A filter material corona charged particle bed and filtering method thereof

Abstract

The invention discloses a filter material corona charged particle bed and a filtering method thereof. The charged particle bed comprises a particle bed shell, an air distribution device and a filter layer filled with filter material particles which are sequentially arranged in the particle bed shell from bottom to top. The particle bed shell is provided with an air inlet located above the filter layer and an air outlet located below the air distribution device. A corona discharge electrode is horizontally buried in the filter layer. A grounding electrode is horizontally placed at a position above the filter layer and below the air inlet. The corona discharge electrode is connected to the high voltage output end of a high voltage pulse switching power supply, the grounding electrode is connected to the grounding end and the ground wire of the high voltage pulse switching power supply, and the space between the corona discharge electrode and the grounding electrode forms an intermittent corona charging zone. The advantage is that the charged filter material particles are used to generate a strong electrostatic attraction to dust with an opposite charge to the charged filter material particles, thereby improving the filtering effect of electrostatic enhancement and significantly improving the filtering efficiency.

Description

Technical Field

[0001] The present invention relates to a particulate bed filtration and dust removal technology, and in particular to a corona charged particulate bed of filter media and its filtration method. Background Art

[0002] In order to improve the filtration efficiency of a particulate bed and reduce the pressure drop during filtration, a Chinese invention patent with the application number 201710754057.4 (authorized announcement number CN 107617295 B) discloses a particulate bed electrostatic enhanced filtration and dust removal device, which includes a housing and a filter media particle layer and a air distribution device arranged in the housing from top to bottom in sequence. The housing is provided with a dust-containing gas inlet and a dust-containing reverse blowing gas outlet above the filter media particle layer, and a clean gas outlet and a clean reverse blowing gas inlet below the air distribution device. A grounded metal dust collecting plate is vertically arranged in the filter media particle layer, and the metal dust collecting plate divides the filter media particle layer into multiple sub-filter media particle layers. A metal electrode rod connected to a high-voltage power supply is vertically inserted at the central position of the sub-filter media particle layer. The sub-filter media particle layer is placed in an electric field formed by the inserted metal electrode rod and the corresponding metal dust collecting plate. A grounded metal charge electrode plate is vertically arranged directly above the metal dust collecting plate, and a corona discharge electrode connected to the high-voltage power supply is vertically arranged directly above the metal electrode rod, so as to form a corona charging area in the area directly above the filter media particle layer. The working principle of this device is to charge the dust through the corona charging area, and then enhance the filtration effect under the action of the electrostatic force of the external electric field of the filter media particle layer, thereby improving the filtration efficiency. However, under high-temperature conditions, the specific resistance of the filter media will decrease, which will reduce the intensity of the external electric field of the filter media particle layer, and further reduce the electrostatic enhanced filtration effect, which is a technical problem that needs to be solved. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a corona charged particulate bed of filter media and its filtration method, which utilizes the strong electrostatic attraction generated by the charged filter media particles on the dust with the opposite polarity to them, improves the electrostatic enhanced filtration effect, and significantly improves the filtration efficiency.

[0004] The technical solution adopted by the present invention to solve the above technical problems is as follows: A corona charged particle bed of filter material includes a particle bed housing, a air distribution device and a filter layer filled with filter material particles which are sequentially arranged in the particle bed housing from bottom to top. An air inlet above the filter layer and an air outlet below the air distribution device are arranged on the particle bed housing. The air outlet is respectively connected to a clean air pipe and a backflush air pipe in series with a switching valve. It is characterized in that: A corona discharge electrode is horizontally embedded in the filter layer, and a grounding electrode is horizontally placed at a position above the filter layer and below the air inlet. The corona discharge electrode is connected to the high-voltage output terminal of a high-voltage pulse switch power supply, and the grounding electrode is connected to the grounding terminal of the high-voltage pulse switch power supply and a ground wire. A space between the corona discharge electrode and the grounding electrode forms an intermittent corona charging area.

