Reduced iron manufacturing method and manufacturing system

Abstract

A technology is disclosed for producing reduced iron containing carbon by cooling metallic iron while increasing the carbon concentration of the metallic iron after a reduction step in a direct reduction process. The method for producing reduced iron containing carbon of the present disclosure includes a reduction step in which a reducing gas is brought into contact with an oxidized iron raw material to obtain metallic iron, and a cooling step in which the metallic iron is cooled. The cooling step includes a first step in which, after the reduction step, methane gas is brought into contact with the metallic iron to carbonize the metallic iron, a second step in which, after the first step, CO gas is brought into contact with the metallic iron to carbonize the metallic iron, and a third step in which, after the second step, methane gas or an inert gas is brought into contact with the metallic iron.

Description

[Technical field]

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

[0002] In the steel industry, a direct reduction process using reducing gas is being considered as an alternative technology to the blast furnace process to reduce CO2 emissions. For example, a process using a shaft furnace is being considered as a direct reduction process (for example, Patent Documents 1 and 2). In the direct reduction process, reducing gas is brought into contact with an iron oxide raw material to obtain direct reduced iron (DRI). In addition, 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 reduces the melting temperature in the subsequent melting and refining processes and ensures the strength of the steel. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2021 / 195160 [Patent Document 2] Japanese Patent Application Publication No. 61-073805 Summary of the Invention [Problem to be solved by the invention]

[0004] There are three types of reduced iron products: cold DRI (CDRI), hot briquetted iron (HBI), and hot DRI (HDRI). When producing CDRI by the direct reduction process, after reducing the iron oxide raw material to obtain metallic iron, a technology is required to cool the metallic iron while increasing its carbon concentration. In conventional technology, when producing reduced iron by the direct reduction process, there is room for improvement in terms of cooling the metallic iron obtained after reduction while increasing its carbon concentration. [Means for solving the problem]

[0005] The present application discloses the following aspects as means for solving the above problems. <Aspect 1> A method for producing reduced iron containing carbon, comprising the steps of: A reduction step in which a reducing gas is brought into contact with the iron oxide raw material to obtain metallic iron; and A cooling step of cooling the metallic iron. having The cooling step comprises: a first step of contacting the metallic iron with methane gas after the reduction step to carbonize the metallic iron; a second step of contacting the metallic iron with CO gas after the first step to carbonize the metallic iron; and A third step of contacting the metallic iron with methane gas or an inert gas after the second step. having A method for producing reduced iron. <Aspect 2> A method for producing reduced iron according to aspect 1, comprising the steps of: The reduction step and the cooling step are carried out in a shaft furnace. A method for producing reduced iron. <Aspect 3> A method for producing reduced iron according to aspect 1, comprising the steps of: The reduction step is carried out in a shaft furnace, The cooling step is carried out in a cooling device provided downstream of the shaft furnace. A method for producing reduced iron. <Aspect 4> A method for producing reduced iron according to aspect 1, comprising the steps of: The reduction step and the first step are carried out in a shaft furnace, The second step and the third step are performed in a cooling device provided downstream of the shaft furnace. A method for producing reduced iron. <Aspect 5> The method for producing reduced iron according to aspect 3 or 4, a transferring step of transferring the metallic iron from the shaft furnace to the cooling device; A method for producing reduced iron. <Aspect 6> A method for producing reduced iron according to any one of aspects 1 to 5, The reducing gas comprises hydrogen gas. A method for producing reduced iron. <Aspect 7> The method for producing reduced iron according to any one of aspects 1 to 6, a dehydration step for dehydrating the exhaust gas from the reduction step to obtain a circulating gas; and A temperature increasing step of increasing the temperature of the circulating gas and the hydrogen gas to obtain the reducing gas containing the circulating gas and the hydrogen gas. having A method for producing reduced iron. <Aspect 8> A method for producing reduced iron according to any one of aspects 1 to 7, A 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. A method for producing reduced iron. <Aspect 9> The method for producing reduced iron according to any one of aspects 1 to 8, A reaction gas of the metallic iron and the methane gas in the first step is added to the reducing gas. A method for producing reduced iron. <Aspect 10> A method for producing reduced iron according to any one of aspects 1 to 9, A reaction gas of the metallic iron and the CO gas in the second step is discharged to the outside of the system downstream of the first step. A method for producing reduced iron. <Aspect 11> A method for producing reduced iron according to any one of aspects 1 to 10, The methane gas or inert gas that has come into contact with the metallic iron in the third step is discharged outside the system downstream of the second step. A method for producing reduced iron. <Aspect 12> A system for producing reduced iron containing carbon, comprising: a reduction section for contacting the iron oxide raw material with a reducing gas to obtain metallic iron; and A cooling section that cools the metallic iron. having The cooling unit is a first section for contacting the metallic iron obtained by the reduction section with methane gas to carbonize the metallic iron; a second portion downstream of the first portion for contacting the metallic iron with CO gas to carbonize the metallic iron; and a third section downstream of the second section, in which methane gas or an inert gas is brought into contact with the metallic iron; having A reduced iron production system. <Aspect 13> A system for producing reduced iron according to embodiment 12, comprising: The reduction section and the cooling section are provided in a shaft furnace. A reduced iron production system. <Aspect 14> A system for producing reduced iron according to embodiment 12, comprising: The reduction section is provided in a shaft furnace, The cooling section is provided in a cooling device downstream of the shaft furnace. A reduced iron production system. <Aspect 15> A system for producing reduced iron according to embodiment 12, comprising: The reduction section and the first section are provided in a shaft furnace, The second portion and the third portion are provided in a cooling device downstream of the shaft furnace. A reduced iron production system. <Aspect 16> The system for producing reduced iron according to embodiment 14 or 15, a moving device for moving the metallic iron from the shaft furnace to the cooling device; A reduced iron production system. <Aspect 17> The reduced iron production system according to any one of aspects 12 to 16, The reducing gas comprises hydrogen gas. A reduced iron production system. <Aspect 18> The reduced iron production system according to any one of aspects 12 to 17, A dehydration device that dehydrates the exhaust gas from the reduction section to obtain a circulating gas; and a temperature raising device for raising the temperatures of the circulating gas and the hydrogen gas to obtain the reducing gas containing the circulating gas and the hydrogen gas; having A reduced iron production system. <Aspect 19> The reduced iron production system according to any one of aspects 12 to 18, a first cooling gas outlet downstream of the reduction section, for discharging a reaction gas of the metallic iron and the methane gas in the first portion to the outside of the system; A reduced iron production system. <Aspect 20> The reduced iron production system according to any one of aspects 12 to 19, The reduction unit and the first portion are connected so that a reaction gas of the metallic iron and the methane gas in the first portion is added to the reducing gas. A reduced iron production system. <Aspect 21> The reduced iron production system according to any one of aspects 12 to 20, 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; A reduced iron production system. <Aspect 22> The reduced iron production system according to any one of aspects 12 to 21, a third cooling gas outlet downstream of the second portion for discharging the methane gas or the inert gas that has come into contact with the metallic iron in the third portion to the outside of the system; A reduced iron production system. Effect of the Invention

