Method for producing hot direct reduced iron

Abstract

Disclosed is a technique by which hot direct reduced iron having a heightened carbon concentration is produced through a direct reduction process.　This method for producing hot direct reduced iron comprises: a reduction step in which a reducing gas is brought into contact with an iron oxide feedstock to obtain iron metal; and a cooling step in which the iron metal is carbonized while being cooled, thereby obtaining hot direct reduced iron. The cooling step comprises a first step, in which after the reduction step, methane gas is brought into contact with the iron metal, and a second step, in which after the first step, CO gas is brought into contact with the iron metal. In the second step, the iron metal in contact with the CO gas has a temperature of 400-700°C. In the second step, the proportion of the volume of a discharge gas that is discharged from the system to the volume of the gas that is supplied is 40% or higher.

Description

Hot reduced iron manufacturing method

[0001] This application discloses a method for producing hot direct reduced iron (HDRI).

[0002] In the steel industry, as an alternative to the blast furnace method, a direct reduction process using reducing gas is used to reduce CO ２ Studies have been conducted to reduce carbon dioxide emissions. For example, a process using a shaft furnace has been studied as a direct reduction process (Patent Document 1). In the direct reduction process, a reducing gas is brought into contact with an iron oxide raw material to obtain direct reduced iron (DRI). DRI includes two forms: cold reduced iron (CDRI) and HDRI. In both CDRI and HDRI, the carbon content may be increased in order to lower the melting temperature in the subsequent melting and refining process and to ensure the strength of the resulting steel.

[0003] International Publication No. 2021 / 195160

[0004] In the prior art, when producing hot reduced iron by a direct reduction process, there is room for improvement in terms of increasing the carbon content of the hot reduced iron while maintaining a high reduction rate.

[0005] The present application discloses the following multiple aspects as means for solving the above-mentioned problems. <Aspect 1> A method for producing hot reduced iron, comprising: a reduction step of bringing a reducing gas into contact with an oxidized iron raw material to obtain metallic iron; and a cooling step of carbonizing the metallic iron while cooling it to obtain hot reduced iron, wherein the cooling step comprises: a first step of bringing methane gas into contact with the metallic iron after the reduction step; and a second step of bringing CO gas into contact with the metallic iron after the first step, wherein the temperature of the metallic iron contacted with the CO gas in the second step is 400°C or higher and 700°C or lower, and wherein the ratio of the volume of exhaust gas discharged outside the system to the volume of gas supplied in the second step is 40% or higher. <Aspect 2> A method for producing hot reduced iron according to Aspect 1, wherein the ratio of the volume of exhaust gas discharged outside the system to the volume of gas supplied in the second step is 70% or higher. <Aspect 3> The method for producing hot reduced iron according to Aspect 1 or 2, wherein the temperature of the metallic iron contacting the CO gas in the second step is 550°C or higher and 700°C or lower. <Aspect 4> The method for producing hot reduced iron according to any of Aspects 1 to 3, wherein the exhaust gas from the first step is used as the reducing gas in the reduction step. <Aspect 5> The method for producing hot reduced iron according to any of Aspects 1 to 4, wherein the reduction step and the cooling step are performed in a shaft furnace. <Aspect 6> The method for producing hot reduced iron according to any of Aspects 1 to 4, wherein the reduction step is performed in a shaft furnace and the cooling step is performed outside the shaft furnace. <Aspect 7> The method for producing hot reduced iron according to any of Aspects 1 to 4, wherein the reduction step and the first step are performed in a shaft furnace and the second step is performed outside the shaft furnace. <Aspect 8> The method for producing hot reduced iron according to any one of Aspects 1 to 7, wherein the reducing gas contains hydrogen gas.<Aspect 9> The method for producing hot reduced iron according to Aspect 8, comprising: a dehydration step of dehydrating exhaust gas from the reduction step to obtain a circulating gas, and a temperature increase step of increasing temperatures of the circulating gas and hydrogen gas to obtain the reducing gas containing the circulating gas and the hydrogen gas. <Aspect 10> The method for producing hot reduced iron according to any of Aspects 1 to 9, wherein the temperature of the metallic iron that comes into contact with the methane gas in the first step is 700°C or higher.

[0006] According to the method for producing hot reduced iron of the present disclosure, it is possible to produce hot reduced iron having an increased carbon concentration while maintaining a high reduction rate.

[0007] FIG. 1 is a schematic diagram for explaining an example of a manufacturing method and manufacturing system for HDRI. FIG. 2 is a schematic diagram for explaining an example of a manufacturing method and manufacturing system for HDRI. FIG. 3 is a schematic diagram for explaining an example of a manufacturing method and manufacturing system for HDRI. FIG. 4 shows simulation conditions for each of Cases 1 to 3. In Case 3, the relationship between the outlet temperature of the transition zone (first step) (the temperature of metallic iron contacting with CO gas in the cooling zone (second step)) and the carbon content and reduction rate of the finally obtained HDRI is shown. In Case 3, the relationship between the outlet temperature of the transition zone (first step) (the temperature of metallic iron contacting with CO gas in the cooling zone (second step)) and the temperature of the finally obtained HDRI is shown.

[0008] An embodiment of a manufacturing method and manufacturing system for hot reduced iron (hereinafter referred to as HDRI) according to the present disclosure will be described below. However, the manufacturing method and manufacturing system for HDRI according to the present disclosure are not limited to the following embodiment. In this application, "iron oxide raw material" refers to a raw material containing iron oxide before the reduction step. "Metallic iron" refers to an intermediate product obtained after the reduction step and up to the completion of the cooling step. For convenience, iron whose carbon concentration has been increased by carbonization or the like is also referred to as "metallic iron." "HDRI" refers to HDRI as a product obtained after the cooling step.

[0009] 1 to 4 , a method for producing HDRI according to one embodiment includes a reduction step S1 in which a reducing gas is brought into contact with an oxidized iron raw material 10 to obtain metallic iron 20, and a cooling step S2 in which the metallic iron 20 is cooled and carbonized to obtain HDRI 30. The cooling step S2 includes a first step S21 in which methane gas is brought into contact with the metallic iron 20 after the reduction step S1, and a second step S22 in which CO gas is brought into contact with the metallic iron 20 after the first step S21. Here, the temperature of the metallic iron 20 that comes into contact with the CO gas in the second step S22 is 400°C or higher and 700°C or lower. Furthermore, the ratio of the volume of the exhaust gas to the volume of the gas supplied in the second step S22 is 40% or higher.

