Method and system for producing reduced iron

Abstract

Disclosed is a technique for producing carbon-containing reduced iron in a direct reduction process, by cooling iron metal resulting from a reduction step while increasing the carbon concentration of the iron metal. This method for producing carbon-containing reduced iron includes a reduction step in which a reducing gas is brought into contact with a raw iron oxide material to obtain iron metal, and a cooling step in which the iron metal is cooled. The cooling step comprises a first step in which, after the reduction step, methane gas is brought into contact with the iron metal to carbonize the iron metal, a second step in which, after the first step, CO gas is brought into contact with the iron metal to carbonize the iron metal, and a third step in which, after the second step, methane gas or an inert gas is brought into contact with the iron metal.

Description

Reduced iron manufacturing method and manufacturing system

[0001] The present application discloses a method and system for producing reduced iron.

[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 emissions. For example, a process using a shaft furnace has been studied as a direct reduction process (see, for example, Patent Documents 1 and 2). In the direct reduction process, a reducing gas is brought into contact with an oxidized iron raw material to obtain direct reduced iron (DRI). In addition, a cooling gas may be brought into contact with the reduced iron in order to cool the reduced iron and increase its carbon concentration. Increasing the carbon concentration of the reduced iron lowers the melting temperature in the subsequent melting and refining process and also ensures the strength of the resulting steel.

[0003] International Publication No. 2021 / 195160 Japanese Patent Application Laid-Open No. 61-073805

[0004] Reduced iron can be produced in three product forms: cold DRI (CDRI), hot briquette iron (HBI), and hot DRI (HDRI). When producing CDRI by a direct reduction process, a technique is required to reduce an iron oxide raw material to obtain metallic iron, and then cool the metallic iron while increasing the carbon concentration of the metallic iron. In conventional techniques, when producing reduced iron by a direct reduction process, there is room for improvement in cooling the metallic iron obtained after reduction while increasing the carbon concentration of the metallic iron.

[0005] The present application discloses the following multiple aspects as means for solving the above-mentioned problems. <Aspect 1> A method for producing reduced iron containing carbon, 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 cooling the metallic iron, wherein the cooling step comprises: a first step of bringing methane gas into contact with the metallic iron to carbonize the metallic iron after the reduction step; a second step of bringing CO gas into contact with the metallic iron to carbonize the metallic iron after the first step; and a third step of bringing methane gas or an inert gas into contact with the metallic iron after the second step. <Aspect 2> The method for producing reduced iron according to Aspect 1, wherein the reduction step and the cooling step are performed in a shaft furnace. <Aspect 3> The method for producing reduced iron according to Aspect 1, wherein the reduction step is performed in a shaft furnace, and the cooling step is performed in a cooling device provided downstream of the shaft furnace. <Aspect 4> The method for producing reduced iron according to Aspect 1, wherein the reduction step and the first step are carried out in a shaft furnace, and the second step and the third step are carried out in a cooling device provided downstream of the shaft furnace. <Aspect 5> The method for producing reduced iron according to Aspect 3 or 4, comprising a transferring step of transferring the metallic iron from the shaft furnace to the cooling device. <Aspect 6> The method for producing reduced iron according to any of Aspects 1 to 5, wherein the reducing gas contains hydrogen gas. <Aspect 7> The method for producing reduced iron according to any of Aspects 1 to 6, 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. <Aspect 8> The method for producing reduced iron according to any one of Aspects 1 to 7, wherein the reaction gas of the metallic iron and the methane gas in the first step is discharged to the outside of the system downstream of the reduction step.<Aspect 9> The method for producing reduced iron according to any one of Aspects 1 to 8, wherein a reaction gas between the metallic iron and the methane gas in the first step is added to the reducing gas. <Aspect 10> The method for producing reduced iron according to any one of Aspects 1 to 9, wherein a reaction gas between the metallic iron and the CO gas in the second step is discharged to the outside of the system downstream of the first step. <Aspect 11> The method for producing reduced iron according to any one of Aspects 1 to 10, wherein the methane gas or inert gas that has come into contact with the metallic iron in the third step is discharged to the outside of the system downstream of the second step. <Aspect 12> A system for producing reduced iron containing carbon, comprising: a reduction unit that brings a reducing gas into contact with an oxidized iron raw material to obtain metallic iron; and a cooling unit that cools the metallic iron, wherein the cooling unit has: a first portion that brings methane gas into contact with the metallic iron obtained by the reduction unit to carbonize the metallic iron, a second portion downstream of the first portion that brings CO gas into contact with the metallic iron to carbonize the metallic iron, and a third portion downstream of the second portion that brings methane gas or an inert gas into contact with the metallic iron. <Aspect 13> The system for producing reduced iron of Aspect 12, wherein the reduction unit and the cooling unit are provided in a shaft furnace. <Aspect 14> The system for producing reduced iron of Aspect 12, wherein the reduction unit is provided in a shaft furnace, and the cooling unit is provided in a cooling device downstream of the shaft furnace. <Aspect 15> The reduced iron manufacturing system of aspect 12, wherein the reduction section and the first portion are provided in a shaft furnace, and the second portion and the third portion are provided in a cooling device downstream of the shaft furnace. <Aspect 16> The reduced iron manufacturing system of aspect 14 or 15, further comprising a transfer device that transfers the metallic iron from the shaft furnace to the cooling device.<Aspect 17> The reduced iron production system of any of Aspects 12 to 16, wherein the reducing gas contains hydrogen gas. <Aspect 18> The reduced iron production system of any of Aspects 12 to 17, comprising: a dehydration device that dehydrates exhaust gas from the reduction section to obtain a circulating gas, and a heating device that heats the circulating gas and hydrogen gas to obtain the reducing gas containing the circulating gas and the hydrogen gas. <Aspect 19> The reduced iron production system of any of Aspects 12 to 18, comprising: a first cooling gas outlet downstream of the reduction section that discharges a reaction gas of the metallic iron and the methane gas in the first section to the outside of the system. <Aspect 20> The reduced iron production system of any of Aspects 12 to 19, wherein the reduction section and the first section are connected so that the reaction gas of the metallic iron and the methane gas in the first section is added to the reducing gas. <Aspect 21> The reduced iron production system of any of Aspects 12 to 20, further comprising a second cooling gas outlet downstream of the first portion, for discharging a reaction gas of the metallic iron and the CO gas in the second portion to the outside of the system. <Aspect 22> The reduced iron production system of any of Aspects 12 to 21, further comprising a third cooling gas outlet downstream of the second portion, for discharging the methane gas or inert gas that has come into contact with the metallic iron in the third portion to the outside of the system.

[0006] According to the method and system for producing reduced iron disclosed herein, it is possible to cool metallic iron while increasing the carbon concentration of the metallic iron in the direct reduction process. According to the method and system for producing reduced iron disclosed herein, it is possible to produce, for example, CDRI having an increased carbon concentration.

