WO2006117426A1

WO2006117426A1 - Lid for electric arc furnace

Info

Publication number: WO2006117426A1
Application number: PCT/FI2006/000133
Authority: WO
Inventors: Tom RÖNNBERG; Janne Ollila; Jouko Kangas
Original assignee: Outotec Oyj; Outokumpu Technology Oyj
Current assignee: Metso Corp
Priority date: 2005-04-29
Filing date: 2006-04-24
Publication date: 2006-11-09
Anticipated expiration: 2007-10-29
Also published as: FI20050448A0; FI20050448L; FI118825B

Abstract

The invention relates to a steel-structured, water-cooled electric arc furnace lid that is fitted in a gas-tight manner on top of the furnace vessel and provided with lead- throughs for electrodes and apertures for material feed, the underneath surface of said lid being provided with refractory lining. The lid is planar and constructed of at least three planar double casing panels, so that the lid meets the vertical edge of the vessel at right angles.

Description

LID FOR ELECTRIC ARC FURNACE

The present invention relates to the structure of an arc furnace used in metallurgy. More precisely, the invention relates to the structure of the lid of an electric furnace, and even more precisely to a closed electric arc furnace as well as to the matching of the lid and the vessel of the furnace.

An electric furnace used in metallurgic processes, for instance in the manufacturing of ferrochromium, is composed of a vessel and a lid, as well as electrodes lead through the lid. The lid is provided with lead-throughs for three generally Sόderberg-type electrodes, and apertures for gas outlet and material feed. The lid is fitted in a gas-tight manner at the vessel edges and supported at several spots against the ground by support beams. The lid also is electrically insulated from the furnace vessel. Generally the gas-tightening and the electric insulation are realized by means of a so-called sand seal, where the gap left between the lid and the vessel is filled with sand.

The lid of an electric furnace is also called a vault, because in traditional arrangements, the lid is made by brick masonry or by casting mass into an upwardly arching vault. From the Finnish patent application 811 ,763, there is known an electric furnace vault constructed of ceramic material, where the center part in which the electrode lead-throughs are arranged is water-cooled by spiral pipeworks. At the same time, the spiral pipeworks constitute part of the vault bearing support. The cooling is mainly directed to the lead-throughs, and the lid insulation is realized by ceramic lining on that surface of the lid that falls on the vessel side.

There also is known an electric arc furnace lid that is made of steel and refractory material. In that case the lid comprises a cover with a steel structure, on the lower surface of which there is arranged a refractory lining. The lining is supported against the lid by steel anchors, so that the anchors in part enhance the cooling of the lining by conducting heat to the steel structure. The steel cover is provided with pipework systems for water cooling. In regular electric arc furnace lids with a steel casing, the lining arranged underneath the lid extends as a uniform lining along the whole area of the lid. When the lid elements require maintenance, for instance in connection with the replacing of the lead-throughs, the lining provided on the interior of the lid must be repaired, and often the whole lining must be replaced. This naturally extends the interruption of the productive process and thus causes extra expenses.

Known steel lids are built to conform to the traditional vault-like lid structure, so that at least the edge part of the lid is inclined with respect to the vessel wall, which again is vertical. Now the lid meets the top edge of the vessel at an angle. This kind of junction between vessel and lid often brings forth several problems. The sand seal between vessel and lid is difficult to build to be reliable owing to the inclined structure of the lid. A particular problem is the comer formed by the lid and the vessel wall, in which feed material accretions are easily accumulated in the furnace. As the accretions become thicker, the lid starts to push into the accretion and finally rises up, detached from the vessel edge.

The feed material fed into an arc furnace is composed of solid grains or pellets. The feed flows must be distributed evenly in the furnace and around the electrodes, so that the electrodes could operate at the best possible efficiency, and that the mechanical forces directed to the electrodes can be eliminated. A danger here is that the electrodes can be broken, if the feed material has a chance to bend the electrode.

Solid feed material is fed through several apertures arranged in the lid. The solid pellet-like material flows to the furnace through the apertures with characteristic dynamics, wherefore the feed flow is spread downwardly at an angle that is nearly constant. The feed flow of ferrochromium pellets is generally spread through downwardly pointed feed apertures at an angle of 100 - 120 degrees. The feed material spread between the lid and the vessel edge forms harmful accretions and damages the sealing between the lid and the vessel. Thus the vessel edge should be sufficiently high with respect to the raw material feed apertures, in order to prevent the feed material from flowing between the vessel and the lid.

The now developed electric arc furnace lid eliminates some of the drawbacks connected to the prior art and results in an extremely reliable and easily maintained lid solution. The arc furnace lid according to the invention is a water- cooled, planar steel structure. Owing to its shape, the lid is connected to the vessel at right angles, so that the junction of the lid and vessel remains sufficiently high with respect to the feed flow expanding towards the furnace, thus reducing the formation of accretions in the critical area. The planar lid is a self-bearing structure, where the steel structure forms a double casing, and between said casings, there is arranged a box-like channel system for the cooling water circulation. The cooling water channel is outlined by the upper and lower casings of the lid steel structure as well as the essentially vertical partition walls arranged between the casings. The partition walls in the cooling water channel system reinforce the self-bearing structure of the steel lid. The cooling water channel system essentially covers the whole area of the lid, because the double casing structure extends over the whole area of the lid. Thus the heat transfer surface of the cooling water channels also covers almost the whole area of the lid. On the underneath surface of the steel lid, there is provided a refractory lining i.e. ceramic brickwork, which is in contact with the steel structure. The lid is provided with steel anchors for supporting the brickwork against the lid.

