Circulation-type reduction system, iron ore reduction method, and blast furnace operation method

Abstract

Provided is a circulating reduction system with which it is possible to efficiently circulate and utilize, as a reduction gas, a CO-rich gas obtained by reforming an exhaust gas that contains CO2 generated in a reduction furnace. In this circulating reduction system 100, an exhaust gas that contains CO2 generated in a reduction furnace 10 is recovered via first piping 81, and hydrogen gas is added to the exhaust gas from a hydrogen gas supply device 30 to produce a hydrogen-added gas. In a catalyst device 40, the CO2 in the hydrogen-added gas is converted to CO through a reverse water gas shift reaction, and a CO-rich gas in which the CO concentration is increased. The CO-rich gas is fed through second piping 82 into the reduction furnace 10 as a reduction gas. No separation device for separating, and recovering or removing, a specific gas component that is not water vapor from a gas passing through the first piping 81 and the second piping 82 is provided partway along the first piping 81 or the second piping 82.

Description

[Technical field]

[0001] The present invention relates to a circulatory reduction system, a method for reducing iron ore, and a method for operating a blast furnace, which are capable of drastically reducing CO2 emissions that promote global warming. [Background technology]

[0002] Amid a global call to reduce CO2 emissions, which contribute to global warming, the steel industry in Japan, which accounts for around 15% of Japan's domestic CO2 emissions, has responded to government policy by declaring that it will be carbon neutral by 2050. To achieve this, it is necessary to develop an iron ore reduction process and reduction furnace to produce crude steel at a low cost close to current levels, but there is currently little prospect of the technical feasibility.

[0003] The hydrogen reduction process, which uses hydrogen as a reducing agent for iron ore, is attracting worldwide attention as an ideal crude steel production technology that does not emit CO2. However, if this method is to be used to maintain Japan's annual molten iron production of approximately 75 million tons, it would require approximately 75 billion Nm 3 This will require 100,000 tons of hydrogen. To meet this demand using water electrolysis, a representative green hydrogen production method, some estimates suggest that 0.34 trillion kWh of electricity would be required per year, even ignoring the electricity required for hydrogen transportation, liquefaction, and storage. Even if the heavy electricity cost issue could be overcome, it must be said that it is extremely unrealistic for Japan, whose annual power consumption is around 1 trillion kWh, to procure this much electricity for domestic blast furnace manufacturers.

[0004] Meanwhile, various attempts are underway to procure large quantities of hydrogen produced using cheap renewable energy from overseas. However, even if the issue of high transportation costs can be overcome, there is still no clear technical prospect of safely storing large quantities of hydrogen, which has a wide explosive concentration range, near steelworks.

[0005] Incidentally, the reason why the domestic steel industry emits around 15% of the country's total CO2 emissions is because high-grade steel is produced mainly using the blast furnace-converter process, which uses coke to reduce iron ore. Crude steel production methods are mainly classified into the blast furnace-converter process and the electric furnace process, with the blast furnace-converter process generating around 2 t of CO2 per ton of steel, and the electric furnace process generating around 0.5 t of CO2 per ton of steel. The electric furnace process is superior in terms of reducing the amount of CO2 emissions. However, high-grade steel used in automobiles and other products is not mass-produced using the electric furnace process, which uses scrap as the raw material, because impurities such as copper tend to adversely affect the quality. Therefore, around 75% of domestic crude steel is produced using the blast furnace-converter process.

[0006] For blast furnaces, which emit a particularly large amount of CO2, for example, Patent Document 1 attempts to reduce the amount of coke used by replacing the high-temperature air blown in from the tuyere with reducing gases such as hydrogen and methane. However, in addition to its role as a reducing agent, coke also plays a role as a heating material that heats the inside of the furnace through a reaction with oxygen blown in from the hot stove, and as an aeration material that ensures ventilation in the furnace. Therefore, it is extremely difficult to drastically reduce the amount of coke used until a new means (other than coke) is found that maintains the temperature inside the furnace and ensures ventilation without adversely affecting the quality of the molten pig iron.

[0007] In light of the above, Japanese steelmakers have no choice but to cut back on the number of blast furnaces in operation and increase the ratio of electric furnaces in order to get by for the time being. As a result, the demand for scrap to be used in electric furnaces is already strong, and it is expected that the fierce competition to procure it will become even more severe in the future.

[0008] Under these circumstances, direct reduction processes that emit less CO2 than the blast furnace-converter process are attracting worldwide attention. In the so-called Midrex process, a representative direct reduction process, iron ore can be reduced in the solid phase with modified natural gas to obtain direct reduced iron (DRI) (see Reference 2). In the early Midrex process, only sponge-like DRI could be produced, and it was considered difficult to handle and transport it from the standpoint of oxidation and ignition. However, since the development and industrialization of hot briquetting equipment, these problems have been almost solved, and a movement to reduce the amount of scrap input and improve the quality of steel by mixing DRI with scrap and feeding it into an electric furnace is spreading worldwide. In addition, attempts are being made to replace natural gas with methane synthesized from CO2 and hydrogen using the methanation reaction (CO2 + 4H2 → CH4 + 2H2O), or with hydrogen itself.

[0009] On the other hand, in the direct reduction process, which is a solid-phase reduction process, in order to maintain the quality of the DRI produced, it is necessary to use high-grade iron ore as a raw material, which is limited in cost and availability. This is a major disadvantage compared to the conventional blast furnace process, in which about 85% of the iron ore raw material can be made into pellets or sintered ore made from low-grade fine ore ore powder.

[0010] Furthermore, in the direct reduction process, crude steel cannot be extracted in the form of molten iron, so refining facilities from the conventional integrated pig iron steel process, such as pretreatment furnaces and converters, cannot be used. This is also one of the reasons why Japanese blast furnace manufacturers are obsessed with the blast furnace process. It is presumed that the reason why the direct reduction process remains at solid-phase reduction is because, as mentioned above, the issues of permeability and maintaining the furnace temperature to obtain molten iron have not been fundamentally resolved.

[0011] In other words, the main obstacles to the blast furnace-converter process are the need for a reducing agent and heating material that can replace coke, and new means of ensuring permeability without adversely affecting the quality of the molten iron, and there is no prospect of a drastic reduction in the amount of coke used. In addition, the direct reduction process, which has lower CO2 emissions than the blast furnace-converter process, has the disadvantages that it cannot use low-quality fine ore ore that can be used in blast furnaces and is easy to obtain at low cost, and that it cannot use refining equipment from the conventional integrated pig iron and steel process because crude steel cannot be extracted as molten iron.

