ZA200904885B

ZA200904885B - Furnace roof

Info

Publication number: ZA200904885B
Application number: ZA200904885A
Authority: ZA
Inventors: Bonawentura Czeslaw Rendecki
Original assignee: Bonawentura Czeslaw Rendecki
Priority date: 2008-07-04
Filing date: 2009-07-13
Publication date: 2010-06-30

Description

I

BACKGROUND TO THE INVENTION

This invention relates to an improved electrical furnace, and particularly to an improved furnace roof for a closed or open submerged arc furnace.

An electrical submerged arc furnace that is used in metallurgical processes, such as in the production of ferrochrome and ferromanganese, generally comprises a furnace vessel defining a hearth, a furnace roof to seal the vessel, and typically either one or three electrodes extending through the furnace roof and into the vessel. The furnace vessel comprises a furnace floor and an upright side wall, extending from the furnace floor, and which the roof engages when the arc furnace is closed and in operation. The furnace roof includes one or more gas outlet apertures, raw material feed apertures, explosion hatches and electrode ports through which the electrodes protrude through the furnace roof and into the vessel.

Both closed and open electrical submerged arc furnaces generally operate under negative pressure, which means that atmospheric air is drawn into the furnace. In open furnace operations, the atmospheric air is necessary to combust carbon monoxide (CO) resulting from chemical reactions in the furnace. In closed furnace operations, however, the ingress of atmospheric air into the furnace is highly undesirable and it is of paramount importance that the furnace is properly sealed. If the furnace is not effectively sealed, burning of the CO co 2 occurs in the vicinity of the electrode, thus increasing furnace gas temperatures around electrode components like pressure rings and electrode contact plates inside the furnace, and causing damage to the electrode equipment and surrounding roof panels. The CO- burning may result in flames escaping from the furnace bed upwards along the electrode. In the event of improper electrode sealing, such flames cause damage not only under the furnace roof, but often burn equipment and cabling surrounding the electrodes above the furnace roof. Furthermore, in a closed furnace such high temperatures directly in the vicinity of the electrode may overbake the electrode paste causing the electrode and surrounding pressure rings to overheat and break. Also, burning of CO is an unnecessary waste of a valuable energy source.

Accordingly, proper airtight sealing of the electrode(s) where it protrudes through the furnace roof is vitally important, especially in closed furnace operations. Electrical insulation and isolation of the electrodes from each other and from the furnace roof are equally important to prevent stray arcing. Most furnace roofs are made of steel, which is electrically conductive and particularly prone to stray arcing. “Stray arcing” refers to arcing between the electrodes, or between the electrode(s) and the furnace roof, which can damage the roof, causing substantial reductions in furnace productivity. Also, stray arcing can rupture water passages in a water-cooled furnace roof, which can lead to water entering the furnace and resulting in severe furnace explosions and potentially also human fatalities.

In South African patent number ZA 2004/10382, which is incorporated herein by reference, the applicant has attempted to eliminate electrode stray arching by patenting an electrode seal arrangement that is adapted to maintain a tight and secure seal around the electrode where it protrudes through the furnace roof so as to prevent ingress of air into the furnace through the electrode port and to electrically isolate the electrode from the furnace roof. The electrode seal arrangement is further adapted to aliow a degree of controlled lateral displacement of the electrode PCD (pitch circle diameter) within the electrode port, and to y 3 facilitate firm and rigid guiding of the electrode position at a vertical lower end of the electrode proximate where it protrudes through the furnace roof. Rigid guiding is essential to prevent uncontrolled lateral displacement of the electrode, which otherwise would damage sealing media, such as sealing ropes, which could then cause the electrode to make arcing contact with the furnace roof. The electrode seal arrangement of South African patent number ZA 2004/10382 sits on top of the furnace roof over six joint roof panels and includes a seal having an electrically insulated circular base, a cylindrical water jacket that extends from the base and surrounds the electrode, a clamping device for adjustably clamping the seal on the furnace roof, and several strong guide rollers. The seal is laterally adjustable relative to the electrode for accommodating concentric misalignment between the electrode and the electrode port.

One of the difficuities that the applicant has encountered with his patented electrode seal arrangement is the ingress of air into the furnace underneath the electrode seal arrangement, and in particular over the great number of joints between adjacent roof panels, which joints are located under the electrically insulating base of the electrode seal. Those who are familiar with the art will appreciate that one of the many challenges associated with assembling a furnace roof is to arrange adjacent roof panels such that they are completely level with each other so that the joints between the roof panels form airtight seals.

