JP2021172861A - Method for producing reduced iron - Google Patents

Abstract

To provide a method for producing reduced iron from iron oxide which enables the realization of energy saving and the reduction of a CO2 output.SOLUTION: The method for producing reduced iron includes: an iron oxide filling step of filling iron oxide into a reduction furnace; a reduction gas blowing step of blowing a reduction gas into the reduction furnace; a mixing step of mixing a furnace top gas exhausted from a furnace top of the reduction furnace and a blast furnace gas exhausted from a furnace top of a blast furnace to generate a mixed gas; a separation step of separating and removing CO2 and H2O from the mixed gas to generate the reduction gas; a heating step of heating the reduction gas; and a reduction step of reducing the iron oxide by the reduction gas in the reduction furnace.SELECTED DRAWING: Figure 1

Description

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

In recent years, against the background of global environmental problems and fossil fuel depletion problems, energy saving and reduction of carbon dioxide (CO ₂ ) emissions have been strongly demanded in various fields. This is no exception in steelworks, and efforts are being made to save energy in each process of the steelworks.

By the way, the raw material of iron is mainly iron oxide, and a reduction process for reducing this iron oxide is indispensable. The most popular and common reduction process in the world is the blast furnace. In this blast furnace, coke or pulverized coal and oxygen in hot air (air heated to about 1200 ° C.) are reacted at the tuyere _{to generate CO and H 2} gas (reduced gas), and these reduced gases are used in the furnace. Iron ore, etc. is being reduced. Due to recent improvements in blast furnace operation technology, the reducing agent ratio (the amount of coke and pulverized coal used per 1 ton of hot metal) has been reduced to about 500 kg / t, but the reduction of the reducing agent ratio has already reached its limit. No further significant reduction in the ratio of reducing agents can be expected.

On the other hand, in areas where natural gas is produced, vertical reduction furnaces are filled with agglomerated iron ore (hereinafter collectively referred to as iron oxide) such as sintered ore and pellets as a raw material for iron oxide, and hydrogen and iron oxide are used. A method of producing reduced iron by blowing 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 raw material 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 reduction furnace to generate a reduction gas. The generated reducing gas is blown into the reduction furnace and reacts with the iron oxide raw material supplied from the upper part of the reduction furnace, and the iron oxide is reduced to become reduced iron. The produced reduced iron is discharged from the lower part of the reduction furnace. The gas after the iron oxide is reduced is discharged from the top of the reduction furnace as the top gas, and after dust collection and cooling, a part of the gas is sent to the reformer as a raw material for the reforming gas. The remaining furnace 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, the exhaust gas of the reduction furnace and the natural gas are reformed by a reformer _{to generate a reduced gas mainly composed of CO and H 2} gas, and this reduction is performed. It is described that gas is blown into a reduction furnace to reduce iron oxide in the reduction furnace to produce reduced iron.

Further, Patent Document 2 _{describes a method of producing reduced iron by reforming coke oven gas and the 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.

Japanese Unexamined Patent Publication No. 2017-888912 Japanese Patent No. 6190522

The method for producing reduced iron described in Patent Document 1 uses natural gas for producing reduced gas, and therefore has a problem that a _{certain amount of CO 2 emission is unavoidable, although it is lower than that of a blast furnace.}

Further, the method described in Patent Document 2 is to produce a reduction gas using coke oven gas or linz-donaw gas generated in a steel mill, but the coke oven gas and linz-donaw gas are heated in an integrated steelworks. Since it is indispensable as a fuel gas for the lower process of a furnace or an annealing furnace, if it is diverted to the reduced iron production process, it will cause a shortage of fuel gas in the lower process. As a result, in the end, natural gas was supplied externally to compensate for the shortage of gas in the lower process, _{and reduction of CO 2} emissions remained an issue without being realized.

