JPH10330824A - Operation of electric furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate a lower temp. zone with the developing position changed in an early stage by measuring the temp. distribution in a furnace hearth with plural temp. sensors in the furnace hearth refractor, estimating an existing position of the low temp. zone in the furnace, controlling gas blowing quantity from tuyeres on the furnace hearth, forming molten metal stream from the high temp. zone to the low temp. zone and promoting the melting. SOLUTION: At the time of melting raw material of scrap, etc., charged in an electric furnace, the gas is blown into the molten metal 1 in the furnace form the tuyeres 7 for gas blowing arranged in the furnace hearth 13 and the melting and refining reaction of the charged mateal in the furnace are promoted by utilizing this stirring force of the gas. At this time, the temp. distribution in the furnace hearth is measured with plural temp. sensors 10 embedded into the furnace hearth refractory 3 and the existing position of the low temp. zone in the furnace caused by remaining the unmelting scrap is estimated from the temp. distribution in the furnace hearth. Based on the estimated position, the gas blowing quantity from the tuyeres 7 is controlled through a gas flow rate control device 11 so as to flow the molten metal 1 from the high temp. zone to the low temp. zone, and promote the melting of scrap.

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 an electric furnace, which efficiently stirs molten metal in an electric furnace to promote melting.

[0002]

2. Description of the Related Art Conventionally, in an electric furnace used for melting and refining a metal, high-speed melting has been aimed at in order to improve productivity. In the process of melting a raw material such as scrap, an auxiliary burner from a furnace wall is required. And an oxygen blowing lance at the top of the furnace body are used.

However, since the electric furnace is generally characterized by a shape whose depth is extremely shallow with respect to its diameter, the stirring efficiency of the molten metal bath is low. Further, since the heat from the arc generated from the electrode is also supplied only to the molten metal surface, heat convection hardly occurs in the molten metal bath, and the temperature distribution such that the surface layer of the metal bath is high and the bottom layer is low is easy to form. .
Therefore, in the melting period of the electric furnace operation, the scrap melting rate at the furnace bottom decreases, and in the refining period, the reaction rate decreases.

[0004] To solve these problems, a method has been proposed in which an oxidizing or inert gas is blown from a plurality of tuyeres provided on a hearth to utilize the stirring effect of the gas.

For example, Japanese Unexamined Patent Publication (Kokai) No. 63-4011 discloses that gas is continuously or intermittently blown from a tuyere at the bottom of a furnace until the melting is completed immediately after charging of scrap to remove molten steel accumulated at the bottom of the furnace. A method of attaching heat to scrap as splash to promote heat transfer has been proposed.

Further, Japanese Patent Application Laid-Open No. 6-18174, Japanese Patent Application Laid-Open No. 3-77251, and
In the gazette, a plurality of hearth tuyeres arranged to circulate a high-temperature molten metal to a place inevitably determined by the electrode arrangement, for example, a low-temperature region in the molten metal generated in a region away from the electrode. A method is disclosed in which the stirring efficiency is improved by injecting a gas from, and the low-temperature region is eliminated.

Furthermore, Japanese Patent Publication No. Hei 7-113517 discloses that a furnace having a furnace shape in which the depth of the molten metal and the furnace diameter are optimal for gas blowing and stirring from the furnace bottom is used, and a small amount of gas is blown. A method for improving the stirring efficiency is disclosed.

[0008]

Generally, scraps of various sizes are used as a metal source to be charged into an electric furnace.
Even heavy materials with large bulk density are included. In the situation of supplying these scraps, if a material with a low bulk density is used, the metal already melted in the initial stage of the operation of the operation enters the scrap gap, heat exchange is activated, and the molten metal flows. And dissolves in a short time.

On the contrary, in the case of a heavy scrap having a high bulk density, since the contact with the molten metal is small, the heat exchange rate is reduced and the melting time is lengthened. Furthermore, in this case,
Scrap does not move regardless of the flow of the molten metal, and a low-temperature region centered on these residual scraps is formed at the bottom of the furnace.As a result, it takes a very long heating time until melting is completed, and the power consumption increases. Invite. The problem of the occurrence of such a low-temperature region starting from the residual scrap having a high bulk density is that the location of occurrence varies depending on the operation charge due to the distribution of the charged scrap.

The technique of promoting agitation by bottom-blown gas described in the above-mentioned publications is based on a low-temperature region which is always generated at the same position, for example, a low-temperature region which is generated near a furnace wall distant from immediately below the upper electrode, or an auxiliary burner. This is effective for a low-temperature region existing at a position away from the flame direction. That is, what can be dealt with by these methods is limited to a low-temperature region generated in a fixed place, and a low-temperature region in which the generated place changes, such as a low-temperature region starting from a heavy scrap having a high bulk density. I can not cope. An object of the present invention is to provide a gas blowing operation method for an electric furnace, which quickly eliminates a low-temperature region where the generation position changes as described above.

