Electrostatic collection device of particles in suspension in a gaseous environment

Abstract

An electrostatic collection device of particles in suspension in a gas including a collecting chamber with a collecting wall, part of which forms a collecting electrode. The collecting electrode faces a discharge electrode in the form of a wire, so as to create a corona discharge between the discharge electrode and the collecting electrode, the collecting wall extends to the periphery of the discharge electrode. The discharge electrode is maintained at a first end by a first holder and at the second end by a second holder, both holders made of electrically insulating material(s). At least one traversal wall protrudes from the collecting wall, and has a shape adapted to deflect the path of a liquid present in the gas and flowing on the collecting wall to the transversal wall such that it does not come into contact with the second holder.

Claims

1. A device for electrostatic collection of particles suspended in a gas, comprising: a collecting chamber including a collecting wall, an inlet opening at an upper end thereof, and an outlet opening at a lower end thereof, at least a part of the collecting wall being a collecting electrode; a discharge electrode disposed inside the collecting chamber, the discharge electrode being a wire extending along a central axis of the collecting chamber, the collecting electrode being disposed to face the discharge electrode, the collecting electrode and the discharge electrode being configured to create a corona discharge in a space delimited therebetween, the collecting wall extending to a periphery of the discharge electrode, the collecting wall being configured to collect, on an inner surface thereof, droplets present in the gas and carrying the particles; a first electrically insulating support disposed at the upper end of the collecting chamber and connected to a first end of the wire; a second electrically insulating support disposed at the lower end of the collecting chamber and connected to a second end of the wire, the first electrically insulating support and the second electrically insulating support being configured to maintain the wire in extension along the central axis of the collecting chamber; and at least one electrically insulating transversal wall disposed below the collecting wall toward the lower end of the collecting chamber, protruding beyond the inner surface of the collecting wall toward the discharge electrode in a direction transverse to the central axis of the collecting chamber, said transversal wall having a shape configured to deflect a flow of the collected droplets along an exterior surface of said transversal wall and to prevent direct contact between the collected droplets and the second electrically insulating support, and defining the outlet opening and a passage through which a portion of the second electrically insulating support extends away from the collecting chamber.

2. The device according to claim 1, wherein the protruding of said transversal wall is along a distance greater than a capillary length of the droplets in the gas.

3. The device according to claim 1, wherein the second electrically insulating support passes through the outlet opening and the passage, and is fixed at an outer wall away from the collecting chamber.

4. The device according to claim 1, wherein the collecting wall is cylindrical, wherein the at least one electrically insulating transversal wall includes n transversal walls angularly spaced apart by 2/n, and wherein the second electrically insulating support comprises a central support and n suspension beams fixed to the central support, also angularly spaced apart by 2/n, the suspension beams individually extending in the delimited space.

5. The device according to claim 4, wherein n is equal to three.

6. The device according to claim 4, wherein at least one suspension beam of the n suspension beams, and the support, are traversed by an electrical supply conductor of the discharge electrode.

7. The device according to claim 1, wherein an electrically insulating material of the first electrically insulating support and the second electrically insulating support is a hydrophobic material.

8. The device according to claim 1, wherein the electrically insulating material of said transversal wall is a hydrophobic material.

9. The device according to claim 6, wherein an electrically insulating material of the first electrically insulating support and the second electrically insulating support is a hydrophobic material, and wherein an assembly including the at least one suspension beam traversed by the electrical supply conductor includes an insulated high-voltage shielded cable of polytetrafluoroethylene (PTFE) or of polyvinylidene fluoride (PVDF).

10. The device according to claim 3, wherein said transversal wall includes at least one tube having an internal diameter such that a distance separating the at least one tube from the portion of the second electrically insulating support passing through the passage is greater than a capillary length of the droplets in the gas.

