Flue gas and dust penetrate through the surface of the filter cloth, and dust is removed in a certain way. After the above two effects are balanced, a thickness of 0.5-0.7 mm is formed in the inner layer (felt layer) of the filter cloth. A layer formed by entangling the dust and the filter cloth fibers, which is called an inner filter layer, corresponds to the primary filter layer of the aforementioned plain weave fabric.
Dust layer filter mechanism:
In the filtration mechanism of filter media, such as diffusion, gravity, inertial collision, static electricity and other effects exist on the dust layer, but the main role is the screening effect. When the bag filter was started up, there was no dust on the new filter bag, and a very thin dust film was formed on the surface of the filter bag after running for several minutes. Because the filter bag is made of fiber weaving, dust will gradually form bridges between the fibers under the effect of diffusion and other effects before the dust layer is formed. Filter bag fiber diameter is generally 20 to 1005mm. Needle felt fiber diameter is mostly 10-205um. The distance between fibers is mostly 10-305um, bridging phenomenon is easy to appear. The 0.3-0.5mm dust layer after completion of the bridging phenomenon is often referred to as dust or primary dust layer. The dust that accumulates on the top of the primary dust layer is called the secondary dust layer.
The dedusting efficiency of the plain fabric filter cloth is 85% to 90%, and the efficiency is relatively low. However, when dust deposits accumulate on the surface of the grate, a high dust removal efficiency of 99.5% or more can be obtained. Therefore, it is necessary to leave a dust layer of 0.3-0.5 mm thick on the surface of the filter cloth after the dust is removed to prevent the dust removal efficiency from decreasing. The problem is how to complete the dust collector during the operation so that the first dust layer is retained, and only the second dust layer is removed. This problem is both a technical problem and a disposal experience for the design manufacturer. Therefore, it can be said that the history of bag filter is a history of continuous improvement. Due to the effect of the dust layer on the efficiency, the dust removal efficiency of the dust layer is drastically reduced. At the same time, the smoke gas is concentrated in this part due to the reduced pressure loss. Therefore, after a few seconds, a dust layer forms on the surface of the filter cloth, and the dust removal efficiency increases. That is, a certain amount of dust can be discharged during each cleaning cycle.
On the other hand, if the filtration wind speed is designed properly, the filter layer on the surface of the filter cloth will have a certain pressure loss (usually 1000 to 1500 Pa). That is, when the filtration layer reaches a certain thickness within the required time, the time is inversely proportional to the filtration wind speed. . Take the filter wind speed n times, the time required is 1/n, the number of dust layers must be removed every hour at least n times, in fact must consider the removal time (10-30s), should take n times. In addition, the non-woven needle felt is used as the filter cloth, generally 1.5 to 2.5 mm thick. This layer is equivalent to the previously mentioned primary dust layer, which is present in the inner layer of the filter cloth.
Flue gas and dust penetrate through the surface of the filter cloth, and dust is removed in a certain way. After the above two effects are balanced, a thickness of 0.5-0.7 mm is formed in the inner layer (felt layer) of the filter cloth. A layer formed by entangling the dust and the filter cloth fibers, which is called an inner filter layer, corresponds to the primary filter layer of the aforementioned plain weave fabric. However, the smoke again accumulates on the surface of the filter cloth and becomes a secondary dust layer. In this way, the inner filter layer is intertwined with the fibers, and the nature of the inner filter layer is very different from that of the secondary dust layer. Therefore, only the secondary dust layer is removed and the inner filter layer is easily retained. Therefore, the dust removal efficiency after dust removal is not Will fall. The adhesion of dust on the filter cloth is very strong. When the filtration speed is 0.28m/min, the adhesion of the dust particles with diameter of 105m on the filter material can reach 1000 times the weight of the particles, and the dust particles of 55m are in the filter media. Adhesion can reach 4200 times the weight of the particles. Therefore, after the filter bag is cleaned, the dust layer will continue to exist. The presence of a dust layer greatly enhances the screening effect during the filtration process and increases the filtration efficiency. The sieve holes formed by the dust layer are much smaller than the gaps of the filter fibers, and the screening effect thereof is obvious.
The formation of dust layer is related to the filtration speed. When the filtration speed is high, the dust layer is formed quickly. When the filtration speed is low, the dust layer is formed slowly. If only considering the filtering effect of the dust layer, ‘the filtration speed is not low. When the dust layer continues to be thickened, it must be removed in a timely manner by means of dust removal, otherwise it will form too high resistance, or the automatic landing of the dust layer, resulting in “leakage” phenomenon between the dust and reduce the effect of dust collection.
Surface filtration mechanism:
Based on the theory that the formation of dust layers is conducive to filtration, the surface of ordinary filter materials is artificially covered with a thin film of micropores to improve the dust removal effect. So the filter surface film is also called artificial dust layer. In order to control the collection efficiency of different particles, the micropore size of microporous surface membranes of different uses varies. For example, when filtering ordinary dust, the micropore pore size is usually less than 25um; when filtering bacteria, the pore size is less than 0.35um; when filtering the virus, the pore size is less than 0.055um. This difference is just like a sieve. According to the requirements of the sieve, the sieve with different meshes is selected.
The surface-filtered film can be overlaid on the surface of an ordinary filter material or on the surface of a plastic plate. Recently, the film covered by the filter cloth was made of fluoroethylene film, with more than 20 base cloth types and only one type of film. The thickness of the film was about 8-30 um. The products of the manufacturers were slightly different.
