WO2024048423A1

WO2024048423A1 - Circulating reduction system, iron ore reduction method, and blast furnace operation method

Info

Publication number: WO2024048423A1
Application number: PCT/JP2023/030590
Authority: WO
Inventors: 寿人野呂; 浩司瀬川; 貴哉久保
Original assignee: Ｊｆｅミネラル株式会社
Priority date: 2022-08-30
Filing date: 2023-08-24
Publication date: 2024-03-07

Abstract

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

Description

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

The present invention relates to a circulating reduction system, a method for reducing iron ore, and a method for operating a blast furnace, which can drastically reduce CO ₂ emissions that promote global warming.

Amid calls for reducing _CO2 emissions, which promote global warming, on a global scale, Japan's steel industry, which accounts for around 15% of _CO2 emissions in Japan, is aiming to become carbon neutral by 2050 in accordance with government policy. declared. In order to achieve this, it is necessary to develop an iron ore reduction process and a reduction furnace to produce crude steel at a low cost close to the current level, but there are almost no technical prospects for this. is the current situation.

Here, the hydrogen reduction process using hydrogen as a reducing agent for iron ore is attracting worldwide attention as an ideal crude steel production technology that does not generate _CO2 . However, if this method were to maintain domestic production of hot metal of approximately 75 million tons per year, approximately 75 billion ^Nm3 of hydrogen would be required. It is estimated that in order to meet this demand using the water electrolysis method, which is a typical green hydrogen production method, 0.34 trillion kWh of electricity would be required annually, even if all electricity required for transportation, liquefaction, and storage of hydrogen is ignored. There is also. Even if we were able to overcome the heavy issue of electricity costs, it must be said that it is extremely unrealistic to procure this much electricity for domestic blast furnace manufacturers in Japan, where annual electricity consumption is on the order of 1 trillion kWh. .

On the other hand, various attempts are underway to procure large amounts of hydrogen produced using cheap renewable energy from overseas. However, even if the heavy problem of transportation costs could be overcome, there is no technical prospect for safely storing large quantities of hydrogen, which has a wide explosive concentration range, around steelworks.

By the way _, the domestic steel industry emits around 15% of the domestic _CO2 emissions, mainly through the use of the blast furnace-converter method, which uses coke to reduce iron ore. This is because they are producing. Crude steel production methods are mainly classified into the blast furnace-converter method and the electric furnace method. The blast furnace-converter method generates about 2 tons of CO 2 per ton of steel, and the electric furnace method generates about 0.5 t of CO ₂ per ton of steel. The electric furnace method is superior in that it can suppress the amount of CO ₂ generated. However, high-grade steel materials used in automobiles and the like are not mass-produced using the electric furnace method, which uses scrap as raw material, because impurities such as copper tend to adversely affect quality. For this reason, approximately 75% of domestic crude steel is produced using the blast furnace-converter method.

For blast furnaces that emit a particularly large amount of _CO2 , for example, Patent Document 1 attempts to reduce the amount of coke used by replacing the high-temperature air blown in from the tuyere with a reducing gas such as hydrogen or methane. There is. However, in addition to its role as a reducing agent, coke also plays a role as a heating material that heats the inside of the furnace through a reaction with oxygen blown in from the hot stove, and as a ventilation material that ensures ventilation inside the furnace. There is. Therefore, until a new means (other than coke) is found to maintain the furnace temperature and ensure ventilation without adversely affecting the quality of the hot metal, the amount of coke used must be drastically reduced. It is extremely difficult to do so.

Given the above background, the current situation is that Japan's steel manufacturers have no choice but to reduce the number of blast furnaces in operation and increase the ratio of electric furnaces to overcome the current situation. For this reason, demand for scrap used in electric furnaces is already strong, and the fierce competition to procure it is expected to become even more intense in the future.

Under these circumstances, the direct reduction process, which produces less CO ₂ emissions than the blast furnace-converter method, is attracting worldwide attention. In the so-called Midrex process, which is a typical direct reduction process, direct reduced iron (DRI) can be obtained by reducing iron ore in its solid phase using modified natural gas (see cited document 2). . The early Midrex process could only produce sponge-like DRI, making it difficult to handle and transport due to oxidation and ignition. However, after the development and industrialization of hot briquetting equipment, these problems have almost been resolved, and there is a movement to reduce the amount of scrap input and improve the quality of steel by mixing DRI with scrap and feeding it into the electric furnace. It is spreading worldwide. Furthermore, attempts have been made to replace natural gas with methane synthesized from CO ₂ and hydrogen using the methanation reaction (CO ₂ + 4H ₂ → CH ₄ + 2H ₂ O), or with hydrogen itself. There is.

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

Furthermore, in the direct reduction process, crude steel cannot be extracted in the form of hot metal, so conventional refining equipment for integrated pig steel processes such as pretreatment furnaces and converters cannot be used. This point is also one of the reasons why Japanese blast furnace manufacturers are obsessed with the blast furnace process. The reason why the direct reduction process is limited to solid-phase reduction is presumed to be because, as mentioned above, the problems of maintaining air permeability and the temperature inside the furnace to obtain hot metal have not been fundamentally solved.

In other words, in the blast furnace-converter process, the main obstacles are reducing agents and heating materials that can replace coke, and new means of ensuring air permeability without adversely affecting the quality of hot metal, and the amount of coke used can be reduced. There is no prospect of drastic reduction. In addition, the direct reduction process, which has lower _CO2 emissions than the blast furnace-converter method, cannot use low-grade fine ore powder or ore, which can be used in blast furnaces at low cost and is easy to procure. The disadvantage is that the refining equipment for the conventional pig steel integrated process cannot be used because it cannot be extracted as a metal.

Against this background, Patent Document 3 proposes a technology that utilizes CO ₂ contained in exhaust gas from a blast furnace. That is, it has been proposed to separate CO ₂ from blast furnace exhaust gas, reform the recovered CO ₂ into CO, and reuse this CO as a reducing agent for the blast furnace.

