Arc furnace and method for operating this arc furnace

Abstract

The invention relates to an arc furnace (1), which can be tilted or remains stationary for tapping the melt or the slag and which comprises an eccentric and/or centric tap (9; 12). The invention also relates to a method for operating an arc furnace (1) of this type. The aim of the invention is to improve an arc furnace with regard to production and to operating characteristics by making structural changes thereto. To this end, the tap (9) is provided inside a separately mounted projection (6) that abuts against a terminating wall (4) of a lower vessel (2). In addition, at least one tapping channel (5) is provided, which connects the furnace trough (2a) and the projection (6) while passing through the terminating wall (4).

Description

[0001] The invention concerns an arc furnace, which can be tilted or remains stationary for tapping the melt or the slag and has an eccentric and/or centric tap, and a method of operating this arc furnace.

[0002] The melt can be tapped on the basis of various well-known designs of the arc furnace: Tapping can be accomplished with an open tapping spout by tilting. Tapping can also be accomplished by a tapping spout with a connected siphon. In arc furnaces of the designated designs, eccentric bottom tapping in a vessel bay (EBT) is well known (DE 82 31 869.7 U1 and DE 198 26 085 A1). Eccentric tapping of this type is also used in an oval vessel (OBT). In addition, centric bottom tapping (CBT) is used in circular vessels.

[0003] Although some of these designs have proven effective, bottom tapping can be further improved to meet operational needs.

[0004] The objective of the invention is to improve production, in-service performance, and the operating sequence.

[0005] In accordance with the invention, this objective is achieved by providing the tap in a separately mounted bay, which abuts a terminal wall of a lower vessel, and by providing at least one tapping channel that passes through the terminal wall to connect the furnace shell and the bay. These design modifications result in more cost-effective production, especially if the vessel is, for example, circular or oval. The terminal wall can be continuously formed in the region of the bay, which results in greater dimensional stability and improved mounting of the refractory lining. The separately mounted bay means high operational flexibility, because this makes a bay of this type interchangeable. An exchange of the nozzle bricks does not have to be carried out in the hot region of the furnace. The tapping channels are readily accessible from the bay. In individual cases, it is possible to dispense with a bay cover. The provision of a taphole valve or a taphole door is not absolutely necessary and can be limited to special cases. In addition, savings of lining material are achieved.

[0006] In an especially advantageous refinement, the bay can be connected to the terminal wall of the lower vessel by a flange joint. Such a flange joint may even be designed as a door that can be swung open.

[0007] To achieve thorough emptying of the lower vessel, it is then advantageous in accordance with other features of the invention for one or more siphon-like tapping channels to run through the terminal wall more or less tangent to the lining profile.

[0008] In this regard, in accordance with additional features of the invention, the tap is arranged in such a way that the taphole of the tap in the bay runs vertically in the zero position, i.e., the horizontal position, of the arc furnace.

[0009] Alternatively, the taphole may be designed with an angle adapted to the tapping angle of the tiltable furnace.

[0010] A method of operating an arc furnace, which is tilted in one swivel direction to tap the melt and in the other swivel direction to tap the slag, such that the melt is tapped eccentrically to the lower vessel, can be carried out in such a way that first the tapping channels are burned out in the lower vessel from the bay side, and, when the melt flows into the bay, the tilting operation is initiated; in that the bay is then sufficiently filled, and the taphole is opened (from the outside); and in that, when the desired amount of melt has been tapped, the arc furnace is tilted back into the zero position or beyond it. This results in a more advantageous operation due to simpler operating sequences.

[0011] Another step is alternatively designed in such a way that first the tapping channels are burned out in the lower vessel from the bay side, and, when the melt flows into the bay through the unclosed taphole, the tilting operation is initiated. This eliminates the need to close the taphole.

[0012] In a refinement of the method, in an additional sequence of steps, after the zero position has been reached, the tapping channel and/or the taphole is cleaned and closed with refractory material.

[0013] In an alternative embodiment, after a suitably long operating time, for relining purposes, the flange joint is disconnected, and the bay is removed and replaced by a relined bay.

[0014] It is also advantageous to add necessary fluxes and alloys or portions of the required amounts of these additives to the bay during the tapping.

