JPH0448189A - Operating method of dc arc fu10rnace - Google Patents

Abstract

PURPOSE:To eliminate biased heating substantially to promote smelting or refining, shorten operating time, permit the reduction of the unit of electrode or electric power and improve efficiency by blowing gas, not reacting to molten metal, through a nozzle arranged on the hearth of a DC are furnace. CONSTITUTION:Fire resistant nozzles 5 are arranged on the hearth of a furnace body 1 near the wall of the furnace and gas, not reacting to molten metal 4, is blown through these nozzles. The blown gas is selected depending on the kind of the molten metal 4 and argon, for example, is used. On the other hand, N2 gas can be used if there is no problem of N2 in the molten steel. The molten metal 4 makes circulating motion so as to move downward through the center of the furnace, pass the upper surface of the hearth and ascend along the wall of the furnace. Accordingly, the gas 6, blown through nozzles 5, promotes the ascending of the molten metal near the wall of the furnace. As a result, the aggitation of the molten metal 4 is advanced synergistically whereby the biased heating of the molten metal in up-and-down direction is reduced and the smelting or refining of materials can be advanced efficiently.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method of operating a DC arc furnace, and more specifically, it suppresses uneven heat in the vertical direction in the furnace to increase thermal efficiency and to melt and/or melt raw materials. The present invention also relates to a method of operating a DC arc furnace that allows efficient refining.

(Prior Art) Arc furnaces are widely used for refining molten steel and manufacturing various special steels. A commonly used furnace consists of a furnace body made of refractory material, an anode placed at the bottom of the furnace body, and a cathode suspended from the top of the furnace body. This creates a high-temperature arc, which uses the heat energy to melt raw materials such as scrap steel charged into the furnace into molten metal.

There are two types of arc furnaces, AC arc furnaces and DC arc furnaces, depending on the current applied, and AC arc furnaces are mainly used.

On the other hand, it is becoming increasingly recognized that DC arc furnaces are more advantageous than AC arc furnaces in terms of preventing pollution (flicker countermeasures), reducing the consumption of electrodes and electric power, and therefore improving productivity. Recently, attempts have been made to install DC arc furnaces mainly in Western countries and Japan.

By the way, an AC arc furnace has three suspended cathodes.
A three-phase alternating current is passed between the two poles to form an arc region. Further, a DC arc furnace has one suspended cathode, and direct current is passed between the two cathodes.

These AC arc furnaces and DC arc furnaces each have the following furnace characteristics.

That is, first, regarding arc characteristics, in the case of an AC arc furnace, arc breakage is likely to occur because the applied voltage and arc current periodically intersect with the zero point. That is, the arc is unstable. On the other hand, in the case of a DC arc furnace, since a predetermined voltage is always applied, arc breakage does not occur, and a stable arc furnace can be obtained during operation.

Regarding the arc flow, in the case of an AC arc furnace,
The interaction between the three cathodes causes a phenomenon in which the arc flow is biased toward the furnace wall. As a result, there is a problem that the melting efficiency of the raw materials in the furnace decreases and the melting state varies, making it difficult to perform uniform melting and refining.

On the other hand, in the case of a DC arc furnace, the arc flow spreads concentrically around the cathode position, and because this spread is uniform, the melting efficiency of raw materials is improved, and a uniform melting and refining state is achieved. can get.

Furthermore, when the raw material is melted and/or refined, the molten raw material moves in the furnace as follows while electricity is being applied. First, in the case of an AC arc furnace, rotational movement is performed in the phase rotation direction of the three-phase alternating current applied to the three cathodes, that is, in the horizontal direction. Therefore, the uneven heat in the vertical direction of the molten metal becomes large, which causes non-uniform melting of raw materials and non-uniform melting before slag formation, which tends to increase heat loss.

On the other hand, in the case of a DC arc furnace, the molten metal performs vertical rotational motion. Therefore, the molten metal circulates up and down in the furnace and is constantly stirred, so that uneven heat in the up and down direction is reduced.

However, the temperature of the arc spot in a DC arc furnace is so high that it is said to be about 6000°C, so even though the above-mentioned circulation of the molten metal occurs in the vertical direction, some degree of uneven heating is unavoidable. .

