JP5061545B2 - Hot metal dephosphorization method - Google Patents

Description

  The present invention relates to a hot metal dephosphorization method, and more particularly to a hot metal dephosphorization method using titanium oxide as a part of a dephosphorization refining agent.

  In steelmaking processes using blast furnace hot metal, most of the silicon (Si) and phosphorus (P) contained in the hot metal are oxidized and removed using oxygen gas or solid iron oxide before decarburization and blowing in the converter. In general, so-called hot metal dephosphorization treatment, or hot metal desulfurization treatment in which sulfur (S) contained in the hot metal is removed under a reducing atmosphere by a desulfurizing agent, is commonly performed. In recent years, quality requirements for steel products have become more stringent than ever, and a lower level of phosphorus concentration has been demanded. 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 at the same time to stably reduce the phosphorus concentration after dephosphorization.

Usually, the hot metal dephosphorization treatment uses a medium solvent mainly composed of CaO such as quicklime as a dephosphorizing refining agent, and the dephosphorizing refining agent and an oxygen source are added to the hot metal, and the phosphorus in the hot metal is used as the oxygen source. The phosphorus oxide (P ₂ O ₅ ) oxidized by the above is taken into a molten dephosphorizing refining agent, and phosphorus in the molten iron is removed.

In this dephosphorization treatment, in order to stably lower the phosphorus concentration after the dephosphorization treatment, it is important to promote the melting (hatching) of CaO which is a dephosphorization refining agent. Conventionally, fluorite (CaF ₂ ) is known as a medium solvent excellent in slag hatching ability including CaO-based slag, and fluorite has also been used in hot metal dephosphorization treatment. However, in recent years, with the strengthening of environmental regulations, the use of a solvent medium containing fluorine, represented by fluorite, has been restricted. Therefore, the dephosphorization reaction by CaO is promoted without using fluorite. Means have been studied and numerous proposals have been made.

As one of the means, a method of reducing the basicity of the dephosphorization slag generated after the treatment has been proposed. For example, Patent Document 1 discloses that the basicity (CaO / SiO ₂ ) of slag after pretreatment is 2 in a hot metal pretreatment method in which refining including dephosphorization is performed while performing bottom blowing gas stirring and oxygen gas top blowing. It is proposed to control to less than .5. This is intended to promote the hatching of CaO by lowering the basicity of the dephosphorized slag and setting the slag composition to be generated outside the CaO saturated composition region. However, when the basicity of the dephosphorization slag is lowered, the dephosphorization ability of the produced slag is lowered. In order to stably lower the phosphorus concentration after the dephosphorization treatment using the dephosphorization slag having a low dephosphorization ability, it is necessary to increase the amount of the dephosphorizing refining agent used. That is, the dephosphorization slag produced | generated increases, As a result, the total discharge | emission amount of the slag in a steelmaking process will increase compared with the past, and it is very unpreferable from the surface of environmental influence.

As another means, a technique using another solvent as a substitute for fluorite has been proposed. For example, Patent Document 2 proposes a method of using a solvent containing aluminum oxide (Al ₂ O ₃ ) as a substitute for fluorite in decarburization refining or dephosphorization of hot metal. However, aluminum oxide promotes hatching of CaO-based slag, but has an effect of increasing the viscosity of CaO-based slag. For this reason, when the dephosphorization slag generated after the dephosphorization treatment is discharged from the reaction vessel, the dephosphorization slag may adhere to the reaction vessel and remain. As a result, there is a problem that so-called “recovery” occurs in which phosphorus in the dephosphorization slag remaining in the dephosphorization process of the next charge returns to the molten iron of the next charge, which adversely affects the dephosphorization process of the next charge.
JP-A-11-269524 JP 2002-309212 A

  The present invention has been made in view of the above circumstances, and the purpose of the present invention is not to excessively use a medium solvent mainly composed of CaO which is a dephosphorizing refining agent in dephosphorizing hot metal, Moreover, it is an object of the present invention to provide a hot metal dephosphorization method that can perform dephosphorization treatment with the same efficiency as the conventional method even if the dephosphorizing refining agent to be used does not contain fluorine.

