JP2006328432A - Blowing method for converter and top-blowing lance for converter blowing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a blowing method for a converter, which can easily adjust a dynamic pressure of a top-blowing oxygen jet, when oxidation-refining molten pig iron or molten steel by spouting an oxygen-containing gas from a top-blowing lance, and adequately coping with various situations occurring even in the same lance. <P>SOLUTION: The top-blowing lance 1 for spouting an oxygen-containing gas onto the molten pig iron or molten steel to oxidation-refine it comprises: one or more main holes 4 with a shape of a Laval nozzle formed in the tip; and a plurality of auxiliary holes 8 concentrically formed around the main holes so that they can have an inclination angle θ<SB>f</SB>equal to a sum of an inclination angle θ<SB>s</SB>of the main hole and 10° or less. The blowing method includes supplying the oxygen-containing gas toward the molten pig iron or molten steel through the auxiliary holes to form a high-temperature region around the oxygen-containing gas which has been spouted from the main holes, due to secondary combustion. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a converter blowing method for performing oxygen refining of hot metal or molten steel by supplying an oxygen-containing gas to the molten iron or molten steel charged in the converter, and an upper blowing for converter blowing used at that time. It is about Lance.

  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 blowing oxygen is blown into the converter as a supersonic or subsonic jet from a top blowing lance having a divergent nozzle called a Laval nozzle as a main hole at its tip. 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 Alternatively, there are some which have some straight portions at the outlet.

  In this decarburization blown converter, 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 dephosphorizing hot metal. The solvent required in the furnace has been greatly reduced. As a result, the amount of slag produced during decarburization blowing, which conventionally exceeded 50 kg (hereinafter referred to as “kg / t”) per ton of molten steel produced, decreased rapidly. For example, if the hot metal phosphorus concentration is reduced to 0.02% by mass or less, which is substantially equal to the phosphorus concentration of the steel product, by the preliminary dephosphorization treatment of the hot metal, The necessary solvent is 10 kg / t or less, and the amount of slag to be generated can be reduced to approximately 25 kg / t or less.

  In the decarburization peak period from the initial stage to the middle stage of decarburization blowing, the decarburization reaction is controlled by oxygen supply, so when aiming at high-speed blowing, the oxygen supply rate (hereinafter referred to as “acid feed rate”) Need to be improved. However, in the decarburization blowing with a small amount of generated slag, the scattering of iron and the generation of dust due to the top-blown oxygen jet become significant, resulting in a decrease in yield and unstable operation. In other words, in the past, a large amount of slag present in the furnace played the role of a cover, but when the amount of slag was reduced, such as when pre-phosphorized hot metal was used, the hot metal affected the oxygen jet. Inconveniences such as a reduction in the yield described above occur directly.

  Conventionally, in order to suppress such deterioration of operating conditions, the number of main holes of the top blowing lance is set to 4 holes or 5 holes to reduce the acid feed rate per hole, that is, the dynamic pressure on the bath surface, and Non-interfering, 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 hard surface of the top blowing lance shape such as the hole diameter and tilt angle of the main hole is optimized, and at the same time, the distance between the tip of the top blowing lance and the bath surface (“lance height Many measures have been proposed to 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 main 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 the hot spots in order to prevent iron scattering and dust generation, Patent Document 2 discloses that the geometric overlap area ratio of the hot spots is 30% or less. In this way, a method has been proposed in which main 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 oxygen supply efficiency to the iron bath, the lance height is reduced to increase the oxygen collision pressure to the iron bath, that is, the dynamic pressure of the oxygen jet. The Laval nozzle as the main hole is usually designed to obtain an optimum jet during the decarburization peak stage of the middle stage of blowing, so if the acid feed rate is low at the end of the blowing stage, it will increase from the appropriate flow rate of the Laval nozzle. Moves downward. Therefore, the effect of the Laval nozzle cannot be obtained, the oxygen jet is attenuated unnecessarily, and the T.V. As seen in the increase of Fe, the decarburization reaction efficiency is reduced. When the jet at the decarburization peak is oriented toward low dynamic pressure, the reduction of dynamic pressure at the end of blowing is even more remarkable. In addition, due to harmful effects such as 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.

