Method for producing reduced iron

Abstract

Provided is a method for producing reduced iron with which it is possible to achieve both energy conservation and reduction of CO2 emissions. A system for recycling furnace top gas, which has a blowing step, a reduction step, a distribution step, a synthesis step and a heating step, is configured, and the amount of gas introduced into the distribution step, the synthesis step and the heating step is controlled in accordance with the CO2 conversion rate of the reverse shift reaction in the synthesis step.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing reduced iron. Background Art

[0002] In recent years, in steel mills, against the backdrop of global environmental problems and fossil fuel depletion problems, there has been a strong demand for energy conservation. The main raw material of iron is iron oxide, and in steel mills, a reduction process for reducing this iron oxide is essential. The most common reduction process worldwide is the blast furnace. In the blast furnace, coke, pulverized coal, and oxygen in hot air (air heated to about 1200°C) react at the tuyeres. Through this reaction, CO and H2, which are reduction gases, are generated, and these reduction gases are used to reduce iron ore in the furnace. With the improvement of blast furnace operation technology in recent years, the reductant ratio (the amount of coke and pulverized coal used per 1 t of hot metal production) has been reduced to about 500 kg / t, and the reductant ratio has almost reached the lower limit. Therefore, a significant reduction in the reductant ratio greater than this cannot be expected.

[0003] On the other hand, in regions where natural gas is produced, a method for manufacturing reduced iron using a vertical reduction furnace (hereinafter also referred to as a shaft furnace) is often used. In this method, lumpy iron ore such as sintered ore and pellet ore (hereinafter, also simply referred to as iron oxide) is filled in the reduction furnace as an iron oxide raw material. Then, a reduction gas containing CO and H2 is blown into the reduction furnace to reduce the iron oxide and manufacture reduced iron. In this method, natural gas or the like can be used as the raw material gas for the reduction gas. This raw material gas is heated and reformed together with the top gas in a reforming device. Thereby, a reduction gas is generated. Here, the top gas is the gas after being supplied to the reduction of iron oxide in the reduction furnace and is generally discharged from the top of the reduction furnace. The generated reduction gas is blown into the reduction furnace and reacts with the iron oxide supplied from the upper part of the reduction furnace. Then, the iron oxide is reduced to reduced iron. Next, the reduced iron is cooled in a region lower than the position where the reduction gas is blown into the reduction furnace and then discharged from the lower part of the reduction furnace.

[0004] In addition, as described above, the top gas, which is the gas after being supplied to the reduction of iron oxide, is discharged from the reduction furnace, for example, from the top. Then, after the top gas is dust-collected and cooled, a part of it is sent to the reforming device as a raw material for the reforming gas. In addition, the remaining top gas is used as the fuel gas for the reforming device. In this method, the top gas used as the fuel gas for the reforming device is usually discharged outside the system.

[0005] As such a reduced iron manufacturing process, for example, Patent Document 1 describes the following method: The exhaust gas of the reduction furnace and natural gas are reformed in a reforming device to generate a reduction gas mainly composed of CO and H2, and this reduction gas is blown into the reduction furnace to reduce the iron oxide in the reduction furnace and manufacture reduced iron.

[0006] In addition, the following method is described in Patent Document 2: Coke oven gas and the top gas of a reduction furnace after removing CO2 are reformed to produce a reducing gas, which is blown into the reduction furnace to produce reduced iron.

[0007] Prior art documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Laid-Open No. 2017-88912

[0010] Patent Document 2: Japanese Patent No. 6190522 Summary of the invention

[0011] In the method described in Patent Document 1, natural gas supplied from the outside is used to produce a reducing gas. Therefore, there is a problem as follows: Although the CO2 emission is less than that of a blast furnace, a certain degree of CO2 emission cannot be avoided.

[0012] In addition, the method described in Patent Document 2 uses coke oven gas or converter gas generated in a steel mill to produce a reducing gas. Here, in an integrated steel mill, coke oven gas or converter gas is required as fuel gas for the next process such as a heating furnace or an annealing furnace. Therefore, if coke oven gas and converter gas are diverted to the reduced iron manufacturing process, there will be a shortage of fuel gas in the next process. As a result, in order to compensate for the shortage of fuel gas in the next process, natural gas will be supplied from the outside. That is, even the method described in Patent Document 2 cannot achieve both energy saving and reduction of CO2 emissions, leaving a problem.

[0013] The present invention has been completed in view of the above situation, and an object thereof is to provide a method for manufacturing reduced iron that can achieve both energy saving and reduction of CO2 emissions.

[0014] The inventors repeatedly studied to achieve both energy saving and reduction of CO2 emissions, and developed a system for recycling top gas.

