Circulation-type reduction system, method for reducing iron ore, and method for operating furnace

Abstract

Provided is a cycle-type reduction system capable of efficiently recycling, as a reducing gas, a CO-rich gas obtained by reforming a CO2-containing exhaust gas generated from a reduction furnace. In this circulation-type reduction system (100), exhaust gas containing CO2 generated in a reduction furnace (10) is recovered via a first line (81), and hydrogen gas is added to the exhaust gas from a hydrogen gas supply device (30) to produce hydrogenated gas. In the catalyst device (40), CO2 in the hydrogenated gas is converted to CO by a reverse water-gas shift reaction, and a CO-rich gas having an increased CO concentration is obtained. The CO-rich gas is supplied to the inside of the reduction furnace (10) as a reducing gas via a second line (82). A separation device for separating, recovering, or removing a specific gas component other than water vapor from the gas passing through the inside is not disposed in the middle of the first conduit (81) and the second conduit (82).

Description

Technical Field

[0001] The present invention relates to a circulation type reduction system, an iron ore reduction method, and a smelting furnace operation method capable of radically reducing the emission of CO2 that contributes to global warming. Background Art

[0002] Amid calls for reducing CO2 emissions that contribute to global warming around the world, Japan's steel industry, which accounts for about 15% of CO2 emissions in Japan, has announced a government policy to achieve carbon neutrality by 2050. To achieve this, it is necessary to develop a reduction process and reduction furnace for iron ore that can produce crude steel at a cost close to current levels, but the current technical goals have hardly been established.

[0003] Here, the hydrogen reduction process, which uses hydrogen as a reducing agent for iron ore, has attracted worldwide attention as an ideal crude steel production technology that does not generate CO2. However, if this method is used to maintain the domestic annual molten iron production of about 75 million tons, about 75 billion Nm 3 In order to provide the above-mentioned approximately 75 billion Nm 3 Even if we completely ignore the electricity required for hydrogen transportation, liquefaction, and storage, it is estimated that 0.34 trillion kWh of electricity is required each year. Assuming that the problem of high electricity costs can be solved, it is extremely unrealistic to supply such a large amount of electricity to domestic blast furnace steelmakers in Japan, where annual electricity consumption is 1 trillion kWh.

[0004] On the other hand, various attempts are being made to supply large quantities of hydrogen produced using cheap renewable energy from overseas. However, even if the problem of high transportation costs can be solved, there is no technical goal of safely storing large quantities of hydrogen with a wide range of explosive concentrations around steel plants.

[0005] However, the domestic steel industry in Japan emits about 15% of Japan's domestic CO2 emissions because it mainly uses the blast furnace-converter method, which uses coke to reduce iron ore, to produce high-grade steel. The production methods of crude steel are mainly divided into the blast furnace-converter method and the electric furnace method. In the blast furnace-converter method, about 2 tons of CO2 are generated for every 1 ton of steel, and in the electric furnace method, about 0.5 tons of CO2 are generated for every 1 ton of steel. The electric furnace method is superior in terms of being able to suppress the amount of CO2 generated. However, high-grade steel used in automobiles, etc., cannot be mass-produced in the electric furnace method that uses scrap as raw materials because impurities such as copper easily have an adverse effect on quality. Therefore, about 75% of crude steel in Japan is produced by the blast furnace-converter method.

[0006] For blast furnaces that emit a particularly high amount of CO2, for example, in Patent Document 1, attempts were made 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 has the role of a heating material that heats the furnace through a reaction with oxygen blown in from a hot blast furnace and a role as a permeable material that ensures air permeability in the furnace. Therefore, it is extremely difficult to fundamentally suppress the amount of coke used until a new method (other than coke) is found for maintaining the temperature in the furnace without adversely affecting the quality of molten iron and ensuring air permeability.

[0007] In view of the above background, the current situation of Japanese steelmakers is that they can only cope with the current situation by reducing the number of blast furnaces in operation and increasing the ratio of electric furnaces. Therefore, the demand for scrap used in electric furnaces has become strong, and the fierce competition for its supply is expected to become more severe in the future.

[0008] Under such circumstances, the direct reduction process, which has less CO2 emissions than the blast furnace-converter process, has attracted worldwide attention. In the representative direct reduction process, the so-called Midrex process, iron ore is reduced in a solid phase by reforming natural gas to obtain direct reduced iron (DRI) (see cited document 2). Since only sponge-like DRI can be produced in the early Midrex process, it is considered difficult to handle and transport it from the perspective of oxidation and ignition. However, after the development and industrialization of hot briquette devices, these problems have been basically solved, and the trend of reducing the amount of waste input and improving the quality of steel by mixing DRI with waste and feeding it into electric furnaces has gradually expanded worldwide. Furthermore, attempts have been made to use methanation reaction (CO2+4H2→4H4+2H2O) to replace natural gas with methane synthesized from CO2 and hydrogen, or to replace natural gas with hydrogen itself.

[0009] On the other hand, in the direct reduction process as solid phase reduction, in order to maintain the grade of the produced DRI, high-grade iron ore, which is limited in cost and supply, has to be used as a raw material. This is a great disadvantage for the existing blast furnace method, which can make about 85% of the iron ore raw material into pellets and sintered ore made of low-grade fine ore or powder ore.

[0010] Furthermore, in the direct reduction process, since crude steel cannot be taken out in the form of molten iron, it is impossible to use the existing refining equipment of the steel integrated process such as the pretreatment furnace and the converter. This is also one of the reasons why Japanese blast furnace steelmakers are obsessed with the blast furnace process. In addition, it can be speculated that the direct reduction process remains at solid phase reduction because, as mentioned above, it cannot fundamentally solve the problems of air permeability and maintaining the furnace temperature for obtaining molten iron.

[0011] That is, in the blast furnace-converter method, the main obstacles are the reducing agent that can replace coke, the heating material, and the new method that does not adversely affect the quality of molten iron and ensures the permeability, and the goal of fundamentally reducing the use of coke has not yet been established. In addition, compared with the blast furnace-converter method, the direct reduction process with less CO2 emissions has the following disadvantages: it cannot use low-grade fine ore and powder ore that can be used in blast furnaces at low cost and easily supplied, and since crude steel cannot be taken out as molten iron, it is also impossible to use the existing refining equipment of the steel integrated process.

[0012] Based on this background, a technology for utilizing CO2 contained in exhaust gas from a blast furnace is proposed in Patent Document 3. That is, a scheme is proposed to separate CO2 from the exhaust gas of the blast furnace, reform the recovered CO2 into CO, and reuse the CO as a reducing agent for the blast furnace.