  Thus, 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 high value in the middle stage of blowing The impact on blowing in the carbon region remains unclear. In addition, in the pretreatment blowing using a converter such as the preliminary dephosphorization of hot metal in the converter, unnecessary decarburization reaction is suppressed and high efficiency of the dephosphorization reaction is achieved by promoting iron oxidation by lowering the dynamic pressure. However, when a large amount of iron scrap is melted in the hot metal preliminary dephosphorization process in the converter, it is required to increase the stirring force by the top blown oxygen jet. Pressure control 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 that a gas jet is in a range from a lance outlet to a bath surface. A method is disclosed in which a flame is surrounded by a flame and a jet of gas is blown into the bath surface at high speed. However, in the method of Patent Document 3, a high-power burner that allows the flame to reach the bath surface is indispensable, and it is practically complicated to install a burner in a high-temperature environment such as in a converter, which is practically complicated. There are many difficult points, and the influence of the flame on refining is unclear.
JP-A-6-228624 JP-A-6-57320 JP-A-10-263384

  As described above, in the converter blowing, the dynamic pressure control of the top blown oxygen jet is possible, so that even in the same lance, the blowing method and the top blow lance can be appropriately dealt with in various situations. However, no effective means have been proposed at present.

  The present invention has been made in view of such circumstances, and when the oxygen-containing gas is blown from the top blowing lance and the hot metal or molten steel is oxidized and refined, the dynamic pressure of the top blowing jet can be easily adjusted. An object of the present invention is to provide a converter blowing method that can appropriately cope with various situations even with a lance, and to provide an upper blowing lance for converter blowing used at that time. .

  The present inventors have conducted intensive research to solve the above problems. As a result, in the top blowing lance, a sub nozzle (referred to as “sub hole”) is arranged around the main hole of the Laval nozzle shape for injecting an oxygen jet, oxygen is supplied from the sub hole, and the main hole is injected. By forming a high temperature zone by secondary combustion of the atmospheric gas so as to surround the oxygen jet around the oxygen jet, the attenuation of the oxygen jet injected from the main hole is remarkably reduced, and the dynamic pressure of the oxygen jet is reduced. The knowledge that it can be adjusted easily was obtained.

  The present invention has been made on the basis of the above knowledge, and the converter blowing method according to the first invention is based on an upper blowing lance in which one or more Laval nozzle-shaped main holes are installed at the tip thereof. Alternatively, when oxygen refining is performed by blowing an oxygen-containing gas toward the molten steel, a plurality of sub-holes having an inclination angle equal to or less than a value obtained by adding 10 ° to the inclination angle of the main hole are arranged around the main hole, An oxygen-containing gas is supplied from the sub-hole, and a high-temperature zone by secondary combustion is formed around the oxygen-containing gas injected from the main hole.

  The converter blowing method according to the second invention is characterized in that, in the first invention, the tilt angle of the auxiliary hole is not more than a value obtained by adding 5 ° to the tilt angle of the main hole.

  A converter blowing method according to a third aspect of the present invention is characterized in that, in the first or second aspect, six or more auxiliary holes are arranged.

  In the converter blowing method according to the fourth aspect of the present invention, in any one of the first to third aspects, the supply flow rate of the oxygen-containing gas from the sub-hole is 20% of the supply flow rate of the oxygen-containing gas from the main hole. % Or less.

  According to a fifth aspect of the present invention, there is provided a converter blowing method according to any one of the first to fourth aspects, wherein the supply amount of the oxygen-containing gas is independently adjusted between the main hole and the sub hole. It is a feature.

  A converter blowing method according to a sixth aspect of the present invention is characterized in that, in any one of the first to fifth aspects, the oxidative refining is a preliminary dephosphorization treatment of hot metal.

  According to a seventh aspect of the present invention, there is provided a converter blowing method according to any one of the first to fifth aspects, wherein the oxidative refining is decarburization blowing of hot metal that has been pretreated, and the formation in the decarburization blowing. The slag amount is 50 kg / t or less.

