Carbon oxide reduction method, steel production method, carbon oxide reduction device, and steel production device

Abstract

To provide a carbon oxide reduction method and a carbon oxide reduction device which can reduce carbon oxide such as carbon dioxide without any catalyst including an expensive material such as Ni, Co, and a noble metal.SOLUTION: A carbon oxide reduction method includes causing gas including hydrogen and carbon oxide including at least one of carbon monoxide and carbon dioxide to flow into a reactor 11, putting reduced iron into the reactor 11, and reducing the carbon oxide by chemical reaction between the gas caused to flow into the reactor 11 as a raw material and the reduced iron as a catalyst.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for reducing carbon oxides, a method for producing iron and steel, an apparatus for reducing carbon oxides, and an apparatus for producing iron and steel. [Background technology]

[0002] In recent years, carbon dioxide is considered to have a significant impact on global warming. Technologies for obtaining useful substances such as hydrocarbons using carbon dioxide as a raw material have attracted attention as an effective measure against this global warming problem. Specific examples of such technologies include a technique for obtaining hydrocarbons such as methane by reacting carbon dioxide or other carbon oxides with hydrogen using a catalyst. Examples of such catalysts include those described in Patent Documents 1 and 2. Patent Document 1 describes a methanation catalyst that is a calcined product of a wet mixture of a Zr salt, a salt of a stabilizing element such as Y, a Ni salt, and an inorganic oxide such as silica. Patent Document 2 describes a methanation catalyst that includes a stabilized zirconia support and Ni supported on the stabilized zirconia support. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-122247 [Patent Document 2] Japanese Patent Application Publication No. 2018-20278 Summary of the Invention [Problem to be solved by the invention]

[0004] When a catalyst is used in a reaction to obtain hydrocarbons as described above, the catalyst's catalytic activity gradually declines due to sintering, carbonization, carbon deposition, and poisoning by impurities such as sulfur compounds. The catalyst is often a catalyst synthesized for the reaction containing Ni, Co, and precious metals, such as those described in Patent Documents 1 and 2. These catalysts are often expensive, and frequent replacement of the catalyst is not practical to maintain high activity of the catalyst used in the reaction. Therefore, in order to suppress the occurrence of sintering, carbonization, and carbon deposition, it is conceivable to set conditions that result in a mild reaction. Specifically, it is conceivable to set reaction conditions, such as temperature, pressure, and composition, that result in a mild reaction that does not cause sintering or carbon deposition (i.e., that results in an extremely slow reaction rate for the carbon deposition reaction). However, such a mild reaction results in a low yield and a low reaction rate. To achieve a favorable reaction, it is necessary to increase the catalyst loading, for example, by increasing the size of the reactor, which may increase the cost of obtaining hydrocarbons. In addition, in order to suppress poisoning by impurities, it is possible to remove impurities from the raw materials of the reaction before the reaction, but this requires pre-treatment, which may increase the cost of obtaining hydrocarbons. For these reasons, when using a catalyst synthesized for a reaction containing Ni, Co, and a noble metal, it is very expensive to maintain the catalytic activity at a high level. Therefore, it is not practical to maintain the catalytic activity of a catalyst synthesized for a reaction containing Ni, Co, and a noble metal at a high level.

[0005] The present invention has been made in view of the above circumstances, and aims to provide a method and apparatus for reducing carbon oxides that can reduce carbon oxides such as carbon dioxide without using a catalyst containing expensive materials such as Ni, Co, precious metals, etc. Another aim of the present invention is to provide a method and apparatus for producing iron and steel that effectively utilizes the reduction method. [Means for solving the problem]

[0006] As a result of various investigations, the present inventors have found that the above object can be achieved by the present invention described below.

[0007] A method for reducing carbon oxides according to one aspect of the present invention includes flowing a gas containing hydrogen and carbon oxides, the carbon oxides including at least one of carbon monoxide and carbon dioxide, into a reactor, introducing reduced iron into the reactor, and reducing the carbon oxides through a chemical reaction using the gas flowed into the reactor as a raw material and the reduced iron as a catalyst.

[0008] A method for producing steel according to another aspect of the present invention includes: flowing a gas containing hydrogen and carbon oxides, the gas including at least one of carbon monoxide and carbon dioxide, into a reactor; introducing reduced iron into the reactor; reducing the carbon oxides through a chemical reaction using the gas introduced into the reactor as a raw material and the reduced iron as a catalyst; measuring the time since the reduced iron was introduced into the reactor; removing the reduced iron from the reactor when the measured time has elapsed a predetermined time; and introducing the reduced iron removed from the reactor into a blast furnace or an electric furnace.

[0009] A carbon oxide reduction device according to another aspect of the present invention includes a reactor, an inlet section through which a gas containing hydrogen and carbon oxides including at least one of carbon monoxide and carbon dioxide flows into the reactor, and an input section through which reduced iron is input into the reactor, and the carbon oxides are reduced by a chemical reaction using the gas that has flowed into the reactor via the inlet section as a raw material and the reduced iron as a catalyst.

[0010] According to another aspect of the present invention, there is provided an apparatus for producing iron and steel, the apparatus comprising: a reactor; an inlet section for introducing a gas containing hydrogen and carbon oxides, the gas including at least one of carbon monoxide and carbon dioxide, into the reactor; an input section for introducing reduced iron into the reactor; an unloading section for removing the reduced iron from the reactor when a predetermined time has elapsed since the reduced iron was introduced into the reactor at the input section; and an iron feeding section for introducing the reduced iron removed from the reactor by the unloading section into a blast furnace or an electric furnace, wherein the reactor reduces the carbon oxides by a chemical reaction using the gas introduced into the reactor as a raw material and the reduced iron as a catalyst. [Effects of the Invention]

[0011] The present invention provides a method and apparatus for reducing carbon oxides that can reduce carbon oxides such as carbon dioxide without using a catalyst containing expensive materials such as Ni, Co, and precious metals. The present invention also provides a method and apparatus for producing iron and steel that effectively utilize the reduction method. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram showing an example of a carbon oxide reduction device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing another example of the carbon oxide reduction device according to an embodiment of the present invention. [Figure 3] FIG. 3 is a schematic diagram showing another example of the carbon oxide reduction device according to an embodiment of the present invention. [Figure 4] FIG. 4 is a schematic diagram showing another example of the carbon oxide reduction device according to an embodiment of the present invention. [Figure 5] FIG. 5 is a schematic diagram showing another example of the carbon oxide reduction device according to an embodiment of the present invention. [Figure 6] FIG. 6 is a schematic diagram showing another example of the carbon oxide reduction device according to an embodiment of the present invention. [Figure 7]FIG. 7 is a schematic diagram showing another example of the carbon oxide reduction device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these.

[0014] [Method for reducing carbon oxides] A carbon oxide reduction method according to an embodiment of the present invention includes: flowing a gas containing carbon oxides, including at least one of carbon monoxide and carbon dioxide, and hydrogen into a reactor; introducing reduced iron into the reactor; and reducing the carbon oxides through a chemical reaction using the gas introduced 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 introduced into the reactor as a raw material and the reduced iron as a catalyst. Examples of the chemical reaction include a reverse shift reaction, a methanation reaction, a Sabatier reaction, and a Fischer-Tropsch reaction. The chemical reaction may be a single reaction or a combination of two or more reactions. By using the gas introduced into the reactor as a raw material and the reduced iron introduced into the reactor as a catalyst through a chemical reaction such as a reverse shift reaction, carbon oxides such as carbon dioxide can be reduced without using a catalyst containing expensive materials such as Ni, Co, or precious metals. The reduction of carbon oxides such as carbon dioxide produces hydrocarbons such as methane and carbon monoxide, which can be used to produce hydrocarbons. This also contributes to the effective utilization of carbon dioxide. Furthermore, since the reduced iron used as a catalyst in the reduction method has carbon precipitated or carbonized, the reduced iron removed from the reactor after the reaction can be effectively used in steel production. This allows the reduced iron catalyst to be replaced frequently while suppressing increases in running costs. Therefore, not only can carbon oxides be reduced, but high catalytic activity can also be maintained by replacing the catalyst before its catalytic activity significantly decreases. While nickel was a relatively inexpensive metal, its use in electric vehicles (EVs) has led to increased demand, raising its price and making it difficult to obtain. Therefore, a carbon oxide reduction method that can reduce carbon oxides such as carbon dioxide without using a Ni-containing catalyst is valuable. Furthermore, as an effective countermeasure against global warming, in addition to the above-mentioned technologies for obtaining useful substances such as hydrocarbons from carbon dioxide as a raw material, technologies for immobilizing atmospheric carbon dioxide, known as negative emission technologies, are also needed.The reduction method also contributes to this negative emission technology in the following ways. In the reduction method, the reaction not only reduces carbon oxides such as carbon dioxide but also generates carbon. Specifically, as described above, carbon is precipitated on the reduced iron used as a catalyst, or the reduced iron is carburized (carburized). Then, steel is produced using the reduced iron on which carbon has been precipitated and the carbonized reduced iron, thereby obtaining steel containing this carbon. Therefore, the reduction method is also a so-called negative emission technology that can convert at least a portion of carbon oxides such as carbon dioxide in the atmosphere into carbon and obtain steel in which this carbon is fixed. In this respect, the reduction method is also significant.

[0015] The carbon oxide is not particularly limited as long as it is a carbon oxide containing at least one of carbon monoxide and carbon dioxide, and 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 generally an inorganic compound composed only of carbon and oxygen, but examples thereof include carbon oxides in which the number of carbon atoms is equal to or less than the number of oxygen atoms, such as carbon monoxide and carbon dioxide. As long as the carbon oxide contains at least one of carbon monoxide and carbon dioxide, it is also possible to use carbon suboxide (CO) and mellitic anhydride (C 12 O9), in which the number of carbon atoms is greater than the number of oxygen atoms, may also be included.

[0016] The reactor is not particularly limited as long as it can use the reduced iron introduced into the reactor as a catalyst to promote the chemical reaction, such as the reverse shift reaction, on the carbon oxides introduced into the reactor. The reactor may be, for example, a flow reactor or a batch reactor. A flow reactor continuously supplies reduced iron as a catalyst to carry out a reaction while maintaining predetermined temperature and pressure conditions, and continuously discharges the reduced iron used as the catalyst (e.g., reduced iron that can be used as a catalyst but has completed its catalytic role). The flow reactor is preferred because of its simple configuration and operating method. Examples of the flow reactor include a shaft furnace, and more specifically, a shaft furnace used in the MIDREX process. A batch reactor is configured such that reduced iron serving as a catalyst is charged into the reactor, and the reaction is allowed to proceed for a predetermined time while maintaining predetermined temperature and pressure conditions, and then the reduced iron used as the catalyst (reduced iron that can be used as a catalyst but has completed its catalytic role) is discharged. A batch reactor is preferable in that it does not require much ingenuity (know-how) for gas sealing of sliding parts when steadily discharging solids such as catalysts that continue to descend within the reactor, as in the case of a flow-through reactor.

