JPS60103109A - Method for operating electric furnace - Google Patents

Abstract

PURPOSE:To heat uniformly steel scraps and a steel bath and to shorten the time required to melt and refine the scraps by blowing an inert gas into each hot zone to transfer the heat of a steel bath present in the hot zone at a high temp. to steel scraps and a steel bath present in each cold zone at a low temp. CONSTITUTION:Three electrodes 5 are put in an electric furnace 1, and steel scraps fed to the furnace 1 are melted and refined with arc heat. At this time, hot zones 6 are formed at parts confronting the electrodes 5, and cold zones 7 are formed at parts close to the wall of the furnace. Each of the cold zones 7 is between the electrodes 5. Three nozzles 12 are set in the hearth 3 in the hot zones 6, and an inert gas is blown into the zones 6 from the nozzles 12 in such directions as the inert gas blown converges on a nearly central part A of the surface of molten metal prepd. by melting steel scraps.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the operation of an electric furnace. The aim is to promote the chemical reaction between slag and metal to shorten the melting time, and to enable the early generation of slag. This article relates to a method of operating an electric furnace.

Conventionally, in the operation of electric furnaces, during the melting stage of charges such as scrap, the use of an auxiliary combustion bar J- from the furnace wall and the use of oxygen to promote melting were combined with melting by arc heat from the electrodes. This results in a considerable reduction in operating time compared to operation using simple arc heat from the electrodes.

However, in recent years, it has been desired to further promote the above-mentioned melting and shorten the refining time. Although it has been proposed to accelerate the refining process and shorten the time required for refining, in reality, this method of operating an electric furnace that also uses gas blowing from the hearth has not been adopted.

Therefore, during the melting period, it is difficult to make the heat distribution uniform in the furnace, so the melting in the cold zone is difficult.
It is difficult to eliminate the delay, and the time required for slag generation cannot be shortened. Therefore, during the refining period, (a) high-temperature slag due to uneven heating causes significant damage to the refractory lining of the furnace, and (b) uneven temperature distribution causes unmelted parts to be (C) The movement speed of C in the steel is slowed down (refining time becomes longer) (d) T and Fe in the slag There are problems such as a large amount of added iron alloy and poor yield.

Next, the above-mentioned means for blowing gas from the hearth and its problems will be explained. That is, as means for blowing gas from the hearth, there are two methods: (1) selecting various gases from the side wall of the electric furnace into the steel bath in the cold zone and blowing them into the steel bath in the cold zone; A large number of gas blowing nozzles are installed in a concentric circle toward the top of the furnace, avoiding temperatures below '7IY, in the hearth, which corresponds to the height of the steel bath. A known method is to inject inert gas during the refining stage.

However, since the former method involves blowing gas into the low-temperature steel bath in the cold zone, the low-grade steel bath merely moves within the furnace, and the melting and refining promotion effect is not as great as expected. cannot be obtained. In addition, in the latter method, there is a risk that the steel bath will leak from the blast gas injection nozzle installed in the hearth, and the sole is difficult, and the nozzle and hearth part are severely damaged, and the cooling mechanism for that purpose is difficult. In addition to being necessary, there are many problems such as heat being taken away from the furnace by cooling.

The present inventors solved the above-mentioned problems, uniformized heating during melting and refining periods, eliminated cold zones, and improved production efficiency and reduced power consumption by shortening melting and refining times. In order to develop a method of operating an electric furnace that can

As a result, by blowing inert gas into the hot zone and transferring the heat from the hot steel bath in the hot zone to the steel scrap and the cold steel bath in the cold zone, the steel scrap and steel bath can be heated evenly. , it was found that the common understanding and refining time could be shortened.

This invention was made based on the findings mentioned in Section 2, and includes blowing gas into the furnace from a nozzle provided in the hearth of the electric furnace, and using the gas to charge the inside of the furnace during the melting period. In a method of operating an electric furnace that uses electrode arc heat to promote melting of materials and chemical reactions in a steel bath during the refining period, 1) 1. During the melting stage, the inert gas is directed to the hot zone in the furnace and the steel after the melting of the charge is completed. The inert gas in the bath is blown into the center of the bath from three or less nozzles provided in the hearth to promote melting of the charge, and then the smelting process is carried out. During the melting period, the inert gas is directed to the hot zone in the furnace from no more than three nozzles provided in the hearth, and the melting of the charge is completed. This method is characterized in that the inert gas is blown in a convergent direction into the substantially central portion of the surface of the steel bath after the steel bath has been heated, thereby promoting the chemical reaction of the steel bath.

