JPH10306984A - Method for melting cold iron source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a facility for melting cold iron source with extremely high efficiency which can not be achieved by a conventional melting facility where scrap is preheated using exhaust gas an in which a cold iron source of next charge can be preheated without requiring a system for feeding a cold iron source to a melting chamber. SOLUTION: A cold iron source is melted using an arc melting facility comprising a melting furnace 1, and a preheating shaft 2 coupled directly to the upper part thereof. Scrap 3 in the melting furnace 1 is melted by arc 7 while being fed continuously or continually to the melting furnace 1 and the preheating shaft 2 such that a continuously existing state is sustained. At a moment of time when a specified quantity of molten steel is stored in the melting furnace 1, the molten steel is delivered to a ladle under a state the scrap 3 is existing in the melting furnace 1 and the preheating shaft 2 and heated in the ladle to raise the temperature thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of melting a cold iron source such as iron scrap, direct reduced iron or the like by an arc.

[0002]

2. Description of the Related Art In recent years, due to resource and environmental issues, processes for melting steel scrap with a large amount of generation using an arc furnace have been increasing. In such an arc furnace, since a large amount of power is consumed for melting the scrap, a method has been proposed in which the scrap is melted while preheating the scrap with exhaust gas generated from the furnace during the melting, thereby reducing the required power as much as possible.

For example, (1) a method in which a horizontal preheater is connected to an arc furnace, exhaust gas from the arc furnace is introduced into the preheater to preheat the scrap, and the preheated scrap is continuously supplied to the arc furnace. And (2) a method in which scrap preheated in the shaft pre-tropical zone by exhaust gas from the arc furnace is continuously supplied to the arc furnace by pushers provided in two stages (a strategy of the ordinary steel electric furnace industry,
P77 and P80; Iron and Steel Institute of Japan, November 1, 1994
4th).

[0004] (3) Two scrap preheating chambers are provided just above the arc furnace, the scrap in the chamber is preheated by exhaust gas generated from the arc furnace, and a stopper called a finger is opened to convert the scrap into the arc furnace. A supply type is also known (Electroheat, No. 82, 1995, P56).

[0005] Further, there is also a method (4) in which a rotary kiln and a shaft type pre-tropical are connected to an arc furnace, scrap is supplied from the shaft to the kiln by a pusher, and further, the scrap is continuously supplied to the arc furnace by the kiln. Kaihei 6
No. 122234).

Further, (5) a shaft-shaped pre-tropical zone is directly connected to a part of the furnace lid of the arc furnace, and one charge of scrap is supplied into the arc furnace and the shaft.
An electrode inserted from the side wall of the furnace while melting the scrap (Japanese Patent Publication No. 6-46145) and (6) a shaft-shaped arc furnace, wherein the scrap for one charge in the shaft is preheated by the exhaust gas. Are known to be dissolved.

[0007] In the arc furnace of the type in which the scrap is preheated by the exhaust gas as described above, the target is an electric power unit of about 250 to 270 kWh / t at a low value.

[0008]

However, the above-mentioned facilities (1) to (6) for preheating scrap with exhaust gas generated from an arc furnace have the following disadvantages.

In the facilities (1) to (4), in order to supply the scrap into the arc furnace, a device for transporting and supplying scrap such as a vibrating conveyor, a pusher, a kiln or a finger is required. There is a limit to the preheating temperature when preheating scrap with exhaust gas from the furnace. That is, when trying to preheat to a high temperature and increasing the amount of oxygen added to the furnace to increase the calorific value of the exhaust gas, hardware problems such as thermal deformation of the above-described apparatus cannot be avoided. In addition, when preheating to a high temperature, there is a problem in that fusion occurs locally and it becomes impossible to convey and supply scrap, and the preheating temperature is limited.

On the other hand, in the equipments of (5) and (6), since the scrap is charged in advance in the arc furnace or the shaft directly connected to the arc furnace and the arc furnace,
There is no need for the above-described device for scrap transport and supply, and therefore, the above-mentioned problems do not occur. However, in these facilities, the scrap in the arc furnace and the shaft is completely melted for each charge, and the molten steel in the furnace is discharged in a state where no scrap remains in the furnace and the shaft. Due to the inability to preheat, it is not sufficient in terms of effective utilization of exhaust gas.