[0017] The reduced iron is not particularly limited, and examples thereof include reduced iron obtained by a direct reduction method. Examples of reduced iron obtained by a direct reduction method include direct reduced iron (DRI), such as hot direct reduced iron (HDRI), and hot briquetted iron (HBI). The direct reduced iron is iron produced by a steelmaking method (direct reduction method) in which iron ore, iron oxide pellets, sintered ore, etc. are directly reduced using a reducing gas produced from natural gas, coal, etc. Examples of the iron ore include stones containing iron oxide in the mined state. Examples of the iron oxide pellets include iron ore, binder, and water, which are mixed and baked. Examples of the sintered ore include iron ore powder, carbon, and lime, which are mixed and baked. Examples of the direct reduction method include the MIDREX process and the HYL process. DRI is preferred because of its high catalytic activity. This is thought to be because oxygen is released from the iron oxide during the reduction of DRI, resulting in the formation of numerous pores in the resulting reduced iron (sponge iron). HBI is obtained by compressing and briquetting DRI at a high temperature (for example, about 700°C). HBI is preferable to DRI with numerous pores because it is easier to handle and can suppress heat generation and ignition (heat generation and ignition due to sponge iron).

[0018] The reduced iron is preferably granular, and more preferably spherical. The reduced iron preferably has an equivalent particle size of 5 mm or more, more preferably 8 to 18 mm, and even more preferably 10 to 16 mm. The equivalent particle size here is the arithmetic mean value of the equivalent particle size (the diameter of a sphere with the same volume as the granular reduced iron: equivalent spherical particle size) assuming that the granular reduced iron is spherical. Granular reduced iron not only allows the carbon oxides contained in the gas to be reduced with the hydrogen, but also facilitates the replacement of the reduced iron catalyst. The reduced iron is often obtained in a granular form. The reduced iron is often produced by, for example, the MIDREX process and the HYL process. The reduced iron obtained by these processes is granular, but it is also possible to obtain spherical reduced iron. In such cases, the reduced iron can be used as is without being crushed, eliminating the need for crushing costs. Moreover, excessive crushing of the reduced iron, which results in excessively fine particles, may result in a reduced yield. Furthermore, if the reduced iron is granular, when the reduced iron removed from the reactor is charged into, for example, a blast furnace or an electric furnace for use in steel production, it is less likely to scatter than powdered reduced iron, thereby preventing a decrease in steelmaking yield and preventing the accumulation of solid dust. Suppressing the accumulation of solid dust also reduces dust recovery costs. Furthermore, if the reduced iron is granular, when the reduced iron removed from the reactor is charged into, for example, a blast furnace for use in steel production, it is possible to prevent an increase in airflow resistance in the blast furnace. Because a gas passage is required in a blast furnace, a molded product such as granules is preferred.

[0019] The reduced iron preferably has a total content of iron compounds, calcium compounds, silicon compounds, magnesium compounds, and aluminum compounds of 90% by mass or more, preferably 95 to 100% by mass, based on the total amount of the reduced iron. Furthermore, the reduced iron preferably has a total content of iron compounds of 75% by mass or more, preferably 85 to 100% by mass, based on the total amount of the reduced iron. The iron compounds are not particularly limited as long as they are compounds containing iron, and examples thereof include iron and iron oxide. The calcium compounds are not particularly limited as long as they are compounds containing calcium, and examples thereof 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 are compounds containing silicon, and examples thereof 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 are compounds containing magnesium, and examples thereof 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 as long as it is a compound containing aluminum. Examples include not only aluminum but also aluminum salts such as aluminum chloride, aluminum sulfate, aluminum phosphate, and aluminum hydroxide. The reduced iron preferably has a metallization rate of 70% or more, more preferably 85 to 100%. The metallization rate here refers to the iron metallization rate, since the reduced iron is reduced iron, and is the ratio (%) of metallic iron contained in the reduced iron to the total iron components contained in the reduced iron [= (metallic iron contained in reduced iron) / (total iron components contained in reduced iron) × 100]. When reduced iron having the equivalent particle size, total content (total content of iron compounds, calcium compounds, silicon compounds, magnesium compounds, and aluminum compounds), iron compound content, and metallization rate within the above-mentioned ranges is used as the reduced iron to be introduced into the reactor, the carbon oxides contained in the gas can be more effectively reduced with the hydrogen.The reduced iron is preferably reduced using a reducing gas containing 50% or more by volume of hydrogen, and more preferably reduced using a reducing gas containing 60% or more by volume of hydrogen. The reduced iron preferably has a carbon content (carbon concentration) of 2.14% by mass or less. By using such reduced iron, the reduced iron is suitably carbonized (carburized), and the carbonized reduced iron contributes to negative emissions. Therefore, not only can the carbon oxides contained in the gas be suitably reduced by the hydrogen, but the carburization and negative emissions effects can be maximized. The reducing gas preferably contains 67% or more by volume and 100% or less by volume of hydrogen. The 2.14% by mass content corresponds to the maximum carbon content in iron alloys classified as carbon steel.

[0020] As described above, the chemical reaction is not particularly limited as long as it is a reaction using the gas flowing into the reactor as a raw material and the reduced iron introduced into the reactor as a catalyst. Examples of the chemical reaction include a reverse shift reaction, a methanation reaction, a Sabatier reaction, and a Fischer-Tropsch reaction.

[0021] The reverse shift reaction is a chemical reaction represented by the following formula (1), which can produce CO from a mixed gas of CO2 and H2.

[0022] CO2 + H2 → CO + H2O (1) The reverse shift reaction is an endothermic reaction, and therefore proceeds more easily at higher equilibrium temperatures.

[0023] The methanation reaction is a chemical reaction typified by the chemical reaction represented by the following formula (2), and can produce methane (CH4) from a mixed gas of CO and H2. The methanation reaction is not particularly limited as long as it is a reaction that can produce methane (CH4), and in addition to the chemical reaction represented by the following formula (2), examples include the chemical reaction represented by the following formula (3).

[0024] CO + 3H2 → CH4 + H2O (2) CO + 2H2 → CH4 + CO2(3) The methanation reaction is an exothermic reaction, and therefore proceeds more easily at low equilibrium temperatures.

[0025] The Sabatier reaction is a chemical reaction represented by the following formula (4), which can produce CH4 from a mixed gas of CO2 and H2.

[0026] CO2 + 4H2 → CH4 + 2H2O (4) The Sabatier reaction is an exothermic reaction, and therefore proceeds more easily at low equilibrium temperatures.

[0027] The Fischer-Tropsch reaction is a chemical reaction represented by the chemical reaction expressed by the following formula (5) and the chemical reaction expressed by the following formula (6), and can produce hydrocarbons from a mixed gas of CO and H2 and a mixed gas of CO2 and H2. The Fischer-Tropsch reaction is not particularly limited as long as it is a reaction that can produce hydrocarbons from the mixed gas, and the chemical reaction expressed by the following formula (5) and the chemical reaction expressed by the following formula (6) are examples. Note that the chemical reaction expressed by the following formula (5) relates to the direct Fischer-Tropsch reaction, which is one of the Fischer-Tropsch reactions, and the chemical reaction expressed by the following formula (6) relates to the indirect Fischer-Tropsch reaction, which is one of the Fischer-Tropsch reactions.

[0028] nCO2+ (3n+1)H2→ C n H 2n+2 + 2nH2O (5) nCO + (2n+1)H2 → C n H 2n+2 + nH2O (6) The chemical reaction may be any reaction using the gas flowing into the reactor as a raw material and the reduced iron as a catalyst, such as a reverse shift reaction, a methanation reaction, a Sabatier reaction, or a Fischer-Tropsch reaction. Whether the reaction is a reverse shift reaction, a methanation reaction, a Sabatier reaction, or a Fischer-Tropsch reaction depends on, for example, the type of gas flowing into the reactor and conditions such as temperature and pressure. Furthermore, the reaction may not be a single reaction, but two or more reactions may occur simultaneously. That is, the chemical reaction may be a single reaction or a combination of two or more reactions. For example, when two or more reactions occur simultaneously, a Sabatier reaction and a direct Fischer-Tropsch reaction may occur, or a methanation reaction and an indirect Fischer-Tropsch reaction may occur.

[0029] The gas flowing into the reactor is not particularly limited as long as it contains the carbon oxides and hydrogen. Because the hydrogen, carbon dioxide, and carbon monoxide serve as raw materials for the reverse shift reaction, methanation reaction, Sabatier reaction, and Fischer-Tropsch reaction, it is preferable that they account for a high proportion of the gas. Specifically, the total volume of the hydrogen, carbon dioxide, and carbon monoxide in the gas is preferably 75% by volume or more, more preferably 85 to 100% by volume, of the total volume of the gas. Furthermore, because water (HO) inhibits the progress of the reverse shift reaction, methanation reaction, Sabatier reaction, and Fischer-Tropsch reaction, it is preferable that the amount of water contained in the gas is small. Specifically, the total volume of the hydrogen and carbon monoxide in the gas is preferably 3 times or more, more preferably 3 to 20 times, and even more preferably 4 to 15 times the total volume of the water and carbon dioxide. When a gas having the above composition is used as the gas to be flowed into the reactor, the carbon oxides contained in the gas can be more effectively reduced by the hydrogen. Furthermore, the gas to be flowed into the reactor preferably does not contain sulfur compounds, both in terms of reducing poisoning by sulfur compounds and improving the quality of steel obtained when the reduced iron used in the reaction is used in steelmaking. Even if the gas contains sulfur compounds, a low sulfur compound content is preferable. The sulfur compound content is preferably, for example, 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). Examples of sulfur compounds include sulfur oxides such as sulfur dioxide and hydrogen sulfide.

[0030] The conditions for the chemical reaction in the reactor, such as the temperature and pressure, are not particularly limited as long as the reaction proceeds. The reduction method does not require a gentle reaction that does not result in carbon precipitation; rather, conditions that increase the reaction rate are preferred, since carbon precipitation allows the reduced iron to be more effectively utilized in iron production. The temperature in the reactor is preferably, for example, 300 to 900°C, more preferably 400 to 900°C. The pressure in the reactor is preferably, for example, atmospheric pressure (approximately 101.325 kPaA) or higher, and more preferably 300 to 5100 kPaA or higher.

[0031] In the reduction method, when a product gas containing carbon monoxide is obtained by reducing the carbon oxides, the carbon monoxide may be separated from the product gas containing carbon monoxide and the separated carbon monoxide may be introduced into the reactor. By doing so, the carbon oxides contained in the gas can be reduced by the hydrogen more efficiently, and hydrocarbons such as methane can be efficiently obtained.

[0032] In the reduction method, it is preferable that all of the hydrogen and carbon dioxide are used after the chemical reaction of the gas flowing into the reactor. However, the product gas obtained after the chemical reaction may contain hydrogen and carbon dioxide that were not used in the chemical reaction. In such a case, the hydrogen and carbon dioxide that were not used in the chemical reaction may be separated from the product gas obtained after the chemical reaction, and the separated hydrogen and carbon dioxide may be flowed into the reactor. By doing so, the hydrogen and carbon dioxide that were not used in the chemical reaction can be reused, and the yields of the conversion rate from hydrogen and the conversion rate from carbon dioxide, etc., can be increased. Therefore, the reduction of the carbon oxides contained in the gas by the hydrogen can be performed more efficiently.

