CA1147785A - Three-phase arc smelting or reducing furnace - Google Patents
Three-phase arc smelting or reducing furnaceInfo
- Publication number
- CA1147785A CA1147785A CA000364912A CA364912A CA1147785A CA 1147785 A CA1147785 A CA 1147785A CA 000364912 A CA000364912 A CA 000364912A CA 364912 A CA364912 A CA 364912A CA 1147785 A CA1147785 A CA 1147785A
- Authority
- CA
- Canada
- Prior art keywords
- electrodes
- vessel
- furnace
- phase
- high tension
- 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.)
- Expired
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F27—FURNACES; KILNS; OVENS; RETORTS
- F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
- F27B3/00—Hearth-type furnaces, e.g. of reverberatory type; Tank furnaces
- F27B3/08—Hearth-type furnaces, e.g. of reverberatory type; Tank furnaces heated electrically, with or without any other source of heat
- F27B3/085—Arc furnaces
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F27—FURNACES; KILNS; OVENS; RETORTS
- F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
- F27D11/00—Arrangement of elements for electric heating in or on furnaces
- F27D11/08—Heating by electric discharge, e.g. arc discharge
- F27D11/10—Disposition of electrodes
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Vertical, Hearth, Or Arc Furnaces (AREA)
- Furnace Details (AREA)
Abstract
ABSTRACT
A three-phase electric arc furnace comprising an elongated non-tilting rectangular vessel having longitudinal and transverse walls, and having six, or an integral multiple of six, electrodes arranged in two longitudinally extending parallel rows within the vessel. Pairs of adjacent electrodes are connected in respective independent single-phase circuits, each circuit being connected to a respective supply transformer by a non-inductively wound pair of high tension conductors.
The electrodes are disposed in a square array with the same number of electrodes in each said row, the spacing of the electrodes with respect to one another and with respect to the walls of the vessel being such that the individual active bath surfaces surrounding the electrodes constitute a coherent bath surface of maximum horizontal area, and the pairs of high tension conductors are symmetrically arranged with respect to the longitudinal axis of the vessel.
A three-phase electric arc furnace comprising an elongated non-tilting rectangular vessel having longitudinal and transverse walls, and having six, or an integral multiple of six, electrodes arranged in two longitudinally extending parallel rows within the vessel. Pairs of adjacent electrodes are connected in respective independent single-phase circuits, each circuit being connected to a respective supply transformer by a non-inductively wound pair of high tension conductors.
The electrodes are disposed in a square array with the same number of electrodes in each said row, the spacing of the electrodes with respect to one another and with respect to the walls of the vessel being such that the individual active bath surfaces surrounding the electrodes constitute a coherent bath surface of maximum horizontal area, and the pairs of high tension conductors are symmetrically arranged with respect to the longitudinal axis of the vessel.
Description
~4 ~ 7~35 This invention relates to three-phase electric arc furnaces. More particularly the invention is concerned with arc smelting furances, and with reducing furnaces for producing ferro-alloys, silicon alloys, or the like.
The furnace of the present invention has an elongated, non-tilting rectangular furnace vessel, the walls of which are at right angles to one another or have slightly rounded corners.
The electrical power is supplied to the furnace through at least six electrodes arranged longitudinally within the furnace vessel at equal intervals, pairs of adjacent electrodes being inter-connected to form respective independent single-phase circuits, and a supply transformer is connected to each such pair of electrodes, through high-tension conductors, which form out-going and return leads wound non-inductively close together and constituting a bifilar cable run.
In the smelting of steel, also more especially in the production of ferro- and silicon-alloys and calcium-carbide, it has hitherto been preferred to use a furnace of circular plan with a triangular arrangement of electrodes. Such an arrangement is disclosed in the periodical "Technische Rundschau", Berne, No. 48, November 1978, pages 21 to 23: U. Becker-Barbrock, W. Felix and G. Papachristos: "Lichtbogenofen Hochleitungsanlagen under ihre Baugruppen".
As a result of expansion of the steel industry, there is a marked increasing need for ferro-alloys. Rapidly increasing the costs of power, raw materials, and labour are subjecting the producers of ferro-alloys to an increasing cost squeeze. In order to take as much advantage as possible of reduced product-related costs resulting from reduced investment costs and lower wage bills, installations of larger capacity than before are continually being designed and built.
The increase in the amount of heat required for metallurgical processes, represented as effective electrical ~1477~35 power of furnace installations, leads to the requirement for electro~sand furnace hearths of ever increasing diameter.
Moreover, the relationship between the amount of power to be transferred through the electrodes, and the possible~or necessary conversion of energy in the hearth, and the increasing need for heat, imposes a technico-economic limit on the power of the circular three-electrode furnace.
