Reduced iron manufacturing method

Abstract

To provide a novel and improved method for producing reduced iron by which reduced iron can be carbonized even when a reducing gas containing hydrogen gas is used as a reducing gas of a shaft furnace.SOLUTION: A method for producing reduced iron using a shaft furnace, comprising: a reduction step in which a raw material, which is iron oxide, is reduced with a reduction gas containing hydrogen gas to produce reduced iron; a dehydration step in which water is removed from the exhaust gas of the reduction step to separate hydrogen gas from the exhaust gas; a cooling step in which the reduced iron is carbonized and cooled with a cooling gas having carbon as an element; and a separation step in which CO gas and CO2 are separated from the exhaust gas of the cooling step. The cooling gas comprises CO gas. The reduction gas comprises hydrogen gas separated in the dehydration step. The cooling gas further comprises CO gas separated in the separation step.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for producing reduced iron. This application claims priority based on Japanese Patent Application No. 2021-168721, filed on October 14, 2021, the contents of which are incorporated herein by reference. [Background technology]

[0002] Direct reduction ironmaking is known as one of the ironmaking methods for obtaining iron from raw materials containing iron oxide (by reducing the iron oxide). Direct reduction ironmaking has continued to develop due to the low construction costs of the plants required for this process, ease of operation, and the ability to operate in small-scale plants. In particular, various improvements have been made to shaft furnace direct reduction ironmaking processes to make effective use of the reducing gas inside the furnace.

[0003] Furthermore, a method for producing iron carbide by adding a carbonization step to the reduced iron to prevent reoxidation of the reduced iron during transportation is also known. Iron carbide also has the advantage of reducing energy consumption when melting in an electric furnace.

[0004] For example, Patent Documents 1 and 2 describe methods for reducing and carburizing iron ore in a fluidized bed direct reduction ironmaking process, specifying the composition, temperature, and pressure of the reducing gas. Patent Document 3 describes methods for reducing and carburizing iron ore in a shaft furnace direct reduction ironmaking process, specifying the composition, temperature, and pressure of the reducing gas.

[0005] Generally, the decomposition reaction of CH4 (methane gas) is an endothermic reaction, and the higher the temperature and pressure, the more easily it progresses. For example, in the atmospheric pressure MIDREX process, the temperature of the reducing gas is increased by enriching it with O2 when heating it, aiming to increase the carbon concentration of the reduced iron. It is also known that the carbon concentration of reduced iron in the high pressure HYL (ENERGIRON) process is higher than that in the MIDREX process (MIDREX process: carbon concentration of reduced iron 0.5-2.5%, ENERGIRON process: 2.0-4.5%).

[0006] Recently, ACT (registered trademark) (Adjustable Carbon Technology) has been developed with the aim of improving the carbon concentration of reduced iron in the MIDREX process (Non-Patent Document 1). In this process, a portion of the natural gas reformed in the reformer is cooled, compressed, and subjected to membrane separation to separate the natural gas into CO2-rich gas and H2-rich gas. The H2-rich gas is then returned to the process gas (i.e., injected into the reduction zone), and the CO2-rich gas is mixed with natural gas and injected into the transition zone, thereby improving and controlling the carbon concentration of the reduced iron. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 11-343512 [Patent Document 2] Japanese Patent Application Publication No. 5-222423 [Patent Document 3] Japanese Patent Publication No. 8-120314 [Non-patent literature]

[0008] [Non-Patent Document 1] http: / / www.midrex.com / wp-content / uploads / MIDREX-ACT-fpo-Brochure.pdf, published September 2017 [Non-patent document 2] Mizutani et al.: CAMP-ISIJ, 33(2020), 483. Summary of the Invention [Problem to be solved by the invention]

[0009] Recently, with the aim of reducing carbon dioxide emissions from the steel industry, development of direct reduction ironmaking processes using hydrogen gas as a reducing gas has been progressing. Typical examples include HYBRIT and MIDREX+H2, which use hydrogen gas obtained by water electrolysis or other methods in shaft furnace direct reduction ironmaking processes. However, because these processes use hydrogen gas as a reducing gas, the reduced iron cannot be recarburized, and a large amount of energy is required for the melting process in an electric furnace.

[0010] Therefore, an object of the present invention is to provide a new and improved method for producing reduced iron that is capable of carburizing reduced iron even when a reducing gas containing hydrogen gas is used as the reducing gas in a shaft furnace. [Means for solving the problem]

[0011] In order to solve the above problems, the gist of the present invention is as follows. (1) A method for producing reduced iron according to aspect 1 of the present invention includes the steps of: A method for producing reduced iron using a shaft furnace, comprising: The method includes a reduction step of reducing a raw material, which is iron oxide, with a reducing gas containing hydrogen gas to produce reduced iron, a dehydration step of removing water from the exhaust gas of the reduction step to separate hydrogen gas from the exhaust gas, a cooling step of cooling the reduced iron while carbonizing it with a cooling gas containing carbon as an element, and a separation step of separating CO gas and CO from the exhaust gas of the cooling step. Has, the cooling gas includes CO gas; the reducing gas contains the hydrogen gas separated in the dehydration step, The cooling gas further contains the CO gas separated in the separation step. (2) A method for producing reduced iron according to aspect 2 of the present invention includes the steps of: In the method for producing reduced iron according to aspect 1, The method further includes a carbon gasification step of gasifying char or coke with CO gas to produce CO gas, The CO2 gas provided in the carbon gasification step includes the CO2 gas separated in the separation step, The cooling gas is the CO gas produced in the carbon gasification process. (3) A third aspect of the present invention is the method for producing reduced iron according to the first aspect, The method further includes a second dehydration step of separating water from the exhaust gas from the cooling step and introducing the exhaust gas into the separation step, and a coal carbonization step of carbonizing coal to produce a coal carbonization gas, The separation step is performed by separating a mixed gas further including methane gas and hydrogen gas produced from the second dehydration step and the coal carbonization step in addition to CO gas and CO gas. Separating hydrogen gas, a mixed gas of CO gas and methane gas, and CO gas; the cooling gas is the mixed gas, In the coal pyrolysis step, the CO2 gas separated in the separation step is used to produce the coal pyrolysis gas. (4) A fourth aspect of the present invention is a method for producing reduced iron according to any one of the first to third aspects, a shaft furnace having, in order from the bottom, a reduced iron discharge section at the bottom for discharging the reduced iron cooled while being carbonized, a cooling gas inlet, a cooling gas outlet, a reducing gas inlet, a reducing gas outlet, and a raw material charging section at the top for charging the raw material, which is iron oxide; In the reduction step, the raw material is reduced with the reducing gas in a reduction zone between the reducing gas inlet and the reducing gas outlet to generate the reduced iron, In the cooling step, the reduced iron is cooled while being carbonized by the cooling gas in a cooling zone between the cooling gas inlet and the cooling gas outlet. [Effects of the Invention]

