Ozone generator

Abstract

An ozone generator (1) is presented comprising a body (2), a first electrode (4), a second electrode (6), an elongate channel within the body extending between the first and second electrodes, an inlet (10) and an outlet (12); the elongate channel being in fluid communication with the inlet and the outlet; the elongate channel isolated from each of the first and second electrodes by a respective dielectric layer (22, 24), whereby an electric field can be generated across the elongate channel between the first and second electrodes. The presented ozone generator allows small quantities of ozone to be produced for use in small scale water treatment. In addition, a method of producing ozone is presented using an ozone generator according to the invention.

Claims

1. An ozone generator comprising: a body; a first electrode; a second electrode; a third electrode, wherein the second electrode is located between the first electrode and the third electrode; an elongate channel within the body, a first portion of the elongate channel extending in a first direction between the first and second electrodes, a second portion of the elongate channel in fluid communication with the first portion of the elongate channel and extending in a second direction opposite the first direction and between the second and third electrodes, and a third portion of the elongate channel coupling the first portion of the elongate channel to the second portion of the elongate channel, the third portion of the elongate channel positioned between the first electrode and the third electrode and extending beyond the second electrode about an axis parallel to a width of the elongate channel in a third direction that is normal to the first direction and the second direction; and an inlet and an outlet, wherein the elongate channel is in fluid communication with the inlet and the outlet, wherein the elongate channel is isolated from either or both of the first and second electrodes by at least one dielectric layer such that a voltage when applied across the first electrode and the second electrode generates periodic electrical discharges across the first and second electrodes through the first portion of the elongate channel, wherein the elongate channel is isolated from either or both of the second and third electrodes by at least one additional dielectric layer such that the voltage when applied across the second electrode and the third electrode generates periodic electrical discharges across the second and the third electrodes through the second portion of the elongate channel, and wherein the first portion of the elongate channel extending between the first and second electrodes is configured to direct a gas along the elongate channel between the first and second electrodes in the first direction, and the second portion of the elongate channel extending between the second and third electrodes is configured to receive the gas after the gas passes through the first portion and the third portion of the elongate channel and to direct the gas along the elongate channel between the second and third electrodes in the second direction.

2. An ozone generator according to claim 1, wherein the elongate channel is isolated from each of the first and second electrodes by a respective dielectric layer.

3. An ozone generator according to claim 1, wherein the first and second and third electrodes are planar.

4. An ozone generator according to claim 1, wherein the elongate channel has an aspect ratio (a length dimension to the width dimension) of 2 to 1.

5. An ozone generator according to claim 1, wherein the elongate channel has a generally rectangular cross section throughout the first portion, the second portion and the third portion of the elongate channel.

6. An ozone generator according to claim 5, wherein the depth dimension of the first portion, the second portion and the third portion of the elongate channel is in a range from 0.6 to 4 millimeters and the width dimension is greater than the depth dimension.

7. An ozone generator according to claim 1, wherein the elongate channel comprises at least one linear portion extending between the first and second electrodes or between the second and third electrodes configured to provide a fluid flow through the elongate channel having a Reynolds number in a range from 5,000 to 15,000.

8. An ozone generator according to claim 1, wherein a gas pathway configured to direct the gas along the elongate channel is free of obstructions, the gas pathway comprising a rectangular shape in cross-section throughout the entirety of the first potion, the second portion, and the third portion of the elongate channel.

9. An ozone generator according to claim 1, wherein at least one of first portion and the second portion of the elongate channel has a length dimension in a range for 1.5 to 15 centimeters, the width dimension of 12 millimeters and the depth dimension of 0.6 millimeters.

10. An ozone generator according to claim 1, wherein the body is generally planar having the entirety of the first portion, the second portion, and the third portion of the elongate channel extending within the body and between a top surface and a bottom surface of the body.

11. An ozone generator according to claim 10, wherein the ozone generator is formed of a flexible material comprising polycarbonate and configured to be rolled up to form a spiral or a cylinder.

