JP2848010B2 - Top blowing lance for refining molten metal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an upper lance used for blowing a refining gas to a molten metal in a converter for steelmaking, for example.

[0002]

2. Description of the Related Art Taking a steelmaking converter as an example, in an LD converter before an upper-bottom blower was developed and put into practical use, a refining gas (oxygen gas) was supplied and an iron bath was stirred. In order to strengthen and promote metallurgical reactions such as decarburization and dephosphorization, so-called hard blow, in which upper blowing refining gas collides with a bath surface with a strong jet, was intended. However, a deep cavity is formed in the bath surface by the hard blow, and accordingly, the spitting in which the granular iron is scattered increases. This spitting causes a reduction in the steelmaking yield, and also causes operational troubles such as sticking of the furnace mouth metal.

[0003] In recent years, in addition to top blowing, a top-bottom blowing converter that blows gas from the furnace bottom has also been put into practical use, and it has become possible to perform strong stirring by the stirring power of the gas blown from the bottom blowing tuyere. The need to do so has diminished. However, in a normal top-bottom blowing converter, the position of the bottom-blowing tuyere is limited to the central part of the furnace bottom due to maintenance such as tuyere replacement or restrictions on operation during tapping. Therefore, the number of tuyeres is also limited in order to avoid interference of gas blown from the tuyeres. In addition, when a large amount of refining gas is blown from one tuyere, there is a problem that blow-by occurs and the life of the tuyere is shortened. For this reason, bottom blown gas is generally 0.05 to 0.3 Nm ³ / min · t (1 ton
0.05 to 0.3 Nm ³ ) per minute, usually 2.5
Most refining gas (oxygen) of ~ 3.5 Nm ³ / min · t is supplied from the upper blowing lance.

On the other hand, the decarburization reaction in the last stage of decarburization is limited by the mass transfer of C (carbon) in molten iron near the flash point. Therefore, if the upper blow is made too soft blow by means such as increasing the lance height or increasing the nozzle diameter, there is a problem that the decarburization reaction rate is reduced. Furthermore, if the soft blow is performed too much, phenomena such as secondary combustion of CO gas occurring in the furnace and collision of the refining gas jet with the furnace wall due to the influence of cover slag may occur, resulting in a decrease in the refining gas reaction efficiency and Problems such as increased refractory wear occur. For this reason, it has been considered that the design of the lance which is somewhat hard-blow is appropriate even in the upper-bottom blower.

On the other hand, recently, for the purpose of melting low-phosphorus steel and reducing steelmaking costs by saving slag-making agents, dephosphorization of hot metal is becoming widespread. In this case, since the hot metal that has been dephosphorized in advance is charged into the converter, the refining function of the converter is mainly decarburization and temperature increase, and dephosphorization is subordinate. Therefore, the so-called less slag blowing, in which slag is reduced and blown, becomes possible, and there is almost no problem of slobbing in which the slag in the furnace overflows from the furnace opening, so the refining gas supply speed is increased to speed up the blowing. It is in the direction of aiming for.

[0006] However, in the case of blowing less slag, since the amount of cover slag is small, the occurrence of spitting is particularly increased, and as described above, the steelmaking yield and operation are hindered.
In other words, suppression of spitting is an important issue in reslag refining.

In order to avoid the problem caused by the excessive soft blowing described above, in order to reduce spitting loss while performing a certain amount of hard blowing, means for increasing the number of nozzles of the upper blowing lance (making the nozzles porous) is required. Optimal. In other words, if the nozzle is made porous, the total amount of stirring energy generated when the gas jet from each nozzle collides with the bath surface is constant, but the collision energy per nozzle hole can be reduced by dispersing the fire point. . The amount of spitting greatly depends on the depth of the cavity in the bath surface generated by the collision energy of the gas jet, and when the depth exceeds a certain depth, spitting starts to occur and increases as the depth increases. Therefore, when the lance nozzle is made porous, the cavity depth is controlled to be less than or equal to the spitting occurrence area or to an area where only a small amount occurs.

