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A filter press is a device that uses a combination of permeable membrane filter elements and pressure to remove fluids from slurries. This process typically entails filling a multi-chambered press with slurry and reducing the internal chamber volumes by applying pressure. This process forces the fluids to exit via the permeable membrane, thus leaving a semi-moist cake of solids in the press. The filter press may be used to recover desirable solids from transport suspensions or to remove undesirable solids from water filtration processes. Filter presses are commonly used in the manufacture of food stuffs and pharmaceuticals and in chemical and water treatment plants.
Many manufacturing and purification processes require solids and their fluid carriers which make up slurry suspensions to be separated. For example, food and pharmaceutical production lines have to remove valuable powder or granular end products from the water which transports them through the production process. Water treatment plants, on the other hand, have to remove undesirable contaminant solids to begin the process of rehabilitating waste water. The filter press is one of the filtering methods which can deal with the speeds and quantities of slurry involved in these processes. These filters are also some of the most efficient and cost effective systems due to the low number of moving parts and system steps involved.
Filter presses generally consist of a series of chambers formed by hollow plate baffles. The surfaces of the baffles are lined with a filtration medium, typically a filter cloth membrane. When the press is open and empty, the gaps or chambers between the plates are fairly large. To start the filtration process, all chambers are pumped full of slurry. Once this step is complete, a hydraulic or electrically powered ram presses the plates together; it then compresses the slurry filled chambers and squeezes liquid out of the slurry through the filter membranes and into the plates' interior spaces. Interconnected filtrate ducts built into each plate then drain the liquid.
When the compression cycle is complete, the press is reopened and the plates are sequentially withdrawn. The filtered solids cake drops out and is collected for later use or disposal and the cycle is started again. After a predetermined number of filter cycles, the plate filters are washed to remove accumulated sludge. The filter press is suitable for a wide range of slurry types including organic and inorganic hydrophilic slurry, inorganic hydrophobic slurry, and oil based slurries. The filter press process is simple and not labor intensive; some filter membrane conditioning is necessary to prevent excessive sludge adherence with certain types of suspensions such as hydrophilic slurries, however.