Displacement Washing of Soda Pulp Cooked from Rapeseed Straw with and without Silique Valves

Abstract

The paper deals with the displacement washing of unbleached pulp cooked from rapeseed straw by the soda 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. The preliminary results obtained for soda rapeseed pulp were compared with those for kraft hardwood pulp published earlier. The pulp yield measured for soda pulp was found to be lower than that for hardwood pulp which manifested lower hydraulic resistance. The presence of silique valves in rapeseed straw has a considerable impact on the exit concentration profile of alkali lignin displaced from the pulp fibre bed.