JP2600736B2 - DC arc furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the invention]

(Industrial application field) The present invention relates to a DC arc furnace mainly used for steelmaking using scrap as a raw material. (Prior Art) Conventionally, in steelmaking, a blast furnace-converter system using iron ore as a raw material has been widely adopted as suitable for mass production. On the other hand, an arc furnace using scrap as a raw material has been used. Electric furnace steelmaking has also been widely adopted. In this electric furnace steelmaking, an AC arc furnace is usually used, and the size and power are gradually increased to the development of a UHP furnace (ultra high power furnace). Has been established as a steelmaking system for mass production. However, in AC arc furnaces operated by UHP, there is a limit to the reduction of circuit impedance for effective use of high power energy, and the flicker problem increases,
Due to the limitation of the electrode current density due to the electrode skin action peculiar to AC, some DC arc furnaces that supply DC between the upper electrode and the furnace bottom electrode have also been considered. Although this DC arc furnace has not made much progress due to the problem of workability, the development of a rectifying facility for AC-DC conversion with a high power capacity in recent years has greatly contributed to its disregard, and it is conventionally known. A DC arc furnace is provided with a plurality of upper electrodes connected to, for example, a cathode side of a DC power supply so as to be able to ascend and descend, penetrating a furnace lid covering an upper part of a furnace main body including a furnace wall and a furnace shell. One or more bottom electrodes connected to, for example, the anode side of the DC power source are provided in the bottom portion of the main body, and a DC arc is generated between the upper electrode and the bottom electrode, thereby mounting the inside of the furnace. The scraps inserted were melted by arc heating. In such a DC arc furnace, compared to the conventional AC arc furnace, the electrode diameter is reduced at the same current value, the reduction of the electrode surface oxidation reduction due to the diameter reduction, and the temperature of the electrode tip compared with AC is reduced. It is possible to provide advantages such as a reduction in electrode unit consumption due to a reduction in graphite sublimation based on the reduction, a reduction in flicker level and a reduction in arc noise. (Problems to be Solved by the Invention) As described above, the conventional DC arc furnace has several advantages as compared with the AC arc furnace, but the preheating burner used at the time of scrap preheating is kept installed in the furnace lid. Occasionally, it has a problem that it is susceptible to thermal damage at the time of melting, and exhaust gas is discharged from an exhaust gas duct provided above a tapping outlet both at the time of scrap preheating and at the time of melting. Because it is inefficient for the flow of exhaust gas peculiar to DC arc furnaces, it has the problem of large energy loss, and is used to reduce energy costs, improve melting efficiency, etc. In addition, there is a demand for further improvement. (Objects of the Invention) The present invention has been made in view of such demands, and aims to improve thermal efficiency, shorten the dissolving time of charged materials, reduce energy costs, and improve dissolving efficiency. It is an object of the present invention to provide a DC arc furnace capable of performing the following.

