1 Equipment Overview The bag filter is a dry dust filter device. It mainly collects coarse dust by inertial collision filter material, and collects fine dust by diffusion and sieving. It is suitable for collecting fine, dry and non-fibrous dust. The filter bag is made of woven filter cloth and non-woven felt. The dust filter is filtered by the filtering effect of the fiber fabric. When the dust-containing gas enters the bag filter, the dust with large particles and large gravity is due to gravity. The effect settles down and falls into the dust hopper. When the gas containing fine dust passes through the filter material, the dust is retained and the gas is purified. Generally, the dust removal efficiency of the new filter material is not high enough. When the filter material is used for a period of time, due to the effects of sieve filtration, collision, retention, diffusion, static electricity, etc., the surface of the filter bag is covered with a layer of dust. This layer of dust is called the primary layer. During the subsequent movement, the primary layer becomes the main filter layer of the filter material. Depending on the function of the primary layer, the filter material with larger mesh size can also obtain higher filtration efficiency. As the dust accumulates on the surface of the filter material, the efficiency and resistance of the dust collector increase accordingly. When the pressure difference between the two sides of the filter material is large, some fine dust particles that have adhered to the filter material are squeezed. Reduce the efficiency of the precipitator. In addition, the excessive resistance of the precipitator will significantly reduce the air volume of the dedusting system. Therefore, after the resistance of the precipitator reaches a certain value, it should be cleaned in time, and the initial layer should not be destroyed during the cleaning to avoid the efficiency drop. The bag filter is mainly composed of an upper box, a middle box, a lower box (ash hopper), a cleaning system and a ash discharging mechanism. The bag filter has the following advantages: (1) The dust removal efficiency is high, and fine dust with a particle diameter larger than 0.3 μm can be collected, and the dust removal efficiency can reach more than 99%. (2) It has strong adaptability and can handle different types of particles, and the processing capacity can be large or small. (3) When the operation flexibility is large and the dust concentration of the inlet gas changes greatly, the dust removal efficiency is not greatly affected. (4) The structure is simple, the operation is relatively stable, the investment is less (compared with the electrostatic precipitator), and the maintenance is convenient. Therefore, bag filter is widely used to eliminate dust pollution, improve the environment, and recycle materials. 2 Analysis of factors affecting dust removal efficiency and filter bag life of bag filter The bag filter is used as a filter device for each dust, and the dust removal performance directly affects the dust removal effect of the device. The main factors affecting the dust removal efficiency of the bag filter and the life of the filter bag are: air cloth ratio, filter material, and cleaning method. (1) Selection of air cloth ratio Air-to-cloth ratio, also known as surface filtration speed, is the ratio of the volume of dust-laden gas treated per unit time to the area of ​​filter cloth. It has the ratio of gross air to cloth and net air to cloth. The former refers to the ratio of the volume of the inlet of the baghouse to the total area of ​​the filter cloth of the dust collector, and the latter refers to the ratio of the volume of the inlet gas to the area of ​​the filter cloth of the running filter bag. For small bag filters, the difference between the two is large. Air-to-cloth ratio is an important design parameter and an important indicator for determining the performance and economy of the precipitator. From the point of view of dust removal performance, the choice of air-to-cloth ratio should take into account factors such as dust collector type, cleaning method, filter material type, dust and gas properties. The value of air-to-cloth ratio is too high. Although the designed bag filter has small volume and low cost, it has large running resistance and frequent cleaning. Dust particles are easily embedded in the filter material, which greatly shortens the service life of the bag and affects bag dust removal. The normal operation of the device. Conversely, if the value of the air-to-cloth ratio is chosen too small, the cost of the bag filter will increase. In addition, different cleaning methods must use different air ratios. (2) Quality of filter material The filter material is the core component of the bag filter. Its performance and quality are directly related to the running effect and service life of the bag filter. There are various kinds of filter materials on the market, and their performances and uses are different. Even if the same materials are used, the products produced by different manufacturers will have great differences in performance. The filtration efficiency determines the outlet emission concentration of the precipitator. As long as the quality of the filter material is qualified, the filtration efficiency can reach more than 99%, thus meeting the current national emission standards. However, as emission requirements become more stringent, the filtration requirements for filter media are gradually increasing. Especially in the case of dust collection of certain dangerous materials or special process requirements, the emission standards are usually not required to be exceeded, so this requires some special treatment of the filter material to ensure. Filtration pressure drop is a factor that directly affects the service life of the filter bag. The filter pressure drop is high and the system resistance is high. Under the same fan