Method for producing reduced iron and system for producing reduced iron

Abstract

Disclosed is a technique with which it is possible to minimize corrosion of equipment when producing reduced iron through a direct reduction process in which a shaft furnace is used. A method for producing reduced iron according to the present disclosure comprises: a reduction step for reducing an iron oxide raw material using a reducing gas in a shaft furnace to obtain reduced iron; an exhaust gas treatment step for treating exhaust gas from the shaft furnace and circulating the treated exhaust gas as a circulating gas; a monitoring step for monitoring at least one of the H2S concentration in the reducing gas, the H2S concentration in the exhaust gas, and the H2S concentration in the circulating gas; and a control step for controlling the H2S concentration.

Description

Reduced iron manufacturing method and reduced iron manufacturing system

[0001] The present application discloses a method and a system 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 For example, a direct reduction process using a shaft furnace is known in which a reducing gas is brought into contact with an iron oxide raw material to obtain direct reduced iron (DRI). Here, in the direct reduction process using a reducing gas, the production and supply of the reducing gas are an issue.

[0003] For example, in a direct reduction process using natural gas, carbon monoxide gas and hydrogen gas contained in the exhaust gas from the shaft furnace are reused (Non-Patent Document 1). In this case, the exhaust gas contains not only carbon monoxide gas and hydrogen gas, but also carbon dioxide gas and water vapor generated when iron oxide is reduced in the shaft furnace. Therefore, the exhaust gas is once cooled to 100°C or less, the water is liquefied and removed, and the natural gas and carbon dioxide gas are reacted in a natural gas reformer, and the generated carbon monoxide- and hydrogen-rich gas is blown back into the shaft furnace. Here, the catalyst used for reforming is H ２ In this respect, the H in natural gas ２ There is an upper limit to the S concentration in the iron oxide raw material (Non-Patent Documents 1 and 2). ２ For natural gas with high sulfur concentration, a chelate iron solution is used to remove sulfur. ２ A technology for converting S into element S has also been developed (Non-Patent Document 2).

[0004] Furthermore, a zero reformer process, which does not have a reformer furnace, is also known as a direct reduction process using natural gas. The zero reformer process has a more relaxed upper limit on the sulfur concentration in natural gas and iron ore than the above-mentioned process using a reformer. However, from the viewpoint of preventing corrosion of equipment, a certain upper limit is set on the sulfur concentration introduced into the system.

[0005] Furthermore, in recent years, development of direct reduction processes using hydrogen gas as a reducing gas has also been underway. As a representative example, a technology is known in which hydrogen gas obtained by electrolysis of water is used in a direct reduction process using a shaft furnace (Patent Document 1). Here, in the direct reduction process using hydrogen gas, unlike the process using natural gas, H is contained in the reducing gas. ２ It does not contain S. However, sulfur in the iron oxide raw material reacts with hydrogen gas to produce H ２ S can be produced.

[0006] DIRECT FROM MIDREX 4TH QUARTER 2019(https: / / www.midrex.com / wp-content / uploads / Midrex-2019-DFM4QTR-Final.pdf)DIRECT FROM MIDREX TECH ARTICLE MAR 2017 PLANT OPS & MAINTENANCE "Midrex Provides SULB Operational Flexibility"(https: / / www.midrex.com / tech-article / midrex-provides-sulb-operational-flexibility / )

[0007] International Publication No. 2020 / 247328

[0008] In conventional direct reduction processes using shaft furnaces, sufficient consideration has not been given to how to manage sulfur from the perspective of suppressing corrosion of equipment.

[0009] The present application discloses the following aspects as one of means for solving the above problems. <Aspect 1> A method for producing reduced iron, comprising: a reduction step of reducing an oxidized iron raw material with a reducing gas in a shaft furnace to obtain reduced iron; an exhaust gas treatment step of treating exhaust gas from the shaft furnace and circulating it as a circulating gas; and a method for producing reduced iron by reducing an oxidized iron raw material with a reducing gas in a shaft furnace. ２ S concentration, H in the exhaust gas ２ S concentration and H in the circulating gas ２ a monitoring step of monitoring at least one of the H concentration and the S concentration;２ and a control step of controlling the S concentration. <Aspect 2> The method for producing reduced iron of Aspect 1, comprising: a reducing gas production step of producing the reducing gas using the circulating gas. <Aspect 3> The method for producing reduced iron of Aspect 2, wherein in the reducing gas production step, the circulating gas and a raw material gas are mixed, and then the circulating gas and the raw material gas are reformed into the reducing gas by a catalyst. <Aspect 4> The method for producing reduced iron of any of Aspects 1 to 3, wherein in the exhaust gas treatment step, a hydrogen-containing gas is produced from water vapor in the exhaust gas by a solid oxide electrolysis cell. <Aspect 5> The method for producing reduced iron of Aspect 4, wherein in the exhaust gas treatment step, at least a portion of the water contained in the hydrogen-containing gas is removed. <Aspect 6> The method for producing reduced iron of any of Aspects 1 to 5, comprising: a heating step of heating the reducing gas by a heating device, and wherein in the monitoring step, ２ S out = H ２ S in +A×(10-3420 / T+0.426×H ２ -H ２ S in ) ... (1) H ２ S out : H in the exhaust gas ２ S concentration [volume %] H ２ S in : H in the reducing gas at the inlet side of the heating device ２ S concentration [vol %] A: constant T: temperature of reducing gas supplied to the shaft furnace [°C] H ２ : Hydrogen gas concentration in reducing gas [vol%] ２Aspect 7 is a method for producing reduced iron according to any one of Aspects 1 to 6, wherein in the control step, at least one of the sulfur content of the oxidized iron raw material, the sulfur content of the reducing gas, and the temperature of the reducing gas is controlled, thereby controlling the H ２ A method for producing reduced iron, in which the S concentration is controlled. <Aspect 8> The method for producing reduced iron of Aspect 7, in which hydrogen gas obtained by electrolysis of water is used as the reducing gas, and in the control step, the proportion of the hydrogen gas in the reducing gas is changed to control the sulfur content of the reducing gas. <Aspect 9> The method for producing reduced iron of Aspect 7 or 8, in which in the control step, the proportion of burned pellets in the oxidized iron raw material is changed to control the sulfur content of the oxidized iron raw material. <Aspect 10> The method for producing reduced iron of any of Aspects 1 to 9, in which the H ２A method for producing reduced iron, in which the sulfur concentration is controlled to 5 ppmv or less. <Aspect 11> A method for producing reduced iron according to any one of Aspects 1 to 10, comprising a raw material pretreatment step of heating the oxidized iron raw material to remove at least a portion of the sulfur contained in the oxidized iron raw material. <Aspect 12> A method for producing reduced iron according to any one of Aspects 1 to 11, in which the temperature of the reducing gas is 700°C or higher and 1100°C or lower. <Aspect 13> A method for producing reduced iron according to any one of Aspects 1 to 12, comprising monitoring the concentration of sulfur contained in the reduced iron. <Aspect 14> A method for producing reduced iron according to any one of Aspects 1 to 13, comprising monitoring the concentration of sulfur contained in the oxidized iron raw material. <Aspect 15> A system for producing reduced iron includes: a shaft furnace; a raw material supply device; a reducing gas supply device; an exhaust gas treatment device; a monitoring device; and a control device, wherein the raw material supply device supplies an oxidized iron raw material to the shaft furnace; the reducing gas supply device supplies a reducing gas to the shaft furnace; the exhaust gas treatment device treats the exhaust gas from the shaft furnace and circulates it as a circulating gas; and the monitoring device monitors the H in the reducing gas. ２ S concentration, H in the exhaust gas ２ S concentration and H in the circulating gas ２ and the control device monitors at least one of the H ２A reduced iron production system that controls the S concentration. <Aspect 16> The reduced iron production system of Aspect 15, comprising a reducing gas production device, wherein the reducing gas production device produces the reducing gas by using the circulating gas. <Aspect 17> The reduced iron production system of Aspect 16, wherein the reducing gas production device comprises a catalyst that reforms the circulating gas and the raw material gas into the reducing gas. <Aspect 18> The reduced iron production system of any of Aspects 15 to 17, wherein the exhaust gas treatment device comprises a solid oxide electrolytic cell, and the solid oxide electrolytic cell produces a hydrogen-containing gas by utilizing water vapor contained in the exhaust gas. <Aspect 19> The reduced iron production system of Aspect 18, comprising a water removal device, wherein the hydrogen-containing gas removes at least a portion of the water contained in the hydrogen-containing gas. <Aspect 20> The reduced iron production system according to any one of aspects 15 to 19, further comprising a heating device, wherein the heating device heats the reducing gas, and the monitoring device is configured to measure a temperature of the reducing gas based on the following formula (1): H ２ S out = H ２ S in +A×(10-3420 / T+0.426×H ２ -H ２ S in ) ... (1) H ２ S out : H in the exhaust gas ２ S concentration [volume %] H ２ S in : H in the reducing gas at the inlet side of the heating device ２ S concentration [vol %] A: constant T: temperature of reducing gas supplied to the shaft furnace [°C] H ２ : Hydrogen gas concentration in reducing gas [vol%] ２Aspect 21 is the system for producing reduced iron according to any one of aspects 15 to 20, wherein the control device controls at least one of the sulfur content of the oxidized iron raw material, the sulfur content of the reducing gas, and the temperature of the reducing gas, thereby monitoring the sulfur concentration of the H. ２ A reduced iron production system that controls the S concentration. <Aspect 22> The reduced iron production system of Aspect 21, wherein hydrogen gas obtained by electrolysis of water is used as the reducing gas, and the control device controls the sulfur content of the reducing gas by changing the proportion of the hydrogen gas in the reducing gas. <Aspect 23> The reduced iron production system of Aspect 21 or 22, wherein the control device controls the sulfur content of the oxidized iron raw material by changing the proportion of fired pellets in the oxidized iron raw material. <Aspect 24> The reduced iron production system of any of Aspects 15 to 23, wherein the H ２ A reduced iron production system, in which the S concentration is controlled to 5 ppmv or less. <Aspect 25> The reduced iron production system of any of Aspects 15 to 24, comprising a raw material pretreatment device, which heats the oxidized iron raw material to remove at least a portion of the sulfur contained in the oxidized iron raw material. <Aspect 26> The reduced iron production system of any of Aspects 15 to 25, in which the temperature of the reducing gas is 700°C or higher and 1100°C or lower. <Aspect 27> The reduced iron production system of any of Aspects 15 to 26, comprising a second monitoring device, which monitors the sulfur concentration contained in the reduced iron. <Aspect 28> The reduced iron production system of any of Aspects 15 to 27, comprising a third monitoring device, which monitors the sulfur concentration contained in the oxidized iron raw material.

