CN119487216A

CN119487216A - Circulation type reduction system, iron ore reduction method and smelting furnace operation method

Info

Publication number: CN119487216A
Application number: CN202380053527.8A
Authority: CN
Inventors: 野吕寿人; 濑川浩司; 久保贵哉
Original assignee: Jiefuyi Mineral Alloy Co ltd
Current assignee: Jiefuyi Mineral Alloy Co ltd
Priority date: 2022-08-30
Filing date: 2023-08-24
Publication date: 2025-02-18
Also published as: TW202426662A; WO2024048423A1; EP4509617A4; KR20250004321A; EP4509617A1; TWI886552B; JPWO2024048423A1; JP7669596B2

Abstract

The present invention provides a circulation type reduction system, which can efficiently recycle the CO-rich gas obtained by reforming the exhaust gas containing _CO2 generated from the reduction furnace as a reducing gas. In the circulation type reduction system (100) of the present invention, the exhaust gas containing _CO2 generated in the reduction furnace (10) is recovered via the first pipeline (81), and hydrogen is added to the exhaust gas from the hydrogen supply device (30) to produce a hydrogenated gas. In the catalyst device (40), 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 CO-rich gas is supplied to the interior of the reduction furnace (10) as a reducing gas via the second pipeline (82). In the middle of the first pipeline (81) and the second pipeline (82), a separation device for separating, recovering or removing specific gas components other than water vapor from the gas passing through the interior is not configured.

Description

Circulation type reduction system, reduction method of iron ore, and operation method of melting furnace

Technical Field

The present invention relates to a cyclic reduction system, a reduction method of iron ore, and an operation method of a smelting furnace capable of fundamentally reducing the amount of CO ₂ discharged to promote global warming.

Background

In the case of reducing the emission amount of CO ₂ which contributes to global warming, the steel industry in japan, which is about 15% of the emission amount of CO ₂ in japan, has been declared to realize carbon neutralization in 2050 according to government guidelines. In order to achieve this, it is necessary to develop a reduction process and a reduction furnace for producing iron ore of coarse steel at low cost close to the existing level, but the technical object is hardly established in the current state.

Here, a hydrogen reduction process using hydrogen as a reducing agent for iron ores has been attracting worldwide attention as an ideal technology for producing coarse steel that does not generate CO ₂. However, when it is intended to maintain a domestic production of about 7500 ten thousand tons of molten iron per year in this way, about 750 hundred million Nm ³ of hydrogen are required. In order to supply about 750 million Nm ³ of hydrogen as described above using water electrolysis as a representative green hydrogen production method, it is estimated that 0.34 megaWh of electric power is required each year even if electric power required for transportation, liquefaction, storage, and the like of hydrogen is completely ignored. Given that even if the problem of high power costs can be solved, it is extremely impractical to supply so much power to blast furnace steelworks in japan, where the annual power consumption is on the scale of 1 megakwh.

On the other hand, various attempts to supply a large amount of hydrogen produced using inexpensive renewable energy from overseas have been advanced. However, even if the problem of high transportation costs can be solved, the technical objective of safely storing a large amount of hydrogen in a wide explosive concentration range around a steel plant has not been established at all.

However, the steel industry in japan has discharged CO ₂ of about 15% of the amount of CO ₂ discharged in japan because the blast furnace-converter method that uses coke to reduce iron ore is mainly used to produce high-grade steel. The production method of the crude steel is largely classified into a blast furnace-converter method in which about 2t of CO ₂ is produced per 1t of steel and an electric furnace method in which about 0.5t of CO ₂ is produced per 1t of steel. The electric furnace method is more excellent in that the amount of CO ₂ generated can be suppressed. However, since the quality of the high-grade steel used in automobiles and the like is easily adversely affected by impurities such as copper, the high-grade steel cannot be mass-produced in an electric furnace method using scrap as a raw material. Thus, about 75% of the raw steel in japan is produced by the blast furnace-converter method.

For a blast furnace with a particularly large amount of CO ₂, for example, patent document 1 discloses an attempt to reduce the amount of coke used by replacing high-temperature air blown from a tuyere with a reducing gas such as hydrogen or methane. However, coke has a function as a reducing agent, a function as a heating material for heating the inside of the furnace by reaction with oxygen blown from the hot blast stove, and a function as a ventilation material for ensuring ventilation of the inside of the furnace. Therefore, it is extremely difficult to fundamentally suppress the amount of coke used before finding a new method (other than coke) for maintaining the temperature in the furnace without adversely affecting the quality of molten iron and also ensuring air permeability.

In view of the above background, the current situation of the steel manufacturer in japan is that the number of blast furnaces can be reduced and the ratio of electric furnaces can be increased to cope with the current situation. Therefore, the demand for waste materials for electric furnaces has become vigorous, and the vigorous competition for the supply is expected to become more serious in the future.

In this case, a direct reduction process with a small emission of CO ₂ as compared with the blast furnace-converter method has received attention worldwide. In a typical direct reduction process, the so-called Midrex (Midrex) process, iron ore is reduced by modifying natural gas while maintaining a solid phase state, and direct reduced iron (DRI: direct Reduced Iron) can be obtained (see reference 2). Since only sponge-like DRI can be produced in the initial midelax process, handling and transportation thereof are considered to be difficult from the viewpoint of oxidation and ignition. However, after the hot briquette (hot briquette) apparatus has been developed and industrialized, these problems have been basically solved, and the worldwide trend of increasing the quality of steel products has been expanding by mixing DRI into waste and charging it into an electric furnace to reduce the amount of waste charged. Further, attempts have been made to replace natural gas with methane synthesized from CO ₂ and hydrogen by methanation reaction (CO ₂+4H₂→4H₄+2H₂ O) or with hydrogen itself.

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

Further, in the direct reduction process, since the crude steel cannot be taken out as molten iron, it is impossible to use refining facilities of the existing steel integrated process such as a pretreatment furnace and a converter. This is also one reason why blast furnace manufacturers in japan have performed the blast furnace process. It is also assumed that the direct reduction process remains on the solid phase reduction because the problems of gas permeability and maintenance of the furnace temperature for obtaining molten iron cannot be fundamentally solved as described above.