[0033] In the reduction method, the reduced iron introduced into the reactor is used as a catalyst to carry out chemical reactions, such as the reverse shift reaction, on the carbon oxides introduced into the reactor. Carbon is deposited on the reduced iron used as a catalyst through the following reaction. Examples of carbon include free carbon (amorphous carbon), graphite (crystalline carbon), soot (solid polymer component), and tar (semi-liquid polymer component). The reduced iron on which carbon has been deposited is then typically at least partially carbonized by the carbon through reactions represented by the following formulas (7) and (8). That is, the reduced iron becomes a metal carbide, bonding with metals such as iron constituting the reduced iron. The carbide (FeC) is commonly called cementite. Metallic iron (Fe) has higher catalytic activity than cementite (FeC).

[0034] 3Fe + C → Fe3C (7) 3Fe + 2CO → Fe3C + CO2(8) The carbon deposited on the reduced iron occurs when the reaction conditions, such as temperature, pressure, and composition, in the reduction method satisfy certain conditions. Specifically, the conditions are such that relatively violent reactions occur in which hydrocarbon decomposition reactions such as the Boudouard reaction shown in the following formula (9), the reaction shown in the following formula (10), and the methane cracking reaction shown in the following formula (11) proceed.

[0035] 2CO → C + CO2(9) CO + H2 → C + H2O (10) CH4 → C + 2H2(11) Carbon deposition reduces catalytic activity. Therefore, when rare metals or the like are used as catalysts, the conditions (temperature, pressure, and composition) are typically adjusted to achieve a mild reaction (i.e., an extremely slow carbon deposition reaction rate) that prevents carbon deposition. However, under conditions that prevent carbon deposition, the reaction rate of the reduction reaction of carbon oxides (e.g., CO) (hydrocarbon synthesis reaction) also typically slows. Therefore, to achieve a predetermined reaction rate, it is necessary to enlarge the reactor and increase the amount of catalyst packed therein, resulting in increased costs. The carbon oxide reduction method according to this embodiment does not require the use of catalysts containing expensive materials such as Ni, Co, and precious metals. Furthermore, since the reduced iron used as a catalyst in the reduction method has carbon deposited or is carbonized, carbon oxides introduced into the reactor can be fixed as carbon in the reduced iron. By using such carbon-immobilized reduced iron (reduced iron with carbon deposited or carbonized) in steel production, the amount of carbon supplied during steel production can be reduced. For these reasons, the reduced iron used in the reduction method can be effectively used in steel production. Because of these factors, the reduced iron used as a catalyst can be replaced frequently, eliminating the need for a mild reaction to prevent carbon precipitation. Furthermore, steel containing carbon can be produced by using the reduced iron with immobilized carbon. Therefore, the reduction method can convert at least a portion of carbon oxides, such as carbon dioxide, in the atmosphere into carbon, thereby producing steel with immobilized carbon. In other words, the reduction method can also achieve so-called negative emissions, absorbing carbon dioxide rather than emitting it.

[0036] To effectively utilize the reduced iron on which carbon has been precipitated or carbonized, the reduction method may be, for example, the following method. First, the reduced iron is removed from the reactor when a predetermined time has elapsed since the reduced iron was introduced into the reactor. Specifically, the time since the reduced iron was introduced into the reactor is measured, and the reduced iron is removed from the reactor when the measured time has elapsed. Then, reduced iron not used as a catalyst (new reduced iron) is introduced into the reactor. This allows the new reduced iron not used as a catalyst to be introduced before the catalytic activity of the reduced iron introduced into the reactor decreases too much, thereby maintaining high catalytic activity of the reduced iron introduced into the reactor. Note that when the reduced iron is used as a catalyst, sintering and poisoning by impurities such as sulfur compounds may occur. However, even if these problems occur, high catalytic activity can be maintained by replacing the reduced iron more frequently than the replacement frequency of a normal catalyst. Therefore, the carbon oxides contained in the gas can be reduced more efficiently by the hydrogen. Furthermore, as described above, the reduced iron that has been introduced into the reactor for a predetermined time has carbon precipitated or been carbonized. This allows for a reduction in the amount of carbon supplied during steel production, and thus allows for effective use in steel production. The predetermined time after the introduction of the reduced iron into the reactor is much shorter than the time (usually one year or more) required for a catalyst adjusted to conditions for a mild reaction that prevents carbon precipitation. The predetermined time may be any time that does not excessively reduce the catalytic activity of the reduced iron, and may be, for example, the time required for the reaction rate to decrease to 70% of the initial reaction rate. The reaction rate can be measured by known methods, such as by Fourier transform infrared spectroscopy (FT-IR) and gas chromatography (gas chromatography mass spectrometry). The predetermined time is preferably 30 minutes to one month, more preferably 30 minutes to one week, and even more preferably 30 minutes to three days. Specific examples of the predetermined time include three days, one week, and one month.

[0037] The reduced iron removed from the reactor can be effectively used in steel production. Specifically, another embodiment of the present invention relates to a method for producing steel, which includes: introducing a gas containing carbon oxides, including at least one of carbon monoxide and carbon dioxide, and hydrogen into a reactor; introducing reduced iron into the reactor; reducing the carbon oxides through a chemical reaction, such as a reverse shift reaction, a methanation reaction, a Sabatier reaction, or a Fischer-Tropsch reaction, using the gas introduced into the reactor as a raw material and the reduced iron as a catalyst; removing the reduced iron from the reactor after a predetermined time has elapsed since the introduction of the reduced iron into the reactor; and introducing the removed reduced iron into a blast furnace or an electric furnace. This allows the reduced iron removed from the reactor to be effectively used as a raw material in steel production. Furthermore, when the reduced iron removed from the reactor is fed into a blast furnace during steel production, carbon precipitates or carbonizes in the reduced iron. This reduces the amount of carbon (coke) separately supplied during steel production. The reduced iron removed from the reactor can be used as a reducing agent in the blast furnace, improving energy efficiency and reducing running costs. The reduced iron removed from the reactor can be used as a heat agent or carburizing agent in an electric furnace, improving energy efficiency and reducing running costs. Furthermore, since steel is produced using the reduced iron with immobilized carbon, the steel containing the immobilized carbon can be obtained. Therefore, the steel production method can convert at least a portion of carbon oxides, such as carbon dioxide, in the atmosphere into carbon, thereby producing steel with immobilized carbon. In other words, the reduction method can achieve so-called negative emissions, absorbing carbon dioxide rather than emitting it. In the production of steel, unreduced iron, reduced iron not used as a catalyst, and the like may be used in addition to the reduced iron removed from the reactor. However, these may not be used, and only the reduced iron removed from the reactor may be used as the iron source. In this way, by using only the reduced iron removed from the reactor as the iron source, negative emissions can be further realized.The method for producing iron and steel may be any known method for producing iron and steel, except that the reduced iron removed from the reactor is added to an iron source to be charged into a blast furnace or an electric furnace.

[0038] The apparatus for performing the reduction method (carbon oxide reduction apparatus) is not particularly limited as long as it can perform the reduction method. The reduction apparatus includes a reactor, an inlet section for introducing a gas containing carbon oxides, including at least one of carbon monoxide and carbon dioxide, and hydrogen into the reactor, and an inlet section for introducing reduced iron into the reactor. The reduction apparatus uses the gas introduced into the reactor via the inlet section as a raw material and the reduced iron as a catalyst to reduce the carbon oxides through a chemical reaction such as a reverse shift reaction, a methanation reaction, a Sabatier reaction, or a Fischer-Tropsch reaction. Since such a reduction apparatus can perform the reduction method, it can reduce carbon oxides such as carbon dioxide without using a catalyst containing expensive materials such as Ni, Co, or precious metals, as in the reduction method. Furthermore, in the reduction apparatus, as in the reduction method, the reduced iron removed from the reactor can be effectively utilized in the production of steel. The reduction apparatus may also be an apparatus for producing steel by utilizing the reduced iron in the production of steel (steel production apparatus). Specifically, an apparatus for producing steel according to another embodiment of the present invention includes a reactor, an inlet section that allows a gas containing hydrogen and carbon oxides including at least one of carbon monoxide and carbon dioxide to flow into the reactor, an input section that introduces reduced iron into the reactor, an unloading section that removes the reduced iron from the reactor when a predetermined time has elapsed since the reduced iron was introduced into the reactor at the input section, and an iron feeding section that introduces the reduced iron removed from the reactor by the unloading section into a blast furnace or an electric furnace, and the carbon oxides are reduced in the reactor by a chemical reaction using the gas that has flowed into the reactor as a raw material and the reduced iron as a catalyst.

[0039] The reduction device may be, for example, a device that causes a Sabatier reaction. A specific example of the reduction device is a reduction device 10 shown in FIG. 1. FIG. 1 is a schematic diagram illustrating an example of a carbon oxide reduction device according to the present embodiment. As shown in FIG. 1, the reduction device 10 includes a reactor 11, an inlet 12, and an input 14. The reduction device 10 supplies a gas containing carbon dioxide and hydrogen to the reactor 11 through the inlet 12, and generates methane by causing a Sabatier reaction using the reduced iron introduced into the reactor 11 through the input 14 as a catalyst. The gas obtained in the reactor 11 contains not only methane but also mainly water (water vapor) in a gaseous state. After the gas is removed from the reactor 11, it is cooled in a heat exchanger 16 provided in the reduction device 10, whereby the gas is separated into methane and water. The gas extracted from the reactor 11 may also contain hydrogen and carbon dioxide that remain unreacted in the reactor 11. However, in FIG. 1 , the unreacted hydrogen and carbon dioxide that may be contained are not shown as the gas extracted from the reactor 11, and only methane and water (water vapor), which mainly constitute the gas, are shown. The separated methane is recovered in a methane recovery unit 171 provided in the reduction device 10, and the separated water is recovered in a water recovery unit 172 provided in the reduction device 10, separately from the separated methane. The reduction device 10 extracts the reduced iron that was used as a catalyst in the reactor 11 in an extraction unit 18. Specifically, as described above, the time since the reduced iron was introduced into the reactor 11 is measured, and when the measured time has elapsed a predetermined time, the reduced iron is extracted from the reactor 11 in the extraction unit 18. As described above, the reduced iron discharged at the discharge unit 18 has carbon precipitated therein or is carbonized, and is then charged into a blast furnace 191 or an electric furnace 192 for use in steel production. After the reduced iron discharged from the reactor 11 or the iron source containing the reduced iron is charged into the blast furnace 191 or the electric furnace 192, the steel production apparatus may be the same as a known steel production apparatus, and steel can be produced by this production apparatus. For this reason, the reduction apparatus 10 also serves as a steel production apparatus.That is, the steel manufacturing apparatus may be any known steel manufacturing apparatus except that the reduced iron removed by the unloading unit 18 is included in the iron source to be charged into the blast furnace 191 or the electric furnace 192. The steel manufacturing apparatus also includes a means for charging the reduced iron removed from the reactor 11 by the unloading unit 18 into the blast furnace 191 or the electric furnace 192, and this means corresponds to an iron feeding unit.

