JPS63290214A - Refining method in top and bottom blowing converter - Google Patents

Abstract

PURPOSE:To produce common steel and low hydrogen steel while maintaining stable service life of tuyere by executing refining using the prescribed bottom blowing gas condition to stabilize eroding speed of the tuyere to low level. CONSTITUTION:The refining is executed by supplying O2 from upper part of a converter 1 through a lance 2 and by blowing mixed gas of O2 and CO2 from inner pipe 3A and CO2 gas or mixed gas of CO2 and hydrocarbon from outer pipe 3B in a tuyere 3 having double pipes at bottom part of the furnace 1. Then, based on hydrogen predicting value in the steel obtd. after refining, at the time of refining the low hydrogen steel, all CO2 gas from the outer pipe 3B as cooling gas and the mixed gas of CO2 and O2 from the inner pipe 3A so that CO2/O2 mixing ratio satisfies the condition of suitable heat balance range at tip of the tuyere 3, are blown. Or, at the time of refining the common steel, the mixed gas of Co2 and hydrocarbon is blown from the outer pipe 3B and the mixed gas of CO2 and O2 is blown from the inner pipe 3A so that CO2/O2 mixing ratio satisfies the above condition. By changing the bottom blowing gas volume and the mixing ratio of each gas kind from the inner pipe 3A and the outer pipe 3B, the common steel and the low hydrogen steel can be produced while maintaining the stable service life of the tuyere.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a refining method using a top-bottom blowing converter.

(Prior Art) A converter refining method is known in which pure oxygen is blown from above and oxygen is also blown from the bottom of the furnace, taking advantage of the respective advantages of pure oxygen top-blown steelmaking and oxygen bottom-blown steelmaking.

For example, Japanese Unexamined Patent Publication No. 55-161014 discloses a technique in which a part of the total amount of oxygen supplied is blown under the bath surface during the blowing operation using top oxygen blowing or until the discharge period after the blowing is completed. A technique has been disclosed in which a mixed gas of oxygen and carbon dioxide is blown below the bath surface until the discharge period after the completion of refining.

(Problems to be Solved by the Invention) According to the technique disclosed in the above-mentioned Japanese Unexamined Patent Publication No. 55-161014, by blowing oxygen gas from the bottom of the furnace,
This solves the disadvantages of increased cost or increased nitrogen content in molten steel due to the injection of inert gas such as argon or neutral gas such as nitrogen, but it There is no consideration given to the lumps of metal (pine mushrooms) that are formed, and as a result, there is a problem that the lifespan of the panels is short, and no equal attention is paid to the reduction of hydrogen in the steel.

On the other hand, the technique disclosed in JP-A-56-23215 uses a mixed gas of oxygen and carbon dioxide as the bottom blowing gas, but the mixing ratio of oxygen and carbon dioxide is between 0.5 and 2.
．． It is only stated that a range of 0 is desirable, but there is no equivalent disclosure regarding the blowing method that takes the life of the tuyere into consideration, and there is no focus on hydrogen in steel at all.
Similar to the technique disclosed in Japanese Patent No. 161014, there was a problem in economically producing steel of desired quality.

Furthermore, in order to reduce the hydrogen content, a technique is disclosed in Japanese Patent Publication No. 56-9250 in which pure oxygen is blown into the inner tube of a double-tube tuyere installed at the bottom of the furnace, and carbon dioxide is blown into it through the outer tube. However, this technology is a pure oxygen bottom blowing method,
This is a completely different technology from the present invention.

(Means for Solving the Problems) The present invention has been made to advantageously solve the problems of the prior art. In the method of refining by blowing a mixed gas of oxygen gas and carbon dioxide gas from the inner pipe of the heavy front panel, and blowing carbon dioxide gas or a mixed gas of carbon dioxide gas and hydrocarbon gas from the outer pipe, after refining. This is a refining method for a top-bottom blowing converter, which is characterized by changing the internal conditions of the double tube tuyere and the mixing ratio of each gas blown from the outer tube based on the obtained predicted value of hydrogen in steel.

