EP0743811B1 - Direct current arc plasma torch, specially conceived for the obtention of a chemical body by decomposition of a plasma gas - Google Patents

Direct current arc plasma torch, specially conceived for the obtention of a chemical body by decomposition of a plasma gas Download PDF

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Publication number
EP0743811B1
EP0743811B1 EP96400770A EP96400770A EP0743811B1 EP 0743811 B1 EP0743811 B1 EP 0743811B1 EP 96400770 A EP96400770 A EP 96400770A EP 96400770 A EP96400770 A EP 96400770A EP 0743811 B1 EP0743811 B1 EP 0743811B1
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EP
European Patent Office
Prior art keywords
plasma
electrode
gas
tubular
plasma torch
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EP96400770A
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German (de)
French (fr)
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EP0743811A1 (en
Inventor
Martine Cadre
Maxime Labrot
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Airbus Group SAS
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Airbus Group SAS
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H1/00—Generating plasma; Handling plasma
    • H05H1/24—Generating plasma
    • H05H1/26—Plasma torches
    • H05H1/32—Plasma torches using an arc
    • H05H1/34—Details, e.g. electrodes, nozzles
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H1/00—Generating plasma; Handling plasma
    • H05H1/24—Generating plasma
    • H05H1/26—Plasma torches
    • H05H1/32—Plasma torches using an arc
    • H05H1/34—Details, e.g. electrodes, nozzles
    • H05H1/341—Arrangements for providing coaxial protecting fluids
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H1/00—Generating plasma; Handling plasma
    • H05H1/24—Generating plasma
    • H05H1/26—Plasma torches
    • H05H1/32—Plasma torches using an arc
    • H05H1/34—Details, e.g. electrodes, nozzles
    • H05H1/3468—Vortex generators
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H1/00—Generating plasma; Handling plasma
    • H05H1/24—Generating plasma
    • H05H1/26—Plasma torches
    • H05H1/32—Plasma torches using an arc
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H1/00—Generating plasma; Handling plasma
    • H05H1/24—Generating plasma
    • H05H1/26—Plasma torches
    • H05H1/32—Plasma torches using an arc
    • H05H1/34—Details, e.g. electrodes, nozzles
    • H05H1/3431—Coaxial cylindrical electrodes
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H1/00—Generating plasma; Handling plasma
    • H05H1/24—Generating plasma
    • H05H1/26—Plasma torches
    • H05H1/32—Plasma torches using an arc
    • H05H1/34—Details, e.g. electrodes, nozzles
    • H05H1/40—Details, e.g. electrodes, nozzles using applied magnetic fields, e.g. for focusing or rotating the arc

