9-06: 2011 Update of the NREL biomass-to-ethanol process design report

A detailed technical and economic analysis is presented for a corn stover-to-ethanol biochemical conversion process. This "design report" builds upon previous issues (Aden et al. 2002; Wooley et al. 1999) and modernizes the process design significantly by considering the latest developments in conversion and process integration research from the intervening decade. The overarching process design is dilute-acid pretreatment of corn stover followed by enzymatic hydrolysis and co-fermentation to ethanol with recombinant Zymomonas mobilis. Ethanol is purified by distillation and the remaining solids are combusted to produce steam and electricity. Material and energy balances generated with the process simulator Aspen Plus are used to determine capital and operating costs for the process. A discounted cash flow analysis computes the minimum ethanol selling price (MESP, $/gallon). The result is a so-called technoeconomic model that reasonably estimates a production cost for this pre-commercial process, which can be used to assess its competitive potential in the marketplace and highlight areas where economic improvements are needed. Major updates to be discussed are (a) an updated representative feedstock composition, (b) updated equipment and raw material costs, (c) replacement of lime conditioning after pretreatment with ammonium hydroxide neutralization, (d) addition of an on-site cellulase enzyme production section, and (e) a newly-designed wastewater treatment section. Sensitivity of costs to feedstock variability and key operating parameters will also be presented.