WO2011020127A2

WO2011020127A2 - Dc furnace electrode

Info

Publication number: WO2011020127A2
Application number: PCT/ZA2010/000041
Authority: WO
Inventors: Tertius Christiaan Pieters
Original assignee: Allied Furnace Consultants (Pty) Limited
Priority date: 2009-08-14
Filing date: 2010-08-11
Publication date: 2011-02-17
Also published as: WO2011020127A3; ZA201200429B; AP2012006113A0

Abstract

The invention provides a DC furnace bottom electrode connector, an electrode, electrode hearth and a DC furnace. The electrode connector includes a circular flat metal plate which is dimensioned to be similar to the circumference of it corresponding furnace. The plate distributes current flow more evenly and non conductive areas provided in the plate can be used to manipulate current flow to minimise arc deflection.

Description

Title: DC Furnace Hearth

Technical field of the invention

This invention relates to DC arc furnaces. In particular, the invention relates to the bottom electrode and hearth of a furnace.

Background to the invention

The most widely used DC arc furnace comprises of the typical bowl shaped monolithic structure lined, for the most part, with refractory bricks. The bottom electrode, usually the anode, is axially aligned with the top electrode. An arc is formed between the top graphite/carbon electrode and the slag and/ or melt from where current flows through the conductive refractory bricks to a cooled metal plate, the anode, which is usually copper. The bottom anode usually includes conductor or metal pins extending from the metal plate through the refractory material to contact the melt.

In practice, the direct current is fed to the current leads from a transformer room horizontally offset from the furnace and it is believed that the magnetic field from these leads caused the angular arc deflection. The negative current lead to the arcing cathode electrode is in the form of a horizontal electrode arm positioned at a substantial height above the arc.

The high current in the electrical conductors to the bottom electrode causes a magnetic field which influences the arc and causes it to deviate from the axial line between the electrodes. The deviations results in loss of efficiency and shortens the life of the refractory lining of the hearth and side walls of the furnace. The hearth, or part thereof, is electrically conductive so that when constructed as part of a DC arc furnace, the arcing power can be transmitted via the hearth to a melt on the hearth and via an arc to an arcing electrode above the melt. Numerous attempts have been made to overcome the problem of arc deflection. For example, by using two or more leads, each passing underneath the furnace and looping back to opposed, or symmetrically arranged, connectors to the bottom electrode to provide opposing magnetic forces in an attempt to balance the magnetic forces. Another attempt to balance the magnetic forces was to use an induction coil to try and align the arc with the electrode axis. However, the use of opposed or balanced magnetic forces still causes magnetic eddies and fluctuations and merely alleviated the problem not solve it.

Another attempt to solve the problem proposed the use of a positive current lead below the bottom of the hearth and having an upper end positioned on the arcing electrode's axis relatively closely below the hearth bottom, this positive current lead extending from its upper end vertically downward on the arcing electrode's axis to a low position where the magnetic field of the positive current lead cannot appreciably affect the arc. This low position can be determined by technical analysis of the factors involved or by actual experimentation. From this low position the positive current lead can then extend horizontally to the transformer room without its magnetic field affecting the arc.

Further, the typical monolithic bowl shaped refractory lining of the hearth and the electrode pins needs to be replaced regularly. The monolithic structure requires a total replacement of the specially shaped refractory lining leading to high costs.

An object of the invention to provide a solution to the problem of arc deflection and to provide a more cost effective furnace of which the hearth and electrode pins can be maintained and replaced at a reduced cost.

General description of the invention

According to one aspect of the invention there is provided a DC furnace bottom electrode connector, which includes a circular flat metal conductor plate which is dimensioned to be similar to the circumference of it corresponding furnace.

The bottom electrode connector may include one or more contact points about its circumferential edge for connecting to the current leads from a transformer and rectifier arrangement for the furnace. Electricity is then conducted from the contact points to electrode pins extending upwards away from the plate and in electrical contact with the plate. The flat metal plate of the bottom electrode connector also functions as an electric current conductor.

