Enlarging the Product Portfolio of a Kraft Pulp Mill via Hemicellulose and Lignin Separation – Process Integration Studies in a Case Mill

Artikel i vetenskaplig tidskrift, 2013

Increased energy and raw material prices along with contracting markets for kraft pulp, have highlighted the need for the pulp industry to enlarge their traditional product portfolio with new value-added products via the implementation of biorefinery concepts. In this paper, we have investigated potentials for enlarging the product portfolio of a kraft pulp mill by extracting hemicellulose prior to digesting and in this way, converting to dissolving pulp production. A case study has been performed on a Swedish kraft pulp mill, in order to evaluate the consequences of the original mill configuration, level of heat integration and choice of by-products produced have on theoverall profitability of the mill upon conversion to dissolving pulp production. For the mill studied, the batch digester is identified to be the bottleneck for both kraft and dissolving pulp production. If the digester capacity is increased by e.g. purchasing new effects, the pulp production could be maintained. The results from the energy study indicate that dissolving pulp production is more heat demanding than kraft production. However, by increasing the heat integration of the mill, it is possible to, not only become self-sufficient in terms of steam, but also to produce significant amounts of excess steam. The steam excess facilitates integration of a lignin separation plant or can be used for power generation. The net annual profit was evaluated for varying prices of electricity and lignin. For the economic conditions studied, lignin separation was always better than power generation, if lignin can be priced as oil.