CH628596A5 - Process for the manufacture of ozone - Google Patents

Description

The present invention relates to a process for manufacturing ozone capable of being applied by means of installations whose simplicity of construction and good energy efficiency must allow the industrial production of this gas under very favorable economic conditions, and make it affordable to solve the problems of sanitation and clean industrial oxidation.

Various types of ozone generators are known in which an alternating voltage is applied between two electrodes, creating between these electrodes an alternating electric field to which the oxygen molecules of the interval are subjected in which air is moved. possibly enriched with oxygen.

The space between the two electrodes generally consists of an air gap in series with a plate of insulating substance.

When the peak voltage across the air gap is less than the priming threshold voltage, the ozonator behaves like an air capacitance in series with a dielectric capacity.

When the peak voltage is greater than the ignition threshold voltage, there are aromas in the air during each positive and negative half-wave of the voltage and, during the duration of these aromas, the ozonator behaves approximately as a variable resistor in series with the capacitance of the dielectric,

Currently known industrial ozonizers generally operate under these conditions: they are constituted by the grouping of several cells connected in parallel between two terminals supplied with high alternating voltage. These ozone generators are either flat plates or consist of concentric tubes.

In the various types of ozone generators, the formation of electric arcs must be avoided, because the arcs are detrimental to the performance of the device: on the one hand, they constitute interruptions in operation, on the other hand, they create conditions required for the destruction of the ozone already formed. To avoid arcing, it is essential to condition the gas (air, oxygen or oxygen enriched air) with which the device is supplied.

This supply gas must be very clean and specially free of dust liable to initiate arcs and traces of oil which may be deposited on the surfaces of the electrodes and the dielectric.

This gas must be extremely dry, because the water vapor promotes the passage of arcs, and the ionization of the resulting water vapor absorbs energy without advantage for the production of ozone.

This gas must be at a temperature lower and at most equal to the ambient temperature, any increase in temperature favoring the instability of ozone.

The electrical power of the emanations is a function of the peak value of the supply voltage; however, this voltage value is limited by the arcing threshold. Electric power is an increasing function of frequency; however, the use of very high frequencies, for example 500 Hz instead of 50 Hz, can only be obtained using complex and expensive installations.

The process according to the invention and the devices using this process make it possible to overcome these difficulties by creating in the treatment duct a state of continuous and stable electrical aromas, thus eliminating the risks of electric arc.

In the process for manufacturing ozone according to the invention:

- a continuous electric field is established between a first limit surface affected by a positive electrical potential of average value chosen in the interval from 1000 to 50,000 V and a second limit surface with zero potential, thus maintaining between the first limit surface and the second surface limits an area of electrical aroma,

An electrical potential gradient is maintained between the first limiting surface and the second limiting surface, the average value of which between the two surfaces is between 500 and 5000 V / cm, thus retaining a stable regime for said electrical tests,

- Passing an air flow through said zone of electrical emanation.

Preferably, the first limit surface is assigned an electrical potential stabilized to within 10%, which is sufficient to obtain a correct application of the process.

The device for implementing the method according to the invention comprises, on the one hand, a conduit made of a conductive material of

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electricity, connecting a first opening leading to an air flow supply means and a second opening opening into a discharge pipe, this pipe being connected to a ground with zero electrical potential and, on the other hand, a body of an electrically conductive material, entirely covered with an insulating, porous and low conductance material, disposed inside the conduit and connected to a high voltage current source of positive polarity.

According to a preferred embodiment, the conduit is a cylinder of revolution, and the body disposed inside the conduit is constituted by a taut metallic wire, of the same axis as the cylinder of revolution constituting the conduit.

In various embodiments, the wire made of an electrically conductive material comprises in its composition only metals whose oxides are porous and of low conductance, the wire being entirely covered with an insulating material, porous and of low conductance.

In other embodiments, the wire made of an electrically conductive material comprises at least one metal whose oxide generated by contact with atmospheric air is porous and of low conductance, the wire being entirely covered with an insulating material porous and low conductance.

