WO2025158712A1 - Method and system for producing reduced iron - Google Patents

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

This application discloses a method and system for producing reduced iron.

In the steel industry, a direct reduction process using reducing gas has been studied as an alternative technology to the blast furnace process to reduce _CO2 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, reducing gas is brought into contact with an oxidized iron 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 lowers the melting temperature in the subsequent melting and refining process and ensures the strength of the resulting steel.

International Publication No. 2021/195160 Japanese Unexamined Patent Publication No. 61-073805

Reduced iron can be produced in three product forms: Cold DRI (CDRI), Hot Briquette Iron (HBI), and Hot DRI (HDRI). When producing CDRI using 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 using the direct reduction process, there is room for improvement in cooling the metallic iron obtained after reduction while increasing its carbon concentration.

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:
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,
The cooling step
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.
A method for producing reduced iron.
<Aspect 2>
A method for producing reduced iron according to aspect 1,
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,
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,
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>
The 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 of dehydrating the exhaust gas from the reduction step to obtain a circulating gas; and a temperature raising step of raising the temperatures of the circulating gas and hydrogen gas to obtain the reducing gas containing the circulating gas and the hydrogen gas.
A method for producing reduced iron.
<Aspect 8>
The method for producing reduced iron according to any one of Aspects 1 to 7,
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.
A method for producing reduced iron.
<Aspect 9>
The method for producing reduced iron according to any one of Aspects 1 to 8,
In the first step, a reaction gas of the metallic iron and the methane gas is added to the reducing gas.
A method for producing reduced iron.
<Aspect 10>
The 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 to the outside of 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 that brings a reducing gas into contact with an iron oxide raw material to obtain metallic iron, and a cooling section that cools the metallic iron,
The cooling unit is
a first section that brings methane gas into contact with the metallic iron obtained by the reduction section to carbonize the metallic iron;
a second section downstream of the first section for bringing CO gas into contact with the metallic iron to carbonize the metallic iron; and a third section downstream of the second section for bringing methane gas or an inert gas into contact with the metallic iron.
Reduced iron production system.
<Aspect 13>
A reduced iron production system according to aspect 12, comprising:
The reduction section and the cooling section are provided in a shaft furnace.
Reduced iron production system.
<Aspect 14>
A reduced iron production system according to aspect 12, comprising:
The reduction unit is provided in a shaft furnace,
The cooling section is provided in a cooling device downstream of the shaft furnace.
Reduced iron production system.
<Aspect 15>
A reduced iron production system according to aspect 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.
Reduced iron production system.
<Aspect 16>
The reduced iron production system according to aspect 14 or 15,
a transfer device for transferring the metallic iron from the shaft furnace to the cooling device;
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.
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 circulation gas, and a temperature raising device that raises the temperatures of the circulation gas and hydrogen gas to obtain the reduction gas containing the circulation gas and the hydrogen gas.
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, which discharges a reaction gas of the metallic iron and the methane gas in the first portion to the outside of the system;
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.
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;
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;
Reduced iron production system.

The reduced iron manufacturing method and manufacturing system disclosed herein make it possible to cool metallic iron while increasing the carbon concentration of the metallic iron during the direct reduction process. The reduced iron manufacturing method and manufacturing system disclosed herein make it possible to produce, for example, CDRI with an increased carbon concentration.

FIG. 1 is a schematic diagram for explaining an example of a method and system for producing reduced iron. FIG. 1 is a schematic diagram for explaining an example of a method and system for producing reduced iron. FIG. 1 is a schematic diagram for explaining an example of a method and system for producing reduced iron. FIG. 1 is a schematic diagram for explaining an example of a method and system for producing reduced iron. FIG. 1 is a schematic diagram for explaining an example of a method and system for producing reduced iron. FIG. 1 is a schematic diagram for explaining an example of a method and system for producing reduced iron. FIG. 1 is a schematic diagram for explaining an example of a method and system for producing reduced iron. This is a schematic diagram to explain the type and introduction position of gas introduced into the cooling section of the shaft furnace for each of Cases 1 to 4. FIG. 2 is a schematic diagram for explaining the types and introduction positions of gases introduced into the shaft furnace and the cooling tower in the first embodiment. FIG. 10 is a schematic diagram for explaining the types and introduction positions of gases introduced into the shaft furnace and the cooling tower, respectively, in Example 2.

