7/30/2019 Design Gas Vapour Biomass http://slidepdf.com/reader/full/design-gas-vapour-biomass 1/15 Pergamon Biomass and Bioenergy, Vol. 9, Nos l-5, pp. 71-285.1995 Else&r Science I&t 0961-9534(95)000968 Printed n Great Britain 0961-9534i95 $9.50 + 0.00 THERMAL GASIFICATION OF BIOMASS TECHNOLOGY DEVELOPMENTS: END OF TASK REPORT FOR 1992 TO 1994 S P BABU IEA Thermal Gasification Activity Leader, Institute of Gas Technology 1700 South Mount Prospect Road, Des Plaines, Illinois 60018-I 804, U.S.A ABSTRACT Th e widely recognised importance of biomass utilisation in controlling carbon build-up in the biosphere and the potential benefits of creating new industries and job opportunities, particularly in the rural areas, have added impetus to the development and commercialisation of advanced biomass energy conversion methods in some Western countries. The world-wide recoverable residues is estimated to be 31 exajoules per year, or 10% of global commercial use. The present biomass combustion power plants have efficiencies in the 15% to 20% range, with electricity costs in the range of US $0.065 to $O.OS/kW h. In contrast, the advanced power-generating cycles utilising gasification have the potential for higher generation efficiencies, 35% to 40%, and lower costs of electricity, $0.045 to $O.O55/kWh. The IEA Biomass Thermal Gasification Activity continued to promote information exchange among the nine participating countries, to ultimately commercialise biomass gasification. The Activity continued to monitor the latest developments in handling herbaceous feedstocks, pilot plant performance of advanced gasification processes, including hot-gas cleanup for demonstration and commercial design, and the testing of a close-coupled prototype gas turbine and a molten carbonate fuel cell. In addition, the participants conducted task studies on Biomass resources for gasification, Biomass feedstock preparation for gasification, Evaluation of biomass feeders, Strategies for sampling analysis of raw gas streams from gasifiers, Altholz gasification, MSW gasification, Hot-gas cleanup, and Combustion characteristics of LCV fuel gases. KEYWORDS Gasification, electricity from biomass, pilot-plant, INTRODUCTION The widely recognised importance of biomass utilisation in controlling carbon build-up in the biosphere and the potential benefits of creating new industries and job opportunities, particularly in the rural areas, have added impetus to the development and commercialisation of advanced biomass energy conversion methods in some of the Western countries. Recent analyses and evaluations have shown that many short rotation energy crops (SREC) produce significant net- energy (i.e., energy yield greater than their energy input ).’ In addition, it is reported that SREC such as willow, poplar, and miscanthus are known to yield up to 20 dry tonnes/ha/year of biomass feed stocks with about 20% moisture after the third year of plantation.2 The benefits of 27 1
Biomass and Bioenergy, Vol. 9, Nos l-5, pp. 71-285.1995
Else&r Science I&t
0961-9534(95)000968 Printedn Great Britain
0961-9534i95 $9.50 + 0.00
THERMAL GASIFICATION OF BIOMASS TECHNOLO GY
DEVELOPM ENTS: END OF TASK REPORT FOR 1992 TO 1994
S P BABU
IEA Therm al Gasification Activity Lead er, Institute o f Gas Technolo gy
1700 South Mount Prosp ect Road, Des Plaines, Illinois 60018-I 804, U.S.A
ABSTRACT
Th e widely recognised importance of biomass utilisation in controlling carbon b uild-up in the biosph ere
and the potential benefits of creating new industries and job opportun ities, particularly in the rural areas,
have added impetus to the development and commercialisation of advanced biomass energy conversion
methods in some Western countries. The world-wide recoverable residues is estimated to be 31
exajoules per year, or 10% of global commercial use. The present biomass combustion power plants
have efficiencies in the 1 5% to 20% range, with electricity costs in the range of US $0.065 to
$O.O S/kW h. In contrast, th e advanced power-ge nerating cycles utilising gasification have the potential
for higher generation efficiencies, 35% to 40% , and lower costs of electricity, $0.045 to $O.O5 5/kWh .
The IEA Biomass Thermal Gasification Activity continued to promote information exchange among the
nine participating countries, to ultimately comm ercialise biomass gasification. The Activity continued to
monitor the latest developments in handling herbaceous feedstocks, pilot plant performance of advanced
gasification proce sses, including hot-ga s cleanup for demons tration and comm ercial design, and thetesting of a close-coup led prototy pe gas turbine and a molten carbonate fuel cell. In addition, the
participants conducted task studies on Biomass resources for gasification, Biomass feedstock
preparation for gasification, Evaluation of biomass feeder s, Strategies fo r sampling analysis of raw gas
streams from gasifiers, A ltholz gasification, MSW gasification, Hot-gas cleanup, and Combustion
characteristics of LCV fuel gases.
