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 excellent for preventing increased electrode consumption. A first agglomerated ore is loaded into the center of a direct reduction furnace and a second agglomerated ore is loaded along the furnace walls of the direct reduction furnace, and the reduction degradability of the first agglomerated ore is made smaller 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 iron-making process, a method (hereinafter also referred to as the DRI production process) for reducing iron oxide by a direct reduction furnace, for example, a vertical shaft furnace, to produce reduced iron is used. In this DRI process, the 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, a reducing gas containing CO and H generated from natural gas is blown into the reduction furnace. Thereby, the iron oxide contained in the agglomerated ore is reduced according to the following formula to produce reduced iron. Fe ２ O ２ O ３ + 3CO → 2Fe + 3CO ２ ... (i) Fe ２ O ３ + 3H ２ → 2Fe + 3H ２ O... (ii)

[0003] Fig. 1 shows an example of the DRI production process. In the figure, reference numeral 1 is a direct reduction furnace, 1a is agglomerated ore, 1b is reduced iron, 3 is a dust removal device, 4 is a dehydration device, 5 is a natural gas supply section, 6 is an air supply section, and 7 is a reforming device.

[0004] In this DRI production process, for example, agglomerated ore is charged from the upper part of the direct reduction furnace and gradually lowered. Then, a high-temperature reducing gas is blown into the middle part of the direct reduction furnace. Thereby, as shown in Fig. 2, heat exchange and reduction reaction occur between the reducing gas and the iron oxide contained in the agglomerated ore, and the iron oxide contained in the agglomerated ore is reduced. Then, reduced iron is discharged from the lower part of the direct reduction furnace. In the figure, reference numeral 8 is the packed bed (reduction region) of agglomerated ore. Next, the reduced iron discharged from the direct reduction furnace is melted in an electric furnace or the like. On the other hand, from the upper part of the direct reduction furnace, mainly CO, CO ２ H ２ and H ２ O-containing top gas is discharged. The top gas is sent to the reforming device as a raw material for the reforming gas after dust collection and cooling. In the reforming device, a reforming reaction occurs between the top gas and the natural gas supplied from the outside, mainly CO and H２ A reducing gas containing [the specified substance] is generated. This reducing gas is then injected into the reduction furnace. The remaining portion 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 from the air.

[0005] Thus, the DRI manufacturing process does not use coke as a reducing agent. Therefore, the DRI manufacturing process produces less greenhouse gas CO2 compared to blast furnaces. ２ The amount emitted is small, CO ２ It is attracting attention as a steelmaking method that leads to a reduction in emissions.

[0006] As a technology relating to such a DRI manufacturing process, for example, Patent Document 1 discloses "a method for producing reduced iron by reducing iron oxide, comprising: a reduced iron production step of reducing the iron oxide to produce reduced iron by bringing the iron oxide into contact with a reducing gas while lowering it from the top of a reducing furnace, and discharging the reduced iron from the bottom of the reducing furnace; a reformed gas production step of extracting the top gas of the reducing furnace, adjusting its moisture content and performing dust removal 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 reduction gas supply step of supplying the generated reformed gas to the reducing furnace as the reducing gas; a cooling step of introducing a cooling gas into a cooling region set at the bottom of the reducing 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 amount of carbon contained in the reduced iron passing through the cooling region."

[0007] Japanese Patent Publication No. 2017-88912

[0008] Incidentally, as mentioned above, reduced iron produced by a conventional DRI manufacturing process, such as that described in Patent Document 1, is subjected to melting in an electric furnace in the next step. However, when reduced iron produced by a conventional DRI manufacturing process is subjected to melting in an electric furnace, the electrode consumption of the electric furnace may increase excessively, and there has been a demand for improvement in this regard.

[0009] The present invention was developed to meet the above-mentioned requirements and aims to provide a method for producing reduced iron that can prevent an excessive increase in the electrode consumption of an electric furnace when melted in an electric furnace (hereinafter also referred to as having excellent electrode consumption increase prevention properties). Furthermore, the present invention aims 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 "~" means a range that includes the numbers before and after "~" as the lower and upper limits, respectively, unless otherwise stated as "greater than" or "less than".