[0012] According to the above viewpoint, even when a reducing gas containing hydrogen gas is used as the reducing gas in the shaft furnace, it is possible to carburize the reduced iron. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a flow chart illustrating a method for producing reduced iron according to a first embodiment of the present invention. [Figure 2]FIG. 4 is a flow chart illustrating a method for producing reduced iron according to a second embodiment of the present invention. [Figure 3] FIG. 10 is a flow chart illustrating a method for producing reduced iron according to a third embodiment of the present invention. [Figure 4] FIG. 10 is a flow chart illustrating a method for producing reduced iron according to a fourth embodiment of the present invention. [Figure 5] FIG. 1 is a flow diagram illustrating an example of a direct reduction system according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, the present embodiment will be described in detail with reference to the drawings. Note that a numerical range indicated using "to" includes the numerical values ​​on both ends of the "to".

[0015] <1. Manufacturing method of reduced iron> The method for producing reduced iron of the present invention will be described below with reference to FIGS. The present invention is a method for producing reduced iron that produces partially carbonized reduced iron using iron oxide as a raw material, and basically comprises a reduction step S1 in which reduced iron is produced by reducing an iron oxide raw material using hydrogen gas as a reducing gas, a dehydration step S3 in which water is removed from the exhaust gas (reduced exhaust gas) of the reduction step S1 to separate hydrogen gas from the exhaust gas, a cooling step S2 in which gas containing carbon as an element is used as a cooling gas to cool the reduced iron produced in the reduction step S1 while partially carbonizing it, and a separation step S4 in which at least a gas containing carbon is separated from the exhaust gas (cooled exhaust gas) of the cooling step S2. The raw materials targeted by this invention are iron ore, mainly composed of iron oxide, and pellets made from iron ore. These may be those used in existing direct reduction processes, and do not require any special pretreatment. According to the present invention, it is possible to produce partially carburized reduced iron even when direct reduction is performed with hydrogen gas. Furthermore, since the separated gas is circulated, efficient gas usage can be achieved.

[0016] The present invention can be defined as various methods for producing reduced iron, as described below, taking into consideration the type of cooling gas, the presence or absence of in-situ production processes for hydrogen gas and CO gas, and differences in gas production methods. Here, from a practical standpoint, methane gas, CO gas, or a mixture of the two is used as the gas containing carbon as an element, but higher hydrocarbons such as propane can also be used.

[0017] (Method for producing reduced iron according to the first embodiment) The method for producing reduced iron according to the first embodiment (FIG. 1) includes a reduction step S1 in which a raw material, which is iron oxide, is reduced with hydrogen gas to produce reduced iron, a dehydration step S3 in which water is removed from the exhaust gas of the reduction step S1 to separate hydrogen gas from the exhaust gas, a cooling step S2 in which the reduced iron is cooled while being carbonized with methane gas, and a separation step S4 in which the exhaust gas of the cooling step S2 is separated into hydrogen gas and methane gas. The hydrogen gas separated in the dehydration step S3, the hydrogen gas separated in the separation step S4, and the methane gas separated in the separation step S4 are circulated as reducing gas and cooling gas, respectively.

[0018] In the reduction step S1, iron oxide is reduced to reduced iron with hydrogen gas. The hydrogen gas is supplied from a reservoir (for example, a gas tank). In the reduction step S1, the reducing gas further includes the hydrogen gas separated in the dehydration step S3 and the hydrogen gas separated in the separation step S4, in addition to the hydrogen gas supplied from the outside (for example, a gas tank). The hydrogen gas may be mixed with other types of gas (for example, nitrogen gas, CO gas, CH4 gas, etc.) within a range that does not impair the effects of this embodiment. The temperature of the hydrogen gas supplied in the reduction step S1 is 700 to 1000°C, and the supply amount is 1000 to 2200 Nm 3 / t-DRI (flow rate per ton of reduced iron (DRI)). The chemical reaction formula for reduction step S1 is shown in equation (1). The metallization rate of the reduced iron produced in reduction step S1 (metallic iron concentration / total iron concentration x 100) is 65-98%. Here, the metallic iron concentration is measured according to ISO 5416, "Measuring metallic iron in reduced iron," using bromine-methanol titration, and the total iron concentration is measured according to JIS M 8212: 2005, "Iron ore - Total iron determination method." Fe2O3+3H2→2Fe+3H2O (1) Since hydrogen gas reacts with iron oxide to form water (water vapor), the reduction exhaust gas discharged from the reduction step S1 consists of water vapor and unreacted hydrogen gas. The reduction exhaust gas is the gas discharged after the reduction reaction in the reduction step S1.

[0019] The reduced exhaust gas is dehydrated in the dehydration step S3, where water is removed and hydrogen is separated. In the dehydration step S3, the reduced exhaust gas is cooled below its dew point, where it is separated into unreacted hydrogen gas and water. The water is discharged outside the system, and the unreacted hydrogen gas is circulated as reducing gas.

[0020] In the cooling step S2, the reduced iron produced in the reduction step S1 is cooled with methane gas. This methane gas is, for example, a gas derived from natural gas. The cooling gas further contains methane gas separated in the separation step S4 in addition to methane gas supplied from the outside (a liquefied natural gas tank). The methane gas may be mixed with other types of gases as long as the effects of this embodiment are not impaired. The methane gas is supplied from a reservoir (for example, a liquefied natural gas tank). The temperature of the methane gas when introduced into the cooling step S2 is 0 to 100°C, and the injection amount is 0 Nm 3 / t-DRI super 400Nm 3 In the cooling step S2, the reduced iron is cooled and carbonized by methane gas. The chemical reaction formula at this time is shown in the following formula (2). The metallization rate of the reduced iron is 70 to 98%, and the amount of carbon contained in the reduced iron is 0 Nm 3 / t-DRI is more than 4.5 mass% or less. The volume ratio of the methane gas separated in the separation step S4 to the total volume of the cooling gas is, for example, 45 vol% to 55 vol%. The volume ratio of the methane gas newly introduced from outside to the total volume of the cooling gas is 45 vol% to 55 vol%. 3Fe+CH4→Fe3C+2H2(2) Since methane gas reacts with reduced iron to form hydrogen gas, the cooled exhaust gas discharged from the cooling step S2 consists of hydrogen gas and unreacted methane gas. The cooled exhaust gas is the gas discharged after cooling in the cooling step S2.