KEYWORDS
Gasification, electricity fro m biomass , pilot-plant,
INTRODUCTION
The widely recognised importance of biomass utilisation in controlling carbon build-up in the
biosphere and the potential benefits of creating new industries and job opportunities, particularly
in the rural areas, have added impetus to the development and comm ercialisation of advanced
biomass energy conversion methods in some of the Western cou ntries. Recent analyses and
evaluations have shown that many short rotation energy crops (SREC ) produce significant net-
energy (i.e., energy yield greater than their energy input ).’ In addition, it is reported that SR EC
such as willow, poplar, and miscanth us are known to yield up to 20 dry tonnes/ha/year of
biomass feed stocks w ith about 20% m oisture after the third year of plantation.2 The benefits of
herbaceous SRE C can be further augmented when value-added by-products, such as cattle feed,
could be produced along with biomas s energy feedstocks.
The availability of bioma ss for energy is dependent on many factors, the most important being
the overall cost of energy production for a given technology and its comparison with
conventional fuels. W ith reasonable assump tions, the energy content of world-wide recoverableresidues is estimated to be 3 1 exajoules per year, which is equivalent to about 10% of global
commercial energy use. It is also well known that the use of advanced biomas s energy
conversion systems can convert wh at is widely regarded as “a marginal (biomass) resource at
best, into a significant global resource3.” The present biom ass power plants use technology that
is similar to coal-fired plants, but normally at a smaller scale with a resulting loss of efficiency.
Today’s boiler/steam turbine p lants average about 20 M W in size and typically have efficiencies
in the 15% to 20% rang e. Electricity costs are in the range of U.S. $0.065 to $O.O8 /kW h. The
advanced systems have the potential for higher generation efficiencies, 35% to 40% , and lower
costs of electricity, $0.045 to $O.O 55/kW h, compared to conventional direct-combustion
systems. Turbine-based systems under consideration include open-cycle gas turbines, steam-injected gas turbines, intercooled steam-injected gas turbines, combined cycle systems, and
cogeneration systems. These observations are also consistent w ith the white-papers presented
by Shell International Petroleum CO .~, and We stinghouse Electric Corporation.
IEA BIOMA SS THERMAL G ASIFICATION ACTIVITY
With the increasing comm itment to fully explore the potential benefits of biomass gasification
as the backdrop, the IEA Biomass Thermal Gasification Activity continued to function through
the last triennium, 1992 to 1994, with the participation of experts from Cana da, D enmark,
Finland, The Netherlands, Norway, Sweden, Sw itzerland, U.K., and U.S. The objective of this
Activity is to promote information exchange on R& D programs, demonstration, and comm ercial
projects am ong the Activity participants in order to eliminate technological impedim ents to
commercialise biomass gasification.
ACCOMPLISHMENTS FOR 1992- 1994
The Activity conducts its business through semi-ann ual meetings held in the participating
countries and by pursuing specific task studies selected collectively by the participants. The first
day of the semi-annu al meetings is usually ded icated to invited ind ustrial and national policypresentations by experts directly involved in bioma ss gasification and energy conversion. These
presentations and the ensuing d iscussion, the exchange of information between participants
during the Activity Me etings, the technical review of selected tas k studies, and the plant visits
scheduled at the end of the Activity Mee tings have been the principal source of current
information on all aspects of developing biomass gasification-based advanced energy
conversion technologies. During the last triennium, six Activity M eetings were held, and more
than thirty ind ustrial experts and policy makers were invited to speak on a variety of subjects
directly related to biomas s gasification. Another benefit of the Activity has been the alliances
made by participating countries to launch joint biomass R& D programs and demonstration
gasification projects, to start with programs in the U.K. and Denm ark, with the participation of
Sweden and Finland, respectively. The following is a summ ary of the developments related to
the technological advances and barriers to scale up and comm ercialise biomass gasification,
current status of demonstration gasification projects in the participating countries, and a brief
summary of the task study reports prepared by the Activity participants during the last
triennium.
Technological Advances and Barriers to Com mercialisation
Feed Preparation and Feeding: The method of bioma ss feed preparation is closely related to the
physical properties of biomass and the type of gasification process. A variety of biomass
feeders designed and tested during the development of many of the gasification processes in
Canad a, Europe, and U.S. have worked satisfactorily for low and high-pressure process
development and pilot plant tests, particularly with woody biom ass. However, some of these
feeders may not be economical and reliable for commercial operations, particularly with
herbaceous feedstocks. The current demonstration projects will identify and evaluate feed
preparation methods and feeders that should be acceptable for commercial gasifier plant designs.
Biomass Gasification Technology Development: During 1 992 to 1994, many of the gasificationtechnologies were evaluated for demonstration projects, a nd the pilot plants at VTT, Espoo,
Varnam o, Sweden; Battelle Columb us (Battelle), Colum bus, Ohio U.S.A.; and Institute of Gas
Technology (IGT), Chicago, Illinois U.S.A., were employed with selected feedstocks to develop
the design data for demonstration projects. Tests were specially designed to investigate biomass
feed preparation and feeding, tar cracking within the gasifier and in a separate tar cracker, high
temperature particulate removal by ceramic candle filters, fuel gas properties for gas turbine
applications, unforeseen process performance and environmental problems du ring extended
operation, and operation of a close-coupled gas turbine and a fuel cell. Significant experimental
data were obtained; however, much of it is treated as proprietary information to provide a
competitive edge to technology developers.
