WO2011015987A1

WO2011015987A1 - Ozone generator

Info

Publication number: WO2011015987A1
Application number: PCT/IB2010/053509
Authority: WO
Inventors: Luigi Civitano; Francesco Muzzi
Original assignee: Luigi Civitano; Francesco Muzzi
Priority date: 2009-08-03
Filing date: 2010-08-03
Publication date: 2011-02-10
Also published as: ITFI20090175A1; IT1395066B1

Abstract

An ozone gas generator apparatus comprising a plurality of electrodes and a plurality of dielectric plates arranged in alternating sequence to form a stack; a plurality of seals interposed between said electrode and said dielectric material plate and adapted to seal said apparatus and maintain the correct distance between said electrodes and said dielectric slab; fastening means adapted to secure said electrode and said dielectric slabs to one another and appropriate cooling means of said electrodes.

Description

OZONE GENERATOR

Field of the invention

The present invention relates to the technical field of ozone generators, in particular to the field of ozone generators for industrial use.

Prior art

Ozone is a powerful oxidizer and bactericide. The bactericide action of ozone is due to its capacity of breaking the cellular membrane of bacteria. Ozone is used in many processes, such as: disinfection of drinking water (in this application, in addition to the bactericide action, it is worth noting that ozone can oxidize any traces of iron present in the water transforming it into easily removable, insoluble oxide), sewage treatment, discoloration of textile industry water, elimination of odors, destruction of phenols, disinfection of water in fish farms, in swimming pools, etc.

Ozone is generally produced using pure oxygen or atmospheric air.

The reactions which transform oxygen into ozone are:

O2 + e* -» O3 + O ^" (1 )

02 + e ^■» 02^" 02^" + O2 = 03 + O ^" (2)

Reaction (1 ) is a resonant dissociation reaction, which requires the presence of free electrons (e*) provided with high energy, typically in the range of 5-7 eV, while reaction (2) occurs by means of an attachment process of a low-energy electron (e) to the oxygen molecule.

Many electrodic geometries have been suggested for the production of ozone using atmospheric air or pure oxygen. However, ozone generators used in industries, where the reliability factor is essential, are mainly based on an electrodic geometry consisting of tubes made of glass or other dielectric material, within which a layer of high electricity conducting material is deposited. These tubes are then coaxially inserted into tubes made of steel or other metal which, preferably, must have a high thermal - in addition to electric - conductivity.

A gap is left between the two tubes through which the gas intended to be enriched with ozone is passed.

In order to produce the free electrons capable of transforming part of the oxygen contained in the primary gas, an alternating voltage generator is connected between the conducting material deposited within the glass tube and the outer metal tube.

By applying an appropriate voltage, a discharge is generated in the gas between these two electrodes, which gives rise to the formation of non-thermalized plasma, the free electrons of which may have average energy in the order of 4-6 eV, and thus capable of dissociating the molecules of oxygen, thus producing ozone by means of reaction (1 ).

The low-energy electrons which allow to favor reaction (2) are mainly produced in the discharge channel and during the step of quenching of the discharge itself. The efficiency of an ozone generator, expressed in grams of ozone produced per kWh of energy transferred to the gas, decreases as the concentration of ozone increases and as the gas temperature increases. Thus, having fixed the desired ozone concentrations, the average gas temperature must be kept low to increase process efficiency.

The average gas temperature is reduced by cooling the surface of the outer metal tube. The gas is cooled mainly by means of a conduction process, and therefore the gas temperature in the gap increases according to the following law:

T(x) = T(O) ₊^-

4 - h₀

where:

T(O) = temperature of the cold wall,

Ps = specific transferred power expressed as w/m² ,

h_o = thermal conductivity of gas passing through the gap,

x = distance from the cold wall.

