JP2007239082A - Method for oxidize-refining molten metal and top-blown lance for refining - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for oxidize-refining molten metal with which, the dynamic pressure in a top-blown jet can be adjusted during oxidize-refining the molten metal by blowing oxygen-contained gas from a top-blown lance and accordingly, the stirring power for giving to the molten metal can easily be increased, and in the same lance, various conditions can be dealt suitably. <P>SOLUTION: The jet of ultra-sonic speed gas is supplied toward the surface of the molten metal from the center hole 4 in a Laval nozzle-shape set at the center of the top-blown lance 1 and also, in the circumference of this jet, a fuel gas supplied from a fuel gas supplying nozzle 6 is burnt to form a flame surrounding zone, and from three holes or more of circumferential holes 5 set in the circumference of the above center hole, the oxygen-contained gas is supplied toward the surface of the molten metal to perform the refining. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a molten metal oxidative refining method performed by blowing an oxygen-containing gas from a top blowing lance toward a molten metal bath surface, and a refining top blowing lance used at that time.

  In the hot metal converter blowing, oxidation refining mainly for decarburization blowing is performed by top blowing oxygen or bottom blowing oxygen. Of these oxygens, the top blown oxygen is blown into the converter as a supersonic or subsonic oxygen jet from a divergent nozzle called a Laval nozzle installed at the tip of the top blow lance. A large stirring force is imparted to the hot metal by the top blowing oxygen. The end part of this Laval nozzle is ideally a curved line, but since it is easy to process, most of it has a conical shape with an extension angle of 2 to 8 °, and the throat part Or there are some which have some straight parts in an exit part.

  In this converter decarburization blowing, in recent years, the need for dephosphorization in the converter has decreased due to the development of hot metal pretreatment (referred to as “preliminary dephosphorization”) for the purpose of dephosphorization of hot metal. The required solvent is greatly reduced. As a result, the amount of slag produced during decarburization blowing, which has conventionally exceeded 50 kg per ton of molten steel produced (hereinafter referred to as “kg / t”), rapidly decreases. For example, preliminary dephosphorization of hot metal When the phosphorus concentration in the hot metal is reduced to 0.02% by mass or less, which is substantially equal to the phosphorus concentration in the steel product, the solvent required for dephosphorization in the decarburization blowing in the converter is 10 kg / The amount of generated slag can be reduced to about 25 kg / t or less.

  In the decarburization peak period (approximately C ≧ 0.6% by mass) from the initial stage to the middle stage of decarburization blowing, the decarburization reaction is controlled by oxygen supply. It is necessary to increase the feed rate (hereinafter referred to as “acid feed rate”). However, when high-speed blowing is aimed at, decarburization blowing with a small amount of generated slag causes significant iron scattering and dust generation due to the top-blown oxygen jet, leading to lower iron yield and unstable operation. . In other words, in the past, a large amount of slag present in the furnace played the role of a coating agent, but when the amount of slag was reduced, such as when pre-dephosphorized hot metal was used, the hot metal was affected by the oxygen jet. This causes inconveniences such as a decrease in the yield described above.

  Conventionally, in order to suppress such deterioration of the operating conditions, the number of holes in the top blowing lance is set to 4 holes or 5 holes to lower the acid feed rate per hole, that is, lower the dynamic pressure on the bath surface, In addition, non-interference and porous lances that prevent the oxygen jets from interfering with each other have been directed. In addition, in order to prevent the oxygen jet from interfering, the distance between the tip of the top blowing lance and the bath surface (“lance height”) is optimized at the same time as optimizing the hard surface of the top blowing lance shape such as the hole diameter and tilt angle of the Laval nozzle. Many measures have been proposed that adjust the operating conditions such as the acid delivery rate.

  For example, Patent Document 1 proposes a blowing method in which the shape of the top blowing lance is optimized, and the acid feed rate and the lance height are controlled within an appropriate range according to the shape of the nozzle hole. However, with such countermeasures, the trajectory and geometric shape of the oxygen jet ejected from the top blowing lance change greatly, so the oxygen concentration change in the oxygen jet and the location of the collision of the oxygen jet with the bath surface (Hereinafter referred to as “fire point”) causes an unnecessary increase in secondary combustion or a decrease in decarburization reaction efficiency.