Configuration of the Invention

(Means for Solving the Problems) In a DC arc furnace according to the first invention of the present invention, a plurality of upper electrodes connected to one side of a DC power supply are passed through electrode through holes provided in a furnace lid. In a DC arc furnace provided so as to be able to ascend and descend and having one or more furnace bottom electrodes connected to the other side of the DC power supply, the electrode through-hole is provided with an opening / closing lid for the electrode through-hole, and the furnace The lid is provided with an opening / closing lid / exhaust gas duct switching connection port that enables the switching connection between the opening / closing lid and the exhaust gas duct. It is characterized in that the exhaust gas is discharged only from the exhaust gas duct connected to the furnace lid, or from both the exhaust gas duct provided above the tapping outlet and the exhaust gas duct connected to the furnace lid. And
If necessary, the opening / closing lid / exhaust gas switching connection port is provided inside an electrode pitch circle formed by the plurality of upper electrodes, particularly at a central portion. Further, the DC arc furnace according to the second invention of the present invention is provided with a plurality of upper electrodes connected to one side of a DC power supply so as to be able to ascend and descend through an electrode through hole provided in a furnace lid, In a DC arc furnace having one or more furnace bottom electrodes connected to the other side of the furnace, the electrode through-hole is provided with an opening / closing lid for the electrode through-hole, and the furnace lid has a preheating burner and an exhaust gas duct. A preheating burner / exhaust gas switching connection port is provided to enable the switching connection of the electrode, and at the time of scrap preheating, the electrode through hole is closed by the opening / closing lid, and a preheating burner is connected to the preheating burner / exhaust gas switching connection port for scrap. Pre-heating, and when melting the scraps, open the electrode through-hole, lower the upper electrode, and replace the pre-heating burner with the exhaust gas duct. Exhaust gas generated at the time of melting is connected only to the exhaust gas duct connected to the furnace lid, or between the exhaust gas duct provided above the tapping port and the exhaust gas duct connected to the furnace lid, which is connected to the heat burner / exhaust gas duct switching connection port. It is characterized by discharging from both, and if necessary, the preheating burner / exhaust gas duct switching connection port is provided inside the electrode pitch circle formed by the plurality of upper electrodes, particularly at the central portion. It is characterized by doing so. (Embodiment) FIG. 1 shows an embodiment of a DC arc furnace according to the second invention of the present invention. The DC arc furnace 1 is tiltably supported on a concave support 3 installed on a foundation 2 via a convex seat 5 provided on the bottom surface of the furnace main body 4. The furnace lid 6 is suspended by a support (not shown), and can be moved up and down and swiveled. Further, in the furnace lid 6, for example, three electrode through holes 7 are formed at equal intervals (120 ° intervals) on the same electrode pitch circle centered on the core C, and these electrode through holes 7 An opening / closing lid 8 for each of the electrode through holes 7 is provided. With these electrode through holes 7 open, an upper electrode 11 made of, for example, a graphite electrode is provided in each of the electrode through holes 7 so as to be able to move up and down by an electrode clamp 12 and other electrode support mechanisms (not shown). The upper electrode 11 is connected to, for example, a cathode side of a DC power supply via an electrode bus, a flexible electric wire, a fixed secondary bus, and the like (not shown). Further, at the position of the core C of the furnace lid 6, a preheating burner
An exhaust gas duct switching connection 15 is provided, and a preheating burner 16
And the exhaust gas duct 17 can be switched and connected (in the illustrated example, the preheating burner 16 is connected). Furthermore, on the furnace bottom side of the furnace body 4, the furnace bottom electrodes 21 are provided at three equally spaced (120 °) intervals on the same electrode pitch circle centered on the core C, and on the left side in the figure. The tapping port 22 is opened and closed by a rotary stopper 23. An exhaust gas duct 24 is provided above the tap hole 22, and a damper 24a is provided in the exhaust gas duct 24 above the tap hole.
Is provided, and a tilting cylinder 25 is provided on the right side of the furnace bottom in the figure. A procedure for melting scraps by the DC arc furnace 1 having such a configuration will be described. First, scraps are charged into the furnace main body 4, the electrode through-hole 7 is closed by the opening / closing lid 8, and the preheating burner 16 is connected to the preheating burner / exhaust gas duct switching connection port 15. Preheating of scraps is started from above by the preheating burner 16. At this time, the exhaust gas after the scraps are preheated through the scraps is discharged through an exhaust gas duct 24 provided above the tapping opening 22. Next, after the preheating of the scraps is completed, the opening / closing lid 8 is opened to open the electrode through-hole 7, and the upper electrode 11 is lowered and inserted into the furnace through the electrode through-hole 7, and the front and back of the same is brought about. The preheating burner / exhaust gas duct switching connection 15 is replaced with an exhaust gas duct instead of the preheating burner 16.
17 is connected, and a DC power supply connected between the upper electrode 11 and the furnace bottom electrode 21 is energized to perform arc heating. Exhaust gas during arc heating is supplied to an exhaust gas duct
By closing the damper 24a provided in the exhaust gas duct 17 connected to the furnace lid 6, that is, discharging only from the center of the furnace, or by opening the damper 24a provided in the exhaust gas duct 24 above the tapping outlet. The exhaust gas is discharged from both the exhaust gas duct 17 connected to the furnace lid 6 and the exhaust gas duct 24 provided above the tapping port 22. In the DC arc furnace 1 according to the first and second aspects of the present invention, the electrode through hole 7 is provided with an opening / closing lid 8 for the electrode through hole 7, and the furnace lid 6 is provided with an opening / closing lid / exhaust gas switching connection port 15.
A or a preheating burner / exhaust gas duct switching connection port 15 is provided, and when the opening / closing lid / exhaust gas duct switching connection port 15A is provided, the opening / closing lid and the exhaust gas duct 17 are switched to the opening / closing lid / exhaust gas duct switching connection port 15A. When the preheating burner and the exhaust gas duct switching connection 15 are provided, the preheating burner / exhaust gas switching connection 15
Since the preheating burner 16 and the exhaust gas duct 17 are connected in a switching manner, the exhaust gas duct 17 is connected with the opening / closing lid of the opening / closing lid / exhaust gas duct switching connection 15A open during melting. By connecting the exhaust gas duct 17 to the exhaust gas duct switching connection port 15,
At the time of melting, the flow of exhaust gas peculiar to the DC arc furnace generated at the center of the furnace can be smoothly discharged as it is from the upper side of the furnace, that is, from the furnace lid 6. Can be adapted to the characteristics of Next, in the DC arc furnace 1 having the above structure, a capacity of 20 to
According to the second invention of the present invention, the electrode through-hole 7 is closed at the time of scrap preheating, and scraps are preheated by the preheating burner 16 connected to the preheating burner / exhaust gas duct switching connection port 15 in accordance with the second invention of the present invention. After that, the electrode through hole 7
And the upper electrode 11 is inserted, and an exhaust gas duct 17 is connected to the preheating burner / exhaust gas duct switching connection 15 in place of the preheating burner 16, and electricity is supplied between the upper electrode 11 and the furnace bottom electrode 21. During the melting, the exhaust gas was discharged from the two exhaust gas ducts 17 and 24, and the preheating burner / exhaust gas switching connection port (15) was provided at the furnace bottom (6) as in the second invention of the present invention. Dissolution time can be reduced by about 25% compared to the conventional case where no switching connection between the preheating burner (16) and the exhaust gas duct (17) is provided.
The energy cost was reduced accordingly.

