EP0660645A1 - Induction heating apparatus for a fluid - Google Patents

Abstract

The invention relates to a device for heating by induction of an electrically conductive fluid (10). According to the invention, the said device comprises: - a closed magnetic circuit (100), - at least one inductor consisting of a winding (200), arranged around the magnetic circuit and supplied with an alternating electric voltage, in such a way that the said inductor generates a magnetic flux in the magnetic circuit, - at least one chamber (300), made of insulating material, containing the fluid to be heated and surrounding each inductor, - a medium-frequency converter supplying each inductor, and - means for causing the converter to resonate. Application to heating fluids of corrosive nature having a conductivity greater than 1 siemens/metre. <IMAGE>

Description

The present invention relates to an induction heating device for an electrically conductive fluid.

The invention finds a particularly advantageous application in the field of metallurgy, of the steel industry, of chemistry, or also of the food industry, for the heating of fluids of corrosive nature.

In the metallurgy and steel industry, acids or mixtures of acids are used in particular for pickling metal parts. In order to increase the effectiveness of acid-based or acid-mixture strippers, it is necessary to heat these products to temperatures generally between 35 and 95 ° C. Likewise, in the field of chemistry , acid or basic solutions are very often used at temperatures above room temperature. For example, the distillation of a mixture of chemical constituents in solution is obtained by heating said mixture to the boiling temperature of the mixture. Finally, in the food industry, it is necessary to heat solutions during cooking and / or pasteurization and sterilization operations.

Various induction heating devices are already known, none of which is satisfactory in the envisaged application.

In particular, an electromagnetic heating device is known which makes it possible to heat fluids having a very high electrical conductivity. This known device comprises a solenoid supplied by a periodic current at very high frequency and surrounding a tank containing the fluid to be heated. This fluid is then the seat of induced currents which cause the heating of said fluid. The major drawback of such a device is that it is very inefficient.

Indeed, very conductive fluids have a low electrical conductivity compared to metals, and the intensity of the induced currents must be very high to heat said fluids. Knowing that the intensity of the induced current is all the more important as the variations of the inductor current are faster, said device must implement inductor currents at very high frequencies of the order of 0.1 to 10 MHz obtained by using high frequency converters which have low efficiencies of the order of 50 to 60%. In addition, the inductive electric currents flowing in the solenoid being large, they cause significant losses. Ultimately, this known heating device must use a large electromagnetic energy to generate a very low active heating energy.

Documents FR-A-1 600 320 and FR-A-516 444 are known, electric induction furnaces which are not suitable for heating fluids and in particular fluids of a corrosive nature.

Finally, document DE-C-318 484 discloses a device comprising a transformer, a primary formed by a winding supplied with alternating current and surrounding a branch of the transformer, and a secondary formed by a water circulation pipe in the form a spiral wrapped around another parallel branch of the transformer. The spiral pipe is made of an insulating material and is closed on itself.

This device has several drawbacks.

First of all, such a device is not suitable for operating on an industrial scale where the rates are high since the quantity of water which it makes it possible to heat during a heating cycle is relatively small. because it is limited to the dimensions of the spiral water circulation pipe. In addition, the dimensions of the transformer do not allow operation at frequencies of the order of several hundred Hertz. Finally, this device causes significant electrical losses.

Also, the invention provides an induction heating device which makes it possible to heat a large quantity of a current conducting fluid. This device operates at medium frequency, that is to say a few hundred Hertz and uses a more efficient frequency converter, which makes it possible to reduce the intensity and the current losses, as well as the proportion of l magnetic energy required relative to the heating energy obtained.

• un circuit magnétique,
• au moins un inducteur constitué par un bobinage disposé autour du circuit magnétique et alimenté par une tension électrique alternative de telle sorte que ledit inducteur engendre un flux magnétique dans le circuit magnétique,
• au moins une cuve réalisée en matériau isolant, contenant le fluide à chauffer et entourant chaque inducteur,
• un convertisseur de moyenne fréquence alimentant chaque inducteur, et des moyens de mise en résonance du convertisseur.

More specifically, the invention proposes a heating device which comprises:

• a magnetic circuit,
• at least one inductor constituted by a coil arranged around the magnetic circuit and supplied with an alternating electric voltage so that said inductor generates a magnetic flux in the magnetic circuit,
• at least one tank made of insulating material, containing the fluid to be heated and surrounding each inductor,
• a medium frequency converter supplying each inductor, and means for resonating the converter.

