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WO2005008157A2 - Installation for induction treatment of a low-conductivity fluid - Google Patents

Installation for induction treatment of a low-conductivity fluid Download PDF

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Publication number
WO2005008157A2
WO2005008157A2 PCT/FR2004/050319 FR2004050319W WO2005008157A2 WO 2005008157 A2 WO2005008157 A2 WO 2005008157A2 FR 2004050319 W FR2004050319 W FR 2004050319W WO 2005008157 A2 WO2005008157 A2 WO 2005008157A2
Authority
WO
WIPO (PCT)
Prior art keywords
enclosure
winding
installation according
terminals
windings
Prior art date
Application number
PCT/FR2004/050319
Other languages
French (fr)
Other versions
WO2005008157A3 (en
Inventor
Roland Ernst
Christian Trassy
Pierre Proulx
Siwen Xue
Original Assignee
Centre National De La Recherche Scientifique
Universite De Sherbrooke
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Centre National De La Recherche Scientifique, Universite De Sherbrooke filed Critical Centre National De La Recherche Scientifique
Publication of WO2005008157A2 publication Critical patent/WO2005008157A2/en
Publication of WO2005008157A3 publication Critical patent/WO2005008157A3/en

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Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/02—Induction heating
    • H05B6/22—Furnaces without an endless core
    • H05B6/24—Crucible furnaces
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B3/00—Charging the melting furnaces
    • C03B3/02—Charging the melting furnaces combined with preheating, premelting or pretreating the glass-making ingredients, pellets or cullet
    • C03B3/026—Charging the melting furnaces combined with preheating, premelting or pretreating the glass-making ingredients, pellets or cullet by charging the ingredients into a flame, through a burner or equivalent heating means used to heat the melting furnace
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B5/00—Melting in furnaces; Furnaces so far as specially adapted for glass manufacture
    • C03B5/02—Melting in furnaces; Furnaces so far as specially adapted for glass manufacture in electric furnaces, e.g. by dielectric heating
    • C03B5/021—Melting in furnaces; Furnaces so far as specially adapted for glass manufacture in electric furnaces, e.g. by dielectric heating by induction heating
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B5/00—Melting in furnaces; Furnaces so far as specially adapted for glass manufacture
    • C03B5/16—Special features of the melting process; Auxiliary means specially adapted for glass-melting furnaces
    • C03B5/18—Stirring devices; Homogenisation
    • C03B5/183—Stirring devices; Homogenisation using thermal means, e.g. for creating convection currents
    • C03B5/185—Electric means
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B14/00—Crucible or pot furnaces
    • F27B14/06—Crucible or pot furnaces heated electrically, e.g. induction crucible furnaces with or without any other source of heat
    • F27B14/061—Induction furnaces
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D11/00—Arrangement of elements for electric heating in or on furnaces
    • F27D11/06—Induction heating, i.e. in which the material being heated, or its container or elements embodied therein, form the secondary of a transformer
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B2213/00—Aspects relating both to resistive heating and to induction heating, covered by H05B3/00 and H05B6/00
    • H05B2213/02—Stirring of melted material in melting furnaces

