JPH0598331A - Blowing operation method for oxygen converter - Google Patents

Abstract

(57) [Summary] [Purpose] To suppress the occurrence of spitting and improve the yield rate and blowing efficiency. [Structure] The bottom blowing nozzle 4 of the upper bottom blowing converter 1 is arranged inside a plane formed by connecting a point P ₁ on the bottom of the furnace directly below the collision point P ₀ between the center axis of the oxygen jet 7 and the steel bath surface. , bottom blowing nozzles per one Ar, N _2, in the case of CO bubbled 0.4 Nm ³ / min · molten steel t following the gas flow rate, in the case of ^{_{O 2, CO 2 0.2Nm 3 /}} min
-Blowing is performed while blowing gas at a flow rate of molten steel t or less. [Effect] Combining the upward flows F _t and F _b due to the top-blown oxygen and bottom-blown gas in the steel bath 5 is avoided, the momentum of the top-blown gas and the bottom-blown gas is offset, and spitting is suppressed. The time required to remove the base metal is shortened. In addition, dephosphorized hot metal can be blown in a low slag amount without spitting.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steelmaking process using a top-bottom blown converter, which can reduce the loss of iron content such as spitting to improve the steel yield and improve the blowing efficiency. Regarding the method.

[0002]

2. Description of the Related Art Top-bottom blowing has become common in converter blowing methods, and many patents have been published regarding the placement of bottom-blowing nozzles. For example, JP-A-57-51212 and JP-A-57-39.
From the viewpoint of strengthening the mixing and stirring of slag and metal in order to promote dephosphorization, Japanese Patent Publication No. 114 has a bottom outside the circumference drawn by the intersection of the oxygen jet extension line of the top-blown oxygen lance and the furnace bottom. An upper and lower blowing converter equipped with a blowing nozzle is disclosed. On the other hand, in JP-A-57-131314, from the viewpoint of slag / metal reactivity, splash prevention, etc., an upper-bottom blowing converter in which a plurality of nozzles are arranged at the furnace bottom in the oxygen injection range from the upper-blowing lance is disclosed. It is disclosed.

As mentioned above, various proposals have been made regarding the position of the bottom blowing nozzle, which causes confusion, but the reason is that the importance of the slag-metal reaction depends on the purpose of converter blowing. It is in.

Recently, the refining load of the converter has been reduced due to the advancement of hot metal pretreatment and secondary refining technology.
Focusing on blowing efficiency rather than strengthening the metal reaction, it has become preferable to increase the oxygen supply rate and shorten the blowing time. For this reason, the scattering of iron such as splash and spitting is increasing, and the need for measures to prevent it is increasing.
In recent years, due to the remarkable progress of hot metal dephosphorization technology in the converter, blowing has become constant in the converter so that the slag / metal reaction need not be considered at all. This causes a decrease in blowing efficiency and a decrease in the yield of steel.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for operating a top-bottom blown converter capable of suppressing the occurrence of splash and spitting even under the above-mentioned high efficiency blowing conditions.

[0006]

The summary of the present invention is as follows.
It is in the blowing operation method of (1) and (2).

(1) The bottom blowing nozzle was arranged only inside the plane formed by connecting the points on the furnace bottom immediately below the point where the central axis of the oxygen jet from the perforated nozzle of the top blowing lance collides with the steel bath surface. Using a bottom-blown converter, per bottom-blown nozzle
Ar, blowing 0.4 Nm ³ / min · molten steel t following the flow of gas in the case of N _2, CO, in the case of O _2, CO ₂ is bubbled 0.2 Nm ³ / min · molten steel t following the flow of the gas A method for operating a bottom-blown converter, which is characterized by performing blowing while carrying out.

(2) The slag generated in the furnace at the end of blowing
The operation method of the above (1) is 50 kg / mol.t or less.

[0009]

The basic idea of the present invention is to provide a bottom-blowing nozzle inside the fire point of the top-blowing jet, and perform operations such that the kinetic energy of the top-blowing oxygen jet and the bottom-blowing gas cancel each other. The point is to suppress the occurrence of splash and spitting.

