JP7272312B2 - Method for producing reduced iron - Google Patents

Description

The present invention relates to a method for producing reduced iron.

BACKGROUND ART In recent years, against the background of global environmental problems and fossil fuel depletion problems, there is a strong demand in various fields for energy saving and reduction of carbon dioxide (CO ₂ ) emissions. Steel works are no exception, and efforts are being made to save energy in each process of the steel works.

Now, the raw material of iron is mainly iron oxide, and a reduction process to reduce this iron oxide is essential. The most popular and common reduction process worldwide is the blast furnace. In this blast furnace, coke or pulverized coal is reacted with oxygen in hot air (air heated to about 1200°C) in the tuyere to generate CO and _H2 gas (reducing gas). of iron ore, etc. Due to recent improvements in blast furnace operating technology, the reducing agent ratio (the amount of coke and pulverized coal used per 1 ton of molten iron) has been reduced to about 500 kg/t, but the reduction of the reducing agent ratio has already reached its limit. A further drastic reduction in the reducing agent ratio cannot be expected.

On the other hand, in areas where natural gas is produced, a vertical reduction furnace is filled with agglomerated iron ore such as sintered ore and pellets (hereinafter collectively referred to as iron oxide) as iron oxide raw materials, and hydrogen and A method of producing reduced iron by blowing in a reducing gas containing carbon oxide to reduce iron oxide is also often used. In this method, natural gas or the like is used as the source gas for the reducing gas. The raw material gas is heated and reformed in the reformer together with the top gas discharged from the top of the reducing furnace to generate a reducing gas. The generated reducing gas is blown into the reducing furnace and reacts with the iron oxide raw material supplied from the upper part of the reducing furnace, whereby the iron oxide is reduced to become reduced iron. The produced reduced iron is discharged from the lower part of the reduction furnace. After the iron oxide has been reduced, the gas is discharged from the top of the reducing furnace as top gas. After dust collection and cooling, part of the gas is sent to the reformer as a raw material for reformed gas. The remaining top gas is used as fuel gas for the heater/reformer.

As the above-mentioned reduced iron production process, for example, in Patent Document 1, exhaust gas from a reducing furnace and natural gas are reformed in a reformer to generate a reducing gas mainly composed of CO and _H gas, and this reduction It describes that gas is blown into a reducing furnace to reduce iron oxide in the reducing furnace to produce reduced iron.

In addition, Patent Document 2 describes a method of producing reduced iron by reforming coke oven gas and top gas of a reducing furnace from which CO ₂ has been removed to produce reducing gas, and blowing it into the reducing furnace. ing.

JP 2017-88912 A Japanese Patent No. 6190522

In the method for producing reduced iron described in Patent Document 1, since natural gas is used to produce reducing gas, there is a problem that a certain amount of CO ₂ emissions cannot be avoided, although the level is lower than that of a blast furnace.

In addition, the method described in Patent Document 2 is for producing reducing gas using coke oven gas or converter gas generated in a steelworks, but in an integrated ironworks, coke oven gas and converter gas are heated. Since it is indispensable as a downstream fuel gas for furnaces, annealing furnaces, etc., if it is diverted to the reduced iron manufacturing process, it will cause a fuel gas shortage in the downstream process. As a result, in the end, natural gas was supplied externally to compensate for the shortage of gas in the downstream process, and the reduction of CO ₂ emissions was not realized and remained an issue.

Furthermore, in the method described in Patent Document 2, coke oven gas is used as a raw material and reformed to produce a reducing gas, but coke oven gas contains a large amount of sulfur, which damages the adsorbent in the CO ₂ separation device. I have concerns. Moreover, it is said that the reduced iron production process can be properly operated when the ratio of _H2 to CO is around 1.5. When converter gas is used in the method described in Patent Document 2, it is difficult to adjust the composition of the reducing gas to the proper composition for operation of the iron reduction process because the converter gas has a low H ₂ content.

The present invention has been devised in view of the above-mentioned current situation, and it is an object of the present invention to provide a method for realizing energy saving and reducing CO ₂ emissions when producing reduced iron from iron oxide. do.