International Publication No. 2021/220555 JP2017-88912A JP2011-225968A

In the technique described in Patent Document 3, the amount of CO 2 generated can be suppressed as a result of reforming CO ₂ separated and recovered from exhaust gas generated in a blast furnace into CO and reusing _it . However, this technology involves multiple steps in which CO ₂ is first separated and recovered from the exhaust gas and then reformed, resulting in a decrease in the circulation efficiency of the reducing components in the exhaust gas and _a reduction in the equipment and equipment used in each process. The cost of operation and maintenance cannot be avoided. Therefore, there has been a desire to recycle and utilize reducing components in the exhaust gas of a reducing furnace such as a blast furnace using a more efficient method.

In view of the above-mentioned problems, the present invention provides a circulating reduction system that is capable of efficiently recycling CO-rich gas obtained by reforming exhaust gas containing CO ₂ generated from a reduction furnace as reducing gas. The purpose is to

In addition, the present invention makes it possible to perform the reduction treatment of iron ore by efficiently circulating and using CO-rich gas obtained by reforming exhaust gas containing CO ₂ generated from a reduction furnace as a reducing gas. The purpose is to provide a method for reducing iron ore.

Another object of the present invention is to provide a method of operating a blast furnace that uses the above-mentioned circulating reduction system to maintain the temperature inside the furnace and ensure air permeability using materials other than coke. .

The present inventors have conducted extensive research into ways to realize an efficient reduction process in which exhaust gas from a reduction furnace can be recycled and used as a starting material for a reducing agent. We have discovered that it is possible to efficiently reuse exhaust gas in a circular manner.

That is, the exhaust gas generated in the iron ore reduction process generally contains excess reducing agents such as CO and H ₂ in addition to CO ₂ and nitrogen derived from the atmosphere. For example, the exhaust gas of 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 derived from air. The present inventors added hydrogen to such exhaust gas and brought this gas into contact with a catalyst for reverse water gas shift reaction (RWGS: CO ₂ + H ₂ → CO + H ₂ O). After significantly changing the balance of CO ₂ and CO in the exhaust gas to a CO-rich one, we came up with the idea of recycling the exhaust gas together with H ₂ and nitrogen as a reducing gas. It has been discovered that if this recycling becomes possible, the amount of conventionally used reducing agents derived from fossil fuels such as coke can be kept to a minimum.

Here, the reason why CO is recycled as the main reducing agent is because the reduction reaction of iron ore with _H2 is an endothermic reaction, whereas the reduction reaction of iron ore with CO is an exothermic reaction. This is because it is the most efficient reducing agent that can maintain the inside of the reduction furnace at a high temperature. Furthermore, in the reduction using CO, the lowering of the freezing point of iron due to the carbon that occurs when coke is used as a reducing agent can be utilized as is. As a result, reduced iron, which does not melt at temperatures above 1500° C. when reduced by H ₂ , melts at about 1200° C. when reduced by CO. This temperature difference of about 300° C. greatly reduces the heat load on the heating furnace for the reducing gas when the reduced iron is taken out as hot metal.

Further, 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 and recovered and used for various purposes. In addition to its uses as a reducing agent and fuel gas, CO is a starting material for the Fischer-Tropsch reaction (nCO+(2n+1)H ₂ →C _n H _2n+2 +nH ₂ O), which is important in the synthesis of various organic substances. Therefore, the CO-rich reducing gas synthesized from the CO _2- rich exhaust gas is a synthesis gas that can be used not only as a reducing agent but also as a raw material for fuel gas and various organic compounds. In particular, if the use of fossil fuels is drastically reduced to prevent global warming, the organic chemical industry that relies on fossil fuels as raw materials will have to find new sources of raw materials. There is great significance in these industries becoming the recipients of the above-mentioned synthesis gas.

As already mentioned, the coke fed into a typical blast furnace has the roles of a heating material and a ventilation material in addition to its role as a reducing agent. Therefore, when taking out reduced iron as hot metal, even if the temperature inside the furnace can be maintained by the reduction heat of CO in the reducing gas, if the amount of coke input is suppressed to the limit, ventilation cannot be ensured (a stable reducing environment cannot be maintained). (becomes unsustainable).

It is newly discovered that this problem can be solved by slowly cooling and crushing a portion of the molten slag that is generated together with hot metal and discharged from the bottom of the furnace, and then mixing it with coke as a ventilation material and reinjecting it from the top of the furnace. was discovered. That is, since the melting point of blast furnace slag is approximately 1400° C., even when the iron whose freezing point has been lowered by carbon in the blast furnace begins to melt, the slag remains solid and serves as a ventilation material. Furthermore, since the slag is a substance originally produced in the blast furnace, the material environment within the blast furnace will not change even if it is recycled.

Furthermore, it is not easy to start up operation of a blast furnace using only slowly cooled and crushed slag as a ventilation material and reducing gas as a reducing agent. Therefore, like a normal blast furnace, coke, which is a reducing agent and ventilation material, and iron source are alternately stacked inside the blast furnace, and then the blast furnace is first operated in "blast furnace mode," which blows high-temperature air heated in a hot blast furnace. Launch. Then, the process is gradually switched to a ``cokeless mode,'' in which slag is gradually mixed with coke and reducing gas is gradually added to the air blown into the blast furnace. When shutting down a blast furnace, re-starting it will be easier if the process is reversed and the operation is ended in blast furnace mode after the cokeless mode.

The present invention has been made based on the above findings, and the gist thereof is as follows.
[1] A reduction furnace that reduces the oxide contained therein;
a first pipe that collects and passes exhaust gas generated in the reduction furnace and containing CO ₂ from the reduction furnace;
a hydrogen gas supply device that is connected to the middle of the first pipe and adds hydrogen gas to the exhaust gas to produce a hydrogenated gas;
A terminal end of the first pipe is connected to a reaction chamber accommodating a catalyst for a reverse water gas shift reaction, and the hydrogenation gas introduced from the first pipe to the reaction chamber contacts the catalyst, a catalytic device in which CO ₂ in the hydrogenated gas is converted to CO by a reverse water gas shift reaction to produce a CO-rich gas with an increased CO concentration;
a second pipe extending from the catalyst device, connected to the reduction furnace, allowing the CO-rich gas to pass therethrough, and supplying the CO-rich gas into the reduction furnace as a reducing gas;
has
A circulating reduction system in which a separation device that separates, recovers or removes specific gas components other than water vapor from the gas passing therethrough is not disposed in the middle of the first pipe and the second pipe.