  The top blowing lance for converter blowing according to the eighth aspect of the invention is provided with one or more main nozzles in the shape of a Laval nozzle at its tip, and is used for oxidizing refining by blowing an oxygen-containing gas toward hot metal or molten steel. It is an upper blowing lance for furnace blowing, and a plurality of sub-holes having an inclination angle equal to or less than a value obtained by adding 10 ° to the inclination angle of the main hole are arranged concentrically around the main hole. It is a feature.

  The top blowing lance for converter blowing according to the ninth invention is characterized in that, in the eighth invention, the inclination angle of the auxiliary hole is not more than a value obtained by adding 5 ° to the inclination angle of the main hole. is there.

  The top blowing lance for converter blowing according to the tenth invention is characterized in that, in the eighth or ninth invention, six or more auxiliary holes are arranged.

  According to the present invention, when oxygen-containing gas is sprayed from the top blowing lance toward hot metal or molten steel to oxidize and refine the molten metal or molten steel, the oxygen-containing gas is surrounded around the oxygen-containing gas sprayed from the main hole in the shape of a Laval nozzle. Since the high temperature zone by secondary combustion is formed so as to surround the atmosphere, the ambient temperature around the oxygen jet becomes high, the density of the ambient gas around the oxygen jet decreases, and as a result, the amount of ambient gas trapped in the oxygen jet Is reduced, the attenuation of the oxygen jet due to the entrainment of the atmospheric gas is suppressed, and the dynamic pressure of the oxygen jet can be increased. This makes it possible to perform blowing with an adjusted dynamic pressure even if the acid feed rate is changed, improving the iron yield in oxygen blowing and stabilizing the operation during high-speed blowing, which is industrially beneficial. Effect.

  Hereinafter, the present invention will be specifically described.

  The present invention relates to a technology for oxidizing and refining hot metal or molten steel by blowing an oxygen-containing gas such as oxygen, air, oxygen-enriched air, or an Ar-oxygen mixed gas from a top blowing lance toward hot metal or molten steel. As an example of this oxidative refining, the hot metal decarburization blowing performed in the converter is taken up, and even if the same top lance is used, the dynamic pressure of the oxygen jet should be able to be accurately decarburized depending on the situation. In order to develop a method that can easily adjust the flow rate, the damping behavior of the top-blowing acid jet was investigated and analyzed in detail, and the nozzle shape and atmosphere affecting the dynamic pressure damping of the oxygen jet injected from the Laval nozzle Clarified the effect of temperature.

  As a result of measuring the flow velocity of the oxygen jet, the density of the ambient gas around the jet decreases in a high-temperature atmosphere, so the entrainment of the ambient gas in the jet is greatly suppressed, resulting in an increase in the flow velocity of the oxygen jet. It was quantitatively understood that the dynamic pressure of the jet increased significantly. In other words, as a method for increasing the dynamic pressure of the oxygen jet on the bath surface, it is not indispensable to generate a flame with a burner as disclosed in Patent Document 3 described above, but by increasing the temperature of the atmospheric gas, the oxygen jet The knowledge that the dynamic pressure of can be increased was obtained.

Therefore, the present inventors installed a sub-hole around the main hole as a method for increasing the temperature of the oxygen jet (also referred to as “main-hole jet”) from the main hole by a simple method. The method of using the heat generated by secondary combustion of CO gas produced by decarburization blowing by supplying oxygen from the atmosphere was studied. Here, the secondary combustion is a reaction (2CO + O ₂ = 2CO ₂ ) in which CO gas generated by decarburization blowing of hot metal is burned by oxygen supplied from a sub-hole or the like.

  First, verification was performed on a small lance in which a plurality of sub holes were arranged around the main hole. In order to simulate the gas in the converter, CO gas was supplied to the outer peripheral atmosphere of the lance. In addition, in order to confirm the influence of the calorific value of CO gas, a test for supplying propane gas was also conducted. As a result, it was confirmed that even a CO gas having a relatively small calorific value can form a high temperature zone around the main hole by oxygen supplied from the sub hole. In addition, a test for supplying propane gas from the sub-hole was also conducted. In this case, it was found that a violent flame was generated near the lance outlet, and the inside surrounded by the flame was remarkably heated.

