JPH01123015A - Method for promoting secondary combustion in converter - Google Patents

Abstract

PURPOSE:To execute secondary combustion of CO generated with decarbonizing reaction in molten iron to CO2 and to efficiently raise temp. of the molten iron with this heat by arranging side blow tuyere at the specific position of belly part in a converter having bottom blow tuyere and blowing oxygen containing gas. CONSTITUTION:At the time of steelmaking refining by oxidizing and decarbonizing C in the molten iron with O2 gas in the bottom blow converter or top and bottom blow converter, plural pieces of side blow tuyeres 3 are arranged at the belly parts in the converter 1 to blow oxidizing gas 10 of O2, etc. C in the molten iron 7 in the converter is oxidized and decarbonized with O2 gas from the bottom blow tuyere 6 or the top blow lance and refined to the molten steel and also CO gas generated by oxidizing C and contained in molten slag 8 is made to secondary combustion with O2 gas from the side blow tuyere 3, and this combustion heat is transmitted to the molten steel 7 and heated, and the temp. of the molten steel 7 is raised. In this case, angle theta formed by component to the horizontal direction of center axis for the side blow tuyere 3 and component to the horizontal direction of line linking the side blow tuyere outlet and bottom blow tuyere 6 outlet is made to <=40 deg., and by making within the radius in the belly at the setting position of the side blow tuyere of the horizontal distance between both tuyere 3, 6 outlets, the temp. raising efficiency in the molten metal 7 is improved and the operation under charging high scrap ratio can be executed.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to an improvement in the decarburization refining of molten iron using a converter, especially a bottom blowing or top blowing converter. , relates to the use of CO gas generated inside the furnace body by the decarburization refining process as a heat source for heating molten iron.

<Conventional technology> Conventionally, CO, which is the reaction product gas of a converter, is released from the furnace mouth without undergoing secondary combustion to CO□ in the converter, and CO is recovered as unburned gas, or Or, for example, it is then burned and released into the atmosphere.

However, recently, the proportion of scrap and ore in the raw materials for converters has increased, and a large amount of heat source has become necessary. In order to make the 8-fusion reduction economically viable, an inexpensive heat source is required.

Here, there is a method of raising the temperature of molten steel by first charging a carbon source such as coke or coal into a furnace and burning it. However, this method inevitably results in an extension of the blowing time, which is a factor that inhibits productivity.

On the other hand, attempts have been made to raise the heat of molten steel by secondary combustion of CO gas generated during decarburization and refining of molten steel in a furnace. 1
No. 017-t discloses that the top-blowing lance is provided with a nozzle for secondary combustion of CO gas in the furnace, separate from the Laval nozzle that is its main nozzle. However, in this method, if the momentum of the gas from the secondary combustion nozzle is large, the secondary combustion heat will melt the refractories on the furnace wall, whereas if the momentum is weak, the cO generated from the molten steel will melt. Due to the upward flow, the gas is discharged from the furnace mouth without being able to sufficiently contribute to heating the molten steel.

In addition, even if the oxygen gas injected from the nozzle reacts with surrounding CO and becomes COt, that gas is blown onto the surface of the molten steel and an endothermic reaction of C + COz -2cot occurs, reducing the temperature rise of the molten steel. Also, JP-A-60
Japanese Patent Application No. 169507 discloses a method of blowing oxygen from an auxiliary lance of upward blowing in order to increase secondary combustion of CO gas in a furnace.

However, in this method, when the force of the oxygen gas jet from the auxiliary lance is strong, so-called hard blowing, it passes through the slag layer and collides with the steel bath surface, resulting in CO and 0 in the gas phase.
2 CO+ -O□→CO, secondary combustion reaction does not occur,
Since the reaction becomes c + -0,→Co, there is a drawback that a high secondary combustion rate cannot be obtained.