Below, one embodiment of the disclosed reduced iron manufacturing method and manufacturing system is described. However, the disclosed reduced iron manufacturing method and manufacturing system are not limited to the following embodiment. In this application, "oxidized iron raw material" refers to raw material containing iron oxide before the reduction process. "Metallic iron" refers to the intermediate product after the reduction process until the completion of the cooling process, and for convenience, "metallic iron" also refers to material whose carbon concentration has been increased by carbonization or the like. "Reduced iron" refers to the product obtained after the cooling process. In addition, in this application, "downstream side" refers to the downstream side in the reduced iron manufacturing process. In other words, when reduced iron containing carbon is manufactured 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.

1. Method for Producing Reduced Iron As shown in FIGS. 1 to 7 , a method for producing reduced iron containing carbon according to an embodiment includes the following steps:
a reduction step S1 in which a reducing gas is brought into contact with the oxidized iron 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 CO gas is brought into contact with the metallic iron 20 to carbonize the metallic iron 20; and
After the second step S22, the method includes a third step S23 in which the metallic iron 20 is brought into contact with methane gas or an inert gas.

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.

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.

When the reduction step S1 is performed in the shaft furnace 100, the above-mentioned 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 filling rate of the packed bed is not particularly limited and may be the same as that in conventional reduced iron manufacturing methods 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 falling, etc. When 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. When focusing on a single 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 depending on the supply amount (feed rate) of the above-mentioned raw material. When moving the packed bed downward, a burden feeder or the like may be used to prevent hanging.

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 pronounced effect. 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 or carbon dioxide, 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. Examples of gases other than hydrogen include CO gas, inert gases, _CO2 gas, and steam. Examples of inert gases 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 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.

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 interior 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 the 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 interior of the furnace via the pipe or the like.

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.

When the reduction step S1 is carried out in the shaft furnace 100, the solid reactant containing metallic iron 20 can be recovered from the outlet 100b provided at the bottom of the shaft furnace 100 (below the supply position of the reducing gas).

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.

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.

In the cooling step S2, (1) the metallic iron 20 is carbonized and cooled using methane gas, followed by (2) carbonization of the metallic iron 20 using CO gas, and then (3) cooling of the metallic iron 20 using methane gas or an inert gas. According to the inventor's findings, the carbon deposition reaction caused by methane gas is likely to proceed in the high-temperature range of 700°C or higher and is an endothermic reaction. On the other hand, the carbon deposition reaction caused by CO gas is most likely to proceed between 400°C and 600°C 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 also tends to lower the temperature of the metallic iron 20 to a temperature suitable for the carbon deposition reaction caused 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) cooling with methane gas or an inert gas may be accompanied by carbon deposition.

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 part or all of the cooling step S2 is performed in the cooling device 200, the exhaust gas from 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 a 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 allows the carbon deposition reaction in the first step S21 to proceed more efficiently. Furthermore, the circulation treatment (hydrogen recovery) of the exhaust gas from the reduction step S21 is facilitated. Furthermore, _CO2 can also be efficiently recovered from the second step S22. As shown in FIGS. 2 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 manufacturing 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 to 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 to the cooling device 200 forms a packed bed in the cooling device 200, a greater effect can be expected.

The cooling step S2 includes a first step S21, a second step S22, and a third step S23. In this 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 rise during the cooling step S2. For example, in the second step S22, an exothermic reaction may occur between the metallic iron 20 and CO gas, causing the temperature of the metallic iron 20 to rise.