  Based on this result, a decarburization blow smelting test of hot metal was conducted in a small converter. As a result, it was found that a high dynamic pressure of the oxygen jet can be obtained on the bath surface of the hot metal by performing acid refining using an upper blowing lance in which auxiliary holes are appropriately arranged around the main hole. In this case, due to the decarburization reaction by the oxygen jet from the main hole, the atmosphere in the converter becomes a high-concentration CO gas atmosphere, and this CO gas and oxygen from the sub-hole react to cause secondary combustion. Normally, secondary combustion is aimed at raising the furnace temperature or bath temperature, but by appropriately arranging the sub-holes, the temperature around the oxygen jet is partially increased, and the atmosphere gas to the jet is increased. It has been found that entrainment is reduced and dynamic pressure is increased, that is, high dynamic pressure can be obtained by appropriately supplying the oxygen-containing gas from the auxiliary hole. In this case, since it is necessary that the periphery of the oxygen jet from the main hole be at a high temperature, it is important that the oxygen from the subhole is injected from the subhole so as to surround the main hole jet. When oxygen from the subhole does not surround the main hole jet, the high temperature zone diffuses, and the effect of suppressing the entrainment of the atmospheric gas is significantly reduced.

  A schematic view of an upper blowing lance according to the present invention having this auxiliary hole is shown in FIGS. 1 is a schematic side sectional view of an upper blowing lance having four main holes and eight sub-holes, FIG. 2 is a schematic view taken along the line XX ′ of FIG. 1, and FIG. It is a schematic sectional drawing of the Laval nozzle which is the shape of the main hole shown in FIG.

  As shown in FIGS. 1 and 2, an upper blow lance 1 according to the present invention 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 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. Four main holes 4 facing vertically downward are installed, and a plurality of (eight in FIG. 2) sub-holes 8 are installed around the main hole 4. The main hole 4 has a Laval nozzle shape, and the sub-hole 8 has a straight shape. The sub-holes 8 are arranged substantially concentrically around the axis of the lance nozzle 3 so as to surround the main hole 4. The main hole 4 may be a vertically downward direction.

  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 tube 11 and the innermost tube 12 serves as a supply flow path for the oxygen-containing gas to the sub-hole 8, and extends from the upper end of the upper blowing lance 1 to the gap between the inner tube 11 and the innermost tube 12. The supplied oxygen-containing gas passes through the gap between the inner tube 11 and the innermost tube 12 and is ejected from the auxiliary hole 8 into the converter. Further, the inside of the innermost pipe 12 serves as a supply flow path for oxygen-containing gas to the main hole 4, and the oxygen-containing gas supplied from the upper end of the upper blowing lance 1 to the inside of the innermost pipe 12 It passes through the inside of the inner pipe 12 and is ejected from the main hole 4 into the converter.

  The main hole 4 for supplying oxygen for oxidative refining has a Laval nozzle shape, and its shape is shown in FIG. As shown in FIG. 3, the main hole 4 has a Laval nozzle shape composed of two cones, a portion whose cross section is reduced and a portion where the cross section is enlarged. In the nozzle of this Laval nozzle shape, the reduced portion is the throttle portion 5. The enlarged portion is the skirt portion 7, and the portion where the narrowed portion 5 transitions from the narrowed portion 5 to the skirt portion 7 is called the throat 6. The oxygen-containing gas that has passed through the upper blowing lance 1 passes through the throttle portion 5, the throat 6, and the skirt portion 7 in this order, and is injected as a supersonic or subsonic jet. In FIG. 3, Dt is the throat diameter, De is the exit diameter, and the spread angle θ of the skirt portion 7 is usually 10 ° or less. The optimum shape of the throat diameter Dt and the outlet diameter De is determined by a theoretical formula based on the operating conditions.

