JPS63153209A - Method for coating bottom of converter fitted with bottom blowing nozzle - Google Patents

Abstract

PURPOSE:To easily form a coating layer of a required thickness on the bottom of a converter fitted with a bottom blowing nozzle without causing blocking trouble by coating the bottom of the converter with molten or semisolid slag and blowing an inert gas from the nozzle at a proper blowing rate during the coating. CONSTITUTION:After steel is tapped from a converter fitted with a bottom blowing nozzle, calcium oxide, light dolomite or the like is added to converter slag to obtain molten or semisolid slag. The converter is then titled to coat the bottom of the empty converter with the slag. In the coating stage, an inert gas is successively blown from the bottom blowing nozzle at >=0.025Nm<3>/ton.min blowing rate per one hole of the nozzle. Thus, a relatively thick protective coating layer of slag can be formed without blocking up vent holes in a mushroom and the service life of the bottom of the converter can be prolonged.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for coating the bottom surface of a converter equipped with a bottom-blowing nozzle (hereinafter referred to as a bottom-blowing converter). The present invention relates to a method for forming a coating layer of sufficient thickness on the bottom of a furnace without clogging a bottom blowing nozzle when applying a slag coating to extend the life of the furnace.

[Prior art] In blowing using a bottom-blowing converter, stirring of hot metal can be promoted by blowing gas such as argon, nitrogen, carbon oxide, etc. from the bottom-blowing nozzle. Although efficiency can be increased, there is a problem in that the thermal shock caused by gas injection significantly shortens the life of the refractory near the bottom blowing nozzle at the bottom of the furnace, and the life of the refractory at the bottom of the furnace is equal to the life of the converter. It becomes apparent. For this reason, various studies are being conducted to extend the life of the refractories at the bottom of converters. Among these, what is currently widely used is slag coating on the bottom of the furnace during or after tapping the steel.

In other words, slag coating is a process in which calcium oxide, light dolomite, etc. are added to the converter slag during or after steel tapping to form a semi-molten slag, and this is coated on the bottom of the converter. The aim is to repair and protect the damaged bottom refractory of the converter, and it has been confirmed that applying a light dolomite slag coating can significantly extend the life of the converter.

In this case, if slag coating is performed with the bottom blowing gas stopped, the inside of the vent hole of the pine mushroom (a porous steel ingot formed by cooling by the bottom blowing gas) formed at the bottom blow nozzle opening will Since molten slag enters and solidifies, causing nozzle blockage, a small amount of bottom-blown gas is continuously flowed into the air furnace, including the coating process, to prevent the vent from clogging.

[Problems to be Solved by the Invention] However, the injection of bottom-blown gas into the air furnace is only for the purpose of preventing nozzle clogging, and does not have a direct positive effect on the operability of the converter. Conventionally, a very small amount (0,01N 1113
Only 7 minutes per ton of bottom-blown gas is flowing, and if the bottom-blowing nozzle is partially blocked, the blowing resistance will increase rapidly, and some of the bottom-blown gas during blowing will reach the furnace wall. This could cause leakage from the joints of the refractory bricks, creating cavities and shortening the lifespan of the furnace bottom. In particular, recently there has been a tendency to make the slag coating thicker in order to further extend the life of the converter, and under such circumstances, nozzle clogging during slag coating becomes more likely to occur.

The present invention was developed in view of these circumstances, and its purpose is to eliminate the clogging of the bottom blowing nozzle during slag coating, and to coat the bottom of each converter with a slag coating layer of an appropriate thickness. The purpose is to provide a method that can be easily formed.

[Means for Solving the Problems] The structure of the method of the present invention that has achieved the above object is that in a method of coating and protecting the bottom of a converter equipped with a bottom blowing nozzle when the furnace is empty, The gist is that in the coating process of semi-molten slag, inert gas is blown at a rate of 0.025 Nm3/ton-minute or more per hole of the bottom blowing nozzle.

[Function] In the conventional slag coating method, accidents often occur when the bottom blowing nozzle is blocked, resulting in a decrease in bottom blowing efficiency in the blowing process of the next charge, or when the furnace bottom is blocked due to gas leakage when the furnace is empty. As mentioned earlier, cavities can form in the joints between refractories, which can actually shorten the life of the converter, but as we have conducted various studies to clarify the reasons why these problems occur, we have discovered the following facts: It was obvious that something had happened.

