Processing of Straw/Corn Stover: Comparison of Life Cycle Emissions

Abstract

The LCA emissions from four renewable energy routes that convert straw/corn stover into usable energy are examined. The conversion options studied are ethanol by fermentation, syndiesel by oxygen gasification followed by Fischer Tropsch synthesis, and electricity by either direct combustion or biomass integrated gasification and combined cycle (BIGCC). The greenhouse gas (GHG) emissions of these four options are evaluated, drawing on a range of studies, and compared to the conventional technology they would replace in a western North American setting. The net avoided GHG emissions for the four energy conversion processes calculated relative to a “business as usual” case are 830 g CO₂e/kWh for direct combustion, 839 g CO₂e/kWh for BIGCC, 2,060 g CO₂e/L for ethanol production, and 2,440 g CO₂e/L for FT synthesis of syndiesel. The largest impact on avoided emissions arises from substitution of biomass for fossil fuel. Relative to this, the impact of emissions from processing of fossil fuel, e.g., refining of oil to produce gasoline or diesel, and processing of biomass to produce electricity or transportation fuels, is minor.

Keywords:

• Renewable energy
• Life cycle analysis
• Agricultural residues
• Lignocellulosic ethanol
• Fisher Tropsch
• BIGCC

ACKNOWLEDGMENTS

The authors gratefully acknowledge financial support from Canada's Natural Sciences and Engineering Research Council, EPCOR, and the Poole Family; all conclusions are the authors'.

Notes

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(S&T)² Consultants Inc., Cheminfo Services Inc., H. MacLean, and Fugacity Technology Consulting. 2008. Sensitivity analysis of bioethanol LCA models to determine assumptions with the greatest influence on outputs.