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 in the amount of CO2 emissions. A system for recycling furnace top gas, which has a blowing step, a reduction step, a distribution step, a generation step, and a heating step, is configured, and the amount of gas introduced into the distribution step, the generation step, and the heating step is controlled in accordance with the CO2 conversion rate of an electrolytic reaction in the generation 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 necessary. The most common reduction process widely used in the world is the blast furnace. In the blast furnace, coke, pulverized coal, and oxygen in hot air (air heated to around 1200°C) react at the tuyere. Through this reaction, CO and H2, which are reduction gases, are generated, and these reduction gases are used to reduce iron ore, etc. 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 ton of hot metal produced) has been reduced to around 500 kg / t, and the reductant ratio has almost reached the lower limit. Therefore, a further significant reduction in the reductant ratio cannot be expected.

[0003] On the other hand, in areas 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 also 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. Moreover, 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 is 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 for 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 in 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 for 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 out of the system.

[0005] As such a reduced iron manufacturing process, for example, Patent Document 1 discloses 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, Patent Document 2 describes the following method: A reducing gas is produced by reforming coke gas and the top gas of a reduction furnace from which CO2 has been removed, and the reducing gas is blown into the reduction furnace to produce reduced iron.

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2017-88912

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

[0011] In the method described in Patent Document 1, a reducing gas is produced using natural gas supplied from the outside. Therefore, there is a problem that although the CO2 emissions are less than those of a blast furnace, a certain degree of CO2 emissions cannot be avoided.

[0012] In addition, the method described in Patent Document 2 uses coke gas or converter gas generated in a steel mill to produce a reducing gas. Here, in an integrated steel mill, coke 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 gas or converter gas is diverted to the reduced iron manufacturing process, a shortage of fuel gas will occur 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 in the method described in Patent Document 2, it is impossible to simultaneously achieve energy saving and a reduction in CO2 emissions, and there is a problem.

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

[0014] The inventors of the present invention repeatedly conducted research in order to simultaneously achieve energy saving and a reduction in CO2 emissions, and developed a system for recycling top gas.

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

[0016] Blowing process, blowing a reducing gas into a reduction furnace;

[0017] Reduction process, reducing iron oxide with a reducing gas in a reduction furnace to obtain reduced iron;

[0018] Distribution process, distributing the top gas discharged from the reduction furnace into a first top gas and a second top gas;

[0019] Generation process, generating a regenerated carbon monoxide gas by an electrolysis reaction using the first top gas; and

[0020] In the heating step, a mixture of the regenerated carbon monoxide gas and the second top gas is heated to produce a reducing gas.

[0021] Furthermore, the present inventors have obtained the following findings as a result of further repeated studies.

[0022] In the above-mentioned circulation system, the CO2 conversion rate η of the electrolysis reaction in the generation step (i.e., the reaction of reforming CO2 contained in the first top gas into CO by electrolysis) C [-] (hereinafter also referred to as CO2 conversion rate) controls the amount of gas introduced into the distribution process, generation process and heating process.

[0023] Thus, it is possible to produce reduced iron with high operational stability without inputting excess energy, that is, while achieving further energy saving and reduction in CO 2 emissions.

[0024] The present invention has been completed as a result of further research based on the above findings.

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

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

[0027] Filling process, filling the reduction furnace with iron oxide;

[0028] a blowing step of blowing reducing gas into the reduction furnace;

[0029] a reduction step of reducing the iron oxide using the reducing gas in the reduction furnace to obtain reduced iron;

[0030] a distribution step of distributing the top gas discharged from the reduction furnace into a first top gas and a second top gas;

[0031] a generating step of generating regenerated carbon monoxide gas by electrolytic reaction using the first top gas; and

[0032] a heating step of heating a mixed gas formed by mixing the regenerated carbon monoxide gas and the second top gas to produce the reducing gas;

[0033] According to the CO2 conversion rate η of the electrolysis reaction in the above-mentioned generation process C [-] Control the amount of gas introduced into the above-mentioned distribution step, the above-mentioned generation step, and the above-mentioned heating step.

[0034] 2. The method for producing reduced iron according to item 1 above, wherein the amount of gas introduced into the distribution step, the generation step, and the heating step is controlled so as to satisfy the following formula (1).

[0035]

[0036] Among them,

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

[0038] V CO2 : The amount of CO2 contained in the gas introduced into the heating process [Nm 3 / t].

