AU2006327784A1

AU2006327784A1 - Compensation system and method for arc skewing for a DC arc furnace

Info

Publication number: AU2006327784A1
Application number: AU2006327784A
Authority: AU
Inventors: Frederik Petrus Greyling; Petrus Hermanus Swart
Original assignee: FREDERICK GREYLING
Current assignee: Greyling Frederick Petrus
Priority date: 2005-12-20
Filing date: 2006-11-29
Publication date: 2007-06-28
Anticipated expiration: 2026-11-29
Also published as: CN101331375B; WO2007072253A1; CN101331375A; AP2309A; AU2006327784B2; AP2008004472A0; ZA200803842B

Description

WO 2007/072253 PCT/IB2006/054509 Title: COMPENSATION SYSTEM AND METHOD FOR ARC SKEWING FOR A DC ARC FURNACE INTRODUCTION AND BACKGROUND This invention relates to DC arc furnaces and more particularly to a 5 system and method of adjusting, for example by reducing or alleviating arc deflection or skewing in an arc region of the furnace. A known DC arc furnace comprises a generally circular vessel in transverse cross section comprising a closed top from which a single 10 electrode extends axially into a chamber defined by the vessel. The electrode is connected as cathode by a main furnace circuit to one pole a DC power supply. The other pole is connected to via an anode conductor to anode terminals on a base of the vessel. Deflection of an arc in an arc region of the furnace and which region extends between 15 a distal end of the electrode and a bath of molten material in the vessel, is a known problem. The deflection is caused by a force resulting from a transverse magnetic field in the arc region and which magnetic field is the result of current in the main circuit. As a consequence of the arc deflection, thermal loading on the wall of the 20 vessel is not symmetrical, which in turn results in uneven wear of the wall and may result in long down times and high refractory costs.

WO 2007/072253 PCT/IB2006/054509 2 There are various systems and methods known for reducing and/or alleviating arc deflection, but they are not suitable for at least some applications. 5 OBJECT OF THE INVENTION Accordingly, it is an object of the present invention to provide an alternative system and method of adjusting, for example by reducing or alleviating arc deflection in a DC arc furnace. 10 SUMMARY OF THE INVENTION According to the invention there is provided a DC arc furnace system comprising - an arc furnace comprising an electrode extending into a vessel; - a main DC power supply connected to the electrode and to an 15 anode region at a base of the vessel by a main furnace circuit comprising an anode conductor connected to the anode region and extending from the anode region externally of the vessel to the main DC power supply; and - an arc deflection compensation system comprising a ?0 compensation circuit separate from the main furnace circuit and which compensation circuit is energized by a compensation power supply which is separate from the main power supply.

WO 2007/072253 PCT/IB2006/054509 3 In this specification the word "separate", when used in relation to the compensation circuit, is used to indicate that a parameter in the compensation circuit, such as current, is independent or independently controllable from a corresponding or associated parameter in the main 5 furnace circuit; and when used in relation to the compensation power supply, that the compensation power supply is independent or independently controllable from the main power supply. The compensation circuit and main circuit may electrically be insulated from one another or may share a common ground or earth. 10 A main plane of the system extends symmetrically through the main furnace circuit and electrode. The compensation circuit is configured such that a current in the 15 compensation circuit causes a magnetic field in an arc region of the furnace, which arc region extends between a distal end of the electrode and a body of material in the furnace, in a direction other than a direction of a magnetic field in the arc region caused by a main current in the main circuit. The other direction may be opposite to the 20 direction of the magnetic field caused by the main current or transverse thereto.

