Reduced iron production method

Abstract

According to one aspect of the present disclosure, this reduced iron production method is for producing reduced iron using a shaft furnace, the method involving an iron oxide charging step for charging an iron oxide raw material into a shaft furnace, and a blowing step for heating a reducing gas mainly composed of hydrogen gas and subsequently blowing same into the shaft furnace, wherein the specific consumption R (Nm3 / t-DRI) of hydrogen gas and the blowing temperature T (K) satisfy R ≥ 0.0051T2 -15.108T +12188. Preferably, the specific consumption R (Nm3 / t-DRI) of hydrogen gas and the blowing temperature T (K) satisfy R ≤ 0.0068T2 -19.792T +15771.

Description

Reduced iron manufacturing method

[0001] The present invention relates to a method for producing reduced iron. This application claims priority to Japanese Patent Application No. 2023-213395, filed on December 18, 2023, the contents of which are incorporated herein by reference.

[0002] Shaft furnace operation, a method for producing reduced iron using a shaft furnace, is a representative example of a direct reduction process for producing reduced iron from iron oxide raw materials. Shaft furnace operation is widespread in areas where natural gas is available at low cost, such as oil-producing countries. Here, an overview of the method for producing reduced iron using a shaft furnace is provided. First, iron oxide raw materials are charged from the top of the shaft furnace. The iron oxide raw materials are the raw materials for reduced iron and are primarily composed of iron oxide. Examples of iron oxide raw materials include iron oxide pellets and lump ore. Reducing gas is then injected from the bottom of the shaft furnace. Here, the reducing gas is heated to a predetermined temperature before being injected into the shaft furnace. The temperature of the reducing gas is, for example, approximately 900 to 950°C. The reducing gas injected into the shaft furnace then reduces the iron oxide raw materials in the shaft furnace. Reduced iron is produced by this direct reduction process. The reduced iron is discharged from the bottom of the shaft furnace and cooled. Hydrogen gas, CO gas, water vapor, and CO are injected from the top of the shaft furnace. ２ After the water vapor is removed from the furnace gas, the hydrogen gas and CO gas in the furnace gas are reused as part of the raw material gas. ２ Gas may also be removed.

[0003] The reducing gas used in the shaft furnace is produced from a raw material gas containing carbon. The raw material gas is, for example, natural gas or coke oven gas. The raw material gas is mixed with water vapor or CO ２ Reducing gas can be obtained by reforming the raw material gas with carbon dioxide, oxygen, etc. Alternatively, the raw material gas may be used in the shaft furnace as the reducing gas without being reformed. The main component of a typical reducing gas is hydrogen gas (H ２ ), CO gas (CO), and CH ４ It's gas.

[0004] By the way, in recent years, CO ２In order to further reduce gas emissions, a technique of using pure hydrogen gas as a reducing gas has been proposed. For example, Patent Document 1 describes a technique of using hydrogen gas separated from coke oven gas (COG) by a PSA method as a reducing gas. Patent Document 2 describes a technique of using hydrogen gas obtained by electrolysis as a reducing gas.

[0005] U.S. Patent No. 9938594B2 International Publication No. 2022-169392

[0006] Yukiaki Hara et al., "Mathematical Model of a Shaft Furnace for Iron Ore Reduction," Iron and Steel, Japan, The Iron and Steel Institute of Japan, 1976, Vol. 62, No. 3, p. 315; Hideyuki Yamaoka et al., "Three-Dimensional Mathematical Model of a Shaft-Type Reduction Furnace and a Cupola-Type Melting Furnace," Iron and Steel, Japan, The Iron and Steel Institute of Japan, 1988, Vol. 74, No. 12, p. 2254

[0007] However, when a gas mainly containing hydrogen gas is used as a reducing gas, there is still no information on the specific operating conditions for operating a shaft furnace. In particular, there is no information on the unit consumption of hydrogen gas required to produce reduced iron.

[0008] Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a method for producing reduced iron that can achieve a high metallization rate.

