FR2694994A1 - 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 - Google Patents

Abstract

A conducting fluid (10) is carried within a tank (300) made from an insulating material such as glass. The tank (300) surrounds one leg (102) of a magnetic yoke (100) which is energised by a winding (200) fed from a frequency convertor. Packing pieces may be introduced into the magnetic circuit which alter its effective inductance and allow the frequency convertor to produce resonance. The varying magnetic flux in the yoke (100) induces currents in the liquid contained in the tank (300) and these heat the liquid by the Joule effect. ADVANTAGE - The equipment functions at medium frequency enabling a more efficient frequency converter to be used and losses to be minimised.

Description

 The present invention relates to an electric heating device by induction of an electrically conductive fluid.

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

 In the metallurgy-steel industry, acids or mixtures of acids are used in particular for pickling metal parts.

In order to increase the effectiveness of the acid-based or acid-mixture strippers, it is necessary to heat these products to temperatures between approximately 35 and 950C, or more depending on the case. Likewise, in the field of chemistry, acid or basic solutions are very often used at temperatures above ambient temperature. For example, the distillation of a mixture of chemical constituents in solution is obtained by heating said mixture to a boiling temperature of the mixture. Finally, in the food industry, it is necessary to heat solutions during cooking and / or pasteurization-sterilization operations.

 Currently, various electrical heating devices are known from the state of the art, none of which is satisfactory.

 Thus, an indirect electric heating device is known comprising a heated metal wall and placed in contact with the fluid to be heated, said heated wall then forming a heat exchange surface making it possible to heat said fluid.

 A major drawback of such a known device lies in the fact that the fluid in contact with the metal wall is brought to a temperature higher than that desired. In the case where the products to be heated are particularly sensitive to high temperatures, such as, for example, food products, this overheating leads to deterioration of the heated products.

 In addition, a direct electric heating device is known, comprising two metal electrodes immersed in the fluid to be heated and connected to a current generator, thus making it possible to heat the fluid, playing the role of resistance, by conduction of the current. The disadvantage of such a device is that it cannot be used to heat corrosive fluids with regard in particular to metals. Indeed, these corrosive fluids tend to attack said metallic electrodes and destroy them.

 Finally, there is known an electromagnetic heating device for heating fluids having a very high electrical conductivity. This known device comprises a solenoid supplied by a periodic current at very high frequency and in which the fluid to be heated is placed. 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 and expensive.

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 inducing current are faster, said device must implement inducing currents at very high frequencies of the order of 0.1 to 10
MHZ using high frequency converters with low efficiency of the order of 50 to 60%. In addition, the inductive electric currents flowing in the solenoid being large, they generate significant losses. Finally, this known heating device must use a large electromagnetic energy to generate a very low active heating energy.

 Also, the technical problem to be solved by the object of the present invention is to propose an electric heating device by induction of a current conducting fluid, operating at medium frequency allowing the use of a more efficient frequency converter. , making it possible to reduce the intensity and the losses of current, as well as the proportion of the magnetic energy used compared to the heating energy obtained.

The solution to the technical problem posed consists, according to the present invention, in that the heating device comprises
- a transformer comprising a closed magnetic circuit in the form of a frame comprising at least one heating column,
at least one inductor constituted by a winding disposed around the transformer and supplied with an electric voltage which varies periodically so that said inductor generates a magnetic flux in said magnetic circuit,
- At least one tank containing said fluid to be heated, surrounding at least one transformer heating column so that said magnetic circuit heats said fluid by creating induced currents in said fluid.

 Thus, according to the invention, said device comprises a transformer 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 lines of magnetic fields created by the inductor, in said closed magnetic circuit, the current losses and therefore the intensity of the useful 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.

 According to the invention, each tank is made of an insulating material.

 Indeed, the heating column of said transformer bathing directly in the fluid to be heated, the tank does not participate at all in the heating and can advantageously be constituted by a material inert from the magnetic point of view, such as PTFE (Polytetrafluoroethylene) or PVDF (Polyvinyldifluoré) or glass.

 According to one embodiment of the device according to the invention, each tank comprises means for entering and leaving said fluid in said tank so as to create at least one flow stream for said fluid around at least one column of heating, said flow stream being perpendicular to said heating column.

 According to a variant of the embodiment of the device according to the invention, each tank comprises means for entering and leaving said fluid in said tank so as to create at least one flow stream for said fluid, parallel to at least one heating column.

 According to one embodiment of the invention, said transformer comprises a closed magnetic circuit in the form of a frame having two substantially parallel heating columns, among which is at least one column around which a coil is surrounded.

