WO2007072253A1

WO2007072253A1 - Compensation system and method for arc skewing for a dc arc furnace

Info

Publication number: WO2007072253A1
Application number: PCT/IB2006/054509
Authority: WO
Inventors: Frederik Petrus Greyling; Petrus Hermanus Swart
Original assignee: Frederik Petrus Greyling; Petrus Hermanus Swart
Priority date: 2005-12-20
Filing date: 2006-11-29
Publication date: 2007-06-28
Also published as: CN101331375A; AP2309A; ZA200803842B; AU2006327784A1; AP2008004472A0; CN101331375B; AU2006327784B2

Abstract

A DC arc furnace system (10) comprises an arc furnace comprising an electrode (24) extending into a vessel (14). A main DC power supply (28) is connected to the electrode and to an anode region (35) at a base of the vessel by a main furnace circuit (25) comprising an anode conductor (40) connected to the anode region and extending from the anode region externally of the vessel to the main DC power supply. The system (10) further comprises an arc deflection compensation system (50) comprising a compensation circuit (52) separate from the main furnace circuit and which compensation circuit is energized by a compensation power supply (54), which is separate from the main power supply (28). The compensation circuit generates a magnetic field (54) in an arc region (44) of the furnace in a direction opposite to the direction of a field (46) generated by the main circuit (25).

Description

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

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

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

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

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. There are various systems and methods known for reducing and/or

alleviating arc deflection, but they are not suitable for at least some

applications.

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.

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

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

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. 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

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.

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

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

direction of the magnetic field caused by the main current or

transverse thereto. 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.

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

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.

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

main plane. 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.

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

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

with an angle a between the planes extend through both the first and

second limbs of the respective coils and wherein 0° < a < 180° .

The compensation power supply may be a single supply, alternatively

the compensation power supply may comprise respective separate

supplies for each of the at least first and second coils. 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

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.

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

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

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.

The arc deflection compensation 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 or control the compensation power supply such that the

current in the compensation circuit changes in sympathy with

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

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

- 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 circuit.

The other direction may be opposite to the direction of the magnetic

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

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

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;

figure 6 is diagrammatic end view of the furnace and compensation

system in figure 5; 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;

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 1 1 is a view similar to figure 5 of the furnace and a fourth

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

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

designated by the reference numeral 10 in figures 1 to 3. 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

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

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

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 L in the main circuit, there

is a resultant transverse magnetic field in an arc region 44 of the

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 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.

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

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

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.

The compensation circuit 52 preferably comprises at least a first and a

second generally rectangular, but could be circular or of other suitable 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

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

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

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

and 60.2 of coil 60. 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

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

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 1 1 and 12, the coils 58 and

60 are positioned adjacent wall 14 of the vessel in diametrically

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 < 180°, extend substantially symmetrically

through both the longer limbs of the respective coils.

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 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 Ic to flow in a

direction opposite to the main current U 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

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

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.

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;

- 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

- 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.

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.

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 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.

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.

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

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.

7. A furnace as claimed in claim 6 wherein each of the at least

first and second coils is generally rectangular in configuration comprising substantially parallel opposed first and second longer

limbs.

8. A furnace system as claimed in claim 7 wherein the first and

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.

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

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

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.

1 1 . 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

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 0° < a < 180°.

12. A furnace system as claimed in any one of claims 1 to 1 1

wherein the compensation power supply comprises a single

supply.

13. A furnace system as claimed in any one of claims 6 to 1 1

wherein the compensation power supply comprises respective

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.

15. A furnace system as claimed in claim 14 wherein the single coil

is generally rectangular in configuration having first and second

opposed limbs.

1 6. 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

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

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

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.

19. An arc deflection compensation system as claimed in claim 18

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.

20. A method of adjusting arc deflection in an arc region adjacent

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

- 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

circuit.