[0007] FIG. 1 is a schematic diagram for explaining an example of a manufacturing method and manufacturing system for reduced iron. FIG. 1 is a schematic diagram for explaining an example of a manufacturing method and manufacturing system for reduced iron. FIG. 2 is a schematic diagram for explaining an example of a manufacturing method and manufacturing system for reduced iron. FIG. 3 is a schematic diagram for explaining an example of a manufacturing method and manufacturing system for reduced iron. FIG. 4 is a schematic diagram for explaining an example of a manufacturing method and manufacturing system for reduced iron. FIG. 5 is a schematic diagram for explaining an example of a manufacturing method and manufacturing system for reduced iron. FIG. 6 is a schematic diagram for explaining an example of a manufacturing method and manufacturing system for reduced iron. FIG. 7 is a schematic diagram for explaining an example of a manufacturing method and manufacturing system for reduced iron. FIG. 8 is a schematic diagram for explaining the type and introduction position of gas introduced into the cooling section of the shaft furnace for each of Cases 1 to 4. FIG. 9 is a schematic diagram for explaining the type and introduction position of gas introduced into each of the shaft furnace and the cooling tower for Example 1. FIG. 10 is a schematic diagram for explaining the type and introduction position of gas introduced into each of the shaft furnace and the cooling tower for Example 2.

[0008] An embodiment of the method and system for producing reduced iron according to the present disclosure will be described below. However, the method and system for producing reduced iron according to the present disclosure are not limited to the following embodiment. In this application, "oxidized iron 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 before the completion of the cooling step. For convenience, "metallic iron" is also used to refer to iron whose carbon concentration has been increased by carbonization or the like. "Reduced iron" refers to a product obtained after the cooling step. In this application, "downstream side" refers to the downstream side in the reduced iron production process. That is, when reduced iron containing carbon is produced from an oxidized iron raw material via metallic iron, the oxidized iron raw material side is the upstream side, and the reduced iron containing carbon is the downstream side.

[0009] 1 to 7 , a method for producing reduced iron containing carbon 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. Here, the cooling step S2 includes a first step S21 in which, after the reduction step S1, methane gas is brought into contact with the metallic iron 20 to carbonize the metallic iron 20, a second step S22 in which CO gas is brought into contact with the metallic iron 20 to carbonize the metallic iron 20 after the first step S21, and a third step S23 in which methane gas or an inert gas is brought into contact with the metallic iron 20 after the second step S22.

[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, and metallic iron 20 is obtained. As shown in FIGS. 1 to 7 , the reduction step S1 may be performed, for example, in a shaft furnace 100. Alternatively, the reduction step S1 may be performed in a reduction device other than the shaft furnace 100 (for example, a fluidized bed or a rotary kiln). In particular, when the reduction step S1 is performed 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 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. In addition to iron oxide, the oxidized iron raw material 10 may also contain, for example, one or both of silicon dioxide and aluminum oxide. The oxidized iron raw material 10 may have a particle size distribution or a uniform particle size. The average particle size 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. Note that the "particle size of the raw material" refers to the sieve size of the raw material, and the "average particle size of the raw material" refers to the weighted average particle size of the raw material. Specifically, the average particle size of the raw material is measured as follows. That is, the average particle size of the 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 the mass-weighted average of the maximum and minimum particle sizes of each sieve as a representative particle size. The iron oxide 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 supplied and filled into the shaft furnace 100 through the raw material supply port 100a of the shaft furnace 100, thereby forming a packed bed. The filling rate of the packed bed is not particularly limited and may be the same as that in a conventional method for producing reduced iron using a shaft furnace. The packed bed moves downward inside the shaft furnace 100. That is, the oxidized iron raw material 10 is substantially filled inside 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 continuously downward 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 may be 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.

[0013] 1.1.2 Reducing Gas The type of reducing gas is not particularly limited as long as it is capable of reducing the oxidized iron raw material 10. In particular, when the reducing gas contains hydrogen gas, the technology of the present disclosure is expected to have a more significant effect. The hydrogen gas may be, for example, obtained by electrolysis of water, obtained by separation (e.g., membrane separation) from synthesis gas (gas obtained by gasifying (partially oxidizing) coal or biomass with steam, air, or oxygen), obtained by separation from gas obtained by reforming natural gas with steam, carbon dioxide, or the like, or obtained by separation from dry distillation gas (gas obtained by heating coal or biomass in an oxygen-free state). The reducing gas may contain gases other than hydrogen in addition to hydrogen gas. Gases other than hydrogen include CO gas, inert gas, and CO ２Examples of the reducing gas include hydrogen gas, nitrogen gas, argon gas, and the like. When the reducing gas contains hydrogen gas, the hydrogen concentration of the reducing gas may be, for example, 40% by volume to 100% by volume, 50% by volume to 100% by volume, 60% by volume to 100% by volume, 70% by volume to 100% by volume, or 80% by volume to 100% by volume. 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 higher. The temperature of the reducing gas is preferably 800°C to 1100°C.

[0014] When the reduction step S1 is performed in the shaft furnace 100, the reducing gas can be supplied into the interior of the furnace from the side wall of the shaft furnace 100. 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 110a provided in the side wall of the shaft furnace 100, and the reducing gas can be supplied from the outside to the interior of the furnace via 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. In addition to metallic iron 20, the solid reactant may also contain 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.

[0016] When the reduction step S1 is carried out in the shaft furnace 100, the solid reactant containing metallic iron 20 can be recovered from an outlet 100b provided at the bottom 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 body portion and a tapered portion located below the body portion, and the inner diameter of the furnace may decrease from top to bottom in 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. Furthermore, the shaft furnace 100 may be equipped with supply ports 121a, 122a, and 123a for supplying various cooling gases and exhaust ports 121b, 122b, and 123b for exhausting various cooling gases below the reducing gas supply port 110a. The supply ports for the various cooling gases may be provided in the side wall of the furnace, or may be provided inside the side wall of the furnace. The exhaust ports for the various cooling gases may be provided in the side wall of the furnace. The shaft furnace 100 may be provided with a raw material supply port 100a in the upper or top part of the furnace, and with an exhaust port 100b in the lower or bottom part of the furnace for recovering metallic iron or reduced iron.

[0018] 1.2 Cooling Step The temperature of the metallic iron 20 immediately after the reduction step S1 is, for example, approximately 700°C to 900°C. 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, reduced iron 30 containing carbon is obtained. By carbonizing the metallic iron 20 to obtain reduced iron 30 containing carbon in this way, the melting temperature in the subsequent melting and refining step is lowered and the strength of the resulting reduced iron as steel is ensured.

[0019] In the cooling step S2, (1) the metallic iron 20 is carbonized and cooled by methane gas, followed by (2) carbonization of the metallic iron 20 by CO gas, and then (3) cooling of the metallic iron 20 by methane gas or an inert gas. According to the inventor's findings, the carbon deposition reaction 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, the carbon deposition reaction 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. 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 carbon deposition reaction to proceed appropriately and efficiently. Furthermore, in addition to the physical endothermic heat caused by contact with methane gas, which has a large specific heat, the endothermic reaction during carbon deposition tends to lower the temperature of the metallic iron 20 to a temperature suitable for the carbon deposition reaction by CO gas. By contacting the metallic iron 20 whose temperature has been reduced in this manner with CO gas, the exothermic reaction, which is a carbon deposition reaction, proceeds appropriately and efficiently, thereby further significantly increasing the carbon concentration in the finally obtained reduced iron 30. At this time, the temperature of the metallic iron 20 may decrease or increase. For example, when the temperature of the CO gas is low, the temperature decrease due to contact with CO gas prevails over the temperature increase due to the exothermic reaction, and the temperature of the metallic iron 20 decreases. By subsequently contacting the metallic iron 20 with methane gas or an inert gas, the temperature of the metallic iron 20 can be decreased to a temperature at which reoxidation is difficult, and reduced iron 30 containing carbon (e.g., carbon-containing CDRI) is obtained. As described above, in the cooling step S2, (1) carbonization with methane gas and (2) carbonization with CO gas are performed in this order, thereby increasing the carbon concentration in the reduced iron 30 compared to when each gas is contacted alone. Because the carbon concentration is sufficiently increased by (1) and (2), (3) cooling with methane gas or an inert gas does not need to be accompanied by carbon deposition. However, (3) the cooling with methane gas or inert gas may be accompanied by carbon deposition.

