comparable interms of premium fuels displacement per tonof biomass. Future developments in refinerytechnology could change this conclusion.

Biomass already supplies substantial quan-tities of chemicals, and an expanded use of

biomass chemicals is a widely discussed sub-ject. Numerous plants produce potentiallyuseful chemicals for industrial synthesis and asa source of natural rubber, mutant cells canproduce highly specialized chemicals, andchemical synthesis from wood and plant herb-age is developing or could be developed in anumber of potentially very interesting direc-tions. Because of the higher value of chemi-cals, as compared to fuel, the economic limita-tions on chemical production from biomassare considerably less severe than for energyproduction.

These topics and related aspects of conver-sion technologies and end use for bioenergyare presented in the following chapters.

Chapter 7

THERMOCHEMICAL CONVERSION

Chapter 7.—THERMOCHEMICAL CONVERSION

PageIntroduction . . . . . . . . . . . . . . . . . . . . . .......123Generic Aspects of Biomass Thermochemistry .. .123Reactor Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127Optimum Size for Thermochemical Conversion

Facil i t ies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .129Biomass Densif icat ion . . . . . . . . . . . . . . . . . . . . .130Direct Combustion of Biomass . ..............131

Cocombustion of Biomass . . . . . . . .131Combustion of Biomass . . . . . ..131W o o d S t o v e s a n d F i r e p l a c e s . . . . . . . . . . . 1 3 3

Gasif icat ion of Biomass . . . . . . . . . . . . . . . . . . . .134Airblown Casifier Types. . . . . . . . . . .135E f f i c i e n c y o f A i r b l o w n G a s i f i e r s . . . . . . 1 3 5Airblown Gasifier Costs . . . . . . . . .137G a s i f i e r s f o r l n t e r n a l C o m b u s t i o n

Engines. . . . . . . . . . . . . . . . . .138Liquid Fuels From Thermal Processes . .........139

Methanol . . . . . . . . . . . . . . . . . . . . . .......139Pyrolytic Oil... . . . . . . . . . . . . . . . . . . . . ..141Ethanol. . . . . . . . . . . . . . . . . . ............142

Environmental lmpacts of Wood andWood Waste Combustion. . ...............143Smal l - Sca le Bu rn ing . . . . . . . . . . . . . . . . . . . . 143Utility and Industrial Boilers . . . . . . . . . .144

Environmental lmpacts of Cofiring Agriculturaland Forest Residues With Coal. . . . . . . . . .. ...147

Environmental impacts of Gasification . ........148Research, Development, and Demonstration

Needs . . . . . . . . . . . . . . . .................149Appendix A.-Optimum Size for a Wood-Fired

Electric Powerplant. . . . . . . . . . . . . . . . . . . . . .151Appendix B.-Analysis of Break-Even Transport

Distance for Pellitized Wood andMiscellaneous Cost Calculations . ...........152

Appendix C.-Survey of Gasifier Research,Development, and Manufacture . ...........154

T A B L E SPage

41 . Proximate Analysis Data for Selected SolidFuels and Biomass Materials . ...........124

42. Ultimate Analysis Data for Selected Solid

4344

4546

Fuels and Biomass Materials . ..........,124Cost of Pelletized Wood. . ..............130Cost of Electric Generation, Cogeneration,and Steam Production From Wood . . . . . 132Small-Scale Heating Device Efficiency .. ..133Cost Estimate for Fuel Gas From WoodUsing a Mass-Produced Airblown Gasifier .. 138

47

48

49

5051

Page

Summary of Cost Estimates for VariousLiquid Fuels from Wood viaThermochemical Processes . . . . . . . . . . . .. 1391979 Cost of Methanol From Wood UsingOxygen Gasification. . . . . . . . . . . . .140Emission Factors for Residential WoodCombustion Processes . . . . . . . . . . . .. ..143Estimates of Total B(a)P Emissions, . . . . .144“Source-to-Power” Air Emissions for Coal,Oil, and Wood Fuel Systems. . . . . . . . . . .. 146

B-1 .

B-2.B-3.

B-4.

B-5.

B-6.

B-7.

B-8.

Electricity From Wood by DirectCombustion. . . . . . . . . . . . . . . . . . . . . .. ..152Steam From Wood by Direct Combustion .152Electricity and Steam From Wood byDirect Combustion . . . . . . . . . . . . . . . . .. .153Medium-Btu Gas From Wood in a DualFluidized-Bed Field Erected Gasifier. . . . . . 153Medium-Btu Gas From Manure in aFluidized-Bed Gasifier . . . . . . . . . , . . . .. 153Methanol From Wood ThroughGasification in a Dual Fluidized-BedGasifier . . . . . . . . . . . . . . . . . . . . . .......153Pyrolysis Oil From Wood by CatalyticD i rect L iquefact ion . . . . . . . . . . . . . . . . . . . 153Ethanol From Wood via Gasification in aDual Fluidized-Bed Gasifier . ...........153

FIGURES

Page16. Effect of Moisture on the Heat Content of

Wood . . . . . . . . . . . . . . . . . . . . . .........12517. Effect of Feedstock Moisture Content on

Boiler Efficiency. . . . . . . . . . . . . . . . . . .12618. A Comparison of Pyrolytic Weight Loss v.

Temperature for Coal and Cellulose .. ....12719. Differential Loss of Weight Curves. . . . .. ..12820. Cost of Electricity From Wood for Various

Wood Costs . . . . . . . . . . . . . . . . . . . . .. ...13221. Cost of Process Steam From Wood for

Various Wood Costs. . . . . . . . . . . . .......13222. Schematic Representation of Various

Gasifier Types . . . . . . . . . . . . . . . . . . . . .. .13623. Boiler Efficiency as a Function of the Btu

Content of the Fuel Gas . ...............13724. Comparison of Oil/Gas Package Boiler

With Airblown Gasifier Costs . ...........13725. Block Flow Diagram of Major Process

Units. . . . . . . . . . . . . . . . . . . . . , . ........140B-1. Two Ways to Produce 106 Btu Steam

From Wood . . . . . . . . . . . . . . . . . . . . .. ...152

Chapter 7

THERMOCHEMICAL CONVERSION

Introduction

During the 1980’s, the conversion processeswith the greatest potential in terms of both thegross energy use and the largest possible dis-placement of oil and natural gas are the ther-mochemical processes, or processes involvingheat-induced chemical reactions. Currentlyabout 1.5 Quads/yr of biomass are combusteddirectly for process steam, electric generation(mostly cogeneration), and space heat. lnter-mediate-Btu gasifiers currently under develop-ment will be useful in retrofitting oil- and gas-fired boilers to biomass fuels and for crop dry-ing and other process heat needs. Develop-ment of medium-Btu gasifiers is also underwayand various processes for producing alcoholsand other liquid fuels can be or are being de-veloped. Also, methanol synthesis from woodcan probably be accomplished with commer-cially available technology, while processes

producing methanol from plant herbage canprobably be demonstrated fairly rapidly. More-over, there are good theoretical reasons for be-lieving that the flexibility, efficiency, and use-fulness of thermochemical processes can besignificantly improved through basic and ap-plied research into the thermochemistry of bio-mass.

Some generic aspects of biomass thermo-chemistry and generic reactor types are givenfirst, followed by a discussion of the optimumsize of some thermochemical conversion facil-it ies and a more detailed consideration ofselect processes including densification, directcombustion, gasification, and direct and in-direct liquefaction. Finally, the environmentalimpacts and research, development, and dem-onstration (RD&D) needs are presented.

Generic Aspects of Biomass Thermochemistry

Possible feedstocks for the thermochemicalconversion processes include any relativelydry plant matter such as wood, grasses, andcrop residues. Some conversion process de-signs accept a wide range of feedstocks, whileothers will be more suited to a specific feed-stock. Although this is sometimes dependenton the chemical properties of the feedstock(e.g., manure), it more often depends on thephysical properties of the material, such as itstendency to clog or bridge the reactor, theease with which it can be reduced to a smallparticle size, and the materials’ density.

Classification systems that provide informa-tion for assisting the designer of conversionequipment are not presently available for bio-mass feedstocks. Standard methods for bio-mass analysis or assays do not exist, althoughit is customary to use coal analyses (ultimateand proximate) for biomass. Some of the prop-erties of some biomass materials using coal

analyses are shown in tables 41 and 42. As afuller understanding of biomass thermochem-istry is developed, however, new classificationschemes and methods of analysis are likely tobe necessary.

Despite the differences in feedstocks, thegeneric thermochemical process consists ofthe following steps:

● moisture removal;● heating the material to and through the

temperature where it decomposes (about4000 to 8000 F);

● decomposition to form gases, liquids, andsol ids; and

● secondary gas phase reactions.

The drying process absorbs the heat neces-sary to evaporate the water. This results in adecrease in the net usable heat from the feed-stock as shown in figure 16. I n this figure, thenet heat content per pound of dry wood is

123

124 . Vol. I/—Energy From Biological Processes

Table 41 .–Proximate Analysis Data for Selected Solid Fuels and Biomass Materials (dry basis, weight percent)

Volatile matter Fixed carbon Ash Reference

CoalsPittsburgh seam coal. . . . . . . . . . . . . . . . . . .Wyoming Elkol coal, . . . . . . . . . . . . . . . . . . .Lignite . . . . . . . . . . . . . . . . . . . . . . . . . . . .Oven dry woodsWestern hemlock . . . . . . . . . . . . . . . . . . . .Douglas fir. . . . . . . . . . . . . . . . . . . . . . . .White fir . . . . . . . . . . . . . . . . . . . . . . . . . . .Ponderosa pine. . . . . . . . . . . . . . . . . . . . . . .Redwood . . . . . . . . . . . . . . . . . . . . . . . . . . .Cedar . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Oven dry barksWestern hemlock . . . . . . . . . . . . . . . . . . . . .Douglas fir.. . . . . . . . . . . . . . . . . . . . . . . . .White fir . . . . . . . . . . . . . . . . . . . . , . . . . . .Ponderosa pine. . . . . . . . . . . . . . . . . . . . . . .Redwood . . . . . . . . . . . . . . . . . . . . . . . . . . .Cedar . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Mill woodwaste samples-4 mesh redwood shavings . . . . . . . . . . . . .-4 mesh Alabama oakchips . . . . . . . . . . . . .Municipal rufuse and major componentsNational average waste . . . . . . . . . . . . . . . . .Newspaper(9.4% of average waste) . . . . . . . .Paperboxes (23.4%) . . . . . . . . . . . . . . . . . .Magazine paper (6.8%) . . . . . . . . . . . . . . . .Brownpaper (5.6%). . . . . . . . . . . . . . . . . . .Pyrolysis charsRedwood (790°to 1,020 F) . . . . . . . . . . . . .Redwood (800°to 1,725 F) . . . . . . . . . . . . .Oak (820°to 1,185 F) . . . . . . . . . . . . . . . . .Oak (1,060°F). . . . . . . . . . . . . . . . . . . . . . .

33.944.443.0

55.851.446.6

10.34.2

10.4

Bituminous Coal Research 1974Bituminous Coal Research 1974Bifumirtous Coal Research 1974

84.886.284.487.083.577.0

15.013.715.112.816.121.0

0.20.10.50.20.42.0

Howlett and Gamache 1977Howlett and Gamache 1977Howlett and Gamache 1977Howlett and Gamache 1977Howlett and Gamache 1977Howlett and Gamache 1977

74.370.673.473.471.386.7

24.027.224.025.927.913.1

1.72.22.60.70.80.2

Howlett and Gamache 1977Hewlett and Gamache 1977Hewlett and Gamache 1977Hewlett and Gamache 1977Howlett and Gamache 1977Howlett and Gamache 1977

76.274.7

23.521.9

0.33.3

Boley and Landers 1969Boley and Landers 1969

65.986.381.769.289.1

9.112.212.97.39.8

25.01.55.4

23.41.1

Klass and Ghosh 1973Klass and Ghosh 1973Klass and Ghosh 1973Klass and Ghosh 1973Klass and Ghosh 1973

30.023.925.827.1

67.772.059.355.6

2.34.1

14.917.3

Howlett and Gamache 1977Howlett and Gamache 1977Howlett and Gamache 1977Howlett and Gamache 1977

SOURCE M Graboskland R Barn, ’’Propertiesof Biomass Relevant lo Gasification, “ in A Swveyo/8/orrrass Gas/ficaf/on (vol. 11: Golden, (Mo, Solar Energy Research Institute, July 1979), TR-33-239

Table 42.–Ultimate Analysis Data for Selected Solid Fuels and Biomass Materials (dry basis, weight percent)

Higher heatingMaterial C H N S O Ash value (Btu/lb) Reference

Pittsburgh seam coal ., . . . . . . . . ., , , , , . 75.5 5.0 1,2 3.1 4 . 9 1 0 . 3West Kentucky No. 11 coal . . . . . . . . . . . . . 74.4 5.1 1.5 3.8 7.9 7.3Utah coal . . . . . . . . . . . . . . . . . . . . . . . . . 77.9 6.0 1.5 0.6 9.9 4.1Wyoming Elkol coal . . . . . . . . . . . . . . . . . . 71.5 5.3 1.2 0.9 16.9 4.2Lignite . . . . . . . . . . . . . . . . . . . . . . . . . . . 64.0 4.2 0.9 1.3 19.2 10.4Charcoal. , . . . . . . . . . . . . . . . . . . . . . . . . 80.3 3.1 0.2 0.0 11.3 3.4Douglas fir . . . . . . . . . . . . . . . ... . . . . . 52.3 6.3 0.1 0 . 0 4 0 . 5 0.8Douglas fir bark. . . . . . . . . . . . . . . . . . . . . 56.2 5.9 0.0 0.0 36.7 1.2Pine bark ., ., . . . . . . . . . . . . . . . . . . . . . 52,3 5.8 0.2 0.0 38.8 2.9Western hemlock. . . . . . . . . . . . . . . . . . . . 50.4 5.8 0.1 0.1 41.4 2.2Redwood. ... , . . . . . . . . . . . . . . . ... , . . 53,5 5.9 0.1 0.0 40.3 0,2Beech. . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.6 6.3 0.0 0.0 41.5 0.6Hickory. . . . . . . . . . . . . . . . . . . . . . . . . . . 49.7 6.5 0.0 0.0 43.1 0.7Maple. . . . . . . . . . . . . . . . . . . . . . . . . . . . 50.6 6.0 0.3 0.0 41,7 1.4Poplar. . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.6 6.3 0.0 0.0 41.5 0.6Rice hulls . . . . . . . . . . . . . . . . . . . . . . . . . 38.5 5.7 0.5 0.0 39.8 15.5Rice straw. . . . . . . . . . . . . . . . . . . . . . . . . 39.2 5.1 0,6 0.1 35.8 19.2Sawdust pellets. . . . . . . . . . . . . . . . . . . . . 47.2 6.5 0.0 0.0 45.4 1.0Paper. . . . . . . . . . . . . . . . . . . . . . . . . . . . 43.4 5.8 0.3 0.2 44.3 6.0Redwood wastewood . . . . . . . . . . . . . . . . 53.4 6.0 0 . 1 3 9 . 9 0.1 0.6Alabama oak woodwaste. . . . . . . . . ., . . . . 49.5 5.7 0.2 0.0 41.3 3,3Animal waste. . . . . . . . , . . . . . . . . . . . . . . 42.7 5.5 2.4 0.3 31.3 17.8Municipal solid waste ... , . . . . 47.6 6.0 1.2 0.3 32.9 12.0

13,65013,46014,17012,71010,71213,3709,0509,5008,7808,6209,0408,7608,6708,5808,9206,6106,5408,8147,5729,1638,2667,3808,546

Tillman 1978Bituminous Coal Research 1974Tillman 1978Bituminous Coal Research 1974Bituminous Coal Research 1974Tillman 1978Tillman 1978Tillman 1978Tillman 1978Tillman 1978Tillman 1978Tillman 1978Tillman 1978Tillman 1978Tillman 1978Tiliman 1978Tillman 1978Wen et al. 1974Bowerman 1969Boley and Landers 1969Boley and Landers 1969Tillman 1978Sanner et al. 1970

C = carbon H = hydrogen N = nitrogen S = sulfur O = oxygen

SOURCE M Graboskl and R Barn, “Properties of Biomass Relevant to Gastf!catlon, ” m A .%rwyof Llornass Gas/f/caf/err, (VOI 11, Golden, Colo Solar Energy Research Institute, July 1979), TR-33-239

Ch. 7—Thermochemical Convers ion ● 1 2 5

Figure 16.— Effect of Moisture on theHeat Content of Wood

9,000

8,000

7,000

6,000

5,000

4,000

3,000

2,000

o 10 20 30 40 50 60

Moisture content(% of fresh weight)

SOURCE: Off Ice of Technology Assessment,

shown for various moisture contents. The heatcontent per pound of moist material, however,decreases much more rapidly with moisturecontent, due to the fact that part of eachpound is water and not combustible material.(Nevertheless, the price of the moist feedstockwill vary with the moisture content, so that$1 5/ton material at 50-percent moisture con-tent is roughly equal to $30/ton of dry material.In this report, the feedstock costs are generallyexpressed as dollars per ton of dry material, sothat variations in cost and heat content per tonare kept at a mini mum.)

There is also a secondary effect of the mois-ture content of the feedstock. If moist feed-stocks are combusted to produce steam, theboiler efficiency will usually drop if the feed-stock moisture content is not that for whichthe boiler was designed. Aside from the heatlost in evaporating the water in the feedstock,high-moisture feedstocks have a lower flametemperature in direct combustion, which canresult in particulate and creosote emissions(which escape without being completely com-busted, if considerable excess combustion airis not used). (1 n poorly designed wood stoves orboilers, simply feeding excess air may not besufficient to suppress these emission s.) In prin-ciple, a reactor can be designed to accommo-date this excess combustion air, vaporizedmoisture, and lower flame temperature with-

out a drop in efficiency, but in practice the ef-ficiency is likely to drop.

A theoretical example of how the boiler effi-ciency drops with feedstock moisture contentis shown in figure 17. Care should be exercisedin applying these results to any given situation,

since some factors which would vary withmoisture content (e. g., excess air) are held con-stant in the calculations, but it does illustratethe point.

With gasification, the s i tuat ion is s l ight lydifferent. In this case the feedstock is decom-posed into a fuel gas before combustion. Theenergy needed to vaporize the feedstock mois-ture is still lost, but the fuel gas can easily bemixed with the combustion air, so that excessair is not required, and the feedstock moistureis already vaporized, so the flame temperaturecan be high. Consequently, it may be possibleto maintain the efficiency of gasification-com-bustion processes over a variety of feedstockmoisture contents better than with direct com-bustion. Depending on reactor design, how-ever, it may be necessary to limit the feedstockmoisture in order to produce a flammable gas,and this point needs further investigation.

The rate that the biomass is heated to andthrough its decomposition temperature is acritical factor in determining the products.Many reactor designs are being developed toachieve high heating rates, as described below.(The heating rate is also determined by the par-ticle size— small particles heating faster— andmoisture content. ) Depending on the productsdesired, however, one may want this heatingrate to be slower.

The details of biomass decomposition arenot well understood, but one can surmise thefollowing. As the material is heated, the large

biomass molecules (cellulose, hemicellulose,and Iignin) begin to break down into intermedi-ate-sized molecules. If the material stays in theheating zone long enough, the intermediate-size molecules decompose into sti l l smallermolecules, such as hydrogen, methane, carbonmonoxide (CO), ethane, ethylene, acetylene,and other chemicals. If the heating rate is tooslow relative to the time the material is in the


Figure 17.—Effect of Feedstock Moisture Content on Boiler Efficiency

90

80

70

60

50

0 10 20 30 40 50 60

Moisture content (o /o )

SOURCE: R. A. Arola, “Wood Fuels – How Do They Stack Up?” Energy and the Wood Products Industry, Forests Products Research Society, Proceeding No. 76-14,

NOV. 15-17, 1976.

heating zone, the intermediate-sized mole-cules will escape and later condense as oilsand tar. (This may also involve some intermedi-ate reactions that are not well understood atpresent. ) It also appears that a slow heatingrate encourages the formation of char. Thus, aslow heating rate (either by design or due to ex-cess moisture in the feedstock) will lead to theformation of varying amounts of char, tar, oil,and gas. With rapid heating, however, virtuallythe entire biomass goes to a gas with only theash remaining.

Finally, the gases and vaporized tars and oilscan react in the gas phase to form a new ormodified set of products. Very Iittle is under-stood about these secondary gas phase reac-tions, but they are of considerable importancein thermochemical processes. Depending onthe oxygen and moisture content, the rate thebiomass was decomposed, the temperature,

the pressure, and other variables not fullyunderstood, the resultant gas can vary fromalmost pure carbon dioxide (C02) and water togases with relatively high contents of materialssuch as hydrogen, methane, or ethylene (seech. 12), or the gas can contain considerablequantities of particulate, various hydrocar-bons, CO, and other pollutants.

Depending on the conditions chosen and thedesign of the reactor, the product(s) can beheat as in direct combustion, an intermediate-or medium-Btu gas suitable for oil- or gas-firedboilers and process heat, a gas suitable forchemical synthesis, oils, and/or char. But con-siderable research into the thermochemistry ofbiomass will be needed, before engineers willhave the necessary information to design reac-tors that can achieve the full potential for thethermochemical conversion of biomass.

Ch. 7—Thermochemical Conversion ● 127

Reactor -Type

Most commercial biomass reactors used fordirect combustion or gasification are modifi-cations of coal technology. The reactors pro-posed for direct liquefaction and densifica-tion, however, do not fall into this categoryand are considered in the sections dealing withthese topics.

Although the technology for coal combus-tion and gasification is considerably more ad-vanced than for biomass, it is generally agreedthat grasses, wood, and crop residues are morereadily gasified than coal or char. The biomassgasifies at a lower temperature and over a nar-rower temperature range than does coal, as il-lustrated in figures 18 and 19, Both of thesepropert ies favor rapid gasi f icat ion. Whi lethese advantages of biomass over coal are par-tially offset by biomass’ higher heat capacity(the amount of heat needed to raise the materi-

Figure 18.—A Comparison of Pyrolytic Weight Loss(on a mass fraction basis) v. Temperature

for Coal and Cellulose1.0

0.9

0.8

0.4

0.3

0.2

Cellulose

0.1100 300 500 700 900

Temperature, “C

SOURCE: M J Antal, Biomass Energy Enhancement—A Report to the Presl.dent’s Counc// on Errv/ronrnental Oua//ty (Princeton, N.J Pr incetonUnlverslty, July 1978)

al’s temperature a given amount)’ coal gasifi-cation in advanced reactors will ultimately belimited by the rate that oxygen, CO2, steam,etc., can diffuse to and into the surface of coalparticles. Biomass gasification and decomposi-tion, on the other hand, do not require thereaction of two or more separate species. Con-sequently, biomass gasification probably willbe limited by the rate that heat can be trans-ferred to the biomass.

In balance, these differences point to theconclusion that there is the potential for build-ing biomass reactors that have considerablyhigher rates of throughput and thus lower coststhan will be achieved with coal or has beenachieved for either material so far. On theother hand, the most rapid heat transfer occurswhen the feedstock particles are pulverized orof relatively small size. Most coals can readilybe pulverized, but the fibrous nature of manytypes of biomass makes it difficult to reducethe particle size. Biomass densification (seebelow) makes it fairly easy to pulverize thebiomass, but this and other pretreatments addto the costs. At present it is impossible topredict whether the difficulty and expense ofreducing the biomass particle size or the in-herent limitations in the rate that coal reactswill dominate the economic differences be-tween the two types of fuel reactors. Neverthe-less, it is clear that dramatic improvements inbiomass reactors are possible and that achiev-ing this full potential will require RD&D spe-cifically aimed at addressing and exploitingthe unique features of biomass. Furthermore,since biomass char is more l ike coal thanwood, grasses, or crop residues, achieving thispotential advantage of biomass will involvereactors that produce Iittle or no char.

Generally, the biomass reactors are classi-fied according to the way the feedstock is fedinto them. Although there are numerous varia-tions, the major types are moving grate, mov-

‘M Graboskl and R Baln, “Properties of Biomass Relevant toCaslflcatton, ” m A S u r v e y of L?iorTra55 Gas//ication (V OI 1 1 ,

Golden, Colo Solar Energy Research Institute, July 1979),TR- 13-239


● These curves represent the derivative of curves similar to those given in figure 18. They were obtained by heating asmall sample of solid material at a given rate and recording fractional weight loss v. temperature. The peak of eachdifferential weight-loss curve (i.e., for cellulose the value is 15% per 10°C at 315 “C) is indicative of the individualmaterial’s pyrolysis kinetics — a higher heating rate would displace all the curves to higher temperatures and would“sharpen” each peak. Thus the position of each peak is not related to “optimum” operating conditions. The curvessimply show that biomass materials pyrolyze much more rapidly at much lower temperatures than coal.

SOURCE: H. H. Lowry, Chemistry of Coal Ufi/ization Supplementary Vo/ume (New York: John Wiley and Sons, Inc. 1963)

ing bed, fluidized bed, and entrained flow. Therate of heat transfer generally follows theorder given, with the moving-grate reactors be-ing the slowest. (There are, however, otherclassification schemes which can be useful aswell. )

Moving-grate reactors consist of a grate thatcarries or moves the biomass through the zonewhere it is heated and decomposes. The heattransfer is relatively inefficient and slow, so anexcess of heat must be generated to sustain thereaction. Therefore this type of reactor is gen-erally best suited to direct combustion wherethe biomass is completely reacted and releasesvirtually all of its heat in the decompositionzone.

A sl ightly faster rate of heat transfer isachieved with moving-bed reactors. In thesethe bed, or clump of biomass, moves in a ver-tical direction as it is decomposed. Additionalbiomass is added at the top, which then grad-ually works its way down the reactor. Twotypes of moving-bed reactors exist: updraftand downdraft.

The updraft moving-bed reactors have astream of air moving up through the bed ofbiomass. The hottest part of the bed is at thebottom. As the hot gases move through thebed, however, they cause relatively largeamounts of tars and oils to form, which cancondense causing maintenance problems and


which may make it more difficult to burn theresultant gas without forming particulate.

The downdraft moving-bed reactors have astream of air moving downward through thebed of biomass. Tars and oils are formed nearthe middle of the bed (where the air is injected)and subsequently move through a relativelylarge hot zone which gives them time to fur-ther decompose. The net result is a fuel gaswith fewer tars and oils, thereby making gascleanup easier and reducing the amount ofparticulate that form when the gas is burned.

Another type is the fluidized-bed reactor. Inthis case, gas is blown through the bed of solidfuel so rapidly that the bed of biomass levi-tates and churns as if it were fluid. In coal-fedfluidized-bed reactors, the fluid bed may con-tain limestone particles to react with and re-move sulfur from the coal. Since biomass usu-ally does not contain significant levels ofsulfur, sand can be used as a fluidizing medi-um or one can rely solely on the biomass itself,with no separate fluidizing medium. Sand has

the advantage, however, of helping to retainheat in the bed, thereby increasing the ratethat new pieces of fuel heat up in the bed.

Fluidized-bed reactors have a considerablyfaster heating rate than moving-bed or travel-ing-grate reactors. The churning in the bed,however, enables material at all stages of de-composition to be found throughout the bed.Consequently, there may be a tendency for oilsand tars to escape from the heating zonebefore they can be fully decomposed.

The last type of reactor considered here isthe suspension or entrained-flow reactor. Inthis type, small particles of feedstock aresuspended in a stream of gas which moves rap-idly into and through the decomposition zone.This type has the most rapid rate of heating,but the feedstock particles must be reduced toa relatively small size. As mentioned above,this would add to the total conversion costsand the details of this economic tradeoff arestill uncertain.

Optimum Size for Thermochemical Conversion Facilities

Electric generating plants fueled with nu-clear power or fossil fuels are generally quitelarge in order to take advantage of economiesof scale. The same is true of most proposals forsynthetic fuel plants. The optimum size of abiomass-fueled electric powerplant or synthet-ic fuels plant, on the other hand, is determinedby a tradeoff between this economy of scaleand the cost of transporting the feedstock tothe conversion plant. Under favorable circum-stances this optimum size could be severalhundred megawatts electric (see app. A), andsome paper-pulping mills do have wood inputsthat would be sufficient for facilities of thissize. z Under more common ci rcumstances,however, the local availability of feedstockmay I imit the s ize of biomass convers ion

2KIp H e w l e t t , Georg!a Pactflc Corp , p r iva te communlcatlon,

1979

facilities to the equivalent of 10- to 60-MWelectric or less.

The economy of scale, however, is oftenmatched by the cost savings associated withmass producing a large number of small units.Furthermore, in many industrial applications(e. g., process heat or steam boilers) the size isdetermined by the needs of that industrialplant rather than a potential economy of scalefor the boiler or heat needs.

Large-scale facilities are technically feasibleunder some circumstances, particularly wherethe biomass arises as a waste byproduct in alarge manufacturing plant. The number of siteswhere large quantities of biomass are avaiIableto a single plant on a continuing basis, how-ever, may be limited. Consequently, the fullestutiIization of the biomass resource for thermo-chemical conversion will require the develop-ment of small-scale, mass-produced units.


Biomass Densification

Freshly harvested biomass usually containsconsiderable moisture, has a relatively largevolume per unit of energy (making it expensiveto transport), and is fibrous (making it oftendifficult to reduce the particle size). These dif-ficulties can be partially overcome by densify-ing the biomass.

There are several types of densificationprocesses including pelletizing, cubing, bri-quetting, extrusion, and rolling-compressing.Pelletizing typifies the advantages and disad-vantages of densification processes and is con-sidered in more detail here.

Pelletization consists of drying the biomass,heating it until the Iignin melts, and compress-ing the material into pellets. The pellets aredenser than the biomass, more easily ground,and easier to handle and feed into reactors.Due to their lower moisture content, pelletsusually burn more efficiently in boilers thandoes green biomass.

At present there are only commercial pelleti-zation processes for wood. The Iignin contentin wood is generally high enough to bind thepellets so that no additional adhesives are re-quired. Densified crop residues or grasses,however, may require the addition of adhe-sives to achieve the necessary binding strengthto prevent the pellets from disintegrating to apowder; and the costs for this are uncertain.

The wood pelletization process has an ener-gy efficiency* of about 90 percent if one startswith wood having 50-percent moisture con-tent. Furthermore, wood pellets would burn inthe boiler depicted in figure 17 to producesteam with an efficiency of about 83 percentas compared with an efficiency of 65 percentfor woodchips with 50-percent moisture. Thusthe overall efficiency (50-percent moisturewoodchips to steam) is increased from 65 per-cent to perhaps 75 percent by including a pel-Ietization process. This efficiency increasecould also be achieved by predrying the wood-

*E fficlency is defined here as the lower heating value of theproduct divided by the lower heating value of the feedstock

chips with heat escaping out the burner’s chim-ney. The exact numbers will vary, however,depending on the specific boiler being con-sidered. If the boiler is designed to accepthigh-moisture woodchips, then there may beno efficiency improvement with wood pellets.

Wood pellet costs are shown in table 43 forvarious feedstock costs. While the costs are

Table 43.–Cost of Pelletized Wood

Wood feedstock cost (dollars/green ton)

$6.50 $10.00 $20,00

Dollars/ton of pellets sold

Wood. ... ., . . . . . . . $14.39 $22.13 $44.26Operation and

maintenance . . . . . , . . 7.95 7.95 7.95Capital charges. . . . . . . . 5.14(30% Of total investment

5.14 5.14

per year)

Total . . . . . . . . . . . . . $27.48 $35.22 $57.35Dollars/ IO” Btu. ... , . . . $1.72 $2.20 $3.58

Input: 540 ton/d of wood (50% moisture)Output: 244 ton/d of pellets (10% moisture) for sale and 56 ton/d of

pellets used to fuel the plant.Load 330 operating days per year

SOURCE OffIce of Technology Assessment, and T B Reed, et al, “Technology and Economics ofClose-Coupled Gaslflers for Relrof!ttmg Gas/Od Combustion Uruts to Biomass Feed-stocks , In Retrof/f ’79, Proceedings 0/a Workshop on M Gas#mal/on, sponsored bythe Solar Energy Research Instltule, Seattle, Wash , Feb 2, t979

considerably higher than those for woodchips,the pellets’ higher energy density allows themto be transported at a lower cost than greenwoodchips. This cost savings in the transporta-tion pays for the pelletization process if thefuel is to be transported more than 50 to 150miles depending on the transport and woodfeedstock costs and the initial moisture con-tent of the wood (see app. B for details of thecalculation). However, this calculation doesnot include the added cost of transporting verybulky material such as plant herbage wherethe volume rather than the weight of thematerial determines the transport cost.

The most common and least expensive useof fuelwood, however, is likely to be in theregion where it is harvested. Consequently, theuse of densification processes may be limited.On the other hand, the increased ease of han-dling and burning pellets may make them at-

Ch. 7—Thermochemical Conversion . 131

tractive in applications where the process has will have to decide whether the higher fuelto be extremely automated such as in very cost is justified in terms of the labor savings.small industrial applications or where the feed- For the remainder of this chapter, it is assumedstock is particularly unwieldy such as with that raw biomass rather than pellets are beingplant herbage. In each application, the user used.

Direct Combustion of

Biomass can be burned together with coal(termed cocombustion) to produce processsteam or electricity. Currently however, thelargest amounts of energy produced from bio-mass come from the combustion of wood andfood-processing wastes such as sugarcane ba-gasse by themselves. Another important use ofdirect combustion is in home heating. Each ofthese applications is considered below.

Cocombustion of Biomass

Currently, outdated — and therefore unusa-ble–seed corn is being cocombusted withcoal by the Logansport, lnd., Municipal Utility.Cocombustion of wood with coal has alsobeen successfully demonstrated by the GrandHaven, Mich., Board of Light and Power. ’ Andseveral assessments of the cocombustion ofcrop residues with coal concluded that it istechnically feasible.4

Abdullah has estimated that the added costsat an electric powerplant needed to modify theboilers and handle the crop residues is $0.20 to$0.50/million Btu. 5 Consequently, for coal cost-ing $1.50 to $2.00/miIlion Btu ($30 to $45/ton),crop residues costing $13 to $24/ton would beeconomically cocombusted. Some crop resi-

dues may be available for these prices, butgenerally delivered crop residue prices are

IPlerre Heroux, Supplemental Wood Fue/ Experiment, report to

Crand Haven Board o f L ight and Power (Crant H a v e n , Mich JB Sims Generating Stat Ion, 1978)

‘See, e g , Wesley t3uechele, D/rect Combustion of Crop /?es-/dues In Furnace Bo//ers (Ames, Iowa Agriculture and Home E co-nomlcs Experiment Stat Ion), paper No J8791

‘Mohammed Abdul Iah, “ E conomles of Corn Stover as a Coa ISupplement In Steam Electrlc Power Plants in the North CentralUnited States, ” ph D thesis, Agricultural Economics Depart-ment, Ohio State Unlverslty, Columbus, Ohio, 1978

l ikely

Biomass

to be higher. Higher coal prices, how-ever, will make residue cocombustion more at-tractive

Cocombustion can also be used to lower sul-fur emissions somewhat. Since the biomassgenerally contains negligible amounts of sul-fur, the quantity of sulfur being released in thecombustion (per million Btu of heat) will de-crease with the percentage of biomass, typical-ly 20 to 30 percent. The economic savings asso-ciated with this will be highly site specific. Themost advantageous situation would be wherecoal-fired boiler emissions are only marginallyabove the emissions standards without the useof sulfur removal equipment. Since the bio-mass costs, air pollution benefits, and feed-stock availability are site specific, the econom-ics of cocombustion wiII have to be deter-mined through site-specific economic analy-ses. The principal determinant, however, willprobably be the availability of a reliable sup-ply of low-cost biomass feedstock.

Combustion of Biomass

Direct combustion of biomass for produc-tion of electricity or steam or for cogeneration(simultaneous production of steam and eitherelectricity or mechanical shaft power) hascommercially ready technology for wood, sug-arcane bagasse, and many other feedstocks.There are also commercially available suspen-sion burner retrofits for oil-fired boilers of 4.5million Btu/hr or larger. The latter retrofittedboilers can return to oil if the biomass feed-stock is temporarily unavailable, but they re-quire a biomass feedstock that is quite dry (lessthan 15-percent moisture) and relatively small

132 . Vol. //—Energy From Biological Processes

in size (less than 1/8” x 1/2’’ -3/4’’). s A few typesof biomass, however, involve special problems(e.g., the high silica content in rice hulls andresidues) and boilers for these are not availa-ble.

In many applications today, feedstocks with40- to 50-percent moisture content are used,resulting in boiler efficiencies of 65 to 70 per-cent. (The retrofit unit mentioned above,which is restricted to low-moisture feedstock,achieves an estimated 75-percent efficiency). 7

There has been little incentive to dry the feed-stock in most current applications, since theyusually involve relatively inexpensive wasteproducts. As the use of biomass for direct com-bustion becomes more widespread and the av-erage feedstock costs increase, however, pre-drying of the feedstock is likely to be morecommon.

As with cocombustion, the feedstock costand availabil ity of a reliable supply of thefeedstock are major determinants of the eco-nomics of using biomass as a fuel. While thesecosts vary considerably from site to site, an av-erage feedstock cost of $30/dry ton ($1 5/greenton) results in the costs of electric generation,cogeneration, and steam production shown intable 44. (More detailed cost calculations aregiven in app. B.) The costs for producing onlyelectricity or only steam are also shown forvarious feedstock costs in figures 20 and 21.

‘Peabody, Cordon-Piatt, Inc , Wlnfleld, Kan , e g , offers sus-pension burner retrofits to oll-fired boilers ranging from 45 mll-Ilon Btu/hr and up. The retrofit cost IS slightly higher than for gas-Iflers, but where dry, small particle feedstock (e g , sawdust) ISavailable at low prices, the system is competitive with fuel 011Prwate communication with Delvln Holdeman, Solld Fuels Mar-keting Dlvlslon, Peabody, Gordon-Platt, November 1979

‘Ibid

Figure 20.—Cost of Electricity From Wood forVarious Wood Costs (field-erected

generating station)

Low 1

I20

10 t I0 $5 $10 $15 $20 $25 $30

Wood cost (dollars/green ton at 500/. moisture


Obviously, where the feedstocks can be ob-tained inexpensively enough, biomass is com-petitive with coal for generating electricityand with oil for process steam. 1 n the case ofelectricity, the investment costs are about thesame as for coal-fired powerplants; but wood-fired boilers cost about three times that of oilor natural gas boilers.8

Wood Stoves and Fireplaces

Wood stoves and fireplaces have long beenused as a means of space heating in residences,but fireplaces are more often used today for

‘A Survey of Biomass Gas/f/cat/on (VOI 1, Golden, Colo SolarEnergy Research Institute, July 1979)

Table 44.–Cost of Electric Generation, Cogenerarion, and Steam Production From Wooda

Wood cost (dollars/green ton, delivered

Product Plant size at 50% moisture) Product cost

Electricity 60 MW (field erected) 15 50-70 mill/kWhSteam 50,000 lb/hr (package boiler) 15 $3.50-$6.00/1 ,000 lbSteam and electricity 390,000 lb/hr 15 $4-$6/1 ,000 Ibb

21,4 MW (field erected) 109-30 mills/kWhb

aSee delafls In app BbAs the steam COSI increases, the electric cost decreases

SOURCE Ofhceot Technology Assessment


Figure 21 .—Cost of Process Steam From Wood forVarious Wood Costs (package boiler)a

L

o $5 $10 $15 $20 $25 $30

Wood cost (dollars/green ton at 500\. moisture)

a.! Ngnlllcant vartatlons (n Installation costs can occur

SOURCE: Off Ice of Technology Assessment.

their recreational or esthetic value. Also manyfireplaces are inefficient because excess airgoes into the fireplace and up the chimney andthis air often is drawn into the house throughcracks in windows and doors. Consequently,while fireplaces do produce some local heat-ing, the overall effect may be a net cooling ofthe house.

The efficiency of fireplaces can be improved(see table 45) through various methods of cir-culating room air past hot parts of the fire-

Table 45.–Small-Scale Heating Device Efficiency

Net efficiencyHeat unit (percent)Fireplace

M a s o n r yMetal prefab, noncirculating

Insert or retrofit, circulating .,Metal prefab, circulatingM e t a l . f r e e s t a n d i n gStoves

Franklin or fireplace stoveC a s t i r o n a i r t i g h tM e t a l a i r t i g h tB o xCirculator, controlled airinlet

Furnace, convertor or adder

– 10- 10%- 1 0 - 1 0

40-5010-30

40

2 5 - 4 55 0 - 6 55 0 - 6 52 5 - 4 540-5540-60

SOURCE Auburn Umverslfy Improwng the Ef!lclency Safety and Uhhly of Wood BurningUmls DOE con!ract reporl DE AS05-77ET 11288 1979

place, through tubes being heated by the fire,or by drawing the combustion air in from out-side through tubes that are heated by the fire.Depending on the complexity of the arrange-ment, the cost can range from as Iittle as $10 to$30 to over $1,000.

Wood stoves generally have a higher effi-ciency than most fireplaces, due to the greaterdegree of air circulation around and the radia-tion of heat from the hot stove. In the betterwood stoves, the combust ion efficiency(amount of heat liberated per pound of wood)is higher than in a fireplace. Often, however,wood stoves do not completely burn the woodgases, leading to deposits of creosote in theflue. The creosote deposits can present a firehazard and, at best, need to be regularlycleaned from the flue. There is no fundamentalreason, however, why these problems cannotbe solved; and research into thermochemistryand development of advanced wood stovesare likely to lead to higher efficiencies, greaterflexibility of operation, and fewer safety prob-lems.

Wood furnaces for centralized heating of ahome also have significantly better efficien-cies than many fireplaces. Efficiencies as highas 80 percent have been reported under certainc i rcumstances . 9 The possibility also exists ofusing wood furnaces as a backup to solar-heated houses. In this case, the heat storagesystem of the active solar heating systemcould be recharged in a few hours and therebyprovide space heating for several days withlow solar insolation. Hill has estimated that awood furnace (300,000 Btu/hr) with hot waterstorage (500 gal) would cost about $3,000 in-stalled. This, however, should be treated as arough estimate and additional work will benecessary to establish a more exact cost.

‘Laatukattlla Oy, Inc , Satamakatu 4, 33201 Tampere 20, Fln-Iand, sells a YR-60 furnace capable of burning either light fuel 011or wood The Fln n Ish Government Cent re for Techn tca I Rewa rch(Valtlon Teknllllnen Tutklmuskeskus) has rated this furnace at793- and 78 8-percent eff Iclency at two-thirds and f Ive-sixths fullload, respect Ively, when u~lng relatively dry blrchwood as ii fuel,according to In forrnatlon supplied to OTA by l.aatukattlla Oy,October 1979

‘“R C H III, Unlverslty of Maine, Orono, Maine, p r i v a t e com-

rnunlcatlon, Oct 26, 1979

134 ● Vol. ii—Energy From Biological Processes

In general wood stove and furnace heatingrequire more labor than oil or natural gas heat.The fuel requires more handling, ashes must beremoved, and the systems must be regularlyserviced to maintain efficient and safe opera-tion. This is less of a problem if wood pellets orwell-dried wood is used or if the wood is usedonly as a solar backup. The use of wood heat-

ing exclusively, however, is likely to be limitedto those people who consider this type of ac-tivity enjoyable or wish to use wood to achievesome degree of energy self-sufficiency. A larg-er number of people are likely to purchasewood stoves as insurance against oil or naturalgas shortages or as a supplement to more con-ventional systems.