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 apparatus (e.g., a shaft furnace), the position (height position) P1 when measuring the "temperature of the metallic iron 20" in the first step S21 is downstream (below) of the position (height position) P2 where the reducing gas is blown in in the reduction step S1 and is within 1 m of this position (height position). Alternatively, when the reduction step S1 and the first step S21 are performed in different apparatuses (e.g., the reduction step S1 is performed in a shaft furnace and the first step S21 is performed in a cooling apparatus provided downstream of the shaft furnace), the position P1 when measuring the "temperature of the metallic iron 20" in the first step S21 is within 1 m downstream (below) of the metallic iron supply port of the apparatus where the first step S21 is performed. The average temperature of the metallic iron 20 in the radial direction can be determined, for example, by installing a rod-shaped member in the radial direction of a shaft furnace or a cooling tower, attaching multiple thermocouples to the member, and measuring multiple temperatures in the radial direction. That is, when the first step S21 is performed in a shaft furnace, the average temperature of the metallic iron 20 in the radial direction is determined by a plurality of thermocouples installed in the radial direction of the shaft furnace. Furthermore, when the first step S21 is performed in a cooling tower, the average temperature of the metallic iron 20 in the radial direction is determined by a plurality of thermocouples installed in the radial direction of the cooling tower. Here, for example, assuming that the temperature between measurement points is linearly distributed in the radial direction, the radial temperature distribution T(r) can be expressed as a combination of linear functions of r. In this case, assuming that the temperature is measured at N points, the average temperature T _ave is defined by the following equation, where _ri is the radius of measurement point i (i = 1 to N). Note that r ₀ and r _N+1 correspond to the positions of the furnace center (r ₀ = 0) and the furnace wall (r _N+1 = R), and the temperatures at these points are determined by extrapolation. According to this method, even if a temperature distribution occurs 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 that five or more thermocouples be provided. 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.

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 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, etc. 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 a carbon deposition reaction (endothermic reaction) caused by methane gas. In the first step S21, as long as such an endothermic reaction caused by methane gas proceeds predominantly, part of the gas that comes into contact with the metallic iron 20 may contain a gas that causes an exothermic reaction (for example, CO gas). However, when the gas that contacts the 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. Also, when the gas that contacts the 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 the individual gases. The gas that contacts the 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.

The reaction gas between the metallic iron 20 and methane gas in the first step S21 may contain methane gas and hydrogen gas. This reaction gas may be discharged to the outside of the system as exhaust gas and used as fuel, or may be used as part of the reducing gas described above. For example, as shown in Figures 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 Figure 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.

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 device (for example, a shaft furnace), the position (height position) P3 when measuring the "temperature of the metallic iron 20" in the second step S22 is a position (height position) downstream (below) of the position (height position) P4 where the methane gas is blown in in the first step S21 and within 1 m of the position P4. Alternatively, if the first step S21 and the second step S22 are performed in different apparatuses (for example, 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 when measuring the "temperature of the metallic iron 20" in the second step S22 is a position within 1 m downstream (downward) 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 that comes into 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 is dominant over the temperature increase due to the exothermic reaction, and the temperature of the metallic iron 20 decreases in the second step S22.

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 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). Note that 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. Furthermore, when the gas that comes into contact with the metallic iron 20 in the second step S22 consists of multiple types of gases, for example, the volumetric proportion of CO gas is the largest among the volumetric proportions of each gas. The gas that comes into contact with the metallic iron 20 in the second step S22 contains, for example, 50% by volume or more, 60% by volume or more, or 70% by volume or more of CO gas.

The reaction gas between the metallic iron 20 and 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 first step S21. In particular, as shown in Figures 1 to 7, the reaction gas between 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.

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 (e.g., 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 CO gas is blown in the second step S22 and is within 1 m of this position (height position). Alternatively, when the second step S22 and the third step S23 are performed in different apparatuses (e.g., 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 at which the "temperature of the metallic iron 20" is measured in the third step S23 is within 1 m downstream (below) of the metallic iron supply port of the apparatus in which the third step S23 is performed. The temperature of the methane gas or inert gas that comes into contact with the metallic iron 20 in the third step S23 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.

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 comes into contact with the metallic iron 20 in the second step S22 may contain methane gas or an inert gas. The gas that comes into contact with 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 comes into contact with the metallic iron 20 in the third step S23 contains methane gas, depending on the temperature of the metallic iron 20, the metallic iron 20 may be further carbonized. Examples of inert gases 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 comes into contact with 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, 50% by volume or more, 60% by volume or more, or 70% by volume or more of methane gas, or 50% by volume or more, 60% by volume or more, or 70% by volume or more of inert gas, or a total of 50% by volume or more, 60% by volume or more, or 70% by volume or more of methane gas and inert gas.

If 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 outside 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, if 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 outside the system or may be reused as the inert gas in the third step S23. For example, as shown in Figures 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 outside the system downstream of the second step S22.

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.

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.

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.

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.

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.