[0040] The reduction device 10 is not particularly limited in the method of introducing the reduced iron into the reactor 11 through the introduction port 14. For example, the introduction may be as follows. For example, the reactor 11 has valves at its upper (the introduction port 14 side) and lower (the removal port 18 side). First, only the lower valve is closed, and the reduced iron (reduced iron before use as a catalyst) is introduced into the reactor 11 from the upper side. Then, the upper valve is closed, and a gas containing carbon dioxide and hydrogen is introduced into the reactor 11 through the inlet port 12, causing a reaction with the reduced iron in the reactor 11 as a catalyst. After a predetermined time has elapsed, the lower valve is opened, and the reduced iron is removed from the reactor 11. Then, the upper valve is opened, the lower valve is closed, and the above-described operation is repeated, starting with the introduction of the reduced iron (reduced iron before use as a catalyst). As another example, a plurality of (two or more) reactors may be connected in parallel to the reduction device. In such a case, for example, while the reduced iron (reduced iron before being used as a catalyst) is being introduced into some of the multiple reactors (reactors constituting the first reactor group), the reaction may be carried out in the remaining reactors (reactors constituting the second reactor group). Thereafter, while the reduced iron used as a catalyst is being removed from the reactors constituting the second reactor group and the reduced iron (reduced iron before being used as a catalyst) is being introduced into the reactors constituting the first reactor group, the reaction may be carried out in the reactors constituting the first reactor group. Furthermore, some of the reactors constituting the first reactor group may be changed to the second reactor group, or some of the reactors constituting the second reactor group may be changed to the first reactor group. Furthermore, some of the reactors constituting the first reactor group may be unused, or some of the reactors constituting the second reactor group may be unused. Furthermore, in the case where two reactors are connected in parallel to the reduction apparatus, for example, while the reduced iron (reduced iron before being used as a catalyst) is being introduced into one reactor, the reaction may be carried out in the other reactor, and thereafter, while the reduced iron used as a catalyst is being removed from the other reactor and the reduced iron (reduced iron before being used as a catalyst) is being introduced into the other reactor, the reaction may be carried out in one reactor.In the reduction method, it is preferable that the reduced iron be taken out and fed at high frequency, as described above. The reactor may be a flow-type reactor or a batch-type reactor, as described above, and these reactors make it easy to take out and feed reduced iron at high frequency.

[0041] The reduction device may be, for example, a device that causes a reverse shift reaction. Another example of the reduction device is specifically a reduction device 20 shown in FIG. 2. FIG. 2 is a schematic configuration diagram showing another example of a carbon oxide reduction device according to the present embodiment. The reduction device 20 is similar to the reduction device 10 except that a reverse shift reaction occurs instead of a Sabatier reaction. As shown in FIG. 2, the reduction device 20 includes a reactor 21, an inlet 22, and an input 24. The reduction device 20 supplies a gas containing carbon dioxide and hydrogen to the reactor 21 from the inlet 22, and causes a reverse shift reaction using the reduced iron input into the reactor 21 from the input 24 as a catalyst to obtain carbon monoxide. The gas obtained in the reactor 21 contains not only carbon monoxide but also mainly water (water vapor) in a gaseous state. After being discharged from the reactor 21, the gas is separated into carbon monoxide and water by cooling it in a heat exchanger 26 provided in the reduction device 20. The gas discharged from the reactor 21 may also contain hydrogen and carbon dioxide that remain unreacted in the reactor 21. However, in FIG. 2, the unreacted hydrogen and carbon dioxide that may be contained are not shown as the gas discharged from the reactor 21, and only carbon monoxide and water (water vapor), which mainly constitute the gas, are shown. The separated carbon monoxide is recovered in a carbon monoxide recovery section 271 provided in the reduction device 20, and the separated water is recovered in a water recovery section 272 provided in the reduction device 20, separately from the separated carbon monoxide. The reduction device 20 discharges the reduced iron used as a catalyst in the reactor 21 to an discharge section 28. The reduced iron discharged at the discharge unit 28 has carbon precipitated therein or is carbonized, as described above, and can be fed into a blast furnace 291 or an electric furnace 292 for use in ironmaking to produce steel.

[0042] The reduction device may be, for example, a device equipped with two or more reactors. Specific examples of the reduction device include a device equipped with a reactor in which a reverse shift reaction occurs and a reactor in which a methanation reaction occurs. Specific examples of the device equipped with two or more reactors include a device in which two reactors are used, each of which is charged with reduced iron, and carbonized reduced iron is removed from both reactors (parallel), and a device in which two reactors are used, each of which is charged with reduced iron, and the carbonized reduced iron removed from the first reactor is charged into the other reactor (series).

[0043] Another example of the reduction device is, for example, a reduction device 30 shown in FIG. 3 in the case of the parallel arrangement. FIG. 3 is a schematic diagram illustrating another example of the carbon oxide reduction device according to the present embodiment. As shown in FIG. 3, the reduction device 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 device 30 supplies a gas containing carbon dioxide and hydrogen to the first reactor 311 from the first inlet 321, and generates carbon monoxide through a reverse shift reaction using the reduced iron input into the first reactor 311 from the first input 341 as a catalyst. The gas extracted from the first reactor 311 may also contain hydrogen and carbon dioxide that remain unreacted in the first reactor 311. However, in FIG. 3 , the gas extracted from the first reactor 311 does not include unreacted hydrogen and carbon dioxide, and instead includes carbon monoxide and water (water vapor), which are the main components of the gas. Because the amount of water (water vapor) accompanying the carbon monoxide obtained in the reverse shift reaction in the first reactor 311 is large, the water accompanying the carbon monoxide may be removed. Specifically, after the carbon monoxide is extracted from the first reactor 311, the carbon monoxide and water may be separated by cooling the carbon monoxide using a heat exchanger 361 provided in the reduction device 30. When water is separated in this manner, the separated water is recovered in a water recovery unit 35. Therefore, the reduction device 30 may or may not include the heat exchanger 361. If the reduction device 30 does not include the heat exchanger 361, the water recovery unit 35 may also not be included. Hydrogen is supplied from the second inlet 322 to the carbon monoxide obtained by the reverse shift reaction (carbon monoxide from which water has been separated, if water has been separated). The reduction device 30 supplies the carbon monoxide to which hydrogen has been supplied to the second reactor 312, and a methanation reaction occurs using the reduced iron introduced into the second reactor 312 from the second introduction port 342 as a catalyst to obtain methane. Note that the gas extracted from the second reactor 312 may also contain hydrogen and carbon dioxide that remain unreacted in the second reactor 312.3, the gas extracted from the second reactor 312 is shown as mainly composed of methane and water (water vapor), omitting the notation of unreacted hydrogen and carbon dioxide that may be contained therein. The gas containing carbon monoxide and hydrogen supplied to the second reactor 312 may be heated by a heat exchanger 362 provided in the reduction device 30 to improve reaction efficiency. The gas obtained in the second reactor 312 contains not only methane but also mainly gaseous water (water vapor). After the methane is extracted from the second reactor 312, it is cooled by a heat exchanger 363 provided in the reduction device 30, thereby separating the gas into methane and water. The separated methane is then recovered by a methane recovery unit 371 provided in the reduction device 30, and the separated water is recovered by a water recovery unit 372 provided in the reduction device 30, separately from the separated methane. In addition, the reduction device 30 discharges the reduced iron used as a catalyst in the first reactor 311 at a first discharge unit 381, and discharges the reduced iron used as a catalyst in the second reactor 312 at a second discharge unit 382. As described above, the reduced iron discharged at the first discharge unit 381 and the second discharge unit 382 has carbon precipitated therein or is carbonized, and can be input into a blast furnace 391 or an electric furnace 392 to be used for ironmaking to produce steel.

[0044] Other examples of the reduction device include, for example, in the case of the series connection, a reduction device 40 shown in Fig. 4 and a reduction device 50 shown in Fig. 5. Figs. 4 and 5 are each a schematic configuration diagram showing another example of the carbon oxide reduction device according to this embodiment.

[0045] As shown in FIG. 4 , the reduction device 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 device 40 supplies a gas containing carbon dioxide and hydrogen to the first reactor 411 through the first inlet 421, inputs reduced iron extracted from the second reactor 412 into the first reactor 411 through the first input 441, and produces carbon monoxide through a reverse shift reaction using the reduced iron as a catalyst. The gas extracted from the first reactor 411 may also contain hydrogen and carbon dioxide that remain unreacted in the first reactor 411. However, in FIG. 4 , the unreacted hydrogen and carbon dioxide that may be contained in the gas extracted from the first reactor 411 are not shown, and only carbon monoxide and water (water vapor), which mainly constitute the gas, are shown. Due to circumstances such as a large amount of water (water vapor) accompanying the carbon monoxide obtained by the reverse shift reaction in the first reactor 411, the water accompanying the carbon monoxide may be removed. Specifically, the carbon monoxide (including the water accompanying the carbon monoxide) may be removed from the first reactor 411 and then cooled by a heat exchanger 461 provided in the reduction device 40, thereby separating the carbon monoxide and the water. When the water is separated in this manner, the separated water is recovered in a water recovery unit 45. Therefore, the reduction device 40 may or may not be provided with the heat exchanger 461, and when the heat exchanger 461 is not provided, the water recovery unit 45 may not be provided either. Hydrogen is supplied from the second inlet 422 to the carbon monoxide obtained by the reverse shift reaction (carbon monoxide from which water is separated, if water is separated). The reduction device 40 supplies the carbon monoxide to which the hydrogen has been supplied to the second reactor 412, and a methanation reaction occurs using the reduced iron introduced into the second reactor 412 from the second input port 442 as a catalyst to obtain methane. The gas extracted from the second reactor 412 may also contain hydrogen and carbon dioxide that remain unreacted in the second reactor 412. However, in FIG. 4, the unreacted hydrogen and carbon dioxide that may be contained in the gas extracted from the second reactor 412 are not shown, and only methane and water (water vapor), which mainly constitute the gas, are shown.The gas containing carbon monoxide and hydrogen supplied to the second reactor 412 may be heated by a heat exchanger 462 provided in the reduction device 40 to increase reaction efficiency. The gas obtained in the second reactor 412 contains not only methane but also mainly gaseous water (water vapor). After the methane is extracted from the second reactor 412, it is cooled by a heat exchanger 463 provided in the reduction device 40 to separate the gas into methane and water. The separated methane is then recovered by a methane recovery unit 471 provided in the reduction device 40, and the separated water is recovered by a water recovery unit 472 provided in the reduction device 40, separately from the separated methane. The reduction device 40 also extracts the reduced iron used as a catalyst in the second reactor 412 from a second extraction unit 482. The reduced iron removed at the second discharge unit 482 is charged into the first reactor 411 at the first charge unit 441, as described above. In addition, the reduction device 40 removes the reduced iron used as a catalyst in the first reactor 411 at the first discharge unit 481. As described above, the reduced iron removed at the first discharge unit 481 has carbon precipitated therein or is carbonized, and can be charged into a blast furnace 491 or an electric furnace 492 to be used for ironmaking to produce steel.

