WO1998000568A1

WO1998000568A1 - Arc furnace with an electrode receiving chamber

Info

Publication number: WO1998000568A1
Application number: PCT/EP1997/001808
Authority: WO
Inventors: Karl-Heinz Klein; Klaus Kimmer
Original assignee: Badische Stahl Engineering Gmbh
Priority date: 1996-07-01
Filing date: 1997-04-11
Publication date: 1998-01-08
Also published as: AU2637697A; EP0909333A1; CA2259180A1; JP2000514910A; KR20000022479A; BR9710120A; DE19626389A1

Abstract

An arc furnace has a furnace vessel, a furnace inner chamber and at least one electrode (4) that projects into the furnace inner chamber. The furnace is characterised by an electrode receiving chamber (5) accessible from one side of the furnace vessel, thermally shielded from the furnace inner chamber and provided with at least one passage (9) for the electrode (4) oriented towards the furnace inner chamber. This electrode receiving chamber (5) designed as a depression allows a furnace vessel with a great overall height to be driven with a relatively short electrode (4) which thanks to its small, free and clamped length has a lesser tendency to break.

Description

Arc furnace with electrode receiving space

The invention relates to an arc furnace, with a furnace vessel, a furnace interior, and with at least one electrode protruding into the furnace interior.

Electric arc furnaces are used, among other things, to melt steel scrap. To improve the thermal efficiency of the furnace, it has already been proposed to use the hot furnace gases for preheating the scrap. For this purpose, EP 0 291 680 B2 proposes to provide a shaft installed on the side of the furnace vessel, through which the scrap is fed. The furnace exhaust gas flows through the shaft and heats up the scrap inside. This design is complicated and requires electrodes that can be moved both horizontally and vertically.

It has already been proposed to build arc furnaces relatively high, so that a comparatively high column of scrap can stand above the molten steel and is heated by furnace exhaust gas. However, this design requires very long graphite or carbon electrodes. If the free clamped electrode length is long, the risk of breakage of the electrode increases, since radial forces acting on the electrode (for example due to collapsing scrap) cause a high bending moment at the clamping point.

The invention has for its object to provide an arc furnace of the type mentioned, which has a high thermal efficiency and is both inexpensive to operate and reliable. The invention solves this problem by means of an electrode receiving space which is accessible from one side of the furnace vessel and is thermally shielded from the furnace interior and has at least one passage opening for the electrode facing the furnace interior.

First, some terms used in the context of the invention are explained. The interior of the furnace is the space in which the steel is melted. It is usually limited at the bottom by the base of the stove or oven. The furnace shaft into which the batch to be melted is poured is also part of the furnace interior.

The electrode receiving space serves to receive at least a part of one or more electrodes required for operating the furnace. An electrode is usually used in a DC arc furnace, and a three-phase arc furnace is usually three electrodes. The electrode receptacle is accessible from the side of the furnace. This means that holding and guiding devices for the electrode can engage in this electrode receiving space from the side. Through the passage opening facing the furnace interior, the lower part of the electrode can be moved from the electrode receiving space into the furnace interior, so that the electrode tip is at the intended site of action. The feature "thermally shielded from the furnace interior" is to be understood in such a way that the electrode receiving space has temperatures during furnace operation which are significantly lower than in the furnace interior and which make it possible to arrange a conventional electrode clamping device, including the devices intended for supplying current, within the electrode receiving space.

The invention enables the operation of an arc furnace of great height with an arc electrode which has a comparatively short free clamped length. In the prior art, the electrode is inserted into the furnace interior through an opening in the furnace cover, and the free clamped length must therefore extend over most of the overall height of the furnace. In contrast, it is proposed according to the invention to provide a separate electrode receiving space which is accessible from one side of the furnace vessel. The electrode clamping head can be arranged in this receiving space, in the operating position of the electrode it can be arranged just above the passage opening of the electrode receiving space to the furnace interior. The The required free, clamped-in electrode length is considerably smaller, it only has to bridge the distance from this through opening arranged in a region below the furnace cover to the intended point of action of the electrode tip. In the case of a built-up furnace, for example, the height of the electrode receiving space can extend over the upper half of the overall height of the furnace vessel. The required free clamped electrode length can be roughly halved.

