Method and Device for Ozone-free Separation of Components in the Corona Discharge Zone

Abstract

In a method and device for separating components in a corona discharge zone an air stream containing water molecules is passed between at least one ionizing electrode and at least one non-ionizing electrode; and high voltage is applied to the electrodes to create a corona discharge zone consisting of a plasma region wherein ozone is formed and a dark region where predominantly hydrogen peroxide is formed. The air flow entering the corona discharge zone is divided into two separate air flows, a first of which passes through the corona discharge plasma region, and a second of which passes through the dark corona discharge region; and a negative pressure gradient is applied to the plasma region only so as to remove the ozone and thereby separate the ozone from the hydrogen peroxide.

Claims

1. A method for efficient production of unipolar ions in a corona discharge zone, said method including: (a) passing an air stream containing water molecules between at least one ionizing electrode (17) and at least one non-ionizing electrode (12); (b) applying high voltage to said electrodes to create a corona discharge zone consisting of a plasma region wherein ozone is formed and a dark region where predominantly hydrogen peroxide is formed; (c) dividing the air flow entering the corona discharge zone into two separate air flows, a first of which passes through the corona discharge plasma region, and a second of which passes through the dark corona discharge region; and (d) applying a negative pressure gradient to the plasma region only so as to remove the ozone and thereby prevent escape of the ozone in the first air flow into an enclosed atmosphere; characterized by: (e) supporting the ionizing electrode (17) at the upper end of a chamber (11) whose inner wall surface serves as the non-ionizing electrode (12) with a non-ionizing part (18) of the ionizing electrode (17) in axial alignment with a hollow air-channel (25) dimensioned to cover the whole area of the plasma region (23) so that a tip of the ionizing electrode (17) protrudes out of an open lower end of the air-channel (25) into the chamber, and (f) applying a unipolar negative or positive corona discharge between the ionizing electrode (17) and the non-ionizing electrode (12).

2. The method according to claim 1, wherein the velocity of the air flowing through the plasma area of the corona discharge is higher than the ion wind velocity for the preset corona discharge current.

3. The method according to claim 1, wherein the air flow though the corona discharge area is generally parallel to the ionizing electrode axis and occurs from a tip of the ionizing electrode towards a non-ionizing part thereof.

4. The method according to claim 1, wherein the directions of the air flow in the first and the second stream coincide.

5. The method according to claim 4, wherein the chamber is circularly cylindrical and the first air stream is coaxial with a geometrical axis of the chamber.

6. The method according to claim 1, wherein preventing escape of the ozone in the first air flow into an enclosed atmosphere includes filtering the ozone.

7. The method according to claim 1, wherein preventing escape of the ozone in the first air flow into an enclosed atmosphere includes conveying the ozone out of the enclosed atmosphere.

8. The method according to claim 1, including disinfecting air in the enclosed atmosphere by releasing hydrogen peroxide formed in the dark area of the corona discharge into the enclosed atmosphere through the at least one second air outlet.

9. The method according to claim 1, including purifying air in the enclosed atmosphere by releasing ions formed in the dark area of the corona discharge into the enclosed atmosphere through the at least one second air outlet.

10. A device (10) comprising: a chamber (11) having a first end (13) and a second end (14) opposite the first end, a first outlet (16) and a second outlet (25), at least one ionizing electrode (17) supported within the second outlet (25) and having a tip, at least one non-ionizing electrode (12) inside the chamber, a high voltage generator (20) coupled to said electrodes so as to generate between the electrodes a corona discharge zone having a plasma area (23) wherein ozone is formed and a dark area (24) where predominantly hydrogen peroxide is formed, the first outlet (16) being fluidly coupled to the dark area, an air inlet (15) formed in the first end (13) of said chamber for conveying an air flow through the corona discharge zone, a suction device (26) coupled to the second outlet (25) for generating negative pressure gradient to the plasma area, and the suction device having an outlet (28) through which ozone is discharged and prevented from escaping into an enclosed atmosphere; characterized in that: the first outlet (16) and the second outlet (25) are formed in the second end (14) of the chamber, the second outlet (25) is a hollow air-channel mounted in spatial relationship with the chamber (11) and is dimensioned to cover the whole area of the plasma corona discharge area (23), the ionizing electrode (17) is supported by a non-ionizing part (18) at the upper end of the chamber in axial alignment with the hollow air-channel (25) so that its tip protrudes out of an open lower end of the air-channel (25) into the chamber, an internal wall of the chamber serves as the non-ionizing electrode (12) whereby the corona discharge zone extends from the tip of the ionizing electrode to the internal wall of the chamber, and the high voltage generator (20) is configured to apply a unipolar negative or positive corona discharge between the ionizing electrode (17) and the non-ionizing electrode (12).