[0009] The gist of the present invention is as follows: (1) A method for producing reduced iron using a shaft furnace according to one aspect of the present invention includes a step of charging an oxidized iron raw material into a shaft furnace and a step of injecting a reducing gas mainly composed of hydrogen gas into the shaft furnace, and ３ / t-DRI) and the blowing temperature T (K) satisfy the following formula (1): R≧0.0051T ２ -15.108T+12000 (1) (2) Preferably, in the method for producing reduced iron described in (1) above, the unit consumption of the hydrogen gas R (Nm ３ / t-DRI) and the blowing temperature T (K) satisfy the following formula (2): R≦0.0068T ２-19.792T+15771 (2) (3) Preferably, in the method for producing reduced iron according to (1) or (2), the unit consumption of the hydrogen gas R (Nm ３ / t-DRI) and the blowing temperature T (K) satisfy the following formula (3): R≧0.0051T ２ −15.108T+12188 (3) (4) Preferably, in the method for producing reduced iron according to any one of (1) to (3) above, the blowing temperature T is controlled based on the hydrogen gas consumption rate R. (5) Preferably, in the method for producing reduced iron according to any one of (1) to (3) above, the hydrogen gas consumption rate R is controlled based on the blowing temperature T.

[0010] According to the present invention, it is possible to provide a method for producing reduced iron that can achieve a high metallization rate.

[0011] Hydrogen gas consumption rate R (Nm ３ 1 is a graph showing the relationship between the sintering time (t / t-DRI) and the blowing temperature T (K) for each metallization rate (%) of reduced iron.

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0013] <1. Findings of the Inventors> First, the findings of the inventors that form the basis of this embodiment will be described. The degree of reduction of the oxidized iron raw material charged into the shaft furnace as raw material is evaluated by the metallization rate of the reduced iron. The metallization rate of the reduced iron can be expressed as a function of the hydrogen gas concentration of the reducing gas blown into the shaft furnace, the blowing temperature of the reducing gas, the blowing amount of the reducing gas, and the blowing time of the reducing gas. The inventors have made the following simplifications with the aim of contributing to the design and efficient operation of the shaft furnace. - The hydrogen gas concentration of the reducing gas is 100% by volume. - The blowing amount and blowing time of the reducing gas are expressed in terms of the basic unit of hydrogen gas (Nm ３ / t-DRI)

[0014] The metallization rate of reduced iron is the relative ratio of the amount of metallic iron in the reduced iron discharged from the shaft furnace to the total iron content of the reduced iron discharged from the shaft furnace. The total iron content is determined by a test specified in JIS M 8212:2005 "Iron ore - Total iron determination method." The amount of metallic iron is determined by a test specified in ISO 5416:2006 (bromine-methanol titration method).

[0015] As a result, the metallization rate of reduced iron is ３ / t-DRI) and the injection temperature T (K). The present inventors then determined this function through simulations using a mathematical model of a shaft furnace. This model was constructed based on the chemical engineering techniques described, for example, in Non-Patent Documents 1 and 2. This model is capable of theoretically analyzing and predicting heat and mass transfer within a shaft furnace, such as chemical reactions and heat transfer phenomena, including the reduction reaction of iron oxide raw materials by hydrogen gas. Using this mathematical model, shaft furnace operation using hydrogen gas was simulated to evaluate macroscopic heat and mass transfer.

[0016] The calculation conditions are as shown in Table 1. The conditions other than the hydrogen reduction rate constant correspond to the operating conditions of the shaft furnace and its peripheral equipment.

[0017] The residence time (minutes) in Table 1 is the time that the oxidized iron raw material charged from the furnace top remains in the region where it comes into contact with hydrogen gas, which is a reducing gas. Specifically, the residence time is the time that the oxidized iron raw material remains in the region between the hydrogen gas inlet and the furnace top charging position. The region where the oxidized iron raw material comes into contact with hydrogen gas is the region where the oxidized iron raw material is reduced by the hydrogen gas. The oxidized iron raw material was assumed to be 90 mass % or more of iron oxide pellets.