[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 in a cooling device 200 provided downstream of the shaft furnace 100. Alternatively, as shown in FIG. 3 , the reduction step S1 and the first step S21 of the cooling step S2 may be performed in the shaft furnace 100, and the second step S22 and the third step S23 of the cooling step S2 may be performed in a cooling device 200 provided downstream of the shaft furnace 100. From the viewpoint of reducing equipment costs, etc., it is preferable that the reduction step S1 and the cooling step S2 be performed in the shaft furnace 100. On the other hand, when a part or all of the cooling step S2 is performed in the cooling device 200, it is possible to prevent the exhaust gas in the cooling device 200 from entering the shaft furnace 100. For example, when the reduction step S1 and the first step S21 of the cooling step S2 are performed in the shaft furnace 100, and the second step S22 and the third step S23 of the cooling step S2 are performed in the cooling device 200 provided downstream of the shaft furnace 100, the exhaust gas (CO gas and CO ２ This prevents CO2 from entering the first step S21. This allows the carbon deposition reaction in the first step S21 to proceed more efficiently. This also facilitates the recycling treatment (hydrogen recovery) of the exhaust gas from the reduction step S21. Furthermore, this also facilitates the recycling treatment (hydrogen recovery) of the exhaust gas from the second step S22. ２2 and 3 , when part or all of the cooling step S2 is performed in a cooling device 200 provided downstream of the shaft furnace 100, the reduced iron production method may include a transfer step of transferring the metallic iron 20 from the shaft furnace 100 to the cooling device 200. Specifically, the metallic iron 20 recovered from the discharge port 100b of the shaft furnace 100 may be transferred to the metallic iron supply port 200a of the cooling device 200. When part or all of the cooling step S2 is performed in a cooling device 200 provided downstream of the shaft furnace 100, a specific example of the cooling device 200 is a cooling tower. There is no particular limitation on the supply rate of the metallic iron 20 to the cooling device 200. The metallic iron 20 supplied into the cooling device 200 may form a packed bed in the cooling device 200 or may be suspended in the airflow. In particular, when the metallic iron 20 supplied into the cooling device 200 forms a packed bed in the cooling device 200, a greater effect can be expected.

[0021] The cooling step S2 includes a first step S21, a second step S22, and a third step S23. In the present embodiment, it is sufficient that the temperature of the reduced iron 30 at the end of the cooling step S2 is lower than the temperature of the metallic iron 20 at the start of the cooling step S2, and the temperature of the metallic iron 20 may increase during the cooling step S2. For example, an exothermic reaction between the metallic iron 20 and CO gas may occur 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 (1) above. That is, in the first step S21, after the reduction step S1, methane gas is brought into contact with the metallic iron 20, thereby carbonizing 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 (e.g., in a cooling device provided downstream of the shaft furnace). In the first step S21, the temperature of the metallic iron 20 when contacted with methane gas is not particularly limited as long as the carbon deposition reaction caused by the methane gas can proceed. In the first step S21, for example, by contacting methane gas with metallic iron 20 at 700°C or higher, the carbon deposition reaction caused by the methane gas can proceed more appropriately and the metallic iron 20 can be appropriately cooled. In the first step S21, there is no particular upper limit on the temperature of the metallic iron 20 when contacted with methane gas. The temperature of the metallic iron 20 brought into contact with the methane gas may be, for example, 1100° C. or less. From the viewpoint of allowing the carbon deposition reaction caused by the methane gas to proceed particularly significantly, the temperature of the metallic iron 20 brought into contact with the methane gas in the first step S21 may be set to 710° C. or more and 1100° C. or less, 730° C. or more and 1100° C. or less, 750° C. or more and 1100° C. or less, 770° C. or more and 1100° C. or less, 790° C. or more and 1100° C. or less, 810° C. or more and 1100° C. or less, 700° C. or more and 1070° C. or less. °C or less, 700°C or more and 1040°C or less, 700°C or more and 1000°C or less, 700°C or more and 970°C or less, 700°C or more and 940°C or less, 700°C or more and 900°C or less, 710°C or more and 1070°C or less, 730°C or more and 1040°C or less, 750°C or more and 1000°C or less, 770°C or more and 970°C or less, 790°C or more and 940°C or less, or 810°C or more and 900°C or less. Note that the "temperature of the metallic iron 20" in the first step S21 refers to the average temperature in the radial direction of the shaft furnace or the cooling tower. When the reduction step S1 and the first step S21 are performed in the same equipment (for example, a shaft furnace), the position (height position) P1 at which the "temperature of the metallic iron 20" is measured in the first step S21 is downstream (below) of the position (height position) P2 at which the reducing gas in the reduction step S1 is blown in, and is a position (height position) within 1 m of the position P2.Alternatively, if the reduction step S1 and the first step S21 are performed in separate devices (for example, if the reduction step S1 is performed in a shaft furnace and the first step S21 is performed in a cooling device provided downstream of the shaft furnace), the position P1 for measuring the "temperature of the metallic iron 20" in the first step S21 is a position within 1 m downstream (downward) from the metallic iron supply port of the device 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 the shaft furnace or cooling tower, providing multiple thermocouples on the member, and measuring multiple temperatures in the radial direction. That is, if 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, if 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, if it is assumed that the temperature between the measured points is distributed linearly in the radial direction, the temperature distribution T(r) in the radial direction 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 proceeds through a carbon deposition reaction caused by methane gas, and other gases may be brought into contact with the metallic iron 20 in addition to methane gas. In other words, the gas that comes into contact with the metallic iron 20 in the first step S21 may be any gas that contains methane gas. In addition to methane gas, the gas that comes into contact with the metallic iron 20 in the first step S21 may be hydrogen gas, nitrogen gas, CO gas, CO ２ The gas may contain gas, water vapor, etc. The 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 carbon deposition reaction (endothermic reaction) caused by methane gas. In the first step S21, as long as the endothermic reaction caused by methane gas proceeds predominantly, part of the gas that comes into contact with the metallic iron 20 may contain an exothermic reaction (e.g., CO gas). However, if the gas that comes into contact with the metallic iron 20 in the first step S21 contains CO gas, the volumetric proportion of the CO gas is smaller than the volumetric proportion of methane gas. Furthermore, if the gas that comes into contact with the metallic iron 20 in the first step S21 is made up of multiple types of gases, for example, the volumetric proportion of methane gas is the largest among the volumetric proportions of the individual gases. The gas that comes into contact with the metallic iron 20 in the first step S21 may contain, for example, 50 vol% or more, 60 vol% or more, or 70 vol% 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 fuel, or may be used as part of the reducing gas described above. For example, as shown in FIGS. 1 to 6, the reaction gas between the metallic iron 20 and methane gas in the first step S21 may be discharged to the outside of the system downstream of the reduction step S1. Alternatively, as shown in FIG. 7, the reaction gas between the metallic iron 20 and methane gas in the first step S21 may be added to the reducing gas described above. In other words, the reaction gas between the metallic iron 20 and methane gas in the first step S21 may be supplied to the reduction step S1. In particular, adding the reaction gas in the first step S21 to the reducing gas described above reduces the amount of reducing gas used, enabling efficient operation.

