There are many forms and types of bag filter, which can be divided into three types according to cleaning methods: mechanical cleaning, reverse airflow cleaning and pulse jet cleaning. According to the filtration mode, it can be divided into two types: internal filtration and external filtration; According to the different positions of import and export, it can be divided into downward suction type and upward suction type.
1, bag filter
Reverse airflow cleaning is to use outdoor or circulating air to pass through the filter bag in the form of reverse airflow opposite to the dusty airflow, so that the dust layer on it falls off and falls into the ash hopper.
In this dust cleaning method, on the one hand, the dust layer is directly peeled off due to the viscous peeling force formed on the dust layer by the dust cleaning airflow in the opposite direction; On the other hand, due to the change of airflow direction, the filter bag produces expansion and contraction vibration, which also helps the dust to fall off.
▲ Bag filter with reverse airflow blowing for dust removal.
2. Pulse soot blowing and ash cleaning method
After the compressed air is ejected at a high speed through the injection port, the surrounding air is induced to inject into the filter bag in a short time, which makes the filter bag expand and contract rapidly.
On the one hand, the stripping of dust layer depends on the stripping force of air blowing, and on the other hand, the dust is thrown out by the reverse acceleration formed when the telescopic filter bag retracts. This method has high dust removal intensity, which can be used for dust removal under filtration working condition, and the allowable filtration wind speed is also high.
Pulse jet cleaning method has gradually become the main cleaning method of bag filter because of its many advantages.
▲ Use pulse jet bag filter for ash cleaning.
3, mechanical ash cleaning type
This cleaning method can include artificial vibration, mechanical vibration, etc. , and it is the simplest method of cleaning ash.
Generally speaking, the vibration distribution of mechanical vibration filter bag along the axial direction is uneven, the acceleration decays quickly, the filter bag length is generally short, and the filtering wind speed is also small. Mechanical vibration bag filter uses mechanical motion device to make the filter bag vibrate periodically, so that the dust particles attached to the filter bag fall into the ash hopper.
▲ Mechanical dust removal bag filter
According to the different vibration modes, it can be divided into three forms: horizontal vibration, vertical vibration and torsional vibration, as shown in the following figure.
▲ Three vibration modes
(a) Horizontal vibration, including top and middle vibration;
(b) When vibrating vertically, the eccentric wheel device is used to vibrate the filter bag frame or periodically lift the filter bag frame for dust removal;
(c) In order to twist the vibration, it uses mechanical transmission device to periodically twist the filter bag by a certain angle, so that dust particles fall off.
4. Internal and external filter types
The dusty airflow with built-in filter first enters the interior of the filter bag and is filtered from the inside out, and dust is deposited on the surface of the filter bag. The outer side of the inner filter bag is the clean air side, which is convenient for inspection and bag change. Internal filter is generally suitable for bag dust collector with mechanical dust removal and reverse airflow dust removal.
The dusty airflow of the external filter dust collector is counted into the filter bag from the outside of the filter bag through the filter material and discharged after purification. In order to facilitate filtration, a supporting skeleton (bag cage) should be set inside the filter bag. The external filter type is suitable for pulse jet bag filter, high-pressure airflow back-blowing bag filter, flat bag filter, etc.
▲ Internal and external filter bag filter
5. Upwind and downwind patterns
Downward air intake: dusty airflow enters the interior of the dust collector from the lower ash hopper of the dust collector.
Updraft: the dusty airflow enters the interior of the dust collector from the upper ash hopper of the dust collector.
▲ Upper (lower) air inlet bag filter
Second, the electrostatic precipitator
When the gas containing dust particles passes through the high-voltage electric field formed between the cathode wire (also called corona electrode) connected to the high-voltage DC power supply and the grounded anode plate, the gas is ionized at the cathode due to corona discharge.