The present invention has been made in view of such circumstances, and does not particularly require a device for transporting and supplying a cold iron source to a melting chamber, and also preheats a cold iron source for the next charge. It is possible to provide an extremely efficient method of melting a cold iron source, which is not possible with a melting facility that preheats scrap using conventional exhaust gas.
It is an object to provide a method for dissolving a cold iron source of less than 50 kWh / t.

[0012]

According to the present invention, there is provided a method for melting a cold iron source using an arc melting apparatus having a melting chamber and a preheating shaft directly connected to the melting chamber. Melting the cold iron source in the melting chamber by an arc while continuously or intermittently supplying the cold iron source to the preheating shaft so as to maintain a state in which the cold iron source is continuously present in the melting chamber and the preheating shaft; When a predetermined amount of molten steel accumulates in the melting chamber, the molten steel is discharged to a molten steel container in a state where a cold iron source is present in the melting chamber and the preheating shaft, and the molten steel in the container is heated and heated. A method for dissolving a cold iron source is provided.

Further, in the above method, during melting and tapping, the melting chamber and the preheating shaft are charged with 5/5 of one charge.
Disclosed is a method for dissolving a cold iron source, wherein 0% or more of the cold iron source remains.

Further, in any one of the above methods, there is provided a method for melting a cold iron source, characterized by supplying an auxiliary heat source such as coke and oxygen into a melting chamber.

Furthermore, the supply amount of oxygen is 25 Nm
Disclosed is a method for dissolving a cold iron source, wherein the method is not less than ³ / t.

Further, in any one of the above methods, there is provided a method for melting a cold iron source, wherein the molten steel is heated during tapping of the molten steel.

In the present invention, since the cold iron source is melted by using an arc melting facility having a melting chamber and a preheating shaft directly connected to the melting chamber, an apparatus for transporting and supplying the cold iron source to the melting chamber. Is not particularly required. In addition, the cold iron source in the melting chamber is melted by an arc while continuously or intermittently supplying the cold iron source to the preheating shaft so as to maintain a state in which the cold iron source is continuously present in the melting chamber and the preheating shaft, When one or more charges of molten steel accumulate in the melting chamber, the molten steel is discharged in a state where the cold iron source is present in the melting chamber and the preheating shaft. Efficient dissolution of cold iron source can be realized. Also,
In this way, the molten steel and scrap always coexist in the melting furnace, so the temperature of the molten steel is low.However, after tapping into the molten steel container, the molten steel in the container is heated to the required temperature by heating the molten steel. Can be warmed.

[0018]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a cross-sectional view showing an arc melting equipment used to carry out the method of the present invention. The arc melting equipment includes a melting furnace 1 for arc melting a cold iron source, and a preheating shaft 2 directly connected above the melting furnace. At the upper end of the preheating shaft 2, an exhaust part 2a connected to an exhaust gas suction system is provided. An iron scrap 3 as a cold iron source is charged into the melting furnace 1 and the preheating shaft 2.

A scrap loading bucket 4 is provided above the preheating shaft 2, and iron scrap 3 is loaded into the preheating shaft 2 from the basket 4. In this case, the loading of the scrap 3 from the basket 4
During operation, the scrap 3 is continuously or intermittently supplied to the preheating shaft 2 so as to keep the scrap 3 continuously present in the melting chamber 1 and the preheating shaft 2. At this time, charging of the scrap 3 may be performed based on a recipe set in advance based on operation results, or the preheating shaft 2 may be used.
It is also possible to provide a sensor capable of detecting the amount of the scrap 3 inside, and to control the input of the scrap 3 by the bucket 4 by an appropriate control means based on a signal from this sensor.

An openable / closable furnace lid 5 is provided on the upper part of the melting furnace 1, and an arc electrode 6 is inserted vertically from above the melting furnace 1 through the furnace lid 5. Further, a furnace bottom electrode 11 is provided at a position of the furnace bottom 10 of the melting furnace 1 facing the arc electrode 6. The scrap 3 is formed by the arc 7 formed by the arc electrode 6.
Is melted to form molten steel 8. A slag 9 is formed on the molten steel 8, and the arc 7 is formed in the slag 9.

