Method for producing reduced iron and system for producing reduced iron

Abstract

Disclosed is a new technology capable of preventing circulative concentration of nitrogen gas and reducing heat deficiency when producing reduced iron using a decomposition gas of ammonia as a reducing gas. The method for producing reduced iron according to the present disclosure involves: decomposing ammonia with an ammonia reformer to obtain a reducing gas containing hydrogen gas and nitrogen gas; reducing an iron oxide raw material with the reducing gas inside a shaft furnace; and discharging an exhaust gas to the outside of the shaft furnace. The exhaust gas discharged from the shaft furnace is divided into a first gas and a second gas. The first gas is used as a heating gas for the ammonia reformer, and then used for another process outside the system or released to the atmosphere. The second gas is used for another process outside the system.

Description

Method for producing reduced iron and system for producing reduced iron

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

[0002] A technique for producing reduced iron by reducing iron oxide with a reducing gas in a shaft furnace is known. For example, Patent Document 1 discloses a technique that uses ammonia decomposition gas as the reducing gas. Ammonia decomposition gas can be obtained, for example, by decomposing ammonia into hydrogen gas and nitrogen gas using an ammonia reformer.

[0003] International Publication No. 2023 / 036475

[0004] When producing reduced iron by reducing iron oxide with a reducing gas in a shaft furnace, it is common practice to recirculate the exhaust gas from the shaft furnace and reuse it as the reducing gas. When recirculating and reusing gas in this way, there is a concern that nitrogen gas in the reduced gas will become concentrated if ammonia decomposition gas is used. Furthermore, for ammonia decomposition, it is desirable to heat the ammonia appropriately and efficiently in an ammonia reformer. In other words, when producing reduced iron using ammonia decomposition gas, there is room for improvement in improving the thermal efficiency for ammonia decomposition. This application discloses a new technology that can prevent the circulation concentration of nitrogen gas and improve thermal efficiency when producing reduced iron using ammonia decomposition gas.

[0005] This application discloses the following multiple embodiments as means for solving the above problems. <Embodiment 1> A method for producing reduced iron, comprising: decomposing ammonia in an ammonia reformer to obtain a reducing gas containing hydrogen gas and nitrogen gas; reducing an iron oxide raw material with the reducing gas inside a shaft furnace; and discharging exhaust gas to the outside of the shaft furnace, wherein the exhaust gas discharged from the shaft furnace is divided into a first gas and a second gas, the first gas is used as a heating gas for the ammonia reformer and then used in other processes outside the system or released into the atmosphere, and the second gas is used in other processes outside the system. <Embodiment 2> A method for producing reduced iron according to Embodiment 1, wherein 35% to 81% by volume of the exhaust gas is divided as the first gas. <Embodiment 3> A method for producing reduced iron according to Embodiment 1 or 2, the following relationship: -5.978 × 10 －２ A method for producing reduced iron, wherein the following conditions are met: X + 127.48 ≤ α 800 ≤ X ≤ 1200 α: proportion (volume %) of the first gas separated from the exhaust gas X: temperature (°C) of the reducing gas supplied to the shaft furnace <Aspect 4> A method for producing reduced iron according to aspect 1 or 2, comprising recovering the sensible heat of the exhaust gas discharged from the shaft furnace in a heat exchanger and using it for heating in the ammonia reformer, and the following relationship: -5.978 × 10 －２ A method for producing reduced iron, wherein the following conditions are met: X - 80Y / X + 127.48 ≤ α 800 ≤ X ≤ 1200 0 < Y ≤ 100 α: proportion (volume %) of the first gas separated from the exhaust gas X: temperature (°C) of the reducing gas supplied to the shaft furnace Y: utilization rate (%) of the heat recovered by heat exchange <Aspect 5> A method for producing reduced iron according to aspect 1 or 2, comprising partially burning the reducing gas with oxygen before supplying it to the shaft furnace, wherein the following relationship: -5.978 × 10 －２A method for producing reduced iron, wherein the following conditions are met: X - ZX / 1200 + 127.48 ≤ α 800 ≤ X ≤ 1200 0 < Z ≤ 14 α: proportion (volume %) of the first gas separated from the exhaust gas X: temperature (°C) of the reducing gas supplied to the shaft furnace Z: partial combustion rate (%) of the hydrogen gas contained in the reducing gas <Aspect 6> A method for producing reduced iron according to aspect 1 or 2, comprising: recovering the sensible heat of the exhaust gas discharged from the shaft furnace in a heat exchanger and utilizing the heat recovered by the heat exchanger for heating in the ammonia reformer, and partially burning the reducing gas with oxygen before supplying it to the shaft furnace, and the following relationship: -5.978 × 10 －２A method for producing reduced iron, wherein the following conditions are met: X - 80Y / X - ZX / 1200 + 127.48 ≤ α 800 ≤ X ≤ 1200 0 < Y ≤ 100 0 < Z ≤ 14 α: proportion (volume %) of the first gas separated from the exhaust gas X: temperature (°C) of the reducing gas supplied to the shaft furnace Y: utilization rate (%) of the heat recovered by heat exchange Z: partial combustion rate (%) of the hydrogen gas contained in the reducing gas <Aspect 7> A system for producing reduced iron, comprising an ammonia reformer, a shaft furnace, and a gas distributor, wherein the ammonia reformer comprises an ammonia supply port, a reaction chamber, a heating device, and a reduced gas outlet, the heating device comprises a heating gas supply port and a post-heated gas outlet, the shaft furnace comprises an iron oxide raw material supply port, a reduced gas supply port, an exhaust gas outlet, and a reduced iron outlet, the gas distributor comprises an exhaust gas supply port, a first gas outlet, and a second gas outlet, the ammonia reformer decomposes ammonia supplied from the ammonia supply port to the reaction chamber using thermal energy from the heating device to produce a reduced gas containing hydrogen gas and nitrogen gas, the reduced gas discharged from the reduced gas outlet of the ammonia reformer is supplied to the inside of the shaft furnace from the reduced gas supply port of the shaft furnace via a first pipe, The shaft furnace produces reduced iron by reducing the iron oxide raw material supplied to the interior of the shaft furnace from the iron oxide raw material supply port with the reducing gas, and discharges the reduced iron to the outside of the shaft furnace from the reduced iron discharge port. The exhaust gas discharged from the exhaust gas discharge port of the shaft furnace is supplied to the exhaust gas supply port of the gas distributor via a second pipe. The gas distributor divides the exhaust gas supplied from the shaft furnace into a first gas and a second gas, discharges the first gas from the first gas discharge port and the second gas from the second gas discharge port. The first gas discharged from the first gas discharge port of the gas distributor is supplied to the heating gas supply port of the heating device via a third pipe.A reduced iron production system. <Aspect 8> A reduced iron production system according to aspect 7, wherein the heating device uses the first gas supplied from the first gas outlet as heating gas when heating the ammonia reformer, the heating device discharges the first gas after it has been used as heating gas from the post-heated gas outlet, the first gas discharged from the post-heated gas outlet of the heating device is supplied to other processes outside the system via a fourth pipe or released into the atmosphere, and the second gas discharged from the second gas outlet of the gas distributor is supplied to other processes outside the system via a fifth pipe. －２ A system for producing reduced iron, wherein the exhaust gas is divided into a first gas and a second gas so as to satisfy the following conditions: X + 127.48 ≤ α 800 ≤ X ≤ 1200 α: proportion (volume %) of the first gas separated from the exhaust gas X: temperature (°C) of the reducing gas supplied to the shaft furnace. <Aspect 10> A system for producing reduced iron according to aspect 7 or 8, comprising a heat exchanger, wherein the heat exchanger recovers the sensible heat of the exhaust gas discharged from the shaft furnace, the heat recovered by the heat exchanger is used for heating in the ammonia reformer, and the gas distributor has the following relationship: -5.978 × 10 －２A system for producing reduced iron, wherein the exhaust gas is divided into a first gas and a second gas such that the following conditions are met: X - 80Y / X + 127.48 ≤ α 800 ≤ X ≤ 1200 0 < Y ≤ 100 α: proportion (volume %) of the first gas separated from the exhaust gas X: temperature (°C) of the reducing gas supplied to the shaft furnace Y: utilization rate (%) of the heat recovered by heat exchange <Aspect 11> A system for producing reduced iron according to aspect 7 or 8, comprising a partial combustion device, wherein the partial combustion device partially combusts the reducing gas with oxygen before supplying it to the shaft furnace, and the gas distributor has the following relationship: -5.978 × 10 －２ A system for producing reduced iron, wherein the exhaust gas is divided into a first gas and a second gas such that the following conditions are met: X - ZX / 1200 + 127.48 ≤ α 800 ≤ X ≤ 1200 0 < Z ≤ 14 α: proportion (volume %) of the first gas separated from the exhaust gas X: temperature (°C) of the reducing gas supplied to the shaft furnace Z: partial combustion rate (%) of the hydrogen gas contained in the reducing gas <Aspect 12> A system for producing reduced iron according to aspect 7 or 8, comprising a heat exchanger and a partial combustion device, wherein the heat exchanger recovers the sensible heat of the exhaust gas discharged from the shaft furnace, the heat recovered by the heat exchanger is used for heating in the ammonia reformer, the partial combustion device partially combusts the reducing gas with oxygen before supplying it to the shaft furnace, and the gas distributor has the following relationship: -5.978 × 10 －２ A system for producing reduced iron, which divides the exhaust gas into a first gas and a second gas so that the following conditions are met: X - 80Y / X - ZX / 1200 + 127.48 ≤ α 800 ≤ X ≤ 1200 0 < Y ≤ 100 0 < Z ≤ 14 α: proportion (volume %) of the first gas separated from the exhaust gas X: temperature (°C) of the reducing gas supplied to the shaft furnace Y: utilization rate (%) of the heat recovered by heat exchange Z: partial combustion rate (%) of the hydrogen gas contained in the reducing gas