11. The device according to claim 10, wherein the air flow though the corona discharge area is generally parallel to the ionizing electrode axis and occurs from a tip of the ionizing electrode (17) towards a non-ionizing part (18) thereof.

12. The device according to claim 10, where the first air outlet (16) is proximate the ionizing electrode (17) outside the corona discharge zone.

13. The device according to claim 10, wherein the first and second air outlets (16, 25) are disposed opposite to the air inlet (15).

14. The device according to claim 10, wherein the chamber (11) is cylindrical and the non-ionizing electrode is an inner wall (12) of the chamber, the ionizing electrode (17) being mounted inside the chamber coaxially with an axis of the chamber.

15. A disinfector comprising the device according to claim 10

16. A unipolar ion generator comprising the device according to claim 10.

17. An electrostatic filter comprising the device according to claim 10.

18. The device according to claim 10, wherein the outlet (28) of the suction device (26) is fluidly coupled to a filter (29) for preventing escape of the ozone into an enclosed atmosphere.

19. The device according to claims 10, wherein the outlet (28) of the suction device (26) is fluidly coupled to an exit tube or pipe for discharging the ozone external to the enclosed atmosphere.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0033] FIG. 1 is a schematic representation of a device according to the invention.

DETAILED DESCRIPTION

[0034] FIG. 1 shows schematically a disinfector 10 comprising a generally hollow cylindrical chamber 11 having an electrically conductive inner wall 12. The cylinder 11 defines least one air inlet aperture 15 at its lower end 13 and an air outlet aperture 16 at its upper end 14. An ionizing electrode 17 is supported by a non-ionizing part 18 at the upper end 14 of the chamber so that its tip protrudes inside the chamber.

[0035] A high voltage generator 20 has supply terminals 21 for connecting to a voltage source such as a main electricity supply and has high voltage output terminals 22, 22′ respectively connected to the ionizing electrode 17 and the inner wall 12 of the chamber 11, which serves as a non-ionizing electrode. The application of high voltage across the two electrodes forms a corona discharge area between them, consisting of a plasma corona discharge area 23 and a dark corona discharge area 24. A hollow air-channel 25 is mounted in spatial relationship with the chamber 11 in axial alignment with the ionizing electrode 17 and is dimensioned to cover the whole area of the plasma corona discharge area 23. It is to be understood that the figure is schematic and is intended to demonstrate the principles of the invention. The air-channel 25 may be supported in a lid (not shown) of the chamber that is attached to a rim of the chamber but which is perforated to allow the free flow of air other than the air which passes through the hollow air-channel 25. Alternatively, the chamber 11 and the hollow air-channel 25 may both be supported in proper spatial alignment within an outer structure (not shown). Also, while the device is depicted in the figure as symmetrical with the hollow chamber 11 coaxial with the longitudinal axis of the chamber 11, this is not a requirement. The only requirement is that the ionizing electrode be coaxial with the hollow air-channel 25. Likewise, although the chamber 11 is described as circularly cylindrical, its cross-section can be of any other polygonal shape.

[0036] A suction device 26 having power supply input terminals 27 is mounted on top of the air-channel 25 in fluid communication therewith and is likewise coupled via a channel 28 to a filter 29, which is typically an activated carbon (AC) filter. The suction device 26 may be a centrifugal fan or a compressor that creates a negative pressure gradient whereby air in the plasma corona discharge area 23 is drawn through the air-channel 25 into the filter 29. The magnitude of the negative pressure gradient required to remove the ozone may be determined experimentally by measuring the maximum possible concentration of ozone when the corona discharge current is at its maximum and the speed of undivided air flow is at its minimum. The maximum desired corona discharge current is selected based on the use of the device i.e. whether its primary use is to emit hydrogen peroxide and, if so, at what desired concentration; or whether the device is an electrostatic filter or ionizer. Once the maximum desired corona discharge current is established, the air flow is increased and the ozone concentration is measured. The air flow is then increased slightly and the ozone concentration is measured again. This is repeated until the ozone concentration no longer increases. Increasing the air flow beyond this value is to no further benefit and establishes the optimum air flow for the prescribed corona discharge current wherein the velocity of the air flowing through the plasma area of the corona discharge is higher than the ion wind velocity for the preset corona discharge current.

