The filter bag is the key component of the bag filter. The temperature of the dust-containing gas plays a key role in the selection of the filter bag. Because the temperature resistance value of the filter bag is limited, for example, the glass fiber temperature resistance value is 280 ℃, so sometimes it When high-temperature dust-containing gas, temperature-lowering measures must be taken to reduce the temperature of the dust-containing gas below the temperature resistance of the filter bag. The main cooling methods are: 1. Use a humidifying tower or flue to spray water directly to cool the temperature. For the bag-type dust collector using glass fiber filter material, the temperature can be reduced to below 260 ℃, but the temperature is much lower, the smoke The air flow rate is much smaller, which is helpful to reduce the filtering wind speed and prolong the service life of the filter bag. 2. Use the cooler to reduce the temperature. In order to improve the efficiency of the cooler, an axial fan can be used to blow the cooler to speed up the exchange of heat and cold. When the air volume of the dusty gas is too large and the temperature is very high, this method will consume a large amount of electricity and be uneconomical. 3. Mixed with cold air, the temperature of dust-containing gas is reduced by mixing cold air to make it below the temperature resistance of the filter bag. This method is simple and requires little investment. Due to the increase in air volume, the bag type dust collector should be considered when selecting the type Use a larger size.
The humidity of the gas has a great influence on the normal use of the bag dust collector 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, the mass of water vapor contained in a unit mass or unit volume of gas. B. Relative humidity, the ratio of the mass of water vapor in a unit volume of gas to the mass of water vapor in the saturated state at the same temperature and pressure. Relative humidity between 30% and 80% is the general state, more 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 conducive to dust capture, but it is difficult to clean the dust. Dust-containing gas tends to generate static electricity in an abnormally dry state, and it is not easy to leak due to high insulation, and it is easy to form a high-voltage charging situation, which is also easy to adhere and difficult to clean. Especially for high-temperature and high-humidity gas, the phenomenon of leakage may occur due to the cooling effect of external air, causing the trapped dust to foul on the surface of the filter bag, also known as the paste bag, which seriously affects the filter function and Service life, but also corrosive materials inside the dust collector. Therefore, controlling the humidity of the gas is very necessary to ensure the normal use of the dust collector and extend the service life of the filter bag.
At present, the filter materials used in bag-type dust collectors mainly include woven filter materials, non-woven filter materials, and composite filter materials. The woven filter material is formed by interweaving twisted warp and weft yarns or single threads. Filtration and separation of dust-containing gas through the gap between the warp and weft, the porosity of the filter material is generally 30% to 40%. The strength of the woven filter material is strong, the wear resistance is strong, but the filter material itself has a large resistance, and the surface filtration can be achieved after coating , Improve the purification efficiency and reduce the working resistance of the filter bag. The non-woven filter material does not go through the general spinning and weaving process, and the filter screen is directly fixed by mechanical, chemical or other methods. The composite filter material is processed into filter material by using two or more distinctive materials in order to make full use of the material.
For the woven filter material, the initial woven filter material is first the dust particles bridging in the hole of the cloth to form a dust layer, and then the dust collection efficiency is increased. Because the pores of the woven filter material are three-dimensional, the dust particles can not only adhere to the fibers to form dust The layer will also enter the inside of the filter cloth. During the period, the dust collection efficiency is 50% to 80%. After the dust layer is formed, the dust collection function is mainly the dust layer, and the dust collection efficiency is more than 99%. The structure of the dust layer changes with time. After half a year or one year, even if it is the same amount of dust layer, due to the clogging of the holes, the resistance loss will become larger. When the resistance loss increases to a large level, the filter bag needs to be replaced. Too. The microporous membrane coated on the surface of the membrane filter material replaces the role of the dust layer, and because the pore size of the microporous membrane is small, the dust particles are difficult and rarely enter the interior of the filter material to block the internal pores, so the resistance to long-term use is higher The material resistance is low.