In addition, the conductor plate may include a non conductive area opposite a contact point to force current around this area to promote uniform distribution of the current flow, in use. The non conductive area may also be shaped and configured to direct current flow to form magnetic fields which counter the magnetic fields from the leads from the transformer. Apart from uniform flow, the non conductive areas can preferably shaped to force current flow around it in a direction and density selected such that most of the magnetic forces are balanced such that minimum deflection of the arc occurs. The non conductive area may be a circular slot opposite its associated contact point or, preferably, a C-shaped slot concentric with the conductor plate with its opening at the side opposite to the leads from the transformer. It will be appreciated that there are several ways to achieve this, in accordance with the invention.

According to another aspect of the invention, there is provided a bottom electrode for a DC furnace, which electrode includes:

bottom electrode connector as described above, which includes a circular flat metal plate which is dimensioned to be similar to the circumference of it corresponding furnace; and

electrode pins extending upwards away from the plate and in electrical contact with the plate.

The conductor plate may include one or more contact points about its circumferential edge for connecting to the current leads from a transformer and rectifier arrangement for the furnace. In the case of two contact points, the contact points should be opposed on a line through the mid point of the conductor plate and more than two contact points should be symmetrically arranged about the circumference of the conductor plate. The electrode may further include a raised portion in the form of a circular metal plate with a dimension smaller than the conductor plate, of which the bottom surface is in full electrical contact with the conductor plate, with the electrode pins extending from the raised portion.

The raised portion may be welded along its circumference to a ring, which ring, in turn, is welded to the conductor plate and the hollow space formed by the raised portion, the ring and the conductor plate may be filled with a graphite machined pad. It will be appreciated that the graphite will assist in heat removal and uniform current distribution to the melt.

In addition, the conductor plate may include a non conductive area opposite a connection point to force current around this area to promote uniform distribution of the current flow, in use.

The invention also extends to a furnace, which furnace includes: a bottom electrode as described above of which the conductor plate is flat; a lining of refractory bricks on top of the conductor plate and about the electrode pins; and

a layer of rammed refractory material on top of the lining and exposed surfaces of the electrode up to a level flush with the top parts of the electrode pins, with the lining and rammed material forming the floor of the furnace.

The invention also extends to a method of energising a DC furnace, which method includes the step of spreading DC current through a circular connector plate through electrode pins and through a melt.

Detailed description of the invention The invention is now described by way of example with reference to the accompanying drawings.

In the drawings: Figure 1 shows a side view of a bottom electrode for a DC furnace, in accordance with the invention;

Figure 2 shows a plan view of the electrode;

Figure 3 shows a plan view of another embodiment of a bottom electrode for a DC furnace, in accordance with the invention;

Figure 4 shows a sectional side view of a DC furnace, in accordance with the invention;

Figure 5 shows details of Figure 4;

Figure 6 shows a current density analysis of a first embodiment of a working electrode;

Figure 7 shows a current density analysis of the working electrode pins of the first embodiment of the working electrode, in accordance with the invention;

Figure 8 shows a current density analysis of a second embodiment of a working electrode, in accordance with the invention;

Figure 9 shows a current density analysis of the working electrode pins of the second embodiment of the working electrode;

Figure 10 shows a current density analysis of a third embodiment of a working electrode, in accordance with the invention;

Figure 11 shows a current density analysis of the working electrode pins of the third embodiment of the working electrode; and

Figure 12 shows a bottom view of another, preferred, embodiment of a bottom electrode according to the invention.

Referring now to the drawings 1 to 11, the bottom electrode for a DC furnace, in accordance with the invention, is generally indicated by reference numeral 10.

The bottom electrode for a DC furnace electrode 10 includes an electric current conductor 12, in the form of a circular metal plate which is dimensioned to be similar to the circumference of its corresponding furnace. The electrode 10 further includes electrode pins 14 extending upwards away from the plate and in electrical contact with the plate. The conductor plate 12 includes one (Figures 2 and 6) or two (Figures 3 and 8) contact points 16 about its circumferential edge for connecting to the current leads from a transformer and rectifier arrangement (not shown) for the furnace. In the case of two contact points, the contact points should be opposed on a line through the mid point of the conductor plate 12.

The electrode further includes a raised portion 18 in the form of a circular metal plate with a dimension smaller than the conductor plate 12, of which the bottom surface is in full electrical contact with the conductor plate, with the electrode pins extending from raised portion. The raised portion 18 is welded and/or bolted along its circumference to a ring 20, which ring, in turn, is welded and/or bolted to the conductor plate 12 and the hollow space 22 formed by the raised portion, the ring and the conductor plate is filled with graphite 24. In addition, the conductor plate includes one or two non conductive area

26 opposite a corresponding connection point 16 to force current around this area to promote uniform distribution of the current flow, in use.