That is, in the blast furnace-converter method, a new method capable of replacing the reducing agent and the heating material of the coke and ensuring the air permeability without adversely affecting the quality of the molten iron has become a major limitation, and the objective of fundamentally reducing the amount of the coke to be used has not been established. Further, the direct reduction process having a smaller amount of CO ₂ emissions than the blast furnace-converter method has a disadvantage in that low-cost and easily available low-grade fine ore or fine ore which can be used in the blast furnace cannot be used, and crude steel cannot be taken out as molten iron, so that conventional refining facilities for the integrated iron and steel process cannot be used.

Against such a background, patent document 3 proposes a technique of using CO ₂ contained in exhaust gas from a blast furnace. That is, it has been proposed to separate CO ₂ from the exhaust gas of a blast furnace, reform the recovered CO ₂ into CO, and reuse the CO as a reducing agent for the blast furnace.

Prior art literature

Patent literature

Patent document 1, international publication No. 2021/220555;

patent document 2, japanese patent application laid-open No. 2017-88912;

Patent document 3 Japanese patent application laid-open No. 2011-225968.

Disclosure of Invention

Problems to be solved by the invention

In the technique described in patent document 3, CO ₂ separated and recovered from the exhaust gas generated in the blast furnace is reformed into CO and reused, and as a result, the amount of CO ₂ generated can be suppressed. However, in this technique, since the CO ₂ is reformed by a plurality of steps of once separating and recovering CO ₂ from the exhaust gas, the reduction in the recycling efficiency of the reducing component in the exhaust gas and the burden of the costs required for the facilities, operation, and maintenance of each step cannot be avoided. Therefore, it is desired to recycle the reducing components in the exhaust gas of a reduction furnace such as a blast furnace by using a more efficient method.

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

Further, an object of the present invention is to provide a method for reducing iron ore, which is capable of efficiently recycling CO-rich gas obtained by reforming exhaust gas containing CO ₂ generated from a reduction furnace as a reducing gas and performing reduction treatment of iron ore.

Further, an object of the present invention is to provide a method of operating a melting furnace capable of maintaining an in-furnace temperature using the above-described circulating reduction system and securing gas permeability by a method other than coke.

Solution for solving the problem

The present inventors have conducted intensive studies on a method for realizing a reduction process capable of recycling an exhaust gas from a reduction furnace as a starting material of a reducing agent, and have found that the recycling of the exhaust gas can be efficiently realized by using a so-called reverse water gas shift reaction.

That is, the exhaust gas generated in the reduction process of iron ore generally contains an excessive reducing agent such as CO, H ₂, and the like in addition to CO ₂ and nitrogen from the atmosphere. For example, the exhaust gas of the blast furnace contains about 23% by volume of CO ₂, the same ratio of CO, about 4% by volume of H ₂, and about 50% by volume of nitrogen from air. The inventors have conceived that by adding hydrogen to such an exhaust gas, the gas is brought into contact with a catalyst for the reverse water gas shift reaction (RWGS: REVERSE WATER GAS SHIFT reaction: CO ₂+H₂→CO+H₂ O), whereby the equilibrium of CO ₂ and CO in the exhaust gas is largely converted into rich CO, and then recycled as a reducing gas together with H ₂ and nitrogen originally contained in the exhaust gas. It has been found that if this recycling is possible, the amount of reducing agent conventionally used, for example, from fossil fuels such as coke, can be limited to a minimum.

Here, the reason why CO is recycled as the main reducing agent is that the reduction reaction of iron ore using H ₂ is an endothermic reaction, and the reduction reaction of iron ore using CO is an exothermic reaction, so CO is the most efficient reducing agent capable of maintaining the inside of the reduction furnace at a high temperature. In addition, in the reduction with CO, the freezing point depression of iron due to carbon, which is exhibited when coke is used as a reducing agent, can be directly utilized. Thus, in the case of reduction with H ₂, if not at 1500 ℃ or higher, the reduced iron that does not melt melts at around 1200 ℃ in the reduction with CO. The presence of the temperature difference of about 300C greatly reduces the heat load of the heating furnace for the reduced iron as the reducing gas at the time of withdrawing the molten iron.

In addition, although the CO-rich reducing gas synthesized from the CO ₂ -rich exhaust gas is mainly supplied to the reduction furnace, the surplus can be discharged, recovered, and reused for various purposes. In addition to its use as a reducing agent or fuel gas, CO is also an important starting material for the fischer-tropsch reaction (nco+ (2n+1) H ₂→n_nH_2n+2+nH₂ O) in the synthesis of various organic compounds. Therefore, the CO-rich reducing gas synthesized from the CO ₂ -rich exhaust gas is not limited to use as a reducing agent, and is a synthesis gas that can be converted into a fuel gas or a raw material of various organic compounds without surplus. In particular, if the amount of fossil fuel used is greatly reduced in order to prevent global warming, the organic chemical industry using this as a raw material has been required to search for suppliers of raw materials again. These industries are significant as acceptors of the above-mentioned synthesis gas.

As described above, the coke charged into a normal blast furnace has functions as a heating material and a ventilation material in addition to the reducing agent. Therefore, in the case of taking out the reduced iron as molten iron, even if the temperature in the furnace can be maintained by the reduction heat of CO in the reducing gas, the gas permeability cannot be ensured (stable reducing environment cannot be maintained) when the amount of coke charged is suppressed to the limit.

It has been found that this problem can be solved by slowly cooling and crushing a part of the molten slag generated together with the molten iron and discharged from the hearth by a mold, mixing the slag into coke as a gas permeable material, and re-charging the coke from the roof. That is, since the melting point of the blast furnace slag is about 1400 ℃, the slag remains in a solid state even when iron, which has a freezing point drop due to carbon in the blast furnace, starts to melt, and functions as a ventilation material. Further, since the slag is originally a substance generated in the melting furnace, the environment of the substance in the melting furnace is not changed even if it is recycled.