Definitions

  • the present invention relates to a plasma arc torch direct current, particularly intended for obtaining of a chemical body by decomposition of a plasma gas.
  • a DC arc plasma torch comprising two coaxial tubular electrodes arranged in extension of each other, on either side of a chamber, into which a stream of plasma gas is injected, for example air.
  • Each of said electrodes is open on the side of said injection chamber, while one of which is further open at its far end of said injection chamber.
  • the arc between said electrodes crosses said injection chamber and ionizes the plasma gas introduced in this one.
  • Said arch hangs by its end feet respectively to the internal face of said electrodes and ionized gas plasma, high pressure (pressure atmospheric at around 5 bar) and at very high temperature (several thousand ° C), crosses the open electrode at both ends and flows out of said torch at through the opening of this last electrode away from said injection chamber.
  • the flow of plasma coming out of said torch comprises ions of the elements composing said gas, as a result of the action of the electric arc on said gas plasmagen.
  • the plasma gas is hydrogen sulfurous
  • the plasma flow contains ions hydrogen and sulfur ions. Therefore, if we submit said plasma flow at thermal quenching it is possible to collect the elements of the plasma gas.
  • sulfurous hydrogen as plasma gas, then quenching the plasma, allow therefore to collect sulfur, on the one hand, and hydrogen, on the other hand.
  • a torch of the type described above can serve as a reactor for the decomposition of gaseous compounds plasmagenics.
  • the object of the present invention is to remedy these drawbacks. It relates to a plasma arc torch of long service life, particularly suitable to be used as a thermochemical decomposition reactor, operating with good energy efficiency and allowing obtaining high purity decomposition products.
  • the plasma leaving the torch conforms to the present invention is particularly pure.
  • said fluid barrier forms a sheath protecting the internal surface of the first electrode against the action erosion of plasma ions. We therefore also improve the lifetime of this electrode.
  • said first tubular part is integral of the first electrode, and it can even form one single piece with the latter, so as to appear as an elongated portion of said electrode.
  • said first tubular part plays no role electric role vis-à-vis the arc in established regime, it can be dimensioned in volume, in diameter and length so that aerothermal conditions (pressure, temperature) optimize the chemical yield and, therefore, energy yield.
  • aerothermal conditions pressure, temperature
  • said first means for forming said fluid barrier are constituted by first means of blowing causing, on the internal wall of said first electrode, a first tubular flow of a gas to pressure at least approximately equal to that of plasma and at a temperature much lower than that of said plasma, said first fluid tubular flow surrounding said flow of plasma and flowing in the same direction as it.
  • a flow of central plasma containing gas decomposition ions plasma and an annular flow formed by the gas blowing and surrounding said central flow of the plasma is at very high temperature (several thousands of ° C) and at high pressure (atmospheric pressure at around 5 bars).
  • the flow blowing ring can be at low temperature (by room temperature) and at a pressure of the order of that of plasma.
  • the central flow and the annular flow have very viscosities different, prohibiting their mixing. The particles of electrodes, torn off by the arc, cannot therefore pass from the annular flow of the blowing gas at the flow of central plasma, surrounded by this annular flow.
  • the blown gas may, for example, be hydrogen.
  • said first electrode has a larger diameter that said first tubular part and that said first blowing means are arranged between said first tubular part and said first electrode.
  • This blowing gas can be blown on the internal wall of said first electrode, parallel to the axis of this last.
  • the gas from said first tubular flow can be blown inside said first electrode, tangentially to the inner wall of the latter, similar to what is generally practiced for the so-called vortex injection of plasma gas into the injection chamber.
  • Such tangential blowing means may have an inner crown and a crown coaxial outer, providing a room between them annular supplied with blowing gas through said outer crown, while the central opening of said inner crown forms at least approximately an extension of the internal surface of said first electrode and that said central crown opening inner is connected to said annular chamber by at at least one orifice tangential to said central opening.
  • said second electrode and its elements partners may have the same features as those mentioned above about the first electrode.
  • the plasma torch according to the present invention includes means for moving the feet arcs, such as those described above.
  • means for moving the feet arcs such as those described above.
  • such means do not have to act on the first and second tubular parts, but only on the electrodes.
  • means are provided, which can be, known manner, of the type with electric discharge produced between both electrodes or short-circuit type, thanks, by example, when using an auxiliary electrode start-up.
  • said arc electric between the parts of said neighboring electrodes of said injection chamber (said first and second tubular parts), then to extend said arc under the effect of the vortex injection of plasma gas, until that the feet of said arc are hooked to the surface internal of said end portions of the electrodes, remote of said injection chamber (electrodes properly say).
  • said means for injecting the plasma gas in said chamber allow to inject it in vortices in planes perpendicular to the common axis electrodes.
  • These means of injection may include (see US-A-5,262,616 mentioned above) a piece of coaxial revolution to said electrodes and defining with these and their supports said injection chamber. Of transverse holes are provided in the room to allow injection of plasma gas from a supply circuit, in the bedroom.
  • the temperatures plasma damage to the torch outlets may exceed 5000 ° C. Also, it is essential to plan cooling circuits for the electrodes, such as this is moreover usual for plasma torches.
  • FIG. 1 shows, in very schematic longitudinal section, a first example of a plasma torch in accordance with this invention, to illustrate the inventive principle of this one.
  • Figure 2 illustrates the section, along line II-II of the Figure 1, the fluid flow at the outlet of the torch to plasma.
  • Figure 3 shows, also in very longitudinal section schematic, a second example of a plasma torch conforming to the present invention.
  • Figure 4 is a simplified longitudinal section of a mode of practical realization of the plasma torch of the figure 1.
  • Figure 5 is a cross section along the line V-V in Figure 4.
  • Figure 6 is a simplified longitudinal section of a mode of practical realization of the plasma torch of the figure 3.
  • the exemplary embodiment I of the plasma torch in accordance with the present invention and shown very schematically in FIG. 1, has an anode 1 and a part cathodic 2, tubular and coaxial, arranged in extension from each other along an X-X axis, on both sides other of a chamber 3 into which is injected, any in known manner, a plasma gas (arrows P).
  • Anode 1 and the cathode part are cooled in any suitable way and known, but not shown.
  • the anode 1 is elongated along the axis X-X and comprises, at its end arranged opposite the injection chamber 3, an opening 4 connecting the interior of said anode 1 with said injection chamber 3. On the other hand, at its end opposite to the injection chamber 3, the anode 1 is closed by a bottom 5.
  • the cathode part 2 comprises, at its end remote from the injection chamber 3, a cathode 2A open towards the outside by an opening 6.
  • the cathode 2A is extended, in the direction of the injection chamber 3, by a part tubular 2B forming an integral part of said cathode 2A.
  • the cathode 2A has a diameter D greater than the diameter d of the tubular part 2B and a shoulder 7 connects the cathode 2A and the tubular part 2B.
  • orifices 8 are provided, distributed around the axis XX and with an axis at least substantially parallel thereto.
  • the tubular part 2B has an opening 9 putting the interior of the cathode part 2 into communication with said injection chamber 3.
  • an electric arc 10 crosses the chamber injection 3 and the tubular part 2B and hooks, by its end legs 10a and 10c, respectively on the internal surface of anode 1 (near bottom 5 opposite to the injection chamber 3) and to that of the cathode 2A.
  • Electromagnetic coils 11 and 12 intended for the rotation of the feet 10a and 10c of the arc 10 around the axis X-X, respectively surround the anode 1 (in the vicinity of the bottom 5) and cathode 2A.
  • the stream of plasma gas P entering the tubular part 2B is transformed, in the latter and under the action of the arc 10, in a plasma flow 13, leaving through opening 6 after passing through the cathode 2A.
  • the tubular part 2B therefore forms a reaction chamber in which the plasma gas is transformed into a plasma, at high pressure and at very high temperature, comprising ions of the components of said plasma gas. It's obvious that the tubular part 2B can be dimensioned to optimize energy efficiency.
  • a gas G for example hydrogen
  • a gas G for example hydrogen
  • the particles of matter from the cathode 2A which are torn off from the inner surface thereof by the arc foot 10c, not only can not mix to the plasma flow 13 but still are evacuated by the annular gas stream 14. They cannot therefore pollute plasma flow 13.
  • particles of material from anode 1, which are torn off at this by the arc foot 10a remain in the anode 1 (this which is obtained from the fact that the anode 1 is long and that the arch 10a is in the vicinity of the bottom 5), the flow plasma 13, comprising ions of the gas components is particularly pure.
  • a quenching device (not shown, but of any type known) allows the annular gas stream 14 to be separated from the plasma flow 13 and then extract the components chemicals contained in the form of ions in said flow plasma 13.
  • the anode part 1 ′ comprises, at its end remote from the injection chamber 3, an anode 1'A open towards the outside by an opening 15.
  • the anode 1'A is extended, in the direction of the injection chamber 3, by a tubular piece 1'B forming an integral part of said anode.
  • the anode 1'A has a diameter D greater than the diameter d of the tubular piece 1'B and a shoulder 16 connects the anode 1'A and the tubular piece 1'B.
  • orifices 17 are provided, distributed around the axis XX and with an axis at least substantially parallel thereto.
  • the tubular part 1'B has an opening 18 putting the interior of the anode part 1 'into communication with the injection chamber 3.
  • the electric arc 10 crosses the chamber injection 3 and the tubular parts 1'B and 2B and hooks, by its feet 10a and 10c, respectively on the surface internal of anode 1'A and cathode 2A.
  • the plasma gas injected into chamber 3 divides in two streams, one of which enters the tubular part 1'B and the other in the tubular part 2B.
  • said plasma gas streams transform into two opposite plasma flows 13 and 19, leaving through openings 6 and 15, after crossing cathode 2A and anode 1'A respectively.
  • Rooms 1'B AND 2B tubular therefore form reaction chambers in which the plasma gas is transformed into plasma.
  • FIG 4 there is shown an embodiment practice of Example I in Figure 1.
  • the tubular body 30 of the plasma torch, surrounding the anode 1 and the cathode part 2 is constituted (at simplicity of construction) of a plurality of sections 30A, 30B, 30C ... coaxial with each other and with said electrodes and tightly assembled one at the end of the other.
  • connection means 31 are provided for sealingly open open end 6, remote from the injection chamber 3, from the cathode 2A to a device quenching (not shown).
  • Conduits 32 and 33 are respectively provided around the anode 1 and the workpiece cathodic 2 for the circulation of a cooling fluid of these.
  • the means 34 for injecting the plasma gas into the chamber 3 are of the vortex injection type, such than those described in US-A-5,262,616. They are made up by a part of revolution, coaxial with the X-X axis and include an annular groove 35, supplied with plasma gas (arrows P) and connected to the injection chamber 3 by transverse holes 36.
  • a short-circuit ignition device 37 is provided, known type with auxiliary starting electrode 38.
  • the arc 10 can be struck between the parts of the anode 1 and of tubular part 2B, adjacent to the injection chamber 3, then stretched out under the effect of the vortex injection plasma gas, until feet 10a and 10b of said arc are attached to the internal surface of anode 1 near the bottom 5 and that of the cathode 2A, in the field coils 11 and 12.
  • the torch of Figure 4 (see also Figure 5) has a section 30E constituting the device S for tangential blowing of the fluid tubular flow 14, surrounding the flow of plasma 13.
  • the blowing device S comprises an inner ring 39 (crossed by the cooling conduits 33) and an outer ring 40 coaxial with the axis XX , forming between them an annular chamber 41, supplied with blowing gas (see arrows G) through said outer ring 40.
  • the central opening 42 of the inner ring 39 has the diameter D and forms at least approximately an extension of the internal surface of cathode 2A. This central opening 42 therefore forms the transition between the internal surface of the tubular part 2B of diameter d and the internal surface of the cathode 2A of diameter D. It is connected to the annular chamber 41 by orifices 43, tangential to its internal surface .
  • Example II of the plasma torch in the practical embodiment of Example II of the plasma torch, according to the present invention and shown in section in Figure 6, we have, compared to the mode of practical embodiment of Figures 4 and 5, replaced the anode 1 by the anode part 1 ', similar (but opposite along from the X-X axis) to the cathode part 2.
  • the part anode 1 ′ comprises the anode 1'A and the tubular part 1'B, connected by a tangential blowing device S '.
  • the anode 1'A, the tubular part 1'B and the device blowing S ′ are respectively identical to cathode 2A, to the tubular part 2B and to the blowing device S.
  • Des connection means 44 are provided for connecting so seals the open end 15 away from the chamber injection 3, from the 1'A anode to a quenching device (not represented).

Description

La présente invention concerne une torche à plasma d'arc à courant continu, particulièrement destinée à l'obtention d'un corps chimique par décomposition d'un gaz plasmagène.The present invention relates to a plasma arc torch direct current, particularly intended for obtaining of a chemical body by decomposition of a plasma gas.

Par exemple, par le brevet américain US-A-5 262 616, on connaít déjà une torche à plasma d'arc à courant continu comportant deux électrodes tubulaires coaxiales disposées en prolongement l'une de l'autre, de part et d'autre d'une chambre, dans laquelle est injecté un courant de gaz plasmagène, par exemple de l'air. Chacune desdites électrodes est ouverte du côté de ladite chambre d'injection, tandis que l'une d'elles est de plus ouverte à son extrémité éloignée de ladite chambre d'injection.For example, by US patent US-A-5,262,616, we already know a DC arc plasma torch comprising two coaxial tubular electrodes arranged in extension of each other, on either side of a chamber, into which a stream of plasma gas is injected, for example air. Each of said electrodes is open on the side of said injection chamber, while one of which is further open at its far end of said injection chamber.

Ainsi, l'arc entre lesdites électrodes traverse ladite chambre d'injection et ionise le gaz plasmagène introduit dans celle-ci. Ledit arc s'accroche par ses pieds d'extrémité respectivement à la face interne desdites électrodes et le plasma de gaz ionisé, à haute pression (de la pression atmosphérique à environ 5 bars) et à très haute température (plusieurs milliers de °C), traverse l'électrode ouverte à ses deux extrémités et s'écoule, hors de ladite torche, à travers l'ouverture de cette dernière électrode éloignée de ladite chambre d'injection.Thus, the arc between said electrodes crosses said injection chamber and ionizes the plasma gas introduced in this one. Said arch hangs by its end feet respectively to the internal face of said electrodes and ionized gas plasma, high pressure (pressure atmospheric at around 5 bar) and at very high temperature (several thousand ° C), crosses the open electrode at both ends and flows out of said torch at through the opening of this last electrode away from said injection chamber.

