Method for producing reduced iron, and shaft furnace

Abstract

Disclosed is a new technique for improving the average reduction rate of raw material in a method for producing reduced iron using a shaft furnace. This method for producing reduced iron comprises supplying a raw material including iron oxide into a shaft furnace through an upper portion thereof, and also supplying a reducing gas including hydrogen gas into the shaft furnace through a side wall thereof, to thereby reduce the iron oxide and obtain the reduced iron from a lower portion of the shaft furnace, and is characterized by comprising performing an action for causing the flow of the reducing gas inside the shaft furnace to be changed from the side wall side of the shaft furnace toward the center of the shaft furnace.

Description

Reduced iron manufacturing method and shaft furnace

[0001] The present application discloses a method for producing reduced iron and a shaft furnace.

[0002] A technology for producing reduced iron by reducing iron oxide using a direct reduction method using a shaft furnace is known. Specifically, raw materials containing iron oxide are supplied from the top to the interior of a shaft furnace, and a reducing gas is supplied from the side wall of the shaft furnace to the interior. The iron oxide is reduced inside the shaft furnace, and reduced iron is obtained from the bottom of the shaft furnace. The reducing gas contains, for example, hydrogen gas. Here, when reducing gas containing hydrogen gas is supplied from the side wall to the interior of the shaft furnace, much of the hydrogen gas rises along the vicinity of the furnace wall, which tends to result in an insufficient supply of hydrogen gas to the central portion (center) of the shaft furnace. As a result, the average reduction rate of the raw materials tends to decrease.

[0003] Patent Document 1 discloses a technique for improving the uniformity of gas within a shaft furnace by dividing the furnace body, but dividing the furnace body increases the equipment cost and reduces the space utilization rate of the furnace.

[0004] Patent Document 2 discloses a technique for dividing a gas discharge system at the top of a shaft furnace. However, simply dividing the gas discharge system makes it difficult to improve the uniformity of the gas inside the furnace. Furthermore, dividing the gas discharge system makes the structure of the furnace top more complicated.

[0005] Patent Document 3 discloses a technique of providing a pipe for introducing a reducing gas in the center of a shaft furnace. However, in this case, the structure of the shaft furnace becomes complicated, increasing the equipment cost, and the pipe in the center of the shaft furnace is easily damaged, for example, due to excessive pressure generated in the pipe during operation.

[0006] Patent Document 4 discloses a technology for controlling the feed position of raw materials into a shaft furnace in the radial direction of the furnace according to the temperature of the exhaust gas at the top of the shaft furnace. However, even if the feed position of raw materials is controlled, it is difficult to improve the uniformity of the gas inside the furnace.

[0007] Patent Document 5 discloses a technology in which hollow tubes are arranged in a staggered pattern inside a shaft furnace, and the hollow tubes disrupt the vertical downward flow of powder and granular material inside the furnace and allow high-temperature gas to circulate through the hollow tubes. However, arranging hollow tubes inside the furnace increases equipment costs and reduces the space utilization rate inside the furnace. Furthermore, the hollow tubes are prone to damage, such as excessive pressure being generated in the hollow tubes during operation.

[0008] Japanese Patent Publication No. 57-019163 Publication No. 59-034763 Japanese Patent Publication No. 62-294127 Publication No. 6-072248 Japanese Patent No. 3083810

[0009] When producing reduced iron using a shaft furnace, a new technology is needed to improve the average reduction rate of the raw material.

