JP5581760B2 - Method for removing copper in steel scrap and method for producing molten steel using steel scrap as an iron source - Google Patents

Description

  The present invention relates to a method for removing copper in steel scrap, which causes quality problems when steel scrap (iron-based scrap) is used as an iron source, and melting after removing copper The present invention relates to a method for producing molten steel for high-grade steel using iron.

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. In the manufacture of iron and steel products, the production of hot metal in a blast furnace requires a great deal of energy to reduce and melt iron ore, whereas steel scraps only require heat of melting. When used, 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.

  Conventionally, steel scrap is often used by directly charging it into a steelmaking furnace such as a converter or an arc furnace. However, when various steel scraps are used as the iron source, there is a problem that it is difficult to adjust the composition of the molten steel to be produced. In addition, since the converter uses the combustion heat of carbon contained in the hot metal as the melting heat of steel scrap, there is a disadvantage that the mixing ratio of steel scrap cannot be increased, whereas the arc furnace has an energy The efficiency was low and there were drawbacks in terms of energy consumption.

  However, in an arc furnace, in order to solve the problem of low energy efficiency, steel waste is preheated by high-temperature exhaust gas generated from the arc furnace during melting, and the preheated steel scrap is melted to reduce the amount of power used. A number of techniques have been proposed to reduce this. The representative average is the technique proposed in Patent Document 1.

  The method for melting steel scrap according to Patent Document 1 uses an arc furnace having a melting chamber and a shaft-type preheating chamber directly connected to the upper portion of the melting chamber and into which exhaust gas generated in the melting chamber is introduced. While supplying the cold iron source to the preheating chamber continuously or intermittently so that the scrap is continuously present in the preheating chamber and the melting chamber, the steel scrap in the melting chamber is melted by an arc to the melting chamber. When the molten iron for at least one heat is collected, the molten iron is discharged in a state where the steel scrap is continuously present in the melting chamber and the preheating chamber. " It has been reported that it is possible to dissolve at a power unit of 200 kWh / t or less.

By the way, when recycling steel scraps, trump elements typified 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 was difficult to use steel scraps that may contain copper or tin as an iron source for producing high-grade steel. However, considering the recent increase in the amount of steel scrap generated and the demand for increased use of steel scrap for reducing CO ₂ generation, it is necessary to promote the recycling of steel scrap.

  The current practical technology for using steel scraps that may contain copper and tin is to physically decompose the steel scraps and separate harmful parts by methods such as human power and magnetic separation. There is no effective method other than blending the part separated into the raw material containing almost no harmful components and using it within the range where there is no problem in the material properties of the steel material. However, with such a method, it is impossible to recycle a large amount of steel scrap such as used automobiles, and as a technology for removing copper in steel scrap corresponding to the era of a large amount of steel scrap expected in the future, It cannot be a sufficient 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 bringing copper-containing high carbon molten iron and FeS-Na ₂ S flux into contact with each other 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 1. It is reported in Patent Document 2. 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 a sulfur (S) component is mixed into the molten iron from the Na ₂ S-based flux. In addition, the distribution ratio, which is the ratio of the Cu concentration in the slag formed on the molten iron by melting the flux and the Cu concentration in the molten iron, is about 30 at most, and the distribution ratio is obtained by giving sufficient stirring to the slag. It is necessary to prevent the deterioration.

As a copper removal treatment method based on this fundamental technical knowledge, Patent Document 2 discloses a flux containing Na ₂ S as a main component after carburizing and melting steel scraps containing copper into copper-containing high carbon molten iron. And a method of separating and removing the copper component in the molten iron as Cu ₂ S in the Na ₂ S-based flux.

  However, Patent Document 2 does not disclose any desulfurization of high carbon molten iron after the copper removal treatment. In addition, a facility for performing the copper removal treatment is necessary separately from the melting furnace, and in order to promote the copper removal reaction, an electric heating device for maintaining a reaction temperature of 1200 to 1500 ° C. is provided, and the atmosphere and A closed reaction vessel is used to cut off the contact, and the equipment is large, and it has not been established as a practical technology.

JP-A-10-292990 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 purpose is to efficiently dissolve steel scrap with a small amount of energy consumption when manufacturing high-grade steel using steel scrap as an iron source, It is to provide a copper removal method capable of removing copper in steel scrap efficiently and without requiring large-scale equipment, and for high-grade steel using molten iron after removing this copper. It is to provide a method for producing molten steel.

  The method for removing copper in steel scraps according to the first invention for solving the above-mentioned problems is a melting chamber and a shaft type preheating that is directly connected to the upper portion of the melting chamber and into which exhaust gas generated in the melting chamber is introduced. A melting chamber using arc heat while supplying the steel scrap to the preheating chamber so that the steel scrap is continuously present in the preheating chamber and the melting chamber. After the steel scrap is carburized and melted to produce molten iron, the sulfur-containing flux is then supplied to the molten iron in the generated melting chamber to remove the copper contained in the molten iron, and then the copper is removed The molten iron is discharged from an arc furnace into a holding container.

  The method for removing copper in the steel scrap according to the second invention is the state in which, in the first invention, the steel scrap is continuously present in the preheating chamber and the melting chamber when the molten iron is discharged from the arc furnace. It is characterized by being.

The method for removing copper in steel scraps according to a third aspect of the present invention is characterized in that, in the first or second aspect, the sulfur-containing flux contains Na ₂ S as a main component.

