JP2022006385A - Top-blown lance for converter dephosphorization treatment and converter blowing method - Google Patents

Abstract

To provide a top-blown lance capable of suppressing the generation of slopping, and a converter blowing method using the top-blown lance.SOLUTION: A top-blown lance for converter dephosphorization treatment has plural circumferential holes rotationally symmetrically arranged with respect to the lance axis, in which jet straightness γ defined by the following equation (1) is 0.31 to 0.75, and a converter blowing method uses the top-blown lance: γ=Xjet/Xlinear(1); where Xi denotes a distance from a lance axis projection position at a bath surface corresponding position under conditions i, the subscript jet denotes the central position of the jet deflected by interference, and the subscript linear denotes the position on the extension of a circumferential hole central axis.SELECTED DRAWING: Figure 3

Description

The present invention relates to a top-blown lance for a converter dephosphorization treatment in which molten iron is oxidatively dephosphorized using oxygen, and a method for blowing a converter using the top-blown lance.

In recent years, since pig iron integrated steelworks are advantageous in terms of cost and quality, dephosphorization is performed as a pretreatment process before decarburization refining in a converter to remove phosphorus in molten iron in advance. The process is widespread. This is because the dephosphorization reaction is more likely to proceed as the refining temperature is lower, and the dephosphorization reaction is more likely to proceed in the molten iron stage than in the molten steel stage, and the dephosphorization can be performed with less auxiliary raw materials.

In this dephosphorization treatment of molten iron, a medium-dissolving material for dephosphorization containing CaO as a main component such as quicklime is added, and an oxygen source such as oxygen gas or iron oxide is added as a dephosphorizing agent. The dephosphorization phenomenon of molten iron is shown in the following reaction formula (3).
2 [P] +2 (FeO) +3 (CaO ・ FeO) (l)
→ (3CaO ・ P _{2O 5} ) (s) + 5 [Fe] ・ ・ ・ (3)
Here, [M] represents the element M in the molten iron, and (S) represents the chemical substance S in the slag.
As can be seen from the equation (3), the dephosphorization reaction is an oxidation reaction, and the presence of iron oxide (FeO) is indispensable. Moreover, since the produced phosphorus oxide (P ₂ O ₅ ) is unstable, it is necessary to react it with lime (CaO) to form (3 CaO · P ₂ O ₅ ) and stabilize it in the slag. Therefore, lime is equally essential for dephosphorization. The (FeO) in the slag is generated by oxidizing the iron by absorbing the oxygen-containing gas ejected from the top-blown lance to the fire point, which is the surface on which the iron bath surface is blown. Further, the melting point of lime that reacts with the phosphorus oxide is 2500 ° C. or higher at the time of charging, and the melting point is overwhelmingly higher than the furnace temperature of 1300 to 1500 ° C., and the reaction efficiency is remarkably low. However, it reacts with iron oxide to form low melting point calcium ferrite (CaO / FeO), which causes slag and contributes to the dephosphorization reaction. From the above, it can be seen that iron oxide not only directly oxidizes P but also contributes to the improvement of the dephosphorization reaction efficiency through the slagging of lime.

As mentioned above, since CaO slag plays an important role in the dephosphorization treatment of molten iron, in order to promote CaO slag, the oxygen jet comes into direct contact with the molten iron, and the fire point where FeO is constantly supplied. A method of promoting CaO slag by supplying calcium oxide is often adopted.

For example, in Patent Document 1, in a dephosphorization treatment method in which a medium-melting material for dephosphorization mainly composed of a CaO source is added to molten iron in a converter and oxygen gas is sprayed from a top-blown slag to the molten iron bath surface. The supply rate of oxygen gas from the top-blown lance was set to 1.5-5.0 Nm ³ / min / molten iron-ton to maintain a high FeO concentration in the slag, and at least a part of the medium-melting material for dephosphorization was oxygen gas. A method has been proposed in which the formation of calcium ferrite is promoted and the phosphorus is efficiently dephosphorized by spraying the fire point generated on the surface of the molten iron bath by spraying.