Based on the license granted by IGT for its IGT RENUG AS@ biom ass gasification and the
U-GA S@ coal gasification processes to Enviropower, Inc., a 15 M W th input capacity
pressurised air-blown gasification pilot plant was built at Tampere, Finland. About 650 hours of
pilot plant tests have been successfully conducted so far with about 3000 tons of wood residue at
the same conditions as a full sized IGCC plant. These pilot plant tests also included testing
different types of biomass steam dryers, a new pressurised bioma ss feeder, and hot-gas clean-up
with ceramic filters. The pilot plant tests show >98% carbon conversion with a low tar content.
The ceramic filter tests demonstrated efficient dust and alkali removal exceeding the
requirements for gas turbine applications. It is reported th at the gas turbine operated well withthe resulting 4 to 6 MJ/Nm 3 fuel gas, with low CO and thermal NOx emissions5
Under a United States Department of Energy (USD OE) sponsored program, the 2 M W th (10
tonnes/day) REN UG AS’ pilot plant gasifier at IGT in Chicago h as recently completed
pressurised air-blown gasification tests with bagasse to test the W estinghouse Electric
Corporation (WE C) hot-gas cleanup unit (HGCU ) train and to characterise the fuel gases for gas
turbine applications. During the recent tests, a bench-scale molten carbonate fuel cell was
successfully operated on the raw product gas slip stream. The HGC U assembly will be installed
in the 10 to 20 MW th (50 to 100 tonnes/day) capacity demonstration gasifier in Haw aii for long
duration tests.
Battelle’s multi-solid fluidised bed (MSF B) pilot plant biomas s gasifier has been operated with
DOE sup port at throughput rates of 14.6 tonnes/m2/hr at W est Jefferson, Ohio. The capacity of
the pilot plant is 2 M W th (10 tons/day). Recent pilot plant tests showed that 90% tar removal
was accomplished with a proprietary Battelle catalyst (D N34) at’ 815°C . The tar conversion
increased to 97% at 870°C w ithout any coke formation. DN 34 also serves as a good waterdg as
shift catalyst, as indicated by the nearly complete conversion of CO to produce a fuel gas with
about 60% HZ . The pilot plant tests also included the successful operation of a 2 00 kW SO LAR
gas turbine.
Man ufacturing and Technology Conversion international (MI‘C I), Colum bia, Maryland, has
recently completed a series of tests in its .pilot gasifier in Baltimore, Ma ryland. The MT CI
process is a pulse-enhanced, indirectly-fired steam reformer gasifier for all types of carbonaceous
materials. Since the combustion zone is isolated from the reformer/gasifier, the low-in-volume and
high-in-heating value fuel gases could be economically cleaned. The combustion of a part of the
product gases instead of biomass to sustain the steam reforming reactions results in reduced NOx
emissions. The steam reformer/gasiIier employs 7 2 resonators or pulse combustors to supply the
endothermic process heat. During the test program, wood chips and wheat straw were gasified at
rates up to 1.2 MW th (6 tons/day). The MTCI process has been scaled up to 1OM Wth (50
tonnes/day) and is presently undergoing tests at the Weyerhauser paper mill at New Bern, NorthCarolina for the gasification of black liquor, a Kraft pulping co-product, with the sponsorship of
Weyerhauser and the DO E Office of Industrial Technology.
The Netherlands’ BTG has published a comprehensive report on the status of small-scale
biomass gasification systems that are developed and operated around the world. The report also
includes a discussion of the technical and operating problems.6 A follow-on report is due to be
published on the economics of these small-scale systems.
The U.K. is supporting biomass gasification test work in the W ellman updraft moving-bed gasifier
near Birmingham. The process uses a novel thermal tar cracker prior to combu sting the gases in a
150-kW Caterpillar en gine. Continuous tests are now in progress. Wh en developed, the Wellm angasifiers w ould be suitable for 3 to 5 MW e capacity range. W ith a proper ga s cleanup method, the
gasifier should operate with low-maintenance and low-labour requirements. The expected
efficiency of biomass conversion to power is about 30% .
Com position and Destruction of Oils and Tars
There has been a considerable amoun t of bench-scale and pilot plant research conducted in
Europe and the U.S. to determine the characteristics of gasification oils and tars and the methods
to crack and gasify them in order to avoid carbon deposition downstream from the gasifier. Thecomposition of oils and tars produced in a gasifier is mainly dependent on the biomass
gasification process. In general, the indirectly heated gasifiers and perhaps the updraft mo ving
bed gasifiers produce more light oils and some tars, while the air blown fluidised bed and
circulating fluidised b ed (CFB) biomass gasification processes produce m ore tars and less oils.
The high temperatures within the oxygen-or air-blown gasifiers thermally crack the lighter oils
into gaseous com ponents, aromatics, and polynuclear aromatics. The current pilot plant tests
conducted in support of the demonstration projects sho uld provide m ore insight into the
susceptibility of the different types of oils and tars to catalytic cracking and carbon deposition,
in particular on ceramic candle filters.