Si, dans une telle torche, on utilise comme gaz plasmagène un corps composé gazeux, l'écoulement de plasma sortant de ladite torche comporte des ions des éléments composant ledit gaz, par suite de l'action de l'arc électrique sur ledit gaz plasmagène. Par exemple, si le gaz plasmagène est de l'hydrogène sulfureux, l'écoulement de plasma comporte des ions hydrogène et des ions soufre. Par suite, si l'on soumet ledit écoulement de plasma à une trempe thermique, il est possible de recueillir les éléments du gaz plasmagène. Dans l'exemple ci-dessus, l'utilisation de l'hydrogène sulfureux comme gaz plasmagène, puis la trempe du plasma, permettent donc de recueillir du soufre, d'une part, et de l'hydrogène, d'autre part.If, in such a torch, one uses as plasma gas a gaseous compound body, the flow of plasma coming out of said torch comprises ions of the elements composing said gas, as a result of the action of the electric arc on said gas plasmagen. For example, if the plasma gas is hydrogen sulfurous, the plasma flow contains ions hydrogen and sulfur ions. Therefore, if we submit said plasma flow at thermal quenching it is possible to collect the elements of the plasma gas. In the example above, the use of sulfurous hydrogen as plasma gas, then quenching the plasma, allow therefore to collect sulfur, on the one hand, and hydrogen, on the other hand.

Ainsi, une torche du type décrit ci-dessus peut servir de réacteur pour la décomposition de corps composés gazeux plasmagènes.Thus, a torch of the type described above can serve as a reactor for the decomposition of gaseous compounds plasmagenics.

Cependant, l'utilisation d'une telle torche en réacteur de décomposition soulève des difficultés :

  • A/ Tout d'abord, il est bien connu que, dans une torche du type décrit ci-dessus, les électrodes s'érodent sous l'action des pieds d'arcs qui arrachent des particules aux parois internes desdites électrodes. Il en résulte donc que, lors de l'utilisation d'une telle torche en réacteur de décomposition, les corps chimiques obtenus sont pollués par ces particules de la matière des électrodes (par exemple du cuivre). Dans une telle application, la pollution est fortement aggravée par l'interaction, au niveau des pieds d'arc, de certains des ions de décomposition (tels que l'ion soufre S-- par exemple) avec la matière des électrodes. Ainsi, non seulement de tels réacteurs de décomposition s'usent rapidement, mais encore les produits de décomposition obtenus ne peuvent être purs.Pour tenter de remédier à de tels inconvénients, on a déjà essentiellement proposé deux mesures. La première consiste à réaliser les électrodes en des matières peu réactives avec le gaz plasmagène utilisé, telles que par exemple le tungstène ou le tungstène rhodié. Quant à la seconde, elle consiste à répartir l'usure des électrodes autour de l'axe de celles-ci en engendrant un champ magnétique susceptible de faire tourner les pieds d'arc autour dudit axe. Des moyens pour obtenir une telle rotation des pieds d'arc sont par exemple décrits dans les documents US-A-3 301 995 et EP-A-0 032 100. Ils sont généralement définis par des bobines électromagnétiques entourant les électrodes. Ainsi, en modulant le champ magnétique axial engendré par les bobines lorsqu'elles sont excitées, les pieds d'accrochage de l'arc électrique se déplacent autour des surfaces internes des électrodes en évitant la formation de cratères locaux et la destruction rapide des électrodes.Les deux mesures connues rappelées ci-dessus permettent effectivement de réduire l'usure des électrodes et la pollution des produits de décomposition. Cependant, une telle réduction est généralement insuffisante pour procurer une durée de vie satisfaisante aux électrodes et assurer la pureté désirée aux produits de décomposition. De plus, la première mesure se révèle généralement onéreuse.
  • B/ Par ailleurs, le rendement énergétique d'une telle torche utilisée en réacteur est faible, de sorte qu'il est nécessaire de dépenser de grandes quantités d'énergie électrique pour décomposer le corps composé gazeux en ses éléments et que le coût de fabrication desdits éléments est élevé.
    • However, the use of such a torch in a decomposition reactor raises difficulties:
  • A / First of all, it is well known that, in a torch of the type described above, the electrodes are eroded under the action of the feet of arcs which tear particles from the internal walls of said electrodes. It therefore follows that, when using such a torch in a decomposition reactor, the chemical bodies obtained are polluted by these particles of the material of the electrodes (for example copper). In such an application, the pollution is greatly aggravated by the interaction, at the level of the arc feet, of some of the decomposition ions (such as the sulfur ion S - for example) with the material of the electrodes. Thus, not only do such decomposition reactors wear out quickly, but also the decomposition products obtained cannot be pure. To try to remedy such drawbacks, two measures have already been proposed. The first consists in producing the electrodes in materials which are not very reactive with the plasma gas used, such as for example tungsten or rhodium tungsten. As for the second, it consists in distributing the wear of the electrodes around the axis of the latter by generating a magnetic field capable of causing the arc feet to rotate around said axis. Means for obtaining such rotation of the arch feet are for example described in the documents US-A-3 301 995 and EP-A-0 032 100. They are generally defined by electromagnetic coils surrounding the electrodes. Thus, by modulating the axial magnetic field generated by the coils when they are excited, the attachment feet of the electric arc move around the internal surfaces of the electrodes, avoiding the formation of local craters and rapid destruction of the electrodes. The two known measures recalled above effectively reduce the wear of the electrodes and the pollution of the decomposition products. However, such a reduction is generally insufficient to provide a satisfactory lifetime for the electrodes and to ensure the desired purity for the decomposition products. In addition, the first measurement is generally expensive.
  • B / Furthermore, the energy efficiency of such a torch used in a reactor is low, so that it is necessary to spend large amounts of electrical energy to decompose the gaseous compound body into its elements and that the manufacturing cost of said elements is high.

    • La présente invention a pour objet de remédier à ces inconvénients. Elle concerne une torche à plasma d'arc de grande durée de vie, particulièrement appropriée à être utilisée comme réacteur thermochimique de décomposition, fonctionnant avec un bon rendement énergétique et permettant l'obtention de produits de décomposition de grande pureté. The object of the present invention is to remedy these drawbacks. It relates to a plasma arc torch of long service life, particularly suitable to be used as a thermochemical decomposition reactor, operating with good energy efficiency and allowing obtaining high purity decomposition products.

    A cette fin, selon l'invention, la torche à plasma d'arc à courant continu, notamment destinée à l'obtention d'un corps chimique à partir d'un gaz plasmagène comportant ledit corps, ladite torche comprenant :

    • une première électrode et une seconde électrode, lesdites électrodes étant tubulaires, coaxiales et disposées en prolongement l'une de l'autre, de part et d'autre d'une chambre d'injection dudit gaz plasmagène, lesdites électrodes étant ouvertes à leurs extrémités en regard de ladite chambre d'injection, et
    • des moyens pour injecter un courant du gaz plasmagène dans ladite chambre d'injection,
    l'arc entre lesdites électrodes traversant ladite chambre d'injection et s'accrochant par des pieds d'extrémité respectivement à la surface interne desdites électrodes, tandis que ladite première électrode est ouverte à son extrémité éloignée de ladite chambre d'injection pour permettre l'écoulement, hors de la torche, du plasma engendré par ledit arc, est remarquable en ce que :
    • ladite première électrode est en communication avec ladite chambre d'injection par l'intermédiaire d'une première pièce tubulaire traversée par ledit arc et constituant une première chambre de réaction dans laquelle ledit gaz plasmagène donne naissance au plasma sous l'action dudit arc électrique ; et
    • il est prévu des premiers moyens permettant de former une barrière fluide entre ladite première électrode et ledit plasma.
    To this end, according to the invention, the direct current arc plasma torch, in particular intended for obtaining a chemical body from a plasma gas comprising said body, said torch comprising:
    • a first electrode and a second electrode, said electrodes being tubular, coaxial and arranged in extension of one another, on either side of an injection chamber of said plasma gas, said electrodes being open at their ends opposite said injection chamber, and
    • means for injecting a stream of plasma gas into said injection chamber,
    the arc between said electrodes passing through said injection chamber and hooking by end feet respectively to the internal surface of said electrodes, while said first electrode is open at its end remote from said injection chamber to allow the the flow, out of the torch, of the plasma generated by said arc, is remarkable in that:
    • said first electrode is in communication with said injection chamber via a first tubular part traversed by said arc and constituting a first reaction chamber in which said plasma gas gives rise to plasma under the action of said electric arc; and
    • first means are provided for forming a fluid barrier between said first electrode and said plasma.