[0046] As shown in FIG. 5 , the reduction device 50 includes a first reactor 511, a first inlet 521, a first input 541, a second reactor 512, a second inlet 522, and a second input 542. The reduction device 50 supplies a gas containing carbon dioxide and hydrogen from the first inlet 521 to the first reactor 511, and generates carbon monoxide through a reverse shift reaction using the reduced iron input from the first input 541 into the first reactor 511 as a catalyst. The gas extracted from the first reactor 511 may also contain hydrogen and carbon dioxide that remain unreacted in the first reactor 511. However, in FIG. 5 , the unreacted hydrogen and carbon dioxide that may be contained in the gas extracted from the first reactor 511 are not shown, and only carbon monoxide and water (water vapor), which mainly constitute the gas, are shown. Due to circumstances such as a large amount of water (water vapor) accompanying the carbon monoxide obtained by the reverse shift reaction in the first reactor 511, the water accompanying the carbon monoxide may be removed. Specifically, after the carbon monoxide is removed from the first reactor 511, the gas may be separated into carbon monoxide and water by cooling it with a heat exchanger 561 provided in the reduction device 50. When water is separated in this manner, the separated water is recovered in a water recovery unit 55. Hydrogen is supplied from the second inlet 522 to the carbon monoxide from which water has been separated. Therefore, the reduction device 50 may or may not be provided with the heat exchanger 561, and if the heat exchanger 561 is not provided, the water recovery unit 55 may not be provided either. Hydrogen is supplied from the second inlet 522 to the carbon monoxide obtained by the reverse shift reaction (carbon monoxide from which water has been separated, if water has been separated). The reduction device 50 supplies the carbon monoxide to which the hydrogen has been supplied to the second reactor 512, and inputs the reduced iron extracted from the first reactor 511 into the second reactor 512 through the second input unit 542. A methanation reaction occurs using the reduced iron as a catalyst to obtain methane. Note that the gas extracted from the second reactor 512 may also contain hydrogen and carbon dioxide that remain unreacted in the second reactor 512.5, the gas extracted from the second reactor 512 is shown as mainly composed of methane and water (water vapor), omitting the notation of unreacted hydrogen and carbon dioxide that may be contained therein. The gas containing carbon monoxide and hydrogen supplied to the second reactor 512 may be heated by a heat exchanger 562 provided in the reduction device 50 to improve reaction efficiency. The gas obtained in the second reactor 512 contains not only methane but also mainly gaseous water (water vapor). After the methane is extracted from the second reactor 512, it is cooled by a heat exchanger 563 provided in the reduction device 50, thereby separating the gas into methane and water. The separated methane is then recovered by a methane recovery unit 571 provided in the reduction device 50, and the separated water is recovered by a water recovery unit 572 provided in the reduction device 50, separately from the separated methane. The reduction device 50 also discharges the reduced iron used as a catalyst in the first reactor 511 at a first discharge unit 581. As described above, the reduced iron discharged at the first discharge unit 581 is charged into the second reactor 512 at the second charge unit 542. The reduction device 50 also discharges the reduced iron used as a catalyst in the second reactor 512 at a second discharge unit 582. As described above, the reduced iron discharged at the second discharge unit 582 has carbon precipitated therein or is carbonized, and can be charged into a blast furnace 591 or an electric furnace 592 for use in ironmaking to produce steel.

[0047] When two reactors are used, such as the reduction device 30, the reduction device 40, and the reduction device 50, and the reverse shift reaction occurs in one reactor and the methanation reaction occurs in the other reactor, as described above, water accompanying the carbon monoxide produced in the reverse shift reaction can be removed from the carbon monoxide, and the carbon monoxide from which the water has been removed can be used in the methanation reaction. Since water inhibits the methanation reaction, the reduction device 30 can increase the methane yield. Furthermore, the methane yield can also be increased by increasing the H2 / CO2 ratio in the reverse shift reaction.

[0048] When two reactors are used, such as the reduction devices 40 and 50, by feeding reduced iron into one reactor and then feeding the carbonized reduced iron removed from that reactor into the other reactor (series), the reduced iron is carbonized in two stages, resulting in a higher FeC content in the removed reduced iron than in a parallel configuration. Therefore, when the removed reduced iron is used for steelmaking, the running costs of the downstream blast furnace or electric furnace are reduced. On the other hand, in a series configuration, the FeC content in the reduced iron fed into the reactor increases more quickly than in a parallel configuration, resulting in a faster decline in catalytic activity and a need for a larger reactor. This increases the cost of the reactor during synthesis.

[0049] When two reactors are used, as in the reduction device 30, with reduced iron fed into each reactor and carbonized reduced iron withdrawn from both reactors (parallel), the FeC content in the withdrawn reduced iron is lower than in the series configuration. Therefore, even if the withdrawn reduced iron is used for steelmaking, the effect of reducing the running costs of the downstream blast furnace or electric furnace is insufficient. On the other hand, in the parallel configuration, the FeC content in the reduced iron fed into the reactors increases more slowly than in the series configuration, so the decrease in catalytic activity is suppressed and the reactors can be made smaller. This reduces the cost of the reactors during synthesis.

[0050] In the reduction device, carbon monoxide or the like separated from the product gas obtained by reacting the gas containing the carbon oxides may be introduced into the reactor and used in the reaction. For example, when a product gas containing carbon monoxide is obtained by reducing the carbon oxides, the carbon monoxide may be separated from the product gas containing carbon monoxide and the separated carbon monoxide may be introduced into the reactor. This allows the carbon oxides contained in the gas to be reduced more efficiently by the hydrogen, and hydrocarbons such as methane can be efficiently obtained. Specific examples of such reduction devices include a reduction device 60 shown in FIG. 6. Note that FIG. 6 is a schematic diagram showing another example of a carbon oxide reduction device according to this embodiment.

[0051] As shown in Fig. 6, the reduction device 60 includes a reactor 61, an inlet 62, and an input 64. The reduction device 60 supplies a gas containing carbon dioxide and hydrogen from the inlet 62 to the reactor 61, and produces carbon monoxide by a reverse shift reaction using the reduced iron introduced into the reactor 61 from the input 64 as a catalyst. The gas extracted from the reactor 61 may also contain hydrogen and carbon dioxide that remain unreacted in the reactor 61. However, in Fig. 6, the unreacted hydrogen and carbon dioxide that may be contained in the gas extracted from the reactor 61 are not shown, and only carbon monoxide and water (water vapor), which mainly constitute the gas, are shown. The gas obtained in the reactor 61 contains not only carbon monoxide but also mainly water (water vapor) in a gaseous state. After the carbon monoxide is removed from the reactor 61, it is cooled in a heat exchanger 66 provided in the reduction device 60, thereby separating the gas into carbon monoxide and water. The separated water is then recovered in a water recovery unit 65 provided in the reduction device 60, separately from the separated carbon monoxide. At least a portion of the separated carbon monoxide is introduced into the gas containing carbon dioxide and hydrogen from the inlet unit 62. Therefore, the gas to be introduced into the reactor 61 is a gas obtained by adding the separated carbon monoxide to the gas supplied from the inlet unit 62. Of the separated carbon monoxide, the carbon monoxide that is not returned to the reactor 61 is recovered in a carbon monoxide recovery unit 67 provided in the reduction device 60, and the reduction device 60 extracts the reduced iron used as a catalyst in the reactor 61 from an outlet unit 68. As described above, the reduced iron discharged from the discharge section 68 has carbon precipitated therein or is carbonized, and can be fed into a blast furnace 691 or an electric furnace 692 for use in ironmaking to produce steel. Carbon monoxide is a reactant not only in the reverse shift reaction but also in the methanation reaction and the Fischer-Tropsch reaction. Therefore, when these reactions are carried out, recycling the carbon monoxide as described above increases the yield (conversion rate from carbon monoxide). Furthermore, in the methanation reaction and the Fischer-Tropsch reaction, the higher the carbon monoxide ratio (the lower the carbon dioxide ratio), the higher the yield of the target product and the reaction rate.Furthermore, since carbon monoxide is an impurity for hydrocarbons such as methane, it is necessary to remove it, and the removed carbon monoxide is returned to the raw material gas. In the above example, carbon monoxide was reused, but it is not limited to carbon monoxide. Alternatively, hydrogen or carbon dioxide may be reused. Since hydrogen serves as a raw material in both reactions, reusing it increases the yield (conversion rate from hydrogen). Furthermore, carbon dioxide serves as a raw material in the reverse shift reaction and the Sabatier reaction. Therefore, reusing carbon dioxide increases the yield (conversion rate from carbon dioxide) when these reactions are performed. Since water slows the reaction rate in both reactions, recovering it as described above rather than reusing it can increase the reaction rate. To recover water, the gas must be heated and cooled, etc. However, water may be recovered as described above depending on various circumstances, such as when there is a high need to increase the reaction rate, or when the gas used in the reaction contains a large amount of water (water vapor) and the reaction rate is too slow. Furthermore, in amine absorption methods, PSA (Pressure Swing Adsorption), and other gas separation methods, water is naturally separated and is often discarded as is. Water also acts as an inhibitor of the carbon deposition reaction on the catalyst. Therefore, when the catalyst is a precious metal or the like, water may be recycled or added externally to suppress carbon deposition on the catalyst. While carbon deposition on the catalyst is suppressed in this way, the carbon oxide reduction method according to this embodiment uses reduced iron as the catalyst, and therefore does not require water recycling, since carbon deposition on the reduced iron does not pose a particular problem.

[0052] The reduction may involve separating the hydrogen and carbon dioxide not used in the chemical reaction from the product gas obtained by chemically reacting the gas containing the carbon oxides flowing into the reactor, and then flowing the separated hydrogen and carbon dioxide into the reactor for use in the chemical reaction. This allows the hydrogen and carbon dioxide not used in the chemical reaction to be reused, thereby increasing the yields of the conversion rate from hydrogen and the conversion rate from carbon dioxide. Therefore, the carbon oxides contained in the gas can be reduced more efficiently by the hydrogen. A specific example of such a reduction device is a reduction device 70 shown in FIG. 7. FIG. 7 is a schematic cross-sectional view showing another example of a carbon oxide reduction device according to this embodiment.

[0053] The reduction device 70 includes a carbon monoxide separation unit 71 in addition to the configuration of the reduction device 60 shown in Fig. 6. The gas extracted from the reactor 61 may also contain hydrogen and carbon dioxide that remain unreacted in the reactor 61. In Fig. 7, the amount of unreacted hydrogen and carbon dioxide is assumed to be greater than in the above-described embodiment, and the gas extracted from the reactor 61 is shown to include not only carbon monoxide and water (water vapor) that mainly constitute the gas, but also the unreacted hydrogen and carbon dioxide.

[0054] The carbon monoxide separation unit 71 is not particularly limited as long as it can separate carbon monoxide from a plurality of gas species, and specific examples include those using various methods such as the above-mentioned PSA (Pressure Swing Adsorption) and cryogenic separation. By providing the carbon monoxide separation unit 71, the carbon monoxide separated in the carbon monoxide separation unit 71 is recovered in the carbon monoxide recovery unit 67 provided in the reduction device 70, while the hydrogen and carbon dioxide not separated in the carbon monoxide separation unit 71, together with a portion of the carbon monoxide, are introduced into the gas containing carbon dioxide and hydrogen from the inlet unit 62. Even with this configuration, it is possible to reuse the hydrogen and carbon dioxide not used in the reaction and increase the yield (the conversion rate from hydrogen and the conversion rate from carbon dioxide).

[0055] As described above, this specification discloses various aspects of the technology, the main technologies of which are summarized below.