  In addition, from the viewpoint that it is important to avoid interference between fire spots in order to prevent iron scattering and dust generation, Patent Document 2 discloses that the geometric overlap area ratio of fire spots is 30% or less. Thus, a method has been proposed in which nozzle holes are arranged in the circumferential direction so that a hot spot is efficiently formed on the bath surface while avoiding interference. However, with this measure, when the acid feed rate is significantly increased, a limit naturally occurs, and it is impossible to cope with a significant change in the acid feed rate.

On the other hand, in the low carbon region (approximately C <0.6% by mass) at the end of decarburization blowing, the supplied oxygen is consumed not only for decarburization but also for iron oxidation. In order to increase the decarbonation efficiency, the acid feed rate is reduced. In this case, in order to maintain the efficiency of supplying oxygen to the iron bath, the lance height is reduced to increase the oxygen collision pressure on the iron bath, that is, the dynamic pressure of the oxygen jet, thereby ensuring the stirring of the bath. Laval nozzles are usually designed to be capable of optimal decarburization in the middle of decarburization during the middle of blowing, and to suppress the scattering of metal and dust, so high flow and low dynamic pressure type nozzles are generally used. is there. Therefore, at the end of blowing, although high dynamic pressure and high agitation force are required, the oxygen jet is unnecessarily attenuated as the acid feed rate decreases, and the T. As seen in the increase of Fe, the decarburization reaction efficiency is reduced. The lance height is also reduced to obtain a high dynamic pressure, but due to the harmful effects of radiant heat, there is a limit to reducing the lance height, and there is a limit to stabilizing the operation at the end of blowing. . T. Fe is the total iron content of all iron oxides (FeO and Fe ₂ O ₃ ) in the slag.

  In this way, when operating with the same lance and changing the acid feed rate between the middle and final stages of blowing, the method of ensuring the dynamic pressure at the final stage of blowing and the middle stage of blowing The impact on blowing in the high-carbon region remains unclear. In addition, with regard to the stirring power of the molten metal, stiffening by bottom blowing gas is also being performed, but problems remain in optimization due to problems such as variable flow rate and nozzle life.

  Also, in the pretreatment blowing using a converter like the hot metal predephosphorization treatment in the converter, the decarburization reaction is suppressed and the dephosphorization reaction is made more efficient by promoting iron oxidation by lowering the dynamic pressure. However, when a large amount of iron scrap is to be melted in this preliminary dephosphorization process, the stirring force by the bottom blowing gas is not sufficient, and the stirring force by the top-blowing oxygen jet must be increased. In this case as well, the control of the dynamic pressure of the top blowing oxygen is an important issue.

By the way, as a technique for increasing the dynamic pressure of an oxygen jet, a technique in which a Laval nozzle and a burner are used together is conventionally known. For example, Patent Document 3 discloses a gas jet in a range from a lance outlet to a molten metal bath surface. A technique is disclosed in which a flame is surrounded by a flame (referred to as a “flame envelope”) and a jet of gas is blown into a molten metal bath surface at a high speed. However, in cases where a high acid feed rate is required, such as in hot metal converter blowing, an upper blowing lance having a plurality of nozzle holes was used to suppress an extreme increase in the oxygen jet dynamic pressure. Fuel feeding is common, and if the technique of Patent Document 3 is applied in such refining with a high flow rate, fuel supply piping for forming a flame envelope around all nozzle holes And an extremely complicated top blowing lance structure. In addition, since a water cooling structure is also required in a high temperature environment such as in a converter, it is practically difficult to provide such a complicated structure in the upper blowing lance, and a simple structure is desired.
JP-A-6-228624 JP-A-6-57320 JP-A-10-263384

  As mentioned above, in converter blowing, the dynamic pressure of the top blown oxygen jet can be adjusted even when the acid feed rate is reduced, and it is suitable for various situations using the same top blow lance. Despite the desire for a blowing method that can be dealt with accurately and an upper blowing lance used therefor, no effective means have been proposed.

