Investigating the influence of pulp types on washing using a new measurement technique

The way in which the washing of pulp is affected by the type of pulp used was investigated in this work by using a new measurement technique. The experimental equipment developed was a test piston press equipped with a γ-radiation source and a scintillation detector that was used to measure concentrations within the pulp bed during the washing process. Three types of pulps were used: sulphite, kraft and mechanical (groundwood) pulp. It was shown that the washing of mechanical pulp differs greatly from the washing of chemical pulp. The dispersion coefficient was found to be a factor 10 larger for mechanical pulp than for chemical pulp. The difference was explained by the difference in fibre properties: the shorter fibres and the large amount of fibres present in groundwood pulp facilitate well-formed beds in which little channelling is present. It was also concluded from the local measurements that the dispersion effect at the top of the bed of the mechanical pulps was mostly attributed to inlet mixing. The influence of inlet mixing on the overall dispersion coefficient was however small. This result illustrates the usefulness of the new measurement technique since it could not have been obtained using traditional measurement techniques