[0015] That is, the inventors developed a top gas recycling and reuse system (hereinafter, also simply referred to as a recycling system), which has the following processes:

[0016] Blowing process: Blow a reducing gas into a reduction furnace.

[0017] Reduction process: Reduce iron oxide with a reducing gas in a reduction furnace to obtain reduced iron.

[0018] Distribution process: Distribute the top gas discharged from the reduction furnace into a first top gas and a second top gas.

[0019] Synthesis step: Using the first top gas and hydrogen to synthesize regenerated carbon monoxide gas through the reverse water-gas shift reaction, and

[0020] Heating step: Heating the gas obtained by mixing the regenerated carbon monoxide gas, the second top gas, and the additionally supplied hydrogen to obtain the reducing gas.

[0021] In addition, the inventors further conducted repeated research and obtained the following insights.

[0022] · In the above-mentioned circulation system, according to the CO2 conversion rate η R [-] (hereinafter, also simply referred to as the CO2 conversion rate) of the reverse water-gas shift reaction in the synthesis step (i.e., the reaction of reforming CO2 into CO by reacting CO2 with H2 using CO2 contained in the first top gas as a gas carbon source), the gas amounts introduced into the distribution step, the synthesis step, and the heating step are controlled.

[0023] · Thereby, it is possible to simultaneously achieve further energy saving without inputting additional energy and reduction of CO2 emissions, and to produce reduced iron with high operation stability.

[0024] The present invention was completed through further research based on the above insights.

[0025] That is, the gist of the present invention is configured as follows.

[0026] 1. A method for manufacturing reduced iron, comprising the following steps:

[0027] Filling step: Filling iron oxide into a reduction furnace,

[0028] Blowing step: Blowing a reducing gas into the above reduction furnace,

[0029] Reduction step: Reducing the iron oxide with the above reducing gas in the above reduction furnace to obtain reduced iron,

[0030] Distribution step: Distributing the top gas discharged from the above reduction furnace into a first top gas and a second top gas,

[0031] Synthesis step: Using the above first top gas and hydrogen to synthesize regenerated carbon monoxide gas through the reverse water-gas shift reaction, and

[0032] Heating step: Heating the gas obtained by mixing the above regenerated carbon monoxide gas, the above second top gas, and the additionally supplied hydrogen to obtain the above reducing gas,

[0033] Controlling the gas amounts introduced into the above distribution step, the above synthesis step, and the above heating step according to the CO2 conversion rate η R [-] based on the reverse water-gas shift reaction in the above synthesis step.

[0034] 2. The method for manufacturing reduced iron according to 1 above, wherein the amount of gas introduced into the above-mentioned distribution process, the above-mentioned synthesis process, and the above-mentioned heating process is controlled in such a way as to satisfy the following formulas (1) and (2).

[0035]

[0036] Here,

[0037] W CO2 : The amount of CO2 contained in the top gas introduced into the distribution process [Nm 3 / t]

[0038] W H2 : The amount of H2 contained in the top gas introduced into the distribution process [Nm 3 / t]

[0039] E H2 : The amount of H2 contained in the hydrogen gas introduced into the synthesis process [Nm 3 / t]

[0040] V CO2 : The amount of CO2 contained in the gas introduced into the heating process [Nm 3 / t]

[0041] V H2 : The amount of H2 contained in the gas introduced into the heating process [Nm 3 / t]

[0042] A H2 : The amount of H2 contained in the additional supplied hydrogen gas [Nm 3 / t].

[0043] 3. The method for manufacturing reduced iron according to 1 or 2 above, wherein in the above-mentioned distribution process, the above-mentioned top gas is separated into separated carbon dioxide gas and first remaining gas,

[0044] The separated carbon dioxide gas is distributed as the above-mentioned first top gas,

[0045] The first remaining gas is distributed as the above-mentioned second top gas.

[0046] 4. The method for manufacturing reduced iron according to 1 or 2 above, wherein in the above-mentioned distribution process, the above-mentioned top gas is separated into separated carbon dioxide gas and first remaining gas,

[0047] The separated carbon dioxide gas is distributed as the above-mentioned first top gas,

[0048] The first remaining gas is separated into separated hydrogen gas and second remaining gas,

[0049] Introduce the separated hydrogen gas mentioned above into the synthesis process described above.

[0050] Distribute the remaining gas of the second mentioned above as the second top gas.

[0051] 5. The method for manufacturing reduced iron according to 1 or 2 above, wherein, in the above-mentioned distribution process, the top gas is separated into separated hydrogen gas and the remaining gas of the third.

[0052] Introduce the separated hydrogen gas mentioned above into the synthesis process described above.