Gasification of Biomass

Gasification is the process of turning solidbiomass into a gas suitable for use as a fuel orfor chemical synthesis. There are several typesof thermal gasification processes, or gasifica-tion induced by heat. Gases produced in blastfurnaces or by the water gas process are low-Btu gases (80 to 180 Btu/stdft3). Other gasifiersuse pure oxygen and partial combustion of thefeedstock to produce a medium-Btu gas (300to 500 Btu/stdft 3) suitable for regional in-dustrial pipelines or chemical synthesis. Stillothers (pyrolysis gasifiers) provide an externalsource of heat to produce a medium-Btu gas(e.g., dual fluidized bed gasifier described inthe next section).

The gasifiers discussed in detail in this sec-tion are the airblown gasifiers. This type blowsair through the feedstock to partially combustit. The heat generated is used to gasify the re-maining material. The resultant gas from up-draft and downdraft airblown gasifiers (termedintermediate-Btu gas) has a lower heat content(120 to 250 Btu/stdft3) than with oxygen or py-rolysis gasification, due to the dilution effectof the nitrogen contained in the air. (Air isabout 78 percent nitrogen and 21 percent oxy-gen.) This lower heat content makes the gas un-suitable for regional pipeline distribution, butit is not a disadvantage if the gasifier is at-tached directly to the boiler being fired (so-called close-coupled gasifier) or used directlyfor process or space heat. Gases with heat con-tents of 250 to 400 Btu/stdft3, however, havebeen produced from an experimental fluid-ized-bed airblown gasifier, but the gas con-tains considerable tar and oil.

‘ ‘Steven R Beck, Department of Chemical Engtneerlng, TexasTech Unlverslty, Lubbock, Tex , private communlcatlon, 1979

Close-coupled ai rblown gasi f ier systemshave the potential for higher efficiencies thandirect combustion when a variety of feed-stocks with different moisture contents areused (see “Generic Aspects of Biomass Ther-mochemistry”), and can be used for processheat. Moreover, they are likely to be more effi-cient and less expensive, in most applications,than oxygen-blown or pyrolysis gasifiers (dueto the energy loss and cost associated with theadded equipment needed to produce oxygenor the external supply of heat). Nevertheless,for methanol synthesis, these gasifiers wouldbe necessary. Moreover, there may be somecircumstances where regional industrial natu-ral gas pipelines could be converted wholly orpartially to gasified biomass. Consequently,cost calculations for two medium-Btu gasifiersare included in appendix B.

Airblown (and other) gasifiers have the flex-ibility of being able to be used together with oras a substitute for oil or natural gas in indus-trial boilers for crop drying, and for processheat. This means that even where biomassfeedstocks are not available in large quan-tities, those that are available can be used todisplace oil and natural gas to the extent oftheir availability; and (barring regulations pro-hibiting it) the users could return to oil ornatural gas if the biomass is temporarily un-available or in short supply. (It should be notedthat the suspension burner retrofit mentionedin the last section also has this advantage butthe types of feedstocks it will accept are morerestricted than for gasifies. ) Furthermore, inproperly designed close-coupled gasifiers, thefuel gas needs only minor cleanup (cycloneprecipitator and perhaps fiberglass filter). This


together with the fact that the volume of fuelgas that needs to be cleaned is less than thevolume of flue gas (from direct combustion)means that the gas cleanup is likely to be lessexpensive for gasifiers.

Gasifiers, however, need further develop-ment to improve their reliability (particularlywith respect to materials clogging), and, insome cases, to lower the tar and char pro-duced. Furthermore, improvements in gasifierefficiency and throughput rates can lower theeffective feedstock costs and capital invest-ment, respectively. The types of airblown gasi-fiers, their efficiency, and the costs are dis-cussed below. Finally, gasifiers for internalcombustion engines (ICES) are consideredbriefly.

Airblown Gasifier Types

The types of reactors suitable for gasifica-tion include updraft, downdraft, fluidized-bed,and entrained-flow reactors. Each of thesetypes is depicted schematically in figure 22.The entrained-flow reactor is the fastest ofthese four. It has the disadvantages, however,that it requires a finely ground feedstock andthe fuel gas contains considerable ash. If theash is cleaned from the gas by wet scrubbing,then the wastewater may contain toxic com-pounds (e. g., phenol). 2

Fluidized-bed reactors can take a wide rangeof particle sizes. In addition the materialthroughput is more than three times as rapid aswith the updraft and downdraft gasifiers 13 andthe particle stays in the gasifier only minutes14

or fractions of a second’ 5 rather than hourswith the slower gasifiers. Fluidized-bed reac-tors release some ash into the gas stream,which must be cleaned from it. Tars in the fuelgas can also be a problem.

The updraft and downdraft gasifiers are theslowest, but they also are the simplest to con-

“Ralph Overend, “Gaslflcatlon – An Overview, ” In Retrofit’79, proceedings of a LVorkshop on AIr Gas/f lcat/on, sponsored bythe Solar Energy Research Institute, Seattle, Wash , Feb 2, 1979

1‘ I b i d“lbld“Beck, OP clt

struct. Updraft gasifiers tend to produce moreash and tar in the fuel gas than with downdraftreactors, but their construction is the simplestof all gasifiers. Both types require relativelylarge feedstock particles so that the gas canflow freely through the bed of biomass.

The ideal gasifier would be simple to con-struct and operate, produce no ash in the fuelgas, completely gasify the feedstock (produc-ing no char or tar), accept a wide range offeedstock sizes and moisture contents, andgasify the feedstock rapidly. The downdraftand fluidized-bed gasifiers appear to be themost favorable types, but further developmentof all types is required before an unambiguouschoice can be made. In the end it may well befound that different gasifier types are superiorfor different feedstocks and applications. Apartial list of gasifiers currently under develop-ment is given in appendix C.

Efficiency of Airblown Gasifiers

The heat content of the fuel gas is an impor-tant consideration in determining the overallefficiency of using a gasifier. The ElectricPower Research Institute has determined theefficiency of a boiler using gases with variousheat values, as shown in figure 23. Both thesensible heat (gas temperature) and the fuelvalue of the gas can contribute to this heatingvalue. 16 Typical gas values range from 120 to200 B tu/ s td f t3 f rom a i rb lown updraf t anddowndraft gasifiers. Some researchers claimthat the energy content of the gas is increasedand its burning characteristics are improved bythe presence of pyrolytic oils (incompletelydecomposed biomass), ” but these oils tend tocondense in fuel lines, clog valves, and in somecases may cause excessive particulate forma-tion when combusted (thereby requiring fluegas cleanup and reducing the combustion effi-ciency and applicability for process heat). De-termining the optimum gas composition and

“T B Reed, et al , “Technology and Economics of Close-Coupled Gaslflers for Retroflttlng Gas/Oil Combustion Units toBiomass Feedstocks, ” In Retrof/t ’79, p r o c e e d i n g s 0 1 a w o r k s h o p

on A/r Caslffcatjon, sponsored by the Solar Energy Research ln-stltute, Seattle, Wash , Feb 2, 1979

1‘Ibid

136 . Vol. n-Energy From Biological Processes

Figure 22.—Schematic Representation of Various Gasifier Types

aNote that other schemes such as moving grate gasifier also exist

SOURCE: From R. Overend, “Gasifiation An Overview, ” Retrofit 79, Proceedings of a Workshop on Air Gasification, Seattle, Wash.,SER1/TP-49-183, Feb. 2, 1979.

Ch. 7—Thermochemical Conversion ● 1 3 7

Figure 23.— Boiler Efficiency as a Function of theBtu Content of the Fuel Gas

Gas fuel Btu/ft3

S O U R C E : Fuels From Municipal Refuse for Uti l i t ies: Technical Assessment(Electric Power Research Institute, March 1975), EPRI report 261-1,prepared by Bechtel Corp.

how to obtain it requires further experimenta-tion and a better understanding of biomasscombustion chemistry. Nevertheless, somedowndraft gasifiers have produced gases ap-proaching 200 Btu/stdft3 from wood with littleoil formation, 18 and there appears to be no fun-damental reason why the optimum energy con-tent (see figure 23) with low tars cannot bereached with additional gasifier development,

The other factor determining the overall ef-ficiency of gasifier-boiler systems is the effi-ciency of the gasifier itself. Since both the sen-sible heat* and the chemical energy in the gascan be utilized with a close-coupled gasifier,the only gasification losses are the heat radi-ated from the gasifier, that lost during fuel gascleanup, and the fuel value lost in condensedtars, oils, or char. Gasifiers have achieved effi-ciencies of 85 to 90 percent l920 and well-insu-lated gasifiers designed to minimize char, oil,and tar formation should be able to reach effi-ciencies of 90 percent or better. This wouldraise the overall efficiency of feedstock tosteam to 85 percent or higher and provide highefficiencies for process heat needs.

‘‘j R Gos~, “The Downdraft Gasifler, ” Retrofit ’79, Proceed-/rigs of a W’orkshop on A/r Ca\/f/cat/on, sponsored by the SolarEnergy Research Institute, Seattle, Wash , Feb 2,1979

‘Sensible heat IS the energy contained In the gas by virtue ofIts be I ng hot, I e , It If the heat that can be sensed or felt directly

“Goss, Op Clt“’Reed, op clt

Airblown Gasifier Costs

It has been estimated that oil- or gas-firedboilers can be retrofitted with mass-producedairblown biomass gasifiers for $4,000 to $9,000/million Btu/hr ($5 to $1 2/lb of steam/h r), withgasifiers ranging from 14 million to 85 millionBtu/hr.21 Retrofit costs, however, can vary con-s iderably dependin g on the difficulty of ac-cessing the boiler and the possible need for anadditional building, to house the gasifier. Voss,for example, has estimated the cost at $20,000/million Btu/hr when new buildings and founda-tions are needed .22

The favorable case cost estimates are com-pared with the costs of new oil/gas- and wood-fired package boilers in figure 24 (similar prob-

Figure 24.—Comparison of Oil/Gas Package BoilerWith Airblown Gasifier Costs

o Air gasifierso Oil/gas package boilers ‘ \

---Forest product laboratory summary

Field-erectedwood-fired

Package wood-fired boilers

boilers

10 20 30 40 50 60 80 100Boiler size

(1,000 lb of steam/hr)

SOURCE: T B. Reed, D E Jantzen, W P Corcoran, and R Wltholder, “Technol-ogy and Economics of Close. Coupled Gastffers for RetrofittingGas/Oil Combustion Units 10 Biomass Feedstocks, ” Retrofit ’79, Pro-ceedings of a Workshop orI A/r Gas/~/cat/on, sponsored by the SolarEnergy Research institute, Seattle, Wash , Feb 2.1979

“ C i t e d In I b i d

“G D Voss, A m e r i c a n Fyr-Feeder E n g i n e e r s , D e s Plalnes, Ill ,

p r ivate communicat ion, 1979


Iems with installation can occur with theseboilers as well). It can be seen that the capitalinvestment for a gasifier retrofit is roughlytwice that for a new oil/gas-fired boiler, butonly two-thirds of that for a new wood-firedboiler. From these preliminary estimates, it ap-pears that a new gasifier-oil/gas boiler combi-nation costs roughly the same as a new woodpackage boiler but more refined data on gasifi-ers are needed before accurate comparisonscan be made.

With costs of $4,000 to $9,000/million Btu/hrand wood fuel at $30/dry ton ($21/air dry ton,30-percent moisture) the resultant gas is esti-mated to cost about $2.70 to $2.90/million Btu(see table 46). In the unfavorable case of$20,000/million Btu/hr, the cost could be $3.35/million Btu with this feedstock cost.

Table 46.–Cost Estimate for Fuel Gas From Wood Usinga Mass-Produced Airblown Gasifier

$4,000-$9,000 per 106

Fixed investment Btu/hr of capacity

Dollars/lO a BtuWood ($21 /ton, 30% moisture,

i.e., $30/dry ton). ., . . . . . . . . $2.38Labor, electricity . . . . . . . . . . . . . . . . 0.20Capital charge (30% of fixed investment

p e r y e a r ) 0.150-0.34

Total ., . . . . . . . . $2,73-$2,92Estimated range ($20-$60/dry ton wood) . $ 2 - $ 6

Input: 38 to 230 tons of air-dried wood (30% moisture) per dayOutput: 14 to 85 106 Btu/hr of intermediate-Btu gasLoad: 330 operating days per year

SOURCE: Office of Technology Assessment

Obviously from table 46, the dominant costis the feedstock cost. If waste byproducts areused to fuel the gasifier, the gas could cost lessthan $1/million Btu. For the larger quantities ofwood, grasses, and residues costing $20 to $60/dry ton, the gas price is estimated to rangefrom $2 to $6/million Btu. These costs are com-pet i t ive with fuel o i l at $6.50/mi l l ion Btu($0.90/gal), but less so with natural gas at about$3.50/million Btu. To achieve the full potentialof gasifiers, however, units in the range of 0.1million to 10 million Btu/hr should also be de-veloped.

F ield-erected gasi f iers are considerablymore expensive (see app. B). They may be eco-nomic, however, in cases where very largequantities of a low-cost feedstock are avail-able. Alternatively, package gasifiers of sev-eral hundred million Btu/hr could be devel-oped, which, together with smaller gasifiers,would cover most situations involving biomassfeedstocks.

Gasifiers for Internal Combustion Engines

Wood and charcoal gasifiers were used dur-ing the 1930’s and 1940’s in Europe to fuelautomobile and truck engines. After some de-velopment, the gasifiers operated satisfactori-ly, but even under favorable circumstances,operation and maintenance required an esti-mated 1 hour per day of operation .23 Becauseof this and the 30-percent power loss associ-ated with switching to the gas,24 it is unlikelythere would be a large market for gasifiersused in automobiles, except under cases of ex-treme shortages of gasoline. Gasifiers could,however, be used to fuel remote ICES for irriga-tion water pumping or electric generation.

The principal difference between gasifyingfor close-coupled boiler operation and processheat and for ICES is that the latter applicationrequires that the gas be cooled before enteringthe engine and requires particularly low tarand ash content. The cooling is required to en-able sufficient gas to be sucked into the cylin-der to fuel the engine and to prevent misfiring.The careful gas cleanup is required to preventfouling or excessive wear in the engine.

These problems were alleviated for charcoaland low-moisture wood by using downdraftgasifiers and various gas cooling and cleanupschemes in Europe before and during WorldWar 11.25 (Charcoal tended to form more ash,while wood more tar, so somewhat differentsystems were required.) The applicability ofthese gasifiers to other feedstocks, however, isuncertain.

*] Swedish Academy of Engineering, Generator Gas– TheSwedish Experience from 7939-1945, Genera lstabens Litograf iskaAnstalts Forlag, Stockholm, 1950, translated by the Solar EnergyResearch Institute, Golden, Colo , 1979

“IbidZSlbld

Ch. 7—Thermochemical Conversion • 139

Gasifiers could be used as the sole fuel forspark ignition (e. g., gasoline) engines or togeth-er with reduced quantities of diesel fuel in die-sel engines (by fumigation, i.e., replacing theair intake with an air-fuel gas mixture). The en-ergy lost in cooling the gas and removing thetar and the added cost of the cooling equip-ment are likely to more than double the gascosts over that for close-coupled gasifiers.(This is based on calculations by Reed, z’ inwhich it is estimated that about half of theclose-coupled gas energy is sensible heat. Theactual value, however, wilI vary with the gas-ifier. )

With waste byproducts having no value orgiving a disposal credit, the gas would be com-

*’Reed, OP clt

petitive with electric irrigation, gasoline, dieselfuel, and, probably, natural gas. With crop resi-dues costing $30/dry ton, the gas cost with con-ventional technology is likely to be over $7/million Btu, which is competitive with electricirrigation and will soon be competitive withgasoline and diesel fuel, but is more expensivethan natural gas at present.

Gasifiers suitable for ICES could probably bemanufactured immediately, but improvementsin the gasifier efficiency and reliability couldimprove the applicability of gasifiers to ICESfor crop irrigation and other uses. The develop-ment could parallel the development of othergasifiers, and improved units could probablybe available in 2 to 5 years.

Liquid Fuels From Thermal Processes

Numerous liquid fuels can be made frombiomass through thermal processes and chemi-cal synthesis. The Iiquid fuels considered hereare methanol, pyrolytic oil, and ethanol. Costestimates for the production of these fuels areshown in table 47, with further details given inappendix B. Each of the processes is discussedbelow.

Methanol

Methanol (“wood alcohol”) was first pro-duced from biomass as a minor byproduct ofcharcoal manufactur ing. Th is process formethanol synthesis, however, is no longer eco-nomic. Most methanol today is produced fromnatural gas. The natural gas is reacted withsteam and CO2 to produce a CO-hydrogen mix-

ture. The gas composition is then adjusted tothe correct ratio of these components and theresultant gas is pressurized in the presence of acatalyst to produce methanol. Finally, thecrude methanol may be distilled to producepure methanol.

Methanol can be produced from biomass bygasifying the biomass with oxygen or throughpyrolytic gasification to produce the CO-hydrogen mixture, with the remainder of theprocess being identical to the processes whichuse natural gas. The oxygen-blown gasifier sys-tems can be built today, whereas pyrolysis gas-ifiers require further development.

Cost estimates for an oxygen-blown gasifierused to produce methanol are given in table 48and a flow diagram of the process is shown infigure 25. The cost is estimated at $0.75 to

Table 47.–Summary of Cost Estimates for Various Liquid FuelsFrom Wood via Thermochemical Processes

Commercial facilities couldFuel $/bbl $/gal $/millIon Btu be available by.

Methanol ., $28-$56 $ 0 . 6 7 - $ 1 . 3 3 $ 1 0 . 5 0 - $ 2 0 . 9 0 NowP y r o l y s i s o i l 30“ 50 0.70-1.20 7 “ 12 Mid to late 1980’sEthanol ., 2 3 - 6 8 0.55-1.62 6.50-19.10 1990’s

SOURCE Off Ice of Technology Assessment


Table 48.–1979 Cost of Methanol From WoodUsing Oxygen Gasification

Fixed investment (field erected) . . ., ., ., $80 millionWorking capital (10% of fixed investment) ., 8 million

Total investment . . , . . $88 million$/bbl

Wood ($15/green ton) . . . . . . . . . . . . . . . . . 10.35Labor, water, chemicals. ., . . . . . . . . . . . . . 1.10Elect r ic i ty (3 .8 kWh/ga l , $0.04 kWh) 6.40Capital charges (15-30% of total

investment per year). ., ., ... . . . . $13.80-$27.60Total, ., . . ... ., ., ., ... ., $31.65-$45.45

($0.75-$1 .08/gal)Estimated range:. ., . . . . . . . ... ., ., . $28-$ 56/bbl

($10-$30/green ton wood) ($0.67-$1 .33/gal)($10.50 -$20.90/10 6 Btu)

Input: 2,000 green ton/d of wood (50% moisture)Output: 2,900 bbl/d methanol (40 million gal/yr)Load: 330 operating days per year

SOURCE Off Ice of Technology Assessment and based on J H Rooker, Davy McKee, Inc.,Cleveland Ohio private commumcahon May 1980 A E Hokanson and R M Rowell,

Methanol From Wood Waste A Techmcal and Economic Study Forest Products Lab.oratory Forest Serwce, U S Oeparfment of Agriculture general technical reportFPL12 June 1977 and E E Badey manager Coal and Biomass Conversion, OavyMcKee Corp Cleveland Ohio, private communication, 1979

$1 .08/gal from $30/dry ton wood, and the capi-tal investment is about $2.00 for each gallonper year of capacity, which is somewhat moreexpensive than grain ethanol distilleries.

Comparable cost calculations are given for adual fluidized-bed pyrolysis gasifier in appen-dix B. In this gasifier, the fluidizing medium isheated in one fluidized-bed reactor whichburns biomass and it is transferred to anotherfluidized bed where it gasifies biomass in theabsence of air or oxygen, Although dual fluid-ized-bed gasifiers are not fully developed, thecalculations in appendix B indicate that thismethod may produce methanol at somewhatlower costs than using oxygen-blown gasifiers,principally because it eliminates the equip-ment needed to produce oxygen. A more accu-rate comparison, however, must await devel-opment and demonstration of dual fluidized-bed and other pyrolysis gasifiers.

Figure 25.—Block Flow Diagram of Major Process Units

Wood hand. Wood Wood

logs gasificationand prep.

plant

oil ILightends Methanol Crude Methanol Acid gasto distillation MeOH synthesis synthesis removalfuel gas

Product Purge gasstorage to fuel

SOURCE: J H. Rooker, &fethano/ V/a Wood Gas/ficat/on (Cleveland, Ohio: Davy Mckee, Inc , 1979)


The only part of methanol synthesis, forwhich there is any uncertainty is the operationof and yield from the gasifier. Oxygen-blownwood gasification can probably be accom-plished with commercial fixed-bed gasifiers,27

but a large part of the gasifier cost would beassociated with cleaning tars, oils, and othercompounds from the gas. Consequently, thecosts would be reduced somewhat by develop-ing advanced oxygen gasifiers that maximizethe CO-hydrogen yields and reduce the tar andoil formation.

With plant herbage as the feedstock, addi-tional problems may arise from the handling ofthis material and possible clogging of the gasi-fier. These problems probably can be solvedwith a relatively straightforward developmentof suitable gasifiers.

Methanol yields from wood would vary de-pending on the type of wood, but have beenestimated at 120 gal/dry ton in a plant that pur-chases i t s e lectr ic i ty.28 If the electricity iscogenerated onsite the yield would be about100 gal/dry ton. ” These yields correspond toconversion efficiencies of 48 and 40 percent,respectively. Yields from plant herbage are notavailable, but based on the above efficiencies,they may be 100 or 80 gal/ton depending onwhether the electricity is purchased or gener-ated onsite. In neither case would additionalboiler fuel be needed. In theory, however,these yields can be increased significantly.

Accessing a large part of the potential bio-mass resource would be aided by the develop-ment of small, inexpensive package methanolplants. However, because small centrifugalcompressors cannot achieve the pressuresneeded for methanol synthesis, plants smallerthan about 3 million to 10 million gal/yr ofmethanol would require a different type ofcompressor, e.g., reciprocal compressor. 30 31

‘7J H Rooker, A4ethano/ Via Wood Gasification [ C l e v e l a n d ,Ohio Davy McKee, Inc , 1979)

I~E E Bailey, Manager, Coal and Biomass conversion, DavyMcKee Corp , Cleveland, Ohio, private communication

29A E Hokanson and R M Rowell, “ M e t h a n o l F r o m WoodWaste A Technical and Economic Study,” Forest Products Labo-ratory, Forest Service, U S Department of Agriculture, generaltechnical report FPL 12, June 1977

\OBalley, op c it“J H Rooker, Davy McKee, lnc , Cleveland, OhJo, private

communlcatlon, May 1980

This could increase the plant cost above thatresult ing f rom the normal diseconomy ofscale, but engineering details and costs areuncertain at present.

There is little doubt that methanol can besynthesized from wood with existing technol-ogy. Since the only uncertainty is with the gasi-fier, the cost estimates are probably accurateto within 20 percent. This would put the costper Btu of methanol from wood at about thesame level as ethanol from grain. However,both alcohols are likely to be more expensivethan methanol from coal, due primarily to theeconomy of scale that can be achieved bybuilding very large coal conversion facilities.

Pyrolytic Oil

Pyrolytic oil can be produced by slowlyheating biomass under pressure and in thepresence of a catalyst. The pressure suppressesgas formation and the catalyst aids the forma-tion of the oil. Other possibilities, however,such as rapid heating and cooling can also pro-duce pyrolytic oils.

The process involving slow heating is cur-rently under development and a pilot plant inAlbany, Oreg., has produced a small quantityof oil, following earlier difficulties. The oil isabout 30 percent lower in heat content (pergallon) than petroleum fuel oil and it may becorrosive but it contains negligible sulfur. Theoil is said to be roughly equivalent to a low-grade fuel oil, but further testing is necessaryto determine how well the oil stores and whatmodifications in boilers may be necessary touse this oil as a boiler fuel.

Since the pyrolytic oil is made from feed-stocks that could be used in close-coupled, airgasifiers and would have some of the sameuses as the gasifier fuel gas, pyrolytic oil pro-duction should be compared to close-coupledgasifiers. The pyrolytic oil is less expensive totransport than raw biomass and it is probablywell suited to fulIy automatic boiler operation.It may also be possible to refine the oil tohigher grade liquid fuels. At present, never-theless, the costs appear to be high in relation


to air gasifiers and the efficiency of using thebiomass feedstock in this way is considerablylower than with gasification, but the oil may becomparable in cost to some other syntheticfuels. Consequently, if gasifiers become widelyavailable, markets for the pyrolytic oils may belimited to those users who are willing to payfor complete automation of their boilers.

Various other thermal processes are possiblefor the production of oils from biomass (seeapp. C), including processes which do not tryto minimize oil production during gasificationand collect the oil as one of the products.These latter types produce gas, oil, and charproducts.

The multi product systems, while being tech-nically easier to develop, have decreased oilyields (since part of the biomass is not con-verted to oil) and the management and eco-nomics are more complicated due to the needto sell each of the various products. A tech-nical solution to these problems being studiedis to slurry the char with the oil. Although thechar contains ash and the oil is corrosive andmay deteriorate under storage, the Depart-ment of Energy (DOE) is funding a feasibilitystudy for burning this slurry of oil and char ingas turbines. j’ Since conventional turbinesmay not be able to tolerate gases with sodiumand potassium the project proposes to use tur-bine combustion technology developed frommiIitary programs. 34

It would seem, however, to be more tech-nically and economically sound to developconversion processes which produce little orno char and which produce only as much gasas can be utilized by the conversion facility.

‘]] W Blrkeland and C 13endersky, “Status of Biomass Wasteand Residue Fuels for Use In Directly Fired Heat Engines, ” pre-sented at the Conference on Advanced Materia/s for A hernateFuel Capable Direct/y Fired Heat Engines, sponsored by the Elec-tric Power Research Institute and the Department of Energy,Maine Marltlme Academy, Castine, Maine, August 1979

J iTeledyne CAE, Toledo, OhIO~ “Gas Turbine Demonstrationof Pyrolysls-Derived Fuels, ” Department of Energy contractE778-C-03-1839

“Btrkeland and Bendersky, op clt

Consequently, OTA has not analyzed the mul-tiproduct liquefaction systems in detail.

Sti l l another type of l iquefaction processwould subject medium-Btu gas to pressure inthe presence of a catalyst (the biomass analogof the South African SASOL process for pro-ducing gasoline from coal). The capital invest-ment, however, appears to be quite high,35 andfurther development will be needed to lowerthese costs.

Ethanol

Conceptually, ethanol can be producedfrom biomass through rapid gasification toproduce ethylene. The ethylene is then sepa-rated from the other gases and converted toethanol using commercial technology.

The critical factor in determining the eco-nomics is the ethylene yield from rapid gasi-fication. Present experimental yields havereached 6 percent (by weight) from biomass, 36

but some researchers’ believe that yields ashigh as 30 percent (by weight) may be possible.If so, then this process could produce fuel eth-anol at prices considerably below those for thefermentation of Iignocellulosic materials andat costs (per million Btu) comparable to thoseprojected for methanol from coal, or roughly$0.65/gal of ethanol.

The process, however, needs considerableresearch to determine if and how such ethyl-ene yields can be achieved. Even under favor-able circumstances, it is unlikely that commer-cial processes could be available before the1 990’s.

“DOW Ctremlcal, U S A , Freeport, “Technical, Economic, andEnvironmental Feaslblllty Study of China Lake Pyrolysts Sys-tern, ” report to the Environmental Protection Agency, 1978

“S Prahacs, H C Barclay, and S P Bhada, “A Study of thePossiblllties of Producing Synthetic Tonnage Chemicals FromLlgnocellulosld Residues,” Pulp and Paper Magazine of Canada,VOI 72, p 69, 1971

J 7See e ~, M j Anta 1, Biomass Energy Enhancement — A ‘e-

port to the President’s Council on Environmental Qua/it y (Prince-ton, N J Princeton Unwerslty, July 1978)


Environmental Impacts of Wood

The major environmental impacts of woodcombustion, aside from any impacts fromgrowing and harvesting the wood fuel, arisefrom the generation of air pollution in thecombustion units. A variety of other impacts,including safety problems with smalI units,water polIution from wood storage and ash dis-posal, and air pollution from wood fuel distri-bution may be of lesser importance, althoughwood appliance safety couId easily become animportant public concern. Because the magni-tude of the impacts, even on a “per ton ofwood burned” basis, is quite dependent on thesize of the operation, this discussion treatsresidential and other small-scale use separate-ly from utility and industrial wood boilers.

Small-Scale Burning

Residential use of wood as a heating fuel isusually a low combustion efficiency, low-tem-perature process compared to larger industrialfossil-fueled or wood boilers. The low combus-tion efficiency is reflected in relatively highemissions of CO and unburned hydrocarbons(see table 49). The low temperature, coupledwith extremely low fuel-bound nitrogen inwood (about 0.1 percent compared to 1.5 per-

Table 49.–Emission Factors for ResidentialWood Combustion Processes

Pollutant g / k g a lb/cord a

Part lculate C 5-19 20-72C a r b o n m o n o x i d e ” 60-130 240-520H y d r o c a r b o n s 2-9 8-40So x : 02 0.8NO X . : : 0.3 12Formaldehyde ., 1.6 6.4Acetaldehyde . . . . . . . 0.7 3Phenols ., 1 4Acetic acid ., ., . . . . 6.4 26Polycyclic organic matter 0.3-4 6% of total particulateElemental metals . . . . . 7 30

aunll~ are ~ram~ of Species eml(fed per kilogram of wood burned Wood mols!ure [s not sPeclfled

In the references clfedbAlternate units are pounds of species emitted per cord of wood burned One cord IS assumed toequal 4000 lb

cpadlculate Includes lnorganlc ash condensable orgamcs and carbon char Note that other en”

tries In the table e g polycyclIc orgamc matter and elemental metals, are somewhat redundant[n fhat they are subcomponenls of particulate matter and not separate species

SOURCE J O Mllrken Airborne Emlsslons From Wood Combushon Environmental Protec.hon Agency /Research Triangle Park N C Feb 20 1979 with rewslons based onprivate commumcahon wNh Mllhken

and Wood Waste Combustion

cent in coal, 38) leads to levels of nitrogen oxide( N OX) emissions well below those of fossil boil-ers. (Old Environmental Protection Agency(EPA) emission factors from “AP-42” showedN OX emissions to be as high as those from coalboilers, but these factors have been demon-strated to be inaccurate.) Wood sulfur levelsare equal to or less than 0.05 percent, 39 a n dsulfur oxide (SOx) emissions consequently arevery low.

Particulate are an especially worrisomecomponent of emissions from residential woodcombustion. Areas with high concentrations ofwood stoves are known to have particulatepollution problems, especially during winterinversion conditions. Rapid deployment ofwood stoves could have significant effects onair quality in New England and the North-west. 40

Condensable organics make up about two-thirds of the particulate matter emitted byresidential wood combustion units .4’ Poly-cyclic organic matter (POM), species of whichare known animal carcinogens, makes up asmuch as 4 or 5 percent of these organics andmay be the most dangerous component. 42

Based on available emission data, POM emis-sions from wood stoves are likely to be fargreater (on a “per Btu” basis) than emissionsfrom the systems they would replace–fossil-fueled powerplants and residential oil or gasfurnaces.

POM is emitted by all combustion sourcesand is spread throughout the environment, al-though usually in low concentrations. Table soshows the major sources of benzo(a)pyrene(B(a) P), which is often used as an indicatorspecies of POM. Aerosols containing B(a)P andother species of POM can survive long enough

“Comparison of Wood and FossI/ FLJe/s (Washington, D C En-vlronmental Protect Ion Agency, March 1976), E PA-60012-76-056

“R H Perry and C H Chlldton, eds , Chemical Eng/neer’sHandbook, 5t/I Edition (McGraw HIII, 1973)

‘“M. D Yokell, et al , E n v i r o n m e n t / Benefits and costs of So/ar

Energy, VOI I [draft), Solar Energy Research lnstltute reportSE R1/TR-52-074, September 1979

“j O. Milllken, Environmental Protection Agency, ResearchTriangle Park, N C , private communlcatlon, Oct 26, 1979

“lbld

144 • Vol. Il—Energy From Biological Processes

Table 50.–Estimates of Total B(a)P Emissions(metric tons/year)

Major sources Minimum Maximum

Burning coal refuse banks. . . . . . . . . . . 280 310Residential fireplaces . . . . . . . . . 52 110Forest fires . . . . . . . . . . . . ., . . . . . ., . 9.5 127Coal-fired residential furnaces . . . . . . . . . . . 0.85 740Coke production. . . . . . . . . . . . . . . . . . . . . 0.05 300

SOURCE Energy and Environmental Analysts, Inc ‘‘Prehmmary Assessment of the Sources,Control and Population Exposure to Airborne Polycyclic Organic Matter (POM) as indi-cated by benzo(a)pyrene [B(a) P], November 1978

to travel 60 miles (100 km) or farther from theirsource .4] However, sources that are far frompopulation centers are less dangerous than ur-ban sources both because of the dispersionthat occurs with distance and because POMseventually can be degraded to less harmfulforms by photo-oxidative processes. ”

POMs are dangerous for a number of rea-sons. First, because of their physical nature,they are more likely than most substances toreach vulnerable human tissues. They areformed in combustion as vapors and then con-dense onto particles in the flue gas. The small-er particles adsorb a proportionately highamount because they have large surface/weight ratios. These smaller particles are bothless likely to be captured by particulate con-trol equipment and more likely to penetratedeep into the lungs if breathed in. Second,several of the POM compounds produced bycombustion are “the same compounds that, inpure form, are known to be potent animal car-cinogens. “45 POM is suspected as a cofactor(contributor) to the added lung cancer risk ap-parently run by urban residents. ” Finally, POMis suspected of causing or contributing toadded incidence of chronic emphysema andasthma. 47

“C Lunde and A Blorjeth, “PolycyclIc Aromatic Hydrocar-bons In Long-Range Transported Aerosols, ” Nature, 268, 1977,Pp 518-519

“M J Svess, “The Environmental Load and Cycle of Polycy-CIIC Aromatic Hydrocarbons, ” The Science of the Tota/ Environ-m e n t , 6 , 2 3 9 , 1 9 7 9

4’J O Milliken, “ Airborne Emissions From Wood Combus-tion, ” presented at the Wood Heating Seminar IV, Portland,Oreg , sponsored by the Wood Energy Institute, Mar 22-24,1979

“J O Mllllken and E G Bobaleck, Po/ycyc/ic O r g a n i c M a t t e r :Review and Analysis (Research Triangle Park, N C SpecialStudies Staff, Industrial Environmental Research Laboratory, En-vironmental ProtectIon Agency, 1979)

“K L Stemmer, “Cllnical Problems Induced by PAH,” In Car-cinogenesis, Volume 1. Polynuclear Aromatic Hydrocarbons:Chem~stry, Metabolism, and Carcinogenests (New York. RavenPress, 1976)

Because POM and other organic emissions,as well as CO, are the products of incompletecombustion, the new airtight stoves, which arebeginning to take an increasing market share,will have to be evaluated carefully for theiremission characteristics, especially under im-proper operation. Airtight stoves achieve ahigher overall heating (but not necessari lycombustion) efficiency by slowing down com-bustion, transferring more of the heat pro-duced into the room rather than up the flue,and avoiding the establishment of an airflowfrom the room into the stove and up the flue.The reduction of excess air allowed into thecombustion zone increases the emissions ofCO and unburned hydrocarbons. Ideally, thesepollutants will be burned in a secondary com-bustion zone fed with preheated air (air that isfirst routed through the primary combustionchamber). However, if the air fed into this zoneis too cool, secondary combustion will not oc-cur; under these circumstances, airtight stoveswould be substantially more polIuting than or-dinary stoves. Also, the lower airflow andcooler exit gases of these stoves cause them todeposit more of their organic emissions– inthe form of creosote—on the interior of theirchimneys. Deposits of creosote from woodstoves and fireplaces have always been a firehazard; this hazard will be increased by great-er use of airtight stoves. An added safety prob-lem associated with ai r t ight stoves i s thepotential for “back-puffing” —surge back offlames–when the stove is opened. Both ofthese safety hazards are controllable by, re-spectively, having the flue cleaned regularlyand increasing the intake airflow before open-ing the stove.

Utility and Industrial Boilers

Large wood-fired boilers should be more ef-ficient energy converters than small units andtherefore should have less problems with COand unburned hydrocarbons. However, the po-tential exists to generate significant quantitiesof these pollutants, and some existing largeboilers are fairly inefficient and thus fulfill thispotential. (For example, emissions of CO fromindustrial boilers range from 1 to 30 g/kg ofwood, compared to 60 to 130 g/kg from small


wood stoves. )48 Inefficient boilers will generatethe same dangerous organic compounds— in-cluding species of POM — as do small residen-tial stoves and fireplaces. These organics aremostly “low-molecular-weight hydrocarbonsand alcohols, acetone, simple aromatic com-pounds, and several short-chain unsaturatedcompounds such as olefins. 49 Some of theseemissions are photochemically reactive, al-though the amounts in question should notcontribute significantly to smog problems. Asthe price of wood and wood waste increases,strong incentives for greater combustion effi-ciency should work to minimize the organicemission problem.

Sulfur dioxide (SO 2) emissions should beminimal because of wood’s low sulfur content.An exception to this is the combustion of blackliquor in the pulp and paper industry; some ofthese boilers should require SO X s c r u b b i n gunder Federal regulations. 50

Although particulate emissions generated bywood-f i red boiIers can be high (6 g/kg, or aboutas high per unit of energy as a wood stove),efficient controls are available for the largerunits. Available devices or combinations of de-vices include multi cyclones coupled with low-energy wet scrubbers, dry scrubbers, electro-static precipitators (ESPs), or baghouses (fabricfi lters). Although ESPs are the most widelyused control mechanism for uti l ity boilers,they have been said to be less practical forwood-f i red boilers because of the very low re-sistivity of both the flyash and unburned car-bon particles from wood combustion .5’ How-ever, ESPs have been successfully used onsome wood-fired boilers, and the problem oflow resistivity apparently can be handled withappropriate precipitator design.

Current regulat ions for emiss ion controlfrom pollution sources do not distinguish par-ticulates by their size. Most control devices in

4* Mllllken, “Airborne E mlsslons From Wood Gaslflcatlon, ” opc It

“M D Yokell, op clt50~n “I r o n menta / ~eadjness D o c u m e n t , W o o d COmmercia/iza-

rIorI (Department of Energy, 1979), draft5 ’ Wood Combu~t/on S y s t e m s A n Assessment of Env/ronmenta/

Concerns (Mlttelhauser Corp , July 1979), draft, contractor reportto Argonne National Laboratory

current use suffer from a severe drop in effi-ciency in controlling the finer, more dangerousparticles. Baghouses appear to be the only fea-sible control devices currently available thatare capable of collecting particles below a fewmicrons in size with 99-percent efficiency orgreater. It appears quite probable that emis-sion standards for the finer particulate even-tually will be promulgated; these standardswould almost certainly lead to extensive use ofbaghouse controls.

Current EPA emiss ion factors show NOX

emissions from wood combustion to be com-parable to emissions from coal combustion. 52

If these factors were correct, large boilers sub-ject to Federal new source performance stand-ards would require NOX reductions of 40 per-cent. This would pose a problem in the shortterm, because there is virtually no experiencein reducing NOX emiss ions f rom wood-f i redboilers. Techniques used for fossil fuel boilersthat may be applicable to wood are:

● low excess air firing,. staged combustion, and● flue gas recirculation.

Recent measurements conducted by OregonState University” and TRW54 show actual NOX

emissions from test boilers to be one-third orless than those predicted by using the currentemission factors. These measurements aremuch more in Iine with the lower combustiontemperatures in wood boilers and wood’s lownitrogen content, EPA and DOE researchersare convinced that the current emission fac-tors are in error 55 56 and it appears likely thatthe factors wilI soon be revised.

In the past, wood boilers have never at-tained the size normally associated with largecoal-fired boilers, Whereas coal-fired util ityboilers are typically a few hundred megawatts

52 Cornpl/ation of Air Po//utant Em/ss/on f a c t o r s R e v / s e a l (Wash-ington, D c Office of Alr Programs, E nvlronmental Protect Ion

Agency, February 1972) , pub l ica t ion No AP-42

“ M e m o r a n d u m f r o m P a u l A B o y s , Alr Surve i l lance and lnves-tlgatlon Section to George Hofer, Chief, Support and SpecialProjects Sect[on, U S Environmental, ProtectIon Agency, “Com-parison of Emlsflons Between Oil Fired Boilers and WoodwasteEloilers, ” November 3, 1978

“J O Mllllken, Envlronrnental Protect Ion Agency, ResearchTriangle Park, N C , private communlcatlon, June 6, 1979

“Mllllken, Oct 26, 1979, op clt“J Harkness, Argonne National Laboratory, private communl-

catlon, Oct 26, 1979


in generating capacity and range up to 1,000MW, a 25- or 50-MW wood-fired boiler wouldbe considered extremely large.

Higher capacities would require using woodsuspension firing, analogous to firing with pul-verized coal, or fluidized-bed combustion. Pul-verizing wood to extreme fineness for suspen-sion fir ing may be costly enough to offsetother economic advantages of going to largersize plants, so future increases in wood boilersize may depend on further development offluidized-bed combustion. The expense oftransporting wood considerable distances hasalso been a constraint on boiler size in thepast, but rising costs for alternative fuels maymake longer distance transport of wood moreattractive, increasing the effective radius ofsupply and the maximum practical size of theboiler.

The local impacts of uti l ity or industrialwood-fired boilers will be moderated by theircomparatively small size. However, the effectsof low stacks (compared to the stacks on largecoal-fired utility boilers) will be to allow less

diffusion of the emissions from the plants; ahigher percentage of the pollution will fall outnear the plants than would normally be ex-pected for large generating facilities or in-dustrial boilers. Also, the high water content ofwood leads to higher concentrations of watervapor in the stack gases and greater visibilityof the plumes. Although not harmful except inan esthetic sense, this increased visibility maylead to added local objections to wood-firedboilers.

In general, emissions from other portions ofthe fuel cycle are quite low compared to emis-sions from combustion. The single exception isCO, which is produced in substantial quanti-ties by harvesting, chipping, and transportequipment. Table 51 presents a comparison ofthe emissions at all stages of the fuel cycle forcoal, oil, and wood boilers. As noted above,CO and organic emissions from wood boilersare far higher than emissions from coal. Notethat the emissions of SO2 and particulate aredependent on the level of control, and can bereduced significantly if required.

Table 51 .–”Source-to-Power” Air Emissions for Coal, Oil, and Wood Fuel Systems

Emissions ton/yr (basis 50-MW plant)

Fuel/energy system SO2a co Particulate Total organic

Low-sulfur Western coalSurface mining . . . . . . . . . . . . . . . . . . . . . – — 113.1Rail transport (1,800 miles), . . . . . . . . . . . .

