Circulating 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

Circulating reduction system, iron ore reduction method, and blast furnace operation method

[0001] The present invention is a method for preventing CO2, which promotes global warming. ２ The present invention relates to a circulatory reduction system, a method for reducing iron ore, and a method for operating a blast furnace, which can drastically reduce CO₂ emissions.

[0002] CO2, which promotes global warming ２ While there is a global call to reduce CO emissions, ２ The country's steel industry, which accounts for around 15% of 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 furnaces that will enable crude steel to be produced at a low cost close to current levels, but there is currently little prospect of this being technologically viable.

[0003] Here, the hydrogen reduction process, in which hydrogen is used as a reducing agent for iron ore, is ２ However, if this method is to be used to maintain Japan's annual production of approximately 75 million tons of hot metal, it would require approximately 75 billion Nm ３ This will require 100,000 tons of hydrogen. To meet this demand using water electrolysis, a typical 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 transporting, liquefying, and storing the hydrogen. 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 on the order of 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 high transportation costs can be overcome, there is no clear technological prospect of safely storing large quantities of hydrogen, which has a wide explosive concentration range, near steelworks.

[0005] By the way, the domestic steel industry is ２ About 15% of CO emissions ２The reason for this is that high-quality steel is produced mainly using the blast furnace-converter method, which uses coke to reduce iron ore. Crude steel production methods are mainly classified into the blast furnace-converter method and the electric furnace method, with the blast furnace-converter method emitting approximately 2 t of CO per ton of steel, and the electric furnace method emitting approximately 0.5 t of CO per ton of steel. ２ CO is generated. ２ The electric furnace method is superior in that it can reduce the amount of copper generated. However, high-quality steel used in automobiles and other applications is not mass-produced using the electric furnace method, which uses scrap as the raw material, because impurities such as copper tend to have a negative impact on quality. For this reason, approximately 75% of crude steel in Japan is produced using the blast furnace-converter method.

[0006] CO ２ For example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2003-149999) has attempted to reduce the amount of coke used in blast furnaces, which have particularly high CO2 emissions, by replacing the high-temperature air blown in through the tuyere with a reducing gas such as hydrogen or methane. However, in addition to its role as a reducing agent, coke also serves as a heating agent that heats the furnace interior through a reaction with oxygen blown in from the hot stove, and as an aerator that ensures ventilation within the furnace. Therefore, until a new means (other than coke) is found that maintains the furnace temperature and ensures ventilation without adversely affecting the quality of the molten pig iron, it will be extremely difficult to drastically reduce the amount of coke used.

[0007] Given the above circumstances, Japanese steelmakers have no choice but to survive for the time being by reducing the number of blast furnaces in operation and increasing the proportion of electric furnaces. As a result, demand for scrap to be used in electric furnaces is already strong, and it is expected that the fierce competition to procure this scrap will become even more severe in the future.

[0008] Under these circumstances, CO ２Direct reduction processes with low emissions are attracting worldwide attention. In the so-called Midrex process, a typical direct reduction process, iron ore is reduced in its solid state using modified natural gas to obtain direct reduced iron (DRI) (see Reference 2). In the early Midrex process, only spongy DRI was produced, making its handling and transportation difficult due to concerns about oxidation and fire. However, with the development and industrialization of hot briquetting equipment, these problems have been largely resolved, and there is a growing global trend 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. Furthermore, natural gas can be used in a methanation reaction (CO ２ +4H ２ →CH ４ +2H ２ O) to CO ２ Attempts are also being made to replace it with methane synthesized from hydrogen and hydrogen, or even hydrogen itself.

[0009] On the other hand, in the direct reduction process, which is a solid-state reduction process, maintaining the quality of the DRI produced requires the use of high-grade iron ore, which is limited in cost and availability, as a raw material. This is a major disadvantage compared to the conventional blast furnace process, where approximately 85% of the iron ore raw material can be converted into pellets or sinter made from low-grade fine ore or fine ore.

[0010] Furthermore, because the direct reduction process does not allow crude steel to be extracted in the form of molten iron, it is not possible to use the refining equipment of conventional integrated steelmaking processes, such as pretreatment furnaces and converters. This is also one of the reasons why Japanese blast furnace manufacturers are so attached to the blast furnace process. It is presumed that the reason the direct reduction process remains limited to solid-phase reduction is because, as mentioned above, it has not been possible to fundamentally resolve the issues of maintaining permeability and the furnace temperature required to obtain molten iron.

[0011] That is, in the blast furnace-converter process, the main obstacles are the need for a reducing agent / heating material that can replace coke and a 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.２ The direct reduction process, which has low emissions, has the disadvantage that it cannot use the low-quality fine ore ore that can be used in blast furnaces, which is low-cost and easy to obtain, and because crude steel cannot be extracted as molten iron, it cannot use the refining equipment of conventional integrated pig iron and steel processes.

