Methods for reducing carbon oxides, methods for manufacturing steel, apparatus for reducing carbon oxides, and apparatus for manufacturing steel.

Abstract

One aspect of the present invention relates to a method for reducing carbon oxides, comprising: flowing a gas containing carbon oxides and hydrogen into a reactor, the carbon oxides comprising at least one of carbon monoxide and carbon dioxide; adding reduced iron into the reactor; and reducing the carbon oxides by performing a chemical reaction using the gas flowing into the reactor as a raw material and the reduced iron as a catalyst.

Description

Technical Field

[0001] This invention relates to a method for reducing carbon oxides, a method for manufacturing steel, an apparatus for reducing carbon oxides, and an apparatus for manufacturing steel. Background Technology

[0002] In recent years, carbon dioxide has been considered to have a significant impact on global warming. As an effective countermeasure to this problem, technologies for obtaining useful substances such as hydrocarbons from carbon dioxide have attracted considerable attention. Specific examples of such technologies include those that use catalysts to react carbon oxides such as carbon dioxide with hydrogen to obtain hydrocarbons such as methane. Furthermore, examples of such catalysts include those described in Patent Document 1 and Patent Document 2. Patent Document 1 describes a methanation reaction catalyst, which is a calcined product of a wet mixture of Zr salt, salts of stabilizing elements such as Y, Ni salt, and inorganic oxides such as silica. Patent Document 2 describes a methanation reaction catalyst comprising: a stabilized zirconium oxide support; and Ni supported on the stabilized zirconium oxide support.

[0003] If a catalyst is used in the above-mentioned reaction to obtain hydrocarbons, the following problem exists: the catalyst's activity gradually decreases due to poisoning caused by impurities such as sintering, carbonization, carbon precipitation, and sulfides. As such catalysts, catalysts containing Ni, Co, and noble metals, as described in Patent Documents 1 and 2, and synthesized specifically for the reaction, are commonly used. These catalysts are often expensive, and maintaining a high level of activity in the reaction by frequently replacing the catalyst is impractical. Therefore, to suppress sintering, carbonization, and carbon precipitation, mild reaction conditions can be considered, for example. Specifically, the reaction conditions, such as temperature, pressure, and composition, can be set to conditions that prevent sintering and carbon precipitation (i.e., reactions with extremely slow carbon precipitation rates). However, under such mild reaction conditions, the yield and reaction rate decrease, and to achieve the ideal reaction, it is necessary to increase the catalyst loading by increasing the size of the reactor, which may lead to higher costs for obtaining hydrocarbons. Furthermore, while removing impurities from the reactants before the reaction could be considered to suppress poisoning, this requires pretreatment, potentially increasing the cost of obtaining hydrocarbons. Based on the above, if a catalyst containing Ni, Co, and noble metals, synthesized specifically for this reaction, is used, maintaining its high activity level would be extremely expensive. Therefore, maintaining a catalyst containing Ni, Co, and noble metals synthesized specifically for this reaction at a high activity level presents certain practical limitations.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Publication No. 2018-122247

[0007] Patent Document 2: Japanese Patent Publication No. 2018-20278 Summary of the Invention

[0008] The present invention was made in view of the above circumstances, and its object is to provide a method and apparatus for reducing carbon oxides such as carbon dioxide even without using catalysts containing expensive materials such as Ni, Co, and precious metals. Furthermore, the present invention aims to provide a method for manufacturing steel and an apparatus for manufacturing steel that effectively utilizes the aforementioned reduction method.

[0009] One aspect of the present invention relates to a method for reducing carbon oxides, comprising: flowing a gas containing carbon oxides and hydrogen into a reactor, the carbon oxides comprising at least one of carbon monoxide and carbon dioxide; adding reduced iron into the reactor; and reducing the carbon oxides by performing a chemical reaction using the gas flowing into the reactor as a raw material and the reduced iron as a catalyst.

[0010] Another aspect of the present invention relates to a method for manufacturing steel, comprising: flowing a gas containing carbon oxides and hydrogen into a reactor, the carbon oxides comprising at least one of carbon monoxide and carbon dioxide; adding reduced iron into the reactor; reducing the carbon oxides by performing a chemical reaction using the gas flowing into the reactor as a raw material and the reduced iron as a catalyst; measuring the time after the reduced iron is added to the reactor, and when the measured time has elapsed for a specified period, removing the reduced iron from the reactor; and feeding the reduced iron removed from the reactor into a blast furnace or an electric furnace.

[0011] Another aspect of the present invention relates to a carbon oxide reduction apparatus comprising: a reactor; an inlet for flowing a gas containing carbon oxide and hydrogen into the reactor, the carbon oxide comprising at least one of carbon monoxide and carbon dioxide; and an input for inputting reduced iron into the reactor; wherein the carbon oxide is reduced by performing a chemical reaction using the gas flowing into the reactor through the inlet as a raw material and the reduced iron as a catalyst.

[0012] Another aspect of the present invention relates to an iron and steel manufacturing apparatus comprising: a reactor; an inflow section for flowing a gas containing carbon oxides and hydrogen into the reactor, the carbon oxides comprising at least one of carbon monoxide and carbon dioxide; an input section for inputting reduced iron into the reactor; an output section for removing the reduced iron from the reactor after a predetermined time has elapsed from the time the reduced iron is input into the reactor at the input section; and an iron supply section for inputting the reduced iron removed from the reactor into a blast furnace or an electric furnace at the output section; wherein, in the reactor, the carbon oxides are reduced by performing a chemical reaction using the gas flowing into the reactor as raw material and the reduced iron as a catalyst.

[0013] The above-described objects, features, and other objects, features, and advantages of the present invention will become more apparent from the following detailed description and accompanying drawings. Attached Figure Description

[0014] Figure 1 This is a schematic diagram illustrating an example of a carbon oxide reduction apparatus according to an embodiment of the present invention.

[0015] Figure 2 This is a schematic diagram illustrating another example of a carbon oxide reduction apparatus according to an embodiment of the present invention.

[0016] Figure 3 This is a schematic diagram illustrating another example of a carbon oxide reduction apparatus according to an embodiment of the present invention.

[0017] Figure 4 This is a schematic diagram illustrating another example of a carbon oxide reduction apparatus according to an embodiment of the present invention.

[0018] Figure 5 This is a schematic diagram illustrating another example of a carbon oxide reduction apparatus according to an embodiment of the present invention.

[0019] Figure 6 This is a schematic diagram illustrating another example of a carbon oxide reduction apparatus according to an embodiment of the present invention.

[0020] Figure 7 This is a schematic diagram illustrating another example of a carbon oxide reduction apparatus according to an embodiment of the present invention. Detailed Implementation

[0021] Through various studies, the inventors have discovered that the above-mentioned objectives can be achieved through the following invention.

[0022] The following describes the embodiments of the present invention, but the present invention is not limited to these embodiments.

[0023] [Methods for reducing carbon oxides]

[0024] The method for reducing carbon oxides according to embodiments of the present invention includes: flowing a gas containing carbon oxides and hydrogen into a reactor, wherein the carbon oxides include at least one of carbon monoxide and carbon dioxide; adding reduced iron into the reactor; and reducing the carbon oxides by performing a chemical reaction using the gas flowing into the reactor as a raw material and the reduced iron as a catalyst. The chemical reaction is not particularly limited as long as it uses the gas flowing into the reactor as a raw material and the reduced iron as a catalyst. Examples of such chemical reactions include reverse shift reaction, methanation reaction, Sabatier reaction, and Fischer-Tropsch reaction. The chemical reaction can be a single reaction or a combination of two or more reactions. By using the gas flowing into the reactor as a raw material and the reduced iron added to the reactor as a catalyst, and performing a chemical reaction such as a reverse shift reaction, carbon oxides such as carbon dioxide can be reduced even without using catalysts containing expensive materials such as Ni, Co, or precious metals. By reducing carbon oxides such as carbon dioxide, hydrocarbons such as methane can be obtained, along with carbon monoxide, thus achieving efficient utilization of carbon dioxide. Furthermore, the reduced iron used as a catalyst in this reduction method, due to the precipitation or carbonization of carbon, can be effectively used in steelmaking after the reaction, as the reduced iron removed from the reactor. This allows for frequent replacement of the reduced iron as a catalyst while suppressing rising operating costs. Therefore, not only can carbon oxides be reduced, but the catalyst activity can also be maintained at a high level by replacing it before it significantly declines. In addition, although Ni is a relatively inexpensive metal, its demand has increased due to its use in electric vehicles (EVs), leading to price increases and making its availability more difficult. Therefore, a method for reducing carbon oxides, such as carbon dioxide, even without using a Ni-containing catalyst is of great significance. Moreover, as an effective countermeasure to global warming, in addition to the aforementioned technologies for obtaining useful substances such as hydrocarbons from carbon dioxide, technologies capable of fixing atmospheric carbon dioxide, i.e., so-called negative emission technologies, are also needed. The reduction method described below also contributes to achieving this negative emission technology. In the reduction method, the reaction can reduce not only carbon oxides such as carbon dioxide, but also produce carbon. Specifically, as described above, carbon is precipitated on the reduced iron used as a catalyst, or the reduced iron is carburized (carburized). Moreover, by using the reduced iron with precipitated carbon and the carburized reduced iron to manufacture steel, steel containing this carbon can be obtained.Therefore, the reduction method described above can convert at least a portion of carbon oxides such as carbon dioxide in the atmosphere into carbon, obtaining steel with the carbon fixed, which is a so-called negative emission technology. From this perspective, the reduction method is also of great significance.

[0025] The carbon oxide is not particularly limited as long as it contains at least one of carbon monoxide and carbon dioxide. It may contain carbon oxides other than carbon monoxide and carbon dioxide, but is preferably composed of at least one of carbon monoxide and carbon dioxide. The carbon oxide is typically an inorganic compound consisting only of carbon and oxygen; examples include carbon oxides such as carbon monoxide and carbon dioxide, which have fewer than or equal to the number of oxygen atoms. As long as the carbon oxide contains at least one of carbon monoxide and carbon dioxide, it may also contain carbon dioxide (C3O2) and calcite anhydride (C2O2). 12 Carbon oxides such as O9 (which have more carbon atoms than oxygen atoms).

[0026] The reactor is not particularly limited as long as it can use the reduced iron fed into the reactor as a catalyst to carry out the chemical reaction, such as the reverse conversion reaction, on the carbon oxides flowing into the reactor. The reactor can be, for example, a flow reactor or a batch reactor. A flow reactor continuously supplies reduced iron as a catalyst while maintaining specified temperature and pressure, and continuously discharges the reduced iron used as a catalyst (reduced iron that can be used as a catalyst but has already completed its catalytic action). Flow reactors are preferred due to their simple structure and operation. Examples of flow reactors include shaft furnaces, and more specifically, shaft furnaces used in the MIDREX process. A batch reactor loads reduced iron as a catalyst into the reactor, maintains specified temperature and pressure, carries out a reaction for a specified time, and then discharges the reduced iron used as a catalyst (reduced iron that can be used as a catalyst but has already completed its catalytic action). Compared to the flow-through reactor, the batch reactor does not require much technical expertise (process ingenuity) in areas such as gas sealing of the sliding section when continuously discharging solids such as catalysts that are constantly sinking inside the reactor, and is therefore preferred.