[0006] According to the manufacturing method and manufacturing system for 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 manufacturing method and manufacturing system for reduced iron disclosed herein, it is possible to manufacture, for example, CDRI having an increased carbon concentration. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram for explaining an example of a method and system for producing reduced iron. [Diagram 2] FIG. 1 is a schematic diagram for explaining an example of a method and system for producing reduced iron. [Diagram 3] FIG. 1 is a schematic diagram for explaining an example of a method and system for producing reduced iron. [Figure 4] FIG. 1 is a schematic diagram for explaining an example of a method and system for producing reduced iron. [Diagram 5] FIG. 1 is a schematic diagram for explaining an example of a method and system for producing reduced iron. [Figure 6] FIG. 1 is a schematic diagram for explaining an example of a method and system for producing reduced iron. [Figure 7] FIG. 1 is a schematic diagram for explaining an example of a method and system for producing reduced iron. [Figure 8] FIG. 4 is a schematic diagram for explaining the type and introduction position of gas introduced into the cooling part of the shaft furnace for each of Cases 1 to 4. [Figure 9] FIG. 2 is a schematic diagram for explaining the types and introduction positions of gases introduced into a shaft furnace and a cooling tower in the first embodiment. [Figure 10] FIG. 11 is a schematic diagram for explaining the types and introduction positions of gases introduced into a shaft furnace and a cooling tower in accordance with a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] An embodiment of the manufacturing method and manufacturing system for reduced iron according to the present disclosure will be described below. However, the manufacturing method and manufacturing system for reduced iron according to the present disclosure are not limited to the following embodiment. In the present application, "oxidized iron raw material" refers to a raw material containing iron oxide before the reduction step. "Metallic iron" refers to an intermediate product produced after the reduction step until the end of the cooling step, and for convenience, the term "metallic iron" is used to refer to a product obtained after the cooling step, even if the carbon concentration has been increased by carbonization or the like. "Reduced iron" refers to a product obtained after the cooling step. In addition, in the present application, "downstream side" refers to the downstream side in the manufacturing process of reduced iron. That is, in the case of manufacturing reduced iron containing carbon 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 side is the downstream side.

[0009] 1. Manufacturing method of reduced iron As shown in FIGS. 1 to 7, a method for producing reduced iron containing carbon according to one embodiment includes the following steps: A reduction step S1 in which a reducing gas is brought into contact with the iron oxide raw material 10 to obtain metallic iron 20; and The method includes a cooling step S2 in which the metallic iron 20 is cooled. Here, the cooling step S2 is After the reduction step S1, a first step S21 is performed in which methane gas is brought into contact with the metallic iron 20 to carbonize the metallic iron 20. After the first step S21, a second step S22 is performed in which the metallic iron 20 is brought into contact with CO gas to carbonize the metallic iron 20; and After the second step S22, a third step S23 is performed in which the metallic iron 20 is contacted with methane gas or an inert gas.

[0010] 1.1 Reduction process 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 Iron oxide raw materials The oxidized iron raw material 10 includes iron oxide. The oxidized iron raw material 10 may be, for example, one or more selected from iron ore pellets, iron ore, and sintered ore. The oxidized iron raw material 10 may include, 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. Note that the "particle diameter of the raw material" means the sieve diameter of the raw material, and the "average particle diameter of the raw material" means the weighted average value of the particle diameters of the raw material. Specifically, the average particle diameter of the raw material is measured as follows. That is, a mass-based particle size distribution is obtained by a dry sieving test described in JIS Z 8815:1995, and the average of the maximum and minimum particle sizes of each sieve is taken as a representative particle size, and the average particle size is weighted by mass to measure the average particle size of the raw material. 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 form.