[0013] Prior art literature

[0014] Patent Literature

[0015] Patent document 1: International Publication No. 2021 / 220555;

[0016] Patent Document 2: Japanese Patent Application Publication No. 2017-88912;

[0017] Patent document 3: Japanese Patent Application Publication No. 2011-225968. Summary of the invention

[0018] Problem that the invention aims to solve

[0019] In the technology described in the above-mentioned patent document 3, CO2 separated and recovered from the waste gas generated in the blast furnace is reformed into CO and reused, and as a result, the amount of CO2 generated can be suppressed. However, in this technology, since CO2 is temporarily separated and recovered from the waste gas and then CO2 is reformed in multiple steps, it is inevitable to reduce the circulation efficiency of the reducing components in the waste gas and the burden of the cost required for the equipment, operation, and maintenance of each step. Therefore, it is expected to use a more efficient method to recycle the reducing components in the waste gas of a reduction furnace such as a blast furnace.

[0020] In view of the above problems, an object of the present invention is to provide a circulation type reduction system capable of efficiently recycling CO-rich gas obtained by reforming exhaust gas containing CO 2 generated from a reduction furnace as a reducing gas.

[0021] Another object of the present invention is to provide a method for reducing iron ore, which can efficiently circulate CO-rich gas obtained by reforming exhaust gas containing CO 2 generated from a reduction furnace as reducing gas to perform reduction treatment of iron ore.

[0022] Another object of the present invention is to provide a method for operating a smelting furnace, which can maintain the temperature in the furnace using the above-mentioned circulation type reduction system and ensure gas permeability by a method other than coke.

[0023] Solutions for solving problems

[0024] The inventors of the present invention have conducted in-depth research on methods for realizing an efficient reduction process capable of recycling exhaust gas from a reduction furnace by using the exhaust gas as a starting material of a reducing agent, and have found that by using the so-called reverse water-gas shift reaction, efficient recycling of the exhaust gas can be realized.

[0025] That is, the exhaust gas generated in the reduction process of iron ore generally contains, in addition to CO2 and nitrogen from the atmosphere, redundant reducing agents such as CO and H2. For example, the exhaust gas from a blast furnace contains about 23% by volume of CO2, the same proportion of CO, about 4% by volume of H2, and about 50% by volume of nitrogen from the air. The inventors of the present invention conceived that by adding hydrogen to such exhaust gas, the gas is brought into contact with a catalyst for the reverse water gas shift reaction (RWGS: Reverse Water Gas Shift reaction: CO2+H2→CO+H2O), thereby greatly converting the balance of CO2 and CO in the exhaust gas to CO-rich, and then recycling it as a reducing gas together with the H2 and nitrogen originally contained in the exhaust gas. It has been found that if this recycling becomes possible, the input amount of reducing agents such as those from fossil fuels such as coke that have been used in the past can be limited to a minimum.

[0026] Here, CO is recycled as the main reducing agent because the iron ore reduction reaction using H2 is an endothermic reaction, while the iron ore reduction reaction using CO is an exothermic reaction, so CO is the most efficient reducing agent that can maintain the high temperature in the reduction furnace. In addition, in the reduction using CO, the freezing point depression of iron caused by carbon, which is manifested when coke is used as a reducing agent, can be directly utilized. As a result, in the case of H2 reduction, the reduced iron that does not melt unless it is above 1500°C melts at around 1200°C in the reduction using CO. The existence of this temperature difference of about 300°C greatly reduces the heat load of the heating furnace for the reducing gas when the reduced iron is taken out as molten iron.

[0027] In addition, although the CO-rich reducing gas synthesized from the CO2-rich waste gas is mainly supplied to the reduction furnace, the excess can be discharged, recovered, and converted to various uses. In addition to being used as a reducing agent and fuel gas, CO is also an important Fischer-Tropsch reaction (nCO+(2n+1)H2→n n H 2n+2 + nH2O). Therefore, the CO-rich reducing gas synthesized from the CO2-rich waste gas is not limited to being used as a reducing agent, but is a synthetic gas that can be converted into a fuel gas or a raw material for various organic compounds without any residue. In particular, if the use of fossil fuels is greatly reduced in order to prevent global warming, the organic chemical industry that has always used these as raw materials must find new suppliers of raw materials. It is of great significance for these industries to become recipients of the above-mentioned synthetic gas.

[0028] As described above, the coke fed into a conventional blast furnace not only functions as a reducing agent, but also functions as a heating material and a breathable material. Therefore, when the reduced iron is taken out as molten iron, even if the temperature in the furnace can be maintained by the reduction heat of CO in the reducing gas, the breathability cannot be ensured (a stable reducing environment cannot be maintained) when the amount of coke fed is suppressed to the limit.

[0029] It has been newly discovered that this problem can be solved by slowly cooling and crushing part of the molten slag produced with the molten iron and discharged from the bottom of the furnace in a mold, mixing it with coke as a breathable material, and re-introducing it from the top of the furnace. That is, the melting point of blast furnace slag is about 1400°C, so even when the iron in the blast furnace begins to melt due to the carbon causing the freezing point to drop, the slag remains in a solid state and acts as a breathable material. In addition, since the slag is originally a substance generated in the smelting furnace, the material environment in the smelting furnace will not change even if it is recycled.

[0030] In addition, it is not easy to start the smelting furnace using only the slowly cooled and crushed slag as the permeable material and only the reducing gas as the reducing agent. Therefore, like a normal blast furnace, after alternately stacking coke and iron source, which are both the reducing agent and the permeable material, in the blast furnace, the smelting furnace is first started in the "blast furnace mode" in which high-temperature air heated in a hot blast furnace is blown in. On this basis, the slag is gradually mixed with the coke, and at the same time, it is switched to the "coke-free mode" in stages in which the reducing gas is gradually added to the air blown into the smelting furnace. In the case of stopping the smelting furnace, it becomes easy to restart it if the operation is ended in the blast furnace mode after the coke-free mode in the reverse procedure.

[0031] The present invention has been accomplished based on the above findings, and the gist of the present invention is as follows.

[0032] [1] A circulation type reduction system comprising:

[0033] a reduction furnace that reduces oxides contained therein;

[0034] A first pipeline, which recovers the exhaust gas containing CO2 generated in the reduction furnace from the reduction furnace and passes it;

[0035] A hydrogen supply device connected to the middle of the first pipeline to add hydrogen to the exhaust gas to produce hydrogenated gas;

[0036] a catalyst device having a reaction chamber connected to the end of the first pipeline and accommodating a catalyst for a reverse water-gas shift reaction, wherein the hydrogenated gas introduced into the reaction chamber from the first pipeline contacts the catalyst, and CO2 in the hydrogenated gas is converted into CO through a reverse water-gas shift reaction to produce a CO-rich gas having an increased CO concentration; and

[0037] a second pipeline extending from the catalyst device and connected to the reduction furnace, allowing the CO-rich gas to pass therethrough, and supplying the CO-rich gas as a reducing gas to the interior of the reduction furnace;

[0038] No separation device for separating, recovering or removing specific gas components other than water vapor from the gas passing through the first pipeline and the second pipeline is arranged in the middle of the first pipeline and the second pipeline.

[0039] [2] The circulation type reduction system according to [1] above, wherein:

[0040] The above-mentioned circulation type reduction system has:

[0041] The gas heating device is arranged in the middle of the second pipeline to heat the CO-rich gas.