WO 2007/072253 PCT/IB2006/054509 4 The compensation circuit may be configured such that the magnetic field caused by the current in the compensation circuit substantially cancels the magnetic field caused by the current in the main circuit. 5 The compensation circuit may comprise a principal compensation limb extending substantially parallel to the anode conductor in a region of the anode conductor towards the anode region. The compensation circuit may comprise at least a first and a second 10 coil. Each coil may comprise a plurality of windings and may have any suitable shape or configuration such as circular, elliptical and rectangular comprising substantially parallel opposed first and second longer limbs. 5 In a first embodiment, the first and second coils may be arranged such that a second plane substantially perpendicular to the main plane and below the base of the vessel extends symmetrically through the first and second limbs of both coils, the coils being arranged in juxtaposition relative to one another and symmetrical relative to the .0 main plane.

WO 2007/072253 PCT/IB2006/054509 5 In a second embodiment, the first and second coils may be arranged below the base of the vessel, so that respective planes parallel and symmetrical to the main plane extend through the first and second limbs of the respective coils. 5 In a third embodiment, the first and second coils may be located adjacent a sidewall of the vessel in diametrically opposite regions of the vessel and at least partially above the base, so that respective planes parallel and symmetrical to the main plane extend through the 10 first and second limbs of the respective coils. In a fourth embodiment, the first and second coils may be located adjacent the vessel in diametrically opposite regions of the vessel, so that respective planes extending symmetrical relative to the main plane 15 with an angle a between the planes extend through both the first and second limbs of the respective coils and wherein 0 <a < 1800. The compensation power supply may be a single supply, alternatively the compensation power supply may comprise respective separate ?0 supplies for each of the at least first and second coils.

WO 2007/072253 PCT/IB2006/054509 6 In other embodiments, the compensation circuit may comprise a single coil of any suitable shape or configuration as aforesaid. The single coil may be generally rectangular in configuration having first and second opposed limbs. The main plane may extend symmetrically through the 5 first and second limbs, the first limb may be located as close as possible to the anode conductor and the coil may be energized such that a compensation current in the first limb flows in a direction opposite to the main current in the anode conductor. 10 The system may comprise a controller configured automatically to cause a parameter in the compensation circuit to follow variations in a corresponding or associated parameter in the main circuit. For example, the controller may be configured to operate the compensation power supply such that the current in the compensation 15 circuit changes in sympathy with variations in the current in the main circuit. The invention also extends to a arc deflection compensation system for a DC arc furnace comprising a main furnace circuit connecting an 20 electrode of the furnace to a main furnace DC power supply, the compensation system comprising a compensation circuit separate from WO 2007/072253 PCT/IB2006/054509 7 the main circuit and a compensation system power supply separate from the main power supply. The arc deflection compensation system may comprise a controller 5 configured automatically to cause a parameter in the compensation circuit to follow variations in a corresponding or associated parameter in the main circuit. For example, the controller may be configured to operate or control the compensation power supply such that the current in the compensation circuit changes in sympathy with 10 variations in the current in the main circuit. Yet further included within the scope of the present invention is a method of adjusting arc deflection in an arc region of a DC arc furnace, which region extends between an end of an electrode of the 15 furnace and material in the furnace and which electrode is connected by a main furnace circuit to a main DC power supply, the method comprising the steps of: - utilizing a separate compensation circuit located in a region of the furnace; and 20 - energizing the compensation circuit with a separate compensation power supply to cause current in the compensation circuit to cause a magnetic field in the arc region WO 2007/072253 PCT/IB2006/054509 8 in a direction other than a direction of a magnetic field in the arc region caused by a main current in the main circuit. The other direction may be opposite to the direction of the magnetic 5 field caused by the main current or transverse thereto. BRIEF DESCRIPTION OF THE ACCOMPANYING DIAGRAMS The invention will now further be described, by way of example only, with reference to the accompanying diagrams wherein 10 figure 1 is a three dimensional representation of a known or prior art DC arc furnace; figure 2 is a side view of the furnace in figure 1; figure 3 is an end view of the furnace in figure 1; figure 4 is a block diagram of a main furnace DC circuit and a 5 separate arc deflection compensation circuit of an arc deflection compensation system according to the invention; figure 5 is a diagrammatic side view of a furnace and a first embodiment of the compensation system according to the invention; .0 figure 6 is diagrammatic end view of the furnace and compensation system in figure 5; WO 2007/072253 PCT/IB2006/054509 9 figure 7 is a view similar to figure 5 of the furnace and a second embodiment of the compensation system; figure 8 is a view similar to figure 6 of the furnace and the second embodiment of the compensation system; 5 figure 9 is a view similar to figure 5 of the furnace and a third embodiment of the compensation system; figure 10 is a view similar to figure 6 of the furnace and the third embodiment of the compensation system; figure 11 is a view similar to figure 5 of the furnace and a fourth 10 embodiment of the compensation system; figure 12 is a view similar to figure 6 of the furnace and the fourth embodiment of the compensation system; and figure 13 is a view similar to figure 5 of the furnace and a fifth embodiment of the compensation system; and 15 figure 14 is a view similar to figure 6 of the furnace and the fifth embodiment of the compensation system. DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION A known Direct Current (DC) arc furnace system is generally .0 designated by the reference numeral 10 in figures 1 to 3.