[0005] The high-voltage pulse switching power supply selects a unipolar pulse switching power supply with a pulse frequency of 1 - 30 Hz, a pulse width of 1 - 255 ms, and an output voltage of 0 - 150 kV or 0 - -150 kV. Here, using a unipolar pulse switching power supply can provide positive or negative pulses. The pulse frequency and pulse width of the high-voltage pulse switching power supply that supplies power to the corona discharge electrode are related to the length of the energization time and the power-off time, which have a great impact on the amount of charge carried by the filter media particles, and even affect whether effective charging can occur. A shorter energization time and a longer power-off time can enable the filter media particles to be fully charged. However, if the pulse width is too large, the energization time is too long, or the power-off time is too short, the amount of charge carried by the filter media particles will be severely reduced because, in the fluidized state, some of the charged filter media particles are thrown towards the grounding electrode by the action of bubbles, adsorbed on the grounding electrode under the action of the electric field force, and leak charge to the grounding electrode. The longer the energization time, the more charge leakage occurs until the electric field force decreases to the point where it cannot overcome gravity and the particles fall back to the filter layer, thus severely reducing the amount of charge carried by the filter media particles. In addition, although the electric field formed between the corona discharge electrode and the air distribution device (containing metal parts) has a small electric field intensity due to the large distance between them, the charged filter media particles are squeezed downward by the action of this electric field force, which is sufficient to squeeze the filter layer into a dead bed, significantly increasing the air flow resistance of the filter layer, causing local perforations, and preventing normal fluidization, thus severely affecting the transmission of charge from the intermittent corona charging area to the entire filter layer. The longer the energization time and the shorter the power-off time, the more serious this situation becomes. Therefore, the energization time should be shorter and the power-off time should be longer to eliminate the dead bed and perforation problems of the filter layer, ensuring normal fluidization of the filter layer and timely transmission of charge. However, it should be noted that if the energization time is too short or the power-off time is too long, it will also lead to an increase in the required charging time. This frequency range allows for flexible adjustment in different application scenarios, being able to adapt to applications that require high-frequency pulses as well as environments with low-frequency requirements; the relatively wide pulse width adjustment range means that the pulse width can be optimized according to different filter media characteristics and filter layer conditions to achieve the best charging effect and dust removal efficiency; the high charge amount of the filter media enhances the electrostatic attraction of the filter media particles to the oppositely charged dust, significantly improving the filtration efficiency and being able to adapt to different working conditions, filter media characteristics, and handle different types of dust.

[0006] The structure of the corona discharge electrode is a slotted screen composed of fine steel wires with a diameter of 2 to 5 mm, and the spacing between adjacent fine steel wires is 10 to 150 mm; the structure of the grounding electrode is a slotted screen composed of thick steel wires with a diameter of 8 to 12 mm, and the spacing between adjacent thick steel wires is 20 to 150 mm; the spacing between the corona discharge electrode and the grounding electrode is 100 to 300 mm. Here, the corona discharge electrode and the grounding electrode adopt the design of a slotted screen, which can provide more discharge points, making the electric field distribution more uniform. This uniform electric field helps to improve the efficiency of corona discharge and the charge-carrying effect of the entire filter layer; the diameter of the fine steel wire is 2 to 5 mm, and the spacing between adjacent fine steel wires is 10 to 150 mm. This design can increase the surface area of corona discharge, thereby improving the discharge efficiency; the diameter of the thick steel wire is 8 to 12 mm, and the spacing between adjacent thick steel wires is 20 to 150 mm. This design helps to avoid abnormal discharge of the grounding electrode and enhance the stability of corona discharge of the corona discharge electrode and the charge-carrying ability of the filter media particles; the spacing between the corona discharge electrode and the grounding electrode is 100 to 300 mm, which can obtain an appropriate electric field strength, avoid breakdown of the air medium or cause unnecessary energy loss, and increase the charge amount of the filter media; the optimized design of the structures of the corona discharge electrode and the grounding electrode enables the filter media particles to be charged more uniformly, thereby increasing the charge amount of the filter media and the electrostatic attraction to the oppositely charged dust, improving the filtration efficiency, making the electrostatic enhanced filtration effect more significant, and helping to capture more dust particles, including very fine dust particles such as submicron particles, etc.; this structural design enables the corona discharge electrode and the grounding electrode to adapt to different working conditions, including different filter media properties, gas temperature and velocity.

[0007] The embedding depth of the corona discharge electrode in the filter layer is 10 to 50 mm. Here, the embedding depth refers to the thickness of the filter media particle layer above the corona discharge electrode; the embedding depth of the corona discharge electrode has a greater impact on the charge amount of the filter media particles and the required charge time. If the embedding depth is large, the additional electric field formed by the charged filter media particles will reduce the electric field strength at the corona discharge electrode, thereby reducing the charge amount of the filter media particles. However, if the embedding depth is small, it will also lead to an increase in the charge time required for the entire filter layer. The embedding depth range of 10 to 50 mm provides a certain degree of flexibility, allowing adjustment according to different working conditions and filter media characteristics to achieve the best dust removal effect; by optimizing the position of the corona discharge electrode, the filter media can be charged quickly and in large amounts, improving the electrostatic enhanced filtration effect.

[0008] The filter layer is composed of at least two upper and lower layers of filter media particle layers. The particle sizes of the filter media particles in each layer of the filter media particle layer decrease layer by layer from top to bottom, and the densities increase layer by layer from top to bottom. When backwashing and cleaning the ash, each layer of the filter media particle layer fluidizes and does not mix with each other. Here, the particle size of the upper layer of filter media particles is larger, which can initially capture large particle dust, while the particle size of the lower layer of filter media particles is smaller, which can capture finer dust, forming a stepped filtration effect and improving the overall filtration efficiency; the filter media particles with larger particle sizes usually have higher air permeability, so the upper layer of filter media particles with larger particle sizes can reduce the pressure loss when the air flow passes through; since each layer of filter media particles fluidizes and does not mix during backwashing and cleaning the ash, each layer of filter media particles can be effectively cleaned, ensuring the cleanliness of the filter media particles and the durability of the stepped filtration performance.

