JP2003138312A - Method for refining molten metal and top-blowing lance for refining molten metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce splashing of molten metal and occurrence of dust at high oxygen feed rate in the high carbon range at the blowing in a converter and further, to restrain oxidization of the molten metal at low oxygen feed rate in the final stage of the blowing in the converter. SOLUTION: In the method for refining molten metal by using a top-blowing lance 1 provided with a sectorial nozzle 4 at its tip part and blowing the oxygen toward the molten metal, the refining is performed by using the top-blowing lance provided with the sectorial nozzle having a straight barrel part 5 whose length (Ls) is determined to be L<=Ls with regard to the length (L) of the sectorial part 6. Thereby, the occurrence of the dust can be reduced at the high oxygen feed rate. Further, the oxidizing of the molten metal can be restrained at the low oxygen feed rate by regulating the ratio (De/Ds) of an outlet diameter De to the inner diameter Ds in the straight barrel part within the range determined by inequality: De/Ds<=1.20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a refining method for oxidizing and refining a molten metal such as hot metal using oxygen, and a refining top blowing lance used therefor.

[0002]

2. Description of the Related Art In the case of refining in which impurities in molten metal are oxidized and removed, refining is generally performed by blowing oxygen from an upper blowing lance. For example, in the blowing of molten iron in a converter, oxidative refining is mainly carried out by means of top blowing oxygen for the purpose of decarburization.

In this converter smelting, not only the demand for refining a large amount of hot metal in a shorter time to obtain high productivity has increased more than ever, but also a large amount of iron ore and A larger amount of oxygen source is required for direct reduction in the furnace to which Mn ore or the like is added and for melting a large amount of iron scrap in the furnace, and a large amount of oxygen can be stably blown in a short time and highly accurate. Technology that enables component control is needed. Also, due to the development of hot metal pretreatment process for the purpose of dephosphorization and desulfurization of hot metal, the amount of slag generated in converter blowing is greatly reduced, and many elements different from the conventional process are generated. There is an urgent need to immediately optimize the converter blowing method to deal with the situation.

In the oxidation refining by the upper blowing lance, oxygen is supplied into the converter as a supersonic or subsonic jet from a nozzle called a Laval nozzle installed at the tip of the upper blowing lance. A Laval nozzle is composed of a part where the cross section shrinks and a part where the cross section expands.The boundary between these is called the throat, and the gas that passes through the part where the cross section is reduced becomes the sonic velocity at the throat and the supersonic velocity at the enlarged part. It has been accelerated to a supersonic jet.

In the blowing of a converter, in order to prevent the reaction efficiency such as decarburization reaction from being lowered, the amount of oxygen supplied (hereinafter referred to as "acid feeding rate") is usually relatively large, and the blowing is carried out from the early stage to the middle stage. The shape of the Laval nozzle is designed based on refining conditions in the high carbon region (about C> 0.6 mass%) up to. In other words, when the oxygen transfer rate is high, the blown oxygen is appropriately expanded by the Laval nozzle so as to be supersonic, and conversely, in the low carbon region (about C ≦ 0. When the oxygen transfer rate corresponding to 6 mass%) is small, oxygen excessively expands in the Laval nozzle, and supersonic speed is inhibited.

When a Laval nozzle based on such a design concept is used for converter blowing in which the oxygen transfer rate is further increased for the purpose of high productivity, the jet velocity of the oxygen jet supplied from the upper blowing lance is used. Is further increased, the jet flow velocity reaching the surface of the molten metal in the converter is increased, and the disorder of the molten metal surface becomes more severe. In the conventional blowing with a large amount of slag (about 50 kg or more per ton of molten steel), this design concept was essential in order to ensure the penetration of the oxygen jet into the slag layer.

However, in blown smelting with a small amount of slag in recent years, the need for such a design concept is becoming low, and conversely, the turbulence of the molten metal surface with the increase in the jet flow velocity is In a small amount of smelting, it causes severe molten metal scattering such as spitting and splashing, increases the metal deposit on the furnace mouth, hood, top blowing lance, and even parts such as exhaust gas equipment, adversely affecting the operation and iron yield. Productivity is deteriorated due to the decrease in In addition, the generation of iron dust due to the scattering is remarkably increased, and the iron yield is reduced from the viewpoint of dust generation.