[0010] 1.1 Reduction Step In the reduction step S1, a reducing gas is brought into contact with the oxidized iron raw material 10. This causes a reduction reaction to occur, resulting in metallic iron 20. As shown in FIGS. 1 to 4, the reduction step S1 may be carried out, for example, in a shaft furnace 100. Alternatively, the reduction step S1 may be carried out in an apparatus other than the shaft furnace 100 (for example, a fluidized bed). In particular, when the reduction step S1 is carried out in the shaft furnace 100, a high effect can be expected.

[0011] 1.1.1 Oxidized Iron Raw Material The oxidized iron raw material 10 contains at least iron oxide. The oxidized iron raw material 10 may be, for example, one or more materials selected from iron ore pellets, iron ore, and sintered ore. The oxidized iron raw material 10 may contain, in addition to iron oxide, for example, one or both of silicon dioxide and aluminum oxide. The oxidized iron raw material 10 may have a particle size distribution or may have a uniform particle diameter. The average particle diameter of the oxidized iron raw material 10 may be, for example, 5.0 mm or more and 30.0 mm or less, or 10.0 mm or more and 15.0 mm or less. The "particle diameter" of the oxidized iron raw material 10 refers to the sieve diameter of the raw material. The "average particle diameter" of the oxidized iron raw material 10 refers to the weighted average value of the particle diameters of the raw material. Specifically, the average particle diameter of the oxidized iron raw material is measured as follows. That is, the average particle size of the oxidized iron raw material can be measured by obtaining a mass-based particle size distribution by a dry sieving test described in JIS Z 8815: 1995, and calculating a mass-weighted average of the maximum and minimum particle sizes of each sieve as a representative particle size. The oxidized iron raw material 10 may be formed into pellets or the like, may be in the form of powder, may be in the form of lumps, or may be in any other shape.

[0012] When the reduction step S1 is performed in the shaft furnace 100, the oxidized iron raw material 10 is filled into the shaft furnace 100 to form a packed bed. The packing rate of the packed bed is not particularly limited and may be the same as that in a conventional reduced iron manufacturing method using a shaft furnace. The packed bed moves downward within the shaft furnace 100. That is, the oxidized iron raw material 10 is substantially filled within the shaft furnace 100 and gradually moves downward by falling or the like. Focusing on a single raw material particle in the packed bed, the raw material particle may move downward continuously at a constant speed or may move intermittently by repeatedly falling and stopping. Focusing on a single raw material particle in the packed bed, the average downward movement speed of the raw material particle is not particularly limited. For example, the average movement speed is adjusted depending on the supply amount (feed rate) of the raw material. When moving the packed bed downward, a burden feeder or the like may be used to prevent hanging. Note that a burden feeder is a rectifying device having a rotation mechanism or the like.

[0013] 1.1.2 Reducing Gas The type of reducing gas is not particularly limited as long as it can reduce the oxidized iron raw material 10. In particular, when the reducing gas contains hydrogen gas, the technology of the present disclosure can be expected to have a more significant effect. The reducing gas may contain not only hydrogen gas but also gases other than hydrogen. Examples of gases other than hydrogen include CO gas, inert gas, and CO ２ Examples of the reducing gas include nitrogen gas and argon gas. When the reducing gas contains hydrogen gas, the hydrogen concentration of the reducing gas may be, for example, 80% by volume or more and 100% by volume or less. The supply temperature of the reducing gas (the temperature immediately before contact with the oxidized iron raw material 10) may be any temperature at which a reduction reaction with the iron oxide occurs, and may be, for example, 700°C or more. The temperature of the reducing gas may be 700°C or more and 1100°C or less, and preferably 800°C or more and 1100°C or less.

[0014] When the reduction step S1 is performed in the shaft furnace 100, the reducing gas is supplied from the side wall of the shaft furnace 100 to the inside of the furnace. The method of supplying the reducing gas is not particularly limited. For example, a pipe or the like can be connected to a reducing gas supply port provided on the side wall of the shaft furnace 100, and the reducing gas can be supplied from the outside to the inside of the furnace through the pipe or the like.

[0015] 1.1.3 Metallic Iron In the reduction step S1, at least a portion of the iron oxide contained in the oxidized iron raw material 10 is reduced to obtain a solid reactant containing metallic iron 20. The solid reactant may contain, in addition to metallic iron 20, iron oxide, silicon dioxide, aluminum oxide, and the like that remain unreduced. The temperature of the metallic iron 20 immediately after reduction may be, for example, 700°C or higher. There is no particular upper limit to the temperature of the metallic iron 20 immediately after reduction, as long as it is a temperature at which the cooling step S2 described below can be carried out. The temperature of the metallic iron 20 immediately after reduction may be, for example, 1100°C or lower. The temperature of the metallic iron 20 immediately after reduction may be 700°C or higher and 1100°C or lower, 700°C or higher and 1050°C or lower, 700°C or higher and 100°C or lower, or 700°C or higher and 900°C or lower.

[0016] When the reduction step S1 is carried out in the shaft furnace 100, the solid reactant containing metallic iron 20 is recovered from the lower part of the shaft furnace 100 (below the supply position of the reducing gas).

[0017] 1.1.4 Shaft Furnace When the reduction step S1 is performed in a shaft furnace 100, the shape of the shaft furnace 100 may be similar to that of a known shaft furnace. For example, the shaft furnace 100 may have a furnace top, a furnace bottom, and a cylindrical portion (cylindrical portion) forming a sidewall between the furnace top and the furnace bottom. In this case, the cylindrical portion may have a barrel portion and a tapered portion located below the barrel portion, and the inner diameter of the furnace may decrease from top to bottom at the tapered portion. The shaft furnace 100 may be equipped with a burden feeder or the like to prevent the packed bed of raw materials from hanging when moving the packed bed downward inside. The shaft furnace 100 may also be equipped with a cooling gas supply port for supplying a cooling gas and a cooling gas discharge port for discharging the cooling gas below the reducing gas supply port. The cooling gas supply port may be provided on the sidewall of the furnace or may be provided inside the sidewall of the furnace. The cooling gas outlet may be provided on the side wall of the furnace. The supply and discharge modes of each gas will be described later.

[0018] 1.2 Cooling Step The temperature of the metallic iron 20 immediately after the reduction step S1 is, for example, 700°C or higher. In the cooling step S2, gas is brought into contact with the metallic iron 20 at such a high temperature, thereby cooling the metallic iron 20 and carbonizing the metallic iron 20. That is, HDRI 30 containing carbon is obtained. By carbonizing the metallic iron 20 in this way to obtain HDRI 30 containing carbon, the melting temperature in the subsequent melting and refining step is lowered and the strength of the resulting steel is ensured.