[0011] The inventors conducted extensive research to solve the above problems. As a result, the inventors obtained the following findings: ・In reduced iron produced by the conventional DRI manufacturing process, there is variation in the reduction rate, that is, variation in the degree of reduction of iron oxide contained in the agglomerate in the reduction process (hereinafter also simply referred to as the degree of reduction). This variation in the degree of reduction leads to an excessive increase in the electrode consumption of the electric furnace. ・To reduce this variation in the degree of reduction, when directly filling the agglomerate into the reduction furnace, it is effective to charge agglomerate with relatively low reducibility to powdering in the center of the direct reduction furnace and agglomerate with relatively high reducibility to powdering in the furnace wall direction of the direct reduction furnace.

[0012] This invention was completed based on the above findings and further investigations. Specifically, the gist of this invention is as follows:

[0013] 1. A method for producing reduced iron, comprising: a filling step of directly filling a reduction furnace with a first agglomerate and a second agglomerate to be used as raw materials; a blowing step of blowing a reducing gas into the direct reduction furnace; and a reduction step of obtaining reduced iron by reducing the iron oxide contained in the raw materials with the reducing gas in the direct reduction furnace, wherein in the filling step, the first agglomerate is filled into the center of the direct reduction furnace and the second agglomerate is filled into the furnace wall of the direct reduction furnace, and the reductivability of the first agglomerate is less than that of the second agglomerate.

[0014] 2. The method for producing reduced iron according to paragraph 1, wherein the central part of the direct reduction furnace is in a region of dimensionless radius 0 to 0.70, and the furnace wall of the direct reduction furnace is in a region of greater than 0.70 to 1.00. Here, the dimensionless radius is the dimensionless radius in the furnace radial direction, with the central 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 claim 1 or 2, wherein the reductive pulverizability of the first agglomerated ore is 0.1 times or more and 0.4 times or less the reductive pulverizability of the second agglomerated ore.

[0016] 4. A direct reduction furnace comprising: hoppers for storing a first agglomerated ore and a second agglomerated ore, respectively, as raw materials; and a raw material charging chute positioned vertically below the hopper and serving as a filling path for the raw materials discharged from the hopper, wherein the reductive pulverizability of the first agglomerated ore is less than that of the second agglomerated ore; and the raw material charging chute has a device for adjusting the filling position of the raw materials in the radial direction of the furnace of the direct reduction furnace.

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

[0018] 6. The direct reduction furnace according to 5, wherein the central part of the direct reduction furnace is in a region of dimensionless radius 0 to 0.70, and the furnace wall portion of the direct reduction furnace is in a region of greater than 0.70 to 1.00. Here, the dimensionless radius is the dimensionless radius in the furnace radial direction, with the central position of the direct reduction furnace being 0 and the furnace wall of the direct reduction furnace being 1.00.

[0019] 7. A direct reduction furnace according to any one of 4 to 6, wherein the reductive pulverization ability of the first agglomerated ore is 0.1 times or more and 0.4 times or less than the reductive pulverization ability of the second agglomerated ore.

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

[0021] This figure shows an example of the DRI manufacturing process. This figure schematically shows the heat exchange (heat transfer) and reduction reaction between the reducing gas and iron oxide contained in the agglomerated ore inside the direct reduction furnace. This figure shows an example of the temperature distribution of the packed bed inside the direct reduction furnace. This figure shows the length of the low-temperature region at each position in the furnace radial direction of the direct reduction furnace. This figure shows an example of a direct reduction furnace according to one embodiment of the present invention. This is a schematic diagram showing an example of a functional block of the control unit. This figure shows an example of the calculation result of the reduction progress rate of the agglomerated ore inside the direct reduction furnace.

[0022] [1] Method for producing reduced iron A method for producing reduced iron according to one embodiment of the present invention comprises: a filling step of directly filling a first agglomerate and a second agglomerate, which are to be used as raw materials, into a reduction furnace; a blowing step of blowing a reducing gas into the direct reduction furnace; and a reduction step of obtaining reduced iron by reducing the iron oxide contained in the raw materials with the reducing gas in the direct reduction furnace. However, the present invention is not limited to the embodiments shown below, as long as it does not depart from the spirit of the present invention.