[0027] The reduced iron is not particularly limited, and examples include reduced iron obtained by direct reduction methods. Examples of reduced iron obtained by direct reduction methods include hot direct reduced iron (HDRI) and other direct reduced iron (DRI), as well as hot briquetted iron (HBI). Direct reduced iron refers to iron produced by a direct reduction process (iron production method) that uses reducing gases derived from natural gas or coal to directly reduce iron ore, iron oxide pellets, and sinter. Examples of iron ore include mined ore containing iron oxide. Examples of iron oxide pellets include sintered products formed by mixing iron ore, binder, and water. Examples of sintered ore include sintered products formed by mixing iron ore powder, carbon, and lime. Examples of direct reduction methods include the MIDREX process and the HYL process. DRI is preferred due to its high catalyst activity. The reason is believed to be that during the reduction process of DRI, oxygen in the iron oxide is removed, resulting in a state with numerous pores (sponge iron) in the obtained reduced iron. HBI is obtained by compressing and molding (bulking) DRI at high temperatures (e.g., about 700°C). Compared to DRI with numerous pores, HBI is easier to process and can suppress heat generation and spontaneous combustion (heat generation and spontaneous combustion caused by the characteristics of sponge iron), therefore it is preferred.

[0028] The reduced iron is preferably granular, more preferably spherical. The equivalent particle size of the reduced iron is preferably 5 mm or more, more preferably 8–18 mm, and even more preferably 10–16 mm. Furthermore, the equivalent particle size here refers to the arithmetic mean of the equivalent particle size assuming the granular reduced iron is spherical (converted to the diameter of a sphere with the same volume as the granular reduced iron: sphere equivalent particle size). If the reduced iron is granular, not only can the hydrogen be used to reduce the carbon oxides contained in the gas, but the reduced iron used as a catalyst can also be easily replaced. The reduced iron is usually obtained in granular form. The reduced iron is usually manufactured using processes such as the MIDREX process and the HYL process, which yield granular reduced iron, and spherical reduced iron can also be obtained. In this case, the reduced iron can be used directly without pulverizing, thus eliminating pulverization costs. Furthermore, if excessive pulverization results in the reduced iron being too fine, the yield may decrease. Furthermore, if the reduced iron is in granular form, it is less prone to scattering than powdered reduced iron when used in steelmaking (e.g., fed into a blast furnace or electric furnace), thus suppressing the decline in ironmaking yield and inhibiting the accumulation of solid dust. Inhibiting the accumulation of solid dust reduces dust recovery costs. Additionally, if the reduced iron is in granular form, the increase in gas resistance within the blast furnace can be suppressed when it is used in steelmaking (e.g., fed into a blast furnace). Since blast furnaces require gas passages, granular or similar shaped materials are preferred.

[0029] In the reduced iron, the total content of iron compounds, calcium compounds, silicon compounds, magnesium compounds, and aluminum compounds relative to the total amount of reduced iron is preferably 90% by mass or more, more preferably 95% to 100% by mass. Furthermore, in the reduced iron, the content of iron compounds relative to the total amount of reduced iron is preferably 75% by mass or more, more preferably 85% to 100% by mass. In addition, the iron compounds are not particularly limited as long as they contain iron, and examples include iron, iron oxide, etc. The calcium compounds are not particularly limited as long as they contain calcium, and examples include not only calcium but also calcium salts such as calcium chloride, calcium sulfate, calcium carbonate, and calcium oxide. The silicon compounds are not particularly limited as long as they contain silicon, and examples include not only silicon but also silicon salts such as silicon dioxide and silicon hydroxide. The magnesium compounds are not particularly limited as long as they contain magnesium, and examples include not only magnesium but also magnesium salts such as magnesium chloride, magnesium sulfate, magnesium carbonate, and magnesium hydroxide. The aluminum compound is not particularly limited to any aluminum-containing compound; for example, it can include not only aluminum, but also aluminum salts such as aluminum chloride, aluminum sulfate, aluminum phosphate, and aluminum hydroxide. The metallization rate of the reduced iron is preferably 70% or more, more preferably 85-100%. Since the target substance is reduced iron, the metallization rate here refers to the metallization rate of iron, that is, the proportion (%) of metallic iron contained in the reduced iron relative to the total iron content [= (metallic iron contained in the reduced iron) / (total iron content in the reduced iron) × 100]. If the reduced iron fed into the reactor has a converted particle size, a total content (total content of iron compounds, calcium compounds, silicon compounds, magnesium compounds, and aluminum compounds), a content of iron compounds, and a metallization rate all within the above ranges, then it is more suitable to use hydrogen to reduce the carbon oxides contained in the gas. The reduced iron is preferably obtained by reducing with a reducing gas containing 50% by volume or more hydrogen, and more preferably by reducing with a reducing gas containing 60% by volume or more hydrogen. The reduced iron is preferably a reduced iron with a carbon content (carbon concentration) of 2.14% by mass or less. By using this type of reduced iron, it is suitably carburized (carburized), thereby contributing to negative emissions. Therefore, not only can the hydrogen be used more appropriately to reduce the carbon oxides contained in the gas, but the effects of carburization and negative emissions can also be maximized. Furthermore, the reducing gas more preferably contains 67% by volume or more and 100% by volume or less hydrogen. Moreover, the 2.14% by mass corresponds to the maximum carbon content in ferroalloys classified as carbon steel (iron).

[0030] The chemical reaction is not particularly limited as long as it is a reaction that uses the gas flowing into the reactor as raw material and the reduced iron added to the reactor as a catalyst, as described above. Examples include: reverse conversion reaction, methanation reaction, Sabatie reaction, and Fischer-Tropsch reaction.

[0031] The reverse conversion reaction is a chemical reaction represented by the following formula (1), which can generate CO from a mixture of CO2 and H2.

[0032] CO2+H2→CO+H2O(1)

[0033] Since the reverse conversion reaction is an endothermic reaction, it is easier to carry out at high temperatures from an equilibrium perspective.

[0034] Methanation is a chemical reaction represented by the chemical reaction shown in equation (2) below, which can generate methane (CH4) from a mixture of CO and H2. In addition, there is no particular limitation on methanation reactions as long as they can generate methane (CH4). In addition to the chemical reaction shown in equation (2) below, chemical reactions represented by equation (3) below can also be listed.

[0035] CO+3H2→CH4+H2O(2)

[0036] CO + 2H₂ → CH₄ + CO₂ (3)

[0037] Since methanation is an exothermic reaction, it is easier to carry out at low temperatures from an equilibrium perspective.

[0038] The Sabatie reaction is a chemical reaction represented by the following formula (4), which can generate CH4 from a mixture of CO2 and H2.

[0039] CO2+4H2→CH4+2H2O(4)

[0040] Since the Sabatie reaction is exothermic, it is easier to carry out at low temperatures from an equilibrium perspective.

[0041] The Fischer-Tropsch reaction is a chemical reaction represented by the chemical reactions expressed in equation (5) and equation (6) below, which can produce hydrocarbons from a mixture of CO and H2 or a mixture of CO2 and H2. The Fischer-Tropsch reaction is not particularly limited to any reaction that produces hydrocarbons from the aforementioned gas mixtures; the chemical reactions expressed in equation (5) and equation (6) below are merely examples. Furthermore, the chemical reaction expressed in equation (5) below involves a direct Fischer-Tropsch reaction, and the chemical reaction expressed in equation (6) below involves an indirect Fischer-Tropsch reaction.

[0042] nCO2 + (3n + 1)H2 → C n H 2n＋2 +2nH2O (5)

[0043] nCO + (2n + 1)H₂ → C n H 2n＋2 +nH2O (6)

[0044] The chemical reaction can be any reaction that uses the gas flowing into the reactor as raw material and the reduced iron as a catalyst. For example, it can be any reaction among reverse shift reaction, methanation reaction, Sabatie reaction, and Fischer-Tropsch reaction. Which reaction, such as reverse shift reaction, methanation reaction, Sabatie reaction, or Fischer-Tropsch reaction, occurs depends on factors such as the type of gas flowing into the reactor and conditions like temperature and pressure. Furthermore, the reaction may not necessarily be a single reaction; two or more reactions may occur simultaneously. That is, the chemical reaction can be a single reaction or a combination of two or more reactions. For example, when two or more reactions occur simultaneously, a Sabatie reaction and a direct Fischer-Tropsch reaction may occur, or a methanation reaction and an indirect Fischer-Tropsch reaction may occur.

[0045] The gas flowing into the reactor is not particularly limited as long as it contains the carbon oxides and the hydrogen. Since the hydrogen, carbon dioxide, and carbon monoxide are raw materials for the reverse shift reaction, methanation reaction, Sabatie reaction, and Fischer-Tropsch reaction, it is preferable that they constitute a high proportion of the gas. Specifically, the combined volume of the hydrogen, carbon dioxide, and carbon monoxide relative to the total volume of the gas is preferably 75% by volume or more, more preferably 85% to 100% by volume. Furthermore, since the reverse shift reaction, methanation reaction, Sabatie reaction, and Fischer-Tropsch reaction are all hindered by water (H₂O), a low water content is preferable. Specifically, the combined volume of the hydrogen and carbon monoxide relative to the combined volume of water and carbon dioxide is preferably 3 times or more, more preferably 3 to 20 times, and even more preferably 4 to 15 times. Using a gas with the above composition as the gas flowing into the reactor allows for more suitable utilization of the hydrogen to reduce the carbon oxides contained in the gas. Furthermore, the gas flowing into the reactor is preferably free of sulfur compounds, both in terms of reducing poisoning caused by sulfur compounds and in terms of improving the quality of steel obtained when using reduced iron in the reaction for iron smelting; even if it contains sulfur compounds, its content is preferably low. The content of the sulfides is preferably 10 ppm or less (i.e., 0 to 10 ppm) relative to the gas, and more preferably 1 ppm or less (i.e., 0 to 1 ppm). In addition, examples of the sulfides include sulfur oxides such as sulfur dioxide and hydrogen sulfide.

[0046] In the reactor where the chemical reaction is carried out, the temperature and pressure conditions within the reactor are not particularly limited as long as the reaction can proceed. The reduction method does not require a mild reaction that does not release carbon; since carbon release allows the reduced iron to be effectively used in ironmaking, conditions that increase the reaction rate are preferred. The temperature within the reactor is preferably, for example, 300–900°C, more preferably 400–900°C. Furthermore, the pressure within the reactor is preferably, for example, atmospheric pressure (approximately 101.325 kPaA) or higher, more preferably 300–5100 kPaA or higher.

[0047] In the reduction method, when a product gas containing carbon monoxide is obtained by reducing the carbon oxides, the carbon monoxide can be separated from the product gas and allowed to flow into the reactor. In this way, the hydrogen can be used more efficiently to reduce the carbon oxides contained in the gas, thereby efficiently obtaining hydrocarbons such as methane.

[0048] In the reduction method, it is preferable that the hydrogen and carbon dioxide are fully utilized after the chemical reaction of the gas flowing into the reactor; however, the product gas obtained after the chemical reaction may sometimes contain hydrogen and carbon dioxide that were not used in the chemical reaction. In this case, the hydrogen and carbon dioxide that were not used in the chemical reaction can be separated from the product gas obtained after the chemical reaction, and the separated hydrogen and carbon dioxide can be allowed to flow into the reactor. In this way, the hydrogen and carbon dioxide that were not used in the chemical reaction can be reused, thereby improving the yield, such as the hydrogen conversion rate and carbon dioxide conversion rate. Therefore, the hydrogen can be used more efficiently to reduce the carbon oxides contained in the gas.