[0009] The filter layer is composed of an upper filter media particle layer and a lower filter media particle layer. The thickness of the upper filter media particle layer is 200 - 300 mm, the corona discharge electrode is horizontally buried in the upper filter media particle layer, and the thickness of the lower filter media particle layer is 40 - 50 mm. Here, the relatively thick upper filter media particle layer can accommodate more dust, extend the ash cleaning cycle, improve the dust holding capacity of the filter layer, and can protect the lower filter media particle layer to avoid large particle dust directly impacting the lower filter media particle layer and extending the service life of the entire filter layer; the filter media particles in the lower filter media particle layer have smaller particle sizes and larger densities, which are suitable for capturing fine dust particles, improving the filtration accuracy, and the finer and thinner lower filter media particle layer can form a more compact structure, improving the capture ability of fine dust and at the same time reducing the total pressure drop of the filter layer.

[0010] The air distribution device is composed of a pre-air distribution perforated plate, a slotted screen, and an air distribution particle layer distributed in sequence from bottom to top. The opening ratio of the pre-air distribution perforated plate is 1 - 3% (take the smaller value at high temperatures). There is a gap between the pre-air distribution perforated plate and the slotted screen. The air distribution particle layer is laid on the slotted screen, and the lowermost layer of the filter media particle layer is laid on the air distribution particle layer. Here, the opening ratio of the pre-air distribution perforated plate is 1 - 3%, and such a design helps to form a uniform air flow above the pre-air distribution perforated plate, reduce the instability of the air flow, and avoid too high or too low flow velocities in local areas. The settings of the slotted screen and the air distribution particle layer are as follows: one is to support the filter layer; the second is to further evenly distribute the air. The slots of the slotted screen can guide the air flow, and the air distribution particle layer can further disperse the air flow to ensure that the air flow passes through the filter layer evenly; the third is to prevent the leakage of fine filter media particles in the lower layer. There is a gap between the pre-air distribution perforated plate and the slotted screen, and this design can conveniently place a static pressure sensor above the pre-air distribution perforated plate (that is, between the pre-air distribution perforated plate and the slotted screen).

[0011] Static pressure sensors are respectively arranged above and below the pre-air distribution perforated plate to measure the static pressure difference above and below the pre-air distribution perforated plate when the air flow passes through, and accordingly monitor the air velocity flowing through the filter layer.

[0012] A filtering method using the filter media corona charged particle bed as described above, characterized in that: in this filtering method, a plurality of the filter media corona charged particle beds are combined in parallel to form a particle bed filter dust collector, and it is ensured that each of the filter media corona charged particle beds can perform a filtering - back - blowing fluidization dust cleaning cycle repeatedly, so as to efficiently remove dust from the dust - containing gas stream; this filtering method includes a back - blowing fluidization dust cleaning process, a filter media corona charging process, and a filtering process.

[0013] The back - blowing fluidization dust cleaning process is as follows:

[0014] When the dust deposition amount in any one of the filter media corona charged particle beds increases, and when the filtration gas velocity of this filter media corona charged particle bed is monitored by the static pressure difference obtained from two static pressure sensors and reduced to a preset gas velocity threshold, through the switching valve, this filter media corona charged particle bed is switched from the filtering state to the back - blowing fluidization dust cleaning state. The clean back - blowing air flow from the back - blowing air pipe enters from the air outlet, flows through the air distribution device and the filter layer in sequence, fluidizes the filter media particles in each layer of the filter media particle layer of the filter layer, and the dust deposited in the voids between the filter media particles is carried out of this filter media corona charged particle bed from the air inlet by the clean back - blowing air flow.

[0015] The filter media corona charging process is as follows:

[0016] When any one of the filter media corona charged particle beds finishes the back - blowing fluidization dust cleaning, then the high - voltage pulse switch power supply is turned on, and the corona discharge electrode discharges intermittently, performing intermittent corona charging on the filter media particles entering the intermittent corona charging area. At the same time, the filter media particles are mixed and collided up and down in the fluidized state, continuously entering and leaving the intermittent corona charging area, promoting the transfer of charges from the intermittent corona charging area to the entire filter layer, enabling all the filter media particles in the entire filter layer to quickly complete charging, and then the high - voltage pulse switch power supply is turned off.

[0017] The filtering stage process is as follows:

[0018] When any one of the filter media corona charged particle beds finishes the filter media corona charging, then through the switching valve, this filter media corona charged particle bed is switched from the filter media corona charging state to the filtering state. The dust - containing gas stream enters this filter media corona charged particle bed from the air inlet. The charged filter media particles in the filter layer generate a strong electrostatic attraction to the dust with the opposite polarity charge to it, significantly improving the filtering efficiency. The purified gas stream after efficient dust removal passes through the air distribution device, flows out from the air outlet, and is finally led out by the clean air pipe.

[0019] Here, a static pressure sensor is used to monitor the dust deposition amount and filtration air velocity of the filter media corona charged particle bed, triggering an automated reverse blowing fluidized ash cleaning process, which improves the timeliness and accuracy of ash cleaning; through the regular reverse blowing fluidized ash cleaning process, excessive accumulation of dust in the filter layer is prevented, maintaining the air permeability and filtration performance of the filter media particles; the effective reverse blowing fluidized ash cleaning process reduces the blockage and wear of the filter media particles, extending the service life of the filter media particles. Through electrostatic enhanced filtration, the same dust removal effect can be achieved at a higher filtration air flow velocity, thereby reducing the equipment size. The ways in which charge is transferred from the intermittent corona charging area to the entire filter layer include: 1) Intermittent corona charging in the charging area: The filter media particles continuously enter and exit the intermittent corona charging area in the fluidized state and directly receive corona charging; 2) Contact transfer charging: The filter media particles tumble up and down, and during mutual collisions, the charged filter media particles transfer charge to the uncharged filter media particles driven by the potential difference.

