MODELING THE FLOW AND THE DEPOSITION OF FILLERS IN PACKED-BEDS OF PULP FIBERS

The process of flow through a packed bed of pulp fibres and the deposition on the fibres of fillers passing through the bed has been modelled theoretically. The flow is described by a residence time distribution and is assumed to be completely segregated so that the bed can be divided into a number of sections, each characterized by a constant fluid velocity. For each section, the transport of fillers is governed by two partial differential equations describing particle transport and the deposition kinetics. The transport through the bed is found by integrating over all sections, using the residence time distribution of the flow through the bed. From this model one can calculate the concentration of fillers at the exit of the bed as a function of time, and the number of fillers deposited on the fibres. It was fouund that particle deposition is controlled by four dimensionless parameters that can be estimated for any bed by knowing the flow conditions and the deposition kinetics. The effect of these parameters on the amount of fillers depositing in the bed and passing through it are presented.