Failure Analysis of Bag Filter in Bag Dust Collector

Bag filter is a dry filter device. It is suitable for the collection of small, dry, non-fibrous dust. The filter bag is made of textile filter cloth or non-woven felt, and the dust-containing gas is filtered by the filtering effect of the fiber fabric. When the dust-laden gas into the bag filter, the particles are large, the proportion of dust, due to the role of gravity settling down, fall into the hopper; containing smaller dust gas through the filter, the dust is blocked, the gas Purification.
China’s “12th Five-Year Plan” put forward higher demand for environmental protection, water, gas, sound, slag will be more application of filter material, filter material industry market prospects. In the dust control field, the bag dust remover is more and more widely used at home and abroad, which accounts for 80% of the dedusting equipment, because of the high dust removal efficiency, no secondary pollution and easy recovery of dry material. At present, China’s bag-type dust removal technology has reached the international advanced level, to meet the increasing environmental requirements for the sustainable development of the national economy to create good conditions.
Although the bag filter has many advantages, but once the bag failure, will result in equipment failure emissions, excessive dust, and the replacement of the other bag is a huge cost. How to recognize and pay attention to the failure of the bag in use, and thus avoid the occurrence is particularly important. The following field of the cement industry often occurs in the bag bag failure, the summary and analysis.
2 bag failure
2.1 Mechanical wear failure
(1) between the bag and bag cage wear. The filter bag has holes in the corresponding ring ribs of the bag cage, apparently due to burrs on the bag cage (Figure 1). This avoid or reduce the wear and tear in the bag cage production process to strictly control the quality of the bag cage, any burr, splash, open welding, broken ribs should be prohibited, or into the dust collector, these defects will directly affect the filter bag The use of results, greatly reducing the filter bag life.

(2) between the filter bag and the shell wear. Due to design or installation reasons, after the installation of the filter bag and the shell (or internal tube support) interference, or filter bag from the shell too close to the filter bag in the injection of shaking and shell friction, the use of a period of time , The filter bag and the shell in contact with parts of the hole, resulting in damage to the bag. At present, in the dust collector shell design, generally considered the filter bag away from the shell at least keep more than 75mm. As the flatness of flower board, the level of the vertical cage, etc. are biased, the installation of adjusted bag and the distance between the shell to be maintained at 60mm.
(3) bag and bag cage with the loose (Figure 2), resulting in the use of bag and bag cage between the damage. In the cement production line kiln commonly used fiberglass bag, the base fabric used glass fiber, the biggest drawback is not bending, if not fixed in the use of the bag cage, bag cage lost support in the work and Cleaning the two states, the filter bag fiber is easy to fracture, resulting in damage to the filter bag. This requires that bag and bag cage in the early stage of mass production with the test to determine the optimal size of bag and filter bag. Take the fiberglass membrane bag as an example, the nominal diameter is Ф160 mm, the cage uses 24 longitudinal ribs, the diameter is Ф156mm, the theoretical circumference is 490mm and the half length of the filter bag is 250mm. Considering the thickness of the filter bag, With the bag and bag cage, with a finger light filter bag without too much deformation, can be firmly fixed in the bag cage.

2.2 Air wear
(1) the working pressure of the pulse valve is too large and the injection tube and the filter bag is not concentric with the filter bag caused by mouth damage (Figure 3 and Figure 4). Fiberglass bag filter bag for the cleaning pressure of 0.2 ~ 0.35MPa, generally put into operation the new bag filter dust 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 compressed air is higher than 0.35MPa, it needs to be adjusted in time. Otherwise, the wear of bag and cage will be increased, which will aggravate the damage of filter bag and shorten the service life of filter bag. Other felt filters, such as P84, polyester, Nomex and other filter bag cleaning pressure can reach 0.5MPa or more.

(2) ash bucket into the dust bag bottom wear. In the use of the dust bag at the bottom of the filter bag due to the erosion of the airflow, showing a side of the wear situation, which is mainly a direct relationship with the air way, if the hopper internal baffle and spoiler Add reasonable can also avoid this happening. The use of side air intake mode of dust can effectively prevent the bag bottom wear.
(3) injection tube problems caused by pocket wear. Injection pipe blowing mouth diameter difference caused by the difference is too large jet air flow is not uniform, poor quality of injection pipe caused by wear and tear, blowing pipe installation problems caused by the injection hole and the bag is not concentric, and so on, will cause the filter bag mouth Damage (Figure 5 and Figure 6).