[0006] According to the technology of the present disclosure, when producing reduced iron using decomposition gas of ammonia as a reducing gas, it is possible to prevent cyclic concentration of nitrogen gas and improve thermal efficiency.

[0007] It is a schematic diagram for explaining a method and a system for producing reduced iron according to an embodiment. It is a schematic diagram for explaining a method and a system for producing reduced iron according to an embodiment. It is a schematic diagram for explaining a method and a system for producing reduced iron according to an embodiment. It is a schematic diagram for explaining a method and a system for producing reduced iron according to an embodiment. It is a schematic diagram for explaining a method and a system for producing reduced iron according to an embodiment. It is a schematic diagram for explaining a method and a system for producing reduced iron according to an embodiment.

[0008] Hereinafter, a method for producing reduced iron and a system for producing reduced iron according to embodiments will be described with reference to the drawings, but the technology of the present disclosure is not limited to the following embodiments.

[0009] 1. Method for Producing Reduced Iron As shown in Fig. 1, the method for producing reduced iron according to an embodiment comprises decomposing ammonia by an ammonia reformer 10 to obtain a reducing gas containing hydrogen gas and nitrogen gas, reducing an iron oxide raw material with the reducing gas inside a shaft furnace 20, and discharging exhaust gas to the outside of the shaft furnace 20. Here, the exhaust gas discharged from the shaft furnace 20 is divided into a first gas and a second gas by a gas distributor 30. After the first gas is used as a heating gas for the ammonia reformer 10, it is used for other processes outside the system or released to the atmosphere. The second gas is used for other processes outside the system.

[0010] 1.1 Production of Reducing Gas In the present embodiment, ammonia is decomposed by the ammonia reformer 10 to produce a reducing gas containing hydrogen gas and nitrogen gas.

[0011] As shown in Fig. 1, the ammonia reformer 10 comprises, for example, an ammonia supply port 11, a reaction chamber 12, a heating device 13, and a reducing gas discharge port 14. As shown in Fig. 1, in the present embodiment, ammonia may be supplied from an ammonia supply source 50 to the reaction chamber 12 via a pipe 47 and the ammonia supply port 11. The ammonia supplied to the reaction chamber 12 is, for example, a gas. In one embodiment, the ammonia supply source 50 may comprise a tank 51 for storing liquefied ammonia and a vaporizer 52 for vaporizing liquefied ammonia, wherein liquefied ammonia is supplied from the tank 51 to the vaporizer 52 via a pipe 46, liquefied ammonia is vaporized in the vaporizer 52, and the ammonia gas obtained by the vaporizer 52 may be supplied to the reaction chamber 12 via the pipe 47 and the ammonia supply port 11. Ammonia supplied to the reaction chamber 12 is decomposed into hydrogen gas and nitrogen gas by utilizing thermal energy from the heating device 13. In the reaction chamber 12, the decomposition reaction of ammonia (e.g., 2NH ３ → N ２ + 3H ２A catalyst may be provided to promote the reaction. As a catalyst, for example, one or both of a noble metal catalyst and a non-noble metal catalyst may be used. Examples of noble metal catalysts include ruthenium and platinum. When a noble metal catalyst is used, for example, the ammonia decomposition reaction can be carried out at a temperature of 300°C to 600°C. Examples of non-noble metal catalysts include nickel and calcium imide. When a non-noble metal catalyst is used, for example, the ammonia decomposition reaction can be carried out at a temperature of 700°C or higher. There are no particular restrictions on the type of catalyst. The heating device 13 heats the inside of the reaction chamber 12 to a temperature suitable for the ammonia decomposition reaction, for example, by heating one or both of the ammonia supplied to the reaction chamber 12 and the catalyst provided in the reaction chamber 12. As will be described later, the heating device 13 uses hydrogen gas contained in the exhaust gas from the shaft furnace 20 as fuel, that is, it uses the heat of combustion of the hydrogen gas to perform heating. The heating temperature by the heating device 13 (the decomposition temperature of ammonia in the reaction chamber 12) may be, for example, 300°C to 1000°C, 600°C to 1000°C, or 700°C to 900°C. The hydrogen gas and nitrogen gas produced by the decomposition of ammonia in the reaction chamber 12 are supplied as reducing gases to the reducing gas supply port 22 of the shaft furnace 20 via the reducing gas outlet 14.

[0012] The reducing gas produced by the ammonia reformer 10 includes hydrogen gas and nitrogen gas, as described above. In addition, the reducing gas may also include ammonia gas that remains without thermal decomposition. Furthermore, the decomposition of ammonia is not limited to the thermal decomposition described above, but can also be partially oxidized using oxygen (for example, 4NH4). ３ +O ２ →2N ２ +2H ２ O+4H ２) may also be used. In this case, the reducing gas may contain water vapor. The hydrogen gas contained in the reducing gas reduces the iron oxide raw material inside the shaft furnace 20, as will be described later. In addition, although the nitrogen gas contained in the reducing gas does not contribute to the reduction of the iron oxide raw material, it may function as a heat source to maintain a high temperature inside the shaft furnace 20. Furthermore, if the reducing gas contains ammonia gas, the ammonia gas may spontaneously thermally decompose into hydrogen gas and nitrogen gas at a temperature of 500°C to 1050°C inside the shaft furnace 20, thereby contributing to the reduction of the iron oxide raw material. Furthermore, if the reducing gas contains water vapor, although the water vapor does not contribute to the reduction of the iron oxide raw material, it may function as a heat source to maintain a high temperature inside the shaft furnace 20. In one embodiment, the reducing gas produced by the ammonia reformer 10 may contain 55% to 75% by volume of hydrogen gas, or 60% to 70% by volume, 25% to 45% by volume of nitrogen gas, or 30% to 40% by volume, and 0% to 20% by volume of other gases other than hydrogen gas and nitrogen gas, or 0% to 10% by volume. Examples of other gases include undecomposed ammonia gas. The concentration of ammonia gas in the reducing gas may be, for example, 0% to 10% by volume, 0% to 5% by volume, 0% to 1% by volume, 0 to 1000 ppm, or 0 to 250 ppm.

[0013] 1.2 Reduction of iron oxide raw material by reducing gas In this embodiment, the iron oxide raw material is reduced by the reducing gas inside the shaft furnace 20, and reduced iron is produced.

