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EP0732866A1 - Process and equipment for heating an electrically conductive liquid - Google Patents

Process and equipment for heating an electrically conductive liquid Download PDF

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Publication number
EP0732866A1
EP0732866A1 EP96400520A EP96400520A EP0732866A1 EP 0732866 A1 EP0732866 A1 EP 0732866A1 EP 96400520 A EP96400520 A EP 96400520A EP 96400520 A EP96400520 A EP 96400520A EP 0732866 A1 EP0732866 A1 EP 0732866A1
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EP
European Patent Office
Prior art keywords
solenoid
liquid
heating
tank
cylinder head
Prior art date
Legal status (The legal status 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 status listed.)
Granted
Application number
EP96400520A
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German (de)
French (fr)
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EP0732866B1 (en
Inventor
Jacques Nuns
Philippe Fache
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Electricite de France SA
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Electricite de France SA
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Publication date
Priority claimed from FR9503054A external-priority patent/FR2731867B1/en
Application filed by Electricite de France SA filed Critical Electricite de France SA
Publication of EP0732866A1 publication Critical patent/EP0732866A1/en
Application granted granted Critical
Publication of EP0732866B1 publication Critical patent/EP0732866B1/en
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    • 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
    • H05B6/10—Induction heating apparatus, other than furnaces, for specific applications
    • H05B6/105—Induction heating apparatus, other than furnaces, for specific applications using a susceptor
    • H05B6/108—Induction heating apparatus, other than furnaces, for specific applications using a susceptor for heating a fluid
    • 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
    • H05B6/36—Coil arrangements
    • H05B6/365—Coil arrangements using supplementary conductive or ferromagnetic pieces

