This article mainly introduces the common damage forms of filter bags in the actual use, and makes a brief theoretical analysis of these damaged forms. According to engineering examples, this phenomenon was demonstrated, and the cause of filter bag failure was analyzed. In order to avoid similar problems later, to extend the service life of filter bags provide a reference.
1 Introduction
As the heart of the bag filter, the filter bag plays a decisive role in the use of the bag filter. In particular, the high temperature filter bag has a large proportion of the value in the entire dust collector. It protects the filter bag and prevents the filter bag from being damaged due to various reasons. On the one hand, it can ensure the filtering effect and meet the emission concentration; on the other hand, it can reduce the economy. Loss to ensure the stable operation of the entire equipment.
2, filter bag damage type
2.1 Mechanical damage
The main performance is that the non-woven layer of the filter material is worn out and detached. This phenomenon is caused by the uneven distribution of the air flow, the erosion of dust on the surface of the filter bag at high filtration speeds, or the failure of the filter bag to install the filter bag. The friction between the two was damaged; or the vertical installation of the spray tube was not vertical, resulting in a hole in the mouth of 30-40 cm, and the filter performance was lost.
Specifically, the filter bag broke at the mouth, the filter bag body was damaged, the bottom of the filter bag was damaged, and the bottom of the filter bag was damaged.
2.1.1 dust filter bag mouth area
The mouth of the filter bag was damaged more than 30-40 cm below the mouth of the bag, and the bottom layer of the filter was blown and peeled. Mostly caused by excessively high compressed air, skewed blowpipes, and deformation of the board. Pay attention to the quality of the installation during installation.
2.1.2 filter bag body position
The contact portion of the filter bag and the skeleton contact part was worn out due to the pulse jet for a long time, showing obvious wear marks in the direction of the horizontal and vertical ribs. Pay attention to the size of the filter bag and the skeleton, the surface roughness of the dust removal frame, etc.
2.1.3 The bottom of the filter bag is damaged
The phenomenon of wear at the bottom of the filter bag is more common. It may be due to the bottom of the bag cage being too small or the filter bag being too long. The bag cage can only make the bottom of the bag. Filter bag cleaning and excessive movement caused filter bag bottom inner wear. Or the dust accumulation is too high to form a vortex wear filter bag.
2.2 Chemical Corrosion
The most obvious manifestation of chemical corrosion is that the strength of the dust bag is greatly reduced. Specifically, acid corrosion, alkali corrosion, oxidative corrosion, and hydrolytic corrosion cause the filter bag to lose the acceptable filtration load, thereby losing the filter performance. This phenomenon is mainly due to problems with the selection of filter bags or the use of working conditions beyond the tolerance of the fiber, resulting in the filter bag loses its filtering performance and failure.
2.2.1 Acid corrosion
High-temperature filter materials generally have acid corrosion, mainly sulfur oxides. Especially in flue gas dedusting of coal-fired boiler plants, high-sulfur coal is used, and in combination with electric bags, the content of sulfur oxides in the flue gas is high and can reach 5000 mg/Nm3. In the high temperature environment, sulfur oxides form sulfurous acid and sulfuric acid, causing acid corrosion to the filter material and failure. If HF is contained in the flue gas, glass fiber filter materials cannot be used, and the acid will cause the filter to fail.
Generally, the flue gas operating temperature can be controlled above the acid dew point. If the temperature is lower than the acid dew point, the dust collector system must be turned off to avoid corrosion of the filter bag. Acidic liquids include hydrochloric acid, sulfuric acid, nitric acid, and hydrofluoric acid.
2.2.2 Alkaline corrosion
Mostly appear in the dust removal of sodium salt and ammonia chemical production process, such as sodium chloride, ammonia, sodium carbonate and other working conditions. For the power plants, cement plants, waste incineration plants, iron and steel plants and other areas of dust dedusting appears less.
2.2.3 Oxidation corrosion
Oxidation corrosion refers to the damage caused to the filter material when there is a certain amount of oxidizing substances, mainly oxidation and corrosion of PPS type filter media, which can cause oxidation damage to PPS type filter media including nitrogen oxide, oxygen, ozone, and strong Sulfuric acid, etc. The performance of PPS fiber became dark and brittle, and the appearance was intact, but the strength decreased sharply, only about 200 N, and it was close to the end of the service life of the filter, losing the filtering effect.
2.2.4 Hydrolysis
Hydrolysis is defined as a chemical reaction that causes water molecules to interfere with the fiber’s polymer and cause decomposition. Synthetic fibers produced from polycondensed polymers are not resistant to hydrolysis. Including: Polyester, Polyimide (P84), NOMEX, COMEX.
High temperatures, humidity, and chemicals must exist to activate hydrolysis. Polyacrylonitrile homopolymers, PPS fibers, and PTFE fibers are not produced from polycondensed polymers and are often selected to replace fibers that have hydrolysis problems. Traces of hydrolysis are mostly fiber color turbidity, filter bag strength is severely reduced, can be easily torn by hand, and the sewing thread is broken after hydrolysis, without strong force.
2.3 High temperature cauterization
The performance of high-temperature cauterization mainly due to high temperature caused by the filter bag severe contraction, severe hardening, and even a hole in the surface of the filter bag, the main reason for the filter bags used in the operating conditions of the temperature exceeds the filter bag tolerance, leading to this phenomenon. Specifically, high-temperature particles, high-temperature flue gas, and high temperature heat shrinkage of the filter bag cause damage to the filter material.
2.4 Dew condensation
The so-called condensation, in layman’s terms, refers to the phenomenon that saturated air is precipitated with moist air under a certain pressure and temperature. The temperature at which moisture is extracted is called the dew point.
The higher the gas pressure in the saturated state, 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 and the moisture-containing air temperature is lower than the dew point temperature, moisture will be formed in the supersaturated air, which will cause condensation; when the air temperature is higher than the dew point, no moisture will be precipitated. No condensation will occur. In addition, if the smoke contains SO2 components, the more SO2 content, the higher the dew point of the flue gas.
Due to the large moisture in the working environment of the filter bag, it adheres to the surface of the filter bag with the dust and the pores on the surface of the filter bag are clogged, resulting in high resistance of the device and the filter bag losing its filtering performance. The specific reasons are as follows:
2.4.1 There is air leakage in the dust collector
Due to the phenomenon of air leakage in the dust collector, a large amount of cold air from the outside is sucked into the dust collector, so that the local air temperature of the dust collector drastically decreases, and water in the air is analyzed, thereby causing condensation.
2.4.2 The moisture content in the flue gas is too high
When the moisture content in the treated flue gas is too high, supersaturated water is analyzed and condensation occurs. This phenomenon is particularly prominent on the kiln-end dust collector of the cement dry-process line. Because the flue gas of the cement-dry-line kiln is generally cooled and tempered using a humidification tower, the amount of water sprayed is too large to cause flue gas. Moisture condensation occurs when moisture is supersaturated.
2.4.3 The smoke temperature is too low
Condensation can also occur when the temperature of the fumes processed by the precipitator approaches or drops below the dew point temperature.
2.4.4 Water entering the dust collector
Due to the “four-tube burst” phenomenon, moisture enters the dust collector and causes the surface of the filter bag to condense and stick.