[0019] In the cooling step S2, (1) carbonization and cooling (and reduction) of the metallic iron 20 by methane gas is followed by (2) carbonization (and reduction) of the metallic iron 20 by CO gas. According to the findings of the present inventors, carbonization of the metallic iron 20 by methane gas is likely to proceed in a high-temperature range of 700°C or higher and is an endothermic reaction. On the other hand, carbonization of the metallic iron 20 by CO gas is most likely to proceed at a temperature of 400°C or higher and 600°C or lower and is an exothermic reaction. Note that, in this application, "carbonization" of the metallic iron 20 by methane gas or CO gas refers to one or more of the following: the metallic iron 20 becoming a carbide due to carbon extracted from methane or CO; the carbon extracted from methane or CO dissolving in the metallic iron 20; and the carbon extracted from methane or CO adhering to and depositing on the surface of the metallic iron 20 as elemental carbon. In the cooling step S2, the high-temperature metallic iron 20 obtained in the reduction step S1 is first contacted with methane gas, thereby allowing the endothermic reaction to proceed appropriately and efficiently. Furthermore, in addition to the physical endothermic reaction due to contact with methane gas, which has a large specific heat, the endothermic reaction during carbonization also tends to lower the temperature of the metallic iron 20 to a temperature suitable for carbonization with CO gas. By contacting the cooled metallic iron 20 with CO gas, the exothermic reaction proceeds appropriately and efficiently, further increasing the carbon concentration in the final HDRI 30. As described above, in the cooling step S2, the carbonization with (1) methane gas and (2) CO gas are carried out in this order, thereby increasing the carbon concentration in the HDRI 30 compared to when each gas is contacted alone. Furthermore, the endothermic reaction with (1) methane gas and the exothermic reaction with CO gas are carried out in this order, making it easier to obtain an HDRI 30 having a temperature above a certain level.

[0020] When the reduction step S1 is performed in a shaft furnace, the cooling step S2 may be performed in the shaft furnace or outside the shaft furnace. That is, as shown in FIG. 1 , the reduction step S1 and the cooling step S2 may be performed in a shaft furnace 100. Alternatively, as shown in FIG. 2 , the reduction step S1 may be performed in the shaft furnace 100, and the cooling step S2 may be performed outside the shaft furnace 100. Alternatively, as shown in FIG. 3 , a first step S21 (described later) of the reduction step S1 and the cooling step S2 may be performed in the shaft furnace 100, and a second step S22 (described later) of the cooling step S2 may be performed outside the shaft furnace 100. When at least a part of the cooling step S2 is performed outside the shaft furnace 100, for example, as shown in FIGS. 2 and 3 , a cooling tower 200 may be provided downstream of the shaft furnace 100, and at least a part of the cooling step S2 may be performed in the cooling tower 200. Note that, in this application, the term "downstream side" refers to the downstream side in the HDRI production process. That is, in the case where HDRI 30 containing carbon is produced from oxidized iron raw material 10 via metallic iron 20, the oxidized iron raw material 10 side is the upstream side, and HDRI 30 containing carbon side is the downstream side.

[0021] The cooling step S2 includes a first step S21 and a second step S22. In this embodiment, it is sufficient that the temperature of the metallic iron 20 is reduced in at least a part of the cooling step S2, and the temperature of the metallic iron 20 may increase during the cooling step S2. For example, as described above, an exothermic reaction may occur between the metallic iron 20 and CO gas in the second step S22, causing the temperature of the metallic iron 20 to increase.

[0022] 1.2.1 First Step The first step S21 corresponds to the above (1). That is, in the first step S21, after the reduction step S1, methane gas is brought into contact with the metallic iron 20. This carbonizes the metallic iron 20. The metallic iron 20 is partially carbonized. When the reduction step S1 is performed in a shaft furnace, the first step S21 may be performed in the shaft furnace or outside the shaft furnace (for example, in a cooling tower provided downstream of the shaft furnace). The method of bringing the methane gas into contact with the metallic iron 20 is not particularly limited. For example, methane gas can be brought into contact with the metallic iron 20 by connecting a pipe or the like to a gas supply port provided on a side wall of the shaft furnace 100 or the cooling tower 200 and supplying methane gas from the outside to the inside through the pipe or the like. The temperature of the metallic iron 20 that comes into contact with methane gas in the first step S21 may be a temperature at which carbonization by methane gas is possible. For example, if the temperature of the metallic iron 20 coming into contact with methane gas in the first step S21 is 700°C or higher, the carbonization of the metallic iron 20 by the methane gas can proceed more appropriately. There is no particular upper limit to the temperature of the metallic iron 20 coming into contact with methane gas in the first step S21. The temperature of the metallic iron 20 coming into contact with methane gas may be, for example, 1100°C or lower. From the viewpoint of allowing the carbonization reaction by methane gas to proceed particularly significantly, the temperature of the metallic iron 20 coming into contact with methane gas in the first step S21 can be set to 710°C or higher and 1100°C or lower, 730°C or higher and 1100°C or lower, 750°C or higher and 1100°C or lower, 770°C or higher and 1100°C or lower, 790°C or higher and 1100°C or lower, 810°C or higher and 1100°C or lower, 700°C or higher and 1070°C or higher. The temperature of the metallic iron 20 in the first step S21 (the temperature of the metallic iron 20 after the reduction step S1) can be controlled by the temperature of the oxidized iron raw material 10 in the reduction step S1, the supply amount of the oxidized iron raw material 10, the temperature of the reducing gas, the supply amount of the reducing gas, etc.Note that the "temperature of the metallic iron 20" in the first step S21 is the average temperature in the radial direction of the shaft furnace or cooling tower. When the reduction step S1 and the first step S21 are performed in the same apparatus (for example, a shaft furnace), the position (height position) P1 when measuring the "temperature of the metallic iron 20" in the first step S21 is downstream (below) the position (height position) P2 where the reducing gas in the reduction step S1 is blown in, and is a position (height position) within 1 m from this position P2. Alternatively, when the reduction step S1 and the first step S21 are performed in different apparatuses (for example, the reduction step S1 is performed in a shaft furnace and the first step S21 is performed in a cooling tower provided downstream of the shaft furnace), the position P1 when measuring the "temperature of the metallic iron 20" in the first step S21 is a position within 1 m downstream (below) from the metallic iron supply port of the apparatus where the first step S21 is performed. The average temperature of the metallic iron 20 in the radial direction can be determined, for example, by installing a rod-shaped member in the radial direction of a shaft furnace or a cooling tower, attaching multiple thermocouples to the member, and measuring multiple temperatures in the radial direction. That is, when the first step S21 is performed in a shaft furnace, the average temperature of the metallic iron 20 in the radial direction is determined by multiple thermocouples installed in the radial direction of the shaft furnace. Also, when the first step S21 is performed in a cooling tower, the average temperature of the metallic iron 20 in the radial direction is determined by multiple thermocouples installed in the radial direction of the cooling tower. Here, for example, assuming that the temperature between the measured points is distributed linearly in the radial direction, the radial temperature distribution T(r) can be expressed as a combination of linear functions of r. In this case, the average temperature T ａｖｅ If the temperature is measured at N points, the radius of the measurement point i (i = 1 to N) is r ｉ is defined by the following formula: ０ , r Ｎ＋１ corresponds to the center of the furnace (r ０ = 0) and the furnace wall (r Ｎ＋１= R), and the temperature at that point is determined by extrapolation. With this method, even if there is a temperature distribution in the radial direction, the average temperature in the radial direction can be determined by averaging multiple measured temperatures. The number of thermocouples is not particularly limited, but it is preferable to arrange five or more thermocouples, for example. In the first step S21, the temperature of the methane gas that comes into contact with the metallic iron 20 is not particularly limited. The temperature of the methane gas may be, for example, 25°C or higher and 600°C or lower.