[0056] A method for reducing carbon oxides according to a first aspect of the present invention is a method for reducing carbon oxides, comprising: flowing a gas containing hydrogen and carbon oxides, the carbon oxides including at least one of carbon monoxide and carbon dioxide, into a reactor; introducing reduced iron into the reactor; and reducing the carbon oxides by a chemical reaction using the gas flowed into the reactor as a raw material and the reduced iron as a catalyst.

[0057] This configuration allows a chemical reaction to occur using the gas flowing into the reactor as a raw material and the reduced iron introduced into the reactor as a catalyst. This reaction allows the carbon oxides contained in the gas to be reduced by the hydrogen. Reducing carbon oxides such as carbon dioxide produces hydrocarbons such as methane and carbon monoxide, which can be used to obtain hydrocarbons, thereby contributing to the effective use of carbon dioxide. This provides a carbon oxide reduction method that can reduce carbon oxides such as carbon dioxide without using a catalyst containing expensive materials such as Ni, Co, and precious metals. Furthermore, the reduced iron is less expensive than catalysts containing expensive materials such as Ni, Co, and precious metals. Furthermore, the reduced iron used as a catalyst in this reduction method has carbon precipitated or is carbonized, making it effective for steel production. These factors limit the increase in running costs even when the reduced iron catalyst is replaced frequently. Therefore, not only can carbon oxides be reduced, but high catalytic activity can also be maintained by replacing the catalyst before its catalytic activity significantly decreases. Furthermore, as described above, the reduced iron used as a catalyst in the reduction method has carbon precipitated thereon or is carbonized, so that carbon oxides introduced into the reactor can be fixed as carbon in the reduced iron. Steel is produced using the reduced iron with fixed carbon, thereby obtaining steel containing carbon. For these reasons, the reduction method can also contribute to negative emissions by absorbing carbon dioxide.

[0058] A method for reducing carbon oxides according to a second aspect of the present invention is the method for reducing carbon oxides according to the first aspect of the present invention, wherein the chemical reaction preferably includes at least one of a Sabatier reaction and a direct Fischer-Tropsch reaction.

[0059] According to this configuration, carbon oxides such as carbon dioxide can be reduced more effectively.

[0060] A method for reducing carbon oxides according to a third aspect of the present invention is the method for reducing carbon oxides according to the first or second aspect of the present invention, wherein the chemical reaction preferably includes at least one of a methanation reaction and an indirect Fischer-Tropsch reaction.

[0061] According to this configuration, carbon oxides such as carbon dioxide can be reduced more effectively.

[0062] A method for reducing carbon oxides according to a fourth aspect of the present invention is the method for reducing carbon oxides according to any one of the first to third aspects of the present invention, wherein the chemical reaction preferably includes a reverse shift reaction.

[0063] According to this configuration, carbon oxides such as carbon dioxide can be reduced more effectively.

[0064] A method for reducing carbon oxides according to a fifth aspect of the present invention is the method for reducing carbon oxides according to any one of the first to fourth aspects of the present invention, wherein the reduced iron is preferably in a granular form.

[0065] According to this configuration, even if the reduced iron introduced into the reactor as a catalyst is granular, the carbon oxides contained in the gas can be reduced by the hydrogen. Furthermore, if the reduced iron is granular, the catalyst reduced iron can be easily replaced. Therefore, high catalytic activity can be maintained. Therefore, the carbon oxides contained in the gas can be more effectively reduced by the hydrogen. Furthermore, the reduced iron is often obtained in a granular form. In such cases, it can be used as is without being crushed, eliminating the need for crushing costs. Furthermore, if the reduced iron is granular, when the reduced iron removed from the reactor is introduced into, for example, a blast furnace for use in steel production, an increase in the airflow resistance in the blast furnace can be suppressed. Because a gas passage is required in a blast furnace, a granular form is also preferable.

[0066] A method for reducing carbon oxides according to a sixth aspect of the present invention is the method for reducing carbon oxides according to any one of the first to fifth aspects of the present invention, wherein the reduced iron has an equivalent particle size of 5 mm or more, the total content of iron compounds, calcium compounds, silicon compounds, magnesium compounds, and aluminum compounds is 90 mass % or more relative to the total amount of the reduced iron, the content of the iron compounds is 75 mass % or more relative to the total amount of the reduced iron, and the metallization rate is 70% or more.

[0067] According to this configuration, the carbon oxides contained in the gas can be reduced more effectively with the hydrogen.

[0068] A method for reducing carbon oxides according to a seventh aspect of the present invention is the method for reducing carbon oxides according to any one of the first to sixth aspects of the present invention, wherein the reduced iron is preferably reduced iron reduced with a reducing gas containing 50% by volume or more of hydrogen, or reduced iron having a carbon content of 2.14% by mass or less.

[0069] According to this configuration, the reduced iron is suitably carbonized (carburized), and the carbonized reduced iron contributes to negative emissions, which not only allows the carbon oxides contained in the gas to be more suitably reduced by the hydrogen but also maximizes the effects of carburization and negative emissions.

[0070] A method for reducing carbon oxides according to an eighth aspect of the present invention is the method for reducing carbon oxides according to any one of the first to seventh aspects of the present invention, wherein the gas to be flowed into the reactor has a total volume of the hydrogen, carbon dioxide, and carbon monoxide of 75% by volume or more relative to the total volume of the gas, and the total volume of the hydrogen and the carbon monoxide is preferably three times or more the total volume of water and the carbon dioxide.

[0071] According to this configuration, the carbon oxides contained in the gas can be reduced more effectively with the hydrogen.

[0072] A method for reducing carbon oxides according to a ninth aspect of the present invention is the method for reducing carbon oxides according to any one of the first to eighth aspects of the present invention, wherein a product gas containing carbon monoxide is obtained by reducing the carbon oxides, the carbon monoxide is separated from the product gas, and the separated carbon monoxide is allowed to flow into the reactor.

[0073] According to this configuration, the carbon oxides contained in the gas can be reduced more efficiently by the hydrogen.

[0074] A method for reducing carbon oxides according to a tenth aspect of the present invention is the method for reducing carbon oxides according to any one of the first to ninth aspects of the present invention, wherein the hydrogen not used in the chemical reaction and the carbon dioxide not used in the chemical reaction are separated from a product gas obtained after the gas flowing into the reactor is subjected to the chemical reaction, and the separated hydrogen and carbon dioxide are flowed into the reactor.

[0075] According to this configuration, the hydrogen and carbon dioxide not used in the chemical reaction can be reused, and the yield of the conversion rate from hydrogen and the conversion rate from carbon dioxide can be increased, etc. Therefore, the reduction of the carbon oxides contained in the gas by the hydrogen can be performed more efficiently.

[0076] A method for reducing carbon oxides according to an eleventh aspect of the present invention is the method for reducing carbon oxides according to any one of the first to tenth aspects of the present invention, wherein the reduced iron is preferably removed from the reactor when a predetermined time has elapsed since the reduced iron was introduced into the reactor, and reduced iron that has not been used as a catalyst is introduced into the reactor.

[0077] According to this configuration, new reduced iron that is not being used as a catalyst can be introduced into the reactor before the catalytic activity of the reduced iron introduced into the reactor decreases too much, so that the reduced iron introduced into the reactor can maintain a high catalytic activity, thereby more efficiently reducing the carbon oxides contained in the gas with the hydrogen.

[0078] A method for reducing carbon oxides according to a twelfth aspect of the present invention is the method for reducing carbon oxides according to the eleventh aspect of the present invention, wherein the predetermined time is preferably from 30 minutes to one month.

[0079] According to this configuration, the catalytic activity of the reduced iron charged into the reactor can be more suitably maintained at a high level, and therefore the carbon oxides contained in the gas can be more efficiently reduced by the hydrogen.

[0080] A method for reducing carbon oxides according to a thirteenth aspect of the present invention is the method for reducing carbon oxides according to any one of the first to twelfth aspects of the present invention, wherein the reactor is preferably a flow reactor or a batch reactor.

[0081] According to this configuration, the reduced iron serving as a catalyst can be easily replaced frequently, and therefore the carbon oxides contained in the gas can be reduced by the hydrogen more efficiently.

[0082] A fourteenth aspect of the present invention is a method for producing steel, comprising: flowing a gas containing hydrogen and carbon oxides, the gas including at least one of carbon monoxide and carbon dioxide, into a reactor; introducing reduced iron into the reactor; reducing the carbon oxides through a chemical reaction using the gas introduced into the reactor as a raw material and the reduced iron as a catalyst; measuring the time since the reduced iron was introduced into the reactor; removing the reduced iron from the reactor when the measured time has elapsed a predetermined time; and introducing the reduced iron removed from the reactor into a blast furnace or an electric furnace.

[0083] According to this configuration, the reduced iron introduced into the reactor is used as a catalyst for reducing the carbon oxides contained in the gas flowing into the reactor with the hydrogen, so that the reduced iron has carbon precipitated thereon or is carbonized. Such reduced iron can be effectively used as a raw material for producing steel. Therefore, a steel production method that effectively utilizes the reduction method can be provided.

[0084] A method for producing iron or steel according to a fifteenth aspect of the present invention is preferably the method for producing iron or steel according to the fourteenth aspect of the present invention, wherein the chemical reaction includes at least one of a Sabatier reaction and a direct Fischer-Tropsch reaction.

[0085] According to this configuration, the reduction method can be used more effectively.

[0086] A method for producing iron or steel according to a sixteenth aspect of the present invention is preferably the method for producing iron or steel according to the fourteenth or fifteenth aspect of the present invention, wherein the chemical reaction includes at least one of a methanation reaction and an indirect Fischer-Tropsch reaction.

[0087] According to this configuration, the reduction method can be used more effectively.

[0088] A method for producing iron and steel according to a seventeenth aspect of the present invention is the method for producing iron and steel according to any one of the fourteenth to sixteenth aspects of the present invention, wherein the chemical reaction preferably includes a reverse shift reaction.

[0089] According to this configuration, the reduction method can be used more effectively.

[0090] An eighteenth aspect of the present invention is a method for producing iron and steel according to any one of the fourteenth to seventeenth aspects of the present invention, wherein the reduced iron taken out of the reactor preferably has carbon precipitated thereon.

[0091] According to this configuration, first, the reduced iron on which carbon has been deposited is usually at least partially carbonized by the carbon. In this way, carbon is deposited on the reduced iron used as a catalyst, or the reduced iron is carbonized. Then, steel is produced using the reduced iron on which carbon has been deposited and the carbonized reduced iron, thereby obtaining carbon-containing steel. Therefore, the steel production method can realize a so-called negative emission technology, which can convert at least a portion of carbon oxides such as carbon dioxide in the atmosphere into carbon, and obtain steel in which this carbon is fixed.

[0092] A 19th aspect of the present invention is a method for producing iron and steel according to any one of the 14th to 18th aspects of the present invention, wherein the temperature inside the reactor when the chemical reaction is carried out is 300 to 900°C, the pressure inside the reactor is atmospheric pressure or higher, the gas flowing into the reactor has a sulfur compound content of 10 ppm or less, and the total volume of the hydrogen and the carbon monoxide is three times or more the total volume of water and the carbon dioxide.

[0093] According to this configuration, the reduced iron used as a catalyst for reducing the carbon oxides contained in the gas flowing into the reactor with the hydrogen has more carbon precipitated or is more carbonized, and such reduced iron can be more effectively used as a raw material for producing steel.