  The sub-hole 8 is for supplying an oxygen-containing gas that forms a high-temperature zone around the oxygen jet from the main hole 4 by burning the CO gas generated by the decarburization reaction. It is necessary to arrange a plurality of auxiliary holes 8 around the oxygen jet. In order to wrap the oxygen jet from the main hole 4 in a high temperature zone, the larger the number of the sub holes 8 is, the more preferable. When there is one main hole 4, three or more sub holes 8 are preferable. In the top blowing lance 1 used in decarburization blowing, there are a plurality of main holes 4, and in this case, it is preferable to arrange 6 or more, preferably 8 or more sub-holes 8. The sub holes 8 are preferably arranged evenly around the main hole 4.

  At this time, from the viewpoint of stabilizing the secondary combustion and improving the total decarbonation efficiency of the main hole 4 and the subhole 8 together, the amount of acid sent from the subhole 8 is the amount of acid sent from the main hole 4. The acid feed rate from the sub-hole 8 is preferably 20% or less of the acid feed rate from the main hole 4.

The sub-hole 8 may be vertically downward, but may be provided with an angle (referred to as “tilt angle”). FIG. 1 shows the inclination angle of the main hole 4 as θ _S and the inclination angle of the sub hole 8 as θ _f . However, if the inclination angle θ _f is excessively widened, the high temperature zone diffuses to the surroundings, and the high temperature zone is separated from the periphery of the oxygen jet injected from the main hole 4, and the attenuation suppression effect of the main hole jet is reduced. For this reason, the tilt angle θ _{f of the} sub-hole 8 is made smaller than the value obtained by adding 10 ° to the tilt angle θ _S of the main hole 4, and preferably from the value obtained by adding 5 ° to the tilt angle θ _S of the main hole 4. It is preferable to reduce the size. When the inclination angles θ _S of the main holes 4 are different, the largest inclination angle θ _S may be used as a reference. The tilt angle θ _f is preferably as small as possible. However, if the tilt angle θ _f is set inwardly toward the main hole 4, the oxygen jet in the main hole 4 is disturbed, so that the above-described effect of the high-temperature zone is difficult to obtain. Therefore, the inclination angle θ _f is preferably in the range of 0 ° (vertically downward) to the inclination angle θ _S of the main hole 4 or less. It may be different from the inclination angle θ _f in each of the sub-ports 8. Further, in order to further surround the oxygen jet from the main hole 4 in the high temperature zone, the effect is further improved if a center hole is provided in addition to the sub holes 8. The sub-hole 8 may have a Laval nozzle shape, but a straight nozzle is preferable in order to stabilize combustion. Here, the inclination angle θ _S of the main hole 4 is usually 20 ° or less. Further, the number of holes in the main hole 4 need not be particularly limited.

  In the main nozzle 4 of the Laval nozzle shape shown in FIG. 3, the throttle portion 5 and the skirt portion 7 are conical, but for the Laval nozzle, the throttle portion 5 and the skirt portion 7 do not need to be conical, and the inner diameter is curved. The throttle portion 5 may be a straight cylindrical shape having the same inner diameter as the throat 6. When the throttle part 5 and the skirt part 7 are configured with curved surfaces whose inner diameter changes in a curved manner, an ideal flow velocity distribution as a Laval nozzle can be obtained, but it is extremely difficult to process the nozzle, while the throttle part 5 In the case of a straight cylindrical shape, it is slightly dissociated from the ideal flow velocity distribution, but there is no problem in use, and the nozzle processing becomes extremely easy. In the present invention, all these divergent nozzles are referred to as Laval nozzles.

  In FIG. 1, the upper blowing lance 1 has a quadruple tube structure, but has a triple tube structure of an outer tube 9, an intermediate tube 10, and an inner tube 11, and the inside of the inner tube 11 is connected to the main hole 4 and the subhole 8. The oxygen-containing gas supply channel may be used. However, in this case, the oxygen-containing gas sent through the inner pipe 11 is injected from the main hole 4 and the sub hole 8 at a ratio corresponding to the cross-sectional area of each nozzle discharge hole of the main hole 4 and the sub hole 8. Therefore, the independent flow path shown in FIG. 1 is more preferable than the dual-purpose flow path in that the supply amount and supply timing of the oxygen-containing gas can be arbitrarily changed between the main hole 4 and the sub hole 8. It is preferable that

  Oxygen-containing gas such as oxygen, air, oxygen-enriched air, Ar-oxygen mixed gas, toward the hot metal or molten steel accommodated in the converter, using the top blow lance 1 according to the present invention configured as described above. And oxidize and refine hot metal or molten steel. Oxidative refining includes hot metal decarburization blowing, hot metal preliminary dephosphorization treatment, iron scrap melting treatment using the combustion heat of carbonaceous materials such as coke, and smelting reduction treatment of Cr ore in the presence of hot metal. Can be implemented. That is, if it is the oxidation refining which CO gas produces | generates, it can refine efficiently using the top blowing lance 1 which concerns on this invention.