According to a fourth aspect of the present invention, there is provided a method for removing copper in steel scraps according to any one of the first to third aspects of the present invention, as a starting material for the sulfur-containing flux, a material mainly composed of Na ₂ CO ₃ and iron It is characterized by using a sulfur alloy.

  In any one of the first to fourth inventions, the method for removing copper in steel scraps according to a fifth aspect of the present invention provides the molten iron before removing the copper with the sulfur-containing flux having a temperature of 1200 ° C to 1500 ° C. The carbon concentration is 2% by mass or more, the copper concentration is 0.1% by mass or more and 1.0% by mass or less, and the sulfur concentration is 0.01% by mass or more.

  The method for removing copper in steel scraps according to a sixth aspect of the present invention is the method for removing copper contained in the molten iron in any one of the first to fifth aspects, together with a carrier gas in the molten iron in the melting chamber. It is characterized by blowing sulfur-containing flux.

  According to a seventh aspect of the present invention, there is provided a method for removing copper in steel scraps according to any one of the first to sixth aspects, wherein the steel scraps are dissolved as a carburizing material and an auxiliary heat source when the steel scraps are carburized and melted. It is characterized by being added indoors.

  According to an eighth aspect of the present invention, there is provided a method for removing copper in steel scraps according to the seventh aspect, wherein the carbonaceous material is derived from biomass.

  According to a ninth aspect of the present invention, there is provided a method for removing copper in steel scraps according to any one of the first to eighth aspects, wherein oxygen gas is supplied into the melting chamber when the steel scraps are carburized and melted. And

  According to a tenth aspect of the present invention, there is provided a method for producing molten steel using steel scrap as an iron source, wherein the method for removing copper in the steel scrap according to any one of the first to ninth aspects is provided in a holding container. First, desulfurization treatment is performed on the molten iron to remove sulfur in the molten iron, and the molten iron after the desulfurization treatment is charged into a converter, and oxygen blowing is performed in the converter to obtain molten iron. It is characterized by producing molten steel by removing carbon and phosphorus therein.

  According to an eleventh aspect of the present invention, there is provided a method for producing molten steel using steel scrap as an iron source. In the tenth aspect, the molten iron in the holding vessel is mixed with molten iron discharged from a blast furnace, and then the desulfurization treatment is performed. It is characterized by giving.

  According to the present invention, steel scrap is melted in an arc furnace having a shaft-type preheating chamber, so that steel scrap can be efficiently melted with a small amount of energy consumption, and melting generated by melting steel scrap. Since the copper removal treatment in iron is performed continuously using the sulfur-containing flux in the same arc furnace, steel that was difficult to separate by the method of separating and removing the steel scraps physically after magnetic decomposition, etc. It becomes possible to remove copper in the scrap efficiently and without requiring large-scale equipment. When manufacturing molten steel for high-grade steel using the molten iron after removing this copper, the oxygen in the converter is removed after removing the sulfur in the molten iron brought from the sulfur-containing flux. Blowing makes it possible to produce molten steel with low copper and sulfur from steel scrap. As a result, steel scrap can be used as an iron source for high-grade steel, and use of steel scrap that may contain copper and tin. Is promoted.

It is a longitudinal section schematic diagram of one example of an arc furnace used by the present invention. It is the longitudinal cross-sectional schematic of the other example of an arc furnace used by this invention.

  Hereinafter, the present invention will be specifically described.

  Processes for producing molten iron containing carbon by carburizing and melting steel scrap include a method using an arc furnace, a method using a converter, a method using a vertical furnace, etc. However, it has excellent melting capacity, can cope with melting of steel scrap generated in large quantities, and can be melted with a low power unit, so that a melting chamber and an upper portion of the melting chamber The steel scrap is carburized and melted using an arc furnace having a shaft type preheating chamber which is directly connected to the shaft and into which exhaust gas generated in the melting chamber is introduced.

When steel scrap is carburized and melted to produce molten iron containing carbon, that is, molten iron, almost all of the copper in the steel scrap is dissolved in the molten iron. In the present invention, as a means for removing copper in the molten iron, the sulfur-containing flux is brought into contact with the molten iron retained in the arc furnace, and the copper in the molten iron is sulfur as copper sulfide (Cu ₂ S). Separate and remove in the flux. First, the copper removal conditions will be described.

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.

  By the way, although copper removal by a sulfur-containing flux has been confirmed in principle, it is a process with a low distribution ratio (ratio of Cu concentration in the flux and Cu concentration in the molten iron). In order to proceed, it is necessary to promote mass transfer on the slag side formed in the holding container by the added sulfur-containing flux. For this purpose, it is important to stir not only the molten iron layer but also the slag layer. In particular, in the present invention, the copper removal treatment is performed at 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 high. Low and slag agitation is important.

  As a method of simultaneously stirring the molten iron and the slag present on the molten iron, in the present invention, since the copper removal treatment is performed in the arc furnace, the material is transported from the blown lance immersed in the molten iron in the arc furnace. It is preferable to use a so-called flux injection method in which powdery sulfur-containing flux is blown into molten iron together with gas. In this case, the powdery sulfur-containing flux blown into the molten iron is in direct contact with the molten iron, and the new unreacted sulfur-containing flux is continuously in contact with the molten iron, so that the slag side material The same effect as when the movement is promoted is exhibited, and the reaction between the molten iron and the sulfur-containing flux is promoted. Moreover, since the carrier gas also functions as a stirring gas, the molten iron and the slag on the molten iron are stirred.

  During the copper removal treatment, an inert gas such as Ar gas or a reducing gas such as propane may be supplied onto the molten iron bath surface in order to prevent air from entering the atmosphere. After the copper removal treatment, the slag formed by adding the sulfur-containing flux is removed from the system.