[0011]

The inventor of the present invention has solved the above-mentioned low-temperature region at an early stage, and has improved the productivity by shortening the melting time.
Various tests were conducted to develop a gas blowing operation method for an electric furnace capable of reducing the power consumption, and the following findings were obtained.

(A) The flow pattern of the molten metal can be controlled by adjusting the amount of gas blown from the hearth tuyere, so that the flow of the molten metal can be directed from a high-temperature region to a low-temperature region of any molten metal. (B) The location of the low-temperature region can be estimated from the hearth temperature distribution measured by a plurality of temperature sensors buried in the hearth refractory.

The present invention has been made based on the above findings, and the gist of the invention is that "gas is blown into the molten metal in the furnace from a tuyere provided on the hearth, and a stirring force by the gas is used. In the method of operating an electric furnace, which promotes melting and refining reactions of furnace interior materials, the furnace temperature distribution measured by a plurality of temperature sensors buried in the hearth refractory indicates that the furnace has not melted due to remaining unmelted scrap. By estimating the location of the inner low-temperature region and controlling the amount of gas blown from the hearth tuyere based on this, a molten metal flow from the high-temperature region to the low-temperature region is formed to promote melting. Of operating electric furnaces

[0014]

FIG. 1 is a longitudinal sectional view showing an example of an electric furnace used in the present invention. The upper electrode 2 provided above the molten metal 1, the hearth electrode 4 embedded in the hearth refractory 3, the water cooling panel 5 arranged on the side wall of the furnace body, and the furnace cover 6 covering the upper part of the furnace body. The body 12 is configured. Hearth 1
A gas injection tuyere 7 is buried in 3, and a gas supply device 8 for supplying gas to the gas injection tuyere 7 and a gas flow valve 9 for controlling a gas flow to each tuyere are installed. . A temperature sensor 10 for temperature measurement is embedded in the hearth refractory, and a gas flow controller 11 for controlling a gas flow to the tuyere from the hearth temperature obtained from the temperature sensor 10 is installed. I have.

FIG. 2 is a schematic view showing a bird's-eye view of the positions of the gas injection tuyeres provided in the hearth, and the black circles indicate the positions of the hearth tuyeres. FIG. 3 is a schematic view of a bird's-eye view of the arrangement of temperature sensors buried in a hearth refractory, and ● indicates the position of the temperature sensor.
As a temperature sensor, a thermocouple thermometer is generally used. FIGS. 4, 5 and 6 show an electric furnace composed of the general top electrode 2 and bottom electrode 4 shown in FIG.
It is a schematic diagram which shows the flow of the molten metal when gas is blown from the hearth tuyere. ● indicates the hearth tuyere position, ○ indicates the position of the upper electrode, arrows indicate the flow direction of the molten metal, and hatched portions indicate the locations where the ascending and descending flows are generated.

FIG. 4 shows a case where the same amount of gas is blown from the four symmetrically arranged hearth tuyeres shown in FIG. 2, wherein FIG. 4 (a) is a molten metal surface, and FIG. The flow of the molten metal in the cross section taken along the line XX of FIG. In this case, a high-temperature descending flow toward the furnace lower part in the central part of the furnace occurs.

FIG. 5 shows the tuyeres 7A, 7B and 7C of FIG.
In this case, gas was blown from the three locations described above, and gas blowing from the tuyere 7D was stopped. FIG. 3A is a molten metal surface, and FIG. 3B is a cross section taken along line YY in FIG. Shows the flow of In this case, a high-temperature descending flow is generated toward the furnace bottom near the tuyere 7D where the gas injection is stopped.
FIG. 6 shows a case where gas is blown from two locations of tuyeres 7A and 7B in FIG. 2 and gas blowing from tuyeres 7C and 7D is stopped. FIG. 6 (a) shows a molten metal surface, and FIG. ) Shows the flow in the cross section taken along the line ZZ in FIG. In this case, a high-temperature descending flow toward the furnace bottom occurs between the tuyeres 7C and 7D where the gas injection is stopped.

FIG. 7 shows the above-mentioned gas blowing conditions, that is, locations where high-temperature descending flows are generated corresponding to gas blowing from four, three and two tuyeres. ● indicates the gas injection position. That is, it corresponds to gas injection from four, three, and two tuyeres, and heads toward the furnace bottom at the positions indicated by the hatched portions in FIGS. (A), (b), and (c), respectively. Heat can be supplied by induction of a high-temperature descending flow. Therefore, when a low-temperature region is generated at the position indicated by the hatched portion in FIG. 3 due to the undissolved scrap of heavy material having a high bulk density, heat is supplied to the low-temperature region by blowing gas from the corresponding tuyere. Becomes possible.

