Graphic explanation of the structure and working principle of various dust collectors
Release Date: 2018-08-13
In recent years, with the rapid development of the economy, boilers using raw coal as fuel have increased a lot. Air pollutants emitted by coal-fired boilers have caused great harm to the surrounding environment. However, the main way to reduce or reduce pollutants emitted by coal-fired boilers is to Various types of smoke and dust collectors for boilers, and the performance and efficiency of dust collectors are the key to determining the degree of damage caused by a boiler to the surrounding environment.
Dust collector can be divided into two categories: ①Dry type dust collector: inertia dust collector, electric dust collector, bag dust collector, cyclone dust collector. ② Wet type dust collector: including spray tower, impact dust collector, Venturi detergent, foam dust collector and water film dust collector. At present, the most commonly used are cyclones, electrostatic precipitators and bag filters.
1. Gravity precipitator <br> The principle of gravity precipitator is to suddenly reduce the airflow velocity and change the flow direction. Large particles of dust are separated from the air under the action of gravity and inertia and settle to the bottom of the cone of the dust collector. It belongs to rough dust removal. The upper part of the gravity precipitator is provided with a shut-off valve, the electric winch is opened, and the lower part of the gravity precipitator is provided with an ash discharge device. Gravity precipitator is a device that separates dust from gas by means of gravity sedimentation of dust. The process of dust settling by gravity is that the flue gas enters the gravity settling equipment from the horizontal direction. Under the action of gravity, the dust particles gradually settle down, and the gas continues to move in the horizontal direction to achieve the purpose of dust removal.
利用粉尘与气体的比重不同的原理，使扬尘靠本身的重力从气体中自然沉降下来的净化设备，通常称为沉降室。 Principle: Using the principle that the specific gravity of dust and gas is different, the purification equipment that makes the dust naturally settle down from the gas by its own gravity is usually called the sedimentation chamber. It is a relatively primitive purification equipment with simple structure, large volume, small resistance, easy maintenance and low efficiency, and can only be used for rough purification. The working process of the gravity dust reduction chamber: the dust-containing gas enters the sedimentation chamber at a uniform speed V in the horizontal direction from one side, and the dust particles independently settle at the sedimentation speed V0. After running for t time, the dust particles settle on the bottom of the chamber. The purified gas is exhausted from the outlet on the other side.
Inertial dust collector
Inertia dust collector is also called inert dust collector. It is a dust removal device that makes the dust-containing gas collide with the baffle or sharply change the direction of the air flow, and uses inertial force to separate and capture dust. Inertia dust collector is also called inert dust collector. Due to the different inertial forces of the dust particles and the gas in the moving airflow, when the dust-containing gas turns sharply or collides with an obstacle, the motion track of the dust particles will be separated to make the gas purified. The equipment is called inertial dust collector or inert dust Device.
Inertial dust collector is divided into two types: collision type and rotary type. The former is to install one or more baffles along the direction of the air flow, and the dust-containing gas collides with the baffles to separate the dust particles from the gas. Obviously, the higher the speed of the gas before it hits the baffle, and the lower it is after the collision, the less dust it carries and the higher the dust removal efficiency. The latter is to change the direction of the dust-containing gas many times, and to separate the dust during the turning process. The smaller the radius of curvature of the gas turn. The more steering speed, the higher the dust removal efficiency.
： 利用粉尘与气体在运动中惯性力的不同，将粉尘从气体中分离出来。 Working principle : The difference between the inertia force of dust and gas in motion is used to separate the dust from the gas. Generally, some form of obstacle is set in front of the dust-laden airflow, which causes the airflow direction to change sharply. At this time, the dust has a much larger inertial force than the gas, and the dust particles are separated from the air flow, and the purified gas is discharged after changing the direction sharply.
This kind of equipment has a simple structure and low resistance, but the dust removal efficiency is not high. This type of equipment is suitable for large particles (above 20 μm) of dry particles.
用一个或几个挡板阻挡气流直线前进，在气流快速转向时，粉尘颗粒在惯性力作用下从气流中分离出来;碰撞式惯性除尘器对气流的阻力较小，但除尘效率也较低;与重力除尘器不同，碰撞式惯性除尘器要求较高的气流速度，约18~20m/s，气流基本上处于紊流状态。 The characteristics of the collision type inertial dust collector are: one or several baffles are used to block the air flow in a straight line. When the air flow is rapidly turning, the dust particles are separated from the air flow under the action of inertial force; It is small, but the dust removal efficiency is also low. Unlike the gravity dust collector, the collision type inertial dust collector requires a higher air velocity, about 18-20m / s, and the airflow is basically in a turbulent state.
