Method for producing reduced iron and system for producing reduced iron

Abstract

Provided is a method which is for producing reduced iron and by which both energy saving and a reduction in CO2 discharge amount can be achieved. This system is configured to circulate and reuse a furnace top gas, and has a blowing step, a reduction step, a distribution step, a synthesis step, and a reforming step, wherein a distribution ratio of the furnace top gas in the distribution step is controlled according to a composition of a raw material gas used in the reforming step.

Description

Reduced iron manufacturing method and reduced iron manufacturing system

[0001] The present invention relates to a method and a system for producing reduced iron.

[0002] In recent years, steelworks have been strongly required to save energy against the backdrop of global environmental issues and the depletion of fossil fuels. The raw material for iron is mainly iron oxide, and a reduction process to reduce this iron oxide is essential in steelworks. The most common reduction process that is widespread worldwide is the blast furnace. In a blast furnace, coke and pulverized coal react with oxygen in hot air (air heated to about 1200°C) in the tuyere. This reaction produces CO and H, which become reducing gases. ２ These reducing gases reduce iron ore and other materials in the furnace. Thanks to recent improvements in blast furnace operation technology, the reducing agent rate (the amount of coke and pulverized coal used to produce 1 ton of molten iron) has been reduced to around 500 kg / t, which is already close to its lower limit. Therefore, a further significant reduction in the reducing agent rate cannot be expected in blast furnaces.

[0003] Meanwhile, in areas where natural gas is produced, a method of producing reduced iron using a vertical reduction furnace (hereinafter also referred to as a shaft furnace) is also commonly used. In this method, a reduction furnace is filled with agglomerated iron ore such as sintered ore and pellets (hereinafter also simply referred to as iron oxide) as the iron oxide raw material. Then, CO and H are added to the reduction furnace. ２ A reducing gas containing the above is injected to reduce iron oxide, thereby producing reduced iron. In this method, natural gas or the like is used as the raw material gas for the reducing gas. This raw material gas is heated and reformed together with the top gas in a reformer. This generates a reducing gas. Here, the top gas is the gas remaining after the reduction of iron oxide in the reduction furnace, and is generally discharged from the top of the reduction furnace. The generated reducing gas is injected into the reduction furnace and reacts with iron oxide supplied from the top of the reduction furnace. The iron oxide is then reduced to produce reduced iron. The reduced iron is then cooled in a region of the reduction furnace below the position where the reducing gas is injected, and is then discharged from the bottom of the reduction furnace.

[0004] As described above, the furnace top gas is discharged from the reducing furnace, for example, from the furnace top. After dust collection and cooling, part of the furnace top gas is fed to the reformer as a raw material for the reformed gas. The remaining furnace top gas is used as fuel gas for the reformer. In this method, the furnace top gas used as fuel gas for the reformer is usually discharged outside the system.

[0005] As an example of such a reduced iron production process, Patent Document 1 discloses a process in which exhaust gas from a reduction furnace and natural gas are reformed in a reformer to produce mainly CO and H. ２ This reducing gas is blown into a reducing furnace to reduce iron oxide therein, thereby producing reduced iron.

[0006] In addition, Patent Document 2 discloses a method for producing a coke oven gas and CO ２ The document describes a method for producing reduced iron by reforming the top gas of a reducing furnace from which sulfur dioxide has been removed to produce a reducing gas, which is then blown into the reducing furnace.

[0007] JP 2017-88912 A Patent No. 6190522

[0008] In the method described in Patent Document 1, natural gas supplied from an external source is used to produce the reducing gas. Therefore, although the amount of CO is lower than that in a blast furnace, a certain amount of CO is generated. ２ The problem is that emissions are unavoidable.

[0009] Furthermore, the method described in Patent Document 2 produces reducing gas using coke oven gas or converter gas generated in a steelworks. In an integrated steelworks, coke oven gas and converter gas are required as fuel gas for downstream processes such as heating furnaces and annealing furnaces. Therefore, if coke oven gas and converter gas are diverted to the reduced iron production process, a fuel gas shortage will occur in the downstream processes. As a result, natural gas will be supplied from an external source to compensate for the shortage of fuel gas in the downstream processes. In other words, the method described in Patent Document 2 also achieves both energy conservation and CO2 reduction. ２ This could not be achieved simultaneously with a reduction in emissions, and so remained a challenge.

[0010] The present invention has been made in consideration of the above-mentioned current situation, and aims to achieve energy saving and CO ２ It is an object of the present invention to provide a method for producing reduced iron that can simultaneously achieve a reduction in the amount of waste generated. Another object of the present invention is to provide a system for producing reduced iron that can be suitably used for the method for producing reduced iron. In this specification, any numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits, respectively.

[0011] The inventors have been working on the energy conservation and CO ２ After extensive investigations to simultaneously achieve a reduction in the amount of carbon dioxide emitted, the inventors have developed a system for circulating and reusing furnace top gas (hereinafter also referred to simply as a circulation system) that includes the following steps: an injection process in which reducing gas is injected into a reducing furnace, a reduction process in which iron oxide is reduced in the reducing furnace with the reducing gas to obtain reduced iron, a synthesis process in which regenerated methane gas is synthesized from the furnace top gas discharged from the reducing furnace and hydrogen gas, and a reforming process in which reducing gas is obtained from the regenerated methane gas as a raw material gas.

[0012] Furthermore, the inventors have further studied and found the following: Energy saving and CO ２ To achieve stable operation while simultaneously reducing emissions, it is important to maintain a healthy material balance in the above circulation system, especially the C (carbon) material balance. ４ It is necessary to synthesize it stably in high yield.

[0013] Incidentally, the furnace gas usually contains CO ２ At the same time, a certain amount of CO that was not used in the reduction of iron oxide in the reduction furnace is also contained. ２ In addition, CO also releases CH ４ is synthesized, where CO ２ From CH ４ is synthesized, CH ４ is synthesized. Also, CO is converted to CH ４is synthesized, CH according to the methanation reaction formula (ii) ４ is synthesized. ２ +4H ２ → CH ４ +2H ２ O ΔH=-165kJ / mol...(i) CO+3H ２ → CH ４ +H ２ O ΔH=-206kJ / mol...(ii)

[0014] However, in the synthesis process, CO ２ From CH ４ and the conversion of CO to CH ４ It is difficult to simultaneously and appropriately control the conversion rate of ethylene to propylene, and it is difficult to maintain a healthy material balance in the circulation system.

[0015] In addition, CO contained in the furnace gas ２ Separating CO from CO requires a huge PSA (pressure swing adsorption) separation device. However, depending on the equipment specifications, it may not be possible to install such a huge device. Even if such a device could be installed, it is not necessarily desirable from the standpoint of compactness of the entire facility and energy efficiency.

[0016] Therefore, the inventors have further studied the above circulation system and have found that the material balance in the circulation system can be kept healthy by carrying out the following control, that is, by controlling the amount of CO contained in the furnace top gas during the production of reduced iron. ２ and CO without separating them. ２ The inventors have found that this technology makes it possible to stably perform operations that simultaneously achieve a reduction in emissions. The furnace top gas discharged from the reduction furnace is divided into a first furnace top gas and a second furnace top gas. The ratio of the furnace top gas distribution is controlled according to the composition of the raw material gas used in the reforming process. Furthermore, from the viewpoint of preventing catalyst poisoning due to C deposition in the synthesis process, H separated and recovered from the regenerated methane gas is used. ２ When O is supplied to the synthesis step, H ２ H supplied to the synthesis step in the O supply step ２ The flow rate of O (hereinafter referred to as H２ H in the O supply process ２ It is preferable to control the distribution ratio of the furnace top gas in accordance with the flow rate of the H2O (also referred to as the supply flow rate of H2O) and the dehydration rate in the dust removal and dehydration process. ２ The O supply step is performed by separating and recovering H from the regenerated methane gas synthesized in the synthesis step. ２ The dedusting and dehydration step is a step of performing at least one of dedusting and dehydration of the furnace gas.

[0017] The present invention has been completed based on the above findings and further investigations. That is, the gist and configuration of the present invention are as follows.