[0023] The filling process will be explained in detail below. The blowing and reduction processes should be carried out according to conventional methods, for example, in the same manner as the conventional DRI manufacturing process described above. Therefore, their explanation will be omitted here.

[0024] - Filling Process: In the filling process, the first and second agglomerates, which serve as raw materials, are directly filled into the reduction furnace. At this time, it is important to charge the agglomerates with relatively low reductive pulverization properties into the center of the direct reduction furnace and the agglomerates with relatively high reductive pulverization properties into the furnace walls. In other words, it is important to fill the center of the direct reduction furnace with the first agglomerate and the furnace walls with the second agglomerate, so that the reductive pulverization properties of the first agglomerate are less than those of the second agglomerate (reductive pulverization properties of the first agglomerate < reductive pulverization properties of the second agglomerate).

[0025] In other words, the inventors conducted various experiments and studies and obtained the following findings.

[0026] In a typical direct reduction furnace (shaft furnace), multiple gas injection holes for reducing gas are arranged circumferentially around the furnace body. Reducing gas is then injected through these injection holes. At this time, the inside of the direct reduction furnace is filled with roughly spherical agglomerated ore, forming a packed bed of agglomerated ore (hereinafter also simply referred to as the packed bed). In the packed bed, as reduction progresses, the agglomerated ore is pulverized (hereinafter also referred to as reduction pulverization). When reduction pulverization occurs, the porosity of the packed bed decreases, and the permeability decreases. Furthermore, reduction pulverization occurs particularly significantly in the temperature range of 500 to 700°C.

[0027] In the packed bed inside a direct reduction furnace, the temperature differs in the radial direction of the furnace, even at the same height. For example, as shown in Figure 3, the temperature is higher at the furnace wall (closer to the gas injection hole for reducing gas) than at the center of the direct reduction furnace. Here, Figure 3 shows the result (contour diagram) of the temperature distribution inside the packed bed of the direct reduction furnace calculated under the same conditions (including analysis conditions and operating conditions) as in Example No. 1 described later.

[0028] Next, Figure 4 shows the length of the temperature region between 500 and 700°C in the vertical direction of the direct reduction furnace at various positions in the furnace radial direction (hereinafter also referred to as the low-temperature region length). Here, the low-temperature region length in Figure 4 was obtained from the calculation results of the temperature distribution shown in Figure 3. In Figure 4, the dimensionless value obtained by dividing the low-temperature region length by the distance from the reducing gas injection point to the top of the furnace is plotted. As shown in Figure 4, in the central part of the direct reduction furnace, particularly in the region with a dimensionless radius of 0 to 0.70, the low-temperature region length increases as you get closer to the center of the direct reduction furnace. On the other hand, in the furnace wall part of the direct reduction furnace, particularly in the region with a dimensionless radius greater than 0.70 to 1.00, the low-temperature region length is approximately constant and shorter than the low-temperature region length in the central part.

[0029] Therefore, the lumpy ore located at the center of the direct reduction furnace stays in a temperature range of 500 to 700 °C longer than the lumpy ore located at the furnace wall of the direct reduction furnace. That is, in the lumpy ore located at the center of the direct reduction furnace, reduction degradation is more prominent than in the lumpy ore located at the furnace wall of the direct reduction furnace. Therefore, in the center of the direct reduction furnace, the air permeability tends to decrease easily. As a result, the lumpy ore filled in the center of the direct reduction furnace becomes less likely to react with the reducing gas than the lumpy ore filled in the furnace wall of the direct reduction furnace, and variations in the degree of reduction occur in the furnace radius direction. In this regard, the first lumpy ore is filled in the center of the direct reduction furnace, and the second lumpy ore is filled in the furnace wall of the direct reduction furnace, and the reduction degradation property of the first lumpy ore is made smaller than that of the second lumpy ore. In other words, in the center of the direct reduction furnace, lumpy ore that is less likely to undergo reduction degradation than the lumpy ore filled in the furnace wall is filled. Thereby, the degree of reduction degradation of the lumpy ore filled in the center of the direct reduction furnace and the lumpy ore filled in the furnace wall of the direct reduction furnace becomes closer. As a result, it becomes possible to reduce variations in the degree of reduction.

