Problems in the design of dust filter bag

The selection of filtering wind speed, pulse dust cleaning air volume and pressure, gas humidity, dust concentration at the inlet, air inlet mode, rising wind speed, the influence of dust cleaning mode on the filter bag, and other factors.

 

  1. Filtering wind speed of low pressure long bag pulse bag dust collector:

One of the important parameters of the bag filter is closely related to the dust concentration of the treated gas, dust characteristics, the material of the filter cloth used and the way of dust removal. The size of the filter speed directly affects the volume size of the whole bag filter and the system resistance of the bag filter, thus affecting the service life of the filter bag. In the same case, the filtering wind speed is higher than that of the filter bag without membrane, because the filter bag is surface filtration, and the resistance will not be increased gradually due to the accumulation of dust in the deep layer of the filter bag. The resistance of the filter bag is squared with the filtering wind speed. If the wind speed is too large, the initial resistance will be too large, which will cause local “perforation” phenomenon on the film, and then the base cloth will be worn and affect the emission and service life. Because the surface treatment is adopted, the deep layer of the filter bag will not accumulate ash, and the pulse type ash cleaning is adopted, with large kinetic energy, thorough ash cleaning, and the resistance will not rise quickly, so this is also the reason why the wind speed of the film covered is larger than that of the film free.

 

  1. Selection of air volume and pressure for pulse ash cleaning:

When the low-pressure long bag pulse bag type dust collector is used for pulse cleaning, besides the selected pressure is lower than the normal pressure and the cycle is longer, the air volume of cleaning should also be determined properly. If it is too large, it is easy to reduce the service life, and if it is too small, it will also affect the service life. Under the same cleaning pressure and gas volume, the pressure of off-line cleaning is lower than that of on-line cleaning, and the gas consumption is smaller and the power consumption is saved.

 

  1. Gas humidity:

When the glass fiber filter bag is wet, its strength will decrease. This is because the alkali component in the alkali containing glass fiber is dissolved by water, resulting in the erosion of the glass fiber surface and the falling off of the film, which affects the service life. Therefore, in addition to limiting the maximum temperature of the working gas, special attention should be paid to controlling the humidity of the glass fiber bag in use to prevent condensation. For example, the glass fiber bag dust collector at the end of the dry process kiln is under the mixed condition at present, that is, a large amount of raw mill waste gas enters, and the humidity increases. If the humidity and air leakage cannot be controlled, the condensation of water vapor in the filter bag will also affect the service life.

 

  1. Dust concentration at the inlet:

The dust concentration of the gas treated by the bag filter directly affects the resistance and service life of the filter bag. The thicker the dust layer on the surface of the filter bag is, the greater the resistance and service life of the filter bag will be. On the other hand, in order to clean the thick dust layer in time, it is bound to strengthen the cleaning of the filter bag, that is to shorten the cleaning cycle (the cleaning cycle of the coated filter material is longer than that of the uncoated filter material), increase the cleaning frequency and extend the cleaning time, which will inevitably increase the wear and damage of the filter bag and affect its service life. It is beneficial to prolong the service life of the filter bag and improve the working condition of the whole dust collector by properly reducing the dust concentration at the inlet.

 

  1. Air inlet mode:

At present, the design of the low-pressure long bag pulse bag dust collector, which air intake method will directly affect the service life of the filter bag, mainly reflected in: the uniformity of air volume. First of all, the uniformity between the rooms is followed by the uniformity of the whole room after entering the ash hopper. When the air inlet pipe is directly into the ash hopper, the horizontal pipe shall be avoided as far as possible to prevent dust accumulation. At the same time, the ash hopper shall be used for dust collection in advance to prevent the direct scouring effect on the filter bag, so as to prolong the life of the filter bag.

 

  1. Rising wind speed:

The low-pressure pulse bag dust collector can be divided into on-line dust removal and off-line dust removal according to the way of dust removal. Online ash cleaning is in the state of simultaneous filtering and ash cleaning, which is easy to produce dust twice, reduce the efficiency of ash cleaning and affect the life of the bag. When cleaning ash online, according to experience, the rising wind speed of the bag room should be controlled within 1.5m/s. During offline ash cleaning, it is because a bag chamber closes the inlet and outlet air valves, stops the filtering work and carries out ash cleaning, so that no dust will be generated twice, and the bag can be protected, but the cost and passive resistance caused by the compartment need to be increased.

 

  1. Influence of ash cleaning method on filter bag

(1) Select the low-pressure pulse mode to clean the dust. It can be seen from the above that the glass fiber in the glass fiber covered filter bag has the characteristics of non folding and non abrasion resistance, which was generally not used in pulse ash cleaning in the past. Since the composite filter material covered with glass fiber is selected, the dust removal cycle is lengthened because the surface filtration is easy and the resistance is not easy to rise. However, due to the external filtration and the bag cage in the glass fiber cloth, the relative movement between the filter bag and the bag cage will produce wear. In addition, the frequent blowing and cleaning, the close contact between the filter bag and the bag cage, and the change of the range with the distance and twists and turns will directly affect the life of the filter bag. In addition, when the filter bag is blown by the pulse air flow, the higher pressure air flow in the bag causes the filter bag in the state of internal contraction to expand rapidly. Under the high pressure, the filter bag will generate the staggered movement between the fibers. The greater the pressure is, the greater the friction force of the staggered contact surface is, and the shorter the life of the filter bag. Therefore, on the premise of not affecting the cleaning effect, reducing the cleaning pressure is also an aspect of prolonging the life of the filter bag. In the use of glass fiber membrane filter bags, low-pressure pulse ash cleaning came into being.

(2) The wind speed of off-line ash cleaning is higher than that of on-line ash cleaning. It is easy to clean ash, and low pressure can be used to save energy. Especially for glass fiber membrane, off-line ash cleaning should be used to extend its life.

 

  1. Other factors

The detailed design of the distance between the blowpipe and the flower plate, the form and size of the nozzle, the distance between the filter bag and the filter bag, the distance between the filter bag and the partition, the number of vertical bars of the bag cage, the distance between the cage rings and so on will affect the service life of the filter bag of the low-pressure long bag pulse bag dust collector.

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