  The present invention has been made in view of such circumstances, and it is possible to adjust the dynamic pressure of the top blowing jet when oxidizing and refining molten metal such as hot metal or molten steel by blowing an oxygen-containing gas from the top blowing lance. Thus, it is possible to easily increase the stirring force applied to the molten metal, and to provide a method for oxidizing and refining molten metal that can appropriately cope with various situations even with the same lance. In addition, an object is to provide an upper blowing lance for refining used at that time.

  The present inventors have conducted intensive research to solve the above problems. As a result, when refining using an upper blowing lance having a plurality of nozzle holes, a flame surrounding zone is formed around the supersonic jet ejected from the central hole of the upper blowing lance, and arranged around the central hole. It has been found that if oxygen-containing gas is supplied from a plurality of nozzle holes and refined, the decrease in the dynamic pressure of the supersonic jet from the central hole is suppressed, and the stirring force due to the top blowing acid can be increased. Obtained.

  The present invention has been made on the basis of the above knowledge, and the method for oxidizing and refining molten metal according to the first invention is characterized in that a supersonic gas jet flows from a central hole in the shape of a Laval nozzle installed at the center of an upper blowing lance Is supplied to the molten metal bath surface by forming a flame encircling zone around the jet, and an oxygen-containing gas is supplied from three or more peripheral holes installed around the central hole. It is characterized by supplying toward the surface.

  The method for oxidizing and refining molten metal according to the second invention is characterized in that, in the first invention, an oxygen-containing gas is supplied from the center hole.

  According to a third aspect of the present invention, in the first or second invention, the peripheral hole is a nozzle having a Laval nozzle shape, and the total flow rate of the oxygen-containing gas supplied from the peripheral hole is the central hole. It is characterized in that it is more than twice the amount of gas supplied from the factory.

  A molten metal oxidative refining method according to a fourth aspect of the present invention is characterized in that, in any of the first to third aspects, the molten metal is molten iron.

  The molten metal oxidative refining method according to the fifth invention is characterized in that, in the fourth invention, the carbon concentration in the molten iron is 0.6% by mass or less.

  A refining top blowing lance according to a sixth aspect of the present invention comprises a center hole in the shape of a Laval nozzle for supplying a supersonic gas jet, and a fuel gas supply nozzle for forming a flame surrounding zone around the jet And three or more peripheral holes are provided around the central hole.

  According to the present invention, since the flame enveloping zone is formed around the jet flow ejected from the central hole, that is, the jet, the amount of the atmospheric gas involved in the jet is reduced, and the attenuation of the jet can be suppressed. By suppressing jet attenuation, that is, by suppressing the decrease in jet dynamic pressure, the stirring power of the molten metal by the top blowing gas increases. As a result, the operation efficiency is improved by reducing the degree of slag oxidation. Stabilization and the like are achieved, and an extremely useful industrial effect is brought about.

  Hereinafter, the present invention will be specifically described.

  TECHNICAL FIELD The present invention relates to a technique for oxidizing and refining molten metal by spraying oxygen-containing gas such as oxygen, air, oxygen-enriched air, Ar-oxygen mixed gas from a top blowing lance toward molten metal such as hot metal or molten steel. It is. As an example of this oxidation refining, hot metal decarburization blown in a converter at atmospheric pressure is taken up, the dynamic pressure of the oxygen jet can be adjusted, and even if the same top blowing lance is used, it is suitable depending on the situation. In order to develop a refining method that enables accurate decarburization blowing, the damping behavior of the top blowing acid jet was investigated and analyzed in detail. Then, the influence of the number of nozzle holes and the ambient temperature on the dynamic pressure attenuation of the oxygen jet injected from the Laval nozzle, that is, the influence of the flame envelope was clarified. Here, as a means for adjusting the dynamic pressure of the oxygen jet, a method of forming a flame surrounding zone disclosed in Patent Document 3 around the oxygen jet was used.

