Hydrogen reduction system and method for manufacturing reduced iron
Patent Information
- Application Number
- AU2025298623
- Authority / Receiving Office
- AU · AU
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2024-07-04
- Filing Date
- 2025-02-20
- Publication Date
- 2026-10-29
Smart Images
Figure 00000000_0000_ABST
Abstract
Description
TITLE: HYDROGEN REDUCTION SYSTEM AND METHOD FOR PRODUCING REDUCED IRON FIELD
[0001] The present application discloses a hydrogen reduction system and a method for producing reduced iron. BACKGROUND
[0002] Reduction in CO2 emission by direct reduction using a reducing gas is being studied in the steel industry as a substitute technique for the blast furnace method. A process using a shaft furnace, for example, has been investigated as a direct reduction process. Known direct reduction processes using shaft furnaces include, for example, techniques in which hydrogen gas is contacted with an iron oxide feedstock to obtain direct reduced iron (DRI). However, production and supply of hydrogen is a challenge for direct reduction processes utilizing hydrogen gas.
[0003] With the increasing development of hydrogen production techniques in recent years, there has been a push to develop green hydrogen that does not result in generation of CO2 during production. Production techniques for green hydrogen include alkaline water electrolysis and polymer electrolyte membrane water electrolysis, and demonstration projects using large-scale modules are under development. Techniques employing solid oxide electrolyzer cells (SOEC) have also been developed, and future implementations of such techniques are considered promising. Hydrogen is produced from liquid water by alkaline water electrolysis or polymer electrolyte membrane water electrolysis, but SOEC allows direct production of hydrogen from high-temperature vapor.
[0004] PTL 1 discloses a method for producing hydrogen by providing an SOEC in a discharge gas circulation system in a direct reduction process using a shaft furnace, utilizing water vapor in the exhaust gas from the shaft furnace. [CITATION LIST] [PATENT LITERATURE]
[0005] [PTL 1] International Patent Publication No. WO2020 / 247328 SUMMARY [TECHNICAL PROBLEM]
[0006] In a direct reduction process using a shaft furnace, production of hydrogen by green hydrogen production technology utilizing water vapor in exhaust gas from the shaft furnace can help reduce the amount of hydrogen that is externally supplied. However, since alkaline water electrolysis or polymer electrolyte membrane water electrolysis produces hydrogen from liquid water, exhaust gas from the shaft furnace must be cooled, and therefore the energy efficiency is poor. On the other hand, since an SOEC produces hydrogen from high-temperature water vapor, it not only eliminates the need for cooling but also eliminates the need for latent heat of phase transition, thus making it possible to reduce the working voltage for electrolysis. However, because the operating temperature is a high temperature of 600 to 900°C, some modification is necessary for it to be incorporated into a direct reduction process using a shaft furnace. [SOLUTION TO PROBLEM]
[0007] The present application discloses the following aspects as one means for solving this problem. <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 an exhaust gas port provided above the gas supply port, 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, 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 feedstock at a temperature of 600°C to 900°C to the raw material supply port, the hydrogen production device has a solid oxide electrolyzer cell, the solid oxide electrolyzer cell uses water vapor-containing gas exhausted from the exhaust gas port to produce hydrogen gas, and the hydrogen gas produced by the solid oxide electrolyzer cell is utilized as the reducing gas. <Aspect 2> A hydrogen reduction system according to aspect 1, wherein the raw material pretreatment device has a mechanism for removing sulfur present in the iron oxide feedstock. <Aspect 3> A hydrogen reduction system according to aspect 1 or 2, wherein the hydrogen reduction system comprises a water removal device, discharge gas from a hydrogen electrode of the solid oxide electrolyzer cell is supplied to the water removal device, and the water removal device removes at least a portion of the water present in the discharge gas. <Aspect 4> A hydrogen reduction system according to aspect 3, wherein the water removal device removes at least a portion of the water in the discharge gas by cooling the discharge gas to 100°C or below, and the water-removed discharge gas is supplied to the reducing gas heating device and is utilized as the reducing gas. <Aspect 5> A method for producing reduced iron, the method comprising: supplying an iron oxide feedstock into a shaft furnace while supplying a reducing gas containing hydrogen gas into the shaft furnace, and reducing the iron oxide feedstock inside the shaft furnace to obtain reduced iron, and exhausting water vapor-containing gas produced by reduction of the iron oxide feedstock out of the shaft furnace, wherein: the iron oxide feedstock is supplied into the shaft furnace after having been heated to 600°C to 900°C, the reducing gas is supplied into the shaft furnace after having been heated, the water vapor-containing gas exhausted from the shaft furnace is supplied to a solid oxide electrolyzer cell, hydrogen gas is produced from the water vapor-containing gas by the solid oxide electrolyzer cell, and the hydrogen gas produced by the solid oxide electrolyzer cell is utilized as the reducing gas. <Aspect 6> The method for producing reduced iron according to aspect 5, wherein the method comprises removing sulfur present in the iron oxide feedstock before supplying the iron oxide feedstock into the shaft furnace. <Aspect 7> The method for producing reduced iron according to aspect 5 or 6, wherein the method comprises removing water present in discharge gas from the hydrogen electrode of the solid oxide electrolyzer cell. <Aspect 8> The method for producing reduced iron according to aspect 7, wherein the method comprises: cooling the discharge gas from the hydrogen electrode of the solid oxide electrolyzer cell to 100°C or below to remove water present in the discharge gas, and heating the water-removed discharge gas and utilizing it as the reducing gas. [EFFECTS OF INVENTION]