[0018] 1. A method for producing reduced iron, comprising: a filling step of filling a reduction furnace with iron oxide; an injection step of injecting a reducing gas into the reduction furnace; a reduction step of reducing the iron oxide with the reducing gas in the reduction furnace to obtain reduced iron; a distribution step of distributing a top gas discharged from the reduction furnace into a first top gas and a second top gas; a synthesis step of synthesizing regenerated methane gas from the first top gas and hydrogen gas; and a reforming step of using the regenerated methane gas and the second top gas as raw material gases to obtain the reducing gas from the raw material gas, wherein a distribution ratio of the top gas in the distribution step is controlled depending on the composition of the raw material gas used in the reforming step.

[0019] 2. The distribution ratio Y (%) to the first furnace gas in the distribution step is set to Y ０ 2. The method for producing reduced iron according to 1 above, wherein Y is controlled to a range of ±10%. ０ = x ＣＨ４ / {(x ＣＯ２ +x ＣＯ +x ＣＨ４ ) × η ÷ 100} × 100, and Y ０ : Standard distribution ratio (%) x ＣＯ２ : CO of the raw material gas used in the reforming process ２ Concentration (volume%) x ＣＯ : CO concentration (vol %) of raw material gas used in the reforming process x ＣＨ４ : CH of raw material gas used in the reforming process ４Concentration (volume %) η: methane conversion rate (%) in the synthesis process. ０ If any part of the range of ±10% exceeds 100%, the upper limit of that range shall be 100%. ０ If any part of the range of ±10% is less than 0%, the lower limit of the range shall be 0%.

[0020] 3. The distribution ratio Y (%) to the first furnace gas in the distribution step is set to Y ０ 3. The method for producing reduced iron according to 2 above, wherein Y is controlled to a range of ±5%. ０ If any part of the range of ±5% exceeds 100%, the upper limit of that range shall be 100%. ０ If any part of the range of ±5% is less than 0%, the lower limit of the range shall be 0%.

[0021] 4. H is generated from the regenerated methane gas between the synthesis step and the reforming step. ２ Separating and recovering O, ２ O separation and recovery step; ２ O is supplied to the synthesis step, ２ 2. The method for producing reduced iron according to 1 above, further comprising: an O supplying step.

[0022] 5. The method further comprises a dust removal and dehydration step of performing at least one of dust removal and dehydration of the furnace gas prior to the distribution step, and the distribution ratio Y (%) to the first furnace gas in the distribution step is set to Y １ 5. The method for producing reduced iron according to 4 above, wherein Y is controlled to a range of ±10%. １ = N Ｈ２Ｏ / (N × z ＣＯ ×2−N×z Ｈ２Ｏ × A) × 100, and Y １ : Standard distribution ratio (%) N Ｈ２Ｏ : H ２ H supplied to the synthesis step in the O supply step ２ O flow rate (Nm ３ / t) N: Flow rate of furnace top gas supplied to the dust removal and dehydration process (Nm ３ / t) z ＣＯ : CO concentration (vol%) of furnace gas supplied to distribution process z Ｈ２Ｏ : H of furnace top gas supplied to distribution process２ O concentration (volume %) A: Dehydration rate in the dust removal and dehydration process. Also, A = 1 - (P １ / P ２ ) and P １ : Saturated vapor pressure (MPa) at the temperature of the furnace gas supplied to the distribution process ２ : Saturated vapor pressure (MPa) at the temperature of the furnace top gas supplied to the dust removal and dehydration process. １ If any part of the range of ±10% exceeds 100%, the upper limit of that range shall be 100%. １ If any part of the range of ±10% is less than 0%, the lower limit of the range shall be 0%.

[0023] 6. The distribution ratio Y (%) to the first furnace gas in the distribution step is set to Y １ 6. The method for producing reduced iron according to 5 above, wherein Y is controlled to a range of ±5%. １ If any part of the range of ±5% exceeds 100%, the upper limit of that range shall be 100%. １ If any part of the range of ±5% is less than 0%, the lower limit of the range shall be 0%.

[0024] 7. The above H ２ The H in the O separation and recovery process ２ 7. The method for producing reduced iron according to any one of 4 to 6, wherein the separation and recovery rate of O is 70 to 90%.

[0025] 8. The above H ２ In the O separation and recovery step, the regenerated methane gas is cooled to 30 to 90°C, thereby ２ 8. The method for producing reduced iron according to any one of 4 to 7, wherein O is separated.

[0026] 9. A system for producing reduced iron, comprising: a reducing furnace; a reducing gas injection device that injects a reducing gas into the reducing furnace; a furnace gas distribution unit that distributes furnace gas discharged from the reducing furnace into a first furnace gas and a second furnace gas; a methane synthesis device that synthesizes regenerated methane gas from the first furnace gas and hydrogen gas; a reformer that uses the regenerated methane gas and the second furnace gas as raw material gases and obtains the reducing gas from the raw material gases; and a control unit, wherein the reducing furnace has: a filling unit that fills iron oxide into the reducing furnace; and a reduction unit that reduces the iron oxide with the reducing gas in the reducing furnace to obtain reduced iron, and the control unit controls the distribution ratio of the furnace gas in the furnace gas distribution unit depending on the composition of the raw material gas used in the reformer.

[0027] 10. The control unit sets the distribution ratio Y (%) of the first furnace top gas in the furnace top gas distribution unit to Y ０ 10. The system for producing reduced iron according to 9 above, wherein Y is controlled within a range of ±10%. ０ = x ＣＨ４ / {(x ＣＯ２ +x ＣＯ +x ＣＨ４ ) × η ÷ 100} × 100, and Y ０ : Standard distribution ratio (%) x ＣＯ２ : CO of the raw material gas used in the reformer ２ Concentration (volume%) x ＣＯ : CO concentration (vol %) of raw gas used in the reformer x ＣＨ４ : CH of raw material gas used in the reformer ４ Concentration (volume%) η: methane conversion rate (%) in the methane synthesis unit. ０ If any part of the range of ±10% exceeds 100%, the upper limit of that range shall be 100%. ０ If any part of the range of ±10% is less than 0%, the lower limit of the range shall be 0%.

[0028] 11. The control unit sets the distribution ratio Y (%) of the first furnace top gas in the furnace top gas distribution unit to Y ０ 11. The system for producing reduced iron according to 10 above, wherein Y is controlled within a range of ±5%.０ If any part of the range of ±5% exceeds 100%, the upper limit of that range shall be 100%. ０ If any part of the range of ±5% is less than 0%, the lower limit of the range shall be 0%.

[0029] 12. A gas supply system for generating H from the regenerated methane gas between the methane synthesis unit and the reformer ２ Separating and recovering O, ２ O separation and recovery device; ２ O is supplied to the methane synthesis unit; ２ 10. The system for producing reduced iron according to 9 above, further comprising an O supply device.

[0030] 13. The furnace gas distribution unit further includes at least one of a dust removal device that removes dust from the furnace gas and a dehydration device that dehydrates the furnace gas, and the control unit adjusts the distribution ratio Y (%) of the first furnace gas in the furnace gas distribution unit to Y １ 13. The system for producing reduced iron according to 12 above, wherein Y is controlled within a range of ±10%. １ = N Ｈ２Ｏ / (N × z ＣＯ ×2−N×z Ｈ２Ｏ × A) × 100, and Y １ : Standard distribution ratio (%) N: Flow rate of furnace top gas supplied to the upstream equipment of the dust removal equipment and dehydration equipment (Nm ３ / t) N Ｈ２Ｏ : H ２ H supplied to the methane synthesis unit by the O supply unit ２ O flow rate (Nm ３ / t) z ＣＯ : CO concentration (vol%) of the furnace gas supplied to the furnace gas distribution section z Ｈ２Ｏ : H of furnace top gas supplied to the furnace top gas distribution section ２ O concentration (volume %) A: Dehydration rate in the dust removal device and dehydration device. Also, A = 1 - (P １ / P ２ ) and P １ : Saturated vapor pressure (MPa) at the temperature of the furnace top gas supplied to the furnace top gas distribution section P ２: Saturated vapor pressure (MPa) at the temperature of the furnace gas supplied to the upstream equipment of the dust removal equipment and the dehydration equipment. １ If any part of the range of ±10% exceeds 100%, the upper limit of that range shall be 100%. １ If any part of the range of ±10% is less than 0%, the lower limit of the range shall be 0%.

