EP0428671A1

EP0428671A1 - Device and process for obtaining high temperatures

Info

Publication number: EP0428671A1
Application number: EP19900908438
Authority: EP
Inventors: Jean Albert François SÜNNEN
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-06-08
Filing date: 1990-06-06
Publication date: 1991-05-29
Also published as: WO1990015516A1

Abstract

Le procédé consiste à établir entre deux ou plusieurs cathodes (1, 2) et une ou plusieurs anodes creuses (3) des arcs distincts (5, 6), à maintenir un débit de gaz inerte entre les cathodes (1, 2) et la ou les anodes (3), à disposer les cathodes (1, 2) sensiblement selon les génératrices d'un cône épousant l'entrée de la première anode (3), et à introduire la matière à traiter par un tube situé dans l'axe du cône et de l'anode. Le fluide de constriction et de guidage des arcs (5, 6) est introduit le long de chaque cathode (selon 9', 9''), de manière à allonger les deux arcs et à déplacer les taches anodiques (12, 13) dans le sens axial vers la sortie de l'anode (3).The method consists in establishing between two or more cathodes (1, 2) and one or more hollow anodes (3) separate arcs (5, 6), in maintaining a flow of inert gas between the cathodes (1, 2) and the or the anodes (3), placing the cathodes (1, 2) substantially along the generatrix of a cone matching the inlet of the first anode (3), and introducing the material to be treated by a tube located in the axis of the cone and the anode. The fluid for constricting and guiding the arcs (5, 6) is introduced along each cathode (along 9 ', 9' '), so as to lengthen the two arcs and to move the anode spots (12, 13) in the axial direction towards the exit of the anode (3).

Description

Method and device for obtaining high temperatures

Devices for obtaining high temperatures are known, in which a fluid at high temperatures is carried by passing it through an arc discharge between two electrodes. Such devices are used in particular in pro ection, welding and chemical reaction at high temperature, the material to be treated being introduced into the plasma in the form of powder, liquid or gas.

In known arrangements, the arc is established between two electrodes, at least one of which is hollow, and the material to be treated is generally introduced downstream of the area where the arc is maintained.

Such devices have several drawbacks: the material to be treated penetrates more or less into the plasma at high temperature, hence low efficiency from the thermal point of view; vaporization of the finest particles, ^" When it comes to powders and as a result of the non-uniformity of thermal exchanges between plasma and material to be treated; obtaining poor coatings, if they are pro ection or solder, and t - ^> chemical reactions not optimized, in the case of synthesis, chemical decomposition or destruction of waste.

The purpose of the following method of the invention is to remedy these drawbacks, while making it possible to operate such installations in one. power of several megawatts.

When one tries, in fact, to increase the dissipated power, one comes up against the problem of the connection e the arc to the electrodes and, in particular, to the cate of, When it is a cooled metal cathode. We note in this case the existence of a cathode spot of very small dimension, that is to say very high current densities, and beyond 1000 A The need to proceed with the displacement of the cathode spot by a gas vortex or an auxiliary magnetic field.

This is accompanied by various drawbacks: unstable operation of the arc; sharp adjustable dimensions of electrodes and flow rates; very high arc voltage (greater than 1 V); limited service life of the electrodes (one hundred hours).

The method according to the invention and the devices intended for s i, realization make it possible to remedy these drawbacks.

Next. The invention The process for obtaining high temperatures is characterized in that it consists in establishing between several cathodes and one or more hollow anodes separate arcs, in maintaining a flow of inert gas between the cathodes and the or the anodes, to dispose the cathodes substantially along the generatrix of a cone matching the entry of the first anode, and to introduce the material to be treated by a tube located in the axis of the cone and the anode.

The method according to the invention also consists in introducing the fluid for constricting and guiding the arcs along each cathode.

To make the invention easier to understand, the invention is now described in more detail on the basis of the appended drawings, by way of examples only, showing in:

Figure 1 a section of a device carrying out the process according to the invention and comprising for reasons of simplicity only two cathodes;

Figure 2 The electrical connection diagram for the device in Figure 1;

Figure 3 a variant of Figure 1, In the case of materials to be treated likely to be highly aggressive vis-à-vis the anode;

FIGS. 4A, 4B, 4C of the variants of the direction of the injection of fluid with respect to the arc in the case of FIG. 3;

Figure 5 a variant of Figure 3, in the case of in ect materials particularly reactive vis-à-vis the anode;

FIGS. 6A and 6B respectively a device with crossed arcs and a view of the configuration of crossed arcs, and Figure 7 a variant of Figures 6.

