JP2007154313A - Method for dephosphorizing molten iron - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform a dephosphorization with the same degree of dephosphorizing efficiency and iron yield as the conventional method, with little lime consumption without using flux containing fluorine, when molten iron is dephosphorized. <P>SOLUTION: In the method for dephosphorizing the molten iron: a dephosphorization refining agent composed mainly of CaO is added; gaseous oxygen source and solid oxygen source as the oxygen source are supplied; the dephosphorization refining agent composed mainly of CaO is reduced to slag; and the dephosphorization is applied to the molten iron. In the dephosphorizing method, at least a part of the solid oxygen source is supplied on the molten iron surface at the same position as the position for supplying the gaseous oxygen source by using a carrier gas. At this time, on the molten iron surface supplying the gaseous oxygen source, the dephosphorization-refining agent composed of CaO is supplied, or it is desirable to use any one or more kinds among sintered ore, mill scale, sand iron, collected dust, iron ore, having ≤1mm grain size as the solid oxygen source. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a hot metal dephosphorization method, and more particularly, to efficiently remove hot metal with high iron yield without using a fluorine source as a solvent for accelerating the hatching of a dephosphorizing refining agent. It is about the method.

  In the steelmaking process using blast furnace hot metal, hot metal dephosphorization treatment in which most of Si and P contained in the hot metal are oxidized and removed using oxygen gas or solid iron oxide before decarburization blowing in the converter. Alternatively, so-called hot metal preliminary treatment such as hot metal desulfurization treatment in which S contained in the hot metal is removed under a reducing atmosphere by a desulfurizing agent is generally performed. In recent years, quality requirements for steel products have become more stringent than ever, and a reduction in phosphorus concentration has been demanded more than ever. In order to meet this quality requirement, it is necessary to increase the amount of hot metal to be dephosphorized in the hot metal pretreatment more than before and to stably reduce the phosphorus concentration after dephosphorization.

  By the way, in order to cope with the environmental impact represented by recent global warming, it is essential to reduce the amount of slag discharged in the steelmaking process. In order to reduce the amount of slag discharged in the hot metal dephosphorization process, the amount of dephosphorization agent that is melted to function as a dephosphorization refining agent (“slag for dephosphorization refining”) is reduced. It is necessary. In hot metal dephosphorization, the main dephosphorizing agent is lime. In order to meet the above quality requirements and reduce slag discharge, the amount of lime used is reduced while maintaining the required dephosphorization amount. Therefore, a technology for efficiently dephosphorizing with a small amount of lime is required.

  In the dephosphorization treatment, lime that does not hatch does not contribute to the dephosphorization reaction. Therefore, in order to reduce the amount of lime used, it is important to promote the hatching of the added lime. Conventionally, fluorite has been known as a medium solvent for promoting hatching which is excellent in hatching ability of slag including lime, and fluorite has been used also in dephosphorization treatment. However, in recent years, with the tightening of environmental regulations, the use of a solvent medium containing fluorine typified by fluorite has been restricted. Therefore, a means for promoting the dephosphorization reaction by lime without using fluorite. Has been studied and a number of proposals have been made.

  As one of the means, a technique using another solvent as a hatching accelerator as a substitute for fluorite has been proposed. For example, Patent Document 1 proposes a method of using a medium solvent containing aluminum oxide as a substitute for fluorite in decarburization refining or dephosphorization of hot metal.

However, aluminum oxide proposed as a substitute for fluorite in Patent Document 1 promotes the hatching of slag, but has the effect of increasing the viscosity of slag. For this reason, when there is much usage-amount of aluminum oxide, when removing slag from a reaction container after a dephosphorization process, the case where slag adheres and remains in a furnace generate | occur | produces. As a result, the so-called “recovery” occurs in which the phosphorus in the residual slag returns to the hot metal during the dephosphorization process of the next charge, which has a problem of adversely affecting the dephosphorization process of the next charge. Furthermore, due to the high viscosity of the slag, there is a problem that a large amount of granular iron is trapped in the slag, and this granular iron is taken out of the furnace when the slag is discharged to reduce the iron yield.
JP 2002-309212 A

  The present invention has been made in view of the above circumstances, and the purpose of the present invention is to reduce the amount of lime used in the conventional method without using a solvent containing fluorine when dephosphorizing the hot metal. It is an object of the present invention to provide a hot metal dephosphorization method that is more advantageous than conventionally proposed, and is capable of dephosphorization with the same dephosphorization efficiency and iron yield.