[0015] An alternative method of operating an arc furnace, which is tilted in one swivel direction to tap the melt, such that the melt is tapped eccentrically to the lower vessel, consists in controlling the tapping rate by controlling the gas pressure in the bay by pressurization of the pressure-tight and vacuum-tight covered bay with inert gas. During this process, the taphole of the tiltable furnace must not be closed. The siphoning effect that develops during ongoing tapping, depending on the length of the tapping channel between the hearth and the bay, and that manifests itself in a negative pressure in the bay above the bath level, can be influenced by controlling the gas pressure.

[0016] Another alternative embodiment of the invention in an arc furnace with a closable taphole, whose lower vessel is stationary and has a bottom taphole, is designed in such a way that the tap is provided in a separately mounted, pressure-tight and vacuum-tight bay, which abuts a terminal wall of the lower vessel, and that at least one tapping channel that passes through the terminal wall to connect the furnace shell and the bay is provided, such that the lower edge of the tapping channel on the bay side and the upper edge of the bay taphole are at about the same level. In this case, the arc furnace no longer needs to be tiltable, which means that the entire tilting mechanism is eliminated. In addition, the operating sequences and the in-service performance change.

[0017] The necessary gas space in the bay is created by providing the bay with a pressure-tight and vacuum-tight cover.

[0018] In addition, the bay taphole can be maintained, despite the cover, by mounting a hollow plug in a hollow plug housing on the pressure-tight and vacuum-tight cover. The housing can be disconnected or connected and opened or closed by a sluice.

[0019] Other design refinements arise from the connection of a gas supply line with a gas valve to the pressure-tight and vacuum-tight cover.

[0020] The aforementioned alternative with a stationary arc furnace can be regarded as the basis for a method of operating an arc furnace that is stationary, has a bay built onto a lower furnace, and is provided with a bay taphole and with a centric bottom taphole. A method of this type consists in opening the bay taphole, pressurizing the bay with inert gas, and then controlling the tapping of the melt in such a way that the ongoing tapping is interrupted by reducing the negative pressure in the bay as soon as the bath level in the lower vessel is below the lower edge of the tapping channel on the bay side. In this way, the tapping can be interrupted with little work.

[0021] Another advantageous measure with respect to the method consists in adjusting the gas pressure in the bay and in the tapping channel to a pressure value at which the bath level is brought to the height of the upper edge of the tapping channel that runs to the lower vessel. After the bay taphole has been closed, the bay and the tapping channel can be kept free of metal in this way. The pressure in the bay can be adjusted in such a way that small, steady gas consumption indicates that a small amount of gas is bubbling into the metal bath on the furnace side of the tapping channel. Lateral burning out or reclosing of the tapping channel becomes superfluous with this method of operation.

[0022] In the method of operation described above, the gas pressure inside the bay automatically drops at once when the bay taphole is opened. Therefore, in accordance with another step of the method, the tapping operation can be started by opening the bay taphole. At this instant, the tapped melt starts to flow through the tapping channels and the bay taphole without any need to tilt the furnace. A sand filling in the bay tap is not encrusted at its surface, because it was not exposed to a molten metal bath. It may be assumed, therefore, that the tap opens smoothly and without problems solely by moving away a sliding plate.

[0023] The bay taphole can be closed from above despite the pressure-tight and vacuum-tight cover. To this end, it is proposed that the tapping is terminated by closing the open bay taphole by means of a hollow plug, which can be moved in through the cover and through which sand can be poured in as far as a slide gate. Therefore, the sand enters the bay taphole in front of the closed slide gate through the hollow plug and fills this entire space. The taphole prevents any pieces of scrap possibly lying on the bay taphole from interfering with the satisfactory functioning of the hollow plug.

[0024] The hollow plug can be changed after it has been used by replacing it on the cover after a sluice has been closed. In addition, a “paddle” is advantageous for preventing the sand from running out of the bay taphole.

[0025] Embodiments of the invention are explained below with reference to the drawings, and several methods of operating the arc furnace are described on the basis of these embodiments.

[0026] FIG. 1 shows a cross section through a tiltable arc furnace, in which only the lower vessel is shown.

[0027] FIG. 2 shows a top view of the arc furnace shown in FIG. 1.

[0028] FIG. 3 shows a cross section through a stationary arc furnace, in which only the lower vessel is shown.

[0029] FIG. 4 shows a top view of the arc furnace shown in FIG. 3.

[0030] The following description refers mainly to FIGS. 1 and 2 for the time being. The drawings show only the lower vessel 2 of an arc furnace 1 with the furnace shell 2a lined towards the hearth 3. The arc furnace 1 can be tilted in both swivel directions for tapping the melt or the slag (FIG. 1).

