JPH0992458A - Method for melting and smelting metal in electric steelmaking furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To cool graphite electrodes by spraying of a coolant without generating hydrogen gas or the like through aquatic reactions inside an electric-arc furnace by greatly reducing original electrode units through the minimizing of the oxidation wear of the graphite electrodes. SOLUTION: A metal is arc melted and smelted in an electric steelmaking furnace by passing current to a line of graphite electrodes which comprises graphite electrodes 1 connected to one another via nipples. In this case, above the furnace lid of the electric steelmaking furnace, the line of graphite electrodes is cooled by spraying of a coolant 2 while the coolant 2, ejected toward the outer peripheries of the line of graphite electrodes, is inclined downwards by an inclination angle of more than 35 deg. but not more than 60 deg. to a horizontal level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for melting and refining metals in an electric steelmaking furnace. More specifically, in an electric steelmaking furnace such as an arc electric furnace, graphite electrodes sequentially connected through nipples are used. Applying electric current to melt metal such as steelmaking
When refining, above the furnace lid of the arc electric furnace,
On the outer peripheral surface of the graphite electrode, while cooling liquid such as cooling water is continuously sprayed and cooled, this cooling liquid is jetted by inclining downward at a predetermined inclination angle, and in addition, The injection amount of the cooling liquid is kept within an appropriate range, the electrode consumption rate is greatly reduced by minimizing the oxidation consumption of the graphite electrode during melting and refining, and the hydrogen gas generated by the aqueous reaction in the arc electric furnace. The present invention relates to a metal melting and refining method that does not cause a deterioration in service life even with a furnace lid made of an inexpensive refractory material such as chamotte.

[0002]

2. Description of the Related Art Conventionally, in the melting and refining of metals in an electric arc furnace such as steelmaking, in addition to the reduction in the cost of electric energy, the consumption of oxidation at the tip and outer peripheral surface of the graphite electrode is suppressed, Therefore, it is desired to reduce the electrode unit consumption. Cooling of the graphite electrode has been proposed and implemented as a means of suppressing this oxidative consumption.As one of the cooling methods, the graphite electrodes in the upper part of the sequentially connected graphite electrodes are cooled by cooling water. Non-consumable electrodes have been proposed. That is, the inside of the non-consumable electrode is water-cooled, but this electrode is limited to cooling the graphite electrode connected to the lower end through a nipple, and the upper non-consumable electrode is cooled by cooling the upper non-consumable electrode during refining operation. This is a method of refining by consuming only the graphite electrode by cooling the graphite electrode.

For example, US Pat. No. 4,416,014,
The water-cooled non-consumable electrode described in each specification of No. 4.417.344 and No. 4.451.926 is composed of a hollow cylinder made of aluminum, and cooling water is introduced into this hollow cylinder to cool this Water cools the wall surface of the hollow cylinder and the graphite electrode connected to the lower end of the non-consumable electrode.

Further, the water-cooled non-consumable electrodes described in JP-A-60-501879 and JP-A-60-501880 are composed of a graphite tubular body, and the central hole of the tubular body is formed. Cooling water is introduced into the inside, and the wall surface of the tubular body and the graphite electrode connected thereto are cooled by this cooling water.

When the non-consumable electrode is used for cooling in this way, the graphite electrode connected to the lower part is cooled, and the graphite electrode is prevented from being oxidized and consumed to some extent.

However, even if the graphite electrode connected to the lower end is cooled by the non-consumable electrode, what is involved in cooling is limited to the connecting end face between the graphite electrode and the non-consumable electrode, and the cooling efficiency is high. Extremely low. Furthermore, the thermal conductivity of graphite itself decreases when it exceeds 100 ° C,
It is difficult to cool the lower graphite electrode that is involved in refining.

Further, when the graphite electrode is removed from the non-consumable electrode, it is moved off-line from the arc electric furnace to remove the used graphite electrode from the nipple, and when necessary, the nipple is also removed from the non-consumable electrode.

When a new graphite electrode is connected, a nipple is attached to the non-consumable electrode and a new graphite electrode is attached to this nipple.

Therefore, when cooling the graphite electrode connected to the lower portion by the water-cooled non-consumable electrode, it is necessary to transfer the graphite electrode offline for replacement, where heavy-duty labor is disconnected and connection work is performed. Therefore, the work becomes extremely complicated. If the graphite electrode is repeatedly removed and connected, the threads of the graphite electrode, the non-consumable electrode, the nipple, etc. may be deformed, crushed or damaged, resulting in poor connection or increase in electrical resistance, thus hindering the operation.