The melting furnace 1 has two lances 12a,
12b is inserted with its tip facing the molten steel surface in the melting chamber, oxygen is supplied from the lance 12a,
Coke as an auxiliary heat source is injected from 2b. Note that a carbon material other than coke may be used as the auxiliary heat source.

A tapping port 14 is formed at the bottom of a protrusion 1a provided at a portion different from the side of the melting furnace 1 to which the preheating shaft 2 is directly connected, and a slag door 15 is provided at the side end. Have been. In addition, a tapping hole may be provided on the same peripheral surface as the slag door 15. Also, the protrusion 1a
, A burner 13 is inserted from above, so that the temperature of molten steel to be tapped can be increased. Note that another heating means such as an arc electrode may be provided instead of the burner 13.

As shown in FIG. 1, the side wall of the preheating shaft 2 has a taper that spreads downward. By providing such a taper, high-temperature scrap can be stably supplied into the molten steel 8 in the melting furnace 1. If the taper is not formed, the scrap 3 is restrained by the wall portion of the preheating shaft 2 and becomes less likely to drop naturally, which causes hanging of the shelf.

The taper of the side wall of the preheating shaft 2 is:
It is preferably in the range of 5 to 7 °. If this taper is less than 2.5 °, it is not possible to effectively prevent the hanging of the shelf. On the other hand, if it exceeds 7 °, the amount of the scrap 3 charged in the preheating shaft 2 decreases, and the residence time of the scrap 3 cannot be sufficiently obtained at the time of preheating, so that a sufficient preheating effect cannot be obtained. Conversely, if the same residence time is to be obtained, the height of the preheating shaft 2 is increased, so that the building must be increased. Furthermore, the cross section of the upper part of the preheating shaft 2 becomes narrow, and the usable scrap amount is limited.

Even if the preheating shaft 2 is tapered, if the preheating shaft 2 is rectangular, the frictional force between the wall surface and the scrap 3 is large, and it is not always possible to effectively prevent hanging from the shelf. Therefore, it is preferable that the cross-sectional shape of the preheating shaft 2 is a shape including a circle, an ellipse, or a curve.

When melting the iron scrap in the melting equipment configured as described above, first, the iron scrap 3 is charged into the melting furnace 1 and the preheating shaft 2, and the iron scrap 3 is put into the melting furnace 1 and the preheating shaft 2. The state exists continuously.

In this state, an arc 7 is formed by the arc electrode 6, and the iron scrap 3 is melted. At this time, oxygen is supplied by the lance 12a to assist in dissolving the scrap. Then, when molten steel accumulates in the furnace, the lance 12
b, coke as an auxiliary heat source is injected into the slag and the operation proceeds to the slag forming operation.
Is buried in the slag 9 so that the arc 7 is formed in the slag 9. The coke as an auxiliary heat source reacts with oxygen supplied separately to generate CO gas, and at the same time, the reaction heat contributes to melting of the scrap 3.

Exhaust gas generated by such scrap melting is discharged through the preheating shaft 2 and the exhaust part 2a, and the heat of the exhaust gas preheats the scrap 3 in the shaft 2. When the scrap 3 is melted in the melting furnace 1, the scrap of the preheating shaft 2 is supplied to the melting furnace 1, so that the upper end position of the scrap 3 in the preheating shaft 2 is lowered. In this case, the scrap 3 is continuously or intermittently supplied from the bucket 4 to the preheating shaft 2 so that the scrap 3 and the like are continuously present in the melting chamber and the preheating shaft. As a result, a state in which a certain amount or more of scrap is always present in the melting furnace 1 and the preheating shaft 2 is maintained. Scrap amount At this time, the charging of the scrap 3 or the like may be performed based on a recipe set in advance based on the operation results as described above, or the amount of the scrap 3 or the like in the preheating shaft 2 can be detected. A sensor may be provided, and the input of the scrap 3 or the like by the bucket 4 may be controlled based on a signal from the sensor.