[0018] Hydrogen gas consumption rate (Nm ３ / t-DRI) is the flow rate of hydrogen gas required to produce 1 ton of reduced iron (DRI). For example, the hydrogen gas consumption rate can be determined by dividing the amount of hydrogen gas used per hour by the amount of reduced iron produced per hour. The amount of hydrogen gas used per hour can be derived by measuring the flow rate and composition of the reducing gas at the inlet side of the shaft furnace and the flow rate and composition of the reducing gas at the outlet side using a flow meter, gas chromatography, or the like. The amount of reduced iron produced per hour can be derived by measuring the weight of reduced iron discharged from the shaft furnace using a load cell, or the like. The amount of reduced iron produced can also be calculated using the following formula. Amount of reduced iron produced (t-DRI / hr) = Amount of raw materials charged (t-raw materials / hr) - {Outlet gas weight of reducing gas (t-outlet gas / hr) - Inlet gas weight of reducing gas (t-inlet gas / hr)} The weight of the reducing gas at the outlet side of the shaft furnace and the weight of the reducing gas at the inlet side of the shaft furnace can be derived from these flow rates and gas compositions.

[0019] The hydrogen gas blowing temperature (K) is the temperature of the hydrogen gas when it is blown into the shaft furnace.

[0020] The furnace top pressure indicates the air pressure at the top of the shaft furnace.

[0021] The raw material particle size indicates the particle size (mm) of the iron oxide raw material. The particle size can be measured by sieving.

[0022] Porosity is the ratio of the pore volume within a raw material pellet particle to the apparent volume of the particle. The method for measuring porosity is specified by JIS M 8716:1990 "Iron ore pellets - Method for calculating apparent density and porosity."

[0023] The hydrogen reduction rate constant represents the rate of reduction reaction by hydrogen and is defined as the movement speed (m / s) of the reaction interface within the particle per unit time.

[0024]

[0025] The results of the simulation are shown in Figure 1. The horizontal axis of Figure 1 represents the hydrogen gas injection temperature (K). The vertical axis of Figure 1 represents the hydrogen gas consumption rate (Nm ３ / t-DRI). Graph L1 shows the hydrogen gas consumption rate R (Nm ３ / t-DRI) and the blowing temperature T (K). Graph L2 shows the relationship between the hydrogen gas consumption rate R (Nm ３ / t-DRI) and the blowing temperature T (K). Graph L3 shows the relationship between the hydrogen gas consumption rate R (Nm ３ / t-DRI) and the blowing temperature T (K). Graph L4 shows the relationship between the hydrogen gas consumption rate R (Nm ３ / t-DRI) and the blowing temperature T (K).

[0026] The graph L1 is expressed by the following formula (3'), and the graph L3 is expressed by the following formula (2'). In formulas (3') and (2'), R is the basic unit of hydrogen gas (Nm ３ / t-DRI), and T is the hydrogen gas injection temperature (K). As is clear from Fig. 1, there is a correlation between the hydrogen gas consumption rate and the hydrogen gas injection temperature, and this correlation differs depending on the metallization rate of reduced iron.

[0027] R = 0.0051T ２ -15.108T+12188 (3') R=0.0068T ２ -19.792T+15771 (2')

[0028] Considering actual operation, the higher the metallization rate of reduced iron, the better. Therefore, the hydrogen gas consumption rate R (Nm ３ It is preferable that the sintering temperature (T / t-DRI) and the blowing temperature T (K) satisfy the following formula (1). This makes it possible to sufficiently increase the metallization rate of reduced iron. ２ -15.108T+12000 (1)

