Dust filter bag can be the heart of the dust collector, filter bag selection is essential, it directly affects the dust collector dust removal effect, dust filter bag fabric and design should try to pursue efficient filtration, easy dust stripping and durable effect. Selection of filter bags should be selected from the following aspects: gas temperature, humidity and chemical; particle size; dust concentration; filter wind speed; cleaning methods and other factors into account.
1Filter bag selection principle And precautions
Bag filter is generally based on the nature of dust-laden gas, the nature of the dust and dust cleaning method of different choice of filter bag, the choice should follow the following principles:
① filter bag performance should meet the production conditions and dust removal process of the general situation and special requirements.
② Under the above conditions, should try to choose a long life of the bag, this is because the long life can not only save operating costs, but also to meet the requirements of long-term gas emissions.
③ choose the filter bag should be a comprehensive comparison of various filter sorting, should not use a so-called "good" filter bag to adapt to a variety of working conditions occasions.
④ in the gas properties, dust properties and cleaning methods, should seize the main factors affecting the filter bag, such as high temperature gas, corrosive gases, flammable dust and so on.
2 According to dustNature selection
① gas temperature. Dust gas temperature is an important factor in the selection of filter bags. Usually less than 130 ℃ dust-containing gas known as room temperature gas, more than 130 ℃ dust-containing gas known as high-temperature gas, so the filter bag can be divided into two categories: the room temperature filter bag and high temperature filter bag should be based on the flue gas temperature Choose the right filter bag was 130-170 ℃ said the temperature of the gas, but the filter bag selected high temperature type.
Filter bag temperature "continuous long-term use temperature", "instant short-term temperature" two. "Continuous long-term use of temperature" refers to the filter bag can be applied to the continuous operation of the long-term temperature, should be used to select the temperature filter bag. "Instantaneous short-term temperature" refers to the filter bag is not allowed every day more than 10 minutes of the maximum temperature, the time is too long, the filter bag will soften deformation.
② gas humidity dust gas according to the relative humidity is divided into three states:. Relative humidity below 30% for the dry gas, easy to produce static electricity, and high humidity gas, dust is easy to attach and difficult to clean relative humidity of 30% to 80% for the general state, the best dust working conditions. Gas relative humidity of 80% or more that is high humidity gas, high humidity gas in a high temperature state, especially dust containing gas containing SO 3, the gas will produce condensation condensation phenomenon. This will not only make the bag surface fouling, clogging, and will corrode structural materials, dust removal devices, filter bags and other serious damage, so pay special attention to the use of wet gas in the choice of filter bags should note the following:
1) containing moisture to the bag surface to capture the dust wetting adhesion, especially for water absorption, deliquescence and wetting dust will cause paste bag. For this purpose should be used nylon and glass fiber and other surface smooth, long fiber, easy to clean the filter bag, and should use the silicone oil bag, fluorocarbon resin to do the invasion treatment, or in the bag surface using acrylic, polytetrafluoroethylene And other substances for coating treatment. Plastic plate and film material has excellent moisture resistance and easy cleaning performance. But as a high humidity gas should be the preferred waterproof and oil dust bag.
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2) When the high temperature and high humidity will exist at the same time will affect the temperature of the filter bag, especially for the nylon, polyester, amide and other hydrolytic stability of the material is so bad, should be avoided as much as possible.
3) the use of wet gas in the dust bag design should adopt a round filter bag, try not to use the shape of complex, very compact layout of the flat filter bag and diamond bag (except plastic plate).
4) dust collector dust gas inlet temperature should be higher than the gas dew point temperature above 30 ℃, in order to avoid paste bag.
5) Chemical properties of gases. In a variety of furnace exhaust and chemical waste gas, often containing acid, alkali, oxidants, organic solvents and other chemical composition, and often by the temperature, humidity and other factors cross the impact of this. Selection of dust bag should be considered thoroughly, so as to avoid unnecessary losses.
Polyester fiber at room temperature with good temperature resistance, chemical resistance, but in high temperature conditions, chemical resistance worse. Polyphenylene sulfide fiber with high temperature and acid and alkali corrosion of good performance for coal-fired flue gas dust, but the antioxidant capacity is poor, although polyimide fiber can make up for its shortcomings, but the hydrolysis stability is not ideal. As the "plastic king" of polytetrafluoroethylene fiber with the best chemical resistance, but the price is more expensive. In the selection of filter media, must be based on the chemical composition of dust-laden gas, seize the ingredients, to seize the main factors, to consider.