[0008] If the temperature of the iron oxide feedstock supplied to the shaft furnace is 600°C to 900°C in the hydrogen reduction system and in the method for producing reduced iron of the disclosure, the temperature of the water vapor-containing gas exhausted from the shaft furnace will tend to be a suitable temperature for operation of an SOEC. That is, in the hydrogen reduction system and the method for producing reduced iron of the disclosure, it is possible to increase the electrolysis efficiency for an SOEC when hydrogen gas is produced by the SOEC using water vapor-containing gas exhausted from a shaft furnace. The hydrogen gas produced by the SOEC can be utilized as a reducing gas for reduction of iron oxide. As a result, it is possible to reduce the amount of hydrogen gas supplied from an external source, for example. BRIEF DESCRIPTION OF DRAWINGS
[0009] Fig. 1 is a schematic view of an example of a hydrogen reduction system and a method for producing reduced iron. Fig. 2 is a schematic view of an example of a hydrogen reduction system and a method for producing reduced iron. Fig. 3 is a schematic view of an example of a hydrogen reduction system and a method for producing reduced iron. Fig. 4 is a schematic view of an example of a hydrogen reduction system and a method for producing reduced iron. Fig. 5 is a schematic view of an example of a hydrogen reduction system and a method for producing reduced iron. DESCRIPTION OF EMBODIMENTS
[0010] A hydrogen reduction system and method for producing reduced iron according to this embodiment will now be described with reference to the accompanying drawings, with the understanding that the hydrogen reduction system and method for producing reduced iron are not limited to these embodiments.
[0011] 1. Hydrogen reduction system As shown in Figs. 1 to 5, the hydrogen reduction system 100 according to one embodiment has 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 has 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 an exhaust gas 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 that has been supplied from the reducing gas supply device 20. The reducing gas that has been 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 feedstock having a temperature of 600°C to 900°C, to the raw material supply port 11. The hydrogen production device 50 has a solid oxide electrolyzer cell 51. The solid oxide electrolyzer cell 51 utilizes the water vapor-containing gas exhausted from the exhaust gas port 14 to produce hydrogen gas. The hydrogen gas produced by the solid oxide electrolyzer cell 51 is utilized as the reducing gas. 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 an exhaust gas port 14 provided above the gas supply port 12. The specific positions and forms of the raw material supply port 11, the gas supply port 12, the reduced iron discharge port 13 and the exhaust gas port 14 in the shaft furnace 10 are not particularly restricted so long as the positional relationships specified above are satisfied. The raw material supply port 11 may also be provided at the top or upper part of the shaft furnace 10, for example. The gas supply port 12 may also be provided directly below the location of the shaft furnace 10 that is to be the reduction zone, for example. The reduction zone is, for example, the zone inside the shaft furnace 10 between the gas supply port 12 and the exhaust gas port 14 (between the height position of the gas supply port 12 and the height position of the exhaust gas port 14). The reduced iron discharge port 13 may be provided at the bottom or lower part of the shaft furnace 10. The exhaust gas port 14 may also be provided at the top or upper part of the shaft furnace 10, at a different section than the raw material supply port 11. If the raw material supply port 11, gas supply port 12, reduced iron discharge port 13 and exhaust gas port 14 satisfy the positional relationships specified above, then it will be possible to supply iron oxide feedstock from the raw material supply port 11 into the shaft furnace 10 to form a packed bed of the iron oxide feedstock inside the shaft furnace 10, to supply a reducing gas containing hydrogen gas from the gas supply port 12 to the packed bed inside the shaft furnace 10, to contact the iron oxide feedstock and the reducing gas inside the shaft furnace 10 for reduction of the iron oxide, and to obtain reduced iron from the reduced iron discharge port 13, while also exhausting water vapor-containing gas from the exhaust gas port 14 out of the shaft furnace 10.
[0013] The iron oxide feedstock supplied to the shaft furnace 10 comprises at least iron oxide. The iron oxide feedstock may be at least one material selected from among iron ore pellets, lump ore and sintered ore, for example. The iron oxide feedstock may also comprise either or both silicon dioxide and aluminum oxide in addition to iron oxide. The iron oxide feedstock may also contain impurities. For example, the iron oxide feedstock may comprise sulfur. When the iron oxide feedstock comprises sulfur, the amount of sulfur in the iron oxide feedstock is preferably reduced by a sulfur removal mechanism as described below. The iron oxide feedstock may be one having a particle size distribution, or one having a uniform particle size. The mean particle size of the iron oxide feedstock may be 5.0 mm to 30.0 mm or 10.0 mm to 15.0 mm, for example. The “particle size” of the iron oxide feedstock is the sieve diameter of the feedstock. The “mean particle size” of the iron oxide feedstock is the weighted average value for the particle size of the feedstock. The mean particle size of the iron oxide feedstock is measured in the following manner. Specifically, the mass-based particle size distribution can be obtained by a dry sieve screening test according to JIS Z 8815:1995, and the weighted average by mass, calculated using the averages for the maximum particle size and minimum particle size of each sieve as the representative particle size, may be used for measurement of the mean particle size of the iron oxide feedstock. The iron oxide feedstock may be formed into pellets, or it may be in a powder state or lump shape, or in any other shape. The feed rate of the iron oxide feedstock into the shaft furnace 10 may be selected as an optimal amount based on the scale and operating conditions of the shaft furnace 10. According to this embodiment, the temperature of the iron oxide feedstock supplied to the shaft furnace 10 is 600°C to 900°C, after treatment by the raw material pretreatment device 40 described below. The temperature of the iron oxide feedstock will be explained below.