On the other hand, regarding the reaction efficiency when the lance nozzle is made porous, the stirring power per one nozzle hole decreases, but the supply amount of the refining gas also decreases correspondingly, so that there is basically no large change.

However, when the lance nozzles are made porous and the upper and lower blowers are blown, overlapping of cavities corresponding to the nozzles (overlap) becomes a problem. That is, when the overlapping area ratio of the cavities becomes larger than a certain value, a phenomenon in which the amount of spitching significantly increases is observed. One solution to such a problem is disclosed in
It is disclosed in JP-A-165313. In this publication, for the purpose of reducing spitting loss, the angle of inclination of the nozzle is determined so that the overlap ratio γ of the cavity is 0.2 or less, and a small nozzle having an opening area of 30% or less of the blowing nozzle is used. An upper-blowing lance has been proposed in which an aperture nozzle is disposed at the center of the lance tip.

When calculating from the definition of γ described in the above-mentioned publication, the inclination angles of the nozzles are the same.
In the case of a porous lance having more than holes, it is necessary to widen the angle of inclination of the nozzle by about 20 ° or more. If the nozzle is widened in this way, it is expected that the lance will be damaged due to the sticking of metal due to spitting at the center of the front of the lance, and as a countermeasure, less than 30% of the blowing nozzle at the center Although it is supposed to arrange a small-diameter nozzle having an opening area, the metal particles generated by spitting are about 1 to 20 mm,
With a jet from such a small-diameter nozzle, it is difficult to remove large metal particles, and it is unavoidable to adhere to the metal. On the other hand, if a nozzle similar to the blowing nozzle is arranged at the center and a strong jet similar to that of the blowing nozzle is flown to prevent sticking of metal, the overlap ratio of the cavity by the center nozzle becomes too large.

Further, as described above, the nozzle inclination angle is set to 20 °.
With the wide angle described above, the secondary combustion of the generated CO gas becomes large, spitting tends to fly to the side, and the refractory near the pool surface is eroded to shorten the furnace life. Occur.

[0012]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems in reslag slag refining, and an object of the present invention is to form a cavity without significantly increasing the inclination angle of a nozzle. An object of the present invention is to provide an upper blowing lance for refining molten metal which can reduce the overlap and reduce the spitting loss without adversely affecting the lance life and the furnace wall refractory.

[0013]

The gist of the present invention is that "two types of Laval nozzles each having three or more holes each having an even number of different inclination angles are alternately arranged in the circumferential direction, and are injected from each of these nozzles. Characterized in that the geometrically overlapping area ratio of the bath cavity formed by the gas jet is 30% or less. The above “total is even” is described later.
Nose excluding small hole nozzle (3 in FIG. 1) at the center of the lance
Means that the sum of the rules is even. Of course, tilt
Each of the two types of Laval nozzles with different oblique angles,
Three or more odd or even numbers may be used.

In order to reduce the spitting loss without adversely affecting the lance life and refractory, it is effective to use a lance having a nozzle having six or more holes and having different inclination angles of adjacent nozzles. It is. This method makes it possible to reduce the overlap of the cavities without increasing the inclination angle of the lance too much, to reduce the spitting loss without adversely affecting the furnace wall refractories, and to some extent near the center of the lance. The presence of the strong jet can prevent the granular iron caused by the spitting from adhering to the center portion of the lance front surface, thereby preventing the lance life from being shortened.

In the present invention, the definition of the geometrical overlapping area ratio of the cavity used for setting the inclination angle of the nozzle is as follows.

FIGS. 1A and 1B schematically show the tip of the upper blowing lance of the present invention, taking a six-hole lance as an example. FIG. 1A is a sectional view taken along the line BB of FIG. FIG. The upper blowing lance 1 has an inclination angle (an angle between the center axis of the nozzle and the center axis of the lance) of θ ₁ and θ, respectively.
₂ (deg.), Two types of nozzles 2 and 2 'are alternately arranged in the circumferential direction at the tip. That is, six nozzles, three and that of the nozzle inclination angle theta _1, those of theta ₂ 3
And they are arranged alternately.

