JP2010163652A - Method for removing copper and sulfur from molten iron - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To produce molten iron having little contents of copper and sulfur, while the copper in the molten iron produced by using copper-contained steel scrap, is effectively removed by using sulfur-containing flux without needing a large-scaled facility and successively, the sulfur in the molten iron, which is brought from the sulfur-contained flux, is efficiently removed in the same reaction vessel without discharging the sulfur-containing flux containing the copper. <P>SOLUTION: In a method for removing the copper and the sulfur from the molten iron, the sulfur-containing flux is added to the molten iron accommodated in the reaction vessel, and the copper in the molten iron is removed by absorbing the copper in the molten iron into this flux and successively, without discharging the sulfur-containing flux containing the copper, a flux for desulfurizing, is added into the reaction vessel to remove the sulfur contained in the molten iron. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention removes copper, which is a quality problem when producing high-grade steel from hot metal produced using steel scrap (iron scrap), and then uses the same reaction vessel to sulfur in the hot metal. In detail, the copper in the hot metal is removed using the sulfur-containing flux, and the sulfur in the hot metal brought about by the sulfur-containing flux is used for the copper removal treatment. The present invention relates to a method for removing the contained sulfur-containing flux in the same reaction vessel without discharging.

The iron source used in the steelmaking process is mainly hot metal obtained by reducing iron ore in a blast furnace, but with the aging of steel scraps, buildings and machinery products generated in the processing process of steel materials A considerable amount of steel scrap is also used. The production of hot metal in the blast furnace requires a great deal of energy to reduce and melt iron ore, whereas steel scrap requires only heat of melting, and when steel scrap is used in the steelmaking process, There is an advantage that the amount of energy used for reducing heat of iron ore can be reduced. Therefore, from the viewpoint of energy saving and prevention of global warming by reducing CO _2, it is desired to promote the use of steel scrap.

By the way, when recycling steel scraps, trump elements represented by copper and tin accompanying these steel scraps are inevitably mixed in the molten iron in the process of steel scrap melting. The trump element is a component that impairs the properties of steel and must be kept below a certain concentration. For this reason, it has been difficult to use low-grade steel scraps that may contain copper or tin as an iron source for producing high-grade steel. However, considering the recent increase in steel scrap generation and the demand for increased use of steel scrap to reduce CO ₂ generation, it is necessary to promote recycling of lower steel scrap.

  As a practical technology for using the current low-grade steel scrap, the steel scrap is physically decomposed and harmful parts are separated by methods such as human power and magnetic separation. There is no effective method other than blending in a raw material containing almost no carbon and using it within a range where there is no problem in the material properties of the steel material. With such a method, it is impossible to recycle a large amount of scrap steel from used cars, etc., and it is sufficient as a technology for removing copper in steel scrap corresponding to the era of the large amount of scrap scrap expected in the future. Cannot be a good solution.

On the other hand, the principle invention described below is known about the copper removal method after mixing in molten iron. That is, the basic technical knowledge of contacting the copper-containing high carbon molten iron with the FeS-Na ₂ S-based flux and separating and removing the copper component in the molten iron as Cu ₂ S is disclosed in Non-Patent Document 1 and Non-Patent Document. 2 is reported. This technique proposes a wider applicability to the above-described physical removal method as a copper removal technique. However, this method has a problem that the sulfur (S) component is mixed into the molten iron from a sulfur-containing flux such as a Na ₂ S-based flux, and the sulfur concentration in the molten iron increases. In addition, the distribution ratio, which is the ratio of the Cu concentration in the slag formed on the molten iron by melting the sulfur-containing flux and the Cu concentration in the molten iron, is about 30 at most, giving sufficient stirring to the slag and the distribution ratio It is necessary to prevent the deterioration.

As a decoppering treatment method based on this fundamental technical knowledge, Patent Document 1 discloses that a copper-containing high-carbon molten iron is obtained by carburizing and melting copper-containing steel scrap, and then contacting with a flux mainly composed of Na ₂ S. A method is disclosed in which the copper component in molten iron is separated and removed in the Na ₂ S flux as Cu ₂ S by reacting.