In addition, it is not easy to start the operation of the melting furnace by using only the slowly cooled and crushed slag as a gas permeable material and only the reducing gas as a reducing agent. Accordingly, similarly to a normal blast furnace, after coke and iron sources of a reducing agent and a permeable material are alternately stacked in the blast furnace, the ore furnace is first started in a "blast furnace mode" in which high-temperature air heated in the hot blast stove is blown in. On this basis, the slag is gradually mixed into the coke, and the mode is switched to a "coke-free mode" in which the reducing gas is gradually added to the air blown into the melting furnace in stages. In the case of stopping the ore smelting furnace, if the operation is ended in the blast furnace mode after the coke-free mode in the reverse step, it becomes easy to restart.

The present invention has been completed based on the above findings, and its gist is as follows.

[1] A cyclical recovery system, having:

a reduction furnace that reduces an oxide contained therein;

a first pipeline for recovering and passing the exhaust gas containing CO ₂ generated in the reduction furnace from the reduction furnace;

A hydrogen supply device connected to a middle of the first pipeline, and configured to add hydrogen to the exhaust gas to produce a hydrogenated gas;

A catalyst device having a reaction chamber connected to the end of the first pipe and containing a catalyst for a reverse water gas shift reaction, wherein the hydrogenation gas introduced into the reaction chamber from the first pipe contacts the catalyst to convert CO ₂ in the hydrogenation gas into CO by the reverse water gas shift reaction to produce a CO-rich gas having an increased CO concentration, and

A second line extending from the catalyst device and connected to the reduction furnace, through which the CO-rich gas passes, and supplying the CO-rich gas as a reducing gas into the reduction furnace,

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 pipeline and the second pipeline.

[2] The cyclic reduction system according to the above [1], wherein,

The above-mentioned cyclic reduction system has:

And a gas heating device disposed in the middle of the second pipeline for heating the CO-rich gas.

[3] The cyclic reduction system according to the above [2], wherein,

The above-mentioned cyclic reduction system has:

a third pipe which branches from a position upstream of the gas heating device in the middle of the second pipe and is connected to the gas heating device,

And supplying a part of the CO-rich gas as combustion gas to the gas heating device via the third pipeline.

[4] The cyclic reduction system according to the above [2] or [3], wherein,

The above-mentioned cyclic reduction system has:

A fourth pipeline extending from the gas heating device and connected to the middle of the first pipeline,

And a fourth pipe line for merging the combustion exhaust gas generated from the gas heating device with the exhaust gas in the first pipe line.

[5] The cyclic reduction system according to any one of the above [1] to [4], wherein,

The catalyst device is provided with a heating device for heating the reaction chamber,

The above-mentioned cyclic reduction system has:

a fifth pipeline which is branched from the second pipeline and is connected with the heating device,

A part of the CO-rich gas is supplied as combustion gas to the heating device via the fifth pipeline.

[6] The cyclic reduction system according to the above [5], wherein,

The above-mentioned cyclic reduction system has:

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

And a sixth pipe line through which the combustion exhaust gas generated by the heating device is merged with the exhaust gas in the first pipe line.

[7] The cyclic reduction system according to any one of the above [1] to [6], wherein,

The above-mentioned cyclic reduction system has:

And a first dehumidifier that is disposed upstream of a portion to which the hydrogen gas supply device is connected, in the middle of the first pipe, and that removes water vapor from the exhaust gas.

[8] The cyclic reduction system according to any one of the above [1] to [7], wherein,

The above-mentioned cyclic reduction system has:

And a second dehumidifier that is disposed in the middle of the second pipeline and removes water vapor from the CO-rich gas.

[9] The cyclic reduction system according to any one of the above [1] to [8], wherein,

The above-mentioned cyclic reduction system has:

a switching valve disposed in the middle of the second pipeline, and

A seventh pipe extending from the switching valve,

A portion of the CO-rich gas is recovered via the seventh line.

[10] The cyclic reduction system according to the above [9], wherein,

The above-mentioned cyclic reduction system has:

And a third dehumidifier that is disposed in the seventh pipeline and removes water vapor from the CO-rich gas passing through the seventh pipeline.

[11] The cyclic reduction system according to any one of the above [1] to [10], wherein the reduction furnace is a fused ore furnace and the oxide is iron ore.

[12] The cyclic reduction system according to [11], wherein the ore smelting furnace is a blast furnace.

[13] A method for reducing iron ore, wherein the recycle type reduction system according to any one of [1] to [12] is used to recycle the CO-rich gas obtained by reforming the exhaust gas as the reducing gas and to perform reduction treatment of iron ore as the oxide.

[14] A method of operating a melting furnace using the cyclic reduction system of [11] or [12],

The method comprises alternately charging (I) at least one selected from the group consisting of sintered ore, lump ore, iron ore pellets and fine ore as the iron ore and (II) a gas permeable material, which is formed of crushed slag obtained by crushing solidified slag obtained by slowly cooling molten slag discharged from the bottom of the ore furnace, into the ore furnace from the top of the ore furnace in a layered state to ensure the gas permeability of the reducing gas in the furnace.

[15] The method of operating a melting furnace according to item [14], wherein the reducing gas and air are supplied as blowing gas into the melting furnace from a tuyere located at a lower portion of the melting furnace,

The proportion of the broken slag to the coke in the gas permeable material and the proportion of the reducing gas to the air in the blowing gas are increased in stages, and the amount of the coke used is suppressed in stages.

Effects of the invention

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

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

According to the operation method of the ore smelting furnace of the present invention, it is possible to maintain the temperature inside the furnace using the above-described circulating type reduction system and secure the gas permeability by a method other than coke.

Drawings

Fig. 1 is a schematic diagram showing the structure of a cyclic reduction system 100 according to an embodiment of the present invention.

Fig. 2 is a schematic diagram showing the structure of a cyclic reduction system 200 according to another embodiment of the present invention.

Fig. 3 is a schematic diagram showing a balance calculation model of the cyclic reduction system of invention example 1.

Fig. 4 is a graph showing the reduction condition in the model of fig. 3 (invention example 1).

Fig. 5 is a schematic diagram showing a balance calculation model of the cyclic reduction system of invention example 2.