[0053] Separate the remaining gas of the third mentioned above into separated carbon dioxide gas and the remaining gas of the fourth.

[0054] Distribute the separated carbon dioxide gas mentioned above as the first top gas, and distribute the remaining gas of the fourth mentioned above as the second top gas.

[0055] According to the present invention, it is possible to perform an operation that simultaneously achieves further energy saving and reduction of CO2 emissions with high operation stability when manufacturing reduced iron. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 It is a diagram showing a conventional manufacturing process of reduced iron.

[0057] Figure 2 It is a diagram showing an example of a manufacturing process of reduced iron based on the method for manufacturing reduced iron according to an embodiment of the present invention. DETAILED DESCRIPTION

[0058] Hereinafter, a method for manufacturing reduced iron according to an embodiment of the present invention will be described with reference to the drawings.

[0059] First, a conventional manufacturing process of reduced iron (hereinafter, also referred to as a conventional manufacturing process) will be described. Figure 1 It is a diagram showing a schematic configuration of an example of a conventional manufacturing process. In the figure, reference numeral 1 is a reduction furnace, 1a is iron oxide, 1b is reduced iron, 3 is a dust removal device, 4 is a dehydration device, 5 is a natural gas supply unit, 6 is an air supply unit, 7 is a reforming device, and 9 is a reducing gas blowing device.

[0060] In an example of a conventional manufacturing process, iron oxide is charged from the upper part of a reduction furnace and made to slowly descend. High-temperature reducing gas is blown into the furnace from the middle part of the reduction furnace to reduce the iron oxide. Then, reduced iron is discharged from the lower part of the reduction furnace. At this time, top gas mainly containing CO, CO2, H2, and H2O is discharged from the upper part of the reduction furnace. The top gas is dust-removed using a dust removal device, and a part of it is sent to a reforming device after moisture adjustment as a raw material gas. A gas containing hydrocarbons such as natural gas from a natural gas supply section is supplied to the reforming device together with the moisture-adjusted top gas. Next, in the reforming device, the supplied gas is heated. Then, a reforming reaction occurs to generate a high-temperature generated reducing gas mainly containing CO and H2. Then, the reducing gas is blown into the reduction furnace. In addition, the remaining part of the top gas is used as heating fuel in the combustion chamber of the reforming device after dehydration. The top gas after combustion as heating fuel is usually discharged to the outside of the system in a state containing CO2. It should be noted that when producing reduced iron by this example of the conventional manufacturing process, about 1 t or more of CO2 is discharged to the outside of the circulation system per 1 t of reduced iron produced.

[0061] On the other hand, in the method for manufacturing reduced iron according to an embodiment of the present invention, for example, as Figure 2 shown, in a top gas distribution section, the top gas discharged from the reduction furnace is distributed into a first top gas and a second top gas. Next, in a carbon monoxide synthesis device, regenerated carbon monoxide gas is synthesized by an inverse conversion reaction using the first top gas and hydrogen. Next, the regenerated carbon monoxide gas, the second top gas, and additional supplied hydrogen are mixed to form a mixed gas. Next, the mixed gas is heated in a heating device. Then, the heated mixed gas is used as a reducing gas and blown into the reduction furnace from a reducing gas blowing device. In the figure, reference numeral 10 is a hydrogen supply section, 11 is a carbon monoxide synthesis device, 12 is a heating device, 13 is a heat source, and 14 is a top gas distribution section.

[0062] Hereinafter, each process of the method for manufacturing reduced iron according to an embodiment of the present invention will be described. It should be noted that the filling process, the blowing process, and the reduction process can be carried out in accordance with a conventional method, for example, in the same manner as the above-described conventional manufacturing process, and thus the description thereof is omitted here.

[0063] · Distribution process

[0064] In the distribution process, for example, in the top gas distribution section, the top gas discharged from the reduction furnace is distributed into a first top gas and a second top gas. In addition, the method for distributing and controlling the flow rate of the top gas is not particularly limited, and a conventional method can be used. For example, a mass flow controller can be used.

[0065] In the distribution process, the top gas can be distributed in its original composition. Additionally, for example, it can also be separated into specific gas species such as CO2 and H2 and then distributed.

[0066] (a) Separate the top gas (CO2 separation) into separated carbon dioxide gas and first remaining gas, distribute the separated carbon dioxide gas as the first top gas, and distribute the first remaining gas as the second top gas.

[0067] (b) Separate the top gas (CO2 separation) into separated carbon dioxide gas and first remaining gas, and distribute the separated carbon dioxide gas as the first top gas.

