Method for producing reduced iron and direct reduction furnace

Abstract

A method for producing reduced iron is provided, the method being capable of producing reduced iron which is highly effective in preventing electrode consumption from increasing. First agglomerated ore is loaded into a central portion in a direct reduction furnace and second agglomerated ore is loaded into a furnace wall portion in the direct reduction furnace, and the reducibility of the first agglomerated ore is made greater than that of the second agglomerated ore.

Description

Method for producing reduced iron and direct reduction furnace

[0001] The present invention relates to a method for producing reduced iron and a direct reduction furnace.

[0002] In the steelmaking process, a method of producing reduced iron by reducing iron oxide in a direct reduction furnace, for example, a vertical shaft furnace (hereinafter also referred to as a DRI production process) is used. In this DRI process, a direct reduction furnace is filled with agglomerated iron ore such as pellets (hereinafter also referred to as agglomerated ore) as the iron oxide raw material. Then, CO and H generated from natural gas are introduced into the reduction furnace. ２ This reduces the iron oxide contained in the agglomerates according to the following formula, producing reduced iron: ２ O ３ +3CO→2Fe+3CO ２ ... (i) Fe ２ O ３ +3H ２ → 2Fe + 3H ２ O... (ii)

[0003] An example of a DRI production process is shown in Figure 1. In the figure, reference numeral 1 denotes a direct reduction furnace, 1a denotes agglomerated ore, 1b denotes reduced iron, 3 denotes a dust remover, 4 denotes a dehydrator, 5 denotes a natural gas supply section, 6 denotes an air supply section, and 7 denotes a reformer.

[0004] In this DRI manufacturing process, for example, agglomerates are charged from the top of a direct reduction furnace and gradually lowered. High-temperature reducing gas is then blown into the furnace from the center. As a result, as shown in Figure 2, heat exchange and a reduction reaction occur between the reducing gas and the iron oxide contained in the agglomerates, reducing the iron oxide contained in the agglomerates. Reduced iron is then discharged from the bottom of the direct reduction furnace. In the figure, reference numeral 8 denotes a packed bed of agglomerates (reduction zone). The reduced iron discharged from the direct reduction furnace is then melted in an electric furnace or the like. Meanwhile, gases, mainly CO, CO2, and CO2, are blown into the furnace from the top. ２ , H ２ and H ２ The furnace top gas containing O is discharged. After dust collection and cooling, a portion of the furnace top gas is sent to the reformer as a raw material for reformed gas. In the reformer, a reforming reaction occurs between the furnace top gas and natural gas supplied from the outside, and mainly CO and H are produced.２ This reducing gas is then blown into the reducing furnace. The remaining part of the furnace top gas is dehydrated and then used as heating fuel in the combustion chamber of the reformer, where it is burned, for example, with oxygen in the air.

[0005] As described above, the DRI manufacturing process does not use coke as a reducing agent, and therefore, compared to blast furnaces, the DRI manufacturing process does not emit CO, a greenhouse gas. ２ The amount of CO generated is low ２ This method is attracting attention as a steelmaking method that can lead to reduced emissions.

[0006] As a technology related to such a DRI production process, for example, Patent Document 1 discloses the following: "A method for producing reduced iron by reducing iron oxide, comprising: a reduced iron production step of reducing the iron oxide in a reduction furnace by bringing the iron oxide into contact with a reducing gas while causing it to fall from the top of the furnace to reduce the iron oxide to produce reduced iron, and discharging the reduced iron from the bottom of the reduction furnace; a reformed gas production step of extracting furnace top gas from the reduction furnace, adjusting the moisture content thereof, and performing dust removal treatment thereon to produce a process gas, and supplying at least the process gas into a reformer to produce a reformed gas containing carbon monoxide and hydrogen in the reformer; a reducing gas supply step of supplying the produced reformed gas to the reduction furnace as the reducing gas; a cooling step of introducing a cooling gas into a cooling region set in a lower part of the reduction furnace to cool the cooling region; and a reformed gas introduction step of extracting a portion of the reformed gas and introducing it into the cooling region to increase the carbon content of the reduced iron passing through the cooling region."