Fig. 6 is a graph showing the reduction condition in the model of fig. 5 (invention example 2).

Fig. 7 is a schematic diagram showing a balance calculation model of the cyclic reduction system of the comparative example.

Fig. 8 is a graph showing the reduction in the model of fig. 7 (comparative example).

Fig. 9 is a graph showing the change in the amount of heat absorbed in the reduction furnace with respect to the number of cycles in examples 1 and 2 and comparative example.

Fig. 10 is a graph showing the change 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 examples 1 and 2 and comparative example.

FIG. 11 is a schematic diagram showing the structure of the experimental recycle type reduction system of invention example 3.

FIG. 12 is a schematic diagram showing the structure of the experimental recycle type reduction system of invention example 4.

Detailed Description

[ Circulation type reduction System ]

Referring to fig. 1, a cyclic reduction system 100 according to an embodiment of the present invention is described. The circulation type reduction system 100 includes the reduction furnace 10, the first dehumidifier 20, the hydrogen gas supply device 30, the catalyst device 40, the second dehumidifier 50, and the gas heating device 60, and includes, as piping devices, 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 a blast furnace or the like, for example. When the reduction furnace 10 is a fused ore furnace, iron ore and coke are charged into the reduction furnace 10 from the furnace roof 12, and a high-temperature reducing gas is blown into the reduction furnace 10 from the tuyere 14 located at the lower portion of the reduction furnace 10, whereby the reduction of the iron ore is performed in the reduction furnace 10.

The first line 81 is a line device for recovering and passing the exhaust gas containing CO ₂ generated in the reduction furnace 10 from the reduction furnace 10. The first pipe 81 has a start end connected to the reduction furnace 10 (in one example, the furnace roof 12) and an end connected to the catalyst device 40. The hydrogen gas supply device 30 is connected to the middle of the first pipe 81. Further, the first dehumidifier 20 is disposed in the middle of the first pipe 81 upstream of the portion to which the hydrogen gas supply device 30 is connected. The first pipe 81 has a pipe 81A extending from the reduction furnace 10 and connected to the first dehumidifier 20 and a pipe 81B extending from the first dehumidifier 20 and connected to the catalyst device 40. In the present specification, "upstream" or "downstream" with respect to a pipe means a direction in which gas flows in the pipe.

While the exhaust gas discharged from the furnace roof 12 of the reduction furnace 10 flows through the first pipe 81, the first dehumidifier 20 performs a dehumidification process, and then hydrogen (H ₂) gas is supplied from the hydrogen gas supply device 30 to become a hydrogenation 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 includes, in addition to steam, 13 to 24% by volume of CO ₂, 21 to 31% by volume of CO, and 3 to 15% by volume of H ₂, with the remainder being composed of N ₂ derived from air. The composition of the hydrogenation gas is not particularly limited, and typically has a composition containing, in addition to steam, 13 to 24% by volume of CO ₂, 21 to 31% by volume of CO, and 10 to 30% by volume of H ₂, the remainder being composed of N ₂ derived from air. The hydrogen supplied from the hydrogen supply device 30 is preferably green hydrogen obtained by electrolysis using renewable energy, but by applying the cyclic reduction system of the present invention in the blast furnace operation, hydrogen purified from coke oven gas can be substituted before the amount of coke used becomes zero.

Further, it is preferable that a dust removing device (not shown) is provided in the middle of the first pipe 81 upstream of the first dehumidifier 20 or downstream of the first dehumidifier 20 and upstream of the portion to which the hydrogen supply device 30 is connected, and dust from the raw material is removed from the exhaust gas by performing dust removing treatment on the exhaust gas.

The catalyst device (inverse reforming type reformer) 40 has a reaction chamber 42 connected to the end of the first pipe 81 and containing a catalyst for the inverse water gas shift reaction, and a heating device 44 for heating the reaction chamber 42. In the catalyst device 40, the hydrogenation gas introduced from the first pipe 81 into the reaction chamber 42 contacts the catalyst, and CO ₂ in the hydrogenation gas is converted into CO by the reverse water gas shift reaction, thereby becoming 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 a composition containing 6 to 20% by volume of CO ₂, 24 to 40% by volume of CO, and 5 to 24% by volume of H ₂ in addition to water vapor, and the remainder is composed of N ₂ derived from air. A variety of catalysts such as nickel-based catalysts and noble metal-based catalysts are known as catalysts that can be used in the reverse water gas shift reaction, but the catalyst used in the present invention may be any of them.

In the case of bringing the hydrogenation gas into contact with the catalyst in the catalyst device 40, it is preferable to set the temperature of the introduced hydrogenation gas to a high temperature as much as possible in a temperature range where the catalyst is not easily deteriorated, from the viewpoint of conversion efficiency of the reverse water gas shift reaction which is an endothermic reaction. Specifically, the inside of the reaction chamber 42 is preferably heated in advance by the heating device 44 so that the temperature of the reaction gas (hydrogenation gas) around the catalyst is 800 ℃ to 1200 ℃.

The second line 82 is a line device that extends from the catalyst device 40 and is connected to the reduction furnace 10 (tuyere 14 in one example), and that passes the CO-rich gas and supplies the CO-rich gas as the reduction gas (via the tuyere 14 in one example) to the inside of the reduction furnace 10. 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 are preferably disposed in the middle of the second pipeline 82. In this case, the gas heating device 60 is preferably disposed downstream of the second dehumidifier 50. At this time, the second pipe 82 has a pipe 82A extending from the catalyst device 40 and connected to the second dehumidifier 50, a pipe 82B extending from the second dehumidifier 50 and connected to the gas heating device 60, and a pipe 82C extending from the gas heating device 60 and connected to the reduction furnace 10 (tuyere 14 in one example).

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

That is, it is preferable 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 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, but in the case of performing solid-phase reduction of the iron ore, the temperature of the reducing gas blown into the reduction furnace 10 is preferably 900 ℃ or higher. Further, when taking out the reduced iron as molten iron at 1500 ℃, it is necessary to maintain the temperature of the molten zone of the iron source and slag formed in the lower zone of the reduction furnace 10 at 1650 ℃ or higher, and therefore, it is preferable to blow the reducing gas after heating the reducing gas, and if the amount of charged coke reaches about 50% of the conventional blast furnace, the temperature of the reducing gas is set to 1200 ℃ or higher, and if the amount of charged coke is lower than 20% of the conventional blast furnace, the temperature of the reducing gas is set to 1500 ℃ or higher.