Definitions

  • the present invention relates to installations for mixing weakly conductive fluids such as gaseous plasma or molten glass.
  • the invention relates more particularly to such an installation using an inductive crucible to heat by induction a body disposed in the crucible so as to maintain the body in the form of a fluid.
  • Many technical fields are concerned with the handling of fluids, and in particular their mixing.
  • Mechanical stirring means such as propellers are known, but such means are inconvenient for stirring corrosive fluids such as fluids at high temperature, because corrosion requires regular replacement of the stirring means.
  • corrosion waste affects the purity of the stirred fluid, which may be undesirable.
  • An object of the present invention is to provide an installation using non-mechanical means for mixing weakly conductive fluids, in particular corrosive fluids.
  • the present invention aims to propose a solution which is compatible with heating the fluid by induction.
  • an induction treatment installation capable of performing electromagnetic stirring of a weakly conductive fluid, comprising: a cylindrical enclosure capable of receiving the fluid; a first winding comprising two first windings respectively formed around two first distinct zones of the enclosure and connected in series opposition so as to be traversed by opposite currents, the terminals of the first winding being able to be connected to the terminals of a first capacitor and across an alternating voltage source; and at least a second winding comprising two second windings respectively formed around two second separate zones of the enclosure, one of which is located between the first two zones of the enclosure, and connected in series opposition so as to be traversed by opposite currents, the terminals of the second winding being able to be connected to the terminals of a second capacitor.
  • the weakly conductive fluid has a resistivity between ÎO- 3 and 1 ⁇ .m.
  • the values of the first and second capacitors are a function of the frequency of the voltage source and of the desired thickness of skin inside the enclosure.
  • the combined inductances of the first and second windings are chosen so as to produce a predetermined heating of a body disposed in the enclosure, said heating being able to maintain said body in the form of a fluid.
  • the weakly conductive fluid is a gaseous plasma.
  • the enclosure is arranged vertically and the voltage source is controlled in such a way that the windings generate an electromagnetic field subjecting the plasma located near the walls of the enclosure at a force acting from bottom to top, and comprising above the center of the enclosure means for introducing a powder into the plasma.
  • the weakly conductive fluid is a liquid glass.
  • the enclosure is arranged vertically and the voltage source is controlled in such a way that the windings generate an electromagnetic field subjecting the liquid glass located near the walls of the enclosure to an acting force. from bottom to top, and comprising above the center of the enclosure means for introducing a powder into the liquid glass.
  • the enclosure is an inductive cold crucible.
  • the enclosure is a crucible made of refractory material.
  • Figure 1 installation of Figure 1;
  • Figure 3 is a partial perspective view of an inductive cold crucible according to the present invention during operation; and
  • Figure 4 shows, schematically and in section, an installation according to the present invention applied to the stirring of gaseous plasma.
  • the same references represent the same elements in the different figures. For reasons of clarity, only the elements necessary for understanding the present invention have been shown in the figures and will be described later. It will be noted that the invention applies equally well to a cold crucible or to a refractory crucible. More generally, it will be noted that the invention can be implemented in any installation using an inductive means around an enclosure containing a weakly conductive fluid, for the purpose of organizing the movements of the fluid.
  • a characteristic of the present invention is to organize an inductive turbulent stirring by means of conductive windings surrounding a crucible containing the weakly conductive fluid.
  • each winding comprises at least two windings connected in opposition series so as to be traversed by opposite currents and nested with the windings of the other windings, only one of the windings being supplied by an alternative source and the terminals of each winding being connected by a capacitor -
  • a weakly conductive fluid is a medium having an electrical resistivity of between approximately 0.1 and 100 ⁇ .cm (10 ⁇ 3 e t 1 ⁇ .m). These are, for example, molten glass, gaseous plasma, salt water, etc.
  • the metallurgy field uses electromagnetic installations for the mixing of molten metals, the electrical resistivity of which is l '' order from 1 to 160 ⁇ .cm (10 ⁇ 8 to 1.6.10 ⁇ ⁇ .m).
  • the thickness of the magnetic skin must be small relative to the diameter of the container (of the order of 10 to 100 times smaller) to allow mixing of the fluid.
  • the skin thickness is the thickness in which the effects of an electromagnetic field are concentrated on the edges of a bath. This skin thickness depends, in particular, on the electrical resistivity of the fluid and on the inverse of the frequency of the electromagnetic field.
  • the forces exerted by the electromagnetic field in the magnetic skin thickness combined with the hydrostatic forces in the bath, generate a turbulent mixing.
  • the document WO 0051400 describes an installation for stirring by induction of liquid metals having skin thicknesses of the order of 1 to 10 millimeters in a crucible of 10 centimeters in diameter.
  • This document provides for a sliding electromagnetic field, generated by polyphase inductors supplied by a single-phase alternating voltage source at a frequency chosen between a few tens of hertz and a few tens of kilohertz.
  • a contribution of the inventors has been to show that, contrary to a prejudice widespread among specialists in the field of electromagnetic induction, it is possible to implement stirring by electromagnetic induction of a weakly conductive fluid.
  • the electrical resistivity of a weakly conducting fluid being appreciably a million times higher than that of a liquid metal, it was considered until then that it would have been necessary to use electromagnetic fields at frequencies more than a hundred gigahertz to obtain a small thickness of skin, which is in practice not feasible.
  • a weakly conducting fluid for example, liquid glass
  • the inventors have obtained a turbulent mixing of weakly conducting fluids with significant skin thicknesses, of the same order of magnitude as the radius of the enclosure containing the fluid.
  • a structure similar to the structure of the installation described in document WO 0051400, once modified to operate at an appropriate frequency is suitable to implement an electromagnetic stirring of a weakly conductive fluid such as liquid glass, gaseous plasma or salt water, having a resistivity between 0.1 and 100 ⁇ .cm (10 ⁇ 3 and 1 ⁇ . m), and preferably between 1 and 10 ⁇ .cm (10 ⁇ 2 and ÎO "1 ⁇ .m).
  • Figure 1 shows, schematically and in section, the application to the mixing of liquid glass of a installation according to a first embodiment of the present invention.
  • the installation comprises an enclosure 1 intended to contain the liquid glass, such as a cold crucible cooled by the circulation of a liquid inside the wall of the crucible.
  • the details constituting the walls of the crucible have not been shown for the sake of clarity.
  • the means for circulating the coolant, for example water, in the thickness of the walls have not been illustrated.
  • the periphery of the crucible is preferably formed by several vertical sectors assembled together.
  • a first winding 5 is wound around the crucible 1 and is connected by its two ends to the terminals of a single-phase alternating generator 3 in parallel with a capacitor C.
  • the winding 5 consists of at least two coils 51 and 52 connected in series opposition, that is to say for example wound around the crucible 1 in opposite directions from a common point.
  • At least a second winding 6 is also wound around the crucible 1 and is connected, by its two ends, to the terminals of a capacitor C.
  • This second winding 6 comprises, like the first winding 5, at least two coils 61, 63 connected in opposition series.
  • the windings 5 and 6 are nested one inside the other, that is to say that the coils are arranged successively in the height of the crucible so as to alternate a coil of the first winding with a coil of the second winding.
  • FIG. 2 represents the electrical circuit of the installation of FIG. 1. This figure shows the elements described in connection with Figure 1 and illustrates in a perspective view the direction of the coils of the windings 5 and 6 in series opposition. It will be noted that, in FIG. 1, the direction of current flow in the respective coils has been indicated by the usual notations (x,.) In electromagnetism.
  • the winding 5 forms, with the capacitor C, a first oscillating circuit connected to the generator 3 and constituting a first phase of excitation of the polyphase system.
  • the second winding 6, spatially offset from the first winding 5 forms, with the capacitor C, a second oscillating circuit.
  • This second oscillating circuit is in magnetic interaction by its mutual inductance with the first oscillating circuit.
  • One can then, by dimensioning, make so that the magnetic field resulting from the superposition of the two phases in presence is a sliding field likely to generate an electromagnetic driving force of pumping on the liquid glass contained in the crucible 1.
  • the windings 5 and 6 also make it possible to generate eddy currents in the glass which keep the glass molten, as in a conventional induction crucible.
  • the respective dimensions of the windings and the capacitors depend on the application and, in particular, on the frequency of the generator 3 and on the diameter of the crucible 1, knowing that the thickness of skin in the fluid can be of the same order of magnitude as the radius of the crucible.
  • the number of turns of the coils of the same winding is identical.
  • the optimization of the system according to the application is within the reach of those skilled in the art by applying the rules of electrical and electromagnetic operation to from the respective inductors, the respective resistors and the respective capacitors of the oscillating circuits, as well as from the mutual inductance of these two circuits and from the pulsation of the single-phase generator.
  • This embodiment finds applications in all industrial fields using the mixing of liquid glass with other bodies, for example the field of treatment of nuclear waste, in which waste, generally reduced to the powder state, are mixed with liquid glass which is then solidified and stored.
  • an appropriate choice of the direction of the current in the windings makes it possible to stir the liquid glass according to a centripetal movement in the upper part.
  • the inventors have shown that, because of the distribution of heat in the glass, higher in the center than at the edges, the previous centripetal brewing promotes a homogeneous inclusion in the glass of a powder 7 spilled at the center of the crucible. , which represents another advantage of the invention.
  • Another advantage of the installation according to the invention is that it requires only a single single-phase generator to generate the stirring magnetic field. Such a generator is less expensive and less complex than a two-phase generator made up of two generators synchronized by active elements.
  • Another advantage of the present invention is that the synchronization of the induced phase (phase obtained by the secondary winding), or of the induced phases in the case where several secondary windings are used, does not pose any particular problem.
  • Another advantage of the present invention is that the system is particularly stable once adapted to the application. In fact, the passive elements (inductors and capacitors) used by the present invention to generate the additional phase or phases are not likely to be out of balance as could be the case with active elements (high power switches).
  • FIG. 3 illustrates, in a perspective view in section, the schematic structure of the inductive cold crucible of Figure 1.
  • This figure shows the sectors (s) of the crucible 1 which are electrically isolated from each other.
  • each coil 61, 51, 62, 52 has four turns.
  • the representation in FIG. 3 illustrates that the number of wheels for stirring the glass depends on the number of sectors of the crucible.
  • stirring is also favored by the sectorized structure of the crucible which improves the mixing.
  • the mixing speeds depend on the intensity of the currents il and ⁇ 2, therefore on the intensity of the current supplied by the generator 3.
  • phase angle between the two oscillating circuits is adjustable by the respective values of the capacitors and of the inductances used. However, as previously indicated, this phase angle is stable once fixed by the dimensions of these elements.
  • the respective values of the capacitors C and C are then fixed as a function of the frequency of the single-phase generator and of the desired skin thickness, which depends on the diameter of the crucible 1 and which may be of the same order of magnitude as the radius of the crucible. It will be noted that the respective relationships between the inductances of the windings and the capacitors C and C must be compatible with the output impedance of the single-phase generator 3.
  • capacitors having values of the order of 0.2 uF may be used with windings whose respective own inductances are of the order of 0.2 ⁇ H and whose resistances are of the order of 80 m ⁇ .
  • a phase shift of the order of 20 ° is obtained between the currents i1 and i2 of the respective windings, and a ratio of the amplitudes of the currents of the order of 1.
  • FIG. 4 represents, schematically and in section, an example of application of the invention to the stirring of a gaseous plasma.
  • the installation comprises an enclosure 1 intended to contain the gaseous plasma, around which are formed at least two nested windings 5 and 6 respectively capable of being connected to a capacitor C in parallel with an alternating voltage source and to a capacitor C alone , linked together and operating in substantially the same way as the elements bearing the same references in FIG. 1.
  • the enclosure 1 waterproof and preferably made of a material such as quartz, comprises a means 8 for introducing a vertical powder 9 to be treated with the plasma vertically from the center of the plasma.
  • the frequency of the voltage source and the characteristics of the windings 5 and 6 and of the capacitors C and C are chosen so that the electromagnetic field generated by the windings 5 and 6, not only heats the gas by eddy currents but also confines the plasma thus formed while creating in the plasma centripetal stirring forces.
  • the inventors have shown that the centripetal brewing forces allow the powder 9 to be mixed from the inside to the outside of the plasma and promote efficient treatment of the powder by the plasma.
  • the choice of the number of turns per coil, the number of coils per winding and the arrangement of the turns is within the reach of the skilled person from the indications given above.
  • the section of the turns will of course depend on the intensity of the currents, and the arrangement in the height of the crucible will depend on the height of the latter and on the number of coils.
  • the average level of the fluid will be chosen to correspond approximately to the middle of the height of the first winding 51 of the first winding 5.
  • the increase in the number of coils of the same winding makes it possible to increase (by cumulative effect due to the increase in the interaction height) the pumping force, therefore the efficiency of the stirring.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Materials Engineering (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Electromagnetism (AREA)
  • Power Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Induction Heating (AREA)
  • Food Preservation Except Freezing, Refrigeration, And Drying (AREA)