[0012] Against this background, Patent Document 3 proposes a technology to utilize CO2 contained in exhaust gas from a blast furnace. That is, it proposes separating CO2 from the exhaust gas of a blast furnace, reforming the captured CO2 into CO, and reusing this CO as a reducing agent for the blast furnace. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] International Publication No. 2021 / 220555 [Patent Document 2] JP 2017-88912 A [Patent Document 3] JP 2011-225968 A Summary of the Invention [Problem to be solved by the invention]

[0014] In the technology described in the above Patent Document 3, the CO2 separated and captured from the exhaust gas generated in a blast furnace is reformed into CO and reused, thereby reducing the amount of CO2 generated. However, this technology involves multiple steps, such as first separating and capturing CO2 from the exhaust gas and then reforming the CO2, which inevitably leads to a decrease in the circulation efficiency of the reducing components in the exhaust gas and the burden of the costs required for the equipment, operation, and maintenance of each step. For this reason, there has been a demand for a more efficient method of circulating and reusing the reducing components in the exhaust gas from a reducing furnace such as a blast furnace.

[0015] In view of the above problems, an object of the present invention is to provide a circulatory reduction system capable of efficiently circulating and utilizing, as a reducing gas, a CO-rich gas obtained by reforming a CO-containing exhaust gas generated from a reducing furnace.

[0016] Another object of the present invention is to provide a method for reducing iron ore, which is capable of efficiently circulating and utilizing a CO-rich gas obtained by reforming a CO-containing exhaust gas generated from a reduction furnace as a reducing gas to perform a reduction treatment of iron ore.

[0017] Another object of the present invention is to provide a method for operating a blast furnace, which uses the above-mentioned circulating reduction system, and is capable of maintaining the temperature inside the furnace and ensuring ventilation without using any material other than coke. [Means for solving the problem]

[0018] The present inventors have conducted extensive research into a method for realizing an efficient reduction process in which exhaust gas from a reduction furnace can be recycled as a starting material for a reducing agent, and have discovered that the use of the so-called reverse water-gas shift reaction allows for efficient recycling of exhaust gas.

[0019] That is, the exhaust gas generated in the reduction process of iron ore generally contains excess reducing agents such as CO and H in addition to CO and nitrogen derived from the atmosphere. For example, the exhaust gas of a blast furnace contains about 23 vol% CO, the same proportion of CO, about 4 vol% H, and about 50 vol% nitrogen derived from the air. The inventors of the present invention have conceived of adding hydrogen to such exhaust gas and contacting this gas with a catalyst for reverse water gas shift reaction (RWGS: Reverse Water Gas Shift reaction: CO + H → CO + H O) to largely change the balance of CO and CO in the exhaust gas to CO-rich, and then circulating and using the hydrogen as a reducing gas together with the H and nitrogen originally contained in the exhaust gas. It has been found that if this circulating use becomes possible, the input amount of reducing agents derived from fossil fuels, such as coke, which have been used in the past, can be minimized.

[0020] Here, CO is recycled as the main reducing agent because the reduction reaction of iron ore with H2 is an endothermic reaction, whereas the reduction reaction of iron ore with CO is an exothermic reaction, making CO the most efficient reducing agent that can maintain a high temperature inside the reduction furnace. In addition, reduction with CO can utilize the freezing point depression of iron caused by carbon that occurs when coke is used as a reducing agent. As a result, reduced iron that melts at 1500°C or higher when reduced with H2 melts at about 1200°C when reduced with CO. This temperature difference of about 300°C significantly reduces the heat load of the reducing gas on the heating furnace when the reduced iron is extracted as molten iron.

[0021] In addition, the CO2-rich reducing gas synthesized from the CO2-rich exhaust gas is mainly supplied to the reduction furnace, but the surplus can be discharged and captured for various uses. In addition to being used as a reducing agent and fuel gas, CO is also used in the Fischer-Tropsch reaction (nCO+(2n+1)H2→C n H 2n+2 +nH2O). Therefore, the CO2-rich reducing gas synthesized from CO2-rich exhaust gas is not only a reducing agent, but is also a synthetic gas that can be used without waste as fuel gas or as a raw material for various organic compounds. In particular, if the use of fossil fuels is to be significantly reduced to prevent global warming, the organic chemical industry that has used fossil fuels as a raw material will have to find new sources of raw materials. There is great significance in these industries becoming a recipient of the above-mentioned synthetic gas.

[0022] As mentioned above, the coke fed into a typical blast furnace not only serves as a reducing agent, but also as a heating and aeration material. Therefore, when reduced iron is extracted as molten iron, even if the temperature inside the furnace can be maintained by the reduction heat of CO in the reducing gas, if the amount of coke fed is kept to a minimum, it becomes impossible to ensure sufficient aeration (a stable reducing environment cannot be maintained).

[0023] It has been newly discovered that this problem can be solved by slowly cooling and crushing part of the molten slag that is generated together with the molten iron and discharged from the bottom of the furnace in a mold, mixing it with the coke as an aeration material, and then re-injecting it from the top of the furnace. In other words, since the melting point of blast furnace slag is about 1400°C, even when the iron in the blast furnace, whose freezing point has been lowered by C, begins to melt, the slag remains in a solid state and plays the role of an aeration material. In addition, since the slag is a material that was originally generated in the blast furnace, recycling it does not change the material environment inside the blast furnace.

[0024] It is not easy to start up a blast furnace using only cooled and crushed slag as an aerating agent and reducing gas as the reducing agent. Therefore, like a normal blast furnace, the blast furnace is first started up in "blast furnace mode" by alternately stacking coke, which acts as both a reducing agent and aerating agent, and iron source in the blast furnace, and then blowing in high-temperature air heated in a hot stove. After that, the blast furnace is gradually switched to "cokeless mode" in which slag is gradually mixed into the coke and reducing gas is gradually added to the air blown into the blast furnace. When the blast furnace is shut down, it is easier to restart it by following the reverse procedure and ending operations in blast furnace mode after cokeless mode.

[0025] The present invention has been made based on the above findings, and the gist of the present invention is as follows. [1] a reduction furnace for reducing an oxide contained therein; a first pipe through which exhaust gas containing CO generated in the reduction furnace is recovered from the reduction furnace and passes; a hydrogen gas supply device connected to the first pipe and adding hydrogen gas to the exhaust gas to produce a hydrogen-added gas; a catalyst device connected to an end of the first pipe, the catalyst device having a reaction chamber containing a catalyst for a reverse water gas shift reaction, the hydrogenated gas introduced from the first pipe into the reaction chamber contacting the catalyst, and CO2 in the hydrogenated gas is converted to CO by the reverse water gas shift reaction to produce a CO-rich gas having an increased CO concentration; a second pipe extending from the catalyst device and connected to the reduction furnace, through which the CO-rich gas passes and through which the CO-rich gas is supplied to the inside of the reduction furnace as a reducing gas; having A circulating reduction system in which a separation device that separates and recovers or removes a specific gas component other than water vapor from the gas passing through the first pipe and the second pipe is not disposed in the first pipe and the second pipe.

[0026] [2] The circulating reduction system according to the above-mentioned [1], further comprising a gas heating device arranged in the second pipe for heating the CO-rich gas.

[0027] [3] The circulating reduction system according to the above item [2], further comprising a third pipe branching off from the second pipe at a position upstream of the gas heating device and connected to the gas heating device, and a part of the CO-rich gas is supplied as a combustion gas to the gas heating device via the third pipe.