[0039] 3. The method for manufacturing reduced iron according to 1 or 2 above, wherein, in the above distribution process, the above top gas is separated into separated carbon dioxide gas and the remaining gas,

[0040] The separated carbon dioxide gas is distributed as the above first top gas,

[0041] The remaining gas is distributed as the above second top gas.

[0042] According to the present invention, when manufacturing reduced iron, it is possible to perform operations that simultaneously achieve further energy saving and reduction of CO2 emissions with high operation stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 is a diagram showing the manufacturing process of conventional reduced iron.

[0044] Figure 2 is a diagram showing an example of the manufacturing process of reduced iron related to the method for manufacturing reduced iron according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0045] The method for manufacturing reduced iron according to an embodiment of the present invention will be described below with reference to the drawings.

[0046] First, the manufacturing process of conventional reduced iron (hereinafter also referred to as the conventional manufacturing process) will be described. Figure 1 is a diagram showing a schematic configuration of an example of the 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 section, 6 is an air supply section, 7 is a reforming device, and 9 is a reducing gas blowing device.

[0047] In an example of a conventional manufacturing process, iron oxide is charged from the upper part of a reduction furnace and allowed to slowly descend. The iron oxide is reduced by blowing high-temperature reducing gas into the furnace from the middle part of the reduction furnace. 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-removing 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, is supplied to the reforming device together with the moisture-adjusted top gas, for example, from a natural gas supply section. Next, in the reforming device, the supplied gas is heated. Then, a reforming reaction occurs to generate high-temperature 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 out of the system in a state containing CO2. It should be noted that if reduced iron is manufactured by this example of the conventional manufacturing process, when manufacturing 1 t of reduced iron, about 1 t or more of CO2 is discharged out of the circulation system.

[0048] On the other hand, in a 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 generation device, regenerated carbon monoxide gas is generated by an electrolytic reaction using the first top gas. Then, the regenerated carbon monoxide gas and the second top gas 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 reducing gas and blown into the reduction furnace from a reducing gas blowing device. In the figure, reference numeral 10 is a water vapor supply section, 11 is a carbon monoxide generation device, 12 is a heating device, 13 is a heat source, and 14 is a top gas distribution section.

[0049] The following describes each process of the method for manufacturing reduced iron according to an embodiment of the present invention. It should be noted that the filling process, the blowing process, and the reduction process are carried out according to a conventional method. For example, they can be carried out in the same manner as the above-described conventional manufacturing process, and thus the description thereof is omitted here.

[0050] · Distribution process

[0051] In the distribution process, for example, 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. In addition, the means for distributing and controlling the flow rate of the top gas is not particularly limited and can be according to a conventional method. For example, a mass flow controller or the like can be used.

[0052] In the distribution process, the top gas can be distributed according to its original composition. Additionally, for example, specific gas species such as CO2 can be separated and distributed as follows. That is, the top gas can be separated into separated carbon dioxide gas and the remaining gas (CO2 separation), the separated carbon dioxide gas can be distributed as the first top gas, and the remaining gas can be distributed as the second top gas.

[0053] Herein, the method for 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-fuel 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. Additionally, these methods also have a track 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 be 100 vol%.

[0054] In addition, the composition of the remaining gas distributed as the second top gas varies according to the amount of separated CO2, and for example, it is CO: 5 - 70 vol%, CO2: 0 - 25 vol%, H2: 25 - 75 vol%, H2O: 0 - 50 vol%, balance: 0 - 30 vol%.

[0055] It should be noted that when the top gas is distributed into the first top gas and the second top gas according to its original composition in the distribution process, a separation process for separating specific gas species such as CO2 from the first top gas and the second top gas can be arbitrarily provided between the above-mentioned distribution process and the subsequent generation process.

[0056] For example, as described above, the first top gas is separated into separated carbon dioxide gas and the remaining gas (CO2 separation), and the separated carbon dioxide gas is used as the first top gas in the generation process. The above-mentioned remaining gas can be directly merged with the second top gas.

[0057] In addition, from the perspective 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, etc. For example, in the combustion chamber of the heating device, using the oxygen supplied from the oxygen supply device, as an example, using the pure oxygen generated by a cryogenic separation process driven by CO2-free electricity, a part of the top gas is burned. Additionally, the burned top gas can be dehydrated as needed and then returned to the original pipeline.

[0058] · Generation process

[0059] In the generation process, for example, in a carbon monoxide generation device, the first top gas distributed in the above-described distribution process is used to generate regenerated carbon monoxide gas through an electrolysis reaction. It should be noted that CO is generated, for example, by electrolyzing CO2 contained in the first top gas according to the reaction formula of the following formula (i).

