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Title:
OZONE GENERATOR
Document Type and Number:
WIPO Patent Application WO/2019/084654
Kind Code:
A1
Abstract:
An ozone generator (10) for generating ozone comprising a first electrode (12), the first electrode (12) having at least a first portion thereof which is electrically conductive, the first portion also being porous to a gas, a second electrode (14) at least partially surrounding and spaced from the first electrode (12), the second electrode (14) being of an electrically conductive and thermally conductive material, and a gas feeding device designed to feed a gas to the interior of the first electrode.

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Inventors:
SALAMA, Amir (600 Robitaille Street, Shefford, Québec J2M 1X2, CA)
SALAMA, Marianne (600 Robitaille Street, Shefford, Québec J2M 1X2, CA)
Application Number:
CA2017/000235
Publication Date:
May 09, 2019
Filing Date:
October 31, 2017
Export Citation:
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Assignee:
OZOMAX INC. (600 Robitaille Street, Shefford, Québec J2M 1X2, CA)
International Classes:
C01B13/11; C01B13/10
Foreign References:
US3023155A1962-02-27
US6106788A2000-08-22
SU1680617A11991-09-30
JP2002087804A2002-03-27
Attorney, Agent or Firm:
FINCHAM, Eric (871 Shefford Street, Suite 304Bromont, Quebec J2L 1C4, CA)
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Claims:
WE CLAIM:

1. An ozone generator (10) for generating ozone comprising:

a first electrode (12), said first electrode (12) having at least a first portion thereof which is electrically conductive, said first portion also being porous to a gas;

a second electrode (14) at least partially surrounding and spaced from said first electrode (12), said second electrode (14) being of an electrically conductive and thermally conductive material; and

a gas feeding device designed to feed a gas to the interior of said first electrode.

2. The ozone generator of Claim 1 wherein said gas feeding arrangement is designed to feed gas through said first electrode under pressure.

3. The ozone generator of Claim 1 wherein said gas feeding device comprises a vortex tube (52), and a nozzle for dividing the vortex into warm and cold factions.

4. The ozone generator of Claim 1 wherein said first electrode (36) is an inner electrode and said second electrode (38) is an outer electrode surrounding said inner electrode.

5. The ozone generator of Claim 4 wherein both said first electrode (36) and second electrode (38) are circular in configuration.

6. The ozone generator of Claim 4 wherein said first electrode (36) is formed of a metallic material.

7. The ozone generator of Claim 4 wherein said first electrode (36) is formed of a material selected from polyaniline and a metal coated quartz substrate.

8. The ozone generator of Claim 4 further including a dielectric (40) located between said first electrode and said second electrode.

9. The ozone generator of Claim 8 further including a power supply operatively connected to said first and second electrodes (36, 38).

10. The ozone generator of Claim 4 wherein said outer electrode has a cooling device (42).

11. The ozone generator of Claim 3 wherein said outer electrode (38) is formed as a coil of metallic material, said coil being hollow to receive a refrigerated liquid flowing therethrough.

12. A method for increasing the amount of ozone in an oxygen containing gas comprising the steps of:

passing a pressurized oxygen containing gas through an electrode formed of a gas porous material;

subjecting said gas to a corona discharge to thereby create an ozone enriched gaseous mixture; and

collecting said ozone enriched gaseous mixture.

13. The method of Claim 12 wherein the step of passing a pressurized oxygen containing gas through an electrode comprises passing air through said electrode.

14. The method of Claim 12 wherein the step of passing a pressurized oxygen containing gas through an electrode comprises passing oxygen through said electrode.

15. A method for increasing the amount of ozone in an oxygen containing gas comprising the steps of:

passing an oxygen containing gas in a vortex to form a hot faction and a cold faction; separating said hot and cold factions;

passing said cold faction through an electrode formed of a gas porous material; and subjecting said gas to a corona discharge to thereby create an ozone enriched gaseous mixture.

16. The method of Claim 15 wherein the step of passing the cold faction through an electrode formed of a gas porous material comprises passing air through said electrode.

17. The method of Claim 15 wherein the step of passing the cold faction through an electrode formed of a gas porous material comprises passing oxygen through said electrode.