[2] The circulating reduction system according to [1] above, including a gas heating device that heats the CO-rich gas, which is disposed in the middle of the second pipe.

[3] A third pipe is branched from a position upstream of the gas heating device in the middle of the second pipe and connected to the gas heating device, and the CO-rich gas is supplied via the third pipe. The circulating reduction system according to [2] above, wherein a part of the gas is supplied as combustion gas to the gas heating device.

[4] A fourth pipe extends from the gas heating device and is connected to the middle of the first pipe, and directs the combustion exhaust gas generated from the gas heating device into the first pipe via the fourth pipe. The circulation type reduction system according to [2] or [3] above, which is made to join the exhaust gas of.

[5] The catalyst device has a heating device that heats the reaction chamber,
The above [1] has a fifth pipe branched from the second pipe and connected to the heating device, and supplies a part of the CO-rich gas to the heating device as a combustion gas via the fifth pipe. ] to [4]. The circulating reduction system according to any one of [4].

[6] A sixth pipe extends from the heating device and is connected to the middle of the first pipe, and the combustion exhaust gas generated from the heating device is transferred to the first pipe through the sixth pipe. The circulation type reduction system according to the above [5], which is made to join the exhaust gas.

[7] The above-mentioned [1] to [2], which includes a first dehumidifier that removes water vapor from the exhaust gas and is disposed in the middle of the first piping upstream of a portion to which the hydrogen gas supply device is connected. 6]. The circulating reduction system according to any one of item 6].

[8] The circulating reduction system according to any one of [1] to [7] above, including a second dehumidifier that is disposed in the middle of the second pipe and removes water vapor from the CO-rich gas.

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

[10] The circulating reduction system according to [9] above, including a third dehumidifier that is disposed 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 according to any one of [1] to [10] above, wherein the reduction furnace is a blast furnace and the oxide is iron ore.

[12] The circulating reduction system according to [11] above, wherein the blast furnace is a blast furnace.

[13] Using the circulating reduction system according to any one of [1] to [12] above, the CO-rich gas obtained by reforming the exhaust gas is recycled as the reducing gas, A method for reducing iron ore, comprising reducing iron ore as the oxide.

[14] A method for operating a blast furnace using the circulating reduction system according to [11] or [12] above,
From the top of the blast furnace, (I) at least one kind of iron ore selected from sintered ore, lump ore, iron ore pellets, and fine ore, and (II) molten slag discharged from the bottom of the blast furnace. Crushed slag obtained by crushing solidified slag obtained by slowly cooling the slag, or a ventilation material made of a mixture of the crushed slag and coke, are charged into the blast furnace in alternating layers, and the reducing gas furnace A method of operating a blast furnace that ensures internal ventilation.

[15] Supplying the reducing gas and air as blowing gas into the inside of the blast furnace from a tuyere located at a lower part of the blast furnace,
The amount of coke used is suppressed in stages by increasing in stages 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 blown gas. The method for operating a blast furnace according to [14].

According to the circulating reduction system of the present invention, CO rich gas obtained by reforming the exhaust gas containing CO ₂ generated from the reduction furnace can be efficiently recycled and used as 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 is efficiently recycled as a reducing gas, and the reduction process of iron ore is carried out. It can be carried out.

According to the method of operating a blast furnace of the present invention, the temperature inside the furnace can be maintained using the above-mentioned circulating reduction system, and ventilation can be ensured using materials other than coke.

1 is a schematic diagram showing the configuration of a circulating reduction system 100 according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing the configuration of a circulating reduction system 200 according to another embodiment of the present invention. FIG. 2 is a schematic diagram showing an equilibrium calculation model of a circulating reduction system according to Invention Example 1. 4 is a graph showing the reduction situation in the model of FIG. 3 (invention example 1). FIG. 7 is a schematic diagram showing an equilibrium calculation model of a circulating reduction system according to Invention Example 2. 6 is a graph showing the reduction situation in the model of FIG. 5 (invention example 2). FIG. 2 is a schematic diagram showing an equilibrium calculation model of a circulating reduction system according to a comparative example. 8 is a graph showing the return situation in the model (comparative example) of FIG. 7. It is a graph showing the change in the amount of heat absorbed in the reduction furnace with respect to the number of cycles in Invention Examples 1 and 2 and Comparative Example. It is a graph showing the change in the amount of heat absorbed in the reduction furnace in the FeO reduction region with respect to the amount of hydrogen in the hydrogenation gas in Invention Examples 1 and 2 and Comparative Example. FIG. 3 is a schematic diagram showing the configuration of an experimental circulating reduction system according to Invention Example 3. FIG. 4 is a schematic diagram showing the configuration of an experimental circulating reduction system according to Invention Example 4.

[Circulating reduction system]
Referring to FIG. 1, a circulating reduction system 100 according to an embodiment of the present invention will be described. The circulating reduction system 100 includes a reduction furnace 10, a first dehumidifier 20, a hydrogen gas supply device 30, a catalyst device 40, a second dehumidifier 50, and a gas heating device 60, and includes a first pipe 81 as piping equipment, It has a second pipe 82, a third pipe 83, a fourth pipe 84, a fifth pipe 85, a sixth pipe 86, a seventh pipe 87, and a switching valve 90.

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

The first piping 81 is piping equipment that collects exhaust gas containing CO ₂ generated in the reduction furnace 10 from the reduction furnace 10 and allows it to pass therethrough. The first pipe 81 has a starting end connected to the reduction furnace 10 (in one example, the furnace top 12), and a terminal 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 includes a pipe 81A that extends from the reduction furnace 10 and connects to the first dehumidifier 20, and a pipe 81B that extends from the first dehumidifier 20 and connects to the catalyst device 40. Note that in this specification, "upstream" or "downstream" with respect to piping refers to the direction of gas flow within the piping.