The hot metal dephosphorization processing method according to the first aspect of the present invention for solving the above problems comprises adding a medium solvent mainly composed of CaO as a dephosphorization refining agent, and using a gaseous oxygen source and / or a solid oxygen source as an oxygen source. In the dephosphorization processing method of removing phosphorus in the hot metal by oxidizing the phosphorus in the hot metal by supplying the catalyst and taking the generated phosphor oxide into the medium solvent which has been hatched , the base of the dephosphorization slag generated after the treatment In addition to the solvent of which the degree is 2.5 or less and containing mainly CaO, a substance containing titanium oxide is used as a part of the dephosphorizing refining agent.

The hot metal dephosphorization method according to the second invention is characterized in that, in the first invention, the content of titanium oxide in terms of TiO _{2 in the} dephosphorization slag is 10% by mass or less. .

  The hot metal dephosphorization method according to the third invention is characterized in that, in the first or second invention, the medium solvent mainly containing CaO and the material containing titanium oxide do not substantially contain fluorine. It is what.

  A hot metal dephosphorization method according to a fourth invention is characterized in that, in any of the first to third inventions, iron sand is used as the substance containing titanium oxide.

  According to the present invention, in the hot metal dephosphorization treatment, in addition to a medium solvent mainly composed of CaO, a substance containing titanium oxide having excellent liquid phase forming ability of CaO-based slag is used as a dephosphorizing refining agent. Since it is used together as a part of the dephosphorizing refining agent, the hatching of the medium solvent mainly composed of CaO is promoted, the dephosphorization reaction is promoted, and the dephosphorization rate is improved. Therefore, it is possible to maintain the same dephosphorization rate as before without increasing the amount of the medium solvent mainly composed of CaO.

  Further, since the basicity of the dephosphorization slag to be generated is 2.5 or less, the proportion of the solid phase in the dephosphorization slag is low, and as a result, the fluidity of the dephosphorization slag itself is improved, The dephosphorization slag is discharged smoothly. In addition, titanium oxide has the effect of reducing the viscosity of the dephosphorized slag to be produced, and in combination with the basicity of the dephosphorized slag being 2.5 or less, the dephosphorized slag is discharged from the reaction vessel. In the dephosphorization process of the next charge, the dephosphorization reaction is not hindered by the dephosphorization by the remaining dephosphorization slag, and the dephosphorization process can be performed efficiently.

  Hereinafter, the present invention will be specifically described.

  The hot metal dephosphorization process is usually performed by using a hot metal conveying container such as a torpedo car or hot metal pan, or a refining furnace such as a converter as a reaction container, and adding a medium solvent mainly composed of CaO as a dephosphorizing refining agent, Further, an oxygen source such as oxygen gas and solid iron oxide is supplied to the hot metal to oxidize phosphorus in the hot metal with the oxygen source, and the generated phosphorous oxide is melted and dephosphorized including a medium solvent mainly composed of CaO. It is carried out by removing the phosphorus in the hot metal by taking it into the smelting agent. The dephosphorizing refining agent generates phosphorus-containing dephosphorization slag on the hot metal bath surface after the dephosphorization treatment. In the present invention, the slag generated by the dephosphorization refining agent hatched before or during the dephosphorization reaction is referred to as “dephosphorization slag” for convenience, and the dephosphorization slag generated after the treatment. It is distinguished from.

  In the present invention, in such hot metal dephosphorization treatment, the basicity of the dephosphorization slag produced after the treatment is adjusted to 2.5 or less. Specifically, the basicity of the dephosphorization slag is controlled to 2.5 or less by adjusting the addition amount or composition of the medium solvent mainly composed of CaO. Thus, in the present invention, since the basicity of the dephosphorization slag is 2.5 or less, the hatching of CaO is promoted, and the incorporation of the phosphor oxide into the dephosphorization refining agent is performed smoothly. That is, the dephosphorization reaction is promoted. Further, since the basicity of the dephosphorization slag to be generated is 2.5 or less, the proportion of the solid phase in the dephosphorization slag is low, and as a result, the fluidity of the dephosphorization slag itself is improved, The dephosphorization slag is discharged smoothly.