  In the present invention, the temperature of the molten iron before the copper removal treatment, that is, the steel containing hot metal containing carbon produced by carburizing and melting steel scrap is 1200 ° C. or higher and 1500 ° C. or lower, desirably 1250 ° C. or higher and 1350 ° C. The following is preferable. When the temperature of the molten iron is less than 1200 ° C., there is a concern that the sulfur-containing flux and the molten iron itself solidify and solidify 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, evaporation of the sulfur-containing flux due to high temperature cannot be ignored. That is, in order to suppress the evaporation of the sulfur-containing flux and efficiently perform the copper removal reaction, the temperature of the molten iron is preferably as low as possible. Therefore, for efficient copper removal reaction, the temperature of the molten iron is set to 1400 ° C. The following is desirable.

  The carbon concentration in the molten iron before the copper removal treatment is preferably 2% by mass or more. It is known that the reaction in which the copper in the molten iron becomes copper sulfide proceeds more thermodynamically as the carbon concentration in the molten iron is higher, and the carbon concentration in the molten iron before the copper removal treatment is 2 mass. If it is less than%, the copper sulfide formation reaction does not occur sufficiently, the liquidus temperature of the molten iron rises, and adhesion of the molten iron to the holding container wall becomes a problem. Furthermore, the copper concentration in the molten iron 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 molten iron 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 molten iron before the copper removal treatment is preferably 0.01% by mass or more, and more preferably 0.05% by mass or more. When the sulfur concentration of the molten iron before the copper removal treatment is less than 0.01% by mass, the amount of sulfur dissolved from the sulfur-containing flux into the molten iron becomes excessive, and the utilization 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 preferable to set it to 0.5 mass% or less.

  As the components of the molten iron other than the 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. If these concentrations are exceeded, the silicon oxide and manganese oxide generated by oxidation during the copper removal treatment of these components move to the slag and the amount of slag increases, making the slag treatment difficult, as well as silicon oxide and manganese oxide. May inhibit the copper removal reaction of the sulfur-containing flux.

  Hereinafter, the present invention will be described along the steps.

  1 and 2 are schematic longitudinal sectional views of an arc furnace used in the present invention. The arc furnace 1 shown in FIG. 1 is an arc furnace in which the method of supplying the carbon material to the melting chamber 2 is only a method of blowing through the carbon material blowing lance 9, while the arc furnace 1A shown in FIG. The supply method of the carbon material to the chamber 2 is an arc furnace that enables the addition of either the method of blowing through the carbon material blowing lance 9 and the addition method of addition from the charging chute 14 or either one of them, Other structures are the same, and the same parts are denoted by the same reference numerals.

  1 and 2, an arc furnace 1 and an arc furnace 1A are provided with a melting chamber 2 and a shaft-type preheating chamber 3, the interior of which is constructed of a refractory, and a melting chamber 2 having a furnace bottom electrode 6 at the bottom. A shaft-type preheating chamber 3 and a water-cooled side wall 4 are disposed in the upper part, and an upper opening of the side wall 4 not covered by the pre-heating chamber 3 is covered with a furnace door 5 having a water-cooling structure that can be freely opened and closed. . An upper electrode 7 capable of moving up and down into the melting chamber 2 through the furnace lid 5 is provided, and the base of the arc furnace 1, 1A is configured. The furnace bottom electrode 6 and the upper electrode 7 are connected to a DC power source (not shown), and an arc 23 is generated between the furnace bottom electrode 6 and the upper electrode 7.

  Above the preheating chamber 3, a bottom-opening type supply bucket 19 suspended from the traveling carriage 26 is provided, and an openable and closable supply port 24 provided at the upper portion of the preheating chamber 3 is provided from the supply bucket 19. Accordingly, the steel scrap 20 is charged into the preheating chamber 3. And the duct 25 connected with a dust collector (not shown) is provided in the upper end part of the preheating chamber 3, and the high temperature exhaust gas generated in the melting chamber 2 is discharged through the preheating chamber 3 and the duct 25 in this order. The steel scrap 20 charged into the preheating chamber 3 by the exhaust gas passing through the preheating chamber 3 is preheated, and the preheated steel scrap 20 is commensurate with the amount of steel scrap 20 melted in the melting chamber 2, and the melting chamber 2. It falls freely into the melting chamber 2 and charged into the melting chamber 2.

An oxygen blowing lance 8, a carbonaceous material blowing lance 9, and a decoppering flux blowing lance 10, which can move up and down in the melting chamber 2 through the furnace lid 5, are provided, and oxygen gas is supplied from the oxygen blowing lance 8. Carbon material made of coke, char, coal, charcoal, charcoal, graphite, biomass charcoal, or a mixture thereof is blown into the melting chamber, and air or nitrogen gas is transferred from the carbon material blowing lance 9 into the melting chamber. From the flux blowing lance 10 for copper removal, an inert gas such as Ar gas or nitrogen gas is used as a carrier gas, and Na ₂ S, Na ₂ CO ₃ , an iron-sulfur alloy, or a mixture thereof. Is blown into the melting chamber as a sulfur-containing flux.

  Further, on the opposite side of the melting chamber 2 from the site where the preheating chamber 3 is installed, the outlet 17 is pressed at the bottom of the furnace by the door 27 and filled with sand or mud agent inside, On the side wall, there is provided an outlet 18 that is pressed on the outlet side by a door 28 and filled with stuffed sand or mud agent. And the burner 16 is attached to the furnace cover 5 of the site | part corresponding to the upper part of the hot water outlet 17 vertically. The burner 16 burns fossil fuel and biomass fuel such as heavy oil, kerosene, pulverized coal, propane gas, and natural gas in the melting chamber 2 with air, oxygen gas, or oxygen-enriched air. The burner 16 can be attached and detached as required.