With DOE suppo rt, the Hawa ii Natural Energy Institute (HN EI) a t the University of Hawa ii isusing a laboratory-scale gasifier to test catalysts for conditioning hot raw product gas to
determine catalyst suitability to produce-.synthesis gas for methanol production and for gas
turbine/fuel cell applications. Current work is being conducted with Ni-based catalysts. Studies
are also underway with nitrogen-rich leguminous tree species, Leucaena spp, on the fate of
nitrogen in biomass gasification systems and to establish nitrogen speciation and destruction of
nitrogen compounds.
The U.K. is participating in a research program with the U.K. Coal Research Establishment,
Germany’s DMT, and Sweden’s Lund Technical University, to study the mechanism of tarformation from high, medium, and low-temperature gasifiers, tar composition and structure, and
the necessary catalytic treatment methods for reducing tars.
The U.K.‘s National Resources Institute and The Netherlands’ BTG are jointly investigating
representative gas sampling techniques and to develop a standard gas quality measurement
method.
Hot-Gas Filtration
The Schumacher ceramic filter elements were first evaluated in biomass gasification tests
conducted at the VTT pilot plant at 200°C (392°F) using a “face velocity” of 100 to 470 m/hour.
The top-held candles are made of filter membranes made of A&O, tibre and Sic. SEM pictures
showed that the filter elements retained high bending strength even at temperatures up to
1000°C. A No. 40 Schumalith filter membrane showed a pressure drop of 55 millibar after
20,000 cycles.
Schumacher supplied filter elements to Bioflow and Enviropower biomass gasification pilot
plants. The Bioflow unit contains 78 candles divided into six groups and designed for operation
at 200°C and 64 bar pressure. The Enviropower unit is designed for operation at 500°C and 20
bar pressure. In general, tars in fuel gases present more problems than alkalis. It is also
determined that pressure drop across the candle filter assembly is indicative of cake build-up and
integrity and failure of filter elements.
Lurgi Lentjes Babcock Energietechnik GmbH developed ceramic candle filters with filter
elements being supported from the bottom. This design incorporates sealing by compression
and provides adequate residence time to preheat the pulse gas prior to pulsing. Also, when a
candle fails, it is expected to be held in place. Candle filter assemblies have been successfully
scaled up from 21 to 56 to 184 filter elements. Several large filter assemblies have been
manufactured (up to 1800 candles, 500,000 Nm3/hour for operation up to 265°C and 25 bar
pressure) for demonstration coal conversion plants in Europe and the U.S.
WEC is currently evaluating several commercial high-temperature filter elements at their research
and demonstration coal conversion facilities in the U.S. WEC has developed proprietary seal
designs for improving the endurance and performance of candle filters. The design also includes
preheating pulse gas to reduce thermal shock and a shut-off mechanism to isolate a filter element
when it fails. So far, the filter elements have been tested up to 24 bar operating pressure, 5OO” C,
and for 4500 hours. The filter elements were obtained from Schumacher, Coors, 3M, and
DuPont.’
Fuel Gas Utilisation
The medium calorific value (MCV) fuel gas, obtained from indirectly heated gasifiers, can be
used in existing gas burners, IC engines, and gas turbine burners, with little or no modifications.
Low calorific value (LCV ) fuel gases (>6 MJ /Nm 3) can be combusted in many industrial burners
without down rating, but some burner modification may be required. For a gas with LCV (< 5
MJ/N m3), significant burner modifications may be required besides downrating. Preheating fuel
gas and/or combustion air would help improve com bustibility of LCV fuel gases. W EC
reported that with LCV fuel gas changes made to the combustor in a gas turbine include
replacing the fuel gas pipeline with a larger diameter p ipeline, increasing burner nozzle size, and
slightly increasing the combustion basket size. The air compressor remained the same, while a
slight change was made to the stationary part of the gas turbine inlet.
Orenda, a Canad ian company, has recently acquired a license for North A merica and Pacific-rim
countries for the Ukrainian MA SHPR OEK T turbine (29% fuel to shaft power efficiency) which
reportedly has run successfully with poor quality oils, in the former Soviet Union.* Evaluating
the suitability of this turbine for converting bioma ss fuel gas to power should be of interest to
the developing biomass gasification demonstration and commercial projects.
Because fuel cells offer modularity and very high-energy conversion efficiency, the DOE isplanning to develop gasification/fuel cell and pyrolysis/catalytic upgrading/fuel cell systems.
The strategy will involve formation of co-operative research and development agreement(s)
(CRA DA ’s) with industry to address specific fuel cell developmental issues, such as molten
carbonate fuel cell material p roblems, sulphur tolerance problems, and carbon dioxide
availability issues. These issues can be evaluated at laboratory scale. Research will concentrate
on defining and solving issues related to interfacing gas production systems with fuel cell
systems. The comm ercialisation of biomass gasification and fuel cell combinations depends on
the satisfactory development of gas conditioning and treatment to link the gasifier w ith the fuel
cell while reducing labour and capital requirements in what will initially be small scale systems
of less than 1 M W output. A first-generation comm ercial prototype will be constructed by mid-
1998 and the evaluation completed in the year 2000, at which time it is anticipated that the
development of economical fuel cells will be completed.
Other small-scale energy conversion equipment suitable for biomass-b ased cogeneration
systems includ es Stirling engines an d indirectly heated hot-air turbines.