[0012] In light of this background, Patent Document 3 describes a method for reducing CO contained in exhaust gas from a blast furnace. ２ A technology has been proposed that utilizes CO from the exhaust gas of a blast furnace. ２ CO separated and recovered ２ It has been proposed to reform CO into CO and reuse this CO as a reducing agent in a blast furnace.

[0013] International Publication No. 2021 / 220555 Japanese Patent Application Laid-Open No. 2017-88912 Japanese Patent Application Laid-Open No. 2011-225968

[0014] In the technology described in Patent Document 3, CO separated and recovered from exhaust gas generated in a blast furnace is ２ is converted into CO and reused, ２ However, this technology can reduce the amount of CO generated from the exhaust gas. ２ is separated and collected, ２ Because the process involves multiple steps to reform the carbon dioxide, the efficiency of circulating the reducing components in the exhaust gas is reduced, and the costs required for the equipment, operation, and maintenance of each step are unavoidable. Therefore, there has been a demand for a more efficient method of circulating and reusing the reducing components in the exhaust gas from reducing furnaces such as blast furnaces.

[0015] In view of the above problems, the present invention provides a method for reducing CO generated from a reduction furnace. ２ The present invention aims to provide a circulating reduction system capable of efficiently circulating and utilizing CO-rich gas obtained by reforming exhaust gas containing CO as a reducing gas.

[0016] Furthermore, the present invention is directed to CO generated from a reduction furnace. ２ The present invention aims to provide a method for reducing iron ore, which can efficiently recycle and reuse CO-rich gas obtained by reforming exhaust gas containing CO 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 that uses the above-mentioned circulating reduction system to maintain the furnace temperature and ensure gas permeability using a material other than coke.

[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 and reused as a starting material for a reducing agent, and have found 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 iron ore reduction process generally contains CO ２ In addition to nitrogen from the atmosphere, CO and H ２ For example, the exhaust gas from a blast furnace contains approximately 23% by volume of CO ２ , the same proportion of CO, and about 4% by volume of H ２ The inventors have discovered that hydrogen is added to such exhaust gas and that this gas undergoes the reverse water gas shift reaction (RWGS). ２ +H ２ →CO+H ２ O) by contacting the exhaust gas with a catalyst for CO ２ After significantly changing the balance of CO and H to CO rich, ２ The researchers came up with the idea of ​​recycling the gas together with nitrogen as a reducing gas. They discovered that if this recycling were possible, it would be possible to minimize the input of reducing agents derived from fossil fuels, such as coke, which have been used in the past.

[0020] Here, CO is recycled as the main reducing agent. ２ This is because the reduction reaction of iron ore with CO is an endothermic reaction, whereas the reduction reaction of iron ore with CO is an exothermic reaction, and therefore CO is the most efficient reducing agent that can maintain a high temperature inside the reduction furnace. Furthermore, in reduction with CO, the freezing point depression of iron caused by carbon, which occurs when coke is used as a reducing agent, can be utilized as is. ２In the case of reduction with CO, reduced iron melts at 1500°C or higher, but in the case of reduction with CO, it melts at about 1200°C. This temperature difference of about 300°C significantly reduces the heat load on the heating furnace of the reducing gas when the reduced iron is extracted as molten iron.

[0021] Also, CO ２ The CO-rich reducing gas synthesized from the CO-rich exhaust gas is mainly supplied to the reduction furnace, but the surplus can be discharged, recovered, and reused for various purposes. In addition to being used as a reducing agent and fuel gas, CO is also used in the Fischer-Tropsch reaction (nCO + (2n + 1)H), which is important for synthesizing various organic compounds. ２ →C ｎ H ２ｎ＋２ +nH ２ O). Therefore, CO ２ The CO2-rich reducing gas synthesized from CO2-rich exhaust gas is not only a reducing agent, but also a synthetic gas that can be used without waste as a fuel gas or a raw material for various organic compounds. In particular, if the use of fossil fuels is to be drastically reduced to prevent global warming, the organic chemical industry that has relied on these as raw materials will have to find new sources of raw materials. It is of great significance that these industries will become recipients of the above-mentioned synthetic gas.

