Dust filtration/removal principle
News Category

Dust filtration/removal principle

Views : 348
Update time : 2018-06-20 20:26:46

Dust filtration/removal principle

 

Inertial collision, interception, diffusion, gravity, electrostatic force and other settlement principles are the theoretical basis of analyzing the dust filtration and removal of dust collector system. The filtration process for bag filters is more complicated, generally speaking, the settlement of dust particles, that is, separation filtration, is not only working result of one kind of filtration mechanism, but working results of several kinds of filtration mechanism. According to the different mechanical characteristics of dust particles moving in the fluid, the mechanism of filtration and dust removal involves the following aspects:

 

Screen filtration: the filter's mesh is usually 5~50 micron. When the dust particle size is larger than the net hole or the pore diameter, or the dust is deposited in inter granular space between the filter materials, the dust is blocked. For the new fabric filter material, the sieve filtration effect is very small because the gap between the fibers is far greater than the particle size of the dust, but the sieve filtration effect is greatly enhanced when a large amount of dust is deposited on the surface of the filter.

 

Inertial collision: dust capture with larger particle size mainly depends on inertial collision. When the dust flow is close to the fiber of the filter material, the air flow will bypass the fiber, of which the larger particles (more than 1 micron) deviate from the airflow streamline because of the inertia effect, and continue to move along the original direction of movement and impact on the fibers. All dust particles in the critical path of dust trajectories can reach the surface of the fiber and be arrested. The inertial collision increases with the increase of dust particle size and airflow velocity. Therefore, increasing the airflow velocity through the filter material can enhance the inertia collision effect.

 

Intercepting action: when the dust flow is close to the filter fiber, the finer particles flow together with the air flow. If the dust particle radius is greater than the distance between the dust center and the edge of the fiber, the dust particles are intercepted by the contact with the fiber.

 

Diffusion: for particles less than 1 micron, especially sub micron particles less than 0.2 micron, the particles are separated from the streamlines under the impact of the gas molecules, and do Brown movement like the gas molecules, and can be separated from the air flow if the fibers are in contact with the fibers. This effect is called diffusion, and it increases with decreasing flow velocity and decreasing diameter of fiber and dust.

 

Electrostatic action: a lot of fiber woven filter material, when the air flow through, due to friction will produce electrostatic phenomenon, and dust in the process of transport will also be charged because of friction and other reasons, which will form a potential difference between the filter and the dust particles, when the dust along with the flow trend filter material, because of the Coulomb force action to promote So that the dust and filter materials collide and enhance the adsorption capacity of the filter material to the dust, and the collection efficiency can be improved.

 

Gravity sedimentation:

When slowly moving dust laden air flows into the dust collector, the dust particles with large particle size and density may settle down naturally due to gravity.

 

Table: the size range of various trap mechanisms

No.

Mechanism

Particle size range

The influence of increasing   wind speed on the mechanism efficiency

1

Intercepting

>1μm

reduced

2

Inertial collision

>1μm

improved

3

Diffusion

<0.010.5μm

reduced

4

Electrostatic

<0.015μm

reduced

5

Screen filtration

> Micro-pore   size of filter layer

reduced

 

Generally speaking, all kinds of dust removal mechanisms are not effective at the same time, but one or several combinations. Moreover, with the change of the void, flow velocity, dust particle size and other causes of the filter material, the influence of various mechanisms on the filtration performance of different filter materials is also different. In fact, the dust removal efficiency of the new filter material is very low at the beginning of dust filtration. After a period of time, coarse dust will form a layer of dust on the surface of the filter cloth.

The air gap, airflow velocity, particle size and other reasons of the filter media also affect the filtration performance of different filter media. In fact, the dust removal efficiency of the new filter material is very low at the beginning of dust filtration. After a period of time, coarse dust will form a layer of dust on the surface of the filter cloth. Because of the dust filtering effect of the dust layer and the dust layer gradually accumulated on the dust layer, the filtration efficiency of the filter material has been improved continuously, but the resistance has also increased correspondingly. When cleaning, the primary layer cannot be destroyed, otherwise the efficiency will drop. The structure of the primary layer of dust plays a very important role in the efficiency, resistance and cleaning effect of the bag filter.