[0042] [3] The circulation type reduction system according to [2] above, wherein:

[0043] The above-mentioned circulation type reduction system has:

[0044] A third pipeline is branched from a position upstream of the gas heating device in the middle of the second pipeline and connected to the gas heating device.

[0045] A part of the CO-rich gas is supplied as combustion gas to the gas heating device via the third pipe.

[0046] [4] The circulation type reduction system according to [2] or [3] above, wherein:

[0047] The above-mentioned circulation type reduction system has:

[0048] a fourth pipeline extending from the gas heating device and connected to the middle of the first pipeline,

[0049] The combustion exhaust gas generated from the gas heating device is merged with the exhaust gas in the first pipe via the fourth pipe.

[0050] [5] The circulation type reduction system according to any one of [1] to [4] above, wherein:

[0051] The catalyst device has a heating device for heating the reaction chamber.

[0052] The above-mentioned circulation type reduction system has:

[0053] a fifth pipeline, which branches off from the second pipeline and is connected to the heating device,

[0054] A part of the CO-rich gas is supplied to the heating device as combustion gas via the fifth pipe.

[0055] [6] The circulation type reduction system according to [5] above, wherein:

[0056] The above-mentioned circulation type reduction system has:

[0057] a sixth pipeline extending from the heating device and connected to the middle of the first pipeline,

[0058] The combustion exhaust gas generated from the heating device is merged with the exhaust gas in the first pipe through the sixth pipe.

[0059] [7] The circulation type reduction system according to any one of [1] to [6] above, wherein:

[0060] The above-mentioned circulation type reduction system has:

[0061] The first dehumidifier is disposed in the middle of the first pipeline and upstream of a portion connected to the hydrogen supply device, and removes water vapor from the exhaust gas.

[0062] [8] The circulation type reduction system according to any one of [1] to [7] above, wherein:

[0063] The above-mentioned circulation type reduction system has:

[0064] The second dehumidifier is arranged in the middle of the second pipeline and removes water vapor from the CO-rich gas.

[0065] [9] The circulation type reduction system according to any one of [1] to [8] above, wherein:

[0066] The above-mentioned circulation type reduction system has:

[0067] a switching valve disposed midway along the second pipeline; and

[0068] a seventh pipeline extending from the switching valve,

[0069] A portion of the CO-rich gas is recovered via the seventh pipeline.

[0070]

[10] The circulation type reduction system according to [9] above, wherein:

[0071] The above-mentioned circulation type reduction system has:

[0072] The third dehumidifier is arranged in the middle of the seventh pipeline and removes water vapor from the CO-rich gas passing through the seventh pipeline.

[0073]

[11] A circulating reduction system according to any one of [1] to

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

[0074]

[12] The circulation reduction system according to

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

[0075]

[13] A method for reducing iron ore, using the circulating reduction system described in any one of [1] to

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

[0076]

[14] A method for operating a smelting furnace, using the circulation type reduction system described in

[11] or

[12] above,

[0077] (I) at least one of sintered ore, lump ore, iron ore pellets and powder ore as the iron ore and (II) breathable material are alternately loaded in layers into the above-mentioned smelting furnace from the top of the above-mentioned smelting furnace to ensure the permeability of the above-mentioned reducing gas in the furnace. The above-mentioned breathable material is composed of crushed slag, or a mixture of the above-mentioned crushed slag and coke. The above-mentioned crushed slag is obtained by crushing the solidified slag obtained by slowly cooling the molten slag discharged from the bottom of the above-mentioned smelting furnace.

[0078]

[15] The method for operating a smelting furnace according to

[14] , wherein the reducing gas and the air are supplied as injection gases into the smelting furnace from a tuyere located at a lower portion of the smelting furnace,

[0079] The ratio of the crushed slag to the coke in the air-permeable material and the ratio of the reducing gas to the air in the blown gas are increased in stages, thereby suppressing the usage amount of the coke in stages.

[0080] Effects of the Invention

[0081] According to the circulation type reduction system of the present invention, it is possible to efficiently circulate and utilize the CO-rich gas obtained by reforming the exhaust gas containing CO 2 generated from the reduction furnace as the reducing gas.

[0082] According to the iron ore reduction method of the present invention, CO-rich gas obtained by reforming exhaust gas containing CO 2 generated from a reduction furnace can be efficiently circulated as a reducing gas to perform reduction treatment of iron ore.

[0083] According to the method for operating a smelting furnace of the present invention, the temperature in the furnace can be maintained using the above-mentioned circulation type reduction system, and the air permeability can be ensured by a method other than coke. BRIEF DESCRIPTION OF THE DRAWINGS

[0084] Figure 1 It is a schematic diagram showing the structure of a circulation type reduction system 100 according to one embodiment of the present invention.

[0085] Figure 2 It is a schematic diagram showing the structure of a circulation type reduction system 200 according to another embodiment of the present invention.

[0086] Figure 3 Schematic diagram showing the equilibrium calculation model of the circulation type reduction system of Inventive Example 1.

[0087] Figure 4 To express Figure 3 A diagram of the reduction condition in the model (Invention Example 1).

[0088] Figure 5Schematic diagram showing the equilibrium calculation model of the circulation type reduction system of Inventive Example 2.

[0089] Figure 6 To express Figure 5 A diagram of the reduction condition in the model (Invention Example 2).

[0090] Figure 7 Schematic diagram showing an equilibrium calculation model of a circulation type reduction system of a comparative example.

[0091] Figure 8 To express Figure 7 A graph showing the reduction condition in the model (comparative example).

[0092] Fig. 9 This is a graph showing the change in the amount of heat absorbed in the reduction furnace relative to the number of cycles in Inventive Examples 1 and 2 and the Comparative Example.

[0093] Fig.10 This is a graph showing changes in the amount of heat absorbed in the reduction furnace in the FeO reduction zone relative to the amount of hydrogen in the hydrogenation gas in Inventive Examples 1 and 2 and the Comparative Example.

[0094] Fig.11 Schematic diagram showing the structure of the experimental circulation type reduction system of Inventive Example 3.

[0095] Fig.12 Schematic diagram showing the structure of the experimental circulation type reduction system of Inventive Example 4. DETAILED DESCRIPTION

[0096] [Circulation type reduction system]

[0097] Reference Figure 1 , a circulation type reduction system 100 according to an embodiment of the present invention is described. The circulation type reduction system 100 includes a reduction furnace 10, a first dehumidifier 20, a hydrogen supply device 30, a catalyst device 40, a second dehumidifier 50, and a gas heating device 60, and as pipeline equipment, includes a first pipeline 81, a second pipeline 82, a third pipeline 83, a fourth pipeline 84, a fifth pipeline 85, a sixth pipeline 86, a seventh pipeline 87, and a switching valve 90.

[0098] The reduction furnace 10 may be a smelting furnace such as a blast furnace. When the reduction furnace 10 is a smelting furnace, iron ore and coke are loaded into the reduction furnace 10 from the furnace top 12, and high-temperature reducing gas is blown into the reduction furnace 10 from a tuyere 14 located at the bottom of the reduction furnace 10, so that the iron ore is reduced in the reduction furnace 10.