In certain embodiments, the porous insulating material of low conductance entirely covering the wire is formed by the oxides of the metals with which the conductive wire is made.

In the preferred embodiments, the diameter of the cylindrical metallic conduit of circular section has a value chosen in the interval from 2 to 50 cm, the wire of material conducting the electricity is metallic and of a diameter chosen in the interval 0, 05 to 1.00 mm.

In such embodiments, the average electrical potential gradient between the wire and the conduit generally has a value between 1000 and 5000 V / cm.

Preferably, the potential of the high voltage source of positive polarity has a value chosen in the range from 5000 to .20000 V, value stabilized to within 10%, the diameter of the cylindrical metallic conduit of circular section has a chosen value in the interval from 2 to 10 cm, the wire of material conducting the electricity is metallic and of a diameter chosen in the interval from 0.1 to 0.5 mm.

In such embodiments, the average electrical potential gradient between the wire and the conduit generally has a value between 1000 and 4000 V / cm.

The invention will be better understood in the description, given by way of example, of a device enabling the method according to the invention to be carried out, device illustrated with the aid of the following figures:

fig. 1 is a block diagram of a cylindrical conduit with coaxial wire,

fig. 2 represents a section of the coaxial wire constituting the positive electrode,

fig. 3 is a perspective view of an industrial device,

fig. 4 is a perspective view of all of the positive electrodes of the device according to FIG. 3,

fig. 5 represents a diagram of electrical supply,

fig. 6 represents the single-phase circuit,

fig. 7 shows the three-phase circuit.

Referring to fig. 1, there is in 1 a cylindrical conduit made of an electrically conductive material made of a sheet of iron or a light metal such as aluminum. The conduit 1 connects a first opening leading to an air supply means, not shown, and a second opening 1b opening into a non-illustrated exhaust duct. The conduit 1 is connected by a conducting wire 2 to a ground 3 with zero potential such as an earth.

A stretched, straight, coaxial metal wire 4 of the conduit 1 extends over the entire length of the conduit 1 supported at its ends by insulating supports that are not shown. The wire 4 is connected to a source of direct electric current of positive polarity. Wire 4, as shown in fig. 2 which gives a cross section thereof, is entirely covered with an insulating material 5, porous and of low conductance.

Fig. 3 gives a perspective view of an industrial device constituted by an assembly of 16 elementary conduits, as described with the aid of FIG. 1, and mounted in parallel, between two end boxes (an inlet box 6 and an outlet box 7) into which said conduits open. Each of the end boxes has, opposite the openings of said conduits, a single opening which, for the inlet box 6, opens into an air supply means 8 and, for the outlet box 7, opens in a drain 9.

All of the conduits, such as 1, are connected by an electrical conductor 2 to a ground 3 with zero potential.

Fig. 4 gives a perspective view of all the positive electrodes of the device according to FIG. 3. Said electrodes are constituted by as many wires, such as wire 4 described with the aid of FIG. 1 of the elementary cylindrical device.

At each end, the wires such as 4 are fixed to the points of intersection of an orthogonal network 10 and 11 consisting of a metal wire made of the same electrically conductive material as that in which the wires such as 4 are made.

One of the end metal networks, for example the network 10, is connected by a metal conductor 12 to the positive terminal of a high voltage direct current generator, not shown.

All of the wires such as 4 and end networks such as 10 and 11 are entirely covered with a porous insulating material which is breathable. The end networks 10 and 11 are fixed inside the boxes 6 and 7 by means of insulating supports not shown.

Fig. 5 illustrates a diagram of a direct current generator usable for supplying the positive electrodes of an ozone generating device.

A transformer 13 supplied with alternating current 14 gives an alternating current of higher potential 15. A diode 16 gives a rectified current 16, and a capacitor 18 interposed between the output of the diode and the homologous output of the transformer gives a certain smoothing of the curve representing the output voltage 19. This constitutes a classic example of a means used for the supply of a pseudo direct or continuous current stabilized at better than ± 10%.

