Hydrogen reduction system and method for manufacturing reduced iron

Abstract

Disclosed is a novel technology for applying SOEC in a direct reduction process in which a shaft furnace is used. A hydrogen reduction system according to the present disclosure has a shaft furnace, a reducing gas supply device, a reducing gas heating device, a source material pretreatment device, and a hydrogen production device. In this hydrogen reduction system, a reducing gas is supplied to the shaft furnace via the reducing gas supply device and the reducing gas heating device, and a 600°C to 900°C iron oxide source material is supplied to the shaft furnace via the source material pretreatment device. The hydrogen production device has an SOEC, and the SOEC uses a steam-containing gas which has been discharged from the shaft furnace to produce hydrogen gas. The hydrogen gas produced by the SOEC is used as a reducing gas.

Description

Hydrogen reduction system and method for producing reduced iron

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

[0002] In the steel industry, as an alternative to the blast furnace method, a direct reduction process using reducing gas is used to reduce CO ２ Studies are being conducted to reduce emissions. For example, a process using a shaft furnace is being considered as a direct reduction process. As a direct reduction process using a shaft furnace, for example, a technology is known in which hydrogen gas is brought into contact with an iron oxide raw material to obtain direct reduced iron (DRI). Here, in a direct reduction process using hydrogen gas, the production and supply of hydrogen are an issue.

[0003] On the other hand, hydrogen production technology has been developed recently, and CO ２ The development of green hydrogen, which does not generate CO₂, is being promoted. Technologies for producing green hydrogen include alkaline water electrolysis and solid polymer membrane water electrolysis, and the development of demonstration technologies for these using large-scale modules is being promoted. In addition, technology using solid oxide electrolyzer cells (SOECs) has also been developed, and its practical application in the future is expected. While alkaline water electrolysis and solid polymer membrane water electrolysis produce hydrogen from liquid water, SOECs are characterized by their ability to produce hydrogen directly from high-temperature steam.

[0004] Patent Document 1 discloses a method for producing hydrogen in a direct reduction process using a shaft furnace, in which an SOEC is provided in an exhaust gas circulation system and water vapor contained in the exhaust gas from the shaft furnace is used.

[0005] International Publication No. 2020 / 247328

[0006] In a direct reduction process using a shaft furnace, if hydrogen could be produced using green hydrogen production technology by utilizing the water vapor contained in the exhaust gas from the shaft furnace, the amount of hydrogen supplied from external sources could be reduced. However, because alkaline water electrolysis and solid polymer water electrolysis produce hydrogen from liquid water, the exhaust gas from the shaft furnace must be cooled once, making them less energy efficient. On the other hand, SOEC produces hydrogen from high-temperature water vapor, eliminating not only the need for cooling but also the need for phase conversion latent heat, making it possible to reduce the operating voltage of the electrolysis. However, its operating temperature is high, at 600 to 900°C, and some ingenuity is required to incorporate it into a direct reduction process using a shaft furnace.

[0007] The present application discloses the following aspects as one of means for solving the above problems. <Aspect 1> A hydrogen reduction system comprising: a shaft furnace; a reducing gas supply device; a reducing gas heating device; a raw material pretreatment device; and a hydrogen production device, wherein the shaft furnace comprises: a raw material supply port; a gas supply port provided below the raw material supply port; a reduced iron discharge port provided below the gas supply port; and a gas discharge port provided above the gas supply port, wherein the reducing gas supply device supplies a reducing gas containing hydrogen gas to the reducing gas heating device, the reducing gas heating device heats the reducing gas supplied from the reducing gas supply device, and the reducing gas heated by the reducing gas heating device is supplied to the gas supply port, the raw material pretreatment device supplies an iron oxide raw material having a temperature of 600°C or more and 900°C or less to the raw material supply port, the hydrogen production device comprises a solid oxide electrolysis cell, and the solid oxide electrolysis cell produces hydrogen gas by utilizing the water vapor-containing gas discharged from the gas discharge port, A hydrogen reduction system, in which the hydrogen gas produced by the solid oxide electrolysis cell is used as the reducing gas. <Aspect 2> The hydrogen reduction system of Aspect 1, in which the raw material pretreatment device has a mechanism for removing sulfur contained in the iron oxide raw material. <Aspect 3> The hydrogen reduction system of Aspect 1 or 2, in which a water removal device is included, in which exhaust gas from a hydrogen electrode of the solid oxide electrolysis cell is supplied to the water removal device, and the water removal device removes at least a portion of the water contained in the exhaust gas. <Aspect 4> The hydrogen reduction system of Aspect 3, in which the water removal device removes at least a portion of the water contained in the exhaust gas by cooling the exhaust gas to 100°C or less, and the exhaust gas after water removal is supplied to the reducing gas heating device and used as the reducing gas.<Aspect 5> A method for producing reduced iron, comprising: supplying an oxidized iron raw material into the interior of a shaft furnace and supplying a reducing gas containing hydrogen gas into the interior of the shaft furnace to reduce the oxidized iron raw material inside the shaft furnace to obtain reduced iron, and discharging a water vapor-containing gas produced by the reduction of the oxidized iron raw material to the exterior of the shaft furnace, wherein the oxidized iron raw material is heated to between 600°C and 900°C and then supplied into the interior of the shaft furnace, the reducing gas is heated and supplied into the interior of the shaft furnace, the water vapor-containing gas discharged from the shaft furnace is supplied to a solid oxide electrolytic cell, hydrogen gas is produced from the water vapor-containing gas by the solid oxide electrolytic cell, and the hydrogen gas produced by the solid oxide electrolytic cell is used as the reducing gas. <Aspect 6> The method for producing reduced iron according to Aspect 5, comprising removing sulfur contained in the oxidized iron raw material before supplying the oxidized iron raw material into the shaft furnace. <Aspect 7> The method for producing reduced iron according to Aspect 5 or 6, comprising removing water contained in the exhaust gas from the hydrogen electrode of the solid oxide electrolysis cell. <Aspect 8> The method for producing reduced iron according to Aspect 7, comprising removing water contained in the exhaust gas from the hydrogen electrode of the solid oxide electrolysis cell by cooling the exhaust gas from the hydrogen electrode of the solid oxide electrolysis cell to 100°C or less, and heating the exhaust gas after water removal to use it as the reducing gas.

