WO1998053643A1

WO1998053643A1 - Electrode seal and holder therefor

Info

Publication number: WO1998053643A1
Application number: PCT/CA1998/000503
Authority: WO
Inventors: Felim P. Mccaffrey
Original assignee: Hatch Associates Ltd.
Priority date: 1997-05-23
Filing date: 1998-05-22
Publication date: 1998-11-26
Also published as: AU7516998A

Abstract

An electrode seal for an arc furnace having at least one electrode passing through an aperture in a refractory zone of the furnace roof has a first water cooled seal member received in the aperture and a second upper water cooled seal member resting on the first member and a sliding fit on the electrode. The seal members are supported from the furnace roof outside of the refractory zone by cantilevers of which that supporting the second seal member can move longitudinally and laterally relative to that supporting the first seal member. Hoses conducting water to and from the seal members are housed within tubular members of the cantilevers, and the seal elements are electrically insulated from the cantilevers.

Description

ELECTRODE SEAL AND HOLDER THEREFOR

This invention relates to electrode seals for electric arc furnaces of the type having at least one depending graphite electrode passing through an aperture in a refractory zone of a furnace roof. It is desirable to minimize the passage of furnace gases through the aperture around the electrode, and to reduce heating of the refractory of the furnace roof within the aperture.

Despite the basic simplicity of the requirement, the development of a satisfactory electrode seal has proved a most intractable problem which has attracted many attempts to solve it without any generally satisfactory solution having been found.

The most promising approach has been to utilize interacting water cooled annular seal members, one engaging and protecting the aperture in the refractory zone of the furnace roof, and the other embracing the seal itself, the two being in sealing interengagement such as to provide for relative movement of the seal members. Telescoping arrangements with one seal member fixed relative to the electrode have been widely proposed and utilized, but are usually not practicable when a wide range of vertical movement of the electrodes must be accommodated.

In International Patent Application No. WO95/17801, the same applicant and inventor proposed an arrangement in which an electrode engaging seal member was resiliently retained upon a bearing surface of a roof engaging member, the electrode engaging seal member being formed segmentally so as to provide a sliding fit on the electrode, the segmental structure accommodating electrode irregularities. Although this arrangement functioned well as an electrode seal, two problems emerged during tests. Firstly, it proved difficult to provide adequate accommodation for the passage between segments of circumferential eddy currents induced in the segmented seal member, and secondly the arrangement presented a potential hazard in the event of catastrophic failure of the refractory zone of the furnace roof in that the water filled seal elements supported thereon might possibly fall into the furnace interior with a subsequent risk of explosion.

It is an object of the present invention to provide an electrode seal providing the same functionality, but which addresses the above problems and is of simplified construction .

The electrode seal of WO95/17801 departed from convention in that it did not attempt to maintain continuous contact between the seal and the electrode. Instead the seal was dimensioned to accommodate the nominal maximum diameter of the seal, the segmental construction of the seal being required only to accommodate material adhering to the electrode surface, and possible irregularities where adjacent electrode segments are connected to one another. In practice it has been found that the strength of adherence of foreign matter to the graphite is relatively low, and provided that adequate control of vertical movement of the seal elements relative to the furnace roof is achieved, such material can simply be scraped off by a metallic seal. Provided that dimensional tolerances are maintained in electrodes, it has been found that irregularities between adjacent electrode segments can also be accommodated without segmentation of the seal. Additionally, small gaps providing passages between adjacent surfaces of components are found not to result in significant leakage provided that the gaps are no more than about 2mm wide and narrow relative to the length of the passage which they form.

According to the invention, there is provided an electrode seal for an arc furnace having a roof and at least one graphite electrode extending downwardly through a refractory zone of said roof, said seal comprising first and second interengaging annular water cooled metal seal members, a first of said seal members engaging the periphery of an opening in said refractory zone, and a second of said seal members being a sliding fit on said electrode, with said second seal member having a downwardly facing bearing surface engaging an upwardly facing bearing surface on said first member for accommodating relative movement of said members in a plane perpendicular to electrode, wherein each seal member is supported independently of said refractory zone by a cantilever extending radially over said refractory zone to a support outside of it, said cantilevers including cooling water supply conduits to and from said annular seals, and further incorporating barriers to the passage of electric current through said cantilevers.

Preferably the cantilevers are arranged concentrically with one having sufficient lateral and longitudinal play within the other to accommodate relative movement of the bearing surfaces of said seal members.

