Efficient washing of paper-grade pulp in the kraft process
Brown stock washing is the first treatment of pulp after the chemical pulping step. If this step is efficient, it saves costs and minimizes an environmental impact for the following oxygen delignification and bleaching.
This project is part of the Industrial Graduate School Resource Smart Process ( www.resurssmarta.se ).
Project description
After pulping the wood chips, the resulting pulp fibers and spent liquor are separated in a series of counter-current washing steps in which water and/or purified condensate from the evaporation plant is used. This separation is of utmost importance to obtain a sufficient pure pulp and an efficient recovery of sodium and sulfur compounds.
The washing can be divided into two parts: a) transport of ions (sodium, hydroxide, hydrosulfide, etc.) and dissolved wood constituents from the fiber wall and lumen to the bulk liquor; and b) removal of this black liquor between the fibers here. The most efficient method is initial filtration/pressing followed by displacement washing of the formed fiber bed. Both parts have been investigated earlier, but relatively few studies can be found. Some of them showed inconsistent results, particularly regarding how mechanical force acting on the fiber influences the quality of the fibers.
The project aims to improve pulp washing efficiency so that less water/condensate is used, thus decreasing the dilution of the black liquor. Still, the pulp's purity and quality are not influenced negatively. The focus will be on the mass transport of larger organic molecules out from the fiber wall at different pH and temperatures for three different pulp qualities (high yield, bleach qualities, and textile pulp). Moreover, studies on how fiber quality is influenced by mechanical forces applied during washing at different pH and temperatures will be carried out. Also, here, different pulp qualities will be investigated.
The project strengthens Swedish competitiveness through expected new fundamental knowledge for developing an efficient pulp washing process and, thus, through an increased pace of innovation in the transition to a circular economy.
Financing
Vinnova
Pulp and paper companies
Collaborators
Olena Sveastyanova, KTH
Gunnar Henriksson, KTH
Merima Hasani, Chalmers University of Technology
Hans Theliander, Chalmers University of Technology
Malin Wohlert, Uppsala University
Tomas Vikström, Valmet
Stora Enso
SCA
Södra skogsägarna ekonomiska förening
BillerudKorsnäs
Holmen