power, the system air volume will decrease, directly affecting the production efficiency; or to maintain the air volume. The fan power must be increased to increase the power consumption cost. A high filtration pressure drop will also result in an increase in the frequency of the cleaning, which will shorten the life of the filter bag. In addition, long-term operation of the filter bag under high resistance will also affect its life. The quality of the filter material directly affects the dust removal efficiency and life of the bag filter. The flue gas characteristics and dust characteristics should be considered when selecting the filter material. The humidity of the flue gas will affect whether the ash adheres to the surface of the filter bag, and the hardness of the particles is directly Affect the service life of the filter material, and choose a lower filtration speed for hard dust. According to the operating environment and medium conditions of various dust collectors, choosing the right filter material is the key to ensure the performance of the bag filter. Due to the high price of the filter material, its cost accounts for a large proportion of the dust collector. If the quality is not guaranteed and the service life is short, the loss is conceivable, and the change of the bag may also affect the production. To be equipped with a good dust collector, first use a filter bag that has good gas permeability, corrosion resistance, wear resistance, and is suitable for on-site process requirements (such as temperature, chemical attack, etc.) and is processed by high-quality sewing technology. If the filter material is improperly selected or the processing quality is poor, it may cause hydrolysis, acid hydrolysis, excessive temperature, peeling of the film, and cracking of the filter bag. (3) Cleaning method The bag filter should be cleaned in time after running for a certain period of time. When the dust is removed, the initial layer cannot be destroyed to avoid the dust removal efficiency. There are three main methods for cleaning the bag filter, namely pulse back blowing, reverse air back blowing and mechanical vibration. The pulse back-blowing method can be divided into high-pressure pulse back-blowing type and low-pressure pulse back-blowing type according to the difference of back-blowing air pressure. The pulse back-flush bag filter can be adjusted due to its pulse back-blowing intensity and frequency, and has a good cleaning effect. It is the most widely used dust-removing device in the world. After the dust-containing gas enters from the inlet of the bag filter, the diversion pipe enters each unit room. Under the action of the flow guiding device, the large particle dust separates directly into the ash hopper, and the remaining dust uniformly enters each chamber with the airflow. In the area, the filtered clean gas is discharged through the upper filter body, the poppet Valve, and the exhaust pipe through the dust filter bag. As the filtration condition progresses, when the surface dust of the filter bag reaches a certain thickness, the purging valve is closed by the cleaning control device according to the set program, the current unit is controlled to be offline, and the electromagnetic pulse valve is opened to blow off the filter bag. Dust. The dust falling into the ash hopper is discharged through the ash discharge valve and sent out by the ash conveying system. The cleaning process does not interrupt the filter material work, and the dust with strong adhesion can be detached, the cleaning time interval is short, and a higher filtration speed can be selected. The disadvantage is that a pulsed blow requires a source of compressed air. The reverse airflow back-blowing method is to blow back air from the opposite direction through the filter bag and the dust layer, and use the airflow to cause the dust to fall off the filter bag. When using airflow cleaning, the cleaning mechanism is simple and easy to maintain, but the filter bag must have a supporting structure, such as a brace or a net frame, to avoid crushing and sticking the filter bag and destroying the primary layer. The backflushing air can be supplied by a special fan or by external suction using the negative pressure of the precipitator itself. The mechanical vibration cleaning method, the top vibration cleaning and the middle vibration cleaning (for the filter bag), is to periodically vibrate the various filter bags by means of mechanical vibration devices to remove the dust on the filter bag. The dust removing device of the cleaning method has the advantages of simple structure and stable performance, and is suitable for dust removal of small air volume, low concentration and scattered dust point, but is not suitable for occasions where the dust collector is continuously operated for a long time. 3 Conclusion With the improvement of people's awareness of environmental protection and energy crisis, the requirements for bag dust removal systems are getting higher and higher. Combined with various working conditions, the design of the bag filter should be based on the premise of ensuring normal use, maximize dust removal efficiency, and improve the operational reliability and service life of the bag filter. 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As a kind of high-efficiency dust removal equipment, bag dust collector was used in industrial production in the middle of the 19th century. Its operation is reliable and stable, flexible in use, simple in operation, high in dust removal efficiency, and can capture dust of about 0.1μm at minimum, which can meet strict environmental protection. Requirements have been widely applied in various dust removal fields. In recent years, with the development of the national economy and increasingly strict environmental protection requirements, the bag filter has experienced considerable growth in both production and sales, and the variety is increasing.