Further features of the invention will become apparent from the following description of a presently preferred embodiment thereof.

SHORT DESCRIPTION OF THE DRAWINGS

Figure 1 is a plan view of a seal in accordance with the invention shown mounted on an electric arc furnace, shown fragmentarily ; Figure 2 is a corresponding side elevation of the seal, adjacent portions of the furnace structure being shown in vertical section, with the electrode omitted; Figure 3 is a plan view of an upper seal member; Figure 4 is a plan view of a lower seal member; and Figure 5 is a vertical cross-section through cantilevers supporting the seal.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to Figures 1 and 2, there is shown an electric arc furnace F, in this case a three phase A.C furnace having a roof 2 with a central refractory zone or insert 4 formed with apertures 6 for three graphite electrodes 8 of which only one is shown in Figure 1. The gaps between the apertures 6 and the electrodes 8 are substantially closed by electrode seal assemblies S of which only one is shown.

Each electrode seal assembly comprises an upper electrode seal member 10 and a lower aperture seal member 12, the latter being provided with a skirt 14 which enters the associated aperture 6. The seal members are formed from highly thermally conductive metal such as copper, although a higher strength copper alloy such as beryllium copper is preferred for the upper electrode seal member 10 because of its strength. Each seal member formed with a circumferential internal water passage 16 extending between ports 18 in an external tangential flange through which the seal member is connected to a manifold by bolts 20.

The manifolds 22 and 24 to which the seal members are secured are located at the distal end of a cantilever assembly C comprising three parallel pipe assemblies 26, 28 secured together by clamps 30, 32, of which the clamp 32 is shown in Figure 5. The outer pipe assemblies 26 are held rigidly in the clamps, while the centre pipe assembly 28 is permitted to move longitudinally and laterally in tubular openings 34, 36 formed in the clamps. The opening 36 in the clamp 32 is shown, and it is wider than the opening 34 in the clamp 30. The clamps 30, 32 are formed in upper and lower parts 38, 40 with vertical flanges 42,44 and a mounting flange 46 whose height relative to the roof 2 of the furnace may be adjusted by screws 50 passing through nuts 48 secured to the flange 46 and locked by lock nuts 47, such that a lower bearing surface 52 of the seal member 12 rests flat on a bearing ring 54 supported by the refractory insert 4. In a presently preferred arrangement, the screws 50 may be adjusted so that there is a very slight clearance between the bearing surface and the bearing ring. This accommodates differential expansion of the parts and minimizes friction, without resulting in excessive leakage provided that the clearance is less than about 2 millimetres.

In order to secure the seal assembly to the furnace roof, chains 41 are wound about ears 43 on the upper parts 40 and lugs 45 on the furnace roof, although other securement means could be used.

The pipe assemblies 26 comprise non-electrically conductive inner cooling water hoses 56 located concentrically within rigid outer tube members 58 by annular insulating spacers 57. Flanges 60 at the distal ends of members 58 are connected to flanges 62 of pipe stubs 64 on the manifold 24 through a coupling assembly comprising a short intermediate pipe coupling 66 flanged at both ends and bolted to the flanges 60 and 62 through electrically insulating spacers 65, the bolts 68 being provided with insulating cups 67 and insulating sleeves so as to avoid short-circuiting the spacers. The hoses 56 are provided with hose couplings 70 connected to couplings 72 within the flanges 62 such that water from one hose 56 passes into one pipe stub 64, through outside the manifold 24 to one port 18 of the passage 16 of the member 12, through the passage and the other port to the other side of the manifold 24, and thence back through the other pipe stub 64 and the other hose 56. The upper and lower portions 38, 40 of the clamps are secured by bolts 39 which can be loosened to adjust the longitudinal position of the assemblies 26 to align the seal portion 12 with an aperture 6. The pipe assembly 28 consists of a rectangular metal casing 74 within which extend two non-electrically conductive hoses 76 maintained in position within the casing by insulating spacers 78 bolted around the hoses. The casing 74 has a flange 80 at its distal end and is connected to a flange 82 of the manifold 22 through a coupling assembly 84 comprising a short intermediate connector flanged at both ends and bolted to the flanges 80 and 82 by bolts 86 through electrically insulating spacers 85, insulating cups 87 and insulating sleeves so as to avoid short-circuiting the spacers. The hoses 76 are provided with hose couplings 88 connected to fixed couplings on the manifold 22 within the flange 80 from which vertically spaced passage extend through the manifold to the ports 18 of the passage 16 in seal member 10, thus providing a continuous passage for water between the hoses 76 and through the seal member 10.