  The hot metal dephosphorization processing method according to the first aspect of the present invention for solving the above problems comprises adding a dephosphorizing refining agent mainly composed of CaO, supplying a gaseous oxygen source and a solid oxygen source as an oxygen source, and adding In the molten iron dephosphorization method, the dephosphorizing agent mainly composed of CaO is hatched to form slag, and the dephosphorization treatment is performed on the molten iron. The same location where the gaseous oxygen source is supplied At least a part of the solid oxygen source is supplied to the hot metal bath surface using a carrier gas.

  The hot metal dephosphorization method according to the second aspect of the present invention is the method of using the lance having at least two supply systems for independently supplying the gaseous oxygen source and the solid oxygen source in the first aspect of the invention. A gaseous oxygen source and a solid oxygen source are supplied.

  According to a third aspect of the present invention, there is provided a hot metal dephosphorization method according to the second aspect of the present invention, wherein the dephosphorizing refining agent mainly composed of CaO is supplied to the hot metal bath surface along with the gaseous oxygen source through the gaseous oxygen source supply system. It is characterized by this.

  In any one of the first to third inventions, the hot metal dephosphorization method according to the fourth invention is characterized in that the solid oxygen source is sintered ore having a particle size of 1 mm or less, mill scale, dust collection dust, iron sand, It is any one or two or more of iron ores.

  The hot metal dephosphorization processing method according to a fifth aspect of the present invention is the hot metal dephosphorization method according to any one of the first to fourth aspects, wherein the transport gas of the solid oxygen source is air, reducing gas, carbon dioxide gas, non-oxidizing gas, It is any one kind or two or more kinds of rare gases, and has an oxygen concentration lower than that of the gaseous oxygen source.

According to the present invention, during the hot metal dephosphorization process, the solid oxygen source is supplied together with the carrier gas to the hot metal bath surface at the same location as the hot metal bath surface supplying the gaseous oxygen source. As a result, the oxygen potential of the dephosphorization slag is rapidly increased, and the dephosphorization ability of the slag is improved. By improving the dephosphorization ability of slag, dephosphorization can be achieved even without using a solvent containing fluorine, even when the amount of lime used is smaller than before, and to improve iron yield. Even if the basicity (CaO / SiO ₂ ) of the smelting slag is lowered as compared with the conventional one or the hot metal temperature after the dephosphorizing treatment is raised compared with the conventional one, the dephosphorization reaction is not hindered and efficient. The hot metal can be dephosphorized. In addition, a gas having a lower oxygen concentration than a gaseous oxygen source such as air, reducing gas, carbon dioxide gas, non-oxidizing gas, or rare gas is used as a transport gas for the solid oxygen source. The oxygen partial pressure at the collision portion, that is, the hot spot of the molten metal surface is lowered, and the dephosphorization reaction can be promoted by suppressing the decarburization reaction.

  The present invention will be specifically described below.

  The hot metal dephosphorization process uses a hot metal transport container such as a torpedo car or hot metal pan, or a refining furnace such as a converter as a reaction vessel, a dephosphorizing refining agent mainly composed of CaO, a gaseous oxygen source such as oxygen gas, and a solid A solid oxygen source such as iron oxide is added to the hot metal, phosphorus in the hot metal is oxidized by a gaseous oxygen source and a solid oxygen source, and the resulting phosphor oxide is obtained from a dephosphorizing refining agent mainly composed of CaO. It is carried out by the method of removing the phosphorus in the hot metal by taking it into the dephosphorizing slag. Gaseous oxygen sources and solid oxygen sources are collectively referred to as oxygen sources.

  In principle, solid oxygen sources are more efficient than gaseous oxygen sources for dephosphorization reactions. This is because the dephosphorization reaction is thermodynamically more advantageous at lower temperatures. When an oxygen source is added to the hot metal, decarburization and dephosphorization occur. However, when a gaseous oxygen source is added, the temperature rises due to decarburization heat generation. On the other hand, when a solid oxygen source is added, an endotherm is generated during decomposition of the solid oxygen source. Therefore, the temperature rise is suppressed. That is, by using a solid oxygen source, a temperature advantageous for the dephosphorization reaction is maintained. However, in order to promote the dephosphorization reaction, a temperature condition that can melt the solid oxygen source is necessary. Further, the solid oxygen source has a function of increasing the FeO component in the dephosphorization slag, which becomes FeO after melting and contributes to the dephosphorization reaction. Promotes the phosphorus reaction.