Thus, according to the invention, said device comprises a magnetic circuit which makes it possible to channel and transport the magnetic flux created in the inductor. As a result, it makes it possible to reinforce the effect of the inductor and to generate a f.e.m (electromotive force) induced large enough in said fluid to heat it. By concentrating the magnetic field lines created by the inductor in said closed magnetic circuit, the current losses and therefore the intensity of the necessary inductive current are considerably reduced. Therefore, said heating device according to the invention operates at medium frequency using an efficient frequency converter having an efficiency of the order of 85 to 95%. In addition, the device according to the invention is more compact. Finally, the tank made of insulating material makes it possible to heat a large quantity of water at a time.

It is interesting to note that the magnetic circuit and the inductor are immersed directly in the fluid to be heated and that the tank does not participate in the heating at all.

This is a concept completely different from that of document DE-C-318 484 which envisaged only the transformer circuit and caused the fluid to be heated to pass through the secondary winding of the transformer.

The tank can advantageously consist of a material inert from the magnetic point of view, such as PTFE (Polytetrafluoroethylene) or PVDF (Polyvinyldifluorinated) or even glass.

According to one embodiment of the device according to the invention, the magnetic circuit is in the form of a frame comprising separable parts including a head and the means for resonating the converter are shims interposed between the head and the other parts carrying each magnetic circuit inductor.

According to an alternative embodiment of the device according to the invention, the means for resonating the converter consist of an inductor placed outside the magnetic circuit, in parallel with the converter to which it is connected.

According to one embodiment of the invention, said magnetic circuit is in the form of a frame having two substantially parallel heating columns, around which two inductors and two tanks are placed respectively.

In addition, according to the invention, in order to channel with better efficiency the magnetic flux created by the winding, it is advantageous for the closed magnetic circuit in the form of a frame having three columns, two lateral columns of section S and one central column of double section of said section S, among which is at least one column around which are placed a winding and a tank.

Similarly, according to another embodiment of the device according to the invention, the magnetic circuit comprising a central column having a section S₁ and a plurality of n peripheral columns arranged radially and having a section n times smaller than said section S₁, said magnetic circuit comprising among said columns at least one column around which are placed a coil and a tank.

• La figure 1 est un schéma en perspective d'un premier mode de réalisation d'un dispositif selon l'invention.
• La figure 2 est une vue en coupe selon le plan A-A du dispositif de la figure 1.
• La figure 3 est un schéma en perspective d'un circuit magnétique muni d'un bobinage d'un deuxième mode de réalisation d'un dispositif selon l'invention.
• La figure 4 est une vue en coupe selon le plan B-B du dispositif de la figure 1.
• La figure 5 est une vue partielle de dessus d'un troisième mode de réalisation du dispositif selon l'invention.
• La figure 6 est une vue en coupe selon le plan C-C du dispositif de la figure 5.
• La figure 7 est un schéma en perspective d'un quatrième mode de réalisation du dispositif selon l'invention.
• La figure 8 est une vue en coupe selon le plan D-D du dispositif de la figure 7.
• La figure 9 est une vue partielle de dessus d'un cinquième mode de réalisation du dispositif selon l'invention.
• La figure 10 est une vue partielle de dessus d'un sixième mode de réalisation du dispositif selon l'invention.

The description which follows with reference to the appended drawings, given by way of nonlimiting examples, will make it clear what the invention consists of and how it can be implemented.

• Figure 1 is a perspective diagram of a first embodiment of a device according to the invention.
• FIG. 2 is a sectional view along the plane AA of the device in FIG. 1.
• Figure 3 is a perspective diagram of a magnetic circuit provided with a coil of a second embodiment of a device according to the invention.
• FIG. 4 is a sectional view along the plane BB of the device of FIG. 1.
• Figure 5 is a partial top view of a third embodiment of the device according to the invention.
• FIG. 6 is a sectional view along the plane CC of the device in FIG. 5.
• Figure 7 is a perspective diagram of a fourth embodiment of the device according to the invention.
• FIG. 8 is a sectional view along the plane DD of the device in FIG. 7.
• Figure 9 is a partial top view of a fifth embodiment of the device according to the invention.
• Figure 10 is a partial top view of a sixth embodiment of the device according to the invention.

(où f est la fréquence), de telle sorte que ledit inducteur engendre un champ magnétique

dans ledit circuit magnétique 100, le flux magnétique résultant s'exprimant comme le produit scalaire φ = NBS (où S est la section de la colonne, ici la section du cadre magnétique).FIG. 1 shows a device for heating an electrically conductive fluid 10 having a conductivity greater than 1 Siemens / meter. This heating device comprises a magnetic circuit 100 closed in the form of a frame, here a square frame of section S, comprising two columns 101, 102 substantially parallel. In addition, the heating device comprises two inductors constituted by two coils 200, arranged respectively around the two columns 101, 102 of the magnetic circuit. The windings 200 comprising N turns, are supplied by a frequency converter not shown delivering a voltage of amplitude U varying periodically over time at a pulsation $\text{ω = 2π f}$

(where f is the frequency), so that said inductor generates a magnetic field

in said magnetic circuit 100, the resulting magnetic flux expressed as the scalar product φ = NBS (where S is the section of the column, here the section of the magnetic frame).

