The driving force for filtration
The driving force for filtration is the pressure difference across the filter media, called the working pressure. The filtration process of the filter press is: introducing the suspension from the feed channel into each filter frame, the filtrate passes under pressure through the filter medium layer, flows to the surface of the filter plate filter, and discharges from the filtrate discharge port on the surface of the filter. The groove is concentrated outside the pores.
Diaphragm filter presses typically use a filter cloth as the filter media. Other filter media can be used if special requirements are met. For example, the fine filtration process of the petroleum industry uses filter paper as a filter medium. At the beginning of the filtration process, the fine solid particles in the suspension often pass through the filter cloth layer, so the filtrate is not very clear, but the larger particles are quickly intercepted or stuck in the channels by the filter cloth fibers. The fiber gap causes the gap through which the filtrate passes to rapidly decrease, and this process is theoretically referred to as filtration bridging.
When the cake layer is formed on the surface of the filter cloth, the actual filter medium is the cake layer and is therefore filtered by a membrane filter press, which is typically filtered through the filter cake layer. In order to filter some suspensions with very low solids content, the filter cloth cannot simply be used as a filter medium in order to obtain a clear filtrate. A more common method is to form a chemically stable and clean precoat on the surface of the filter cloth. The layer in which the precoat layer is used as a filter medium is referred to as a precoat layer.
The liquid content of the filter cake is a particular indicator of interest for separator filter presses. The filter cake layer on the surface of the filter cloth is extruded through the entire filter cake layer during filtration, so its sealing property is greater than other parts, and the filter cake in contact with the suspension is loose with the increase of the thickness of the filter cake, and the sides of the filter chamber The filter cake layer is connected, and the filter cake in the middle part has a high liquid content and is in a semi-fluid state.