What are the common dust removal equipment and technologies?
Gravity dust collector
The working principle of this dust collector is: Dust-containing gas passes through the enlarged part of the pipeline (gravity settling chamber), the flow rate is greatly reduced, and the larger dust particles are Settling under the influence of gravity. In order to prevent the air vortex from picking up settled dust particles, baffles are often added to the settling chamber. The airflow speed through the settling chamber shall not be greater than 3 m/s, and the pressure loss is generally 10-20 mm water column, which can capture dust particles with a particle size greater than 50 microns. Gravity dust collectors are divided into dry and wet types. The dry dust removal efficiency is 40-60%, and the wet dust removal efficiency is 60-80%. Gravity dust collector is suitable for pre-purification of dusty gas. In order to improve the dust removal efficiency, the height of the settling chamber can be reduced or a multi-layer settling chamber can be set up.
Inertia force dust collector
The working principle is: the dust-containing airflow impacts on the baffle or filter layer, the airflow turns sharply, and the dust particles are collided with each other under the action of inertia force Air flow separation. There are two types: collision type and rotary type. Among them, 1 and 2 are collision type, 3 and 4 are rotary type, and 4 is also called louver type). The inertial force dust collector is suitable for collecting dust particles with a particle size of 10 microns or more. Because it is easy to block, it is not suitable for cohesive and fibrous dust. Its pressure loss varies depending on the structure, generally 30 to 70 mm of water column. The dust removal efficiency is 50~70%.
Centrifugal dust collector
It is a device that uses the centrifugal force generated by the vortex motion of the air flow to remove dust particles in the air flow. ?The most commonly used is the cyclone dust collector. ?When the cyclone dust collector is working, the airflow enters the dust collector from the upper part along the tangential direction and performs rotational motion. The dust particles are thrown to the inner wall of the cylindrical part of the dust collector under the action of centrifugal force and fall to the dust collecting chamber. Centrifugal dust collectors began to be used in 1885 and have been developed into various types, such as axial introduction of air flow, axial configuration of dust outlet or peripheral configuration. It is characterized by simple structure, low cost, no moving parts, pressure loss is generally 40-150 mm water column, and is suitable for removing dust particles larger than 5 microns. The dust removal efficiency of protective film is about 70~90%. The multi-tube cyclone dust collector (referred to as multi-tube dust collector) is composed of several single-tube cyclone plastic fired plates.
Several cyclone dust collectors with smaller diameters can be connected in parallel, or the cyclones can be connected in series. A cyclone dust collector with a larger diameter is used in the front stage, and a cyclone dust collector with a smaller diameter is used in the rear stage. . ?Parallel multi-tube dust collector can be made into various structures such as vertical, horizontal and inclined types. ?The multi-tube dust collectors produced in China are available in cylinder diameters of 150 and 250 mm, and in specifications of 9 tubes, 12 tubes and 16 tubes. The multi-tube dust collector can remove dust particles with a particle size of more than 3 microns, the pressure loss is 50-200 mm water column, and the dust removal efficiency is 85-95%.
Washing dust collector
A device that uses water to wash dust-containing gas to purify the gas. ?There are various types as follows: Gravity spray dust collector is also called spray tower or washing tower. When the dust-containing gas passes through the droplet space of the spray liquid, due to the collision, interception and condensation between the dust particles and the droplets, the larger dust particles settle due to gravity, and together with the washing liquid, are discharged from the bottom of the tower Drain away. ?To ensure uniform air flow in the tower, porous distribution plates or packed beds are commonly used. The pressure loss of gravity spray dust collector is less than 25 mm water column, and it is often used to remove dust particles with a particle size greater than 50 microns. This kind of plastic fired board has the characteristics of simple structure, low resistance and easy operation; but it consumes a lot of water, covers a large area and has low efficiency.
Cyclone scrubbing dust collector
This type of dust collector captures dust particles with a particle size less than 5 microns, and is suitable for occasions with large air volumes and high dust concentrations. Commonly used ones include cyclone water film dust collector, cylindrical water film dust collector and central spray cyclone dust collector.
?Cyclone water film dust collector uses a nozzle on the upper part of the dust collector cylinder to spray water mist along the tangential direction to the wall of the device, so that a thin flowing water film is formed on the wall. The dust-containing gas flows from the lower layer of the cylinder at the inlet flow rate. It enters tangentially at a speed of about 15-22 meters/second, rotates and rises, and the dust particles are thrown toward the wall by centrifugal force, adhere to the water film, and are discharged with the water flow. The air flow pressure loss is 50~75 mm water column, and the dust removal efficiency can reach 90~95%.
Horizontal cyclone water film dust collector
Also known as drum dust collector or cylindrical dust collector. After the airflow enters the dust collector, it rotates along the spiral channel. Under the action of centrifugal force, the dust particles are thrown toward the cylinder wall. ?The air flow hits the water surface in the water tank at high speed, and the dust particles fall into the water. The water droplets and dust particles stirred up by the air flow hitting the water surface collide, and the dust particles can also be captured. The airflow carrying the water droplets continues to rotate, and the water droplets are thrown toward the wall of the device, forming a water film, which captures the dust particles falling on the wall. ?The air flow pressure loss is ?80~100 mm water column.