Thus, indicating with d the distance (gap) between the inner surface of the cooled metal tube and the outer surface of the glass tube, the maximum temperature reached by the gas is:

Ps -d

T(d) = T(0) +

4- K

From this ratio, it is apparent that with the power transferred to the gas per unit of surface being equal, the maximum temperature of the gas is reduced by decreasing the size of the gap; and conversely, with the thermal rise being equal, the power transferred to the gas per unit of surface can be increased by decreasing the gap dimensions, thus reducing by far the dimensions of the ozone generator.

This is the reason why, in devices for the generation of ozone gas of the prior art, all efforts are addressed to reducing the dimensions of the gap described above, i.e. the distance between the inner surface of the cooled metal tube and the outer surface of the glass tube.

In industrial ozone generators, glass tubes with diameter in the order of 5-10 cm and length in the order of one meter are generally used; for these geometries, the gap is approximately 0.7-1 mm. Smaller gaps may be made, but this causes an exponential increase of production costs.

Furthermore, the cooling system generally used in tube ozone generators has the drawback of poor water turbulence near the metal tubes to be cooled. This causes the presence of a limit layer of non-negligible dimensions near the tube to be cooled, and thus a low heat exchange between water and tube.

Other ozone generators of the prior art are made using the so-called slab technique. According to this technique, the electrodes consist of two flat metal slabs, parallel to one another. The dielectric is generally deposited on either one of or both the electrodes. The drawback generally presented by this solution consists in that the deposited dielectric acts as thermal insulator, and thus reduces the heat transfer from the gas to the cooled metal electrode. The deposit on alumina on the electrodes by means of the plasma spray technique has been proven to be poorly reliable and not usable in industrial ozone generators. The cost of coating an electrode with an alumina plate is prohibitive. Furthermore, another reason for which this technique has not yet been used for industrial applications is related to the difficulty of introducing gas into the gaps, and thus the difficulty of making medium and high power commercial generators capable of high hourly ozone production rates at acceptable costs.

Only the electrode connected to ground is normally cooled in medium and high power ozone generators. For example, in patent application US 2004/0076560 A1 (April 22, 2004), this choice is explained by asserting that cooling only the electrode connected to ground allows to use non-demineralized water for cooling. The cooling of both electrodes (both those connected to ground and those connected to high voltage) does not in actual fact have any drawback and offers considerable advantages. Indeed, in the system described in patent application

US 2004/0076560, if the cooling system is of the closed circuit type equipped with chiller, the water used must contain additives to prevent fouling (i.e. use of common tap water is not convenient); if instead the cooling system is of the open type, i.e. the cooling water is lost, the problem of water conductivity does not exist.

With the type and thickness of the dielectric used, the working frequency and the maximum temperature reached by the gas being equal, cooling both the electrodes connected to ground and the electrodes connected to high voltage allows to transfer a specific power to the electrodic structure which is double with respect to that which can be transferred by cooling only one electrode (with consequent halving of the electrodic surface, with the hourly production rate of O₃ and the maximum temperature reached by the gas being equal) and to increase the cosφ of the electrodic structure; the latter effect allows to reduce the apparent power required by the voltage generator, and consequently favors a cost reduction of the voltage generator and a reduction of electric loss.

Brief description of the figures

Fig. 1 shows a section view of the basic element of the device according to the present invention.

Fig. 2 shows a section view of a preferred embodiment of the device according to the present invention made by a stack of basic elements.

Fig. 3 shows a plan view of an intermediate electrode used in a preferred embodiment of the device according to the present invention concerning a stack of basic elements.

Fig. 4 shows a first section view of an intermediate electrode used in a preferred embodiment of the device according to the present invention concerning a stack of basic elements.

Fig. 5 shows a second section view of an intermediate electrode used in a preferred embodiment of the device according to the present invention concerning a stack of basic elements.

Fig. 6 shows a section view of a detail of the device according to the present invention concerning a fastening point, and in particular the insulation of the screws used in said fastening point.

Fig. 7 shows a plan view of the electric material plate used in a preferred embodiment of the present invention.

Fig. 8 shows diagrammatic overview of the cooling system of the electrodes of the device according to the present invention.