(2) Reflow type
把进气流用挡板分割成小股气流。 The characteristic of the return type inertial dust collector is that the baffle of the intake air is divided into small air currents. In order to make any airflow have the same smaller turning radius and larger turning angle, various louver baffle structures can be used.
The louver baffle can increase the speed before the sharp turning of the airflow, effectively improving the separation efficiency. However, the speed should not be too high, otherwise it will cause the secondary flying of the captured particulate dust, so generally the air velocity of 12-15m / s is used.
The size of the louver baffle also has a certain effect on the separation efficiency. Generally, the length of the baffle (in the direction of the air flow) is about 20mm; the distance between the baffles is about 3 ~ 6mm; the installation bevel of the baffle (with the vertical line The included angle is about 30 °, and the airflow rotation angle is about 150 °.
(3) Bell type
The bell-type inertial dust collector has a simple structure, low resistance, does not require an induced draft fan, and can be directly installed on an exhaust tube or an air duct. However, the dust removal efficiency of this type of dust collector is relatively low, generally only about 50%.
The bell-type dust collector is mainly designed by using the principle of collision and the rapid turning of airflow to cause some dust particles to settle by gravity. Before the dust-containing flue gas enters the large-section settling chamber from the long smoke pipe, the flow direction is changed rapidly due to the obstruction of the conical fume hood. At the same time, the velocity of the flue gas is sharply reduced due to the enlarged cross-section, so that some of the smoke is settled and separated by gravity. come out. The separated dust particles are discharged from the ash discharge port in the lower part of the sedimentation chamber. The purified flue gas is discharged into the atmosphere through the flue pipe in the upper part of the sedimentation chamber.
(4) Louver settlement
The louver settling dust collector is suitable for small vertical boilers, which can be directly installed on steel chimneys. The dust removal efficiency for coarse dust particles is generally about 60%. The louver-type inertial dust collector is composed of a louver-type ash barrier and a cyclone dust collector, among which the louver-type ash barrier mainly concentrates dust particles, and has two types of cone and "V" shape. The shutter type inertial dust collector also uses the airflow to suddenly change the direction, so that the particulate dust is separated from the gas under the effect of inertia force. After the dust-containing gas enters the louver-type ash fence 1, most of the gas enters the pipeline through the gap between the ash fence blades and is discharged into the atmosphere. This part of the gas is separated from the particulate dust due to a sudden change of direction, and is purified. Particle dust still moves forward in the original direction due to inertia. The gas purified by bypassing the ash barrier generally accounts for 90% of the total gas volume, and another 10% of the gas containing the concentrated particulate dust enters the coarse particle removal chamber 3, which is removed by inertia, and then enters the cyclone dust collector and removes the fine Dust (if the exhaust volume is not large or the dust concentration is not high, the coarse particle removal chamber can be canceled and the gas directly enters the cyclone dust collector). The processed 10% gas can be returned to the ash barrier by the fan 2. , Can also be discharged directly into the atmosphere.
3. Cyclone separator
旋风除尘器的工作原理如下图所示，含尘气体从入口导入除尘器的外壳和排气管之间，形成旋转向下的外旋流。 Working principle: The working principle of the cyclone dust collector is shown in the figure below. Dust-containing gas is introduced into the dust collector from the inlet and between the exhaust pipe to form a downward swirling external swirl. The dust suspended in the outer swirling flow moves to the wall of the device under the action of centrifugal force, and then moves to the lower part of the dust collector with the outer swirling flow, and is discharged through the dust discharge hole. The purified gas forms a rising internal swirl and is discharged through the exhaust pipe.
旋风除尘器适用于净化大于5~10微米的非粘性、非纤维的干燥粉尘。 Application scope and characteristics: Cyclone dust collector is suitable for purifying non-viscous, non-fiber dry dust larger than 5-10 microns. It is a purification equipment with simple structure, convenient operation, high temperature resistance, low equipment cost and resistance (80 ~ 160 mm water column). Cyclone dust collector is most widely used in purification equipment.
4. Bag dust collector
(1) Gravity sedimentation effect—When dust-containing gas enters the bag filter, the dust with large particles and large specific gravity settles down under the effect of gravity, which is exactly the same as the sedimentation chamber.