Conventional arc furnaces have a height / diameter ratio that is approximately 0.35. According to the invention, furnaces with a corresponding ratio of, for example, 0.85 can be built, which nevertheless require no or only an insignificantly greater free clamped electrode length. The large height enables the furnace exhaust gases to be used effectively for preheating scrap, while the comparatively small free clamped electrode length ensures safe and cost-effective operation.

The electrode is preferably arranged on a support arm which projects into the electrode receiving space from the side. This support arm usually runs essentially horizontally, the support arm and the electrode arranged thereon can be moved vertically within this space. This vertical method allows the electrode to be moved into and out of the furnace interior through the passage opening. The support arm can comprise a conventional electrode clamping head, which clamps a graphite or carbon electrode, which may be nipped together from several lengths, and supplies the electrode current. However, a so-called combination electrode can also be used within the scope of the invention. In the case of such a combination electrode, an electrode head designed as a permanent electrode is arranged on the support arm, to which a wear electrode is attached, usually nippled, in the lower region.

The electrode receiving space is advantageously designed as an inward indentation of a side wall of the furnace vessel. The essentially vertical walls of the indentation separate the electrode receiving space from the furnace interior. As a lower boundary with respect to the interior of the furnace, the indentation advantageously has a bottom with the passage opening for the electrode arranged therein. The height of the indentation preferably extends over approximately one third to two thirds of the overall height of the furnace. Arc furnaces are usually approximately circular in cross section. In this case, the indentation preferably extends radially from the furnace circumference to the center of the furnace. It preferably extends at least to the middle of the furnace cross section, so that the electrode receiving space can receive the support arm and the upper part of an electrode arranged centrally in the furnace. The indentation can taper radially from the outside inwards, roughly speaking, its cross-sectional area then has the shape of a trapezoid. However, the indentation can also extend with a substantially constant cross section radially from the outside to the center, its essentially vertical boundary walls running from the side wall to the center of the furnace are then arranged essentially parallel to one another.

The passage opening for the electrode facing the furnace interior is preferably formed in the bottom of the electrode receiving space.

In a particularly preferred embodiment of the invention, the electrode receiving space extends to the upper edge of the furnace vessel and is additionally accessible from above. In this embodiment of the invention, the electrode and the support arm can be moved upward out of the receiving space if necessary. This makes maintenance and electrode replacement easier. In the preferred embodiment of the electrode receiving space as an indentation, this indentation is left open at the top.

The walls of the electrode receiving space facing the furnace interior or at least some of these walls are preferably provided with cooling devices. As cooling devices, cooling media (preferably water), for example, can flow through

Pipelines serve. These cooling devices improve the thermal shielding of the electrode receiving space from the interior of the furnace and increase the service life of the furnace vessel. As a rule, cooling devices are also provided on or in the other walls of the furnace vessel.

The side walls of the furnace vessel can run essentially vertically in one embodiment of the invention. The free cross-sectional area of the furnace interior is then reduced in the upper part of the furnace by the electrode receiving space, but it does not change due to the course of the walls of the furnace vessel. However, it is within the scope the invention also possible that at least a portion of the side walls of the furnace vessel run obliquely inwards from top to bottom. The inclination of the corresponding wall sections can be approximately up to 10 ° to the vertical.

