MIT22_081JF10_lec19b

MIT22_081JF10_lec19b - Biomass Part II: Producing Biofuels...

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Unformatted text preview: Biomass Part II: Producing Biofuels William H. Green Sustainable Energy MIT November 16, 2010 Biomass needs to be converted to useful fuels. Biomass Conventional Fuels State • Generally solids • Liquids or gases Energy Density • Low • High [Lignocellulose: [Gasoline: 43.4 MJ/kg] ~10-20 MJ/kg] Moisture Content • High • No moisture content [Corn: 15% moisture delivered] Oxygen Content • High • No oxygen content [Often 10-40% oxygen] [<1% oxygen] Compatibility • Generally not compatible • Combust efficiently in with existing engines, existing engines, boilers, boilers, and turbines and turbines Biomass contains more oxygen and is structurally different from fuels. O H HO H HO H H OH H OH OH D-glucose O O O O O Carbohydrates Fats Proteins Cellulose Lignin H 2 CH 4 Hydrogen Natural Gas Propane Gasoline Diesel Methane LPG / NGL Petrol Autogas Naptha Lignin image from wikimedia foundation, peptide image from http://www.steve.gb.com . Most first-generation biofuels are imperfect fuel replacements. OH Ethanol OCH 3 O Biodiesel O DME “Synthetic” natural gas CH 4 43.4 MJ/kg 42.8 MJ/kg 46.3 MJ/kg 26.9 MJ/kg Gasoline 37.5 MJ/kg Diesel 28.9 MJ/kg Propane 49.5 MJ/kg Natural gas CH 4 49.5 MJ/kg Ethanol: the original biofuel.-7000 -6000 -5000 -4000 -3000 -2000 -1000 0 1000 2000 ~7000 B.C. 750 1000 1250 1500 1750 2000 Oldest idence of evidence of ethanol fermentation (pottery in China) ~800 A.D. Ethanol first distilled in Middle East 1908 Model T runs on ethanol 1885 Daimler’s 1 st gasoline- powered car 1859 Drake drills first oil well in Pennsylvania 1796 Lowitz produces absolute (pure) ethanol u Ethanol is made by yeast when no oxygen is present. 3000 If oxygen is available, cells use it- 2500 C 6 H 12 O 6 + 6 O 2 → 6 CO 2 + 6 H 2 O + (36 or 38) ATP 2000 Without oxygen, cells salvage a little energy with fermentatio C 6 H 12 O 6 → 2 C 2 H 5 OH + 2 CO 2 + 2 ATP C 6 H 12 O 6 → 2 C 2 H 5 OH + 2 CO 2 + 2 ATP n- 1500 O H HO H HO H H OH H OH OH D-glucose OH Ethanol Fuel upgrading 27 MJ/kg, 16 MJ/kg, liquid solid 1000 500 0 enthalpy of comb bustion, kJ/mol Glucose Ethanol Ethanol processing is much more complex than fermentation. Liquification & Milling Fermentation Purification Harvest Transportation Conversion Corn Ethanol Saccharification Courtesy of Jeremy Johnson. Used with permission. Careful accounting must be made of the energy used to make ethanol. Argonne (1999) USDA (2004) ORNL (1990) UCBerkeley A (2006) UCBerkeley B (2006) Amoco (1989) Iowa State (1992) Pimentel (2005) Effect of common system boundaries, coproduct credit Energy in Ethanol Production Total Ethanol Distill/Dry Electricity Distribution Other Corn 10 20 30 40 MIT (2006) 0.5 0.75 1 1.25 1.5 1.75 Net Energy Ratio MJ/kg EtOH Machinery Seeds Electricity Pesticide Lime P-K Nitrogen Irrigation Fossil Fuels 5 MJ/kg EtOH 0 kg EtOH Feed Ethanol Production B ij C ij Corn 3.4 kg Nat Gas 1 kg 13.5 MJ Electricity .95 kg 1.3 MJ Corn Production Nitrogen Nat Gas Electricity B C ij...
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This note was uploaded on 02/24/2012 for the course MECHANICAL 2.650J taught by Professor Johnc.wright during the Fall '10 term at MIT.

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MIT22_081JF10_lec19b - Biomass Part II: Producing Biofuels...

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