  In the case of the arc furnace 1A shown in FIG. 2, a hopper 12, a cutting device 13 connected to the lower portion of the hopper 12, and a lower portion of the cutting device 13 are connected to the furnace lid above the melting chamber 2. A charcoal charging device 11 including a charging chute 14 penetrating through 5 is installed. The hopper 12 stores a carbon material 15 made of coke, char, coal, charcoal, graphite, biomass charcoal, or a mixture thereof, and the carbon material 15 cut out by the cutting device 13 has a charging chute 14. Via the melting chamber 2.

  In addition, a traveling crane (not shown) is installed above the melting chamber 2, and includes an upper electrode 7, an oxygen blowing lance 8, a carbonaceous material blowing lance 9, a copper removal flux blowing lance 10, a burner 16, and a carbonaceous material. The charging device 11 (however, only in the case of the arc furnace 1 </ b> A in FIG. 2) has a structure in which the steel lid 20 can be directly charged into the melting chamber 2 by opening the furnace cover 5 that has been removed in advance.

  In the operation method in the DC arc 1, 1 </ b> A configured as described above, first, steel scrap 20 is charged into the preheating chamber 3 by the supply bucket 19. The steel scrap 20 charged in the preheating chamber falls into the melting chamber 2 and is charged, and eventually fills the inside of the preheating chamber 3. In order to uniformly charge the steel scrap 20 into the melting chamber 2, the steel scrap 20 and the carbonaceous material 15 are loaded inside the melting chamber 2 opposite to the preheating chamber 3 with the furnace lid 5 opened. You can also enter. In addition, the hot metal discharged from the blast furnace (hereinafter referred to as “blast furnace hot metal”) can be charged into the melting chamber 2 when the steel scrap 20 is charged. By using the blast furnace hot metal, it becomes possible to reduce the amount of power used by the heat of the blast furnace hot metal. The blast furnace hot metal may be charged into the melting chamber 2 using hot metal (not shown) connected to the ladle for supply or the melting chamber 2.

  Next, while feeding a direct current between the furnace bottom electrode 6 and the upper electrode 7, the upper electrode 7 is moved up and down, or between the furnace bottom electrode 6 and the upper electrode 7 or between the charged steel scrap 20 and the upper part. An arc 23 is generated between the electrodes 7. And the steel scrap 20 is melt | dissolved with the generated arc heat, and the molten iron 21 is produced | generated. As the molten iron 21 is generated, a flux such as quick lime or fluorite is charged into the melting chamber 2 to form the molten slag 22 on the molten iron 21, thereby preventing the molten iron 21 from being oxidized and the molten iron 21. Keep warm. If the amount of the molten slag 22 is too large, it can be discharged from the spout 18 even during operation.

  If the oxygen blowing lance 8 and the carbon material blowing lance 9 can be inserted into the melting chamber after energization, oxygen gas from the oxygen blowing lance 8 and carbon material from the carbon material blowing lance 9 are transferred to the melting chamber. It is preferable to blow into the molten iron 21 or the molten slag 22. The carbon material can also be supplied from the carbon material charging device 11. However, the supplying method from the carbonaceous material charging device 11 is addition on top, and is different from the method of blowing directly into the molten iron 21 or the molten slag 22.

The carbon material blown and dissolved in the molten iron 21 or the carbon material suspended in the molten slag 22 reacts with the oxygen gas to be blown to generate combustion heat and acts as an auxiliary heat source to save power consumption. At the same time, the CO gas of the reaction product forms the molten slag 22 and the arc 23 is encased in the molten slag 22, so that the so-called slag forming operation is performed. Moreover, the high-temperature CO gas generated in large quantities and the CO ₂ gas generated by combustion of this CO gas efficiently preheat the steel scrap 20 in the preheating chamber.

The total amount of oxygen gas, i.e., the total amount of the oxygen gas blown into the dissolution start to tapping is, 15 Nm ³ or more per ton of molten iron 21 is dissolved (hereinafter referred to as "Nm ³ / t") to be higher than that preferable. Further, the total amount of carbonaceous material added, that is, the total amount of carbonaceous material blown from the start of melting to the hot water is determined in accordance with the amount of oxygen gas added. That is, it is preferable to add a carbon material equal to or more than the chemical equivalent of the oxygen gas addition amount. If the amount of carbonaceous material added is smaller than the amount of oxygen gas added, the molten iron 21 is excessively oxidized and the carbon concentration in the molten iron is lowered, that is, it is not preferable.

  As the steel scrap 20 is melted in the melting chamber, the steel scrap 20 in the preheating chamber falls to the melting chamber 2 in accordance with the amount melted in the melting chamber and decreases. Steel scrap 20 is charged into the preheating chamber 3 through the bucket 19. The steel scrap 20 is charged into the preheating chamber 3 continuously or intermittently so that the steel scrap 20 is continuously present in the preheating chamber 3 and the melting chamber 2. The charging of the steel scrap 20 at this time may be performed based on a preset recipe based on the operation results, or a sensor capable of detecting the amount of the steel scrap 20 in the preheating chamber is provided. The charging of the steel scrap 20 by the supply bucket 19 may be controlled based on the signal. In that case, it is preferable that the amount of the steel scrap 20 existing continuously in the preheating chamber 3 and the melting chamber 2 is 50 mass% or more of the steel scrap 20 for one heat.