Referring to FIG. 1, the cathodes 1 and 2 are usually metal made up of a refractory tip 14 ′ and 14 ", welded and brazed on metal supports 15 * and 15", cooled by an injected fluid in 10 'by the 16' and 16 "tubes and evacuated by 10".

The anode 3 is common and two arcs 5 and 6 are introduced. The material to be treated is introduced by the injector 4 using a fluid 8. The hottest zone of the combined arcs 5 and 6 found in 7.

The fluid for constricting and guiding the arcs 5 and 6 is introduced along each cathode at 9 ', 9 ", so as to lengthen the two arcs and to move the anodic spots 12 and 13 in the axial direction towards the outlet. of the anode 3. In this way, stable arcs of good length and relatively high voltages are obtained, therefore an important electrical power, mainly dissipated in the zone 7 through which the material to be treated travels. electrodes are cooled by a suitable fluid (10 ', 10 "for the cathodes; 11', 11" for the anode).

For a device as shown in Figure 1 The electrical connection is made in accordance with Figure 2. Each cathode is connected to the negative pole of a direct current generator or rectifier 17,18, the positive pole of which is connected to the 'anode, which in the case shown is common.

Current 11 flowing in the arc between cathode 1 and anode 3 and current 12 flowing in the arc ent re L a ca t hode 2 and Anode 3 are adjusted and adjusted if ndép end ammen t pa rlesd eu x red re ss eu rs 1 7, 1 8.

The example of this figure 2 can easily be extended to a larger number of cathodes and to the same number of rectifiers. At startup, use will be made of a known means, such as a high frequency pilot discharge between each cathode and the input of the anode. In order to ensure a long service life for the electrodes, it is preferable to limit the current at each cathode spot to a value of around 1000 A. The problems are less acute on the side of the anode spot, which is distributed naturally over a larger area, which results in lower current densities.

On the other hand, it is very important to position the anode spots 12 and 13 as far downstream as possible downstream in the hollow anode, so as to benefit for the same intensity from an arc voltage and therefore from such a high power. as possible. A larger heating zone 7 will also be obtained in this way and therefore a better theoretical exchange with the material to be treated.

Frequently it is necessary to treat highly aggressive materials chemically at high temperature. This is why, use will preferably be made of inert fluids at 9 ', 9 "along the cathodes, and the presence of an inert fluid at the height of the anode spots 12 and 13 will be ensured. for this purpose an inert or non-oxidizing gas, such as Argon, Nitrogen, Helium or hydrogen, or a Liquid such as water. The subject to be treated is likely to be. Jtement aggressive vis-à-vis the anode, for example if it is to react at high temperature of atomic oxygen with TiCL4 in order to obtain Ti02, we will usefully use the variant shown in Figure 3. In this device The hollow anode is divided into several parts 3a, 3b, 3c, 3d electrically isolated from each other.

Here, the arcs 6 and 7 are first struck between the cathodes 1 and 2 and the nearest anode-3a by the action of the switches 19a, 20a. These two arcs are then progressively lengthened by increasing the gas flow rates 9 ′ and 9 ", so as to move the anode spots 12 and 13 towards the second part of the anode 3b, at the same time the switches 19b are engaged, 20b and, as soon as the anode spots have reached the anode 3b, the connection of the first anode 3a is interrupted by opening the switches 19a, 20a. It is possible, if this is desirable, to introduce at this time an additional fluid 22a per 1 'intei— valle 21a separating the anode 3a from the anode 3b. In this way we ensure a better guidance of the a "- towards the exit of the Anode 3b.

This injection of fluid can take various directions with respect to the arc, parallel, inclined or tangential as shown respectively in FIGS. 4A, 4B, 4C.

This upe of cold fluid stabilizes the discharge, prevents parasitic discharges to the previous anode, maintaining the anode spots 12 and 13 towards the outlet of the anode 3b, and provides additional cooling of this anode. By gradually increasing the fluid flow rates 9 ', 9 "and 22a, the anode spots are dragged towards the anode 3c, the switch 19c is closed, then 19b is opened, an additional fluid 22b by 21b is introduced and thus transferred gradually the anodic spots towards the exit of the torch on the 3d anode.

The fine adjustments of the different flow rates make it possible to obtain very stable arcs, of great length, operating at one or more kV, that is to say at one or more HW for an intensity per cathode not exceeding 1 kA.

The perfect stability of the discharge makes it possible to avoid the very sudden variations in current which are encountered during flash back on traditional installations, which results in a very significant increase in the service life of the electrodes. , a sine qua non condition for the use of these torches in chemical or metallurgical processes intended to operate for long weeks without interruption or disassembly.

The various anodes are naturally cooled, if necessary, by an appropriate fluid as shown in 11 * and 11 "in FIG. 1.

