BIOMASS COFIRING IN UTILITY BOILERS. Harding & Associates Presentation Outline Introduction Benefits...

BIOMASS COFIRING IN UTILITY BOILERS

N. S. Harding

N. S. Harding & Associates

Utah Biomass Resource Group

August 23, 2012

N.S. Harding & Associates

Presentation Outline

Introduction

Benefits of Cofiring

Fuel Preparation/Handling

Torrefaction

Utilization in PC Boilers

Summary

Questions


Introduction


Biomass Utilization


Benefits to Biomass Cofiring Convenient or low cost disposal of wood wastes;

Establish early market for biomass, encourage industry to produce these renewable fuels;

Reduce Hg, SO2 and potentially NOx emissions;

Considered CO2 neutral;

Requires low capital investments relative to building new power plants; and

Converts wood to electricity at higher thermal efficiencies than wood-fired power plants.

No. 1 Problem – Energy Density


Cofiring Demonstrations

Continent Country Location Plant Name OwnerCofiring

TypeBoiler Burner Config.

Output

(MWe)

Output

(MWth)

Biomass

%Notes Primary Fuel Cofired Fuel

No. America USA Pittsburgh, PA NIOSH NIOSH Direct Grate Stoker grate 55,000 lb/hr,

200 psig40% Mass 5 burns Coal Wood chips

No. America USA Pittsburgh, PA Pittsburgh Brewing Pittsburgh Brewing Direct Grate Travelling grate42,000 lb/hr,

140 psig40% Mass

15 burns of 4-16

hours, one 72

hour

Coal Wood chips

No. America USA Port Wentworth, GA Kraft/Riverside #2 Southern Company Direct PFT-fired with 2

elevations46 36% Heat

11 tests, 8-10

hours/dayPulverized Coal Sawdust from pallets

No. America USA Prewitt, NM Escalante #1Tri-State Generating &

TransmissionDirect PF

T-fired with 5

elevations250 1% Mass 2 years Pulverized Coal Waste paper sludge

No. America USA Rumford, ME Rumford Cogen Co. Rumford Cogen Co. Direct CFB 76 260 Coal Oil, wood

No. America USA Savannah, GA SEPCO Direct PF 54 Pulverized Coal Waste wood

No. America USA Spring Grove, PASpring Grove Paper

MillP.H. Glatfelter Co. Direct CFB 132 Coal Anthracite, wood, oil

No. America USA Stillwater, MN Allen S. King Unit #1 Northern States Power Direct PF Cyclone 560 5% Mass 2 years Pulverized CoalKiln dried wood, pet coke,

PRB blend

No. America USA Tacoma, WACity of Tacoma Steam

Plant No. 2Tacoma Public Utilities Direct BFB 18 80% Heat Ongoing Coal Wood, RDF

No. America USA Tampa, FL Gannon #3 Tampa Electric Co. Direct PF Cyclone 165 5% Mass21 days over 60

day periodPulverized Coal Paper pellets

No. America USA Columbia, MOThomas Hill Energy

Center #2

Associated Electric

Cooperative, Inc.Direct PF Cyclone 175 7% Mass 1 week PRB Coal Railroad ties

No. America USA Tuscumbia, AL Colbert #1 TVA Direct PF Front-wall fired 182 5% Mass Ongoing Pulverized Coal Sawdust

Over 150 worldwide

Over 50 in the USA


Continent Country Location Plant Name OwnerCofiring

TypeBoiler Burner Config.

Output

(MWe)

Output

(MWth)

Biomass

%Notes Primary Fuel Cofired Fuel

Europe UK Cockenzie Scottish Power Direct PF 1200 Trial Pulverized Coal Wood

Europe UK Cottam EdF Direct PF 2000 Trial Pulverized Coal Wood

Europe UK Didcot Innogy Direct PF 2100 Trial Pulverized Coal Wood

Europe UK Ironbridge Powergen Direct PF 970 Trial Pulverized Coal Wood

Europe UK Tilbury Innogy Direct PF 1085 Trial Pulverized Coal Wood

No. America USA Ames, IA Ames Municipal Direct PF 75 Pulverized Coal RDF

No. America USA Ashland, WI Bay Front Station Northern States Power Direct Grate Stoker grate 44 100% Continuous CoalWood, shredded rubber

railroad ties

No. America USA Bismark, ND ND State PenitentiaryND Dept. of

CorrectionsDirect Grate Travelling grate

28,000 lb/hr,

200 psigNot finished Lignite Wood waste

No. America USA Burlington, VTMcNeil Generating

Station

Future Energy

ResourcesIndirect Grate Stoker grate 50 15% Heat Since 1998 Coal Wood chips

No. America USA Chesterton, INBailly Generating

StationNIPSCO Direct PF Cyclone 160 10% Mass

57 Tests, 300

hoursCoal

Urban wood waste,

petroleum coke

No. America USA Coosa, GA Hammond Unit 1 Southern Company Direct PF Front-fired 100 13% 3 days Pulverized Coal Sawdust and tree trim

