USDA Study Underscores Ethanol Efficiency Gains

June 22, 2010 03:21 AM

The U.S. ethanol industry continues to see improved efficiency, according to a new report released by USDA's Office of the Chief Economist.

Based on results of the Agricultural Resource Management Survey of corn growers for the year 2005 and the 2008 survey of dry mill ethanol plants, the report measures all conventional fossil fuel energy used in the production of one gallon of corn ethanol.

What the study found relative to the amount of energy used to produce corn:

Nitrogen use measured on a per bushel basis has declined by about 20% since the mid-90s. Similarly, all direct energy components have declined by about 50% since the mid-90s. Together, the nitrogen and direct energy reductions result in a 30% decline in the energy required to produce a bushel of corn.

Overall, 65,285 BTU/bu (British thermal unit per bushel) were required for corn production in 1996, whereas 41,029 BTU/bu were required in 2005.

Energy in corn that is actually used for ethanol production, expressed per gallon of ethanol, which is important for an evaluation of ethanol production. Ethanol yields have increased by about 10% in the last 20 years, so proportionately less corn is required 14,866 BTU/gal in 2005. Further, only the starch fraction of the corn plant (66%) is used for ethanol production. So the net corn energy used for ethanol production is 9,811 BTU/gallon.

The corn energy input to ethanol production declined to 9,811 BTU/gal from 16,346 over the most recent 10-year period.

As for the ethanol processing side, the report concluded the following (based on a survey of ethanol producers in Iowa, Minnesota, Nebraska, and eastern South Dakota conducted in the fall of 2008 and the winter of 2009):

The ethanol processing yield of survey respondents has a mean of 2.76 gal/bu of corn. Further, the standard deviation is 0.07 gal/bu. Hence, processing yields continue a slow but steady improvement—the 2009 average yield is 3.7% higher than the average for the 2002 USDA survey, and 4.7% higher than the 1998 survey.

Those responding to the survey regarding external thermal energy showed that several firms were using between 10% and 50% biomass power.

A 50% biomass fraction would reduce the energy use of a dry mill with dry instead of wet distillers grain (dg) dg by about half.

The heat required to dry dgs accounts for 44% of the energy required for ethanol production with dry dg with typical moisture standards.

As for the issue of the energy balance for ethanol, this study would seem to contradict those who often make claims ethanol production is inefficient. The study found:

The various components of energy use are compared to the heat content of ethanol (76,300 BTU/gal). Together, the recent energy use estimates show that the ratio of energy in ethanol to the external energy used to produce ethanol is about 1.4, even without allowing for the processing component of the byproduct credit. After fully allowing for heat used to produce byproducts, the energy ratio is between 1.9 and 2.3.

If biomass is used at the plant for some of the power, the energy balance ratio increases to 2.8, even using the lower byproduct credit from the regression results.

The overall conclusions of the report are summarized as follows:

A dry grind ethanol plant that produces and sells dry distiller’s grains and uses conventional fossil fuel power for thermal energy and electricity produces nearly two times more energy in the form of ethanol delivered to customers than it uses for corn, processing, and transportation. The ratio is about 2.3 BTU of ethanol for 1 BTU of energy in inputs, when a more generous means of removing byproduct energy is employed.

Some dry mills are already using up to 50 percent biomass power. The energy output for these plants is near 2.8 times energy inputs, even using the conservative byproduct allowance. As processors master the logistics of handling bulky biomass, the energy balance ratio could reach 26 BTUs of ethanol per BTU of inputs used.

Overall then, ethanol has made the transition from an energy sink, to a moderate net energy gain in the 1990s, to a substantial net energy gain in the present. And there are still prospects for improvement.

Here's a link to read the full report.

Meanwhile, USDA's National Ag Statistics Service (NASS) announced it is seeking stakeholder input as it develops an annual program to collect and publish data about agriculture's production and use of renewable energy. In the 2007 Census of Agriculture, NASS for the first time included a question about on-farm energy production. Based on the information gathered from the census, NASS is currently conducting USDA's first On-Farm Renewable Energy Production Survey, focusing on farms and ranches that produced renewable energy via solar panels, wind turbines and methane digesters in 2009.

A release from USDA said, the survey will serve as an "important baseline" with plans to expand the effort into an annual survey program beginning in 2012. NASS said it would look at "all aspects of renewable energy production and use, including issues such as the costs and benefits, the motivators and obstacles, and the handling and use of energy co-products."


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