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

 Similarly, according to another embodiment of the device according to the invention, said transformer comprises a magnetic circuit comprising a central heating column having a section S1 and a plurality of n peripheral heating columns arranged radially and having a section n times more weaker than said section S1, said magnetic circuit comprising among said columns at least one column around which a coil is surrounded.

 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.

 - Figure 2 is a sectional view along the plane A-A of the device of Figure 1.

 - Figure 3 is a perspective diagram of a transformer of a second embodiment of a device according to the invention.

 - Figure 4 is a sectional view along plane B-B of the device of Figure 1.

 - Figure 5 is a partial top view of the third embodiment of the device according to the invention.

 - Figure 6 is a sectional view along the plane C-C of the device of Figure 5.

 - Figure 7 is a perspective diagram of a fourth embodiment of the device according to the invention.

 - Figure 8 is a sectional view along the plane D-D of the device of Figure 7.

 - Figure 9a is a partial top view of a fifth embodiment of the device according to the invention.

 - Figure 9b is a partial top view of a sixth embodiment of the device according to the invention.

 - Figure 10 is a partial top view of a seventh embodiment of the device according to the invention.

 Referring to Figure 1, there is shown an electric heating device of an electrically conductive fluid 10 preferably having a conductivity greater than 1 Siemens / meter. This heating device comprises a transformer comprising a magnetic circuit 100 closed in the form of a frame, here a square frame of section S, comprising two substantially parallel heating columns 101, 102. In addition, the heating device comprises an inductor constituted by a winding 200, called the primary winding, arranged around a heating column 101 of the transformer. This heating column 101 comprising the inductor will be called subsequently for more understanding, induction column. On the other hand, each column not carrying the winding will remain under the designation heating column. The primary winding 200 comprising N turns, is supplied by a frequency converter not shown delivering a voltage of amplitude U varying periodically over time to a pulsation w = 2 f (where f is the frequency), so that said inductor generates a magnetic field B in said magnetic circuit 10, the resulting magnetic flux being expressed as the dot product cP = NBS (where S is the section of the induction column, here the section of the magnetic frame).

It is interesting to note that the aforementioned parameters N, U, w, B, and S satisfy the relation expressed as follows
U
NS xw x B
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 a tank made of an insulating material, such as PTFE or glass, containing the fluid 10 to be heated and surrounding said heating column 102 of the transformer so that the magnetic circuit heats the fluid by creating in the fluid 10 induced currents. More particularly, the transformer channels the magnetic flux created in the inductor, and generates an induced f.e.m in the fluid 10. The current-conducting fluid 10 in which said heating column 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 FIG. I, the induction 101 and heating 102 columns 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 primary winding 200 and the tank 300 containing the fluid 10, respectively around the induction and heating columns. In addition, the frequency converter operating at resonance conditions, this arrangement makes it possible to interpose shims, not shown in FIG. 1, between the head 103 and the rest of the magnetic circuit. These cables represent means of operation of said frequency converter, ensuring the resonance conditions required by the converter. Indeed, the assembly constituted by the inductor, the transformer and the fluid behaves like an electrical circuit composed of an inductance L in series with a resistor R, and the frequency converter consists of a voltage source put in parallel with a capacitor C. The electrical diagram representative of the device shown in Figure 1, consists of the voltage source put in parallel simultaneously with capacitor C and inductance L in series with resistor R.

Thus, the resonance conditions of the frequency converter is expressed as LC w2 = 1 or also Lw / R> 2, where the product L w is called the reactance. In the case where the ratio> LwlR is less than 2, said shims then make it possible to adjust the reactance Lw of said device to recover the resonance condition Lw / R> 2 and ensure the operation of said frequency converter.

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

 Likewise, to use the device of FIG. 1 at low frequencies between about 250 HZ and 6kHZ, said transformer 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 transformer consists of ferrites. In both cases, in order to prevent said magnetic circuit 100 from heating up, the latter includes a cooling circuit.

 As shown better in FIG. 2, said cooling circuit comprises for example "heat pullers" constituted by copper plates 110 cooled on the banks using copper pipes 111 traversed by water 112. For a transformer 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 transformer 100 'forming part of a heating device according to the invention. This transformer has a magnetic circuit 100 'closed in the form of a frame, having three heating columns 101', 102 ', 103', two lateral columns 101 ', 103' of section S and a central column 102 'having a double section 2S of said section S. Among the three heating columns 101 ′, 102 ′, 103 ′ is a column 102 ′ carrying the primary winding 200. This transformer with three columns makes it possible to channel with better efficiency the magnetic flux created by the winding primary 200.

 In this way, as will be seen in detail later, it is possible to envisage, according to another embodiment, an electric induction heating device comprising a transformer having a magnetic circuit comprising a central heating column of section S1 and a plurality of n peripheral heating columns arranged radially and having a section n times smaller than section S1.

