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 synthesis 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 synthesis step, and the heating step are regulated in accordance with the degree of CO2 conversion by inverse shift reaction in the synthesis 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 synthesis step of synthesizing regenerated carbon monoxide gas by a reverse shift reaction using the first furnace top gas and hydrogen gas; a heating step of heating a mixture of the regenerated carbon monoxide gas, the second furnace gas and the additionally supplied hydrogen 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 reverse shift reaction in the synthesis process (i.e., the reaction in which CO2 contained in the first furnace gas is used as a gaseous carbon source and CO2 is reformed into CO by reacting with H2) R The amounts of gas introduced into the distribution step, synthesis step, and heating step 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 synthesis step of synthesizing regenerated carbon monoxide gas by a reverse shift reaction using the first furnace gas and hydrogen gas; a heating step of heating a mixture of the regenerated carbon monoxide gas, the second furnace gas and the additionally supplied hydrogen gas to obtain the reducing gas; having CO2 conversion rate η by the reverse shift reaction in the synthesis process R The method for producing reduced iron, further comprising controlling the amounts of gas introduced into the distributing step, the synthesizing 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 synthesis step, and the heating step are controlled so as to satisfy the following formulas (1) and (2):

number

number

[0016] 3. In the distribution step, the furnace gas is separated into a separated carbon dioxide gas and a first 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 first residual gas is distributed as the second top gas.

[0017] 4. In the distribution step, the furnace gas is separated into a separated carbon dioxide gas and a first remaining gas, Distributing the separated carbon dioxide gas as the first top gas; The first remaining gas is separated into a separated hydrogen gas and a second remaining gas; The separated hydrogen gas is introduced into the synthesis step; 3. The method for producing reduced iron according to 1 or 2, wherein the second remaining gas is distributed as the second top gas.

[0018] 5. In the distribution step, the furnace gas is separated into a separated hydrogen gas and a third remaining gas, The separated hydrogen gas is introduced into the synthesis step; The third remaining gas is separated into a separated carbon dioxide gas and a fourth remaining gas; 3. The method for producing reduced iron according to item 1 or 2, wherein the separated carbon dioxide gas is distributed as the first top gas, and the fourth remaining gas is distributed as the second top gas. Effect of the Invention

[0019] 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]

[0020] [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

[0021] Hereinafter, a method for producing reduced iron according to an embodiment of the present invention will be described with reference to the drawings.

[0022] 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.

[0023] 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.

[0024] 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 top gas distribution section, the furnace top gas discharged from a reducing furnace is distributed into a first furnace top gas and a second furnace top gas. Then, in a carbon monoxide synthesis device, a regenerated carbon monoxide gas is synthesized by a reverse shift reaction using the first furnace top gas and hydrogen gas. Then, the regenerated carbon monoxide gas, the second furnace top gas, and the additionally supplied hydrogen gas are mixed to obtain a mixed gas. Then, the mixed gas is heated in a heating device. 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 hydrogen supply section, 11 denotes a carbon monoxide synthesis device, 12 denotes a heating device, 13 denotes a heat source, and 14 denotes a furnace top 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.

[0025] ·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.

[0026] In the distribution step, the top gas may be distributed with its composition as is, or specific gas species such as CO2 and H2 may be separated and distributed, for example, as follows: (a) The top gas is separated into a separated carbon dioxide gas and a first residual gas (CO2 separation), and the separated carbon dioxide gas is distributed as the first top gas, and the first residual gas is distributed as the second top gas. (b) The top gas is separated into a separated carbon dioxide gas and a first remaining gas (CO2 separation), and the separated carbon dioxide gas is distributed as a first top gas. The first remaining gas is separated into a separated hydrogen gas and a second remaining gas (H2 separation). The separated hydrogen gas is then introduced (supplied) to a synthesis step, and the second remaining gas is distributed as a second furnace top gas. (c) The top gas is separated into a separated hydrogen gas and a third remaining gas (H2 separation). Next, the separated hydrogen gas is introduced (supplied) to the synthesis step, and the third remaining gas is separated into a separated carbon dioxide gas and a fourth remaining gas (CO2 separation). Then, the separated carbon dioxide gas is distributed as a first top gas, and the fourth remaining gas is distributed as a second top gas.