Biomass Gasification Demonstration Projects
European Biomass Gasification Demonstration Programs: The European Com mission ha s
developed a plan to implement commercial bioma ss gasification projects und er the THER MIEprogram initiated in 1990. The goal of this program is to introduce IGCC power plants in the 8
to 15 MW e rang e by the late 19 90’s, 20 to 30 MW e ran ge by the end of this century, to be
followed by 50 to 80 M We units by 2005. The three important requirements for these projects
include:
?? Dedicated biomass supply system based on high-yield energy crops;
?? Demo nstration of advanced energy conversion systems;
?? Assurance of environmental benefits.
In 1994, out of seven proposals received for such demonstration projects, three proposals from
Denm ark, U.K. and Italy were selected. These three demonstration projects are listed, along
with the demonstration projects in U.S. and Brazil, in Table 1. The Denm ark BIOC YCL E
project will use the pressurised fluidised bed air-blown gasification technology from
Enviropower, Inc., and employ tar cracking w ith dolomite and particulate removal by ceramic
CFB gasitier, based on the pilot plant performance data obtained at the two gasification facilities
in Sweden. The downstream gas clean-up will be determined by the selected gasification
technology. The GE-LM 2500 ga s turbine will be used to convert the fuel gas to electricity.
TPS-Studsvik completed the required gasification tests with eucalyptus in its 2 M W th pilot
plant. Bioflow is expected to complete the gasification tests by now, in its 18 MW th pilot plant.
The Haw aii Biomass Gasification Demo nstration Project: The Haw aii Biomass G asification
Facility (BGF) project is part of a major USD OE initiative to demonstrate high-efficiency
biomass gasification systems. The project will provide a near-term demonstration for total
system integration of gasification and HGC U com ponents, with gas turbines for power
generation. The objective of the project is to scale up the 2M W th (IO-tonnes/day) IGT
REN UGA S’ pressurised air-blown fluidised-bed gasification pilot plant to a 10 to 20M W th (50
to 100 tonnes/day) demonstration unit using bagasse and wood as feed. The BGF is located a t
the Haw aii C omm ercial and Sugar Company’s (HC& S) Paia sugar mill on the island of Ma ui in
Hawaii, IJ.S.A.
Process scale-up will be completed in several phases. Phase 1, which is now underway, consists
of the design, construction, and preliminary operation of the gasitier to generate hot,
unprocessed gas which will be flared. The gasification system is presently undergoing
comm issioning. The gasifier has been designed to operate with either air or oxygen at pressures
up to 2.07 MP a at typical operating temperatures of 850” to 900°C . In Phase 2, to begin later in
1995, the gasifier will be operated at a feed rate of 10 M Wth (45 tonnes/day) and at about 1.04
MPa. The slip-stream HGC U, tested by W EC and IGT and described above, will be installed in
the demonstration gasifier and operated to obtain long-term performance evaluation information.
At the same time, the necessary design and environmental permitting will be completed for the
succeeding full-scale HGC U and gas turbine operation. The turbine may utilise supplementary
fuel to obtain an output tha t would permit com mercial operation at the completion of the
demonstration phase. In mid-199 6, a HGC U and gas turbine w ill be added to the system.
Options are being ev aluated for up to 5 MW e of electrical capacity. In this phase, the gasitier
feed rate will be a minim um of 20 MW th (90 tonnes/day), and the system will operate at
pressures up to 2.07 MPa. A third phase is being considered in which the gasifier will be
operated in an oxygen-blown mode to produce electricity and a clean synthesis gas for methanol
production.
Participants in the project are the Pacific International Centre for High Technology Research,
IGT, WEC , HC&S, HNE I, and Parsons, the architectural and engineering firm for the project.
Industry and the State of Haw aii have contributed US $4.2 million to Phase 1, with D OEcontributing $6.0 million. In Phase 2, the project will be co-funded by the State of Hawa ii,
industry, and DOE .
The Vermont Biomass Gasification Project: The Vermont project is part of the DO E initiative
to demonstrate biomass gasification. The Vermont Project has been undertaken to demonstrate
the integration of the Battelle “indirectly-heated” gasifier with a high efficiency gas turbine. The
goal of the Vermont project is to scale up the Battelle pilot plant g asifier from its present
2M W th (10 tonnes/day) capacity to 40 MW th (200 tonnes/day) capacity dem onstration project
to provide MC V gas for a nominal 15 MW e gas turbine. The demonstration and validation of
this gasification/gas turbine system is being undertaken at the existing McN eil Power
Generating Power S tation, a 50 M We wood-fired boiler/steam turbine station in Burlington,
Vermont, thereby significantly reducing the time-scale for deployment. The industrial partner is
Future Energy Resources Company (FERC O), Atlanta, Georgia, wh ich is putting u p the 50%
non-DO E cost share for the overall project. Other project participants include the co-owners of
the McN eil gene rating station located in Burlington, Vermont, and operated by the Burlington
Electric Department. Currently, Z um Nepco, a Portland, Maine -based engineering company
with extensive experience in the design and construction of biomass-fired power plan ts, is
preparing the detailed engineering design and permitting process for the start of construction,
which is scheduled for late 1995. Operation of the gasifier is forecast for late 1996, and the
addition of the gas turbine is forecast for late 1997.