[0021] In the separation step S4, at least hydrogen gas is separated from the exhaust gas (cooled exhaust gas) from the cooling step S2. Specifically, in the separation step S4, the exhaust gas from the cooling step S2 is separated into hydrogen gas and methane gas. For example, a membrane separation method can be used for the separation. The pressure during membrane separation is 1.0 to 2.0 MPa, and the temperature is 0 to 100°C. The separated methane gas is circulated as a cooling gas, and the separated hydrogen gas (H2) is circulated as a reducing gas. If H2 is not separated in the separation step, the H2 concentration in the cooling step increases, and the rate of the carburization reaction with CH4 decreases. This reduces the carbon concentration (C concentration) of the reduced iron. Furthermore, by circulating the separated H2 as a reducing gas, the amount of H2 introduced from outside in the reduction step can be reduced. This allows for cost reduction.

[0022] The concentration of the separated hydrogen gas is preferably 95 vol% or more. The upper limit of the concentration of the separated hydrogen gas is not particularly limited and may be 100 vol%. The concentration of the separated methane gas is preferably 95 vol% or more.

[0023] The upper limit of the concentration of the separated methane gas is not particularly limited, and may be 100 vol %.

[0024] The reduced iron manufacturing method of the first embodiment is characterized by the use of methane gas as the cooling gas, as compared with other methods described later. The reduced iron manufacturing method of the first embodiment can decompose methane gas in the cooling step S2, which makes it possible to omit the conventional reforming step for producing reducing gas, and to efficiently obtain reducing gas.

[0025] (Method for producing reduced iron according to the second embodiment) The reduced iron manufacturing method of the second embodiment (FIG. 2) includes a reduction step S1A in which a raw material, which is iron oxide, is reduced with hydrogen gas to produce reduced iron; a dehydration step 3A in which water is removed from the exhaust gas of the reduction step S1A to separate hydrogen gas from the exhaust gas; a cooling step S2A in which the reduced iron produced in the reduction step S1A is cooled while being carbonized with CO gas; and a separation step S4A in which the cooled exhaust gas discharged from the cooling step S2A is separated into CO gas and CO gas. The hydrogen gas separated in the dehydration step 3A and the CO gas separated in the separation step S4A are circulated as reducing gas and cooling gas, respectively.

[0026] In the method for producing reduced iron according to the second embodiment, hydrogen gas and CO gas are supplied from an external source, stored in a reservoir, and then used. The hydrogen gas and CO gas can also be obtained by separating coal gas obtained by coal gasification. Coal gasification is a method for obtaining hydrogen gas and CO gas by decomposing coal using a small amount of oxygen.

[0027] The reduction step S1A and the dehydration step 3A in the method for producing reduced iron according to the second embodiment are the same as those in the method for producing reduced iron according to the first embodiment.

[0028] In the cooling step S2A in the method for producing reduced iron according to the second embodiment, the reduced iron produced in the reduction step S1A is cooled with CO gas, which is a cooling gas. The cooling gas further contains CO gas separated in the separation step S4A in addition to the CO gas supplied from the outside. The CO gas may be mixed with other types of gases as long as the effects of this embodiment are not impaired. The CO gas is supplied from a reservoir (for example, a gas tank). The temperature of the CO gas when introduced into the cooling step S2A is 0 to 100°C, and the blowing amount is 0 Nm. 3 / t-DRI super 400Nm 3 / t-DRI or less. In the cooling step S2A, the reduced iron is cooled and carbonized by CO gas. The chemical reaction formula at this time is represented by the following formula (3). The metallization rate of the reduced iron is 70 to 98%, and the amount of carbon contained in the reduced iron is more than 0 mass% and 4.5 mass% or less with respect to the total mass of the reduced iron. The volume ratio of the CO gas separated in the separation step S4A to the total volume of the cooling gas is preferably 45 vol% to 55 vol%. In the cooling step S2A, the volume ratio of the CO gas newly introduced from outside to the total volume of the cooling gas is preferably 45 vol% to 55 vol%. Fe+2CO→FeC+CO2(3) Since CO gas reacts with reduced iron to become CO2, the cooled exhaust gas discharged from the cooling step S2A consists of CO2 gas and unreacted CO gas.

[0029] In the separation step S4A in the reduced iron production method of the second embodiment, the exhaust gas from the cooling step S2A is separated into CO gas and CO2 gas. For example, chemical absorption (https: / / www.course50.com / technology / technology02 / ) can be used for separation. Chemical absorption is a method in which an alkaline aqueous solution (absorption liquid) of an amine or the like is brought into contact with a CO2-containing gas in an absorption tower to selectively absorb CO2 into the absorption liquid, and then the absorption liquid is heated in a regeneration tower to separate and capture high-purity CO2. The CO2 gas separated in the separation step S4A is circulated as a cooling gas. Meanwhile, the handling of the CO2 gas separated in the separation step S4A is not particularly limited in the reduced iron production method of the second embodiment.

[0030] The concentration of the CO gas separated in the separation step S4A is preferably 99% by mass or more. The concentration of the CO gas may be 100%. The concentration of the CO gas separated in the separation step S4A is preferably 99% by mass or more. The concentration of the CO gas may be 100%.

[0031] The reduced iron manufacturing method of the second embodiment is characterized in that CO gas is used as the cooling gas, as compared with the reduced iron manufacturing method of the first embodiment. Since CO is separated and circulated in the separation step S4A, the cooling gas can be obtained efficiently.

[0032] When coal gas obtained by coal gasification is separated into hydrogen gas and CO gas and used as the hydrogen gas and CO gas supplied in the method for producing reduced iron of the second embodiment, the ratio of hydrogen gas to CO gas in the coal gas can be adjusted by using oxygen gas and steam in combination as decomposition gases in the coal gasification process. Therefore, by adjusting the reducing gas and cooling gas requirements, all required gases can be supplied by coal gasification.

[0033] In the reduced iron production method of the second embodiment, the ratio of hydrogen gas consumed in the reduction step S1A to CO gas consumed in the cooling step S2A is approximately 4:1. Therefore, if all of the cooling CO gas is supplied from aqueous gas (a 1:1 mixed gas of hydrogen gas and CO gas obtained when coal is decomposed using only steam), one-quarter of the reducing hydrogen gas will be supplied from aqueous gas. For example, it is recommended to provide four direct reduction apparatuses based on the reduced iron production method of the second embodiment and one aqueous gas production apparatus. This configuration is efficient because it can provide the reducing hydrogen gas for one apparatus and the cooling CO gas for all four apparatuses.