[0020] Compared with the prior art, the advantages of the present invention are as follows:

[0021] 1) The filter media particles have a large amount of corona charge: Firstly, by using a high-voltage pulse switching power supply, intermittent corona discharge of the corona discharge electrode is realized, with a short power-on time and a long power-off time. This method helps to reduce the contact leakage time between the charged filter media particles and the grounding electrode, reducing charge leakage, and thus increasing the charge amount of the filter media particles. In addition, intermittent corona discharge helps to eliminate the dead bed (stationary filter media particle area) and perforation (holes formed by blown-away filter media particles) problems in the filter layer caused by the DC corona electric field, ensuring that the charged filter layer can be fluidized normally, enabling charge to be effectively transmitted between the filter media particles, making the filter media particles in the entire filter layer more uniformly charged, with a faster charging speed and a larger charge amount. Secondly, the corona discharge electrode is horizontally buried in the filter layer. The corona discharge electrode divides the filter layer into two parts. The part above the corona discharge electrode is in the intermittent corona charging area. Since the filter media layer in this part is thin, it can effectively reduce the influence of the additional electric field formed by the charged filter media particles on the electric field intensity at the corona discharge electrode, effectively preventing corona blockage, and thus increasing the charge amount of the filter media. Thirdly, the horizontal placement method of the corona discharge electrode and the grounding electrode helps to optimize the uniformity and stability of the electric field, enabling the filter media particles in the filter layer to be quickly, uniformly, and fully charged in the fluidized state.

[0022] 2) The electrostatic enhanced filtration effect is large: Due to the large amount of corona charge of the filter media particles, the electrostatic attraction of the charged filter media particles to the oppositely charged dust is significantly enhanced. This enhanced electrostatic attraction is much greater than simple mechanical filtration or inertial collision filtration, and can effectively improve the dust capture ability of the electric particle bed, thereby significantly improving the filtration efficiency. Under the action of static electricity, even very fine dust particles such as submicron particles can be effectively captured, significantly improving the dust removal efficiency.

[0023] 3) Reducing the equipment size: Due to the electrostatic enhancement effect, the same dust removal effect can be achieved at a higher filtration air velocity, so that the equipment size can be reduced when processing the same air flow rate. Brief Description of the Drawings

[0024] Figure 1 It is a schematic diagram of the simple structure of the filter media corona charged particle bed of the present invention;

[0025] Figure 2 It is a curve showing the change of the charge amount per unit surface area of the filter media particles at different depths in the filter layer of the filter media corona charged particle bed of the present invention with the charging time. Detailed Description of the Invention

[0026] The present invention will be further described in detail below with reference to the embodiments in the drawings.

[0027] This embodiment provides a filter media corona charged particle bed, as Figure 1 shown, which includes a particle bed housing 1, a air distribution device 2 and a filter layer 3 filled with filter media particles arranged in the particle bed housing 1 in sequence from bottom to top. The particle bed housing 1 is the main structure of the particle bed. The air distribution device 2 is used to evenly distribute the air flow. The filter layer 3 is used to capture dust. An air inlet 4 is provided above the filter layer 3 on the particle bed housing 1, and an air outlet 5 is provided below the air distribution device 2. The air inlet 4 is used to guide the dusty air flow into or the backwash air flow out. The air outlet 5 is used to guide the purified air flow out or the clean backwash air flow in. The air outlet 5 is respectively connected to a clean air pipe (not shown in the figure) and a backwash air pipe (not shown in the figure) in series with a switching valve (not shown in the figure). A corona discharge electrode 7 is horizontally buried in the filter layer 3. The corona discharge electrode 7 is used to generate corona discharge. A grounding electrode 8 is horizontally placed at a position above the filter layer 3 and below the air inlet 4. The grounding electrode 8 is opposite to the corona discharge electrode 7 and is used to form an electric field. The corona discharge electrode 7 is connected to the high-voltage output terminal of a high-voltage pulse switch power supply 9. The grounding electrode 8 is connected to the grounding terminal and the ground wire of the high-voltage pulse switch power supply 9. The high-voltage pulse switch power supply 9 provides intermittent high voltage, causing the air around the corona discharge electrode 7 to be intermittently ionized to form charged ions and electrons. These charged particles then collide with the filter media particles to charge the filter media particles. A space between the corona discharge electrode 7 and the grounding electrode 8 forms an intermittent corona charging area 10, which can charge the filter media particles and increase the electrostatic attraction between the dust particles and the filter media particles, thereby improving the filtration efficiency.