Now, the distance between the center of the nozzle outlet of each of the nozzles 2 and 2 'and the center of the lance surface is rr ₁ , rr ₂ (cm).
, The nozzle throat diameters are dt ₁ and dt ₂ (cm), the nozzle outlet diameters are de ₁ and de ₂ (cm), and the number of nozzles is n (in the lance in FIG. 1, n
= 6).

1 is a small hole nozzle provided at the center of the lance, which is not essential in the lance of the present invention.

FIG. 2 is a view showing a use state of the upper blowing lance of the present invention, and is a longitudinal sectional view schematically showing a geometric positional relationship between a lance nozzle and a cavity corresponding thereto.

FIG. 3 is a diagram schematically showing the geometrical overlap of the cavities corresponding to the adjacent nozzles on the molten metal bath surface.

As shown in FIG. 2, the refining gas jet from the nozzles 2 and 2 'spreads at a divergence angle of about 20 ° in a turbulent flow region.
You. Here, in the case of a Laval nozzle, one
During a fixed distance, there is a transition region that attenuates from supersonic to sonic speed.
The spread angle of the jet gas in this region is
Although it is said to be smaller than the divergence angle,
Φ is defined as an average spread angle including the shift region. Then, when the lance height H (cm) indicating the distance from the lance tip to the molten metal bath surface, the cavity having a diameter D _i (cm) represented by the following equation (1) is obtained from the geometric relationship shown in FIG. Is formed. The distance R _i (cm) between the center of the cavity and the point C immediately below the center of the lance can be calculated by the following equation (2).

D _i ≒ 2H / cos θ _i × tan (φ / 2) + de, i (1) R _i = H tan θ _i + rr _i (2) where i is the nozzle number and In case, nozzle 2,
1 and 2 corresponding to 2 '.

Now, in the geometric relationship shown in FIG.
The angle formed by a straight line connecting the point C immediately below the center of the lance on the molten metal bath surface and the center of the cavity corresponding to each nozzle is δ (d
eg.) = 360 / n, distance L between centers of adjacent cavities
(cm) is represented by the following equation (3).

L = (R ₁ ² + R ₂ ² −2 R ₁ R ₂ cos δ) ^1/2 (3) The straight line connecting the centers of the adjacent cavities, the overlapping point of the cavity outer circumference circle, and the Assuming that angles formed by the straight line connecting the centers are β ₁ and β ₂ , respectively, the overlapping area ratio Sr of the geometric cavity is expressed by the following equation (4).

[0025]

(Equation 1)

Here, β ₁ and β ₂ are represented by the following (5) and (6)
Satisfies the formula.

D ₁ sin β ₁ = D ₂ sin β ₂ (5) L = D ₁ cos β ₁ + D ₂ cos β ₂ (6) As shown in the examples described later, the overlapping area ratio Sr of the cavity is If it exceeds 30%, the pitching loss increases significantly. Therefore, in the present invention, the inclination angles θ ₁ and θ ₂ of the adjacent nozzles are determined so that the Sr becomes 30% or less. Further, when the number n of nozzles of the upper blowing lance is 5 or less, even if the inclination angle of the nozzles is alternately changed, the effect of reducing the overlap of the cavities is small. That is, in order to ensure the effect, the number of nozzles is preferably set to 6 or more.

The nozzle throat diameter dt and the outlet diameter de are desirably equal for each nozzle in order to uniformly disperse the kinetic energy of the refining gas jet and make the cavity shape uniform. It is desirable that the angle of inclination of the nozzle is kept substantially constant between two types of θ ₁ and θ ₂ in order to maintain the point symmetry and keep the inside of the reaction vessel uniform. If θ ₁ > θ ₂ , θ ₂ is preferably around 10 ° in order to prevent a granular iron from adhering to the lance by allowing a strong jet to exist to a certain extent directly below the center of the lance and to avoid overlapping of the cavities at the center. . θ
_{Although 1} is determined in relation to θ _2, it is desirably about 15 to 20 ° in order to avoid an adverse effect on the furnace wall refractory due to widening of the angle and to reduce the overlap of the cavities.