[0034] (Method for producing reduced iron according to the third embodiment) The reduced iron production method of the third embodiment (FIG. 3) includes, in addition to the reduced iron production method of the second embodiment, a carbon gasification step S5 in which char or coke is gasified with CO gas to produce CO gas. The carbon gasification reaction is a reaction represented by formula (4). By allowing the carbon gasification reaction to proceed at 900°C or higher, the gas produced can be mostly CO gas. C+CO2→2CO (4)

[0035] Here, it is desirable that the char or coke to be gasified have a small residual volatile content so as not to produce hydrogen gas or water vapor, which inhibit the carbonization reaction of the reduced iron in the cooling step S2B. The CO2 gas used in gasification is obtained by circulating the CO2 gas separated in the separation step S5B, and the deficiency is supplied from a reservoir. The amount of CO2 gas supplied from the reservoir to the carbon dioxide gasification step S5 is adjusted so that the cooling gas is the CO2 gas produced in the carbon dioxide gasification step S5, i.e., so that the amount of CO2 produced in the carbon dioxide gasification step S5 matches the amount of CO2 required as cooling gas, thereby eliminating the need to introduce CO2 gas from an external source. The cooled exhaust gas discharged from the cooling step S2B consists of CO2 gas and unreacted CO2 gas. During gasification, oxygen gas can also be used in combination with CO2 gas.

[0036] The reduced iron production method of the third embodiment is different from the reduced iron production method of the second embodiment in that it adds a carbon gasification step S5, and therefore does not release CO2 gas outside the system. Furthermore, the reduced iron production method of the third embodiment has the effect of fixing CO2 gas as carbon in iron carbide, and therefore using the recovered CO2 gas as the CO2 gas supplied from the reservoir also contributes to suppressing CO2 gas release.

[0037] (Method for producing reduced iron according to the fourth embodiment) The reduced iron manufacturing method of the fourth embodiment (FIG. 4) includes a reduction step S1C in which a raw material, iron oxide, is reduced with hydrogen gas to produce reduced iron; a dehydration step S3C in which hydrogen gas is separated from the exhaust gas of the reduction step S1C by removing water from the exhaust gas; a cooling step S2C in which the reduced iron is cooled while carbonizing it with a cooling gas that is a mixture of CO2 and methane; a coal carbonization step S7 in which coal is carbonized to produce coal carbonization gas; another dehydration step (second dehydration step) S6 in which water is separated from the exhaust gas of the cooling step S2C; and a separation step S4C in which the dehydrated cooled exhaust gas and coal carbonization gas are separated into hydrogen gas, a mixture of CO2 and methane, and CO2 gas. The separated hydrogen gas and mixture are circulated as part or all of the reducing gas and cooling gas, respectively. CO2 gas is also used in the coal carbonization step S7.

[0038] The reduction step S1C and the dehydration step S3C in the method for producing reduced iron according to the fourth embodiment are the same as the reduction step S1 and the dehydration step S3 in the method for producing reduced iron according to the first embodiment.

[0039] In the cooling step S2C in the method for producing reduced iron according to the fourth embodiment, cooling is performed with a mixed gas of methane gas and CO gas. The cooling gas is the mixed gas of methane gas and CO gas separated in the separation step S4C. The mixed gas temperature when introduced into the cooling step S2C is 0 to 100°C, and the blowing amount is 0 Nm 3 / t-DRI super 400Nm 3 In the cooling step S2C, the reduced iron is cooled and carbonized by the mixed gas. At this time, the carbonization reactions of formulas (2) and (3) proceed simultaneously. The metallization rate of the reduced iron is 70 to 98%, and the amount of carbon contained in the reduced iron is more than 0 mass% and not more than 4.5 mass% with respect to the total mass of the reduced iron.

[0040] Furthermore, since oxygen and hydrogen coexist as elements in the cooling gas, water is also produced in parallel, for example, according to formula (4). The method for producing reduced iron of the fourth embodiment has another dehydration step (second dehydration step) S6 in which water is separated from the cooling exhaust gas in order to discharge this water out of the system. CO2+H2→H2O+CO (4)

[0041] In the separation step S4C, the cooled flue gas after the second dehydration step S6 and the coal carbonization gas produced in the coal carbonization step S7 are separated into hydrogen gas, a mixed gas of methane gas and CO gas, and CO gas. The separation step S4C includes a single step or multiple steps for separating the dehydrated cooled flue gas and coal carbonization gas. For example, a membrane separation method can be used for the separation. In a single step, the dehydrated cooled flue gas (the cooled flue gas after the second dehydration step S6) and the coal carbonization gas may be separated into hydrogen gas, a mixed gas of methane gas and CO gas, and CO gas. In multiple steps, the dehydrated cooled flue gas and coal carbonization gas may be separated into hydrogen gas, a mixed gas of methane gas and CO gas, and CO gas.

[0042] When separation is performed in multiple steps, in the first step, only CO2 gas is separated from the dehydrated cooled exhaust gas and coal carbonization gas. In the second step, CO2 gas is separated and CO gas is separated from the gas remaining (first residual gas). In the third step, CO gas is separated from the first residual gas and methane gas is separated from the gas remaining (second residual gas). In the fourth step, methane gas is separated from the second residual gas and hydrogen gas is separated from the gas remaining (third residual gas). CO gas and methane gas are mixed and used as a mixed gas. The separation method may be changed, for example, CO2 gas is separated in the first step using chemical adsorption and pressure swing adsorption is used in the second to fourth steps.

[0043] The coal carbonization gas is, for example, coke oven gas. The pressure during membrane separation is 1.0 to 2.0 MPa, and the temperature is 0 to 100°C. The separated mixed gas is circulated as a cooling gas, and the hydrogen gas is circulated as a reducing gas. In the coal carbonization step S7, the CO2 gas separated in the separation step S4C is used to produce the coal carbonization gas.

[0044] The reduced iron manufacturing method of the fourth embodiment, in addition to the reduced iron manufacturing method of the first embodiment and the reduced iron manufacturing method of the second embodiment, further includes a coal carbonization step S7 of carbonizing coal to produce coal carbonization gas. Coal carbonization is a process in which coal is heated to 1100°C using, for example, a coke oven to gasify the volatile components in the coal and obtain char or coke. The coal carbonization gas is a gas generated when coal is carbonized and contains hydrogen gas, methane gas, and CO gas. The coal carbonization gas contains approximately 50 vol% H2, 30 vol% CH4, and 8 vol% CO.