[0010] According to the technology of the present disclosure, sulfur can be controlled in a direct reduction process using a shaft furnace, and corrosion of equipment and the like can be suppressed.

[0011] 3A and 3B are schematic diagrams showing an example of a method and system for producing reduced iron. 3B and 3C are schematic diagrams showing an example of a method and system for producing reduced iron. 3C and 3D are schematic diagrams showing an example of a relationship between a reducing gas temperature and an S concentration in reduced iron. 3D and 3E are schematic diagrams showing an example of a relationship between a reducing gas temperature and an S concentration in exhaust gas. 3D and 3E are plotted by changing the value of constant A. The plot when constant A is 0.5 substantially matches the plot in FIG. 3A. 3D and 3E are plotted by changing the value of constant A. The plot when constant A is 0.5 substantially matches the plot in FIG. 3B.

[0012] Hereinafter, a method for producing reduced iron and a system for producing reduced iron according to embodiments will be described with reference to the drawings. However, the method for producing reduced iron and the system for producing reduced iron according to the present disclosure are not limited to the following embodiments.

[0013] 1 and 2, a method for producing reduced iron according to one embodiment includes a reduction step S1 in which an oxidized iron raw material is reduced with a reducing gas in a shaft furnace 10 to obtain reduced iron, an exhaust gas treatment step S2 in which exhaust gas from the shaft furnace 10 is treated and circulated as a circulating gas, and a reduction step S3 in which H in the reducing gas is removed. ２ S concentration, H in the exhaust gas ２ S concentration and H in the circulating gas ２ a monitoring step S3 for monitoring at least one of the H ２ and a control step S4 of controlling the S concentration.

[0014] 1.1 Reduction Step In the reduction step S1, an oxidized iron raw material is reduced with a reducing gas in a shaft furnace 10 to produce reduced iron. The shaft furnace 10 may have 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 relationships are 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 from the gas supply port 12 to the gas discharge port 14 (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 the top or upper part of the shaft furnace 10, at a location different from the raw material supply port 11. By having 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-mentioned positional relationship, it is possible to supply oxidized iron raw material from the raw material supply port 11 into the interior of the shaft furnace 10 and form a packed bed of oxidized iron raw material inside the shaft furnace 10, and to supply a reducing gas containing hydrogen gas from the gas supply port 12 to the packed bed inside the shaft furnace 10, so that the oxidized iron raw material and the reducing gas can be brought into contact with each other inside the shaft furnace 10 to reduce iron oxide, thereby obtaining reduced iron from the reduced iron discharge port 13, and discharging water vapor-containing gas as exhaust gas to the outside of the shaft furnace 10 from the gas discharge port 14.

[0015] The supply of the oxidized iron raw material to the shaft furnace 10 may be performed by the raw material supply device 20. The oxidized iron raw material supplied from the raw material supply device 20 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, 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. 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 particle diameter of the raw material. The average particle size of the oxidized iron raw material is measured as follows. That is, a mass-based particle size distribution is obtained by a dry sieving test described in JIS Z 8815:1995, and the average value of the maximum and minimum particle sizes of each sieve is used as a representative particle size, and the mass-weighted average is calculated to measure the average particle size of the oxidized iron raw material. The oxidized iron raw material may be formed into pellets or the like, may be in powder form, may be in a lump form, or may be in any other form. The amount of the oxidized iron raw material supplied to the shaft furnace 10 may be optimally selected depending on the size and operating conditions of the shaft furnace 10, etc.

[0016] The supply of reducing gas to the shaft furnace 10 may be performed by a reducing gas supply device 30. The reducing gas supplied from the reducing gas supply device 30 to the shaft furnace 10 contains, for example, hydrogen gas and optionally other gases. 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 ２The 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.