[0028] Furthermore, the high-voltage pulse switching power supply 9 is preferably a unipolar pulse switching power supply, with a pulse frequency of 1 to 30 Hz, preferably 5 to 10 Hz, a pulse width of 1 to 255 ms, preferably 20 to 60 ms, and an output voltage of 0 to 150 kV or 0 to -150 kV, preferably 0 to 60 - 100 kV. Here, using a unipolar pulse switching power supply can provide positive or negative pulses. In specific implementation, a positive unipolar pulse switching power supply is selected. The pulse frequency and pulse width of the high-voltage pulse switching power supply 9 that supplies power to the corona discharge electrode 7 are related to the on-time and off-time lengths, and have a great impact on the amount of charge carried by the filter media particles, and even affect whether effective charging can be achieved. A shorter on-time and a longer off-time can enable the filter media particles to be fully charged. However, if the pulse width is too large, the on-time is too long, or the off-time is too short, the amount of charge carried by the filter media particles will be severely reduced. Because in the fluidized state, some of the charged filter media particles are thrown towards the grounding electrode 8 under the action of air bubbles, adsorbed on the grounding electrode 8 under the action of the electric field force, and charge leakage occurs to the grounding electrode 8. The longer the on-time, the more charge leakage, until the electric field force decreases to the point where it cannot overcome gravity and the particles fall back to the filter layer 3, thus severely reducing the amount of charge carried by the filter media particles. In addition, although the electric field formed between the corona discharge electrode 7 and the air distribution device 2 (containing metal parts) has a small electric field strength due to the large distance between them, the charged filter media particles are squeezed downward under the action of this electric field force, which is sufficient to squeeze the filter layer 3 into a dead bed. The air flow resistance of the filter layer 3 increases significantly, local perforations occur, and normal fluidization cannot be achieved, thus seriously affecting the transmission of charge from the intermittent corona charging area 10 to the entire filter layer 3. The longer the on-time and the shorter the off-time, the more serious this situation is. Therefore, the on-time should be shorter and the off-time should be longer to eliminate the dead bed and perforation problems of the filter layer 3 and ensure the normal fluidization of the filter layer 3 and the timely transmission of charge. However, it should be noted that if the on-time is too short or the off-time is too long, the required charging time will also increase. This frequency range allows for flexible adjustment in different application scenarios, and can adapt to applications that require high-frequency pulses as well as environments with low-frequency requirements; the relatively wide pulse width adjustment range means that the pulse width can be optimized according to different filter media characteristics and filter layer 3 conditions to achieve the best charging effect and dust removal efficiency; the high charge amount of the filter media enhances the electrostatic attraction of the filter media particles to the oppositely charged dust, significantly improves the filtration efficiency, and can adapt to different working conditions, filter media characteristics, and handle different types of dust.

[0029] Further defined, the structure of the corona discharge electrode 7 is a slotted screen composed of thin steel wires with a diameter of 2 - 5 mm, and the distance between adjacent thin steel wires is 10 - 150 mm, preferably 100 mm; the structure of the grounding electrode 8 is a slotted screen composed of thick steel wires with a diameter of 8 - 12 mm, and the distance between adjacent thick steel wires is 20 - 150 mm, preferably 100 mm; the distance between the corona discharge electrode 7 and the grounding electrode 8 is 100 - 300 mm. Here, the corona discharge electrode 7 and the grounding electrode 8 adopt the design of slotted screens, which can provide more discharge points, making the electric field distribution more uniform. This uniform electric field helps to improve the efficiency of corona discharge and the charge effect of the entire filter layer 3; the diameter of the thin steel wires is 2 - 5 mm, and the distance between adjacent thin steel wires is 10 - 150 mm. This design can increase the surface area of corona discharge, thus improving the discharge efficiency; the diameter of the thick steel wires is 8 - 12 mm, and the distance between adjacent thick steel wires is 20 - 150 mm. This design can avoid abnormal discharge of the grounding electrode 8, enhance the stability of corona discharge of the corona discharge electrode 7 and the charge ability for filter media particles; the distance between the corona discharge electrode 7 and the grounding electrode 8 is 100 - 300 mm, which can obtain an appropriate electric field strength, avoid breakdown of the air medium or cause unnecessary energy loss, and increase the charge amount of the filter media; the optimized structural design of the corona discharge electrode 7 and the grounding electrode 8 enables the filter media particles to be charged more evenly, thereby increasing the charge amount of the filter media and the electrostatic attraction for heteropolar charged dust, improving the filtration efficiency, making the electrostatic enhanced filtration effect more significant, and helping to capture more dust particles, including very fine dust particles such as submicron particles, etc.; this structural design enables the corona discharge electrode 7 and the grounding electrode 8 to adapt to different working conditions, including different filter media properties, gas temperature and velocity.

[0030] Further defined, the embedding depth of the corona discharge electrode 7 in the filter layer 3 is 10 - 50 mm, preferably 20 - 30 mm. Here, the embedding depth refers to the thickness of the filter media particle layer above the corona discharge electrode 7; the embedding depth of the corona discharge electrode 7 has a greater impact on the charge amount of the filter media particles and the required charging time. If the embedding depth is large, the additional electric field formed by the charged filter media particles will reduce the electric field strength at the corona discharge electrode 7, thereby reducing the charge amount of the filter media particles. However, if the embedding depth is small, it will also lead to an increase in the charging time required for the entire filter layer 3. The embedding depth range of 10 - 50 mm provides a certain degree of flexibility, allowing adjustment according to different working conditions and filter media characteristics to achieve the best dust removal effect; by optimizing the position of the corona discharge electrode 7, the filter media can be charged quickly and in large amounts, improving the electrostatic enhanced filtration effect.

