JPH0587467A - Operating method for dc arc furnace - Google Patents

Abstract

PURPOSE:To provide a method of operating an arc furnace which has no problem in the matters of equipment cost and easiness of maintenance as well by suppressing rationally a directional deflection of the arc caused by the magnetic field that is generated by the DC current flowing through the conductive bodies and making possible a stable operation and, at the same time, arranging the conductive bodies effectively. CONSTITUTION:The arrangement of the conductive bodies 10 with respect to an upper electrode 6 and electrode 7 in the furnace bottom is made to keep the relation L/R, where L is the directional deflection of the arc caused by magnetic field and R the inner radius of the furnace in the range below 0.05. With this arrangement the thermal load to the furnace wall is the same as when the arc 9 flies vertically and it is possible to make a rational arrangement of the conductive bodies 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of operating a DC arc furnace for melting and heating a metal to be melted such as scrap by forming an arc between an upper electrode and a furnace bottom electrode.

[0002]

2. Description of the Related Art With the recent increase in the capacity of power semiconductor devices such as thyristors, a DC arc furnace has come into general use as an arc furnace for steelmaking. Unlike the AC arc furnace, the DC arc furnace does not require three movable electrodes, and an arc is formed between at least one movable electrode (upper electrode) and the furnace bottom electrode to melt scrap or the like. It is a method of melting and heating a metal, and has an advantage that the structure is simple. In the case of a DC electric furnace with a single upper electrode, by locating the upper electrode in the center of the furnace body, the melting of scrap, etc. charged into the furnace will cause the arc generated from the upper electrode in the center of the furnace body. It has the advantage that the heat source advances uniformly in a concentric circle, and there is no generation of hot spots or cold spots as in an AC arc furnace, and the thermal efficiency is high.

However, a direct current flowing through the conductors connected to the upper electrode and the bottom electrode forms a direct magnetic field in the arc generation region, and the magnetic field and the arc current are mutually compliant with Fleming's left-hand rule. By the action
The force (Lorentz force) acts on the arc and the arc is deflected, and the heat quantity of the arc is concentrated in a specific direction, so the melting and heating of scrap etc. is unevenly performed and the thermal efficiency decreases, It becomes a hot spot, and there is a problem that the wear of the furnace wall refractory and water cooling box becomes severe. This phenomenon also occurs in arc welding or the like, and is called magnetic spraying. As a countermeasure, a method is generally used in which the arrangement of conductors is adjusted to cancel the magnetic field generated by a direct current flowing through the conductors.

The principle is the same in a DC arc furnace, and various measures have been considered. However, in Japanese Utility Model Laid-Open No. 2-24290, etc., it is appropriate to dispose a part of the lower conductor connected to the furnace bottom electrode. There has been proposed a technique for generating a magnetic field that cancels the magnetic field in the arc generation region. In addition, Japanese Patent Application Laid-Open No. HEI 2-
No.-208354 proposes a technique for offsetting a change in arc deflection force caused by a change in position of the upper conductor by moving a part of the lower conductor connected to the furnace bottom electrode.

[0005]

However, it is difficult to completely eliminate the magnetic field in the arc generation region by the conductor arrangement, and the conductor arrangement becomes complicated in order to minimize the magnetic field in the arc generation region. Therefore, the cost of expensive conductor equipment made of copper or aluminum increases, the equipment cost increases, and the maintainability of the arc furnace deteriorates due to the complicated arrangement of the conductors. There is a problem that the proper conductor placement technology that enables stable operation in the arc furnace is not clear.

In view of such problems of the prior art, the main object of the present invention is to eliminate the operational problems of uneven heating and melting due to arc deflection and local wear of furnace wall refractory / water cooling box. Another object of the present invention is to provide a method of operating an electric arc furnace that does not increase facility costs and maintainability.

[0007]

According to the present invention, the object of the invention is to provide a method of operating a DC arc furnace having an upper electrode and a furnace bottom electrode, in which the inner radius R and the deflection amount L of the arc are set. It is achieved by providing a method for operating a DC arc furnace, characterized in that the upper and lower conductor routes are effectively arranged so that the relation of L / R = 0.05 or less.

[0008]

[Function] When the arc generated from the upper electrode is regarded as a hot air column, when the hot air column is blown perpendicularly to the molten metal surface, the hot air is evenly dispersed in all directions after colliding with the molten metal surface. It will be. At this time, the heat load on the surrounding furnace wall is also uniform. However, if the hot air column enters at an angle of inclination with respect to the surface of the molten metal, the hot air after the collision will not be uniformly dispersed, but a large amount of hot air will fly in the inclined direction, and the heat load on the furnace wall will also increase. Similarly, it becomes non-uniform and the slope side becomes higher. This leads to uneven melting and hot spots on the furnace wall. The heat load on the furnace wall is uniform in the circumference according to the relationship between the portion of the hot air column having this inclination angle that collides with the molten metal surface and the amount of eccentricity from the center of the furnace, that is, the amount of arc deflection L and the radius R of the furnace. Although the sex changes, the relationship is shown in FIG. As can be seen from the figure, as the L / R increases, the furnace wall heat load in the deflection direction increases under the same arc heating conditions, and particularly when L / R exceeds 0.05, the increase becomes rapid.