Definitions

  • the present invention relates to a method and an instrument for heating an electrically conductive liquid.
  • Induction ovens are used to heat metals, but in the case of a much less conductive electrolyte, the supply frequencies would be too high.
  • the liquid is contained in a metal container, it is essentially the container which would be heated by induction, and this heat would then be communicated to the liquid. This could cause damage to the anticorrosive coating of the container.
  • the invention also applies to Joule heating of metals or non-ferrous metal alloys (aluminum, copper, zinc, bronze, etc.).
  • a magnetic circuit is provided, generally made of magnetic sheets, extending partly inside the crucible containing the molten metal and partly outside.
  • An inductor winding is wound around the magnetic circuit in the outside of the crucible. This winding forms the primary of a transformer, the secondary of which consists of a stream of liquid metal around the magnetic circuit.
  • This type of oven causes significant energy losses, like traditional induction ovens, because the inductor is located outside the container containing the material to be heated.
  • the channel that is to say the zone inside the crucible situated between the magnetic circuit and the wall of the crucible, where the heating is most effective, tends to become blocked during the operation of the oven.
  • These channel ovens are limited in frequency. They are generally used at 50 Hz, but the circuits necessary to balance the three phases are then very bulky and they disturb the network.
  • the invention also relates to the heating of molten glasses which are often fairly good electrical conductors. It is known to heat glasses by induction in so-called "direct coil” ovens. In such an oven, a copper coil placed in the molten glass is fed at very high frequency (several hundred kHz) to generate the heat sink eddy currents. A serious drawback of these ovens is the risk of dielectric breakdown in the interval between the connection points of the coil, where the electric field is high. To mitigate this drawback, a so-called “cold cage” oven is sometimes used in which copper tubular sectors are placed axially inside the coil, cooling water circulating in these sectors. The circulation of the current in the coil induces other currents in the sectors, which generate the eddy currents in the molten glass. If these cold cage ovens limit the risks of dielectric breakdown, they have the disadvantage of having mediocre yields.
  • An object of the present invention is to provide a method for heating an electrically conductive liquid by the Joule effect with good efficiency.
  • the invention thus proposes a method of heating an electrolytic liquid consisting in immersing in said liquid a heating instrument comprising an inductor circuit electrically isolated from the liquid, and in supplying the inductor circuit with alternating current.
  • the invention is applicable to a liquid having a significant electrical conductivity, that is to say to an electrolytic liquid but also to a molten metal or alloy or even to a molten glass.
  • a method according to the invention thus consists in placing the liquid in a tank in which there is also an inductor circuit comprising a solenoid electrically isolated from the liquid and a cylinder head made of soft magnetic material extending axially inside the solenoid, and to supply the solenoid with alternating current.
  • inductor circuit By an appropriate dimensioning of the inductor circuit and by an adjustment of the supply frequency, one can essentially confine in the liquid the magnetic field induced outside the heating instrument. This gives excellent energy yields (over 90%). There are also the advantages of induction heating: low thermal inertia; possibility of finely regulating power and temperature; possibility of transmitting strong powers.
  • the invention also provides a heating instrument making it possible to carry out the above method in the case of an electrolytic liquid.
  • the instrument according to the invention comprises a solenoid arranged coaxially in an electrically insulating cylindrical tube and closed at its lower end, terminals for connecting the solenoid to an AC power supply, and a cylinder head made of soft magnetic material extending axially to inside the solenoid.
  • This cylinder head may have, at its end adjacent to the lower end of the tube, a flange directed radially towards the outside of the solenoid, this in order to improve efficiency.
  • the cylinder head is arranged to concentrate the induced magnetic field in the liquid. It is then possible to use greater depths of skin effect while maintaining an excellent energy yield, which makes it possible to use a power supply with a frequency that is significantly lower, and therefore more economical.
  • the invention further provides an oven for heating an electrically conductive liquid, comprising a tank for receiving said liquid, a solenoid electrically isolated from the liquid, extending inside the tank, a cylinder head extending axially to inside the solenoid, and an AC power supply connected to the solenoid.
  • Figure 1 shows a cylindrical tank 10 containing an electrolytic liquid to be heated, typically between room temperature and a temperature of 100 to 150 ° C, or even higher.
  • An inductor winding constituted here by a solenoid 12
  • the solenoid 12 is part of a heating instrument further comprising the terminals for connection to the generator 14 and means electrical insulation between the liquid and the copper of the solenoid and the connection terminals.
  • These means of electrical insulation also provide chemical protection of the copper against the liquid to be heated.
  • They can be constituted by an insulating and anticorrosive coating applied to the turns of the solenoid or even by a double cylindrical casing surrounding the solenoid.
  • Such a box can also be arranged to allow the circulation of a cooling fluid for the turns of the solenoid 12.
  • the liquid to be heated is located both around and inside the solenoid 12.
  • the alternating current applied induces in the liquid a magnetic field of which flow lines 16 are shown. Due to the conductivity of the liquid, which is for example between 10 and 100 S / m, this magnetic field generates eddy currents which heat the liquid by the Joule effect.
  • the frequency of supply is chosen according to the diameter of the solenoid, the diameter of the tank and the electrical conductivity of the liquid, taking into account that the latter generally increases with temperature.
  • the frequency selected is inversely proportional to the conductivity of the liquid and to the square of the desired skin effect depth. If necessary, an optimal supply frequency can be sought by preliminary tests. If the tank 10 is metallic, the frequency is chosen so that the walls of the tank 10 are not heated directly, that is to say so that the magnetic field induced outside the solenoid 12 remains essentially confined in the liquid. In practice, the supply frequency will often be greater than 50 kHz.
  • FIG. 2 shows a heating instrument allowing the method to be implemented at lower supply frequencies.
  • this instrument comprises a cylinder head 24 and a container tube 26.
  • the tube 26 is made of electrically insulating anti-corrosion material. He has a cylindrical shape which surrounds the solenoid 22 and the yoke 24, with a closed lower end 28.
  • the yoke 24 is for example made of magnetic sheets arranged in a star for supply frequencies of the order of 5 kHz or, for higher frequencies (typically 20 kHz) from ferrite bars.
  • the cylinder head 24 may have a flange 32, 34 extending radially outwards, as shown in FIG. 4.
  • the cylinder head 24 has a structure capable of concentrating the power transmitted opposite the turns of the solenoid 22.
  • the flux lines bend at a significant angle in the lower edge 32.
  • FIG. 3 illustrates the distribution of the magnetic field lines 36 in the example of a power of 237 kW, a frequency of 20 kHz and a conductivity of 37 S / m.
  • the bottom of the tank is not heated at all.
  • the upper rim 34 of the yoke limits the extension of the magnetic field above the surface of the liquid.
  • FIG. 4 shows an oven usable for heating a conductive liquid to higher temperatures.
  • the liquid in question can be a molten metal (or metallic alloy), or even a molten glass.
  • the oven comprises a tank 110 made of refractory material.
  • the refractory material of the wall of the tank is placed in a metal casing 111.
  • the tank is covered with a cover 113, provided with an opening 115 for the introduction of the material (liquid or solid not yet melted) to be heated .
  • a pouring spout 117 is provided at the upper part of the tank 110 for removing the heated liquid from the tank.
  • a solenoid 122 provided with an inner cylinder head 124 is placed inside the tank 110.
  • the solenoid is connected to an alternating current generator 114.
  • a path is formed around the solenoid 122 and of the cylinder head 124 to allow the passage of a cooling fluid, such as water, which circulates a pump 119.
  • the inductor constituted by the solenoid 122 and its cylinder head 124 is placed in a refractory sheath 126 integrated into the bottom of the tank 110.
  • the sheath 126 electrically and thermally insulates the solenoid 122 and its cylinder head 124 of the liquid.
  • the solenoid is placed vertically towards the middle of the tank, and is dimensioned so that the induced magnetic field is essentially confined in the liquid to be heated.
  • the electrical conductivity is very high (resistivities of the order of 10 to 20.10 -8 ⁇ .m).
  • the cylinder head 124 can then be produced from magnetic sheets, and the solenoid can be supplied at a frequency greater than 100 Hz, typically of 300 to 500 Hz.
  • the refractory materials of the tank 110 and of the sheath 126 are chosen from those usually used in metallurgy (adobe for example).
  • the conductivity is lower (up to 150 to 200 S / m) so that we have to increase the supply frequency for the same heating power .
  • a yoke 124 made from ferrite bars, and supply frequencies greater than 10 kHz, typically around 20 kHz.
  • the refractory materials of the tank 110 and of the sheath 126 can be ceramics such as those usually used in the glass industry.
  • the furnace shown in Figure 5 differs from that of Figure 4 in that the refractory sheath 226 containing the solenoid 222 and the cylinder head 224 is suspended from the cover 213 of the tank 210 instead of being fixed or integrated into the wall of the bottom of the tank. It will be understood that many other arrangements of the inductor inside the tank are possible.
  • FIG. 6 shows another example of an oven which can in particular be used for galvanizing sheets.
  • the solenoid 322, the cylinder head 324 and the refractory sheath 326 are placed near the bottom of the tank 310, with their axis parallel to this bottom.
  • the sleeve 326 for example crosses the width of the tank as shown. It may then be necessary to subdivide the solenoid 322 into several winding sections supplied separately.
  • the heated liquid being molten zinc, it is possible, thanks to a conventional arrangement of rollers, to slide a sheet in the space between the inductor and the bottom of the tank to apply a coating of zinc to it.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • General Induction Heating (AREA)
  • Resistance Heating (AREA)
  • Furnace Details (AREA)

Abstract

The method involves plunging a heating device in the liquid. The heating device has an inductive circuit (12) electrically insulated from the liquid. The inductive circuit is supplied by an alternative current to induce Foucault currents in the electrolytic liquid. The liquid can be placed in a tank (10) made of electrically conductive material. The inductive circuit may be supplied at a frequency selected in such a way that the induced magnetic field will be confined outside the heating device. The heating device may have a system for cooling the inductive circuit.

Description

La présente invention concerne un procédé et un instrument de chauffage d'un liquide électriquement conducteur.The present invention relates to a method and an instrument for heating an electrically conductive liquid.