[0094] A carbon oxide reduction device according to a twentieth aspect of the present invention includes a reactor, an inlet section through which a gas containing hydrogen and carbon oxides including at least one of carbon monoxide and carbon dioxide flows into the reactor, and an input section through which reduced iron is input into the reactor, and the carbon oxides are reduced by a chemical reaction using the gas that has flowed into the reactor at the inlet section as a raw material and the reduced iron as a catalyst.

[0095] According to this configuration, it is possible to provide a carbon oxide reduction device that can reduce carbon oxides such as carbon dioxide without using a catalyst containing expensive materials such as Ni, Co, and precious metals, as in the carbon oxide reduction method described above.

[0096] A carbon oxide reduction apparatus according to a twenty-first aspect of the present invention is the carbon oxide reduction apparatus according to the twentieth aspect of the present invention, wherein the chemical reaction preferably includes at least one of a Sabatier reaction and a direct Fischer-Tropsch reaction.

[0097] According to this configuration, carbon oxides such as carbon dioxide can be reduced more effectively.

[0098] A carbon oxide reduction apparatus according to a twenty-second aspect of the present invention is the carbon oxide reduction apparatus according to the twentieth or twenty-first aspect of the present invention, wherein the chemical reaction preferably includes at least one of a methanation reaction and an indirect Fischer-Tropsch reaction.

[0099] According to this configuration, carbon oxides such as carbon dioxide can be reduced more effectively.

[0100] The carbon oxide reduction device according to a 23rd aspect of the present invention is the carbon oxide reduction device according to any one of the 20th to 22nd aspects of the present invention, wherein the chemical reaction preferably includes a reverse shift reaction.

[0101] According to this configuration, carbon oxides such as carbon dioxide can be reduced more effectively.

[0102] A carbon oxide reduction device according to a twenty-fourth aspect of the present invention is the carbon oxide reduction device according to any one of the twentieth to twenty-third aspects of the present invention, wherein the reduced iron is preferably in a granular form.

[0103] With this configuration, even if the reduced iron introduced into the reactor as a catalyst is granular, the carbon oxides contained in the gas can be reduced by the hydrogen. Furthermore, if the reduced iron is granular, the reduced iron serving as a catalyst can be easily replaced. Therefore, a high catalytic activity can be maintained. Therefore, the carbon oxides contained in the gas can be more effectively reduced by the hydrogen.

[0104] A carbon oxide reduction device according to a 25th aspect of the present invention is the carbon oxide reduction device according to any one of the 20th to 24th aspects of the present invention, wherein the reduced iron has an equivalent particle size of 5 mm or more, the total content of iron compounds, calcium compounds, silicon compounds, magnesium compounds, and aluminum compounds is 90 mass % or more relative to the total amount of the reduced iron, the content of the iron compounds is 75 mass % or more relative to the total amount of the reduced iron, and the metallization rate is 70% or more.

[0105] According to this configuration, the carbon oxides contained in the gas can be reduced more effectively with the hydrogen.

[0106] A carbon oxide reduction device according to a 26th aspect of the present invention is the carbon oxide reduction device according to any one of the 20th to 25th aspects of the present invention, wherein the reduced iron is preferably reduced iron reduced with a reducing gas containing 50% by volume or more of hydrogen, or reduced iron having a carbon content of 2.14% by mass or less.

[0107] According to this configuration, the reduced iron is suitably carbonized (carburized), and the carbonized reduced iron contributes to negative emissions, which not only allows the carbon oxides contained in the gas to be more suitably reduced by the hydrogen but also maximizes the effects of carburization and negative emissions.

[0108] A carbon oxide reduction apparatus according to a 27th aspect of the present invention is the carbon oxide reduction apparatus according to any one of the 20th to 26th aspects of the present invention, wherein the gas introduced into the reactor at the inlet section has a total volume of the hydrogen, carbon dioxide, and carbon monoxide of 75 volume % or more relative to the total volume of the gas, and the total volume of the hydrogen and the carbon monoxide is preferably three times or more the total volume of water and the carbon dioxide.

[0109] According to this configuration, the carbon oxides contained in the gas can be reduced more effectively with the hydrogen.

[0110] The carbon oxide reduction apparatus according to a 28th aspect of the present invention is preferably the carbon oxide reduction apparatus according to any one of the 20th to 27th aspects of the present invention, further comprising a reuse unit that separates carbon monoxide from a product gas containing carbon monoxide produced by reducing the carbon oxides, and uses the separated carbon monoxide as at least a part of the gas to be flowed into the reactor.

[0111] According to this configuration, the carbon oxides contained in the gas can be reduced more efficiently by the hydrogen.

[0112] A carbon oxide reduction apparatus according to a 29th aspect of the present invention is preferably the carbon oxide reduction apparatus according to any one of the 20th to 28th aspects of the present invention, wherein the hydrogen not used in the chemical reaction and the carbon dioxide not used in the chemical reaction are separated from the product gas obtained after the chemical reaction is performed on the gas flowing into the reactor, and the separated hydrogen and carbon dioxide are flowed into the reactor.

[0113] According to this configuration, the hydrogen and carbon dioxide not used in the chemical reaction can be reused, and the yield of the conversion rate from hydrogen and the conversion rate from carbon dioxide can be increased, etc. Therefore, the reduction of the carbon oxides contained in the gas by the hydrogen can be performed more efficiently.

[0114] A carbon oxide reduction apparatus according to a 30th aspect of the present invention is the carbon oxide reduction apparatus according to any one of the 20th to 29th aspects of the present invention, further comprising an unloading unit that unloads the reduced iron from the reactor when a predetermined time has elapsed since the reduced iron was loaded into the reactor by the loading unit, and it is preferable that the loading unit loads reduced iron that has not been used as a catalyst into the reactor after the unloading unit unloads the reduced iron from the reactor.

[0115] According to this configuration, new reduced iron that is not being used as a catalyst can be introduced into the reactor before the catalytic activity of the reduced iron introduced into the reactor decreases too much, so that the reduced iron introduced into the reactor can maintain a high catalytic activity, thereby more efficiently reducing the carbon oxides contained in the gas with the hydrogen.

[0116] A carbon oxide reduction device according to a thirty-first aspect of the present invention is the carbon oxide reduction device according to the thirtieth aspect of the present invention, wherein the predetermined time is preferably 30 minutes to one month.

[0117] According to this configuration, the catalytic activity of the reduced iron charged into the reactor can be more suitably maintained at a high level, and therefore the carbon oxides contained in the gas can be more efficiently reduced by the hydrogen.

[0118] A carbon oxide reduction apparatus according to a 32nd aspect of the present invention is the carbon oxide reduction apparatus according to any one of the 20th to 31st aspects of the present invention, wherein the reactor is preferably a flow reactor or a batch reactor.

[0119] According to this configuration, the reduced iron serving as a catalyst can be easily replaced frequently, and therefore the carbon oxides contained in the gas can be reduced by the hydrogen more efficiently.

[0120] A thirty-third aspect of the present invention provides an apparatus for producing iron and steel, comprising: a reactor; an inlet section for introducing a gas containing hydrogen and carbon oxides, the gas including at least one of carbon monoxide and carbon dioxide, into the reactor; an input section for introducing reduced iron into the reactor; an unloading section for removing the reduced iron from the reactor when a predetermined time has elapsed since the reduced iron was introduced into the reactor at the input section; and an iron feeding section for introducing the reduced iron removed from the reactor by the unloading section into a blast furnace or an electric furnace, wherein the reactor reduces the carbon oxides by a chemical reaction using the gas introduced into the reactor as a raw material and the reduced iron as a catalyst.

[0121] According to this configuration, the reduced iron introduced into the reactor is used as a catalyst for reducing the carbon oxides contained in the gas flowing into the reactor with the hydrogen, so that the reduced iron has carbon precipitated thereon or is carbonized. Such reduced iron can be effectively used as a raw material for producing steel. Therefore, a steel production apparatus that effectively utilizes the reduction method can be provided.

[0122] A thirty-fourth aspect of the present invention relates to the apparatus for manufacturing iron and steel according to the thirty-third aspect of the present invention, and it is preferable that the chemical reaction includes at least one of a Sabatier reaction and a direct Fischer-Tropsch reaction.

[0123] According to this configuration, the reduction method can be used more effectively.

[0124] An apparatus for manufacturing iron and steel according to a 35th aspect of the present invention is the apparatus for manufacturing iron and steel according to the 33rd or 34th aspect of the present invention, wherein the chemical reaction preferably includes at least one of a methanation reaction and an indirect Fischer-Tropsch reaction.

[0125] According to this configuration, the reduction method can be used more effectively.

[0126] An apparatus for producing iron and steel according to a thirty-sixth aspect of the present invention is the apparatus for producing iron and steel according to any one of the thirty-third to thirty-fifth aspects of the present invention, wherein the chemical reaction preferably includes a reverse shift reaction.

[0127] According to this configuration, the reduction method can be used more effectively.

[0128] A thirty-seventh aspect of the present invention is the apparatus for manufacturing iron and steel according to any one of the thirty-third to thirty-sixth aspects of the present invention, wherein the reduced iron taken out from the reactor preferably has carbon precipitated thereon.

[0129] According to this configuration, first, the reduced iron on which carbon has been deposited is usually at least partially carbonized by the carbon. In this way, carbon is deposited on the reduced iron used as a catalyst, or the reduced iron is carbonized. Then, by manufacturing steel using the reduced iron on which carbon has been deposited and the carbonized reduced iron, the carbon-containing steel is obtained. Thus, the steel manufacturing apparatus can convert at least a portion of carbon oxides, such as carbon dioxide, in the atmosphere into carbon, and can obtain steel in which the carbon is fixed, thereby realizing so-called negative emission technology.

[0130] A 38th aspect of the present invention is an apparatus for manufacturing iron and steel according to any one of the 33rd to 37th aspects of the present invention, wherein, when the chemical reaction is carried out, the temperature inside the reactor is 300 to 900°C, the pressure inside the reactor is atmospheric pressure or higher, the gas introduced into the reactor at the inlet portion has a sulfur compound content of 10 ppm or less, and the total volume of the hydrogen and the carbon monoxide is three times or more the total volume of water and the carbon dioxide.

[0131] According to this configuration, the reduced iron used as a catalyst for reducing the carbon oxides contained in the gas flowing into the reactor with the hydrogen has more carbon precipitated or is more carbonized, and such reduced iron can be more effectively used as a raw material for producing steel.

[0132] The present invention provides a method and apparatus for reducing carbon oxides that can reduce carbon oxides such as carbon dioxide without using a catalyst containing expensive materials such as Ni, Co, and precious metals. The present invention also provides a method and apparatus for producing iron and steel that effectively utilize the reduction method.