[0014] For this embodiment, reduction of the iron oxide by the reducing gas occurs in the reduction zone inside the shaft furnace 10. The temperature of the reducing gas supplied from the gas supply port 12 to the interior of the shaft furnace 10 (the temperature at the gas supply port 12) may be 700°C to 1100°C, for example. The flow rate of the reducing gas supplied from the gas supply port 12 into the shaft furnace 10 (the flow rate at the gas supply port 12) may be 1000 Nm3 / t-DRI to 2200 Nm3 / t-DRI, for example. The temperature of the iron oxide feedstock in the reduction zone may be 600°C to 900°C, for example. The reduction rate of the reduced iron discharged from the reduced iron discharge port 13 through the reduction zone may be 65% to 98%, for example. The temperature of the water vapor-containing gas exhausted from the exhaust gas port 14 to the outside of the shaft furnace 10 through the reduction zone corresponds to the temperature of the iron oxide feedstock supplied from the raw material supply port 11, i.e. 600°C to 900°C.
[0015] 1.2 Reducing gas supply device The reducing gas supply device 20 supplies the reducing gas containing hydrogen gas to the reducing gas heating device 30 described below. The reducing gas supply device 20 may also 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 comprise any one or more from among a flow meter, pressure gauge and thermometer, and it may also comprise a control mechanism that controls either or both the flow rate and pressure of the reducing gas. The reducing gas supply device 20 may also be constructed so that it is connected to a reducing gas source or to the solid oxide electrolyzer cell (SOEC) 51 described below via piping, and gas comprising hydrogen gas is supplied from the reducing gas source or SOEC to the reducing gas supply device 20, or it may be constructed so that it is connected to the reducing gas heating device 30 described below via piping, and supplies the reducing gas to the reducing gas heating device 30.
[0016] The flow rate of the reducing gas supplied from the reducing gas supply device 20 may be 1000 Nm3 / t-DRI to 2200 Nm3 / t-DRI, for example. The pressure of the reducing gas supplied from the reducing gas supply device 20 may be 0.1 MPa to 0.8 MPa, for example. The temperature of the reducing gas supplied from the reducing gas supply device 20 may be from room temperature up to 100°C, for example. The reducing gas supply device 20 used may be a commercially available product. An example of a commercially available reducing gas supply device is an on-site supply unit by Air Water Inc.
[0017] The reducing gas supplied from the reducing gas supply device 20 comprises hydrogen gas, and optionally other gases. The reducing gas may comprise hydrogen gas at 40 vol% to 100 vol%. Gases other than hydrogen gas include CO gas, hydrocarbon gases and inert gases. The inert gas may be one or more selected from among, for example, nitrogen gas, noble gases such as argon gas, and CO2 gas or water vapor. The proportion of hydrogen gas in the reducing gas may be 40 vol% or greater, 45 vol% or greater, 50 vol% or greater, 55 vol% or greater, 60 vol% or greater, 65 vol% or greater, 70 vol% or greater, 75 vol% or greater, 80 vol% or greater, 85 vol% or greater, 90 vol% or greater or 95 vol% or greater. The proportion of hydrogen gas in the reducing gas is most preferably 90 vol% to 100 vol%.
[0018] 1.3 Reducing gas heating device The reducing gas heating device 30 heats the reducing gas that has been supplied from the reducing gas supply device 20. The reducing gas that has been 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 also supply the reducing gas to the gas supply port 12 while controlling the flow rate, pressure and temperature of the reducing gas, for example. In other words, the reducing gas heating device 30 may comprise a heating mechanism that heats gas, and may also comprise a control mechanism that controls the gas temperature. The reducing gas heating device 30 may further comprise any one or more from among a flow meter, pressure gauge and thermometer, and it may also comprise a control mechanism that controls either or both the flow rate and pressure of the reducing gas. The heating mechanism may be any mechanism that is able to heat gas, and it may be a heat exchanger, a heater with external heating, or one that causes partial combustion of gas (a mechanism that causes reaction between oxygen and a portion of the hydrogen in the reducing gas to cause combustion, thus heating the gas by the heat of combustion).