Elle concerne notamment le chauffage par effet Joule d'un liquide électrolytique corrosif. Dans un liquide corrosif tel qu'un acide, il n'est guère envisageable de plonger deux électrodes pour faire circuler un courant électrique, car le matériau conducteur des électrodes serait attaqué par l'acide. Un montage de type four à induction, avec des enroulements inducteurs placés autour du récipient contenant le liquide, permettrait un chauffage par effet Joule provoqué par des courants induits dans la cuve, donc sans contact direct entre le liquide et un conducteur. Dans ces conditions, le rendement énergétique serait dégradé par perte supplémentaire dans l'inducteur, même si des culasses externes sont prévues. Les fours à induction sont utilisés pour chauffer des métaux, mais dans le cas d'un électrolyte beaucoup moins conducteur, les fréquences d'alimentation seraient trop élevées. En outre, si le liquide est contenu dans un récipient métallique, c'est essentiellement le récipient qui serait chauffé par induction, et cette chaleur serait ensuite communiquée au liquide. Ceci risquerait de provoquer une altération du revêtement anticorrosif du récipient.It relates in particular to the heating by the Joule effect of a corrosive electrolytic liquid. In a corrosive liquid such as an acid, it is hardly possible to immerse two electrodes to circulate an electric current, because the conductive material of the electrodes would be attacked by the acid. An induction oven type assembly, with inductor windings placed around the container containing the liquid, would allow heating by Joule effect caused by currents induced in the tank, therefore without direct contact between the liquid and a conductor. Under these conditions, the energy efficiency would be degraded by additional loss in the inductor, even if external cylinder heads are provided. Induction ovens are used to heat metals, but in the case of a much less conductive electrolyte, the supply frequencies would be too high. In addition, if the liquid is contained in a metal container, it is essentially the container which would be heated by induction, and this heat would then be communicated to the liquid. This could cause damage to the anticorrosive coating of the container.

L'invention s'applique également au chauffage par effet Joule de métaux ou d'alliages métalliques non ferreux (aluminium, cuivre, zinc, bronze...). Dans un four à canal, parfois utilisé pour chauffer des métaux non ferreux, il est prévu un circuit magnétique, généralement en tôles magnétiques, s'étendant en partie à l'intérieur du creuset contenant le métal fondu et en partie à l'extérieur. Un enroulement inducteur est bobiné autour du circuit magnétique dans la partie extérieure au creuset. Cet enroulement forme le primaire d'un transformateur dont le secondaire est constitué par une veine du métal liquide autour du circuit magnétique. Ce type de four provoque des pertes énergétiques non négligeables, comme les fours à induction traditionnels, du fait que l'inducteur est situé à l'extérieur du récipient contenant le matériau à chauffer. En outre, le canal, c'est-à-dire la zone intérieure au creuset située entre le circuit magnétique et la paroi du creuset, où le chauffage est le plus efficace, a tendance à se boucher au cours du fonctionnement du four. Ces fours à canal sont limités en fréquence. Ils sont généralement utilisés à 50 Hz, mais les circuits nécessaires pour équilibrer les trois phases sont alors très encombrants et ils perturbent le réseau.The invention also applies to Joule heating of metals or non-ferrous metal alloys (aluminum, copper, zinc, bronze, etc.). In a channel furnace, sometimes used to heat non-ferrous metals, a magnetic circuit is provided, generally made of magnetic sheets, extending partly inside the crucible containing the molten metal and partly outside. An inductor winding is wound around the magnetic circuit in the outside of the crucible. This winding forms the primary of a transformer, the secondary of which consists of a stream of liquid metal around the magnetic circuit. This type of oven causes significant energy losses, like traditional induction ovens, because the inductor is located outside the container containing the material to be heated. In addition, the channel, that is to say the zone inside the crucible situated between the magnetic circuit and the wall of the crucible, where the heating is most effective, tends to become blocked during the operation of the oven. These channel ovens are limited in frequency. They are generally used at 50 Hz, but the circuits necessary to balance the three phases are then very bulky and they disturb the network.

L'invention concerne également le chauffage de verres en fusion qui sont souvent d'assez bons conducteurs électriques. Il est connu de chauffer des verres par induction dans des fours dits "à spire directe". Dans un tel four, une spire de cuivre placée dans le verre fondu est alimentée à très haute fréquence (plusieurs centaines de kHz) pour générer les courants de Foucault dissipateurs de chaleur. Un grave inconvénient de ces fours est le risque de claquage diélectrique dans l'intervalle séparant les points de raccordements de la spire, où le champ électrique est élevé. Pour atténuer cet inconvénient, on utilise parfois un four dit "à cage froide" dans lequel des secteurs tubulaires en cuivre sont placés axialement à l'intérieur de la spire, de l'eau de refroidissement circulant dans ces secteurs. La circulation du courant dans la spire induit d'autres courants dans les secteurs, lesquels génèrent les courants de Foucault dans le verre fondu. Si ces fours à cage froide limitent les risques de claquage diélectrique, ils ont l'inconvénient de présenter des rendements médiocres.The invention also relates to the heating of molten glasses which are often fairly good electrical conductors. It is known to heat glasses by induction in so-called "direct coil" ovens. In such an oven, a copper coil placed in the molten glass is fed at very high frequency (several hundred kHz) to generate the heat sink eddy currents. A serious drawback of these ovens is the risk of dielectric breakdown in the interval between the connection points of the coil, where the electric field is high. To mitigate this drawback, a so-called "cold cage" oven is sometimes used in which copper tubular sectors are placed axially inside the coil, cooling water circulating in these sectors. The circulation of the current in the coil induces other currents in the sectors, which generate the eddy currents in the molten glass. If these cold cage ovens limit the risks of dielectric breakdown, they have the disadvantage of having mediocre yields.

Un but de la présente invention est de proposer un procédé permettant de chauffer un liquide électriquement conducteur par effet Joule avec un bon rendement.An object of the present invention is to provide a method for heating an electrically conductive liquid by the Joule effect with good efficiency.

L'invention propose ainsi un procédé de chauffage d'un liquide électrolytique consistant à plonger dans ledit liquide un instrument de chauffage comportant un circuit inducteur électriquement isolé du liquide, et à alimenter le circuit inducteur en courant alternatif.The invention thus proposes a method of heating an electrolytic liquid consisting in immersing in said liquid a heating instrument comprising an inductor circuit electrically isolated from the liquid, and in supplying the inductor circuit with alternating current.

