Ozone generation at high pressures

Abstract

A method for producing ozone at elevated pressure with a capacity of at least 1 kg ozone/hour by an ozone generator having a high voltage electrode and a counter electrode. The electrodes delimit a gap in which a dielectric is arranged and through which a gas containing oxygen and having a gas pressure of p.sub.gas flows. The high voltage electrode and the counter electrode with a connection for an electric power supply to generate discharges are provided in at least one discharge gap. The power supply provides a voltage in a range from 1 kV to 50 kV and wherein stroke widths di of the discharge are distributed between a minimum stroke width d.sub.min and a maximum stroke width d.sub.max. The gas pressure p.sub.gas of the gas containing oxygen at the outlet of the ozone generator is at least 3 bar.

Claims

1. A method for producing ozone at elevated pressure with a capacity of at least 1 kg ozone/hour by an ozone generator having an inlet, an outlet, a high voltage electrode and at least one counter electrode, wherein the high voltage electrode and the at least one counter electrode delimit a gap in which at least one dielectric is arranged, said method comprising the steps of: distributing a gas containing oxygen through the gap, generating discharges in at least one discharge gap using the high voltage electrode and the at least one counter electrode, which are each connected to an electric power supply, and providing a voltage using the power supply in a range from 1 kV to 50 kV, wherein stroke widths d.sub.i between the dielectric and the high voltage electrode are distributed between a minimum stroke width d.sub.min and a maximum stroke width d.sub.max, and wherein gas pressure p.sub.gas of the gas containing oxygen at the outlet of the ozone generator is at least 3 bar in excess of atmospheric pressure.

2. The method according to claim 1, wherein the voltage provided using the power supply is in a range from 10 kV to 30 kV.

3. The method according to claim 1, wherein the voltage provided using the power supply is in a range from 15 kV to 20 kV.

4. The method according to claim 1, wherein the gas containing oxygen has an ozone concentration of at least 10% by weight at the outlet of the ozone generator.

5. The method according to claim 1, wherein the gas pressure p.sub.gas of the gas containing oxygen is at least 6 bar in excess of the atmospheric pressure at the outlet of the ozone generator.

6. The method according to claim 1, wherein the gas pressure p.sub.gas of the gas containing oxygen is between 10 bar and 12 bar in excess of the atmospheric pressure at the outlet of the ozone generator.

7. The method according to claim 1, wherein the capacity is at least 20 kg ozone/hour.

8. The method according to claim 1, wherein the capacity is at least 100 kg ozone/hour.

9. The method according to claim 1, comprising distributing the gas containing oxygen into the gap at a feed-in rate in the range from 500 kg/hour O.sub.2 to 800 kg/hour O.sub.2.

10. The method according to claim 1, wherein the minimum stroke width d.sub.min is zero.

11. The method according to claim 1, wherein the ozone generator has a single counter electrode and the dielectric is arranged on the counter electrode.

12. The method according to claim 1, wherein the high voltage electrode comprises at least in part a fabric made of wire.

13. The method according to claim 12, wherein the high voltage electrode consists of the fabric made of wire.

14. The method according to claim 1, further comprising a fabric made of wire filling the gap delimited by the high voltage electrode and the at least one counter electrode.

Description

BRIEF DESCRIPTION OF THE DRAWING FIGURES

(1) A preferred embodiment of the invention is described below in more detail with reference to the drawings. In the drawings:

(2) FIG. 1: shows a perspective view of an electrode arrangement from the prior art and

(3) FIG. 2: shows a basic progression of the energy consumption of a conventionally operated ozone generator and an ozone generator operated with the method according to the invention by gas pressure.