When the basicity of the dephosphorization slag after the treatment is less than 1.0, the proportion of CaO in the dephosphorization slag is lowered, resulting in poor dephosphorization. On the other hand, when the basicity of the dephosphorization slag exceeds 2.5, the flow rate of the dephosphorization slag decreases because the proportion of the solid phase in the dephosphorization slag is high, and the dephosphorization slag remains in the processing vessel. There is a possibility that rephosphorization will occur in the dephosphorization treatment of the next charge, which is not preferable. From such a viewpoint, the basicity of the dephosphorization slag after the dephosphorization treatment is more preferably 2.2 or less. The basicity of slag in the present invention is the ratio (mass% CaO / mass% SiO ₂ ) between the CaO content and the SiO ₂ content in the slag.

  In the present invention, as a dephosphorization refining agent in the hot metal dephosphorization treatment, a substance containing titanium oxide is used in combination as a part of the dephosphorization refining agent in addition to a medium solvent mainly composed of CaO. The added titanium oxide-containing substance is melted together with a medium solvent mainly composed of CaO to form dephosphorization slag on the hot metal.

Titanium oxide generally acts as an acidic oxide in a CaO-based slag produced when a solvent mainly composed of CaO is used as a dephosphorizing refining agent. Excellent hatching effect. As an example, FIG. 1 shows the relationship between the liquid phase ratio of dephosphorization slag calculated using thermodynamic calculation software (Fact Sage) and the TiO ₂ concentration in the slag. As shown in FIG. 1, it can be seen that the liquid phase ratio of the dephosphorization slag increases with the increase of the TiO ₂ component within the basicity range of the present invention. That is, it can be seen that the addition of a substance containing titanium oxide promotes the hatching of the medium solvent mainly composed of CaO and promotes the dephosphorization reaction.

  Titanium oxide has the effect of reducing the viscosity of CaO-based slag produced from a solvent medium mainly composed of CaO. Thereby, after the dephosphorization process, there exists an effect that discharge | emission of the dephosphorization slag from a reaction container becomes easy. For this reason, the residual amount of dephosphorization slag in the reaction vessel after the dephosphorization slag is discharged is negligibly small. In the dephosphorization treatment of the next charge, the dephosphorization reaction is not hindered by dephosphorization or the like, and the efficiency is reduced. Dephosphorization can be performed well.

The amount of titanium oxide in the dephosphorization slag produced in the reaction vessel is preferably 10% by mass or less in terms of TiO ₂ . When it exceeds 10 mass%, CaO required for a dephosphorization reaction will be diluted, and the dephosphorization capability will be 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 viscosity of dephosphorized 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. .

As the substance containing titanium oxide, generally available sand iron, ilmenite ore (titanite), rutile ore (goldenite), iron oxide-containing iron ore, and the like can be used. Among these, iron sand is particularly preferable because it is a fine particle having a size of 1 mm or less and is rapidly melted in the reaction vessel. Furthermore, it has been found that the iron oxide concentration of the dephosphorization slag produced by hatching the dephosphorization refining agent is increased by adding iron sand. Thereby, the oxygen potential of the dephosphorization slag is increased, and the dephosphorization ability of the dephosphorization slag is improved. Therefore, even if the amount of CaO is reduced, the dephosphorization ability of the dephosphorization slag is maintained. That is, even if the amount of the medium solvent mainly composed of CaO is reduced, the same dephosphorization rate as before can be maintained. Incidentally, although the quality of sand iron varies depending on the production area, it contains about 5 to 8% by mass of TiO _2, and about 13% by mass of TiO ₂ . Ilmenite red stone and rutile ore usually contain 30% by mass or more of TiO ₂ .

