Greenhouse gas emissions from cellulosic biofuels: A field to wheel analysis
Abstract
The production of biofuel feedstocks result in greenhouse gas fluxes to the atmosphere as a result of fertilizer application, land management practices and land use changes. While the life cycle greenhouse gas emissions associated with feedstock conversion to liquid fuels through final combustion are fairly well understood, emissions from agricultural lands used to grow feedstocks for biofuel production continue to be poorly accounted for in life cycle assessment. There exists a lot of variability in the results reported to date due to dependence of trace gas fluxes on soil, weather, management practices and plant type. This study evaluates the soil biogeochemical model DAYCENT for six bioenergy cropping systems and provides a framework for calculating the lifecycle greenhouse gas emissions combining the soil emissions from DAYCENT with the life cycle emissions from GREET. Indirect land use change emissions from the GTAP model are added to the total life cycle emissions to fully evaluate the potential of these feedstocks to reduce greenhouse gas emissions. This approach is applied to two counties in Indiana to explore the greenhouse gas fluxes associated with the production of cellulosic feedstocks; corn stover, miscanthus and switchgrass. Greenhouse gas flux results show that energy crops have higher yields and fare better in terms of emissions reduction, with miscanthus showing great promise due to its carbon sequestration potential. The collection of residues for biofuel production from croplands has higher emission compared to energy crops, due to N2O flux from extra fertilizer additions and loss of carbon from the soil. Miscanthus has the highest reduction compared with gasoline (90-95%), followed by switchgrass (56-60%), and corn stover (33-69%) for the two conversion pathways considered. The study provides a holistic framework for the estimation of emissions associated with cellulosic biofuel production that is more complete than any other previous analysis. This form of carbon accounting is necessary in the establishment of effective carbon policy for alternative fuels.
Degree
M.S.E.
Advisors
Tyner, Purdue University.
Subject Area
Environmental Studies|Environmental science|Environmental engineering
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