Farm-scale production of fuel ethanol and wet grain from corn in a batch process.
The batch production of fuel grade ethanol and distillers' wet grain (wet solids) in a farm-scale process (1240-15,580 L/batch) is described. The employs yeast fermentation of amylase-treated corn mash and a two-stage distillation. Primary emphasis in this study was on the cooking, fermentation, and centrifugation steps. Without recycling, fermentation of the mash yield beers with 10.0-10.5% ethanol. Recycling of stillage supernatant at full, 75, or 50% strengths produced enriched mashes that after 48-h fermentation yielded beers with 5-;14% more ethanol. Recycling twice with full-strength supernatant at pH 7.0 increased the ethanol yield in the final beer 16.5%; however, the time to complete the final fermentation was extended form 48 to 72 h and salt buildup occurred. By recycling at pH 5.4, it was possible to avoid rapids salt buildup and obtain beers with 10.3-10.5% ethanol. Recycling resulted in increased levels of glucose, starch, crude protein, and fat in the beer and a reduced moisture content while the wet solids showed an increased starch content. Centrifugation after cooking or fermentation yield in the subsequently produced beer. Fermentation of a volume-resorted mash supernatant gave a beer with only 9.25% ethanol. Mash wet solids varied somewhat chemically from beer and stillage solids. An economic and energy balance analysis of various modes of plant operation are provided and plant considerations are suggested.
Department of Microbiology and Alcohol Fuel Research Laboratory, South Dakota State University, Brookings, South Dakota 57007.
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Westby
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Gibbons