[0099] The first pipeline 81 is a pipeline device that recovers the exhaust gas containing CO2 generated in the reduction furnace 10 from the reduction furnace 10 and passes it. The starting end of the first pipeline 81 is connected to the reduction furnace 10 (in one example, the furnace top 12), and the end is connected to the catalyst device 40. A hydrogen supply device 30 is connected in the middle of the first pipeline 81. In addition, in the middle of the first pipeline 81, a first dehumidifier 20 is arranged upstream of the part connected to the hydrogen supply device 30. The first pipeline 81 has a pipeline 81A extending from the reduction furnace 10 and connected to the first dehumidifier 20, and a pipeline 81B extending from the first dehumidifier 20 and connected to the catalyst device 40. In addition, in this specification, "upstream" or "downstream" with respect to the pipeline refers to the gas flow direction in the pipeline.

[0100] 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 pipeline 81, and then hydrogen (H2) gas is supplied from the hydrogen supply device 30 to become hydrogenated gas. The dehumidification treatment is preferably performed 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, and typically has the following composition: in addition to water vapor, it also contains CO2: 13 to 24 volume%, CO: 21 to 31 volume%, and H2: 3 to 15 volume%, and the remainder is composed of N2 from the air. The composition of the hydrogenated gas is not particularly limited, and typically has the following composition: in addition to water vapor, it also contains CO2: 13 to 24 volume%, CO: 21 to 31 volume%, and H2: 10 to 30 volume%, and the remainder is composed of N2 from the air. The hydrogen supplied from the hydrogen supply device 30 is preferably green hydrogen obtained by water electrolysis using renewable energy, but by applying the circulation type reduction system of the present invention to blast furnace operation, it can be replaced with hydrogen purified from coke oven gas before the amount of coke used becomes zero.

[0101] In addition, it is preferred to install a dust removal device (not shown) in the middle of the first pipeline 81, upstream of the first dehumidifier 20, or downstream of the first dehumidifier 20 and upstream of the part connected to the hydrogen supply device 30, to perform dust removal treatment on the exhaust gas to remove dust from the raw materials from the exhaust gas.

[0102] The catalyst device (reverse shift reformer) 40 has a reaction chamber 42 connected to the end of the first pipeline 81 and accommodating a catalyst for a 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 into the reaction chamber 42 from the first pipeline 81 contacts the catalyst, and the CO2 in the hydrogenated gas is converted into CO through the reverse water gas shift reaction to become 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, and typically has the following composition: in addition to water vapor, it also contains CO2: 6 to 20 volume%, CO: 24 to 40 volume%, and H2: 5 to 24 volume%, and the remainder is composed of N2 from air. Catalysts that can be used for the reverse water gas shift reaction are known to include a variety of catalysts such as nickel-based catalysts and precious metal-based catalysts, but the catalyst used in the present invention may be any of them.

[0103] When the hydrogenated gas is brought into contact with the catalyst in the catalyst device 40, from the viewpoint of the conversion efficiency of the reverse water-gas shift reaction, which is an endothermic reaction, the temperature of the introduced hydrogenated gas is preferably set as high as possible within a temperature range in which the catalyst is not easily degraded. Specifically, the reaction chamber 42 is preferably heated in advance 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.

[0104] The second pipeline 82 is a pipeline device that extends from the catalyst device 40 and is connected to the reduction furnace 10 (in one example, the tuyere 14), passes the CO-rich gas, and supplies the CO-rich gas as the reducing gas (in one example, via the tuyere 14) to the inside of the reduction furnace 10. Preferably, a second dehumidifier 50 for removing water vapor from the CO-rich gas and a gas heating device 60 for heating the CO-rich gas are arranged in the middle of the second pipeline 82. In this case, the gas heating device 60 is preferably arranged downstream of the second dehumidifier 50. In this case, the second pipeline 82 has a pipeline 82A extending from the catalyst device 40 and connected to the second dehumidifier 50, a pipeline 82B extending from the second dehumidifier 50 and connected to the gas heating device 60, and a pipeline 82C extending from the gas heating device 60 and connected to the reduction furnace 10 (in one example, the tuyere 14).

[0105] The CO-rich gas that has passed through the catalyst device 40 is dehumidified by the second dehumidifier 50 while flowing through the second pipeline 82 , and then heated by the gas heating device 60 , and then blown into the reduction furnace 10 as a reducing gas.

[0106] That is, it is preferred that the temperature of the CO-rich gas (reducing gas) blown into the reduction furnace 10 is adjusted by the gas heating device 60 after the above-mentioned reaction using the catalyst. The higher the temperature of the reducing gas, the more advantageous the reduction efficiency of the iron ore in the reduction furnace 10 is, but in the case of solid phase reduction of the iron ore, the temperature of the reducing gas blown into the reduction furnace 10 is preferably 900°C or higher. In addition, when the reduced iron is taken out as molten iron at 1500°C, it is necessary to maintain the temperature of the molten area of ​​the iron source and slag formed in the lower area of ​​the reduction furnace 10 at 1650°C or higher. Therefore, it is preferred that the reducing gas is blown after heating the reducing gas, and the temperature of the reducing gas is made to be 1200°C or higher if the input amount of coke reaches about 50% of that of the existing blast furnace, and the temperature of the reducing gas is made to be 1500°C or higher if the input amount of coke is less than 20% of that of the existing blast furnace.

[0107] The preferred operation of the gas heating device 60 is as follows. The circulation type reduction system 100 of the present embodiment preferably has a third pipeline 83, and the third pipeline 83 is connected to the gas heating device 60 by branching from a position upstream of the gas heating device 60 and downstream of the second dehumidifier 50 in the middle of the second pipeline 82. Moreover, it is preferred that a part of the CO-rich gas flowing through the second pipeline 82 is supplied to the gas heating device 60 as a combustion gas via the third pipeline 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 reduction gas can be increased to the above-mentioned desired temperature. Although in Figure 1 Although omitted, the oxygen-containing gas supplied to the gas heating device 60 in order to burn the combustion gas is preferably oxygen (not containing non-consumable nitrogen).

[0108] The circulation type reduction system 100 preferably has a fourth pipeline 84 extending from the gas heating device 60 and connected to the middle of the first pipeline 81. Furthermore, it is preferred that the combustion exhaust gas generated from the gas heating device 60 is merged with the exhaust gas in the first pipeline 81 via the fourth pipeline 84 and reused. The fourth pipeline 84 is preferably connected to a position upstream of the first dehumidifier 20 in the middle of the first pipeline 81. When the combustion exhaust gas generated from the gas heating device 60 is heat-exchanged with (1) the reduction gas pipeline between the catalyst device 40 and the gas heating device 60 and (2) the hydrogenation gas pipeline between the hydrogen supply device 30 and the catalyst device 40 and then merged with the exhaust gas in the first pipeline 81 upstream of the first dehumidifier 20, the reduction gas and the hydrogenation gas can also be preheated.