From the structural point of view, there are two limita-tions to be observed in the design of high power furnaces. One of these is the maximum available electrode diameter (in the case of graphite electrodes about 560 mm; for carbon electrodes about 1400 mm; and for Soderberg electrodes about 2000 mm). The other limitation is imposed by the maxiumum diameter of the circular furnace, since the efficiency of the circular furnace decreases with increasing size.
It has been found that, in the case of a circular three-electrode furnace, these limits may be exceeded by doubling the number of electrodes and adapting the capacity of the hearth accordingly, but this is not economical.
It is therefore the main object of the present invention to provide a three-phase electric furnace of the type mentioned initially which will preferably have a higher productive capacity and an output which exceeds the limits imposed by the production techniques and economics of conventional electric furnaces and which, while retaining the advantages of known rectangular furnaces having six electrodes, will achieve increased electro-thermal efficiency by improved utilization of the entire hearth-surface as a process-active surface, defined as the quotient of the power supplied less the total of electrical and thermal losses and the power supplied. At the same time, the electrical and metallurgical conditions of the process are to be improved by more uniform loading of the bath and by extensive electrical balancing.
~14'7~35 The furnace is also to have lower operating costs, and the installation is to be of simpler design.
According to the invention there is provided a three-phase electric arc furnace comprising an elongated non-ti~ting rectangular vessel having longitudinal and transverse walls, and having six, or an integral multiple of six, electrodes arranged in two longitudinally extending parallel rows within the vessel~ Pairs of adjacent electrodes are connected in respective independent single-phase circuits, each circuit being connected to a respective supply transformer by a non-inductively wound pair of high tension conductors. The electrodes are disposed in a square array with the same number of electrodes in each said row, the spacing of the electrodes with respect to one another and with respect to the walls of the vessel being such that the individual active bath surfaces surrounding the electrodes constitute a coherent bath surface of maximum horizon-tal area, and the pairs of high tension conductors are symmet-rically arranged with respect to the longitudinal axis of the vessel .
German Patent No. 677 279 discloses an arc furnace having a rectangular vessel, but this is a typical tilting arc furnace for producing steel products only, the six electrodes being arranged in two rows and being connected in a star circuit arrangement to two three-phase alternating current systems. The electrodes are arranged on the longitudinal sides of the furnace vessel. During tilting, the vessel is rotated about a vertical axis, so that the narrow side, upon which a tap hole is located, assumes a sharply inclined position. The use of six electrodes is presumably intended to improve the distribution of the power introduced. On the other hand, since the vessel rotates about a vertical axis, the elctrodes must be arranged centrally. As a result of this, large inactive areas are produced at the two ends of the vessel, and these impair the electrothermal efficiency of S
the furnace. In this known furnace, furthermore, there is a sharp increase in the negative effect of power asymmetry.
German OS 25 35 207 discloses an electrical furnace for obtaining steel from pre-reduced material, in small lumps, containing iron, more particularly pellets, lump-ore, and sponge-iron. This furnace is of elongated rectangular shape, with more than three electrodes arranged in one or more rows upon the longitudinal axis of the vessel. The purpose of this invention is to produce a flow of material in the furnace vessel, which passes through different processing zones.
Various arrangements of transformers and cable runs for furnaces having three or six electrodes are described in an article b~ Dr.-Ing. Mollenkamp and Dr.-Ing. Kallfelz: "Moderne Elektro-Reduktionsofen fur die Gewinning von Ferro-Leg;erungen, Roheisen und Kalzium-Karbid", Electrowarme International, Vol.B,
The furnace of the present invention has an elongated, non-tilting rectangular furnace vessel, the walls of which are at right angles to one another or have slightly rounded corners.
The electrical power is supplied to the furnace through at least six electrodes arranged longitudinally within the furnace vessel at equal intervals, pairs of adjacent electrodes being inter-connected to form respective independent single-phase circuits, and a supply transformer is connected to each such pair of electrodes, through high-tension conductors, which form out-going and return leads wound non-inductively close together and constituting a bifilar cable run.
In the smelting of steel, also more especially in the production of ferro- and silicon-alloys and calcium-carbide, it has hitherto been preferred to use a furnace of circular plan with a triangular arrangement of electrodes. Such an arrangement is disclosed in the periodical "Technische Rundschau", Berne, No. 48, November 1978, pages 21 to 23: U. Becker-Barbrock, W. Felix and G. Papachristos: "Lichtbogenofen Hochleitungsanlagen under ihre Baugruppen".
As a result of expansion of the steel industry, there is a marked increasing need for ferro-alloys. Rapidly increasing the costs of power, raw materials, and labour are subjecting the producers of ferro-alloys to an increasing cost squeeze. In order to take as much advantage as possible of reduced product-related costs resulting from reduced investment costs and lower wage bills, installations of larger capacity than before are continually being designed and built.
