Enhanced expression of filter cakes using a local thermal supply

A thermal-dewatering system was studied to investigate alternative processes to enhance conventional dewatering device efficiency. The main idea in this work was to heat the filter medium at a temperature higher than the liquid boiling point. In this particular case a fast decrease of the filter cake thickness was observed during the expression stage. This phenomenon that we have called “cake collapse”, occurs in a quite short time as compared to the expression time and depends on many different parameters such as applied pressure, temperature, cake compressibility, …. Mechanisms involved are complex and combine thermal and mechanical effects. Experimental results show that “cake collapse” is closely linked to boiling at the filter medium level. In order to provide basic interpretation of this phenomenon, influence of capillary forces was also experimentally investigated and the role of capillary forces on “cake collapse” was highlighted. It appeared that formation of menisci in the pores of the cake modified pressure liquid distribution and contributed to cake destabilization.