(2) Screening effect-When the particle diameter of the dust is larger than the gap between the fibers of the filter material or the dust between the filter material, the dust is blocked when the airflow passes through. This is called the filtering effect. . When the dust accumulation on the filter material increases, this effect becomes more significant.
(3) Inertial force effect-When the airflow passes through the filter material, it can pass around the fiber, but under the action of the inertia force of the larger dust particles zai, it still moves in the original direction, and then collides with the filter material and is captured.
(4) Thermal motion effect—Light and small dust (less than 1 micron) moves with the airflow, is very close to the airflow streamline, and can bypass the fiber. However, after they are collided by gas molecules that perform thermal motion (ie, Brownian motion), they change their original direction of motion, which increases the chance of dust and fiber contact, so that the dust can be captured. The smaller the filter fiber diameter, the smaller the porosity and the higher the capture rate, so it is more conducive to dust removal.
Bag dust collectors have been widely used in various industrial sectors for a long time, used to capture non-adhesive and non-fibrous industrial dust and volatiles, and capture dust particles up to 0.1 microns. However, when using it to treat water vapor-containing gases, condensation problems should be avoided. The bag type dust collector has high purification efficiency, even the fine dust collection efficiency can reach more than 99%, and its efficiency ratio is high.
5. Electrostatic Precipitator
含有粉尘颗粒的气体，在接有高压直流电源的阴极线(又称电晕极)和接地的阳极板之间所形成的高压电场通过时，由于阴极发生电晕放电、气体被电离，此时，带负电的气体离子，在电场力的作用下，向阳板运动，在运动中与粉尘颗粒相碰，则使尘粒荷以负电，荷电后的尘粒在电场力的作用下，亦向阳极运动，到达阳极后，放出所带的电子，尘粒则沉积于阳极板上，而得到净化的气体排出防尘器外。 The working principle of electrostatic precipitator: When the gas containing dust particles passes through the high-voltage electric field formed between the cathode line (also known as the corona electrode) connected to the high-voltage DC power supply and the grounded anode plate, a corona discharge occurs in the cathode. The gas is ionized. At this time, the negatively charged gas ions move under the action of the electric field force, and the sun plate moves and collides with the dust particles during the movement, so that the dust particles are negatively charged, and the charged dust particles are in the electric field. Under the action of force, it also moves toward the anode. After reaching the anode, the electrons are released, and the dust particles are deposited on the anode plate, and the purified gas is discharged out of the dust collector.
Application scope Cement, fertilizer, and other industries, such as various mills, crushing point discharge, packaging machines and dryers, and similar dispersing sources for disposal.
6.Explosion-proof dust collector
Because the explosive dust of aluminum powder is at a certain concentration, it is likely to explode or extinguish when it encounters sparks or static electricity.
Due to the explosion of aluminum powder, the most critical factor is the concentration of aluminum powder. The most effective way to control the explosion of aluminum powder is to control the concentration of aluminum powder. The tool for controlling the concentration of aluminum powder in this equipment is a dust collector. As long as the working condition of the dust blasting machine is good and the dust removal effect is good, the aluminum powder concentration of the entire shot blasting machine equipment will not increase. Therefore, ensuring the good dust removal effect of the dust removal appliance is the key to the normal operation of the equipment. The quality of the dust removal effect mainly depends on the filtering data. When the filtering data is blocked, the dust removal effect will be greatly reduced. When the filtering data is well ventilated and filtered, the pressure difference between the static pressure chamber and the dynamic pressure chamber of the dust collector will be stable within a fixed range. Therefore, controlling the pressure difference of the dust collector is the most effective way to control the working status of the dust collector. method. Based on this, DISA has created an explosion-proof dust collector. The main method is to install the pressure difference controller in the center of the shot blasting machine dust collector without vibration. When the shot blasting machine duster works for a period of time, the The pressure difference value detected by the instrument will change. When the detection value exceeds the set upper and lower limits, the pressure difference controller will control the cleaning mechanism of the filter bag of the dust collector, such as the shock or backflush mechanism to filter the dust filter material. The appearance of dust is removed to ensure a good working condition for dust removal. When the automatic cleaning still fails to meet the request, the differential pressure controller will control the alarm and control the device to automatically shut down to prevent accidents.