[0012] When the reduction step S1 is performed in the shaft furnace 100, the iron oxide raw material 10 is supplied and filled into the shaft furnace 100 through the raw material supply port 100a of the shaft furnace 100, and a packed bed can be formed. The packing rate of the packed bed is not particularly limited, and may be the same as the packing rate in a conventional method for producing reduced iron using a shaft furnace. The packed bed moves downward inside the shaft furnace 100. That is, inside the shaft furnace 100, the iron oxide raw material 10 is substantially filled, and gradually moves downward by dropping or the like. When focusing on one raw material particle in the packed bed, the raw material particle may move continuously downward at a constant speed, or may move intermittently by repeating dropping and stopping. When focusing on one raw material particle in the packed bed, the average downward moving speed of the raw material particle is not particularly limited. For example, the average moving speed can be adjusted according to the supply amount (feed speed) 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 the reducing gas is not particularly limited as long as it can reduce the iron oxide raw material 10. In particular, when the reducing gas contains hydrogen gas, the effect of the technology of the present disclosure can be more remarkable. The hydrogen gas may be, for example, one obtained by electrolysis of water, one obtained by separation (for example, membrane separation) from synthesis gas (gas obtained by gasifying (partially oxidizing) coal or biomass with steam, air, or oxygen), one obtained by separation from gas obtained by reforming natural gas with steam or carbon dioxide, or one obtained by separation from dry distillation gas (gas obtained by heating coal or biomass in an oxygen-free state). The reducing gas may contain gas other than hydrogen in addition to hydrogen gas. Examples of gas other than hydrogen include CO gas, inert gas, CO2 gas, and steam. Examples of inert 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, 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 contacting with the iron oxide 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 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 110a 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. In addition to metallic iron 20, the solid reactant may contain iron oxide, silicon dioxide, aluminum oxide, and the like that remain unreduced. The temperature of metallic iron 20 immediately after reduction may be, for example, 700°C or higher. There is no particular limit to the upper limit of the temperature of metallic iron 20 immediately after reduction, and it may be any temperature at which the cooling step S2 described below can be carried out. The temperature of 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 the metallic iron 20 can be collected from an outlet 100b provided in 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 furnace body of the shaft furnace 100 may be the same as the shape of the furnace body of a known shaft furnace. For example, the furnace body of the shaft furnace 100 may have a furnace top, a furnace bottom, and a tubular part (cylindrical part) constituting a side wall between the furnace top and the furnace bottom. In this case, the tubular part may have a body part and a reduced diameter part provided below the body part, and the inner diameter of the furnace may be reduced from top to bottom in the reduced diameter part. The shaft furnace 100 may be equipped with a burden feeder or the like for preventing the packed bed from hanging when the packed bed of the raw material is moved downward inside. In addition, 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 have a raw material supply port 100a in the upper or top part of the furnace, and may have an exhaust port 100b in the lower or bottom part of the furnace for recovering metallic iron or reduced iron.

[0018] 1.2 Cooling process The temperature of the metallic iron 20 immediately after the reduction step S1 is, for example, about 700°C to 900°C. In the cooling step S2, the metallic iron 20 at such a high temperature is brought into contact with gas, 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 manner, the melting temperature in the subsequent melting and refining step is lowered and the strength as steel is ensured.

[0019] In the cooling step S2, (1) the metallic iron 20 is carbonized and cooled by methane gas, (2) the metallic iron 20 is carbonized by CO gas, and (3) the metallic iron 20 is cooled by methane gas or an inert gas. According to the knowledge of the present inventor, the carbon deposition reaction by methane gas is likely to proceed in a high temperature range of 700°C or more, 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 more and 600°C or less, 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, so that the endothermic reaction, which is the carbon deposition reaction, proceeds appropriately and efficiently. In addition to the physical endothermic reaction due to contact with methane gas, which has a large specific heat, the temperature of the metallic iron 20 is likely to decrease to a temperature suitable for the carbon deposition reaction by CO gas due to the endothermic reaction during carbon deposition. By contacting the metallic iron 20 whose temperature has been reduced in this way with CO gas, the exothermic reaction, which is a carbon precipitation reaction, proceeds appropriately and efficiently, and the carbon concentration in the finally obtained reduced iron 30 can be further increased. 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 the CO gas becomes dominant over the temperature increase due to the exothermic reaction, and the temperature of the metallic iron 20 decreases. Thereafter, by 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., CDRI containing carbon) is obtained. As described above, in the cooling step S2, by going through (1) carbonization with methane gas and (2) carbonization with CO gas in this order, the carbon concentration in the reduced iron 30 increases compared to the case of contacting each gas alone. Since 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 precipitation. However, (3) cooling with methane gas or an 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, it is preferable that the reduction step S1 and the cooling step S2 are performed in the shaft furnace 100. On the other hand, when a part or the whole of the cooling step S2 is performed in the cooling device 200, the exhaust gas in the cooling device 200 can be prevented 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 (including CO gas and CO2 gas) from the second step S22 is prevented from entering the first step S21. This makes it possible to more efficiently proceed with the carbon deposition reaction in the first step S21. In addition, the circulation treatment (hydrogen recovery) of the exhaust gas from the reduction step S21 becomes easy. Furthermore, CO2 can be efficiently recovered from the second step S22. 2 and 3, when a part or the whole of the cooling step is performed in a cooling device 200 provided downstream of the shaft furnace 100, the method for producing reduced iron may include a moving step of moving the metallic iron 20 from the shaft furnace 100 to the cooling device 200. Specifically, the metallic iron 20 recovered from the discharge outlet 100b of the shaft furnace 100 may be moved to the metallic iron supply port 200a of the cooling device 200. When a part or the whole 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 may be a cooling tower.There is no particular limit to the supply rate of metallic iron 20 to cooling device 200. The metallic iron 20 supplied into cooling device 200 may form a packed bed within cooling device 200, or may be suspended in the air current. In particular, when the metallic iron 20 supplied into cooling device 200 forms a packed bed within cooling device 200, a higher 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, in the second step S22, an exothermic reaction between the metallic iron 20 and CO gas may occur, 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, the metallic iron 20 is brought into contact with methane gas, and the metallic iron 20 is carbonized. 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, 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 by methane gas can proceed. In the first step S21, for example, by contacting the metallic iron 20 at 700°C or higher with methane gas, the carbon deposition reaction 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 limit to the upper limit of the temperature of the metallic iron 20 contacted with methane gas. The temperature of the metallic iron 20 contacted with the methane gas may be, for example, 1100° C. or less. From the viewpoint of allowing the carbon deposition reaction by methane gas to proceed particularly significantly, the temperature of the metallic iron 20 contacted with the methane gas in the first step S21 is 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, and the like. ° C. or less, 700° C. to 1040° C., 700° C. to 1000° C., 700° C. to 970° C., 700° C. to 940° C., 700° C. to 900° C., 710° C. to 1070° C., 730° C. to 1040° C., 750° C. to 1000° C., 770° C. to 970° C., 790° C. to 940° C., or 810° C. to 900° C. In addition, 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 the cooling tower. When the reduction step S1 and the first step S21 are performed in the same equipment (e.g., a shaft furnace), the position (height position) P1 for measuring the "temperature of metallic iron 20" in the first step S21 is a position (height position) downstream (below) of the position (height position) P2 where the reduction gas in the reduction step S1 is blown in, and is within 1 m of said position P2.Alternatively, when the reduction step S1 and the first step S21 are performed in different devices (for example, when 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 when 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 in which the first step S21 is performed. The average temperature of the metallic iron 20 in the radial direction can be specified, 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, when the first step S21 is performed in a shaft furnace, the average temperature of the metallic iron 20 in the radial direction is specified 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 specified by multiple thermocouples installed in the radial direction of the cooling tower. Here, for example, if we assume 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. N+1 corresponds to the center of the furnace (r0=0) and the furnace wall (r N+1 =R), and the temperature at that point is determined by extrapolation. According to this method, even if there is a temperature distribution in the radial direction, it is possible to identify the average temperature in the radial direction by averaging a plurality of measured temperatures. The number of thermocouples is not particularly limited, but it is preferable that five or more points are arranged, 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.

