Method for producing reduced iron and molten iron

Abstract

To provide reduced iron which can avoid the aggregation and floating of the reduced iron charged into an electric furnace, and to provide a method for producing molten iron using the reduced iron as a raw material.SOLUTION: When the mass of all the reduced-iron particles is W (kg), the mass of particles having a longest side of 80 to 0g among particles on a sieve having a mesh size of 10mm is W1 (kg), the mass of particles having a longest side of 50 to 150mm is W2 (kg), and the mass of particles on the sieve having a mesh size of 10mm and under the sieve having a mesh size of 2mm is (kg), the following relationship is satisfied: / 150mm> W (kg). 5mm cm3 W3, reduced iron having a particle size distribution satisfying all of the following formulae (1) to (3): 0.60 ≤ W1 / W (1) 0.80 ≤ W2 / W (2) 0.005 ≤ W3 / W ≤ 0.02 (3) SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to reduced iron and a method for producing molten iron using the reduced iron as a raw material. [Background technology]

[0002] In recent years, there has been a demand to reduce the use of fossil fuels in order to prevent global warming. In the steelmaking process, which uses iron ore as a raw material and produces molten iron using the blast furnace method, coke is used as a reducing agent to reduce the iron ore. Coke is a fossil fuel derived from coal, so in order to reduce the amount of fossil fuel used in the steelmaking industry, it is necessary to switch to processes that use less reducing agent or to use reducing agents that do not emit CO2 when reducing iron ore.

[0003] Against this background, attention has been focused on technologies for producing solid reduced iron using the minimum amount of reducing agent necessary for reducing iron ore. Reduced iron produced by these technologies is sometimes called solid reduced iron, sponge iron, granular metallic iron, or other names, but hereafter will be referred to as reduced iron. Many techniques for producing reduced iron have been published, as disclosed in Patent Document 1, for example. Producing steel products using reduced iron as a raw material can reduce the amount of fossil fuel used. In this case, using a reducing agent that does not generate CO2, such as H2, during the reduction of iron ore can further reduce the amount of CO2 generated.

[0004] The production of molten iron using reduced iron or scrap as raw material is widely carried out using electric furnaces. For example, Patent Document 2 discloses a method in which reduced iron containing specified amounts of SiO2, Al2O3, and C and having a metallization rate of 90% or more is heated and melted in an electric furnace, followed by slag separation and decarburization to produce molten steel. Patent Document 2 also discloses a technology that suppresses oxidation loss of iron by not introducing oxygen for decarburization until the slag removal process, making it possible to use low-grade iron ore containing a large amount of gangue as a raw material for reduced iron. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-337264 [Patent Document 2] Patent Publication No. 2021-102798 Summary of the Invention [Problem to be solved by the invention]

[0006] When replacing the blast furnace method for producing steel products with a method for producing molten iron in an electric furnace using reduced iron as a raw material, it is necessary to melt the reduced iron in a short time to ensure productivity equivalent to that of a blast furnace. In a typical electric furnace, the upper limit of the amount of reduced iron charged per minute (t) is approximately 0.03 times the amount of steel tapped per heat (t) due to heat balance, and this also roughly corresponds to the amount of reduced iron described in Patent Document 2. When reduced iron is charged at such a high speed into the electric furnace, a problem often arises: the reduced iron particles agglomerate and float to the surface of the molten iron (hereinafter simply referred to as "agglomeration flotation"). Because the agglomerated and floated reduced iron contains a complex mixture of iron, slag, and voids, its thermal conductivity is low, which lengthens the time required for melting and reduces productivity. Therefore, a technology to prevent agglomeration flotation of reduced iron is needed to improve the productivity of electric furnaces.

