Compression Mechanism in Multilayered Filter Cakes

Sedimentation combined with a broad particle size distribution in the suspension results in multilayered filter cakes, where a fine particle layer forms on top of a compressible bottom layer. Owing to their high resistance, the fine particles act as a stiff layer and compress the bottom layer during filtration. This was investigated using a model cake composed of a compressible bottom layer and an artificial fine layer. Compression was determined via a volumetric porosity measurement. A reduction in porosity due to compression increased the filter cake resistance significantly. The use of different types of fine particles demonstrated that if the top layer resistance is higher than that of the bottom, a differential pressure results that pulls the top layer down and compresses the bottom layer.