How to choose industrial filter bag according to working condition
Bag dust removal technology is developing rapidly in China. At present, domestic bag dust removal technology can keep up with the international pace. The industrial filter bag is the top priority in the field of bag dust removal and needs to be replaced regularly. Our purpose under each dust removal condition is to select the appropriate filter bag material. So how to select such industrial filter bag?
We need to know all about our industrial filter bags:
The long-time working temperature and instantaneous service temperature (shutdown and startup temperature) of industrial filter bag directly determine the service life of dust removal cloth bag. Long-time over temperature resistant work will shorten the service life of dust removal cloth bag or even burn it directly.
2. Wettability and adhesion of dust
The wettability and wettability of dust can be characterized by wetting angle. It is generally said that those less than 60°are hydrophilic and those greater than 90°are hydrophobic. When the humidity of hygroscopic dust increases, the cohesion and viscosity of particles increase, and the fluidity and electrification decrease. It adheres to the surface of the filter bag. Over time, the ash removal fails and the dust cake hardens. Some dusts, such as Cao, CaCl, KCl, MgCl2 and NaCO3, undergo further chemical reaction after moisture absorption to deliquesce and paste the bag, which is taboo for industrial filter bags.
3. Flammability and charging of dust
Some dust will burn or explode when it meets sparks in the air at a specific concentration. The ignition sources of dust combustion or explosion are usually caused by friction sparks, electrostatic sparks, hot particles, etc., among which the charging hazard is great. This is because the chemical fiber filter bag is usually easy to be charged. If the dust is charged at the same time, it is easy to produce sparks. Therefore, for combustible and easily charged dust such as pulverized coal, coke powder, aluminum oxide powder and magnesium powder, flame retardant filter bags and conductive filter bags should be selected. For example, PVC, PPS, P84, PTEF and other filter bags woven with fibers with oxygen index greater than 30, while for fibers with oxygen index less than 30, such as polypropylene, nylon, polyester, amide and other filter bags can be impregnated with flame retardant.
Secondly, determine the nature of dust gas: inlet dust concentration, outlet emission concentration, dust type and dust particle size (0.1 can be filtered after dust cake is formed by dust removal cloth bag) μ M above), moisture content, whether there is viscosity, whether it can produce or have acid and alkali corrosive components, whether there is the possibility of explosion, or even open fire, etc. At this time, we can consider appropriate post-treatment methods (such as explosion-proof, waterproof and oil proof, film covering, coating, high-temperature setting, flame retardant, acid and alkali resistant impregnation, etc.) according to the bag material to deal with the complex working environment.
4. Dust flow and friction
When the dust flow and friction are strong, it will directly wear the filter bag and reduce the service life. The wear resistance of particles with rough surface and irregular diamond shape is 10 times greater than that of spherical particles with smooth surface. The particle size is 90 μ The wear resistance of dust particles of M is large, and when the particle size is reduced to 5 μ m～l0 μ M, the wear resistance is very weak. The wear property is directly proportional to the 2 ~ 3 power of air velocity and the 1.5 power of particle size. Therefore, the air velocity and its uniformity must be strictly controlled. Among the common dusts, aluminum powder, silicon powder, coke powder, carbon powder and sinter powder belong to high wear dust. For abrasive dust, filter bags with good wear resistance should be selected.
Filtration wind speed: the filtration wind speed is mostly controlled above 1.2m/min and less than 0.8m/min under a few working conditions (glass fiber). Here, we know the filtering wind speed and the air volume of industrial filter bags, so we can calculate the filtering area, and then calculate the size of dust removal cloth bags according to the estimated number of dust removal cloth bags.
5. Select according to the nature of dusty gas
Chemical properties of gas.
In all kinds of furnace flue gas and chemical waste gas, it often contains a variety of chemical components such as acid, alkali, oxidant and organic solvent, which are often affected by temperature, humidity and other factors. Therefore, when selecting filter bags, we must grasp the main factors and comprehensively consider them according to the chemical composition of dusty gas.
The temperature of dusty gas is an important factor in the selection of filter bag. Generally, the dusty gas less than 130 ℃ is called normal temperature gas, and the dusty gas greater than 130 ℃ is called high temperature gas. Therefore, filter bags can be divided into two categories: normal temperature filter bags lower than 130 ℃ and high temperature filter bags higher than 130 ℃. Therefore, appropriate filter bags shall be selected according to the flue gas temperature. In practice, some people call 130 ~ 200 ℃ gas medium temperature gas, but the filter bag is mostly high-temperature type.
The dusty gas is divided into three states according to the relative humidity: when the relative humidity is less than 30%, it is dry gas, when the relative humidity is between 30% ~ 80%, it is general state, and when the relative humidity of the gas is more than 80%, it is high humidity gas. For high humidity gas, when it is at high temperature, especially when SO2 is contained in dusty gas, condensation will occur when the gas is cooled. This will not only scale and block the surface of the filter bag, but also corrode the structural materials, so special attention should be paid.
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