In order to suppress such deterioration of the operating condition, the distance between the tip of the upper blowing lance and the bath surface (hereinafter referred to as "lance height" is optimized while optimizing the hard surface of the upper blowing lance shape such as the hole diameter and inclination of the Laval nozzle. ]) And a number of measures to control the operating conditions such as the oxygen transfer rate have been proposed. For example, Japanese Unexamined Patent Publication No. 6-228624 discloses a blowing method in which the shape of the upper blowing lance is optimized and the rate of feeding acid and the height of the lance are controlled within an appropriate range according to the shape of the Laval nozzle. . However, when changing the structure of the Laval nozzle and the lance height in order to suppress iron scattering and dust when the flow rate is increased as in the same publication, the trajectory of the oxygen jet ejected from the upper blowing lance is changed. In addition, since the geometrical shape greatly changes, unnecessary secondary combustion occurs, and a secondary adverse effect occurs that reaction efficiency deteriorates due to a change in the reaction interface area. Further, when it is difficult to change the lance height physically or operationally, this method cannot deal with it.

On the other hand, in the low carbon region at the end of blowing, the oxygen supplied is consumed not only for the decarburization reaction but also for the oxidation of iron, so that the oxidation of iron is suppressed and the efficiency of decarboxylation is increased. The acid transfer rate is reduced. In this case, since the acid transfer rate largely deviates from the proper flow rate value of the Laval nozzle, the maximum effect of the Laval nozzle cannot be obtained, and the oxygen jet is unnecessarily damped, and the T.O. As seen in the increase in Fe, the decarburization reaction efficiency is reduced. In addition, the unsteady turbulence of the oxygen jet also becomes large, the refining reaction cannot be stabilized and stabilized, and the variation of the components at the end of the blowing becomes large. Incidentally, T. Fe is the total value of iron content of all iron oxides (FeO and Fe ₂ O ₃ ) in the slag.

In order to suppress these phenomena, in order to improve and stabilize the reaction efficiency in the final stage of blowing, the lance height is further reduced, and the dynamic pressure of the oxygen jet on the molten metal surface is increased. However, in this case, since the oxygen transfer rate at the end of blowing is also greatly reduced, it is necessary to maintain the lance height at a considerably low level, and it is necessary to maintain the lance height on the top blowing lance. Negative effects such as iron adhesion cannot be ignored, leading to lower yield and worse operability. Further, the reduction of the height of the lance reduces the area of collision of the oxygen jet with the bath surface, so that the reaction interface area is reduced, and Fe
It is difficult to obtain a large effect on the reduction of

To solve this problem, Japanese Patent Laid-Open No. 10-
In JP 30110, an upper blowing lance having an outlet diameter of 0.85D to 0.94D is used in a high carbon region with respect to an appropriate expansion outlet diameter D of the Laval nozzle which is determined by the throat diameter of the Laval nozzle and the acid feeding rate. , In the low carbon region 0.9
A converter blowing method using an upper blowing lance having an outlet diameter of 6D to 1.15D is disclosed. Even if the same Laval nozzle is used, the outlet diameter can be changed within the above range with respect to the proper expansion outlet diameter D by changing the acid feeding rate and the nozzle pressure P of the Laval nozzle.

However, in this blowing method, two or more types of top blowing lances having different shapes must be used in order to surely control refining, and the complexity of equipment and operation cannot be ignored. . Also, when the same top blowing lance is used, it is necessary to keep it within the optimum range in both the high carbon region and the low carbon region, which complicates the design of the Laval nozzle, and especially from the early stage to the middle stage of blowing. In the high carbon region of, in order to secure a high acid transfer rate for the purpose of shortening the blowing time and high productivity, and to keep the oxygen transfer rate low at the end of blowing, deviate from the above range. I will end up. That is, the adjustment range of the acid transfer rate is limited, and there arises a problem that the acid transfer rate cannot be freely changed according to the situation in the furnace.

[0013]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances. An object of the present invention is to provide a wide adjustment range of the oxygen transfer rate, and to freely change the oxygen transfer rate according to the in-furnace conditions. It is possible to reduce the scattering of molten metal and dust generation at the time of high acid feeding rate such as in high carbon region in converter blowing, and to reduce the low acid feeding such as in the final stage of converter blowing. It is an object of the present invention to provide a molten metal refining method capable of suppressing the oxidation of a molten metal at a high speed and improving the stabilization of a reaction, and a refining upper blowing lance used for the refining method.

[0014]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies and research in order to solve the above problems. As a result, in the shape design of the end-spreading nozzle for blowing oxygen, by providing a straight body portion having a length equal to or greater than the length of the enlarged cross-section on the upstream side of the enlarged cross-section, it is possible to reduce It is possible to reduce the scattering of molten metal and dust, and further to set the ratio (De / Ds) of the outlet diameter of the enlarged cross section, that is, the outlet diameter De of the nozzle and the inner diameter Ds of the straight body portion to 1.20 or less. As a result, it was found that stable operation is possible at low acid transfer rates such as the final stage of blowing. Hereinafter, the study results will be described by taking converter blowing as an example. The blowing nozzle according to the present invention is an improved nozzle of the Laval nozzle, but will be referred to as a “divergent nozzle” to distinguish it from the Laval nozzle.