From this point, it is found that
In the publication, in order to cool the graphite electrode connected through the nipple, without using a water-cooled non-consumable electrode, the graphite electrode surface protruding upward from the furnace lid of the arc electric furnace is used. A cooling device for spraying and cooling cooling water is described.

As shown in FIG. 4, this cooling device has a furnace lid 1
A graphite electrode array is vertically inserted through the column 1. In the graphite electrode array, a graphite electrode is connected to the lower portion of the upper graphite electrode 12 via a nipple, and the graphite electrodes 12 are sequentially connected via the nipple. In one graphite electrode array, the lower graphite electrode is in the arc electric furnace, and the graphite electrode in the arc electric furnace is involved in refining during steelmaking. Above the furnace lid 11, the upper graphite electrode 12 is held by the electrode holder 13, and on the lower surface of the electrode holder 13, an annular cooling pipe 14 that surrounds the outer periphery of the upper graphite electrode 12 is provided.
A plurality of vertical pipes 15 are projected downward from the annular cooling pipe 14, and a nozzle 16 directed to the surface of the graphite electrode is provided on the inner surface of each vertical pipe 15. Therefore, the cooling water supplied to the annular cooling pipe 14 descends along each vertical pipe 15, and the cooling water is supplied from each nozzle 16 on the inner surface to the upper graphite electrode 1.
The outer peripheral surface of 2 is sprayed and cooled.

However, in the cooling device shown in FIG. 4, the cooling water is jetted from each nozzle 16 in a horizontal level or in a direction parallel to the horizontal level. For this reason, the cooling water is used for the graphite electrode 1.
When colliding with the outer peripheral surface of 2, a considerable amount of light is reflected and scattered, and the scattered cooling water is large, and the electrode holder 13 and the furnace lid 11 are severely contaminated and damaged. The lid is rarely made of expensive high-alumina refractory, and most of it is made of chamotte or other refractory, which is susceptible to contamination and wear.

The colliding cooling water 16 is almost reflected and hardly descends along the graphite electrode. Therefore, the graphite electrode to be cooled is limited only to the collision of the cooling water, and unless the amount of the cooling water used is abnormally increased, the graphite electrode in the lower part cannot be cooled, which is extremely uneconomical.

It should be noted that an increase in the amount of the cooling water used tends to enter the scattered electric water in the arc electric furnace, which affects the reaction in the furnace, and among them, the steelmaking of steel types that are difficult to produce, such as hydrogen embrittlement. In this case, hydrogen gas generated by an aqueous reaction in the furnace easily enters the molten steel and cannot be used.

Further, from the cooling pipe 14 to the many vertical pipes 15
Projects downward, and the projecting length is extremely long. For this reason, this long vertical pipe 15 becomes an obstacle when the cooling device is removed during electrode replacement, and handling is extremely troublesome.

Further, since the electromagnetic force is shielded by the cooling pipe 14, a considerable part of the current flowing through the graphite electrode 12 is cut off, which seriously hinders the operation.

Further, as described above, when the cooling liquid such as the cooling water is sprayed on the graphite electrode, there are the following problems.

That is, a part of the cooling liquid sprayed on the graphite electrode is scattered, and it inevitably enters a part of the arc electric furnace. When this cooling water is placed under high temperature conditions in the arc electric furnace, hydrogen is generated by the water gas reaction. It has been a concern from the beginning that when this hydrogen enters molten steel, it causes hydrogen embrittlement depending on the type of steel to be refined. For this reason, the operation of spraying the cooling liquid on the graphite electrode has not been carried out for steel making of steel grades that are required to have a high toughness, and as described above, the cooling device shown in Japanese Utility Model Publication No. 59-23357 has been proposed. However, this cooling device is not used.

Although it is preferable to spray the cooling liquid to cool the graphite electrode mainly from the viewpoint of preventing oxidation and consumption and reducing the power consumption rate, if the graphite electrode is excessively cooled, the supercooling of the graphite electrode is prevented. Electric power is consumed by that amount, and instead, the power consumption rate rises, which greatly increases the cost, which is not preferable.

