1 bag filter application overview
Bag filter is a dry filter device. It is suitable for capturing fine, dry, non-fibrous dust. The filter bag is made of a textile filter cloth or a non-woven felt, and the dust-containing gas is filtered using the filtering action of the fiber fabric. When the dust-laden gas enters the bag filter, the dust with large particles and large specific gravity settles down due to the action of gravity and falls into the ash hopper. When the gas containing fine dust passes through the filter material, the dust is trapped and the gas is obtained. Purification.
China’s “Twelfth Five-Year Plan” puts forward a higher demand for environmental protection. Water, gas, sound, and slag will all be used more as filter materials, and the market prospect of filtration materials industry is promising. Among them, in the field of dust control, bag dust collectors have high dust removal efficiency, do not cause secondary pollution, and facilitate the recovery of dry materials, and are widely used at home and abroad, accounting for 80% of the dust removal equipment used. At present, China’s bag type dust removal technology has reached the international advanced level, can meet the increasing environmental protection requirements, and can create favorable conditions for the sustainable development of the national economy.
Although the bag filter has many advantages, once the filter bag fails, failure of the device will be caused, the dust will be exceeded, and the replacement of the filter bag will also be a huge expense. It is especially important to understand how to use the filter bag and to pay attention to it in order to prevent it from happening. The following summarizes and analyzes the problem of filter bag failure that often occurs on the site of the cement industry.
2 filter bag failure
2.1 Mechanical wear failure
(1) Wear between the filter bag and the bag cage. The filter bag had holes in the corresponding ring ribs of the bag cage, which was apparently caused by the burr abrasion filter bag on the bag cage. To avoid or reduce this kind of wear, it is necessary to strictly control the quality of the bag cage during the bag cage production process. Any burrs, splashes, open welds, or broken bars must be prohibited. Otherwise, these defects will directly affect the filter bag when installed in the dust collector. The use of the effect greatly reduces the service life of the filter bag.
(2) Wear between filter bag and housing. Due to design or installation reasons, the filter bag may interfere with the housing (or internal tube support) after installation, or the filter bag may be too close to the housing and cause the filter bag to sway with the housing during blowing, after being used for a period of time. The filter bag has holes in the parts that are in contact with the housing, resulting in breakage of the filter bag. At present, in the design of the dust collector housing, it is generally considered that the distance of the filter bag from the housing is maintained at least 75 mm or more. Since the flatness, levelness, and verticality of the bag cage are all deviated, the distance between the installed filter bag and the housing should be kept at 60mm.
(3) The filter bag and the bag cage are too loosely fit and cause breakage between the filter bag and the bag cage during use. The glass fiber filter bag is widely used in the kiln end of the cement production line. The biggest drawback of the fiberglass used in the base fabric is that it cannot resist folding. If it cannot be fixed on the bag cage during use, the bag cage loses its support meaning at work and In the two states of cleaning, the fibers of the filter bag are likely to fatigue and fracture, resulting in breakage of the filter bag. This requires mating tests in the early stages of mass production of filter bags and bag cages to determine the optimal size of bag cages and filter bags. Take the glass fiber membrane filter bag as an example, the nominal diameter is mm160 mm, the bag cage uses 24 vertical bars, the diameter is Ф156mm, the theoretical perimeter is 490mm, and the filter bag’s half-circumference (outer diameter) is 250mm. Consider the thickness of the filter bag. With the filter bag and bag cage, lightly press the filter bag with your fingers without much deformation, and it can be tightly fixed on the bag cage.
2.2 Airflow wear
(1) Excessive working pressure of the pulse valve and damage to the upper mouth of the filter bag due to misalignment of the injection pipe and filter bag. Glass fiber membrane filter bag suitable cleaning pressure is 0.2 ~ 0.35MPa, the newly put into operation bag filter cleaning pressure can be adjusted to 0.25MPa. To achieve this pressure, a filter and a pressure reducing valve are provided before the compressed air enters the pulse valve. If the pressure of the compressed air is higher than 0.35 MPa, it needs to be adjusted in time, otherwise it will cause the filter bag and the bag cage to wear out, intensify the damage of the filter bag, and shorten the service life of the filter bag. Other filter materials such as P84, Dacron, Nomex and other filter bags can reach a cleaning pressure of 0.5 MPa or more.
(2) The bottom of the hopper dust collector is worn out. The dust collector adopts the ash bucket air inlet method. In use, the bottom of the filter bag is exposed to wear due to the erosion of the air flow. This is mainly related to the air inlet method. If the inner ash bucket has a baffle and a baffle plate, Adding reasonableness can also prevent this from happening. The use of side-intake dust collectors can effectively prevent the bottom of the bag from wear.
(3) The bag mouth wear caused by the injection pipe problem. The difference in the diameters of the injection nozzles is too large, resulting in uneven spraying air flow, poor quality of the injection pipe, wear and tear, injection pipe holes and filter bag misalignment, etc., which can cause the filter bag mouth. damaged.