  As a result of measuring the flow velocity of the oxygen jet, in the single hole nozzle, the density of the ambient gas around the jet is reduced by forming a flame surrounding zone near the nozzle exit, so the entrainment of the ambient gas in the jet is greatly increased. As a result, it was quantitatively grasped that the flow velocity of the oxygen jet was increased and the dynamic pressure on the bath surface was remarkably increased as compared with the case where no flame envelope was formed. However, in the case of a multi-hole nozzle, even if one large flame envelope is formed so as to surround a plurality of oxygen jets by the multi-hole nozzle, the entrainment of atmospheric gas cannot be sufficiently suppressed, and the dynamic pressure It turned out that the effect which raises is hardly acquired. From this result, it was found that in order to suppress the attenuation of the oxygen jet of the multi-hole nozzle, it is necessary to form a flame band in each oxygen jet.

  However, in the case of a multi-hole nozzle, it is not necessary to suppress attenuation for all oxygen jets in order to increase the stirring force of the hot metal by the oxygen jet. It was found that the stirring force increased. By doing so, it was also found that highly efficient oxygen supply was achieved.

  Therefore, first, the effect of the flame surrounding zone on the porous nozzle was verified by a blowing experiment (100 kg scale) with a small lance. A central nozzle in the shape of a Laval nozzle was installed in the center of a small lance, and an oxygen jet was ejected at supersonic speed. At this time, the ejection Mach number was in the range of 1.5 to 2.0. Then, a flame envelope was formed around the oxygen jet by burning propane gas. As a result, it was confirmed from the measurement result of the dynamic pressure by the water-cooled Pitot tube that the dynamic pressure was remarkably increased when the flame envelope was formed compared to the case where the flame envelope was not formed. In this case, there is no particular limitation on the method for forming the flame enveloping zone, and a nozzle for supplying propane gas and its combustion oxygen around the center hole may be installed on the circumference, and a laval nozzle in the center hole It is also possible to supply propane gas from the inner wall. When propane gas is supplied from the inner wall of the Laval nozzle, the fuel gas supply mechanism is facilitated.

  This small lance was further provided with three peripheral holes with the center hole as a symmetry point. Here, the number of surrounding holes is required to be three or more in order to ensure symmetry on the bath surface and reduce bath surface vibration. Using this top blowing lance, decarburization blowing experiments were conducted. As a comparison object, an experiment was also performed under the condition that no flame siege was formed. The lance height was the same for all levels, but was set so that the flame did not reach the bath surface in order to ensure the stability of the flame.

  As a result of the experiment, the iron oxide concentration in the slag after blowing (carbon concentration = 0.05% by mass) was halved from about 40% by mass to 20% by mass due to the formation of the flame envelope. Moreover, although the experiment which formed the flame surrounding zone in all the surrounding holes was also conducted, the iron oxide density | concentration in slag was about 20 mass%, and there was no big difference. However, in the experiment in which a flame band was formed in all the surrounding holes, the fluctuation of the bath surface during blowing was extremely large, and the scattering of iron and dust was remarkably increased. Moreover, due to the complicated structure of the lance nozzle, an increase in the cooling water temperature due to insufficient cooling was observed.

  As described above, as a result of the small experiment, it was found that the stirring force can be increased and the oxidation degree of the slag can be reduced by forming the flame surrounding zone in the jet part of the oxygen jet. Moreover, in the case of a multi-hole nozzle, it was found that a sufficient stirring effect can be obtained without causing severe iron scattering by forming a flame envelope only in the oxygen jet in the center hole, not in all nozzle holes. In addition, as a result of performing the same experiment while increasing the lance height, a decrease in the decarbonation efficiency was observed when the flame encircling zone was not formed, but it was removed by forming the flame encircling zone in the center hole. It was possible to maintain high carbon dioxide efficiency. It is considered that this is because the stirring in the vicinity of the bath surface is strengthened, and the oxygen jet of the peripheral holes is accompanied, and the reach of all the oxygen transported oxygen including the peripheral holes is maintained at a high level.

  The refining top blow lance according to the present invention is based on these test results. Hereinafter, an example of the refining top blow lance according to the present invention in which a flame surrounding band is formed around the oxygen jet in the center hole. Will be described.

