Process integration studies on Kraft pulp-mill-based biorefineries producing ethanol

Doktorsavhandling, 2012

Large scale, sustainable production of biofuels will require commercialization of processes using lignocellulosic feedstocks. These processes are still not competitive with existing pathways, however. The competitiveness of lignocellulosic biofuel production plants could potentially be improved if they were integrated with already existing facilities. One such example being explored currently is connected to the fact that the pulping industry is showing a growing interest in expanding their product portfolio, namely the complete or partial conversion of pulp mills into biorefineries for production of transport fuels. The objective of the work presented in this thesis has been to study different potential biorefinery concepts connected to chemical pulping, and more specifically the Kraft pulping process. Three different process combinations have been assessed in the project; a process where a Kraft pulp mill is repurposed to ethanol production (no pulp is produced), a process where ethanol and dimethyl- ether is produced in a repurposed Kraft pulp mill, and finally a process where an ethanol plant is co-located with a modern Kraft pulp mill. The findings from the studies reveal that an increasing degree of heat integration leads to a lower production cost of ethanol both if the ethanol plant is based on a repurposed mill and if the plant is co-located with a modern mill. In the ethanoland di-methyl-ether process, which has much higher conversion efficiency from feedstock to biofuel than the other processes, it was shown that the process could be competitive with the other combinations in terms of production cost, if the biofuel price is high and if the biorefinery is perceived as a low risk investment.