For non-woven filter materials, most of the bag-type dust collectors currently use needle-punched felts. Needle-punched felts are classified into base fabric and base fabric. Increasing the base fabric can increase the strength. Put the pre-woven base fabric between the upper and lower fiber webs, strengthen them by pre-needle punching and main needle punching, and then perform necessary post-processing to become the required needle felt filter material. The fibers in the needle-punched felt filter material are arranged in a three-dimensional staggered manner, which is conducive to the formation of a dust layer, there is no straight gap, and the dust capture rate is higher than that of the general woven filter material. Needle felt filter material has no or only a small amount of base fabric, so the void ratio is generally 70% to 80%, good permeability and low resistance.
For composite filter material, because it is made of two or more materials with different characteristics, this filter material basically maintains the good properties of various materials, such as needle felt filter material or woven filter material. The coated filter material made of microporous membrane on the surface can realize surface filtration and improve the capture rate, and because the dust only adheres to the surface of the filter bag, it is easy to peel off. Membrane filter material itself has increased resistance compared with that without membrane, but after the dust collector is operated, it is surface filtered, with good peelability, easy to clean dust, and dust particles are not easy to block the pores of the filter material. The pressure loss during normal use is more The growth rate is low and slow, and the service life is longer than the uncoated filter material. For uncoated filter media, due to the dust blocking the pores of the filter media, the resistance of the filter bag continues to rise with the increase of working time. The resistance of the filter bag at the end of its service life is very large, which is not economical from the perspective of power consumption and treatment effects. Should be replaced with a new filter bag.
For the treatment of high-temperature flue gas, most of them currently use glass fiber filter material, which is made of glass liquid and is an inorganic non-metallic material with high tensile strength and low relative elongation. It has good high temperature resistance and Chemical stability. The glass fiber filter material has a shrinkage rate of 0 at 280 ° C and can be operated stably at 260 ° C. It is an ideal filter material for processing high temperature and high humidity flue gas. At present, the glass fiber filter materials that are used more are glass fiber open-width filter materials, glass fiber expanded yarn filter materials, and glass fiber needle felt filter materials. Glass fiber filter fabric is a fabric interwoven with warp and weft yarns, and is currently the leading product in the domestic market. Glass fiber bulk yarn filter material is a filter material woven with glass fiber bulk yarn in the weft yarn of traditional filter material. Due to its bulky yarn and strong covering ability, compared with glass fiber flat width 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, particles with a particle size of about 1 μm can be collected, and the dust capture rate is above 99.5%. At present, the amount of foreign use accounts for glass fiber filter material About 70% of the total. The glass fiber needle punched felt filter material has a three-dimensional microporous structure with high porosity and low resistance to gas filtration. It is a high-temperature filter material with high gas distribution and high dust collection rate, which enables the glass fiber filter material to pulse at high speed. It can be applied to bag dust collector. According to the requirements of the pressure and dust removal effect of the bag dust collector system, different filter materials are selected. Under normal circumstances, the anti-blowing bag type dust collector uses glass fiber open-width filter material or glass fiber expanded yarn filter material, and the pulse bag type dust collector uses glass fiber needle felt filter material. Filter materials of different thicknesses are selected according to the filtering air speed. High wind speed requires the thickness of the filter material. Excessively high filtering air speed has a negative impact on the service life of the filter material, dust collection efficiency, dust removal effect, and system operating resistance.
The selection of filter material should consider 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. Ordinary glass fiber filter material is used. The filtering air speed is low. The volume of the dust collector is much larger and the steel is also used much for the same air volume. The dust collector cost is high. The service life of the filter bag is generally about 1 year. The membrane filter material and P84 filter material are selected, and 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 longer, generally 2 to 3 years. In order not to affect the normal production of equipment and environmental protection compliance emissions as much as possible, the filter bags of domestic high-temperature bag dust collectors mostly use membrane-coated filter materials and P84 filter materials.
Three-point equipment, seven-point management, during the operation of the equipment, we must obtain the stability of the dust collector operation and the standard emission from the stability of the system.
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