The inventors have made intensive studies to solve the above-mentioned problems of the prior art, and as a result, have developed a novel method for producing reduced iron as described below.
That is, the gist of the present invention is as follows.
1. A method for producing reduced iron from iron oxide using a reducing furnace,
An iron oxide filling step of filling the iron oxide into the reducing furnace;
a reducing gas blowing step of blowing a reducing gas into the reducing furnace;
A mixing step of mixing the top gas discharged from the top of the reducing furnace and the blast furnace gas discharged from the top of the blast furnace to generate a mixed gas;
a separation step of separating and removing CO ₂ and H ₂ O from the mixed gas to generate the reducing gas;
a heating step of heating the reducing gas;
a reducing step of reducing the iron oxide with the reducing gas in the reducing furnace;
A method for producing reduced iron having

2. 2. The method for producing reduced iron according to 1 above, wherein the blast furnace is a blast furnace that uses oxygen gas for air blowing.

According to the present invention, whereas natural gas is conventionally used to produce the reducing gas for iron oxide raw materials, the exhaust gas from the reducing furnace and the blast furnace gas discharged from the blast furnace are mixed, and CO ₂ is produced from this mixed gas. and H ₂ O are appropriately removed to adjust the composition to produce a reducing gas, and this reducing gas is subjected to a reduction treatment of iron oxide. CO ₂ emissions in the manufacturing process can be greatly reduced. In addition, when oxygen gas is used as the blast gas and blast furnace gas from a blast furnace is used to produce the reducing gas, the concentration of the resulting reducing gas can be maintained at a high level, so that the reduction efficiency in the reduced iron production process can be further increased. can.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows the reduced iron manufacturing equipment used for one Embodiment of this invention. It is a schematic diagram which shows the reduced iron manufacturing equipment used for a comparative example. It is a schematic diagram which shows the reduced iron manufacturing equipment used for a comparative example.

The present invention is a method for producing reduced iron from iron oxide using a reducing furnace,
An iron oxide filling step of filling the reducing furnace with the iron oxide, a reducing gas blowing step of blowing reducing gas into the reducing furnace, and a top gas discharged from the top of the reducing furnace and from the top of the blast furnace. A mixing step of mixing with discharged blast furnace gas to generate a mixed gas; a separation step of separating and removing CO ₂ and H ₂ O from the mixed gas to generate the reducing gas; and heating the reducing gas. It has a heating step and a reducing step of reducing the iron oxide with the reducing gas in the reducing furnace.
Below, the method for producing reduced iron of the present invention will be described in detail according to embodiments.

One embodiment of the present invention will be described with reference to a reduced iron manufacturing facility schematically shown in FIG. In the figure, 1 is a reducing furnace, 2 is iron oxide, 3 is reduced iron, 4 is a dust remover, 5 is a mixing device, 6 is a dehydrator, 7 is a heating device, 8 is a separator, 11 is a blast furnace, and 12 is A tuyere, 13 a dewatering device and 14 a burner.

[Method of operating the reducing furnace]
In this embodiment, reduced iron is produced according to the following procedure. First, the iron oxide 2 is charged from above into the reducing furnace 1, which is the center of the reduced iron manufacturing process, and the iron oxide 2 is gradually lowered. During the descent process of the iron oxide 2 , the iron oxide 2 is reduced by blowing a high-temperature reducing gas containing CO and H ₂ from the middle portion of the reducing furnace 1 , and the reduced iron 3 is discharged from the lower portion of the reducing furnace 1 . During the reduction treatment in the reducing furnace 1, a furnace top gas mainly containing CO, _CO2 , _H2 and _H2O is discharged from the upper part of the reducing furnace 1. This furnace top gas is dust-removed by the dust remover 4 and then partly sent to the mixer 5 as a raw material gas for reducing gas. The remaining top gas is dehydrated in the dehydrator 6 and then used as a heating fuel in the heating device 7 . When burning the furnace top gas in the heating device 7, air may be used as a combustion support gas.

In this embodiment, if CO ₂ -free electricity is used as the energy source for the production of oxygen and the separation of CO ₂ and H ₂ O described later, CO ₂ emissions can be reduced to zero in principle. can be done. Here, as the CO ₂ -free electric power, electric power generated by, for example, solar power generation or nuclear power generation may be used.