[0031] Further defined, the filter layer 3 is composed of at least two upper and lower filter media particle layers. The particle sizes of the filter media particles in each layer decrease layer by layer from top to bottom, and the densities increase layer by layer from top to bottom. When backwashing and cleaning the ash, each layer of filter media particle layer fluidizes and does not mix with each other. Here, the upper layer of filter media particles has a larger particle size and can initially capture large particle dust. The lower layer of filter media particles has a smaller particle size and can capture finer dust, forming a stepped filtration effect and improving the overall filtration efficiency. The filter media particles with a larger particle size usually have higher air permeability. Therefore, the upper layer of filter media particles with a larger particle size can reduce the pressure loss when the air flow passes through. Since each layer of filter media particles fluidizes and does not mix during backwashing and cleaning the ash, each layer of filter media particles can be effectively cleaned, ensuring the cleanliness of the filter media particles and the durability of the stepped filtration performance.

[0032] Preferably, as Figure 1 shown, the filter layer 3 is composed of an upper filter media particle layer 31 and a lower filter media particle layer 32. The thickness of the upper filter media particle layer 31 is 200 - 300 mm, preferably 250 mm. The corona discharge electrode 7 is horizontally embedded in the upper filter media particle layer 31. The thickness of the lower filter media particle layer 32 is 40 - 50 mm, preferably 45 mm. The filter media particles in the upper filter media particle layer 31 are cenospheres with a diameter of 2 - 3 mm, and the filter media particles in the lower filter media particle layer 32 are emery sands with a diameter of 0.4 - 0.6 mm. Here, the thicker upper filter media particle layer 31 can accommodate more dust, extend the ash cleaning cycle, improve the dust holding capacity of the filter layer 3, and can protect the lower filter media particle layer 32 from direct impact of large particle dust, extending the service life of the entire filter layer 3. The filter media particles in the lower filter media particle layer 32 have a smaller particle size and a larger density, which are suitable for capturing fine dust particles, improving the filtration accuracy. The thinner and finer lower filter media particle layer 32 can form a more compact structure, improve the capture ability of fine dust, and at the same time reduce the total pressure drop of the filter layer 3.

[0033] Further limitation: The air distribution device 2 is composed of a pre-air distribution perforated plate 23, a slotted sieve 22, and an air distribution particle layer 21 that are distributed in sequence from bottom to top. The aperture ratio of the pre-air distribution perforated plate 23 is 1-3% (take the smaller value at high temperatures). There is a gap between the pre-air distribution perforated plate 23 and the slotted sieve 22. The air distribution particle layer 21 is laid on the slotted sieve 22, and the lowermost filter material particle layer is laid on the air distribution particle layer 21. Here, the aperture ratio of the pre-air distribution perforated plate 23 is 1-3%. Such a design helps to form a uniform air flow above the pre-air distribution perforated plate 23, reduce the instability of the air flow, and avoid too high or too low flow velocity in local areas. The settings of the slotted sieve 22 and the air distribution particle layer 21 are as follows: one is to support the filter layer 3; the second is to further evenly distribute the air. The slots of the slotted sieve 22 can guide the air flow, and the air distribution particle layer 21 can further disperse the air flow to ensure that the air flow passes through the filter layer 3 evenly; the third is to prevent the leakage of fine filter material particles in the lower layer. There is a gap between the pre-air distribution perforated plate 23 and the slotted sieve 22. This design can conveniently place the static pressure sensor 61 above the pre-air distribution perforated plate 23.

[0034] Further limitation: Static pressure sensors 61 and 62 are respectively arranged above and below the pre-air distribution perforated plate 23 to measure the static pressure difference above and below the pre-air distribution perforated plate 23 when the air flow passes through, and accordingly monitor the air velocity flowing through the filter layer 3.

[0035] This embodiment also proposes a filtering method using a corona-charged particle bed of filter material. This filtering method combines multiple corona-charged particle beds of filter material in parallel to form a particle bed filter dust collector, and ensures that each corona-charged particle bed of filter material can cycle through the filtration-backwashing fluidization dust cleaning process, so that the dust-containing air flow can be efficiently dust-removed; this filtering method includes a backwashing fluidization dust cleaning process, a corona charging process of filter material, and a filtering process.

[0036] The backwashing fluidization dust cleaning process is as follows:

[0037] When the dust deposition amount of any corona-charged particle bed of filter material increases, and the static pressure difference obtained by the two static pressure sensors 61 and 62 monitors that the filtration air velocity of this corona-charged particle bed of filter material drops to a preset air velocity threshold value (which can be set according to the situation), through the switching valve, this corona-charged particle bed of filter material is switched from the filtration state to the backwashing fluidization dust cleaning state. The clean backwashing air flow from the backwashing air pipe enters from the air outlet 5, flows through the air distribution device 2 and the filter layer 3 in sequence, fluidizes the filter material particles in each layer of the filter material particle layer of the filter layer 3, and the dust deposited in the gaps between the filter material particles is carried out of this corona-charged particle bed of filter material by the clean backwashing air flow from the air inlet 4.