The present invention will be explained below based on the drawings.

FIG. 1 is an explanatory diagram illustrating the present invention, and FIG. 2 is a sectional view illustrating a double pipe tuyere according to the present invention.

As shown in FIGS. 1 and 2, the present invention supplies pure oxygen from above a converter l through a lance 2, and from an inner tube 3A of a double-tube tuyere 3 provided at the bottom of the furnace. Oxygen gas source 6
A and 0.0 from carbon dioxide source 6B. Gas and CO gas are taken out at a predetermined ratio and blown in as a mixed gas, and from the outer tube 3B, propane gas from the hydrocarbon gas source 5A,
In the refining method of a top-bottom blowing converter in which refining is performed while blowing CO and gas from the carbon dioxide gas source 5B alone or in a well-mixed manner, the inner tube 3A is Refining is performed by changing the mixing ratio of the gas blown in from the outer tube 3B.

In the figure, 30 is a rib, 7A and 7B are setting devices that set the ratio of mixed gas and issue opening commands to each flow control valve 9A to 9D, and 8 is a control device that controls the type of steel to be refined, the refining conditions, It has a function of setting the ratio of mixed gas based on the values of the components of hot metal, temperature, etc., and inputting the ratio to the setting devices 7A and 78.

FIG. 3 is a diagram illustrating a pattern of the amount of top-blown oxygen, the composition and mixing ratio of bottom-blown gas according to the present invention.

The present invention will be further explained based on FIG.

The figure shows the top-bottom blowing refining pattern of 300 using a converter for ordinary steel with a less strict hydrogen content and 2.0pp of hydrogen content.
- The following is shown for the low hydrogen steel.

As shown in the figure, when refining ordinary steel by top-bottom blowing, the top-blowing oxygen amount is 6
7,000 N+s'/H, and CO2 and 0.0% from the inner tube 3A. A total of 5000 Nll1i/■ is injected, and in this case, COt is 30 to 40% and Of is 60 to 70%.

In addition, from the outer tube 3B, a total of 500 LPG and COt
It was decided to blow in at Nm'/H, and the comparison was 30 LPG.
%, CO, is 7θ%.

On the other hand, when refining low hydrogen steel, the gas injected from the inner pipe 3A is a mixed gas of COt and O2, and the total amount of gas is 5,000 yen.
Nm3/H is blown in, and the mixing ratio in this case is 70% to 70%, 30 to 40%.

On the other hand, the gas blown from the outer tube 3B is cotto.

%, and blowing is carried out under these conditions until the start of steel tapping.

However, the blow end (H) is the input at the final stage of converter blowing [■1
], it is sufficient that the bottom blowing gas pattern for low hydrogen steel refining is continued from the middle of blowing until the start of tapping. The top-blown oxygen flow rate is 6700011+s'/H.

As described above, according to the hydrogen content obtained after refining, the composition and mixing ratio of the gas injected from the inner and outer tubes of the double-tube tuyere are determined by dividing the steel into, for example, ordinary steel and low-hydrogen steel. It is something that is simultaneously changed and refined.

Next, we will discuss the thermal balance for stabilizing the bottom blow tuyere.

In order to stabilize the bottom-blown tuyere, it is necessary to optimize the heat balance at the tip of the tuyere.

The appropriate heat balance at the tip of the tuyere is defined in the following range by using the heat of reaction shown in Table 1.

Table 1 The inner tube heat generation rate per tuyere is defined by the following formula.

Inner tube 0. Gas flow rate (Nl13/Hr・unit)
,8Kcal/Hr・book)・・・・・・・・・・・・(
1) Define the outer tube heat absorption rate per tuyere using the following formula.

