KR20010109928A - A Method for Manufacturing Molten Steel by Direct Electric Furnace - Google Patents

Abstract

The present invention relates to a method for manufacturing molten steel using a mini mill DC electric furnace, and in a method of manufacturing molten steel by dissolving scrap in a mini mill DC electric furnace, an abnormality occurs in a power supply device or a furnace refractory or a lower electrode is damaged. If the normal power supply is impossible, to provide a method for manufacturing molten steel by mini-mill DC electric furnace that can carry out the heating and refining process of molten steel by injecting gaseous oxygen and powdered carbon material into molten steel without supplying power to the lower electrode. It has a purpose

The present invention provides a method for producing molten steel by mini-mill direct current electric furnace for melting and raising the scrap metal using the arc heat generated by supplying power to the upper and lower parts of the furnace,

When the normal power supply is impossible during the heating step, the main purpose of the molten steel by mini-mill electric furnace is to blow gas oxygen and powder carbon material into molten steel to heat and refine the molten steel by heat of reaction of oxygen and carbon.

Description

Method for Manufacturing Molten Steel by Direct Electric Furnace

The present invention relates to a method for manufacturing molten steel using a mini mill DC electric furnace, and more particularly, to a method for manufacturing molten steel using a mini mill DC electric furnace that can be suitably applied even when power supply is impossible.

In general, a method of manufacturing molten steel using an electric furnace is generally classified into a direct current electric furnace method for supplying electric power to the hearth part and a lower electrode electrode, and a three phase alternating current electric furnace method for supplying electric power only from the hearth part.

As shown in FIG. 1, the mini-mill DC furnace 1 is provided with one rod-shaped graphite electrode rod 2 and an upper electrode power supply tube 3 at the top thereof, and two billet-type lower electrodes 6 at the bottom thereof. And a lower electrode power supply tube 7, the upper electrode power supply tube 3 is connected to a negative pole of a rectifier (not shown), and the lower electrode power supply tube 7 is a rectifier (not shown). Is connected to the + pole.

In Fig. 1, reference numerals "4" and "5" denote "body bottom" and "lower electrode sleeve", respectively.

Mini Mill DC Furnace has the merit of using less graphite electrode compared to AC method and reducing electric power input per ton of molten steel by 20KWH. On the other hand, careful management of furnace walls is required due to the installation of the lower electrode on the furnace bottom. have.

That is, the lower electrode installed on the furnace has high power input and melt remains all the time, causing erosion and abrasion due to thermal damage and performing periodic repairs.If the lower electrode is damaged or the refractory is damaged, The sensor installed in each part of the electrode detects this, and it can be checked in the central control room. The operation temperature of the lower electrode is automatically stopped when the temperature rises above 40-60 ℃ or 80-100 ℃.

The lower electrode is usually subjected to total replacement at 1000 levels.

Referring to the configuration of the lower electrode in detail with reference to Figure 2, the two round rod-shaped lower electrode (6) is installed through the furnace from the bottom to the furnace side, the lower electrode sleeve (5) is set in three stages to the outside and the lower electrode The lower end is provided with a jacket-type cooling panel and a cooling water supply pipe, and the power supply pipe 7 is connected to the lower end of the lower electrode 6.

The rod-shaped lower electrode configured as described above maintains a solid shape when power is not supplied, but when the power is supplied, the rod-shaped lower electrode is melted by heat loss from the upper end of the lower electrode, and the lower electrode is used for a long time or the non-conductor remains on the lower electrode part. If the normal power supply is not made, the sleeve edges outside the round bar type lower electrode are destroyed, and molten steel is leaked to the damaged part.

On the other hand, in the electric furnace operation technology applied in the prior art, the main purpose of the oxygen injection was scrap cutting of the discharging outlet side and decarburization and slag forming to control the carbon in the molten steel of the refiner. Arc heat of the electric power is the main heat source.

In the prior art, when the temperature of the lower electrode during molten steel rises, the lower electrode is not melted in a method of applying the method of re-powering the steel after refining the furnace steel after waiting for a predetermined time. Molten steel flows out to the bottom of the furnace when the sleeve is damaged, and the furnace equipment is burned or damaged by the scattering of the melt, causing secondary equipment accident.

On the other hand, when the sensor temperature for the lower electrode temperature is rapidly increased, the furnace floor refractory or the lower electrode is a sign of damage, the power supply is immediately stopped.

At this time, if the scrap is charged in the furnace, the scrap should be taken out using a collector or the like. If molten steel is formed, the scrap should be cooled and the current and the lower electrode should be simultaneously taken out using a crane.

After the molten steel cooling in the furnace, drawing out work is a long-term repair work that usually takes more than 20 days will have a direct impact on production.

