Effect of Rapeseed Straw Composition upon Washing Efficiency of Soda Pulp

Abstract

The aim of this work was to investigate the displacement washing process of soda pulp cooked from rapeseed straw containing stalks and silique valves. Displacement washing process was described by breakthrough washing curves recorded for alkali lignin like a tracer. Mathematical treatment of the washing curves, which were obtained as a response to the step input signal, gave the dimensionless number known as the Péclet number characterizing the displacement of lignin from the pulp pad. For detailed description of displacement washing process, further parameters, such as the traditional wash yield, as well as time parameters, were also evaluated. The preliminary results obtained showed that, similarly as for kraft hardwood fibres, the wash yield determined for soda rapeseed pulp was found to be lower than that for non-porous incompressible particles. The differences between the mean residence time of alkali lignin and holding time of the wash liquid in the bed were greater for soda pulp cooked from stalks only in comparison with the soda pulp cooked from a blend of stalks and silique valves.