  First, the refining top blow lance according to the present invention in which the fuel gas supply nozzle and the combustion oxygen supply nozzle are arranged around the center hole will be described. 1 and 2 are schematic views of a refining top blow lance according to the present invention in which a fuel gas supply nozzle and a combustion oxygen supply nozzle are arranged around a central hole. FIG. 1 is a schematic view of a refining top blow lance according to the present invention as viewed from the front end side, and FIG. 2 is a schematic cross-sectional view of the X-X ′ cross section of FIG. 1.

  As shown in FIGS. 1 and 2, an upper blow lance 1 for refining according to the present invention includes 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 lance body 2 is composed of four types of concentric steel pipes consisting of an outer pipe 9, an intermediate pipe 10, an inner pipe 11, and an innermost pipe 12, that is, a quadruple pipe, and a lance nozzle 3 made of copper. The center hole 4 that is directed vertically downward is provided at the center, and three peripheral holes 5 are provided symmetrically around the center hole 4 with the center hole 4 as a symmetric point. It is essential that the center hole 4 has a Laval nozzle shape, while the peripheral hole 5 may have a straight shape. However, from the viewpoint of improving oxygen efficiency, it is preferable to have a Laval nozzle shape as shown in FIG. Further, from the viewpoint of preventing the vibration of the bath surface, the total flow rate of the oxygen-containing gas supplied from the peripheral hole 5 is preferably at least twice as much as the amount of oxygen-containing gas supplied from the central hole 4. It is preferable to determine the sizes of the central hole 4 and the peripheral hole 5 so that the total area of the diameters (minimum part diameter) is at least twice the area of the central hole 4 diameter (minimum part diameter).

  Around the center hole 4, the fuel gas supply nozzles 6 and the combustion oxygen supply nozzles 8 are alternately arranged on the same circumference centered on the axis of the lance nozzle 3. The fuel gas supply nozzle 6 is a nozzle that supplies fuel gas such as propane gas, natural gas, hydrogen-containing gas, and CO-containing gas around the center hole 4, and the combustion oxygen supply nozzle 8 is the fuel gas supply nozzle 6. It is a nozzle which supplies the oxygen containing gas for burning the fuel gas supplied by this. The fuel gas supplied from the fuel gas supply nozzle 6 is burned by the oxygen-containing gas supplied from the combustion oxygen supply nozzle 8 to form a flame envelope around the jet ejected from the center hole 4. In FIG. 1, the fuel gas supply nozzles 6 and the combustion oxygen supply nozzles 8 are alternately arranged on the same circumference, but the fuel gas supply nozzles 6 are arranged in the vicinity of the center hole 4 and burned outside thereof. An oxygen supply nozzle 8 may be arranged. In FIG. 1, there are six fuel gas supply nozzles 6 and six oxygen supply nozzles 8 for combustion, but this is for the convenience of drawing, and there is no problem even if more nozzles are arranged. . The fuel gas supply nozzle 6 and the combustion oxygen supply nozzle 8 are straight nozzles without any problem.

  The gap between the outer tube 9 and the middle tube 10 and the gap between the middle tube 10 and the inner tube 11 serve as a cooling water flow path for cooling the upper blowing lance 1. The cooling water supplied from a water supply joint (not shown) provided in the pipe passes through the gap between the intermediate 10 and the inner pipe 11 to reach the lance nozzle 3 and is reversed at the lance nozzle 3 to be reversed to the outer pipe. The water is discharged from a drainage joint (not shown) provided in the upper part of the upper blowing lance 1 through a gap between the intermediate pipe 10 and the middle pipe 10. In this case, the water supply / drainage path may be reversed.

  The gap between the inner pipe 11 and the innermost pipe 12 is a fuel gas supply flow path, and the fuel gas supplied from the upper end of the upper blowing lance 1 to the gap between the inner pipe 11 and the innermost pipe 12 is The gas passes through the gap between the inner pipe 11 and the innermost pipe 12 and is ejected from the fuel gas supply nozzle 6. Further, the inside of the innermost pipe 12 serves as a supply flow path for the oxygen-containing gas, and the oxygen-containing gas supplied from the upper end of the upper blowing lance 1 to the inside of the innermost pipe 12 flows into the innermost pipe 12. Through the center hole 4, the peripheral hole 5 and the combustion oxygen supply nozzle 8. In the figure, the oxygen-containing gas supplied from the combustion oxygen supply nozzle 8 and the oxygen-containing gas supplied from the center hole 4 and the peripheral hole 5 have the same path, but the lance body 2 has a five-pipe structure. Both may be made independent.

