TWI886552B - Circulating reduction system, iron ore reduction method and smelting furnace operating method - Google Patents

Abstract

The present invention provides a circulating reduction system that can efficiently circulate and utilize CO-rich gas obtained by reforming exhaust gas containing CO ₂ generated from a reduction furnace as reducing gas. In the circulating reduction system 100 of the present invention, the exhaust gas containing CO ₂ generated in the reduction furnace 10 is recovered through the first pipe 81, and hydrogen is added to the exhaust gas from the hydrogen supply device 30 to produce hydrogenated gas. In the catalyst device 40, CO ₂ in the hydrogenated gas is converted into CO by a reverse water gas shift reaction, thereby becoming CO-rich gas with an increased CO concentration. The CO-rich gas is supplied to the inside of the reduction furnace 10 as reducing gas through the second pipe 82. A separation device for separating specific gas components other than water vapor from the gas passing through the inside and recovering or removing them is not arranged in the middle of the first pipe 81 and the second pipe 82.

Description

Circulating reduction system, iron ore reduction method and smelting furnace operating method

The present invention relates to a circulation reduction system, an iron ore reduction method and a smelting furnace operating method capable of radically reducing the emission of _CO2 which contributes to global warming.

Amid calls for a reduction in _CO2 emissions that contribute to global warming, Japan's steel industry, which accounts for about 15% of _CO2 emissions in Japan, has been influenced by government policy and has announced that it will achieve carbon neutrality by 2050. To achieve this, it is necessary to develop an iron ore reduction process and reduction furnace that can produce crude steel at a low cost close to current levels, but the current technical goal has hardly been established.

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 produce _CO2 . However, if the domestic production of molten iron of about 75 million tons per year is to be maintained using this method, about 75 billion ^Nm3 of hydrogen is required. In order to meet this demand using water electrolysis, which is a representative green hydrogen production method, even if all the electricity required for hydrogen transportation, liquefaction, and storage is ignored, it is estimated that 0.34 trillion kWh of electricity is required per year. Even if 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 manufacturers in Japan, where annual electricity consumption is 1 trillion kWh.

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, the technical goal of safely storing large quantities of hydrogen with a wide range of explosive concentrations around steel smelters has not yet been established.

The reason why the domestic steel industry emits about 15% _of the country's _CO2 emissions is that it mainly produces high-grade steel using the blast furnace-converter process, which uses coke to reduce iron ore. The production methods of crude steel are mainly classified into the blast furnace-converter process and the electric furnace process. In the blast furnace-converter process, about 2 tons of _CO2 are generated for every ton of steel, and in the electric furnace process, about 0.5 tons of _CO2 are generated for every ton of steel. The electric furnace process is superior in terms of suppressing the amount of _CO2 generated. However, high-grade steel used in automobiles, etc., is easily adversely affected by impurities such as copper, so it is not mass-produced in the electric furnace process that uses scrap iron as raw materials. Therefore, about 75% of crude steel in the country is produced using the blast furnace-converter process.

For blast furnaces that emit a particularly high amount of CO ₂ , for example, in Patent Document 1, attempts have been made to reduce the amount of coke used by replacing the high-temperature air blown in from the tuyere with a reducing gas such as hydrogen or methane. However, coke not only functions as a reducing agent, but also functions as a heating material for heating the furnace by reacting with oxygen blown in from the hot blast furnace, and as a ventilation material for ensuring ventilation in the furnace. Therefore, it is extremely difficult to fundamentally reduce the amount of coke used until a new means (other than coke) is found for maintaining the temperature in the furnace and ensuring ventilation without adversely affecting the quality of molten iron.

Against this backdrop, Japanese steelmakers are now forced to reduce the number of blast furnaces in operation and increase the ratio of electric furnaces to cope with the current situation. As a result, demand for scrap iron used in electric furnaces has become strong, and fierce competition for its supply is expected to become more severe in the future.

Under such circumstances, the direct reduction process, which has less CO ₂ emissions than the blast furnace-converter process, has come to the fore. In the so-called Midrex process, which is a representative direct reduction process, iron ore is reduced in a solid phase using reformed natural gas to obtain direct reduced iron (DRI) (see reference 2). In the early days of the Midrex process, only spongy DRI could be produced, so it was difficult to handle or transport it from the perspective of oxidation or ignition. However, after the development and industrialization of hot-pressed equipment, these problems were basically solved, and the trend of reducing the amount of scrap iron input and improving the quality of steel by mixing DRI with scrap iron and feeding it into the electric furnace has gradually expanded around the world. Furthermore, attempts have been made to replace natural gas with methane synthesized from CO ₂ and hydrogen by utilizing the methanation reaction (CO ₂ +4H ₂ →CH ₄ +2H ₂ O), or to replace it with hydrogen itself.

On the other hand, in the direct reduction process as solid phase reduction, if the quality of the DRI produced is to be maintained, high-grade iron ore, which has cost and supply constraints, must be used as a raw material. This is a major disadvantage compared to the previous blast furnace method, which can produce about 85% of the iron ore raw material in the form of pellets or sintered ore made from low-grade fine ore or powder ore.

Furthermore, in the direct reduction process, crude steel cannot be taken out in the form of molten iron, so the refining equipment of the previous integrated steelmaking process, such as the pre-treatment furnace or converter, cannot be used. This is also one of the reasons why Japanese blast furnace manufacturers insist on the blast furnace process. Furthermore, it is speculated that the reason why the direct reduction process remains at solid phase reduction is that, as mentioned above, it is impossible to fundamentally solve the problem of maintaining the permeability and the temperature in the furnace for obtaining molten iron.

That is, in the blast furnace-converter process, the main obstacles are the reducing agent that can replace coke, the heating material, and the new means to ensure the permeability without adversely affecting the quality of the molten iron, and the goal of fundamentally reducing the amount of coke used has not yet been established. In addition, compared with the blast furnace-converter process, the direct reduction process with less _CO2 emissions has the following disadvantages: it cannot use the low-cost and easy-to-supply low-grade fine ores or powder ores that can be used in the blast furnace, and crude steel is not taken out as molten iron, so the refining equipment of the previous steelmaking process cannot be used.