[0017] The temperature of the iron oxide raw material supplied into the shaft furnace 10 (the temperature at the raw material supply port 11) may be, for example, 600°C or higher and 900°C or lower. According to the findings of the present inventors, when the iron oxide raw material supplied into the shaft furnace 10 is 600°C or higher and 900°C or lower, the temperature of the exhaust gas discharged from the shaft furnace 10 also becomes 600°C or higher and 900°C or lower, and, for example, the temperature of the exhaust gas tends to become a temperature corresponding to the operating temperature of the SOEC described below. The temperature of the reducing gas supplied into the shaft furnace 10 (the temperature at the gas supply port 12) may be, for example, 25°C or higher and 1100°C or lower, 100°C or higher and 1100°C or lower, 300°C or higher and 1100°C or lower, 500°C or higher and 1100°C or lower, 700°C or higher and 1100°C or lower, 800°C or higher and 1100°C or lower, or 900°C or higher and 1100°C or lower. Here, when sulfur is contained in the oxidized iron raw material, the reducing gas, etc., the higher the temperature of the reducing gas, the lower the sulfur concentration of the reduced iron and the more likely it is that the sulfur concentration contained in the exhaust gas from the shaft furnace 10 will increase. In other words, the higher the temperature of the reducing gas, the more likely it is that H ２ It can be said that it is important to monitor and control the S concentration. In this regard, the temperature of the reducing gas may be 700°C or higher and 1100°C or lower, 800°C or higher and 1100°C or lower, or 900°C or higher and 1100°C or lower. The flow rate of the reducing gas supplied into the shaft furnace 10 (flow rate at the gas supply port 12) is, for example, 1000 Nm ３ / t-DRI or more 2200Nm ３ / t-DRI or less. In this embodiment, the iron oxide comes into contact with the reducing gas in a reduction zone inside the shaft furnace 10, causing reduction of the iron oxide. The temperature of the iron oxide raw material in the reduction zone may be, for example, 700°C or higher and 1000°C or lower. The reduction rate of the reduced iron that has passed through the reduction zone and is discharged from the reduced iron outlet 13 may be, for example, 65% or higher and 98% or lower. The temperature of the exhaust gas (water vapor-containing gas) that has passed through the reduction zone and is discharged to the outside of the shaft furnace 10 from the gas outlet 14 may be, for example, 600°C or higher and 1000°C or lower, or 600°C or higher and 900°C or lower.

[0018] 1.2 Exhaust Gas Treatment Step In the exhaust gas treatment step S2, the exhaust gas from the shaft furnace 10 is treated and then circulated as a circulating gas. In this way, when the exhaust gas from the shaft furnace 10 is treated and circulated, H ２ Although corrosion of equipment is likely to become more pronounced due to the generation and concentration of S gas, the method for producing reduced iron according to the present embodiment can suppress corrosion of equipment even in such cases.

[0019] The exhaust gas from the shaft furnace 10 contains reducing gases (hydrogen gas, carbon monoxide gas, etc.) that are discharged without contributing to the reduction reaction, as well as dust, water vapor, carbon dioxide gas, H ２ In this regard, the exhaust gas treatment step S2 includes, for example, a dust removal step S2-1 for removing dust contained in the exhaust gas, a water removal step S2-2 for removing water contained in the exhaust gas, a carbon dioxide removal step S2-3 for removing carbon dioxide contained in the exhaust gas, and a H 2 O 3 removal step S2-4 for removing carbon dioxide contained in the exhaust gas. ２ Remove S, H ２ The exhaust gas from the shaft furnace 10 may be treated by an exhaust gas treatment device 40. For example, the exhaust gas treatment device 40 may include a dust removal device, a water removal device, a carbon dioxide removal device, a H ２ The system may include at least one device 41 selected from an S removal device and a hydrogen production device.

[0020] 1.2.1 Dust Removal Step The exhaust gas treatment device 40 may be equipped with a dust removal device for removing dust contained in the exhaust gas. As the dust removal device, a known device such as a dust collector or a dust removal filter may be used.

[0021] 1.2.2 Water Removal Step The exhaust gas treatment device 40 may be equipped with a water removal device for removing water contained in the exhaust gas. The water removal step S2-2 may include, for example, cooling the exhaust gas to liquefy and remove the water in the exhaust gas. In other words, the water removal device provided in the exhaust gas treatment device 40 may be equipped with a cooling mechanism for cooling the exhaust gas. Alternatively, the water removal device may be one that separates hydrogen gas and water vapor using a molecular sieve or the like. Alternatively, the water removal device may be one that removes water by selectively reacting with or adsorbing water using a material that is inert to hydrogen and reactive with water.

[0022] 1.2.3 Carbon Dioxide Removal Step The exhaust gas treatment device 40 may be equipped with a carbon dioxide removal device for removing carbon dioxide contained in the exhaust gas. The carbon dioxide removal step S2-3 may be a step in which hydrogen gas and carbon dioxide gas are separated using a molecular sieve or the like. Alternatively, the carbon dioxide removal step S2-3 may be a step in which carbon dioxide is removed by selectively reacting with or adsorbing carbon dioxide using a material that is inert to hydrogen and reactive with carbon dioxide.

[0023] 1.2.4 H ２ S removal process The exhaust gas treatment device 40 removes H contained in the exhaust gas. ２ H to remove S ２ An S removal device may be provided. ２ The S removal step S2-4 separates hydrogen gas and H using a molecular sieve (a substance that has the property of separating molecules according to the size of the molecules to be separated). ２ Alternatively, the gas may be separated from the H ２ The S removal step S2-4 is carried out using a catalyst that is inert to hydrogen and is free of H ２ H by materials reactive to S ２By selectively reacting or adsorbing S, H ２ In particular, as will be described below, when hydrogen gas is produced by using water vapor contained in exhaust gas with an SOEC, the H contained in the exhaust gas is removed in order to suppress deterioration or poisoning of the catalyst in the SOEC. ２ It is preferable to remove S.

[0024] 1.2.5 Hydrogen Production Process The exhaust gas treatment device 40 may include a hydrogen production device for producing hydrogen gas using water vapor contained in the exhaust gas. The hydrogen production device may include, for example, a solid oxide electrolyzer cell (SOEC). The SOEC electrolyzes water vapor contained in the exhaust gas discharged from the gas outlet 14 of the shaft furnace 10 to produce a hydrogen-containing gas. The hydrogen-containing gas produced by the SOEC may be used as a circulating gas and as the reducing gas described above. The SOEC may include, for example, a hydrogen electrode, an oxygen electrode, and an electrolyte layer disposed between them. The water vapor-containing gas discharged from the gas outlet 14 is supplied to the hydrogen electrode of the SOEC. At the hydrogen electrode, hydrogen gas is produced by electrolysis of water vapor. Meanwhile, at the oxygen electrode, electrons are released from oxygen radicals to produce oxygen gas. That is, exhaust gas containing hydrogen gas is discharged from the hydrogen electrode of the SOEC, and exhaust gas containing oxygen gas is discharged from the oxygen electrode. The hydrogen electrode is, 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 SOEC may include a ceramic electrolyte such as a ceramic electrolyte. In the hydrogen production device, a plurality of SOECs may be stacked with metal separators interposed therebetween to form an SOEC stack. The temperature (temperature of the water vapor-containing gas) when the SOEC is operated may be, for example, 600°C or higher and 900°C or lower. The power density when the SOEC is operated may be, for example, 0.5 A / m ２ 1.0A / m or more ２ It may be the following:

[0025] In addition, when the exhaust gas treatment device 40 is equipped with an SOEC as a hydrogen production device, the gas supplied to the SOEC contains H ２ If a large amount of S is contained, there is a concern that the catalyst of the SOEC may be poisoned or the electrode function may be deteriorated. ２ The S concentration is monitored and controlled, resulting in a reduction in the H concentration of the gas supplied to the SOEC. ２ In this respect, in the present embodiment, even when a hydrogen-containing gas is produced from water vapor in the exhaust gas from the shaft furnace 10 by the SOEC in the exhaust gas treatment step S40, catalyst poisoning of the SOEC and deterioration of electrode function can be suppressed. In particular, before the exhaust gas from the shaft furnace 10 reaches the SOEC, the H concentration in the exhaust gas is controlled. ２ It is preferable to monitor and control the S concentration.