Outer tube CO, flow rate (Nl13/Hr・units) X (21
,8Kcal/sol
...(2) Considering that the inner pipe gas that contributes to the heat balance at the tip of the tuyere is a part of the inner pipe gas flowing near the inner periphery of the inner pipe, the outer pipe contains the inner pipe gas flowing near the inner periphery of the inner pipe. It is necessary to flow enough cooling gas to balance the heat generation rate of a portion of the pipe gas with the sensible heat of the molten steel near the tuyere. This appropriate heat balance region is expressed as in equation (3) using equations (1) and (2).

Appropriate heat balance area Inner tube heat generation rate > 0 The inner and outer tube bottom-blown gas amounts and gas type mixing ratio must ensure a linear flow rate that is above the hot water pitch limit, as well as the appropriate heat balance area expressed by equation (3). If it is determined to satisfy the following, it is possible to enjoy the metallurgical effect for a long period of time while maintaining a stable tuyere life.

(Function) In the present invention, the mixing ratio of bottom-blown gas is changed during low-hydrogen steel refining and ordinary steel refining, and the heat balance at the tuyere tip is set in the above-mentioned range for the following reason.

(1) In the case of low hydrogen steel refining, (H) pickup is
Because of this problem, CO gas is passed through all the outer tubes as a cooling gas. The Cot10s gas mixture ratio of the inner pipe gas is (3)
It is determined to satisfy the formula.

(2) In the case of ordinary steel refining, [11] LPG is used as a cooling gas for the outer tube because pick-up is not a problem. However, the cooling CO and gas required for low hydrogen steel are LI
Compared to 'G, the cooling capacity is smaller, so a large amount of CO2 needs to be injected when low hydrogen steel is melted.

In order to use the same tuyeres to ensure that the outer pipe line flow rate during low hydrogen steel refining and the outer pipe line flow rate during ordinary steel refining are above the limit line flow rate, it is necessary to It becomes necessary to flow not only LPG but also a mixed gas of LPG+GO and other gases.

Therefore, when refining ordinary steel, LPG and Co are used in the outer tube.

Flow the mixed gas of the inner tube gas according to equation (3).
10. The gas mixture ratio will be determined.

(Example) Table 2 shows the values of blow-off [H) when ordinary steel and low hydrogen steel were refined using the pattern shown in FIG.

As shown in the table above, the blow-off [H) is significantly reduced by using the low-hydrogen steel refining bottom-blowing gas pattern. When the low hydrogen steel refining bottom blowing gas pattern ratio was 10.2%, the tuyere nozzle erosion rate over one furnace was as low as 0.28 am/ch.

(Effects of the Invention) As described above, by carrying out refining using the bottom-blown gas conditions according to the present invention, ordinary steel and low hydrogen steel can be produced while keeping the tuyere erosion rate low and stable. .

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram illustrating the present invention, FIG. 2 is a sectional view illustrating the double pipe body opening according to the present invention, and FIG. 3 is a diagram showing the amount of top-blown oxygen, the composition of bottom-blown gas, and It is a figure which patterned and illustrated the mixing ratio. 1...Converter 2...Lance 3...Double tube body opening 3A...Inner tube 3B...Outer tube 5A...Hydrocarbon gas source 6A ...Oxygen gas sources 5B, 6B...Carbon dioxide gas source 8...Control device Applicant Nippon Steel Corporation No. 1 Plan

Claims (1)

[Claims] (1) Oxygen gas is supplied from above the converter, and a mixed gas of oxygen gas and carbon dioxide gas is blown from the inner tube of the double-tube tuyere installed at the bottom of the furnace, and carbon dioxide gas or carbon dioxide gas is blown from the outer tube. In the method of refining by blowing a mixed gas of carbon gas and hydrocarbon gas, the mixing ratio of each gas injected from the inner and outer tubes of the double-tube tuyere is determined based on the predicted value of hydrogen in steel obtained after refining. A refining method using a top-bottom blowing converter characterized by