  However, Patent Document 1 does not disclose any desulfurization of high carbon molten iron after copper removal. Moreover, although the copper removal treatment is performed by stirring the hot metal and slag by blowing Ar gas from the bottom of the reaction vessel (hot metal ladle), stirring of the slag is insufficient. In order to compensate for this, it is equipped with an electric heating device for maintaining a reaction temperature of 1200 to 1500 ° C., and uses a covered reaction vessel for cutting off the contact with the atmosphere. It is not an established technology.

Japanese Patent Laid-Open No. 4-198431

Masato Imai, iron and steel, vol.74 (1988) No.4. p. 640 Oshio et al., Iron and Steel, vol.77 (1991) No.4. p. 504

  The present invention has been made in view of the above circumstances, and its object is to use copper in hot metal produced using copper-containing steel scrap, using a sulfur-containing flux without the need for extensive equipment. The sulfur in the hot metal brought about by the sulfur-containing flux was removed efficiently, and used for copper removal treatment in the same reaction vessel without discharging the sulfur-containing flux containing copper. It is an object of the present invention to provide a method for removing copper and sulfur from hot metal, which can be efficiently removed and can produce hot metal with low copper content and low sulfur content.

  The method for removing copper and sulfur from the hot metal according to the first invention for solving the above-described problem is a method of removing sulfur from the hot metal contained in a reaction vessel produced by carburizing and dissolving copper-containing steel scrap. The copper in the hot metal is absorbed into the flux to remove the copper in the hot metal, and then the desulfurization flux is added into the reaction vessel without discharging the sulfur-containing flux containing copper. Thus, sulfur contained in the molten iron is removed.

The method for removing copper and sulfur from the hot metal according to the second invention uses, in the first invention, a material mainly composed of Na ₂ CO ₃ and an iron-sulfur alloy as a starting material for the sulfur-containing flux. It is characterized by.

  The method for removing copper and sulfur from the hot metal according to the third invention is characterized in that, in the first or second invention, the copper and sulfur removal process from the hot metal is performed by a mechanical stirring type refining apparatus. Is.

  The method for removing copper and sulfur from the hot metal according to a fourth aspect of the present invention is the method according to any one of the first to third aspects, wherein the hot metal contains the copper using a vertical furnace in which a carbon material bed is formed. It is characterized by carburizing and melting steel scrap.

  According to the present invention, copper in hot metal produced by carburizing and dissolving copper-containing steel scrap is separated and removed by the sulfur-containing flux. Copper, which was difficult to separate, can be separated and removed efficiently, and after separation and removal of copper, desulfurization flux is added to the same reaction vessel without discharging the sulfur-containing flux that has absorbed copper. Since the hot metal desulfurization treatment is performed, that is, the copper removal treatment step and the desulfurization treatment step are carried out continuously, it is possible to improve productivity and prevent the hot metal temperature from being lowered. In addition, it is possible to efficiently produce hot metal with less sulfur.

It is the schematic of the cross-sectional composition distribution of the slag produced | generated after implementing a copper removal process and a desulfurization process continuously.

  The present invention will be specifically described below.

When the hot metal for steelmaking containing carbon is produced by carburizing and dissolving copper-containing steel scrap, almost all of the copper in the steel scrap is dissolved in the hot metal. In the present invention, as a means for removing the copper (referred to as “copper removal treatment”), the sulfur-containing flux is brought into contact with the hot metal, and the copper in the hot metal is separated and removed into the sulfur-containing flux as copper sulfide (Cu ₂ S). . As the sulfur-containing flux, those containing an alkali metal or alkaline earth metal sulfide as a main component are suitable. In order to increase the sulfur content in the sulfur-containing flux, FeS (iron sulfide) may be mixed. Particularly suitable is a flux mainly composed of Na ₂ S. In the case of a flux mainly composed of Na ₂ S, if Na ₂ CO ₃ (soda ash) widely used industrially is used as the Na source, and an iron-sulfur alloy (ferrosulfur) is used as the sulfur source, This is advantageous in terms of cost. As the composition of the sulfur-containing flux, it is desirable that the molar fraction of Na ₂ S in the flux is 0.2 or more from the viewpoint of efficient copper removal. There is no particular upper limit for the molar fraction of Na ₂ S in the flux, and a desired copper removal reaction can be expected as long as it is 0.2 or more.