[0007] An object of the present invention is to provide reduced iron capable of preventing agglomeration and floating of reduced iron charged into an electric furnace, and a method for producing molten iron using the reduced iron as a raw material. [Means for solving the problem]

[0008] That is, the gist of the present invention is as follows. [1] Reduced iron that is supplied to an electric furnace and used as a raw material for molten iron, and the apparent density of the reduced iron is 4.0 g / cm 3The reduced iron is characterized by having a particle size distribution that satisfies all of the following formulas (1) to (3), where W (kg) is the mass of all the reduced iron particles, W1 (kg) is the mass of particles that have a longest side of 80 to 150 mm among the particles that sieve with a 10 mm mesh, W2 (kg) is the mass of particles that have a longest side of 50 to 150 mm among the particles that sieve with a 10 mm mesh, and W3 (kg) is the mass of particles that sieve with a 2 mm mesh and sieve with a 5 mm mesh. 0.60≦W1 / W (1) 0.80≦W2 / W (2) 0.005≦W3 / W≦0.02 (3) [2] The reduced iron according to [1], wherein the reduced iron has a metallization rate of 80 to 98 mass %. [3] The reduced iron according to [1], characterized in that the reduced iron contains 3.5 to 11.5 mass% in total of CaO, SiO2, Al2O3, and MgO.

[0009] [4] A method for producing molten iron, comprising a melting step of charging the reduced iron according to any one of [1] to [3] into an electric furnace, heating and melting it. [5] The method for producing molten iron according to [4], wherein the reduced iron used in the melting step in the electric furnace is 10 to 100 mass % of the total iron raw material melted in the furnace. [6] A method for producing molten iron according to [4], characterized in that after the melting step in the electric furnace, a slag discharge step is carried out in which slag is discharged outside the furnace to separate it from the molten iron, and in which at least a portion of the slag is left in the furnace in the slag discharge step and is held in the furnace until the next melting step. [7] A method for producing molten iron according to [6], characterized in that the electric furnace has a means for measuring the vertical thickness of the slag in the furnace, and the amount of slag discharged outside the furnace in the slag removal process is controlled so that the vertical thickness of the slag remaining in the furnace is 20 mm or more. [Effects of the Invention]

[0010] The present invention makes it possible to produce molten iron from reduced iron as a raw material without causing a decrease in productivity due to the agglomeration and flotation of the reduced iron charged into an electric furnace. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic front cross-sectional view showing an example of an electric furnace. DETAILED DESCRIPTION OF THE INVENTION

[0012] As shown in Figure 1, a three-phase AC electric furnace 1 can be used as the electric furnace. The electric furnace 1 consists of a lower furnace shell 3 and an upper furnace lid 4. Three graphite electrodes 2 penetrate the furnace lid 4 and are inserted into the furnace. The furnace lid 4 also has a main raw material inlet 5 and an auxiliary raw material inlet 6. Reduced iron and alloys can be added through the main raw material inlet 5, and auxiliary raw materials such as slag formers can be added through the auxiliary raw material inlet 6. The furnace shell 3 is designed to discharge the processed molten iron 10 outside the furnace using an eccentric bottom tapping method. It also has a slag discharge port 7 on the side wall. By tilting the furnace, the slag 11 inside the furnace can be discharged through the slag discharge port 7 and separated from the molten iron 10.

[0013] Furthermore, the electric furnace 1 preferably has an oxygen supply lance 9 connected to a manipulator 8 to supply oxygen gas into the furnace for the purposes of assisting melting by oxidation heat and oxidative refining. The oxygen supply lance 9 is inserted into the furnace through the slag discharge port 7, and can spray oxygen gas toward the raw materials and molten iron.

[0014] The present inventors focused on the mechanism by which reduced iron agglomeration and flotation occur in an electric furnace. Using a test furnace containing molten iron and molten slag, the reduced iron agglomeration phenomenon can be observed by charging the reduced iron into the test furnace. The reduced iron that agglomerated during melting was recovered and observed. As a result, it was found that the bridges connecting the agglomerated reduced iron particles consisted primarily of metallic iron. The metallic iron that bridged the reduced iron particles is believed to be solidified molten iron in the test furnace. Specifically, the inventors found that the molten iron in the furnace was cooled by contact with the charged reduced iron, and the cooled molten iron solidified, forming bridges between the surrounding reduced iron and the reduced iron, thereby causing the agglomeration of reduced iron. Furthermore, they found that if slag gets between the reduced iron and the bridges, the corresponding parts are prone to peeling.