  Conventionally, the solid oxygen source has been generally dropped and introduced from a hopper installed above the reaction vessel during the dephosphorization process. In this case, in order to prevent the solid oxygen source from being sucked into the exhaust system, a granular or lump of several mm to several tens mm has been used. The granular or lump solid oxygen source does not melt immediately when it is put into the reaction vessel, and may remain until the end of the dephosphorization treatment. In addition, FeO in the slag rises as the solid oxygen source melts, but the FeO in the slag reacts with the carbon in the hot metal and is reduced, so the melting rate of the solid oxygen source and the reduction rate of FeO Are equivalent, the FeO concentration in the slag does not increase. That is, unless the melting rate of the solid oxygen source is increased faster than the reduction rate of FeO in the slag, the oxygen potential in the slag does not increase, and an improvement in the dephosphorization rate cannot be expected.

  In the present invention, air, reducing gas, carbon dioxide gas, non-oxidizing gas is applied to the hot metal bath surface where the gaseous oxygen source is supplied, i.e., where the gaseous oxygen source collides with the hot metal bath surface. A rare gas or the like is used as a carrier gas, and a solid oxygen source is supplied together with the carrier gas. Here, the reducing gas is a hydrocarbon gas such as propane gas and CO gas, the non-oxidizing gas is a gas having no oxidizing ability such as nitrogen gas, and the rare gas is Ar gas or He. An inert gas such as a gas. On the hot metal bath surface, the location where the gaseous oxygen source collides with the hot metal bath surface (referred to as “fire point”) is heated by the reaction between the gaseous oxygen source and the carbon in the hot metal, and the solid oxygen supplied to the hot oxygen bath surface. The source melts quickly and increases the FeO component in the slag. As a result, the oxygen potential of the slag rises, that is, the slag optimum for the dephosphorization reaction is rapidly formed, and the dephosphorization process is possible even at a small amount of slag and at a high temperature.

  Here, the "hot metal bath surface at the same location as the place where the gaseous oxygen source is supplied" as used in the present invention is a surface where the supplied gaseous oxygen source first contacts the molten iron. For example, when supplying a gaseous oxygen source from an upper blowing lance, the gaseous oxygen source injected from the upper blowing lance is a position where the gaseous oxygen source collides with the hot metal bath surface, that is, a fire point, and the gaseous oxygen source is inserted into an injection lance or tuyere. When it is used to inject (blow) into the hot metal, it becomes a surface where the gaseous oxygen source enters the hot metal at the injection lance or the exit of the tuyere (also defined as “fire point” in this case).

  Some solid oxygen sources contain a small amount of metallic iron, which may burn in a pure oxygen stream and damage equipment. Carrying the solid oxygen source with a carrier gas having a lower oxygen concentration than air is also effective from the industrial viewpoint of avoiding accidents.

  In the present invention, the dephosphorizing refining agent mainly composed of CaO may be added separately from the gaseous oxygen source from a hopper or the like. However, in a preferred embodiment of the present invention, a dephosphorizing refining agent mainly composed of CaO is supplied to the hot metal bath surface together with a gaseous oxygen source. That is, since the dephosphorizing refining agent mainly composed of CaO is supplied simultaneously with the solid oxygen source to the fire point, the dephosphorizing refining agent itself mainly composed of CaO is also heated in a high temperature atmosphere. Melting and slag can be made even faster. That is, the dephosphorization reaction can be further promoted.

  The dephosphorizing refining agent mainly composed of CaO used in the present invention is not particularly limited as long as it contains CaO and can be dephosphorized as intended. Usually, it consists of CaO alone, or contains 50 mass% or more of CaO, and contains other components as necessary.

As other components, hatching accelerators are generally used. That is, although the present application is a technique that enables reduction or omission of a hatching accelerator, it does not prohibit further improvement of hatching efficiency by adding a hatching accelerator. As the hatching accelerator, in particular, a substance containing titanium oxide or aluminum oxide (Al ₂ O ₃ ) having an action of promoting the hatching by lowering the melting point of CaO can be mentioned, and these are preferably used. Among these, addition of titanium oxide is preferable from the viewpoint of slag viscosity. Fluorine-containing materials such as fluorite can also be used as hatching accelerators. However, it is preferable not to use a fluorine-containing substance as a solvent from the viewpoint of protecting the environment by suppressing the amount of fluorine eluted from the slag when the slag is disposed of. A substance in which fluorine is inevitably mixed as an impurity component may be used. Of course, when using a substance containing titanium oxide or a substance containing aluminum oxide, it is preferable from this point of view that it does not contain fluorine.