Abstract

The invention concerns an installation for stirring a low-conductivity fluid, comprising: a cylindrical chamber (1) for receiving the fluid; a first winding (5) including two first coils (51, 52) respectively formed around two separate first regions of the chamber (1) and connected oppositely in series, the terminals of the first winding (5) being adapted to be connected to the terminals of a first capacitor (C) and to the terminals of an alternating current voltage source (3); and at least a second winding (6) including two second coils (62, 62) respectively formed around two separate second regions of the chamber (1) and connected oppositely in series, one of which is located between the two separate first regions of the chamber, and connected oppositely in series, the terminals of the second winding (6) being adapted to be connected to the terminals of a second capacitor (C').

Description

INSTALLATION DE TRAITE EaSiT PAR INDUCTION D'UN FLUIDE FAIBLEMENT CONDUCTEUR EaSiT TREATMENT PLANT BY INDUCTION OF A LOW CONDUCTIVE FLUID
La présente invention concerne les installations de brassage de fluides faiblement conducteurs tels que du plasma gazeux ou du verre en fusion. L'invention concerne plus particulièrement une telle installation ayant recours à un creuset inductif pour chauffer par induction un corps disposé dans le creuset de manière à maintenir le corps sous forme d'un fluide. De nombreux domaines techniques sont concernés par la manipulation de fluides, et notamment leur brassage. Des moyens mécaniques de brassage tels que des hélices sont connus, mais de tels moyens sont peu commodes pour brasser des fluides corrosifs tels que des fluides à haute température, car la corrosion nécessite de remplacer régulièrement les moyens de brassage. En outre, les déchets de corrosion affectent la pureté du fluide brassé, ce qui peut être indésirable. Un objet de la présente invention est de prévoir une installation utilisant des moyens non mécaniques de brassage de fluides faiblement conducteurs, en particulier de fluides corrosifs. L'invention vise également à proposer une solution qui soit compatible avec un chauffage du fluide par induction. Pour atteindre ces objets, ainsi que d'autres, la présente invention prévoit une installation de traitement par induction apte à réaliser un brassage électromagnétique d'un fluide faiblement conducteur, comportant : une enceinte cylin- drique apte à recevoir le fluide ; un premier enroulement comprenant deux premiers bobinages respectivement formés autour de deux premières zones distinctes de l'enceinte et reliés en série opposition de manière à être parcourus par des courants opposés, les bornes du premier enroulement étant aptes à être reliées aux bornes d'un premier condensateur et aux bornes d'une source de tension alternative ; et au moins un deuxième enroulement comprenant deux deuxièmes bobinages respectivement formés autour de deux deuxièmes zones distinctes de l'enceinte dont l'une est située entre les deux premières zones de l'enceinte, et reliés en série opposition de manière à être parcourus par des courants opposés, les bornes du deuxième enroulement étant aptes à être reliées aux bornes d'un deuxième condensateur. Selon un mode de réalisation de l'invention, le fluide faiblement conducteur présente une résistivité comprise entre ÎO-3 et 1 Ω.m. Selon un mode de réalisation de l'invention, les valeurs des premier et deuxième condensateurs sont fonction de la f équence de la source de tension et de 1 ' épaisseur de peau souhaitée à l'intérieur de l'enceinte. Selon un mode de réalisation de l'invention, les inductances combinées des premier et deuxième enroulements sont choisies de manière à produire un échauffement prédéterminé d'un corps disposé dans l'enceinte, ledit échauffement étant apte à maintenir ledit corps sous forme d'un fluide. Selon un mode de réalisation de l'invention, le fluide faiblement conducteur est un plasma gazeux. Selon un mode de réalisation de l'invention, l'enceinte est disposée verticalement et la source de tension est commandée de telle manière que les enroulements génèrent un champ électromagnétique soumettant le plasma situé à proximité des parois de l'enceinte à une force agissant de bas en haut, et comportant au dessus du centre de l'enceinte un moyen pour introduire une poudre dans le plasma. Selon un mode de réalisation de l'invention, le fluide faiblement conducteur est un verre liquide. Selon un mode de réalisation de l'invention, l'enceinte est disposée verticalement et la source de tension est commandée de telle manière que les enroulements génèrent un champ électromagnétique soumettant le verre liquide situé à proximité des parois de l'enceinte à une force agissant de bas en haut, et comportant au dessus du centre de l'enceinte un moyen pour introduire une poudre dans le verre liquide. Selon un mode de réalisation de l'invention, l'enceinte est un creuset froid inductif. Selon un mode de réalisation de l'invention, l'enceinte est un creuset en matériau réfractaire. Ces objets, caractéristiques et avantages, ainsi que d' autres de la présente invention seront exposés en détail dans la description suivante de modes de réalisation particuliers faite à titre non-limitatif en relation avec les figures jointes parmi lesquelles : la figure 1 représente, de façon schématique et en coupe, une installation selon la présente invention appliquée au brassage de verre liquide ; la figure 2 illustre le circuit électrique deThe present invention relates to installations for mixing weakly conductive fluids such as gaseous plasma or molten glass. The invention relates more particularly to such an installation using an inductive crucible to heat by induction a body disposed in the crucible so as to maintain the body in the form of a fluid. Many technical fields are concerned with the handling of fluids, and in particular their mixing. Mechanical stirring means such as propellers are known, but such means are inconvenient for stirring corrosive fluids such as fluids at high temperature, because corrosion requires regular replacement of the stirring means. In addition, corrosion waste affects the purity of the stirred fluid, which may be undesirable. An object of the present invention is to provide an installation using non-mechanical means for mixing weakly conductive fluids, in particular corrosive fluids. The invention also aims to propose a solution which is compatible with heating the fluid by induction. To achieve these and other objects, the present invention provides an induction treatment installation capable of performing electromagnetic stirring of a weakly conductive fluid, comprising: a cylindrical enclosure capable of receiving the fluid; a first winding comprising two first windings respectively formed around two first distinct zones of the enclosure and connected in series opposition so as to be traversed by opposite currents, the terminals of the first winding being able to be connected to the terminals of a first capacitor and across an alternating voltage source; and at least a second winding comprising two second windings respectively formed around two second separate zones of the enclosure, one of which is located between the first two zones of the enclosure, and connected in series opposition so as to be traversed by opposite currents, the terminals of the second winding being able to be connected to the terminals of a second capacitor. According to one embodiment of the invention, the weakly conductive fluid has a resistivity between ÎO- 3 and 1 Ω.m. According to one embodiment of the invention, the values of the first and second capacitors are a function of the frequency of the voltage source and of the desired thickness of skin inside the enclosure. According to one embodiment of the invention, the combined inductances of the first and second windings are chosen so as to produce a predetermined heating of a body disposed in the enclosure, said heating being able to maintain said body in the form of a fluid. According to one embodiment of the invention, the weakly conductive fluid is a gaseous plasma. According to one embodiment of the invention, the enclosure is arranged vertically and the voltage source is controlled in such a way that the windings generate an electromagnetic field subjecting the plasma located near the walls of the enclosure at a force acting from bottom to top, and comprising above the center of the enclosure means for introducing a powder into the plasma. According to one embodiment of the invention, the weakly conductive fluid is a liquid glass. According to one embodiment of the invention, the enclosure is arranged vertically and the voltage source is controlled in such a way that the windings generate an electromagnetic field subjecting the liquid glass located near the walls of the enclosure to an acting force. from bottom to top, and comprising above the center of the enclosure means for introducing a powder into the liquid glass. According to one embodiment of the invention, the enclosure is an inductive cold crucible. According to one embodiment of the invention, the enclosure is a crucible made of refractory material. These objects, characteristics and advantages, as well as others of the present invention will be explained in detail in the following description of particular embodiments given without limitation in relation to the attached figures among which: FIG. 1 represents, of schematically and in section, an installation according to the present invention applied to the mixing of liquid glass; Figure 2 illustrates the electrical circuit of