Based on this background, Patent Document 3 proposes a technology for utilizing CO ₂ contained in exhaust gas from a blast furnace. That is, it proposes a technology for separating CO ₂ from the exhaust gas of a blast furnace, reforming the recovered CO ₂ into CO, and reusing the CO as a reducing agent for the blast furnace. [Prior Art Document] [Patent Document]

[Patent Document 1] International Publication No. 2021/220555 [Patent Document 2] Japanese Patent Publication No. 2017-88912 [Patent Document 3] Japanese Patent Publication No. 2011-225968

[Problems to be Solved by the Invention] In the technology described in the aforementioned patent document 3, CO ₂ separated and recovered from the exhaust gas generated in the blast furnace is reformed into CO for reuse, thereby suppressing the amount of CO ₂ generated. However, in this technology, since CO ₂ is temporarily separated and recovered from the exhaust gas and CO ₂ is reformed through multiple steps, it is inevitable that the recycling efficiency of the reducing components in the exhaust gas is reduced and the cost of the equipment, operation, and maintenance of each step is incurred. Therefore, it is desired to use a more efficient method to recycle the reducing components in the exhaust gas of a reducing furnace such as a blast furnace.

In view of the above-mentioned subject, an object of the present invention is to provide a circulating reduction system which can efficiently circulate and utilize CO-rich gas obtained by reforming exhaust gas containing CO ₂ generated from a reduction furnace as reducing gas.

In addition, the object of the present invention is to provide an iron ore reduction method, which can efficiently circulate the CO-rich gas obtained by reforming the exhaust gas containing _CO2 generated from the reduction furnace as reducing gas to carry out the reduction treatment of iron ore.

In addition, the object of the present invention is to provide a method for operating a smelting furnace, which is capable of maintaining the temperature in the furnace using the circulating reduction system and ensuring the permeability by means other than coke. [Means for Solving the Problem]

The inventors of the present invention have conducted intensive research on a method for realizing an efficient reduction process that can circulate and utilize the exhaust gas from a reduction furnace as a starting material of a reducing agent, and have found that the exhaust gas can be efficiently circulated and reused by using the so-called reverse water gas shift reaction.

That is, the exhaust gas generated in the reduction process of iron ore generally contains not only CO ₂ and nitrogen from the atmosphere, but also residual reducing agents such as CO and H _2. For example, the exhaust gas from a blast furnace contains about 23% by volume of CO ₂ , the same proportion of CO, about 4% by volume of H ₂ , and about 50% by volume of nitrogen from the air. The inventors of the present invention have thought that by adding hydrogen to such exhaust gas and bringing the gas into contact with a catalyst for reverse water gas shift reaction (RWGS: Reverse Water Gas Shift reaction: CO ₂ +H ₂ →CO+H ₂ O), the balance of CO ₂ and CO in the exhaust gas is largely shifted to be rich in CO, and then recycled as reducing gas together with H ₂ and nitrogen originally contained in the exhaust gas. The inventors have recognized that if such recycling is possible, the input amount of reducing agents derived from fossil fuels such as coke, which have been used in the past, can be limited to a minimum.

Here, CO is circulated as the main reducing agent because the reduction reaction of iron ore by _H2 is an endothermic reaction, while the reduction reaction of iron ore by CO is an exothermic reaction, so CO is the most efficient reducing agent that can maintain the temperature in the reduction furnace at a high temperature. In addition, in the reduction by CO, the freezing point of iron caused by carbon found when coke is used as a reducing agent can be directly utilized. Thereby, the reduced iron that does not melt unless it is 1500°C or above in the case of reduction by _H2 melts at about 1200°C in the reduction by CO. The presence 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.

In addition, the CO-rich reducing gas synthesized from _CO2 -rich exhaust gas is mainly supplied to the reduction furnace, but the surplus can be discharged, recovered, and converted to various uses. CO is not only used as a reducing agent or fuel gas, but also an important starting material for the Fischer-Tropsch reaction (nCO+(2n+1) _H2 → _{CnH2n +2} + _nH2O ) in the synthesis of various organic substances. Therefore, the CO-rich reducing gas synthesized from _CO2- rich exhaust gas is not limited to a reducing agent, but also a synthesis gas that can be converted to a fuel gas or a raw material for various organic compounds without surplus. In particular, if the use of fossil fuels is greatly reduced in order to prevent global warming, the organic chemical industry that has been using them as raw materials must find new suppliers of raw materials. It is of great significance for these industries to become acceptors of the synthesis gas.

As mentioned above, the coke put into a general blast furnace not only acts as a reducing agent, but also as a heating material and a ventilation material. Therefore, when the reduced iron is taken out as molten iron, even if the reduction heat of CO in the reducing gas can be used to maintain the temperature in the furnace, if the amount of coke put in is suppressed to the limit, ventilation cannot be ensured (a stable reducing environment cannot be maintained).

It was newly recognized that this problem can be solved by using a mold to slowly cool and crush part of the molten slag that is produced with the molten iron and discharged from the bottom of the furnace, and then mixing it with the coke as a ventilation material and re-introducing it from the top of the furnace. That is, the melting point of blast furnace slag is about 1400℃, so even when the iron in the blast furnace, whose solidification point is lowered by C, begins to melt, the slag remains in a solid state and acts as a ventilation material. In addition, since the slag is originally a substance generated in the smelting furnace, even if it is recycled, it will not change the material environment in the smelting furnace.

Furthermore, it is not easy to start the melting furnace operation using only the slowly cooled and crushed slag as the ventilation material and only the reducing gas as the reducing agent. Therefore, as with a normal blast furnace, the melting furnace is first started in the "blast furnace mode" where high-temperature air heated by a hot blast furnace is blown in after alternating layers of coke and iron source, which are both reducing agents and ventilation materials, in the blast furnace. Then, the melting furnace is gradually switched to the "coke-free mode" where the slag is gradually mixed with the coke and the reducing gas is gradually added to the air blown into the melting furnace. When the melting furnace is shut down, restarting becomes easy if the operation is terminated in the blast furnace mode after the coke-free mode in the reverse order.

The present invention is based on the above findings, and its main purpose is as follows. [1] A circulating reduction system, comprising: a reduction furnace, which reduces oxides contained therein; a first pipe, which recovers exhaust gas containing _CO2 generated in the reduction furnace from the reduction furnace and passes the exhaust gas through the reduction furnace; a hydrogen supply device, which is connected to the middle of the first pipe and adds hydrogen to the exhaust gas to produce hydrogenated gas; a catalyst device, which is connected to the end of the first pipe and has a reaction chamber for containing a catalyst for a reverse water gas shift reaction, wherein the hydrogenated gas introduced into the reaction chamber from the first pipe contacts the catalyst, and the CO2 in the hydrogenated gas is reduced by the reverse water gas shift reaction. ₂ is converted into CO, thereby producing a CO-rich gas with an increased CO concentration; and a second pipe extending from the catalyst device and connected to the reduction furnace, allowing the CO-rich gas to pass through, and supplying the CO-rich gas to the interior of the reduction furnace as a reducing gas, and no separation device is arranged in the middle of the first pipe and the second pipe, and the separation device separates specific gas components other than water vapor from the gas passing through the interior and recovers or removes them.

