Method for producing reduced iron

Abstract

This method for producing reduced iron includes a raw material charging step of charging raw materials into a shaft furnace, a reduction step of reacting the raw materials with a reducing gas in the shaft furnace to obtain reduced iron and exhaust gas after reduction, and an exhaust gas circulation step of circulating the exhaust gas after reduction and using it as part of the reducing gas. The raw material charging step includes, in order, a pressure reduction step, a first purge step, a raw material input step, a second purge step, a pressure equalization step, and a raw material discharge step. The exhaust gas circulation step includes a dehydration step of removing water from the exhaust gas after reduction. The purge gas is an inert gas, and the pressure equalization gas is the gas from which water has been removed from the exhaust gas in the dehydration step.

Description

Technical Field

[0001] The present invention relates to a method for producing reduced iron. This application claims priority based on Japanese Patent Application No. 2024-059600 filed in Japan on April 2, 2024, the content of which is incorporated herein by reference.

Background Art

[0002] Currently, reduced iron is produced by shaft furnace operation using natural gas (NG) as a reducing gas, such as the HyL method and the Midrex method.

[0003] In the production of reduced iron, iron oxide as a raw material is charged from the upper part of the shaft furnace through a plurality of hoppers. When charging the raw material into the charging hopper for filling the raw material, the pressure in the hopper must be atmospheric pressure. However, when supplying the raw material from the hopper to the shaft furnace, the pressure in the hopper must be the pressure of the shaft furnace. Therefore, it is necessary to equalize the pressure so that the pressures become equal before the raw material is transferred from the hopper to the shaft furnace.

[0004] For the gas used for pressure equalization, an inert gas (usually nitrogen gas) is used for a purge operation to prevent an oxidation reaction with the reducing gas remaining in the pressure equalization hopper (pressure equalization hopper) after raw material charging and a pressure increase operation to make the pressure in the hopper equal to that in the furnace before raw material charging.

[0005] This inert gas enters the furnace together with the raw material and mixes into the reducing gas. Then, it accumulates in the gas during the process of the reducing gas circulation, reducing the reducing ability of the reducing gas. Therefore, conventionally, it has been necessary to appropriately release the circulating gas to prevent this concentration.

[0006] On the other hand, in the method for producing carburized sponge iron disclosed in Patent Document 1, the raw material gas is hydrogen gas, and carbon dioxide is used as the pressure equalization gas.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, in the method used in Patent Document 1, since carbon dioxide gas is used as the pressure-equalizing gas, there is a risk that more carbon dioxide than the amount consumed in carburizing will enter the shaft furnace. There is a problem that the reducing power decreases when the concentration of carbon dioxide increases in the shaft.

[0009] The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for producing reduced iron capable of suppressing the concentration of unnecessary components such as nitrogen and carbon dioxide and maintaining reduction performance. Here, the unnecessary components refer to components not used in the reduction reaction such as nitrogen, carbon dioxide, and water.

Means for Solving the Problems

[0010] In order to solve the above problems, the present invention proposes the following means. (1) The method for producing reduced iron using the shaft furnace according to Embodiment 1 of the present invention includes a raw material charging step of charging the raw material from a charging hopper for storing the raw material into the furnace of the shaft furnace operating at a pressure higher than atmospheric pressure via a pressure equalizing hopper for pressure adjustment, a reduction step of reacting the raw material and a reducing gas in the shaft furnace after the raw material charging step to obtain reduced iron and exhaust gas after reduction, an exhaust gas circulation step of circulating the exhaust gas after reduction and using it as a part of the reducing gas after the reduction step, and includes the raw material charging step includes a decompression step of decompressing the pressure of the pressure equalizing hopper from the pressure in the shaft furnace to atmospheric pressure, a first purge step of replacing the gas in the pressure equalizing hopper with a purge gas after the decompression step, After the first purge step, a raw material charging step of transferring the raw material from the charging hopper to the pressure equalizing hopper replaced with the purge gas; After the raw material charging step, a second purge step of replacing the air introduced into the pressure equalizing hopper in the raw material charging step with the purge gas; After the second purge step, a pressure equalizing step of increasing the pressure of the pressure equalizing hopper from atmospheric pressure to the pressure in the shaft furnace with the pressure equalizing gas; After the pressure equalizing step, a raw material discharging step of transferring the raw material from the pressurized pressure equalizing hopper into the shaft furnace; including; The exhaust gas circulation step is including a dehydration step of removing water from the exhaust gas after reduction, The purge gas is an inert gas, The pressure equalizing gas is the gas from which water has been removed from the exhaust gas in the dehydration step. (2)Aspect 2 of the present invention is, in the method for producing reduced iron of Aspect 1, The exhaust gas circulation step further includes a carbon dioxide removal step of removing carbon dioxide from the exhaust gas, The pressure equalizing gas is the gas from which water and carbon dioxide have been removed from the exhaust gas in the dehydration step and the carbon dioxide removal step.

