The dust layer of a high-temperature dust-removing bag in a power plant plays a very important role in the actual dust removal process. The dust layer on the surface of the filter cloth is composed of dust particles of different sizes, with various structural and void properties. Under normal circumstances, it affects the dust removal efficiency and resistance of the bag filter and determines the performance of the operation. The filter cloth is a skeleton that forms and supports the dust layer.
1. In the process of filtering and removing dust, the role of the dust layer.
(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 voids, the air permeability is good, and the dust removal resistance and dust removal efficiency are low.
(3) When the dust ratio is large, the inertia of the dust removal is large, and it is easy to separate from the surface of the filter bag after being shaken to enhance the dust removal effect.
(4) When the dust layer is highly viscous, it is not easy to clean the dust and the resistance is also high.
The degree to which the remaining dust layer enters the filter cloth or is attached to the surface of the filter cloth directly affects the resistance and dust removal effect of the dust collector.
2. The formation process of the dust layer can be roughly divided into three stages.
(1) The process of filling the gaps of the filter cloth with dust within a few minutes or hours after the new filter cloth is used.
(2) After the filter cloth is used for a week or longer, clean the dust several times until a stable remaining dust layer is established.
(3) The amount of ash removed from the filter bag each time is approximately equal to the amount of ash deposited on the cloth bag before the next cleaning, and the resistance is the same under the condition of the same.
The adhesion in the unstable dust layer is related to factors such as sulfur trioxide, water vapor, calcium or other alkali metal components, particle size, and electric charge in the flue gas during the dust removal process. High-sulfur fuel has greater resistance to the filter bag than low-sulfur fuel. With the thickening of the dust layer, the resistance of the filter bag also increases. From the beginning of use to the maximum resistance, the relationship between the two is not completely linear, but there is no sudden change, and it is stable most of the time.
3. The effect of different dust removal methods on the dust layer.
The unstable dust layer and the filter cloth are separated on the outer surface of the filter cloth during dust removal. In the process of use, the diameter of the filter cloth, the holes, and grooves of the weft interlaced yarns first accumulate dust in a prismatic shape, and then gradually develop to the outer surface of the filter cloth to form a dust layer. Under normal circumstances, the adhesion force between the filter cloth and the ash layer, and between the ash layer and the dust particles, and the latter is much larger, so the unstable dust layer is separated from the filter cloth on the outer surface of the filter cloth This is where the binding force is weakest.
The thickness of the dust layer on the surface of the filter cloth varies by 5-20 times. When reverse blowing is used to clean the dust, the remaining dust layer is highly uneven and easy to fall off in spots. Most of the remaining dust layer remains on the cloth bag, so the amount of remaining dust is large. The section of the dust layer on the filter cloth section is like The hills are undulating. When used again, the pressure loss rises quickly, which shows that although the resistance loss of the filter bag after cleaning has decreased, it does not mean that the cleaning has reached a satisfactory level. Because the large remaining dust still works. The remaining dust layer of the filter cloth for vibrating dust removal is thinner and more uniform, with a smaller amount of dust per unit area, and the dust layer profile on the section of the filter cloth is relatively gentle.
Rapping and cleaning are carried out when the airflow is static, and the filter cloth is smooth and the resistance is also small, because the remaining dust layer after rapping and cleaning is less, and the emission concentration in a very short period of time is better than that of back-blowing cleaning. The gray ones are bigger. It is usually about 3 times in a few minutes, but its cleaning cycle is very long. Reverse blowing and ash cleaning often make the attached ash layer perforate and ventilate, so that the reverse blowing pressure is sharply reduced. After the pressure is relieved, there is no ability to continue blowing off the attached ash, resulting in less dust blown off each time, so under the same resistance condition, Rewind cleaning is much more frequent than rapping and vibration cleaning. The speed of back-blowing cleaning is less than 0.61m/min. Increasing the number of back-blowing will not reduce the resistance of the dust layer. Instead, it will increase the emission concentration and reduce the efficiency of dust removal. Using a high back-blowing speed may cause damage to the filter bag. The dust layer that was cleaned by rapping began to fall a lot, and then gradually decreased, but the fall has always been relatively uniform, and the section of the remaining dust layer is also relatively uniform.
The dust attachment to the filter bag of the bag filter is a process of gradual accumulation. The dust removal efficiency can only reach normal when the dust accumulates to a certain thickness. At this time, the resistance of the filter bag is relatively stable for a period of time. When the resistance of the filter bag and the thickness of the dust layer reaches a predetermined value Clean the dust after the limit.
From the perspective of the mechanism of rapping and dust removal, rapping produces high-frequency vibration force, which is evenly transmitted on the rigid body of the pull filter bag frame, and the tensioned filter bag also vibrates at the same time. During the vibration process, the dust layer has inertial force, if sufficient Overcoming the adhesive force between the filter bag and the filter bag, the filter bag can fall off with one impact and rapping. In the process of impact rapping, the falling dust of one impact rapping occupies most of the dust layer. Continue rapping to make the dust attached to the filter bag, especially the denser dust on the surface of the filter bag, absorbed Vibration energy becomes loosely attached. The more the energy absorbed and the more adsorbed air, the looser it is, thereby reducing the friction between dust particles and making them gradually fluidized. When the adhesion force with the filter bag is less than the falling gravity, finally Separate from the surface of the filter bag.
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