[2] The circulating reduction system described in [1] above, further comprising a gas heating device, wherein the gas heating device is disposed in the middle of the second pipe and heats the CO-rich gas.

[3] The circulating reduction system as described in [2] has a third pipe, which branches 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 to the gas heating device as combustion gas through the third pipe.

[4] The circulation reduction system as described in [2] or [3] has a fourth pipe, which extends from the gas heating device and is connected to the middle of the first pipe, so that the combustion exhaust gas generated from the gas heating device is combined with the exhaust gas in the first pipe through the fourth pipe.

[5] A circulating reduction system as described in any one of [1] to [4], wherein the catalyst device has a heating device for heating the reaction chamber, and the circulating reduction system has a fifth pipe, the fifth pipe is branched from the second pipe and connected to the heating device, and a portion of the CO-rich gas is supplied to the heating device as combustion gas through the fifth pipe.

[6] The circulation reduction system described in [5] has a sixth pipe extending from the heating device and connected to the middle of the first pipe, and the combustion exhaust gas generated from the heating device is combined with the exhaust gas in the first pipe through the sixth pipe.

[7] The circulation reduction system described in any one of [1] to [6] has a first dehumidifier, which is arranged in the middle of the first pipe and upstream of the position connected to the hydrogen supply device, and removes water vapor from the exhaust gas.

[8] The recycling reduction system described in any one of [1] to [7] has a second dehumidifier, which is arranged in the middle of the second pipe and removes water vapor from the CO2-rich gas.

[9] A circulation reduction system as described in any one of [1 to [8], comprising: a switching valve disposed in the middle of the second pipe; and a seventh pipe extending from the switching valve, and recovering a portion of the CO-rich gas through the seventh pipe.

[10] The recycling reduction system described in [9] has a third dehumidifier, which is arranged in the middle of the seventh pipe and removes water vapor from the CO-rich gas passing through the seventh pipe.

[11] The circulating reduction system as described in any one of [1] to [10], wherein the reduction furnace is a smelting furnace and the oxide is iron ore.

[12] The circulating reduction system as described in [11], wherein the smelting furnace is a blast furnace.

[13] A method for reducing iron ore, using the circulating reduction system as described in any one of [1] to [12], wherein the CO-rich gas obtained by reforming the exhaust gas is circulated as the reducing gas to reduce the iron ore as the oxide.

[14] A method for operating a smelting furnace using the circulating reduction system described in [11] or [12], wherein: (I) at least one of the iron ore selected from sintered ore, lump ore, iron ore pellets and powdered ore, and (II) crushed slag 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 are alternately loaded into the smelting furnace in layers from the top of the smelting furnace, thereby ensuring the in-furnace permeability of the reducing gas.

[15] A method for operating a melting furnace as described in [14], wherein the reducing gas and air are supplied as injection gas to the interior of the melting furnace from a tuyere located at the bottom of the melting furnace, so that the ratio of the crushed slag to the coke in the ventilation material and the ratio of the reducing gas to the air in the injection gas are increased in stages, thereby gradually suppressing the amount of coke used. [Effect of the invention]

According to the circulating reduction system of the present invention, CO-rich gas obtained by reforming exhaust gas containing CO ₂ generated from a reduction furnace can be efficiently circulated and utilized as reducing gas.

According to the iron ore reduction method of the present invention, CO-rich gas obtained by reforming _CO2- containing exhaust gas generated from a reduction furnace can be efficiently circulated as reducing gas to carry out the reduction treatment of iron ore.

According to the smelting furnace operating method of the present invention, the circulating reduction system can be used to maintain the temperature in the furnace and ensure the permeability by means other than coke.

[Circulation reduction system] Referring to FIG. 1 , a circulation reduction system 100 according to an embodiment of the present invention is described. The circulation reduction system 100 has 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 piping equipment, has a first piping 81, a second piping 82, a third piping 83, a fourth piping 84, a fifth piping 85, a sixth piping 86, a seventh piping 87, and a switching valve 90.

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

The first piping 81 is a piping device for recovering the exhaust gas containing _CO2 generated in the reducing furnace 10 from the reducing furnace 10 and passing it. The starting end of the first piping 81 is connected to the reducing furnace 10 (in one example, the furnace top 12), and the terminal end is connected to the catalyst device 40. The hydrogen supply device 30 is connected in the middle of the first piping 81. In addition, the first dehumidifier 20 is arranged in the middle of the first piping 81 at a position upstream of the portion connected to the hydrogen supply device 30. The first piping 81 has a piping 81A extending from the reducing furnace 10 and connected to the first dehumidifier 20, and a piping 81B extending from the first dehumidifier 20 and connected to the catalyst device 40. In this specification, the term "upstream" or "downstream" in relation to piping refers to the term in relation to the direction in which gas flows in the piping.

The exhaust gas discharged from the top 12 of the reduction furnace 10 flows in the first pipe 81, and after being dehumidified by the first dehumidifier 20, hydrogen (H ₂ ) gas is supplied from the hydrogen supply device 30, thereby becoming hydrogenated gas. In order to suppress the water gas shift reaction and promote the reverse water gas shift reaction, it is preferable to perform the dehumidification treatment. The composition of the exhaust gas is not particularly limited, but typically has the following composition: except for water vapor, it contains CO ₂ : 13 volume % to 24 volume %, CO: 21 volume % to 31 volume %, and H ₂ : 3 volume % to 15 volume %, and the remainder contains N ₂ derived from air. The composition of the hydrogenated gas is not particularly limited, but typically has the following composition: in addition to water vapor, it contains CO ₂ : 13 volume % to 24 volume %, CO: 21 volume % to 31 volume %, and H ₂ : 10 volume % to 30 volume %, and the remainder contains N ₂ from air. The hydrogen supplied from the hydrogen gas supply device 30 is ideally green hydrogen obtained by water electrolysis using renewable energy, but before the use of coke is reduced to zero by applying the circulating reduction system of the present invention to blast furnace operation, hydrogen purified from coke furnace gas can be used instead.

Furthermore, it is preferable to install a dust removal device (not shown) in the middle of the first piping 81, upstream of the first dehumidifier 20, or downstream of the first dehumidifier 20 and upstream of the portion connected to the hydrogen gas supply device 30, to perform dust removal treatment on the exhaust gas, thereby removing dust originating from the raw materials from the exhaust gas.