Advantages of the Invention

[0011] According to each of the above aspects of the present invention, it is possible to provide a method for producing reduced iron that can suppress the concentration of unnecessary components such as nitrogen and carbon dioxide and maintain the reduction performance.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0013] (First Embodiment) Hereinafter, with reference to the drawings, a direct reduced iron manufacturing apparatus 100 for implementing the method for manufacturing reduced iron according to the first embodiment will be described. FIG. 1 is a flowchart showing an example of a direct reduction apparatus according to the first embodiment of the present invention. The direct reduced iron manufacturing apparatus 100 includes a charging hopper 12 for storing iron oxide as a raw material, a pressure equalizing hopper 14 for adjusting the pressure between the atmosphere and the pressure inside the shaft furnace, a shaft furnace 20 for manufacturing direct reduced iron using hydrogen as a raw material gas, a dehydration apparatus 30 for dehydrating the exhaust gas of the shaft furnace 20 to obtain a circulating gas, a pressure boosting apparatus 40 for boosting the circulating gas, and a heating apparatus 50 for heating the dehydrated circulating gas together with the raw material gas to obtain a reducing gas.

[0014] (Charging Hopper 12) The charging hopper 12 stores iron oxide. The charging hopper 12 transfers the iron oxide as a raw material to the pressure equalizing hopper 14 at atmospheric pressure via the raw material inlet 14a.

[0015] (Pressure Equalizing Hopper 14) After transferring the raw material into the pressure equalizing hopper 14, the pressure equalizing hopper 14 adjusts the pressure inside the pressure equalizing hopper 14. After pressure adjustment, the pressure equalizing hopper 14 sends the raw material to the raw material charging section 24 of the shaft furnace 20. The pressure equalizing hopper 14 includes a raw material inlet 14a for transferring the raw material from the charging hopper 12, a raw material discharge port 14b for sending the raw material to the raw material charging section 24 of the shaft furnace 20 after pressure equalization, a purge gas inlet 14c for injecting purge gas, a gas outlet 14d for discharging purge gas and the like, and a pressure equalizing gas inlet 14e for introducing pressure equalizing gas into the pressure equalizing hopper 14. The raw material inlet 14a is connected to the charging hopper 12, and the raw material discharge port 14b is connected to the raw material charging section 24 of the shaft furnace 20.

[0016] The operation of the pressure equalizing hopper 14 will be described below. The pressure equalizing hopper 14 closes the raw material inlet 14a, the raw material outlet 14b, the purge gas inlet 14c, and the pressure equalizing gas inlet 14e, and opens the gas outlet 14d to reduce the pressure inside the pressure equalizing hopper 14 so that it becomes atmospheric pressure. Next, the purge gas inlet 14c is opened, and an inert gas, which is the purge gas, is introduced into the pressure equalizing hopper 14. As a result, the furnace gas remaining inside the pressure equalizing hopper 14 can be replaced with the inert gas. Next, the pressure equalizing hopper 14 closes the purge gas inlet 14c, opens the raw material inlet 14a, and transfers the raw material from the charging hopper 12 to the pressure equalizing hopper 14 filled with the inert gas. After the raw material transfer, the purge gas inlet 14c is opened, and the inert gas is introduced into the pressure equalizing hopper 14. As a result, the air introduced into the pressure equalizing hopper 14 together with the raw material can be replaced with the inert gas. Here, examples of the inert gas include nitrogen gas, noble gas, CO2, H2O gas, and a mixed gas thereof. Generally, nitrogen gas is used as the inert gas. The inert gas used as the purge gas is supplied from outside the system.

[0017] Here, the purge gas refers to an inert gas introduced into the pressure equalizing hopper 14 so that the flammable reducing gas and air do not come into contact. The pressure of the purge gas is, for example, 0.2 to 1.0 MPa, and the blowing amount of the purge gas is 1V to 3V with respect to the capacity V of the pressure equalizing hopper 14. The pressure equalizing gas is a gas introduced into the pressure equalizing hopper to reduce the difference between the pressure inside the shaft furnace 20 and the pressure inside the pressure equalizing hopper 14, and refers to a gas from which moisture has been removed to about 2 vol% from the exhaust gas in the dehydration process. The pressure of the pressure equalizing gas is, for example, 0.2 to 0.8 MPa, and the blowing amount of the pressure equalizing gas is 1V to 8V with respect to the capacity V of the pressure equalizing hopper 14. Here, purging means sending gas A (here, an inert gas) into a certain space (here, the pressure equalizing hopper 14), replacing gas B (here, the reducing gas) staying in that space with gas A, and removing gas B. Equalizing pressure means making the pressure uniform.

[0018] After replacement with an inert gas, the pressure equalizing hopper 14 closes the raw material inlet 14a, the purge gas inlet 14c, and the gas outlet 14d, opens the pressure equalizing gas inlet 14e, and introduces the pressure equalizing gas into the pressure equalizing hopper 14 to increase the pressure. This pressure equalizing gas is pressurized to the pressure inside the shaft furnace 20 by a pressure increasing device 40 described later. In order to discharge the inert gas remaining inside at the initial stage of pressure increase, it is preferable to keep the gas outlet 14d open for a certain period of time. For example, it is possible to monitor whether the inert gas has been discharged using gas chromatography or the like, and close the gas outlet 14d when the amount of inert gas discharged from the gas outlet 14d no longer fluctuates.