[0049] In the reduction method, if the reduced iron fed into the reactor is used as a catalyst to carry out the chemical reaction such as the reverse conversion reaction on the carbon oxides flowing into the reactor, the reduced iron used as a catalyst will precipitate carbon due to the following reactions. Examples of such carbon include free carbon (amorphous carbon), graphite (crystalline carbon), carbon black (solid polymeric component), and tar (semi-liquid polymeric component). Furthermore, the reduced iron that precipitates carbon will usually be at least partially carbonized due to the carbon through reactions such as those shown in formulas (7) and (8). That is, it will be converted into a metal carbide that is bonded to the iron or other metals constituting the reduced iron. Furthermore, the carbide (Fe3C) is usually called cementite. The catalytic activity of metallic iron (Fe) is higher than that of cementite (Fe3C).

[0050] 3Fe+C→Fe3C(7)

[0051] 3Fe + 2CO → Fe3C + CO2 (8)

[0052] The carbon precipitated in the reduced iron is produced in the reduction method when the reaction conditions, such as temperature, pressure, and composition, meet specified conditions. Specifically, these conditions are relatively vigorous reaction conditions that allow the following reactions to proceed: the Boudouard reaction shown in equation (9), the reaction shown in equation (10), and the methane cracking reaction shown in equation (11), as well as other hydrocarbon decomposition reactions.

[0053] 2CO→C+CO2(9)

[0054] CO+H2→C+H2O(10)

[0055] CH4→C+2H2(11)

[0056] If carbon is released, the catalyst activity will decrease. Therefore, when using rare metals or the like as catalysts, the conditions (temperature, pressure, and composition) are usually adjusted to a mild reaction that does not release carbon (i.e., a reaction with a very low carbon release rate). However, even under reaction conditions where carbon release does not occur, the reduction rate of carbon oxides (such as CO2) (i.e., hydrocarbon synthesis reactions) usually slows down. Therefore, to obtain the desired reaction rate, the reactor must be enlarged and the amount of catalyst packed in it must be increased, leading to increased costs. In the carbon oxide reduction method according to this embodiment, catalysts containing expensive materials such as Ni, Co, and precious metals are not required. Moreover, the reduced iron used as a catalyst in the reduction method releases or carbonizes, thus fixing the carbon oxides flowing into the reactor as carbon on the reduced iron. By using such carbon-fixed reduced iron (i.e., reduced iron that has released or carbonized) in steel manufacturing, the amount of carbon supplied during steel manufacturing can be reduced. Therefore, based on these factors, the reduced iron used in the reduction method can be effectively used in steel manufacturing. Given these circumstances, since the reduced iron acting as a catalyst can be replaced frequently, there is no need to design it as a mild reaction that does not release carbon. Furthermore, by using the reduced iron with fixed carbon to manufacture steel, steel containing that carbon can be obtained. Thus, the reduction method can convert at least a portion of carbon oxides such as carbon dioxide in the atmosphere into carbon, obtaining steel with fixed carbon. In other words, the reduction method can achieve so-called negative emissions, that is, not only does it not emit carbon dioxide, but it can also absorb carbon dioxide.

[0057] To effectively utilize the reduced iron that has precipitated carbon or undergone carbonization, the reduction method can be, for example, as follows: First, the reduced iron is added to the reactor and, after a specified time, is removed from the reactor. Specifically, the time after the reduced iron is added to the reactor is measured, and when the measured time has elapsed to a specified time, the reduced iron is removed from the reactor. Subsequently, reduced iron not used as a catalyst (new reduced iron) is added to the reactor. In this way, new reduced iron not used as a catalyst can be added before the catalytic activity of the reduced iron added to the reactor becomes too low, thereby maintaining the reduced iron added to the reactor at a high catalytic activity level. Furthermore, if the reduced iron is used as a catalyst, sintering or poisoning due to impurities such as sulfides may occur, but even if these situations occur, by setting the replacement frequency of the reduced iron to be higher than that of conventional catalysts, a high catalytic activity level can be maintained. Therefore, the reduction of carbon oxides contained in the gas by hydrogen can be achieved more efficiently. Furthermore, the reduced iron, after being fed into the reactor and undergoing a specified time, precipitates carbon or undergoes carbonization as described above, thus reducing the amount of carbon supplied during steelmaking and enabling its efficient use in steel production. In addition, the predetermined time after the reduced iron is fed into the reactor is much shorter than the time required for the catalyst used to adjust to mild reaction conditions that do not precipitate carbon (typically more than one year). The specified time is simply the time during which the catalytic activity of the reduced iron does not decrease excessively; for example, it can be the time when the reaction rate drops to 70% of the initial reaction rate. Furthermore, the reaction rate can be measured using known methods, for example, calculated using a gas analyzer based on measurements from Fourier transform infrared spectroscopy (FT-IR) and gas chromatography (gas chromatography-mass spectrometry, etc.). For example, the specified time is preferably 30 minutes to 1 month, more preferably 30 minutes to 1 week, and even more preferably 30 minutes to 3 days. Specifically, examples of the specified time include 3 days, 1 week, and 1 month.

[0058] The reduced iron removed from the reactor can be effectively utilized in steelmaking. Specifically, other embodiments of the present invention involve a steelmaking method comprising: flowing a gas containing carbon oxides and hydrogen into a reactor, wherein the carbon oxides include at least one of carbon monoxide and carbon dioxide; adding reduced iron into the reactor; reducing the carbon oxides by performing chemical reactions such as reverse conversion reaction, methanation reaction, Sabatie reaction, and Fischer-Tropsch reaction, using the gas flowing into the reactor as raw material and the reduced iron as a catalyst; removing the reduced iron from the reactor after a specified time has elapsed since it was added; and feeding the reduced iron removed from the reactor into a blast furnace or electric furnace. In this way, the reduced iron removed from the reactor can be effectively used as a raw material in steelmaking. Furthermore, when manufacturing steel, if the reduced iron taken from the reactor is fed into the blast furnace, the amount of additional carbon (coke) required for steelmaking can be reduced because the reduced iron taken from the reactor has already precipitated carbon or undergone carbonization. Additionally, the reduced iron taken from the reactor can be used as a reducing agent in the blast furnace, thereby improving energy efficiency and reducing operating costs. Furthermore, if the reduced iron taken from the reactor is fed into an electric furnace, it can be used as a flux or carburizing agent, thereby improving energy efficiency and reducing operating costs. Moreover, by using the reduced iron with fixed carbon to manufacture steel, steel containing that carbon can be obtained. Therefore, by employing this steelmaking method, at least a portion of carbon oxides such as carbon dioxide in the atmosphere can be converted into carbon, thereby obtaining steel with fixed carbon. In other words, this reduction method can achieve so-called negative emissions, that is, not only does it not emit carbon dioxide, but it can also absorb carbon dioxide. In steel manufacturing, in addition to the reduced iron taken from the reactor, unreduced iron or reduced iron not used as a catalyst may also be used; however, these substances may not be used, and only the reduced iron taken from the reactor may be used as the iron source. By using only the reduced iron taken from the reactor as the iron source as described above, negative emissions can be further achieved. Furthermore, in the steel manufacturing method, apart from including the reduced iron taken from the reactor in the iron source fed into the blast furnace or electric furnace, the rest can be done using known steel manufacturing methods.

[0059] The apparatus for implementing the reduction method (a carbon oxide reduction apparatus) is not particularly limited as long as it can implement the reduction method. Examples of such an apparatus include: a reactor; an inlet section for flowing a gas containing carbon oxides and hydrogen into the reactor, wherein the carbon oxides include at least one of carbon monoxide and carbon dioxide; and an input section for feeding reduced iron into the reactor. The carbon oxides are reduced by performing chemical reactions such as reverse conversion reaction, methanation reaction, Sabatie reaction, and Fischer-Tropsch reaction, using the gas flowing into the reactor through the inlet section as raw material and the reduced iron as a catalyst. Because this type of reduction apparatus can implement the reduction method, it can reduce carbon oxides such as carbon dioxide even without using catalysts containing expensive materials such as Ni, Co, and precious metals, similar to the reduction method. Furthermore, similar to the reduction method, the reduced iron taken from the reactor in this reduction apparatus can be effectively utilized in steel manufacturing. The reduction apparatus can also be an apparatus for manufacturing steel using the reduced iron during steel manufacturing (a steel manufacturing apparatus), as described above. Specifically, other embodiments of the present invention involve an iron and steel manufacturing apparatus comprising: a reactor; an inflow section for flowing a gas containing carbon oxides and hydrogen into the reactor, the carbon oxides comprising at least one of carbon monoxide and carbon dioxide; an input section for inputting reduced iron into the reactor; an output section for removing the reduced iron from the reactor after a predetermined time has elapsed from the time the reduced iron is input into the reactor at the input section; and an iron supply section for inputting the reduced iron removed from the reactor into a blast furnace or an electric furnace at the output section; wherein, in the reactor, the carbon oxides are reduced by performing a chemical reaction using the gas flowing into the reactor as raw material and the reduced iron as a catalyst.

[0060] Examples of such reduction devices include, for instance, devices that initiate the Sabatie reaction. Specifically, examples of such reduction devices include... Figure 1 The reduction apparatus 10 shown is an example. Furthermore, Figure 1 This is a schematic diagram illustrating an example of the carbon oxide reduction apparatus according to this embodiment. Figure 1As shown, the reduction apparatus 10 includes a reactor 11, an inlet 12, and an input 14. The reduction apparatus 10 supplies a gas containing carbon dioxide and hydrogen to the reactor 11 through the inlet 12, and uses reduced iron introduced into the reactor 11 from the input 14 as a catalyst to initiate the Sabatie reaction to obtain methane. The gas obtained in the reactor 11, in addition to methane, mainly contains water (water vapor) in the gaseous phase; after the gas is removed from the reactor 11, it is cooled by a heat exchanger 16 provided in the reduction apparatus 10, thereby separating the gas into methane and water. Furthermore, the gas removed from the reactor 11 may also contain unreacted hydrogen and carbon dioxide from the reactor 11. However, in Figure 1 In this description, the unreacted hydrogen and carbon dioxide that may be present are omitted from the description of the gas extracted from the reactor 11; only methane and water (water vapor), which are the main components of the gas, are listed. Furthermore, the separated methane is recovered in the methane recovery unit 171 of the reduction unit 10, while the separated water is separated from the separated methane and recovered in the water recovery unit 172 of the reduction unit 10. The reduction unit 10 extracts the reduced iron used as a catalyst in the reactor 11 via the extraction unit 18. Specifically, the time after the reduced iron is added to the reactor 11 is measured as described above, and when the measured time has elapsed to a specified time, the reduced iron is extracted from the reactor 11 via the extraction unit 18. As described above, the reduced iron extracted via the extraction unit 18 has precipitated carbon or undergone carbonization and is then fed into the blast furnace 191 or electric furnace 192 for ironmaking. Furthermore, the steelmaking apparatus, after feeding the reduced iron or an iron source containing the reduced iron from the reactor 11 into the blast furnace 191 or electric furnace 192, can be the same as a known steelmaking apparatus, and steel can be manufactured by this apparatus. Accordingly, the reduction apparatus 10 is also a steelmaking apparatus. That is, as the steelmaking apparatus, except that the iron source fed into the blast furnace 191 or electric furnace 192 includes the reduced iron extracted by the extraction section 18, all other known steelmaking apparatuses can be used. Moreover, this steelmaking apparatus also includes a mechanism for feeding the reduced iron extracted from the reactor 11 through the extraction section 18 into the blast furnace 191 or electric furnace 192, which is equivalent to an iron feeding section.

