JPH05226074A - Power feeding method for dc arc furnace - Google Patents

Abstract

PURPOSE:To reduce space for installation by detecting heat generated by the current running in a metal rod based on the increase in the temperature of the metal rod measured by a thermocouple provided in the metal rod, and whereby adjusting arc current. CONSTITUTION:A lower conductor 11 connected to a feeding terminal of a furnace bottom electrode is converged on the lower conductor 11 of a system or systems less than number of the furnace bottom electrode. A power source circuit connected to the positive electrode side of a rectifier is thus formed through a dc reactor 12 in an electric chamber provided on a point away from a dc arc furnace. An arc current is adjusted based on the measurement of the increase in the temperature of a metal rod 6 by means of a thermocouple provided on the metal rod 6, according to the conductive condition of each furnace bottom. Namely, the current running in each metal rod 6 is estimated based on the measurement result of the ratio of the increase in the temperature of the thermocouple, and when it is found out that an excessive current larger than a set level runs in any of the metal rod 6, feeding current is reduced, and thus is adjusted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for supplying electric power to a bottom electrode of a DC arc furnace for melting and refining metals and a method for adjusting an arc current.

[0002]

2. Description of the Related Art Conventionally, as shown in Japanese Patent Publication No. 63-43675, there is a metal rod and a power feeding terminal connected to the metal rod, and the metal rod and the power feeding terminal are cooled by a cooling fluid. Cooling bottom electrodes are used in DC arc furnaces.

In a DC arc furnace that supplies a large current exceeding about 50,000 amperes, a plurality of bottom electrodes are used, and the power feeding method is that a power supply circuit is provided for each bottom electrode. (Industrial heating Vo1.25
No.2 P. 26-28).

[0004]

The metal rod and the power feeding terminal connected to the metal rod and the metal rod penetrating the hearth refractory of the DC arc furnace are cooled by a cooling fluid. In the furnace bottom electrode, the metal rod is melted by heat conduction from the molten metal in the furnace and Joule heat generated by the electric current. The melting line is located at a portion where the amount of heat removed by cooling the lower portion of the metal rod is equal to the amount of heat transfer from the molten metal in the furnace and the amount of Joule heat generated by the current.

At this time, when the current flowing through the metal rod body is less than the set current, the melting line is located at a predetermined hearth refractory portion, but the current significantly exceeds the set current, for example, twice the set current density. When an electric current is applied, the melting line may reach the mold that cools the metal rod outside the DC arc furnace. In this case, the molten metal comes into contact with the mold, so that a thermal shock is applied to the mold. Frequent thermal shocks significantly reduce mold life.

Further, even when the cross-sectional area of the metal rod is increased and the allowable current per furnace bottom electrode is increased, the cooling capacity of the metal rod against the increase in the amount of heat transferred from the molten metal in the furnace is increased. The cross-sectional area of the metal rod cannot be increased so much because the melting line is lowered due to the relative reduction.

On the other hand, installing a current detector in the vicinity of the furnace in order to measure the current flowing through the conductor connected to each furnace bottom electrode means that the current detector becomes large in size.
This is not done because it is difficult to secure an installation space and because the atmosphere near the furnace is high temperature and a lot of dust makes it unsuitable for installing a current detector. If the same number of conductors as the number of bottom electrodes is installed at a position where the current detector can be installed, for example, up to the electric room, and the conductors are combined into one system or a system with less than the number of bottom electrodes at this position, equipment cost and installation The reduction effect cannot be expected in terms of space.

For the above reasons, the metal rod body penetrated through the hearth refractory of the DC arc furnace and the power feed terminal connected to the metal rod body are provided, and the metal rod body and the power feed terminal are cooled by the cooling fluid. Currently, about 50000 amperes is the permissible current for the bottom electrode, and in the case of a DC arc furnace that supplies a large current exceeding about 50000 amperes, a plurality of bottom electrodes with a cross section that can ensure sufficient cooling capacity are used. Even if it is provided and one of these electrodes is covered with a non-conductive material such as slag or refractory, or if there is insufficient contact between the raw material charged into the furnace and the furnace bottom electrode A power supply circuit including a rectifier, a DC reactor, and a conductor is provided for each electrode so that a current larger than a set current does not flow to other conductive electrodes.

As described above, providing a power supply circuit for each bottom electrode causes the number of rectifiers, DC reactors and conductors to be greater than the number required for electrical equipment capacity, resulting in higher equipment and construction costs. . Furthermore, the required space of the electric room where the rectifier and the DC reactor are installed becomes large. There is a problem.

Therefore, an object of the present invention is not to increase the number of rectifiers, DC reactors and conductors more than necessary, and
An object of the present invention is to provide a power feeding method in which an excessive current exceeding a set current does not flow through each furnace bottom electrode.

[0011]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and its gist is to have a metal rod protruding outside the furnace body and a power supply terminal connected to the metal rod. In a power supply method of a DC arc furnace having a plurality of furnace bottom electrodes for cooling a rod body and the power supply terminals with a cooling fluid, a conductor connected to the power supply terminals of the furnace bottom electrodes is provided under the furnace body in one system or in the furnace. A power supply circuit is collectively formed with conductors of a system smaller than the number of bottom electrodes, and current is supplied, from the rate of temperature rise of the metal rod body measured by a thermocouple provided inside the metal rod body, By detecting the amount of heat generated by the current flowing through the metal rod, the arc current is adjusted so that the current flowing through the metal rod does not exceed a preset value.

