Method for producing reduced iron

Abstract

Provided is a method for producing reduced iron, the method rendering energy saving and a reduction in CO2 emission possible at the same time. This method employs a system which comprises a blowing step, a reduction step, a distribution step, a generation step, and a heating step and in which a furnace gas is circulated and reutilized. The amounts of gases to be introduced into the distribution step, the generation step, and the heating step are regulated in accordance with the degree of CO2 conversion by electrolysis in the generation step.

Description

[Technical field]

[0001] The present invention relates to a method for producing reduced iron. [Background technology]

[0002] In recent years, energy conservation has been strongly demanded in steelworks against the backdrop of global environmental problems and fossil fuel depletion problems. The raw material of 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 or pulverized coal reacts with oxygen in hot air (air heated to about 1200°C) at the tuyere. This reaction produces reducing gases CO and H2, which are used to reduce iron ore and other materials in the furnace. With the recent improvement of blast furnace operation technology, the reducing agent ratio (the amount of coke and pulverized coal used to produce 1 ton of molten iron) has been reduced to about 500 kg / t, which is already almost at the lower limit. Therefore, no further significant reduction in the reducing agent ratio is expected.

[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 often used. In this method, a reduction furnace is filled with agglomerated iron ore such as sintered ore or pellets (hereinafter also simply referred to as iron oxide) as an iron oxide raw material. Then, a reducing gas containing CO and H2 is blown into the reduction furnace to reduce the iron oxide and produce reduced iron. In this method, natural gas or the like is used as a raw material gas for the reducing gas. This raw material gas is heated and reformed in a reformer together with the top gas. This produces a reducing gas. Here, the top gas is a gas after being used for 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 blown into the reduction furnace and reacts with the iron oxide supplied from the top of the reduction furnace. Then, the iron oxide is reduced to produce reduced iron. Next, the reduced iron is cooled in a region below the position where the reducing gas is blown into the reduction furnace, and then discharged from the bottom of the reduction furnace.

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

[0005] As such a reduced iron production process, for example, Patent Document 1 describes a method in which exhaust gas from a reduction furnace and natural gas are reformed in a reformer to generate a reducing gas mainly composed of CO and H, and this reducing gas is blown into a reduction furnace to reduce iron oxide in the reduction furnace, thereby producing reduced iron.

[0006] Furthermore, Patent Document 2 describes a method for producing reduced iron by reforming coke oven gas and top gas of a reducing furnace from which CO2 has been removed to produce reducing gas, and then injecting the reducing gas into a reducing furnace. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2017-88912 A [Patent Document 2] Patent No. 6190522 Summary of the Invention [Problem to be solved by the invention]

[0008] In the method described in Patent Document 1, natural gas supplied from an external source is used to produce the reducing gas, and therefore, although the amount of CO2 emitted is lower than that emitted from a blast furnace, a certain amount of CO2 is unavoidable.

[0009] Moreover, the method described in Patent Document 2 produces reducing gas using coke oven gas or converter gas generated in a steelworks. Here, 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 or converter gas is diverted to the reduced iron production process, it will cause a fuel gas shortage in the downstream processes. As a result, natural gas will be supplied from outside to compensate for the shortage of fuel gas in the downstream processes. In other words, even with the method described in Patent Document 2, energy saving and reduction of CO2 emissions cannot be achieved at the same time, and problems remain.

[0010] The present invention has been made in consideration of the above-mentioned current situation, and has an object to provide a method for producing reduced iron that can simultaneously achieve energy saving and reduction in CO2 emissions. [Means for solving the problem]

[0011] The inventors conducted extensive research to simultaneously achieve energy savings and reduction in CO2 emissions, and developed a system for circulating and reusing furnace gas. That is, the inventors a blowing step of blowing a reducing gas into the reduction furnace; a reduction step of reducing the iron oxide with a reducing gas in a reduction furnace to obtain reduced iron; a distribution step of distributing a top gas discharged from the reducing furnace into a first top gas and a second top gas; a generating step of generating regenerated carbon monoxide gas by an electrolytic reaction using the first furnace top gas; a heating step of heating the mixed gas of the regenerated carbon monoxide gas and the second furnace gas to obtain a reducing gas; We have developed a top gas circulation and reuse system (hereinafter simply referred to as the circulation system) that has the following features.