[0031] 14. The control unit sets the distribution ratio Y (%) of the first furnace top gas in the furnace top gas distribution unit to Y １ 14. The system for producing reduced iron according to 13 above, wherein Y is controlled within a range of ±5%. １ If any part of the range of ±5% exceeds 100%, the upper limit of that range shall be 100%. １ If any part of the range of ±5% is less than 0%, the lower limit of the range shall be 0%.

[0032] According to the present invention, energy saving and CO ２ Furthermore, according to the present invention, even if the grade of iron ore used during operation fluctuates, it is possible to achieve both energy saving and CO2 reduction. ２ The quality of iron ore refers to the content (% by mass) of Fe contained in the iron ore.

[0033] It is a diagram showing a conventional manufacturing process of reduced iron. It is a diagram showing an example of a manufacturing process of reduced iron by a manufacturing method of reduced iron according to an embodiment of the present invention. It is a schematic diagram showing an example of a schematic configuration of a manufacturing system of reduced iron according to an embodiment of the present invention. It is a schematic diagram showing an example of functional blocks of a control unit.

[0034] [1] Method for Producing Reduced Iron Hereinafter, a method for producing reduced iron according to one embodiment of the present invention will be described with reference to the drawings.

[0035] First, a conventional process for producing reduced iron (hereinafter also referred to as the conventional production process) will be described. Fig. 1 is a diagram showing a schematic configuration of an example of the conventional production process. In Fig. 1, reference numeral 1 denotes a reduction furnace, 1a denotes iron oxide, 1b denotes reduced iron, 3 denotes a dust removal device, 4 denotes a dehydration device, 5 denotes a natural gas supply unit, 6 denotes an air supply unit, 7 denotes a reformer, and 9 denotes a reducing gas injection device.

[0036] In one example of a conventional manufacturing process, iron oxide is charged into the top of a reduction furnace and gradually lowered. High-temperature reducing gas is then blown into the furnace from the center to reduce the iron oxide. The reduced iron is then discharged from the bottom of the reduction furnace. At this time, mainly CO, CO ２ , H ２ and H ２ A furnace top gas containing O is discharged. This furnace top gas is subjected to dust removal in a dust removal device, and a portion thereof is fed to a reformer as a raw material gas after adjusting its moisture content. A gas containing hydrocarbons, for example, natural gas from a natural gas supply unit, is fed to the reformer together with the moisture-adjusted furnace top gas. Next, the fed gas is heated in the reformer. Then, a reforming reaction occurs, and mainly CO and H are produced. ２ A high-temperature reducing gas containing CO is generated. This reducing gas is then blown into the reducing furnace. The remaining part of the furnace gas is dehydrated and then used as a heating fuel in the combustion chamber of the reformer, where it is burned with oxygen in the air, for example. After being burned as a heating fuel, the furnace gas usually contains CO ２ It is discharged from the system still containing

[0037] On the other hand, in a method for producing reduced iron according to one embodiment of the present invention, the furnace top gas discharged from the reducing furnace is divided into a first furnace top gas and a second furnace top gas in a furnace top gas distribution section, as shown in Fig. 2. Then, methane gas (hereinafter also referred to as regenerated methane gas) synthesized from the first furnace top gas and hydrogen gas is used instead of a hydrocarbon gas such as natural gas supplied from an external source in the conventional process shown in Fig. 1. In Fig. 2, reference numeral 1 denotes a reducing furnace, 1a denotes iron oxide, 1b denotes reduced iron, 3 denotes a dust removal device, 4 denotes a dehydration device, 4-1 denotes H ２ O separation and recovery device, 4-2 is H ２2 shows an example in which the regenerated methane gas produced in the methane synthesis unit 11 and the second furnace gas are joined in the gas joining unit 14, and the joined gas is supplied to the reformer 7 to be used as the raw material gas for the reducing gas.

[0038] Each step of the method for producing reduced iron according to one embodiment of the present invention will be described below. Note that the filling step, blowing step, and reducing step may be performed in accordance with a conventional method, for example, in the same manner as in the conventional production process described above, and therefore, description thereof will be omitted here.

[0039] In the distribution step, for example, in a furnace gas distribution section, the furnace gas discharged from the reducing furnace is distributed into a first furnace gas and a second furnace gas. At this time, the composition of the raw material gas used in the reforming step, preferably further including H ２ H in the O supply process ２ It is important to control the distribution ratio of the furnace gas in the distribution step depending on the O supply flow rate and the dehydration rate in the dust removal and dehydration step. The reason for this will be described later. The means for controlling the distribution and flow rate of the furnace gas are not particularly limited and may be conventional. For example, a mass flow controller may be used.

[0040] In the synthesis step, for example, in a methane synthesis apparatus, regenerated methane gas is synthesized from the first furnace top gas distributed in the distribution step and hydrogen gas. ４ is the CO contained in the first furnace gas ２ and at least one of CO and H ２ CO is synthesized according to the methanation reaction formulas (i) and (ii) below. ２ +4H ２ → CH ４ +2H ２ O ΔH=-165kJ / mol...(i) CO+3H ２ → CH ４ +H ２ O ΔH=-206kJ / mol...(ii)

[0041] For example, the first furnace gas and hydrogen gas supplied from outside the circulation system are supplied to a methane synthesis apparatus. Then, in the methane synthesis apparatus, CH ４ is synthesized. ４ The synthesis conditions are not particularly limited, and may be carried out in accordance with conventional methods.

[0042] The composition of the first furnace gas and the second furnace gas described later is basically the same as the composition of the furnace gas. In this case, the composition of the first furnace gas is CO: 5 to 50% by volume, CO ２ : 5 to 30% by volume, H ２ : 5 to 80% by volume, H ２ O: 0 to 35% by volume, balance: 0 to 20% by volume. The composition of the second furnace top gas described below is similar.

[0043] In the synthesis step, in addition to the first furnace gas, CO and CO ２ Any other gas containing at least one of the above (hereinafter also referred to as "other gas") can also be used. Examples of other gases include gases produced as by-products in the steelmaking process, specifically blast furnace gas (BFG) and coke oven gas (COG).

[0044] The source of hydrogen gas used in the synthesis step is not particularly limited, and it may be supplied and produced by any method. Examples of methods for producing hydrogen gas include synthesis by electrolysis of water and synthesis by decomposition of ammonia, hydrocarbons, and organic hydrides. However, when hydrocarbons and organic hydrides are used as raw materials, CO is generated during the hydrogen synthesis process. ２ Therefore, CO ２ From the viewpoint of further reducing CO emissions, it is preferable to synthesize hydrogen by at least one of the electrolysis of water and the decomposition of ammonia. In addition, when producing hydrogen gas by electrolysis of water, green hydrogen produced using electricity obtained from green energy sources such as solar, wind, and geothermal energy can be used to reduce CO emissions. ２ The amount of hydrogen gas emitted can be reduced to virtually zero. ２The concentration is not particularly limited, but is preferably 90% by volume or more, and more preferably 95% by volume or more. ２ The concentration may be 100% by volume.

[0045] Furthermore, the amount of hydrogen gas supplied in the synthesis step (the amount of hydrogen gas supplied to the methane synthesis apparatus) is determined based on the methanation reaction formula shown in the above formula (i) and the amount of CO contained in the first furnace top gas. ２ It is preferred to use a stoichiometric amount.

[0046] CH ４ In the synthesis of , commonly used methanation catalysts can be used. Specifically, transition metal catalysts such as Fe, Ni, Co, and Ru can be used. Among them, Ni-based catalysts have high activity. Ni-based catalysts also have high heat resistance and can be used at temperatures up to about 500°C. Therefore, Ni-based catalysts are particularly preferred. Iron ore may also be used as a catalyst. In particular, high-water-of-crystallization ores have an increased specific surface area when the water of crystallization is dehydrated, making them suitable for use as catalysts.

