Energy, carbon dioxide and water use implications of hydrous ethanol production

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Saffy, HA 
Northrop, WF 
Kittelson, DB 
Boies, AM 

Sub-azeotropic hydrous ethanol has been demonstrated as an effective diesel fuel replacement when used in dual-fuel compression ignition engines. Previous studies have also suggested that hydrous ethanol may be more efficient to produce from corn than anhydrous ethanol. In this study, we investigate corn ethanol production from a dry-mill, natural gas-fired corn ethanol refinery, producing ethanol with a range of ethanol concentrations from 58°wt% - 100°wt% to determine the effect on energy use, water consumption and greenhouse gas (GHG) emissions in the refining stage of the corn ethanol lifecycle. A second law (exergy) analysis of anhydrous ethanol refining revealed the overall process to be 70% efficient, whereby 86% of the exergy losses could be accounted for by three processes: fermentation (34%), steam generation (29%) and distiller’s grains and solubles drying (23%).

We found that producing 86°wt% ethanol is optimal as thermal energy consumption decreases by a maximum of 10% (from 7.7°MJ/L to 6.9°MJ/L). These savings have the potential to reduce energy costs by approximately 8% ($0.34 /L) and reduce refinery emissions by 8% (2°g°CO_2e/MJ). Production of hydrous ethanol reduced refinery water use due to decreased evaporative losses in the cooling towers, leading to water savings of between 3 - 6% at 86°wt% ethanol.

Ethanol, Hydrous ethanol, Greenhouse gas, Water
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Energy Conversion and Management
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Elsevier BV
This work was supported in part by the Minnesota Corn Growers Association under contract number 1051-14EU and St Edmund’s College (Cambridge, United Kingdom).