1.6 _CO2 Gas Separation Step As shown in FIG. 6 , the method for producing reduced iron according to one embodiment may include a _CO2 gas separation step of separating _CO2 gas contained in the exhaust gas of the second step S22. This allows, for example, the _CO2 gas and CO gas contained in the exhaust gas of the second step S22 to be separated. The CO2 gas separated from the exhaust gas can be used, for example, as the CO gas in the second step S22. Furthermore, the _CO2 gas separated from the exhaust gas is discharged outside the system and can be 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.

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 may be performed below the reduction step S1 in the shaft furnace 100. In this case, as shown in FIG. 7 , the reaction gas between the 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, and used for reduction. Furthermore, as shown in FIGS. 1 to 7 , the reaction gas between 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, CO gas and _CO2 gas discharged from the second step S22 are removed from the reduction step S1. That is, 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 consist only of reducing gas (e.g., hydrogen gas) and water vapor. By subjecting such exhaust gas to the dehydration step S3, it can be reused as reducing gas. Note that methane gas remains in the reaction gas between 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 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 contain methane, it is only about 1% by volume. Therefore, there is almost no effect of concentration of carbon-containing gases due to circulation. In other words, this can be achieved by simply partially discharging the reducing gas outside the system, and no special _CO2 removal step or the like is required when circulating the exhaust gas.

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 or 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, or a _CO2 gas separation step as shown in Figure 6 may be performed. As shown in Figure 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.

2. Reduced Iron Manufacturing System The technology of the present disclosure also has an aspect as a system for manufacturing reduced iron containing carbon. That is, as shown in FIGS. 1 to 7 , a system for manufacturing 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 that cools the metallic iron 20.
Here, the cooling unit 120 has
a first portion 121 in which methane gas is brought into contact with the metallic iron 20 obtained by the reduction portion 110 to carbonize the metallic iron 20;
The apparatus has a second portion 122 downstream of the first portion 121, which brings CO gas into contact with the metallic iron 20 to carbonize the metallic iron 20, and a third portion 123 downstream of the second portion 122, which brings methane gas or an inert gas into contact with the metallic iron 20.

In this embodiment, the reduction step S1 is performed in the reduction section 110, and the cooling step S2 is performed in the cooling section 120. The configurations of the reduction section 110 and the cooling section 120 need only be such that they can perform the reduction step S1 and the cooling step S2, respectively. As shown in Figures 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 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 the 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 the reaction gas of the metallic iron 20 and the CO gas in the second section 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. As shown in Figures 2 and 3, when the cooling device 200 is provided downstream of the shaft furnace 100, the reduced iron production system may also 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 perspective of reducing equipment costs, 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.

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

The reduced iron production system according to this embodiment may include other components in addition to the reduction section 110 and cooling section 120 described above. For example, the reduced iron 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 circulation gas. The reduced iron production system according to one embodiment may also include a heating device 140 that heats the exhaust gas from the reduction section 110 or heats the circulation gas obtained by dehydrating the exhaust gas. The heating device 140 may also heat the exhaust gas from the reduction section 110 or the circulation gas obtained by dehydrating the exhaust gas, and hydrogen gas, to produce a reduction gas containing hydrogen gas and one or both of the exhaust gas and the circulation gas. The dehydration device 130 and heating device 140 described above may also be combined. For example, as shown in FIG. 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 heating device 140 that heats the circulating gas and hydrogen gas to obtain a reducing gas containing the circulating gas and hydrogen gas. The dehydration device 130 and the heating device 140 are used to perform the dehydration step S3 and the heating step S4, respectively. Details are as described above.

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

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 one embodiment of the manufacturing system, 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 one embodiment of the manufacturing system, 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 one embodiment of the manufacturing system, 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.

Furthermore, in the manufacturing system of the present disclosure, when a shaft furnace 100 is used 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 installed at the shaft furnace top.

Furthermore, in the manufacturing system of the present disclosure, if 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 installed at the top of the cooling tower.

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.

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).

The present invention will be further described below with reference to examples, but the present invention is not limited to the following examples. The present invention allows various conditions to be adopted as long as the object is achieved without departing from the gist of the present invention. In the following examples, conditions for increasing the amount of carbonization of reduced iron were investigated by numerical simulation. The numerical simulation in the present examples 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 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)

1. Study on the Reduction Process and Cooling Process 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 iron oxide pellets charged into the shaft furnace to promote the reduction reaction. 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 simultaneously cool the metallic iron. Then, CO gas at 25°C was blown from below the _CH4 blowing port to promote carbon deposition of CO. Then, for Case 1, Case 2, Case 3, and Case 4, _CH4 was blown further from below to lower the temperature to the target temperature for CDRI.