[0007] JP 2017-88912 A

[0008] Incidentally, reduced iron produced by the conventional DRI production process such as that disclosed in Patent Document 1 is subjected to melting in an electric furnace in the next step, as described above. However, when reduced iron produced by the conventional DRI production process is subjected to melting in an electric furnace, the consumption of electrodes in the electric furnace may increase excessively in some cases, and an improvement in this respect has been desired.

[0009] The present invention has been developed to meet the above-mentioned demand, and an object of the present invention is to provide a method for producing reduced iron that can prevent an excessive increase in electrode consumption in an electric furnace when the reduced iron is melted in the electric furnace (hereinafter also referred to as having excellent electrode consumption prevention properties). Another object of the present invention is to provide a direct reduction furnace that can be suitably used in the above-mentioned method for producing reduced iron.

[0010] In this disclosure, any numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower limit and upper limit, respectively, except when written as "greater than" or "less than."

[0011] The inventors conducted extensive research to solve the above-mentioned problems. As a result, the inventors discovered the following: Reduced iron produced by a conventional DRI production process has variations in reduction rate, i.e., variations in the degree of reduction of iron oxide contained in the agglomerates during the reduction process (hereinafter simply referred to as the reduction degree). This variation in the reduction degree causes an excessive increase in electrode consumption in an electric furnace. In order to reduce this variation in the reduction degree, it is effective to charge agglomerates with a relatively high reducibility toward the center of the direct reduction furnace in the radial direction of the direct reduction furnace and to charge agglomerates with a relatively low reducibility toward the furnace wall. The present invention was completed based on the above-mentioned findings and further research.

[0012] That is, the gist and configuration of the present invention are as follows.

[0013] 1. A method for producing reduced iron, comprising: a filling step of filling a direct reduction furnace with first and second agglomerates as raw materials; an injection step of injecting a reducing gas into the direct reduction furnace; and a reduction step of reducing iron oxide contained in the raw materials with the reducing gas in the direct reduction furnace to obtain reduced iron, wherein in the filling step, the first agglomerates are filled in a center portion of the direct reduction furnace and the second agglomerates are filled in a furnace wall portion of the direct reduction furnace, and the reducibility of the first agglomerates is greater than the reducibility of the second agglomerates.

[0014] 2. The method for producing reduced iron according to 1 above, wherein the center of the direct reduction furnace is in a region where the dimensionless radius is 0 to 0.57, and the furnace wall of the direct reduction furnace is in a region where the dimensionless radius is greater than 0.81 to 1.00. Here, the dimensionless radius is a dimensionless radius in the furnace radial direction, with the center position of the direct reduction furnace being 0 and the furnace wall of the direct reduction furnace being 1.00.

[0015] 3. The method for producing reduced iron according to 2 above, wherein the raw materials further include a third agglomerate, the third agglomerate is charged into a middle section of the direct reduction furnace in the charging step, the middle section of the direct reduction furnace has a dimensionless radius of more than 0.57 to 0.81, and the relationship of the following formula (1) is satisfied: [reducibility of first agglomerate] > [reducibility of third agglomerate] > [reducibility of second agglomerate] ... (1)

[0016] 4. A direct reduction furnace comprising: hoppers for storing first and second agglomerated ores, which are raw materials; and a raw material charging chute arranged vertically below the hoppers and serving as a charging path for the raw materials discharged from the hoppers, wherein the reducibility of the first agglomerated ores is greater than the reducibility of the second agglomerated ore, and the raw material charging chute has a device for adjusting the charging position of the raw materials in the radial direction of the direct reduction furnace.

[0017] 5. The direct reduction furnace according to claim 4, further comprising a control unit that controls charging positions of the raw materials by the raw material charging chute so that the first agglomerated ore is charged in a center portion of the direct reduction furnace and the second agglomerated ore is charged in a furnace wall portion of the direct reduction furnace.