1 ' installation de la figure 1 ; la figure 3 est une vue partielle en perspective d'un creuset froid inductif selon la présente invention en cours de fonctionnement ; et la figure 4 représente, de façon schématique et en coupe, une installation selon la présente invention appliquée au brassage de plasma gazeux. De mêmes références représentent de mêmes éléments aux différentes figures. Pour des raisons de clarté, seuls les éléments nécessaires à la compréhension de la présente invention ont été représentés aux figures et seront décrits par la suite. On notera que l'invention s'applique aussi bien à un creuset froid ou à un creuset réfractaire. Plus généralement, on notera que 1 ' invention peut être mise en oeuvre dans toute installation utilisant un moyen inductif autour d'une enceinte contenant un fluide faiblement conducteur, à des fins d'organisation des mouvements du fluide. Une caractéristique de la présente invention est d'organiser un brassage turbulent inductif au moyen d'enrou- lements conducteurs entourant un creuset contenant le fluide faiblement conducteur. Selon l'invention, chaque enroulement comprend au moins deux bobinages reliés en série opposition de manière à être parcourus par des courants opposés et imbriqués avec les bobinages des autres enroulements, un seul des enroulements étant alimenté par une source alternative et les bornes de chaque enroulement étant reliées par un condensateur- Au sens de la présente invention, un fluide faiblement conducteur est un milieu présentant une résistivité électrique comprise entre environ 0,1 et 100 Ω.cm (10~3 et 1 Ω.m). Il s'agit, par exemple, de verre en fusion, de plasma gazeux, d'eau salée, etc... Le domaine de la métallurgie utilise des installations électromagnétiques pour le brassage de métaux en fusion, dont la résistivité électrique est de l'ordre de 1 à 160 μΩ.cm (10~8 à 1,6.10~ Ω.m). Dans ce domaine, on considère que l'épaisseur de peau magnétique doit être faible par rapport au diamètre du contenant (de l'ordre de 10 à 100 fois plus faible) pour permettre un brassage du fluide. L'épaisseur de peau est l'épaisseur dans laquelle les effets d'un champ électro- magnétique se concentrent sur les bords d'un bain. Cette épaisseur de peau dépend, notamment, de la résistivité électrique du fluide et de 1 ' inverse de la fréquence du champ électromagnétique. Dans les métaux en fusion, les forces exercées par le champ électromagnétique dans l'épaisseur de peau magnétique, combinées aux forces hydrostatiques dans le bain, génèrent un brassage turbulent. Par exemple, le document WO 0051400 décrit une installation de brassage par induction de métaux liquides ayant des épaisseurs de peau de l'ordre de 1 à 10 millimètres dans un creuset de 10 centimètres de diamètre. Ce document prévoit un champ électromagnétique glissant, généré par des inducteurs polyphasés alimentés par une source de tension alternative monophasée à une fréquence choisie entre quelques dizaines de hertz et quelques dizaines de kilohertz . Un apport des inventeurs a été de montrer que, contrairement à un préjugé répandu parmi les spécialistes du domaine de l'induction électromagnétique, il est possible de mettre en oeuvre un brassage par induction électromagnétique d'un fluide faiblement conducteur. La résistivité électrique d'un fluide faiblement conducteur (par exemple, du verre liquide) étant sensiblement un million de fois plus élevée que celle d'un métal liquide, on considérait jusqu'alors qu'il aurait fallu utiliser des champs électromagnétiques à des fréquences de plus de cent gigahertz pour obtenir une faible épaisseur de peau, ce qui n'est en pratique pas réalisable. De façon surprenante et contrairement à un préjugé répandu, les inventeurs ont obtenu un brassage turbulent de fluides faiblement conducteurs avec des épaisseurs de peau importantes, du même ordre de grandeur que le rayon de l'enceinte contenant le fluide. Ainsi, pour les inventeurs, une structure semblable à la structure de 1 ' installation décrite dans le document WO 0051400, une fois modifiée pour fonctionner à une fréquence appropriée (de préférence comprise entre environ 0,1 MHz et environ 20 MHz) , est apte à mettre en oeuvre un brassage électromagnétique d'un fluide faiblement conducteur tel que du verre liquide, un plasma gazeux ou de l'eau salée, ayant une résistivité comprise entre 0,1 et 100 Ω.cm (10~3 et 1 Ω.m), et de préférence comprise entre 1 et 10 Ω.cm (10~2 et ÎO"1 Ω.m) . La figure 1 représente, de façon schématique et en coupe, l'application au brassage de verre liquide d'une installation selon un premier mode de réalisation de la présente invention. L'installation comporte une enceinte 1 destinée à contenir le verre liquide, telle qu'un creuset froid refroidi par la circulation d'un liquide à l'intérieur de la paroi du creuset. Les détails constitutifs des parois du creuset n'ont pas été représentés par souci de clarté. En particulier, les moyens de circulation du liquide de refroidissement, par exemple de l'eau, dans l'épaisseur des parois n'ont pas été illustrés. Afin d'éviter le bouclage des courants induits, le pourtour du creuset est de préférence formé de plusieurs secteurs verticaux assemblés les uns aux autres. Selon la présente invention, un premier enroulement 5 est bobiné autour du creuset 1 et est raccordé par ses deux extrémités aux bornes d'un générateur alternatif monophasé 3 en parallèle avec un condensateur C. L'enroulement 5 est constitué d'au moins deux bobines 51 et 52 reliées en série opposition, c ' est-à-dire par exemple enroulées autour du creuset 1 dans des sens opposés depuis un point commun. Au moins un deuxième enroulement 6 est également bobiné autour du creuset 1 et est raccordé, par ses deux extrémités, aux bornes d'un condensateur C. Ce deuxième enroulement 6 comporte, comme le premier enroulement 5, au moins deux bobines 61, 63 reliées en série opposition. Les enroulements 5 et 6 sont imbriqués l'un dans l'autre, c'est-à-dire que les bobines sont disposées successivement dans la hauteur du creuset de façon à alterner une bobine du premier enroulement avec une bobine du deuxième enroulement . Dans 1 ' exemple d'un système diphasé tel que représenté à la figure 1, on trouve ainsi depuis le haut du creuset 1 : le premier bobinage 61 de l'enroulement 6, le premier bobinage 51 de l'enroulement 5, le deuxième bobinage 62 de l'enroulement 6 et le deuxième bobinage 52 de l'enroulement 5. Selon la présente invention, le deuxième enroulement 6 joue le rôle d'un circuit induit dont l'énergie provient du premier enroulement 5. La figure 2 représente le circuit électrique de 1 ' ins- tallation de la figure 1. Cette figure reprend les éléments décrits en relation avec la figure 1 et illustre par une vue en perspective le sens des bobines des enroulements 5 et 6 en série opposition. On notera que, à la figure 1, le sens de circulation du courant dans les bobines respectives a été indiqué par les notations habituelles (x, .) en électromagnétisme. L'enroulement 5 forme, avec le condensateur C, un premier circuit oscillant connecté au générateur 3 et constituant une première phase d'excitation du système polyphasé. Le deuxième enroulement 6, décalé spatialement par rapport au premier enroulement 5 forme, avec le condensateur C, un deuxième circuit oscillant. Ce deuxième circuit oscillant se trouve en interaction magnétique par sa mutuelle inductance avec le premier circuit oscillant. On peut alors, par dimension- nement, faire en sorte que le champ magnétique résultant de la superposition des deux phases en présence soit un champ glissant susceptible d'engendrer une force motrice électromagnétique