[0015] Based on the above findings, the present inventors came up with a method for preventing the aggregation and flotation of reduced iron. Specifically, they considered that the following would be effective, while ensuring heat transfer to the reduced iron: (A) reducing the heat removal from the molten iron by the reduced iron, (B) increasing the distance between reduced iron particles, and (C) bringing the surface of the reduced iron into contact with slag. They then investigated the conditions that the reduced iron should have to achieve these goals.

[0016] In order to prevent the agglomeration and floating of reduced iron in an electric furnace, the present inventors have focused on the apparent density and particle size of reduced iron.

[0017] Regarding the former, the apparent density, by increasing the apparent density of the reduced iron, it is possible to prevent the reduced iron charged into the electric furnace from floating up and remaining on the slag layer in the furnace, and the reduced iron can quickly reach the molten iron layer below the slag layer, thereby ensuring heat transfer from the molten iron to the reduced iron. Tests conducted by the inventors have shown that the apparent density of reduced iron is 4.0 g / cm 3 It has been found that agglomeration and flotation can be prevented when the density is above 100%. The apparent density of reduced iron can be adjusted by means of compression molding the reduced iron, etc. The apparent density of reduced iron can be evaluated by the underwater weighing method described in JIS Z 8807-2012.

[0018] Regarding the particle size of the reduced iron, we investigated the heat removal and flow of reduced iron particles as follows. When a large particle size is contained in the reduced iron, the ratio of surface area to volume (hereinafter referred to as specific surface area) of the large particle size decreases, resulting in reduced heat removal and difficulty in bridging between particles. On the other hand, large particle size particles are less likely to flow, making them more likely to approach each other. Considering these factors, we believe there is an optimal content range for large particle size reduced iron. Briquettes made by compressing reduced iron with a longest side of 150 mm or less are commonly used. Therefore, when the mass of all reduced iron particles is W (kg), we defined the mass of large particle size reduced iron particles, which are those with a longest side of 80 to 150 mm among particles passing through a 10 mm mesh sieve, as W1 (kg) and those with a longest side of 50 to 150 mm as W2 (kg). We evaluated the effect of the proportion of these particle sizes on the flotation and separation of reduced iron. The size of the longest side of each particle can be measured by taking an image of the reduced iron being transported by the conveyor and determining the shape of each particle by image analysis.

[0019] When reduced iron contains a large amount of small-particle size particles, the specific surface area increases, facilitating heat transfer and making the particles more likely to crosslink. Therefore, it is believed that there is a suitable upper limit for the content of small-particle size particles. On the other hand, small-particle size reduced iron generates a large amount of gas, which stirs the molten iron, facilitating the flow of the reduced iron and maintaining the distance between particles. Therefore, it is believed that there is a suitable lower limit for the content of small-particle size particles. The reduced iron with small particle size that is fed into an electric furnace contains fine particles that were broken during the transportation of the briquetted reduced iron. Typical particle sizes are approximately 2 mm to 5 mm. Therefore, we defined W3 (kg) as the mass of particles that fell above the 2 mm sieve and below the 5 mm sieve among particles that fell below the 10 mm sieve. We evaluated the effect of the proportion of particles of this size on the flotation and separation of reduced iron.

[0020] That is, the inventors came up with the idea of ​​mixing reduced iron with large particle diameters and reduced iron with small particle diameters in an appropriate ratio, thereby stirring the molten iron while minimizing heat removal ((A) above) and ensuring a sufficient distance between the reduced iron particles ((B) above).