[0023] In the first step S21, it is sufficient that the carbonization of the metallic iron 20 by the methane gas proceeds, and other gases may be brought into contact with the metallic iron 20 in addition to the methane gas. In other words, the gas (first contact gas) that comes into contact with the metallic iron 20 in the first step S21 may be any gas that contains methane gas. The first contact gas that comes into contact with the metallic iron 20 in the first step S21 may be any gas other than methane gas, such as hydrogen gas, nitrogen gas, CO gas, CO ２ The first contact gas that comes into contact with the metallic iron 20 in the first step S21 may be, for example, natural gas. As described above, in the first step S21, the temperature of the metallic iron 20 is lowered by a carbonization reaction (endothermic reaction) of the metallic iron 20 by methane gas. In the first step S21, as long as the endothermic reaction by methane gas proceeds predominantly, part of the first contact gas that comes into contact with the metallic iron 20 may contain a gas that is accompanied by an exothermic reaction (e.g., CO gas). However, when the first contact gas that comes into contact with the metallic iron 20 in the first step S21 contains CO gas, the volume fraction of the CO gas is smaller than the volume fraction of methane gas. Furthermore, when the first contact gas that comes into contact with the metallic iron 20 in the first step S21 is composed of multiple types of gases, for example, the volume fraction of methane gas is the largest among the volume fractions of the individual gases. The first contact gas that comes into contact with the metallic iron 20 in the first step S21 contains, for example, 50% by volume or more, 60% by volume or more, or 70% by volume or more of methane gas.

[0024] The reaction gas between the metallic iron 20 and methane gas in the first step S21 may contain methane gas and hydrogen gas. The reaction gas may be discharged to the outside of the system as an exhaust gas and used as a fuel, or may be used as the reducing gas described above. In particular, by using the reaction gas between the metallic iron 20 and methane gas in the first step S21 as the reducing gas in the reduction step S1, efficient operation can be achieved while reducing the amount of reducing gas used.

[0025] 1.2.2 Second Step The second step S22 corresponds to (2) above. That is, in the second step S22, after the first step S21, CO gas is brought into contact with the metallic iron 20. This further carbonizes the metallic iron 20. The metallic iron 20 is partially carbonized. When the reduction step S1 is performed in a shaft furnace, the second step S22 may be performed in the shaft furnace or outside the shaft furnace (for example, in a cooling tower provided downstream of the shaft furnace). Note that when the first step S21 is performed outside the shaft furnace, the second step S22 is necessarily performed outside the shaft furnace as well. The method of bringing the CO gas into contact with the metallic iron 20 is not particularly limited. For example, CO gas can be brought into contact with the metallic iron 20 by connecting a pipe or the like to a gas supply port provided on a side wall of the shaft furnace 100 or the cooling tower 200 and supplying CO gas from the outside to the inside through the pipe or the like. In the second step S22, the temperature of the metallic iron 20 that comes into contact with the CO gas is set to 400°C or higher and 700°C or lower, which allows the carbonization reaction by the CO gas to proceed appropriately and also allows HDRI 30 having an appropriate temperature to be obtained after the second step. From the viewpoint of allowing the carbonization reaction by CO gas to proceed particularly significantly, the temperature of the metallic iron 20 that comes into contact with the CO gas in the second step S22 may be 410°C or higher and 700°C or lower, 420°C or higher and 700°C or lower, 430°C or higher and 700°C or lower, 440°C or higher and 700°C or lower, 450°C or higher and 700°C or lower, 460°C or higher and 700°C or lower, 470°C or higher and 700°C or lower, 480°C or higher and 700°C or lower, 490°C or higher and 700°C or lower, 500°C or higher and 700°C or lower, 510°C or higher and 700°C or lower, 520°C or higher and 700°C or lower, 530°C or higher and 700°C or lower, 540°C or higher and 700°C or lower, 550°C or higher and 700°C or lower, 560°C or higher and 700°C or lower, 570°C or higher and 700°C or lower, or 580°C or higher and 700°C or lower. In particular, when the temperature of the metallic iron 20 that comes into contact with the CO gas in the second step S22 is 550° C. or higher and 700° C. or lower, the temperature of the HDRI 30 obtained after the second step S2 becomes higher, and the HDRI 30 is likely to reach a temperature suitable for briquetting (for example, 650° C. or higher). In other words, it is also possible to obtain HBI (Hot Briquette Iron) by briquetting the HDRI 30 as is.The temperature of the metallic iron 20 in the second step S22 (the temperature of the metallic iron 20 after the first step S21) can be controlled by the temperature of the metallic iron 20 in the first step S21, the supply amount of the metallic iron 20, the temperature of the methane gas, the supply amount of the methane gas, etc. Note that, as with the first step S21, the "temperature of the metallic iron 20" in the second step S22 is the average temperature in the radial direction of the shaft furnace or the cooling tower. That is, when the second step S22 is performed in a shaft furnace, the average temperature of the metallic iron 20 in the radial direction is determined by a plurality of thermocouples installed in the radial direction of the shaft furnace. Furthermore, when the second step S22 is performed in a cooling tower, the average temperature of the metallic iron 20 in the radial direction is determined by a plurality of thermocouples installed in the radial direction of the cooling tower. When the first step S21 and the second step S22 are performed in the same apparatus (e.g., a shaft furnace), the position (height position) P3 at which the "temperature of the metallic iron 20" is measured in the second step S22 is downstream (below) of the position (height position) P4 at which the methane gas is blown in in the first step S21 and is within 1 m of this position (height position). Alternatively, when the first step S21 and the second step S22 are performed in different apparatuses (e.g., the first step S21 is performed in a shaft furnace and the second step S22 is performed in a cooling tower located downstream of the shaft furnace), the position P3 at which the "temperature of the metallic iron 20" is measured in the second step S22 is within 1 m downstream (below) of the metallic iron supply port of the apparatus in which the second step S22 is performed. The temperature of the CO gas that comes into contact with the metallic iron 20 in the second step S22 is not particularly limited. The temperature of the CO gas may be, for example, 25°C or higher and 700°C or lower.