[0014] The iron oxide raw material contains iron oxide. The amount of iron oxide contained in the iron oxide raw material may be, for example, 40% by mass or more and 100% by mass or less, or 70% by mass or more and 100% by mass or less. The iron oxide raw material may be one or more selected from, for example, iron ore pellets, iron ore, and sintered ore. In addition to iron oxide, the iron oxide raw material may contain components other than iron oxide. The iron oxide raw material may contain recycled materials. The iron oxide raw material may contain impurities. For example, the iron oxide raw material may contain oxides or hydroxides of elements such as silicon, aluminum, calcium, and magnesium, or compounds such as carbonates. The iron oxide raw material may have a particle size distribution or a uniform particle size. The iron oxide raw material may be molded into pellets, or it may be in the form of lumps, or it may be in other shapes. The particle size of the iron oxide raw material may be, for example, 5.0 mm or more and 20.0 mm or less, or 10.0 mm or more and 15.0 mm or less. Furthermore, the average particle size of the iron oxide raw material may be, for example, 5.0 mm or more and 20.0 mm or less, or 10.0 mm or more and 15.0 mm or less. In this application, the "particle size" of the iron oxide raw material is measured by the diameter of the sieve (sieve opening) when the iron oxide raw material is sieved. When measuring the particle size of the iron oxide raw material, several sieves with different openings are prepared. Specifically, a total of five types of sieves with openings of 20.0 mm, 16.0 mm, 12.5 mm, 9.5 mm, and 6.3 mm are prepared, and the iron oxide raw material is sieved according to the dry sieving test described in JIS Z 8815:1994. At this time, the particle size D of the iron oxide raw material that did not pass through the sieve with the largest opening of 20.0 mm is measured. １ It is assumed to be 20.0 mm. Furthermore, the particle size D of the iron oxide raw material that passed through the sieve with a mesh size of 20.0 mm but did not pass through the sieve with a mesh size of 16.0 mm is also considered. ２ This is considered to be the average of 20.0 mm and 16.0 mm, which is (20.0 + 16.0) / 2 mm. Similarly, for iron oxide raw materials that passed through a sieve with a mesh size of 16.0 mm but did not pass through a sieve with a mesh size of 12.5 mm, particle size D ３Assuming that the particle size is (16.0 + 12.5) / 2 mm, the particle size D of the iron oxide raw material that passed through a sieve with a mesh size of 12.5 mm but did not pass through a sieve with a mesh size of 9.5 mm is calculated. ４ Assuming that the particle size is (12.5 + 9.5) / 2 mm, the particle size D of the iron oxide raw material that passed through a sieve with a mesh size of 9.5 mm but did not pass through a sieve with a mesh size of 6.3 mm is calculated. ５ Assuming that the particle size is (9.5 + 6.3) / 2 mm, the particle size D of the iron oxide raw material that passed through the smallest sieve with a mesh size of 6.3 mm is calculated. ６ It is assumed that (6.3 + 0.0) / 2 mm. Furthermore, in this application, the "average particle size" of the iron oxide raw material means the weighted average value of the particle size of the iron oxide raw material. Specifically, the average particle size of the iron oxide raw material can be measured by obtaining a mass-based particle size distribution by the dry sieving test described in JIS Z 8815:1994, and using the average of the maximum and minimum diameters of each sieve as the representative diameter, and weighting the average by mass. More specifically, as described above, a total of five types of sieves with mesh openings of 20.0 mm, 16.0 mm, 12.5 mm, 9.5 mm, and 6.3 mm are prepared, and the iron oxide raw material is sieved according to the dry sieving test described in JIS Z 8815:1994. At this time, the iron oxide raw material that did not pass through the sieve with the largest mesh opening of 20.0 mm (particle size D １ The mass of 20.0 mm is X １ (g) represents the iron oxide raw material (particle size D) that passed through a sieve with a mesh size of 20.0 mm and did not pass through a sieve with a mesh size of 16.0 mm. ２ The mass of (20.0 + 16.0) / 2 mm is X ２ (g) is the iron oxide raw material (particle size D) that passed through a sieve with a mesh size of 16.0 mm and did not pass through a sieve with a mesh size of 12.5 mm. ３ The mass of (16.0 + 12.5) / 2 mm is X ３ (g) represents iron oxide raw material (particle size D) that passed through a sieve with a mesh size of 12.5 mm and did not pass through a sieve with a mesh size of 9.5 mm. ４ The mass of (12.5 + 9.5) / 2 mm is X ４ (g) represents the iron oxide raw material (particle size D) that passed through a sieve with a mesh size of 9.5 mm and did not pass through a sieve with a mesh size of 6.3 mm.５ The mass of (9.5 + 6.3) / 2 mm is X ５ (g) represents the iron oxide raw material that passed through the smallest sieve with a mesh size of 6.3 mm (particle size D ６ The mass of 3.15 mm is X ６ If (g), the average particle size of the iron oxide raw material (weighted average value of the particle size of the iron oxide raw material) D ａｖｅ D is calculated as follows: ａｖｅ = [X １ ×D １ +X ２ ×D ２ +X ３ ×D ３ +X ４ ×D ４ +X ５ ×D ５ +X ６ ×D ６ ] / [X １ +X ２ +X ３ +X ４ +X ５ +X ６ ]

[0015] The iron oxide raw material is supplied into the shaft furnace 20 via an iron oxide raw material supply port 21 provided in the shaft furnace 20. The iron oxide raw material supply port 21 is located at any position above the reducing gas supply port 22. The iron oxide raw material supply port 21 is located, for example, at the top or apex of the shaft furnace 20. The iron oxide raw material may also be supplied into the shaft furnace 20 by known supply devices such as chutes or hoppers. The temperature of the iron oxide raw material supplied into the shaft furnace 20 (temperature at the iron oxide raw material supply port 21) is not particularly limited. In one embodiment, the temperature may be, for example, above room temperature and below 1100°C, above 500°C and below 1000°C, or above 600°C and below 900°C.

[0016] The reducing gas generated by the ammonia reformer 10 is supplied, for example, from the reducing gas outlet 14 of the ammonia reformer 10 to the reducing gas supply port 22 of the shaft furnace 20 via the first piping 41. The reducing gas supplied into the shaft furnace 20 comes into contact with the aforementioned iron oxide raw material, reducing the iron oxide raw material and generating reduced iron. The position of the reducing gas supply port 22 is any position below the iron oxide raw material supply port 21. The temperature X of the reducing gas supplied into the shaft furnace 20 (temperature of the reducing gas at the reducing gas supply port 22) is not particularly limited and should be any temperature at which the reduction reaction of the iron oxide raw material by hydrogen gas can proceed. The temperature X of the reducing gas supplied into the shaft furnace 20 may be, for example, 800°C to 1200°C, 850°C to 1150°C, or 900°C to 1100°C. The amount of reducing gas supplied into the shaft furnace 20 is not particularly limited, and should be such that the metallization rate of the reduced iron produced by reducing the iron oxide raw material reaches the target metallization rate. The reduced iron generated inside the shaft furnace 20 is discharged to the outside of the shaft furnace 20 through the reduced iron outlet 24. The position of the reduced iron outlet 24 is any position below the reducing gas supply port 22. The reduced iron generated inside the shaft furnace 20 may be cooled inside the shaft furnace 20 before being discharged from the reducing gas supply port 22. The reduced iron discharged from the reduced iron outlet 24 may have a metallization rate of, for example, 80% to 100%. The reduced iron may be porous.

[0017] 1.3 Discharge of gas from the shaft furnace In this embodiment, exhaust gas is discharged to the outside of the shaft furnace 20. Specifically, the reducing gas supplied to the inside of the shaft furnace 20 rises through the inside of the shaft furnace 20 while coming into contact with the iron oxide raw material and causing a reduction reaction, and is discharged to the outside of the shaft furnace 20 as exhaust gas through the exhaust gas outlet 23.

[0018] The exhaust gas outlet 23 is located at any position above the reduction gas supply port 22, and may be located at the same position as the iron oxide raw material supply port 21, or at a different position. The exhaust gas contains nitrogen gas, as well as water vapor produced by the reduction reaction and hydrogen gas not consumed in the reduction reaction. As will be described later, a portion of the exhaust gas containing hydrogen gas is used as the first gas, which is used as the heating gas (fuel) for the heating device 13 of the ammonia reformer 10, and the remainder is used as the second gas, which is used in other processes outside the system. The temperature of the exhaust gas (temperature of the exhaust gas at the exhaust gas outlet 23) is not particularly limited and may be, for example, 300°C to 1100°C, or 400°C to 900°C.

[0019] 1.4 Splitting of exhaust gas by gas distributor In this embodiment, the exhaust gas discharged from the shaft furnace 20 is split into a first gas and a second gas by the gas distributor 30.