The increase in the amount of heat required for metallurgical processes, represented as effective electrical ~1477~35 power of furnace installations, leads to the requirement for electro~sand furnace hearths of ever increasing diameter.
Moreover, the relationship between the amount of power to be transferred through the electrodes, and the possible~or necessary conversion of energy in the hearth, and the increasing need for heat, imposes a technico-economic limit on the power of the circular three-electrode furnace.
From the structural point of view, there are two limita-tions to be observed in the design of high power furnaces. One of these is the maximum available electrode diameter (in the case of graphite electrodes about 560 mm; for carbon electrodes about 1400 mm; and for Soderberg electrodes about 2000 mm). The other limitation is imposed by the maxiumum diameter of the circular furnace, since the efficiency of the circular furnace decreases with increasing size.
It has been found that, in the case of a circular three-electrode furnace, these limits may be exceeded by doubling the number of electrodes and adapting the capacity of the hearth accordingly, but this is not economical.
It is therefore the main object of the present invention to provide a three-phase electric furnace of the type mentioned initially which will preferably have a higher productive capacity and an output which exceeds the limits imposed by the production techniques and economics of conventional electric furnaces and which, while retaining the advantages of known rectangular furnaces having six electrodes, will achieve increased electro-thermal efficiency by improved utilization of the entire hearth-surface as a process-active surface, defined as the quotient of the power supplied less the total of electrical and thermal losses and the power supplied. At the same time, the electrical and metallurgical conditions of the process are to be improved by more uniform loading of the bath and by extensive electrical balancing.
~14'7~35 The furnace is also to have lower operating costs, and the installation is to be of simpler design.
According to the invention there is provided a three-phase electric arc furnace comprising an elongated non-ti~ting rectangular vessel having longitudinal and transverse walls, and having six, or an integral multiple of six, electrodes arranged in two longitudinally extending parallel rows within the vessel~ Pairs of adjacent electrodes are connected in respective independent single-phase circuits, each circuit being connected to a respective supply transformer by a non-inductively wound pair of high tension conductors. The electrodes are disposed in a square array with the same number of electrodes in each said row, the spacing of the electrodes with respect to one another and with respect to the walls of the vessel being such that the individual active bath surfaces surrounding the electrodes constitute a coherent bath surface of maximum horizon-tal area, and the pairs of high tension conductors are symmet-rically arranged with respect to the longitudinal axis of the vessel .
German Patent No. 677 279 discloses an arc furnace having a rectangular vessel, but this is a typical tilting arc furnace for producing steel products only, the six electrodes being arranged in two rows and being connected in a star circuit arrangement to two three-phase alternating current systems. The electrodes are arranged on the longitudinal sides of the furnace vessel. During tilting, the vessel is rotated about a vertical axis, so that the narrow side, upon which a tap hole is located, assumes a sharply inclined position. The use of six electrodes is presumably intended to improve the distribution of the power introduced. On the other hand, since the vessel rotates about a vertical axis, the elctrodes must be arranged centrally. As a result of this, large inactive areas are produced at the two ends of the vessel, and these impair the electrothermal efficiency of S
the furnace. In this known furnace, furthermore, there is a sharp increase in the negative effect of power asymmetry.
German OS 25 35 207 discloses an electrical furnace for obtaining steel from pre-reduced material, in small lumps, containing iron, more particularly pellets, lump-ore, and sponge-iron. This furnace is of elongated rectangular shape, with more than three electrodes arranged in one or more rows upon the longitudinal axis of the vessel. The purpose of this invention is to produce a flow of material in the furnace vessel, which passes through different processing zones.
Various arrangements of transformers and cable runs for furnaces having three or six electrodes are described in an article b~ Dr.-Ing. Mollenkamp and Dr.-Ing. Kallfelz: "Moderne Elektro-Reduktionsofen fur die Gewinning von Ferro-Leg;erungen, Roheisen und Kalzium-Karbid", Electrowarme International, Vol.B,
2/79. The arrangement of transformers for a six-electrode furnace is shown in Fig. 4. However, this is a furnace arrange-ment with six electrodes connected in a row, the total power being divided between three single-phase transformers. The row of transformers extends parallel with the longitudinal side of the furnace.
An arrangement of this kind would have been unsatisfactory for the production of ferro- and silicon-alloys. The book by Durrer/Volkert: "Metallurgie der Ferro-Legierungen", 2nd Edition, Springer-Verlag, Berlin 1972, pages 130 and 131, describes cable runs to three-electrode furnaces, paying particular attention to the problems of electrical asymmetry, which impairs the distri-bution of total power.