[0012] Furthermore, the inventors conducted further studies and obtained the following findings. In the above circulation system, the CO2 conversion rate η due to the electrolytic reaction in the generation process (i.e., the reaction in which the CO2 contained in the first furnace gas is reformed into CO by electrolysis) C The amounts of gas introduced into the distribution process, the production process, and the heating process are controlled according to [-] (hereinafter also referred to simply as CO2 conversion rate). This makes it possible to produce reduced iron with high operational stability without inputting extra energy, thereby achieving further energy savings and reducing CO2 emissions at the same time. The present invention was completed based on the above findings and through further investigation.

[0013] That is, the gist and configuration of the present invention are as follows.

[0014] 1. A charging step of charging 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 a top gas discharged from the reducing furnace into a first top gas and a second top gas; a generating step of generating regenerated carbon monoxide gas by an electrolytic reaction using the first furnace top gas; a heating step of heating a mixed gas obtained by mixing the regenerated carbon monoxide gas and the second furnace gas to obtain the reducing gas; having CO2 conversion rate η by electrolysis reaction in the generation process C The method for producing reduced iron, further comprising controlling the amounts of gas introduced into the distributing step, the generating step, and the heating step in response to [-].

[0015] 2. The method for producing reduced iron according to item 1, wherein the amounts of gas introduced into the distribution step, the generation step, and the heating step are controlled so as to satisfy the following formula (1):

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[0016] 3. In the distribution step, the furnace gas is separated into a separated carbon dioxide gas and a remaining gas, Distributing the separated carbon dioxide gas as the first top gas; 3. The method for producing reduced iron according to 1 or 2, wherein the remaining gas is distributed as the second top gas. Effect of the Invention

[0017] According to the present invention, in the production of reduced iron, it is possible to carry out an operation that simultaneously achieves further energy saving and reduction in CO2 emissions under highly stable operation. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram showing a conventional process for producing reduced iron. [Diagram 2] FIG. 2 is a diagram showing an example of a process for producing reduced iron according to a method for producing reduced iron according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, a method for producing reduced iron according to an embodiment of the present invention will be described with reference to the drawings.

[0020] First, a conventional manufacturing process for reduced iron (hereinafter also referred to as the conventional manufacturing process) will be described. Fig. 1 is a diagram showing a schematic configuration of an example of the conventional manufacturing process. In the figure, reference numeral 1 denotes a reduction furnace, 1a denotes iron oxide, 1b denotes reduced iron, 3 denotes a dust remover, 4 denotes a dehydrator, 5 denotes a natural gas supply section, 6 denotes an air supply section, 7 denotes a reformer, and 9 denotes a reducing gas blowing device.

[0021] In one example of the conventional manufacturing process, iron oxide is charged from the top of the reduction furnace and gradually lowered. High-temperature reducing gas is 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, furnace top gas containing mainly CO, CO2, H2, and H2O is discharged from the top of the reduction furnace. This furnace top gas is dusted in a dust collector, and a portion of the top gas is adjusted in moisture and sent to the reformer as a raw material gas. A gas containing a hydrocarbon, for example, natural gas from a natural gas supply unit, is supplied to the reformer together with the moisture-adjusted top gas. The supplied gas is then heated in the reformer. A reforming reaction occurs, and a high-temperature reducing gas containing mainly CO and H2 is generated. This reducing gas is then blown into the reduction furnace. The remaining part of the top gas is dehydrated and used as heating fuel in the combustion chamber of the reformer. After being burned as a heating fuel, the top gas is usually discharged outside the system while still containing CO2. When reduced iron is produced using one example of the conventional manufacturing process, approximately 1 ton of CO2 is discharged outside the circulation system per ton of reduced iron produced.

[0022] On the other hand, in a method for producing reduced iron according to an embodiment of the present invention, as shown in FIG. 2, for example, in a furnace gas distribution section, the furnace gas discharged from a reducing furnace is distributed into a first furnace gas and a second furnace gas. Then, in a carbon monoxide generator, the first furnace gas is used to generate regenerated carbon monoxide gas by an electrolytic reaction. Then, the regenerated carbon monoxide gas and the second furnace gas are mixed to generate a mixed gas. Then, in a heating device, the mixed gas is heated. Then, this heated mixed gas is blown into the reducing furnace as a reducing gas from a reducing gas blowing device. In the figure, reference numeral 10 denotes a steam supply section, 11 denotes a carbon monoxide generator, 12 denotes a heating device, 13 denotes a heat source, and 14 denotes a furnace gas distribution section. 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, the blowing step, and the reducing step may be performed in a conventional manner, for example, in the same manner as in the above-mentioned conventional production process, and therefore the description thereof will be omitted here.

