JP2000303114A - Method for refining molten metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a refining method for preventing spitting developed with a top-blown lance blowing to molten metal. SOLUTION: In the refining method, in which gas for refining is blown onto the molten metal surface from the lance for refining the molten metal, which is arranged with nozzles 2, 3 in the same direction on two concentric circles with a lance axis as the center, when using D1 and D2 as diameters of recessions 6a, 6b respectively formed with two gas jets 4a, 4b jetted in the same direction on the molten metal surface 5, and D12 for distance between the centers of two recessions, gas pressure for refining before the lance, nozzle diameter, nozzle inclining angle and lance height are set so as to satisfy the formula 0.75<2D12/(D1+D2)<1.60.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for refining molten metal by blowing a refining gas from a lance to the molten metal.

[0002]

2. Description of the Related Art A converter steelmaking process will be described below as an example. In order to improve productivity in the steelmaking process, it is important to increase the acid supply rate and shorten the blowing time. However, when the acid supply speed is increased, slopping (a phenomenon in which formed slag overflows from a furnace port) and spitting (a phenomenon in which molten steel is scattered by an upper jet) occur, thereby causing a problem of a reduction in yield.

In recent years, since the amount of slag has been reduced due to the spread of hot metal pretreatment equipment, slopping is relatively unlikely to occur, and spitting is the main problem during high-speed blowing.

In order to reduce this spitting,
It is effective to make the lance porous for the purpose of dispersing the collision energy of the jet with the bath surface, and a porous lance is generally used in the current steelmaking converter.

In general, a porous lance is one in which three or more nozzles having a constant inclination angle are arranged on the same circumference, and the greater the number of holes, the greater the effect of dispersing the jet collision energy. In the current top-bottom blow composite converter, a 4-hole or 6-hole lance is generally used.

In the case of such a porous lance, when the jets jetted from each nozzle overlap with the dents formed on the bath surface,
It has been pointed out that spitting increases, and several methods have been disclosed as means for solving this.

For example, Japanese Unexamined Patent Publication (Kokai) No. 60-165313 discloses an overlap ratio γ, which is the ratio of the diameter D of this dent to the distance d between two dents on a straight line connecting the centers of adjacent dents. A method has been proposed in which the nozzle inclination angle θ is made large using (= d / D) as an index to reduce the overlap of the dents.

[0008] However, when θ is increased, the secondary combustion rate of CO gas and oxygen generated in the furnace increases, so that decarbonation efficiency (reaction efficiency between top-blown oxygen and carbon in molten steel) is increased.
Decreased, the blowing time was prolonged, and T.C. A problem such as an increase in Fe (total Fe) occurs. That is, reducing the overlap of dents by increasing θ is
Although effective in reducing spitting, it cannot be said to be an effective means for improving the productivity of the steelmaking process, which is the original purpose.

On the other hand, in Japanese Patent Application Laid-Open No. 6-57320,
As a method for reducing the overlap of the depressions, a method is disclosed in which the inclination angles of the adjacent nozzles with respect to the lance axis are alternately changed.

In the present invention, since the inclination angle does not need to be increased for all nozzles, the above-mentioned problem caused by increasing θ is reduced. However,
According to the experimental results of the present inventors, JP-A-6-57320
It has been found that even if the lance described in Japanese Patent Application Laid-Open No. H10-209400 is used, if the acid feed rate (flow rate) from the lance is ³ Nm ³ / min or more per ton of molten steel, it is not sufficient to suppress spitting.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to provide a spinning machine which tends to occur when the acid supply rate is ³ Nm ³ / min or more per ton of molten steel in a high-speed blowing condition of molten metal, for example, in a converter steelmaking process. It is an object of the present invention to provide a refining method capable of effectively suppressing the refining.

[0012]

The present inventors have studied various methods in a water model experiment in order to reduce spitting, and have obtained the following findings.

(A) When refining gas is blown upward from two nozzles inclined in the same direction, spitting may be suppressed even if the dents formed by the two jets overlap.

(B) FIG. 1 is a schematic view showing a state in which a jet of a refining gas is blown onto the surface of a molten metal.
(a) shows the case where there is only one dent, and (b) shows the case where there are two dents.