Fig. 6 gives a diagram of a generator making it possible, from a single-phase current, to rectify the two half-waves instead of one, as only the device according to FIG. 5.

From the arrival of the sector, we note the presence of a variable autotransformer 20 which immediately precedes the step-up transformer 13. The variable autotransformer 20 makes it possible to pass from current 14 to current 14 '. Instead of a diode 16, the device comprises a diode bridge 16. On the output and before the filtering capacitor 18 is arranged in series a resistor of small value 21.

The stabilization of this classic type of supply is that of the sector at ± 10% in general.

In order to further improve the filtering, one can opt for a supply from a three-phase sector of which the two half-waves will be rectified for each phase. Fig. 7 shows the diagram of such a generating device.

In fig. 7, there are elements homologous to those shown in FIG. 6, either: a three-phase variable-ratio autotransformer 20, a step-up transformer 13, a diode bridge, or Graetz bridge 16, a small-value resistor 21 and a filtering capacitor 5.

The stabilization of this conventional supply is that imposed by the sector.

The advantage of a three-phase circuit lies in better filtering obtained by rectifying the two half-waves of each of the three phases.

In an industrial device of the type described with the aid of FIGS. 3 and 4, the diameter of the cylindrical conduits is chosen in the range 2 to 10 cm and the diameter of the metal wire 4 is chosen in the range 0.1 to 0.5 mm.

The metal wires 4 being connected to the positive polarity terminal of a direct current generator stabilized better than ± 10%, the

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average value of the potential gradient at any point situated in the interior space of the cylindrical conduits 1 is between 1000 and 4000 V / cm.

Under these conditions, there is established between the wires 4 and the internal surface of the conduits 1 a regime of continuous electrical aromas.

The various experiments pursued with various models of cylindrical conduits with coaxial wire, as defined by the invention, have led to the following observations:

The diameter of the cylindrical duct determines the value of the maximum potential that can be applied, as well as the optimal value of the potential to apply to the coaxial wire.

When the diameter of the wire varies from 2 to 10 cm, the optimal value of the potential varies from 1000 to 20000 V.

The diameter of the metal wire must be sufficient for the wire to have good mechanical strength and sufficient longevity having regard to the particular conditions of corrosion in an oxidizing medium. This diameter must not be too large so that the current density on the external contour of the wire remains as high as possible, in order to favor the initiation of the corona. The diameters used are between 0.1 and 0.5 mm.

With a bare metal wire, an insignificant increase in the value of the potential, beyond that which produces the initiation of the corona, causes the initiation of the arc, and this all the more easily as the air is more humid and dusty. Under these conditions, with a bare metal wire, the amount of ozone produced per hour remains minimal.

With a metal wire covered with a continuous layer of oxide, for example of the oxide of the metal itself, provided that this oxide is porous, it becomes possible to increase considerably for the same potential the value of the intensity of the current. Under these conditions, around 10,000 V for a tube with a diameter of 6 cm and a length of 100 cm, a production of 600 mg / h is observed for an absorbed power of 10 W, ie a yield of approximately 60 mg of O3 / W / h. The current flowing through the cell is then 1000 | xA.

Tubes of the same diameter, fitted with a wire of the same characteristics and brought to the same potential, give an ozone production, in mg / h, substantially proportional to their length, up to a value of this length from which growth becomes less than proportional. In this case, the electric effluvium destroys the ozone with a speed whose value, apparently, increases according to the ozone content of the air.

For a tube of diameter 6 cm equipped with a metal wire of diameter 0.3 mm for the conductive part, it has been observed that the production of ozone ceases to be proportional to the length from a length of approximately 100 cm.

In many applications, particularly for small productions, an increase in productivity can be obtained by placing two or more tube elements in series. In large production ozone production plants, the increase in productivity should rather be sought by means of parallel arrangements such as that described with the aid of FIGS. 3 and 4.