[0023] ·Distribution process In the distribution step, for example, in the top gas distribution section, the top gas discharged from the reducing furnace is distributed into a first top gas and a second top gas. The distribution and flow rate control means of the top gas are not particularly limited and may be in accordance with a conventional method. For example, a mass flow controller may be used.

[0024] In the distribution step, the top gas may be distributed with its composition unchanged. In addition, for example, a specific gas species such as CO2 may be separated and distributed as follows. That is, the top gas may be separated into a separated carbon dioxide gas and a residual gas (CO2 separation), and the separated carbon dioxide gas may be distributed as a first top gas, and the residual gas may be distributed as a second top gas.

[0025] 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, oxygen combustion method, chemical looping combustion method, etc. can be used. Among them, chemical absorption method represented by amine absorption method and adsorption separation method represented by PSA method have a long history of use in chemical plants and industrial CO2 production. In addition, these methods have a track record of recovering gas with a CO2 concentration of 99% or more by volume. Therefore, these methods are preferred. The CO2 concentration in the separated carbon dioxide gas is preferably 90% by volume or more. The CO2 concentration in the separated carbon dioxide gas may be 100% by volume.

[0026] The composition of the remaining gas distributed as the second furnace gas varies depending on the amount of CO2 separated, but is, for example, CO: 5-70 volume %, CO2: 0-25 volume %, H2: 25-75 volume %, H2O: 0-50 volume %, and the remainder: 0-30 volume %.

[0027] In addition, when the top gas is distributed into the first top gas and the second top gas with the same composition in the distribution step, a separation step for separating specific gas species such as CO2 from the first top gas and the second top gas may be optionally included between the above distribution step and the production step described later. For example, as described above, the first furnace gas may be separated into a separated carbon dioxide gas and a residual gas (CO2 separation), and the separated carbon dioxide gas may be used as the first furnace gas in the production step. The residual gas may be directly merged with the second furnace gas.

[0028] 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 may be used as a 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 combusted using oxygen supplied from an oxygen supply device, for example, pure oxygen produced by a cryogenic separation process driven by CO2-free electricity. In addition, the top gas after combustion may be dehydrated as necessary and then returned to the original line.

[0029] ·Generation process In the generating step, for example, in a carbon monoxide generating device, the first top gas distributed in the above-mentioned distribution step is used to generate regenerated carbon monoxide gas by an electrolytic reaction. Note that CO is generated, for example, by electrolyzing CO2 contained in the first top gas according to the following reaction formula (i). CO2 → CO+1 / 2O2 (i)

[0030] In addition, when the first furnace gas contains H2O or when steam is introduced together with the first furnace gas, it is preferable to electrolyze H2O simultaneously with CO2. In this case, H2 is generated according to the following reaction formula (ii). HO → H2+1 / 2O2 (ii) In addition, the simultaneous electrolysis of CO2 and H2O according to the above formulas (i) and (ii) is hereinafter also referred to as a co-electrolysis reaction.

[0031] That is, in the reducing furnace, CO and H2 are consumed in the reduction reaction of iron oxide to become CO2 and H2O. Therefore, when comparing the composition of the reducing gas blown into the reducing furnace with the composition of the top gas discharged from the reducing furnace, 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-mentioned circulation system, it is preferable to carry out a co-electrolysis reaction to adjust the fluctuations in not only CO but also H2.

[0032] The conditions for electrolysis of CO2 and H2O are not particularly limited, and may be in accordance with conventional methods.