[0047] The reactor used in the synthesis process of the methane synthesis apparatus can be a fixed-bed reactor, a fluidized-bed reactor, an entrained-bed reactor, or the like. The physical properties of the catalyst can be selected appropriately depending on the type of reactor. In addition, a heat exchanger can be disposed in the gas flow path downstream of the reactor to recover the reaction heat (gas sensible heat) of the methanation reaction in each reactor. The recovered thermal energy can be used, for example, to heat the reduction furnace and the reformer. The recovered thermal energy can also be used to heat other processes, such as the reforming process.

[0048] The methanation catalyst is also ２ It shows a stable high conversion rate during methanation of CO and CO. However, as mentioned above, carbon is produced as an intermediate during methanation of CO. This causes carbon precipitation and catalyst poisoning. In order to prevent such catalyst poisoning, it is necessary to add steam (H ２ It is preferred to add O).

[0049] Furthermore, it is preferable to control the reaction temperature of the synthesis step, that is, the temperature inside the reactor of the methane synthesis apparatus where the methanation reaction occurs, in the range of 200 to 550°C. If the reaction temperature of the synthesis step is less than 200°C, the reaction rate will be slow and the activity of the methanation catalyst may not be sufficient. On the other hand, if the reaction temperature of the synthesis step exceeds 550°C, the deactivation of the catalyst may be accelerated. Furthermore, as shown in the above formulas (i) and (ii), the methanation reaction is an exothermic reaction. Therefore, if the reaction temperature of the synthesis step is excessively high, the reaction equilibrium will shift to the left side (CO ) of the above formulas (i) and (ii). ２ Therefore, it is preferable to control the reaction temperature in the synthesis step within the range of 200 to 550°C.

[0050] In addition, it is preferable to control the pressure in the synthesis step, that is, the pressure in the reactor of the methane synthesis apparatus where the methanation reaction occurs, in the range of 3 to 10 atm. As shown in the above formulas (i) and (ii), the methanation reaction is a molecular reduction reaction. Therefore, according to Le Chatelier's principle, the higher the pressure in the synthesis step, the more the reaction equilibrium shifts to the right (CH ４ This increases the tendency for the methane to be biased toward the NH 3 side, improving the methane yield. However, if the pressure in the synthesis step becomes excessively high, safety issues may arise. Therefore, it is preferable to control the pressure in the synthesis step within the range of 3 to 10 atm.

[0051] Regenerated methane gas CH ４ The concentration is not particularly limited. ２ In the regenerated methane gas from which O has been removed, for example, the regenerated methane gas obtained by dehydrating the gas at the outlet of the methane synthesis unit using a dehydrator, ４ The concentration is preferably 80% by volume or more, more preferably 90% by volume or more. ２ CH in regenerated methane gas excluding O ４ The concentration may be 100% by volume.

[0052] ・H ２ O separation and recovery process H generated as a by-product of methane synthesis ２ If a large amount of O is supplied to the reformer, H２ Therefore, while taking into consideration the material balance of the entire circulation system, H is extracted from the regenerated methane gas between the synthesis step and the reforming step. ２ Separating and recovering O, ２ The method may further include a step of separating and recovering O from the regenerated methane gas. ２ The separation and recovery of O can be performed, for example, by a dehydration device (hereinafter referred to as H ２ This can be done using a device called an O separation and recovery device.

[0053] H ２ H in the O separation and recovery process ２ O separation and recovery rate (hereinafter simply referred to as H ２ The separation and recovery rate of H is preferably 70 to 90%. ２ The separation and recovery rate of O is defined by the following formula: [H ２ O separation recovery rate (%)] = [H ２ H in the O separation and recovery process ２ Separation and recovery amount of O (Nm ３ / t)] / [H contained in the regenerated methane gas synthesized in the synthesis step ２ O amount (Nm ３ / t)] x 100

[0054] In addition, H ２ H in the O separation and recovery process ２ The amount of O separated and recovered can be calculated by, for example, ２ H in the tank that temporarily stores O ２ The change in the amount of O and H from the tank ２ The amount of O discharged can be calculated.

[0055] Also, H ２ To control the separation and recovery rate of O to 70 to 90%, for example, the regenerated methane gas is cooled to 30 to 90°C to reduce the H contained in the regenerated methane gas. ２ O is condensed to produce H from regenerated methane gas. ２ It is preferable to separate O. The cooling method is not particularly limited, and for example, a heat exchanger may be used.

[0056] ・H ２ O supply process H separated and recovered from regenerated methane gas２ O is added to the catalyst in order to prevent the catalyst from being poisoned by the above-mentioned C deposition. ２ The H separated and recovered from the regenerated methane gas may be supplied to the synthesis step after being heated to form steam by an O supply device. ２ The water vapor obtained by heating O does not contain impurities and is already at an appropriate pressure, so there is no need to increase the pressure, making it very advantageous for supplying to the synthesis process. ２ H in the O supply process ２ The supply flow rate of O is preferably controlled (changed) in accordance with the risk of catalyst poisoning in the synthesis step, the reaction rate, and the like. For example, it is preferably controlled within a range of 1.5 to 2.5 equivalents of the amount of CO contained in the first furnace top gas.

[0057] - Combining step: A combining step of combining the regenerated methane gas and the second furnace gas may be optionally provided before the reforming step. In this case, the regenerated methane gas and the second furnace gas are combined and then supplied to the reforming step (combined gas). If the combining step is not provided, the regenerated methane gas and the second furnace gas are supplied separately to the reforming step.

[0058] In the reforming step, the regenerated methane gas and the second furnace gas are used as raw material gases to obtain a reducing gas from the raw material gases. For example, the regenerated methane gas and the second furnace gas are combined as raw material gases, or the regenerated methane gas and the second furnace gas are individually supplied to a reformer. Next, the raw material gas is heated in the reformer. Then, in the reformer, CO and H are converted by the reforming reactions of the following formulas (iii) and (iv): ２ In addition, the reformer generates a reducing gas containing water vapor (H ２ By supplying O), the reforming reaction shown in formula (iv) proceeds. ４ +CO ２ → 2CO + 2H ２ ΔH=247kJ / mol...(iii) CH ４ +H ２ O → CO + 3H ２ ΔH=206kJ / mol...(iv)

[0059] The gas composition of the reducing gas is, for example, CO: 1 to 60% by volume, H ２ : 40 to 99 volume %, and the remainder: 0 to 30 volume %.

[0060] As can be seen from the fact that the formation enthalpies of the above formulas (iii) and (iv) are positive, the reactions of the above formulas (iii) and (iv) are both endothermic reactions. Therefore, by using green energy such as solar, wind, or geothermal energy as the energy source for the reforming reaction, it is possible in principle to reduce CO ２ Emissions can be reduced to zero.

[0061] Next, the reducing gas is supplied to the reducing furnace through an injection process. For example, the reducing gas is supplied to the reducing furnace using a reducing gas injection device. Then, in the reducing furnace, the iron oxide is reduced by the reducing gas to obtain reduced iron. Meanwhile, the reducing gas after being used to reduce the iron oxide is discharged from the reducing furnace as furnace top gas.

[0062] The amount of CO relative to the amount of CO contained in the furnace gas ２ The ratio of CO ２ / CO is preferably 0.25 or more and 4.0 or less. ２ CO relative to the total amount of CO ２ Amount ratio CO ２ / (CO ２ +CO) represents the degree of reaction progress in the reduction reaction of iron oxide by CO in the following formula (v), and depends on the equilibrium constant and reaction rate constant of formula (v): 3CO + Fe ２ O ３ →3CO ２ +2Fe ΔH=-247kJ / kg-Fe...(v) 3H ２ +Fe ２ O ３ →3H ２ O+2Fe ΔH=858kJ / kg-Fe...(vi)

[0063] For example, if the quality of the raw material, iron ore, declines, ２ This increases the activation energy of the reduction by CO. This decreases the reaction rate of the above formula (vi) while increasing the reaction rate of the above formula (v).２ / (CO ２ In addition, the reduction by CO in the above formula (v) is an exothermic reaction, whereas the reduction by H in the above formula (vi) ２ The reduction by CO is an endothermic reaction. Therefore, when the temperature inside the reduction furnace increases, the reaction rate of the above formula (vi) increases, while the reaction rate of the above formula (v) decreases. As a result, CO ２ / (CO ２ +CO) value becomes smaller.

