ELECTRIC ARC FURNACE AND METHOD OF OPERATING SAME

Abstract

The invention relates to an electric arc furnace and a method for operating same. The electric arc furnace comprises a lower vessel and a lid 120 placed on said lower vessel. The lower vessel has a tapping device for tapping molten metal. At least one electrode protrudes through the lid into the interior of the electric arc furnace, said electrode being held by an electrode holding device. A supply voltage device 150 is provided for supplying an electric direct current or alternating current to the electrode 130. The aim of the invention is to allow a continuous operation of the electric arc furnace. This is achieved in that the electrode holding device has an electrode adjusting device for adjusting the electrode dependent on the wear of the electrode and an electrode nippling device for nippling the electrode during the operation of the electric arc furnace. According to the invention, both the electrode adjusting device as well s the electrode nippling device 144 operate when the supply voltage of the electrode is switched on.

Claims

1. (canceled)

3-18. (canceled)

19. An electrical arc furnace (100) for a quasi-continuous operation, comprising: a lower vessel (100) for melting iron carries, wherein the lower vessel has a tapping device (115) for tapping melt; a lid (120) placeable on the lower vessel and having a first opening (122) for receiving at least one electrode (130), and at least one second opening for charging iron carriers and additive in the electrical arc furnace; the at least one electrode (130) extending vertically through the first opening (122) and into an interior of the electrical arc furnace; an electrode holding device (140) for holding the at least one electrode (130); and a supply voltage device (150) for making available an electrical supply voltage for the at least one electrode (130); wherein the electrode holding device (140) has an electrode adjusting device (142) for adjusting the at least one electrode and an electrode nippling device (144) for nippling the at least one electrode (130) for adjusting the at least one electrode in accordance with its wear and for nippling the at least one electrode, respectively, during operation of the electrical arc furnace, wherein the tapping device (115) is so arranged on the lower vessel (110) that a regular tapping is possible when the lower vessel is upright and stationary, and wherein the supply voltage device (150) is formed as d.c. voltage source or a.c. voltage source for making available supply voltage for the electrode in form of d.c. voltage or a.c. voltage, and wherein the supply voltage device (150) has a transformer (152) which is located directly above the at least one electrode (130), the at least one electrode (130) being connected with the transformer (152) by a conductor (130a) extending vertically between the at least one electrode (130) and the transformer (152).

20. The electrical arc furnace according to claim 19, wherein the lid (120) is formed as a truncated cone, and wherein the first opening (122) is formed in a top surface of the truncated cone and the second opening is formed in one of side surfaces of the truncated cone.

21. The electrical arc furnace (100) according to claim 20, comprising a blow-in device (160) for introducing rinsing material in an interior of the electrical arc furnace and provided in another one of the side surfaces of the truncated cone.

22. The electrical arc furnace (100) according to claim 19, comprising, a cooling device (170) for cooling the lid.

23. The electrical arc furnace (100) according to claim 19, wherein the lid (120) is vertically displaceable relative to the stationary lower vessel (110) during operation of the electrical arc furnace.

24. The electrical arc furnace according to claim 19, wherein with the supply voltage device being formed as an a.c. voltage source, the transformer (152) has three single-phase transformers which are symmetrically arranged relative to each other at an angle of 120.

25. The electrical arc furnace (100) according to claim 19, wherein, the lower vessel (110) is lined up with a fire-resistant material.

26. A method of operating, in a quasi-continuous operation, an electrical arc furnace (100) having a lower vessel (110), a lid (120) placeable on the lower vessel and having a first opening (122) for receiving, at least one electrode (130), the at least one electrode being displaceable through the first opening (122) in the lid (120) into an interior of the electrical arc furnace, and at least one second opening (124), and a supply voltage device (150) having a transformer (152) located directly above the at least one electrode (130), wherein the at least one electrode (130) is connected with the transformer (152) a conductor (130a) extending vertically between the at least one electrode (130) and the transformer (152), the method comprising the following steps: charging iron carriers or additives into the electrical arc furnace through the at least one second opening (124) in the lid, time-continuously feeding supply voltage from the transformer to the at least one electrode (130) for melting an iron carrier introduced into the electrical arc furnace for the continuous operation of the electrical arc furnace over several melts, and adjusting and nipping that at least one electrode during operation of the electrical arc furnace, and wherein tapping of the melt takes place at the upright and stationary lower vessel (110).