The behavior in the converter during oxygen blowing is roughly classified into a high carbon region (C> 0.6 mass%) and a low carbon region (C ≦ 0.6 mass%) due to the difference in reaction behavior. In high carbon regions,
Almost all of the oxygen supplied is consumed for decarburization, the reaction is the rate-determining supply of oxygen, and blowing is performed at a high acid transfer rate. On the other hand, in the low carbon region, the rate-controlling of oxygen is changed to the rate-determining transfer of carbon, and part of the oxygen is also spent on the oxidation of iron.
In order to suppress iron oxidation and increase decarboxylation efficiency, the rate of acid transfer is reduced.

At this time, in blowing in a high carbon region, in order to reduce iron scattering and dust generation, it is necessary to keep the dynamic pressure of the oxygen jet on the molten metal surface low while maintaining a high acid transfer rate. is there. However, in order to avoid unnecessary secondary combustion and maintain the decarboxylation efficiency at a high level, it is necessary to keep the geometrical shape and trajectory of the oxygen jet under the same conditions as much as possible. On the other hand, in the low carbon region, the rate of oxygen transfer is reduced in order to increase the efficiency of decarboxylation, but the dynamic pressure of the oxygen jet is also greatly reduced with this, and as a result, the efficiency of decarboxylation is reduced, that is, iron. Results in increased oxidation of. Further, the degree of deterioration becomes greater as the acid transfer rate is lowered. for that reason,
We want to keep the dynamic pressure of the oxygen jet on the bath surface as high as possible, but lowering the lance height to increase the dynamic pressure of the oxygen jet means that the radiation from the bath surface causes wear of the tip of the top blowing lance and There is a limit to significantly increase the metal deposit on the top-blown lance due to the iron scattering from the surface. In this way, there are conflicting requirements between high carbon and low carbon,
Moreover, it is necessary to avoid changes in operating conditions such as lance height as much as possible.

Therefore, the inventors investigated the blowing behavior of the converter with respect to blowing nozzles of various shapes having different design guidelines. As a result, in the structure of the end-spreading type blowing nozzle, by providing a straight body part longer than the length of the end-spreading part on the upstream side of the enlarged cross-section part (hereinafter referred to as the “spread-out part”), it is possible to achieve high feed rate at the peak of decarburization By reducing the molten metal scattering and dust at the time of acid velocity, and further by setting the ratio (De / Ds) of the outlet diameter De of the diverging nozzle to the inner diameter Ds of the straight body portion to 1.20 or less, it is possible to reduce In the oxygen region, while suppressing the oxidation of iron, it has achieved extremely stable operation compared to conventional operations.

The structure of a normal Laval nozzle has a divergent portion (also referred to as a "skirt portion") at the tip of a reduced cross-section portion (hereinafter referred to as "throttle portion"), and the boundary portion between these portions forms a throat. There is. Ideally, it is desirable that the entire surface has a smooth curved surface shape, but it may have a conical shape due to processing. The gas that has passed through the throttle portion becomes sonic velocity at the throat portion, and is accelerated to supersonic velocity at the end widening portion to obtain a supersonic jet.

Normally, the design of the Laval nozzle in the converter blowing is designed by the acid feeding rate Fh (Nm ³ / hr) and the throat diameter per hole of the Laval nozzle obtained from the acid feeding rate F (Nm ³ / hr) in the high carbon region. The nozzle absolute pressure Po (kPa) is determined from the Dt (mm) and the following equation (3), and this nozzle absolute pressure Po
(KPa) and atmosphere pressure Pe (kPa) and throat diameter Dt (m
m) and the outlet diameter De (m
m). Here, the oxygen transfer rate Fh per Laval nozzle can be obtained by multiplying the oxygen transfer rate F by the ratio of the sectional area of each Laval nozzle throat diameter Dt to the total sectional area of the throat diameter Dt of the Laval nozzle. Normally, when a plurality of Laval nozzles are installed, the throat diameters Dt of the Laval nozzles are substantially the same, so the acid transfer rate F
Can be calculated by dividing by the number of installed Laval nozzles. The atmosphere pressure Pe is the atmosphere pressure outside the Laval nozzle, in other words, the gas atmosphere pressure inside the converter, and is usually atmospheric pressure.

[0020]

[Equation 1]

[0021]

[Equation 2]

When the Laval nozzle designed according to the equations (3) and (4) is used and the nozzle pressure P in actual operation is made to coincide with the absolute nozzle pressure Po, the oxygen jet is almost optimally expanded. , The energy of the oxygen jet itself is maximum.

In the peak stage of decarburization, in the case of blowing with a large amount of slag, it is necessary to maximize the energy of the oxygen jet to penetrate the slag and supply oxygen to the molten metal surface in recent years. In the case of blowing with a small amount of slag, it is not necessary to maximize the energy, that is, to optimize the oxygen jet. From the viewpoint of dust and iron scattering, a weak jet having a large energy loss is preferable.

