How to more accurately determine the type and form of the dust collector?

How to determine the type and form of the filter more accurately? Here we introduce the relevant knowledge:

(1) Dispersion of dust

When selecting the form of the dust remover, it is first necessary to accurately grasp the dispersion of the dust. As pointed out in Figure 1-7, when the particle size is above lOMm, the centrifugal dust collector should be selected. When the particle size is less than several microns, most of the dust particles should be electrostatic precipitator, filter dust collector or scrubber. For specific options, preliminary selections can be made based on the particle size distribution and other requirements, with reference to the Common Dust Collector Types and Performance Table (Table 1-19). Then determine the performance and design requirements of the type and form of dust collector discussed in the following chapters.

(2) By dust density

Dust density has a great influence on the dust removal performance of the dust collector. The most obvious effects of this effect are gravity, inertial force, and centrifugal dust collectors. The common point of all dust collectors is that the smaller the bulk density is, the more difficult it is for dust particles to be separated and trapped, and the more serious the secondary flying of dust is. Therefore, special measures should be taken in the operation and equipment structure.

According to experience, dust with a ratio of dust particle density ft to dust particle packing density of 10 or more requires special attention to the secondary flying of dust. For example, the ft/in of carbon soot is greater than 46, so its secondary flight is very serious, and the separation and collection of dust is also very difficult.

(3) According to dust concentration

1 In gravity, inertial force and centrifugal dust collectors, in general, the greater the concentration of imported dust, the higher the dust removal efficiency. However, in general, the concentration of dust contained in the outlet will be increased. Therefore, it cannot be considered that the dust treatment is good only from the high dust removal efficiency.

(2) In dust collectors such as Wänter scrubbers and jet scrubbers, it is desirable that the initial dust concentration is below 10 g/m3 (standard), taking into account factors such as friction loss in the throat section and nozzle clogging.

3 In the filter dust collector, the lower the initial dust concentration, the better the overall dust removal performance. At high initial dust concentrations, it is desirable to use a continuous cleaning method with a small change in pressure loss.

(4) Electrostatic precipitators are generally used within the range of initial dust concentration below 30g/m3 (standard).

(4) Dust adhesion

Dust and wall adhesion mechanism is very complex, but experience has known that it has a large relationship with the specific surface area of ​​dust. The specific surface area Fb of the dust is the surface area per unit volume of dust particles. If d represents the diameter of the spherical dust particles, Fb will be expressed as follows:

Fb — /(.nd3 / 6) = -^r (1-36)

a

The smaller the particle diameter d of the dust, the larger the specific surface area Fb and the greater its adhesion.

In a cyclone dust collector, dust adheres to the wall surface due to centrifugal force and there is a risk of clogging. On the other hand, bag filter is easy to block the pores of the filtered gas, and it is easy for the electrostatic precipitator to accumulate the discharge electrode hypertrophy and the dust collector. Experiments have shown that the adhesion of dust plays an important role in the formation of a filter-dust dust primary layer.

Of course, the adhesion of dust is not only related to its specific surface area, but also related to the composition of the dust and the nature of the gas, as well as the characteristics of adhesion to the dust.

(5) Dust resistivity

The dust resistivity of the electrostatic precipitator should be in the range of 10••lO^n•cm. The resistivity of dust with dust gas

The temperature and humidity vary greatly. Generally between 100 and 200 °C, the maximum value. If we humidify dust-containing gas, the resistivity decreases. Therefore, when selecting an electrostatic precipitator, it is necessary to know the resistivity of the dust in advance and fully consider the selection of dust gas temperature and the adjustment of the nature of the dust-laden gas.

(6) Handling dust gas temperature

Dry dedusting equipment must, in principle, be carried out at a temperature above the dew point of the exhaust gas.

In the dust gas containing sulfur trioxide, even if the amount of sulfur trioxide is small, the dew point will be greatly increased. In addition:

1 In scrubbing and dust removal, due to evaporation of water and condensation after discharge into the atmosphere, it should be treated as low as possible;

2 In filter dust removal, the temperature of direct or indirect treatment of dust-laden gas should be reduced below the heat-resistant temperature of the filter cloth. The use temperature of glass fiber filter cloth is generally below 300°C, and other filter cloths are generally below 250X:

3 In the electrostatic precipitator, the use temperature can be up to 400 乞. The dust resistivity should be considered to select the temperature of the dust-containing gas.

The majority of wet dust removal is water. If the dust-generating equipment is of a small scale and needs to remove harmful gases at the same time, or when it is necessary to completely capture dust such as extremely fine carbon black, wet dust removal is often used. The low temperature of the dust-laden gas emitted by the wet dust collector will cause the effect of atmospheric diffusion to be reduced, resulting in long smoke flow and smoke falling. In addition, wet scrubbers must take measures to deal with the problem of washing wastewater.

(7) Dust gas properties

In order to effectively use the dust collector, the following dust and dust gas properties should be treated according to the circumstances.

1 oxidation of carbon monoxide gas. When dealing with exhaust fumes containing carbon monoxide, air is introduced into the high-temperature part of the furnace exit flue to prevent the explosion, and carbon monoxide is oxidized to carbon dioxide.

2 Improve the cohesion of dust. Indirect cooling by a heat exchanger or the like, or direct cooling and humidification of a water spray, or electrostatic agglomeration or the like can be used to increase dust flocculation effect.

3 Change the resistivity of dust. In the case of high-resistance dust, such as in fuel coal, mixed heavy oil with high-sulfur coal is mixed, or water, steam, sulfur trioxide and other regulators are sprayed to reduce the dust's resistivity. On the other hand, when the heavy oil is burned, dust generated when the heavy oil is too low can be sprayed with ammonia gas to generate high-resistance ammonium sulfate, and the resistivity of all the dust can be adjusted within the range of 104 to 10 UQ • cm.

(8) Capacity decision

The nature of the dust-laden gas can vary significantly depending on the operating conditions or the combustion conditions, and has a great influence on the dust removal performance. After the dust remover enters the actual operation, it is actually very difficult to obtain dust that meets the specification of the juice. On the other hand, it is not easy to predict the environmental conditions of operation and equipment installation locations, whether the equipment performance is deteriorating or improving. Therefore, when deciding the capacity of the equipment, it must be ensured that there is a certain margin or some space may be added to increase the equipment.

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