[0068] In addition, separate the above-mentioned first remaining gas (H2 separation) into separated hydrogen and second remaining gas. Then, introduce (supply) the separated hydrogen into the synthesis process, and distribute the second remaining gas as the second top gas.

[0069] (c) Separate the top gas (H2 separation) into separated hydrogen and third remaining gas. Then, introduce (supply) the separated hydrogen into the synthesis process, and separate the third remaining gas (CO2 separation) into separated carbon dioxide gas and fourth remaining gas. Next, distribute the separated carbon dioxide gas as the first top gas, and distribute the fourth remaining gas as the second top gas.

[0070] Here, the method of CO2 separation is not particularly limited, and various methods such as chemical absorption method, physical absorption method, adsorption separation method, membrane separation method, cryogenic separation method, oxy-combustion method, chemical looping combustion method, etc. can be used. Among them, in particular, the chemical absorption method represented by the amine absorption method and the adsorption separation method represented by the PSA method have a long history of use in chemical plants, industrial CO2 production, etc. In addition, these methods also have a record of recovering gases with a CO2 concentration of 99 vol% or more. Therefore, these methods are preferred. It should be noted that the CO2 concentration in the separated carbon dioxide gas is preferably 90 vol% or more. The CO2 concentration in the separated carbon dioxide gas can also be 100 vol%.

[0071] The method of H2 separation is also not particularly limited, and various methods such as adsorption separation method and membrane separation method can be used. The concentration of H2 in the separated hydrogen is preferably 90 vol% or more. The concentration of H2 in the separated hydrogen can also be 100 vol%.

[0072] In addition, the compositions of the first remaining gas, the second remaining gas, and the fourth remaining gas distributed as the second top gas vary according to the amounts of CO2 and H2 separated. For example, CO: 5 - 70 vol%, CO2: 0 - 25 vol%, H2: 0 - 75 vol%, H2O: 0 - 50 vol%, balance: 0 - 30 vol%.

[0073] It should be noted that when the top gas is distributed into the first top gas and the second top gas with the original composition in the distribution process, a separation process for separating specific gas species such as CO2 and H2 from the first top gas and the second top gas can be arbitrarily provided between the above-mentioned distribution process and the subsequent synthesis process.

[0074] For example, as in the above (a) and (b), the first top gas can be separated (CO2 separation) into separated carbon dioxide gas and the first remaining gas, and the separated carbon dioxide gas can be used as the first top gas in the synthesis process. The above-mentioned first remaining gas can be directly merged with the second top gas. In addition, the above-mentioned first remaining gas can also be separated (H2 separation) into separated hydrogen gas and the second remaining gas. Then, the separated hydrogen gas is introduced into the synthesis process, and the second remaining gas is merged with the second top gas.

[0075] In addition, as in the above (c), the first top gas is separated into separated hydrogen gas and the third remaining gas. Then, the separated hydrogen gas is introduced into the synthesis process, and the third remaining gas is separated (CO2 separation) into separated carbon dioxide gas and the fourth remaining gas. Then, the separated carbon dioxide gas can be used as the first top gas in the synthesis process, and the fourth remaining gas is merged with the second top gas.

[0076] In addition, from the viewpoint of controlling the flow rate of the top gas introduced into the distribution process, a part of the top gas can be used as heating fuel for a heating device or the like. For example, in the combustion chamber of the heating device, a part of the top gas is burned using oxygen supplied by an oxygen supply device, such as pure oxygen generated by a cryogenic separation process driven by CO2-free electricity as an example. In addition, the burned top gas can be dehydrated as needed and then returned to the original pipeline.

[0077] ·Synthesis process

[0078] In the synthesis process, for example, in a carbon monoxide synthesis device, regenerated carbon monoxide gas is synthesized from the first top gas distributed in the above-mentioned distribution process and hydrogen supplied from outside the circulation system. It should be noted that CO is synthesized, for example, from CO2 contained in the first top gas and H2 contained in hydrogen supplied from outside the circulation system according to the reverse shift reaction formula of the following formula (i).

[0079] CO2 + H2 → CO + H2O ··· (i)

[0080] For example, the first top gas and the above-mentioned hydrogen supplied from outside the circulation system are introduced into the carbon monoxide synthesis device. Then, in the carbon monoxide synthesis device, CO is synthesized according to the reaction formula of the above formula (i). The synthesis conditions of CO and the like are not particularly limited, and conventional methods can be used.

[0081] When the composition of the first top gas becomes the same as that of the separated carbon dioxide gas obtained by using the above-described distribution process or separation process, the composition of the first top gas is the same as that of the separated carbon dioxide gas. In addition, when the top gas is distributed in its original composition in the distribution process and does not go through the separation process, the composition of the first top gas is basically the same as the composition of the top gas introduced into the distribution process. For example, the composition of the first top gas in this case is CO: 5 to 50% by volume, CO2: 5 to 30% by volume, H2: 5 to 80% by volume, H2O: 0 to 35% by volume, and the balance: 0 to 20% by volume. The same applies to the composition of the second top gas described below.

