TEST METHOD AND EQUIPMENT FOR THE DETERMINATION OF CAKE DISCHARGE PERFORMANCE OF FILTER MEDIA FOR INDUSTRIAL LIQUID FILTRATION APPLICATIONS

摘要

When a filter media is asessed for its suitability for application to an industrial liquid filtrationrnapplication, it is usual that several aspects of its performance are evaluated in the laboratoryrnprior to field trials. These tests are focussed on performance criteria such as particle sizernretention efficiency, filtrate throughput, cake moisture content, and the resistance of the mediarnto dimensional change in service (ie shrinkage) (1).rnOne of the most important aspects of filter media performance is the ease with which the cakerncan be removed from the media itself – ie the cake discharge performance. It is desirable thatrnthe cake can be removed easily from the cloth, as this can reduce cycle times and labor costs.rnNevertheless, this is an area that is not routinely benchmarked by filter media manufacturersrnin a laboratory environment, and cake discharge is only assessed during plant trials. Thernavailability of a test method for assessing cake discharge performance would provide extrarnevidence for the suitability of a filter medium for a particular application.rnThis paper describes a test rig and test method that have been developed to assess the cakerndischarge performance of filter media for liquid filtration applications. The test equipmentrncomprises a laboratory scale high pressure filter press consisting of mini-filter plates andrnspacers – the filter medium is placed between plate and spacer, and the cake forms in thernspacers. Filtrate passes through the cloth and can be gathered in a vessel on a top pan balancernwith RS232 output connected to a PC data logger to determine filtrate throughput.rnAfter a filtration cycle is run, the press can be opened, and the filter media is often adhered tornthe cake in the spacer. The spacer fixture itself is designed to be removed with the cake in siturnand cloth attached, and can be attached to a tensile test machine. The filter medium can thenrnbe pulled from the cake, ie subjected to a shear test, and the peak load is measured, producingrna ‘Cake Discharge Load’.rnThe test equipment is discussed in detail, and a case study is presented which illustrates howrnthis test method can be employed in benchmarking the cake discharge performance of filterrnmedia against specific slurries. The use of this technique for generating fundamentalrnunderstanding of cake discharge physics is also addressed.