GB2454458A

GB2454458A - Plasma discharge ozone generator

Info

Publication number: GB2454458A
Application number: GB0721705A
Authority: GB
Inventors: Kui Zhang; David Glover
Original assignee: PLASMA CLEAN Ltd
Current assignee: PLASMA CLEAN Ltd
Priority date: 2007-11-06
Filing date: 2007-11-06
Publication date: 2009-05-13
Also published as: GB0721705D0

Abstract

An apparatus (1) is disclosed for producing ozone which comprises a pair of opposed spaced electrodes (5,6), a solid dielectric material (2) in contact with the electrodes (5,7) and extending therebetween, means (6) for applying a potential difference across the electrodes (5,7) to provide an electric field in a direction between the electrodes (5,7), and means for providing an air flow in a direction parallel to the electrodes (5,7). The means to provide an air flow may be a fan. The electrodes may be a metal film, foil, gauze or mesh. The metal may be stainless steel or nickel. The dielectric material may be glass, quartz, ceramic or a polymer such as polyethylene, polypropylene or PTFE.

Description

OZONE GENERATING MEANS AND APPLICATIONS

ABSTRACT

The present invention relates to an ozone generating device for air and surface treatment wherein ozone is produced directly from air by a plasma discharge. In particular this invention relates to an ozone generating device which is used for odour abatement and grease reduction in a kitchen ventilation canopy and ductwork.

DESCRIPTION

Ozone is well known for its ability to oxidise airborne and water borne pollutants and has excellent cleansing, deodonsing and disinfecting properties.

Where ozone is produced at low levels (100mg per hour or less), there are many affordable units on the market which are either battery or mains operated and which produce ozone from air as a feedstock. These are often used in washrooms for odour control purposes. Further there are many applications where the oxidising properties of ozone are utilised.

Where ozone is required at higlier levels (5-50g per hour and above), products are available but these can be expensive and unreliable and often cumbersome in size in relation to their chosen application. In particular where air is used as a feedstock the high power requirement and associated heat build up results in the production of nitrogen oxide (NOx) gas. To overcome this issue, complex cooling systems are included in the design or alternatively oxygen is used as a feedstock which is supplied either from oxygen cylinders or through oxygen concentrators. This facilitates the production of high levels of ozone which is NOx-free, but the additional system complexity means that these products are very expensive.

A further issue for many ozone generators is that the ozone production rate drops rapidly in high humidity environments which necessitates the need for complex and expensive oxygen-fed systems or in-line air drying which is seldom practical in commercial installations.

There is a requirement to produce ozone relatively cheaply in the 5-5Ogfhr range, using ambient air as a feedstock, while using a relatively high flow, low back pressure reactor design that requires no cooling, generates no NOx, is tolerant of wide variations in air humidity and is compact, robust and easy to construct and which can be powered from cheap commercially available high frequency power supplies, such as those used to power neon tubes. Existing designs of ozone generation discussed below do not address these key requirements.

The generation of ozone by the action of electrical discharge in air has been known for over a century. The Siemens tube or Siemens ozoniser consists of two concentric glass or quartz tubes. The inner surface of the inner tube being connected to a high voltage alternating current and the outer surface of the outer tube being connected to earth. A corona discharge is generated in the gap between the two concentric tubes through which air or oxygen-enriched air passes which results in the production of ozone and oxygen ions. This type of ozoniser has been used for industrial scale ozone generation since the beginning of the twentieth century for municipal water purification amongst other applications. Such applications require extremely high levels of ozone (50kg/day and greater) which in turn requires high power consumptions (1 5-3OkwHr per kg ozone is typical). Due to the low energy efficiency of such devices heat is produced which needs to be dissipated by cooling means which adds to the complexity of the design. There is also a requirement to dry the feed gas which adds further complexity to the design of such devices. Whilst such devices are well known for industrial scale applications, they are seldom used for smaller scale applications where the ozone is required in the 5-5ogfhr range due to the apparent complexity of design taking into account the requirements to cool the device and to remove moisture from the feed gas.

Ozone is produced during electrical discharge or by UV at 1 85nm and there are many examples of devices to generate ozone. W02005021 135 describes ozone generation for odour removal using UV light. The invention comprises two banks of UV light sources, the first operating at I SSnm to generate ozone and a downstream bank operating at 254nm to decompose residual ozone. The use of UV lamps to generate ozone is not desirable in kitchen extract applications as oil and grease residues from cooking can result in unwanted deposits on the surface of the UV tubes which reduce performance.

