ES2409739T3 - Cuba furnace heated electrically - Google Patents

Abstract

Tank furnace (5, 10) electrically heated for melting reduction by induction heating with at least one inductor (12), the inductor (12) being formed of graphite composite electrical conductors, and in which the tank furnace ( 5, 10) comprises an inner lining (11) of refractory material and presents in its inner surface grooves (20) in which conductors formed of graphite are provided.

Description

Cuba furnace heated electrically.

The invention relates to an electrically heated bowl oven with at least one heating element formed of electrical conductors.

In WO 2006/079132 A1 a procedure and a device for the reduction of slag or vitrified slag with content of metal oxides and / or degassing of mineral laundry have been proposed, in which the molten slags have been fed to a bed of inductively heated coke. In this case, the load has been supplied to a vat furnace and the coke bed inductively heated to temperatures that ensure that until the end of the sangria a casting is formed or the melting temperature is maintained. By means of the use of inductively heated coke, a bed with a high reduction potential was made available, so that it has been possible to easily reduce the oxidic slags or loaded with organic substances and metallurgical powders also with high slag contents. chrome oxide or vanadium oxide. Inductively heated ovens are also known as crucible furnaces. In the case of electrically heated ovens, the electrical resistance of the laundry and the application of electrical energy by means of the electrodes immersed in the laundry are generally used. For inductive heating, copper coils had already been proposed, with induction heat transmission only being successful with high efficiency when only short distances should be covered between the induction coil and the medium to be inductively heated. In the case of castings, this means that the corresponding heat is also radiated to the induction coils, so that in the case of copper windings, water-cooled copper tubes have been proposed as conductors. However, water-cooled conductors have a considerable loss of power.

Document DE 2 235 706 discloses a dome oven for the production of a metal casting, the dome oven comprising an overheating chamber, in which a coating containing graphite content is provided in which they are located arranged induction coils cooled by which the existing load material in the superheating chamber is heated. Similar furnaces are known from JP 06-074.653 A, WO 2006/079132 A1 and US document

2,122,241.

By CN 86-108.553 a furnace for the fusion of metals and alloys is disclosed, this furnace being equipped with an inductive heating whose inductor is composed of a graphite tape. In this case, the graphite tape is arranged behind a graphite jacket provided behind an electrical insulation.

However, the invention proposes to create a configuration for the electric heating of a vat furnace in which with a low loss of power it is possible to introduce high frequency energy or, optionally, to perform other forms of electric heating and with which it is It is possible to avoid the complicated water cooling provided in the current state of the art.

To achieve this objective, an electrically heated vat furnace for melting reduction is made available by induction heating with at least one inductor, the inductor being configured of graphite composite electrical conductors, and in which the vat furnace comprises an inner lining of refractory material and has grooves on its inner surface in which conductors formed of graphite are provided. The graphite selection for the driver, and with it for the inductor, results here in the use of a refractory material that no longer requires complicated cooling. The conductivity of graphite increases with increasing temperature, so that a corresponding stepped heating appears to be advantageous, for which, for example, at the beginning the conductor can also be connected in the manner of a resistance heater.

Particularly advantageously, the inductor can be formed of rings or annular segments of graphite or, alternatively, of graphite bars.

Graphite generally has less than half the conductivity of copper, so graphite inducers or correspondingly larger graphite conductor sections must be provided. In accordance with the present invention, this is achieved because the configuration is such that the inner lining of the vat furnace is made of refractory material and on its inner surface it has grooves, in particular grooves in the form of helical lines for the accommodation of conductor tracks. formed of graphite. In this case, the conductive layer

or the graphite rings can be incorporated directly into the refractory lining of the vat furnace, the graphite itself being an excellent refractory material and which remains undeformable, even at very high temperatures. Because in the case of inductive heating, induction losses increase in the square of the distance between the inductor and the material to be coupled, for example a coke bed, induction losses can be minimized by incorporating the conductor directly to the refractory material, whereby only a corresponding electrical insulation between a coke bed and the inductor is necessary, for which, however, particularly simple measures are sufficient.