de pompage sur le verre liquide contenu dans le creuset 1. Les enroulements 5 et 6 permettent également de générer dans le verre des courants de Foucault qui maintiennent le verre en fusion, comme dans un creuset à induction classique. Les dimensionnements respectifs des enroulements et des condensateurs dépendent de l'application et, en particulier, de la fréquence du générateur 3 et du diamètre du creuset 1, sachant que l'épaisseur de peau dans le fluide peut être du même ordre de grandeur que le rayon du creuset. De préférence, le nombre de spires des bobines d'un même enroulement est identique. L'optimisation du système en fonction de l'application est à la portée de l'homme du métier en mettant en application les règles de fonctionnement électrique et électromagnétique à partir des inductances respectives, des résistances respectives et des condensateurs respectifs des circuits oscillants, ainsi que de la mutuelle inductance de ces deux circuits et de la pulsation du générateur monophasé. Pour obtenir un effet de champ glissant linéaire permettant l'effet de pompage en périphérie du contenant, on cherchera, de préférence, à ce que les produits LC62 et L'C'ω2, où L et L' représentent les inductances respectives des enroulements 5 et 6 et où ω représente la pulsation du générateur monophasé 3, soient le plus proche possible de l'unité afin d'optimiser le fonctionnement des circuits oscillants. Un avantage de ce premier mode de réalisation est de permettre de brasser du verre liquide, très corrosif, sans devoir introduire des moyens mécaniques de brassage dans le verre. Ce mode de réalisation trouve des applications dans tous les domaines industriels mettant en oeuvre le mélange de verre liquide avec d'autres corps, par exemple le domaine du traitement des déchets nucléaires, dans lequel des déchets, généralement réduits à l'état de poudre, sont mélangés à du verre liquide qui est ensuite solidifié et stocké. En outre, comme l'illustrent les flèches de la figure 2, un choix approprié du sens du courant dans les bobinages permet de brasser le verre liquide selon un mouvement centripète en partie supérieure. Les inventeurs ont montré que, du fait de la répartition de la chaleur dans le verre, plus élevée au centre que sur les bords, le brassage centripète précédent favorise une inclusion homogène dans le verre d'une poudre 7 déversée au niveau du centre du creuset, ce qui représente un autre avantage de l'invention. Un autre avantage de l'installation selon l'invention est de ne nécessiter qu'un seul générateur monophasé pour générer le champ magnétique de brassage. Un tel générateur est moins coûteux et moins complexe qu'un générateur biphasé constitué de deux générateurs synchronisés par des éléments actifs. Un autre avantage de la présente invention est que la synchronisation de la phase induite (phase obtenue par l'enroulement secondaire), ou des phases induites dans le cas où plusieurs enroulements secondaires sont utilisés, ne pose pas de problème particulier. Un autre avantage de la présente invention est que le système est particulièrement stable une fois adapté à l'application. En effet, les éléments passifs (inducteurs et condensateurs) utilisés par la présente invention pour générer la ou les phases supplémentaires ne risquent pas de se dérégler comme cela pourrait être le cas d'éléments actifs (commutateurs haute puissance) . La figure 3 illustre, par une vue en perspective et en coupe, la structure schématique du creuset froid inductif de la figure 1. Cette figure fait apparaître les secteurs (s) du creuset 1 qui sont isolés électriquement les uns des autres. Dans l'exemple de la figure 3, chaque bobine 61, 51, 62, 52 comporte quatre spires . La représentation de la figure 3 illustre que le nombre de roues de brassage du verre dépend du nombre de secteurs du creuset. Ainsi, non seulement la présente invention permet de favoriser 1 ' inclusion des particules au centre du bain par un brassage centripète, mais, dans cette application, le brassage est également favorisé par la structure sectorisée du creuset qui améliore le mélange. Les vitesses de brassage dépendent de l'intensité des courants il et ι2 , donc de 1 ' intensité du courant fourni par le générateur 3. On notera que, selon la présente invention, l n'est pas nécessaire d'avoir un déphasage de 90° entre les deux circuits oscillants. Un déphasage de l'ordre de 20 à 40° est suffisant en terme d'efficacité pour le brassage opéré. On notera également que 1 ' angle de phase entre les deux circuits oscillants est réglable par les valeurs respec- tives des condensateurs et des inductances utilisés. Toutefois, comme cela a été indiqué précédemment, cet angle de phase est stable une fois fixé par les dimensionnements de ces éléments. En pratique, lorsque l'application concerne un chauffage par induction, on commencera de préférence par fixer les valeurs requises pour les inductances respectives des enroule¬ ments. Ces valeurs conditionnent en effet le chauffage du verre liquide ou autre fluide. On tiendra cependant compte de l'exis¬ tence de la phase induite qui participe également au chauffage. On fixe ensuite les valeurs respectives des condensa- teurs C et C en fonction de la fréquence du générateur monophasé et de l'épaisseur de peau souhaitée, qui dépend du diamètre du creuset 1 et qui pourra être du même ordre de grandeur que le rayon du creuset. On notera que les rapports respectifs entre les inductances des enroulements et les condensateurs C et C doivent être compatibles avec l'impédance de sortie du générateur monophasé 3. A titre d'exemple particulier de réalisation, pour un creuset ayant un diamètre de l'ordre d'une dizaine de centimètres et pour un générateur monophasé ayant une fréquence de fonctionnement de l'ordre de 400 kHz, on pourra utiliser des condensateurs ayant des valeurs de l'ordre de 0,2 uF avec des enroulements dont les inductances propres respectives sont de l'ordre de 0,2 μH et dont les résistances sont de l'ordre de 80 mΩ. Dans un tel exemple, on obtient un déphasage de l'ordre de 20° entre les courants il et i2 des enroulements respectifs, et un rapport des amplitudes des courants de 1 ' ordre de 1. La figure 4 représente, de façon schématique et en coupe, un exemple d'application de l'invention au brassage d'un plasma gazeux. L'installation comporte une enceinte 1 destinée à contenir le plasma gazeux, autour de laquelle sont formés au moins deux enroulements imbriqués 5 et 6 respectivement aptes à être reliés à un condensateur C en parallèle avec une source de tension alternative et à un condensateur C seul, reliés entre eux et fonctionnant sensiblement de la même manière que les éléments portant les mêmes références en figure 1. L'enceinte 1, étanche et de préférence réalisée en un matériau tel que le quartz, comporte un moyen 8 d'introduire à la verticale du centre du plasma une poudre 9 à traiter par le plasma. Selon ce mode de réalisation de l'invention, la fré- quence de la source de tension et les caractéristiques des enroulements 5 et 6 et des condensateurs C et C sont choisies de telle manière que le champ électromagnétique généré par les enroulements 5 et 6, non seulement échauffe le gaz par courants de Foucault mais également confine le plasma ainsi formé tout en créant dans le plasma des forces de brassage centripètes. Les inventeurs ont montré que les forces de brassage centripètes permettent un mélange de la poudre 9 de l'intérieur vers 1 ' extérieur du plasma et favorisent un traitement efficace de la poudre par le plasma. Bien que l'invention ait été décrite ci-dessus en relation avec un système diphasé, elle peut également être mise en oeuvre avec plus de deux phases . A cet égard, on notera que plus le nombre de phases est important, plus le système est contrôlable, par exemple, pour brasser le fluide sur une hauteur plus importante. L'adaptation du système décrit ci-dessus à un nombre plus important de phases est à la portée de l'homme du métier. On veillera toutefois à respecter l'imbrication des différents enroulements dans la hauteur du creuset ainsi que les associations en série opposition des bobinages constituant les différents enroulements. Bien entendu, la présente invention est susceptible de diverses variantes et modifications qui apparaîtront à l'homme de l'art. En particulier, bien que l'invention ait été décrite ci-dessus en relation avec le brassage du verre et d'un plasma gazeux, elle s'adapte sans difficulté au brassage d'autres fluides faiblement conducteurs tels que des électrolytes, ou au brassage de fluides conducteurs non corrosifs. De plus, le choix du nombre de spires par bobine, du nombre de bobines par enroulement et de la disposition des spires est à la portée de l'homme du métier à partir des indications données ci-dessus. En particulier, la section des spires dépendra bien entendu de l'intensité des courants, et la disposition dans la hauteur du creuset dépendra de la hauteur de ce dernier et du nombre de bobines. Par exemple, en se référant au mode de réalisation décrit ci-dessus en relation avec la figure 3, le niveau moyen du fluide sera choisi pour correspondre approximativement au milieu de la hauteur du premier bobinage 51 du premier enroulement 5. L'augmentation du nombre de bobines d' un même enroulement permet d' augmenter (par effet de cumul dû à l'augmentation de la hauteur d'interaction) la force de pompage, donc l'efficacité du brassage. 