[0030] Here, for example, the center of the direct reduction furnace is a region with a dimensionless radius of 0 to 0.70, and the furnace wall of the direct reduction furnace is a region with a dimensionless radius exceeding 0.70 to 1.00. The dimensionless radius is the dimensionless radius in the furnace radius direction with the center position of the direct reduction furnace being 0 and the furnace wall of the direct reduction furnace being 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 of the inner diameter)).

[0031] Further, the reduction degradation property of the first lumpy ore is preferably 0.1 times or more, more preferably 0.2 times or more, that of the second lumpy ore. The reduction degradation property of the first lumpy ore is preferably 0.4 times or less, more preferably 0.3 times or less, that of the second lumpy ore. The degree of reduction degradation of the lumpy ore filled in the center of the direct reduction furnace and the lumpy ore filled in the furnace wall of the direct reduction furnace becomes closer, and it becomes possible to more effectively reduce variations in the degree of reduction.

[0032] The index of the reduction degradation property is not limited, but in particular, the reduction degradation index (%) (hereinafter also referred to as RDI) defined in JIS M 8720 (2009) is suitable.

[0033] RDI can be calculated by the following formula according to the iron ore - low - temperature reduction degradation test method conforming to JIS M 8720 (2009). Here, m ０ : The mass (g) of the measurement sample (lump ore) before rolling after reduction, and m １ : The mass (g) of the measurement sample remaining on a 2.8 - mm sieve.

[0034] For example, taking the lump ore used in a direct reduction furnace as the measurement sample, weigh 500 g of the lump ore and load it into a reaction tube with an inner diameter of 75 mm. Then, use a reducing gas of CO: 70 vol% and N ２ : 30 vol% to reduce the measurement sample in the reaction tube for 30 minutes. After reduction, measure the mass of the measurement sample and set it as m ０ . Then, fill the measurement sample into a cylindrical container with an inner diameter of 914 mm and a height of 457 mm, and rotate it 900 times at a rotation speed of 30 rpm. After that, take out the measurement sample and sieve it with a 2.8 - mm sieve. Then, measure the mass of the measurement sample remaining on the 2.8 - mm sieve and set it as m １ .

[0035] The above - mentioned filling process can be carried out, for example, by using the raw material charging chute of the direct reduction furnace described later and adjusting the charging position of the lump ore in the radial direction of the furnace radius of the direct reduction furnace. As an example, when discharging the first lump ore from the hopper, the charging position can be adjusted using the raw material charging chute so that the first lump ore is filled in the central part of the direct reduction furnace. Similarly, when discharging the second lump ore from the hopper, the charging position can be adjusted using the raw material charging chute so that the second lump ore is filled in the furnace wall part of the direct reduction furnace. Note that the first lump ore can be referred to as the lump ore filled in the central part of the direct reduction furnace. Similarly, the second lump ore can be referred to as the lump ore filled in the furnace wall part of the direct reduction furnace.

[0036] Also, the reduction degradation property of the lump ore can be adjusted, for example, by the pore structure and porosity of the lump ore, and the blending of auxiliary raw materials (such as limestone) during the production of the lump ore.

[0037] Conditions other than the above are not particularly limited and may follow conventional methods.

[0038] For example, the composition of the reducing gas is H ２ Preferably, the composition is: 60-90% by volume for the main component, 10-40% by volume for CO, and 0-5% by volume for the remainder. The amount of reducing gas blown in should be 1500-2000 Nm³. ３ / t is preferable. Here, Nm ３ / t represents the flow rate (converted to standard conditions) per ton of reduced iron (DRI) produced. The injection temperature of the reducing gas is preferably 850 to 1050°C.