  In this way, the steel scrap 20 is carburized and melted to generate molten iron 21 in the melting chamber 2, and the molten iron 21 for one heat or more is stored in the melting chamber 2. The carbon concentration of the accumulated molten iron 21 is measured, and if necessary, the carbon material is supplied from the carbon material blowing lance 9 or the carbon material charging device 11 to adjust the carbon concentration of the molten iron 21 to 2% by mass or more. Moreover, the supply amount of arc heat is adjusted and the temperature of the molten iron 21 is adjusted to 1200-1500 degreeC. Furthermore, preferably, the sulfur concentration of the molten iron 21 is adjusted to 0.01% by mass or more. Generally, the carbonaceous material contains sulfur, and the sulfur concentration of the molten iron 21 is increased by carburizing and melting. However, when the sulfur concentration does not reach 0.01% by mass even in the carburizing and melting step. Is preferably prepared by adding an iron-sulfur alloy or the like.

  When the temperature and chemical composition of the molten iron 21 in the melting chamber are adjusted within a predetermined range, the tip of the decoppering flux blowing lance 10 is immersed in the molten iron 21, and the decoppering flux blowing lance 10 is transported together with the carrier gas. Desulfurization treatment is started by blowing a sulfur-containing flux into the molten iron. When a predetermined amount of sulfur-containing flux is supplied and a predetermined time has elapsed, the copper removal treatment is terminated. In addition, when the sulfur-containing flux containing CuS that is blown and reacts with the molten iron 21 floats on the molten iron 21 and mixes with the molten slag 22 generated during melting, the sulfur-containing flux is diluted, Since the CuS absorption capacity of the sulfur-containing flux may be reduced, it is preferable to discharge the molten slag 22 from the tap outlet 18 before the copper removal treatment.

  After the copper removal treatment, the melting chamber 2 is tilted toward the hot water outlet 17 by a tilting device (not shown), and the steel scrap 20 is continuously left in the melting chamber 2 and the preheating chamber 3 while leaving the state. The door 27 that has closed the gate 17 is opened, and the molten iron 21 for one heat is discharged from the outlet 17 into a holding container (not shown). In this case, since the steel scrap 20 is buried in the molten iron 21 and coexists, the molten iron 21 cannot be given a high degree of superheat. Therefore, in order to prevent troubles such as blockage of the hot water outlet 17 caused by the temperature drop of the molten iron 21, it is preferable to heat the molten iron 21 with the burner 16 at the time of hot water.

  After the molten iron 21 is tapped and the melted sulfur-containing flux (including the flux mixed with the molten slag 22) is discharged, the melting chamber 2 is returned to a horizontal position by a tilting device, Fill with stuffed sand or mud material and then start melting the next heat. It should be noted that several tons to several tens of tons of molten iron 21 may remain in the melting chamber at the time of the hot water to resume melting of the next heat. By doing so, the initial dissolution is promoted and the dissolution efficiency is improved.

  By heating and melting the steel scrap 20 in this manner, the next heat can start melting with the preheated steel scrap 20, so that productivity can be improved and the power consumption can be greatly reduced. .

  With the above copper removal treatment, sulfur in the sulfur-containing flux inevitably moves into the molten iron, so that the sulfur concentration in the molten iron increases. Therefore, in this invention, the process which removes the sulfur in molten iron is further performed with respect to the molten iron 21 after tapping a hot water in a holding container. This desulfurization treatment may be any of a method using a known mechanical stirring type refining device, a method by blowing powder from a lance, a method using a converter, and the desulfurizing agent used is CaO. Various desulfurization agents such as a desulfurization agent mainly composed of calcium carbide, a desulfurization agent mainly composed of calcium carbide, a desulfurization agent mainly composed of soda ash, and metallic Mg can be used. Among these desulfurization methods, since a high desulfurization rate can be obtained even using an inexpensive desulfurization agent mainly composed of CaO, it is preferable to perform a desulfurization treatment using a mechanical stirring type refining apparatus. That is, a desulfurization agent mainly composed of CaO is used as a desulfurization agent, the molten iron is stirred with an impeller immersed in the molten iron 21, and the added desulfurization agent and the molten iron 21 are mixed and stirred to desulfurize. It is preferable.

  When carrying out the desulfurization process, the blast furnace hot metal may be additionally mixed with the molten iron 21 in the holding container, and then the mixed molten iron 21 may be desulfurized. Furthermore, you may mix a blast furnace hot metal with the molten iron 21 after a desulfurization process.

  The desulfurized molten iron 21 is charged into the converter, oxygen gas is supplied from the top blowing lance or bottom blowing tuyer in the converter, and oxygen blowing is performed to remove carbon and phosphorus in the molten iron. Manufactures molten steel for high-grade steel.

  As described above, according to the present invention, since the steel scrap 20 is melted in the arc furnace 1, 1A having the shaft-type preheating chamber 3, the steel scrap 20 can be efficiently melted with a small amount of energy consumption. Moreover, since the copper removal process in the molten iron produced | generated by melt | dissolution of the steel scrap 20 is continuously performed using a sulfur containing flux in the same arc furnace, magnetic separation etc. are performed after physically decomposing the steel scrap. Thus, it is possible to remove copper in steel scrap, which has been difficult to separate by the method of separation and removal, efficiently and without requiring large-scale equipment.