[0082] It should be noted that in the synthesis process, in addition to the first top gas, any other gas containing CO2 (hereinafter also referred to as other gas) can also be used. As other gases, for example, gases by-produced in the steelmaking process, specifically blast furnace gas (BFG) and coke oven gas (COG), can be cited. In addition, other gases can be introduced into the above-described separation process together with the first top gas, separated into separated carbon dioxide gas and the remaining gas, and then the separated carbon dioxide gas can be supplied to the synthesis process.

[0083] In addition, the supply source of hydrogen used in the synthesis process is not particularly limited, and it can be supplied and produced by any method. As a method for producing hydrogen, for example, synthesis based on electrolysis of water, and synthesis carried out by using decomposition reactions of ammonia or hydrocarbons and organic hydrides can be cited. However, if hydrocarbons or organic hydrides are used as raw materials, CO2 is discharged during the hydrogen synthesis process. Therefore, from the viewpoint of further reducing CO2 emissions, it is preferable to synthesize by at least one of electrolysis of water and decomposition of ammonia. In addition, when hydrogen is produced by electrolysis of water, by using green hydrogen produced by using electricity obtained from green energy such as sunlight, wind power, and geothermal energy, CO2 emissions can be made zero. The H2 concentration of hydrogen is not particularly limited, and it is preferably 90% by volume or more, more preferably 95% by volume or more. It should be noted that the H2 concentration of hydrogen can also be 100% by volume.

[0084] In the synthesis of CO in the reverse water-gas shift reaction, generally used catalysts can be utilized. Specifically, metals containing transition metals such as Fe, Cu, Ni, Zr, and Ti, and oxide-based catalysts can be used.

[0085] As the reactor of the carbon monoxide synthesis device used in the synthesis process, a fixed-bed reactor, a fluidized-bed reactor, a entrained-flow reactor, etc. can be used. As long as the physical properties of the catalyst are appropriately selected according to the form of these reactors.

[0086] It should be noted that it is not preferred to introduce a large amount of H2O by-produced through the reverse conversion reaction into the heating device. Therefore, considering the material balance of the entire circulation system, it is preferred to appropriately dehydrate the regenerated carbon monoxide gas using a dehydration device before the heating process described below.

[0087] In addition, the CO concentration of the regenerated carbon monoxide gas is not particularly limited. In the regenerated carbon monoxide gas after removing H2O, for example, in the regenerated carbon monoxide gas dehydrated by the above-mentioned dehydration device, the CO concentration is preferably 80% by volume or more, more preferably 90% by volume or more. It should be noted that the CO concentration in the regenerated carbon monoxide gas after removing H2O can also be 100% by volume.

[0088] ·Heating process

[0089] In the heating process, the gas obtained by mixing the regenerated carbon monoxide gas, the second top gas, and the additionally supplied hydrogen (hereinafter also referred to as the mixed gas) is heated to obtain a reducing gas. The mixing of the regenerated carbon monoxide gas, the second top gas, and the additionally supplied hydrogen can be carried out on the upstream side of the heating device as shown in Figure 2 or these gases can be directly supplied to the heating device from their respective independent pipelines and mixed inside the heating device. It should be noted that in Figure 2 , an example of supplying the second top gas and the additionally supplied hydrogen to the circulation pipeline of the regenerated carbon monoxide gas between the dehydration device and the heating device is shown, but it is not limited thereto. For example, the second top gas and the additionally supplied hydrogen can be supplied to the circulation pipeline of the regenerated carbon monoxide gas between the carbon monoxide synthesis device and the dehydration device. In addition, one of the second top gas and the additionally supplied hydrogen can be supplied to the circulation pipeline of the regenerated carbon monoxide gas between the dehydration device and the heating device, and the other can be supplied to the circulation pipeline of the regenerated carbon monoxide gas between the carbon monoxide synthesis device and the dehydration device.

[0090] Here, the additionally supplied hydrogen refers to the hydrogen supplied from outside the circulation system for mixing with the regenerated carbon monoxide gas and the second top gas, which is distinguished from the hydrogen supplied from outside the circulation system in the synthesis process. It should be noted that the supply source, H2 concentration, etc. of the additionally supplied hydrogen are not particularly limited as long as they are the same as the hydrogen supplied from outside the circulation system in the synthesis process. Examples of the specific supply location of the additionally supplied hydrogen are as described above.