WO 2007/072253 PCT/IB2006/054509 10 The system 10 comprises a known arc furnace 12 comprising an elongate tubular vessel 14 defining a chamber 16. The vessel comprises a wall 18, which is substantially circular in transverse cross section, a closed roof 20 and a base 22. A single electrode 24 5 connected to a main furnace circuit 25 extends centrally into the vessel from the roof towards the base 22. The electrode 24 is connected by the main circuit as cathode to a negative pole of a known and main furnace DC power supply 28. The power supply comprises a transformer and rectifier 30 and a coil 32 (both shown in 10 figure 4). A positive pole 34 of the power supply 28 is connected to an anode region 35 of the furnace vessel at the base 22 thereof. The cathode is connected to the negative terminal 26 of the main power supply by a cathode arm 36 and flexible conductors 38. The anode region is connected to the positive terminal 34 by an anode conductor 15 in the form of a bus-tube 40. As best shown in figure 1, a north-south main plane 42 extends symmetrically through the main circuit 25 components 36,38,26,32,30,34 and 40. It is known that with such an arrangement and due to a main current Im in the main circuit, there is a resultant transverse magnetic field in an arc region 44 of the 20 furnace in a direction out of the paper, as shown at 46 in figure 2. This resultant magnetic field causes an arc deflecting force Fi, causing the arc 48 to deflect in a northern direction. The disadvantages and WO 2007/072253 PCT/IB2006/054509 11 problems with this deflection are set out in the introduction of this specification. With the aforementioned symmetry about plane 42, substantially no deflection in an east-west direction is expected. 5 Referring to figures 4 to 14, to alleviate or compensate for the aforementioned deflection and according to the applicant's invention, there is provided a compensation system 50 comprising a separate compensation circuit 52 which is electrically insulated from the main circuit and a separate compensation DC power supply 54 which is 10 electrically insulated from the main power supply and circuit. The compensation system 50 is configured such that a compensating transverse magnetic field is generated thereby in the arc region 44 and in another direction, preferably opposite (that is into the paper as 15 shown at 56) to the magnetic field 46 caused by the main current in the main circuit. The compensating magnetic field causes a distributed compensating force Fc, in a direction substantially opposite to force Fi, to be exerted on the arc 48, thereby to alleviate or compensate for the aforementioned undesirable deflection of the arc. 20 The compensation circuit 52 preferably comprises at least a first and a second generally rectangular, but could be circular or of other suitable WO 2007/072253 PCT/IB2006/054509 12 shape or configuration, multi-winding coils 58 and 60 and these coils may be configured relative to the vessel 14 in various configurations or embodiments to compensate for the aforementioned deflection, as will hereinafter be described, merely as examples. The two coils may 5 be energized by a common DC power supply 54, or each may be energized by a respective DC power supply (not shown). As best shown in figure 4, the coils 58 and 60 are configured such that current flow in a principal compensation limb namely adjacent legs 58.1 and 60.1 extending in a southern direction parallel to anode 10 conductor 40 is in a direction opposite to Im and also such that symmetry about the plane 42 (shown in figure 1), is maintained. In a first embodiment shown in figures 5 and 6, the coils 58 and 60 are positioned in a second, typically horizontal plane 61 perpendicular 15 to main plane 42 below the vessel. Bearing in mind the inverse square law rule, it will be appreciated that the closer the aforementioned adjacent legs 58.1 and 60.1 are to the arc region 44, the more advantageous. The plane 61 extends symmetrically through both the parallel longer limbs 58.1 and 58.2 of coil 58 and longer limbs 60.1 20 and 60.2 of coil 60.