[0064] From the viewpoint of stable operation, CO ２ / (CO ２ +CO) is preferably 0.2 or more and 0.8 or less, more preferably 0.4 or more and 0.6 or less. That is, 0.2≦CO ２ / (CO ２ +CO) is transformed to 0.25≦CO ２ / CO. CO ２ / (CO ２ +CO)≦0.8 is transformed to CO ２ / CO≦4.0. Also, 0.4≦CO ２ / (CO ２ +CO) is transformed to 0.67≦CO ２ / CO 2 . ２ / (CO ２ +CO)≦0.6 is transformed to CO ２ / CO≦1.5. That is, CO ２ / CO is preferably 0.25 or more and 4.0 or less. ２ / CO is more preferably 0.67 or more. ２ / CO is more preferably 1.5 or less.

[0065] The amount of CO relative to the amount of CO contained in the furnace gas ２ The ratio of CO ２The method for measuring the CO / CO is not particularly limited, but for example, it can be measured as follows. That is, the flow rate (standard condition conversion) of the top gas is measured using a flow meter at an arbitrary point in the top gas flow section. In addition, the top gas is sampled from a sampling port, and the CO / CO content of the gas is measured by gas chromatography. ２ and CO volume concentrations are measured. ２ By dividing the volume concentration of CO by the volume concentration of CO ２ / CO is calculated. Note that the flow rate of the furnace gas (standard condition conversion) [Nm ３ / h] is the flow rate (standard condition equivalent) [Nm ３ In addition, the CO contained in other gases, such as the regenerated methane gas and the second furnace gas that are the raw material gases used in the reforming step, and the combined gas of these, can be converted into CO . ２ , CO, CH ４ and H ２ The volume concentration and flow rate of O can be measured in a similar manner.

[0066] Dust Removal and Dehydration Step: It is also preferable to perform at least one of dust removal and dehydration of the top gas prior to the distribution step. Any dust removal device can be used for dust removal. The dust removal device may be capable of dehydration in addition to dust removal. Any dehydration device can be used for dehydration. The order of dust removal and dehydration is not particularly limited, but in the example shown in FIG. 2, the top gas is first dusted by a dust removal device and then dehydrated by a dehydration device, and then the top gas is distributed into a first top gas and a second top gas. At least one of dust removal and dehydration may be performed on the first top gas after the distribution step.

[0067] The distribution ratio of the furnace top gas in the distribution step (furnace top gas distribution section) and the method for producing reduced iron according to one embodiment of the present invention are also advantageous in that the composition of the raw material gas used in the reforming step (reformer) is preferably adjusted. ２ H in the O supply process ２It is important to control the distribution ratio of the furnace top gas in the distribution step (furnace top gas distribution section) (hereinafter simply referred to as the distribution ratio of the furnace top gas) depending on the supply flow rate of O and the dehydration rate in the dust removal and dehydration step.

[0068] For example, the distribution ratio Y (%) to the first furnace gas is preferably Y ０ ±10%, more preferably Y ０ ±5%, more preferably Y ０ ±3%, and even more preferably Y ０ The distribution ratio Y (%) to the first furnace top gas is most preferably controlled within the range of Y ０ (%), where Y ０ = x ＣＨ４ / {(x ＣＯ２ +x ＣＯ +x ＣＨ４ ) × η ÷ 100} × 100, and Y ０ : Standard distribution ratio (%) x ＣＯ２ : CO of the raw material gas used in the reforming process (reformer) ２ Concentration (volume%) x ＣＯ : CO concentration (vol %) of raw material gas used in the reforming process (reformer) x ＣＨ４ : CH of raw material gas used in the reforming process (reformer) ４ Concentration (volume %) η: methane conversion rate (%) in the synthesis process (methane synthesis unit). ０ If any part of the range of ±10% exceeds 100%, the upper limit of that range shall be 100%. ０ If any part of the range of ±10% is less than 0%, the lower limit of the range shall be 0%. ０ The same is true for more suitable ranges such as ±5%.

[0069] Here, the distribution ratio Y (%) to the first furnace gas is defined by the following formula: Y (%) = [amount of furnace gas distributed to the first furnace gas in the distribution step (Nm ３ / t)]÷[amount of furnace gas supplied to the distribution process (Nm ３ / t)] × 100 The distribution ratio to the second furnace gas is also defined in the same manner as in the above formula. Since the furnace gas is basically distributed to the first furnace gas and the second furnace gas, by appropriately controlling the distribution ratio to the first furnace gas, the distribution ratio to the second furnace gas can also be appropriately controlled. In this case, the distribution ratio (%) to the second furnace gas is 100-Y. In addition, a portion of the top gas may be supplied to another load depending on the operating conditions, etc., as long as it is 10% by volume or less of the amount of top gas. The amount of top gas supplied to another load is not included in the amount of top gas supplied to the distribution process.

[0070] The methane conversion rate η (%) in the synthesis step is defined by the following formula: η (%) = (1-([(CH in the synthesis step ４ CO of regenerated methane gas (emitted after synthesis of ２ amount (CO ２ (Nm ３ / t)] + [CO content of regenerated methane gas (Nm ３ / t)])÷([CO supplied to synthesis step ２ Amount (Nm ３ / t)] + [amount of CO supplied to the synthesis step (Nm ３ / t)])) × 100

[0071] Next, the standard distribution ratio Y ０ First, let us assume that the C mass balance of the entire circulation system is kept healthy and that C is conserved without going in or out of the circulation system. In this case, the C mass balance can be expressed as follows: [Total C amount in the furnace gas (gas flow rate of all C-containing molecules contained in the furnace gas) (Nm ３ / t)] = [CO of furnace gas ２ Amount (Nm ３ / t)] + [CO content of furnace gas (Nm ３ / t)] ... (a) [Total C amount of raw material gas (used in the reforming process) (gas flow rate of all C-containing molecules contained in the raw material gas) (Nm ３ / t)] = [CO of raw material gas ２ Amount (Nm ３ / t)] + [CO content of raw material gas (Nm ３ / t)] + [CH of raw material gas４ Amount (Nm ３ / t)] = (x ＣＯ２ +x ＣＯ +x ＣＨ４ ) × [total flow rate of raw material gas (Nm ３ / t)] ... (b) [Total C content of furnace gas (Nm ３ / t)] = [Total C content of raw material gas (Nm ３ / t)] ...(c)

[0072] These can be summarized as follows: ２ Amount (Nm ３ / t)] + [CO content of furnace gas (Nm ３ / t)] = (x ＣＯ２ +x ＣＯ +x ＣＨ４ ) × [total flow rate of raw material gas (Nm ３ / t)] ...(d)

[0073] In addition, the CO supplied to the synthesis step ２ The amount of CO and the amount of CO supplied to the synthesis step are respectively expressed by the following formulas: ２ Amount (Nm ３ / t)] + [amount of CO supplied to the synthesis step (Nm ３ / t)]) × η ÷ 100 = [CH of regenerated methane gas ４ Amount (Nm ３ / t)] ...(e) [CO supplied to the synthesis step ２ Amount (Nm ３ / t)] = [CO of furnace gas ２ Amount (Nm ３ / t)] × Y ​​÷ 100 ... (f) [Amount of CO supplied to the synthesis step (Nm ３ / t)] = [CO content of furnace gas (Nm ３ / t)]×Y÷100...(g)

[0074] Here, by substituting the formulas (f) and (g) into the formula (e), the following formula is obtained: ([CO of furnace top gas] ２ Amount (Nm ３ / t)] + [CO content of furnace gas (Nm ３ / t)]) × Y ÷ 100 × η ÷ 100 = [CH of regenerated methane gas ４ Amount (Nm ３ / t)] ...(h)

[0075] From equations (d) and (h), the following equation is obtained: Y = [CH of regenerated methane gas] ４ Amount (Nm ３ / t)] / {(x ＣＯ２ +x ＣＯ +x ＣＨ４ ) × [total flow rate of raw material gas (Nm ３ / t)]×η÷100}×100...(i)

[0076] The furnace gas basically contains CH ４ does not contain CH ４ CH of regenerated methane gas emitted after synthesis of ４ The amount can be expressed by the following formula: [CH of regenerated methane gas] ４ Amount (Nm ３ / t)] = x ＣＨ４ × [Total flow rate of raw material gas (Nm ３ / t)] ...(j)

[0077] Here, when equation (j) is substituted into equation (i), the following equation is obtained: Y=x ＣＨ４ / {(x ＣＯ２ +x ＣＯ +x ＣＨ４ ) × η ÷ 100} × 100

[0078] Therefore, the distribution ratio Y (%) to the first furnace gas is set to Y ０ (%), especially Y ０ ±10%, more preferably Y ０ By controlling the CO concentration in the furnace top gas within the range of ±5%, it is possible to maintain a healthy material balance in the circulation system. ２ and CO without separating them. ２ This will enable stable operations that simultaneously achieve reductions in emissions.