In this case, the configuration is advantageously adopted so that the inner lining is covered with a refractory material or insulating sheet or mat, the refractory material and / or insulating layer being formed, preferably, of MgO or Al2O3. Alternatively to this use of a sheet, with correspondingly narrow grooves and an appropriate sizing of the conductor tracks or of the graphite rings with, simultaneously, an appropriate particle size of the coke load, it is possible to proceed so that the depth of the grooves in the lining are chosen greater than the width of the conductor tracks or graphite rings and the radial distance of the conductor tracks of the shaft or the inner diameter of the graphite rings is chosen greater than the inner diameter of the furnace liner from Cuba.

In a particularly simple way, the electrical connection to the conductor tracks is achieved when the graphite rings are configured open in their circumference and the free ends of the rings are applicable in parallel or in series to a current source. In this case, the configuration can be carried out, advantageously, in such a way that the conductor paths are composed of rammed graphite powder or electroconductive substances, in particular provided with thermally dissociating salts.

Alternatively to the described configuration, in which the inductor is formed of carbon pathways along a helical line or in the form of a circular ring, the configuration can be carried out particularly easily so that the inductor is formed of graphite bars . In this case, the configuration is preferably adopted so that the bars are essentially arranged parallel to the axis of the tubular tub furnace, the cuvette furnace being configured cylindrical and a plurality of bars arranged on a concentric circle to be found. axis. In this configuration it is possible to work with graphite bars such as those also used as electrodes in electric furnaces. The corresponding electrode material can be graphitized and stands out for extremely high stability, even mechanical. The arrangement of such bars parallel to the axis of a Cuba furnace allows, to top it off, to perform any circuit of these bars, the configuration being able to be carried out, advantageously, such that the bars are connected, in each case, at one end with the adjacent end of a contiguous bar in the circumferential direction of the vat furnace. In such a configuration, it is advantageously possible to connect adjacent bars, the bars being able to be optionally connected to each other or separated from the current source. Therefore, seen in a circumferential direction, it is possible to operate different bars connected in series or in parallel, being able, to top it off, individual bars or groups of bars with different frequencies can be used for inductive heating.

The design as a tank furnace in which the entire lining has inductive heating elements with which it is possible to carry out extremely high temperatures without problems allows, in this case, especially preferred uses of a bowl oven of this type. According to the invention, such a preferred use is that the Cuba furnace is used for the smelting of silicon, silicon carbide, silicon iron or phosphorus.

In principle, a conductor formed of carbon or graphite is suitable for use in an extremely large range of frequencies, producing in the case of direct current or alternating current with frequency f = 0 a purely conductive heating of the graphite conductor pathway, in particular bars or annular segments, due to ohmic resistance. When alternating current is applied, resistance heating or induction heating of the load material will take place, depending on the frequency of the alternating current, for example a coke bed or, in the case of a crucible, an iron casting, being the use of graphite as a particularly advantageous conductor where neutral even reductive conditions prevail. Here is a possible example of application induction smelting furnaces in which alloys of high melting steel are melted under vacuum or inert gas. Regarding water-cooled copper coils, in this case, the potential danger of explosion is eliminated, because in the case of leakage points the water outlet can produce detonating gas, and there may be, in addition, a diffusion of hydrogen in the steel casting. The use of highly refractory conductive material allows the conductor temperature to be selected essentially equal to the temperature of the material to be treated, thereby increasing the conductivity significantly. Another increase in conductivity at high temperatures is achieved, as already mentioned above, by the addition of thermally dissociating metal salts which, at high temperatures, are very good conductors.

The electrically heated tub furnace according to the invention is operated as an induction furnace, being able, in the case of electro-conductive loads and, in particular, in the case of a coke bed or a crucible with steel casting, to carry out temperature problems without problems. about 2300 ° C. In a reducing atmosphere, graphite remains non-deformable up to temperatures of approximately 3400 ° C.

