THEORY AND PRACTICE OF FILTRATION IN THE ALUMINA INDUSTRY

Continuous rotary filters like disc, drum or pan filters are of great importance in the industrial practice of solid/liquid separation and especially in alumina refineries they are standard technology for a variety of filtration duties. In the daily practice however the knowledge of the theory of cake forming filtration, which is the precondition for understanding the operation behavior of these filters, is rather basic. Essential interrelations of the physical conditions of the filtration process, product characteristics and filter design are insufficiently understood and consequently the operation behavior of running filters is often misinterpreted. Operation issues like incomplete cake discharge on disc or drum filters, increased Na₂Ocontent in the filter cake of pan or drum filters or lack of capacity are often referred to OEMs in terms of “your filter is not performing”. What is the reason for incomplete cake discharge on disc or drum filters? Why do results of cake wash fall off in quality on pan or drum filters? A correct analysis and adequate answers to such operational problems are not possible without knowledge the basic functions and interrelations described by the filtration theory.