Exhaust gas discharged from the furnace top 12 of the reduction furnace 10 is dehumidified by the first dehumidifier 20 while flowing through the first pipe 81, and then hydrogen (H ₂ ) gas is supplied from the hydrogen gas supply device 30. is replenished and becomes hydrogenated gas. The dehumidification treatment is preferably performed in order to suppress the water gas shift reaction and promote the reverse water gas shift reaction. The composition of the exhaust gas is not particularly limited, but typically contains _CO2 : 13 to 24% by volume, CO: 21 to 31% by volume, and _H2 : 3 to 15% by volume, excluding water vapor. The remainder has a composition of _N2 derived from air. The composition of the hydrogenation gas is not particularly limited, but typically contains 13 to 24% by volume of CO ₂ , 21 to 31% by volume of

H

2 , and 10 to 30% by volume of H ₂ , excluding water vapor. , the remainder being _N2 derived from air. The hydrogen supplied from the hydrogen gas supply device 30 is preferably green hydrogen obtained by water electrolysis using renewable energy, but by applying the circulating reduction system of the present invention to blast furnace operation, it is possible to use coke. Until the amount reaches zero, it can be replaced with hydrogen purified from coke oven gas.

In addition, a dust removal device (not shown) is installed 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 part to which the hydrogen gas supply device 30 is connected. It is preferable to provide a filter (1) to perform dust removal treatment on the exhaust gas to remove dust originating from the raw materials from the exhaust gas.

The catalyst device (reverse shift type reformer) 40 has a reaction chamber 42 to which the terminal end of the first pipe 81 is connected and accommodates a catalyst for the reverse water gas shift reaction, and a heating device 44 that heats the reaction chamber 42. . In the catalyst device 40, the hydrogenated gas introduced into the reaction chamber 42 from the first pipe 81 comes into contact with the catalyst, and _CO2 in the hydrogenated gas is converted to CO by a reverse water gas shift reaction, increasing the CO concentration. It becomes a CO-rich gas. The composition of the CO-rich gas after the reverse water gas shift reaction is not particularly limited, but typically, excluding water vapor, it contains CO ₂ : 6-20% by volume, CO: 24-40% by volume, and H ₂ : 5-24%. % by volume, with the remainder being _N2 derived from air. There are many known catalysts that can be used in the reverse water gas shift reaction, including those based on nickel and noble metals, and any of them may be used in the present invention.

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

The second pipe 82 extends from the catalyst device 40 and is connected to the reduction furnace 10 (in one example, the tuyere 14), and allows the CO-rich gas to pass through the reduction furnace using the CO-rich gas as a reducing gas (in one example, via the tuyere 14). This is piping equipment that supplies the inside of 10. Preferably, a second dehumidifier 50 that removes water vapor from the CO-rich gas and a gas heating device 60 that heats the CO-rich gas are disposed in the middle of the second pipe 82. In this case, it is preferable that the gas heating device 60 is arranged downstream of the second dehumidifier 50. In this case, the second pipe 82 includes a pipe 82A extending from the catalyst device 40 and connecting to the second dehumidifier 50, a pipe 82B extending from the second dehumidifier 50 and connecting to the gas heating device 60, and a pipe 82B extending from the gas heating device 60. It has a pipe 82C 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 through the second pipe 82, heated by the gas heating device 60, and then returned to the reduction furnace 10 as a reducing gas. is blown into.

That is, after the reaction with the catalyst, it is desirable to adjust the temperature of the CO-rich gas (reducing gas) blown into the reduction furnace 10 using the gas heating device 60. The higher the temperature of the reducing gas, the better the reduction efficiency of iron ore in the reduction furnace 10, but when performing solid-phase reduction of iron ore, it is desirable that the temperature of the reducing gas blown into the reduction furnace 10 be 900 ° C. or higher. . In addition, when taking out reduced iron as hot metal at 1500°C, it is necessary to maintain the temperature of the melting region of the iron source and slag formed in the lower area of the reduction furnace 10 at 1650°C or higher, so the amount of coke input must be maintained at 1650°C or higher. If the amount of coke input is less than 20% of that of a conventional blast furnace, the temperature of the reducing gas is heated to 1,500 degrees Celsius or higher. It is preferable to blow in at the top.

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

It is preferable that the circulation type reduction system 100 has a fourth pipe 84 extending from the gas heating device 60 and connected to the middle of the first pipe 81. Preferably, the combustion exhaust gas generated from the gas heating device 60 is joined to 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 . The combustion exhaust gas generated from the gas heating device 60 is transferred to (1) the reducing gas piping between the catalyst device 40 and the gas heating device 60, (2) the hydrogenation gas piping between the hydrogen gas supply device 30 and the catalyst device 40, and heat. If the exhaust gas is exchanged and then merged with the exhaust gas in the first pipe 81 upstream of the first dehumidifier 20, the reducing gas and the hydrogenation gas can be preheated.

Note that if the reducing gas cannot be raised to the desired temperature using the indirect heating type gas heating device 60 as illustrated in FIG. It is also possible to directly combust some of the CO and H ₂ contained in the fuel. Furthermore, if oxygen-rich air is used in the hot air blown into the reduction furnace 10 when starting up in blast furnace mode, the heat load on the gas heating device 60 that is taken away by nitrogen heating will be reduced. It becomes easier to raise the temperature of the reducing gas.

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

It is preferable that the circulating reduction system 100 has a sixth pipe 86 extending from the heating device 44 and connected to the middle of the first pipe 81. Preferably, the combustion exhaust gas generated from the heating device 44 is joined to the exhaust gas in the first pipe 81 via the sixth pipe 86 and reused. Note that in this embodiment, since the upstream portion 86A of the sixth piping 86 is connected to the middle of the fourth piping 84, which is the fuel exhaust gas passage from the gas heating device 60, the downstream portion 86B of the sixth piping 86 also serves as the downstream portion 84 of the fourth pipe 84. However, the present invention is not limited to this, and it goes without saying that the sixth pipe 86 may be directly connected to the first pipe 81 independently of the fourth pipe 84. The combustion exhaust gas generated from the heating device 44 is heat exchanged with the hydrogenation gas piping between the hydrogen gas supply device 30 and the catalyst device 40, and then the exhaust gas in the first piping 81 is transferred upstream of the first dehumidifier 20. The hydrogenation gas can also be preheated by merging it with the hydrogen gas.