WO 2007/072253 PCT/IB2006/054509 13 In a second embodiment shown in figures 7 and 8, the coils 58,60 are arranged below the base 22 of the vessel, so that respective planes 64, 66, which are symmetrical and parallel to main plane 42, extend substantially symmetrical through both longer limbs of the respective 5 coil. In a third embodiment shown in figures 9 and 10, the coils 58 and 60 are positioned at least partially above base 22 and adjacent the wall 14 of the vessel in diametrically opposed regions thereof, so that 10 respective planes 68, 70, which are substantially symmetrical and parallel to main plan 42, extend through both longer limbs of the coils. In a fourth embodiment shown in figures 11 and 12, the coils 58 and 60 are positioned adjacent wall 14 of the vessel in diametrically 5 opposed regions thereof, so that respective planes 71 and 73, which are symmetrical relative to plane 42 and with an angle a between them wherein 0< a < 1800, extend substantially symmetrically through both the longer limbs of the respective coils. 0 In a fifth embodiment shown in figures 13 and 14, a single coil 74, which may have any suitable shape, such as rectangular, is used. The coil comprises a first and principal compensation limb 76 and a second WO 2007/072253 PCT/IB2006/054509 14 opposed limb 77. The main plane 42 extends symmetrically through both limbs and the first limb is located as close as possible to the anode conductor of the main circuit 25 and/or the arc region 44. The DC power supply 54 causes a compensation current I to flow in a 5 direction opposite to the main current Im in the anode conductor 40. As illustrated in figures 4 and 13 merely as example, the system 10 or compensation system 50 may in any embodiment thereof further comprise a controller 80 configured to control the voltage or current at 10 output 82 of the separate power supply 54 to change in sympathy with any variations in the voltage at the output poles 26,34 of the main power supply 28 or in the current Im in the main circuit 25. In embodiments wherein the coils 58 an 60 are energized by 5 respective separate power supplies, the respective power supplies may be separately controllable, to compensate for any possible east-west deflection of the arc due to any non south-north symmetry, for example. !0 Alternatively, the separate power supplies may be utilized to adjust the arc in any desired direction, thereby to alleviate or prevent hot spot formation in any part of the furnace wall, for example.

Claims

1. A DC arc furnace system comprising: - an arc furnace comprising an electrode extending into a vessel; 5 - a main DC power supply connected to the electrode and to an anode region at a base of the vessel by a main furnace circuit comprising an anode conductor connected to the anode region and extending from the anode region externally of the vessel to the main DC power supply; and 10 - an arc deflection compensation system comprising a compensation circuit separate from the main furnace circuit and which compensation circuit is energized by a compensation power supply which is separate from the main power supply. 15

2. A furnace system as claimed in claim 1 wherein a main plane of the system extends symmetrically through the main furnace circuit and electrode. .0

3. A furnace system as claimed in claim 1 or claim 2 wherein the compensation circuit is configured such that a current in the compensation circuit causes a magnetic field in an arc region of WO 2007/072253 PCT/IB2006/054509 16 the furnace in a direction substantially opposite to a direction of a magnetic field in the arc region caused by a main current in the main circuit. 5

4. A furnace system as claimed in claim 3 wherein the compensation circuit is configured such that the magnetic field caused by the current in the compensation circuit substantially cancels the magnetic field caused by the main current in the main circuit. 10

5. A furnace system as claimed in any one of claims 1 to 4 wherein the compensation circuit comprises an elongate principal compensation limb extending substantially parallel to the anode conductor in a region of the anode conductor towards 15 the anode region.

