WO2002020397A1

WO2002020397A1 - Flat plate ozone generator

Info

Publication number: WO2002020397A1
Application number: PCT/EP2000/008734
Authority: WO
Inventors: Jan BORGSTRÖM
Original assignee: Ozonator Limited
Priority date: 2000-09-05
Filing date: 2000-09-05
Publication date: 2002-03-14
Also published as: AU2001212705A1

Abstract

An ozone generating apparatus comprising a flat plate double cell arrangement, said apparatus including a first corona cell comprising a first spacing and a first dielectric member arranged between a first pair of conductive surfaces; a second corona cell comprising a second spacing and a second dielectric member arranged between a second pair of conductive surfaces. The invention is characterized in that a first of said first pair of conductive surfaces, and a first of said second pair of conductive surfaces are opposing sides of a first type electrode.

Description

FLATPLATE OZONEGENERATOR

Field of the Invention

The present invention relates generally to devices which generate ozone by applying a high voltage across a gap to create a corona discharge, and more specifically to a new type of flat plate ozone generating cell having a double cell arrangement.

Description of the Prior Art Ozone is a very powerful gaseous reactant, and its usefulness has been well established for many years in a wide range of industrial applications. Recently its value in all types of water purification applications has been coming to the fore because of its ability to act as a powerful oxidant, microflocculant and disinfectant without producing toxic side-products. The most widely used method of generating ozone is to flow dry air or oxygen through a narrow gap bordered on one side by a conductive electrode and on the other side by a dielectric electrode (surfaced on the side which faces away from the gap with an electrical conductor). An alternating high voltage is connected across the electrodes, producing a high voltage field across the gap which creates a corona discharge. This discharge, which is also known as a "silent discharge" or "cold plasma discharge" and is actually composed of many transient microdischarges, converts a percentage of the gas to ozone. The dielectric is necessary to prevent these microdischarges from becoming arcs between the conductive electrodes, which would rapidly destroy the electrode surfaces. The majority of high quality prior art corona ozone generators have been designed for large-scale industrial-type applications. Today there is a great need in numerous water treatment applications for small stand-alone cells which are very reliable and yet reasonable in cost and easily maintained. Much of the prior art that has addressed this need consists of scaled down versions of previous designs, and because they still retain many of the large-scale design features, are often extremely expensive, and are difficult to assemble and service. Corona ozone generators usually fall into one of two general categories: either the concentric tubular type, in which an elongate annular corona gap is created between a metal tube and a dielectric tube, or the flat plate type, in which a flat corona gap is formed between a metal plate and a dielectric plate. Both types are well known in prior art, with numerous patents having been issued, for designs in both categories.

US 5,211,919 to Conrad, hereby included by reference and illustrated in Fig. 1, discloses a flat plate type ozone generator, which involves two essentially flat electrodes 12,30 held in parallel by intermediate spacers 32, defining a corona gap between the flat portions of the electrodes. As is obvious from Fig. 1, although the electrodes are preferably circular, and the corona cell defined there between is at the perimeter of the electrode pair delimited by an outer shell 14, which is sealed towards the electrodes. At said perimeter the gap of the corona cell is substantially increased, thus defining a distribution area extending around said perimeter. The distribution area is devised with inlet ports 18 for gas in the form of fresh air or oxygen, which gas is first distributed around the distribution area before it flows centripetally through the narrow corona gap towards the center of the corona chamber, where an outlet port 20 is arranged in one or both of the electrodes.

During the passage between the electrodes from the distribution area to the outlet port, a high voltage at high frequency is applied over the electrodes, causing oxygen present in the introduced gas to convert into ozone. The dielectric 28 necessary for the corona discharge is a flat element arranged between, and in parallel with, the flat portions of the electrodes. In one embodiment the dielectric is suspended by said spacers, and is arranged in between the electrodes without contact to any of said electrodes. In this embodiment, the dielectric is preferably suspended by the spacers on a few discrete perimeter points, thus allowing gas to flow from one side of the dielectric to the other side. In another embodiment the dielectric is arranged directly attached to one of the electrodes.