11. The device according to claim 1, wherein said device is an air purifier.

12. A method of electrostatic collection of particles suspended in a gas, comprising: providing a collecting chamber including a collecting wall, an inlet opening at an upper end thereof, and an outlet opening at a lower end thereof, at least a part of the collecting wall being a collecting electrode; providing a discharge electrode inside the collecting chamber, the discharge electrode being a wire extending along a central axis of the collecting chamber, the collecting electrode facing the discharge electrode, the collecting wall extending to a periphery of the discharge electrode; providing a first electrically insulating support at the upper end of the collecting chamber and connected to a first end of the wire; providing a second electrically insulating support at the lower end of the collecting chamber and connected to a second end of the wire, the first electrically insulating support and the second electrically insulating support maintaining the wire in extension along the central axis of the collecting chamber, providing at least one electrically insulating transversal wall below the collecting wall toward the lower end of the collecting chamber, said transversal wall protruding beyond the inner surface of the collecting wall toward the discharge electrode in a direction transverse to the central axis of the collecting chamber, and defining the outlet opening and a passage through which a portion of the second electrically insulating support extends away from the collecting chamber; creating a corona discharge in a space delimited between the collecting electrode and the discharge electrode; and collecting, on an inner surface of the collecting wall, droplets present in the gas and carrying the particles, wherein said transversal wall deflects a flow of the collected droplets along an exterior surface of said transversal wall and prevents direct contact between the collected droplets and the second electrically insulating support.

13. The method according to claim 12, wherein said transversal wall protrudes along a distance greater than a capillary length of the droplets in the gas.

14. The method according to claim 12, wherein the second electrically insulating support passes through the outlet opening and the passage, and is fixed at an outer wall away from the collecting chamber.

15. The method according to claim 12, wherein the collecting wall is cylindrical, wherein the providing at least one electrically insulating transversal wall further comprises providing n transversal walls angularly spaced apart by 2/n, and wherein the second electrically insulating support comprises a central support and n suspension beams fixed to the central support, also angularly spaced apart by 2/n, the suspension beams individually extending in the delimited space.

16. The method according to claim 15, wherein n is equal to three.

17. The method according to claim 15, wherein at least one suspension beam of the n suspension beams, and the support, are traversed by an electrical supply conductor of the discharge electrode.

18. The method according to claim 12, wherein an electrically insulating material of the first electrically insulating support, of the second electrically insulating support, and of said transversal wall is a hydrophobic material.

19. The method according to claim 17, wherein an electrically insulating material of the first electrically insulating support and the second electrically insulating support is a hydrophobic material, and wherein an assembly including the at least one suspension beam traversed by the electrical supply conductor includes an insulated high-voltage shielded cable of polytetrafluoroethylene (PTFE) or of polyvinylidene fluoride (PVDF).

20. The method according to claim 14, wherein said transversal wall includes at least one tube having an internal diameter such that a distance separating the at least one tube from the portion of the second electrically insulating support passing through the passage is greater than a capillary length of the droplets in the gas.

21. The device according to claim 1, further comprising an electrically insulating evacuation duct disposed below and in fluid communication with the at least one electrically insulating transversal wall and the outlet opening, the electrically insulating evacuation duct being configured to carry the gas, free of the collected droplets carrying the particles, from an interior of said transversal wall away from the collecting chamber.

22. The method according to claim 12, further comprising providing an electrically insulating evacuation duct disposed below and in fluid communication with said transversal wall and the outlet opening, wherein the electrically insulating evacuation duct carries the gas, free of the collected droplets carrying the particles, from an interior of said transversal wall away from the collecting chamber.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) Other advantages and characteristics of the invention will become clearer on reading the detailed description of the invention made with reference to the following figures, among which:

(2) FIG. 1 is a longitudinal sectional schematic view of an electrostatic collection device according to the invention;

(3) FIG. 2 is a transversal sectional schematic view of a device according to FIG. 1.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

(4) In the description that follows, the terms inlet, outlet, upstream, downstream are used with reference to the direction of suction of the air which takes place vertically from the top to the bottom. Similarly, the terms upper, lower, above, below are used with reference to the vertical physical orientation of the electrostatic collection device according to the representation of the invention in the figures.