1 installation of Figure 1; Figure 3 is a partial perspective view of an inductive cold crucible according to the present invention during operation; and Figure 4 shows, schematically and in section, an installation according to the present invention applied to the stirring of gaseous plasma. The same references represent the same elements in the different figures. For reasons of clarity, only the elements necessary for understanding the present invention have been shown in the figures and will be described later. It will be noted that the invention applies equally well to a cold crucible or to a refractory crucible. More generally, it will be noted that the invention can be implemented in any installation using an inductive means around an enclosure containing a weakly conductive fluid, for the purpose of organizing the movements of the fluid. A characteristic of the present invention is to organize an inductive turbulent stirring by means of conductive windings surrounding a crucible containing the weakly conductive fluid. According to the invention, each winding comprises at least two windings connected in opposition series so as to be traversed by opposite currents and nested with the windings of the other windings, only one of the windings being supplied by an alternative source and the terminals of each winding being connected by a capacitor - Within the meaning of the present invention, a weakly conductive fluid is a medium having an electrical resistivity of between approximately 0.1 and 100 Ω.cm (10 ~ 3 e t 1 Ω.m). These are, for example, molten glass, gaseous plasma, salt water, etc. The metallurgy field uses electromagnetic installations for the mixing of molten metals, the electrical resistivity of which is l '' order from 1 to 160 μΩ.cm (10 ~ 8 to 1.6.10 ~ Ω.m). In this area, it is considered that the thickness of the magnetic skin must be small relative to the diameter of the container (of the order of 10 to 100 times smaller) to allow mixing of the fluid. The skin thickness is the thickness in which the effects of an electromagnetic field are concentrated on the edges of a bath. This skin thickness depends, in particular, on the electrical resistivity of the fluid and on the inverse of the frequency of the electromagnetic field. In molten metals, the forces exerted by the electromagnetic field in the magnetic skin thickness, combined with the hydrostatic forces in the bath, generate a turbulent mixing. For example, the document WO 0051400 describes an installation for stirring by induction of liquid metals having skin thicknesses of the order of 1 to 10 millimeters in a crucible of 10 centimeters in diameter. This document provides for a sliding electromagnetic field, generated by polyphase inductors supplied by a single-phase alternating voltage source at a frequency chosen between a few tens of hertz and a few tens of kilohertz. A contribution of the inventors has been to show that, contrary to a prejudice widespread among specialists in the field of electromagnetic induction, it is possible to implement stirring by electromagnetic induction of a weakly conductive fluid. The electrical resistivity of a weakly conducting fluid (for example, liquid glass) being appreciably a million times higher than that of a liquid metal, it was considered until then that it would have been necessary to use electromagnetic fields at frequencies more than a hundred gigahertz to obtain a small thickness of skin, which is in practice not feasible. Surprisingly and contrary to a widespread prejudice, the inventors have obtained a turbulent mixing of weakly conducting fluids with significant skin thicknesses, of the same order of magnitude as the radius of the enclosure containing the fluid. Thus, for the inventors, a structure similar to the structure of the installation described in document WO 0051400, once modified to operate at an appropriate frequency (preferably between approximately 0.1 MHz and approximately 20 MHz), is suitable to implement an electromagnetic stirring of a weakly conductive fluid such as liquid glass, gaseous plasma or salt water, having a resistivity between 0.1 and 100 Ω.cm (10 ~ 3 and 1 Ω. m), and preferably between 1 and 10 Ω.cm (10 ~ 2 and ÎO "1 Ω.m). Figure 1 shows, schematically and in section, the application to the mixing of liquid glass of a installation according to a first embodiment of the present invention. The installation comprises an enclosure 1 intended to contain the liquid glass, such as a cold crucible cooled by the circulation of a liquid inside the wall of the crucible. The details constituting the walls of the crucible have not been shown for the sake of clarity. In particular, the means for circulating the coolant, for example water, in the thickness of the walls have not been illustrated. In order to avoid looping of the induced currents, the periphery of the crucible is preferably formed by several vertical sectors assembled together. According to the present invention, a first winding 5 is wound around the crucible 1 and is connected by its two ends to the terminals of a single-phase alternating generator 3 in parallel with a capacitor C. The winding 5 consists of at least two coils 51 and 52 connected in series opposition, that is to say for example wound around the crucible 1 in opposite directions from a common point. At least a second winding 6 is also wound around the crucible 1 and is connected, by its two ends, to the terminals of a capacitor C. This second winding 6 comprises, like the first winding 5, at least two coils 61, 63 connected in opposition series. The windings 5 and 6 are nested one inside the other, that is to say that the coils are arranged successively in the height of the crucible so as to alternate a coil of the first winding with a coil of the second winding. In the example of a two-phase system as shown in Figure 1, there is thus from the top of the crucible 1: the first winding 61 of the winding 6, the first winding 51 of the winding 5, the second winding 62 of the winding 6 and the second winding 52 of the winding 5. According to the present invention, the second winding 6 plays the role of an induced circuit whose energy comes from the first winding 5. FIG. 2 represents the electrical circuit of the installation of FIG. 1. This figure shows the elements described in connection with Figure 1 and illustrates in a perspective view the direction of the coils of the windings 5 and 6 in series opposition. It will be noted that, in FIG. 1, the direction of current flow in the respective coils has been indicated by the usual notations (x,.) In electromagnetism. The winding 5 forms, with the capacitor C, a first oscillating circuit connected to the generator 3 and constituting a first phase of excitation of the polyphase system. The second winding 6, spatially offset from the first winding 5 forms, with the capacitor C, a second oscillating circuit. This second oscillating circuit is in magnetic interaction by its mutual inductance with the first oscillating circuit. One can then, by dimensioning, make so that the magnetic field resulting from the superposition of the two phases in presence is a sliding field likely to generate an electromagnetic driving force of pumping on the liquid glass contained in the crucible 1. The windings 5 and 6 also make it possible to generate eddy currents in the glass which keep the glass molten, as in a conventional induction crucible. The respective dimensions of the windings and the capacitors depend on the application and, in particular, on the frequency of the generator 3 and on the diameter of the crucible 1, knowing that the thickness of skin in the fluid can be of the same order of magnitude as the radius of the crucible. Preferably, the number of turns of the coils of the same winding is