[0037] Operation of the disinfector 10 is as follows:

[0038] As voltage is applied to the terminals 21 of the high voltage source 20, a corona discharge area is generated between the ionizing electrode 17 and the non-ionizing electrode constituted by the inner wall 12 of the chamber 11. Plasma corona discharge 23 is generated close to the tip of the ionizing electrode 17, while the remaining volume of the corona discharge constitutes the dark corona discharge area 24. At the same time, power is applied to the supply terminals 27 of the suction device 26, thus generating a negative pressure gradient in the air-channel 25, which draws ozone formed in the plasma corona discharge area 24 through the channel 28 to the filter 29 where it is neutralized. Ozone-free air now exits from the ozone filter and reaches the air to be disinfected.

[0039] In the air flowing through the dark area of the corona discharge 24 some of the water molecules are converted to hydrogen peroxide molecules due to the interaction with ions in the corona discharge electric field and also reach the environment with the air flowing via the outlet aperture 16 in the lid 14 as shown by arrows A.

[0040] As a result, the ozone is separated from most of the hydrogen peroxide, of which a small amount will also pass through the air channels 25 and 28 and will be neutralized by the filter 29. However, the majority of the hydrogen peroxide passes through the outlet aperture 16 into the atmosphere, which is therefore disinfected, while ozone-free air passes into the atmosphere from the filter outlet. Since the ozone is prevented by the filter from escaping into an enclosed atmosphere, the corona discharge current can be safely increased to a level which generates a much higher quantity of hydrogen peroxide as evidenced by Table 1 below showing the technical specification of a disinfector manufactured and tested according to the invention.

[0041] The filter 29 in effect neutralizes the ozone in order that the concentration of ozone released into an enclosed atmosphere in which the device is deployed will be below the permitted maximum. However, the same objective can be achieved without the filter by conveying the ozone out of the enclosed atmosphere through an exit tube or pipe that may simply be envisaged as an extension of the channel 28.

TABLE-US-00001 TABLE 1 1 Diameter of the inlet hole of air channel 11  8 mm 2 Distance between the tip of electrode 17 and  3 mm the inlet aperture of the air-channel 25 3 Air-flow velocity in channel 25 8 m/sec 4 Diameter of the non-ionizing electrode (i.e. wall 12) 40 mm 5 Corona discharge type Negative 6 Corona discharge current 10.sup.−2 mA 7 The tested room volume 7 m.sup.3 8 H.sub.2O.sub.2 concentration 15 ppb 9 O.sub.3 concentration  5 ppb

[0042] The following devices were used to measure the H.sub.2O.sub.2 and O.sub.3 concentration: [0043] a) For H.sub.2O.sub.2 concentration: Portable gas detector OC-905 [0044] Resolution —0.01 ppm, precision ± 3%

[0045] For O.sub.3 concentration: [0046] Ozone analyzer Dasibi Model 1008. [0047] Resolution —1 ppb, precision ± 2%.

[0048] Although the invention has been described with particular reference to a disinfection device and method, it will be appreciated that the principles of the invention are equally applicable for other devices based on corona discharge where the maximum permissible concentration of ozone limits the efficiency. Thus, the same principles may also be applied to electrostatic filters and ionizers.

[0049] It should also be noted that while the ozone filter has been described with regard to an active carbon filter, the term “filter” is to be construed in its broadest sense as a device that separates the ozone from the air and prevents it from escaping into the atmosphere. Whether the ozone is merely trapped or destroyed is not crucial to the invention, because once its passage into the atmosphere is prevented the corona discharge current can safely be increased. Other approaches to preventing the ozone from escaping into the atmosphere include chemical oxidation where the ozone is passed through a titanium reaction chamber. It is also known to use catalytic processes involving reactions with chlorine, bromine, nitrogen, hydrogen, and oxygen gases or a destruction catalyst such as a mixture of copper and manganese dioxides.