Further, in the method described in Patent Document 2, the coke oven gas is reformed as a raw material to obtain a reducing gas, but since the coke oven gas contains a large amount of sulfur, the adsorbent in the _{CO 2 separator is damaged.} There are concerns. In addition, it is said that the reduced iron production process can be operated properly when the ratio _{of H 2 to CO is around 1.5.} When the linz-Donaw gas is used in the method described in Patent Document 2, it is difficult to adjust the composition of the reduction gas to the above-mentioned operation-appropriate composition of the reduction production iron process because the linz-Donaw gas has a low _{H 2 content.}

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

As a result of diligent research to solve the above-mentioned problems of the prior art, the inventors have developed a new method for producing reduced iron described below.
That is, the gist of the present invention is as follows.
1. 1. A method of producing reduced iron from iron oxide using a reduction furnace.
An iron oxide filling step of filling the reduction furnace with the iron oxide, and
The reduction gas blowing process of blowing the reducing gas into the reduction furnace and
A mixing step of mixing the top gas discharged from the top of the reduction 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, and
The heating step of heating the reducing gas and
A reduction step of reducing the iron oxide with the reducing gas in the reduction furnace,
A method for producing reduced iron having.

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

According to the present invention, in contrast to the conventional method of producing reduced gas as a raw material for iron oxide using natural gas, 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.} As a result of realizing a reduced iron production process using blast furnace gas, which appropriately removes H ₂ O and adjusts the composition to produce reduced gas, and uses this reduced gas for the reduction treatment of iron oxide, reduced iron. _{CO 2} emissions in the manufacturing process can be significantly reduced. Further, when the reduction gas is produced by using the blast furnace gas of the blast furnace, which uses oxygen gas as the blowing gas, the concentration of the obtained reduction gas can be maintained high, so that the reduction efficiency in the reduced iron production process can be further improved. can.

It is a schematic diagram which shows the reduced iron production facility used in one Embodiment of this invention. It is a schematic diagram which shows the reduced iron production facility used for a comparative example. It is a schematic diagram which shows the reduced iron production facility used for a comparative example.

The present invention is a method for producing reduced iron from iron oxide using a reduction furnace.
From the iron oxide filling step of filling the reduction furnace with the iron oxide, the reduction gas blowing step of blowing the reduction gas into the reduction furnace, and the top gas discharged from the top of the reduction furnace and the top of the blast furnace. A mixing step of mixing the 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 reduced gas, and heating the reduced gas. It has a heating step and a reduction step of reducing the iron oxide with the reducing gas in the blast furnace.
Hereinafter, the method for producing reduced iron of the present invention will be described in detail according to the embodiment.

An embodiment of the present invention will be described with reference to the reduced iron production facility schematically shown in FIG. In the figure, reference numeral 1 is a reduction furnace, 2 is iron oxide, 3 is reduced iron, 4 is a dust remover, 5 is a mixing device, 6 is a dehydrating device, 7 is a heating device, 8 is a separation device, 11 is a blast furnace, and 12 is. The tuyere, 13 is a dehydrator and 14 is a burner.

[Operation method of reduction furnace]
In this embodiment, reduced iron is produced according to the following procedure. First, iron oxide 2 is charged from above into the reduction furnace 1 which is the center of the reduced iron production process, and the iron oxide 2 is gradually lowered. In the process of lowering the iron oxide 2, the iron _{oxide 2 is reduced by blowing a reducing gas containing high temperature CO and H 2} from the intermediate portion of the reduction furnace 1, and the reduced iron 3 is discharged from the lower part of the reduction furnace 1. In the reduction treatment in the reduction furnace 1, the furnace top gas containing _{CO, CO 2} , H ₂ and H _{2 O is mainly discharged from the upper part of the reduction furnace 1.} After the furnace top gas is dust-removed by the dust removing device 4, a part of the furnace top gas is sent to the mixing device 5 as a raw material gas for reducing gas. The remaining furnace top gas is dehydrated by the dehydrating device 6 and then used as heating fuel in the heating device 7. When the furnace top gas is burned by the heating device 7, air may be used as the combustion assisting gas.