6. A furnace system as claimed in any one of claims 1 to 5 wherein the compensation circuit comprises at least first and second coils, each comprising a plurality of windings. ?0

7. A furnace as claimed in claim 6 wherein each of the at least first and second coils is generally rectangular in configuration WO 2007/072253 PCT/IB2006/054509 17 comprising substantially parallel opposed first and second longer limbs.

8. A furnace system as claimed in claim 7 wherein the first and 5 second coils are arranged such that a second plane substantially perpendicular to the main plane and below the base of the vessel extends symmetrically through the first and second limbs of both coils, the coils being arranged in juxtaposition relative to one another and symmetrical relative to the main plane. 10

9. A furnace system as claimed in claim 7 wherein the first and second coils are arranged below the base of the vessel, so that respective planes parallel and symmetrical to the main plane extend through the first and second limbs of the respective 15 coils.

10. A furnace system as claimed in claim 7 wherein the first and second coils are located adjacent a sidewall of the vessel in diametrically opposite regions of the vessel and at least partially .O above the base, so that respective planes parallel and symmetrical to the main plane extend through the first and second limbs of the respective coils. WO 2007/072253 PCT/IB2006/054509 18

11. A furnace system as claimed in claim 7 wherein the first and second coils are located adjacent the vessel in diametrically opposite regions of the vessel, so that respective planes 5 extending symmetrical relative to the main plane with an angle a between the planes extend through both the first and second limbs of the respective coils and wherein 00 < a < 1800.

12. A furnace system as claimed in any one of claims 1 to 11 10 wherein the compensation power supply comprises a single supply.

13. A furnace system as claimed in any one of claims 6 to 11 wherein the compensation power supply comprises respective 15 power supplies for each of the at least first and second coils.

14. A furnace system as claimed in any one of claims 1 to 5 wherein the compensation circuit comprises a single coil. ?0

15. A furnace system as claimed in claim 14 wherein the single coil is generally rectangular in configuration having first and second opposed limbs. WO 2007/072253 PCT/IB2006/054509 19

16. A furnace system as claimed in claim 15 wherein the main plane extends symmetrically through the first and second limbs, wherein the first limb is located as close as possible to the 5 anode conductor, wherein the coil is energized such that a compensation current in the first limb flows in a direction opposite to the main current in the anode conductor.

17. A furnace system as claimed in any one of claims 1 to 16 10 comprising a controller configured automatically to cause a parameter in the compensation circuit to follow variations in a corresponding or associated parameter in the main circuit.

18. An arc deflection compensation system for a DC arc furnace 5 comprising a main furnace circuit connecting an electrode of the furnace to a main furnace DC power supply, the compensation system comprising a compensation circuit separate from the main circuit and a compensation system power supply separate from the main power supply. 0

19. An arc deflection compensation system as claimed in claim 18 comprising a controller configured automatically to cause a WO 2007/072253 PCT/IB2006/054509 20 parameter in the compensation circuit to follow variations in a corresponding or associated parameter in the main circuit.

20. A method of adjusting arc deflection in an arc region adjacent 5 an electrode of a DC arc furnace and which electrode is connected by a main furnace circuit to a main DC power supply, the method comprising the steps of: - utilizing a separate compensation circuit located in a region of the furnace; and 10 - energizing the compensation circuit with a separate compensation power supply to cause current in the compensation circuit to cause a magnetic field in the arc region in a direction other than a direction of a magnetic field in the arc region caused by a main current in the main 15 circuit.