[0019] (Shaft furnace 20) The shaft furnace 20 includes a raw material charging section 24 for charging iron oxide as a raw material, a reduced iron discharging section 25 for discharging reduced iron, a reducing gas injection port 28 disposed at the lower part of the shaft furnace 20 for injecting a reducing gas, and an exhaust gas discharge port 29 disposed at the upper part of the shaft furnace 20 for discharging exhaust gas. Iron oxide as a raw material is charged from the pressure equalizing hopper 14 through the raw material charging section 24 at the top of the shaft furnace 20. The furnace pressure inside the shaft furnace 20 is higher than atmospheric pressure. For example, the pressure near the reducing gas injection port 28 is 0.1 to 1 MPa, and is discharged from the exhaust gas discharge port 29 at a pressure reduced by the pressure loss inside the furnace. The iron oxide is reduced by the reducing gas while descending inside the shaft furnace 20 to become reduced iron. The reduced reduced iron is discharged from the reduced iron discharging section 25. The reducing gas is heated to 900 °C or higher by a heating device 50 and blown into the furnace of the shaft furnace 20 from the reducing gas injection port 28. The iron oxide is reduced by the blown reducing gas. When the reducing gas becomes hydrogen gas, the specific reaction between iron oxide and hydrogen gas is as shown in the following formula (1A). As shown in the following formula (1A), hydrogen gas becomes water (water vapor) by reacting with iron oxide. The unreacted hydrogen gas (H2) and water vapor (H2O) are sent to the dehydration device 30 through the exhaust gas discharge port 29. Fe2O3 + 3H2 → 2Fe + 3H2O (1A)

[0020] (Dehydration device 30) The dehydration device 30 dehydrates the exhaust gas discharged from the exhaust gas outlet 29. The exhaust gas discharged from the exhaust gas outlet 29 contains unreacted hydrogen gas and water vapor generated by the reduction reaction of iron oxide. The dehydration device 30 dehydrates, for example, by cooling the exhaust gas after dust removal. Since water inhibits the reduction reaction, it is preferable that the moisture concentration in the exhaust gas is as low as possible. For example, when the moisture concentration in the exhaust gas is 25 vol%, it is preferable to remove moisture until the moisture concentration is 2 vol% or less by dehydration. The dehydrated exhaust gas (circulation gas) is sent to the pressure boosting device 40. The exhaust gas may be dust-removed by a dust removal device (not shown) before being dehydrated by the dehydration device 30. The dust removal method is not particularly limited, and examples include a cyclone and a scrubber.

[0021] (Pressure boosting device 40) The pressure boosting device 40 boosts the pressure of the circulation gas dehydrated by the dehydration device 30 to atmospheric pressure or higher and sends it to the heating device 50. A part of the pressurized circulation gas is introduced into the equalizing hopper 14 as equalizing gas through the equalizing gas inlet 14e. The pressure boosting device 40 is, for example, a compressor.

[0022] (Heating device 50) The heating device 50 heats the circulation gas and the raw material gas pressurized by the pressure boosting device 40 and blows it into the reduction gas injection port 28. The reduction gas is a gas that reduces iron oxide as a raw material. In this embodiment, it becomes the circulation gas and the raw material gas. The temperature of the injected reduction gas is generally 700 to 1000 °C. Also, the injection amount of the reduction gas is generally 1000 to 2000 Nm 3 / t-DRI. The injection is performed from the reduction gas injection ports 28 evenly arranged in the circumferential direction of the shaft furnace 20. As the raw material gas, it is preferable to use hydrogen gas obtained by electrolysis of water or the like.

[0023] (Method for producing reduced iron) Next, the method for manufacturing reduced iron according to the first embodiment will be described. FIG. 2 is a flowchart of the method for manufacturing reduced iron according to the first embodiment. The method for manufacturing reduced iron according to the first embodiment includes a raw material charging step S10 of charging raw materials from a charging hopper 12 for storing the raw materials into the furnace of a shaft furnace 20 operating at a pressure higher than atmospheric pressure via a pressure equalizing hopper 14 for pressure adjustment; a reduction step S20 of reacting the raw materials with a reducing gas in the shaft furnace 20 after the raw material charging step S10 to obtain reduced iron and exhaust gas after reduction; an exhaust gas circulation step S30 of circulating the exhaust gas after reduction and using it as a part of the reducing gas after the reduction step S20; and a raw material gas supply step S40. Hereinafter, each step will be described.

[0024] (Raw material charging step S10) In the raw material charging step S10, raw materials are charged from a charging hopper 12 for storing the raw materials into the furnace of a shaft furnace 20 operating at a pressure higher than atmospheric pressure via a pressure equalizing hopper 14 for pressure adjustment. The raw material charging step S10 includes a pressure reduction step S1 of reducing the pressure of the pressure equalizing hopper 14 from the pressure in the shaft furnace 20 to atmospheric pressure; a first purging step S2 of replacing the furnace gas in the pressure equalizing hopper with a purging gas after the pressure reduction step S1; a raw material input step S3 of transferring raw materials from the charging hopper 12 to the pressure equalizing hopper 14 replaced with the purging gas after the first purging step S2; a second purging step S4 of replacing the air introduced into the pressure equalizing hopper 14 in the raw material input step S3 with a purging gas after the raw material input step S3; a pressure equalizing step S5 of increasing the pressure of the pressure equalizing hopper 14 from atmospheric pressure to the furnace pressure with a pressure equalizing gas after the second purging step S4; and a raw material discharge step S6 of transferring raw materials from the pressure equalizing hopper 14 with increased pressure into the shaft furnace 20 after the pressure equalizing step S5.

[0025] (Pressure reduction step S1) In the pressure reduction step S1, the pressure of the pressure equalizing hopper 14 is reduced from the pressure in the shaft furnace 20 to atmospheric pressure. Specifically, by closing the raw material discharge port 14b and opening the gas outlet 14d, the pressure of the pressure equalizing hopper 14 is reduced from the pressure in the shaft furnace 20 to atmospheric pressure.