[0022] As mentioned above, the coke charged into a typical blast furnace not only serves as a reducing agent but also as a heating and aeration material. Therefore, when direct-reduced iron is extracted as molten iron, even if the temperature inside the furnace can be maintained by the heat of reduction of CO in the reducing gas, if the amount of coke charged 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 a portion of the molten slag that is generated along with the molten pig iron and discharged from the hearth, mixing it with coke as an aerator, and then re-injecting it into the furnace from the top. Since the melting point of blast furnace slag is approximately 1,400°C, even when the iron in the blast furnace begins to melt after its freezing point is lowered by C, the slag remains solid and functions as an aerator. Furthermore, because the slag is a substance originally produced in the blast furnace, recycling it does not alter 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 aerator and reducing gas as the reducing agent. Therefore, the blast furnace is first started up in "blast furnace mode," in which coke, which acts as both aerator and aerator, and iron source are alternately stacked inside the furnace, just like in a conventional blast furnace, and high-temperature air heated in a hot stove is blown into it. Then, the 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 furnace. When shutting down a blast furnace, restarting it is easy if the above procedure is reversed, with operations ending in blast furnace mode after cokeless mode.

[0025] The present invention has been made based on the above findings, and its gist is as follows: [1] A reduction furnace for reducing oxides contained therein; ２ a first pipe through which exhaust gas containing CO2 is recovered from the reduction furnace and passes; a hydrogen gas supply device connected to the middle of the first pipe and adding hydrogen gas to the exhaust gas to produce a hydrogenated gas; and a reaction chamber connected to an end of the first pipe and containing a catalyst for a reverse water gas shift reaction, wherein the hydrogenated gas introduced from the first pipe into the reaction chamber comes into contact with the catalyst to remove CO2 from the hydrogenated gas by a reverse water gas shift reaction. ２a catalytic device in which water vapor is converted into CO to produce a CO-rich gas having an increased CO concentration; and a second pipe extending from the catalytic device and connected to the reduction furnace, through which the CO-rich gas passes and which supplies the CO-rich gas to the inside of the reduction furnace as a reducing gas, wherein no separation device is disposed between the first pipe and the second pipe, which separates a specific gas component other than water vapor from the gas passing through an interior of the reduction furnace and recovers or removes it.

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

[0027] [3] The circulation-type reduction system according to the above [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 supplying a portion of the CO2-rich gas as 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 to the middle 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.

[0029] [5] The circulating reduction system according to any one of [1] to [4] above, wherein the catalytic device has a heating device that heats the reaction chamber, and a fifth pipe that branches off from the second pipe and is connected to the heating device, and a portion of the CO-rich gas is supplied to the heating device as combustion gas via the fifth pipe.

[0030] [6] The circulation-type reduction system according to the above-mentioned [5], further comprising a sixth pipe extending from the heating device and connected to the middle of 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 circulatory reduction system according to any one of [1] to [6] above, further comprising a first dehumidifier that removes water vapor from the exhaust gas and is arranged in the first piping upstream of a portion to which the hydrogen gas supply device is connected.

[0032] [8] The circulating reduction system according to any one of [1] to [7] above, further comprising a second dehumidifier arranged in the second pipe to remove water vapor from the CO2-rich gas.

[0033] [9] The circulating reduction system according to any one of [1] to [8] above, further comprising: a switching valve disposed midway along the second pipe; and a seventh pipe extending from the switching valve, wherein a portion of the CO2-rich gas is recovered via the seventh pipe.

[0034]

[10] The circulating reduction system according to [9], further comprising a third dehumidifier disposed midway along the seventh pipe and configured to remove water vapor from the CO2-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 circulating reduction system according to the above

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

[0037]

[13] A method for reducing iron ore, using the circulation-type reduction system according to any one of [1] to

[12] above, to recycle the CO-rich gas obtained by reforming the exhaust gas as the reducing gas, and performing a reduction treatment on iron ore as the oxide.

[0038]

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

[11] or

[12] above, comprising: (I) at least one 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 made of a mixture of the crushed slag and coke, which are alternately charged into the blast furnace from the top of the blast furnace in layers to ensure ventilation of the reducing gas inside the furnace.

[0039]

[15] The method for operating a blast furnace according to the above

[14] , wherein the reducing gas and air are supplied as injection gases into the interior of the blast furnace from a tuyere located at the bottom of the blast furnace, and the ratio of the crushed slag to the coke in the aerating material and the ratio of the reducing gas to the air in the injection gas are gradually increased, thereby gradually reducing the amount of coke used.

[0040] According to the circulating reduction system of the present invention, CO generated from the reduction furnace ２ The CO-rich gas obtained by reforming exhaust gas containing CO can be efficiently recycled and reused as a reducing gas.

[0041] According to the iron ore reduction method of the present invention, CO generated from the reduction furnace ２ The CO-rich gas obtained by reforming exhaust gas containing CO can be efficiently recycled and reused as a reducing gas for the reduction treatment of iron ore.

[0042] According to the method for operating a blast furnace of the present invention, the above-mentioned circulating reduction system can be used to maintain the temperature inside the furnace and ensure gas permeability using materials other than coke.