  The oxygen-containing gas jet injected from the Laval nozzle-shaped main hole 4 is optimally expanded at a predetermined oxygen feed rate determined by the throat diameter Dt and the outlet diameter De of the main hole 4, and is an ideal supersonic jet. Injected as. When hot metal or molten steel is subjected to oxidative refining, there is a case where it is necessary to change the acid feed rate during refining, for example, decarburization blowing of hot metal. In that case, if the acid delivery rate deviates from the predetermined acid delivery rate determined by the throat diameter Dt and the outlet diameter De and becomes inadequate acid delivery conditions, there will be a shortage of jets when the acid delivery rate exceeds the predetermined acid delivery rate. On the other hand, when it falls below a predetermined acid feed rate, both the energy loss occurs due to excessive expansion of the jet, and the ideal supersonic speed that is theoretically required cannot be obtained. descend. In particular, when the acid delivery rate is decreased, a significant decrease in dynamic pressure occurs on the bath surface, including a decrease in dynamic pressure due to low acid delivery.

  On the other hand, by supplying the oxygen-containing gas from the sub-hole 8 of the upper blowing lance 1 according to the present invention, the CO gas in the atmospheric gas generated by the decarburization reaction by the jet from the main hole 4 is changed to the sub-hole. Secondary combustion is performed by oxygen supplied from 8, and a high-temperature zone is generated around the jet portion of the main hole 4. Therefore, the temperature around the main hole jet becomes partially high, and the density of the atmospheric gas around the jet decreases, so that the amount of atmospheric gas entrained in the main hole jet decreases, in other words, due to the atmospheric gas. The attenuation of the main hole jet is suppressed, and the dynamic pressure of the main hole jet on the bath surface can be increased as compared with the conventional case. That is, by using the top blowing lance 1 according to the present invention, the attenuation of the main hole jet due to the atmospheric gas is suppressed even under an inappropriate acid feeding condition in which the dynamic pressure of the main hole jet itself is lowered. Therefore, the dynamic pressure of the main hole jet on the bath surface can be maintained at a high value substantially equal to the dynamic pressure at the outlet of the main hole 4. In this case, no fuel gas is required to use the CO gas generated by the decarburization reaction. In addition, when the high temperature zone is not closely attached to the periphery of the main hole jet, the above effect is remarkably reduced.

  Thus, even if the acid feed rate is reduced, the dynamic pressure of the main hole jet increases compared to the conventional case, so that the reaction efficiency of oxygen is increased and the reaction rate such as decarburization reaction can be promoted. . When there is no need to increase the dynamic pressure, such as when the acid feed rate is in an appropriate range where an ideal supersonic jet can be obtained, it is not necessary to supply the oxygen-containing gas from the auxiliary hole 8. Even in such a case, it is preferable to supply a small amount of oxygen-containing gas or inert gas from the sub-hole 8 in order to prevent clogging of the sub-hole 8 and to cool the lance nozzle 3. Here, even if the acid supply conditions are within an appropriate range in which an ideal supersonic jet can be obtained, if it is necessary to increase the dynamic pressure, the present invention can further increase the dynamic pressure. Needless to say.

  As described above, in the present invention, the dynamic pressure of the jet from the main hole 4 can be controlled by supplying the oxygen-containing gas from the sub-hole 8. In particular, various benefits can be obtained by applying this dynamic pressure control method to converter decarburization blowing of hot metal that has been subjected to preliminary dephosphorization.