[0018] 6. The direct reduction furnace according to 5 above, wherein the center of the direct reduction furnace is in a region where the dimensionless radius is 0 to 0.57, and the furnace wall of the direct reduction furnace is in a region where the dimensionless radius is greater than 0.81 to 1.00. Here, the dimensionless radius is a dimensionless radius in the furnace radial direction, with the center position of the direct reduction furnace being 0 and the furnace wall of the direct reduction furnace being 1.00.

[0019] 7. The direct reduction furnace according to 6, wherein the control unit further controls the charging position of the raw materials by the raw material charging chute so as to charge a third agglomerate ore serving as the raw material in an intermediate portion of the direct reduction furnace, the intermediate portion of the direct reduction furnace having a dimensionless radius of more than 0.57 to 0.81, and the relationship of the following formula (1) is satisfied: [reducibility of first agglomerate ore] > [reducibility of third agglomerate ore] > [reducibility of second agglomerate ore] ... (1)

[0020] According to the present invention, it is possible to produce reduced iron that is excellent in preventing an increase in electrode consumption, and therefore the present invention is extremely advantageous from an industrial perspective.

[0021] 1 is a diagram showing an example of a DRI manufacturing process.

[0023] FIG. 1 is a diagram showing an example of a DRI manufacturing process.

[0024] FIG. 1 is a diagram showing an example of a DRI manufacturing process.

[0025] FIG. 2 is a diagram showing an example of a direct reduction furnace.

[0026] FIG. 3 is a diagram showing an example of a direct reduction furnace according to an embodiment of the present invention.

[0027] FIG. 4 is a diagram showing an example of a direct reduction furnace according to an embodiment of the present invention.

[0028] FIG. 5 is a diagram showing an example of a calculation result of the reduction progress rate of the agglomerated ore inside the direct reduction furnace (contour diagram).

[0029] FIG. 6 is a diagram showing the calculation domain of FIG. 5.

[0029] FIG. 7 is a diagram showing the achieved reduction rate of No. 3 plotted against the dimensionless radius in the furnace radial direction of the direct reduction furnace.

[0030] FIG. 8 is a diagram showing an example of a direct reduction furnace according to an embodiment of the present invention.

[0031] FIG. 9 is a diagram showing an example of a direct reduction furnace according to an embodiment of the present invention.

[0032] FIG. 10 is a diagram showing an example of a direct reduction furnace according to an embodiment of the present invention.

[0033] FIG. 11 is a diagram showing an example of a direct reduction furnace according to an embodiment of the present invention.

[0034] FIG. 12 is a diagram showing an example of a direct reduction furnace according to an embodiment of the present invention.

[0035]

[0022] [1] A method for producing reduced iron according to one embodiment of the present invention includes: a charging step of charging first and second agglomerates as raw materials into a direct reduction furnace; an injecting step of injecting a reducing gas into the direct reduction furnace; and a reducing step of reducing iron oxide contained in the raw materials with the reducing gas in the direct reduction furnace to obtain reduced iron. Note that the present invention is not limited to the embodiments shown below as long as it does not deviate from the gist of the present invention.

[0023] The filling step will be described in detail below. The blowing step and the reduction step may be performed in the usual manner, for example, in the same manner as in the conventional DRI manufacturing process described above, and therefore, a description thereof will be omitted here.

[0024] In the charging step, the first and second agglomerates serving as raw materials are charged into the direct reduction furnace. It is important to charge the agglomerates with a relatively high reducibility in the center of the direct reduction furnace and the agglomerates with a relatively low reducibility in the furnace wall. In other words, it is important to charge the first agglomerates in the center of the direct reduction furnace and the second agglomerates in the furnace wall, respectively, so that the reducibility of the first agglomerates is greater than that of the second agglomerates.

[0025] That is, the inventors have conducted various experiments and studies and have obtained the following findings.