number

[0023] In the first step S21, it is sufficient that the carbonization of the metallic iron 20 proceeds by the carbon deposition reaction due to the methane gas, and other gases may be brought into contact with the metallic iron 20 together with the methane gas. In other words, the gas that comes into contact with the metallic iron 20 in the first step S21 may contain methane gas. The gas that comes into contact with the metallic iron 20 in the first step S21 may contain hydrogen gas, nitrogen gas, CO gas, CO2 gas, water vapor, and the like in addition to methane gas. 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 the carbon deposition reaction (endothermic reaction) due to the methane gas. In the first step S21, as long as such an endothermic reaction due to the methane gas proceeds predominantly, a part of the gas that comes into contact with the metallic iron 20 may contain a gas that is accompanied by an exothermic reaction (for example, CO gas). However, when the gas contacting metallic iron 20 in the first step S21 contains CO gas, the volumetric percentage of the CO gas is smaller than the volumetric percentage of methane gas. When the gas contacting metallic iron 20 in the first step S21 is made up of multiple types of gas, for example, the volumetric percentage of methane gas is the largest among the volumetric percentages of each gas. The gas contacting metallic iron 20 in the first step S21 contains, for example, 50 volume % or more, 60 volume % or more, or 70 volume % or more of methane gas.

[0024] The reaction gas of the metallic iron 20 and the 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 a part of the above-mentioned reducing gas. For example, as shown in Figs. 1 to 6, the reaction gas of the metallic iron 20 and the 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 of the metallic iron 20 and the methane gas in the first step S21 may be added to the above-mentioned reducing gas, in other words, the reaction gas of the metallic iron 20 and the methane gas in the first step S21 may be supplied to the reduction step S1. In particular, by adding the reaction gas in the first step S21 to the above-mentioned reducing gas, efficient operation is possible while reducing the amount of reducing gas used.

[0025] 1.2.2 Second process The second step S22 corresponds to the above (2). That is, in the second step S22, after the first step S21, the metallic iron 20 is brought into contact with CO gas, and the metallic iron 20 is carbonized. 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, a cooling device provided downstream of the shaft furnace). When the first step S21 is performed outside the shaft furnace, the second step S22 is necessarily performed outside the shaft furnace. In the second step S21, the temperature of the metallic iron 20 when it is brought into contact with the CO gas is not particularly limited as long as the carbon deposition reaction by the CO gas can proceed. In the second step S22, for example, by bringing the CO gas into contact with the metallic iron 20 at 400°C or more and 600°C or less, the carbon deposition reaction by the CO gas described above can proceed more appropriately. The temperature of the metallic iron 20 contacted with the CO gas in the second step S22 may be 410°C to 600°C, 420°C to 600°C, 430°C to 600°C, 440°C to 600°C, 450°C to 600°C, 400°C to 590°C, 400°C to 580°C, 400°C to 570°C, 400°C to 560°C, 400°C to 550°C, 410°C to 590°C, 420°C to 580°C, 430°C to 570°C, 440°C to 560°C, or 450°C to 550°C, from the viewpoint of allowing the carbon deposition reaction by the CO gas to proceed particularly significantly. Note that 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, 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 metallic iron 20" is measured in the second step S22 is downstream (lower) than the position (height position) P4 at which the methane gas is blown in the first step S21, and is a position (height position) within 1 m from the position P4. 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 device provided downstream of the shaft furnace), the position P3 at which the "temperature of metallic iron 20" is measured in the second step S22 is a position within 1 m downstream (lower) from the metallic iron supply port of the apparatus in which the second step S22 is performed. In the second step S22, the temperature of the CO gas in contact with the metallic iron 20 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, the carbonization of the metallic iron 20 may proceed by a carbon precipitation reaction due to 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 that comes into contact with the metallic iron 20 in the second step S22 may contain CO gas. The gas that comes into contact with the metallic iron 20 in the second step S22 may contain nitrogen gas, hydrogen gas, CO2 gas, etc. in addition to CO gas. The gas that comes into contact with the metallic iron 20 in the second step S22 may be, for example, converter gas (LDG). In addition, when the gas that comes into contact with the metallic iron 20 in the second step S22 contains methane gas, the volumetric ratio of the methane gas is smaller than the volumetric ratio of the CO gas. In addition, 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 ratio of CO gas is the largest among the volumetric ratios of each gas. The gas that comes into contact with the metallic iron 20 in the second step S22 contains, for example, CO gas at 50 vol % or more, 60 vol % or more, or 70 vol % or more.

[0027] The reaction gas of the metallic iron 20 and the CO gas in the second step S22 may contain CO gas and CO2 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 above-mentioned first step S21. In particular, as shown in Figures 1 to 7, the reaction gas of the metallic iron 20 and the CO gas in the second step S22 is discharged to the outside of the system downstream of the first step S21, so that the endothermic reaction with methane gas can proceed more appropriately, enabling efficient operation.