[0026] Furthermore, when the exhaust gas treatment device 40 includes a water removal device and an SOEC as a hydrogen production device, it is preferable that the dehydration of the exhaust gas by the water removal device be performed after the hydrogen-containing gas is produced by the SOEC. That is, in the present embodiment, after the hydrogen-containing gas is produced from the water vapor in the exhaust gas by the SOEC in the exhaust gas treatment device 40, at least a portion of the water contained in the hydrogen-containing gas may be removed.

[0027] 1.3 Monitoring Step In the monitoring step S3, the H in the reducing gas supplied to the shaft furnace 10 is monitored. ２ S concentration, H in the exhaust gas from the shaft furnace 10 ２ S concentration and H in the circulating gas from the exhaust gas treatment device 40 ２ At least one of the following is monitored: H ２ The monitoring of the S concentration may be performed by the monitoring device 51.

[0028] In the direct reduction process using the shaft furnace 10, if natural gas is used as the reducing gas, H contained in the natural gas ２The S gas does not contribute to the reduction reaction in the reduction step S1 and is discharged as exhaust gas from the shaft furnace 10. Alternatively, even if a sulfur-free reducing gas is used in the direct reduction process using the shaft furnace 10, the iron oxide raw material and the reducing gas may react inside the shaft furnace 10, and the sulfur contained in the iron oxide raw material may be converted to H. ２ The H ２ The S gas is discharged as exhaust gas from the shaft furnace 10. In this way, the H gas derived from the iron oxide raw material ２ H derived from S gas and reducing gas ２ All of the S gases are discharged to the outside of the shaft furnace 10 as exhaust gases from the shaft furnace 10. ２ S gas may corrode the exhaust gas system and circulation system of the shaft furnace 10 (for example, the exhaust gas treatment device 40 and the reducing gas production device 80 described later, particularly the part where the gas is cooled, such as a scrubber). In this embodiment, in the monitoring step S3, H in the reducing gas supplied to the shaft furnace 10 is monitored. ２ S concentration, H in the exhaust gas from the shaft furnace 10 ２ S concentration and / or H in the circulating gas from the exhaust gas treatment device 40 ２ In particular, at least the H concentration in the exhaust gas is monitored. ２ S concentration and H in the circulating gas ２ By monitoring one or both of the concentration of H in the reducing gas and the concentration of S, corrosion in the exhaust gas system and the circulation system can be more appropriately reduced. ２ S concentration and H in the exhaust gas ２ By monitoring both the H and S concentrations, it is possible to ２ The accuracy of managing the S concentration can be improved, and deterioration and poisoning of the water decomposition catalyst and reforming catalyst can be suppressed even when reducing gas is produced in an SOEC using exhaust gas as described above, or when reducing gas is produced by gas reforming as described below.

[0029] In the monitoring step S3, H ２The S concentration may be monitored by the following actual measurement method, the following estimation method, or a combination of these.

[0030] 1.3.1 Measurement method H by measurement method ２ The monitoring of the sulfur concentration is carried out by measuring the concentration of sulfur components in the gas using a method that utilizes ultraviolet fluorescence or a method that utilizes an oxidation catalyst. The sulfur concentration in the oxidized iron raw material and the product reduced iron can be measured by ICP or the like. The monitoring device 51 measures the sulfur concentration in the oxidized iron raw material and the product reduced iron by these methods. ２ A device for measuring the S concentration may be provided.

[0031] 1.3.2 Estimation method H in gas ２ S concentration (H ２ S out ) may be estimated as follows: First, the material balance in the shaft furnace 10 is given by the following equation (3): H ２ S out = H ２ S in +S ore -S DRI …(3)

[0032] Here, the amount of sulfur transferred from the iron oxide raw material into the gas (=S ore -S DRI ) can be estimated as follows. First, assume the following:

[0033] Assumption 1: The gasification reaction of sulfur on the surface of the iron oxide raw material is in an equilibrium state based on the following formula (2): FeS(s) + H ２ (g)=Fe(s)+H ２ S(g) ... (2)

[0034] Assumption 2: The rate of gasification of sulfur in the oxidized iron raw material is controlled by the rate at which hydrogen sulfide gas diffuses from the surface of the oxidized iron raw material into the gas bulk.

[0035] Assumption 3: The hydrogen gas concentration on the surface of the iron oxide raw material is equal to that in the bulk (hydrogen gas diffusion is sufficiently fast).

[0036] According to the above assumption 2, the rate of gasification of sulfur in the oxidized iron raw material (the rate of generation of hydrogen sulfide gas from the oxidized iron raw material) is proportional to the difference in hydrogen sulfide concentration between the surface and the bulk (the following formula (4)). ore -S DRI ) / dt = a × (H ２ S 表面 -H ２ S バルク ) … (4)

[0037] On the other hand, the equilibrium constant K (= P H2S / P H2 ) is derived, for example, by the following formula (5) (Non-Patent Document 3: Shoji Hayashi et al.: Nagoya Institute of Technology Bulletin, Vol. 26 (1974), p. 247): −log K=3420 / T−0.426 (5)

[0038] From assumptions 1 and 3, the hydrogen sulfide concentration on the surface of the iron oxide raw material is ２ S 表面 = 10-3420 / T+0.426×H ２ バルク Therefore, the above formula (4) becomes d(S ore -S DRI ) / dt = a × (10-3420 / T + 0.426 × H ２ バルク -H ２ S バルク ) …(6).

[0039] Furthermore, the sulfur balance in the entire furnace (the above formula (3)) ore -S DRI Considering the same as equation (6), H ２ S out = H ２ S in +A×(10-3420 / T+0.426×H ２ バルク -H ２ S in )…(1).

[0040] where a and A are constants, T is the reducing gas temperature, and H ２ バルク : Hydrogen gas concentration in reducing gas (bulk), where A x (10-3420 / T + 0.426 x H ２バルク -H ２ S in ) is S ore It will never exceed.

[0041] H ２ バルク is the bulk hydrogen gas concentration surrounding the iron ore in the reducing gas, which varies depending on the position in the furnace as it is consumed by the reduction. ２ Concentration (H ２ out ) and H in the reducing gas at the inlet side of the heating device for heating the reducing gas. ２ Concentration (H ２ in ) can be used as the average value.

[0042] Furthermore, a and A are constants specific to the iron oxide raw material and the process, respectively. The constant A is a factor determined by the properties of the iron oxide raw material (FeS, iron oxide, generated metallic iron, pore shape, etc.), and once the type of iron oxide raw material is determined, A can be derived from the results of experiments and actual operations.