In the lance of the present invention, in order to more reliably prevent the adhesion of granular iron to the central portion of the lance, it is necessary to form a cavity on the steel bath surface that interferes with the cavity corresponding to another nozzle. It is also possible to arrange a small-diameter nozzle (nozzle indicated by 3 in FIG. 1) at the center of the lance, which produces a weak jet.

[0030]

A water model experiment was carried out to clarify the effect of the geometric overlapping area ratio of the cavity formed on the bath surface by the jet from the perforated nozzle lance on spitting.

As a water model, an actual converter having a furnace belly diameter of about 66 cm with a size reduced to 1/9 was used. Water volume is about 390 l
(Liter), and air is blown from the upper lance about 1020 l / min
The lance height was about 35 cm. About 51 l / min of air was blown from the four tuyeres as bottom blowing gas.
The upper blowing lances are all 6-hole nozzles with the same diameter, the lances each having 6 fixed angles of 10 °, 12 °, 15 °, and 20 °, and the angle of adjacent nozzles.
A lance according to the invention, alternating between 10 ° and 20 °, 10 ° and 18 °, and 10 ° and 15 °. Using these, the change in the amount of spitting was investigated.

FIG. 4 shows the relationship between the geometrical overlapping area ratio of the cavities and the spiking occurrence index. The spitting index is an amount of spitching when the lance pitching amount of a lance having six nozzles having an inclination angle of 10 ° is set to 100.

As shown in FIG. 4, the amount of spitching greatly depends on the geometrical overlapping area ratio Sr of the cavity. That is, when Sr exceeds 30%, the amount of spitching sharply increases. From this, it can be said that it is effective to reduce Sr to 30% or less in order to reduce the spitting loss.

Further, in the lance of the present invention in which the angles of adjacent nozzles are alternately changed (indicated by △ in FIG. 4), all the nozzles are
Lance widened to 15 ° or 20 ° (Fig. 4
A, D) can be adjusted to almost the same level as Sr.
The amount of spitching can be made substantially the same.
Therefore, it is possible to reduce the spitting loss without increasing the nozzle inclination angle too much, and it is possible to avoid the deposition of metal on the nozzles that occurs when the nozzle inclination angle is increased.

The lance of the present invention is optimally used in a steelmaking process using an upper-bottom blower, but is not limited to this, and is not limited to this, and may be used in a steelmaking process using only an upper-blower lance, and other AOD furnaces and converters for copper refining. The present invention is applicable to any metal refining process in which a refining gas is supplied from an upper blowing lance.
In addition, when using the lance of the present invention, it is formed on the bath surface.
The outer circumference of the entire cavity is not strictly circular,
Therefore, the distance between the outer periphery and the inner periphery of the furnace wall is not constant. I
However, this is no obstacle to the actual refining reaction.
No.

Hereinafter, the effects of the present invention will be described with reference to examples in a converter for steelmaking.

[0037]

EXAMPLE In an upper-bottom blowing converter with a molten steel amount of about 260 t / ch, low carbon steel was melted using the upper blowing lance of the present invention, and the spitting loss, lance life, and furnace wall refractory wear were determined. A comprehensive survey was conducted.

Blowing is all slag blowing using dephosphorized hot metal, the top blowing oxygen amount is 55,000 Nm ³ / hr, and the bottom blowing gas is
CO ₂ was fixed at 2000 Nm ³ / hr. The nozzle throat diameter of each lance was determined so that the pressure before the lance was constant at an oxygen gas amount of 55,000 Nm ³ / hr. The nozzle inclination angle is constant for each nozzle in the comparative example, and the angles of the adjacent nozzles are alternately different in the example. The lance height was constant at about 3.2m. A lance in which a small-diameter nozzle corresponding to 30% of the opening area of the multi-hole nozzle was disposed in the center of the lance, and a lance which was provided around a nozzle having the same diameter as the nozzle disposed in the circumferential direction were also tested.

