The filter bag is a key component of the bag filter. The temperature of the dust-containing gas plays a key role in the selection of the filter bag. Since the temperature resistance of the filter bag is limited, for example, the temperature resistance of the glass fiber is 280 ° C, so sometimes it is processed. When high temperature dusty gas is used, cooling measures must be taken to lower the temperature of the dusty gas below the temperature resistance of the filter bag. The main methods of cooling are as follows: 1. Use a humidification tower or a flue to directly spray water mist to cool down. For a bag type dust collector using a glass fiber filter, the temperature drops below 260 ° C, but the temperature drops much, the smoke The air flow is much smaller, which helps to reduce the filtering wind speed and extend the life of the filter bag. 2. Use a cooler to cool down. In order to improve the efficiency of the cooler, an axial fan can be used to blow the cooler to speed up the hot and cold exchange. When the air volume of the dust-containing gas is too large and the temperature is high, this method consumes a large amount of electricity and is uneconomical. 3. Mix cold air, reduce the temperature of dust-containing gas by adding cold air to lower it below the temperature resistance value of the filter bag. This method is simple and the investment is small. Due to the increase of air volume, the selection of bag type dust collector should be considered. Use larger specifications.
The humidity of the gas has a great influence on the normal use of the bag filter and the service life of the filter bag. The humidity of a gas indicates how much water vapor is contained in the gas. There are generally two ways to express it: A. Absolute humidity, mass per unit volume or mass of water vapor per unit volume of gas. B. Relative humidity, the mass ratio of the water vapor in a gas per unit volume to the water vapor in the same temperature and saturated state. The relative humidity is between 30% and 80% in general, greater than 80% is high humidity, and less than 30% is abnormally dry. When the dust-containing gas is in a high humidity state, a water film may be formed on the surface of the dust particles to increase the adhesion, which is advantageous for dust capture, but it is difficult to remove dust. When the dust-containing gas is in an abnormally dry state, static electricity is likely to be generated, and since the insulation is high, it is not easy to leak electricity, and it is easy to form a high-voltage charging state, and it is also easy to adhere to the cleaning. Especially for high temperature and high humidity gas, it may cause junction leakage due to the cooling effect of external gas, so that the trapped dust will be fouled on the surface of the filter bag, which is commonly known as the paste bag, which seriously affects the filter function of the filter bag and It has a long service life and also corrodes the internal material of the dust collector. Therefore, controlling the humidity of the gas is necessary to ensure the normal use of the dust collector and extend the life of the filter bag.
At present, the filter materials used in the bag type dust collector mainly include a woven filter material, a non-woven filter material, and a composite filter material. The woven filter material is formed by interlacing warp and weft yarns or single threads of ply. The dust-containing gas is separated by filtration through the gap between the latitude and longitude lines, and the void ratio of the filter material is generally 30% to 40%. The strength of the woven filter material is large, and the wear resistance is strong, but the resistance of the filter material itself is large, and the surface filter can be realized after the film is coated. Improve purification efficiency and reduce the working resistance of the filter bag. The nonwoven filter material is directly subjected to a mechanical spinning, weaving process, and the screen is directly fixed by mechanical, chemical or other means. The composite filter material is processed into a filter material by using two or more materials with different characteristics in order to exert the strength of the material.
For the woven filter material, the initial woven filter material firstly forms dust particles in the pores of the cloth to form a dust layer, and then the dust collection efficiency is increased. Since the woven filter material pores are three-dimensional, the dust particles can not only adhere to the fibers to form dust. The layer will also enter the interior of the filter cloth. During the period, the dust collection efficiency is 50%~80%. The dust collection layer is mainly composed of dust layer after dust layer formation. At this time, the dust collection efficiency is above 99%. The structure of the dust layer changes with time. After half a year or one year, even for the same amount of dust layer, the resistance loss will increase due to the clogging of the hole. When the resistance loss increases to a large extent, the filter bag needs to be replaced. It is. The microporous membrane coated on the surface of the membrane filter replaces the role of the dust layer, and since the pore size of the microporous membrane is small, it is difficult for the dust particles to enter the inside of the filter material to block the internal pores, so the long-term use resistance is smaller than that of the uncoated membrane. Material resistance is low.