[0008] In the hydrogen reduction system and reduced iron production method disclosed herein, the temperature of the iron oxide raw material supplied to the shaft furnace is 600°C or higher and 900°C or lower, which makes it easier for the temperature of the steam-containing gas discharged from the shaft furnace to be a temperature suitable for operating the SOEC. In other words, in the hydrogen reduction system and reduced iron production method disclosed herein, when hydrogen gas is produced by the SOEC using the steam-containing gas discharged from the shaft furnace, the electrolysis efficiency of the SOEC can be improved. The hydrogen gas produced by the SOEC can be used as a reducing gas for reducing iron oxide. As a result, for example, the amount of hydrogen gas supplied from an external source can be reduced.

[0009] 1A and 1B are schematic diagrams showing an example of a hydrogen reduction system and a method for producing reduced iron; 1C are schematic diagrams showing an example of a hydrogen reduction system and a method for producing reduced iron; 1D are schematic diagrams showing an example of a hydrogen reduction system and a method for producing reduced iron; 1E are schematic diagrams showing an example of a hydrogen reduction system and a method for producing reduced iron; 1F are schematic diagrams showing an example of a hydrogen reduction system and a method for producing reduced iron;

[0010] Hereinafter, a hydrogen reduction system and a method for producing reduced iron according to embodiments will be described with reference to the drawings. However, the hydrogen reduction system and the method for producing reduced iron according to the present disclosure are not limited to the following embodiments.

[0011] 1 to 5 , a hydrogen reduction system 100 according to one embodiment includes a shaft furnace 10, a reducing gas supply device 20, a reducing gas heating device 30, a raw material pretreatment device 40, and a hydrogen production device 50. The shaft furnace 10 includes a raw material supply port 11, a gas supply port 12 provided below the raw material supply port 11, a reduced iron discharge port 13 provided below the gas supply port 12, and a gas discharge port 14 provided above the gas supply port 12. The reducing gas supply device 20 supplies a reducing gas containing hydrogen gas to the reducing gas heating device 30. The reducing gas heating device 30 heats the reducing gas supplied from the reducing gas supply device 20. The reducing gas heated by the reducing gas heating device 30 is supplied to the gas supply port 12. The raw material pretreatment device 40 supplies an iron oxide raw material having a temperature of 600° C. or higher and 900° C. or lower to the raw material supply port 11. The hydrogen production device 50 includes a solid oxide electrolysis cell 51. The solid oxide electrolysis cell 51 produces hydrogen gas by utilizing the water vapor-containing gas discharged from the gas outlet 14. The hydrogen gas produced by the solid oxide electrolysis cell 51 is used as the reducing gas.

[0012] 1.1 Shaft Furnace The shaft furnace 10 has at least a raw material supply port 11, a gas supply port 12 provided below the raw material supply port 11, a reduced iron discharge port 13 provided below the gas supply port 12, and a gas discharge port 14 provided above the gas supply port 12. In the shaft furnace 10, the raw material supply port 11, the gas supply port 12, the reduced iron discharge port 13, and the gas discharge port 14 are not particularly limited in terms of their specific positions or shapes as long as the above-described positional relationship is satisfied. The raw material supply port 11 may be provided, for example, at the top or upper part of the shaft furnace 10. The gas supply port 12 may be provided, for example, directly below a position that will become the reduction zone of the shaft furnace 10. The reduction zone refers to, for example, the area inside the shaft furnace 10 from the gas supply port 12 to the gas discharge port 14 (i.e., the area between the height positions of the gas supply port 12 and the gas discharge port 14). The reduced iron discharge port 13 may be provided at the bottom or lower part of the shaft furnace 10. The gas discharge port 14 may be provided at a location different from the raw material supply port 11, which is at the top or upper part of the shaft furnace 10. When the raw material supply port 11, the gas supply port 12, the reduced iron discharge port 13, and the gas discharge port 14 satisfy the above-described positional relationship, an oxidized iron raw material can be supplied from the raw material supply port 11 into the interior of the shaft furnace 10 to form a packed bed of the oxidized iron raw material inside the shaft furnace 10, a reducing gas containing hydrogen gas can be supplied from the gas supply port 12 to the packed bed inside the shaft furnace 10, and the oxidized iron raw material can be brought into contact with the reducing gas inside the shaft furnace 10 to reduce the iron oxide, thereby obtaining reduced iron from the reduced iron discharge port 13 and discharging a water vapor-containing gas from the gas discharge port 14 to the outside of the shaft furnace 10.