[0021] Using compressed reduced iron briquettes and crushed reduced iron, the flotation behavior of reduced iron with various particle size distributions was investigated. It was found that flotation could be prevented when reduced iron with the following particle size distribution was used. Specifically, when the mass of all reduced iron particles is W (kg), the mass of particles with a longest side of 80 to 150 mm among particles that sieved a 10 mm mesh is W1 (kg), the mass of particles with a longest side of 50 to 150 mm among particles that sieved a 10 mm mesh is W2 (kg), and the mass of particles that sieved a 2 mm mesh and sieved a 5 mm mesh among particles that sieved a 10 mm mesh is W3 (kg), it was found that flotation could be prevented when reduced iron with a particle size distribution that satisfied all of the following formulas (1) to (3) was used: 0.60≦W1 / W (1) 0.80≦W2 / W (2) 0.005≦W3 / W≦0.02 (3)

[0022] Preferred embodiments of the present invention will be described in detail below.

[0023] Carbon monoxide is generated when unreduced iron oxide remaining in the reduced iron reacts with the molten iron or carbon in the reduced iron. This carbon monoxide functions as a gas to fluidize the reduced iron. Therefore, it is desirable for a certain amount of iron oxide to remain in the reduced iron when implementing the present invention. On the other hand, if the content of iron oxide in the reduced iron is too high, the temperature of the molten iron decreases significantly due to the endothermic reduction reaction, which actually promotes agglomeration. Experiments conducted by the inventors have found that stirring of the molten iron due to gas generation is promoted when the proportion of reduced metallic iron (mass %, hereinafter referred to as the metallization rate) of the total iron present in the reduced iron is 80 to 98%, more preferably 90 to 98%. The metallization rate of the reduced iron can be controlled by adjusting one or more of the amount of solid reducing agent added to the raw material, the flow rate of the reducing gas used in the reduction treatment, and the treatment temperature. The metallization rate of reduced iron can be evaluated by measuring the total iron content according to JIS M 3212 and the metallic iron content according to JIS A 5011-2.

[0024] As described above, to bring the surface of the reduced iron into contact with the slag (see (C) above), a layer of molten slag is formed on the surface of the molten iron in the electric furnace. It is preferable to leave the slag formed in the previous heat in the electric furnace. Alternatively, auxiliary materials may be added to the electric furnace to produce molten slag. Reduced iron contains gangue components composed of oxides, which melt into slag in the electric furnace. As the reduced iron melts, slag resulting from the gangue components accumulates in the furnace. If the reduced iron contains too many gangue components, the heat required for melting increases, resulting in reduced productivity. However, as described above, from the perspective of bringing the reduced iron into contact with the slag, it is preferable that the reduced iron contain a certain amount of gangue components. Based on experiments conducted by the present inventors, it was found that a reduced iron containing a total of 3.5 to 11.5 mass% of CaO, SiO2, Al2O3, and MgO is preferable from the perspective of productivity. The gangue components contained in the reduced iron can be adjusted by adjusting the blending of raw materials, etc. The gangue components contained in the reduced iron can be measured in accordance with the method described in JIS G0321:2017.

[0025] The metallization rate and gangue components of the reduced iron can be adjusted independently, but from the viewpoint of carrying out the present invention, it is preferable to use reduced iron having a combination of these components.

[0026] When reduced iron satisfying the above-described preferred conditions of the present invention is used as a raw material for molten iron, it is possible to use it by mixing it with an iron source other than reduced iron, such as scrap, etc. When an iron source other than reduced iron is used, it becomes difficult to obtain the stirring effect due to the gas generation described above. Therefore, it is preferable to use reduced iron in the melting step in an amount of 10% by mass or more, more preferably 50% by mass or more, of the total iron raw materials to be melted in the furnace.