[0026] In the second step S22, it is sufficient that the carbonization of the metallic iron 20 is promoted by the CO gas, and other gases may be brought into contact with the metallic iron 20 together with the CO gas. In other words, the gas (second contact gas) that comes into contact with the metallic iron 20 in the second step S22 may be one that contains CO gas. The second contact gas that comes into contact with the metallic iron 20 in the second step S22 may be nitrogen gas, hydrogen gas, CO gas, etc., in addition to CO gas. ２The second contact gas that comes into contact with the metallic iron 20 in the second step S22 may contain, for example, converter gas (LDG). When the second contact gas that comes into contact with the metallic iron 20 in the second step S22 contains methane gas, the volumetric proportion of the methane gas is smaller than the volumetric proportion of CO gas. When the second contact gas that comes into contact with the metallic iron 20 in the second step S22 is made up of multiple types of gases, for example, the volumetric proportion of CO gas is the largest among the volumetric proportions of the individual gases. The second contact gas that comes into contact with the metallic iron 20 in the second step S22 contains, for example, 50 vol% or more, 60 vol% or more, or 70 vol% or more of CO gas.

[0027] As described above, the gas supplied in the second step S22 contains CO gas and optionally other gases. On the other hand, the reaction gas between the metallic iron 20 and CO gas in the second step S22 is mainly CO gas and CO ２The reaction gas may contain a gas. The reaction gas may be discharged outside the system and used as fuel, or may be used as part of the cooling gas or the like in the first step S21 described above. In the production method of the present disclosure, it is important that the ratio of the volume of the discharged gas to the volume of the gas supplied in the second step S22 ([(volume of discharged gas to the system) / (volume of supplied gas)] × 100) is 40% or more. This allows the reduction reaction in the reduction step S1 and the carbonization reaction by methane gas in the first step S21 to proceed more appropriately, thereby increasing the reduction rate and carbon concentration in the HDRI 30. In one embodiment, the ratio of the volume of the discharged gas to the volume of the gas supplied in the second step S22 may be 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, or 100%. In particular, when the ratio of the volume of the discharged gas to the volume of the gas supplied in the second step S22 is 70% or more, the carbon content and reduction rate of the finally produced HDRI are likely to be more significantly improved. For example, if the gas from the first step S21 flows into the second step S22 within the system, the volume of gas discharged to the outside of the system may be greater than the volume of gas supplied in the second step S22. When the volume of gas discharged to the outside of the system is greater than the volume of gas supplied in the second step S22, the ratio of the volume of the gas discharged to the outside of the system to the volume of the gas supplied in the second step S22 is considered to be "100%." ​​The method for discharging the exhaust gas from the second step S22 to the outside of the system is not particularly limited. For example, the exhaust gas may be discharged to the outside of the system through a gas outlet provided in the side wall of the shaft furnace 100 or the cooling tower 200. The gas outlet may be provided downstream of the reduction step S1 or downstream of the first step S21. By controlling the flow rate of the exhaust gas at the gas outlet, the proportion of the gas discharged to the outside of the system from the second step S22 can be controlled.

[0028] 1.2.3 Hot Reduced Iron (HDRI) Through the reduction step S1 and cooling step S2, HDRI 30 is produced. In this application, "HDRI" refers to DRI having a surface temperature of 100°C or higher.

[0029] In addition to carbon and iron, HDRI 30 may also contain unreduced iron oxide, silicon dioxide, aluminum oxide, etc. The carbon content of HDRI 30 may be, for example, 2.5% by mass or more and 5% by mass or less.

[0030] 1.3 Dehydration Step and Temperature-Raising Step The HDRI manufacturing method according to this embodiment may include other steps in addition to the reduction step S1 and cooling step S2 described above. For example, the HDRI manufacturing method according to one embodiment may include a dehydration step S3 in which the exhaust gas from the reduction step S1 is dehydrated to obtain a circulating gas. The HDRI manufacturing method according to one embodiment may also include a temperature-raising step S4 in which the exhaust gas from the reduction step S1 is heated or the circulating gas obtained by dehydrating the exhaust gas is heated. The temperature-raising step S4 may be a step in which the exhaust gas from the reduction step S1 or the circulating gas obtained by dehydrating the exhaust gas is heated, together with hydrogen gas, to obtain a reducing gas containing hydrogen gas and one or both of the exhaust gas and the circulating gas. The dehydration step S3 and temperature-raising step S4 may also be combined. For example, as shown in FIG. 4 , a method for producing HDRI according to one embodiment may include a dehydration step S3 in which the exhaust gas from the reduction step S1 is dehydrated to obtain a circulating gas, and a heating step S4 in which the circulating gas and hydrogen gas are heated to obtain a reducing gas containing the circulating gas and hydrogen gas.

[0031] 1.3.1 Dehydration Step In the dehydration step S3, the exhaust gas from the reduction step S1 is dehydrated to obtain a circulation gas. The dehydration may be performed using a known dehydration device. In the reduction step S1, water may be produced by the reaction between the reducing gas and the oxidized iron raw material 10. However, in the reduction step S1, the reducing gas is not necessarily used 100%. That is, the reducing gas remains in the exhaust gas from the reduction step S1 together with water. By dehydrating such exhaust gas, a circulation gas containing the reducing gas is obtained.