[0028] [4] The circulation-type reduction system according to [2] or [3] above, further comprising a fourth pipe extending from the gas heating device and connected midway to the first pipe, and wherein the combustion exhaust gas generated from the gas heating device is merged with the exhaust gas in the first pipe via the fourth pipe.

[0029] [5] The catalytic device has a heating device for heating the reaction chamber, The circulating reduction system according to any one of the above-mentioned [1] to [4], further comprising a fifth pipe branching from the second pipe and connected to the heating device, and a part of the CO-rich gas is supplied as a combustion gas to the heating device via the fifth pipe.

[0030] [6] The circulation-type reduction system according to [5] above, further comprising a sixth pipe extending from the heating device and connected midway to the first pipe, and wherein the combustion exhaust gas generated from the heating device is merged with the exhaust gas in the first pipe via the sixth pipe.

[0031] [7] The circulating reduction system according to any one of the above-mentioned [1] to [6], further comprising a first dehumidifier that removes water vapor from the exhaust gas, the first dehumidifier being disposed in the first piping, upstream of a portion to which the hydrogen gas supply device is connected.

[0032] [8] The circulatory reduction system according to any one of the above-mentioned [1] to [7], further comprising a second dehumidifier disposed in the second pipe for removing water vapor from the CO-rich gas.

[0033] [9] A switching valve disposed midway through the second pipe; and a seventh pipe extending from the switching valve, The circulating reduction system according to any one of the above-mentioned [1] to [8], wherein a portion of the CO-rich gas is recovered via the seventh pipe.

[0034]

[10] The circulatory reduction system according to the above-mentioned [9], further comprising a third dehumidifier disposed midway along the seventh pipe and configured to remove water vapor from the CO-rich gas passing through the seventh pipe.

[0035]

[11] The circulating reduction system according to any one of the above [1] to

[10] , wherein the reduction furnace is a blast furnace, and the oxide is iron ore.

[0036]

[12] The circulation-type reduction system according to the above

[11] , wherein the blast furnace is a blast furnace.

[0037]

[13] A method for reducing iron ore, comprising the steps of: using the circulating reduction system according to any one of the above-mentioned [1] to

[12] ; and circulating and utilizing the CO-rich gas obtained by reforming the exhaust gas as the reducing gas to perform a reduction treatment of iron ore as the oxide.

[0038]

[14] A method for operating a blast furnace using the circulation type reduction system according to

[11] or

[12] above, A method for operating a blast furnace, comprising: charging, into the blast furnace from the top of the blast furnace, alternate layers of (I) at least one type of iron ore selected from sintered ore, lump ore, iron ore pellets, and fine ore; and (II) crushed slag obtained by crushing solidified slag obtained by slowly cooling molten slag discharged from the bottom of the blast furnace, or a ventilation material consisting of a mixture of the crushed slag and coke, to ensure ventilation of the reducing gas inside the furnace.

[0039]

[15] The reducing gas and air are supplied as blown gases into the inside of the blast furnace from a tuyere located at the bottom of the blast furnace; The method for operating a blast furnace according to the above-mentioned

[14] , wherein the ratio of the crushed slag to the coke in the aeration material and the ratio of the reducing gas to the air in the blown gas are gradually increased, thereby gradually reducing the amount of coke used. Effect of the Invention

[0040] According to the circulation-type reduction system of the present invention, the CO-rich gas obtained by reforming the exhaust gas containing CO2 generated from the reduction furnace can be efficiently circulated and reused as a reducing gas.

[0041] According to the method for reducing iron ore of the present invention, the CO-rich gas obtained by reforming the exhaust gas containing CO2 generated from a reduction furnace can be efficiently recycled and used as a reducing gas to perform the reduction treatment of iron ore.

[0042] According to the method for operating a blast furnace of the present invention, the above-mentioned circulation type reduction system can be used to maintain the temperature inside the furnace and ensure gas permeability without using any material other than coke. [Brief description of the drawings]

[0043] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a circulatory reduction system 100 according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram showing the configuration of a circulating reduction system 200 according to another embodiment of the present invention. [Diagram 3]FIG. 2 is a schematic diagram showing an equilibrium calculation model of a circulating reduction system according to Example 1 of the present invention. [Figure 4] 4 is a graph showing the reduction state in the model of FIG. 3 (Example 1). [Diagram 5] FIG. 11 is a schematic diagram showing an equilibrium calculation model of a circulating reduction system according to Example 2 of the present invention. [Figure 6] 6 is a graph showing the reduction state in the model of FIG. 5 (Example 2). [Figure 7] FIG. 1 is a schematic diagram showing an equilibrium calculation model of a circulating reduction system according to a comparative example. [Figure 8] 8 is a graph showing the reduction state in the model of FIG. 7 (comparative example). [Figure 9] 1 is a graph showing changes in the amount of heat absorbed in a reducing furnace versus the number of cycles in Examples 1 and 2 and a comparative example. [Figure 10] 1 is a graph showing the change in the amount of heat absorbed in a reduction furnace in an FeO reduction region versus the amount of hydrogen in a hydrogen-added gas in Examples 1 and 2 and a comparative example. [Figure 11] FIG. 13 is a schematic diagram showing the configuration of an experimental circulatory reduction system according to Example 3 of the present invention. [Figure 12] FIG. 13 is a schematic diagram showing the configuration of an experimental circulatory reduction system according to Example 4 of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] [Circulation-based return system] A circulatory reduction system 100 according to one embodiment of the present invention will be described with reference to Fig. 1. The circulatory reduction system 100 has a reduction furnace 10, a first dehumidifier 20, a hydrogen gas supply device 30, a catalyst device 40, a second dehumidifier 50, and a gas heating device 60, and has a first pipe 81, a second pipe 82, a third pipe 83, a fourth pipe 84, a fifth pipe 85, a sixth pipe 86, a seventh pipe 87, and a switching valve 90 as piping equipment.

[0045] The reduction furnace 10 may be, for example, a blast furnace or other blast furnace. When the reduction furnace 10 is a blast furnace, iron ore and coke are charged into the reduction furnace 10 from a furnace top 12, and high-temperature reducing gas is blown into the reduction furnace 10 from tuyere 14 located at the bottom of the reduction furnace 10, thereby reducing the iron ore in the reduction furnace 10.

[0046] The first pipe 81 is a pipe facility that recovers and passes exhaust gas containing CO2 generated in the reduction furnace 10 from the reduction furnace 10. The first pipe 81 is connected at its beginning to the reduction furnace 10 (furnace top 12 in one example) and at its end to the catalytic device 40. The hydrogen gas supply device 30 is connected to the middle of the first pipe 81. In addition, the first dehumidifier 20 is disposed in the middle of the first pipe 81, upstream of the portion where the hydrogen gas supply device 30 is connected. The first pipe 81 has a pipe 81A that extends from the reduction furnace 10 and connects to the first dehumidifier 20, and a pipe 81B that extends from the first dehumidifier 20 and connects to the catalytic device 40. In this specification, the terms "upstream" and "downstream" in relation to the pipes refer to the gas flow direction in the pipes.