  As a specific example of the dephosphorization refining agent mainly composed of CaO, it is preferable to use quick lime or limestone because it is inexpensive and has excellent dephosphorization ability. Also, slag generated when decarburizing and refining light burned dolomite and hot metal after dephosphorization treatment in the converter of the next process is used as a dephosphorizing refining agent mainly composed of CaO. You can also The decarburized soot is mainly composed of CaO and has a low phosphorus content, and therefore can be sufficiently used as a dephosphorizing refining agent mainly composed of CaO.

  As the gaseous oxygen source used in the present invention, oxygen gas (including industrial pure oxygen), air, oxygen-enriched air, a mixed gas of oxygen gas and inert gas, and the like can be used. In the case of normal dephosphorization treatment, it is preferable to use oxygen gas because the dephosphorization reaction rate is faster than when other gases are used. In the case of a mixed gas, the oxygen concentration is preferably higher than that of air in order to ensure the dephosphorization reaction rate.

  In addition, as the solid oxygen source used in the present invention, iron ore sintered ore, mill scale, dust collection dust, iron sand, iron ore and the like can be used. Dust collection dust is dust containing iron that is recovered from exhaust gas in a blast furnace, converter, and sintering process. From the viewpoint of promoting melting of the solid oxygen source, the solid oxygen source is preferably a granular material having a particle size of 1 mm or less. When the particle size exceeds 1 mm, rapid melting is difficult, and it is difficult to increase the FeO component of the slag. Here, the particle size of 1 mm or less means that the particle size passes through a sieving machine with an opening size of 1 mm, and the spindle has a spindle shape with a major axis exceeding 1 mm as long as it passes through a sieving machine with an opening size of 1 mm. It doesn't matter. From the viewpoint of handling, the particle size is preferably 1 μm or more.

  Among the above solid oxygen sources, iron sand and fine iron ore are particularly preferable because they are fine powders of 1 mm or less in generation form and do not require pulverization. Among these, iron sand not only functions as a solid oxygen source, but also has a function as a hatching accelerator of a dephosphorizing refining agent mainly composed of CaO because it contains titanium oxide, and is particularly suitable. is there.

  Titanium oxide acts as an acidic oxide in the slag composition during the dephosphorization treatment, and is excellent in the effect of hatching CaO, which is the main component of the dephosphorization refining agent. That is, by adding sand iron containing titanium oxide, hatching of a dephosphorizing refining agent mainly composed of CaO is promoted, and a dephosphorization reaction is promoted. Titanium oxide has the effect of lowering the viscosity of slag composed of a dephosphorizing refining agent mainly composed of CaO, and this has the effect of facilitating the discharge of slag from the reaction vessel after the dephosphorization treatment. . For this reason, the amount of slag remaining in the reaction vessel after slag discharge is negligibly small. In the dephosphorization process of the next charge, the dephosphorization reaction is not hindered by dephosphorization and the dephosphorization process is efficiently performed. can do.

The amount of titanium oxide in the slag is preferably 10% by mass or less in terms of TiO ₂ . If it exceeds 10% by mass, the ratio of CaO as the main component is reduced, so the effect of improving the dephosphorization ability is offset and the effect of addition is reduced. On the other hand, the amount of titanium oxide is preferably 1% by mass or more in terms of TiO ₂ in order to surely enjoy the above effects such as a decrease in the viscosity of slag. Here, the meaning in terms of TiO ₂ means that titanium oxide has the forms of TiO, TiO ₂ , Ti ₂ O ₃ , and Ti ₃ O ₅ , and these Ti contents are converted into TiO ₂ for display. .