Fig. 9 shows an example of embodiment of an intermediate electrode obtained by extrusion with the head terminals 90 and 91 adapted to allow the introduction, exiting and recirculation of the cooling fluid. The electrode is provided with flared holes 92 to allow the passage of gas to the contiguous electrodes. The channels

93 obtained within the electrode and obtained by means of extrusion are shown with a circular section.

Fig. 10 shows an example of embodiment of an intermediate electrode obtained by casting, provided with a steel serpentine necessary to cool the electrode 1 and openings 100 which allow the passage of gas to the continuous electrodes.

Summary of the invention

The present invention concerns an ozone gas generator apparatus comprising the following basic elements: an upper, slab-shaped metal electrode 1 ; a lower electrode V, also slab-shaped, and facing said upper electrode 1 , both such electrodes being cooled by means of a specific fluid and not coated with dielectric material, which would reduce the gas cooling capacity; a dielectric material slab 3 interposed between said upper 1 and lower electrodes 1 ' and distanced from both so as to form two gaps 2, 2', such that, by applying an alternating voltage between said two electrodes 1 , 1' a dielectric barrier discharge is generated between each electrode and said dielectric slab; a plurality of seals 6, 6^! interposed between said electrodes and said dielectric slab and adapted to seal said apparatus and maintain the correct distance between said electrodes and said dielectric plate; fastening means adapted to secure said upper and lower electrodes and said dielectric slab to one another.

The gas to be enriched with ozone enters into gaps gap 2 and 2' through inlet hole

10 and cavities 4, 4" and 4'. The gas enriched with ozone exits from hole 11 through cavities 4a, 4a' and 4a". The gas inlet and outlet are situated on the two ends of the electrodes, and therefore the gas to be treated crosses the entire volume occupied by the discharge present in gaps 2 and 2'.

Intermediate metal electrodes are inserted between these basic elements in order to increase the hourly ozone production rate. Dielectric material slabs separate the contiguous intermediate metal electrodes and the surfaces of the dielectric slabs are distanced from the surfaces of the electrodes so as to form further gaps in which the gas passes and the discharge is generated. These intermediate electrodes are cooled by means of specific fluid and are not coated with dielectric.

Detailed description of the invention

The present invention consists in an ozone generator made using the slab technique and solving the previously described technical drawbacks.

Patent application US 2004/0076560 mentioned above, for example, contains a long description of the prior art of ozone generators and the aforesaid patent suggests a simpler electrodic geometry than the existing ones.

The present invention introduces an electrodic geometry further simplified with respect to the one shown in patent application US 2004/0076560 because the electrodes used in the present invention - both those connected to ground and those connected to high voltage - are made of simple metal slabs, which require simple mechanical machining operations, do not require any material to be deposited on their surface, and - if they are made of aluminum-based alloys - they may also be obtained by extrusion or casting. If electrodes are made of aluminum or other material with a low melting point, said electrodes may be subjected to anodic oxidation or nickel-plating or chrome-plating, etc., in order to increase the surface hardness of the electrode and avoid the phenomenon of material sputtering induced by the discharge.

The absence of dielectric coating on the electrodes, connected to high voltage and/or to ground, combined with the electrodic geometry simplicity drastically reduces the cost of the ozone generator according to the present invention, even if it is has gaps of only 0.1-0.2 mm in size.

Furthermore, with respect to patent application US 2004/0076560, our invention displays the following further advantages:

• The cooling of the electrodes connected to high voltage allows to decrease the electrodic surface, the hourly production rate of ozone being equal.

• Less apparent power required from the supply voltage generator.

• Dielectric is not deposited on the electrodes and therefore said dielectric does not need high thermal conductivity; consequently, the dielectric may be made also using commercial glass or borosilicate glass sheets, i.e. a low cost material which is easy to procure.

• The volume occupied by the gas within the ozone generator is very small and this facilitates compliance with safety standards.

• The ozone generator according to the present invention is intrinsically proof and therefore no supplementary container is needed.

The ozone generator according to the present invention allows to drastically reduce the costs of ozone generators, and will consequently increase the use of ozone in activities until now precluded because of the high investment cost.

