Preliminary design and energy efficiency analysis of a kraft pulp mill converted to a biorefinery producing ethanol and DME from softwood

Abstract

In this study a conceptual biorefinery process is evaluated. The process is based on conversion of softwood to biofuels, and consists of a digester according to the soda cooking principle, a cellulose to ethanol production line, and a black liquor gasification line. The main products are ethanol and DME. The focus of the study is to combine knowledge from previous research in order to generate a preliminary design and energy balance for the process. This information is then used as input in a heat integration analysis in order to assess the potential for energy efficiency measures. Since the gasification leg of the process is a heat source and the ethanol leg, pretreatment and evaporation plant are heat sinks, an important result of the heat integration analysis is to give an indication of whether the process is self sufficient with respect to heat. The study shows that large opportunities for heat integration exist. The results from the study indicate that the steam surplus from the gasification plant cannot fully satisfy the steam demand of the balance of the process, even if the process is well heat-integrated. The demand is however considerably lower compared to when pulp is produced.