Ainsi, on peut ajuster en conséquence le circuit magnétique 100 aux caractéristiques du convertisseur de fréquence et du fluide à chauffer, et réciproquement.The aforementioned parameters N, U, ω, B, and S satisfy the relation expressed as follows:

Thus, the magnetic circuit 100 can be adjusted accordingly to the characteristics of the frequency converter and of the fluid to be heated, and vice versa.

Furthermore, the device comprises two tanks here of parallelepiped shape, made of an insulating material, such as PTFE or glass, containing the fluid 10 to be heated. The two tanks respectively surround the two columns 101, 102 of the magnetic circuit in such a way that the magnetic circuit heats the fluid by creating in the fluid 10 induced currents. The magnetic circuit channels the magnetic flux created in each inductor, and generates an induced fem in the fluid 10. The fluid 10 conducting current, in which each column 101, 102 is immersed behaves like a resistor. When said fluid 10 is crossed by the induced currents, it heats by Joule effect.

As can be seen in Figure 1, the columns 101, 102 are separable from the other parts of the closed frame and more particularly from the upper part 103, called the head. Thus, such an assembly makes it possible to introduce, without difficulty, the windings 200 and the tanks 300 containing the fluid 10, respectively around the two columns 101, 102. In addition, the frequency converter operating at resonance conditions, this assembly allows spacers, not shown in Figure 1, to be interposed between the head 103 and the rest of the magnetic circuit. These shims represent means for resonating said frequency converter. Indeed, the assembly constituted by the inductors, the magnetic circuit and the fluid behaves like an electrical circuit composed of an inductance L in series with a resistance R, and the frequency converter consists of a voltage source parallel with a capacitor C. The electrical diagram representative of the device shown in Figure 1, consists of the voltage source paralleled simultaneously with the capacitor C and the inductor L in series with the resistor R.

ou encore $\text{Lω / R > 2}$

, où le produit Lω est appelé la réactance. Dans le cas où le rapport Lω / R est inférieur à 2, lesdites cales permettent alors d'ajuster la réactance Lω dudit dispositif pour retrouver la condition de résonance $\text{Lω / R > 2}$

et assurer le fonctionnement dudit convertisseur de fréquence.Thus, the resonance conditions of the frequency converter is expressed as $\text{LCω² = 1}$

or $\text{Lω / R> 2}$

, where the product Lω is called the reactance. In the case where the ratio Lω / R is less than 2, said shims then make it possible to adjust the reactance Lω of said device to regain the resonance condition $\text{Lω / R> 2}$

and ensuring the operation of said frequency converter.

Furthermore, said frequency converter is an efficient medium frequency converter with thyristors or transistors, having a yield of between approximately 85 and 95%.

According to an alternative embodiment, it is possible to envisage as means for bringing the converter into resonance, another inductor placed outside the magnetic circuit in parallel with the converter to which it is connected.

To use the device of Figure 1 at low frequencies between about 250 HZ and 6 kHZ, the magnetic circuit 100 is constituted by magnetic sheets, such as silicon sheets, preferably having small thicknesses between 0.1 and 0.35 millimeter, so as to minimize the heating of said transformer. For higher frequencies, for example greater than 3 kHZ, said magnetic circuit consists of ferrites. In both cases, in order to prevent the magnetic circuit 100 from heating up, the latter includes a cooling circuit.

As best shown in FIG. 2, said cooling circuit includes “heat pumps” constituted by copper plates 110 cooled on the banks using copper pipes 111 traversed by water 112. For a circuit magnetic constituted by magnetic sheets, these "heat-pullers" are arranged parallel to said magnetic sheets.

In Figure 3, there is shown a second embodiment of a magnetic circuit 100 'forming part of a heating device according to the invention. This magnetic circuit 100 'closed in the form of a frame, has three columns 101', 102 ', 103', two lateral columns 101 ', 103' of section S and a central column 102 'having a section 2S double of said section S. Among the three columns 101 ′, 102 ′, 103 ′ is a column 102 ′ carrying a coil 200. This circuit with three columns makes it possible to channel with better efficiency the magnetic flux created by the coil 200.

As will be seen in detail later, it is possible to envisage, according to another embodiment, an electric induction heating device comprising a magnetic circuit comprising a central column of section S centrale and a plurality of n peripheral columns arranged radially and having a section n times weaker than section S₁. This magnetic circuit has several columns, each carrying an inductor, and care must be taken to ensure that the magnetic fluxes created by the inductors add up well.