Further benefits connected to the ozone generator according to the present invention are:

• Extreme assembly ease of a multitude of electrodes for making generators with a high hourly ozone production rate.

• Possibility of obtaining very small gaps, even smaller than 0.2 mm. The best cost/benefit ratio is obtained with slab size in the order of 0.2 mm.

• Possibility of making the dielectric with insulating material slabs having any thermal conductivity, because the dielectric is not deposited on the electrodes but is positioned between the electrodes and thus does not prevent the electrodes from cooling the gas; furthermore, the discharge gaps are made between each of the two electrodes and the dielectric: therefore each intermediate electrode has two discharge channels, both cooled by the electrode itself.

• Efficient electrode cooling system by virtue of the high speed of the cooling water within the electrode to be cooled for producing high turbulence and reducing the size of the water limit layer.

• Lower apparent power required by the voltage generator due to the higher cosφ, characteristic of the electrodic structure of the present invention.

With reference to appended figure 1 , a first preferred embodiment of the device according to the present invention concerns an ozone generator device comprising two electrodes.

The structure comprises: an upper, slab-shaped electrode 1 ; a lower electrode 1', also slab-shaped, and facing said upper electrode 1 ; said metal electrodes are cooled by a specific fluid and do not need to be coated with any dielectric material, which would reduce their gas cooling efficiency; a slab of dielectric material 3 interposed between said upper 1 and lower 1' electrodes and distanced from both so as to form two gaps 2, 2', in which a discharge is generated; a plurality of seals 6, 6' interposed between said electrodes and said dielectric material slab and having the twofold function of sealing the device in accordance with the present invention while maintaining the correct distance between electrodes and dialectic slab; fastening means adapted to secure said upper and lower electrodes and said dialectic slab to one another. Said upper and lower electrodes further comprise grooves 4, 4', 4a and 4a' made near the side edges and positioned on two opposite sides, preferably on the short sides of said electrodes, as shown, for example, in appended figure 7. Said dielectric material slab comprises two openings 4" and 4a", arranged in position corresponding to said grooves 4, 4', 4a and 4a'. Said upper electrode 1 further comprises at least one through hole adapted to let the gas in/out; in a preferred embodiment of the present invention, said upper electrode 1 comprises two through holes 10, 11 such as to put said grooves 4, 4', 4a and 4a' into communication with the outside and adapted to be connected to external tubes for introduction and emission of gas.

The operation of the ozone generator device comprising two electrodes according to the present invention is: the gas to be enriched with ozone enters into gaps 2, 2' - where the discharge occurs - through a chamber 4, 4', 4", constituted by the grooves belonging to said upper 1 and lower V electrodes and by the opening 4" of said slab of dielectric material and arranged at the gas inlet tube; similarly, the gas let out from the gaps flows into a similar chamber, also constituted by the grooves 4a, 4a' belonging to said upper 1 and lower 1' electrode and by the opening 4a" of said dielectric material slab and arranged at the gas output tube 11. In principle, if the dielectric is 20 times thicker that the gaps, the cavities 4, 4' 4a and 4a' may not be made because the probability of a discharge being sparked between the two electrodes is virtually null. In presence of cavities 4, 4', 4a and

4a', the cavities 4" and 4a", present in the dielectric slabs must preferably have smaller linear dimensions than the cavities 4, 4', 4a and 4a' to extend the discharge path between the electrodes.

The seals 6 and 6', which may be replaced by an o-ring, are used to seal the slab, while the size of the gap is adjusted by tying the upper electrode to the lower one by means of said fastening means adapted to secure said upper and lower electrodes and said dielectric slab to one another, preferably made with appropriately electrically insulated screws.

The possible slots 5 and 5', on the entire outer perimeter of the upper and lower electrodes allow to extend the discharge path and are used to avoid partial discharges between electrodes and dielectric slab into the external atmosphere. A

U-shaped seal 8, made of appropriate elastic material, adapted to protect the dielectric slab from accidental knocks and polluting agents, may be inserted along the entire perimeter of the device according to the present invention, between the electrodes and the dielectric plate.