In the present invention, a substance containing titanium oxide is a substance containing 3% by mass or more of titanium oxide in terms of TiO ₂ , and a substance having a lower content is not defined as a substance containing titanium oxide. Even if a substance having a titanium oxide content of less than 3% by mass in terms of TiO ₂ is added, it is difficult to obtain the effect of titanium oxide described above, and when trying to obtain the effect, the addition amount increases and the amount of slag increases. This is because CaO necessary for the dephosphorization reaction is diluted, and instead the dephosphorization ability is lowered. Therefore, a substance in which titanium oxide is inevitably mixed as an impurity is not included in the substance containing titanium oxide in the present invention.

The medium solvent mainly composed of CaO is not particularly limited as long as it contains CaO and can be subjected to the dephosphorization treatment intended in the present invention. Usually, CaO is simple or 50 masses of CaO. % Or more and, if necessary, a hatching accelerator such as Al ₂ O ₃ or CaF ₂ as the other components. However, when dephosphorizing slag is disposed of, fluorine-containing substances such as fluorite should not be added to the dephosphorizing refining agent from the viewpoint of protecting the environment by reducing the amount of fluorine eluted from the dephosphorizing slag. Is preferred. A substance in which fluorine is inevitably mixed as an impurity component may be used. Of course, the substance containing titanium oxide is also preferably free of fluorine from this viewpoint.

  As a solvent medium mainly composed of CaO, it is preferable to use quick lime powder because it is inexpensive and has excellent dephosphorization ability. In addition, slag (also referred to as “decarburization slag”) generated when the hot metal after dephosphorization is decarburized and refined in a converter in the next step can be used as a solvent medium mainly composed of CaO. The decarburized slag contains CaO as a main component and has a low phosphorus content, so that it can be sufficiently used as a medium solvent mainly composed of CaO.

  As a method for adding a medium solvent mainly composed of CaO, it may be placed on top, injected into hot metal, or a combination thereof. Further, it may be added by spraying toward the hot metal bath surface. The addition method of the substance containing titanium oxide may be any method, but in order to quickly exhibit the above-described effect of titanium oxide, it is mixed from the same location as the medium solvent mainly composed of CaO. It is preferable to add.

  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, in order to promote the dephosphorization process, a gaseous oxygen source and / or a solid oxygen source is supplied to the molten iron as an oxygen source. As this gaseous oxygen source, oxygen gas or oxygen-containing gas is used, and as the solid oxygen source, iron oxide such as iron ore or mill scale is used. Of these, for gaseous oxygen sources, by any method such as top blowing by lance, injection into hot metal or bottom blowing, and for solid oxygen sources by any method such as top loading or injection, respectively. Supply to hot metal. 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 and latent heat of the solid oxygen source itself are larger than the oxidation reaction heat, so the hot metal temperature. Descends. 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. Further, in order to efficiently perform the dephosphorization reaction, it is preferable to stir the hot metal. As this stirring, generally, gas stirring using a dipping lance or a nozzle embedded in the furnace bottom may be performed.

  By performing the hot metal dephosphorization treatment in this manner, the dephosphorization treatment can be performed while maintaining the same dephosphorization rate as before even if the amount of the medium solvent mainly composed of CaO is reduced. As a result, it is possible to reduce the generated dephosphorization slag and bring about industrially beneficial effects such as resource saving and reduction of waste slag. In addition, titanium oxide has an action of lowering the viscosity of the dephosphorization slag to be generated, whereby the dephosphorization slag is smoothly discharged from the reaction vessel, and remains in the dephosphorization process of the next charge. The dephosphorization treatment can be efficiently performed without hindering the dephosphorization reaction by dephosphorization by dephosphorization slag or the like. Furthermore, it is possible to maintain the same amount of dephosphorization as before without adding a fluorine-containing substance to the dephosphorizing refining agent. In this case, it is not necessary to take measures for leakage of fluorine to the environment. This makes it possible to reuse the dephosphorized slag.