Further, in Patent Document 2, the average tilt angle of the main holes of the upper blowing lance is set to 13 ° or more, and the interference rate between jets from adjacent main holes is set within the range of 30 to 60% to combine the jets. It is designed so that the wear of the nozzle is reduced even if the medializing material is sprayed, while the supersonic jet with less attenuation can be obtained. In Patent Document 2, it is stated that the powdery medium-melting material has a trajectory similar to that of a coalesced jet and can be effectively projected to a fire point.

Japanese Unexamined Patent Publication No. 2008-266666 Japanese Unexamined Patent Publication No. 2006-336033

However, the above-mentioned prior art has the following problems.
In the technique disclosed in Patent Document 1, although an appropriate range is specified for the amount of acid feed, the above-mentioned appropriate range is based on the premise that the generated FeO will continue to be consumed for the dephosphorization / decarburization reaction. No mention is made to meet.

In order for the generated FeO to contribute to the dephosphorization / decarburization reaction and be consumed, P and C in the molten iron, which is a reactant, must be supplied to the slag metal interface where FeO exists or the fire point region. .. However, if the bath surface dynamic pressure of the top-blown lance jet is insufficient and the stirring of molten iron is insufficient, the supply will be delayed and the dephosphorization / decarburization reaction will be low. Therefore, the consumption of FeO is reduced, and it accumulates excessively in the slag. In order to avoid this problem, when designing a lance, the target bath surface dynamic pressure is determined for each operation, and it is common to set the lance shape so that the above can be achieved.

However, it is difficult to constantly obtain the bath surface dynamic pressure as designed in actual operation. Since the jet flow discharged from the lance reaches the bath surface while entraining the atmospheric gas and continuing to attenuate the flow velocity, the distance from the lance to the bath surface (lance height) is an important factor when considering the dynamic pressure of the bath surface. Contribute. On the other hand, in an actual converter, the shape and volume of the inside of the furnace change from moment to moment due to the undissolved residue of scrap input as a cold iron source and the metal adhering to the inside of the furnace. As a result, the bath surface position frequently increases or decreases by about 100 to 300 mm with respect to the design position. In particular, when the position of the bath surface is lowered, the distance from the lance to the bath surface is increased by the amount of the lowered bath surface, the jet is excessively attenuated, and the dynamic pressure of the bath surface becomes insufficient. At this time, a large amount of surplus FeO that does not contribute to the reaction is present in the slag.

In the above environment, the reaction proceeds between C in the granular iron suspended in the slag and the excessive FeO that does not contribute to dephosphorization or decarburization, and a large amount of CO gas is generated in the slag. As a result, a phenomenon called sloping occurs in which the slag foams excessively and overflows from the furnace opening. The slag that overflows due to sloping scatters under the furnace and blocks the track for the pot trolley for hot water discharge and drainage, so it is necessary to clean the furnace frequently, which hinders operations. Therefore, in the injection of the oxygen-containing gas from the top-blown lance, it is necessary to supply an appropriate amount of FeO and at the same time to appropriately continue the reaction with P and C in the molten iron.

Patent Document 1 refers to the oxygen supply amount required to enrich the supply amount of FeO required for dephosphorization, but as described above, the position of the molten metal is lowered during the operation and the lance height is increased. There is no countermeasure against the problem that the reaction with P and C in the molten iron is delayed when the stirring power becomes insufficient. This problem is an important issue because it causes sloping, which is an operational inhibitor, and significantly deteriorates productivity.