[0039] Furthermore, the composition of the first and second agglomerate ores used as raw materials is as follows (in mass%): Iron: 61-68%, FeO: 0.1-0.6%, SiO ２ Examples include 1.1–5.7% for iron and 0.15–0.78% for CaO. Here, the value for iron (T.Fe) is the mass fraction of all Fe atoms (including Fe atoms in FeO) contained in the agglomerated ore. The RDI of the first agglomerated ore is preferably 3–10%, and the RDI of the second agglomerated ore is preferably 11–19%.

[0040] [2] Direct Reduction Furnace Next, a direct reduction furnace according to one embodiment of the present invention will be described. The direct reduction furnace according to one embodiment of the present invention can be suitably used in the method for producing reduced iron according to the above embodiment of the present invention.

[0041] A direct reduction furnace according to one embodiment of the present invention comprises a hopper for storing a first agglomerated ore and a second agglomerated ore, respectively, as raw materials, and a raw material charging chute positioned vertically below the hopper and serving as a filling path for the raw materials discharged from the hopper, wherein the reducibility of the first agglomerated ore is less than that of the second agglomerated ore, and the raw material charging chute has a device for adjusting the filling position of the raw materials in the radial direction of the furnace of the direct reduction furnace.

[0042] The hopper is not particularly limited as long as it can store the first and second agglomerates, which are the raw materials. For example, one configuration is to have multiple hoppers, each independent for each agglomerate to be stored. Specifically, as shown in Figure 5, one configuration is to have two hoppers (a first hopper for storing the first agglomerate and a second hopper for storing the second agglomerate). In the figure, reference numeral 9 denotes the hopper and 10 denotes the raw material charging chute. Another configuration is to have a single hopper with separate storage sections for each agglomerate (for example, having a first storage section for storing the first agglomerate and a second storage section for storing the second agglomerate). The hopper has, for example, a raw material charging inlet, a storage section, and a raw material discharge port. Furthermore, in the aforementioned alternative configuration, a raw material charging port may be provided for each storage section, or there may be only one raw material charging port, and a valve or the like may be used to allow switching between the first and second storage sections for the raw material to be charged. The same applies to the raw material discharge port.

[0043] The raw material charging chute is positioned vertically below the hopper and constitutes the filling 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 filling position of the raw materials in the furnace radial direction of the direct reduction furnace. This allows the filling position of the raw materials in the furnace radial direction of the direct reduction furnace to be adjusted according to the type of raw material discharged from the hopper.

[0044] As a raw material filling position adjustment device, for example, one configuration is one in which the chute body is tilted in a manner adjustable with respect to the vertical direction by a drive device. For example, as shown in Figure 5, one end of the chute body is positioned so that it is approximately at the center of the direct reduction furnace and on the upper side in the vertical direction, and the chute body is tilted in a manner adjustable with respect to the vertical direction by a drive device using this end as the tilt axis. For example, when discharging the first agglomerated ore from the hopper (hereinafter also referred to as the first discharge pattern), the tilt angle of the raw material charging chute (the angle between the vertical direction and the chute body) is reduced to fill the first agglomerated ore into the center of the direct reduction furnace. When discharging the second agglomerated ore from the hopper (hereinafter also referred to as the second discharge pattern), the tilt angle of the raw material charging chute is increased to fill the second agglomerated ore into the furnace wall of the direct reduction furnace. The raw material charging chute may also have a rotating device that rotates the chute body in the circumferential direction of the direct reduction furnace by a drive device. Examples of the drive device include electric and pneumatic types.

[0045] In addition, a direct reduction furnace according to one embodiment of the present invention may have a control unit that controls the filling position of the raw materials (particularly the filling position of the raw materials in the radial direction of the furnace) by a raw material charging chute so as to fill the center of the direct reduction furnace with a first agglomerated ore and the furnace wall portion of the direct reduction furnace with a second agglomerated ore.

[0046] As an example, the control unit may include an input unit for inputting the type of agglomer ore discharged from the hopper, a calculation unit for processing the input, a storage unit for storing various data, and an output unit for outputting an operation signal that changes the filling position of the raw material by the raw material charging chute based on the calculation results from the calculation unit.

