Permeability Parameters of Pulp Fibers from Filtration Resistance Data and Their Application to Pulp Dewatering

The drainage resistance of pulp fibers can be characterized by means of a specific surface area and the specific volume. These parameters can be used to determine the impact not only of processing the pulp fibers but also to compare and distinguish between different pulp mixes. We determined the specific surface area and specific volume of hardwood kraft pulp fibers by measuring the rate of filtrate flow under different applied pressures by a modified filtration apparatus. The specific surface area and specific volume can be used as parameters for monitoring fiber changes due to source and variation, determination of polymer dosage (retention, drainage aids, and flocculation control), and so on. The specific surface area serves as an indicator of the flocculation state of the pulp suspension, while the specific volume indicates the hydration of the fibers. Two mathematical models to describe dewatering of fibrous suspensions under varying pressure were applied. The first is based on conventional cake filtration theory, whereas the second is based on multiphase flow theory. The phenomena of cake filtration and sedimentation are included in the models, and the measured specific surface area and specific volume were found to predict the dewatering curves satisfactorily.