[0060] CO2 → CO + 1 / 2O2 ··· (i)

[0061] In addition, when H2O is contained in the first top gas or when steam is introduced together with the first top gas, it is preferable to electrolyze H2O simultaneously with CO2. In this case, H2 is generated according to the reaction formula of the following formula (ii).

[0062] H2O → H2 + 1 / 2O2 ··· (ii)

[0063] It should be noted that hereinafter, the reaction of simultaneously electrolyzing CO2 and H2O according to the above formulas (i) and (ii) is also referred to as a co-electrolysis reaction.

[0064] That is, in the reduction furnace, CO and H2 are consumed in the reduction reaction of iron oxide and become CO2 and H2O. Therefore, by comparing the composition of the reducing gas blown into the reduction furnace with the composition of the top gas discharged from the reduction furnace, it can be known that CO and H2 decrease, and CO2 and H2O increase. Therefore, from the viewpoint of maintaining the composition of the reducing gas within a certain range in the above-described circulation system, it is preferable to perform a co-electrolysis reaction and adjust the variation amount of H2 in addition to CO.

[0065] The electrolysis conditions of CO2 and H2O are not particularly limited, and conventional methods can be used.

[0066] In addition, when using the separated carbon dioxide gas obtained in the above-described distribution process or separation process, the composition of the first top gas is the same as the composition of the separated carbon dioxide gas. When the top gas is distributed according to the original composition in the distribution process and does not pass 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. The composition of the first top gas in this case is, for example, CO: 5 to 50% by volume, CO2: 5 to 30% by volume, H2: 5 to 80% by volume, H2O: 0 to 35% by volume, balance: 0 to 20% by volume. The composition of the second top gas described later is the same.

[0067] It should be noted that in the production 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 the other gas, for example, the gas by-produced in the steelmaking process can be cited, and specifically, blast furnace gas (BFG) and coke oven gas (COG) can be cited. In addition, the other gas and the first top gas can be introduced into the above separation process together, and after being separated into separated carbon dioxide gas and the remaining gas, the separated carbon dioxide gas can be supplied to the production process.

[0068] In addition, in the production process, steam can be introduced together with the first top gas in consideration of the overall material balance of the circulation system. For example, steam can be introduced into the carbon monoxide generation device after being supplied to the flow production line of the first top gas, or can be directly introduced into the carbon monoxide generation device from an independent production line. Steam can be supplied from outside the above circulation system, or the dehydrated H2O in the dehydration device can be reused.

[0069] In addition, from the viewpoint of electrolysis efficiency, the following method is preferred. That is, in the above distribution process, the top gas is separated into separated carbon dioxide gas and the remaining gas (CO2 separation). Then, the separated carbon dioxide gas is introduced into the production process as the first top gas, and steam is introduced into the production process. It should be noted that the remaining gas is the second top gas.

[0070] The electrolysis device used as the carbon monoxide generation device is not particularly limited, and a generally used device can be used. In addition, the electric power used in electrolysis is not particularly limited. The electric power used in electrolysis is particularly preferably CO2-free electric power, for example, the electric power supplied by solar power generation or wind power generation.

[0071] It should be noted that it is not preferable to introduce a large amount of H2O in the heating process described below. Therefore, it is preferable to appropriately dehydrate the regenerated carbon monoxide gas using a dehydration device before the heating process described below in consideration of the overall material balance of the circulation system.

[0072] In addition, the composition of the regenerated carbon monoxide gas is not particularly limited. After removing H2O, in the regenerated carbon monoxide gas, for example, in the regenerated carbon monoxide gas dehydrated by the above dehydration device, its composition is CO: 1 to 60% by volume, H2: 40 to 99% by volume, and the balance: 0 to 30% by volume.

[0073] It should be noted that oxygen, which is a by-product generated when carbon monoxide is produced, is separated from the gas in the above-mentioned circulation system. That is, generally, the gas in the circulation system (regenerated carbon monoxide gas) and oxygen have been separated in the carbon monoxide generation device. Therefore, there is no need to specifically provide an oxygen separation device, but this does not limit the setting of the separation device. The separated oxygen can be released into the atmosphere, but it is preferably appropriately used for other purposes such as combustion oxygen when heating the gas in the above-mentioned circulation system or supplementing the required oxygen in other processes inside and outside the steel plant.