7.Electric dust collector
The electrostatic precipitator is built on the foundation of the electrostatic precipitator and dust source control method, and it is a new way to deal with the dust removal of small scattered dust spots. It uses the exhaust pipe or airtight cover of the consumer equipment as the pole plate, puts electrodes in the cover or tube, and connects the high voltage power source to form an electric field. When the dust-containing gas passes through the electric field, the dust is collected on the cover or the wall of the tube under the force of the electric field, and the purified gas is discharged through the exhaust pipe. The dust is cleaned by artificial vibration or by weight. It is especially suitable for dispersing dust spots such as crushing, screening workshops and sintered conveyor belts, as well as the dust purification of mine tunnels and small boilers. Although there are many types of simple electric dust collectors, there are three types: hood, tube and open.
Dust removal process of electric precipitator
According to the current domestic types of electrostatic precipitator, it can be roughly divided into the following categories: vertical and horizontal according to the direction of air flow, plate and tube according to the type of precipitation pole, and methods for removing dust on the plate Divided into dry and wet.
Second, wet dust collector
There are many types of dust collectors, with different structural forms, and the dust removal effects are different. Wet dust collector is commonly known as "water dust collector". It is a device that keeps dust-containing gas in close contact with liquid (usually water), and uses the inertia collision of water droplets and particles to catch particles or make them larger. 水磨。 The main working principle of dust removal is: there are two ways of gas and liquid contact in the dust collector, contact with liquid (usually water) which is pre-dispersed (atomization or water film), or drum when the gas impacts (liquid) layer Bubble to form fine water droplets or water mill. For dust particles larger than 1 μm, the collision efficiency between dust particles and water droplets depends on the inertia of the particles. When the gas and water droplets move relative to each other, as the water droplets surround the air film, when the gas approaches the water droplets, the gas streamline will bypass the water droplets and change the flow direction. The movement trajectory changes from a straight line to a curve, and the dust with a large particle size and a high density The particles try to keep the original streamline and collide with the water droplets. The dust particles contact the water droplets and condense into large particles and are carried away by the water flow. Obviously, the more contact area with the dust-containing gas (the smaller the diameter of the water droplets) , The more water droplets), the higher the collision agglutination efficiency; the higher the dust particle density, particle size, and relative velocity, the higher the collision agglutination efficiency; the greater the viscosity of the gas, the diameter of the water droplets, and the greater the surface tension of the water, the higher the collision agglomeration effect Over the bottom; when the gas contains condensable substances (mainly moisture), because the dust-containing gas may reach below the dew point after washing, the condensed substances are condensed with dust particles as the core and covered on the surface. When dealing with high-temperature gas (especially hydrophobic dust), you can humidify the dust-containing gas or spray steam to improve purification efficiency.
1.Spray tower scrubber
In the counter-current spray tower, the dust-containing gas moves upward, and the liquid droplets are ejected downward by the nozzle. Due to the inertial collision, interception, and condensation of droplets and particles, larger particles are captured by the droplets. The spray tower has the characteristics of simple structure, small pressure loss, stable operation, etc. It is often used in combination with high-efficiency scrubbers to capture particles with larger particle sizes.
It is mainly composed of venturi tube (with shrink tube, throat tube and enlarged tube) and cyclone separator. Working principle: Dust-containing gas enters the shrink tube, and the flow rate gradually increases along the tube. Water or other liquid is sprayed from the throat, and it is atomized by the high-speed airflow. The dust particles in the gas come into contact with the droplets and are lubricated. After entering the expansion tube, the flow rate gradually decreases, and the dust particles adhere to each other, making the particles larger and easier to remove. Finally, it enters the cyclone separator. Due to the centrifugal force, water and lubricated dust particles are thrown on the inner wall of the separator and flow out of the separator downward. The cleaned gas is discharged from the central tube of the separator. Its advantages are simple structure and high dust removal efficiency. The disadvantage is that the resistance is large, and it cannot be used for the net production of gases that do not allow contact with liquids. In addition to dust removal, it also has a cooling effect.
3.Impact dust collector
The impact type water bath dust collector is used for the industrial waste gas with high humidity, large emission and large dust content, which has good purification and dust removal. It is especially suitable for purifying non-fibrous, non-corrosive, dust-containing gas at a temperature not higher than 300 ° C. Dust removal in viscous quicklime transport systems can be very effective. The flue gas coming out of the boiler enters from the inlet of the dust collector and hits the water surface at a relatively high speed. Most of the dust particles are left in the water due to the weight increase or adhesion with the water. This stage is the impact stage. At this stage After the generation, the water surface forms a parabolic region of water droplets, water mist and foam due to the movement of the gas, and the dust-containing gas is further purified by water droplets and water mist in this region. This is the shower stage. When entering the equipment, the temperature of the flue gas is very high, and water mist is formed under the impact of the flue gas in the cylinder. When the dust particles change direction and move upward, they are further purified by the water mist. This stage is atomizing and removing dust. After purification through the above three methods, clean gas enters the chimney from the outlet of the impact water bath desulfurization and dust collector.