[0047] The exhaust gas discharged from the furnace top 12 of the reduction furnace 10 is dehumidified by the first dehumidifier 20 while flowing through the first pipe 81, and then hydrogen (H2) gas is supplied from the hydrogen gas supply device 30 to become hydrogen-added gas. The dehumidification is preferably performed in order to suppress the water-gas shift reaction and promote the reverse water-gas shift reaction. The composition of the exhaust gas is not particularly limited, but typically contains 13 to 24 volume % of CO2, 21 to 31 volume % of CO, and 3 to 15 volume % of H2, excluding water vapor, with the remainder being N2 derived from air. The composition of the hydrogen-added gas is not particularly limited, but typically contains 13 to 24 volume % of CO2, 21 to 31 volume % of CO, and 10 to 30 volume % of H2, excluding water vapor, with the remainder being N2 derived from air. It is desirable that the hydrogen supplied from the hydrogen gas supply device 30 be green hydrogen obtained by water electrolysis using renewable energy; however, by applying the circulatory reduction system of the present invention to blast furnace operation, it can be substituted with hydrogen refined from coke oven gas until the amount of coke used becomes zero.

[0048] It is preferable to provide a dust removal device (not shown) in the first piping 81 upstream of the first dehumidifier 20, or downstream of the first dehumidifier 20 and upstream of the portion where the hydrogen gas supply device 30 is connected, to subject the exhaust gas to a dust removal process and remove dust derived from the raw materials from the exhaust gas.

[0049] The catalyst device (reverse shift type reformer) 40 has a reaction chamber 42 to which the end of the first pipe 81 is connected and which contains a catalyst for the reverse water gas shift reaction, and a heating device 44 for heating the reaction chamber 42. In the catalyst device 40, the hydrogenated gas introduced from the first pipe 81 into the reaction chamber 42 comes into contact with the catalyst, and the CO2 in the hydrogenated gas is converted to CO by the reverse water gas shift reaction, resulting in a CO-rich gas with an increased CO concentration. The composition of the CO-rich gas after the reverse water gas shift reaction is not particularly limited, but typically contains 6 to 20 volume % of CO2, 24 to 40 volume % of CO, and 5 to 24 volume % of H2, excluding water vapor, and the remainder is N2 derived from air. Many catalysts are known that can be used for the reverse water gas shift reaction, such as nickel-based and precious metal-based catalysts, and any of them may be used in the present invention.

[0050] When the hydrogenated gas is brought into contact with the catalyst in the catalytic device 40, it is desirable to set the temperature of the hydrogenated gas to be introduced as high as possible within a temperature range in which the catalyst is unlikely to deteriorate, from the viewpoint of the conversion efficiency of the reverse water gas shift reaction, which is an endothermic reaction. Specifically, it is preferable to heat the inside of the reaction chamber 42 by the heating device 44 so that the temperature of the reaction gas (hydrogenated gas) around the catalyst is 800°C or higher and 1200°C or lower.

[0051] The second pipe 82 is a pipe facility that extends from the catalytic device 40 and is connected to the reducing furnace 10 (in one example, the tuyere 14), passes the CO-rich gas through, and supplies the CO-rich gas to the inside of the reducing furnace 10 as a reducing gas (through the tuyere 14 in one example). It is preferable that a second dehumidifier 50 that removes water vapor from the CO-rich gas and a gas heating device 60 that heats the CO-rich gas are disposed midway along the second pipe 82. In this case, it is preferable that the gas heating device 60 is disposed downstream of the second dehumidifier 50. In this case, the second pipe 82 has a pipe 82A that extends from the catalytic device 40 and connects to the second dehumidifier 50, a pipe 82B that extends from the second dehumidifier 50 and connects to the gas heating device 60, and a pipe 82C that extends from the gas heating device 60 and connects to the reducing furnace 10 (in one example, the tuyere 14).

[0052] The CO-rich gas that has passed through the catalytic device 40 is dehumidified by the second dehumidifier 50 while flowing through the second pipe 82, and then heated by the gas heating device 60. Thereafter, the CO-rich gas is blown into the reduction furnace 10 as a reducing gas.

[0053] That is, after the reaction in the catalyst, it is desirable to adjust the temperature of the CO-rich gas (reducing gas) to be blown into the reduction furnace 10 by the gas heating device 60. The higher the temperature of the reducing gas, the more advantageous the reduction efficiency of the iron ore in the reduction furnace 10 is. However, when performing solid-phase reduction of the iron ore, it is desirable to set the temperature of the reducing gas to be blown into the reduction furnace 10 to 900°C or higher. When the reduced iron is taken out as molten pig iron at 1500°C, it is necessary to maintain the temperature of the molten region of the iron source and slag formed in the lower region of the reduction furnace 10 at 1650°C or higher. Therefore, it is desirable to blow the reducing gas after heating it so that the temperature of the reducing gas is 1200°C or higher if the amount of coke charged is up to about 50% of that of the conventional blast furnace, and the temperature of the reducing gas is 1500°C or higher if the amount of coke charged is less than 20% of that of the conventional blast furnace.

[0054] The preferred operation of the gas heating device 60 is as follows. The circulation type reduction system 100 of this embodiment preferably has a third pipe 83 that branches from a position upstream of the gas heating device 60 and downstream of the second dehumidifier 50 in the middle of the second pipe 82 and is connected to the gas heating device 60. Then, it is preferable to supply a part of the CO-rich gas flowing through the second pipe 82 to the gas heating device 60 as a combustion gas via the third pipe 83. In this way, by burning a part of the CO-rich gas as a fuel gas in the gas heating device 60, the temperature of the reducing gas can be raised to the desired temperature. Although omitted in FIG. 1, the oxygen-containing gas supplied to the gas heating device 60 for burning the combustion gas is preferably oxygen gas (not including unconsumed nitrogen).

[0055] The circulation type reduction system 100 preferably has a fourth pipe 84 extending from the gas heating device 60 and connected to the middle of the first pipe 81. The combustion exhaust gas generated from the gas heating device 60 is preferably merged with the exhaust gas in the first pipe 81 via the fourth pipe 84 for reuse. The fourth pipe 84 is preferably connected to a position upstream of the first dehumidifier 20 in the middle of the first pipe 81. The combustion exhaust gas generated from the gas heating device 60 is heat exchanged with (1) the reducing gas pipe between the catalytic device 40 and the gas heating device 60 and (2) the hydrogen-added gas pipe between the hydrogen gas supply device 30 and the catalytic device 40, and then merged with the exhaust gas in the first pipe 81 upstream of the first dehumidifier 20, so that the reducing gas and the hydrogen-added gas can be preheated.

[0056] 1, if the reducing gas cannot be heated to a desired temperature by an indirect heating type gas heating device 60, a part of CO and H2 contained in the reducing gas may be directly burned by adding oxygen near the tip of the gas heating device 60. In addition, if oxygen-enriched air made by cryogenic separation or the like is used as the hot air blown into the reducing furnace 10 when starting up in the blast furnace mode, the heat load of the gas heating device 60 lost by heating the nitrogen is reduced, making it easier to raise the temperature of the reducing gas.