[0027] Furthermore, if the electric furnace has a function for separating slag and molten iron by means such as tilting after melting the raw materials, a slag removal process can be provided after the melting process of the previous heat, in which the slag is discharged outside the furnace and separated from the molten iron. To ensure the contact between the reduced iron and the slag, it is desirable to leave at least a portion of the slag remaining in the furnace when separating the slag generated in the previous heat in the slag removal process and retain it in the furnace until the melting process of the current heat. After various investigations into the thickness of the slag to be left in the furnace, the inventors found that a thickness of 20 mm or more is effective for ensuring sufficient contact between the slag and the reduced iron. To achieve this, it is preferable to have a means for measuring the vertical thickness of the slag in the electric furnace and to control the amount of slag discharged outside the furnace in the slag removal process so that the vertical thickness of the slag remaining in the furnace is 20 mm or more.

[0028] By installing weighing scales in three locations in the electric furnace 1 shown in Figure 1—the furnace shell 3, the ladle (not shown) that receives the molten iron tapped from the electric furnace, and the slag ladle (not shown) that receives the discharged slag—the mass and thickness of the slag remaining in the furnace can be measured based on the contents of the furnace and the weighing values ​​of each scale. That is, the masses of the molten iron and slag in the furnace are measured before slag discharge from the amounts of main and auxiliary materials supplied in the previous heat and the weighing value of the furnace shell. Then, the masses of the molten iron and slag that have moved out of the furnace are measured from the weighing values ​​of the slag ladle at the time of slag discharge and the weighing value of the ladle at the time of tapping, and the mass of the slag 11 remaining in the furnace before the start of the current heat can be evaluated. Furthermore, assuming a density of molten slag of 3000 kg / m 3 The volume of the slag can be calculated using the above equation, and the position and surface area of ​​the stationary molten iron surface can be calculated from the mass of the molten iron remaining in the furnace, and using these, the vertical thickness of the slag 11 present on the molten iron 10 can be estimated. This method can be used to measure the vertical thickness of the slag in an electric furnace.

[0029] The amount of reduced iron and the thickness of the remaining slag can be determined independently, but from the viewpoint of implementing the present invention, it is preferable to use them in combination.

[0030] The electric furnace can be a general steelmaking arc furnace, in which case an arc can be used as the main heat source for melting the reduced iron. It is also possible to use heat of oxidation from the supply of oxygen gas. The main raw materials can be charged into the electric furnace by charging them through the main raw material charging port 5 as shown in FIG. 1 , or by sequentially charging them using a charging chute or horizontal conveyor while melting them using an arc, or by charging them all at once using a bucket or the like before heating and melting them. The following examples will describe in detail one embodiment of the present invention, but they are not intended to limit the scope of the present invention. The heating method, raw material charging method, etc. can be modified within the spirit and scope of the present invention. [Example]

[0031] The present invention was implemented in a three-phase AC electric furnace 1 shown in FIG. 1, with an inner diameter of 6.5 m, a tapping capacity of 110 t, and 65 t of seed molten iron remaining in the furnace during tapping. The reduced iron used as the main raw material for molten iron 10 in the electric furnace 1 had the particle size distribution, metallization rate, gangue, and apparent density shown in Table 1. The reduced iron used here was briquette-formed by compression molding after reduction. The maximum longest side of the briquettes was 150 mm. Briquettes whose longest side had changed due to breakage during transportation or other reasons were classified. The particle size distribution of the reduced iron that overflowed a 10 mm sieve was determined based on the longest side, and that of the reduced iron that underflowed the sieve was determined based on the sieve classification. The particle size distributions are listed in Table 1. The apparent density of the reduced iron was measured by underwater weighing as specified in JIS Z 8807-2012, and the components of the reduced iron were measured according to the method specified in JIS G0321:2017. The metallization rate of the reduced iron was calculated from the total iron content measured by the method described in JIS M 3212 and the metallic iron content measured by the method described in JIS A 5011-2.