[0091] It should be noted that the gas composition of the reducing gas (mixed gas) is, for example, CO: 1 - 60% by volume, H2: 40 - 99% by volume, balance: 0 - 30% by volume.

[0092] The heating temperature and heating means of the reducing gas (mixed gas) are not particularly limited and can be carried out according to conventional methods. For example, the heating temperature of the reducing gas (mixed gas) can be exemplified as 750 to 1100 °C.

[0093] In addition, by using green energy sources such as sunlight, wind power, and geothermal energy as the heat source of the heating device, it is possible to theoretically make the CO2 emission zero.

[0094] Next, the reducing gas is introduced into the reduction furnace via a blowing process. For example, it is introduced into the reduction furnace using a reducing gas blowing device. Then, in the reduction furnace, iron oxide is reduced using the reducing gas to obtain reduced iron. On the other hand, the reducing gas after being used for the reduction of iron oxide is discharged from the reduction furnace in the form of top gas.

[0095] In addition, it is preferable to perform at least one of dust removal and dehydration of the top gas before the above-mentioned distribution process. Any dust removal device can be used as the dust removal device for dust removal. In addition, any dehydration device can be used as the dehydration device for dehydration. It should be noted that the order of dust removal and dehydration is not particularly limited. In Figure 2 In the example shown, for the top gas, after dust removal using a dust removal device, dehydration is performed using a dehydration device, and then the top gas is distributed into the first top gas and the second top gas.

[0096] · Control of the gas volume introduced into the distribution process, synthesis process, and heating process

[0097] Moreover, in the method for manufacturing reduced iron according to an embodiment of the present invention, it is important to control the gas volume introduced (supplied) into the distribution process, synthesis process, and heating process according to the CO2 conversion rate. Thereby, the composition of the reducing gas blown into the reduction furnace, particularly the ratio of the amount of H2 to the amount of CO contained in the reducing gas, i.e., H2 / CO (hereinafter, also referred to as the H2 / CO of the reducing gas), can be stabilized. As a result, it is possible to continuously perform the operation of further energy saving and reduction of CO2 emissions with high operation stability. Specifically, it is a stable operation in which CO2 is not discharged outside the circulation system, CO is supplied from outside the circulation system, and the composition of the reducing gas is maintained within a constant range.

[0098] Here, the CO2 conversion rate represents the ratio of CO2 contained in the first top gas introduced into the synthesis process being converted into CO through the reverse shift reaction. For example, the CO2 conversion rate can be calculated by the following formula.

[0099] CO2 conversion rate η R [-]=1-(the amount of CO2 contained in the regenerated carbon monoxide gas discharged after synthesizing CO in the synthesis process [Nm 3 / t])÷(the amount of CO2 contained in the first top gas introduced into the synthesis process [Nm3 / t])

[0100] It should be noted that the CO2 conversion rate can be adjusted mainly by the reactor used in the synthesis process, such as the type or amount of catalyst used in the reactor, the volume of the reactor, the temperature of the reactor, etc. In addition, when a gas containing hydrogen or the like other than the first top gas is introduced into the synthesis process, the amount of CO2 contained in this gas is also included in (the amount of CO2 contained in the first top gas introduced into the synthesis process [Nm 3 / t]).

[0101] In addition, Nm 3 / t and kg / t are raw material units per 1 t of direct reduced iron (DRI) produced.

[0102] Moreover, for example, it is suitable to control the gas amounts introduced into the distribution process, the synthesis process, and the heating process in a manner that satisfies the following formulas (1) and (2).

[0103]

[0104] Here,

[0105] W CO2 : The amount of CO2 contained in the top gas introduced into the distribution process [Nm 3 / t]

[0106] W H2 : The amount of H2 contained in the top gas introduced into the distribution process [Nm 3 / t]

[0107] E H2 : The amount of H2 contained in the hydrogen introduced into the synthesis process [Nm 3 / t]

[0108] V CO2 : The amount of CO2 contained in the gas introduced into the heating process [Nm 3 / t]

[0109] V H2 : The amount of H2 contained in the gas introduced into the heating process [Nm 3 / t]

[0110] A H2 : The amount of H2 contained in the additional supplied hydrogen [Nm 3 / t].[[]]END]]

[0111] It should be noted that V CO2 and V H2The total amount of CO2 and H2 contained in the gas introduced into the heating process. The gas introduced into the heating process is basically the recycled carbon monoxide gas, the second top gas, and the additionally supplied hydrogen (or a mixed gas thereof). In addition, the hydrogen introduced into the synthesis process is the hydrogen introduced from outside the circulation system and does not include the separated hydrogen and the H2 in the first top gas mentioned above.