  The reaction vessel used for the dephosphorization treatment is not particularly limited, and a ladle type vessel such as a hot metal ladle or a charging ladle, a torpedo car, a converter type vessel or the like can be used. In the dephosphorization process of the present invention, both a gaseous oxygen source and a solid oxygen source are supplied as oxygen sources in order to promote the dephosphorization reaction. Of these, the gaseous oxygen source can be supplied by any method such as top blowing with an upper blowing lance, injection into hot metal with an injection lance or tuyere, or bottom blowing. It is necessary to supply to the hot metal bath surface in the same place as the location where the oxygen source is supplied. Therefore, when the gaseous oxygen source is blown up, the solid oxygen source must also be fed from above. In the case where the gaseous oxygen source is injected, the same is injected and supplied from the same location as the solid oxygen source.

  In the dephosphorization treatment of the present invention, the dephosphorization refining agent mainly composed of CaO is also preferably supplied to the hot metal bath surface at the same location as the location where the gaseous oxygen source is supplied. In order to supply a source and a solid oxygen source, and further a dephosphorizing refining agent mainly composed of CaO, for example, at least two supply systems are installed in an upper blowing lance or an injection lance or tuyere for supplying them, By supplying a dephosphorization refining agent mainly composed of CaO together with a gaseous oxygen source from one of the supply systems, and supplying a solid oxygen source together with the above-described carrier gas from the other supply system, Can be achieved. The supply means may be any means such as an upper blowing lance, injection lance, tuyere, etc. However, it is preferable to supply from the upper blowing lance because it is easy to operate.

  The top blow lance has at least two supply systems, one of which supplies a gaseous oxygen source and the other one supplies a solid oxygen source together with the carrier gas toward the fire point, thereby providing solid oxygen. The source will be supplied to the fire point. Since the solid oxygen source is supplied with a carrier gas having a lower oxygen concentration than the gaseous oxygen source, the temperature of the portion does not increase excessively, and the good reactivity of the solid oxygen source prevents dephosphorization. Promoted. As such a configuration, for example, the upper blowing lance is at least a double tube structure, one is a flow path for oxygen gas, the other is a flow path for solid oxygen source and carrier gas, and the gaseous oxygen source is centered on the lance central axis. A method of supplying from a nozzle hole arranged on a concentric circle at the center while supplying a solid oxygen source and a carrier gas from a nozzle hole arranged on the center axis of the lance can be adopted. Also, a plurality of nozzle holes may be arranged on a concentric circle with the lance center axis as the center, and the gaseous oxygen source and the solid oxygen source may be supplied from the alternate holes.

It is not necessary to supply all of the solid oxygen source to be supplied to the hot metal bath surface where the gaseous oxygen source is supplied, and only a part of the solid oxygen source is supplied with the gaseous oxygen source. You may supply to the hot metal bath surface of the same place. However, if there is a small amount of solid oxygen source supplied to the hot metal bath surface in the same place where the gaseous oxygen source is supplied, the increase in the FeO component in the slag will be small. Accordingly, an amount that sufficiently increases the FeO component in the slag may be set as the lower limit. Moreover, as an upper limit, what is necessary is just to suppress to the quantity which does not become excessive heat removal according to equipment specifications. For example, when dephosphorization is performed in a container of about 100 to 350 tons, a solid oxygen source supplied to the same location as the location where the gaseous oxygen source is supplied with respect to 1 m ^{3 of} pure oxygen gas of the gaseous oxygen source. It is preferable to add in the range of 0.1 kg or more and 2 kg or less. If the amount is less than 0.1 kg, the effect expected in the present invention cannot be sufficiently obtained. On the other hand, if the amount exceeds 2 kg, the heat removal on the supply surface of the solid oxygen source is increased, and the slag is insufficiently hatched to remove phosphorus. Will be reduced.

  What is necessary is just to supply the solid oxygen source supplied to places other than the same place as the bath surface of the hot metal to which the gaseous oxygen source is supplied by an appropriate method such as top addition or injection addition. Similarly, when supplying a dephosphorizing refining agent mainly composed of CaO to a place other than the same place as the hot metal to which the gaseous oxygen source is supplied, it may be supplied by an appropriate method such as top addition or injection addition. . The dephosphorizing refining agent mainly composed of CaO is also preferably 1 mm or less from the viewpoint of promoting hatching, and the influence is particularly great when it is supplied to the hot metal bath surface to which a gaseous oxygen source is supplied.

  When a gaseous oxygen source is used, the hot metal temperature rises due to the oxidation reaction heat. When a solid oxygen source is used, the sensible heat, latent heat, and decomposition heat of the solid oxygen source itself are higher than the oxidation reaction heat. Because it is large, the hot metal temperature drops. Therefore, the use ratio of the gaseous oxygen source and the solid oxygen source is set according to the temperature before and after the hot metal treatment while maintaining the above range. Further, in order to efficiently perform the dephosphorization reaction, it is preferable to stir the hot metal. As this stirring, generally, gas stirring using an injection lance or a nozzle embedded in the furnace bottom may be performed.