  Moreover, when manufacturing the molten steel for high-grade steel using the molten iron 21 after removing this copper, after performing the removal process of the sulfur in the molten iron brought from the sulfur containing flux, a converter Since oxygen blowing is performed at the steel, molten steel with less copper and sulfur can be obtained from the steel scrap 20, and as a result, the steel scrap 20 can be used as an iron source for high-grade steel and may contain copper and tin. Utilization of the steel scrap 20 is promoted.

  Using the DC arc furnace shown in FIG. 1, steel scrap mixed with copper, called so-called city scrap, is carburized and melted to produce carbon-containing molten iron (steel making iron). A test was conducted in which the molten iron was decopperized in the melting chamber, and the hot water was discharged after the decoppering process. The arc furnace used has a melting chamber with a furnace diameter of 7.2 m, a height of 4 m, a preheating chamber with a width of 3 m, a length of 5 m, a height of 7 m, and a furnace capacity of 180 tons.

First, about 70 tons of room temperature steel scraps are charged into the preheating chamber, and then about 50 tons of room temperature steel scraps and 1 ton of coke are charged into the melting chamber, and the graphite upper part with a diameter of 30 inches. Using the electrode, electricity was passed between the furnace bottom electrode with a maximum power supply capacity of 750 V and 130 kA, and melting of the steel scrap was started. Immediately after energization, quick lime and fluorite were charged into the melting chamber, oxygen gas was blown into the melting chamber from the oxygen blowing lance at 1800 Nm ³ / hr, and coke was blown into the melting chamber from the carbonaceous material blowing lance at 96 kg / min. . Quicklime and fluorite were heated to form molten slag, and the molten slag was formed by CO gas, which is a reaction product of oxygen gas and coke, and the tip of the upper electrode was buried in the formed molten slag. The voltage at this time was set to 550V.

When the steel scrap in the preheating chamber descends as the steel scrap is melted in the melting chamber, the steel scrap is supplied into the preheating chamber by the supply bucket arranged above the preheating chamber, and the height of the steel scrap in the preheating chamber is increased. Melting was continued while maintaining a substantially constant height, and when about 140 tons of molten iron was produced in the melting chamber, the process shifted to copper removal treatment. By dissolving in this manner, the amount of power used was 270 kWh / t under the conditions of an oxygen gas blowing rate of 15 Nm ³ / t and a coke blowing rate of 120 kg / t.

  During the copper removal treatment, the blowing of oxygen gas from the oxygen blowing lance and the blowing of carbonaceous material from the carbonaceous blowing lance were stopped, and the energization to the electrodes was also stopped.

The sulfur-containing flux used for the copper removal treatment is a flux mainly composed of FeS-Na ₂ S (test No. 1) in which the molar fraction of Na ₂ S in the flux is 0.4, and iron-sulfur. It is a flux (test No. 2) made of a mixture of an alloy (a sulfur concentration in the alloy of 48% by mass) and soda ash (Na ₂ CO ₃ ). These sulfur-containing fluxes were blown into the molten iron via a copper removal flux blowing lance.

  After the copper removal treatment, about 140 tons of molten iron was poured into a ladle through a tap. When the hot water was discharged, the molten iron was discharged while heating the molten iron using a burner disposed above the hot water outlet. After the hot water is discharged, the slag in the furnace is discharged from the tap, and after the slag is discharged, energization of the electrode is resumed, oxygen gas is blown from the oxygen blowing lance, and coke is blown from the carbon material blowing lance. Then, the melting of the next heat was started. The melting of the next heat is carried out by a method according to the melting method of the first heat, and when the molten iron of 140 tons or more is formed in the melting chamber, the copper removal treatment is performed. 140 tons of hot water was repeatedly carried out.

  Table 1 shows the transition of the test conditions and the copper concentration in the molten iron. Test No. 3 is a comparative example in which no copper removal treatment is performed. Although not described in Table 1, the carbon concentration of the molten iron before the copper removal treatment was 4.4 to 4.7% by mass, and the temperature of the molten iron was 1400 ° C.

  As shown in Table 1, in test No. 1, the copper concentration in the molten iron changed from 0.30 mass% to 0.10 mass%, and in test No. 2, the copper concentration in the molten iron increased from 0.30 mass%. It was reduced to 0.14% by mass. By blowing and adding a sulfur-containing flux, the copper removal rate (= (copper concentration in hot metal before treatment−copper concentration in hot metal after treatment) × 100 / copper concentration in hot metal before treatment) is 40% or more, and copper removal It was confirmed that this was done well.

  In addition, about the immersion depth of the flux blowing lance for copper removal, when the bath depth of molten iron is H (m) and the distance from the molten iron bath surface to the tip of the flux blowing lance for copper removal is L (m), It has been confirmed by a separate experiment that the blown flux can contribute to the copper removal reaction if L / H is 0.3 or more. Moreover, as a specification of the flux blowing lance for copper removal to be used, what kind of thing may be used if it can endure the process which immerses in molten iron and blows a flux. Further, the relationship between the transfer gas flow rate and the flux blowing speed has no effect on the metallurgical characteristics as long as flux clogging does not occur in the lance. There is no problem as long as the kind of the carrier gas is an inert gas, for example, Ar gas may be used.

  Using molten iron containing carbon melted in the arc furnace shown in FIG. 1 and having different temperature and composition, the decopper refining flux is melted in the molten iron in the arc furnace melting chamber via a decoppering flux blowing lance. The test which carries out a copper removal process by blowing in was performed (test No. 4-13).