The catalyst device (reversal reformer) 40 is connected to the terminal of the first pipe 81 and includes: a reaction chamber 42 for accommodating a catalyst for the reverse water gas shift reaction; and a heating device 44 for heating the reaction chamber 42. In the catalyst device 40, the hydrogenated gas introduced into the reaction chamber 42 from the first pipe 81 contacts the catalyst, and _CO2 in the hydrogenated gas is converted into CO in the reverse water gas shift reaction, thereby becoming 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 contains CO ₂ : 6 vol% to 20 vol%, CO: 24 vol% to 40 vol%, and H ₂ : 5 vol% to 24 vol%, and the remainder contains N ₂ from air. There are many known catalysts that can be used for the reverse water gas shift reaction, such as nickel substrates or precious metal substrates, but the catalyst used in the present invention may be any of them.

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, it is desirable to set the temperature of the introduced hydrogenated gas as high as possible within a temperature range in which the catalyst is not easily degraded. Specifically, it is preferred to preheat the reaction chamber 42 by the heating device 44 so that the temperature of the reaction gas (hydrogenated gas) around the catalyst is 800° C. or higher and 1200° C. or lower.

The second pipe 82 is a pipe device extending from the catalyst device 40 and connected to the reduction furnace 10 (in one example, the tuyere 14), allowing the CO-rich gas to pass through, and supplying the CO-rich gas as reducing gas (in one example, through the tuyere 14) to the inside of the reduction furnace 10. It is preferable to arrange the second dehumidifier 50 for removing water vapor from the CO-rich gas and the gas heating device 60 for heating the CO-rich gas in the middle of the second pipe 82. In this case, it is preferable to arrange the gas heating device 60 downstream of the second dehumidifier 50. In this case, the second piping 82 includes a piping 82A extending from the catalyst device 40 and connected to the second dehumidifier 50, a piping 82B extending from the second dehumidifier 50 and connected to the gas heating device 60, and a piping 82C extending from the gas heating device 60 and connected to the reduction furnace 10 (in one example, the tuyere 14).

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

That is, it is desirable to adjust the temperature of the CO-rich gas (reducing gas) to be blown into the reduction furnace 10 by the gas heating device 60 after the reaction using the catalyst. Regarding the reduction efficiency of the iron ore in the reduction furnace 10, the higher the temperature of the reducing gas, the more advantageous it is. However, in the case of solid phase reduction of the iron ore, it is desirable to set the temperature of the reducing gas blown into the reduction furnace 10 to 900° C. or higher. In addition, when the reduced iron is taken out as molten iron at 1500°C, the temperature of the molten zone of the iron source and slag formed in the lower area of the reduction furnace 10 needs to be maintained at above 1650°C. Therefore, it is ideal that if the amount of coke input reaches about 50% of the previous blast furnace, the reducing gas is heated in such a way that the temperature of the reducing gas becomes above 1200°C and then blown in. If the amount of coke input is less than 20% of the previous blast furnace, the reducing gas is heated in such a way that the temperature of the reducing gas becomes above 1500°C and then blown in.

The preferred operation of the gas heating device 60 is as follows. The circulation reduction system 100 of the present embodiment preferably has a third pipe 83, which branches from a position more upstream than the gas heating device 60 and more downstream than the second dehumidifier 50 in the middle of the second pipe 82 and is connected to the gas heating device 60. Furthermore, it is preferred to supply a portion of the CO-rich gas flowing in the second pipe 82 as a combustion gas to the gas heating device 60 via the third pipe 83. In this way, by burning a portion 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 desired temperature. Although omitted in FIG. 1 , the oxygen-containing gas supplied to the gas heating device 60 for burning the combustion gas is preferably oxygen gas (not containing unconsumed nitrogen).

The circulation reduction system 100 preferably has a fourth pipe 84 extending from the gas heating device 60 and connected to the middle of the first pipe 81. The fourth pipe 84 has an upstream portion 84A and a downstream portion 84B. 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 pipe 81 through the fourth pipe 84 and reused. The fourth pipe 84 is preferably connected to a position upstream of the first dehumidifier 20 in the middle of the first pipe 81. When the combustion exhaust gas generated from the gas heating device 60 is subjected to heat exchange with (1) the reducing gas piping between the catalyst device 40 and the gas heating device 60 and (2) the hydrogenated gas piping between the hydrogen supply device 30 and the catalyst device 40, and then merges with the exhaust gas in the first piping 81 upstream of the first dehumidifier 20, the reducing gas and the hydrogenated gas can be preheated.

Furthermore, when the reducing gas cannot be completely raised to the desired temperature by the indirect heating type gas heating device 60 as shown in FIG1 , oxygen or the like may be added near the front end of the gas heating device 60 to directly burn a portion of CO or _H2 contained in the reducing gas. In addition, when the hot air blown into the reducing furnace 10 at the time of startup in the blast furnace mode is oxygen-enriched air made by cryogenic separation or the like, the heat load of the gas heating device 60 taken away by the heating of nitrogen is reduced, so that the temperature of the reducing gas can be easily raised.

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 reduction system 100 of the present embodiment preferably has a fifth pipe 85, which branches from the second pipe 82 and is connected to the heating device 44 of the catalyst device 40. The fifth pipe 85 is preferably branched from the middle of the second pipe 82, from a position more upstream than the gas heating device 60 and more downstream than the second dehumidifier 50. And, it is preferred to supply a part of the CO-rich gas as the combustion gas to the heating device 44 through the fifth pipe 85. Although omitted in FIG. 1 , the oxygen-containing gas supplied to the heating device 44 for burning the combustion gas is preferably oxygen gas (not containing unconsumed nitrogen).

The circulation 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. Furthermore, it is preferred that the combustion exhaust gas generated from the heating device 44 is merged with the exhaust gas in the first pipe 81 through the sixth pipe 86 and reused. Furthermore, in the present embodiment, since the upstream portion 86A of the sixth pipe 86 is connected to the middle of the fourth pipe 84 which is the fuel exhaust gas flow path from the gas heating device 60, 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 thereto, 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 hydrogen gas piping between the hydrogen gas supply device 30 and the catalyst device 40 and then merges with the exhaust gas in the first piping 81 upstream of the first dehumidifier 20, the hydrogen gas can be preheated.

