Experimental an theoretical studies on the improved application of displacement washing for cracked filter cakes

Cake filtration is a flexible, generally well-controllable, and relatively cost-effective technology for solid-liquid separation. In many cases, on-spec separation result regarding soluble components can only be achieved through additional displacement washing, during which the wash liquid penetrates the surface of the filter cake and displaces the pore liquid. The standard preliminary tests for the subsequent design of industrial filtration systems are typically conducted for this purpose in small laboratory setups under defined conditions.

In actual industrial processes, crack formation frequently occurs in the filter cake (for example, due to partial desaturation leading to shrinkage processes). Such filter cakes typically elude standardized laboratory methodologies because the cracks occur stochastically with regard to their size, shape, and distribution. Since cracks exhibit a significantly lower flow resistance, the wash liquid preferentially flows through these defects, bypassing the actual filter cake. The process engineering consequences of this bypass flow (channeling) are uncertain plant designs, highly heterogeneous washing, an increased demand for wash liquid, as well as an undesirable dilution of the filtrate. To date, there is a lack of quantitative fundamental knowledge to evaluate the process engineering impacts of cracks. This is the starting point for the current research project.