    Ainsi, grâce à l'invention :

    • le plasma est formé dans une zone de réaction découplée des pieds d'arc. Par suite, lors de sa formation, ledit plasma ne peut être pollué par les particules arrachées à la matière des électrodes ; et
    • les particules de matière de la première électrode, arrachées par le pied d'arc correspondant, sont empêchées de s'incorporer au plasma.
    Thus, thanks to the invention:
    • the plasma is formed in a reaction zone decoupled from the arc feet. Consequently, during its formation, said plasma cannot be polluted by the particles torn from the material of the electrodes; and
    • the particles of material from the first electrode, torn off by the corresponding arc foot, are prevented from incorporating into the plasma.

    Par suite, le plasma sortant de la torche conforme à la présente invention est particulièrement pur.As a result, the plasma leaving the torch conforms to the present invention is particularly pure.

    De plus, ladite barrière fluide forme une gaine protégeant la surface interne de la première électrode contre l'action d'érosion des ions du plasma. On améliore donc en outre la durée de vie de cette électrode.In addition, said fluid barrier forms a sheath protecting the internal surface of the first electrode against the action erosion of plasma ions. We therefore also improve the lifetime of this electrode.

    De préférence, ladite première pièce tubulaire est solidaire de la première électrode, et elle peut même ne former qu'une seule pièce avec cette dernière, de façon à apparaítre comme une partie allongée de ladite électrode.Preferably, said first tubular part is integral of the first electrode, and it can even form one single piece with the latter, so as to appear as an elongated portion of said electrode.

    On remarquera que, puisque ladite première pièce tubulaire ne joue aucun rôle rôle électrique vis-à-vis de l'arc en régime établi, elle peut être dimensionnée en volume, en diamètre et en longueur pour que les conditions aérothermiques (pression, température) permettent d'optimiser le rendement chimique et, donc, le rendement énergétique. Ainsi, grâce à la présente invention, on peut définir la géométrie de la torche en fonction des critères liés à l'optimisation des réactions thermochimiques à établir, et non pas uniquement en fonction de critères fonctionnels liés, par exemple, au développement de l'arc électrique et/ou à la résistance dans le temps des électrodes (comme cela est le cas pour les torches connues).It will be noted that, since said first tubular part plays no role electric role vis-à-vis the arc in established regime, it can be dimensioned in volume, in diameter and length so that aerothermal conditions (pressure, temperature) optimize the chemical yield and, therefore, energy yield. Thus, thanks to the present invention, one can define the torch geometry based on criteria related to optimization of the thermochemical reactions to be established, and not only according to functional criteria related, for example, to the development of the electric arc and / or the resistance over time of the electrodes (as this is the case for known torches).

    L'invention permet donc d'obtenir une torche à plasma, à moindre usure :

    • capable de produire des composés chimiques non pollués par les produits d'érosion des électrodes ; et
    • apte à optimiser, sans limitation de puissance, les conditions aérothermiques des réactions par ajustement du dimensionnement de la zone de réaction.
    The invention therefore makes it possible to obtain a plasma torch, with less wear:
    • capable of producing chemical compounds not polluted by the erosion products of the electrodes; and
    • able to optimize, without power limitation, the aerothermal conditions of the reactions by adjusting the dimensioning of the reaction zone.

    Avantageusement, lesdits premiers moyens pour former ladite barrière fluide sont constitués par des premiers moyens de soufflage engendrant, sur la paroi interne de ladite première électrode, un premier écoulement tubulaire d'un gaz à pression au moins approximativement égale à celle du plasma et à température très inférieure à celle dudit plasma, ledit premier écoulement tubulaire fluide entourant ledit écoulement du plasma et s'écoulant dans le même sens que celui-ci.Advantageously, said first means for forming said fluid barrier are constituted by first means of blowing causing, on the internal wall of said first electrode, a first tubular flow of a gas to pressure at least approximately equal to that of plasma and at a temperature much lower than that of said plasma, said first fluid tubular flow surrounding said flow of plasma and flowing in the same direction as it.

    Ainsi, les particules de matière de la première électrode, arrachées par le pied d'arc, sont évacuées par ledit premier écoulement fluide hors de la torche, sans contact avec le plasma.So the matter particles from the first electrode, torn off by the arch foot, are evacuated by said first fluid flow out of the torch, without contact with the plasma.

    On remarquera que, à la sortie de la torche à plasma conforme à la présente invention, on obtient donc un écoulement de plasma central contenant les ions de décomposition du gaz plasmagène et un écoulement annulaire constitué par le gaz de soufflage et entourant ledit écoulement central du plasma. Comme on l'a mentionné ci-dessus, l'écoulement central de plasma est à très haute température (plusieurs milliers de °C) et à haute pression (de la pression atmosphérique à environ 5 bars). Par ailleurs, l'écoulement annulaire de soufflage peut être à faible température (par exemple la température ambiante) et à une pression de l'ordre de celle du plasma. Par suite, l'écoulement central et l'écoulement annulaire présentent des viscosités très différentes, interdisant leur mélange. Les particules des électrodes, arrachées par l'arc, ne peuvent donc passer de l'écoulement annulaire du gaz de soufflage à l'écoulement de plasma central, entouré par cet écoulement annulaire. It will be noted that, at the exit of the plasma torch conforms to the present invention, a flow of central plasma containing gas decomposition ions plasma and an annular flow formed by the gas blowing and surrounding said central flow of the plasma. As mentioned above, the flow plasma center is at very high temperature (several thousands of ° C) and at high pressure (atmospheric pressure at around 5 bars). By the way, the flow blowing ring can be at low temperature (by room temperature) and at a pressure of the order of that of plasma. As a result, the central flow and the annular flow have very viscosities different, prohibiting their mixing. The particles of electrodes, torn off by the arc, cannot therefore pass from the annular flow of the blowing gas at the flow of central plasma, surrounded by this annular flow.

    Ainsi :

    • le plasma n'est pas originellement pollué par les particules arrachées aux électrodes, grâce au découplage entre la zone de réaction et les pieds d'arc ; et
    • le plasma ne peut être pollué aux sorties de la torche par lesdites particules, à cause de l'impossibilité du mélange entre le plasma et l'écoulement de soufflage.
    So :
    • the plasma is not originally polluted by the particles torn from the electrodes, thanks to the decoupling between the reaction zone and the arc feet; and
    • the plasma cannot be polluted at the torch exits by said particles, because of the impossibility of the mixture between the plasma and the blowing flow.

    Le gaz soufflé peut, par exemple, être de l'hydrogène.The blown gas may, for example, be hydrogen.

    Afin de faciliter l'enrobage de l'écoulement de plasma par ledit écoulement tubulaire de barrière, il est avantageux que ladite première électrode présente un plus grand diamètre que ladite première pièce tubulaire et que lesdits premiers moyens de soufflage soient disposés entre ladite première pièce tubulaire et ladite première électrode.In order to facilitate the coating of the plasma flow by said tubular barrier flow it is advantageous that said first electrode has a larger diameter that said first tubular part and that said first blowing means are arranged between said first tubular part and said first electrode.

    Ce gaz de soufflage peut être soufflé sur la paroi interne de ladite première électrode, parallèlement à l'axe de cette dernière.This blowing gas can be blown on the internal wall of said first electrode, parallel to the axis of this last.

    En variante, le gaz dudit premier écoulement tubulaire peut être soufflé à l'intérieur de ladite première électrode, tangentiellement à la paroi interne de cette dernière, de manière semblable à ce qui est généralement pratiqué pour l'injection, dite tourbillonnaire, du gaz plasmagène dans la chambre d'injection. De tels moyens de soufflage tangentiel peuvent comporter une couronne intérieure et une couronne extérieure coaxiales, ménageant entre elles une chambre annulaire alimentée en gaz de soufflage à travers ladite couronne extérieure, tandis que l'ouverture centrale de ladite couronne intérieure forme au moins approximativement un prolongement de la surface interne de ladite première électrode et que ladite ouverture centrale de la couronne intérieure est reliée à ladite chambre annulaire par au moins un orifice tangentiel à ladite ouverture centrale. Alternatively, the gas from said first tubular flow can be blown inside said first electrode, tangentially to the inner wall of the latter, similar to what is generally practiced for the so-called vortex injection of plasma gas into the injection chamber. Such tangential blowing means may have an inner crown and a crown coaxial outer, providing a room between them annular supplied with blowing gas through said outer crown, while the central opening of said inner crown forms at least approximately an extension of the internal surface of said first electrode and that said central crown opening inner is connected to said annular chamber by at at least one orifice tangential to said central opening.