Unfortunately, in practice this is rarely achieved, which results in inter-panel joints that are vulnerable to ingress of air into the furnace through these joints, and especially under the base of the electrode seal. As such the applicant has identified a need for a specially dedicated electrode seal support base designed to minimize the number of joints under the electrode seal so as to minimize the ingress of air into the furnace over the non-level inter- panel joints.

Moreover, a furnace roof generally has a multi-facetted periphery. It comprises a number of steel panels that are bolted together, some of which are insulated from each other by means of refractory material forced into the inter-panel joints. The roof is vertically displaceable above the vessel and is supported by both suspension means, from which the roof hangs, and roof support legs, which stand on the ground and on which the furnace roof sits. The roof includes a substantially planar central portion, and a peripheral tapered portion, which extends radially outwardly from the planar central portion and which is tapered downwardly in the direction of the vessel. The tapered portion of the roof extends as far as the vessel's edges and is generally insulated from the vessel and the ground.

The peripheral tapered portion of the furnace roof defines a tapered corer zone between the underside of the roof, the sidewall of the vessel and the top surface of a molten bath inside the vessel. Conditions inside the vessel are volatile and frothing and sparking take place, the level of the molten bath changes, and the composition and rate of the feed material fluctuates. A common problem during operation of a closed submerged arc furnace is that material, such as slag, is displaced during the melting process onto the sidewall and roof-of the furnace. The level of the molten bath may rise so high in the tapered corner zone that it pushes the furnace roof upwardly, lifting the roof support legs from the ground. The roof becomes unstable and starts moving sideways, “dancing” about the vessel, which may cause bending of the roof.

SUMMARY OF THE INVENTION

According to the invention there is provided a furnace roof for an electric submerged arc furnace, the furnace roof comprising a water-cooled roof structure made of steel and including at least one electrode port through which an electrode protrudes through the furnace roof into the furnace, the furnace roof further comprising an electrode seal support base for supporting an electrode seal that sits on top of the furnace roof, the electrode seal support base being characterised therein that it comprises two dedicated furnace roof panels that are connected to each other to define a level electrode seal support base for receiving the electrode seal, and that cooperate with each other to define the electrode port.

The electrode seal support base may be adapted to support the electrode seal as described in South African patent number ZA 2004/10382.

The two dedicated roof panels of the electrode seal support base may be connected to each other at two opposing joints at radially opposite sides from each other such that together they are concentrically aligned with the electrode port and between them define the electrode port. These two roof panels of the electrode seal support base may be connected at mutually electrically insulating joints. In particular, the insulating joints between the two roof panels of the electrode seal support base may be filled with refractory or the like non- conductive material for electrically insulating and isolating the panels from each other.

Alternatively, the two dedicated roof panels of the electrode seal support base may be hard- bolted to each other.

The two dedicated roof panels of the electrode seal support base may, when connected to each other, have an annular, hexagonal or octagonal periphery.

In one form of the invention the furnace roof may include three electrode ports extending through the roof for allowing three electrodes to protrude through the furnace roof into the furnace. In this arrangement, the furnace roof may include three electrode seal support bases, respectively defining the three electrode ports, and a central roof panel arranged centrally amidst the three electrode seal support bases such that the central roof panel is at least partially surrounded by the three electrode seal support bases. The arrangement may be characterised therein that the electrode seal support bases are electrically insulated from the central roof panel and from each other, thereby electrically isolating the electrodes from each other. The electrode seal support bases may be arranged about the central roof panel in a substantially triangular configuration.

The electrode seal support bases may be separated from each other by three intermediate spacer roof panels arranged intermediate neighbouring electrode seal support bases, the arrangement being such that the three electrode seal support bases and the three spacer roof panels together surround the central panel such that the three electrode seal support bases, the three intermediate spacer roof panels and the central panel together form a substantially planar, inner zone of the furnace roof, referred to as the “Delta section”. The spacer roof panels may be arranged in electrically isolated contact with the electrode seal support bases and with the central roof panel.