<Problems to be Solved by the Invention> The present invention eliminates the above-mentioned drawbacks, increases the secondary combustion rate extremely efficiently, and makes it possible to absorb combustion heat into molten steel. It was done for the purpose of getting used to it.

<Means for Solving the Problems> As a result of extensive research into a method for achieving a high secondary combustion rate of the generated CO gas in the converter, the present inventors discovered that the oxygen Alternatively, the inventors found that the object can be achieved by blowing an oxidizing gas, particularly by defining the position of the side blowing tuyeres and the axial direction thereof, and based on this knowledge, the present invention was accomplished.

The present invention has the following features: (1) A side-blowing tuyere is installed in the belly of a bottom-blowing or top-bottom-blowing converter, and oxygen is blown into the slag from the tuyere toward the gas generated in the furnace containing carbon monoxide. The characteristic method of promoting secondary combustion in a converter is: ■ The angle formed by the horizontal component of the center axis of the side blowing tuyere and the horizontal component of the line connecting the side blowing tuyere outlet and the bottom blowing tuyere outlet is 40°. and the horizontal distance between the bottom blowing tuyere outlet and the side blowing tuyere outlet is within the radius of the furnace belly at the side blowing tuyere installation position. This is the method described in item 0. However, "horizontal" here refers to the horizontal state when the converter body is in the standard blowing position, so-called "standing" state.

In other words, oxidizing gas is supplied through a bottom blowing tuyere that opens below the bath surface of the molten iron housed in the converter, or a top blowing lance that hangs above the bath surface to decarburize the molten iron or to refining the molten iron. In performing decoaling and heat generation while supplying oxygen or oxidizing gas, oxygen or oxidizing gas is injected from the side blow tuyeres installed above the bath surface of the molten iron through the shell and refractories of the furnace belly. , side blowing tuyere so that 0□ supplied from part or all of the bottom blowing tuyeres reacts with carbon in the molten iron and the CO gas that floats up is likely to burn above the molten iron and become COz gas. Oxygen or oxidizing gas is blown orally onto the CO gas. For this purpose, it is important that the bottom blowing tuyere tips and the side blowing tuyere tips should be close to each other when viewed from a plan view.

On the other hand, according to this method, since the 02 from the side blowing tuyere only passes through the slag layer, the secondary combustion rate hardly changes depending on the strength of the jet's momentum. The shortcomings of 1986-169507 were completely resolved.

Figure 1 shows a joint cross-sectional view of a top-bottom blowing converter. In Figure 2, 1 is the converter refractory, 2 is the iron shell, 3 is the side blowing tuyere, 4 is the top blowing lance (optional), 5 is the furnace mouth, 6 is the bottom blowing tuyere, 7 is the molten iron, 8 is slag. The oxidizing gas 12 injected from the side blowing tuyere 3 collides with the gas bubbles 9 containing co generated from the oxidizing gas injected from the bottom blowing tuyere 6. By colliding, CO and 02 stop the combustion reaction of CO+ -O□→CO, and heat is transferred from COz to the slag layer to the molten iron, resulting in a high heat transfer rate. Of course, this is effectively achieved by stirring the slag or molten steel, and bottom-blown or side-blown gas stirring guarantees this.

FIG. 2 is a cross-sectional view taken along line A-A in FIG. The effect is sustained when the angle formed by the horizontal component of the line connecting the component and the side-blowing tuyere outlet and the bottom-blowing tuyere outlet is within 40''.

In addition, 6' is the tuyere position which is a comparative example of this patent.

According to the present invention, CO gas from the bottom blow and 02 from the side blow are efficiently combusted in the slag layer, and the combustion heat is efficiently transferred to the steel bath layer by strong stirring in the slag layer.

<Example> The converter 5 has a bottom diameter of 1.4 m, a bottom diameter of 1.8 m, and a height of 3.5 m from the bottom to the furnace mouth. Pipe inner diameter 0.01 m, outer pipe gap 0.00
A 0.08 m double pipe tuyere is used as a top blowing lance, a throat diameter of 0.01 m, and a spread angle of 12° from the vertical direction.
It was installed with a 3-hole Laval nozzle.