Biomass Power for Rural D evelopment: It is the mutual goal of DOE an d the U.S. Department
of Agriculture (USD A) to demonstrate and deploy cost-competitive renewable biomas s power
systems that spur rural development. A key aspect of this goal is to demonstrate sustainable
biomass energy feedstocks, e.g., woody and herbaceous crops such as hybrid poplars or
switchgrass, coupled w ith high-efficiency power conversion systems. In support of this, DOE
initiated through the National Renew able Energy Laboratory (NREL) ten 50/50 cost-shared
subcontracts with private industry to conduct feasibility studies and develop b usiness plans for
integrated biom ass feedstock production and advanced pow er/liquid fuel conversion systems.
States included for study are California, Florida, Ha waii (2 systems), Kans as, Iowa, Minne sota,New York, and North Carolina, plus the Com monw ealth of Puerto Rico. The systems b eing
studied include gasification with gas turbines or fuel cells, advanced direct combustion, re-
powering or co-tiring, pyrolysis, and ethanol production via simultaneous saccarification and
fermentation. Following these efforts and given the high level of private-sector interest in
pursuing integrated bioma ss power projects, DOE in collaboration with USD A is planning to
select through competitive solicitation up to five integrated biomass power projects w ith 50/50
cost-shared co-operative agreements with private industry. These projects will be the first step
in demon strating the successful integration of biomass feedstock production with advanced
energy conversion technologies. It is expected that the average plant size will be between 25 to
75 M W while utilising an environmentally and economically sustainable biomass feedstock.
Through this collaborative DOE /USD A effort, these projects will also emph asise rural economic
development and job creation and the introduction of alternative industrial/energy crops for the
nation to potentially offset federal agricultural subsidy paymen ts.
Summ ary of Activity Task Study Reports
Biomass R esources for Gasification’: This task report presents estimated wo rld-wide biomass
resources av ailable for power generation using gasification processes. The analysis addresses
dry renewable feedstocks, such as agricultural residues a nd plantation biomass, but excludes
aquatic bioma ss. The methodology uses two scenarios: A continuation of existing policies, a ndan adoption of intensive energy plantations strategy. In both cases there will be a substantial
market of several thousan d M W in the period up to 2025. It is concluded that exploitation of
this potential will be expedited in geographical areas where environmental concern is the driving
policy towards the development of cost-effective renewable energy.
Biomass Feedstock Preparation for Gasification”: This task study report was prepared to
describe the “state of the art” of the handling characteristics and preparation of straw, a major
source of herbaceous feedstock in some countries, for energy conversion. The dema nds of the
various conversion technologies on the quality of straw and the quality control measures during
feeder, Putzmeister piston pump , Ingersoll R and reciprocating screw pistons, and plug screwfeeders developed or manufactured by Koppers, Fuller-Kinyon Gard, Inc., and General Electric
Co. These feeders have been developed for handling a variety of solids, and they have certain
limitations in handling either certain types of biomass and/or operating in conjunction with
pressurised gasifiers. Therefore, these feeders sh ould first be modified for handling the
heterogeneous and fibrous herbaceous biomass feedstocks. It is also necessary to demonstrate
the reliability and durability of these feeders for advanced bioma ss gasification applications.
Related to feeder selection is the safety aspects of handling large quantities of bioma ss dust.
Increased operating pressure increases the susceptibility of dust to spontaneous ignition an d
severity of dust explosion. Hence, it is necessary to design solids handling and storage b ins to
ensure free mass flow of solids and dust.
Strategies for Samp ling Analysis of Raw Gas Streams From Biomass Gasifiers’3: This task
study report presents a review of the sampling and analytical procedures developed from process
development and pilot plant research conducted with coal, peat, and bioma ss gasification. The
general on-line gas analysis for major components with gas chromatography is well developed.
This report discusses primarily the methods to improve sampling and analysis of raw gas
streams particularly for the measurem ent of tars, nitrogen comp ounds, sulphur compound s, and
particulates so that the precision of elemental balances could be improved.
All samp ling and analysis techniqu es should be designed to minimise changes in compositionand properties of samp les between the point of sampling and the analytical device. The
important parameters to watch include the method of sample withd rawal, raw gas chemical
composition, moisture and particulate content of raw gases, gas temperature, material of
construction of the samp ling probe, dimensions, and the temperature and residence time in the
probe. T he recommended guidelines include:
1) well designed and operated isokinetic samp ling probe;
2) any sample filter employed should be preferably maintained at a temperature close to gasifier
temperature to avoid condensation, but definitely > 175°C;
4) minimise probe lengths to reduce or eliminate secondary reactions;
5) hot-gas filters should have hot gas back flushing provisions;
6) rapid quenching and stabilisation and storage in amber coloured glass containers to preserve
the original sample composition;
7) blockage of sample collecting devices could be minimised by using two parallel sampling
lines with provision for purging and solvent wash ing.
