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Corrosion is one of the common reasons for the damage of the filter bag of bag filter. Because the flue gas contains many corrosive substances, and the corrosion effect is greater in high temperature environment, the filter bag will be damaged. The main causes of corrosion are hydrolysis, oxidation, acid and alkali corrosion. Among them, hydrolysis and oxidation mainly cause more damage, while acid corrosion is less and alkali corrosion is less. (1) Acid and alkali corrosion The main reason for corrosion is that the flue gas contains acid and alkaline components, and the dew point changes with the change of the concentration of these chemical gases. If the dust collector is started or stopped below the dew point, SO2 in the waste gas will form H2SO4 when it meets water, which will cause the filter bag fibers to harden and deform, thus losing strength and being damaged. The traces of corrosion damage are mostly radial, and a large area of discoloration is formed on the surface of the filter bag, which causes the filter bag to become hard and brittle and a small number of irregular circumferential holes appear, but it is different from the irregular circumferential holes produced by Mars burning through the filter bag and can be distinguished by naked eyes. Figure 8 shows that the HCI content in the flue gas of chlorination section of a magnesium oxide factory in Henan Province is very high. The average service life of PTFE filter bag is less than 3 months, and it is corroded and can not be used any more. Therefore, if the filter bag is cleaned by pulse under this condition, the damage of the filter bag will be accelerated. In addition to acid and alkali corrosion, the corrosion of organic solvents on the dust removal bag can not be ignored. For example, the damage of some trace substances in the waste incineration tail gas to the filter bag can not be reasonably explained at present, because the content of these substances is too low to be detected by the * * * method, but they actually exist in the tail gas, causing harm. Such as bromine vapor (Br2), although its content is very small, but the damage to the filter bag is fatal. (2) Hydrolysis Fiber hydrolysis is a process in which water molecules enter the fiber and react with polymers to break their molecular chains and generate new small molecular substances. As the molecular weight becomes smaller, the tensile strength of the fiber is weakened and damaged. Synthetic fibers produced by polycondensation polymers are not resistant to hydrolysis. For example, commonly used filter materials such as polyester and Nomex are easily hydrolyzed. Only under the combined action of high temperature, humidity and chemicals can molecules be activated and hydrolysis occur. The higher the content and temperature of water molecules in flue gas, the more serious the hydrolysis of filter bag. Different filter materials have different hydrolysis temperatures. Among them, P84 is one of the currently used filter bags with poor hydrolysis resistance. Hydrolysis marks are turbid in color, and the strength of the filter bag is seriously reduced, which is easy to be damaged. After the sewing thread is hydrolyzed, the filter bag cracks from the sewing thread, so that the filter bag is no longer cylindrical. (3) oxidation Fiber oxidation is a process in which molecules in the fiber lose (or dissociate) electrons, such as PPS fiber. At high temperature (150°C), oxygen molecules attack the "S" in the molecule and combine with it. The PPS fiber is discolored, hardened and brittle, and the strength is reduced and damaged. In severe cases, the fiber web will be broken and separated from the base fabric (as shown in Figure 10). Oxidation is another major factor of track damage. The filter materials with poor oxidation resistance mainly include polypropylene and polyphenylene sulfide (PPS).