Types of Damage to Dust Filter Bags

Filter bags, as the heart of baghouse dust collectors, play a decisive role in the effectiveness of baghouse dust collectors. Especially for high-temperature filter bags, their value within the entire dust collector is considerable. Protecting the filter bags and preventing them from being damaged for various reasons is essential. On the one hand, it ensures filtration efficiency and meets emission concentration requirements; on the other hand, it reduces economic losses and ensures the stable operation of the entire equipment.

Types of Filter Bag Damage

1.Mechanical Damage

Mechanical damage mainly manifests as the abrasion and detachment of the nonwoven layer of the filter material. This phenomenon is caused by uneven airflow distribution, dust abrasion on the filter bag surface under high filtration air velocity, improper installation causing friction between filter bags, or misalignment of pulse jet pipes resulting in holes within 30-40 cm from the mouthpiece. Specific manifestations include damage to the mouthpiece, body, lower part, and bottom of the filter bag.

a.Damage to the mouthpiece of the dust filter bag: This type of damage mostly occurs within 30-40 cm below the mouthpiece, often manifesting as the blowing and shedding of the bottom layer of the filter material. It is mainly caused by excessive compressed air pressure, misalignment of pulse jet pipes, or deformation of the flower plate. Attention should be paid to the quality of installation during the installation process.

b.Damage to the body of the dust filter bag: Prolonged contact between the filter bag and the frame due to pulse jet cleaning causes wear at the contact part, manifesting as obvious wear marks in the horizontal and vertical bar directions. Attention should be paid to the dimensional coordination between the filter bag and the frame, as well as the smoothness of the dust collector frame surface.

C.Damage to the bottom of the dust filter bag: Wear at the bottom of the filter bag is common, possibly due to the bottom of the cage being too small or the filter bag being too long, causing the cage to only support the bottom of the bag locally. Excessive agitation during filter bag cleaning and filtering causes wear on the inner side of the filter bag bottom, or dust accumulation causes vortex wear on the filter bag.

2.Chemical Corrosion

The most obvious manifestation of chemical corrosion is a significant decrease in the strength of the dust filter bag. Specific manifestations include acid corrosion, alkali corrosion, oxidation corrosion, and hydrolysis corrosion, resulting in the filter bag losing its ability to withstand the filtering load and thus losing its filtering performance. This phenomenon is mainly due to problems in the selection of filter bag materials or operating conditions exceeding the fiber's tolerance range, resulting in the filter bag losing its filtering performance and failing.

a.Acid corrosion: High-temperature filter materials generally suffer from acid corrosion, mainly sulfur oxidation. Especially in the flue gas dust removal of coal-fired power plants using high-sulfur coal and electrostatic bag combination projects, the content of sulfur oxides in the flue gas is high, reaching up to 5000 mg/Nm3. At high temperatures, sulfur oxides form sulfurous acid and sulfuric acid, causing acid corrosion and failure of the filter material. If the flue gas contains HF, glass fiber filter materials cannot be used, as they are prone to acid corrosion and filter material failure. Generally, controlling the operating temperature of the flue gas above the acid dew point is sufficient. If the temperature is lower than the acid dew point, the dust collector system must be shut down to avoid corroding the filter bags. Acidic liquids also include hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, etc.

b.Alkali corrosion: Mostly found in the dust removal of sodium salt and ammonia in chemical production processes, such as sodium chloride, ammonia water, sodium carbonate, etc. It occurs less frequently in the dust removal of power plants, cement plants, waste incineration plants, steel plants, and other industries.

c.Oxidation corrosion: Oxidation corrosion refers to damage to filter materials caused by a certain amount of oxidative substances. PPS filter materials are mainly affected by oxidation corrosion, which can be caused by nitrogen oxides, oxygen, ozone, concentrated sulfuric acid, etc. Manifestations include darkening and embrittlement of PPS fibers, with no apparent external damage, but a significant decrease in strength to only about 200N, close to the end of the filter material's service life, resulting in the loss of filtering effects.

d.Hydrolysis: Hydrolysis is a chemical reaction in which water molecules intervene in the decomposition of high polymer fibers. Synthetic fibers produced from condensation-type polymers are not resistant to hydrolysis. They include polyester, polyimide (P84), NOMEX, and COMEX. High temperature, humidity, and chemicals must all be present to activate hydrolysis. Polyacrylonitrile copolymer, PPS fibers, and PTFE fibers are not produced from condensation-type polymers and are often used instead of fibers with hydrolysis problems. The traces of hydrolysis are mostly turbid fiber colors, severe decrease in filter bag strength, easy tearing by hand, and breakage of sewing threads after hydrolysis, with no strength.

3.High-Temperature Burning The main manifestations of high-temperature burning are severe shrinkage, hardening, and even surface holes in the filter bag due to high temperatures, mainly caused by operating conditions exceeding the filter bag's tolerance range. Specific causes include high-temperature particles, high-temperature flue gas, excessive thermal shrinkage of filter bags, causing damage to the filter material.

4.Condensation Blocking Condensation refers to the phenomenon of saturated water separating from moist air at a certain pressure and temperature. The temperature at which moisture separates is called the dew point. The higher the pressure of saturated air, the lower the dew point. The higher the moisture content in the air, the higher the dew point temperature. When the moisture content in the air is constant, if the temperature of the moist air is lower than the dew point temperature, supersaturated air will condense water, resulting in condensation; if the air temperature is higher than the dew point, no water will condense, and condensation will not occur. In addition, if the flue gas contains SO2 components, the higher the SO2 content, the higher the dew point of the flue gas. Due to the high moisture content in the operating environment, moisture adheres to the surface of the filter bag, causing micro-pores on the filter bag surface to block, resulting in high equipment operating resistance and loss of filtering performance.

Specific reasons include:

a.Air leakage in the dust collector: Due to air leakage in the dust collector, a large amount of cold air from the outside is drawn into the dust collector, causing a rapid decrease in local air temperature within the dust collector, leading to condensation as moisture in the air condenses.

b.High moisture content in the flue gas: When the processed flue gas contains a high moisture content, supersaturated moisture separates, resulting in condensation. This phenomenon is particularly prominent in the tail-end dust collectors of dry-process cement kilns. Due to the use of a humidification tower for cooling and conditioning, excessive water spraying can lead to supersaturation of moisture in the flue gas, causing condensation.

c.Low flue gas temperature: Condensation can also occur when the temperature of the flue gas being treated by the dust collector is close to or below the dew point temperature.

d.Moisture entering the dust collector: Moisture can enter the dust collector due to the "four-tube burst" phenomenon, causing condensation and bag caking on the surface of the filter bag.

If further information is needed, please feel free to contact Shanghai Sffiltech Co., Ltd. We will be happy to assist you.