_{In this embodiment, if CO 2-} free electric power is used as an energy source for producing the oxygen and _{separating CO 2} and H ₂ O, which will be described later, in principle, CO ₂ emissions are reduced to zero. Can be done. Here, as the CO _2- free electric power, for example, electric power generated by solar power generation or nuclear power generation may be used.

In the present embodiment, a mixed gas in which a blast furnace gas is mixed in addition to the furnace top gas is used as the raw material gas for the reduction gas. Conventionally, natural gas has been supplied from the outside as a hydrocarbon gas for reforming the furnace top gas components (CO, CO ₂ , H ₂ and H ₂ O) into reducing components (CO and H _2). Is as described above, but in the embodiment according to the present invention, a mixed gas of the blast furnace gas and the furnace top gas discharged from the blast furnace 11 is adjusted instead of the hydrocarbon gas supplied from the outside such as natural gas. It is important to use it as a reducing gas.
This embodiment is a method that is advantageous when a reduced iron production process is installed in a steel mill having a blast furnace for producing hot metal.

[Blast furnace operation method]
First, the operation method of the blast furnace, which is the supply source of the blast furnace gas which is the raw material gas of the reduction gas in the embodiment of the present invention, will be described. As shown in FIG. 1, sinter, lump ore, pellets (hereinafter, also referred to as ore raw materials), coke, etc., which are raw materials, are charged into the blast furnace from the top of the blast furnace 11 (not shown). Further, the blowing gas and the reducing agent are blown into the blast furnace 11 from the tuyere 12 installed in the lower part of the blast furnace 11. The reducing agent blown from the tuyere 12 into the blast furnace 11 is also referred to as a blown reducing material in order to distinguish it from coke.
Then, the ore raw material charged in the blast furnace 11 is reduced by the carbon monoxide gas and hydrogen gas generated by the reaction between the blower gas and the reducing agent. In the reduction reaction of the ore raw material, carbon dioxide is generated, and it is discharged from the top of the blast furnace as a by-product gas together with carbon monoxide and hydrogen that did not react with the ore raw material. Since the top of the blast furnace 11 is under a high pressure condition of about 2.5 atm, the blast furnace gas (by-product gas) discharged from the top of the blast furnace is condensed by expansion and cooling when it returns to normal pressure. Then, in the dehydrator 13, the condensed water is removed.

At least a part of the blast furnace gas generated in the operation of the blast furnace is introduced into the mixing device 5 described above. Then, in the mixing device 5, the mixed gas is generated by mixing with the top gas of the reduction furnace 1. Since the inside of the blast furnace has a reducing atmosphere, the blast furnace gas contains almost no sulfur content, which causes deterioration trouble of the adsorbent in the later separation step. Further, since the blast furnace gas contains 5 to 20% hydrogen, there is an advantage that it is easy to properly adjust _{the proper gas composition of the reduced iron process, that is, the H 2 / CO ratio.}

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

_{Next, CO 2} and H ₂ O are separated and removed by the separation device 8 in order to increase the reduction potential of the mixed gas. By this separation step, the concentration of the reducing component (CO and H ₂ ) is increased to generate a reducing gas from the mixed gas. Here, the CO ₂ and H ₂ O separation and removal, it is preferable to remove as much as possible CO ₂ and H ₂ O.

For the separation device 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 reduction gas thus obtained is heated by the heating device 7 described above and supplied to the reduction furnace 1 as a high-temperature reduction 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 that _{CO 2 emissions from the blast furnace can be reduced. Assuming the total CO 2} emissions of the blast furnace and the reduced iron manufacturing process, the _{increase in CO 2} emissions of the steelworks when the reduced iron manufacturing process is added is zero. CO ₂ emissions will be zero. By charging the reduced iron produced in the reduction furnace 1 into the blast furnace 11 as a raw material, the ratio of the reducing material in the blast furnace can be reduced, and further CO ₂ reduction can be performed.