At this time, under the action of electric field force, the negatively charged gas ions move towards the anode plate, and when they collide with dust particles during the movement, the dust particles are negatively charged, and the charged dust particles also move towards the anode under the action of electric field force, and when they reach the anode, they release the carried electrons, and the dust particles are deposited on the anode plate, and the purified gas is discharged from the dust collector.
▲ Corona electrode characteristics
▲ Schematic diagram of dust removal process of electrostatic precipitator
1, classified according to the form of dust collector, and divided into tube electrostatic precipitator and plate electrostatic precipitator according to the form of dust collector.
(1) tubular electrostatic precipitator
The electrode of this electrostatic precipitator consists of one or a group of circular, hexagonal or square tubes, with a diameter of 200-300mm and a length of 3-5m. Corona wires with circular or star-shaped cross sections are installed in the center of the pipe, and dusty gas passes through the pipe from top to bottom.
▲ Principle of single-tube electrostatic precipitator
▲ Single tube electrostatic precipitator
(2) Plate electrostatic precipitator
The dust collecting plate of this electrostatic precipitator is composed of several flat plates. In order to reduce the secondary flying of dust and enhance the rigidity of the plates, the plates are generally tied into various cross-sectional shapes, and corona electrodes are installed in the middle of the channels formed by each row of dust collection plates.
▲ Plate electrostatic precipitator
2. Classification according to different configurations of dust removal plate and corona electrode.
According to the different configuration of dust removal plate and corona electrode, it can be divided into single-zone electrostatic precipitator and double-zone electrostatic precipitator.
(1) single-zone electrostatic precipitator
The dust collecting plate and corona electrode of this electrostatic precipitator are installed in the same area, so the charging and collecting of dust are in the same area, so the charging and collecting of dust are completed in the same area. Single-zone electrostatic precipitator is a widely used electrostatic precipitator.
▲ Plate single-zone electrostatic precipitator
(2) Double-zone electrostatic precipitator
The dust removal system and corona system of the electrostatic precipitator are installed in two different areas respectively.
Corona electrode and anode plate are installed in the front end area, where dust is charged. This area is the ionization area, and the dust collecting electrode and cathode plate are installed in the back area, and dust is collected in this area, which is called the dust collecting area. Because the ionization zone and the dust collection zone are separated, it is called a double-zone dust collector.
▲ Plate double-zone electrostatic precipitator
▲ Single-tube double-zone electrostatic precipitator
3. According to the different classification of electrode cleaning methods
According to different electrode cleaning methods, it can be divided into dry electrostatic precipitation, wet electrostatic precipitation, mist particle trap and semi-wesp.
( 1) wesp
Spray water on the dust collected by the vacuum cleaner or form a layer of water film on the surface of the vacuum cleaner in an appropriate way, so that the dust and water deposited on the vacuum cleaner can flow to the lower part of the vacuum cleaner and be discharged. The electrostatic precipitator using this dust cleaning method is called wesp.
▲ Schematic diagram of wet electrostatic dust removal process
(2) Dry electrostatic precipitator
A dust collector that captures the dust in the flue gas in a dry state and removes the dust deposited on the dust removal plate through mechanical vibration is called a dry electrostatic precipitator.
(3) Electric mist particle catcher
This electrostatic precipitator collects droplets such as sulfuric acid fog and tar fog, and then flows down in liquid state to be removed. It also belongs to wesp.
(4) Semi-wesp
Absorbing the advantages of dry and wet electrostatic precipitator, dry-wet hybrid electrostatic precipitator appeared, also known as semi-wet electrostatic precipitator. The high temperature flue gas first passes through the dry dust removal chamber, then through the wet dust removal chamber, and then is discharged through the chimney.
The washing water in the wet dust removal room can be recycled, and the discharged mud is sent to the dryer by the mud pump through the concentration pool for drying, and the dried dust enters the ash hopper of the dry dust removal room and is discharged.
4. Classification according to the moving direction of gas in electrostatic precipitator.
According to the moving direction of gas in electrostatic precipitator, it can be divided into vertical electrostatic precipitator and horizontal electrostatic precipitator.
(1) vertical electrostatic precipitator
Gas moves vertically from bottom to top in electrostatic precipitator, which is called vertical electrostatic precipitator. This electrostatic precipitator is suitable for occasions with small gas flow, low dust removal efficiency, easy dust removal and narrow installation site.
(2) Horizontal electrostatic precipitator
The gas moving in the horizontal direction in electrostatic precipitator is called horizontal electrostatic precipitator.
Third, the mechanical dust collector
1, gravity settling chamber
The principle of gravity dust collector is to suddenly reduce the airflow speed and change the flow direction. Under the action of gravity and inertia force, the dust with larger particles is separated from the gas and settled at the bottom of the cone of the dust collector, which belongs to coarse dust removal.
The process of gravity settling dust is that flue gas enters gravity settling equipment from horizontal direction. Under the action of gravity, the dust particles gradually settle, while the gas continues to move forward in the horizontal direction, thus achieving the purpose of dust removal.
Gravity settling chamber can be divided into single-layer gravity settling chamber and double-layer gravity settling chamber.
▲ Single-layer gravity settling chamber
▲ Multi-layer gravity settling chamber
2. Cyclone separator
The dusty airflow enters the cylinder from the intake pipe and spirals downward along the inner wall. Dust is thrown to the wall of the device under the action of centrifugal force, falls into the ash hopper under the action of gravity, and the purified gas is discharged from the central pipe.
▲ Cyclone separator
There are many kinds of cyclone separators with different classifications. According to the structural type, it can be divided into long cone type, cylindrical type, diffusion type and bypass type. According to its combination and installation mode, it can be divided into internal cyclone separators (installed in reactors or other equipment), external cyclone separators, vertical and horizontal cyclone separators, and single-tube and multi-tube cyclone separators.
According to airflow guidance, it can be divided into tangential guidance or axial guidance; After the airflow enters the cyclone separator, there are different forms such as countercurrent, downstream and secondary air.
▲ Axial inlet cyclone separator-direct inlet cyclone separator
▲ Axial inlet cyclone separator-reverse type
▲ tangential inlet cyclone separator
According to its performance, it is divided into:
(1) high-efficiency cyclone separator, with small cylinder diameter, is used to separate fine dust, and the efficiency is over 95%.
(2) Large-flow cyclone separator with large cylinder diameter is used to treat large-flow gas, and the dust removal efficiency is 50% ~ 80%.
(3) The general cyclone separator between the above two is used to treat moderate airflow, and its dust removal efficiency is 80% ~ 95%.
Four, wet dust collector
The basic principle of all wet dust collectors is to make liquid droplets contact/combine with relatively small dust particles to produce larger particles, which is convenient for collection. In this process, dust particles grow into large particles in several ways.
These methods include combining dust particles with larger droplets, and the dust particles absorb water to increase their mass (or density), or forming and increasing condensable particles at a lower temperature in a dust collector.
According to its structure, there are the following types:
1, gravity spray wet dust collector
Gravity spray wet dust collector, such as spray washing tower.
▲ spray scrubber
2. Cyclone wet dust collector
Cyclone wet dust collector, such as cyclone water film dust collector and water film dust collector.
▲ Vertical cyclone water film dust collector
▲ Horizontal cyclone water film dust collector
3. Self-excited wet dust collector
Self-excited wet dust collectors, such as pulse dust collectors and water bath dust collectors.
▲ Self-excited wet dust collector
4, packaging wet dust collector
Packed wet dust collector, such as packed tower and turbulent ball tower.
▲ packed tower
▲ Turbulent ball tower
5, foam wet dust collector
Foam wet dust collector, such as foam dust collector and cyclone dust collector.
▲ Foam scrubber
6, Venturi wet dust collector
Venturi wet dust collector, such as Venturi dust collector.
▲ Venturi scrubber