—20.2 218.1 21.8 22.2

Power generation. . . . . . . . . . . ., ., . . 2,664.8 87.2 113.1 25.8Total . . . . . . . . . . . . . . ., . . . . . . 2,685.0 305.3 248,0 28.0

Crude oilDomestic oil pipeline. . . . . . . . . . . . . . . 25.8 0.0 3.2 0.5New Jersey refined with desulfurization . . . . 193,8 4.8 3.2 40.4Rail transport (300 miles) . . . . . . . . . . . . 1.5 16.3 1.6 1.7Power generation . . ., ., . . . . . . . 854.3 – 80.8 16.2

Total . . . . . . . . . . . . . . . . . . . . . . ., 1,075.4 21.1 88.8 58.8WoodWood recovery. . . . . . . . . . . . . . . . . 6.5 48.5 3.2 8.1Process chipping . . . . . . . . . . . . . . . . . . . . 14.5 116.3 6.5 19,4Truck transport (60 miles). . . ... . . . . 4.4 36.3 2.1 6.0Power generation. . . . . . . . . . . . . . . . 119.5 398.9 339.2 398.9

Total ... . . . . . . . . . . . . . . . . . . . . . . 144.9 600.2 351.0 432.4

NOTE NOX levels may be slgmflcant for wood fuel There IS Inadequate data on NOX emfsslon levels There are also production tradeoffs for various con.version systems

asoj emlsslons from coal-fired powerplant assume no scrubbers 90% control required by new source performance standards would lower emissions

from 2,6648 tons 10266 Ions

SOURCE E H Hall, et al , Corrrpar/sorr 0( FossI/ arrd Woud fuels (Washington, O C Enwronmentai ProtectIon Agency, March 1976), EPA-600/2-76-056

Ch. 7— Thermochemical Conversion ● 147

Environmental Impacts of Cofiring Agriculturaland Forest Residues With Coal

Cofiring of coal and agricultural or forestresidues has been proposed both as a means ofexpanding energy supply and as an economicalway to lower sulfur emissions (from burninglocal high-sulfur coal) without importing low-sulfur coal. Since wood and most crop residueshave very low sulfur contents (cotton gin trashis one exception), total SO2 emissions can besignificantly lowered if the residues can re-place a large fraction of the coal normallyburned in the boilers. Two situations wherecofiring would appear to be attractive are:

●

●

r e d u c i n g S O2 emi s s ions f rom ex i s t i ngcoal-fired powerplants that are marginallyout of compliance with their State imple-mentation plans, andal lowing very high-sul fur coals to beused with scrubbers in new powerplants(achievement of the current 1.2 lb/millionBtu SO, standard may be difficult withsome very high-sulfur coals)

There are few examples of cofiring experi-ments in the literature and these examplesgenerally do not examine emission changescaused by the addition of crop and woodwastes to the coal fuel. Because SO2 is the onlypollutant whose formation generally does notvary with combustion conditions (except thatsulfur may be captured in the char from apyrolytic reaction), it is probably the onlypollutant that can be predicted reliably at thistime. However, general emission trends forsome pollutants can be predicted. For exam-ple, hydrocarbon and CO emissions may in-crease slightly, because combustion tempera-tures are lowered and complete combustion ismore difficult to achieve when residues areadded to the boiler fuel. The lower combustiontemperature and low fuel-bound nitrogen inthe residues should cause NOX emissions to belowered. If dryers are used for high-moisture-content res idues, thei r emiss ions must beadded to those of the boiIer.

Particulate emissions are difficult to predictbecause they are affected by several site-spe-

cific factors. However, there appears to besome potential for increased particulate emis-sions under certain conditions. Although bio-mass residues generally have lower inorganicash contents than the coal they would replace,they tend to generate more organics in particu-late form. The ability of the boiler to maintainnearly complete combustion conditions willthus strongly affect particulate emissions. Inlarge facilities with ESPs, the lower resistivityof the particles generated from combustion ofthe residues may allow a higher percentage toescape control. If the biomass is fed moist intothe boiler, the steam generated during com-bustion will increase the flow of hot combus-tion gases and conceivably may lead to moreentrainment of bottom ash and higher particu-late emissions. On the other hand, if the bio-mass is first artificially dried, particulate emis-sions from the dryer could be high unless theyare carefully controlled. The significance ofany of these effects is uncertain at the presenttime.

The importance of these emission changesdepends on the original quality of the coal, thenature of the residues added, the percentagefuel mixture, the type of pollution controls onthe boiler, and its operating conditions. All ofthese factors vary considerably from site tosite. However, it seems Iikely that emission in-creases will be small except in cases where thecofiring seriously degrades the operating char-acteristics of the boiIer (it is unIikely that cofir-ing would continue under such conditions un-less noneconomic pressures– such as the pos-sibility of adverse publicity and/or embarrass-ment of company management— preventedcessation of operations). In addition, emissionschanges will be limited by constraints on theamount of biomass that can be mixed with thecoal. Logging residues and high-moisture cropresidues have a considerably lower energy con-tent per unit volume than coal, Because boilersystems are sized to allow a certain volumetricflow rate of fuel feed, a high percentage of bio-mass volume in the feed wiII limit boiIer out-


put capacity. An additional limit may be pre- content of the biomass may cause condensa-sented by the additional volume of combustion problems in the stack unless the biomasstion gases that would be generated if the bio- content is limited, stack temperatures are in-mass is fed moist into the boiler. These con- creased (by removing less energy from the gasstraints do not apply when the energy output and thus lowering system efficiency), or therequired is much lower than the boiler’s rated biomass is first dried (which may also lowercapacity, or when the system is specifically system efficiency).designed for cofiring. Also, the high-moisture

Environmental Impacts of Gasification

Gasification technologies have a number ofpotential air and water impacts. Because fewsuch gasifiers are in operation, quantificationof these impacts is premature. The low concen-trations of trace metals and sulfur in the bio-mass feedstocks and the lack of extreme tem-perature and pressure conditions imply thatimpacts should be substantially less than thoseassociated with coal gasification. However,scientists working for DOE’s Fuels from Bio-mass Branch profess to be unsure as towhether this supposed biomass “advantage”actually exists, especially in the water effluentstream; although the hydrocarbons present inbiomass gasification wastewater should bemore amenable to biological treatment thancoal gasification hydrocarbons (they are moreoxygenated), they may be produced in greaterquantities and have a higher biological oxygendemand than those of a coal system.57 Also,the potential for proliferation of small-scalebiomass gasifiers may present monitoring andenforcement problems that would not existwith a few large coal gasifiers. Therefore, bio-mass gasification may require as much atten-tion and concern as coal gasification.

The quantity and mix of air pollutants pro-duced by biomass gasification plants will de-pend in large part on the combustion/gasifica-tion conditions maintained as well as the en-vironmental controls and the chemical make-up of the feedstock. For example, the concen-tration of hydrogen in the reaction chamberand of suIfur and nitrogen in the feedstock wilIinfluence the formation of ammonia (NH 3) ,

‘7 Richard Doctor, Science Appllcatlons, Inc , prwate commu-nlcatlon, November 1979

hydrogen sulfide (H2S), and hydrogen cyanide(HCN). Other products of the gasification proc-ess include carbonyl sulfide (COS) and carbondisulfide (CS 2) as well as phenols and poly-nuclear aromatic (PNA) compounds. 58 Gasifi-cation processes that are closer in their natureto pyrolysis and that produce considerable by-product char will have lower nitrogen and sul-fur-derived emissions; about half of the origi-nal sulfur and nitrogen in the biomass shouldremain in the char. 59

The gas produced will either be burned on-site (producer gas) or cleaned and upgraded topipeline gas. Either process should eliminate orreduce most of the more toxic pollutants, withthe onsite burning oxidizing them to CO2, SO2,N O2, and water. Recent tests of a close-cou-pled gasifier/boiler combination using wood-chips for fuel showed emissions of CO, particu-Iates, and hydrocarbons–which are of majorconcern in wood combustion — to be well be-low emissions expected from a direct-firedwood boiler, although a fuel oil boiler re-placed by such a gasifier would have had con-siderably lower particulate and hydrocarbonemiss ions. NO X emissions from the gasifier/boiler combination were lower than those ex-pected from either oil- or wood-fired boilers. 60

“Solar Program Assessment: Environmental Factors, Fuels FromB/ornass (Washington, D C Energy Research and DevelopmentAdministration, March 1977), ERDA 77-47/7

“lbld“’Ca[ifornla Alr Resources Board, “source Test Report NO C-G-

O(I2-C, Source Test of Exhaust Gas From a Boiler Fired by Produc-tion Gas Generated From an Experimental Gaslfler Unit UsingWood Chips for Fuel, ” Stationary Source Control Dlvlslon,March 1978


Wood Oi lGasifier boiler boiler

Carbon monox ide ( lb /hr ) . 0 1.8-54 0 . 3 3Part icu lates ( lb /hr ) 0 7 0 4 5 - 1 3 5 0 1 3H y d r o c a r b o n s ( l b / h r ) 0 . 9 0 6 3 0 0 7Nitrogen oxides (lb/hr) 039 9 1.46

These results cannot be readily extrapolatedto other situations, but they imply that the useof gasifiers may offer a less polIuting alter-native to direct combustion of biomass when ashift to renewable (from oil) is being con-templated.

Leaks of raw product gas represent a poten-tial for significant impacts, especially on thosein the immediate vicinity of the gasifier. Theprobability of such leakage is not known. Al-though impact analyses of high-pressure coalgasification technologies have identified fugi-tive hydrocarbon emissions as a likely prob-lem, it is not clear that similar problems wouldoccur with (lower pressure) biomass gasifiers.

The combustible char produced by the gasi-fication process is another potential source ofair pollution. It may be used as a fuel sourceelsewhere or else used to heat the bed in a flu-idized-bed gasifier. In either case, its combus-tion will produce NOX, flyash, and SOx as wellas trace metals either adsorbed on the flyash(potassium, magnesium, sodium, iron, boron,barium, cadmium, chromium, copper, lead,strontium, and zinc) or in gaseous form (beryl-lium, arsenic compounds, fluorides).61 62

Because most biomass feedstocks usedgasification processes have concentrations

6’So/ar Program Assessment, op clt“Doctor, op clt

inof

trace elements, ash, and sulfur that are sub-stantially lower than concentrations found incoal, combustion of the char should emitlower concentrations of related pollutantsthan would coal combustion. Depending onthe farming and harvesting techniques, how-ever, the feedstock may be somewhat contami-nated with pesticides, ferti l izers, and soil,which should add to combustion pollutants,Also, some forms of biomass—for example,cotton trash, with 1.7 percent— have sulfurlevels comparable to levels in coal.

Aside from water impacts caused by con-struction activities and leaching from biomassstorage piles, gasification facilities will have tocontrol potential impacts from disposal andstorage of process wastes and byproducts.Water initially present in the feedstock andthat formed during the combustion accompa-nying gasification should provide significantamounts of effluent requiring disposal (al-though in close-coupled systems, the moistlow-Btu gas may be fed directly into the boil-er). Air polIutants identified above may appearalso as water contaminants: NH3 (as ammoni-um hydroxide), HCN and its ionized form, phe-nols, and trace elements found in the ash.Leaching from byproduct chars may be a prob-lem if the char is (incompletely carbonized)brown char although (carbonized) black charshouId be similar to charcoal and far less likelyto be polluting. Finally, the tars produced bygasification may well be carcinogenic; as yetno data confirm this potential. These watercontaminants present a potential occupationalas well as ecological and public health con-cern, because plant operators may be exposedunless stringent “housekeeping” is enforced.

Research, Development, and

Thermochemical conversion includes theleast expensive, near-term processes for usingthe major biomass resources — wood and plantherbage. Moreover, R&D is likely to lead to in-teresting new possibilities for the productionof fuels and chemicals from biomass. Some ofthe more important areas are:

Demonstration Needs

● Thermochemistry of biomass. — Basic andapplied research into the thermochemis-try of biomass, including secondary gasphase reactions, is needed to better definethe possibilities for fuel synthesis and toaid engineers in designing advanced reac-tors. The research should include studies


●

●

of the effects of the various operating pa-rameters on the nature and compositionof products and ways to maximize theyields of various desirable products suchas CO and hydrogen, ethylene, methane,and other Iight hydrocarbons.Gasifier development and demonstration. –Gasifiers should be developed further anddemonstrated, so as to improve their relia-bility, efficiency, and flexibility with re-spect to feedstock type and moisture con-tent. This should include airblown gasifi-ers for process heat, boiler retrofits, andICES, and oxygen-blown and pyrolysis gas-if iers for methanol synthesis. It shouldalso include the demonstration of gasifi-ers suitable for converting pIant herbageto methanol and should investigate thetradeoff between densifying herbage be-fore gasification versus gasification ofherbage directly. Each of the uses for gasi-fiers will have unique requirements, whichprobably will dictate separate develop-ment and demonstration efforts.Compressor development.– One of themajor costs of producing methanol insmall plants is the relativley high price ofsmall compressors. The cost of methanolsynthesis from biomass would be loweredsubstantially if small, inexpensive com-pressors suited to the process are devel-oped.

Each of the new biomass conversion tech-nologies will require environmental assesment

to ensure the development of appropriate con-trol technologies and incorporation of environ-mental considerations in system design, siting,and operation. In general, the larger scale tech-nologies are Iikely to be assessed as part ofnormal EPA and DOE envi ronmental pro-grams. The smaller technologies generally willnot come under Federal new source perform-ance standards (specifications of allowableemissions), but there is growing recognition inEPA and DOE of the potential environmentaldangers of small-scale technologies such aswood stoves.

Key environmental R&D areas in thermo-chemical conversion are:

●

●

●

●

●

development of wood stove designs (orcontrols) that achieve complete combus-tion and minimize emissions of unburnedhydrocarbons;

development of combustion controls thatwill allow efficient — and pollutant mini-mizing— thermochemical reactions re-gardless of feedstock characteristics;assessment of the potential health effectsof emissions from wood stoves and otherbiomass conversion technologies, with afocus on part iculate with a h igh un-burned hydrocarbon component;evaluation of toxicity and carcinogenicityof biomass gasifier/pyrolysis tars and oils;and

design of controls for gasifier/pyrolysis ef-fIuent streams.


Appendix A. —Optimum Size for a Wood-Fired Electric Powerplant

The annual cost, C, of producing electricity in awood-fired electric powerplant can be expressedas:

c = cc + Cf + ct (1)Where CC represents the capital and other fixedcharges, Cf represents the fuel and other variablecosts, and Ct the cost of transporting the fuel.

Letting S represent a dimensionless scaling pa-rameter

c c = CcoS 0.7

(2)Here CC

O represents the fixed charges for a basecase and it is assumed that these charges scale witha 0.7 scaling factor. Furthermore, the variable costsare:

Cf = CfoS [3)Where Cf

O represents the base case.Assuming the fuel is collected from a circular

area surrounding the powerplant, the transportcosts can be expressed as:

C t = C t

O Q o S r (4)Where Ct

O is the transport cost per ton-mile, Qo isthe annual quantity of wood transported in thebase case, and r is the average transport distance.

For a given scaling parameter S, the quantity ofwood transported is:

Q = Q OS = enr2 (5)where e is the average availability of fuel wood col-lected in dry tons per square mile year and r is theradius of the circle from which wood is collected.

If one assumes that the actual transport distancefrom a harvest site to the powerplant is J2 timesthe direct Iine distance,

Taking the derivative of C with respect to S and set-ting it to zero (in order to find the minimum costper kilowatthour) yields

(9)

This represents the optimum size for the power-plant.

Evaluating the parameters for the base casegiven in appendix B results in:

S = 11.7 Q06)5 (lo)where Q is in dry tons per acre year, the base casecorresponds to a 62-MW powerplant, and the trans-port costs are assumed to be $0.20/dry ton-mile($0.10/green ton-mile).

As expected, the higher the density of biomassavailability, e, the larger is the optimum-sized pow-erplant. IronicalIy, however, as Q increases, the av-erage transport distance decreases. I n other words,it is more economic to keep the powerplant sizesmaller than to transport large quantities of woodfor greater distances.

If one assumes that Q = 0.5 dry ton/acre-yr, thenthe optimum powerplant size is over 500 MW andthe radius of the collection circle is about 50 miles.With Q = 0.05 dry ton/acre-yr, the optimum size is110 MW and the circle radius is 75 miles. If thetransport charges double, then for these values ofe, the optimum sizes are reduced to 200 and 50MW, respectively, with collection radii of 30 and 50miles, respectively,

In principle, then, large-scale biomass conver-sion facilities are not unrealistic. The values as-sumed for Q are probably less than what can beachieved in a region where the infrastructure forfuelwood harvests is fully developed. In practice,however, it is likely to be difficult to develop amature harvest-supply infrastructure devoted to asingle conversion facility. As the infrastructure isbeing developed, many small users are likely tocompete for the fuelwood and the resultant availa-bility to a single user may never reach the hundredsof thousands or milIions of dry tons per year neces-sary for the larger faciIities.

Clearly biomass farms dedicated to a single con-version facility would overcome these problems ofobtaining a large feedstock source, It is unlikely,however, that these farms will be developed as de-scribed in the section on “Unconventional BiomassProduct ion.”


Appendix B.—Analysis of Break-Even Transport Distance forPellitized Wood and Miscellaneous Cost Calculations

Two ways for producing 1 million Btu of steamfrom woodchips containing 50-percent moistureare presented in figure B-1. In the first case 389 lbof greenwood are transported to the boiler andburned directly; in the second 339 lb of greenwoodare pelletized first and then transported to theboiler for burning.

In the first case the cost of the fuel needed toproduce this steam is:

C = CW W W + Ct W W d (1)where CW is the cost per ton of wood at a centralyard, WW is the weight of wood to be transported,Ct is the transport cost per ton-mile, and d is the dis-tance from the yard to the boiler.

I n the second case:C = CP W P + C t W P d (2)

when C is the cost of the pellets at the pellet mill,W Pis the weight of pellets to be transported andthe other symbols are as before (assuming the pel-let mill is located at the wood yard).

Setting these two costs equal to one another andusing the weights of wood and pellets as above,one finds that:

d = (0.65 CP – 1.65 CW) / Ct (3)With transport costs of $0.10/ton mile and the

wood and pellet costs given in the text, the break-even transport distance varies from 43 to 71 miles.If, however, the original wood is 40-percent mois-ture, only 324 lb are needed in the boiler (with thesame efficiency) and the break-even transport dis-tance becomes 123 to 134 miles. If the transportcharges are lower, the break-even distance will in-crease. Conversely, where transport is more expen-sive, the break-even distance wilI be less. Numer-ous other local variables can also change the re-sults.

Miscellaneous Cost CalculationsFollowing are estimates for the costs of various

thermochemical conversion processes.

Figure B-1.-Two Ways to Produce 106 Btu Steam From Wood

I 1

●

Pellet mill Wood boilerCase 2 339 lb wood 153 lb

1 x 106 Btu steam(50% moisture) 9(3% efficiency pellets

83% efficiency

Table B-1 .-Electricity From Wood by Direct Combustion Table B-2.-Steam From Wood by Direct Combustion

Input 2,000 green ton/d of wood (50% moisture)output 62-MW electricityLoad 300 operating days per yearFixed investment (field erected) $50 millionWorking capital (10% of fixed

Investment) 5 million

Total Investment $55 million

Mills/kWh Million $/yr

Wood ($15/green ton) 20 9 0Labor and water 9 4 0Capital charges (15’%o of total

Investment per year) 19 825

Total 48 213Estimated range 45-70 mills/kWh

(package boiler)

Input: 270 green ton/d of wood (50% moisture)output, 50,000 lba of steam/hrLoad 330 operating days per yearFixed investment (package boiler) $600,000

$1,000 lb steamW o o d ( $ 1 5 / g r e e n t o n ) 338L a b o r ( $ 7 5 , 0 0 0 / y r ) 0 1 9Capital charges(15-30’%0 of fixed

Investment per year) O 23-0.46

T o t a l 380-403E s t i m a t e d r a n g e : $350-$6 00/

1,000 lb steam($2 ‘O-$4 80/106 Btu)

‘1 ,O@I lb of steam = 1 25 mllllon Btu of steam

SOURCE OTA from A Survey of B/omam Gas/f (car/on (Golden, Colo Solar EnergyResearch Institute, July 1979)


Table B-3.–Electricity and Steam From Woodby Direct Combustion

I npu t 2,000 green ton/d of wood (50%. moisture)output 21.4-MW electricity and 390,000 lb steama/hrLoad 300 operating days per yearFixed Investment (field erected) $40 millionWorking capital (10% of fixed


Total Investment $44 millionMillion $/yr

Wood ($15/green ton) 109Labor and water 4Capital charges (15’XO of total

Investment per year) 66-132

T o t a l 2 1 5 - 2 8 1Product costs S team E I e c t r i c i t y

(assumed cost ) ( d e r i v e d )

$/1,000 Ib m i l l s / k W h

4 67-109

5 48-91

6 30-73

‘1 000 lb ot steam = 1 25 mll I Ion Iltu ot steam

SOURCE OTA trom Ste\ en R Beck Department ot ( hem,{ al t nglneerlng TexasTIX h Unl\ersttv I ubbrx k Tex prlk ate c ommunlt atmn 1 9 7 9

Table B-4.–Medium-Btu Gas From Wood in a DualFluidized-Bed Field Erected Gasifier

Input 2,000 green ton/d of wood (50%. moisture)output 460 106 Btu/hr medium-Btu gasLoad 330 operating days per yearFixed investment (field erected) $43 millionWorking capital (10% of fixed


Tota l Investment $ 4 7 3 m i l l i o n

$ 1 06 Btu gas

Wood ($15/green ton) 326Labor and water O 82Capital charges(15% of total

Investment per year) $195-$390

Total $6.03-$7.98Estimated range $550-$9.00/10 6 Btu

SOU R( E O T A t r n m Ste\ en R B(>( k Department ot ( hemlc a l F nglneer!ng lexa~Te( h Unl\erslty 1 ubb{,( k Tex prlk ~tc { {,mmunl( dt!on 1979

Table B-5.–Medium-Btu Gas From Manurein a Fluidized-Bed Gasifier

Input 1,000 dry tend of manureoutput 400 10’ Btu/hr medium-Btu gasLoad 330 operating days per yearFixed investment (field erected) $36 millionWorking capital (10% of fixed



$/106Btu of gas

Manure ($3/dry ton) 031Labor, water, chemicals, ash disposal,

electricity 164Capital charges (15Y0 of total

Investment per year) $188-$375

Total $383-570Estimated range $350-$7 00/10’ Btu

SOLJ K( E () T A trom St(,\ en R t~~[ k [lepart ment ot C hem I{ a I E ngfneerlng TexasTVI h EJnl\erslt~ I ubb[)r k Tex I)riv ate ( fjmmunlc atlon 1979

~ -- q L ~ -1 - 80 - 1:

Table B-6.-Methanol From Wood Through Gasificationin a Dual Fluidized-Bed Gasifier

Input, 2,000 green ton/d of wood (50%. moisture)output 3,150 bbl methanol/d (44 million gal/yr)Load 330 operating days per yearFixed Investment (field erected) $64 millionWorking capital (10% of fixedInvestment) 64 million


$/bbl

Wood ($1 S/green ton) 952Labor, water, and chemical 491Capital charges (15-30~0 of total

Investment per year) 10.16-2032

Total $2459-$3475($0 58-$0 83/gal)

Estimated range $22-$40/bbl($0 52-$0 95/gal)

($8 20-14 96/106 Btu)SOURCE OTA trom Ste\en R Beck, Department of Chemlc al E nglneermg. Tcwa$

Tech Unlkers(tv Lubbock Tex prlk ate communication, 1979

Table B-7.-Pyrolysis Oil From Wood byCatalytic Direct Liquefaction

Input 2,000 green ton/d of wood (50%. moisture)output 2,500 bbl/d of pyrolytic oil (4 2 106 Btu/bbl)Load 330 operating days per yearFixed Investment (field erected) $50 millionWorking capital (10% of fixed



$/bbl

Wood ($1 S/green ton) 1200Labor, water, and chemicals 7.27Capital charges (15-30% of total

Investment per year) 1000-20.00Total $29.27-$39.37

Estimated range $30-$50/bbl(.$7-$1 2/106 Btu)

SOURCE OTA trom Steven R Be{ k Department of Chemical Engineering, TexasTech Uni\er\ttk Lubbock Tex prltate ( ommunl[ atlon, 1979

Table B-8.-Ethanol From Wood via Gasificationin a Dual Fluidized-Bed Gasifier

Input 2,000 green ton/d of wood (50% moisture)output 1,620 bbl/d of ethanol (assuming 14 wt. %. yield of

ethylene from dry wood)Load. 330 operating days per yearFixed Investment (field erected) $60 millionWorking capital (10% of fixed



$/bbl

Wood ($15/green ton) 1827Labor, water, chemicals, and electricity 1253Capital charges (15-30% of total

Investment per year) 1852-3704

Total $49.32-$67.84($1 17-$1 62/gal)

($13.90-$19.20/10 6Btu)With ethylene yield of 30 wt % $23-$32/bbl

($0 55-$0 76/gal)(.%6 50-$9 00/106 Btu)

S O U R C E O T A f r o m Stewen R 13ec k D e p a r t m e n t of ( hemtcal f ngineerlcrg, TexasT e c h Unl\ ersltv I ubboc k T ex prtvate ( ommunic atlon 1979

. ..


Appendix C. —Survey of Gasifier Research,Development, and Manufacture

Gasifier type Size

Contact OperatingOrganization lnput mode Fuel products units Btu/hr

Air gasification of biomassAlberta Industrial Dev. , Edmonton, Alb , CanApplied Engineering Co , Orangeburge, S C 29115Bat te l l e -Nor thwes t , R ich land , Wash 99352 . , . , Century Research, Inc., Cardena, Calif. 90247Davy Powergas, Inc., Houston, Tex. 77036Deere & Co., Moline, Ill. 61265E c o - R e s e a r c h L t d . , W i l l o d a l e , O n t . N 2 N 5 5 8 Forest Fuels, Inc., Keene, N H 03431.Foster Wheeler Energy Corp., Livingston, N H 07309Fue l Convers ion Pro jec t , Yuba C i ty , Ca l i f . 95991 H a l c y o n A s s o c . I n c . , E a s t A n d o v e r , N . Y . 0 3 2 3 1Industrial Development & Procurement, Inc.,

Carie Place, N.Y. 11514 ., .,Pulp & Paper Research Inst.,b Pointe Claire, Quebec H9R 3J9 Agricultural Engr. Dept., Purdue University, W. Lafayette, Ind. 47907Dept. of Chem. Engr., Texas Tech University, Lubbock, Tex. 79409.Dept. of Chem. Engr., Texas Tech University, Lubbock, Tex, 79409Vermont Wood Energy Corp., Stowe, Vt. 05672Dept. of Ag. Engr., Univ. of Calif., Davis, Calif. 95616 ., Dept. of Ag. Engr., Univ. of Calif., Davis, Calif. 95616Westwood Polygas (Moore)Bio-Solar Researc & Development Corp., Eugene, Oreg. 97401 .,

Oxygen gasification of biomassE n v i r o n m e n t a l E n E n g . , M o r g a n t o w n , W VI G T - R e n u g a s

Pyrolysis gasification of biomassW r i g h t - M a l t a , B a l l s t o n S p a , N . Y .c

C o o r s / U . o f M O .U . o f A r k a n s a sA & G Corp., Jonesboro, Ark, ., ...E R C O , C a m b r i d g e , M a s s ,E N E R C O , L a n g h a m , P a .Garrett Energy Research ...Tech Air Corp., Atlanta, Ga. 30341. ...M. Antal, Princeton Univ., NS ., ., M R e n s f e i t , S w e d e n .T e x a s T e c h , L u b b o c k , T e x . .B a t t e l l e - C o l u m b u s , C o l u m b u s , O h i o

Air gasification solid muncipal waste (SMW)Andco-Torrax, a Buffalo, N. Y.. . . . . . . . . . . . . . . ., ... . . . .B a t t e l l e - N o r t h w e s t , R i c h l a n d , W a s h . 9 9 3 5 2 ,

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Table Notation (by columns)InputContact modeFuel products

Operating unitsSize

A = alr gaslfier, O = oxygen gaslfler, P = pyrolysts process, PC = pyrolysis gaslfter, S = steam, C = char combustionU = updraft, D = downdraft, O = other (sloping bed, movmg grate), FI = fluidlzed bed, S = suspended flow, MS = molten salt, MH = multiple hearthLEG = low energy gas ( -150-200 Btu/SCF) produced m air gaslflcation, MEG = medium energy gas produced In oxygen and pvrolysls gaslflcatlon (350500 Btu/SCF,PO = pyrolysls 011, typically 12,000 fltu/lb, C = char, typically 12,(x)0 Btu/lbR = research, P = pilot, C = commercial size, Cl =commerclal Installation, D =demonstratlonCaslflers are rated m a variety of units Listed here are Btu/h derived from feedstock throughput on the basis of biomass containing 16 MBtu/ton or 8,000 Btu/lb,SMW with 9 MBtu/ton ( ) mdtcate planned or under construction‘Unless noted otherwise, the gaslfwrs Ilsted here produce drv ash (T > 1,100” C) and operate at 1 atm pressure (Coal gaslfwrs and future biomass gastfiers may

operate at much higher pressures )b operate s at 1.3 atm PressurecOperates at 10 atm pressuredThese ~aslflers produce slagglng (T > 1,3fM0 C) Instead of clw ash

SOURCE A Surieyof B/omass Gas/f /cdtlon (Golden, Colo Solar Energy Reseqrch Instttute, JUIV 1979)


Gasifier type Size

Contact OperatingOrganization Input mode Fuel products units Btu/hr

Oxygen gasification of SMWUnion Carbide (Linde), Tonowanda, N.Y.d

Catorican, Murray HiIIs, NS

Pyrolysis gasification of SMWMonsanto, Landgard, Enviro-chemEnvirotech, Concord, Calif.Occidental Res. Corp., El Cajon, Calif.Garrett En. Res. & Eng., Hanford, Calif.Michigan Tech., Houghton, Mich.U. of W. Va. -Wheelebrator, Morgantown, W. Va.Pyrex, JapanN i c h o l s E n g i n e e r l n gERCO, Cambridge, MassRockwell International, Canoga Park, Calif.M.J. Antal, Princeton, NS

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MEG, CMEG

MEG, CMEG, C

1 100 M9 M

I D 20 (375)1P1C1P

1P1C

1P 161P 162R —

Table Notation (by columns)Input A = alr ga$lfter, O = oxygen gaslfler, P = pyrolysis process, PG = pvrolysls gaslfler, S = steam, C = char combustmnContact mode U = updraft, D = downdraft O = other (sloping bed, moving grate), FI = fluldlzed bed, S = suspended flow, MS = molten salt, MH = multlple hearthFuel products I F(; = low energy gas ( -150-200 FIIuSCF) produced !n alr gaslf!catton, MEG = medium energy gas produced In oxvgen and pkrolv$ls gaslflcatmn ( 150-500 f3tu/SCF,

PO = pvrolvsls oil, typically 12,000 fltu lb, C = char, tvplcally 12,0CM) Btu/lbOperating untt$ R = research, P = pilot, C = commerc Ial SIZe C I = commercial m$tallatlon, D = demonstrationSlrf’ Caslflers are rated (n a varletv ot ucr!ts I !sted here are Btu h derwed trczm feedstock throughput on the basis of bmmass containing 16 MFltu ton or t3,0cK) Fltu, lb,

SMW with 9 MBtu ton ( ) Incflc ate planned or under crm$tructlon‘Unless noted otherwise, the ga$tfler$ I Isted here produce riry ash [ T 1 1 ()()0 C) and operate at 1 atm pressure [Coal gaslfler$ and future biomass ga$lfters mav operate at mu{ h

Chapter 8

FERMENTATION

Chapter 8.– FERMENTATION

Introduction . . . . . . . . . . . . . . . . . . . . . . . . .Ethanol From Starch and Sugar Feedstocks . . .

Energy Consumption . . . . . . . . . . . . . . .,Process Byproducts . . . . . . . . . . . . . . . . .Ethanol Production Costs. . . . . . . . . . . . .Onfarm Distillation . . . . . . . . . . . . . . . . .

Cellulosic Feedstocks. . . . . . . . . . . . . . . . . . .Generic Aspects and Historical Problems

With Pretreatment . . . . . . . . . . . . . .Processes Currently Under DevelopmentGeneric Economics of Lignocellulosic

Materials to Ethanol. . . . . . . . . . . . . . .Environmental lmpact of Ethanol Production. .Process Innovations. . . . . . . . . . . . . . . . . . . .

Crain and Sugar Processing ..., . . . . . . .Fermentation . . . . . . . . . . . . . . . . . . .Distillation. , . . . . . . . . . . . . . . . . . . . . . .Producing Drv Ethanol. . . . . . . . . . . . . . .

Page. . . 159. . . 160. . . 160 52. . . 162. . . 164 53

166. . . 167 54

55. . . 169. . . 169

. . . 172

. . . 173

TABLESPage

Energy Consumption in a DistilleryProducing Fuel Ethanol From Corn . ......161Early 1980 Production Costs for EthanolFrom Grain and Sugar Crops. . . . . . . . . ....165Cost of Ethanol From Various Sources. ....165Plausible Cost Calculation for FutureProduction of Ethanol From Wood,Classes, or Crop Residues . .............173

FIGURES

Page. . . 175 26. Process Diagram for the Production of. . . 175 Fuel Ethanol From Grain . ..............160. . . 175 27. Process Diagram for the Production of

176 Fuel Ethanol From Sugarcane or Sweet. . .. . . 176 Sorghum. . . . . . . . . . . . . . . . . . . . . . ......160

Chapter 8

FERMENTATION

Introduction

Ethanol, or “grain alcohol,” is a versatileand commercially important liquid which hasbeen used for a variety of purposes for centu-ries. Ethanol is the intoxicant in alcoholic bev-erages and, prior to the industrial age, society’smost common contact with ethanol was as aningredient of beer, wine, or liquor.

Beverage alcohol is a major item of com-merce and a source of substantial tax reve-nues. In addition, ethanol is also a key industri-al chemical and is used as a solvent or reactantin the manufacture of organic chemicals, plas-tics, and fibers. Ethanol has a long history as acombustible fuel for transportation vehiclesand space heating. Except under unusual cir-cumstances (e. g., wartime Europe), ethanol hasbeen little used for these purposes in the 20thcentury, having been largely displaced by pe-troleum-based motor and boiler fuels.

Beverage alcohol is usually produced by fer-mentation processes, but the processes are de-signed to achieve various qualities of taste andaroma which are irrelevant to fuel alcohol pro-duction. Most industrial ethanol is producedfrom ethylene, a gas derived from petroleumor natural gas liquids. Rising oil prices havemade biomass-derived ethanol competitivewith ethanol derived from petroleum but it isunclear whether the chemical industry wil lturn to biomass or coal for its supply of etha-nol.

All processes for the production of ethanolthrough fermentation consist of four basicsteps: 1 ) first the feedstock is treated to pro-duce a sugar solution; 2) the sugar is then con-verted to ethanol and carbon dioxide (CO2) byyeast or bacteria in a process called fermenta-tion; 3) the ethanol is removed from the fer-

mented solution by a disti l lation* processwhich yields a solution of ethanol and waterthat cannot exceed 95.6 percent ethanol (atnormal pressures) due to the physical proper-ties of the ethanol-water mixture; and 4) in thefinal step, the water is removed to produce dryethanol. This is accomplished by disti l l ingonce again in the presence of another chemi-cal.

The main distinctions among the processesusing different feedstocks are the differencesin the pretreatment steps. Sugar crops such assugarcane, sweet sorghum, and sugar beetsyield sugar directly, but the sugar often mustbe concentrated to a syrup or otherwisetreated for storage or the sugar will be de-stroyed “by bacteria. Starch feedstocks such ascorn and other grains require a rather mildtreatment with enzymes (biological catalysts)or acid to reduce the starch to sugar. And. cel-Iulosic (cellulose containing) feedstocks suchas crop residues, grasses, wood, and municipalwastepaper require more extensive treatmentto reduce the more inert cellulose to sugar.

Processes utilizing each of the ethanol feed-stock types are considered below. I n addition,the environmental effects of ethanol distill-eries are discussed as are various processchanges that could lower costs. Although etha-nol is emphasized in this chapter, it should beremembered that other alcohols (e. g., butanol)and chemicals could be produced from thesugar solutions, but technical and economicuncertainties are too great to include a de-tailed consideration of these alternatives atpresent.

*Distillation consists of heating the ethanol-water solutionand passing the vapor through a column in which the vapor con-densed and revaporized numerous times, a process that succes-sively concentrates the ethanol and removes the water

159

160 Ž Vol. II—Energy From Biological Processes

Ethanol From Starch

Ethanol can be produced from starch andsugar feedstocks with commercially availabletechnology. Starch feedstocks are primarilygrain crops such as corn, wheat, grain sor-ghum, oats, etc., but also include various rootpIants such as potatoes. The sugar feedstocksare plants such as sugarcane, sweet sorghum,sugar beets, and Jerusalem artichokes. Sincethese feedstocks are all crops grown on agri-cultural lands under intensive cultivation andcan be converted with commercial technology,they are considered together.

The processes for producing ethanol fromstarch and sugar feedstocks are shown sche-matically in figures 26 and 27. The energy con-sumption of these processes is discussed next,followed by a description of process byprod-ucts, cost calculations, and onfarm processes.

Figure 26.—Process Diagram for the Production ofFuel Ethanol From Grain

and Sugar Feedstocks

Figure 27.—Process Diagram for the Production ofFuel Ethanol From Sugarcane or Sweet Sorghum

Energy Consumption

Most ethanol distilleries in the United Statestoday were designed for beverage alcohol pro-duction, with little emphasis on energy usage.A fuel ethanol distillery can take advantage ofnewer technology and the low purity require-ments of fuel ethanol to reduce its energy con-sumption. Nevertheless, both the type of fuelused and the amount of energy consumed atthe distillery will continue to be important de-terminants of the efficacy of fuel ethanol pro-duction in displacing imported fuels.

In the plant currently producing most of thefuel ethanol today, the germ (protein) in theSOURCE Office of Technology Assessment

Ch. 8—Fermentat ion . 161

corn feedstock is removed in a separate feedprocessing plant. Consequently, the distilleryreceives a more or less pure starch from thegrain processing plant and the waste still age(material left in the fermentation broth afterthe ethanol has been removed) is fed into amunicipal sewage system, so that the energyneeded to pretreat the corn and to process thewaste stream is not included in the distilleryenergy usage. Nevertheless, the distillery con-sumes 30,000 Btu/gal of ethanol and 96.5 per-cent of this is in the form of natural gas.1 If allprocessing energy inputs are included, fuelconsumption is about 65,000 to 75,000 Btu/galof ethanol (exclusive of the energy needed forwaste stream treatment). z Furthermore, theeconomics of this process are predicated on in-come from process byproducts, such as cornoil, for which the markets are uncertain if largevolumes are produced.

OTA’s analysis indicates that the fuel usedat the distillery cannot soon be reduced to aninsignificant fraction of the energy containedin the ethanol. Thus, if the displacement of im-ported fuels (oil and natural gas) is to be max-imized, fuel ethanol distiIIeries should be re-quired to use abundant or renewable domesticfuels such as coal or solar energy (includingbiomass).

A distillery that might be more common in alarge-scale ethanol program has been designedby Raphael Katzen Associates. ’ This distillerywould produce a dry animal feed byproduct,known as distillers’ grain (DC) (see next sectionon byproducts). Although the disti l lery usessome equipment to dry the DC which is not incommon use in ethanol distilleries, all of theequipment is commercially available. The de-sign reduces the number of distillation col-umns to the minimum using conventional tech-nology (two columns: one to produce 95 per-cent ethanol and one to produce dry ethanol)

‘ R Strasma, “Domestic Crude 011 Entitlements, Applicationfor Petroleum Substitutes, E RA-03° submitted to the Departmentof Energy by Archer Danlels Midland, Co , Decatur, Ill , May 17,1979 update

* I b}d‘Raphael Katzen Associates, Grain Motor Fuel Alcohol, Tech-

n/ca/ and Econorn(c Assessment Study (Washington, D C Assist-ant Secretary for Pol Icv Evaluation, Department of Energy, June1979), CPO stock No 061-000-00308-9

and uses “vapor recompression” evaporationfor drying the DG. The distillery is coal-firedand consumes 42,000 Btu of coal and 13,000Btu of purchased electricity* to produce 1 galof ethanol which has a lower heating value of76,000 Btu. ** The energy breakdown for theKatzen design is shown in table 52.

Table 52.–Energy Consumption in a DistilleryProducing Fuel Ethanol From Corn

Thousand Btu ofProcess step coal/gal of ethanola

Receiving, storage, and milling, . . . . . . . . . . . . 0.8Conversion to sugar (including enzyme production). 16.0Fermentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.6Distillation . . . . . . , . . . . . . . . 24.8Distillers’ grain recovery . . . . . . . . . . . . . . . . . . . . 6.2Miscellaneous . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.6

Total . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55.0

aA55ume5 10,000 Btu of cod per kllowatthour of electricity

SOURCE Raphael Katzen Assoclales, Gram Molor Fuel Alcohol, Technical and Econorrvc Assess.rrml Study (Washington, D C Assistant Secretary for Policy Evaluation, Departmentof Energy, June 1979), GPO stock No 061-000 .00308-8

At first thought, one might expect the energydemand of a distillery using sugar plant feed-stocks to be less than that for starch feed-stocks, since the energy needed to reduce thestarch to sugar is no longer required. The situ-ation is, in fact, quite the opposite. The proc-esses for extracting the sugar from the feed-stock and concentrating it to a syrup (highlyconcentrated sugar solution) are quite energyintensive. The average energy usage for a sugarfeedstock (based on sugarcane) would beabout 85,000 Btu of coal per gal Ion of ethanolproduced on the average, ’ or slightly morethan the energy content in the ethanol. If thebagasse, i.e., plant matter left over after thesugar is extracted, is used to fuel the boiler,then 110,000 Btu of bagasse would be neededto produce 1 gal of ethanol. (This assumes a 70-percent boiler efficiency for bagasse, as op-posed to 90 percent for coal.)

For both the grain and sugar feedstocks,crop residues could be used to fuel the dis-tilleries. In both cases there is sufficient resi-

*1O,OOO Btu/kilowatthour* *Lower heating value is measured when water vapor iS the

product of combustion The higher heat value, when liquid wateriS the product, iS 84,000 Btu/gal

‘Ibid


due produced together with the starch or sugarto fuel an energy-efficient distillery, althoughthe quantity may be only marginally adequatefor sugar feedstocks.5 If one requires that suffi-cient residues be left on the land to provideadequate soil erosion protection, then theavailable residues are not adequate in mostcases. 6* Crop residues gathered from adjacentcroplands where the crops are not used for eth-anol production could easily supplement theshortfall, however.

Since the sugar feedstocks are generally de-livered to the distillery with much of the resi-due, which subsequently arises as a waste by-product of the sugar extraction step, it is morelikely that residues will be used to fuel thesedistilleries, although it is technically feasible inboth cases.

If crop residues are used to fuel distilleries,then the fossil fuel usage at the distillery willbe negligible. The fossil energy used to collectand transport residues and replace their nutri-ent value to the soil would have to be in-cluded. OTA estimates this energy to be about10,000 Btu/gal of ethanol for grain feedstocksand about 3,000 Btu/gal for sugar feedstocks.(These estimates assume that no grain residuesare normally harvested with the grain and thatthe entire sugar plant is harvested and trans-ported to the distillery. Therefore, the grain-fed distillery needs 10.3 lb of residue per gal-lon of ethanol and the sugar-fed disti l leryneeds a supplement of 3 lb of residue per gal-lon of ethanol.)

‘R A Nathan, “Fuels From Sugar Crops, ” published by Techni-cal Information Center, Department of Energy, TID-22781, July1978.