[0013] The oxidized iron raw material supplied to the shaft furnace 10 contains at least iron oxide. The oxidized iron raw material may be, for example, at least one selected from iron ore pellets, lump ore, and sintered ore. The oxidized iron raw material may contain, in addition to iron oxide, for example, one or both of silicon dioxide and aluminum oxide. The oxidized iron raw material may contain various impurities. For example, the oxidized iron raw material may contain sulfur. When the oxidized iron raw material contains sulfur, it is preferable to reduce the amount of sulfur contained in the oxidized iron raw material by a sulfur removal mechanism described below. The oxidized iron raw material may have a particle size distribution or a uniform particle diameter. The average particle diameter of the oxidized iron raw material may be, for example, 5.0 mm or more and 30.0 mm or less, or 10.0 mm or more and 15.0 mm or less. The "particle diameter" of the oxidized iron raw material refers to the sieve diameter of the raw material. The "average particle diameter" of the oxidized iron raw material refers to the weighted average value of the particle diameters of the raw material. The average particle diameter of the oxidized iron raw material is measured as follows. That is, the average particle size of the oxidized iron raw material can be measured by obtaining a mass-based particle size distribution by a dry sieving test described in JIS Z 8815:1995, and then calculating a mass-weighted average using the average of the maximum and minimum particle sizes of each sieve as a representative particle size. The oxidized iron raw material may be formed into pellets or the like, or may be in the form of a powder, a lump, or other shapes. The amount of oxidized iron raw material supplied to the shaft furnace 10 may be selected optimally depending on the size and operating conditions of the shaft furnace 10. This embodiment is characterized in that the temperature of the oxidized iron raw material supplied to the shaft furnace 10 is adjusted to 600°C or higher and 900°C or lower by a raw material pre-treatment device 40 described later. The temperature of the oxidized iron raw material will be described later.

[0014] In this embodiment, reduction of iron oxide by the reducing gas occurs in a reduction zone inside the shaft furnace 10. The temperature of the reducing gas supplied from the gas supply port 12 to the inside of the shaft furnace 10 (the temperature at the gas supply port 12) may be, for example, 700°C or higher and 1100°C or lower. The flow rate of the reducing gas supplied from the gas supply port 12 to the inside of the shaft furnace 10 (the flow rate at the gas supply port 12) may be, for example, 1000 Nm ３ / t-DRI or more 2200Nm ３ / t-DRI or less. The temperature of the oxidized iron raw material in the reduction zone may be, for example, 600°C or higher and 900°C or lower. The reduction rate of the reduced iron that has passed through the reduction zone and is discharged from the reduced iron discharge port 13 may be, for example, 65% or higher and 98% or lower. The temperature of the water vapor-containing gas that has passed through the reduction zone and is discharged from the gas discharge port 14 to the outside of the shaft furnace 10 corresponds to the temperature of the oxidized iron raw material supplied from the raw material supply port 11, that is, may be 600°C or higher and 900°C or lower.

[0015] 1.2 Reducing Gas Supply Device The reducing gas supply device 20 supplies a reducing gas containing hydrogen gas to the reducing gas heating device 30 described later. The reducing gas supply device 20 may supply the reducing gas to the reducing gas heating device 30 while controlling the flow rate, pressure, and temperature of the reducing gas, for example. In other words, the reducing gas supply device 20 may include at least one of a flow meter, a pressure gauge, and a thermometer, and may also include a control mechanism for controlling one or both of the flow rate and pressure of the reducing gas. The reducing gas supply device 20 may be connected to a reducing gas source or a solid oxide electrolysis cell (SOEC) 51 described later via a pipe so that a gas containing hydrogen gas is supplied from the reducing gas source or the SOEC to the reducing gas supply device 20, or may be connected to the reducing gas heating device 30 described later via a pipe so that a reducing gas is supplied to the reducing gas heating device 30.

[0016] The flow rate of the reducing gas supplied from the reducing gas supply device 20 is, for example, 1000 Nm ３ / t-DRI or more 2200Nm ３ / t-DRI or less. The pressure of the reducing gas supplied from the reducing gas supply device 20 may be, for example, 0.1 MPa or more and 0.8 MPa or less. The temperature of the reducing gas supplied from the reducing gas supply device 20 may be, for example, room temperature or more and 100°C or less. A commercially available reducing gas supply device may be used as the reducing gas supply device 20. An example of a commercially available reducing gas supply device is an on-site supply unit manufactured by Air Water Inc.

[0017] The reducing gas supplied from the reducing gas supply device 20 contains hydrogen gas and may contain other gases as desired. The reducing gas may contain 40% by volume or more and 100% by volume or less of hydrogen gas. Examples of gases other than hydrogen gas include CO gas, hydrocarbon gas, and inert gas. Examples of inert gases include rare gases such as nitrogen gas and argon gas, CO ２ The reducing gas may be at least one selected from the group consisting of hydrogen gas, water vapor, etc. The proportion of hydrogen gas in the reducing gas may be 40% by volume or more, 45% by volume or more, 50% by volume or more, 55% by volume or more, 60% by volume or more, 65% by volume or more, 70% by volume or more, 75% by volume or more, 80% by volume or more, 85% by volume or more, 90% by volume or more, or 95% by volume or more. In particular, the proportion of hydrogen gas in the reducing gas is preferably 90% by volume or more and 100% by volume or less.