The preferred operation of the gas heating device 60 is as follows. The circulation type reduction system 100 of the present embodiment preferably includes a third pipe 83, and the third pipe 83 is branched from a position upstream of the gas heating device 60 and downstream of the second dehumidifier 50 in the middle of the second pipe 82 and connected to the gas heating device 60. Further, it is preferable that a part of the CO-rich gas flowing through the second pipe 82 is supplied as the combustion gas to the gas heating device 60 via the third pipe 83. In this way, by burning a part of the CO-rich gas as the fuel gas in the gas heating device 60, the temperature of the reducing gas can be raised to the above-described 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 (without containing unconsumed nitrogen) oxygen.

The circulation type reduction system 100 preferably has a fourth pipe 84, and the fourth pipe 84 extends from the gas heating device 60 and is connected to the middle of the first pipe 81. Further, it is preferable that the combustion exhaust gas generated from the gas heating device 60 is merged with the exhaust gas in the first pipe 81 via 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 caused to flow into (1) the reducing gas line between the catalyst device 40 and the gas heating device 60 and (2) the hydrogenation gas line between the hydrogen gas supply device 30 and the catalyst device 40, and then merged with the exhaust gas in the first line 81 upstream of the first dehumidifier 20, the reducing gas and the hydrogenation gas can also be preheated.

In addition, as shown in fig. 1, when the reducing gas cannot be completely increased to a desired temperature by the indirectly heated gas heating device 60, oxygen or the like may be added from the vicinity of the tip of the gas heating device 60 to directly combust a part of CO or H ₂ contained in the reducing gas. In addition, when the blast furnace mode is started, if air enriched with oxygen by a cryogenic separation method or the like is used for hot air blown into the reduction furnace 10, the heat load of the gas heating device 60 taken away by heating of nitrogen is reduced, and therefore the temperature of the reducing gas is easily increased.

Next, for the preferred operation of the catalyst device 40, it is also preferable to use a part of the CO-rich gas as the combustion gas. That is, the circulation-type reduction system 100 of the present embodiment preferably has a fifth pipe 85, and the fifth pipe 85 is branched from the second pipe 82 and connected to the heater 44 of the catalyst device 40. The fifth conduit 85 is preferably branched from a position upstream of the gas heating device 60 and downstream of the second dehumidifier 50 midway in the second conduit 82. Further, it is preferable that a part of the CO-rich gas is supplied as the combustion gas to the heating device 44 via the fifth line 85. Although omitted in fig. 1, the oxygen-containing gas supplied to the heating device 44 for burning the combustion gas is preferably (without containing unconsumed nitrogen) oxygen.

The circulation type reduction system 100 preferably has a sixth pipe 86, and the sixth pipe 86 extends from the heating device 44 and is connected to the middle of the first pipe 81. Further, it is preferable that the combustion exhaust gas generated from the heating device 44 and the exhaust gas in the first pipe 81 are merged and reused via the sixth pipe 86. 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 off-gas flow path from the gas heating device 60, the downstream portion 86B of the sixth pipe 86 doubles as the downstream portion 84B of the fourth pipe 84. However, the present invention is not limited thereto, and 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 line between the hydrogen supply device 30 and the catalyst device 40 and then merges with the exhaust gas in the first line 81 upstream of the first dehumidifier 20, the hydrogenation gas can also be preheated.

In the present embodiment described above, the cycle process in which the reduction step of blowing the iron ore with the reducing gas, the recovery step of the off-gas from the reduction furnace, the dust removal and dehumidification step (any step) of the off-gas, the hydrogen addition step to the off-gas, the step of generating the CO-rich gas from the hydrogenation gas by the reverse water gas shift reaction, the dehumidification step (any step) of the CO-rich gas, the heating step (any step) of the CO-rich gas, and the blowing step of the CO-rich gas as the reducing gas are repeated is realized, and the off-gas from the reduction furnace 10 is reused in the closed cycle system.

Unconverted CO ₂ remaining in the CO-rich gas as the reducing gas will be a source of CO during the recycle process early and late and thus does not need to be separated from the reducing gas. That is, in the present embodiment, it is important that 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 midway between the first pipe 81 and the second pipe 82. In this embodiment, since a new separation and concentration process is not required, besides the dust removal and dehumidification of the related art can be applied, the recycling efficiency of the reducing gas is high.

In this embodiment, since the reverse water gas shift reaction in which CO ₂ is converted into CO with equimolar hydrogen is used, the supply amount of hydrogen per CO ₂ can be suppressed to about 1/4 as compared with the above-described conventional reduction method in which methane generated by the methanation reaction requiring 4 times the molar amount of hydrogen of CO ₂ is used as a reducing agent.

In the present embodiment, since the reducing gas mainly composed of CO modified from the exhaust gas can be supplied into the reduction furnace 10 at a high temperature and impurities in the iron ore can be separated from the molten iron as molten slag, low-grade fine ore and fine ore, which are advantageous in terms of cost and easy to supply, can be formed into pellets and sintered ore in the same manner as a normal blast furnace.

In addition, an excess portion of the CO-rich gas (in the present embodiment, the excess 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 includes the switching valve 90 disposed in the middle of the second pipeline 82 and the seventh pipeline 87 extending from the switching valve 90, and can recover a part of the CO-rich gas through the seventh pipeline 87. The recovered CO-rich gas can be used, for example, as synthesis gas as a feedstock for organic compounds. In the present embodiment, since the system for converting the CO ₂ -rich exhaust gas discharged from the reduction furnace 10 into the CO-rich reducing gas and recycling the same is realized, the excess CO-rich gas can be effectively utilized as the synthesis gas in the organic chemical industry or the like, whereby the CO ₂ emission amount to the atmosphere can be suppressed to zero level.