1A and 1B are views showing an example of a top-bottom blowing converter used in the method of the present invention. FIG. 1A is a vertical sectional view and FIG. 1B is a plan view.

The upper blowing lance 2 usually has about 3 to 7 oxygen blowing nozzles 3, and each nozzle 3 is inclined at an angle θ with respect to the vertical axis. Assuming that the distance between the lance and the steel bath surface is H, at the point P ₀ of H · tan θ from the center of the steel bath surface,
The central axis of the oxygen jet 7 jetted from each nozzle 3 collides with the steel bath surface. As a result, the steel bath surface forms a depression centered around the collision point, and an upward flow F _t obliquely upward is formed outside the depression.

On the other hand, the gas blown from the bottom-blowing nozzle 4 forms a violent upflow F _b , so that when the ascending position coincides with the upflow F _t due to top-blowing oxygen, it causes a violent splash on the steel bath surface, Spitting 6 occurs. In order to avoid such a situation, it is necessary to provide the bottom blow nozzle position inside the plane connecting the collision points P ₀ between the top blow oxygen and the steel bath surface or near the side wall of the furnace.

In the top-blown converter 1 of the present invention, the inside of the plane connecting the point P ₁ on the furnace bottom immediately below the collision point P ₀ between the central axis of the top-blown oxygen jet 7 and the steel bath surface (where the nozzle is In the case of four, the furnace bottom nozzles 4 are arranged in the shaded area in FIG. 1 (b). Therefore, the upward flow F _t by upflow F _t and the bottom-blown gas by top-blown oxygen never coalesce.

With the arrangement of the bottom blowing nozzle as described above, the apparent specific gravity of the steel bath is lowered by the bottom blowing bubbles, and the impact at the time of collision between the top blowing oxygen jet 7 and the steel bath 5 can be weakened. . Further, the momentums of the bottom-blown gas and the top-blown oxygen cancel each other out, so that the formation of splash can be suppressed and the spitting caused by the splash can be reduced. Such an effect cannot be expected when the bottom blowing nozzle is arranged near the furnace wall.

FIG. 2 shows the results of examining the relationship between the bottom blowing nozzle position and the spitting generation amount in a 15t converter. The symbols of the bottom blow nozzle positions on the horizontal axis in FIG. 2 are the same as the position symbols shown in FIG. Bottom blowing gas flow rate per nozzle
0.3 Nm ³ / min for N ₂ and molten steel t, 0.15 Nm ³ / m for O ₂
In and molten steel t were kept constant. The number of bottom-blowing nozzles is 2 except for the case of 1 hole (x mark) in the center of the furnace bottom.

Comparing the effects of the position of the bottom-blowing nozzle with the spitting amount without bottom blowing (marked with ⊚) being 1, the bottom-blown gas amount in one hole at the center of the furnace bottom (marked with ×) is the other half amount. , The least spitting. Next, when there was a nozzle inside the oxygen jet collision point (● mark), the number of spitting was the highest when the nozzle was placed just outside the oxygen jet collision point (○ mark).

[0017] When using the O ₂ in the bottom-blown gas because it produces twice the volume CO gas blow O ₂ by reaction with in the steel bath carbon was bubbled O ₂ for half of N ₂ .. As a result, the same relationship as N ₂ blowing was obtained.

FIG. 4 shows the blow-through limit bottom-blowing flow rate in a 15t converter in which the bottom-blowing nozzle is installed in the region defined by the present invention. The case bottom blowing nozzle of the central first hole (× mark), but bottom-blown N ₂ gas flow rate is less spitting up 0.4 Nm ³ / min · molten steel t, exceeds 0.4 Nm ³ / min · molten steel t It increased sharply.

When the bottom blowing nozzle has two holes and is inside the oxygen impact point (marked by ●), spitting is more than in the case of one hole at the center, but the flow rate per nozzle is 0.3. Nm ³ / min · Molten steel t minimizes spitting,
When 0.4Nm ³ / min ・ molten steel t was exceeded, spitting increased sharply. This is because the steel bath directly above the bottom blowing nozzle is substantially shallowed by top blowing oxygen, and when the bottom blowing gas flow rate exceeds the limit flow rate, blow-through occurs and metal is violently blown up.