This magnetic circuit includes at least one induction column among said columns. In the case where said magnetic circuit comprises several heating columns each carrying an inductor, care must be taken to ensure that the magnetic fluxes created by each inductor add up well.

 In Figure 4, there is shown in detail an example of flow of the fluid 10 to be heated, around the heating column 102 of said heating device of Figure 1. From a fluid supply line not shown , using a feeder 130 placed in the tank 300, two flow streams 10a, 10b of said fluid 10 are created around said heating column 102, 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.

 FIGS. 5 and 6 show the flow of the fluid 10 around the heating columns 102 and induction 101 of the transformer of FIG. 1. Likewise, the flow of the fluid is perpendicular to said heating columns and d induction and comprises a distribution in three streams of fluid flow 10a10b, 10c 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, a variant of the embodiment of the device in FIG. 4 has been shown. As can be seen in these figures, the tank 300 having a cylindrical shape, comprises in the lower part an inlet 301 for the fluid 10 and in the upper part, an outlet 302 of said fluid 10, so as to create a cyclindric flow stream for the fluid parallel to the heating column 102.

 Similarly, in FIGS. 9a and 9b, two other variants of the embodiment of the device in FIG. 5 are shown.

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

 On the other hand, in FIG. 9b, there are two tanks 300, 300 'of cylindrical shape which respectively surround the heating column 102 and the induction column 101.

 According to the two alternative embodiments presented in FIGS. 9a and 9b, the tanks also comprise means for entering and leaving the fluid 10, not shown, so that the fluid 10 flows along two streams of cylindrical flow parallel to said heating and induction columns respectively.

 It should be noted that the device in FIGS. 9a and 9b is more efficient than that in FIGS. 7 and 8, since the device in FIGS. 9a and 9b has a heating efficiency which can be equal to 85% while the device in FIGS. 7 and 8 has a yield which is 70% under the same conditions of use.

 FIG. 10 shows another embodiment of the heating device, comprising a central column 104a and three peripheral columns 110a, 102a, 103a, arranged radially. Said peripheral columns have a section S, and the central column then has a section equal to three times said section S. Among said columns 101a, 102a, 103a is at least one induction column.

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

 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.

 For example, one can imagine a variant of the embodiment of the device of FIG. 10, comprising a flow of the fluid along flow paths perpendicular to said heating and induction columns.

Claims (11)

 1. Electric heating device by induction of an electrically conductive fluid (10), characterized in that it comprises  - a transformer comprising a magnetic circuit (100) closed in the form of a frame comprising at least one heating column (102),  - at least one inductor constituted by a coil (200) disposed around the transformer and supplied with an electric voltage which varies periodically so that said inductor generates a magnetic flux in said magnetic circuit (100),  - at least one tank (300) containing said fluid (10) to be heated, surrounding at least one heating column (102) of the transformer so that said magnetic circuit (100) heats said fluid (10) by creating in said fluid (10) induced currents.  2. Heating device according to claim 1, characterized in that each tank (300) consists of an insulating material.  3. Heating device according to one of claims 1 or 2, characterized in that said device comprising a frequency converter operating at resonance conditions to supply said inductor, said device comprises operating means for ensuring said resonance conditions of the frequency converter.  4. A heating device according to any one of claims 1 to 3, characterized in that said magnetic circuit (100) consists of magnetic sheets.  5. Heating device according to any one of claims 1 to 3, characterized in that said magnetic circuit (100) is constituted by ferrites.  6. Heating device according to any one of claims 1 to 5, characterized in that it comprises a cooling circuit (110,111,112) of said magnetic circuit (100).  7. Heating device according to any one of claims 1 to 6, characterized in that each tank (300) comprises means for input and output of said fluid (10) in said tank (300) so as to create at at least one flow stream of said fluid (10) around at least one heating column (102), said flow stream being perpendicular to said heating column (102).  8. Heating device according to any one of claims 1 to 6, characterized in that each tank (300) comprises means for input and output of said fluid (10) in said tank (300) so as to create at at least one flow stream for said fluid (10), parallel to at least one heating column (102).  9. Heating device according to any one of claims 1 to 8, characterized in that said transformer comprises a magnetic circuit (100) closed in the form of a frame having two substantially parallel heating columns (101,102), among which is located at least one column (101) around which a winding (200) is surrounded.  10. Heating device according to any one of claims 1 to 8, characterized in that the transformer comprises a magnetic circuit (100 ') closed in the form of a frame having three heating columns (101', 102 ', 103') , two side 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 is surrounded a winding (200).  11. Heating device according to any one of claims 1 to 8, characterized in that said transformer comprises a magnetic circuit comprising a central heating column having a section S 1 and a plurality n of peripheral heating 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 a winding is surrounded.