Furthermore, spacers, made of rigid materials (dielectric or conducting) having size such as to make the required gap, may be inserted between the outer perimeter of the seal and the end of the electrodes.

The dielectric slab 3 may be made of alumina, polycarbonate, glass or other dielectric material. However, the most convenient solution from the economic and from the implementation point of view is to use approximately 4 mm thick glass sheets. Commercial glass sheets (3-6 mm thick) have high planarity and very low cost. Therefore, in order to obtain 0.2 mm thick gaps, it is sufficient to mill the surfaces of the electrodes facing the dielectric plate with tolerances of 0.05-0.1 mm.

With reference to appended figure 2, a second preferred embodiment of the device according to the present invention concerns an ozone generator device comprising a plurality of electrodes and a stack of electrodes.

Increasing the total surface of the electrodes of the device described above comprising two electrodes would consequently increase the hourly ozone production rate. However, use of electrodes wider than some tens of centimeters and longer than 1.5 meters is not convenient for this type of planar electrodic geometry.

For high hourly ozone production rates, the first embodiment of this present invention comprising two electrodes is thus modified by inserting a plurality of intermediate metal electrodes 9, appropriately cooled and free from dielectric coatings which could reduce the gas cooling capacity, and a plurality of dielectric slabs 3, arranged in alternating sequence, between the head or upper electrode 1 and the final or lower electrode 1 ', as shown in Fig. 2.

For the gas flow to be homogenous throughout all gaps of the stack, said additional intermediate electrodes 9, shown in appended figures 3, 4 and 5, comprise two openings 12, 13 at the openings 4", 4a" in said dielectric material slabs, as shown in Fig. 2. The whole of these openings forms a channel which crosses the entire stack and allows to feed all the gaps in the stack itself with homogenous flow rates. The holes may have any shape: rectangular, square, circular, etc. Furthermore, said openings in the electrodes and in the dielectric slabs may be made by means of a single hole or several holes of smaller size. Said head or upper electrode 1 further comprises two through holes 10, 11 , such as to put into communication said grooves 4, 4a or 4a' with the outside and be connected to external tubes for the introduction of gas to be enriched with ozone and to introduce gas enriched with ozone. Said final or lower electrode 1 ' may possibly comprise at least one through hole 11', arranged on the same side as the through outlet hole 11 of said head or upper electrode 1. In this manner, the gas may be let in and out to/from the same electrode, or in order to improve the pressure gradient to/from the two electrodes arranged on the ends of the stack. In order to avoid any possibility of discharges between electrodes within the stack, preferably the openings made in the electrodes are larger than the openings made in the dielectric slabs.

As clearly apparent in appended Fig. 2, each electrode of the stack in accordance with the second preferred embodiment of the device according to the present invention, allows the formation of two discharge gaps.

The head, intermediate and final electrodes are connected alternatively to ground and to the high voltage terminal of the generator. In this manner, a dielectric barrier discharge is generated in the gaps formed by the surface of an electrode and one side of the dielectric slab and between the opposite side of the dielectric slab and the surface of the contiguous electrode connected to the other terminal of the voltage generator. No electrode— neither those connected to ground nor those connected to high voltage - is coated with dielectric having low thermal conductivity, and therefore the gas circulating the gaps and subjected to discharge is cooled in the most effective manner possible.

The metal tubes which carry the gas to be enriched with ozone and those which carry the gas enriched with ozone are connected to the head and final electrode, and therefore the total number of the electrodes must be an odd number. Indeed, this solution allows to connect the two end electrodes to the same polarity of the voltage generator, and thus they can be both connected to ground.

The entire stack or even multiple stacks may be closed in a chamber provided with an oxygen concentration measurer in order to send an alarm and/or to interrupt, by means of a solenoid valve, the flow of oxygen to the stack if the concentration of oxygen in the chamber exceeds a predetermined value due to possible loss of oxygen from the ozone generator.

