Bag filter collector ‘paste bag’ and ‘burning bag’ can not distinguish? No!

Bag filter collector ‘paste bag’ and ‘burning bag’ can not distinguish? No! A text lets you understand the difference, the detailed reasons and solutions

When the bag is operated in the dust collector, the filter performance is often lost or partially lost for one reason or another, and the actual service life of the bag is greatly shortened compared as expected, so that the maintenance and operation cost of the factory is greatly increased. ‘Paste Bag’ and ‘Burning Bag’ are typical problems. Although there is only one word difference between them, the causes and solutions of the faults are very different.

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Dust collector ‘Paste Bag’

What is a ‘paste bag’?

‘Paste bag’ is a phenomenon in which the dust condenses, adheres or knots on the filter surface of the dust bag or the inside filter material,and cannot be effectively removed by the online cleaning system, then causes running resistance increasing a large degree in the working condition where the high humidity or oily substance comes into contact with the filter material during the long-term operation or shutdown of the dust bag.

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The harm of ‘paste bag’

After the dust bag is paste, the dust is densely covered on the surface of the filter bag, so that the effective filtration area of the filter material is greatly reduced, the air permeation volume of the filter material is drastically decreased, the running resistance becomes so high, and the load of induced draft fan is increased, resulting in energy consumption rising, and more seriously the induced draft fan can be overwhelmed and unable to operate. At the same time, the pressure drop of the dust bag is high, so that the online dust cleaning system is frequently deashing, which not only consumes a large amount of compressed air, but also causes serious loss of mechanical strength of the filter material, and the service life is greatly shortened.

The reason for the formation of ‘paste bag’

1. Dew formation paste bag

Under normal circumstances, the operating temperature requirement of the bag dust collector must be higher than the acid dew point temperature of 25 ° C or more, which is safe for the bag. This is mainly to avoid the occurrence of dew formation. When the operating temperature is lower than the dew point, liquid water is formed, and the liquid water is mixed with the dust and gathered on the surface of the filter bag to form paste bag.

Secondly, compressed air of pulsed dedusting is also one of the possible causes of dew formation. The compressed air temperature is generally much lower than the operating temperature of the precipitator. At the moment of the pulse, the low temperature compressed air will rapidly lower the temperature of the upper part of the filter bag. When it is lower than the dew point temperature, the dew formation will occur on the outer surface of  filter bag at this part.

In addition, the air leakage rate of the precipitator is also a possible cause of dew formation. The air leakage rate of the general dust collector is about 1% to 2%. However, as the running time increases, the air leakage rate will increase slightly. If it is in the cold winter of North, the problem becomes bigger. The higher the air leakage rate, the greater influence on the local temperature in the precipitator, and the risk of the bag in the leaking position becomes paste because of dew formation will be higher and higher.

2. Cohesiveness paste bag

Mainly because the dust adhesion is relatively high, although there is no dew formationn occurrence, the dust still adheres to the surface of the fiber, and the online dust cleaning system cannot remove it. The reason for the cohesiveness paste bag may be due to the following conditions.

(1) The viscosity of the dust itself is relatively high, and when it is in contact with the filter fiber, the intermolecular force is relatively strong. For example, oily particles, ammonium sulfate formed by denitration, and slaked lime used for desulfurization.

(2) Although some dusts are not sticky, they are easily deliquescent. When they are trapped on the fiber surface, they absorb moisture in the air and form a solution on the surface of the fiber.

(3) Some dust adhesion may not be strong, but it can absorb the moisture in the flue gas and carry out the chemical process of recrystallization to generate new hydration hardening  substances or crystals, and the formed “crusting” covers the filter material surface. For example: cement clinker, desulfurization products, Calcium sulfate.

(4) Even if the dust itself is not sticky, if the dust particles are fine and the water content of the dust is relatively large, the dust is easily adsorbed evenly on the surface of the filter material to form a layer of ‘floating ash’, and the adhesion is not very strong, but it is difficult to remove. The longer the running time, the thicker of ‘floating ash’ it will be. This may happen in general coal-fired power plants, especially for filter bags longer than 6 meters. 

filtering and deashing

3. Operation errors

(1) The pre-spraying is not carried out as required, so that the oil mist in the ignition directly invades the filter material, resulting in paste bag.

(2) When the startup and shutdown (especially before a long shutdown), the deashing operation is not performed in the correct procedure.

(3) The filter bag is not properly treated and remedied when there is an accident such as a pipe burst of boiler during operation.

‘Paste bag’ solution

1. Strictly control the operating temperature to prevent dew formation

To prevent the bag dust collector filter bag from dewing paste bag, the process gas temperature must be kept above its dew point by 25 ° C to 35 ° C. When the dust collector is used to treat high temperature and high humidity gas, a temperature detection alarm device should be installed at the entrance for monitoring, and thermal insulation materials such as rock wool should be installed outside the casing for heat preservation.