The furnace roof also may include an outer, substantially planar, peripheral zone comprising of a number of mutually electrically insulating panels arranged adjacent each other and extending radially outwardly from the Delta section. The furnace roof may be characterised therein that the roof diameter is at least equal to, but preferably greater than, the diameter of a furnace vessel on which it sits. In particular, the furnace roof does not include a peripheral tapered portion. Instead, the outer, substantially planar, peripheral zone of the furnace roof extends at least as far as, but preferably beyond, the vessel's edges, such that the outer, substantially planar, peripheral zone defines a square corner zone between the underside of the furnace roof, a sidewall of the vessel and the top surface of a molten bath inside the vessel.

In one form of the invention, the furnace roof may terminate in a circumferential flange extending downwardly at a right angle from the substantially planar, peripheral zone, such that when the furnace roof is seated on the vessel, the circumferential flange is substantially parallel with the sidewall of the vessel. The downwardly extending circumferential flange may be dimensioned either to meet the sidewall of the vessel, or at least partially to overlap with the sidewall of the vessel.

The furnace roof panels may be electrically insulated and isolated from each other by intermediate insulation joints, which are filled with refractory or the like non-conductive material.

Moreover, the furnace roof may include at least three insulated compensation joints extending radially outwardly from the central roof panel to the circumferential flange and dividing the furnace roof into three equally-sized, magnetically and electrically insulated roof segments. The compensation joints may be filled with refractory or the like non-conductive material.

The furnace roof may be supported by at least one suspension anchor, from which the roof hangs, and at least one, but preferably a number of support legs that stand on the ground surrounding the furnace and on which the roof sits.

The furnace roof may be characterised therein that it has an annular periphery.

The furnace roof may be insulated from the vessel, for example by a circumferential sand seal, as well as insulated from the ground.

The furnace roof may be applied to closed or open, AC or DC submerged arc furnaces.

The invention extends to a furnace roof comprising a water-cooled roof structure made of steel and being characterised therein that the roof diameter is at least equal to, but preferably greater than, the diameter of a furnace vessel on which it sits. The furnace roof may have an annular periphery.

L2009/048g 5

The invention also includes a furnace roof for an electric submerged arc furnace, comprising a water-cooled roof structure made of steel, the furnace roof comprising a substantially planar, inner zone (“Delta section”) and an outer, substantially planar, peripheral zone extending radially outwardly from the inner zone of the roof such that the outer, substantially planar, peripheral zone defines a square corner zone between the underside of the furnace roof, a sidewall of the furnace vessel and the top surface of a molten bath inside the furnace vessel. In one form of the invention, the outer, substantially planar, peripheral zone may terminate in a circumferential flange extending downwardly at a right angle from the substantially planar, peripheral zone, such that when the furnace roof is seated on the vessel, the circumferential flange is substantially parallel with the sidewall of the vessel.

SPECIFIC EMBODIMENT OF THE INVENTION

The invention will now further be described by way of the following non-limiting examples only, wherein —

FIGURE 1 is a plan view of a furnace roof according to the invention comprising three octagonal electrode seal support bases;

FIGURE 2 is a plan view of a furnace roof according to an alternative embodiment of the invention, comprising three hexagonal electrode seal support bases; and

FIGURE 3 is a cross-sectional view of a furnace, showing the planar character of the furnace roof.

A furnace roof according to the invention is designated by reference numeral [10] and is applied to closed or open, AC or DC submerged arc furnaces. In the illustrated embodiments, the furnace roof [10] comprises a water-cooled steel structure and three electrode ports [12] through which an electrode [14] protrudes into the furnace [16]. The

- 9 2009/0483 5 furnace roof [10] includes an electrode seal support base [18] for supporting an electrode seal [8] that sits on top of the furnace roof [10]. The electrode seal support base [18] comprises of two dedicated roof panels [18.1 and 18.2] that are connected to each other to define a level electrode seal support base. The two roof panels [18.1, 18.2] are mutually electrically insulating panels that cooperate so as between them to define the electrode port

[12].

The electrode seal support base [18] is specifically adapted to support the electrode seal as described in South African patent number ZA 2004/10382.

The two dedicated roof panels [18.1, 18.2] of the electrode seal support base [18] are connected to each other at two opposing insulation joints [20] at radially opposite sides of the electrode port [12], such that the electrode seal support base [18] is concentrically aligned with the electrode port [12]. The insulation joints [20] are filled with refractory or the like non-conductive material for electrically insulating and isolating the roof panels [18.1, 18.2] of the electrode seal support base from each other.

