The present invention relates to a device for generating ozone with the features of the preamble of claim 1.

Ozone is a powerful oxidizing medium for organic as well as for inorganic compounds. There are diverse areas of application for ozone, one of which is its use in water treatment.

Technically, ozone can be generated by silent electrical discharge in an oxygen-containing gas. Silent electrical discharge is, in contrast to spark discharge, to be understood as a stable plasma discharge or corona discharge. Molecular oxygen is dissociated into atomic oxygen. The reactive oxygen atoms subsequently attach themselves to molecular oxygen in an exothermic reaction and form tri-atomic molecules, i.e. ozone. The ozone yield depends inter alia on the electric field strength and operating temperature. The dependence on operating temperature rests on the fact that ozone

decomposes more rapidly again into molecular oxygen at higher temperatures and, due to the resulting displacement of the equilibrium between the originating and disintegrating ozone, the available ozone concentration is less.

Electrode assemblies with multiple discharge gaps for ozone generation are known. They offer several advantages over single gap systems, e.g. better utilization of the reactor volume, lower space requirements, lower investment cost, and higher discharge areas. However the main difficulty is a sufficient cooling, which is needed to achieve high ozone concentrations with good efficiency. To avoid excessive heat build-up, commonly water is arranged to directly cool the outer electrode. However with multiple-gap arrangements, these known cooling systems are too inefficient.

Document JP 2001-210448 discloses a corona discharge device to be used for gas processing device, such as a deodorizer with an electrode arrangement with one gap. A central heat pipe is in airtight contact with an inside of a discharge electrode. The cooling effect is improved by removing

the heat generated in the electric discharges by the central rod-shaped heat pipe.

It is an objective of the present invention to provide a device for generating ozone, which is able to remove excessive heat from the at least one discharge gap and from components of the generating device.

This problem is solved by a device for generating ozone with the features listed in claim 1.

Accordingly, a device for generating ozone from oxygen-containing gas with an electrode arrangement with at least one high-voltage electrode and at least one annular ground electrode is provided, wherein between the at least one high-voltage electrode and the at least one ground electrode an annular dielectric is arranged, and the at least one high-voltage electrode is

surrounded by at least one annular heat pipe. The at least one high-voltage electrode, the at least one ground electrode and/or an annular dielectric can be designed to be an annular heat pipe.

An annular heat pipe has radially spaced inner and outer walls defining an annular space in cross section. The annular heat pipe allows cooling of the discharge gap or components of the electrode arrangement with high efficiency. In addition a cooling medium and pumping systems are not necessary and the cooling section can be placed in proximity to the discharge gap. The systems are therefore much smaller.

Preferably, the central high-voltage electrode is formed by a metal heat pipe with a circular cross-section. This way, heat can be efficiently transported out of the internal structure. In another preferred embodiment, the central high- voltage electrode is formed by a filler material arranged on a heat pipe with a circular cross-section. This heat pipe can be an insulator. The filler material can be a stainless steel mesh or fabric. This is advantageous in particular in the event of a breakdown, because the electrode arrangement can

demonstrate intrinsically safe electrical behaviour since, during the

breakdown, the substantially lighter inner electrode, which consists solely of the filler material, can evaporate without damaging the substantially higher- mass outer electrode. The ozone generator can generally remain in operation in spite of the breakdown.

Advantageously, at least one of the annular heat pipes forms an electrode. The electrode is directly cooled and installation space can be further saved.

In one embodiment, at least two discharge gaps are formed, which are traversed by the gas, wherein one of said gaps is formed between the high- voltage electrode and the dielectric and the other gap is formed between said dielectric and the ground electrode. In another embodiment, four discharge gaps are formed, which are traversed by the gas, wherein one high-voltage electrode and one ground electrode are formed each by an annular heat pipe. Multiple discharge gaps for ozone generation offer the above mentioned advantages. By usage of an annular heat pipe, the system can be efficiently cooled even inside.

The annular heat pipes are preferably heat exchange systems with an air- cooled finned condenser. In another preferred embodiment a heat exchanger is arranged within the condensation zone of the annular heat pipe, wherein a cooling jacket of the heat exchanger is directly connected to the heat pipe.

It is advantageous, if each of the at least one annular heat pipes is a closed heat exchange system.

Preferably, ozone is generated from oxygen-containing gas with silent electric discharge.