[0010] The present application discloses the following multiple aspects as one of means for solving the above problems: <Aspect 1> A method for producing reduced iron, comprising: supplying a raw material containing iron oxide from an upper part of a shaft furnace to the inside thereof, and supplying a reducing gas containing hydrogen gas from a side wall of the shaft furnace to the inside thereof, and reducing the iron oxide to obtain reduced iron from a lower part of the shaft furnace, and also comprising performing an action of changing the flow of the reducing gas inside the shaft furnace from the side wall side of the shaft furnace to the center side of the shaft furnace. <Aspect 2> The method for producing reduced iron according to Aspect 1, wherein the action is at least one of the following actions 1 to 4: Action 1: Cooling at least an inner wall of the shaft furnace at least between a feed position of the raw materials and a feed position of the reducing gas; Action 2: Mixing an inert gas with the reducing gas; Action 3: Dividing the reducing gas to be supplied into the shaft furnace into a first gas having a relatively low reducing power and a second gas having a relatively high reducing power, and supplying the first gas from above the second gas; Action 4: Making the average particle diameter of the raw materials supplied to the center of the shaft furnace larger than the average particle diameter of the raw materials supplied to the side wall of the shaft furnace. <Aspect 3> The method for producing reduced iron according to Aspect 2, wherein the action 1 is the following action 1A: Action 1A: Cooling at least an inner wall of the shaft furnace by water at least between a feed position of the raw materials and a feed position of the reducing gas. <Aspect 4> The method for producing reduced iron according to aspect 2 or 3, wherein Action 4 is Action 4A below: Action 4A: The raw materials are supplied to the side wall of the interior of the shaft furnace so that the average particle diameter of the raw materials supplied to the center side of the shaft furnace is larger than the average particle diameter of the raw materials supplied to the side wall side of the shaft furnace.<Aspect 5> The method for producing reduced iron according to any one of Aspects 2 to 4, wherein the first gas and the second gas in Action 3 satisfy one or both of the following conditions A and B: Condition A: The temperature of the first gas is lower than the temperature of the second gas; Condition B: The hydrogen gas concentration of the first gas is lower than the hydrogen gas concentration of the second gas. <Aspect 6> The method for producing reduced iron according to any one of Aspects 2 to 5, comprising: estimating information related to a reduction rate of the raw materials inside the shaft furnace; and performing the action based on the estimated information. <Aspect 7> The method for producing reduced iron according to Aspect 6, wherein the information is a reduction rate of the raw materials on the side wall side inside the shaft furnace or an index representative of the reduction rate, and the action is performed when the estimated reduction rate or the index representative of the reduction rate is greater than a first threshold. <Aspect 8> The method for producing reduced iron according to Aspect 6, wherein the information is a deviation in the furnace radial direction of the reduction rate of the raw materials inside the shaft furnace or an index representative of the reduction rate, and the action is performed when the estimated deviation is greater than a second threshold. <Aspect 9> A shaft furnace comprising: a raw material supply inlet, a gas supply inlet, a reduced iron discharge outlet, a gas discharge outlet, and an action execution device, wherein the raw material supply inlet is provided in an upper part of the shaft furnace, the gas supply inlet is provided in a side wall of the shaft furnace below the raw material supply inlet, the reduced iron discharge outlet is provided below the gas supply inlet, and the gas discharge outlet is provided above the gas supply inlet, and the action execution device is configured to perform an action to change the flow of reducing gas inside the shaft furnace from the side wall side of the shaft furnace to the center side of the shaft furnace.<Aspect 10> The shaft furnace of Aspect 9, wherein the action execution device is at least one of a cooling device, a mixing device, a gas supply device, and a raw material supply device, the cooling device is configured to cool at least an inner wall of the shaft furnace at least between the raw material supply port and the gas supply port, the mixing device is configured to mix the reducing gas with an inert gas, the gas supply device is configured to supply a first gas having a relatively low reducing power and a second gas having a relatively high reducing power from the gas supply port into the interior of the shaft furnace, and the supply position of the first gas is configured to be higher than the supply position of the second gas, and the raw material supply device is configured to supply the raw materials into the interior of the shaft furnace through the raw material supply port so that the average particle diameter of the raw materials supplied to the center side of the shaft furnace is larger than the average particle diameter of the raw materials supplied to the side wall side of the shaft furnace. <Aspect 11> The shaft furnace of Aspect 10, wherein the cooling device is configured to cool at least the inner wall of the shaft furnace by water cooling at least between the raw material supply port and the gas supply port. <Aspect 12> The shaft furnace of Aspect 10 or 11, wherein the raw material supply device is configured to supply the raw materials to a side wall side of the interior of the shaft furnace. <Aspect 13> The shaft furnace of any of Aspects 10 to 12, wherein the gas supply device is configured so that the first gas and the second gas satisfy one or both of the following conditions A and B. Condition A: The temperature of the first gas is lower than the temperature of the second gas; Condition B: The hydrogen gas concentration of the first gas is lower than the hydrogen gas concentration of the second gas. <Aspect 14> The shaft furnace of any one of Aspects 9 to 13, further comprising an estimation device and a control device, wherein the estimation device is configured to estimate information relating to a reduction rate of raw materials inside the shaft furnace, and the control device controls the action execution device so that the action is performed based on the estimated information.<Aspect 15> The shaft furnace of Aspect 14, wherein the information is a reduction rate of the raw materials on the side wall side inside the shaft furnace or an index representative of the reduction rate, and the control device controls the action execution device to take the action when the estimated reduction rate or the index representative of the reduction rate is greater than a first threshold. <Aspect 16> The shaft furnace of Aspect 14, wherein the information is a deviation in the furnace radial direction of the reduction rate of the raw materials inside the shaft furnace or an index representative of the reduction rate, and the control device controls the action execution device to take the action when the estimated deviation is greater than a second threshold.

[0011] According to the technology of the present disclosure, when reduced iron is produced using a shaft furnace, the average reduction rate of raw materials can be increased.

[0012] 1 schematically shows an example of a state before a predetermined action is performed in a method for producing reduced iron. 1 schematically shows an example of a state after action 1 is performed in a method for producing reduced iron. 1 schematically shows an example of a state after action 2 is performed in a method for producing reduced iron. 1 schematically shows an example of a state after action 3 is performed in a method for producing reduced iron. 1 schematically shows an example of a state after action 4 is performed in a method for producing reduced iron. 1 schematically shows an example of action 4. 1 schematically shows an example of action 4. 1 schematically shows an example of a configuration for performing a predetermined estimation in a method for producing reduced iron. 1 schematically shows an example of a configuration for performing a predetermined estimation in a method for producing reduced iron. 1 schematically shows a furnace body structure adopted in the calculations of the examples.

[0013] Hereinafter, a method for producing reduced iron according to an embodiment and a shaft furnace according to an embodiment will be described with reference to the drawings, but the technology of the present disclosure is not limited thereto.