Parallel plate and tubular type ozone generators, which operate under the principle of silent discharge, are known. A parallel plate design, where the ozone is generated in a narrow gap, typically less than a few millimetres, between a dielectric coated electrode and an exposed electrode is an effective mechanism of ozone generation however it is severely limited in many practical applications by the low flow rates and high back pressures associated with the narrow electrode gap. For many applications an open tube design is desirable to maximise flow rate and minimise back pressure.

Tubular designs typically include an outer electrically conductive tubular electrode, a dielectric tube positioned within the outer tubular electrode and spaced therefrom to form a discharge gap, together with an inner electrode which contacts the inner surface of the dielectric tube. These designs also suffer from low flow rates and high back pressures associated with the narrow electrode gap. US42 16096, uses an improved version of a tubular silent discharge plasma reactor to produce ozone. While this design claims improved discharge stability it still suffers from the existence of a narrow inter-electrode gap.

US367 1417 describes a tubular design of ozone generator with a concentrically mounted metal rod internal electrode, however, this again requires one end of the reactor to be plugged and hence the back pressure is increased and the flow rate reduced.

US4234800 describes a further improved tubular design of ozone generator but in this case fluid cooling of electrodes is required.

US65 17787 discloses an ozone generator for producing low NOx however this is achieved via drying the process air stream and by cooling the reactor.

US6235090 describes a kitchen hood treatment system using ozone. In this example the ozone is generated from a high voltage DC corona discharge from an electrostatic precipitator In this invention a pair of parallel electrodes separated by a single dielectric has been designed to generate modest amounts of ozone when powered by high voltage alternating current.

Further, individual ozone generating modules may be connected electrically in series or parallel to facilitate the increased production of ozone in a modular fashion. This invention enables ozone to be produced relatively cheaply in the 5-50g/hr range, using ambient air as a feedstock, while using a relatively high flow, low back pressure reactor design that is cooled simply by means of the feedstock gas passing through the apparatus. Given the relatively low power requirement the system generates no NOx, is tolerant of wide variations in air humidity and is compact, robust and easy to construct. The invention can also be powered from affordable commercially available high frequency power supplies, such as those used to power neon tubes. As such, and this is the crux of the invention, we have taken a heretofore industrial scale ozone generating means and have scaled this down to produce a simple and elegant self-cooling ozone generating means for smaller scale industrial, commercial and domestic use.

A specific embodiment of the invention is in the form of a standalone ozoniser wherein ozone is injected directly into a chamber, a room, or ductwork carrying polluted air, for example a kitchen extract canopy, where it can react with and neutralise odour, grease and smoke molecules.

The Unit comprises an air inlet and outlet means and a pathway there between through which the air flows through the ozone generating device. Said air stream being pushed through the device by means of a fan located at the air inlet, alternatively said air stream being pulled through the device by the Venturi effect caused by air flowing through any ductwork connected to the outlet of the device, or a combination of both. The unit being modulated by an airflow switch located in a position such that the unit is switched on by the Venturi effect caused by air flowing through any ductwork connected to the outlet of the device.

This invention incorporates the possibility of moving the mesh electrodes, which will affect the discharge that is produced and hence the levels of ozone. For purposes of this invention the inner mesh electrode is smaller in length than the external mesh electrode and it can either be fixed in place, in order to keep the discharge constant, or moved to allow the movement and overlap of the mesh electrodes. Another unique part of this invention is the use of a clip that holds the wires in place and is setup for ease of use and to allow easy changing of the cylinder glass tubes.

In such an application there are clear advantages given the high humidity of the environment.

Further, there is no resultant nitric acid from NOx which is known to affect the ductwork of kitchen canopies.

The invention will be further described by way of example only with reference to the accompanying drawings, in which: Figure 1 schematically illustrates one embodiment of the ozone generating apparatus in accordance with the invention; Figure 2 schematically illustrates one embodiment of the ozone generating apparatus in accordance with the invention; Figure 3 schematically illustrates one embodiment of a plurality of ozone generating apparatus which is in accordance with the invention; Figure 4 represents graphically the relationship between power (W) and ozone output (g/hr); Figure 5 schematically illustrates one embodiment of the apparatus when used as an ozone generator product for, by means of example only, a commercial kitchen extraction system.

