In September I wrote about an study to be released by researchers at the University of Nebraska at Lincoln that concluded that ethanol production was more energy efficient than previously thought. Previous studies were done or relied on data acquired before the most recent ethanol plant building boom occurred. These new plants, built since January 2005, will represent about 75% of all plants operating by the end of this year and produce ethanol with much greater efficiency than older plants.
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.
This study more thoroughly evaluates the effect of these new plants as well as improvements in crop production and co-product utilization on the net energy yield and green house gas reduction of ethanol. Below is a summary of the conclusions of the study.
Recent improvements in crop production, biorefinery operation, and coproduct utilization in U.S. corn-ethanol systems result in greater GHG emissions reduction, energy efficiency, and ethanol-to-petroleum output/input ratios compared to previous studies. Direct-effect GHG emissions reductions were found to be 48% to 59% compared to gasoline, which is two to three times greater than estimated in previous reports (Farrell et al. 2006). The NER (Net Energy Ratio) has improved from 1.2 in previous studies to 1.5 to 1.8 on the basis of updated data. Ethanol-to-petroleum ratios were 10:1 to 13:1 for today’s typical corn-ethanol systems but could increase to 19:1 with progressive crop management that increases both yield and input use efficiency.
Source : Improvements in Life Cycle Energy Efficiency and Greenhouse Gas Emissions of Corn-Ethanol