Study Finds Recent Improvements in Corn Ethanol Production Result in 48-59% Less Direct-Effect GHG Than Gasoline
Direct-effect GHG emissions from corn ethanol are equivalent to a 48% to 59% reduction compared to gasoline—a twofold to threefold greater reduction than reported in previous studies—as a result of recent improvements in efficiency throughout the production process, according to a study by researchers at the University of Nebraska-Lincoln (UNL).
The team of UNL researchers evaluated dry-mill ethanol plants that use natural gas. Such plants account for nearly 90% of current production capacity. An open-access paper on the study was published 21 January in the Journal of Industrial Ecology.
The direct-effect emissions assessment considered the energy used for feedstock production and harvesting (e.g., fossil fuels for field operations and electricity for grain drying and irrigation) as well as upstream costs for the production of fertilizer, pesticides, and seed; depreciable cost of manufacturing farm machinery; and the energy required in the production of fossil fuels and electricity.
Energy used in the conversion of corn to ethanol includes transportation of grain to the biorefinery, grain milling, starch liquefaction and hydrolysis, fermentation to biofuel, and coproduct processing and transport. The study included energy used for the construction of the biorefinery itself, prorated over the life of the facility.
The research is the first to quantify the impact of recent improvements throughout the corn-ethanol production process, including crop production, biorefinery operations and co-product use, according to Professor Ken Cassman, UNL agronomist who was part of the research team. Previous studies, which found ethanol to have a much smaller edge over gasoline in GHG emissions, relied on estimates based on corn production, ethanol plant performance and co-product use as they were seven years ago.
|“Critics claim that corn ethanol has only a small net energy yield and little potential for direct reductions in GHG emissions compared to use of gasoline. This is the first peer-reviewed study to document that these claims are not correct.”|
More recently built and more energy-efficient plants now represent about 60% of total ethanol production and will account for 75% by the end of 2009. Also, many are located near cattle feeding or dairy operations, which allows efficient use of the co-product distillers grains as cattle feed. For example, the distillers grains don’t have to be dried to facilitate long-distance travel; drying uses up to 30% of total energy use in the ethanol plant.
Also contributing to corn ethanol’s GHG performance are improvements in how the crop is grown, including improved crop and soil management, and better hybrids that help farmers achieve a steady increase in corn yields without having to increase fertilizer or energy inputs.
Ethanol-to-petroleum output/input ratios ranged from 10:1 to 13:1 but could be increased to 19:1 if farmers adopted high-yield progressive crop and soil management practices, according to the study. An advanced closed-loop biorefinery with anaerobic digestion reduced GHG emissions by 67% and increased the net energy ratio to 2.2, from 1.5 to 1.8 for the most common systems. Earlier studies gad pegged the net energy ratio at an average of 1.2 to 1.
The range in the ethanol-oil replacement value, as well as the ranges measured for net energy efficiency and GHG emissions reduction, are due to differences in crop management practices and ethanol plant performance.
Such improved technologies have the potential to move corn-ethanol closer to the hypothetical performance of cellulosic biofuels, according to the study. Likewise, the larger GHG reductions estimated in this study allow a greater buffer for inclusion of indirect-effect land-use change emissions while still meeting regulatory GHG reduction targets.
The research is a component of a regional, multi-university research initiative known as NC506, to assess the economic and environmental sustainability of the rapidly expanding Midwestern corn ethanol industry. This project is funded by the US Department of Agriculture and the North Central Bioeconomy Consortium. Other sources of funding include the Western Governors Association, Environmental Defense, and the Agricultural Research Division at UNL, and the Nebraska Center for Energy Sciences Research.
Researchers used the UNL-developed Biofuel Energy Systems Simulator, or BESS, to make their calculations. This software is available for download online. BESS analyzes energy yield and efficiency, greenhouse gas emissions and resource requirements for individual biofuel production systems. This “seed-to-fuel” tool quantifies lifecycle carbon savings and environmental impact of individual biofuel systems. It factors in energy use and greenhouse gases from crop production, ethanol conversion, co-product use, and transportation.
Adam J. Liska, Haishun S. Yang, Virgil R. Bremer, Terry J. Klopfenstein, Daniel T. Walters, Galen E. Erickson, and Kenneth G. Cassman (2009) Improvements in Life Cycle Energy Efficiency and Greenhouse Gas Emissions of Corn-Ethanol, Journal of Industrial Ecology, doi: 10.1111/j.1530-9290.2008.00105.x