[0029] In addition, the unit consumption of hydrogen gas R (Nm ３It is more preferable that the hydrogen gas consumption rate R and the blowing temperature T (K) satisfy the following formula (3). This can further increase the metallization rate of reduced iron. It is believed that by controlling the hydrogen gas consumption rate R and the blowing temperature T under the conditions shown in Table 1 so as to satisfy formula (3), it is possible to achieve a metallization rate of reduced iron of 92% or more. R≧0.0051T ２ -15.108T+12188 (3)

[0030] On the other hand, if hydrogen gas is blown in at a rate exceeding 100% metallization, excessive hydrogen gas will be blown into the shaft furnace. Therefore, the hydrogen gas consumption rate R (Nm ３ It is preferable that the temperature (T / t-DRI) and the blowing temperature T (K) satisfy the following formula (2): R≦0.0068T ２ -19.792T+15771 (2)

[0031] By adjusting the hydrogen gas consumption rate and the injection temperature so as to satisfy the formula (1), the metallization rate of reduced iron can be sufficiently increased. Furthermore, by adjusting the hydrogen gas consumption rate and the injection temperature so as to satisfy the formula (2), excessive injection of hydrogen gas can be avoided. The method for producing reduced iron according to this embodiment of hydrogen gas has been made based on the above findings.

[0032] Instead of formula (1), the hydrogen gas consumption rate R and the injection temperature T may be defined using the following formula (4): R≧0.0051T ２ −15.108T+X (4) Here, X is any number greater than 12,000. When X is 12,188, Equation (4) is the same as Equation (3) above. In Equation (4), X may be 12,050, 12,100, 12,200, 12,300, 12,500, 12,500, or 12,600. Increasing X increases the lower limit of the hydrogen gas consumption rate R, further improving the metallization rate of reduced iron.

[0033] Furthermore, instead of formula (2), the hydrogen gas consumption rate R and the blowing temperature T may be defined using the following formula (5): R≦0.0068T ２−19.792T+Y (5) Here, Y is any number less than 15771. In formula (5), Y may be 15700, 15600, 15500, 15400, or 15300. When Y is reduced, the upper limit of the hydrogen gas consumption unit R decreases, and the amount of hydrogen used can be further reduced.

[0034] Alternatively, instead of formula (1), the hydrogen gas consumption rate R and the injection temperature T may be defined using the following formula (6): R≧0.0062T ２ -18.066T+14388 (6) In formula (6), R is the basic unit of hydrogen gas (Nm ３ / t-DRI), where T is the hydrogen gas injection temperature (K). Equation (6) corresponds to graph L2 in FIG. 1. By adjusting the hydrogen gas consumption rate and injection temperature so as to satisfy Equation (6), the metallization rate of reduced iron can be increased to approximately 96% or more.

[0035] <2-1. Reduced Iron Manufacturing Apparatus> Next, a reduced iron manufacturing apparatus 1A according to this embodiment will be described with reference to FIG. 2. As shown in FIG. 2, the reduced iron manufacturing apparatus 1A according to this embodiment includes a shaft furnace 1, a heating furnace 2, and a dehydration device 3. The shaft furnace 1 is the same as a conventional one. That is, the oxidized iron raw material 4 is charged from above the shaft furnace 1. There is no particular restriction on the type of oxidized iron raw material 4, as long as it is the same as in existing shaft furnace operation. Examples of the oxidized iron raw material 4 include iron oxide pellets. The oxidized iron raw material 4 preferably contains 90 mass % or more of iron oxide pellets, and more preferably is composed only of iron oxide pellets. Examples of the oxidized iron raw material 4 other than iron oxide pellets include lump ore, sintered ore, and unsintered agglomerates.