This task study report discusses in detail the design of isokinetic probes; method of samp ling for
selective analysis of certain organic compound s in the raw gases; choice of a solvent to collect
and preserve condensables; samp ling for inorganic compoun ds such as H2S, NH3 , HCN , and
HCl; preparation and fractionation of condensed tar samples; tar characterisation; and analyses
of the aqueous phase.
Altholz (D emolition Woo d) Gasification14: This study investigated the fate of contaminan ts inAltholz d uring gasification followed by combustion of LCV gas and during direct combustion of
Altholz. The distribution of Cl, F, Cd, Hg, As, Cu, Ni, Cr, Pb, and Zn between the residual ash,
fly ash, and flue gases was studied. Gasification tests were conducted in Lurgi CFB , Wamsler
cocurrent-downdraft moving bed, and Juch cocurrent-downdraft moving bed pilot plant
gasifiers. Comp arison of gasification LCV fuel gas combustion with direct combustion showed
that chlorine was completely released in both cases. On the other hand, only 25% of sulphur
was released during combustion while it was completely released during gasification. During
combustion, Cr, Ni, and Cu were expected to form non-volatile compound s with ash
constituents; however, during gasification and combustion in CFB units, a significant amount of
these elements were found in the gas phase. It is postulated that the gas phase co ntaminationcould be attributed to high carry over of fine solids in the CFB units. It was also observed that
the dioxin emissions were lower with gasification followed by LCV gas combustion compared
to direct combustion of Altholz. This difference could be attributed to the deposition of dioxins
on fly ash released at lower temperatures in gasification compared to direct combustion. In
general, the gas cleaning costs for LCV should be cheaper than the cost of cleaning a
comparatively large volume of flue gases. This is a first attempt to understand the behaviour of
inorganic contaminan ts during gasification and combustion; further detailed studies are required
to ascertain the technoeconomic comparisons.
Mu nicipal Solid W aste (MSW ) Gasification”: The purpose of this task report is to summ arise
the state of the art of M SW gasification. The report also includes a brief description of MS W
gasifiers that have been developed, tested, and those that are still in operation. MS W
gasification was first developed 30 years ago, 20 processes were developed to some extent
during the 1970s. Of these. five gasifiers were tested at 1 to 10 tonnes/day and 13 gasitiers were
run at capacities more than 10 tonnes/day. Of all these processes the Andco-Torrax process had
some success. Out of the five Andco-Torrax plants that were built, only one may be still in
operation outside Paris, France. The failure of many M SW gasifiers is attributed to feeding
MS W without any separation and this has led to serious mechanical operating problems. In
addition, processes may have been scaled up with inadequate technology development. The
more recent processes include the Siemens-Kiener, TPS-Studsvik, Thermoselect, and Plasm a
Wa ste offer several environmental benefits with built-in provisions for emissions control. Theseprocesses were tested in pilot units and the TPS-Studsvik process is scaled up to a 15 MW th
Table 2. Tolerance level of contaminan ts in energy conversion equipment
28 3
The Netherlands BTG has recently published a report with details of TPS-Studsvyk and
Thermoselect processes for gasifying MSW .16
Hot-Gas Cleanup 17: The hot-gas cleanup task study investigated the characteristics ofparticulates, tars, alkalis, hydrocarbons, and amm onia in raw fuel gases leaving the gasifier, un it
operations and processes for gas cleanup, and the strategies for gas cleanup for selected end use
applications. The particles in raw gas may include biomass derived ash , char, aerosols of
alkalis. The nature of tars produced varies with the operating temperature, and the composition
changes further as the fuel gas containing tars is transported through the gasitier downstream gas
clean-up system. The alkali compoun ds are mainly in the form of sodium and potassium oxides,
and they could be deposited on fly ash and carryover char when the temperature drops below
650°C . Hydrocarbons in fuel gas is preferable, except when synthesis gas is used for producing
methanol or other chemicals and fertilisers. Amm onia should either be decomposed to
elemental nitrogen and hydrogen or removed prior to fuel gas combustion in order to reduceNOx production.
Many of the available options for gas cleanup have been initially developed under the advanced
coal conversion programs. A variety of ceramic candle filters that have been developed for the
removal of particulates in coal combustion and gasification systems has already been
successfully tested in bioma ss gasification pilot plants. The chemical a nd physical b ehaviour of
biomass derived tars in gasification reactors containing dolomite and catalytic tar reduction are
well known, and they are currently under consideration in some of the biomass gasification
demonstration projects. Controlling fuel gas temperature to promote alkali compoun ds
withdraw al along with carryover ash and char and the use of alkali absorption materials are
some of the main options for alkali removal. The evaluation of these hot-gas clean-up
techniques is an integral part of all advanced bioma ss d emonstration projects that are now under
various stages of development.
Further in sight into the characteristics of fuel gas contaminan ts, particularly for advanced power
cycle applications, will be developed when the advanced gasifiers are scaled-up and operated for
extended durations with commercial feedstocks. The specifications for limiting contaminant
level for the major end use applications for biomas s gasification are summ arised in Table 2.
Comb ustion Characteristics of LCV Fuel Gases:‘* LCV gases obtained from blast furnace
operations are very low in heating value, but they are combustible in specially designed burners.The biomass-derived LCV fuel gas may be about 50% higher in heating value compared to blast
furnace gas. Its exact composition and combustion characteristics are dependent upon many
factors, including the type of feedstock and most importantly on the gasification process.
