4 reasons and solutions for the failure of the bag filter bag

The filter bag is the core part of the bag filter. The quality of the filter bag directly determines the performance of the dust removal. The main factors of filter bag failure are unreasonable filter material selection, improper processing, mechanical wear, chemical corrosion, excessively high smoke temperature, condensation and bonding. Common filter bag failures such as filter bag wear, filter bag burning, filter bag embrittlement, filter bag clogging, etc.

　　 1. Filter bag breaking loss effect

　　The common locations of filter bag damage are the breakage of the filter bag mouth, bag body, bottom and filter bag sutures, as shown in Figure 1. Due to the difference in air intake method, filter bag filtering method and dust cleaning method, the filter bag will cause different reasons for wear and failure. Filter bag wear can be divided into mechanical wear and air flow erosion.

　　1) Mechanical wear

　　 The chaotic stacking of filter bags and filter cages during installation in the project will often cause deformation of the filter cage and mechanical damage of the filter bag. The deformation of the flower plate or the deviation of the flower plate hole caused by the use conditions will cause the mechanical wear of the bag mouth to increase.

　　 At the same time, the non-vertical filter cage will cause mechanical abrasion between the filter bag and the filter bag (or with the shell), which will cause the lower part of the filter bag to wear and fail, and the wear can be observed on the outside of the filter bag.

　　 When the installation of the filter bag and the filter cage is too tight or loose, the mechanical abrasion will be caused by the violent expansion, contraction, distortion and stretching of the filter bag during the cleaning process. In particular, the rust, weld scars, burrs and other surface irregularities caused by the rough processing of the filter cage will accelerate the wear and tear of the filter bag. Such abrasion is on the inside of the bag body.

　　2) Air flushing

　　 The destructive effect caused by air flow is mainly caused by the high-pressure air flow directly sprayed to the upper part of the filter bag during cleaning, the flue gas inlet method, the flue gas concentration is too large, the flue gas filtration rate is too high, and the flue gas rising speed is too high.

　　For example, the tilt of the filter cage caused by installation and deformation of the flower plate will not only cause mechanical wear, but also cause the centerline of the filter cage to shift and cause airflow to scour. Excessive cleaning gas pressure, nozzle tilt, and uneven air flow distribution between nozzles are common causes of upper air scour.

　　The scour caused by the flue gas inlet method is mainly due to the uneven distribution of the airflow in the bag chamber caused by the air intake. The local airflow is too large, causing the dust to impact the filter bag, which accelerates the wear and tear of the filter bag. Especially for the abrasive gas, the local flue gas flow rate is too large, and the problem of filter bag breaking loss efficiency is more likely to occur frequently.

　　2. Chemical failure of the filter bag caused by the characteristics of the flue gas

　　 When the selection of filter material is not considered comprehensively, the filter bag will quickly become invalid. The failure of the filter bag caused by chemical action is chemical failure, mainly hydrolysis reaction, oxidation corrosion and acid-base corrosion.

　　The commonly used polyester, polypropylene and Nomex filter materials in chemical fiber filter materials are most prone to hydrolysis reaction. After the hydrolysis reaction occurs, the tensile strength of the filter media fiber is reduced, and it is more prone to wear. The water leakage from the top of the dust collector and the condensation of the flue gas produce water vapor, which causes the filter material to be hydrolyzed in a high temperature environment. The higher the moisture content in the gas and the higher the temperature, the faster the hydrolysis.

　　3. Filter bag failure caused by high temperature flue gas

　　 Excessive smoke temperature is divided into instantaneous high temperature and continuous operating temperature too high. Too high temperature will cause irreversible failure of the filter bag, such as bag burning, oxidation corrosion, deflagration and high temperature shrinkage. According to the factors affecting the hydrolysis and oxidation corrosion process, when the flue gas continues to run at a high temperature, the process of hydrolysis and oxidation corrosion will be accelerated. Therefore, the flue gas needs to be cooled to help extend the life of the filter bag.

　　1) Burning bag

　　Each type of filter bag has a corresponding upper temperature limit. When the temperature is higher than the upper limit, it will cause loss of the base fabric, film and filter bag sutures of the filter bag.