The proposed solution in us 5,211,919 is a single corona cell, meaning that each generated corona extends between the first and the second electrode, regardless of the space between the electrodes being divided by the dielectric into two gas chambers or not. Therefore, during operation there will always be a different electric potential or phase on the two electrodes of one cell, caused by the alternating current used for the oxygen-to-ozone conversion. One problem associated with the referred to solution is cooling of the generator. A great deal of heat is generated during ozone generation in a corona cell. Heat has a negative effect on the ozone output, and some form of cooling is thus required. The most efficient way of cooling the electrodes is by means of a cooling liquid, which is also one example proposed by the author. However, since the two electrodes of a common cell have different potential or phase, the use of a common water cooling system for cooling the two electrodes is inhibited due to the risk of spark-over in the cooling system. An alternative to the use of water is to use a non-conductive cooling oil. However, this has obvious negative effects in terms of cost, handling and maintenance.

A second problem is associated with having different voltage or phase on the outer electrodes. The consequence is that either one or both of the outer surfaces of the electrodes will have to be incapsulated in order to obtain an ozone generator which is safe to handle. A third problem with the proposed solution, having a freely suspended dielectric dividing the corona cell into two gas chambers, is associated with the general desire to decrease the gap width. If a corona gap of 0,2 mm is to be divided by a dielectric in half, two gaps of only 0,1 mm will be obtained. Needless to say, it will then be much more difficult to ensure that the same gap width will occur in both gas chambers over the entire corona cell. Where the gap is larger on one side of the dielectric than on the other side, the corona will also be concentrated to that side. There is thus a risk for coronas to appear on different sides of the dielectrode throughout the corona cell, placing uneven strain on the dielectric. The result is an increased risk for failure due to cracks in the dielectric.

A fourth problem is related to gas pressure, in combination with the small corona gap width. When trying to improve the productivity of ozone generators, an increased gas input pressure is one alternative. In order to prevent the walls from bulging, i.e. the inside surfaces of the corona cell, the electrode elements will have to be made with a certain thickness in order to achieve a desired rigidity. However, in order to improve the efficiency of the oxygen-to-ozone conversion, also a reduced width of the corona gap is desired. But with a gap width of 0.2 millimetre or less, any gas pressure above atmospheric means that even with a fairly thick second type electrode 101,101 ', its walls will bulge to a degree that is quite significant in relation to the gap width. Since the ozone generator is preferably tuned to operate optimally at the chosen gap width, an increased pressure may actually decrease the ozone output.

Summary of the Invention For the purpose of solving the problems related to the prior art, the present invention relates to an ozone generating apparatus comprising a flat plate double cell arrangement, said apparatus including a first corona cell comprising a first spacing and a first dielectric member arranged between a first pair of conductive surfaces; a second corona cell comprising a second spacing and a second dielectric member arranged between a second pair of conductive surfaces. The invention is characterized in that a first of said first pair of conductive surfaces, and a first of said second pair of conductive surfaces are opposing sides of a first type electrode.

In an embodiment said first type electrode comprises two electrically connected electrode elements, which may be connected by a conductive wire, or be arranged in contact with each other with mechanical connection. In another embodiment said first type electrode is a single electrode element. The first type electrode is preferably devised to be connected to an alternating high voltage. The second of said first pair of conductive surfaces is preferably an inner side surface of a first second type electrode, and the second of said second pair of conductive surfaces is preferably an inner side surface of a second type electrode. The second type electrodes are preferably connectable to a common electric potential of equal phase. Said second type electrodes preferably comprise passage means for a fluid cooling agent. Said spacing of each corona cell preferably comprises a first type spacing, delimited by a surface of the dielectric member facing away from the first type electrode and the inner surface of the second type electrode of the respective corona cell. Gas inlet means to the first type spacing of each cell are preferably connected to a common gas inlet. In one embodiment said spacing of each corona cell comprises a second type spacing, delimited by the surface of the first type electrode and a surface of the dielectric member facing said first type electrode of the respective corona cell. Gas inlet means to the second type spacing of each cell are connected to a common gas inlet. First spacing elements are preferably arranged in said first type spacing of each cell, in direct contact with the inner surface of the second type electrode and the surface of the dielectric element delimiting said first type spacing. Second spacing elements are preferably arranged in said second type spacing of each cell, in direct contact with the surface of the first type electrode and the surface of the dielectric element delimiting said second type spacing. In a preferred embodiment each corona cell comprises a gas passage orifice formed in the respective second type electrode, and a first aperture is formed in the first type electrode, said first aperture opposing the gas outlet orifice of both corona cells. Said first aperture preferably has a diameter, which is at least as large as the diameter of said outlet orifices. In one embodiment a second aperture is formed in each of said dielectric member, overlapping said first aperture. Said second aperture preferably has a diameter, which is less than the diameter of the first aperture is. Said first aperture preferably has an inner envelope, said envelope being covered by a dielectric shield.