[0043] For example, if the S concentration in the iron oxide raw material is 0.025%, the S concentration in the reducing gas is 5 ppmv, and the H ２ The graphs in Figures 3A and 3B were obtained by examining the S concentrations in the reduced iron and the exhaust gas under various reducing gas temperature conditions with a concentration of 90% by volume. Meanwhile, Figures 4A and 4B are plots of equations (1) and (3) with different values ​​of constant A. Comparing Figures 3 and 4, the value of constant A that most accurately estimates this case can be determined to be 0.5.

[0044] In summary, the method for producing reduced iron according to one embodiment may include a heating step of heating the reducing gas by a heating device, and a monitoring step of detecting a reaction rate determined by the following formula (1): H ２ S out = H ２ S in +A×(10-3420 / T+0.426×H ２ -H ２ S in ) ... (1) H ２ S out : H in the exhaust gas２ S concentration [volume %] H ２ S in : H in the reducing gas at the inlet side of the heating device ２ S concentration [vol %] A: constant T: temperature of reducing gas supplied to the shaft furnace [°C] H ２ : Hydrogen gas concentration in reducing gas [vol%] ２ The S concentration may be monitored. That is, the reducing gas production step S5 described later may involve heating the reducing gas by a heating device. The monitoring device 51 used in the monitoring step S3 may measure the H concentration contained in the exhaust gas based on the above formula (1). ２ The apparatus may be provided with an estimation device (various measuring devices and calculation devices) for estimating the S concentration.

[0045] 1.4 Control Step In the control step S4, the above H ２ More specifically, the H concentration monitored in the monitoring step S3 is controlled. ２ The H is then adjusted so that the S concentration is equal to or less than the threshold. ２ The S concentration may be controlled. ２ The S concentration may be controlled by the control device 60 controlling the raw material supply device 20, the reducing gas supply device 30, the exhaust gas treatment device 40, and the like.

[0046] In the control step S4, H ２ A specific method for controlling the S concentration is as follows, for example. That is, in the control step S4 according to one embodiment, at least one of (A) the sulfur content of the oxidized iron raw material, (B) the sulfur content of the reducing gas, and (C) the temperature of the reducing gas is controlled, thereby reducing the H ２ The S concentration may be controlled. The "sulfur content" may be derived from elemental sulfur or from sulfur compounds. For example, in the iron oxide raw material, sulfur exists as FeS or the like. In the reducing gas, sulfur exists as H ２ S and SO ｘ etc. exist.

[0047] In the control step S4, as described above, (D) H in the exhaust gas is removed in the exhaust gas treatment step S2, etc. ２ When S is removed (H ２ S removal process) ２ By controlling the amount of S removed, ２ The S concentration may be controlled.

[0048] When the monitoring step S3 is performed by the actual measurement method, H in the exhaust gas or the circulating gas ２ In the control step S4, the measured value of the S concentration is fed back and H is controlled by at least one of the above (A) to (D). ２ When the monitoring step S3 is performed by an estimation method, the H concentration in the exhaust gas or the circulating gas that is set in advance may be controlled. ２ The manipulated variables for (A) to (D) above may be determined based on the above formula (1) so that the upper limit of the S concentration is not exceeded.

[0049] 1.4.1 Control of sulfur content of iron oxide raw material In a direct reduction process using a shaft furnace, for example, when hydrogen gas is produced from water vapor in exhaust gas by SOEC, it is necessary to strictly control the amount of S supplied into the system from the viewpoint of preventing poisoning of the catalyst in the SOEC. In this case, it is particularly preferable to control (reduce) the sulfur content in the iron oxide raw material. However, in a direct reduction process using a shaft furnace, it may be difficult to use only iron oxide raw materials with low sulfur contents due to the supply and demand of raw materials. In this regard, in this embodiment, for example, both iron oxide raw materials with a relatively high sulfur content and iron oxide raw materials with a relatively low sulfur content are prepared, and the H content monitored in the monitoring step S3 is controlled. ２ The type of iron oxide raw material supplied to the shaft furnace 10 may be changed depending on the S concentration.

[0050] To reduce the sulfur content in the oxidized iron raw material, for example, the blending ratio of iron ore with a low sulfur content in the oxidized iron raw material may be increased. Iron ore with a low sulfur content includes the following iron ores and agglomerates. As shown in Table 1, the sulfur content of iron ore varies depending on the country and producing region, with iron ore from southern Brazil and South Africa having a particularly low sulfur content. These ores can be agglomerated into lump ore or unfired briquettes and used directly in the direct reduction process using the shaft furnace 10. On the other hand, the sulfur content of Australian iron ore and iron ore from northern Brazil varies depending on the producing region and mining area. Therefore, iron ore with a high sulfur content is not used as lump ore directly in the shaft furnace 10, but is fired in an oxidizing atmosphere to form fired pellets, for example, to convert the sulfur in the iron ore into SO ｘ It is preferable to remove the sulfur as a pretreatment before use. In this regard, in the control step S4 according to one embodiment, the sulfur content of the oxidized iron raw material may be controlled by changing the proportion of the fired pellets in the oxidized iron raw material. Furthermore, as will be described later, in the method for producing reduced iron according to one embodiment, at least a portion of the sulfur contained in the oxidized iron raw material may be removed in the raw material pretreatment step S0.

[0051] 1.4.2 Control of sulfur content of reducing gas Depending on the type of reducing gas, the sulfur content (H ２ In addition, it may be difficult to use only sulfur-free reducing gas (for example, hydrogen gas obtained by electrolysis of water) due to supply and demand. In this regard, in this embodiment, for example, both a reducing gas source with a high sulfur content and a reducing gas source with a low sulfur content are prepared, and the H content monitored in the monitoring step S3 is used. ２ The type of reducing gas supplied to the shaft furnace 10 may be switched depending on the S concentration. For example, when hydrogen gas obtained by electrolysis of water is used as the reducing gas, the proportion of the hydrogen gas in the reducing gas may be changed in the control step S4 to control the sulfur content of the reducing gas.

[0052] 1.4.3 Control of the temperature of the reducing gas According to the findings of the present inventors, when the temperature of the reducing gas is lowered, the amount of H generated in the system decreases. ２ For example, in the reducing gas production process described later, by lowering the gas heating temperature, a reducing gas having a relatively low temperature is supplied to the shaft furnace 10, and the H in the exhaust gas and circulating gas from the shaft furnace 10 is reduced. ２ In other words, in this embodiment, the H concentration monitored in the monitoring step S3 may be reduced. ２ The temperature of the reducing gas supplied to the shaft furnace may be changed depending on the S concentration.

[0053] 1.4.4 H ２ S concentration threshold value H in control step S4 ２ When controlling the S concentration, H ２ The threshold value of the S concentration is not particularly limited. ２ The S concentration is preferably controlled to 5 ppmv or less. The "v" in ppmv means that it is on a volume basis. ２ By controlling the S concentration to 5 ppmv or less, corrosion of the equipment in the exhaust gas system and the circulating gas system can be more appropriately suppressed. ２ By controlling the S concentration to 5 ppmv or less, it is also possible to suppress deterioration and poisoning of the water splitting catalyst in the SOEC described above and the gas reforming catalyst described below.