[0074] · Heating process

[0075] In the heating process, the gas formed by mixing the regenerated carbon monoxide gas and the second top gas (hereinafter also referred to as the mixed gas) is heated to obtain a reducing gas. The mixing of the regenerated carbon monoxide gas and the second top gas can be carried out as shown Figure 2 upstream of the heating device, or these gases can be directly supplied to the heating device from independent production lines and mixed inside the heating device. It should be noted that Figure 2 in the example, the second top gas is supplied to the circulation production line of the regenerated carbon monoxide gas between the dehydration device and the heating device, but it is not limited thereto. For example, the second top gas can also be supplied to the circulation production line of the regenerated carbon monoxide gas between the carbon monoxide generation device and the dehydration device.

[0076] It should be noted that the gas composition of the reducing gas (mixed gas) is, for example, CO: 1 to 60% by volume, H2: 40 to 99% by volume, and the balance: 0 to 30% by volume.

[0077] There is no particular limitation on the heating temperature and heating means of the reducing gas (mixed gas), and conventional methods can be used. For example, as the heating temperature of the reducing gas (mixed gas), 750 to 1100 °C can be exemplified.

[0078] In addition, by using green energy such as sunlight, wind energy, and geothermal energy as the heat source of the heating device, theoretically, the CO2 emissions can be made zero.

[0079] Next, the reducing gas is introduced into the reduction furnace via the blowing process. For example, a reducing gas blowing device is used to introduce it into the reduction furnace. Then, in the reduction furnace, iron oxide is reduced with 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.

[0080] 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 for the dust removal device used in dust removal. In addition, any dehydration device can be used for the dehydration device used in dehydration. It should be noted that the order of dust removal and dehydration is not particularly limited.Figure 2 In the example shown, after dust removal of the top gas using a dust removal device, dehydration is performed using a dehydration device. Thereafter, the top gas is distributed into a first top gas and a second top gas.

[0081] · Control of the gas amounts introduced into the distribution process, generation process, and heating process

[0082] Then, in the method for manufacturing reduced iron according to an embodiment of the present invention, it is important to control the gas amounts introduced (supplied to) the distribution process, generation 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. Thereby, under high operation stability, an operation that simultaneously achieves further energy saving and reduction in CO2 emissions can be continuously performed. Specifically, a stable operation of maintaining the composition of the reducing gas within a certain range without discharging CO2 outside the circulation system or supplying CO from outside the circulation system can be continuously performed.

[0083] Here, the CO2 conversion rate represents the ratio of CO2 contained in the first top gas introduced into the generation process that is converted into CO through an electrolytic reaction. For example, the CO2 conversion rate can be calculated by the following formula.

[0084] CO2 conversion rate η C [-] = 1 - (amount of CO2 [Nm 3 / t] contained in the regenerated carbon monoxide gas discharged after CO is generated in the generation process) ÷ (amount of CO2 [Nm 3 / t] contained in the first top gas introduced into the generation process)

[0085] It should be noted that the CO2 conversion rate can be mainly adjusted by the reactor itself used in the generation process. For example, the type, amount, surface area, thickness of the materials used for the electrodes or electrolytes used in the reactor, as well as the temperature of the reactor and the amount of electric power supplied to the reactor. In addition, when there is a gas introduced into the generation process in addition to the first top gas such as water vapor, the amount of CO2 contained in this gas is also included in (amount of CO2 [Nm 3 / t] contained in the first top gas introduced into the generation process).

[0086] In addition, Nm 3 / t and kg / t are basic units per ton of reduced iron (DRI) manufactured.

[0087] Moreover, for example, it is preferable to control the gas amounts introduced into the distribution process, generation process, and heating process in a manner that satisfies the following formula (1).

[0088]

[0089] Among them,

[0090] W CO2 : The amount of CO2 contained in the top gas introduced into the distribution process [Nm 3 / t]

[0091] V CO2 : The amount of CO2 contained in the gas introduced into the heating process [Nm 3 / t].

[0092] It should be noted that V CO2 is the total amount of CO2 contained in the gas introduced into the heating process. The gas introduced into the heating process is basically the recycled carbon monoxide gas and the second top gas (or their mixed gas).

[0093] 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 proportion of 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 from CO2 to CO in the generation process is insufficient, and CO2 remains 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.

[0094] In summary, it is preferable to control the gas amounts of the distribution process, the generation process, and the heating process in such a way as to satisfy the above formula (1).

[0095] 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.