[0018] 1.3 Reducing Gas Heating Device The reducing gas heating device 30 heats the reducing gas supplied from the reducing gas supply device 20. The reducing gas heated by the reducing gas heating device 30 is supplied to the gas supply port 12 of the shaft furnace 10. The reducing gas heating device 30 may, for example, supply the reducing gas to the gas supply port 12 while controlling the flow rate, pressure, and temperature of the reducing gas. In other words, the reducing gas heating device 30 may include a heating mechanism for heating the gas and a control mechanism for controlling the gas temperature. The reducing gas heating device 30 may also include at least one of a flow meter, a pressure meter, and a thermometer, and may also include a control mechanism for controlling one or both of the flow rate and pressure of the reducing gas. The heating mechanism may be any mechanism capable of heating the gas, and may be a heat exchanger, an external heater, or a mechanism for partially combusting the gas (a mechanism that reacts and burns part of the hydrogen contained in the reducing gas with oxygen, thereby heating the gas using the combustion heat).

[0019] The flow rate of the reducing gas supplied from the reducing gas heating device 30 is, for example, 1000 Nm ３ / t-DRI or more 2200Nm ３ / t-DRI or less. The pressure of the reducing gas supplied from the reducing gas heating device 30 may be, for example, 0.1 MPa or more and 0.8 MPa or less. The temperature of the reducing gas supplied from the reducing gas heating device 30 (the temperature at the gas supply port 12) may be, for example, 700°C or more and 1100°C or less. A commercially available reducing gas heating device may be used as the reducing gas heating device 30. An example of a commercially available reducing gas heating device is a gas heater manufactured by Izumi Denetsu Co., Ltd.

[0020] 1.4 Raw Material Pretreatment Device The raw material pretreatment device 40 supplies the iron oxide raw material having a temperature of 600° C. or more and 900° C. or less to the raw material supply port 11 of the shaft furnace 10. The raw material pretreatment device 40 may be, for example: (1) a device having a heating mechanism for heating the iron oxide raw material, or (2) a raw material manufacturing device for manufacturing high-temperature iron oxide raw material.

[0021] (1) The raw material pre-treatment device 40 may be configured to heat the oxidized iron raw material to 600°C or higher and 900°C or lower using a heating mechanism and then supply the oxidized iron raw material to the raw material supply port 11 of the shaft furnace 10. There are no particular limitations on the heating mechanism, and any mechanism that can heat the oxidized iron raw material to 600°C or higher and 900°C or lower can be used. The heating mechanism may be configured to heat the oxidized iron raw material in a batch manner or a continuous manner. The raw material pre-treatment device 40 may be configured to include a hopper, a raw material discharge device, a thermometer, a heating mechanism, and a control mechanism that controls the heating temperature of the raw material.

[0022] (2) The raw material pre-treatment device 40 may be a calcination furnace that produces pellets as the iron oxide raw material. That is, the raw material pre-treatment device 40 according to one embodiment may be configured so that pellets produced in the pellet calcination furnace are transferred to the raw material supply port 11 of the shaft furnace 10 while the pellets have a temperature of 600°C or higher and 900°C or lower.

[0023] The temperature of the oxidized iron raw material supplied from the raw material pretreatment device 40 to the raw material supply port 11 of the shaft furnace 10 is 600°C or higher, and may be 650°C or higher, or 700°C or higher, or 900°C or lower, or 850°C or lower, or 800°C or lower. By heating the oxidized iron raw material before being supplied to the shaft furnace 10 in this way, the temperature of the steam-containing gas discharged from the shaft furnace 10 is likely to be a temperature suitable for operating the solid oxide electrolysis cell (SOEC) 51, as will be described later. Furthermore, by heating the oxidized iron raw material before being supplied to the shaft furnace 10, the thermal efficiency of the entire system is increased, and the reduction efficiency of the oxidized iron raw material inside the shaft furnace 10 is also thought to be increased. The "temperature of the oxidized iron raw material" refers to the surface temperature of the oxidized iron raw material. The surface temperature of the oxidized iron raw material may be an actual value measured using a thermocouple or the like, or an estimated value estimated by simulation or the like.

[0024] As described above, the oxidized iron raw material may contain sulfur. The sulfur contained in the oxidized iron raw material is gasified and circulated within the hydrogen reduction system. Here, the presence of sulfur in the hydrogen reduction system may cause corrosion of various devices and may poison the catalyst of a solid oxide electrolysis cell (SOEC) 51, which will be described later. In this regard, when the oxidized iron raw material contains sulfur, it is preferable to reduce the amount of sulfur in the oxidized iron raw material. For example, as shown in FIG. 2 , the raw material pretreatment device 40 may have a mechanism 41 that removes sulfur contained in the oxidized iron raw material. The sulfur removal mechanism 41 may be, for example, a mechanism that removes sulfur contained in the oxidized iron raw material as sulfur dioxide gas by heating the oxidized iron raw material in an oxidizing atmosphere.

[0025] 1.5 Hydrogen Production Device The hydrogen production device 50 includes a solid oxide electrolysis cell (SOEC) 51. The SOEC 51 produces hydrogen gas by utilizing the water vapor-containing gas discharged from the gas outlet 14 of the shaft furnace 10. The hydrogen gas produced by the SOEC 51 is used as the reducing gas. For example, the hydrogen gas produced by the SOEC 51 may be supplied to at least one of the reducing gas supply device 20, the reducing gas heating device 30, and the gas supply port 12, or may be supplied to one or both of the reducing gas heating device 30 and the gas supply port 12. The temperature of the hydrogen gas produced by the SOEC 51 is usually high. In this regard, when the hydrogen gas produced by the SOEC 51 is supplied to one or both of the reducing gas heating device 30 and the gas supply port 12, the thermal energy of the hydrogen gas is likely to be effectively utilized.