Therefore, various studies were conducted on the throat portion of the Laval nozzle, and it was concluded that the energy of the oxygen jet is lost and a soft blow is achieved by providing the straight body portion on the throat portion. To confirm this effect,
In a laboratory-scale divergent nozzle with a throat portion having a straight body shape, the length (Ls) of the straight body portion and the length (L) of the divergent portion were changed to measure the flow velocity in front of the divergent nozzle. The divergent nozzle used is the inner diameter D of the straight body
The s is 7.9 mm, the outlet diameter De is 9.2 mm, and the nozzle absolute pressure Po is 527 kPa.

In the test, the ratio (Ls / L) of the length (Ls) of the straight body portion and the length (L) of the divergent portion is 0, 0.5, 0.
The central flow velocity was measured with a Pitot tube at 6 positions of 9, 1.0, 2.0, and 4.0, and at a position 200 mm away from the divergent nozzle outlet. The measurement result is 203m /
s, 206m / s, 204m / s, 190m / s, 185m /
It was s, 184 m / s. The measurement results are shown in FIG.
As is clear from FIG. 1, when the ratio (Ls / L) is 1.0 or more, that is, the straight body part length (Ls) is within the range of the following formula (1) with respect to the end spread part length (L). It has been found that the jet damping effect is obtained when satisfied.

[0026]

[Equation 3]

As described above, it has been found that by providing the straight body portion in the throat portion, an optimum jet cannot be obtained, that is, soft blow is performed and dust and iron scattering are reduced. At the same time, it was found that in order to maximize this effect, the length (Ls) of the straight body portion needs to be equal to or longer than the length (L) of the divergent portion. This is because in a Laval nozzle, a jet that normally passes through the throat at a constant speed of sound velocity has a velocity distribution or turbulence in the straight body in the divergent nozzle according to the present invention, which prevents proper expansion of the jet in the divergent portion downstream. Therefore, it is considered that the jet will be improper as a result. Here, the length (L) of the divergent end portion is determined by the divergence angle, and an angle of 10 degrees or less is usually selected, and there are many cases of about 5 degrees. The smaller this angle, the slower the jet expands, so larger turbulence in the straight body part is required for soft blow, but the length (Ls) of the straight body part is the length of the divergent part. If it is (L) or more, there is no great difference in effect.

When the throat portion is formed in a straight body shape, the lance nozzle is extremely easily processed, and the secondary effect is that the manufacturing cost of the lance nozzle can be significantly reduced.

The expansion degree of such a jet is
For Laval nozzle, outlet diameter De and throat diameter Dt
(De / Dt), and in the divergent nozzle of the present invention, the ratio (De) between the outlet diameter De and the straight body portion inner diameter Ds.
/ Ds). Here, the inner diameter Ds of the straight body portion of the divergent nozzle of the present invention corresponds to the throat diameter Dt of the Laval nozzle, and therefore the ratio (D
e / Dt) and the ratio (De / Ds) have the same influence on the expansion degree of the jet, and the ratio (De / D) on the expansion degree of the jet in the divergent nozzle of the present invention.
The influence of s) can be determined from the influence of the ratio (De / Dt) on the jet in the Laval nozzle.

Since this ratio (De / Dt) is determined by the above-mentioned equation (4), it is a function of only the nozzle absolute pressure Po. Therefore, in order to obtain a further jet damping effect, the outlet diameter De should be designed according to the equation (4) by using a numerical value different from the nozzle absolute pressure Po, that is, different from the pressure during actual operation. It can be obtained by designing the outlet diameter De with pressure. This is because the nozzle pressure (hereinafter referred to as "designed nozzle pressure") used during design is normally matched with the nozzle absolute pressure Po, but in actual operation, the nozzle pressure P and the nozzle absolute pressure Po are always matched. However, it is known that the nozzle pressure P and the nozzle absolute pressure Po naturally differ when the oxygen transfer rate is changed according to the operating condition, and when this difference occurs, the oxygen jet is attenuated. This phenomenon is clear, and is clear from this phenomenon.

Therefore, a detailed study was conducted on the design nozzle pressure. As a result, it was found that if the design nozzle pressure was designed to be extremely low with respect to the nozzle absolute pressure Po corresponding to the high oxygen transfer rate region during the peak decarburization period, an extremely large damping effect could be obtained. The effect is that the design nozzle pressure is set to 58.
It was found that it becomes large when the pressure is 8 kPa (6 kgf / cm ² ) or less. By the way, the nozzle pressure P is near 980 kPa (10 kgf / cm ² ) in the high carbon region of ordinary converter blowing, so conventionally, the outlet diameter De is designed with the designed nozzle pressure near 980 kPa. Design nozzle pressure 5
Setting the pressure to 88 kPa or less can be regarded as an extremely low design nozzle pressure as compared with the related art.