[0028] 1.2.3 Third step The third step S23 corresponds to the above (3). 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 (for example, a cooling device provided downstream of the shaft furnace). 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, since the carbon deposition reaction in the second step S22 is an exothermic reaction, the temperature of the metallic iron 20 immediately after the second step S22 is unlikely to be a temperature appropriate for CDRI. In other words, the metallic iron 20 immediately after the second step S22 is in a state that is easily reoxidized. By performing the third step S23 after the second step S22, the temperature of the metallic iron 20 can be reduced to a temperature appropriate for CDRI. In the third step S23, the temperature of the metallic iron 20 when it comes into contact with the methane gas or the inert gas is not particularly limited. In the third step S23, for example, the metallic iron 20 at a temperature of less than 400° C. may be brought into contact with the methane gas or the inert gas to lower the temperature of the metallic iron 20 to a temperature appropriate for CDRI. Note that the "temperature of the metallic iron 20" in the third step S23 is the average temperature in the radial direction of the shaft furnace or the cooling tower, as in the first step S21 and the second step S22. 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. Also, 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 equipment (e.g., a shaft furnace), the position (height position) P5 for measuring the “temperature of the metallic iron 20” in the third step S23 is a position (height position) downstream (below) of the position (height position) P6 where the CO gas is blown in in the second step S22, and is within 1 m of said position P6.Alternatively, when 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 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 the methane gas or inert gas, and other gases may be contacted with the metallic iron 20 together with 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, etc. 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 is made up of multiple types of gases, for example, the volume ratio of methane gas or the volume ratio of the inert gas is the largest among the volume ratios 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 volume % or more, 60 volume % or more, or 70 volume % or more, or an inert gas at 50 volume % or more, 60 volume % or more, or 70 volume % or more, or a total of methane gas and an inert gas at 50 volume % or more, 60 volume % or more, or 70 volume % or more.

[0030] When methane gas is used in the third step S23, the exhaust gas in 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 in the third step S23 may contain an 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 above-mentioned reduction step S1 and 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, in addition to carbon and iron, iron oxide, silicon dioxide, aluminum oxide, and the like that remain without being reduced. The carbon content of the reduced iron 30 may be, for example, more than 0 mass% and 5 mass% or less. 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, 150°C or less, or 80°C or less. When the reduction step S1 and the cooling step S2 are performed in the shaft furnace 100, the reduced iron 30 may be recovered, for example, from an outlet 100b provided in the lower part of the shaft furnace 100. When a part or the whole of the cooling step S2 is performed in the cooling device 200, the reduced iron 30 may be recovered, for example, from an outlet 200b provided in the lower part of the cooling device 200.

[0032] 1.4 Dehydration process and heating process The method for producing reduced iron according to the present embodiment may include other steps in addition to the reduction step S1 and the cooling step S2 described above. For example, the method for producing reduced iron according to an 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 method for producing reduced iron according to an embodiment may include a temperature increase 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 increase step S4 may be a step of heating the exhaust gas from the reduction step S1 or the circulation gas obtained by dehydrating the exhaust gas, and hydrogen gas, to obtain a reduction gas containing one or both of the exhaust gas and the circulation gas, and hydrogen gas. The dehydration step S3 and the temperature increase step S4 described above 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 circulating gas, and a heating 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 process 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 a reaction between the reducing gas and the iron oxide 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 Heating process Although the circulation gas obtained by the dehydration step S3 contains the reducing gas, the amount of the reducing gas is not sufficient. In addition, since the temperature of the circulation gas obtained by the dehydration step S3 is low, it is not efficient to use it as it is in the reduction step S1. Therefore, in the temperature increase 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 hydrogen gas as a make-up gas is heated and mixed with the circulation gas to obtain the reducing gas. In the temperature increase step S4, the circulation gas and hydrogen gas may be mixed after being heated, or the circulation gas and hydrogen gas may be mixed and heated after being mixed. The hydrogen gas may be obtained by electrolysis of water or membrane separation from a synthesis gas (a gas obtained by steam reforming or partial combustion of coal or biomass). The temperature increase step S3 may be performed by a known temperature increase device (heating device) 140.

[0035] 1.5 Hydrogen gas separation process 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 of the first step S21. This makes it possible to separate, for example, hydrogen gas and methane gas contained in the exhaust gas of the first step S21. 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 CO2 gas separation process As shown in Fig. 6, the method for producing reduced iron according to an embodiment may include a CO2 gas separation step of separating CO2 gas contained in the exhaust gas in the second step S22. This allows, for example, separation of CO2 gas and CO gas contained in the exhaust gas in the second step S22. The CO gas separated from the exhaust gas can be used, for example, as the CO gas in the above-mentioned second step S22. In addition, the CO2 gas separated from the exhaust gas can be discharged outside the system and captured by a CO2 capture device or the like. The CO2 gas separation step can be performed by a known CO2 gas separation device 500. The configuration of the CO2 gas separation device 500 is not particularly limited.

[0037] 1.7 Other matters As described above, in the manufacturing method of 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 in the shaft furnace 100 below the reduction step S1. In this case, as shown in FIG. 7, the reaction gas of the metallic iron 20 and methane gas in the first step S21 may rise in the furnace as it is and be added to the reducing gas in the reduction step S1 and used for reduction. Also, 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 CO2 gas discharged from the second step S22 are removed from the reduction step S1. That is, the CO gas and CO2 gas are not mixed into the exhaust gas from the reduction step S1, and the exhaust gas from the reduction step S1 is likely to be only the reducing gas (e.g., hydrogen gas) and water vapor. By subjecting such exhaust gas to the dehydration step S3, it can be reused as a 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 the methane gas can be decomposed in the reduction zone. The methane gas is also mixed with other gases in the reduction zone and diluted. That is, the exhaust gas from the reduction step S1 contains almost no methane gas, and even if it does, 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, it can be handled with only a normal partial discharge step of the reducing gas outside the system, and a special CO2 decomposition step or the like is not required when circulating the exhaust gas.

[0038] In the manufacturing method of the present disclosure, the forms 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 or a temperature increasing step S5 as shown in Figure 4 may be performed, a hydrogen gas separation step as shown in Figure 5 may be performed, or a CO2 gas separation step as shown in Figure 6 may be performed, or the reaction gas of metallic iron 20 and methane gas in the first step S21 may rise directly in the furnace and be added to the reducing gas in the reduction step S1 as shown in Figure 7, or a combination of these may be performed.