[0054] 1.5 Other Steps The method for producing reduced iron according to this embodiment may include other steps in addition to the above steps S1 to S4.

[0055] 1.5.1 Raw Material Pretreatment Step For example, a method for producing reduced iron according to one embodiment may include a raw material pretreatment step S0 in which the oxidized iron raw material is heated to remove at least a portion of the sulfur contained in the oxidized iron raw material. The raw material pretreatment step S0 may be performed, for example, by a raw material pretreatment device 70 described below. The atmosphere in which the oxidized iron raw material is heated is not particularly limited. For example, as described above, by heating the oxidized iron raw material in an oxidizing atmosphere, the sulfur contained in the oxidized iron raw material can be converted into SOｘ When sulfur-containing iron oxide raw material is supplied to the shaft furnace 10, the sulfur is gasified in the shaft furnace 10 and circulates within the system as exhaust gas and circulating gas. In this case, the sulfur circulating within the system may corrode each device and may poison the catalyst of the SOEC. In the raw material pretreatment step S0, at least a portion of the sulfur contained in the iron oxide raw material is removed by heating, making such problems less likely to occur.

[0056] 1.5.2 Reducing Gas Production Step Furthermore, the method for producing reduced iron according to one embodiment may include a reducing gas production step S5 in which the reducing gas is produced using the circulating gas. The reducing gas production step S5 may be performed by a reducing gas production apparatus 80. The reducing gas produced in the reducing gas production step S5 is supplied to the shaft furnace 10. In this regard, the reducing gas production apparatus 80 may also function as the reducing gas supply apparatus 30 described above.

[0057] The reducing gas production step S5 may include, for example, at least one of a reforming step, a heating step, and a combustion step. The reforming step may be performed by a reformer having a catalyst for reforming the gas. The heating step may be performed by a heating device for heating the reducing gas. The combustion step may be performed by a combustion device for combusting a portion of the reducing gas.

[0058] In the reducing gas production step S5, the above-mentioned circulation gas and raw material gas may be mixed, and then the circulation gas and raw material gas may be reformed into a reducing gas by a catalyst. An example of the raw material gas is natural gas. As described above, the circulation gas may contain carbon dioxide or the like. In this case, a gas rich in carbon monoxide and hydrogen can be produced by reforming natural gas as the raw material gas and carbon dioxide gas contained in the circulation gas using a catalyst. Also, a gas rich in carbon monoxide and hydrogen can be produced by reforming natural gas as the raw material gas and steam obtained from waste heat recovery or the like using a catalyst. An example of the catalyst is a Ni-based catalyst. The raw material gas may be supplied by a raw material gas supply device 90. When the reducing gas production step S5 includes a reforming step, the H of the catalyst used for the reforming may be ２ In the method for producing reduced iron according to the present embodiment, the poisoning by S is a concern. However, as described above, the H ２ Since the sulfur concentration is monitored and controlled, it is also possible to prevent the catalyst used for reforming from being poisoned. ２ It is preferable to monitor and control the concentration of S. The reaction temperature in the reforming step is not particularly limited as long as reforming is possible.

[0059] The reducing gas production step S5 may include a heating step of heating the reducing gas. As described above, in one embodiment, water contained in the circulating gas may be removed by cooling. That is, the temperature of the circulating gas may decrease, and if the circulating gas is supplied to the shaft furnace 10 as is, the efficiency of the reduction step S1 may decrease. In addition, from the viewpoint of reduction efficiency, it is often better to heat the circulating gas and the reducing gas before supplying them to the shaft furnace 10. For example, the reducing gas may be heated by a heating device to reach the target temperature in the reduction step S1, and then supplied to the shaft furnace 10. As described above, by changing the heating temperature of the reducing gas, the H in the exhaust gas from the shaft furnace 10 and the circulating gas may be reduced. ２ The S concentration can also be controlled.

[0060] In the reducing gas production step S5, a part of the reducing gas may be partially burned by blowing in oxygen, etc. This makes it possible to increase the temperature of the reducing gas.

[0061] 1.5.3 Step of Monitoring Sulfur Concentration in Reduced Iron The reduced iron manufacturing method according to one embodiment may include monitoring the sulfur concentration contained in the reduced iron (reduced iron monitoring step S6). The reduced iron monitoring step S6 may be performed by the second monitoring device 52. The sulfur concentration contained in the reduced iron can be measured by ICP or the like, as described above. That is, the reduced iron monitoring step S6 may be a step of confirming the sulfur concentration contained in the reduced iron by sampling a portion of the reduced iron and analyzing the sulfur contained in the reduced iron by ICP or the like. When sulfur is contained in the oxidized iron raw material or the reducing gas, the higher the temperature of the reducing gas, the lower the sulfur concentration of the reduced iron produced, and the higher the sulfur concentration of the exhaust gas from the shaft furnace 10. In other words, when the sulfur concentration contained in the reduced iron monitored in the reduced iron monitoring step S6 is higher than the target value, the sulfur concentration of the reduced iron produced thereafter can be brought closer to the target value by increasing the temperature of the reducing gas. In this case, increasing the temperature of the reducing gas reduces the H contained in the exhaust gas from the shaft furnace 10. ２ The S concentration increases, and the H in the exhaust gas monitored in the monitoring step S3 is ２ In this case, H is extracted from the exhaust gas in the exhaust gas treatment step S2. ２ By removing sulfur, etc., H in the exhaust gas system and circulation system, etc. ２ In this way, according to the present embodiment, the H concentration in the exhaust gas from the shaft furnace 10 can be reduced. ２ By appropriately controlling the balance between the S concentration and the sulfur concentration in reduced iron, ２ It can be said that reduced iron with a target sulfur concentration can be produced while suppressing equipment corrosion due to S.

[0062] 1.5.4 Step of Monitoring Sulfur Concentration in Oxidized Iron Raw Material The reduced iron manufacturing method according to one embodiment may include monitoring the sulfur concentration contained in the oxidized iron raw material (oxidized iron raw material monitoring step S7). The oxidized iron raw material monitoring step S7 may be performed by the third monitoring device 53. The sulfur concentration contained in the oxidized iron raw material can be measured by ICP or the like, as described above. That is, the oxidized iron raw material monitoring step S6 may be a step of confirming the sulfur concentration contained in the oxidized iron raw material by sampling a portion of the oxidized iron raw material before being supplied to the shaft furnace 10 or the oxidized iron raw material being supplied to the shaft furnace 10 and analyzing the sulfur contained in the oxidized iron raw material by ICP or the like. As described above, the sulfur contained in the oxidized iron raw material is transferred into the gas by reaction with the reducing gas or the like, and is discharged from the shaft furnace 10 as exhaust gas. Therefore, if the sulfur concentration contained in the oxidized iron raw material monitored in the oxidized iron raw material monitoring step S7 is higher than the target value, the H contained in the exhaust gas from the shaft furnace 10 may be monitored. ２ The S concentration increases, and the H in the exhaust gas monitored in the monitoring step S3 is ２ In this case, H is extracted from the exhaust gas in the exhaust gas treatment step S2. ２ By removing sulfur, etc., H in the exhaust gas system and circulation system, etc. ２ It is preferable to reduce the concentration of S. Furthermore, if the concentration of sulfur contained in the oxidized iron raw material monitored in the oxidized iron raw material monitoring step S7 is higher than a target value, the sulfur contained in the oxidized iron raw material may be removed by performing the above-mentioned raw material pretreatment step S0, or the type of oxidized iron raw material may be switched by performing the above-mentioned control step S4, so that the concentration of sulfur contained in the oxidized iron raw material falls below the target value.