As a solution to the above-mentioned problems, a top-blown lance has been developed in which the attenuation of the jet flow with respect to the height of the lance is small. For example, in the technique disclosed in Patent Document 2, the jets discharged from the porous nozzles are designed to interfere with each other and deflect each other, and the jets are combined to form a jet with less attenuation, so that the jets are not affected by the height of the lance. The dynamic pressure of is stably obtained. However, the method disclosed in Patent Document 2 does not show the grounds that the powder supplied from the lance nozzle can obtain a trajectory similar to that of a jet. Therefore, there is a possibility that the region where the oxidizing gas jet is absorbed by the molten iron to generate FeO and the region where the dephosphorizing agent, which is an auxiliary raw material required for dephosphorization, reaches are different. Therefore, it is a problem that the reaction formula of the above formula (3), which requires the coexistence of FeO, P, and CaO, progresses poorly. In a lance as shown in Patent Document 2, a powder dephosphorizing agent having a high density and a large inertial force has a higher straightness than a jet, and even if the jet interferes or deflects, the followability to the jet deteriorates. Many dephosphorizers that do not contribute to the reaction are generated. Therefore, the efficiency of the dephosphorization reaction also deteriorates.

The present invention has been made in view of such circumstances, and an object thereof is to minimize the influence of the lance height, which is a parameter that fluctuates in continuous operation and is difficult to control, and sloping. It is an object of the present invention to provide a top-blown lance having a higher reaction efficiency of a dephosphorizing agent and to propose a method for blowing a converter using the top-blown lance, while achieving the ability to suppress the occurrence of the above-blown lance.

The top-blown lance for converter dephosphorization treatment of the present invention, which advantageously solves the above problems, has a plurality of peripheral holes arranged rotationally symmetric with respect to the lance axis, and has the following equation (1) (in the equation, Xi). Represents the distance from the lance axis projection position on the bath surface equivalent surface under the condition i, the subscript jet indicates the center position of the jet deflected by the interference, and the subscript liner indicates the extension of the peripheral hole center axis. The jet straightness γ defined by) is characterized by being 0.31 or more and 0.75 or less.
γ = X _jet / X _linear ... (1)

In the top-blown lance for converter dephosphorization according to the present invention, the molten iron for dephosphorization containing CaO as a main component is sprayed on the molten iron in the converter together with oxygen gas from the top-blown lance. It is a top-blown lance for oxidizing and removing phosphorus from molten iron, and it is designed so that the lap ratio λ of the medialable material defined by the following equation (2) is 0.19 or more. It could be a preferred solution.
λ = (total weight of the medial material projected into the fire point) / (total weight of the supplied medial material) ・ ・ ・ (2)

The converter blowing method that advantageously solves the above problems is a converter blowing method that uses a top-blown lance and blows oxygen gas from the top-blown lance to oxidize and remove phosphorus from molten iron. Is characterized by having a plurality of peripheral holes arranged rotationally symmetrically with respect to the lance axis, and having a jet flow straightness γ defined by the above equation (1) of 0.31 or more and 0.75 or less. ..

In the converter blowing method according to the present invention, oxygen gas is blown from a top-blown lance to the molten iron in the converter, and a medium-melting material for dephosphorization containing CaO as a main component is supplied to the molten iron in the converter. It is a converter blowing method for oxidizing and removing phosphorus from molten iron, and when at least a part of the medium-melting material for dephosphorization is sprayed from a top blowing lance toward a molten iron bath surface in a converter and added, the above (2). It is considered that setting the wrap ratio λ of the insoluble material defined by the formula) to 0.19 or more can be a more preferable solution.

According to the present invention, sloping can be suppressed by positively interfering with the oxygen jet supplied from the porous lance to form a coalesced jet and obtaining a jet with a small attenuation due to the fluctuation of the lance height. As a result, the dephosphorization treatment can be performed stably.

In addition, preferably, the effects of design item parameters such as nozzle shape, powder medium particle size, and acid feed rate on the orbits of the oxidizing gas and powder medium and melt are estimated in advance, and under jet coalescence. It can provide a lance that can maximize the amount of medial material that reaches the fire point. As a result, stable operation is possible without fear of sloping, and the cost of auxiliary raw materials is suppressed.

FIG. 3 is an enlarged schematic view of a vertical cross section of the tip of a top blown lance according to an embodiment of the present invention. FIG. 3 is an enlarged cross-sectional view of the nozzle shape of the peripheral hole shown in FIG. 1. It is a schematic diagram which shows the concept of the jet straightness degree γ which concerns on one Embodiment of this invention. It is a figure which shows the distribution of lime with respect to the distribution of the fire point on the surface corresponding to the bath surface obtained by the numerical analysis.