    Afin d'augmenter encore le rendement de la torche conforme à la présente invention, tout en éliminant les particules arrachées par l'arc à la seconde électrode, il est de plus avantageux que :

    • ladite seconde électrode soit également ouverte à son extrémité éloignée de ladite chambre d'injection, de sorte que l'écoulement dudit plasma est double et s'effectue à travers chacune desdites électrodes ;
    • ladite seconde électrode soit également en communication avec ladite chambre d'injection par l'intermédiaire d'une seconde pièce tubulaire traversée par ledit arc et constituant une seconde chambre de réaction dans laquelle ledit gaz plasmagène donne naissance au plasma sous l'action dudit arc électrique ;
    • il soit prévu des seconds moyens permettant de former une barrière fluide entre ladite seconde électrode et ledit plasma.
    In order to further increase the efficiency of the torch in accordance with the present invention, while eliminating the particles torn off by the arc from the second electrode, it is more advantageous that:
    • said second electrode is also open at its end remote from said injection chamber, so that the flow of said plasma is double and takes place through each of said electrodes;
    • said second electrode is also in communication with said injection chamber by means of a second tubular part traversed by said arc and constituting a second reaction chamber in which said plasma gas gives rise to plasma under the action of said electric arc ;
    • second means are provided for forming a fluid barrier between said second electrode and said plasma.

    Bien entendu, ladite seconde électrode et ses éléments associés peuvent comporter les mêmes particularités que celles mentionnées ci-dessus à propos de la première électrode.Of course, said second electrode and its elements partners may have the same features as those mentioned above about the first electrode.

    De préférence, la torche à plasma conforme à la présente invention comporte des moyens de déplacement des pieds d'arc, tels que ceux décrits ci-dessus. Bien entendu, de tels moyens n'ont pas à agir sur les première et seconde pièces tubulaires, mais uniquement sur les électrodes.Preferably, the plasma torch according to the present invention includes means for moving the feet arcs, such as those described above. Of course, such means do not have to act on the first and second tubular parts, but only on the electrodes.

    Par ailleurs, pour amorcer l'arc électrique entre les électrodes, on prévoit des moyens, qui peuvent être, de façon connue, du type à décharge électrique produite entre les deux électrodes ou du type à court-circuit, grâce, par exemple, à l'utilisation d'une électrode auxiliaire de démarrage. Ainsi, il est possible d'amorcer ledit arc électrique entre les parties desdites électrodes, voisines de ladite chambre d'injection (lesdites première et seconde pièces tubulaires), puis d'allonger ledit arc sous l'effet de l'injection tourbillonnaire du gaz plasmagène, jusqu'à ce que les pieds dudit arc se trouvent accrochés à la surface interne desdites parties d'extrémité des électrodes, éloignées de ladite chambre d'injection (électrodes proprement dites).Furthermore, to initiate the electric arc between the electrodes, means are provided, which can be, known manner, of the type with electric discharge produced between both electrodes or short-circuit type, thanks, by example, when using an auxiliary electrode start-up. Thus, it is possible to strike said arc electric between the parts of said neighboring electrodes of said injection chamber (said first and second tubular parts), then to extend said arc under the effect of the vortex injection of plasma gas, until that the feet of said arc are hooked to the surface internal of said end portions of the electrodes, remote of said injection chamber (electrodes properly say).

    Avantageusement, lesdits moyens d'injection du gaz plasmagène dans ladite chambre permettent d'injecter celui-ci en tourbillons selon des plans perpendiculaires à l'axe commun des électrodes. Ces moyens d'injection peuvent comprendre (voir US-A-5 262 616 mentionné ci-dessus) une pièce de révolution coaxiale auxdites électrodes et définissant avec celles-ci et leurs supports ladite chambre d'injection. Des orifices transversaux sont prévus dans la pièce pour autoriser l'injection du gaz plasmagène, issu d'un circuit d'alimentation, dans la chambre.Advantageously, said means for injecting the plasma gas in said chamber allow to inject it in vortices in planes perpendicular to the common axis electrodes. These means of injection may include (see US-A-5,262,616 mentioned above) a piece of coaxial revolution to said electrodes and defining with these and their supports said injection chamber. Of transverse holes are provided in the room to allow injection of plasma gas from a supply circuit, in the bedroom.

    Dans la torche conforme à l'invention, les températures atteintes par le plasma aux sorties de la torche peuvent dépasser les 5000°C. Aussi, il est indispensable de prévoir des circuits de refroidissement pour les électrodes, comme cela est d'ailleurs usuel pour les torches à plasma.In the torch according to the invention, the temperatures plasma damage to the torch outlets may exceed 5000 ° C. Also, it is essential to plan cooling circuits for the electrodes, such as this is moreover usual for plasma torches.

    Dans un mode de réalisation de la torche à plasma conforme à la présente invention et spécialement appropriée à la décomposition de l'hydrogène sulfureux, les particularités sont les suivantes :

    • puissance électrique : 500 KW
    • intensité : de 200 à 700 A
    • débit de gaz plasmagène : de 35 à 150 Nm3/h
    • débit de gaz soufflé : de 3 à 15 Nm3/h.
    In one embodiment of the plasma torch in accordance with the present invention and especially suitable for the decomposition of sulfurous hydrogen, the features are as follows:
    • electric power: 500 KW
    • intensity: from 200 to 700 A
    • plasma gas flow: 35 to 150 Nm 3 / h
    • blown gas flow: from 3 to 15 Nm 3 / h.

    De ce qui précède, on comprendra aisément que si, à la sortie ou à chacune des sorties de ladite torche, on dispose un dispositif de trempe (de tout type connu) sur le trajet du plasma, on obtient des produits de très grande pureté.From the above, it will be readily understood that if, at the outlet or at each outlet of said torch, there are a quenching device (of any known type) on the way plasma, you get very high purity products.

    Les figures du dessin annexé feront bien comprendre comment l'invention peut être réalisée. Sur ces figures, des références identiques désignent des éléments semblables.The figures in the accompanying drawing will make it clear how the invention can be realized. In these figures, references identical denote similar elements.

    La figure 1 montre, en coupe longitudinale très schématique, un premier exemple de torche à plasma conforme à la présente invention, permettant d'illustrer le principe inventif de celle-ci.FIG. 1 shows, in very schematic longitudinal section, a first example of a plasma torch in accordance with this invention, to illustrate the inventive principle of this one.

    La figure 2 illustre la section, selon la ligne II-II de la figure 1, de l'écoulement fluide à la sortie de la torche à plasma.Figure 2 illustrates the section, along line II-II of the Figure 1, the fluid flow at the outlet of the torch to plasma.

    La figure 3 montre, également en coupe longitudinale très schématique, un second exemple de torche à plasma conforme à la présente invention.Figure 3 shows, also in very longitudinal section schematic, a second example of a plasma torch conforming to the present invention.

    La figure 4 est la coupe longitudinale simplifiée d'un mode de réalisation pratique de la torche à plasma de la figure 1.Figure 4 is a simplified longitudinal section of a mode of practical realization of the plasma torch of the figure 1.

    La figure 5 est une coupe transversale, selon la ligne V-V de la figure 4.Figure 5 is a cross section along the line V-V in Figure 4.

    La figure 6 est la coupe longitudinale simplifiée d'un mode de réalisation pratique de la torche à plasma de la figure 3.Figure 6 is a simplified longitudinal section of a mode of practical realization of the plasma torch of the figure 3.

    L'exemple de réalisation I de la torche à plasma, conforme à la présente invention et représentée de façon très schématique sur la figure 1, comporte une anode 1 et une pièce cathodique 2, tubulaires et coaxiales, disposées en prolongement l'une de l'autre le long d'un axe X-X, de part et d'autre d'une chambre 3 dans laquelle est injecté, de toute manière connue, un gaz plasmagène (flèches P). L'anode 1 et la pièce cathodique sont refroidies de toute façon appropriée et connue, mais non représentée.The exemplary embodiment I of the plasma torch, in accordance with the present invention and shown very schematically in FIG. 1, has an anode 1 and a part cathodic 2, tubular and coaxial, arranged in extension from each other along an X-X axis, on both sides other of a chamber 3 into which is injected, any in known manner, a plasma gas (arrows P). Anode 1 and the cathode part are cooled in any suitable way and known, but not shown.

    L'anode 1 est allongée le long de l'axe X-X et comporte, à son extrémité disposée en regard de la chambre d'injection 3, une ouverture 4 mettant en communication l'intérieur de ladite anode 1 avec ladite chambre d'injection 3. En revanche, à son extrémité opposée à la chambre d'injection 3, l'anode 1 est obturée par un fond 5.The anode 1 is elongated along the axis X-X and comprises, at its end arranged opposite the injection chamber 3, an opening 4 connecting the interior of said anode 1 with said injection chamber 3. On the other hand, at its end opposite to the injection chamber 3, the anode 1 is closed by a bottom 5.