[0063] 1.6 Effects As described above, the method for producing reduced iron according to this embodiment includes the reduction step S1, the exhaust gas treatment step S2, the monitoring step S3, and the control step S4, and therefore, the H in the exhaust gas system and the circulation system can be reduced. ２ The S concentration can be managed and controlled, and corrosion of equipment can be suppressed.

[0064] 2. Reduced iron production system The technology of the present disclosure also has an aspect as a reduced iron production system. That is, as shown in FIGS. 1 and 2 , a reduced iron production system 100 according to one embodiment includes a shaft furnace 10, a raw material supply device 20, a reducing gas supply device 30, an exhaust gas treatment device 40, a monitoring device 51, and a control device 60. The raw material supply device 20 supplies oxidized iron raw materials to the shaft furnace 10. The reducing gas supply device 30 supplies reducing gas to the shaft furnace 10. The exhaust gas treatment device 40 treats the exhaust gas from the shaft furnace 10 and circulates it as a circulating gas. The monitoring device 51 monitors the H in the reducing gas. ２ S concentration, H in the exhaust gas ２ S concentration and H in the circulating gas ２ The control device 60 monitors at least one of the H ２ Control the S concentration.

[0065] The raw material supply device 20 may, for example, supply the iron oxide raw material to the shaft furnace 10 while controlling the supply amount of the iron oxide raw material. The raw material supply device 20 may include a chute, a hopper, or the like. That is, the raw material supply device 20 may be configured to supply the iron oxide raw material from the top of the shaft furnace 10 to the inside of the shaft furnace 10 via a chute, a hopper, or the like.

[0066] The reducing gas supply device 30 may supply the reducing gas to the shaft furnace 10 while controlling, for example, the flow rate, pressure, and temperature of the reducing gas. The reducing gas supply device 30 may include at least one of a flow meter, a pressure meter, and a thermometer, and may also include a control mechanism that controls one or both of the flow rate and pressure of the reducing gas.

[0067] As described above, the exhaust gas treatment device 40 treats and circulates the exhaust gas from the shaft furnace 10, and includes a dust removal device, a water removal device, a carbon dioxide removal device, a H ２ The system may include at least one device 41 selected from an S removal device and a hydrogen production device.

[0068] As described above, the monitoring device 51 monitors the H in the reducing gas, exhaust gas, and / or recycle gas. ２ It monitors the S concentration and H in the gas. ２ A mechanism for measuring the S concentration (such as a fluorescence analyzer) and / or a method for measuring the H concentration in the exhaust gas based on the above formula (1) ２ The monitoring device 51 may be provided with an estimation device (various measuring devices and calculation devices) for estimating the S concentration. ２ It is preferable that the monitoring device 51 monitors the S concentration. Alternatively, the monitoring device 51 monitors at least the H concentration of both the reducing gas and the exhaust gas. ２ Preferably, the S concentration is monitored.

[0069] As described above, the control device 60 ２ The S concentration is controlled by, for example, the operation of the raw material supply device 20, the reducing gas supply device 30, the exhaust gas treatment device 40, etc. (switching of the type of iron oxide raw material, switching of the type of reducing gas, H ２ S removal, the amount of heat applied to the iron oxide raw material in the raw material pretreatment device 70, the amount of heat applied to the reducing gas in the reducing gas production device 80, switching of the type of raw material gas from the raw material gas supply device 90, etc.) are controlled to ２ The control device 60 may be one that controls the concentration of S. The control device 60 may be one that includes a measuring device, a computing device, and the like for performing such control.

[0070] In this embodiment, other specific aspects of the reducing gas production system correspond to those of the reducing gas production method. That is, the reduced iron production system 100 according to an embodiment may include a raw material pretreatment device 70, which may heat the oxidized iron raw material (e.g., heat in an oxidizing atmosphere) to remove at least a portion of the sulfur contained in the oxidized iron raw material. In other words, the raw material pretreatment device 70 may include a heating mechanism for heating the oxidized iron raw material. The raw material pretreatment device 70 may be provided separately from the raw material supply device 20, or the raw material supply device 20 may function as the raw material pretreatment device 70. In other words, the raw material supply device 20 may include the heating mechanism. Furthermore, the reduced iron production system 100 according to an embodiment may include a reducing gas production device 80, which may produce the reducing gas using the circulating gas. Furthermore, the reducing gas production device 80 may include a catalyst for reforming the circulating gas and the raw material gas into the reducing gas. In this case, the raw material gas supply device 90 may be configured to supply the raw material gas to the reducing gas production device 80 .

[0071] In the reduced iron production system 100 according to one embodiment, the exhaust gas treatment device 40 may include a solid oxide electrolytic cell, and the solid oxide electrolytic cell may produce a hydrogen-containing gas by utilizing water vapor contained in the exhaust gas. In addition, the reduced iron production system 100 according to one embodiment may include a water removal device, and the hydrogen-containing gas may be treated by removing at least a portion of the water contained in the hydrogen-containing gas.

[0072] Furthermore, the reduced iron production system 100 according to one embodiment may include a heating device, and the heating device may heat the reducing gas. The monitoring device 51 may be configured to calculate a temperature of the reducing gas by calculating the temperature of the reducing gas based on the following formula (1): ２ S out = H ２ S in +A×(10-3420 / T+0.426×H ２ -H２ S in ) ... (1) H ２ S out : H in the exhaust gas ２ S concentration [volume %] H ２ S in : H in the reducing gas at the inlet side of the heating device ２ S concentration [vol %] A: constant T: temperature of reducing gas supplied to the shaft furnace [°C] H ２ : Hydrogen gas concentration in reducing gas [vol%] ２ The S concentration may be monitored.

[0073] In the reduced iron production system 100 according to one embodiment, the control device 60 controls at least one of the sulfur content of the oxidized iron raw material, the sulfur content of the reducing gas, and the temperature of the reducing gas, thereby ２ The control device 60 may control the sulfur concentration in the reducing gas by changing the proportion of the hydrogen gas in the reducing gas. In addition, the control device 60 may control the sulfur content in the reducing gas by changing the proportion of the fired pellets in the reducing gas.

[0074] In the reduced iron production system 100 according to one embodiment, the H ２ The S concentration may be controlled to 5 ppmv or less.

[0075] In the reduced iron production system 100 according to an embodiment, the temperature of the reducing gas supplied to the shaft furnace 10 may be 700° C. or higher and 1100° C. or lower. For example, the temperature of the reducing gas can be increased to 700° C. or higher and 1100° C. or lower by the heating device or the combustion device described above.

[0076] Furthermore, the reduced iron production system 100 according to the embodiment may include a second monitoring device 52, which may monitor the concentration of sulfur contained in the reduced iron. As described above, the second monitoring device 52 may be configured to be able to check the concentration of sulfur contained in the reduced iron by ICP or the like.

[0077] Furthermore, the reduced iron production system 100 according to one embodiment may include a third monitoring device 53, which may monitor the concentration of sulfur contained in the oxidized iron raw material. As described above, the third monitoring device 53 may be configured to be able to check the concentration of sulfur contained in the reduced iron by ICP or the like.