[0109] In addition, if Figure 1As shown, when the reducing gas cannot be completely raised to the desired temperature by the indirect heating type gas heating device 60, oxygen or the like may be added near the front end of the gas heating device 60 to directly burn a part of CO and H2 contained in the reducing gas. In addition, when starting in the blast furnace mode, if air enriched with oxygen by a cryogenic separation method or the like is used as hot air blown into the reducing furnace 10, the heat load of the gas heating device 60 taken away by the heating of nitrogen will decrease, so it is easy to raise the temperature of the reducing gas.

[0110] Next, for the preferred operation of the catalyst device 40, it is also preferred 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 pipeline 85, which branches from the second pipeline 82 and is connected to the heating device 44 of the catalyst device 40. The fifth pipeline 85 preferably branches from the second pipeline 82 at a position upstream of the gas heating device 60 and downstream of the second dehumidifier 50. Moreover, it is preferred to supply a part of the CO-rich gas as the combustion gas to the heating device 44 via the fifth pipeline 85. Although Figure 1 Although omitted, the oxygen-containing gas supplied to the heating device 44 in order to burn the combustion gas is preferably oxygen (not containing nitrogen that cannot be consumed).

[0111] 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. Moreover, it is preferable to merge the combustion exhaust gas generated from the heating device 44 with the exhaust gas in the first pipe 81 through the sixth pipe 86 and reuse it. In addition, in the present embodiment, since the upstream portion 86A of the sixth pipe 86 is connected to the middle of the fourth pipe 84 as the fuel exhaust gas flow path from the gas heating device 60, the downstream portion 86B of the sixth pipe 86 also serves as the downstream portion 84B of the fourth pipe 84. However, the present invention is not limited to this, and of course the sixth pipe 86 may be directly connected to the first pipe 81 independently of the fourth pipe 84. When the combustion exhaust gas generated from the heating device 44 is heat-exchanged with the hydrogenation gas pipe between the hydrogen supply device 30 and the catalyst device 40 and then merged with the exhaust gas in the first pipe 81 upstream of the first dehumidifier 20, the hydrogenation gas can also be preheated.

[0112] In the present embodiment described above, by repeatedly performing a reduction process of iron ore using the blowing of reducing gas, a recovery process of exhaust gas from the reduction furnace, a dust removal and dehumidification process of the exhaust gas (an arbitrary process), a hydrogen addition process to the exhaust gas, a process of generating a CO-rich gas from the hydrogenated gas through a reverse water-gas shift reaction, a dehumidification process of the CO-rich gas (an arbitrary process), a heating process of the CO-rich gas (an arbitrary process), and a blowing process of the CO-rich gas as a reducing gas, a circulation process for reusing the exhaust gas from the reduction furnace 10 in a closed circulation system is realized.

[0113] The unconverted CO2 remaining in the CO-rich gas as the reducing gas will sooner or later become a CO source during the circulation process, so it does not need to be separated from the reducing gas. That is, in this embodiment, it is important that a separation device for separating, recovering or removing specific gas components other than water vapor from the gas passing through the first pipeline 81 and the second pipeline 82 is not configured. In this embodiment, in addition to the dust removal and dehumidification that can be applied to the existing technology, no new separation and concentration process is required, so the circulation efficiency of the reducing gas is high.

[0114] In this embodiment, since the reverse water gas shift reaction is utilized to convert CO2 into CO using an equal mole of hydrogen, the supply amount of hydrogen per CO2 can be suppressed to about 1 / 4 compared to the above-mentioned conventional reduction method in which methane produced by a methanation reaction requiring 4 times the moles of hydrogen as CO2 is used as a reducing agent.

[0115] In the present embodiment, since the reducing gas mainly composed of CO after the exhaust gas is modified can be supplied to the reduction furnace 10 at a high temperature, the impurities in the iron ore can be separated from the molten iron as molten slag. Therefore, the low-grade fine powder ore and powder ore which are cost-effective and easy to supply can be made into pellets and sintered ore for use in the same way as a conventional blast furnace.

[0116] In addition, the excess portion of the 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 arranged in the middle of the second pipeline 82 and a seventh pipeline 87 extending from the switching valve 90, and a part of the CO-rich gas can be recovered through the seventh pipeline 87. The recovered CO-rich gas can be used as a synthesis gas as a raw material of an organic compound, for example. In this embodiment, since a system is implemented that converts the CO2-rich exhaust gas discharged from the reduction furnace 10 into a CO-rich reducing gas and recycles it, the CO2 emission to the atmosphere can be suppressed to zero level by effectively using the excess portion of the CO-rich gas as a synthesis gas in the organic chemical industry, etc.

[0117] In addition, the molten slag separated from the molten iron is slowly cooled in a mold to form solidified slag, and the solidified slag is crushed to form crushed slag, which can be reused as a permeable material. When part of the pig iron discharged from the reduction furnace (smelting furnace) adheres to the permeable material from the slag, the pig iron can be returned to the reduction furnace as an iron source via the permeable material.

[0118] In addition, since the molten slag is automatically discharged to the surface of the molten iron due to the difference in specific gravity, even if it is recycled, it has almost no adverse effect on the quality of the molten iron. In addition, the recycled molten slag has the same quality as ordinary blast furnace slag, so it can be used industrially as a raw material for blast furnace cement, etc.

[0119] Reference Figure 2 , describing a circulation type reduction system 200 of another embodiment of the present invention. The circulation type reduction system 200 does not have the second dehumidifier 50, but has the same structure as the circulation type reduction system 100 except that the third dehumidifier 70 is arranged in the middle of the seventh pipeline 87. That is, in the present invention, the second dehumidifier 50 is not a necessary structure. In the case where the second dehumidifier 50 is not arranged, it is preferred to remove water vapor from the CO-rich gas passing through the seventh pipeline 87 by the third dehumidifier 70.

[0120] The above mainly describes the case where the reduction furnace 10 is a molten ore furnace such as a blast furnace and the reduction object is iron ore, but the present invention is not limited thereto. The reduction furnace 10 may also be a solid reduction furnace. In addition, the reduction object 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.

[0121] [Iron ore reduction method]

[0122] The iron ore reduction method according to one embodiment of the present invention uses the above-mentioned circulation type reduction system 100, 200 to circulate the CO-rich gas obtained by reforming the exhaust gas as the reducing gas to perform the reduction treatment of the iron ore as an oxide. Thus, the CO-rich gas obtained by reforming the exhaust gas containing CO2 generated from the reduction furnace 10 can be efficiently circulated as the reducing gas to perform the reduction treatment of the iron ore.

[0123] In addition, according to the reduction method of this embodiment, since an efficient reduction process is realized in which the exhaust gas from the reduction furnace 10 can be recycled as a starting material of the reducing agent, the amount of CO2 generated can be significantly reduced. Furthermore, the input amount of the reducing agent from fossil fuels such as coke, which is conventionally used in the reduction process of iron ore, can be fundamentally suppressed.