　　 Therefore, for flammable flue gas, measures such as dust collectors, cooling spray towers, and spark trapping devices should be installed to prevent sparks from entering, and anti-static filter bags or metal wire and other anti-static measures should be adopted. For working conditions where flue gas temperature fluctuates due to process reasons, attention should be paid to the flue gas temperature at the inlet of the dust collector, and a high temperature alarm control system should be set up.

　　 When the flue gas temperature exceeds the set value, the flue gas temperature is reduced by spray cooling and cooling air valve suction cooling. It is worth mentioning that, according to the characteristics of process flue gas, recovering flue gas waste heat through heat exchangers, waste heat boilers, etc., and reducing the flue gas temperature is an effective way to save energy.

　　2) High temperature shrinkage

　　 When the flue gas temperature is continuously used or the instantaneous temperature exceeds the normal use temperature of the filter bag, due to the temperature characteristics of the filter material fiber, the heat shrinkage rate in the warp and weft directions will increase. When the heat shrinkage rate is too large, the filter bag becomes smaller in the warp direction and is tightly wrapped on the filter cage, which easily affects the dust removal effect and cannot withdraw the filter cage from the filter bag. At the same time, the filter bag becomes shorter in the vertical direction, and the bottom of the bag is easily broken by the filter cage.

　　4. Other failures of the filter bag

　　1) Condensation

　　 For flue gas with a certain pressure, when its temperature is lower than the dew point temperature, the water vapor in the flue gas will produce condensation. If the design is improperly operated, condensation and agglomeration will occur. In order to ensure the stable operation of the bag filter above the dew point temperature, measures such as coated filter material, shell insulation and hot air mixing are usually adopted.

　　 Under cold conditions, the cold start and cold shutdown of the dust collector equipment will also cause condensation of water vapor in the high-temperature flue gas and cause the filter bag to fail.

　　 Therefore, according to the use environment and the nature of the flue gas, the auxiliary heat cannot be stopped when the bag filter that requires auxiliary heat is shut down. For bag filter equipment that needs to be reopened, it should be fully preheated if necessary before it can be put into use.

　　 In addition, when spray cooling and cold air valve suction cooling are used to reduce the flue gas temperature, it may cause condensation at the flue gas inlet of the dust collector. Therefore, in the design stage, we should fully understand the characteristics of the process flue gas and the environmental characteristics of the location, and make a reasonable plan based on the actual situation.

　　 Furthermore, the condensation at the inlet of the filter bag of the bag filter is due to the low temperature or high humidity of the compressed gas used, or both. When compressed air is used to clean the dust, it also causes condensation at the inlet of the filter bag. By heating compressed air, dehumidifying, or using venturi nozzles to increase the amount of air flow to reduce the amount of air, condensation at the inlet of the filter bag can be avoided.

　　 2) Blockage

When the dust-laden fume airflow filter bag, the dust stays on the filter bag to form a dust layer. The existence of the dust layer will improve the filtration efficiency. As the thickness of the dust layer increases, the filtration efficiency becomes higher and higher, but the operation resistance of the dust collector is also higher. . When the running resistance exceeds the limit value, clean the dust by means of mechanical vibration, back blow or pulse. However, the flue gas contains tar, water vapor, or ultra-fine dust entering the filter material, which will cause the dust to block the filter bag, resulting in large running resistance and failure of the filter bag.

　　 When the bag filter is used to process high-temperature flue gas, high-humidity flue gas, or the operating environment temperature is low, avoid condensation and cause deliquescent dust to stick to the surface of the filter bag and cause blockage, or even paste the bag problem to cause the filter bag to fail.

　　The flue gas dust particles processed by are relatively fine, which can easily cause the problem of dust entering the filter material. Generally, in this case, the membrane filter material is used or the pre-coating is manually made on the surface of the filter bag before the formal dust removal operation. The pre-coating can protect the filter material while improving the efficiency of the bag filter and reducing the running resistance.

　　The bag filter is an indispensable equipment for the treatment of atmospheric dust pollution. The frequent damage of the filter bag causes not only economic losses to the enterprise, but also brings difficulties to the enterprise management. Correct installation, reasonable operation and maintenance can effectively improve the efficiency of the dust collector.