Plus généralement, l'invention est applicable à un liquide ayant une conductivité électrique notable, c'est-à-dire à un liquide électrolytique mais également à un métal ou alliage fondu ou encore à un verre en fusion. Un procédé selon l'invention consiste ainsi à placer le liquide dans une cuve dans laquelle se trouve en outre un circuit inducteur comprenant un solénoïde électriquement isolé du liquide et une culasse en matériau magnétique doux s'étendant axialement à l'intérieur du solénoïde, et à alimenter le solénoïde en courant alternatif.More generally, the invention is applicable to a liquid having a significant electrical conductivity, that is to say to an electrolytic liquid but also to a molten metal or alloy or even to a molten glass. A method according to the invention thus consists in placing the liquid in a tank in which there is also an inductor circuit comprising a solenoid electrically isolated from the liquid and a cylinder head made of soft magnetic material extending axially inside the solenoid, and to supply the solenoid with alternating current.

Par un dimensionnement approprié du circuit inducteur et par un réglage de la fréquence d'alimentation, on peut confiner essentiellement dans le liquide le champ magnétique induit à l'extérieur de l'instrument de chauffage. On accède ainsi à d'excellents rendements énergétiques (supérieurs à 90%). On bénéficie en outre des avantages propres au chauffage par induction : faible inertie thermique ; possibilité de réguler finement la puissance et la température ; possibilité de transmettre de fortes puissances.By an appropriate dimensioning of the inductor circuit and by an adjustment of the supply frequency, one can essentially confine in the liquid the magnetic field induced outside the heating instrument. This gives excellent energy yields (over 90%). There are also the advantages of induction heating: low thermal inertia; possibility of finely regulating power and temperature; possibility of transmitting strong powers.

L'invention propose également un instrument de chauffage permettant de mettre en oeuvre le procédé ci-dessus dans le cas d'un liquide électrolytique. D'autres types d'instruments seraient néanmoins utilisables. L'instrument selon l'invention comprend un solénoïde disposé coaxialement dans un tube cylindrique électriquement isolant et fermé à son extrémité inférieure, des bornes de raccordement du solénoïde à une alimentation en courant alternatif, et une culasse en matériau magnétique doux s'étendant axialement à l'intérieur du solénoïde. Cette culasse peut présenter, à son extrémité adjacente à l'extrémité inférieure du tube, un rebord dirigé radialement vers l'extérieur du solénoïde, ceci afin d'améliorer l'efficacité.The invention also provides a heating instrument making it possible to carry out the above method in the case of an electrolytic liquid. Other types of instruments would nevertheless be usable. The instrument according to the invention comprises a solenoid arranged coaxially in an electrically insulating cylindrical tube and closed at its lower end, terminals for connecting the solenoid to an AC power supply, and a cylinder head made of soft magnetic material extending axially to inside the solenoid. This cylinder head may have, at its end adjacent to the lower end of the tube, a flange directed radially towards the outside of the solenoid, this in order to improve efficiency.

La culasse est agencée pour concentrer dans le liquide le champ magnétique induit. On peut alors utiliser de plus grandes profondeurs d'effet de peau en conservant un excellent rendement énergétique, ce qui permet d'utiliser une alimentation de fréquence sensiblement plus basse, donc plus économique.The cylinder head is arranged to concentrate the induced magnetic field in the liquid. It is then possible to use greater depths of skin effect while maintaining an excellent energy yield, which makes it possible to use a power supply with a frequency that is significantly lower, and therefore more economical.

L'invention propose en outre un four de chauffage d'un liquide électriquement conducteur, comprenant une cuve pour recevoir ledit liquide, un solénoïde électriquement isolé du liquide, s'étendant à l'intérieur de la cuve, une culasse s'étendant axialement à l'intérieur du solénoïde, et une alimentation en courant alternatif reliée au solénoïde.The invention further provides an oven for heating an electrically conductive liquid, comprising a tank for receiving said liquid, a solenoid electrically isolated from the liquid, extending inside the tank, a cylinder head extending axially to inside the solenoid, and an AC power supply connected to the solenoid.

D'autres particularités et avantages de la présente invention apparaîtront dans la description ci-après d'exemples de réalisation préférés mais non limitatifs, en référence aux dessins annexés, dans lesquels :

  • la figure 1 est un schéma illustrant la mise en oeuvre d'un procédé selon l'invention ;
  • la figure 2 est une vue schématique en coupe axiale d'un instrument de chauffage selon l'invention ;
  • la figure 3 est un schéma illustrant la répartition des lignes de flux magnétique dans un liquide chauffé par l'instrument représenté sur la figure 2 ; et
  • les figures 4 à 6 sont des schémas en coupe de trois exemples de four selon l'invention.
Other particularities and advantages of the present invention will appear in the description below of preferred but nonlimiting exemplary embodiments, with reference to the appended drawings, in which:
  • Figure 1 is a diagram illustrating the implementation of a method according to the invention;
  • Figure 2 is a schematic view in axial section of a heating instrument according to the invention;
  • Figure 3 is a diagram illustrating the distribution of magnetic flux lines in a liquid heated by the instrument shown in Figure 2; and
  • Figures 4 to 6 are sectional diagrams of three examples of an oven according to the invention.