On the other hand, when the bottom blowing gas is O ₂ , the amount of half the amount of N ₂ is
When O _{2 was} blown in, the same spitting generation behavior as N ₂ bottom blowing was shown, and the blow-through limit flow rate was 0.2 Nm ³ / min · molten steel t. Note exactly the same relationship as that of O ₂ even when using CO ₂ instead of O ₂ was obtained.

As described above, the bottom blowing nozzle is arranged only inside the plane formed by connecting the points on the furnace bottom immediately below the point where the central axis of the oxygen jet collides with the steel bath surface, and N ₂ per nozzle is arranged. In the case of inert gas such as 0.4Nm ³ / min · molten steel t or less, in the case of O ₂ and CO ₂ , blow at a flow rate of 0.2Nm ³ / min · molten steel t or less to suppress the generation of splash. The amount of spitting can be reduced.

When the hot metal dephosphorization is sufficiently carried out and dephosphorization is not required in the converter, it is desirable to reduce the amount of slag and reduce the loss of iron content transferred into the slag to improve the yield rate. However, it is usually necessary to use more than a certain amount of slag to prevent spitting, and the slag cannot be reduced unnecessarily. According to the method of the present invention, spitting can be effectively prevented as described above, so that it is possible to operate the slag minimum in which the slag is significantly reduced.

FIG. 5 shows the relationship between the spitting amount and the slag amount at the end of blowing in a 15t converter in which the bottom blowing nozzle is provided inside and outside the region defined by the present invention. The nozzle arrangement is shown by the symbols corresponding to FIG. 3 described above, and the N ₂ flow rate of the bottom blowing gas is constant at 0.3 Nm ³ / min · molten steel t. In the case without bottom blowing (marked with ⊚), the spitting amount increased rapidly when the slag amount became 50 kg / molten steel t or less. Even if bottom blowing is performed, in the case where the bottom blowing nozzle is provided outside the area defined by the present invention, the amount of spitting increases when the slag amount decreases as in the case of no bottom blowing. On the other hand, when the bottom blowing nozzle is arranged at the position defined by the present invention and bottom blowing is performed under the conditions of the present invention (marked by ●), even if the slag amount is reduced to 50 kg / mol. The increase in the amount of tings was slight.

As mentioned above, according to the method of the present invention,
Even if the pre-dephosphorized hot metal is used and the slag amount is reduced to 50 kg / mol.t or less, it is possible to perform high-efficiency blowing without spitting.

Examples of the present invention will be described below.

[0026]

Example 1 Ordinary molten pig metal was blown using an upper-bottom blowing converter as shown in FIG. The top-bottom blowing converter used was a nominal 15t converter with a steel bath surface diameter of 1.8m, and one bottom-blowing nozzle was placed either at the center of the furnace bottom or 0.25m to the left and right, and the top-blown oxygen jet center axis was used. The bottom blowing nozzle was located inside the plane connecting the points on the furnace bottom immediately below the collision point with the steel bath surface. The top blowing lance has four nozzles and has a nozzle inclination angle of 15 ° with respect to the vertical axis.

First, in a converter, normal hot metal 14 having the composition shown in Table 1 is used.
t, scrap 1t, quick lime 500kg and fluorspar 40kg, the distance between the lance and the steel bath surface is 1.3m (In this case, the collision position between the top-blown oxygen jet central axis and the steel bath surface is the steel bath surface). 0.35m from the center), supply speed 3000Nm ^{3 /} h (3.3Nm ³
/ min · Molten steel t) is top-blown with oxygen and the feed rate is 270 Nm ³ / h
(0.3 Nm ³ / min · molten steel t) was blown with nitrogen to produce molten steel having the composition shown in Table 1.