[0027] 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.

[0028] The method of H2 separation is not particularly limited, and various methods such as adsorption separation and membrane separation can be used. The concentration of H2 in the separated hydrogen gas is preferably 90% by volume or more. The concentration of H2 in the separated hydrogen gas may be 100% by volume.

[0029] The compositions of the first remaining gas, the second remaining gas and the fourth remaining gas distributed as the second top gas vary depending on the amounts of CO2 and H2 separated, but are, for example, CO: 5-70 volume %, CO2: 0-25 volume %, H2: 0-75 volume %, H2O: 0-50 volume %, and balance: 0-30 volume %.

[0030] In addition, when the top gas is distributed into the first top gas and the second top gas with the composition unchanged in the distribution step, a separation step for separating specific gas species such as CO2 and H2 from the first top gas and the second top gas may be optionally included between the above distribution step and the synthesis step described later. For example, as in (a) and (b) above, the first furnace gas may be separated into a separated carbon dioxide gas and a first residual gas (CO2 separation), and the separated carbon dioxide gas may be used as the first furnace gas in the synthesis step. The first residual gas may be directly merged into the second furnace gas. Alternatively, the first residual gas may be separated into a separated hydrogen gas and a second residual gas (H2 separation), and then the separated hydrogen gas may be introduced into the synthesis step, and the second residual gas may be merged into the second furnace gas. Alternatively, as in (c) above, the first furnace gas is separated into a separated hydrogen gas and a third remaining gas. Then, the separated hydrogen gas is introduced into a synthesis step, and the third remaining gas is separated into a separated carbon dioxide gas and a fourth remaining gas (CO2 separation). Then, the separated carbon dioxide gas may be used as the first furnace gas in the synthesis step, and the fourth remaining gas may be merged with the second furnace gas.

[0031] 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.

[0032] ·Synthesis process In the synthesis step, for example, in a carbon monoxide synthesis device, regenerated carbon monoxide gas is synthesized from the first furnace gas distributed in the distribution step and hydrogen gas supplied from outside the circulation system. Note that CO is synthesized, for example, from CO2 contained in the first furnace gas and H2 contained in hydrogen gas supplied from outside the circulation system according to the reverse shift reaction formula shown in the following formula (i). CO2+H2→ CO+H2O (i) For example, the first furnace gas and hydrogen gas supplied from outside the circulation system are introduced into a carbon monoxide synthesis apparatus. Then, in the carbon monoxide synthesis apparatus, CO is synthesized according to the reaction formula (i) above. The CO synthesis conditions are not particularly limited and may be performed according to a conventional method.

[0033] When the separated carbon dioxide gas obtained in the above-mentioned distribution step or separation step is used, 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 in 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 synthesis step. Examples of other gases include gases by-produced 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 separation step together with the first furnace gas, separated into separated carbon dioxide gas and remaining gas, and then the separated carbon dioxide gas may be supplied to the synthesis step.

[0035] In addition, the supply source of hydrogen gas used in the synthesis step is not particularly limited, and may be supplied and produced by any method. Examples of methods for producing hydrogen gas include synthesis by electrolysis of water, and synthesis by decomposition reaction of ammonia, hydrocarbons, and organic hydrides. However, when hydrocarbons or organic hydrides are used as raw materials, CO2 is emitted during the hydrogen synthesis process. Therefore, from the viewpoint of further reducing CO2 emissions, it is preferable to synthesize hydrogen by at least one of electrolysis of water and decomposition of ammonia. In addition, when producing hydrogen gas by electrolysis of water, CO2 emissions can be reduced to zero by using green hydrogen produced using electricity obtained from green energy sources such as solar, wind, and geothermal energy. The H2 concentration of the hydrogen gas is not particularly limited, but is preferably 90% by volume or more, more preferably 95% by volume or more. The H2 concentration of the hydrogen gas may be 100% by volume.