‘Ibid● As an example, the national average available crop residues

for corn are about 7,3 lb/gal of ethanol (see ch 3) With a 70-per-cent boiler efficiency, this would provide 70 percent of the ener-gy needed at the distillery (assuming 6,500 Btu/lb)

For sugarcane and sweet sorghum (syrup variety), the totalcrop residues are about 11 lb of combustible matter per gallon ofethanol The residues required to protect against soil erosionvary greatly If all of the residue IS used, one gets about 80 to 85percent of the distillery energy requirement (assuming 30-percentleaves with 6,500 Btu/lb and 70-percent cane with 9,000 Btu/lband 70-percent boiler efficiency) And in areas where residues areneeded to protect the soil from erosion, the available residuesmight be only the cane, which would be about 60 percent of thedistillery energy requirement

Process Byproducts

All of the material in the feedstock, exceptfor the sugar or starch (most of which is con-verted to alcohol), become byproducts of dis-tillation. in addition, the excess yeast or bacte-ria grown in the fermentation step can alsoserve as a byproduct. The grain feedstocks arehigh in protein and, consequently, the byprod-uct credits will be larger than with sugar feed-stocks.

The grain protein can be removed as “glu-ten” before distillation and oil, such as cornoil, can be extracted. As mentioned above,however, the oil market is uncertain and the re-quired selling price for such oil is too high forit to be considered as a fuel.

The grain processes considered most likelyfor large-scale fuel ethanol production wouldferment a mash (crushed, cooked, and treatedgrain plus water) that still contains all the non-starch components of the grain. The materialleft after the ethanol has been removed, called“still age,” has in it protein, dead yeast, andbacteria as well as various other materials con-tained in the grain. This stillage can be fed toanimals directly or can be dried (to produceDG) for transport and, again, used as an animalfeed. The wet stillage, however, spoils in 1 to 2days, so care must be exercised when feedingthe still age wet. 7

The high protein content makes DG a suita-ble protein supplement to animal feed, al-though its high fiber content limits the quanti-ty that can be fed and the types of animals thatcan consume it. Although DG contains abouthalf the protein per pound of material as doessoybean meal, a common protein supplement,the types of protein in DG are such that thecattle use it more effectively and experimentsindicate that 1.5 lb of DG can substitute for 1

‘E W Kienholz, et al , “Craln Alcohol Fermentation Byprod-ucts for Feeding In Colorado, ” Department of Animal Sciences,Colorado State Unlverslty, Fort Colllns, Colo , 1979

Ch. 8—Fermentation ● 163

lb of soybean meal. * 89 Consequently, the by-product of distilling 1 bu of corn can displacethe meal from about 0.25 bu of soybeans.**

Other experiments have indicated that DCcauses the cattle to digest more of the starchin their feed than would be digested withoutD G10 thereby giving DC an enhanced feed val-ue, since less total corn could be fed to ani-mals if part of the corn were converted to etha-nol and the resulting DC fed in place of thecorn. These results, however, occur only whenthe animal is fed a starch-rich and protein-poordiet. Feed rations commonly used today havea more nearly optimum protein-starch bal-ance, so this effect would not occur, and thefeed value of DC is only as a replacement forother protein concentrates used in animal ra-tions.

The quantity of DC that can be fed to cattlehas been estimated to correspond to an etha-nol production level of 2 billion to 3 billiongal/yr. 1 2 As mentioned above, the protein inthe grains could be removed before fermenta-tion, and this protein feed (“gluten”) would besuitable for a larger variety of animals. Theo-retically, if the byproduct replaces all domes-tic consumption of crushed soybeans used foranimal feed, 13 a production level of 7 billiongal/yr could be achieved before all crushedsoybeans had been replaced with distillery by-

‘ C a t t l e b r e a k ciown some p r o t e i n s In the rumen ancf later use

t h e re~ultant ammonia tn the I n t e s t i n e s t o s~ntheslze n e w pro-

teins Other p r o t e i n s pa~s t h r o u g h the rumen anci are absorbeci

cflrectly In the intestine Depencllng on the relatlve propor t ions of

the two c lasses o f p ro te ins , the effective qwantltv of usable pro-

tein WIII vdry

‘T K Iopfenstein, D e p a r t m e n t o f Animal Sclence$, Unlver$lty

of Nebraska, Lincoln, Nebr , private communlcdtion, 1979

‘ M 1 Poo\ and T Klopfensteln, “Nutrltiondl Value o f BVpro~-

uc t~ ot Alcohol Produ( t Ion for L lve~tock Eeecls, Cooperat Ive E x-

tenslon Servl( e, Unlver$itV o f Nebrdska, I Incoln, Nebr , An!malSctence Publlcatlon No 79-4, 1979

‘ ‘One bujhel of Cflstllled corn Vlelc!s about 18 lb of DC Onebu~hel of soybeans produces about 48 lb of ~oybean meal

‘“W P Carrigu~, Unlverslty of Kentu[ ky, Proceedjng$ of IothD/\t///ws’ Feed Conference, Clnclnatti, Ohio, Mar }, 1955

‘‘Klopfen$tein, op clt‘‘R L Meekhof, W E TVner, and F D Holland, “Agricultural

Policy and Cd$ohol, ” purdue (_Jn!versltV, west LdfdVette, I nd ,Mav 1979, contractor report to OTA These authors assume a 21

subst itut Ion of D~ for soybean mea I a nci ) bl j ! Ion ga I of ethanolper Vear as the saturation point Using 1 51 as the ratio, how-ever, reduces this to 225 bllllon gal/yr

‘ ‘ARr/cu/tura/ $t.?(I\tIc$, / <)79 (Wa~hlngton, D C IJ S D e p a r t -

ment of Agriculture, 1979), GPO stoc-k No 001- 000-04069-1

product (assuming the byproduct of ferment-ing 1 bu of corn displaces the soybean mealfrom 0.25 bu of soybeans). The byproduct,however, is not a perfect substitute for soy-bean meal and the actual level at which theanimal feed market becomes saturated is prob-ably considerably lower than this.

Other uses for DC are possible. Brewers’yeast is used as a B vitamin source by somepeople and the protein could possibly be usedas a human protein source. It is not clear, how-ever, whether this source of protein will gainconsumer acceptance. The distiller byproductcould also be exported as an animal feed sup-plement, but if it competes with indigenoussoybean meal producers (such as in Europe),import tariffs or quotas may be imposed.

While there are numerous possibilities, mostproposals are vague and involve some obviousproblems. Consequently, byproduct creditscould drop or disappear in a large-scale etha-nol program based largely on grain feedstocks.

If the protein in grains is removed in thepretreatment or sugar feedstocks are used, thestill age consists primarily of yeast or bacteria,and has smaller feed value than DC. (The dis-tillery producing most of the fuel ethanol usedtoday removes the protein in the pretreatmentand returns the still age to sewage treatment.)Although there is a limited market for this stil-Iage, it is likely that it will either be dried andused as a fuel or subjected to anaerobic diges-tion with the resulting biogas used as a fuel.Drying and burning the byproduct result inslightly more energy— an estimated 8,000 Btu/gal of ethanol. *

Other possible byproducts of fermentationinclude oils, vitamins, other alcohols, variousorganic acids (e. g., vinegar), fusel oil (a mixtureof alcohols), and other chemicals. The proc-esses, however, are generally controlled sothat the major chemical byproduct is fusel oil.This would probably be combined with the

‘If the rnaterlal IS cirleci, 11,000 Btu (2 lb) of material result pergallon of ethanol The cfrytng however, requires an estlmateci1,000 tltu additional Input energy Anaerobic dlgestlon woulcfprociuce about 5,0oo Htu of blogas (assum[ng 4 ft blogds/lb sol-Icis) wlt h the process requ Irlng about 1,000 13tu


fuel alcohol, resulting in a 0.7-percent increasein the quantity of fuel produced.

C O2 is also a byproduct of fermentationwhich is used in carbonated beverages, dry ice,and, to a small extent, in chemical processes.Moreover, CO2 has many interesting propertiesthat are currently being researched and recov-ery may eventually become more widespreadand profitable.

Ethanol Production Costs

Raphael Katzen Associates has performed adetailed cost calculation on a 50-million-gal/yrcoal-fired distillery that purchases its electrici-ty from an electric utility. 14 Including coal-han-dling and pollution control equipment and al-lowing the production of dried DC, the totaldistillery would cost an estimated $53 million.

Inflating this to early 1980 dollars (20 per-cent) results in a distillery investment of $64million. (These figures do not include engineer-ing fees which could be small if a large numberof disti l leries are built, but which are esti-mated at $6 million, in 1978 for a single dis-til lery.)

A distillery designed solely for sugar cropfeedstocks would cost considerably more. Asmentioned above, the sugar has to be concen-trated to a syrup for storage, since the feed-stock is available for only part of the year, dur-ing and somewhat after the harvesting season.Hence, the pretreatment equipment has to beable to handle a larger capacity than the distil-lery for part of the year, while standing idle forpart of the year. In addition storage tanks areneeded for the syrup. if the bagasse and cropresidues are used as fuel, however, then someof the pollution control equipment needed toremove sulfur emissions can be eliminated,due to the very low sulfur content of thebiomass. In all, a 50-miIl ion-gal/yr disti l leryfor sugarcane or sweet sorgham would cost anest imated $100 mi l l ion in 197815 16 or $120

‘“Raphael Katzen Associates, op clt‘Slbid“F C Schaffer, Inc , in E S Llplnsky, et al , Sugar Crops as a

Source of Fuels, Vol // Processing and Conversion Research,final report to Department of Energy, Aug 31, 1978

mill ion in 1980, assuming the feedstock isavailable for half of the year and half year’ssyrup storage is required. These assumptionsabout the length of time that the feedstockwill be available may be somewhat optimisticfor Midwestern grown sweet sorghum, how-ever, and the cost could be higher. If the rawfeedstock is available for only 3 months peryear, OTA estimates the distillery would costabout $140 million in 1978 dollars.

Although it might be possible to avoid con-centrating the extracted sugar solution to asyrup by using antibiotics or various chemi-cals, a major cost of the pretreatment is theequipment needed to remove the sugar solu-tion from the raw plant material. Furthermore,storage of large quantities of dilute sugar solu-tion would be expensive. Consequently, im-provements in the economics of using sugarfeedstock will require methods for storing theraw sugar feedstocks inexpensively and in away that the sugar need not be removed andconcentrated. Possibil it ies include pretreat-ment with chlorine gas, ammonia, or sulfurdioxide (to change the acidity and provide atoxic environment for bacteria). OTA is un-aware, however, of any work in this area thatwould serve as a basis for cost calculation.

An alternate approach is to build a distillerycapable of handling either starch or sugarfeedstocks. Katzen has calculated that this 50-million-gal/yr distillery would cost $93 millionin 1978 dolIars.17

The ethanol costs are influenced by the cap-ital investment in and financing of the distil-lery, the disti l lery operating costs, and thebyproduct credits. For a coal-fired 50-mill ion-gal/yr distillery using starch feedstock, the cap-ital charges are about $0.21 to $0.42/gal of eth-anol, depending on the financing arrange-ments. These charges, however, can vary sig-nificantly with interest rates, depreciation al-lowances, tax credits, and other economic in-centives.

The major operating expense is the feed-stock cost less the byproduct credit. For cornat $2.50/bu, the feedstock costs $0.96/gal of

1‘Raphael Katzen Associates, op clt

Ch. 8—Fermentat ion ● 1 6 5

ethanol and the byproduct credit is about$0.38/gal ($110/ton of DG), resulting in a netfeedstock cost of $0.58/gal. Because farm com-modity prices are extremely volatile, the netfeedstock and resultant ethanol cost could bequite variable. A $0.50/bu increase in corngrain prices (and a proportionate increase inthe byproduct credit), for example, would raisethe ethanol cost by $0.1 2/gal.

Tables 53 and 54 show the cost of ethanolproduced from various feedstocks. Althoughthe costs will vary depending on the size of thedistillery, ethanol can be produced from corn($2.50/bu) in a coal-fired 50-million-gal/yr dis-tillery for $0.95 to $1 .20/gal. About $0.10 to$0.30/gal should be added to these costs fordeliveries of up to 1,000 miles from the distil-lery. (Most ethanol is currently delivered in

Table 53.–Early 1980 Production Costs for Ethanol From Grain and Sugar Crops(in a 50-million-gal/yr distillery)

Graln a Sugarb

Fixed capital. ., ., ., ., ... ., ., ., ., ., ., . . . . . . . $64 million $120 millionWorking capital (10% of fixed capital) ... ., . . . . 6.4 million 12 million

Total Investment ., ., ., ., ., ... ., ., ., ., ., ... ., $70.4 million $132 million

$ per gallon of 99.6% ethanol

Operating costsLabor . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . . . ... . . . . . . $0.08 $0.09Chemicals . . . . . . . . . . . . . . . . . . . . . . . . . . 0.01 0.01Water . . ., . . . . ., . ... ... . ., . . . . . . . 0.01 0.01Fuel (coal at $30/ton for grain feedstock and crop residues at $30/ton for

sugar feedstock) . . . . . . . . . . . . . . . . . . . . . . . 0.08 0.04c

Subtotal . . . . . . . . . . . . . . . . . $0.18 $0.15Capital charges15 to 30% of total investment per yeard . . . . . . . . . . . . . . . . . . 0.21-0.42 0.40-0.79

Total . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $0.37-$0.60 $0.55-$0.94

alncludes drying Of distillers grambln~lude~ eqU,pmen( for extracting the sugar from the feedsfock Concentratlflg If to a sYrUP for stora9ec~gasse.fueled dlsllllery appropriate for sweef sorghum and sugarcane supplemental fuel requirement Is 3 lb of residue Per 9allon of ethanoldTh ere are M any oflen complex formulae [ocOmpufe ac[ualcapl[a(cOs[s Economic factors considered mcludedebl/equity ratio dePrecfatlon schedule In”

come lax credit rate of Inflallon terms 01 debt repay menl, Operating capital requirements and Investment hfet!me However, a reahstlc range of posslbll.thes for annual capital costs would he between 15 and 30% of total capital mves[ment

The upper extreme of 30% may be obtained assuming 100% equity finance and a 13% aftertax rale of return on Investment The lower extreme of15% may be obtained assuming 100VO debl flnanclng a! a 9% rate of Interest Both calculations assume constant dollars, a Zo.year protect Mehme, andinclude a charge for local taxes and Insurance equal to 3% of fixed cap!fal costs For a more detaded treatment of capital costs see OTA, Apphcarlon 01Solar Tecfrno/ogy /0 Today’s Energy Needs VOI II ch 1

SOURCE Off Ice of Technology Assessment and Raphael Kalzen Assoclales Gram Moror Fue/A/coho/, Techrvcalarrd Ecorromfc Assessmen/ Study (Washmgfon D C Asslstanl Secretary for Policy Evaluation Department of Energy, June 1979), GPO stock No 061.000 -00308-9

Table 54,–Cost of Ethanol From Various Sources

Net feedstock costb Ethanol cost YieldsC (gallons ofFeedstock Price a ($/gal ethanol) ($/gal) ethanol per acre)

Corn . . . . . . ... $2.44/bu $0.57 $0.94-$1.17 220Wheat ., ., ., ., ., 3.07-4.04/bud 0.73-1.08 d 1,10-1.68 86Grain sorghum 2.23/bu 0.49 0.86-1.09 130Oats. . . . . . 1.42/bu 0.59 0,96-1.19 75Sweet sorghum, ., ., 15.00/tone 0.79 1.34-1.73 380e

Sugarcane . . . . . 17.03/tonf 1.26 1.81-2.20 f 520

aAverage of 1974-77 seasonal average viceshhe feedslock cost less the byproduct credit The dltference In feedslock costs might not hold over the longer term due to equdlbrahon of prices throughlarge-scale ethanol production

cAverage of 1974.77 national avera9e yieldsdRange due tO d! fferent prices for different tYPeS of MeateA55umlng 20 fre5h We!ghf tons/acre yteld $300/acre ProductIon costs‘Excludes 1974 data due 10 the anomalously high sugar Prices that Year

SOURCE Agr/cu/fura/ Slaf/sOcs 1978 (Washmglon O C U S Oeparfmerl of Agriculture), and Office of Technology Assessment


tank trucks, but as production volume growsother forms of transportation, such as bargeshipments, rail tank cars, and petroleum prod-uct pipelines, * could decrease the transporta-tion cost to as low as $0.03 to $0.05/gaI underfavorable circumstances.)

As shown in tables 53 and 54 the majortradeoff between starch and sugar feedstocksis that the starch-fed distilleries require con-siderably less investment than the sugar-fedones, but the ethanol yield per acre cultivatedmay be larger with the sugar feedstocks. Asnoted in chapter 3, however, these yield figuresare highly unreliable for sweet sorghum, andsugarcane cannot be grown on most croplandpotentially available for energy crop produc-tion. If comparative studies of potential eth-anol feedstocks grown under comparable con-ditions show that certain sugar crops producemore ethanol per acre than the starch crops,then there may be a tendency to turn to sugarfeedstocks as farmland prices rise. Moreover,if the grain byproducts are difficult to sell,then economics could favor sugar crop feed-stocks. For now, however, the lower capital in-vestment required for grain-fed disti l leriesgives them an advantge over sugar-fed distil-leries.

Onfarm Distillation

Apart from commercial distilleries, consider-able interest has been expressed in individualfarmers or farm coops producing ethanol. Anumber of factors, however, could limit theprospects of such production.

Technology for producing 90 to 95 percentethanol (5 to 10 percent water) is relatively sim-ple. Several farmers are or have constructedtheir own distilleries for this purpose. In addi-

‘Various strategies can be used to eliminate potential prob-lems with the water sometimes found in petroleum pipelines. Ifethanol is being transported, the total volume of ethanol in thebatch can be kept large enough so that the percentage of waterin the delivered ethanol iS within tolerable limits If gasohol istransported, it can be preceded by a few hundred barrels of etha-nol which will absorb any water found in the pipeline, therebykeeping the gasohol dry. Other strategies also exist or can be de-veloped 18

‘8L J Barbe, Jr , Manager of Otl Movements, EXXON PlpellneCo , Houston, Tex , private communication, August 1979

tion prefabricated distilleries for producing 9 0to 95 percent ethanol are available both at thefarm size (15,000 gal/yr)19 and coop size (sev-eral hundred thousand gallons per year) 20 for acost of about $1 for each gallon per year of ca-pacity, but there is insufficient onfarm operat-ing experience to establish the reliability or ex-pected operating life of these distilleries. OTAis not aware of smaller distilleries, but there isno fundamental reason why they cannot bebuilt. There will, however, be a tradeoff be-tween the cost of small distilleries and theamount of labor required to operate them.

A farmer must consider a number of site-specific factors before deciding to invest in anonfarm skill. Some of the more important ofthese are:

●

●

●

●

●

●

Investment. – How much does the still andrelated equipment cost?Use of the ethanol. –Will the ethanol beused onfarm or sold? What equipmentmodif icat ions are necessary? Wi l l thefarmer be dependent on a single buyer,such as a large distillery that will upgrade95 percent ethanol to dry ethanol?Labor. – Does the farmer have access tocheap, qualified labor, or is it better tomake a larger investment for an automat-ic distillery?Skill.– Although ethanol can be producedeasily, the process yield—and thus thecost — as well as the safety of the opera-tion can depend critically on the skill ofthe operator.Equipment lifetime.– Less expensive distil-leries may be constructed of materialsthat are destroyed by rust after a fewyears’ operation.Fuel.– Does the farmer have access towood, grass, or crop residues and combus-tion equipment that can use these fuels?Can reliable, inexpensive solar sti l ls beconstructed for the distiIlation step?

If oil or natural gas is used in the distil-Iery, would it be less expensive to use this

“Paul Harback, United International, Buena Vista, Ga , pri-vate communication, October 1979

ZORobert Chambers, president, ACR Process Corp , Urbana, Ill ,

private communication, September 1979

Ch. 8—Fermentat ion ● 1 6 7

●

●

fuel directly as a diesel fuel supplement ina retrofitted diesel engine?Byproduct. – Can the farmer use the wetbyproduct on his/her farm? Will this un-duly complicate the feeding operations ormake the animal operation dependent onan unreliable still? What will drying equip-ment cost and how much energy will itconsume?Water. – Does the farmer have access tosufficient water for the distiIIery?

Under favorable circumstances, it might bepossible to produce 95 percent ethanol for aslittle as $1/gal* plus labor with a labor-inten-sive distillery. If the ethanol is used in a dieseltractor, the ethanol would be equivalent todiesel fuel costing $1.70/gal, or about twice thecurrent diesel fuel prices, Under unfavorablecircumstances, the cost could be several timesas great. Due to a lack of experience with on-farm distilleries, however, these cost estimatesmay be low.

Onfarm or coop production of dry ethanolcould become competitive with commerciallydistilled ethanol, however, if relatively auto-matic, mass-produced distilleries capable ofusing fuels found onfarm and producing dryethanol and dry DC could be sold for about $1for each gallon per year of capacity and iffarmers charge little for their labor. OTA is notaware of any package distiIIeries for producingdry ethanol that are available at this price.

*Assuming equipment costs of $1 for each gallon per year ofcapacity, the costs per gallon of ethanol are: $0.58 for net feed-stock cost, $0.20 for equipment costs (operated at 75 percent ofcapacity), $020 for fuel (assuming $3/m million Btu and 67,000Btu/gallon), and $0.05 for enzymes and chemicals, resulting in$1 03/gal of ethanol or $0.98/gal of 95 percent ethanol

Cellulosic

The feedstocks with the largest potential forethanol production –both in terms of the ab-solute quantity of ethanol and in terms of thequantity of ethanol per acre of cultivatedland– are the cellulosic, or cellulose contain-ing, feedstocks. These include wood, crop resi-dues, and grasses, as well as the paper fractionof municipal solid waste.

Meeting this price goal for automatic, on-farm, dry ethanol production facil it ies wil lprobably require process innovations, particu-larly in the ethanol-drying step, and could wellinvolve the use of small, inexpensive comput-ers (microprocessors) for monitoring the proc-ess. A major constraint, however, could be thecost of sensors, automatic valves, etc. thatwould be required.

For some farmers, however, the cost or laborrequired to produce ethanol may be of second-ary importance. The value of some degree ofliquid fuel self-sufficiency and the ability todivert l imited amounts of corn and othergrains when the market price is low may out-weigh the inconvenience and/or costs. 1 n otherwords, farmers may consider the technology tobe an insurance against diesel shortages andhope that it will raise grain prices. Althoughinsurance against diesel shortages certainly canbe achieved by purchasing large diesel storagetanks at a cost below an ethanol distillation andstorage system, increased grain prices for the en-tire crop would make the economics consider-ably more favorable to farmers but would be avery expensive way for the nonfarm sector toprovide fuel to farmers. As evidence of the inter-est, the Bureau of Alcohol, Tobacco, and Fire-arms had received over 2,800 applications foronfarm disti l lation permits by mid-1979 andthey expected 5,000 by the end of the year. 2’

As a profitable venture in the absence of largesubsidies or grain price increases, however, on-farm production of ethanol is, at best, margin-al with current technology.

1’Wllllam Davis, Bureau of Alcohol, Tobacco, and Firearms,U S Treasury, Washington, D C , private communlcatlon, July1979

Feedstocks

Wood, grasses, and crop residues containcellulose, hemicellulose, and lignin. The cellu-lose can be reduced, or hydrolyzed, to sugarsthat can be fermented to alcohol. The hemicel-Iulose can also be reduced to sugars capableof being converted to ethanol with other typesof bacteria. The Iignin, however, does not con-vert to alcohol and can be used as a source of


chemicals or dried and used as a fuel. General-ly, paper is primarily cellulose with varyingamounts of partially broken Iignin.

The removal of hemicellulose from wood,grass, or crop residues and its reduction tosugar are relatively straightforward. In fact,hemicellulose from biomass is the prinicpalsource of the chemical feedstock furfural.Although hemicellu lose is not now used as asource of ethanol, the fermentation step canprobably be developed without excessive dif-ficulty.

The cellulose, on the other hand, is em-bedded with Iignin, which protects it from bio-logical, but to a much lesser extent chemical,attack. Thus, the reduction of cellulose in-volves treating the IignocelIulose material withacid or pretreating the material either chem-ically or mechanically to make it susceptibleto biological reduction with enzymes.

What was apparently the first acid hydroly-sis of wood was described in a German patentissued in 1880.22 Modifications of this processwere used to produce animal fodder in severalcountries (mostly for the sugar) during WorldWar 1. At the end of the war, the economic ba-sis became obsolete. Between World Wars 1and 11, however, other acid hydrolysis proc-esses were used mostly in Germany to producesugar and alcohol, partly because of materialsshortages but partly in an attempt at self-suffi-c iency. 23 Other plants were also built in Swit-zerland and Korea.

During World War 1, pilot plants were builtin the United States for producing ethanolfrom wood wastes. Acid hydrolysis processesunderwent a series of modifications duringWorld War I l. Following World War II, how-ever, virtually all of the wood-ethanol plantswere closed for economic reasons. * Todaycommercial wood sugar plants are in opera-tion only in the U.S.S.R. and in Japan but sever-

Z~H F J wenz I ~~e Chemica / Tec/?nO/ogy of wood, t r a n s -lated by F E Braun’s (New York: Academic Press, 1970).

~ ‘Ibid*One ethanol plant that uses the sugar-containing waste

stream of a sulfite paper-pulping plant IS still in operation. It is,however, primarily a waste treatment plant and less than 10 per-cent of the paper-pulping processes used in the United Statesproduce a suitable waste stream

al other countries have expressed interest indeveloping the technology, and one plant inSwitzerland is again being used for pilot stud-ies. 24

Clearly it is technically possible to produceethanol from Iignocellulosic feedstocks today.The failure of these processes to remain eco-nomically viable except under special circum-stances has been due, in large part, to the rela-tively low costs of petrochemicals and ethyl-ene-derived ethanol. With oil prices rising, theprimary competitor is likely to be grain- andsugar-derived ethanol. There are, however, im-provements and developments in the lignocel-Iulose processes which can make them com-petitive with the current costs of ethanol fromthese other feedstocks. Alternatively, largerises in farm commodity prices could make thecellulosic processes competitive without tech-nical developments.

While there are processes whose economicsrely on large byproduct credits or special fi-nancing that could be in commercial operationbefore 1985, the key to achieving economiccompetitiveness without these conditions is todevelop processes which:

● produce high yields of ethanol per ton ofbiomass,

● do not require expensive equipment,● allow nearly complete recovery of any ex-

pensive process chemicals, and● do not produce toxic wastes.

No processes currently in existence fully satis-fy all of these criteria, although there are proc-esses that satisfy two and sometimes three ofthe criteria. Nevertheless, R&D currently un-derway could yield significant results in 3 to 5years. With a normal scaleup of 5 years, one ormore processes satisfying these criteria couldbecome commercial by the late 1980’s.

The generic aspects and historical problemswith producing sugars from Iignocellulosicfeedstocks are now discussed, followed by aSlightly more detailed description of variousprocesses currently under investigation. Final-

24) L Zerbe, Program Manager, Forest Service Energy Re-search, U S Department of Agriculture, Forest Products Labora-tory, Madison, WIS , private communication, 1980


Iy, a generic economic analysis is presented fora hypothetical advanced distillery for produc-ing ethanol from IignocelIulosic feedstocks.

Generic Aspects and HistoricalProblems With Pretreatment

As mentioned above, Iignocellulosic materi-als consist of cellulose, hemicellulose, and lig-nin. Typically, such material would first betreated with dilute acid to remove the hemicel-Iulose, which then would be fermented in aseparate step to ethanol. The remaining lignin-cellulose combination would be treated withconcentrated acid at low temperatures (per-haps 100° to 110° F) or dilute acid at high tem-peratures (300 0 to 4000 F) to either dissolve thecellulose from the Iignin or to cause the mate-rial to swell, thereby exposing the cellulose forhydrolysis. Alternatively, the material can beexposed to a number of different chemical ormechanical pretreatments which render thecellulose susceptible to hydrolysis. The hydrol-ysis is then accomplished by further exposureto acid or by the action of enzymes (biologicalcatalysts).

The relative amounts of cellulose, hemicel-Iulose, and Iignin can vary considerably amongthe various Iignocellulosic materials. If purecellulose is converted completely to ethanol,however, the theoretical maximum yield is 170gal of ethanol per ton of cellulose. The yieldsper ton of hemicellulose are similar. Conse-quently for a Iignocellulosic material that is sopercent cellulose, 20 percent hemicellulose,and 25 percent Iignin, the theoretical yield isabout 120 gal/dry ton of biomass fermented. Ayield of 85 to 90 percent of this is a reasonablepractical goal, which would result in yields of100 to 110 gal of ethanol per ton of biomassfermented. The expected yield, however, willvary with the exact composition of the feed-stock. For municipal solid waste (29 percentpaper and 21 percent yard wastes and woodpackaging 25), the average yield could be about60 gal of ethanol per ton assuming a 90-per-cent overall conversion efficiency.

~ ~~a ~erla /~ a n~ f~efgy ~rorn MU njclpa / Waste (VOI 1, wash lng-

ton, D C Office of Technology Assessment, 1979), GPO stockNo 052-001-00692-8

The historical processes have generally usedacid hydrolysis. The dilute acid methods (Mod-ified Rheinau, Scholler-Tornesch, Madison,Tennessee Valley Authority, and Russian Modi-fication of Percolation processes) all sufferfrom a similar ailment, 26 The h igh tempera-tures and acidic conditions needed in the proc-esses cause the resultant sugars to decompose,thereby lowering the overall ethanol yield. Theconcentrated acid processes (Rheinau-Bergiusand Hokkaido), on the other hand, have re-sulted in good product yields. The economics,however, have historically suffered due to theloss of large quantities of acid in the processes,Nevertheless, one of the oldest concentratedacid processes (Rheinau-Bergius) is currentlybeing reexamined to see if this economic con-clusion necessarily pertains today (see below).

Publications over the past 20 years in the So-viet Union have reported good experimentalresults with impregnating wood with acid fol-lowed by mechanical grinding. The details foran assessment of the commercial viability ofthis process, however, are not available. Onthe other hand, a mechanical pretreatment isalso involved in the Emert (formerly Gulf OilChemicals) process discussed below. Histori-cally, the mechanical pretreatments neededhave been quite expensive, but the researchersindicate that this is not a problem with theEmert process. 27 F ina l l y , a v a r i e t y o f o t h e r

processes or combinations of processes aimedat exposing the cellulose to hydrolysis are cur-rently being researched. The most important ofthese are considered below.

Processes Currently UnderDevelopment

Emert Process

The development of this process started in1971 under Gulf Oil Chemicals Corp., but wastransferred to the University of Arkansas Foun-

1~1 Gold5teln D~partm~nt of Wood and Paper Science, North

Carollna State Unwerstty, Ralefgh, N C , private communlcatlon,1979

“G H Emert and R Katzen, “Chemicals From Biomass by lm-proved Enzyme Technology, ” presented In the fymposlum f3iGm a s s a s a Non-Fue/ S o u r c e , sponfored b y t h e A C S/CSJ JointChemical Congress, Honolulu, Hawal}, Apr 1-6, 1979

67-968 0 - 80 - 12


dation for scaleup (the transfer reportedly oc-curred because Gulf had made a managementdecision to concentrate its efforts on fossilfuels). This process is the most advanced of theenzymatic hydrolysis methods and, with prop-er financing, can probably be brought to com-mercial-scale operation by 1983-85.

The method consists of a pretreatment de-veloped for this process which involves grind-ing and heating the feedstock followed by hy-drolysis with a mutant bacterium also devel-oped for this purpose. A unique feature is thatthe hydrolysis and fermentation are performedsimultaneously in the same vessel, thereby re-ducing the time requirements for a separatehydrolysis step, reducing the costs and increas-ing the yield (since a sugar buildup during hy-drolysis could slow the hydrolysis and de-crease the overall yield). Also the process doesnot use acids, which would increase equip-ment costs. The sugar yields from the celluloseare about 80 percent of what is theoreticallyachievable, 28 but the small amount of hemicel-Iulose in the sawdust is not being converted.

The process has been brought to the pilotplant stage and funds are currently beingsought for a demonstration (1 million gaI/yr) fa-cility as part of the scaleup process. Based onthe pilot plant experience, Emert estimates theselling price for the ethanol to be $1 .49/gal(1983 dollars, 100-percent private equity fi-nancing, and 10-year amortization).29 With 80-percent municipal bond financing, he esti-mates the selling price to be $1.01/gal (1983dollars, 20-year amortization).

These cost estimates are based on a feed-stock of So-percent “air classified” municipalsolid waste (i. e., the paper and plastic fraction)at $14/ton, 25-percent saw mill waste at $21/ton, and 25-percent pulp mill waste at $14/ton.These costs are all on the low end of estimatesfor 1978-79 prices and consequently representoptimistic estimates. Furthermore, by 1983, in-flation would increase these costs. More realis-tic 1983 feedstock costs (50 to 100 percenthigher than those cited) would raise the etha-nol cost by about $0.10 to $0.20/gal.

“lbtd“lbld

The cost estimates also assume a large by-product credit for dried fermentation yeastand hydrolysis bacteria ($0.40/gal ethanol).Most of this comes from the hydrolysis bacte-ria and an animal feed value for this materialhas not been established. In addition, large-scale production could lead to a saturatedanimal feed market similar to that with graindistillation and subsequent loss of the byprod-uct credit.

Furthermore, problems encountered withscaling up a process virtually always lead tocost increases above those estimated. Conse-quently, these cost estimates could be too lowby $0.20 to $0.70 or more per gallon of ethanol.Nevertheless, with municipal bond financing,this process could well be competitive withethanol produced from corn in a privately fi-nanced distillery by 1983. (Assuming 7-percentannual inflation as apparently was done inEmert’s calculations, $1 .10/gal ethanol in 1979would sell for about $1 .45/gal in 1983).

While no cost estimates are available forthis process using woodchips, grasses, or cropresidues as feedstocks, Emert reports that ex-periments have shown that modifications inthe thermal-mechanical pretreatment enablesethanol yields of 70 to 75 gal/ton of feed-stock .30 The increased costs for these feed-stocks ($40 to $50/ton in 1983 up from $30 to$40/ton in 1979) would add $0.30 to $().45/galto the ethanol price. Consequently, it is lesslikely that this process using these feedstockswould be competitive with corn-derived etha-nol, unless corn and other grain prices risemore rapidly than general inflation.

In sum, it appears that this process could becompetitive with grain-derived ethanol if mu-nicipal wastepaper is used as a feedstock andthe distillery receives special financing. A re-liable determination of the competitive posi-tion of other feedstocks and financing arrange-ments are less certain and probably cannot bedetermined until a full-scale plant has beenbuilt.

‘“G H Emert, private ~ommunlcation, October 1979


Reexamination ofRheinau-Bergius Process

Much of the detailed information on theRheinau-Bergius process has been lost. Sincethe acid hydrolysis of wood involves subtlechemical processes which can change dramat-ically with small changes in the process condi-tions, the detailed process chemistry of hydrol-ysis with concentrated hydrochloric acid is be-ing reexamined at North Carolina State Univer-sity. The research should provide a basis forreevaluating the process as a source of ethanoland chemicals and determining whether suffi-cient quantities of the acid can be recoveredto make the process economic at today’sprices.

Tsao Process

This process is being developed at PurdueUniversity with the major emphasis on cropresidues as a feedstock and is currently pro-gressing to the pilot plant stage. Althoughthere have been numerous changes in the proc-ess as the research has proceeded, in the cur-rently preferred process hemicelIulose is re-moved first with dilute acid and then, the cel-lulose and Iignin are dissolved in concentrated(70 percent) sulfuric acid. The acid is recov-ered by precipitating the celIulose-lignin fromthe acid through the addition of methanol,then the methanol is removed from the acid bydisti l lation. Following this pretreatment, en-zymes hydrolyze the cellulose.

The use of methanol to aid in recovering theacid is a novel aspect of this process. As therecovery has been proposed, however, themethanol is likely to react to form toxic by-products such as dimethyl sulfate, dimeth-yl ether, dimethyl sulfoxide, and other com-pounds. The loss of process methanol as wellas the disposal of these toxic wastes would in-crease the costs. I n addition, there are severalplaces in the process where more expensiveequipment will be needed than has been in-cluded in most cost calculations due primarilyto the corrosive effects of the acid. 31 32 A l -though novel acid recovery processes of this

‘‘I?aphael Katzen Associates, op clt’11 Goldsteln, op clt

type should be thoroughly investigated, it hasnot yet been satisfactorily demonstrated thatthe process proposed would be economicallycompetitive as a source of fuel ethanol.

University of Pennsylvania—General Electric Process

In this process, woodchips are heated in analkaline solution containing water, sodium car-bonate, and butanol (a higher alcohol). Sincebutanol is only partly soluble in water, thesolution consists of two phases (similar to oilfloating on water). The hemicellulose goes tothe water phase, the Iignin dissolves in the bu-tanol, and the cellulose remains undissolved.Following removal of the cellulose, and clean-ing to remove traces of butanol, it can be hy-drolyzed either with acid or enzymes and thehemicellulose can be converted to ethanolwithout removing it from solution. The butanolis then cooled, which causes the Iignin to pre-cipitate from solution, the solution is filtered,and the butanol recycled to the process.

Clearly the process economics will dependheavily on the cost of producing the processbutanol and the quantity of butanol lost to thewaste stream. On the other hand, the butanol-water sodium carbonate solution is consider-ably less corrosive than other chemicals usedto remove Iignin and therefore could result inlower equipment costs. At this stage, however,the processes are not well enough defined toprovide a meaningful cost calculation.

U.S. Army —Natick Laboratories

Work done at this laboratory has contrib-uted substantially to the basic knowledgeabout the enzyme system that converts cellu-lose to sugar. ’3 These researchers first identi-fied the three-enzyme system involved in thehydrolysis and have developed fungus mutantswith improved enzyme productivities. N o tonly is this research applicable to ethanol pro-duction, but it also provides information forthose interested in retarding cellulose degrada-tion such as that which occurs with jungle rot.

“E T Reese, “History of the Cellulose Program at the U SArmy Natlck Development Center, ” Biotechnology and B/oener-gy Syf71POS/Uf?l, No 6, p 9, 1976


The system developed at Natick, however,requires relatively pure cellulose (such as inpaper); it has not been effective on lignin-containing materials such as grasses, crop resi-dues, and wood. Recently, attention has beendirected at a mechanical process (ball milling)for reducing raw materials to extremely fineparticles in order to use the Natick fungus, butthis pretreatment is expensive and would prob-ably make the process uneconomic, althoughdetailed economic analyses are not availablefrom the current pilot plant operation.

University of California at Berkeley (Wilke)

Wilke has concentrated on changing the pre-treatment step of the Natick process by usingacid and hammer milling of the wastepaperand field residues feedstocks. Nevertheless, acritical step involving the recycling of enzymeshas not yet been demonstrated.

Iotech Process

This process is proprietary and the subject ofpatent applications in the name of the Cana-dian Research and Development Corp. Appar-ently, the novel aspect of the process is thepretreatment of the material before hydrolysis.In this process woodchips are exposed to high--pressure steam for several seconds, followedby explosive decompression. The product issaid to be highly susceptible to hydrolysis.

Generic Economics of LignocellulosicMaterials to Ethanol

The processes described above represent asampling of the possible approaches to etha-nol production from lignocellulosic materials.The descriptions were necessarily brief andcould not include all of the ramifications oraspects of the various research groups’ efforts.

The chemistry and physics of Iignocellulosicmaterials are complex, and there are few pre-dictive theories that enable one to evaluateunambiguously the various approaches. Fur-thermore, the competition between researchgroups is enormous and details are often pro-prietary.

Nevertheless, the process at the most ad-vanced stage of development (of those beingdeveloped) appears to be the Emert process.But as this process now stands and with a suc-cessful scaleup, the ethanol could sell for$0.30 to $0.60/gal more than corn-derived eth-anol and the price difference could be greaterif woodchips rather than sawdust are used as afeedstock. As mentioned above, however, spe-cial financing of the distillery (and an inexpen-sive feedstock source) could lower the sellingprice to a level competitive with the corn-de-rived ethanol from distilleries not specially fi-nanced. (Because of the larger investment, spe-cial financing lowers the price more than itwouId for corn distiIleries. )

Alternatively, distilleries based on the olderacid hydrolysis methods can be built to pro-duce ethanol and chemical feedstocks. KatzenAssociates, for example, has reevaluated theMadison process* on this basis and found thatthe ethanol could be sold at about $1 .50/galwithout byproduct credits (1978 dollars) .34 Theeconomics, however, depend on the byproductcredits for the chemical feedstocks, but thechemical industry is unlikely to make the com-mitment necessary to support a large fuel etha-nol industry until more information is avail-able on the relative merits of biomass- andcoal-derived chemical feedstocks.

As suggested earlier, the key to producingethanol from Iignocellulosic materials at aprice competitive with corn-derived ethanolwithout relying on special financing or largebyproduct credits is the R&D currently aimedat reducing equipment costs, increasing over-all yields, and ensuring a good recovery ofprocess chemicals without the production oftoxic wastes.

*Dilute acid hydrolysis process Products are ethanol, furfural,and phenol

“Raphael Katzen Associates In The Feasib///ty of Uti/izing For-est Res/dues for frtergy and Chernica/s (Madison, W I S ForestProducts Laboratories, March 1976), report NO PB-258-630

Ch. 8—Fermentation . 173

R&D currently underway could fulfill thesecriteria. If so, the production costs might looksomething like those in table 55. These costsrepresent plausible cost goals for the produc-tion of ethanol from IignocelIulosic materials.

Disti l leries can and may be built beforethese criteria are fulfilled, but the economicswill depend on favorable financing and atypi-calIy low feedstock costs or in securing a mar-ket for chemical byproducts. Some distilleriesbased on these circumstances are likely to bebuilt before the late 1980’s. It is unlikely, how-ever, that such circumstances will sustain alarge fuel ethanol industry.

Table 55.-Plausible Cost Calculation for Future Productionof Ethanol From Wood, Grasses, or Crop Residues

(in a 50-million-gal/yr distillery, early 1980 dollars)

Dollars

Fixed investment ... , ... ., ., ... ., ... $120 millionWorking capital ... . . ., ., . . ., . . ., 12 million

Total investment ... . . ., ., ... . . ... . . $132 million

$/gallon

Labor, chemicals, fuel ., ., ., . . . ., . . $0.30Feedstock ($30/ton, 110 gal/ton) ., ., ., . . . 0.27Capital charges (15 to 30% of total investment) . . . . . 0.36-0.72

Total . . ... . . ., ., . . . . . . . ., ., ... $0.93-$1.29

SOURCE : Office of Technology Assessment

Environmental Impact of Ethanol Production

The major potential causes of environmen-tal impacts from ethanol production are theemissions associated with i t s substant ialenergy requirements, wastes from the distilla-tion process, and hazards associated with theuse of toxic chemicals (especially in smallplants). A variety of controls and design alter-natives are available to reduce or eliminateadverse effects, however, so actual impactswill depend more on design and operation ofthe plants than on any inevitable problemswith the production process.

New large energy-efficient ethanol plantsprobably will require at least 50,000 Btu/gal ofethanol produced to power corn milling, dis-tilling, still age drying, and other operations(see “Energy Consumption” discussion). Smallplants will be less efficient. Individual distill-eries of 50-milIion-gal/yr capacity wilI useslightly more fuel than a 30-MW powerplant; *a 10-billion-gal/yr ethanol industry (the ap-proximate requirement for a 10 percent alco-hol blend in all autos) will use about the sameamount of fuel needed to supply 6,000 to 7,000MW of electric power capacity.