[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, thereby carbonizing 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 (e.g., in a cooling device installed 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. In the second step S21, the temperature of the metallic iron 20 when contacted with CO gas is not particularly limited as long as the carbon deposition reaction caused by the CO gas can proceed. In the second step S22, for example, by contacting CO gas with metallic iron 20 at a temperature of 400°C or higher and 600°C or lower, the carbon deposition reaction caused by the CO gas can proceed more appropriately. From the viewpoint of allowing the carbon deposition reaction by the CO gas to proceed particularly significantly, the temperature of the metallic iron 20 contacted with the CO gas in the second step S22 may be 410°C or higher and 600°C or lower, 420°C or higher and 600°C or lower, 430°C or higher and 600°C or lower, 440°C or higher and 600°C or lower, 450°C or higher and 600°C or lower, 400°C or higher and 590°C or lower, 400°C or higher and 580°C or lower, 400°C or higher and 570°C or lower, 400°C or higher and 560°C or lower, 400°C or higher and 550°C or lower, 410°C or higher and 590°C or lower, 420°C or higher and 580°C or lower, 430°C or higher and 570°C or lower, 440°C or higher and 560°C or lower, or 450°C or higher and 550°C or lower. Note that the "temperature of the metallic iron 20" in the second step S22 refers to the average temperature in the radial direction of the shaft furnace or the cooling tower, as in the first step S21. 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. 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 (lower) from 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 apparatus provided 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 (lower) from 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 400°C or lower. When the temperature of the CO gas is within this range, the temperature decrease due to contact with the CO gas becomes dominant over the temperature increase due to the exothermic reaction, and the temperature of the metallic iron 20 decreases in the second step S22.

[0026] In the second step S22, it is sufficient that carbonization of the metallic iron 20 proceeds through a carbon deposition reaction caused by CO gas, and other gases may be brought into contact with the metallic iron 20 in addition to CO gas. In other words, the gas that comes into contact with the metallic iron 20 in the second step S22 may be any gas that contains CO gas. In addition to CO gas, the gas that comes into contact with the metallic iron 20 in the second step S22 may be nitrogen gas, hydrogen gas, CO ２ The gas that comes into contact with the metallic iron 20 in the second step S22 may contain, for example, converter gas (LDG). When the 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 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 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] The reaction gas between the metallic iron 20 and CO gas in the second step S22 is CO gas and CO ２ The reaction gas may contain CO gas. The reaction gas may be discharged to the outside of the system and used as fuel, or may be used as part of the cooling gas in the first step S21. In particular, as shown in FIGS. 1 to 7 , the reaction gas of the metallic iron 20 and CO gas in the second step S22 is discharged to the outside of the system downstream of the first step S21, which allows the endothermic reaction with methane gas to proceed more appropriately and enables efficient operation.

[0028] 1.2.3 Third Step The third step S23 corresponds to (3) above. That is, in the third step S23, methane gas or an inert gas is brought into contact with the metallic iron 20 after the second step S22. When the reduction step S1 is performed in a shaft furnace, the third step S23 may be performed in the shaft furnace or outside the shaft furnace (e.g., in a cooling device provided downstream of the shaft furnace). Note that when the second step S22 is performed outside the shaft furnace, the third step S23 is necessarily performed outside the shaft furnace. As described above, the carbon deposition reaction in the second step S22 is an exothermic reaction, and therefore the temperature of the metallic iron 20 immediately after the second step S22 is unlikely to reach a temperature appropriate for CDRI. In other words, the metallic iron 20 immediately after the second step S22 is in a state where it is easily reoxidized. By performing the third step S23 after the second step S22, the temperature of the metallic iron 20 can be lowered to a temperature appropriate for CDRI. In the third step S23, the temperature of the metallic iron 20 when it is brought into contact with methane gas or an inert gas is not particularly limited. In the third step S23, for example, it is preferable to bring methane gas or an inert gas into contact with metallic iron 20 at a temperature of less than 400°C, thereby lowering the temperature of the metallic iron 20 to a temperature appropriate for CDRI. Note that, as in the first step S21 and the second step S22, the "temperature of the metallic iron 20" in the third step S23 refers to the average temperature in the radial direction of the shaft furnace or cooling tower. That is, when the third step S23 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 third step S23 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 second step S22 and the third step S23 are performed in the same apparatus (for example, a shaft furnace), the position (height position) P5 at which the "temperature of the metallic iron 20" is measured in the third step S23 is downstream (below) of the position (height position) P6 at which the CO gas is blown in in the second step S22, and is a position (height position) within 1 m of said position P6.Alternatively, if the second step S22 and the third step S23 are performed in different apparatuses (for example, the second step S22 is performed in a shaft furnace, and the third step S23 is performed in a cooling apparatus provided downstream of the shaft furnace), the position P5 for measuring the "temperature of the metallic iron 20" in the third step S23 is a position within 1 m downstream (downward) from the metallic iron supply port of the apparatus in which the third step S23 is performed. In the third step S23, the temperature of the methane gas or inert gas that comes into contact with the metallic iron 20 is not particularly limited. The temperature of the methane gas or inert gas may be, for example, 25°C or higher and 100°C or lower.

[0029] In the third step S23, it is sufficient that the metallic iron 20 is cooled by methane gas or an inert gas, and other gases may be brought into contact with the metallic iron 20 in addition to the methane gas or inert gas. In other words, the gas that contacts the metallic iron 20 in the second step S22 may contain methane gas or an inert gas. The gas that contacts the metallic iron 20 in the third step S23 may contain hydrogen gas, water vapor, or the like in addition to methane gas or an inert gas. When the gas that contacts the metallic iron 20 in the third step S23 contains methane gas, the metallic iron 20 may be further carbonized, depending on the temperature of the metallic iron 20. Examples of the inert gas in the third step S23 include gases that do not substantially react with the metallic iron 20, such as nitrogen gas. When the gas that contacts the metallic iron 20 in the third step S23 consists of multiple types of gases, for example, the volume proportion of methane gas or the volume proportion of the inert gas is the largest among the volume proportions of each gas. The gas that comes into contact with the metallic iron 20 in the third step S23 contains, for example, methane gas at 50 vol% or more, 60 vol% or more, or 70 vol% or more, or an inert gas at 50 vol% or more, 60 vol% or more, or 70 vol% or more, or a total of methane gas and an inert gas at 50 vol% or more, 60 vol% or more, or 70 vol% or more.

[0030] When methane gas is used in the third step S23, the exhaust gas from the third step S23 may contain methane gas and hydrogen gas. The exhaust gas may be discharged to the outside of the system and used as fuel, or may be used as part of the reducing gas described above, or may be used as part of the gas in the first step S21 described above, or may be used as part of the gas in the second step S22 described above. On the other hand, when an inert gas is used in the third step S23, the exhaust gas from the third step S23 may contain the inert gas. The exhaust gas may be discharged to the outside of the system or may be reused as the inert gas in the third step S23. For example, as shown in FIGS. 1 to 7 , the methane gas or inert gas that has come into contact with the metallic iron 20 in the third step S23 may be discharged to the outside of the system downstream of the second step S22.