identical. The optimization of the system according to the application is within the reach of those skilled in the art by applying the rules of electrical and electromagnetic operation to from the respective inductors, the respective resistors and the respective capacitors of the oscillating circuits, as well as from the mutual inductance of these two circuits and from the pulsation of the single-phase generator. To obtain a linear sliding field effect allowing the pumping effect at the periphery of the container, it will preferably be sought that the products LC62 and L'C'ω 2 , where L and L 'represent the respective inductances of the windings 5 and 6 and where ω represents the pulsation of the single-phase generator 3, be as close as possible to the unit in order to optimize the operation of the oscillating circuits. An advantage of this first embodiment is that it makes it possible to brew liquid glass, which is very corrosive, without having to introduce mechanical stirring means into the glass. This embodiment finds applications in all industrial fields using the mixing of liquid glass with other bodies, for example the field of treatment of nuclear waste, in which waste, generally reduced to the powder state, are mixed with liquid glass which is then solidified and stored. In addition, as illustrated by the arrows in FIG. 2, an appropriate choice of the direction of the current in the windings makes it possible to stir the liquid glass according to a centripetal movement in the upper part. The inventors have shown that, because of the distribution of heat in the glass, higher in the center than at the edges, the previous centripetal brewing promotes a homogeneous inclusion in the glass of a powder 7 spilled at the center of the crucible. , which represents another advantage of the invention. Another advantage of the installation according to the invention is that it requires only a single single-phase generator to generate the stirring magnetic field. Such a generator is less expensive and less complex than a two-phase generator made up of two generators synchronized by active elements. Another advantage of the present invention is that the synchronization of the induced phase (phase obtained by the secondary winding), or of the induced phases in the case where several secondary windings are used, does not pose any particular problem. Another advantage of the present invention is that the system is particularly stable once adapted to the application. In fact, the passive elements (inductors and capacitors) used by the present invention to generate the additional phase or phases are not likely to be out of balance as could be the case with active elements (high power switches). Figure 3 illustrates, in a perspective view in section, the schematic structure of the inductive cold crucible of Figure 1. This figure shows the sectors (s) of the crucible 1 which are electrically isolated from each other. In the example of Figure 3, each coil 61, 51, 62, 52 has four turns. The representation in FIG. 3 illustrates that the number of wheels for stirring the glass depends on the number of sectors of the crucible. Thus, not only does the present invention make it possible to favor the inclusion of the particles in the center of the bath by centripetal stirring, but, in this application, stirring is also favored by the sectorized structure of the crucible which improves the mixing. The mixing speeds depend on the intensity of the currents il and ι2, therefore on the intensity of the current supplied by the generator 3. It will be noted that, according to the present invention, it is not necessary to have a phase shift of 90 ° between the two oscillating circuits. A phase shift of the order of 20 to 40 ° is sufficient in terms of efficiency for the brewing carried out. It will also be noted that the phase angle between the two oscillating circuits is adjustable by the respective values of the capacitors and of the inductances used. However, as previously indicated, this phase angle is stable once fixed by the dimensions of these elements. In practice, when the application relates to an induction heating, we start preferably by setting the required values for the respective inductances of wraps ¬ ments. These values condition the heating of the liquid glass or other fluid. However, we will consider the exis ¬ tence of the induced phase also involved heating. The respective values of the capacitors C and C are then fixed as a function of the frequency of the single-phase generator and of the desired skin thickness, which depends on the diameter of the crucible 1 and which may be of the same order of magnitude as the radius of the crucible. It will be noted that the respective relationships between the inductances of the windings and the capacitors C and C must be compatible with the output impedance of the single-phase generator 3. As a particular embodiment, for a crucible having a diameter of the order of about ten centimeters and for a single-phase generator having an operating frequency of the order of 400 kHz, capacitors having values of the order of 0.2 uF may be used with windings whose respective own inductances are of the order of 0.2 μH and whose resistances are of the order of 80 mΩ. In such an example, a phase shift of the order of 20 ° is obtained between the currents i1 and i2 of the respective windings, and a ratio of the amplitudes of the currents of the order of 1. FIG. 4 represents, schematically and in section, an example of application of the invention to the stirring of a gaseous plasma. The installation comprises an enclosure 1 intended to contain the gaseous plasma, around which are formed at least two nested windings 5 and 6 respectively capable of being connected to a capacitor C in parallel with an alternating voltage source and to a capacitor C alone , linked together and operating in substantially the same way as the elements bearing the same references in FIG. 1. The enclosure 1, waterproof and preferably made of a material such as quartz, comprises a means 8 for introducing a vertical powder 9 to be treated with the plasma vertically from the center of the plasma. According to this embodiment of the invention, the frequency of the voltage source and the characteristics of the windings 5 and 6 and of the capacitors C and C are chosen so that the electromagnetic field generated by the windings 5 and 6, not only heats the gas by eddy currents but also confines the plasma thus formed while creating in the plasma centripetal stirring forces. The inventors have shown that the centripetal brewing forces allow the powder 9 to be mixed from the inside to the outside of the plasma and promote efficient treatment of the powder by the plasma. Although the invention has been described above in relation to a two-phase system, it can also be implemented with more than two phases. In this regard, it will be noted that the greater the number of phases, the more the system is controllable, for example, to stir the fluid over a greater height. The adaptation of the system described above to a larger number of phases is within the reach of those skilled in the art. However, care must be taken to respect the nesting of the different windings in the height of the crucible as well as the associations in opposite series of the windings constituting the different windings. Of course, the present invention is susceptible to various variants and modifications which will appear to those skilled in the art. In particular, although the invention has been described above in relation to the stirring of glass and a gaseous plasma, it easily adapts to the stirring of other weakly conductive fluids such as electrolytes, or to the stirring non-corrosive conductive fluids. In addition, the choice of the number of turns per coil, the number of coils per winding and the arrangement of the turns is within the reach of the skilled person from the indications given above. In particular, the section of the turns will of course depend on the intensity of the currents, and the arrangement in the height of the crucible will depend on the height of the latter and on the number of coils. For example, with reference to the embodiment described above in relation to FIG. 3, the average level of the fluid will be chosen to correspond approximately to the middle of the height of the first winding 51 of the first winding 5. The increase in the number of coils of the same winding makes it possible to increase (by cumulative effect due to the increase in the interaction height) the pumping force, therefore the efficiency of the stirring.