New source performance standards have notbeen formulated for industrial combustion fa-cilities, and the degree of control and subse-quent emissions are not predictable. The most

* Assuming 1 (),0()() Btu k Ilowatthour

l ikely fuels for these plants wil l be coal orbiomass (crop residues and wood), however,and thus the most likely source of problemswill be their particulate emissions. Coal andbiomass combustion sources of the size re-quired for distil leries —especially disti l leriesdesigned to serve small local markets–mustbe carefully designed and operated to avoidhigh emission levels of unburned particulatehydrocarbons (including polycyclic organicmatter). Fortunately, most distilleries will belocated in rural areas; this will reduce totalpopulation exposure to any harmful pollut-ants. Particulate control equipment with effi-ciencies of 99 percent and greater are avail-able, especially for the larger plants. If allenergy requirements are provided by a singleboiler, high efficiency control would be easierto provide. This is also true for any sulfur oxide(SO x) controls (scrubbers) that may be requiredif the faciIity is fueled with high-sulfur coal.

Other air emissions associated with ethanolproduction include fugitive dust from raw ma-terial and product handling; emissions of or-ganic vapors from the distillation process (asmuch as 1 percent of the ethanol, as well asother volatile organics, may be lost in the proc-ess); and odors from the fermentation tanks.These emissions may be tightly controlled bywater scrubbing (for odors and organics) andcyclones (for dust).


The “still age” — the waste product from thefirst sti l l (or “beer sti l l’’)–wil l be extremelyhigh in organic material with high biologicaland chemical oxygen demand, and will alsocontain inorganic salts, and possibly heavymetals and other pollutants. When corn is thebiomass feedstock, the stillage is the source ofdried DC, which is a valuable cattle feedwhose byproduct value is essential to the eco-nomics of the process. Thus, it will be recov-ered as an integral part of the plant operationand does not represent an environmentalhazard. On the other hand, sugarcane stillagehas far lower economic potential as a byprod-uct; its recovery is unlikely except as a re-sponse to regulation.

The stillage and other wastes from all etha-nol plants have severe potential for damagingaquatic ecosystems if they are mishandled.The high biological and chemical oxygen de-mand levels in the stillage, which would resultin oxygen depletion in any receiving waters,will be the major problem. 35 Control tech-niques are available for reducing impacts fromthese wastes. Biological treatment methods(activated sludge, biological filters, anaerobicdigestion, etc.] and land disposal techniquesused in the brewing industry are suitable forethanol production, but controls for stillagesfrom some crop materials will require furtherdevelopment and demonstration.

Because fermentation and distillation tech-nologies are available in a wide range of sizes,small-scale onfarm alcohol production mayplay a role in a national gasohol program. Thescale of such operations may simplify water ef-fluent control by allowing land disposal ofwastes. On the other hand, environmental con-trol may in some cases be more expensive be-cause of the loss of scale advantages. Currentexperience with combustion sources indicatesthat high emissions of unburned particulatehydrocarbons, including polycyclic organicmatter, are a more common problem with

JsCarjbbean Rum Study,. Effects of Distillery Wastes on (he Na-rine Environment (Washington, D C Off Ice of Research and De-velopment, Environmental Protect Ion Agency, April 1979)

smaller units. Because smaller units are unlike-Iy to have highly efficient particulate controls,this problem will be aggravated. Also, SO X

scrubbers are impractical for small boilers, andeffective SOX control may be achieved onlywith clean fuels or else forgone. Because localcoals in the Midwest tend to have high sulfurcontents (5 percent sulfur content is not unusu-al), small distiIIeries in this region may have ob-jectionably high SO X emission rates. Finally,small plants will be less efficient than largeplants and will use more fuel to produce eachgallon of alcohol.

The decentralization of energy processingand conversion facilities as a rule has beenviewed favorably by consumer and environ-mental interests. Unfortunately, a proliferationof many small ethanol plants may not providea favorable setting for careful monitoring ofenvironmental conditions and enforcement ofenvironmental protection requirements. Regu-latory authorities may expect to have prob-lems with these facilities similar to those theyrun into with other small pollution sources. Forexample, the attempts of the owners of late-model automobiles to circumvent pollutioncontrol systems conceivably may provide ananalog to the kinds of problems that might beexpected from small distilleries if their con-trols prove expensive and/or inconvenient tooperate.

The same may be true for considerations ofoccupational safety. The current technologyfor the f inal dist i l lat ion step, to produceanhydrous (water-free) alcohol, uses reagentssuch as cyclohexane and/or ether that couldpose severe occupational danger (these chemi-cals are toxic and highly flammable) at inade-quately operated or maintained disti l leries.Similar problems may exist because of the useof pressurized steam in the distillation process.Although alternative (and safer) dehydratingtechnologies may be developed and automaticpressure/leak controls may eventually be madeavailable (at an attractive cost) for smallplants, in the meantime special care will haveto be taken to ensure proper design, operation,and maintenance of these smaller plants.


Process Innovations

The processes for producing ethanol fromsugar and grains are well established, but thetraditional concern of the industries who oper-ate them has been the flavor (or, in some cases,chemical purity) of the product. With the pro-duction of fuel ethanol, on the other hand, theprincipal concerns are cost and energy effi-ciency. There are several possible processimprovements — at various stages of develop-ment — which can result in modest reductionsin the processing cost and energy usage. Ex-cept for improvements in grain and sugar proc-essing, the R&D could also be applicable to theproduction of ethanol from cellulosic materi-als. Some possible improvements in grain proc-essing, fermentation, and alcohol recovery arementioned below.

Grain and Sugar Processing

Developments in the last 20 years have ledto more or less continuous grain preprocessingtechniques which have lowered the costs overthe traditional batch processes. Novel meth-ods have been proposed, however, such asheating the mash with electrical current ratherthan process steam. This allows production ofa more concentrated sugar solution, therebyreducing the load on evaporators at laterstages in the operation. While this is a moreenergy-intensive pretreatment, it could lowerthe overall processing energy. 36

The pr incipal problem with sugar feed-stocks, as noted, is the necessity of processinglarge quantities of feedstock to a syrup forstorage. At Ieast one research group is studyingways to store the sugar crops without reduc-tion to syrup,37 but the details are proprietary.

Fermentation

The key to cost reductions in fermentation isthe use of methods for maintaining a highyeast or bacteria concentration in the mash, so

“Raphael Katzen Associates, Crain Motor Fue/ A/coho/, Tech-nical and Econom(c A~sessment Study, op c[t

“E Llplnsky, Battelle C o l u m b u s L a b o r a t o r i e s , C o l u m b u s ,Ohio, private communtcatlon, 197!I

that the fermentation proceeds rapidly—there-by reducing the size and number of fermenta-tion vessels required. The two ways of doingth i s a re th rough c o n t i n u o u s f e r m e n t a t i o n o rthrough recycling of the yeast.

Continuous fermentation processes havebeen tested in full-scale operation. Due to thepossibility of infection of the mash (resulting inthe production of products other than etha-nol), the processes have two complete fermen-tation systems to allow periodic switchoverand ster i l i zat ion. The added cost for th isequipment effectively nullifies the cost advan-tage of continuous fermentation. 38 Improvedhandling techniques, which can assure sterileoperation, may obviate the necessity for thisredundancy in equipment.

One type of continuous fermentation that isunder R&D uses a vacuum over the fermenta-tion mash. The ethanol is drawn off by thevacuum as it is produced, with the necessaryheat for the evaporation of the alcohol beingsupplied by the fermentation process itself.This would reduce the need for cooling wateras well as accelerate the fermentation (whichis slowed by high ethanol concentrations).While added equipment costs might reduce ornullify the potential savings, the question ofwhether this will be the case has not been re-solved.

Another way of maintaining a high yeastconcentration is by recycling the yeast (after itis separated from any grain solids that are tobe sold as a byproduct). A hybrid of yeast re-cycling and continuous fermentation involvesa device called a countercurrent flow fermen-tation tower,39 in which the yeast flows oneway (counter to the current) whiIe the sugars tobe fermented flow in the opposite direction.The high yeast concentrations require addi-tional cooling of the mash, which increases thecooling equipment costs somewhat, but re-search in this area can probably result in someoverall cost savings.

“Raphael Katzen Associates, Grain Motor Fuel Alcohol, Tech-nica/ and Economic Assessment Study, op. clt

“lbld

176 • Vol. Il—Energy From Biological Processes

Distillation

The distillation process in the corn-to-fuel-ethanol distillery considered above consumesnearly half of the energy used at the distillery.Lowering the energy requirements for separat-ing the ethanol from the mash is desirable for afuel ethanol facility in any case, but the in-creased equipment costs for advanced ethanolseparation techniques could counter part or allof the potential cost savings from lower fueluse and smaller boiler and fuel-handling re-quirements. Consequently, R&D into this areamust address both the energy use and theequipment cost.

One way to lower the energy requirementsof distillation is to produce a mash with anethanol concentration higher than the usual 10percent. This would require development ofyeast or bacteria that are tolerant of the highalcohol concentrations. Since it would be ex-pected that any yeast or bacteria producingethanol would produce it more slowly at thehigher ethanol concentrations, this might re-quire longer fermentation times with a conse-quent increase in the cost of fermentationequipment. It may be possible, however, tocombine this with advanced fermentationmethods to provide an overall savings.

Several methods have been suggested for re-moving the ethanol from the water. These in-clude:

●

●

●

membranes using reverse osmosis (some-thing like a super filter that allows thewater or ethanol to pass through the mem-brane while preventing the other compo-nent from doing so);absorption agents (solids which selective-ly absorb the ethanol are then separatedfrom the solution, with the ethanol finallybeing removed from the solid); andliquid-liquid extraction (extracting the eth-anol into a liquid that is not soluble inwater, physically separating the liquids,and removing the ethanol from the otherliquid).

All of these processes, however, are likely torequire that the yeast and grain sol ids be re-

moved from the mash first, so that they do notinterfere with the ethanol concentration step(e.g., by clogging the membrane). Little re-search has been done in producing a clarifiedsolution from the mash, hence, the costs forthese methods are highly uncertain.

Numerous other suggestions exist, and re-search in these areas may eventually produceusable results. One example is the use of super-critical CO2. When gases are subject to highpressures at suitable temperatures, they form afluid which is neither gas nor l iquid, but iscalled a supercritical fluid. The properties ofsupercritical fluids are largely unresearched,but there are proprietary claims that super-critical CO 2 could be suitable for extractingethanol from the mash. The pressure wouldthen be lowered, the CO2 would become a gas,and the ethanol would Iiquefy.

Another possibility is the use of phase sep-arating salts. Salts, when dissolved in a liquidchange the liquid’s structure and properties. Ithas been suggested that there may be saltswhich would attract the water (or ethanol) sovigorously and selectively that the ethanol-water mixture wouId separate into two phases,with one being predominantly water and theother predominantly ethanol.

These novel approaches should be investi-gated, but it is not possible to predict when orif results applicable to commercial fuel etha-nol production will emerge.

Producing Dry Ethanol

In a large, commercial distillery, the produc-tion of dry ethanol only costs $0.01 to $0.03/gal(of ethanol) more than the production of 95percent ethanol .40 (The difference in the sellingprice per gallon of 99.5 percent ethanol and 95percent ethanol is due primarily to the factthat the latter contains 4.5 percent less ethanolper gallon of product.) Furthermore, with mod-ern heat recovery systems, the production ofdry ethanol requires very little additional ener-gy. Consequently, little economic or energysavings are available here.

‘“I bid


On the other hand, the additional cost ofequipment for producing dry ethanol automat-ically onfarm with conventional technologymay be prohibitive. If the distillery is of thelabor-intensive type, however, the additionalequipment cost would be small since the samestill could be used to produce 95 percent etha-nol and then later used to distilI to dry ethanol.

Drying agents or desiccants, however, maybe a suitable substitute for the conventionalprocess. These materials would selectively re-

move the water from 95 percent ethanol. vari-ous chemicals are known to do this and recentresearch indicates that corn stover or corngrain may even be suitable.41 It is not known,however, how much ethanol would be lost inthe process or, if grain is used, whether the ab-sorbed ethanol would inhibit the production ofsugar from the starch. While the processes areundoubtedly technicalIy possible, the econom-ics are still highly uncertain.

4’M. R Ladlsch and K Dyck, Science, vol 205, p 898, 1979

Chapter 9

ANAEROBIC DIGESTION

Chapter 9.–ANAEROBIC DIGESTION

PageIntroduction . . . . . . . . . . . . . . . . . . . . . .181Generic Aspects of Anaerobic Digestion. . .181

Basic Process . . . . . . . . . . . . .181F e e d s t o c k s . . . . . . . . . . . . . 1 8 2Byproducts. . . . . . . . . . . . . . . . . . ....182

Reactor Types. . . . . . . . . . . . . . . . . . . . . . . . . . . . 184Single-Tank Plug Flow . . . . . . . . . . . . . . .184Multitank Batch System. . . . . . . . . . . . . 184Single-Tank Complete Mix. . . . . . . . . . . .184Anaerobic Contact, . . . . . . . . 184Two or Three Phase . . . . . . . . . ...187Packed Bed . . . . . . . . . . . . . . . . . . . . . . . . . . . . .188Expanded Bed . . . . . . . . . . . . . . . . . . . . . 189Variable Feed. . . . . . . . . . . . . . . . . . . . . .189

Existing Digester Systems . . . . . . . . . ..................191Economic Analysis. . . . . . . .. . . . . . ......................191Environmental lmpacts of Biogas Production:

Anaerobic Digestion of Manure. . . . . . . .........,195Research, Development, and Demonstration

Needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..198Microbiology . . . . .198Eng ineer ing . . . . . . . . . . . . . . . . . . 198Agriculture. . . . . . . . . . .. . . . . . . . . . . . . . 98

TABLESPage

56. Suitability of Various Substrates forAnaerobic Digestion. . . . . . .183

Page57. Anaerobic Digester Systems. . . . . . . . . . ...18558. investment Cost for Various Anaerobic

Digester System Options . ..............19259. Anaerobic Digestion: Energy Balance, or

the Energy Production Potential andEnergy Consumption Potential ofindividual Farms in Major Producing States. 193

60. Cost of Various Digesters With ElectricGenerating Capabilities . . . . . . . . . . . . . . .194

61. Annual Costs and Returns From DigesterEnergy Only . . . . . . . . . . . . . . . . . . . . ....194

62. Economic Feasibility of AnaerobicDigestion , . . . . . . . . . . . . . . . . . . . . . . . . . 195

FIGURES

Page28. Chinese Design of a Biogas Plant. . . . . ..18529. Diagram of a Gobar Gas Plant . ..........18630. Plug Flow Digestion System . , . . . . . . . . . .18631, Single-Tank Complete Mixed Digester .. ...18732. Two-Stage Digester . . . . . . . . . . . . . . . . ..18733. Two-Phase Digestion of Cellulosic Feed. ...18834. Packed-Bed Digester . . . . . . . . . . . . . . . . .18935. Expanded-Bed Reactor. . . . . . . . . . . ..19036. Variable Feed Systems . . . . . . . . . .190

Chapter 9

ANAEROBIC DIGESTION

Introduction

Anaerobic (“without air”) digestion is theprocess that occurs when various kinds of bac-teria consume plant or animal material in anairtight container called a digester. Tempera-tures between 950 and 140°F favor bacteriathat release biogas (50 to 70 percent methane— essentially natural gas — with most of the re-mainder as carbon dioxide — CO2). The bacte-ria may be present in the original materialwhen charged (as is the case with cattle ma-nure) or may be placed in the digester when itis initially charged. The gas has the heat valueof its methane component, 500 to 700 Btu/stdft3, and can be used directly as a heat fuelor in internal combustion engines. I n somecases there is enough hydrogen sulfide (H 2S )present to cause corrosion problems, particu-larly in engines. H2S can be removed by a sim-

ple, inexpensive, existing technology. CO2 canbe removed by a somewhat more complex andexpensive technology, which would need to beemployed if the gas is to be fed into a naturalgas pipeline.

The anaerobic digestion process is especial-ly well adapted to slurry-type wastes and hasenvironmental benefits in the form of treatingwastes to reduce pollution hazards and to re-duce odor nuisances. Furthermore, the residualfrom the process can be returned to land, ei-ther directly or through animal refeeding tech-nologies, and thus retain nitrogen and organiclevels of soil. Most other biomass energy con-version processes more nearly totally destroythe input material.

Generic Aspects of Anaerobic Digestion

The anaerobic digestion process involves anumber of different bacteria and a digester’sperformance depends on a large number ofvariables. The basic process is considered firstand then the feedstocks and byproducts of theprocess.

Basic Process

Not all of the bacteria involved in anaerobicdigestion have been identified and the exactbiochemical processes are not fully under-stood. Basically, however, the process consistsof three steps: 2 1 ) decomposition (hydrolysis)of the plant or animal matter to break it downto usable-sized molecules such as sugar, 2)conversion of the decomposed matter to or-

1 j j WOIIS, Arnerlcan /ourna/ 01 C /inlcal Nutrition, 27 (11), p

1120, 1974

‘E C Clausen and I L Caddy, “Stagewlse F e r m e n t a t i o n o ff310mass to Methane, r’ Department of Chemical E nglneerlng,Unlverslty ot Ml~~ourl, Rolla, Mo , 1977

ganic acids, and 3) conversion of the acids tomethane. Accomplishing these steps involvesat least two different types of bacteria.

The rate at which the biogas forms will de-pend on the temperature (higher temperatureusually gives a faster rate) and the nature ofthe substrate to be digested. Cellulosic mate-rials, such as crop residues and municipal solidwaste, produce biogas more slowly than sew-age sludge and animal manure. Disturbancesof the digester system, changes in temperature,feedstock composition, toxins, etc., can leadto a buildup of acids that inhibit the methane-producing bacteria. Generally, anaerobic di-gestion systems work best when a constanttemperature and a uniform feedstock aremaintained.

When a digester is started, the bacterialcomposition is seldom at the optimum. But ifthe feedstock and operating conditions areheld constant a process of natural selection

181


takes place until the bacteria best able tometabolize the feedstock (and thus grow) dom-inate. Biogas production begins within a day orso, but complete stabilization sometimes takesmonths.

Numerous sources for good anaerobic bac-teria have been tried, though the process is ba-sically one of hit and miss. The potential forimprovement cannot be assessed at this time.Future developments could produce superiorgenetic strains of bacteria, but too little isknown about the process to judge if or whenthis can be accomplished. It is quite possiblethat if such strains are to be effective, the in-put material may first require pasteurization.

Biogas yields vary considerably with feed-stock and operating conditions. Operating adigester at high temperatures usually increasesthe rate at which the biogas is formed, but rais-ing the temperature can actually decrease thenet fuel yield as more energy is required toheat the digester. The optimum conditions forbiogas yields have to be determined separatelyfor each feedstock or combination of feed-stocks.

Feedstocks

A wide range of plant and animal matter canbe anaerobically digested. Both the gas yieldsand rates of digestion vary, Generally materi-als that are higher in Iignin (e. g., wood andcrop residues3) are poor feedstocks becausethe Iignin protects the cellulose from bacterialattack. Pretreatment could increase their sus-ceptibility to digestion. ’ However, even thendigestion energy efficiencies generally do notexceed 50 to 75 percent. Thus, more usable en-ergy can generally be obtained through com-bustion or thermal gasification of these feed-stocks (see ch. 5).

The best feedstocks for anaerobic digestionusually are wet biomass such as fresh animal

‘See also, J T Pfeffer, “131010 glcal Conversion of Crop Resi-dues to Methane, ” In Proceedings of the Second A nnual S ympo~i-urn on Fue/\ for Bioma\s, Troy, N Y , June 20-22, 1978

4P L McC~rty, et al , “Heat Treatment of Biomass for increas-ing Blodegradabllity, ” In Proceeding~ of the Third Annual Bio-mass Energy Systems Conference, sponsored by the Solar EnergyResearch Institute, Golden, Colo , June 1979, TP-33-285

manure, various aquatic plants, and wet food-processing wastes such as those that occur inthe cheese, potato, tomato, and fruit-process-ing industries. See table 56 for a summary ofthe suitability of various feedstocks for diges-tion.

The digesterwell as most of

Byproducts

effluent contains bacteria asthe undigested material in the

feedstock (mostly Iignocellulose) and the solu-bilized nutrients. The process has the potentialfor killing most disease-causing bacteria, butvolatile losses of ammonia may increase withanaerobic digestion. 5

The most generally accepted technology fordisposal of the effluent is to use it as a soil con-ditioner (low-grade fertilizer). Animal manureis already used widely for this but there is somecontroversy over whether the digester effluentis a better source of nitrogen than the undi-gested manure. * The actual added value (ifany) as a fertilizer, however, will have to bedetermined experimentally and is likely to behighly feedstock specific. The effluent mayalso be used as fertilizer for aquatic plant sys-tems. In one case the effluent is dewatered andused as animal bedding in place of sawdust. G

Another potential use of the effluent is as ananimal feed. It has been claimed that the pro-tein mix in the cake obtained from dewateringthe effluent is superior to that of undigestedmanure. 7 Biogas of Colorado has concluded asuccessful animal feeding trial of digester cakeand Hamilton Standard has also done feedingtr ia ls .8

‘J A. Moore, et al , “Ammonia Volatilization From Animal Ma-nures, ” in Biomass Uti/lzation in Minnesota, Perry Black shear,ed , National Technlcai Information Service

● The nitrogen IS more concentrated In the effluent, but It ISalso more volatile

‘John Mart[n, Scheaffer and Roland, Inc , Chicago, Ill, privatecommunication, 1980

‘B G Hashlmoto, et al , “Thermophllllc Anaerobic Fermenta-tion of Beef Cattle Residues, ” In Symposium on Energy From Bio-mass and Wastes, Institute of Gas Technology, Washington,D C , Aug 14-18, 1978

‘D J Llzdas, et al , “Methane Generation From Cattle Resi-dues at a Dirt Feedlot, ” DOE report COO-2952-20, September1979

Ch. 9—Anaerobic Digestion ● 1 8 3

Table 56.-Suitability of Various Substrates for Anaerobic Digestion

Feedstock Availability Suitability for digestion Special problems

Animal wastesDairy . . . . . . . . . . . .Beef cattle ., ., .,

Swine . . . . . . . .

Chicken . . . . . . . . .

Turkey. . . . . . . .

Municipal wastesSewage sludge . . . . .Solid wastes . . . . . . .

Crop residuesW h e a t s t r a w . .

Corn stover. . . . . . . .

GrassesK e n t u c k y b l u e .

O r c h a r d g r a s s .

Aquatic plantsWater hyacinth . . . . .

Algae. . . . . ., . . .Ocean kelp . . . . . . .

Various woods. . . .

Kraft paper. . . . . . . .

Small- to medium-sized farms, 30-150 headFeedlots, up to 1,000-100,000 cattle

100-1,000 per farm

10,000-1,000,000 per farm

30,000-500,000 per farm

All towns and citiesAll towns and cities

Same cropland

Same cropland

Individual home lawns

Midwest

Southern climates, very high reproductionratesWarm or controlled climatesWest coast, Pacific Ocean, large-scale kelpfarms

Total United States

Limited

ExcellentExcellent

Excellent

Excellent

Excellent

ExcellentBetter suited to directcombustion

Poor, better suited todirect combustion

Poor, better suited todirect combustion

Very good

Fair

Very good

GoodVery good

Poor, better for directcombustion or pyrolysis

No major problems, some systems operating.Rocks and grit in the feed require degritting, somesystems operating.

Lincomycin in the swine feed will inhibitdigestion–full-scale systems on university farms.

Degritting necessary, broiler operations need specialdesign due to aged manure, tendency to sour.

Bedding can be a problem, manure is generally aged, nocommercial systems operating.

Vast experience.Designed landfill best option

Particle size reduction necessary, low digestibility, nocommercial systems.

No commercial systems, no data available, particle sizereduction necessary.

Distribution of feedstock disperse, no commercialsystems.

No commercial systems, no data on sustainability ofyields.

No commercial operations, needs pregrinding.

Longer reaction time than for animal wastes.Full-scale operations not proven, no present value foreffluent.

Will not digest.

Excellent, need to evaluate Premixing watering necessary.recycle potential andother conversion

SOURCE Tom Abeles and David Ellsworth, ‘‘Blologlcal Production of Gas, contractor report to OTA by I E Associates, Inc., Minneapolis, Minn. , 1979

Although most of the disease-causing bacte-ria are killed by digestion of the manure, sev-eral questions about refeeding of digester ef-fluents need to be resolved. Buildup of toxicmaterials, development of resistance to antibi-otics by organisms in the cake, permissiblequantities of cake in the diet, storage, andproduct quality are all issues that have beenraised. There is no firm evidence that these willpresent significant problems, however.

To avoid some of these problems, the Foodand Drug Administration has generally favoredcross-species feeding, but has not sanctioned

its use as a feed or feed ingredient.9 The use ofdigester effluents as an animal feed, however,would greatly improve the economics of ma-nure digestion. Consequently, the value, use,and restrictions on using digester effluents asanimal feeds should be thoroughly investi-gated. Moreover, the animal feed value of ef-fluents from the digestion of feedstocks otherthan manure should also be investigated.

9T P Abeles, “Design and Englneerlng Conslderatlons In PlugFlow Farm Digesters, ” In Symposium on C/can Fue/s From Bio-mass, Institute of Gas Technology, 1977

184 . Vol. Ii—Energy From Biological Processes

Reactor Types

There are numerous possible designs for an-aerobic digesters, depending on the feedstock,the availability of cheap labor, and the pur-pose of the digestion. The most complex andexpensive systems are for municipal sewagesludge digestion, but the primary purpose ofthese has been to stabilize the sludge and notto produce biogas.

Digester processes have been classified intothree types, depending on the operating tem-perature: 1 ) psychrophilic (under 680 F), 2) mes-ophilic (680 to 1130 F), and 3) thermophilic(11 30 to 150° F). The cost, complexity, and en-ergy use of the systems increase with the tem-perature, as does the rate of gas production.The amount of gas produced per pound offeedstock, however, can either increase or de-crease with temperature. Retention time is alsoan important consideration, wherein maximumgas production per pound of feedstock is sacri-ficed for reduced size and cost of the digester.Anaerobic digesters in the mesophilic and ther-mophilic ranges have used agricultural wastes,residues, and grasses, to produce biogas. Theoptimum temperature appears to be both siteand feedstock specific. There are still unre-solved technical questions about the tradeoffsbetween mesophilic and thermophilic digest-ers, but most onfarm systems have been meso-philic.

Other design parameters include continuousversus batch processes, mixed versus unmixedreactors, and other features. Some of the ma-jor types are summarized in table 57 and dis-cussed briefIy.

Single-Tank Plug Flow

This system is the simplest adaptation ofAsian anaerobic digester technology (figures28-30). The feedstock is pumped or allowed toflow into one end of a digester tank and re-moved at the other. Biogas is drawn off fromthe top of the digester tank. The feed rate ischosen to maintain the proper residence time*

● The time the feedstock remains in the digester

in the digester and the feed or digester con-tents can be heated as needed. Depending onthe placement of the heating pipes, some con-vective mixing can also occur.

Multitank Batch System

This system consists of a series of tanks orchambers which are filled sequentially withbiomass and sealed. As each unit completesthe digestion process, it is emptied and re-charged. This type of reactor is best suited tooperations where the feedstock arrives inbatches, for example, grass or crop residuesthat are collected only at certain times of theyear or turkey or broiler operations that arecleaned only when the flocks are changed.This digester system, however, is relativelylabor intensive.

Single-Tank Complete Mix

The single-tank complete mix system (figure31) has a single rigid digester tank which isheated and mixed several times a day. It hasbeen argued that mixing enhances the contactof bacteria with the feedstock and inhibitsscum formation, which can interfere with di-gester operation. Theoretical calculations, ’”however, indicate that the mixing does not im-prove bacterial contact, and these calculationshave been confirmed experimentally in onec a s e . Single-tank complete-mixed digestersare used to treat municipal sewage sludge andhave been used in the larger anaerobic digestersystems (exclusive of landfills).

Anaerobic Contact

The single-tank complete-mix system efflu-ent can be transferred to a second unmixed

‘(’P C Augensteln, “Technical Prlnclples of Anaerobic Diges-tion, ” Dynatech R&D CO , presented at course fl/otechno/ogy for

Ut//izat/on of o r g a n i c Wastes, Unlversldad Autonoma Metropoll-tana, Iztapalapa, Mexico, 1978

“K D Smith, et al , “Destgn and First Year Operation of a50,000 Gallon Anaerobic D[gester at the State Honor Farm Dairy,Monroe, Washington, ” Department of Energy contract EG-77-C-06-1016, ECOTOPE Group, Seattle, Wash , 1978

Ch. 9—Anaerobic Digestion • 185

Table 57.–Anaerobic Digester Systems

Type of system Application and inputs Scale a Stage of development Advantages Disadvantages

Landfill municipal solid wastes,sewage sludge, warmclimates

All types of organics, farmand feedlot operations

Low cost, tanks not re- Gas generation may Iast onlywaste and up landfills, controlled land quired, high loading rates 10 years in “as is” land-(28-acreIandfill)

Small to large

filling in pilot stages

Commercial

possible, no moving parts

Low cost, simple designcan run high solidswastes, can have gravityfeed and discharge

Simple, low maintenance,low cost, complete diges-

tion of materials

Proven reliability, workswell on all types ofwastes

Smaller tank sizes,operation not overlycritical

Allows more completedecomposition, greatergas yields, greater load-ing rates, lower retentiontimes

High loading ratespossible, short retentiontimes

High loading rates, lowtemperature digestion,high quality gas, shortretention times

Fast throughput, highloading rates, highersolids input than packedbeds

Allows seasonal peaking of

fills, gas usage onsite maypresent problems

Low solids wastes maystratify

Single-tank plugflow

Multitank batchsystem

Can accept all types ofwastes, limited applicationcrop residues, grasses,chicken broilers, turkeys

All types of organics sewagetreatment, farm and feedlot,municipal solid wastes

Sewage sludge and otherorganics, limited apphcation(see variable feed)

Celluloslc feedstocks

Small to large Commercial, in Asia Gas generation notcontinuous, labor-intensive

feed and discharge, low gasproduction per day

Greater input energy to runmixers, higher cost thanplug flow

Two tanks necessary

Single-tankcomplete mix

Anaerobic contact

Small to large Commercial

Commercial, for sewagetreatment

Pilot scale

Medium tolarge

Medium tolarge

Two or three phase Feed rates vary withfeedstocks, have not beenattempted full scale, requiretight controls and manage-ment of the operation

Tends to clog with organicparticles, Iimited to dilutewastes

Packed bed Dilute organics–sewage,food-processing wastes,very dilute animal wastes—Industrial and commercial

Dilute organics-sewage,food-processing wastes,very dilute animal wastes

Medium tolarge

Commercial, as wastetreatment technology

LaboratoryExpanded bed Undetermined Not developed, high energyinput to operate pumps, nooperating data

Tends to clog, high pumpingenergy input no operatingdata

Feed-discharge may requireextra pump

Mixed bed

Variable feed

Sewage sludge, animalwastes, food-processingwastes–fairly dilutemixtures

All types of organics, farmsand feedlots

Small to large Pilot scale

Small to Conceptual–combinesmedium plug flow with anaerobic gas production, pre-

contact serves nutrient value ofmaterial, low cost

ascaje def[ned as small–o to 30,000 gal med!um–30 000 to 80000 gal. andlarge–over 80,000 gal

SOURCE Tom Abeles and David Ellsworth Blologlcal Produchon of Gas ‘‘ contractor report to OTA by I E Associates Inc M!nneapohs, Mlnn 1979

Figure 28.—Chinese Design of a Biogas Plant

Gas ventpipe Outlet C o v e r Gas outlet pipeInlet

S l u d g e c h a m b e rOver-

flow

Base

SOURCE: K. C. Khandeleval, “Dome-Shaped Biogas Plan,” Compost Science, March/Apr!l 1978.


Figure 29.—Diagram of a Gobar Gas Plant (Indian)

rrypit

All dimensions in meters

SOURCE: R. B. Singh, “Biogas Plant,” Gobar Gas Research Station, Ajitmal, Etaweh (V.P.), India, 1971

Figure 30.-Plug Flow Digestion System

Cross section

Gas utilization system

SOURCE: W. J. Jewell, et al., “Low Cost Methane Generation on Small Farms,” presented at Third Annual Symposium on Biomass Energy Systems, Solar EnergyResearch Institute, Golden, Colo., June 1979

Ch. 9—Anaerobic Digestion . 187

Figure 31. —Single-Tank Complete Mixed Digester

Digester gast

Raw Active

sludge 4 zoneexchanger

Digested sludge

SOURCE Environmental Protection Agency, “Process Design Manual, SludgeTreatment and Disposal ,” EPA 625/1-29-001, September 1979

and unheated storage tank. Here the biomassundergoes further digestion and solids settleout (figure 32). In other words, by adding a sec-ond, inexpensive digester tank gas yields canbe improved. These systems have been u s e dextensively in sewage treatment and may re-ceive wide application where preservation ofthe effluents nutrient value requires coveredlagoons or in short throughput systems locatedin warm climates.

Two or Three Phase

As mentioned previously under “Generic As-pects of Anaerobic Digestion, ” the basic proc-ess consists of a series of biochemical steps in-volving different bacteria. The idea behind themultitank systems is to have a series of digest-er tanks (figure 33) each of which is separatelyoptimized for one of the successive digestionsteps. The rationale behind such system is thehypothesis that they: 1 ) can accept higher feed-stock concentrations without inhibiting thereactions in successive stages, 2) have greaterprocess stability, 3) produce higher methaneconcentrations in the biogas, and 4) requirelower retention times in the digester than withmost single-phase digesters. The majority ofthe work on this approach has been on munici-pal sewage sludge, although the Institute forGas Technology hopes to eventually transferthe technique to kelp digestion. The need foruniform feed rates and controls may limit theuse of two or muItiphased systems to larger orextremely well-managed operations; but thistype of reactor should be carefully examinedfor other anaerobic digestion applications be-cause of its potentialIy high efficiencies.

Figure 32.—Two-Stage Digester

Digester

Primary digester

Transfer

gas

Supernatant

sludge

1 Digested

sludge -

Secondary digester

SOURCE Environmental Protect Ion Agency, “Process Design Manual, Sludge Treatment and Disposal,” EPA 625/29-001, September 1979


Figure 33.—Two-Phase Digestion of Cellulosic Feed

Gas

SOURCE S Ghos and D. L Klass, “Two Phase Anaerobic Digestion,” Symposium on Clean Fuels f rom Biomass ( Inst i tute of Gas Technology, 1977)

Packed Bed (Anaerobic Filter)

In this system a dilute stream of feedstock isfed up through a verticle column packed withsmall stones, plastic balls, ceramic chips, orother inert materials (figure 34). Because thebacteria attach themselves to the inert mate-rial, it is possible to pass large quantities offeedstock through it while maintaining a highbacterial concentration in the digester. Thesystem is best suited to municipal sewage (andother dilute feedstocks). More concentratedfeedstocks tend to clog the column.

Analyses of bench-scale laboratory resultson the AN FLOW system indicate that the sys-tem could produce enough energy to make thissewage treatment step energy self-sufficient. 12

‘JR K Genung and C D S c o t t , “ A n Aneroblc Bloreactor(AN F1.OW) for Wastewater Treatment and Process Appl(ca-tlons, ” briefing presented to the Subcommittee on E nergv andPower, HOLJJ(J I nter$tate and Foreign Commerce Committee,Nov 1, 1979

As it now exists, however, it is not well suitedto energy production.

Like the packed and expanded bed, themixed-bed systems are intended to provide aninert substance to which the bacteria can at-tach, thereby preventing them from beingflushed out with the effluent. The digestermaintains a higher bacteria population. Vari-ous designs include netting,13 strips of plastic,and rough porous digester walls. In all cases,the inert substance increases the resistance toflow and thus the energy needed for pumpingincreases too, but it decreases the necessaryreactor size. Sufficient data are not yet avail-able for a detailed analysis of this tradeoff.

‘ ‘S A St’rfl Ing and C Alsten, “An I nt~gratd, Controlled E nvl-ronment A q u i c u l t u r e Lagoon Proce\\ t o r S e c o n d a r y o r Ad-vanced Wastt>water Treatment ,“ Sol ar Aqua\ y\tem\, I nc , En-clnltas, Cal If , 1978

Ch. 9—Anaerobic Digestion ● 189

Figure 34.—Packed-Bed

System gasp r e s s u r e

Digester

Process gaschromatography

G a s p u m p

F l o w Magne t i c

contro l va lve f l o w

pH andtemperature

probescomposite

samp les

5 ft diax

10 ft highpackedsection

gas meter

pH andtemperature

probes

Weir box composite

flow meter samplers

Bar screens

SOURCE R K Genung. W W Pitt, Jr , G M Davis, and J H Koon, “Energy Conservation and Scale-Up Studies for a Wastewater Treatment System Based on a Fixed-Film, Anaerobic Bioreactor,” presented at 2nd Symposium on Biotechnology in Energy Production, Gatlinburg, Term Oct 2-5, 1979

Expanded Bed

A var ia t ion on the packed-bed concept is the

expanded-bed reactor ( f igure 35) . I n th is case

the co lumn pack ing is sand or o ther very smal l

p a r t i c l e s . T h e f e e d s t o c k s l u r r y i s f e d u pthrough the column and the bed of inert mate-rial expands to allow the material to passthrough. A semifluidized state results, reduc-i n g t h e p o t e n t i a l f o r c l o g g i n g w h e n r e l a t i v e l y

c o n c e n t r a t e d m a t e r i a l i s f e d i n t o t h e r e a c t o r ,

T h e process has been found to be qu i te s tab le

wi th h igh organic inputs , shor t res idence t imes

in the digester, and relatively low temperatures(50° to 70° F).14 The study did indicate, how-

ever, that the process would not be a net ener-gy producer due to the energy required to ex-pand the bed.

Variable Feed

The idea behind variable feed systems (fig-ure 36) is to store undigested manure in timesof low gas demand for use during periods ofhigh demands. The key is to be able to storethe manure for long periods (e. g., 6 months)without excessive deterioration. The effect oflong-term storage is being investigated,15 butthe systems may be limited to areas with coolsummers or to operations in which the gas isused to generate electricity for export duringthe peak electric demand periods in summer.

‘“W J Jewel 1, (.orn[~l I Un Iveriitp, I t ha( ,1, N } , {)rlv,ltt> c onlnjLl-

nlc,l tlon, 1978


Figure 35.—Expanded Bed Reactor

I

Feed

Pump

Gas

IRecycle AAFEB

IIpump Effluent

SOURCE: M. S., Switzenbaum and W. J. Jewell, “Anaerobic Attached Film Expanded Bed Reactor Treatment of DiluteOrganics,” presented at 51st Annual Water Pollution Control Federation Conference, Anaheim, Calif., 1978.

Figure 36.—Variable Feed Systems

H2O

Manure

SOURCE Tom Abeles and Oawd Ellsworth, “Blologlcal Produchon of Gas, contractor report to OTA by I E Associates, Inc , Mmneapolm, Mmn 1979


Existing Digester Systems

Fourteen experimental and prototype digest-ers of animal manure were identified as opera-tional in 1978. ’6 The capacity of these plantsvaries from less than 1,500 gal to 4 million gal.Two of the prototypes are owned by individualfarmers and are sized for farm use. The 12others are owned by private firms, universities,or the Federal Government.

Since then, however, the field of anaerobicdigestion has been advancing rapidly, and anylist of existing operations would be quicklyoutdated. Several companies currently designand sell digesters and the support equipment.Most systems are currently designed for cattlemanure. One example of an apparently suc-cessful digester system is on a dairy farm inPennsylvania. The digester is fed by 700 head

“D L Klass, “Energy From Biomass and Wastes, ” In Syrnposi-urn on Energy from L?lomass and Waste, I nstltute of Gas Technol-ogy, Washington, D C , Aug 14-18, 1978

Economic

Aside from the paper and other digestablematter in municipal solid waste (which is notincluded in this report), the best feedstocks foranaerobic digestion are animal manure, sometypes of grasses, aquatic plants, and variousprocessing wastes. The supply of aquaticplants is likely to be small in the next 10 yearsand l i t t le information is avai lable on thedigester requirements for grasses. Furthermore,with grass at $30/dry ton, the feedstock costalone would be $4.50/milIion Btu. More energyat a lower cost can usually be produced fromgrass by thermal gasification or combustion.Hence, animal manure and some processingwastes are the most promis ing near-termsources of biogas by far. The larger of thesetwo sources is animal manure.

More than 75 percent of the animal manureresource istions that hequivalent250,000 chi

located on confined animal opera-ave less than 800 dairy cows or theweight of other animals (e. g.,

ckens). Large feedlots account for

of cattle and has been functioning since latefall 1979. The biogas is fed into a dual-fueldiesel engine and supplies about 90 percent ofthe engine’s fuel needs. The engine drives a125-kW generator (for peak electric demands)and the generator has an average output of 45kW. The system supplies essentially all of theoperation’s direct energy needs.

Other systems are operational or are likelyto become operational soon. Nevertheless, op-erating experience is limited and suitable di-gesters for all types of manures and combinedanimal operations are currently not available.Consequently, commercialization of the tech-nology could be helped by demonstrating awide range of digester systems in a variety ofconfined animal operations so as to provideoperating experience and increase the numberof operations for which suitable digester sys-tems exist.

Analysis

less than 15 percent of the resource or lessthan 0.04 Quad/yr (see ch. 5 in pt. l). Since it isrelatively expensive to transport manure longdistances, this economic analysis concentrateson digesters appropriate for onfarm use.

The system analyzed consists of a plug flowdigester operating at 700 to 90° F, with a feed-stock pond and effluent residue storage pit.(See top schematic, figure 36.) After removal ofthe hydrogen su l f ide (H2S), the biogas isburned in an internal combustion engine togenerate electricity. The electricity is used onthe farm (replacing retail electricity) and theexcess is sold wholesale to the electric utility.The waste heat from the generator engine isalso used onfarm, but any excess heat goes towaste. On the average,15 percent of the ener-

gy produced is used to heat the manure enter-ing the digester and for the other energy needsof the digester (e. g., pumping). (Other systemsvary from 10 to 40 percent, depending on thetype of digester and the operating conditions.)


There is sufficient gas storage capacity tolimit electric generation to those times of theday when the utility or the farmer has peakelectric demands; and the feedstock storageallows for seasonal variations in the averagedaily energy production. Therefore, this sys-tem can be used either as a peakload or base-Ioad electric generating system. In a maturesystem, the electric utility would be able tocall for more or less electric generation fromonfarm units by sending coded signals alongthe electric powerlines.

Other systems are possible, including one inwhich the water in the digester effluent islargely removed (dewatered) and the resultantmaterial sold as a fertilizer or animal feed.Table 58 shows the cost of various systems; thebasic digester cost represents the sum of thecosts for digester, pumps, pipes, hot waterboilers, H2S scrubber, low-pressure gas com-pressor, heat exchangers, and housing. Thecost of the manure premixing equipment isalso included with tanks larger than 40,000 gal.However, these costs should be viewed as pre-liminary and approximate.