In the present embodiment described above, a process of reducing iron ore by blowing reducing gas, a process of recovering exhaust gas from a reduction furnace, a process of dust removal and dehumidification of exhaust gas (optional process), and a process of adding hydrogen gas to exhaust gas. , a step of generating CO-rich gas from hydrogenated gas by a reverse water gas shift reaction, a step of dehumidifying the CO-rich gas (optional step), a step of heating the CO-rich gas (optional step), and a step of blowing the CO-rich gas as a reducing gas. By returning the exhaust gas, a circulation process is realized in which the exhaust gas from the reduction furnace 10 is reused in a closed circulation system.

The unconverted CO ₂ remaining in the CO-rich gas used as the reducing gas becomes a CO source in the course of the circulation process, so there is no need to separate it from the reducing gas. That is, in this embodiment, it is important that a separation device that separates, recovers, or removes specific gas components other than water vapor from the gas passing through them is not disposed in the middle of the first pipe 81 and the second pipe 82. be. In this embodiment, since no new separation and concentration process is required other than dust removal and dehumidification to which existing techniques can be applied, the circulation efficiency of the reducing gas is high.

In this embodiment, in order to utilize a reverse water gas shift reaction that converts _CO2 into CO with an equimolar amount of hydrogen, methane produced by a methanation reaction that requires four times the mole of hydrogen as _CO2 is used as a reducing agent. Compared to the conventional reduction method described above, the amount of hydrogen procured per CO ₂ can be reduced to about 1/4.

In this embodiment, a CO-based reducing gas modified from exhaust gas is supplied into the reduction furnace 10 at high temperature, and impurities in the iron ore can be separated from the hot metal as molten slag. Low-grade fine ore or fine ore, which is cost-effective and easy to procure, can be used in the form of pellets or sintered ore.

Note that the surplus of the CO-rich gas (in this embodiment, the remainder 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 a switching valve 90 disposed in the middle of the second pipe 82 and a seventh pipe 87 extending from the switching valve 90. A portion of the rich gas can be recovered. The recovered CO-rich gas can be used, for example, as synthesis gas, which is a raw material for organic compounds. In this embodiment, a system is realized in which the CO2 _- rich exhaust gas discharged from the reduction furnace 10 is converted into CO-rich reducing gas and recycled, so the surplus CO2-rich gas is used as synthesis gas for the organic chemical industry, etc. By making effective use of CO2, it will be possible to suppress _CO2 emissions into the atmosphere to zero levels.

In addition, the molten slag separated from the hot metal is slowly cooled in a mold to become solidified slag, and this solidified slag is crushed to become crushed slag, which can be reused as a ventilation material. If part of the pig iron discharged from the reduction furnace (blast furnace) is attached to this slag-derived ventilation material, the pig iron can be returned to the reduction furnace as an iron source through this ventilation material.

Note that the molten slag is automatically discharged to the surface of the hot metal due to the difference in specific gravity, so even if it is recycled, it will have almost no negative effect on the quality of the hot metal. In addition, since the recycled molten slag has the same quality as normal blast furnace slag, it can be used industrially as a raw material for blast furnace cement and the like.

With reference to FIG. 2, a circulating reduction system 200 according to another embodiment of the present invention will be described. The circulation type reduction system 200 has the same configuration as the circulation type reduction system 100 except that the second dehumidifier 50 is not provided and a third dehumidifier 70 is placed in the middle of the seventh pipe 87 instead. have That is, the second dehumidifier 50 is not an essential component in the present invention. When the second dehumidifier 50 is not disposed, it is preferable that the third dehumidifier 70 removes water vapor from the CO-rich gas passing through the seventh pipe 87.

In the above description, the case where the reduction furnace 10 is a blast furnace such as a blast furnace and the object to be reduced is iron ore has been mainly described, but the present invention is not limited thereto. The reduction furnace 10 may be a solid reduction furnace. Further, the object to be reduced is not limited to iron ore as long as it is an oxide, and may be, for example, manganese ore, which is a raw material for ferromanganese or silicomanganese.

[Iron ore reduction method]
A method for reducing iron ore according to an embodiment of the present invention uses the above-described circulating

reduction system

100, 200 to circulate and utilize CO-rich gas obtained by reforming exhaust gas as a reducing gas, and convert it into oxides. The company conducts reduction processing of iron ore. Thereby, the CO rich gas obtained by reforming the exhaust gas containing CO ₂ generated from the reduction furnace 10 can be efficiently circulated and used as a reducing gas, and the iron ore can be reduced.

Further, according to the reduction method of this embodiment, in order to realize an efficient reduction process in which the exhaust gas from the reduction furnace 10 can be recycled and used as a starting material for the reducing agent, the amount of CO ₂ generated can be significantly reduced. can be reduced. Furthermore, it becomes possible to drastically reduce the input amount of reducing agents derived from fossil fuels such as coke, which are conventionally used in the iron ore reduction process.

[How to operate a blast furnace]
A method for operating a blast furnace according to an embodiment of the present invention is performed using the above-described circulating

reduction system

100, 200. From the top of the reduction furnace (blast furnace) 10, (I) at least one type of iron ore (iron source) selected from sintered ore, lump ore, iron ore pellets, and fine ore, and (II) the blast furnace. Crushed slag obtained by crushing solidified slag obtained by slowly cooling the molten slag discharged from the bottom of the blast furnace, or a ventilation material made of a mixture of this crushed slag and coke, are charged into a blast furnace in alternating layers. Therefore, it is important to ensure ventilation of the reducing gas inside the furnace. Thereby, using the above-mentioned circulating

reduction systems

100, 200, it is possible to maintain the temperature inside the furnace and ensure ventilation with materials other than coke.

In the operation according to this embodiment, reducing gas and air are supplied from the tuyere 14 into the inside of the blast furnace as blowing gas. At this time, it is preferable to gradually increase the ratio of crushed slag to coke in the ventilation material and the ratio of reducing gas to air in the blown gas to gradually suppress the amount of coke used.

According to the method of operating a blast furnace according to the present embodiment, it is possible to obtain reduced iron in the form of hot metal using low-cost and easily procured low-grade fine ore powder or powdered ore. The conventional integrated pig steel process can be used as is.

