Filter bags are selected according to dust properties
Dust wetness and adhesion. The wettability and wettability of dust are achieved by capillary action formed between dust particles, which is related to atomic chain, state of dust, surface tension of liquid and other factors, and can be represented by wetting Angle. Generally, those less than 60 degrees are called hydrophilic, and those greater than 90 degrees are called hydrophobic. With the increase of humidity, the cohesion and viscosity of the particles increase, and the fluidity and charge decrease. They stick to the surface of the filter bag.
Some dust, such as CaO, CaCl2, KCL, MgCL2, NaCO3 and so on, undergo further chemical reactions after moisture absorption, and their properties and morphology change, which is called deliquescence. After deliquescent dust pastes the surface of filter bag, this is the most taboo of bag filter.
For wetting and deliquescence dust, attention should be paid to the smoothness, non-fluffiness and water quality of the filter material when selecting the filter material, among which plastic burning plate of plastic coated filter bag is the best.
Dust with strong wettability has strong adhesive force, which is inextricably related to adhesion. If the adhesive force of bag precipitator is too small, it will lose the ability to collect dust, while the adhesive force is too large, which will cause dust aggregation and dust removal difficulties.
For the strong adhesion of dust should also choose filament fabric filter bag, or by surface burning, calendering, mirror treatment of needled felt filter bag, for impregnation, coating, mulching technology should make full use of. Nylon and glass fiber are superior to other varieties in terms of the material of dusting bag.
(2) the flammability and charge-ability of dust. Some dust in a particular concentration of the state, in the air sparks will occur combustion or explosion. The flammability of dust is related to its particle size, composition, concentration, combustion heat and combustion speed. The smaller the particle size, the larger the surface area, the easier the ignition. An important condition of dust explosion is a closed space, in this space the lower limit of the explosion concentration is generally dozens to hundreds of grams per cubic meter, the higher the combustion heat and combustion speed of dust, the greater the explosive power.
Dust combustion or explosive source is usually caused by friction spark, electrostatic spark, hot particles, etc. This is because chemical fiber filtration is usually easy to charge, if the dust is also charged, it is easy to produce sparks, so for combustible and easily charged dust such as coal powder, coke powder, aluminum oxide powder and magnesium powder, it is appropriate to choose flame retardant filter material and antistatic dust bag.
It is generally believed that the fibers with oxygen index greater than 30 are mixed with conductive fibers to make the filter material conductive in meridionic or meridionic direction, so that the resistance is less than 1*109 ohms. Commonly used conductive fibers are stainless steel fibers and modified (carbonized) chemical fibers. Compared with the former, the conductivity is stable and reliable, while the latter is liable to decline after a certain period of time. The amount of conductive fiber is about 2% ~ 5% of the basic fiber.
(3) dust flow and friction. Dust flow and strong friction, will directly wear the filter bag, reduce the service life. Particles with rough, irregular rhomboids are 10 times more abrasive than spherical particles with smooth surfaces. Dust particles with a particle size of about 90 microns had the greatest wear, but when the particle size was reduced to 5 ~ 10 microns, the wear was very weak. Abrasion is proportional to the speed of the airflow to the power of 20,000 to 30,000 and to the power of 1.5 square of the particle. Therefore, the airflow velocity and its uniformity must be strictly controlled. Among the common dust, aluminum powder, silicon powder, coke powder, carbon powder, sinter powder and so on belong to high wear dust. Wear - resistant filter bags should be selected for wear - resistant dust.
The wear parts and forms of dust removal filter bag are varied. According to experience, the wear of filter bag is in the lower part, which is because the upper part of the filter bag has a low filtration rate and a small concentration of gas containing dust. In order to prevent the lower part of the filter bag from fraying, the design should limit the speed of air flow up the lower part of the bag room.