Preferably said passage means of each second type electrode comprises a cooling chamber with input and output cooling agent apertures, said cooling chamber extending over an area substantially corresponding to the corona cell diameter. The ozone generating apparatus preferably comprises a pressure control unit, devised to control and equalize the pressure of gas input to said corona cells and pressure of said fluid cooling agent input to said cooling chamber .

Brief description of the drawings

Preferred embodiments of the present invention will be described in greater detail below, at the same time referring to the drawings. It should be noted that the drawings are merely schematic, and for the purpose of being easy to interpret the dimensional relationships are not necessarily representative of a functional embodiment of the present invention. This concerns e.g. the gap width of the corona cells, which in reality preferably is only a fraction of a millimetre. Furthermore, not all details are marked with references in every drawing. Details that are not explicitly indicated with references in some drawings can however easily be identified through at least one of the other drawings where the same detail is identified with a reference. In the drawings

Fig. 1 is an exploded perspective view of the flat plate corona cell of the prior art; Fig. 2 illustrates schematically an embodiment of the present invention, wherein the center electrode comprises two separate, spaced-apart elements;

Fig.3 illustrates schematically an embodiment of the present invention, wherein the center electrode comprises two separate elements arranged in contact;

Fig.4 illustrates schematically an embodiment of the present invention, wherein the center electrode comprises one electrode element;

Fig. 5 illustrates schematically an embodiment of the present invention, wherein the center electrode comprises one thin electrode element;

Fig. 6 illustrates schematically an embodiment of the present invention, comprising spacing elements in the corona cells; Fig. 7 illustrates schematically an embodiment of the present invention, wherein each corona cell comprises two gas chambers divided by the respective dielectric member;

Fig. 8 illustrates schematically an embodiment according to Fig. 7, comprising spacing elements in the corona cells; Fig. 9 illustrates schematically an embodiment of the present invention, having a distribution chamber at the perimeter of each corona cell;

Fig. 10 illustrates schematically an embodiment of the present invention, comprising an opening in the center electrode and the dielectric members;

Fig. 11 illustrates schematically an embodiment according to Fig. 10, as seen from the front, with circles representing the corona cell perimeter, the center electrode opening diameter, the dielectric member opening diameter, and the outlet opening;

Fig. 12 illustrates schematically an embodiment according to Fig. 6 or 8, as seen from the front, with circles representing the corona cell perimeter and the outlet opening, and radial markings representing the spacing elements, and

Fig 13 illustrates schematically a preferred embodiment of the invention having a recessed portion for passage of a fluid cooling agent in the second type electrodes, and an arrangement of mounting two double cells together, with coupled passages for a cooling agent. Detailed description of the Invention

The present invention solves the problems related with the prior art by providing a flat plate ozone generator having a double cell arrangement. A first type electrode is arranged centrally between a pair of second type electrodes. By electrode is intended a conductive electrode member, useable for application of an electrical current for the purpose of generating a corona.

A first corona cell 102 is thereby defined between a first surface 103 of said first type electrode 100 and an inner surface 104 of one 101 of said second type electrodes, and a second corona cell 102' is defined between a second surface 103 ' of the first type electrode 100, opposing said first side 103, and an inner surface 104' of the other 101 ' second type electrode. Each corona cell 102, 102' of the double cell ozone generator further comprises a dielectric member 110, 110'. A first dielectric member 110 is positioned between the first type electrode 100 and said one 101 of the second type electrodes in the first corona cell 102. A second dielectric member 110' is positioned between the first type electrode 100 and said other 101 ' of the second type electrodes in the second corona cell 102 '.The suspension arrangement of the dielectric members 110, 110' and the first type electrode 100 is such that there is a first type spacing 129 between the first dielectric member 110 and said one 101 of the second type electrodes, and also a first type spacing 129' between the second dielectric member 110' and said other 101 ' of the second type electrodes, said first type spacing allowing gas to flow between the respective second type electrode 101, 101 ' and the respective dielectric member 110, 110'.