It may be desirable, when the injected materials are particularly reactive with respect to the anode 3, to displace before injection of these materials the anodic spots on the face downstream of the latter anode, as shown in FIG. 5, to keep it there by injecting fluid The anodic spots 12 and 13 on an anode 23 insulated from 3d and protected active elements of the plasma by an inert fluid 24. The stability of the discharge can usefully be improved by rotating the anode spots under the action of an auxiliary magnetic field 25 produced by the winding 26.

When the arcs 6 and 7, after closing of the switches 19 and 20, have been hooked by their anode spot 12, 13 to the anode 23, the switches 19d and 20d are opened.

It goes without saying that the anode 23 can be cooled by known means, not shown.

In the devices described above, it is sometimes desirable to work at high enthalpy with relatively low plasma fluid flow rates and non-peated axial flow Lonna re of the La¬ mineral type. If the internal diameter of the anodes is relatively large, then there will be a certain number of arcs, as many as cathodes, which are substantially parallel. In this case, it is possible that the axial part of the plasma is at a lower temperature than that of the peripheral zone. In order to remedy this drawback, use is made according to the invention of a device with crossed arcs, as shown in FIG. 6A. Each anode is divided into as many segments as there are cathodes. The positive pole of each rectifier being systematically connected to the anode segment angularly offset from the cathode connected to the negative pole of the same generator.

FIG. 6A shows a device with two cathodes 1, 2 and an anode made up of four years rings 3'a, 3'b, 3'c, 3'd, these rings being composed of two cooled segments, electrically isolated and each connected to the positive pole of one of the two rectifiers.

The inclination of the cathodes 1, 2 and the auxiliary jets 9 ',. 9 "allows, after arcing between the arcs and the anode 3'a, to pass the anodic spot of each arc to an anode segment offset angularly by 60 ° on Anode 3 'b, 120 ° on the anode 3'c and 180 ° on the anode 3' This gives the configuration of crossed arcs 6 and 7 shown in Figure 6B.

In a variant of this embodiment, each cathode is followed by an initiating and guiding nozzle and the plasma jet, which leaves this initiating nozzle, is directly oriented towards the anode segment arranged at 180 ° . The device is shown in FIG. 7. In another variant, these nozzles are replaced by a single anode pierced with a number of passages as much as with cathodes and serving to channel and orient the plasmas at priming.

The devices described above are only examples. It goes without saying that either of these devices can be combined with other known means intended to bring more energy into the plasma, such as, for example, exothermic reactions, induction heating or low or medium frequency high voltage discharge in the turbulent flow at the outlet of the anode.

In particular, in the case of destruction of waste, the latter can be introduced after having been preheated by passage through a traditional burner.

Claims

claims

1. Process. For obtaining high temperatures for a fluid, characterized in that it consists in establishing between two or more cathodes (1, 2 ^N and one or more hollow anodes (3) separate arcs (5, 6) , to maintain a flow of inert gas between the methods (1, 2) and the year (s) of (3), to arrange the cathodes (1, 2) substantially according to the generators of a cone matching L ' inlet of the or the first anode (3), and introduce the material to be treated by a tube located in the axis of the cone and the anode.

2. Method according to the claim on 1, characterized in that it consists in introducing the fluid for constricting and guiding the arcs (5, 6) along each cathode (along 9 ', 9 "), so to lengthen the two arcs and to move the anode spots (12, 13) in the axial direction towards the outlet of the anode (3).

3. Method according to claim 2, characterized in that it consists in positioning the anodic spots (12, 13) as far downstream as possible in the hollow anode (3), so as to obtain for the same intensity an arc voltage, and therefore a power, as high as possible.

4. Next method The claim on 1, characterized in that the hollow anode (3) is divided into several parts' 3a, 3b, 3c, 3d) electrically insulated from each other with gas injection between the parts anode.

5. Method according to claim 4, characterized in that it consists in moving, before injection of particularly reactive materials vis-à-vis the A¬ node (3), the anode spots (12, 13) on the face downstream of the last anode (3d ⁾ and to be maintained there by injection of fluid The anode spots ( 12,13) on an anode (23) isolated from the anode (3d) and protected from the active elements of the plasma by an inert fluid (24).

6. Method according to claim 5, characterized in that it. consists in rotating the anodic spots (12, 13) under the action of an auxiliary magnetic field (25) produced by a winding (26).

7. Method according to one or more of the preceding claims, characterized in that each anode (3) is divided into as many segments as there are cathodes, the positive pole of each rectifier being systematically connected to the anode segment dec- random angularly with respect to the cathode connected to the negative pole of the same rectifier.