In the present embodiment described above, by repeatedly performing the following steps, namely, a reduction step of iron ore by blowing in reducing gas, a recovery step of exhaust gas from the reduction furnace, a dust removal and dehumidification step of the exhaust gas (optional step), a hydrogenation step of the exhaust gas, a step of generating a CO-rich gas from the hydrogenated gas by a reverse water gas shift reaction, a dehumidification step of the CO-rich gas (optional step), a heating step of the CO-rich gas (optional step) and a blowing step of the CO-rich gas as reducing gas, a circulation process for reusing the exhaust gas from the reduction furnace 10 in a closed circulation system is realized.

The unconverted _CO2 remaining in the CO-rich gas as the reducing gas will always 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 is not arranged in the middle of the first pipe 81 and the second pipe 82, and the separation device separates specific gas components other than water vapor from the gas passing through the inside and recovers or removes them. In this embodiment, in addition to the dust removal and dehumidification of the existing technology, no new separation and concentration process is required, so the circulation efficiency of the reducing gas is high.

In this embodiment, since the reverse water gas shift reaction is used to convert _CO2 into CO with equimolar hydrogen, the supply amount of hydrogen per _CO2 can be suppressed to about 1/4 compared to the previous reduction method that uses methane generated by a methanation reaction requiring 4 times the molar amount of hydrogen as _CO2 as a reducing agent.

In the present embodiment, reducing gas mainly composed of CO after reforming the exhaust gas is supplied to the reduction furnace 10 at a high temperature, 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 powder ore or powder ore, which is cost-effective and easy to supply, can be used as pellets or sintered ore.

Furthermore, the remaining portion of the CO-rich gas (in this embodiment, the reduced gas, the combustion gas of the gas heating device 60, and the residual portion of the CO-rich gas used as the combustion gas of the heating device 44) can be recovered. That is, the recycling reduction system 100 has a switching valve 90 disposed in the middle of the second pipe 82 and a seventh pipe 87 extending from the switching valve 90, and a portion of the CO-rich gas can be recovered through the seventh pipe 87. The recovered CO-rich gas can be used as a synthesis gas that becomes a raw material of an organic compound, for example. In this embodiment, a system is realized that converts the _CO2 -rich exhaust gas discharged from the reduction furnace 10 into a CO-rich reducing gas and circulates it for utilization. Therefore, by effectively utilizing the remaining CO-rich gas as synthesis gas in the organic chemical industry, etc., the _CO2 emission to the atmosphere can be suppressed to zero level.

In addition, the molten slag separated from the iron water is slowly cooled in a casting mold to form solidified slag, and the solidified slag is crushed to form crushed slag, which can be reused as a breathable material. If a part of the pig iron discharged from the reduction furnace (melting furnace) is attached to the breathable material derived from the slag, the pig iron as an iron source can be returned to the reduction furnace through the breathable material.

Furthermore, the molten slag is automatically discharged to the surface of the molten iron due to the difference in specific gravity, so even if it is recycled, it will hardly have any 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.

Referring to FIG. 2 , a recycling reduction system 200 according to another embodiment of the present invention is described. The recycling reduction system 200 does not have the second dehumidifier 50, but instead, a third dehumidifier 70 is arranged in the middle of the seventh piping 87. In other respects, the recycling reduction system 200 has the same structure as the recycling reduction system 100. That is, the second dehumidifier 50 is not an essential structure in the present invention. Preferably, when the second dehumidifier 50 is not arranged, water vapor is removed from the CO-rich gas passing through the seventh piping 87 by the third dehumidifier 70.

In the above description, the reduction furnace 10 is mainly a melting furnace such as a blast furnace, and the reduction object is iron ore. However, the present invention is not limited to this. The reduction furnace 10 may also be a solid reduction furnace. In addition, if the reduction object is an oxide, it is not limited to iron ore, and for example, it may be manganese ore as a raw material of iron manganese or silicon manganese.

[Iron Ore Reduction Method] The iron ore reduction method according to one embodiment of the present invention uses the above-mentioned circulating reduction system 100 and circulating reduction system 200 to circulate the CO-rich gas obtained by reforming the exhaust gas as a reducing gas, thereby reducing the iron ore as an oxide. In this way, the CO-rich gas obtained by reforming the exhaust gas containing _CO2 generated from the reduction furnace 10 can be efficiently circulated as a reducing gas to reduce the iron ore.

In addition, the reduction method of this embodiment realizes an efficient reduction process that can circulate the exhaust gas from the reduction furnace 10 as a starting material of the reducing agent, thereby significantly reducing the amount of _CO2 generated. Furthermore, the input amount of reducing agents such as coke derived from fossil fuels that have been used in the iron ore reduction process can be fundamentally suppressed.

[Method for operating a smelting furnace] A method for operating a smelting furnace according to an embodiment of the present invention is performed using the circulating reduction system 100 and the circulating reduction system 200. Furthermore, it is important that (I) at least one of iron ore selected from sintered ore, lump ore, iron ore pellets and powdered ore (iron source) and (II) crushed slag obtained by slowly cooling molten slag discharged from the bottom of the molten furnace or a mixture of the crushed slag and coke are alternately charged into the molten furnace in layers at the top of the reduction furnace (melting furnace) 10, thereby ensuring the in-furnace permeability of the reducing gas. In this way, the circulating reduction system 100 and the circulating reduction system 200 can be used to maintain the furnace temperature and ensure the permeability by means other than coke.

In the operation based on this embodiment, reducing gas and air are supplied as injection gas into the melting furnace from the tuyere 14. At this time, it is preferable to increase the ratio of crushed slag to coke in the ventilation material and the ratio of reducing gas to air in the injection gas in stages, thereby gradually reducing the amount of coke used.

By using the smelting furnace operation method according to the present embodiment, it is possible to obtain reduced iron in the form of molten iron using low-grade micro-powder ore or powder ore that is low-cost and easily available, so that the previous steelmaking integrated process can be directly switched to after the next step.

The ventilation level of the blast furnace can be adjusted by the particle size of the crushed slag. For example, by adding vents to the slowly cooled slag for casting, ventilation can be further ensured. Furthermore, there are no special problems even if ordinary molten furnace slag is used as the ventilation material.

In the smelting furnace operation method based on this embodiment, the amount of molten slag produced in the circulating smelting furnace 100 and the circulating smelting furnace 200 is greater than that in a conventional blast furnace because the slag re-injected from the furnace top 12 is re-melted after the fusion zone. In addition, if more slag is added, 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 ideal to adjust the layer thickness ratio of the iron source layer and the ventilation layer in advance so that the iron source layer is more enriched than that of a conventional blast furnace. [Example]

[Example 1] As described below, as Invention Example 1, Invention Example 2, and Comparative Example, a balance calculation was performed to confirm the effect of the reduction method of the present invention.

