Biofuel Life Cycle Analysis with the GREET Model
Jennifer B. Dunn, Ph.D.
Argonne National Laboratory
Biofuels are often considered to be among the technologies that can reduce the greenhouse gas (GHG) impacts of the transportation sector. Yet several concerns are associated with their adoption, including the changes in land use and associated GHG emissions that could accompany the production of biofuel feedstocks. Life cycle analysis (LCA) is a widely-used tool that aims to quantify the environmental impacts of biofuels over their entire life-cycle, from farm-to-wheels.
At Argonne National Laboratory, the GREETTM (Greenhouse Gases, Regulated Emissions and Energy use in Transportation) model, an LCA tool for advanced fuel and vehicle technologies, is developed and used to conduct biofuel LCA. Recently, several notable updates have been incorporated into this model. For example, new estimates of LUC GHG emissions associated with the production of ethanol from corn, corn stover, switchgrass, and miscanthus have been developed. These estimates are calculated with new, state-level carbon emission factors for domestic LUC.1 Combined with other recent updates to the GREET ethanol pathways2,3, they predict that on net, miscanthus ethanol production sequesters GHGs (up to -8.5 g CO2e /MJ). Ethanol produced from switchgrass, a lower yielding crop than miscanthus, however, emits GHGs (10 to 26 g CO2e/MJ).
Additionally, GREET’s pyrolysis pathway (producing drop-in hydrocarbon fuels) allows users to examine alternative uses for the biochar co-product and different hydrogen supply options for the upgrading step.4 Maximum emission reductions compared to gasoline are achieved when a portion of the pyrolysis oil is reformed to produce hydrogen and the biochar is used as a soil amendment. On the other hand, reforming natural gas to produce hydrogen and converting all pyrolysis oil to fuel minimized fossil fuel consumption. GREET also allows for analysis of renewable diesel (RD), produced by lipid extraction or hydrothermal liquefaction (HTL) of algal feedstocks.5 Generally, RD produced from HTL has lower life-cycle GHG emissions but higher petroleum usage than RD produced from lipid extraction. Results for the HTL pathway are dependent on key variables of oil yield, hydrogen demand during upgrading and the nitrogen content of HTL oil. Finally, an aviation module in GREET allows users to compare conventional and biofuels for powering aircraft.6 A number of feedstocks and conversion options are available. Overall, renewable jet fuels produced from pyrolysis offered the greatest GHG reductions as compared to baseline petroleum-derived jet fuel.
- H. Kwon, M. M. Wander, S. Mueller, and J. B. Dunn. Modeling state-level soil carbon emissions factors under various scenarios for direct land use change associated with United States biofuel feedstock production. Biomass and Bioenergy. 2013. In press.
- M. Wang, J. Han, J. B. Dunn, H. Cai, and A. Elgowainy. Well-to-Wheels Energy Use and Greenhouse Gas Emissions of Ethanol from Corn, Sugarcane, and Cellulosic Biomass for U.S. Use. Environmental Research Letters. 2012, 7:045905.
- J. B. Dunn, S. Mueller, M. Wang, J. Han. Energy consumption and greenhouse gas emissions from enzyme and yeast manufacture for corn and cellulosic ethanol production. Biotechnology Letters. 2012, 34: 2259-2263
- J. Han, A. Elgowainy, J. B. Dunn, and M. Q. Wang. Life Cycle Analysis of Fuel Production from Fast Pyrolysis of Biomass. Bioresource Technology. 2013. In press.
- E. D. Frank, A. Elgowainy, J. Han, Z. Wang. Life cycle comparison of hydrothermal liquefaction and lipid extraction pathways to renewable diesel from algae. Mitigation and Adaptation Strategies for Global Change. 2012, 18: 137-158
- A. Elgowainy, J. Han, M. Wang, N. Carter, R. Stratton, J. Hileman, A. Malwitz, S. Balasubramanian. Life-Cycle Analysis of Alternative Aviation Fuels in GREET. 2012. ANL/ESD/12-8.
Dr. Jennifer Dunn is an Environmental Analyst at Argonne National Laboratory. She investigates life cycle energy consumption and environmental impacts of advanced transportation and fuel technologies, including biofuels and battery-powered electric drive vehicles. Through this work, Jennifer contributes to the development of Argonne’s GREET (Greenhouse gases, Regulated Emissions, and Energy use in Transportation) software model for life-cycle analysis of advanced vehicle technologies and new fuels. At present, GREET has more than 20,000 registered users worldwide. Prior to joining Argonne, Jennifer led life cycle analysis projects in the United States for URS Corporation and supported mobile source emission reduction programs at the United States Environmental Protection Agency. She holds a Ph.D. in Chemical Engineering from the University of Michigan.