  That is, in converter decarburization blowing of hot metal that has been subjected to preliminary dephosphorization, conventionally, in the decarburization peak period from the initial stage to the middle stage of decarburization, the top blown due to the small amount of slag in the furnace. Iron scattering and dust generation due to oxygen jets become prominent, leading to a decrease in iron yield and operational instability.On the other hand, at the end of decarburization blowing, the acid feed rate is increased to increase decarbonation efficiency. By reducing the flow rate, the flow rate of the Laval nozzle greatly deviates downward, the effect of the Laval nozzle is not obtained, and the oxygen jet is unnecessarily attenuated. As seen in the increase of Fe, the decarburization reaction efficiency was reduced.

  On the other hand, in order to achieve low dynamic pressure and high acid feed operation in the decarburization peak period from the initial stage to the middle stage of decarburization, for example, low dynamics that can obtain an optimum jet at a low pressure in the main hole 4 are achieved. The top blowing lance 1 of the present invention is designed as a pressure Laval nozzle shape, and using this top blowing lance 1, converter decarburization blowing of hot metal preliminarily dephosphorized is performed as follows. That is, in the initial to middle stage of decarburization, oxygen jet is supplied from the main hole 4 at a low dynamic pressure and a high acid feed rate, and from the sub-hole 8, only blockage due to metal scattering is avoided. The minimum necessary oxygen or inert gas is supplied. On the other hand, at the end of decarburization blowing, although the acid feed rate from the main hole 4 is reduced, oxygen is supplied from the sub-hole 8 to move the main hole jet. Prevents pressure decay and ensures higher dynamic pressure than before. By decarburizing and blowing in this way, the dynamic pressure of the oxygen jet is kept low from the beginning to the middle of the decarburization blowing, so iron scattering and dust generation by the top blowing oxygen jet are suppressed. The iron yield is improved and the operation is stabilized. At the end of decarburization, the stirring pressure of the molten metal is improved by increasing the dynamic pressure of the oxygen jet even at a low acid feed rate. As a result, iron oxidation is suppressed and the iron yield is improved, and at the same time, the decarburization reaction is promoted. In the operation of adding Mn ore into the converter and reducing the Mn ore, a dramatic improvement in Mn yield can be obtained. These effects are remarkable when the amount of slag in the furnace is 50 kg / t or less, and particularly remarkable when the amount of slag is 20 kg / t or less.

  In addition, if oxygen is supplied from the sub-hole 8 in the decarburization peak period from the initial stage to the middle stage of the decarburization, the dynamic pressure of the oxygen jet from the main hole 4 is further increased. An effect etc. are acquired. Further, since the stirring by the oxygen jet is strengthened, the necessity for bottom blowing stirring is eliminated, and further, the height of the lance can be increased while maintaining the same oxygen jet trajectory. Metal adhesion can also be reduced.

  Further, in the hot metal preliminary dephosphorization process using the top blowing lance 1 of the present invention, the dynamic pressure of the oxygen jet is increased, so that the stirring of the hot metal is promoted and the melting of the iron scrap is promoted. Iron scrap can be melted.

  In the present invention, since CO gas generated by the decarburization reaction is used, it is optimal to use a converter that is close to the hermetic seal so that the generated CO gas does not diffuse from the container. When using a dust collector and exhaust gas equipment that suppresses the present invention, the present invention can be implemented even in a pot-type container.

Examples of the present invention are shown below together with comparative examples. About 260 tons of hot metal was charged into a top-bottom-blown combined blowing converter that had a capacity of 260 tons, oxygen was blown up, and stirring gas was blown at the bottom, and decarburization blowing was mainly performed. The hot metal used was the hot metal for the same steel type that was desulfurized and dephosphorized in the hot metal pretreatment facility, which was the previous process of converter decarburization blowing, and the silicon concentration of the hot metal was 0.10 mass%. Hereinafter, the phosphorus concentration was 0.007 to 0.018 mass%. Lime-based flux is added into the converter to generate slag. The basicity (CaO / SiO ₂ ) of slag determined from the analysis value of slag was about 2.8 to 3.7, and the amount of slag in the furnace was determined from the CaO balance. From the tuyere installed at the bottom of the converter, Ar or nitrogen was blown at a rate of about 10 to 25 Nm ³ per minute for the purpose of stirring the molten metal.