A perimeter encapsulation 122 is devised to enclose the respective cell 102, 102' at a perimeter thereof. In the illustrated embodiments of Figs. 2- 10, the perimeter encapsulation is schematically illustrated as a single element surrounding the cells 102, 102', but naturally separate parts for the different cells 102, 102' may be used. In one embodiment, the encapsulation 122 is made of an electrically insulating material, and may thus be arranged in direct contact with both the first 100 and the second 101, 101 ' electrode type, and is optionally integrated with said spacer means 105, 105'. In an alternative embodiment, center first type electrode 100 is suspended by electrically insulating spacer means 105, 105', electrically separated from the encapsulation 122, whereas the encapsulation 122 is made of a conductive element arranged in contact with, or as an integrated part of, the second type electrodes 101,101 '.

At least a portion of said surfaces 103, 103', 104, 104' of the electrodes are essentially flat, and are held in a substantially parallel arrangement together with the dielectric members 110, 110' by spacer means 105, 105', located between the respective second type electrode 101, 101 ' and the respective dielectric member 110, 110'. First spacer means 105 are arranged between the first dielectric member 110 adjacent the first surface 103 of the central first type electrode 100, and the inner surface 104 of said one 101 of the second type electrodes, said first spacer means thus defining a first corona gap width of the first type spacing, relating to said first corona cell 102. Second spacer means 105' are arranged between the second dielectric member 110' adjacent the second surface 103 ' of the first type electrode 100 and the inner surface 104' of said other 101' second type electrode, said second spacer means 105' thus defining a second corona gap width of the first type spacing relating to said second corona cell 102'. By corona gap is here meant the distance between the second type electrode 101, 101' and the dielectric member 110, 110' of a corona cell 102, 102'. In combination with the thickness of the respective dielectric member 110, 110', spacer means 105, 105' control the electrode distance, which is the distance between surfaces 103,103' and 104, 104', respectively, of a corona cell 102, 102' .In an alternative embodiment, spacer means 105, 105' are directly devised to control the electrode distance. In such an embodiment, the position of dielectric members 110, 110' may also be directly controlled by the said spacer means 105, 105', or by separate spacer means. In one embodiment, spacer means 105, 105', which are merely schematically illustrated in Figs 2 -10, may be arranged to interact with the first type electrode 100 and the dielectric members 110, 110' on discrete perimeter points, rather than around the entire circumference of the respective corona cell 102, 102', thus providing the capability for gas to flow between the corona cells 102, 102' at the perimeter of the cells 102, 102'.

Each corona cell is provided with gas inlet means 106, 106' and gas outlet 107, 107' means. Furthermore, said inlet means 106, 106' are connected to, or devised to be connected to, a single tee 108 for gas supply from a single source. Hence, any pressure variations originating from said source, such as pressure shocks occurring as the gas flow is turned on or of, will be distributed equally to every orifice 109, 109' of said inlet means 106, 106'. Preferably, the orifices 109, 109 ' of the inlet means 106, 106' are arranged at an outer portion of the respective cell, whereas the outlet means 107,107' preferably have orifices 121,121' at a central position of each cell 102, 102'. In a preferred embodiment, wherein the corona cells 102, 102' are essentially circular in shape, the inlet means orifices 109, 109' are preferably arranged at the perimeter of the respective circular corona cell, and the outlet means orifices 121, 121 ' at the circular center of the respective cell 102, 102'. Preferably the inlet 106, 106' and outlet 107, 107' means are arranged as channels and orifices formed in the second type electrodes 101, 101'. In an alternative embodiment, the inlet means 106, 106' are arranged at the center of the respective cell, whereas the outlet means 107, 107' are arranged at said perimeter. The second type electrodes 101, 101' are preferably manufactured in aluminum, stainless steel, or other metal, or as a combination or alloy comprising different metals. Furthermore, the second type electrodes 101, 101 ' are rigid elements which are designed to be essentially unaffected by any foreseeable gas pressure within the corona cells 102, 102'. For the purpose of cooling the ozone generator, each second type electrode 101, 101 ' is devised passage means 111, 111 ', e.g. conduits, for a liquid cooling agent, preferably water. During operation, each second type electrode 101, 101 ' is devised to be connected to an alternating high voltage having the same potential Pj and the same phase. Consequently, the same cooling system can be used for both second type electrodes 101, 101' of the ozone generator, even though the cooling agent is conductive. Preferably the second type electrodes 101, 101 ' are grounded, further decreasing the risk of spark -over in an attached cooling system devised to circulate the cooling agent.