The above publications contain no mention of measures whereby the thermal efficiency of a furnace may be increased by improved utilization of the total hearth area and by the functional relationship between the shape of the furnace vessel and the electrode arrangement. Nor do they contain any 1~4'7'7~S
instructions for improving the process-related and electrical conditions under which the furnace operates, whereas it is precisely upon these considerations that the present invention is based.
Norwegian Patent Publication 139 796 describes a current supply circuit for a direct current reducing furnace having four electrodes arranged in a square. This does not deal with problems related to alternating-current furnaces.
The invention is based upon the following considerations:
In the case of a circular furnace, the hearth resistance of the furnace vessel, in which the power required for the process is converted under the electrodes, decreases with increasing electrode diameter. The current must be increased as a function of the decreasing hearth resistance, in order to obtain the necessary power. This means that the effective force of the current decreases with increasing electrode diameter.
In view of these relationships, a rectangular furnace having six electrodes, for example, according to the above-mentioned article by Drs. Mollenkamp and Kallfelz: "Moderne 20 Elektro-Reduktionsofen ", has the following advantages:
- as compared with a circular furnace having three electrodes and of comparable effective power, the rectangular six-electrode furnace operates with smaller electrodes and there-for has higher electrical efficiency;
- with smaller electrode diameter, smaller conductor cross sections are used in the vicinity of the electrodes;
- since the height of the hearth is dependent upon electrode diameter, among other things, the height is less in a six-electrode furnace and the system conductors in the vicinity of the electrodes are shorter;
- since this furnace permits shorter high tension conductors of smaller cross section, the inductance of the conduc~or system is substantially reduced;
li47~713~i - the reduced inductance achieved (and therefore the reduced inductive-resistance~ leads, in conjunction with comparably lower electrode currents, to lower reactive powers;
- the use of single-phase systems permits a bifilar conductor arrangement from transformer to electrode tips;
- by a suitable choice of phase-sequence, and thus predeter-mination of the direction of the current in the electrodes, the whole six-electrode system may be designed as a bifilar conductor system;
- the considerable reduction in impedance losses makes it possible to equip a furnace according to the invention, which has an improved power factor, with lower power transformers and reactive power compensating installations;
- the bifilar arrangement, by lowering the inductance, avoids a rotating field whereby the bath in conventional furnaces is caused to rotate, thus making it more difficult to separate the metal and the slag, especially in the boundary area;
- a rectangular furnace vessel is structually simpler to build and less costly than a circular furnace; this applies both to the steel structure and to the refractory lining.
As compared with the last-mentioned known rectangular furnace having six electrodes, a furnace according to the present invention of comparable effective power provides a number of additional advantages which have the effect of increasing the electrothermal efficiency.
The configuration of the furnace vessel, and the arrange-ment of the electrodes, together provide reaction zones which cover almost the whole horizontal cross-sectional area of the vessel.
The active reaction surface, together with the previously mentioned reduced hearth height, produces substantially smaller radiation surfaces. From the metallurgical point of view, this leads to better utilization of the hearth area and to improved 1~477~
electrical conditions; this has, above all, a positive effect upon the electrothermal efficiency of the furnace.
Utilizing the whole hearth area as a process-active area makes it possible to eliminate the rotation or movement of the furnace vessel which in the case of circular furnaces is required in order to distribute the power over the hearth.
By dividing the total power among three (,or a multiple of three~ single-phase systems arranged symmetrically in relation to the longitudinal axis of the furnace, and making use of the above-mentioned extensive bifilarity of the system as a whole, the disruptive effects of geometrical and electrical asymmetry are eliminated.
The symmetrical arrangement of the transformers in relation to the longitudinal axis of the furnace vessel make it,, possible to keep one transverse wall of the furnace vessel free for tapping equipment and the like.
The structural arrangement of the entire high tension installation is greatly simplified in that charging hoppers may be arranged in two parallel rows; where two furnaces are arranged side by side, the charging hoppers may be arranged in only three rows running parallel with the rows of electrodes.
Investigations and measurements carried out in the course of testing have shown that a 40 MW furnace according to the invention has substantially more favourable economic factors than a 40 MW circular furnace with three electrode or a 40 MW
rectangular furnace with six electrodes arranged in a row.
The results of the comparison measurements are given in Table 1.
Three embodiments of the inventîon will now be described by way of example with reference to the accompanying diagrammati-cal drawings, in which:
Fig. 1 is a plan view of an electric furnace according to the invention having six electrodes;
1~7~35 Fig. 2 is a plan view of a modification having twelve electrodes; and Fig. 3 is a plan view of another design of the twelve-electrode furnace according to the invention, with another arrangement of high-tension conductors.