[0019] The flow rate of the reducing gas supplied from the reducing gas heating device 30 may be 1000 Nm3 / t-DRI to 2200 Nm3 / t-DRI, for example. The pressure of the reducing gas supplied from the reducing gas heating device 30 may be 0.1 MPa to 0.8 MPa, for example. The temperature of the reducing gas supplied from the reducing gas heating device 30 (the temperature at the gas supply port 12) may be 700°C to 1100°C, for example. The reducing gas heating device 30 used may be a commercially available product. An example of a commercially available reducing gas heating device is a gas heater by Izumi Dennetsu Co., Ltd.
[0020] 1.4 Raw material pretreatment device The raw material pretreatment device 40 supplies an iron oxide feedstock having a temperature of 600°C to 900°C, to the raw material supply port 11 of the shaft furnace 10. The raw material pretreatment device 40: (1) may have a heating mechanism that heats the iron oxide feedstock, or (2) may be a feedstock production apparatus that produces a high-temperature iron oxide feedstock.
[0021] (1) The raw material pretreatment device 40 may be one that, after heating the iron oxide feedstock to 600°C to 900°C by a heating mechanism, supplies the iron oxide feedstock to the raw material supply port 11 of the shaft furnace 10. There are no particular restrictions on the heating mechanism, and any one may be employed that can heat the iron oxide feedstock to between 600°C and 900°C. The heating mechanism may be one that heats the iron oxide feedstock in a batch process, or it may be one that heats it in a continuous manner. The raw material pretreatment device 40 may also comprise a hopper, a feedstock discharger, a thermometer, a heating mechanism, and a control mechanism that controls the feedstock heating temperature.
[0022] (2) The raw material pretreatment device 40 may be a firing furnace that produces pellets as iron oxide feedstock. That is, the raw material pretreatment device 40 according to one embodiment may be constructed so that the pellets produced in the pellet firing furnace are transferred to the raw material supply port 11 of the shaft furnace 10 while at a temperature of 600°C to 900°C.
[0023] The temperature of the iron oxide feedstock supplied from the raw material pretreatment device 40 to the raw material supply port 11 of the shaft furnace 10 may be 600°C or higher, 650°C or higher or 700°C or higher, and 900°C or lower, 850°C or lower or 800°C or lower. By thus having the iron oxide feedstock heated before it is supplied into the shaft furnace 10, the temperature of the water vapor-containing gas exhausted from the shaft furnace 10 will tend to be a temperature suitable for operation of the solid oxide electrolyzer cell (SOEC) 51, as explained below. Heating of the iron oxide feedstock before it is supplied into the shaft furnace 10 also increases the overall thermal efficiency of the system while further increasing the reduction efficiency of the iron oxide feedstock inside the shaft furnace 10. The “temperature of the iron oxide feedstock” is the surface temperature of the iron oxide feedstock. The surface temperature of the iron oxide feedstock may be the actual measured value with a thermocouple, or it may be an estimated value obtained by simulation.
[0024] As mentioned above, the iron oxide feedstock may comprise sulfur. The sulfur in the iron oxide feedstock gasifies and circulates in the hydrogen reduction system. When sulfur is present in a hydrogen reduction system, the devices in it may undergo corrosion and the catalyst of the solid oxide electrolyzer cell (SOEC) 51 may become poisoned. When sulfur is present in the iron oxide feedstock, therefore, the amount of sulfur in the iron oxide feedstock is preferably reduced. For example, as shown in Fig. 2, the raw material pretreatment device 40 may have a mechanism 41 that removes sulfur in the iron oxide feedstock. The sulfur-removing mechanism 41 may be a mechanism that heats the iron oxide feedstock with an oxidizing atmosphere, for example, to remove the sulfur in the iron oxide feedstock as sulfur dioxide gas.
[0025] 1.5 Hydrogen production device The hydrogen production device 50 comprises a solid oxide electrolyzer cell (SOEC) 51. The SOEC 51 utilizes the water vapor-containing gas exhausted from the exhaust gas port 14 of the shaft furnace 10 to produce hydrogen gas. The hydrogen gas produced by SOEC 51 is utilized as the reducing gas. For example, the hydrogen gas produced by the SOEC 51 may be supplied to any or all of the reducing gas supply device 20, reducing gas heating device 30 and gas supply port 12, or it may be supplied to only either or both the reducing gas heating device 30 and the gas supply port 12. The temperature of the hydrogen gas produced by the SOEC 51 will usually be a high temperature. When hydrogen gas produced by the SOEC 51 is supplied to either or both the reducing gas heating device 30 and the gas supply port 12, it is easier to effectively utilize the thermal energy of the hydrogen gas.
[0026] The structure of the SOEC 51 itself is known (see Japanese Unexamined Patent Publication No. 2005-232525 and Japanese Unexamined Patent Publication No. H7-109592, for example). Specifically, the SOEC 51 has, for example, a hydrogen electrode, an oxygen electrode, and an electrolyte layer situated between them. The water vapor-containing gas exhausted from the exhaust gas port 14 is supplied to the hydrogen electrode of the SOEC 51. At the hydrogen electrode, hydrogen gas is generated by electrolysis of water vapor. At the oxygen electrode, on the other hand, electrons are released from oxygen radicals, generating oxygen gas. That is, hydrogen gas-containing discharge gas is discharged from the hydrogen electrode of the SOEC 51, while oxygen gas-containing discharge gas is discharged from the oxygen electrode. The hydrogen electrode may comprise a metal catalyst-co-catalyst such as Ni-CeO2, or a metal catalyst-support for example. The oxygen electrode may comprise a ceramic catalyst such as LaCoO3, for example. The electrolyte layer may comprise a ceramic electrolyte such as ZrO2. The hydrogen production device 50 may also have a plurality of SOECs 51 stacked via metal separators to form an SOEC stack. The electric power density during operation of the SOEC 51 may be 0.5 A / m2 to 1.0 A / m2, for example.