[0026] (First purging step S2) In the first purge step S2, after the pressure reduction step S1, the gas in the pressure equalizing hopper 14 is replaced with the purge gas. Specifically, the purge gas inlet 14c is opened to introduce an inert gas, which is the purge gas, into the pressure equalizing hopper 14. Thereby, the furnace gas in the pressure equalizing hopper 14 mixed when charging the raw material from the pressure equalizing hopper 14 into the shaft furnace 20 can be replaced with the inert gas. It is preferable to replace with an inert gas that is three times or more the volume of the pressure equalizing hopper 14. The end of the first purge step S2 may be determined by measuring the gas components and confirming that the concentration of the gas to be replaced (reduction gas) has become equal to or lower than the specified value.

[0027] (Raw material charging step S3) In the raw material charging step S3, after the first purge step S2, iron oxide, which is the raw material, is transferred from the charging hopper 12 to the pressure equalizing hopper 14 replaced with the purge gas. Specifically, the purge gas inlet 14c is closed, the raw material inlet 14a is opened, and the raw material is transferred from the charging hopper 12 to the pressure equalizing hopper 14 that has been depressurized and replaced.

[0028] (Second purge step S4) In the second purge step S4, after the raw material charging step S3, the air introduced into the pressure equalizing hopper 14 in the raw material charging step S3 is replaced with the purge gas. The purge gas is an inert gas. Specifically, the purge gas inlet 14c is opened to introduce an inert gas, which is the purge gas, into the pressure equalizing hopper 14. Thereby, the air introduced into the pressure equalizing hopper 14 together with the raw material in the raw material charging step S3 can be replaced with the inert gas.

[0029] (Pressure equalizing step S5) In the pressure equalizing step S5, after the second purge step S4, the pressure of the pressure equalizing hopper 14 is increased to the pressure in the shaft furnace 20 from the atmospheric pressure with the pressure equalizing gas. The pressure in the shaft furnace 20 is usually controlled. The pressure equalizing gas may be increased in pressure targeting the control value of the pressure of the shaft furnace 20. Specifically, close the raw material inlet 14a and the gas outlet 14d, open the pressure equalizing gas inlet 14e, introduce the pressure equalizing gas into the pressure equalizing hopper 14, and increase the pressure. The pressure equalizing gas is pressurized to the pressure inside the shaft furnace (furnace internal pressure) by the pressure increasing device 40. The pressure equalizing gas is a part of the circulating gas that has been dehydrated by the dehydration device 30. At the initial stage of the pressure equalizing step S5, it is preferable that the inert gas (nitrogen gas) introduced in the second purge step S4 can be pushed out by the pressure equalizing gas so that the inert gas (nitrogen gas) does not accumulate in the shaft furnace 20. When pushing out the nitrogen gas with the pressure equalizing gas, open the gas outlet 14d for a while to exhaust the inert gas (nitrogen gas). The opening time when the gas outlet 14d is open can be determined by checking the variation of the inert gas with gas chromatography or the like.

[0030] (Raw material discharge step S6) In the raw material discharge step S6, after the pressure equalizing step S5, the raw material is transferred from the pressurized pressure equalizing hopper 14 into the shaft furnace 20. Specifically, by closing the pressure equalizing gas inlet 14e and opening the raw material discharge port 14b, the raw material in the pressure equalizing hopper is transferred from the pressurized pressure equalizing hopper into the shaft furnace. After the completion of the raw material discharge step S6, by returning to the pressure reduction step S1, the raw material can be continuously charged into the shaft furnace 20.

[0031] (Reduction step S20) In the reduction step S20, after the raw material charging step S10, the raw material and the reducing gas are reacted in the shaft furnace 20 to obtain reduced iron and the exhaust gas after reduction. Specifically, in the shaft furnace 20, it is reduced by the reducing gas blown from the reducing gas injection port 28 to become reduced iron (direct reduced iron), and is discharged from the reduced iron discharge part 25. When the raw material gas is hydrogen gas, the iron oxide reacts with the hydrogen gas as shown in the above formula (1A), and reduced iron and water are generated. The unreacted hydrogen gas and water vapor are discharged as exhaust gas (exhaust gas after reduction) from the exhaust gas outlet 29.

[0032] (Exhaust gas circulation step S30) In the exhaust gas circulation step S30, after the reduction step S20, the exhaust gas (the exhaust gas after reduction) discharged in the reduction step S20 is circulated and used as part of the reducing gas. When hydrogen gas is used as the raw material gas, the exhaust gas becomes hydrogen gas and water. The exhaust gas circulation step S30 includes a dehydration step of removing water from the exhaust gas after reduction. The exhaust gas discharged from the exhaust gas outlet 29 is dehydrated using the dehydration device 30. The dehydrated exhaust gas (circulation gas) is pressurized by the pressure boosting device 40, and a part of the circulation gas is used as the pressure equalizing gas in the pressure equalizing step S5. That is, the pressure equalizing gas is the gas from which water has been removed from the exhaust gas in the dehydration step. The remaining circulation gas not used in the pressure equalizing step S5 is heated by the heating device 50 and recycled as the reducing gas. That is, the remaining circulation gas not used in the pressure equalizing step S5 and heated by the heating device 50 and introduced into the shaft furnace 20 is used as part of the reducing gas.