[0014] 1 , a method for producing reduced iron according to one embodiment includes: supplying a raw material 10 containing iron oxide from an upper portion of a shaft furnace 100 to the interior thereof; and supplying a reducing gas containing hydrogen gas from a side wall 100 a of the shaft furnace 100 to the interior thereof; and reducing the iron oxide to obtain reduced iron 30 from a lower portion of the shaft furnace 100. Here, one feature of the method for producing reduced iron according to one embodiment is that it includes an action of changing the flow of the reducing gas inside the shaft furnace 100 from the side wall side of the shaft furnace 100 to the center side of the shaft furnace 100.

[0015] 1.1 Raw Material Raw material 10 includes at least iron oxide. Raw material 10 may be, for example, at least one selected from iron ore pellets, lump ore, and sintered ore. In addition to iron oxide, raw material 10 may also include, for example, one or both of silicon dioxide and aluminum oxide. Raw material 10 may have a particle size distribution or may have a uniform particle diameter. The average particle diameter of raw material 10 may be, for example, 10.0 mm or more and 15.0 mm or less. Raw material 10 may be formed into pellets or the like, or may be in the form of a powder, a lump, or other shapes.

[0016] The amount of raw material 10 supplied to the shaft furnace 100 may be optimally selected depending on the size and operating conditions of the shaft furnace 100, etc. The raw material 10 is supplied from the top of the shaft furnace 100 to the interior. The supply position of the raw material 10 may be any position above the supply position of the reducing gas. The raw material 10 may be supplied, for example, through a raw material supply port 101 provided at the top of the shaft furnace 100, etc. The method of supplying the raw material 10 is not particularly limited, and may be supplied, for example, by a hopper, a chute, etc. The raw material 10 may be supplied by free fall. In particular, when a rotating chute is used, action 4 described below can be more easily performed.

[0017] As the raw materials 10 are supplied from the top to the inside of the shaft furnace 100, a packed bed 20 is formed inside the shaft furnace 100. The packing rate of the packed bed 20 is not particularly limited. The packing rate of the packed bed 20 may be the same as the packing rate in a conventional method for producing reduced iron using a shaft furnace.

[0018] The raw materials 10 move downward inside the shaft furnace 100. That is, the raw materials 10 are substantially filled inside the shaft furnace 100 and gradually move downward by falling or the like. When focusing on a single raw material particle in the packed bed 20, the raw material particle may move downward continuously at a constant speed, or may move intermittently by repeatedly falling and stopping. When focusing on a single raw material particle in the packed bed 20, the average downward movement speed of the raw material particle is not particularly limited. For example, the average movement speed can be adjusted depending on the supply amount (feed speed) of the raw material. When moving the packed bed 20 downward, a burden feeder or the like may be used to prevent hanging. The configuration of a burden feeder in the shaft furnace 100 is known.

[0019] In the packed bed 20, the raw material 10 may have a particle size distribution and a temperature distribution from the top to the bottom of the shaft furnace 100 and / or in the radial direction of the shaft furnace 100. The particle size distribution of the raw material 10 may be, for example, a particle size distribution achieved by Action 4 described below. Alternatively, the raw material 10 may have an irregular particle size distribution in the packed bed 20. The temperature distribution of the packed bed 20 is not particularly limited. The packed bed 20 has a temperature at which reduction by the reducing gas can proceed. The packed bed 20 may be cooled below the supply position of the reducing gas. For example, the packed bed 20 can be cooled by supplying a cooling gas to the packed bed 20 below the supply position of the reducing gas. The cooling gas may be, for example, at least one selected from an inert gas, natural gas, hydrogen gas, etc.

[0020] 1.2 Reducing Gas The reducing gas contains at least hydrogen gas. The reducing gas may contain, in addition to hydrogen gas, a gas other than hydrogen gas. Examples of gases other than hydrogen gas include carbon monoxide gas and inert gases. The inert gas may be, for example, at least one selected from rare gases such as nitrogen gas and argon gas, carbon dioxide gas, and water vapor. The hydrogen gas concentration of the reducing gas (when the reducing gas contains the first gas and second gas described below, the average hydrogen gas concentration) may be, for example, 80% by volume or more and 100% by volume or less. The supply temperature of the reducing gas (the temperature immediately before contacting the packed bed) may be any temperature at which a reduction reaction with iron oxide occurs, and may be, for example, 700°C or more and 1000°C or less, or 800°C or more and 1000°C or less.

[0021] The reducing gas is supplied from the side wall 100a of the shaft furnace 100 to the interior of the shaft furnace 100. The method of supplying the reducing gas is not particularly limited. For example, a pipe or the like can be connected to a gas supply port 102 provided in the side wall 100a of the shaft furnace 100, and the reducing gas can be supplied from the outside of the shaft furnace 100 to the interior of the shaft furnace 100 via the pipe or the like. Here, the tip of the pipe or the like connected to the gas supply port 102 does not need to protrude inward beyond the inner wall 100ax inside the shaft furnace 100.

[0022] 1.3 Reduced Iron At least a portion of the iron oxide contained in the raw material 10 is reduced by the reduction reaction described above, thereby obtaining reduced iron 30, which is a solid reactant containing at least metallic iron. In addition to metallic iron, the reduced iron 30 may also contain unreduced iron oxide, silicon dioxide, aluminum oxide, and the like. The reduced iron 30 containing metallic iron can be recovered from the lower part of the shaft furnace 100 (below the supply position of the reducing gas).