Removal of the CO2 and sales of the gas tonatural gas pipelines were assumed not to befeasible in small operations because: 1) the gaspipelines often are not readily accessible, 2)the cost of CO2 removal equipment is high,and 3) revenues from the gas sales would prob-ably be relatively low. In very large systems,though, production of pipeline quality gas maybe feasible.

Table 59 gives the energy that could be pro-duced with onfarm digesters. It also shows thequantities that could be used onfarm and ex-ported for various animal operations in someof the major producing States if farm energyuse stays at 1974-75 levels or if it decreases 25percent due to energy conservation. In mostcases, the digester energy output is sufficientto meet the energy needs of the Iivestock oper-ation and in more than half of the cases con-sidered, it also fills the farmer’s home energyneeds and enables a net export of electricity.With conservation, the situation is even morefavorable with respect to energy exports. Thelower revenue that the farmer receives forsurplus energy as opposed to the replacementof retail energy, however, makes conservationless economically attractive unless the farmeris not energy self-sufficient without conserva-tion. In other words, it is more economicallyattractive to replace retail electricity than togenerate surplus electricity for sales at whole-sale rates.

The digester size, capital investment, andoperating costs for anaerobic digester-electricgeneration systems for these various opera-tions are shown in table 60. Assuming the farm-ers can displace retail electricity costing 50mi l l /kWh, sel l wholesale electr ic i ty for 25milI/kWh, and displace heating oil used on-farm costing $6/million Btu, the returns fromthe digester system are shown in table 61. Alsoshown are the farmer’s costs for two assumedcapital charges: 1 ) wherecharges are 10.8 percent 01

Table 58.–investment Cost for Various Anaerobic Digester System Options

thethe

annual capitalinvestment, i.e.,

Median capital costs ($1 ,000)

Options

Tank size (gallons) Basic digester Dewatering Electric generator Feedstock Iagoonb Residue pitc

10,000 . . . . . . . . . . . . . $ 19.6 $34.0 $ 4 . 0 $ 6.7 $ 0 . 420,000 . . . . . . . . . . . . . 33.7 34.0 5.0 13.4 0.840,000 . . . . . . . . . . . . . 48.1 34.0 6.0 26.9 1.680,000 . . . . . . . . . . . . . 65.6 45.0 12.0 53.7 3.2200,000 . . . . . . . . . . . . 98.8 60.0 45.0 133.0 7,5400,000 . . . . . . . . . . . . 143.6 90.0 70.0 268.3 15.2

aGeRerator IS In operation 12 hours each daybStorage for 6 monthscStorage for 9 months.

SOURCE Tom Abeles and Dawd Ellsworlh, ‘Biological ProductIon of Gas, ” contractor repofl 10 OTA by I E Associates, Inc , Mmneapolls, Mmn , 1979


Table 59.–Anaerobic Digestion: Energy Balance, or the Energy Production Potential and Energy Consumption Potentialof Individual Farms in Major Producing States

Methane energy Demands of livestock Household use Excess energy Excess energyoptions operation (1975 levels) (1974 levels) (25% conservation

Direct Electricity 1974 levels 25% conserv. Direct Electricity Direct Electricity

use Waste use Waste use Wasteonly heat only heat only heat

1974 livestock average number sold 1,000 1,000 1,000 1,000 1,000 1,000(inventory )/farm Btu 106 kWh Btu 106Btu 106 kWh Btu 106 kWh Btu 106 kWh Btu 106 kWh Btu 106Btu 106 kWh Btu 106

TurkeysMinnesota (124,000). . . . . ., 14,914 877California (98,000) . . . . . . .. . ..11,787 693North Carolina (89,000 . . . . . . . . . . . . .. .10,705 630BroilersMinnesota (52,000), . . . . . . . . 522 31

(198,000). .. . . . . . . . . . . . . . . . . . . . 1,986 117California (56,000) . . . . . . . . . . . . . 562 33

( 1 , 3 7 7 , 0 0 0 ) . . . . . . . . . . 1 3 , 8 1 2 8 1 2Arkansas (63,200) ., ., ., . . 634 37

(186,000) . . . . 1,866 110Swinelowa ., ., ... ., ... ., 325a 19Missouri . . 325a 19North Carolina (500) ., . . . . . 325a 19Dairy cowsWisconsin (36) ., ., . . . . . ., ., 261 15New York (71) ., ., ., 521 31California (337) . . . . . . . . . . . . . . . 2,459 145Laying hensMinnesota (13,000). ., . . . ., 846 50

(41,000) . . . . . . . . . . 2,670 157Georgia (14,000) . . . . . . . . . . . . 912 54

(41,000) . . . . . . . . . . . . . . . . . . . . . . 2,670 157California (14,000) . . . . 912 54

(105,000) . . . . . . . . 6,838 402Beef(500) . . . . . . . . . 1,527 90

9,545 8,7547,544 4,7146,851 1,931

248147160

6,5593,5361,448

186 326110 180120 128

161622

5,835 6136,893 5308,646 448

465 8,0292,650 8,0714,792 9,129

675567488

2,6603,8285,275

11 16341 163

8 90183 180

7 10720 107

888

1699

2 9457 54122 15

5,026 552213 19822 74

-186 91- 2 5 8 7 9 9

-80 21054 7,178

- 1 5 291150 1.056

126817

6132181

- 9 784

82,206

63384

334 3571,271 1,366

360 3508,840 8,606

406 3141 , 1 9 4 9 3 7

145510

2449

27

2681,024

2626,454

236703

208 147208 69208 29

282213

1105222

21 15516 13610 64

88

11

2 3 - 1 71 2 0 - 1 1232 -5

-94 603 137

115 239

– l o- 5- 2

- 5 720

123

-5 92182 376934 1,911

- 2188

1,026

167 11333 25

1,574 370

1633

133

819

278

12 16125 126

100 270

88

24

89 -93 7 0 - l o

1 , 8 1 9 - 1 2

- 5- 221

541 2131 , 7 0 9 6 7 2

584 1401 , 7 0 9 4 1 0

584 2244,376 1,680

977 –

34106349855

414—

160504105308168

1,260—

26 16380 16326 7274 7241 90

310 180— 160

88

10108

1610

470 81,835 43

700 102,188 49

598 -94 , 9 7 8 – 2 81.427 80

165 523874 2,003372 735

1,227 2,290270 654

2,516 5,398817 –

16691873

576—

2181,042’ 4 0 7

1,329326

2,936—

alncludes breeding stockAssumptions 15% of blogasused lorun digester system electrrc generational 20% effmency,and80% of the engmewaste heatcanbe recaptured

SOURCE Tom Abelesand David Ellsworth “Bloloqlcal ProducNon of Gas contractor reporl to OTA by I E Associates Inc , MmneaDohs, Mlnn 1979, Enerayafld L/ S Awrcu/ture, 1974 Da/a Base(Washington DC Energy Research and_Development AdmmlstraNon, 1974)

9-percent interest loan with 20-year amoritiza-tion, and 2) where the annual capital chargesare 15 percent of the investment.

The principal cost factor in anaerobic diges-tion is the capital charge, or the cost of the di-gester itself—thus, favorable financing is themost effective way of reducing the cost to thefarmer.

Financing aside, the anaerobic digestion op-erations that are most economically attractiveare relatively large poultry, dairy, beef, orswine operations (enabling an economy ofscale) which are also relatively energy inten-sive (enabling the displacement of relativelyIarge quantities of energy at retail prices) Forexample, anaerobic digestion on a broiler farm

“.

with 198,000 birds in Minnesota is more eco-nomically attractive than an equivalent oper-ation with only 52,000 birds (see table 61). Onthe other hand, the 52,000-bird broiler farm(equivalent to 250 head of cattle in terms ofthe quantity and quality of manure) is moreeconomically attractive than a 500-head cattlefeedlot, because the poultry operation con-sumes considerably more energy, and thuscould better utilize the digester output withinits own enterprise.

Based on 1978 fuel prices, the feasibility ofanaerobic digestion was assessed for varioustypes of farm animal operations in the variousregions of the country. It was found that itwould be feasible to digest so percent of the


Table 60.–Cost of Various Digesters WithElectric Generating Capabilities

Table 61 .–Annual Costs and Returns From Digester Energy Only

Return from1974 livestock Capital Annualaverage number sold Digester size investment operating costs(inventory )/farm (1,000 gal) ($1 ,000) ($1 ,000)

energydisplacement Digester costsand sales of (operating + capital) ($1,000)

1974 livestock electricity 10.8% annual 15% annual(inventory )/farm ($1,000) capital charge capital charge

TurkeysMinnesota (124,000) .California (98,000) . . . .North Carolina (89,000). .

BroilersMinnesota (52,000) . . . .

(198,000). . . .California (56,000) . . . . .

(1 ,377,000). . .Arkansas (63,200) . . . . .

(186,000) . . . .

SwineIowa (500). . . . . . . . . . .Missouri (500) . . . . . . .North Carolina (500) ... ,

Dairy cowsWisconsin (32). . . . . . . .New York (64) . . . . . . . .California (337). . . . . . . .

Laying hensMinnesota (13,000) . . . .

(41,000) . . . .Georgia (14,000) . . . . . .

(41,000) . . . . . .California (14,000) . . . . .

(105,000) . . . .

Beef(500).. . . . . . . . .

300250225

220195182

4.63.93.7

TurkeysMinnesota (124,000). . . .California (98,000) . . . . .North Carolina (89,000)..

BroilersMinnesota (52,000) . . . .

(198,000) . . .California (56,000) . . . . .

(1,377,000). . .Arkansas (63,200) . . . . .

(186,000) . . . .

Swinelowa (500). . . . . . . . . . .Missouri (500) . . . . . . . .North Carolina (500) . . . .

Dairy cowsWisconsin . . . . . . . .NewYork (64) . . . . . . . .California (337) . . . . . . .Laying hensMinnesota (13,000) . . . .

(41,000) . . . .Georgia (14,000) . . . . . .

(41,000) . . . . . .California (14,000) . . . . .

(105,000) . . . .

600/(500) . . . . . . . . .. . .

81 2851 2536 12

38333112

4513

3001440

256227

2202859

0.92.60.94.41.02.6

3,3 3.612 9.33.4 3.8

80 283.8 4.09.9 9.0

4.7125.0

375.2

11101010

272727

0.80.80.8 2.2 3.7

2.2 3.71.5 3.7

4.94.94,910

1080

243092

0.60.81.6 1.8 3.2

2.5 4.011 12

4.25.3

153410034

10035

250

20

5010350

10351

169

43

1.61.71.61.71.63.0

0.7

4.6 712 133.7 7.9.5 134.6 7.1

31 21

3.2 5.3

9.1179.1

179.3

28

7.2SOURCE SOURCE Tom Abeles and David Ellsworth, ’’Biological Production of Gas,’’ contractorreport to OTA by l. E Associates, lnc ,Minneapolis, Minn. ,1979

animal manure to produce electricity and on-site heat if the effective annual capital chargeswere 6.6 percent of the investment. (Digestionwas deemed feasible if the returns from dis-placing onsite energy use and wholesaling ex-cess electricity were greater than the capitaland operating costs for the anaerobic diges-tion energy system.) This effective capitalcharge could be achieved by a 9-percent in-terest, 20-year loan with 4.2-percent annual taxwriteoff. Other possible credits could be avail-able through combinations of AgriculturalStabil ization and Conservation Service pol-lution abatement cost sharing, soil conserva-tion district cost sharing, energy credits, andother incentives, although these are not in-cluded in the feasibility calculations. In table62, the percent of the manure resource thatwould be feasible for energy production withthe 6.6-percent capital charge is shown forvarious manure types and regions. Also shown

SOURCE SOURCE Tom Abeles and David Ellsworth, “Biological Production of Gas, ” contractorreport to OTA by I E Associates, Inc. , Minneapolis, Minn., 1979.

are the quantities of manure that would be fea-sible if the digester effluent were dewateredand sold as a fertilizer at $1 O/dry ton over therevenues available from sales of the raw ma-nure as a fertilizer. Furthermore, if the dewa-tered effluent could be sold for feed, highercredits may be possible based on the proteincontent of the effIuent.17 Although the feasibil-ity of these higher credits is unproven as yet,the selling of digester effluent as feed or fertil-izer would substantially expand the quantityof manure that could be digested economi-cally.

Turkey farms tend to be the most economicbecause of their rather large average size and

17 Blogas of Colorado, “Energy Potential Through Bloconver-sion of Agricultural Wastes, ” Phase //, Fina/ Report to the FourCorners Regiona/ Commission, demonstration pro]ect FCRC No672-366,002, Arvada, Colo , 1977


Table 62.–Economic Feasibility of Anaerobic Digestion (percent of total manure resource that can be utilized economicallya)

Total usableRegion manure problem Layers Broilers Turkeys Cattle on feed Dairy SwineNortheast . . . . . . . . . . . . . . . . . 52% 68% 82% 98% 6% 43%Southeast . . . . . . . . . . . . . . . . . . . .

—65 54 75 90 45 80

Appalachia . . . . . . . . . . . . . . . . . . .—

47 51 85 89 8 26Corn Belt . . . . . . . . . . . . . . . . . . .

—17 38 67 89 9 19 8%

Lake States . . . . . . . . . . . . . . . . . . 30 50 90 98 6 23 8North Plains . . . . . . . . . . . . . . . . . . 39 37 46 96 55 12Delta . . . . . . . . . . . . . . . . . . . . . . .

—69 68 82 86 21 37

South Plains . . . . . . . . . . . . . . . . . .—

82 76 87 94 90 49Mountain. . . . . . . . . . . . . . . . . . . .

—75 82 44 95 83 49

Pacific . . . . . . . . . . . . . . . . . . . .—

88 78 97 98 90 89Alaska. . . . . . . . . . . . . .

—69 0 0 0 0 82

Hawaii. ..., . . . . . . . . . . . . .—

70 35 82 0 89 99 —

National totals 4 9 + 2 0b

With fertilizer enhancement59 81 94 61 41 5

assumption of $10/dry ton . . . . . 69 + 30b 85 95 99 72 60 35

Investment Also assumes 1978 energy costs as follows home healing $3 80/mdhon Btu, farming heat $5 40/mlHlon Blu, retadelectrlclty accordlngto DOE, Typca/Hectm Ms. .larruary 1978, October1978, and wholesale elecrrlclty 25 mdl/kWh

bEstlmated uncertainty These correspond to weighted average percentages

SOURCE Tom Abeles and Dawd Ellsworfh, ‘Blologlcal Produchon of Gas, ‘‘ contractor report to OTA by I E Associates, Inc , Mmneapolls, Mmn , 1979

the relatively large amount of thermal energyconsumed by them. Swine operations, how-ever, are usually too small to be economicallyattractive, for the energy alone, but because ofodor problems these may also be attractive.

If 50 percent of the animal manure on con-fined animal operations in the United States isconverted to electricity and heat, about 7 bil-lion kWh of electricity per year (equivalent toabout 1,200 MW of electric generating capaci-ty) and about 0.08 Quad/yr of heat would beproduced by 0.12 Quad/yr of biogas. At 70- per-cent utilization, electricity equivalent to about1,600 MW of electr ic generat ing capacitywould be produced along with 0.11 Quad/yr ofheat.

In either case some of the heat would bewasted in the systems described above. There

is, however, the possibility of expanding theoperation to use the excess heat, for example,by building greenhouses. This could improvethe economics, but it would require major ad-justments in the farmer’s operation. In the end,site-specific economics and the inclination ofthe individual farmer will determine whethersuch options are adopted.

Care should be exercised when using thesedata. They are based on a number of approxi-mations and they cannot be taken too Iiterally.They do, though, indicate the general trends asto economic feasibility and they show that asubstantial quantity of the manure producedon livestock operations could be used econom-ically to produce energy, if the effective capi-tal charges are reduced through various eco-nomic incentives.

Environmental Impacts of Biogas Production:Anaerobic Digestion of Manure

Anaerobic digestion of feedlot manure is nure (which often represents a substantial dis-considered to be an environmentally benefi- posal problem) into a more benign sludgecial technology because it is an adaptation of waste. Where the manure was used as a fertil-a pollution control process. The energy prod- izer and soil amendment, the digestion wastesuct–biogas–is basically a byproduct of the can substitute for the manure while eliminat-control process, which converts the raw ma- ing some of its drawbacks.


The environmental benefits associated withreducing feedlot pollution are extremely im-portant. The runoff from cattle feedlots is asource of high concentrations of bacteria, sus-pended and dissolved solids, and chemical andbiological oxygen demand (COD/BOD). Thistype of runoff has been associated with: largeand extensive fish kil ls because of oxygendepletion of receiving waters; high nitrogenconcentrations in ground and surface waters,which can contribute to the aging of streamsand to nitrate poisoning of infants and live-stock; transmission of infectious disease orga-nisms (including salmonella, leptospirosis, andcoliform and enterococci bacteria) to man,livestock, and wi ldl i fe; a n d c o l o r i n g o fstreams. 8 Other problems associated withfeedlots include attraction of flies and obnox-ious odors.

Because anaerobic digestion is a relativelysimple process not requiring extreme operatingconditions or exotic controls, biogas facilitiesmay be designed for very small (10 cow) oper-ations as well as large feedlots. The environ-mental impacts will vary accordingly. For ex-ample, recycling of wastewater may be possi-ble for the larger operations; it is not likely tobe possible for the small onfarm digesters be-cause of high water treatment costs. The prod-uct gas from the smaller units is likely to beused onsite and, depending on its use, may ormay not be scrubbed of its HIS and ammonia(N H,) content; the product from very largeunits may be upgraded to pipeline quality byremoving these pollutants as well as the 30 to40 percent of the CO, fraction in the biogas.

The major problem associated with the di-gestion process is waste disposal and the asso-ciated water polIution impacts that could re-sult. As noted above, anaerobic digestion isbasically a waste treatment technology, but al-though it reduces the organic pollution con-tent of manure it does not eliminate it. Thecombination of liquid and solid effluent fromthe digester contains organic solids, fairly high

concentrations of inorganic salts, some con-centrat ions of H2S and NH3, and variableamounts of potentially toxic metals such asboron, copper, and iron. For feed lot operationswhere the manure is collected only intermit-tently, small concentrations of pesticides usedfor fly control may be contained in the manureand passed through to the waste stream.

A variety of disposal options for the liquidand sludge wastes exist. Generally, wastes willbe ponded to allow settling to occur. The liq-uid, which is high in organic content, can bepumped into tank trucks (or, for very largeoperations, piped directly to fields) to be usedfor irr igation and ferti l ization. The high saltcontent and the small concentrations of met-als in the fluid make it necessary to rotate landused for this type of disposal. Large operationsmay conceivably treat the water and recycle it,but treatment cost may prove to be prohibi-tive. Other disposal methods include evapora-tion (in arid climates), discharge into water-ways (although larger operations are likely tobe subject to zero discharge requirements bythe Environmental Protection Agency), and dis-charge into public sewage treatment plants.In all cases, infiltration of wastewater into theground water system is a possibility where soilsare porous and unable to purify the effluentthrough natural processes. As with virtually alldisposal problems of this nature, this is a de-sign and enforcement problem rather than atechnological one; if necessary, ponds can belined with clay or other substances for groundwater protection.

The organic content of the effluent, whichvaries according to the efficiency of the digest-er, will represent a BOD problem if allowed toenter surface waters that cannot dilute the ef-fluent sufficiently. Similar problems can occurwith organics leached from manure storagepiles. However, this problem exists in moresevere form in the original feedlot operation.

The sludge product can be disposed of in alandfill, but it appears that the sludge has

1‘Environmental Impllcation$ ot [rends In Agriculture and S/lvi-culture, Volume I I En vlronmenta I t ffect~ of Trencfj (Wa shlngton,D C Environmental Protection Agency, December 1978), E PA-600/ 1-78-102

‘vSolar Program A~se$$ment Environmental factors, Fue/s FromBiomass (Washington, D C Energy Research and DevelopmentAcimlnlstratlon, March 1977), ERDA 77-477


value either as a fertilizer or cattle feed if theheavy metals content is not too great. Success-ful experience with anaerobically digested mu-nicipal sludges, which clearly have higher con-centrations of heavy metals, indicates that useof the feedlot-der ived s ludge as fert i l i zershould present no metals problem. 20 I n numer-ous applications overseas, the sludge is consid-ered a substantial improvement over the previ-ously used manure fertilizer. I n areas w h e r echemical fertiIizers are not available or are tooexpensive, the retention of the manure’s fer-tilizer value is a particularly critical benefit ofthe biogas process.

Although the H2S (and related compounds)content of the effluent may present some odorproblems, this problem, as well as that of thevery small pesticide content, should be negligi-ble. 21

The gas produced by the digester will con-tain small (less than l-percent each)22 concen-trations of H2S and NH3. If the gas is burnedonsite without scrubbing out these pollutants,combustion will oxidize these contaminants tosulfur and nitrogen oxides. Because the H2Swill form mostly sulfurous and sulfuric acids,which are extremely corrosive to metal, thebiogas has limited use if it is not scrubbed. Forexample, scrubbing is a requirement if the gasis to be used in an internal combustion engine.Simple and inexpensive scrubbing methods areavailable, using an “iron sponge” of ferric ox-ide and wood shavings to react the gas with theiron to form ferric sulfide.23 However, even ifthe gas were not scrubbed, the pollutant con-centrations caused by biogas combustionshould be of l ittle consequence to publichealth as long as the combustion did not takeplace in a confined area. For example, combus-tion of biogas produced from fresh cow ma-nure might generate sulfur oxides on the order

‘ O Me t h a n e Gerrerat/on F r o m H u m a n , A n / m a / , and Agricultural

Waste$ (Washington, D C National Research Council, NationalAcademy ot Sciences, 1977), Library ot Congress catalog No77-92794

) ‘M C T Kuo ancl J L Jones, “ E nvlronmental and F nerg,y Out-put Ana]ysls for the Conver\lon of Agrlcult ura I Re\Idues to Met h-ane, ” Sympos/um o n Energy F r o m Bioma$$ and W a$te, I n~t Ituteot Gas Technology, Washington, D C , Aug 14-18, 1978

‘J So/ar Program A ~jej$men[, op ( It‘‘Kuo ancl jone~, op clt

of 0.1 lb/million Btu,24 compared to the Feder-al requirement of 1.2 lb/million Btu for coalcombustion in large utility boilers.

The major air pollution problem of anaer-obic digestion, therefore, is not from combus-tion of the product gas, but from leaks of rawgas from the system. For a manure sulfur con-tent of 0.2 percent and digester pH of 7.2, theraw biogas can contain H2S in concentrationsof nearly 2,000 parts per million (ppm). 25 A l -though exposure to this full concentrationseems extremely unlikely, concentrations of500 ppm can lead to unconsciousness anddeath within 30 minutes to 1 hour, and concen-trations of 100 ppm to respiratory problems ofgradually increasing severity over the courseof a few hours; the Occupational Safety andHealth Administration’s standard is a max-imum permissible exposure level of 20 ppm.26

Because of rapid diffusion of the gas, healthproblems associated with H2S exposures arelikely to be confined to these occupational ex-posures. However, venting of raw gas cancause severe odor problems to the genera Ipublic. In this case, odor problems associatedwith gas venting should be compared to thesimilar (but more certain) odor problems asso-ciated with the sometimes haphazard treat-ment of manure that the biogas operation re-places.

Because methane is explosive when mixedwith air, strong precautions must be taken toavoid biogas leakage into confined areas andto prevent any possibility of the gas cominginto contact with sparks or flames. Althoughthis will be a universal problem with biogas fa-cilities, it is particularly worrisome if smallunits proliferate.

If normal operating conditions hold biogasleakage to near-zero levels, the powerful odorof the H2S contaminant would serve as anearly warning of a leak. Because low concen-trations of H 2S wil l deactivate the sense ofsmell, the acceptance of small leaks as “stand-

“lbld“$o/ar Program As\e$$ment, op c It“)1 blci


ard operating practice” would eliminate thissafety factor.

The institutional problems associated withassuring that there is adequate control of di-gester impacts are very similar to those of eth-anol plants: there is an attraction towardssmaller size (“on farm”) plants which may havesome advantages (mainly ease of locating sitesfor waste disposal and smaller scale local im-pacts) but which cannot afford sophisticatedwaste treatment, are unlikely to be closely

monitored, and may be operated and main-tained by untrained (and/or part-time) person-nel. Some of the potential safety and healthproblems probably will respond to improvedsystem designs if small onfarm systems be-come popular and the size of the market justi-fies increased design efforts on the part of themanufacturers. The ease of building home-made systems, however, coupled with farmers’traditional independence should provide po-tent competition to the sale of manufactured(and presumably safer) systems.

Research, Development, and Demonstration Needs

Below, the more important research, devel-opment, and demonstration needs for anaero-bic digestion are divided into the general areasof microbiology, engineering, and agriculture.

Microbiology

The whole range of studies related to howanaerobic digestion works shou ld be ad-dressed. This includes identifying the bacteriaand enzymes involved, studying the bacteria’snutr ient requirements ( includin g t race ele-ments), identifying optimum conditions for thevarious conversion stages, and investigatingwhy some feedstocks are superior to others.Much of this is in the realm of basic researchneeded to understand the processes involvedso that the yields, rates, control, and flexibilityof anaerobic digestion can be improved.

Engineering

A large number of different digester typesneed to be demonstrated to aid in optimizingthe safety and reliability of digester systemswhile reducing the cost for onfarm use or forlarge-scale systems. The unique problems andopportunities of various types of animal opera-tions should also be addressed by the various

digester systems. There are also numerous de-sign alternatives that could lower the digestercosts, and these should be thoroughly exam-ined.

Electric power generation and the relatedfeedstock pumping is a weak area in digestersystems, particularly with respect to reliabiIity,maintenance, and efficiency of the engine-gen-erator units. Development work for small en-gines intended to use biogas and the relatedpumps could lead to improvements in theseareas, and fuel cells capable of using biogasshould be developed. Development work isalso needed into the best ways the farm gener-ator can supply the electric utility grid duringperiods of high demand without undue incon-venience for the Iivestock operation.

Agriculture

More needs to be known about the differ-ence between digested and undigested ma-nure. The digested manure should be investi-gated in order to determine its value as a fertil-izer, animal feed, and nutrient source for aqua-tic plants. High-value uses for the digester ef-fluent, proved through thorough testing, couldsignificantly improve the economics of anaer-obic digestion.

Chapter 10

USE OF ALCOHOL FUELS

Chapter 10.– USE OF ALCOHOL FUELS

PageIntroduction . . . . . . . . . . . . . . . . . . . . . .......201Spark Ignition Engines–Ef

and Blends . . . . . . . .Gasohol . . . . . . . . .Ethanol. . . . . . . . .Methanol-Gasoline BMethanol . . . . . . .Summary . . . . . . . . .

ects From Alcohols. . . . . . . . . . . . . . . . . . . 201. . . . . . . . . . . . 203, . . . . . . . . 206ends. . . . 207. . . . . . . . . . . . 208. . . . . . . . . . . . . . 208

D i e s e l E n g i n e s . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 0 9Environmental impacts of Automotive Use of

B i o m a s s F u e l s . . . . . . . . . . . . . . . . . . . . . . . . . 2 1 0Air Pol lut ion— Spark Ignit ion Engines. .. ...210Air Pollution—Diesel Engines . . 213Occupational Exposures to Fuels and

Emissions . . . . . 213Safety Hazards. . . . . . . . . . . . . . . . . . . . . ...214E n v i r o n m e n t a l E f f e c t s o f S p i l l s . . . . . . . . . . . 2 1 4H a z a r d s t o t h e P u b l i c . . . . . . . . . . . . . . . . . . . 2 1 4

Page

Gas Turb ines . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215Air Pollution Effects of Alcohol Fuel Use in

63.

64.

37

Gas Turbines. . . . . . . . . . . . ....215

TABLESPage

Various Estimates of Refinery EnergySavings From Use of Ethanol as Octane-Boosting Additive. . . . . . . . . . . . . . . . . . ..205Emission Changes From Use of AlcoholFuels and Blends. . . . . . . . . . . . . . . . . . . . . 211

FIGURE

PageEfficiency, Power, and Emissions as aFunction of Equivalence Ratio. . .........202

Chapter 10

USE OF ALCOHOL FUELS

Introduction

Liquid fuels have some unique advantagesover sol ids and gases that make them impor-tant fuels in some applications. They contain alarge amount of energy per unit volume (ascompared to gases) and their combustion caneasily be controlled (as compared to solids).However, there are substantial differencesamong Iiquid fuels. At one end of the spectrumis residual fuel oil, which can produce consid-erable emissions when burned and is generallybest suited as a boiler fuel (an application alsoopen to solid fuels). At the other end are lightdistillate oils, gasolines, and alcohol fuels. Theoils and gasolines are superior to alcohols withrespect to their energy content per unit weight(ethanol has two-thirds and methanol one-halfof the energy per gallon of gasoline), whichmakes them better suited for aviation. The al-cohols are superior to oils with respect to theirlower particulate emissions and higher octanevalues. These properties make them particu-larly useful for marine and ground transporta-tion where energy density is not critical and forgas turbines used for peak load electric genera-tion, the applications considered here.

While both ethanol and methanol are alco-hols, they have different physical and chemi-cal properties. Of the two, methanol is less sol-uble in gasoline, separates easier, and canmore easily damage certain plastics, rubbers,and metals used in current automobiles. Fur-

thermore, methanol requires more heat to va-porize it. Both alcohols, as contrasted to gas-oline, contain oxygen and conduct electricity.These properties are important when consider-ing the use of alcohol fuels.

While oil and hydrocarbon (HC) crops maysome day produce fuels for transportation,their costs and yields are highly uncertain atthis time. For the near to mid-term, the mostlikely biomass substitutes for gasoline, diesel,and light fuel oil are the alcohol fuels.

Biomass is the only solar technology for pro-ducing liquid fuels. The biomass can be con-verted to methanol (“wood alcohol”) throughthermochemical conversion or to ethanol(“grain alcohol”) through fermentation or,possibly, thermochemical conversion. Ethanolproduction from sugars and starches is current-ly commercial technology. Wood-to-methanolplants can be built with existing technology,although none currently exists, and plant-herb-age-to-methanol technology needs to be dem-onstrated.

Most cost calculations indicate that metha-nol from coal will be less expensive than eitheralcohol from biomass. Until and unless a do-mestic liquid fuels surplus develops, however,this cost difference is not likely to exclude thebiomass alcohols from the market.

Spark Ignition Engines— Effects From Alcohols and Blends

Alcohols make excellent fuels for spark-ignited engines which are designed for theiruse. However, when considering alcohol or al-cohol-gasoline blend use in gasoline engines,there are four specific factors that are of over-riding importance. One factor is the materialfrom which the engine is constructed. Anotheris the ratio of air to fuel (A/F ratio) in the mix-ture that is burned in the engine. A third is

proper fuel distribution among the cylinders,and a fourth is cold-starting ability.

Some materials in some automobiles are in-compatible with alcohols. Contact with alco-hols can damage some gaskets, fuel pump dia-phragms, and other plastic and rubber parts. Ifthese parts are adversely affected or fail, theengine is likely to malfunction. Furthermore,

201

67-968 0 - 80 - 14


some electric fuel pumps are mounted in thefuel tank. Electric currents induced in thealcohol fuels by these motors may cause theprotective terneplate coating on fuel tanks todissolve and leave the tank susceptible to cor-rosion. There may also be a fire hazard associ-ated with electrical shorting. Under certain cir-cumstances, not totally understood at present,the alcohols or blends can also chemicallyr e m o v e t h e t e r n e p l a t e c o a t i n g .123 F i n a l I y ,alcohols can cause some deposits in the fueltanks and lines to loosen and dislodge, leadingto a blockage in the fuel filter or carburetor.

Three major classes of automobiles are inuse today: pre-1 975 cars, oxidation (two-way)catalyst cars (most post-1 975 cars in Statesother than California), and California three-way catalyst cars. The range of A/F ratios* in-tended for each class of cars is shown in figure37 together with the effect of this ratio on theengine power, efficiency, and emissions. If theA/F ratio extends beyond the ranges of this fig-ure, most engines will hesitate or stall. (Strati-fied-charge engines like the Honda CVCC andFord Proco have somewhat wider ranges.)

Since the pre-1975 cars and oxidation cata-lyst cars usually have carburetors with fixedfuel metering passageways, the alcohol blendfuels, which require less air per volume of fuelthan gasoline, will make the effective fuel mix-ture leaner (i. e., move the effective A/F ratio toless fuel and more air). California three-waycatalyst cars, however, have a sensor that ad-justs the fuel delivery system to the A/F valueintended by the manufacturer. Nevertheless,exhausts from alcohol fuels “fool” this sensorsomewhat, so the compensation is not com-

‘K R Stamper, “50,000 Mile Methanol/Gasollne Blend FleetStudy– A Progress Report, ” in Proceeding of the Alcohol FuelsTechnology Third /nterr-tationa/ Syrrrposlum, Asllomar, Callf (Bar-tlesvllle, Okla Bartlesvllle Energy Technology Center, Depart-ment of Energy, May 1979)

‘S. Gratch, Director of Chemical Science Lab, Ford Motor Co ,Dearborn, Mlch , private communlcatlon, 1979

‘j L Keller, G M Nakaguckl, and j C Ware, “Methanol FuelModlflcatlon for Highway Vehicle Use, ” Union 011 Co ofCalifornia, Brea, Callf , final report to the Department of Energy,contract No FY 76-04-3683, j uly 1978

● The ftgure shows the equivalence ratio which is found by di-viding the stolchlometnc A/F rat to which IS exactly sufficient tocompletely burn all of the fuel by the actual AIF ratio used In thecar Leaner mixtures are to the left and richer to the right

Figure 37.—Efficiency, Power, and Emissions as aFunction of Equivalence Ratio

1 10.85 0.90 0.95 1.0 1.05

Stoichiometric Rich

Equivalence ratio (+)

The equivalence ratio is the ratio of the A/F ratio which is exactlysufficient to completely burn all of the fuel to the actual A/F ratioused in the car. Leaner mixtures have an excess of air, while richerones have an excess of fuel.

SOURCE: H Adelman, et al., “End Use of Fluids From Biomass as Energy Re-sources in Both Transportation and Nontransportation Sectors, ” Uni-versity of Santa Clara, Santa Clara, Cal If., contractor report to OTA,1979

plete. 4 Consequently, while the difference be-tween the A/F ratio for alcohol fuels and puregasoline is less for California three-way cata-lyst cars than for other cars, the A/F ratio is stillsomewhat leaner with alcohol fuels comparedto gasoline.

For pure alcohols the fuel metering ratemust be increased significantly relative to gas-01 inc. This increased rate can result in stream-ing flow rather than well-disbursed droplets asthe fuel enters the air stream when carburetorsare retrofitted for alcohol fuel. This change

‘Gratch, private communlcatlon, op clt

Ch. 10—Use of Alcohol Fuels ● 2 0 3

can seriously aggravate the variation in the A/Fratio among the cylinders which in turn can re-duce performance and economy and increaseemissions. Proper design of the fuel deliverysystem and intake manifold can avoid thispenalty.

The alcohols do not inherently provide goodcold engine starting. Below 400 F, special at-tention must be paid to avoid cold-startingproblems with alcohol. Aids such as electricheating in the intake manifold, blendingagents such as gasoline, butane, or pentaneadded to the alcohols, or auxiliary cold-startfuel are providing solutions to this problem inthe alcohol vehicle fleets now in operation.

Gasohol

Materials Compatibility

Gasohol is a mixture of 10 percent ethanoland 90 percent unleaded gasoline. The ethanolblended in gasohol must be dry (anhydrous) orthe blend will separate into two phases or lay-ers under certain conditions. Typically, gaso-hol can hold more water than gasoline, but itcan contain no more than about 0.3 percent ifseparation is to be avoided down to –400 F.Various additives have been tried to improvethe water tolerance of gasohol, but none haveproved satisfactory to dates

Although the use of anhydrous ethanolshould minimize water tolerance problemswith gasohol, phase separation has been ob-served to occur in four service stations inIowa. ’ This phase-separated blend was sold tosome customers and caused their vehicles tostall. Both the vehicle tanks and the servicestation tanks were drained and up to 0.3 per-cent by volume water was found in the mix-ture, but the origin of the water contaminationis not known.

5 H Adelman, et al , “End Use of Flu Ids From Biomass as Ener-gy Resources In Both Transportation and Non-TransportationSectors, ” University of Santa Clara, Santa Clara, Callf , contrac-tor report to OTA, 1979,

‘Douglas Snyder, lowa Development Commission, privatecommunication, 1979

Gasohol does not appear to significantly af-fect engine wear as compared to gasoline butmore experience with gasohol is needed beforea definitive statement can be made. However,an unknown fraction of existing automobileshave specific components that are not com-patible with gasohol, which can result in somefuel system failures.

As older cars are replaced with newer oneswarranted for gasohol use and as experiencedevelops in handling ethanol-gasoline blends,these problems should gradually disappear.

Thermal Efficiency

The leaning effect of gasohol relative to gas-oline wiII affect the three classes of cars some-what differently. For precatalyst and oxidationcatalyst cars, the thermal efficiency can eitherincrease or decrease with gasohol dependingon the original A/F setting (see figure 37). Ingeneral, automobiles that operate rich will in-crease in efficiency, while those that operatelean will decrease in thermal efficiency withgasohol.

The Nebraska “ t w o m i l l i o n m i l e ” t e s tshowed a large average mileage increase (7percent) with gasohol. ’ However, the spread ofdata points is so large that the uncertainty inthis difference is greater than the differenceitself. * This is a generic problem in trying todeduce small differences in mileage with roadtests.

Laboratory tests, however, indicate an in-crease in thermal efficiency of 1 to 2 percent

‘W A Scheller, Nebraska 2 Million Mile Gasohol Road TestProgram, Sixth Progress Report (Lincoln, Nebr Unlversit~ of Ne-braska, January 1977)

*Taking data from figure 4 of Scheller, OTA has analyzed theuncertainty in the average mileage difference Using a standardstatistical test (“t” test) reveals that the spread In data points(standard deviation) IS so large that the mileage difference be-tween gasohol and regular unleaded would have to be more than30 percent (two times the standard deviation) before OTA wouldconsider that the test had demonstrated a difference In mileageWhile more sophisticated statistical tests might Indicate that themeasured difference in mileage is meaningful, the validity ofthese statistical methods IS predicated on all the errors beingstrictly random, and the assumption of random errors IS suspectunless the number of vehicles in the test fleet is orders of magni-tude larger than any tests conducted to date


with gasohol in precatalyst and oxidation cata-lyst cars, which is within the measurementerrors. 8 The changes in thermal efficiency withthree-way catalyst cars will be less and there-fore negligible.

Since gasohol contains 3.5 percent less ener-

gy per gallon than gasoline, precatalyst and OX-

idation catalyst cars are expected to experi-ence about a zero- to 4-percent decrease inmiles per gallon. Three-way catalyst cars areexpected to experience about a 3- to 4-percentdecrease in mileage. Probably neither of thesedecreases would be noticeable by motoristsand, as stated above, will depend on the A/Fsetting of the automobile for all but the three-way catalyst cars.

These conclusions are in complete agree-ment with the results of an American Petrole-um Institute study released in the spring of1980, 9 in which all available data on gasoholmileage were compared, averaged, and treatedstatistically to determine the significance ofthe results.

Drivability

Pos t -1970 nonca ta lys t and ox ida t ion ca ta lys tcars that are set at lean A/F rat ios on gasol inecan exper ience dr ivabi l i ty problems such asstumbling, surging, hesitation, and stall ingwith gasohol due to further mixture leaning.While no drivability problems have been re-ported for precatalyst cars, laboratory tests on1978 and 1979 oxidation catatlyst cars sug-gested slight deterioration in drivability .’” Ifthe percentage of ethanol is increased beyond10 percent, more and more cars are expectedto experience drivability problems due to theleaning effect.

Since three-way catalyst cars largely com-pensate for the leaning effect of gasohol, no

‘R K Pefley, et al., “Characterization and Research investiga-tion of Methanol and Methyl Fuels, ” University of Santa Clara,Santa Clara, Calif , contractor report to the Department ofEnergy, contract No FY 76-5-02-1258, 1979

‘Mueller Associates, Inc , “A Comparative Assessment of Cur-rent Gasohol Fuel Economy Data, ” commissioned by the Amer-ican Petroleum Institute, 1980

‘“R Lawrence, “Gasohol Test Program, ” Technology Assess-ment and Evaluation Branch, Environmental Protection Agency,Ann Arbor, Mlch , December 1978

drivability problems are expected with gaso-hol, as long as the mixture does not go beyondthe capability of the compensation mechanismin these cars.

In most cars there may also be some minorproblems with vapor lock, if the vapor pressureof the blend is not adjusted properly by remov-ing some butanes from the gasoline.

Octane

Addition of ethanol to gasoline increases theoctane* for the mixture over that of the gaso-line. The exact increase will depend on the gas-oline, of which there is a great variety. On theaverage, for the range of 5 to 30 percent etha-nol, each percent of ethanol added to one baseunleaded regular gasoline (88 octane) raisedthe octane number by 0.3. However, the oc-tane increases per unit alcohol are larger forlower percentages of ethanol and lower octanegasolines and level off at higher alcohol per-centages and gasoline octane. A 10-percentblend would raise the octane by about 2 to 4using an “average gasoline. ”

The octane-boosting properties of ethanolcan be exploited in either of two ways to saveenergy: 1 ) by reducing the oil refinery energyby producing a lower octane gasoline or 2) byincreasing the octane of all motor fuels so thatautomobile manufacturers can increase thecompression ratios and thus the efficiency ofnew cars.

There is considerable uncertainty and varia-bility in the amount of premium fuel that canbe saved at refineries by using ethanol as anoctane-boosting additive. As shown in table 63,reported or derived values vary from nearlyzero to more than 60,000 Btu/gal of ethanol,depending on the average octane of the refin-ery gasoline pool, the octane boost assumedfrom ethanol, the type of gasoline and theratio of gasoline to middle distillates producedby the refinery, the refinery technology used,and other specifics.

*Octane here refers to the average of research octane andmotor octane.

‘ ‘Keller, Nakagucki, and Ware, op cit


Table 63.–Various Estimates of Refinery Energy Savings FromUse of Ethanol as Octane-Boosting Additive

103 Btu saved/gal ofethanol blended

Source 10% in gasoline Conditions

Energy ResearchAdvisory Boarda. . . . . 8 Unknown

Kozinski b . . . . . . . . . 16 86 pool octane, reduction ingasoline to distillate ratio,3 octane number boostby ethanol

OTA C. . . . . . . . . . . . 40-45 91 pool octane, reduction ingasoline to distillate ratio,3 octane number boostby ethanol

Adelman d ., . . . . . . . . 53 Pool of 91 and 96 researchoctane, 5 research octaneboost by ethanol

Office of Alcohol Fuels e 6 3 Unknown

a Energy Research Adwsory Board. “Gasohol. ” Oeparfment of Energy, Apr 29, 1980bA A Kozlnskl, Amoco 011 CO , Naperwlle, HI private commumcatlon, 1980 from data In O K

Lawrence, et al , ‘‘Automotwe Fuels–Refinery Energy and Economics, ’ Amoco 011 Co , SAEtechmcal paper scrles No 800225, 1980

COTA from data In Lawrence, Op Clt , and from figure 5 In G W Mlchalskt and G H Unzelman !