The molten steel outflow and the withdrawal after molten steel cooling in the furnace have been frequent accidents since the initial operation and have had a direct impact on production.

The present inventors have conducted research and experiments to solve the above problems of the conventional method, and based on the results, the present invention has been proposed, and the present invention relates to a method for producing molten steel by melting scrap in a mini mill DC electric furnace. If the power supply device is abnormal or the furnace refractory or the lower electrode is damaged and normal power supply is impossible, the gaseous oxygen and powder carbon material is blown into the molten steel without supplying power to the lower electrode, thereby raising the temperature and refining the molten steel. To provide a method for producing molten steel by mini-mill direct current electric furnace that can carry out the process, the purpose is

1 is a cross-sectional view of a mini mill DC electric furnace to which the present invention is applied

2 is an enlarged cross-sectional view of a part of the mini-mill DC electric furnace of FIG.

3 is a cross-sectional view of a mini-mill direct current furnace showing a process of blowing oxygen and carbon material by an oxygen injection lance and a carbon retake lance;

Explanation of symbols on the main parts of the drawings

One . . . Mini Mill DC Furnace 6. . . Bottom electrode

8 . . . Oxygen blowing lance 9. . . Carbon reentry lance

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

The present invention provides a method for producing molten steel by mini-mill direct current electric furnace for melting and raising the scrap metal using the arc heat generated by supplying power to the upper and lower parts of the furnace,

The present invention relates to a method for manufacturing molten steel by mini-mill DC electric furnace, in which gaseous oxygen and powder carbon material are blown into molten steel and the temperature of molten steel is heated and refined by heat of reaction of oxygen and carbon when normal heating is not possible.

The present invention provides a method of manufacturing molten steel using a mini-mill direct current electric furnace equipped with an oxygen injection lance for blowing oxygen and a carbon injection lance for blowing carbon material,

Determining whether normal power supply is impossible; And

If it is determined that the normal power supply is impossible, the step of heating the molten steel to the target tap temperature by injecting oxygen and carbon material through the oxygen injection lance and the carbon material injection lance, respectively,

When the power input is less than 32000KWH, the oxygen blowing type through the oxygen blowing lance is performed by hard blowing, and the oxygen blowing flow rate through the oxygen blowing lance is less than 20 minutes after the power injection. 6000-7000Nm ³ / h and in the case of 20-40 minutes, the 7000-8000Nm ³ / h and in the case of 40-60 minutes in the case minutes, and 60-80 in 8000-9000Nm ³ / h, the 7000-8000Nm ³ / h, 5000-10000 Nm ³ / h in the case of 80-100 minutes, and the amount of carbon ash injection through the carbon ash injection lance is 60-80kg / min when the elapsed time after the power input is less than 20 minutes, It is 80-100kg / min for 20-40 minutes, 100-120kg / min for 40-60 minutes, 80-100kg / min for 60-80 minutes, and the power input is 32000KWH or more. In the case of oxygen blowing type through the oxygen blowing lance is soft blow ing), 5000-6000 Nm ³ / h if the elapsed time after power input is less than 20 minutes, 5000-7000 Nm ³ / h for 20-40 minutes, and 6000- for 40-60 minutes. 8000Nm ³ / h and in the case of 60-80 minutes when minutes 5000-7000Nm ³ / h and a, 80-100, the amount of carbon material blown over, and the carbon material and blowing lance 5000-6000Nm ³ / h is power If the elapsed time after the input is less than 40 minutes, 60-100kg / min, if more than 40 minutes relates to a method of manufacturing molten steel by a DC electric furnace that is not blown or less than 100kg / min.

Further, in the present invention described above, the tilt angle of the oxygen injection lance is 15 ° or more, preferably 15-20 °, the oxygen injection jet angle is 40-55 °, and from the molten steel surface to the lower part of the oxygen injection lance. The height is 300-700mm, the tilt angle of the carbon material injection lance is 15 ° or more, preferably 15-20 °, the carbon material injection angle is 30-40 °, and the carbon material is blown from the molten steel bath surface. It is preferable that the height to the bottom of the lance is 200-250mm so that the oxygen and the carbon material react at 500-600mm in the molten steel.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

The present invention is applied when the abnormality in the power supply device during the refining process after the melting of the scrap or molten iron in the mini-mill DC furnace, or when the normal power supply is impossible due to damage to the lower electrode is injected into the furnace molten steel surface in the form of powder or powder. The carbon material such as coke is mixed with gaseous oxygen to heat the reaction heat generated at this time to the molten steel side to perform molten steel heating and component control.

In the present invention, as shown in FIG. 3, oxygen is introduced through the oxygen injection lance 8, and carbon material is introduced through the carbon retake lance 9.