When the design nozzle pressure is 588 kPa or less
In the above formula (4), the nozzle absolute pressure Po
Instead, substitute the design nozzle pressure = 588 kPa, and
By substituting the atmospheric pressure Pe = 101 kPa (atmospheric pressure)
Ratio of the outlet diameter De and the throat diameter Dt (De / Dt)
Can be uniquely determined. In this case, the ratio (D
e / Dt) is 1.20 or less. In addition, design nozzle pressure
To 490 kPa (5 kgf / cm ² ) By doing the following,
A more stable damping effect can be obtained, and in this case
Has a ratio (De / Dt) of 1.15 or less. Same as this
Similarly, in the divergent nozzle of the present invention, the outlet diameter De
The ratio (De / Ds) between the inner diameter of the straight body and Ds is given in (2) below.
By setting it within the range of the formula, it is possible to achieve a high acid transfer rate range at the peak of decarburization.
The jet can be greatly dampened. This place
If the ratio (De / Ds) is 1.15 or less,
A more stable damping effect can be obtained.

[0033]

[Equation 4]

Even if the outlet diameter De is designed by making the designed nozzle pressure extremely higher than the absolute nozzle pressure Po, the desired damping effect can be obtained in the high oxygen transfer rate range. In the final stage of blowing, when the velocity is reduced, the oxygen jet is attenuated more than in the conventional nozzle to cause improperness, and the reaction in the final stage of blowing is obstructed, so that the object of the present invention cannot be achieved.

FIG. 2 shows that the ratio of the outlet diameter De to the inner diameter Ds of the straight body portion (De / Ds) is changed by using a nozzle to blow the converter, and the dust generation rate and the ratio ( De /
It is a figure which shows the result of having investigated the relationship with Ds). As is clear from FIG. 2, it is understood that the dust generation amount can be suppressed by setting the ratio (De / Ds) to 1.20 or less.

On the other hand, in the low carbon region in the final stage of blowing in which the acid transfer rate is reduced, in the conventional nozzle designed on the basis of the nozzle absolute pressure Po at the high acid transfer rate, the nozzle pressure P associated with the decrease in the acid transfer rate is set. The decrease in oxygen jet causes the oxygen jet to be attenuated, resulting in a decrease in decarburization reaction efficiency, but the design nozzle pressure is 588 kPa (6
With a nozzle of less than kgf / cm ² ), the oxygen jet tends to be optimized because the nozzle pressure P at the end of blowing at the time of founding approaches the design nozzle pressure. Reduction of Fe, promotion of reaction and stabilization are naturally achieved.

The present invention has been made on the basis of the above-mentioned examination results. The molten metal refining method according to the first invention uses an upper blowing lance having a nozzle that spreads toward the tip of the molten metal and uses a top blowing lance to supply oxygen toward the molten metal. In the molten metal refining method of spraying and refining, the end-spreading nozzle has a straight body portion having a length (Ls) determined by the above formula (1) with respect to the length (L) of the end-spread portion, on the upstream side of the end-spread portion. It is characterized by having in.

In the molten metal refining method according to the second invention, in the first invention, the ratio (De / Ds) of the outlet diameter De of the divergent nozzle to the inner diameter Ds of the straight body portion is the above (2).
It is characterized in that the range is determined by the formula.

A molten metal refining method according to a third invention is the molten metal refining method according to the first invention or the second invention, wherein the upper blowing lance has a plurality of divergent nozzles, and at least one of them is provided.
The two divergent nozzles satisfy the above formula (1).

A molten metal refining method according to a fourth aspect of the present invention is the method for refining molten metal according to any one of the first to third aspects, wherein the molten metal is hot metal, and the hot metal is decarburized, dephosphorized, and desiliconized. It is characterized in that it is refining aimed at at least one of the treatments.

A molten metal refining method according to a fifth aspect of the present invention is the refining method according to any one of the first to third aspects, wherein the refining is a refining for the purpose of decarburizing hot metal using a converter. The amount of slag in the converter is less than 50 kg per ton of molten steel.

A molten metal refining top-blowing lance according to a sixth aspect of the present invention is a molten metal refining top-blowing lance in which an end-spreading nozzle is installed at the tip thereof, wherein the end-spreading nozzle has a length (L) at the end-spreading portion. On the other hand, the present invention is characterized by having a straight body portion having a length (Ls) determined by the above formula (1) on the upstream side of the divergent portion.

The molten metal refining top-blowing lance according to the seventh invention is the sixth invention, wherein the ratio (De / Ds) between the outlet diameter De of the divergent nozzle and the inner diameter Ds of the straight body portion is as described above (De / Ds). It is characterized in that the range is determined by the equation (2).