[0045] The method for producing reduced iron according to the fourth embodiment includes the coal carbonization step S7, and can produce reducing gas and cooling gas in the system. Furthermore, by changing the type of coal, the ratio of hydrogen gas and other components in the coal carbonization gas can be adjusted. For example, the lower the coal rank, such as lignite, the higher the hydrogen gas content. Therefore, by adjusting the type of coal, it is possible to supply both the reducing gas and the cooling gas from the coal carbonization gas alone.

[0046] (Method for producing reduced iron according to the fifth embodiment) The method for producing reduced iron of the present invention is preferably carried out using one shaft furnace. As shown in Fig. 5, the shaft furnace is provided with, in order from the bottom 25A, a reduced iron discharge section 25 for discharging carbonized and cooled reduced iron at the bottom 25A, a cooling gas inlet 26, a cooling gas outlet 27, a reducing gas inlet 28, and a reducing gas outlet 29, and a raw material charging section 24 at the top 24A for charging the raw material, which is iron oxide. A cooling step S2 is performed in a cooling zone between the cooling gas inlet 26 and the cooling gas outlet 27. In the cooling step S2, the reduced iron is cooled while being carbonized by the cooling gas in the cooling zone between the cooling gas inlet 26 and the cooling gas outlet 27. A reduction step S1 is performed in a reduction zone between the reducing gas inlet 28 and the reducing gas outlet 29. In the reduction step S1, the raw material, which is iron oxide, is reduced with a reducing gas (hydrogen gas) in the reduction zone between the reducing gas inlet 28 and the reducing gas outlet 29 to produce reduced iron.

[0047] Specifically, in an embodiment using a shaft furnace, heated hydrogen gas is blown into the lower part of the reduction zone, while methane gas is blown into the lower part of the cooling zone. Iron oxide, the raw material charged from the upper part of the shaft furnace, descends while being reduced by hydrogen gas in the reduction zone.

[0048] Meanwhile, hydrogen gas rises while reducing the iron oxide. Unreacted hydrogen gas and water (steam) produced by the reduction of iron oxide are extracted from the top of the reduction zone as reduction exhaust gas. The reduction exhaust gas is cooled and separated into hydrogen gas and water (liquid). The hydrogen gas is circulated as reduction gas.

[0049] In the cooling zone, the reduced iron descends while being cooled and carbonized by the methane gas. The partially carbonized reduced iron is then discharged from the bottom of the cooling zone. Meanwhile, the methane gas ascends while carbonizing the reduced iron. During this process, hydrogen gas is generated by the reaction between the reduced iron and the methane gas. A cooled exhaust gas, which is a mixture of hydrogen gas and unreacted methane gas, is discharged from the top of the cooling zone. The cooled exhaust gas is separated into hydrogen gas and methane gas. The methane gas is circulated as a cooling gas, and the hydrogen gas is circulated as a reducing gas.

[0050] The reduced iron production method of the present invention can be carried out using one shaft furnace divided into a reduction zone and a cooling zone as described above, or can be carried out using two shaft furnaces in series, or can be carried out using one shaft furnace in two stages as shown in the examples.Furthermore, the method is not limited to a shaft furnace, and can also be carried out using a multi-stage fluidized bed.

[0051] <2. Direct Rebate System Configuration> A method using one shaft furnace divided into a reduction zone and a cooling zone will be described in detail below with reference to Fig. 5. Fig. 5 is a diagram showing the configuration of a direct reduction system 10-1 according to this embodiment. The direct reduction system 10-1 is a system for implementing the reduced iron production method according to this embodiment, and includes a shaft furnace 20, a heating furnace 30, a cooling device 40, a compressor 50, a cooling device 60, a compressor 70, and a separator 80. The shaft furnace 20 includes the raw material charging section 24, the reduced iron discharge section 25, the cooling gas inlet 26, the cooling gas outlet 27, the reducing gas inlet 28, and the reducing gas outlet 29 described above.

[0052] The shaft furnace 20 is divided into a reduction zone 21, a transition zone 22, and a cooling zone 23. The reduction zone 21 is a region between the center of the reducing gas inlet 28 and the center of the reducing gas outlet 29, and is a region where the oxidized iron raw material is reduced to iron. The transition zone 22 is a region between the center of the cooling gas outlet 27 and the center of the reducing gas inlet 28, and is a material seal region that separates the reduction zone and the cooling zone. The cooling zone 23 is a region between the center of the cooling gas inlet 26 and the center of the cooling gas outlet 27, and is a region where the reduced iron produced in the reduction zone is cooled while being carbonized.

[0053] In the reduction zone 21, heated hydrogen gas is injected as a reducing gas from a reducing gas inlet 28 at the bottom of the reduction zone. The hydrogen gas includes gas supplied from outside the system as well as gas circulated in a process described below. The hydrogen gas supplied from outside the system is, for example, hydrogen gas produced by electrolysis of water.

[0054] Iron oxide as a raw material is charged into the shaft furnace 20 through a raw material charging section 24 at the top of the shaft furnace 20. The iron oxide is reduced by hydrogen gas as it descends in the reduction zone 21 to become reduced iron.

[0055] A mixed gas of unreacted hydrogen gas and water (steam) generated by the reduction of iron oxide is discharged from a reduction gas outlet 29 at the top of the reduction zone 21. After passing through a transition zone 22, the reduced iron descends from the reduction zone 21 to a cooling zone 23.

[0056] In the cooling zone 23, methane gas is blown in as a cooling gas from a cooling gas blowing port 26 at the bottom of the cooling zone 23 (a cooling gas blowing step).

[0057] Meanwhile, methane gas rises while carbonizing the reduced iron. Hydrogen gas is generated by the reaction between the reduced iron and methane gas. A cooled exhaust gas consisting of hydrogen gas and unreacted methane gas is discharged from a cooled gas outlet 27 at the top of the cooling zone (cooled exhaust gas discharge step).

[0058] The heating furnace 30 heats the hydrogen gas and then injects it into the lower part of the reduction zone 21. The cooling device 40 cools the reduction exhaust gas (a mixed gas of unreacted hydrogen gas and water (steam) generated by the reduction of iron oxide) extracted from the upper part of the reduction zone 21 to dehydrate it and separate the hydrogen gas (dehydration step S3). The hydrogen gas is compressed by the compressor 50 and then introduced into the heating furnace 30. That is, the hydrogen gas is circulated as a reducing gas.