The molten slag separated from the molten iron is slowly cooled by a mold to form solidified slag, and the solidified slag is crushed to form crushed slag, which can be reused as a gas permeable material. When a part of pig iron discharged from a reduction furnace (a ore smelting furnace) adheres to a permeable material derived from the slag, the pig iron can be returned to the reduction furnace as an iron source via the permeable material.

Further, since the molten slag is automatically discharged to the surface of the molten iron due to the difference in specific gravity, there is little adverse effect on the quality of the molten iron even if it is recycled. In addition, the recycled molten slag has the same quality as normal blast furnace slag, and thus can be industrially used as a raw material for blast furnace cement and the like.

Referring to fig. 2, a cyclic reduction system 200 according to another embodiment of the present invention is illustrated. 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 disposed in the middle of the seventh pipe 87. That is, in the present invention, the second dehumidifier 50 is not an essential structure. In the case where the second dehumidifier 50 is not provided, it is preferable to remove water vapor from the CO-rich gas passing through the seventh line 87 by the third dehumidifier 70.

The above description mainly describes the case where the reduction furnace 10 is a blast furnace or other ore melting furnace and the reduction target is iron ore, but the present invention is not limited thereto. The reduction furnace 10 may be a solid reduction furnace. The object to be reduced is not limited to iron ore as long as it is an oxide, and may be manganese ore as a raw material of ferromanganese or manganese silicon, for example.

[ Method for reducing iron ore ]

The method for reducing iron ore according to one embodiment of the present invention uses the above-described cyclic reduction systems 100 and 200 to recycle CO-rich gas obtained by reforming exhaust gas as a reducing gas and perform reduction treatment of iron ore as an oxide. This enables efficient recycling of the CO-rich gas obtained by reforming the exhaust gas containing CO ₂ generated from the reduction furnace 10 as the reducing gas, and reduction treatment of the iron ore.

Further, according to the reduction method of the present 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 CO ₂ generation amount can be significantly reduced. Further, the amount of the reducing agent added from fossil fuels such as coke, which have been conventionally used in the reduction process of iron ore, can be fundamentally suppressed.

[ Method of operating Ore melting furnace ]

The operation method of the ore smelting furnace according to an embodiment of the present invention is performed using the above-described circulating reduction systems 100 and 200. It is important that (I) at least one kind (iron source) selected from the group consisting of sintered ore, lump ore, iron ore pellets and fine ore as iron ore and (II) a gas permeable material consisting of crushed slag obtained by crushing solidified slag obtained by slowly cooling molten slag discharged from the bottom of the ore furnace are alternately charged into the ore furnace in layers from the top of the reduction furnace (ore furnace) 10 to ensure the gas permeability in the furnace of the reducing gas, or a mixture of the crushed slag and coke. Thus, the circulating reduction systems 100 and 200 can be used to maintain the temperature in the furnace and ensure the gas permeability by a method other than coke.

In the operation of the present embodiment, the reducing gas and air are supplied as the blowing gas from the tuyere 14 to the inside of the ore furnace. In this case, it is preferable to increase the ratio of the broken slag to the coke in the gas permeable material and the ratio of the reducing gas to the air in the blown gas in stages, and to suppress the amount of the coke used in stages.

According to the operation method of the melting furnace of the present embodiment, reduced iron can be obtained as molten iron using low-grade fine ore and fine ore which are easily supplied at low cost, and therefore, the conventional steel integrated process can be directly transferred after the subsequent steps.

The ventilation degree of the melting furnace can be adjusted by crushing the grain size of the slag, for example, if casting is in a form of adding ventilation ports to the slow-cooling slag, it becomes easier to ensure ventilation. In addition, there is no particular problem in using normal blast furnace slag for the ventilation material.

In the method of operating the melting furnace according to the present embodiment, the amount of molten slag generated in the circulating reduction systems 100 and 200 is larger than that of a normal blast furnace by the amount of remelted slag after the slag newly charged from the furnace roof 12 enters the reflow zone. In addition, when the amount of slag to be charged increases, the amount of heat taken away as the heat of fusion of the slag increases. Therefore, when the operation is started in the blast furnace mode, the layer thickness ratio of the iron source layer and the ventilation layer is preferably adjusted in advance so as to be richer in the iron source layer than in a usual blast furnace.

Examples

Example 1

As described below, as inventive examples 1,2 and comparative example, balance calculation for confirming the effect of the reduction method of the present invention was performed.

(Inventive example 1)

Fig. 3 shows a model of balance calculation of the cyclic reduction system of invention example 1. As an initial state, a state was assumed in which the reduction furnace 10 containing 25 moles of iron (III) oxide (Fe ₂O₃) was connected to an inverse reforming type reformer (hereinafter simply referred to as "reformer 40") as the catalyst device 40 containing 100 moles of a mixed gas consisting of 22 moles of CO, ₂:22.8 moles of CO, 4.2 moles of H ₂:4.2 moles, and 51 moles of N ₂:51, which corresponds to a blast furnace off 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 for maintaining the number of moles of H ₂ in the reformer at 22.8 moles (corresponding to the concentration of CO ₂ in the blast furnace off-gas) is placed between the first dehumidifier and the reformer. When the reduction furnace and the reformer are not fed with and discharged from the hydrogen gas supply device other than the H ₂ and the H ₂ O removed by the first dehumidifier and the second dehumidifier, the total amount of H ₂ O is generated by the consumed H ₂, and therefore, it can be considered that the total number of moles of the mixed gas circulated through 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 were both maintained at 900 ℃. In practice, a gas delivery system is required for gas circulation between the reduction furnace and the reformer, but the energy consumed here is neglected for the sake of confirming the principle. Likewise, the energy consumed for 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 the equilibrium reaction is reached, although it is affected by the performance of the catalyst used.