[0061] In the reduction apparatus 10, there are no particular limitations on how the reduced iron is fed into the reactor 11 from the feeding section 14. For example, it can be fed in the following manner: The reactor 11 has valves at the upper part (the feeding section 14 side) and the lower part (the taking-out section 18 side). First, only the lower valve is closed, and then the reduced iron (reduced iron before use as a catalyst) is fed into the reactor 11 from the upper part. Afterward, the upper valve is closed, and a gas containing carbon dioxide and hydrogen flows into the reactor 11 through the inflow section 12, allowing the reduced iron in the reactor 11 to react as a catalyst. After a specified time, the lower valve is opened, and the reduced iron is taken out of the reactor 11. Then, the upper valve is opened, the lower valve is closed, and the above operation is repeated, starting from the feeding of the reduced iron (reduced iron before use as a catalyst). As another example, multiple (two or more) reactors can be connected in parallel to the reduction apparatus. In this scenario, for example, among multiple reactors, while the reduced iron (reduced iron before use as a catalyst) is introduced into one reactor (the reactor constituting the first reactor group), the reaction is carried out in the remaining reactors (the reactor constituting the second reactor group). Then, while the reduced iron used as a catalyst is removed from the reactor constituting the second reactor group and the reduced iron (reduced iron before use as a catalyst) is introduced, the reaction can be carried out in the reactor constituting the first reactor group. Furthermore, a portion of the reactor constituting the first reactor group can be converted into the second reactor group, or a portion of the reactor constituting the second reactor group can be converted into the first reactor group. Moreover, a portion of the reactor constituting the first reactor group can be left unused, or a portion of the reactor constituting the second reactor group can be left unused. Furthermore, if two reactors are connected in parallel to the reduction apparatus, for example, while the reduced iron (reduced iron before use as a catalyst) is being added to one reactor, the reaction can be carried out in the other reactor; then, while the reduced iron used as a catalyst is being removed from the other reactor and the reduced iron (reduced iron before use as a catalyst) is being added back, the reaction can be carried out in one reactor. Moreover, in the reduction method, as mentioned above, it is preferable to perform the removal and addition of reduced iron at a high frequency. As for the reactor, as described above, it can be a flow-through reactor or a batch reactor; any of these reactors facilitates the high-frequency removal and addition of reduced iron.

[0062] Examples of such reduction devices include, for instance, devices that initiate an inverse conversion reaction. More specifically, examples of such reduction devices include... Figure 2 The reduction apparatus 20 shown is an example. Furthermore... Figure 2 This is a schematic diagram illustrating another example of the carbon oxide reduction apparatus according to this embodiment. The reduction apparatus 20 is identical to the reduction apparatus 10, except that it initiates the reverse conversion reaction (Sabatier reaction). Figure 2 As shown, the reduction apparatus 20 includes a reactor 21, an inlet 22, and an input 24. The reduction apparatus 20 supplies a gas containing carbon dioxide and hydrogen to the reactor 21 through the inlet 22, and uses reduced iron introduced into the reactor 21 from the input 24 as a catalyst to initiate a reverse conversion reaction to obtain carbon monoxide. The gas obtained in the reactor 21 mainly contains water (water vapor) in the gaseous phase, in addition to carbon monoxide. After the gas is removed from the reactor 21, it is cooled by a heat exchanger 26 provided in the reduction apparatus 20, thereby separating the gas into carbon monoxide and water. Furthermore, the gas removed from the reactor 21 may also contain unreacted hydrogen and carbon dioxide from the reactor 21. However, in Figure 2 In this description, the unreacted hydrogen and carbon dioxide that may be present in the gas extracted from the reactor 21 are omitted; only carbon monoxide and water (water vapor), which are the main components of the gas, are listed. Furthermore, the separated carbon monoxide is recovered in the carbon monoxide recovery unit 271 of the reduction device 20, while the separated water is separated from the carbon monoxide and recovered in the water recovery unit 272 of the reduction device 20. The reduction device 20 extracts the reduced iron, which serves as a catalyst in the reactor 21, from the extraction unit 28. As described above, the reduced iron extracted through the extraction unit 28 has undergone carbon precipitation or carbonization and is fed into the blast furnace 291 or electric furnace 292 for iron smelting, which can produce steel.

[0063] The reduction apparatus may be, for example, an apparatus comprising two or more reactors. Specifically, examples of such a reduction apparatus include an apparatus comprising a reactor for initiating a reverse conversion reaction and a reactor for initiating a methanation reaction. Furthermore, examples of an apparatus comprising two or more reactors include: using two reactors, where reduced iron is fed into each reactor separately and the carbonized reduced iron is removed from both reactors (parallel connection); and using two reactors, where reduced iron is fed into one reactor and the carbonized reduced iron removed from that reactor is fed into another reactor (series connection).

[0064] As another example of the reduction device, specifically in the parallel connection case, examples can be listed. Figure 3 The reduction apparatus 30 shown is an example. Furthermore... Figure 3 This is a schematic diagram illustrating another example of the carbon oxide reduction apparatus according to this embodiment. Figure 3 As shown, the reduction apparatus 30 includes a first reactor 311, a first inlet 321, a first input 341, a second reactor 312, a second inlet 322, and a second input 342. The reduction apparatus 30 supplies a gas containing carbon dioxide and hydrogen to the first reactor 311 through the first inlet 321, and uses the reduced iron introduced into the first reactor 311 from the first input 341 as a catalyst to initiate a reverse conversion reaction to obtain carbon monoxide. Furthermore, the gas extracted from the first reactor 311 may also contain unreacted hydrogen and carbon dioxide from the first reactor 311. However, in Figure 3 In this text, the description of the gas extracted from the first reactor 311 omits the inclusion of unreacted hydrogen and carbon dioxide, only listing carbon monoxide and water (water vapor) as the main components of the gas. Given the large amount of water (water vapor) accompanying the carbon monoxide obtained in the reverse conversion reaction in the first reactor 311, the water accompanying the carbon monoxide can be removed. Specifically, after the carbon monoxide is extracted from the first reactor 311, it can be cooled by the heat exchanger 361 provided in the reduction device 30, thereby separating the carbon monoxide from the water. If water is separated in this manner, it will be recycled in the water recovery unit 35. Therefore, the reduction device 30 may or may not include the heat exchanger 361; if the heat exchanger 361 is not included, the water recovery unit 35 may also be omitted. Hydrogen is supplied from the second inlet 322 to the carbon monoxide obtained through the reverse conversion reaction (or, if water has been separated, carbon monoxide with separated water). The reduction device 30 supplies carbon monoxide infused with hydrogen to the second reactor 312, and uses the reduced iron introduced into the second reactor 312 from the second input section 342 as a catalyst to initiate a methanation reaction to obtain methane. Furthermore, the gas extracted from the second reactor 312 may also contain unreacted hydrogen and carbon dioxide from within the second reactor 312. However, in Figure 3In this description, the gas extracted from the second reactor 312 is omitted from the labeling of unreacted hydrogen and carbon dioxide, and only methane and water (water vapor), which mainly constitute the gas, are listed. To improve reaction efficiency, the gas containing carbon monoxide and hydrogen supplied to the second reactor 312 can be heated by the heat exchanger 362 provided in the reduction device 30. The gas obtained in the second reactor 312 mainly contains water (water vapor) in a gaseous state, in addition to methane. After the methane is extracted from the second reactor 312, it is cooled by the heat exchanger 363 provided in the reduction device 30, thereby separating the gas into methane and water. Furthermore, the separated methane is recovered in the methane recovery section 371 provided in the reduction device 30, while the separated water is separated from the separated methane and recovered in the water recovery section 372 provided in the reduction device 30. Furthermore, the reduction device 30 removes the reduced iron used as a catalyst in the first reactor 311 via the first extraction section 381, and removes the reduced iron used as a catalyst in the second reactor 312 via the second extraction section 382. As described above, the reduced iron extracted via the first extraction section 381 and the second extraction section 382 has precipitated carbon or undergone carbonization, and is fed into the blast furnace 391 or electric furnace 392 for iron smelting, which can produce steel.

[0065] As another example of the reduction device, specifically in the case of the series connection, examples can be listed. Figure 4 The reduction device 40 shown and Figure 5 The reduction apparatus 50 shown is an example. Furthermore... Figure 4 and Figure 5 These are schematic diagrams illustrating another example of a carbon oxide reduction apparatus according to this embodiment.

[0066] like Figure 4 As shown, the reduction apparatus 40 includes a first reactor 411, a first inlet 421, a first input 441, a second reactor 412, a second inlet 422, and a second input 442. The reduction apparatus 40 supplies a gas containing carbon dioxide and hydrogen to the first reactor 411 through the first inlet 421, and inputs reduced iron taken from the second reactor 412 into the first reactor 411 through the first input 441. This reduced iron acts as a catalyst to initiate a reverse conversion reaction to obtain carbon monoxide. Furthermore, the gas taken from the first reactor 411 may also contain unreacted hydrogen and carbon dioxide from the first reactor 411. However, in... Figure 4In this text, the description of the gas extracted from the first reactor 411 omits the inclusion of unreacted hydrogen and carbon dioxide, only listing carbon monoxide and water (water vapor) as the main components of the gas. Given the large amount of water (water vapor) accompanying the carbon monoxide obtained in the reverse conversion reaction in the first reactor 411, the water accompanying the carbon monoxide can be removed. Specifically, after the carbon monoxide (including the water accompanying it) is extracted from the first reactor 411, it can be cooled by the heat exchanger 461 of the reduction device 40 to separate the carbon monoxide from the water. If water is separated in this manner, it will be recovered in the water recovery unit 45. Therefore, the reduction device 40 may or may not include the heat exchanger 461; if the heat exchanger 461 is not included, the water recovery unit 45 may also be omitted. Hydrogen is supplied from the second inlet 422 to the carbon monoxide obtained through the reverse conversion reaction (or, if water has been separated, carbon monoxide with separated water). The reduction device 40 supplies carbon monoxide infused with hydrogen to the second reactor 412, and uses the reduced iron introduced into the second reactor 412 from the second input section 442 as a catalyst to initiate a methanation reaction to obtain methane. Furthermore, the gas extracted from the second reactor 412 may also contain unreacted hydrogen and carbon dioxide from within the second reactor 412. However, in Figure 4In this description, the gas extracted from the second reactor 412 is omitted from the labeling of unreacted hydrogen and carbon dioxide, and only methane and water (water vapor), which mainly constitute the gas, are listed. To improve reaction efficiency, the gas containing carbon monoxide and hydrogen supplied to the second reactor 412 can be heated by the heat exchanger 462 provided in the reduction device 40. The gas obtained in the second reactor 412 mainly contains gaseous water (water vapor) in addition to methane; after the methane is extracted from the second reactor 412, it is cooled by the heat exchanger 463 provided in the reduction device 40, thereby separating the gas into methane and water. Furthermore, the separated methane is recovered in the methane recovery section 471 provided in the reduction device 40, while the separated water is separated from the separated methane and recovered in the water recovery section 472 provided in the reduction device 40. Moreover, the reduction device 40 extracts the reduced iron used as a catalyst in the second reactor 412 via the second extraction section 482. As described above, the reduced iron taken out through the second extraction section 482 is fed into the first reactor 411 through the first input section 441. Furthermore, the reduction device 40 extracts the reduced iron used as a catalyst in the first reactor 411 through the first extraction section 481. As described above, the reduced iron extracted through the first extraction section 481 has precipitated carbon or undergone carbonization, and is fed into the blast furnace 491 or electric furnace 492 for iron smelting, which can produce steel.