As the flux for copper removal refining, 50 kg of iron-sulfur alloy (ferrosulfur, sulfur content: 48% by mass) per ton of molten iron and 35 kg of soda ash (Na ₂ CO ₃ ) per ton of molten iron were added. .

  In Table 2, the components and temperature of the molten iron before the copper removal treatment and the components of the molten iron after the copper removal treatment are listed. In addition, about the component of molten iron other than having shown in Table 2, silicon concentration is 0.05-0.4 mass%, manganese concentration is 0.05-0.4 mass%, phosphorus concentration is 0.02-0. It was the range of 2 mass%.

  In Test Nos. 4 to 9, the temperature of the molten iron is 1200 ° C. or more and 1500 ° C. or less, the carbon concentration is 2 mass% or more, the copper concentration is 0.1 mass% or more and 1.0 mass% or less, and the sulfur concentration is 0.00. It was confirmed that it was within the range of 01% by mass or more, that is, the preferable condition of the present invention, the copper removal rate was 40% or more, and copper removal was performed well. On the other hand, in Test Nos. 10 to 13, the copper removal rate was less than 40% because the copper removal treatment was performed under conditions that deviated from the preferred conditions of the present invention.

  A decoppering test was carried out by changing the carbonaceous material charging method when steel scrap was carburized and melted using the DC arc furnace shown in FIG. 2 (Test Nos. 14 to 17).

  Addition of the carbon material during melting is only from the carbon material blowing lance in the test No. 14 and the test No. 16, and both from the carbon material blowing lance and the carbon material charging device in the test No. 15 and the test No. 17. I went from. Moreover, the kind of charcoal used the coke in test No.14 and test No.15, and used coconut husk charcoal (PKS charcoal) as bio-coke in test No.16 and test No.17.

First, about 70 tons of normal steel scraps are charged into the preheating chamber, and then about 50 tons of normal steel scraps and 1 ton of coke or PKS charcoal are charged into the melting chamber. Using a graphite upper electrode, electricity was passed between the furnace bottom electrode with a maximum power supply capacity of 750 V and 130 kA to start melting steel scrap. Immediately after energization, quick lime and fluorite are charged into the melting chamber, oxygen gas from the oxygen blowing lance is 1800 Nm ³ / hr, and coke or PKS charcoal is blown from the charcoal blowing lance at a rate of 96 kg / min. Infused into. Quicklime and fluorite were heated to form molten slag, and the molten slag was formed by CO gas, which is a reaction product of oxygen gas and carbonaceous material, and the tip of the upper electrode was buried in the formed molten slag. The voltage at this time was set to 550V.

  Thereafter, the carbon material is supplied from the carbon material blowing lance in the test No. 14 and the test No. 16, and from both the carbon material blowing lance and the carbon material charging device in the test No. 15 and the test No. 17. It was.

  When the steel scrap in the preheating chamber descends as the steel scrap melts in the melting chamber, the steel scrap is supplied into the preheating chamber from the supply bucket placed above the preheating chamber, and the height of the steel scrap in the preheating chamber is increased. Melting was continued while maintaining a substantially constant height, and when molten iron of 140 tons or more was generated in the melting chamber, the process shifted to copper removal treatment. During the copper removal treatment, the blowing of oxygen gas from the oxygen blowing lance and the blowing of carbonaceous material from the carbonaceous blowing lance were stopped, and the energization to the electrodes was also stopped.

The sulfur-containing flux used for the copper removal treatment is a mixture of 50 kg of iron-sulfur alloy (48% by mass of sulfur in the alloy) per ton of molten iron and 35 kg of soda ash (Na ₂ CO ₃ ) per ton of molten iron. This sulfur-containing flux was blown into molten iron through a flux blowing lance for copper removal.

  Table 3 shows the transition of the test conditions and the copper concentration in the molten iron. Although not described in Table 3, the carbon concentration of the molten iron before the copper removal treatment was 4.4 to 4.7% by mass, and the temperature of the molten iron was 1400 ° C.

  As shown in Table 3, there was no significant difference in the copper removal rate even when the carbon material addition method and the type of carbon material were changed, the copper removal rate was 40% or more, and copper removal was performed well. Was confirmed.

  From the above results, it was confirmed that the copper removal treatment is possible even when the carbon material is supplied from the carbon material charging device or when bio-coke is used as the carbon material.

  Using the arc furnace shown in FIG. 1, molten iron containing carbon is produced by melting steel scraps, and this molten iron is decoppered, and after decoppering, the hot water is discharged from the arc furnace to a ladle. The test which desulfurizes the molten iron in a pan using a CaO type | system | group desulfurization agent was implemented (test No. 18-20).

First, about 70 tons of room temperature steel scraps are charged into the preheating chamber, and then about 50 tons of room temperature steel scraps and 1 ton of coke are charged into the melting chamber, and the graphite upper part with a diameter of 30 inches. Using the electrode, electricity was passed between the furnace bottom electrode with a maximum power supply capacity of 750 V and 130 kA, and melting of the steel scrap was started. Immediately after energization, quick lime and fluorite were charged into the melting chamber, oxygen gas was blown into the melting chamber from the oxygen blowing lance at 1800 Nm ³ / hr, and coke was blown into the melting chamber from the carbonaceous material blowing lance at 96 kg / min. . Quicklime and fluorite were heated to form molten slag, and the molten slag was formed by CO gas, which is a reaction product of oxygen gas and coke, and the tip of the upper electrode was buried in the formed molten slag. The voltage at this time was set to 550V.