[0026] In a typical direct reduction furnace (shaft furnace), multiple gas injection holes for reducing gas are arranged in the circumferential direction of the furnace body. Reducing gas is injected through these gas injection holes. At this time, the direct reduction furnace is packed with spherical agglomerates, forming a packed layer of agglomerates (hereinafter simply referred to as a packed layer). The reducing gas injected into the direct reduction furnace is attenuated in the packed layer and therefore does not easily reach the center of the direct reduction furnace. As shown in FIG. 3 , the reducing gas flowing through the center of the direct reduction furnace (hereinafter also referred to as a center reducing gas) flows downward once after being injected into the furnace, and then reaches the center. As a result, the center reducing gas has a lower reduction ability for agglomerates (iron oxide) than the reducing gas flowing at other positions in the furnace radial direction, particularly the reducing gas flowing through the furnace wall of the direct reduction furnace (hereinafter also referred to as a furnace wall reducing gas).

[0027] On the other hand, among the reducing gases injected into the direct reduction furnace, the volumetric flow rate of the reducing gas at the furnace wall is greater than the volumetric flow rate of the reducing gas at the center. This is because the so-called wall effect increases the permeability near the furnace wall of the direct reduction furnace, that is, in a packed bed, the closer to the furnace wall, the more voids there are (the higher the void ratio). As a result, the agglomerates packed at the furnace wall of the direct reduction furnace react more easily with the reducing gas than the agglomerates packed at the center of the direct reduction furnace.

[0028] That is, in a direct reduction furnace, the reaction between the agglomerates and the reducing gas is more readily promoted in the furnace wall than in the center in the furnace radial direction. As a result, variations in the reduction rate of the produced reduced iron occur. In this regard, by filling the first agglomerates in the center of the direct reduction furnace and the second agglomerates in the furnace wall, respectively, and making the reducibility of the first agglomerates greater than that of the second agglomerates (filling the center of the direct reduction furnace with agglomerates that are more easily reduced than the furnace wall), the decrease in the reducing ability of the reducing gas in the center can be compensated for. As a result, variations in the degree of reduction within the direct reduction furnace can be reduced.

[0029] Here, for example, the center of the direct reduction furnace is in a region where the dimensionless radius is 0 to 0.57, and the furnace wall of the direct reduction furnace is in a region where the dimensionless radius is greater than 0.81 to 1.00. The dimensionless radius is a dimensionless radius in the furnace radial direction, where the center position of the direct reduction furnace is 0 and the furnace wall of the direct reduction furnace is 1.00 (the value obtained by dividing the distance from the center position of the direct reduction furnace by the inner radius of the direct reduction furnace (half the inner diameter)).

[0030] In addition, a third agglomerate may be filled in the intermediate section of the direct reduction furnace. The third agglomerate also serves as a raw material. The reducibility of the third agglomerate is not particularly limited. From the viewpoint of further reducing the variation in the degree of reduction inside the direct reduction furnace, it is preferable to satisfy the relationship of the following formula (1). In this case, the intermediate section of the direct reduction furnace is in a region where the dimensionless radius is greater than 0.57 to 0.81. The cross section of the direct reduction furnace is divided into approximately three equal parts: the center section, the furnace wall section, and the intermediate section. In other words, the areas of the center section, the furnace wall section, and the intermediate section of the direct reduction furnace are each approximately one-third of the area of ​​the cross section of the direct reduction furnace. [Reducibility of the first agglomerate] > [Reducibility of the third agglomerate] > [Reducibility of the second agglomerate] (1)

[0031] The reducibility (index of reducibility) is not limited, but the achieved JIS reduction rate (%) (hereinafter also referred to as RI) defined in JIS M 8713 (2021) is particularly suitable.

[0032] The RI can be calculated by the following formula (4) using a measurement method in accordance with JIS M 8713 (2021). Here, W０ W: Mass (g) of the measurement sample (agglomerate) immediately before the start of reduction １ W: Mass of the weighed sample (g) Ｆ where A is the total Fe content (mass%) in the measurement sample before reduction and B is the FeO content (mass%) in the measurement sample before reduction.