As shown in FIG. 3A, when the overlap between the two dents is too large, the two jets are in a united state, and as in the case where the dent alone exists, a large amount of liquid drops from the outer edge of the dent. (C) If the two dents are too far apart, the two jets will be completely separated as shown in Fig. 2 (b), the bath surface between them will be torn by the shear force of both jets, Many occur.

(D) That is, there is an optimum range of the inter-dent distance where the spitting is minimized.

Based on the above findings, the gist of the present invention is as follows. A refining method in which a refining gas is blown onto a surface of a molten metal from a lance for refining molten metal in which nozzles are arranged in the same direction on two concentric circles around a lance axis, and two gas jets ejected in the same direction The diameters of the depressions formed on the surface of the molten metal by D ₁ and D
_2, and when the distance between the centers of the two indentations and D _12, refining method of molten metal which they are characterized by satisfying the following formula (1). 0.75 <2D ₁₂ / (D ₁ + D ₂ ) <1.60 (1)

[0018]

FIG. 2 is a schematic longitudinal sectional view schematically showing a state of a refining gas jet in one direction of a lance according to the present invention. The figure shows the geometrical positional relationship between the depressions 6 a and 6 b formed by the two nozzles 2 and 3 on the molten metal bath surface 5.

As shown in FIG. 2, the jet 4a ejected from the inclination angle theta ₁ is smaller nozzle 2 and the inclination angle theta ₂ is larger nozzle 3 in the orientation relative lance axis at supersonic speed, 4b Form a supersonic core of length X ₁ , X ₂ . After that, it develops into a completely turbulent flow through the transition region and spreads at a spreading angle of 2φ (about 20 °).

Here, the length X _i of the supersonic core is expressed by the following (2)
Is calculated from the empirical formula. X _i = 2.47 · P ₀ · d _i (2) where P ₀ is the gas pressure for refining before the lance (kgf / c
m ^2), d _i is the nozzle outlet diameter (mm). Also, i is the number of the nozzle, in this case, 1 and 2 corresponding to nozzles 2 and 3.

[0021] When the lance tip lance height H ₀ indicating the distance to the molten metal bath surface 5 of (mm), from a geometrical relation shown in FIG. 2, recess diameter D _i shown in the following equation (3) 6a , 6b are formed. Distance R _i between the center and the lance center immediately below the recess can be calculated by the following equation (4).

D _i = (H ₀ −X _c · cos θ _i ) · (tan (θ _i + φ) −tan
(Θ _i −φ)) + d _i (3) R _i = H ₀ · tan θ _i + r _i (4) The distance D ₁₂ between the centers of the two dents corresponding to the nozzles 2 and 3 is
It is expressed by equation (5).

D ₁₂ = R ₂ −R ₁ (5) As shown in the examples described below, when 2D ₁₂ / (D ₁ + D ₂ ) is 0.75 or less, or 1.60 or more, the spitting loss is reduced. Increase significantly. Therefore, in the method of the present invention, this 2D ₁₂ / (D ₁ + D ₂ ) exceeds 0.75 and 1.6.
The inclination angles θ ₁ and θ ₂ of the nozzles 2 and 3 are set to be less than 0.
Is determined.

The present inventors investigated the effect of the distance between two recesses in the same direction on the droplet scattering behavior by a water model experiment.

FIG. 3 is a schematic diagram of a 1/10 scale water model experiment.

FIG. 4 is a schematic view schematically showing the lance used in the water model experiment. FIG. 4 (a) is a longitudinal sectional view, and FIG.
Is a plan view. As shown in FIG. 4 (a), the inclination angles θ ₁ and θ of each nozzle are changed so that the distance between two recesses having the same orientation changes.
Various combinations of ₂ (> θ ₁ ) were changed.

The distance between the lance and the water surface was set to 270 mm, and compressed air was blown upward from the lance 1 at a flow rate of 200 Nl / min for a certain period of time. In the meantime, the water-absorbing paper 8 was attached 700 mm above the water surface 5, and the scattering speed of the droplet 7 was calculated from the weight change before and after that.

FIG. 5 shows the results obtained by arranging the droplet scattering speeds at 2D ₁₂ / (D ₁ + D ₂ ) for various values of the nozzle inclination angles θ ₁ and θ ₂ for two recesses having the same orientation. As is clear from the figure, the droplet scattering speed is 2D ₁₂ / (D ₁
+ D ₂ ), and 2D ₁₂ / (D ₁ +
D ₂ ) is almost constant in the range of more than 0.75 and less than 1.60, but tends to increase sharply in the range of 0.75 or less and 1.60 or more.