(Problems to be Solved by the Invention) As described above, operation using a DC arc furnace can be said to be industrially advantageous compared to that using an AC arc furnace.

However, in terms of production efficiency, it is still difficult to say that it is highly efficient.

Therefore, an object of the present invention is to provide a DC arc that substantially eliminates uneven heat and promotes melting and/or refining, thereby shortening operating time and reducing electrode and electric power consumption, thereby increasing efficiency. The purpose is to provide a method for operating a furnace.

(Means for Solving the Problems) In order to achieve the above-mentioned object, in the present invention, when melting and/or refining the raw material charged into the DC arc furnace, the molten metal of the raw material is There is provided a method for operating a DC arc furnace, characterized in that a gas that does not react with the molten metal is blown from a nozzle disposed at the bottom of the DC arc furnace to promote flow.

The operating method of the present invention will be explained with reference to the drawings. In FIG. 1, a furnace body 1 made of refractory material has a bottom electrode 2, which is an anode, disposed at the bottom, and an upper electrode 3, which is a cathode, suspended from the top.

A raw material is charged into a furnace body 1, and an arc is blown between a bottom electrode 2 and an upper electrode 3 to melt the raw material.

At this time, the molten metal 4 rotates clockwise or counterclockwise in the vertical direction depending on the current value, as described above. Now, consider the case where the molten metal 4 flows in the direction of the arrow p as shown in the figure.

In this case, refractory nozzles 5, 5 are provided at the bottom of the furnace body 1 near the furnace wall, and a gas 6.6 that does not react with the molten metal 4 is blown from these nozzles.

The gas to be blown is selected depending on the type of molten metal 4, or is, for example, Ar. Further, N2 gas can also be used as long as there is no problem with N2 in the molten steel.

The molten metal 4 moves downward through the center of the furnace, passes through the upper surface of the bottom of the furnace, and rises along the furnace wall, making a circular movement.

Therefore, the gas 6.6 blown from the nozzle 5.5
This promotes the rise of the molten metal near the furnace wall. As a result, the stirring of the molten metal 4 proceeds synergistically, so that the uneven heat of the molten metal in the vertical direction becomes small, and the melting and/or refining of the raw materials proceeds efficiently.

In addition, when operating with a current value that causes circulation of the molten metal to be opposite to that shown in the figure, the nozzles 5, 5 may be placed near the bottom electrode 2.

Note that the amount of waste blown at this time is not particularly limited as long as it is an amount that promotes the flow of the molten metal 4, but it is 0.001 to 0.01 NM/min per ton of molten metal.
It is sufficient as long as it is of a certain extent.

(Example) Example 1. 2. Comparative Examples 1 and 2 Thirty tons of scrap steel was charged into the DC arc furnace shown in FIG. 1 and arc melted.

At this time, gas was blown at the flow rate shown in Table 1 only during the melting process (Example 1), and gas was blown at the indicated flow rate during both the melting and refining processes (Example 2).

For comparison, 30 tons of scrap steel was charged into an AC arc furnace, and gas was blown during both melting and refining processes (Comparative Example 1).

Melting and refining were performed by blowing gas at the indicated flow rate during both refining processes (Comparative Example 2).

For each 100 charges in each of these cases, the time required for melting and refining, electric power consumption, and electrode consumption were measured. Those average values are collectively shown in Table 1 as relative values when Comparative Example 1 is set to 1.00.

(Left below) 4゜(Effects of the invention) As is clear from the above explanation, the method of the present invention can shorten the steelmaking time, reduce the electricity consumption rate and the electrode consumption rate, and improve the AC arc furnace operation. It is possible to operate with higher efficiency than in the case of

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing one example of a DC arc furnace used in the method of the present invention. 1...Furnace body, 2...Furnace bottom electrode, 3...Top electrode,
4... Molten metal, 5... Nozzle, 6... Gas.

Claims (1)

[Claims] When melting and/or refining the raw material charged into the DC arc furnace, the molten metal is discharged from a nozzle disposed at the bottom of the DC arc furnace so as to promote the flow of the molten raw material in the furnace. A method of operating a DC arc furnace characterized by injecting a gas that does not react with.