An upper-blown lance for refining molten metal according to an eighth invention is the upper-blown lance for refining molten metal according to the sixth or seventh invention, wherein the upper-blown lance for refining molten metal is a converter blower for decarburizing hot metal. It is a top-blown lance and is used for blowing in which the amount of slag in the converter is less than 50 kg per ton of molten steel.

[0045]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 3 is a schematic sectional view of an upper blowing lance according to an embodiment of the present invention, and FIG. 4 is a schematic enlarged sectional view of the divergent nozzle shown in FIG.

As shown in FIG. 3, the upper blowing lance 1 is composed of a cylindrical lance body 2 and a lance nozzle 3 connected to the lower end of the lance body 2 by welding or the like. The main body 2 includes an outer tube 7, a middle tube 8 and an inner tube 9.
The three types of concentric steel pipes, that is, triple pipes, are provided. The copper lance nozzle 3 is provided with a divergent nozzle 4 in a vertically downward direction or in a vertically oblique downward direction.

The gap between the outer pipe 7 and the middle pipe 8 and the gap between the middle pipe 8 and the inner pipe 9 serve as cooling water flow paths for cooling the upper blowing lance 1. The cooling water supplied from the water supply joint (not shown) provided in the upper part of 1 reaches the portion of the lance nozzle 3 through the gap between the middle pipe 8 and the inner pipe 9, and is reversed at the portion of the lance nozzle 3. Through the gap between the outer pipe 7 and the middle pipe 8 and is discharged from a drain joint (not shown) provided on the upper portion of the upper blowing lance 1. The water supply and drainage route may be reversed. In addition, the inside of the inner tube 9 spreads toward the end and the nozzle 4
Oxygen supplied to the inner pipe 9 from the upper end of the upper blowing lance 1 passes through the inner pipe 9,
It is ejected from the divergent nozzle 4 into a converter (not shown).

The divergent nozzle 4 is, as shown in FIG.
It is composed of the straight body part 5 and the end widening part 6 following the straight body part 5. The spread angle θ of the end widening part 6 is usually 10 degrees or less, and the length (Ls) of the straight body part 5 is equal to that of the end widening part 6. It has a length equal to or longer than the length (L). The lance nozzle 3 is provided with one or a plurality of divergent nozzles 4 having such a shape. Oxygen that has passed through the inside of the lance body 2 is supplied into the converter through the straight body portion 5 and the diverging portion 6 in order.

In this case, as described above, in order to further attenuate the oxygen jet in the high oxygen transport rate region and optimize the oxygen jet in the low oxygen transport rate region, the inner diameter Ds of the straight body portion 5 and the outlet diameter The ratio to De (De / Ds) is 1.
It is preferably 20 or less, and more preferably 1.15 or less.

The inner diameter Ds of the straight body portion 5 can be determined as follows. That is, the acid transfer rate F (Nm ³ from the top blowing lance 1 in the high carbon region from the early stage to the middle stage of blowing)
/ Hr) to one end-spreading nozzle 4, and the acid transfer rate Fh
(Nm ³ / hr) is calculated, and this acid transfer rate Fh (Nm ³ / hr) and the nozzle absolute pressure Po at that time are substituted into the above-mentioned equation (3) to calculate the throat diameter Dt, and the calculated throat diameter Dt Is defined as the inner diameter Ds of the straight body portion 5 of the nozzle 4 which spreads toward the end.
Similarly, the inner diameter Ds of the straight barrel portion 5 can be obtained from the acid transfer rate F in the low carbon region at the final stage of blowing and the nozzle absolute pressure Po at that time. In this way, by using the acid transfer rate F and the nozzle absolute pressure Po at that time, it is possible to obtain an arbitrary acid transfer rate.

In the end-spreading nozzle 4 shown in FIG. 4, the end-spreading portion 6 is a conical body, but the end-spreading portion 6 does not have to be a conical body, and may be constituted by a curved surface whose inner diameter changes curvilinearly. . When the lance nozzle 3 has a plurality of end-spreading nozzles 4, only some of the end-spreading nozzles 4 may have the above-described shape. However, in this case, the intended effect is slightly reduced. Further, a throttle portion such as a Laval nozzle may be installed on the upstream side of the straight body portion 5.

Then, using the upper blowing lance 1, the molten pig iron produced in a blast furnace or the like is blown in the converter. In this blowing, the high carbon region (C>
0.6 mass%), regardless of the acid feeding rate and the nozzle pressure P, the upper blowing lance 1 is used to blow at a high acid feeding rate and a high nozzle pressure P under any conditions suitable for the refining reaction. It is possible.