[0043] FIG. 1 is a schematic diagram showing the configuration of a circulatory reduction system 100 according to one embodiment of the present invention. FIG. 2 is a schematic diagram showing the configuration of a circulatory reduction system 200 according to another embodiment of the present invention. FIG. 3 is a schematic diagram showing an equilibrium calculation model of a circulatory reduction system according to Invention Example 1. FIG. 4 is a graph showing the reduction status in the model of FIG. 3 (Invention Example 1). FIG. 5 is a schematic diagram showing the reduction status in the model of FIG. 5 (Invention Example 2). FIG. 6 is a schematic diagram showing the equilibrium calculation model of a circulatory reduction system according to a comparative example. FIG. 7 is a graph showing the reduction status in the model of FIG. 7 (Comparative Example). FIG. 8 is a graph showing the change in the heat absorption amount in a reduction furnace with respect to the number of cycles in Invention Examples 1 and 2 and the comparative example. FIG. 9 is a graph showing the change in the heat absorption amount in a reduction furnace in the FeO reduction zone with respect to the amount of hydrogen in the hydrogen-added gas in Invention Examples 1 and 2 and the comparative example. FIG. 10 is a schematic diagram showing the configuration of an experimental circulatory reduction system according to Invention Example 3. FIG. 11 is a schematic diagram showing the configuration of an experimental circulatory reduction system according to Invention Example 4.

[0044] [Circulation-Type Reduction System] A circulation-type reduction system 100 according to one embodiment of the present invention will be described with reference to Fig. 1. The circulation-type reduction system 100 includes a reduction furnace 10, a first dehumidifier 20, a hydrogen gas supply device 30, a catalytic device 40, a second dehumidifier 50, and a gas heating device 60, and also includes 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 reducing furnace 10 may be, for example, a blast furnace or other blast furnace. When the reducing furnace 10 is a blast furnace, iron ore and coke are charged into the reducing furnace 10 from a furnace top 12, and high-temperature reducing gas is blown into the reducing furnace 10 from tuyere 14 located at the bottom of the reducing furnace 10, thereby reducing the iron ore in the reducing furnace 10.

[0046] The first pipe 81 is for discharging CO generated in the reduction furnace 10. ２ The first pipe 81 is a piping facility that recovers and passes exhaust gas containing the hydrogen from the reducing furnace 10. The first pipe 81 has a starting end connected to the reducing furnace 10 (furnace top 12, for example) and a terminal end connected to the catalytic device 40. A hydrogen gas supply device 30 is connected to the first pipe 81. In addition, a first dehumidifier 20 is disposed in the first pipe 81, upstream of the portion where the hydrogen gas supply device 30 is connected. The first pipe 81 includes a pipe 81A that extends from the reducing 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" with respect to a pipe refer to the direction of gas flow in the pipe.

[0047] The exhaust gas discharged from the furnace top 12 of the reducing furnace 10 is dehumidified by the first dehumidifier 20 while flowing through the first pipe 81, and then hydrogen (H ２ ) gas is replenished to form a hydrogen-added gas. The dehumidification treatment is preferably carried out 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, except for water vapor, CO ２ : 13 to 24 vol%, CO: 21 to 31 vol%, and H ２: Contains 3 to 15 volume % N, the remainder being air-derived N ２ The composition of the hydrogenation gas is not particularly limited, but typically contains, excluding water vapor, CO ２ : 13 to 24 vol%, CO: 21 to 31 vol%, and H ２ : Contains 10 to 30% by volume, the remainder being N derived from air ２ The hydrogen supplied from the hydrogen gas supply device 30 is preferably green hydrogen obtained by water electrolysis using renewable energy, but by applying the circulatory reduction system of the present invention to blast furnace operation, hydrogen refined from coke oven gas can be used instead 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 point where the hydrogen gas supply device 30 is connected, to perform a dust removal process on the exhaust gas and remove dust derived from the raw materials from the exhaust gas.

[0049] The catalytic 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 catalytic device 40, the hydrogenated gas introduced into the reaction chamber 42 from the first pipe 81 comes into contact with the catalyst, and the CO in the hydrogenated gas is converted by the reverse water gas shift reaction. ２ is converted to CO, 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, excluding water vapor, CO ２ : 6 to 20% by volume, CO: 24 to 40% by volume, and H ２ : Contains 5 to 24 volume % N, the remainder being air-derived N ２ There are many known catalysts that can be used in the reverse water gas shift reaction, such as nickel-based and noble metal-based catalysts, and any of these 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 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 with 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 piping facility that extends from the catalytic device 40 and is connected to the reducing furnace 10 (in one example, the tuyere 14). The second pipe 82 passes the CO-rich gas and supplies the CO-rich gas as a reducing gas to the inside of the reducing furnace 10 (in one example, via the tuyere 14). 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 preferably disposed along the second pipe 82. In this case, the gas heating device 60 is preferably disposed downstream of the second dehumidifier 50. In this case, the second pipe 82 includes 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 subjected to a dehumidification process by the second dehumidifier 50 while flowing through the second pipe 82, and is then heated by the gas heating device 60, and is then blown into the reducing furnace 10 as a reducing gas.