[0032] 1.3.2 Temperature-Raising Step Although the circulation gas obtained in the dehydration step S3 contains reducing gas, the amount thereof is insufficient. Furthermore, since the temperature of the circulation gas obtained in the dehydration step S3 is low, it is inefficient to use it directly in the reduction step S1. Therefore, in the temperature-raising step S4, the circulation gas and hydrogen gas are heated to obtain a reducing gas containing the circulation gas and hydrogen gas. In other words, the reducing gas is obtained by heating and mixing the circulation gas and hydrogen gas as a make-up gas. In the temperature-raising step S4, the circulation gas and hydrogen gas may be heated and then mixed, or the circulation gas and hydrogen gas may be mixed and then heated. The hydrogen gas may be obtained by electrolysis of water or membrane separation from synthesis gas (gas obtained by steam reforming or partial combustion of coal or biomass). The temperature-raising step S3 may be performed using a known heating device.

[0033] 1.3.3 Other Matters As described above, in the method for producing HDRI according to one embodiment, the reduction step S1 and the cooling step S2 may be performed in the shaft furnace 100. For example, the first step S21 may be performed below the reduction step S1 in the shaft furnace 100. In this case, as shown in FIG. 4, the exhaust gas from the first step S21 may rise directly within the furnace and be added to the reducing gas in the reduction step S1 and used for reduction. Furthermore, as shown in FIGS. 1 to 4, the exhaust gas from the second step S22 may be discharged outside the system downstream of the first step S21. With these configurations, CO gas and CO ２ Gas is removed from the reduction step S1. That is, CO gas and CO are removed from the exhaust gas of the reduction step S1. ２There is no gas contamination, and the exhaust gas from the reduction step S1 consists only of reducing gas (e.g., hydrogen gas) and water vapor. By subjecting such exhaust gas to the above-mentioned dehydration step S3, it can be reused as reducing gas. Note that methane gas remains in the exhaust gas from the first step S21, but this methane gas is decomposed in the reduction zone. Furthermore, this methane gas is combined with other gases in the reduction zone and diluted. In other words, the exhaust gas from the reduction step S1 contains almost no methane gas, and even if it does contain methane, it is only about 1% by volume. Therefore, there is almost no effect of concentration of carbon-containing gases due to circulation. In other words, this can be achieved by only a normal partial out-of-system discharge step of the reducing gas, and no special de-CO2 treatment is required when circulating the exhaust gas. ２ No process is required.

[0034] In the manufacturing method of the present disclosure, the embodiments shown in Figures 1 to 4 may be combined. For example, in the manufacturing method shown in Figures 1 to 3, the dehydration step S4 and the temperature increasing step S5 as shown in Figure 4 may be performed.

[0035] 2. HDRI Production System In addition to the above-described HDRI production method, the technology disclosed herein also includes an HDRI production system. That is, as shown in Figures 1 to 4, an HDRI production system according to one embodiment includes: a reduction section 110 that brings a reducing gas into contact with an oxidized iron raw material 10 to obtain metallic iron 20; and a cooling section 120 that cools and carbonizes the metallic iron 20 to obtain HDRI 30. Here, the cooling section 120 includes: a first section 121 that brings methane gas into contact with the metallic iron 20 downstream of the reduction section 110; and a second section 122 that brings CO gas into contact with the metallic iron 20 downstream of the first section 121. Furthermore, the HDRI manufacturing system according to one embodiment is configured so that the temperature of the metallic iron 20 that comes into contact with the CO gas in the second portion 121 is 400°C or higher and 700°C or lower, and the ratio of the volume of the gas discharged outside the system to the volume of the gas supplied in the second portion 121 is 40% or higher.

[0036] In this embodiment, the reduction step S1 is performed in the reduction section 110, and the cooling step S2 is performed in the cooling section 120. The configurations of the reduction section 110 and the cooling section 120 only need to be capable of performing the reduction step S1 and the cooling step S2, respectively. For example, as shown in FIG. 1, the reduction section 110 and the cooling section 120 may be provided in the shaft furnace 100. Alternatively, as shown in FIG. 2, the reduction section 110 may be provided in the shaft furnace 100, and the cooling section 120 may be provided separately from the shaft furnace 100. Alternatively, as shown in FIG. 3, the reduction section 110 and a first portion 121 of the cooling section 120 may be provided in the shaft furnace 100, and a second portion 122 of the cooling section 120 may be provided separately from the shaft furnace 100. When at least a portion of the cooling section 120 is provided separately from the shaft furnace 100, the cooling section 120 may be, for example, a cooling tower 200 provided downstream of the shaft furnace 100.

[0037] A reducing gas is supplied to the reduction unit 110. The type and supply form of the reducing gas are as described above. The reducing gas may contain, for example, hydrogen gas.

[0038] 4, an HDRI manufacturing system according to one embodiment may include a dehydration device 130 that dehydrates the exhaust gas from the reduction section 110 to obtain a circulating gas, and a temperature raising device 140 that raises the temperatures of the circulating gas and hydrogen gas to obtain a reducing gas containing the circulating gas and hydrogen gas. The dehydration device 130 and the temperature raising device 140 are used to perform the dehydration step S3 and the temperature raising step S4, respectively. Details are as described above.

[0039] The exhaust gas systems from the reduction unit 110 and the cooling unit 120 are also as described above. That is, in one embodiment of the production system, the ratio of the volume of the exhaust gas discharged to the outside of the system (corresponding to the exhaust gas discharged to the outside of the system in the above-described second step S22) to the volume of the gas supplied in the second portion 122 is 40% or more. In particular, when the ratio of the volume of the exhaust gas discharged to the outside of the system to the volume of the gas supplied in the second portion 122 is 70% or more, the carbon content and reduction rate of the HDRI finally produced are likely to be more significantly improved. Furthermore, in one embodiment of the production system, the exhaust gas from the first portion 121 (corresponding to the exhaust gas in the above-described first step S21) may be used as the reducing gas in the reduction unit 110.