【The invention's effect】

As described above, in the DC arc furnace according to the first invention of the present invention, a plurality of upper electrodes connected to one side of the DC power supply can be moved up and down through electrode through holes provided in the furnace lid. A DC arc furnace having a furnace bottom electrode connected to the other side of the DC power supply, wherein the electrode through-hole is provided with an opening / closing lid for the electrode through-hole, and the furnace lid is provided with an opening / closing lid and exhaust gas. Since the switching lid and exhaust gas duct switching connection that enables switching connection with the duct are provided, the exhaust gas with a flow unique to the DC arc furnace generated at the center of the furnace during melting is discharged to the upper side of the furnace. In other words, the gas can be discharged smoothly through the exhaust gas duct connected to the furnace lid, and the energy can be discharged from the exhaust gas duct above the tapping port during melting, as compared with the conventional case. Improved efficiency, it is possible to realize a shortening of the melting time, reduce energy costs,
A remarkably excellent effect is achieved in that the dissolution efficiency can be improved. Further, the DC arc furnace according to the second invention of the present invention is provided with a plurality of upper electrodes connected to one side of a DC power supply so as to be able to move up and down through electrode through holes provided in the furnace lid, In a DC arc furnace provided with a furnace bottom electrode connected to the other side of a power supply, the electrode through-hole is provided with an opening / closing lid for the electrode through-hole, and the furnace lid is provided with a switching connection between a preheating burner and an exhaust gas duct. Preheating burner that enables
Since the exhaust gas duct switching connection is provided, exhaust gas having a flow peculiar to the DC arc furnace generated at the center of the furnace during melting is discharged smoothly through the exhaust gas duct connected to the upper part of the furnace, that is, the furnace lid. It is possible to improve the energy efficiency and shorten the melting time compared to the conventional case where exhaust gas is discharged from the exhaust gas duct above the tapping port both during preheating and melting of scraps. This makes it possible to reduce energy costs and improve melting efficiency.By connecting an exhaust gas duct instead of a preheating burner during melting, the preheating burner This has the significant advantage that damage can be prevented.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing one embodiment of a DC arc furnace according to the present invention. 1 DC arc furnace, 6 Furnace lid, 7 Electrode through hole, 8 Opening / closing lid for electrode through hole, 11 Upper electrode, 15 Preheating burner / exhaust gas duct switching connection, 15A … Opening / closing lid / exhaust gas duct switching connection, 16 …… Preheating burner, 1 …… Exhaust gas duct, 21 …… Bottom electrode, 24 …… Exhaust gas duct above the tapping outlet.

Claims (4)

(57) [Claims] A plurality of upper electrodes connected to one side of a DC power supply are provided so as to be able to move up and down through electrode through holes provided in a furnace lid, and a furnace bottom connected to the other side of the DC power supply. In a DC arc furnace equipped with electrodes, an opening / closing lid for the electrode through-hole is provided in the electrode through-hole, and the furnace lid is capable of switching between an opening / closing lid and an exhaust gas duct for switching the opening / closing lid / exhaust gas duct. A DC arc furnace having a connection port. 2. The direct current as claimed in claim 1, wherein the opening / closing lid / exhaust gas duct switching connection port is provided at a central portion of an electrode pitch circle formed by a plurality of upper electrodes. Arc furnace. 3. A furnace bottom connected to one side of a DC power supply so as to be able to move up and down through an electrode through hole provided in a furnace lid and to be connected to the other side of the DC power supply. In a DC arc furnace equipped with electrodes, an opening / closing lid for the electrode through-hole is provided in the electrode through-hole, and a preheating burner / exhaust gas duct switchover is provided on the furnace lid to enable switching connection between a preheating burner and an exhaust gas duct. A DC arc furnace having a connection port. 4. A direct current according to claim 3, wherein the preheating burner / exhaust gas duct switching connection port is provided at a central portion of an electrode pitch circle formed by a plurality of upper electrodes. Arc furnace.