The effect of dust layer of dust filter bag on filtration

According to the mechanism of filtration and dust removal, dust layer plays a very important role in the actual dust removal process. The dust layer on the surface of the filter cloth is composed of dust particles of different sizes and has various structural and void properties. Under normal circumstances, it affects the dust removal efficiency and resistance of the bag filter and determines the performance of operation. The press cloth is the skeleton that forms the dust layer and supports the dust layer. Dust bag quotation

1. The role of dust layer in the process of filtration and dust removal

(1) When the dust layer is thick enough, high dust removal efficiency can be achieved.

(2) When the dust layer is thin or multi-void, the permeability is good, and the dust removal resistance and efficiency are low.

(3) When the dust ratio is heavy, the inertia of dust cleaning is large, and it is easy to separate from the surface of the filter bag after earthquake, so as to strengthen the effect of dust cleaning.

(4) When the dust layer is sticky, it is not easy to remove ash and the resistance is high.

The degree to which the remaining dust layer enters into the press cloth or is attached to the surface of the press cloth directly affects the resistance and dust removal effect of the dust collector.

2. The generation process of dust layer can be roughly divided into three sections

(1) The process by which dust fills the gaps in the press cloth within minutes or hours after the new press cloth is put into use.

(2) After using the press cloth for a week or longer, dust should be removed several times until a stable residual dust layer is established.

(3) each time the amount of ash from the filter bag is about equal to the amount of ash deposited on the cloth bag before the last time of ash removal, and the resistance is the same under the same condition of ash removal.

The adhesion force in the unstable dust layer is related to sulfur trioxide, water vapor, calcium or other alkali metal components, particle size and charge in the process of dust removal. The high sulfur fuel has more resistance to the filter bag than the low sulfur fuel. With the thickening of dust layer, the resistance of filter bag also increases, from the beginning of use to the maximum resistance, the relationship between the two is not completely linear, but there is no mutation phenomenon, most of the time is stable.

3. The influence of different ash cleaning methods on dust layer

The separation of the unstable dust layer from the press cloth occurs on the outer surface of the press cloth. In the process of use, dust first accumulates in the diameter of the press cloth, holes and grooves of weft interwoven yarn, and then gradually develops to the outer surface of the press cloth to form a dust layer. Under normal conditions, there is adhesion between the press cloth and the ash layer, and between the ash layer and the dust particles, and the latter is much greater, so that the separation of the unstable dust layer from the press cloth occurs on the outer surface of the press cloth, where the binding force is weakest.

The thickness of the dust layer on the surface of the press cloth varies by 5-20 times. When backblowing is used to remove dust, the residual dust layer is highly uneven and prone to appear as spots and fall off. Most of the residual dust layer remains on the cloth bag, so the residual ash content is large. The dust layer profile on the filter cloth section is like mountains. When used again, the pressure loss rises quickly, which indicates that although the resistance loss of filter bag decreases after ash removal, it does not mean that ash removal has reached a satisfactory degree. Because of the large amount of residual dust that still plays a role. On the other hand, the remaining ash layer of the vibrating dust cleaning press cloth is thinner and more uniform, the amount of ash per unit area is smaller, and the dust layer profile on the section of the press cloth is also gentle.

Vibration dust cleaning is carried out under the condition of static air flow, and the filter cloth is smooth and the resistance is small, so the residual dust layer after vibration dust cleaning is less, and the emission concentration in a very short time is larger than that of reverse blowing dust cleaning. In a few minutes is generally about 3 times but it has a very long cleaning cycle. Reverse blowing dust often make the attached ash layer perforation ventilation, so that the back blowing air pressure sharply reduced, pressure relief after no continue to blow ash ability, resulting in less dust each time blow, so under the condition of maintaining the same resistance, the back blowing dust than vibration, vibration dust is more frequent. The back blowing speed is less than 0.61m/min. Increasing the number of back blowing can not reduce the resistance of dust layer, but increase the emission concentration and reduce the dust removal efficiency. High back blowing speed may lead to the damage of filter bag. Vibration dust layer, began to fall more, later gradually reduced, but the fall has been relatively uniform, the rest of the dust layer section is also relatively uniform.

The dust attached to the filter bag of the bag filter is a process of gradual accumulation, dust accumulation to a certain thickness, dust removal efficiency can reach normal, at this time the resistance of the filter bag is relatively stable for a period of time, until the resistance of the filter bag and the thickness of the dust layer reaches the predetermined limit after the dust removal.

From the mechanism of dust removal by vibration, high-frequency vibration force is generated by vibration, which is uniformly transmitted on the rigid body of the filter bag frame, and the stretched filter bag vibrates at the same time. In the process of vibration, there is inertial force in the dust layer, and if it is enough to overcome the adhesive force between the filter bag, the filter bag can fall off in one impact and vibration. In the process of shock shaking, a vibration impact lay down for most of the dust of the dust layer, to continue shaking, make with on the filter bag with gray, especially in a relatively dense layer of dust on the surface of the filter bag to absorb the vibration energy, closely attached to loosely adherent, energy absorption, adsorption volume more loosely, thereby reducing the friction between the dust particles of fluidization gradually, When the adhesive force of the filter bag is less than the falling gravity, it is finally separated from the surface of the filter bag.