Corrosion is one of the most common causes of dust bag filter bag damage, because the smoke contains a variety of corrosive substances, and in the high temperature environment, a greater effect of corrosion, resulting in damage to the filter bag. The main causes of corrosion are hydrolysis, oxidation, acid and alkali corrosion. Among them, the main causes are hydrolysis and oxidation, and the acid corrosion is less and the alkali corrosion is less.
(1) Acid, alkali corrosion
The main cause of corrosion is the presence of acid and alkaline components in the flue gas. The dew point changes as the concentration of these chemical gases changes. If the dust remover is turned on or off below the dew point, the SO2 in the exhaust water will form H2SO4 in water. Causes the filter bag fibers to harden, deform and lose their strength and damage.
The traces of corrosion damage are mostly radial and form a large area of discoloration on the surface of the filter bag, causing the filter bag to become hard, brittle, and with a few irregular holes. However, unlike the irregular circular holes generated by Mars burning filter bags, Can be distinguished with the naked eye. Figure 8 shows that the content of HCl 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 the PTFE filter bag is less than 3 months. Therefore, if the filter bag is pulsed under this condition, the filter bag will be damaged.
In addition to acid and alkali corrosion, the corrosion of dust bags by organic solvents can not be ignored. For example, some micro-contents in waste incineration waste damage the filter bags, and it is still impossible to give a reasonable explanation because of the content of these substances. It is too low, even low to detect, but they are actually present in the exhaust gas, and the damage is enormous. For example, although bromine vapor (Br2) is extremely small, damage to filter bags is fatal.
(2) Hydrolysis
Fiber hydrolysis is the process by which water molecules enter the fiber and chemically react with the polymer, causing the molecular chain to break down and generate new small molecules. As the molecular weight becomes smaller, the tensile strength of fibers is weakened and damaged. Synthetic fibers produced from polycondensed polymers are not resistant to hydrolysis. Such as commonly used polyesters, Nomex and other filter media are prone to hydrolysis.
Only when the three factors of high temperature, humidity, and chemicals work together to activate the molecule, hydrolysis occurs. The higher the water molecule content and temperature in the flue gas, the more severe the hydrolysis of the filter bag. Different filters have different hydrolysis temperatures. P84 is one of the poorest hydrolysis resistance in the filter bags currently used.
The traces of hydrolysis are turbid, and the strength of the filter bag is severely reduced and easily damaged. After the sewing thread is hydrolyzed, the filter bag is cracked from the sewing thread so that the filter bag is no longer cylindrical. The filter bag sewing thread is broken as shown in Figure 9.
(3) Oxidation
Fiber oxidation is the process by which molecules in a fiber lose (or dissociate) electrons, such as PPS fibers, and molecules of oxygen attack the “S” in the molecule at high temperatures (150°C) and bind to it. As a result, the PPS fiber discolors, becomes hard, becomes brittle, and breaks down in strength. In severe cases, the web breaks off from the base fabric (see Figure 10). Oxidation is another major factor in filter bag damage. Poor anti-oxidation properties of the filter are: polypropylene, polyphenylene sulfide (PPS) and so on.