The planar lid of the arc furnace according to the invention is formed of at least three segments that are bolted together, said segments being planar double casing panels. In each panel, there is arranged a panelwise channel for water circulation, a refractory lining layer and lead-throughs. The lid advantageously comprises three panels that form, when seen from above, three radial segments. In addition, the panels are suitably provided with apertures for gas outlet and raw material feed. A lid according to a preferred embodiment of the invention is made of three planar panels that form the center part of the lid, as well as of two panel segments following the perimeter, said segments forming the edge part of the lid. The lead-throughs for the electrodes are arranged in the segments of the center part, one in each segment. Each segment has its own, separate cooling water channel.

According to the invention, the lining provided on the underside of the lid is made separately in each panel, so that the lid segments can be easily replaced in a short time without having to replace the whole lining in other parts of the lid. In a solution according to the invention, the thickness of the refractory lining need not be particularly thick, because water cooling is realized in an effective way that reduces the need for insulation because of the lining. The efficiency of the water cooling is based on the fact that the heat transfer surface extends essentially over the whole area of the underneath surface of the lid. In the invention, the thickness of the lining provided on the underside of the lid is advantageously 80 - 180 mm, preferably 100 - 150 mm.

The invention is described in more detail below, with reference to the appended drawings. Figure 1 illustrates a lid according to the invention, fitted in place on top of the vessel of an electric arc furnace. Figure 2 illustrates a sand seal arranged between the planar lid and vessel according to the invention.

Figure 1 illustrates the lid 10 and vessel 11 of an electric arc furnace. Electrodes 102 are lead through the lid 10, and the lead-throughs 12 are gas- tight and water-cooled. The sand seal 14 arranged between the lid 10 and the vessel 11 passes in a ring between the vessel edge and the lid. The lid is provided with gas outlet apertures 104, apertures 105, 106 for raw material feed and an inspection door 103 that can also serve as a material feed aperture. The lid 10 is straight and meets the vessel 11 at right angles with respect to the edge. The steel-structured lid is composed of several panels 13, 15. In the embodiment illustrated in figure 1 , the number of center part panels 15 is nine, and they are arranged in radial segments that together constitute the center part of the lid. The panels in the center part outline the lead-throughs for the electrodes as well as part of the raw material feed apertures 106. The outer perimeter of the lid is formed by nine panels 13 arranged in a ring. All panels are bolted together, and their ceramic lining 24 on the furnace side is made before the panels are installed in place.

Figure 2 shows the lid 10 and the vessel edge as well as the sand seal 200 in vertical section. The lid 10 is provided with a water flow channel 22 outlined by the lid casings, i.e. the top casing 27 and the bottom casing 26, as well as essentially vertical walls 25. The bottom casing 26 is provided with anchors 23 that fasten the refractory mass layer 24 to the lid 10. The lid 10 is sealed against the vessel edge 21 by a sand seal 200 made of ceramic refractory wool 202 and sand 201. The lid 10 is supported against the ground through a lid support structure 210. In between the lid 10 and the vessel wall 28, there is left a gap that serves, among others, as play for the expansion caused by thermal expansion and as electric insulation. Said gap is provided with a sand seal 200, where the ceramic wool 202 is arranged in between the lid and the vessel, which prevents sand 201 from getting into the furnace. Figure 2 illustrates the steel casing 29 of the vessel wall and the lining 21 of the inner furnace wall.

Claims

1. A steel-structured water-cooled lid of an electric arc furnace, fitted in a gas- tight manner on top of the furnace vessel, provided with lead-throughs for electrodes and apertures for material feed, the underneath surface of said lid being provided with refractory mass lining, and that the lid is planar and constructed of at least three planar double-casing panels, characterized in that the lid 10 meets the vertical vessel edge 28 at right angles when in between the lid 10 and the vertical edge 28 of the vessel, there is arranged a sand seal insulation 200 comprising ceramic wool 202 and sand 201 , so that the wool 202 prevents the sand from flowing into the furnace.

2. A lid according to claim 1 , characterized in that the double casing panels comprise parallel, superimposed steel casings, a top steel casing 27 and a bottom steel casing 26, between which there is arranged a cooling water channel that outlines the steel casings 26, 27 and the partition walls 25 arranged between the essentially vertical casings.

3. A lid according to claim 1 or 2, characterized in that the heat transfer surface of the cooling water channels 22 of the double casing panels essentially covers the whole furnace-side area of the panel.

4. A lid according to claims 1 - 3, characterized in that the furnace-side surface of the double casing panels is prior to the installation provided with a refractory lining with a thickness of 80 - 180 mm, preferably 100 - 150 mm.