[0124] [Operation method of melting furnace]

[0125] The method for operating a smelting furnace according to one embodiment of the present invention is performed using the above-mentioned circulation type reduction system 100, 200. Furthermore, it is important to alternately load (I) at least one (iron source) selected from sintered ore, lump ore, iron ore pellets and powder ore as iron ore and (II) a permeable material in layers from the top of the reduction furnace (smelting furnace) 10 into the smelting furnace to ensure the permeability of the reducing gas in the furnace, wherein the permeable material is composed of crushed slag or a mixture of the crushed slag and coke, wherein the crushed slag is obtained by crushing the solidified slag obtained by slowly cooling the molten slag discharged from the bottom of the smelting furnace. Thus, the above-mentioned circulation type reduction system 100, 200 can be used to maintain the furnace temperature and ensure the permeability by a method other than coke.

[0126] In the operation of this embodiment, reducing gas and air are supplied as injection gas into the interior of the molten metal furnace from the tuyere 14. At this time, it is preferable to increase the ratio of crushed slag to coke in the permeable material and the ratio of reducing gas to air in the injection gas in stages, and to suppress the amount of coke used in stages.

[0127] According to the method for operating the smelting furnace of this embodiment, since reduced iron can be obtained in the form of molten iron using low-grade fine ore and powder ore that are low-cost and easily available, the existing steel integration process can be directly used after the next step.

[0128] The permeability of the smelting furnace can be adjusted by crushing the particle size of the slag. For example, if the slowly cooled slag is cast in a form with permeable holes, it becomes easier to ensure permeability. In addition, there is no particular problem in using ordinary blast furnace slag as the permeable material.

[0129] In the method for operating the smelting furnace of the present embodiment, the amount of molten slag generated in the circulation type reduction system 100, 200 is greater than that of a normal blast furnace by the amount of slag re-injected from the furnace top 12 and then melted in the soft melting zone. In addition, as the amount of slag injected increases, the amount of heat taken away as the melting heat of the slag also increases. Therefore, when starting the operation in the blast furnace mode, it is preferable to adjust the layer thickness ratio of the iron source layer and the gas permeable layer in advance so that the iron source layer is richer than that of a normal blast furnace.

[0130] Example

[0131] [Example 1]

[0132] As described below, as Inventive Examples 1 and 2 and Comparative Examples, equilibrium calculations were performed to confirm the effects of the reduction method of the present invention.

[0133] (Invention Example 1)

[0134] The equilibrium calculation model of the circulation type reduction system of Invention Example 1 is shown in Figure 3 As an initial state, the following state is assumed: a reduction furnace 10 filled with 25 moles of iron (III) oxide (Fe2O3) is connected to a reverse conversion type reformer (hereinafter referred to as "reformer 40") as a catalyst device 40 filled with a total of 100 moles of mixed gas, and the mixed gas is composed of CO: 22 moles, CO2: 22.8 moles, H2: 4.2 moles, and N2: 51 moles, which is equivalent to blast furnace exhaust gas. The first dehumidifier 20 is placed on the inlet side of the reformer, the second dehumidifier 50 is placed on the outlet side of the reformer, and a hydrogen 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 (equivalent to the CO2 concentration in the blast furnace exhaust gas). When there is no entry or exit of gas in the reduction furnace and the reformer except H2 supplied from the hydrogen supply device and H2O removed by the first dehumidifier and the second dehumidifier, since all H2O is generated from the consumed H2, it can be considered that the total number of moles of the mixed gas circulating in the reformer and the reduction furnace will not change.

[0135] In Example 1 of the present invention, the temperature in the reduction furnace and the reformer is maintained at 900°C by heat supplied from the outside. In fact, a gas delivery system is required to circulate gas between the reduction furnace and the reformer, but the energy consumed in this process is ignored in order to confirm the principle. Similarly, the energy consumed by driving the first dehumidifier, the second dehumidifier, and the hydrogen supply device is also ignored. Since the reverse water-gas shift reaction in the reformer sometimes cannot reach an equilibrium state, it is assumed that an equilibrium reaction is reached, although it is affected by the performance of the catalyst used.

[0136] Here, a circulation process is considered in which the following operation is regarded as a cycle and the cycle is repeated: all the reducing gas generated when the hydrogenated gas becomes stable in the reformer is sent to the reduction furnace, the gas in the reduction furnace when the reduction reaction becomes stable is taken out as exhaust gas, and a certain level of hydrogen is added to it until it becomes hydrogenated gas again. The equilibrium state of the gas components and the iron source in the reformer and the reduction furnace in each cycle of sending the reducing gas from the reformer to the reduction furnace is calculated using the thermodynamic equilibrium calculation software & thermodynamic database FactSage8.1 produced by the Computational Dynamics Research Center Co., Ltd. The results are shown in Figure 4 In addition, methane and the like are also included in the compounds generated in the reformer and the reduction furnace, but trace components of less than 0.005 mol are ignored.

[0137] In the reduction furnace, the iron source is reduced by CO supplied from the reformer and the excess H2 not consumed in the reverse water-gas shift reaction. The solid Fe2O3 introduced as the iron source changes to 2 times the mole of FeO (solid phase) in the first cycle. After the second cycle, FeO is gradually reduced and changes to α-Fe (solid phase), and the reduction is completed in the seventh cycle. The main reduction reaction is the reaction from FeO to α-Fe, which is consistent with the known view in the blast furnace. The amount of H2 consumed in the reduction of the iron source is 89 moles.

[0138] (Invention Example 2)

[0139] The equilibrium calculation model of the circulation type reduction system of Invention Example 2 is shown in Figure 5 . It is similar to the reformer except that no second dehumidifier is provided at the outlet side of the reformer. Figure 3 The calculation conditions are the same as those of Invention Example 1, and the equilibrium state of the gas components and the iron source in the reformer and the reduction furnace is calculated. The results are shown in Figure 6 .

[0140] The solid phase Fe2O3 introduced as the iron source changes to 2 times the mole of FeO (solid phase) in the first cycle. After the third cycle, FeO is gradually reduced and changes to α-Fe (solid phase), and the reduction is completed in the ninth cycle. The main reduction reaction is the reaction from FeO to α-Fe, which is consistent with the known view in blast furnaces. The amount of H2 consumed for the reduction of this iron source is 85 moles.

[0141] (Comparative Example)

[0142] The equilibrium calculation model of the circulation type reduction system of the comparative example is shown in Figure 7 . Except that the reformer and the second dehumidifier are not provided, Figure 3 The calculation conditions are the same as those of Invention Example 1, and the equilibrium state of the gas components and the iron source in the reformer and the reduction furnace is calculated. The results are shown in Figure 8 .

[0143] In the reduction furnace of the comparative example, the iron source is reduced only by H2 directly fed into the reduction furnace from the hydrogen 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. After the second cycle, FeO is gradually reduced and changes to α-Fe (solid phase), and the reduction is completed in the ninth cycle as in Example 2 of the invention. The main reduction reaction is the reaction from FeO to α-Fe, which is the same as in Examples 1 and 2 of the invention. The amount of H2 consumed in the reduction of the iron source is 75 moles, which is 10 moles less than that in Example 2 of the invention.