In the following, the invention is explained in detail by means of an embodiment of a tub furnace schematically represented in the drawing. In it, Figure 1 shows a plan view of an open graphite ring, Figure 2 a sectional representation in the direction of arrow II-II of Figure 1, and Figure 3 a sectional representation in the direction of the arrow III - III of figure 1. The sectional representation according to figures 2 and 3 shows, in this case, only in section half of the vat furnace. Figure 4 shows an axial section through a modified configuration of the tub furnace with rod-shaped inductor, Figure 5 a section according to line V, V of Figure 4 not according to the invention, Figure 6 a modified configuration in a representation corresponding to figure 5 not according to the invention, and figure 7 a cross section through a modified configuration with extended conductor tracks parallel to the axis.

In figure 1 an open graphite ring is designated with 1 whose free ends flow into front faces 2 and 3. By means of these front faces 2 and 3, the open graphite rings can be contacted electrically and applied, correspondingly, by current continuous, alternating current of low frequency or alternating current of high frequency.

In the representation according to figure 2, in each case, the contact faces 3 can be seen which, in graphite rings arranged one above the other in the direction of the axis 4 of the bowl furnace 5, are connected to each other. In this case, as it turns out in combination with the representation according to figure 3, in the sector the graphite rings are connected in series, while in the sector b two graphite rings are operated in parallel with each other.

In the representation according to figure 3, the front faces 2 of the open rings can be seen respectively. In combination with the representation of figure 2 with the front faces 3, it is therefore that in the sector a current is applied to the lower front face 2 and then the contact with the graphite ring 1 follows by means of the adjacent front faces 3 in the vertical direction, after which, on the other hand, rotated at an angle of approximately 180 °, a contact of adjacent front faces 2 is produced to achieve a serial connection of the rings. In this case, low frequency alternating current can be supplied via connections 6 and 7. For the supply of high frequency alternating current and, in particular, for the application of frequencies of more than 60 kH, specifically up to approximately 350 kHz, a parallel connection is convenient, such as that seen in the axial sector b, the respective connections indicated here with 8 and 9, and there are, respectively, two consecutive rings 1 in axial direction connected in parallel. A parallel connection of this type produces a reduction in the voltage required in the case of inductive heating, so that the potential for risk and discharge decreases.

In principle, the configuration by means of the axial height of the bowl furnace 5 can be chosen flexibly and, optionally, a parallel connection or a serial connection can be made in different axial widths to take into account the temperature profiles required in each case.

Figure 4 shows a cross section through a bowl furnace 10 in whose refractory lining 11, heating elements 12 in the form of bars have been incorporated. In this case, the heating elements 12 in the form of bars are formed of graphite bars. The contiguous ends of such graphite bars 12 may, in each case, be connected to each other, optionally, by means of conductive connections 13 at one end and conductive connections 14 at the other end of the bars, whereby it is possible to make a serial connection of three graphite bars 12 arranged adjoining. The ends of the total resistance and the total inductivity achieved by this series connection can be used both as inductive heating with alternating current connection, and for conductive heating with direct current connection. The connection of the different bars results, in this case, from the sectional representation according to Figure 7, and a graphite bar cage can be configured as a whole, the different bars of the cage being able to be connected in parallel or in series.

The slightly modified configuration according to Figure 6, whose representation corresponds, essentially, to the representation of Figure 5, allows a multilayer structure of the coating to be recognized and is preferably used at maximum temperatures to cause graffiti reactions. In this case, the heating elements 12 are coated with a first graphite cover, this first coating 15 being able to be composed of individual segments. In this case, the graphite bars or independent graphite electrodes can, if necessary, be swept, if necessary, by inert gas, for which input openings are provided

16.

 The graphite jacket 15 is wrapped externally by another lining of refractory material, designated with

17.