[0038] The corona charging process of filter material is as follows:

[0039] After any one of the filter media corona charged particle beds completes backflush fluidization dust cleaning, the high-voltage pulse switch power supply 9 is then turned on. The corona discharge electrode 7 discharges intermittently, corona charging the filter media particles entering the intermittent corona charging area 10 intermittently. At the same time, the filter media particles are mixed and collided up and down in the fluidized state, continuously entering and leaving the intermittent corona charging area 10, promoting the transfer of charges from the intermittent corona charging area 10 to the entire filter layer 3, enabling all the filter media particles in the entire filter layer 3 to complete charging quickly, and then the high-voltage pulse switch power supply 9 is turned off;

[0040] The filtration process is as follows:

[0041] After any one of the filter media corona charged particle beds completes filter media corona charging, then through the switching valve, this filter media corona charged particle bed is switched from the filter media corona charging state to the filtration state. The dusty gas flow enters this filter media corona charged particle bed from the air inlet 4. The charged filter media particles in the filter layer 3 generate a strong electrostatic attraction to the dust with the opposite charge polarity to theirs, significantly enhancing the filtration efficiency. The purified gas flow after high-efficiency dust removal passes through the air distribution device 2 and flows out from the air outlet 5, and finally is led out by the clean gas pipe.

[0042] Here, the dust deposition amount and filtration gas velocity of the filter media corona charged particle bed are monitored by the static pressure sensor to trigger the automated backflush fluidization dust cleaning process, improving the timeliness and accuracy of dust cleaning; through the regular backflush fluidization dust cleaning process, preventing excessive accumulation of dust in the filter layer 3, maintaining the air permeability and filtration performance of the filter media particles; the effective backflush fluidization dust cleaning process reduces the blockage and wear of the filter media particles, extending the service life of the filter media particles. Through electrostatic enhanced filtration, the same dust removal effect can be achieved at a higher filtration gas flow rate, thus reducing the equipment size. The ways of charge transfer from the intermittent corona charging area 10 to the entire filter layer 3 include: 1) Charging in the intermittent corona charging area 10: The filter media particles continuously enter and leave the intermittent corona charging area 10 in the fluidized state and directly obtain corona charging; 2) Contact transfer charging: The filter media particles tumble up and down, and during the mutual collision, the charged filter media particles transfer charges to the uncharged filter media particles under the drive of the potential difference.

[0043] For a filter media corona charged particle bed of this embodiment, the pulse frequency of the positive monopolar pulse switch power supply is set to 5 Hz, the pulse width is set to 40 ms, that is, the power-on time is 40 ms and the power-off time is 160 ms, the output voltage is set to 0 - 90 kV, the distance between the corona discharge electrode 7 and the grounding electrode 8 is set to 200 mm, the thickness of the filter media particles above the corona discharge electrode 7 is set to 20 mm, that is, the buried depth of the corona discharge electrode 7 in the filter layer 3 is 20 mm, the temperature is 450 °C, and the fluidization gas velocity is 2.1u mf (u mf(which is the critical fluidization velocity of the upper filter media), the charge amount per unit surface area (μC / m) of the filter media particles at different depths (surface layer, 37.5 mm, 75 mm, 112.5 mm, 175 mm) in the filter layer 3 2 ) is as Figure 2 shown. It can be seen from Figure 2 that the charge amounts of the filter media particles at different depths in the filter layer 3 are basically the same, indicating that the filter media particles are strongly mixed in the fluidized state and the charge of the filter media particles in the filter layer 3 is uniform. It can also be seen from Figure 2 that the charge amount of the filter media particles is large, reaching 30 μC / m 2 , which is more than 10 times the charge amount of the filter media particles due to fluidization friction.

[0044] The initial filtration gas velocity is 0.45 m / s, the final filtration gas velocity is 0.25 m / s, the dust concentration in the dust-containing gas flow entering from the air inlet 4 is 10 g / m 3 , and the temperature is 450 °C. Filtration comparisons were made under two working conditions. Working condition 1: The filter media particles are positively charged and the dust is negatively charged; Working condition 2: The filter media particles are not charged and the dust is not charged. The results show that the initial outlet dust concentration of the particle bed filtration under working condition 1 is 12.5 mg / Nm 3 , and the average outlet dust concentration during the filtration cycle is 4.82 mg / Nm 3 , while the initial outlet dust concentration of the particle bed filtration under working condition 2 is 44.38 mg / Nm 3 , and the average outlet dust concentration during the filtration cycle is 13.47 mg / Nm 3 . It can be seen that the electrostatic enhanced filtration effect under working condition 1 is very obvious.

