JPS62164810A - Method for operating top and bottom blown converter - Google Patents

Abstract

PURPOSE:To advantageously recover a converter gas enriched with CO by executing flux injection with bottom blowing in the initial and end periods of blowing and controlling slag forming in the middle period thereby adjusting the height of slag forming. CONSTITUTION:The flux injection from a bottom blowing tuyere is executed in the initial and end periods of blowing when the concn. of CO is low to suppress the slag forming. The converter gas is recovered in the middle period of blowing when the concn. of CO is high. The control of the slag forming including the stopping and restarting of the flux injection, continuous throwing of iron ore, temporary stopping thereof, etc. is executed during this time so that the height of the slag forming is maintained in the 50-80% range of the furnace throat height. The converter gas having a high concn. of CO is generated by such slag forming control, by which the energy from the converter is recovered with high efficiency.

Description

[Detailed Description of the Invention] (Industrial Application Field) Regarding the operation of a top-bottom blowing converter equipped with a top-blowing lance, this specification describes the development of an operating method aimed at recovering converter gas with a high concentration of CO gas. Describe the results of the research.

Blowing of molten steel in a top-bottom blowing converter is advantageous, for example, in low-hot metal operations using scrap, because secondary combustion occurs in the furnace due to the 0° gas jet from the top-blowing lance, and the heat source can be improved.

However, when converter gas is recovered, secondary combustion in the furnace reduces the CD concentration in the recovered gas, which is a major disadvantage in terms of the calorie consumption of the recovered gas.

(Prior art) Regarding the recovery of CO gas from a converter, Japanese Patent Laid-Open No. 54-126
No. 610 can be referred to, but there is no disclosure about increasing the COa content in the recovered gas.

(Problems to be Solved by the Invention) It is an object of the present invention to achieve operation of a top-bottom blowing converter that is advantageous for recovery of CD-rich converter gas by slag control.

(Means for Solving the Problems) This invention provides a flux that suppresses slag forming from the bottom blowing tuyere during a period of low CO gas generation at the beginning and end of blowing when blowing molten steel in a top and bottom blowing converter. Injection should be carried out, and the slag forming height should be 50 to 8 m
This is a method of operating a top-bottom blowing converter that combines the following: controlling the slag to within a range of 0%.

Now, the blowing pattern shown in FIG. 1 will be explained.

First, the initial and final stages of blowing are inappropriate periods for gas recovery because the CD concentration of the gas generated in the furnace is low, and flux injection is performed from the bottom blowing tuyere during this period to suppress slag forming. . C as a flux
Using aO, blow Can into molten steel along with 0° gas.

Further, in the middle stage of blowing, the CD concentration in the converter gas becomes sufficiently high, so the converter gas is recovered. At this time, in order to increase the CD concentration in the converter gas, slag forming control is performed to maintain the slag forming height within a range of 50 to 80% of the furnace mouth height. As shown in FIG. 2, the slag forming height and furnace mouth height are the heights from the stationary steel bath surface A, respectively, and the slag forming height is expressed as a percentage of the furnace mouth height.

In order to control the slag forming height to 50 to 80% of the furnace mouth height, the following operations (1) and (2) are performed.

(1) Slag forming height 50% First, stop the flux injection, start continuous injection of iron ore, and if the slag forming height is still low after that, add auxiliary materials such as fluorite from the furnace mouth.

(2) Slag forming height > 80% If the slag forming height exceeds 80% and there is a risk of slopping, start flux injection and temporarily stop the introduction of iron ore. In addition, in top-bottom blowing converters such as the bottom-blowing inert gas type (LD-KGC) where the top-blowing lance greatly contributes to the stirring force, lowering the top-blowing lance can also reduce the slag forming height. It is possible.

The slag forming height is JP-A-55-12521.
As disclosed in Publication No. 7, the acceleration based on the movement of the slag generated by the reaction in the furnace is detected by an acceleration detector attached to the top blowing lance, and this acceleration, the method of immersing the detector in the slag, and the acid flow rate are measured. Estimate using the functional relationship between

(Function) The decarburization reaction in the converter takes place through primary combustion (C+1/202→CO) at the top blowing lance and the fire point near the bottom blowing tuyere, and the CO2 content (CO7/ (CO+
CD□)X100) is 5 to 10%. However, in top-bottom blown converters, secondary combustion (CO
+1/20□→CO□) occurs, and the CD2 content is 15~
Increases to 20%.

By the way, CD□ is a strong oxidizing agent in the high temperature range,
Fe+CD□=F'e[]+CD (a Fe= a
The co□-co content in the reaction of P@o”1) is the third
As shown in the figure (Tetsu to Hagane vol. 51. (see page 19651194)), the furnace atmosphere temperature is 1500
℃, the CD content is high at 15 vol% CO2 and 85 vol% CO. Also, during slag forming, 5 to 10 wt.
% of granulated iron is contained, the COz in the exhaust gas is reduced to CD by the granulated iron, and the cod degree in the exhaust gas increases.

Furthermore, the contact area between the top-blown gas jet and the primary combustion gas decreases due to the increase in the slag forming height, and the secondary combustion rate decreases, which is also a factor in increasing the CD concentration.

Therefore, by increasing the slag forming height, it is possible to increase the CD concentration in the converter gas.For this purpose, the slag forming height needs to be at least 50% of the furnace mouth height, and from the viewpoint of preventing slopping. The upper limit of height is 80%.

(Example) In a 250 ton top-bottom blowing converter, the first
The operation was carried out according to the blowing pattern shown in the figure, and the slag forming height in the middle stage of blowing was +a: 38% of the furnace mouth height.
B: 5% and C: 49%, respectively. These a
- C of converter gas recovered after generation in three types of C blowing
The D concentration is shown in FIG.

Upper bottom blowing oxygen flow rate 2.3Nm37min・t ~3
．． 4Nm37min ・Bottom blowing oxygen flow rate 0.6~0
．． 7Nm'/m1ntCaO injection amount (Tot) 13
~27kg/l is the initial amount of CaO injection 6~8kg/l, and the final amount of CaO injection is 10~18kg/l.
From Figure 4, it can be seen that as the slag forming height is increased, the COa degree increases, and b In the type, the CD concentration reaches about 83%.

(Effects of the Invention) The present invention can generate converter gas with a high CD concentration by controlling the slag in the furnace, and can recover energy from the converter with high efficiency.

[Brief explanation of drawings]

Figure 1 is a graph showing the blowing pattern, Figure 2 is an explanatory diagram of a top-bottom blowing converter, and Figure 3 is a CD. -Graph showing CO content, Figure 4 is C
It is a graph showing the relationship between D concentration and blowing time. Figure 1 Figure 2

Claims (1)

[Claims] 1. When blowing molten steel in a top-bottom blowing converter, flux injection is performed to suppress slag forming from the bottom blowing tuyeres during periods when CO gas is generated at the beginning and end of blowing. A method for operating a top-bottom blowing converter comprising: performing slag-forming control such that the slag forming height is in the range of 50 to 80% of the furnace mouth height during the middle stage of refining, when a large amount of CO gas is generated.