  Since the top blowing lance 1 according to the present invention is used for refining with a high acid feed rate, it is a perforated nozzle having a central hole 4 and a peripheral hole 5, and it is necessary to install at least three peripheral holes 5. However, in order to suppress the scattering of iron and dust during refining, it is necessary to reduce it to an appropriate dynamic pressure on the bath surface. It is preferable to have 6 holes or more. Here, if the inclination angle (θ) of the peripheral hole 5 is too large, the jet of the peripheral hole 5 is too far from the jet of the central hole 4, and it becomes difficult to obtain the effect of increasing the dynamic pressure. In order to prevent this, the inclination angle (θ) of the peripheral hole 5 is preferably 20 ° or less. When the flame envelope is formed around the oxygen jet from the central hole 4, the dynamic pressure of the oxygen jet from the peripheral hole 5 is equal to or slightly higher than that when the flame envelope is not formed. I have confirmed.

  Next, the refining top blow lance according to the present invention in which the fuel gas supply nozzle that opens to the inner wall of the center hole is arranged will be described. FIG. 3 is a schematic side cross-sectional view of a refining top blowing lance according to the present invention in which a fuel gas supply nozzle that opens to the inner wall of the center hole is arranged. This upper blowing lance is denoted by reference numeral 1A in order to be distinguished from the upper blowing lance 1 described above.

  As shown in FIG. 3, the upper blowing lance 1 </ b> A according to the present invention is provided with a fuel gas supply nozzle 7 that opens on the side wall of the center hole 4. A plurality of fuel gas supply nozzles 7 are arranged concentrically on the side wall of the center hole 4. Since the fuel gas supplied from the fuel gas supply nozzle 7 is burned by the oxygen-containing gas supplied from the center hole 4, the combustion oxygen supply nozzle disposed in the above-described upper blowing lance 1 is provided in the upper blowing lance 1 </ b> A. 8 is not required and is not installed. The other structure of the upper blowing lance 1A is the same as that of the upper blowing lance 1 shown in FIGS. 1 and 2, and the same parts are denoted by the same reference numerals and the description thereof is omitted.

  That is, in the upper blow lance 1A, the fuel gas supplied to the gap between the inner pipe 11 and the innermost pipe 12 passes through the gap between the inner pipe 11 and the innermost pipe 12 and passes from the fuel gas supply nozzle 7 to the center hole 4. Is spouted into the inside. The fuel gas ejected into the center hole 4 is combusted by the oxygen-containing gas supplied from the center hole 4 to form a flame surrounding zone around the oxygen jet ejected from the center hole 4. In the case of such a lance structure, the structure is simple, and it becomes easy to use liquid fuel as the fuel.

  Using the top blow lance 1, 1A according to the present invention configured as described above, oxygen, air, oxygen-enriched air, Ar-oxygen mixed gas, and the like are directed toward a molten metal bath surface such as hot metal or molten steel. Oxygen-containing gas is blown to smelt the molten metal. Specific examples of oxidative refining include hot metal decarburization blowing, hot metal preliminary dephosphorization treatment, iron scrap melting treatment using the combustion heat of carbon materials such as coke, and smelting reduction of Cr ore in the presence of hot metal. Processing. That is, if it is the oxidation refining which CO gas produces | generates as a reaction product, it can refine efficiently using the top blowing lances 1 and 1A which concern on this invention.

