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Global Warming Impact of Corn Ethanol

The Global Warming and Land Use Impact of Corn Ethanol Produced at the Illinois River Energy Center Executive Summary

This study assessed the global warming impact (GWI) of ethanol produced at the Illinois River

Energy ethanol plant (IRE) on a life cycle basis. IRE is located 80 miles west of Chicago. The plant currently produces 58 million gallon per year of ethanol with an expansion underway to double capacity.

The life cycle assessment includes the GWI contributions from corn agriculture, corn to ethanol conversion at the IRE biorefinery, distribution to the terminal, and combustion. The analysis was performed using Argonne National Laboratory's GREET model with customizations based on different data sets:

1. We collected detailed data on agricultural practices within the corn draw area around IRE. A survey was conducted with 29 corn growers supplying 2,528,850 bushels of corn to IRE or 12% of all delivered bushels (representative of about 6.9 million gallon of ethanol production). The survey assessed key agricultural variables including fertilizer application rates, tractor fuel use and other on-farm fuel consumption, and yields.

2. Using the USDA NASS Cropland Data Layer (developed from satellite imagery) combined with the National Land Cover Dataset we determined the crop rotations and land use changes (including land conversions from non agricultural uses) within the IRE corn draw area.

3. From a literature survey we determined different methodologies that account for the nitrogen and carbon adjustments from land use changes. Based on these methodologies we determined nitrogen emissions and carbon sequestration rates for the IRE corn draw area.

The three data sets were used to parameterize GREET. The results show that IRE produced corn ethanol has a substantially lower GWI of 54.8 g CO2e/MJ than the current GREET default value for corn ethanol of 69.1 g CO2e/MJ (a 21% reduction). This reduction is primarily due to higher corn yields, reduced on-farm energy consumption, and reduced energy consumption at the biorefinery. Compared to gasoline, the GWI of IRE corn ethanol is 40% lower (54.8 g CO2e/MJ vs. 92.1 g CO2e/MJ for gasoline). These results exclude the impact from indirect and international land use changes. Including the current GREET default factor for land use change would increase the GWI of IRE ethanol by 0.7 g CO2e/MJ to 55.5 g CO2e/MJ.

IRE is currently exploring advanced technologies that may further reduce the GWI of its ethanol product including corn fractionation and a digester to offset natural gas consumption with biogas. The results also indicate that if advanced agricultural management practices such as no-till and winter crops were promoted, the GWI of IRE corn ethanol could drop to as low as 41.4 g CO2e/MJ or a 55% reduction from gasoline.

Finally, the study finds a much lower on-farm energy consumption of 7,855 Btu per bushel for IRE supplied corn than the current GREET default value of 22,500 Btu per bushel (representing US national average). The large difference should prompt a reassessment of GREET's agricultural energy default value.

For the full report, click here.

 
 
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