[0020]

DISCLOSURE OF THE INVENTION The present invention is intended to solve the above-mentioned drawbacks. Specifically, in an electric steelmaking furnace such as an arc electric furnace, cooling is performed on graphite electrodes that are sequentially connected through nipples. When a current is applied to this graphite electrode to melt and refine the metal while spraying the liquid, it is tilted downward from the horizontal level at a predetermined tilt angle above the furnace lid of the arc electric furnace. While spraying and spraying the cooling liquid on the outer periphery of the graphite electrode, the spraying amount or spraying amount of the cooling liquid is kept within a predetermined range, and the graphite electrode in the arc electric furnace involved in refining and melting is also effective. Of the graphite gas in the arc electric furnace is suppressed by the water gas reaction of the cooling liquid entering the arc electric furnace. AC power or DC power with almost no Suggest dissolution and refining method of the metal that can be easily realized while current facilities at high power operation by.

[0021]

That is, according to the method of the present invention, a graphite electrode array in which graphite electrodes are sequentially connected through a nipple is energized to arc-melt and refine a metal in an electric steelmaking furnace. At this time, above the furnace lid of this electric steelmaking furnace, the cooling liquid was jetted toward the outer periphery of the graphite electrode of the graphite electrode array by inclining downward with an inclination angle of more than 35 ° and 60 ° or less with respect to the horizontal level. And spraying the graphite electrode array to cool it.

In other words, according to the method of the present invention, when the cooling liquid is sprayed and cooled on the outer peripheral surface of the graphite electrodes sequentially connected through the nipple, the cooling liquid has a predetermined inclination with respect to the horizontal level. Take an angle and incline downward and spray. Therefore, most of the cooling liquid comes into contact with the outer peripheral surface of the graphite electrode and descends along the outer peripheral surface, and the cooling liquid descending along the outer peripheral surface is always in contact with the outer peripheral surface of the graphite electrode. The graphite electrode in the arc electric furnace is cooled to the outer peripheral surface and the tip.

Also in the arc electric furnace, the invading cooling liquid always flows along and contacts the outer peripheral surface of the graphite electrode. Therefore, the invading cooling liquid is almost evaporated and scattered during the descent, and there is no possibility that the water-gas reaction occurs.

Further, when the cooling liquid contains an oxidation resistant agent, when the cooling liquid descends along the outer peripheral surface of the graphite electrode, the oxidation resistant agent contained therein adheres, and is formed by this adhesion. The oxidation resistant coating effectively prevents the graphite electrode from being consumed by oxidation.

Further, the spray amount of the cooling liquid remains within the proper range. For this reason, even if a part of the cooling liquid enters the arc electric furnace, most of it is vaporized in the middle, no water-gas reaction occurs in the furnace, and no hydrogen gas is generated. From that point, when refining in this way, hydrogen and the like are not mixed in the molten steel, and it is possible to easily refine even the steel type having a problem of hydrogen embrittlement.

The structure and operation of these means will be described below in detail with reference to the drawings.

FIG. 1 is a front view showing an example of refining a metal while spraying a cooling liquid on a graphite electrode to cool the graphite electrode by the method of the present invention.

FIG. 2 is an explanatory view showing a part of FIG. 1 in an enlarged manner.

FIG. 3 is an explanatory view showing a part of the cooling pipe of FIG. 2 in an enlarged manner.

First, reference numeral 1 in FIGS. 1, 2 and 3 indicates graphite electrodes which are located above the furnace lid in the graphite electrodes which are sequentially connected through the nipple. Graphite electrode 1
The upper part of the graphite electrode 1 is gripped by an electrode holder (not shown), the graphite electrodes are sequentially connected to the lower end of the graphite electrode 1 through a nipple, and the lower graphite electrode is of an arc electric furnace (not shown). It is inserted into the electric furnace, and the graphite electrode
It is heated and refined such as steelmaking.

In the case of heating with three-phase AC power in an arc electric furnace, three-phase power is provided at intervals on a circle circle having a predetermined radius with its center as the center. Thus, three graphite electrode rows are arranged in which the graphite electrodes 1 are sequentially connected via the nipple.

Instead of heating with AC power,
In the case of heating with direct current power, one graphite electrode array is arranged, and in this graphite electrode array, the graphite electrodes 1 are sequentially connected through the nipple, and according to the energization heating with direct current power, a large current flows. , A large amount of refining can be done.