The wall section running obliquely inwards from top to bottom can be arranged in the height section of the furnace in which the electrode receiving space is located. If, for example, the electrode receiving space extends over the upper half of the furnace vessel, the wall of the furnace vessel is inclined in this upper furnace section, so that the furnace vessel tapers from top to bottom at this height section. In this embodiment, the free cross-section of the furnace interior or furnace shaft is initially limited by the electrode receiving space and continues to decrease due to the inclined furnace walls extending down to the lower limit of the electrode receiving space. The free cross-section widens below this range, since it is no longer restricted by the electrode receiving space. Since the furnace walls run vertically in this area, there is no further narrowing of the cross-section. The described slightly inclined furnace wall course makes it easier for the cargo (scrap) to slide down without bridging.

In the context of the invention, the open vessel can be composed of a lower part and an upper part. The electrode receiving space is then arranged in the upper part. The lower part of the furnace has an essentially cylindrical or frustoconical cross section and can be designed as in a conventional arc furnace. The upper part of the furnace has the indentation forming the electrode receiving space, the lower end of the indentation is provided with a base plate, which in turn has a passage opening for the electrode. This two-part construction is structurally simple and inexpensive.

If a larger quantity of charge is introduced and preheated in the furnace shaft, it may be advantageous to control the supply of the charge (scrap) to the immediate area of the arc, i.e. to the melting zone. For this purpose, according to the invention arranged in the furnace interior above the hearth catcher for cargo. The term safety gear includes everything Devices that at least hinder the sliding of cargo from the upper area of the furnace interior towards the hearth.

These folding devices are preferably arranged approximately at the level of the lower boundary of the electrode receiving space. That part of the furnace shaft whose free

Cross section through the electrode receiving space is then used as a storage space for the scrap, the scrap contained therein is preheated by the hot exhaust gases. The part of the furnace interior that is no longer delimited by the electrode receiving space in its free cross section serves as the melting zone. The catching devices are preferably fingers which can be pushed into the furnace interior through openings in the side walls of the furnace and which, when pushed in, together form a type of grating which holds the charged goods. The clear distance between two fingers is preferably in the range of about 500 to 1000 mm, the cross section of the fingers preferably tapers in the direction of their end located in the furnace interior.

The lid of the furnace vessel can be made in one piece and close the furnace shaft during operation. It is adapted to the shape of the furnace vessel. If the electrode receiving space extends to the upper edge of the furnace vessel, the cover has an incision corresponding to the shape of the indentation. In this embodiment, the furnace cover and the electrode are usually together on one

Structure arranged. To load the furnace, the lid is lifted, and at the same time the electrode is moved out of the furnace. As soon as the lid and electrode are raised to such an extent that the electrode tip is no longer in the interior of the furnace but in the electrode receiving space, the lid and electrode can be swiveled away to the side and the furnace can be loaded. The upper opening of the indentation is expediently closed during the scrap loading in order to prevent scrap from falling into this indentation. For this purpose, a separate cover can be provided, which closes the indentation during loading. Alternatively, a correspondingly designed scrap basket can be provided which fits exactly on the furnace vessel and closes the indentation at the top.

In another embodiment of the invention, the furnace has a two-part cover. The lower lid part is designed as a scrap feed hopper The top lid closes this scrap feed hopper. The lower part of the lid expediently covers the upper opening of the indentation and thus prevents scrap from falling into the indentation. The part of the bottom of the lid lower part located above the indentation is expediently inclined towards the furnace shaft, so that the scrap scrap slides into the furnace shaft. To load the furnace, just lift the top lid and fill in scrap. This upper part of the lid can be lifted and swung out independently of the electrode. Only for changing the electrodes or for other maintenance work must the lower part of the lid also be raised so that the electrode and the support arm can be moved upwards out of the electrode receiving space. The lower lid part and the electrode can therefore be arranged on a common supporting structure. Expediently, however, the electrode can be moved independently of the lower part of the lid, so that the electrode can be completely or partially moved upwards out of the furnace interior while the furnace is being loaded with scrap, in order to protect it from the mechanical effects of collapsing scrap.

Embodiments of the invention are explained below with reference to the drawings. In it show:

Figure 1 is a side view of an arc furnace according to the invention.