Here, in the present embodiment, it is preferable to use oxygen gas as the blowing gas for the tuyere 12 instead of hot air (air heated to about 1200 ° C.).
That is, when hot air (air heated to about 1200 ° C.) is used as the blowing gas, about 50% by volume of nitrogen that does not contribute to the combustion reaction is contained in the combustion gas, and about 50% of the nitrogen gas is contained in the blast furnace gas. Since it is contained, it causes a disadvantage that the concentration as a reducing gas obtained by using this blast furnace gas as a raw material gas becomes low. Therefore, it is advantageous to use the blast furnace gas discharged from the blast furnace that uses oxygen gas as a blower as the raw material gas. At this time, the nitrogen concentration in the blast furnace gas becomes almost zero, and the blast furnace gas contains _{only CO, CO 2} and H _2, which makes it suitable as a raw material for the reducing gas.

Incidentally, in the tuyere 12, the blowing reducing agent and the oxygen gas are mixed, and the mixed gas is rapidly ignited and rapidly burned immediately after being blown into the blast furnace 11 from the tuyere 12. Then, in the blast furnace at the tip of the tuyere 12, a raceway is formed, which is a region where a blown reducing agent such as regenerated methane gas or coke reacts with oxygen gas.

If the oxygen concentration in the blown gas increases, the amount of gas in the furnace decreases, and the temperature rise of the charged material in the upper part of the blast furnace may become insufficient. In this case, as shown in FIG. 1, a part of the blast furnace gas downstream of the dehydrator 13 is partially burned by the burner 14 so as to be about 800 ° C. to 1000 ° C., and then blown into the blast furnace shaft portion. It is preferable to blow in preheated gas.

Hereinafter, examples of the present invention will be described. Here, the operating specifications are described as the basic unit for producing 1 ton of reduced iron (DRI). For example, when considering a reduced iron plant of 3000 tons / day, multiplying the following by 3000 gives the specifications per day.
[Invention Example 1]
The following reduction furnace operation was performed using the reduced iron production equipment attached to the blast furnace schematically shown in FIG. 1. That is, 1394 kg / t of sinter was charged as iron oxide 2 from the upper part of the reduction furnace 1, and the high temperature reducing gas 2205 Nm ³ / t (H ₂ : 42% by volume) heated to 800 ° C. from the middle part of the furnace 1. , 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, the blast furnace gas (H 2} : 24% by volume, CO: 33% by volume, CO ₂ : 43% by volume) generated from the blast furnace that uses oxygen gas as the blast gas is taken out equivalent to ^{1430 Nm 3} / t after dehydration, and it rains heavily. In the apparatus 5, it was mixed with the above-mentioned furnace top gas and used as a raw material gas for the reduction gas. Then, feeds feeding a mixed gas 3280Nm ³ / t of a mixture of top gas and blast furnace gas to the separation device 8, performs dehydration (H ₂ O separated off) and CO ₂ separated from a mixed gas of 154 kg / t Water and 885 Nm ³ / t CO ₂ were removed. The reducing gas 2205 Nm ³ / t obtained by dehydration and CO ₂ separation was heated by the heating device 7 to obtain a high-temperature reduced gas. Here, in the heating device 7, the remaining gas of the furnace top gas, which was not used as the raw material gas, was 354 Nm ³ / t, which was used as the heating fuel gas. 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 reduced gas.

_{In the above operation, CO 2} is generated when a part of the furnace top gas is burned in the heating device 7, while CO and CO ₂ discharged from the blast furnace are reused in the reducing iron process. As a result, CO ₂ reduction was realized, and when viewed in total, the increase or decrease _{in CO 2 emissions from the steelworks when the reduced iron process was added was zero.}