Fig. 1 represents a closed reducing furnace having a stationary, elongated, rectangular furnace vessel 7. As shown in the figure, 8iX electrodes 1 to 6 are spaced equally apart in two rows running parallel with the longitudinal axis of the furnace vessel, in such a manner that each row contains three electrodes. As seen in plan view, electrodes 1, 2, 5, 6 and 2, 3, 4, 5 are located at the corners of imaginary squares, that i8, they are disposed in a square array.
In order to achieve optimal power distribution over the bath, the electrodes are spaced from each other, and from the walls of the vessel in such a manner that the surfaces of the bath which are technically active in the process, and which extend around the electrodes 1 to 6, form a coherent surface.
Adjacent electrodes 1 and 2, 3 and 4, 5 and 6 are combined into respective, independent single-phase circuits. Electrodes 1 and 2 are connected, through high tension conductors, to a supply transformer A; the pair of electrodes 3, 4 are connected to a transformer B; and pair of electrodes 5 and 6 are connected to a transformer C.
The supply transformers A and C, with their respective high tension conductors, are positioned at the longitudinal sides of the furnace vessel, and the supply transformer B at one of the ; transverse sides. As may be seen in the figure, the arrangement of the high tension conductors is symmetrical with respect to 30 the longitudinal axis of the furnace vessel 7. The tap-hole, not shown, is located on the free transverse side of vessel 7.
As may be seen in all of the figures, the outgoing and return conductors between each transformer and the electrodes ~4'~ 3S
connected thereto are laid close together, thus forming a non-inductive bifilar cable-run, which considerably reduces the inductive reactive power from electromagnetic fields with currents flowing in opposite directîons.
In the example illustrated, the supply transformers A, B and C have their primary sides connected to a three-phase system, the secondary sides of the single-phase circuits connected to the transformers being connected, through the metallic product in the furnace, to a three-phase system which is balance with respect to the pr~mary system.
For the purpose of regulating the voltage in each of the single-phase systems, each supply transformer is provided with a regulating power circuit-breaker. Each electrode may be adjustable individually according to its process-effective power-input. Power is supplied to the furnace illustrated in Fig. 2 by twelve electrodes 21 to 32, the spacing of which, in relation to each other and to the walls of the vessel is similar to the arrangement in Fig. 1. Three transformers with high tension conductors 8 are provided at each longitudinal side of vessel 7.
The arrangement in Fig. 3 is similar to that in Fig. 2, except that of the six transformers D, E, F, G, H, K, four, namely D, E and H, G, are arranged at the longitudinal sides of the vessel, whereas transformers F and K, with their high tension leads, are located at the transverse sides.
_ g _ 1~4~77~5 Comparison of data for 40 MW furnaces of circular design (with
An arrangement of this kind would have been unsatisfactory for the production of ferro- and silicon-alloys. The book by Durrer/Volkert: "Metallurgie der Ferro-Legierungen", 2nd Edition, Springer-Verlag, Berlin 1972, pages 130 and 131, describes cable runs to three-electrode furnaces, paying particular attention to the problems of electrical asymmetry, which impairs the distri-bution of total power.
The above publications contain no mention of measures whereby the thermal efficiency of a furnace may be increased by improved utilization of the total hearth area and by the functional relationship between the shape of the furnace vessel and the electrode arrangement. Nor do they contain any 1~4'7'7~S
instructions for improving the process-related and electrical conditions under which the furnace operates, whereas it is precisely upon these considerations that the present invention is based.
Norwegian Patent Publication 139 796 describes a current supply circuit for a direct current reducing furnace having four electrodes arranged in a square. This does not deal with problems related to alternating-current furnaces.
The invention is based upon the following considerations:
In the case of a circular furnace, the hearth resistance of the furnace vessel, in which the power required for the process is converted under the electrodes, decreases with increasing electrode diameter. The current must be increased as a function of the decreasing hearth resistance, in order to obtain the necessary power. This means that the effective force of the current decreases with increasing electrode diameter.