The degree of ventilation in the blast furnace can be adjusted by the particle size of the crushed slag. For example, if the slowly cooled slag is cast with ventilation holes added, it will be easier to ensure ventilation. Note that there is no particular problem even if common blast furnace slag is used as the ventilation material.

In the blast furnace operating method according to the present embodiment, the amount of molten slag generated in the circulating

blast furnaces

100, 200 is larger than that in a normal blast furnace because the slag re-injected from the furnace top 12 is remelted after the cohesive zone. There will be more. Furthermore, as the amount of slag added increases, the amount of heat taken away as heat of fusion of the slag also increases. Therefore, when starting up operations in blast furnace mode, it is desirable to adjust the thickness ratio of the iron source layer and the aeration layer in advance so that the iron source layer is richer than in a typical blast furnace.

[Example 1]
As described below, equilibrium calculations were performed to confirm the effects of the reduction method of the present invention as Invention Examples 1 and 2 and a comparative example.

(Invention example 1)
An equilibrium calculation model of the circulating reduction system according to Invention Example 1 is shown in FIG. In the initial state, the reduction furnace 10 containing 25 moles of iron (III) oxide (Fe ₂ O ₃ ) contains 22 moles of CO, 22.8 moles of CO ₂ , 4.2 moles of H ₂ , and 4.2 moles of N ₂ : A state is assumed in which a reverse shift type reformer (hereinafter simply referred to as "reformer 40") is connected as a catalyst device 40 containing a mixed gas of 51 moles equivalent to a total of 100 moles of blast furnace exhaust gas. A first dehumidifier 20 is installed on the inlet side of the reformer, a second dehumidifier 50 is installed on the outlet side of the reformer, and between the first dehumidifier and the reformer, the number of _H2 moles in the reformer (blast furnace exhaust gas A hydrogen gas supply device 30 is installed to maintain the CO ₂ concentration at 22.8 mol (corresponding to the CO 2 concentration in the tank). Assuming that no gas enters or exits the reduction furnace and reformer other than H ₂ supplied from the hydrogen gas supply device and H ₂ O removed by the first and second dehumidifiers, all H ₂ O is consumed. It can be considered that the total number of moles of the mixed gas circulating through the reformer and the reduction furnace does not change because it is generated from the H ₂ that was removed.

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

Here, the entire reducing gas generated when the hydrogenation gas reaches a steady state in the reformer is sent to the reducing furnace, and the gas in the reducing furnace when the reduction reaction reaches a steady state is taken out as exhaust gas. Let us consider a circulation process in which one cycle is defined as adding hydrogen up to a certain level to hydrogen and turning it into hydrogenated gas again, and repeating this cycle. The equilibrium state of gas components and iron sources inside the reformer and the reduction furnace that occurs in each cycle of sending reducing gas from the reformer to the reduction furnace is calculated using thermodynamic equilibrium calculation software and thermodynamics database Fact Sage manufactured by Computational Mechanics Research Center Co., Ltd. Calculated in 8.1. The results are shown in FIG. Although methane and the like are included in the compounds produced in the reformer and reduction furnace, trace components of 0.005 mol or less were ignored.

In the above-mentioned reduction furnace, reduction of the iron source proceeds with CO supplied from the reformer and surplus H ₂ not consumed in the reverse water gas shift reaction. The solid phase Fe ₂ O ₃ input as an iron source changes to twice the molar amount of FeO (solid phase) in the first cycle, and after the second cycle, FeO is gradually reduced to α-Fe (solid phase). The reduction is completed in the 7th cycle. The fact that the main reduction reaction is from FeO to α-Fe is consistent with the knowledge known in blast furnaces. The amount of _H2 consumed in reducing this iron source is 89 moles.

(Invention example 2)
FIG. 5 shows an equilibrium calculation model of the circulating reduction system according to Invention Example 2. This is the same as the equilibrium calculation model of the circulating reduction system according to Invention Example 1 shown in FIG. 3, except that the second dehumidifier is not provided on the outlet side of the reformer. The calculation conditions were also the same as in Invention Example 1, and the equilibrium state of the gas components and iron source in the reformer and reduction furnace was calculated. The results are shown in FIG.

The solid phase Fe ₂ O ₃ input as an iron source changes to twice the molar amount of FeO (solid phase) in the first cycle, and after the third cycle, FeO is gradually reduced to α-Fe (solid phase). The reduction is completed in the 9th cycle. The fact that the main reduction reaction is from FeO to α-Fe is consistent with the knowledge known in blast furnaces. The amount of _H2 consumed in the reduction of this iron source is 85 moles.

(Comparative example)
FIG. 7 shows an equilibrium calculation model of a circulating reduction system according to a comparative example. This is the same as the equilibrium calculation model of the circulating reduction system according to Invention Example 1 shown in FIG. 3, except that the reformer and the second dehumidifier are not provided. The calculation conditions were also the same as in Invention Example 1, and the equilibrium state of the gas components and iron source in the reformer and reduction furnace was calculated. The results are shown in FIG.

In the reduction furnace of the comparative example, reduction of the iron source progresses only with H ₂ directly introduced into the reduction furnace from the hydrogen gas supply device. 25 mol of Fe ₂ O ₃ (solid phase) input as an iron source changes into 8.2 mol of Fe ₃ O ₄ (solid phase) and 22.5 mol of FeO (solid phase) in the first cycle. After the second cycle, FeO is gradually reduced and changed to α-Fe (solid phase), and the reduction is completed at the ninth cycle, which is the same as in Invention Example 2. This is the same as Invention Examples 1 and 2 in that the main reduction reaction is the reaction from FeO to α-Fe. The amount of H ₂ consumed in reducing this iron source was 75 mol, which was 10 mol less than that in Invention Example 2.

(Amount of heat absorbed in the reduction furnace)
The major difference between Invention Examples 1 and 2 and Comparative Example is the amount of heat absorbed in the reduction furnace. The reaction heat (endothermic amount) in the reduction furnace calculated from the reaction heat of each reaction calculated using Fact Sage 8.1 is shown in FIGS. 9 and 10.

