Dust removal principle of bag filter

2021-10-23 10:37

The sedimentation mechanism of dust particles such as inertial collision, barrier diffusion, gravity and electrostatic force is the theoretical basis for analyzing the dust filtering mechanism of filter dust collectors. The dust filtering process of the filter dust collector is more complicated. Generally speaking, the sedimentation of dust particles on the trapping group, that is, separation and filtration, is not only one sedimentation and filtration mechanism at work, but the result of the combined action of multiple sedimentation separation and filtration mechanisms.


  According to the different mechanical characteristics of the movement of dust of different particle sizes in the fluid, the filtering and dust removal mechanism involves the following aspects:


  1 sieve filtration effect


  The filter material mesh of the filter is generally 5~50um. When the dust particle size is larger than the mesh or pore diameter or the dust is deposited in the gap between the dust particles between the filter materials, the dust will be blocked. For the new fabric filter material, because the voids between the fibers, that is, the pore size is much larger than the dust particle size, the sieving effect is small, but when a large amount of dust is deposited on the surface of the filter material to form a dust layer, the sieving effect is significantly enhanced.


   2 Inertial collision effect


   Generally, dust with larger particle size is mainly collected by inertial collision. When the dust-containing airflow approaches the fibers of the filter material, the airflow will bypass the fibers, and the larger particles (greater than 1um) will deviate from the airflow streamline due to inertia, continue to move along the original direction of movement, and hit the fibers. Capture. All large dust particles within the critical line of the dust trajectory can reach the surface of the fiber and be trapped. This inertial collision effect increases with the increase of dust particle size and air flow velocity. Therefore, increasing the flow rate of the airflow through the filter material can increase the inertial collision effect.


  3 block effect


   When the dust-containing airflow approaches the filter material fiber, the finer dust particles circulate along with the airflow. If the radius of the dust particle is larger than the distance from the dust particle to the edge of the fiber, the dust particle will be blocked due to contact with the fiber.


  4 diffusion effect


For dust particles smaller than 1um, especially sub-micron particles smaller than 0.2um, they break away from the streamline under the impact of gas molecules and perform Brownian motion like gas molecules. If they come in contact with fibers during the movement, they can be separated from the airflow. come out. This effect is called diffusion, and it increases as the flow rate decreases and the diameter of fibers and dust decreases.


  5 electrostatic effect


Many fiber woven filter materials will generate static electricity due to friction when airflow passes through. At the same time, dust will also be charged due to friction and other reasons during the transportation process, which will form a potential difference between the filter material and the dust particles. When the dust tends to the filter material along with the airflow, the Coulomb force promotes the collision of the dust and the filter material fiber and enhances the adsorption force of the filter material to the dust to be trapped, which improves the collection efficiency.


  6 gravity sedimentation


   When the slowly moving dust-laden airflow enters the dust collector, the dust particles with large particle size and density may naturally settle down due to gravity.


   Generally speaking, various dust removal mechanisms are not effective at the same time, but one or several kinds of combined action. Moreover, as the gaps of the filter media, air flow rate, dust particle size and other reasons change, various mechanisms have different effects on the filtration performance of different filter media. In fact, when the new filter material starts to filter dust, the dust removal efficiency is very low. After a period of use, coarse dust will form an initial layer of dust on the surface of the filter cloth.


  The changes in the gaps of the filter media, air flow rate, dust particle size and other reasons, various mechanisms have different effects on the filtration performance of different filter media. In fact, when the new filter material starts to filter dust, the dust removal efficiency is very low. After a period of use, coarse dust will form an initial layer of dust on the surface of the filter cloth. The dust filtering process of the filter cloth is shown in Figure 10-2. Due to the dust filtering effect of the first layer of dust and the dust layer that gradually accumulates on it, the filtration efficiency of the filter material is continuously improved, but the resistance is also increased accordingly. When cleaning the dust, the primary layer cannot be destroyed, otherwise the efficiency will decrease. The structure of the first layer of dust plays a very important role in the efficiency, resistance and dust removal effect of the bag filter.


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