[0059] The cooled exhaust gas (a mixed gas of hydrogen gas generated in the cooling zone and unreacted methane gas) extracted from the upper part of the cooling zone is cooled by the cooling device 60. The cooled exhaust gas is then compressed by the compressor 70. The cooled exhaust gas is then introduced into the separation device 80. The separation device 80 separates the cooled exhaust gas into hydrogen gas and methane gas, for example, by membrane separation or the like (separation step S4). The methane gas is circulated as a cooling gas, and the hydrogen gas is circulated as a reducing gas. That is, the methane gas is blown into the lower part of the cooling zone 23, and the hydrogen gas is introduced into the heating furnace 30.

[0060] <3. Method for producing reduced iron according to this embodiment> Next, a method for producing reduced iron using the above-described direct reduction system 10-1 will be described. First, hydrogen gas is heated in a heating furnace 30 and then introduced into the lower part of the reduction zone 21. The temperature of the hydrogen gas is approximately 700 to 1000°C. The injection rate of the hydrogen gas is approximately 1000 to 2200 Nm3. 3The process is / t-DRI. Meanwhile, iron oxide, the raw material, is charged from the top of the reduction zone 21. As the iron oxide descends within the reduction zone 21, it is reduced by hydrogen gas to form reduced iron. As the hydrogen gas ascends within the reduction zone 21, it reduces the iron oxide. The chemical reaction at this time is represented by the above-mentioned formula (1). The metallization rate is approximately 65 to 98%.

[0061] A reduction exhaust gas, which is a mixed gas of unreacted hydrogen gas and water (water vapor) generated by the reduction of iron oxide, is extracted from the upper part of the reduction zone 21. A cooling device 40 cools the reduction exhaust gas extracted from the upper part of the reduction zone 21 and separates it into water (liquid) and hydrogen gas. The hydrogen gas is compressed by a compressor 50 and then introduced into the heating furnace 30. That is, the hydrogen gas is circulated as a reducing gas.

[0062] Meanwhile, the reduced iron descends through the transition zone 22 into the cooling zone 23. Methane gas is injected as a cooling gas from the bottom of the cooling zone 23 (cooling gas injection step). The temperature of the methane gas is approximately 0 to 100°C, and the injection rate is 0 Nm 3 / t-DRI super 400Nm 3 In the cooling zone 23, the reduced iron descends while being cooled and carbonized by methane gas.

[0063] The carbonized reduced iron is then discharged from the bottom of the cooling zone. The metallization rate of the reduced iron is approximately 70 to 98%, and the amount of carbon contained in the reduced iron is approximately more than 0 mass% and 4.5 mass% or less with respect to the total mass of the reduced iron.

[0064] Meanwhile, methane gas rises while carbonizing the reduced iron. Hydrogen gas is generated by the reaction between the reduced iron and methane gas. A cooled exhaust gas containing hydrogen gas and unreacted methane gas is discharged from the top of the cooling zone 23 (cooled exhaust gas discharge step).

[0065] The cooled exhaust gas extracted from the upper part of the cooling zone 23 is cooled by the cooling device 60 (cooling step). Next, the cooled exhaust gas is compressed by the compressor 70. Next, the cooled exhaust gas is introduced into the separation device 80. The separation device 80 separates the cooled exhaust gas into hydrogen gas and methane gas by, for example, membrane separation (separation step). The pressure during the separation step is approximately 1.0 to 2.0 MPa, and the temperature is 0 to 100°C. The methane gas is circulated as a cooling gas, and the hydrogen gas is circulated as a reducing gas. That is, the methane gas is blown into the lower part of the cooling zone 23, and the hydrogen gas is introduced into the heating furnace 30.

[0066] As described above, according to this embodiment, even when a reducing gas containing hydrogen gas is used as the reducing gas in the shaft furnace, it is possible to carburize the reduced iron. Furthermore, since the methane gas separated in the separation process is circulated as a cooling gas, the methane gas can be used efficiently. Furthermore, since the hydrogen gas separated in the separation process is blown into the reduction zone 21, the hydrogen gas can be used efficiently. Furthermore, the amount of CO2 generated is zero.

[0067] Furthermore, because methane gas is used as the cooling gas, the amount of cooling gas is reduced due to the endothermic reaction of the methane gas. As a result, the compressor 70 can be downsized. Furthermore, because hydrogen gas generated within the system is circulated as the reducing gas, the amount of hydrogen gas supplied from outside the system can be reduced. Furthermore, carbonizing the reduced iron can suppress reoxidation of the reduced iron. Furthermore, because the reduced iron contains carbon, energy consumption in the electric furnace is reduced (the melting of the reduced iron in the electric furnace is promoted; a small amount of carbon rapidly increases the solubility). [Example]

[0068] Next, examples of this embodiment will be described. In the following examples, the reduction step and the cooling step were carried out separately using an adiabatic countercurrent moving bed shaft furnace simulator (hereinafter referred to as a shaft-type test apparatus or simply as the apparatus) with a height of 4 m and a diameter of 100 mm, as described in Non-Patent Document 2. Note that the examples described below are examples of the present invention, and the present invention is not limited to the following examples.

[0069] Example 1 In Example 1, a shaft-type test apparatus was used. Brazilian acid pellets (iron content: 65.9%, SiO2: 3.1%) were supplied from the top as the iron oxide raw material, and the following reduction treatment was performed. The "top" refers to the very top of the apparatus. First, a gas (a mixture of hydrogen gas, CO gas, and CO2 gas) with the composition shown in Table 1 was blown into the bottom of the apparatus. The bottom of the apparatus is located 0.75 m above the bottom. In Table 1, "Inlet" indicates the composition of the gas blown into the bottom of the apparatus (input gas), and "Outlet" indicates the composition of the gas discharged from the top of the apparatus (output gas). The top of the apparatus refers to the position 0.25 m below the top of the apparatus. The composition values ​​in Table 1 and the tables described below indicate the volume percentage of each component relative to the total gas. The gas composition was measured using a gas chromatography-mass spectrometry (GC / MS). Specifically, each gas was supplied to the GC / MS, and the components of each gas were continuously measured. The values ​​in the tables indicate their average values. The input gas temperature was 950°C and the flow rate was 1400 Nm 3 The reduced iron discharged from the bottom of the device had a metallization rate of 96%, and the carbon content of the reduced iron was 1.5 mass%. The bottom of the device refers to the very bottom of the device. The carbon content was measured in accordance with JIS G 1211-3, combustion-infrared absorption method.