In view of these relationships, a rectangular furnace having six electrodes, for example, according to the above-mentioned article by Drs. Mollenkamp and Kallfelz: "Moderne 20 Elektro-Reduktionsofen ", has the following advantages:
- as compared with a circular furnace having three electrodes and of comparable effective power, the rectangular six-electrode furnace operates with smaller electrodes and there-for has higher electrical efficiency;
- with smaller electrode diameter, smaller conductor cross sections are used in the vicinity of the electrodes;
- since the height of the hearth is dependent upon electrode diameter, among other things, the height is less in a six-electrode furnace and the system conductors in the vicinity of the electrodes are shorter;
- since this furnace permits shorter high tension conductors of smaller cross section, the inductance of the conduc~or system is substantially reduced;
li47~713~i - the reduced inductance achieved (and therefore the reduced inductive-resistance~ leads, in conjunction with comparably lower electrode currents, to lower reactive powers;
- the use of single-phase systems permits a bifilar conductor arrangement from transformer to electrode tips;
- by a suitable choice of phase-sequence, and thus predeter-mination of the direction of the current in the electrodes, the whole six-electrode system may be designed as a bifilar conductor system;
- the considerable reduction in impedance losses makes it possible to equip a furnace according to the invention, which has an improved power factor, with lower power transformers and reactive power compensating installations;
- the bifilar arrangement, by lowering the inductance, avoids a rotating field whereby the bath in conventional furnaces is caused to rotate, thus making it more difficult to separate the metal and the slag, especially in the boundary area;
- a rectangular furnace vessel is structually simpler to build and less costly than a circular furnace; this applies both to the steel structure and to the refractory lining.
As compared with the last-mentioned known rectangular furnace having six electrodes, a furnace according to the present invention of comparable effective power provides a number of additional advantages which have the effect of increasing the electrothermal efficiency.
The configuration of the furnace vessel, and the arrange-ment of the electrodes, together provide reaction zones which cover almost the whole horizontal cross-sectional area of the vessel.
The active reaction surface, together with the previously mentioned reduced hearth height, produces substantially smaller radiation surfaces. From the metallurgical point of view, this leads to better utilization of the hearth area and to improved 1~477~
electrical conditions; this has, above all, a positive effect upon the electrothermal efficiency of the furnace.
Utilizing the whole hearth area as a process-active area makes it possible to eliminate the rotation or movement of the furnace vessel which in the case of circular furnaces is required in order to distribute the power over the hearth.
By dividing the total power among three (,or a multiple of three~ single-phase systems arranged symmetrically in relation to the longitudinal axis of the furnace, and making use of the above-mentioned extensive bifilarity of the system as a whole, the disruptive effects of geometrical and electrical asymmetry are eliminated.
The symmetrical arrangement of the transformers in relation to the longitudinal axis of the furnace vessel make it,, possible to keep one transverse wall of the furnace vessel free for tapping equipment and the like.
The structural arrangement of the entire high tension installation is greatly simplified in that charging hoppers may be arranged in two parallel rows; where two furnaces are arranged side by side, the charging hoppers may be arranged in only three rows running parallel with the rows of electrodes.
Investigations and measurements carried out in the course of testing have shown that a 40 MW furnace according to the invention has substantially more favourable economic factors than a 40 MW circular furnace with three electrode or a 40 MW
rectangular furnace with six electrodes arranged in a row.
The results of the comparison measurements are given in Table 1.
Three embodiments of the inventîon will now be described by way of example with reference to the accompanying diagrammati-cal drawings, in which:
Fig. 1 is a plan view of an electric furnace according to the invention having six electrodes;
1~7~35 Fig. 2 is a plan view of a modification having twelve electrodes; and Fig. 3 is a plan view of another design of the twelve-electrode furnace according to the invention, with another arrangement of high-tension conductors.
Fig. 1 represents a closed reducing furnace having a stationary, elongated, rectangular furnace vessel 7. As shown in the figure, 8iX electrodes 1 to 6 are spaced equally apart in two rows running parallel with the longitudinal axis of the furnace vessel, in such a manner that each row contains three electrodes. As seen in plan view, electrodes 1, 2, 5, 6 and 2, 3, 4, 5 are located at the corners of imaginary squares, that i8, they are disposed in a square array.
In order to achieve optimal power distribution over the bath, the electrodes are spaced from each other, and from the walls of the vessel in such a manner that the surfaces of the bath which are technically active in the process, and which extend around the electrodes 1 to 6, form a coherent surface.
Adjacent electrodes 1 and 2, 3 and 4, 5 and 6 are combined into respective, independent single-phase circuits. Electrodes 1 and 2 are connected, through high tension conductors, to a supply transformer A; the pair of electrodes 3, 4 are connected to a transformer B; and pair of electrodes 5 and 6 are connected to a transformer C.
The supply transformers A and C, with their respective high tension conductors, are positioned at the longitudinal sides of the furnace vessel, and the supply transformer B at one of the ; transverse sides. As may be seen in the figure, the arrangement of the high tension conductors is symmetrical with respect to 30 the longitudinal axis of the furnace vessel 7. The tap-hole, not shown, is located on the free transverse side of vessel 7.
As may be seen in all of the figures, the outgoing and return conductors between each transformer and the electrodes ~4'~ 3S
connected thereto are laid close together, thus forming a non-inductive bifilar cable-run, which considerably reduces the inductive reactive power from electromagnetic fields with currents flowing in opposite directîons.