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

[0040] 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 reduction section 110 and the cooling section 120 may be configured to perform the reduction step S1 and the cooling step S2, respectively. As shown in FIGS. 1 to 5, the reduction section 110 may include a reduction gas supply port 110a for supplying a reduction gas and an outlet 110b for discharging a gas after the reduction reaction. The first section 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 section 121. The second section 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 section 122. Further, the third portion 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 portion 123. The reduction portion 110 and the cooling portion 120 may be integrated or separate. For example, as shown in FIG. 1, the reduction portion 110 and the cooling portion 120 may be provided in the shaft furnace 100. Alternatively, as shown in FIG. 2, the reduction portion 110 may be provided in the shaft furnace 100, and the cooling portion 120 may be provided in the cooling device 200 downstream of the shaft furnace 100. Alternatively, as shown in FIG. 3, the reduction portion 110 and the first portion 121 of the cooling portion may be provided in the shaft furnace 100, and the second portion 122 and the third portion 123 of the cooling portion 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 and a cart. From the viewpoint of reducing equipment costs, it is preferable that the reduction section 110 and the cooling section 120 are provided in the shaft furnace 100.In the case where 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] The reduction unit 110 may be supplied with a reduction gas through the reduction gas supply port 110a. The first portion 121 of the cooling unit 120 may be supplied with methane gas through the first cooling gas supply port 121a. The second portion 122 may be supplied with CO gas through the second cooling gas supply port 122a. The third portion 123 may be supplied with methane gas or an inert gas through the third cooling gas supply port 123a. The supply systems of each gas are not particularly limited, and may be, for example, a gas source and a supply port connected by a pipe or the like. The type of reduction gas is as described above. The reduction gas may include, for example, hydrogen gas. The type of gas supplied to the cooling unit 120 is 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 include a temperature raising device 140 that raises the temperature of the exhaust gas from the reduction unit 110 or raises the temperature of the circulation gas obtained by dehydrating the exhaust gas. The temperature raising device 140 may be a device that raises the temperature of the exhaust gas from the reduction unit 110 or the circulation gas obtained by dehydrating the exhaust gas, and hydrogen gas, and produces a reduction gas containing one or both of the exhaust gas and the circulation gas, and hydrogen gas. The dehydration device 130 and the temperature raising device 140 described above may be combined. For example, as shown in Fig. 4, a production system according to one embodiment may include a dehydrator 130 that dehydrates the exhaust gas from the reduction section 110 to obtain a circulating gas, and a temperature increasing device 140 that increases the temperature of the circulating gas and hydrogen gas to obtain a reducing gas containing the circulating gas and hydrogen gas. The dehydrator 130 and the temperature increasing device 140 are for carrying out the above-mentioned dehydration step S3 and temperature increasing step S4, respectively. Details are as described above.

[0043] The exhaust gas system from the reduction section 110 and the cooling section 120 is also as described above. For example, as shown in Figs. 1 to 6, the production system according to an embodiment may have a first cooling gas outlet 121b downstream of the reduction section 110, which discharges the reaction gas of the metallic iron 20 in the first section 121 and the methane gas to the outside of the system. Alternatively, as shown in Fig. 7, the production system according to an embodiment may be connected to the reduction section 110 and the first section 121 so that the reaction gas of the metallic iron 20 in the first section 121 and the methane gas (corresponding to the reaction gas in the first step S21 described above) is added to the reduction gas. In addition, the production system according to an embodiment may have a second cooling gas outlet 122b downstream of the first section 121, which discharges the reaction gas of the metallic iron in the second section 122 and the CO gas (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 to the outside of the system.

[0044] The temperatures of the metallic iron 20 in each of the reduction section 110 and the cooling section 120 are also as described above. For example, in the 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 more and 900°C or less. In addition, in the 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 more and 600°C or less. In addition, in the 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 less than 400°C.

[0045] In the manufacturing system of the present disclosure, when the shaft furnace 100 is used as the reduction section 110, the shaft top pressure is not particularly limited, but may be in the range of 0 MPa to 0.8 MPa in terms of gauge pressure. The pressure can be measured, for example, using a pressure gauge provided at the shaft top.

[0046] In the manufacturing system of the present disclosure, when a cooling tower is used as the cooling unit 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 terms of 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 dehydrator 130 and a heating device 140 as shown in Figure 3.

[0048] 3.Effects As described above, according to the manufacturing method and manufacturing system of this 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 by methane gas, followed by (2) carbonizing the metallic iron 20 by CO gas, and then (3) cooling the metallic iron 20 by 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). EXAMPLES

[0049] 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 gist of the invention is not deviated from and the object is achieved. In the following examples, conditions for increasing the amount of carbonization of reduced iron were examined by numerical simulation. The numerical simulation in the present examples was performed by adding the reactions described as (7), (9), and (10) in the following non-patent document 2 to a shaft furnace mathematical model developed by applying the blast furnace mathematical model described in the following non-patent document 1. Non-patent literature 1: Nishioka et al., "Development of a mathematical model for blast furnaces," Nippon Steel & Sumitomo Metal Technical Review 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 case where reduction process and cooling process are performed in a shaft furnace 1.1 Simulation method A numerical simulation was performed assuming operation in a shaft furnace. First, H2 at 950°C was blown into the iron oxide pellets put into the shaft furnace to allow the reduction reaction to proceed. The temperature of the metallic iron immediately after the reduction reaction was 858°C. Then, for Case 2 and Case 4 (Example), CH4 at 25°C was blown into the metallic iron to perform carbon deposition and cool the metallic iron at the same time. Then, CO gas at 25°C was blown in from below the CH4 blowing port to allow carbon deposition of CO to proceed. Then, for each of Case 1, Case 2, Case 3, and Case 4, CH4 was further blown in from the bottom to lower the temperature to the target temperature as CDRI.