[0023] 1.4 Action In the method for producing reduced iron according to one embodiment, an action is performed to change the flow of reducing gas inside the shaft furnace 100 from the side wall side of the shaft furnace 100 to the center side of the shaft furnace 100. This action is performed, for example, by the action execution device 110. By performing the action to change the flow of reducing gas inside the shaft furnace 100 from the side wall side of the shaft furnace 100 to the center side of the shaft furnace 100, uneven flow of reducing gas inside the shaft furnace 100 can be eliminated, and the average reduction rate of the raw materials 10 can be improved.

[0024] According to the inventor's findings, when the action in question is, for example, at least one of the following actions 1 to 4, the flow of reducing gas inside the shaft furnace 100 can be changed from the side wall side of the shaft furnace 100 to the center side of the shaft furnace 100 without adopting a complex configuration in the shaft furnace 100.

[0025] Action 1: Cooling at least the inner wall 100ax of the shaft furnace 100 at least between the feed position of the raw material 10 and the feed position of the reducing gas.

[0026] Action 2: Mixing the reducing gas with an inert gas.

[0027] Action 3: Divide the reducing gas supplied to the inside of the shaft furnace 100 into a first gas having a relatively low reducing power and a second gas having a relatively high reducing power, and supply the first gas from above the second gas.

[0028] Action 4: Making the average particle diameter of the raw material 10 supplied to the center side of the shaft furnace 100 larger than the average particle diameter of the raw material 10 supplied to the side wall side of the shaft furnace 100.

[0029] According to at least one of the above actions 1 to 3, for example, it is considered that the position at which the reduction reaction by the reducing gas on the side wall side inside the shaft furnace 100 is completed moves downward, and the flow of the reducing gas inside the shaft furnace 100 changes from the side wall side of the shaft furnace 100 to the center side of the shaft furnace 100. Furthermore, according to the above action 4, it is considered that the shape of the packed bed inside the shaft furnace 100 is controlled, the supply of gas to the center side of the shaft furnace 100 is promoted, and the flow of the reducing gas inside the shaft furnace 100 changes from the side wall side of the shaft furnace 100 to the center side of the shaft furnace 100.

[0030] 1.4.1 Action 1 As shown in FIG. 2 , according to Action 1, at least the inner wall 100ax of the shaft furnace 100 is cooled between the raw material 10 supply position and the reducing gas supply position (above the reducing gas supply position, between the raw material supply port 101 and the gas supply port 102; for example, the reduction zone 100ay where iron oxide is reduced). By cooling the inner wall 100ax between the raw material 10 supply position and the reducing gas supply position, the position where the reduction reaction is completed can be moved closer to the reducing gas supply position. This increases the area occupied by a reaction gas (e.g., steam) with a viscosity and density greater than that of hydrogen gas near the furnace wall, thereby increasing the pressure loss near the furnace wall. This allows the amount of reducing gas supplied to the inside of the vicinity of the furnace wall, i.e., the center of the shaft furnace 100.

[0031] In order to promote the reduction reaction of iron oxide by hydrogen, the temperatures of the reducing gas and the raw material 10 must be at a certain high temperature (e.g., 700°C or higher). On the other hand, because the reduction reaction of iron oxide by hydrogen is an endothermic reaction, the temperature in the system drops and the reduction reaction becomes difficult to proceed unless thermal energy is supplied from the outside. Therefore, conventional common sense dictates that the inner walls of the shaft furnace are not cooled, but rather the system is heated to maintain a high temperature inside the shaft furnace. In contrast, in Action 1, by deliberately adopting an operation that is unfavorable to the reduction reaction of iron oxide (cooling the inner walls of the shaft furnace), the position where the reduction reaction is completed is moved closer to the supply position of the reducing gas, thereby improving the uniformity of the gas inside the shaft furnace 100 and suppressing uneven reaction of iron oxide. As a result, the proportion of iron oxide contained in the reduced iron after the reduction reaction may decrease and the proportion of metallic iron may increase, compared to when the inner walls of the shaft furnace 100 are not cooled. That is, the average reduction rate R ａｖｅ can be improved.

[0032] In Action 1, the method for cooling the inner wall of the shaft furnace 100 is not particularly limited. For example, the inner wall of the shaft furnace 100 can be cooled by a known cooling device 111. Depending on the configuration of the furnace wall, for example, the inner wall of the shaft furnace 100 may be water-cooled by providing a mechanism for circulating cooling water inside the furnace wall between the supply position of the raw materials 10 and the supply position of the reducing gas. That is, in the method for producing reduced iron according to one embodiment, the above Action 1 may be the following Action 1A.

[0033] Action 1A: Cooling at least the inner wall 100ax of the shaft furnace 100 by water cooling, at least between the supply position of the raw material 10 and the supply position of the reducing gas.