[0047] In this case, specifically, the control unit is an information processing device. Figure 6 shows an example of the functional blocks of the control unit. A reduction furnace may have a control unit as shown in Figure 6. As shown in Figure 6, the control unit has an input unit and an output unit that are connected to external devices for data communication, a calculation unit and a storage unit that stores various types of data, all of which are connected to each other for data communication.

[0048] The input and output sections are, for example, interfaces provided to enable data communication with external devices.

[0049] The arithmetic unit is, for example, a CPU. The arithmetic unit controls the operation of the entire control unit. Based on various setting values ​​and measurement data input from the external input unit or stored in the memory unit, the arithmetic unit calculates how to change the filling position of the raw material by the raw material charging chute and generates an operation signal to change the filling position of the raw material. The output unit outputs the operation signal. The arithmetic unit realizes the above functions, for example, by executing a program stored in the memory unit.

[0050] The storage unit is, for example, a writable non-volatile memory such as EPROM. While the storage unit is not particularly limited, for example, an HDD and an SSD can be used.

[0051] The raw material charging chute then receives an operation signal output from the output unit and adjusts the raw material charging position using a raw material filling position adjustment device. This fills the raw material as described in [1] above.

[0052] Other configurations are not particularly limited and may be the same as those of conventionally known direct reduction furnaces. The first agglomerate, the second agglomerate, and the central part and furnace wall of the direct reduction furnace are described in [1] above. The configuration of the direct reduction furnace having the control unit described above is just one example, and the method for adjusting the raw material charging position is not limited to the method by the control unit described above, but any method is acceptable as long as charging to the desired position can be achieved.

[0053] The following describes an example. In the direct reduction furnace shown in Figure 5, when the first agglomerate is packed into the center of the direct reduction furnace and the second agglomerate is packed into the furnace wall, the reduction rate of the agglomerate in the packed bed inside the direct reduction furnace was calculated using a two-dimensional mathematical model. Here, the reduction rate of the agglomerate is the reduction rate A(x) of the agglomerate at an (arbitrary) position x in the packed bed. A(x) can be calculated, for example, by the following formula: [A(x) (unit: %)] = ([Amount of oxygen in the agglomerate before reduction (mass of oxygen atoms, the same applies below) (unit: mass%)] - [Amount of oxygen in the agglomerate at position x (unit: mass%)]) / [Amount of oxygen in the agglomerate before reduction (unit: mass%)] × 100

[0054] The analysis conditions and assumed manufacturing conditions in the calculations using the above two-dimensional mathematical model are as follows and in Table 1. (Analysis conditions) ・Calculation domain dimensions: 4m x 8m ・30 x 56 divisions ・Size of the gas injection hole for reducing gas: Φ150mm ・Furnace void ratio: 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, 40% by volume of CO; reducing gas injection rate: 300,000 Nm³ ３ / h (2000 Nm) ３ ( / t) • Injection temperature of reducing gas: 950°C • Pressure of reducing gas: 120 kPa • Operating period: 30 days • Production rate of reduced iron: 150 t / h

[0055] From the obtained calculation results, the average value of the reduction rate of agglomerated ore at the level (vertical position) of the gas injection hole of the reducing gas at dimensionless radii of 0, 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, and 0.70 of the direct reduction furnace (hereinafter also referred to as the achievable reduction rate) was determined, and this average value was set as the achievable reduction rate at the center of the direct reduction furnace (hereinafter also referred to as the center reduction rate). In addition, the average value of the achievable reduction rate at dimensionless radii of 0.80, 0.90, and 1.00 of the direct reduction furnace (hereinafter also referred to as the furnace wall reduction rate) was determined, and this average value was set as the achievable reduction rate at the furnace wall of the direct reduction furnace (hereinafter also referred to as the furnace wall reduction rate). Then, an evaluation of the reduction of variation in the degree of reduction, that is, an evaluation of the ability to prevent an increase in electrode consumption, was performed according to the following criteria. The results are shown in Table 1. A (Pass, Excellent): The difference between the reduction rate of the furnace wall (%) and the reduction rate of the center (%) (hereinafter also referred to as the reduction rate difference) is 5% or less. B (Pass, Excellent): The reduction rate difference is greater than 5% but 10% or less. C (Fail, Poor): The reduction rate difference is greater than 10%.