‘‘Effeclwe Use of Armknocks During the 1980’ s.’ American Petroleum Institute preprint No22.79, from 44th Refinery Midyear Meeting, May 16, 1979

‘ H Adelman, et al , “End Use of FluIds From Biomass as Energy Resources m Both Transporfa-tlon and Nontransporfatlon Sectors, ’ Unwerslty of Santa Clara, Santa Clara, Cahf contractorreport to OTA, 1979

eofflce Of AicOhOl Fuels, Department of Energy, “Commenls by the DOE Off Ice of Alcohol Fuels onthe Energy Research Advisory Board, Aprd 29, 1980, Gasohol Study Group, Repod. June 3,1980


Based on published computer simulations ofan oil refinery,12 Kozinski has estimated a sav-ings of about 16,000 Btu/gal of ethanol on thebasis of an average gasoline pool octane of 86,and appropriate reduction in the gasoline-to-distillate ratio, which is appropriate for thecurrent situation where the octane of abouthalf the gasoline is raised with tetraethyllead. ” In the future, if most of the gasolineproduced is unleaded, then the pool will haveto increase to at least 89 octane, which is thecurrent average after lead has been added.Moreover, the octane requirements of newcars is increasing, which will induce refinersto increase the pool octane further.

Assuming an average pool octane require-ment of 91, which can be reduced to 88 by theaddition of 10 percent ethanol, and assuming

an 8-percent reduction in the gasoline-to-distil-Iate ratio from the ethanol, the refinery energysavings from using ethanol as an octane-boost-ing additive are about 40,000 to 45,000 Btu/galof ethanol. 15 16 This corresponds to about 0.3to 0.4 gal of gasoline equivalent per gallon ofethanol.

The refinery energy savings are nonlinearwith the pool octane and the greatest savingsoccur with the first increment of ethanol used.Consequently, since the supply of ethanol willlikely be limited to less than a universal 10-percent blend, 0.4 gal of gasoline equivalentper gallon of ethanol is used in the calcula-tions.

If the energy savings from ethanol representthe major economic incentive to the refiner,then refineries with the highest potential forenergy savings would be the most likely to useit and savings would be maximized. Some re-fineries, however, may have additional incen-tives for using ethanol, including capital sav-ings and greater gasoline yields from reducedreforming requirements, and access to strongermarkets with gasohol. These incentives maynot coincide with maximum energy savings.Moreover, the widespread use of technicallyadvanced refining methods could reduce thepotential for energy savings through ethanoluse. Clearly, there are numerous factors whichcan lower the actual savings below that whichis technically possible for the refineries mod-e led prev ious ly .l 7 1 8 Consequently, although0.4 gal of gasoline equivalent per gallon of eth-anol is used as the refinery energy savings, itshould be viewed as a potential savings, whichprobably will not be achieved in practice forall cases. However, too many assumptionsabout future refinery operations are requiredin calculating the energy savings to be able todetermine a single, correct value; and the ac-tual savings achieved will be very site specific.

“D K Lawrence, et al , “Automotive Fuels– Refinery Energyand Economic s,” Amoco 011 Co , SAE technical Series NO800225, 1980

11A A Kozinskl, Amoco 011 Co , Napervllle, Ill , private com-munication, 1980

“Bob Tlppee, “U S Refiners Adjusting to Changing Require-merits, ” 0// and Gas /ourna/, june 23, 1980

“Based on Lawrence, et al , op clt“Based on figure 5 of G W Mlchalskl and C H Unzelman,

“Effective Use of Antiknocks During the 1980’ s,” American Pe-troleum Institute preprint No 22-79, from 44th Refinery MidyearMeeting, May 16,1979

“Lawrence, et al , op clt18 Mlchalskl and Unzelman, op clt


The other possibility is to use the ethanol na-tionwide to gradually increase the octane ofmotor fuels. Auto manufacturers could use theincreased octane to improve engine efficien-cies by increasing the compression ratios inautomobile engines. The energy savings pergallon of ethanol would be comparable to thatcalculated above, but there would be Iittle sav-ings before higher octane fuels were readilyavailable and older automobiles had been re-placed with the newer, more efficient engines.

Some stratified-charge engines (e.g., FordProco) do not require high-octane fuels and thebenefits from a high-octane fuel would be sub-stantially less than for conventional engines. Ifthese or other such engines are used extensive-ly, the octane-boosting properties of ethanolwould be of little value, but it is likely thatlarge numbers of automobiles will need high-octane fuels well into the 1990’s.

Value of Ethanol in Gasohol

The value of ethanol or the price at which itbecomes competitive as a fuel additive can becalculated in several ways. Two alternativesare presented here.

At the oil refinery, each gallon of ethanolused as an octane booster saves the refinerythe equivalent of 0.4 gal of gasoline by allow-ing the production of a lower octane gasoline(see section on octane above). in addition, 1gal of ethanol will displace about 0.8 gal ofgasoline when used as a gasohol blend (i.e.,gasohol mileage is assumed to be 2 percentless than gasoline mileage). At the refinerygate, unleaded regular costs about 1.6 timesthe crude oil price. Assuming that the fuelssaved by the octane boost, which are of lowervalue than gasoline, cost about the same ascrude oil, the ethanol is valued at about (gaso-line saved) x (gasoline price) + (refinery fuelsaved) x fuel price = 0.8 X 1.6 + 0.4 X 1.0 =1.7 times the crude oil price. *

‘This IS in agreement with the value of 16 to 1 8 times thecrude oil price that can be calculated using Bonner andMoore’s” estimates based on $12 25/bbl crude 011

“A Formu/a for Estimating Refinery Cost Changes AssociatedWith Motor Fue/ Reformation (Houston, Tex Bonner and MooreAssociates, Inc., Jan 13, 1978)

If the gasoline retailer blends the gasohol,the value of the ethanol is somewhat different.Gasoline retailers bought regular unleadedgasoline for about $0.70/gal in July 1979 andsold gasohol for a rough average of $().()3/galmore than regular unleaded. (The differencebetween this and the retail price of gasoline isdue to taxes and service station markup, whichtotal about $0.29/gal.) One-tenth gallon of eth-anol displaces $0.07 worth of gasoline and themixture sold for $0.03/gal more. Therefore, 0.1gal of ethanol was valued at $0.10 or $1 .00/gal. This is 2.5 times the July 1979 averagecrude oil price of $0.40/gal.

Both of these estimates are approximate,and changing price relations between crude oiland gasoline couId affect them. Moreover, sev-eral other factors can change the estimatedvalue of ethanol. If a special, low-octane, lowvapor pressure gasoline is sold for blendingwith ethanol, at low sales volumes the whole-saler might assign a larger overhead charge pergallon sold. Also, the refinery removes relative-ly inexpensive gasoline components in order tolower the vapor pressure* of the gasoline, andthis increases its cost. On the other hand, inareas where gasohol is popular, the large salesvolumes lower service station overhead pergallon thus raising ethanol’s value. These fac-tors can change the value of ethanol by asmuch as $0.40/gal in either direction (i. e.,$0.04/gal of gasohol) and the pricing policies ofoil refiners and distributors will, to a large ex-tent, determine whether ethanol is economi-calIy attractive as an octane-boosting additive.

Ethanol

If pure ethanol is used, carburetors have tobe modified to accommodate this fuel. Newengines designed for ethanol could have

*The more’ volatile components of gasoline (e.g., butanes) maybe removed to decrease evaporative emissions and reduce thepossibility of vapor lock Although these components can beused as fuel, removing them decreases the quantity of gasolineand the octane boost achieved by the ethanol Consequently, theadvantages of having a less volatile gasoline must be weighedagainst the resultant decrease in the gasoline quantity and thevalue of the ethanol This IS a matter of business economics ineach refinery and there are no simple rules which would be uni-versally applicable


higher compression ratios (due to the higheroctane of ethanol) and burn leaner fuel mix-tures which would improve engine efficiency;and laboratory tests indicate the improvementcould be 10 to 20 percent. 20 21 Furthermore, theincreased compression ratio provides morepower, so engine sizes could also be reduced,thereby increasing the efficiency stilI further.

In cold climates there can be problems start-ing and during warmup of engines fueled bypure ethanol, due to its low volatility and highheat of vaporization. Consequently, specialequipment will be necessary to enable coldstarting in vehicles fueled with straight etha-nol. Alternatively, it may be possible to blendsmall quantities of light hydrocarbons in thealcohol to alleviate the cold-start problem, orone couId use a combination of these strate-gies.

Methanol= Gasoline Blends

In general the effects of adding methanol togasoline are similar to those for ethanol addi-tion, but more extreme. Thus methanol sepa-rates from gasoline at lower moisture levelsand damages alcohol-susceptible parts andsome paints 22 more quickly or extensively.Therefore, there would be some added costassociated with using metals, plastic and rub-ber parts, or paints that are tolerant to metha-nol over using those tolerant to ethanol, butthe added cost is probably quite small.

As with ethanol, the change in thermal effi-ciency for methanol-gasoline blends dependson the original gasoline A/F ratio, but wouldgenerally be in the range of zero to 4 percentfor a 10 percent methanol blend, leading to anestimated 1- to 5-percent drop in mileage(miles per gallon).

‘(’H Menrad, “Recent Progre$s In Automotive Alcohol Fuel Ap-pl Icatlon, ” In Proceedings of the Fourth /nternationa/ Symposiumon Automotive Propulsion Systems, held on Apr 18-22, 1977,(NATO Committee on the Challenges of Modern Society, Febru-ary 1978)

‘‘Wlnfrled Berhardt, “Posslbllltles for Co~t-Effective Use of Al-cohol Fuels In Otto E nglne-Powered Vehicles, ” In Proceed/rigs of

t h e i n t e r n a t i o n a l Symposium o n A l c o h o l F u e l T e c h n o l o g y ,

A4ethano/ and Ethano/, West Germany, Nov 21-23, 1973, engllshtranslation by the Department of Energy

llKel jer, Nak aguck I, and Ware, oP c ‘t

The octane boost that can be achieved withmethanol is comparable to that for ethanol, orabout 3 octane numbers for a 10-percentblend .23 24

For cars adjusted lean on gasoline, drivabili-ty problems will occur with a 10 percent meth-anol blend due to additional leaning. However,at lower percentages of methanol, these prob-lems decrease. Indeed methanol is used as ade-icer at concentrations of about 0.5 percent,with no apparent impairment of drivability. 25

The p r inc ipa l p rob lems w i th methano lblends are the large increase in vapor pressurewhen methanol is added and the poor watertolerance of the blends. The higher vapor pres-sure can lead to increased evaporative emis-sions and possibly vapor lock. The decreasedwater tolerance can lead to fuel separation(into layers), which can lead to poorer drivabil-ity in automobiles.

The vapor pressure of the blend can be de-creased by reducing the gasoline vapor pres-sure, but this significantly reduces the volumeof gasoline blending stock and can result inless total automotive fuel.26 Newer cars, how-ever, are fitted with charcoal to trap evapora-t ive emiss ions f rom fuel tanks,27 but thesefilters may have to be replaced yearly in orderto maintain their effectiveness.28 Evaporativeemissions from carburetor boiloff increasewith alcohol blends. However, charcoal air fil-ters are being used on some 1980 model vehi-cles to trap the evaporative emissions from thecarburetor and may reduce blend evaporativeemissions. Moreover, fuel injection systemshave less fuel losses. Vapor lock may also be aproblem in some cases, 29 but studies indicate

‘lAdelman, et al , op clt“F W Cos, “The Physical Properties of Casollne/Alcohol Au-

tomotive Fuels, ” In Proceedings of the Third /nternationa/ S ym-posium on A/coho/ Fue/ Technology, vo/, //, Asllomar, Callf May28-31, 1979

2’Adelman, et al , op clt“Keller, Nakaguckl, and Ware, op clt“lbld‘“K R Stamper, Bartlesvllle Energy Technology Center, De-

partment of Energy, Bartlesvllle, Okla , 1979“Keller, Nakaguckl, and Ware, op clt


that proper vehicle design can also eliminatethis problem .30

The water tolerance problem may requiresome sort of cosolvent, or additive, whichhelps to retain methanol in gasoline. * Onesuch cosolvent, t-butanol (another alcohol), iscurrently being test marketed in t-butanol-methanol-gasoline blends by Sun Oil. 32 T h eenergy cost of producing the t-butanol, how-ever, is not known. Alternatively, hexanol (stillanother alcohol) has been used successfully torecombine the phases in a separated methanol-gasoline blend .33

Each of the problems with methanol blendshas numerous solutions, but it is unclear atpresent which will be the most effective at in-creasing motor fuel supplies at the least costto consumers. Additional work is needed toclarify this matter.

Methanol

In o r d e r t o u s e m e t h a n o l , c a r b u r e t o r s s u i t -a b l e f o r m e t h a n o l h a v e t o b e i n s t a l l e d o n t h eengine or old ones modified. New engines de-signed for methanol could have higher com-pression ratios and burn leaner fuel mixtures,leading to a potential 20-percent improvementin thermal efficiency .34 35 As with ethanol,slightly smaller engines could be used becauseof the greater power associated with the highercompression ratio, which could provide stillgreater efficiency improvements.

‘“A W. Crowley, et al , “Methanol-Gasoline Blends Perform-ance in Laboratory Tests and Vehicles, ” Inter Industry EmissionContro/ Progran?-2, Progress Report No. 1 (Society of AutomotiveEngineers, 1975)

● Nevertheless, one test of automobiles operating on a phase-separated blend showed fewer drivability problems than wouldhave been expected ‘1

“Stamper, “50,000 Mile Methanol/Gasoline Blend FleetStudy,” OP. cit.

“B C Davis and W H Douthut, “The Use of Alcohol Mix-tures as Gasoline Additwes, ” Suntech, Inc , Marcus Hook, Pa ,presented at 1980 National Petroleum Refiners Association An-nual Meeting, March 1980.

“Stamper, private communication, op cit“W j Most and j P Longwell, “Single Cylinder Engine Eval-

uation of Methanol-Improved Energy Economy and ReducedNOX,” SAE paper No 750119, February 1975

I%pef ley, et a I , oP Cit

Another possible approach with methanol isto decompose the alcohol into carbon monox-ide (CO) and hydrogen in the carburetor. Thisgas mixture is then used to fuel the engine. Ex-haust heat from the engine is used to fuel thedecomposition; and the CO-hydrogen mixturecontains 20 percent more energy than themethanol from which it came. This offers thepossibility of improving the engines thermal ef-ficiency by 20 percent, but it is too soon toknow whether this potential increase can beachieved in practice.

Methanol can cause gasoline fuel injectionpumps to fail, due to its low lubricity. ” Othertests indicate that methanol combustion cor-rodes cast iron piston rings and may affect nor-mal lubricating oils, particularly in very coldweather starting. ” However, in actual engineand vehicle tests in warm weather conditions,methanol has not been found to cause prema-ture engine wear. 38

Below about 400 F, methanol-fueled enginescan experience starting probIems, due to thesame factors that affect ethanol-fueled vehi-cles. As with ethanol, special equipment and/or blending of volatile hydrocarbons in thefuel will be needed to enable cold starting.

Summary

Ethanol-gasoline blends are currently beingmarked commercially, and methanol blends(with a cosolvent) are being test marketed. Inaddition, automobiles fueled with straightethanol are being used in Brazil and extensivetests with methanol-fueled vehicles are under-way. Nevertheless, because the alcohols arenot fully compatible with the existing liquidfuels delivery system and automobile fleet,some initial difficulties in using alcohol fuels

“j C Ingamells and R H Llndqulst, “Methanol as a MotorFuel or a Gasoline Blendlng Component, ” SAE paper No 750123,Automotwe Englneerlng Congress and Exposltton, Detroit, Mich ,February 1975

“E, C, Owens, “Methanol Effects on Lubrication and EngineWear,” in Proceedings of the International Symposium on AICOho/ Fue/ Teclmo/ogy, Methane/ and Ethano/, Wolfsburg, WestGermany, Nov. 21-23,1977.

]apef Icy, et al , oP Clt


are to be expected. These problems should dis- cause of the energy saved by allowing refinersappear with time, however, as more experience to produce a lower octane gasoline. The situa-is gained at handling and using the alcohol tion with methanol is less clear because of thefuels and as older automobiles are replaced greater difficulties associated with methanol

with vehicles designed for use with these fuels. blends and the possible need for cosolvents.The use of methanol both in blends and as a

For ethanol the preferred use probably is as straight fuel is currently being pursued.an octane-boosting additive to gasoline be-

Diesel Engines

Alcohols have only l imited volubi l i ty indiesel fuel, making diesel-alcohol blends im-practical at present. * If “ignition acceler-ators”* * are dissolved in the alcohols toenable them to ignite in diesel engines, theycan be used as a replacement for diesel fuel,but the fuel metering system would have to bemodified to provide the fuII range of power forwhich the engine was designed and some pro-visions made for the decreased lubricity of thealcohols.

Alternatively, the alcohols can be used indual fuel systems, i.e., where the alcohol anddiesel fuel are kept in separate fuel tanks andseparate fuel metering systems are used. Thetwo main possibilities are fumigation and dualinjection. In a fumigation system, the alcoholis passed through a carburetor or injected intothe air intake stream and the alcohol-air mix-ture replaces the intake air. In dual injection,each fuel is injected separately into the com-bustion chamber.

Most diesel engines are speed governed, i.e.,more or less diesel fuel is injected automatical-ly to maintain a constant engine speed for agiven accelerator setting. If alcohol is fumi-gated into the cylinder, the diesel injectiondecreases automatically when the engine isnot at full power to compensate for the addi-tional power from the alcohol. At full power,the alcohol will give the engine additionalpower. Consequently, once a fumigation sys-tem is installed, alcohol usage is optional,

since the engine will run normally without thealcohol present, but the higher power at fullpower can cause additional engine wear if theengine is not designed for this power. Alter-natively, the diesel injection can be modifiedto allow less fuel to be injected, but it wouldhave to be returned to its original state whenalcohol is not being used. Dual injection sys-tems also can be designed to run with or with-out alcohol, but the injection controls wouldprobably be more complicated.

If the fuel systems are separate, alcohol con-taining up to 20 percent water probably can beused. However, the diesel engines must bemodified to accommodate the alcohols. Themodifications for alcohol fumigation are rela-tively simple and can be performed for an esti-mated $150 if, for example, a farmer does ithimself and uses mostly spare parts. ” Costscould range up to $500 to $1,500 if installed bya mechanic using stainless steel fuel tanks andall new parts.40 Cost estimates for modifyingengines for dual injection are not available,however, but would be more expensive. In ei-ther case the long-term effects, such as possi-bly increased engine wear, are unknown at thepresent time.

Fumigation systems will generally be limitedto 30 to 45 percent ethanol or about 20 percentmethanol, because evaporation of the alcoholcools the combustion air and the cooling fromhigher concentrations is sufficient to preventthe diesel fuel from igniting. However, consid-

*E mulslons are possible, but still In the R&D phase● ● Although alkyl nitrates have generally been used as Ignltlon

accelerates, sunflower 5CW! 011 and other vegetable OIIS havebtwn suggested for biomass-derived ethanol

“Pefley, et al , op cit‘(’lbld


erably higher proportions of alcohol can beused with dual injection systems.41

In fumigat ion systems, some tests haveshown thermal efficiency increases of up to 30percent for certain combinations of alcoholand diesel fuel. 42 Other tests 43 showed s l ightincreases (5 percent) in thermal efficiencywhen the engine is at two-thirds to full load,while there are large decreases (25 percent) inefficiency at one-third full load. Similar am-

41 F, F plschlnger and C Haven ith, “A New Way of Direct In-

jectton of Methanol In a Diesel E nglne, ” in Proceedings of theThird International Symposium on Alcohol Fuels Technology,vo/. //, Asilomar, Callf , May 1979

“K Bro and P S Pederson, SAE paper No. 770794, September1977

4’K D Barnes, D B Kittleson, and T E Murphy, SAE paperNo 750469, Automotive Engineering Congress and Exposltlon,Society of Automotwe Engineers, Detroit, Mlch , February 1975.

biguities exist for dual injection systems. 4 4

These differences in efficiency are due to dif-ferences in engine tuning and design. An accu-rate determination is not available at present,but it is unlikely that there will be significantdifferences in the thermal efficiencies of en-gines optimized for the respective fuels.

Considerable uncertainty exists about thethermal efficiencies that can be obtained inpractice if, for example, tractors are convertedto alcohol use. Assuming, however, that thethermal efficiency does not change, 1 gal ofethanol would replace 0.61 gal of diesel fuel,and 1 gal of methanol would replace 0.45 galof diesel fuel.

44~ Holmer, “Methanol as a Substitute Fuel in the Diesel En-gine, “ In Proceed~ngs of the International Symposium on AlcoholFue/ Techrto/ogy,’ Methane/ and .Ethano/, West Germany, Novem-ber 1977

Environmental Impacts of Automotive Use of Biomass Fuels

The use of alcohol fuels and gasoline-alco-hol blends in automobiles will have a numberof environmental impacts associated withchanges in automotive emissions as well as dif-ferences in the toxicity and handling character-istics of the fuel alternatives. The potentialchanges in automotive emissions have beenidentified as the impact of major concern andare treated in the greatest detail in this discus-sion.

Air Pollution—Spark Ignition Engines

Predictions of emissions changes can bebased on a combination of theoretical consid-erations, laboratory tests, and field measure-ments. Unfortunately, the results of the emis-sions tests that have been completed to dateare varied and confusing. Difficulties withusing these results for predicting emissionschanges include:

. Tests are rarely comparable because ofdifferent base fuels (gasolines), fuel mix-tures, automobiles, state of “tune,” driv-ing cycle, etc.

●

●

In some important tests, methodologicalproblems may seriously weaken the de-rived conclusions. For example, the Envi-ronmental Protection Agency’s (EPA) 1978tests of “gasohol” (10 percent ethanolblend) included some vehicles that eitheroperated too “fuel-rich” initially (fourvehicles) or exceeded the nitrogen’ oxide( N Ox) standard on indolene (two vehi-cles).45 If these noncompliance vehiclesare dropped from the test sample, thechanges caused by using gasohol are lessthan test-to-test variabil ity in exhaustemissions for the same vehicle.46

Test results have generally been obtainedfrom laboratory engines or, in testingalcohol blends, from relatively unmodi-fied automobile engines. A strategy thatprovided reliable and plentiful supplies ofalcohol fuels would presumably be ac-

45 Characterization Report: Analyses of Gasohol Fleet Data toCharacterize the Impact of Gasohol on Tailpipe and EvaporativeEmissions (Washington, D C Technical Support Branch, MobileSource Enforcement Division, Environmental Protection Agency,December 1978)

“’Wiplore K juneja, et al , “A Treatise on Exhaust EmissionTest Varlabillty,” Society of Automotive Engineers, VOI 86, paper770136, 1977


companied by design changes that wouldtake advantage of the different propertiesof these fuels. Thus, extrapolations fromcurrent test data may be overly pessimis-tic, at least for the long run.

Aside from test results, emission changescan be explained in great part by the depend-ence of emissions on the operating conditionsof the engine. Emissions of CO, HC, NOX, andaldehydes are strongly influenced by the“equivalence ratio @“ (stoichiometric A/F ra-tio/actual A/F ratio) and the emission controlsystem (none, oxidation catalyst, etc.). Figure37 shows how CO, HC, NOX, and aldehydes arelikely to vary with @.

Both methanol (6.4:1 ) and ethanol (9:1) havelower stoichiometric A/F ratios than gasoline(14. s: I). Thus, blends of either alcohol fuel re-sult in lower equivalence ratios (“leaner” oper-ation) if no changes are made in the fuel meter-ing devices. Examining figure 37, emissionschanges can be predicted qualitatively by ob-serving that adding alcohol pushes the equiva-lence ratio to the left. For an automobile nor-mally operating “lean,” CO may be expectedto remain about the same, HC remain thesame or increase slightly, and NOX decrease.

For out-of-tune automobiles, which usuallyoperate in a “fuel rich” mode, CO and HC maybe expected to decrease while NOX increases.Vehicles equipped with three-way catalystshave feedback-controlled systems that operateto maintain a predetermined value of @ andthus should be less affected by the blend lean-ing effect of the alcohol fuels. However, thisfeedback system is usually overridden duringcold starting to deliver a fuel-rich mixture; dur-ing this time period, HC and CO are more like-ly to decrease and NOX to increase withalcohol fuels. Also, catalysts with oxygen sen-sors can be fooled into adjusting to leaneroperation because the exhaust emissions fromalcohol blends oxidize faster than gasoline-based exhausts and drive down the oxygen lev-el in the exhaust stream (giving the appearanceof overly fuel-rich operation);47 this should alsotend to decrease HC and CO and increase NOX

emissions when alcohol blends are used in ve-hicles equipped with such catalysts.

Table 64 provides a summary of the type ofemissions changes that may be expected bycombining knowledge of test results and the

47 Cratch, op cit

Table 64.–Emission Changes (compared to gasoline) From Use of Alcohol Fuels and Blends

Pollutant/fuel Methanol Methanol/gasoline Ethanol Ethanol/gasoline ‘‘gasohol’

Hydrocarbonor unburnedfuels

Carbonmonoxide

Nitrogenoxides

Oxygenatedcompounds

Particulate

Other

About the same or slightly higher, May go up or down in unmodifiedbut much less photochemically vehicles, unchanged when @reactive, and virtual elimination remains constant. Compositionof PNAs; can be catalytically changes, the, and PNAs gocontrolled down. Can be controlled. Higher

evaporative emissionsAbout the same, slightly less for Essentially unchanged if@

rich mixtures; can be catalytically remains constant, lower ifcontrolled; primarily a function -

of @1/3 to 2/3 less at same A/F ratio,

can be lowered further by goingvery lean; can be controlled

Much higher aldehydes, particu-larly significant with precatalystvehicles

Virtually none

No sulfur compounds, no HCN orammonia

leaning is allowed to occur

Mixed; decreases when is heldconstant, but may increase fromfuel ‘‘leaning’ effect in unmodi-fied vehicles

Aldehydes increase somewhat,most significant inprecatalyst vehicles

Little data

Unknown

Not very much data, should be May go up or down in unmodifiedabout the same or higher but less vehicles, about the same when +reactive. Expected reduction in remains constant; compositionPNA may change, expected reduction

in PNAs. Evaporative emissionsup

About the same, can be controlled ;Decrease in unmodified vehiclesprimarily a function of * (i.e., leaning occurs), about the

same when @ remains constant

Lower, but not as Iow as with Slight effect, small decrease whenmethanol; can be controlled 4 is held constant, but may

increase or decrease further fromfuel ‘‘leaning’ effect inunmodified vehicles

Much higher aldehydes, particu- Aldehydes increase, most signifi-Iarly significant with precatalyst cant in precatalyst vehiclesvehicles

Expected to be near zero Little data, no significant changeexpected

No sulfur compounds No data



theoretical model discussed above. The mostsignificant changes, and their environmentalimplications, are:

● Substantial reductions in reactive HC andNOX exhaust emissions with 100 percent(neat) methanol and, to a lesser extent, eth-anol.— Although HC emiss ions are ex-pected to remain approximately the samewith alcohol fuel use at the same *,4 8 4 9

the reactivity of these emissions is muchlower than that of gasoline-based HCemissions. Reductions in reactive HC andN OX should reduce photochemical smogformation, although predictions of themagnitude of these effects are difficult.

● Increase in aldehyde emissions with neat al-cohols and blends.— Use of pure alcoholfuels yields several-fold increases in alde-hydes,50 51 whereas blends increase alde-hyde emissions to a lesser extent. Becausecatalytic converters are effective in re-moving aldehydes, catalyst-equipped ve-hicles tend to have low aldehyde emis-sions whether or not alcohol is used;52 53

the major problem l ies with cars notequipped with catalysts.

Aldehydes cause eye and respiratory ir-ritations and are photochemically reac-tive. Despite this, aldehydes are not spe-cifically regulated in automobiles, and

“aDavid L Hllden and Fred B Parks, “A Single Cyllnder EngineStudy of Methanol Fuel – Emphasis on Organic Emlsslons, ” Soci-ety of Automotive E nglneers paper No 760378, presented at theAutomotive Engineering Congress, Dearborn, Mich , Feb 23-27,1976

“Samuel O Lowry and R S Devoto, “Exhaust Emissions Froma Single-Cyl Inder Engine Fueled With Gasoline, Methanol, andEthanol, ” CornbustiorI Science and Technology, VOI 12, Nos 4, 5,and 6, 1976, pp 177-82

“W Lee and W Geffers, “Engine Performance and ExhaustEmission Characteristics of Spark Ignited Engines Burning Meth-anol and Methanol-Gasoline Mixtures, ” Volkswagen Researchand Development Division, Wolfsburg, West Germany, pre-sented at AICLE meeting, Boston, Mass , September 1975

“Comparative Automotive Eng\ne Operation When FueledWith Ethano/ and Methane/ (Washington, D C Alcohol FuelsProgram, Alternative Fuels Utlllzatlon Program, Department ofEnergy, May 1978)

“j R Altsup, “Experimental Results Using Methanol andMethanol/G asollne Blends as Automotive Engine Fuel, ” Bartles-vllle Energy Technology Center, No B9RC/Rl-76/l 5, january1977

“j R Allsup and D El Eccleston, “Ethanol/Gasollne Blends asAutomotive Fuels, ” Bartlesvllle Energy Technology Center, draftNo 4

●

●

the most abundant aldehyde in automo-tive emissions–formaldehyde – is not de-tectable with conventional HC measuringinstrumentation. Aldehyde increases maysomewhat negate the positive effects ofreductions in emissions of HC as well as inN OX emissions from alcohol use. The mag-nitude of the potential impacts, however,is not well understood.Substantial. reductions in particulate emis-sions if neat alcohol fuels are used. — Use ofneat alcohol fuels may reduce particulateemissions virtually to zero. This is particu-larly significant when the fuel substitutedfor is leaded gasoline; particulate emis-sions from autos using leaded gasoline areon the order of 0.6 g/mile on the Federalemission test cycle, and most of the par-ticles are toxic (mostly lead by weight,with polynuclear aromatic (PNA) com-pounds adsorbed on their surfaces) and inthe inhalable size range (whereas particu-late emissions from autos using unleadedgasoline are on the order of 0.2 g/mile onthe same test cycle, are about 90-percentcontrolIable with catalytic converters,and are composed mainly of carbon par-t ic les.55

Substantial reductions in PNA compoundswith neat alcohols and blends. — PNA com-pounds emitted in small quantities in au-tomobile exhausts are toxic and carcino-genic. 56 Methanol and methanol blendsappear to provide substantial reductionsin these emissions (methanol exhaust con-tains only about 1 percent of the PNAcompounds observed in gasol ine ex-haus t ) ,57 which may be of some signifi-cance in reducing the cancer hazards ofurban air pollution. Ethanol and ethanolblends may be expected to provide similareffects, but this has not yet been verified.

“R E Sampson and G S Sprtnger, “Effects of Exhaust GasTemperature and Fuel Composltlon on Particulate EmlsslonFrom Spark Ignited Engines, ” Environmental Science and Tech-nology, VOI 7, No 1, january 1973

551 bid“American Petroleum Institute, “API Toxlcologlcal Review

Gasoline, ” 1967“On the Trai/ of New Fue/s – Alternative Fue/s for Motor Vehi-

c/es (Bonn, West Germany Federal Ministry for Research andTechnology, 1974), translated by Addls Translation International


Air Pollution—Diesel Engines

Very l ittle data is available to allow theprediction of emission changes from the use ofalcohol fuels and blends in diesel engines.Predictions of some limited reliability may bemade from the small number of tests, extrap-olation from spark ignition tests, and knowl-edge of diesel characteristics.

The major environmental reason why alco-hol fuels appear to be attractive for diesels istheir ability to burn without producing par-ticulate emissions. Domestic manufacturersare having problems meeting the proposedEPA particulate standard of 0.6 g/mile. Par-ticulate emissions from diesel engines are 50 to100 times those from gasoline engines58 a n dmay contain more PNA; particulate reductionsthus appear to be especially attractive environ-mentally.

HC emissions from diesels are more photo-chemicalIy reactive than automobile HC emis-sions. Although a switch to alcohol fuels by it-self will have an uncertain effect on uncon-trolled emissions, the elimination of particu-late emissions may allow the use of oxidationcatalysts to improve HC control (because par-ticulates otherwise would plug up the cata-lyst). 59

If alcohol fuels behave in diesels in a man-ner similar to their behavior in spark ignitionengines, they should cause NOX emissions todecrease and aldehydes to increase. CO levelshave been observed in tests to double theiroriginally low values when shifting from dieselfuel to alcohol;60 however, this is thought to bea correctable problem with the fuel injectionsystems.

Alcohol fuels have poor ignition capabilitieswhen injected into the compressed and heatedair in a diesel engine. To counteract this dif-

“ K j Springer and T M Ra Ines, “E mlsslons F r o m D i e s e l Ver-sions of Prociuct Ion Passenger Cars, $oclery of A utornotlve ErtgI-

neer$ Tran/at/ens, VOI 86, 5PC 4, paper No 770818, 1977“ M Amano, et al , “Approaches to Low Emission Levels for

Light-Duty Diesel Vehicles, ” Soc[ety of Automotive Engineerspaper No 760211, February 1976

‘“W F Marshall, Experlrnents W i t h Nove/ FL I P/ 5 f o r D/ese/ En-

gines ( Bartlesvll Ie, ok la 13artlesvll Ie Energy Technology Center,Department of Energy, February 1978), II ERCITPR-7718

ficulty, ignition accelerating agents containingnitrates can be added to the fuel to provide anignition source for the alcohol. There appearsto be some potential for the formation of hy-drogen cyanide or ammonia in the combustionprocess when these additives are used. Labora-tory testing will be necessary to verify the ex-istence of this effect.

Emission characteristics of mixed fuel oper-ation with alcohol and diesel fuels depend onthe method of introducing the alcohol into thecombustion chamber.

When the alcohol is mixed with the intakeair (fumigation), the following changes havebeen observed to occur:61

● increase in HC emissions and aldehydes,. little change in CO,. increase or decrease in NOx, and

● decrease in particulate.

The emissions effects of other fuel systemsare poorly understood.

Occupational Exposures to Fuelsand Emissions

In general, the effects of gasoline and gas-oline-based emissions are more acute, in anoccupational setting, than those of methanoland ethanol. For example:

. Short-term exposure to gasoline is consid-ered more poisonous, tissue disruptive,and irritative than methanol when effectsof eye contact, inhalation, skin penetra-tion, skin irritation, or ingestion are con-s idered. 62 Effects of the more severe (in-gestion) exposures to methanol are gener-alIy reversible, although in some extremecases there can be irreversible effects onthe central nervous system, optic nerveend, and heart. 63

“ B S Murthy and L G Pless, “Et fectlvenes$ of Fuel CetaneNumber for Combustion Control In BI-FLJel Diesel E ng,lne, ” /our-

nal of the Institution 01 Engineers [India), VOI 45, No 7, pt ME 4,March 1965

“N V Steer, ed , Handbook of Laboratory Sa/etv ( C l e v e l a n d ,Ohio Chemical Rubber Co , 1971)

‘‘M N Gleason, et al , C/frt)ca/ Toxicology of Cornrnercla/ PoI-Jor15, W i I I lams and W I I I la ms


●

●

The effects of both acute and chronic ex-posure to ethanol are considered to bemuch less disruptive than methanol and,therefore, gasoline.The automotive exhaust emissions thatare most dangerous in an enclosed space— such as a garage without adequate ven-tilation —are CO from gasoline and COand formaldehyde from methanol. If afleet of methanol-powered cars is com-pared directly to a fleet of gasoline-powered cars, CO will be the most danger-ous pollutant (and equally dangerous forboth fleets, because methanol should notsubstantially change CO emissions)—solong as three-way catalysts are used. With-out catalysts, formaldehyde emissionscould be more dangerous than CO in themethanol-powered fleet.

It is interesting to observe that, for thecatalyst-equipped methanol fleet, formal-dehyde will act as a “tracer” for CO; if eyeand respiratory irritation from formalde-hyde becomes acute, this will be an al-most sure sign that CO is at dangerous lev-els.

Safety Hazards

The risks of fire and explosion appear to belower with alcohol fuels than with gasoline,although evidence is mixed:

●

●

●

●

●

gasoline has a lower flash point and igni-tion temperature and is more flammableand explosive in open air than either etha-nol or methanol, 64

alcohols are the greater hazard in closedareas, 65

higher electrical conductivity of alcohollessens danger of spark ignition,high volubil ity in water makes alcoholfires easier to fight than gasoline fires, andalcohol fires are virtually invisible, addingto their danger (but addition of trace ma-terials could overcome this drawback).

Alcohol blends will be similar to gasolinebut they may be more ignitable in open spacesand less ignitable in closed containers when

“CRC Handbook of Laboratory Safety, op clt“lbd

the blends have higher evaporation rates thanthe pure gasoline. Diesel fuels and dieselalcohol emulsions are considered to be saferthan gasoline or alcohol fuels. 66

Environmental Effects of Spills

To the extent that domestic alcohol produc-tion substitutes for significant quantities of im-ported oil, a reduction in fuel transportationand a consequent reduction in spills can be ex-pected. If alcohol is shipped by coastal tanker,the poss ibi l i ty of large alcohol spi l l s i s arealistic one, and the effects of such spillsshould be compared to the effects of oilspilIs.

Alcohol fuels appear to be less toxic than oilin the initial acute phase of the spill and havefewer long-term effects. Except in areas wherealcohol concentrations reach or exceed 1 per-cent, the immediate effects of a spill should beminimal. For example, a concentration ofabout 1 percent methanol in seawater is toler-ated by many common components of inter-tidal, mud-flat, and estuarine ecosystems un-less the alcohol is contaminated with heavymetals. b’ I n contrast, crude oil contains severalhighly toxic water soluble components thatcan be damaging at low concentrations. Fur-thermore, alcohols are extremely biodegrad-able— toxic effects may be eliminated in hours—whereas the effects of heavy fuel oils canlast for years.

Hazards to the Public

The widespread distribution and use of alco-hol fuels will result in the public facing thesame potential dangers as exist in the occupa-tional environment. A true assessment of etha-nol and methanol public health risks must in-corporate an analysis of probable exposure,however, and such an analysis is likely to showthat both alcohol fuels may have considerably

“M E LePera, “Fine Safe Diesel Emulsions, ’’Conference orITrarrsportation Synfue/s, sponsored by the Department of Energy,San Antonio, Tex , November 1978

‘7P N D’E Iiscu, “Biological Effects of Methanol Spills IntoMarine, Estuarine, and Freshwater Habitats, ” in Proceedings ofthe International Symposium on Alcohol Fuel Technology, Meth-anol and Ethanol, Wolfsburg, West Germany, Nov 21-23, 1977

Ch. 10—Use of Alcohol Fuels ● 215

greater potential than gasoline to harm thepublic. For example, although methanol andgasoline are comparably toxic upon ingestion,methanol has a long history of improper inges-tion and gasoline does not. Ethanol is evenmore Iikely to be improperly used, and the eth-anol used for motor fuel blending will be con-taminated with dangerous toxic chemicals. Al-though vile tasting and smelling denaturantsmay be added to fuel ethanol to discourageimproper use, enterprising individuals are Iike-Iy to try to filter out these additives. Also, fuelethanol may be diverted to consumption be-

fore these denaturants are added. The prob-ability of such diversion will be especially highif small, onfarm ethanol stilIs are widely used.

A careful risk assessment of ethanol andmethanol fuels and blends could identify andquantify these types of risks and would be in-valuable both in setting priorities for researchand in devising risk mitigation strategies thatmust accompany promotion of alcohol fueluse. Such an assessment has not as yet beenconducted by DOE.

Gas Turbines

Alcohol fuels can be used readily in gas tur-bine generators used to generate peakloadelectric power. The fuel metering system hasto be modified to meter the larger volumes ofalcohols necessary to maintain the same pow-er output and to accommodate the lower lu-bricity of alcohols relative to l ight fuel oil.These modifications are minor. In some cases,however, the alcohols may attack the turbineblades or other metal parts and the modifica-tions needed to use alcohol fuels would beconsiderably more expensive.

If alcohol fuels are used, care must be takento ensure that no salts are dissolved in thealcohols by, for example, contamination withseawater during barge transport. The saltscould greatly reduce the Iife of the turbines.

The thermal efficiency of a gas turbine is de-termined by the ratio of the pressures at theturbine inlet and outlet. This ratio is limited bythe combustion temperature. The alcoholshave slightly lower combustion temperaturesand should allow higher efficiencies than withlight fuel oil in redesigned turbines. In unmod-ified turbines, the thermal efficiency of thealcohol fuels is about the same (within ± 2 per-cent) as for light fuel oils. 6869 Thus, 1 gal of

ethanol would replace 0.67 gal of light oil and1 gal of methanol would replace 0.48 gal oflight fuel oil.

Currently about 0.25 Quad/yr of oil and 0.2Quad/yr of natural gas are consumed for peak-Ioad electric generation .70 This representsabout 6 percent of the electricity generated inthe United States. Use of alcohol fuels herewould save about 0.2 trillion ft3 of natural gasper year and about 130,000 bbl/d of light distil-late oil.

Air Pollution Effects of Alcohol FuelUse in Gas Turbines

Although alcohol fuels have been tested ingas turbines and the resulting emissions levelshave been measured, there is some doubt as towhether those levels represent true indicatorsof emissions to be expected from an optimizedsystem. For example, methanol use in an auto-motive gas turbine produced a tenfold in-crease in HC emissions in one test, 71 but it is

quite possible that more optimal design of thefuel injection nozzles could lower these valuesconsiderable y.

““l W Huellmantt’lf 5 C Te(i(jle{ dncl K) C Hammond, J r ,

( ombujt Ion ot Methano l tn an A u t o m o t i v e (;a5 Turbine, ” In Fu-

(UV? A u(orno~IL e f l i e / \ . j IM ( ; OILICC I and N E Gal Idpoulou$, t%

(NPW York P lenum f)rt~$$, 1977)

““P M J arvis, ‘ ‘ M e t h ~ n o l as Gas Turb ine Fue l , ” presenteci at

the 1974 E ngl neerlng Fou nda t Ion C o n f e r e n c e , M e t h a n e / a \ an

~1 /ternate Fue/, Henneker, N H , j u Iy 1974

7“Adelman, et al , op clt“C W Ldpolnte and W L S{ hultz, “C’omparlson of E mlfslon

ln~lce$ Wlthln a Turbine Combustor Operated on Diese l FLIPI or

Methano l , ” Soc ie ty o f Automot ive Engineer$ paper No 710669 ,

June 1971


The most significant emission change should distillate fuels. ’z Ethanol, which has a combus-be a substantial drop in NOx emissions, which tion temperature intermediate between metha-are typically quite high in gas turbines. Metha- nol and distillates, should achieve somewhatnol has achieved 76-percent reductions in NOX smalIer reductions.emissions in large turbines because it has a sig-nificantly lower combustion temperature than ‘2JdrVlS, op clt

Chapter

ENERGY BALANCES FORALCOHOL FUELS

Chapter 11.-ENERGY BALANCES FOR ALCOHOL FUELS

Page PageEthanol From Grains and Sugar Crops.... . . . . . . 219 66. Net Displacement of Premium Fuels FromMethanol and Ethanol From Wood, Grasses, and Various Feedstocks and Two End Uses. . . . .221

crop Residues ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● 222 67. Net Displacement of Premium Fuels WithGeneral Considerations . . . . . . . . . . . . . . . . . . . . 223 Alcohol Production From Various Feedstocks

and Two End Uses . . . . . . . . . . . . . . . . .. ..22268. Net Displacement of Premium Fuel per

TABLES Dry Ton of Wood for Various Uses. . . . . . . . 222Page

65. Energy Balance of Gasohol From Corn: Oiland Natural Gas Used and Displaced. .. ...220

II

Chapter 11

ENERGY BALANCES FOR ALCOHOL FUELS

The energy objective of using alcohol fuelsfrom biomass is the displacement of foreign oiland gas with domestic synthetic fuels. The ef-fectiveness of a fuel alcohol program dependson the energy consumed in growing and har-vesting the feedstock and converting it intoalcohol, the type of fuel used in the conversionprocess, and the use of the alcohol.