[0079] In addition, the CO contained in the furnace gas ２ A part of the CO contained in the top gas is methanated in the synthesis step and then supplied to the reforming step. ２is supplied to the reforming step as the second furnace gas without going through the synthesis step. Here, when paying attention to the material balance of the whole C atom, in the above circulation system, the distribution ratio to the first furnace gas is ２ , CO and CH ４ of the source gas relative to the total amount of ４ The optimum ratio is

[0080] In addition, H is produced from recycled methane gas. ２ O is separated and recovered, and the H ２ When O is supplied to the synthesis step, H ２ H in the O supply process ２ It is preferable to control the distribution ratio of the furnace gas in the distribution step according to the supply flow rate of O and the dehydration rate in the dust removal and dehydration step. For example, the distribution ratio Y (%) to the first furnace gas is preferably set to Y １ ±10%, more preferably Y １ ±5%, more preferably Y １ ±3%, and even more preferably Y １ The distribution ratio Y (%) to the first furnace top gas is most preferably controlled within the range of Y １ (%). This reduces the CO contained in the furnace gas during the production of reduced iron. ２ Energy saving and CO ２ It also achieves both reduction of emissions and prevention of catalyst poisoning during the synthesis process. ２ It is possible to carry out stable operation that also realizes optimization of the material balance of the circulating system by reusing O. １ = N Ｈ２Ｏ / (N × z ＣＯ ×2−N×z Ｈ２Ｏ × A) × 100, and Y １ : Standard distribution ratio (%) N Ｈ２Ｏ : H ２ In the O supply step, ２ H supplied to the methane synthesis unit by the O supply unit ２ O flow rate (Nm ３ / t) N: Flow rate (Nm m) of furnace top gas supplied to the dust removal and dehydration process (the device located upstream of the dust removal device and the dehydration device). ３ / t) z ＣＯ : CO concentration (vol%) of the furnace gas supplied to the distribution process (furnace gas distribution section) z Ｈ２Ｏ : H of the furnace gas supplied to the distribution process (furnace gas distribution section) ２ O concentration (volume %) A: Dehydration rate in the dust removal and dehydration process (dust removal device and dehydration device). Also, A = 1 - (P １ / P ２ ) and P １ : Saturated vapor pressure (MPa) at the temperature of the furnace gas supplied to the distribution process (furnace gas distribution section) P ２ : Saturated vapor pressure (MPa) at the temperature of the furnace gas supplied to the dust removal and dehydration process (the device located upstream of the dust removal device and the dehydration device). １ If any part of the range of ±10% exceeds 100%, the upper limit of that range shall be 100%. １ If any part of the range of ±10% is less than 0%, the lower limit of the range shall be 0%. １ The same is true for more suitable ranges such as ±5%.

[0081] The distribution ratio to the first furnace gas in the distribution step may be constant or may be changed at any timing.

[0082] The conditions other than those mentioned above are not particularly limited, and may be those according to conventional methods.

[0083] For example, the flow rate of the reducing gas supplied to the reducing furnace (hereinafter also referred to as the blowing amount of the reducing gas) is 1500 Nm ３ / t or more 3500Nm ３ / t or less is preferable. In other words, if the amount of reducing gas injected is too small, it will lead to a decrease in production volume and deterioration of product properties. On the other hand, if the amount of reducing gas injected is too large, the gas flow resistance in the reduction furnace will increase, and the raw material (pellets) in the reduction furnace will not descend. Therefore, the amount of reducing gas injected is preferably 1500 Nm ３ / t or more 3500Nm ３The reducing gas blowing temperature is preferably 700 to 1200°C.

[0084] Furthermore, the iron oxide raw material used in the reduced iron production method according to one embodiment of the present invention is, for example, iron ore. Specific examples include lump iron ore (lump ore) and pellets (spherical iron ore formed by solidifying powdered iron ore). The grade of the iron ore used as the iron oxide raw material, i.e., the iron content, is not particularly limited, but is generally preferably 65% ​​by mass or more from the viewpoint of reduction in a shaft furnace. However, in recent years, a rise in the price of high-grade iron ore, such as that produced in South America, is predicted due to its depletion. Therefore, it is preferable to use low-grade iron ore with an iron content of 63% by mass or less as needed. Such low-grade iron ore is inexpensive and abundant, and examples of sources include Australia.

[0085] Additionally, in the method for producing reduced iron according to one embodiment of the present invention, a method using a shaft furnace as a direct reduction ironmaking method has been described. However, the type of reduction furnace is not limited to this, and methods using a fluidized bed, rotary kiln, rotary hearth furnace (RHF), etc. may also be used. Note that a shaft furnace is preferred as the reduction furnace because of its high production efficiency, availability, and operational stability. Furthermore, the majority of direct reduction furnaces operating around the world are shaft furnace-type Midrex (registered trademark) and Hyl (registered trademark).

[0086] [2] Reduced iron production system Next, a reduced iron production system according to an embodiment of the present invention will be described. The reduced iron production system according to an embodiment of the present invention can be suitably used in the above-described reduced iron production method according to an embodiment of the present invention.

[0087] A reduced iron manufacturing system according to one embodiment of the present invention includes, for example, a reduction furnace; a reducing gas injection device that injects reducing gas into the reduction furnace; a furnace top gas distribution unit that distributes furnace top gas discharged from the reduction furnace into a first furnace top gas and a second furnace top gas; a methane synthesis unit that synthesizes regenerated methane gas from the first furnace top gas and hydrogen gas; a reformer that uses the regenerated methane gas and the second furnace top gas as raw material gases and obtains the reducing gas from the raw material gases; and a control unit, wherein the reduction furnace includes: a filling unit that fills iron oxide into the reduction furnace; and a reduction unit that reduces the iron oxide with the reducing gas in the reduction furnace to obtain reduced iron, and optionally, a gas separator that converts the regenerated methane gas into H ２ Separating and recovering O, ２ O separation and recovery device; ２ O is supplied to the methane synthesis unit; ２ and at least one of a dust removal device for removing dust from the furnace gas and a dehydration device for dehydrating the furnace gas, which are disposed before the furnace gas distribution unit, and the control unit controls the composition of the raw material gas used in the reforming unit, and preferably further controls H ２ H supplied to the methane synthesis unit by the O supply unit ２ The distribution ratio of the top gas in the top gas distribution unit is controlled according to the flow rate of O and the dehydration rates in the dust removal device and the dehydration device. Figure 3 is a schematic diagram showing an example of the overall configuration of a reduced iron production system according to an embodiment of the present invention. In Figure 3, reference numeral 15 denotes a control unit.

[0088] The configuration of the reducing furnace is not particularly limited, and a general one can be used. As an example, the reducing furnace has a filling section (filling port) for filling the reducing furnace with iron oxide, and a reduction section for reducing the iron oxide with a reducing gas in the reducing furnace to obtain reduced iron. The reduction section is a region through which the reducing gas blown in through the reducing gas blowing port flows and which serves as a descending path for the iron oxide filled from the filling section.

[0089] In addition, the furnace top gas distribution unit, methane synthesis unit, reformer, H ２ O separation and recovery device, H ２The O supply device, dust removal device, and dehydration device are not particularly limited, and common devices can be used. For example, a mass flow controller or the like can be used to distribute and control the flow rate of the furnace top gas in the furnace top gas distribution section.

[0090] The control unit controls the distribution ratio of the furnace top gas in accordance with the composition of the raw material gas used in the reformer. The preferred control mode in the control unit is as described in [1] above.