For non-woven filter materials, most of the bag-type dust collectors used today are needle-punched felts, which are divided into two types: base cloth and base-free cloth. Increasing the base fabric can increase the strength. The pre-woven base fabric is placed between the upper and lower webs, pre-needled and main-needle-reinforced, and then subjected to necessary post-treatment to become the desired needle felt filter. The fibers in the needle felt filter material are arranged in a three-dimensional staggered manner, which is favorable for forming a dust layer, and there is no straight space, and the dust collection rate is higher than that of the general woven filter material. The needle felt filter has no or only a small amount of base fabric, so the void ratio is generally 70% to 80%, and the gas permeability is good and the resistance is low.
For the composite filter material, since it is a filter material processed from two or more different materials, the filter material basically maintains good properties of various materials, such as needle felt filter or woven filter material. The surface is coated with a laminated filter made of a microporous membrane to achieve surface filtration, which improves the capture rate, and is easy to peel off because the dust adheres only to the surface of the filter bag. The resistance of the membrane filter itself is increased compared with that when the membrane is not coated. However, after the dust collector is operated, it is surface-filtered, and has good peelability and easy cleaning. The dust particles are not easy to block the pores of the filter material, and the pressure loss during normal use period is higher. Low and slow growth, and long service life compared to uncoated filter media. Uncoated membrane material, due to the clogging of the filter material by the dust particles, the resistance of the filter bag increases with the increase of working time, and the resistance of the filter bag is very large after the service life, which is uneconomical in terms of power consumption and treatment effect. You should replace it with a new filter bag.
For the treatment of high temperature flue gas, most of the glass fiber filter materials are currently used. The glass fiber filter material is made of glass liquid and is an inorganic non-metal material with high tensile strength, low relative elongation and good high temperature resistance. Chemical stability. The glass fiber filter material has a shrinkage rate of 0 at 280 ° C and can be stably operated at 260 ° C. It is an ideal filter material for treating high temperature and high humidity flue gas. The glass fiber filter materials used nowadays are glass fiber flat filter material, glass fiber bulk yarn filter material and glass fiber needle felt filter material. The glass fiber flat filter material is a fabric made of warp and weft yarns, and is currently the leading product in the domestic market. The glass fiber bulky yarn filter material is a filter material woven from glass fiber bulked yarn in the weft yarn of the traditional filter material. Because of its bulky yarn, the covering ability is strong, compared with the glass fiber flat web filter material. Under the same capacity, the filtration wind speed can be increased by 1/3, the system running resistance can be reduced by 1/4, and the particles with a particle size of about 1 μm can be collected, and the dust collection rate is above 99.5%. At present, the amount of the foreign material accounts for the glass fiber filter material. About 70% of the total. The glass fiber needle felt filter fiber has a three-dimensional microporous structure, high void ratio, low filtration resistance to gas, high-temperature filter material with high air cloth and high dust-collecting rate, so that the glass fiber filter material can be pulsed at high speed. The bag dust collector is applied. According to the pressure and cleaning effect of the bag filter system, different filter materials are selected. Under normal circumstances, the reverse blow bag type dust collector uses a glass fiber flat filter material or a glass fiber bulk yarn filter material, and the pulse bag type dust collector uses a glass fiber needle felt filter material. Filter materials of different thickness are selected according to the filtering wind speed. The high wind speed requires the filter material to be thick, and the excessively high filtering wind speed has a negative impact on the service life of the filter material, the dust collecting efficiency, the cleaning effect, and the system running resistance.
The filter material should be selected to take into account the dust concentration of the flue gas, the fineness of the dust, the temperature of the flue gas, the moisture, the emission requirements, and the strength of the filter material. At present, the high temperature resistant filter materials mainly include ordinary glass fiber filter materials, coated glass fiber filter materials, PPS filter materials, P84 filter materials, PTFE fiber filter materials, and high temperature composite material filter materials. The ordinary glass fiber filter material is selected, the filtering wind speed is low, the same air volume, the volume of the dust collector is much larger, the steel is also used much, the dust collector is expensive, and the service life of the filter bag is generally about one year. The membrane filter material and the P84 filter material are selected. The price of the filter bag is high. The price of the filter bag often exceeds the cost of the dust collector body, and the service life is relatively long, generally 2 to 3 years. In order to prevent the normal production of the equipment and the environmental protection of the standard as far as possible, the filter bags of the domestic high-temperature bag type dust collectors mostly use the membrane filter material and the P84 filter material.
Three-point equipment, seven-point management, in the operation of the equipment to obtain stable and standard discharge of the dust collector from the stability of the system.
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