Corn Ethanol Even Better for Greenhouse Gas Emissions

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Using corn ethanol could be more effective in reducing greenhouse gases than at first thought, writes TheBioenergySite senior editor, Chris Harris.

A report by researchers at the University of Nebraska, Improvements in Life Cycle Energy Efficiency and Greenhouse Gas Emissions of Corn-Ethanol, has shown that it could produce between 48 per cent and 59 per cent reduction in greenhouse gas emissions compared to using petrol or gasoline.

The researchers say that this is between two and three fold better than previous estimates, and they have discovered that the effectiveness of corn ethanol in reducing emissions could be even higher, depending on the technology used and the way the corn, ethanol and byproducts are handled.

The report shows that the importance of this reduction in emission is growing as the production, use and consumption of corn ethanol increases. In the USA production of corn ethanol has risen from 12.9 billion litres in 2004 from 81 biorefineries, to 29.9 billion litres from 139 biorefineries by January 2008.

“These newer biorefineries have increased energy efficiency and reduced GHG emissions through the use of improved technologies.”

University of Nebraska study.

The US has a further 20.8 billion litres of capacity under construction from a further 61 biorefineries, bringing a potential total capacity in the US to 50.7 billion litres over the next one to two years. The Energy Independence Security Act in the US has issued a mandate that capacity has to reach 57 billion litres by 2015.

The report shows that when this is achieved, the US will have 10 per cent of its petrol or gasoline replaced by corn ethanol.

The 2007 EISA also mandates that life cycle greenhouse gas emissions of corn-ethanol, cellulosic ethanol, and advanced biofuels achieve 20 per cent, 60 per cent, and 50 per cent greenhouse gas emissions reductions relative to gasoline, respectively.

The research shows a correlation between the growth in the development of technology with building new and modern biorefineries and the greater efficiency of production and the reduction in CO2 emissions.

“These newer biorefineries have increased energy efficiency and reduced GHG emissions through the use of improved technologies, such as thermocompressors for condensing steam and increasing heat reuse; thermal oxidizers for combustion of volatile organic compounds (VOCs) and waste heat recovery; and raw-starch hydrolysis, which reduces heat requirements during fermentation,” the report says.

It adds that the newer refineries tend also to be near to cattle feed lots or to dairy farms that use the byproducts of ethanol production, dried distillers grains with solubles more than pig and poultry operations.

This means that the refineries do not have to transport their byproducts long distances to get rid of them and hence their carbon foot print is reduced.

Increases in corn yields because of improved genetics has also helped to boost not only productivity but the greenhouse gas emission profile of corn-ethanol. The have increased nitrogen use efficiency through reduced fertiliser use and on-farm practices of less tillage have also reduced the amount of diesel needed to tend the field.

The Nebraska University researchers carried out a series of life cycle assessment studies for the cultivation and use of corn for ethanol production and then the use of the byproducts for animals feed.

The study analysed crop production data using USDA and national agricultural statistics.

It also examined ethanol biorefinery data using performance information from dry mill plants in different regions.

It then examined the information about feeding DDGS to cattle, examining the distance of the feedlots from the refineries and the cattle performance and other data including the co-product energy credits and the impact on greenhouse gas emissions.

“When GHG emissions from crop production, biorefinery, and co-product savings are evaluated according to recent data, the magnitude of direct-effect GHG emission reductions is twofold to threefold greater than the 17 per cent to 24 per cent previously reported from existing models with older performance data,” the report finds.

The report goes on: “GHG emissions trading markets could provide an additional revenue stream if the corn-ethanol systems can achieve verifiable reductions in GHG emissions compared to gasoline. For example, when the mandated annual production capacity of 57 billion litres occurs by 2022, a 50 per cent GHG reduction could have an annual value of $330 million at current Chicago Climate Exchange prices of $6 per Mg CO2e. Under a fully implemented cap-and-trade program, however, GHG prices are projected to be $49 per Mg CO2e (Kintisch 2007), which gives a total GHG trading value of $2.7 billion per year.”

The report adds that current prices under the European Union’s Emissions Trading Scheme are €23 per Mg, which is equivalent to $31 at current exchange rates.

The research also stresses that the newer discoveries of fossil fuels through tar sands will have a greater greenhouse gas impact so that the practicality of corn ethanol becomes even more appealing.

It shows that a close loop biorefinery with an anaerobic digester “reduces greenhouse gas emission by 67 per cent – approaching the levels achieved by cellulosic ethanol.

  • Note: The research was carried out by Adam J. Liska, Haishun S. Yang, Virgil R. Bremer, Terry J. Klopfenstein, Daniel T. Walters, Galen E. Erickson, and Kenneth G. Cassman at the University of Nebraska.

Further Reading

You can view the full report by clicking here.

March 2009

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