    La pièce cathodique 2 comporte, à son extrémité éloignée de la chambre d'injection 3, une cathode 2A ouverte vers l'extérieur par une ouverture 6. La cathode 2A est prolongée, en direction de la chambre d'injection 3, par une pièce tubulaire 2B faisant partie intégrante de ladite cathode 2A. La cathode 2A présente un diamètre D supérieur au diamètre d de la pièce tubulaire 2B et un épaulement 7 relie la cathode 2A et la pièce tubulaire 2B. Dans cet épaulement 7, sont prévus des orifices 8, répartis autour de l'axe X-X et d'axe au moins sensiblement parallèle à celui-ci. A son extrémité opposée à la cathode 2A, la pièce tubulaire 2B comporte une ouverture 9 mettant en communication l'intérieur de la pièce cathodique 2 avec ladite chambre d'injection 3.The cathode part 2 comprises, at its end remote from the injection chamber 3, a cathode 2A open towards the outside by an opening 6. The cathode 2A is extended, in the direction of the injection chamber 3, by a part tubular 2B forming an integral part of said cathode 2A. The cathode 2A has a diameter D greater than the diameter d of the tubular part 2B and a shoulder 7 connects the cathode 2A and the tubular part 2B. In this shoulder 7, orifices 8 are provided, distributed around the axis XX and with an axis at least substantially parallel thereto. At its end opposite to the cathode 2A, the tubular part 2B has an opening 9 putting the interior of the cathode part 2 into communication with said injection chamber 3.

    En régime établi, un arc électrique 10 traverse la chambre d'injection 3 et la pièce tubulaire 2B et s'accroche, par ses pieds d'extrémité 10a et 10c, respectivement sur la surface interne de l'anode 1 (au voisinage du fond 5 opposé à la chambre d'injection 3) et sur celle de la cathode 2A.In steady state, an electric arc 10 crosses the chamber injection 3 and the tubular part 2B and hooks, by its end legs 10a and 10c, respectively on the internal surface of anode 1 (near bottom 5 opposite to the injection chamber 3) and to that of the cathode 2A.

    Des bobines électromagnétiques 11 et 12, destinées à la rotation des pieds 10a et 10c de l'arc 10 autour de l'axe X-X, entourent respectivement l'anode 1 (au voisinage du fond 5) et la cathode 2A. Electromagnetic coils 11 and 12, intended for the rotation of the feet 10a and 10c of the arc 10 around the axis X-X, respectively surround the anode 1 (in the vicinity of the bottom 5) and cathode 2A.

    Ainsi, le courant de gaz plasmagène P pénétrant dans la pièce tubulaire 2B se transforme, dans cette dernière et sous l'action de l'arc 10, en un écoulement de plasma 13, sortant par l'ouverture 6 après avoir traversé la cathode 2A. La pièce tubulaire 2B forme donc une chambre de réaction dans laquelle le gaz plasmagène est transformé en un plasma, à haute pression et à très haute température, comportant des ions des composants dudit gaz plasmagène. Il est évident que la pièce tubulaire 2B peut être dimensionnée pour optimiser le rendement énergétique.Thus, the stream of plasma gas P entering the tubular part 2B is transformed, in the latter and under the action of the arc 10, in a plasma flow 13, leaving through opening 6 after passing through the cathode 2A. The tubular part 2B therefore forms a reaction chamber in which the plasma gas is transformed into a plasma, at high pressure and at very high temperature, comprising ions of the components of said plasma gas. It's obvious that the tubular part 2B can be dimensioned to optimize energy efficiency.

    De plus, à travers les orifices 8 de l'épaulement 7, est soufflé à la périphérie de l'écoulement de plasma 13 un gaz G, par exemple de l'hydrogène, formant un courant gazeux annulaire 14 à température ambiante et à une pression au moins approximativement égale à celle du plasma s'écoulant dans le même sens que le plasma. Par suite, dans la traversée de la cathode 2A et à la sortie de celle-ci (en aval de l'ouverture 6), l'écoulement de plasma 13 est complètement entouré par une gaine formée par le courant annulaire gazeux 14 et établissant une barrière fluide entre la cathode 2A et l'écoulement de plasma 13 (voir également la figure 2).In addition, through the openings 8 of the shoulder 7, is blown at the periphery of the plasma flow 13 a gas G, for example hydrogen, forming a gas stream ring 14 at room temperature and at pressure less approximately equal to that of flowing plasma in the same direction as plasma. As a result, in the crossing cathode 2A and at the exit of it (downstream of opening 6), the plasma flow 13 is completely surrounded by a sheath formed by the annular gas stream 14 and establishing a fluid barrier between the cathode 2A and plasma flow 13 (see also Figure 2).

    Il en résulte que les particules de matière de la cathode 2A, qui sont arrachées à la surface intérieure de celle-ci par le pied d'arc 10c, non seulement ne peuvent se mélanger à l'écoulement de plasma 13, mais encore sont évacuées par le courant annulaire gazeux 14. Elles ne peuvent donc polluer l'écoulement de plasma 13. Comme de plus, les particules de matière de l'anode 1, qui sont arrachées à celle-ci par le pied d'arc 10a, restent dans l'anode 1 (ce qui est obtenu du fait que l'anode 1 est longue et que le pied d'arc 10a se trouve au voisinage du fond 5), l'écoulement de plasma 13, comportant des ions des composants du gaz plasmagène, est particulièrement pur. As a result, the particles of matter from the cathode 2A, which are torn off from the inner surface thereof by the arc foot 10c, not only can not mix to the plasma flow 13 but still are evacuated by the annular gas stream 14. They cannot therefore pollute plasma flow 13. As well, particles of material from anode 1, which are torn off at this by the arc foot 10a, remain in the anode 1 (this which is obtained from the fact that the anode 1 is long and that the arch 10a is in the vicinity of the bottom 5), the flow plasma 13, comprising ions of the gas components is particularly pure.

    On conçoit aisément que, en aval de l'ouverture 6, un dispositif de trempe (non représenté, mais de tout type connu) permet de séparer le courant gazeux annulaire 14 de l'écoulement de plasma 13, puis d'extraire les composants chimiques contenus sous forme d'ions dans ledit écoulement de plasma 13.It is easily understood that, downstream of the opening 6, a quenching device (not shown, but of any type known) allows the annular gas stream 14 to be separated from the plasma flow 13 and then extract the components chemicals contained in the form of ions in said flow plasma 13.

    Dans la variante d'exemple de réalisation II de la torche à plasma, conforme à la présente invention et représentée de façon très schématique sur la figure 3, on retrouve les éléments 2, 2A, 2B, 3 et 6 à 14 de la figure 1. Toutefois, dans cette variante, l'anode 1 est remplacée par une pièce anodique 1' de constitution semblable à celle de la pièce cathodique 2.In variant embodiment II of the torch at plasma, in accordance with the present invention and represented by very schematically in Figure 3, we find the elements 2, 2A, 2B, 3 and 6 to 14 of FIG. 1. However, in this variant, the anode 1 is replaced by a part anodic 1 'of constitution similar to that of the coin cathodic 2.

    A cet effet, la pièce anodique 1' comporte, à son extrémité éloignée de la chambre d'injection 3, une anode 1'A ouverte vers l'extérieur par une ouverture 15. L'anode 1'A est prolongée, en direction de la chambre d'injection 3, par une pièce tubulaire 1'B faisant partie intégrante de ladite anode. L'anode 1'A présente un diamètre D supérieur au diamètre d de la pièce tubulaire 1'B et un épaulement 16 relie l'anode 1'A et la pièce tubulaire 1'B. Dans cet épaulement 16, sont prévus des orifices 17, répartis autour de l'axe X-X et d'axe au moins sensiblement parallèle à celui-ci. A son extrémité opposée à l'anode 1'A, la pièce tubulaire 1'B comporte une ouverture 18 mettant en communication l'intérieur de la pièce anodique 1' avec la chambre d'injection 3.For this purpose, the anode part 1 ′ comprises, at its end remote from the injection chamber 3, an anode 1'A open towards the outside by an opening 15. The anode 1'A is extended, in the direction of the injection chamber 3, by a tubular piece 1'B forming an integral part of said anode. The anode 1'A has a diameter D greater than the diameter d of the tubular piece 1'B and a shoulder 16 connects the anode 1'A and the tubular piece 1'B. In this shoulder 16, orifices 17 are provided, distributed around the axis XX and with an axis at least substantially parallel thereto. At its end opposite the anode 1'A, the tubular part 1'B has an opening 18 putting the interior of the anode part 1 'into communication with the injection chamber 3.