4.Water film dust collector
Dust-containing gas is used to impact the water film on the inner wall of the dust collector or other special components, so that the dust is captured by the water film, and the gas is purified. This type of purification equipment is called water film dust collector. Including impact water film, inert (louver) water film and centrifugal water film dust collector.
含尘气体由筒体下部顺切向引入，旋转上升，尘粒受离心力作用而被分离，抛向筒体内壁，被筒体内壁流动的水膜层所吸附，随水流到底部锥体，经排尘口卸出。 The working principle of the water film dust collector is: the dust-containing gas is introduced tangentially from the lower part of the cylinder, and it rotates and rises. The dust particles are separated by the centrifugal force, thrown to the inner wall of the cylinder, and absorbed by the water film layer flowing on the inner wall of the cylinder. Follow the water to the bottom cone and unload it through the dust outlet. The water film layer is formed by several nozzles arranged on the upper part of the cylinder to spray water tangentially to the wall of the device. In this way, the inner wall of the cylinder is always covered with a very thin water film that rotates downward to achieve the purpose of improving the dust removal effect. The wet dust collector has a simple structure, small metal consumption and small water consumption. The disadvantages are that the height is large, the layout is difficult, and the phenomenon of water carry is found in actual operation.
5.Foam dust collector
含尘气体由进气口进入下部筒体，急剧翻转向上，较大的尘粒由于惯性作用，从气流中分离出来落入下部锥体。 Working principle: Dust-containing gas enters the lower cylinder from the air inlet, and it flips up sharply. Larger dust particles are separated from the air flow and fall into the lower cone due to inertia. The upward moving air flow collides with the water entering from the water inlet through the sieve plate, and some dust particles are carried away by the water. When the air flow passes through the small holes on the sieve plate, the air and water are fully contacted, a boiling foam layer is formed on the sieve plate, and most of the dust particles are washed. The purified gas is removed from the water mist through the baffle and discharged through the exhaust port. Compared with other wet dust suppression methods, foam dust suppression can reduce water consumption by 50% to 80%, and the dust suppression efficiency is 3 to 5 times higher than that of spray water spraying. Foam dust suppression has the characteristics that foam can cover the dust source without voids, and fundamentally prevent the dust from spreading outward; after the liquid forms foam, the total volume and total surface area are greatly increased, increasing the collision efficiency with dust, and purifying the underground mining surface The working environment of the foam; the liquid film of the foam contains a special additive that can quickly change the wet performance of the dust and increase the speed at which the dust is wetted; the foam has good viscosity, and the dust and foam will be quickly adhered by the foam after contact. Suppress the sparks generated by the cuttings of the roadheader and the action of coal and rock, and prevent the gas and coal dust explosion accidents caused by it. The small water consumption avoids the subsidence of the comprehensive excavator caused by the large water consumption of water mist and dust removal, which improves the work efficiency. The dust removal efficiency is high, the sight of the driver of the roadheader is greatly improved, the hidden safety hazards caused by it are eliminated, and the section quality and production efficiency are improved.
6. High temperature ceramic dust collector
For the coal-fired combined cycle power generation system (IGCC), it is very important to develop a high-temperature gas purification system that can meet the requirements of gas turbines and environmental protection. It is one of the most critical technologies for the true commercialization of coal-fired combined cycle power generation technology. One. High temperature ceramic filter is currently considered as the most promising high temperature dust removal equipment. Ceramic filters are used to filter the dust in high-temperature gas. Grit layer (particle layer dust collector) or fiber layer (bag dust collector) are used to purify the gas based on the same filtering theory.
Ceramic filter elements currently use high-density materials, ceramic filter elements are mainly produced in three types: rod, management, cross-flow. The figure below shows a cross-flow ceramic filter element. It consists of a thin, multi-void ceramic plate, which is sintered to form a ribbed whole with channels. Dust-containing gas enters the filter from the short channel end, and then enters the longer clean gas end of the channel after filtering in each channel. One end of the clean gas channel is sealed, and the clean gas flows into the clean gas collection box. Dust particles are periodically removed by a reverse pulsed airflow.
Source: Chemical 707