[0040] The temperatures of the metallic iron 20 in each of the reduction section 110 and the cooling section 120 are also as described above. That is, the production system according to one embodiment is configured so that the temperature of the metallic iron 20 in contact with CO gas in the second section 122 is 400°C or higher and 700°C or lower. In particular, as described above, it is preferable that the temperature of the metallic iron 20 in contact with CO gas in the second section 122 is 550°C or higher and 700°C or lower. Furthermore, the production system according to one embodiment may be configured so that the temperature of the metallic iron 20 in contact with methane gas in the first section 121 is 700°C or higher. The temperature of the metallic iron 20 in the first section 121 can be controlled by the temperature of the oxidized iron raw material 10 in the reduction section 110, the supply amount of the oxidized iron raw material 10, the temperature of the reducing gas, the supply amount of the reducing gas, etc. Furthermore, the temperature of the metallic iron 20 in the second section 122 can be controlled by the temperature of the metallic iron 20 in the first section 121, the supply amount of the metallic iron 20, the temperature of the methane gas, the supply amount of the methane gas, etc.

[0041] Furthermore, in the production system of the present disclosure, when the shaft furnace 100 is employed as the reduction section 110, the shaft furnace top pressure is not particularly limited, but may be in the range of 0 MPa to 0.8 MPa in gauge pressure. The pressure can be measured, for example, using a pressure gauge provided at the shaft furnace top.

[0042] Furthermore, in the manufacturing system of the present disclosure, when a cooling tower 200 is used as the cooling section 120, the pressure at the top of the cooling tower is not particularly limited, but may be in the range of 0 MPa to 0.8 MPa in gauge pressure. The pressure can be measured, for example, using a pressure gauge provided at the top of the cooling tower.

[0043] In the manufacturing system of the present disclosure, the configurations shown in Figures 1 to 4 may be combined. For example, the manufacturing system shown in Figures 1 to 3 may be combined with a dehydration device 130 and a heating device 140 as shown in Figure 4.

[0044] 3. Effects As described above, according to the production method and production system of the present embodiment, (1) metallic iron 20 is obtained by reducing iron oxide raw material 10, (2) metallic iron 20 is carbonized and cooled with methane gas, and then (3) metallic iron 20 is carbonized with CO gas, thereby making it possible to efficiently produce HDRI 30 with an increased carbon concentration while maintaining a high reduction rate.

[0045] The present invention will be further described below with reference to examples, but the present invention is not limited to the following examples. The present invention allows various conditions to be adopted as long as the object is achieved without departing from the gist of the present invention. In the following examples, conditions for increasing the reduction rate and carbonization amount of HDRI were investigated by numerical simulation. The numerical simulation in this example was performed using a shaft furnace mathematical model developed by applying the blast furnace mathematical model described in Non-Patent Document 1 below, to which the reactions (7), (9), and (10) described in Non-Patent Document 2 below were added. Non-patent document 1: Nishioka et al. "Development of Mathematical Models for Blast Furnaces", NIPPON STEEL & SUMITOMO METAL TECHNICAL REPORT No. 120(2018) Non-patent document 2: Hamzeh Hamadeh et al., "Detailed Modeling of the Direct Reduction of Iron Ore in a Shaft Furnace", Materials 2018, 11(10), 1865 (https: / / doi.org / 10.3390 / ma11101865)

[0046] 1. Simulation conditions A numerical simulation was carried out assuming operation in a shaft furnace. First, iron oxide pellets were placed in the shaft furnace and heated to 950°C. ２ The temperature of the metallic iron immediately after the reduction reaction was 861°C. The metallic iron at 861°C was then subjected to one of the following cooling steps, Case 1 to Case 3. The pressure at the top of the shaft furnace was 0.04 MPa or 0.7 MPa (gauge pressure). Case 1 (corresponding to a comparative example): CH ４ Case 2 (equivalent to a comparative example): In the transition zone of the shaft furnace, CH ４A mixed gas (400°C) of CH and CO was blown into the shaft furnace, and the metallic iron was cooled simultaneously with carbonization. ４ (25°C) was blown into the furnace to cool the metallic iron while carbonizing it, and CO (25°C or 400°C) was blown into the lower part of the cooling zone of the shaft furnace to further carbonize it.

[0047] FIG. 5 shows the types and introduction positions of gases introduced into the transition zone and cooling zone of the shaft furnace for each of Cases 1 to 3. The structure shown in FIG. 5 (the black portion in FIG. 5) is the left-half structure when the furnace internal structure in a cross section passing through and along the central axis of the shaft furnace is divided into right and left halves with the central axis as the boundary. For Case 3, the reduction zone in FIG. 5 corresponds to the reduction step S1, the transition zone corresponds to the first step S21 of the cooling step S2, and the lower part of the cooling zone corresponds to the second step S22 of the cooling step S2. Under some calculation conditions, a predetermined amount of gas was extracted from the upper part of the cooling zone, and under other calculation conditions, the amount of gas extracted from the upper part of the cooling zone was set to zero.

[0048] 2. Calculation Results 1 Tables 1 and 2 below show the shaft furnace top pressure, the gas injection mode (Case 1 to Case 3 above), the calculation results for the temperature of metallic iron coming into contact with gas in the transition zone (first step), the type, supply amount, and temperature of gas in the transition zone (first step), the calculation results for the temperature of metallic iron coming into contact with gas in the cooling zone (second step), the type, supply amount, and temperature of gas in the cooling zone (second step), the amount of exhaust gas in the cooling zone (second step) and the amount extracted to the outside of the system, and the discharge rate of exhaust gas in the cooling zone (second step) to the outside of the system, as well as the calculation results for the temperature, carbon content, and reduction rate of HDRI discharged from the lower end of the shaft furnace.

[0049] In this example, when the carbon content of HDRI is 2.5% or more and the reduction rate is 91.0% or more, it is determined that the HDRI has both a high carbon content and a high reduction rate.

[0050]

[0051] The results in Tables 1 and 2 reveal the following: CH ４ Case 3 (Examples 1-1 to 1-5, 2-1 to 2-4), in which CO and CO are cooled separately, is better. ４ Case 1 (Comparative Example 1-1) with single cooling and CH ４ Compared to Case 2 (Comparative Example 1-2), in which mixed cooling with CO was performed, the carbon content of the finally obtained HDRI was increased. Furthermore, in Case 3, when the amount of exhaust gas extracted from the system in the second step was insufficient (Comparative Examples 1-3, 1-4, and 2-1), the carbon content and reduction rate of the finally obtained HDRI decreased. From the results shown in Tables 1 and 2, it can be said that in order to maintain a high reduction rate of the finally obtained HDRI, the ratio of the volume of the exhaust gas extracted from the system to the volume of the gas supplied in the second step needs to be 40% or more. In particular, when the ratio of the volume of the exhaust gas extracted from the system to the volume of the gas supplied in the second step is 70% or more, the carbon content and reduction rate of the finally obtained HDRI can be more significantly improved. Furthermore, when the temperature of the metallic iron contacting the CO gas in the second step was high (Comparative Example 1-5), the carbon content of the finally obtained HDRI could not be sufficiently increased. Furthermore, when the temperature of the metallic iron that comes into contact with the CO gas in the second step is low (Comparative Example 1-6), the reduction rate of the finally obtained HDRI cannot be increased sufficiently.