Figure 6 illustrates the setup of the mesh electrodes and the positioning of the clip, which is used to easily attach the tubes.

The apparatus I illustrated in Figure 1 comprises a solid dielectric material 2 formed with an inlet 3 and an outlet 4. Located on the inner surface of the dielectric is an electrode 5 connected to a high voltage high frequency power supply 6. Located on the outer surface of the dielectric is an electrode 7 connected to earth.

The apparatus I illustrated in Figure 2 comprises a solid dielectric material 2 formed with an inlet 3 and an outlet 4. Located on the inner surface of the dielectric is an electrode 5 connected to a high voltage high frequency power supply 6. Located on the outer surface of the dielectric is an electrode 7 connected to a high voltage high frequency power supply 6.

The apparatus I illustrated in Figure 3 comprises a plurality of ozone generating apparatus.

The apparatus I illustrated in Figure 5 represents an embodiment of the invention consisting of an ozone resistant material 2 formed with an inlet 3 and an outlet 4. A prefilter 5 a means of drawing air through the unit 6 and passing through the ozone generating device 7. Said outlet 4 capable of releasing ozone gas directly into the treatment area by means of a louvre fitting or spigot-type connector.

The apparatus I illustrated in Figure 6 represents the clip and its positioning in the tubular dielectric 2 to facilitate ease of electrical connection of the high voltage alternating current with the internal electrode.

Claims

Claims 1. An apparatus for producing ozone comprising: a. a pair of opposed spaced electrodes, b. a solid dielectric material in contact with the electrodes and extending between the electrodes, c. means for applying a potential difference across the electrodes to provide an electric field in a direction between the electrodes, and d. means for providing an air flow in a direction parallel to the electrodes.
2. An apparatus according to claim 1, wherein the means for applying a potential difference across the electrodes is adapted to provide a potential difference of Vpk.pk 1- 30kV at up to 50kHz.
3. An apparatus according to claim 1, wherein the means to provide air flow through the apparatus is a fan.
4. An apparatus according to claim 1, wherein the electrodes are formed of a metal film, foil, gauze or mesh.
5. An apparatus according to claim 4, wherein the metal is comprised of stainless steel or nickel.
6. An apparatus according to claim 1, wherein the dielectric material is glass, quartz, a ceramic or organic polymer material.
7. An apparatus according to claim 6 wherein the organic polymer material is polyethylene, polypropylene or Teflon.
8. An apparatus according to claim 6, wherein the dielectric material has a dielectric constant of less than 1000.
9. An apparatus according to claim 6, wherein the dielectric material has a dielectric constant of less than 500.
10. An apparatus according to claim 6, wherein the dielectric material has a dielectric constant of less than 200.
11. An apparatus according to claim 6, wherein the dielectric material has a dielectric constant of less than 100,
12. An apparatus according to claim 6, wherein the dielectric material has a dielectric constant of less than 20.
13. An apparatus according to claim 6, wherein the dielectric is coated with a catalyst layer.
14. An apparatus according to claim 6, wherein the dielectric has a thickness of 1mm-6mm.
15. An apparatus according to claim 6, wherein the dielectric is in tubular form
16. An apparatus according to claim 6, wherein the dielectric is in the form of a flat or curved plate.
17. An apparatus according to claims 1 -16 consisting of a plurality of ozone generating devices which are connected electrically in series or in parallel.
18. A method of producing ozone comprising one or more units which contain a pair of opposed spaced electrodes, a solid dielectric material in contact with the electrodes and extending between the electrodes, a means for applying a potential difference across the electrodes to provide an electric field in a direction between the electrodes, and a means for providing an air flow in a direction parallel to the electrodes.
19. A method of treating air according to claim 18 wherein ozone is injected into a polluted air stream and reacts with and oxidises airborne and surface pollutants.
20. An apparatus according to claim 6, which comprises of two mesh electrodes, with the internal electrode length being less than that of the external electrode. The inner mesh electrode is fixed in position and the external mesh electrode may be fixed or moved.
21. An apparatus according to claim 6, in which a clip is utilised to hold the wires in place and give ease of access when changing the glass tubes.