[0032] [Table 1]

[0033] The electric furnace 1 consists of a lower furnace shell 3 and an upper furnace lid 4. Three graphite electrodes 2 are inserted into the furnace through the furnace lid 4, and a main raw material inlet 5 and an auxiliary raw material inlet 6 also penetrate the furnace lid 4. Reduced iron and alloys can be added through the main raw material inlet 5, and auxiliary raw materials such as slag formers can be added through the auxiliary raw material inlet 6. The furnace shell 3 is designed to discharge the processed molten iron 10 outside the furnace using an eccentric bottom tapping method, and has a slag discharge port 7 on the side wall that is 1,000 mm wide and 995 mm high. By tilting the furnace body, the slag 11 inside the furnace can be discharged outside the furnace through the slag discharge port 7 and separated from the molten iron 10.

[0034] In addition, weighing scales are provided in three locations: the furnace shell 3, the ladle (not shown) that receives the molten iron tapped from the electric furnace, and the slag receiving ladle (not shown) that receives the discharged slag. The mass of the slag remaining in the furnace can be measured based on the contents of the furnace and the weighing values ​​of each weighing scale.

[0035] Prior to the addition of the main raw materials for this heat, a slag removal process was performed after the melting process of the previous heat, in which slag was removed from the furnace and separated from the molten iron. The masses of the molten iron and slag in the furnace were measured before slag removal based on the amounts of the main raw materials and auxiliary materials supplied for the previous heat and the weighing value of the furnace shell. The masses of the molten iron and slag that had moved outside the furnace were measured based on the weighing values ​​of the slag receiving ladle at the time of slag removal and the weighing values ​​of the ladle at the time of tapping, and the mass of the molten iron and slag 11 remaining in the furnace before this heat was evaluated. The density of the molten slag was set at 3000 kg / m 3 The volume of the slag was calculated using the above equation, and the position and surface area of ​​the stationary molten iron surface were calculated from the mass of the molten iron remaining in the furnace, and the height of the slag 11 present above the molten iron 10 was estimated using these.

[0036] The electric furnace 1 also has one oxygen supply lance 9 with an inner diameter of 28 mm connected to a manipulator 8 to supply oxygen gas into the furnace for the purposes of assisting melting by oxidation heat and oxidative refining. The oxygen supply lance 9 is inserted into the furnace through the slag discharge port 7, and can spray oxygen gas toward the raw materials and molten iron.

[0037] Table 2 shows examples in which molten steel was produced from the reduced iron listed in Table 1 using electric furnace 1, along with comparative examples.

[0038] [Table 2]

[0039] During the slag removal process of the previous heat prior to this heat, slag was left in the furnace, and the vertical thickness of the slag remaining in the furnace was evaluated using the method described above. The evaluation results are shown in the "Slag thickness after previous slag removal" column in Table 2.

[0040] In the melting process for producing molten steel for this heat, reduced iron or a mixture of reduced iron and scrap (hereinafter referred to as the main raw materials) was fed into the furnace, which had 65 tons of seed molten iron remaining, from the main raw material inlet 5 at a feed rate of 3.2 tons / min., while arc current was started. Five minutes after the start of reduced iron feeding, 3200 Nm was fed from the oxygen supply lance 9.3 The main raw materials were melted by supplying oxygen at a rate of 1 / min. After the charging of 110 t of the main raw materials was completed, 3.4 t of quicklime was charged as a slag-forming material through auxiliary raw material inlet 6, and electricity was again applied and oxygen was supplied. After the slag was discharged outside the furnace, the temperature of the molten steel was measured. After confirming that the temperature of the molten steel had reached 1550°C or higher, electricity was again applied to raise the temperature to 1650°C and the molten steel was then poured into the ladle.

[0041] When reduced iron agglomerates and floats, extra energy is required to melt it, which is thought to extend the time required to reach 1550°C under constant input power conditions. The time required for melting was defined as the time from the start of main raw material charging until the temperature rose to 1550°C or higher, and is shown in Table 2 together with the relative value when the required melting time in Comparative Example 1 was set to 100. In addition, to evaluate agglomerate flotation, visual inspection was performed through the slag discharge port 7 50 minutes after the start of main raw material charging. If unmelted slag was found in the slag, an "X" was marked in the "Evaluation" column of Table 2, and if no unmelted slag was found, an "O" was marked.