[0020] The first gas is used as heating gas (fuel) for the heating device 13 of the ammonia reformer 10 described above, and then either used in other processes outside the system or released into the atmosphere. On the other hand, the second gas is used in other processes outside the system. In this way, by using a portion of the exhaust gas discharged from the shaft furnace 20 to heat the ammonia reformer 10, the thermal efficiency within the system can be improved and the amount of fuel added from outside the system can be reduced. Furthermore, since the first gas, after being used to heat the ammonia reformer 10, is not circulated within the system but is used in other processes outside the system or released into the atmosphere, and the second gas, which is divided by the gas distributor 30, is not circulated within the system but is used in other processes outside the system, the circulation and concentration of nitrogen gas within the system can be prevented. The distribution ratio of the first gas and the second gas by the gas distributor 30 is not particularly limited. Specific examples of distribution ratios will be described later.

[0021] 1.5 Utilization of the First Gas In this embodiment, as described above, the first gas divided by the gas distributor 30 is used as a heating gas for the ammonia reformer 10, and then either used in other processes outside the system or released into the atmosphere.

[0022] In this embodiment, the first gas contains hydrogen gas, which can serve as the heating gas (fuel) for the ammonia reformer 10. In this embodiment, as shown in Figure 1, the first gas, which has been divided by the gas distributor 30, is supplied to the heating device 13, for example, from the first gas outlet 32 ​​via the third pipe 43 and the heating gas supply port 13a. The hydrogen gas contained in the first gas is used as fuel in the heating device 13, and heating is performed by the heating device 13 by burning the hydrogen gas.

[0023] The first gas, after being used as a heating gas in the heating device 13, has a high temperature and may be used as a heat source in other processes outside the system. Alternatively, if hydrogen gas remains in the first gas after being used as a heating gas in the heating device 13, this hydrogen gas may be used as fuel in other processes outside the system. In this application, "other processes outside the system" refers to processes that are different from the liquefied ammonia vaporization process, the ammonia decomposition process in the ammonia reformer 10, the reduction process of iron oxide raw materials in the shaft furnace 20, and the exhaust gas splitting process in the gas distributor 30, and are processes downstream of the splitting process. For example, the first gas, after being used as a heating gas in the heating device 13, may be used as a heat source or fuel in furnaces other than the shaft furnace in the steelworks (for example, one or more of the following: blast furnace, pellet firing furnace, ignition furnace (sintering machine), converter, electric furnace, and rolling mill heating furnace). Alternatively, the first gas, after being used as a heating gas in the heating device 13, may be used for power generation. In one embodiment, the first gas, which is used as a heating gas in the heating device 13 and then discharged from the post-heating gas outlet 13b, may be supplied to a gas tank via the fourth pipe 44, temporarily stored in the gas tank, and then supplied to other processes outside the system, or it may be supplied directly to other processes outside the system via the fourth pipe 44.

[0024] The first gas, after being used as a heating gas in the heating device 13, may be released directly into the atmosphere if the amount of active gas such as hydrogen gas has been reduced. This release into the atmosphere may be done by opening the post-heating gas outlet 13b to the atmosphere, or by connecting a fourth pipe 44 to the post-heating gas outlet 13b and opening the fourth pipe 44 to the atmosphere.

[0025] 1.6 Utilization of the Second Gas In this embodiment, the second gas separated by the gas distributor 30 is used in other processes outside the system. The other processes outside the system in which the second gas is used may be the same processes as those described above in which the first gas is used, or they may be different processes. The second gas after being separated by the gas distributor 30 contains hydrogen gas. This hydrogen gas may be used, for example, as fuel in other processes outside the system. For example, the second gas separated by the gas distributor 30 may be used as fuel in furnaces other than shaft furnaces in a steel mill (for example, one or more of the following: blast furnace, pellet firing furnace, ignition furnace (sintering machine), converter, electric furnace, and rolling mill heating furnace). Alternatively, the second gas separated by the gas distributor 30 may be used for power generation. In one embodiment, the second gas discharged from the second gas outlet 33 of the gas distributor 30 may be supplied to a gas tank via the fifth pipe 45, temporarily stored in the gas tank, and then supplied to other processes outside the system, or it may be supplied directly to other processes outside the system via the fifth pipe 45.

[0026] In this embodiment, as described above, the exhaust gas from the shaft furnace 20 is divided into a first gas and a second gas by the gas distributor 30. Here, the second gas refers to gases other than the first gas. In this embodiment, the second gas, other than the first gas, may be further divided into multiple gases in the gas distributor 30 and supplied to other processes outside the system. For example, the gas distributor 30 may have a third gas outlet (not shown) in addition to the first gas outlet 32 ​​and the second gas outlet 33, and a portion of the second gas may be discharged from the second gas outlet 33, and a portion of the second gas may be discharged from the third gas outlet (a gas outlet arbitrarily provided in addition to the first gas outlet 32 ​​and the second gas outlet 33).

[0027] 1.7 Other Steps The method for producing reduced iron according to this embodiment may include other steps in addition to the ammonia decomposition step in the ammonia reformer 10, the reduction step of the iron oxide raw material in the shaft furnace 20, and the exhaust gas splitting step in the gas distributor 30, as described above. An example of other steps will be described below.

[0028] 1.7.1 Heat exchange of exhaust gas As shown in Figure 2, a method for producing reduced iron according to one embodiment may include recovering the sensible heat of the exhaust gas discharged from the shaft furnace 20 in a heat exchanger 60 and using it for heating in the ammonia reformer 10. More specifically, the exhaust gas discharged from the shaft furnace 20 may be supplied to the heat exchanger 60, and the exhaust gas after sensible heat has been recovered in the heat exchanger 60 may be supplied to the gas distributor 30, while the heat recovered by the heat exchanger 60 may be used for heating in the ammonia reformer 10. In this way, by using the sensible heat of the exhaust gas for heating in the ammonia reformer 10, the thermal efficiency in the system is further improved. The specific form of the heat exchanger 60 is not particularly limited, and it is sufficient if it can recover the sensible heat of the exhaust gas and make the recovered heat available for heating in the ammonia reformer 10. In this embodiment, the utilization rate Y of the heat recovered by heat exchange in the heat exchanger 60 is not particularly limited and may be, for example, 0% or more and 100% or less, or greater than 0% and 100% or less. In particular, a higher utilization rate Y tends to improve the overall efficiency of the process. In this regard, the utilization rate Y may be 10% or more and 100% or less, 20% or more and 100% or less, 30% or more and 100% or less, 40% or more and 100% or less, 50% or more and 100% or less, 60% or more and 100% or less, 70% or more and 100% or less, 80% or more and 100% or less, or 90% or more and 100% or less. In this application, "utilization rate of heat recovered by heat exchange" indicates what percentage of the thermal energy (J) of the exhaust gas recovered by heat exchange was used for heating in the ammonia reformer 10. The utilization rate Y of the heat recovered by heat exchange can be calculated from the amount of heat energy (Je) of the exhaust gas recovered by heat exchange that is used in the ammonia reformer 10, using the following formula. When calculating Je, the reaction heat of ammonia decomposition may also be taken into consideration. Y = Je / J × 100 (%) J = W × Cp × (Tin - Tout) W: Flow rate of the first gas (Nm³) ３ ( / s, or kg / s) Cp: Specific heat of the first gas (J / Nm ３( / K, or J / kg / K) Tin: Temperature of the first gas at the heat exchanger inlet (K) Tout: Temperature of the first gas at the heat exchanger outlet (K) Je = We × Cpe × (Tein - Tout) We: Flow rate of ammonia (Nm³) ３ ( / s, or kg / s) Cp: Specific heat of ammonia (J / Nm ３ ( / K, or J / kg / K) Tein: Temperature (K) at the heat exchanger inlet of ammonia Teout: Temperature (K) at the heat exchanger outlet of ammonia

[0029] 1.7.2 Partial Combustion of Reducing Gas As shown in Figure 3, a method for producing reduced iron according to one embodiment may include partially combusting the reducing gas with oxygen before supplying it to the shaft furnace 20. Partial combustion of the reducing gas is performed, for example, by a partial combustion device 70 provided downstream of the ammonia reformer 10 and upstream of the reducing gas supply port 22 of the shaft furnace 20. The partial combustion device 70 burns a portion of the hydrogen gas contained in the reducing gas with oxygen. By burning a portion of the hydrogen gas contained in the reducing gas in this way, the temperature of the reducing gas can be increased, and the thermal efficiency in the system is further improved. The partial combustion rate Z of the hydrogen gas contained in the reducing gas is not particularly limited and may be, for example, 0% or more and 20% or less, or more than 0% and 15% or less. In this application, "partial combustion rate of hydrogen gas contained in the reducing gas" indicates what volume percentage of the hydrogen gas contained in the reducing gas is partially combusted with oxygen. The partial combustion rate Z of the hydrogen gas contained in the reducing gas can be determined from the concentration of hydrogen gas contained in the reducing gas, the flow rate of the reducing gas, and the amount of oxygen supplied to the reducing gas by the partial combustion device 70.

