Filter media is the heart of all filtering equipment. At present, the principle of filtration operation can be divided into three categories: cake filtration, deep filtration and surface filtration.
Filter Media Filtration Principle
Ceramic foam filter cake filtration uses fabric, porous solid or pore membrane as the filtering medium. The pore size of the medium is generally smaller than the filtered particles. When filtering, the liquid can pass through the small hole of the medium, and the particles larger than the small hole are intercepted by the medium to form filter cake. Therefore, the filter cake mainly depends on screening.
In fact, although the pore size of the filter medium is very small, some small particles will enter the small hole of the medium, and some particles will pass through the medium to make the filtrate turbid.
With the continuous filtration, many particles rush to the medium orifice, forming bridging phenomenon in the hole and on the orifice. When the concentration of solid particles is high, bridging phenomenon will be formed quickly. At this time, the role of the medium begins to realize. Because of the small space of filter cake, more and more fine particles are intercepted, forming a dense filter cake layer, which makes the filtrate clear. After that, filtration can be carried out effectively.
Deep filtering is to use sand, coke, ceramic, plastic and after processing of metal powder, such as fiber porous granular bed layer for clarification filtration. The characteristics of the deep filtration is solid particle capture is formed inside the filter medium pore and can stop the particles smaller than filter medium pore. Deep filter can get rid of sub-micron particles, so that small particles is difficult to use precipitation or average filtering method to deal with.
The common requirements for all kinds of filter media are excellent filtration characteristics; good physical and mechanical properties (high strength, creep resistance, steel flexibility, high wear resistance); good chemical stability (corrosion resistance, temperature resistance and microbial action) under certain process operation conditions and environment; convenient cleaning and regeneration, low price and reliable source.