It should be noted that two insulating spacers are provided in each cantilever to provide redundancy in the event that one insulator loses its effectiveness in the adverse environment found adjacent a furnace. The non-electrically conductive hoses are of sufficient length that the water within them provide an adequate barrier to the passage of significant electric currents. The spacers 57 and 75 keep the hoses away from the outer tube members 58 and casing 74 thus protecting the hoses from flame emissions which may impinge on the cantilevers.

A planar surface 90 on the underside of member 10 is held against an upper planar surface 92 on the seal member 12, movement relative to the seal member 12 being accommodated by angular and longitudinal movement of the casing 74 within the tubular openings 29.

The pipe assemblies 26 and 28 provide cantilever support for the seal members 12 and 10 respectively with respect to the support rods 50 from points well outside the insert 4. The seal members are continuous conductive rings, but are electrically insulated from the furnace roof by the spacers 65 and 85, which form barriers to the passage of electric current through the cantilevers.

In operation, the aperture in the seal member 10 is dimensioned just to accommodate an electrode 8 of diameter at the upper end of the tolerance range for electrode diameter, and the cantilever formed by the pipe assemblies and clamps supports it sufficiently rigidly that material adhering the outer surface of the electrode to bring it over tolerance will simply be scraped off as the electrode moves through the seal member. The system is set up so as to maintain gaps between the various seal and support members, and the seal member 10 and the electrode 8 less than about 2mm. If the insert 4 should collapse, the seal members will remain supported by the cantilever assembly. The seal members are free of projections which might promote flashover between electrodes and are simple and robust in construction, and the water supply hoses are well protected and do not extend over the insert 4. The seals are electrically isolated from the rest of the seal assembly.

Claims

CLAIMS :

1. An electrode seal for an arc furnace having a roof (2) and at least one graphite electrode (8) extending downwardly through a refractory zone (4) of said roof, said seal comprising first and second interengaging annular water cooled metal seal members (10,12), a first of said seal members (12) engaging the periphery of an opening (6) in said refractory zone, and a second of said seal members

(10) being a sliding fit on said electrode, with said second seal member having a downwardly facing bearing surface (90) engaging an upwardly facing bearing surface

(92) on said first member for accommodating relative movement of said members in a plane perpendicular to electrode, characterised in that each seal member (10,12) is supported independently of said refractory zone by a cantilever assembly (C) extending radially over said refractory zone (4) to a support (30,32) outside of it, said cantilever assembly including cooling water supply conduits (56,76) to and from said annular seals, and further incorporating barriers (65,85) to the passage of electric current through said cantilever assembly.

2. An electrode seal according to claim 1 characterised in that the cantilever assembly comprises pipe assemblies (26,28) arranged concentrically with one having sufficient lateral and longitudinal play within the other to accommodate relative movement of the bearing surfaces of said seal members.

3. An electrode seal according to claim 1 characterised in that the pipe assemblies (26,28) are tubular, and the conduits are hoses (56,76) located within the tubular pipe assemblies and carrying water to and from water passages (16) extending circumferentially within said seal members.

4. An electrode seal according to claim 3 , characterised in that insulating spacers (57,78) maintain the hoses spaced from the tubular pipe assemblies.

5. An electrode seal according to claim 3, characterised in that the support includes clamps (30,32) securing the pipe assemblies to the roof (2) of the furnace radially outwards of said refractory zone, the clamps allowing lateral and longitudinal movement of the pipe assembly supporting the second seal member.

6. An electrode seal according to claim 4, characterised in that the clamps (30,32) have means (39) for adjusting the position of the cantilevers supporting the first seal member (12) to align the latter with an opening (6) in the refractory zone.

7. An electrode seal according to claim 1, characterised in that the second seal member (10) is formed by a continuous annulus of beryllium copper.

8. An electrode seal according to claim 3, characterised in that electrically insulating spacers (65,85) are secured between the tubular pipe assemblies and manifolds connecting the hoses to the water passages.

9. An electrode seal according to claim 8, characterised in that a connecting member (66,84) sandwiched between two insulating spacers (65,85) is secured between each tubular pipe assembly and the manifold to which it is connected.