A Life-Cycle Analysis of the Greenhouse Gas Emissions of Corn Based Ethanol

Jan 2017

The primary purpose of this report is to consider a more complete set of information now available related to the life-cycle emissions for corn-based ethanol and based on this information, assess its current (i.e., in 2014) GHG emissions profile.
This report also develops two projected emissions profiles for corn ethanol in 2022 (the last year of the RFS2). Starting with the current emissions profile, the first projection, labeled the business-as-usual (BAU) scenario, assumes that recent trends observed in corn inputs and per-acre yields, refinery technologies, vehicle fleets, and other factors continue through 2022. The continuation of these trends has implications for the path that GHG emissions attributable to corn ethanol production will follow over the next few years. The second projection, labeled the Building-Blocks scenario, adds to the BAU
the assumption that refineries adopt a set of currently available GHG reducing technologies and practices in corn production, transportation, and co-products. The Building-Blocks scenario can be viewed as a best-case assessment of corn ethanol’s potential to mitigate GHG emissions given currently available technologies and production practices.
Chapter 2 reviews the scientific papers, technical reports, data sets, and other information that has become available since 2010 and relate to current emission levels in each emission category.
Chapter 3 develops current GHG emission values for each emission category included in the EPA RIA based on the literature review. Chapter 3 considers each emission category separately. For each emission category, the section includes a summary of the methods, data sources, and emissions projection developed in the EPA RIA, describes the methods ICF used to quantify the contribution to corn ethanol’s current GHG profile attributable to that category, and quantifies that contribution.
Based on the current GHG emissions profile of corn ethanol developed in Chapter 3, Chapter 4 develops two projected profiles for corn ethanol in 2022. The first projection considers a continuation through 2022 of observable trends in corn yields (per acre), process fuel switching toward natural gas, and fuel efficiency in trucking. The second projection adds a number of changes refineries could make in their value chain to further reduce the GHG intensity of corn ethanol. These changes include contracting with farmers to reduce tillage and manage nitrogen applications, switch to biomass as a process fuel, and locating confined livestock operations in close proximity to refineries.


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