GB2102303A

GB2102303A - Ozone generation and water treatment

Info

Publication number: GB2102303A
Application number: GB08119191A
Authority: GB
Inventors: Douglas Barry Fox; Brian Victor Catton
Original assignee: AQUA ELECTRONICS Ltd
Current assignee: AQUA ELECTRONICS Ltd
Priority date: 1981-06-22
Filing date: 1981-06-22
Publication date: 1983-02-02
Also published as: GB2102303B

Abstract

Air is compressed in a compressor 1, cooled to ambient temperature in a heat exchanger 7, and (after separation of condensed water in a trap 9) is fed alternately through two desiccators 13, 14 to an expansion valve 18 which feeds dry air at approximately ambient pressure to an ozone generator 27. Excess compressed air is returned through a valve 21 to the inoperative one of the desiccators to expel moisture which has been collected. The ozone generator 27 has outer and inner tubular electrodes with a tubular insulator between them. A passageway for air to be ozonised is defined between at least one of tie electrodes and the insulator, and the electrode surface delimiting the passageway is provided with grooving. The ozone is used to treat water, which may then be electrolysed to generate hypochlorite ions from chloride ions present in the water (Fig. 11). <IMAGE>

Description

SPECIFICATION Ozone generation This invention relates to apparatus for generating ozone, an ozone generator suitable for use in such apparatus, and a method and apparatus for treating water with ozone.

The equipment presently available for generating ozone is very bulky and is therefore unsuited to domestic use or to use in the field, e.g.

on vehicles. One aim of the present invention is to provide ozone generating apparatus which is compact and only occupies a small space.

Ozone is produced by the action of a glow discharge on molecules of oxygen. Basically, an ozone generator comprises two electrodes with an insulator of dielectric material between to prevent direct arcing between the electrodes. An air passage is defined on one or both sides of the insulator, and a sufficient potential difference is applied across the electrodes to obtain electron flow in the (or each) passageway. There are two main forms of electrode assembly, employing either flat components or tubular components.

The present invention provides apparatus for generating ozone, comprising a compressor having an inlet communicating with the ambient air, and an outlet for compressed air at above ambient temperature; a heat exchanger for cooling the compressed air by heat exchange with ambient air; a water trap in which water which has condensed during cooling of the compressed air separates from the compressed air; two elongate desiccators; first valve means for selectively connecting one end of one desiccator to the compressed air outlet of the water trap and connecting one end of the other desiccator to an air discharge outlet, and vice versa; an expansion valve having a compressed air inlet and an expanded air outlet; second valve means for selectively connecting the other end of the said one desiccator to the compressed air inlet of the expansion valve and disconnecting the other end of the said other desiccator from the compressed air inlet of the expansion valve, and vice versa; control means for reversing the operation of each of the first and second valve means; means for supplying surplus air from the said other end of the desiccator which is under pressure to the said other end of the desiccator which is not under pressure; an ozone generator comprising an inner tubular electrode, an outer tubular electrode, and a tubular insulator of dielectric material disposed between the electrodes and forming with at least one of them an elongate passageway communicating at one end with the expanded air outlet of the expansion valve and at the other end with an ozonised air outlet; and electronic means for applying a high voltage across the electrodes so as to cause a glow discharge in the passageway.

Thus the desiccators are used alternately. One desiccator dries the compressed air while the other desiccator is being dried out by the (dry) air which is surplus to the requirements of the expansion valve. The use of compression of the air followed by desiccation of the compressed air, to dry the air supplied to the ozone generator, is much more efficient than using desiccation alone, and also utilises less space.

The present invention also provides an ozone generator comprising an inner tubular electrode, an outer tubular electrode, and a tubular insulator of dielectric material disposed between the electrodes and forming with at least one of them an elongate passageway in which a glow discharge is to be produced by the application of a high voltage across the electrodes, the passageway communicating at one end with an air inlet and at the other end with an ozonised air outlet, the electrode surface delimiting the passageway being provided with grooving extending over at least a major part of the area facing the other electrode.

The grooving may run substantially circumferentially. In particular, it may comprise annular grooves; however, it is more easy to cut a helical groove in the manner of a screwthread.

Alternatively, or additionally, the grooving may comprise longitudinal grooves. The provision of grooving in the electrode surface produces sharp edges at which the electrical field is intensified, thus facilitating the production of a glow discharge which is highly efficient in converting oxygen into ozone. It appears that, by grooving the electrode surface, it is possible to increase the rate of ozone generation by a factor of about 2 without difficulty.