[0027] The moisture content of the water vapor-containing gas supplied to the SOEC 51 is not particularly restricted. The water vapor-containing gas may also comprise other gases in addition to water vapor. The water vapor-containing gas may comprise one or more selected from among hydrogen gas, carbon monoxide gas, carbon dioxide gas, hydrocarbon gas and inert gases, although this will depend on the composition of the iron oxide feedstock or reducing gas. The flow rate and pressure of the water vapor-containing gas supplied to the SOEC 51 are also not particularly restricted, and may be appropriately adjusted depending on the scale of the hydrogen production device 50.
[0028] The operating temperature of the SOEC 51 will normally be 600°C to 900°C. For this embodiment, the temperature of the water vapor-containing gas exhausted from the exhaust gas port 14 of the shaft furnace 10 corresponds to the temperature of the iron oxide feedstock supplied from the raw material supply port 11 into the shaft furnace 10, or in other words, it is a temperature near 600°C to 900°C. That is, according to this embodiment the temperature of the water vapor-containing gas exhausted from the exhaust gas port 14 tends to be a temperature suitable for operation of the SOEC 51. For this embodiment, therefore, the water vaporcontaining gas exhausted from the exhaust gas port 14 of the shaft furnace 10 may be directly supplied to the SOEC without heating or cooling by an external device.
[0029] 1.6 Other components The hydrogen reduction system 100 may also comprise other devices in addition to the shaft furnace 10, reducing gas supply device 20, reducing gas heating device 30, raw material pretreatment device 40 and hydrogen production device 50 described above. Examples of such other devices will now be described.
[0030] 1.6.1 Water removal device As mentioned above, water vapor is present in the gas discharged from the shaft furnace 10. The water vapor-containing gas is supplied to the SOEC 51, and hydrogen is produced. At the SOEC 51, a portion of the water vapor in the water vapor-containing gas is circulated throughout the system without being converted to hydrogen, and this can increase the water vapor concentration in the system. The hydrogen reduction system 100 according to one embodiment may therefore have a water removal device 60, as shown in Fig. 3. For example, in the hydrogen reduction system 100, the construction may be such that discharge gas from the hydrogen electrode of the SOEC 51 (gas comprising water vapor in addition to hydrogen) is supplied to the water removal device 60, with the water removal device 60 removing at least a portion of the water in the discharge gas. The water removal device 60 may be disposed further downstream than the hydrogen electrode of the SOEC 51, and further upstream than the gas supply port 12 of the shaft furnace 10, for example. For example, the water removal device 60 may be disposed between the hydrogen electrode of the SOEC 51 and the reducing gas heating device 30, as explained below.
[0031] There are no particular restrictions on the water removal system in the water removal device 60. For example, the water removal device 60 may be one that cools the discharge gas from the hydrogen electrode of the SOEC 51 to 100°C or below to remove at least a portion of the water in the discharge gas. In this case, the temperature of the discharge gas after water removal is low, and therefore if it is supplied directly into the shaft furnace 10 as the reducing gas, it can lower efficiency of the iron oxide reduction reaction. When the water is removed by cooling in the water removal device 60, therefore, the water-removed discharge gas (which comprises hydrogen gas) is preferably supplied to the reducing gas heating device 30 and heated before being utilized as the reducing gas, as shown in Fig. 4.
[0032] The flow rate of the water vapor-containing gas supplied to the water removal device 60 may be 1000 Nm3 / t-DRI to 2200 Nm3 / t-DRI, for example. The pressure of the water vaporcontaining gas supplied to the water removal device 60 may be 0.1 MPa to 0.8 MPa, for example. The temperature of the water vapor-containing gas supplied to the water removal device 60 may be 600°C to 900°C, for example. The water removal device 60 used may be a commercially available product. An example of a commercially available water removal device is a gas cooling (quenching) device by Hipotec Co.
[0033] Alternatively, the water removal device 60 may be one that separates the hydrogen gas and water vapor using a device such as a molecular sieve. The water removal device 60 may also, alternatively, remove water by selectively reacting or adsorbing water using a material that is inert to hydrogen but reactive with water.