[0031] 1.3 Reduced Iron Through the reduction step S1 and the cooling step S2, reduced iron 30 containing carbon (e.g., CDRI with an increased carbon concentration) is produced. The reduced iron 30 containing carbon may contain unreduced iron oxide, silicon dioxide, aluminum oxide, and the like in addition to carbon and iron. The carbon content of the reduced iron 30 may be, for example, more than 0 mass% and not more than 5 mass%. The temperature of the reduced iron 30 immediately after the third step S23 (the temperature of the reduced iron 30 at the outlet of the third step S23) may be, for example, not more than 150°C or not more than 80°C. When the reduction step S1 and the cooling step S2 are performed in the shaft furnace 100, the reduced iron 30 can be recovered, for example, from an outlet 100b provided in the lower part of the shaft furnace 100. When part or all of the cooling step S2 is performed in the cooling device 200, the reduced iron 30 can be recovered, for example, from an outlet 200b provided in the lower part of the cooling device 200.

[0032] 1.4 Dehydration Step and Temperature-Raising Step The reduced iron manufacturing method according to this embodiment may include other steps in addition to the reduction step S1 and the cooling step S2 described above. For example, the reduced iron 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 circulation gas. The reduced iron 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 circulation 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 circulation gas obtained by dehydrating the exhaust gas is heated, and hydrogen gas, to obtain a reduced gas containing hydrogen gas and one or both of the exhaust gas and the circulation gas. The dehydration step S3 and the temperature-raising step S4 may be combined. For example, as shown in FIG. 4 , a method for producing reduced iron 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 circulation gas, and a temperature increase step S4 in which the circulation gas and hydrogen gas are heated to obtain a reducing gas containing the circulation gas and hydrogen gas.

[0033] 1.4.1 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 by a known dehydration device 130. In the reduction step S1, water may be produced by the reaction between the reducing gas and the oxidized iron raw material 10. On the other hand, 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.

[0034] 1.4.2 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, for example, 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 by a known heating device (heating device) 140.

[0035] 1.5 Hydrogen Gas Separation Step As shown in FIG. 5 , the method for producing reduced iron according to one embodiment may include a hydrogen gas separation step of separating hydrogen gas contained in the exhaust gas from the first step S21. This allows, for example, the hydrogen gas and methane gas contained in the exhaust gas from the first step S21 to be separated. The hydrogen gas separated from the exhaust gas can be used, for example, as part of the reducing gas. Furthermore, the methane gas separated from the exhaust gas can be used, for example, as part of the methane gas in the first step S21. The hydrogen gas separation step can be performed by a known hydrogen gas separation device 400. The configuration of the hydrogen gas separation device 400 is not particularly limited.

[0036] 1.6 CO ２ Gas Separation Step As shown in FIG. 6, in the method for producing reduced iron according to one embodiment, CO contained in the exhaust gas in the second step S22 is separated. ２ Separating gases, CO ２ A gas separation step may be provided, whereby, for example, CO contained in the exhaust gas from the second step S22 is separated. ２The CO gas separated from the exhaust gas can be used as the CO gas in the second step S22. ２ The gas is discharged outside the system, and CO ２ It can be recovered by a recovery device, etc. ２ The gas separation process is carried out using a known CO ２ This can be achieved by the gas separation device 500. ２ The configuration of the gas separation device 500 is not particularly limited.

[0037] 1.7 Other Matters As described above, in the method for producing reduced iron according to one embodiment, the reduction step S1 and the cooling step S2 may be performed in the shaft furnace 100. In this case, for example, the first step S21 is performed below the reduction step S1 in the shaft furnace 100. In this case, as shown in FIG. 7 , the reaction gas of the metallic iron 20 and methane gas in the first step S21 rises directly within the furnace and is added to the reducing gas in the reduction step S1, and can be used for reduction. Furthermore, as shown in FIGS. 1 to 7 , the reaction gas of the metallic iron 20 and CO gas in the second step S22 may be discharged outside the system downstream of the first step S21. With these configurations, the 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. ２ Gas contamination is eliminated, and the exhaust gas from the reduction step S1 is likely to consist only of reducing gas (e.g., hydrogen gas) and water vapor. By performing the dehydration step S3 on such exhaust gas, it can be reused as reducing gas. Note that methane gas remains in the reaction gas of the metallic iron 20 and methane gas in the first step S21, but this methane gas can be decomposed in the reduction zone. Furthermore, this methane gas is diluted by merging with other gases in the reduction zone. In other words, the exhaust gas from the reduction step S1 contains almost no methane gas, and even if it does contain methane gas, it is only about 1% by volume. Therefore, there is almost no effect of concentration of carbon-containing gas 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 CO 2 removal is required when circulating the exhaust gas.２ No process is required.

[0038] In the manufacturing method of the present disclosure, the embodiments shown in Figures 1 to 7 may be combined. For example, in the manufacturing method shown in Figures 1 to 3, a dehydration step S4 and a temperature raising step S5 as shown in Figure 4 may be performed, a hydrogen gas separation step as shown in Figure 5 may be performed, and a CO ２ A gas separation step may be performed, or as shown in FIG. 7, the reaction gas of metallic iron 20 and methane gas in the first step S21 may rise directly within the furnace and be added to the reducing gas in the reduction step S1, or a combination of these may be performed.

[0039] 2. Reduced Iron Production System The technology disclosed herein also has an aspect as a system for producing reduced iron containing carbon. That is, as shown in Figures 1 to 7, the system for producing reduced iron containing carbon according to one embodiment includes a reduction unit 110 that brings a reducing gas into contact with an oxidized iron raw material 10 to obtain metallic iron 20, and a cooling unit 120 that cools the metallic iron 20. Here, the cooling unit 120 includes: a first portion 121 that brings methane gas into contact with the metallic iron 20 obtained by the reduction unit 110 to carbonize the metallic iron 20; a second portion 122 that brings CO gas into contact with the metallic iron 20 downstream of the first portion 121 to carbonize the metallic iron 20; and a third portion 123 that brings methane gas or an inert gas into contact with the metallic iron 20 downstream of the second portion 122.

[0040] In this embodiment, the reduction step S1 is performed in the reduction unit 110, and the cooling step S2 is performed in the cooling unit 120. The reduction unit 110 and the cooling unit 120 may be configured to be able to perform the reduction step S1 and the cooling step S2, respectively. As shown in FIGS. 1 to 5 , the reduction unit 110 may include a reduction gas supply port 110a for supplying a reduction gas and an outlet 110b for discharging gas after the reduction reaction. The first portion 121 may include a first cooling gas supply port 121a for supplying a cooling gas containing methane gas and a first cooling gas outlet 121b for discharging a reaction gas of the metallic iron 20 and the methane gas in the first portion 121. The second portion 122 may include a second cooling gas supply port 122a for supplying a cooling gas containing CO gas and a second cooling gas outlet 122b for discharging a reaction gas of the metallic iron 20 and the CO gas in the second portion 122. Furthermore, the third section 123 may include a third cooling gas supply port 123a for supplying a cooling gas containing methane gas or an inert gas, and a third cooling gas discharge port 123b for discharging the methane gas or the inert gas that has come into contact with the metallic iron 20 in the third section 123. The reducing section 110 and the cooling section 120 may be integrated or separate. For example, as shown in FIG. 1, the reducing section 110 and the cooling section 120 may be provided in the shaft furnace 100. Alternatively, as shown in FIG. 2, the reducing section 110 may be provided in the shaft furnace 100, and the cooling section 120 may be provided in a cooling device 200 downstream of the shaft furnace 100. Alternatively, as shown in FIG. 3, the reducing section 110 and a first portion 121 of the cooling section may be provided in the shaft furnace 100, and the second portion 122 and the third portion 123 of the cooling section may be provided in the cooling device 200 downstream of the shaft furnace 100. 2 and 3 , when the cooling device 200 is provided downstream of the shaft furnace 100, the reduced iron production system may include a moving device 300 that moves the metallic iron 20 from the shaft furnace 100 to the cooling device 200. Specific examples of the moving device 300 include a conveyor, a cart, and the like. From the viewpoint of reducing equipment costs, etc., it is preferable that the reduction section 110 and the cooling section 120 be provided in the shaft furnace 100.When the cooling device 200 is provided in the reduced iron production system, a specific example of the cooling device 200 is a cooling tower.

