Repurposing a Kraft Pulp and Paper Mill to the Production of Ethanol

Wide commercial production of cellulosic ethanol has been impeded because of both high capital investment, and scarcity of low cost biomass feedstock. Both issues can be mitigated by Repurposing an existing kraft pulp mill to ethanol production, and attractive financial returns can be earned. Under "Reasonable but Optimistic" assumptions, capital cost required to produce ethanol from Forest Biomass can be reduced by 40-50% (compared to Greenfield Dilute Acid Process), and cash costs of $1.60 per gallon can be achieved. We have prepared a rigorous process simulation model of a 6-step ethanol production process that includes: (1) hot water pre-cooking of the wood to extract hemicellulosic material; (2) high yield kraft pulping to reduce lignin content and physically open up the fiber structure; (3) enzymatic hydrolysis of the pulp stream using a cocktail of cellulose enzymes found in our lab to efficiently convert hardwood cellulosic material to simple sugars; (4) fermentation of the streams produced in Steps (1) and (3); (5) distillation of the ethanol produced in Step (4) to 95% (V/V) in water; (6) dehydration of the ethanol solution to 99% + concentration using molecular sieves. A number of cases were simulated and financial proforma analysis was prepared on each case. The financial outcomes are most significantly impacted by assumptions for ethanol revenues per gallon and less so by fiber cost or cost of hydrolysis enzymes. We conclude that our technical approach has significant financial merit, with only minor compromises for re-using existing mill equipment. Repurposing takes advantage of proven manufacturing equipment and skilled operating personnel in place, and, perhaps most important, takes advantage of existing supply chain of growth, harvesting and delivery of forest biomass, without creating new demand. Further simplification of the process is currently under study, along with opportunities to Repurpose the Forest as well as the conversion plant.