[0033] (Raw material gas supply step S40) In the raw material gas supply step S40, the amount of hydrogen gas consumed for the reduction of the raw material (iron oxide) in the reduction step S20 is introduced into the shaft furnace 20 as the raw material gas via the heating device 50. The amount of hydrogen gas introduced is analyzed for the hydrogen concentration in the exhaust gas. When the hydrogen concentration exceeds the upper limit of the specified range, the amount of hydrogen gas introduced is decreased, and when the hydrogen concentration is less than the specified value range, the amount of hydrogen gas introduced is increased.

[0034] As described above, the method for producing reduced iron according to the first embodiment and the manufacturing apparatus 100 for directly reduced iron used in the manufacturing method have been described. According to the method for producing reduced iron according to the first embodiment, by purging the combustible gas with an inert gas (nitrogen gas), it is possible to operate safely even when using the hydrogen-containing circulation gas as the pressure equalizing gas. As a result of using the exhaust gas after reduction as the pressure equalizing gas, it is possible to prevent the concentration of nitrogen, carbon dioxide, etc. accompanying the circulation of the exhaust gas, so that the reducing power of the reducing gas is not reduced. In addition, since there is no concentration, there is no need for regular emission of exhaust gas.

[0035] (Second Embodiment) Next, a direct reduction iron manufacturing apparatus 100A for implementing the method for manufacturing reduced iron according to the second embodiment will be described. FIG. 3 is a flowchart showing an example of a direct reduction apparatus according to the second embodiment of the present invention. The direct reduction iron manufacturing apparatus 100A includes a charging hopper 12 for storing iron oxide as a raw material, a pressure equalizing hopper 14 for adjusting the pressure between the atmosphere and the shaft furnace internal pressure, a shaft furnace 20 for manufacturing direct reduction iron using methane gas as a raw material gas, a dehydration apparatus 30 for dehydrating the exhaust gas of the shaft furnace 20 to obtain a circulating gas, a carbon dioxide removal apparatus 60 for removing carbon dioxide from the circulating gas, a pressure boosting apparatus 40 for boosting the circulating gas after removing water and carbon dioxide, and a heating apparatus 50 for heating the boosted circulating gas together with the raw material gas to obtain a reducing gas.

[0036] (Charging Hopper 12) The charging hopper 12 stores iron oxide. The charging hopper 12 transfers the stored iron oxide, which is the raw material, to the pressure equalizing hopper 14 at atmospheric pressure through the raw material inlet 14a.

[0037] (Pressure Equalizing Hopper 14) The pressure equalizing hopper 14 performs pressure adjustment after transferring the raw material, and sends the raw material after pressure adjustment to the raw material charging section 24 of the shaft furnace 20. The pressure equalizing hopper 14 includes a hopper main body, a raw material inlet 14a for charging the raw material from the charging hopper 12, a raw material discharge port 14b for sending the raw material to the raw material charging section 24 of the shaft furnace 20 after pressure equalization, a purge gas inlet 14c for introducing purge gas, a gas outlet 14d for discharging purge gas and the like, and a pressure equalizing gas inlet 14e for introducing pressure equalizing gas into the pressure equalizing hopper 14. The raw material inlet 14a is connected to the charging hopper 12, and the raw material discharge port 14b is connected to the raw material charging section 24 of the shaft furnace 20.

[0038] The operation of the pressure equalizing hopper 14 will be described below. The pressure equalizing hopper 14 closes the raw material inlet 14a, the raw material outlet 14b, the purge gas inlet 14c, and the pressure equalizing gas inlet 14e, and opens the gas outlet 14d to reduce the pressure inside the pressure equalizing hopper 14 so that it becomes atmospheric pressure. Next, the purge gas inlet 14c is opened, and an inert gas, which is the purge gas, is introduced into the pressure equalizing hopper 14. Thereby, the furnace gas remaining in the pressure equalizing hopper 14 can be replaced with the inert gas. Next, the pressure equalizing hopper 14 closes the purge gas inlet 14c, opens the raw material inlet 14a, and transfers the raw material from the charging hopper 12 to the pressure equalizing hopper 14 filled with the inert gas. After the raw material transfer, the purge gas inlet 14c is opened, and the inert gas is introduced into the pressure equalizing hopper 14. Thereby, the air introduced into the pressure equalizing hopper 14 together with the raw material can be replaced with the inert gas. Here, examples of the inert gas include nitrogen gas, rare gas, CO2, H2O gas, and a mixed gas thereof. As the inert gas, nitrogen gas is preferable.

[0039] After replacement with the inert gas, the pressure equalizing hopper 14 closes the raw material inlet 14a and the gas outlet 14d, opens the pressure equalizing gas inlet 14e, and introduces the pressure equalizing gas into the pressure equalizing hopper 14 to increase the pressure. Here, whether or not replacement has been completed may be determined when an inert gas three times or more the volume of the pressure equalizing hopper 14 has been introduced into the pressure equalizing hopper 14, or it may be determined by measuring the gas component and confirming that the concentration of the gas to be replaced (reducing gas) has become equal to or lower than the specified value. This pressure equalizing gas is pressurized to the pressure inside the shaft furnace 20 by a pressure increasing device 40 described later. In order to discharge the inert gas remaining inside at the initial stage of pressure increase, the gas outlet 14d may be left open for a certain period of time. For example, whether or not the inert gas has been discharged may be monitored using gas chromatography or the like, and the gas outlet 14d may be closed when the amount of the inert gas discharged from the gas outlet 14d no longer fluctuates.