La figure 1 montre une cuve cylindrique 10 contenant un liquide électrolytique à chauffer, typiquement entre la température ambiante et une température de 100 à 150°C, voire plus élevée. Un enroulement inducteur, constitué ici par un solénoïde 12, est immergé dans le liquide et alimenté par un générateur de courant alternatif 14. Le solénoïde 12 fait partie d'un instrument de chauffage comportant en outre les bornes de raccordement au générateur 14 et des moyens d'isolation électrique entre le liquide et le cuivre du solénoïde et les bornes de raccordement. Ces moyens d'isolation électrique assurent également la protection chimique du cuivre vis-à-vis du liquide à chauffer. Ils peuvent être constitués par un revêtement isolant et anticorrosif appliqué sur les spires du solénoïde ou encore par un boîtier cylindrique double entourant le solénoïde. Un tel boîtier peut également être agencé pour permettre la circulation d'un fluide de refroidissement des spires du solénoïde 12.Figure 1 shows a cylindrical tank 10 containing an electrolytic liquid to be heated, typically between room temperature and a temperature of 100 to 150 ° C, or even higher. An inductor winding, constituted here by a solenoid 12, is immersed in the liquid and supplied by an alternating current generator 14. The solenoid 12 is part of a heating instrument further comprising the terminals for connection to the generator 14 and means electrical insulation between the liquid and the copper of the solenoid and the connection terminals. These means of electrical insulation also provide chemical protection of the copper against the liquid to be heated. They can be constituted by an insulating and anticorrosive coating applied to the turns of the solenoid or even by a double cylindrical casing surrounding the solenoid. Such a box can also be arranged to allow the circulation of a cooling fluid for the turns of the solenoid 12.

Dans l'agencement de la figure 1, le liquide à chauffer se trouve à la fois autour et à l'intérieur du solénoïde 12. Le courant alternatif appliqué induit dans le liquide un champ magnétique dont des lignes de flux 16 sont représentées. Du fait de la conductivité du liquide, qui est par exemple comprise entre 10 et 100 S/m, ce champ magnétique génère des courants de Foucault qui chauffent le liquide par effet Joule.In the arrangement of FIG. 1, the liquid to be heated is located both around and inside the solenoid 12. The alternating current applied induces in the liquid a magnetic field of which flow lines 16 are shown. Due to the conductivity of the liquid, which is for example between 10 and 100 S / m, this magnetic field generates eddy currents which heat the liquid by the Joule effect.

La fréquence d'alimentation est choisie en fonction du diamètre du solénoïde, du diamètre de la cuve et de la conductivité électrique du liquide, en tenant compte du fait que cette dernière augmente en général avec la température. En première approximation, la fréquence retenue est inversement proportionnelle à la conductivité du liquide et au carré de la profondeur d'effet de peau désirée. Si nécessaire, une fréquence d'alimentation optimale peut être recherchée par des essais préalables. Si la cuve 10 est métallique, on choisit la fréquence de façon que les parois de la cuve 10 ne soient pas chauffées directement, c'est-à-dire de façon que le champ magnétique induit à l'extérieur du solénoïde 12 reste essentiellement confiné dans le liquide. En pratique, la fréquence d'alimentation sera souvent supérieure à 50 kHz.The frequency of supply is chosen according to the diameter of the solenoid, the diameter of the tank and the electrical conductivity of the liquid, taking into account that the latter generally increases with temperature. As a first approximation, the frequency selected is inversely proportional to the conductivity of the liquid and to the square of the desired skin effect depth. If necessary, an optimal supply frequency can be sought by preliminary tests. If the tank 10 is metallic, the frequency is chosen so that the walls of the tank 10 are not heated directly, that is to say so that the magnetic field induced outside the solenoid 12 remains essentially confined in the liquid. In practice, the supply frequency will often be greater than 50 kHz.

La figure 2 montre un instrument de chauffage permettant de mettre en oeuvre le procédé à des fréquences d'alimentation plus basses. Outre un solénoïde 22 et ses bornes de raccordement non représentées, cet instrument comporte une culasse 24 et un tube conteneur 26. Le tube 26 est en matériau anti-corrosif électriquement isolant. Il a une forme cylindrique qui entoure le solénoïde 22 et la culasse 24, avec une extrémité inférieure fermée 28. La culasse 24 est par exemple réalisée en tôles magnétiques disposées en étoile pour des fréquences d'alimentation de l'ordre de 5 kHz ou, pour des fréquences plus élevées (typiquement 20 kHz) à partir de barreaux de ferrite. Elle a une forme générale cylindrique coaxiale au solénoïde 22 et au tube 26, avec un alésage axial 30 permettant de faire circuler un fluide de refroidissement du solénoïde et de la culasse, par exemple de l'eau. A chacune des extrémités axiales du solénoïde 22, la culasse 24 peut présenter un rebord 32, 34 s'étendant radialement vers l'extérieur, comme le montre la figure 4.FIG. 2 shows a heating instrument allowing the method to be implemented at lower supply frequencies. In addition to a solenoid 22 and its connection terminals not shown, this instrument comprises a cylinder head 24 and a container tube 26. The tube 26 is made of electrically insulating anti-corrosion material. He has a cylindrical shape which surrounds the solenoid 22 and the yoke 24, with a closed lower end 28. The yoke 24 is for example made of magnetic sheets arranged in a star for supply frequencies of the order of 5 kHz or, for higher frequencies (typically 20 kHz) from ferrite bars. It has a generally cylindrical shape coaxial with the solenoid 22 and the tube 26, with an axial bore 30 making it possible to circulate a coolant for the solenoid and the cylinder head, for example water. At each of the axial ends of the solenoid 22, the cylinder head 24 may have a flange 32, 34 extending radially outwards, as shown in FIG. 4.

La culasse 24 a une structure propre à concentrer la puissance transmise face aux spires du solénoïde 22. En particulier, les lignes de flux se courbent selon un angle important dans le rebord inférieur 32. Ainsi, lorsque l'instrument est plongé verticalement dans la cuve 10 contenant le liquide électrolytique à chauffer, on peut induire un champ magnétique élevé sans que ce champ soit important au niveau du fond de la cuve. Le champ est bien concentré dans le liquide, même si la profondeur de l'effet de peau est relativement importante, c'est-à-dire si la fréquence d'alimentation est relativement basse. Le solénoïde peut alors être alimenté à des fréquences à partir de 5 kHz seulement pour une puissance transmise de plusieurs centaines de kW et une conductivité du liquide de l'ordre de 30 à 50 S/m. La figure 3 illustre la distribution des lignes de champ magnétique 36 dans l'exemple d'une puissance de 237 kW, d'une fréquence de 20 kHz et d'une conductivité de 37 S/m. A une fréquence de 20 kHz, le fond de la cuve n'est pas du tout chauffé. De même, le rebord supérieur 34 de la culasse limite l'extension du champ magnétique au-dessus de la surface du liquide.The cylinder head 24 has a structure capable of concentrating the power transmitted opposite the turns of the solenoid 22. In particular, the flux lines bend at a significant angle in the lower edge 32. Thus, when the instrument is immersed vertically in the tank 10 containing the electrolytic liquid to be heated, a high magnetic field can be induced without this field being significant at the bottom of the tank. The field is well concentrated in the liquid, even if the depth of the skin effect is relatively large, that is to say if the frequency of feeding is relatively low. The solenoid can then be supplied at frequencies from 5 kHz only for a transmitted power of several hundred kW and a conductivity of the liquid of the order of 30 to 50 S / m. FIG. 3 illustrates the distribution of the magnetic field lines 36 in the example of a power of 237 kW, a frequency of 20 kHz and a conductivity of 37 S / m. At a frequency of 20 kHz, the bottom of the tank is not heated at all. Likewise, the upper rim 34 of the yoke limits the extension of the magnetic field above the surface of the liquid.