The first type electrode 100 is not suitable for connection to the same cooling agent as the second type electrodes 101, 101 ' as previously explained. During operation, however, the corona triggered oxygen-to-ozone conversion between a conductive surface and a dielectric surface will be concentrated to the area of the corona gap closest to the conductive surface, which is also where most of the heat will be generated. With the arrangement according to the present invention, wherein the conductive surface 104, 104' delimiting each respective corona gap is a cooled second type electrode 101, 101 ', generated heat is effectively taken care of. Furthermore, since the first type electrode 100 is situated in-between two cooled second type electrodes 101, 101 ', only separated therefrom by the small corona gap, any heat generated in the vicinity of the first type electrode 100 is swiftly transferred to the surrounding cooled second type electrodes 101, 101 '. Hence, the center first type electrode 100 is preferably left uncooled. In alternative embodiment, the center first type electrode 100 is separately cooled by a non-conductive agent, e.g. by circulating oil or air in channels formed in said first type electrode 100. With the proposed arrangement, three things are achieved: -Cooling is readily achieved using plain water;

-Since the most exterior electrodes 101, 101' in the preferred embodiment are grounded, non of the parts of the ozone generator facing its exterior will be charged with an electric potential during operation. Thus, the double cell ozone generator body does not have to be electrically shielded, and is therefore easy to handle and operate;

-With the proposed double cell arrangement with flat parallel electrodes, the length of each corona will be essentially constant throughout each corona cell, and the length of the corona will furthermore be the same on opposite sides of the respective corona cell. This means that the entire surface 104, 104' of the respective corona cell, apart from any present apertures in any of the opposing electrodes of a cell, will be fully utilized during operation for the purpose of ozone generation. In one embodiment of the present invention, as illustrated in Fig. 2, the center first type electrode 100 comprises a pair of first type electrode elements 100', 100", which are electrically connected to each other. During operation the first type electrode 100 pair 100', 100"are devised to be coupled to the same high voltage potential P2. The electrical connection is achieved e.g. by a conductive wire, as indicated in Fig. 2, or by placing the sides of the respective first type electrode elements 100', 100"opposing the respective dielectric member 110, 110' in direct contact with each other, as indicted in Fig. 3. In yet another embodiment, illustrated in Fig. 4, the first type electrode 100 contains only one electrode element, having opposing sides 103, 103' facing the respective dielectric member 110, 110'. The embodiments illustrated in Figs 2-4 provide capability of cooling the first type electrode 100 separately, e.g. by circulating a non-conductive fluid cooling agent, such as oil, or by blowing air, between the separated but wire-connected first type electrode elements 100', 100" Said cooling agent can also be circulated through channels in the single first type electrode elements 100', 100 "arranged in contact with each other, or a single first type element 100.

Another embodiment is illustrated in Fig. 5, and is especially devised to reduce size. The center electrode 100 of the first type is a single element, and is left uncooled. It is also made quite thin -with the proposed solution a thickness of a couple of microns is possible, although any desired thickness there above is possible. With decreasing size of the first type electrode 100, there is an increased risk for said first type electrode 100 to bend, and thereby to crack the dielectric elements 110, 110', due to sudden pressure variations in one of the corona cells. However, with the inlet means 106, 106' to the two cells being connected, or being devised to be connected to, the same gas supply source, any pressure variation occurring in one cell 102 will also occur in the other cell 102'. This way pressure compensation is achieved. As a consequence, there is no resulting force acting perpendicularly on any side of the respective dielectric members 110, 110', whereby the risk for damage to the dielectric members 110, 110' is clearly minimized or eliminated.

In one embodiment, illustrated in Figs. 10 and 11, an aperture 112 is made in the central first type electrode 100. In one embodiment an aperture 114, 114' is made also in the dielectric elements 110, 110'. When the orifice 121 , 121 ' of the outlet means 107, 107' from a corona cell 102, 102' is arranged in the center of the second type electrode 101, 101 ', there is of course no conductive material on that side of the corona gap. Hence, no corona can be formed there, and consequently there is no need for the first type electrode 100 to cover the area opposing said orifice 121, 121' of the outlet means 107, 107'. By eliminating a portion of the first type electrode 100 corresponding to said orifice 121, 121', i.e. introducing an aperture 112 in the first type electrode 100, the total surface area of the first type electrode 100 is decreased. As a result, the capacitance is decreased in the corresponding amount. This means that also the impedance is decreased, whereby power loss in the corona cell 102, 102' during operation is decreased. Furthermore, the speed of the gas flow close to the outlet orifice 121, 121' is significantly higher than at the outer parts of the cell 102, 102', close to the perimeter. Consequently, the productivity in the vicinity of the center is significantly less than at the outer parts, and does not contribute to a great extent to the overall ozone productivity .