27. The method according to claim 26, comprising the step of blowing-in of a rinsing material in the electrical arc furnace.

28. The method according to claim 12, comprising the step the electrical arc furnace is continuously operated at an average temperature of about 1600 C.

29. The method according to claim 26, wherein the tapping is so carried out that after tapping, height of the sump level (h) in the lower vessel remains at least 500 mm.

30. The method according to claim 26, wherein the electrical arc furnace (100) is operated for a short time with a temperature of about 1650 for tapping the melt.

31. The method according to claim 26, wherein the adjustment and nippling of the at least one electrode can take place during charging.

32. The method according to claim 26, comprising the step of forming the lid (120) as a truncated cone, forming the first opening (122) in a top surface of the truncated cone, and forming the at least one second opening (124) in one of side surfaces of the truncated cone.

33. The method according to claim 32, comprising the step of providing, in another one of the side surfaces of the truncated cone, a blow-in device (160) for introducing rinsing material in interior in an interior of the electrical arc furnace. The adjustment and nippling of the at least one electrode can take place during charging.

Description

[0019] The description is accompanied by two figures, wherein:

[0020] FIG. 1 shows a cross-sectional view of an electrical arc furnace according to the present invention; and

[0021] FIG. 2 shows a process of operating the electrical arc furnace according to the present invention.

[0022] The invention will be described below with reference to the above-mentioned drawings by way of exemplary embodiments.

[0023] FIG. 1 shows an inventive electrical arc furnace 100 having a lower vessel 110 and a lid 120 which is placed on the lower vessel. The lid is formed, e.g., conically and has a cooling device 170 for cooling its surface. The cooling device is formed, e.g., of tubular conduits in which cooling water flows. The lid has, in its center or its tip, at least one large first opening for receiving an electrode 130 that is advanced in the electrical arc furnace 100.

[0024] In addition to the first opening 122, the lid 120 has a second opening 124 for charging iron carriers and/or additives into the electrical arc furnace at the turned-on supply voltage. As an iron carrier, e.g., scrap, direct reduced iron (DRI) hot briquette iron (HBI) and/or liquid, and/or solid pig iron. Further, a blow-in device 160 is provided in the surface of the lid for feeding, e.g., rinsing material, or oxygen, or carbon in the interior of the electrical arc furnace, preferably, at turned-on supply voltage. As shown in FIG. 1, the blow-in device enables a targeted feeding of materials in an immediate vicinity of slag or melt.

[0025] During operation of the electrical arc furnace, the lower vessel 110 is upright and stationary. Therefore, the lid 120 must be displaced only in vertical direction, i.e., it can be lifted or lowered only in direction of the double arrow in FIG. 1. There can be provided a device for swinging of the lid, however, it is not absolutely necessary. E.g., for maintenance purposes, the lower vessel can be displaced.

[0026] The lower vessel is lined up with a fire-resistant material 112. After maintenance, the fire-resistant material must have such thickness in the lower vessel that it retains a sufficient residual thickness even after operation of the electrical arc furnace for several days. The lower vessel has a tapping device 115 for tapping the melt, preferably so that after each tapping, the sump level h remains at least 550 mm in the stationary lower vessel.

[0027] For holding the electrode 130 in the electrical arc furnace 100, there is provided an electrode holding device 140. It includes an electrode adjusting device 142 for adjusting the electrode 130 in accordance with its wear, and an electrode nippling device for nippling the electrode 130. According to the invention, both the electrode adjusting device 142 and the electrode nippling device 144 are so formed that they make possible adjustment and nippling of the electrode during the operation of the electrical arc furnace, at the turned-on supply voltage to the electrode 130. Thereby, in particular, a continuous operation of the electrical arc furnace over several tapping cycles or melts becomes generally possible.