[0030] As shown in Figure 4, a method for producing reduced iron according to one embodiment may include recovering the sensible heat of the exhaust gas discharged from the shaft furnace 20 in the heat exchanger 60 and using it for heating in the ammonia reformer 10, and partially burning the reduced gas with oxygen before supplying it to the shaft furnace 20. Details of the recovery of sensible heat by heat exchange and the partial combustion of the reduced gas are as described above.

[0031] 1.7.3 The exhaust gas from the dust removal shaft furnace 20 contains dust derived from iron oxide raw materials, etc. As shown in Figure 5, a method for producing reduced iron according to one embodiment may include dust removal from the exhaust gas discharged from the shaft furnace 20. Dust removal from the exhaust gas may be performed by a known dust removal device 80. For example, the dust removal device 80 may be a combination of a dust catcher and a dust collector. The dust collector may be a wet dust collector or a dry dust collector, but a dry dust collector is particularly preferred. The dry dust collector may be a bag filter and an electrostatic precipitator, or both. Dust removal may be performed upstream of the gas distributor 30, as shown in Figure 5, or downstream of the gas distributor 30, or in the gas distributor 30. The exhaust gas after dust removal is in a state more suitable for use as fuel in an ammonia reformer, or as a heat source or fuel in other processes outside the system.

[0032] 1.7.4 Dehydration As described above, the exhaust gas from the shaft furnace 20 contains water vapor generated by the reduction reaction. As shown in Figure 6, a method for producing reduced iron according to one embodiment may include dehydrating the exhaust gas discharged from the shaft furnace 20. Dehydration of the exhaust gas may be carried out by a known dehydration device 90. The dehydration device 90 may have, for example, a mechanism that liquefies water vapor by lowering the temperature of the exhaust gas. Dehydration may be carried out downstream of the gas distributor 30, as shown in Figure 6, or upstream of the gas distributor 30, or in the gas distributor 30. The exhaust gas after dehydration is in a state suitable for use as fuel in an ammonia reformer, or as a heat source or fuel in other processes outside the system.

[0033] 1.8 Specific Examples of Gas Distribution by Gas Distributor In this embodiment, as described above, the exhaust gas discharged from the shaft furnace 20 is divided into a first gas and a second gas by the gas distributor 30, and the first gas is used to heat the ammonia reformer 10, thereby improving the thermal efficiency within the system and reducing the amount of fuel added from outside the system. The distribution ratio of the exhaust gas by the gas distributor 30 is not particularly limited. The more the proportion of the first gas in the total exhaust gas is increased, the more a sufficient amount of heating gas can be supplied to the ammonia reformer 10, thereby supplying or replenishing thermal energy to the ammonia reformer 10 and improving the thermal efficiency within the system. However, if the proportion of the first gas in the total exhaust gas becomes excessive, the first gas will be supplied in excess to the ammonia reformer 10, and the effect of improving thermal efficiency will saturate. In this regard, in this embodiment, the proportion of the first gas in the total exhaust gas may be kept within a predetermined range. From the viewpoint of further improving the thermal efficiency within the system and further reducing the amount of fuel added from outside the system, for example, in the method for producing reduced iron according to one embodiment, 35% to 81% by volume, 39% to 81% by volume, 45% to 75% by volume, or 50% to 70% by volume of the exhaust gas may be divided into first gases.

[0034] In this embodiment, the distribution ratio of the exhaust gas by the gas distributor 30 may be determined based on the temperature X of the reducing gas supplied to the shaft furnace 20, the utilization rate Y of the heat recovered by heat exchange in the heat exchanger 60, and the partial combustion rate Z of the hydrogen gas contained in the reducing gas. In other words, the gas distributor 30 may have a control unit that controls the distribution ratio of the exhaust gas, and the control unit may determine the distribution ratio of the exhaust gas in the gas distributor 30 based on one or more of the temperature X of the reducing gas supplied to the shaft furnace 20, the utilization rate Y of the heat recovered by heat exchange, and the partial combustion rate Z of the hydrogen gas contained in the reducing gas, and control the division of the exhaust gas by the gas distributor 30 based on the determined distribution ratio. For example, if the temperature X of the reducing gas blown into the shaft furnace 20 is high, it is possible to produce reduced iron even if the flow rate of the reducing gas is low. When the temperature X is high and the flow rate of the reducing gas is low, the temperature of the exhaust gas discharged from the shaft furnace 20 is high, but the flow rate of the exhaust gas decreases, and the amount of heat contained in the first gas after distribution by the gas distributor 30 also decreases. On the other hand, if the flow rate of the reducing gas is small, the amount of ammonia decomposed in the ammonia reformer 10 can also be reduced. As a result, even if the amount of first gas distributed to the ammonia reformer 10 is reduced, a heat deficiency in the ammonia reformer 10 is less likely to occur. If the utilization rate Y of the heat recovered by heat exchange in the heat exchanger 60 is high, the ammonia reformer 10 can be heated using the sensible heat of the exhaust gas, so even if the amount of first gas distributed to the ammonia reformer 10 is reduced, a heat deficiency in the ammonia reformer 10 is less likely to occur. Furthermore, when the partial combustion rate Z of hydrogen gas contained in the reducing gas is increased, the proportion of hydrogen gas that contributes to the endothermic reduction reaction in the reducing gas blown into the shaft furnace 20 relatively decreases, while the proportion of nitrogen gas and water vapor that do not contribute to the reduction reaction but function as heat sources relatively increases. As a result, the temperature of the exhaust gas discharged from the shaft furnace 20 increases, and the amount of heat contained in the first gas after distribution by the gas distributor 30 also increases. Consequently, even if the amount of first gas distributed to the ammonia reformer 10 is reduced, a heat deficiency in the ammonia reformer 10 becomes less likely.

[0035] As a result of diligent research, the inventors have found the following: Based on the temperature X of the reducing gas injected into the shaft furnace 20, the utilization rate Y of the heat recovered by heat exchange in the heat exchanger 60, and the partial combustion rate Z of the hydrogen gas contained in the reducing gas, the proportion α (volume %) of the first gas separated from the exhaust gas is determined such that the following relationship is satisfied. This ensures that a sufficient amount of the first gas is supplied to the ammonia reformer 10, preventing heat deficiency in the ammonia reformer 10, improving the thermal efficiency within the system, and reducing the amount of fuel added from outside the system.

[0036] That is, as shown in Figures 2 and 4, if the method for producing reduced iron according to one embodiment includes recovering the sensible heat of the exhaust gas discharged from the shaft furnace 20 in the heat exchanger 60 and using it for heating in the ammonia reformer 10, then the following relationship: -5.978 × 10 －２ X - 80Y / X + 127.48 ≤ α 800 ≤ X ≤ 1200 0 < Y ≤ 100 α: proportion (volume %) of the first gas separated from the exhaust gas X: temperature (°C) of the reducing gas supplied to the shaft furnace Y: utilization rate (%) of the heat recovered by heat exchange The exhaust gas may be divided into a first gas and a second gas by the gas distributor 30 so as to satisfy the following conditions.

[0037] Alternatively, as shown in Figures 3 and 4, if the method for producing reduced iron according to one embodiment includes partially burning the reducing gas with oxygen before supplying it to the shaft furnace 20, then the following relationship applies: -5.978 × 10 －２ X - ZX / 1200 + 127.48 ≤ α 800 ≤ X ≤ 1200 0 < Z ≤ 14 α: proportion (volume %) of the first gas separated from the exhaust gas X: temperature (°C) of the reducing gas supplied to the shaft furnace Z: partial combustion rate (%) of the hydrogen gas contained in the reducing gas The exhaust gas may be divided into a first gas and a second gas by the gas distributor 30 so as to satisfy the following conditions.