Referring now to Figure 4, the furnace 11 includes a bottom electrode 10 as described above of which the conductor plate 12 is flat. The furnace further includes a lining of refractory bricks 26 on top of the conductor plate and about the electrode pins 14 and a layer of rammed refractory material 28 on top of the lining and exposed surfaces of the electrode up to a level flush with the top parts of the electrode pins 14, with the lining and rammed material forming the floor of the furnace.

As can be seen from the current density analysis, the conductor plate with one contact point 16 provides an excellent uniform distribution of current flow to the melt 30, while the use of two connecting points 16 improves the distribution. The use of non conductive areas 26 further improves the distribution.

Referring now to Figure 12, the bottom electrode for a DC furnace, in accordance with the invention, is generally indicated by reference numeral 10. The bottom electrode for a DC furnace electrode 10 includes an electric current conductor 12, in the form of a circular metal plate which is dimensioned to be similar to the circumference of its corresponding furnace. The electrode 10 further includes electrode pins (not visible in this bottom view) extending upwards away from the plate and in electrical contact with the plate.

The conductor plate 12 includes two contact points 16 about its circumferential edge for connecting to the current leads 40 from a transformer and rectifier arrangement (not shown) for the furnace. The contact points are opposed to each other on a line through the mid point of the conductor plate 12 and which line is perpendicular to the leads 40.

The conductor plate includes one C-shaped non conductive area 26 spanning opposite the connection points 16 to force current around this area to promote uniform distribution of the current flow, and with its opening opposite the direction of the leads 40 is shaped and configured to direct current flow to form magnetic fields which counter the magnetic fields from the leads from the transformer. It shall be understood that the examples are provided for illustrating the invention further and to assist a person skilled in the art with understanding the invention and are not meant to be construed as unduly limiting the reasonable scope of the invention.

Claims

1. A DC furnace bottom electrode connector, which includes a circular flat metal conductor plate which is dimensioned to be similar to the circumference of it corresponding furnace.

2. A connector as claimed in Claim 1, which includes one or more contact points about its circumferential edge for connecting to the current leads from a transformer and rectifier arrangement for a furnace.

3. A connector as claimed in Claim 2, which includes a non conductive area opposite a contact point.

4. A connector as claimed in Claim 3, wherein the non conductive area is shaped and configured to direct current flow, in use, to form magnetic fields which counter the magnetic fields from leads from a transformer.

5. A connector as claimed in Claim 4, wherein the non conductive area is a circular slot opposite its associated contact point.

6. A connector as claimed in Claim 4, wherein the non conductive area is a C-shaped slot concentric with the conductor plate with its opening at the side opposite to leads from a transformer.

7. A bottom electrode for a DC furnace, which electrode includes: a bottom electrode connector as claimed in Claim 1 to 6; and

electrode pins extending upwards away from the conductor plate and in electrical contact with the plate.

8. An electrode as claimed in Claim 7, which includes a raised portion in the form of a circular metal plate with a dimension smaller than the conductor plate, of which the bottom surface is in full electrical contact with the conductor plate, with the electrode pins extending from the raised portion. K p_{CT/ZA2010/000|)41}

9. An electrode as claimed in Claim 8, wherein the raised portion is welded along its circumference to a ring, which ring, in turn, is welded to the conductor plate and the hollow space formed by the raised portion, the ring and the conductor plate is filled with graphite.

10. A furnace, which furnace includes:

a bottom electrode as claimed in Claim 7 or Claim 8;

a lining of refractory bricks on top of the conductor plate and about the electrode pins; and

11. A method of energising a DC furnace, which method includes the step of spreading DC current through a circular bottom electrode connector plate, through electrode pins and through a melt.

12. A DC furnace bottom electrode connector, substantially as described herein with reference to the accompanying drawings.

13. A bottom electrode for a DC furnace, substantially as described herein with reference to the accompanying drawings.

14. A furnace, substantially as described herein with reference to the accompanying drawings.

15. A method of energising a DC furnace, substantially as described herein with reference to the accompanying drawings.