[0042] In Comparative Examples 1 to 5, the melting time was long, and unmelted iron was observed at 50 minutes. It is believed that in Comparative Examples 1, 2, and 4, a large amount of reduced iron with a small particle size was included, which resulted in increased heat removal and flotation of the reduced iron particles. On the other hand, in Comparative Example 3, the reduction iron with a small particle size, which generates a large amount of gas, was excluded, which presumably reduced the flow of the reduced iron particles due to stirring of the molten iron to a small extent, leading to flotation of the reduced iron particles. Furthermore, in Comparative Example 5, in which the apparent density of the reduced iron was low, the reduced iron floated on the slag, which presumably resulted in insufficient heat transfer from the molten iron to the reduced iron.

[0043] In contrast, in Examples 1 to 14, the required melting time was short and no undissolved material was observed, suggesting that agglomeration and flotation were successfully suppressed. In particular, Examples 1 to 4 exhibited a particularly significant effect of suppressing agglomeration and flotation compared to Examples 5 and 6, which had high or low metallization rates, Example 7, which contained a large amount of gangue components, and Example 8, which contained a low amount. Furthermore, in Examples 1 and 9 to 11, which contained a high reduced iron content, agglomeration of the main raw materials was suppressed by the stirring of the molten iron caused by gas generation from the reduced iron, and thus the required melting time was shorter compared to Example 12, which contained a low reduced iron content. Prior to Example 13, all of the slag was removed, and prior to Example 14, the amount of removed slag was increased. Consequently, the required melting time was extended compared to Example 1. This is thought to be due to the reduction in slag coming into contact with the reduced iron. [Explanation of symbols]

[0044] 1 electric furnace 2. Graphite electrodes 3 Furnace shell 4 Hearth lid 5 Main raw material input port 6 Auxiliary material input port 7. Slag outlet 8 Manipulator 9 Oxygen supply lance 10 Molten Iron 11 Slag

Claims

1. Reduced iron that is supplied to an electric furnace and used as a raw material for molten iron, wherein the apparent density of the reduced iron is 4.0 g / cm ３ The mass of all the reduced iron particles is W (kg), and the mass of particles on a sieve with a mesh size of 10 mm and having a longest side of 80 to 150 mm is W １ (kg), the mass of the object whose longest side is 50 to 150 mm is W ２ (kg), and the mass of particles that fall on a 2 mm sieve and below a 5 mm sieve among particles that fall under a 10 mm sieve is W ３ (kg) and has a particle size distribution that satisfies all of the following formulas (1) to (3): 0.60≦W １ / W (1) 0.80≦W ２ / W (2) 0.005≦W ３ / W≦0.02 (3)

2. The reduced iron according to claim 1, wherein the metallization rate of the reduced iron is 80 to 98 mass%.

3. The reduced iron contains CaO, SiO ２ , Al ２ O ３ and MgO in a total content of 3.5 to 11.5 mass%.

4. A method for producing molten iron, comprising a melting step of charging the reduced iron according to any one of claims 1 to 3 into an electric furnace, heating and melting the reduced iron.

5. 5. The method for producing molten iron according to claim 4, wherein the amount of reduced iron used in the melting step in the electric furnace is 10 to 100 mass % of the total iron raw material melted in the furnace.

6. 5. The method for producing molten iron according to claim 4, further comprising a slag removal process in which slag is discharged outside the electric furnace after the melting process to separate it from the molten iron, and in the slag removal process, at least a portion of the slag is left in the furnace and held in the furnace until the next melting process.

7. 7. The method for producing molten iron according to claim 6, further comprising the step of controlling the amount of slag discharged from the electric furnace in the slag removal step so that the vertical thickness of the slag remaining in the furnace is 20 mm or more.

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