2.3 Failure of Filter Bag Caused by High or Low Temperature
(1) The temperature is too low. In the flue gas, there is inevitably moisture. If the temperature is too low, condensation on the surface of the filter bag is likely to occur. The liquid water and dust gather together into the surface of the filter bag and is difficult to clean. The filter bag becomes air-pervious for a long time. Poor, high resistance, no effect. The first thing to do is to find out what causes the temperature to be too low. If the temperature of the bag room decreases due to the insulation problem, or if the temperature caused by the air leakage drops, or the inlet temperature of the process system determines that the inlet temperature is too low, then take the appropriate Technical measures.
(2) Filter bag burned due to excessive temperature. Any filter bag has a normal temperature range of use, the use of materials determines the upper limit temperature, beyond this temperature, the loss caused by the filter bag is irreversible. Take glass fiber membrane filter as an example, its normal operating temperature range is less than 260°C. This temperature value is for the base fabric, film, and suture. Exceeding this temperature value, any one of the three materials appears. The problem will inevitably lead to the failure of the filter bag. At this temperature, the filter material can work for a short time. If it exceeds this temperature, it can easily cause permanent damage to the filter material. The service life of the filter bag is reduced or even damaged. Therefore, the inlet temperature of the dust collector should be closely watched during use, and over-temperature operation is strictly prohibited. When the temperature exceeds 220°C, the system should start a protection program to prevent the burning of bags. For high temperature alarm control systems, the upper limit should be adjusted to 220°C. All other kinds of filter media have their own use temperature. In actual work, different alarm temperatures should be set according to different filter media.
The common filter material use temperature range of the building material industry, such as: Nomex filter bags widely used in cement production line kiln head, the normal use temperature range of 200 ~ 240 °C, but due to the kiln head temperature changes quickly, it is recommended that the alarm temperature is set at about 200 °C, Once over-temperature, the cold air valve in the system is opened or the outlet valve on the dust collector is closed to ensure that the filter bag is not damaged by high temperatures.
2.4 Failure of filter bags caused by lack of pretreatment at the initial stage of operation
Before the new dust collector is put into operation, the surface of the filter bag should be pre-coated with raw material powder so as to prevent fumes from sticking to the surface of the filter bag during ignition. Some operators of the production line are eager to put into production and do not care or omit this. Work, causing irreversible filter bag resistance increases.
2.5 filter bag failure due to unreasonable parameter setting
(1) Short cleaning cycle leads to shortening the service life of the filter bag. The setting of injection parameters is mainly to meet the needs of on-site production. When the injection time interval is too long, the resistance of the whole filter of the dust remover increases and the ventilation of the system is not smooth; and when the injection time interval is too short, the service life of the filter bag will be reduced. , because once the cleaning of the filter bag will cause some damage. If the number of blows is constant during the normal service life of the filter bag, it is obvious that increasing the middle blow time interval is the best way to extend the service life of the filter bag. The reasonable setting of the cleaning cycle parameters depends on the continuous exploration and adjustment of the production lines. If it is timed cleaning method, it is recommended to set the entire cleaning cycle at 30~400min in the initial stage of operation. If the fixed resistance cleaning method is used, set the upper and lower limits according to the actual value of the system resistance. After the parameter adjustment, other personnel should not Changes should be handled by a specialist.
(2) Pulse width. It turns out that the increase in the pulse width does not improve the cleaning effect, but intensifies the wear of the filter bag and the bag cage. Therefore, the pulse width is generally set to 0.1 to 0.15 s, and it is not necessary to set 0.2 s or more.
2.6 Compressed air quality
Impurities in the compressed air will affect the operation of the pressure reducing valve and the pulse valve. If impurities enter the pressure reducing valve, the pressure reducing valve will fail, and the pressure cannot be adjusted. If impurities enter the pulse valve, the pulse valve diaphragm will be damaged, resulting in leakage and loss. Dust removal or long-term spraying of the filter bag can cause damage to the filter bag.
Water in the compressed air will cause corrosion of the bag cage. After the bag cage corrodes, it will not meet the requirements of the filter bag. Even the rough surface of the bag cage will aggravate the wear of the filter bag. Secondly, after the water is sprayed on the inner surface of the filter bag, It is easy to cause paste bags and cause the resistance of the dust collector to rise. To reduce the resistance, only the cleaning cycle can be shortened and the service life of the filter bags can be reduced. Third, excessive moisture can also cause hydrolysis of the filter bags, resulting in a decrease in the strength of the filter bags. Causes the filter bag to break; In addition, in the cold winter of Northeast, if the moisture in the air box and the air tank will freeze, then cause the whole blowing system to fail. Therefore, it is necessary to determine the distribution box and the gas tank.
Drain water to avoid entering the cleaning system. The general waterproof cycle can not exceed one week, it is best to carry out waterproofing every day.
2.7 Filter bag selection error
In the design of the bag filter, it is very important to choose the appropriate filter speed and choose different filter media for different working conditions. If the choice of filter bag material can not be used correctly, it is beyond doubt. In addition, the use of different sutures for different filter media must also be considered in the filter bag manufacturing process.
3 Conclusion
Although there are many problems in bag dedusters in engineering practice, as long as sufficient considerations are taken in the above-mentioned large areas, effective measures are taken to avoid related problems, bag filter can fully meet the increasingly stringent national dust emission standards. Its application prospects are very optimistic.