In Figure 4, there is shown in detail an example of flow of the fluid 10 to be heated, around the column 102 of said heating device of Figure 1. From a fluid supply line not shown, we creates, using a nurse 130 placed in the tank 300, two flow veins 10 _a , 10 _{b of} said fluid 10 around said column 102, substantially perpendicular to said column. These two flow streams in parallel, converge at the outlet 120 of said tank 300 towards a collector not shown.

As can be seen in FIG. 4, the induced currents flow in said fluid according to arrow i, in the direction of flow of said fluid.

In FIGS. 5 and 6, the flow of the fluid 10 has been shown around the columns 101, 102 of the magnetic circuit of FIG. 1. Likewise, the flow of the fluid is substantially perpendicular to the said columns and has a distribution in three veins fluid flow 10 _a , 10 _b , 10 _c in parallel, perpendicular to said columns. In this case, the distribution is carried out using a reservoir 20.

Furthermore, as can also be seen in FIGS. 5 and 6, the induced currents flow in the fluid according to the arrows i representing the direction of the flow of the fluid 10.

In FIGS. 7 and 8, an alternative embodiment has been shown according to which each tank 300 has a cylindrical shape and comprises in the lower part an inlet 301 of the fluid 10 and in the upper part an outlet 302 of the said fluid 10, so as to create a cylindrical flow stream of the fluid substantially parallel to each column 101, 102.

Similarly, in FIG. 9, another variant of the embodiment of the device in FIG. 7 has been shown.

As can be seen in FIG. 9, the tank 300 has a substantially cylindrical shape, comprising two recesses so as to surround the two columns 101, 102.

According to the alternative embodiment presented in FIG. 9, the tank also comprises means for entering and leaving the fluid 10, not shown, so that the fluid 10 flows in two substantially cylindrical flow streams parallel respectively to said columns 101, 102.

It should be noted that the devices of FIGS. 7, 8 and 9 have a heating efficiency which can reach 85%.

FIG. 10 shows another embodiment of the heating device, comprising a central column 104 _a and three peripheral columns 101 _a , 102 _a , 103 _a , arranged radially. Said peripheral columns have a section S, and the central column then has a section equal to three times said section S. All the columns carry a winding.

In addition, said device comprises a tank comprising four recesses surrounding the four columns and containing the fluid 10.

Of course, the present invention is in no way limited to the embodiment described and shown, but a person skilled in the art will know how to make any variant which conforms to his spirit.

Claims (9)

Induction heating device for an electrically conductive fluid (10), characterized in that it comprises: - a closed magnetic circuit (100), - at least one inductor constituted by a coil (200) arranged around the magnetic circuit (100) and supplied by an alternating electric voltage, so that said inductor generates a magnetic flux in the magnetic circuit (100), - at least one tank (300) made of insulating material, containing the fluid (10) to be heated and surrounding each inductor (200), - a medium frequency converter supplying each inductor, and - means for resonating the converter. Heating device according to claim 1, characterized in that the magnetic circuit (100) is in the form of a frame comprising separable parts (101, 102, 103, 104) including a head (103), and in that the means for resonance of the converter are shims interposed between the head (103) and the other parts (101, 102) carrying each inductor (200) of the magnetic circuit (100). Heating device according to claim 1, characterized in that the means for resonating the converter consist of an inductor placed outside the magnetic circuit (100), in parallel with the converter to which it is connected. Heating device according to any one of claims 1 to 3, characterized in that it comprises a cooling circuit (110, 111, 112) of said magnetic circuit (100). Heating device according to any one of claims 1 to 4, characterized in that each tank (300) has means for entering and leaving said fluid (10) in said tank (300) so as to create a flow around of each inductor (200). Heating device according to any one of Claims 1 to 5, characterized in that the magnetic circuit is in the form of a frame having two substantially parallel heating columns (101, 102) around which two inductors (200) and two are placed respectively. tanks (300). Heating device according to any one of claims 1 to 5, characterized in that the magnetic circuit (100 ') closed in the form of a frame has three columns (101', 102 ', 103'), two lateral columns (101 ' , 103 ') of section S and a central column (102') of double section of said section S, among which is at least one column around which are placed an inductor (200) and a tank (300). Heating device according to any one of Claims 1 to 5, characterized in that the said magnetic circuit comprising a central column having a section S₁ and a plurality n of peripheral heating columns arranged radially and having a section n times smaller than the said section S₁ said magnetic circuit comprising among said columns at least one column around which are placed a coil and a tank. Heating device according to any one of Claims 4 to 8, characterized in that the cooling circuit consists of copper plates (110) cooled on the banks using pipes (111) traversed by water (112).

Images