[0053] That is, after the reaction in the catalyst, it is desirable to adjust the temperature of the CO2-rich gas (reducing gas) to be injected into the reducing furnace 10 using the gas heating device 60. Although the efficiency of iron ore reduction in the reducing furnace 10 is improved as the reducing gas temperature increases, when solid-phase reduction of iron ore is performed, it is desirable to set the temperature of the reducing gas to 900°C or higher. Furthermore, when removing reduced iron as molten iron at 1500°C, the temperature of the molten region of the iron source and slag formed in the lower region of the reducing furnace 10 needs to be maintained at 1650°C or higher. Therefore, it is desirable to inject 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 a conventional blast furnace, and that the temperature of the reducing gas is 1500°C or higher if the amount of coke charged is less than 20% of that of a conventional blast furnace.

[0054] The gas heating device 60 is preferably operated as follows. The circulation-type reduction system 100 of this embodiment preferably includes a third pipe 83 that branches off from the second pipe 82 at a position upstream of the gas heating device 60 and downstream of the second dehumidifier 50 and is connected to the gas heating device 60. A portion of the CO-rich gas flowing through the second pipe 82 is preferably supplied to the gas heating device 60 as combustion gas via the third pipe 83. In this manner, by burning a portion of the CO-rich gas as fuel gas in the gas heating device 60, the temperature of the reducing gas can be raised to the desired temperature. Although not shown in FIG. 1 , the oxygen-containing gas supplied to the gas heating device 60 for combusting the combustion gas is preferably oxygen gas (not containing unconsumed nitrogen).

[0055] The circulation-type reduction system 100 preferably includes a fourth pipe 84 extending from the gas heating device 60 and connected to 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 the first pipe 81 at a position upstream of the first dehumidifier 20. The combustion exhaust gas generated from the gas heating device 60 may be 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, thereby preheating the reducing gas and hydrogen-added gas.

[0056] In addition, when the reducing gas cannot be heated to a desired temperature by the indirect heating type gas heating device 60 as exemplified in FIG. 1, oxygen may be added from the tip of the gas heating device 60 to reduce CO and H contained in the reducing gas. ２ Furthermore, if oxygen-enriched air obtained by a cryogenic separation method 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 heater 60 that is lost due to heating of the nitrogen is reduced, making it easier to raise the temperature of the reducing gas.

[0057] Next, with regard to suitable operation of the catalytic device 40, it is also preferable to use a portion of the CO-rich gas as the combustion gas. That is, the circulating reduction system 100 of this embodiment preferably has a fifth pipe 85 branching from the second pipe 82 and connected to the heating device 44 of the catalytic device 40. The fifth pipe 85 preferably branches off from the second pipe 82 at a position upstream of the gas heating device 60 and downstream of the second dehumidifier 50. It is then preferable to supply a portion of the CO-rich gas as the combustion gas to the heating device 44 via the fifth pipe 85. Although not shown in FIG. 1 , the oxygen-containing gas supplied to the heating device 44 for combusting the combustion gas is preferably oxygen gas (not including unconsumed nitrogen).

[0058] The circulation-type reduction system 100 preferably includes a sixth pipe 86 extending from the heating device 44 and connected to the first pipe 81. The combustion exhaust gas generated from the heating device 44 is preferably merged with the exhaust gas in the first pipe 81 via the sixth pipe 86 for reuse. In this embodiment, the upstream portion 86A of the sixth pipe 86 is connected to the fourth pipe 84, which is the fuel exhaust gas flow path from the gas heating device 60, and 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 with the combustion exhaust gas generated from the heating device 44 through a hydrogen-added gas pipe between the hydrogen gas supply device 30 and the catalytic device 40 and then merging the combustion 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 reducing furnace 10 is reused in a closed circulation system is realized by repeating the steps of reducing the iron ore by injecting a 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 CO2-rich gas from the hydrogen-added gas by the reverse water gas shift reaction, dehumidifying the CO2-rich gas (optional step), heating the CO2-rich gas (optional step), and injecting the CO2-rich gas as a reducing gas.