[0056] * Center of the direct reduction furnace: Region with a dimensionless radius of 0 to 0.70. Furnace wall of the direct reduction furnace: Region with a dimensionless radius greater than 0.70 to 1.00. Dimensionless radius: Dimensionless radius in the furnace radial direction, with the center of the direct reduction furnace being 0 and the furnace wall of the direct reduction furnace being 1.00.

[0057] For reference, Figure 7 shows an example of the calculated reduction rate of agglomerate ore inside the No. 4 direct reduction furnace (contour plot).

[0058] As shown in Table 1, in all of the inventive examples, the variation in the degree of reduction is effectively reduced. Therefore, when the reduced iron produced according to these inventive examples is subjected to melting in an electric furnace, the increase in the electrode consumption of the electric furnace is effectively suppressed. In particular, in Nos. 3 to 5, where the reductive pulverization property of the first agglomerate is within the range of 0.2 to 0.3 times that of the reductive pulverization property of the second agglomerate, the variation in the degree of reduction is extremely effectively reduced. Therefore, when the reduced iron produced according to Nos. 3 to 5 is subjected to melting in an electric furnace, the increase in the electrode consumption of the electric furnace is extremely effectively suppressed.

[0059] Furthermore, when calculating the reduction rate of agglomerate ore during the production of reduced iron using a two-dimensional mathematical model under various direct reduction furnace and manufacturing conditions, similar results were obtained.

[0060] 1. Reduction furnace 1a. Agglomerated ore 1b. Reduced iron 3. Dust removal device 4. Dehydration device 5. Natural gas supply unit 6. Air supply unit 7. Reforming device 8. Packed bed 9. Hopper 10. Raw material charging chute

Claims

1. A method for producing reduced iron, comprising: a filling step of directly filling a reduction furnace with a first agglomerate and a second agglomerate to be used as raw materials; a blowing step of blowing a reducing gas into the direct reduction furnace; and a reduction step of obtaining reduced iron by reducing the iron oxide contained in the raw materials with the reducing gas in the direct reduction furnace, wherein in the filling step, the first agglomerate is filled into the center of the direct reduction furnace and the second agglomerate is filled into the furnace wall of the direct reduction furnace, and the reducibility of the first agglomerate is less than that of the second agglomerate.

2. The method for producing reduced iron according to claim 1, wherein the central part of the direct reduction furnace is in a region with a dimensionless radius of 0 to 0.70, and the furnace wall portion of the direct reduction furnace is in a region with a dimensionless radius of greater than 0.70 to 1.

00. Here, the dimensionless radius is the dimensionless radius in the furnace radial direction, with the central 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 1 or 2, wherein the reductive pulverizability of the first agglomerated ore is 0.1 times or more and 0.4 times or less the reductive pulverizability of the second agglomerated ore.

4. A direct reduction furnace comprising: hoppers for storing a first agglomerated ore and a second agglomerated ore, respectively, as raw materials; and a raw material charging chute positioned vertically below the hopper and serving as a filling path for the raw materials discharged from the hopper, wherein the reducibility of the first agglomerated ore is less than that of the second agglomerated ore, and the raw material charging chute has a device for adjusting the filling position of the raw materials in the radial direction of the furnace of the direct reduction furnace.

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

6. The direct reduction furnace according to claim 5, wherein the central part of the direct reduction furnace is in a region of dimensionless radius 0 to 0.70, and the furnace wall portion of the direct reduction furnace is in a region of greater than 0.70 to 1.

00. Here, the dimensionless radius is the dimensionless radius in the furnace radial direction, with the central 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 any one of claims 4 to 6, wherein the reductive pulverization ability of the first agglomerated ore is 0.1 times or more and 0.4 times or less than the reductive pulverization ability of the second agglomerated ore.

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