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Biomass Conversion to Electricity
John R. Shelly, UC Berkeley
Woody Biomass Workshop
Eureka, CA
March 25, 2010
John Shelly, UC Berkeley Cooperative Extension
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Combustion of Woody Biomass to produce heat and/or power
Large scale – California has biomass power plants that consume large quantities
of woody biomass
Small scale – units are available for space or process heat. Combined heat and power may be feasible
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Combustion of Wood
Wood + Air + Ignition Wood + Air + Ignition COCO22 + H+ H22O + OO + O22 + N+ N22
++ HeatHeat++ AshAsh++ EmissionsEmissions
particulates, Nox, Sox, etc.particulates, Nox, Sox, etc.
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20 MW Biomass Power Plant
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Biomass Gasification Unit coupled to an Internal Combustion Engine and Generator - 500 Kw
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2004 CA Electricity Production
Biomass2%
Imports19%
Solar & Wind 2%
Nuclear11%
Hydro12%
Oil0%
Coal10%
Geothermal5%
Natural Gas39%
Total Production: 275,091 GWhBiomass: 5, 997 GWh
Source: 2004 Net System Power Calculation Report, CEC-300-2005-004, CA Energy Commission
(18%)
(15%)
(15%)(2%) (31%)
(0.02%)
(13%)(5%)(1.5%)
(values in parenthesisare for year 1999)
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30 + MW 20 - 30 MW 10 - 20 MW 0 - 10 MW
Sawmill Cogen Other Biomass Power Plants
California Biomass Energy Facilities
A 10 MW (megawatt) generator can supply electricity to about 10,000 homes.
27 facilities with total capacity of about 626 MW using 4.5 million bone dry tons of biomass per year • 22% forest-based
• 29 % manuf. residue
• 28% landfill diverted
• 21% ag residue
About 15% of total biomass available and about 12% of forest-based biomass available
The 7 cogeneration facilities are co-located with sawmills
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Typical Biomass-Fired Powerplant
John Shelly, UC Berkeley Cooperative Extension
• 20 MW capacity, combustion/steam turbine• Installed cost = $1700 - $3500 per kW• Processes 140 - 200 thousand tons/yr (1BDT/MW/hour)
• Biomass transported up to 50 miles• Delivered biomass valued at $15 - 60 per BDT• Average production cost ~ $0.07 - $0.10/kWh
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Biomass Combustion Concerns
• Availability and cost of Fuel
• Emissions
• Higher maintenance compared to other fuel types– Inorganic (ash) transformations lead to fouling of combustion chamber
surfaces and slag formation on bottom– Increased corrosion from acidic gases
• Maintenance issues can lead to reduced capacity and efficiency
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Example of Costs of Forest Thinning or Salvage Operations with a 50 Mile Haul
0
5
10
15
20
25
30
35
40
Thin/Salvage Cost
$ / B
DT Haul
Chip
Skid
Fell/Bunch
Value of biomass delivered to a powerplant ranges from about $15 - $40 per BDT
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0
10
20
30
40
50
60
70
80
0 10 20 30 40
Quantity (Million dry tons/y)
Co
st (
$/
dry
to
n)
Manure
s/Pro
cess
ing
Bio
solid
s/S
hells
/Pits
Orc
hard
Pru
nin
gs
Field
Cro
p R
esi
dues
Vegeta
ble
Cro
p R
esi
dues
MS
W--
Div
ert
ed
In-F
ore
st
Shru
b/C
haparr
al
Dedic
ate
d C
rops
Mill
Resi
dues/
Manure
s
California Statewide Resource Supply Curve
Source: California Biomass Collaborative
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Emissions by type of Combustion in pounds emitted per ton of Woody Biomass consumed
PM- 2.5 NOx CO VOC N2O
Industrial (dry fuel)
0.7 – 6.5 8.8 10.8 0.31 0.23
Industrial (wet fuel)
0.4 – 5.0
Residential Stove
6 - 23 45 – 100 2 – 14
Prescribed Burn
12 - 34 3 300 19.0 0.46
Wildfire 17 4.0 140 12 - 24 0.46
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Environmental ImpactAir Emissions Open Field
BurningBiomass Fueled Boiler
Natural Gas Boiler
lb/Million BtuCO 6.89 2.267 0.058CO2 fossil 0 114.6CO2 non fossil 100 - 350 350.0 0NOx 0.36 0.250 0.301SOx 0.03 0.013 0.073VOC 0.74 0 0.009Methane 0 0.003Particulates 0.66 0.028 0.009
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Power Plant EfficiencyHeat Rate (Btu/kWh)
Efficiency (%)
Natural gas combined-cycle
7,500 45.5
Coal-fired steam/electricity
10,000 34.1
Biomass-fired steam/electricity
15,000 22.7
Biomass-fired, combined heat and power (co-gen)
8,500 70.0
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Barriers
• Emissions• Grid Interconnect• Fuel Availability
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– Biomass utilization policies– Relative price of natural gas and electricity– Environmental issues
• Emissions – particulates, CO2
• Carbon Accounting -- does biomass CO2 have a zero emission impact?
– Societal value placed on biomass disposal/use (e.g. reducing wildfire hazards)
The Future of Biomass Power Plants Depends on …
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How Can We Increase Woody Biomass-Produced Electricity?
• Offset high costs of processing in thinning and salvage operations– Assign values to environmental and social benefits– Apply economic incentives
• Educate public to the value of well managed, sustainable, and productive forests
• Improve the conversion efficiency of powerplants• Compare life cycle assessments of various energy
alternatives• Encourage policies and incentives that level the playing
field with other fuels