In this embodiment, a mixed gas obtained by mixing blast furnace gas in addition to the furnace top gas is used as the raw material gas of the reducing gas. Conventionally, natural gas was supplied from the outside as a hydrocarbon gas for reforming the top gas components (CO, CO ₂ , H ₂ and H ₂ O) into reducing components (CO and H ₂ ). As described above, in the embodiment according to the present invention, instead of the hydrocarbon gas supplied from the outside such as natural gas, the mixed gas of the blast furnace gas and the top gas discharged from the blast furnace 11 is adjusted. It is important to use the gas as a reducing gas.
This embodiment is a method that is advantageously established when a reduced iron production process is installed in a steelworks having a blast furnace for producing molten iron.

[Blast furnace operation method]
First, a method of operating a blast furnace, which is a supplier of the blast furnace gas that is the raw material gas of the reducing gas in the embodiment of the present invention, will be described. As shown in FIG. 1, raw materials such as sintered ore, lump ore, pellets (hereinafter also referred to as ore raw materials), coke, and the like are charged from the top of a blast furnace 11 into the blast furnace (not shown). Further, a blowing gas and a reducing agent are blown into the blast furnace 11 from tuyeres 12 installed in the lower part of the blast furnace 11 . In order to distinguish the reducing agent injected into the blast furnace 11 from the tuyere 12 from coke, it is also called the injected reducing agent.
The ore raw material charged into the blast furnace 11 is reduced by carbon monoxide gas and hydrogen gas generated by the reaction between the blowing gas and the reducing agent. In the reduction reaction of the ore raw material, carbon dioxide is generated and discharged from the top of the blast furnace as a by-product gas together with carbon monoxide, hydrogen, etc. that have not reacted with the ore raw material. Since the top of the blast furnace 11 is under a high pressure condition of about 2.5 atmospheres, the blast furnace gas (by-product gas) discharged from the top of the blast furnace is expanded and cooled to condense water vapor when returning to normal pressure. Then, in the dehydrator 13, the condensed water is removed.

At least part of the blast furnace gas generated in the operation of the blast furnace described above is introduced into the mixing device 5 described above. Then, in the mixing device 5, it is mixed with the furnace top gas of the reduction furnace 1 to generate a mixed gas. Since the inside of the blast furnace is a reducing atmosphere, the blast furnace gas contains almost no sulfur content, which causes deterioration troubles of the adsorbent in the subsequent separation step. In addition, since blast furnace gas contains 5 to 20% hydrogen, there is an advantage that the proper gas composition for the reduced iron process, that is, the H ₂ /CO ratio can be easily adjusted.

Here, the mixing ratio of the blast furnace gas and the furnace top gas in the mixed gas to be generated does not need to be particularly regulated, but the gas composition after mixing should have a H ₂ /CO value of between 0.5 and 4. from the viewpoint of stable operation of the reduced iron process.

Next, CO ₂ and H ₂ O are separated and removed from the mixed gas in a separator 8 in order to increase the reduction potential. This separation step enriches the concentration of reducing components (CO and H ₂ ) to produce a reducing gas from the mixed gas. Here, in separating and removing CO ₂ and H ₂ O, it is preferable to remove CO ₂ and H ₂ O as much as possible.

As for the separator 8, for example, PSA can be used for CO ₂ separation, and a gas-liquid separation tank can be used for H ₂ O separation, but the device configuration is not limited to these.

The reducing gas thus obtained is heated by the heating device 7 and supplied to the reduction furnace 1 as a high-temperature reducing gas.

In this embodiment, since CO ₂ from the blast furnace is reused as a raw material for the reducing gas in the reduced iron process, there is an effect of reducing CO ₂ emissions from the blast furnace. Assuming the total CO ₂ emissions of the blast furnace and the reduced iron production process, the increase in CO ₂ emissions from the ironworks when the reduced iron production process is expanded is zero. CO ₂ emissions will be zero. By charging the reduced iron produced in the reducing furnace 1 into the blast furnace 11 as a raw material, it is possible to reduce the reducing agent ratio of the blast furnace and further reduce CO ₂ .