[0091] As an example, the control unit may have an input unit that inputs various set values ​​and measurement data such as the composition of the reducing gas, a calculation unit that processes the input set values ​​and measurement data, a memory unit that stores the set values ​​and measurement data, and an output unit that outputs an operation signal that changes the distribution ratio of the furnace gas based on the calculation results of the calculation unit.

[0092] In this case, specifically, the control unit is an information processing device. Fig. 4 shows an example of functional blocks of the control unit. The reducing furnace may have a control unit as shown in Fig. 4. As shown in Fig. 4, the control unit includes an input unit and an output unit connected to external devices so as to be able to perform data communication, a calculation unit, and a storage unit that stores various data, all of which are connected to each other so as to be able to perform data communication. In Fig. 4, reference numeral 16 denotes the input unit, 17 denotes the calculation unit, 18 denotes the storage unit, and 19 denotes the output unit.

[0093] The input unit and the output unit are, for example, interfaces that are provided to enable data communication with external devices.

[0094] The calculation unit is, for example, a CPU. The calculation unit controls the operation of the entire control unit. The calculation unit receives various set values ​​input from the input unit from the outside or stored in the storage unit, as well as the composition of the raw material gas used in the reforming device, H ２ H supplied to the methane synthesis unit by the O supply unit ２The calculation unit calculates how to change the distribution ratio of the top gas based on information (e.g., measurement data) such as the flow rate of O and the dehydration rates in the dust collector and dehydrator, and generates an operation signal for changing the distribution ratio of the top gas. The output unit outputs the operation signal. The calculation unit realizes the above-mentioned functions by, for example, executing a program stored in the storage unit.

[0095] The storage unit is, for example, a writable nonvolatile memory such as an EPROM, etc. The storage unit is not particularly limited, but may be, for example, an HDD or SSD.

[0096] The furnace top gas distribution unit receives the operation signal output from the output unit and controls the distribution ratio of the furnace top gas as described in [1] above.

[0097] The configuration other than that described above is not particularly limited, and may be the same as that of a conventionally known reduction furnace manufacturing system.

[0098] Examples will be described below, which are based on numerical calculations.

[0099] Example 1 In the circulation system shown in Figure 2 or 3, reduced iron is produced under the following conditions and the conditions shown in Table 1. In the distribution process, the entire amount of furnace gas is distributed to the first furnace gas and the second furnace gas, and is not supplied to other loads. Other conditions are the same as in the conventional method. In No. 1-15, the distribution ratio is not controlled and the entire amount of furnace gas is supplied to the synthesis process. Injection rate of reducing gas: 2200 Nm ３ / t Composition of reducing gas: H ２ 56% by volume, CO 35% by volume, and the balance 8% by volume. Reducing gas injection temperature: 900°C. Iron ore used: 65% by mass (normal quality, such as that produced in Brazil). Operation period: 28 days.

[0100]

[0101] In all of the invention examples No. 1-1 to 1-14, stable operation was possible over the entire 28-day operation period under a sound material balance in the circulation system shown in Figure 2, i.e., the system in which the furnace gas is circulated and reused, which is extremely advantageous for realizing energy savings. Here, being able to operate stably under a sound material balance means that the CO contained in the furnace gas in the circulation system during the operation period is ２ This means that reduced iron can be produced continuously without separating CO from the circulating system. ２ Emissions can also be reduced to zero.

[0102] On the other hand, in Comparative Example No. 1-15, stable operation under a sound material balance cannot be performed midway through the operation period.

[0103] Example 2 In the circulation system shown in Figure 2 or 3, reduced iron is produced in the same manner as in Example 1, except that No. 1-1 in Table 1 is used as the base condition and the quality (brand) of the iron ore used is changed sequentially as follows: Quality of iron ore used Days 1 to 10: 65 mass% Days 11 to 20: 67 mass% Days 20 to 28: 63 mass%

[0104] Here, in No. 2-1 and No. 2-2, the distribution ratio of the furnace gas in the distribution step is controlled according to the composition of the raw material gas used in the reforming step. Specifically, the distribution ratio Y (%) to the first furnace gas in the distribution step is set to Y ０ ±10% and Y ０ It is controlled to be within the range of ±5%.

[0105] On the other hand, in No. 2-3, the distribution ratio Y (%) to the first furnace gas is constant (33%), and the distribution ratio of the furnace gas in the distribution step according to the composition of the raw material gas used in the reforming step is not controlled.

[0106]

[0107] In the invention examples No. 2-1 and 2-2, stable operation was possible over the entire 28-day operation period under a sound material balance in the circulation system shown in Figure 2, i.e., the system in which the furnace top gas is circulated and reused, which is extremely advantageous for realizing energy savings. ２ Emissions can also be reduced to zero.

[0108] On the other hand, in the comparative example No. 2-3, stable operation under a sound material balance cannot be performed midway through the operation period.

[0109] Note that, when reduced iron is produced using Nos. 1-2 to 1-14 in Table 1 as base conditions and the grade (brand) of the iron ore used is sequentially changed in the same manner as above, the same results as above can be obtained.

[0110] In addition, even when the grade of iron ore used in various reduction furnaces and operating conditions is changed sequentially, the distribution ratio Y (%) to the first furnace top gas in the distribution step can be changed to Y ０ If the value is controlled to be within the range of ±10%, the same results as above can be obtained.

[0111] Example 3 In the circulation system shown in Figure 2 or 3, No. 1-1 in Table 1 was used as the base condition, and H ２ H in the O supply process ２ Reduced iron was produced in the same manner as in Example 1, except that the O supply flow rate was changed in various ways.

[0112] Here, in No. 3-1 and 3-2, H ２ H in the O supply process ２ The distribution ratio of the furnace top gas in the distribution step is controlled according to the supply flow rate of O and the dehydration rate in the dust removal and dehydration step. Specifically, the distribution ratio Y (%) to the first furnace top gas in the distribution step is set to Y １ ±10% and Y １ It is controlled to be within the range of ±5%.

[0113] On the other hand, in No. 3-3, the distribution ratio Y (%) to the first furnace top gas is constant (33%), and the distribution ratio of the furnace top gas in the distribution process is not controlled.

[0114]

[0115] In the invention examples No. 3-1 and 3-2, stable operation was possible over the entire 28-day operation period under a sound material balance in the circulation system shown in Figure 2, i.e., the system in which the furnace top gas is circulated and reused, which is extremely advantageous for realizing energy savings. ２ Emissions can also be reduced to zero.

[0116] On the other hand, in the comparative example No. 3-3, stable operation under a sound material balance cannot be performed midway through the operation period.

[0117] In addition, No. 1-2 to 1-14 in Table 1 were used as base conditions, and H ２ H in the O supply process ２ The same results as above can be obtained when reduced iron is produced by varying the O supply flow rate.

[0118] In addition, H ２ H in the O supply process ２ Even when the supply flow rate of O is changed, the distribution ratio Y (%) to the first furnace gas in the distribution step can be changed to Y １ If the value is controlled to be within the range of ±10%, the same results as above can be obtained.

[0119] 1 Reduction furnace 1a Iron oxide 1b Reduced iron 3 Dust removal device 4 Dehydration device 4-1 H ２ O separation and recovery device 4-2 H ２ O2 supply device 5 Natural gas supply section 6 Air supply section 7 Reforming device 9 Reducing gas injection device 10 Hydrogen supply section 11 Methane synthesis device 12 Steam supply section 13 Furnace top gas distribution section 14 Gas junction section 15 Control section 16 Input section 17 Calculation section 18 Memory section 19 Output section

Claims

1. The filling process involves filling the reduction furnace with iron oxide, A blowing step in which reducing gas is blown into the aforementioned reduction furnace, In the reduction furnace, a reduction step is performed in which the iron oxide is reduced by the reducing gas to obtain reduced iron, A distribution step, which divides the top gas discharged from the reduction furnace into a first top gas and a second top gas, A synthesis step for synthesizing regenerated methane gas from the first furnace top gas and hydrogen gas, A reforming step in which the regenerated methane gas and the second furnace top gas are used as raw material gases to obtain the reduced gas from the raw material gases, It has, A method for producing reduced iron, comprising controlling the distribution ratio of the furnace top gas in the distribution step according to the composition of the raw material gas used in the reforming step.