[0067] like Figure 5 As shown, the reduction apparatus 50 includes a first reactor 511, a first inlet 521, a first feed 541, a second reactor 512, a second inlet 522, and a second feed 542. The reduction apparatus 50 supplies a gas containing carbon dioxide and hydrogen to the first reactor 511 through the first inlet 521, and uses the reduced iron fed into the first reactor 511 from the first feed 541 as a catalyst to initiate a reverse conversion reaction to obtain carbon monoxide. Furthermore, the gas extracted from the first reactor 511 may also contain unreacted hydrogen and carbon dioxide from the first reactor 511. However, in Figure 5In this description, the gas extracted from the first reactor 511 is listed without specifying unreacted hydrogen and carbon dioxide, only carbon monoxide and water (water vapor) are listed as the main components of the gas. Given the large amount of water (water vapor) accompanying the carbon monoxide obtained from the reverse conversion reaction in the first reactor 511, the water accompanying the carbon monoxide can be removed. Specifically, after the carbon monoxide is extracted from the first reactor 511, it can be cooled by the heat exchanger 561 of the reduction device 50, thereby separating the gas into carbon monoxide and water. If water is separated in this manner, it will be recovered in the water recovery unit 55. Hydrogen is supplied to the separated carbon monoxide from the second inlet 522. Therefore, the reduction device 50 may or may not include the heat exchanger 561; if the heat exchanger 561 is not included, the water recovery unit 55 may also be omitted. Hydrogen gas is supplied from the second inlet 522 to the carbon monoxide (or, in the case of water separation) obtained through the reverse conversion reaction. The reduction device 50 supplies this hydrogen-supplied carbon monoxide to the second reactor 512, and through the second input 542, reduces iron taken from the first reactor 511 is introduced into the second reactor 512. This reduced iron acts as a catalyst to initiate a methanation reaction to obtain methane. Furthermore, the gas extracted from the second reactor 512 may also contain unreacted hydrogen and carbon dioxide from within the second reactor 512. However, in… Figure 5In this description, the gas extracted from the second reactor 512 is omitted from the labeling of unreacted hydrogen and carbon dioxide, and only methane and water (water vapor), which mainly constitute the gas, are labeled. To improve reaction efficiency, the gas containing carbon monoxide and hydrogen supplied to the second reactor 512 can be heated by the heat exchanger 562 provided in the reduction device 50. The gas obtained in the second reactor 512, in addition to methane, mainly contains water (water vapor) in the gaseous phase; after the methane is extracted from the second reactor 512, it is cooled by the heat exchanger 563 provided in the reduction device 50, thereby separating the gas into methane and water. Furthermore, the separated methane is recovered in the methane recovery section 571 provided in the reduction device 50, while the separated water is separated from the separated methane and recovered in the water recovery section 572 provided in the reduction device 50. Moreover, the reduction device 50 extracts the reduced iron used as a catalyst in the first reactor 511 through the first extraction section 581. As described above, the reduced iron taken out through the first extraction section 581 is fed into the second reactor 512 through the second input section 542. Furthermore, the reduction device 50 extracts the reduced iron used as a catalyst in the second reactor 512 through the second extraction section 582. As described above, the reduced iron extracted through the second extraction section 582 has undergone carbon precipitation or carbonization, and is fed into the blast furnace 591 or electric furnace 592 for iron smelting, which can produce steel.

[0068] In reduction devices 30, 40, and 50, where two reactors are used—one initiating the reverse shift reaction and the other initiating the methanation reaction—as described above, the water accompanying the carbon monoxide produced in the reverse shift reaction can be removed from the carbon monoxide. This dehydrated carbon monoxide is then used in the methanation reaction. Since water hinders the methanation reaction, the methane yield can be increased in reduction device 30. Furthermore, the methane yield can also be increased by increasing the H2 / CO2 ratio in the reverse shift reaction.

[0069] In the reduction apparatus 40 and 50, where two reactors are used (connected in series), reduced iron is fed into one reactor and the carbonized reduced iron taken from that reactor is fed into the other reactor, the Fe3C content in the extracted reduced iron is higher than that in the parallel reactor because the reduced iron undergoes two stages of carbonization. Therefore, when the extracted reduced iron is used for ironmaking, the operating cost of the subsequent blast furnace or electric furnace is reduced. On the other hand, since the Fe3C content in the reduced iron fed into the reactor in series increases faster than in the parallel reactor, the catalyst activity decreases more rapidly, thus requiring a larger reactor. Therefore, the reactor cost during synthesis is higher.

[0070] In the reduction apparatus 30 described above, where two reactors are used, and reduced iron is fed into each reactor and then removed from both reactors (in parallel), the Fe3C content in the removed reduced iron is lower than that in the series reactor. Therefore, even if the removed reduced iron is used for ironmaking, the reduction effect on the operating cost of the subsequent blast furnace or electric furnace is not sufficient. On the other hand, since the Fe3C content in the reduced iron fed into the reactors in parallel increases more slowly than in the series reactor, the decrease in catalyst activity can be suppressed, and the reactor size can be reduced accordingly. Therefore, the reactor cost during synthesis is lower.

[0071] As the reduction apparatus, carbon monoxide and the like, separated from the product gas obtained by reacting a gas containing the carbon oxides, can be fed into the reactor for use in the reaction. For example, when a product gas containing carbon monoxide is obtained by reducing the carbon oxides, the carbon monoxide can be separated from the product gas containing carbon monoxide and fed into the reactor. In this way, the hydrogen can be used more efficiently to reduce the carbon oxides contained in the gas, thereby efficiently obtaining hydrocarbons such as methane. Specifically, examples of such reduction apparatus can be listed... Figure 6 The reduction apparatus 60 shown is an example. Furthermore... Figure 6 This is a schematic diagram illustrating another example of the carbon oxide reduction apparatus according to this embodiment.

[0072] like Figure 6 As shown, the reduction apparatus 60 includes a reactor 61, an inlet 62, and an input 64. The reduction apparatus 60 supplies a gas containing carbon dioxide and hydrogen to the reactor 61 through the inlet 62, and uses the reduced iron introduced into the reactor 61 from the input 64 as a catalyst to initiate a reverse conversion reaction to obtain carbon monoxide. Furthermore, the gas extracted from the reactor 61 may also contain unreacted hydrogen and carbon dioxide from the reactor 61. However, in Figure 6In this description, the gas extracted from the reactor 61 is omitted from the labeling of unreacted hydrogen and carbon dioxide, and only carbon monoxide and water (water vapor) are listed as the main components of the gas. The gas obtained in the reactor 61 mainly contains gaseous water (water vapor) in addition to carbon monoxide. After the carbon monoxide is extracted from the reactor 61, it is cooled by a heat exchanger 66 provided in the reduction device 60, thereby separating the gas into carbon monoxide and water. Furthermore, the separated water is separated from the separated carbon monoxide and recovered by a water recovery unit 65 provided in the reduction device 60. At least a portion of the separated carbon monoxide is fed into a gas containing carbon dioxide and hydrogen from the inlet 62. Therefore, the gas flowing into the reactor 61 is a gas to which the separated carbon monoxide has been added to the gas supplied from the inlet 62. Of the separated carbon monoxide, the carbon monoxide that does not return to the reactor 61 is recovered by the carbon monoxide recovery unit 67 of the reduction device 60; the reduction device 60 removes the reduced iron used as a catalyst in the reactor 61 from the extraction unit 68. As described above, the reduced iron extracted by the extraction unit 68 has precipitated carbon or undergone carbonization, and is fed into the blast furnace 691 or electric furnace 692 for ironmaking, which can produce steel. Carbon monoxide is a reactant not only in the reverse conversion reaction, but also in the methanation reaction and the Fischer-Tropsch reaction. Therefore, by reusing it as described above during these reactions, the yield (conversion rate of carbon monoxide) can be increased. Moreover, in the methanation reaction and the Fischer-Tropsch reaction, the higher the ratio of carbon monoxide (the lower the ratio of carbon dioxide), the higher the yield of the target product and the reaction rate. Furthermore, for hydrocarbons such as methane, carbon monoxide is an impurity, so it is necessary to remove carbon monoxide and return the removed carbon monoxide to the feed gas. Furthermore, while carbon monoxide is reused in the above example, it is not limited to carbon monoxide; hydrogen or carbon dioxide can also be reused. Since hydrogen is a reactant in any reaction, reuse can increase the yield (i.e., the hydrogen conversion rate). Moreover, carbon dioxide is also a reactant in the reverse shift reaction and the Sabatie reaction; therefore, reuse in these reactions can increase the yield (carbon dioxide conversion rate). Since water reduces the reaction rate in any reaction, it is better to recover it as described above rather than reuse it, thus increasing the reaction rate. To recover water, the gas needs to be treated by heating and cooling, but in cases where there is a high necessity to increase the reaction rate, or where the gas used in the reaction contains a high amount of water (water vapor), resulting in a low reaction rate, water can be recovered as described above, depending on the specific circumstances.Furthermore, in gas separation methods such as amine absorption or PSA (Pressure Swing Adsorption), water is usually discarded directly because it separates naturally. Additionally, since water can also inhibit carbon deposition on the catalyst, when the catalyst is a precious metal, it is possible to reuse the water or add water externally to suppress carbon deposition on the catalyst. Although carbon deposition on the catalyst is suppressed as described above, in the carbon oxide reduction method according to this embodiment, since reduced iron is used as the catalyst, even if carbon is deposited on the reduced iron, it will not cause a particular problem, and therefore there is no need to reuse water.

[0073] As a reduction, hydrogen and carbon dioxide that were not used in the chemical reaction can be separated from the product gas obtained after the chemical reaction of the gas containing the carbon oxides flowing into the reactor. The separated hydrogen and carbon dioxide are then fed back into the reactor for use in the chemical reaction. In this way, the hydrogen and carbon dioxide that were not used in the chemical reaction can be reused, thereby improving the yield, such as the hydrogen conversion rate and carbon dioxide conversion rate. Therefore, the hydrogen can be used more efficiently to reduce the carbon oxides contained in the gas. As an example of such a reduction apparatus, specifically, the following can be listed... Figure 7 The reduction apparatus 70 shown is an example. Furthermore... Figure 7 This is a schematic cross-sectional view showing another example of the carbon oxide reduction apparatus according to this embodiment.

[0074] The reduction device 70, in addition to having Figure 6 In addition to the structure of the reduction apparatus 60 shown, it also includes a carbon monoxide separation unit 71. Furthermore, the gas extracted from the reactor 61 may also contain unreacted hydrogen and carbon dioxide from the reactor 61. Figure 7 In this embodiment, the amount of unreacted hydrogen and carbon dioxide is greater than that in the above embodiment. Therefore, as the gas taken out from the reactor 61, in addition to carbon monoxide and water (water vapor) which mainly constitute the gas, the unreacted hydrogen and carbon dioxide are also labeled.

[0075] The carbon monoxide separation unit 71 is not particularly limited as long as it can separate carbon monoxide from multiple gas components. Specifically, structures based on various methods such as PSA (Pressure Swing Adsorption) and cryogenic separation methods can be listed. By providing the carbon monoxide separation unit 71, on the one hand, the carbon monoxide separated by the carbon monoxide separation unit 71 is recovered by the carbon monoxide recovery unit 67 provided in the reduction device 70. On the other hand, hydrogen and carbon dioxide that are not separated by the carbon monoxide separation unit 71 flow together with a portion of the carbon monoxide into a gas containing carbon dioxide and hydrogen from the inflow unit 62. According to this configuration, hydrogen and carbon dioxide that are not used in the reaction can also be reused, thereby improving the yield (conversion rate of hydrogen and conversion rate of carbon dioxide).

[0076] This specification discloses various implementation techniques as described above, and the main technical features are summarized below.

