Displacement washing of pulp with urea solutions

Two basic mechanisms of displacement washing of pulp fibres were investigated. Experiments were carried out in a laboratory washing cell that simulated a single stage of displacement washing. The step-change method has been employed in investigation of alkali lignin profile in outlet stream of washing effluents. The addition of urea to wash water resulted in a decrease of the liquid layer immobilized on the fibre surface. It had a positive effect on the washing efficiency expressed in terms of the void local efficiency. Presented at the 33rd International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 22–26 May 2006.