[0144] (Heat absorption in the reduction furnace)

[0145] The major difference between Inventive Examples 1 and 2 and Comparative Example is the amount of heat absorbed in the reduction furnace. The heat of reaction (heat absorbed) in the reduction furnace calculated from the heat of reaction of each reaction calculated by Fact Sage 8.1 is shown in FIG. Fig. 9 and Fig.10 .

[0146] Except for the reaction from Fe2O3 to Fe3O4 that is completed in the early stage, the direct reduction of the iron source using H2 is an endothermic reaction. In contrast, in the reduction of the iron source using CO and excess H2 in Example 1, the exothermic heat generated by the CO reduction compensates for the endothermic heat generated by the H2 reduction, so the total endothermic heat can be greatly suppressed (see Fig. 9 ). In addition, in the reduction region of FeO in Invention Example 2, the exothermic amount generated by CO reduction exceeds the endothermic amount generated by H2 reduction, so the reduction temperature of FeO is spontaneously maintained at a high temperature (refer to Fig. 9 ). If the amount of iron source input increases, the reduction stage of FeO will be further prolonged. Generally, it is extremely difficult to supply heat from outside the tuyere and the furnace top for a reduction furnace that needs to maintain a high temperature inside. Therefore, when considering that the absorption heat needs to be compensated by the combustion heat of the coke input into the reduction furnace, the superiority of the present invention example is obvious.

[0147] In addition, from Fig.10 It is estimated that the amount of H2 supplied to the reformer to maximize the heat release in the FeO reduction zone is about the same as the molar amount of CO2 in the exhaust gas. Since it is believed that if the amount of H2 supplied to the reformer is suppressed, the reduction rate will also decrease, the amount of H2 supplied is actually adjusted based on the balance between the temperature in the reduction furnace and the reduction rate.

[0148] [Example 2]

[0149] As described below, as Invention Examples 3 and 4, reduction of iron ore was performed using an experimental circulation type reduction system.

[0150] (Invention Example 3)

[0151] The structure of the experimental circulation type reduction system of Inventive Example 3 is shown in FIG. Fig.11 .exist Fig.11 In the process, a raw material block A is formed on a tungsten mesh separating the bottom of an experimental reduction furnace, i.e., a BF simulator (hereinafter referred to as "reduction furnace 10"), which is set on a weight scale. The raw material block A is 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.

[0152] Furthermore, a raw material block B is formed on the raw material block A. The raw material block B is formed by alternately stacking 1.1 kg of the above-mentioned coke with 2.8 kg of a material obtained by crushing blast furnace slow cooling slag into about 5 mm and 5.0 kg of lump ore crushed into about 3 mm.

[0153] The exhaust gas discharged from the top of the furnace passes through the dust removal device, the dehumidifier 20, the first electric tube furnace 40, the dehumidifier, the second electric tube furnace 40, the dehumidifier 50 and the heat storage type gas heating furnace 60, and is connected to the exhaust gas treatment device on one side and to the nozzle 92 at the bottom of the reduction furnace on the other side through the switching valve 91. The second electric tube furnace 40 is a ceramic electric tube furnace with a quartz reaction tube containing 51g of platinum catalyst set in the center.

[0154] Sampling tubes for gas composition analysis are provided at two locations, one in front of the first electric tube furnace 40 and one between the second electric tube furnace 40 and the dehumidifier 50, and are connected to a micro gas chromatograph (micro GC). In addition, a hydrogen line 30 is connected between the dehumidifier 20 and the first electric tube furnace 40 via a switching valve 93 and a mass flow controller (MFC) 94.

[0155] A nozzle 96 is provided at the lower part of the reduction furnace 10 on the side opposite to the nozzle 92, which feeds 2.3% oxygen-enriched air via a regenerative gas heating furnace 95. The flow rate of the air introduced from the nozzle 96 is controlled by a mass flow controller (MFC) 97.

[0156] In order to completely exhaust the exhaust gas remaining in the reduction furnace 10 after the reduction experiment, a nitrogen purge line is connected between the dehumidifier 20 and the switching valve 93 via a switching valve 98 .

[0157] First, the switching valve 91 is set to the exhaust gas treatment device side to separate the exhaust gas from the reduction furnace 10. On this basis, air heated to 1200°C by MFC97 is introduced into the reduction furnace 10 at a flow rate of 17L / min from the nozzle 96 of the reduction furnace 10. The internal temperature of both electric tube furnaces 40 is set to 800°C using thermocouples (TC) provided around the catalyst.

[0158] The representative composition of the exhaust gas generated by the reduction of the lump ore in the raw material block A and the mixed gas after passing through the second electric tube furnace 40 (when hydrogen is not supplemented at the inlet side of the first electric tube furnace 40) is shown in Table 1. It can be seen that after passing through the second electric tube furnace 40, CO increases by 2.7% and CO2 and H2 decrease by 2.7% respectively by using the reverse water gas shift reaction of the excess H2 in the exhaust gas.

[0159] When the 2.2 kg of coke in the raw material block A is completely consumed as exhaust gas, the flow rate of air introduced from the nozzle 96 is changed to 8.5 L / min by MFC97. At the same time, the switching valve 93 is switched to the hydrogen pipeline 30 side, hydrogen is introduced, and the MFC94 is adjusted so that the H2 concentration (the same as the CO2 concentration in the initial exhaust gas) in the mixed gas before entering the first electric tube furnace 40 is 22.8%. On this basis, the switching valve 91 is switched to the reduction furnace 10 side, and the reduction gas is introduced from the nozzle 92. In addition, it is judged that the coke in the raw material block A is completely consumed based on the weight change of the reduction furnace 10.

[0160] In this state, wait for all the 1.1 kg of coke in the raw material block B to be consumed, stop the air introduced from the nozzle 96, stop the two electric tube furnaces and the two gas heating furnaces. On this basis, wait for the water temperature in the water cooling jacket to reach 30°C, cut off the hydrogen with the switching valve 93, switch the switching valve 91 to the exhaust gas treatment device side, switch the switching valve 98 to the nitrogen introduction side, and discharge all the exhaust gas remaining in the reduction furnace 10 to the exhaust gas treatment device. Then, disassemble the reduction furnace 10 to confirm the situation inside the furnace.

[0161] The total of 10 kg of lump ore, 3.3 kg of coke, and 2.8 kg of blast furnace slow cooling slag in raw material blocks A and B were almost not found on the tungsten mesh. A mixture of ferrite (α-Fe) and cementite (Fe3C) and slag deposited thereon were confirmed at the bottom of the furnace separated by the tungsten mesh. X-ray diffraction confirmed that the mixture was composed of ferrite and cementite. In addition, the carbon in the same mixture measured by a combustion-type carbon-sulfur analysis device was approximately 4.3% by mass. When the upper and lower parts of the mixture were compared, a tendency of carbon increasing by about 0.3% by mass was shown in the lower part.

[0162] The above experiments confirmed that after the total amount of raw material block A equivalent to the blast furnace mode was reduced, in the reduction step of raw material block B equivalent to a 50% carbon reduction operation using slag as the air permeable material, the lump ore input as the raw material can also be completely reduced.

