BIOMASS COFIRING IN UTILITY BOILERS. Harding & Associates Presentation Outline Introduction Benefits...
Transcript of 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
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Introduction
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Biomass Utilization
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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
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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
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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
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Typical Biomass Quality
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Fuel Preparation/Handling
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
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Fuel Preparation/Handling
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
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Fuel Preparation/Handling
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
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Fuel Preparation/Handling
Pulverizing
Volatile release and explosion is a possibility at the operating temperatures of typical pulverizers.
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Grinding Characteristics of Blends
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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!
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Torrefaction Pilot Tests
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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
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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
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Biomass Utilization in PC Units
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
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Biomass Utilization in PC Units
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.
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Biomass Utilization in PC Units
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
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Ash Deposition
High “water soluble” alkalis
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Ash Deposition
Can reduce ash fusion temperatures especially with eastern bituminous coals
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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
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Ash Deposition
General Trends
Deposition rates depend strongly on both individual fuel properties and interactions between the cofired fuels
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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)
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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.
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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.
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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.
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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.
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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.
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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.
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QUESTIONS