Next, in the graphite electrode array, a cooling liquid 2 such as cooling water is formed on the outer peripheral surface of the graphite electrode 1 above the furnace lid.
Is continuously sprayed downward at an inclination angle of more than 35 [deg.] And not more than 60 [deg.] To spray and spray, while the spray amount of the cooling liquid 2 is maintained in the range of 0.8 to 35 liters / minute.

That is, while the cooling liquid 2 is sprayed downward at a predetermined inclination angle as described above, the amount of the cooling liquid 2 is controlled according to the diameter of the graphite electrode 1, that is, the thickness. preferable. By the way, the appropriate range is 1
The diameter (inch) of the graphite electrode 1 is 16 ″, 18 ″, 2
In case of 0 ″, 22 ″, 24 ″, 26 ″, 28 ″, 30 ″, the cooling liquid amount (liter / min) is 6 to 9 and 8 respectively.
~ 12, 10-14, 12-17, 15-20, 17-
24, 20 to 28, 23 to 32 are preferable, and in this range, the electrode unit unit (kg / t) is reduced by 14 to 19% as compared with the conventional example (when cooled by a consumable electrode), and the power consumption is reduced. The basic unit (kwh / t) is reduced by 3 to 5%.

The cooling liquid can be sprayed by any method under the above conditions, but the cooling liquid can be sprayed using the cooling pipe 3 as follows.

A cooling pipe 3 is arranged around the graphite electrode 1 to be sprayed with the cooling liquid, and the cooling liquid is sent into the cooling pipe 3,
The cooling liquid is sprayed by inclining downward from the spray nozzle 4 on the inner peripheral surface of the cooling pipe 3 and spraying it. The cooling tube 3 is a graphite electrode 1
Between the electrode holder (not shown) that holds the upper part of the plate and the furnace lid (not shown) of the arc electric furnace.

Further, each spray nozzle 4 on the inner peripheral surface of the cooling pipe 3
Is directed in the radial direction toward the center of the graphite electrode 1, and the tip nozzle portion 4a of each spray nozzle 4 is inclined obliquely downward at an inclination angle θ of less than 60 ° and more than 35 ° as shown in FIG. Let When the spray nozzle 4 is attached in this manner, the cooling liquid 2 that is continuously supplied is jetted obliquely downward from each of the spray nozzles 4 of the cooling pipe 3, and the cooling liquid 2 becomes the outer peripheral surface of the graphite electrode 1. Of the lower graphite electrode 1 involved in refining while sequentially cooling the graphite electrode 1 while the cooling liquid 2 descends downward along the outer peripheral surface of each graphite electrode 1 of the graphite electrode array. Even when the cooling liquid is cooled to the tip and enters the arc electric furnace, the cooling liquid is vaporized by the internal heat and there is no room for an aqueous reaction.

In this way, by tilting downward, 0.8 to 3
When a cooling liquid of 5 liters / minute is sprayed and cooled, the cooling liquid 2 hardly scatters, most of the cooling liquid 2 flows on the outer peripheral surface of each graphite electrode 1 of the graphite electrode group, and the arc electric Enter the furnace and cool to the tip of the lower graphite electrode.

In this case, when the downward inclination angle θ is 35 ° or less, the ratio of collision and reflection on the outer peripheral surface of the graphite electrode 1 increases. For this reason, if the injection pressure is not properly adjusted, the amount reflected in the cooling liquid increases, and the reflected cooling water stains the dropped furnace lid and the like, and greatly deteriorates the durability.

If the downward inclination angle θ exceeds 60 ° or more, the descending speed of the cooling liquid becomes faster, and a part of the released cooling liquid undergoes a water gas reaction in the furnace to generate hydrogen gas. , Explosion occurs locally, which is not preferable. Furthermore, if the inclination angle is set to be 70 ° or less, the electrode unit unit is increased by 10 to 20%, as shown in Examples below.
This is also not preferable.

Further, the flow rate of the cooling liquid is 0.8 liter /
If the flow rate is 6 liters / minute or less, the predetermined effect cannot be achieved because the flow rate of the cooling liquid is insufficient even if the inclination angle θ is within the above range.

On the other hand, when the flow rate of the cooling liquid exceeds 35 liters / minute, the entire graphite electrode array is excessively cooled,
On the contrary, extra power is required to heat the supercooled portion, and the power consumption rate increases, which is not preferable. Further, the excess cooling liquid damages the furnace lid, and the durability is greatly reduced.