[0112] The left side of the above formula (1) can be rewritten as (W CO2 -V CO2 ) / W CO2 , which can be said to represent the ratio of the CO2 converted to CO in the CO2 introduced into the distribution process. Here, when the above formula (1) is not satisfied, the conversion amount of CO2 to CO in the synthesis process is insufficient, and CO2 becomes excessive in the circulation system. As a result, in order to perform stable operation under a sound material balance, it may be necessary to discharge CO2 outside the circulation system.

[0113] In addition, the left side of the above formula (2) can be rewritten as (W H2 +E H2 +A H2 -V H2 ) / (W H2 +E H2 ), which can be said to represent the ratio of the amount of H2 used for the reverse shift reaction in the synthesis process to the amount of H2 contained in the top gas and the amount of H2 contained in the hydrogen introduced into the synthesis process. Here, when the CO2 conversion rate is less than the left side value of the above formula (2), the reaction efficiency of the reverse shift reaction in the synthesis process is insufficient, and H2 becomes excessive in the circulation system. As a result, stable operation may sometimes not be possible under a sound material balance.

[0114] In summary, it is suitable to control the gas amounts introduced into the distribution process, the synthesis process, and the heating process in a manner that simultaneously satisfies the above formulas (1) and (2).

[0115] It should be noted that the left side of the above formula (1) is more preferably 1 - V CO2 / W CO2 + 0.015. In addition, the left side of the above formula (1) is further preferably 1 - V CO2 / W CO2 + 0.03.

[0116] The left side of the above formula (2) is more preferably 1 + (A H2 -V H2 ) / (W H2 +E H2 ) + 0.015. In addition, the left side of the above formula (2) is further preferably 1 + (A H2 -V H2 ) / (W H2 +EH2 ) + 0.03。

[0117] In addition, as long as the gas amounts introduced into the distribution process, synthesis process, and heating process simultaneously satisfy the above formulas (1) and (2), they can be constant or can be changed at any timing. In addition, the gas amounts introduced into the distribution process, synthesis process, and heating process at the start-up of the equipment are determined, for example, from the past operating history, and the gas amounts introduced into the distribution process, synthesis process, and heating process can be appropriately changed and controlled according to the subsequent operating conditions.

[0118] In addition, the iron oxide raw material used in the method for manufacturing reduced iron according to an embodiment of the present invention is, for example, iron ore. As specific examples, lump iron ore (lump ore), pellet (a substance obtained by solidifying powdered iron ore into a spherical shape), etc. can be cited. The quality of the iron ore used as the iron oxide raw material, that is, the iron content, is not particularly limited, and from the viewpoint of reduction in a shaft furnace, it is generally preferably 65% by mass or more.

[0119] In addition, in the method for manufacturing reduced iron according to an embodiment of the present invention, a method using a shaft furnace as a direct reduction ironmaking method will be particularly described. However, the type of reduction furnace is not limited thereto, and it can also be a method using a fluidized bed, rotary kiln, rotary hearth furnace (RHF), etc. It should be noted that since the production efficiency, operation rate, and operation stability are high, a shaft furnace is preferably used as the reduction furnace. In addition, most of the direct reduction furnaces operating in the world are of the shaft furnace type, such as Midrex (registered trademark) and Hyl (registered trademark).

[0120] Examples

[0121] Hereinafter, examples will be described.

[0122] In Figure 2 In the shown circulation system, reduced iron was manufactured according to the conditions described in Table 1. Under any conditions, the operation time was 28 days. In Table 1, the operation specifications are described in terms of the raw material unit per 1 t of reduced iron manufactured. For example, when 1300 kg of iron oxide pellets are used in manufacturing 1 t of reduced iron, the usage amount of the iron oxide pellets is expressed as 1300 kg / t. When manufacturing 3000 t / day of reduced iron, as long as this amount is enlarged by 3000 times, it is the specification for each day.