[0036] Meanwhile, reducing gas 5 is injected into the shaft furnace 1 from the lower side of the shaft furnace 1. The reducing gas 5 injected into the shaft furnace 1 rises within the shaft furnace 1. The reducing gas 5 reduces the iron oxide raw material 4 in the shaft furnace 1 to produce reduced iron (DRI) 6. The reduced iron 6 is discharged from the bottom of the shaft furnace 1 and cooled. The metallization rate of the reduced iron 6 is preferably, for example, 92% or more. Meanwhile, top gas 7 (exhaust gas) is discharged from the top of the shaft furnace 1. The top gas 7 contains unreacted hydrogen gas as well as water vapor, dust, CO ２ The furnace gas 7 is subjected to dust removal by a dust removal device (not shown), and further subjected to chemical adsorption or the like to remove CO ２ After the gas is removed, the top gas 7 is introduced into the dehydration device 3. The dehydration device 3 dehydrates the top gas 7. As a result, hydrogen gas is produced. The produced hydrogen gas is introduced into the heating furnace 2.

[0037] A reducing gas 5 is introduced into the heating furnace 2. The reducing gas 5 is mainly composed of hydrogen gas, and preferably consists of hydrogen gas. Specifically, the reducing gas 5 preferably contains hydrogen gas at a ratio of 90% by volume or more. The reducing gas 5 may contain other gases at a ratio of 10% by volume or less. Examples of other gases include CO gas, CO ２ Gas, H ２ O gas (water vapor), CH ４ Examples of hydrogen gas that can be used include electrolytic hydrogen gas, coke oven gas (COG), and hydrogen gas obtained by separating hydrogen from gas obtained by an aqueous gas shift reaction using a PSA method or a membrane separation method.

[0038] The heating furnace 2 heats the reducing gas 5 to a predetermined temperature and then injects it into the shaft furnace 1. The temperature of the reducing gas 5 when injected into the shaft furnace 1 is called the injection temperature. The heating furnace 2 can be realized by an existing electric furnace or the like. Here, the heating furnace 2 heats the reducing gas 5 so that the above-mentioned formula (1), and preferably also formula (2), is satisfied. In other words, the amount of hydrogen gas introduced into the heating furnace 2 and the heating temperature by the heating furnace 2 are adjusted so that the above-mentioned formula (1), and preferably also formula (2), is satisfied.

[0039] The heating furnace 2 and the shaft furnace 1 are connected by a pipe. The reducing gas 5 is blown into the shaft furnace 1 through this pipe. Here, the blowing temperature of the reducing gas 5 is measured by, for example, a thermocouple. The thermocouple is provided at the connecting portion between the above-mentioned pipe and the shaft furnace 1. The blowing temperature of the reducing gas 5 is measured using this thermocouple. The thermocouple may be provided somewhere in the pipe or at the outlet of the heating furnace 2.

[0040] <2-2. Method for Producing Reduced Iron> Next, a method for producing reduced iron using the reduced iron production apparatus 1 A will be described. This production method includes an iron oxide charging step of charging an iron oxide raw material 4 into the shaft furnace 1, and an injection step of heating a reducing gas 5 mainly composed of hydrogen gas and then injecting it into the shaft furnace 1.

[0041] In the blowing step, one or both of the unit consumption R of hydrogen gas and the blowing temperature T are controlled so as to satisfy the above-mentioned formula (1), and preferably also the formula (2). The means for controlling these values ​​is not particularly limited.

[0042] For example, the blowing temperature T can be controlled based on the hydrogen gas consumption rate R. In this case, only the blowing temperature T is controlled. Increasing the blowing temperature T lowers the lower limit of the hydrogen gas consumption rate R required to ensure a high metallization rate. Therefore, by increasing the blowing temperature T, the blowing amount of reducing gas 5 can be reduced. The blowing temperature T can be set to any value by changing the output of the heating furnace 2. After the reducing gas 5 is heated by the heating furnace 2, it is blown into the shaft furnace 1.

[0043] Furthermore, the hydrogen gas consumption rate R may be controlled based on the blowing temperature T. In this case, only the hydrogen gas consumption rate R is controlled. If there is some constraint on the blowing temperature T, it is preferable to satisfy the above formula by controlling the hydrogen gas consumption rate R. The hydrogen gas consumption rate R can be set to any value by changing the amount of blowing of the reducing gas 5 or the amount of reduced iron produced. Increasing the amount of blowing of the reducing gas 5 lowers the lower limit of the blowing temperature T necessary to ensure a high metallization rate. Therefore, by increasing the amount of blowing of the reducing gas 5, the blowing temperature T of the reducing gas 5 can be lowered.

