Process design and economic studies of alternative fermentation methods for the production of ethanol

TLDR

Cell‑recycle and vacuum fermentation processes are presented as continuous methods for ethanol production. Preliminary process designs compare the economics of these continuous schemes to conventional continuous and batch fermentations, assuming a 78,000‑gal‑per‑day capacity with molasses as substrate. The analyses show continuous operation cuts fixed capital by 57 % versus batch, with cell‑recycle and vacuum schemes reducing it further by 68 % and 71 %; although molasses accounts for over 75 % of costs, net production costs fall to 82.3 and 80.6 ¢/gal when yeast by‑product credits are included.

Abstract

Abstract Cell recycle and vacuum fermentation processes are described for the continuous production of ethanol. Preliminary process design studies are employed to make an economic comparison of these alternative fermentation schemes with continuous and batch fermentation technologies. Designs are based on a production capacity of 78,000 gal 95% ethanol (EtOH)/day employing molasses as the fermentation substrate. The studies indicate that a 57% reduction in fixed capital investment is realized by continuous rather than batch operation. Further decreases in required capital investment of 68 and 71% over batch fermentation were obtained for cell recycle and vacuum operation, respectively. However, ethanol production costs were dominated by the cost of molasses, representing over 75% of the total manufacturing cost. But, when a reasonable yeast by‐product credit was assumed, the net production cost for 95% ethanol was estimated at 82.3 and 80.6 cent/gal, for the cell recycle and vacuum processes, respectively.