The benefits of pre-thickening

The feed solids concentration has a profound effect on the performance of any cake filtration equipment. It affects the capacity and the cake resistance, as well as the penetration of the solids into the cloth (which influences filtrate clarity and medium resistance). Thicker feeds lead to improved performance of most filters through higher capacity and lower cake resistance. 

The effect on solids yield can be easily demonstrated using the following equation derived in appendix I of Svarovsky (neglecting medium resistance)  

For given operating conditions and submergence, the dry cake production rate increases with the speed of rotation (see equation 9.40) and the limiting factor is usually the minimum cake thickness which can still be successfully discharged by the method used in the filter. Equation 9.41 (also derived by Svarovsky ) shows the dependence of the solids yield on cake thickness  

For those filters which allow variations in cake formation time within a fixed cycle time (such as the horizontal vacuum belt filter, for example), the advantage of pre-thickening is that for thicker feeds the cake formation time can be shortened, thus giving more time for dewatering, washing or other cake-processing operations. On the other hand, it can be shown (see Svarovsky or section 12.2.1.3) that in an optimum cycle time, at 

The physical reason for the higher feed concentrations to reduce the specific cake resistance has been the subject of a computer modelling project. The model used was similar to that of hard spheres used in molecular studies. The determining factor in the formation of local voids and higher 

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