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a schematic horizontal cross-sectional view of the bottom of an electric furnace showing one embodiment of the method of the present invention, and FIG. 2 is a schematic vertical cross-sectional view of the bottom of the electric furnace. As shown in the drawing, three electrodes 5 are inserted into an electric furnace 1 whose inner wall 2 is made of refractory material, whose hearth 3 is lined with an MgO stamp, and whose periphery is covered with an iron shell 4.
The arc heat melts and refines the steel scrap fed into the electric furnace. At this time, a hot zone 6 is generated in the area facing the electrodes 5, and a cold sea 77 is generated near the furnace wall between the electrodes 5. In FIG. 1, 8 is unmelted steel scrap, 9 is a tapping trough, and in FIG. 2, 10 is an auxiliary combustion burner provided on the furnace wall, and 11 is molten steel.

In this invention, three nozzles 12 are provided in the hearth 3 of the hot zone 6, and inert gas is blown in from the nozzles 12. The molten metal surface after the steel scrap has melted down is in the direction of convergence in the IT central part A.

The inert gas to be blown is, for example, nitrogen gas, argon gas, etc., and the blown metal is preferably in the range of 01 to (LINm3/min) per ton of molten steel.

That is, if the injection amount is less than 0.01 Nm/min per ton of molten steel, the desired effect cannot be obtained; If the temperature exceeds 1Nm for 37 minutes, cooling will be facilitated, but unnecessary movement will occur in the steel bath, which will adversely affect power input. Furthermore, when an active gas such as an oxidizing gas is injected, there is a problem in that the hearth is damaged. Therefore, no active gas is used in the present invention.

According to the above, the number of nozzles 12 for blowing inert gas should be three or less. That is, if the number of nozzles 12 exceeds three, the hearth refractories around the nozzles 12 will be damaged, which will require a lot of time to repair, which will impede production efficiency and cause unnecessary movement of the steel bath. This causes disadvantages such as loss of power efficiency. In this invention, the nozzle 12 for blowing inert gas is made of, for example, a Mgo-c-based capillary porous refractory.

When the cine active gas is injected by the method described above, the melt in the hot zone 6 is strongly agitated during the melting period,
By this stirring, the molten material in the hot sea 76 is scattered onto the unmelted steel scrap 8 present in the cold sea 77, and the melting of the steel scrap 8 is promoted by the molten material. Incidentally, since the temperature of the scattered molten material increases due to the arc heat, the melting of the steel scrap 7 is further promoted.

Conventionally, during the melting stage, it was necessary to perform auxiliary combustion by spraying petroleum fuel using an auxiliary combustion burner, and to blow oxygen using a burner and a lance as auxiliary combustion energy, but according to the present invention, the auxiliary combustion In addition to the combined effect of auxiliary combustion energy, almost all of the melting period
Since stirring can be carried out throughout the period, dissolution efficiency is significantly improved. As a result, the power consumption per unit of production is reduced and slag formation becomes possible at an early stage, so that the reaction efficiency is improved and the quicklime consumption rate can be reduced.

Next, during the refining period, as the high-temperature steel bath in the hot zone 6 is moved, the temperature deviation and non-uniformity of the composition of the molten steel are reduced, and as a result, the power consumption rate is reduced and the refining time is shortened. In addition, the influence of high-temperature slag on refractories is also reduced, and the unit consumption of refractories is reduced.

Furthermore, improved decarburization efficiency facilitates refining of low-carbon steel, and as a result of promoting the reaction between slag and molten steel, the loss of Ill and Fe is reduced, and the Fe steel extraction yield is improved. , the deoxidizing conditions have improved, and Fe-8i and F
The yield of additive elements such as e-Mn is also improved. Also, de-P1
Reactions such as S1 removal and O removal are also promoted, and the CaO basic unit is reduced.

Next, the present invention will be further explained using examples.

Tables 1 and 2 show examples and conventional examples in which operations were carried out according to the method of the present invention described above. Table 1 shows examples of raw material charging, steelmaking time, electric power consumption, operating consumption, melting efficiency, and tapping yield, and Table 2 shows the molten steel temperature, C value, and S value during refining. ,
This figure shows the values of Ill, lit, and ferroalloy yield in the slag.

Conventional Example 1 For example, oxygen is blown with a lance onto the surface of the steel bath and the steel bath in the furnace, and oil is blown onto the surface from the furnace wall or furnace lid with a burner. System fuel F)
This is the case where a% combustion is achieved by the auxiliary combustion method using k spray. In conventional example 2, a large number of gas blowing nozzles are provided concentrically upward in the furnace, avoiding the area under the electrodes, in the hearth where the steel bath depth is below Σ. This figure shows an example in which the values obtained when a bottom blowing method in which oxygen and inert gas are blown into a steel bath are carried out in an experimental furnace are converted to those in an actual furnace.

In addition, in both the above-mentioned embodiment and conventional example 2, the auxiliary combustion method of sub-q (example) was also used.

02 in the operating unit in Table 1 is the amount of spray from the lance by the above-mentioned auxiliary combustion method.