[0034] In action 1, the height position at which the inner wall of the shaft furnace 100 is cooled is at least between the feed position of the raw material 10 and the feed position of the reducing gas (above the feed position of the reducing gas, between the raw material feed port 101 and the gas feed port 102; for example, the reduction zone 100ay where iron oxide is reduced). In action 1, the inner wall of the shaft furnace 100 may be cooled over the entire area between the feed position of the raw material 10 and the feed position of the reducing gas, or may be cooled only in a portion between the feed position of the raw material 10 and the feed position of the reducing gas.

[0035] In Action 1, the entire circumference of the inner wall of the shaft furnace 100 may be cooled, or only a part of the inner circumference may be cooled. In particular, a greater effect can be expected when the entire circumference of the inner wall of the shaft furnace 100 is cooled.

[0036] 1.4.2 Action 2 As shown in FIG. 3, according to Action 2, an inert gas is mixed with the reducing gas supplied into the shaft furnace 100 .

[0037] By mixing the reducing gas with an inert gas, as in Action 1, the position where the reduction reaction near the furnace wall inside the shaft furnace 100 is completed can be moved closer to the supply position of the reducing gas, and the area occupied by a reaction gas (e.g., water vapor) with a viscosity and density greater than that of hydrogen gas near the furnace wall can be increased, increasing the pressure loss near the furnace wall. This makes it possible to increase the amount of reducing gas supplied to the inside of the vicinity of the furnace wall, i.e., the center of the shaft furnace 100, improving the uniformity of the gas inside the shaft furnace 100 and suppressing uneven reaction of iron oxide inside the shaft furnace 100. As a result, compared to when an inert gas is not mixed with the reducing gas, the proportion of iron oxide contained in the solid product after the reduction reaction can be reduced and the proportion of reduced iron can be increased. That is, the average reduction rate R ａｖｅ can be improved.

[0038] In Action 2, for example, an inert gas supply system may be connected to the reducing gas supply system, and the inert gas may be mixed with the reducing gas via the inert gas supply system. In Action 2, the method for mixing the reducing gas and the inert gas is not particularly limited. The mixing of the reducing gas and the inert gas may be performed, for example, by an appropriate mixer 112. The amount of the inert gas mixed with the reducing gas is not particularly limited. For example, the inert gas may be mixed with the reducing gas so that the concentration of the inert gas in the total of the reducing gas and the inert gas is 5% by volume or more and 15% by volume or less. The inert gas may be at least one selected from rare gases such as nitrogen and argon. Nitrogen is particularly preferred.

[0039] 1.4.3 Action 3 As shown in FIG. 4, according to Action 3, the reducing gas supplied to the inside of the shaft furnace 100 is divided into a first gas having a relatively low reducing power and a second gas having a relatively high reducing power, and the first gas is supplied from above the second gas.

[0040] By supplying the first gas, which has a relatively low reducing power, from above the second gas, which has a relatively high reducing power, the position where the reduction reaction is completed can be moved closer to the supply position of the reducing gas, as in Action 1. This increases the area occupied by a reaction gas (e.g., steam) with a viscosity and density greater than that of hydrogen gas near the furnace wall, thereby increasing the pressure loss near the furnace wall. This allows the amount of reducing gas supplied to the interior of the furnace, i.e., the center of the furnace, to be increased, improving the uniformity of the gas in the furnace and suppressing uneven reaction of iron oxide in the furnace. As a result, compared to when only one type of reducing gas is supplied, the proportion of iron oxide contained in the reduced iron after the reduction reaction can be reduced and the proportion of metallic iron can be increased. That is, the average reduction rate R ａｖｅ can be improved.

[0041] In Action 3, for example, when the temperature of the first gas is lower than the temperature of the second gas and / or when the hydrogen gas concentration of the first gas is lower than the hydrogen gas concentration of the second gas, the reducing power of the first gas is relatively lower than the reducing power of the second gas. That is, the first gas and the second gas in Action 3 may satisfy one or both of the following conditions A and B:

[0042] Condition A: The temperature of the first gas is lower than the temperature of the second gas.

[0043] Condition B: The hydrogen gas concentration of the first gas is lower than the hydrogen gas concentration of the second gas.

[0044] As in the above condition A, lowering the temperature of the first gas not only improves the reduction rate but also reduces the energy required for heating. Regarding condition A, the difference between the temperature of the first gas and the temperature of the second gas is not particularly limited. The difference between the temperature of the first gas and the temperature of the second gas can be adjusted appropriately depending on the target average reduction rate, etc. When condition A is satisfied, the composition of the first gas and the composition of the second gas may be the same or different. The first gas may or may not contain hydrogen gas. On the other hand, the second gas essentially contains hydrogen gas. The first gas and the second gas may contain gases other than hydrogen gas in addition to hydrogen gas. Examples of gases other than hydrogen gas include carbon monoxide and inert gases. Examples of inert gases include nitrogen, argon, carbon dioxide, and water vapor.

[0045] As in the above condition B, by reducing the hydrogen gas concentration of the first gas, the reduction rate can be improved and the amount of hydrogen gas required can be reduced. Regarding condition B, the difference between the hydrogen gas concentrations of the first gas and the second gas is not particularly limited. The difference between the hydrogen gas concentrations of the first gas and the second gas can be adjusted appropriately depending on the target average reduction rate, etc. The method for reducing the hydrogen gas concentration of the first gas to be lower than the hydrogen gas concentration of the second gas is not particularly limited, and examples thereof include a method of mixing an inert gas with the first gas. The first gas may or may not contain hydrogen gas. On the other hand, the second gas essentially contains hydrogen gas. The first gas and the second gas may contain gases other than hydrogen gas in addition to hydrogen gas. Examples of gases other than hydrogen gas include carbon monoxide and inert gases. Examples of inert gases include nitrogen, argon, carbon dioxide, and water vapor. When condition B is satisfied, the temperatures of the first gas and the second gas may be the same or different.