Table 1 shows the spitting loss, the lance life, and the state of wear of the refractory of the furnace wall during operation using the lance nozzles of the example and the comparative example. In Table 1, the geometrical overlapping area ratio of the cavities is calculated by the above equation (4). The spitting loss is expressed in terms of% by weight based on Comparative Example 1, and the wear of the furnace wall refractories is a relative comparison based on Comparative Example 1. The lance life is the number of charges before the metal arrives at the nozzle and becomes unusable. Since a number of lances were used, their life expectancy was indicated.

First, the following tendency is apparent from a comparative example in which the nozzle inclination angle in Table 1 is fixed.

At the same nozzle inclination angle, the geometric overlap area ratio Sr of the six-hole lance (Comparative Example 2) is larger than that of the four-hole lance (Comparative Example 1). as a result,
Lance life and furnace wall refractory wear remain unchanged, but spitting loss increases.

Comparing Comparative Example 2, Comparative Example 3, and Comparative Example 6 with the same number of nozzles and different nozzle inclination angles, the larger the nozzle inclination angle, the shorter the lance life and the greater the wear of the refractory.

Even if a small-diameter nozzle is disposed at the center of the lance as in Comparative Example 4, the effect of improving the lance life is very small. Furthermore, in the seven-hole lance (Comparative Example 5) provided with a nozzle having the same diameter as the center, the geometrical overlapping area ratio of the cavity becomes 30% or more, and the spitting loss increases.

On the other hand, in the case of using the lances of the present invention in which the inclination angles of the adjacent nozzles are alternately changed (Examples 1 and 2), the adverse effect on the lance life and refractory wear is small, and Spitching loss is reduced.
In the case where a small hole is provided in the center (Example 3), substantially the same effect can be obtained.

[0045]

[Table 1]

[0046]

EFFECT OF THE INVENTION In a refining process in which a refining gas is blown onto a molten metal bath surface, the use of the lance of the present invention greatly reduces spitting loss without adversely affecting lance life and refractory wear. Can be.
Therefore, it is possible to improve the yield in refining and reduce operational troubles such as adhesion of furnace mouth metal, thereby reducing the total cost of refining.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing a tip portion of an upper blowing lance of the present invention, wherein (a) is a longitudinal sectional view, and (b) is a plan view taken along the line AA of (a).

FIG. 2 is a longitudinal sectional view schematically showing a geometrical positional relationship between a lance nozzle and a cavity corresponding to the lance nozzle in a use state of the upper blowing lance of the present invention.

FIG. 3 is a plan view schematically showing the geometrical overlap of the cavities on the molten metal bath surface corresponding to FIG. 2;

FIG. 4 is a diagram showing a relationship between a geometrical overlapping area ratio of a cavity and a spitting occurrence index.

──────────────────────────────────────────────────続 き Continued on the front page (72) Keiichi Maya Inventor 4-33, Kitahama, Chuo-ku, Osaka-shi, Osaka Sumitomo Metal Industries, Ltd. (56) References JP-A-2-11716 (JP, A) JP-B-62-46611 (JP, B2) JP-B-53-36344 (JP, Y2) (58) Fields investigated (Int. Cl. ⁶ , DB name) C21C 5/46 101 C21C 5/32 C21C 7 / 072 C22B 9/05 F27D 3/16

Claims (1)

(57) [Claims] 1. A bath cavity formed by gas jets jetted from each of two types of Laval nozzles having three or more holes each having an even number of different Laval nozzles having different inclination angles. An upper blowing lance for refining molten metal, characterized in that the geometrical overlapping area ratio of the metal is 30% or less.