(Invention Example 1) The equilibrium calculation model of the cyclic reduction system based on Invention Example 1 is shown in FIG3. As an initial state, the following state is assumed: a reduction furnace 10 charged with 25 mol of iron (III) oxide ( _Fe2O3 ) _is connected to a reverse conversion type reformer (hereinafter referred to as "reformer 40 _" ) as a catalyst device 40 charged with a mixed gas equivalent to blast furnace exhaust gas _containing 100 mol in total of CO: 22 mol, _CO2 : 22.8 mol, H2: 4.2 mol, and N2: 51 mol. A first dehumidifier 20 is provided at the inlet side of the reformer, a second dehumidifier 50 is provided at the outlet side of the reformer, and a hydrogen supply device 30 is provided between the first dehumidifier and the reformer to maintain the _H2 molar number in the reformer at 22.8 moles (equivalent to the _CO2 concentration in the blast furnace exhaust gas). If the _H2 supplied from the hydrogen supply device and the gas other than the _H2O removed by the first dehumidifier and the second dehumidifier do not enter or exit the reduction furnace and the reformer, since all the _H2O is generated from the consumed _H2 , it can be considered that the total molar number of the mixed gas circulating in the reformer and the reduction furnace does not change.

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 transport system is required for gas circulation between the reduction furnace and the reformer, but for the purpose of confirming the principle, the energy consumed by it is ignored. 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 a balanced state, it will be affected by the performance of the catalyst used, but it is assumed that a balanced reaction is achieved.

Here, a cyclic process is considered in which the following operation is repeated as one cycle: all the reducing gas generated when the hydrogenated gas reaches a stable state in the reformer is sent to the reducing furnace, the gas in the reducing furnace when the reduction reaction reaches a stable state is taken out as waste gas, and a certain level of hydrogen is added to it until hydrogenated gas is produced again. The thermodynamic balance calculation software & thermodynamic database Fact Sage 8.1 manufactured by the Computational Mechanics Research Center Co., Ltd. is used to calculate the gas composition and iron source equilibrium state in the reformer and the reducing furnace in each cycle of sending reducing gas from the reformer to the reducing furnace. The results are shown in Figure 4. Furthermore, the compounds generated in the reformer and the reducer also include methane, etc., but trace components below 0.005 mol are ignored.

In the reduction furnace, the iron source is reduced by CO supplied from the reformer and the remaining _H2 not consumed by the reverse water gas shift reaction. _The solid _Fe2O3 introduced as the iron source is converted into 2 times the mole of FeO (solid phase) in the first cycle. After the second cycle, FeO is gradually reduced and converted into 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.

(Invention Example 2) The equilibrium calculation model of the circulation reduction system based on Invention Example 2 is shown in FIG5. It is the same as the equilibrium calculation model of the circulation reduction system based on Invention Example 1 shown in FIG3, except that the second dehumidifier is not provided on the outlet side of the reformer. The calculation conditions are also the same as those of Invention Example 1, and the equilibrium state of the gas composition and the iron source in the reformer and the reduction furnace are calculated. The result is shown in FIG6.

_The solid _Fe2O3 introduced as the iron source changes to 2 moles of FeO (solid phase) in the first cycle. After the third cycle, FeO is gradually reduced to α-Fe (solid phase), and the reduction is completed in the ninth cycle. The main reduction reaction is from FeO to α-Fe, which is consistent with the known view in the blast furnace. The amount of _H2 consumed for the reduction of this iron source is 85 moles.

(Comparative Example) The equilibrium calculation model of the circulation reduction system based on the comparative example is shown in FIG7. It is the same as the equilibrium calculation model of the circulation reduction system based on the inventive example 1 shown in FIG3 except that the reformer and the second dehumidifier are not provided. The calculation conditions are also the same as those of the inventive example 1 to calculate the equilibrium state of the gas composition and the iron source in the reformer and the reduction furnace. The result is shown in FIG8.

In the reduction furnace of the comparative example, the iron source is reduced only by using _H2 directly fed into the reduction furnace from the _hydrogen gas supply device. 25 mol of _Fe2O3 (solid phase) fed as the iron source changes to 8.2 mol _{of Fe3O4} (solid phase) and 22.5 mol of FeO (solid phase) in the first cycle. After the second cycle, FeO is gradually reduced and changes to α-Fe (solid phase). At the same time, as in Invention Example 2, the reduction is completed in the ninth cycle. The main reduction reaction is the reaction from FeO to α-Fe, which is the same as Invention Example 1 and Invention Example 2. The amount of _H2 consumed in the reduction of the iron source is 75 mol, which is 10 mol less than that of Invention Example 2.

(Heat absorption in the reduction furnace) The biggest difference between Invention Example 1 and Invention Example 2 and the comparative example is the heat absorption in the reduction furnace. The heat of reaction (heat absorption) in the reduction furnace calculated based on the heat of reaction of each reaction calculated using Fact Sage 8.1 is shown in Figures 9 and 10.

Regarding the direct reduction of the iron source using _H2 , except for the reaction _{from Fe2O3} to _Fe3O4 that is completed in _the initial stage, all reactions are endothermic reactions. In contrast, in the reduction of the iron source using CO and excess _H2 in Invention Example 1, the heat generated by CO reduction supplements the heat absorbed by _H2 reduction, so the total heat absorbed can be greatly suppressed (see Figure 9). In addition, in Invention Example 2, in the reduction area of FeO, the heat generated by CO reduction exceeds the heat absorbed by _H2 reduction, so the reduction temperature of FeO is spontaneously maintained at a high temperature (see Figure 9). If the amount of iron source input increases, the reduction stage of FeO is further extended. Generally, it is extremely difficult to supply heat from outside the tuyere and the furnace top to a reduction furnace that needs to maintain a high temperature inside. Therefore, considering that the absorption heat must be supplemented by the combustion heat of the coke fed into the reduction furnace, the superiority of the present invention is obvious.

In addition, according to Figure 10, the amount of _H2 supplied to the reformer to maximize the calorific value of FeO in the reduction zone is expected to be about the same as the molar amount of _CO2 in the exhaust gas. It is considered that if the amount of H2 supplied to the reformer is suppressed, the reduction rate will also decrease, so the amount of _H2 supplied is actually adjusted based on the balance between the temperature in the reduction furnace and the reduction _rate .

[Example 2] As described below, as Invention Examples 3 and 4, reduction of iron ore was performed using an experimental cycle reduction system.