 Such a configuration can be used, for example, for the graphitization of carbon rods, as indicated schematically, by a coke extrudate 18 that can be transported through the bowl furnace in the direction of arrow 19. At an appropriately high temperature and a corresponding residence time, coke extrusion graffiti 18 can be achieved, in addition to continuous cooking, whereby carbon crystallization occurs in coke extrudate 18.

Figure 7 shows, schematically, different examples of application of the vat furnace, with a modified configuration of the vat furnace being provided again. In the lining 11 of refractory material, in this case, grooves or grooves 20 formed with shapes of dovetails and housing the conductor tracks and / or graphite bars 21 are provided. In this case, the inner surface of this Graphite bar or conductor track is a greater radial distance from the axis 22 of the Cuba furnace than the inner wall 23 of the refractory lining, so that in the case of the use of a coke bed for melting reduction, a Direct conductor contact between the coke bed and the graphite bar. A food of this type or an application of this type of a coke bed is sketched by pieces of coke. Alternatively, as shown in a cross section in another segment of the bowl oven, it is possible to produce a laundry and use the bowl oven as a crucible for steel casting. In this case, the laundry is indicated, schematically, with 24. In another section 25, which clarifies another possible use of the vat furnace, the procedure can be used in such a way that a graphite heat exchanger, indicated with reference 25 , is applied for the production of three component slag.

Claims (15)

one.

Tank furnace (5, 10) electrically heated for melting reduction by induction heating with at least one inductor (12), the inductor (12) being formed of graphite electrical conductors, and in which the furnace Cuba (5, 10) comprises an inner lining (11) of refractory material and has grooves (20) on its inner surface in which conductors formed of graphite are provided.

2.

Tank furnace according to claim 1, characterized in that the inductor (12) is formed of graphite conductors arranged circumferentially in the form of rings, ring segments (1) or in a helical line.

3.

 Tank furnace according to claim 1, characterized in that the inductor is formed of graphite bars (12).

Four.

Tank oven according to claim 3, characterized in that the graphite bars (12) are arranged parallel to the axis (22) of the tubular tank oven (5, 10).

5.

Tank oven according to claims 3 or 4, characterized in that the tank oven (5, 10) is configured cylindrical and a plurality of graphite bars (12) are arranged on a concentric circle to the shaft (22).

6.

Tank furnace according to one of claims 1 to 5, characterized in that the grooves are made as helical grooves.

7.

Tank furnace according to one of claims 1 to 6, characterized in that the inner jacket (11) is covered with a refractory layer or sheet or insulating mat (17).

8.

Tank furnace according to claim 7, characterized in that the refractory material and / or the insulating layer is formed of MgO, Al2O3 or chamotte.

9.

Tank furnace according to claim 2, characterized in that the graphite rings (1) are configured open in their circumference and the free ends (2, 3) of the graphite rings (1) are applicable in parallel or in series to a source of current.

10.

Tank furnace according to one of claims 1 to 9, characterized in that the conductor tracks are composed of rammed graphite powder or provided with electroconductive substances.

eleven.

Tank furnace according to claim 10, characterized in that the conductor paths are provided with thermally dissociating substances.

12.

Tank furnace according to one of claims 1 to 11, characterized in that the depth of the grooves (20) in the coating (11) is greater than the width of the conductor tracks (21), preferably of the graphite rings (1 ), and the radial distance of the conductor tracks (21) from the shaft (22), preferably the inner diameter of the graphite rings (1), has been chosen greater than the inner diameter of the liner (11) of the bowl furnace (5, 10).

13.

Tank furnace according to one of claims 3 to 5, characterized in that the graphite bars (12) are connected, in each case, at one end with the adjacent end of a graphite bar (12) contiguously circumferential to the furnace of Cuba.

14.

Tank furnace according to claim 13, characterized in that the connection of adjacent graphite bars (12) is switchable and the graphite bars (12) can optionally be connected to each other or separated with the current source.

fifteen.

 Use of a bowl oven according to claims 1 to 14 for the reductive fusion of Si, SiC, FeSi or P.