  Since copper removal with a sulfur-containing flux is a process with a low distribution ratio (ratio of Cu concentration in the flux and Cu concentration in the molten iron), the sulfur-containing flux should be added in order to sufficiently proceed with copper removal. Therefore, it is necessary to promote the mass transfer on the slag side formed in the reaction vessel. For this purpose, it is important to also stir the slag layer. In particular, in the present invention, the copper removal treatment is performed in the hot metal stage, the hot metal temperature range (1200 to 1400 ° C.) is lower than the molten steel temperature range (1550 to 1700 ° C.), and the slag fluidity is also low. Slag agitation is important.

  As a method of simultaneously stirring the molten iron and the slag present on the molten iron, the stirring slag is blown from the injection lance immersed in the molten iron in the reaction vessel or the tuyere installed at the bottom of the reaction vessel, and the slag and molten iron are stirred. Although a method (referred to as a “gas stirring method”) can also be employed, in the present invention, it is preferable to perform a copper removal treatment using a mechanical stirring type refining apparatus because good stirring can be obtained. As a mechanical stirring type refining apparatus, stirring using an impeller (also referred to as “stirring blade”) is typical. In other words, the impeller is immersed in the hot metal contained in a ladle-shaped reaction vessel, and the impeller is rotated about the axis of rotation to forcibly stir the hot metal and the sulfur-containing flux added on the hot metal. Is the method. In the mechanical stirring type refining apparatus, the sulfur-containing flux charged on the hot metal is sufficiently entrained in the hot metal, and the hot metal and the sulfur-containing flux are sufficiently stirred. On the other hand, in the gas stirring method disclosed in Patent Document 1, the slag is not easily caught in the hot metal, and stirring is insufficient.

  Further, a method of blowing a powdery sulfur-containing flux into the hot metal together with the conveying gas from an injection lance immersed in the hot metal, so-called flux blowing method, is also a preferable processing method. In this case, the powdered sulfur-containing flux blown into the hot metal is in direct contact with the hot metal, and new unreacted sulfur-containing flux is continuously in contact with the hot metal, facilitating mass transfer on the slag side. The effect equivalent to the case where it is made to develop is exhibited, and the reaction between the hot metal and the sulfur-containing flux is promoted. Further, since the carrier gas also functions as a stirring gas, although the stirring strength is not as high as that of the mechanical stirring type refining apparatus, the hot metal and the hot metal slag are stirred.

  In the copper removal treatment, an inert gas such as Ar gas or a reducing gas such as propane may be supplied onto the hot metal bath surface in order to prevent air from entering the atmosphere.

  In the present invention, the temperature of the hot metal before the copper removal treatment, that is, the hot metal for steelmaking containing carbon produced by carburizing and melting the copper-containing steel scrap is 1200 ° C. or higher and 1500 ° C. or lower, preferably 1250 ° C. or higher and 1350 It is preferable that it is below ℃. If the hot metal temperature is less than 1200 ° C., there is a concern about solidification and solidification of the flux and the hot metal itself due to the low temperature. In particular, considering the temperature guarantee in the subsequent desulfurization process and converter decarburization process, it is desirable to set the temperature to 1250 ° C. or higher. On the other hand, at 1500 ° C. or higher, the evaporation of flux due to high temperature cannot be ignored. That is, in order to suppress the evaporation of the sulfur-containing flux and perform the copper removal reaction efficiently, the lower the hot metal temperature is preferable, and therefore, the hot metal temperature should be 1350 ° C. or lower for efficient copper removal reaction. Is desirable.

  The carbon concentration in the hot metal before the copper removal treatment is preferably 2% by mass or more. It is known that the reaction in which the copper in the hot metal becomes copper sulfide proceeds more thermodynamically as the carbon concentration in the hot metal is higher. If the carbon concentration in the hot metal before the copper removal treatment is less than 2% by mass, the formation reaction of copper sulfide does not occur sufficiently, the liquidus temperature of the hot metal rises, and the hot metal adheres to the vessel wall. It becomes a problem. The upper limit of the carbon concentration is not particularly required, but it is preferably up to about 5.5% by mass in consideration of reduction of the amount of carbon material used. Even if excessive carburizing is performed, only graphite is deposited on the hot metal surface, and the contribution to the copper removal reaction is small. Furthermore, the copper concentration in the hot metal before the copper removal treatment is preferably 0.1% by mass or more and 1.0% by mass or less. When the copper concentration in the hot metal before the copper removal treatment exceeds 1.0% by mass, the amount of the sulfur-containing flux necessary for removing copper becomes excessive, and the practical load is large. On the other hand, when it is less than 0.1% by mass, it can be dealt with by, for example, diluting with a hot metal having a low copper content without performing a copper removal treatment.