Preferred embodiments of the present invention will be described with reference to the drawings. In all figures the same reference signs denote the same components or functionally similar components.

Figure 1 shows a schematic cross-sectional view of a multi-gap discharge unit of an ozone generator with a central heat pipe made of glass; Figure 2 shows a schematic cross-sectional view of a multi-gap discharge unit of an ozone generator with a central high-voltage electrode formed by a metal heat pipe and a stainless steel wire mesh;

Figure 3 shows a schematic cross-sectional view of a multi-gap discharge unit of an ozone generator with a central heat pipe functioning as a high-voltage electrode; and

Figure 4 shows a schematic view of a heat pipe arrangement in a discharge gap.

Figure 1 shows an electrode arrangement 1 of a device for generating ozone with a group of annular shaped electrodes and a central heat 2 pipe with a circular cross-section made of glass which are installed in a nesting manner. The isolator 2 (central heat pipe) is surrounded by a stainless steel mesh 3, which forms a high voltage electrode 4. The high voltage electrode 4 is concentrically surrounded by a ground electrode 5, wherein in between the electrodes 4,5 a dielectric 6 is arranged. The ground electrode 5 is again surrounded by a dielectric 7 which is covered by a high voltage electrode 8. Gaps 9 are formed both between the high-voltage electrodes 4,8 and the dielectric 6,7 and between the dielectric 6,7 and the ground electrode 5.

The central heat pipe 2 is a hollow cylindrical tube filled with a material that will vaporize at operating temperatures of the inner high-voltage electrode. The tube, as shown in figure 4, can extend into a bonnet 10 wherein it is provided with some extended surface 11. The extended surface 11 can be realized by helically wound fins, studs, longitudinally organized fins or other known forms of extended surface. In the condensation zone of the heat pipe 2 the tube 2 is cooled by air which is circulated through the bonnet 10. The vaporizing and condensing material typically may be water, or methyl alcohol or ethyl alcohol or ammonia.

Heat pipes are heat transfer devices which provide high heat transport efficiency. Heat pipes have an enclosed cavity filled with a condensable heat transfer medium. Heat is put into the heat pipe at an evaporator section where the working fluid is vaporized and the vapour travels to a condenser section of the heat pipe where it condenses, thereby giving up heat which is radiated or conducted to an external load or sink. The condensed working fluid is then returned to the evaporator section typically by refluxing or through a wick which conducts the liquid by capillary action.

Annular heat pipes 12 with a double wall structure form the ground electrode 5 and the outer high-voltage electrode 8. These heat pipes typically may be made of various grades of steel, aluminium alloys or chromium-nickel-iron alloys.

Each heat pipe 2,12 has preferably its own closed heat exchange system.

In figure 2 the inner high-voltage electrode 4 is formed by the mesh 3 and the central heat pipe 2, which are both made of metal.

In the electrode arrangement of figure 3, the central heat pipe 2 solely forms the inner high-voltage electrode 4. A mesh is not provided.

Figure 4 shows the arrangement of the central heat pipe 2 surrounded by a discharge gap 9. The cooling section 10 is placed outside of the discharge gap. The cooling fins 11 are cooled with air.

In practical use, the number of the at least one ground electrode, the at least one insulating layer and the at least one high voltage electrode may be determined according to actual needs. The device according to the invention can be used for systems in which one or a plurality of gaps is used for the discharge. The at least one annular heat pipe allows to efficiently cool the at least one discharge gap. Additional cooling with water is not required. The use of an annular heat pipe leads to significant design advantages; the reaction zone does not need to be cooled directly, a cooling medium and pumping systems are not necessary, the cooling section can be placed in proximity to the discharge gap. The systems are therefore much smaller and can be developed as "plug and play" solutions.

Preferably, a heat exchanger with a cooling jacket is arranged in the

condensation zone of the heat pipe. This allows transfer of the heat generated by the heat pipe to the cooling water of the heat exchanger. For larger systems with multiple high voltage electrodes it is advantageous, if an interlocking connection between the cooling jacket of the heat exchanger and the heat pipe is used. The heat pipe can but does not need to be made of an electrically conductive material. Therefore the components of the electrode arrangement, the high voltage electrodes, the ground electrodes and the even the dielectric can be designed as a heat pipe.

The present invention significantly improves the efficiency of ozone generators and the concentration of the ozone output. Heat balancing between areas of high and low temperature is possible, which results in less NOx generation because less power input per surface area is required.