  By using the top blowing lances 1, 1 </ b> A according to the present invention, a fuel gas is supplied from the fuel gas supply nozzle 6 or the fuel gas supply nozzle 7 to form a flame envelope around the oxygen jet in the center hole 4. When the temperature around the oxygen jet ejected from the hole 4 becomes high, and the density of the atmospheric gas around the oxygen jet decreases, the amount of atmospheric gas entrained in the oxygen jet decreases, in other words, the atmosphere Attenuation of the oxygen jet in the central hole 4 by the gas is suppressed, and the dynamic pressure of the oxygen jet on the bath surface can be increased as compared with the case where no flame enclosure is formed. As the dynamic pressure of the oxygen jet increases, the stirring power of the molten metal by the top blowing gas also increases.

  Such refining that can particularly effectively utilize the effect of the top blowing lances 1 and 1A according to the present invention includes hot metal decarburization blowing in a converter, and the following effects can be obtained.

  That is, from the initial stage to the middle stage (approximately C ≧ 0.6% by mass), the center hole 4 and the peripheral hole 5 are designed as low dynamic pressure, that is, soft blow in order to achieve low dynamic pressure and high acid feed operation. Therefore, when a flame enveloping zone is formed around the oxygen jet in the center hole 4, the fluctuation of the bath surface becomes large, so that fine spitting or dust can be reduced. Although large-diameter iron scattering increases, the amount of generation depends on the amount of acid delivered, and in the method of the present invention, oxygen supply from the peripheral hole 5 is the main, so the degree of increase can be minimized. Moreover, since the stirring force by top blowing oxygen increases, even if there is no bottom blowing stirring, blowing can be performed without any problem. Further, even when the height of the lance is increased for the purpose of reducing adhesion of the metal to the top blowing lances 1 and 1A, a high decarbonation efficiency can be obtained and the effect of stabilizing the operation is remarkable.

  On the other hand, in the final stage of blowing (approximately C <0.6% by mass) in which the decarbonation efficiency decreases, the purpose of increasing the decarbonation efficiency is to form a flame envelope around the oxygen jet in the center hole 4. Even when the acid feed rate is reduced by this, the dynamic pressure of the oxygen jet is high, the stirring power of the molten metal is maintained at a high level, and iron oxidation is suppressed. That is, T. in the slag. Fe concentration can be reduced and iron yield can be improved. In addition, with respect to the oxygen jet from the peripheral hole 5 at which the dynamic pressure decreases at the same time, it is possible to suppress a decrease in oxygen efficiency due to the jet suction effect toward the center by the central hole having a high dynamic pressure. In addition, when reducing Mn ore in hot metal decarburization blowing, it is possible to dramatically improve the Mn yield. On the other hand, when the flame envelope is not formed, the decrease in the decarburization rate and the oxidation of iron are promoted along with the decrease in the acid feeding rate, and the T and Fe concentrations in the slag are remarkably increased. As described above, the effect is particularly remarkable by using the top blowing lances 1 and 1A according to the present invention at the end of blowing. Moreover, these effects are remarkable when the amount of slag in the furnace is 50 kg / t or less, and are particularly remarkable when the amount of slag is 20 kg / t or less.

  In addition, in the hot metal preliminary dephosphorization treatment using the top blowing lance 1, 1A of the present invention, the stirring pressure of the hot metal is promoted by increasing the dynamic pressure of the oxygen jet, and the melting of the iron scrap is promoted. A large amount of iron scrap can be melted.

  As described above, according to the present invention, since the flame envelope is formed around the oxygen jet ejected from the center hole 4, the dynamic pressure of the oxygen jet increases, and as the dynamic pressure of the oxygen jet increases, The stirring force by the top blowing gas is increased, and for example, effects such as improvement of iron yield and promotion of smelting reduction of Mn ore can be obtained. Further, the necessity of bottom blowing stirring is eliminated, and dust can be reduced. Furthermore, since the dynamic pressure of the oxygen jet is high, the lance height can be increased, and adhesion of metal to the top blowing lance can be reduced. Furthermore, the effect of promoting the melting of iron scrap by controlling the dynamic pressure during hot metal pretreatment such as dephosphorization blowing can also be obtained. These effects spread to the surrounding holes, and the maximum effect can be obtained with a simple nozzle structure.

