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Filter Presses ClothFilter presses cloth is used for Pressure Filters which are semi-continuous type machines that enter a wash and cake discharge mode at the end of the filtration cycle. The filtration cycle may extend from 5-10 minutes on cake filtration applications and up to 8 or even more hours for the polishing of liquids. Since the operation is in batches, that are usually fed from and discharged to a continuous process, a surge tank is required upstream the filter and batch collection of cake downstream the filter. The collection of filtrate depends on the operating mode of the filter which can be constant flow rate, constant pressure or both with pressure rising and flow rate reducing as for a centrifugal pump. Most Pressure Filters are batch operated but continuous filters are also available. However, owing to the difficulty in removing the cake they are mechanically complex and expensive so mainly applied in fine chemical processes where the added value to the product is high. There are two constraining factors that determine the duration of the filtration cycle: For cake filtration it is the volume available for cake build-up and once the volume is filled the cycle must terminate even if the permissible pressure was not reached. For polishing, or when the solids are fast blinding, the cycle must terminate once the permissible pressure has been reached regardless of cake thickness. The filtration rate is influenced, in broad terms, by the properties of the slurry. The trend is that the rate goes up with increased pressure, coarser particles, particle distribution with high uniformity, non-slimy or non-gelatinous solids, non-compressible cakes, lower liquid viscosity and higher temperatures. The Types of Pressure FiltersFilterpress up to 1000 m2 and 20 m3 cake. |