For an apparatus of this type, defined by the respective diameters of the tube and of the wire, the value of the potential to which the wire must be carried is chosen according to the production of ozone which it is desired to produce per 10 hours. The choice of the value of the potential entails fixing the intensity of the current which flows through the device.

For high potentials, having regard to the diameter of the tube, a high speed of air makes it possible to delay the passage from the effluvium to the arc, but causes a greater dilution of the ozone, because the speed of l The air in the tube, or the air flow, does not significantly affect the productivity of the device.

With wires coated with a continuous layer of insulating oxide, porous and low conductance, which allows iron and very many iron-based alloys and which eliminates aluminum for this use, it is observed that the device operation is not affected by the dust content of the supply air. It is also the same with artificial coatings meeting the requirements for insulation, porosity and low conductance, and not comprising 25 oxides of the metal with which the electrode wire is made.

The advantages of the new process compared to all those which have been reported to date are:

- the use of a DC voltage which can be developed without special precautions for its regulation from the mains

30 three-phase,

- a very simple technology corresponding to a very light and inexpensive construction; the cost of an installation of the same productivity is considerably reduced,

- an energy efficiency higher than that of current industrial devices, since it is necessary to take into account, in order to assess the performance of the latter, the energies consumed in the various annexed mechanical installations, in particular in devices for prior enrichment of the air by oxygen, in drying and dedusting devices,

40 - negligible maintenance.

Such advantages make it possible to economically use ozone in water purification, in the depollution of numerous biological effluents and in industrial treatments of oxidation by gas.

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2 sheets of drawings

Claims (9)

628596 1. Ozone manufacturing process in which: - a continuous electric field is established between a first limit surface affected by a positive electrical potential of average value chosen in the interval from 1000 to 50,000 V and a second limit surface with zero potential, thus maintaining between the first limit surface and the second surface limits an area of electrical aroma, An electrical potential gradient is maintained between the first limiting surface and the second limiting surface, the average value of which is between 500 and 5000 V / cm, thus maintaining a stable regime for said electrical scents, - Passing an air flow through said zone of electrical emanation. 2. Method according to claim 1, wherein the first limit surface is affected by an electrical potential stabilized to within 10%. 2 3. Device for implementing the method according to claim 1, comprising a conduit, made of an electrically conductive material, connecting a first opening opening onto an air flow supply means and a second opening opening into an evacuation pipe, this pipe being connected to a ground with zero electrical potential, and a body, made of an electrically conductive material, entirely covered with an insulating, porous and low conductance material, arranged inside of the conduit and connected to a high voltage current source of positive polarity. 4. Device according to claim 3, in which the conduit is a cylinder of revolution, and in which the body, disposed inside the conduit, is constituted by a taut metallic wire of the same axis as the cylinder of revolution constituting the conduit. 5. Device according to claim 4, in which the wire of an electrically conductive material comprises in its composition metals whose oxides are porous and of low conductance, the wire being entirely covered with an insulating material, porous and of low conductance. 6. Device according to claim 4, in which the wire made of an electrically conductive material comprises at least one metal whose oxide generated by contact with atmospheric air is porous and of low conductance, the wire being completely covered with 'a porous insulating material with low conductance. 7. Device according to one of claims 4 or 5, in which the porous insulating material of low conductance entirely covering the wire is constituted by the oxides of the metals with which the conductive wire is made. 8. Device according to claim 3, in which the diameter of the cylindrical metallic conduit of circular section has a value chosen in the interval from 2 to 50 cm, the wire of material conducting the electricity is metallic and of a diameter chosen in the interval 0.05 to 1.00 mm. 9. Device according to claim 3, in which the potential of the high voltage source of positive polarity has a value chosen in the range from 5000 to 20000 V, value stabilized to within 10%, the diameter of the cylindrical metallic section pipe. circular has a value chosen in the range of 2 to 10 cm, the wire of electrically conducting material is metallic and of a diameter chosen in the range of 0.1 to 0.5 mm.