[0034] 1.6.2 Carbon dioxide removal device As mentioned above, the reducing gas supplied to the shaft furnace 10 or the exhaust gas from the shaft furnace 10 can potentially comprise carbon dioxide. Carbon dioxide is inert to reduction reaction during a direct reduction process, but a high carbon dioxide concentration in the system can relatively lower the reducing gas concentration and lower the efficiency for iron oxide reduction reaction. The hydrogen reduction system 100 according to one embodiment may therefore have a carbon dioxide removal device 70, as shown in Fig. 5. For example, the construction of the hydrogen reduction system 100 may be such that discharge gas from the hydrogen electrode of the SOEC 51 (gas comprising water vapor and carbon dioxide in addition to hydrogen) is supplied to the water removal device 60, the water removal device 60 removes at least a portion of the water in the discharge gas, and the water-removed discharge gas is supplied to the carbon dioxide removal device 70, with the carbon dioxide removal device 70 removing at least a portion of the carbon dioxide in the discharge gas. The carbon dioxide removal device 70 may be installed at any position in the gas circulation line of the hydrogen reduction system 100. The carbon dioxide removal device 70 may be disposed further downstream than the hydrogen electrode of the SOEC 51, and further upstream than the gas supply port 12 of the shaft furnace 10, for example. 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 the hydrogen gas and carbon dioxide gas by a device such as a molecular sieve. Alternatively, the carbon dioxide removal device 70 may remove carbon dioxide by selectively reacting or adsorbing the carbon dioxide with a material that is inert to hydrogen but reactive with carbon dioxide.
[0036] 1.6.3 Sulfur removal device The above explanation illustrates a case where the raw material pretreatment device 40 comprises a sulfur-removing mechanism 41, but the hydrogen reduction system 100 may also comprise a sulfur removal device (not shown) separate from the raw material pretreatment device 40. For example, sulfur may be present in the water vapor-containing gas that is exhausted from the shaft furnace 10. When present, the sulfur in the gas is preferably removed by the sulfur removal device before the water vapor-containing gas exhausted from the shaft furnace 10 reaches the SOEC 51 of the hydrogen production device 50. The hydrogen reduction system 100 may also be constructed so that the sulfur concentration in the gas circulating through circulating line is monitored by a sulfur concentration monitoring device, and when the sulfur concentration in the circulating gas has exceeded a threshold value, the sulfur is removed from the circulating gas by the sulfur removal device to lower the sulfur concentration of the circulating gas to below the threshold value.
[0037] The system used to monitor the sulfur concentration in the circulating gas may be an actual measuring system or an estimating system. An actual measuring system may be a system that measures the sulfur concentration in a circulating gas or iron oxide feedstock by a gas chromatography method, atomic absorption method, UV fluorescence method or ICP. An estimating system may be a system that theoretically estimates the amount of sulfur migrating from the iron oxide feedstock into the circulating gas.
[0038] The system for lowering the sulfur concentration in the circulating gas may be (1) a system in which the temperature of the reducing gas is varied to lower the sulfur concentration in the circulating gas, (2) a system in which the type of iron oxide feedstock supplied to the raw material supply port 11 is switched to supply iron oxide feedstock with a low sulfur concentration, thereby lowering the sulfur concentration in the circulating gas, (3) a system in which the type of reducing gas supplied to the gas supply port 12 is switched to supply the reducing gas with a low sulfur concentration, thereby lowering the sulfur concentration in the circulating gas, or (4) a system in which a desulfurizing mechanism is provided in part of the circulating line to lower the sulfur concentration in the circulating gas. The desulfurizing mechanism may be one that removes at least a portion of the sulfur (such as hydrogen sulfide) in the circulating gas by a filter method or adsorption method, for example.
[0039] 1.7 Supplement The constructions shown in Figs. 1 to 5 may be combined in any desired manner in the hydrogen reduction system 100. Specifically, the hydrogen reduction system 100 may comprise, in addition to the shaft furnace 10, reducing gas supply device 20, reducing gas heating device 30, raw material pretreatment device 40 and hydrogen production device 50, also one or more from among the sulfur-removing mechanism 41, water removal device 60, carbon dioxide removal device 70 and sulfur removal device (not shown). The hydrogen reduction system 100 may also comprise other devices in addition to the devices mentioned above.
[0040] 2. Method for producing reduced iron As shown in Figs. 1 to 5, the method for producing reduced iron according to one embodiment comprises supplying an iron oxide feedstock into the shaft furnace 10 while also supplying a reducing gas containing hydrogen gas into the shaft furnace 10, the iron oxide feedstock being reduced inside the shaft furnace 10 to obtain reduced iron, and exhausting out of the shaft furnace 10 the water vapor-containing gas produced by reduction of the iron oxide feedstock. The iron oxide feedstock is supplied into the shaft furnace 10 after having been heated to 600°C to 900°C. The reducing gas is also supplied into the shaft furnace 10 after being heated. The water vapor-containing gas exhausted from the shaft furnace 10 is supplied to the solid oxide electrolyzer cell (SOEC) 51, and hydrogen gas is produced from the water vaporcontaining gas by the SOEC 51. The hydrogen gas produced by the SOEC 51 is utilized as the reducing gas. The shaft furnace 10, SOEC 51, iron oxide feedstock, reducing gas and water vapor-containing gas are as described above, and will not be explained again here.
