The "RFM" filtration process developed by Schenk Filterbau GmbH, which can be fully automated and is suitable for both polishing and sterile filtration, uses a "ZHF/Z Primus" horizontal pressure leaf filter in conjunction with filter aids consisting of polyethylene and cellulose fibres mixed with ceramic powder. A suspension of filter aid, the properties of which vary according to the proportions of its constituents and the particle size composition of the ceramic, is prepared in a mixing tank and fed in at the bottom of the filtration vessel, rising up a central column and spreading out over each successive filter element to form a precoat which is much more uniform in thickness and composition than is the case with some older filters. The filter is rinsed after each filtering operation and chemically regenerated (with caustic followed by acid) after every third rinse. The filter cake, which remains in place after rinsing, is discharged, remixed and precoated again after regeneration. Up to 5% of the filter aid may be lost during this procedure, and must then be replaced during mixing, but otherwise it may remain in use indefinitely, thus avoiding the solid waste disposal problems created by used filter sheets, spent kieselguhr, etc., from other filtration systems.
Keywords : automatic filter aid filtration pressure leaf filter recycling sterile filtration