Here, a cycle process is considered in which all of the reducing gas generated when the hydrogenation gas is in a steady state in the reformer is fed to the reduction furnace, the reducing furnace gas in the steady state in the reduction reaction is taken out as an exhaust gas, and hydrogen is added thereto to a certain level until the hydrogen gas is again changed to a hydrogenation gas, and the cycle is repeated. The equilibrium state of the gas components and the iron source in the reformer and in the reduction furnace occurring in each cycle of sending the reducing gas from the reformer to the reduction furnace was calculated by thermodynamic equilibrium calculation software & thermodynamic database Fact sage8.1 manufactured by the computer research center of the co. The results are shown in FIG. 4. In addition, the compounds produced in the reformer and the reduction furnace also contain methane and the like, but the trace components of 0.005 mol or less are ignored.

In the reduction furnace, reduction of the iron source is performed by CO supplied from the reformer and surplus H ₂ not consumed in the reverse water gas shift reaction. The solid phase of Fe ₂O₃ fed as the iron source was changed to 2-fold mol of FeO (solid phase) in the first cycle, and after the second cycle, feO was gradually reduced to α -Fe (solid phase), and the reduction was completed in the seventh cycle. The main reduction reaction is a reaction from FeO to alpha-Fe, which is consistent with the known findings in blast furnaces. The amount of H ₂ consumed for the reduction of the iron source was 89 moles.

(Inventive example 2)

Fig. 5 shows a model of balance calculation of the cyclic reduction system of invention example 2. The same as the balance calculation model of the circulation type reduction system of the invention example 1 shown in fig. 3, except that the second dehumidifier was not provided on the outlet side of the reformer. The equilibrium state of the gas components and the iron source in the reformer and the reduction furnace was calculated in the same manner as in inventive example 1. The results are shown in FIG. 6.

The solid phase of Fe ₂O₃ fed as the iron source was changed to 2-fold mol of FeO (solid phase) in the first cycle, and after the third cycle, feO was gradually reduced to α -Fe (solid phase), and the reduction was completed in the ninth cycle. The main reduction reaction is a reaction from FeO to alpha-Fe, which is consistent with the known findings in blast furnaces. The amount of H ₂ consumed for the reduction of the iron source was 85 moles.

Comparative example

Fig. 7 shows a model of balance calculation of the cyclic reduction system of the comparative example. Except that the reformer and the second dehumidifier were not provided, the balance calculation model of the circulation type reduction system of the invention example 1 shown in fig. 3 was the same. The equilibrium state of the gas components and the iron source in the reformer and the reduction furnace was calculated in the same manner as in inventive example 1. The results are shown in FIG. 8.

In the reduction furnace of the comparative example, the reduction of the iron source was performed only by the H ₂ directly fed into the reduction furnace from the hydrogen gas supply device. In the first cycle, 25 moles of Fe ₂O₃ (solid phase) charged as the iron source was changed to 8.2 moles of Fe ₃O₄ (solid phase) and 22.5 moles of FeO (solid phase), and after the second cycle, feO was gradually reduced to α -Fe (solid phase), and the reduction was completed in the ninth cycle in the same manner as in example 2. The main reduction reaction was the reaction from FeO to α -Fe, which was the same as that of invention examples 1 and 2. The amount of H ₂ consumed in the reduction of the iron source was 75 moles, which was 10 moles less than that of invention example 2.

(Heat absorption amount in reduction furnace)

The great difference between examples 1 and 2 and comparative example is the heat absorption amount in the reduction furnace. Fig. 9 and 10 show the heat of reaction (heat absorption amount) in the reduction furnace calculated from the heat of reaction of each reaction calculated by the Fact Sage 8.1.

Except for the initial completion of the reaction from Fe ₂O₃ to Fe ₃O₄, the direct reduction of the iron source with H ₂ is an endothermic reaction. In contrast, in the reduction of the iron source using CO and excess H ₂ in inventive example 1, the heat release amount by the CO reduction compensates for the heat release amount by the H ₂ reduction, and thus the total heat release amount can be greatly suppressed (see fig. 9). In addition, in the invention example 2, since the amount of heat released by CO reduction exceeds the amount of heat absorbed by H ₂ reduction in the FeO reduction region, the FeO reduction temperature is spontaneously maintained at a high temperature (see fig. 9). If the iron source input increases, the FeO reduction stage becomes further longer. In general, it is extremely difficult to supply heat from outside the tuyere and the furnace roof to a reduction furnace in which the inside is required to be maintained at a high temperature. Therefore, when considering that the heat of combustion of the coke charged into the reduction furnace is required to compensate for the heat of absorption, the advantages of the present invention are apparent.

It is also predicted from fig. 10 that the amount of H ₂ supplied to the reformer for maximizing the amount of heat released in the FeO reduction zone is the same as the molar amount of CO ₂ in the exhaust gas. Since it is considered that if the supply amount of H ₂ to the reformer is suppressed, the reduction rate is also lowered, the supply amount of H ₂ is actually adjusted according to 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 using a circulating reduction system for experiment was performed.

Inventive example 3

Fig. 11 shows the structure of the cyclic reduction system for experiment of invention example 3. In FIG. 11, a raw material block A, which is obtained by alternately stacking 2.2kg of coke pulverized to about 5mm and 5.0kg of lump ore pulverized to about 3mm, was formed on a tungsten wire mesh that separates the bottom of a BF simulator (hereinafter referred to as "reduction furnace 10") serving as an experimental reduction furnace provided on a weight scale.

Further, a raw material block B was formed on the raw material block A, and the raw material block B was formed by alternately stacking 2.8kg of a material obtained by uniformly mixing about 5mm of crushed blast furnace slag and about 5.0kg of about 3mm of crushed lump ore into 1.1kg of the coke.

The exhaust gas discharged from the top of the furnace passes through the dust removing 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 then is connected to the exhaust gas treatment device on one side and to the nozzle 92 on the lower portion of the reduction furnace via the switching valve 91. The second electric tube furnace 40 is a ceramic electric tube furnace in which a quartz reaction tube containing 51g of platinum catalyst is provided in the center.

Sampling tubes for gas composition analysis are provided at two positions between the first electric tube furnace 40 and the second electric tube furnace 40 and the dehumidifier 50, and connected to a micro gas chromatograph (micro GC). Further, between the dehumidifier 20 and the first electric tube furnace 40, the hydrogen line 30 is connected via a switching valve 93 and a Mass Flow Controller (MFC) 94.

