How is the dust filter bag corroded

- Dec 14, 2019-

How is the dust filter bag corroded


Corrosion is one of the most common causes of bag filter bag damage, because the smoke contains a variety of corrosive substances, and in the environment of high temperature corrosion greater, will cause damage to the filter bag. The main causes of corrosion are hydrolysis, oxidation, acid and alkali corrosion. The main reasons are hydrolysis and oxidation, but acid corrosion and alkali corrosion are less.


(1) acid and alkali corrosion


The main reason for corrosion is that the flue gas contains acid and alkaline components, which change the dew point with the concentration of these chemical gases. If the dust collector is started or shut down below the dew point, the SO2 in the exhaust gas meets water to form H2SO4, which will cause the filter bag fiber to harden, deform and lose its strength and damage.


Most of the corrosion damage traces are radial, and large area of color change is formed on the surface of the filter bag, causing the filter bag to become hard and brittle, and a small number of irregular circular holes appear, but different from the irregular circular holes caused by Mars burning through the filter bag, it can be distinguished by the naked eye. Figure 8 shows the HCl content in the flue gas of the chlorination section of a magnesium oxide plant in henan province is very high, and the average service life of PTFE filter bag is less than 3 months, which is so badly corroded that it cannot continue to be used. Therefore, if the filter bag is washed by pulse under this condition, the damage of the filter bag will be accelerated.


In addition to acid, alkali corrosion, organic solvents, such as corrosion of dust bag also nots allow to ignore, such as waste incineration exhaust gas in some of the micro content of material damage to the filter bag, it is unable to make a reasonable explanation to its, because these substances content is too low, low to even cannot be detected, but they are actually consist in tail gas, the harm is great. For example, bromine vapor (Br2), though extremely small in content, can be fatal to the filter bag.


(2) hydrolysis


Fiber hydrolysis is a process in which water molecules enter into fibers and react with macromolecules to break their chains to form new small molecules. As the molecular weight becomes smaller, the tensile strength of the fiber is weakened and damaged. Synthetic fibers made from polycondensation polymers are not resistant to hydrolysis. Such as commonly used polyester, nomex and other filter materials are easy to hydrolyze.


Only under the combined action of high temperature, humidity and chemicals can molecules be activated and hydrolyzed. The higher the water molecular content and temperature in flue gas, the more serious the hydrolysis of filter bag is. The hydrolysis temperature of different filter materials is also different. P84 is one of the filter bags with poor hydrolysis resistance.


The hydrolytic mark is color cloudy, the strength of filter bag decreases seriously, easy to be damaged. After the sewing thread hydrolyzed, the filter bag cracked from the sewing thread, making the filter bag no longer tubular. The sewing thread of the filter bag is broken as shown in figure 9.


(3) oxidation


Fiber oxidation is the process by which molecules in fibers lose (or dissociate) electrons, such as PPS fibers, and oxygen molecules attack and bind to the "S" in molecules at high temperatures (150 ° c). This causes PPS fibers to change color, become hard and brittle, reduce strength and break, and break off the base cloth when serious (see figure 10). Oxidation is another major factor in bag damage. The main filter materials with poor oxidation resistance are polypropylene, polyphenylene sulfide (PPS), etc.

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