On the other hand, in the low carbon region at the end of blowing, the nozzle pressure P is set to 588 kP in order to suppress the decrease in dynamic pressure of the oxygen jet.
a It is preferable to blow as below. In this case, if the carbon concentration of the molten metal reaches 0.6 mass%, it is not necessary to immediately set the nozzle pressure P to 588 kPa or less, and it is necessary to change the acid transfer rate for blowing in the low carbon region in accordance with the timing. It should be carried out.

When the amount of slag in the furnace at the time of blowing the converter is small, the ratio of the molten metal covered with the slag decreases, and the amount of dust and iron scattering in the high carbon region increases. The end-spreading nozzle 4 of the present invention has a strong effect of suppressing the generation of dust and iron scattering in the high carbon region. Therefore, the present invention is applied to the blowing in which the amount of slag in the furnace is less than 50 kg per ton of molten steel, preferably 30 kg or less. By doing so, the effect can be further exerted.

By blowing the hot metal in the converter in this way, it is possible to reduce the jet flow velocity in the high acid transport rate region of the high carbon region, and to maintain the oxygen jet energy at a low level. It is possible to reduce iron scattering and dust generation. When the ratio (De / Ds) is 1.20 or less, it is possible to further optimize the jet velocity of the oxygen jet at the end of blowing, that is, increase the dynamic pressure of the oxygen jet at the end of blowing. It becomes possible and the oxidation of iron can be suppressed. As a result, the iron yield in the entire blowing can be improved, and the operation can be stabilized.

Further, in the top blowing lance 1 of the present invention, it is possible to arbitrarily set the acid transfer rate in the high carbon range with respect to the acid transfer rate in the low carbon range, that is, a wide range of acid transfer rates. It is possible to carry out the blowing with the adjustment range of 1. Therefore, there is also an advantage that the acid transfer rate can be freely changed according to the situation in the furnace.

Although the above description is about the decarburizing treatment of the hot metal, the present invention is not limited to this, and is applied to the refining of the hot metal such as the dephosphorization treatment and the desilvering treatment using the top blowing lance. can do.

[0058]

[Example] With a capacity of 250 tons, top-blown oxygen and top-blown converter for blow-blown agitation gas were used to change the shape of the end-spreading nozzle attached to the top-spraying lance to expand the end-spreading. Nozzle shape, dust generation, and slag in slag at the end of blowing A test was conducted to investigate the relationship with the Fe concentration. The top-blowing lance used for the test is a 5-hole nozzle type top-blowing lance in which five end-spreading nozzles are installed.

The inner diameter Ds of the divergent nozzle is determined by the acid transfer rate F = 60,000 Nm ³ in the high carbon region from the early stage to the middle stage of blowing.
Designed based on the condition of / hr. That is, the inner diameter Ds of the straight body part
Nozzle 1 in all divergent nozzles tested
The throat diameter Dt = 55.0 mm was calculated from the equation (3) from the conditions of the acid transport rate per hole Fh = 12000 Nm ³ / hr and the nozzle absolute pressure Po = 870 kPa, and this throat diameter Dt
Was defined as the inner diameter Ds of the straight body part.

In Examples 1 and 2, the outlet diameter De was set to 62.0 mm by setting the design nozzle pressure to 445 kPa and substituting 445 kPa into the equation (4) for the nozzle absolute pressure Po.
In Examples 3 to 4 and Comparative Examples 1 to 2, the nozzle absolute pressure Po was used.
= (870 kPa), obtained by the equation (4), 73.4
defined as mm. At the time of calculating the outlet diameter De, the atmospheric pressure Pe
Was set to 101 kPa (atmospheric pressure) for all nozzles.

The ratio (Ls / L) of the length (Ls) of the straight body portion of the divergent nozzle to the length (L) of the divergent portion is two levels of 1.0 and 1.5 in the embodiment, and the comparative example. Then, there are two levels of 0 and 0.5. Incidentally, Comparative Example 2 does not have a straight body portion, and is a conventional Laval nozzle. Table 1 shows the shape of the divergent nozzle used.

[0062]

[Table 1]

In the test, about 250 tons of hot metal was charged into the converter, and decarburization blowing was mainly performed. The hot metal used was hot metal that had been desulfurized and dephosphorized in the hot metal pretreatment facility that was the pre-converter process.In the converter, lime flux was added and a small amount of slag (per ton of molten steel) Less than 50 kg)
Is being generated. From the tuyere installed at the bottom of the converter, argon or nitrogen was blown at about 10 Nm ³ per minute for the purpose of stirring the molten metal. From the upper blowing lance inserted into the converter from the upper side, from the early stage to the middle stage of blowing, the acid feeding rate F was 60,000 Nm ³ / hr, and the carbon concentration of the molten metal was 0.6 mass% or less. In the final stage of blowing, the acid was fed under the condition that the acid feeding rate F was 28000 to 35000 Nm ³ / hr. The nozzle pressure P at the end of blowing was 500 kPa or less in all tests.