[0028]

[Comparative Example 1] One bottom-blowing nozzle was placed 0.45 m to the left and right from the center of the furnace bottom, and outside the plane connecting the point on the furnace bottom immediately below the collision point between the central axis of the top-blown oxygen jet and the steel bath surface. The bottom blowing nozzle is located at the bottom. Other top blowing lance conditions and gas supply conditions were the same as in Example 1, and normal molten iron having the composition shown in Table 1 was used to produce molten steel having the composition shown in Table 1.

[0029]

[Example 2] 15 tons of dephosphorized hot metal shown in Table 1 was charged without using scrap as an iron source material of a converter, and 15 kg of raw coal / molten steel t was charged as a raw material of slag and blown. Molten steel having the composition shown in Table 1 was produced under the same conditions as in Example 1 except that the amount of slag at the end was 50 kg / molt steel t or less.

[0030]

[Comparative Example 2] Molten steel having the composition shown in Table 1 was prepared by using the dephosphorized hot metal shown in Table 1 under the same conditions as in Example 2 except that one bottom blowing nozzle was placed 0.45 m to the left and right from the center of the furnace. Manufactured.

Table 2 shows the results obtained by averaging the blowing of 10 times for each of Examples and Comparative Examples.

[0032]

[Table 1]

[0033]

[Table 2]

As shown in Table 2, in Example 1 in which normal hot metal was used, spitting was reduced as compared with Comparative Example 1, and the amount of the metal at the furnace mouth was reduced to about 1/3. Therefore, the yield rate of the tapped steel was improved by 0.4% as compared with Comparative Example 1. Also, the work of dropping the metal at the furnace mouth was reduced, the time for Tap to Tap was shortened, and the operation efficiency was greatly improved.

In Example 2 using dephosphorized hot metal, Example 1 was used.
Although the amount of slag was smaller, the amount of the metal at the furnace mouth by spitting was about the same as in Example 1. On the other hand, the yield rate of the tapped steel was further improved as compared with Example 1. Comparing Example 2 and Comparative Example 2 having different bottom blow nozzle positions, Example 2 has a smaller amount of metal attached to the furnace mouth and a higher steel yield.

[0036]

According to the operation method of the top-bottom blowing converter of the present invention, the bottom-blowing nozzle is properly arranged at the jet collision position of the top-blowing oxygen and the bottom blowing is performed at a gas flow rate below the blow-through limit. Splash is suppressed, spitting is reduced, and steel yield can be improved. In particular,
Since spitting can be suppressed even in the low-slag amount blowing of dephosphorized hot metal, the present invention can be applied to the recent high-efficiency blowing of slag minimum to obtain good results.

[Brief description of drawings]

1A and 1B are diagrams showing an example of a top-bottom blowing converter used in the method of the present invention, in which FIG. 1A is a vertical sectional view and FIG. 1B is a plan view.

FIG. 2 is a diagram showing a relationship between a bottom blowing nozzle position of a converter and a spitting generation amount.

FIG. 3 is the same view as FIG. 1B showing the symbols of the bottom blowing nozzle positions.

FIG. 4 is a diagram showing a blow-through limit bottom-blowing flow rate in a converter in which a bottom-blowing nozzle is provided in a region defined by the present invention.

FIG. 5 is a diagram showing a relationship between a spitting amount and a slag amount at the end of blowing in a converter in which a bottom blowing nozzle is provided inside and outside a region defined by the present invention.

Claims (2)

[Claims] 1. A bottom blowing nozzle is arranged only inside a plane formed by connecting a point on the furnace bottom immediately below the point where the central axis of the oxygen jet from the perforated nozzle of the top blowing lance collides with the steel bath surface. Using a bottom blowing converter, Ar per bottom blowing nozzle,
For N ₂ and CO, blow gas at a flow rate of 0.4 Nm ³ / min · molten steel t or less, and for O ₂ and CO ₂ , blow gas while blowing gas at a flow rate of 0.2 Nm ³ / min · molten steel t or less A method of operating a top-bottom blown converter characterized by performing. 2. The slag generated in the furnace at the end of blowing is 50k.
The operating method according to claim 1, wherein g / molten steel t is set.