On peut bien entendu plonger plusieurs instruments de chauffage dans une même cuve. On prend alors toutefois la précaution de les raccorder de façon que le champ magnétique créé par l'un ne soit pas en opposition de phase avec celui créé par ses voisins.It is of course possible to immerse several heating instruments in the same tank. We then take the take care to connect them so that the magnetic field created by one is not in phase opposition with that created by its neighbors.

La figure 4 montre un four utilisable pour le chauffage d'un liquide conducteur à des températures plus élevées. Le liquide en question peut être un métal (ou alliage métallique) fondu, ou encore un verre en fusion. Le four comporte une cuve 110 en matériau réfractaire. Le matériau réfractaire de la paroi de la cuve est placé dans une enveloppe métallique 111. La cuve est recouverte d'un couvercle 113, pourvu d'une ouverture 115 pour l'introduction de la matière (liquide ou solide non encore fondu) à chauffer. Un bec de coulée 117 est prévu à la partie supérieure de la cuve 110 pour évacuer de la cuve le liquide chauffé.Figure 4 shows an oven usable for heating a conductive liquid to higher temperatures. The liquid in question can be a molten metal (or metallic alloy), or even a molten glass. The oven comprises a tank 110 made of refractory material. The refractory material of the wall of the tank is placed in a metal casing 111. The tank is covered with a cover 113, provided with an opening 115 for the introduction of the material (liquid or solid not yet melted) to be heated . A pouring spout 117 is provided at the upper part of the tank 110 for removing the heated liquid from the tank.

Un solénoïde 122 pourvu d'une culasse intérieure 124 est placé à l'intérieur de la cuve 110. Le solénoïde est relié à un générateur de courant alternatif 114. Comme dans le cas de la figure 2, un trajet est ménagé autour du solénoïde 122 et de la culasse 124 pour permettre le passage d'un fluide de refroidissement, tel que de l'eau, que fait circuler une pompe 119.A solenoid 122 provided with an inner cylinder head 124 is placed inside the tank 110. The solenoid is connected to an alternating current generator 114. As in the case of FIG. 2, a path is formed around the solenoid 122 and of the cylinder head 124 to allow the passage of a cooling fluid, such as water, which circulates a pump 119.

Dans l'exemple de réalisation de la figure 4, l'inducteur constitué par le solénoïde 122 et sa culasse 124 est placé dans un fourreau réfractaire 126 intégré au fond de la cuve 110. Le fourreau 126 isole électriquement et thermiquement le solénoïde 122 et sa culasse 124 du liquide. Le solénoïde est placé verticalement vers le milieu de la cuve, et est dimensionné pour que le champ magnétique induit soit essentiellement confiné dans le liquide à chauffer.In the embodiment of FIG. 4, the inductor constituted by the solenoid 122 and its cylinder head 124 is placed in a refractory sheath 126 integrated into the bottom of the tank 110. The sheath 126 electrically and thermally insulates the solenoid 122 and its cylinder head 124 of the liquid. The solenoid is placed vertically towards the middle of the tank, and is dimensioned so that the induced magnetic field is essentially confined in the liquid to be heated.

Dans le cas où le liquide à chauffer est un métal non ferreux ou un alliage de métaux non ferreux, la conductivité électrique est très élevée (résistivités de l'ordre de 10 à 20.10-8 Ω.m). La culasse 124 peut alors être réalisée à partir de tôles magnétiques, et le solénoïde peut être alimenté à une fréquence supérieure à 100 Hz, typiquement de 300 à 500 Hz. Les matériaux réfractaires de la cuve 110 et du fourreau 126 sont choisis parmi ceux habituellement utilisés en métallurgie (pisé par exemple).In the case where the liquid to be heated is a non-ferrous metal or an alloy of non-ferrous metals, the electrical conductivity is very high (resistivities of the order of 10 to 20.10 -8 Ω.m). The cylinder head 124 can then be produced from magnetic sheets, and the solenoid can be supplied at a frequency greater than 100 Hz, typically of 300 to 500 Hz. The refractory materials of the tank 110 and of the sheath 126 are chosen from those usually used in metallurgy (adobe for example).

Dans le cas où le liquide à chauffer est un verre en fusion, la conductivité est moins élevée (jusqu'à 150 à 200 S/m) de sorte qu'on est amené à augmenter la fréquence d'alimentation pour une même puissance de chauffage. On utilise alors une culasse 124 réalisée à partir de barreaux de ferrite, et des fréquences d'alimentation supérieures à 10 kHz, typiquement d'environ 20 kHz. Les matériaux réfractaires de la cuve 110 et du fourreau 126 peuvent être des céramiques telles que celles habituellement utilisées dans l'industrie du verre.In the case where the liquid to be heated is a molten glass, the conductivity is lower (up to 150 to 200 S / m) so that we have to increase the supply frequency for the same heating power . We then use a yoke 124 made from ferrite bars, and supply frequencies greater than 10 kHz, typically around 20 kHz. The refractory materials of the tank 110 and of the sheath 126 can be ceramics such as those usually used in the glass industry.

