NUMBER OF IDEAL STAGES AS AN EFFICIENCY PARAMETER FOR DISPLACEMENT WASHING OF PULP

In this paper, the concept of the number of ideal stages of dilution and thickening commonly used for the description of counter-current washing systems was applied to quantify the efficiency of displacement washing of pulp. Two kraft pulps cooked from beech and spruce, along with one soda pulp obtained from rapeseed straw and delignified to a relatively high kappa number ranging from 49.7 to 51.6, were subjected to displacement washing, using water as the wash liquid. Besides the traditional displacement ratio, the efficiency of displacement washing was expressed by the number of ideal counter-current washing stages as a function of the Peclet number and dimensionless dispersion length. The results described by the correlation equations showed that the kraft pulps cooked from beech and spruce were more easily washable, compared to soda rapeseed pulp.