Summary of key points in the structural design of

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Summary of key points in the structural design of single machine bag filter

the processing air volume determines the size of single machine bag filter. Generally, the handling air volume is the working condition air volume. Attention must be paid to the use place and flue gas temperature of the dust collector in the design. If the flue gas treatment temperature of the single bag dust collector has been determined and the gas is cooled by dilution method, the amount of diluted air should also be considered in the treatment air volume; Considering the future process changes, the air volume design index value should increase the safety factor of 5% - 10% on the basis of the normal air volume. Otherwise, once the process adjustment increases the air volume in the future, the filtration speed of the single bag dust collector will increase, which will increase the resistance of the equipment, and even shorten the service life of the filter bag, which will also become the reason for the sharp rise of other failure frequencies. However, if the safety factor is too large, the investment and operation cost of the dust collector will be increased; The filtration wind speed varies greatly due to the form of single bag filter, the type and characteristics of filter materials. Once the treatment air volume is determined, the necessary filtration area can be determined according to the determined filtration wind speed

2. Service temperature

the service temperature of a single bag filter is an important basis for design. Deviation between the service temperature and the design temperature will lead to serious consequences, because the temperature is restricted by the following two conditions: first, the maximum allowable temperature of different filter materials (instantaneous allowable temperature and long-term operating temperature) is strictly limited; Second, to prevent condensation, the gas temperature must be kept above the dew point of 20 ℃. For high-temperature gas, it must be cooled below the temperature that the filter material can withstand. There are many kinds of cooling methods, such as natural air duct cooling, forced air cooling, water cooling, etc. specifically, it can be designed according to different processes, cooling temperatures, layout and size requirements, and load calculation and load meter selection

3. Gas composition

except for special cases, the gas handled by single bag dust collector is mostly ambient air or furnace flue gas. Generally, the design of single bag dust collector is calculated according to the treated air, and the composition of gas is considered only when the parameters such as density, viscosity, mass heat capacity and so on are related to the calculation of wind power performance and pipe resistance and the design of cooling device. In many working conditions, the flue gas mostly contains moisture. With the increase of moisture in the flue gas, the equipment resistance and fan energy consumption of single bag filter also change. The water content in dusty gas can be determined by actual measurement or calculated according to the material balance of combustion and cooling. Whether there is corrosive gas in the flue gas is a factor that must be considered in the selection of filter material, dust collector shell material and corrosion prevention. In addition, if there is toxic gas in the flue gas, it is generally trace, which has little impact on the performance of the device. However, when dealing with this kind of dusty flue gas, the single bag filter must adopt a gas tight structure, and it must be regularly maintained and overhauled to avoid the leakage of toxic gas, which will cause Jinan new era gold assay instrument Co., Ltd. to choose a hydraulic universal testing machine, First of all, you should make clear what kind of material experiment the equipment is used for

4. Inlet dust concentration

the inlet dust concentration is often expressed by the dust mass of the standard state volume. As for the inlet dust concentration, the following considerations should be taken into account in the design of single machine bag filter

(1) equipment resistance and ash cleaning cycle. When the dust concentration at the inlet increases, the equipment resistance also increases under the same filtering area. In order to maintain a certain equipment resistance, the ash removal cycle is also shortened correspondingly

(2) wear of filter material and box. Under the condition of high concentration of dust with strong wear, the wear amount is directly proportional to the dust concentration. There should be treatment technologies such as diversion and wear resistance at the inlet of the dust collector, such as sintering dust, aluminum oxide powder, silica sand powder, etc

(3) pre deduster and filtration wind speed. In the case of high dust concentration at the inlet, a lower filtering wind speed and a pre dust collector should be designed, but if a structural form with primary sedimentation function is designed, the pre dust collector can also be cancelled; (4) Ash discharge device. The ash discharge capacity is based on the ability to discharge all the collected dust. The amount of dust discharged is equal to the product of the difference between the dust concentration at the inlet and outlet and the treatment air volume. The capacity design of the multi-stage ash discharge device should be based on the ash discharge capacity of the lower level greater than that of the upper level

5. The dust concentration at the outlet

the dust concentration at the outlet must be lower than the specified value of environmental protection regulations and national health standards. The dust concentration at the outlet of a single bag dust collector varies according to the structural form of the dust collector, the type of filter material and the nature of the dust, generally between 1-50mg/m3. In the case of containing harmful substances such as lead and cadmium, the outlet concentration is required to be particularly low. During the design, different single machine bag filter structures and filter materials are selected according to different uses and process characteristics

6. Dust properties

the properties of dust have a great impact on the design of single machine bag filter. For some special properties of dust, effective measures should be taken according to design experience

(1) adhesion and cohesion. When the adhesive and cohesive dust enters the single bag dust collector, the dust will become larger after a little condensation. The dust accumulated on the surface of the filter bag can continue to condense in the process of shaking off. The dust removal efficiency and the amount of dust passing through the filter material are also related to the adhesion and cohesion of the dust. Therefore, for dust with significant adhesion and cohesion, or almost no adhesion and cohesion, different treatment measures must be taken according to different types and uses of dust and design experience

(2) particle size. The main influence of particle size distribution on single bag filter is resistance loss and wear. Fine dust has a greater impact on pressure loss, and coarse dust plays a decisive role in wear, but only particles with high dust concentration and high hardness at the inlet have a greater impact

(3) particle shape. It is generally believed that needle shaped crystalline particles and sheet shaped particles are easy to block the pores of the filter material and reduce the dust removal efficiency. Fibrous particles that can condense into flocs are difficult to fall off the surface of the filter material if the filtration speed of shortening the gap is very high. Different filtration speeds are selected according to the particle shape and characteristics in the design

(4) particle density. The bulk density of dust is related to particle size, cohesion and adhesion, as well as the resistance loss of single bag filter The filtering area has "our goal is to provide the strongest and lightest material. The smaller the stacking density, the more difficult it is to remove the ash. In addition, the lower the filtering wind speed should be selected in the design. In addition, the stacking density of the dust is very important for the selection of the ash hopper of the dust collector and the ability of the ash discharge device.

(5) Hygroscopicity and deliquescence. Dust with strong hygroscopicity and deliquescence is very easy to absorb moisture and solidify on the surface of the filter material during the operation of the single bag dust collector, or deliquesce with water and become a thick substance, resulting in difficulty in dust removal, increased equipment resistance, and even affecting the normal operation of the dust collector. For example, necessary technical measures should be taken for dust containing KCl, MgCl2, NaCl, Cao and other strong deliquescent substances

(6) electrostatic. Once the easily charged dust generates static electricity on the filter material, it is not easy to fall off. For the very easily charged dust, technical measures such as anti-static filter material must be taken to avoid explosion caused by sparks generated by static electricity

(7) flammability. Although combustible dust may not always cause explosion, if sparks appear in the process flow in front of the dust collector and can enter the dust collector, explosion-proof measures should be taken, such as adding spark catchers, setting explosion-proof doors, etc

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