[0051] 1.2 Calculation conditions FIG. 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 FIG. 8 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 a right half and a left half with the central axis as a boundary. For Cases 2 and 4, the reduction zone in FIG. 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 outside the system downstream of the first step S21. The exhaust gas from the third step S23 was used as the cooling gas for the second step S22 as it is.

[0052] Details of Cases 1 to 4 are as follows. Case 1 (Comparative Example): The first step S21 and the second step S22 were not performed, and CH4 was 1400 Nm 3 / min, the temperature of the reduced iron at the outlet of the third process S23 was lowered to the target temperature for CDRI. The pressure at the top of the shaft was 0.04 MPa (gauge pressure). Case 2 (Example): CH4 is 300 Nm in the first step S21 3 / min, and in the second step S22, CO is injected at a flow rate of 700 Nm 3 / min, and in the third step S23, CH4 is injected at a flow rate of 1500 Nm 3 / min, the temperature of the reduced iron at the outlet of the third process S23 was lowered to the target temperature for CDRI. The pressure at the top of the shaft was 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): CH4 is 300 Nm in the first step S21 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, CH4 is injected at a flow rate of 1850 Nm 3 / min, the temperature of the reduced iron at the outlet of the third process S23 was lowered to the target temperature for CDRI. The pressure at the top of the shaft was 0.7 MPa (gauge pressure).

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

[0054] [Table 1]

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

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

[0057] [Table 2]

[0058] The results in Table 2 show the following: In both Case 3 and Case 4, the reduction degree in the product reduced iron was 93 to 94%, and a high reduction degree was ensured. In Case 3 (Comparative Example), although the reduced iron was discharged in a cooled state, a sufficient amount of carbonization was not obtained. In Case 4 (Example), the carbonization amount (carbon concentration) of the discharged reduced iron was high, and the discharge temperature was also reduced to a temperature that was practically sufficiently low.

[0059] 1.4 Calculation result 2 In Case 2, the amount of CH4 injected in the first step S21 was changed so that the temperature of the metallic iron after the first step S21 was about 400 to 600°C (Cases 5 to 11), and the amount of carbonized reduced iron discharged was investigated. For Cases 5 to 11, the flow rates of CH4 injected in the first step S21 are as follows. The calculation conditions and results are shown in Table 3.

[0060] [Table 3]

[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 more and 600° C. or less, preferably 450° C. or more and 550° C. or less. In all of Cases 5 to 11, the reduction degree in 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 amount of CH4 injected in the first step S21 was changed so that the temperature of the metallic iron after the first step S21 was about 400 to 600°C, and nitrogen gas (flow rate: 1700 Nm) was used instead of CH4 in the third step S23. 3 / min) (Cases 12 to 15). The calculation conditions and results are shown in Table 4.

[0063] [Table 4]

[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 decreased. In all of Cases 12 to 15, the reduction degree in 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 condition 1 2.1.1 Comparative Example 1 The simulation conditions for Comparative Example 1 were the same as those for Case 1. That is, first, H2 at 950°C was blown into the iron oxide pellets charged into the shaft furnace to allow the reduction reaction to proceed. The temperature of the metallic iron immediately after the reduction reaction was 858°C. Thereafter, CH4 at 25°C was blown into the metallic iron to perform carbon precipitation and simultaneously cool the metallic iron, thereby obtaining the reduced iron product. The shaft furnace top pressure was 0.04 MPa (gauge pressure). The amount of CH4 supplied, 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 performed assuming that a shaft furnace and a cooling tower were combined and operated. Figure 9 shows the type and introduction position of gas introduced into each of the shaft furnace and the cooling tower. The structure shown in Figure 9 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 and the cooling tower is divided into a right half and a left half with the central axis of the shaft furnace and the cooling tower as a boundary. First, H2 at 950 ° C was blown into the iron oxide pellets put into the shaft furnace to advance the reduction reaction. The temperature of the metallic iron immediately after the reduction reaction was 858 ° C. Then, CH4 at 25 ° C was blown into the metallic iron to perform carbon deposition and cool the metallic iron at the same time. The temperature of the metallic iron at the outlet of the shaft furnace was 533.6 ° C. The supply amount of CH4 in the shaft furnace is as shown in Table 5 below. Next, metallic iron recovered from the outlet of the shaft furnace was charged into the top of the cooling tower, CO at 25°C was blown in downstream of the top to precipitate carbon, and CH4 at 25°C was blown in further downstream to cool the metallic iron and obtain the product reduced iron. The pressure at the top of the shaft furnace and the pressure at the top of the cooling tower were 0.04 MPa (gauge pressure). The amounts of CO and CH4 supplied to the cooling tower, and the temperature and carbon concentration of the product reduced iron are as shown in Table 5 below.

[0067] 2.1.3 Example 2 A simulation was performed in the same manner as in Example 1, except that 100% of the exhaust gas cooled by CH4 was extracted between the CO supply position and the CH4 supply position of the cooling tower as shown in Fig. 10. The supply amounts of CO and CH4 in the cooling tower, 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] [Table 5]

[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 by only performing the reduction of the oxidized iron raw material and the cooling of the metallic iron by methane gas in the shaft furnace. In contrast, as in Examples 1 and 2, the reduction of the oxidized iron raw material and the cooling of the metallic iron are performed in the shaft furnace, and then, in a cooling tower provided separately from the shaft furnace, the metallic iron is carbonized by CO gas, and further, the metallic iron is cooled by methane gas downstream of the cooling device, so that the carbon concentration of the product reduced iron can be improved. That is, 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 is further improved by extracting the exhaust gas cooled by CH4 between the supply position of CO and the supply position of CH4 in the cooling tower. In addition, as in Examples 1 and 2, the shaft furnace and the cooling tower are provided separately, so that the exhaust gas in the cooling tower can be prevented from entering the shaft furnace.