[0026] The configuration of the SOEC 51 itself is publicly known (see, for example, Japanese Patent Application Laid-Open No. 2005-232525 and Japanese Patent Application Laid-Open No. 7-109592). That is, the SOEC 51 has, for example, a hydrogen electrode, an oxygen electrode, and an electrolyte layer disposed therebetween. The water vapor-containing gas discharged from the gas outlet 14 is supplied to the hydrogen electrode of the SOEC 51. At the hydrogen electrode, hydrogen gas is generated by electrolysis of the water vapor. On the other hand, at the oxygen electrode, electrons are released from oxygen radicals to generate oxygen gas. That is, exhaust gas containing hydrogen gas is discharged from the hydrogen electrode of the SOEC 51, and exhaust gas containing oxygen gas is discharged from the oxygen electrode. The hydrogen electrode is made of, for example, Ni—CeO ２ The oxygen electrode may contain, for example, a metal catalyst-cocatalyst or a metal catalyst-support. ３ The electrolyte layer may contain a ceramic catalyst such as ZrO ２ The hydrogen production device 50 may include a ceramic electrolyte such as a SOEC 51. In addition, in the hydrogen production device 50, a plurality of SOECs 51 may be stacked with metal separators interposed therebetween to form an SOEC stack. The power density when operating the SOEC 51 is, for example, 0.5 A / m ２ 1.0A / m or more ２ It may be the following:

[0027] The amount of water in the water vapor-containing gas supplied to the SOEC 51 is not particularly limited. The water vapor-containing gas may contain other gases in addition to water vapor. Depending on the compositions of the iron oxide raw material and the reducing gas, the water vapor-containing gas may contain at least one gas selected from, for example, hydrogen gas, carbon monoxide gas, carbon dioxide gas, hydrocarbon gas, and inert gas. The flow rate and pressure of the water vapor-containing gas supplied to the SOEC 51 are also not particularly limited and may be adjusted appropriately depending on the scale of the hydrogen production device 50, etc.

[0028] The operating temperature of the SOEC 51 is usually 600°C or higher and 900°C or lower. On the other hand, in the present embodiment, the temperature of the water vapor-containing gas discharged from the gas outlet 14 of the shaft furnace 10 corresponds to the temperature of the iron oxide raw material supplied from the raw material supply port 11 into the shaft furnace 10, that is, is a temperature in the vicinity of 600°C or higher and 900°C or lower. In other words, in the present embodiment, the temperature of the water vapor-containing gas discharged from the gas outlet 14 is likely to be a temperature suitable for operating the SOEC 51. Therefore, in the present embodiment, the water vapor-containing gas discharged from the gas outlet 14 of the shaft furnace 10 may be supplied directly to the SOEC without being heated or cooled by an external device.

[0029] 1.6 Other Configurations The hydrogen reduction system 100 may include other devices in addition to the above-described shaft furnace 10, reducing gas supply device 20, reducing gas heating device 30, raw material pretreatment device 40, and hydrogen production device 50. An example of the other devices will be described below.

[0030] 1.6.1 Water Removal Device As described above, the exhaust gas from the shaft furnace 10 contains water vapor. The water vapor-containing gas is supplied to the SOEC 51 to produce hydrogen. Here, in the SOEC 51, some of the water vapor contained in the water vapor-containing gas circulates within the system without being converted to hydrogen, which may result in an increased water vapor concentration within the system. In this regard, the hydrogen reduction system 100 according to one embodiment may include a water removal device 60 as shown in FIG. 3 . For example, in the hydrogen reduction system 100, exhaust gas (gas containing hydrogen and water vapor) from the hydrogen electrode of the SOEC 51 may be supplied to the water removal device 60, and the water removal device 60 may be configured to remove at least a portion of the water contained in the exhaust gas. The water removal device 60 may be located, for example, downstream of the hydrogen electrode of the SOEC 51 and upstream of the gas supply port 12 of the shaft furnace 10. For example, the water removal device 60 may be located between the hydrogen electrode of the SOEC 51 and the reducing gas heating device 30, as described below.

[0031] There are no particular limitations on the water removal method used in the water removal device 60. The water removal device 60 may, for example, remove at least a portion of the water contained in the exhaust gas from the hydrogen electrode of the SOEC 51 by cooling the exhaust gas to 100°C or less. In this case, the temperature of the exhaust gas after water removal is low, and if this is supplied directly to the shaft furnace 10 as a reducing gas, the efficiency of the reduction reaction of iron oxide may decrease. In this regard, when water is removed by cooling in the water removal device 60, it is preferable that the exhaust gas (containing hydrogen gas) after water removal be supplied to the reducing gas heating device 30, heated, and then used as a reducing gas, as shown in FIG. 4.

[0032] The flow rate of the water vapor-containing gas supplied to the water removal device 60 is, for example, 1000 Nm ３ / t-DRI or more 2200Nm ３ / t-DRI or less. The pressure of the water vapor-containing gas supplied to the water removal device 60 may be, for example, 0.1 MPa or more and 0.8 MPa or less. The temperature of the water vapor-containing gas supplied to the water removal device 60 may be, for example, 600°C or more and 900°C or less. A commercially available device may be used as the water removal device 60. An example of a commercially available water removal device is a gas cooling device (quenching) manufactured by Hipotec.

[0033] Alternatively, the water removal device 60 may be one that separates hydrogen gas and water vapor using a molecular sieve or the like. Alternatively, the water removal device 60 may be one that removes water by selectively reacting with or adsorbing water using a material that is inactive to hydrogen and reactive with water.