[0060] Unconverted CO remaining in the CO-rich gas used as the reducing gas ２ Since water vapor will eventually become a CO source during the circulation process, it does not need to be separated from the reducing gas. That is, in this embodiment, it is important that no separation device that separates, recovers, or removes specific gas components other than water vapor from the gas passing through the first pipe 81 or the second pipe 82 is disposed midway through 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, CO ２ In order to utilize the reverse water gas shift reaction, which converts CO with an equimolar amount of hydrogen,２ Compared to the conventional reduction method described above, which uses methane generated in a methanation reaction as a reducing agent, which requires four times the molar amount of hydrogen as CO ２ The amount of hydrogen required per unit can be reduced to about one-fourth.

[0062] In this embodiment, a reducing gas mainly composed of CO converted 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 with a general blast furnace, low-grade fine ore or powder ore, which is cost-effective and easy to procure, can be used in the form of pellets or sintered ore.

[0063] It should be noted that the surplus CO-rich gas (in this embodiment, the remaining portion 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 disposed midway through the second pipe 82 and a seventh pipe 87 extending from this switching valve 90, and can recover a portion of the CO-rich gas via this seventh pipe 87. The recovered CO-rich gas can be used, for example, as synthesis gas that is a raw material for organic compounds. In this embodiment, the CO discharged from the reduction furnace 10 ２ This will realize a system that converts rich exhaust gas into CO2-rich reducing gas and recycles it, and by effectively utilizing the surplus CO2-rich gas as synthesis gas in the organic chemical industry, etc., it will reduce CO2 emissions into the atmosphere. ２ It will be possible to reduce emissions to zero levels.

[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 aerating material. If part of the pig iron discharged from the reducing furnace (blast furnace) adheres to the slag-derived aerating material, the pig iron can be returned to the reducing furnace as an iron source via the aerating material.

[0065] Furthermore, 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. Furthermore, because recycled molten slag has the same quality as regular blast furnace slag, it can be used industrially as a raw material for blast furnace cement and other products.

[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 it does not include the second dehumidifier 50 and instead includes a third dehumidifier 70 disposed midway through the seventh pipe 87. In other words, the second dehumidifier 50 is not an essential component of the present invention. If the second dehumidifier 50 is not disposed, it is preferable to use the third dehumidifier 70 to remove water vapor from the CO2-rich gas passing through the seventh pipe 87.

[0067] Although the above description has been given mainly of the case where the reduction furnace 10 is a blast furnace or other blast furnace and the material to be reduced is iron ore, the present invention is not limited to this. The reduction furnace 10 may be a solid reduction furnace. Furthermore, the material 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 for reducing iron ore] In a method for reducing iron ore according to an embodiment of the present invention, the above-described circulation-type reduction system 100, 200 is used to recycle CO-rich gas obtained by reforming exhaust gas as a reducing gas, and the CO generated from the reduction furnace 10 is used for reduction treatment of iron ore as an oxide. ２ The CO-rich gas obtained by reforming exhaust gas containing CO can be efficiently recycled and reused as a reducing gas for the reduction treatment of iron ore.

[0069] Furthermore, according to the reduction method of this embodiment, an efficient reduction process is realized in which the exhaust gas from the reduction furnace 10 can be recycled and used as a starting material for the reducing agent. ２ Furthermore, it will be possible to drastically reduce the amount of fossil fuel-derived reducing agents, such as coke, that are conventionally used in the iron ore reduction process.

[0070] [Method for Operating a Blast Furnace] A method for operating a blast furnace according to one embodiment of the present invention is carried out using the above-described circulating reduction system 100, 200. It is essential to alternately charge into the blast furnace from the top of the reducing furnace (blast furnace) 10 layers of (I) at least one iron ore (iron source) 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, thereby ensuring permeability of the reducing gas within the furnace. This allows the above-described circulating reduction system 100, 200 to maintain the furnace temperature and ensure permeability without using coke.

[0071] In the operation according to this 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 aerating 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 of this 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. 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 particle size of the crushed slag. For example, if air holes are added to the cooled slag, ventilation can be ensured more easily. There is no particular problem with using ordinary blast furnace slag as the ventilation material.

[0074] In the method for operating a blast furnace according to this embodiment, the amount of molten slag generated in the circulation blast furnace 100, 200 is greater than that in a conventional blast furnace, due to the amount of slag recharged from the furnace top 12 that remelts after the cohesive zone. Furthermore, the amount of heat absorbed as heat of slag fusion also increases as the amount of slag charged increases. Therefore, when starting up operation in blast furnace mode, it is desirable to adjust in advance the thickness ratio of the iron source layer to the permeable layer so that the iron source layer is richer than in a conventional blast furnace.