  As the dephosphorizing slag, the FeO concentration in the slag is preferably in the range of 10% by mass to 30% by mass. Therefore, the supply amount of the solid oxygen source is maintained so that the FeO concentration in the slag can maintain this range. Is preferably adjusted. When the FeO concentration in the slag is less than 10% by mass, the oxygen potential of the slag is low and the dephosphorization efficiency is poor. On the other hand, when the FeO concentration in the slag exceeds 30% by mass, the CaO necessary for the dephosphorization reaction is obtained. Will reduce the dephosphorization ability.

  By performing dephosphorization of the hot metal in this manner, it is possible to perform dephosphorization while maintaining the same dephosphorization rate as before without using a fluorine-containing material as a medium solvent for promoting hatching. It becomes. As a result, the slag can be reused without taking measures for fluorine leakage to the environment, and the environmental load can be avoided. In addition, even if the dephosphorization temperature is increased, it is possible to maintain the same dephosphorization amount as in the past. In this case, the iron yield in the dephosphorization process can be increased, which is an industrially beneficial effect. Is brought about.

The hot metal discharged from the blast furnace was desiliconized in the blast furnace casting floor, and then transferred to a 300-ton capacity converter, and a total of four dephosphorization processes were performed in the converter (Invention Examples 1 to 4). The phosphorus concentration of the hot metal before the dephosphorization treatment was unified to 0.12% by mass, the phosphorus concentration of the hot metal after the dephosphorization treatment was set to 0.020% by mass or less, and the iron yield was set to 98% or more. The iron yield (η) is the amount of hot metal discharged after dephosphorization relative to the total mass (W ₀ + W _s ) of the mass (W ₀ ) of the hot metal charged in the converter and the mass (W _s ) of the scrap. The mass (W) was calculated as a percentage (η = 100 W / (W ₀ + W _s )).

  The dephosphorization process has two separate supply systems in addition to the cooling water supply and drainage system, supplies oxygen gas and quicklime powder from one supply system, and uses nitrogen gas from the other supply system as a carrier gas. This was carried out using an upper blowing lance that supplied a solid oxygen source of powder. The two supply systems are separated to the tip of the top blowing lance, but the solid oxygen source and quicklime are mixed and supplied onto the same bath surface after being ejected from the tip of the lance. It processed without adding fluorine-containing substances such as fluorite. That is, dephosphorization treatment was performed by supplying only quicklime powder of 1 mm or less, a powdered solid oxygen source, and oxygen gas.

As the solid oxygen source, any one of powdered iron ore (average particle size 50 μm), iron sand (average particle size 100 μm), mill scale (average particle size 500 μm), iron ore sintered ore (average particle size 100 μm) Was sprayed onto the hot metal bath surface. The oxygen gas sending conditions were 15000 to 25000 Nm ³ / hr. The oxygen basic unit was 12 Nm ³ / t excluding oxygen necessary for desiliconization.

  In addition, as a comparative example, a dephosphorization treatment was performed in which granular iron ore (average particle size 20 mm) was placed and put in from the furnace hopper. Other dephosphorization treatment conditions in the comparative example were performed in accordance with the examples of the present invention. Table 1 shows the hot metal components and operating conditions before and after the dephosphorization treatment in the examples of the present invention and the comparative examples.

  As shown in Table 1, in all the examples of the present invention in which the solid oxygen source was supplied to the blowing surface of the oxygen gas from the top blowing lance, the phosphorus concentration in the hot metal after the dephosphorization treatment was 0.020% by mass or less. And the iron yield was 98% or more. On the other hand, in the comparative example, the phosphorus concentration in the hot metal after the dephosphorization treatment was higher than 0.020% by mass, or the iron yield was lower than 98%, and it was confirmed that both were incompatible.

  The hot metal discharged from the blast furnace is desiliconized in the blast furnace casting floor, and then transferred to a 300-ton capacity converter. A total of 10 dephosphorization treatments are performed in this converter using the top blow lance used in Example 1. (Invention Examples 11 to 20). The phosphorus concentration in the hot metal after the dephosphorization treatment was set to 0.020% by mass or less, and the iron yield was set to 98% or more. The iron yield was determined by the same calculation method as in Example 1.