[0033] For example, 500 g of agglomerated ore used in a direct reduction furnace is used as a measurement sample, and the agglomerated ore is weighed and loaded into a reaction tube with an inner diameter of 75 mm. ２ The measurement sample in the reaction tube is reduced for 180 minutes using 30% by volume of reducing gas. ０ , W １ and W Ｆ Furthermore, A is measured, for example, in accordance with JIS M 8212 (2022), and B is measured, for example, in accordance with JIS M 8213 (1995).

[0034] The above-mentioned charging step can be performed by, for example, adjusting the charging position of the agglomerates in the radial direction of the direct reduction furnace using a raw material charging chute of the direct reduction furnace, which will be described later. For example, when discharging the first agglomerates from the hopper, the charging position can be adjusted using the raw material charging chute so that the first agglomerates are charged in the center of the direct reduction furnace. Similarly, when discharging the second agglomerates from the hopper, the charging position can be adjusted using the raw material charging chute so that the second agglomerates are charged in the furnace wall of the direct reduction furnace. More preferably, when discharging the third agglomerates from the hopper, the charging position can be adjusted using the raw material charging chute so that the third agglomerates are charged in the middle of the direct reduction furnace. The first agglomerates can be referred to as the agglomerates charged in the center of the direct reduction furnace. Similarly, the second agglomerates can be referred to as the agglomerates charged in the furnace wall of the direct reduction furnace, and the third agglomerates can be referred to as the agglomerates charged in the middle of the direct reduction furnace.

[0035] The conditions other than those mentioned above are not particularly limited, and may be those according to conventional methods.

[0036] For example, the composition of the reducing gas is H ２: 60 to 90 vol%, CO: 10 to 40 vol%, and the balance: 0 to 5 vol%. The amount of blown reducing gas is 1500 to 2000 Nm ３ / t is preferred. ３ / t is the flow rate (standard state conversion) per ton of reduced iron (DRI) produced. The reducing gas blowing temperature is preferably 850 to 1050°C.

[0037] The compositions of the first, second and third agglomerates, which are raw materials, are, in mass %, iron: 61 to 68%, FeO: 0.1 to 0.6%, SiO ２ Examples of the RI include: Iron: 1.1 to 5.7%, and CaO: 0.15 to 0.78%. Here, the value of the iron content (T.Fe) is the mass fraction of all Fe atoms (including Fe atoms of FeO) contained in the agglomerates. The RI of the first agglomerates is preferably 72 to 75%, the RI of the second agglomerates is preferably 60 to 68%, and the RI of the third agglomerates is preferably 69 to 71%. Preferably, the difference between the RI of the first agglomerate and the RI of the second agglomerate ([RI of the first agglomerate] - [RI of the second agglomerate]) is 4 to 15%, the difference between the RI of the first agglomerate and the RI of the third agglomerate ([RI of the first agglomerate] - [RI of the third agglomerate]) is 1 to 6%, and the difference between the RI of the third agglomerate and the RI of the second agglomerate ([RI of the third agglomerate] - [RI of the second agglomerate]) is 1 to 11%.

[0038] [2] Direct Reduction Furnace Next, a direct reduction furnace according to an embodiment of the present invention will be described. The direct reduction furnace according to an embodiment of the present invention can be suitably used in the above-described method for producing reduced iron according to an embodiment of the present invention.

[0039] A direct reduction furnace according to one embodiment of the present invention includes: hoppers for storing first and second agglomerates, which are raw materials; and a raw material charging chute that is arranged vertically below the hoppers and serves as a charging path for the raw materials discharged from the hoppers, wherein the reducibility of the first agglomerates is greater than the reducibility of the second agglomerates, and the raw material charging chute has a device for adjusting the charging position of the raw materials in the radial direction of the direct reduction furnace.