[0041] A reducing gas may be supplied to the reducing unit 110 via a reducing gas supply port 110a. Furthermore, methane gas may be supplied to the first portion 121 of the cooling unit 120 via a first cooling gas supply port 121a. Furthermore, CO gas may be supplied to the second portion 122 via a second cooling gas supply port 122a. Furthermore, methane gas or an inert gas may be supplied to the third portion 123 via a third cooling gas supply port 123a. The supply systems for each gas are not particularly limited, and may be, for example, any gas source and supply port may be connected by piping or the like. The types of reducing gases are as described above. The reducing gas may include, for example, hydrogen gas. The types of gases supplied to the cooling unit 120 are as described above.

[0042] The reduced iron production system according to the present embodiment may include other components in addition to the reduction unit 110 and the cooling unit 120 described above. For example, the reduced iron production system according to an embodiment may include a dehydration device 130 that dehydrates the exhaust gas from the reduction unit 110 to obtain a circulation gas. The reduced iron production system according to an embodiment may also include a temperature raising device 140 that raises the temperature of the exhaust gas from the reduction unit 110 or the circulation gas obtained by dehydrating the exhaust gas. The temperature raising device 140 may also raise the temperature of the exhaust gas from the reduction unit 110 or the circulation gas obtained by dehydrating the exhaust gas, and hydrogen gas, to produce a reducing gas containing hydrogen gas and one or both of the exhaust gas and the circulation gas. The dehydration device 130 and the temperature raising device 140 described above may also be combined. 4, a production 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 temperature 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.

[0043] The exhaust gas systems from the reduction unit 110 and the cooling unit 120 are also as described above. For example, as shown in FIGS. 1 to 6 , a production system according to an embodiment may have a first cooling gas outlet 121b downstream of the reduction unit 110, which discharges the reaction gas of the metallic iron 20 and methane gas in the first portion 121 to the outside of the system. Alternatively, as shown in FIG. 7 , a production system according to an embodiment may connect the reduction unit 110 and the first portion 121 so that the reaction gas of the metallic iron 20 and methane gas in the first portion 121 (corresponding to the reaction gas in the first step S21 described above) is added to the reducing gas. Furthermore, a production system according to an embodiment may have a second cooling gas outlet 122b downstream of the first portion 121, which discharges the reaction gas of the metallic iron and CO gas in the second portion 122 (corresponding to the reaction gas in the second step S22 described above). In addition, the manufacturing system according to one embodiment may have a third cooling gas outlet 123b downstream of the second portion 122, which discharges methane gas or an inert gas that has come into contact with the metallic iron 20 in the third portion 123 outside the system.

[0044] The temperatures of the metallic iron 20 in the reduction section 110 and the cooling section 120 are also as described above. For example, in a production system according to an embodiment, the temperature of the metallic iron 20 in contact with methane gas in the first section 121 may be 700°C or higher and 900°C or lower. In addition, in a production system according to an embodiment, the temperature of the metallic iron 20 in contact with CO gas in the second section 122 may be 400°C or higher and 600°C or lower. In addition, in a production system according to an embodiment, the temperature of the metallic iron 20 in contact with methane gas or an inert gas in the third section 123 may be lower than 400°C.

[0045] 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.

[0046] Furthermore, in the manufacturing system of the present disclosure, when a cooling tower 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.

[0047] In the manufacturing system of the present disclosure, the configurations shown in Figures 1 to 7 may be combined. For example, the manufacturing system shown in Figure 1 may be combined with a dehydration device 130 and a heating device 140 as shown in Figure 3.

[0048] 3. Effects As described above, according to the production method and production system of the present embodiment, metallic iron 20 is obtained by reducing the oxidized iron raw material 10, and then (1) the metallic iron 20 is carbonized and cooled with methane gas, followed by (2) carbonizing the metallic iron 20 with CO gas, and then (3) cooling the metallic iron 20 with methane gas or an inert gas, thereby making it possible to efficiently produce reduced iron 30 containing carbon (e.g., CDRI with an increased carbon concentration).

[0049] The present invention will be further described below with reference to examples, but the present invention is not limited to these examples. Various conditions can be adopted according to the present invention as long as they do not deviate from the gist of the present invention and the object thereof is achieved. In the following examples, conditions for increasing the amount of carbonization of reduced iron 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 a Blast Furnace Mathematical Model," Nippon Steel & Sumitomo Metal Technical Report No. 410 (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)

[0050] 1. Study on the reduction process and cooling process in a shaft furnace 1.1 Simulation method 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 858°C. After that, in Case 2 and Case 4 (Examples), CH ４ was blown in to precipitate carbon and cool the metallic iron at the same time. ４ CO gas at 25°C was blown in from below the blowing port to promote carbon deposition of CO. Then, for each of Case 1, Case 2, Case 3, and Case 4, CH ４ was blown in and the temperature was lowered to the target temperature for CDRI.

[0051] 1.2 Calculation Conditions Figure 8 shows the type and introduction position of gas introduced into the cooling section of the shaft furnace for each of Cases 1 to 4. The structure shown in Figure 8 is the left half of the furnace interior structure when a cross section passing through and along the central axis of the shaft furnace is divided into right and left halves along the central axis. For Cases 2 and 4, the reduction zone in Figure 8 corresponds to the reduction step S1, the transition zone corresponds to the first step S21 of the cooling step S2, the upper part of the cooling zone corresponds to the second step S22 of the cooling step S2, and the lower part of the cooling zone corresponds to the third step S23 of the cooling step S2. In Cases 2 and 4, the exhaust gas from the first step S21 was introduced directly into the reduction step S1. The exhaust gas from the second step S22 was extracted from the system downstream of the first step S21. The exhaust gas from the third step S23 was used as the cooling gas in the second step S22 as it was.

[0052] Details of Cases 1 to 4 are as follows: Case 1 (Comparative Example): The first step S21 and the second step S22 are not performed, and CH ４ is 1400Nm ３ / min, the temperature of the reduced iron at the outlet of the third step S23 was lowered to the target temperature as CDRI. The pressure at the shaft top was set to 0.04 MPa (gauge pressure). Case 2 (Example): In the first step S21, ４ is 300Nm ３ / min, and in the second step S22, CO was blown in at a flow rate of 700 Nm ３ / min, and in the third step S23 ４ is 1500Nm ３ / min, the temperature of the reduced iron at the outlet of the third step S23 was lowered to the target temperature as CDRI. The pressure at the shaft top was set to 0.04 MPa (gauge pressure). Case 3 (Comparative Example): The same as Case 1 except that the pressure at the shaft top was changed to 0.7 MPa (gauge pressure). Case 4 (Example): In the first step S21, CH ４ is 300Nm ３ / min, and in the second step S22, CO is injected at a flow rate of 500 Nm ３ / min, and in the third step S23 ４ is 1850Nm ３ / min, the temperature of the reduced iron at the outlet of the third step S23 was lowered to the target temperature as CDRI. The pressure at the shaft top was 0.7 MPa (gauge pressure).