[0041] The construction of the hydrogen reduction system 100 as described above may be employed directly in the method for producing reduced iron according to one embodiment. For example, the method for producing reduced iron according to one embodiment may comprise removing the sulfur in the iron oxide feedstock before the iron oxide feedstock is supplied into the shaft furnace 10. The method for producing reduced iron according to one embodiment may also comprise removing water present in the discharge gas from the hydrogen electrode of the SOEC 51. The method for producing reduced iron according to one embodiment may also comprise cooling discharge gas from the hydrogen electrode of the SOEC 51 to 100°C or below to remove the water in the discharge gas, and heating the water-removed discharge gas for use as the reducing gas. The method of removing sulfur in the iron oxide feedstock and the method of removing water in the gas are the same as described above and will not be repeated here.
[0042] 3. Effect As explained above, in the hydrogen reduction system 100 and the method for producing reduced iron according to one embodiment, water vapor-containing gas exhausted from the shaft furnace 10 is supplied to the SOEC 51, and hydrogen gas is produced by water-splitting reaction at the SOEC 51. If the temperature of the iron oxide feedstock supplied to the shaft furnace 10 is 600°C to 900°C, the temperature of the water vapor-containing gas exhausted from the shaft furnace 10 will tend to be a suitable temperature for operation of the SOEC 51. That is, when water vapor-containing gas exhausted from the shaft furnace 10 is used to produce hydrogen gas by the SOEC 51, the electrolysis efficiency of the SOEC 51 can be increased even without additional heating of the water vapor-containing gas exhausted from the shaft furnace 10. The hydrogen gas produced by the SOEC 51 can be utilized as a reducing gas for reduction of iron oxide. As a result, it is possible to reduce the amount of hydrogen gas supplied from an external source, for example. Maximizing the electrolysis efficiency of the SOEC 51 makes it possible to convert the total amount of water vapor exhausted from the shaft furnace 10 into hydrogen, so that initial supply of the reducing gas is sufficient without requiring later additional external supply of hydrogen.
[0043] The hydrogen gas produced by the SOEC 51 has a temperature of 600°C to 900°C which corresponds to the operating temperature of the SOEC 51, and such high-temperature hydrogen gas can be utilized as is for direct reduction in the shaft furnace 10. That is, less heating is required for the produced hydrogen gas, or further heating may be unnecessary.
[0044] In the hydrogen reduction system 100 and the method for producing reduced iron according to one embodiment, the sulfur present in the iron oxide feedstock may be removed before it is supplied into the shaft furnace 10, as mentioned above. The sulfur in the iron oxide feedstock, reacting with the reducing gas, is converted to hydrogen sulfide and is exhausted out of the shaft furnace 10. If the sulfur in the iron oxide feedstock is removed beforehand, then it is possible to reduce the amount of sulfur (such as hydrogen sulfide) present in the water vapor-containing gas exhausted from the shaft furnace 10, and to help prevent poisoning or deterioration of the SOEC 51 catalyst by sulfur during production of hydrogen gas using the water vapor-containing gas in the SOEC 51. EXAMPLES
[0045] The effect of the technology of the disclosure will now be described in greater detail using Examples, with the understanding that these Examples are not intended to be limitative on the technology of the disclosure in any way.
[0046] An example of a design for a hydrogen reduction system that is able to produce reduced iron at 15 kg / hr will now be described.
[0047] (1) A shaft furnace with a diameter of 0.1 m and an effective height of 4 m was prepared. (2) An iron oxide feedstock heated to 850°C was supplied from a raw material supply port provided at the top of the shaft furnace, into the shaft furnace. (3) Reducing gas was supplied from a gas supply port provided in the side wall of the shaft furnace into the shaft furnace at a flow rate of 2000 Nm3 / t-DRI. The composition and temperature of the supplied reducing gas are shown in Table 1. (4) Exhaust gas was exhausted out of the shaft furnace from an exhaust gas port provided in the side wall of the shaft furnace and above the gas supply port. The composition and temperature of the exhaust gas are shown in Table 1. (5) Steps (2) to (4) above were carried out simultaneously, and the reduced iron was continuously discharged from the reduced iron discharge port provided at the bottom section of the shaft furnace. The reduction rate of the reduced iron was 95%.
[0048] [Table 1]_____________________________________________________________________ H2 H2O CO CO2 N2 Temp vol% vol% vol% vol% vol% °C Supply gas 95 0 0 0 5 980 Exhaust gas 60 35 0 0 5 840
[0049] As shown in Table 1, heating the iron oxide feedstock to 850°C and then supplying it to the shaft furnace allowed the temperature of exhaust gas from the shaft furnace to be controlled to near 850°C (840°C). This temperature is within the range of the operating temperature of an SOEC, or in other words, the result suggests that supplying exhaust gas from the shaft furnace directly to the SOEC allows water vapor in the exhaust gas to be converted to hydrogen. The temperature of the exhaust gas from the shaft furnace thus corresponds to the supply temperature for the iron oxide feedstock. Considering that the operating temperature of the SOEC will usually be 600°C to 900°C, if the supply temperature of the iron oxide feedstock is 600°C to 900°C, then the exhaust gas temperature from the shaft furnace will also be near 600°C to 900°C, as a temperature suitable for operating the SOEC.