[0046] In Action 3, for example, the gas supply system in the gas supply device 113 may be divided into two systems, an upper system and an lower system, or three or more systems, including an upper system, a middle system, and a lower system, and the first gas may be supplied from at least one system on the upper side, and the second gas may be supplied from at least one system on the lower side. The supply position of the first gas may be directly above the supply position of the second gas or may be diagonally above. However, a more effective supply position directly above the supply position is particularly likely to be directly above the supply position. In Action 3, the supply amount or supply rate of the first gas and the supply amount or supply rate of the second gas may be the same or different. For example, in Action 3, the ratio of the first gas to the total of the first gas and the second gas supplied into the shaft furnace 100 (first gas / (first gas + second gas)) may be greater than 0 vol% and less than 10 vol%. In Action 3, the exhaust gas discharged from the gas outlet 104 of the shaft furnace 100 may be reused as the first gas (a gas with a relatively lower hydrogen concentration than the second gas and / or a gas with a relatively lower temperature than the second gas).

[0047] 1.4.4 Action 4 As shown in FIG. 5 , in Action 4, the average particle size of the raw materials 10 supplied to the center side of the shaft furnace 100 (the central region 20a of the packed bed 20) is made larger than the average particle size of the raw materials 10 supplied to the side wall side of the shaft furnace 100 (the region 20b radially outward of the central region 20a in the packed bed 20).

[0048] In this application, the "particle diameter" of the raw material refers to the maximum outer diameter of the raw material particles. Furthermore, the "average particle diameter" of the raw material refers to the harmonic mean of the maximum outer diameter of the raw material particles. Furthermore, in this application, a predetermined position between the center and the inner wall of the shaft furnace is defined as the boundary, and the area between this boundary and the center is defined as the "center side of the shaft furnace," and the area between this boundary and the inner wall is defined as the "side wall side of the shaft furnace." Specifically, the range from the center of the shaft furnace to 1 / 4 of the furnace inner diameter (up to 1 / 2 of the radius) is defined as the "center side of the shaft furnace," and the range outside this range is defined as the "side wall side of the shaft furnace."

[0049] In Action 4, coarse particles are arranged in the center of the shaft furnace 100 and fine particles are arranged on the sidewalls of the shaft furnace 100, which increases the gas pressure loss near the furnace wall of the packed bed 20 and makes it easier for the reducing gas to be supplied to the center of the furnace. That is, the gas uniformity inside the shaft furnace 100 is improved, and uneven reaction of iron oxide inside the shaft furnace 100 can be suppressed. As a result, compared to when the average particle diameter of the packed bed 20 is not controlled, the proportion of iron oxide contained in reduced iron after the reduction reaction may decrease and the proportion of metallic iron may increase. That is, the average reduction rate may be improved.

[0050] In one embodiment of the method for producing reduced iron, when, for example, the following Action 4A or Action 4B is employed as Action 4, the average particle size of the raw material 10 supplied to the center of the shaft furnace 100 is likely to be larger than the average particle size of the raw material 10 supplied to the sidewall of the shaft furnace 100. Action 4A: As shown in FIG. 6 , a rotating chute is used as the raw material supply device 114. When a mountain or slope of raw material 10 particles is formed on the sidewall of the shaft furnace 100, coarse particles tend to gather in the center of the shaft furnace 100. Specifically, the raw material 10 is supplied into the shaft furnace 100 so that the top 20x of the packed bed 20 is formed on the sidewall of the shaft furnace 100. Action 4B: As shown in FIG. 7 , multiple hoppers are provided as the raw material supply device 114 in the radial direction of the shaft furnace 100. Fine-grained raw material is supplied through the hoppers on the sidewall of the shaft furnace 100, and coarse-grained raw material is supplied through the hoppers on the central side of the shaft furnace 100.

[0051] In particular, Action 4A as shown in Fig. 6 is simple. That is, in the method for producing reduced iron according to one embodiment, Action 4 may be Action 4A described below.

[0052] Action 4A: Supply raw material 10 to the side wall side (inner wall 100ax side) of the shaft furnace 100 so that the average particle diameter of raw material 10 supplied to the center side of the shaft furnace 100 is larger than the average particle diameter of raw material 10 supplied to the side wall side (inner wall 100ax side) of the shaft furnace 100.

[0053] In the packed bed 20 formed after action 4, the average particle size of the raw materials 10 may decrease continuously or intermittently from the center of the shaft furnace 100 to the sidewall of the shaft furnace 100. In the packed bed 20 formed after action 4, for example, when the overall average particle size of the raw materials 10 is 10.0 mm to 15.0 mm, it is preferable that the difference between the average particle size of the raw materials 10 on the sidewall side and the average particle size of the raw materials 10 on the center side be 1.0 mm or more.

