Filtered classification
1) According to the change of the nature of impurities in the filtration process, it can be divided into physical filtration and chemical filtration. The bag filter system is a physical filtration method and is a dead end filtration method for removing solid or colloidal particles in a liquid.
2) According to the filtering object, it is divided into gas filtration and liquid filtration: gas filtration mainly refers to the removal of oil, water and other particulate impurities in the gas; we refer to the liquid filtration mainly refers to solid-liquid separation, concentrated in the field of physical filtration; Color and deodorization are done by chemical treatment, so it is not completely within the scope of the liquid filtration we refer to, but a small amount of decolorization and deodorization can be done by adsorption in our activated carbon filter bag.
Impurity retention mechanism for physical filtration:
- Mechanical retentate: It has the effect of trapping impurities such as particles having a larger pore diameter or a pore diameter, that is, sieving.
- Physical action or adsorption retention: In addition to considering the pore size factor, other factors, including adsorption and electrical properties (such as static electricity), are also considered.
- Bridging effect: It can be observed by electron microscopy that at the entrance of the hole, the particles can also be trapped due to bridging.
- internal entrapment: this entrapment is to trap the particles inside the membrane, not on the surface of the membrane
Liquid filtration can be divided into deep filtration and absolute filtration
1) Deep filtration is a filtering method that intercepts the surface and inside of the filter layer.
Non-woven fabrics in non-woven fabrics (also known as non-woven fabrics) are randomly intertwined. Large particles are first intercepted on the outside of the non-woven fabric, and penetrated slightly, but are intercepted to a certain depth, and are smaller. The impurities are further deepened, and finally passed through particles smaller than a certain size and a small amount of particles larger than this size.
Generally used for depth filtration, such as polypropylene, polyester, NOMEX, PTFE, etc., the internal structure of the filter materials such as non-woven fabrics, the thickness of the material, and the fiber surface will produce the interception efficiency of the depth filter. influences.
Usually, this filtration is also called relative filtration, and the filtration accuracy is often defined by the filtration efficiency of impurities of a certain pore size. Different companies have different requirements for the test method of filter bag accuracy and the required filter efficiency. Some are defined as 80~85%, and some are defined as 50~70%. The actual filtration effect is different after using filter bags of the same precision from different companies. Sam can help choose a filter bag of the right precision.
2) Absolute filtration is a surface interception filtration method. 95-99.9% of particles larger than a certain size are intercepted, and particles smaller than this size are all passed.
Commonly used for absolute filtration, such as polypropylene, polyester, nylon, etc., monofilament or multifilament and stainless steel filter mesh.
The single fiber absolute filter has good slag discharge capacity; the multi-fiber absolute filter has high strength and filter colloid ability.
The diameter of the surface of the filter bag material must be the same size. The fiber weaving must be tight and firm. After the material is joined, it is required to withstand a large pressure to prevent leakage, and the absolute filtration effect is strictly guaranteed.
At present, nylon bags can achieve absolute filtration accuracy of 25μm. If the absolute filtration requirement is less than 25μm, it can be achieved with filter elements or other filter bags.
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