Next, in order to clarify the reason for the above results, the state of the experiment was photographed with a high-speed video camera, and the manner in which droplets scattered was observed. As a result, the following was confirmed.

(A) When 2D ₁₂ / (D ₁ + D ₂ ) is 0.75 or less, the state becomes as shown in FIG. 1A, and the two jets having the same orientation are almost united, and the dent is formed. Droplets violently scatter from the outer edge of the outer dent, as if it were alone.

(B) When 2D ₁₂ / (D ₁ + D ₂ ) is 1.60 or more, the two jets having the same orientation are completely separated from each other as shown in FIG. Drops are generated.

From the above, it is apparent that when two gas jets are blown upward in the same direction, there is an optimum distance between the depressions that can suppress the generation of droplets, which is expressed by the following equation (1). It became.

0.75 <2D ₁₂ / (D ₁ + D ₂ ) <1.60 (1) When the method of the present invention is applied to oxygen top blowing in a top-bottom blowing converter, the nozzle inclination angle of the top blowing lance theta _1, theta _2, and lance - between the melt surface distance H ₀ is for spitting suppression, while satisfying the expression (1) is determined in consideration of the following.

FIG. 4 shows the nozzle arrangement of the lance according to the present invention.
As shown in (b), two nozzles are arranged in the same direction on the concentric circle. Therefore, although the number of nozzle holes is even,
It is preferably 6 or 8. With two or four holes, the symmetry around the lance axis is poor, and with ten or more holes, the cooling structure at the tip of the lance becomes complicated and the cost increases.

Further, as described in JP-A-6-57320, if the nozzle inclination angle is too large, the CO gas generated by the decarburization reaction excessively burns secondary,
Problems such as reduction in decarbonation efficiency and wear of refractories are caused.

Even when θ ₂ is large, a dent can be formed near the center of the bath surface by reducing the lance height H ₀ , but melting and thermal deformation of the lance due to spitting are likely to occur. And the lance life is shortened.

On the other hand, if the lance height H ₀ is too large, the spread of the jet becomes large, and as in the case where the nozzle inclination angle is too large, the decarbonation efficiency decreases due to the secondary combustion of CO gas and the refractory This causes wear problems.

When the present invention is applied to a top blowing lance, the appropriate ranges of the two types of nozzle inclination angles θ ₁ and θ ₂ and the lance height H ₀ are, for example, 270 tons / charge in a converter having an inner diameter of 6 m, Acid supply rate is ³ ~ 3.7Nm ³ / min per ton of molten steel
6 ° ≦ θ ₁ ≦ 15 °, 10 ° ≦ θ ₂ ≦ 25 °, 2200 mm ≦ H ₀ ≦ 3300 mm.

The refining method of the present invention is not limited to the top-bottom blow converter, but also includes a steelmaking process such as a top blow converter, an electric furnace, and an AOD furnace, and a refining gas from a top blow lance such as a copper refining furnace. Is applicable to any metal refining process.

[0040]

EXAMPLES (Example 1) In a top and bottom blown converter with a molten steel amount of 270 ton / charge, low carbon steel was melted by oxygen top blowing to which the method of the present invention was applied, and the amount of spitting loss was investigated.

The blowing was all slag blowing using dephosphorized iron (30-35 kg per slag of molten steel ton), the top blown oxygen flow rate was 3.4 Nm ³ / hr, and the bottom blown gas was CO ₂ 0.
The lance height was constant at 12 Nm ³ / min and about 2.7 m.
The end point [C] was fixed at about 0.05%.

The lances were all six-hole lances having a throat diameter of 44 mmφ and an outlet diameter of 60 mmφ. The nozzles were inclined at the same angle (Comparative Examples 1 and 2) and two nozzles having different inclination angles were arranged in the same direction. (Comparative Examples 3, 4 and Example) were used. The nozzles were uniformly arranged in the circumferential direction by shifting the nozzle directions by 60 ° in the former case and 120 ° in the latter case. The distance from the center of the lance to the center of the nozzle outlet was 100 mm for all nozzles in the former case, 65 mm for the inner nozzle, and 140 mm for the outer nozzle in the latter.