In the preferred molten steel manufacturing method according to the present invention, if the power input is less than 32000KWH, the hard blowing method should be adopted as the oxygen blowing type, because the undissolved scrap in the furnace is dissolved using only oxygen. If the input amount is 32000KWH or more, the soft blowing method should be adopted as the oxygen blowing type because the scraps charged in the furnace are melted and strengthened.

In other words, excessive blowing of oxygen may cause molten steel to be peroxidated.

On the other hand, in the present invention, when the height from the molten steel surface to the lower portion of the oxygen injection lance is 700 mm or more, the reaction efficiency may be low and a splash may occur. When the diameter is less than 300 mm, the molten steel is adsorbed to the lance nozzle. Since the nozzle may be clogged and the furnace refractory may be damaged, the height from the molten steel surface to the lower portion of the oxygen blowing lance is preferably limited to about 300 to 700 mm.

In addition, it is preferable to set the tilt angle of the carbon material injection lance to 15 ° or more, because the carbon material is mixed with oxygen in the molten steel to form slag forming, so that the tilt angle is more than 15 ° to obtain the effect. It is preferable to reduce it, but if it is too large, the slag forming reaction efficiency is improved, but the solvent is adsorbed to the carbon material insertion lance nozzle part, so that the equipment may be damaged or nozzle clogging may occur. Therefore, the upper limit should be set to 20 °. desirable.

On the other hand, the reason why the injection angle of carbon material injection is set to 30-40 ° is that when the oxygen lance tilt angle is 15-20 °, the injection angle of carbon material becomes 30-40 ° due to the characteristics of a conventional electric furnace. The reason for setting the height from the hot water surface to the lower part of the carbon material injection lance is 200-250mm. The reason for setting the height of the carbon material injection lance to prevent the molten steel from contacting or scattering the molten steel adsorbed to the lance nozzle is too high. If it is low, the carbon material is blown into the molten steel to improve the reaction efficiency, but there is a risk of the above-described molten steel contact or molten steel adsorption, and if the height is too high, the slag forming reaction efficiency is low.

The more preferable example of this invention is demonstrated as follows.

In other words, if the tilt angle of the oxygen injection lance is 15-20 °, the oxygen injection angle is 40-50 °, and the nozzle part of the oxygen injection lance will be about 300-700mm in height from the molten steel surface and the tilt angle of the carbon material injection lance. At this 15-20 °, the carbon material injection angle is 30-40 °, and the carbon material injection lance is located at a height of 200-250mm from the molten steel bath surface, and the tilt angle of the oxygen lance and the carbon material injection lance (15-20). At °), oxygen and carbon materials are reacted at 500-600mm inside the molten steel.

In the method for producing molten steel according to the present invention, the amount of oxygen and carbon reblowing according to elapsed time according to a more preferable power input amount is shown in Table 1 below.

Pattern No. Power input standard Blown medium Oxygen and carbon reblowing by elapsed time according to power input Oxygen Blowing Type Less than 20 minutes 20-40 minutes 40-60 minutes 60-80 minutes 80-100 minutes One 26000KWH Oxygen (Nm ³ / h) 6000-7000 7000-8000 9000 8000 5000-6000 Hard Blowing Carbon material (Kg / Min) 80 80 100 80 Not taken 2 28000KWH Oxygen (Nm ³ / h) 6000-7000 7000-8000 9000 7000 5000-6000 Carbon material (Kg / Min) 80 80 100 80 Not taken 3 30000KWH Oxygen (Nm ³ / h) 6000-7000 7000-8000 8000 7000 5000-6000 Carbon material (Kg / Min) 80 80 100 80 Not taken 4 32000KWH Oxygen (Nm ³ / h) 5000-6000 5000-7000 8000 7000 5000 Soft Blowing Carbon material (Kg / Min) 80 80 80 Not taken Not taken 5 34000KWH Oxygen (Nm ³ / h) 5000 6000-7000 7000 7000 5000 Carbon material (Kg / Min) 80 80 80 Not taken Not taken 6 36000KWH Oxygen (Nm ³ / h) 5000 6000-7000 6000 5000 5000 Carbon material (Kg / Min) 80 80 80 Not taken Not taken 7 More than 38000KWH Oxygen (Nm ³ / h) 5000 5000-7000 6000 5000 5000 Carbon material (Kg / Min) 80 80 80 Not taken Not taken

In Table 1, in the case of hard blowing pattern when heating up from the molten steel temperature below 1500 ° C to 1630 ° C, the oxygen injection flow rate is about 5000-6000 Nm ³ / h since the slag forming must be pre-adjusted to the surface of the furnace steel at the beginning of oxygen injection. However, since the slag forming is stabilized, it is blown at a high speed of 8000-9000 Nm ³ / h, and the carbon material injection amount is 80-100Kg / Min.

At this time, the total oxygen injection amount is 12000-15000Nm ³ , the carbon material is 5000-6000Kg when the molten steel temperature is increased by more than 1630 ℃.

