Filter press

Generally, the slurry needed to be dewatered is injected into the center of the press and each chamber filled. The filling time should be as quick as possible in order to avoid cake formation in the first chamber before the last chamber is filled. While the chambers are being filled up, the pressure inside the system will increase due to the formation of thick sludge. Then, the liquid is filtered out through the filter cloths by adding streams of compressed air or water. The use of pressurized water requires more time to pass into the chamber compared to pressurized air, however this method is much more cost efficient.

The first form of filter press was invented in the United Kingdom in 1853, used in obtaining seed oil through the use of pressure cells. However, there were many disadvantages associated with them, such as high labour requirement and discontinuous process. Major developments in filter press technology started in the middle of 20th century. In Japan in 1958, Kenichiro Kurita and Seiichi Suwa succeeded in developing the world's first automatic horizontal-type filter press to improve the cake removal efficiency and moisture absorption. Nine years later, Kurita Company began developing flexible diaphragms to decrease moisture in filter cakes. The device enables optimisation of the automatic filtration cycle, cake compression, cake discharge and filter-cloth washing leading to the increment in opportunities for various industrial applications. A detailed historical review, dating back to when the Shang Dynasty used presses to extract tea from camellia the leaves and oil from the hips in 1600 BC, was compiled by K. McGrew.

There are three main basic types of filter presses: plate and frame filter presses, recessed plate and frame filter presses and automatic filter presses.

A plate and frame filter press is the most fundamental design, and many now refer it as a "membrane filter plate". This type of filter press consists of many plates and frames assembled alternately with the supports of a pair of rails. The presence of a centrifuge pump ensures the remaining suspended solids do not settle in the system, and its main function is to deliver the suspension into each of the separating chambers in the plate and frame filter. For each of the individual separating chambers, there is one hollow filter frame separated from two filter plates by filter cloths. The introduced slurry flows through a port in each individual frame, and the filter cakes are accumulated in each hollow frame. As the filter cake becomes thicker, the filter resistance increases as well. So when the separating chamber is full, the filtration process is stopped as the optimum pressure difference is reached. The filtrate that passes through filter cloth is collected through collection pipes and stored in the filter tank. Filter cake (suspended solid) accumulation occurs at the hollow plate frame, then being separated at the filter plates by pulling the plate and frame filter press apart. The cakes then fall off from those plates and are discharged to the final collection point.

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Wikipedia