Further, when using this top blowing lance, the lance height (distance between the static bath surface and the tip of the lance) was set to 0.5 m. The top blow Ot flow rate is 15 Nm3/min. The number of side blowing tuyere installed in the furnace belly shall be 1 to 2, and if there are two, they shall be equally spaced, the inner diameter of the tuyeres shall be 0.008 m, and the height from the bottom blowing to the above tuyere shall be 1 m. , the depth of molten steel is approximately 0.5 m when approximately 5 mm is charged.

Approximately 5 tons of hot metal was charged into the converter, and blowing was performed under the first condition using the bottom blowing tuyere 6 or the top blowing lance, and oxygen was also injected from the side blowing tuyere 3. The effect of this invention can be seen from the amount of scrap required to obtain a predetermined molten steel composition C=0.05% and a temperature of 1700°C. The thickness of the foamed slag at this time is about 1 m, and it is effective to control this slag thickness by adding, for example, a carbon source.

In addition, the hot metal components here are C-4, 4 to 4.6%, Si-
0.15~0.2, Mn=0.4~0.5, P
-0,1~0.11, -52=0.01~0.015
The temperature of the hot metal after charging is 1250 to 1260°C, the molten steel composition is 10-0.04 to 0.05, and the temperature is 1700 to 17.
The temperature was set at 10°C. Further, as a comparative example, two sub-lances (inner diameter 0.006 mφ, 2 holes, inclination angle 10°) were installed and blowing was performed simultaneously with top blowing and bottom blowing at a lance height of 0.6 m.

As shown in Table 1, the position of the bottom blowing tuyere with respect to the axis of the side blowing tuyere is within ±40°, and the horizontal distance between the bottom blowing tuyere outlet and the side blowing tuyere outlet is It has a remarkable effect when the angle is within the antral radius, and as shown in Comparative Examples ■ and ■, there is no significant increase in the secondary combustion rate at ±40° or more.
Comparative examples ■ and ■ are 4 Nm'/
This is an example in which 0□ of a+in was injected, and as can be seen from this, the effect of increasing the secondary combustion rate due to 02 from the top blowing sub-lance is different from that in the example. This is because in the almost horizontal case of the present invention, less heat is transferred into the base slag.

<Effects of the Invention> According to the present invention, the secondary combustion rate in the converter was significantly improved, and the smelting and reduction of ore due to the heating effect on molten iron, high scrap operation, and low Si operation were performed without any problems.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of a top-bottom blowing converter, and FIG. 2 is a cross-sectional view taken along the line A-A in FIG. 1. 1... Converter refractory, 2... Steel shell, 3... 2
Tuyere for subsequent combustion, 4... Top blowing lance, 5... Furnace mouth, 6... Bottom blowing tuyere, 6'... Bottom blowing tuyere (comparative example), 7... Molten steel, 8...Slag, 9...
・Bubbles containing CO, 10...Oxidizing gas, 11.
... Hearth bottom center, 12... Permissible bottom blowing tuyere position. Patent applicant: Kawasaki Steel Corporation

Claims (2)

[Claims] (1) A side-blowing tuyere is provided in the furnace belly of a bottom-blowing or top-bottom-blowing converter, and oxygen is blown into the slag through the tuyere toward the gas generated in the furnace containing carbon monoxide. A method for promoting secondary combustion in a converter. (2) The angle formed by the horizontal component of the center axis of the side blowing tuyere and the horizontal component of the line connecting the side blowing tuyere outlet and the bottom blowing tuyere outlet is within 40 degrees, and the bottom blowing tuyere outlet and the horizontal 2. The method according to claim 1, wherein oxygen is blown from the side blowing tuyeres in which the horizontal distance between the blowing tuyere outlets is within the radius of the furnace belly at the installation position of the side blowing tuyere.