Le four représenté sur la figure 5 diffère de celui de la figure 4 en ce que le fourreau réfractaire 226 contenant le solénoïde 222 et la culasse 224 est suspendu au couvercle 213 de la cuve 210 au lieu d'être fixé ou intégré à la paroi du fond de la cuve. On comprendra que de nombreux autres agencements de l'inducteur à l'intérieur de la cuve sont envisageables.The furnace shown in Figure 5 differs from that of Figure 4 in that the refractory sheath 226 containing the solenoid 222 and the cylinder head 224 is suspended from the cover 213 of the tank 210 instead of being fixed or integrated into the wall of the bottom of the tank. It will be understood that many other arrangements of the inductor inside the tank are possible.

La figure 6 montre un autre exemple de four pouvant notamment être utilisé pour zinguer des tôles. Le solénoïde 322, la culasse 324 et le fourreau réfractaire 326 sont placés près du fond de la cuve 310, avec leur axe parallèle à ce fond. Le fourreau 326 traverse par exemple la largeur de la cuve comme représenté. Il peut alors être nécessaire de subdiviser le solénoïde 322 en plusieurs tronçons d'enroulement alimentés séparément. Le liquide chauffé étant du zinc fondu, on peut, grâce à un agencement conventionnel de rouleaux, faire défiler une tôle dans l'intervalle situé entre l'inducteur et le fond de la cuve pour lui appliquer un revêtement de zinc.FIG. 6 shows another example of an oven which can in particular be used for galvanizing sheets. The solenoid 322, the cylinder head 324 and the refractory sheath 326 are placed near the bottom of the tank 310, with their axis parallel to this bottom. The sleeve 326 for example crosses the width of the tank as shown. It may then be necessary to subdivide the solenoid 322 into several winding sections supplied separately. The heated liquid being molten zinc, it is possible, thanks to a conventional arrangement of rollers, to slide a sheet in the space between the inductor and the bottom of the tank to apply a coating of zinc to it.

Claims (16)

Procédé de chauffage d'un liquide électrolytique, caractérisé en ce qu'on plonge dans ledit liquide au moins un instrument de chauffage comportant un circuit inducteur (12;22) électriquement isolé du liquide, et en ce qu'on alimente le circuit inducteur en courant alternatif de manière à induire des courants de Foucault dans le liquide électrolytique.Method for heating an electrolytic liquid, characterized in that at least one heating instrument is immersed in said liquid comprising an inductor circuit (12; 22) electrically isolated from the liquid, and in that the inductor circuit is supplied with alternating current so as to induce eddy currents in the electrolytic liquid. Procédé selon la revendication 1, caractérisé en ce que, le liquide étant placé dans une cuve (10) en matériau électriquement conducteur, on alimente le circuit inducteur à une fréquence sélectionnée pour confiner sensiblement dans le liquide le champ magnétique induit à l'extérieur de l'instrument de chauffage.Method according to claim 1, characterized in that, the liquid being placed in a tank (10) of electrically conductive material, the inductor circuit is supplied at a selected frequency to substantially confine the magnetic field induced outside of the liquid. the heating instrument. Procédé selon la revendication 1 ou 2, caractérisé en ce que l'instrument de chauffage comporte des moyens de refroidissement du circuit inducteur.Method according to claim 1 or 2, characterized in that the heating instrument comprises means for cooling the inductor circuit. Procédé selon l'une quelconque des revendications 1 à 3, caractérisé en ce que le circuit inducteur est un solénoïde (22), et en ce que l'instrument de chauffage comporte en outre une culasse (24) en matériau magnétique doux s'étendant axialement à l'intérieur du solénoïde, la culasse présentant, à au moins une extrémité axiale du solénoïde, un rebord (32,34) dirigé radialement vers l'extérieur du solénoïde.Method according to any one of Claims 1 to 3, characterized in that the inductor circuit is a solenoid (22), and in that the heating instrument also comprises a cylinder head (24) made of soft magnetic material extending axially inside the solenoid, the cylinder head having, at at least one axial end of the solenoid, a flange (32, 34) directed radially towards the outside of the solenoid. Instrument de chauffage pour un liquide électrolytique, caractérisé en ce qu'il comprend un solénoïde (22) disposé coaxialement dans un tube cylindrique électriquement isolant (26) fermé à son extrémité inférieure (28), des bornes de raccordement du solénoïde à une alimentation en courant alternatif (14), et une culasse (24) en matériau magnétique doux s'étendant axialement à l'intérieur du solénoïde.Heating instrument for an electrolytic liquid, characterized in that it comprises a solenoid (22) arranged coaxially in an electrically insulating cylindrical tube (26) closed at its lower end (28), terminals for connecting the solenoid to a supply of alternating current (14), and a yoke (24) of soft magnetic material extending axially inside the solenoid. Instrument de chauffage selon la revendication 5, caractérisé en ce que la culasse présente, à son extrémité adjacente à l'extrémité inférieure du tube, un rebord (32) dirigé radialement vers l'extérieur du solénoïde.Heating instrument according to claim 5, characterized in that the cylinder head has, at its end adjacent to the lower end of the tube, a flange (32) directed radially towards the outside of the solenoid. Instrument de chauffage selon la revendication 6, caractérisé en ce que la culasse comporte un autre rebord (34) dirigé radialement vers l'extérieur du solénoïde (22), à son extrémité opposée à l'extrémité inférieure du tube (26).Heating instrument according to claim 6, characterized in that the cylinder head has another flange (34) directed radially towards the outside of the solenoid (22), at its end opposite the lower end of the tube (26). Instrument de chauffage selon l'une quelconque des revendications 5 à 7, caractérisé en ce que la culasse (24) comporte un alésage axial (30) pour la circulation d'un fluide de refroidissement.Heating instrument according to any one of Claims 5 to 7, characterized in that the cylinder head (24) has an axial bore (30) for the circulation of a cooling fluid. Procédé de chauffage d'un liquide électriquement conducteur, caractérisé en ce qu'on place ledit liquide dans une cuve (10;110;210;310) dans laquelle se trouve en outre au moins un solénoïde (22;122;222;322) électriquement isolé du liquide, avec une culasse (24;124;224;324) en matériau magnétique doux s'étendant axialement à l'intérieur du solénoïde, et en ce qu'on alimente le solénoïde en courant alternatif.Method of heating an electrically conductive liquid, characterized in that said liquid is placed in a tank (10; 110; 210; 310) in which there is also at least one solenoid (22; 122; 222; 322) electrically isolated from the liquid, with a yoke (24; 124; 224; 324) of soft magnetic material extending axially inside the solenoid, and in that the solenoid is supplied with alternating current. Procédé selon la revendication 9, caractérisé en ce que ledit liquide électriquement conducteur est un métal non ferreux fondu ou un alliage métallique non ferreux fondu.A method according to claim 9, characterized in that said electrically conductive liquid is a molten non-ferrous metal or a molten non-ferrous metal alloy. Procédé selon la revendication 10, caractérisé en ce que la culasse (124;224;324) est réalisée en tôles magnétiques, et en ce que la fréquence d'alimentation du solénoïde est supérieure à 100 Hz.Method according to claim 10, characterized in that the yoke (124; 224; 324) is made of magnetic sheets, and in that the supply frequency of the solenoid is greater than 100 Hz. Procédé selon la revendication 9, caractérisé en ce que ledit liquide électriquement conducteur est un verre en fusion.A method according to claim 9, characterized in that said electrically conductive liquid is a molten glass. Procédé selon la revendication 12, caractérisé en ce que la culasse (124;224;324) est réalisée à base de ferrite, et en ce que la fréquence d'alimentation du solénoïde est supérieure à 10 kHz.Method according to claim 12, characterized in that the yoke (124; 224; 324) is produced on the basis of ferrite, and in that the supply frequency of the solenoid is greater than 10 kHz. Four de chauffage d'un liquide électriquement conducteur, caractérisé en ce qu'il comprend une cuve (10;110;210;310) pour recevoir ledit liquide, un solénoïde (22;122;222;322) électriquement isolé du liquide, s'étendant à l'intérieur de la cuve, une culasse (24;124;224;324) s'étendant axialement à l'intérieur du solénoïde, et une alimentation (14;114) en courant alternatif reliée au solénoïde.Oven for heating an electrically conductive liquid, characterized in that it comprises a tank (10; 110; 210; 310) for receiving said liquid, a solenoid (22; 122; 222; 322) electrically isolated from the liquid, s '' extending inside the tank, a cylinder head (24; 124; 224; 324) extending axially inside the solenoid, and an alternating current supply (14; 114) connected to the solenoid. Four selon la revendication 14, caractérisé en ce qu'il comprend en outre des moyens (119) de refroidissement du solénoïde et de la culasse.Oven according to claim 14, characterized in that it further comprises means (119) for cooling the solenoid and the cylinder head. Four selon la revendication 14 ou 15, caractérisé en ce que le solénoïde (322) est placé près du fond de la cuve (310), avec son axe parallèle audit fond.Oven according to claim 14 or 15, characterized in that the solenoid (322) is placed near the bottom of the tank (310), with its axis parallel to said bottom.
EP96400520A 1995-03-16 1996-03-13 Process and equipment for heating an electrically conductive liquid Expired - Lifetime EP0732866B1 (en)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
FR9503054 1995-03-16
FR9503054A FR2731867B1 (en) 1995-03-16 1995-03-16 METHOD AND INSTRUMENT FOR HEATING AN ELECTROLYTIC LIQUID
FR9600737A FR2731868B1 (en) 1995-03-16 1996-01-23 METHOD AND EQUIPMENT FOR HEATING AN ELECTRICALLY CONDUCTIVE LIQUID
FR9600737 1996-01-23