[0077] The first embodiment of the present invention relates to a method for reducing carbon oxides, comprising: flowing a gas containing carbon oxides and hydrogen into a reactor, wherein the carbon oxides contain at least one of carbon monoxide and carbon dioxide; adding reduced iron into the reactor; and reducing the carbon oxides by performing a chemical reaction using the gas flowing into the reactor as a raw material and the reduced iron as a catalyst.

[0078] According to this configuration, a chemical reaction can be carried out using the gas flowing into the reactor as raw material and the reduced iron added to the reactor as a catalyst. Through this reaction, the carbon oxides contained in the gas can be reduced using hydrogen. By reducing carbon oxides such as carbon dioxide, hydrocarbons such as methane can be obtained, along with carbon monoxide for obtaining hydrocarbons, thereby achieving efficient utilization of carbon dioxide. Therefore, a method for reducing carbon oxides such as carbon dioxide can be provided even without using catalysts containing expensive materials such as Ni, Co, and precious metals. Moreover, the reduced iron is cheaper than catalysts containing expensive materials such as Ni, Co, and precious metals. Furthermore, the reduced iron used as a catalyst in this reduction method can be effectively used in steel manufacturing because it precipitates carbon or undergoes carbonization. For these reasons, even with frequent replacement of the reduced iron as a catalyst, the increase in operating costs can be suppressed. Therefore, not only can carbon oxides be reduced, but the catalyst activity can also be maintained at a high level by replacing the catalyst before its activity significantly declines. Furthermore, the reduced iron used as a catalyst in the reduction method, due to the precipitation or carbonization of carbon as described above, can fix the carbon oxides flowing into the reactor into the reduced iron in the form of carbon. By using the carbon-fixed reduced iron to manufacture steel, steel containing this carbon can be obtained. In summary, the reduction method can also contribute to achieving negative emissions by absorbing carbon dioxide.

[0079] The preferred method for reducing carbon oxides according to the second embodiment of the present invention is as follows: In the method for reducing carbon oxides according to the first embodiment of the present invention, the chemical reaction includes at least one of the Sabatie reaction and the direct Fischer-Tropsch reaction.

[0080] Based on this composition, carbon oxides such as carbon dioxide can be reduced more effectively.

[0081] The preferred method for reducing carbon oxides according to the third embodiment of the present invention is as follows: In the method for reducing carbon oxides according to the first or second embodiment of the present invention, the chemical reaction includes at least one of methanation reaction and indirect Fischer-Tropsch reaction.

[0082] Based on this composition, carbon oxides such as carbon dioxide can be reduced more effectively.

[0083] The preferred method for reducing carbon oxides according to the fourth embodiment of the present invention is that, in the method for reducing carbon oxides according to any one of the first to third embodiments of the present invention, the chemical reaction includes an inverse conversion reaction.

[0084] Based on this composition, carbon oxides such as carbon dioxide can be reduced more effectively.

[0085] The fifth embodiment of the present invention relates to a preferred method for reducing carbon oxides: in the method for reducing carbon oxides according to any of the first to fourth embodiments of the present invention, the reduced iron is in granular form.

[0086] According to this configuration, even if the reduced iron, which is added to the reactor as a catalyst, is in granular form, the carbon oxides contained in the gas can be reduced using hydrogen. Furthermore, if the reduced iron is in granular form, it is easy to replace the reduced iron used as a catalyst. Therefore, a high catalyst activity can be maintained. Thus, the carbon oxides contained in the gas can be reduced more appropriately using hydrogen. Moreover, since the reduced iron is typically obtained in granular form, it can be used directly without pulverization, eliminating pulverization costs. Furthermore, if the reduced iron is in granular form, the increase in gas flow resistance within the blast furnace can be suppressed when the reduced iron taken from the reactor is used in steelmaking (e.g., fed into a blast furnace). Since blast furnaces require gas passages, granular form is also preferable from this perspective.

[0087] The preferred method for reducing carbon oxides according to the sixth embodiment of the present invention is as follows: In the method for reducing carbon oxides according to any one of the first to fifth embodiments of the present invention, the reduced iron satisfies the following conditions: the equivalent particle size is 5 mm or more; the total content of iron compounds, calcium compounds, silicon compounds, magnesium compounds and aluminum compounds relative to the total amount of reduced iron is 90% by mass or more; the content of iron compounds relative to the total amount of reduced iron is 75% by mass or more; and the metallization rate is 70% or more.

[0088] According to this configuration, the hydrogen gas can be used to more appropriately reduce the carbon oxides contained in the gas.

[0089] The preferred method for reducing carbon oxides according to the seventh embodiment of the present invention is as follows: In the method for reducing carbon oxides according to any one of the first to sixth embodiments of the present invention, the reduced iron is reduced iron obtained by reducing with a reducing gas containing 50% by volume or more hydrogen, or reduced iron with a carbon content of 2.14% by mass or less.

[0090] According to this configuration, the reduced iron is suitably carburized (carburized), thereby facilitating negative emissions. Therefore, not only can the hydrogen be used more appropriately to reduce the carbon oxides contained in the gas, but the effects of carburization and negative emissions can also be maximized.

[0091] The carbon oxide reduction method according to the eighth embodiment of the present invention is preferably as follows: In the carbon oxide reduction method according to any one of the first to seventh embodiments of the present invention, the gas flowing into the reactor satisfies the following: the total volume of the hydrogen, the carbon dioxide and the carbon monoxide is 75% or more relative to the total volume of the gas; and the total volume of the hydrogen and the carbon monoxide is 3 times or more relative to the total volume of water and the carbon dioxide.

[0092] According to this configuration, the hydrogen gas can be used to more appropriately reduce the carbon oxides contained in the gas.

[0093] The preferred method for reducing carbon oxides according to the ninth embodiment of the present invention includes: obtaining a generated gas containing carbon monoxide by reducing the carbon oxide; separating the carbon monoxide from the generated gas; and feeding the separated carbon monoxide into the reactor.

[0094] According to this configuration, the hydrogen can be used more efficiently to reduce the carbon oxides contained in the gas.

[0095] The preferred method for reducing carbon oxides according to the tenth embodiment of the present invention includes: in any of the first to ninth embodiments of the present invention, the method for reducing carbon oxides includes: separating hydrogen gas and carbon dioxide gas that are not used in the chemical reaction from the generated gas obtained after the gas flowing into the reactor undergoes the chemical reaction; and flowing the separated hydrogen gas and carbon dioxide gas into the reactor.

[0096] According to this configuration, hydrogen and carbon dioxide that were not used in the chemical reaction can be reused, thereby improving yields such as hydrogen conversion rate and carbon dioxide conversion rate. Therefore, the hydrogen can be used more efficiently to reduce the carbon oxides contained in the gas.

[0097] The preferred method for reducing carbon oxides according to the eleventh embodiment of the present invention includes: in any of the first to tenth embodiments of the present invention, the method for reducing carbon oxides includes: after a specified time has elapsed after the reduced iron is added to the reactor, removing the reduced iron from the reactor; and adding reduced iron that is not used as a catalyst to the reactor.

[0098] According to this configuration, new reduced iron that has not been used as a catalyst can be added before the catalytic activity of the reduced iron added to the reactor becomes too low, thereby maintaining the reduced iron added to the reactor at a high catalytic activity level. Therefore, the hydrogen can be used more efficiently to reduce the carbon oxides contained in the gas.

[0099] The preferred method for reducing carbon oxides according to the twelfth embodiment of the present invention is as follows: In the method for reducing carbon oxides according to the eleventh embodiment of the present invention, the specified time is 30 minutes to 1 month.

[0100] Based on this configuration, the catalytic activity of the reduced iron added to the reactor can be maintained at a higher level more appropriately. Therefore, the hydrogen can be used more efficiently to reduce the carbon oxides contained in the gas.

[0101] The preferred method for reducing carbon oxides according to the thirteenth embodiment of the present invention is as follows: in the method for reducing carbon oxides according to any one of the first to twelfth embodiments of the present invention, the reactor is a flow-through reactor or a batch reactor.

[0102] According to this configuration, the reduced iron, which serves as a catalyst, can be replaced at a high frequency, thereby enabling more efficient use of hydrogen to reduce the carbon oxides contained in the gas.

[0103] The fourteenth embodiment of the present invention relates to a method for manufacturing steel, comprising: flowing a gas containing carbon oxides and hydrogen into a reactor, wherein the carbon oxides include at least one of carbon monoxide and carbon dioxide; adding reduced iron into the reactor; reducing the carbon oxides by performing a chemical reaction using the gas flowing into the reactor as raw material and the reduced iron as a catalyst; measuring the time after the reduced iron is added to the reactor, and when the measured time has elapsed for a specified period, removing the reduced iron from the reactor; and adding the reduced iron removed from the reactor to a blast furnace or an electric furnace.

[0104] According to this configuration, the reduced iron introduced into the reactor is used as a catalyst when hydrogen is used to reduce the carbon oxides contained in the gas flowing into the reactor, thereby causing the reduced iron to precipitate carbon or undergo carburization. This reduced iron can be effectively used as a raw material in steel manufacturing. Therefore, a steel manufacturing method that effectively utilizes the reduction method can be provided.

[0105] The preferred method for manufacturing steel according to the fifteenth embodiment of the present invention is as follows: In the method for manufacturing steel according to the fourteenth embodiment of the present invention, the chemical reaction includes at least one of the Sabatie reaction and the direct Fischer-Tropsch reaction.

[0106] Based on this configuration, the reduction method can be utilized more effectively.

[0107] The steel manufacturing method according to the sixteenth embodiment of the present invention is preferably: in the steel manufacturing method according to the fourteenth or fifteenth embodiment of the present invention, the chemical reaction includes at least one of methanation reaction and indirect Fischer-Tropsch reaction.

[0108] Based on this configuration, the reduction method can be utilized more effectively.

[0109] The preferred method for manufacturing steel according to the seventeenth embodiment of the present invention is that, in the method for manufacturing steel according to any one of the fourteenth to sixteenth embodiments of the present invention, the chemical reaction includes an inverse conversion reaction.

[0110] Based on this configuration, the reduction method can be utilized more effectively.

[0111] The steel manufacturing method according to the eighteenth embodiment of the present invention is preferably characterized in that, in the steel manufacturing method according to any one of the fourteenth to seventeenth embodiments of the present invention, carbon is precipitated in the reduced iron taken out from the reactor.

[0112] According to this structure, firstly, the reduced iron with carbon deposits is typically at least partially carbonized by the carbon. As described above, carbon is deposited on the reduced iron used as a catalyst, or the reduced iron is carbonized. Moreover, by using the reduced iron with carbon deposits and the carbonized reduced iron to manufacture steel, steel containing the carbon can be obtained. Therefore, the steel manufacturing method described above can convert at least a portion of carbon oxides such as carbon dioxide in the atmosphere into carbon, obtaining steel with the carbon fixed, thereby achieving so-called negative emission technology.

[0113] The preferred method for manufacturing steel according to the nineteenth embodiment of the present invention is as follows: In the method for manufacturing steel according to any one of the fourteenth to eighteenth embodiments of the present invention, the temperature inside the reactor during the chemical reaction is 300 to 900°C, and the pressure inside the reactor is atmospheric pressure or above. The gas flowing into the reactor satisfies the following conditions: the content of sulfides is less than 10 ppm; and the total volume of hydrogen and carbon monoxide is more than three times the total volume of water and carbon dioxide.

[0114] According to this configuration, when the reduced iron is used as a catalyst in reducing the carbon oxides contained in the gas flowing into the reactor with the hydrogen, carbon is further precipitated or further carbonized. This reduced iron can be used more effectively as a raw material in the manufacture of steel.