[0033] In addition, when using the separated carbon dioxide gas obtained in the above-mentioned distribution step or separation step, the composition of the first furnace gas is the same as that of the separated carbon dioxide gas. When the furnace gas is distributed in the distribution step with its composition as it is and does not go through the separation step, the composition of the first furnace gas is basically the same as that of the furnace gas introduced into the distribution step. In this case, the composition of the first furnace gas is, for example, CO: 5-50 volume %, CO2: 5-30 volume %, H2: 5-80 volume %, H2O: 0-35 volume %, and the balance: 0-20 volume %. The composition of the second furnace gas described later is also the same.

[0034] In addition to the first furnace gas, any other gas containing CO2 (hereinafter also referred to as other gas) can also be used in the production process. Examples of other gases include gases produced as by-products in the steelmaking process, specifically blast furnace gas (BFG) and coke oven gas (COG). In addition, the other gas may be introduced into the above-mentioned separation process together with the first furnace gas, and separated into separated carbon dioxide gas and remaining gas, and then the separated carbon dioxide gas may be supplied to the production process.

[0035] In the generation step, steam may be introduced together with the first furnace gas while taking into consideration the material balance of the entire circulation system. For example, the steam may be supplied to the distribution line of the first furnace gas and then introduced into the carbon monoxide generator, or may be directly introduced into the carbon monoxide generator from an independent line. The steam may be supplied from outside the circulation system, or H2O dehydrated in a dehydrator may be reused.

[0036] In addition, from the viewpoint of the efficiency of electrolysis, the following embodiment is preferable. That is, in the above-mentioned distribution process, the furnace gas is separated into a separated carbon dioxide gas and a remaining gas (CO2 separation). Then, the separated carbon dioxide gas is introduced into the production process as a first furnace gas, and water vapor is introduced into the production process. The remaining gas is the second furnace gas.

[0037] The electrolysis device used as the carbon monoxide generator is not particularly limited, and a commonly used device can be used. The power used for the electrolysis is also not particularly limited. It is preferable to use CO2-free power, for example, power supplied by solar power generation or wind power generation, as the power used for the electrolysis.

[0038] It is not preferable to introduce a large amount of HO into the heating step described later. Therefore, it is preferable to dehydrate the regenerated carbon monoxide gas using a dehydrator as appropriate, taking into consideration the material balance of the entire circulation system, prior to the heating step described later.

[0039] The composition of the regenerated carbon monoxide gas is not particularly limited. The regenerated carbon monoxide gas excluding H2O, for example, the regenerated carbon monoxide gas after dehydration by the above-mentioned dehydrator, has a composition of CO: 1 to 60 volume %, H2: 40 to 99 volume %, and the balance: 0 to 30 volume %.

[0040] Incidentally, oxygen obtained as a by-product when carbon monoxide is generated is separated from the gas in the circulation system. That is, usually, the gas in the circulation system (regenerated carbon monoxide gas) and oxygen are already separated in the carbon monoxide generating device. Therefore, there is no particular need to provide an oxygen separator, but this does not limit the installation of a separator. The separated oxygen may be released into the atmosphere, but it is preferable to use it for other purposes as appropriate, such as oxygen for combustion when heating gas in the circulation system, or to supplement the oxygen required in other processes inside and outside the steelworks.

[0041] ·Heating process In the heating step, a gas obtained by mixing the regenerated carbon monoxide gas and the second furnace gas (hereinafter also referred to as a mixed gas) is heated to obtain a reducing gas. The regenerated carbon monoxide gas and the second furnace gas may be mixed upstream of the heating device as shown in FIG. 2, or these gases may be directly supplied to the heating device from independent lines and mixed in the heating device. Note that FIG. 2 illustrates an embodiment in which the second furnace gas is supplied to a distribution line for the regenerated carbon monoxide gas between the dehydrator and the heating device, but the present invention is not limited to this. For example, the second furnace gas may be supplied to a distribution line for the regenerated carbon monoxide gas between the carbon monoxide generator and the dehydrator.

[0042] The gas composition of the reducing gas (mixed gas) is, for example, CO: 1 to 60 volume %, H2: 40 to 99 volume %, and the balance: 0 to 30 volume %.

[0043] The heating temperature and heating means of the reducing gas (mixed gas) are not particularly limited and may be in accordance with a conventional method. For example, the heating temperature of the reducing gas (mixed gas) may be 750 to 1100°C.

[0044] Furthermore, by using green energy such as solar, wind, or geothermal energy as the heat source for the heating device, it is possible in principle to reduce CO2 emissions to zero.