[0057] Next, for the suitable operation of the catalytic device 40, it is preferable to use a part of the CO-rich gas as the combustion gas. That is, the circulation type reduction system 100 of the present embodiment preferably has a fifth pipe 85 that branches off from the second pipe 82 and is connected to the heating device 44 of the catalytic device 40. The fifth pipe 85 preferably branches off from a position upstream of the gas heating device 60 and downstream of the second dehumidifier 50 in the middle of the second pipe 82. Then, it is preferable to supply a part of the CO-rich gas as the combustion gas to the heating device 44 via the fifth pipe 85. Although omitted in FIG. 1, the oxygen-containing gas supplied to the heating device 44 to combust the combustion gas is preferably oxygen gas (not including unconsumed nitrogen).

[0058] The circulation type reduction system 100 preferably has a sixth pipe 86 extending from the heating device 44 and connected to the middle of the first pipe 81. It is preferable that the combustion exhaust gas generated from the heating device 44 is merged with the exhaust gas in the first pipe 81 through the sixth pipe 86 and reused. In this embodiment, the upstream portion 86A of the sixth pipe 86 is connected to the middle of the fourth pipe 84, which is the fuel exhaust gas flow path from the gas heating device 60, so that the downstream portion 86B of the sixth pipe 86 also serves as the downstream portion 84 of the fourth pipe 84. However, the present invention is not limited to this, and it goes without saying that the sixth pipe 86 may be directly connected to the first pipe 81 independently of the fourth pipe 84. The hydrogen-added gas can also be preheated by exchanging heat between the combustion exhaust gas generated from the heating device 44 and the hydrogen-added gas pipe between the hydrogen gas supply device 30 and the catalyst device 40 and then merging it with the exhaust gas in the first pipe 81 upstream of the first dehumidifier 20.

[0059] In the present embodiment described above, a circulation process in which the exhaust gas from the reduction furnace 10 is reused in a closed circulation system is realized by repeating the steps of reducing the iron ore by injecting the reducing gas, recovering the exhaust gas from the reduction furnace, removing dust and dehumidifying the exhaust gas (optional step), adding hydrogen gas to the exhaust gas, generating a CO-rich gas from the hydrogen-added gas by the reverse water gas shift reaction, dehumidifying the CO-rich gas (optional step), heating the CO-rich gas (optional step), and injecting the CO-rich gas as a reducing gas.

[0060] Unconverted CO2 remaining in the CO-rich gas used as the reducing gas will eventually become a CO source during the circulation process, and so there is no need to separate it from the reducing gas. That is, in this embodiment, it is important that no separation device that separates and recovers or removes specific gas components other than water vapor from the gas passing through the first pipe 81 and the second pipe 82 is disposed in the middle of the first pipe 81 and the second pipe 82. In this embodiment, no new separation and concentration process is required other than dust removal and dehumidification, for which existing technology can be applied, and therefore the circulation efficiency of the reducing gas is high.

[0061] In this embodiment, the reverse water gas shift reaction is used to convert CO2 to CO with an equimolar amount of hydrogen. This makes it possible to reduce the amount of hydrogen required per CO2 to approximately 1 / 4 compared to the conventional reduction method described above, which uses methane produced by a methanation reaction, which requires four times the amount of hydrogen in moles relative to CO2, as the reducing agent.

[0062] In the present embodiment, a reducing gas mainly composed of CO transformed from exhaust gas is supplied at a high temperature into the reducing furnace 10, and impurities in the iron ore can be separated from the molten iron as molten slag. Therefore, as in the case of a general blast furnace, low-grade fine ore ore powder, which is cost-effective and easy to procure, can be made into pellets or sintered ore and used.

[0063] In addition, the surplus of the CO-rich gas (in this embodiment, the remaining part of the CO-rich gas used as the reducing gas, the combustion gas of the gas heating device 60, and the combustion gas of the heating device 44) can be recovered. That is, the circulation type reduction system 100 has a switching valve 90 arranged in the middle of the second pipe 82 and a seventh pipe 87 extending from the switching valve 90, and a part of the CO-rich gas can be recovered through the seventh pipe 87. The recovered CO-rich gas can be used as a synthesis gas that is a raw material for organic compounds, for example. In this embodiment, a system is realized in which the CO2-rich exhaust gas discharged from the reduction furnace 10 is converted into a CO-rich reducing gas and recycled, so that the surplus of the CO2-rich gas can be effectively used as a synthesis gas in the organic chemical industry, etc., thereby suppressing CO2 emissions into the atmosphere to zero.

[0064] In addition, the molten slag separated from the molten pig iron is slowly cooled in a mold to form solidified slag, which is then crushed to form crushed slag, which can be reused as aeration material. If some of the pig iron discharged from the reduction furnace (blast furnace) adheres to the aeration material derived from the slag, the pig iron can be returned to the reduction furnace as an iron source via the aeration material.

[0065] In addition, because the difference in specific gravity causes the molten slag to automatically drain onto the surface of the molten pig iron, recycling it has almost no adverse effect on the quality of the molten pig iron. In addition, recycled molten slag has the same quality as regular blast furnace slag, so it can be used industrially as a raw material for blast furnace cement, etc.

[0066] A circulatory reduction system 200 according to another embodiment of the present invention will be described with reference to Fig. 2. The circulatory reduction system 200 has the same configuration as the circulatory reduction system 100, except that the circulatory reduction system 200 does not have the second dehumidifier 50, and instead has a third dehumidifier 70 disposed midway through the seventh pipe 87. That is, the second dehumidifier 50 is not an essential component in the present invention. When the second dehumidifier 50 is not disposed, it is preferable to remove water vapor from the CO2-rich gas passing through the seventh pipe 87 by the third dehumidifier 70.

[0067] In the above description, the reduction furnace 10 is a blast furnace or other smelting furnace, and the object to be reduced is iron ore. However, the present invention is not limited to this. The reduction furnace 10 may be a solid reduction furnace. In addition, the object to be reduced is not limited to iron ore as long as it is an oxide, and may be, for example, manganese ore, which is a raw material for ferromanganese and silicomanganese.

[0068] [Method of reducing iron ore] In the method for reducing iron ore according to one embodiment of the present invention, the CO-rich gas obtained by reforming exhaust gas is recycled as a reducing gas to reduce iron ore as an oxide using the above-mentioned circulation-type reduction system 100, 200. This makes it possible to efficiently recycle and use the CO-rich gas obtained by reforming the exhaust gas containing CO2 generated from the reduction furnace 10 as a reducing gas to perform the reduction process of iron ore.

[0069] In addition, according to the reduction method of the present embodiment, an efficient reduction process is realized in which the exhaust gas from the reduction furnace 10 can be recycled as a starting material for the reducing agent, and therefore the amount of CO2 generated can be significantly reduced. Furthermore, it becomes possible to drastically reduce the input amount of the reducing agent derived from fossil fuels, such as coke, which has been conventionally used in the iron ore reduction process.