In greater detail and with reference to appended figures 3, 4 and 5, said intermediate electrode substantially consists of a metal slab 9 comprising two openings 12, 13 placed at the end of said electrode and such to allow the passage of gas both to the adjacent electrodes and to the gaps. In this figure, the openings made by the electrode have a rectangular shape.

A plurality of through holes 15' situated in the lower peripheral parts of the electrode allow to insert the screws which fix it to the electrode underneath. The electrode underneath is provided with threaded holes 14 at the through screws of the electrode above. Fig. 4 shows section A:A of said intermediate electrode, while Fig. 5 show section B:B. As apparent in figure 6, the screw head is accommodated in a cavity obtained in the electrode itself.

With reference to appended figure 6, the electric insulation between the upper electrode and the lower electrode is obtained by means of an insulating bushing 61 which coats the screw 60 and is also used to centre the dielectric plate. Said insulating bushing 61 is adapted to be inserted on the shank of said screws 60 and to accommodate the head of said screws 60 in the upper part. The following is further present: a threaded cap 62, made of dielectric material, having an outer threading adapted to engage the threading present on the inner part of the upper part of said insulating bushing 61 and a disc 63 of elastic, insulating material, adapted to be placed on the head of said screws 60 and compressed by said threaded cap 62.

The air gap which is formed between the shank of the bushing and the hole made in the dielectric slab could favor the formation of discharges between two contiguous electrodes, and therefore specific silicon rubber washers are inserted on the shank of the insulating bushing.

The arrangement of the through holes and of the treaded holes in the electrodes is such that, by turning an electrode upside-down with respect to the adjacent one, each through hole of an electrode is at a threaded hole of the adjacent electrode. With reference to appended Fig. 3 and Fig. 6, in order to avoid discharges between the fastening screws and the electrode on which the head of the fastening screw is situated, a part of the surface of the electrodes is not used for active discharging for the production of ozone. In order to reduce the unused surface, metal screws can be replaced with screws made of insulating material (e.g. nylon).

The apparatus according to the present invention, both in the two electrode and in the multiple electrode or stack version, may be made using seals made of rigid material, both metal and insulating, adapted to determine the gap size. In this manner, the electrodes and the dielectric plates may be maintained in the correct position by means of specific radial slings, thus eliminating all the screws and holes (threaded and through) adapted to fix the electrodes and the dielectric plates to one another. According to this preferred embodiment, the apparatus according to the present invention is preferably enclosed in a sealed container.

The described electrodes may be cooled by constructing (by extrusion) slabs provided with channels, within which cooling fluid is circulated. The channels may have a pure circular section or a circular section with protuberances to increase the thermal exchange surface. The central part of the channel may be choked to increase the cooling water speed near the metal. Alternatively, the electrode may be cooled by making electrodes of aluminum casting and inserting a steel serpentine in the casting. Fig. 8 shows an example, while fig. 9 and 10 show some examples of assembly drawings of the intermediate electrodes obtained respectively by extrusion and by casting. In the example of the electrodes shown in Fig 8 and Fig.10, it is apparent that because the adjacent electrodes need to be turned reciprocally upside-down, all the electrodes which must be connected to a terminal of the voltage generator have water inlet and outlet tubes on the opposite side with respect to those which must be connected to the other terminal of the voltage generator. This particularity simplifies the electric connection of the stack.

Claims

1. An ozone gas generator apparatus comprising: an upper, slab-shaped electrode (1) provided with at least one hole (10, 11) adapted to let gas in and/or out; a lower electrode (1 '), also slab-shaped, and facing said upper electrode (1 ); a slab of dielectric material (3), provided with openings (4", 4a") at said inlet (10) and outlet (11) holes of the gas, arranged between said upper (1 ) and lower (1') electrodes and distanced from both so as to form two gaps (2, 2'); fastening means, adapted to secure said upper and lower electrodes (1 , 1') and said electric slab (3) to one another; a plurality of seals (6, 6') interposed between said electrodes (1 , 1') and said dielectric material slab (3) and adapted to seal said apparatus and maintain the correct distance between said electrodes and said dielectric slab, characterized in that said electrodes (1 , 1 ') are free from any dielectric coating on their surface which is in contact with the gas and comprise fluid cooling means.

