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