[0031] A tap 9 for the melt is located in a separately mounted bay 6, which abuts a terminal wall 4 of the circular or oval lower vessel 2. The terminal wall 4 is formed as an upper flange (FIG. 2). One or more siphon-like tapping channels 5 run from the hearth 3 transversely through the terminal wall 4 and completely through the bay wall more or less tangent to the lining profile 10.

[0032] The bay 6 is detachably connected to the terminal wall 4 of the lower vessel 2a by a flange joint 8. Corresponding flanges 7 are provided on the bay and on the lower vessel. The bay taphole 9a runs vertically in the zero position 11 of the arc furnace 1. Alternatively, the tap 9 can be designed with its axis at an angle adapted to the tapping angle of the furnace 1.

[0033] The arc furnace 1 can be tipped in one swivel direction or the other to tap the melt and the slag, such that the melt is tapped eccentrically to the lower vessel 2. In this regard, first the tapping channels 5 are burned out in the lower vessel 2, and, when the melt flows into the bay 6, the tilting operation is initiated. The bay 6 is then sufficiently filled, and the bay taphole 9a is opened. When the desired amount of melt has been tapped, the arc furnace 1 is tilted back into its zero position 11 or beyond it.

[0034] Another method of operation can be carried out in such a way that first the tapping channels 5 are burned out in the lower vessel 2 from the bay side, and, when the melt flows into the bay 6 through the unclosed tap 9, the tilting operation is initiated.

[0035] After the zero position 11 has been reached, the tapping channel 5 and/or the bay taphole 9a is cleaned and, if necessary, closed with refractory material.

[0036] Alternatively, for relining purposes after suitably long production, the flange joint 8 is disconnected, and the bay 6 is removed and replaced by a relined bay 6.

[0037] The bay 6 can also be advantageously used for the addition of necessary fluxes and alloys or portions of the required amounts of these additives to the bay 6 during the tapping.

[0038] The following description pertains to the stationary furnace shown in FIGS. 3 and 4.

[0039] FIG. 3 shows a process situation in which a hollow plug 14 is inserted through a hollow plug housing 15 with the sluice 13 opened and through the pressure-tight and vacuum-tight cover 16 (with gas valve 17 closed). The bay 6 is pressurized with the gas valve 17 open. A slide gate 18 below the bay taphole 9a is closed. In a subsequent step of the method, the hollow plug 14 is moved into a standby or changing position (as illustrated) with the bay taphole 9a closed by the slide gate 18. The bay 6 is pressurized, and inert gas bubbles out at the upper edge of the tapping channel 5 in the hearth 3. In a third step of the method, the tapping begins. The slide gate 18 is opened, the sand filling that is present runs out, and the bay is unpressurized relative to the atmosphere. The molten metal is then tapped. A few seconds after the start of the tapping, the molten metal flows through the bay taphole 9a. In a fourth step of the method, a negative pressure develops in the bay by the siphon principle. The hollow plug 14 is still in the standby or changing position. In a fifth step of the method, the hollow plug 14 moves in, the slide gate 18 closes, sand runs in, and the bay 6 is pressurized with gas. The bay 6 runs empty, as does the tapping channel 5. The hollow plug 14 moves out into the standby or changing position.

[0040] The furnace can be completely emptied, if necessary, from the bottom taphole 12.

[0041] List of Reference Numbers

[0042] 1 arc furnace

[0043] 2 lower vessel

[0044] 2 a furnace shell

[0045] 3 (circular) hearth

[0046] 4 terminal wall

[0047] 5 tapping channel

[0048] 6 bay

[0049] 7 flange

[0050] 8 flange joint

[0051] 9 tap

[0052] 9 a bay taphole

[0053] 10 lining profile

[0054] 11 zero position

[0055] 12 bottom taphole

[0056] 13 sluice

[0057] 14 hollow plug

[0058] 15 hollow plug housing

[0059] 16 pressure-tight and vacuum-tight cover

[0060] 17 gas valve

[0061] 18 slide gate

Claims

1. Arc furnace (1), which can be tilted or remains stationary for tapping the melt or the slag and has an eccentric or centric tap (9; 12), wherein the tap (9) is provided in a separately mounted bay (6), which abuts a terminal wall (4) of a lower vessel (2), and that at least one tapping channel (5) is provided, which passes through the terminal wall (4) to connect the furnace shell (2a) and the bay (6), such that the taphole (9a) of the tap (9) in the bay (6) runs vertically in the zero position (11), i.e., the horizontal position, of the arc furnace (1), and the tapping channel (5) runs at an angle.