On the other hand, when the molten steel temperature is raised from 1500 ° C or higher to 1630 ° C or higher, in the case of the soft blowing pattern, the slag forming is first adjusted in the same manner as the hard blowing pattern at the beginning of the oxygen blowing, and then the oxygen injection amount is 6000-7000Nm ³ / After setting to h, it is blown at high speed for about 40-60 minutes. Oxygen injection amount is 8000-10000Nm ³ , and carbon material is 3500-5000Kg.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1

The abnormality of the power supply device of the mini-mill DC electric furnace was found, and the molten steel was raised and lowered to the target tapping temperature 1620-1630 ° C. under the conditions shown in Table 1 below.

The temperature of the molten steel when the abnormality of the power supply device was found was 1520 ° C, and the amount of power input was as shown in Table 2 below.

Example No. Power input standard Blown medium Oxygen and carbon reblowing by elapsed time according to power input Oxygen Blowing Type Less than 20 minutes 20-40 minutes 40-60 minutes 60-80 minutes 80-100 minutes Inventive Example 1 28000KWH Oxygen (Nm ³ / h) 7000 8000 9000 8500 6500 Hard Blowing Carbon material (Kg / Min) 80 100 80 Not taken Inventive Example 2 30000KWH Oxygen (Nm ³ / h) 6500 7000 8000 7500 6000 Carbon material (Kg / Min) 90 100 80 Not taken Inventive Example 3 34000KWH Oxygen (Nm ³ / h) 5500 6000 7500 7000 5000 Soft Blowing Carbon material (Kg / Min) 90 80 Not taken Not taken Inventive Example 4 36000KWH Oxygen (Nm ³ / h) 5000 5500 7000 5500 5000 Carbon material (Kg / Min) 80 80 Not taken Not taken

As a result of injecting oxygen and carbon material under the conditions of Table 2, the target tapping temperature 1620-1630 ° C was obtained.

As described above, the present invention can increase the molten steel temperature without supplying power to the furnace body when abnormality occurs in the power system and the lower electrode part in the mini-mill DC furnace facility, so that the molten steel in the furnace can be pulled out without stagnation. There is an effect that can be perfected to improve and manage the body.

Claims (2)

In the method of manufacturing molten steel using a mini mill DC electric furnace equipped with an oxygen blowing lance for blowing oxygen and a carbon blowing lance for blowing carbon material, Determining whether normal power supply is impossible; And If it is determined that the normal power supply is impossible, the step of heating the molten steel to the target tap temperature by injecting oxygen and carbon material through the oxygen injection lance and the carbon material injection lance, respectively, When the power input is less than 32000KWH, the oxygen blowing type through the oxygen blowing lance is performed by hard blowing, and the oxygen blowing flow rate through the oxygen blowing lance is less than 20 minutes after the power injection. 6000-7000Nm ³ / h and in the case of 20-40 minutes, the 7000-8000Nm ³ / h and in the case of 40-60 minutes in the case minutes, and 60-80 in 8000-9000Nm ³ / h, the 7000-8000Nm ³ / h, 5000-10000 Nm ³ / h in the case of 80-100 minutes, and the amount of carbon ash injection through the carbon ash injection lance is 60-80kg / min when the elapsed time after the power input is less than 20 minutes, It is 80-100kg / min for 20-40 minutes, 100-120kg / min for 40-60 minutes, 80-100kg / min for 60-80 minutes, and the power input is 32000KWH or more. In the case of oxygen blowing type through the oxygen blowing lance is soft blow ing), 5000-6000 Nm ³ / h if the elapsed time after power input is less than 20 minutes, 5000-7000 Nm ³ / h for 20-40 minutes, and 6000- for 40-60 minutes. 8000Nm ³ / h and in the case of 60-80 minutes when minutes 5000-7000Nm ³ / h and a, 80-100, the amount of carbon material blown over, and the carbon material and blowing lance 5000-6000Nm ³ / h is power If the elapsed time after the input is less than 40 minutes, 60-100kg / min, and if it exceeds 40 minutes unmelted or less than 100kg / min method of manufacturing molten steel by a mini mill DC electric furnace The method of claim 1, wherein the tilt angle of the oxygen blowing lance is 15-20 °, the oxygen blowing injection angle is 40-55 °, the height from the molten steel surface to the bottom of the oxygen blowing lance is 300-700mm, and Oxygen and carbon steel are molten steel with the tilt angle of the carbon material injection lance set to 15-20 °, the carbon material injection angle set to 30-40 °, and the height from the molten steel surface to the bottom of the carbon material injection lance set to 200-250mm. Method for producing molten steel by mini-mill direct current electric furnace, characterized in that the reaction is made in the interior 500-600mm