In addition, in the embodiment of the present invention, N2 was used during almost the entire period of the melting period and the refining period, Ar was blown into the hot zone from three nozzles installed in the hearth, and Ar was used during the refining period. This is the amount of air blown into the hot zone during the last 3 minutes of . Note that the injection of N2 may be started after some molten steel has been generated. Further, in Conventional Example 2, the bottom blowing 02 is the blowing amount during the melting period, and the bottom blowing Ar is the blowing amount during the refining period.

As is clear from Tables 1 and 2, in the case of the non-explosion J method, compared to the auxiliary combustion method of Conventional Example 1, the steelmaking time, electric power consumption rate, and CaO consumption rate # are reduced. The melting efficiency and tapping yield are improved, and the deviations in molten steel temperature and C value are small, making it possible to improve the S removal rate, reduce the T and Fe values in slag, and improve the yield of ferroalloy. Ta.

In addition, in the case of the bottom blowing method of Conventional Example 2, the melting time is faster than in the example of the method of the present invention, but on the other hand, the refractories around the gas injection nozzle in the hearth are severely worn out, so they need to be repaired. As a result, the overall steel manufacturing time is shorter in the example, and the unit consumption of the sprayed repair material is also higher. Furthermore, in the case of Conventional Example 2, gas is blown in from a large number of nozzles, which increases bubbling on the surface of the molten metal, making the current flowing between the electric charge and the molten steel unstable and increasing power consumption. As a result, the electricity consumption rate during the refining period was higher than that of the example.

Next, the functions and effects of the method of the present invention will be listed.

■ During the dissolution stage, the dissolution of steel scrap is accelerated1
- As a result, it is possible to improve raw t2'f', improve efficiency, and reduce electric power consumption.In addition, early slag formation enables high basicity operation from the initial stage of melting, reducing CaO consumption. Ru.

■ During the refining period, the reaction between slag and metal is promoted, resulting in the following effects.

a. Since the Ill and Fe values in the slag decrease, F
The tapping yield of e is improved.

b. Since the O value in the steel is reduced, the yield of deoxidizer and ferroalloy is improved.

Since the C2 removal efficiency and S removal efficiency are improved, the basic unit of CaO is reduced.

d. Since the Mn value in molten steel increases, the amount of Mn input decreases.

e. Since the C removal efficiency is improved, it becomes possible to manufacture low C materials.

f. Since the composition of molten steel becomes uniform, variations in quality are reduced.

■ Since the temperature of the steel bath during the refining period is uniform, there is less erosion of the furnace wall reinforcements, and the basic unit of spraying repair work is improved.

■ Since refining time is shortened, it is possible to improve production efficiency and reduce power consumption.

As described above, according to the method of the present invention, heating during the melting and refining periods is made uniform, there is no cold zone, the melting and refining times are shortened, production efficiency is improved, and electric power and other operating basic units are reduced. Many excellent industrial effects are brought about, such as the ability to reduce

[Brief explanation of drawings]

FIG. 1 is a schematic horizontal cross-sectional view of the bottom of an electric furnace showing one embodiment of the method of the present invention, and FIG. 2 is a schematic vertical cross-sectional view of the bottom of the electric furnace. In the drawings, ]... Electric furnace 2... Inner wall 3... Hearth 4... Steel shell 5... Electrode 6... Hot zone 7... Cold sea 78... Steel scrap 9 ...
Steel tapping trough 10... Burner for auxiliary combustion I】... Molten steel 12
...Nozzle applicant Toshin Steel Co., Ltd. Agent Natsuo Shioya (and 2 others) (N \r

Claims (2)

[Claims] (1) Gas is blown into the furnace from a nozzle installed in the hearth of the electric furnace, and the gas accelerates the melting of the charge in the furnace during the melting period, and the steel bath during the refining period. A method of operating an electric furnace that uses melting and refining using arc heat of an electrode to promote a chemical reaction, in which an inert gas is used as the gas blown into the furnace, and the inert gas is Three points are provided in the hearth part toward the hot zone in the furnace and in a direction such that the inert gas converges at approximately the center of the steel bath surface after the melting of the charge is completed. A method for operating an electric furnace, characterized in that melting of the charge is promoted by blowing from the following nozzle. (2) Gas is blown into the furnace from a nozzle installed in the hearth of the electric furnace, and the gas accelerates the melting of the charge in the furnace during the melting period, and the steel bath during the refining period. A method of operating an electric furnace that uses melting and refining using arc heat of an electrode to promote a chemical reaction, wherein an inert gas is used as the gas blown into the furnace, and during the melting period towards the hot zone in the furnace,
Further, the inert gas is blown in from three or less nozzles provided in the hearth part in a direction such that the inert gas converges on approximately the center of the steel bath surface after the melting of the charge is completed. , to promote the dissolution of the charge, and then during the refining stage, the inert gas, ? 1 (Similar to the above melting period, from three or less nozzles provided in the hearth part, towards the hot zone in the furnace and on the steel bath surface after the melting of the charge is completed) A method for operating an electric furnace, characterized in that a chemical reaction in a steel bath is promoted by blowing the inert gas in a converging direction approximately at the center.