[0070] [How to operate a blast furnace] The method of operating a blast furnace according to an embodiment of the present invention is carried out using the above-mentioned circulating reduction system 100, 200. It is essential to alternately charge layers of (I) at least one type (iron source) of iron ore selected from sintered ore, lump ore, iron ore pellets, and (II) crushed slag obtained by crushing solidified slag obtained by slowly cooling molten slag discharged from the bottom of the blast furnace, or aeration material made of a mixture of the crushed slag and coke, into the blast furnace from the top of the reduction furnace (blast furnace) 10 to ensure permeability of the reducing gas in the furnace. This makes it possible to maintain the temperature in the furnace and ensure permeability without using coke by using the above-mentioned circulating reduction system 100, 200.

[0071] In the operation according to the present embodiment, reducing gas and air are supplied as injection gases into the blast furnace through the tuyere 14. At this time, it is preferable to gradually increase the ratio of crushed slag to coke in the aeration material and the ratio of reducing gas to air in the injection gas, thereby gradually reducing the amount of coke used.

[0072] According to the method for operating a blast furnace according to the present embodiment, it is possible to obtain reduced iron in the form of molten pig iron by using low-grade fine ore ore powder, which is low cost and easy to procure, and therefore a conventional integrated pig iron and steel process can be used as is for the subsequent steps.

[0073] The degree of ventilation in a blast furnace can be adjusted by the grain size of the crushed slag. For example, if air holes are added to the cooled slag, it becomes easier to ensure ventilation. There is no problem in using ordinary blast furnace slag as the ventilation material.

[0074] In the method of operating a blast furnace according to the present embodiment, the amount of molten slag generated in the circulation type blast furnace 100, 200 is greater than that in a normal blast furnace, since the slag recharged from the furnace top 12 is remelted after the cohesive zone. In addition, when more slag is charged, the amount of heat taken away as the heat of fusion of the slag also increases. Therefore, when starting up operations in the blast furnace mode, it is desirable to adjust in advance the layer thickness ratio between the iron source layer and the ventilation layer so that the iron source layer is richer than in a normal blast furnace. EXAMPLES

[0075] [Example 1] As described below, equilibrium calculations were carried out for Invention Examples 1 and 2 and a Comparative Example to confirm the effects of the reduction method of the present invention.

[0076] (Example 1) An equilibrium calculation model of the circulatory reduction system according to the first embodiment is shown in Fig. 3. As an initial state, a reduction furnace 10 containing 25 moles of iron oxide (III) (Fe2O3) is assumed to be connected to a reverse shift type reformer (hereinafter simply referred to as "reformer 40") as a catalytic device 40 containing a mixed gas equivalent to a total of 100 moles of blast furnace exhaust gas, consisting of 22 moles of CO, 22.8 moles of CO2, 4.2 moles of H2, and 51 moles of N2. A first dehumidifier 20 is placed on the inlet side of the reformer, a second dehumidifier 50 is placed on the outlet side of the reformer, and a hydrogen gas supply device 30 is placed between the first dehumidifier and the reformer to maintain the number of moles of H2 in the reformer at 22.8 moles (corresponding to the CO2 concentration in the blast furnace exhaust gas). If we assume that no gas flows in or out of the reduction furnace and the reformer other than H2 supplied from the hydrogen gas supply device and H2O removed by the first dehumidifier and the second dehumidifier, then all H2O is generated from the consumed H2, and it can be considered that the total number of moles of the mixed gas circulating through the reformer and the reduction furnace does not change.

[0077] In Example 1 of the present invention, the temperatures in the reduction furnace and reformer are both maintained at 900°C by heat supplied from outside. A gas transport system is required to actually circulate gas between the reduction furnace and reformer, but the energy consumed by this system is ignored because the purpose is to confirm the principle. Similarly, the energy consumed to drive the first dehumidifier, the second dehumidifier, and the hydrogen gas supply device is also ignored. The reverse water gas shift reaction in the reformer may not reach an equilibrium state, so it is assumed that an equilibrium reaction is reached, although this depends on the performance of the catalyst used.

[0078] Here, we consider a circulation process in which the reducing gas generated when the hydrogenation gas reaches a steady state in the reformer is sent in its entirety to the reduction furnace, the gas in the reduction furnace when the reduction reaction reaches a steady state is taken out as exhaust gas, and hydrogen is added to this gas up to a certain level to produce hydrogenation gas again, with this cycle being considered as one cycle. The equilibrium state of the gas components and iron source in the reformer and reduction furnace that occurs in each cycle in which the reducing gas is sent from the reformer to the reduction furnace was calculated using thermodynamic equilibrium calculation software and thermodynamic database Fact Sage 8.1 made by Computational Mechanics Research Center Co., Ltd. The results are shown in Figure 4. Note that compounds generated in the reformer and reduction furnace include methane, but trace components of 0.005 moles or less were ignored.

[0079] In the reduction furnace, the reduction of the iron source proceeds with the CO supplied from the reformer and the excess H2 not consumed in the reverse water gas shift reaction. The solid phase Fe2O3 introduced as the iron source changes to twice the moles of FeO (solid phase) in the first cycle, and from the second cycle onwards, FeO is gradually reduced and changes to α-Fe (solid phase), completing the reduction in the seventh cycle. The fact that the main reduction reaction is from FeO to α-Fe coincides with knowledge known from blast furnaces. The amount of H2 consumed in the reduction of this iron source is 89 moles.

[0080] (Example 2) An equilibrium calculation model of the circulating reduction system according to Example 2 of the present invention is shown in Fig. 5. This is the same as the equilibrium calculation model of the circulating reduction system according to Example 1 of the present invention shown in Fig. 3, except that no second dehumidifier is provided on the outlet side of the reformer. The calculation conditions were also the same as in Example 1 of the present invention, and the equilibrium states of the gas components and the iron source in the reformer and the reduction furnace were calculated. The results are shown in Fig. 6.

[0081] The solid phase Fe2O3 added as the iron source changes to twice the moles of FeO (solid phase) in the first cycle, and from the third cycle onwards, FeO is gradually reduced and changes to α-Fe (solid phase), completing the reduction in the ninth cycle. The fact that the main reduction reaction is from FeO to α-Fe is consistent with knowledge known from blast furnaces. The amount of H2 consumed in the reduction of this iron source is 85 moles.

[0082] (Comparative Example) An equilibrium calculation model of a circulating reduction system according to a comparative example is shown in Fig. 7. This is the same as the equilibrium calculation model of the circulating reduction system according to Example 1 of the invention shown in Fig. 3, except that a reformer and a second dehumidifier are not provided. The calculation conditions were also the same as those of Example 1 of the invention, and the equilibrium states of the gas components and the iron source in the reformer and the reduction furnace were calculated. The results are shown in Fig. 8.

[0083] In the reduction furnace of the comparative example, the reduction of the iron source proceeds only with H2 directly fed into the reduction furnace from a hydrogen gas supply device. 25 moles of Fe2O3 (solid phase) fed as the iron source changes to 8.2 moles of Fe3O4 (solid phase) and 22.5 moles of FeO (solid phase) in the first cycle, and from the second cycle onwards, FeO is gradually reduced and changes to α-Fe (solid phase), completing the reduction in the 9th cycle, the same as in Example 2. Similar to Examples 1 and 2, the main reduction reaction is the reaction from FeO to α-Fe. The amount of H2 consumed in the reduction of this iron source is 75 moles, 10 moles less than in Example 2.