    En régime établi, l'arc électrique 10 traverse la chambre d'injection 3 et les pièces tubulaires 1'B et 2B et s'accroche, par ses pieds 10a et 10c, respectivement sur la surface interne de l'anode 1'A et de la cathode 2A. In steady state, the electric arc 10 crosses the chamber injection 3 and the tubular parts 1'B and 2B and hooks, by its feet 10a and 10c, respectively on the surface internal of anode 1'A and cathode 2A.

    Ainsi, le gaz plasmagène injecté dans la chambre 3 se divise en deux courants, dont l'un pénètre dans la pièce tubulaire 1'B et l'autre dans la pièce tubulaire 2B. Dans ces pièces tubulaires 1'B et 2B, lesdits courants de gaz plasmagène se transforment en deux écoulements de plasma opposés 13 et 19, sortant par les ouvertures 6 et 15, après avoir traversé respectivement la cathode 2A et l'anode 1'A. Les pièces tubulaires 1'B ET 2B forment donc des chambres de réaction dans lesquelles le gaz plasmagène est transformé en plasma.Thus, the plasma gas injected into chamber 3 divides in two streams, one of which enters the tubular part 1'B and the other in the tubular part 2B. In these rooms 1'B and 2B tubular tubes, said plasma gas streams transform into two opposite plasma flows 13 and 19, leaving through openings 6 and 15, after crossing cathode 2A and anode 1'A respectively. Rooms 1'B AND 2B tubular therefore form reaction chambers in which the plasma gas is transformed into plasma.

    A travers les orifices 8 et 17 des épaulements 7 et 16, sont soufflés, respectivement à la périphérie des écoulements de plasma 13 et 19, des courants gazeux annulaires 14 et 20, à température ambiante et à une pression au moins approximativement égale à celle du plasma, s'écoulant respectivement dans le même sens que lesdits écoulements de plasma 13 et 19. Par suite, dans la traversée de l'anode 1'A et de la cathode 2A et à la sortie de celles-ci (en aval des ouvertures 6 et 15), les écoulements de plasma 13 et 19 sont complètement entourés par des gaines formées respectivement par les courants annulaires gazeux 14 et 20. Ces courants annulaires établissent donc une barrière fluide entre les écoulements de plasma 13 et 19 et la cathode 2A et l'anode 1'A, respectivement, évitant toute pollution desdits écoulements de plasma par les particules de matière arrachées aux électrodes par les pieds d'arc 10a et 10c. Dans l'exemple de réalisation II de la figure 3, on prévoit un dispositif de trempe (non représenté) en aval de chacune des ouvertures 6 et 15.Through the openings 8 and 17 of the shoulders 7 and 16, are blown, respectively at the periphery of the flows of plasma 13 and 19, annular gas streams 14 and 20, at room temperature and at a pressure at least approximately equal to that of plasma, flowing respectively in the same direction as said plasma flows 13 and 19. Consequently, in the crossing of the anode 1'A and the cathode 2A and at the exit of these (downstream of the openings 6 and 15), the plasma flows 13 and 19 are completely surrounded by sheaths formed respectively by the annular gas streams 14 and 20. These streams annulars therefore establish a fluid barrier between the plasma flows 13 and 19 and cathode 2A and anode 1'A, respectively, avoiding any pollution of said flows of plasma by the particles of material torn from the electrodes by the arc feet 10a and 10c. In the example of embodiment II of FIG. 3, a device is provided quenching (not shown) downstream of each of the openings 6 and 15.

    Sur la figure 4, on a représenté un mode de réalisation pratique de l'exemple I de la figure 1. On peut y voir que le corps tubulaire 30 de la torche à plasma, entourant l'anode 1 et la pièce cathodique 2, est constitué (à des fins de simplicité de construction) d'une pluralité de tronçons 30A, 30B, 30C ... coaxiaux entre eux et auxdites électrodes et assemblés de façon étanche l'un au bout de l'autre. De plus, des moyens de raccord 31 sont prévus pour raccorder de façon étanche l'extrémité ouverte 6, éloignée de la chambre d'injection 3, de la cathode 2A à un dispositif de trempe (non représenté). Des conduits 32 et 33 sont respectivement prévus autour de l'anode 1 et de la pièce cathodique 2 pour la circulation d'un fluide de refroidissement de celles-ci.In Figure 4, there is shown an embodiment practice of Example I in Figure 1. We can see that the tubular body 30 of the plasma torch, surrounding the anode 1 and the cathode part 2, is constituted (at simplicity of construction) of a plurality of sections 30A, 30B, 30C ... coaxial with each other and with said electrodes and tightly assembled one at the end of the other. In addition, connection means 31 are provided for sealingly open open end 6, remote from the injection chamber 3, from the cathode 2A to a device quenching (not shown). Conduits 32 and 33 are respectively provided around the anode 1 and the workpiece cathodic 2 for the circulation of a cooling fluid of these.

    Les moyens 34 d'injection du gaz plasmagène dans la chambre d'injection 3 sont du type à injection en tourbillons, tels que ceux décrits dans US-A-5 262 616. Ils sont constitués par une pièce de révolution, coaxiale à l'axe X-X et comportent une gorge annulaire 35, alimentée en gaz plasmagène (flèches P) et reliée à la chambre d'injection 3 par des orifices transversaux 36.The means 34 for injecting the plasma gas into the chamber 3 are of the vortex injection type, such than those described in US-A-5,262,616. They are made up by a part of revolution, coaxial with the X-X axis and include an annular groove 35, supplied with plasma gas (arrows P) and connected to the injection chamber 3 by transverse holes 36.

    Pour amorcer l'arc électrique 10 entre les électrodes, il est prévu un dispositif d'amorçage à court-circuit 37, du type connu avec électrode auxiliaire de démarrage 38. Ainsi, l'arc 10 peut être amorcé entre les parties de l'anode 1 et de la pièce tubulaire 2B, voisines de la chambre d'injection 3, puis allongé sous l'effet de l'injection tourbillonnaire du gaz plasmagène, jusqu'à ce que les pieds 10a et 10b dudit arc se trouvent accrochés à la surface interne de l'anode 1 près du fond 5 et à celle de la cathode 2A, dans le champ des bobines 11 et 12.To strike the electric arc 10 between the electrodes, it a short-circuit ignition device 37 is provided, known type with auxiliary starting electrode 38. Thus, the arc 10 can be struck between the parts of the anode 1 and of tubular part 2B, adjacent to the injection chamber 3, then stretched out under the effect of the vortex injection plasma gas, until feet 10a and 10b of said arc are attached to the internal surface of anode 1 near the bottom 5 and that of the cathode 2A, in the field coils 11 and 12.

    Entre la pièce tubulaire 2B et la cathode 2A, la torche de la figure 4 (voir également la figure 5) comporte un tronçon 30E constituant le dispositif S de soufflage tangentiel de l'écoulement tubulaire fluide 14, entourant l'écoulement de plasma 13.Between the tubular part 2B and the cathode 2A, the torch of Figure 4 (see also Figure 5) has a section 30E constituting the device S for tangential blowing of the fluid tubular flow 14, surrounding the flow of plasma 13.

    Par analogie avec les moyens 33 d'injection du gaz plasmagène dans la chambre d'injection 3, le dispositif de soufflage S comporte une couronne intérieure 39 (traversée par les conduits de refroidissement 33) et une couronne extérieure 40 coaxiales à l'axe X-X, ménageant entre elles une chambre annulaire 41, alimentée en gaz de soufflage (voir les flèches G) à travers ladite couronne extérieure 40. L'ouverture centrale 42 de la couronne intérieure 39 présente le diamètre D et forme au moins approximativement un prolongement de la surface interne de la cathode 2A. Cette ouverture centrale 42 forme donc la transition entre la surface interne de la pièce tubulaire 2B de diamètre d et la surface interne de la cathode 2A de diamètre D. Elle est reliée à la chambre annulaire 41 par des orifices 43, tangentiels à sa surface interne.By analogy with the means 33 for injecting the plasma gas into the injection chamber 3, the blowing device S comprises an inner ring 39 (crossed by the cooling conduits 33) and an outer ring 40 coaxial with the axis XX , forming between them an annular chamber 41, supplied with blowing gas (see arrows G) through said outer ring 40. The central opening 42 of the inner ring 39 has the diameter D and forms at least approximately an extension of the internal surface of cathode 2A. This central opening 42 therefore forms the transition between the internal surface of the tubular part 2B of diameter d and the internal surface of the cathode 2A of diameter D. It is connected to the annular chamber 41 by orifices 43, tangential to its internal surface .