[0040] The hopper is not particularly limited as long as it can store the first agglomerate and the second agglomerate, preferably the third agglomerate, respectively. For example, a configuration having multiple independent hoppers for each agglomerate to be stored may be used. Specifically, as shown in FIG. 4 , a configuration having three hoppers (a first hopper for storing the first agglomerate, a second hopper for storing the second agglomerate, and preferably a third hopper for storing the third agglomerate) may be used. In the figure, reference numeral 9 denotes a hopper and reference numeral 10 denotes a raw material charging chute. Another configuration may be one in which a single hopper is provided with separate storage sections capable of storing each agglomerate (for example, a first storage section for storing the first agglomerate, a second storage section for storing the second agglomerate, and preferably a third storage section for storing the third agglomerate). The hopper may have, for example, a raw material charging port, a storage section, and a raw material discharge port. In the other embodiment described above, a raw material charging port may be provided for each storage section, or a single raw material charging port may be provided, and the raw material charging destination may be switchable between the first storage section, the second storage section, and the third storage section by a valve or the like.

[0041] The raw material charging chute is disposed vertically below the hopper and constitutes a charging path (hereinafter also referred to as the chute body) for the raw materials discharged from the hopper. The raw material charging chute has a device for adjusting the charging position of the raw materials in the radial direction of the direct reduction furnace. This makes it possible to adjust the charging position of the raw materials in the radial direction of the direct reduction furnace depending on the type of raw material discharged from the hopper.

[0042] An example of the raw material charging position adjustment device is a mode in which the chute body is adjustably tilted relative to the vertical direction by a drive device. As shown in FIG. 4 , one end of the chute body is positioned vertically above the approximate center of the direct reduction furnace, and the drive device adjustably tilts the chute body relative to the vertical direction around the end as a tilt axis. For example, when discharging a first agglomerate from the hopper (hereinafter also referred to as a first discharge pattern), the inclination angle of the raw material charging chute (the angle between the vertical direction and the chute body) is reduced to charge the first agglomerate at the center of the direct reduction furnace. When discharging a second agglomerate from the hopper (hereinafter also referred to as a second discharge pattern), the inclination angle of the raw material charging chute is increased to charge the second agglomerate against the furnace wall of the direct reduction furnace. More preferably, when discharging the third agglomerated ore from the hopper, the inclination angle of the raw material charging chute is adjusted between the inclination angle in the first discharge pattern and the inclination angle in the second discharge pattern to charge the third agglomerated ore into the intermediate portion of the direct reduction furnace. The raw material charging chute may have a swivel device that rotates the chute body in the circumferential direction of the direct reduction furnace by a drive device. The drive device may be, for example, an electric or pneumatic type.

[0043] In addition, the direct reduction furnace according to one embodiment of the present invention may include a control unit that controls the charging positions of the raw materials by the raw material charging chute (particularly, the charging positions of the raw materials in the radial direction of the furnace) so that the first agglomerate is charged in the center portion of the direct reduction furnace, the second agglomerate is charged in the furnace wall portion of the direct reduction furnace, and preferably the third agglomerate is charged in the middle portion of the direct reduction furnace.

[0044] As an example, the control unit may include an input unit for inputting the type of agglomerated ore to be discharged from the hopper, a calculation unit for processing the input, a memory unit for storing various data, and an output unit for outputting an operation signal for changing the charging position of the raw material by the raw material charging chute based on the processing result of the calculation unit.

[0045] In this case, specifically, the control unit is an information processing device. Fig. 9 shows an example of functional blocks of the control unit. The reducing furnace may have a control unit as shown in Fig. 9. As shown in Fig. 9, the control unit has an input unit and an output unit connected to external devices so as to be able to perform data communication, a calculation unit, and a storage unit that stores various data, all of which are connected to each other so as to be able to perform data communication.

[0046] The input unit and the output unit are, for example, interfaces that are provided to enable data communication with external devices.

[0047] The calculation unit is, for example, a CPU. The calculation unit controls the operation of the entire control unit. The calculation unit calculates how to change the filling position of the raw material by the raw material charging chute based on various setting values ​​and measurement data input from the outside to the input unit or stored in the memory unit, and generates an operation signal to change the filling position of the raw material. The output unit outputs the operation signal. The calculation unit realizes the above-mentioned functions, for example, by executing a program stored in the memory unit.