As the solid oxygen source, iron sand having an average particle size of 100 μm was used. This iron sand was used in combination with the supply from the top blowing lance by the carrier gas and the top loading from the furnace hopper. Moreover, as a dephosphorizing refining agent mainly composed of CaO, quick lime powder (average particle diameter of 1 mm or less) supplied from a gaseous oxygen source supply system, and massive lime (average diameter of about 10 mm) to be placed on top from a furnace hopper And the basicity of slag (weight ratio of CaO component and SiO ₂ component in slag) was adjusted. In addition, with respect to Inventive Example 19, quick lime powder was not supplied from the supply system of the gaseous oxygen source, and only massive lime was placed on top from the furnace hopper. Furthermore, about this invention example 20, in addition to the quick lime powder from the supply system of the gaseous oxygen source, limestone powder (average particle size of 1 mm or less) was supplied.

  Moreover, the dephosphorization process was performed also about the case where a solid oxygen source (sand iron) is not supplied from an upper blowing lance as Comparative Examples 11-14. Other dephosphorization treatment conditions in the comparative example were performed in accordance with the examples of the present invention. Table 2 shows the hot metal components and operating conditions before and after the dephosphorization treatment in the present invention example and the comparative example.

  As shown in Table 2, even when a part of the solid oxygen source is placed on top, in the present invention example, the phosphorus concentration in the hot metal after the dephosphorization treatment is 0.020% by mass or less, and iron Yield was over 98%. On the other hand, in the comparative example, the phosphorus concentration in the hot metal after the dephosphorization treatment: 0.020% by mass or less and the iron yield: 98% or more could not be made compatible.

The hot metal discharged from the blast furnace was desiliconized in the blast furnace casting floor, and then transferred to a 300-ton capacity converter, and dephosphorization treatment was carried out twice in total (Invention Examples 31 to 32). As bottom blowing gas, oxygen gas was blown in as a stirring gas from the inner tube of the double tube structure tuyeres provided at the bottom of the converter furnace, at a flow rate of about 0.8 Nm ³ / min per ton of hot metal. The dephosphorization treatment was carried out using the top blowing lance used in Example 1 while blowing propane gas for cooling the tuyere. As the solid oxygen source, a mill scale having an average particle size of 500 μm was used. The phosphorus concentration in the hot metal after the dephosphorization treatment was set to 0.020% by mass or less, and the iron yield was set to 98% or more. The iron yield was determined by the same calculation method as in Example 1. Table 3 shows the hot metal components and operating conditions before and after the dephosphorization treatment in the examples of the present invention.

  As shown in Table 3, even when oxygen gas was blown from the tuyere as the stirring gas, in the present invention example, the phosphorus concentration in the hot metal after dephosphorization was 0.020 mass% or less, and iron Yield was over 98%.

Claims (5)

  A dephosphorizing refining agent mainly composed of CaO is added, a gaseous oxygen source and a solid oxygen source are supplied as an oxygen source, and the dephosphorizing refining agent mainly composed of CaO is hatched to form slag. In the hot metal dephosphorization method for performing dephosphorization treatment on the hot metal bath, at least a part of the solid oxygen source is transferred to the hot metal bath surface in the same place as the place where the gaseous oxygen source is supplied using a carrier gas. A method for dephosphorizing hot metal, which comprises supplying the hot metal.   The gas oxygen source and the solid oxygen source are supplied using a lance having at least two supply systems for independently supplying the gaseous oxygen source and the solid oxygen source, respectively. The hot metal dephosphorization processing method of description.   3. The hot metal dephosphorization method according to claim 2, wherein the dephosphorizing agent mainly composed of CaO is supplied to the hot metal bath surface along with the gaseous oxygen source through the gaseous oxygen source supply system.   The solid oxygen source is one or more of sintered ore having a particle size of 1 mm or less, mill scale, dust collection dust, iron sand, and iron ore. Item 4. The hot metal dephosphorization method according to any one of Items 3 to 4.   The gas for transporting the solid oxygen source is any one or more of air, reducing gas, carbon dioxide gas, non-oxidizing gas, and rare gas, and more than the gaseous oxygen source. The method for dephosphorizing hot metal according to any one of claims 1 to 4, wherein the oxygen concentration is low.