[0040] (Shaft furnace 20) The shaft furnace 20 includes a raw material charging section 24 for charging iron oxide as a raw material, a reduced iron discharging section 25 for discharging reduced iron, a reducing gas injection port 28 disposed at the lower part of the shaft furnace 20 for injecting reducing gas, and an exhaust gas discharge port 29 disposed at the upper part of the shaft furnace 20 for discharging exhaust gas. Iron oxide as a raw material is charged from the equalizing hopper 14 through the raw material charging section 24 at the top of the shaft furnace 20. The furnace pressure inside the shaft furnace 20 is higher than atmospheric pressure. For example, the furnace pressure is 0.1 to 1 MPa. The iron oxide is reduced by carbon monoxide (CO) and hydrogen gas (reducing gas) generated from methane gas while descending inside the shaft furnace 20 to become reduced iron. The reduced iron is discharged from the reduced iron discharging section 25. The reducing gas is heated by the heating device 50 and injected into the furnace of the shaft furnace 20 from the reducing gas injection port 28. The injected reducing gas reduces the iron oxide. Next, the generation of reduced iron based on methane gas inside the shaft furnace 20 will be described.

[0041] The methane gas introduced as a raw material gas reacts with water inside the shaft furnace 20 to generate carbon monoxide and hydrogen as shown in Equation (2A). Similarly, the methane gas introduced as a raw material gas reacts with carbon dioxide inside the shaft furnace 20 to generate carbon monoxide and hydrogen as shown in Equation (2B). The carbon monoxide generated in the above reaction reacts with iron oxide as shown in Equation (2C) to generate reduced iron and carbon dioxide. As shown in Equation (2D), the reduced iron further reacts with methane gas, contributing to an increase in the carbon concentration in the reduced iron. When the carbon concentration in the reduced iron increases, the melting point of the reduced iron decreases, making it easier to use in an electric furnace or the like.

[0042] The hydrogen gas generated in the reaction of (2D) is used for the reduction of iron oxide to generate reduced iron and water. Specifically, the reaction between iron oxide and hydrogen gas is as shown in the above Equation (1A). The unreacted methane gas (CH4), hydrogen gas (H2) generated by the reaction, carbon monoxide, carbon dioxide, and water vapor (H2O) are sent to the dehydration device 30 through the exhaust gas discharge port 29. H2O + CH4 → CO + 3H2 (2A) CO2 + CH4 → 2CO + 2H2 (2B) Fe2O3 + 3CO → 2Fe + 3CO2 (2C) 3Fe + CH4 → Fe3C + 2H2 (2D)

[0043] (Dehydration device 30) The dehydration device 30 dehydrates the exhaust gas discharged from the exhaust gas outlet 29. The exhaust gas discharged from the exhaust gas outlet 29 contains unreacted methane gas, water vapor, hydrogen gas, carbon monoxide, and carbon dioxide generated by the reduction reaction of iron oxide. The dehydration device 30 dehydrates, for example, by cooling the exhaust gas after dust removal. Since water inhibits the reduction reaction, it is preferable that the moisture concentration in the exhaust gas is as low as possible. For example, when the moisture concentration in the exhaust gas is 25 vol%, it is preferable to remove moisture until the moisture concentration is 2 vol% or less by dehydration. The dehydrated exhaust gas (circulation gas) is sent to the carbon dioxide removal device 60. The exhaust gas may be dust-removed by a dust removal device (not shown) before being dehydrated by the dehydration device 30. The dust removal method is not particularly limited, and examples include a cyclone and a scrubber.

[0044] The carbon dioxide removal device 60 removes carbon dioxide in the circulated gas after dehydration. Since carbon dioxide inhibits the reduction reaction, it is preferably removed as much as possible. The carbon dioxide removal device 60 preferably removes 90 vol% or more of carbon dioxide from the circulated gas. Thereby, the concentration of carbon dioxide in the circulated gas can be prevented. For the separation of carbon dioxide in the circulated gas, for example, a chemical adsorption method can be used. The circulated gas after separating carbon dioxide is sent to the pressure booster 40.

[0045] (Pressure booster 40) The pressure booster 40 boosts the pressure of the circulated gas after carbon dioxide removal to atmospheric pressure or higher and sends it to the heating device 50. A part of the boosted circulated gas is introduced into the equalizing hopper 14 as equalizing gas through the equalizing gas inlet 14e. The pressure booster 40 is, for example, a compressor.

[0046] (Heating device 50) The heating device 50 heats the circulating gas and the raw material gas pressurized by the pressure boosting device 40 and blows them into the reduction gas injection port 28. The temperature of the injected reduction gas is approximately 700 to 1000 °C. Also, the injection amount of the reduction gas is approximately 1000 to 2000 Nm 3 / t-DRI. It is preferable to use methane gas as the raw material gas.

[0047] (Method for manufacturing reduced iron) Next, the method for manufacturing reduced iron according to the second embodiment will be described. FIG. 4 is a flowchart of the method for manufacturing reduced iron according to the second embodiment. The method for manufacturing reduced iron according to the second embodiment includes a raw material charging step S10A of charging raw materials from a charging hopper 12 for storing the raw materials, via a pressure equalizing hopper 14 for performing pressure adjustment, into the furnace of a shaft furnace 20 operating at a pressure higher than atmospheric pressure; after the raw material charging step S10A, a reduction step S20A of reacting the raw materials with a reduction gas in the shaft furnace 20 to obtain reduced iron and exhaust gas after reduction; an exhaust gas circulation step S30A of circulating the exhaust gas after reduction and using it as a part of the reduction gas; and a raw material gas supply step S40A. Hereinafter, each step will be described.