When the melting of the scrap proceeds and a predetermined amount of molten steel, for example, one charge or more, accumulates in the furnace, the melting is continued while the scrap is continuously present in the melting furnace 1 and the melting shaft 2. Tilting furnace 1 and tapping port 1
4 to 1 charge of molten steel is discharged into a molten steel container, for example, a ladle. At the time of tapping, tapping port 14 due to solidification of molten steel
In order to prevent clogging, molten steel may be heated by the burner 13. Then, after tapping the molten steel into the ladle, the molten steel in the ladle is heated by an appropriate heating means, and the temperature is raised to a predetermined temperature. At this time, for example, an arc electrode can be used as the heating means.

When the scrap is melted in this manner, the preheating shaft 2 is not provided with a device for transporting and supplying the scrap such as a pusher or a finger. The amount of oxygen used can also be increased, and the exhaust gas temperature can be increased. Therefore, it becomes possible to preheat the scrap to a higher temperature than conventional melting equipment.

Further, the scrap 3 is supplied to the preheating shaft 2 so that the scrap 3 is always kept continuous with the melting furnace 1 and the preheating shaft 2, and molten steel for one charge or more is formed in the melting furnace 1. When tapping the steel, the scrap is continuously present in the melting furnace 1 and the preheating shaft 2, so that the scrap preheating efficiency by the exhaust gas is high.
In this case, 50 parts for one charge during melting and tapping.
By making the scrap of not less than% continuously exist in the melting furnace 1 and the preheating shaft 2, the preheating efficiency becomes extremely high.

From the viewpoint of efficiently dissolving scrap, it is desirable to use an auxiliary heat source such as coke. Injecting coke as an auxiliary heat source from the lance 12b and supplying oxygen from another lance 12a. Thereby, CO gas is generated and heat can be generated. In this case, the supplied oxygen amount is preferably 25 Nm ³ / t or more. Thereby, the scrap can be more efficiently melted.
More preferably, it is 40 Nm ³ / t. FIG. 2 shows that the oxygen unit consumption was 15 to 4 in the melting furnace in the embodiment described later.
This shows the basic unit of power when 5 Nm ³ / t is set. As shown in this figure, the power consumption decreases as the oxygen consumption increases. In particular, when the power consumption becomes 25 Nm ³ / t or more, the power consumption becomes an extremely low value of 200 kWh / t or less. 4 more
If it exceeds 0 Nm ³ / t, it will be about 120 kWh / t or less, and the value will be even lower.

Further, when melting is performed in a state where scrap is always present, the molten steel temperature is as low as about 1550 ° C., and the molten steel may be clogged in the tap hole 14.
By heating the molten steel with the burner 13 as described above, such a fear can be avoided.

Even if the molten steel is heated by using the burner 13 to prevent the molten steel from clogging the tap hole 14, the temperature of the molten steel itself is low. However, as described above, the molten steel is tapped into a ladle or the like and the molten steel is heated by an appropriate heating means therein, so that the molten steel can be heated to a sufficient temperature.

[0035]

【Example】

(Example 1) Scrap 1 was placed in a melting furnace and a preheating shaft of a DC arc facility in which a melting furnace (furnace diameter: 7.2 m, height 4 m) and a preheating shaft (5 mW x 3 mD) were directly connected.
50 tons were charged, an arc was formed in a melting furnace with a 28-inch graphite electrode at a maximum power supply capacity of 600 V and 100 kA, and the scrap was melted. A water-cooling lance is inserted from the working port provided on the furnace side wall, and 6000 Nm from there.
^The acid was fed in an amount of ³ / hr. When molten steel had accumulated in the furnace, coke was injected into the slag at 80 kg / min, and the slag forming operation was started, and the tip of the graphite electrode was buried in the forming slag. The voltage at this time was set to 400V. When the scrap in the preheating shaft descended with the melting of the scrap in the melting furnace, the scrap was supplied from the scrap charging bucket from the upper part of the preheating shaft, and the height of the scrap in the preheating shaft was maintained at a constant height. .

As described above, the melting is advanced in a state where the scrap is continuously present in the melting furnace and the preheating shaft, and when 180 tons of molten steel is generated in the melting furnace, the melting temperature is increased.
0 tons were left in the furnace, and 120 tons of molten steel for one charge was tapped from a tapping port to a ladle. The temperature of molten steel during tapping is 1
550 ° C. The C concentration in the molten steel was 0.1%. The molten steel near the tap hole was heated by an oxygen-oil burner.