[0078] 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 raw material supply device 30 reducing gas supply device 40 exhaust gas treatment device 51 monitoring device 52 second monitoring device 53 third monitoring device 60 control device 70 raw material pretreatment device 80 reducing gas production device 90 raw material gas supply device 100 reduced iron production system

Claims

1. A method for producing reduced iron, comprising: a reduction step in which an oxidized iron raw material is reduced with a reducing gas in a shaft furnace to obtain reduced iron; an exhaust gas treatment step in which exhaust gas from the shaft furnace is treated and circulated as a circulating gas; and a method for producing reduced iron, comprising the steps of: ２ S concentration, H in the exhaust gas ２ S concentration and H in the circulating gas ２ a monitoring step of monitoring at least one of the H concentration and the S concentration; ２ and a control step of controlling the S concentration.

2. The method for producing reduced iron according to claim 1, comprising: a reducing gas producing step of producing the reducing gas using the circulating gas.

3. A method for producing reduced iron according to claim 2, wherein in the reducing gas production step, the circulating gas and the raw material gas are mixed together, and then the circulating gas and the raw material gas are reformed into the reducing gas by a catalyst.

4. A method for producing reduced iron according to any one of claims 1 to 3, wherein in the exhaust gas treatment step, a hydrogen-containing gas is produced from water vapor in the exhaust gas by a solid oxide electrolysis cell.

5. The method for producing reduced iron according to claim 4, wherein at least a portion of the water contained in the hydrogen-containing gas is removed in the exhaust gas treatment step.

6. A method for producing reduced iron according to any one of claims 1 to 5, comprising: a heating step of heating the reducing gas by a heating device; and in the monitoring step, a reaction rate determined by the following formula (1): H ２ S out = H ２ S in +A×(10-3420 / T+0.426×H ２ -H ２ S in ) ... (1) H ２ S out : H in the exhaust gas ２ S concentration [volume %] H ２ S in : H in the reducing gas at the inlet side of the heating device ２ S concentration [vol %] A: constant T: temperature of reducing gas supplied to the shaft furnace [°C] H ２ : Hydrogen gas concentration in reducing gas [vol%] ２ A method for producing reduced iron, in which the S concentration is monitored.

7. The method for producing reduced iron according to any one of claims 1 to 6, wherein in the control step, at least one of the sulfur content of the oxidized iron raw material, the sulfur content of the reducing gas, and the temperature of the reducing gas is controlled, thereby reducing the H ２ A method for producing reduced iron, in which the S concentration is controlled.

8. A method for producing reduced iron according to claim 7, wherein hydrogen gas obtained by electrolysis of water is used as the reducing gas, and in the control step, the proportion of hydrogen gas in the reducing gas is changed to control the sulfur content of the reducing gas.

9. A method for producing reduced iron according to claim 7 or 8, wherein in the control step, the sulfur content of the oxidized iron raw material is controlled by changing the proportion of fired pellets in the oxidized iron raw material.

10. The method for producing reduced iron according to any one of claims 1 to 9, wherein the H ２ A method for producing reduced iron, wherein the S concentration is controlled to 5 ppmv or less.

11. A method for producing reduced iron according to any one of claims 1 to 10, comprising a raw material pretreatment step of heating the oxidized iron raw material to remove at least a portion of the sulfur contained in the oxidized iron raw material.

12. A method for producing reduced iron according to any one of claims 1 to 11, wherein the temperature of the reducing gas is 700°C or higher and 1100°C or lower.

13. A method for producing reduced iron according to any one of claims 1 to 12, comprising monitoring the concentration of sulfur contained in the reduced iron.

14. A method for producing reduced iron according to any one of claims 1 to 13, comprising monitoring the concentration of sulfur contained in the oxidized iron raw material.

15. A reduced iron manufacturing system comprising: a shaft furnace; a raw material supply device; a reducing gas supply device; an exhaust gas treatment device; a monitoring device; and a control device, wherein the raw material supply device supplies iron oxide raw materials to the shaft furnace; the reducing gas supply device supplies reducing gas to the shaft furnace; the exhaust gas treatment device treats the exhaust gas from the shaft furnace and circulates it as a circulating gas; and the monitoring device detects H in the reducing gas. ２ S concentration, H in the exhaust gas ２ S concentration and H in the circulating gas ２ and the control device monitors at least one of the H ２ A reduced iron production system that controls sulfur concentration.

16. A reduced iron production system according to claim 15, comprising a reducing gas production device, wherein the reducing gas production device produces the reducing gas using the circulating gas.

17. A reduced iron production system according to claim 16, wherein the reducing gas production device has a catalyst that reforms the circulating gas and the raw material gas into the reducing gas.

18. A reduced iron production system according to any one of claims 15 to 17, wherein the exhaust gas treatment device has a solid oxide electrolytic cell, and the solid oxide electrolytic cell produces a hydrogen-containing gas by utilizing water vapor contained in the exhaust gas.

19. A reduced iron production system according to claim 18, further comprising a water removal device, wherein the hydrogen-containing gas removes at least a portion of the water contained in the hydrogen-containing gas.

20. A reduced iron production system according to any one of claims 15 to 19, further comprising a heating device, wherein the heating device heats the reducing gas, and the monitoring device is configured to calculate a value calculated by the following formula (1): H ２ S out = H ２ S in +A×(10-3420 / T+0.426×H ２ -H ２ S in ) ... (1) H ２ S out : H in the exhaust gas ２ S concentration [volume %] H ２ S in : H in the reducing gas at the inlet side of the heating device ２ S concentration [vol %] A: constant T: temperature of reducing gas supplied to the shaft furnace [°C] H ２ : Hydrogen gas concentration in reducing gas [vol%] ２ A reduced iron production system that monitors S concentration.

21. The system for producing reduced iron according to any one of claims 15 to 20, wherein the control device controls at least one of the sulfur content of the oxidized iron raw material, the sulfur content of the reducing gas, and the temperature of the reducing gas, thereby controlling the H ２ A reduced iron production system that controls sulfur concentration.

22. A reduced iron production system according to claim 21, wherein hydrogen gas obtained by electrolysis of water is used as the reducing gas, and the control device controls the sulfur content of the reducing gas by changing the proportion of the hydrogen gas in the reducing gas.

23. A reduced iron production system according to claim 21 or 22, wherein the control device controls the sulfur content of the oxidized iron raw material by changing the proportion of fired pellets in the oxidized iron raw material.

24. A reduced iron production system according to any one of claims 15 to 23, wherein the H ２ A reduced iron production system in which the S concentration is controlled to 5 ppmv or less.

25. A reduced iron production system according to any one of claims 15 to 24, comprising a raw material pretreatment device, wherein the raw material pretreatment device heats the oxidized iron raw material to remove at least a portion of the sulfur contained in the oxidized iron raw material.

26. A reduced iron production system according to any one of claims 15 to 25, wherein the temperature of the reducing gas is 700°C or higher and 1100°C or lower.

27. A reduced iron production system according to any one of claims 15 to 26, comprising a second monitoring device, wherein the second monitoring device monitors the concentration of sulfur contained in the reduced iron.

28. A reduced iron production system according to any one of claims 15 to 27, comprising a third monitoring device, wherein the third monitoring device monitors the concentration of sulfur contained in the oxidized iron raw material.

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