[0048] (Raw material charging step S10A) In the raw material charging step S10A, raw materials are charged from a charging hopper 12 for storing the raw materials, via a pressure equalizing hopper 14 for performing pressure adjustment, into the furnace of a shaft furnace 20 operating at a pressure higher than atmospheric pressure. The raw material charging step S10A includes a pressure reduction step of reducing the pressure of the pressure equalizing hopper 14 from the pressure in the shaft furnace 20 to atmospheric pressure; after the pressure reduction step S1, a first purging step S2 of replacing the furnace gas in the pressure equalizing hopper with a purging gas; after the first purging step S2, a raw material input step S3 of transferring raw materials from the charging hopper 12 to the pressure equalizing hopper 14 replaced with the purging gas; after the raw material input step S3, a second purging step S4 of replacing the air introduced into the pressure equalizing hopper 14 in the raw material input step S3 with the purging gas; after the second purging step S4, a pressure equalizing step S5A of increasing the pressure of the pressure equalizing hopper 14 from atmospheric pressure to the furnace pressure with a pressure equalizing gas; and after the pressure equalizing step S5A, a raw material discharge step S6 of transferring raw materials from the pressure increased pressure equalizing hopper 14 into the shaft furnace 20.

[0049] (Pressure reduction step S1) In the pressure reduction step S1, the pressure in the equalizing hopper 14 is reduced from the pressure in the shaft furnace 20 to atmospheric pressure. Specifically, by closing the raw material discharge port 14b and opening the gas outlet 14d, the pressure in the equalizing hopper 14 is reduced from the pressure in the shaft furnace 20 to atmospheric pressure.

[0050] (First purge step S2) In the first purge step S2, after the pressure reduction step S1, the gas in the equalizing hopper 14 is replaced with purge gas. Specifically, the purge gas inlet 14c is opened to introduce an inert gas, which is the purge gas, into the equalizing hopper 14. Thereby, the furnace gas in the equalizing hopper 14 mixed when charging the raw material from the equalizing hopper 14 into the shaft furnace 20 can be replaced with the inert gas.

[0051] (Raw material charging step S3) In the raw material charging step S3, after the first purge step S2, iron oxide, which is the raw material, is transferred from the charging hopper 12 to the equalizing hopper 14 replaced with the purge gas. Specifically, the purge gas inlet 14c is closed, the raw material inlet 14a is opened, and the raw material is transferred from the charging hopper 12 to the equalizing hopper 14 whose pressure has been reduced and replaced.

[0052] (Second purge step S4) In the second purge step S4, after the raw material charging step S3, the air introduced into the equalizing hopper 14 in the raw material charging step S3 is replaced with purge gas. Specifically, the purge gas inlet 14c is opened to introduce an inert gas, which is the purge gas, into the equalizing hopper 14. Thereby, the air introduced into the equalizing hopper 14 together with the raw material in the raw material charging step S3 can be replaced with the inert gas.

[0053] (Equalizing step S5A) In the pressure equalization step S5A, after the second purge step S4, the pressure in the pressure equalization hopper 14 is increased from atmospheric pressure to the pressure in the shaft furnace 20 using a pressure equalization gas. Specifically, the raw material inlet 14a and the gas outlet 14d are closed, the pressure equalization gas inlet 14e is opened, and the pressure equalization gas is introduced into the pressure equalization hopper 14 to increase the pressure. The pressure equalization gas is pressurized by a pressure boosting device 40 to the pressure (furnace internal pressure) in the shaft furnace. The pressure equalization gas is a part of the circulated gas that has been dehydrated by a dehydration device 30. At the initial stage of the pressure equalization step S5A, it is preferable that the inert gas (nitrogen gas) introduced in the second purge step S4 can be pushed out by the pressure equalization gas so that the inert gas (nitrogen gas) does not accumulate in the shaft furnace 20. When pushing out the nitrogen gas with the pressure equalization gas, the gas outlet 14d is opened for a while to exhaust the inert gas (nitrogen gas). The opening time of the gas outlet 14d, the opening time, can be determined by checking the variation of the inert gas (e.g., nitrogen gas) using gas chromatography or the like.

[0054] (Raw material discharge step S6) In the raw material discharge step S6, after the pressure equalization step S5A, the raw material is transferred from the pressurized pressure equalization hopper 14 into the shaft furnace 20. Specifically, by closing the pressure equalization gas inlet 14e and opening the raw material discharge port 14b, the raw material in the pressure equalization hopper is transferred from the pressurized pressure equalization hopper into the shaft furnace. After the completion of the raw material discharge step S6, by returning to the pressure reduction step S1, the raw material can be continuously charged into the shaft furnace 20.