[0071] 2.3 Simulation condition 2 Comparative Example 2 is performed under the same conditions as Case 3, that is, under the same conditions as Comparative Example 1 except that the shaft top pressure is 0.7 MPa (gauge pressure). Example 3 is performed under the same conditions as Example 1 except that the shaft top pressure is 0.7 MPa (gauge pressure). Example 4 is performed under the same conditions as Example 1 except that the shaft top pressure and the cooling tower top pressure are 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] [Table 6]

[0074] The results shown in Table 6 reveal the following: As in Comparative Example 2, the carbon concentration of the product reduced iron cannot be sufficiently increased by only performing the reduction of the oxidized iron raw material in the shaft furnace and the cooling of the metallic iron with methane gas. In contrast, as in Examples 3 and 4, the reduction of the oxidized iron raw material and the cooling of the metallic iron are performed in the shaft furnace, and then, in a cooling tower provided separately from the shaft furnace, the metallic iron is carbonized with CO gas, and further, the metallic iron is cooled with methane gas downstream of the cooling device, thereby improving the carbon concentration of the product reduced iron. That is, reduced iron containing carbon (e.g., CDRI with an increased carbon concentration) can be efficiently produced. Furthermore, as in Examples 3 and 4, the shaft furnace and the cooling tower are provided separately, thereby preventing the exhaust gas in the cooling tower from entering the shaft furnace.

[0075] The same calculation was performed when nitrogen gas was used instead of CH4 in the cooling tower, and the calculation results showed the same tendency as the results shown in Table 5. That is, even if 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 through the following reduction step and cooling step.

[0077] In the reduction step, a reducing gas is brought into contact with the 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. [Explanation of symbols]

[0078] 10. Iron oxide raw materials 20 Metallic Iron 30 Carbon-containing reduced iron 100 Shaft Furnace 100a Raw material supply port 100b outlet 110 Reduction Section 110a Reduction gas supply port 110b reduction gas outlet 120 Cooling section 121 Part 1 121a First cooling gas supply port 121b First cooling gas outlet 122 Part 2 122a Second cooling gas supply port 122b Second cooling gas outlet 123 Part 3 123a 3rd cooling gas supply port 123b 3rd cooling gas outlet 200 Cooling device

Claims

1. A method for producing reduced iron containing carbon, comprising the steps of: A reduction step in which a reducing gas is brought into contact with the iron oxide raw material to obtain metallic iron; and A cooling step of cooling the metallic iron. having The cooling step comprises: a first step of contacting the metallic iron with methane gas after the reduction step to carbonize the metallic iron; a second step of contacting the metallic iron with CO gas after the first step to carbonize the metallic iron; and A third step of contacting the metallic iron with methane gas or an inert gas after the second step. having A method for producing reduced iron.

2. The method for producing reduced iron according to claim 1, 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, The reduction step is carried out in a shaft furnace, 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, The reduction step and the first step are carried out in a shaft furnace, The second step and the third step are performed 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, a transferring 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, The reducing gas comprises hydrogen gas. A method for producing reduced iron.

7. The method for producing reduced iron according to any one of claims 1 to 5, a dehydration step for dehydrating the exhaust gas from the reduction step to obtain a circulating gas; and A temperature increasing step of increasing the temperature of the circulating gas and the hydrogen gas to obtain the reducing gas containing the circulating gas and the hydrogen gas. having A method for producing reduced iron.

8. The method for producing reduced iron according to any one of claims 1 to 5, A 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. A method for producing reduced iron.

9. The method for producing reduced iron according to any one of claims 1 to 5, A reaction gas of the metallic iron and the methane gas in the first step is added to the reducing gas. A method for producing reduced iron.

10. The method for producing reduced iron according to any one of claims 1 to 5, A reaction gas of the metallic iron and the CO gas in the second step is discharged to the outside of the system downstream of the first step. A method for producing reduced iron.

11. The method for producing reduced iron according to any one of claims 1 to 5, The methane gas or inert gas that has come into contact with the metallic iron in the third step is discharged outside the system downstream of the second step. A method for producing reduced iron.

12. A system for producing reduced iron containing carbon, comprising: a reduction section for contacting the iron oxide raw material with a reducing gas to obtain metallic iron; and A cooling section that cools the metallic iron. having The cooling unit is a first section for contacting the metallic iron obtained by the reduction section with methane gas to carbonize the metallic iron; a second portion downstream of the first portion for contacting the metallic iron with CO gas to carbonize the metallic iron; and a third section downstream of the second section, in which methane gas or an inert gas is brought into contact with the metallic iron; having A reduced iron production system.

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

14. The reduced iron production system according to claim 12, The reduction section is provided in a shaft furnace, The cooling section is provided in a cooling device downstream of the shaft furnace. A reduced iron production system.

15. The reduced iron production system according to claim 12, The reduction section and the first section are provided in a shaft furnace, The second portion and the third portion are provided in a cooling device downstream of the shaft furnace. A reduced iron production system.

16. The reduced iron production system according to claim 14, a moving device for moving the metallic iron from the shaft furnace to the cooling device; A reduced iron production system.

17. The reduced iron production system according to any one of claims 12 to 16, The reducing gas comprises hydrogen gas. A reduced iron production system.

18. The reduced iron production system according to any one of claims 12 to 16, A dehydration device that dehydrates the exhaust gas from the reduction section to obtain a circulating gas; and a temperature raising device for raising the temperatures of the circulating gas and the hydrogen gas to obtain the reducing gas containing the circulating gas and the hydrogen gas; The reduced iron production system includes:

19. The reduced iron production system according to any one of claims 12 to 16, a first cooling gas outlet downstream of the reduction section, for discharging a reaction gas of the metallic iron and the methane gas in the first portion to the outside of the system; A reduced iron production system.

20. The reduced iron production system according to any one of claims 12 to 16, The reduction unit and the first portion are connected so that a reaction gas of the metallic iron and the methane gas in the first portion is added to the reducing gas. A reduced iron production system.

21. The reduced iron production system according to any one of claims 12 to 16, 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; A reduced iron production system.

22. The reduced iron production system according to any one of claims 12 to 16, a third cooling gas outlet downstream of the second portion for discharging the methane gas or the inert gas that has come into contact with the metallic iron in the third portion to the outside of the system; A reduced iron production system.

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