Possibilities for lignin extraction versus maximized power production in a process integrated pulp mill converted to ethanol production plant

Other conference contribution, 2008

In this paper process integration opportunities in a conceptual ethanol production process, based on conversion of an existing pulp mill, are discussed. The process uses alkaline pre-treatment, softwood as raw material, and the ethanol is assumed to be produced by way of fermentation of hexoses. A pinch analysis has been performed on the process, and possibilities for decreasing steam demand have been evaluated. Several alternatives are presented and discussed. To visualise possible effects on the economics of the ethanol production plant, when implementing energy efficiency measures, two alternative steam saving measures are used in a techno-economic analysis. The steam savings are presented in economic terms as increased exports of by-products, in this case lignin extraction for use as biofuel, or power production. The results show that steam savings have a positive effect on economics of ethanol production, and that choice of option between lignin extraction and increased power production differs from similar pulp mill studies. It is shown that the possibility of in-site production of CO2, which is used in lignin extraction, is one important reason for this difference.