Reasons for dust emission exceeding the standard in the use of dust filter bags

The dust-proof filter bag refers to the matched cloth bag in the dust remover. In the production process of thermal power generation, iron and steel, coking, non-ferrous smelting and cement industries, a large amount of dust will be produced, which will cause serious pollution to the environment. Therefore, the state has set strict requirements on the atmospheric emissions of such enterprises. Bag type dust removal is an ideal dust removal method widely used. The dust removal bag (dust removal filter bag) is called the heart of the bag type dust remover, and plays a very important role in the dust removal effect. The dedusting efficiency is 99.999%. However, recently, many users reported that the dust emission exceeded the standard in the use of dust removal bags. So, what is the reason?

Generally speaking, insufficient initial layer on the surface of the filter bag, damaged filter bag and poor filter bag assembly are all related to excessive dust emission. The details are as follows:

1. Insufficient initial layer on the filter bag surface

During the operation of the dust remover, if the emissions exceed the standard and the operating pressure of the dust remover is too low than the design, it is very likely that the initial powder layer on the surface of the filter bag is insufficient. The reasons may be that the filtering speed of the dust filter bag is too high, the cleaning cycle of the filter bag is too short, the pressure of the compressed air injection is too high, and the load of the dust is reduced.

Some studies have shown that: if the filtering speed is too high, the dust discharge rate will increase. If the filtering gas speed is too high, the initial dust layer will be broken, and the dust will impact the filter bag, causing excessive wear. If the number of times to clean the filter bag is too high at this time, it is very easy to cause the fabric of the filter bag to be loose, which will cause the dust remover to discharge beyond the standard.

When setting the pulse cleaning cycle of the dust remover, it is better to ensure that the dust remover can work under a stable pressure, the set pulse cleaning cycle time is the longest, the pulse cleaning time can ensure that the initial dust does not fall off, and the set time for cleaning is the shortest. If the initial dust layer is insufficient, you can extend the cleaning cycle as a reward, and if you use differential pressure control, you can improve the stability of the pressure setting at the inlet and outlet of the dust remover.

If the excessive discharge of the precipitator only occurs after cleaning the filter bag, it is only necessary to check whether the pressure of the compressed air for pulse cleaning is too high.

The reduction of dust load may be caused by the reduction of productivity, or the maintenance and adjustment of the control system of the dust remover. The solution is to slowly start loading with light load or to use pre coated dust.

2. Damaged filter bag (worn, burnt, corroded)

The use of dust-proof filter bag accounts for the largest maintenance cost of the dust remover, which can reach more than 70% of the maintenance cost. The basic conditions are wear, burning, corrosion, etc. The following solutions can be adopted:

(1) Wear

Excessive filtering gas velocity will cause dust impact and wear of filter bag, and also damage the fabric fiber tension of dust filter bag. The solution is to adjust the waste gas flow of the dust remover. When the expected flow changes greatly, the automatic flow control system can be increased to ensure that the dust remover works at a stable gas flow.

The air inlet distribution of the dust remover is uneven, which is easy to make the high content of dusty waste gas directly impact the local filter bags, which is easy to make some filter bags at the exhaust gas inlet perforated, and the service life is too short. The solution is to install the air inlet distribution guide at the inlet duct of the dust remover, or replace the filter bags at the frequently worn parts with wear resistant filter bags.

If the distance between filter bags is too small and the cage bone is bent, it is easy to cause wear between filter bags. For example, glass fibers are very sensitive to wear, so it is necessary to adjust and install a solid dust-proof filter bag and replace the bent cage bone.

The diameter difference between the filter bag and the cage bone is not good when the cleaning effect is too small. The cleaning cycle should be increased and the pressure of the blowing air should be increased. If the friction between the filter bag and the cage is too large, the wear will be accelerated. The better combination is that the filter bag is 10~20mm larger than the perimeter of the keel, and the length should be consistent. Special attention should be paid to some filter fabrics that change greatly with temperature and have elongation characteristics.

When there are holes or burrs at the cage bone weld, or the rough surface caused by corrosion, the wear of the filter bag will also be accelerated.

The filter bag and the perforated plate are not tightly sealed, which will cause wear at the top of the anti dust filter bag. It is better to use an elastic ring instead.

The Venturi tube or pulse tube is misaligned with respect to the filter bag, which is easy to cause mechanical friction on the upper section of the filter bag, so it should be adjusted.

If the filter bag is cleaned too frequently, it will accelerate the wear of the dust proof filter bag, so it should be adjusted.

The dust content in the exhaust gas exceeds the design standard, which will also accelerate the wear of the filter bag.

Excessive dust stored in the ash hopper of the precipitator will also accelerate the wear of the filter bag.

The above reasons will cause the dust remover to discharge beyond the standard, and will also reduce the service life of the dust remover components, which should be paid attention to.

(2) Burn

The burning of the filter bag of the precipitator is mainly caused by the high temperature of the exhaust gas

If the temperature of the exhaust gas treated by the dust remover for a long time exceeds the working conditions of the dust filter bag, it is easy to make the filter bag harden and shrink, or cause holes when melting, and the sparks in the exhaust gas flow in, or the dust heats, it may also cause the dust filter bag to burn into holes, which is particularly important when selecting the filter bag.

If it is necessary to cool the waste gas, pay attention to the humidity of the cold air and whether it contains acid and alkali, and try to ensure that the air temperature of the waste gas treated by the dust remover is higher than the dew point, and prevent water droplets from directly entering the dust filter bag.

In order to prevent sparks from entering the bag filter and burning the filter bag, pretreatment methods can be used, such as pre coating a protective layer on the surface of the filter bag, using kaolin, limestone powder, etc. At the same time, the unburned carbon shall be prevented from secondary combustion in the dust remover.

(3) Corrosion

The main cause of corrosion is that the waste gas contains acid and alkaline components, and the dew point will change with the concentration change of these chemical gases. If the dust remover is started or stopped below the dew point, SO2 in the waste gas will form H2SO2 when it meets water, causing the fiber of the dust filter bag to deform and lose its strength. The prevention method is to use acid and alkali resistant filter bags, heat the inlet pipe and shell of the dust remover, and heat the dust remover if possible.

The condensed water in the exhaust gas will also cause the filter bag to be blocked. When the initial dust layer on the surface of the dust-proof filter bag is dry due to moisture, the dust will condense and harden, which will cause the filter bag to lose its elasticity. If the filter bag is cleaned by pulse under this condition, the damage of the filter bag will be accelerated.

It is beneficial to protect the filter bag by using pulse back blowing to clean the dust filter bag several times after the dust remover is shut down.