(5) The device 1 according to the invention constitutes a device for collecting particles in suspension in a fluid containing air as gaseous phase and thus is an electrostatic precipitator for purifying the air. In such a device, a liquid, for example water or an aqueous solution, may be admitted: either in a simultaneous manner to the gas treated by the device (for example in the form of water vapour or droplets), and this is then known as a wet (injection of droplets) or semi-wet (injection of vapour) electrostatic precipitator, or following the treatment of a gas, and, in this case, along the collecting wall, in order to collect the collected particles, or prior to the treatment of a gas, and, in this case, along the collecting wall, in order to clean the device before its use.

(6) These different types of admission of liquid in the device (before treatment, during treatment, following treatment) may be cumulated.

(7) In all instances, droplets of liquid form and/or flow along the collecting wall, and, when the liquid is conductive, it is necessary to avoid said droplets accumulating and forming an electrical bridge between the two electrodes of the device, at the surface of the maintaining means.

(8) Gas is taken to mean a fluid medium comprising a gas or a gaseous mixture, knowing that said medium may also comprise solid particles as well as a liquid dispersed in the form of droplets or vapour.

(9) Treatment of a gas is taken to mean the electrostatic extraction of particles carried along by said gas and their collection by means of the collecting electrode.

(10) The device 1 firstly comprises a collecting chamber 2 with an inlet opening 20 in the upper part through which the air containing particles in suspension to be collected penetrates through suction from an outlet opening 21 in the lower part of the chamber. The collecting chamber 2 is delimited by a collecting wall 3, including a first electrode 30 called collecting electrode. When the device is in operation, said collecting electrode 30 may be earthed. As illustrated, the collecting wall 3 comprises the collecting electrode 30 over its whole height, but may also extend upstream and/or downstream of said electrode.

(11) Inside the collecting chamber 2 is arranged a second electrode 4 called discharge electrode in the form of a wire. In this example, the discharge electrode 4 extends along the axis of the collecting electrode 3. The surface of the collecting electrode 30 facing the second electrode 4 forms part of the collection surface, because it is intended to receive the particles separated by the electric field defined between the discharge electrode 4 and the annular collecting electrode 30. In this example, the collecting electrode 30 totally surrounds the discharge electrode 4, in order to obtain an optimal collection surface.

(12) The collecting electrode 30 may also only partially surround the discharge electrode 4, defining not a cylinder but a portion of cylinder.

(13) The collecting electrode 30 may also be flat, and situated facing the discharge electrode 4.

(14) The discharge electrode 4 is typically a conductive wire of diameter comprised between 10 and several hundreds of microns (m): it is adapted to create a corona discharge between itself and the collecting electrode 3 when supplied with an electric voltage comprised between several kV and several tens of kV.

(15) For example, the device represented may be an electrostatic precipitator of wet or semi-wet type in which the gas to be treated comprises vapour and/or a liquid phase, for example in the form of droplets. In these different cases, droplets are likely to form on the collecting wall. Thus, when the device is in operation, the gas containing particles in suspension, as well as the vapour and/or and the liquid employed to facilitate the capture of the particles collected, penetrates into the chamber 2 through the inlet 20 between the discharge electrode 4 and the collecting electrode 30. The particles in suspension in the air are then collected on the collecting electrode 30, by corona discharge, and the gas is evacuated, downstream of the collecting chamber, through the outlet openings 5 in communication with the outlet 21 of chamber 2 as detailed hereafter.

(16) As described previously, by addition of a liquid dispersed in the form of droplets or in vapour phase, simultaneously with the gas, droplets are collected, carrying along the extracted particles, on the collecting wall.

(17) It is also possible to inject a liquid following the treatment of the gas, in order to form droplets at the surface of the collecting wall, said droplets then carrying along the particles extracted during the treatment.