2. Arc furnace in accordance with claim 1, wherein the bay (6) can be connected to the terminal wall (4) of the lower vessel (2a) by a flange joint (8).

3. Arc furnace in accordance with claim 1, wherein one or more siphon-like tapping channels (5) run through the terminal wall (4) more or less tangent to the lining profile (10).

4. Arc furnace in accordance with claim 1, wherein the taphole (9a) is designed with an angle adapted to the tapping angle of the tiltable furnace (1).

5. Method of operating an arc furnace (1), which is tilted in one swivel direction to tap the melt and in the other swivel direction to tap the slag, such that the melt is tapped eccentrically to the lower vessel (2), wherein first the tapping channels (5) are burned out in the lower vessel (2) from the side of a separately mounted bay (6), and, when the melt flows into the bay (6), the tilting operation is initiated; in that the bay (6) is then sufficiently filled, and the taphole (9a) is opened; and in that, when the desired amount of melt has been tapped, the arc furnace (1) is tilted back into the zero position (11) or beyond it.

6. Method of operating an arc furnace (1), which is tilted in one swivel direction to tap the melt and in the other swivel direction to tap the slag, such that the melt is tapped eccentrically to the lower vessel (2), wherein first the tapping channels (5) are burned out in the lower vessel (2) from the bay side, and, when the melt flows into the bay (6) through the unclosed taphole (9a), the tilting operation is initiated.

7. Method in accordance with claim 5, wherein, after the zero position (11) has been reached, the tapping channel (5) and/or the taphole (9a) is cleaned and closed with refractory material.

8. Method in accordance with claim 5, wherein, for relining purposes, the flange joint (8) is disconnected, and the bay (6) is removed and replaced by a relined bay (6).

9. Method in accordance with claim 5, wherein necessary fluxes and alloys or portions of the required amounts of these additives are added to the bay (6) during the tapping.

10. Method of operating an arc furnace (1), which is tilted in one swivel direction to tap the melt, such that the melt is tapped eccentrically to the lower vessel (2), wherein the tapping rate is controlled by controlling the gas pressure in the bay (6) by pressurization of the pressure-tight and vacuum-tight covered bay (6) with inert gas.

11. Arc furnace (1) with a closable taphole (9a), whose lower vessel (2) is stationary and has a bottom taphole (12), wherein the tap (9) is provided in a separately mounted, pressure-tight and vacuum-tight bay (6), which abuts a terminal wall (4) of the lower vessel (2), and that at least one tapping channel (5) that passes through the terminal wall (4) to connect the furnace shell (2a) and the bay (6) is provided, such that the lower edge of the tapping channel (5) on the bay side and the upper edge of the bay taphole (9a) are at about the same level.

12. Arc furnace in accordance with claim 11, wherein the bay (6) is provided with a pressure-tight and vacuum-tight cover (16).

13. Arc furnace in accordance with claim 11, wherein a hollow plug (14) in a hollow plug housing (15) is mounted on the pressure-tight and vacuum-tight cover (16), and that the hollow plug housing can be detached or connected and opened or closed by a sluice (13).

14. Arc furnace in accordance with claim 11, wherein a gas supply line with a gas valve (17) is connected to the pressure-tight and vacuum-tight cover (16).

15. Method of operating an arc furnace (1) that is stationary, has a bay (6) built onto the lower furnace (2a), and is provided with a bay taphole (9a) and with a centric bottom taphole (12), wherein, after the bay taphole (9a) has been opened, and the bay (6) has been pressurized with inert gas, the tapping of the melt is controlled in such a way that the ongoing tapping is interrupted by reducing the negative pressure in the bay (6) as soon as the bath level in the lower vessel (2) is below the lower edge of the tapping channel (5) on the bay side.

16. Method in accordance with claim 15, wherein the gas pressure in the bay (6) and in the tapping channel (5) is adjusted to a pressure value at which the bath level is brought to the height of the upper edge of the tapping channel (5) that runs to the lower vessel (2).

17. Method in accordance with claim 15, wherein the tapping operation is started by opening the bay taphole (9a).

18. Method in accordance with claim 15, wherein the tapping is terminated by closing the open bay taphole (9a) by means of a hollow plug (14), which can be moved in through the cover (16) and through which sand can be poured in as far as a slide gate (18).

19. Method in accordance with claim 15, wherein the hollow plug (14) is replaced on the cover (16) after a sluice (13) has been closed.