GWI comparison of gasoline, ethanol modeled using GREET defaults, and the IRE results using the new data sets. Click to enlarge. Source: Mueller (2008)

Illinois River Energy study. The Mueller study assessed the current global warming impact (GWI) of ethanol produced at the Illinois River Energy ethanol plant (IRE) on a life cycle basis. The plant 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. The researchers 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, the team determined the crop rotations and land use changes (including land conversions from non agricultural uses) within the IRE corn draw area.

3. A literature survey provided determined different methodologies that account for the nitrogen and carbon adjustments from land use changes. Based on these methodologies, the team 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, the authors argue.

We looked at the global warming and land use impact of corn ethanol produced at the Illinois River Energy ethanol plant—which is a modern, natural gas fueled facility—on a full life-cycle basis. We found conclusively that the global warming impact of the modern ethanol plant is 40 percent lower than gasoline. This is a sizable reduction from numbers currently being used by public agencies and in the public debate. The study also documents the significant net energy benefits of ethanol when compared to gasoline. And, additional opportunities exist to expand that margin even more through technological improvements and on farm changes in corn production that reduce green house gas emissions. Furthermore, corn supply for the ethanol plant was primarily met through yield increases in the surrounding area and, as documented with satellite imagery, without conversion of non agricultural land to corn.

—Steffen Mueller

Projected increases in corn yield through 2030. Click to enlarge. Source: Korves (2008)

Korves. The Korves study is broader in scope and analyzed the consequences of a technology-driven increase in average corn yield from 155 bushels per acre today to 289 bushels per acre by 2030 corn crop with total production of 24.6 billion bushels. Korves concluded that with no increase in harvested corn acreage from the 2007 level of 85 million acres and growth in other uses of corn, corn available for use in ethanol production would be 12 billion bushels from the 2030 corn crop. This compares to 2.2 billion bushels used for ethanol from the 2006 crop.

If ethanol yield per bushel of corn remains at the current level of 2.75 gallons per bushel, total corn ethanol production in 2030 would be 33 billion gallons, compared to estimates of 7.1 billion gallons for calendar year 2007. If ethanol output per bushel of corn increases to 3.0 gallons per bushel, corn ethanol production would be 36 billion gallons. The current Renewable Fuel Standard (RFS) in EISA 2007 mandates a 15-billion cap on corn ethanol on a 36-billion gallon target for 2022.

Efficiency of use of commercial nitrogen fertilizer per bushel of corn produced will likely continue to improve from the current level of 0.9 pounds per bushel, Korves said. The improved efficiency would reduce the amount of nitrous oxide (N₂O), a significant greenhouse gas, released per bushel of corn produced. Continuation of the current trend of less use of anhydrous ammonia would also reduce the amount of N₂O released in corn production. Commercial applications of phosphate and potash per bushel produced are also expected to decline, but not continue at the trend decline of the last 25 years.

A continued shift to more no-till corn production could reduce the amount of CO₂ released in corn production because no-till corn is considered by some researchers as a carbon sink (more carbon is taken up by the soil than is released to the air in corn production). Some research indicates that minimum tillage programs can also reduce the amount of CO₂ released.

The Agricultural Research Service (ARS) of USDA has begun a five year program, the Renewable Energy Assessment Project (REAP), to determine the amount of corn stover that can be removed without reducing long-term soil productivity. From a review of literature, the researchers estimate that more productive soils that are not highly erodible can be managed to allow some removal of stover.

About 20 percent of nation’s corn production is irrigated and continued improvements in irrigation management and higher yields per acre should decrease the amount of water used per bushel of corn produced, according to the study. Additional ethanol production per acre of corn produced could be achieved by using fiber from the corn kernel and some stover fiber to produce cellulosic ethanol. Poet, an ethanol plant builder and ethanol producer, is building an ethanol plant that is expected to produce 11% more ethanol from a bushel of corn by using the corn kernel fiber and 27% more ethanol from an acre of corn by using the corn kernel fiber and corn cobs for cellulosic ethanol production.

Improvements in the efficiencies of dry mill ethanol plants are expected to reduce the thermal energy used in the average dry mill ethanol plant on a per gallon produced basis in 2030 by 27% compared to 2007 and reduce electricity use by 46%.

A life cycle analysis of carbon intensity using the GREET model from Argonne National Laboratory using the production estimates in the Korves report shows the Global Warming Impact (GWI) from corn agriculture (on farm energy use for agricultural practices) could decline by 22% from 26,610 g CO₂eq/MMBtu (grams of CO₂ equivalent per million Btus) in 2010 to 20,755 g CO₂eq/MMBtu by 2030. This is 25% below the current GREET default value of 27,469 g CO₂eq/MMBtu.

The GWI of the average ethanol plant could decline from 63,959 g CO₂eq/MMBtu in 2010 to 46,479 g CO₂eq/MMBtu by 2030, a 27% decline. The GWI of ethanol produced from the averaged ethanol plant in place in 2030 may be half the GWI of gasoline. The GWI of corn ethanol processed in a plant using a biomass combined heat and power (CHP) system in 2030 could be less than one-third of the GWI of gasoline, 30,502 g CO₂eq/MMBtu vs. 98,134 g CO₂eq/MMBtu.

At this level of reduction, corn to ethanol could be categorized as an advanced biofuel based on the performance requirements in the Energy Independence and Security Act of 2007, said the ICGA.

Resources

• Steffen Mueller, Ken Copenhaver and Michelle Wander (2008) The Global Warming and Land Use Impact of Corn Ethanol Produced at the Illinois River Energy Center

• Ross Korves (2008) The Potential for Corn Ethanol in Meeting the Energy Needs of the United States in 2016-2030