DETAILED DESCRIPTION OF THE INVENTION

(4) FIG. 1 shows an electrode arrangement as known from DE 10 2011 008 947 A1. Ozone generators of this type are used in an ozone generator in groups. The ozone generators are thereby arranged parallel to one another between two tube plates in the manner of a tube bundle heat exchanger and connected in an electrically parallel manner. The ozone generator shown has a tubular outer electrode 1, an also tubular dielectric 2 and an internal rod 3, wherein shortened versions of the individual components are shown stretched out from one another in an axial direction. The arrangement is rotationally symmetrical. The outer electrode 1, the dielectric 2 and the rod 3 are oriented concentrically to one another. There is a wire mesh 4 between the outer electrode 1 and the dielectric 2 that fills the gap. Accordingly, a wire mesh 5 is provided between the dielectric 2 and the rod 3 which also fills the gap there. The outer electrode 1 is designed in the form of a stainless steel tube. The waste heat generated during the ozone production is cooled by means of cooling water which is passed along the outer side of the outer electrode between the bases of the tubes. The dielectric 2 is a glass tube. The wire meshes 4 and 5 are preferably manufactured as what are known as circular hollow strings made of a stainless steel wire mesh. The rod 3 arranged in the centre of the electrode arrangement is an insulator, for example made of glass of another material compatible with oxygen and ozone. The rod 3 can be designed to be massive. During operation, pressure is exerted on the electrode arrangement by means of a gas containing oxygen having a gas pressure of 1 to 2 bar which flows through the wire meshes 4 and 5 in the direction of the arrow 6. An electric power supply 7 is schematically indicated, which power supply is in contact with the outer electrode 1 on the one side and with the mesh 5 on the other. The operating voltage supplied by the power supply 7 a silent electrical discharge in the space between the electrodes 1, 5 and the dielectric 2 which generates ozone from the oxygen flowing through the meshes 4 and 5 in the direction of the arrow 6.

(5) In the structure shown the inner electrode is formed solely from the mesh 5 while the rod 3 exercises a supporting function as an insulator which ensures the even filling of the inside of the dielectric 2 with the wire mesh 5. This shape of the electrode results in an overlapping of volume and surface charge.

(6) FIG. 2 shows curves of the specific energy consumption of ozone generators. With reference to the method according to the invention,

(7) U(t)=U.sub.0*sin(2*f*t) even at comparatively high gas pressures and voltage amplitudes (in the range indicated), there are still surface points on the high voltage electrodes from which silent discharges originate. It is surprising in this context that the specific energy consumption of the ozone generator measured in kWh/kg of ozone is significantly lower as a result of this operation 10 according to the invention at high pressures compared to conventional ozone generators 11. The above-mentioned characteristic optimal operating pressure for ozone generators described above depending on the specific energy consumption is in a narrow range about the minimum of a parabolic distribution (see curve 11). In contrast to this, an ozone generator with a profiles high voltage electrode has a significantly flatter distribution (see curve 10). The specific energy consumption is still comparatively low at high pressures, for example of more than 3 bar, or even higher pressures. Since the minimum distribution is flatter, the operating pressure can be in a wide range, for example in a range from 1 to 12 bar with almost the same level of efficiency in terms of ozone generation.

(8) The advantage of this method is further that no compromise has to be made between gas pressure and capacity and/or ozone concentration.

(9) According to the invention the ozone generator is operated at capacities of one to several hundred kg of ozone/h. In one embodiment the ozone concentration is at least 12% by weight ozone.

(10) The method according to the invention is therefore suitable for ozone production in the paper industry as high ozone concentrations and high ozone capacities can be produced effectively at high pressures.

(11) The high voltage electrode is an electrically conductive material, preferably stainless steel with a profiled surface. The high voltage electrode can be a wire mesh or a knitted fabric, a fabric or even a wire winding or a granulate placed on a surface. Fibrous fabrics such as fleece or felts are also suitable as structures that are placed on the electrode by means of mechanical processing or by coating. The profiling is stochastically or periodically distributed and is distributed in both a longitudinal and a peripheral direction of the electrode.

(12) It is also conceivable, however, to profile the dielectric instead of the electrode, with the same effect being able to be achieved.

(13) The method according to the invention is not limited to tubular electrode arrangements. It can be used in both tubular and flat ozone generators. Use in single-gap and multi-gap systems is provided for. The electrically conductive material of the electrode can be introduced into the discharge hap with or without carrier material.

(14) The method of ozone generation according to the invention can of course also be used more generally in plasma generators.

(15) The ozone generator can be adapted to customer-specific requirements by means of the method according to the invention. This is economical due to the increasing energy prices, and is also ecologically advantageous. Ozone generation at the high pressures at the outlet of the ozone generator of up to 12 bar are technically and economically possible. The water ring compressors that are usually required are therefore not necessary.