[0123] Here, under any conditions, iron oxide pellets as raw materials are charged into a reduction furnace at a rate of 1394 kg / t during the charging process. In the blowing process, a reducing gas heated to 980 °C is blown into the middle of the reduction furnace to reduce the iron oxide pellets and obtain reduced iron. Then, the top gas discharged from the reduction furnace is dust-removed and appropriately dehydrated to balance the material input and output. Next, the top gas is introduced into the distribution process and distributed into the first top gas and the second top gas. In the distribution process, the top gas introduced into the top gas distribution section is appropriately separated into carbon dioxide gas by any of the above (a) to (c) methods to balance the material input and output, and the separated carbon dioxide gas is distributed as the first top gas. The separated hydrogen is also introduced into the synthesis process in the form of the first top gas together with the separated carbon dioxide gas. In addition, the remaining gas (the first remaining gas, the second remaining gas, or the fourth remaining gas) is distributed as the second top gas. Next, the first top gas (a part, also including the separated hydrogen) and hydrogen from outside the circulation system are introduced into the carbon monoxide synthesis device. Then, regenerated carbon monoxide gas is synthesized by the reverse water-gas shift reaction in the reactor of the carbon monoxide synthesis device. After the synthesized regenerated carbon monoxide gas is dehydrated, it is mixed with the regenerated carbon monoxide gas, the second top gas, and the additional supplied hydrogen to form a mixed gas. Next, the mixed gas is introduced into the heating device, and the mixed gas is heated in the heating device to obtain a reducing gas. It should be noted that the total amount of the introduced gas in the heating process in Table 1 is the mixed gas, that is, the total amount of the regenerated carbon monoxide gas, the second top gas, and the additional supplied hydrogen. In addition, the conditions other than those described above and in Table 1 are in accordance with the conventional methods.

[0124]

[0125] In the inventive examples, during the entire operation period of 28 days, it is extremely advantageous in terms of energy conservation Figure 2 in the shown circulation system, that is, the system for recycling the top gas, to operate stably under a sound material balance. In addition, the CO2 emissions from this circulation system can also be made zero.

[0126] On the other hand, in the comparative examples where the gas volume is not controlled according to the CO2 conversion rate in the synthesis process, the composition of the reducing gas cannot be maintained within a constant range during the middle of the operation period, resulting in unstable reactions in the reduction furnace and the operation has to be interrupted.

[0127] Symbol Explanation

[0128] 1 Reduction furnace

[0129] 1a Iron oxide

[0130] 1b Reduced iron

[0131] 3 Dust removal device

[0132] 4 Dehydration device

[0133] 5 Natural gas supply section

[0134] 6 Air supply section

[0135] 7 Reforming device

[0136] 9 Reduction gas blowing device

[0137] 10 Hydrogen supply section

[0138] 11 Carbon monoxide synthesis device

[0139] 12 Heating device

[0140] 13 Heat source

[0141] 14 Top gas distribution section

Claims

1. A method for manufacturing reduced iron, comprising the following steps: A filling step of filling iron oxide into a reduction furnace; A blowing step of blowing 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 the top gas discharged from the reduction furnace into a first top gas and a second top gas; A synthesis step of synthesizing a regenerated carbon monoxide gas by an inverse water-gas shift reaction using the first top gas and hydrogen; and A heating step of heating a gas obtained by mixing the regenerated carbon monoxide gas, the second top gas, and additionally supplied hydrogen as the reducing gas; According to the CO2 conversion rate η of the reverse conversion reaction in the synthesis process R [-] Control the amount of gas introduced into the distribution process, the synthesis process, and the heating process.

2. The method for manufacturing reduced iron according to claim 1, wherein, Controlling the amounts of gases introduced into the distribution step, the synthesis step, and the heating step in such a manner as to satisfy the following formulas (1) and (2); Here, W CO2 : The amount of CO2 contained in the top gas introduced into the distribution process [Nm 3 / t] W H2 : Amount of H2 contained in top gas introduced into the distribution process [Nm 3 / t] E H2 : Amount of H2 contained in hydrogen introduced into the synthesis process [Nm 3 / t] V CO2 : Amount of CO2 contained in the gas introduced into the heating process [Nm 3 / t] V H2 : The amount of H2 contained in the gas introduced into the heating process [Nm 3 / t] A H2 : The amount of H2 contained in the additional supplied hydrogen [Nm 3 / t].

3. The method for manufacturing reduced iron according to claim 1 or 2, wherein, In the distribution step, separating the top gas into a separated carbon dioxide gas and a first remaining gas; Distributing the separated carbon dioxide gas as the first top gas; Distributing the first remaining gas as the second top gas.

4. The method for manufacturing reduced iron according to claim 1 or 2, wherein, In the distribution step, separating the top gas into a separated carbon dioxide gas and a first remaining gas; Distributing the separated carbon dioxide gas as the first top gas; Separating the first remaining gas into a separated hydrogen gas and a second remaining gas; Introducing the separated hydrogen gas into the synthesis step; Distributing the second remaining gas as the second top gas.

5. The method for manufacturing reduced iron according to claim 1 or 2, wherein, In the distribution step, separating the top gas into a separated hydrogen gas and a third remaining gas; Introducing the separated hydrogen gas into the synthesis step; Separating the third remaining gas into a separated carbon dioxide gas and a fourth remaining gas; Distributing the separated carbon dioxide gas as the first top gas and distributing the fourth remaining gas as the second top gas.

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