The main use for ozone is in the treatment of water, since it is a highly efficient agent for the inactivation of viruses and for the decomposition of certain pollutants such as phenols. However, it does not persist in water and thus cannot provide a stable residual sterilant which will protect the treated water against further contamination. In contrast, chlorine which is an efficient germicide, can provide a residual disinfectant, but it may form objection compounds with some pollutants, overdosing produces undesirable effects, and the application of chlorine in the form of gas or as hypochlorite requires the transport, storage, and handling of hazardous chemicals.

The present invention provides a method of treating water, comprising passage air through a glow discharge to ozonise it, introducing the ozonised air into water, and subjecting the resulting water to electrolysis generating hypochlorite ions from chloride ions present in the water.

The invention also provides apparatus for treating water, comprising passing air through a having two electrodes and an insulator of dielectric material disposed between the electrodes and forming with at least one of them a passageway communicating between an air inlet and an ozonised air outlet; a waver conduit; means for introducing the ozonised air into water in the conduit; an electrolyser to which water is supplied by the conduit, the electrolyser having two electrodes between which the water flows; and electronic means for applying a high voltage across the electrodes of the ozone generator to produce the glow discharge and for applying a low voltage across the electrodes of the electrolyser to generate hypochlorite ions from chloride ions present in the water.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic elevation of apparatus for producing ozone, which is mounted in a cabinet shown in vertical section; Figure 2 is a transverse section through the ozone generator of the apparatus; Figure 3 is a part-sectioned elevation of the ozone generator; Figure 4 is an enlarged detail of Figure 3; Figure 5 is an elevation of the ozone generator, provided with fins, on a reduced scale; Figure 6 is an end view corresponding to Figure 5; Figures 7 and 8 are views corresponding to Figure 4 of two different embodiments of ozone generators; Figures 9 and 10 are views corresponding to the left-hand side of Figure 2, of two further embodiments of ozone generators; and Figure 11 diagrammatically illustrates apparatus for treating water.

Referring first to Figure 1, a piston compressor 1 draws in air through a pipe 2 from an air filter 3 mounted in an aperture in the cabinet 4 containing the ozone generating apparatus. Warm compressed air at a pressure of about 4.5 bars leaves the compressor 1 through a pipe 6 and enters a heat exchanger in the form of a honeycomb radiator 7 mounted adjacent an aperture 8 in the cabinet 4. If necessary, ambient air can be driven through the radiator 7 by a fan (not shown).

The compressed air follows a sinuous path through the radiator 7 and is cooled to approximately ambient temperature with the result that water condenses out of the compressed air. The water is separated from the compressed air in a trap 9 from which the water is periodically automatically vented. The compressed air then passes through a pipe 11 to an electrically controlled slide valve 12.

In the situation shown in Figure 1, the valve 12 connects the pipe 11 to the lower end of a desiccator 13, which is one of two molecular sieve desiccators 13, 14 which work in alternation. In Figure 1, the desiccators are shown side-by-side for the sake of clarity, but in practice they will be mounted one in front of the other in order to save space. The compressed air passes through the desiccator 13, in which the molecular sieve takes up its water content, and then passes to a pressure operated slide valve 16, which, in the situation illustrated in Figure 1, connects the upper end of the desiccator 13 to a pipe 1 7 leading to the compressed air inlet of a needle valve 18 from which the compressed air expands into a pipe 19.The air in the pipe 19 is approximately at ambient pressure, is at less than ambient temperature (owing to the expansion), and is very dry; it thus has the optimum properties for ozone generation.

The surplus compressed air from the desiccator 13 which is under pressure is returned through a needle valve 21 to the upper end of the other desiccator 14. The dry air passes through the desiccator 14, sweeping out any moisture which has been stored in that desiccator, and leaves the lower end of the desiccator 14, which, in the situation illustrated in Figure 1, is connected to an air discharge outlet 22. This air may be discharged to the atmosphere, as shown, or it may be discharged into the cabinet 4 at one or more points so as to provide a flow of air in the cabinet for the purpose of cooling.A control unit 23, including a timer, periodically changes over the operation of the desiccators 13 and 14 by operating the slide valve 12 so that the incoming compressed air flows up through the desiccator 14, operates the slide valve 16, and enters the pipe 17, while the surplus air expands through the needle valve 21 and flows down through the desiccator 13, clearing it of the moisture previously collected.