Examples of the present invention are shown below together with comparative examples. About 5 tons of hot metal was charged into an upper bottom blown combined blowing smelting converter having a capacity of 5 tons, oxygen blown up, and stirring gas blown into the bottom, and the upper blow lance shown in FIG. 3 was used. Mainly decarburization blowing. The hot metal used had a silicon concentration of 0.05% by mass or less and a phosphorus concentration of 0.007 to 0.018% by mass. Lime-based flux is added into the converter to generate slag. The basicity of slag (CaO / SiO ₂ ) determined from the analysis value of slag was about 2.6 to 3.9 in mass% ratio, and the amount of slag in the furnace was determined by the CaO balance. From the tuyere installed at the bottom of the converter furnace, Ar or nitrogen was blown in at about 0.5 Nm ³ per minute for the purpose of stirring the molten metal.

The acid feeding was performed by a 4-hole top lance mainly having one central hole and three peripheral holes (inclination angle θ: 10 °), and a lance having a part of five peripheral holes was also used. Oxygen-flow-rate of toward its peak from decarburization early 1200 Nm ³ / hr, the blow end and 600 Nm ³ / hr, the oxygen supply ratio of the surrounding hole and center hole was kept constant during the blowing. In addition, the blowing pattern such as the lance height was made the same as much as possible in any operation.

  The flame envelope was formed at the outlet of the center hole by mixing propane gas from the inner wall of the Laval nozzle in the center hole and burning the propane gas. The furnace body vibration increased when the flame reached the bath surface. The end goal of decarburization blowing was the time when the carbon concentration in the molten steel reached 0.05 mass%, and the ultimate temperature was 1650 ° C. Moreover, the slag at the time of completion | finish of blowing was extract | collected, and T.Fe density | concentration in slag was evaluated. Mn ore was added at 5 kg / t during blowing, and the Mn yield at the end of blowing was also evaluated. Table 1 shows the operation conditions and operation results of the inventive examples and the comparative examples.

  As shown in Table 1, in the examples of the present invention, the T.V. It was confirmed that the Fe concentration was low and the iron yield was improved. In the present invention example, the T.I. It was confirmed that the reduction yield of Mn ore was improved because the Fe concentration was low. In Comparative Example 3 in which the flame surrounding zone was formed in both the center hole and the surrounding hole, the fluctuation of the bath surface during blowing was extremely large, and the scattering of iron and dust was remarkably increased. On the other hand, in the example of the present invention, the scattering of iron and dust was stable at a low level.

It is the schematic which shows an example of the top blowing lance which concerns on this invention. It is a schematic sectional drawing of the X-X 'cross section of FIG. It is a schematic side sectional view showing another example of the top blowing lance according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Top blowing lance 1A Top blowing lance 2 Lance main body 3 Lance nozzle 4 Center hole 5 Perimeter hole 6 Fuel gas supply nozzle 7 Fuel gas supply nozzle 8 Combustion oxygen supply nozzle 9 Outer pipe 10 Middle pipe 11 Inner pipe 12 Innermost pipe

Claims (6)

  A supersonic gas jet is supplied from a central hole in the shape of a Laval nozzle installed at the center of the upper blowing lance toward a molten metal bath surface by forming a flame envelope around the jet, and the central hole A method for oxidizing and refining molten metal, characterized in that an oxygen-containing gas is supplied toward the molten metal bath surface from three or more peripheral holes installed around the metal.   The method for oxidizing and refining molten metal according to claim 1, wherein an oxygen-containing gas is supplied from the center hole.   The peripheral hole is a nozzle having a Laval nozzle shape, and the total flow rate of the oxygen-containing gas supplied from the peripheral hole is at least twice the amount of gas supplied from the central hole. 3. The method for oxidizing and refining molten metal as described in 2.   The method for oxidizing and refining molten metal according to any one of claims 1 to 3, wherein the molten metal is molten iron.   The method for oxidizing and refining molten metal according to claim 4, wherein the carbon concentration in the molten iron is 0.6% by mass or less.   It has a Laval nozzle-shaped central hole for supplying a supersonic gas jet, a fuel gas supply nozzle for forming a flame surrounding zone around the jet, and has three or more peripheral holes. An upper blow lance for refining, which is provided around the center hole.

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