[0052] 3. Calculation Result 2 In Case 3, the relationship between the outlet temperature of the transition zone (first step) (the temperature of metallic iron contacting with CO gas in the cooling zone (second step)) and the carbon content and reduction rate of the finally obtained HDRI was investigated in detail. The results are shown in FIG. 6. In FIG. 6, among the plots corresponding to the above-mentioned Calculation Result 1, the plot for the C concentration (carbon content) is represented by an open square, and the plot for the reduction rate is represented by an open circle. In FIG. 6, among the plots corresponding to the calculation results other than the above-mentioned Calculation Result 1, the plot for the C concentration (carbon content) is represented by a filled square, and the plot for the reduction rate is represented by a filled circle. In Calculation Result 2, the outlet temperature of the first step was changed in the range of 250°C to 750°C by changing the gas flow rate and temperature in the cooling step.

[0053] As shown in Figure 6, it was found that the carbon content of HDRI increases as the outlet temperature of the first step is lowered to approach a temperature at which carburization by CO easily proceeds. On the other hand, it was also found that excessively lowering the outlet temperature of the first step reduces the reduction rate of HDRI. From the results shown in Figure 6, it can be said that in order to increase the carbon content while maintaining the reduction rate of HDRI, it is effective for the temperature of the metallic iron that comes into contact with CO gas in the second step to be 400°C or higher and 700°C or lower.

[0054] 4. Calculation Result 3 In Case 3, the relationship between the exit temperature of the transition zone (first step) (the temperature of the metallic iron that comes into contact with CO gas in the cooling zone (second step)) and the temperature of the HDRI finally obtained was investigated in detail. The results are shown in Figure 7. In Figure 7, the plots corresponding to the above-mentioned Calculation Result 1 are represented by open circles, and the other plots are represented by filled circles. In Calculation Result 3, the exit temperature of the first step was changed in the range of 250°C to 750°C by changing the gas flow rate and temperature in the cooling step.

[0055] As shown in Figure 7, the lower the temperature of the metallic iron after the first step, the lower the temperature of the HDRI. When performing the subsequent briquetting step, the temperature of the HDRI is preferably 650°C or higher. Taking this into consideration, when producing HBI using HDRI, it can be said that the temperature of the metallic iron that comes into contact with CO gas in the second step is preferably 550°C or higher and 700°C or lower.

[0056] 5. Supplementary Note: In the above embodiment, hydrogen gas is used as the reducing gas, but the type of reducing gas is not limited to this. If a gas other than hydrogen gas (for example, CO gas or CH ４ When a carbon-containing gas such as a carbon dioxide gas is used, carburization occurs during the reduction process as iron oxide is reduced, and the carbon concentration in the metallic iron after the reduction process is thought to be high. By subjecting metallic iron with such a high carbon concentration to the cooling process of the present disclosure, it is thought that the carbon concentration of the finally obtained HDRI can be further increased.

[0057] 5. Summary From the above results, it can be said that the carbon content of HDRI can be increased while maintaining the reduction rate by undergoing the following reduction step and cooling step.

[0058] In the reduction step, a reducing gas is brought into contact with an oxidized iron raw material to obtain metallic iron. In the cooling step, the metallic iron is carbonized while being cooled to obtain HDRI. Here, the cooling step includes a first step in which methane gas is brought into contact with the metallic iron after the reduction step, and a second step in which CO gas is brought into contact with the metallic iron after the first step. The temperature of the metallic iron that comes into contact with the CO gas in the second step is 400°C or higher and 700°C or lower. In the second step, the ratio of the volume of exhaust gas discharged to the outside of the system to the volume of gas supplied is 40% or higher.

[0059] 10 Iron oxide raw material 20 Metallic iron 30 HDRI 100 Shaft furnace 110 Reduction section 120 Cooling section 121 First section 122 Second section 200 Cooling tower

Claims

1. A method for producing hot reduced iron, comprising: a reduction step of bringing a reducing gas into contact with an oxidized iron raw material to obtain metallic iron; and a cooling step of carbonizing the metallic iron while cooling it to obtain hot reduced iron, wherein the cooling step comprises: a first step of bringing methane gas into contact with the metallic iron after the reduction step; and a second step of bringing CO gas into contact with the metallic iron after the first step, wherein the temperature of the metallic iron that comes into contact with the CO gas in the second step is 400°C or higher and 700°C or lower, and wherein the ratio of the volume of exhaust gas discharged to the outside of the system to the volume of gas supplied in the second step is 40% or higher.

2. A method for producing hot reduced iron according to claim 1, wherein the ratio of the volume of the exhaust gas discharged to the outside of the system to the volume of the gas supplied in the second step is 70% or more.

3. A method for producing hot reduced iron according to claim 1 or 2, wherein the temperature of the metallic iron that comes into contact with the CO gas in the second step is 550°C or higher and 700°C or lower.

4. A method for producing hot reduced iron according to any one of claims 1 to 3, wherein exhaust gas from the first step is used as the reducing gas in the reduction step.

5. A method for producing hot reduced iron according to any one of claims 1 to 4, wherein the reduction step and the cooling step are carried out in a shaft furnace.

6. A method for producing hot reduced iron according to any one of claims 1 to 4, wherein the reduction step is carried out in a shaft furnace, and the cooling step is carried out outside the shaft furnace.

7. A method for producing hot reduced iron according to any one of claims 1 to 4, wherein the reduction step and the first step are carried out in a shaft furnace, and the second step is carried out outside the shaft furnace.

8. A method for producing hot reduced iron according to any one of claims 1 to 7, wherein the reducing gas contains hydrogen gas.

9. A method for producing hot reduced iron according to claim 8, comprising: a dehydration step of dehydrating exhaust gas from the reduction step to obtain a circulating gas; and a heating step of heating the circulating gas and hydrogen gas to obtain the reducing gas containing the circulating gas and the hydrogen gas.

10. A method for producing hot reduced iron according to any one of claims 1 to 9, wherein the temperature of the metallic iron that comes into contact with the methane gas in the first step is 700°C or higher.

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