3 According to the nature of the dust
① wetness and adhesion of dust. Dust wetness, wettability is formed by the formation of capillary between the dust particles to complete, and the dust of the atomic chain, the state and the liquid surface tension and other factors related to the wet angle can be used to characterize. Usually less than 60 degrees are known as hydrophilic, greater than 90 degrees are known as hydrophobic. After the increase of humidity, the cohesion and viscous force of the particles increase with the increase of the humidity, and the mobility and chargeability decrease, and the surface of the bag is prolonged.
Some of the dust, such as CaO, calcium chloride, KCL, magnesium chloride, sodium carbonate on the asparagus and other moisture after further chemical reaction, its nature and shape are changed, said the deliquescence. After the deliquescence of the dust paste the bag surface, which is the most taboo of the bag filter.
For wetting, deliquescence of dust, in the selection of filter media should pay attention to the smooth filter, not cashmere and water delivery, of which the film filter bag plastic plate for the best.
Wetting strong dust, many strong adhesion, in fact, and sticky inseparable link. For the bag filter if the adhesion is too small, will lose the ability to capture dust, and the adhesion is too large and cause dust condensation, cleaning difficult.
For the strong adhesion of the dust should also use the filament can not afford fabric bag, or the surface singeing, calendering, mirror treatment of needle felt filter bag, for impregnation, coating, film technology should be fully utilized. Polyester from the dust bag material, glass fiber is better than other varieties.
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② dust flammability and charge. Some dust in a particular concentration state, in the air when the spark will occur burning or explosion. Dust flammability and its particle size, composition, concentration, combustion heat and burning speed and other factors. The smaller the particle size, the larger the surface area, the easier it is to ignite. Dust explosion is an important condition is closed air, in this space, the lower limit of its explosive concentration is generally tens of hundreds of grams per cubic meter, the dust burning heat and burning speed higher, the greater the power of its explosion.
Dust burning or explosive fire source is usually caused by friction sparks, static sparks, hot particles and other substances, which charge the greatest harm. This is because the chemical fiber filter is because the chemical fiber filter is usually easy to charge, if the dust at the same time charge is easy to produce sparks, so for flammable and easy to charge dust such as coal, coke powder, alumina powder and magnesium Powder, etc., should choose flame retardant filter and anti-static dust bag.
Generally believed that the oxygen index of more than 30 fibers mixed with conductive fibers, so that the filter in the warp or Wei to have conductive properties, the resistance is less than 1 × 109 ohms. Commonly used conductive fibers are made of stainless steel fibers and modified (carburized) chemical fibers. Both compared to the former conductive performance is stable and reliable, the latter after a certain period of time after the conductivity is easy to decline. The amount of conductive fiber mixed is about 2% to 5% of the basic fiber.
③ dust flow and friction. Dust flow and friction are strong, will directly wear the filter bag, reducing the service life. Rough surface, irregular diamond particles than the surface smooth spherical particles wear 10 times. Particles with a particle size of about 90 microns are the most abrasive, and when the particle size is reduced to 5 to 10 microns, the abrasion is very weak. Wear and air velocity of 2 ~ 3 million times with the grain of the 1.5 power is proportional to, therefore, the air velocity and its uniformity must be strictly controlled. In the common dust, aluminum powder, silicon powder, coke powder, toner, sintered ore powder are high abrasive dust. For wearable dust should choose a good wear resistance of the bag.
Dust filter bag wear parts and forms varied, according to experience, filter bag wear in the lower part, this is because the upper filter bag filter speed is low, the concentration of gas dust small reason. In order to prevent the lower part of the filter bag wear, the design should be limited to the lower part of the bag air flow rate.
For the strong wear of dust, the choice of filter bag should pay attention to three points:
① chemical fiber is better than glass fiber, puffed glass fiber is superior to the general glass, fine, short, curly type fiber is better than coarse, long, smooth fiber.
② felt in the use of acupuncture need to strengthen the fiber between the texture, the fabric to satin fabric is the best, the fabric surface is also to improve the wear resistance of the measures, but the felt, satin fabric and cashmere Filter bag will increase the resistance value.
③ for ordinary filter surface coating, calendering and other post-processing can also improve wear resistance. For glass fiber filter bag, silicone oil, graphite, PTFE resin treatment can improve wear resistance folding. However, the film filter for the strong wear conditions, the film will prematurely worn, loss of film effect.