Claims

REVENDICATIONS
1. Installation de traitement par induction apte à réaliser un brassage électromagnétique d'un fluide faiblement conducteur, comportant : une enceinte cylindrique (1) apte à recevoir le fluide ; un premier enroulement (5) comprenant deux premiers bobinages (51, 52) respectivement formés autour de deux premières zones distinctes de l'enceinte (1) et reliés en série opposition de manière à être parcourus par des courants opposés, les bornes du premier enroulement (5) étant aptes à être reliées aux bornes d'un premier condensateur (C) et aux bornes d'une source de tension alternative (3) ; et au moins un deuxième enroulement (6) comprenant deux deuxièmes bobinages (61, 62) respectivement formés autour de deux deuxièmes zones distinctes de l'enceinte (1) dont l'une est située entre les deux premières zones de l'enceinte, et reliés en série opposition de manière à être parcourus par des courants opposés, les bornes du deuxième enroulement (6) étant aptes à être reliées aux bornes d'un deuxième condensateur (C) . 1. Induction treatment installation capable of carrying out electromagnetic stirring of a weakly conductive fluid, comprising: a cylindrical enclosure (1) capable of receiving the fluid; a first winding (5) comprising two first coils (51, 52) respectively formed around two first distinct zones of the enclosure (1) and connected in opposition series so as to be traversed by opposite currents, the terminals of the first winding (5) being able to be connected to the terminals of a first capacitor (C) and to the terminals of an alternating voltage source (3); and at least one second winding (6) comprising two second windings (61, 62) respectively formed around two second separate zones of the enclosure (1) one of which is located between the first two zones of the enclosure, and connected in series opposition so as to be traversed by opposite currents, the terminals of the second winding (6) being able to be connected to the terminals of a second capacitor (C).
2. Installation selon la revendication 1, dans laquelle le fluide faiblement conducteur présente une résistivité comprise entre 10-3 et 1 Ω.m. 2. Installation according to claim 1, wherein the weakly conductive fluid has a resistivity between 10-3 and 1 Ω.m.
3. Installation selon la revendication 1 ou 2, dans laquelle les valeurs des premier et deuxième condensateurs (C, C) sont fonction de la fréquence de la source de tension (3) et de l'épaisseur de peau souhaitée à l'intérieur de l'enceinte. 3. Installation according to claim 1 or 2, in which the values of the first and second capacitors (C, C) are a function of the frequency of the voltage source (3) and of the desired skin thickness inside. the enclosure.
4. Installation selon l'une quelconque des revendications précédentes dans laquelle les inductances combinées des premier (5) et deuxième (6) enroulements sont choisies de manière à produire un échauffement prédéterminé d'un corps disposé dans l'enceinte, ledit échauffement étant apte à maintenir ledit corps sous forme d'un fluide. 4. Installation according to any one of the preceding claims, in which the combined inductances of the first (5) and second (6) windings are chosen so as to produce a predetermined heating of a body disposed in the enclosure, said heating being suitable maintaining said body in the form of a fluid.
5. Installation selon la revendication 4, dans laquelle le fluide faiblement conducteur est un plasma gazeux. 5. Installation according to claim 4, wherein the weakly conductive fluid is a gaseous plasma.
6. Installation selon la revendication 5, dans laquelle l'enceinte (1) est disposée verticalement et la source de tension (3) est commandée de telle manière que les enroulements (5, 6) génèrent un champ électromagnétique soumettant le plasma situé à proximité des parois de l'enceinte à une force agissant de bas en haut, et comportant au dessus du centre de l'enceinte un moyen (8) pour introduire une poudre (9) dans le plasma. 6. Installation according to claim 5, wherein the enclosure (1) is arranged vertically and the voltage source (3) is controlled such that the windings (5, 6) generate an electromagnetic field subjecting the plasma located nearby walls of the enclosure at a force acting from bottom to top, and comprising above the center of the enclosure means (8) for introducing a powder (9) into the plasma.
7. Installation selon la revendication 4, dans laquelle le fluide faiblement conducteur est un verre liquide. 7. Installation according to claim 4, wherein the weakly conductive fluid is a liquid glass.
8. Installation selon la revendication 7, dans laquelle l'enceinte est disposée verticalement et la source de tension (3) est commandée de telle manière que les enroulements (5, 6) génèrent un champ électromagnétique soumettant le verre liquide situé à proximité des parois de l'enceinte (1) à une force agissant de bas en haut, et comportant au dessus du centre de l'enceinte (1) un moyen pour introduire une poudre (7) dans le verre liquide. 8. Installation according to claim 7, wherein the enclosure is arranged vertically and the voltage source (3) is controlled such that the windings (5, 6) generate an electromagnetic field subjecting the liquid glass located near the walls of the enclosure (1) at a force acting from bottom to top, and comprising above the center of the enclosure (1) means for introducing a powder (7) into the liquid glass.
9. Installation selon l'une quelconque des revend!- cations précédentes, dans laquelle l'enceinte (1) est un creuset froid inductif. 9. Installation according to any one of the resellers - previous cations, in which the enclosure (1) is an inductive cold crucible.
10. Installation selon l'une quelconque des revendications 1 à 8, dans laquelle l'enceinte (1) est un creuset en matériau réfractaire. 10. Installation according to any one of claims 1 to 8, wherein the enclosure (1) is a crucible of refractory material.
PCT/FR2004/050319 2003-07-10 2004-07-09 Installation for induction treatment of a low-conductivity fluid WO2005008157A2 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR03/50316 2003-07-10
FR0350316A FR2857522A1 (en) 2003-07-10 2003-07-10 INDUCTION TREATMENT SYSTEM FOR LOW-CONDUCTIVE FLUID

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WO2005008157A2 true WO2005008157A2 (en) 2005-01-27
WO2005008157A3 WO2005008157A3 (en) 2005-08-18

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US8367008B2 (en) 2008-03-14 2013-02-05 Christian Claude Cyprien Trassy Method for purifying silicon for photovoltaic applications
CN114303035A (en) * 2019-08-30 2022-04-08 法国原子能源和替代能源委员会 Induction furnace including additional resonant circuit

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CN100419365C (en) * 2005-11-04 2008-09-17 丰宝科技（中山）有限公司 Thyristor intermediate frequency heating industrial medium boiler and its heating method
CN101509730B (en) * 2008-08-08 2012-01-04 张森林 Bottom assembling electromagnetic agitator for direct current excitation smelting furnace
CN101782324B (en) * 2010-02-05 2011-09-28 新星化工冶金材料(深圳)有限公司 Electromagnetic induction electric melting furnace for controlling average nominal diameter of TiB2(TiC) particle group in Al-Ti-B (Al-Ti-C) alloy
CN107421328A (en) * 2017-06-13 2017-12-01 石家庄爱迪尔电气有限公司 Heating seethes rabble furnace with stirring interlock type electromagnetism

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WO2000051400A1 (en) * 1999-02-26 2000-08-31 Centre National De La Recherche Scientifique Electromagnetic stirring of a melting metal
WO2002054831A2 (en) * 2001-01-08 2002-07-11 Inductotherm Corp. Induction furnace with improved efficiency coil system

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FR713498A (en) * 1930-03-18 1931-10-28 Improvements to electric induction furnaces
US2635125A (en) * 1949-09-30 1953-04-14 American Optical Corp Glass induction furnace
WO2000051400A1 (en) * 1999-02-26 2000-08-31 Centre National De La Recherche Scientifique Electromagnetic stirring of a melting metal
WO2002054831A2 (en) * 2001-01-08 2002-07-11 Inductotherm Corp. Induction furnace with improved efficiency coil system

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Publication number Priority date Publication date Assignee Title
US8367008B2 (en) 2008-03-14 2013-02-05 Christian Claude Cyprien Trassy Method for purifying silicon for photovoltaic applications
CN114303035A (en) * 2019-08-30 2022-04-08 法国原子能源和替代能源委员会 Induction furnace including additional resonant circuit

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FR2857522A1 (en) 2005-01-14

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