[0045] Next, the reducing gas is introduced into the reducing furnace through an injection process. For example, the reducing gas is introduced into 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 a top gas.

[0046] In addition, it is preferable to perform at least one of dust removal and dehydration of the top gas prior to the above distribution step. Any dust removal device can be used for the dust removal. Any dehydration device can be used for the dehydration. The order of dust removal and dehydration is not particularly limited. In the example shown in FIG. 2, the top gas is subjected to dust removal by the dust removal device, and then dehydration by the dehydration device, and then the top gas is distributed into a first top gas and a second top gas.

[0047] Controlling the amount of gas introduced into the distribution, production and heating processes In the method for producing reduced iron according to one embodiment of the present invention, it is important to control the amount of gas introduced (supplied) to the distribution step, the generation step, and the heating step according to the CO2 conversion rate. This makes it possible to stabilize the composition of the reducing gas blown into the reduction furnace, in particular the ratio of the amount of H2 to the amount of CO contained in the reducing gas (hereinafter also referred to as H2 / CO of the reducing gas). This makes it possible to simultaneously achieve further energy saving and reduction in CO2 emissions under high operational stability, specifically, to continuously perform stable operation in which the composition of the reducing gas is maintained within a certain range without discharging CO2 outside the circulation system or supplying CO from outside the circulation system.

[0048] Here, the CO2 conversion rate indicates the ratio of CO2 contained in the first furnace gas introduced into the production step that is converted to CO by the electrolysis reaction. For example, the CO2 conversion rate can be calculated by the following formula. CO2 conversion rate η C [-] = 1-(Amount of CO2 contained in the regenerated carbon monoxide gas discharged after the generation of CO in the generation process [Nm 3 / t])÷(Amount of CO2 contained in the first furnace gas introduced into the generation process [Nm 3 / t]) The CO2 conversion rate can be adjusted mainly by the reactor itself used in the production process, for example, the type and amount, surface area and thickness of the materials used for the electrodes and electrolytes used in the reactor, as well as the temperature of the reactor and the amount of electricity supplied to the reactor. In addition, when there is a gas other than the first furnace gas, such as steam, introduced into the production process, the amount of CO2 contained in the gas (the amount of CO2 contained in the first furnace gas introduced into the production process [Nm 3 / t]). Also, Nm 3 / t and kg / t are the basic units per ton of reduced iron (DRI) produced.

[0049] For example, it is preferable to control the amounts of gas introduced into the distribution step, the generation step, and the heating step so as to satisfy the following formula (1).

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[0050] The left side of the above equation (1) is (W CO2 -V CO2 ) / W CO2This can be rewritten as: CO2 / CO2=CO2 / ...

[0051] For the above reasons, it is preferable to control the amounts of gas introduced into the distribution step, the generation step, and the heating step so as to satisfy the above formula (1).

[0052] The left side of the above formula (1) is 1-V CO2 / W CO2 It is more preferable to set the value to +0.015. Also, the left side of the above formula (1) is 1-V CO2 / W CO2 More preferably, it is +0.03.

[0053] In addition, the amounts of gas introduced into the distribution process, the generation process, and the heating process may be constant or may be changed at any timing as long as the above formula (1) is satisfied. In addition, the amounts of gas introduced into the distribution process, the generation process, and the heating process at the time of starting up the equipment may be determined, for example, from the past operating history, and the amounts of gas introduced into the distribution process, the generation process, and the heating process may be appropriately changed and controlled according to the subsequent operating conditions.

[0054] Furthermore, the iron oxide raw material used in the method for producing reduced iron according to one embodiment of the present invention is, for example, iron ore. Specific examples include lump iron ore (lump ore) and pellets (iron ore powder solidified into a spherical shape). The quality 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 mass% or more from the viewpoint of reduction in a shaft furnace.