The flow rate of the air in the pipe 19 is indicated by a gauge 24 visible through a window 26 in the front of the cabinet 4. The air enters the upper end of an ozone generator 27 (described below) and the ozonised air leaves the ozone generator through a pipe 28. A high voltage at a high frequency (e.g. 5 to 10 kV or more at 5 to 10 kHz) is produced by an electronic unit 29 connected to the ozone generator 27 by a high tension lead 31 , the exterior of the ozone generator being earthed. The unit 29 is powered by the mains and comprises a transformer, a rectifier, and an inverter. Alternatively, the inve,rter can be powered by a battery, e.g. a vehicle battery, and the apparatus is thus readily transportable.

Furthermore, the apparatus is very compact: the cabinet 4 is less than 1 metre in height and width, and has a depth of about 200 mm.

The ozone generator 27 (see Figures 2 to 4) has an outer tubular electrode 32 with an air inlet nipple 33 (to which the pipe 19 is attached) and an ozonised air outlet nipple 34 (to which the pipe 28 is attached). The electrode 32 is of stainless steel and has end caps 36, 37 which locate a coaxial tubular insulator 38 of glass or other dielectric material. Between the nipples 33 and 34, the inner surface of the insulator 38 is provided with an inner tubular electrode 39 formed by electroplating copper onto an electrolessly deposited film of silver. The electrode 39 is covered by an insulating layer of resin 41, except where it is connected to the high tension lead 31, which enters through the end cap 36.

When the high voltage at high frequency is applied to the inner electrode 39, the outer electrode 32 being earthed, a glow discharge is produced in the passageway 42 defined between the electrode 32 and the insulator 38. The inner surface of the electrode 32 is provided with grooving in the form of a helical groove 43 resembling a screwthread. It has been found that the presence of this grooving has a very advantageous effect on the efficiency of the ozonisation of the air passing along the passageway 42. The provision of the groove 43 results in two sharp edges being formed at the internal surface of the electrode 32, and the electric field is intensified at these edges.

Furthermore, the machining of the groove 43 in the electrode 32 causes these sharp edges to be irregular and to contain many sharp points which produce intense local electric fields facilitating the production of an effective glow discharge along the whole of the path of the air.

The stainless steel electrode 32 acts as a heat sink for the heat generated in ozonising the air in the passageway 42. Given the fact that the air entering the generator through the pipe 19 is cooler than ambient temperature, the electrode 32 will normally conduct away sufficient heat to prevent the temperature in the passageway 42 from becoming excessive, at ozone production rates of 1 to 5 g/h. If required, however, an additional heat sink can be provided in the form of an extruded metal member 44 with longitudinal fins 46, this member being in contact with the electrode 32 along most of its length. An air flow over the fins can be provided by convection, by a fan (not shown), or by the air discharged from the pipe 22.

Figures 7 and 8 show different forms of the grooving of the internal surface of the electrode 32. These Figures show longitudinal grooves 47 and annular circumferential grooves 48. In Figure 8 the two types of groove are used together, resulting in sharp corners as well as sharp edges.

Although the grooves in Figures 4, 7, and 8 are shown as V-shaped in section, they could be of any other convenient shape.

Figures 9 and 10 show two alternative arrangements of the insulator 38 in relation to the electrodes 32 and 39. In Figure 9, the insulator 38 is directly adjacent the outer electrode 32 and is spaced from the inner electrode 39, which is supported by the end caps 36, 37. Here the external surface of the electrode 39 is provided with grooving 49 having any of the three forms described above with reference to Figures 4, 7, and 8. The air is passed through the passageway 51 defined between the insulator 38 and the conductor 39. In Figure 10 the insulator 38 is spaced from both electrodes 32 and 39 and with them defines two passageways 52 and 53 along which the air is passed. In this case both the inner surface of the outer electrode 32 and the outer surface of the inner electrode 39 are provided with grooving.