[0012]

When feeding power using the above power supply circuit, a plurality of furnace bottom electrodes are installed in order to always hold the melting line of the metal rod body of the furnace bottom electrode in a predetermined hearth refractory part. It is necessary to adjust the arc current when an excessive current flows in any of the furnace bottom electrodes by detecting the current flowing in each of the.

The rate of temperature rise of the metal rod body measured by a thermocouple provided on the metal rod body of the furnace bottom electrode depends on the amount of heat generated by the current flowing through the metal rod body.

FIG. 3 shows the relationship between the time (current elapsed time) during which the current flows and the temperature rise of the metal rod. The current is 25 kA.
Three examples of 50 kA and 100 kA are shown. The temperature of the metal rod increases with time, but the rate of increase increases as the current increases. Therefore, the arc current can be adjusted by estimating the current flowing through the metal rod by detecting the temperature rise rate. By adopting this adjusting method, the conductors of the respective bottom electrodes can be connected in the lower part of the furnace.

[0015]

FIG. 1 is a schematic view of a DC arc furnace showing an example for carrying out the method of the present invention. FIG. 2 shows a partially enlarged view of the furnace bottom electrode of FIG. The inside of the furnace body is lined with refractory 1 and the outside is covered with a steel shell 2. At the bottom of the furnace,
One end contacts the metal or molten metal 3 inside the furnace body,
A plurality of metal rods 6 having the other end penetrating the iron shell 2 of the furnace body connected to the power supply terminal 4 and being cooled by the cooling fluid through the mold 5 outside the iron shell 2 of the furnace body Bottom electrodes are installed.

On the cathode side of the rectifier 7, an upper conductor 8
It is connected to a movable electrode 10 which moves up and down through an electrode through hole provided in the furnace lid 9.

On the other hand, the lower conductors 11 connected to the power supply terminals of the furnace bottom electrode are grouped into one system or a system of lower conductors 11 less than the number of furnace bottom electrodes in the lower part of the furnace body, and separated from the DC arc furnace. A power supply circuit connected to the anode side of the rectifier 7 is configured through the DC reactor 12 in the electric room provided at the position.

Further, by configuring the above power supply circuit,
Due to the conduction state of each furnace bottom electrode, the arc current when an excessive current exceeding the set current flows to any of the furnace bottom electrodes is adjusted by a metal rod body provided by a thermocouple 13 provided on the metal rod body 6. It becomes possible by measuring the temperature rise rate of 6.

That is, as a result of estimating the current flowing through each of the metal rods 6 from the measurement result of the temperature rise rate of the thermocouple 13, an excessive current exceeding the set current flows in any of the metal rods 6. If it is found, the total supply current is reduced so that the current of the metal rod body 6 becomes equal to or less than the set current. Furthermore, when it is confirmed by the measurement of the thermocouple 13 that the current has flowed uniformly through all the metal rods 6, the entire supply current may be returned to the original value again. In this way, the current does not flow evenly in each metal rod, but an excessive current flows only in a specific metal rod because the upper surface of the metal rod is covered with a non-conductor such as slag, or as a charging raw material. When the contact between the two is insufficient, it does not occur frequently and is solved in a relatively short time. Therefore, it is a temporary measure to reduce the total supply current in order to suppress an excessive current, and there is no hindrance to the operation.

[0020]

According to the present invention, conventionally, a plurality of furnace bottom electrodes having a metal rod and a power feeding terminal connected to the metal rod and cooling the metal rod and the power feeding terminal with a cooling fluid are provided. In a single DC arc furnace, the power supply circuit consisting of the same number of conductors, DC reactors, and rectifiers as the number of furnace bottom electrodes can be converted into one system or a power supply circuit with a system less than the number of furnace bottom electrodes. It is possible to reduce equipment cost, construction cost and installation space.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of a power supply circuit of a DC arc furnace according to the present invention.

FIG. 2 is a partially enlarged view of the bottom electrode showing an installation example of a thermocouple for detecting a current flowing through the bottom electrode according to the present invention.

FIG. 3 is a diagram showing an electric current flowing through a metal rod and a metal rod in a furnace bottom electrode having a metal rod and a power supply terminal connected to the metal rod and cooling the metal rod and the power supply terminal with a cooling fluid. The figure which shows the relationship of the temperature rise rate of a body.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Refractory 2 ... Iron shell 3 ... Metal or molten metal 4 ... Power supply terminal 5 ... Mold 6 ... Metal rod 7 ... Rectifier 8 ... Upper conductor 9 ... Furnace lid 10 ... Movable electrode 11 ... Lower conductor 12 ... DC reactor 13 …thermocouple

Claims (1)

[Claims] 1. A plurality of furnace bottom electrodes each having a metal rod protruding outside the furnace body and a power feeding terminal connected to the metal rod and cooling the metal rod and the power feeding terminal with a cooling fluid. In a DC arc furnace power feeding method having the above, a conductor connected to a power feeding terminal of the hearth bottom electrode is integrated into a conductor of one system or a system of less than the number of the hearth bottom electrode in the lower part of the furnace body to form a power supply circuit. , By supplying an electric current and detecting the amount of heat generated by the current flowing through the metal rod from the rate of temperature rise of the metal rod measured by a thermocouple provided inside the metal rod. A power supply method for a DC arc furnace that adjusts the arc current so that the current flowing through the rod does not exceed a certain set value.