No. America USA Dresden, NY Greenidge Unit 6 NYSEG Direct PFT-fired with 4

elevations108 30% 16 hrs/day Pulverized Coal Wood chips

No. America USA Dresden, NY Dunkirk #1Niagara Mohawk

Power Corp.Direct PF

T-fired, natural

circulation90 20% Heat

Long-term (6

months)Pulverized Coal

Wood Residue and willow

(energy crop)

No. America USA Dublin, GA Southeast Paper Direct CFB 65 125 Coal Sludge

No. America USA Beesleys Point, NJ BL England #1 Rockland Capital Direct PFFront-wall-fired

cyclone120 12%

2 months, 2

days with TDF,

wood, and coal

Pulverized Coal Shredded pallet wood waste

No. America USA Fort Drum, NY Fort Drum Cogen 1 Black River Partners Direct CFB 168 Coal Anthracite, wood

No. America USA Gadsden, AL Gadsden #2 Southern Company Direct PFT-fired with 3

elevations60 12$ 3-4 Weeks Pulverized Coal Switchgrass

No. America USA Hammond Georgia Power Direct PF 100 Pulverized Coal Waste wood

No. America USA Shawville, PA Shawville #3 Reliant Energy Direct PF T-fired twin furnace 190 3%7 days, 3-4

hoursPulverized Coal Various ground wood

No. America USA Shawville, PA Shawville #2 Reliant Energy Direct PF Wall-fired 138 3%7 days, 3-4

hoursPulverized Coal Various ground wood

No. America USA Kansas City, KS La Cygne #1Kansas City Power &

LightDirect PF

Supercritical

cyclone840 5%

1 month, 2

shifts/dayPulverized Coal Chipped railroad ties/PRB

No. America USA Lake Michigan, IN Michigan City #12 NIPSCO Direct PF Cyclone 469 20%6 tests over 5

daysPulverized Coal

Urban wood waste/

Shoshone coal/PRB blend

No. America USA Lakeland, FL Lakeland Electric #3 Lakeland Electric Direct PF Wall-fired 350 2% Heat Pulverized Coal RDF

No. America USA Madison, WI Blount StreetMadison Gas and

ElectricDirect PF Wall-fired 2 x 500 15% Pulverized Coal Switchgrass

No. America USA Marshalltown, IA Ottumwa #1 IES Utilities, Inc. Direct PFT-fired with 6

elevations650 2.5% Heat Ongoing Pulverized Coal Switchgrass

No. America USA Memphis, TN Allen Plant TVA Direct PF Cyclone 272 20% Mass10-24 Tests, 3-6

hours eachPulverized Coal Sawdust

No. America USA Milbank, SD Big Stone #1 Otter Tail Power Direct PF Cyclone 450 1% HeatContinuous

(several years)Pulverized Coal Seed corn and soy beans

No. America USA Milledgeville, GA Harlee Branch Southern Company Direct PF Opposed-fired250, 319,

480, 4901% Heat

Continuous

(several years)Pulverized Coal Sander dust

No. America USA Moncks Corner, SC Jefferies Units 3 & 4 Santee Cooper Direct PF Wall-fired 165 20% Mass 6 months Pulverized Coal Wood chips

No. America USA Niagara Falls CHR Niagara Falls 1UDG Niagara

GoodyearDirect CFB 149 Coal Tires

No. America USA Oakridge, TN Kingston #5 TVA Direct PFT-fired with 3

elevations180 5% Mass

9 Tests, 3-4

hours eachPulverized Coal Hardwood sawdust

No. America USA Oakwood, IL Vermilion #1 Illinois Power Direct PF T-fired 75 25% Heat 3 Hours Bituminous Coal Railroad ties

No. America USA Pelzer, SC Lee #3 Duke Power Direct PFT-fired with 5

elevations170 5% Mass 2 days Pulverized Coal Shredded railroad ties

No. America USA Seward, PA Seward #12 Reliant Energy Direct PF Wall-fired 32 12% Mass Ongoing Pulverized Coal Sawdust


Typical Biomass Quality



Drying

Heating – too costly

Natural – too long

Quality Control

Delivery & Transportation

Dust control

Scheduling – Trucks hold 20-23 tons

For 300 tph plant @5% requires 30 trucks/day



Screening

Shaker – less expensive

Trommel – preferred, better control

Mixing/Blending

Meter biomass on coal belt – mixed in crusher

Storage

Must be covered

Spontaneous combustion issues



Pulverizing

Much lower HGI values than coal due to their fibrous nature and moisture content;

Grinding of biomass/coal mixtures requires more mill power;

Milling systems can be ranked as:

General cutting and hammer mill systems

Bowl mills (due to shearing action) and ball-race mills

Ball mills



Pulverizing

Volatile release and explosion is a possibility at the operating temperatures of typical pulverizers.