(Invention Example 3) The structure of the experimental cyclic reduction system based on Invention Example 3 is shown in FIG11. In FIG11, raw material blocks A obtained by alternating layers of 2.2 kg of coke crushed to about 5 mm and 5.0 kg of lump ore crushed to about 3 mm are formed on a tungsten mesh that separates the furnace bottom of a BF simulator (hereinafter referred to as "reduction furnace 10") set on a weighing scale as an experimental reduction furnace.

Furthermore, on the raw material block A, a raw material block B was formed. The raw material block B was obtained by uniformly mixing 2.8 kg of blast furnace slow-cooling slag crushed to about 5 mm in 1.1 kg of the above coke and 5.0 kg of lump ore crushed to about 3 mm, and stacking them alternately.

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

Sampling tubes for gas composition analysis are provided in front of the first electric tubular furnace 40 and between the second electric tubular furnace 40 and the dehumidifier 50 and are connected to a micro gas chromatography analysis device (micro GC (Gas Chromatograph)). In addition, a hydrogen pipe 30 is connected between the dehumidifier 20 and the first electric tubular furnace 40 via a switching valve 93 and a mass flow controller (MFC) 94.

A nozzle 96 for introducing 2.3% oxygen-enriched air via a regenerative gas heating furnace 95 is provided on the opposite side of the nozzle 92 at the lower portion of the reduction furnace 10. The flow rate of the air introduced from the nozzle 96 is controlled by a mass flow controller (MFC) 97.

In order to completely exhaust the waste gas remaining in the reduction furnace 10 after the reduction experiment, a nitrogen purge pipe is connected between the dehumidifier 20 and the switch valve 93 via the switch valve 98.

First, the switching valve 91 is set on the exhaust gas treatment device side to separate the exhaust gas from the reduction furnace 10. Then, the air heated to 1200°C is introduced into the reduction furnace 10 at a flow rate of 17 L/min from the nozzle 96 of the reduction furnace 10 using the MFC 97. Both sets of electric tubular furnaces 40 use thermocouples (TC) set around the catalyst to set the internal temperature to 800°C.

The representative composition of the exhaust gas generated by the reduction of the ore in the raw material block A and the mixed gas after passing through the second set of electric tubular furnace 40 (in the case of no hydrogen supplementation at the inlet side of the first set of electric tubular furnace 40) is shown in Table 1. It can be seen that after passing through the second set of electric tubular furnace 40, CO increased by 2.7% in the reverse water gas shift reaction caused by the residual _H2 in the exhaust gas, and _CO2 and _H2 decreased by 2.7% respectively.

When 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 using the MFC 97. At the same time, the switching valve 93 is switched to the hydrogen distribution pipe 30 side and hydrogen is introduced, and the MFC 94 is adjusted so that the H ₂ concentration in the mixed gas before entering the first set of electric tubular furnaces 40 (the same as the CO ₂ concentration in the initial exhaust gas) becomes 22.8%. Then, the switching valve 91 is switched to the reduction furnace 10 side and the reducing gas is introduced from the nozzle 92. In addition, the complete consumption of the coke in the raw material block A is determined based on the weight change of the reduction furnace 10.

In this state, wait until 1.1 kg of coke in the raw material block B is completely consumed, stop the air introduced from the nozzle 96, stop the two sets of electric tube furnaces and the two sets of gas heating furnaces. Then, wait until the water temperature in the water cooling jacket reaches 30°C, use the switching valve 93 to shut off the hydrogen gas, 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. After that, dismantle the reduction furnace 10 and confirm the condition inside the furnace.

A 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 lump A and raw material B were almost not confirmed on the tungsten mesh. A mixture of ferrite (α-Fe) and cementite (Fe ₃ C) and slag accumulated on it were confirmed at the bottom of the furnace separated by the tungsten mesh. X-ray diffraction confirmed that the mixture contained ferrite and cementite. Furthermore, the carbon in the mixture measured by a combustion-type carbon-sulfur analyzer was approximately 4.3 mass%. When comparing the upper and lower parts of the mixture, the carbon in the lower part showed a tendency to increase by about 0.3 mass%.

Through the above experiments, it was 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 the operation of 50% carbon reduction using slag as a ventilation material, the lump ore input as raw material can also be completely reduced.

(Invention Example 4) The structure of the experimental circulation reduction system based on Invention Example 4 is shown in FIG12. It is the same as the circulation reduction system of Invention Example 3 shown in FIG11, except that the electric tubular furnace 40 is set as one set and no dehumidifier is arranged downstream of the electric tubular furnace 40. The electric tubular furnace 40 uses a thermocouple (TC) arranged around the catalyst to set the internal temperature to 900°C. The test was conducted under the same conditions as Invention Example 3.

The representative composition of the exhaust gas generated by the reduction of the ore in the raw material block A and the mixed gas after passing through the electric tubular furnace 40 (in the case of no hydrogen supplementation at the inlet side of the electric tubular furnace 40) is shown in Table 1. It can be seen that after passing through the electric tubular furnace 40, CO increased by 1.8% in the reverse water gas shift reaction caused by the residual _H2 in the exhaust gas, and _CO2 and _H2 decreased by 1.8% respectively.

After the test, similar to Invention Example 3, almost no lump ore, coke, and blast furnace slow cooling slag were confirmed on the tungsten mesh. A mixture of ferrite (α-Fe) and cementite (Fe ₃ C) and slag deposited thereon were confirmed at the furnace bottom separated by the tungsten mesh. X-ray diffraction confirmed that the mixture contained ferrite and cementite. Furthermore, the carbon in the mixture measured by a combustion-type carbon-sulfur analyzer was approximately 4.3 mass %, and when comparing the upper and lower parts of the mixture, the carbon in the lower part showed a tendency to increase by about 0.3 mass %.

Through the above experiments, it was 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 the operation of 50% carbon reduction using slag as a ventilation material, all the lump ore input as raw material can be reduced.