[0053] 1.3 Calculation Results 1 The calculation results for Case 1 and Case 2 are shown in Table 1 below.

[0054]

[0055] The results in Table 1 reveal the following. In both Cases 1 and 2, the reduction rate of the product reduced iron was 93 to 94%, ensuring a high reduction rate. In Case 1 (Comparative Example), the reduced iron was discharged in a cooled state, but a sufficient amount of carbonization was not obtained. In Case 2 (Example), the amount of carbonization (carbon concentration) of the discharged reduced iron was high, and the discharge temperature was also reduced to a temperature sufficiently low for practical use.

[0056] The calculation results for Case 3 and Case 4 are shown in Table 2 below.

[0057]

[0058] The results in Table 2 reveal the following. In both Case 3 and Case 4, the reduction rate of the product reduced iron was 93 to 94%, ensuring a high reduction rate. In Case 3 (Comparative Example), the reduced iron was discharged in a cooled state, but a sufficient amount of carbonization was not obtained. In Case 4 (Example), the amount of carbonization (carbon concentration) of the discharged reduced iron was high, and the discharge temperature was also reduced to a temperature sufficiently low for practical use.

[0059] 1.4 Calculation result 2 In Case 2, the CH injected in the first step S21 is set so that the temperature of the metallic iron after the first step S21 is about 400 to 600°C. ４ The amount of carbonized reduced iron discharged was investigated when the amount of CH injected in the first step S21 was changed (Cases 5 to 11). ４ The flow rate of is as follows: The calculation conditions and results are shown in Table 3.

[0060]

[0061] As shown in Table 3, it can be seen that the carbon concentration of the finally obtained reduced iron is particularly high when the temperature of the metallic iron after the first step is 400° C. or higher and 600° C. or lower, preferably 450° C. or higher and 550° C. or lower. In all of Cases 5 to 11, the reduction degree of the product reduced iron was 92 to 94%, and a high reduction degree was ensured.

[0062] 1.5 Calculation result 3 In Case 2, the CH injected in the first step S21 is set so that the temperature of the metallic iron after the first step S21 is about 400 to 600°C. ４ In the third step S23, the amount of CH ４ Instead, nitrogen gas (flow rate: 1700 Nm ３ / min) (Cases 12 to 15). The calculation conditions and results are shown in Table 4.

[0063]

[0064] As shown in Table 4, even when an inert gas such as nitrogen gas was used in the third step S23, the carbon concentration of the finally obtained reduced iron was hardly reduced. In all of Cases 12 to 15, the reduction degree of the product reduced iron was 92 to 94%, and a high reduction degree was ensured.

[0065] 2. Study on the case where the reduction process is performed in a shaft furnace and the cooling process is performed in a cooling tower 2.1 Simulation Conditions 1 2.1.1 Comparative Example 1 The simulation conditions for Comparative Example 1 are the same as those for Case 1. That is, first, iron oxide pellets are charged into a shaft furnace and heated to 950°C. ２ The temperature of the metallic iron immediately after the reduction reaction was 858°C. ４ The carbon was deposited and the metallic iron was cooled at the same time, and the reduced iron product was obtained. The shaft furnace top pressure was 0.04 MPa (gauge pressure). ４ The supply amount of sintered iron, the temperature of the product reduced iron, and the carbon concentration are as shown in Table 5 below.

[0066] 2.1.2 Example 1 A numerical simulation was carried out assuming a case where a shaft furnace and a cooling tower were combined and operated. Figure 9 shows the types and positions of gases introduced into each of the shaft furnace and the cooling tower. The structure shown in Figure 9 is the left half of the furnace structure in a cross section passing through and along the central axis of the shaft furnace or the cooling tower, when the furnace interior structure is divided into right and left halves with the central axis of the shaft furnace or the cooling tower as the boundary. First, iron oxide pellets were charged into the shaft furnace and heated to 950°C. ２ The temperature of the metallic iron immediately after the reduction reaction was 858°C. ４ The temperature of the metallic iron at the outlet of the shaft furnace was 533.6°C. ４The amount of carbon dioxide supplied is as shown in Table 5 below. Subsequently, metallic iron recovered from the outlet side of the shaft furnace is introduced into the top of the cooling tower, and CO2 at 25°C is blown in downstream of the top to deposit carbon. Further downstream, CH2 at 25°C is blown in. ４ The pressure at the top of the shaft furnace and the top of the cooling tower was 0.04 MPa (gauge pressure). ４ The supply amount of sintered iron, the temperature of the product reduced iron, and the carbon concentration are as shown in Table 5 below.

[0067] 2.1.3 Example 2 As shown in Figure 10, the CO supply position of the cooling tower and the CH ４ Between the supply position of ４ The simulation was carried out in the same manner as in Example 1, except that 100% of the cooled exhaust gas was extracted. ４ The amount of the sintered iron supplied, the temperature of the product reduced iron, and the carbon concentration are as shown in Table 1 below.

[0068] 2.2 Calculation Results The following Table 5 shows the calculation results for each of Comparative Example 1 and Examples 1 and 2. In each of Comparative Example 1 and Examples 1 and 2, the reduction rate of the product reduced iron was 93% or more.

[0069]

[0070] The results shown in Table 5 reveal the following. As in Comparative Example 1, the carbon concentration of the product reduced iron cannot be sufficiently increased simply by reducing the oxidized iron raw material in a shaft furnace and cooling the metallic iron with methane gas. In contrast, as in Examples 1 and 2, the reduction of the oxidized iron raw material and cooling of the metallic iron are performed in a shaft furnace, followed by carbonization of the metallic iron with CO gas in a cooling tower provided separately from the shaft furnace, and further cooling of the metallic iron with methane gas downstream of the cooling device. This makes it possible to improve the carbon concentration of the product reduced iron. In other words, reduced iron containing carbon (e.g., CDRI with an increased carbon concentration) can be efficiently produced. In particular, as in Example 2, the carbon concentration of the product reduced iron can be increased by adjusting the CO supply position of the cooling tower and the CH ４ Between the supply position of４ By extracting the cooling exhaust gas from the shaft furnace, the carbon concentration of the product reduced iron is further improved. In addition, by providing the shaft furnace and the cooling tower separately as in Examples 1 and 2, it is possible to prevent the exhaust gas from the cooling tower from entering the shaft furnace.

[0071] 2.3 Simulation Conditions 2 Comparative Example 2 was conducted under the same conditions as Case 3 above, that is, under the same conditions as Comparative Example 1 except that the shaft top pressure was set to 0.7 MPa (gauge pressure). Example 3 was conducted under the same conditions as Example 1 except that the shaft top pressure was set to 0.7 MPa (gauge pressure). Example 4 was conducted under the same conditions as Example 1 except that the shaft top pressure and the cooling tower top pressure were both set to 0.7 MPa (gauge pressure).