[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] (Invention Example 1) An equilibrium calculation model of the circulating reduction system according to Invention Example 1 is shown in FIG. 3. As an initial state, 25 moles of iron (III) oxide (Fe ２ O ３ The reduction furnace 10 containing CO: 22 moles, CO ２ : 22.8 mol, H ２ : 4.2 mol, N ２ It is assumed that the catalytic converter 40 is connected to a reverse shift type reformer (hereinafter simply referred to as "reformer 40") containing a mixed gas equivalent to a total of 100 moles of blast furnace exhaust gas, consisting of 51 moles of blast furnace exhaust gas. A first dehumidifier 20 is provided on the inlet side of the reformer, a second dehumidifier 50 is provided on the outlet side of the reformer, and a H ２ The number of moles of CO in the blast furnace exhaust gas is ２ A hydrogen gas supply device 30 is installed to maintain the hydrogen concentration at 22.8 moles (corresponding to the concentration). ２ and H removed by the first and second dehumidifiers ２ If there is no gas other than O entering or leaving, all H ２ O is the consumed H ２ Therefore, it can be considered that the total number of moles of the mixed gas circulating between the reformer and the reduction furnace does not change.

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

[0078] Here, we consider a recirculation 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. When the reduction reaction reaches a steady state, the gas in the reduction furnace is extracted as exhaust gas, and hydrogen is added to this to a certain level to produce hydrogenation gas again. This cycle is considered a repetitive cycle. The equilibrium state of the gas components and iron source in the reformer and reduction furnace, which occurs during each cycle in which the reducing gas is sent from the reformer to the reduction furnace, was calculated using the thermodynamic equilibrium calculation software and thermodynamic database Fact Sage 8.1 from Computational Mechanics Research Center, Inc. The results are shown in Figure 4. Note that compounds generated in the reformer and reduction furnace include methane, but trace components below 0.005 moles were ignored.

[0079] In the reduction furnace, CO supplied from the reformer and excess H that was not consumed in the reverse water gas shift reaction are ２ The reduction of the iron source proceeds by the solid phase Fe introduced as the iron source. ２ O ３ is converted to twice the molar amount of FeO (solid phase) in the first cycle, and from the second cycle onwards, FeO is gradually reduced and converted to α-Fe (solid phase), with the reduction being completed in the seventh cycle. The fact that the main reduction reaction is from FeO to α-Fe is in agreement with knowledge known from blast furnaces. H consumed in the reduction of this iron source ２ The amount is 89 moles.

[0080] (Example 2) An equilibrium calculation model of the circulating reduction system according to Example 2 is shown in Figure 5. This is the same as the equilibrium calculation model of the circulating reduction system according to Example 1 shown in Figure 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, and the equilibrium states of the gas components and iron source in the reformer and the reducing furnace were calculated. The results are shown in Figure 6.

[0081] Solid Fe added as iron source ２ O ３is converted to twice the molar amount of FeO (solid phase) in the first cycle, and from the third cycle onwards, FeO is gradually reduced and converted to α-Fe (solid phase), with the reduction being completed in the ninth cycle. The fact that the main reduction reaction is from FeO to α-Fe is in agreement with knowledge known from blast furnaces. H consumed in the reduction of this iron source ２ The amount is 85 moles.

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

[0083] In the reduction furnace of the comparative example, H 2 was directly introduced into the reduction furnace from the hydrogen gas supply device. ２ The reduction of the iron source proceeds only with 25 moles of Fe added as the iron source. ２ O ３ (solid phase) is 8.2 moles of Fe in the first cycle ３ O ４ (solid phase) and 22.5 moles of FeO (solid phase). From the second cycle onwards, FeO is gradually reduced and changes to α-Fe (solid phase), and reduction is completed in the ninth cycle, the same as in Example 2. Similar to Examples 1 and 2, the main reduction reaction is from FeO to α-Fe. H consumed in the reduction of this iron source ２ The amount is 75 moles, which is 10 moles less than that in Invention Example 2.

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

[0085] H ２ The direct reduction of the iron source by Fe ２ O ３ From Fe ３ O ４ All reactions are endothermic except for the reaction to CO and excess H２ In the reduction of the iron source by H ２ The heat absorbed by the reduction is compensated for by the heat generated by the CO reduction, so the total heat absorbed can be significantly reduced (see FIG. 9). ２ Since the heat absorbed by the reduction exceeds the heat absorbed by the reduction, the reduction temperature of FeO is maintained at a high temperature spontaneously (see FIG. 9). If the amount of iron source charged increases, the FeO reduction stage becomes even longer. Normally, it is extremely difficult to supply heat to a reduction furnace that needs to maintain a high temperature inside from sources other than the tuyere and the furnace top. Therefore, considering that this absorbed heat must be supplemented by the heat of combustion of the coke charged into the reduction furnace, the superiority of the example of the present invention is clear.