During blowing, the amount of dust in the exhaust gas was measured using a wet dust measuring device. At the end of blowing, the slag in the converter is collected and the T. The Fe concentration was investigated. The amount of dust generated in each test blowing over 10 heats, and the T.A. in the slag when the blowing was stopped at a carbon content of 0.05 mass%. The results of the Fe concentration investigation are also shown in Table 1 above. The ⊚ mark in the evaluation column of Table 1 indicates the dust generation amount and T.I. The case where both the Fe concentrations are low is represented, the mark ◯ represents the case where the amount of dust generated is low, and the mark x represents that there is no improvement effect.

As is clear from Table 1, when the length (Ls) of the straight body portion is equal to or longer than the length (L) of the divergent portion, the dynamic pressure of the oxygen jet in the high carbon region is suppressed, Generation of dust was suppressed compared to the conventional method. In addition to this, the ratio of the inner diameter Ds of the straight body part to the outlet diameter De (De / Ds)
When the ratio is less than 1.2, the amount of dust generated is further reduced, and the dynamic pressure of the oxygen jet in the final stage of blowing is optimized so that the T. It was possible to reduce the Fe concentration.

[0066]

As described above, according to the present invention,
It is possible to secure a wide range of adjustment of the oxygen transfer rate, and it is possible to reduce the jet flow velocity in the high carbon acid range and other high oxygen transfer rates, thus suppressing dust generation at high oxygen transfer rates. It is also possible to suppress the oxidation of iron by optimizing the acid transfer in the low acid transfer rate region such as the final stage of converter blowing, and as a result, the iron yield in the entire blowing is improved. It can be greatly improved and the stabilization of the operation is achieved, resulting in extremely beneficial effects in industry.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a ratio (Ls / L) and a flow velocity of ejected gas.

FIG. 2 is a diagram showing the relationship between the ratio (De / Ds) and the dust generation rate during the peak decarburization period.

FIG. 3 is a schematic cross-sectional view of an upper blowing lance according to an embodiment of the present invention.

FIG. 4 is a schematic enlarged cross-sectional view of the divergent nozzle shown in FIG.

[Explanation of symbols]

1 Top blowing lance 2 Lance body 3 lance nozzle 4 end spread nozzle 5 straight body 6 end spread part

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Ryo Kawabata             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. (72) Inventor Satoshi Kodaira             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. (72) Shinichi Akai             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. F-term (reference) 4K070 AB02 AB03 AB06 AB14 AB17                       AB18 BA05 CF02 EA15

Claims (8)

[Claims] 1. A molten metal refining method in which oxygen is blown toward a molten metal for refining using an upper blowing lance having an end-diverging nozzle installed at its tip, wherein the end-diverging nozzle has a length (L) of the flared portion. On the other hand, a molten metal refining method characterized by having a straight body portion having a length (Ls) determined by the following formula (1) on the upstream side of the divergent portion. L ≦ Ls (1) 2. The ratio (De / Ds) between the outlet diameter De of the diverging nozzle and the inner diameter Ds of the straight body portion is in a range determined by the following equation (2). Molten metal refining method. De / Ds ≦ 1.20 (2) 3. The upper blowing lance has a plurality of end-spreading nozzles, and at least one of the end-spreading nozzles satisfies the formula (1). Molten metal refining method. 4. The molten metal is hot metal, and is a refining for the purpose of at least one of decarburizing treatment, dephosphorizing treatment and desiliconizing treatment of the hot metal. Item 4. A molten metal refining method according to any one of Items 3. 5. The refining is refining for the purpose of decarburizing hot metal using a converter, and the amount of slag in the converter is less than 50 kg per ton of molten steel.
The molten metal refining method according to any one of claims 1 to 3. 6. A molten metal refining top-blowing lance having an end-spreading nozzle installed at the tip thereof, wherein the end-spreading nozzle has the following (1) with respect to the length (L) of the end-spreading part.
An upper blowing lance for molten metal refining, which has a straight body portion having a length (Ls) determined by a formula on the upstream side of the divergent portion. L ≦ Ls (1) 7. The ratio (De / Ds) between the outlet diameter De of the diverging nozzle and the inner diameter Ds of the straight body portion is in a range determined by the following equation (2). Top blow lance for molten metal refining. De / Ds ≦ 1.20 (2) 8. The molten metal refining top-blown lance is a converter-blown top-blown lance for decarburizing molten pig iron, wherein the amount of slag in the converter is less than 50 kg per ton of molten steel. It is used and Claim 6 or Claim 7 characterized by the above-mentioned.
A top-blown lance for refining molten metal according to.