  Furthermore, the sulfur concentration of the hot metal before the copper removal treatment is preferably 0.01% by mass or more, and more preferably 0.05% by mass or more. If the sulfur concentration of the hot metal before the copper removal treatment is less than 0.01% by mass, the amount of sulfur dissolved from the sulfur-containing flux into the hot metal becomes excessive, and the use efficiency of the sulfur-containing flux is lowered, which is not economical. The upper limit of the sulfur concentration does not need to be specified in particular, but if it is too high, the desulfurization treatment will be hindered, so it is desirable to set it to 0.5% by mass or less.

  As the hot metal components other than those described above before the copper removal treatment, for example, the silicon concentration is preferably 0.5% by mass or less and the manganese concentration is preferably 0.5% by mass or less. When these concentrations are exceeded, silicon oxide and manganese oxide generated by oxidation of these components during the copper removal treatment are transferred to slag to increase the amount of slag, making slag treatment difficult, as well as silicon oxide and manganese oxide. May inhibit the copper removal reaction of the sulfur-containing flux.

  In addition, the hot metal for steelmaking manufactured by carburizing and melting copper-containing steel scrap is mixed with hot metal discharged from the blast furnace (hereinafter referred to as “blast furnace hot metal”) as necessary to dilute the copper concentration. Thereafter, copper contained in the mixed hot metal may be removed using a sulfur-containing flux.

  As a process for producing hot metal containing carbon by carburizing and dissolving copper-containing steel scrap, there are a method using an electric furnace, a method using a converter, a method using a vertical furnace, etc. Since the energy efficiency is higher than that of a converter or a converter, a method using a vertical furnace in which a carbon material bed is formed is preferable.

  Here, a vertical furnace with a charcoal bed formed inside is a steel containing copper-containing steel scraps and coke from the upper part of the vertical furnace and, if necessary, a slagging agent, and is provided at the lower part of the vertical furnace. The coke is burned by blowing air, oxygen-enriched air, oxygen gas, hot air, etc. from the heated tuyere, and the copper-containing steel scrap and iron making agent are melted by the combustion heat of the coke, and the hot metal is melted from the tap at the bottom of the furnace. And an apparatus for taking out molten slag. In this case, only the coke is filled in the range from the furnace bottom to a certain height above the tuyere, and this is burned to melt the copper-containing steel scrap charged in the upper part of the coke. The coke that fills the bottom of the furnace is called a “charcoal bed”, and the charcoal bed burns and wears out. To compensate for this, the coke is charged from the top of the furnace body. The molten iron produced by melting the copper-containing steel scraps flows down the coke gap and is carburized by the coke to produce hot metal.

  When hot metal is produced using such a vertical furnace in which a carbon material bed is formed, the sulfur concentration in the hot metal is generally higher than that in the blast furnace hot metal. Taking advantage of this high sulfur concentration, copper removal with a sulfur-containing flux can be advantageously advanced. Since the sulfur concentration in the hot metal is high, there is little movement of sulfur from the sulfur-containing flux into the hot metal, and the utilization efficiency of the sulfur-containing flux can be increased.

  Along with the above copper removal treatment, sulfur in the sulfur-containing flux inevitably moves into the hot metal, so that the sulfur concentration in the hot metal increases. Accordingly, when the hot metal is decopperized using the sulfur-containing flux, after the decoppering process, a desulfurization process for removing sulfur in the hot metal is required. In the present invention, the desulfurization treatment is performed without discharging the sulfur-containing flux used in the decopperization treatment from the reaction vessel for the purpose of improving productivity and preventing the hot metal temperature from decreasing. The desulfurization flux is added to the performed reaction vessel, and the reaction is performed in the same reaction vessel as the reaction vessel in which the copper removal treatment is performed.