[0044] Naturally, both the blowing temperature T and the hydrogen gas consumption rate R may be controlled so as to satisfy the above-mentioned formula.

[0045] The reducing gas 5 injected into the shaft furnace 1 rises within the shaft furnace 1. The reducing gas 5 reduces the iron oxide raw material 4 within the shaft furnace 1 to produce reduced iron (DRI) 6. The reduced iron 6 is discharged from the bottom of the shaft furnace 1 and cooled. The metallization rate of the reduced iron 6 is preferably, for example, 92% or more. Meanwhile, top gas 7 (exhaust gas) is discharged from the top of the shaft furnace 1. Dust is removed from the top gas 7 by a dust removal device (not shown), and CO 2 is further removed by a chemical adsorption method or the like. ２ After the gas is removed, the top gas 7 is introduced into the dehydration device 3. The dehydration device 3 dehydrates the top gas 7. As a result, hydrogen gas is produced. The produced hydrogen gas is introduced into the heating furnace 2.

[0046] Other operating conditions are not particularly limited. For example, the reduced iron manufacturing apparatus 1A may be operated under the operating conditions shown in Table 1. On the other hand, the operation may be performed under operating conditions other than those shown in Table 1. For example, the residence time may be longer than 70 minutes. The longer the residence time, the longer the time required to manufacture reduced iron, but the higher the metallization rate of the reduced iron. Increasing the residence time does not adversely affect the metallization rate of the reduced iron.

[0047] According to this embodiment, the reduced iron manufacturing apparatus 1A having the shaft furnace 1 is operated so that formula (1), and preferably formula (2), is satisfied. Therefore, the unit consumption R of hydrogen gas necessary to produce reduced iron 6 can be identified. This makes it possible to identify the minimum unit consumption R of hydrogen gas necessary to obtain reduced iron 6. By minimizing the amount of hydrogen injected into the shaft furnace 1, it is possible to reduce the size and simplify the hydrogen supply means in the shaft furnace 1 and its peripheral equipment. Therefore, according to this embodiment, the shaft furnace 1 and its peripheral equipment can be designed and operated efficiently.

[0048] Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to these examples. It is clear that a person skilled in the art to which the present invention pertains can conceive of various modifications and alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

[0049] 1A Reduced iron manufacturing apparatus 1 Shaft furnace 2 Heating furnace 3 Dehydration device 4 Iron oxide raw material 5 Reducing gas 6 Reduced iron 7 Furnace top gas T Injection temperature R Hydrogen gas consumption

Claims

1. A method for producing reduced iron using a shaft furnace, comprising the steps of: charging an iron oxide raw material into a shaft furnace; and blowing a reducing gas mainly composed of hydrogen gas into the shaft furnace, wherein the unit consumption of the hydrogen gas R (Nm ３ / t-DRI) and the blowing temperature T (K) satisfy the following formula (1): ２ -15.108T+12000 (1) 2. The unit of hydrogen gas consumption R (Nm ３ 2. The method for producing reduced iron according to claim 1, wherein R≦0.0068T / t-DRI and the blowing temperature T (K) satisfy the following formula (2). ２ -19.792T+15771 (2) 3. The unit of hydrogen gas consumption R (Nm ３ The method for producing reduced iron according to claim 1 or 2, characterized in that R≧0.0051T ２ -15.108T+12188 (3) 4. A method for producing reduced iron as set forth in claim 1 or 2, characterized in that the blowing temperature T is controlled based on the unit consumption R of the hydrogen gas.

5. A method for producing reduced iron as set forth in claim 1 or 2, characterized in that the unit consumption R of the hydrogen gas is controlled based on the blowing temperature T.

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