All direct reductions of iron sources with H ₂ are endothermic reactions, except for the reaction of Fe ₂ O ₃ to Fe ₃ O ₄ which is completed initially. On the other hand, in the reduction of the iron source using CO and surplus H ₂ in Invention Example 1, the amount of heat absorbed by the reduction of H ₂ is supplemented by the amount of heat absorbed by the reduction of CO, so the total amount of heat absorbed can be significantly suppressed (Fig. 9 reference). Furthermore, in Inventive Example 2, since the calorific value due to CO reduction exceeds the endothermic amount due to H ₂ reduction in the FeO reduction region, the FeO reduction temperature is spontaneously maintained at a high temperature (see FIG. 9). If the input amount of iron source increases, the FeO reduction stage will become longer. Normally, it is extremely difficult to supply heat from other than the tuyere and furnace top to a reduction furnace, which needs to maintain its interior at a high temperature. Therefore, considering that it is necessary to supplement this absorption heat with the combustion heat of coke introduced into the reduction furnace, the superiority of the example of the present invention is obvious.

Note that from FIG. 10, the amount of H ₂ supplied to the reformer in order to maximize the calorific value in the FeO reduction region is expected to be approximately the same as the molar amount of CO ₂ in the exhaust gas. If the amount of H ₂ replenishment to the reformer is suppressed, it is thought that the reduction rate will also decrease, so in reality, the amount of H ₂ replenishment is adjusted based on the balance between the temperature inside the reduction furnace and the reduction rate.

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

(Invention example 3)
The configuration of an experimental circulating reduction system according to Invention Example 3 is shown in FIG. In FIG. 11, coke 2 crushed to about 5 mm is placed on a tungsten mesh that partitions the bottom of the BF simulator (hereinafter referred to as "reduction furnace 10"), which is an experimental reduction furnace installed on a weight scale. A raw material block A was formed by alternately stacking .2 kg of lump ore and 5.0 kg of lump ore crushed to around 3 mm.

Furthermore, on top of the raw material block A, a mixture of 1.1 kg of the coke and 2.8 kg of slowly cooled blast furnace slag crushed to around 5 mm, and 5.0 kg of lump ore crushed to around 3 mm are alternately stacked. A raw material block B was formed.

Exhaust gas discharged from the top of the furnace is passed through a dust removal device, a dehumidifier 20, a first electric tubular furnace 40, a dehumidifier, a second electric tubular furnace 40, a dehumidifier 50, and a regenerative gas heating furnace 60. After passing through, one side was connected to the exhaust gas treatment device and the other side was connected to a nozzle 92 at the lower part of the reduction furnace via a switching valve 91. The two electric tube furnaces 40 are ceramic electric tube furnaces in which a quartz reaction tube holding 51 g of platinum catalyst is set in the center.

Sampling tubes for gas composition analysis are provided at two locations, immediately before the first electric tubular furnace 40 and between the second electric tubular furnace 40 and the dehumidifier 50. ) was connected. Further, a hydrogen pipe 30 was connected between the dehumidifier 20 and the first electric tubular furnace 40 via a switching valve 93 and a mass flow controller (MFC) 94.

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

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

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

Typical composition of exhaust gas generated by reduction of lump ore in raw material block A and mixed gas after passing through the second electric tubular furnace 40 (no hydrogen replenishment at the entrance side of the first electric tubular furnace 40) ) are as described in Table 1. After passing through the second electric tubular furnace 40, CO increases by 2.7% due to a reverse water gas shift reaction due to excess H ₂ in the exhaust gas, and CO ₂ and H ₂ each decrease by 2.7%. I understand that.

When 2.2 kg of coke in raw material block A was completely consumed as exhaust gas, the flow rate of air introduced from nozzle 96 was changed to 8.5 L/min by MFC 97. At the same time, the switching valve 93 is switched to the hydrogen pipe 30 side to introduce hydrogen gas, so that the H ₂ concentration in the mixed gas before entering the first electric tubular furnace 40 (the CO ₂ concentration in the initial exhaust gas) Same) Adjusted with MFC94 to 22.8%. Then, the switching valve 91 was switched to the reducing furnace 10 side, and the reducing gas was introduced from the nozzle 92. In addition, it was judged from the weight change of the reduction furnace 10 that the coke in the raw material block A was completely consumed.

In this state, after 1.1 kg of coke in the raw material block B was completely consumed, the air introduced from the nozzle 96 was stopped, and the two electric tube furnaces and the two gas heating furnaces were stopped. Then, wait until the water temperature in the water cooling jacket reaches 30°C, then cut off the hydrogen gas with the switching valve 93, switch the switching valve 91 to the exhaust gas treatment device side, and switch the switching valve 98 to the nitrogen gas introduction side. All of the exhaust gas remaining in the reduction furnace 10 was discharged to the exhaust gas treatment device. Thereafter, the reduction furnace 10 was disassembled and the situation inside the furnace was confirmed.

A total of 10 kg of lump ore, 3.3 kg of coke, and 2.8 kg of slowly cooled blast furnace slag in raw material blocks A and B were hardly recognized on the tungsten mesh. A mixture of ferrite (α-Fe) and cementite (Fe ₃ C) and slag deposited thereon were confirmed at the bottom of the furnace, which was partitioned with a tungsten mesh. It was confirmed by X-ray diffraction that the mixture was composed of ferrite and cementite. The carbon content of the mixture measured with a combustion-type carbon-sulfur analyzer was approximately 4.3% by mass, and when comparing the upper and lower parts of the mixture, the carbon content in the lower part was about 0.3% higher by mass. showed a trend.

Through the above experiments, it was found that after the entire amount of raw material block A, which corresponds to blast furnace mode, has been reduced, even in the reduction process of raw material block B, which corresponds to 50% carbonless operation using slag as an aeration material, the lump ore input as a raw material It has been confirmed that the entire amount can be returned.

(Invention example 4)
FIG. 12 shows the configuration of an experimental circulating reduction system according to Invention Example 4. This is the same as the circulating reduction system of Invention Example 3 shown in FIG. 11, except that there is only one electric tubular furnace 40 and no dehumidifier is disposed downstream of the electric tubular furnace 40. The electric tubular furnace 40 was set to have an internal temperature of 900° C. using a thermocouple (TC) provided around the catalyst. The test was conducted under the same conditions as in Invention Example 3 except for the above.