  This desulfurization treatment may be any of a method using a known mechanical stirring type refining device, a method by blowing powder from an injection lance, a method using a converter, and the like. As the desulfurization agent, various desulfurization agents such as a desulfurization agent mainly composed of CaO, a desulfurization agent mainly composed of calcium carbide, a desulfurization agent mainly composed of soda ash, and metallic Mg can be used. However, since a high desulfurization rate can be obtained even if an inexpensive desulfurizing agent mainly composed of CaO is used, it is preferable to perform the desulfurization treatment using a mechanical stirring type refining apparatus. Here, the desulfurizing agent containing CaO as a main component is quick lime itself, or one obtained by adding several mass% to ten and several tens mass% of quick lime and alumina.

  When desulfurization processing is performed with the same mechanical stirring type refining equipment after performing decopperization processing with a mechanical stirring type refining device, the transition period from the decoppering treatment process to the desulfurization processing step can be minimized, and production The improvement of the property and the prevention of the hot metal temperature from being lowered are further achieved. Moreover, when performing a desulfurization process, a blast furnace hot metal may be mixed with the hot metal which performed the copper removal process, a sulfur concentration may be diluted, and the mixed hot metal desulfurization process may be performed after that. Furthermore, you may mix a blast furnace hot metal with the hot metal after a desulfurization process.

After the desulfurization treatment, it is necessary to remove the slag in the reaction vessel (a mixture of the sulfur-containing flux and the desulfurization flux) from the reaction vessel. If this slag is not removed and decarburized and refined in a converter, for example, the copper sulfide (Cu ₂ S) in the sulfur-containing flux is decomposed and returned to the molten steel, not only increasing the copper concentration in the molten steel but also desulfurizing. This is because the sulfur in the flux for use returns to the molten steel, the sulfur concentration in the molten steel increases, and a molten steel with less copper and sulfur cannot be obtained.

  The slag removal operation may be any of a method using a known slag dragger, a method using a slag suction machine, a method of discharging the slag in the container by inclining the hot metal container, and is suitable for the equipment situation possessed by each steelworks You can select the one you want.

  As described above, according to the present invention, the copper in the hot metal produced by carburizing and melting copper-containing steel scrap is separated and removed by the sulfur-containing flux. It is possible to efficiently separate and remove copper, which was difficult to separate by the method of separating and removing by the above, and after separating and removing the copper, desulfurization in the same reaction vessel without discharging the sulfur-containing flux that absorbed the copper. Flux is added and the hot metal desulfurization treatment is performed, that is, since the copper removal treatment step and the desulfurization treatment step are carried out continuously, improvement of productivity and prevention of lowering of the hot metal temperature are realized. It becomes possible to efficiently produce hot metal containing less copper and sulfur from copper-containing steel scrap.

  Using a vertical furnace with a charcoal bed formed inside, copper-containing steel scrap is melted to produce hot metal for steelmaking. About 5 tons of the hot metal produced is received in the hot metal ladle and removed in this hot metal ladle. The test which performs a copper process and a desulfurization process continuously was implemented 8 times (test No. 1-8).

As the sulfur-containing flux for copper removal, an iron-sulfur alloy (ferrosulfur, sulfur content: 48% by mass) and soda ash (Na ₂ CO ₃ ) were used. As a method for stirring hot metal in the hot metal ladle and adding sulfur-containing flux, a sulfur-containing refining flux is added from a refining agent supply hopper provided on the pan, and an impeller covered with a refractory is immersed in the hot metal. Rotating the impeller, stirring the molten iron and the sulfur-containing flux (mechanical stirring method), immersing the refractory-coated injection lance in the hot metal, and using nitrogen gas as the carrier gas through the injection lance Two methods of blowing and adding a sulfur-containing flux into the hot metal (flux blowing method) were used. After completion of the decoppering treatment, desulfurization refining was carried out by adding the desulfurization flux without removing the sulfur-containing flux (decoppering slag) after the decoppering treatment floating on the hot metal.

  On the other hand, as a comparative example, after removing the copper removal slag floating on the hot metal after the copper removal treatment with a slag dragger, a test for carrying out a desulfurization scouring by adding a desulfurization flux was also performed (Test Nos. 9 to 12). ).