[0034] 1.6.2 Carbon Dioxide Removal Device As described above, the reducing gas supplied to the shaft furnace 10 and the exhaust gas from the shaft furnace 10 may contain carbon dioxide. Carbon dioxide is inert to the reduction reaction in the direct reduction process. However, when the carbon dioxide concentration in the system increases, the reducing gas concentration decreases relatively, which may result in a decrease in the efficiency of the reduction reaction of iron oxide. In this regard, the hydrogen reduction system 100 according to one embodiment may include a carbon dioxide removal device 70, as shown in FIG. 5 . For example, the hydrogen reduction system 100 may be configured such that exhaust gas (gas containing hydrogen, water vapor, and carbon dioxide) from the hydrogen electrode of the SOEC 51 is supplied to a water removal device 60, which removes at least a portion of the water contained in the exhaust gas. Furthermore, the exhaust gas after water removal may be supplied to the carbon dioxide removal device 70, which removes at least a portion of the carbon dioxide contained in the exhaust gas. The carbon dioxide removal device 70 may be installed anywhere in the gas circulation system of the hydrogen reduction system 100. The carbon dioxide removal device 70 may be disposed, for example, downstream of the hydrogen electrode of the SOEC 51 and upstream of the gas supply port 12 of the shaft furnace 10. For example, the carbon dioxide removal device 70 may be disposed between the hydrogen electrode of the SOEC 51 and the reducing gas heating device 30.

[0035] The carbon dioxide removal device 70 may be one that separates hydrogen gas and carbon dioxide gas using a molecular sieve or the like. Alternatively, the carbon dioxide removal device 70 may be one that removes carbon dioxide by selectively reacting with or adsorbing carbon dioxide using a material that is inert to hydrogen and reactive with carbon dioxide.

[0036] 1.6.3 Sulfur Removal Device In the above description, the case where the raw material pretreatment device 40 includes the sulfur removal mechanism 41 has been exemplified. However, the hydrogen reduction system 100 may also include a sulfur removal device (not shown) separate from the raw material pretreatment device 40. For example, sulfur may be contained in the steam-containing gas discharged from the shaft furnace 10. In this case, it is preferable that the sulfur in the steam-containing gas discharged from the shaft furnace 10 be removed by the sulfur removal device before the gas reaches the SOEC 51 of the hydrogen production device 50. Furthermore, the hydrogen reduction system 100 may be configured to monitor the sulfur concentration in the gas circulating through the circulation system with a sulfur concentration monitoring device, and, when the sulfur concentration in the circulation gas exceeds a threshold value, remove sulfur from the circulation gas with the sulfur removal device to reduce the sulfur concentration of the circulation gas to below the threshold value.

[0037] The sulfur concentration in the circulating gas may be monitored by either an actual measurement method or an estimated method. Examples of actual measurement methods include measuring the sulfur concentration in the circulating gas or the iron oxide raw material by gas chromatography, atomic absorption spectrometry, ultraviolet fluorescence spectrometry, ICP, etc. Examples of estimated methods include theoretically estimating the amount of sulfur transferred from the iron oxide raw material to the circulating gas.

[0038] Methods for reducing the sulfur concentration in the circulating gas include: (1) a method for reducing the sulfur concentration in the circulating gas by changing the temperature of the reducing gas, (2) a method for reducing the sulfur concentration in the circulating gas by switching the type of iron oxide raw material supplied to the raw material supply port 11 and supplying an iron oxide raw material with a low sulfur concentration, (3) a method for reducing the sulfur concentration in the circulating gas by switching the type of reducing gas supplied to the gas supply port 12 and supplying a reducing gas with a low sulfur concentration, and (4) a method for reducing the sulfur concentration in the circulating gas by providing a desulfurization mechanism in part of the circulating system, etc. Examples of desulfurization mechanisms include those that remove at least a portion of the sulfur (e.g., hydrogen sulfide) in the circulating gas by a filter method or an adsorption method.

[0039] 1 to 5 may be combined in any manner in the hydrogen reduction system 100. That is, the hydrogen reduction system 100 may include at least one of a sulfur removal mechanism 41, a water removal device 60, a carbon dioxide removal device 70, and a sulfur removal device (not shown), in addition to the shaft furnace 10, the reducing gas supply device 20s, the reducing gas heating device 30, the raw material pretreatment device 40, and the hydrogen production device 50. Furthermore, the hydrogen reduction system 100 may include devices other than the above-mentioned devices.

[0040] 1 to 5 , a method for producing reduced iron according to one embodiment includes supplying an oxidized iron raw material into a shaft furnace 10 and supplying a reducing gas containing hydrogen gas into the shaft furnace 10 to reduce the oxidized iron raw material in the shaft furnace 10 to obtain reduced iron, and discharging a steam-containing gas produced by the reduction of the oxidized iron raw material to the outside of the shaft furnace 10. Here, the oxidized iron raw material is heated to 600°C or higher and 900°C or lower and then supplied into the shaft furnace 10. The reducing gas is heated and then supplied into the shaft furnace 10. The steam-containing gas discharged from the shaft furnace 10 is supplied to a solid oxide electrolysis cell (SOEC) 51, and hydrogen gas is produced from the steam-containing gas by the SOEC 51. The hydrogen gas produced by the SOEC 51 is used as the reducing gas. The shaft furnace 10, the SOEC 51, the iron oxide raw material, the reducing gas, the steam-containing gas, etc. are as described above, and therefore will not be described here.