12. An ozone generator according to claim 1, wherein a first end of the first electrode and a first end of the third electrode extend beyond a first end of the body of the ozone generator, and a first end of the second electrode extends beyond a second end of the body of the ozone generator opposite the first end of the body, wherein the inlet extends from a first planar surface at a top of the body to a first end of the first portion of the elongate channel and adjacent to a second end of the first electrode, and the outlet extends from a second planar surface at a bottom of the body to a second end of the second portion of the elongate channel and adjacent to a second end of the third electrode, and wherein the third portion of the elongate channel is coupled to a second end of the first portion of the elongate channel and to a first end of the second portion of the elongate channel, the third portion of the elongate channel positioned adjacent to a second end of the third electrode.

13. An ozone generator according to claim 1, wherein the body of the ozone generator, the at least one dielectric layer, and the at least one additional dielectric layer are formed of a material comprising a flexible polycarbonate.

14. An ozone generator according to claim 1, wherein the ozone generator is configured to generate ozone at a rate of 39 grams/nanometer.sup.3 at the outlet when an oxygen gas flowing at no more than 1 liter/minute and having a pressure of no more than 220 millibars is received at the inlet.

15. An ozone generator according to claim 1, wherein the ozone generator is configured to utilize no more than 3.5 watts of power per gram of ozone produced.

16. A stack of ozone generators comprising: a plurality of ozone generators, each of the ozone generators comprising: a body; a first electrode; a second electrode; a third electrode, wherein the second electrode is located between the first electrode and the third electrode; an elongate channel within the body, a first portion of the elongate channel extending in a first direction between the first and second electrodes, a second portion of the elongate channel in fluid communication with the first portion of the elongate channel and extending in a second direction opposite the first direction and between the second and third electrodes, and a third portion of the elongate channel coupling the first portion of the elongate channel to the second portion of the elongate channel, the third portion of the elongate channel positioned between the first electrode and the third electrode and extending beyond the second electrode about an axis parallel to a width of the elongate channel in a third direction that is normal to the first direction and the second direction; and an inlet and an outlet, wherein the elongate channel is in fluid communication with the inlet and the outlet, wherein the elongate channel is isolated from either or both of the first and second electrodes by at least one dielectric layer such that a voltage when applied across the first electrode and the second electrode generates periodic electrical discharges across the first and second electrodes through the first portion of the elongate channel, wherein the elongate channel is isolated from either or both of the second and third electrodes by at least one additional dielectric layer such that the voltage when applied across the second electrode and the third electrode generates periodic electrical discharges across the second and the third electrodes through the second portion of the elongate channel, and wherein the first portion of the elongate channel extending between the first and second electrodes is configured to direct a gas along the elongate channel between the first and second electrodes in the first direction, and the second portion of the elongate channel extending between the second and third electrodes is configured to receive the gas after the gas passes through the first portion and the third portion of the elongate channel to direct the gas along the elongate channel between the second and third electrodes in the second direction.

17. A method of producing ozone for use in sterilization comprising the steps of: providing an ozone generator comprising a body, a first electrode, a second electrode, a third electrode, wherein the second electrode is located between the first electrode and the third electrode, an elongate channel within the body, a first portion of the elongate channel extending in a first direction between the first and second electrodes, a second portion of the elongate channel in fluid communication with the first portion of the elongate channel and extending in a second direction opposite the first direction and between the second and third electrodes, and a third portion of the elongate channel coupling the first portion of the elongate channel to the second portion of the elongate channel, the third portion of the elongate channel positioned between the first electrode and the third electrode and extending beyond the second electrode about an axis parallel to a width of the elongate channel in a third direction that is normal to the first direction and the second direction, and an inlet and an outlet, wherein the elongate channel is in fluid communication with the inlet and the outlet, wherein the elongate channel is isolated from either or both of the first and second electrodes by at least one dielectric layer such that a voltage when applied across the first electrode and the second electrode generates periodic electrical discharges across the first and second electrodes through the first portion of the elongate channel, wherein the elongate channel is isolated from either or both of the second and third electrodes by at least one additional dielectric layer such that the voltage when applied across the second electrode and the third electrode generates periodic electrical discharges across the second and the third electrodes through the second portion of the elongate channel, wherein the first portion of the elongate channel extending between the first and second electrodes is configured to direct a gas along the elongate channel between the first and second electrodes in the first direction, and the second portion of the elongate channel extending between the second and third electrodes is configured to receive the gas after the gas passes through the first portion and the third portion of the elongate channel and to direct the gas along the elongate channel between the second and third electrodes in the second direction; introducing an oxygen containing gas into the inlet of the ozone generator such that the oxygen containing gas flows from the inlet to the outlet via the elongate channel; applying an electric field across the elongate channel sufficient to initiate the periodic electrical discharges across the elongate channel; wherein the periodic electrical discharges across the elongate channel interact with the oxygen within the oxygen containing gas such that ozone is produced; and at least some of the produced ozone flows out of the outlet.