In the example illustrated, the supply transformers A, B and C have their primary sides connected to a three-phase system, the secondary sides of the single-phase circuits connected to the transformers being connected, through the metallic product in the furnace, to a three-phase system which is balance with respect to the pr~mary system.
For the purpose of regulating the voltage in each of the single-phase systems, each supply transformer is provided with a regulating power circuit-breaker. Each electrode may be adjustable individually according to its process-effective power-input. Power is supplied to the furnace illustrated in Fig. 2 by twelve electrodes 21 to 32, the spacing of which, in relation to each other and to the walls of the vessel is similar to the arrangement in Fig. 1. Three transformers with high tension conductors 8 are provided at each longitudinal side of vessel 7.
The arrangement in Fig. 3 is similar to that in Fig. 2, except that of the six transformers D, E, F, G, H, K, four, namely D, E and H, G, are arranged at the longitudinal sides of the vessel, whereas transformers F and K, with their high tension leads, are located at the transverse sides.
_ g _ 1~4~77~5 Comparison of data for 40 MW furnaces of circular design (with
3 electrodes) and of rectangular design (with 6 electrodes).
_ ,.
Designation Design Data ISymbol Dim. (a~ (b~ (c~
_ r ~onnected Furnace Load s MVA 83 62 68 Primary Current Il - 1380 1040 1100 Necessary Capacitor Power for Reactive- P MVar 5129 35 Power Compensation C
. , rurraentoS all Secondary I2 kA 430 475 545 Elect. Power Loss Pv kW335030803140 In otal Furnace Design A m2 990 1090 1350 onverted Area of VG m389002285028700 Furnace Building C as Activation f VH Nm3/m2h 46 49 40 earth Surface _ _ eat-Radiation Area in he Vicinity of Bottom ABM m2277 271 339 nd Bath of Metal C Radiation Surface in 2 . icinity of Burden AMO m 150 153 197 o adiation Surface of A m2 246 228 282 essel Cover D
_ ~a~* Circular design: three electrodes.
(b)* Rectangular design: six electrodes in two rows.
(c)* Rectangular design: six electrodes in single row.
_ ,.
Designation Design Data ISymbol Dim. (a~ (b~ (c~
_ r ~onnected Furnace Load s MVA 83 62 68 Primary Current Il - 1380 1040 1100 Necessary Capacitor Power for Reactive- P MVar 5129 35 Power Compensation C
. , rurraentoS all Secondary I2 kA 430 475 545 Elect. Power Loss Pv kW335030803140 In otal Furnace Design A m2 990 1090 1350 onverted Area of VG m389002285028700 Furnace Building C as Activation f VH Nm3/m2h 46 49 40 earth Surface _ _ eat-Radiation Area in he Vicinity of Bottom ABM m2277 271 339 nd Bath of Metal C Radiation Surface in 2 . icinity of Burden AMO m 150 153 197 o adiation Surface of A m2 246 228 282 essel Cover D
_ ~a~* Circular design: three electrodes.
(b)* Rectangular design: six electrodes in two rows.
(c)* Rectangular design: six electrodes in single row.
Claims (7)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A three-phase electric arc furnace comprising an elongated non-tilting rectangular vessel having longitudinal and transverse walls, and having six, or an integral multiple of six, electrodes arranged in two longitudinally extending parallel rows within the vessel, pairs of adjacent electrodes being connected in respective independent single-phase circuits, each circuit being connected to a respective supply transformer by a non-inductively wound pair of high tension conductors, wherein the electrodes are disposed in a square array with the same number of electrodes in each said row, the spacing of the electrodes with respect to one another and with respect to the walls of the vessel being such that the individual active bath surfaces surrounding the electrodes constitute a coherent bath surface of maximum horizontal area, and wherein said pairs of high tension conductors are symmetrically arranged with respect to the longitudinal axis of the vessel.
2. A furnace according to claim 1, wherein the length-to-width ratio of the vessel is approximately equal to the number of electrodes at the longitudinal sides and the number of electrodes at the transverse sides of the furnace vessel.
3. A furnace according to claim 1, in which there are six electrodes and in which one of the transformers with the respective high tension conductors connecting said one trans-former to one pair of electrodes is arranged at a transverse side of the furnace vessel.
4. A furnace according to claim 1 or claim 2, in which there are more than six electrodes, and in which one trans-former with the respective high tension conductors connecting this transformer to a pair of electrodes is arranged at each transverse side of the furnace vessel.
5. A furnace according to any one of claims 1, 2 and 3, wherein three of the supply transformers provided are connected on the primary side, to a three-phase system the single-phase circuits connected to these three transformers being connected, on the secondary side, through the furnace contents to a three-phase system constituting a balance load to the primary system.