Hereinafter, in explaining the present invention based on a preferred embodiment, first, the results of studies leading to the present invention will be described. FIG. 1 is an enlarged schematic view of a vertical cross section of a top blown lance tip portion 2 according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view of the shape of the nozzle portion 3 of the peripheral hole shown in FIG.

Conventionally, the top blown lance 1 for converter dephosphorization treatment has been designed to promote the generation of FeO for the purpose of promoting the dephosphorization reaction expressed by the above equation (3). Specifically, (A) the amount of FeO accumulated in the slag is increased by the low dynamic pressure on the bath surface, and (B) the area of the fire point where oxygen is absorbed on the iron bath surface is expanded. That is, in order to satisfy the above conditions A and B, a lance design aimed at dispersing the jet using a porous lance having a plurality of nozzles, reducing the collision pressure, and expanding the firing point area. Was done. When a plurality of nozzles are installed at the tip portion 2 of the top blown lance, the nozzles installed at the center position (coaxial with the lance axis) are referred to as the center hole, and the nozzles installed around the center hole are referred to as the peripheral hole 4. ing. The peripheral holes 4 are evenly arranged rotationally symmetrically about the lance axis. On the other hand, it is known that when the number of holes in the lance is increased and the nozzle spacing is narrowed, the jets interfere with each other and coalesce.

Further, in the conventional design, a lance design in which the nozzle spacing is large, the interference between jets is avoided, and the nozzle tilt angle θ is increased in order to increase the fire point has been widely adopted. Here, the nozzle tilt angle θ is an angle formed by the central axis (lance axis) 11 of the upper blowing lance and the discharge direction central axis 42 of each peripheral hole 4. If the nozzle tilt angle θ is excessively increased, the oxidizing gas jet discharged from the lance tip portion 2 directly collides with the inner wall of the converter and significantly wears the bricks in the furnace. Therefore, there is an upper limit to the nozzle tilt angle θ. As described above, the conventional top-blown lance 1 for converter dephosphorization treatment has used an independent jet type porous lance.

In order to examine the above effects, the inventors conducted a dephosphorization smelting test using a 340 ton scale converter using porous lances of various shapes, and each lance was charged with 40 to 80 charges. At that time, in order to quantitatively evaluate the degree of interference of the oxidizing gas jet, the jet straightness γ was defined by the following equation (1). The concept is shown in FIG. The jet straightness γ is calculated as follows. First, assuming that the oxygen jet advances linearly and does not deflect, the calculated bath surface arrival position (= lance height H equivalent position 100) at the center of the oxidizing gas jet, that is, the extension line of the peripheral hole central axis 42. The denominator is the distance (X _linear ) between the position on the bath surface equivalent surface 100 and the projection position of the lance axis 11 on the bath surface equivalent surface 100. Then, in consideration of the influence of jet interference, the distance (X) between the position on the bath surface equivalent surface 100 of the jet center 101 and the projection position of the lance axis 11 on the bath surface equivalent surface 100 calculated by numerical fluid analysis. It is a numerical value expressing _jet ) as a molecule. The higher the jet straightness γ, the higher the independence of the jet, and the lower the jet straightness γ, the more the jet is deflected and the tendency to coalesce becomes stronger. STAR-CCM + was used for the computational fluid dynamics to calculate the jet trajectory 101. In the calculation, the center position O at the lower end of the upper blow lance 1 was set as the origin, the horizontal line including the center position of the peripheral hole outlet 41 was set as the X axis, and the lance axis 11 was set as the Z axis vertically downward. The jet start position on the X-axis (Z = 0) was set to be half the diameter P of the circle connecting the center of the peripheral hole outlet 41 at the lower end position of the upper blow lance.
γ = X _jet / X _linear ... (1)
Here, Xi represents the distance from the lance axis projection position on the surface corresponding to the bath surface under the condition i.
The subscript jet indicates the center position 101 of the jet deflected by the interference.
The subscript liner represents a position on the extension of the peripheral hole center axis 42.