  When the steel scrap in the preheating chamber descends as the steel scrap melts in the melting chamber, the steel scrap is supplied into the preheating chamber from the supply bucket placed above the preheating chamber, and the height of the steel scrap in the preheating chamber is increased. Melting was continued while maintaining a substantially constant height, and when molten iron of 140 tons or more was generated in the melting chamber, the process shifted to copper removal treatment. During the copper removal treatment, the blowing of oxygen gas from the oxygen blowing lance and the blowing of carbonaceous material from the carbonaceous blowing lance were stopped, and the energization to the electrodes was also stopped.

The sulfur-containing flux used for the copper removal treatment is a mixture of 50 kg of iron-sulfur alloy (48% by mass of sulfur in the alloy) per ton of molten iron and 35 kg of soda ash (Na ₂ CO ₃ ) per ton of molten iron. This sulfur-containing flux was blown into molten iron through a flux blowing lance for copper removal.

  After the copper removal treatment, about 140 tons of molten iron was poured into a ladle and the molten iron was subjected to desulfurization treatment. However, in test No.18, about 140 tons of molten iron after tapping is desulfurized as it is, and in test No.19, about 140 tons of molten iron after tapping is mixed with about 160 tons of blast furnace hot metal and mixed. In the test No. 20, about 140 tons of molten iron after tapping is divided into about 1/2, and about 70 tons of molten iron is divided into about 70 tons of molten iron. 230 tons of blast furnace hot metal was mixed, and about 300 tons of molten iron after mixing was desulfurized.

  In the desulfurization treatment, both test No. 18, test No. 19 and test No. 20 were performed by immersing an impeller coated with a refractory in molten iron in a mechanical stirring type refining apparatus, rotating the impeller, and molten iron and desulfurizing agent. The desulfurization treatment was carried out with stirring. The amount of CaO-based desulfurizing agent added was 20 kg / t. Table 4 shows the test conditions and the transition of the copper concentration and sulfur concentration in the molten iron. Although not described in Table 4, the carbon concentration of the molten iron before the copper removal treatment was 4.4 to 4.7% by mass, and the temperature of the molten iron before the desulfurization treatment was 1350 ° C.

  As shown in Table 4, it was found that by performing desulfurization treatment after the decoppering treatment, it is possible to finally obtain molten iron having both a low copper concentration and a low sulfur concentration, and can be used without any problem as a hot metal for steelmaking for high-grade steel. .

DESCRIPTION OF SYMBOLS 1 Arc furnace 1A Arc furnace 2 Melting chamber 3 Preheating chamber 4 Side wall 5 Furnace lid 6 Furnace electrode 7 Upper electrode 8 Oxygen blowing lance 9 Carbon material blowing lance 10 Decapping flux blowing lance 11 Carbon material feeding device 12 Hopper 13 Cutting device 14 Charging material 15 Charcoal material 16 Burner 17 Outlet 18 Outlet 19 Supply bucket 20 Steel scrap 21 Molten iron 22 Molten slag 23 Arc 24 Supply port 25 Duct 26 Traveling carriage 27 Door 28 Door

Claims (10)

Using an arc furnace having a melting chamber and a shaft-type preheating chamber directly connected to the upper portion of the melting chamber and into which exhaust gas generated in the melting chamber is introduced, steel scraps are continuously connected to the preheating chamber and the melting chamber. While supplying steel scrap to the preheating chamber so as to maintain the existing state, the steel scrap is carburized and dissolved in the melting chamber using arc heat to generate molten iron, and then the generated melting chamber by blowing sulfur-containing flux together with carrier gas into the molten iron to remove the copper contained in the molten iron, characterized by tapping the holding vessel a molten iron after removal of copper from the arc furnace , A method for removing copper in steel scraps.   The method for removing copper in steel scrap according to claim 1, wherein the steel scrap is continuously present in the preheating chamber and the melting chamber when the molten iron is discharged from the arc furnace. . The method for removing copper in steel scraps according to claim 1 or 2, wherein the sulfur-containing flux contains Na ₂ S as a main component. The steel scrap according to any one of claims 1 to 3, wherein a material mainly composed of Na ₂ CO ₃ and an iron-sulfur alloy are used as a starting material for the sulfur-containing flux. How to remove copper inside.   The molten iron before removing copper by the sulfur-containing flux has a temperature of 1200 ° C. or more and 1500 ° C. or less, a carbon concentration of 2 mass% or more, a copper concentration of 0.1 mass% or more and 1.0 mass% or less, and a sulfur concentration. The method for removing copper in steel scraps according to any one of claims 1 to 4, characterized in that is 0.01 mass% or more. The steel scrap according to any one of claims 1 to 5 , wherein when the steel scrap is carburized and melted, a carbonaceous material is added to the melting chamber as a carburized material and an auxiliary heat source. Copper removal method. The method for removing copper in steel scraps according to claim 6 , wherein the carbonaceous material is derived from biomass. The method for removing copper in steel scrap according to any one of claims 1 to 7 , wherein oxygen gas is supplied into the melting chamber when the steel scrap is carburized and melted. The sulfur in the molten iron is first subjected to desulfurization treatment with respect to the molten iron in the holding container manufactured by the method for removing copper in steel scraps according to any one of claims 1 to 8. The molten iron after this desulfurization treatment is charged into a converter, and oxygen blown in the converter to remove carbon and phosphorus in the molten iron to produce molten steel, A method for producing molten steel using steel scrap as an iron source. The method for producing molten steel using steel scrap as an iron source according to claim 9 , wherein the molten iron in the holding container is mixed with molten iron discharged from a blast furnace, and then the desulfurization treatment is performed.

Images