[0055] In addition, in the method for producing reduced iron according to one embodiment of the present invention, a method using a shaft furnace has been described as a direct reduction ironmaking method. However, the type of reduction furnace is not limited to this, and a method using a fluidized bed, a rotary kiln, a rotary hearth furnace (RHF), or the like may also be used. Note that a shaft furnace is preferable as the reduction furnace because of its high production efficiency, operating rate, and operational stability. Also, most of the direct reduction furnaces operating around the world are shaft furnace type Midrex (registered trademark) and Hyl (registered trademark). EXAMPLES

[0056] Examples will now be described. In the circulation system shown in Figure 2, reduced iron was produced under the conditions listed in Table 1. For all conditions, the operation period was 28 days. In Table 1, the operation specifications are listed in terms of the basic unit per ton of reduced iron produced. For example, if 1,300 kg of iron oxide pellets are used to produce 1 ton of reduced iron, the amount of iron oxide pellets used is expressed as 1,300 kg / t. If 3,000 t / day of reduced iron is produced, multiply this amount by 3,000 to obtain the specifications per day.

[0057] Here, in either condition, in the filling step, the raw material iron oxide pellets were filled into the reduction furnace under the condition of 1394 kg / t. In the injection step, reducing gas heated to 980°C was injected from the center of the reduction furnace to reduce the iron oxide pellets and obtain reduced iron. Then, the furnace gas discharged from the reduction furnace was dedusted and appropriately dehydrated so that the material balance was balanced. Next, the furnace gas was introduced into the distribution step and distributed into a first furnace gas and a second furnace gas. In the distribution step, the furnace gas introduced into the furnace gas distribution section was appropriately separated into a separated carbon dioxide gas and a remaining gas (CO2 separation) so that the material balance was balanced. Then, the separated carbon dioxide gas was added with an appropriate amount of steam as the first furnace gas, and introduced into a carbon monoxide generator. Next, in the carbon monoxide generator, regenerated carbon monoxide gas was generated by a co-electrolytic reaction. After the generated regenerated carbon monoxide gas was appropriately dehydrated, the regenerated carbon monoxide gas was mixed with the second furnace gas to obtain a mixed gas. The mixed gas was then introduced into a heating device, and heated in the heating device to obtain a reducing gas. The total amount of gas introduced in the heating step in Table 1 is the mixed gas, i.e., the total amount of the regenerated carbon monoxide gas and the second furnace gas. W H2 is the amount of H2 contained in the top gas introduced into the distribution process. V H2 is the amount of H2 contained in the gas (regenerated carbon monoxide gas and second furnace gas) introduced into the heating process. In addition, the conditions other than those described above and in Table 1 were in accordance with conventional methods.

[0058] [Table 1]

[0059] In all of the invention examples, stable operation was achieved over the entire 28-day operation period under a sound material balance in the circulation system shown in Figure 2, which is extremely advantageous for realizing energy savings, that is, the system in which the top gas is circulated and reused. In addition, CO2 emissions from the circulation system were reduced to zero. On the other hand, in all of the comparative examples in which the gas amount was not controlled according to the CO conversion rate in the generation process, the composition of the reducing gas could not be maintained within a certain range during the operation period, and the reaction in the reduction furnace became unstable, which forced the interruption of operation. [Explanation of symbols]

[0060] 1. Reduction furnace 1a Iron oxide 1b Reduced iron 3 Dust removal equipment 4 Dehydration equipment 5. Natural Gas Supply Department 6 Air supply section 7. Reformer 9. Reducing gas injection device 10. Water vapor supply section 11 Carbon monoxide generator 12 Heating device 13 Heat source 14 Top gas distribution section

Claims

1. a charging step of charging the 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 a top gas discharged from the reducing furnace into a first top gas and a second top gas; a generating step of generating regenerated carbon monoxide gas by an electrolytic reaction using the first furnace top gas; a heating step of heating a mixed gas obtained by mixing the regenerated carbon monoxide gas and the second furnace gas to obtain the reducing gas; having CO produced by the electrolytic reaction in the production process ２ Conversion rate η Ｃ the amounts of gas introduced into the distributing step, the generating step, and the heating step are controlled according to [-] so as to satisfy the following formula (1): [0010] Where: W CO2 : Amount of CO 2 contained in the furnace gas introduced into the distribution process [Nm 3 / t] V CO2 : Amount of CO 2 contained in the gas introduced into the heating step [Nm 3 / t] It is.

2. In the distribution step, the furnace gas is separated into a separated carbon dioxide gas and a remaining gas, Distributing the separated carbon dioxide gas as the first top gas; The method for producing reduced iron according to claim 1 , wherein the remaining gas is distributed as the second top gas.

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