Dust collector selection principle

First, dust collector selection principle

1. Standard discharge principle

The selected dust collector must meet the emission concentration specified in the emission standard. For systems with unstable operating conditions, attention should be paid to the influence of changes in flue gas treatment volume on dust removal efficiency and pressure loss. For example, the dust removal efficiency and pressure loss of cyclone dust collectors increase with the increase of treated smoke volume, but the efficiency of most dust collectors (such as electric dust collectors) decreases with the increase of treated smoke volume.

Emission standards include emission standards based on concentration control and total volume control standards. The emission standards are limited by time and space, and the emission standards are different when the boiler or production unit is installed and established. Different functional areas have different emission standards. When the dust collector discharge outlet is in the workshop, the emission concentration should not be higher than the allowable concentration of the workshop.

2. No secondary pollution principle

The dust removal process can not eliminate particulate pollutants, but the pollutants in the exhaust gas transfer to solid waste (such as dry dust removal) and water pollutants (such as water pollution caused by wet dust removal), so the selection of dust collectors must be examined at the same time. In some factories, the process itself has a mud wastewater treatment system or adopts hydraulic ash transport, in which case wet dust removal can be considered and the mud and wastewater from the dust removal system can be returned to the process system.

3. Economic principles

Under the premise of pollutant discharge meeting environmental standards, economic factors should be taken into account, that is, choose the dust collector with the same environmental effect and the lowest cost.

In the selection of dust collectors must also consider the location of the equipment, available space, environmental factors, etc., equipment investment (equipment, installation and engineering, etc.) and operation and maintenance costs and other economic factors must also be considered. In addition, it is also necessary to consider that the equipment is easy to operate, easy to maintain and manage.

Bag _ filter canister _ cyclone _ electrostatic precipitator selection points

Second, dust collector selection points

There are many factors and conditions that affect the selection of dust collector, and the following aspects should be considered at least.

1. Consider the gas flow of the treatment

The size of the treatment gas flow is a decisive factor in determining the type and specification of the dust collector. Large size dust collector should be selected for large flow, if multiple small size dust collectors are used in parallel, not only the air flow is difficult to distribute evenly, but also uneconomical. For small flow should be as far as possible to choose easy to make the emission concentration of the standard surface and economic dust collector.

2. Consider the properties of dusty gases

When the dust concentration of the gas is high, the initial purification equipment with low resistance should be set up before the electrostatic precipitator or bag precipitator to remove coarse dust particles so that the equipment can play a better role. For example, reducing the dust concentration of the dust collector population can improve the filter speed of the bag dust collector, prevent the electric dust collector from producing corona block, and reduce the amount of mud treatment for the wet dust collector, save investment and reduce the operation and maintenance workload. Generally speaking, in order to reduce the wear of the throat and prevent the blockage of the nozzle, the wet dust collector such as the Venturi and spray tower can be used for cleaning. It is hoped that the dust concentration is below 10g/m, the ideal dust concentration of the bag dust collector is 0.2~ 10g/m2, and the electric dust collector hopes that the dust concentration is below 30g/m2.

Gas temperature and other properties are also factors that must be considered when selecting dust removal equipment. Bag type dust collector is not suitable for high temperature and high humidity gas. If the flue gas also contains gaseous pollutants such as SO2.NO, you can consider using a wet dust collector, but you must pay attention to the corrosion problem.

In the dry dust collector, the temperature of the treated gas should be higher than the dew point temperature of 20~30C, and the temperature in the bag dust collector should be smaller than the allowable use temperature of the filter material. The gas temperature in the electrostatic precipitator should be < 350, otherwise the internal components are easy to deform at high temperatures, making the distance between the poles smaller, and the voltage rise is not high, which directly affects the efficiency of the electrostatic precipitator.

3. Consider dust properties

The physical properties of dust have great influence on the performance of dust collector. For example, the dust with large viscosity is easy to bond on the surface of the dust collector, and it is not suitable to use dry dust removal; The specific resistance is too large or too small dust, should not use electric dust removal; Fibrous or hydrophobic dust is not suitable for wet dust removal.

The dust removal efficiency of different dust collectors for different particle sizes is completely different. When selecting dust collectors, we must first understand the particle size distribution of the dust to be captured, and then select the appropriate dust collector according to the dust removal classification efficiency and dust removal requirements.

(1) Consider the dispersion and density of dust

The common feature of all dust collectors is that the finer the dust and the smaller the density, the more difficult it is to capture, and the more serious the dust secondary flying. Therefore, the dispersion and density of dust have a great impact on the performance of the dust collector. Even if the dispersion and density are the same, and the selected dust collector is the same, but there are great differences due to different operating conditions. If the general dust density is larger, and the particle size is > 10μm, the dust removal efficiency requirements are not very high, you can choose gravity dust collector, inertia dust collector or cyclone dust collector. On the contrary, the particle size is less than a few micrometers, or the ratio of true density Pz and bulk density pd > 10 dust, should choose an efficient electrostatic precipitator or bag dust collector. When selecting, it can be preliminatively selected according to the type and performance table of the commonly used dust collector (Table 1-1), and then the final selection is made according to other conditions and the performance of the dust collector described later in this paper.

(2) Consider the adhesion of dust

Although the mechanism of adhesion between dust and the wall is very complicated, experience has proved that the adhesion is closely related to the specific surface area and wet content of dust, that is, the larger the specific surface area and the higher the wet content of dust, the stronger the adhesion. The dust with large adhesion is easy to adhere to the wall of the dust hopper of the dust collector, making it difficult to discharge ash, and it will block the lower ash mouth in serious cases. Sticky dust is easy to block the filter bag of the bag dust collector, which increases the resistance of the dust collector; The dust attached to the plate and pole line of the electrostatic precipitator is difficult to shake down, which will seriously affect the performance of the electrostatic precipitator.

(3) Consider the specific resistance of dust

The specific resistance of dust is the most important factor in the selection of electrostatic precipitator, which should be controlled in the range of 1011~ 1040.cm. If the specific resistance is greater than 10112.cm, tempering measures should be taken, otherwise the expected effect cannot be achieved. At present, the most effective and economical tempering measure is to spray water into the flue gas to increase the humidity of the flue gas and reduce the temperature, because the specific resistance of the dust depends on the size of the humidity and temperature. On the other hand, when the specific resistance <10*0.> 1042.cm.