Here, in the present embodiment, it is preferable to use oxygen gas instead of hot air (air heated to about 1200° C.) as the blowing gas for the tuyeres 12 .
That is, when hot air (air heated to about 1200 ° C.) is used as the blowing gas, the combustion gas contains about 50% by volume of nitrogen that does not contribute to the combustion reaction, and the blast furnace gas contains about 50% of nitrogen gas. Since the blast furnace gas is contained, the concentration of the reducing gas obtained by using the blast furnace gas as the raw material gas is lowered. Therefore, it is advantageous to use blast furnace gas discharged from a blast furnace that uses oxygen gas as the source gas. At this time, the nitrogen concentration in the blast furnace gas becomes almost zero, and the blast furnace gas consists almost exclusively of CO, CO ₂ and H ₂ , making it suitable as a raw material for reducing gas.

Incidentally, in the tuyeres 12, the blown reducing material and oxygen gas are mixed, and the mixed gas undergoes rapid ignition and rapid combustion immediately after being blown into the blast furnace 11 from the tuyeres 12. A raceway is formed in the blast furnace ahead of the tuyeres 12, which is a region where oxygen gas reacts with injected reducing agents such as regenerated methane gas and coke.

In addition, when the oxygen concentration in the blast gas increases, the amount of gas in the furnace decreases, and the temperature rise of the charge in the upper part of the blast furnace may become insufficient. In this case, as shown in FIG. 1, part of the blast furnace gas downstream of the dehydrator 13 is partially burned by the burner 14 to a temperature of about 800° C. to 1000° C., and then blown into the blast furnace shaft. Preheating gas blowing is preferably carried out.

Examples of the present invention are described below. In addition, here, the operational specifications are described as a basic unit per 1 ton of reduced iron (DRI) production. For example, when considering a 3000 t/day reduced iron plant, multiply the following by 3000 to get the specifications per day.
[Invention Example 1]
Using the reduced iron manufacturing facility attached to the blast furnace schematically shown in FIG. 1, the following reducing furnace operation was performed. That is, 1394 kg/t of sintered ore is charged as iron oxide 2 from the upper part of the reduction furnace 1, and 2205 Nm ³ /t (H ₂ : 42% by volume) of high-temperature reducing gas heated to 800° C. , CO: 57% by volume) was blown. At this time, 2205 Nm ³ /t (H ₂ : 32% by volume, CO: 43% by volume, CO ₂ : 15% by volume, H ₂ O: 10% by volume) of furnace top gas was discharged from the upper part of the furnace 1. .

On the other hand, blast furnace gas (H ₂ : 24% by volume, CO: 33% by volume, CO ₂ : 43% by volume) generated from a blast furnace using oxygen gas as the blast gas is taken out after dehydration, equivalent to 1430 Nm ³ /t, It was mixed with the furnace top gas in the device 5 and used as a raw material gas for the reducing gas. Next, a mixed gas of 3280 Nm ³ /t, which is a mixture of the top gas and blast furnace gas, is fed to the separation device 8, where dehydration (H ₂ O separation removal) and CO ₂ separation are performed, and 154 kg / t of gas is extracted from the mixed gas. Water and 885 Nm ³ /t of CO ₂ were removed. A reducing gas of 2205 Nm ³ /t obtained by dehydration and CO ₂ separation was heated by the heating device 7 to obtain a high-temperature reducing gas. Here, 354 Nm ³ /t of the furnace top gas that was not used as the raw material gas was used as the heating fuel gas in the heating device 7 . This heated fuel gas was dehydrated and then burned in the combustion chamber of the heating device to serve as a heat source for heating the reducing gas.

In the above operation, CO ₂ is generated when part of the furnace top gas is burned in the heating device 7, but on the other hand, the CO and CO ₂ discharged from the blast furnace are reused in the reduced iron process. As a result, CO ₂ reduction was realized, and when viewed in total, there was no increase or decrease in CO ₂ emissions from the ironworks when the reduced iron process was expanded.

Furthermore, when the reduced iron obtained in the above-described reduced iron production process was charged into the blast furnace 11 as a raw material and the blast furnace was operated, the amount of coke used in the blast furnace could be reduced, and a further CO ₂ reduction effect was obtained.