In the water treatment apparatus illustrated in Figure 11 the ozone generator 27 is supplied with the high voltage at high frequency by an electronic unit 54 having a mains input 56 and a battery input 57, used alternatively. Water supplied through a conduit 58 entrains ozonised air from the pipe 28 in a venturi 59, and the mixture of ozone and water discharged into the bottom of a vessel 61 in which the ozone dissolves in the water. Undissolved ozonised air escapes through a vent 62. The water flows from the top of the vessel 61 through an electrolyser 63 having upper and lower plate electrodes 64, 66 between which the water flows. The electronic unit 54 applies a low voltage at low frequency (e.g. 6 to 12 volts with polarity changes taking place at intervals measured in seconds or minutes) across the electrodes 64, 66, in order to generate hypochlorite ions from chloride ions present in the water. If the natural chloride content of the water is too low, it may be increased by adding common salt (e.g. in the vessel 61). A switch 67 is provided, for disconnecting the electrolyser 63 from the unit 54. This operation may be manual or can be controlled by a chlorine sensing device in the body of water which is fed by the electrolyser 63.

Claims

1. Apparatus for generating ozone, comprising a compressor having an inlet communicating with the ambient air and an outlet for compressed air at above ambient temperature; a heat exchanger for cooling the compressed air by heat exchange with ambient air; a water trap in which water which has condensed during cooling of the compressed air separates from the compressed air; two elongate desiccators; first valve means for selectively connecting one end of one desiccator to the compressed air outlet of the water trap and connectinSone end of the other desiccator to an air discharge outlet and vice versa; an expansion valve having a compressed air inlet and an expanded air outlet; second valve means for selectively connecting the other end of the said one desiccator to the compressed air inlet of the expansion valve and disconnecting the other end of the said other desiccator from the compressed air inlet of the expansion valve, and vice versa; control means for reversing the operation of each of the first and second valve means; means for supplying surplus air from the said other end of the desiccator which is under pressure to the said other end of the desiccator which is not under pressure; an ozone generator comprising an inner tubular electrode, an outer tubular electrode, and a tubular insulator of dielectric material disposed between the electrodes and forming with at least one of them an elongate passageway communicating at one end with the expanded air outlet of the expansion valve and at the other end with an ozonised air outlet; and electronic means for applying a high voltage across the electrodes so as to cause a glow discharge in the passageway.

2. Apparatus as claimed in claim 1 , in which the electronic means applies a high frequency voltage across the electrodes.

3. Apparatus as claimed in claim 1 or 2, in which the desiccators comprise molecular sieves.

4. An ozone generator comprising an inner tubular electrode, an outer tubular electrode, and a tubular insulator of dielectric material disposed between the electrodes and forming with at least one of them an elongate passageway in which a glow discharge is to be produced by the application of a high voltage across the electrodes, the passageway communicating at one end with an air inlet and at the other end with an ozonised air outlet, the electrode surface delimiting the passageway being provided with grooving extending over at least a major part of the area facing the other electrode.

5. An ozone generator as claimed in claim 4, in which the grooving comprises a helical groove or circumferential annular grooves.

6. An ozone generator as claimed in claim 4 or 5, in which the grooving comprises longitudinal grooves.

7. An ozone generator as claimed in any of claims 4 to 6, in which the electrodes define two said passageways, respectively, with the insulator, the inner surface of the outer electrode and the outer surface of the inner electrode both being provided with grooving.

8. A method of treating water, comprising passing air through a glow discharge to ozonise it, introducing the ozonised air into water, and subjecting the resulting water to electrolysis generating hypochlorite ions from chloride ions present in the water.

9. Apparatus for treating water, comprising an ozone generator having two electrodes and an insulator of dielectric material disposed between the electrodes and forming with at least one of them a passageway communicating between an air inlet and an ozonised air outlet: a water conduit; means for introducing the ozonised air into water in the conduit; an electrolyser to which water is supplied by the conduit, the electrolyser having two electrodes between which the water flows; an electronic means for applying a high voltage across the electrodes of the ozone generator to produce the glow discharge and for applying a low voltage across the electrodes of the electrolyser to generate hypochlorite ions from chloride ions present in the water.

10. Apparatus as claimed in claim 9, in which the high voltage is at high frequency.

1 Apparatus as claimed in claim 9 or 10, in which the low voltage is at low frequency.

12. Apparatus for generating ozone, substantially as described with reference to, and as shown in, the accompanying drawings.

13. An ozone generator substantially as described with reference to, and as shown in, the accompanying drawings.

14. A method of treating water substantially as described with reference to Figure 11 of the accompanying drawings.

1 5. Apparatus for treating water substantially as described with reference to, and as shown in, Figure 11 of the accompanying drawings.