[0038] Alternatively, as shown in Figure 4, if the method for producing reduced iron according to one embodiment includes recovering the sensible heat of the exhaust gas discharged from the shaft furnace 20 in the heat exchanger 60 and using the heat recovered by the heat exchanger 60 for heating in the ammonia reformer 10, and partially burning the reduced gas with oxygen before supplying it to the shaft furnace 20, then the following relationship applies: -5.978 × 10 －２ X - 80Y / X - ZX / 1200 + 127.48 ≤ α 800 ≤ X ≤ 1200 0 < Y ≤ 100 0 < Z ≤ 14 α: proportion (volume %) of the first gas separated from the exhaust gas X: temperature (°C) of the reducing gas supplied to the shaft furnace Y: utilization rate (%) of the heat recovered by heat exchange Z: partial combustion rate (%) of the hydrogen gas contained in the reducing gas The exhaust gas may be divided into a first gas and a second gas by the gas distributor 30 so as to satisfy the following conditions.

[0039] Alternatively, in this embodiment, the following relationship may be satisfied regardless of whether the sensible heat of the exhaust gas is recovered by the heat exchanger 60 or whether or not there is partial combustion of the reducing gas. That is, in the method for producing reduced iron according to one embodiment, the following relationship: -5.978 × 10 －２ X + 127.48 ≤ α 800 ≤ X ≤ 1200 α: proportion (volume %) of the first gas separated from the exhaust gas X: temperature (°C) of the reducing gas supplied to the shaft furnace The exhaust gas may be divided into a first gas and a second gas by the gas distributor 30 so as to satisfy the following conditions. In this case, the method for producing reduced iron may or may not include recovering the sensible heat of the exhaust gas discharged from the shaft furnace 20 in a heat exchanger 60 and using the heat recovered by the heat exchanger 60 for heating in the ammonia reformer 10, and may or may not include partially burning the reducing gas with oxygen before supplying it to the shaft furnace 20.

[0040] 2. Reduced Iron Production System In addition to the reduced iron production method described above, the technology of this disclosure also includes the following reduced iron production system. That is, as shown in Figure 1, a reduced iron production system 100 according to one embodiment comprises an ammonia reformer 10, a shaft furnace 20, and a gas distributor 30. The ammonia reformer 10 comprises an ammonia supply port 11, a reaction chamber 12, a heating device 13, and a reduced gas outlet 14. The heating device 13 comprises a heating gas supply port 13a and a post-heated gas outlet 13b. The shaft furnace 20 comprises an iron oxide raw material supply port 21, a reduced gas supply port 22, an exhaust gas outlet 23, and a reduced iron outlet 24. The gas distributor 30 comprises an exhaust gas supply port 31, a first gas outlet 32, and a second gas outlet 33. The ammonia reformer 10 decomposes the ammonia supplied from the ammonia supply port 11 to the reaction chamber 12 using thermal energy from the heating device 13 to produce a reduced gas containing hydrogen gas and nitrogen gas. The reduced gas discharged from the reduced gas outlet 14 of the ammonia reformer 10 is supplied to the inside of the shaft furnace 20 via the first piping 41 through the reduced gas supply port 22 of the shaft furnace 20. The shaft furnace 20 reduces the iron oxide raw material supplied to the inside of the shaft furnace 20 from the iron oxide raw material supply port 21 with the reduced gas to produce reduced iron, and discharges the reduced iron to the outside of the shaft furnace from the reduced iron outlet 24. The exhaust gas discharged from the exhaust gas outlet 23 of the shaft furnace 20 is supplied to the exhaust gas supply port 31 of the gas distributor 30 via the second piping 42. The gas distributor 30 divides the exhaust gas supplied from the shaft furnace 20 into a first gas and a second gas, and discharges the first gas from the first gas outlet 32 ​​and the second gas from the second gas outlet 33. The first gas discharged from the first gas outlet 32 ​​of the gas distributor 30 is supplied to the heating gas supply port 13a of the heating device 13 via the third pipe 43.The heating device 13 uses the first gas supplied from the first gas outlet 32 ​​as heating gas when heating the ammonia reformer 10. The heating device 13 discharges the first gas, after it has been used as heating gas, from the post-heated gas outlet 13b. The first gas discharged from the post-heated gas outlet 13b of the heating device 13 is supplied to other processes outside the system via the fourth pipe 44 or released into the atmosphere. The second gas discharged from the second gas outlet 33 of the gas distributor 30 is supplied to other processes outside the system via the fifth pipe 45.

[0041] The ammonia reformer 10, shaft furnace 20, gas distributor 30, piping 41-47, and ammonia supply source 50 are as described above, and a detailed explanation is omitted here. In the reduced iron production system according to this embodiment, the distribution ratio of the exhaust gas by the gas distributor 30 may be as follows, similar to the reduced iron production method described above.

[0042] In other words, in a reduced iron production system according to one embodiment, the gas distributor 30 may divide the exhaust gas into first gases that are 35% to 81% by volume, 39% to 81% by volume, 45% to 75% by volume, or 50% to 70% by volume.

[0043] Furthermore, as shown in Figures 2 and 4, the reduced iron production system according to one embodiment may also include a heat exchanger 60. Here, the heat exchanger 60 recovers the sensible heat of the exhaust gas discharged from the shaft furnace 20, and the heat recovered by the heat exchanger 60 may be used for heating in the ammonia reformer 10. In this case, the gas distributor 30 has the following relationship: -5.978 × 10 －２ X - 80Y / X + 127.48 ≤ α 800 ≤ X ≤ 1200 0 < Y ≤ 100 α: proportion (volume %) of the first gas separated from the exhaust gas X: temperature (°C) of the reducing gas supplied to the shaft furnace Y: utilization rate (%) of the heat recovered by heat exchange The exhaust gas may be divided into a first gas and a second gas so as to satisfy the following conditions.

[0044] Furthermore, as shown in Figures 3 and 4, the reduced iron production system according to one embodiment may include a partial combustion device 70. Here, the partial combustion device 70 may partially combust the reducing gas with oxygen before supplying it to the shaft furnace 20. In this case, the gas distributor 30 has the following relationship: -5.978 × 10 －２ X - ZX / 1200 + 127.48 ≤ α 800 ≤ X ≤ 1200 0 < Z ≤ 14 α: proportion (volume %) of the first gas separated from the exhaust gas X: temperature (°C) of the reducing gas supplied to the shaft furnace Z: partial combustion rate (%) of the hydrogen gas contained in the reducing gas The exhaust gas may be divided into a first gas and a second gas so as to satisfy the following conditions.

[0045] Furthermore, as shown in Figure 4, the reduced iron production system according to one embodiment may also include a heat exchanger 60 and a partial combustion device 70. Here, the heat exchanger 60 recovers the sensible heat of the exhaust gas discharged from the shaft furnace 20, and the heat recovered by the heat exchanger 60 may be used for heating in the ammonia reformer 10. The partial combustion device 70 may partially combust the reduced gas with oxygen before supplying it to the shaft furnace 20. In this case, the gas distributor 30 has the following relationship: -5.978 × 10 －２ X - 80Y / X - ZX / 1200 + 127.48 ≤ α 800 ≤ X ≤ 1200 0 < Y ≤ 100 0 < Z ≤ 14 α: proportion (volume %) of the first gas separated from the exhaust gas X: temperature (°C) of the reducing gas supplied to the shaft furnace Y: utilization rate (%) of the heat recovered by heat exchange Z: partial combustion rate (%) of the hydrogen gas contained in the reducing gas The exhaust gas may be divided into a first gas and a second gas so as to satisfy the following conditions.

[0046] Alternatively, in one embodiment of the reduced iron production system, the distribution ratio by the gas distributor 30 may be determined according to the temperature of the reducing gas supplied to the shaft furnace, regardless of the presence or absence of the heat exchanger 60 and partial combustion device 70 described above. That is, the gas distributor 30 has the following relationship: -5.978 × 10 －２X + 127.48 ≤ α 800 ≤ X ≤ 1200 α: proportion (volume %) of the first gas separated from the exhaust gas X: temperature (°C) of the reducing gas supplied to the shaft furnace The exhaust gas may be divided into a first gas and a second gas so as to satisfy the following conditions.