[Comparative Example 1]
A general reducing furnace operation using the reduced iron production equipment shown in FIG. 2 was performed. This general reduction furnace operation is Comparative Example 1 in which natural gas is used as the raw material added to the furnace top gas used as the raw material gas in the above-described invention examples. That is, 2200 Nm ³ /t (H ₂ : 62% by volume, CO: 38% by volume) of high-temperature reducing gas heated to 800° C. was blown from the middle portion of the reducing furnace 1 to operate the reducing furnace. At this time, 2200 Nm ³ /t (H ₂ : 46% by volume, CO: 29% by volume, CO ₂ : 10% by volume, H ₂ O: 15% by volume) of furnace top gas was discharged from the upper part of the furnace. After removing dust from the top gas, 1501 Nm ³ /t was used as the source gas, and the remaining 699 Nm ³ /t of the top gas was used as the heating fuel gas for the reformer 10 . The furnace top gas used as the raw material gas was sent to the reformer 10 after removing 86 kg/t of water in the dehydrator 9 for moisture adjustment. After being dehydrated, the heated fuel gas was combusted with air in the combustion chamber of the reformer 10, and the flue gas was released into the atmosphere. In the reformer 10, 269 Nm ³ /t of natural gas was flowed together with the raw material gas to produce a reducing gas.
In the operation described above, the amount of CO ₂ emitted as flue gas from the reformer 10 was converted to 528 kg-CO ₂ /t, and CO ₂ emissions could not be suppressed.

[Comparative Example 2]
A general reducing furnace operation using the reduced iron manufacturing equipment shown in FIG. 3 was performed. This general reduction furnace operation is Comparative Example 2 in which coke oven gas is used as the raw material added to the furnace top gas used as the raw material gas in the above-described invention examples. That is, in Comparative Example 2, reduced iron is produced by flowing coke oven gas of 524 Nm ³ /t into the gas heating device 10 instead of natural gas in Comparative Example 1. Therefore, as in Comparative Example 1, the CO ₂ released as the combustion exhaust gas from the gas heating device 10 is converted to 456 kg-CO ₂ /t, which is part of the coke oven gas generated in the steelworks. Since it was diverted to the reduced iron process, the CO ₂ emissions from the coke oven side also decreased by 456 kg-CO ₂ /t, and the balance is zero for the ironworks. However, unlike blast furnace gas, coke oven gas is used as a process gas in downstream processes, so it cannot be replaced by CO ₂ -free power or hydrogen obtained by water electrolysis using CO ₂ -free power. Therefore, in the method of Comparative Example 2, it is necessary to introduce 284 Nm ³ /t of external methane (natural gas, etc.) in the downstream process. As a result, the steelworks as a whole increased CO ₂ emissions by 557 kg/t, and CO ₂ emissions could not be suppressed. In addition, coke oven gas contains a large amount of sulfur, and the reaction-promoting catalyst provided in the gas heating device is vulnerable to sulfur, so it was necessary to additionally install large-scale desulfurization equipment.

The coke oven gas used in Comparative Example 2 is an important process gas used as a fuel for downstream processes in an integrated steelworks, such as a burner fuel for a heating furnace, so a large amount is used in the reduced iron process. And the problem of running out of fuel in the downstream process occurs. The amount of coke oven gas generated when producing coke used in a steel plant having a 10,000 t/day blast furnace is 1,690,000 Nm ³ /day. If the production amount of reduced iron is 3000 t/day, the coke oven gas consumed in the reduced iron production process of the present invention is 1,570,000 Nm ³ /t, and almost the entire amount of generated coke oven gas is used up. become. Therefore, the method of Comparative Example 2 cannot be applied to an actual ironworks.

1 reducing furnace 2 iron oxide 3 reduced iron 4 dust removal device 5 mixing device 6 dehydration device 7 heating device 8 separation device 9 dehydration device 10 reformer 11 blast furnace 12 tuyere 13 dehydration device 14 burner

Claims (1)

A method for producing reduced iron from iron oxide using a reducing furnace,
An iron oxide filling step of filling the iron oxide into the reducing furnace;
a reducing gas blowing step of blowing a reducing gas into the reducing furnace;
A mixing step of mixing the top gas discharged from the top of the reducing furnace with the blast furnace gas discharged from the top of the blast furnace using oxygen gas for blowing as it is to generate a mixed gas;
a separation step of separating and removing CO ₂ and H ₂ O from the mixed gas to generate the reducing gas;
a heating step of heating the reducing gas;
a reducing step of reducing the iron oxide with the reducing gas in the reducing furnace;
A method for producing reduced iron having

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