(1) Select filter material according to the characteristics of dusty gas
The filter material is usually made of natural fibers or synthetic fibers such as cotton and wool. Raw materials have different physical and chemical properties, and it is impossible to have completely excellent performance and resistance in terms of temperature, humidity and chemical resistance. Therefore, as the principle of selecting filter materials, it is necessary to fully grasp the characteristics of dust-containing gas (including the temperature, humidity, corrosiveness, flammability and explosiveness of dust-containing gas, etc.), carefully compare the properties of various fibers, and make reasonable choices. .
(2) Select filter material according to the properties of dust
The properties of dust include chemical and physical properties of dust. The selection of material, structure and post-processing of the filter material is mainly considered from the perspective of the physical properties of the dust. These properties mainly include the shape and particle size distribution of the dust, the adhesion and cohesion of the dust, the hygroscopicity and deliquescence of the dust, and the abrasiveness of the dust.
(3) Select the filter material according to the cleaning method of the dust collector
The cleaning method of the bag filter is a major factor in selecting the type of filter material structure. Due to the difference in cleaning energy and filter bag deformation characteristics of bag filters with different cleaning methods, filter materials with different structures and varieties should be selected.
(4) Select filter material according to other special requirements
It mainly includes high-concentration dust collection process, high-standard discharge and occasions with purification requirements, occasions with stable and low-resistance operation requirements, treatment of viscous dust gases such as oil mist, and requirements for special-structure dust collectors. The principle of selecting the filter material of waste incineration flue gas dust collector from the perspective of use
(1) Good filtration performance and low resistance;
(2) Uniform texture, stable size, high mechanical strength and long service life;
(3) Good chemical stability, acid and alkali resistance, high temperature resistance, and oxidation resistance;
(4) The source of raw materials is wide and the price is relatively cheap.
Obviously, it is very difficult to satisfy all the above conditions, because these conditions contradict and restrict each other. Therefore, the main factors should be considered when selecting filter media.
At present, the filter materials used in the bag filter of waste incinerators mainly include PPS filter material, P84 filter material, glass fiber bulk yarn and membrane filter material, glass fiber needle felt, PTFE fiber composite filter material and GORE-TEX, etc. varieties, and others include PTFE fiber or PTFE membrane filter material. Among them, the most widely used are PPS filter material and P84 filter material, especially in foreign waste incinerator bag filter, the use of these two filter materials is relatively large; glass fiber bulk yarn coated filter material and glass fiber Needle felt is widely used in China and Japan.
At present, the main properties of the commonly used filter materials for waste incinerator bag filter at home and abroad are as follows:
(1) Polyphenylene Sulfide (PPS)
Polyphenylene sulfide (PPS) fiber can work continuously at 190°C, and can withstand a high temperature of 232°C in an instant (without the influence of other chemical components). In addition to weak oxidation resistance, PPS fiber filter material has excellent acid and alkali resistance, so it is widely used in waste incinerators. However, when the oxygen (O2) content in the flue gas being treated exceeds 10% and the operating temperature exceeds 165°C, the PPS fibers will also decompose.
(2) Glass fiber
Glass fiber can be used to make glass fiber cloth, glass fiber bulk yarn cloth or needle felt. The maximum continuous temperature of glass fiber filter material can reach 260 ℃, and the instantaneous temperature resistance is 290 ℃. At temperatures above 260°C, the glass fiber filter material itself will not be directly destroyed, but the post-treatment substances used to increase the lubricity between the glass fibers (yarns) will be evaporated, which will eventually lead to mechanical damage between the glass fibers (yarns). wear. Fiberglass media is flame retardant, is virtually non-hygroscopic (no hydrolysis occurs), has excellent dimensional stability and reasonable strength properties. Fiberglass woven fabric has good tensile strength, but relatively weak bending resistance, so bending and friction should be avoided when handling. The acid resistance of glass fiber filter media is relatively good, but HF, concentrated sulfuric acid and hot phosphoric acid will have a corrosive effect on glass fiber filter media. At high temperature, weak alkalis, acid anhydrides and metal oxides will also damage the glass fiber filter media. . Therefore, glass fiber filter media generally cannot be used at dew point temperatures.
(3) Polyimide (P84)
Polyimide fiber filter material is a kind of flame retardant fiber filter material with stable temperature resistance. Under the condition of 240℃, the mechanical properties of P84 fiber filter material will not change, and the maximum temperature resistance can reach 260℃. P84 fiber filter material has no melting temperature and is naturally golden yellow. The fiber can be used as the base cloth of filter material and spinning filament yarn. P84 fiber filter material is not a hygroscopic fiber filter material (at a relative temperature of 65%, the water absorption is about 3%). In addition, since P84 fiber has a special-shaped (leaf-shaped) cross-sectional structure, which has a large filtering area and excellent filtering performance, P84 fiber is usually implanted in the surface layer of the filter material (dust-facing side) to improve the filtering performance of the filter material. Since the P84 fiber filter material has a certain degree of hydrolysis, it is recommended that the water vapor content in the conditions of use should be less than 38%. The filter material has strong adaptability to SO2 concentration, and has no special requirements for the oxygen content of flue gas.
(4) Polytetrafluoroethylene (PTFE)
PTFE synthetic fiber filter material is a unique material that can withstand acid attack of any acidity under the condition of operating temperature of 240°C and instantaneous temperature of 260°C. Polytetrafluoroethylene synthetic fiber filter material has excellent self-wetting, does not absorb moisture, and can withstand ultraviolet radiation. However, the wear resistance of PTFE fibers is general, so there are strict requirements on the smoothness of the filter bag frame. PTFE fiber can be used in harsh corrosive conditions and occasions where the service life of the filter material is high, and it can also be mixed with glass fiber to make a more cost-effective filter material.
(5) PTFE membrane filter material
The surface of the PTFE membrane is smooth and resistant to chemical substances. When it is laminated to the surface layer of ordinary filter materials, all dust can be trapped on the membrane surface to achieve surface filtration; because of the smooth surface of the membrane, it has excellent chemical stability. , water repellent, no aging, so that the dust trapped on the surface is easy to peel off, thus improving the service life of the filter material. Compared with ordinary filter media, it has the following advantages:
1) The pore size of the membrane is 0.2 to 3 μm, the filtration efficiency can reach more than 99.99%, and there is almost zero emission. The porosity does not change after cleaning, and the dust removal efficiency is stable.
2) At the beginning of use, the pressure loss of the film-coated filter material is higher than that of the ordinary filter material, but after being put into operation, with the increase of the use time, the pressure loss does not change much, while the pressure loss of the ordinary filter material will change with the It gets bigger and bigger over time.
3) When the ordinary filter material is in use, the dust can easily enter the interior and accumulate more and more until the pores of the filter material are blocked, resulting in the inability to continue to use. The PTFE membrane filter material can easily remove the filtered dust from the surface of the membrane, with good cleaning effect, long cycle and low cleaning pressure, which can improve the service life of the filter material and reduce the operating cost of the product. . The PTFE membrane filter materials commonly used in waste incinerators include PPS, P84 and glass fiber bulk yarn woven cloth.