[0086] 10, it is possible to maximize the amount of heat generated in the FeO reduction region by increasing the amount of H ２ The amount of replenishment is determined by the CO ２ The molar amount of H in the reformer is expected to be about the same. ２ If the amount of H is reduced, the reduction rate will also decrease. ２ The amount of supply will be adjusted.

[0087] Example 2 As inventive examples 3 and 4, reduction of iron ore was carried out using an experimental circulating reduction system as follows.

[0088] (Invention Example 3) The configuration of an experimental circulating reduction system according to Invention 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 approximately 5 mm and 5.0 kg of lump ore crushed to approximately 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, on the raw material block A, a raw material block B was formed by alternately stacking a mixture of 1.1 kg of the coke and 2.8 kg of slowly cooled blast furnace slag crushed to about 5 mm and 5.0 kg of lump ore crushed to about 3 mm.

[0090] The exhaust gas discharged from the top of the furnace passed 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 was then connected via a selector valve 91 to an exhaust gas treatment device on one side and a nozzle 92 at the bottom of the reducing furnace on the other side. The two electric tubular furnaces 40 were ceramic electric tubular furnaces in which a quartz reaction tube holding 51 g of platinum catalyst was set in the center.

[0091] Sampling pipes 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 reducing 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 selector valve 93 via a selector 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 1,200°C by an MFC 97 was introduced into the reducing furnace 10 from a nozzle 96 of the reducing furnace 10 at a flow rate of 17 L / min. The internal temperature of each of the two electric tubular furnaces 40 was set to 800°C using thermocouples (TCs) provided around the catalyst.

[0095] The representative composition 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 was not replenished at the inlet side of the first electric tubular furnace 40) is shown in Table 1. After passing through the second electric tubular furnace 40, the excess H in the exhaust gas ２ The reverse water gas shift reaction caused an increase in CO by 2.7%, and CO ２ and H ２It can be seen that each of these has decreased 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 H in the mixed gas before entering the first electric tubular furnace 40 was removed. ２ The concentration of CO in the initial exhaust gas ２ The concentration of the coke in the raw material block A was adjusted to 22.8% (the same as the concentration) by the MFC 94. Then, the switching valve 91 was switched to the reducing furnace 10 side, and the reducing gas was introduced from the nozzle 92. It was determined from the change in weight of the reducing furnace 10 that the coke in the 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 being 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 with selector valve 93, selector valve 91 was switched to the exhaust gas treatment device side, and selector valve 98 was switched 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, and the condition inside the furnace was confirmed.

[0098] Of the 10 kg of lump ore, 3.3 kg of coke, and 2.8 kg of slowly cooled blast furnace slag in the raw material blocks A and B, almost none were found on the tungsten mesh. ３ The mixture was confirmed to consist of ferrite and cementite using X-ray diffraction. The carbon content of the mixture measured using a combustion-type carbon-sulfur analyzer was approximately 4.3 mass%, and when comparing the upper and lower parts of the mixture, the carbon content in the lower part tended to be approximately 0.3 mass% higher.

[0099] From the above experiments, it was confirmed that 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, the entire amount of lump ore charged as raw material can be reduced.

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

[0101] The typical 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. After passing through the electric tubular furnace 40, the excess H in the exhaust gas ２ The reverse water gas shift reaction caused an increase of 1.8% in CO, and CO ２ and H ２ It can be seen that each of these has decreased by 1.8%.

[0102] After the test, almost no lump ore, coke, or slowly cooled blast furnace slag was observed on the tungsten mesh, as in Example 3. The hearth bottom separated by the tungsten mesh contained ferrite (α-Fe) and cementite (Fe ３ The mixture was confirmed to consist of ferrite and cementite using X-ray diffraction. The carbon content of the mixture measured using a combustion-type carbon-sulfur analyzer was approximately 4.3 mass%, and when comparing the upper and lower parts of the mixture, the carbon content in the lower part tended to be approximately 0.3 mass% higher.

[0103] From the above experiments, it was confirmed that 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, the entire amount of lump ore charged as raw material can be reduced.

[0104]

[0105] 100 Circulation-type reduction system 200 Circulation-type reduction system 10 Reduction furnace 12 Furnace top 14 Tuyere 20 First dehumidifier 30 Hydrogen gas supply device 40 Catalytic device 42 Reaction chamber 44 Heating device 50 Second dehumidifier 60 Gas heating device 70 Third dehumidifier 81 First pipe 82 Second pipe 83 Third pipe 84 Fourth pipe 85 Fifth pipe 86 Sixth pipe 87 Seventh 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 as a reducing gas to an inside of the reduction furnace; 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.