[0054] 1.5 Timing of Taking Action In the method for producing reduced iron, the above-described action may be taken at any timing, may be taken periodically, or may be taken based on a predetermined criterion.

[0055] For example, the above action may be performed at any timing at the discretion of the operator based on operational experience.

[0056] Alternatively, information regarding the reduction rate of the materials 10 inside the shaft furnace 100 may be estimated, and the above action may be performed based on the estimated information. The information may be, for example, the reduction rate of the materials 10 on the side wall side inside the shaft furnace 100 or an index representing the reduction rate (first form below). Alternatively, the information may be, for example, the deviation in the furnace radial direction of the reduction rate of the materials 10 inside the shaft furnace 100 or an index representing the reduction rate (second form below).

[0057] 1.5.1 First Form As shown in FIG. 8 , in a method for producing reduced iron according to one embodiment, the information is the reduction rate R of the raw materials 10 on the side wall side inside the shaft furnace 100 or an index I representing the reduction rate R, and the action may be taken when the estimated reduction rate R or the index I representing the reduction rate R is greater than a first threshold value.

[0058] The "reduction rate of the raw materials on the side wall side of the shaft furnace or an index representing the reduction rate" refers to the reduction rate R or an index I representing the reduction rate R of the raw materials 10 located close to the side wall inside the shaft furnace 100. Specifically, this refers to the reduction rate R or an index I representing the reduction rate R of the raw materials 10 located at a distance from the side wall inside the shaft furnace 100 within ¼ of the inner radius of the shaft furnace 100. The height position of the side wall inside the shaft furnace 100 at which the reduction rate R of the raw materials 10 is estimated may be, for example, a region ranging from 0.2 to 0.7, where the height of the gas supply port 102 is 0 and the raw material stock level (the upper end of the packed bed 20) is 1.0. This region may vary depending on the furnace shape, etc. As shown in FIG. 8 , the reduction rate R of the raw materials 10 or an index I representing the reduction rate R can be estimated using various estimation devices 107. The reduction rate R of the raw materials 10 may be estimated by sampling and analyzing the raw materials 10. It can also be estimated based on a numerical simulation of the operating conditions in the shaft furnace 100. Alternatively, the gas may be sampled and analyzed to determine an index I representative of the reduction rate R. The index I representative of the reduction rate R may be, for example, a hydrogen gas concentration.

[0059] In the first embodiment, the action is taken when the estimated reduction rate R or the index I representing the reduction rate R is greater than a first threshold value. The "threshold value" in this case can be determined, for example, by numerical simulation, operational analysis, or the like. For example, the action may be taken when the reduction rate R of the raw material 10 on the side wall side inside the shaft furnace 100 is estimated to be 33% or more (when the raw material 10 is estimated to have been reduced to wüstite or more). Alternatively, the action may be taken when the hydrogen utilization rate on the side wall side inside the shaft furnace 100 is estimated to be 30 mol% or more.

[0060] In the first embodiment, when the estimated reduction rate R or the index I representing the reduction rate R is large, this indicates that the reduction reaction by the reducing gas is completed near the furnace wall and at the upper part (near the furnace top) of the shaft furnace 100. In this case, the reducing gas inside the shaft furnace 100 tends to flow near the furnace wall, making it difficult for the reducing gas to be sufficiently supplied to the center of the shaft furnace 100. In other words, the proportion of hydrogen gas near the furnace wall increases, reducing pressure loss and impeding gas supply to the center. By taking the above action in such a case, the amount of reducing gas supplied to the center of the shaft furnace 100 can be increased, thereby improving the uniformity of the gas inside the shaft furnace 100 and suppressing uneven reaction of iron oxide inside the shaft furnace 100. As a result, the proportion of iron oxide contained in the reduced iron after the reduction reaction can decrease and the proportion of metallic iron can increase. In other words, the average reduction rate R can be improved.

[0061] 1.5.2 Second Form As shown in FIG. 9 , in a method for producing reduced iron according to one embodiment, the information is a deviation D in the furnace radial direction for the reduction rate R of the raw materials 10 inside the shaft furnace 100 or an index I representing the reduction rate R, and the action described above may be performed if the estimated deviation D is greater than a second threshold value.

[0062] Compared to the first mode, the second mode simultaneously uses information from the center of the shaft furnace 100 as well as the side wall of the shaft furnace 100, and therefore can more accurately determine the timing of action execution.