Therefore, in order to even further decrease the electrical impedance, the center aperture 112 in the first type electrode 100 can be made even larger than the opposing ozone outlet orifices 121, 121 ' in the second type electrodes 101, 101 '. In an exemplary embodiment the diameter of the aperture 112 in the first type electrode 100 can be up to 50% of the corona cell diameter 113, which corona cell diameter 113 defines the perimeter limit of the portion where a parallel arrangement of the electrodes is maintained so that a corona can appear during operation. Preferably the diameter of the aperture 112 is within 10- 25% of the corona cell diameter 113. However, the preferred specific or relative size of the aperture 112 in the first type electrode 100 is dependent on other parameters. Such parameters are e.g. the flow speed of the gas at the center of the cell, which in turn is dependent on the input pressure, and the physical dimensions of the cell 102, 102'. In one embodiment, as illustrated in Figs 10 and 11, apertures 114, 114' are made also in the dielectric elements 110, 110'. Apertures 114, 114' can be of the same size as aperture 112 in the first type electrode 100, but as evidenced by Figs 10 and 11, apertures 114, 114' are in one embodiment slightly smaller in diameter than aperture 112, in order to minimize the risk of spark-over within the cells 102, 102'. In an alternative embodiment, also the inner envelope of aperture 112 is covered by a dielectric shield. In an embodiment where the first type electrode 100 is a single element, as in Figs 6- 10, the aperture 112 therein provides a passage between the opposing corona cells 102, 102' of the inventive double cell arrangement. In an embodiment where two elements 100', 100 "are comprised in the first type electrode 100, each element 100', 100" will have an aperture 112, 112'. These apertures 112, 112' may be connected through a pipe, or they may be sealed towards each other. Fig 11 shows a front view of a corona cell 102, indicating the cell diameter 113, aperture 112 of the first type electrode 100, aperture 114 of the dielectric member 110 and orifice 121 of the outlet means 107.

In one embodiment of the present invention, the respective dielectric members 110, 110' are arranged directly towards opposing sides 103, 103 ' of the first type electrode 100, in mechanical contact therewith. In an alternative embodiment, illustrated in Fig 11, a second type spacing 115 is formed between the first type electrode 100 and each of the respective dielectric members 110, 110' .In such an embodiment, the second type spacing 115 of the respective corona cell 102, 102' are preferably connectable with gas inlet means 116, 116' to a tee 117 connectable to a common gas supply source. Furthermore, the previously mentioned first type spacing between the respective dielectric member 110, 110' and the respective second type electrode 101, 101 ' are also connectable via inlet means 106, 106' to the same common gas supply source as said second type spacings 115. This means that pressure variations originating from said supply source will act on both sides of each dielectric member 110, 110', as well as on both sides of the first type electrode 100. This makes it possible to manufacture the dielectric elements 110, 110' as well as the first type electrode 100 very thin, and still be able to operate the ozone generator with an increased gas pressure. Consequently, an increased ozone productivity is made possible, at the same time as the physical dimensions of the ozone generator can be minimized.

In one embodiment of the invention, illustrated e.g. in Figs 6 and 12, first spacing elements 118, 118' are arranged in the first type spacing between, and in contact with, the respective second type electrode 101, 101 ' and the respective dielectric member 110, 110'. These spacing elements 118, 118' are preferably arranged as ribs in a radial pattern, as illustrated in Fig. 12, and are devised to secure that an even gap distance is maintained throughout the corona cell 102, 102'. In an embodiment where said second type spacing 115, 115' is formed, illustrated in Fig 12, also the gap distance of this second type spacing 115 is preferably controlled by second spacing elements 119, 119' between, and in contact with, both one side 103, 103' of the first type electrode 100 and the side of the respective dielectric element 110, 110' facing the first type electrode 100. The spacing elements 118, 118', 119, 119' may be conductive or dielectric.

In a preferred embodiment the gap distance between the first type electrode 100 and each of the second type electrodes 101, 101 ' is greatly increased at the perimeter of the respective corona cell 102, 102' , thus defining a gas distribution chamber 120, 120', into which said inlet means 106, 106' discharges through orifices 109, 109'.

