The influence of non-ideal effects on cake washing and their experimental analysis

The investigations described herein focus on phenomena normally omitted in the description of cake washing. The topics discussed are the shrinkage behavior of the cake during washing, the influence of the non uniform structure of the cake near the cloth and the effect of dewatering the cake mechanically by gas differential pressure before washing. Shrinkage during washing is divided in capillary shrinkage and shrinkage due to; the loss of electrolyte. The first type has to be regarded when gas is present in the cake and includes the second one. The second type is important if the cake is saturated. By means of shrinkage experiments a method for the determination of an optimized compressive pressure is derived. Caused by the non uniform structure of the cake nearby the cloth this zone has a higher load of pollution in the regime of diffusion than expected for a homogeneous cake. This zone contributes in addition to other effects to the tendency of a higher reachable purity with growing height of the cake at a constant specific consumption of wash fluid. The influence of the residual moisture of the cake before washing is shown and the experimentally spotted consequences for each mechanisms regime are explained in detail.