Central spray cyclone dust collector
There is a spray porous tube in the center. The dust-containing airflow is introduced tangentially from the lower part. The dust particles are thrown towards the wall by centrifugal force. Since the water droplets are mixed with the dust, The dust particles are removed by the collision of particles and the adhesion of the water film on the wall to the dust particles. The air flow pressure loss is 50 to 200 mm water column. ?Suitable for dust particles smaller than ?0.5 micron, with a dust removal efficiency of 95~98%.
Diaphragm pump dust collector
A dust collector that relies on the kinetic energy of the air flow itself to impact the liquid surface and stir up water droplets and splashes. ?For example, in an impact water bath type dust collector, the dust-laden airflow is sprayed in at high speed from the nozzle, ?and changes direction after impacting the water surface, so that large particles of dust are captured by the water. ?The airflow continues to flow through the water layer, stirring up a large amount of water splash, foam and mist droplets, and the dust particles are captured again, and the dust removal efficiency can reach 80~95%. The pressure loss is about 100~150 mm water column. In addition, there are impulse and double-blade impulse dust removal units based on the same working principle.
Foam dust collector
Also known as foam scrubber, or simply foam tower. There is one or several porous sieve plates in the tower. The washing liquid flows to the tray to maintain a certain liquid layer height. The dust-containing airflow is introduced from the bottom of the tower and evenly passes through the small holes on the tray to be dispersed in the liquid flow. During the process, a large amount of foam is produced at the same time, which increases the contact surface area of the gas and liquid phases, causing dust particles to be captured by the liquid. ?The dust removal efficiency mainly depends on the thickness of the foam layer. When the foam layer is 30 mm thick, the dust removal efficiency is 95~99%; when the foam layer is 120 mm thick, the dust removal efficiency can reach more than 99.5%. Air flow pressure loss is 50~80 mm water column.
Jet washing dust collector
The working principle of this dust collector is: water is injected into the ejector under high pressure (3.5~7 kgf/cm2) to suck the dust-containing gas , causing dust particles in the airflow to collide with water droplets and be captured. ?Then the mixture of water droplets and gas enters the settling chamber, and?the water droplets and dust particles are separated from the air flow,?to achieve the purpose of dust removal. ?This kind of dust collector is suitable for removing dust particles with a particle size of ?0.5 micron or more, and the dust removal efficiency is about 90%. Due to the large water consumption and high operating costs, it is not suitable for the treatment of large amounts of dust-containing gas.
Packed bed scrubber and dust collector
Also known as packed tower. ?The filler layer wetted by the spray liquid has a large wet surface. ?When the dust-laden airflow passes through the packing layer, the dust particles hit the surface of the wet packing and are captured and removed. ?This kind of dust collector can remove dust particles with a particle size of ?3 microns or more, and the dust removal efficiency is about 90%. Air flow pressure loss is 15~50 mm water column. Packed bed scrubbers include vertical and horizontal types, single-layer packing and multi-layer packing, fixed bed, moving bed and fluidized bed, advection type and cross-flow type.
Venturi dust collector
Also known as Venturi dust collector, it consists of a Venturi condenser and a demister. The condenser consists of a shrink tube, a throat tube and a diffusion tube.
?After the dust-containing gas enters the shrink tube, the flow rate increases. When entering the throat, the flow rate reaches the maximum value. When the washing liquid is added from the shrink tube or throat, the relative flow rate between the gas and liquid phases is very large, the liquid droplets are atomized under the high-speed air flow, the gas humidity reaches saturation, and the dust particles are moistened by water. Violent collisions and agglomeration occur between dust particles and liquid droplets or between dust particles and dust particles. In the diffusion tube, the air flow speed decreases, the pressure rises, and the condensation effect with dust particles as condensation nuclei accelerates, condensing into dust-containing droplets with larger particle sizes, which are easily captured.
The venturi dust collector is suitable for removing dust particles with a particle size of 0.1 to 100 microns, with a dust removal efficiency of 80 to 95% and a pressure loss of 300 to 800 mm water column. If the venturi is equipped with a device for adjusting the diameter of the throat, the dust removal efficiency will not be reduced when the gas flow rate processed changes. There are many forms of venturi structures, which are divided into round and square according to the cross-sectional shape; according to the throat structure, they are divided into two types: adjustable throat diameter and fixed throat diameter; according to the liquid atomization method, they can be divided into Pre-atomized and non-pre-atomized. Since the early 1970s, some factories have used steam and hot water wet dust collectors. The dust removal efficiency can be increased to 99.9%, and the waste heat of the factory can be used.
