Washing thin and nonuniform filter cakes: Effects of wash liquor maldistribution

To maximise solid and liquid production rates, vacuum filters are usually operated with as thin a cake as is permitted by the method of cake discharge utilised. This introduces problems with cake washing; thicker cakes can be washed more effectively, and there is a greater tendency for wash liquid to channel through thinner cakes, and also slight nonuniformities in cake thickness have a great effect on the distribution of wash liquid over the cake surface. The paper describes the results from an experimental investigation into the washing of thin cakes, indicating the effects of process variables on washing effectiveness. Equations are developed which permit the effects of wash liquor maldistributions to be assessed. Causes of poor cake coverage by wash liquor are discussed, and differences between washing thick and thin cakes are indicated.