[0048] The storage unit is, for example, a writable nonvolatile memory such as an EPROM, etc. The storage unit is not particularly limited, but may be, for example, an HDD, an SSD, etc.

[0049] The raw material charging chute then receives the operation signal output from the output unit, adjusts the raw material charging position using the raw material charging position adjustment device as described in [1] above, and then charges the raw material.

[0050] The configuration other than the above is not particularly limited, and may be the same as that of a conventionally known direct reduction furnace. The first agglomerate, the second agglomerate, and the third agglomerate, as well as the center, middle, and furnace wall of the direct reduction furnace, are as described in [1] above. The configuration of the direct reduction furnace having the control unit described above is one example, and the method of adjusting the charging position of the raw materials is not limited to the method using the control unit described above, and any method may be used as long as it is possible to charge the raw materials at the desired position.

[0051] Examples will be described below. In the direct reduction furnace shown in FIG. 4 , the first agglomerate ore is packed in the center of the direct reduction furnace, the second agglomerate ore is packed in the furnace wall, and the third agglomerate ore is packed in the middle of the furnace to produce reduced iron. The reduction progress rate of the agglomerates in the packed bed inside the direct reduction furnace was calculated using a two-dimensional mathematical model. Here, the reduction progress rate of the agglomerates is the reduction rate A(x) of the agglomerates at an (arbitrary) position x in the packed bed. A(x) can be calculated, for example, by the following formula: [A(x) (unit: %)] = ([oxygen content of agglomerates before reduction (unit: mass %)] - [oxygen content of agglomerates at position x (unit: mass %)]) / [oxygen content of agglomerates before reduction (unit: mass %)] × 100

[0052] The analytical conditions and assumed manufacturing conditions for the calculations using the above two-dimensional mathematical model are as follows and shown in Table 1. (Analysis conditions) Calculation domain size: 4m x 8m Division: 30 x 56 Size of gas injection hole for reducing gas: Φ150mm Void ratio in furnace: 0.3 Continuity equation and Navier-Stokes equation discretized using the SMAC method (Assumed operating conditions) Composition of reducing gas: H ２ 60% by volume, CO 40% by volume. Reducing gas blowing amount: 300,000 Nm ３ / h (2000 Nm ３ / t) Reducing gas blowing temperature: 900 ° C.

[0053] *Center of direct reduction furnace: Dimensionless radius range of 0 to 0.57. Wall of direct reduction furnace: Dimensionless radius range of more than 0.81 to 1.00. Middle of direct reduction furnace: Dimensionless radius range of more than 0.57 to 0.81. Dimensionless radius: Dimensionless radius in the furnace radial direction, with the center position of the direct reduction furnace at 0 and the wall of the direct reduction furnace at 1.00.

[0054] For reference, Fig. 5 shows an example of the calculation results (contour diagram) of the reduction progress rate of the agglomerate ore inside the direct reduction furnace No. 3. Fig. 6 shows the calculation domain of Fig. 5. Fig. 7 shows a diagram in which the reduction progress rate of the agglomerate ore at the level (vertical position) of the gas injection hole of the reducing gas No. 3 (hereinafter also referred to as the achieved reduction rate) is plotted against the dimensionless radius in the furnace radial direction. Fig. 8 shows a diagram in which the achieved reduction rates of Nos. 1 to 3 are plotted against the dimensionless radius in the furnace radial direction.

[0055] As shown in Fig. 7, in No. 3 (comparative example) in which the same reducible agglomerates were packed in the radial direction of the direct reduction furnace, the achieved reduction degree was significantly lowered in the central portion, particularly in the region where the dimensionless radius was 0 to 0.16, and it was found that a large variation in the degree of reduction occurred in the radial direction of the furnace.

