GREENHOUSE GAS EMISSIONS FROM BIO- ETHANOL AND BIO-DIESEL FUEL SUPPLY SYSTEMS

摘要

Analyses of the yield, energy consumption and GHG emissions for current systems to produce ethanol and bio-diesel are reviewed in the context of European Union (EU-15) application. Energy consumption and net GHG emissions are compared on a per unit fuel and per unit land basis for various systems: corn, sugar cane, wheat, and sugar beet to ethanol; and rapeseed to rape methyl ester (RME). Gross yield of RME is approximately 1 toe ha~(-1), ethanol from wheat 1.2 toe ha~(-1), and ethanol from sugar beet 3.4 toe ha~(-1) limiting the quantity of gasoline or diesel fuel use that could be replaced by biofuels using set-aside land available in the EU-15. Energy consumption for crop production and processing to make ethanol or RME in current processes account for about 58-106% of the produced RME or ethanol fuel energy content. Avoided GHG emissions resulting from gasoline or diesel fuel use replaced by biofuels, accounting for fuel system energy use, and crediting GHG offsets for animal feed byproducts, result in 0.4 tC_(eq) ha~(-1) for ethanol from wheat, 1.3 tC_(eq) ha~(-1) for ethanol from sugar beet, 0.6 tC_(eq) ha~(-1) for RME with a wide range of uncertainty stemming from, e.g., uncertainty in agricultural N_2O emissions and byproduct credits. Fluxes of avoided GHG emissions from these biofuel production systems are found to be much less than those from afforestation or reforestation in temperate regions.