Further, in order to prevent the adhesion of granular iron to the center of the lance, a nozzle of 20 mmφ was arranged at the center of each lance.

Table 1 shows the increase of the tapping yield during the operation of the inventive examples and the comparative examples. These values are approximately 20 for each lance.
This is the average value when charging is used. The table shows (2) ~
2D ₁₂ / (D ₁ + D ₂ ) calculated using equation (5) is also shown. In addition, the tapping yield (%) was shown as an increase or decrease with respect to Comparative Example 1 as a reference value.

First, Comparative Examples 1 and 2 and Invention Example 1 will be described in comparison. Comparative Example 1 is a case where the nozzle inclination angle is set to 8 °, which is the same as that of the nozzle of the present invention example 1 having a smaller inclination angle. Since the spitting loss is larger than in Example 1, the tapping yield is lower.

On the other hand, Comparative Example 2 is a case where the nozzle inclination angle is set to 20 ° which is the same as that of the outer nozzle of Example 1 of the present invention. Since the spitting in the vertical direction is reduced as compared with Comparative Example 1, the tapping yield is slightly increased, but not as high as that of Example 1 of the present invention.

Next, two nozzles having different inclination angles are arranged in the same direction (Comparative Examples 3 and 4, and Examples 1 to 5 of the present invention).
Compare 3).

As can be seen from Table 1, 2D ₁₂ / (D ₁ +
In Examples 1 to 3 of the present invention in which D ₂ satisfies the expression (1), the tapping yield is greatly improved to 0.8 to 0.9% with respect to the reference value of Comparative Example 1. On the other hand, Comparative Example 3, which is out of the range of Expression (1),
4 is not much different from the reference value.

This phenomenon is explained as follows. 2D ₁₂ /
When (D ₁ + D ₂ ) is 0.75 or less, the two jets having the same orientation are in a united state, and spitting is violently generated from the outer edge of the outer dent as in the case where the dent is present alone. 2D ₁₂ / (D ₁ + D ₂ ) is 1.
If it is more than 60, the two jets will be completely separated, and the bath surface between them will be broken by the shearing force of the jets on both sides, and a lot of spitting will occur. In other words, 2D ₁₂ / (D ₁ +
D ₂ ) must satisfy the expression (1).

From the above results, it was found that the top blowing method of the present invention is the most suitable method for reducing the spitting loss.

[0051]

[Table 1]

[0052]

According to the refining process in which a refining gas is blown onto the surface of a molten metal bath, spitting can be greatly reduced by the top blowing method of the present invention.

As a result, it is possible to improve the smelting yield and to avoid operational troubles such as the adhesion of metal at the furnace mouth, thereby improving the productivity.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a state in which a jet of a refining gas is sprayed on a surface of a molten metal. FIG. 1 (a) shows a case where a single dent is provided, and FIG. 1 (b) shows a case where two dents are provided.

FIG. 2 is a schematic longitudinal sectional view schematically showing a state of a refining gas jet in one direction of a lance according to the present invention.

FIG. 3 is a schematic diagram of a 1/10 scale water model experiment.

FIG. 4 is a schematic diagram schematically showing a lance used in a water model experiment, wherein FIG. 4 (a) is a longitudinal sectional view and FIG. 4 (b) is a plan view.

FIG. 5: 2D ₁₂ / (D ₁ +) obtained by a water model experiment
9 is a graph showing the relationship between D ₂ ) and the droplet generation speed.

[Explanation of symbols]

 1: Lance 2: Nozzle 3: Nozzle 4a, 4b: Jet 5: Molten metal bath surface or water surface 6a, 6b: Depression 7: Droplet 8: Water absorbing paper

Claims (1)

[Claims] 1. A refining method in which a refining gas is blown onto a surface of a molten metal from a lance for refining the molten metal in which nozzles are arranged in the same direction on two concentric circles centered on a lance axis. When the diameters of the depressions formed on the surface of the molten metal by the two gas jets are D ₁ and D _2, and the distance between the centers of the two depressions is D ₁₂ , these are as follows:
A method for refining molten metal, characterized by satisfying the formula. 0.75 <2D ₁₂ / (D ₁ + D ₂ ) <1.60 (1)