2.  Do a good job of the dust collector body sealing work

The dust collector must be tightly sealed and the air leakage rate is less than 3%. Welding quality is critical during the installation of the equipment. All welding must be carried out in accordance with the relevant specifications and standards. After the welding is completed, the phosphors are used for leak inspection, and the leaks must be re-welded. The inspection door of the dust collector must be sealed with rubber strips and checked frequently. Carefully inspect the unloader and flange to seal. Reducing the air leakage of the dust collector can effectively protect the filter bag, avoid the occurrence of the paste bag, and ensure the smooth running of the device under lower resistance.

3. The correct switch operation

During the start up and shutdown process (especially for long-term shutdown), the program operation should be carried out in strict accordance with the instructions of the startup and shutdown. For example, before the dust removal system stops running, the wet gas in the dust collector must be completely discharged and replaced with dry air to prevent dew formation, that is, after the production equipment is shut down, the dust removal fan should be extended for a period of time before it stops.


Dust collector ‘burning bag’

In addition to the high temperature burnout of the bag filter bag, the damage of spark in the flue gas to the bag of the dust collector is also quite serious, such as coke oven, drying kiln, chain furnace, cupola, electric furnace, blast furnace, mixed iron furnace, etc. During production process, there will be a large number of sparks entering the flue gas. If spark is not treated in time, especially when the dust layer on the surface of the filter bag is thin, spark will burn the filter bag and form an irregular round hole. When the dust layer on the surface of the filter bag is thin, spark will not directly burn through the filter bag, and a dark color baking mark will be formed on the surface of the filter bag.

The reason for ‘burning bag’

1. High temperature burn down dust bag

High temperature damage to the dust bag is fatal. For example, in a pulverized coal drying kiln, since the pulverized coal particles are very fine and particularly sticky after drying, the deashing is not ideal, so that a large amount of dried coal powder remains on the surface of the filter bag, and the dried coal powder has a very low ignition point. When the high-temperature flue gas enters the dust collector, it will quickly ignite the coal powder on the surface of the filter bag, causing the dust bag and the dust-removing skeleton of the entire dust collector to be completely burned.

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2. Spark burned through the dust bag

In addition to the high temperature burnout, the damage of sparks in the flue gas to the dust bag is also very serious.  Coke oven, drying kiln, chain furnace, cupola, electric furnace, blast furnace, mixed iron furnace, etc. in the production process, a large number of sparks will be mixed into the flue gas, if such treatment of sparks is not timely, especially the dust layer on the surface of the dust filter bag is thinner, sparks will burn through the dust bag and form an irregular round hole. However, when the dust layer on the surface of the dust bag is thicker, sparks will not directly burn through the dust bag, which will cause a deep color baking mark on the surface of the bag.

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3. High temperature shrink dust bag

Another damage caused by high-temperature flue gas to the dust bag is high temperature shrinkage. Although the temperature of each filter material is different, when the flue gas temperature exceeds its use temperature, if the warp-wise shrinkage rate is too large, the dust bag will be shortened in the length direction and the bottom of the dust bag is held against the skeleton and damaged by force. If the weft-wise heat shrinkage of the dust bag is too large, the dust bag will become smaller in the warp-wise direction, and the dust bag will be tightly hung on the skeleton, and even cannot be extracted from the skeleton. Therefore, the dust bag is always under stress, causing the filter bag to shrink deformation, hardening, brittle, accelerating the strength loss, and shortening the life of the filter bag. Since the filter bag is tightly hooped on the skeleton after being deformed, the filter bag is difficult to be deformed during the deashing, which is not advantageous for jetting deashing, resulting in high resistance of the filter bag.

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4. Ash bucket dust storage heat and burn down dust bag

After the high-temperature dust is collected into the ash bucket, if it cannot be discharged in time, the dust will accumulate in the ash bucket for a long time, causing the temperature inside the ash bucket to rise continuously. The dust-removing cloth bag will become brittle, hard, burnt down more seriously under long-term baking at high temperature, especially the flammable substances contained in the dust, will burn in the ash hopper, thus burn down the dust bag.


‘Burning bag’ solution

If it is necessary to cool the exhaust gas, when using the cooling method, pay attention to the humidity of the air and whether it contains acid and alkali components. At the same time, try to ensure that the temperature of the exhaust gas treated by the dust collector is higher than the dew point and avoid water droplets directly entering the filter bag.

In order to prevent sparks from entering the dust collector and causing the filter bag to be burnt, pretreatment methods may be used. For example, a protective layer may be pre-coated on the surface of the filter bag, and kaolin, limestone powder or the like may be used. At the same time, it is necessary to prevent unburned carbonaceous materials from being burned again in the dust collector.

There are many reasons for ‘paste bag’ and ‘burning bag’ of the dust collector filter bag. Therefore, in the daily operation and maintenance process, care should be taken to avoid these situations. Regularly replace the powder layer on the surface of the filter bag and avoid this two types of faults from the source.  If it has already occurred, relevant emergency treatment should be carried out in time to avoid further deterioration.

Post time: Mar-03-2019
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