[0084] (Amount of heat absorbed in the reduction furnace) The major difference between Examples 1 and 2 and the Comparative Example is the amount of heat absorbed in the reduction furnace. Figures 9 and 10 show the reaction heat (amount of heat absorbed) in the reduction furnace calculated from the reaction heat of each reaction calculated using Fact Sage 8.1.

[0085] Direct reduction of the iron source with H2 is an endothermic reaction, except for the reaction from Fe2O3 to Fe3O4, which is completed in the early stage. In contrast, in the reduction of the iron source with CO and excess H2 in Example 1, the amount of heat absorbed by H2 reduction is compensated for by the amount of heat generated by CO reduction, so the total amount of heat absorbed can be significantly reduced (see Figure 9). In addition, in Example 2, the amount of heat generated by CO reduction exceeds the amount of heat absorbed by H2 reduction in the FeO reduction region, so the reduction temperature of FeO is spontaneously maintained at a high temperature (see Figure 9). If the amount of iron source input increases, the reduction stage of FeO becomes even longer. Normally, it is extremely difficult to supply heat to a reduction furnace that needs to be kept at a high temperature inside from any source other than the tuyere and the furnace top. Therefore, considering that this absorbed heat needs to be compensated for by the combustion heat of the coke input into the reduction furnace, the superiority of the present invention is clear.

[0086] From Fig. 10, it is expected that the amount of H2 supplied to the reformer to maximize the heat generation in the FeO reduction region is approximately the same as the molar amount of CO2 in the exhaust gas. Since it is considered that the reduction rate will also decrease if the amount of H2 supplied to the reformer is suppressed, in practice the amount of H2 supplied is adjusted based on the balance between the temperature in the reduction furnace and the reduction rate.

[0087] [Example 2] As described below, in Examples 3 and 4 of the present invention, reduction of iron ore was carried out using an experimental circulation-type reduction system.

[0088] (Example 3) The configuration of an experimental circulatory reduction system according to Example 3 is shown in Fig. 11. In Fig. 11, a raw material block A was formed by alternately stacking 2.2 kg of coke crushed to about 5 mm and 5.0 kg of lump ore crushed to about 3 mm on a tungsten mesh that partitioned the furnace bottom of a BF simulator (hereinafter referred to as "reduction furnace 10"), which was an experimental reduction furnace installed on a weighing scale.

[0089] Furthermore, raw material block B was formed by alternately stacking on top of raw material block A a uniform mixture of 1.1 kg of the above coke and 2.8 kg of slowly cooled blast furnace slag crushed to approximately 5 mm and 5.0 kg of lump ore crushed to approximately 3 mm.

[0090] The exhaust gas discharged from the top of the furnace passes through a dust collector, a dehumidifier 20, a first electric tubular furnace 40, a dehumidifier, a second electric tubular furnace 40, a dehumidifier 50, and a regenerative gas heating furnace 60, and is then connected via a switching valve 91 to an exhaust gas treatment device on one side and a nozzle 92 at the bottom of the reduction furnace on the other side. The two electric tubular furnaces 40 are ceramic electric tubular furnaces in which a quartz reaction tube holding platinum catalyst 51g is set in the center.

[0091] Sampling tubes for gas composition analysis were provided at two locations, immediately before the first electric tubular furnace 40 and between the second electric tubular furnace 40 and the dehumidifier 50, and were connected to a micro gas chromatograph (micro GC). In addition, a hydrogen pipe 30 was connected between the dehumidifier 20 and the first electric tubular furnace 40 via a switching valve 93 and a mass flow controller (MFC) 94.

[0092] On the opposite side of the nozzle 92 at the bottom of the reduction furnace 10, a nozzle 96 was provided for feeding 2.3% oxygen-enriched air via a regenerative gas heating furnace 95. The flow rate of the air introduced from the nozzle 96 was controlled by a mass flow controller (MFC) 97.

[0093] In order to completely exhaust the exhaust gas remaining in the reduction furnace 10 after the reduction experiment was completed, a nitrogen gas purge pipe was connected between the dehumidifier 20 and the switching valve 93 via a switching valve 98.

[0094] First, the switching valve 91 was set to the exhaust gas treatment device side to separate the exhaust gas from the reducing furnace 10. Then, air heated to 1200°C by the MFC 97 was introduced into the reducing furnace 10 from the nozzle 96 of the reducing furnace 10 at a flow rate of 17 L / min. Both of the two electric tubular furnaces 40 were set to have an internal temperature of 800°C using thermocouples (TC) provided around the catalyst.

[0095] The representative compositions of the exhaust gas generated by the reduction of lump ore in raw material block A and the mixed gas after passing through the second electric tubular furnace 40 (when hydrogen is not replenished at the inlet side of the first electric tubular furnace 40) are shown in Table 1. It can be seen that after passing through the second electric tubular furnace 40, CO increases by 2.7% due to the reverse water gas shift reaction caused by excess H2 in the exhaust gas, and CO2 and H2 each decrease by 2.7%.

[0096] When 2.2 kg of coke in raw material block A was completely consumed as exhaust gas, the flow rate of air introduced from nozzle 96 was changed to 8.5 L / min by MFC 97. At the same time, the switching valve 93 was switched to the hydrogen pipe 30 side to introduce hydrogen gas, and the H2 concentration in the mixed gas before entering the first electric tubular furnace 40 was adjusted by MFC 94 to 22.8% (the same as the CO2 concentration in the initial exhaust gas). Then, the switching valve 91 was switched to the reducing furnace 10 side, and reducing gas was introduced from nozzle 92. It was determined from the change in weight of the reducing furnace 10 that the coke in raw material block A had been completely consumed.

[0097] In this state, after waiting for 1.1 kg of coke in raw material block B to be completely consumed, the air introduced from nozzle 96 was stopped, and the two electric tubular furnaces and the two gas heating furnaces were stopped. Then, after waiting for the water temperature in the water-cooled jacket to reach 30°C, the hydrogen gas was shut off by switching valve 93, switching valve 91 to the exhaust gas treatment device side and switching valve 98 to the nitrogen gas introduction side, and all of the exhaust gas remaining in the reducing furnace 10 was discharged to the exhaust gas treatment device. Thereafter, the reducing furnace 10 was disassembled to confirm the condition inside the furnace.

[0098] The total of 10 kg of lump ore, 3.3 kg of coke, and 2.8 kg of slowly cooled blast furnace slag in raw material blocks A and B were hardly observed on the tungsten mesh. A mixture of ferrite (α-Fe) and cementite (Fe3C) was observed in the hearth bottom separated by the tungsten mesh, along with slag deposited on top of it. X-ray diffraction confirmed that the mixture was composed of ferrite and cementite. The carbon content of the mixture measured with a combustion-type carbon-sulfur analyzer was approximately 4.3 mass%, and when comparing the upper and lower parts of the mixture, the lower part tended to have a carbon content about 0.3 mass% higher.