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EP0732866B1 EP0732866B1 (en) 2002-02-20

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CA (1) CA2171788A1 (en)
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Publication number Priority date Publication date Assignee Title
FR2821647A1 (en) * 2001-03-02 2002-09-06 Robert Lipp OMNIDIRECTIONAL SUBMERSIBLE HYDRAULIC TURBINE WITH PERPENDICULAR AXIS
WO2014202683A1 (en) * 2013-06-19 2014-12-24 Behr-Hella Thermocontrol Gmbh Heating device

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US3936625A (en) * 1974-03-25 1976-02-03 Pollutant Separation, Inc. Electromagnetic induction heating apparatus
FR2694994A1 (en) * 1992-08-24 1994-02-25 Electricite De France Electric induction appts. for heating conducting corrosive fluid e.g. acid used for cleaning of metallic article - using insulated tank which encloses limb of magnetic yoke energised by alternating current winding
JPH0729673A (en) * 1993-07-13 1995-01-31 Fuji Electric Co Ltd High frequency electromagnetic induction heater

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US1362622A (en) * 1920-04-26 1920-12-21 Gen Electric Electric heater
US3936625A (en) * 1974-03-25 1976-02-03 Pollutant Separation, Inc. Electromagnetic induction heating apparatus
FR2694994A1 (en) * 1992-08-24 1994-02-25 Electricite De France Electric induction appts. for heating conducting corrosive fluid e.g. acid used for cleaning of metallic article - using insulated tank which encloses limb of magnetic yoke energised by alternating current winding
JPH0729673A (en) * 1993-07-13 1995-01-31 Fuji Electric Co Ltd High frequency electromagnetic induction heater

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2821647A1 (en) * 2001-03-02 2002-09-06 Robert Lipp OMNIDIRECTIONAL SUBMERSIBLE HYDRAULIC TURBINE WITH PERPENDICULAR AXIS
WO2014202683A1 (en) * 2013-06-19 2014-12-24 Behr-Hella Thermocontrol Gmbh Heating device
CN105284185A (en) * 2013-06-19 2016-01-27 贝洱海拉温控系统公司 heating equipment
CN105284185B (en) * 2013-06-19 2017-10-31 贝洱海拉温控系统公司 heating equipment

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DE69619285D1 (en) 2002-03-28
JPH08315971A (en) 1996-11-29
DE69619285T2 (en) 2002-11-21
EP0732866B1 (en) 2002-02-20
FR2731868B1 (en) 1997-06-06
FR2731868A1 (en) 1996-09-20
CA2171788A1 (en) 1996-09-17

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