[0096] In addition, the gas amounts of the distribution process, the generation process, and the heating process only need to satisfy the above formula (1), and can be constant or changed at any time. In addition, the gas amounts of the distribution process, the generation process, and the heating process at the start of the equipment can be determined according to, for example, past operation experience, and the gas amounts of the distribution process, the generation process, and the heating process can be appropriately changed and controlled according to the subsequent operation conditions.

[0097] 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.

[0098] 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 reduced steelmaking method has been particularly described. However, the type of reduction furnace is not limited thereto, and it may also be a method using a fluidized bed, a rotary kiln, a rotary hearth furnace (RHF), etc. It should be noted that, from the viewpoint of high production efficiency, operation rate, and operation stability, a shaft furnace is preferably used as the reduction furnace. In addition, most of the direct reduction furnaces operating globally are of the shaft furnace type, such as Midrex (registered trademark) and Hyl (registered trademark).

[0099] Examples

[0100] Examples will be described below.

[0101] In Figure 2 In the circulation system shown, reduced iron is manufactured according to the conditions described in Table 1. Regardless of the conditions, the operation period is 28 days. In Table 1, the operation specifications are described in basic units per 1 t of reduced iron manufactured. For example, when 1300 kg of iron oxide pellets are used to manufacture 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, this amount is multiplied by 3000 times as the daily specification.

[0102] Here, under any conditions, in the filling process, iron oxide pellets as raw materials are filled into the reduction furnace under the condition of 1394 kg / t. In the blowing process, reduction gas heated to 980 °C is blown from the middle of the reduction furnace to reduce the iron oxide pellets to obtain reduced iron. Then, after dust removal of the top gas discharged from the reduction furnace, dehydration is appropriately carried out in a manner that matches the material balance. 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 separated carbon dioxide gas and the remaining gas (CO2 separation) to balance the material income and expenditure. Then, the separated carbon dioxide gas is used as the first top gas and introduced into the carbon monoxide generation device on the basis of adding an appropriate amount of water vapor. Next, in the carbon monoxide generation device, regenerated carbon monoxide gas is generated through a co-electrolysis reaction. After appropriately dehydrating the generated regenerated carbon monoxide gas, the regenerated carbon monoxide gas and the second top gas are mixed to form a mixed gas. Then, the mixed gas is introduced into the heating device, and the mixed gas is heated in the heating device to obtain reduction 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 and the second top gas. W H2 The amount of H2 contained in the top gas introduced into the distribution process. V H2 The amount of H2 contained in the gas (regenerated carbon monoxide gas and the second top gas) introduced into the heating process. In addition, conditions other than the above and those described in Table 1 can be in accordance with conventional methods.

[0103]

[0104] In the inventive examples, it is possible to achieve extremely favorable energy conservation throughout the entire operation period of 28 days Figure 2 in the shown circulation system, that is, the system that recycles the top gas, and stably operate under a sound material balance. In addition, it is also possible to make the CO2 emission amount from this circulation system zero.

[0105] On the other hand, in the comparative examples without controlling the gas volume according to the CO2 conversion rate in the generation process, during the middle of the operation period, the composition of the reduction gas could not be maintained within a certain range, the reaction in the reduction furnace was unstable, and the operation had to be interrupted.

[0106] Symbol Explanation

[0107] 1 Reduction Furnace

[0108] 1a Iron Oxide

[0109] 1b Reduced Iron

[0110] 3 Dust Removal Device

[0111] 4 Dehydration device

[0112] 5 Natural gas supply section

[0113] 6 Air supply section

[0114] 7 Reforming device

[0115] 9 Reduction gas blowing device

[0116] 10 Steam supply section

[0117] 11 Carbon monoxide generation device

[0118] 12 Heating device

[0119] 13 Heat source

[0120] 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 generation step of generating regenerated carbon monoxide gas by an electrolysis reaction using the first top gas; And A heating step of heating a mixed gas formed by mixing the regenerated carbon monoxide gas and the second top gas to produce the reducing gas, According to the CO2 conversion rate η of the electrolysis reaction in the generation process C [-]Control the gas amounts introduced into the distribution process, the generation process, and the heating process.

2. The method for manufacturing reduced iron according to claim 1, controlling the gas amounts introduced into the distribution step, the generation step, and the heating step in a manner that satisfies the following formula (1), wherein, W CO2 : The amount of CO2 contained in the top gas introduced into the distribution process, in Nm 3 / t, V CO2 : The amount of CO2 contained in the gas introduced into the heating process, in Nm 3 / t.

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

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