6. A furnace according to any one of claims 1, 2 and 3, wherein each supply transformer of each single-phase circuit is fitted with a regulating power contact-breaker for voltage control purposes.
7. A furnace according to any one of claims 1 J 2 and 3, wherein each electrode is individually adjustable according to its process effective power input.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE2946588A DE2946588C2 (en) | 1979-11-19 | 1979-11-19 | Three-phase arc melting or reduction furnace |
| DEP2946588 | 1979-11-19 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1147785A true CA1147785A (en) | 1983-06-07 |
Family
ID=6086346
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000364912A Expired CA1147785A (en) | 1979-11-19 | 1980-11-18 | Three-phase arc smelting or reducing furnace |
Country Status (4)
| Country | Link |
|---|---|
| CA (1) | CA1147785A (en) |
| DE (1) | DE2946588C2 (en) |
| MX (1) | MX148234A (en) |
| ZA (1) | ZA807156B (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3024223A1 (en) * | 1980-06-27 | 1982-01-28 | Mannesmann Demag Ag, 4100 Duisburg | Three=phase electric arc furnace - with rectangular hearth and six electrodes or multiple of six in specified circuitry |
| DE102005051232A1 (en) * | 2005-10-26 | 2007-05-03 | Sms Demag Ag | Control device for alternating current reduction furnaces |
| DE102011083036A1 (en) * | 2011-05-13 | 2012-11-15 | Sms Siemag Ag | reduction furnace |
| WO2017220726A1 (en) * | 2016-06-23 | 2017-12-28 | Sms Group Gmbh | Electric reduction device |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE677279C (en) * | 1938-02-19 | 1939-06-22 | Demag Elektrostahl G M B H | Arc furnace, especially for the production of iron and steel |
| DE973715C (en) * | 1952-08-31 | 1960-05-19 | Demag Elektrometallurgie Gmbh | Electric arc or reduction furnace |
| DE2535207C3 (en) * | 1975-08-07 | 1983-11-03 | Mannesmann AG, 4000 Düsseldorf | Method and device for extracting steel from pre-reduced small pieces of ferrous material, in particular pellets or lump ores or sponge iron, in an electric furnace |
-
1979
- 1979-11-19 DE DE2946588A patent/DE2946588C2/en not_active Expired
-
1980
- 1980-11-14 MX MX184765A patent/MX148234A/en unknown
- 1980-11-18 CA CA000364912A patent/CA1147785A/en not_active Expired
- 1980-11-18 ZA ZA00807156A patent/ZA807156B/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| ZA807156B (en) | 1981-11-25 |
| DE2946588C2 (en) | 1982-08-12 |
| MX148234A (en) | 1983-03-28 |
| DE2946588A1 (en) | 1981-05-21 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4821284A (en) | Scrap-melting process and electric furnace for carrying out the process | |
| US3949151A (en) | Arc furnaces | |
| US5138630A (en) | Direct current electric arc furnace | |
| CA1147785A (en) | Three-phase arc smelting or reducing furnace | |
| US3431344A (en) | Control system providing supply circuit impedance balance control for electric arc furnaces | |
| US3634592A (en) | System for charging electric-arc furnaces | |
| US4856021A (en) | Electric direct-current scrap-melting furnace | |
| US4406008A (en) | Three phase arc melting and reduction furnace | |
| US3598888A (en) | Electric smelting furnace | |
| US4388108A (en) | Method and apparatus for smelting charge materials in electric arc furnace | |
| RU2040864C1 (en) | Direct current smelting furnace | |
| US3857697A (en) | Method of continuously smelting a solid material rich in iron metal in an electric arc furnace | |
| DE3024223A1 (en) | Three=phase electric arc furnace - with rectangular hearth and six electrodes or multiple of six in specified circuitry | |
| RU2192713C1 (en) | Power supply unit | |
| Robinson et al. | Ultra-high power electric steel furnace operation | |
| US2808324A (en) | Method of smelting ilmenite | |
| Stewart | An analysis of the electrical circuit of submerged-arc furnaces | |
| US3131246A (en) | Electric furnace | |
| Lupi et al. | Arc Furnaces | |
| US5844933A (en) | Electrode arrangement for direct current and furnace | |
| RU2075840C1 (en) | Method of realization of optimum control of electric furnace | |
| DE3825984A1 (en) | ELECTRIC REDUCTION STOVES | |
| Gusev et al. | Scientific foundation for the production of carbothermal manganese alloys | |
| Sarapulov et al. | Electromagnetic model of a multiphase inductive crucible furnace | |
| AU2020392060A1 (en) | DC brush-arc furnace with arc deflection compensation |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |