Cake washing plug flow

The washing analysis presented here is for a steady state, completely mixed system where the wash water and the water entrained by the solid matrix are in equilibrium When filter cakes are washed, the operation is batch, the system is not well mixed because flow is close to plug flow, and the operation is not at equilibrium since the entrained fluid has to diffuse into the wash liquid. This case is analyzed by Harrison et al. 20031. 

Figure 10.4 A typical washing curve for a cake initially saturated, also showing one for ideal plug flow...

Washing in a continuous decanter is fairly effective on solid particles larger than 80 jam (200 mesh), provided the particles are reasonably uniform in size with porous structure. Otherwise, the wash flows across the cake surface with little penetration because the pores at the cake surface are plugged by fines. Rinsing efficiency, the proportion of soluble impurities displaced from the sohds, is in the range of 50 to 80... 

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