Claims

1. A filter material corona charged granular bed, comprising a granular bed shell and an air distribution device and a filter layer filled with filter material particles arranged in the granular bed shell from bottom to top, the granular bed shell is provided with an air inlet located above the filter layer and an air outlet located below the air distribution device, the air outlet is respectively connected to a clean air pipe and a back-blowing air pipe connected in series with a switching valve, characterized in that: A corona discharge electrode is horizontally buried in the filter layer, and a grounding electrode is horizontally placed at a position above the filter layer and below the air inlet. The corona discharge electrode is connected to the high-voltage output end of the high-voltage pulse switching power supply, and the grounding electrode is connected to the grounding end and the ground wire of the high-voltage pulse switching power supply. The pulse frequency of the high-voltage pulse switching power supply is 1 to 30 Hz, and the pulse width is 1 to 255 ms. The space between the corona discharge electrode and the grounding electrode forms an intermittent corona charging zone.

2. A filter material corona charged particle bed according to claim 1, characterized in that: The high-voltage pulse switching power supply is a unipolar pulse switching power supply with an output voltage of 0 to 150 kV or 0 to -150 kV.

3. A filter material corona charged particle bed according to claim 1, characterized in that: The structure of the corona discharge electrode is a slotted screen composed of thin steel wires with a diameter of 2 to 5 mm, and the spacing between adjacent thin steel wires is 10 to 150 mm; the structure of the grounding electrode is a slotted screen composed of thick steel wires with a diameter of 8 to 12 mm, and the spacing between adjacent thick steel wires is 20 to 150 mm; the spacing between the corona discharge electrode and the grounding electrode is 100 to 300 mm.

4. A filter material corona charged particle bed according to any one of claims 1 to 3, characterized in that: The corona discharge electrode is embedded in the filter layer to a depth of 10 to 50 mm.

5. A filter material corona charged particle bed according to claim 4, characterized in that: The filter layer is composed of at least two layers of filter material particles, the particle size of the filter material particles in each layer decreases layer by layer from top to bottom, and the density increases layer by layer from top to bottom. During backblowing cleaning, the filter material particles in each layer are fluidized and do not mix with each other.

6. A filter material corona charged particle bed according to claim 5, characterized in that: The filter layer consists of an upper filter material particle layer and a lower filter material particle layer, the thickness of the upper filter material particle layer is 200-300 mm, the corona discharge electrode is horizontally buried in the upper filter material particle layer, and the thickness of the lower filter material particle layer is 40-50 mm.

7. A filter material corona charged particle bed according to claim 5, characterized in that: The air distribution device consists of a pre-air distribution porous plate, a slit screen and an air distribution particle layer which are distributed in sequence from bottom to top. The opening rate of the pre-air distribution porous plate is 1-3%. There is a gap between the pre-air distribution porous plate and the slit screen. The air distribution particle layer is spread on the slit screen, and the bottom layer of the filter material particle layer is spread on the air distribution particle layer.

8. A filter material corona charged particle bed according to claim 7, characterized in that: Static pressure sensors are respectively arranged above and below the pre-air distribution porous plate.

9. A filtering method using the filter material corona charged particle bed according to claim 8, characterized in that: The filtering method combines a plurality of filter material corona charged particle beds in parallel into a particle bed filter dust collector, and ensures that each of the filter material corona charged particle beds can perform filtering-backblowing fluidized dust cleaning cycle repeatedly, so that the dust-laden airflow can be dusted efficiently; the filtering method includes backblowing fluidized dust cleaning process, filter material corona charging process and filtering process, The back-flushing fluidized dust cleaning process is as follows: As the amount of dust deposition in any filter material corona charged particle bed increases, when the static pressure difference obtained by the two static pressure sensors monitors that the filtration air velocity of this filter material corona charged particle bed is reduced to a preset air velocity threshold, the filter material corona charged particle bed is switched from the filtration state to the back-blowing fluidized cleaning state through the switching valve, and the clean back-blowing airflow from the back-blowing air pipe enters from the air outlet, flows through the air distribution device and the filter layer in turn, so that the filter material particles in each layer of the filter material particle layer of the filter layer are fluidized, and the dust deposited in the gaps between the filter material particles is carried out of the filter material corona charged particle bed from the air inlet by the clean back-blowing airflow; The filter material corona charging process is: When any filter material corona charged particle bed completes back-flushing fluidized cleaning, then the high-voltage pulse switch power supply is turned on, the corona discharge electrode performs intermittent corona discharge, and the filter material particles entering the intermittent corona charging area are intermittently corona charged. At the same time, the filter material particles are mixed and collided up and down in the fluidized state, and continuously enter and exit the intermittent corona charging area, which promotes the transfer of charge from the intermittent corona charging area to the entire filter layer, so that all the filter material particles in the entire filter layer are quickly charged, and then the high-voltage pulse switch power supply is turned off; The filtering process is: When any filter material corona charged particle bed completes the filter material corona charging, the switching valve is then used to switch the filter material corona charged particle bed from the filter material corona charged state to the filtering state, and the dust-laden airflow enters the filter material corona charged particle bed from the air inlet. The charged filter material particles in the filter layer generate a strong electrostatic attraction to the dust with the opposite charge to its polarity. The purified airflow after efficient dust removal passes through the air distribution device, flows out from the air outlet, and is finally led out by the clean air pipe.

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