[0036] The synthesis of CO by the reverse shift reaction can utilize commonly used catalysts, including transition metals such as Fe, Cu, Ni, Zr, and Ti, as well as oxide-based catalysts.

[0037] The reactor for the carbon monoxide synthesis apparatus used in the synthesis step may be a fixed bed reactor, a fluidized bed reactor, an entrained bed reactor, etc. The physical properties of the catalyst may be appropriately selected depending on the type of the reactor.

[0038] It is not preferable to introduce a large amount of H2O, which is generated as a by-product of the reverse shift reaction, into the heating device. Therefore, it is preferable to dehydrate the regenerated carbon monoxide gas using a dehydrator as appropriate prior to the heating step described below, while taking into consideration the material balance of the entire circulation system.

[0039] The CO concentration of the regenerated carbon monoxide gas is not particularly limited. In the regenerated carbon monoxide gas excluding HO, for example, the regenerated carbon monoxide gas after dehydration by the above-mentioned dehydrator, the CO concentration is preferably 80% by volume or more, more preferably 90% by volume or more. The CO concentration in the regenerated carbon monoxide gas excluding HO may be 100% by volume.

[0040] ·Heating process In the heating step, a gas (hereinafter also referred to as a mixed gas) containing the regenerated carbon monoxide gas, the second furnace gas, and the additionally supplied hydrogen gas is heated to obtain a reducing gas. The regenerated carbon monoxide gas, the second furnace gas, and the additionally supplied hydrogen 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 and the additionally supplied hydrogen gas are supplied to the regenerated carbon monoxide gas distribution line between the dehydrator and the heating device, but the present invention is not limited to this. For example, the second furnace gas and the additionally supplied hydrogen gas may be supplied to the regenerated carbon monoxide gas distribution line between the carbon monoxide synthesis device and the dehydrator. Also, one of the second furnace gas and the additionally supplied hydrogen gas may be supplied to the regenerated carbon monoxide gas distribution line between the dehydrator and the heating device, and the other may be supplied to the regenerated carbon monoxide gas distribution line between the carbon monoxide synthesis device and the dehydrator.

[0041] Here, the additionally supplied hydrogen gas is hydrogen gas supplied from outside the circulation system to be mixed with the regenerated carbon monoxide gas and the second furnace gas, and is to be distinguished from hydrogen gas supplied from outside the circulation system in the synthesis process. The supply source and H2 concentration of the additionally supplied hydrogen gas are not particularly limited, and may be the same as the hydrogen gas supplied from outside the circulation system in the synthesis process. Examples of specific supply points of the additionally supplied hydrogen gas are as described above.

[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, synthesis 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, synthesis step, and heating step in accordance with 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). As a result, it becomes possible to simultaneously achieve further energy saving and reduction in CO2 emissions under high operational stability, specifically, to continue 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 synthesis step that is converted to CO by the reverse shift reaction. For example, the CO2 conversion rate can be calculated by the following formula. CO2 conversion rate η R [-] = 1-(Amount of CO2 contained in the regenerated carbon monoxide gas discharged after the synthesis of CO in the synthesis process [Nm3 / t])÷(Amount of CO2 contained in the first furnace gas introduced into the synthesis process [Nm 3 / t]) The CO2 conversion rate can be adjusted mainly by the reactor used in the synthesis process, for example, the type and amount of catalyst used in the reactor, the volume of the reactor, the temperature of the reactor, etc. In addition, when there is a gas other than the first furnace gas, such as separated hydrogen gas, introduced into the synthesis process, the amount of CO2 contained in the gas (the amount of CO2 contained in the first furnace gas introduced into the synthesis 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, synthesis step, and heating step so as to satisfy the following formulas (1) and (2).

number

number

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

[0051] In addition, the left side of the above equation (2) is (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 in the reverse shift reaction in the synthesis process to the amount of H2 contained in the furnace gas and the amount of H2 contained in the hydrogen gas introduced into the synthesis process. Here, if 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 surplus in the circulation system. As a result, it may become impossible to perform stable operation under a healthy material balance.