[0070] [Table 1]

[0071] Next, the discharged reduced iron was again fed from the top of the shaft-type test device, and a gas (methane gas) with the composition shown in Table 2A was blown into the bottom of the device. Inlet in Table 2A shows the composition of the gas blown into the bottom of the device (input gas), and Outlet shows the composition of the gas discharged from the top of the device. The temperature of the input gas was 25°C, and the flow rate was 150 Nm 3 The reduced iron discharged from the bottom of the apparatus had a metallization rate of 97%, and the carbon content of the reduced iron was 4.5 mass%. The cooled exhaust gas was separated into hydrogen gas and methane gas using a separation membrane. The concentrations of each component in the separated gas are shown in Table 2B. The cooled exhaust gas was cooled and then separated. The separated hydrogen gas was mixed with a reducing gas having the composition shown in Table 1 to reduce iron oxide. The reduced iron had a metallization rate of 96%, and the carbon content of the reduced iron was 1.5 mass%. Similarly, the separated methane gas was mixed with the cooling gas shown in Table 2A and cooled. The reduced iron had a metallization rate of 97%, and the carbon content of the reduced iron was 4.5 mass%. The amount of methane gas from the separation process in the cooling process was 55 vol% of the total volume of the cooling gas, and the amount of newly introduced methane gas was 45 vol% of the total volume of the cooling gas. The separated gas is circulated for reduction and cooling, which reduces the amount of hydrogen that should be supplied through reduction, resulting in reduced energy consumption and cost.

[0072] [Table 2A]

[0073] [Table 2B]

[0074] As described above, according to Example 1, even when hydrogen gas (or a gas mainly composed of hydrogen gas) was used as the reducing gas, reduced iron with a carbon content of 4.5 mass % could be produced.

[0075] Example 2 In Example 2, the same raw materials as in Example 1 were used, and the following reduction treatment was carried out using a shaft-type test apparatus. First, a gas having the composition shown in Table 3, i.e., hydrogen gas (containing a trace amount of nitrogen gas), was blown into the bottom of the apparatus. In Table 3, "Inlet" indicates the composition of the gas blown into the bottom of the apparatus (input gas), and "Outlet" indicates the composition of the gas discharged from the top of the apparatus (output gas). The temperature of the input gas was 980°C, and the flow rate was 1200 Nm 3 The reduced iron discharged from the bottom of the apparatus had a metallization rate of 85%, and the carbon content in the reduced iron was less than 0.1% by mass.

[0076] [Table 3]

[0077] Next, the discharged reduced iron was fed back into the shaft-type test device, and a gas (methane gas) with the composition shown in Table 4A was blown into the bottom of the device. Inlet in Table 4A shows the composition of the gas blown into the bottom of the device (input gas), and Outlet shows the composition of the gas discharged from the top of the device. The temperature of the input gas was 30°C, and the flow rate was 250 Nm 3 The reduced iron discharged from the bottom of the apparatus had a metallization rate of 90%, and the carbon content of the reduced iron was 4.0 mass%. Next, the cooled exhaust gas was separated into hydrogen gas and methane gas using a separation membrane. The concentrations of each component in the separated gas are shown in Table 4B. The cooled exhaust gas was cooled and then separated. The resulting hydrogen gas was mixed with a reducing gas having the composition shown in Table 3 to reduce iron oxide. The reduced iron had a metallization rate of 85%, and the carbon content of the reduced iron was less than 0.1 mass%. The methane gas obtained by similar separation was mixed with a cooling gas having the composition shown in Table 4A and cooled. The reduced iron had a metallization rate of 90%, and the carbon content of the reduced iron was 4.0 mass%. The amount of methane gas from the separation process in the cooling process was 46 vol% of the total volume of the cooling gas, and the amount of newly introduced methane gas was 54 vol% of the total volume of the cooling gas. The separated gas is circulated for reduction and cooling, which reduces the amount of hydrogen that should be supplied through reduction, resulting in reduced energy consumption and cost.

[0078] [Table 4A]

[0079] [Table 4B]

[0080] As described above, according to Example 2, even when hydrogen gas was used as the reducing gas, reduced iron with a carbon content of 4.0 mass % could be produced.

[0081] Example 3 In Example 3, the same raw material as in Example 1 was subjected to the following reduction treatment using a shaft-type test apparatus. First, a gas having the composition shown in Table 5, i.e., hydrogen gas (containing a trace amount of nitrogen gas), was blown into the bottom of the apparatus. In Table 5, "Inlet" indicates the composition of the gas blown into the bottom of the apparatus (input gas), and "Outlet" indicates the composition of the gas discharged from the top of the apparatus (output gas). The temperature of the input gas was 980°C, and the flow rate was 1200 Nm 3 The reduced iron discharged from the bottom of the apparatus had a metallization rate of 85%, and the carbon content in the reduced iron was less than 0.1% by mass.

[0082] [Table 5]

[0083] Next, the discharged reduced iron was fed back into the shaft-type test apparatus, and gas (CO gas) with the composition shown in Table 6A was injected into the lower part of the apparatus. Inlet in Table 6A shows the composition of the gas (input gas) injected into the lower part of the apparatus, and Outlet shows the composition of the gas discharged from the upper part of the apparatus. The temperature of the input gas was 30°C, and the flow rate was 200 Nm 3The reduced iron discharged from the bottom of the apparatus had a metallization rate of 90%, and the carbon content of the reduced iron was 3.5% by mass. The cooled exhaust gas was separated into CO gas and CO2 gas using a separation membrane. The concentrations of the separated gases are shown in Table 6B. The cooled exhaust gas was cooled before separation. The separated CO was mixed with a cooling gas having the composition shown in Table 6A, and the reduced iron was cooled. The metallization rate of the reduced iron was 90%, and the carbon content of the reduced iron was 3.5% by mass. The amount of CO gas from the separation process in the cooling process was 55 vol% of the total volume of the cooling gas, and the amount of newly introduced CO gas was 45 vol% of the total volume of the cooling gas. The separated gas is circulated and cooled, which reduces the amount of CO that would otherwise be supplied through reduction, resulting in reduced energy consumption and cost.

[0084] [Table 6A]

[0085] [Table 6B]

[0086] As described above, according to Example 3, even when hydrogen gas was used as the reducing gas, reduced iron with a carbon content of 3.5 mass % could be produced.