As a result, by arranging the conductors so that L / R is 0.05 or less, the uniformity of the heat load on the furnace wall is
As in the case where the arc is generated almost perpendicularly to the molten metal surface, it is possible to provide a method of operating an arc furnace that enables stable operation without arranging conductors in a complicated manner.

[0010]

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. FIG. 1 is a cross-sectional view of an arc furnace to which the present invention is applied, FIG. 2 is a state diagram of forces acting on the arc, FIG. 3 is a calculation example diagram of conductor arrangement and arc locus, and FIG. 4 is deflection amount (L) of arc / It is a relationship diagram of a furnace inner radius (R) and a furnace wall heat load.

The DC arc furnace 1 shown in FIG. 1 comprises a furnace body 4 covered with a refractory 2 and a water-cooled box 3, and a furnace lid 5 arranged above the furnace body 4, which can be lifted and lowered from the center of the furnace lid 5. Between the molten metal 8 such as scrap charged in the DC arc furnace 1 and the tip of the upper electrode 6 by the DC current supplied to the upper electrode 6 and the furnace bottom electrode 7 installed on the furnace bottom. The metal 8 to be melted is melted and heated by the arc 9 formed on. A direct current is passed through the conductor 10 taken out of the electric equipment for the furnace such as a transformer or a thyristor (not shown), but at this time, a magnetic field B is generated around the conductor according to the Biot-Savart law (Fig. 2). Therefore, an arc deflection force F, which will be described later, acts on the arc 9, causing the arc to fly obliquely, and a deflection amount L is generated in the arc 9. The deflection amount L is determined by the relationship of the magnetic field B determined by the arrangement of the conductor 10. In the present invention, the relationship L / R between the arc deflection amount L and the furnace radius R is set to 0.05 or less.

The magnitude of the magnetic field B generated in the arc 9 generation region in the DC arc furnace 1 is easily determined according to the Biot-Savart law, and as shown in the state diagram of the force acting on the arc in FIG. The deflection force F acts on the arc 9 passing through. The arc 9 is an electric current, and when the electric current, that is, the arc 9 flows in the magnetic field B, the Lorentz force acts on the arc 9 according to Fleming's left-hand rule, and this becomes the deflection force F. On the other hand, since the arc 9 is a gas and not a rigid body, it will fly away if there is no force against the deflection force F, but the arc 9 is displaced from the center of the upper electrode 6 of the arc generation source by the deflection force F. Then, the centripetal force F1 is generated by the magnetic field B1 created by the current flowing through the upper electrode 6, and the centripetal force F1 is generated.
The arc 9 maintains the state in which the deflection force F is balanced with the deflection force F.

When this balanced state is calculated for each distance d from the upper electrode 6, the locus 11 of the arc 9 is obtained. FIG. 3 shows a calculation example in which the deflection state of the arc 9 is obtained as the locus 11. It goes without saying that the locus 11 changes depending on the arrangement of the conductor 10. In this way, the deflection amount L is obtained from the trajectory 11 of the arc 9, and the degree of change in the furnace wall heat load of the furnace body 4 due to the deflection amount L of the arc 9 is shown in FIG. 4 as the deflection amount L of the arc 9 and the radius R of the furnace. The relationship L / R is shown as an index.

This is the result of the inventors' testing the degree of change in the heat load on the furnace wall of the furnace body 4 by changing the arrangement of the conductors 10 and changing the deflection amount L of the arc 9. It is understood that there is not much change when L / R is in the range up to 0.05, and the increase phenomenon becomes large when L / R exceeds 0.05. Increasing the heat load on the furnace wall means that the arc 9
2 becomes prominent, the molten metal 8 becomes non-uniformly melted, which not only deteriorates the thermal efficiency but also adversely affects the wear of the refractory 2 and the water cooling box 3.

[0015]

As described above, according to the present invention, by setting the relationship between the furnace radius R and the arc deflection amount L to be L / R = 0.05 or less, uneven heating and melting due to arc deflection, It is a technology that enables the local wear of refractory and water-cooled boxes on the furnace wall to be corrected, and has established a technique for designing a conductor arrangement that enables stable operation without unnecessarily complicating the conductor arrangement. Therefore, stable operability of the DC arc furnace can be achieved, thermal efficiency can be improved, equipment reliability can be improved, and more rational conductor arrangement can be achieved.
It also contributes to maintainability and its effect is extremely large.

[Brief description of drawings]

FIG. 1 is a sectional view of an arc furnace to which the present invention is applied.

FIG. 2 is a state diagram of a force acting on an arc.

FIG. 3 is a diagram showing an example of calculation of conductor arrangement and arc locus.

FIG. 4 is a diagram showing a relationship between an arc deflection amount (L) / furnace inner radius (R) and furnace wall heat load.

[Explanation of symbols]

 1 DC arc furnace 6 Upper electrode 7 Furnace bottom electrode 9 Arc 10 Conductor F Deflection force F1 Centripetal force B Magnetic field L Arc deflection amount R Inner radius

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Kimiyoshi Goto 46-59, Nakahara, Tobata-ku, Kitakyushu, Fukuoka Prefecture, Nippon Steel Plant Design Co., Ltd.

Claims (1)

[Claims] 1. A method for operating a DC arc furnace having an upper electrode and a bottom electrode, wherein the inner radius R and the arc deflection amount L are used.
And L / R = 0.05 or less.