[0052] In view of the above, it is preferable to control the amounts of gas introduced into the distribution step, synthesis step, and heating step so as to simultaneously satisfy the above formulas (1) and (2).

[0053] The left side of the above formula (1) is 1-V CO2 / W CO2It 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. The left side of the above equation (2) is 1+(A H2 -V H2 ) / (W H2 +E H2 ) + 0.015. In addition, the left side of the above formula (2) is 1 + (A H2 -V H2 ) / (W H2 +E H2 ) +0.03 is even more preferable.

[0054] The amounts of gas introduced into the distribution step, synthesis step, and heating step may be constant or may be changed at any timing as long as the above formulas (1) and (2) are satisfied simultaneously. The amounts of gas introduced into the distribution step, synthesis step, and heating step at the time of starting up the equipment may be determined, for example, from the past operation history, and the amounts of gas introduced into the distribution step, synthesis step, and heating step may be appropriately changed and controlled according to the subsequent operating conditions.

[0055] 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.

[0056] 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

[0057] Examples will be described below. 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.

[0058] 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 the first furnace gas and the second furnace gas. In the distribution step, the furnace gas introduced into the furnace gas distribution section was appropriately obtained as a separated carbon dioxide gas by any one of the above modes (a) to (c) so that the material balance was balanced, and the separated carbon dioxide gas was distributed as the first furnace gas. The separated hydrogen gas was also introduced into the synthesis step as the first furnace gas together with the separated carbon dioxide gas. In addition, the residual gas (the first residual gas, the second residual gas, or the fourth residual gas) was distributed as the second top gas. Next, the first top gas (including a part of the separated hydrogen gas) and hydrogen gas from outside the circulation system were introduced into a carbon monoxide synthesis device. Then, in the reactor of the carbon monoxide synthesis device, regenerated carbon monoxide gas was synthesized by a reverse shift reaction. After the synthesized regenerated carbon monoxide gas was dehydrated, the regenerated carbon monoxide gas, the second top gas, and the additionally supplied hydrogen gas were mixed to obtain a mixed gas. Next, the mixed gas was introduced into a heating device, and the mixed gas was heated in the heating device to obtain a reducing gas. Note that the total amount of gas introduced in the heating step in Table 1 is the mixed gas, that is, the total amount of the regenerated carbon monoxide gas, the second top gas, and the additionally supplied hydrogen gas. In addition, the conditions other than those described above and in Table 1 were in accordance with the usual method.

[0059] [Table 1]

[0060] 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 CO2 conversion rate in the synthesis 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]

[0061] 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 Hydrogen supply unit 11 Carbon monoxide synthesis device 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 synthesis step of synthesizing regenerated carbon monoxide gas by a reverse shift reaction using the first furnace gas and hydrogen gas; a heating step of heating a mixture of the regenerated carbon monoxide gas, the second furnace gas and the additionally supplied hydrogen gas to obtain the reducing gas; having CO from the reverse shift reaction in the synthesis process ２ Conversion rate η Ｒ the amounts of gas introduced into the distributing step, the synthesizing step, and the heating step are controlled according to [-] so as to satisfy the following formulas (1) and (2): [0010] [0025] Where: W CO2 : Amount of CO 2 contained in the furnace gas introduced into the distribution process [Nm 3 / t] W H2 : Amount of H 2 contained in the furnace gas introduced into the distribution process [Nm 3 / t] E H2 : Amount of H 2 contained in hydrogen gas introduced into the synthesis step [Nm 3 / t] V CO2 : Amount of CO 2 contained in the gas introduced into the heating step [Nm 3 / t] V H2 : Amount of H 2 contained in the gas introduced into the heating step [Nm 3 / t] A H2 : Amount of H 2 contained in additionally supplied hydrogen gas [Nm 3 / t] It is.

2. In the distribution step, the furnace gas is separated into a separated carbon dioxide gas and a first 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 first remainder gas is distributed as the second top gas.

3. In the distribution step, the furnace gas is separated 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; The separated hydrogen gas is introduced into the synthesis step; The method for producing reduced iron according to claim 1 , wherein the second remainder gas is distributed as the second top gas.

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

Images