In other words, in the conventional slag coating method, the emphasis is on reducing the bottom blown gas, so the amount of bottom blown gas during the empty furnace (including during slag coating) is suppressed to a minimum, and therefore, the amount of bottom blown gas during slag coating is reduced to a minimum. It is not possible to reliably prevent the semi-molten slag from entering the vent hole of the pine mushroom, and as a result, the slag adheres to the inner wall of the vent hole and solidifies, resulting in increased ventilation resistance and blockage of the vent hole. A situation develops. This kind of intrusion of molten or semi-molten slag into the vent holes becomes more likely to occur as the slag coating layer becomes thicker, so in the end the slag coating layer cannot be thickened to the target level, and as a result, the converter It was not possible to extend the life span to a satisfactory degree.

However, as a result of further research aimed at developing a means to prevent blockage of the ventilation holes in the pine mushroom, it was found that if the bottom blowing gas is flowed at a flow rate of 0.025 N m3/min or more per hole of the bottom blowing nozzle, a considerable thickness can be achieved. Even when trying to form a slag coating layer on meat, there is no risk of clogging the vents in the pine mushroom room, and there is no phenomenon of cavities being created in the joints of the hearth bottom refractory during the slag coating process. It has become clear that by repeating this for each blowing charge, the life of the bottom of the converter can be dramatically increased.

Furthermore, the appropriate flow rate of the gas blown during lag coating will vary slightly depending on the target thickness of the slag coating layer, the type of slag, and the fluidity of the slag (which varies depending on the processing temperature, slag composition, etc.). In the present invention, which targets calcium oxide-based or light dolomite-based slag for inner surface coating and is carried out immediately after discharging molten steel after converter blowing, the amount of gas blown during slag coating is O.025Nm3. By setting the value to /'F-n.min or more, clogging of the bottom blow nozzle can be reliably prevented.

The specific method of slag coating is not different from the conventional method except that the amount of blown gas is increased.
For example, C in the refining slag during or after the completion of blowing.
AO, light dolomite, etc. may be added to form slag in a semi-molten state, and after completion of tapping, the converter may be tilted to adhere the slag to the bottom of the furnace.

During this period, while the molten slag is in a molten or semi-molten state, it is necessary to continue blowing gas at the specified amount or more from the bottom blowing nozzle, but after the slag coating layer has solidified, the gas blowing amount should be reduced to the conventional level. Even if the blowing is reduced to a certain level or the blowing is stopped, it will not have a negative effect on the life of the converter, and if it is applicable to a converter equipped with multiple bottom-blowing nozzles, it is natural to take precautions to prevent clogging for each nozzle. Therefore, the amount of gas blown into each nozzle was set at 0.025 N m.
Must be at least 3/ton/minute.

[Example] According to the following standard converter operating conditions, the average life of the bottom blowing nozzle in the conventional method in which 0.01 Nm3/min/ton of N2 gas was blown from the bottom blowing nozzle in the slag coating process after tapping was 1090 charge is enough, but according to the same standard converter operating conditions, the amount of 82 gas blown from the bottom blowing nozzle during slag coating was 0.025 N.
The nozzle life is 231 m3/ )-min.
2 charges, and it was confirmed that the converter life could be extended by more than twice that of the conventional example. Note that this converter life approximately corresponds to the erosion life of the refractories near the slag line on the furnace wall.

Standard converter operating conditions〉 Test converter (actual machine) Capacity: 85 tons/charge bottom blowing nozzle
...Single hole SA nozzle (Single Annealer) Large furnace bottom material...Mg0-C Hot metal charging amount -aa tons/Charge refining slag...4 tons/Charge top-blown oxygen -tsoooNm3/hr Bottom-blowing oxygen ...None Slag coating material...During steel tapping, 6 kg of light dolomite per ton of molten steel was put into the refining slag to make it semi-molten and used as coating slag.

Figure 1 also shows the case where the bottom blowing gas flow rate during slag coating was changed according to the above method (slag thickness: approximately 300 mm).
Fig. 3 is a graph showing changes in total iron content in mm) in comparison with a case without slag coating.

[Effects of the Invention] The present invention is configured as described above, and although the gas consumption increases slightly due to the increase in the amount of bottom-blown gas during slag coating, it is possible to dramatically extend the life of the converter. Therefore, overall, the cost required for converter blowing could be significantly reduced.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the bottom blowing gas flow rate and the total iron content during slag coating. April 15, 1988 Patent Application No. 301957 of 1988 2, Title of the invention 3, Relationship with the case of the person making the amendment Patent applicant 4, Agent 5, Subject of amendment Errata

Claims (1)

[Claims] In a method of coating and protecting the bottom of a converter equipped with a bottom-blowing nozzle when the furnace is empty, in the coating process of molten or semi-molten slag, an amount of 0.025 Nm^3/ton-min or more per hole of the bottom-blowing nozzle is applied. A method for coating the bottom surface of a converter equipped with a bottom blowing nozzle, which is characterized by blowing inert gas at a bottom blowing speed.