In an embodiment, illustrated schematically in Fig. 13, passage means 111 for the cooling liquid in second type electrode 101 comprises as a recessed portion 123. In the illustrated example, outlet means 107 for ozone preferably leads inside the second type electrode 101 to the perimeter encapsulation 122. In an alternative embodiment, the outlet means 107 discharges directly out through the side of the second type electrode 101, as illustrated e.g. in Fig. 2. In such an embodiment, the recessed portion 123 preferably does not involve the central portion of the second type electrode 101, said central portion including the outlet means 107 and the vicinity thereof. However, for the purpose of making the drawing easy to understand, neither inlet means 106, 106' nor outlet means 107, 107' are shown in Fig. 13. As illustrated in Fig. 13, the recessed portion 123 is covered by a lid 124, fastened by screws, nuts, rivets or the like 125. In the illustrated embodiment, cooling agent apertures 126, 127 are arranged at the perimeter portion of the recessed portion 123, providing the capability of circulating a cooling agent, such as water, through the passage means 111 defined by the recess 123 and the lid 124. An advantage with this embodiment is that it is easy to form complex patterns of cooling ducts as recesses 123 by milling. The ducts are closed when the lid 124 is applied, and this way a cooling agent entered in aperture 126 is forced to run in the pattern determined by the recessed ducts before exiting through aperture 127, which provides the capability of improved cooling. Preferably an endless seal 128, such as an O-ring, is arranged to seal the lid 124 towards the second type electrode 101. Obviously, the features described with reference to Fig. 13 is also applicable to the other corona cell 102', with its second type electrode. However, as illustrated in Fig. 13, second type electrode 101 ' is in one embodiment connected to yet another second type electrode 101 " of a second double cell arrangement. Apart from the comiected second type electrodes 101 ' and 101 ", being connectable to the same electric potential and phase Pi , they are also devised to form a common set of cooling agent ducts through the respective recesses 123 ' and 123 " In the embodiment according to Fig. 13, there is no lid between the connected electrodes 101 ' and 101 ", and preferably only one seal 128' is needed between said two electrodes. The combination of two double cells as illustrated in Fig. 13 can of course include even more double cells, connected by the second type electrodes 101, 101 ', 101 ", etc, with lids 124 arranged only at the outermost second type electrodes 101, 101 ". Obviously, any type of first type electrode arrangement according to the embodiments illustrated in Figs. 2 -10 is, with no or minor adjustments, applicable to the embodiment of Fig. 13.

Another preferred embodiment of the invention can be described with reference to Fig. 13, solving the problem relating to the gas pressure in combination with a small gap width. In the proposed embodiment, the recessed portion 123 forms a cooling chamber with a large outer diameter, preferably covering, or almost covering, the entire corona cell diameter 113. Furthermore, during operation the fluid cooling agent, preferably water, is pressurized to the same degree as the gas input into the corona cells 102, 102'. Hence, pressure equilibrium is obtained on the opposing sides of each second type electrode, thus eliminating the risk of the inner surface 104, 104' to bulge as the input gas pressure through inlet means 106, 106', 116, 116' is raised above atmospheric pressure. Preferably a pressure control unit (not shown) is coupled both to the gas supply source and the cooling agent system, and including means for obtaining the same pressure in the gas fed to the corona cells 102,102' and the fluid cooling agent fed to the cooling chambers 123, 123', In a preferred embodiment, the ozone generator of the present invention is devised, by said pressure control unit, to be operated with an input pressure of both gas and cooling fluid of 3 bar.

It should also be noted that by a flat plate ozone generator type is intended cells which are delimited by a first and a second surface which at each point are essentially parallel to each other, and which surfaces are limited in two dimensions. This means that the present invention is fully applicable to a design resembling a traditional flat plate generator arrangement, but where the limiting surfaces are bent, folded or in any other way deviating from an overall flat form, though still being parallel to each other. While this invention has been described in connection with preferred embodiments thereof, it is obvious that modifications and changes therein may be made by those skilled in the art to which it pertains without departing from the spirit and scope of this invention. Needless to say, several combinations of the presented embodiments can be realized, without departing from the scope of the invention as defined by the appended claims.

Claims

1. Ozone generating apparatus comprising a flat plate double cell arrangement, said apparatus including:

-a first corona cell (102) comprising a first spacing (129,115) and a first dielectric member (110) arranged between a first pair (103,104) of conductive surfaces; -a second corona cell (102') comprising a second spacing (129', 115) and a second dielectric member (110') arranged between a second pair (103', 104') of conductive surfaces; characterised in that a first (103) of said first pair of conductive surfaces, and a first of said second pair of conductive surfaces are opposing sides of a first type electrode (100).

