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14, food feed industry bag filter use of some suggestions

Number of visits: Date:2013-4-24


① strict sense, for the bag-type pulse filter "selection" one that is wrong. A bag-type dust removal system is made up of independent systems with multiple technologies. It is designed separately for different dusts, different handling volumes, and different process environments. Direct purchase of the corresponding processing of air flow models, or to the weight of the dust tank unit for the tender bid. Blindly "selection" in the application of dust removal equipment often produce a variety of "failure" accident.

② in the dust removal equipment manufacturing industry and users, there is a common misunderstanding that the dust removal equipment is not the main equipment, installation of dust removal equipment purposes, only to passively meet environmental requirements. But in fact, in more food feed mill, the dust removal equipment is indeed the main product production and processing equipment, in these production processes, the efficiency of dust removal equipment will directly affect the production of production. The main function of these dust removal equipment is in the key process of grading dust recovery.

③ In the food and feed industry in the current debugging and maintenance issues are particularly prominent. To solve this problem first to correct the dust removal equipment is not the main equipment of the misunderstanding, improve the dust system operating norms system. Second, carefully read the instructions and the use of the necessary dust removal mechanism, principles and other knowledge.

④ bag-type pulse dust collector cleaning system is an independent control of the operation of the independent unit, good debugging does not require manual cleaning. When the filter bag is fouling, check the cleaning time, strength, shutdown sequence and other related factors. It is an extremely wrong practice to clean up the door by hand. This will not solve the problem, but will also cause new problems such as damage to the bag, skeleton deformation, so that the filter bag seal failure. This will affect the effective operation of the entire dust removal system, reducing the life of the dust collector.

Filtration Mechanism and Cleaning of Bag Filter

The use of fibrous fabric layer to achieve suspended in the gas medium of solid particles or liquid droplets from the gas medium separation process device called bag filter. The purpose of cleaning the bag filter is to remove the dust from the appearance of the filter bag, control system running resistance fluctuates within a certain range to ensure the effective operation of the dust removal system. The filter mechanism of the bag filter to understand the purpose of cleaning and the proper use of cleaning means.

1. Filtering mechanism

1.1 Typical filtration mechanism

Dust particles can be separated from the air flow, which mainly rely on inertia, collision, interception and diffusion effects, followed by static electricity, gravity, electrophoresis force and so on. In fact, any dust is separated from the air flow is the result of the combination of several effects, it is difficult to use an isolated collection mechanism to establish a model for efficiency analysis, the effect of the simultaneous effect of the series mode is more reasonable to deal with Way, called the integrated filtration efficiency method.

1.2 Fiber fabric layer filtration theory

Fiber fabric layer filtration theory is to study the filter material, the development of filter media and the design of bag filter, bag filter performance parameters supporting the theory. Fiber fabric layer filtration is divided into two types: internal filtration and surface filtration. Filter fiber diameter is generally 20 ~ 100μm; needle felt fiber diameter of 10 ~ 20μm, the distance between the fibers are mostly 10 ~ 30μm. When the dust-laden gas through the clean filter pore channel, in a variety of filtration mechanism under the action of dust separation, accumulation in the fiber inside, dust particles in a short period of time constantly deposited in the filter fiber, making the filter pore gradually Reduce the hole in a certain value, the dust in the fiber between the bridge phenomenon. After the completion of the phenomenon of dust particles began to filter the surface of the filter and quickly formed 0.3 ~ 0.5mm dust layer, often referred to as the inner filter layer or a dust layer. And then deposited again in a dust layer above the dust, said surface filter layer or secondary dust layer. The secondary dust layer and the primary dust are involved in the filtration of dust-laden gases. This is from the internal filter to the surface of the process of change, but also "dust dust" concept.

2. The main factors affecting the efficiency of dust removal

The concept of "dust dust" is a very important concept. The importance is reflected in the dust removal efficiency of the precipitator. Bag filter efficiency is a comprehensive efficiency, the efficiency of the level depends mainly on the filter, to enhance the efficiency depends on the secondary dust layer. Generally speaking plain weave filter itself dust removal efficiency of 85% to 90%, the efficiency is relatively low. But the filter cloth surface after the formation of secondary dust layer in addition to the efficiency will be increased to 99.5% or more. This is because the dust layer formed by the sieve than the filter fiber gap is much smaller, to strengthen the dust layer on the dust sieving effect, dust removal efficiency also increases.

3. The purpose of cleaning

From the fiber fabric layer filtration theory we know that the secondary dust layer formation and thickness is extremely important. So is not the secondary dust layer thicker the better? actually not. When the secondary dust layer reaches a certain thickness when the dust layer will automatically fall off, it will lead to the dust layer of the local "leak", but reduce the ability to capture dust. Moreover, the higher the dust layer, the higher the resistance of the filter bag, the formation of the system resistance is too high, resulting in dust system can not run properly. The pressure loss of the precipitator itself depends on the filter material, and the 80% pressure loss of the filter material is caused by the dust layer.

In order to ensure the normal and effective operation of the dust removal system, it is necessary to clean the dust layer and reduce the thickness of the dust layer. This is a contradictory body, the purpose of cleaning is to remove the dust layer to reduce the resistance, but also to ensure that the filter bag surface of about 0.3 ~ 0.5mm thick layer of dust to ensure that dust removal efficiency will not decline. So the use of dust in the process, the cleaning is a problem, it is not only to solve the dust collector design technology, but also by the actual situation with the operating experience of the injection system to adjust the system.

Then the ability to clean up the secondary dust layer and keep a dust layer? The answer is yes. The adhesion of dust to the filter is very strong. The data show that the adhesion of dust particles with a diameter of 10μm can reach 1000 times of the weight of the particles when the filtration rate is 0.28 m / min. 5μm dust particles in the filter on the adhesion can reach the particle weight of 4200 times. As long as the reasonable adjustment of the bag blowing bag cleaning, the dust layer will continue to exist. The formation of the dust layer is fast and is related to the filtration wind speed. Filtration of high dust layer formation faster, low filtration rate of the formation of low dust layer.

4. Effective benchmarking for cleaning

In fact the result of cleaning directly to clean up the secondary dust layer and retain a dust layer. This should be the benchmark for our adjustment of the jetting system. But the secondary dust layer by the amount of dust, filtration wind speed, filtration resistance, cleaning time, strength of the impact, it is a stable and long time unsteady filter state. For a large gap of the filter, such as ordinary needle felt inside the filter is a pre-indispensable process; for the film filter is the main surface filtration, filter outside the peritoneum to form a role in the formation of dust layer. So different dust collector, different filter, different conditions of the injection system is not the same adjustment, can not be stereotyped.

The pulse controller is the main device that implements the adjustment, and it has two key parameters, the pulse interval and the pulse width. Pulse interval is to control when the solenoid valve action; pulse width is to control the length of the solenoid valve action time. The image of the pulse interval is to control when the secondary dust layer to clean up; pulse width is to control the secondary dust layer to clean up the extent. Of course, the two are complementary and complementary.

Cleaning the two problems: 1. Clear enough, the secondary dust layer damage is insufficient, resulting in increased system resistance; 2. Excessive cleaning, destruction of a dust layer or local secondary dust layer damage is too large, Causing the system to run ash.

5 Conclusion

From the filter theory to know the filter is the basis for the formation of secondary dust layer, secondary dust layer is the guarantee of dust removal efficiency, dust layer and affect the dust filter running resistance. Only to fully understand the bag filter mechanism can be targeted, in order to adjust the injection system tends to be reasonable, to achieve the effective cleaning dust. To ensure the normal operation of dust removal system.

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