18. A method according to claim 17, wherein the oxygen containing gas is at least 90% oxygen.

19. A method according to claim 17, wherein the oxygen containing gas is introduced into the inlet at a pressure of less than 1 bar.

20. A method according to claim 19, wherein the oxygen containing gas is introduced into the inlet at a pressure of less than 0.1 bar.

21. A method according to claim 17, wherein the periodic electrical discharges across the elongate channel are produced when the charge applied across the elongate channel between the electrodes is defined by the following equation: $\stackrel{\_}{Q}=k\frac{d}{}$ where Q is the average charge transferred per microdischarge, k is proportional to the relative permittivity of the dielectric of the at least one dielectric layers, d is the depth of the elongate channel and is the total thickness of the at least one dielectric layer.

22. A method according to claim 17, wherein the voltage is applied as a repeating asymmetric waveform.

23. A method according to claim 22, wherein the asymmetric waveform has a primary peak and one or more secondary peaks subsequent to the primary peak.

Description

DESCRIPTION OF THE DRAWINGS

(1) An example embodiment of the present invention will now be illustrated with reference to the following Figures in which:

(2) FIG. 1 is a schematic side view of an ozone generator;

(3) FIG. 2 is a perspective view of an ozone generator from the side;

(4) FIG. 3 is a schematic side view of an alternative ozone generator;

(5) FIG. 4 is a schematic side view of an ozone generator comprising a stack of channels;

(6) FIG. 5 is a perspective view of an array of ozone generators;

(7) FIG. 6 is a schematic side view of an ozone generator;

(8) FIG. 7 is a perspective view of the channel of an ozone generator;

(9) FIG. 8 is a plot of ozone produced as a function of time at a fixed pressure of 200 mbar;

(10) FIG. 9 is a plot of ozone produced as a function of flow rate for a 15 cm elongate channel;

(11) FIG. 10 is a plot of ozone produced as a function of flow rate for a 7 cm elongate channel compared to that for a 15 cm elongate channel;

(12) FIG. 11 is a plot of voltage applied across the elongate channel (square waveform) and the measured current across the said channel;

(13) FIG. 12 a plot of voltage applied across the elongate channel and the measured current across the said channel; and

(14) FIG. 13 is a plot of voltage applied across the elongate channel and the measured current across the said channel.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

EXAMPLE 1

(15) With reference to FIGS. 1 to 3, an ozone generator 1 comprises a body 2, the body having a first electrode 4, a second electrode 6, a channel 8 (acting as an elongate channel), an inlet 10 and an outlet 12. The first electrode is arranged above the second electrode. The channel extends between the first and second electrodes and has a first end 14 and a second end 16, the first end in fluid communication with the inlet and the second end in fluid communication with the outlet.

(16) The body of the ozone generator has a top surface 18 (acting as a first surface) and a bottom surface 20 (acting as a second surface). The inlet extends from the top surface of the body to the first end of the channel, and the outlet extends from the second end of the channel to the second surface.

(17) A first polycarbonate sheet 22 and a second polycarbonate sheet 24 (both acting as a dielectric layer) isolate the channel from the first and second electrodes respectively. That is, the first polycarbonate sheet isolates the channel from the first electrode and the second polycarbonate sheet isolates the channel from the second electrode.

(18) During use, oxygen (acting as an oxygen containing gas) is introduced into the inlet and allowed to flow from the inlet to the outlet via the channel. An electric field is applied across the channel between the first and second electrodes. The voltage applied across the gap between the first and second electrodes must be greater than the breakdown voltage of the system. The breakdown voltage is proportional to the distance between the first and second electrodes.