Grinding Characteristics of Blends


Torrefaction

Increases heating value, energy density

Slow heating at 450-570oF

Removes moisture, oxygen

Raises heating value to ~10,000 Btu/lb

Pelletize to increase energy density more

Pellets hydrophobic, can store outside

Must balance with cost!


Torrefaction Pilot Tests


Torrefaction Demonstrations

Portland General Electric

Boardman Station

Gulf Power

Plant Schultz – this fall

50 MW wall-fired; 25-50% torrefied product

Torrefied product – Earth Care Products, KS

Ontario Power

Antikokan Plant

210 MW – Conversion to biomass in 2013


Biomass Utilization in PC Units

Fired WITH coal

Type of boiler (wall- or tangentially-fired);

Heat release characteristics of the boiler (e.g., Btu/ft3-hr);

Type of pulverizer;

Coal characteristics, especially HGI and moisture content;

Due to low amount, not many operating changes



Fired WITH coal

Method of operation, and the capacity- limiting feature of the boiler, particularly—

is the boiler operating with a spare pulverizer, or is the boiler pulverizer limited;

is the boiler FD fan limited or ID fan limited; or

is the unit turbine limited.

Up to 8% by mass in Atrita mills

Biomass < ¼” top size



SEPARATE from coal

Outside air, or ambient air, is always used as transport air. Changes the amount of air transported by the FD fans through the air heater, and alters the heat transfer characteristics of that operation;

The relationship of the biomass flame to the coal flame, and the synergies between the two systems and their fuels, must be carefully considered.



SEPARATE from coal

Control systems must accommodate the new fuel delivery system. If mill or coal delivery system has been altered, the biomass fuel must compensate for the lost Btu’s. The reduced energy density of the biofuel can have consequences for firing practices.

Can fire up to 10-20% by mass

@ 15-20% biomass – ~1-1.5% efficiency loss


Ash Deposition

High “water soluble” alkalis


Ash Deposition

Can reduce ash fusion temperatures especially with eastern bituminous coals


Ash Deposition

General Trends

Ash deposition rates should not be affected significantly when cofiring wood or similar low-ash, low-alkali, low-chlorine fuels; even at elevated cofiring ratios

As deposition rates should increase when cofiring high-chlorine, high-alkali, high-ash fuels such as many herbaceous and agricultural residue materials


Ash Deposition

General Trends

Deposition rates depend strongly on both individual fuel properties and interactions between the cofired fuels


Emissions and Ash Utilization Cofiring reduces emissions of: SO2

Trace elements, i.e., Hg

Can reduce NOx if properly injected

Ash Utilization Cannot use ash in concrete if cofired

(ASTM C618)


Summary

Successful biomass cofiring can be done if care is taken to evaluate the biomass source, the desired cofiring level and boiler characteristics.

There have been over 150 biomass cofiring demos worldwide including +50 in the US.

In addition, there are several torrified biomass demonstrations that have been completed or are soon to be completed both in Europe and the US.


Summary There are many benefits of biomass cofiring to the utility, including: Low-cost disposal of waste woods, etc.; Reduces mercury, SO2 and when properly

designed, NOx emissions; and Is considered CO2 neutral.

Due to the biomass energy density being about 10% that of coal, cofiring biomass at a 10% heat input rate (20% by mass) results in volumetric coal and biomass flow rates of comparable magnitude.


Summary Torrefaction followed by pelletization can overcome the energy density difference between the biomass and coal.

In general, biomass has less ash and sulfur than coal but higher moisture and alkali and alkaline earth metals in its ash.

Quality control of the biomass fuel as well as the torrified biomass product at the power plant is critical to avoid potential problems in the mill or boiler; this will at least include size screening.


Summary

Because of the density difference biomass fuel deliveries will be frequent; storage requirements will be large if stored on site.

Atrita mills tend to allow the highest percentages of biomass cofiring.

While overall costs are lower if the biomass is directly injected with the coal in pulverized coal boilers, the limit of biomass cofiring is about 2-3% on a heat input basis.


Summary

Biomass cofiring in pulverized coal units using separate feed locations permits higher cofiring percentages, up to about 10-15% on a heat input basis.

For US demonstrations there has not been a concern over increased boiler slagging or fouling; there is a small decrease in boiler efficiency due to the increased moisture; usually there is a capacity decrease due to the inability to introduce the required coal quantity.


Summary Biomass particle size should be less than about ¼ inch.

Due to the alkali and alkaline earth metals in most biomass ashes, there are some small effects potentially on an SCR system.

Currently ASTM does not allow ash from a cofiring installation to be used in concrete. If the flyash from a plant is currently being sold to this market, that loss of revenue needs to be accounted for in determining overall cofiring costs.


QUESTIONS

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