[0028] For feeding electrical energy into the electrical arc furnace, there is provided a supply voltage device 150 for making available electrical supply voltage for at least one electrode. The supply voltage device can be formed as a d.c. source for making available supply voltage in form of d.c. voltage or as an a.c. source for making available supply voltage in form of a.c. voltage for the electrode 130. It includes a transformer 152 that according to the invention is located above the furnace lid. In case the supply voltage device is formed as the a.c. voltage source and the electrical arc furnace operates as alternating current AC-furnace, the transformer 152 has three single-phase transformers symmetrically arranged relative to each other at an angle of 120.

[0029] Below, a method with which the electrical arc furnace operates according to the invention will be described in detail.

[0030] The main characteristic of the inventive method consists in that the electrical arc furnace operates in a quasi continuous operation over several days and a plurality of melts or tapping cycles. Only for maintenance purposes, after several days, the continuous operation is interrupted, and maintenance takes place.

[0031] The continuous operation becomes possible, on one hand, by using the electrode adjustment device which so advances the electrode 130 in the interior of the furnace during the operation of the electrical arc furnace that ideally the electrical arc length remains substantially constant despite the wear and burn-up of the electrode. In order that the operation of the electrical arc furnace even when a minimal length of the electrode 130 is reached, need not be interrupted, the present invention contemplates that in addition to the electrode adjusting device 142, there is provided an electrode nippling device 144 which insures that the electrode 130 again is lengthen at the top before reaching the minimal length. The so-called nippling typically is carried out by screwing on a lengthening electrode or a new electrode strand at the end of the electrode remote from the furnace. According to the invention, the electrode nippling device 144 insures the nippling of the electrode when the supply voltage is turned on so that the operation of the electrical arc furnace can continue during nippling.

[0032] However, not only the adjustment and nippling of the electrode 130, but also charging of the furnace with iron carriers or additives, blowing in of rinsing material, refining of the melt by addition of alloy materials, and in particular, tapping of the melt or slag takes place advantageously, according to the invention, with turned-on supply voltage for arbitrary time period during the operation. The advantage of this consists in that for the above-mentioned processes, the operation of the electrical arc furnace need not be interrupted, which results in noticeable costs savings in comparison with an interrupted operation of an electrical arc furnace.

[0033] The costs savings results from elimination of time-off that occurs in a discontinuous operation of an electrical arc furnace, during the production according to the inventive continuous operation. The available electrical power can be optimally used with the present invention. There is no need for any storage for the electrical energy and no other electrical consumer should be available for consuming the electrical power supplied by the supply voltaging device during off-times of an electrical arc furnace that operates intermittently. Also, the energy losses during feed-in are reduced because of a noticeably reduced number of turning-on and turning-off operation.

[0034] A timely continuous energy supply, i.e., with a continuous turned-on supply voltage for the electrode 130 over several tapping cycles or melt is shown in FIG. 2 graphically in an idealized form.

[0035] According to the present operating method, the electrical arc furnace operates during the continuous operation on average at a temperature of about 1,600 C. At the start of a planned tapping process that takes place at the turned-on supply voltage and in the upright position of the lower vessel, the melt temperature advantageously is slightly raised by about 50 C. to prevent a premature undesired cooling of the melt after it exits the electrical arc furnace. The tapping is preferably conducted in such a way that after tapping the height of the sump level remains at least at 500 mm in the deepest point of the lower vessel. The advantage of this consists in that the lower vessel is not damaged during an empty operation without melt at supplied voltage. Because of the available sump, the temperature variation of the melt and, thus, of the lower vessel are kept within limits. In this way, the load applied to the fire-resistant material is reduced and the service life of the lower vessel is increased. Not only tapping but also the adjustment and/or nippling of the electrode can take place during charging at a feed supply voltage.