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.

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 injected at a flow rate of 1,400 ^Nm3 /min in the third step S23, thereby lowering the temperature of the reduced iron at the outlet of the third step S23 to the target temperature as CDRI. The pressure at the shaft top was 0.04 MPa (gauge pressure).
Case 2 (Example): In the first step S21, _CH4 was injected at a flow rate of 300 ^Nm3 /min, in the second step S22, CO was injected at a flow rate of 700 ^Nm3 /min, and in the third step S23, _CH4 was injected at a flow rate of 1500 ^Nm3 /min, thereby lowering the temperature of the reduced iron at the outlet of the third step S23 to the target temperature as CDRI. The pressure at the shaft top was 0.04 MPa (gauge pressure).
Case 3 (Comparative Example): The same as Case 1 except that the pressure at the shaft furnace top was changed to 0.7 MPa (gauge pressure).
Case 4 (Example): In the first step S21, _CH4 was injected at a flow rate of 300 ^Nm3 /min, in the second step S22, CO was injected at a flow rate of 500 ^Nm3 /min, and in the third step S23, _CH4 was injected at a flow rate of 1,850 ^Nm3 /min, thereby lowering the temperature of the reduced iron at the outlet of the third step S23 to the target temperature as CDRI. The pressure at the shaft top was 0.7 MPa (gauge pressure).

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

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), 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 practically low enough.

Table 2 below shows the calculation results for Case 3 and Case 4.

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), 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 low enough.

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 would be approximately 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 were as follows. The calculation conditions and results are shown in Table 3.

As shown in Table 3, when the temperature of the metallic iron after the first step is between 400°C and 600°C, and preferably between 450°C and 550°C, the carbon concentration of the ultimately obtained reduced iron is particularly high. Furthermore, in all of Cases 5 to 11, the reduction rate of the product reduced iron was 92 to 94%, ensuring a high reduction rate.

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 would be approximately 400 to 600°C, and similar calculations were also performed for cases (Cases 12 to 15) in which nitrogen gas (flow rate: 1700 ^Nm3 /min) was used instead of _CH4 in the third step S23. The calculation conditions and results are shown in Table 4.

As shown in Table 4, even when an inert gas such as nitrogen gas is used in the third step S23, the carbon concentration of the final reduced iron is hardly reduced. Furthermore, in all of Cases 12 to 15, the reduction rate of the product reduced iron was 92 to 94%, ensuring a high reduction rate.

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 cause a reduction reaction. 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 precipitate carbon and simultaneously cool the metallic iron, thereby obtaining reduced iron as a product. The shaft furnace top pressure was 0.04 MPa (gauge pressure). The _CH4 supply rate, the temperature, and the carbon concentration of the product reduced iron are as shown in Table 5 below.

2.1.2 Example 1
A numerical simulation was performed assuming operation using a shaft furnace and a cooling tower in combination. Figure 9 shows the types and introduction positions of gases introduced into the shaft furnace and the cooling tower. The structure shown in Figure 9 is the left half of a cross section of the furnace interior taken along the central axis of the shaft furnace or the cooling tower, divided into right and left halves along the central axis of the shaft furnace or the cooling tower. First, _H2 at 950°C was blown into iron oxide pellets introduced into the shaft furnace to promote a 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 simultaneously precipitate carbon and cool the metallic iron. The temperature of the metallic iron at the outlet of the shaft furnace was 533.6°C. The _CH4 supply rate to the shaft furnace is 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, thereby obtaining reduced iron as a product. 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, the temperature of the product reduced iron, and the carbon concentration are as shown in Table 5 below.

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 in the cooling tower, as shown in Figure 10. The amounts of CO and _CH4 supplied to the cooling tower, the temperature of the product reduced iron, and the carbon concentration are as shown in Table 1 below.

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.

The results shown in Table 5 reveal the following:
The carbon concentration of the product reduced iron cannot be sufficiently increased simply by reducing the oxidized iron raw materials in a shaft furnace and cooling the metallic iron with methane gas, as in Comparative Example 1. In contrast, as in Examples 1 and 2, 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, the metallic iron is cooled with methane gas downstream of the cooling device. This 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. In particular, as in Example 2, the carbon concentration of the product reduced iron is further increased by extracting the exhaust gas cooled with _CH4 between the CO supply position and the _CH4 supply position of the cooling tower. Furthermore, as in Examples 1 and 2, the shaft furnace and the cooling tower are provided separately, thereby preventing the exhaust gas from the cooling tower from entering the shaft furnace.