[0099] Through the above experiments, it was confirmed that the lump ore charged as raw material can be completely reduced even in the reduction process of raw material block B, which corresponds to 50% carbonless operation using slag as an aerator, after the entire amount of raw material block A, which corresponds to the blast furnace mode, has been reduced.

[0100] (Example 4) The configuration of an experimental circulatory reduction system according to Example 4 of the invention is shown in Fig. 12. This is the same as the circulatory reduction system of Example 3 of the invention shown in Fig. 11, except that one electric tubular furnace 40 is used and no dehumidifier is placed downstream of the electric tubular furnace 40. The electric tubular furnace 40 was set to have an internal temperature of 900°C using a thermocouple (TC) provided around the catalyst. Tests were conducted under the same conditions as in Example 3 of the invention.

[0101] The representative compositions of the exhaust gas generated by the reduction of lump ore in raw material block A and the mixed gas after passing through the electric tubular furnace 40 (when hydrogen is not replenished at the inlet side of the electric tubular furnace 40) are shown in Table 1. It can be seen that after passing through the electric tubular furnace 40, CO increases by 1.8% due to the reverse water gas shift reaction caused by excess H2 in the exhaust gas, and CO2 and H2 each decrease by 1.8%.

[0102] After the test, almost no lump ore, coke, or blast furnace slag was found on the tungsten mesh, as in Example 3. A mixture of ferrite (α-Fe) and cementite (Fe3C), and slag deposited on it, were found in the hearth, which was partitioned off by the tungsten mesh. X-ray diffraction confirmed that the mixture was composed of ferrite and cementite. The carbon content in the mixture, as measured by a combustion-type carbon-sulfur analyzer, was approximately 4.3% by mass, and when comparing the upper and lower parts of the mixture, the lower part tended to have a higher carbon content of about 0.3% by mass.

[0103] Through the above experiments, it was confirmed that the lump ore charged as raw material can be reduced in its entirety even in the reduction process of raw material block B, which corresponds to 50% carbonless operation using slag as an aerating material, after the entire amount of raw material block A, which corresponds to the blast furnace mode, has been reduced.

[0104] [Table 1] [Explanation of symbols]

[0105] 100 Circulation-based Reduction System 200 Circulation-type Reduction System 10 Reduction furnace 12 Hearth top 14 Tuyere 20 1st dehumidifier 30 Hydrogen gas supply device 40 Catalytic device 42 Reaction chamber 44 Heating device 50 2nd dehumidifier 60 Gas Heating Equipment 70 Third dehumidifier 81 First Pipe 82 Second Pipe 83 Third Pipe 84 4th Pipe 85 5th Pipe 86 6th Pipe 87 7th Pipe 90 Switching valve

Claims

1. a reduction furnace, which is a smelting furnace for reducing oxides contained therein; CO generated in the reduction furnace ２ a first pipe through which an exhaust gas containing the above-mentioned is recovered from the reduction furnace and passes; a hydrogen gas supply device connected to the first pipe and adding hydrogen gas to the exhaust gas to produce a hydrogen-added gas; The terminal end of the first pipe is connected to a reaction chamber that contains a catalyst for a reverse water gas shift reaction, and the hydrogenated gas introduced into the reaction chamber from the first pipe comes into contact with the catalyst to react with CO in the hydrogenated gas by the reverse water gas shift reaction. ２ a catalyst device in which the above-mentioned is converted into CO to produce a CO-rich gas having an increased CO concentration; a second pipe extending from the catalyst device and connected to the reduction furnace, through which the CO-rich gas passes and through which the CO-rich gas is supplied to the inside of the reduction furnace as a reducing gas; having A circulating reduction system in which a separation device that separates and recovers or removes a specific gas component other than water vapor from the gas passing through the first pipe and the second pipe is not disposed midway through the first pipe and the second pipe.

2. 2. The circulating reduction system according to claim 1, further comprising a gas heating device arranged in the second pipe for heating the CO-rich gas.

3. 3. The circulation-type reduction system according to claim 2, further comprising a third pipe that branches off from the second pipe at a position upstream of the gas heating device and is connected to the gas heating device, and a portion of the CO-rich gas is supplied as a combustion gas to the gas heating device via the third pipe.

4. 4. The circulation-type reduction system according to claim 2 or 3, further comprising a fourth pipe extending from the gas heating device and connected to a midpoint of the first pipe, and wherein the combustion exhaust gas generated from the gas heating device is merged with the exhaust gas in the first pipe via the fourth pipe.

5. the catalytic device has a heating device for heating the reaction chamber, 4. The circulation type reduction system according to claim 1, further comprising a fifth pipe branched from the second pipe and connected to the heating device, and a part of the CO-rich gas is supplied to the heating device as a combustion gas via the fifth pipe.

6. 6. The circulation-type reduction system according to claim 5, further comprising a sixth pipe extending from the heating device and connected to a middle of the first pipe, wherein the combustion exhaust gas generated from the heating device is merged with the exhaust gas in the first pipe via the sixth pipe.

7. 4. The circulation-type reduction system according to claim 1, further comprising a first dehumidifier that removes water vapor from the exhaust gas and is disposed in the first piping upstream of a portion to which the hydrogen gas supply device is connected.

8. 4. The circulating reduction system according to claim 1, further comprising a second dehumidifier arranged in the second pipe to remove water vapor from the CO-rich gas.

9. A switching valve is disposed in the middle of the second pipe, and a seventh pipe extends from the switching valve, 4. The circulating reduction system according to claim 1, wherein a portion of the CO-rich gas is recovered through the seventh pipe.

10. 10. The circulating reduction system according to claim 9, further comprising a third dehumidifier disposed midway along the seventh pipe to remove water vapor from the CO-rich gas passing through the seventh pipe.

11. A circulating reduction system described in any one of claims 1 to 3, wherein the oxide is iron ore.

12. The circulating reduction system according to claim 11 , wherein the smelting furnace is a blast furnace.

13. A method for reducing iron ore, comprising: using the circulation-type reduction system according to any one of claims 1 to 3, circulating and utilizing the CO-rich gas obtained by reforming the exhaust gas as the reducing gas, and performing a reduction process of iron ore as the oxide.

14. A method for operating a blast furnace using the circulating reduction system according to claim 11, comprising: A method for operating a blast furnace, comprising: charging, into the blast furnace from the top of the blast furnace, alternate layers of (I) at least one type of iron ore selected from sintered ore, lump ore, iron ore pellets, and fine ore; and (II) crushed slag obtained by crushing solidified slag obtained by slowly cooling molten slag discharged from the bottom of the blast furnace, or a ventilation material consisting of a mixture of the crushed slag and coke, to ensure ventilation of the reducing gas inside the furnace.

15. The reducing gas and air are supplied as blown gases into the inside of the blast furnace from a tuyere located at the bottom of the blast furnace; 15. The method for operating a blast furnace according to claim 14, wherein the ratio of the crushed slag to the coke in the aeration material and the ratio of the reducing gas to the air in the blown gas are gradually increased to gradually reduce the amount of coke used.

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