The dust layer of filter bag with high temperature resistance plays a very important role in the actual dust removal process. The dust layer on the surface of filter cloth is composed of dust particles of different sizes, and has various structures and gap properties. Under normal circumstances, it will affect the dust removal efficiency and resistance of bag filter, and determine the operation performance. The filter cloth is the skeleton that forms and supports the dust layer.

The function 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 has many gaps, it has good air permeability, low dust removal resistance and low dust removal efficiency.

(3) When the dust ratio is large, the dust removal inertia is large, and it is easy to separate from the filter bag surface after the earthquake, thus enhancing the dust removal effect.

(4) When the viscosity of dust layer is large, it is difficult to clean the dust and the resistance is high.

The residual dust layer enters the filter cloth or adheres to the surface of the filter cloth, which directly affects the resistance and dust removal effect of the dust remover.

Dust filter bag manufacturers divide the generation of dust layer into three parts:

(1) within a few minutes or hours after the new filter cloth is used, dust fills the gap of the filter cloth.

(2) After the filter cloth is used for one week or more, remove dust for many times until a stable residual dust layer is established.

(3) The amount of ash removed from the filter bag every time is about equal to the amount of ash attached to the bag before the next ash removal, and the resistance is the same under the condition of constant ash removal.

The cohesive force of unstable dust layer is related to sulfur trioxide, water vapor, calcium or other alkali metal components, particle size and charge in the treated flue gas. The resistance of high sulfur fuel to filter bag is greater than that of low sulfur fuel. With the thickening of dust layer, the resistance of filter bag also increases, from use to resistance. The relationship between them is not completely linear, but there is no mutation, and it is stable most of the time.

When different dust removal methods affect the dust removal layer, the unstable separation between the dust removal layer and the filter cloth occurs on the outer surface of the filter cloth. During use, dust first accumulates in the holes and grooves of diameter and weft interwoven yarns of filter cloth, and then gradually develops to the surface of filter cloth to form a dust layer. Under normal circumstances, the adhesion between filter cloth and ash layer, ash layer and dust particles is much larger, so the unstable ash layer is separated from filter cloth and occurs on the outer surface of filter cloth, which is the place where the binding force is weak.

The thickness of dust layer on the surface of filter cloth changes by 5-20 times. When back blowing is used for dust removal, the remaining dust layer is highly uneven, and spots are easy to fall off. Most of the remaining dust layer remains on the bag, so the amount of remaining dust is large, and the dust layer profile on the filter cloth section fluctuates like a mountain. After being used again, the pressure loss rises rapidly, which shows that although the resistance loss of the filter bag after dust removal decreases, it does not mean that dust removal has reached a satisfactory level. Because a large amount of residual dust still works. The residual ash layer of vibrating dust-removing filter cloth is thin and uniform, the ash content per unit area is small, and the dust layer profile of filter cloth section is relatively flat.

Vibration dust removal is carried out under the condition of static airflow, with smooth filter cloth and low resistance. Therefore, there are few remaining dust layers after vibration dust removal, and the emission concentration in a very short time is greater than that of back air dust removal. Generally, it is about 3 times in a few minutes, but the dust cleaning cycle is very long. The dust removal by reverse blowing often makes the ash-attached layer perforated and ventilated, which makes the pressure of reverse blowing decrease sharply. After the pressure is released, there is no ability to continue blowing off the ash attached, resulting in less dust in each reverse blowing. Therefore, under the condition of keeping the same resistance, the dust removal by reverse blowing is much more frequent than that by vibration and vibration. Back-blowing dust removal speed is less than 0.61m/min. Increasing back-blowing times can not reduce dust layer resistance, but increase emission concentration and reduce dust removal efficiency. Using high back-blowing speed may lead to filter bag damage. The dust layer of vibration cleaning began to decline, and then gradually decreased, but the decline has been relatively uniform, and the remaining dust layer cross section is relatively uniform.

It is a gradual accumulation process that dust is attached to filter bags filtered by high temperature resistant dust removal filter bags. Only when the dust has accumulated to a certain thickness can the dust removal efficiency be normal. At this time, the resistance of the filter bag is relatively stable for a period of time, and dust removal is carried out after the resistance of the filter bag and the thickness of the dust layer reach the predetermined limit.

According to the mechanism of vibration dust removal, high frequency vibration force is generated by vibration, which is uniformly transmitted on the rigid body pulling the filter bag frame, and the tightened filter bag vibrates at the same time. During vibration, the dust layer has inertial force. If it is enough to overcome the adhesion between filter bags, the filter bags can fall off with one impact vibration. In the process of impact vibration, the dust dropped by one impact vibration accounts for most of the dust layer. Continue to vibrate, so that the dust attached to the filter bag absorbs vibration energy, especially the layer on the surface of the filter bag absorbs vibration energy, and becomes tightly attached as loose attachment. The more energy absorbed and gas adsorbed, the more loose it is, thus reducing the friction between dust particles and making it flow gradually. When the adhesive force with the filter bag is less than the falling gravity, it is separated from the surface of the filter bag.