(18) On account of the absence of its own sufficient rigidity of the conductive wire constituting the discharge electrode, according to the invention it is provided to maintain it in the collecting chamber 2 on the one hand by first maintaining means 6 arranged above the inlet opening 20. Said first means 6 consist of a central support 60 made of electrically insulating material in which the upper end 40 of the wire is maintained, and of suspension beams 61 also made of electrically insulating material each fixed on the one hand to the central support 60 and on the other hand to peripheral supports 62 made of electrically insulating material itself fixed to the upper end of the collecting wall 3.

(19) Second maintaining means 7 arranged below the outlet opening 21 of the collecting chamber 2 are moreover provided. Said second means 7 consist of a central support 70 made of electrically insulating material in which the lower end 41 of the wire is maintained, and of suspension beams 71 also made of electrically insulating material each fixed on the one hand to the central support 70 and on the other hand to another peripheral wall 80 delimiting a duct 8 for evacuating the purified air as explained below. Preferably, the evacuation ducts 8 are made of electrically insulating material(s).

(20) More exactly, according to the invention, the second maintaining means 7 are designed so that the suspension beams 71 each extend inside an outlet opening 5 delimited by a wall 9 transversal to the collecting wall 3 downstream of the actual collecting chamber 2.

(21) The transversal wall 9, preferably a tube, or a portion of tube, of circular or polygonal section, has a shape adapted to deflect the path of the droplets flowing along the collecting electrode 30, carried along by gravity and by the suction effect up to said transversal wall 9 such that they cannot come directly into contact with the suspension beams 71. Said transversal wall, in the form of tube or portion of tube, protrudes from the collecting wall, along a length d greater than or equal to the capillary length of the liquid within the fluid.

(22) When the transversal wall is in tube form, it may be advantageously bevelled, such that the distance between the end of the tube and the peripheral collecting wall of the chamber 3 decreases along the direction of flow of the liquid.

(23) Preferably, the supports 60, 70 and the suspension beams 61, 71 are made of an electrically insulating material non wetting for the liquid(s) employed in the device, in other words circulating in the collecting chamber 2. In so far as the liquids employed are often aqueous solutions, the electrically insulating material is advantageously hydrophobic such as for example polytetrafluoroethylene (code PTFE) such as Teflon, or polyvinylidene fluoride (code PVDF).

(24) As shown in FIG. 2, the suspension beams are preferentially three in number spread out angularly at 120 to each other and centre the central support 70 of the discharge electrode 4 along the axis of the cylindrical collecting chamber 2. It is possible to provide to have an identical assembly at the two ends 40, 41 of the wire of the discharge electrode 4 a same number of suspension beams 61 with the same relative layout with respect to each other and with respect to the central support 60.

(25) Similarly, the transversal walls 9 are preferably made of an electrically insulating material non wetting for the liquid(s) employed in the device, in other words circulating in the collecting chamber 2. Like the maintaining means 7, the electrically insulating material constituting the transversal walls is advantageously hydrophobic such as for example polytetrafluoroethylene (code PTFE) such as Teflon, or polyvinylidene fluoride (code PVDF).

(26) When the device is in operation, the purified air or exempt of particles in suspension initially is sucked up by the outlet openings 5 delimited between tubes 9 and suspension beams 71, to the evacuation duct 8 delimited by the walls 80, 81 and connected to pumping means (ventilation) not represented. In other words, in operation the purified gas is sucked up through the openings 5 delimited by the tubes 9, which has the advantage moreover of potentially drying the suspension beams 71.

(27) In order to limit the power thereof and incidentally their level of emitted noise, care is advantageously taken so that the total surface of the outlet openings 5 is sufficiently big so as not to create too great a resistance to the flow of the air.

(28) According to an embodiment, a supply cable of the discharge electrode is integral with a second maintaining means. Thus, the second maintaining means, apart from its functions of mechanically maintaining and electrically insulating the discharge electrode, acts as support for the supply cable of the collecting electrode. Thus, according to an advantageous embodiment variant, at least one suspension beam 71 is traversed by an electrical supply conductor of the wire 4: it may thus be an insulated HT high voltage shielded cable made of PTFE or PVDF. The cable may also be arranged in the same way as the second maintaining elements, while being independent (in other words non integral) of the latter.