[0041] In the method for producing reduced iron according to an embodiment, the configuration of the hydrogen reduction system 100 described above may be employed as is. For example, the method for producing reduced iron according to an embodiment may include removing sulfur contained in the oxidized iron raw material before supplying the oxidized iron raw material to the inside of the shaft furnace 10. The method for producing reduced iron according to an embodiment may also include removing water contained in an exhaust gas from the hydrogen electrode of the SOEC 51. The method for producing reduced iron according to an embodiment may also include removing water contained in the exhaust gas from the hydrogen electrode of the SOEC 51 by cooling the exhaust gas from the hydrogen electrode of the SOEC 51 to 100°C or less, and heating the exhaust gas after water removal to use it as the reducing gas. The method for removing sulfur contained in the oxidized iron raw material and the method for removing water contained in the gas are as described above, and therefore will not be described here.

[0042] 3. Effects As described above, in the hydrogen reduction system 100 and the method for producing reduced iron according to one embodiment, the water vapor-containing gas discharged from the shaft furnace 10 is supplied to the SOEC 51, and hydrogen gas is produced by a water decomposition reaction in the SOEC 51. Here, by setting the temperature of the iron oxide raw material supplied to the shaft furnace 10 to be 600°C or higher and 900°C or lower, the temperature of the water vapor-containing gas discharged from the shaft furnace 10 is likely to be a temperature suitable for operating the SOEC 51. In other words, when hydrogen gas is produced by the SOEC 51 using the water vapor-containing gas discharged from the shaft furnace 10, the electrolysis efficiency in the SOEC 51 can be improved without additionally heating the water vapor-containing gas discharged from the shaft furnace 10. The hydrogen gas produced by the SOEC 51 can be used as a reducing gas for reducing iron oxide. As a result, for example, the amount of hydrogen gas supplied from an external source can be reduced. If the electrolysis efficiency of the SOEC 51 can be improved to the maximum extent possible, all of the water vapor discharged from the shaft furnace 10 can be converted into hydrogen, and it will be necessary to supply reducing gas initially, eliminating the need for additional hydrogen to be supplied from outside thereafter.

[0043] Furthermore, the hydrogen gas produced by the SOEC 51 has a temperature of 600°C or higher and 900°C or lower, which corresponds to the operating temperature of the SOEC 51, and such high-temperature hydrogen gas can be used as is for direct reduction in the shaft furnace 10. In other words, the amount of heating required for the produced hydrogen gas is small, or heating is not required at all.

[0044] Furthermore, in the hydrogen reduction system 100 and the method for producing reduced iron according to one embodiment, as described above, sulfur contained in the oxidized iron raw material may be removed before the oxidized iron raw material is supplied into the shaft furnace 10. Here, the sulfur contained in the oxidized iron raw material reacts with the reducing gas to form hydrogen sulfide or the like, and is discharged to the outside of the shaft furnace 10. By removing the sulfur contained in the oxidized iron raw material in advance, the amount of sulfur (hydrogen sulfide or the like) contained in the steam-containing gas discharged from the shaft furnace 10 can also be reduced, and when hydrogen gas is produced in the SOEC 51 using the steam-containing gas, poisoning or deterioration of the catalyst in the SOEC 51 by sulfur can also be suppressed.

[0045] The effects of the technology of the present disclosure will be described in more detail below with reference to examples, but the technology of the present disclosure is not limited to the following examples.

[0046] An example of the design of a hydrogen reduction system having a reduced iron production capacity of 15 kg / hr is shown below.

[0047] (1) A shaft furnace with a diameter of 0.1 m and an effective height of 4 m was prepared. (2) Iron oxide raw material heated to 850°C was supplied into the shaft furnace from a raw material supply port provided at the top of the shaft furnace. (3) A gas supply port provided on the side wall of the shaft furnace was used to supply 2000 Nm of iron oxide raw material into the shaft furnace. ３ A reducing gas was supplied at a flow rate of 1 / t-DRI. The composition and temperature of the supplied reducing gas are as shown in Table 1 below. (4) Exhaust gas was discharged to the outside of the shaft furnace from a gas outlet provided on the side wall of the shaft furnace and above the gas supply port. The composition and temperature of the exhaust gas are as shown in Table 1 below. (5) The above steps (2) to (4) were carried out simultaneously, and reduced iron was continuously discharged from a reduced iron outlet provided at the bottom of the shaft furnace. The reduction rate of the reduced iron was 95%.

[0048]

[0049] As shown in Table 1, by heating the iron oxide raw material to 850°C before supplying it to the shaft furnace, the temperature of the exhaust gas from the shaft furnace could be controlled to around 850°C (840°C). This temperature is within the operating temperature range of the SOEC. In other words, it is believed that by supplying the exhaust gas from the shaft furnace directly to the SOEC, the water vapor contained in the exhaust gas can be converted to hydrogen. In this way, the temperature of the exhaust gas from the shaft furnace corresponds to the supply temperature of the iron oxide raw material. Considering that the operating temperature of an SOEC is typically between 600°C and 900°C, by setting the supply temperature of the iron oxide raw material to between 600°C and 900°C, the temperature of the exhaust gas from the shaft furnace also becomes close to between 600°C and 900°C, which is believed to be a suitable temperature for operating the SOEC.

[0050] Specific examples of SOECs include the following: Operating temperature: 800°C Power density: 1.0 A / m ２ Hydrogen electrode: Ni—CeO ２ Mixed material Electrolyte: ZrO ２ Oxygen electrode: LaCoO ３ Separator: SUS304

[0051] In summary, it is believed that the hydrogen reduction system having the following configurations (A1) to (I1) and the method for producing reduced iron having the following configurations (A2) to (E2) make it easier for the temperature of the steam-containing gas discharged from the shaft furnace to become a temperature suitable for operating the SOEC, thereby increasing the electrolysis efficiency of the SOEC and reducing the amount of hydrogen gas supplied from the outside.

