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Session 12 biomass energy

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biomass energy

biomass energy

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  • 1. Session 12 - Biomass • Definition • Photosynthesis Again • Examples – Heat and Power from Wood and Wood Waste – Biogas – Ethanol • Environmental Impacts • R&D T. Ferguson, University of
  • 2. Definition of Biomass • Living Plant Matter and Organic Wastes – Trees – Grasses1 – Animal Dung – Sewage – Garbage – Wood Construction Residues • Biomass second only to hydro T. Ferguson, University of 1 This includes corn, other grains
  • 3. Photosynthesis 6 CO2 + 6 H2O → C6H12O6 + 6 O2 ΔH = +2800 kJ = 668 kcal • • Electromagnetic to Chemical Energy Of the solar radiation not reflected: – – – – – • 1 Light penetration of canopy is 80 % efficient Only visible light, or 43 % of total light, is useful Glucose formation from photons is 28.6 % efficient Respiration reduces energy by 33% (67 % efficiency factor) All told, of absorbed light energy, about 7 % is stored chemically1 Plants are a great energy storage medium! From upei.ca/~physics/p261/Content/Sources_Conversion/Photo-_synthesis/photo-_synthesis T. Ferguson, University of
  • 4. Photosynthesis Rate of production of Energy = Rate of production of dry biomass/land area X Total growing area available X Unit energy content of dry biomass X Efficiency of conversion My backyard: • • • • • 1 acre yields 500 mature poplar trees/20 years or 25 tons/yr/acre At 7000 Btu/lb, or 14 E 6 Btu/ton, annual energy is 350 E6 Btu Conversion efficiency = 20% (crude genset) Rate of Energy Production = 70 E6 Btu/yr or 2.3 kW continuously At 8 c/kWh, I could purchase this electrical energy for $1640. T. Ferguson, University of
  • 5. Biomass Properties • Heating value similar to lignite (7000-9000 Btu/lb) • H/C (1.2-2) better than coal, less than CH4 • Low sulfur, nitrogen oxide emissions • Drawbacks – – – – Water content Non-organic content Non-beneficial oxygen adds to bulk Expensive to haul, low production density, competition • Supplies about 1.4% of US generating capacity T. Ferguson, University of
  • 6. Biomass: For Heat or Power? For Heat/Steam: 2.5 Quads Biomass 3.1 Quads For Electrical Generation: 0.6 Quads (input) T. Ferguson, University of Figures are for the US for 2005. Source: EIA (renewables/electricity net gen)
  • 7. Biomass Properties Heat Contents in MMBtu/ton • • • • • • • Wood/wood waste Utility Poles Tires Peat Paper Pellets Municipal Solid Waste Agricultural Byproducts T. Ferguson, University of Source: EIA, 2008 9.961 12.500 26.865 8.000 13.029 9.945 8.248
  • 8. Heat and Power from Wood • 2007 Electrical Generation: 55 million MWh from Biomass – 39 million from wood • Pulp and paper use vast majority for steam • Minnesota Power (based in Duluth): – Three wood-fired plants (including co-firing): • Hibbard (Duluth) • Cloquet Energy Center • Rapids Energy Center T. Ferguson, University of 48 MW 23 MW 30 MW
  • 9. Virginia (MN) Public Utilities Biomass Generating Station • Co-generation: municipal steam (~1500 homes) + electrical generation • Fuel: 75% PRB coal + 25% wood (reverse in future) • Annually: 175,000 tons of wood – 75 economic radius for wood • Daily: 20 truck loads @ 25 tons (4-5 trucks/hour); 15 hour inventory • Rankine Cycle: 800 °F turbine inlet, 40-50 °F lake temp • Generators: 18.5 MW, 6.5 MW • Issues: Fugitive dust, boiler performance, attaining capacity factor (86% target), lake mist T. Ferguson, University of
  • 10. Biogas from Wet Biomass • • • • • • Anaerobic Digestion of Wet Biomass Produces ~50/50 mix of CH4 and CO2 With pure CH4, get ~ 1000 Btu/cubic foot Biogas, then, yields ~ 500 Btu/SCF Largest producers in US are landfills Why pursue? – Environmental hazards of dairy farms, feedlots (coliform bacteria, methane) – Methane is a significant GHG (GWP of 56 times CO2 over 30 years) – Heat and power may be secondary benefits T. Ferguson, University of
  • 11. Biogas Production • Bacteria digest biomass in absence of oxygen, in a digester • Operates between 68 °F and 150 °F • Higher temp accelerates production • Farm Scale: 500 dairy cows: 8000 gallons of manure/day = 1070 ft3 = 30 m3. • Landfill Scale: >40 ft deep and > 1 million tons of waste (Landfill is fastest growing biomass electricity source: 4%/yr) • Production: 30 m3/day*1.0m3gas/day/m3 = 30 m3 of biogas/day = 1070 ft3, or 500 SCF of CH4 or 0.5 million Btu. Across 24 hours at 35% conversion efficiency, this represents 6.1 kW. T. Ferguson, University of Source: Oregon.gov/Biomass Energy Home Page; text p. 438
  • 12. Ethanol from Corn • Biomass to ethyl alcohol • From Text, page 240, for corn fermentation: – Input for 1 gallon of ethanol: • Corn Production • Fermentation/Distillation » Total – Output in combustion: 55,300 Btu 74,300 129,600 Btu 76,000 Btu • Gasoline: Output to input ~ 7 • Sustainability Rule of Thumb: Ratio > 4 • Cellulosic Ethanol: T. Ferguson, University of
  • 13. Biomass R&D Focus is on: – Production yields – Harvesting costs – Conversion efficiencies T. Ferguson, University of