Description:
OZONE GENERATOR

FIELD OF THE INVENTION

The present invention relates to an ozone generator and more particularly, relates to an ozone generator wherein the feed gas in subjected to a cooling step prior to passing through the inner electrode of a corona discharge generator and where the outside dielectric is cooled with a water jacket in contact with the electric electrode.

BACKGROUND OF THE INVENTION

Ozone generators are well known in the art and different approaches have been utilized including UV and corona discharge.

Ozone generators are used to generate ozone for various purposes such as sterilization. Thus, they may be used for manufacturing in dying and bleaching as well as waste water treatment and the like.

In a corona discharge apparatus, the dual atoms of oxygen are caused by electrical discharge to disassociate and to recombine as three atom molecules ozone (O 3 ). The corona discharge is a phenomenon characterized by low current electrical discharge across a gaseous gap at a voltage which exceeds a certain critical value. A typical corona cell configuration comprises two metallic electrodes separated by a gas filled gap and a dielectric material. The net ozone that may be produced with a corona cell will depend upon the reaction variables. These reaction variables can include the oxygen content and temperature of the feed gas, contaminants in the feed gas, the power density in the corona, coolant temperature and flow, and other factors.

An enemy of the ozone is heat. Accordingly, it is desirable to operate an ozone generator at a lower temperature which increases the efficiency of the ozone generating process. SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an ozone generator which achieves a high level of efficiency.

According to one aspect of the present invention, there is provided an ozone generator comprising a first electrode, the first electrode having at least a first portion thereof which is electrically conductive, the first portion also being porous to a gas, a second electrode at least partially surrounding and spaced from the first electrode, the second electrode being of an electrically conductive and thermally conductive material, a cooling device arranged to cool at least one of the electrodes, and a gas feeding device designed to feed a gas to the interior of the first electrode.

According to a further aspect of the present invention, there is provided a method for generating ozone which comprises the steps of passing pressurized oxygen containing gas through an electrode formed of a gas porous material, subjecting the gas to a corona discharge to thereby create an ozone enriched gaseous mixture.

According to a still further aspect of the present invention, there is provided a method of generating ozone which comprises the steps of creating a vortex of an oxygen containing gas to thereby form a hot faction and a cold faction, separating the hot and cold factions, passing the cold faction through an electrode formed of a gas porous material, and subjecting the gas to a corona discharge to thereby create an ozone enriched gaseous mixture.

The first electrode is made of an electrically and thermally conductive porous or partially porous material which may be metallic, such as porous aluminum or porous stainless steel, or non-metallic, such as electrically conductive polymers like poly-aniline for example, or metal coated porous substrates such as ceramics or plastics. The length of the porous section of the inner electrode is designed such that cooling is optimised for a desired set of or range of operating conditions including flow rate, inlet temperature and inlet pressure. The inner electrode need not necessarily be entirely porous.

The feed gas can be oxygen containing air or oxygen. Naturally, the higher the percentage of oxygen in the feed gas, the higher the output of ozone.

The electrodes can come in several different forms as is known in the art. In a preferred embodiment, the first electrode will be an inner electrode with the second electrode surrounding the first electrode and being spaced therefrom. In a preferred embodiment, the electrodes are circular and concentric.

The first or inner electrode is porous to the gas with the gas being fed interiorly thereof. The nature of the porosity of the electrode can vary with passages being mechanically formed therein or alternatively, the electrode could be formed of a foamed metal wherein the cells are open such that gas can egress from the interior of the electrode to the space between the inner and outer electrodes. As is known in the art, a dielectric may also be used in the space between the inner and outer electrodes.

The inner electrode is hollow in the middle, is open at one end and is closed at the other. An oxygen containing gas is introduced under pressure through the open end and is forced to exit the inner electrode through its pores. As it does so, it loses pressure, expands and cools. The degree of cooling can be controlled using high inlet gas pressure.