The major sources of biomass alcohol fuelsare grains, sugar crops, wood, grasses, and

crop residues. Ethanol from grains and sugarcrops is considered first, including a compar-ison of various feedstocks and end uses. Meth-anol and ethanol from the other feedstocks arethen considered, and the use of these feed-stocks directly as fuels is compared with theproduction of alcohols from them. Finally,some general considerations about the energybalance of these fuels are given.

Ethanol From Grains and Sugar Crops

Corn is currently a principal feedstock forethanol production, but other grains and sugarcrops could also be used. The energy balancefor gasohol from corn is discussed in detailbelow, followed by a summary of the energybalance for various possible feedstocks andfor use of the ethanol either as an octanebooster or as a standalone fuel.

For each gallon of ethanol derived fromcorn, farming and grain drying consume, onthe average, the energy equivalent of 0.29 galof gasoline’ in the form of oil (for fuel andpetrochemicals) and natural gas (for nitrogenfertilizers). (See ch. 3 in pt. l.) The exactamount will vary with farming practices (e. g.,irrigation) and yields. I n general, however, thefarming energy input per gallon of ethanol pro-duced will increase when the farmland is ofpoorer quality (e. g., setaside acreage) and/or indryer or colder climates (i.e., most of thewestern half of the country, excluding Hawaii).

The type of fuel used in the distillation proc-ess is perhaps the most important factor in de-termining the displacement potential of etha-

● Some authors have Included the energy used to manufacturefarming equipment and the materials from which they are madeas part of the farm energy inputs However, for consistency oneshould aIso Include, as a credit, the energy used in manufactur-ing the goods that would have been exported to pay for import-ing the 011 displaced by the ethanol Because of the uncertaintyin these factors, and the fact that they are relatively small, theyare not incIuded in the energy balance caIcuIations

nol. Even under the most favorable circum-stances, distillery energy consumption is sig-nificant. The distillery producing most of thefuel ethanol used today reportedly consumes0.25 gal of gasoline equivalent (0.24 in theform of natural gas) per gallon of ethanol pro-duced. 1 This number, however, involves somearbitrary decisions about what energy inputsshouId be attributed to the faciIity’s food-proc-essing operations. Total processing energy in-puts in this plant amount to about 0.55 gal ofgasoline equivalent per gallon of ethanol (seech. 7).

Energy-efficient standalone fuel ethanol dis-tilleries would consume the equivalent ofabout 0.45 gal of gasoline per gal Ion of ethanolproduced (see ch. 7). Because the energy con-sumption of distilleries is not Iikely to be insig-nificant in relation to the alcohol produced inthe foreseeable future, it is essential that dis-tilleries use abundant or renewable domesticenergy sources such as coal, biomass, and/orsolar heat or obtain their heat from sourcesthat would otherwise be wasted. Reliance onthese fuels would reduce the total use of oiland gas at the distillery to insignificant levels.

‘Archer Dantels Mtdland Co , Decatur, III , “Update of Domes-tic Crude C)ll Entitlements, Application for Petroleum Substi-tutes, ” ERA-O 1, submitted to the Department of Energy, May 17,1979

219


The amount of petroleum displaced by etha-nol fuel also depends on the manner in whichit is used. As a standalone fuel, each gallon ofethanol displaces about 0.65 gal of gasolineequivalent. As an additive in gasohol, each gal-lon of ethanol displaces about 0.8 (± 0.2) galof gasoline. * (See ch. 10. ) If the oil refinery pro-duces a lower grade of gasoline to take advan-tage of the octane-boosting properties of etha-nol, up to 0.4 gal of gasoline energy equivalentcan be saved in refinery processing energy (seech. 10) for each gallon of ethanol used.

Additional energy savings are achieved byusing the byproduct disti l lers’ grain as ananimal feed. To the extent that crop produc-tion is displaced by this animal feed substitute,the energy required to grow the feed crop isdisplaced.

Table 65 summarizes the oil and natural gasused and displaced for the entire gasohol fuelcycle. The energy is expressed as gallons ofgasoline energy equivalent for each gallon ofethanol produced and used in gasohol (i. e., 1.0in the table represents 117,000 Btu/gal of eth-anol, 0.5 represents 58,500 Btu/gal of ethanol,etc.) The three cases presented correspond to:1) two ways to calculate the present situation,2) future production of ethanol from the lessproductive land that can be brought into cropproduction and using coal as a distillery fuel,

*The greater displacement results from the alcohol’s Ieaningeffect

and 3) the same as (2) except that the octane ofthe gasoline is lowered to exactly compensatefor ethanol’s octane-boosting properties. Theyresult in net displacements of: 1 ) from zero toone-third gal, 2) about one-half gal, and 3)slightly less than 1 gal of gasoline and naturalgas equivalent per gallon of ethanol used.

In all, the total displacement of premiumfuels (oil and natural gas) achieved per gallonof ethanol can be nearly 1 gal of gasolineequivalent per gallon of ethanol if petroleumand natural gas are not used to fuel ethanoldistilleries and 2) lower octane gasoline is usedin gasohol blends. Failure to take these steps,however, can result in the fuel cycle consum-ing slightly more oil and natural gas than itdisplaces leading to a net increase in oil andgas consumption with ethanol production anduse. This is the situation that is alluded to inmost debates over gasohol’s energy balance,but it is a situation that can be avoided withappropriate legislation.

Nevertheless in the most favorable case(case 3) and with an energy-efficient distillery,the ratio of total energy displaced to totalenergy consumed is 1.5 ( ± 0.4), i.e., the energybalance is positive (a ratio greater than 1). Andif the feedstocks are derived from more pro-ductive farmland, or local conditions allowenergy savings at the distillery, e.g., not havingto dry the distillers’ grain, then the balance iseven more favorable. Alternatively, an energy

Table 65.–Energy Balance of Gasohol From Corn: Oil and Natural Gas Used(+) and Displaced ( - )(in gallons of gasoline equivalent per gallon of ethanol produced and useda)

Set-aside and potential cropland

PresentCoal-fired distillery and

lowering of gasolineEntire plant Ethanol only Coal-fired distillery octane Uncertainty

Farming. . . . . . . . . . . . . . . . . . . . . 0 . 3b 0 . 3b 0.4c 0.4C

?0.15Distillery . . . . . . . . . . . . . . . . . . . . 0.55 0.24 0 e Oe

Distillery byproduct . . . . . . . . . . .—

- 0 . 0 9 d o - 0 . 0 9d – 0 . 0 9 d ±0.03Automobile. . . . . . . . . . . . . . . . . . . - 0 . 8 - 0 . 8 - 0 . 8 - 0 . 8 ± 0 . 2Oil refinery. . . . . . . . . . . . . . . . . . . — — — - 0 . 4 ± 0.2

Total. . . . . . . . . . . . . . . . . . . . . . - 0 . 0 - 0 . 3 - 0 . 5 - 0 . 9 * 0 . 3

aLower heat content Of gasoline and ethanol taken to be 117,000 Btu/gal and 76,000 Btu/gal, resPectlve&bo 16 as nitrogen ferflhzer (from natural gas) and 0.13 tTI05tly as Petroleum ProductscEQlmated “nce~alnly of tO 15, assumes 75% of the yield achievable on avera9e croplanddBa5~ on soy~an ‘Ultlvatlon and ~rushlng energy The byproduct of 1 gal of ethanol from corn displaces 12 lb of crushed soybeans, whtch requires 009 gal Of gasoline eqUIValenf tO produce private COM-

murrlcatlon with R Thomas, Van Arsdall, National Council of Farmer Cooperatese5 5,000 BIU Ot COaI per gallon of ethanol

SOURCE Offtce of Technology Assessment

Ch. 11-Energy Balances for Alcohol Fuels ● 221

credit could be taken for the crop residues,which would also improve the calculated bal-ance. This general approach to the energy bal-ance, however, does not consider the differentvalues of Iiquid versus solid fuels.

The uncertainty factor in table 65 of ± 0.3gal of gasoline per gallon of ethanol is dueprimarily to inherent differences in farmingpractices and yields, errors in fuel efficiencymeasurements, uncertainties in oil refinerysavings, and the magnifying effect on theseerrors of the low (10 percent) ethanol contentof gasohol. These factors make more preciseestimates unlikely in the near term.

Not only does the farming energy used forgrain or sugar crop production vary consider-ably from State to State, but also the averageenergy usage displays some differences be-tween the various feedstocks. A more signifi-cant difference arises, however, between useof the ethanol as an octane-boosting additiveto gasoline and as a standalone fuel, e.g., indiesel tractors or for grain drying. As an oc-tane-boosting additive, each gallon of ethanoldisplaces up to 1.2 gal of gasol ine energyequivalent in the automobile and at the re-finery (see table 65). * As a standalone fuel,however, the displacement at the end use isonly 0.65 to 0.8 gal of gasoline energy equiv-alent per gallon of ethanol.**

Table 66 summarizes the net displacementof premium fuels (oil and natural gas) forvarious feedstocks and the two end uses. I neach case it was assumed that the feedstockswould be grown on marginal cropland withyields that are 75 percent of those obtained onaverage U.S. cropland.

The striking feature displayed in table 66 isthat use of ethanol as a standalone fuel is con-siderably less efficient in displacing premiumfuels than use of it as an octane-boosting ad-ditive. In some cases, e.g., with grain sorghumand in areas with poor yields of the other

*O 4 gal of gasoline equivalent IS due to the octam-boostingproperties of ethanol and () 15 gal 15 due to the leaning effect ofthe a Icohol

● * Used as a standalone fuel in spark-ignition engines, alcohol-fueled engines can have a 20 percent higher thermal efflclencvthan their gasollne-fuelwf counterparts (see ch 10)

Table 66.–Net Displacement of Premium Fuels (oil andnatural gas) From Various Feedstocks and Two End Uses

(energy expressed as gallons of gasoline equivalent per gallonof ethanol produced and useda)

Ethanol used as an octane-boosting additive to Ethanol used as a

Feedstock gasolineb standalone fuelc

Corn . . . . . . . . . . . . 0.9 0.4Grain sorghum . . . 0.7 0.1Spring wheat . . . . . . 1.0 0.5Oats. ., 1.0 0.5Barley ... ., ., . 1,0 0.4S u g a r c a n e 0.9 0.3

%ssut-mflg lower fl@ content of gasoline and ethanol to be 117000 Btu/gal and 76000 Btu/galrespectwely, crops grown on margmal cropland wlfh yields of 75 percent of average croplandyields, distillers’ gram energy credts as In table 65 for all grams and no credit for sugars, dlst[l-Iers fueled with nonpremmm fuels, nahonal average energy Inputs S Barber et al The Po-tential of Producing Energy From Agriculture. contractor report 10 OTA

bUncerfamty * O 3CUncertamfy t O 2


grains, ethanol produced from grains and usedas a standalone fuel (e. g., onfarm as a dieselfuel substitute) may actually lead to an in-creased use of premium fuels, even if nonpre-mium fuels are used in the distilIery. Conse-quently, caution should be exercised if onfarmethanol production and use are encouraged asa means of reducing the U.S. dependence onimported fuels.

Furthermore, the agricultural system is socomplex and interconnected that it is virtuallyimpossible to ensure that large levels of grainproduction for standalone ethanol fuel wouldnot lead to a net increase in premium fuel con-sumption. Two examples illustrate this point. Ifgrain sorghum from Nebraska is used as an eth-anol feedstock (to produce a standalone fuel),the net displacement of premium fuels per gal-lon of ethanol is similar to the national aver-age for corn. A secondary effect of this, how-ever, could be an increase in grain sorghumproduction on marginal cropland in Texas, andthe increased energy required to grow thisgrain sorghum could more than negate the fueldisplaced by the Nebraska sorghum. Similarly,ethanol production from corn could raise cornprices and lead to some shift from corn tograin sorghum as an animal feed. Dependingon where the shifts occurred, U.S. p r e m i u mfuel consumption could either increase or de-crease as a resuIt.

222 . Vol. It—Energy From Biological Processes

The crucial point is that the energy usage in In order to avoid this situation, care should beagriculture is an important consideration in taken to ensure that ethanol derived fromdetermining the effectiveness of a fuel ethanol grains and sugar crops be used in the most en-

program. Because of this, there can be situa- ergy-efficient manner possible, i.e., as antions where energy from agriculture does not octane-boosting additive.result in a net displacement of premium fuels.

Methanol and Ethanol From Wood, Grasses, and Crop Residues

Methanol, like ethanol, can be used as anoctane-boosting additive and the oil refineryenergy saved per gallon of methanol is roughlyequivalent to that of ethanol. The lower energycontent (per gal Ion) of methanol, however,leads to a smaller displacement of gasoline inthe automobile per gallon of alcohol (0.6 gal ofgasoline equivalent per gallon of methanolversus 0.8 for ethanol; see ch. 10). On the otherhand, the energy used to grow, collect, andtransport wood and plant herbage for metha-nol production is less than for ethanol f e e d -stocks such as grain and sugars. There are,however, considerable local variations andwhere, for example, crop residues are col-lected on lands with poor yields, the energyconsumed in collection could be comparableto that needed to produce some grains andsugar crops.

Table 67 presents a summary of the net dis-placement per gallon of alcohol for the vari-ous Iignocellulosic feedstocks and two enduses. The net displacement per gal Ion of meth-anol is comparable to that obtained for etha-nol from grains and sugar crops, because thelower energy content of methanol (as com-pared to ethanol) is largely compensated forby the lower energy required to obtain metha-nol feedstocks.

Another aspect of the energy balance for theIignocellulosic feedstocks is the net displace-ment of premium fuels per ton of feedstock. Intable 68, direct combustion, airblown gasifica-tion, and alcohol fuels production are com-pared with wood as the feedstock. Similar re-sults can also be derived for crop residues andgrasses.

Table 67.–Net Displacement of Premium Fuels (oil and naturalgas) With Alcohol Production From Various Feedstocks and

TWO End Uses (energy expressed as gallons of gasoline equivalentper gallon of alcohol produced and useda)

Used as an octane-boosting additive Used as a

Feedstock Fuel to gasoline standalone fuel

Wood . . . . . . . . . . . . Methanol 0 . 9b 0.4C

Grasses or cropresidues. . Methanol 0 . 8b 0.3C

Wood. . . . . . . . . . . . Ethanol 1.1 d 0 . 6d

Grasses or cropresidues. . . . . Ethanol 1.0 d

0 . 5d

aA55ume5 I ) [ower healing values of 57,000, 76,000, and 117,000 i3w/9al !Or Methanol. @tha”nol, and gasoline, respeclwely, 2) culhvatton (grasses) collection and transport (all Ieedslocks)energy of O 75 mlll!on Btu/dry Ion for wood and 2 mdhon Btu/dry ton for grasses and crop resi-dues (mcludmg fertilizers for grasses and fertdlzer replacements needed when crop res!dues arecollected), 3) methanol ytelds of 120 gal/ton for wood and 100 gal/ton for grasses and crop resl.dues (50V0 energy conversion efflclency), 4) ethanol yields are 100 gal/ton of Ieedstock fer-mented, but addlhonal feedstock amountmg to 25,000 Btu/gal of ethanol IS required for dlshlleryenergy over and above that obtained from burmng the byproduct hgnm (based on G H Emertand R Katz@n, “Chemicals From Biomass by Improved Enzyme Technology, ” presented at theSyrrrposIurn orr tlorrrass as a Non-Foss// Fuel Source, ACWCST Joint Chemical Congress, Hono-lulu, Hawall, Apr 1-6, t979), resulting m net yields of 86 and 84 gal/ton of feedstock for woodand grasses/crop residues, respechvely, 5) methanol and ethanol displace 1 0 and 1 2 gal, r@-spectlvely, of gasollne energy equivalent (per gallon of alcohol) at the refinery and m the automo-bile when used as octane-boosting addlwes 10 gasohne, 6) they replace O 48 and O 65 gal ofgasollne equwalent (per gallon of alcohol) al the end use when used as standalone fuels

bUncertamty *O 3cUncertamty *O 1dunce~alnly large, since future processes for producing ethanol from these f@edstocks are not

fully defined (see footnote a)

SOURCE Offlceof Technology Assessment

Table 68.-Net Displacement of Premium Fuel (oil andnatural gas) per Dry Ton of Wood for Various Uses

Net displacement of premium fuel

(106 Btu/dry ton (% of feedstockUse of feedstock) energy content)

Direct combustion (68% efficiency). 1 2ab

75Air gasification and combustion of fuel

gas (85% overall efficiency) . . . . . 1 5ab

95Methanol (used as octane-boostingadditive). . . . . . . . . . . . . . . . . . . . 13C

80Ethanol (used as octane-boostingadditive). . . . . . . . . . . . . . . . . 11C

70Methanol (standalone fuel). . . . . . . 6C

40Ethanol (standalone fuel) . . . . . . . . . 6C

40

aASSUrnln9 16 rllllllofl Btuld~ 10rl, 075 mllhon Btu/ton requwed for collechon and IransporfbAssumlng It replaces 011 burned with 85% @fflcl@ncycBased on table 67


Ch. 11-Energy Balances for Alcohol Fuels ● 223

Care should be exercised when interpreting boosting additives can be nearly as efficient intable 68. The ethanol yields (per ton of wood) displacing premium fuels as the direct com-and the energy that will be required by wood- bustion or airblown gasification of wood. Onto-ethanol distilleries are still highly uncertain. the other hand, if the alcohols are used asNevertheless, this table does display the gener- standalone fuels, the premium fuels displace-

al feature that alcohol fuels used as octane- ment is considerably smaller.

General Considerations

The results presented in tables 65 through 68are based on OTA’s estimates of average val-ues for the energy consumed and displaced bythe various feedstocks. These figures, however,cannot be taken too literally since local vari-ations and changing circumstances can influ-ence the results. Two of the more importantfactors which influence the results–the ener-gy required to obtain the feedstock and theend use of the fuel — are discussed below.

The energy needed to grow, harvest, andtransport the feedstocks varies considerably,depending on a number of site-specific factorssuch as quantity of available biomass per acre,terrain, soil productivity, plant type, harvest-ing techniques, etc. Generally, however, fac-tors that increase the energy requirements alsoincrease the costs. For example, where thequantity of collectable crop residues per acreis small both the energy used and the cost (perton of residue) will be higher than the average.The economics will therefore usually dictatethat— locally, at least—the more energy-effi-cient source of a given feedstock be used.

As the use of bioenergy increases, however,the tendency will be to move to less energy-efficient sources of feedstocks, and large Gov-ernment incentives could lead to the use ofbioenergy that actually increases domesticconsumption of premium fuels. The danger ofthis is minimal with wood, but somewhat great-er for grasses and crop residues due to thelarger amount of energy needed to grow and/orcollect them. The danger is even greater when

grain or sugar feedstocks are used for the pro-duction of standalone fuel ethanol.

Another important factor in the energy bal-ance is the end use of the alcohol fuel. As hasbeen emphasized above, there is a significantincrease in the displacement of premium fuelswhen the alcohol is used as an octane-boostingadditive. In the 1980’s, however, there could bean increased use of automobile engines thatdo not require high-octane fuels and that haveautomatic carburetor adjustment to maintainthe proper air to fuel ratio (see ch. 10). Withthese engines, the octane-boosting propertiesof the alcohols are essentially irrelevant. Con-sequently, if the automobile fleet is graduallyconverted in this way, there will be a gradualreduction in the fuel displacement per gallonof alcohol, until the energy balances derivedfor standalone fuels pertain. The same conclu-sion would hold if oil refineries convert tomore energy-efficient processes for producinghigh-octane gasoline.

Another consequence of these possiblechanges would be to increase the importanceof the energy required to obtain the feedstock.For example, if ethanol only displaces as muchpremium fuel as indicated when used as astandalone fuel, then, as mentioned above,cultivating and harvesting the grains or sugarcrops used as feedstocks may require morepremium fuel than is displaced by the ethanol.The danger of this is considerably less forgrasses and crop residues and virtually nonex-istent for forest wood used as feedstock foralcohol production.

CHEMICALS FROMChapter 12

BIOMASS

Chapter 12.-CHEMICALS FROM BIOMASS

Page 227 74.

~ ~ b t i b • • ● ● ● ● ● ● ● ● . • • 2 2 7Chemical Synthesis From Lignocellulose........ 229

75.

Page1974 Production of Plastics, SyntheticFibers, and Rubber, and EstimatedLignocellulose Raw Material Base Required 231Product Results in Fast Pyrolysis ofBiomass and Its Constituents. . ..........233

TABLESPage

69. Species With Long-Chain Fatty Acids inSeed Oil . . . . . . . . . ..................228

70. Species With Hydroxy and Keto FattyFIGURES

PageAcids ... , ...: . . . . . . . . . . . . . . . . . . . . .. ..228 38. Synthesis Routes for Converting

71. Potential Sources of Epoxy Fatty Acids ... 228 Lignocellulose Into Select Chemical72. Sources of Conjugated Unsaturates. .. ....228 Feedstocks . . . . . . . . . . . . . . . . . . . . .. ....23073. Major Petrochemicals That Can Be 39. Chemical Synthesis Involving Thermal

Synthesized From Lignocellulose. . .......231 Processes and Microwaves. . . . . . . . . . .. ..232

Chapter 12

CHEMICALS FROM BIOMASS

Introduction

Biomass is used as a source of several indus-trial chemicals, including dimethyl sulphoxide,rayons, vanillin, tall oil, paint solvents, tannins,and specialty chemicals such as alkaloids andessential oils. Biomass is also the source of fur-fural which is used to produce resins and adhe-sives and can be used in the production of ny-ion. ’ Aside from paper production, biomasscurrently is the source of cellulose acetatesand nitrates and other cellulose derivatives (4billion lb annually). Other chemicals includetall oil resin and fat acid, Iignosulfonate chem-icals, Kraft Iignin, bark chemicals, various seedoils, and many more. Every petroleum-derivedchemical currently being used could be pro-duced from biomass and nonpetroleum miner-als, but some (e. g., carbon disulphide) wouldrequire rather circuitous synthesis routes.

In the future biomass-derived chemicalscould play an increasing role in the petro-chemical industries. The economic decisionsto use or not to use biomass will be based onan assessment of the overall process fromfeedstock to end product and it will probably

‘ I S Goldstein, “Potential for Converting Wood Into Plastics, ”S( /ence, vol 189, p 847, 1975

involve consideration of various alternativesynthesis routes in most cases. At present, how-ever, too little information is available aboutthe relative merits of biomass-versus coal-de-rived chemicals to expect widespread, new in-dustrial commitments to biomass chemicals inthe near future. This uncertainty depends asmuch on uncertainties surrounding the costsand possibilities of coal syntheses as on thosesurrounding biomass chemicals. Continued re-search into both options is needed to resolvethe problem and it is likely (as has been thecase in the past) that a mix of feedstocks willresult.

Biomass-derived chemicals can be dividedinto two major areas: 1 ) those in which theplant has performed a major part of the syn-thesis and 2) those in which chemical industryfeedstocks are derived by chemical synthesisfrom the more abundant biomass resourcessuch as wood, grasses, and crop residues. Someexamples of each type are given below. Thepossibilities are so enormous, only an incom-plete sampling can be given here. A thoroughanalysis of the options for chemicals frombiomass is beyond the scope of this study.

Chemicals Synthesized by Plants

Several plant species produce relatively have properly placed chemical groups whichlarge quantities of chemicals that can be used are susceptible to chemical attack so that theyto produce plastics, plasticizers, lubricants, can be readily converted to the needed indus-coating products (e. g., paints), and various trial chemicals. There is also the possibi l i ty ofchemicals that can serve as intermediates in using biologicalIy derived chemicals to pro-the syntheses used for numerous industrial duce products (such as plastics) which wouldproducts. 2 be expected to have similar properties to the

The biologically synthesized chemicals thatproducts currently produced. For example, ny-lon could be made from acids and amines

are most easily used in the chemical industriesother than the six carbon acids and amines cur-

are those that are either: 1 ) identical to existingfeedstock or intermediate chemicals, or 2 )

rently used for nylon synthesis.

‘1 H Prlnc en, ‘ Potential Wealth Is New Crops. Research anclllevf~l(jpm[~nt ,“ ( rop l?e~ource} ( N e w Y o r k Academic Pres$, S o m e p l a n t species producin g various1’977) c l a s s e s o f c h e m i c a l s a r e s h o w n i n t a b l e s 6 9

227

228 ● Vol. I I -Energy From Biological Processes

through 72. (Note that these lists are incom-plete and used only to illustrate some possi -bilities.) Included are the following types:

●

●

●

long-chain fatty acids which might beused for the production of polymers, lu-bricants, and plasticizers;hydroxy fatty acids which could displacethe imported castor oil currently used as asupply of these fatty acids;epoxy fatty acids which may be useful inplastics and coating materials; and

Table 69.–Species With Long-Chain Fatty Acids in Seed Oil

Component inCommon name Species triglyceride oil

Crambe. . . . . . . . Crambe abyssinica 60% C22

Money plant . . . . Lunaria annua 40% C22, 20% C24

Meadowfoam. Limnanthes alba 95% C 22 + C20

Selenia . . . . . . . Selenia grandis 58% C22

— Leavenworthia alabamica 50 % C22

Marshallia. . . . . . . . Marshallia caespitosa 44% C22

SOURCE : L. H. Prlncen, ‘‘Potenllal Wealth in New Crops Research and Development, Crop Re-sources (New York Academic Press, Inc. ), 1977

Table 70.–Species With Hydroxy and Keto Fatty Acids

Component inCommon name Species triglyceride oil

B ladde rpod .Consessi

H o l a r r h e n a .B i t t e r c r e s s . ,

Thistle . . . . . . .Bladderpod . . . .Blueeyed

Capemarigold. .

Myrtle Coriaria. . .

Lesquerella gracilis

Holarrhena antidysentericaCardamine impatiens

Chamaepeuce afraLesquerella densipila

Dimorphotheca sinuata

Coriaria myrtifolia

Cuspedaria pterocarpa

14-OH-C 20 (70%)

9-OH-C,8 (70%)Dihydroxy C22 and C24

(23%)Trihydroxy C18 (35%)12-OH-C 18 diene (50%)

9-OH-C 18 conj. diene(67%)

13-OH-C 18 conj. diene(65%)

Keto acids (25%)

SOURCE L H Prmcen, ‘‘Polenhal Wealth m New Crops Research and Oevelopmenl, Crop /?e.sources (New York Academic Press, Inc ), 1977

Table 71 .–Potential Sources of Epoxy Fatty Acids

Epoxy acidCommon name Species content,%

Kinkaoil ironweed. . . . Vernonia anthelmintica 68-75%Euphorbia Euphorbia Iagascae 60-70Stokesia Stokesia Iaevis 75

— . . . . . . . Cephalocroton pueschellii 67— Erlangea tomentosa 50

Hartleaf Christmasbush Alchornea cordifolia 50 (c20)— Schlectendalia Iuzulaefolia 45

SOURCE L H Prmcen, ‘‘Potenllal Wealth In New Crops Research and Development, Crop Re-sources (New York Academic Press, Inc ), 1977

Table 72.–Sources of Conjugated Unsaturates

Common name Species Type of saturation

Common valeriana. . . . . . Valeriana officinalis 40% 9,11,13Potmarigold colendula . . . Calendula officinalis 55% 8,10,12Spurvalerian centrathus. .Centranthus macrosiphon 65% 9,11,13Snapweed . . . . . . . . . . . Impatiens edgeworthii 60% 9,11,13,15Blueeyed Capemarigold . Dimorphotheca sinuata 60% 10,12

( + hydroxy)Myrtle Coriaria . . . . . . . . Coriaria myrtifolia 65% 9,11

(+ hydroxy)

SOURCE L H Prmcen, ‘‘Potential Wealth m New Crops” Research and Development, Crop l?e-

●

sources (New York Academic Press, Inc ), 1977

conjugated unsaturates potentially usefulas intermediates in the synthesis of vari-ous industrial products. (These can also beobtained from structural modification ofsoybean and linseed fatty acids.3).

Other possible new sources of chemicalsand materials include natural rubber from gua-yule (Parthenium argentaturn),4 and possibly jo-joba (Sirnmondia chinensis) and paper pulpfrom kenaf (H ib iscus cannabinus) .5 Some ofthese plants have also received considerableattention because it may be possible to growthem on marginal lands or land where the irri-gation water is insufficient to support conven-tional crops (see ch. 4). It is risky, however, toextrapolate unambiguous conclusions abouttheir economic viability from incomplete dataon the cultivation. In many cases they wouldalso compete with food production for theavailable farmland. Nevertheless, continuedscreening of plant species together with cul-tivation tests should provide numerous addi-tional options for the cultivation of cropsyielding chemicals for industrial use.

Another type of chemical synthesis involvesthe use of specific bacteria, molds, or yeasts tosynthesize the desired chemicals or substance.Commercial production of alcohol beveragesby fermentation is one example. Mutant bac-teria designed to produce insulin or other

‘W j De Jarlals, L E Cast, and j C Cowan, / Am, Oi/ Chem,SOC., VOI 50, P 18, 1973

‘K E Foster, “A Sociotechnlcal Survey of Eluyule Rubber Com-mercla Iizat Ion, ” report to the National Science Foundation,Dlvlslon of Policy Research and Analysis, grant No PRA78-11632, April 1979

‘M O f3agby, “Kenaf A Practical Fiber Resource, ” TAPP/Press Report Non-Wood Plant Fiber Pulping Process Report, No8, p 175, Atlanta, Ca , 1977

Ch. 12—Chemicals From Biomass . 229

drugs is another. ’ 7 Furthermore, other basicbiochemical processes such as the reductionof nitrates to ammonia may also be used even-tual ly.8

“Pe~r( e Wright, 1 Ime for Bug Valley, ” New Sc/ent/sL p 27,Julv 5, 1979

“’Where Genctlc Englneerlng Will Change Industry, ” f3usJnessWee&, p 160, Oct 22, 1979

‘P Candan, C Manzano, and M Losada, “Bloconverslon ofLight Into Chemical Energy Through Reduction With Water ofNitrate to Ammonia, ” Nature, VOI 262, p 715, 1976

Further study into the details of photosyn-thesis, the biochemistry of plants, and molecu-lar genetics could lead to the development ofother plants or micro-organisms that could syn-thesize specific, predetermined chemicals. Theoptions seem enormous at this stage of devel-opment, but considerable additional R&D isneeded before the full potential of this ap-proach can be evaluated.

Chemical Synthesis From Lignocellulose

The second major area of chemicals frombiomass involves using the abundant biomassresources of wood, grasses, and crop residues(Iignocellulosic material) to synthesize large-volume chemical feedstocks, which are con-verted in the chemical industry to a wide varie-ty of more complex chemicals and materials.The large (polymer) molecules in lignocellulo-sic materials are converted to the desiredchemical feedstocks either: 1 ) by chemicalmeans or 2) with heat or microwaves. The dis-tinction between these two approaches, how-ever, is not always clear cut.

The chemical means include treatment withacids, alkaline chemicals, and various bacteri-al processes. Pretreatments also often involvesome heating and mechanical grinding (see ch.8). The three basic polymers– Iignin, cellulose,and hemicellulose — are reduced to sugars andvarious benzene-based (so called aromatic)chemicals, which can be used to synthesize thechemical feedstocks by rather direct and effi-cient chemical synthesis or fermentation (seefigure 38). Some of the major petrochemicalfeedstocks that can be produced in this wayare shown in table 73, together with the quan-tities of these chemicals (derived mostly frompetroleum) which were used by the chemicalindustries in 1974.

The quantities of wood that would be re-quired to satisfy the 1974 U.S. demand for plas-tics, synthetic fibers, and synthetic rubberfrom the above chemical feedstocks are shownin table 74 for the various types of products.

These estimates were derived by Goldstein’using optimistic assumptions about the yieldsof the sugars- and benzene-based chemicalsfrom wood. Obtaining these sugars- and ben-zene-based compounds from wood is currentlythe subject of considerable R&D. (See ch. 8.)The yields for the other chemical reactionswere based on established experimental andindustrial data.

About 95 percent of these synthetic poly-mers (plastics, synthetic fibers, and syntheticrubbers) can be derived from wood or otherIignocellulosic materials, although the cir-cuitous synthesis route required for some ofthem might make such processes uneconomicat this time. I n al 1, SIightly less than 60 milliondry tons (about 1 Quad) of wood per yearcould supply 95 percent of these synthetic pol-ymer needs; and the ratio of cellulose to Iigninrequired (2:1) would be about the same as theirnatural abundance in wood. This quantity ofwood is relatively modest in comparison toOTA estimates of the quantities that can bemade available, and in all cases it serves as adirect substitute for chemicals derived fromfossil fuels (mostly oil and natural gas). Aboutthree to five times as much wood would beneeded to supply all petrochemical needsusing more or less established chemical syn-thesis routes, 10 and again there appears to beno technical barrier to supplying these quan-tities of wood. In both cases, however, addi-

‘Goldsteln, op clt1 “1 S Goldstein, Department of Wood and Paper Sc Ien( e,

No r t h Carolln~ State Unlverslty, Raleigh, N C , prlvdte communi-

cdtlon, 1980

230 . Vol. I/—Energy From Biological Processes

Figure 38.—Synthesis Routes for Converting Lignocellulose Into Select Chemical Feedstocks

HydrolysisHydrogenation Phenolic C 6H 50 H C 6H 6

LigninPyrolysis Benzene

SOURCE: 1. S. Goldstein, “Chemicals From Lignocellulose,” Biotechnol. and Bioen. Symp. No. 6, (New York: John Wiley and Sons, Inc., 1976), p. 293.

Ch. 12—Chemicals From Biomass . 231

Table 73.–Major Petrochemicals That Can Be SynthesizedFrom Lignocellulose

1974 U.S. production(in billions of pounds)

Total IignocelluloseAmmonia ., . . . . . . . . . ., 31.4Methanol ., ., . . . . . . . . 6.9HemicelluloseEthanol. ., ., ., ... ., ., ., . . 2.0celluloseEthanol, . . . . . ., ., ., ... ., 2.0Ethylene . . . . . . . . . . 23,5Butadiene ., . . 3.7LigninPhenol . . . . . ., ., ... 2.3Benzene . . 11.1

SOURCE: From l. S. Goldstein Chemicals From Lignocellulose in Biotechnology and Bioener-gy Symposium No 6( John Wiley&Sons Inc. p 293 1976)

tional energy would be needed to provide heatfor the syntheses; and, in some cases, this ismore than the energy content of the chemicalfeedstock.11 As of 1976, the petrochemical in-dustry consumed 1.2 Quads/yr of oil and natu-ral gas for fuel and 2.3 Quads/yr for feed-stocks. 12

Another approach to chemicals from ligno-cellulose involves heat, partial combustion, orthe use of microwave radiation to break thenatural polymers into smaller molecules suit-able for the synthesis. Biogas derived from theanaerobic digestion of biomass could also beused in some of these processes, but the yieldsare Iikely to be lower than for the more directprocesses. Some possible synthetic routes areshown in figure 39.

‘1“ BIg Future for SVnthetlcs, ” Science, VOI 208, p 576, May 9,1980

12G B Hegeman, Report to the Petrochemical Energy G r o u pon 1976 Petrochem/ca/ /ndustry Prof//e (Cambr idge, Mass Ar-thur D Little, Inc , June 28, 1977)

Table 74.–1974 Production of Plastics, Synthetic Fibers,and Rubber, and Estimated Lignocellulose

Raw Material Base Required

LignocelluloseProduction required a

Material (10 3 tons) (10 3 tons)

PlasticsThermosetting resins

Epoxies . . . . . . . . . . . . . . . . . .Polyesters ., ., .,Urea . . . . . . . . . . . . . . . . . . . .Melamine. . . . . . . . . . . . . . . . .Phenolic and other tar-acid resins

Thermoplastic resinsPolyamide . . . . . . . . . . . . . . . .Polyethylene

Low density. . . . . . . . .High density . . . .

Polypropylene and copolymersStyrene and copolymers, . ,P o l y v i n y l c h l o r i d e . ,Other vinyl resins . . . . . . . . . . .

125455420

80670

100

2,9851,4201,1252,5052,425

175

T o t a l p l a s t i c s . . , 12,485

Synthetic fibersCellulosic

Rayon . . . . . . . . . . . . . . . . . . .Acetate ... . . ... .,

NoncellulosicNylon. . . . . . . . . . . . . . .Acrylic, . . . . . . ... . .Polyester . . . . . . . . . . . . . .Olefin . . . . . . . . . . . . . . . . . . .

Total noncellulosic fibers,

Synthetic rubberStyrene-butadiene . . . . . . .

Butyl. . . . . . . . . . . . . . . . . . . . .Nitrile . . . . . . . . . . . . . . . . . . . .Polybutadiene . . . . . . . . . . . . . . .P o l y i s o p r e n eE t h y l e n e - p r o p y l e n e . . ,Neoprene and others. . . . . . .

Total synthetic rubber. . . .

Total plastics, noncellulosic fibers,and rubber. . . . .

Obtainable from IignocelluloseCellulose drived (C). ., . . . . .Lignin derived (L) . . . . . . .

410190

1,065320

1,500230

3,115

1,615

18095

360100140280

2,770

18,37017,490

355 (L)1,220 (L)

——

1,915 (L)

285 (L)

11,940 (c)5,680 (C)4,500 (c)7,445 (L)4,225 (C)

440 (c)

——

3,045 (L)640 (C)

4,020 (L)920 (C)

5,700 (c)1,920 (L)1,060 (C)

190 (c)2,120 (c)

—825 (C)

—

58,44538,240 (C)20,205 (L)

aEstlmated from Opllmlstlc approximate yields of monomers obtainable (C) cellulose derived (L)hgmn derwed

SOURCE I S Goldstein. “Potent ial for Converrlng Wood Into Plasttcs, Science VOI 189, P

847, 1975


Figure 39.—Chemical Synthesis Involving Thermal Processes and Microwaves


The production of ammonia’ 3 and methanolfrom wood can be accomplished with commer-cial technology (see ch. 7 for further details ofthe methanol synthesis). The Fischer Tropschprocess is commercial in South Africa (al-though the source of the synthesis gas is coalrather than biomss). The economics of theprocesses other than methanol synthesis havenot been assessed by OTA for this report.

The other processes yielding various chemi-cals are considerably less developed. Theyields of some chemicals that have been pro-duced in laboratory experiments using rapidheating and gasification (pyrolysis) of various

1‘R W Rutherford and K Ruschln, “Product ion of AmmoniaSynthesis Ca$ From Wood Euel In Incfla, ” presented at a meetingof the Institute of Chem Ica I E nglneers, London, Oct 11, 1949

types of biomass are shown in table 75. Pre-sumably by learning more about pyrolysis, theyields of select chemicals would be increasedto a level where it could be economical to ex-tract that chemical from the gas. An examplemight be the conceptual equation:

C 1 0H 1 4O 6 - 3CO2 + 3.5 C2H4

Wood Carbon dioxide Ethylene(solid) (gas) (gas)

where 43 weight percent of the dry wood isconverted to ethylene (which is by far the Iarg-est volume petrochemical used for chemicalsynthesis in the world). If it becomes practicalto achieve relatively high (e. g., 30 weight per-cent) yields of ethylene, then this processcould be competitive with petroleum-derived

Ch. 12—Chemicals From Biomass ● 233

I

I I

I

1

I

I


References to Table 75

Antal, M. J., W. E. Edwards, H. C. Friedman, and F. E. Rogers, ‘‘A Study of the Steam Gasification of Organic Wastes, Environmental Protection AgencyUniversity grant No. R 804836010, final report, 1979.

Berkowitz-Mattuck, J, B. and T. Noguchi, “Pyrolysis of Untreated and APO-THPC Treated Cotton Cellulose During l-See. Exposure to Radiation Flux Lev-els of 5-25 cal/mc2 sec.1, J. App/ied Po/ymer Science, vol. 7, p. 709, 1963.

Brink, D. 1.., ‘ ‘Pyrolysis –Gasification–Combustion: A Process for Utilization of Plant Material, Applied Polymer Symposium IVO. 28, p. 1377, 1976.Brink, D. L, and M. S. Massoudi, ‘‘A Flow Reactor Technique for the Study of Wood Pyrolysis. 1. Experimental, J. Fire and flammability T, p. 176, 1978.Diebold, J. P. and G. D. Smith, ‘‘Noncatalytic Conversion of Biomass to Gasoline, “ ASME paper No. 70-Sol-29, 1979.Hileman, F. D., L. H. Wojeik, J. H. Futrell, and 1. N. Einhorn, ‘(Comparison of the Thermal Degradation Products of Cellulose and Douglas Fir Under Inert

and Oxidative Environments, Therma/ Uses and Properties of Carbohydrates and Lignins Symposium, Shafizadek, Sarkenen, and Tillman, ed. (Aca-demic Press, 1976), p. 49.

Lewellen, P. C., W. A. Peters, and J. B. Howard, “Cellulose Pyrolysis Kinetics and Char Formation Mechanism, Sixteenth Symposium (International onCombustion (The Combustion Institute, 1976), p. 1471.

Lincoln, K. A., ‘‘Flash Vaporization of Solid Materials for Mass Spectrometry by Intense Thermal Radiation,Ana/ytica/ Chemistry, VOI 37, p. 541, 1965.Martin, S., “Diffusion-Controled Ignition of Cellulosic Materials by Intense Radiant Energy, ’ Tenth Symposium (/niernationa/) on Combustion (The Com-

bustion Institute, 1965), p. 877.Prahacs, S., “Pyrolytic Gasification of Na-, Ca-, and Mg- Base Spent Pulping Liquors in an AST Reactor, ’ Advances in Chemistry Series, vol. 69, p. 230,

1967.Prahacs, S., H. G, Barclay, and S. P. Bhaba, ‘‘A Study of the Possibilities of Producing Synthetic Tonnage Chemicals From Lignocellulosic Residues,

Pu/p and Paper Magazine of Canada, vol. 72, p. 69, 1971.Rensfelt, E., G. Blomkvist, C. Ekstrom, S. Engstrom, B. G. Espenas, and L. Liinanki, ‘‘Basic Gasification Studies for Development of Biomass Medium-Btu

Gasification Processes.Stern, E. W., A. S. Logindice, and H. Heinerman, ‘‘Approach to Direct Gasification of Cellulosics, Industrial Engineering Chemistry Process Design and

Development, vol. 4, p. 171, 1965.

ethylene. The ethylene could be converted to netic radiation) could possibly be used toethanol, and overall processing costs (wood to break specific predetermined chemical bondsethanol) may be considerably lower than those in order to guide and control the decomposi-projected for fermentation processes (see chs. tion of the biomass.7 and 8).

Rapid pyrolysis, cracking, and microwaveThe liquefaction process for producing a py- processes are still at the research stage and

rolytic oil (see ch. 7) might also be carried fur- considerable work is required to determinether by cracking the oil in a way that is analo- their feasibility. Efforts along these directions,gous to current oil refinery technology. In ad- might lead to significant advances in the use ofdition, microwave energy (or other electromag- biomass for chemicals and fuels.

U . S . GOVERNMENT PRINTING OFFICE : 1980 0 - 67-968 : Q L 3

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