Displacement Washing of Kraft Spruce Pulp Cooked to Low Kappa Number

Abstract

The paper deals with the displacement washing of unbleached pulp cooked from spruce wood by kraft pulping process under laboratory conditions. Using the step function input change method, the washing breakthrough curves measured for alkali lignin as a tracer were described by the dispersed plug flow model, containing dimensionless criterion, the Péclet number. Besides the traditional wash yield, the relationship between the Péclet and Reynolds numbers was investigated as well. The results obtained for spruce pulp were compared with those for kraft beech pulp published earlier. The pulp yield achieved for spruce pulp was found to be lower than that for beech pulp.