After the tapping of 120 tons, the slag forming operation was performed while carrying out acid supply and coke injection to continue melting, and when the molten steel amount in the melting furnace reached 180 tons, the tapping of 120 tons was repeated. . An average of 120 tons of molten steel was obtained in about 40 minutes of tap-tap. Oxygen amount 33Nm ³ / t, Coke basic unit 26kg
The power consumption rate of 175 kWh / t was obtained at / t.

The temperature of 120 tons of molten steel discharged into the ladle is raised to 1620 ° C. by a ladle furnace (LF), that is, by an arc electrode inserted into the ladle, and 175 × 1 by continuous casting.
A 75 mm billet was produced. The average power consumption of LF was 60 kW / t. On the other hand, in the case where the same apparatus was used and the scrap was melted one charge at a time without continuously supplying the scrap (similar to the related art (5)), the power source unit was similarly obtained.

Table 1 shows the results. As shown in Table 1, the amount of oxygen used is almost the same, and the continuously supplied Example 1 has a power source unit lower by about 130 kWh / t than the comparative example. However, the power consumption was as low as about 100 kWh / t. In addition, the power consumption per unit of the present invention is 60 kWh / t or more, and the power consumption per unit required before reaching LF is lower than that of the reported examples of other processes shown in the prior art. It was confirmed that the preheating efficiency of the scrap was very high.

Example 2 The same melting as in Example 1 was carried out in the above melting furnace, except that the oxygen amount was 45 Nm ³ / t and the basic unit of coke was 36 kg / t. Table 1 also shows the results. The power consumption at this time is extremely low at 120 kW, and molten steel having an average temperature of 1550 ° C. has a tap-tap of about 3
Obtained in 7 minutes.

[0041]

[Table 1]

[0042]

As described above, according to the present invention,
Since a cold iron source such as scrap is melted using an arc melting facility having a melting chamber and a preheating shaft directly connected to the melting chamber, a device for transporting and supplying the cold iron source to the melting chamber is not particularly required. . Also, the cold iron source in the melting chamber is melted by an arc while supplying the cold iron source to the preheating shaft so as to maintain a state in which the cold iron source is continuously present in the melting chamber and the preheating shaft, and a predetermined amount is supplied to the melting chamber. For example, when molten steel of one charge or more accumulates, molten steel is tapped in a state where a cold iron source is present in the melting chamber and the preheating shaft. Dissolution of the iron source can be realized. Further, since the molten steel is heated after tapping, the temperature of the molten steel can be raised to a sufficient temperature.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an arc melting equipment used to carry out the method of the present invention.

FIG. 2 is a diagram showing a relationship between an oxygen consumption rate and an electricity consumption rate when an operation is performed using the apparatus of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Melting furnace 2 ... Preheating shaft 3 ... Iron scrap 4 ... Scrap loading basket 6 ... Electrode 7 ... Arc 8 ... Molten steel 9 ... Slag 12a ... Oxygen lance 12b ... Coke lance 13 ... … Burner 14… Steel outlet

Claims (5)

[Claims] 1. A method for melting a cold iron source using an arc melting apparatus having a melting chamber and a preheating shaft directly connected to the melting chamber, wherein the cold iron source is continuously provided in the melting chamber and the preheating shaft. The cold iron source in the melting chamber is melted by an arc while continuously or intermittently supplying the cold iron source to the preheating shaft so as to maintain the state of melting, and when a predetermined amount of molten steel has accumulated in the melting chamber, the melting chamber and preheating A method for melting a cold iron source, comprising: discharging molten steel into a molten steel container in a state where a cold iron source is present on a shaft; and heating the molten steel in the container to increase the temperature. 2. The melting of the cold iron source according to claim 1, wherein 50% or more of the cold iron source for one charge remains in the melting chamber and the preheating shaft during melting and at the time of tapping. Method. 3. The method for melting a cold iron source according to claim 1, wherein an auxiliary heat source such as coke and oxygen are further supplied into the melting chamber. 4. The method according to claim 3, wherein the supply amount of the oxygen is 25 Nm ³ / t or more. 5. The method for melting a cold iron source according to claim 1, wherein the molten steel is heated during tapping of the molten steel.