[0115] The carbon oxide reduction apparatus according to the twentieth embodiment of the present invention includes: a reactor; an inlet section for flowing a gas containing carbon oxide and hydrogen into the reactor, the carbon oxide including at least one of carbon monoxide and carbon dioxide; and an input section for inputting reduced iron into the reactor; wherein the carbon oxide is reduced by performing a chemical reaction using the gas flowing into the reactor in the inlet section as raw material and the reduced iron as a catalyst.

[0116] Based on this configuration, a carbon oxide reduction apparatus can be provided that can reduce carbon oxides such as carbon dioxide even without using catalysts containing expensive materials such as Ni, Co, and precious metals, similar to the carbon oxide reduction method described above.

[0117] The carbon oxide reduction apparatus according to the twenty-first embodiment of the present invention preferably includes, in the carbon oxide reduction apparatus according to the twenty-twentieth embodiment of the present invention, at least one of the Sabatie reaction and the direct Fischer-Tropsch reaction.

[0118] Based on this composition, carbon oxides such as carbon dioxide can be reduced more effectively.

[0119] The carbon oxide reduction apparatus according to the twenty-second embodiment of the present invention preferably includes, in the carbon oxide reduction apparatus according to the twenty or twenty-first embodiment of the present invention, at least one of methanation reaction and indirect Fischer-Tropsch reaction.

[0120] Based on this composition, carbon oxides such as carbon dioxide can be reduced more effectively.

[0121] The carbon oxide reduction apparatus according to the twenty-third embodiment of the present invention preferably includes a reverse conversion reaction in the carbon oxide reduction apparatus according to any one of the twenty to twenty-second embodiments of the present invention.

[0122] Based on this composition, carbon oxides such as carbon dioxide can be reduced more effectively.

[0123] The carbon oxide reduction apparatus according to the twenty-fourth embodiment of the present invention preferably has the following characteristics: in the carbon oxide reduction apparatus according to any one of the twenty to twenty-third embodiments of the present invention, the reduced iron is in granular form.

[0124] According to this configuration, even if the reduced iron added to the reactor as a catalyst is in granular form, the carbon oxides contained in the gas can be reduced using hydrogen. Furthermore, if the reduced iron is in granular form, it is easy to replace the reduced iron as a catalyst. Therefore, a high catalyst activity can be maintained. Thus, the carbon oxides contained in the gas can be reduced more appropriately using hydrogen.

[0125] The carbon oxide reduction apparatus according to the twenty-fifth embodiment of the present invention is preferably provided that, in the carbon oxide reduction apparatus according to any one of the twenty to twenty-fourth embodiments of the present invention, the reduced iron satisfies the following conditions: the equivalent particle size is 5 mm or more; the total content of iron compound, calcium compound, silicon compound, magnesium compound and aluminum compound relative to the total amount of reduced iron is 90% by mass or more; the content of iron compound relative to the total amount of reduced iron is 75% by mass or more; and the metallization rate is 70% or more.

[0126] According to this configuration, the hydrogen gas can be used to more appropriately reduce the carbon oxides contained in the gas.

[0127] The carbon oxide reduction apparatus according to the twenty-sixth embodiment of the present invention is preferably: in the carbon oxide reduction apparatus according to any of the twenty to twenty-fifth embodiments of the present invention, the reduced iron is reduced iron obtained by reduction using a reducing gas containing 50% by volume or more hydrogen, or reduced iron with a carbon content of 2.14% by mass or less.

[0128] According to this configuration, the reduced iron is suitably carburized (carburized), thereby facilitating negative emissions. Therefore, not only can the hydrogen be used more appropriately to reduce the carbon oxides contained in the gas, but the effects of carburization and negative emissions can also be maximized.

[0129] The carbon oxide reduction apparatus according to the twenty-seventh embodiment of the present invention preferably has the following characteristics: In the carbon oxide reduction apparatus according to any one of the twenty to twenty-sixth embodiments of the present invention, the gas flowing into the reactor at the inlet section satisfies the following: the total volume of the hydrogen, the carbon dioxide and the carbon monoxide is 75% or more relative to the total volume of the gas; and the total volume of the hydrogen and the carbon monoxide is 3 times or more relative to the total volume of water and the carbon dioxide.

[0130] According to this configuration, the hydrogen gas can be used to more appropriately reduce the carbon oxides contained in the gas.

[0131] The carbon oxide reduction apparatus according to the twenty-eighth embodiment of the present invention preferably includes, in any of the twenty to twenty-seventh embodiments of the present invention, a carbon oxide reduction apparatus further comprising: a recycling unit that separates the carbon monoxide from the generated gas, the generated gas containing carbon monoxide generated by reducing the carbon oxide, and uses the separated carbon monoxide as at least a portion of the gas flowing into the reactor.

[0132] According to this configuration, the hydrogen can be used more efficiently to reduce the carbon oxides contained in the gas.

[0133] The carbon oxide reduction apparatus according to the twenty-ninth embodiment of the present invention preferably includes the following: In the carbon oxide reduction apparatus according to any of the twenty to twenty-eighth embodiments of the present invention, hydrogen gas and carbon dioxide gas that are not used in the chemical reaction are separated from the generated gas obtained after the gas flowing into the reactor undergoes the chemical reaction; and the separated hydrogen gas and carbon dioxide gas are then flowed into the reactor.

[0134] According to this configuration, hydrogen and carbon dioxide that were not used in the chemical reaction can be reused, thereby improving yields such as hydrogen conversion rate and carbon dioxide conversion rate. Therefore, the hydrogen can be used more efficiently to reduce the carbon oxides contained in the gas.

[0135] The carbon oxide reduction apparatus according to the thirtieth embodiment of the present invention preferably includes, in any of the twenty to twenty-ninth embodiments of the present invention, a carbon oxide reduction apparatus further comprising: a take-out section that takes out the reduced iron from the reactor after a predetermined time has elapsed from the time the reduced iron is taken out of the reactor by the take-out section, wherein the take-out section takes out the reduced iron from the reactor by the take-out section and then takes out the reduced iron from the reactor by the take-out section and puts the reduced iron, which is not used as a catalyst, into the reactor.

[0136] According to this configuration, new reduced iron that has not been used as a catalyst can be added before the catalytic activity of the reduced iron added to the reactor becomes too low, thereby maintaining the reduced iron added to the reactor at a high catalytic activity level. Therefore, the hydrogen can be used more efficiently to reduce the carbon oxides contained in the gas.

[0137] The carbon oxide reduction apparatus according to the thirty-first embodiment of the present invention is preferably wherein, in the carbon oxide reduction apparatus according to the thirty-twentieth embodiment of the present invention, the specified time is 30 minutes to 1 month.

[0138] Based on this configuration, the catalytic activity of the reduced iron added to the reactor can be maintained at a higher level more appropriately. Therefore, the hydrogen can be used more efficiently to reduce the carbon oxides contained in the gas.

[0139] The carbon oxide reduction apparatus according to the thirty-second embodiment of the present invention is preferably, in any of the twenty to thirty-first embodiments of the present invention, the reactor is a flow-through reactor or a batch reactor.

[0140] According to this configuration, the reduced iron, which serves as a catalyst, can be replaced at a high frequency, thereby enabling more efficient use of hydrogen to reduce the carbon oxides contained in the gas.

[0141] The steel manufacturing apparatus according to the thirty-third embodiment of the present invention includes: a reactor; an inflow section for flowing a gas containing carbon oxides and hydrogen into the reactor, wherein the carbon oxides include at least one of carbon monoxide and carbon dioxide; an input section for inputting reduced iron into the reactor; an output section for removing the reduced iron from the reactor after a predetermined time has elapsed from the time the reduced iron is input into the reactor at the input section; and an iron supply section for inputting the reduced iron removed from the reactor into a blast furnace or an electric furnace at the output section; wherein, in the reactor, the carbon oxides are reduced by performing a chemical reaction using the gas flowing into the reactor as raw material and the reduced iron as a catalyst.

[0142] According to this configuration, the reduced iron introduced into the reactor is used as a catalyst when hydrogen is used to reduce the carbon oxides contained in the gas flowing into the reactor, thereby causing the reduced iron to precipitate carbon or undergo carburization. This reduced iron can be effectively used as a raw material in the manufacture of steel. Therefore, an apparatus for manufacturing steel that effectively utilizes this reduction method can be provided.

[0143] The steel manufacturing apparatus according to the thirty-fourth embodiment of the present invention preferably includes, in the steel manufacturing apparatus according to the thirty-third embodiment of the present invention, at least one of the Sabatie reaction and the direct Fischer-Tropsch reaction.

[0144] Based on this configuration, the reduction method can be utilized more effectively.

[0145] The steel manufacturing apparatus according to the thirty-fifth embodiment of the present invention preferably includes, in the steel manufacturing apparatus according to the thirty-third or thirty-fourth embodiment of the present invention, at least one of methanation reaction and indirect Fischer-Tropsch reaction.

[0146] Based on this configuration, the reduction method can be utilized more effectively.

[0147] The steel manufacturing apparatus according to the thirty-sixth embodiment of the present invention preferably includes, in the steel manufacturing apparatus according to any one of the thirty-third to thirty-fifth embodiments of the present invention, the chemical reaction comprising an inverse conversion reaction.

[0148] Based on this configuration, the reduction method can be utilized more effectively.

[0149] The steel manufacturing apparatus according to the thirty-seventh embodiment of the present invention preferably contains carbon precipitated in the reduced iron taken out from the reactor in any of the thirty-third to thirty-sixth embodiments of the present invention.

[0150] According to this configuration, firstly, the reduced iron with carbon deposits typically undergoes at least partial carbonization due to the carbon. As described above, carbon is deposited on the reduced iron used as a catalyst, or the reduced iron is carbonized. Furthermore, by using the carbon-deposited reduced iron and the carbonized reduced iron to manufacture steel, steel containing that carbon can be obtained. Therefore, the steel manufacturing apparatus can convert at least a portion of carbon oxides such as carbon dioxide in the atmosphere into carbon, obtaining steel with that carbon fixed, thereby enabling so-called negative emission technology.

[0151] The steel manufacturing apparatus according to the thirty-eighth embodiment of the present invention is preferably as follows: In the steel manufacturing apparatus according to any one of the thirty-third to thirty-seventh embodiments of the present invention, the temperature inside the reactor during the chemical reaction is 300 to 900°C, and the pressure inside the reactor is atmospheric pressure or above. The gas flowing into the reactor at the inlet section satisfies the following conditions: the sulfide content is 10 ppm or less; and the total volume of hydrogen and carbon monoxide is more than three times the total volume of water and carbon dioxide.

[0152] According to this configuration, when the reduced iron is used as a catalyst in reducing the carbon oxides contained in the gas flowing into the reactor with the hydrogen, carbon is further precipitated or further carbonized. This reduced iron can be used more effectively as a raw material in the manufacture of steel.

[0153] According to the present invention, a method and apparatus for reducing carbon oxides, such as carbon dioxide, can be provided even without using catalysts containing expensive materials such as Ni, Co, and precious metals. Furthermore, according to the present invention, a method for manufacturing steel and an apparatus for manufacturing steel that effectively utilize the reduction method can be provided.

[0154] The present invention will be further described in detail below through embodiments, but the scope of the present invention is not limited to these embodiments.

