Analysis of filter cake formation using computational fluid dynamics - discrete element method (CFD-DEM) simulation

Cake filtration is one of the basic solid-fluid separation process. It is known that in many cases the cake has a non-uniform structure. Depending on a number of factors, the formed cake may or may not consolidate during compression. In short, an in-depth understanding of cake formation is required for the optimal design of the filtration process. In this work, we aim to acquire an in-depth understanding of the various factors affecting the structure of the cake with the help of numerical studies. As the suspension is dense, the flow is affected by the suspended particles which in turn affect the particle dynamics. This effect is captured by two-way coupling between the flow and the particle solvers (OpenFoam-LIGGGHTS). Moreover, the suspended particles come in contact with each other after which they may deform rebound, permanently stick at the point of contact, or may remain in contact but roll down to new positions. The Discrete Element Method (DEM) is used to model such micromechanisms. The contact model used in DEM has a set of input parameters like coefficient of restitution, sliding friction, rolling friction, and the work of adhesion. The measurement of these parameters for micron sized particles is a challenging task. In this study, we obtained a set of parameters by comparing the volume averaged void fraction of the cake predicted by CFD-DEM simulation to the experimental values. It is observed that the work of adhesion is the most important parameter affecting the cake structure of fine particles. Further the factors affecting the pressure drop across compressible and incompressible cake are discussed based on the results of numerical studies.