2. An apparatus according to claim 1 , wherein said lower electrode (1 ') is provided with at least one hole (11 ') adapted to let gas in and/or out.

3. An apparatus according to claims 1-2, wherein said at least one hole (10, 11 , 11') is located at the ends of said electrodes (1 , 1^!) so that gas to be enriched with ozone crosses the entire volume occupied by the discharge.

4. An apparatus according to claims 1-3, wherein said lower and lower electrodes (1 , 1') comprise grooves (4, 4a, 4' and 4a'), made at holes (10, 11 , 11') and openings (4", 4a") of said dielectric slab (3).

5. An apparatus according to claims 1-4, wherein said upper and lower electrodes (1 , V) further comprise slots (5, 5'), made along the entire outer perimeter of the upper and lower electrodes and adapted to extend the discharge path between said electrodes and prevent the formation of partial discharges between said electrodes (1 , 1 ') and said dielectric material slab (3) in the space outside said gaps (2, 2').

6. An apparatus according to claims 1-5, comprising a plurality of additional intermediate electrodes (9) and a plurality of dielectric slabs (3) arranged in alternating sequence to form a stack, said intermediate electrodes (9) being free from any dielectric coating on their surface which is in contract with the gas and comprising fluid cooling means.

7. An apparatus according to claim 6, wherein said additional intermediate electrodes (9) comprise two openings (12, 13) corresponding to the openings (4", 4a") in said dielectric material slabs (3).

8. An apparatus according to claims 1-7, comprising: seals made of rigid materials, both metal and insulating, adapted to determine the size of the gap and specific radial slings adapted to maintain said electrodes and said dielectric slabs assembled in the correct position without needing screws or holes, neither threaded nor through.

9. An apparatus according to claims 1-7, wherein said fastening means are adapted to secure said electrodes and said dielectric slab to one another chosen from the group comprising: appropriately insulated metal screws, screws made of electrically insulating material.

10. An apparatus according to claims 1-7 and 9, wherein said fastening means adapted to clamp said electrodes and said dielectric slab to one another comprise screws (60), in turn comprising an insulating bushing (61) adapted to be inserted on the shank of said screws (60) and to accommodate the head of said screws (60) in the upper part thereof; a threaded cap (62), made of dielectric material, having an outer threading adapted to engage the threading present in the inner part of the upper part of said insulating bushing (61); a disc (63) made of elastic and insulating material and adapted to be placed on the head of said screws (60) and compressed by said threaded cap (62).

11. An apparatus according to claims 1-10, further comprising a "U"-shaped seal (8), arranged along the entire perimeter of said apparatus, between said electrodes and said dielectric slab and adapted to protect the dielectric slab from accidental knocks and polluting agents.

12. An apparatus according to claims 1-11 , wherein said electrodes (1 , 1 ', 9) comprise a series of channels adapted to make cooling fluid circulate.

13. An apparatus according to claims 1-12, wherein said electrodes (1 , 1', 9) are made of aluminum or other low melting point material.

14. An apparatus according to claim 13, wherein said electrodes (1, V, 9) are treated by means of anodic oxidation or nickel-plating or chrome-plating, in order to increase the surface hardness of said electrode and avoid the phenomenon of sputtering of the electrodic material induced by the discharge.

15. An apparatus according to claims 1-14, wherein said electrodes (1 , 1', 9) are made by extrusion or casting.

16. An apparatus according to claims 1-15, comprising a chamber adapted to contain said apparatus provided with an oxygen concentration measurer adapted to send an alarm and/or to interrupt by means of a solenoid valve the flow of oxygen to said apparatus if the concentration of oxygen in the chamber exceeds a predetermined value caused by the possible loss of oxygen from the ozone generator.