[0133] The present invention will be explained in more detail below with reference to examples, but the scope of the present invention is not limited to these examples. [Example]

[0134] Specifically, for example, the following reaction was carried out. Reduced iron (reduced iron reduced with a reducing gas containing 50% by volume of hydrogen, having an equivalent particle size of approximately 10 to 13 mm, a total content of iron compounds, calcium compounds, silicon compounds, magnesium compounds, and aluminum compounds of 99% by mass relative to the total amount of the reduced iron, a content of the iron compounds of 96% by mass relative to the total amount of the reduced iron, and a carbon content of approximately 0% by mass) was introduced into a reactor. Specifically, the reduced iron had a composition of approximately 95% by mass of metallic Fe (an iron compound), less than 1% by mass of FeO, less than 1% by mass of CaO (a calcium compound), approximately 2% by mass of SiO (a silicon compound), less than 1% by mass of MgO (a magnesium compound), less than 1% by mass of AlO (an aluminum compound), and a total sulfur content of less than 100 ppm by mass. A raw material gas (66% by volume of hydrogen, 17% by volume of carbon dioxide, and 17% by volume of nitrogen; the total volume of the hydrogen, carbon dioxide, and carbon monoxide was approximately 83% by volume, which was 80% or more by volume, relative to the total volume of the gas; and the total volume of the hydrogen and carbon monoxide was approximately four times the total volume of the water and carbon dioxide) was introduced into the reactor. The raw material gas did not contain sulfur compounds, i.e., the sulfur compound content was 0 ppm relative to the raw material gas. The temperature inside the reactor was set to 350 to 450°C, the pressure inside the reactor was set to 500 kPaA, and the raw material gas was reacted with the reduced iron for a contact time of approximately several seconds. This resulted in a reaction mainly consisting of the Sabatier reaction. The reaction rate was calculated by measuring the gas discharged from the reactor using gas chromatography-mass spectrometry. As a result, the reaction rate sometimes reached a methane conversion rate of 20% or more. Furthermore, when the reduced iron was analyzed after the reaction, carbon deposition on its surface was confirmed. It was also confirmed that the methane conversion rate could be increased by increasing the contact time between the raw material gas and the reduced iron. [Explanation of symbols]

[0135] 10, 20, 30, 40, 50, 60 reduction device 11, 21, 61 reactors 311, 411, 511 First Reactor 312, 412, 512 Second reactor 12, 22, 62 Inlet 321, 421, 521 1st inflow section 322, 422, 522 2nd inflow section 14, 24, 64 Input section 341, 441, 541 1st input section 342, 442, 542 2nd input section 16, 26, 361, 362, 363, 461, 462, 463, 561, 562, 563, 66 heat exchanger 18, 28, 68 Removal section 381, 481, 581 1st extraction section 382, 482, 582 2nd extraction section 172, 272, 35, 372, 45, 472, 55, 572, 65 Water recovery section 271, 67 Carbon Monoxide Recovery Section 171, 371, 471, 571 Methane Recovery Section 191, 291, 391, 491, 591, 691 blast furnace 192, 292, 392, 492, 592, 692 electric furnace 71 Carbon monoxide separator

Claims

1. A gas containing carbon oxides including at least one of carbon monoxide and carbon dioxide and hydrogen is introduced into a reactor; charging reduced iron into the reactor; a method for reducing carbon oxides, the method comprising: reducing the carbon oxides by a chemical reaction using the gas flowed into the reactor as a raw material and the reduced iron as a catalyst;

2. 2. The method for reducing carbon oxides according to claim 1, wherein the chemical reaction comprises at least one of a Sabatier reaction and a direct Fischer-Tropsch reaction.

3. 2. The method for reducing carbon oxides according to claim 1, wherein the chemical reaction comprises at least one of a methanation reaction and an indirect Fischer-Tropsch reaction.

4. 2. The method for reducing carbon oxides according to claim 1, wherein the chemical reaction comprises a reverse shift reaction.

5. 2. The method for reducing carbon oxides according to claim 1, wherein the reduced iron is in a granular form.

6. The reduced iron is The equivalent particle size is 5 mm or more, a total content of the iron compound, the calcium compound, the silicon compound, the magnesium compound, and the aluminum compound is 90% by mass or more based on the total amount of the reduced iron, the content of the iron compound is 75% by mass or more based on the total amount of the reduced iron, 2. The method for reducing carbon oxides according to claim 1, wherein the metallization rate is 70% or more.

7. 2. The method for reducing carbon oxides according to claim 1, wherein the reduced iron is reduced with a reducing gas containing 50% by volume or more of hydrogen, or reduced iron having a carbon content of 2.14% by mass or less.

8. The gas flowing into the reactor is the total volume of the hydrogen, the carbon dioxide, and the carbon monoxide is 75% by volume or more relative to the total volume of the gas; 2. The method for reducing carbon oxides according to claim 1, wherein the total volume of the hydrogen and the carbon monoxide is at least three times the total volume of the water and the carbon dioxide.

9. By reducing the carbon oxides, a product gas containing carbon monoxide is obtained, Separating the carbon monoxide from the product gas; 2. The method of claim 1, wherein the separated carbon monoxide is flowed into the reactor.

10. separating the hydrogen and the carbon dioxide that were not used in the chemical reaction from a product gas obtained after the gas that was flowed into the reactor is subjected to the chemical reaction; 2. The method for reducing carbon oxides according to claim 1, wherein the separated hydrogen and carbon dioxide are flowed into the reactor.

11. When a predetermined time has elapsed since the reduced iron was introduced into the reactor, the reduced iron is removed from the reactor; 2. The method for reducing carbon oxides according to claim 1, wherein reduced iron not used as a catalyst is charged into the reactor.

12. 12. The method for reducing carbon oxides according to claim 11, wherein the predetermined time period is between 30 minutes and 1 month.

13. 2. The method for reducing carbon oxides according to claim 1, wherein the reactor is a flow reactor or a batch reactor.

14. A gas containing carbon oxides including at least one of carbon monoxide and carbon dioxide and hydrogen is introduced into a reactor; charging reduced iron into the reactor; reducing the carbon oxides through a chemical reaction using the gas flowing into the reactor as a raw material and the reduced iron as a catalyst; When a predetermined time has elapsed since the reduced iron was introduced into the reactor, the reduced iron is removed from the reactor; The method for producing steel, wherein the reduced iron removed from the reactor is charged into a blast furnace or an electric furnace.

15. 15. The method of claim 14, wherein the chemical reaction comprises at least one of a Sabatier reaction and a direct Fischer-Tropsch reaction.

16. The method of claim 14, wherein the chemical reaction comprises at least one of a methanation reaction and an indirect Fischer-Tropsch reaction.

17. The method of claim 14, wherein the chemical reaction comprises a reverse shift reaction.

18. The method for producing steel according to claim 14, wherein carbon is precipitated in the reduced iron removed from the reactor.

19. When the chemical reaction is carried out, the temperature inside the reactor is 300 to 900°C, and the pressure inside the reactor is atmospheric pressure or higher; The gas flowing into the reactor is The content of sulfur compounds is 10 ppm or less, The method for producing steel according to claim 14, wherein the total volume of the hydrogen and the carbon monoxide is three times or more the total volume of the water and the carbon dioxide.

20. a reactor; an inlet portion for introducing a gas containing hydrogen and carbon oxides including at least one of carbon monoxide and carbon dioxide into the reactor; an input unit that inputs reduced iron into the reactor, a carbon oxide reduction device that reduces the carbon oxides by a chemical reaction using the gas that has been made to flow into the reactor at the inlet section as a raw material and the reduced iron as a catalyst.

21. 21. The apparatus for reducing carbon oxides according to claim 20, wherein the chemical reaction comprises at least one of a Sabatier reaction and a direct Fischer-Tropsch reaction.

22. 21. The apparatus for reducing carbon oxides according to claim 20, wherein the chemical reaction comprises at least one of a methanation reaction and an indirect Fischer-Tropsch reaction.

23. 21. The apparatus for reducing carbon oxides according to claim 20, wherein the chemical reaction comprises a reverse shift reaction.

24. 21. The apparatus for reducing carbon oxides according to claim 20, wherein the reduced iron is in a granular form.

25. The reduced iron is The equivalent particle size is 5 mm or more, a total content of the iron compound, the calcium compound, the silicon compound, the magnesium compound, and the aluminum compound is 90 mass% or more based on the total amount of the reduced iron, the content of the iron compound is 75% by mass or more based on the total amount of the reduced iron, 21. The apparatus for reducing carbon oxides according to claim 20, wherein the metallization rate is 70% or more.

26. 21. The apparatus for reducing carbon oxides according to claim 20, wherein the reduced iron is reduced with a reducing gas containing 50% by volume or more of hydrogen, or reduced iron having a carbon content of 2.14% by mass or less.

27. The gas introduced into the reactor at the inlet section is the total volume of the hydrogen, the carbon dioxide, and the carbon monoxide is 75% by volume or more relative to the total volume of the gas; 21. The apparatus for reducing carbon oxides according to claim 20, wherein the total volume of the hydrogen and the carbon monoxide is three times or more the total volume of the water and the carbon dioxide.

28. 21. The apparatus for reducing carbon oxides according to claim 20, further comprising: a recycling section that separates the carbon monoxide from a product gas containing the carbon monoxide produced by reducing the carbon oxides, and uses the separated carbon monoxide as at least a part of the gas to be flowed into the reactor.

29. separating the hydrogen and the carbon dioxide that were not used in the chemical reaction from a product gas obtained after the chemical reaction of the gas that has flowed into the reactor; 21. The apparatus for reducing carbon oxides according to claim 20, wherein the separated hydrogen and carbon dioxide are flowed into the reactor.

30. the reduced iron production system further includes an unloading unit that unloads the reduced iron from the reactor when a predetermined time has elapsed since the reduced iron was loaded into the reactor by the loading unit, 21. The apparatus for reducing carbon oxides according to claim 20, wherein the input unit inputs reduced iron that is not used as a catalyst into the reactor after the output unit removes the reduced iron from the reactor.

31. 31. The apparatus for reducing carbon oxides according to claim 30, wherein the predetermined time period is between 30 minutes and one month.

32. 21. The apparatus for reducing carbon oxides according to claim 20, wherein the reactor is a flow reactor or a batch reactor.

33. a reactor; an inlet portion for introducing a gas containing hydrogen and carbon oxides including at least one of carbon monoxide and carbon dioxide into the reactor; an input section for inputting reduced iron into the reactor; an unloading unit that unloads the reduced iron from the reactor when a predetermined time has elapsed since the reduced iron was loaded into the reactor by the loading unit; and an iron feeding unit that feeds the reduced iron removed from the reactor by the removal unit into a blast furnace or an electric furnace, In the reactor, the gas flowing into the reactor is used as a raw material, and the carbon oxides are reduced by a chemical reaction using the reduced iron as a catalyst.

34. 34. The apparatus of claim 33, wherein the chemical reaction comprises at least one of a Sabatier reaction and a direct Fischer-Tropsch reaction.

35. 34. The apparatus of claim 33, wherein the chemical reaction comprises at least one of a methanation reaction and an indirect Fischer-Tropsch reaction.

36. 34. The apparatus of claim 33, wherein the chemical reaction comprises a reverse shift reaction.

37. 34. The apparatus for producing steel according to claim 33, wherein the reduced iron removed from the reactor has carbon precipitated thereon.

38. When the chemical reaction is carried out, the temperature inside the reactor is 300 to 900°C, and the pressure inside the reactor is atmospheric pressure or higher; The gas introduced into the reactor through the inlet section is The content of sulfur compounds is 10 ppm or less, 34. The apparatus for producing steel according to claim 33, wherein the total volume of the hydrogen and the carbon monoxide is three times or more the total volume of the water and the carbon dioxide.

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