[0047] Furthermore, the reduced iron production system according to one embodiment may include a dust removal device 80, as shown in Figure 5, or a dewatering device 90, as shown in Figure 6.

[0048] 3. Supplementary Information In the method for producing reduced iron and the reduced iron production system according to this embodiment, the components shown in Figures 1 to 6 may be combined in any way. For example, the method for producing reduced iron and the reduced iron production system shown in Figures 1 to 4 may be equipped with either or both of the dust removal device 80 shown in Figure 5 and the dewatering device 90 shown in Figure 6.

[0049] 4. Effects As described above, the method for producing reduced iron and the system for producing reduced iron according to this embodiment make it possible to prevent the circulation and concentration of nitrogen gas when producing reduced iron using ammonia decomposition gas as the reducing gas, and to improve thermal efficiency.

[0050] The effects of the technology of this disclosure will be explained in more detail below with reference to examples. In the following examples, preferred conditions for the distribution ratio of exhaust gas by the gas distributor (the proportion α of the first gas separated from the exhaust gas) in the method for producing reduced iron and the reduced iron system according to the above embodiment are shown by simulation. However, the distribution ratio α of exhaust gas by the gas distributor in the technology of this disclosure is not limited to the following examples.

[0051] 1. Calculation conditions: Ammonia is decomposed in an ammonia reformer (2NH ３ →N ２ +3H ２To simulate the production of reduced iron (metallization rate: 95%) by supplying a reducing gas to the inside of a shaft furnace and supplying iron oxide raw material (iron content: 65%, temperature: room temperature) to the inside of the shaft furnace and reducing the iron oxide raw material with the reducing gas, a simulation was performed using a one-dimensional model. The one-dimensional model corresponds to a mathematical model of the shaft furnace and was constructed based on chemical engineering methods described in non-patent literature ("Hara et al., Iron and Steel, Vol. 62 (1976), No. 3, p. 315", "Yamaoka et al., Iron and Steel, Vol. 74 (1988), No. 12, p. 2254"), and can theoretically analyze and estimate heat and mass transfer inside the shaft furnace, including chemical reactions such as the reduction reaction of iron oxide by the reducing gas and heat transfer phenomena. In this simulation, the supply temperature X of the reducing gas, the utilization rate Y of the heat recovered by heat exchange, the partial combustion rate Z of the reducing gas, and the distribution ratio α of the exhaust gas were changed as shown in (1) to (4) below. (1) Ammonia decomposition gas is supplied to the shaft furnace at a temperature of X (°C) as a reducing gas. (2) Sensible heat of the exhaust gas from the shaft furnace is recovered by heat exchange, and the heat recovered by said heat exchange is used for the decomposition of ammonia at a utilization rate of Y (%). (3) Before supplying the reducing gas to the shaft furnace, a portion of the hydrogen gas contained in the reducing gas is burned with oxygen at a partial combustion rate of Z (%). (4) The exhaust gas from the shaft furnace is divided into a first gas and a second gas, and the first gas is used as a heating gas for the decomposition of ammonia. Here, α (volume %) of the exhaust gas is divided as the first gas.

[0052] In this embodiment, the required amount of reducing gas corresponding to each reducing gas temperature was calculated using a one-dimensional model. That is, in this embodiment, the amount of reducing gas injected into the shaft furnace was varied according to the reducing gas injection temperature X so that the reduction rate of the ultimately produced reduced iron would be the same. Specifically, the calculation was performed while ensuring that the amount of reducing gas injected and the reducing gas injection temperature satisfied the following relationship (A). The basis for deriving relationship (A) is described in paragraphs 0043 to 0044 of Patent Document: International Publication No. 2025 / 169851 (WO2025 / 169851A1), etc.

[0053] R = 0.0068X ２ -16.074X + 10875 (A) R: Amount of reducing gas supplied (Nm) ３ / t-DRI) X: Supply temperature of reducing gas (°C)

[0054] Next, the reaction heat, the sensible heat of reduced iron, and the sensible heat of the exhaust gas were calculated.

[0055] Finally, the thermal balance of the entire system, including the exhaust gas system, was calculated under each condition. The required heat (reaction heat for ammonia decomposition, reaction heat for reduction, sensible heat of reduced iron, and sensible heat of exhaust gas) was calculated under the same standard conditions (0°C, 101325 Pa). Furthermore, when exhaust gas heat exchange was performed, it was assumed that the introduction temperature of the exhaust gas into the heat exchanger was approximately the same as the furnace top gas temperature, and the heat exchange efficiency was set to 85%. Additionally, when partial combustion of the raw material gas with oxygen was performed, the calculation was performed assuming that the temperature of the reducing gas increased due to this partial combustion to reach the supply temperature X.

[0056] 2. Calculation Results Tables 1 to 4 below show the conditions under which operation was possible without additional fuel being added from outside the system (i.e., no heat deficiency occurred in the ammonia reformer or shaft furnace), by performing calculations while varying the supply temperature X of the reducing gas, the utilization rate Y of the heat recovered by heat exchange, the partial combustion rate Z of the reducing gas, and the distribution ratio α of the exhaust gas.

[0057] The results shown in Tables 1-4 indicate that 35% to 81% of the exhaust gas from the shaft furnace is separated as the first gas and used as heating gas for the ammonia reformer, enabling operation without the need to add additional fuel from outside the system.

[0058] Furthermore, from the results shown in Tables 1 to 3, the relationship between the supply temperature X of the reducing gas, the utilization rate Y of the heat recovered by heat exchange, the partial combustion rate Z of the reducing gas, and the distribution ratio α of the exhaust gas can be determined to be one of the following conditions (A) to (D) under which operation is possible without adding additional fuel from outside the system.

[0059] (A) When the sensible heat of the exhaust gas discharged from the shaft furnace is recovered in a heat exchanger and used for heating in the ammonia reformer, the following relationship applies: -5.978 × 10 －２ The following conditions are met: X - 80Y / X + 127.48 ≤ α 800 ≤ X ≤ 1200 0 < Y ≤ 100 α: proportion (volume %) of the first gas separated from the exhaust gas X: temperature (°C) of the reducing gas supplied to the shaft furnace Y: utilization rate (%) of the heat recovered by heat exchange.

[0060] (B) When the reducing gas is partially combusted with oxygen before being supplied to the shaft furnace, the following relationship applies: -5.978 × 10 －２ X - ZX / 1200 + 127.48 ≤ α 800 ≤ X ≤ 1200 0 < Z ≤ 14 α: proportion (volume %) of the first gas separated from the exhaust gas X: temperature (°C) of the reducing gas supplied to the shaft furnace Z: partial combustion rate (%) of the hydrogen gas contained in the reducing gas The conditions are met.

[0061] (C) When the sensible heat of the exhaust gas discharged from the shaft furnace is recovered in a heat exchanger and the heat recovered by the heat exchanger is used for heating in the ammonia reformer, and the reducing gas is partially combusted with oxygen before being supplied to the shaft furnace, the following relationship: -5.978 × 10 －２X - 80Y / X - ZX / 1200 + 127.48 ≤ α 800 ≤ X ≤ 1200 0 < Y ≤ 100 0 < Z ≤ 14 α: proportion (volume %) of the first gas separated from the exhaust gas X: temperature (°C) of the reducing gas supplied to the shaft furnace Y: utilization rate (%) of the heat recovered by heat exchange Z: partial combustion rate (%) of the hydrogen gas contained in the reducing gas The conditions are met.

[0062] (D) Regardless of whether or not sensible heat is recovered from the exhaust gas discharged from the shaft furnace, or whether or not partial combustion is performed with oxygen before supplying the reducing gas to the shaft furnace, the following relationship applies: -5.978 × 10 －２ The following conditions are met: X + 127.48 ≤ α 800 ≤ X ≤ 1200 α: proportion (volume %) of the first gas separated from the exhaust gas X: temperature (°C) of the reducing gas supplied to the shaft furnace.