[Table 1] Table 1 Differentiation Gas CO CO _{2 H2} N _{2 H2O} vol% vol% vol% vol% vol% Invention Example 3 Exhaust gas 22.0 22.8 4.2 51.0 - Mixed gas 24.7 20.1 1.5 51.0 0.8 Invention Example 4 Exhaust gas 22.0 22.8 4.2 51.0 - Mixed gas 23.8 21.0 2.4 51.0 1.8

10: Reduction furnace 12: Furnace top 14: Tuyere 20: First dehumidifier/dehumidifier 30: Hydrogen supply device/hydrogen piping 40: Catalyst device (reversing reformer)/electrode furnace 42: Reaction chamber 44: Heating device 50: Second dehumidifier/dehumidifier 60: Gas heating device 70: Third dehumidifier 81: First piping 81A, 81B, 82A, 82B, 82C: Piping 82: Second piping 83: Third piping 84: Fourth piping 85: Fifth piping 86: Sixth piping 84A, 86A: Upstream part 84B, 86B: Downstream part 87: Seventh pipe 90, 91, 93, 98: Switch valve 92, 96: Nozzle 94, 97: MFC 95: Gas heating furnace 100, 200: Circulating reduction system/circulating smelting furnace A, B: Raw material block

FIG. 1 is a schematic diagram showing the structure of a recycling reduction system 100 according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing the structure of a recycling reduction system 200 according to another embodiment of the present invention. FIG. 3 is a schematic diagram showing a balance calculation model of a recycling reduction system according to Invention Example 1. FIG. 4 is a graph showing the reduction state in the model of FIG. 3 (Invention Example 1). FIG. 5 is a schematic diagram showing a balance calculation model of a recycling reduction system according to Invention Example 2. FIG. 6 is a graph showing the reduction state in the model of FIG. 5 (Invention Example 2). FIG. 7 is a schematic diagram showing a balance calculation model of a recycling reduction system according to a comparative example. FIG8 is a graph showing the reduction state in the model (comparative example) of FIG7. FIG9 is a graph showing the change in the heat absorption in the reduction furnace relative to the number of cycles in Invention Example 1, Invention Example 2 and the comparative example. FIG10 is a graph showing the change in the heat absorption in the reduction furnace in the FeO reduction zone relative to the amount of hydrogen in the hydrogenation gas in Invention Example 1, Invention Example 2 and the comparative example. FIG11 is a schematic diagram showing the structure of the experimental cyclic reduction system based on Invention Example 3. FIG12 is a schematic diagram showing the structure of the experimental cyclic reduction system based on Invention Example 4.

10: Reduction furnace

12: stove top

14: Wind outlet

20: First dehumidifier/dehumidifier

30: Hydrogen supply device/hydrogen piping

40: Catalyst device (reversing reformer)/tube furnace

42: Reaction room

44: Heating device

50: Second dehumidifier/dehumidifier

60: Gas heating device

81: First piping

81A, 81B, 82A, 82B, 82C: piping

82: Second piping

83: Third piping

84: Fourth pipe

85: Fifth pipe

86: Sixth pipe

84A, 86A: Upstream part

84B, 86B: Downstream part

87: Seventh pipe

90: Switching valve

100: Circulating reduction system/circulating smelting furnace

Claims (15)

A circulating reduction system comprises: a reduction furnace for reducing oxides contained therein; a first pipe for recovering exhaust gas containing _CO2 generated in the reduction furnace from the reduction furnace and passing the exhaust gas; a hydrogen supply device connected to the middle of the first pipe for adding hydrogen to the exhaust gas to produce hydrogenated gas; a catalyst device connected to the end of the first pipe and having a reaction chamber for containing a catalyst for a reverse water gas shift reaction, so that the hydrogenated gas introduced into the reaction chamber from the first pipe contacts the catalyst, and CO2 in the hydrogenated gas is reduced by the reverse water gas shift reaction. ₂ is converted into CO, thereby producing a CO-rich gas with an increased CO concentration; and a second pipe extending from the catalyst device and connected to the reduction furnace, allowing the CO-rich gas to pass through, and supplying the CO-rich gas to the interior of the reduction furnace as a reducing gas, and no separation device is arranged in the middle of the first pipe and the second pipe, and the separation device separates specific gas components other than water vapor from the gas passing through the interior and recovers or removes them. The circulation reduction system as described in claim 1 has a gas heating device, which is arranged in the middle of the second pipe to heat the CO-rich gas. The circulating reduction system as described in claim 2 has a third pipe, which branches from the middle of the second pipe and is further upstream than the gas heating device and is connected to the gas heating device, and a portion of the CO-rich gas is supplied to the gas heating device as combustion gas through the third pipe. The circulation reduction system as described in claim 2 or 3 has a fourth pipe, which extends from the gas heating device and is connected to the middle of the first pipe, so that the combustion exhaust gas generated from the gas heating device and the exhaust gas in the first pipe are combined through the fourth pipe. A circulation reduction system as described in any one of claims 1 to 3, wherein the catalyst device has a heating device for heating the reaction chamber, and the circulation reduction system has a fifth pipe, the fifth pipe is 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 through the fifth pipe. The circulation reduction system as described in claim 5 includes a sixth pipe extending from the heating device and connected to the middle of the first pipe, and the combustion exhaust gas generated from the heating device is merged with the exhaust gas in the first pipe through the sixth pipe. The circulation reduction system as described in any one of claims 1 to 3 has a first dehumidifier, which is arranged in the middle of the first pipe and upstream of the position connected to the hydrogen supply device, and removes water vapor from the exhaust gas. The recycling reduction system as described in any one of claims 1 to 3 has a second dehumidifier, which is arranged in the middle of the second pipe and removes water vapor from the CO-rich gas. The circulation reduction system as described in any one of claims 1 to 3 comprises: a switching valve disposed in the middle of the second piping; and a seventh piping extending from the switching valve, and recovering a portion of the CO-rich gas through the seventh piping. The circulation reduction system as described in claim 9 has a third dehumidifier, which is arranged in the middle of the seventh pipe and removes water vapor from the CO-rich gas passing through the seventh pipe. A circulating reduction system as described in any one of claims 1 to 3, wherein the reduction furnace is a smelting furnace and the oxide is iron ore. A circulating reduction system as described in claim 11, wherein the smelting furnace is a blast furnace. A method for reducing iron ore, using the circulating reduction system as described in any one of claims 1 to 12, wherein the CO-rich gas obtained by reforming the exhaust gas is circulated as the reducing gas to reduce the iron ore as the oxide. A method for operating a smelting furnace using a circulating reduction system as described in claim 11 or 12, wherein: (I) at least one of sintered ore, lump ore, iron ore pellets and powdered ore as the iron ore, and (II) crushed slag obtained by crushing solidified slag obtained by slowly cooling molten slag discharged from the bottom of the smelting furnace, or a ventilation material containing a mixture of the crushed slag and coke are alternately loaded into the smelting furnace in layers from the top of the smelting furnace, thereby ensuring the in-furnace permeability of the reducing gas. A method for operating a melting furnace as described in claim 14, wherein the reducing gas and air are supplied as injection gas to the interior of the melting furnace from a tuyere located at the bottom of the melting furnace, so that the ratio of the crushed slag to the coke in the ventilation material and the ratio of the reducing gas to the air in the injection gas are increased in stages, so as to gradually suppress the use of the coke.

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