2.3 The temperature caused by the failure of the bag
(1) the temperature is too low. In the flue gas are inevitably there is moisture, too low temperature easily lead to condensation on the surface of the bag, liquid water and dust gathered into the particles bonded to the surface of the filter bag, easy to clean up, over time caused by bag permeability Poor, increased resistance, loss of function (Figure 7). First of all, to deal with the reasons for what is the cause of the temperature is too low, the case of insulation problems caused by bag room around the temperature decreases, or air leakage caused by temperature drops, or process system determines the entrance temperature is too low, and then targeted to take the appropriate Technical measures.

(2) the temperature is too high caused by the burning bag. Any filter bag has a normal temperature range, the use of materials determines the maximum temperature, beyond this temperature, the loss caused by the filter bag is irreversible. Glass fiber coated filter media, for example, the normal use temperature range of less than 260 ℃, the temperature value is for the base fabric, film and suture in terms of, beyond this temperature value, any of the three materials The problem will inevitably lead to the failure of the filter bag. At this temperature, the filter can be a short time, beyond this temperature, can easily lead to irreversible permanent damage filter, filter bag to reduce or even damage the service life. Therefore, the use should pay close attention to the inlet temperature of the precipitator, is strictly prohibited over-temperature operation. When the temperature exceeds 220 ℃ when the system should start the protection program to prevent the occurrence of burning bags. For high temperature alarm control system, the upper limit should be adjusted to 220 ℃. Other various media have their own temperature, in the actual work, should be set according to different filter different alarm temperature.
Commonly used in the building materials industry, the use of temperature range in Table 1. Such as: widely used in cement production line kiln Nomex bag, the normal use temperature range of 200 ~ 240 ℃, but the temperature changes fast kiln, the proposed alarm temperature set at about 200 ℃, once the over-temperature, the system of cold air valve Open or dust on the outlet valve closure and other measures to ensure that the filter bag from high temperature damage. Figure 8 for the use of more than 280 ℃ after the temperature of glass fiber coated bag suture fracture.

2.4 The early operation of the lack of pretreatment caused by the failure of the bag
New dust collector in the put into operation before the use of raw material powder on the filter bag surface pre-coating, so as to avoid the ignition of the oil filter attached to the surface of the bag can not afford to remove some of the production line operators eager to put into operation, do not pay attention to or omit this Work, resulting in irreversible increase in resistance to the filter bag, see Figure 9.

2.5 parameter set unreasonable caused by the failure of the bag
(1) cleaning cycle is too short lead to shorten the filter bag life. The injection parameters are mainly set to meet the needs of on-site production, injection time interval is too long, the dust collector machine resistance increases, the system ventilation is poor; and injection time interval is too short, will reduce the bag life , Because every time the dust on the filter bag will cause some damage. If the filter bag in the normal life of the number of injection is certain, obviously increasing the middle of the injection interval is the best way to extend the life of the filter bag. Cleaning cycle of this parameter is a reasonable set, depending on the production line of continuous exploration and adjustment of the scene. If it is fixed ash cleaning method, according to the actual value of the system resistance to set the upper and lower limits, the parameters of other personnel do not adjust after the arbitrarily Changes, should be responsible for the person.
(2) pulse width. It turns out that the pulse width increases and does not enhance the cleaning effect, but increased the bag and bag cage wear. Therefore, the pulse width is generally set to 0.1 to 0.15 s, and it is not necessary to set the pulse width at 0.2 s or more.
2.6 Compressed air quality
Impurities in the compressed air will affect the work of the pressure reducing valve and pulse valve, if the impurities into the valve, resulting in failure of pressure reducing valve, can not adjust the pressure; if impurity into the pulse valve will damage the pulse valve diaphragm, Cleaning effect or a long time on the filter bag injection, will cause damage to the filter bag.
Compressed air in the water will cause the corrosion of the bag cage, bag cage corrosion can not meet with the filter bag with the requirements, and even after the bag cage surface roughness increased wear on the filter bag; Secondly, the water sprayed into the filter bag inside surface, Third, the excessive moisture will cause the hydrolysis of the filter bag, resulting in reduced strength of the filter bag, and then to reduce the dust bag cycle, reduce the filter bag life; Causing damage to the filter bag; In addition, in the cold northeast winter, if the distribution box and the gas tank will have ice in the water, thus causing the entire injection system failure. Therefore, the distribution box and gas tank to be set
When the water to avoid water into the cleaning system. General waterproofing cycle can not be more than a week, it is best to be waterproof every day.
2.7 The selection of the filter bag is incorrect
Bag filter machine machine design, the choice of appropriate filtering wind speed and for different conditions of choice of different filter is critical. If the filter bag material selection error certainly can not be normal use, this is no doubt; another different filter selection of different sutures, but also in the bag making process must be considered.
3 Conclusion
Although the bag filter in the engineering practice of many problems, but as long as the above several major aspects of the full consideration and take effective measures to avoid the problems associated with the bag filter can meet the increasingly stringent national dust emission standards , Its application prospect is very optimistic.