This parameter can be controlled and can lead to significant cooling. Thermodynamics show that the relationship between pressure and temperature during isoentropetic expansion is

T 2 /Ti = (P 2 /Pi) [1 - Cv/Cp]

where, T 2 = Gas temperature after expansion (in degrees Kelvin)

Ti = Gas temperature before expansion (in degrees Kelvin)

P 2 = Gas absolute pressure after expansion (in atmospheres)

Pi = Gas absolute pressure before expansion (in atmospheres)

Cv = Gas specific heat at constant volume

C P = Gas specific heat at constant pressure

Using this equation, the cooling effect resulting from the expansion through the porous inner electrode may be estimated. Table 1 shows the resulting temperatures for oxygen

expanding through the inner electrode in two cases:

In the first case: The inlet 0 2 pressure = 7.8 atm absolute pressure (100 psig)

In the second case: The inlet 0 2 pressure = 4.4 atm absolute pressure (50 psig) Table 1 shows the resulting cold temperatures at different pressure exit pressures. In practise, the exiting oxygen pressure is determined by the porosity of the inner electrode. The C p and Cv of oxygen are 0.919 kJ/kg*K and 0.659 kJ/kg*K respectively. In both cases, we assume that the oxygen gas enters the electrode assembly at room temperature, that is, at 25C (298.15 K).

Table 1. Cooling of Oxygen Gas by Expansion through the Porous Inner Electrode at Various Pressures

P 2 = 2.4 atm (20 psig) T 2 = 213.6K (-59.6C)

P 2 = 1 atm (0 psig) T 2 = 166.7K (-106.4C)

Case 2: Pi = 4.4 atm (50 psig)

P 2 = 3.7 atm (40 psig) T 2 = 283.8K (10.7C)

P 2 = 3.0 atm (30 psig) T 2 = 267.5K (-5.6C)

P 2 = 2.4 atm (20 psig) T 2 = 251.2K (-22.0C)

P 2 = 1.7 atm (10 psig) T 2 = 227.8K (-45.3C)

P 2 = 1 atm (0 psig) T 2 = 196.0K (-77.1C)

Table 1 shows that at reasonable operating pressures, significant gas cooling can be achieved.

Other operating parameters that may be used to enhance cooling: a. Lower than ambient inlet gas temperature b. Recycling a portion of the inlet gas continuously through the inner electrode in order to achieve progressively lower temperatures c. Spiking the inlet gas with a high Joules Thompson coefficient gas such as carbon dioxide.

The inner electrode is made of an electrically and thermally conductive non-porous material which may be metallic, such as aluminum or stainless steel, or metal coated non-metals such as ceramics or plastics.

In one embodiment, the inner electrode is configured such that the inlet air or oxygen enters it tangentially through a nozzle and is thus made to flow in a vortex pattern with a rotational frequency of up to several million rpms (revolutions per minute). This rotation separates the feed gas into a cold stream and a hot stream. These streams exit the inner electrode assembly at opposite ends of the inner electrode. The hot air stream may be exhausted to the ambient or collected, cooled and recycled back to the electrode assembly. The cold air stream proceeds to the high voltage section of the inner electrode. The length of the high voltage section is defined by the length of the outer, shorter electrode. The cold air enters the high voltage section of the corona lamp at a temperature that can be as low as -50C or less. The hot air exits the opposite end of the inner electrode at a temperature that can be as high as 150C or more. The temperatures of each of these air streams are controlled by the feed gas inlet pressure, the inlet gas flow rate and the degree of throttling of the hot air flow exiting the electrode. Throttling may be achieved using a manual or electrical valve, or some other similar means, that may be either incorporated in the electrode assembly or installed outside of the assembly.

The inner electrode combines the aforementioned designs as follows: The inner electrode is divided into two cooling sections. The first section is configured such that the inlet air or oxygen enters it tangentially and is cooled as described above. The cold air stream proceeds to the second section of the inner electrode which is composed of an electrically and thermally conductive porous or partially porous material as described above. One may also combine the two designs, i.e. cooling by expansion through porous material and vortex cooling.

