The principle of crossflow filtration can be seen from the diagram below.
The liquid suspension to be filtered is passed through a porous tube. As a result of a differential pressure, some of the liquid passes through the membrane tube and is collected as particulate-free filtrate. The remainder of the liquid flows through the channels of the element, back into the processing tank and is recycled through the system. Eventually enough clean liquid is extracted from the process volume that liquid containing a higher concentration of the particulate material is left in the processing tank. Frequently the liquid can even be reduced to the consistency of a light slurry. Due to the high efficiency of the ceramic filter elements, very small particles may be removed from liquid streams that cannot effectively, or economically, be removed using conventional filter cartridge technology. Generally, the ceramic filter does not remove material or salts that are in a truly dissolved state, however with proper ceramic membrane selection, many oils and grease compounds can be separated from the base liquid and collected in the retenate. Depending upon the characteristics of the liquid and of the particulate, a ceramic cross-flow filtration system may utilize “back-pulsation” during operation to clear any particulate material from the filter surface by briefly reversing the flow of liquid through the ceramic filter tube. The ceramic filter elements are not replaced regularly, as are traditional filter elements, since they actively inhibit particulate build-up or clogging by maintaining a high cross-flow velocity through the tube and by means of the back-pulsation process. Ceramic elements are constructed from pure aluminum oxide and are impervious to basic and acidic solutions, can withstand wide temperature ranges and can operate at elevated pressures.
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