FIG. 8 is a schematic diagram showing the transition of the hearth temperature distribution by the temperature sensor when the charge obtained by adding the high bulk density scrap to the low bulk density scrap is melted. This corresponds to the temperature sensor shown in FIG. FIG. 9 is an explanatory diagram showing the position of the high bulk density scrap in the case of FIG. 8, in which the hatched portion S indicates the charging position and ● indicates the position of the gas blowing tuyere.

As shown in FIG. 8, the temperature sensors D, E, G, H
It is guessed that the temperature rise of the portions L and L is slow, and a low-temperature region starting from the undissolved scrap exists at this position. That is, by comparing hearth temperature distributions measured by a plurality of temperature sensors buried in the hearth refractory, it is possible to estimate the location of the low-temperature region.

Therefore, the generation position of the low-temperature region is estimated from the measurement of the hearth temperature, and a high-temperature molten metal flow can be induced in this low-temperature region by controlling gas injection from the tuyere. Can be eliminated at an early stage, and the time required for dissolving the entire amount of scrap can be reduced.

It is desirable that four or more gas injection tuyeres be provided at a half of the hearth radius on a concentric circle and point-symmetrically. Further, the gas blowing control is specifically performed by reducing or stopping the air flow from the tuyeres near the detected low-temperature region relative to the other tuyeres.

[0023]

【Example】

(Example 1) The electric furnace has a furnace capacity of 50 ton and a hearth inner diameter of 5
m. In the hearth, as shown in FIG.
Four gas injection tuyeres were arranged at 90 ° intervals, and the inner diameter of the tuyeres was 1.0 cm. Thermocouple thermometers were installed at 13 places on the hearth shown in FIG. 3 as temperature sensors.

A low bulk density scrap having a unit weight of 250 kg or less is charged with 49 tons, and the unit weight is 1 ton.
On, high bulk density scrap was charged, and carbon steel was melted at a total scrap of 50 ton and a scrap ratio of 100%.

FIG. 10 is an explanatory view showing the position of a high bulk density scrap charging place, and ● represents a gas blowing tuyere.
As shown in the figure, a high bulk density scrap was placed at the position S. The amount of heat input by electric power was 25.6 MJ / sec, and Ar gas at a flow rate of 20 Nm ³ / hour was blown in from each of the four tuyeres for 15 minutes. At this time, based on the hearth temperature distribution by the temperature sensor, in order to raise the temperature of the portion where the temperature rise was delayed, the gas blowing amount was adjusted by the gas flow controller and the gas flow valve shown in FIG. . That is, since the temperature rise near the tuyere 7D, that is, the temperature sensors D, E, G, H, and L, is delayed, the correspondence between the gas injection position and the flow of the molten metal shown in FIG. Based on the relationship, the tuyere 7A, 7 shown in FIG.
From the three locations B and 7C, the flow rate was 25 Nm ³
/ Hour gas was blown into the tuyere 7D, and in order to prevent clogging, the gas blowing conditions were changed to only Ar gas at a flow rate of 2.5 Nm ³ / hour, and the entire amount was dissolved.

In the comparative example, the control of the gas injection amount based on the hearth temperature distribution was not performed, and Ar gas was injected at a flow rate of 20 Nm ³ / hour from each of the four tuyeres from the start to the end of melting. Except for the above, dissolved under the same conditions as in Example 1.

FIG. 11 shows the transition of the hearth temperature distribution by the temperature sensor of Example 1 and FIG. In the first embodiment, after changing the blowing conditions, the temperature sensors D, E, G, H
The rate of temperature increase in the portions L and L is large, and the low-temperature region is eliminated earlier than in Comparative Example 1.

Table 1 shows the test results of Example 1 in comparison with Comparative Example 1.

[0029]

[Table 1]

As shown in Table 1, the total dissolution time of Example 1 was about 62 minutes, which was about 13 minutes shorter than Comparative Example 1. In addition, the unit power consumption of the first embodiment is about 1.90 × 1
0 ³ MJ / ton, which is about 17% lower than that of Comparative Example 1.