The furnace roof [10] includes a central roof panel [22] and three electrode seal support bases [18], respectively defining and surrounding the three electrode ports [12], and arranged in electrically isolated contact with the central roof panel [22]. The electrode seal support bases [18] are arranged about the central roof panel [22] in a triangular configuration. The electrode seal support bases [18] are separated and electrically insulated from each other by three intermediate spacer roof panels [24], arranged intermediate the electrode seal support bases [18] and in electrically isolated contact with the electrode seal support bases [18] and the central roof panel [22]. In particular, the arrangement is such that the central roof panel [22], the surrounding three electrode seal support bases [18] and the three intermediate spacer roof panels [24] together form a substantially planar, inner zone [26] of the roof [10], referred to as the Delta section. The Delta section is preferably manufactured from non-magnetic stainless steel.

The furnace roof [10] also includes an outer, substantially planar and circular, peripheral zone [28] comprising of a number of mutually electrically insulating panels [30] arranged adjacent each other and extending radially outwardly from the inner zone [26] of the roof

[10]. The roof [10] is characterised therein that it is round and the roof diameter is at least equal to, but preferably greater than, the diameter of a furnace vessel [32] on which it sits. in particular, the furnace roof [10] does not include a peripheral tapered portion. Instead, the outer, substantially planar, peripheral zone [28] of the furnace roof [10] extends at [east as far as, but preferably beyond, the vessel's edges, such that the substantially planar, peripheral zone [28] defines a square corner zone [34] between the underside of the roof [10.2], a sidewall [36] of the vessel [32] and the top surface of a molten bath inside the vessel [32].

The furnace roof [10] may terminate in a circumferential flange (vertical side panel) [38] extending downwardly at a right angle from the substantially planar, peripheral zone [28], such that when the furnace roof [10] is seated on the vessel [32], the circumferential flange

[38] is substantially parallel with the sidewall [38] of the vessel [32].

The roof panels [30] are hard-bolted to each other. Moreover, the roof [10] includes at least three insulated compensation joints [42] extending radially outwardly from the central roof panel [22] and dividing the roof [10] into three equally-sized, magnetically and electrically insulated zones. The compensation joints are filled with refractory or the like non-conductive material to prevent stray arching between electrodes. Even the connecting means (not shown) at the compensation joints [42] are electrically insulated in themselves.

The furnace roof [10] has an annular periphery and is supported by at least one suspension anchor (not shown), from which the roof [10] hangs and a number of support legs (not shown) that stand on the ground surrounding the furnace and on which the roof sits. The furnace roof [10] is insulated from the vessel [32] by a circumferential sand seal [44] to prevent the ingress of air. The furnace roof [10] is also insulated from the ground.

It will be appreciated that other embodiments of the invention may be possible without departing from the spirit or scope of the invention as claimed.

Claims

i Him CLAIMS cL I

1. A furnace roof for an electric submerged arc furnace, the furnace roof comprising a water-cooled roof structure made of steel and including at least one electrode port through which an electrode protrudes through the furnace roof into the furnace, the furnace roof further comprising an electrode seal support base for supporting an electrode seal that sits on top of the furnace roof, the electrode seal support base being characterised therein that it comprises two dedicated furnace roof panels that are connected to each other to define a level electrode seal support base for receiving the electrode seal, and that cooperate with each other to define the electrode port.

2. The furnace roof as claimed in claim 1 wherein the electrode seal is the electrode seal claimed in South African patent number ZA 2004/10382.

3. The furnace roof as claimed in claim 1 wherein the two dedicated roof panels of the electrode seal support base are connected to each other at two opposing joints at radially opposite sides from each other such that together they are concentrically aligned with the electrode port and between them define the electrode port.

4. The furnace roof as claimed in claim 3 wherein the joints between the two roof panels are mutually electrically insulating joints for electrically insulating and isolating the two roof panels from each other.

5. The furnace roof as claimed in claim 3 wherein the two dedicated roof panels of the electrode seal support base are hard-bolted to each other.

6. The furnace roof as claimed in claim 1 wherein the two dedicated roof panels of the electrode seal support base, when connected to each other, have an annular, hexagonal or octagonal periphery.