2. The distribution ratio Y (%) to the first top gas in the distribution process is Y ０ A method for producing reduced iron according to claim 1, wherein the reduction is controlled within a range of ±10%. Here, Y ０ =x ＣＨ４ / {(x ＣＯ２ +x ＣＯ +x ＣＨ４ )×η÷100}×100 And, Y ０ Baseline allocation ratio (%) x ＣＯ２ : CO of the source gas used in the modification process ２ Concentration (volume%) x ＣＯ CO concentration (volume %) of the raw material gas used in the reforming process x ＣＨ４ CH4 is the raw material gas used in the reforming process. ４ concentration (volume %) η: Methane conversion rate in the synthesis process (%) That is the case. Also, Y ０ If a portion of the ±10% range exceeds 100%, the upper limit of that range shall be 100%. ０ If a portion of the ±10% range falls below 0%, the lower limit of that range shall be set to 0%.

3. The distribution ratio Y (%) to the first top gas in the distribution process is Y ０ A method for producing reduced iron according to claim 2, wherein the reduction is controlled within a range of ±5%. Here, Y ０ If a portion of the ±5% range exceeds 100%, the upper limit of that range shall be 100%. ０ If a portion of the ±5% range falls below 0%, the lower limit of that range shall be set to 0%.

4. Between the synthesis step and the reforming step, H is extracted from the regenerated methane gas. ２ O is separated and recovered, H ２ O separation and recovery process, The aforementioned H ２ O is supplied to the synthesis step, H ２ O supply process, A method for producing reduced iron according to claim 1, further comprising the above.

5. Prior to the distribution step, the process further includes a dust removal and dewatering step, which performs at least one of dust removal and dewatering of the top gas of the furnace. The distribution ratio Y (%) to the first top gas in the distribution process is Y １ A method for producing reduced iron according to claim 4, wherein the range is controlled to ±10%. Here, Y １ =N Ｈ２Ｏ / (N×z ＣＯ ×2-N×z Ｈ２Ｏ ×A)×100 And, Y １ Baseline allocation ratio (%) N Ｈ２Ｏ : H ２ In the supply process, H is supplied to the synthesis process. ２ Flow rate of O (Nm ３ / t) N: Flow rate of furnace top gas supplied to the dust removal and dewatering process (Nm³) ３ / t) z ＣＯ : CO concentration (volume %) of top gas supplied to the distribution process z Ｈ２Ｏ : H of the top gas supplied to the distribution process ２ O concentration (volume %) A: Dewatering rate in the dust removal and dewatering process That is the case. Also, A=1-(P １ / P ２ ) And, P １ : Saturated vapor pressure (MPa) at the temperature of the top gas supplied to the distribution process. P ２ : Saturated vapor pressure (MPa) at the temperature of the furnace top gas supplied to the dust removal and dewatering process. That is the case. In addition, Y １ If a portion of the ±10% range exceeds 100%, the upper limit of that range shall be 100%. １ If a portion of the ±10% range falls below 0%, the lower limit of that range shall be set to 0%.

6. The distribution ratio Y (%) to the first top gas in the distribution process is Y １ A method for producing reduced iron according to claim 5, wherein the range is controlled to ±5%. Here, Y １ If a portion of the ±5% range exceeds 100%, the upper limit of that range shall be 100%. １ If a portion of the ±5% range falls below 0%, the lower limit of that range shall be set to 0%.

7. The aforementioned H ２ H in the O separation and recovery process ２ A method for producing reduced iron according to any one of claims 4 to 6, wherein the separation and recovery rate of O is 70 to 90%.

8. The aforementioned H ２ In the O separation and recovery process, the regenerated methane gas is cooled to 30 to 90°C, thereby separating the H from the regenerated methane gas. ２ A method for producing reduced iron according to any one of claims 4 to 6, wherein oxygen is separated.

9. A reduction furnace and A reducing gas injection device for injecting reducing gas into the aforementioned reducing furnace, A top gas distribution unit that distributes the top gas discharged from the reduction furnace into a first top gas and a second top gas, A methane synthesis apparatus for synthesizing regenerated methane gas from the first furnace top gas and hydrogen gas, A reforming apparatus that uses the regenerated methane gas and the second furnace top gas as raw material gases to obtain the reduced gas from the raw material gases, It has a control unit and The aforementioned reduction furnace is A filling section for filling the reduction furnace with iron oxide, The reduction furnace has a reduction section which reduces the iron oxide with the reducing gas to obtain reduced iron, A system for producing reduced iron, wherein the control unit controls the distribution ratio of the top gas in the top gas distribution unit according to the composition of the raw material gas used in the reforming apparatus.

10. The control unit sets the distribution ratio Y (%) to the first top gas in the top gas distribution unit, Y ０ A system for producing reduced iron according to claim 9, which controls the range to ±10%. Here, Y ０ =x ＣＨ４ / {(x ＣＯ２ +x ＣＯ +x ＣＨ４ )×η÷100}×100 And, Y ０ Baseline allocation ratio (%) x ＣＯ２ CO2 used as raw material gas in reforming equipment ２ concentration (volume %) x ＣＯ CO concentration (volume %) of the raw material gas used in the reforming unit x ＣＨ４ CH4 is the raw material gas used in the reforming plant. ４ concentration (volume %) η: Methane conversion rate (%) in the methane synthesis plant That is the case. Also, Y ０ If a portion of the ±10% range exceeds 100%, the upper limit of that range shall be 100%. ０ If a portion of the ±10% range falls below 0%, the lower limit of that range shall be set to 0%.

11. The control unit sets the distribution ratio Y (%) to the first top gas in the top gas distribution unit, Y ０ A system for producing reduced iron according to claim 10, which controls the range to ±5%. Here, Y ０ If a portion of the ±5% range exceeds 100%, the upper limit of that range shall be 100%. ０ If a portion of the ±5% range falls below 0%, the lower limit of that range shall be set to 0%.

12. Between the methane synthesis apparatus and the reforming apparatus, H is extracted from the regenerated methane gas. ２ O is separated and recovered, H ２ O separation and recovery device, The aforementioned H ２ O is supplied to the methane synthesis apparatus, H ２ O supply device and A method for producing reduced iron according to claim 9, further comprising the above.

13. The furnace top gas distribution section is further provided with at least one of a dust removal device for removing dust from the furnace top gas and a dewatering device for dewatering the furnace top gas. The control unit sets the distribution ratio Y (%) to the first top gas in the top gas distribution unit, Y １ A system for producing reduced iron according to claim 12, which controls the range to ±10%. Here, Y １ =N Ｈ２Ｏ / (N×z ＣＯ ×2-N×z Ｈ２Ｏ ×A)×100 And, Y １ Baseline allocation ratio (%) N: Flow rate (Nm³) of the top gas supplied to the device located upstream of the dust removal and dewatering devices. ３ / t) N Ｈ２Ｏ : H ２ H supplied to the methane synthesis plant by the oxygen supply device. ２ Flow rate of O (Nm ３ / t) z ＣＯ CO concentration (volume %) of the top gas supplied to the top gas distribution section of the furnace. z Ｈ２Ｏ : The H of the top gas supplied to the top gas distribution section ２ O concentration (volume %) A: Dehydration rate in dust removal and dehydration equipment That is the case. Also, A=1-(P １ / P ２ ) And, P １ : Saturated vapor pressure (MPa) at the temperature of the top gas supplied to the top gas distribution section. P ２ : The saturated vapor pressure (MPa) at the temperature of the furnace top gas supplied to the upstream equipment among the dust removal and dewatering equipment. That is the case. In addition, Y １ If a portion of the ±10% range exceeds 100%, the upper limit of that range shall be 100%. １ If a portion of the ±10% range falls below 0%, the lower limit of that range shall be set to 0%.

14. The control unit controls the distribution ratio Y (%) of the first top gas in the top gas distribution unit to be within the range of Y １ ±5%, and the reduction iron manufacturing system according to claim 13. Here, Y １ If a portion of the ±5% range exceeds 100%, the upper limit of that range shall be 100%. １ If a portion of the ±5% range falls below 0%, the lower limit of that range shall be set to 0%.