The acid feeding is performed by an upper blowing lance having 4 holes and a main hole with an inclination angle θ _S of 12 ° and 3 to 8 holes, and the acid feeding rate from the main hole is from the initial stage to the middle stage of the blowing process. 60000Nm ³ / hr, the blow end and 30000Nm ³ / hr, blowing patterns such as lance height was also the utmost identical in any operation. As shown in FIG. 1, the main hole and the sub hole made the oxygen supply path independent, and oxygen was supplied from the sub hole at the end of blowing. The acid feed rate from the sub-hole was set to 3000 Nm ³ / hr because there was a tendency for flame abnormality in the furnace and large wear of the refractory when the acid feed rate of the main hole was 20% or more. The end target of decarburization blowing was the time when the carbon concentration in the molten steel reached 0.05 mass%, and the molten steel temperature at the end was set to 1650 ° C. During blowing, 5 kg / t of Mn ore was charged into the furnace, and the Mn yield at the end of blowing was investigated. Also, slag at the end of blowing was collected and T. The concentration of Fe was investigated.

  Moreover, the operation of the top blowing lance which has four main holes which are not provided with the subhole as a comparative example was also implemented. In the comparative example, it carried out according to the operating conditions of the example of this invention except not supplying oxygen from a subpore. Table 1 shows the operation conditions and operation results of the inventive examples and the comparative examples.

As shown in Table 1, in the example 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. It was also confirmed that these effects become significant by increasing the number of sub-holes installed and reducing the tilt angle θ _f of the sub-holes.

It is a schematic side sectional view of the top blowing lance according to the present invention. It is the schematic by the X-X 'arrow of FIG. It is a schematic sectional drawing of the Laval nozzle which is the shape of the main hole shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Top blowing lance 2 Lance main body 3 Lance nozzle 4 Main hole 5 Constriction part 6 Throat 7 Skirt part 8 Subhole 9 Outer pipe 10 Middle pipe 11 Inner pipe 12 Innermost pipe

Claims (10)

  When an oxygen-containing gas is blown toward the hot metal or molten steel from an upper blowing lance having one or more Laval nozzle-shaped main holes at its tip, an inclination angle is formed around the main hole. A plurality of sub-holes that are equal to or less than the value obtained by adding 10 ° to the tilt angle are concentrically arranged, oxygen-containing gas is supplied from the sub-holes, and secondary combustion is generated around the oxygen-containing gas injected from the main holes. A converter blowing method characterized by forming a high temperature zone.   2. The converter blowing method according to claim 1, wherein an inclination angle of the auxiliary hole is equal to or less than a value obtained by adding 5 ° to an inclination angle of the main hole.   The converter blowing method according to claim 1 or 2, wherein six or more sub-holes are arranged.   The supply flow rate of the oxygen-containing gas from the sub-hole is 20% or less of the supply flow rate of the oxygen-containing gas from the main hole, according to any one of claims 1 to 3. Converter blowing method.   The converter blowing method according to any one of claims 1 to 4, wherein the supply amount of the oxygen-containing gas is independently adjusted in the main hole and the sub hole.   6. The converter blowing method according to any one of claims 1 to 5, wherein the oxidative refining is a hot metal preliminary dephosphorization treatment.   The oxidative refining is decarburization blowing of hot metal that has been pretreated, and the amount of generated slag in the decarburization blowing is 50 kg / t or less, according to any one of claims 1 to 5. The converter blowing method as described in one.   One or more laval nozzle-shaped main holes are installed at the tip of the top blow lance for converter smelting by blowing oxygen-containing gas toward hot metal or molten steel, and surrounding the main hole. The upper blow lance for converter blowing is characterized in that a plurality of sub-holes having an inclination angle equal to or less than a value obtained by adding 10 ° to the inclination angle of the main hole are arranged concentrically.   The upper blowing lance for converter blowing according to claim 8, wherein the inclination angle of the auxiliary hole is not more than a value obtained by adding 5 ° to the inclination angle of the main hole.   The upper blow lance for converter blowing according to claim 8 or 9, wherein six or more sub-holes are arranged.

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