[0072] 2.4 Calculation Results The following Table 6 shows the calculation results for each of Comparative Example 2 and Examples 3 and 4. In each of Comparative Example 2 and Examples 3 and 4, the reduction rate of the product reduced iron was 93% or more.

[0073]

[0074] The results shown in Table 6 reveal the following. Simply performing the reduction of the oxidized iron raw materials in a shaft furnace and cooling the metallic iron with methane gas, as in Comparative Example 2, does not sufficiently increase the carbon concentration of the product reduced iron. In contrast, as in Examples 3 and 4, the reduction of the oxidized iron raw materials and cooling of the metallic iron are performed in a shaft furnace, followed by carbonization of the metallic iron with CO gas in a cooling tower provided separately from the shaft furnace. Furthermore, cooling of the metallic iron with methane gas downstream of the cooling device increases the carbon concentration of the product reduced iron. In other words, reduced iron containing carbon (e.g., CDRI with an increased carbon concentration) can be efficiently produced. Furthermore, providing the shaft furnace and the cooling tower separately, as in Examples 3 and 4, prevents exhaust gas from the cooling tower from entering the shaft furnace.

[0075] In addition, CH ４Similar calculations were also performed when nitrogen gas was used instead of inert gas, and the calculation results showed a tendency similar to the results shown in Table 5. That is, even when an inert gas such as nitrogen gas is used in the cooling tower, the carbon concentration of the finally obtained reduced iron is not significantly reduced.

[0076] 3. Summary From the above results, it can be said that reduced iron containing carbon can be efficiently produced by performing the following reduction step and cooling step.

[0077] In the reduction step, a reducing gas is brought into contact with an iron oxide raw material to obtain metallic iron. In the cooling step, the metallic iron is cooled. Here, the cooling step includes a first step of bringing methane gas into contact with the metallic iron after the reduction step to carbonize the metallic iron, a second step of bringing CO gas into contact with the metallic iron after the first step to carbonize the metallic iron, and a third step of bringing methane gas or an inert gas into contact with the metallic iron after the second step.

[0078] REFERENCE SIGNS LIST 10 iron oxide raw material 20 metallic iron 30 reduced iron containing carbon 100 shaft furnace 100a raw material supply port 100b outlet 110 reduction section 110a reducing gas supply port 110b reducing gas outlet 120 cooling section 121 first section 121a first cooling gas supply port 121b first cooling gas outlet 122 second section 122a second cooling gas supply port 122b second cooling gas outlet 123 third section 123a third cooling gas supply port 123b third cooling gas outlet 200 cooling device

Claims

1. A method for producing reduced iron containing carbon, comprising: a reduction step of bringing a reducing gas into contact with an iron oxide raw material to obtain metallic iron; and a cooling step of cooling the metallic iron, wherein the cooling step includes: a first step of bringing methane gas into contact with the metallic iron after the reduction step to carbonize the metallic iron; a second step of bringing CO gas into contact with the metallic iron after the first step to carbonize the metallic iron; and a third step of bringing methane gas or an inert gas into contact with the metallic iron after the second step. A method for producing reduced iron.

2. The method for producing reduced iron according to claim 1, wherein the reduction step and the cooling step are carried out in a shaft furnace. A method for producing reduced iron.

3. The method for producing reduced iron according to claim 1, wherein the reduction step is carried out in a shaft furnace, and the cooling step is carried out in a cooling device provided downstream of the shaft furnace. A method for producing reduced iron.

4. The method for producing reduced iron according to claim 1, wherein the reduction step and the first step are carried out in a shaft furnace, and the second step and the third step are carried out in a cooling device provided downstream of the shaft furnace. A method for producing reduced iron.

5. The method for producing reduced iron according to claim 3 or 4, further comprising a transfer step of transferring the metallic iron from the shaft furnace to the cooling device. A method for producing reduced iron.

6. The method for producing reduced iron according to any one of claims 1 to 5, wherein the reducing gas contains hydrogen gas. A method for producing reduced iron.

7. The method for producing reduced iron according to any one of claims 1 to 6, further comprising: a dehydration step of dehydrating the exhaust gas of 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 hydrogen gas. A method for producing reduced iron.

8. The method for producing reduced iron according to any one of claims 1 to 7, wherein the reaction gas of the metallic iron and the methane gas in the first step is discharged out of the system downstream of the reduction step. A method for producing reduced iron.

9. A method for producing reduced iron according to any one of claims 1 to 8, wherein the reaction gas of the metallic iron and the methane gas in the first step is added to the reducing gas.

10. A method for producing reduced iron according to any one of claims 1 to 9, wherein the reaction gas of the metallic iron and the CO gas in the second step is discharged out of the system on the downstream side of the first step.

11. A method for producing reduced iron according to any one of claims 1 to 10, wherein the methane gas or the inert gas that has contacted the metallic iron in the third step is discharged out of the system on the downstream side of the second step.

12. A production system for reduced iron containing carbon, comprising: a reduction unit that brings a reducing gas into contact with an iron oxide raw material to obtain metallic iron; and a cooling unit that cools the metallic iron, wherein the cooling unit has: a first part that brings methane gas into contact with the metallic iron obtained by the reduction unit to carbonize the metallic iron; a second part that brings CO gas into contact with the metallic iron on the downstream side of the first part to carbonize the metallic iron; and a third part that brings methane gas or inert gas into contact with the metallic iron on the downstream side of the second part.

13. A production system for reduced iron according to claim 12, wherein the reduction unit and the cooling unit are provided in a shaft furnace.

14. A production system for reduced iron according to claim 12, wherein the reduction unit is provided in a shaft furnace, and the cooling unit is provided in a cooling device on the downstream side of the shaft furnace.

15. A production system for reduced iron according to claim 12, wherein the reduction unit and the first part are provided in a shaft furnace, and the second part and the third part are provided in a cooling device on the downstream side of the shaft furnace.

16. A production system for reduced iron according to claim 14 or 15, comprising a transfer device that transfers the metallic iron from the shaft furnace to the cooling device.

17. A system for producing reduced iron according to any one of claims 12 to 16, wherein the reducing gas contains hydrogen gas, the system for producing reduced iron.

18. A system for producing reduced iron according to any one of claims 12 to 17, comprising a dehydration device that dehydrates the exhaust gas from the reduction section to obtain a circulating gas, and a temperature raising device that raises the temperature of the circulating gas and hydrogen gas to obtain the reducing gas containing the circulating gas and the hydrogen gas, the system for producing reduced iron.

19. A system for producing reduced iron according to any one of claims 12 to 18, having a first cooling gas discharge port that discharges the reaction gas of the metallic iron and the methane gas in the first part to the outside of the system on the downstream side of the reduction section, the system for producing reduced iron.

20. A system for producing reduced iron according to any one of claims 12 to 19, wherein the reduction section and the first part are connected such that the reaction gas of the metallic iron and the methane gas in the first part is added to the reducing gas, the system for producing reduced iron.

21. A system for producing reduced iron according to any one of claims 12 to 20, having a second cooling gas discharge port that discharges the reaction gas of the metallic iron and the CO gas in the second part to the outside of the system on the downstream side of the first part, the system for producing reduced iron.

22. A system for producing reduced iron according to any one of claims 12 to 21, having a third cooling gas discharge port that discharges the methane gas or the inert gas that has contacted the metallic iron in the third part to the outside of the system on the downstream side of the second part, the system for producing reduced iron.

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