In the above description, an example in which the cooling liquid is blown out from a plurality of nozzles is shown, but under the above conditions, the cooling liquid can be blown out from one nozzle,
In this case, the structure of the cooling device itself can be made compact.

[0044]

【Example】

Embodiment 1 FIG. First, graphite electrodes having various diameters as shown in Table 1 were connected via a nipple, and the upper end of the graphite electrode above the furnace lid in this graphite electrode array was held by an electrode holder. As shown in FIG. 3, the cooling liquid 2 is sprayed downward from the spray nozzle 4 of the cooling pipe 3 with an inclination angle θ, and the scrap material is melted in an arc electric furnace for steelmaking. -Ku refined. Tap water was used as this cooling liquid, and this cooling water was continuously supplied and sprayed from each spray nozzle 4 toward the outer peripheral surface of the graphite electrode 1.

The injection conditions of the cooling water at this time are as shown in Table 1, and the improvement effect was examined mainly in terms of the electrode unit.

[0046]

[Table 1]

In Table 1, the optimum amount of water is as follows.

The amount of cooling water, including the case where the cooling liquid is cooling water, must be determined in relation to the diameter of the graphite electrode. From this, the optimum amount of cooling water was obtained as described above.

An experiment was conducted by setting the amount of water in relation to the diameter of the graphite electrode within the range of this optimum amount of cooling water.

As is clear from Table 1, for injection, that is, when the inclination angle θ is 60 ° or more, it is important in the operation of the electric furnace even within the range of the optimum amount of water corresponding to each electrode diameter. The basic unit of electrode was large.

Further, when the same experiment was conducted with one spray nozzle, the same results as shown in Table 1 were obtained.

[0052]

As described in detail above, according to the method of the present invention, a graphite electrode array in which graphite electrodes are sequentially connected through a nipple is energized to arc-melt and refine a metal in an electric steelmaking furnace. At the upper part of the furnace lid of the electric steelmaking furnace, the cooling liquid is jetted downward toward the outer periphery of the graphite electrode of the graphite electrode array with an inclination angle of more than 35 ° and 60 ° or less with respect to the horizontal level. To cool the graphite electrode array.

Further, regarding the spray amount of the cooling liquid, the optimum spray amount is determined within the range of 0.8 to 35 liters / min in relation to the diameter of the graphite electrode to be cooled, and the cooling liquid of this optimum spray amount is obtained. To spray.

When the metal is melted and refined while the cooling liquid is sprayed in this way, the oxidation consumption of the graphite electrode during the melting and refining is suppressed to a minimum and the electrode unit consumption is greatly reduced. No hydrogen gas is generated in the furnace due to aqueous reaction, and even a furnace lid made of an inexpensive refractory such as chamotte does not impair the service life.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example from the front when refining a metal while spraying a cooling liquid on a graphite electrode to cool it by the method of the present invention.

FIG. 2 is an explanatory view showing a part of FIG. 1 in an enlarged manner.

FIG. 3 is an explanatory view showing a part of the cooling pipe of FIG. 2 in an enlarged manner.

FIG. 4 is an explanatory diagram of a conventional cooling device.

[Explanation of symbols]

 1 Graphite electrode 2 Cooling liquid 3 Cooling pipe 4 Spray nozzle θ Inclination angle

Claims (4)

[Claims] 1. A furnace lid of an electric steelmaking furnace, when electric current is applied to a graphite electrode row in which graphite electrodes are sequentially connected through a nipple to arc melt and refine a metal in the electric steelmaking furnace. In the upper part, a cooling liquid is jetted and sprayed by inclining downward at an inclination angle of more than 35 ° and 60 ° or less with respect to the horizontal level toward the outer periphery of the graphite electrode array of the graphite electrode array, A method for melting and refining a metal in an electric steelmaking furnace characterized by cooling. 2. The method for melting and refining a metal in an electric steelmaking furnace according to claim 1, wherein water is injected as the cooling liquid. 3. The method for melting and refining a metal in an electric steelmaking furnace according to claim 1, wherein the cooling liquid is a cooling liquid containing an antioxidant and the balance being substantially water. . 4. The spraying amount of the cooling liquid is set to 0.8 to 35 liters / minute.
A method for melting and refining a metal in an electric steelmaking furnace as described.