Lo 13

7. The furnace roof as claimed in claim 1 wherein the furnace roof includes three electrode ports extending through the roof for allowing three electrodes to protrude through the furnace roof into the furnace; three electrode seal support bases, respectively defining the three electrode ports; and a central roof panel arranged centrally amidst the three electrode seal support bases such that the central roof panel is at least partially surrounded by the electrode seal support bases.

8. The furnace roof as claimed in claim 7 wherein the electrode seal support bases are electrically insulated from the central roof panel and from each other, thereby electrically isolating the electrodes from each other.

9. The furnace roof as claimed in claim 7 wherein the electrode seal support bases are arranged about the central roof panel in a substantially triangular configuration.

10. The furnace roof as claimed in claim 7 wherein the electrode seal support bases are separated from each other by three intermediate spacer roof panels arranged intermediate neighbouring electrode seal support bases, the arrangement being such that the three electrode seal support bases and the three spacer roof panels together surround the central panel such that the three electrode seal support bases, the three intermediate spacer roof panels and the central panel together form a substantially planar, inner zone of the furnace roof, referred to as the “Delta section”.

11. The furnace roof as claimed in claim 10 wherein the intermediate spacer roof panels are arranged in electrically isolated contact with the electrode seal support bases and with the central roof panei.

12. The furnace roof as claimed in claim 10 wherein the furnace roof also includes an outer, substantially planar, peripheral zone comprising of a number of mutually electrically insulating panels arranged adjacent each other and extending radially outwardly from the Delta section.

LT 14

13. The furnace roof as claimed in claim 1 wherein the furnace roof has a roof diameter that is at least equal to, but preferably greater than, the diameter of a furnace vessel on which it sits.

14. The furnace roof as claimed in claim 12 wherein the outer, substantially planar, peripheral zone of the furnace roof extends at least as far as, but preferably beyond, the diameter of a furnace vessel on which it sits, such that the outer, substantially planar, peripheral zone defines a square corner zone between the underside of the furnace roof, a sidewall of the vessel and the top surface of a molten bath inside the vessel.

15. The furnace roof as claimed in claim 14 wherein the furnace roof terminates in a circumferential flange extending downwardly at a right angle from the substantially planar, peripheral zone, such that when the furnace roof is seated on the furnace vessel, the circumferential flange is substantially parallel with the sidewall of the vessel.

16. The furnace roof as claimed in claim 15 wherein the downwardly extending circumferential flange either meets the sidewall of the vessel, or at least partially overlaps with the sidewall of the vessel.

17. The furnace roof as claimed in claim 12 wherein the furnace roof panels are electrically insulated and isolated from each other by intermediate insulation joints, which are filled with refractory or the like non-conductive material.

18. The furnace roof as claimed in claim 15 wherein the furnace roof include at least three insulated compensation joints extending radially outwardly from the central roof panel to the circumferential flange and dividing the furnace roof into three equally- sized, magnetically and electrically insulated roof segments.

19. The furnace roof as claimed in claim 1 wherein the Le roof £0488.5 periphery.

20. A furnace roof comprising a water-cooled roof structure made of steel and being characterised therein that the roof diameter is at least equal to, but preferably greater than, the diameter of a furnace vessel on which it sits.

21. The furnace roof as claimed in claim 20 wherein the furnace roof has an annular periphery.

22. A furnace roof for an electric submerged arc furnace comprising a water-cooled roof structure made of steel, the furnace roof comprising a substantially planar, inner zone (“Delta section”) and an outer, substantially planar, peripheral zone extending radially outwardly from the inner zone of the furnace roof such that the outer, substantially planar, peripheral zone defines a square corner zone between the underside of the furnace roof, a sidewall of a furnace vessel on which the furnace roof sits, and the top surface of a molten bath inside the furnace vessel.

23. The furnace roof as claimed in claim 22 wherein the outer, substantially planar, peripheral zone terminates in a circumferential flange extending downwardly at a right angle from the substantially planar, peripheral zone, such that when the furnace roof is seated on the furnace vessel, the circumferential flange is substantially parallel with the sidewall of the vessel.

24. A novel furnace roof according to anyone of claims 1, 20 or 22 substantially as herein described, illustrated and exemplified. DATED THIS 13™ DAY OF JULY 2009 SPOOR & FISHER APPLICANTS PATENT ATTORNEYS