[0055] (Reduction step S20A) In the reduction step S20A, after the raw material charging step S10A, the raw material and the reduction gas are reacted in the shaft furnace 20 to obtain reduced iron and exhaust gas after reduction. Specifically, in the shaft furnace 20, it is reduced by the reduction gas blown from the reduction gas injection port 28 to become reduced iron (direct reduced iron), and is discharged from the reduced iron discharge part 25. When the raw material gas is methane gas, carbon monoxide generated from iron oxide and methane gas reacts as shown in the above formulas (2A) - (2D), and reduced iron and carbon dioxide are generated. The unreacted methane gas, hydrogen gas, carbon monoxide, carbon dioxide, and water vapor generated in the above reaction are discharged as exhaust gas from the exhaust gas outlet 29.

[0056] (Exhaust gas circulation step S30A) In the exhaust gas circulation step S30A, the exhaust gas (exhaust gas after the reduction reaction) discharged in the reduction step S20 is circulated and used as part of the reducing gas. When methane gas is used as the raw material gas, the exhaust gas becomes unreacted methane gas, hydrogen gas, carbon monoxide, carbon dioxide, and water vapor generated in the above reaction. The exhaust gas discharged from the exhaust gas outlet 29 is dehydrated by the dehydrator 30, and then carbon dioxide is removed by the carbon dioxide removal device 60. That is, the exhaust gas circulation step S30A includes a dehydration step of dehydrating the exhaust gas and a carbon dioxide removal step of removing carbon dioxide from the exhaust gas. The circulated gas from which carbon dioxide has been removed is pressurized by the booster 40, and a part of the circulated gas is used as the equalizing pressure gas in the equalizing pressure step S5A. The remaining circulated gas not used in the equalizing pressure step S5A is heated by the heating device 50 and recycled as the reducing gas. That is, the equalizing pressure gas is the gas from which water and carbon dioxide have been removed from the exhaust gas in the dehydration step and the carbon dioxide removal step. The equalizing pressure gas may be burned in a heating furnace or the like outside the direct reduced iron production apparatus 100, and the combustion exhaust gas after removing carbon dioxide may be added.

[0057] (Raw material gas supply step S40A) In the raw material gas supply step S40A, the amount of methane gas corresponding to the amount consumed for reducing the raw material (iron oxide) in the reduction step S20 is introduced as the raw material gas into the shaft furnace 20 via the heating device 50. The introduction amount of methane gas is calculated based on the required blowing amount of methane gas, and the methane blowing amount is increased or decreased.

[0058] As described above, the method for producing reduced iron according to the second embodiment and the direct reduced iron production apparatus 100A used in the production method have been described. According to the method for producing reduced iron according to the second embodiment, by purging the combustible gas with an inert gas (nitrogen gas), it is possible to operate safely even when using the circulating gas containing hydrogen as the equalizing pressure gas. As a result of using the exhaust gas after reduction as the equalizing pressure gas, it is possible to prevent the concentration of nitrogen accompanying the circulation of the exhaust gas, so that the reducing power of the reducing gas is not reduced. In addition, since there is no concentration, there is no need for regular emission of exhaust gas.

[0059] Note that the technical scope of the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. In addition, within the scope not departing from the spirit of the present invention, it is possible to appropriately replace the components in the above-described embodiments with well-known components, and the above-described modification examples may be appropriately combined.

Industrial Applicability

[0060] The method for producing reduced iron according to the present disclosure can suppress the concentration of unnecessary components such as nitrogen and carbon dioxide and maintain the reduction performance, so it has high industrial applicability.

Explanation of Reference Numerals

[0061] 12 charging hopper, 14 pressure equalizing hopper, 20 shaft furnace, 24 raw material charging section, 25 reduced iron discharge section, 28 reducing gas injection port, 29 exhaust gas discharge port, 30 dehydration device, 40 pressure boosting device, 60 carbon dioxide removal device

Claims

1. A raw material charging step of charging the raw material from a charging hopper for storing the raw material into the furnace of a shaft furnace operating at a pressure higher than atmospheric pressure via a pressure equalizing hopper for pressure adjustment; A reduction step of reacting the raw material with a reducing gas in the shaft furnace after the raw material charging step to obtain reduced iron and exhaust gas after reduction; An exhaust gas circulation step of circulating the exhaust gas after reduction and using it as a part of the reducing gas; comprising: The raw material charging step includes: A pressure reduction step of reducing the pressure of the pressure equalizing hopper from the pressure in the shaft furnace to atmospheric pressure; A first purging step of replacing the gas in the pressure equalizing hopper with a purging gas after the pressure reduction step; A raw material input step of transferring the raw material from the charging hopper to the pressure equalizing hopper replaced with the purging gas after the first purging step; A second purging step of replacing the air introduced into the pressure equalizing hopper in the raw material input step with a purging gas after the raw material input step; A pressure equalizing step of increasing the pressure of the pressure equalizing hopper from atmospheric pressure to the pressure in the shaft furnace with a pressure equalizing gas after the second purging step; A raw material discharge step of transferring the raw material from the pressure equalizing hopper with increased pressure into the shaft furnace after the pressure equalizing step; comprising: The exhaust gas circulation step includes: A dehydration step of removing water from the exhaust gas after reduction; The purging gas is an inert gas, and the pressure equalizing gas is a gas from which water has been removed from the exhaust gas in the dehydration step. A method for producing reduced iron, characterized in that.

2. The exhaust gas circulation step further includes a carbon dioxide removal step of removing carbon dioxide from the exhaust gas, and the pressure equalizing gas is a gas from which water and carbon dioxide have been removed from the exhaust gas in the dehydration step and the carbon dioxide removal step. The method for producing reduced iron according to claim 1, characterized in that.

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