(19) For example, for a system having a channel depth, d, of 1 mm under standard conditions, the approximate resulting breakdown voltage, V.sub.B, would be:
V.sub.B4.510.sup.6d=4.5kV

(20) Therefore, an applied voltage of greater than 4.5 kV is required to create discharges across the channel.

(21) In addition, the linear nature of the above equation (i.e. V.sub.Bd) means that for an ozone generator with a larger gap to produce higher volumes of ozone, a proportionately larger voltage must be applied.

(22) The average charge transferred per discharge across the gap is proportional to the relative permittivity of the dielectric layer, the total thickness of dielectric between the two electrodes and the thickness of the gap.

(23) Whilst the voltage is applied across the channel, periodic electric discharges occur across the channel with a power density following the following equation;

(24) $W1.8{10}^2\frac{f{\mathrm{.Math.}}_r{d}^2}{}$
where f is the frequency of the power supply, .sub.r is the relative permittivity of the dielectric layer and is the total depth of the or both dielectric layers. Therefore, for a system applying an alternating voltage with a frequency of 17 kHz, comprising polycarbonate (.sub.r=2.9) dielectric layers of total thickness, , 2 mm and a channel depth of 1 mm, the power density of the device is approximately 4.4 kW m.sup.2.

(25) Molecules within the volume of the period electrical discharge interact with the electrons within the volume of the electrical discharge, being either ionised (loss of electrons from the molecules) or split (chemical bonds are broken). For example, diatomic oxygen may be ionised to form O.sub.2.sup.+, for example, or it may be split into two oxygen atoms, 2{dot over (O)}.
e.sup.+O.sub.2.fwdarw.2{dot over (O)}+e.sup.

(26) Oxygen atoms may recombine to reform diatomic oxygen or may react with diatomic oxygen, in the presence of a third collision partner, M, to form ozone, O.sub.3. The collision partner is required to absorb some of the energy released by the formation of the new chemical bond to prevent spontaneous decomposition.
2{dot over (O)}.fwdarw.O.sub.2
{dot over (O)}+O.sub.2+M.fwdarw.O.sub.3

(27) Once formed, ozone continues to flow along the channel and exits the ozone generator via the outlet, where it may enter a water supply to react with impurities within the water, for example.

(28) Due to the low pressure the oxygen gas is introduced into the inlet of the ozone generator, the number of collisions experienced by any particular molecule within the oxygen gas is lower than would be the case at higher pressures. Therefore, as chemical reactions can only occur when two or more species are close enough for the interaction of electrons between the species, a higher proportion of the ozone produced within the channel will reach the outlet of the ozone generator than would be the case at higher pressure.

(29) The device of the above embodiment produces ozone efficiently. For example, a device having a channel 15 cm long, 12 mm wide and 0.6 mm deep produced 54 gm.sup.3 ozone flowing at a rate of 0.6 to 0.7 Lmin.sup.1. A 5 kV potential difference was applied across the depth of the channel at a frequency of 17 kHz. Similar results have been obtained for devices having the same width and depth but with a channel 7.5 cm long and a channel 1.5 cm long.

(30) In an alternative embodiment the inlet 26 and outlet 28 are linear extensions of the channel such that the oxygen gas is introduced into the inlet on one side face 30 of the body and exits the outlet on the opposed side face 32 of the body.

(31) With reference to FIG. 4, in an alternative embodiment, the ozone generator comprises a stack of electrodes and elongate channels 34, such that each elongate channel (for example, 36) extends between two electrodes adjacent within the stack (for example, 38 and 40).

(32) With reference to FIG. 5, in an alternative embodiment, the ozone generator comprises an array of bodies 42 arranged in parallel, each body having a channel 44 extending between a separate first electrode 46 and second electrode 48.

(33) Typical ozone generators comprising heavy duty blocks of aluminium (approximately 4 kg) are able to treat approximately 28 liters of water per second, using 12 watts of power per gram of ozone produced. The device according Example 1 weighing 380 g produces sufficient ozone to treat 13 liters of water per second, using only 3.5 watts of power per gram of ozone produced. Therefore, the ozone generator described in Example 1 above is capable of producing ozone at a much higher efficiency (power used per gram of ozone produced) than existing ozone generator. In addition, due to the relatively low cost of the materials that may be used to construct the above ozone generator (copper electrodes, polypropylene body, polycarbonate dielectric).