[0056] In contrast, in Nos. 1 and 2 (invention examples), in which the reducibility of the first agglomerate was greater than that of the second agglomerate, the decrease in the achieved reduction degree at the center was mitigated and the variation in the reduction degree in the furnace radial direction was reduced compared to No. 3, as shown in Figure 8. In particular, in No. 2, which satisfied the relationship of formula (1), the variation in the reduction degree in the furnace radial direction was more effectively reduced. Therefore, when the reduced iron produced in Nos. 1 and 2 was melted in an electric furnace, the increase in electrode consumption in the electric furnace was effectively suppressed.

[0057] Furthermore, when the reduction progress rate of the agglomerated ore during the production of reduced iron was calculated using a two-dimensional mathematical model under various direct reduction furnaces and production conditions, similar results to those described above were obtained.

[0058] REFERENCE SIGNS LIST 1 reduction furnace 1a agglomerated ore 1b reduced iron 3 dust removal device 4 dewatering device 5 natural gas supply section 6 air supply section 7 reformer 8 packed bed 9 hopper 10 raw material charging chute

Claims

1. A method for producing reduced iron, comprising: a filling step of filling a direct reduction furnace with first and second agglomerates as raw materials; an injection step of injecting a reducing gas into the direct reduction furnace; and a reduction step of reducing iron oxide contained in the raw materials with the reducing gas in the direct reduction furnace to obtain reduced iron, wherein in the filling step, the first agglomerates are filled in a center portion of the direct reduction furnace and the second agglomerates are filled in a furnace wall portion of the direct reduction furnace, and the reducibility of the first agglomerates is greater than the reducibility of the second agglomerates.

2. The method for producing reduced iron according to claim 1, wherein the center of the direct reduction furnace is in a region where the dimensionless radius is 0 to 0.57, and the furnace wall of the direct reduction furnace is in a region where the dimensionless radius is greater than 0.81 to 1.

00. Here, the dimensionless radius is a dimensionless radius in the furnace radial direction, with the center position of the direct reduction furnace being 0 and the furnace wall of the direct reduction furnace being 1.

00.

3. The method for producing reduced iron according to claim 2, wherein the raw materials further include a third agglomerate, the third agglomerate is charged into an intermediate section of the direct reduction furnace in the charging step, the intermediate section of the direct reduction furnace has a dimensionless radius in a range of more than 0.57 to 0.81, and the relationship of the following formula (1) is satisfied: [Reducibility of the first agglomerate] > [Reducibility of the third agglomerate] > [Reducibility of the second agglomerate] ... (1) 4. A direct reduction furnace comprising: hoppers for storing first agglomerated ores and second agglomerated ores, which are raw materials; and a raw material charging chute arranged vertically below the hoppers and serving as a charging path for the raw materials discharged from the hoppers, wherein the reducibility of the first agglomerated ores is greater than the reducibility of the second agglomerated ores, and the raw material charging chute has a device for adjusting the charging position of the raw materials in the radial direction of the direct reduction furnace.

5. The direct reduction furnace according to claim 4, further comprising a control unit that controls charging positions of the raw materials by the raw material charging chute so that the first agglomerated ore is charged in a center portion of the direct reduction furnace and the second agglomerated ore is charged in a furnace wall portion of the direct reduction furnace.

6. The direct reduction furnace according to claim 5, wherein the center of the direct reduction furnace is in a region where the dimensionless radius is 0 to 0.57, and the furnace wall of the direct reduction furnace is in a region where the dimensionless radius is greater than 0.81 to 1.00, where the dimensionless radius is the dimensionless radius in the furnace radial direction, with the center position of the direct reduction furnace being 0 and the furnace wall of the direct reduction furnace being 1.

00.

7. The direct reduction furnace according to claim 6, wherein the control unit further controls the charging position of the raw materials by the raw material charging chute so that the third agglomerate ore serving as the raw material is charged into an intermediate portion of the direct reduction furnace, the intermediate portion of the direct reduction furnace having a dimensionless radius of greater than 0.57 to 0.81, and the relationship of the following formula (1) is satisfied: [Reducibility of the first agglomerate ore] > [Reducibility of the third agglomerate ore] > [Reducibility of the second agglomerate ore] ... (1)

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