When the dephosphorization and smelting results were carried out in a 340t scale converter, the inventors found that the lance with a higher jet straightness γ tended to have a higher sloping frequency. It was also found that the frequency of sloping is low in the lance with a low jet straightness γ. Considering that the main cause of sloping is insufficient dynamic pressure of the upper jet as described above, in the lance with high jet straightness, the charge whose dynamic pressure drops below the design bath surface dynamic pressure at the time of blowing is high in frequency. It is presumed that it was. This is because even if the oxygen gas supplied from the top-blown lance has the same total flow rate, the surface area of the jet is larger and the atmospheric gas is more likely to be entrained in the case of an independent jet. It is thought that one of the reasons is that it becomes sensitive to the influence of height. In addition to that, it is qualitatively explained if the environment inside the furnace fluctuates with each smelting and the bath surface height changes from moment to moment during operation, and a state deviating from the design value may occur. It is possible.

Generally, a sublance is used to measure the bath surface height, but since the blowing time is extended by the amount of time during which the bath surface is measured by the sublance, frequent measurement significantly reduces productivity. Since it is difficult to measure the bath surface height in a stable manner, it is necessary to satisfy the insensitivity to the influence of the lance height, that is, the jet flow that is difficult to attenuate, as a condition for providing the top blow lance for converter dephosphorization treatment. I found out that there is. From the above, it was found that a combined jet type porous lance should be adopted, which makes it difficult for the jets to interfere with each other and be attenuated. In order to confirm the above findings, a test was conducted using a jet coalescence type lance by lowering the jet straightness γ, which is an index indicating the jet coalescence, from the test results. When the jet straightness γ was set to 0.75 or less, sloping It was confirmed that the frequency could be reduced. On the other hand, when the jet straightness is made smaller than 0.31, the jets are completely united, and the behavior is similar to that of a single-hole nozzle (lance with only the central hole), resulting in uncontrollable high bath surface dynamic pressure. rice field. As a result, it was found that the molten iron may be scattered and troubles such as lance with bullion may occur. Further, at a level smaller than 0.31, the generated FeO was consumed for decarburization due to the excessively strong stirring force of the high bath surface dynamic pressure, and the dephosphorization efficiency also deteriorated. From the above, it was judged that the jet straightness γ should be in the range of 0.31 or more and 0.75 or less. More preferably, the jet straightness γ is in the range of 0.31 or more and 0.50 or less.

In order to promote the slagging of CaO, an operation is performed in which a powdery refining medium containing lime is sprayed from a top-blown lance to a fire point, which is a FeO generation site, together with an oxidizing gas. When the jet-combined lance was adopted for such an operation, it was raised as a concern that the jet and lime trajectories were different. This is due to the fact that the powdery medium-welded material, which is a solid with a high density and a large inertial force, has high straightness with respect to a jet that is easily deflected due to its low density and low inertial force. In order to evaluate the above quantitatively, the lap ratio λ defined by the following equation (2) was adopted in the present invention. As an example of the above study, using numerical fluid analysis by STAR-CCM +, lime with an average particle size of 200 μm was projected from a lance nozzle with 8 peripheral holes and a nozzle tilt angle of θ = 16 ° together with oxygen gas of 30,000 Nm ³ / h. FIG. 4 shows the results of calculating and comparing the area corresponding to the fire point 6 and the lime distribution (lime projection area) 7. Here, the region corresponding to the fire point 6 is defined as a region to which a dynamic pressure of 0.1 kPa or more is applied. As can be seen from this analysis, the followability of the powder when the jet is deflected is low, and the insoluble material that cannot reach the area corresponding to the fire point 6 is generated, and the efficiency of contribution to dephosphorization and blowing is reduced.
λ = (total weight of the medial material projected into the fire point) / (total weight of the supplied medial material) ・ ・ ・ (2)

The above-mentioned drawbacks can be improved by increasing the followability of the powder or by increasing the straightness of the jet within a range that does not cause sloping. However, in order to improve the followability of the powder, it is necessary to make the particle size of lime finer, and the finer the particle size, the higher the unit price per weight of the medial material and the higher the cost. Moreover, since the powder having an excessively fine particle size is easily affected by static electricity, it easily sticks to the inside of the transport pipe during feeding and causes clogging. Therefore, in the present embodiment, it is selected to improve the straightness of the jet in the region where sloping does not occur.

In order to improve the straightness of the jet, it is possible to increase the inertial force of the jet or reduce the interference between the jets. The former can be achieved by increasing the acid transfer flow rate, but excessive acid transfer promotes decarburization and raises the hot metal temperature, which is disadvantageous for the dephosphorization reaction. Therefore, in this embodiment, it is adopted to reduce the interference between jets. Reducing the interference between jets is synonymous with increasing the distance between jets, and in the top blow lance, it is adjusted by changing the number of nozzle holes and the inclination angle. Also in this embodiment, the number of nozzle holes and the tilt angle θ are used as parameters to change the interference of the jet, and each lap ratio λ at this time is evaluated from the numerical fluid analysis. Regarding this study, the region corresponding to the fire point 6 is a region where dynamic pressure of 0.1 kPa or more is applied, and the powdered lime having an average particle size of 200 μm is 5 kg / t-molten iron together with oxygen gas of 30,000 Nm ³ / h. I set the case of projecting. In addition, dephosphorization was carried out in a 340t converter under the same conditions.

From the results of the above examination, it was found that the lap ratio λ tended to increase as the nozzle tilt angle θ increased, but the lap ratio λ decreased when the tilt angle θ was 20 °. The above phenomenon is that lime with high straightness is geometrically projected to a place away from the center of the lance by the lance height × tan θ as the inclination angle θ increases, but the improvement of the jet straightness γ cannot follow. to cause. In addition, since the lime dephosphorization ability improved as the lap ratio λ increased, it was confirmed that the lap ratio λ can express the lime dephosphorization efficiency. At this time, if the lap ratio λ is smaller than 0.19, the amount of de-P is less than 1.0 kg / t, so it is desirable to set λ to 0.19 or more at least. Considering the appropriate range of the jet straightness γ described above, the upper limit of the lap ratio λ is about 0.55. More preferably, the lap ratio λ is 0.20 or more, and even more preferably, it is in the range of 0.20 to 0.50.

Hereinafter, examples of the invention are shown together with comparative examples. With a capacity of 340 tons, about 340 tons of molten iron was charged into a converter for top-bottom-blown compound blowing, in which oxygen was top-blown and a stirring gas was bottom-blown, and dephosphorization was performed. The molten iron used was molten iron after desulfurization treatment, and the silicon concentration of the molten iron was 0.3 to 0.5% by mass and the phosphorus concentration was 0.12 to 0.14% by mass. A lime-based flux was projected into the converter from a top-blown lance together with refined oxygen to a concentration of 5 kg / t-molten iron. Argon or nitrogen was blown in the range of 10 to 50 Nm ³ / min to stir the molten metal from the tuyere installed for bottom blowing of the converter. In addition, acid feeding was performed by a top-blown lance, and about 50,000 Nm ³ / h was blown in the first half of the smelting de-Si period and about 30,000 Nm ³ / h in the latter half of the dephosphorization period. The lance height H was set for each lance nozzle so that the dynamic pressure was as equal as possible. The target molten iron temperature at the start of blowing was about 1250 ° C, and the target molten iron temperature at the end of blowing was 1380 ° C. The upper blown lance of the invention example used is a nozzle in which only 6 to 8 peripheral holes are installed, and the inclination angle θ is 14 to 20 °, the jet straightness γ is 0.31 to 0.75, and the lap ratio λ is 0. It was 19 to 0.56.

Further, as a comparative example, a 4-hole nozzle (No. 1) with a tilt angle θ = 14 ° designed so that the jet straightness γ is 1.00, and a tilt angle θ designed so that the jet straightness γ is 0.84. A test of a 5-hole nozzle (No. 2) at = 14 ° was carried out. The lap ratio λ was 1.00 and 0.87, respectively. The operating conditions are the same as those of the invention example.

Table 1 shows the nozzle conditions and operation results. For each condition, about 40 to 80 charges were carried out. In Table 1, the sloping frequency is an index obtained by counting the number of sloping charges generated when each condition is implemented, dividing by the total number of implemented charges for each condition, and taking a percentage. For the dephosphorization amount ΔP, the average value of the implemented charges was calculated for each condition.

As shown in Table 1, in the examples of the invention, the sloping frequency is reduced as compared with the comparative example, and the amount of dephosphorization is improved even under the condition that the auxiliary raw material (powder medium and molten material) per molten iron is the same. It was confirmed that efficient dephosphorization can be realized.

The top-blown lance of the present invention is suitable for application to dephosphorization and smelting using a converter.

1 Top blow lance 11 Lance shaft 2 Lance tip 3 Nozzle 4 Peripheral hole 41 Peripheral hole exit 42 Peripheral hole central axis 5 Throat part 6 Fire point equivalent area 7 Lime distribution (lime projection area)
100 Bath surface equivalent surface position 101 Jet locus P Diameter of the circle connecting the center of the peripheral hole outlet at the lower end position of the upper blow lance H Top blow lance height (distance from the lower end of the upper blow lance to the equivalent position of the bath surface)
θ Nozzle tilt angle O Top blow lance lower end center position

Claims (4)

It is a top-blown lance for converter dephosphorization.
A converter characterized by having a plurality of peripheral holes arranged rotationally symmetrically with respect to the lance axis and having a jet straightness γ defined by the following equation (1) of 0.31 or more and 0.75 or less. Top-blown lance for dephosphorization treatment.
γ = X _jet / X _linear ... (1)
Here, Xi represents the distance from the lance axis projection position on the surface corresponding to the bath surface under the condition i.
The subscript jet indicates the center position of the jet deflected by the interference.
The subscript liner represents a position on the extension of the central axis of the peripheral hole. It is a top-blown lance for oxidatively removing phosphorus from the molten iron by spraying the molten iron in the converter with oxygen gas from the top-blown lance and a medium for dephosphorization containing CaO as the main component. The top blown lance for converter dephosphorization treatment according to claim 1, wherein the lap ratio λ of the insoluble material defined by the following equation (2) is designed to be 0.19 or more.
λ = (total weight of the medial material projected into the fire point) / (total weight of the supplied medial material) ・ ・ ・ (2) It is a converter blowing method that uses a top-blown lance and blows oxygen gas from the top-blown lance to oxidize and remove phosphorus from molten iron.
The top blown lance has a plurality of peripheral holes arranged rotationally symmetrically with respect to the lance axis, and the jet straightness γ defined by the following equation (1) is set to 0.31 or more and 0.75 or less. A converter jet method characterized by.
γ = X _jet / X _linear ... (1)
Here, Xi represents the distance from the lance axis projection position on the surface corresponding to the bath surface under the condition i.
The subscript jet indicates the center position of the jet deflected by the interference.
The subscript liner represents a position on the extension of the central axis of the peripheral hole. Oxygen gas is blown from the top-blown lance to the molten iron in the converter, and a medium for dephosphorization containing CaO as the main component is supplied to the molten iron in the converter to oxidize and remove phosphorus from the molten iron. Therefore, when at least a part of the dephosphorization medium-melting material is sprayed and added from the top-blown lance toward the molten iron bath surface in the converter, the lap ratio λ of the medium-melting material defined by the following equation (2) is determined. , The converter blowing method according to claim 3, wherein the value is 0.19 or more.
λ = (total weight of the medial material projected into the fire point) / (total weight of the supplied medial material) ・ ・ ・ (2)

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