  The desulfurization treatment includes a mechanical stirring method in which the impeller is rotated to stir the molten iron and a desulfurization flux is added from a hopper for supplying a refining agent, and a flux blowing method in which a desulfurization flux is blown into the hot metal together with nitrogen gas from the injection lance. Two ways were done. The most common quick lime was used as the desulfurization flux.

  Table 1 shows a list of test conditions and test results. As for the hot metal components before the copper removal treatment, the components other than those in Table 1 are 4.5 to 4.7% by mass of carbon, 0.20% by mass of silicon, 0.15% by mass of manganese, and 0.050 of phosphorus. The test was performed with the mass% aligned. The hot metal temperature before the copper removal treatment was 1350 ° C.

  In this example, the test was performed by two methods of the mechanical stirring method and the flux blowing method. As can be seen from Table 1, there is no significant difference in the refining characteristics between the mechanical stirring method and the flux blowing method regarding the copper removal treatment. I couldn't.

  On the other hand, with regard to the desulfurization treatment, although the sulfur concentration is low in the desulfurization treatment by the mechanical stirring method, a slight amount of recovered copper (a phenomenon in which the copper in the decopper slag returns to the hot metal) has occurred. In the case of the mechanical stirring method, the stirring force is strong, and the copper removal slag and quicklime are entrained in the hot metal bath, so it is considered that the copper removal reaction occurs due to the reaction between the copper removal slag and the hot metal.

  On the other hand, in the case of the flux blowing method, although the recovery copper does not occur at all, the reached sulfur concentration was slightly high. This is presumably because the flux blowing method is weaker than the mechanical stirring method, and there is less entrainment of the copper removal slag into the hot metal bath.

Incidentally, as a result of collecting, observing and investigating slag samples after continuously performing the copper removal treatment and the desulfurization treatment, it was confirmed that granular slag having a concentration distribution as shown mainly in the conceptual diagram of FIG. 1 was obtained. I understood. That is, the shape is such that desulfurization flux (desulfurization slag: CaO-CaS system) having a high melting point composition is coated around the decopperization slag (Na ₂ S—FeS—Cu ₂ S system) having a low melting point composition. Therefore, it is presumed that the copper reaction was difficult to occur because of this shape.

  In this way, the sulfur concentration of the hot metal is reduced to about 0.006 to 0.009% by mass by adding the flux for desulfurization without removing the copper removal slag after the copper removal treatment, and the recovered copper. Was found to hardly occur. If it is this level of sulfur concentration, it cannot be applied to low-sulfur steel or ultra-low-sulfur steel, but it is at a level that can be sufficiently used for thin steel plates and general thick steel plates. Moreover, when comparing the hot metal temperature after the desulfurization scouring treatment, the test No. 1-8 that does not remove the decopper slag after the decoppering treatment is approximately 20 ° C. than the test No. 9-12 in which the decopper slag is removed. The hot metal temperature can be kept high.

  That is, according to the present invention, the hot metal applicable to the thin steel plate material and the general thick steel plate material can be melted with one processing facility without going through the waste removal step of removing the copper removal slag after the copper removal treatment. In addition, it is possible to enjoy merits such as labor saving by omitting the process and securing thermal margin after the next process.

Claims (4)

  A sulfur-containing flux is added to the hot metal contained in the reaction vessel, which is produced by carburizing and dissolving copper-containing steel scrap, and the copper in the hot metal is absorbed by the flux to remove the copper in the hot metal, and then Removing sulfur contained in hot metal by adding a desulfurization flux to the reaction vessel without discharging the sulfur-containing flux containing copper. Method. It said sulfur-containing material and iron as the main component Na ₂ CO ₃ as starting material for the flux - characterized by the use of sulfur alloy, copper and method for removing sulfur from molten iron according to claim 1.   The method for removing copper and sulfur from hot metal according to claim 1 or 2, wherein the copper and sulfur removal treatment from the hot metal is performed with a mechanical stirring type refining apparatus.   The hot metal is obtained by carburizing and melting the copper-containing steel scrap using a vertical furnace in which a carbon material bed is formed. A method for removing copper and sulfur from the hot metal as described.

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