The typical composition of the exhaust gas generated by reducing the lump ore in raw material block A and the mixed gas after passing through the electric tubular furnace 40 (in the case of no hydrogen replenishment at the entrance side of the electric tubular furnace 40) is shown in Table 1. As described. It can be seen that after passing through the electric tubular furnace 40, CO increases by 1.8% due to a reverse water gas shift reaction due to excess H ₂ in the exhaust gas, and CO ₂ and H ₂ each decrease by 1.8%.

After the test, as in Invention Example 3, hardly any lump ore, coke, or slow-cooled blast furnace slag was observed on the tungsten mesh. A mixture of ferrite (α-Fe) and cementite (Fe ₃ C) and slag deposited thereon were confirmed at the bottom of the furnace, which was partitioned with a tungsten mesh. It was confirmed by X-ray diffraction that the mixture was composed of ferrite and cementite. The carbon content of the mixture measured with a combustion-type carbon-sulfur analyzer is approximately 4.3% by mass, and when comparing the upper and lower parts of the mixture, the carbon content in the lower part is about 0.3% higher by mass. showed a trend.

100 Circulating reduction system 200 Circulating reducing system 10 Reduction furnace 12 Furnace top 14 Tuyere 20 First dehumidifier 30 Hydrogen gas supply device 40 Catalyst device 42 Reaction chamber 44 Heating device 50 Second dehumidifier 60 Gas heating device 70 Third Dehumidifier 81 First pipe 82 Second pipe 83 Third pipe 84 Fourth pipe 85 Fifth pipe 86 Sixth pipe 87 Seventh pipe 90 Switching valve

Claims

a reduction furnace that reduces the oxide contained therein;
a first pipe that collects and passes exhaust gas generated in the reduction furnace and containing CO 2 from the reduction furnace;
a hydrogen gas supply device that is connected to the middle of the first pipe and adds hydrogen gas to the exhaust gas to produce a hydrogenated gas;
The terminal end of the first pipe is connected to a reaction chamber accommodating a catalyst for a reverse water gas shift reaction, and the hydrogenation gas introduced from the first pipe to the reaction chamber comes into contact with the catalyst, A catalytic device in which CO 2 in the hydrogenated gas is converted to CO by a reverse water gas shift reaction to produce a CO-rich gas with an increased CO concentration;
a second pipe extending from the catalyst device, connected to the reduction furnace, allowing the CO-rich gas to pass therethrough, and supplying the CO-rich gas into the reduction furnace as a reducing gas;
has
A circulating reduction system in which a separation device that separates, recovers or removes specific gas components other than water vapor from the gas passing through the first pipe and the second pipe is not disposed in the middle of the first pipe and the second pipe.
The circulating reduction system according to claim 1, further comprising a gas heating device that heats the CO-rich gas and is placed in the middle of the second pipe.
A third pipe is branched from a position upstream of the gas heating device in the middle of the second pipe and connected to the gas heating device, and a part of the CO-rich gas is supplied through the third pipe. The circulating reduction system according to claim 2, wherein the combustion gas is supplied to the gas heating device.
A fourth pipe extends from the gas heating device and is connected to the middle of the first pipe, and the combustion exhaust gas generated from the gas heating device is transferred to the exhaust gas in the first pipe through the fourth pipe. The circulating reduction system according to claim 2 or 3, which is made to join the gas.
The catalyst device includes a heating device that heats the reaction chamber,
Claim 1, further comprising a fifth pipe branched from the second pipe and connected to the heating device, and supplying a portion of the CO-rich gas as combustion gas to the heating device via the fifth pipe. The circulating reduction system according to any one of 3 to 3.
A sixth pipe extends from the heating device and is connected to the middle of the first pipe, and the combustion exhaust gas generated from the heating device is transferred to the exhaust gas in the first pipe via the sixth pipe. The circulating reduction system according to claim 5, wherein the system is made to merge.
Any one of claims 1 to 3, further comprising a first dehumidifier for removing water vapor from the exhaust gas, the first dehumidifier being disposed in the middle of the first piping upstream of a portion to which the hydrogen gas supply device is connected. Circulating reduction system as described in Section.
The circulating reduction system according to any one of claims 1 to 3, further comprising a second dehumidifier disposed in the middle of the second pipe to remove water vapor from the CO-rich gas.
comprising a switching valve disposed in the middle of the second pipe, and a seventh pipe extending from the switching valve,
The circulating reduction system according to any one of claims 1 to 3, wherein a part of the CO-rich gas is recovered via the seventh pipe.
The circulating reduction system according to claim 9, further comprising a third dehumidifier disposed in the middle of the seventh pipe to remove water vapor from the CO-rich gas passing through the seventh pipe.
The circulating reduction system according to any one of claims 1 to 3, wherein the reduction furnace is a blast furnace and the oxide is iron ore.
The circulating reduction system according to claim 11, wherein the blast furnace is a blast furnace.
Using the circulating reduction system according to any one of claims 1 to 3, the CO-rich gas obtained by reforming the exhaust gas is recycled as the reducing gas, and the iron ore as the oxide is produced. A method for reducing iron ore by reducing stone.
A method of operating a blast furnace using the circulating reduction system according to claim 11,
From the top of the blast furnace, (I) at least one kind of iron ore selected from sintered ore, lump ore, iron ore pellets, and fine ore, and (II) molten slag discharged from the bottom of the blast furnace. Crushed slag obtained by crushing solidified slag obtained by slowly cooling the slag, or a ventilation material made of a mixture of the crushed slag and coke, are charged into the blast furnace in alternating layers, and the reducing gas furnace A method of operating a blast furnace that ensures internal ventilation.
Supplying the reducing gas and air as blowing gases into the inside of the blast furnace from a tuyere located at a lower part of the blast furnace,
A ratio of the crushed slag to the coke in the ventilation material and a ratio of the reducing gas to the air in the blown gas are increased in stages to suppress the amount of coke used in stages. Item 15. The method for operating a blast furnace according to item 14.