    Dans le mode de réalisation pratique de l'exemple II de la torche à plasma, conforme à la présente invention et représentée en coupe sur la figure 6, on a, par rapport au mode de réalisation pratique des figures 4 et 5, remplacé l'anode 1 par la pièce anodique 1', semblable (mais opposée le long de l'axe X-X) à la pièce cathodique 2. En effet, la pièce anodique 1' comporte l'anode 1'A et la pièce tubulaire 1'B, reliées par un dispositif de soufflage tangentiel S'. L'anode 1'A, la pièce tubulaire 1'B et le dispositif de soufflage S' sont respectivement identiques à la cathode 2A, à la pièce tubulaire 2B et au dispositif de soufflage S. Des moyens de raccord 44 sont prévus pour raccorder de façon étanche l'extrémité ouverte 15, éloignée de la chambre d'injection 3, de l'anode 1'A à un dispositif de trempe (non représenté).In the practical embodiment of Example II of the plasma torch, according to the present invention and shown in section in Figure 6, we have, compared to the mode of practical embodiment of Figures 4 and 5, replaced the anode 1 by the anode part 1 ', similar (but opposite along from the X-X axis) to the cathode part 2. Indeed, the part anode 1 ′ comprises the anode 1'A and the tubular part 1'B, connected by a tangential blowing device S '. The anode 1'A, the tubular part 1'B and the device blowing S ′ are respectively identical to cathode 2A, to the tubular part 2B and to the blowing device S. Des connection means 44 are provided for connecting so seals the open end 15 away from the chamber injection 3, from the 1'A anode to a quenching device (not represented).

    Claims (20)

    1. A DC arc plasma torch, in particular intended for obtaining a chemical substance from a plasma-generating gas (P) which includes said substance, said torch comprising,
      a first electrode and a second electrode, said electrodes being tubular, coaxial and arranged in extension of each other, on either side of a chamber (3) for injection of said plasma-generating gas, said electrodes being open at their ends which face said injection chamber, and
      means (34) for injecting a stream of the plasma-generating gas into said injection chamber, the arc (10) between said electrodes passing through the said injection chamber and being anchored by end feet (10c, 10a) respectively to the internal surface of said electrodes, while said first electrode (2) is open at its end remote from the said injection chamber in order to allow the plasma (13) generated by said arc to flow out of the torch, characterized in that:
      said first electrode (2A) is in communication with said injection chamber (3) via a first tubular piece (2B) through which said arc (10) passes and which constitutes a first reaction chamber in which said plasma-generating gas (P) gives rise to the plasma (13) under the action of said electric arc (10); and
      first means (7, 8, S) are provided which make it possible to form a fluid barrier (14) between said first electrode (2A) and said plasma (13).
    2. The plasma torch as claimed in claim 1, characterized in that said first tubular piece (2B) is securely joined to said first electrode (2A).
    3. The plasma torch as claimed in claim 2, characterized in that said first tubular piece (2B) and said first electrode (2A) form a single piece (2).
    4. The plasma torch as claimed in any one of claims 1 to 3, characterized in that said first means for forming said fluid barrier consist of first blowing means (7, 8, S) which generate, on the internal wall of said first electrode (2A), a first tubular flow (14) of a gas at a pressure at least approximately equal to that of the plasma and at a temperature very much lower than that of said plasma (13), said first tubular fluid flow (14) surrounding said flow of the plasma (13) and flowing in the same direction as the latter.
    5. The plasma torch as claimed in claim 4, characterized in that the gas (G) of said first tubular flow is hydrogen.
    6. The plasma torch as claimed in either of claims 4 and 5, characterized in that said first electrode (2A) has a larger diameter (D) than said first tubular piece (2B) and in that said first blowing means (7, 8, S) are arranged between said first tubular piece and said first electrode.
    7. The plasma torch as claimed in one of claims 4 to 6, characterized in that the gas of said first tubular flow is blown along the internal wall of said first electrode, parallel to the axis of the latter.
    8. The plasma torch as claimed in one of claims 4 to 6, characterized in that the gas of said first tubular flow is blown inside said first electrode, tangentially to the internal wall of the latter.
    9. The plasma torch as claimed in claim 8, characterized in that said first tangential blowing means (S) include an inner ring (39) and an outer ring (40) which are coaxial and form between them an annular chamber (41) fed with blowing gas (G) through said outer ring (40), while the central opening (42) in said inner ring (39) at least approximately forms an extension of the internal surface of said first electrode (2A) and said central opening (42) in the inner ring is joined to said annular chamber by at least one orifice (43) which is tangential to said central opening.
    10. The plasma torch as claimed in one of claims 1 to 9, characterized in that:
      said second electrode (1'A) is also open at its end remote from said injection chamber (3), so that there are two said plasma flows (13, 19) taking place through each of said electrodes;
      said second electrode (1'A) is also in communication with said injection chamber (3) via a second tubular piece (1'B) through which said arc (10) passes and which constitutes a second reaction chamber in which said plasma-generating gas (P) gives rise to the plasma under the action of said electric arc;
      second means (16, 17, S') are provided which make it possible to form a fluid barrier (20) between said second electrode (1'A) and said plasma (19).
    11. The plasma torch as claimed in claim 10, characterized in that said second tubular piece (1'B) is securely joined to said second electrode (1'A).
    12. The plasma torch as claimed in claim 11, characterized in that said second tubular piece (1'B) and said second electrode (1'A) form a single piece (1').
    13. The plasma torch as claimed in any one of claims 10 to 12, characterized in that said second means for forming said fluid barrier consist of second blowing means (16, 17, S) which generate, on the internal wall of said second electrode (1'A), a second tubular flow (20) of a gas at a pressure at least approximately equal to that of the plasma and at a temperature very much lower than that of said plasma (13), said second tubular fluid flow (20) surrounding said flow of the plasma (19) and flowing in the same direction as the latter.
    14. The plasma torch as claimed in claim 13, characterized in that the gas of said second tubular flow is hydrogen.
    15. The plasma torch as claimed in either of claims 13 and 14, characterized in that said second electrode (1'A) has a larger diameter (D) than said second tubular piece (1'B) and wherein said second blowing means are arranged between said second tubular piece and said second electrode.
    16. The plasma torch as claimed in one of claims 13 to 15, characterized in that the gas of said second tubular flow is blown along the internal wall of said second electrode, parallel to the axis of the latter.
    17. The plasma torch as claimed in one of claims 13 to 15, characterized in that the gas of said second tubular flow is blown inside said second electrode, tangentially to the internal wall of the latter.
    18. The plasma torch as claimed in claim 17, characterized in that said second tangential blowing means (S') include an inner ring (39) and an outer ring (40) which are coaxial and form between them an annular chamber (41) fed with blowing gas (G) through said outer ring (40), while the central opening (42) in said inner ring (39) at least approximately forms an extension of the internal surface of said second electrode (1'A) and said central opening (42) in the inner ring is joined to said annular chamber by at least one orifice (43) which is tangential to said central opening.
    19. The plasma torch as claimed in any one of claims 1 to 18, characterized in that it consists of a plurality of sections (30A, 30B, ...) coaxial with one another and with said electrodes and assembled in leaktight fashion one after the other.
    20. The plasma torch as claimed in any one of claims 1 to 19, characterized in that it includes means (31, 44) for leaktight connection of the open end, remote from the injection chamber (3), of an electrode to a device for quenching said plasma.
    EP96400770A 1995-05-19 1996-04-10 Direct current arc plasma torch, specially conceived for the obtention of a chemical body by decomposition of a plasma gas Expired - Lifetime EP0743811B1 (en)

    Applications Claiming Priority (2)

    Application Number Priority Date Filing Date Title
    FR9505972 1995-05-19
    FR9505972A FR2734445B1 (en) 1995-05-19 1995-05-19 CONTINUOUS CURRENT ARC PLASMA TORCH, ESPECIALLY INTENDED FOR OBTAINING A CHEMICAL BODY BY DECOMPOSITION OF A PLASMAGEN GAS

    Publications (2)

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    EP0743811A1 EP0743811A1 (en) 1996-11-20
    EP0743811B1 true EP0743811B1 (en) 1998-11-04

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    EP (1) EP0743811B1 (en)
    JP (1) JPH08339893A (en)
    CA (1) CA2174571A1 (en)
    DE (1) DE69600904T2 (en)
    FR (1) FR2734445B1 (en)
    ZA (1) ZA962967B (en)

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    FR2734445A1 (en) 1996-11-22
    DE69600904T2 (en) 1999-04-01
    DE69600904D1 (en) 1998-12-10
    ZA962967B (en) 1996-10-22
    EP0743811A1 (en) 1996-11-20
    US5688417A (en) 1997-11-18
    CA2174571A1 (en) 1996-11-20
    JPH08339893A (en) 1996-12-24
    FR2734445B1 (en) 1997-07-18

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