2.3 Simulation Condition 2
Comparative Example 2 was performed under the same conditions as Case 3 above, i.e., 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 performed under the same conditions as Example 1 except that the shaft top pressure was set to 0.7 MPa (gauge pressure). Example 4 was performed 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).

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.

The results shown in Table 6 reveal the following:
As in Comparative Example 2, simply reducing the oxidized iron raw materials in a shaft furnace and cooling the metallic iron with methane gas does not sufficiently increase the carbon concentration of the product reduced iron. In contrast, as in Examples 3 and 4, reducing the oxidized iron raw materials in a shaft furnace and cooling the metallic iron are performed, followed by carbonizing the metallic iron with CO gas in a cooling tower provided separately from the shaft furnace. Furthermore, cooling 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, as in Examples 3 and 4, providing the shaft furnace and the cooling tower separately prevents exhaust gas from the cooling tower from entering the shaft furnace.

Similar calculations were also performed when nitrogen gas was used in place of _CH4 in the cooling tower, 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.

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.

In the reduction process, a reducing gas is brought into contact with the iron oxide raw material to obtain metallic iron. In the cooling process, the metallic iron is cooled. Here, the cooling process includes a first process in which, after the reduction process, methane gas is brought into contact with the metallic iron to carbonize the metallic iron; a second process in which, after the first process, CO gas is brought into contact with the metallic iron to carbonize the metallic iron; and a third process in which, after the second process, methane gas or an inert gas is brought into contact with the metallic iron.

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 (22)

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,
The cooling step
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.
A method for producing reduced iron. 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. 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. 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. The method for producing reduced iron according to claim 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. 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. The method for producing reduced iron according to any one of claims 1 to 6,
a dehydration step of dehydrating the exhaust gas from the reduction step to obtain a circulating gas; and a temperature raising step of raising the temperatures of the circulating gas and hydrogen gas to obtain the reducing gas containing the circulating gas and the hydrogen gas.
A method for producing reduced iron. The method for producing reduced iron according to any one of claims 1 to 7,
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.
A method for producing reduced iron. The method for producing reduced iron according to any one of claims 1 to 8,
In the first step, a reaction gas of the metallic iron and the methane gas is added to the reducing gas.
A method for producing reduced iron. The method for producing reduced iron according to any one of claims 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. The method for producing reduced iron according to any one of claims 1 to 10,
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.
A method for producing reduced iron. A system for producing reduced iron containing carbon, comprising:
a reduction section that brings a reducing gas into contact with an iron oxide raw material to obtain metallic iron, and a cooling section that cools the metallic iron,
The cooling unit is
a first section that brings methane gas into contact with the metallic iron obtained by the reduction section to carbonize the metallic iron;
a second section downstream of the first section for bringing CO gas into contact with the metallic iron to carbonize the metallic iron; and a third section downstream of the second section for bringing methane gas or an inert gas into contact with the metallic iron.
Reduced iron production system. The reduced iron production system according to claim 12,
The reduction section and the cooling section are provided in a shaft furnace.
Reduced iron production system. The reduced iron production system according to claim 12,
The reduction unit is provided in a shaft furnace,
The cooling section is provided in a cooling device downstream of the shaft furnace.
Reduced iron production system. 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.
Reduced iron production system. The reduced iron production system according to claim 14 or 15,
a transfer device for transferring the metallic iron from the shaft furnace to the cooling device;
Reduced iron production system. The reduced iron production system according to any one of claims 12 to 16,
The reducing gas comprises hydrogen gas.
Reduced iron production system. The reduced iron production system according to any one of claims 12 to 17,
a dehydration device that dehydrates the 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. The reduced iron production system according to any one of claims 12 to 18,
a first cooling gas outlet downstream of the reduction section, which discharges a reaction gas of the metallic iron and the methane gas in the first portion to the outside of the system;
Reduced iron production system. The reduced iron production system according to any one of claims 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.
Reduced iron production system. The reduced iron production system according to any one of claims 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;
Reduced iron production system. The reduced iron production system according to any one of claims 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;
Reduced iron production system.