Example 2 Using the same electric furnace, the same amount and the same constitution as in Example 1, a high bulk density scrap having a unit weight of 1 ton was put into a position T shown in FIG. The amount of heat input by electric power was the same as in Example 1, and Ar flow rate of 20 Nm ³ / hour was obtained from four tuyeres.
Gas was bubbled in for 15 minutes. At this point, based on the hearth temperature distribution by the temperature sensor, the tuyere
In order to increase the temperature between the tuyeres 7A and 7B,
The gas is blown at a flow rate of 30 Nm ³ / hour from each of the ^three locations, and the gas blowing conditions are changed from the tuyeres 7C and 7D to only Ar gas at a flow rate of 2.5 Nm ³ / hour to prevent clogging. Then, the whole amount was dissolved.

Comparative Example 2 was the same as Comparative Example 1, except that the gas injection was not controlled, and that Ar gas was injected from the four tuyeres at a flow rate of 20 Nm ³ / hour from the start to the end of melting. The operation was performed under the same conditions as in Example 2.

FIG. 13 shows the transition of the hearth temperature distribution by the temperature sensor of Example 2 and FIG. In Example 2, after the gas blowing conditions were changed, the heating rates of K, D, H, and E near the high-bulk-density scrap charging position increased, and the low-temperature region was eliminated earlier than Comparative Example 2. I have. Table 2 shows the results of Example 2 in comparison with Comparative Example 2.

[0034]

[Table 2]

As shown in Table 2, the total dissolution of Example 2 was completed in about 60 minutes, which was about 18 minutes shorter than Comparative Example 2. In addition, the unit power consumption of the second embodiment is about 1.84 × 10
³ MJ / ton, which is about 23% lower than that of Comparative Example 2. As described above, by controlling the gas injection amount corresponding to the generation position of the low-temperature region, the effect of shortening the melting time and reducing the power consumption is apparent.

[0036]

According to the method of the present invention, by controlling the amount of gas blown from the tuyere corresponding to the position of the low temperature region generated by the bulk density distribution of the scrap of the charge, The high-temperature molten metal flow can be directed to the low-temperature region, the low-temperature region can be eliminated early, and the time required for melting the entire amount can be reduced. As a result, it is possible to improve the productivity of the electric furnace and to reduce the electric power consumption, thereby bringing about economic effects.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing an electric furnace for carrying out an electric furnace operating method according to the present invention.

FIG. 2 is a schematic view showing a position of a tuyere for gas injection buried in a hearth refractory of an electric furnace for carrying out the present invention.

FIG. 3 is a schematic diagram showing a position of a temperature sensor buried in a hearth refractory of an electric furnace for carrying out the present invention.

FIG. 4 is a schematic diagram showing a flow of a molten metal when gas is blown from four places of a hearth tuyere.

FIG. 5 is a schematic diagram showing a flow of a molten metal when gas is blown from three places of a hearth tuyere.

FIG. 6 is a schematic diagram showing a flow of a molten metal when gas is blown from two places of a hearth tuyere.

FIG. 7 is a schematic view showing a place where a high-temperature descending flow is generated by gas injection from a hearth tuyere. FIG.
FIG. 3B shows the case from three tuyeres, and FIG. 3C shows the case from two tuyeres.

FIG. 8 is a schematic diagram showing a transition of a hearth temperature distribution by a temperature sensor when a charge obtained by adding high bulk density scrap to low bulk density scrap is melted.

FIG. 9 is an explanatory view showing a high bulk density scrap input position in the case of FIG. 8;

FIG. 10 is an explanatory diagram showing a high bulk density scrap charging position in the embodiment.

FIG. 11 is an explanatory diagram showing a transition of a hearth temperature distribution by the temperature sensor according to the first embodiment.

FIG. 12 is an explanatory diagram showing a transition of a hearth temperature distribution by the temperature sensor of Comparative Example 1.

FIG. 13 is an explanatory diagram showing transition of a hearth temperature distribution by the temperature sensor according to the second embodiment.

FIG. 14 is an explanatory diagram showing a transition of a hearth temperature distribution by the temperature sensor of Comparative Example 2.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 molten metal 8 gas supply device 2 upper electrode 9 gas flow valve 3 hearth refractory 10 temperature sensor 4 hearth electrode 11 gas flow controller 5 water cooling panel 12 furnace body 6 furnace cover 13 hearth 7 tuyere for gas injection

Claims (1)

[Claims] A method of operating an electric furnace in which a gas is blown into a molten metal in a furnace from a tuyere provided in a hearth portion, and a melting and refining reaction of materials inside the furnace is promoted by utilizing a stirring force by the gas. In the hearth temperature distribution measured by a plurality of temperature sensors embedded in the hearth refractory, the location of the low-temperature region in the furnace due to the remaining unmelted scrap was estimated, and based on this, A method for operating an electric furnace, comprising forming a molten metal flow from a high-temperature region to a low-temperature region by controlling a gas blowing amount to promote melting.