[0155] Example

[0156] Specifically, for example, the following reaction was carried out. Reduced iron (reduced iron obtained by reducing with a reducing gas containing 50% by volume hydrogen, which meets the following requirements: equivalent particle size of about 10-13 mm; total content of iron compounds, calcium compounds, silicon compounds, magnesium compounds and aluminum compounds of 99% by mass relative to the total amount of reduced iron; content of iron compounds of 96% by mass relative to the total amount of reduced iron; and carbon content of almost 0% by mass) was added to the reactor. It should be noted that the composition of the reduced iron is as follows: metallic Fe, which is an iron compound, about 95% by mass; FeO, less than 1% by mass; CaO, which is a calcium compound, less than 1% by mass; SiO2, which is a silicon compound, about 2% by mass; MgO, which is a magnesium compound, less than 1% by mass; Al2O3, which is an aluminum compound, less than 1% by mass; total sulfur content, less than 100 ppm by mass. A feedstock gas (66% by volume of hydrogen, 17% by volume of carbon dioxide, and 17% by volume of nitrogen relative to the total volume of the gas, with the total volume of hydrogen, carbon dioxide, and carbon monoxide being approximately 83% by volume and exceeding 80% by volume, and the total volume of hydrogen and carbon monoxide being approximately four times that of water and carbon dioxide) is introduced into the reactor. It should be noted that the feedstock gas does not contain sulfides; that is, the sulfide content relative to the feedstock gas is 0 ppm. The temperature inside the reactor is set to 350–450°C, and the pressure inside the reactor is set to 500 kPaA, thereby allowing the feedstock gas to react with the reduced iron in contact for approximately a few seconds. This initiates a reaction primarily based on the Sabatie reaction. The reaction rate is calculated by measuring the gas discharged from the reactor using gas chromatography-mass spectrometry. As a result, the reaction rate, in some cases, represents a methane conversion rate of over 20%. Furthermore, analysis of the reduced iron after the reaction confirmed the presence of carbon adhering to its surface. It was also confirmed that extending the contact time between the feed gas and the reduced iron could improve the methane conversion rate.

[0157] This application is based on Japanese Patent Application No. 2024-025194, filed on February 22, 2024, the contents of which are included in this application.

[0158] To illustrate the invention, the present invention has been appropriately and sufficiently described above through embodiments. However, it should be recognized that those skilled in the art can readily make changes and / or modifications to the above embodiments. Therefore, any changes or modifications implemented by those skilled in the art that do not depart from the scope of protection of the claims set forth in the claims can be interpreted as being included within the scope of protection of the claims.

[0159] Industrial availability

[0160] According to the present invention, a method and apparatus for reducing carbon oxides, such as carbon dioxide, can be provided even without using catalysts containing expensive materials such as Ni, Co, and precious metals. Furthermore, according to the present invention, a method for manufacturing steel and an apparatus for manufacturing steel that effectively utilize the reduction method can be provided.

Claims

1. A method for reducing carbon oxides, characterized in that... include: A gas containing carbon oxides and hydrogen is fed into the reactor, wherein the carbon oxides include at least one of carbon monoxide and carbon dioxide; Reduced iron is added to the reactor. and, The carbon oxides are reduced by carrying out a chemical reaction using the gas flowing into the reactor as raw material and the reduced iron as catalyst.

2. The method for reducing carbon oxides according to claim 1, characterized in that, The chemical reaction described includes at least one of the Sabatie reaction and the direct Fischer-Tropsch reaction.

3. The method for reducing carbon oxides according to claim 1, characterized in that, The chemical reaction includes at least one of methanation and indirect Fischer-Tropsch reaction.

4. The method for reducing carbon oxides according to claim 1, characterized in that, The chemical reaction includes an inverse transformation reaction.

5. The method for reducing carbon oxides according to claim 1, characterized in that, The reduced iron is in granular form.

6. The method for reducing carbon oxides according to claim 1, characterized in that, The reduced iron satisfies: The equivalent particle size is 5mm or larger; The total content of iron compounds, calcium compounds, silicon compounds, magnesium compounds and aluminum compounds is 90% by mass or more relative to the total amount of reduced iron. The content of the iron compound is 75% by mass or more relative to the total amount of reduced iron; and, The metallization rate is over 70%.

7. The method for reducing carbon oxides according to claim 1, characterized in that, The reduced iron is obtained by reduction using a reducing gas containing more than 50% by volume of hydrogen, or reduced iron with a carbon content of less than 2.14% by mass.

8. The method for reducing carbon oxides according to claim 1, characterized in that, The gas flowing into the reactor satisfies: The combined volume of the hydrogen, carbon dioxide, and carbon monoxide is 75% or more relative to the total volume of the gases; and, The combined volume of hydrogen and carbon monoxide is more than three times that of water and carbon dioxide combined.

9. The method for reducing carbon oxides according to claim 1, characterized in that... include: A gas containing carbon monoxide is obtained by reducing the carbon oxide. Separate the carbon monoxide from the generated gas; and, The separated carbon monoxide flows into the reactor.

10. The method for reducing carbon oxides according to claim 1, characterized in that... include: From the product gas obtained after the chemical reaction of the gas flowing into the reactor, hydrogen gas and carbon dioxide gas that were not used in the chemical reaction are separated; and... The separated hydrogen and carbon dioxide flow into the reactor.

11. The method for reducing carbon oxides according to claim 1, characterized in that... include: After a specified time has elapsed since the reduced iron was added to the reactor, the reduced iron is removed from the reactor. and, Reduced iron that was not used as a catalyst was added to the reactor.

12. The method for reducing carbon oxides according to claim 11, characterized in that, The specified time ranges from 30 minutes to 1 month.

13. The method for reducing carbon oxides according to claim 1, characterized in that, The reactor is either a flow-through reactor or a batch reactor.

14. A method for manufacturing steel, characterized in that... include: A gas containing carbon oxides and hydrogen is fed into the reactor, wherein the carbon oxides include at least one of carbon monoxide and carbon dioxide; Reduced iron is added to the reactor. The carbon oxides are reduced by carrying out a chemical reaction using the gas flowing into the reactor as raw material and the reduced iron as catalyst. After a specified time has elapsed since the reduced iron was added to the reactor, it is removed from the reactor; and... The reduced iron taken from the reactor is fed into a blast furnace or electric furnace.

15. The method for manufacturing steel according to claim 14, characterized in that, The chemical reaction includes at least one of the Sabatie reaction and the direct Fischer-Tropsch reaction.

16. The method for manufacturing steel according to claim 14, characterized in that, The chemical reaction includes at least one of methanation and indirect Fischer-Tropsch reaction.

17. The method for manufacturing steel according to claim 14, characterized in that, The chemical reaction includes an inverse transformation reaction.

18. The method for manufacturing steel according to claim 14, characterized in that, Carbon is precipitated from the reduced iron taken out of the reactor.

19. The method for manufacturing steel according to claim 14, characterized in that, In the reactor where the chemical reaction is carried out, the temperature inside the reactor is 300–900°C, and the pressure inside the reactor is above atmospheric pressure. The gas flowing into the reactor satisfies: The sulfide content is below 10 ppm; and, The combined volume of hydrogen and carbon monoxide is more than three times that of water and carbon dioxide combined.

20. A device for reducing carbon oxides, characterized in that... have: Reactor; The inlet section allows a gas containing carbon oxides and hydrogen to flow into the reactor, wherein the carbon oxides comprise at least one of carbon monoxide and carbon dioxide; and, The input section feeds reduced iron into the reactor; wherein, The carbon oxides are reduced by carrying out a chemical reaction using the gas flowing into the reactor at the inlet as raw material and the reduced iron as catalyst.

21. The apparatus for reducing carbon oxides according to claim 20, characterized in that, The chemical reaction includes at least one of the Sabatie reaction and the direct Fischer-Tropsch reaction.

22. The apparatus for reducing carbon oxides according to claim 20, characterized in that, The chemical reaction includes at least one of methanation and indirect Fischer-Tropsch reaction.

23. The carbon oxide reduction apparatus according to claim 20, characterized in that, The chemical reaction includes an inverse transformation reaction.

24. The carbon oxide reduction apparatus according to claim 20, characterized in that, The reduced iron is in granular form.

25. The apparatus for reducing carbon oxides according to claim 20, characterized in that, The reduced iron satisfies: The equivalent particle size is 5mm or larger; The total content of iron compounds, calcium compounds, silicon compounds, magnesium compounds and aluminum compounds is 90% by mass or more relative to the total amount of reduced iron. The content of the iron compound is 75% by mass or more relative to the total amount of reduced iron; and, The metallization rate is over 70%.

26. The carbon oxide reduction apparatus according to claim 20, characterized in that, The reduced iron is obtained by reduction using a reducing gas containing more than 50% by volume of hydrogen, or reduced iron with a carbon content of less than 2.14% by mass.

27. The apparatus for reducing carbon oxides according to claim 20, characterized in that, The gas flowing into the reactor at the inlet section satisfies: The combined volume of the hydrogen, carbon dioxide, and carbon monoxide is 75% or more relative to the total volume of the gases; and, The combined volume of hydrogen and carbon monoxide is more than three times that of water and carbon dioxide combined.

28. The carbon oxide reduction apparatus according to claim 20, characterized in that... It also has: The recycling section separates the carbon monoxide from the generated gas, the generated gas containing carbon monoxide generated by reducing the carbon oxide, and uses the separated carbon monoxide as at least a portion of the gas flowing into the reactor.

29. The carbon oxide reduction apparatus according to claim 20, characterized in that, From the product gas obtained after the chemical reaction of the gas flowing into the reactor, hydrogen gas and carbon dioxide gas that were not used in the chemical reaction are separated; and... The separated hydrogen and carbon dioxide flow into the reactor.

30. The carbon oxide reduction apparatus according to claim 20, characterized in that... It also has: The extraction section removes the reduced iron from the reactor after a specified time has elapsed since the reduced iron was introduced into the reactor at the input section. After the reduced iron is removed from the reactor by the take-out section, the input section adds the reduced iron that was not used as a catalyst into the reactor.

31. The apparatus for reducing carbon oxides according to claim 30, characterized in that, The specified time ranges from 30 minutes to 1 month.

32. The carbon oxide reduction apparatus according to claim 20, characterized in that, The reactor is either a flow-through reactor or a batch reactor.

33. An apparatus for manufacturing steel, characterized in that... have: Reactor; The inlet section allows a gas containing carbon oxides and hydrogen to flow into the reactor, wherein the carbon oxides include at least one of carbon monoxide and carbon dioxide. The input section feeds reduced iron into the reactor. The extraction section removes the reduced iron from the reactor after a predetermined time has elapsed since the reduced iron was introduced into the reactor at the input section; and, The iron supply section, in which the reduced iron taken from the reactor is fed into the blast furnace or electric furnace from the extraction section; wherein... In the reactor, the carbon oxides are reduced by a chemical reaction using the gas flowing into the reactor as raw material and the reduced iron as a catalyst.

34. The steel manufacturing apparatus according to claim 33, characterized in that, The chemical reaction includes at least one of the Sabatie reaction and the direct Fischer-Tropsch reaction.

35. The steel manufacturing apparatus according to claim 33, characterized in that, The chemical reaction includes at least one of methanation and indirect Fischer-Tropsch reaction.

36. The steel manufacturing apparatus according to claim 33, characterized in that, The chemical reaction includes an inverse transformation reaction.

37. The steel manufacturing apparatus according to claim 33, characterized in that, Carbon is precipitated from the reduced iron taken out of the reactor.

38. The steel manufacturing apparatus according to claim 33, characterized in that, In the reactor where the chemical reaction is carried out, the temperature inside the reactor is 300–900°C, and the pressure inside the reactor is above atmospheric pressure. The gas flowing into the reactor at the inlet section satisfies the following: The sulfide content is below 10 ppm; and, The combined volume of hydrogen and carbon monoxide is more than three times that of water and carbon dioxide combined.

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