Preliminary experiments were conducted with a gas having a composition of 10% HZ, 16% CO ,
4% CH ,, 17% COz, and 53% N2 and with LCV fuel gas and natural gas mixtures to determine
the maxim um experimental safe gap (MES G), laminar burning velocities, and flame geometry.
The results are preliminary, and further experiments have to be conducted to ascertain whether
biomass-derived LCV g ases should be mixed w ith natural g as for use in existing industrial
burners and gas turbines. It is also the purpose of this task study to investigate the benefits of
LCV g ases in reducing NOx w hen it is fired along with conventional fuels.
ACKNOWLEDGEMENT
The author is grateful for the support and the many valuable contributions made by the
participants and their countries’ energy agencies, wh ich makes the IEA Bioma ss Thermal
Gasification Activity productive and successful. The technical information provided by Dr. R.
L. Bain, NREL, on the U.S. programs is extensively used in this publication. The author is also
grateful for the guidance provided by Dr. Carl W allace, NR EL, the Operating Agent for the IEA
Bioenergy Agreement.
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REFERENCES
Abstracts From the Eighth European C onference on Biomass Energy, Environm ent,
Agriculture an d Industry. Sponsored by European Com mission, Bundesm inisterium fur
W issenscaft und Forschung, Austria, International Energy Agency, and AD EM E, France,
Vienna, Austria, p. 2-ORA L.A, Oct. 3 to 5, 1995.
Reference 1, p. 28-0RA L.A.
D. 0. Hall, F. Rosillo-Calle, R. H. W illiams and J Woo ds, Ch apter 3: Biom ass for
Energy: Supply Prospects in Renewa ble Energy, Sources for Fuels and Electricity,”
edited by Thomas B. Johansson , Henry Kelly, Am ulya K. N. Reddy, and Robert H.
W illiams. pp. 593-65 1, Island Press, Washin gton, D.C., U.S.A. 1993.
P. Elliott and R. Booth, Su stainable Biom ass Energy, Selected P apers, published by
Shell International Petroleum Co., Shell Center, London, U.K. 1990.
Reference 1, p. 105-OR AL.D2 .
H. E. Stassen, UNDPW B Small-Scale Biom ass Gasifier Monitoring Report, Volume I -
Findings. Prepared for W orld Bank/U NDP by BTG Bioma ss Technology Group,
University of Twente, P. 0. Box 217,750O AE Enschede, The Netherlands. 1993.
R. A. Newby and R. L.. Bannister, Advanced Hot Gas Cleaning System for Coal
Gasification Processes. Paper presented at the International Gas Turbine and Aeroengine
Congress and Exposition, Cincinnati, Ohio, 93-GT-338, The American Society of
Mec hanical Engineers, 345 E. 47th Street, New York, NY 10 017. 1993 .
K. Fulton, Russia Pushing In dustrialized Aeroengines for Gas Pum ping and Powergen,”
J. of Gas Turbine Wo rld, pp . 42-44. 1994.
D. 0. Hall, Bioma ss Resources for Gasification. Prepared for ETSU for the Departme nt
of Trade and Industry, Harwell, D idcot, Oxfordshire OX 1 IORA , U.K. Task Study
Report prepared for the IEA Biomass Thermal G asification Activity (1992 -94). 1995.
T. Koch, Feed Preparation of Straw. Energi, Industrivaenget 1, 47 11 Kalvehave,
Denm ark. Prepared for Danish Energy Agency, Copenh agen, D enmark. Task Study
Report prepared for the IEA Biomass Thermal Gasification Activity (1992-94). 1995.T. R. Miles and T. R. Miles, Jr Feed Preparation. Report prepared for the IEA Thermal
14. Ph. Hasler and R. Btihler, Gasification of Urban Waste Wood (Altholz). T ask Study
report prepared for the IEA Biom ass Thermal Gasification Activity (1992-94). 1994.
15. E. Rensfelt and Anders Gstman, Gasification of W astes, Summ ary and Conclusions of
Twenty-Five Years of Development,“, Task Study Report, prepared for the IEA Biomass
Thermal Gasification Activity (1992-94). 1995.
16 . BTG Biomass Technology Group B.V KEM A, Gasification of W aste, Evaluation of the
W aste Processing Facilities of the Thermoselect and TPS/Greve. Prepared for NOV EM ,
NOV EM Task Number 355100/023, No. 9420, Netherlands Organization for Energy andEnvironment, Sint Jacobsstraat 61, P. 0. Box 8242, 3503 RE Utrecht, The Netherlands.
1994.
17 . R. G. Graham and R. Bain, Biomass Gasification: Hot Gas Clean-U p. Task Study
Report prepared for the IEA Biomass Thermal G asification Activity (1992-94 ). 1993.
18 . T. Engebretsen, M. Fossum and J. E. Hustad, Co mbustion Characteristics and Low Value
Gases From Biomass Gasification -- Preliminary Study. Task Study Report prepared for
the IEA Bioma ss Thermal G asification Activity (1992-94). 1995.