[0163] (Invention Example 4)

[0164] The structure of the experimental circulation type reduction system of Inventive Example 4 is shown in FIG. Fig.12Except that the electric tube furnace 40 is set as one and no dehumidifier is arranged downstream of the electric tube furnace 40, Fig.11 The circulation type reduction system of the inventive example 3 shown is the same. The internal temperature of the electric tube furnace 40 is set to 900° C. by using a thermocouple (TC) provided around the catalyst. The test is performed in the same manner as in the inventive example 3 under other conditions.

[0165] The representative composition of the exhaust gas generated by the reduction of the lump ore in the raw material block A and the mixed gas after passing through the electric tube furnace 40 (when hydrogen is not supplemented at the inlet side of the electric tube furnace 40) is shown in Table 1. It can be seen that after passing through the electric tube furnace 40, due to the reverse water gas shift reaction of the excess H2 in the exhaust gas, CO increases by 1.8%, and CO2 and H2 decrease by 1.8%, respectively.

[0166] After the test, similar to Invention Example 3, lump ore, coke and blast furnace slow cooling slag were hardly found on the tungsten mesh. A mixture of ferrite (α-Fe) and cementite (Fe3C) and slag deposited thereon were confirmed at the furnace bottom separated by the tungsten mesh. X-ray diffraction confirmed that the mixture was composed of ferrite and cementite. In addition, the carbon in the same mixture measured by a combustion-type carbon-sulfur analysis device was approximately 4.3% by mass. When the upper and lower parts of the mixture were compared, a tendency of carbon increasing by about 0.3% by mass was shown in the lower part.

[0167] The above experiments confirmed that after the total amount of raw material block A equivalent to the blast furnace mode was reduced, in the reduction step of raw material block B equivalent to a 50% carbon reduction operation using slag as the air permeable material, the lump ore input as the raw material can also be completely reduced.

[0168] [Table 1]

[0169]

[0170] Description of Reference Numerals

[0171] 100: Circulation reduction system;

[0172] 200: Circulation reduction system;

[0173] 10: Reduction furnace;

[0174] 12: furnace top;

[0175] 14: vent;

[0176] 20: First dehumidifier;

[0177] 30: Hydrogen supply device;

[0178] 40: Catalyst device;

[0179] 42: reaction chamber;

[0180] 44: Heating device;

[0181] 50: Second dehumidifier;

[0182] 60: Gas heating device;

[0183] 70: The third dehumidifier;

[0184] 81: first pipeline;

[0185] 82: Second pipeline;

[0186] 83: the third pipeline;

[0187] 84: the fourth pipeline;

[0188] 85: Fifth pipeline;

[0189] 86: sixth pipeline;

[0190] 87: seventh pipeline;

[0191] 90: Switching valve.

Claims

1. A circulation type reduction system, comprising: a reduction furnace that reduces oxides contained therein; a first pipeline which recovers from the reduction furnace the exhaust gas containing CO2 generated in the reduction furnace and passes the exhaust gas through; A hydrogen supply device connected to the middle of the first pipeline to add hydrogen to the exhaust gas to produce hydrogenated gas; a catalyst device having a reaction chamber connected to the end of the first pipeline and accommodating a catalyst for a reverse water-gas shift reaction, wherein the hydrogenated gas introduced into the reaction chamber from the first pipeline contacts the catalyst, and CO2 in the hydrogenated gas is converted into CO through a reverse water-gas shift reaction to produce a CO-rich gas with an increased CO concentration; as well as a second pipeline extending from the catalyst device and connected to the reduction furnace, allowing the CO-rich gas to pass therethrough, and supplying the CO-rich gas as a reducing gas to the interior of the reduction furnace, No separation device for separating, recovering or removing specific gas components other than water vapor from the gas passing through the first pipeline and the second pipeline is arranged in the middle of the first pipeline and the second pipeline.

2. The circulation type reduction system according to claim 1, wherein: The circulation type reduction system has: A gas heating device is arranged in the middle of the second pipeline to heat the CO-rich gas.

3. The circulation type reduction system according to claim 2, wherein: The circulation type reduction system has: a third pipeline which branches off from a position upstream of the gas heating device midway through the second pipeline and is connected to the gas heating device, A portion of the CO-rich gas is supplied as combustion gas to the gas heating device via the third pipeline.

4. The circulation type reduction system according to claim 2 or 3, wherein: The circulation type reduction system has: a fourth pipeline extending from the gas heating device and connected to the middle of the first pipeline, The combustion exhaust gas generated from the gas heating device is merged with the exhaust gas in the first pipe through the fourth pipe.

5. The circulation type reduction system according to any one of claims 1 to 3, wherein: The catalyst device has a heating device for heating the reaction chamber. The circulation type reduction system has: a fifth pipeline, which branches off from the second pipeline and is connected to the heating device, A portion of the CO-rich gas is supplied to the heating device as combustion gas via the fifth pipe.

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

7. The circulation type reduction system according to any one of claims 1 to 3, wherein: The circulation type reduction system has: The first dehumidifier is disposed in the middle of the first pipe and upstream of a portion connected to the hydrogen supply device, and removes water vapor from the exhaust gas.

8. The circulation type reduction system according to any one of claims 1 to 3, wherein: The circulation type reduction system has: The second dehumidifier is arranged in the middle of the second pipeline and removes water vapor from the CO-rich gas.

9. The circulation type reduction system according to any one of claims 1 to 3, wherein: The circulation type reduction system has: a switching valve disposed midway along the second pipeline; and a seventh pipeline extending from the switching valve, A portion of the CO-rich gas is recovered via the seventh pipeline.

10. The circulation type reduction system according to claim 9, wherein: The circulation type reduction system has: The third dehumidifier is arranged in the middle of the seventh pipeline and removes water vapor from the CO-rich gas passing through the seventh pipeline.

11. The circulation type reduction system according to any one of claims 1 to 3, wherein: The reduction furnace is a smelting furnace, and the oxide is iron ore.

12. The circulation type 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, recycling the CO-rich gas obtained by reforming the exhaust gas as the reducing gas, and performing a reduction treatment of the iron ore as the oxide.

14. A method for operating a smelting furnace, using the circulation type reduction system according to claim 11, (I) at least one selected from sintered ore, lump ore, iron ore pellets and powder ore as the iron ore and (II) a permeable material are alternately charged into the smelting furnace in layers from the top of the smelting furnace to ensure the permeability of the reducing gas in the furnace, The air-permeable material is composed of crushed slag, which is obtained by crushing solidified slag obtained by slowly cooling molten slag discharged from the bottom of the smelting furnace, or a mixture of the crushed slag and coke.

15. The method for operating a smelting furnace according to claim 14, wherein: The reducing gas and air are supplied as injection gas into the interior of the smelting furnace from a tuyere located at a lower portion of the smelting furnace, The ratio of the crushed slag to the coke in the air-permeable material and the ratio of the reducing gas to the air in the blown gas are increased in stages, thereby suppressing the amount of coke used in stages.

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