  The hot metal discharged from the blast furnace was desiliconized in the blast furnace cast floor, and then transferred to a 300-ton capacity converter, and a total of seven dephosphorization processes were performed in the converter (Invention Examples 1 to 7). The phosphorus concentration of the hot metal before the dephosphorization treatment was unified to 0.12% by mass, and the target phosphorus concentration of the hot metal after the dephosphorization treatment was set to 0.020% by mass or less.

As the dephosphorization treatment conditions, the supply ratio of the gaseous oxygen source and the solid oxygen source was adjusted so that the hot metal temperature before and after the dephosphorization treatment was in the range of 1270 to 1350 ° C. As the dephosphorizing refining agent, CaO-based quick lime not containing a fluorine source such as fluorite is used, and iron oxide (TiO ₂ content: 7.5 mass%) or high Ti ore (TiO ₂ ) is used as a titanium oxide source. ₂ content: 20% by mass) was added as a dephosphorizing refining agent, and the mixture was placed on top. Then, oxygen gas was supplied by an upper blowing lance and a solid oxygen source mainly composed of iron ore was placed on top. 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.

Moreover, as a comparative example, when a TiO ₂ source is not used as a dephosphorizing refining agent and only quick lime is used (Comparative Examples 1 to 3), when quick lime and fluorite are used in combination (Comparative Example 4), and The dephosphorization process was performed also about the case (comparative example 5) which used quick lime and the lump cake. Other dephosphorization treatment conditions in Comparative Examples 1 to 5 were performed in accordance with the examples of the present invention. Ingot casting is a general term for slag generated from a ladle that contains and conveys molten steel and slag generated from a tundish of a continuous casting facility.

  After dephosphorization treatment, dephosphorization slag was collected and analyzed, and the composition of dephosphorization slag was investigated. As a result, the concentrations of MgO and MnO, which are representative components of dephosphorization slag, were in the range of 1 to 5% by mass and 1 to 10% by mass, respectively, in both the inventive examples and the comparative examples. Further, the iron oxide concentration in the dephosphorized slag was 10% by mass or more. 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 examples of the present invention in which a TiO ₂ source was used in combination as a dephosphorizing refining agent, the phosphorus concentration in the hot metal after the dephosphorization treatment was the same as in the case of using fluorite in Comparative Example 4 together. 0.020% by mass or less. In contrast, in Comparative Examples 1 to 3 and Comparative Example 5, the phosphorus concentration in the hot metal after the dephosphorization treatment was higher than 0.020% by mass, and it was confirmed that the phosphorus was not sufficiently dephosphorized.

In Comparative Examples 1 to 5, TiO ₂ is present in the dephosphorization slag, but this is not brought from the dephosphorization refining agent, but is carried over from the blast furnace slag adhering to the hot metal transfer container. In addition, Ti contained in the blast furnace hot metal is generated by oxidation by dephosphorization.

It is a diagram showing the relationship between the liquid phase ratio and slag TiO ₂ concentration of dephosphorization for slag calculated using the thermodynamic calculation software.

Claims (4)

A medium in which a medium solvent mainly composed of CaO is added as a dephosphorizing refining agent, a gaseous oxygen source and / or a solid oxygen source is supplied as an oxygen source to oxidize phosphorus in the hot metal, and the generated phosphor oxide is hatched. In the dephosphorization treatment method for removing phosphorus in the hot metal by taking it into the solvent, the basicity of the dephosphorization slag generated after the treatment is 2.5 or less, and in addition to the medium solvent mainly composed of CaO, A method for dephosphorizing hot metal, characterized by using a substance containing titanium oxide as a part of a dephosphorizing refining agent. _2. The hot metal dephosphorization method according to claim 1, wherein the content of titanium oxide in terms of TiO _{2 in the} dephosphorization slag is 10% by mass or less.   3. The hot metal dephosphorization method according to claim 1 or 2, wherein the CaO-based medium solvent and the titanium oxide-containing substance contain substantially no fluorine.   4. The hot metal dephosphorization method according to any one of claims 1 to 3, wherein iron sand is used as the substance containing titanium oxide.

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