2 is a top view;

Fig. 3 is an axial section along the line A-A in Fig. 2;

4 shows a corresponding axial section of another embodiment with an upper part of the furnace vessel tapering from top to bottom;

5 shows an axial section of a third embodiment with fingers protruding into the furnace interior as catching devices for the cargo.

Fig. 6 shows an axial section of a further embodiment with a two-part cover. The arc furnace has a vessel base or hearth 1 lined with refractory stones. A furnace vessel part 2 with an essentially cylindrical cross section is arranged above the stove. The electrode 4 projects into the section of the furnace interior enclosed by the furnace vessel part 2.

A further furnace vessel part 3 is arranged above the furnace vessel part 2 and has an indentation 5 pointing radially inward over its entire height and extending beyond the center of the essentially circular cross-sectional area. The outer wall of the upper furnace vessel part 3 is thus recessed on a certain circumferential angle, a substantially vertical wall 6 delimits the electrode receiving space or the indentation 5 with respect to the furnace interior 7 formed, in which a preferably circular passage opening 9 is provided for the electrode 4. The passage opening 9 is preferably concentric with the center of the furnace.

The electrode 4 is arranged on a support arm 10 and is held by a clamping head 11, via which the current is also supplied. The support arm 10 protrudes into the indentation 5, it can be moved vertically together with the electrode 4.

The wall 6 of the indentation 5 and its base plate 8 thermally shield the electrode receiving space 5 from the furnace interior. The wall 6 and the base plate 8 are water-cooled.

On the walls of the furnace vessel parts 2 and 3 facing the furnace interior, water-cooled wall elements 12 are arranged, which are preferably replaceable as wearing parts.

In the embodiment of the arc furnace shown in FIG. 3, the upper furnace vessel part 3 has an essentially cylindrical cross section, which is only through the

Indentation 5 is interrupted. The walls of the furnace vessel part 3 run essentially vertically. In the embodiment shown in FIG. 4, the walls of the upper furnace vessel part 3 run obliquely inwards from top to bottom. The free cross section of the furnace shaft 7 within the upper furnace vessel part 3 tapers from top to bottom. The angle of inclination of the inclined wall is preferably less than 10 ° to the vertical. This slightly conical design of the upper furnace vessel part 3 facilitates scrap sliding without undesirable bridging.

In the embodiment shown in FIG. 5, a plurality of fingers 13 are arranged distributed over the circumference of the upper furnace vessel part 3, which are mounted on rollers 14 and can be inserted into the furnace shaft 7 through openings 15. The clear distance between two neighboring fingers is about 500 to 1000 mm. These fingers 13 make it possible to initially hold the charged goods in the furnace shaft 7 of the upper furnace vessel part 3 and to have them preheated by the hot exhaust gases. By pulling back the fingers 13, scrap can then be added in a targeted manner into the lower furnace vessel part 2, where it is melted by the arc emanating from the electrode 4.

The lid of the furnace vessel (not shown in FIGS. 1-5) is adapted to the shape of the vessel and in particular has an incision corresponding to the shape of the indentation 5. Therefore, even when the furnace cover is in place, the electrode 4 and the electrode support arm 10 can be moved upward out of the indentation 5 if necessary. If the furnace is to be loaded with scrap, the electrode 4 is moved out of the furnace to such an extent that the free end of the electrode 4 protrudes into the furnace interior to such an extent that it cannot be damaged by subsequent scrap. The furnace lid is raised and swung out to the side. Possibly. As already described above, the furnace lid and the electrode can be arranged on a common supporting structure and can thus be lifted and swung out together. The upper opening of the indentation 5 is expediently closed during the scrap loading in order to prevent scrap from falling into the indentation 5. For this purpose, a separate cover can be provided for the indentation 5.