Bag dust collector
It is a filter dust collector. ?It is a device that separates and captures dust by passing the dust-containing airflow through the filter material. The dust-containing gas is introduced into the cylindrical filter bag from the bottom. When passing through the gaps in the filter cloth, the dust particles are intercepted due to inertia, contact and diffusion. If the dust particles and the filter material have opposite charges, the dust particles will be adsorbed on the filter material, which can improve the dust removal efficiency, but it will be difficult to clean the dust; if they have the same charge, the dust removal efficiency will be reduced, but the dust removal will be difficult. easier. The bag dust collector can remove dust particles with a particle size of 0.1 micron or more, and the dust removal efficiency reaches 99%. Air flow pressure loss is 100~200 mm water column. Bag materials can be made of natural fiber or synthetic fiber textiles or felt products; when purifying high-temperature gases, glass fiber can be used as filter material.
According to the different methods of cleaning dust from the filter cloth, it can be divided into three types: The intermittent cleaning type temporarily stops the work and uses tapping or oscillator to remove the dust. Compressed air can also be used to clean the dust. The periodic cleaning type is composed of several groups of bag dust collectors, which stop the work of one group at certain intervals in sequence, and then cleans them; the continuous cleaning type uses a continuously moving air ring to backflush or pulses to backflush air. Remove accumulated dust. A pulse dust collector is called a pulse dust collector. The disadvantage of the bag dust collector is that it has no cooling effect on the passing gas and occupies a large area; the advantage is that the device is simple, the dust removal efficiency is high, and the recovered dry dust can be directly used.
Sonic dust collector
Under the vibration of sonic waves, dust-containing gas causes dust particles to vibrate, and the dust particles collide with each other and then condense. The sonic dust collector consists of an acoustic wave generator, a condensation tower, a dust collector, etc., and is often used in series with a centrifugal dust collector. ?The sound wave source is located at the upper part of the condensation tower, and ?produces sound waves with an intensity of about ?150 decibels in the condensation tower, causing dust particles to collide and condense. The dust particles stay in the tower with an effective height of 10 to 20 meters, and then are collected by the dust collector after staying for a few to more than ten seconds. The sonic dust collector can handle dust particles with a particle size of 0.1 to 100 microns, the pressure loss is 60 to 100 mm water column, and the dust removal efficiency is 80 to 95%. It is characterized by great adaptability, can handle high-temperature and high-concentration dust-containing gases, and can also be used in wet conditions, but it is noisy. The electrostatic precipitator was first successfully developed by F.G. Cottrell in 1906, so it is also called Cottrell electrostatic precipitator. It uses a strong electric field
to ionize the gas. The dust in the gas also has charges and is separated from the gas under the action of the electric field.
There are two types of electrodes in dust collectors: flat type and tubular type. The negative electrode is usually called the discharge electrode, and the positive electrode is called the dust collecting electrode (or settling electrode).
?For example, a tubular electrostatic precipitator converts ?220 volt (or 380 volt) alternating current into a high-voltage direct current of about 30,000 to 60,000 volts through a boost rectifier device. The insulation enters the corona wire, and the cylindrical wall is the dust collection pole. The wire is grounded, and an electrostatic field is formed between the corona wire and the cylinder wall. The air around the corona wire is ionized, forming a large number of negative ions and electrons, which move toward the dust collection pole. Dust-containing gas enters the dust collector from the inlet of the dust collector. The uncharged dust particles combine with negative ions and become negatively charged. After moving to the dust collecting pole, they lose their charge and become neutral. They fall into the ash hopper along the dust collecting pole through vibration. The purified gas is discharged from the dust collector outlet. The electrostatic precipitator consumes less energy than other dust collectors. The air flow pressure loss is generally 10 to 50 mm of water column. The dust removal efficiency is as high as 90 to 99.9%. It is suitable for removing dust particles with a particle size of 0.05 to 50 microns. It can be used for high temperature and high pressure. In some cases, it can operate continuously. The disadvantage is that the equipment is huge and the investment is high.
Other types of dust collectors
In addition to the above-mentioned various dust collectors that have been produced, there are also high gradient magnetic dust collectors, electrostatic wet dust collectors, and ceramic filter dust collectors. Devices etc. ?More than 70% of the dust particles in the exhaust gas from the steel industry are highly magnetic, so high gradient magnetic filters can be used. For example, converter smoke dust is mainly strong magnetic particles. A magnetic filter is used to capture dust particles with a particle size of 0.8 microns or more, with an efficiency of 99% and a pressure loss of 170 mm water column.
The electrostatic wet precipitator is equipped with a high-voltage ionizer, which causes the dust particles in the airflow to be charged before entering the washing area with fillers. The charged dust particles are attracted by the fillers and washed away by water. ?This dust collector has an efficiency of 90% in removing dust particles with a particle size of ?0.1 micron. Ceramic filter dust collector uses microporous ceramics as filter material and can be used to remove dust from high-temperature gases. The micropores of the filter material can be made into different pore sizes. If the pore size is 1 micron, all dust with a particle size of 1 micron or above can be captured. According to tests, when the pore size is 0.85 microns, dust particles larger than 0.1 microns can also be captured.