[0050] Specific examples of conditions for the SOEC include the following. Operating temperature: 800°C Power density: 1.0 A / m Hydrogen electrode: Ni-CeO2 mixed material Electrolyte: ZrO2 Oxygen electrode: LaCoO3 Separator: SUS304
[0051] To summarize the above, it is believed that with a hydrogen reduction system having the following constructions (A1) to (I1) and a method for producing reduced iron having the following constructions (A2) to (E2), the temperature of the water vapor-containing gas exhausted from the shaft furnace will tend to be a temperature suitable for operation of an SOEC, the electrolysis efficiency of the SOEC can be increased, and the amount of externally supplied hydrogen gas can be reduced.
[0052] (A1) The hydrogen reduction system has 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 has 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 an exhaust gas port provided above the gas supply port. (C1) The reducing gas supply device supplies reducing gas containing hydrogen gas to the reducing gas heating device. (D1) The reducing gas heating device heats the reducing gas that has been supplied from the reducing gas supply device. (E1) The reducing gas that has been heated by the reducing gas heating device is supplied to the gas supply port. (F1) The raw material pretreatment device supplies an iron oxide feedstock having a temperature of 600°C to 900°C, to the raw material supply port. (G1) The hydrogen production device has a solid oxide electrolyzer cell. (H1) The solid oxide electrolyzer cell utilizes the water vapor-containing gas exhausted from the exhaust gas port to produce hydrogen gas. (I1) The hydrogen gas produced by the solid oxide electrolyzer cell is utilized as the reducing gas.
[0053] (A2) The method for producing reduced iron comprises supplying an iron oxide feedstock into a shaft furnace while also supplying a reducing gas containing hydrogen gas into the shaft furnace, the iron oxide feedstock being reduced inside the shaft furnace to obtain reduced iron, and exhausting out of the shaft furnace the water vapor-containing gas produced by reduction of the iron oxide feedstock. (B2) The iron oxide feedstock is supplied into the shaft furnace after having been heated to 600°C to 900°C. (C2) The reducing gas is supplied into the shaft furnace after being heated. (D2) The water vapor-containing gas exhausted from the shaft furnace is supplied to the solid oxide electrolyzer cell, and hydrogen gas is produced from the water vapor-containing gas by the solid oxide electrolyzer cell. (E2) The hydrogen gas produced by the solid oxide electrolyzer cell is utilized as the reducing gas. REFERENCE SIGNS LIST
[0054] 10 Shaft furnace 11 Raw material supply port 5 12 Gas supply port 13 Reduced iron discharge port 14 Exhaust gas port 20 Reducing gas supply device 30 Reducing gas heating device 10 40 Raw material pretreatment device 41 Sulfur-removing mechanism 50 Hydrogen production device 51 Solid oxide electrolyzer cell (SOEC) 60 Water removal device 15 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, anda hydrogen production device,whereinthe 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, andan exhaust gas port provided above the gas supply port,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,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 feedstock at a temperature of 600°C to 900°C to the raw material supply port,the hydrogen production device comprises a solid oxide electrolyzer cell,the solid oxide electrolyzer cell uses water vapor-containing gas exhausted from the exhaust gas port to produce hydrogen gas, andthe hydrogen gas produced by the solid oxide electrolyzer cell is utilized as the reducinggas.
2. A hydrogen reduction system according to claim 1, whereinthe raw material pretreatment device comprises a mechanism for removing sulfur present in the iron oxide feedstock.
3. A hydrogen reduction system according to claim 1 or 2, whereinthe hydrogen reduction system comprises a water removal device,discharge gas from a hydrogen electrode of the solid oxide electrolyzer cell is supplied to the water removal device, andthe water removal device removes water present in the discharge gas.
4. A hydrogen reduction system according to claim 3, whereinthe water removal device removes at least a portion of the water in the discharge gas by cooling the discharge gas to 100°C or below, andthe water-removed discharge gas is supplied to the reducing gas heating device and is utilized as the reducing gas.
5. A method for producing reduced iron, the method comprising:supplying an iron oxide feedstock into a shaft furnace while supplying a reducing gas containing hydrogen gas into the shaft furnace, and reducing the iron oxide feedstock inside the shaft furnace to obtain reduced iron, andexhausting water vapor-containing gas produced by reduction of the iron oxide feedstock out of the shaft furnace,wherein:the iron oxide feedstock is supplied into the shaft furnace after having been heated to 600°C to 900°C,the reducing gas is supplied into the shaft furnace after having been heated,the water vapor-containing gas exhausted from the shaft furnace is supplied to a solid oxide electrolyzer cell,hydrogen gas is produced from the water vapor-containing gas by the solid oxide electrolyzer cell, andthe hydrogen gas produced by the solid oxide electrolyzer cell is utilized as the reducing gas.
6. The method for producing reduced iron according to claim 5, whereinthe method comprises removing sulfur present in the iron oxide feedstock before supplying the iron oxide feedstock into the shaft furnace.The method for producing reduced iron according to claim 5 or 6, whereinthe method comprises removing water present in discharge gas from the hydrogen electrode of the solid oxide electrolyzer cell.5
8. The method for producing reduced iron according to claim 7, whereinthe method comprises:cooling the discharge gas from the hydrogen electrode of the solid oxide electrolyzer cell to 100°C or below to remove water present in the discharge gas, and10 heating the water-removed discharge gas and utilizing it as the reducing gas.