Alternatively, the scrap loading can be carried out by means of an appropriately designed scrap basket which fits exactly on the furnace vessel and closes the indentation 5 towards the top. It should be noted that the electrode 4 and the electrode support arm 10 must not be moved so far upwards during loading that they hinder the closing of the indentation 5 towards the top by means of the special cover or the specially adapted scrap basket.

6 shows an embodiment of the arc furnace with a two-part furnace cover. The lower lid part 17 is designed as a scrap feed hopper. It covers the upper opening of the indentation 5 and in this area has an inclined floor 20 which allows the scrap contained therein to slide to the furnace shaft 7. The lid upper part 18 is removable for loading the funnel 17 with scrap. An exhaust gas outlet 19 serves to discharge the exhaust gases rising from the area of the arc after these have been located in the furnace shaft 7 and in the lower lid part 17

Flowed through and preheated scrap. To load the furnace with scrap, just lift the top lid and swing it out. Possibly. can the electrode 4 be moved up slightly so that it may falling scrap is protected. The lower lid part 17 only has to be raised and swung out when the indentation 5 must be accessible from above. This can be necessary, for example, when changing electrodes or for other maintenance work.

After loading with scrap, the lid (or the lid upper part 18) is placed on the furnace, the electrode 4 is moved into its operating position and the arc is ignited. In the embodiments shown in FIGS. 5 and 6, the scrap supply from the furnace shaft 7 can be controlled in a targeted manner by moving the fingers 13.

Claims

claims

1. arc furnace, with a furnace vessel, a furnace interior, and with at least one electrode protruding into the furnace interior, characterized by an electrode receiving space (5) accessible from one side of the furnace vessel and thermally shielded from the furnace interior, with at least one passage opening facing the furnace interior (9) for the electrode.

2. Arc furnace according to claim 1, characterized in that the electrode (4) is arranged on a support arm (10) which projects from the side into the electrode receiving space (5).

3. Arc furnace according to claim 1 or 2, characterized in that the electrode receiving space (5) is designed as an inward indentation of a side wall (3, 16) of the furnace vessel.

4. Arc furnace according to one of claims 1 to 3, characterized in that the electrode receiving space (5) from the side wall (3, 16) of the furnace vessel extends to at least the middle of the furnace cross section.

5. Arc furnace according to one of claims 1 to 4, characterized in that the passage opening facing the furnace interior (9) for the electrode (4) is formed in the bottom of the electrode receiving space (5).

6. Arc furnace according to one of claims 1 to 5, characterized in that the electrode receiving space (5) extends to the upper edge of the furnace vessel and is additionally accessible from above.

7. Arc furnace according to one of claims 1 to 6, characterized in that the walls facing the furnace interior (6, 8) of the electrode receiving space (5) have cooling devices.

8. Arc furnace according to one of claims 1 to 7, characterized in that at least a part (16) of the side walls of the furnace vessel run obliquely inwards from top to bottom.

9. Arc furnace according to claim 8, characterized in that the obliquely inwardly extending wall section (16) is arranged in that height section of the furnace in which the electrode receiving space (5) is located.

10. Arc furnace according to one of claims 1 to 9, characterized in that the furnace vessel is composed of a lower part (2) and an upper part (3, 16) and that the electrode receiving space (5) is arranged in the upper part (3, 16) .

1 1. Arc furnace according to one of claims 1 to 10, characterized in that in the furnace interior above the hearth (1) catching devices (13) are arranged for cargo.

12. Arc furnace according to claim 1 1, characterized in that these catching devices (13) are arranged approximately at the level of the lower limit of the electrode receiving space (5).

13. Arc furnace according to claim 11 or 12, characterized in that the catching devices through openings (15) of the side walls of the furnace in the furnace interior sliding fingers (13).

14. Arc furnace according to one of claims 6 to 13, characterized in that it has a two-part cover, the lower part is designed as a scrap feed hopper (17) and the upper part (18) closes the scrap feed hopper (17).