On the side of the lower part of the reduction furnace 10 opposite to the nozzle 92, a nozzle 96 for feeding 2.3% oxygen enriched air via a heat accumulating type gas heating furnace 95 is provided. The flow rate of the air introduced from the nozzle 96 is controlled by a Mass Flow Controller (MFC) 97.

In order to completely treat the exhaust gas remaining in the reduction furnace 10 after the completion of the reduction experiment, a purge nitrogen line was connected between the dehumidifier 20 and the switching valve 93 via the switching valve 98.

First, the switching valve 91 is set on the exhaust gas treatment device side, and the exhaust gas is separated from the reduction furnace 10. On this basis, air heated to 1200 ℃ by MFC97 was introduced into the reduction furnace 10 from the nozzle 96 of the reduction furnace 10 at a flow rate of 17L/min. Both the electric tube furnaces 40 set the internal temperature to 800 ℃ by using Thermocouples (TC) provided around the catalyst.

The typical composition of the exhaust gas generated by reducing the lump ore in the raw material lump a and the mixed gas after passing through the second electric tube furnace 40 (in the case where the inlet side of the first electric tube furnace 40 is not supplemented with hydrogen) is shown in table 1. It was found that after passing through the second electric tube furnace 40, CO increased by 2.7% and CO ₂ and H ₂ decreased by 2.7% respectively by using the reverse water gas shift reaction of excess H ₂ in the exhaust gas.

At the time point when 2.2kg of coke in the raw material block a was consumed as the exhaust gas, the flow rate of the air introduced from the nozzle 96 was changed to 8.5L/min by MFC 97. At the same time, the switching valve 93 was switched to the hydrogen line 30 side, and hydrogen gas was introduced and adjusted by the MFC94 so that the concentration of H ₂ (the same concentration as the concentration of CO ₂ in the initial off-gas) in the mixed gas before entering the first electric tube furnace 40 was 22.8%. In addition, the switching valve 91 is switched to the reduction furnace 10 side, and the reducing gas is introduced from the nozzle 92. Further, the total consumption of coke in the raw material block a was determined based on the weight change of the reduction furnace 10.

In this state, 1.1kg of coke in the raw material block B was completely consumed, and the air introduced from the nozzle 96 was stopped, and 2 electric tube furnaces and 2 gas heating furnaces were stopped. After that, the water temperature in the water jacket was set to 30 ℃, the hydrogen gas was shut off by the switching valve 93, the switching valve 91 was switched to the exhaust gas treatment device side, the switching valve 98 was switched to the nitrogen gas introduction side, and all the exhaust gas remaining in the reduction furnace 10 was discharged to the exhaust gas treatment device. Then, the reduction furnace 10 was disassembled, and the condition in the furnace was confirmed.

The aggregate of 10kg of lump ore, 3.3kg of coke, and 2.8kg of blast furnace slag in the raw material lump A, B was hardly found on the tungsten net. A mixture of ferrite (α -Fe) and cementite (Fe ₃ C) and slag deposited thereon were confirmed at the bottom of the furnace separated by a tungsten net. The mixture was confirmed to be composed of ferrite and cementite by X-ray diffraction. The carbon content in the same mixture measured by the combustion type carbon-sulfur analyzer was about 4.3 mass%, and when the upper and lower portions of the mixture were compared, the carbon content tended to be increased by about 0.3 mass% in the lower portion.

From the above experiments, it was confirmed that, in the reduction step of the raw material block B corresponding to the carbon reduction operation of 50% using slag as a gas permeable material after the total amount of the raw material block a corresponding to the blast furnace mode was reduced, the whole of the lump ore charged as the raw material was reduced.

Example 4 of the invention

Fig. 12 shows the structure of the cyclic reduction system for experiment of invention example 4. Except that the number of the electric tube furnaces 40 is 1, a dehumidifier is not disposed downstream of the electric tube furnaces 40, and the same is true for the circulation type reduction system of the invention example 3 shown in fig. 11. The electric tube furnace 40 was set to an internal temperature of 900 ℃ by using Thermocouples (TC) provided around the catalyst. Other conditions were the same as in inventive example 3.

The representative composition of the exhaust gas produced by the reduction of the lump ore in the raw material lump a and the mixed gas after passing through the electric tube furnace 40 (in the case where the inlet side of the electric tube furnace 40 is not supplemented with hydrogen) is as described in table 1. It was found that after passing through the electric tube furnace 40, CO increased by 1.8% and CO ₂ and H ₂ decreased by 1.8%, respectively, due to the reverse water gas shift reaction of the excess H ₂ in the exhaust gas.

After the completion of the test, the lump ore, coke and the blast furnace slag were hardly found on the tungsten wire as in invention example 3. A mixture of ferrite (α -Fe) and cementite (Fe ₃ C) and slag deposited thereon were confirmed at the bottom of the furnace separated by a tungsten net. The mixture was confirmed to be composed of ferrite and cementite by X-ray diffraction. The carbon content in the same mixture measured by the combustion type carbon-sulfur analyzer was about 4.3 mass%, and the carbon content in the upper part and the lower part of the mixture tended to be increased by about 0.3 mass% when compared.

TABLE 1

Description of the reference numerals

100, A circulating type reduction system;

200, a circulating type reduction system;

10, a reduction furnace;

12, the furnace top;

14, a tuyere;

20, a first dehumidifier;

30, a hydrogen supply device;

40, catalyst device;

42, a reaction chamber;

44 a heating device;

50, a second dehumidifier;

60, a gas heating device;

70, a third dehumidifier;

81 a first pipeline;

82, a second pipeline;

83 a third pipeline;

84, a fourth pipeline;

85, a fifth pipeline;

86 a sixth line;

87 a seventh pipeline;

90, switching valve.

Claims

1. A circulation type reduction system, comprising:

a reduction furnace that reduces oxides contained therein;

a first pipeline which recovers exhaust gas containing _CO2 generated in the reduction furnace from the reduction furnace and passes it;

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; and

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:

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:

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 claim 1 , 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 the air are supplied as the blowing 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.