(34) In an alternative embodiment, the inlet and the outlet are in the same plane as the elongate channel (see FIG. 3).

(35) With reference to FIGS. 8 and 9, the device according to the main embodiment has been shown to produce ozone at a constant rate over periods of at least 400 seconds, without any degradation in the rate due to heating of the electrodes. For example, FIG. 8 shows that for oxygen gas flowing along a channel having dimension 15 cm0.12 cm0.005 cm, at a rate of 1 L/min at 200 mbar pressure, a constant amount of ozone is produced (approximately 39 g/Nm.sup.3). Furthermore, with reference to FIG. 8, when the mean ozone output is plotted as a function of the flow rate at a constant pressure, the data can be fitted by a curve of the equation

(36) $y=\frac{39}{x},$
where y is the ozone produced and x is the flow rate of the oxygen along the channel. This fit is almost the expected form of fit for a perfect case (which would be fitted by an equation such as

(37) $y=\frac{40}{x}).$
Therefore, the ozone production of the device of the above example is surprisingly efficient.

(38) In addition, it has been found that the ozone produced is proportional to the length of the elongate channel. For example, with reference to FIG. 10, the ozone produced by an ozone generator having a channel 7 cm in length (other dimensions the same as in the previous example) can be fitted by an equation

(39) $y=\frac{397/15}{x}$
and shows that the amount of ozone produced is directly proportional to the length of channel (at least for the channel lengths used so far).

(40) It has been found that the major discharges across the channel occur at the first tallest peak in the waveform of the applied voltage. For example, peaks in current 82 are observed for a number of different waveforms as shown in FIGS. 11 to 13, ranging from an almost square waveform (FIG. 11) to an approximately triangular waveform (FIG. 13).

EXAMPLE 2

(41) With reference to FIGS. 6 and 7, an ozone generator 50 comprises a body 52, the body having a first electrode 54, a second electrode 56, and a third electrode 58 arranged such that the second electrode extends between the first and third electrodes, an inlet 60 and an outlet 62. The body comprises a channel (acting as an elongate channel). The channel has a first linear section 64 extending between the first and second electrodes, a second linear section 66 extending between the second and third electrodes, and a third section 68 (acting as a bend) connecting the first and second linear sections. The channel and the electrodes are arranged so as to form distinct layers arranged in the order; first electrode, first linear section of the channel, second electrode, second linear section of the channel, third electrode. The third section of the channel extends beyond the second electrode across three layers; the first linear section of the channel, the second electrode and the second linear section of the channel.

(42) The first linear section of the channel is isolated from the first electrode by a first dielectric layer 70 and is isolated from the second electrode by a second dielectric layer 72. The second linear section of the channel is isolated from the second electrode by a third dielectric layer 74, and isolated from the third electrode by a fourth dielectric layer 76. The four dielectric layers are polycarbonate.

(43) The body has a top surface 78 (acting as a first surface) and a bottom surface 80 (acting as a second surface). The inlet extends from the top surface to the first section of the channel. The outlet extends from the second section of the channel to the bottom surface such that a gas introduced into the inlet may flow to the outlet via the first, third and second sections of the channel sequentially.

(44) During use, oxygen gas is introduced into the inlet and allowed to flow from the inlet to the outlet via the channel. A voltage is applied across the first and second electrodes, and the third and second electrodes. The first and third electrodes are of a first polarity (for example, the cathode) and the second electrode is of a second polarity (for example, the anode).

(45) When a voltage greater then the breakdown voltage of the system is applied across each pair of electrodes, electrical discharges occur across the first and second electrodes through the first section of the channel, and across the second and third electrodes through the second section of the channel and ozone is produced by the same method as for the first embodiment.

EXAMPLE 3

(46) An ozone generator of the first and second examples is formed of flexible materials such that the ozone generator is flexible and rolled up before use to form a spiral or cylinder that may be inserted into a pipe or other water conduit, such that the top surface of the body forms the outer surface of the spiral and the bottom surface of the body forms the inner surface of the spiral.

(47) Further variations and modifications may be made within the scope of the invention herein disclosed.