This cooling of the feed gas favours the production of ozone since the production rate of ozone is inversely proportional to gas temperature. The production of ozone occurs inside the corona lamp according to the reaction

O + O 2 → O 3

for which the reaction rate dependence on gas temperature T z is given by the following expression k = 2.5 x IO- 35 exp (970/T g ) [cm 6 s "1 ] where T g is given in degrees Kelvin Based on this equation, the percent increase in the production of ozone due only to gas cooling can be estimated as shown in Table 2 below. We use a temperature of 25C as the reference case, that is, when no gas cooling is performed. We limit this analysis to a cooled gas temperature of -35C as most air dryers or oxygen concentrators commonly used in ozone applications will achieve dew points of -40C. Therefore cooling the gas below this point would cause the electrode assembly to become filled with condensation and ice. Table 1 shows that within the defined temperature range ozone production can increase up to 126% thanks solely to gas cooling.

Table 2. Theoretical Effect of Gas Cooling on the Ozone Production of a Corona

Discharge Ozone Generator

To favour ozone production even further the outer electrode may also be cooled. The outer electrode is made of an electrically conductive, thermally conductive, flexible, and hollow material such as, but not limited to copper tubing, aluminum tubing, brass tubing, or any flexible, thermally and electrically conductive polymer or composite coil. The outer electrode is electrically connected to the outside surface of the dielectric by some practical means such as, but not limited to, an electrically conductive epoxy, by brazing, or by soldering. Alternatively the outer surface of the dielectric can be metallised through a suitable process such as evaporation, sputtering, electroless plating, electroplating or some similar means.

This would then allow the outer electrode to be electrically and physically connected to the metallised dielectric by soldering, by gluing or by means of a conductive epoxy or similar conductive polymer or any other such means. The outer electrode is coiled around the outer surface of the dielectric to form a serpentine around it. A cooling fluid such as chilled water, chilled oil, or any other suitable chilled or non-chilled thermally conductive liquid or gas, flows through the outer electrode to cool it and the surface of the dielectric simultaneously. This outer electrode design increases the efficiency of the electrode assembly in two ways. The first is by means of reducing the temperature of the electrode assembly and thereby increasing the overall ozone production of the electrode assembly and second by, through its coiled shape and lack of sharp edges, eliminating corona and consequently ozone from being formed on the outside of the electrode assembly. The overall mechanical strength of this electrode assembly design would allow ozone to be delivered at high pressures.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus generally described the invention, reference will be made to the

accompanying drawings illustrating embodiments thereof, in which:

Figure 1 is a schematic cross-sectional view of an ozone generator;

Figure 2 is a schematic cross-sectional view of a further embodiment of an ozone generator; and Figure 3 is a perspective view of a cooling coil used in the embodiments of Figures 1 and 2.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings in greater detail and by reference characters thereto, there is illustrated in Figure 1 an ozone generator which is generally designated by reference numeral 10.

Ozone generator 10 includes an inner electrode 12 and an outer electrode 14 spaced therefrom. Inner electrode 10 is preferably formed of a porous metal such as stainless steel, copper, aluminium, or ceramic coated with a metallic material. Intermediate inner 12 and outer electrode 14 is a dielectric 16. The arrangement is such that there is a gap 18 to which a gaseous oxygen containing material is fed.

Ozone generator 10 also includes a lower cap 20 and an upper cap 22 as is known in the art.

Outer electrode 14 may be formed of any suitable material; in one embodiment, it may be an epoxy filled with a metallic material or a conductive ceramic which would be highly thermally conductive. Encasing outer electrode 14 is tubing 24 for the coolant. Tubing 24 is provided with an inlet 26 and an outlet 28.

After having been subjected to a corona discharge, the ozone enriched gas is discharged through an outlet 30.

In the embodiment of Figure 2, there is provided a further version of an ozone generator 34. Ozone generator 34 has an inner electrode 36 which is also formed of a porous metallic material. Surrounding inner electrode 36 is an outer electrode 38 while a dielectric 40 is provided therebetween. As in the previous embodiment, there is provided a cooling coil 42 designed to receive a suitable cooling through an inlet 44 and discharge the same through outlet 46.

Ozone generator 34 also has an upper cap 48 and a lower cap 50. Ozone generator 34 includes a vortex tube 52 which is designed to feed an oxygen containing gas through a valve (not shown) which will divide the gaseous flow into a cold faction 56 which extends downwardly into inner electrode 36 and a hot faction which can then be discharged or used otherwise. The tube containing cold faction 56 includes a plug at the bottom thereof such that the cold gas will exit as indicated by arrows 62.