Further, when the reduced iron obtained in the above-mentioned reduced iron production process was charged into the blast furnace 11 as a raw material and operated in the blast furnace, 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 reduction furnace operation using the reduced iron production equipment shown in FIG. 2 was carried out. This general reduction furnace operation is Comparative Example 1 in which the raw material added to the furnace top gas as the raw material gas is natural gas in the above-mentioned invention example. ^{That is, the reduction furnace was operated by blowing 2200 Nm 3} / t (H ₂ : 62% by volume, CO: 38% by volume) of high-temperature reduction gas heated to 800 ° C. from the middle portion of the reduction furnace 1. At this time, 2200Nm ³ / t from the furnace top (H _2: 46 vol%, CO: 29 vol%, CO _2: 10 vol%, H ₂ O: 15% by volume) furnace top gas is discharged. After removing the dust from the top gas, 1501 Nm ³ / t was used as the raw material gas, and the remaining 699 Nm ³ / t of the top gas was used as the heating fuel gas for the reformer 10. As the raw material gas, the furnace top gas was sent to the reformer 10 after removing 86 kg / t of water with the dehydrator 9 for adjusting the water content. After dehydration, the heated fuel gas was burned with air in the combustion chamber of the reformer 10, and the combustion exhaust gas was released to the atmosphere. In the reformer 10, natural gas 269 Nm ³ / t was poured together with the raw material gas to produce a reduced gas.
_{In the above operation, the CO 2} emitted as the combustion exhaust gas of the reformer 10 was converted to 528 kg-CO ₂ / t, and the CO ₂ emission could not be suppressed.

[Comparative Example 2]
A general reduction furnace operation using the reduced iron production equipment shown in FIG. 3 was carried out. This general reduction furnace operation is Comparative Example 2 in which the raw material added to the furnace top gas as the raw material gas is the coke oven gas in the above-mentioned invention example. That is, in Comparative Example 2, in Comparative Example 1, ^{reduced iron is produced by pouring 524 Nm 3} / t coke oven gas into the gas heating device 10 instead of natural gas. _{Therefore, as in Comparative Example 1, the CO 2} emitted as the combustion exhaust gas of the gas heating device 10 is 456 kg-CO ₂ / t, which is a part of the coke oven gas generated in the steelworks. Since it was diverted to the reduced iron process, CO ₂ emissions on the coke oven side are also reduced by 456 kg-CO ₂ / t, which is zero for a steel mill. However, unlike blast furnace gas, coke oven gas is used as a process gas in the lower process, so it cannot be replaced by hydrogen obtained by _{CO 2-} free power or _{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 or the like) in the lower step. When this by viewed as a whole steelworks, become a CO ₂ emission increase of 557kg / t, it was not able to suppress the emission of CO _2. Further, since the coke oven gas contains a large amount of sulfur and the reaction promoting catalyst provided in the gas heating device is vulnerable to sulfur, it is necessary to additionally install a large-scale desulfurization facility.

Since the coke oven gas used in Comparative Example 2 is an important process gas used as a fuel for the lower process in an integrated steel mill, for example, a burner fuel for a heating furnace, it is used in a large amount in the reduced iron process. And the problem of running out of fuel in the lower process occurs. The amount of coke oven gas generated when producing coke used in a steel mill with a blast furnace of 10000 t / day is 1.69 million Nm ³ / day. Assuming that the production amount of reduced iron is 3000 tons / day, the coke oven gas consumed in the reduced iron production process of the present invention is 1.57 million Nm ³ / t, and almost all of the generated coke oven gas is used up. become. Therefore, the method of Comparative Example 2 cannot be applied to an actual steel mill.

1 Reduction furnace 2 Iron oxide 3 Reduced iron 4 Dust remover 5 Mixing device 6 Dehydrating device 7 Heating device 8 Separator 9 Dehydrating device 10 Reformer 11 Blast furnace 12 Tuft 13 Dehydrating device 14 Burner

Claims (2)

A method of producing reduced iron from iron oxide using a reduction furnace.
An iron oxide filling step of filling the reduction furnace with the iron oxide, and
The reduction gas blowing process of blowing the reducing gas into the reduction furnace and
A mixing step of mixing the top gas discharged from the top of the reduction 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, and
The heating step of heating the reducing gas and
A reduction step of reducing the iron oxide with the reducing gas in the reduction furnace,
A method for producing reduced iron having. The method for producing reduced iron according to claim 1, wherein the blast furnace is a blast furnace that uses oxygen gas for blowing air.

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