[0052] (A1) The hydrogen reduction system includes a shaft furnace, a reducing gas supply device, a reducing gas heating device, a raw material pretreatment device, and a hydrogen production device. (B1) The shaft furnace includes a raw material supply port, a gas supply port provided below the raw material supply port, a reduced iron discharge port provided below the gas supply port, and a gas discharge port provided above the gas supply port. (C1) The reducing gas supply device supplies a reducing gas containing hydrogen gas to the reducing gas heating device. (D1) The reducing gas heating device heats the reducing gas supplied from the reducing gas supply device. (E1) The reducing gas heated by the reducing gas heating device is supplied to the gas supply port. (F1) The raw material pretreatment device supplies an iron oxide raw material having a temperature of 600°C or higher and 900°C or lower to the raw material supply port. (G1) The hydrogen production device includes a solid oxide electrolysis cell. (H1) The solid oxide electrolysis cell produces hydrogen gas by utilizing the water vapor-containing gas discharged from the gas outlet. (I1) The hydrogen gas produced by the solid oxide electrolysis cell is used as the reducing gas.

[0053] (A2) A method for producing reduced iron includes supplying oxidized iron raw material into a shaft furnace and supplying a reducing gas containing hydrogen gas into the shaft furnace to reduce the oxidized iron raw material inside the shaft furnace to obtain reduced iron, and discharging a water vapor-containing gas produced by the reduction of the oxidized iron raw material to the outside of the shaft furnace. (B2) The oxidized iron raw material is heated to 600°C or higher and 900°C or lower and then supplied into the shaft furnace. (C2) The reducing gas is heated and then supplied into the shaft furnace. (D2) The water vapor-containing gas discharged from the shaft furnace is supplied to a solid oxide electrolytic cell, and hydrogen gas is produced from the water vapor-containing gas by the solid oxide electrolytic cell. (E2) The hydrogen gas produced by the solid oxide electrolytic cell is used as the reducing gas.

[0054] REFERENCE SIGNS LIST 10 shaft furnace 11 raw material supply port 12 gas supply port 13 reduced iron discharge port 14 gas discharge port 20 reducing gas supply device 30 reducing gas heating device 40 raw material pretreatment device 41 sulfur removal mechanism 50 hydrogen production device 51 solid oxide electrolysis cell (SOEC) 60 water removal device 70 carbon dioxide removal device

Claims

1. A hydrogen reduction system comprising: a shaft furnace; a reducing gas supply device; a reducing gas heating device; a raw material pretreatment device; and a hydrogen production device; wherein the shaft furnace comprises: a raw material supply port; a gas supply port provided below the raw material supply port; a reduced iron discharge port provided below the gas supply port; and a gas discharge port provided above the gas supply port; wherein the reducing gas supply device supplies a reducing gas containing hydrogen gas to the reducing gas heating device; the reducing gas heating device heats the reducing gas supplied from the reducing gas supply device; and the reducing gas heated by the reducing gas heating device is supplied to the gas supply port; the raw material pretreatment device supplies an iron oxide raw material having a temperature of 600°C or more and 900°C or less to the raw material supply port; the hydrogen production device comprises a solid oxide electrolysis cell; and the solid oxide electrolysis cell produces hydrogen gas using the water vapor-containing gas discharged from the gas discharge port; A hydrogen reduction system, wherein the hydrogen gas produced by the solid oxide electrolysis cell is used as the reducing gas.

2. A hydrogen reduction system according to claim 1, wherein the raw material pretreatment device has a mechanism for removing sulfur contained in the iron oxide raw material.

3. A hydrogen reduction system according to claim 1 or 2, further comprising a water removal device, wherein exhaust gas from the hydrogen electrode of the solid oxide electrolysis cell is supplied to the water removal device, and the water removal device removes water contained in the exhaust gas.

4. A hydrogen reduction system according to claim 3, wherein the water removal device removes at least a portion of the water contained in the exhaust gas by cooling the exhaust gas to 100°C or less, and the exhaust gas after water removal is supplied to the reducing gas heating device and used as the reducing gas.

5. A method for producing reduced iron, comprising: supplying an oxidized iron raw material into the interior of a shaft furnace, and supplying a reducing gas containing hydrogen gas into the interior of the shaft furnace to reduce the oxidized iron raw material inside the shaft furnace to obtain reduced iron; and discharging a water vapor-containing gas produced by the reduction of the oxidized iron raw material to the outside of the shaft furnace, wherein the oxidized iron raw material is heated to between 600°C and 900°C and then supplied into the interior of the shaft furnace, the reducing gas is heated and then supplied into the shaft furnace, the water vapor-containing gas discharged from the shaft furnace is supplied to a solid oxide electrolytic cell, hydrogen gas is produced from the water vapor-containing gas by the solid oxide electrolytic cell, and the hydrogen gas produced by the solid oxide electrolytic cell is used as the reducing gas.

6. A method for producing reduced iron according to claim 5, comprising removing sulfur contained in the oxidized iron raw material before supplying the oxidized iron raw material into the shaft furnace.

7. A method for producing reduced iron according to claim 5 or 6, comprising removing water contained in exhaust gas from the hydrogen electrode of the solid oxide electrolysis cell.

8. A method for producing reduced iron according to claim 7, comprising: removing water contained in exhaust gas from the hydrogen electrode of the solid oxide electrolysis cell by cooling the exhaust gas to 100°C or less; and heating the exhaust gas after water removal and using it as the reducing gas.

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