[0087] Example 4 In Example 4, the same raw material as in Example 1 was subjected to the following reduction treatment using a shaft-type test apparatus. First, a gas having the composition shown in Table 7, i.e., hydrogen gas (containing a trace amount of nitrogen gas), was blown into the bottom of the apparatus. In Table 7, "Inlet" indicates the composition of the gas blown into the bottom of the apparatus (input gas), and "Outlet" indicates the composition of the gas discharged from the top of the apparatus (output gas). The temperature of the input gas was 980°C, and the flow rate was 1200 Nm 3 The reduced iron discharged from the bottom of the apparatus had a metallization rate of 85%, and the carbon content in the reduced iron was less than 0.1% by mass.

[0088] [Table 7]

[0089] Next, the discharged reduced iron was fed back into the shaft-type test device, and a gas (a mixture of methane and CO gas) with the composition shown in Table 8A was blown into the bottom of the device. Inlet in Table 8A shows the composition of the gas blown into the bottom of the device (input gas), and Outlet shows the composition of the gas discharged from the top of the device. The temperature of the input gas was 30°C, and the flow rate was 150 Nm 3 The reduced iron discharged from the bottom of the apparatus had a metallization rate of 91%, and the carbon content of the reduced iron was 3.0% by mass. The cooled exhaust gas was separated into hydrogen gas, CO gas, CO2 gas, and methane gas using a separation membrane. The concentrations of each component in the separated gases are shown in Table 8B. The cooled exhaust gas was cooled before separation. HO was separated as liquid water when the cooled exhaust gas was cooled. The separated hydrogen gas was introduced into a reducing gas with the composition shown in Table 7A to reduce iron oxide. The reduced iron had a metallization rate of 85%, and the carbon content of the reduced iron was less than 0.1% by mass. The CO gas and methane gas mixture obtained by separation was mixed with a gas with the composition shown in Table 8A, and the reduced iron was cooled. The reduced iron had a metallization rate of 91%, and the carbon content of the reduced iron was 3.0% by mass. The amount of the mixed gas obtained in the separation step was 55 vol% of the total volume of the cooling gas, and the amount of the newly introduced mixed gas of Table 8A was 45 vol% of the total volume of the cooling gas. The separated gas is circulated for reduction and cooling, which reduces the amount of CO that would otherwise be supplied through reduction, resulting in reduced energy consumption and cost.

[0090] [Table 8A]

[0091] [Table 8B]

[0092] As described above, according to Example 4, even when hydrogen gas was used as the reducing gas, reduced iron with a carbon content of 3.0 mass % could be produced.

[0093] Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person skilled in the art to which the present invention pertains can conceive of various modifications and alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present invention. [Explanation of symbols]

[0094] 10-1 Direct Redemption System 20 Shaft furnace 30 Furnace 40 Cooling device 50 Compressor 60 Cooling device 70 Compressor 80 Separation equipment

Claims

1. A method for producing reduced iron using a shaft furnace, comprising: The present invention includes a reduction step in which a raw material, which is iron oxide, is reduced with a reducing gas, which is hydrogen gas, to produce reduced iron; a dehydration step in which water is removed from the exhaust gas of the reduction step to separate hydrogen gas from the exhaust gas; a cooling step in which the reduced iron is cooled while being carbonized with a cooling gas containing carbon as an element; and a cooling step in which CO gas and CO are extracted from the exhaust gas of the cooling step. ２ and a separation step of separating the Has, the cooling gas includes CO gas; the reducing gas contains the hydrogen gas separated in the dehydration step, The method for producing reduced iron, wherein the cooling gas further contains the CO gas separated in the separation step.

2. A method for producing reduced iron using a shaft furnace, comprising: The method includes a reduction step of reducing a raw material, which is iron oxide, with a reducing gas containing hydrogen gas to produce reduced iron, a dehydration step of removing water from the exhaust gas of the reduction step to separate hydrogen gas from the exhaust gas, a cooling step of cooling the reduced iron while carbonizing it with a cooling gas containing carbon as an element, and a separation step of separating CO gas and CO 2 from the exhaust gas of the cooling step. Has, the cooling gas includes CO gas; the reducing gas contains the hydrogen gas separated in the dehydration step, In the method for producing reduced iron, the cooling gas further contains the CO gas separated in the separation step, CO ２ The method further comprises a carbon gasification step of gasifying char or coke with the gas to produce CO gas; CO provided in the carbon gasification step ２ The gas is the CO separated in the separation step. ２ Contains gas, The method for producing reduced iron, wherein the cooling gas is the CO gas produced in the carbon gasification step.

3. A method for producing reduced iron using a shaft furnace, comprising: The method includes a reduction step of reducing a raw material, which is iron oxide, with a reducing gas containing hydrogen gas to produce reduced iron, a dehydration step of removing water from the exhaust gas of the reduction step to separate hydrogen gas from the exhaust gas, a cooling step of cooling the reduced iron while carbonizing it with a cooling gas containing carbon as an element, and a separation step of separating CO gas and CO 2 from the exhaust gas of the cooling step. Has, the cooling gas includes CO gas; the reducing gas contains the hydrogen gas separated in the dehydration step, In the method for producing reduced iron, the cooling gas further contains the CO gas separated in the separation step, a second dehydration step of separating water from the exhaust gas from the cooling step and introducing the exhaust gas into the separation step; and a coal carbonization step of carbonizing coal to produce a coal carbonization gas, The separation step is performed by separating CO gas and CO ２ a mixed gas further comprising methane gas and hydrogen gas produced from the second dehydration step and the coal carbonization step in addition to the gas; A mixture of hydrogen gas, CO gas and methane gas, and CO ２ gas and, the cooling gas is the mixed gas, In the coal carbonization step, the CO separated in the separation step ２ The coal carbonization gas is produced using the gas.

4. a shaft furnace having, in order from the bottom, a reduced iron discharge section at the bottom for discharging the reduced iron cooled while being carbonized, a cooling gas inlet, a cooling gas outlet, a reducing gas inlet, a reducing gas outlet, and a raw material charging section at the top for charging the raw material, which is iron oxide; In the reduction step, the raw material is reduced with the reducing gas in a reduction zone between the reducing gas inlet and the reducing gas outlet to generate the reduced iron, 4. The method for producing reduced iron according to claim 2, wherein in the cooling step, the reduced iron is cooled while being carbonized by the cooling gas in a cooling zone between the cooling gas inlet and the cooling gas outlet.

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