2. Ozone generating apparatus according to claim 1, wherein said first type electrode (100) comprises two electrically connected electrode elements (100',100").

3. Ozone generating apparatus according to claim 2, wherein said two electrically connected electrode elements (100', 100") are connected by a conductive wire.

4. Ozone generating apparatus according to claim 2, wherein said two electrically connected electrode elements (100', 100") are arranged in contact with each other with mechanical connection.

5. Ozone generating apparatus according to claim 1, wherein said first type electrode (100) is a single electrode element.

6. Ozone generating apparatus according to claim 1, wherein said first type electrode (100) is devised to be connected to an alternating high voltage.

7. Ozone generating apparatus according to claim 1, wherein the second (104) of said first pair of conductive surfaces is an inner side surface of a first (101) second type electrode, and the second (104') of said second pair of conductive surfaces is an inner side surface of a second (101 ') second type electrode.

8. Ozone generating apparatus according to claim 7, wherein said second type electrodes (101,101 ') are connectable to a common electric potential of equal phase.

9. Ozone generating apparatus according to claim 8, wherein said second type electrodes (101,101') comprise passage means (111,111 ',123,126,127) for a fluid cooling agent.

10. Ozone generating apparatus according to claim 7, wherein said spacing of each corona cell comprises a first type spacing (129,129'), delimited by a surface of the dielectric 111 ember (110,110') facing away from the first type electrode (100) and the inner surface (104,104') of the second type electrode (101,101 ') of the respective corona cell (102,102').

11. Ozone generating apparatus according to claim 7, wherein gas inlet means (106,106') to the first type spacing {129,129') of each cell (102,102') are connected to a common gas inlet (108).

12. Ozone generating apparatus according to claim 7, 10 or 11, wherein said spacing of each corona cell comprises a second type spacing (115,115'), delimited by the surface (103,103') of the first type electrode (100) and a surface of the dielectric member (110,110') facing said first type electrode (100) of the respective corona cell (102,102').

13. Ozone generating apparatus according to claim 12, wherein gas inlet means (116,116') to the second type spacing (115,115') of each cell (102,102') are connected to a common gas inlet (117).

14. Ozone generating apparatus according to claim 10, wherein first spacing elements (118,118') are arranged in said first type spacing (129,129') of each cell (102,102'), in direct contact with the inner surface { 104,104') of the second type electrode (101,101 ') and the surface of the dielectric element (110,110') delimiting said first type spacing (129,129').

15. Ozone generating apparatus according to claim 12 and 14, wherein second spacing elements (119,119') are arranged in said second type spacing (115,115') of each cell (102,102'), in direct contact with the surface (103,103') of the first type electrode (101,101 ') and the surface of the dielectric element (110,110') delimiting said second type spacing (129,129').

16. Ozone generating apparatus according to claim 1 and 7, wherein each corona cell (102,102') comprises a gas passage orifice (121,121 ') formed in the respective second type electrode (101,101 '), and where a first aperture (112) is formed in the first type electrode (100), said first aperture opposing the gas outlet ori fice (121,121 ') of both corona cells (102,102').

17. Ozone generating apparatus according to claim 16, said first aperture (112) having a diameter which is at least as large as the diameter of said outlet orifices (121,121 ').

18. Ozone generating apparatus according to claim 16, wherein a second aperture (114,114') is formed in each of said dielectric member (110,110'), overlapping said first aperture (112).

19. Ozone generating apparatus according to claim 18, wherein said second aperture (114,114') has a diameter which is less than the diameter of the first aperture (112) is.

20. Ozone generating apparatus according to claim 19, wherein said first aperture (112) has an inner envelope, said envelope being covered by a dielectric shield.

21. Ozone generating apparatus according to claim 9, wherein said passage means (111,111 ') of each second type electrode (101,10 1') comprises a cooling chamber

(123,123') with input and output cooling agent apertures (126,127), said cooling chamber extending over an area substantially corresponding to the corona cell diameter (113).

22. Ozone generating apparatus according to claim 21, comprising a pressure control unit, devised to control and equalize the pressure of gas input to said corona cells (102,102') and pressure of said fluid cooling agent input to said cooling chamber (123).