[0063] 100 Reduced Iron Production System 10 Ammonia reformer 11 Ammonia supply port 12 Reaction chamber 13 Heating device 13a Heating gas supply port 13b Post-heating gas outlet 14 Reduced gas outlet 20 Shaft furnace 21 Iron oxide raw material supply port 22 Reduced gas supply port 23 Exhaust gas outlet 24 Reduced iron outlet 30 Gas distributor 31 Exhaust gas supply port 32 First gas outlet 33 Second gas outlet 41, 42, 43, 44, 45 Piping 50 Ammonia supply source 51 Tank 52 Vaporizer 60 Heat exchanger 70 Partial combustion device 80 Dust removal device 90 Dehydration device

Claims

1. A method for producing reduced iron, comprising: decomposing ammonia in an ammonia reformer to obtain a reducing gas containing hydrogen gas and nitrogen gas; reducing iron oxide raw materials with the reducing gas inside a shaft furnace; and discharging exhaust gas to the outside of the shaft furnace, wherein the exhaust gas discharged from the shaft furnace is divided into a first gas and a second gas by a gas distributor; the first gas is used as a heating gas for the ammonia reformer and then used in other processes outside the system or released into the atmosphere; and the second gas is used in other processes outside the system.

2. A method for producing reduced iron according to claim 1, wherein 35% by volume or more and 81% by volume or less of the exhaust gas is separated as the first gas.

3. A method for producing reduced iron according to claim 1 or 2, wherein the following relationship: -5.978 × 10 －２ A method for producing reduced iron, wherein the following conditions are met: X + 127.48 ≤ α 800 ≤ X ≤ 1200 α: proportion (volume %) of the first gas separated from the exhaust gas X: temperature (°C) of the reducing gas supplied to the shaft furnace.

4. A method for producing reduced iron according to claim 1 or 2, comprising recovering the sensible heat of the exhaust gas discharged from the shaft furnace in a heat exchanger and using it for heating in the ammonia reformer, with the following relationship: -5.978 × 10 －２ A method for producing reduced iron, wherein the following conditions are met: X - 80Y / X + 127.48 ≤ α 800 ≤ X ≤ 1200 0 < Y ≤ 100 α: proportion (volume %) of the first gas separated from the exhaust gas X: temperature (°C) of the reducing gas supplied to the shaft furnace Y: utilization rate (%) of the heat recovered by heat exchange 5. A method for producing reduced iron according to claim 1 or 2, comprising partially burning the reducing gas with oxygen before supplying it to the shaft furnace, the following relationship: -5.978 × 10 －２ A method for producing reduced iron, wherein the following conditions are met: X - ZX / 1200 + 127.48 ≤ α 800 ≤ X ≤ 1200 0 < Z ≤ 14 α: proportion (volume %) of the first gas separated from the exhaust gas X: temperature (°C) of the reducing gas supplied to the shaft furnace Z: partial combustion rate (%) of the hydrogen gas contained in the reducing gas 6. A method for producing reduced iron according to claim 1 or 2, comprising: recovering the sensible heat of the exhaust gas discharged from the shaft furnace in a heat exchanger and utilizing the heat recovered by the heat exchanger for heating in the ammonia reformer; and partially burning the reduced gas with oxygen before supplying it to the shaft furnace, with the following relationship: -5.978 × 10 －２ A method for producing reduced iron, wherein the following conditions are met: X - 80Y / X - ZX / 1200 + 127.48 ≤ α 800 ≤ X ≤ 1200 0 < Y ≤ 100 0 < Z ≤ 14 α: proportion (volume %) of the first gas separated from the exhaust gas X: temperature (°C) of the reducing gas supplied to the shaft furnace Y: utilization rate (%) of the heat recovered by heat exchange Z: partial combustion rate (%) of the hydrogen gas contained in the reducing gas 7. A system for producing reduced iron, comprising an ammonia reformer, a shaft furnace, and a gas distributor, wherein the ammonia reformer comprises an ammonia supply port, a reaction chamber, a heating device, and a reduced gas outlet, the heating device comprises a heating gas supply port and a post-heated gas outlet, the shaft furnace comprises an iron oxide raw material supply port, a reduced gas supply port, an exhaust gas outlet, and a reduced iron outlet, the gas distributor comprises an exhaust gas supply port, a first gas outlet, and a second gas outlet, the ammonia reformer decomposes ammonia supplied from the ammonia supply port to the reaction chamber using thermal energy from the heating device to produce a reduced gas containing hydrogen gas and nitrogen gas, the reduced gas discharged from the reduced gas outlet of the ammonia reformer is supplied through a first pipe to the interior of the shaft furnace from the reduced gas supply port of the shaft furnace, The shaft furnace produces reduced iron by reducing the iron oxide raw material supplied to the interior of the shaft furnace from the iron oxide raw material supply port with the reducing gas, and discharges the reduced iron to the outside of the shaft furnace from the reduced iron discharge port. The exhaust gas discharged from the exhaust gas discharge port of the shaft furnace is supplied to the exhaust gas supply port of the gas distributor via a second pipe. The gas distributor divides the exhaust gas supplied from the shaft furnace into a first gas and a second gas, and discharges the first gas from the first gas discharge port and the second gas from the second gas discharge port. The first gas discharged from the first gas discharge port of the gas distributor is supplied to the heating gas supply port of the heating device via a third pipe. When the heating device heats the ammonia reformer, it uses the first gas supplied from the first gas discharge port as heating gas. The heating device discharges the first gas, after it has been used as heating gas, from the post-heated gas discharge port. The first gas discharged from the post-heating gas outlet of the heating device is supplied to other processes outside the system via the fourth piping, or released into the atmosphere.A reduced iron production system wherein the second gas discharged from the second gas outlet of the gas distributor is supplied to other processes outside the system via a fifth pipe.

8. A system for producing reduced iron according to claim 7, wherein the gas distributor divides 35% by volume or more and 81% by volume or less of the exhaust gas as the first gas.

9. A system for producing reduced iron according to claim 7 or 8, wherein the gas distributor has the following relationship: -5.978 × 10 －２ A system for producing reduced iron, which divides the exhaust gas into a first gas and a second gas so that the following conditions are met: X + 127.48 ≤ α 800 ≤ X ≤ 1200 α: proportion (volume %) of the first gas separated from the exhaust gas X: temperature (°C) of the reducing gas supplied to the shaft furnace 10. A system for producing reduced iron according to claim 7 or 8, comprising a heat exchanger, the heat exchanger recovering the sensible heat of the exhaust gas discharged from the shaft furnace, the heat recovered by the heat exchanger being used for heating in the ammonia reformer, and the gas distributor having the following relationship: -5.978 × 10 －２ A system for producing reduced iron, which divides the exhaust gas into a first gas and a second gas such that the following conditions are met: X - 80Y / X + 127.48 ≤ α 800 ≤ X ≤ 1200 0 < Y ≤ 100 α: proportion (volume %) of the first gas separated from the exhaust gas X: temperature (°C) of the reducing gas supplied to the shaft furnace Y: utilization rate (%) of the heat recovered by heat exchange 11. A system for producing reduced iron according to claim 7 or 8, comprising a partial combustion device, wherein the partial combustion device partially combusts the reducing gas with oxygen before supplying it to the shaft furnace, and the gas distributor has the following relationship: -5.978 × 10 －２ A system for producing reduced iron, which divides the exhaust gas into a first gas and a second gas such that the following conditions are met: X - ZX / 1200 + 127.48 ≤ α 800 ≤ X ≤ 1200 0 < Z ≤ 14 α: proportion (volume %) of the first gas separated from the exhaust gas X: temperature (°C) of the reducing gas supplied to the shaft furnace Z: partial combustion rate (%) of the hydrogen gas contained in the reducing gas 12. A system for producing reduced iron according to claim 7 or 8, comprising a heat exchanger and a partial combustion device, wherein the heat exchanger recovers the sensible heat of the exhaust gas discharged from the shaft furnace, the heat recovered by the heat exchanger is used for heating in the ammonia reformer, the partial combustion device partially combusts the reduced gas with oxygen before supplying it to the shaft furnace, and the gas distributor has the following relationship: -5.978 × 10 －２ A system for producing reduced iron, which divides the exhaust gas into a first gas and a second gas so that the following conditions are met: X - 80Y / X - ZX / 1200 + 127.48 ≤ α 800 ≤ X ≤ 1200 0 < Y ≤ 100 0 < Z ≤ 14 α: proportion (volume %) of the first gas separated from the exhaust gas X: temperature (°C) of the reducing gas supplied to the shaft furnace Y: utilization rate (%) of the heat recovered by heat exchange Z: partial combustion rate (%) of the hydrogen gas contained in the reducing gas

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