[0063] The "radial deviation (%) of the reduction rate of the raw material or the index representing the reduction rate" refers to the variation in the reduction rate R (%) of the raw material 10 or the index I representing the reduction rate R in the radial direction inside the shaft furnace 100. The radial position of the furnace is preferably between the side wall and the center, since this allows for greater deviation detection. The radial deviation D of the reduction rate R of the raw material 10 or the radial deviation D of the index I representing the reduction rate R of the raw material 10 can be estimated based on a numerical simulation of the operating conditions of the shaft furnace 100. In this case, the height position within the furnace at which the reduction rate of the raw material 10 is estimated may be, for example, a region in the range of 0.2 to 0.7, where the height of the gas supply port 102 is 0 and the raw material stock level (the upper end of the packed bed 20) is 1.0. Alternatively, as shown in FIG. 9 , various devices 120, such as a flow rate measuring device or a gas analyzer, may be used to analyze the exhaust gas components in the radial direction at the furnace top, and the hydrogen distribution in the radial direction of the exhaust gas at the furnace top may be determined. This may then determine the hydrogen utilization rates on the furnace wall side and the furnace center side, and the difference between the hydrogen utilization rates on the furnace wall side and the furnace center side may be determined. Information obtained from the gas information at the furnace top represents the entire height of the packed bed 20. Based on this information, the deviation D of the reduction degree R of the raw material 10 in the radial direction may be estimated. Alternatively, as shown in FIG. 9 , various devices 120 may be used to measure the gas flow rate in the radial direction of the exhaust gas at the furnace top, and the deviation D of the reduction degree R of the raw material 10 in the radial direction may be estimated from the deviation of the gas flow rate in the radial direction. Alternatively, as shown in FIG. 9 , the hydrogen distribution and gas flow rate of the exhaust gas at the furnace top measured using various devices 120 may be directly used as an index I representing the reduction degree R. From this information, the deviation D in the furnace radial direction may be estimated.

[0064] In a second embodiment, the action is taken when the estimated deviation D is greater than a second threshold. The second threshold can be determined, for example, by numerical simulation, operational analysis, or analysis of operational performance. The second threshold is a coefficient of variation (2 × (sidewall value − median value) / (sidewall value + median value)), and is preferably set, for example, to 0.1 or more and 0.3 or less. Alternatively, when the gas flow rates at the sidewall and the center are measured and converted to standard conditions, the action may be taken when the sidewall value is greater than the median by a predetermined amount (for example, 10% or more).

[0065] In the second embodiment, a large estimated deviation D indicates a large difference between the reduction rate of the raw materials 10 near the furnace wall and the reduction rate of the raw materials 10 near the center of the shaft furnace 100. This reflects a state in which the reducing gas easily flows near the furnace wall and is not sufficiently supplied to the center of the shaft furnace 100. In other words, the reduction reaction by the reducing gas is completed near the furnace wall and at the upper part of the shaft furnace (near the furnace top), and the proportion of hydrogen gas near the furnace wall increases, reducing pressure loss and impeding gas supply to the center. By taking the above action in such a case, the amount of reducing gas supplied to the inner side of the furnace wall, i.e., the center of the shaft furnace 100, can be increased. This improves gas uniformity within the shaft furnace 100 and suppresses uneven iron oxide reaction within the shaft furnace 100. As a result, the proportion of iron oxide contained in the solid product after the reduction reaction decreases and the proportion of reduced iron increases. In other words, the average reduction rate can be improved.

[0066] 1.6 Supplementary Information In the above-described method for producing reduced iron, only one type of action may be performed, or multiple types of actions may be performed. For example, although FIGS. 2 to 7 illustrate an embodiment in which one of Actions 1 to 4 is performed in the method for producing reduced iron according to an embodiment, only one of Actions 1 to 4 may be performed, two or more of Actions 1 to 4 may be performed, three or more of Actions 1 to 4 may be performed, or all of Actions 1 to 4 may be performed. Furthermore, in the method for producing reduced iron according to an embodiment, one action may be performed followed by another action. For example, in the method for producing reduced iron according to an embodiment, an action other than Action 1 (e.g., one of Actions 2 to 4, or Action 1 under different conditions) may be performed simultaneously with or after Action 1. Furthermore, in the method for producing reduced iron according to an embodiment, after a predetermined action is performed, the action may be interrupted or stopped as desired. In any case, in the method for producing reduced iron according to an embodiment, the average reduction rate of the raw material may be improved by performing the above-described action. In other words, in the method for producing reduced iron according to one embodiment, the reduced iron produced after the action has been performed has a higher reduction rate than the reduced iron produced before the action has been performed, and can be a better product reduced iron.

[0067] 2. Shaft Furnace The technology disclosed herein also has an aspect as a shaft furnace. As shown in FIGS. 1 to 7 , a shaft furnace 100 according to one embodiment includes a raw material supply inlet 101, a gas supply inlet 102, a reduced iron discharge outlet 103, a gas discharge outlet 104, and an action execution device 110. The raw material supply inlet 101 is provided at the top of the shaft furnace 100, the gas supply inlet 102 is provided on a side wall of the shaft furnace 100 below the raw material supply inlet 101, the reduced iron discharge outlet 103 is provided below the gas supply inlet 102, and the gas discharge outlet 104 is provided above the gas supply inlet 102. The action execution device 110 is configured to perform an action to change the flow of reducing gas inside the shaft furnace 100 from the side wall side of the shaft furnace 100 to the center side of the shaft furnace 100.

[0068] 2.1 Raw Material Supply Port, Gas Supply Port, Reduced Iron Discharge Port, and Gas Discharge Port In the shaft furnace 100, the raw material supply port 101, gas supply port 102, reduced iron discharge port 103, and gas discharge port 104 are not particularly limited in shape as long as the above-described positional relationship is satisfied. The raw material supply port 101 may be provided, for example, at the top of the shaft furnace 100. The gas supply port 102 may be provided, for example, directly below the position that will become the reduction zone 100ay of the shaft furnace 100. The reduced iron discharge port 103 may be provided at the bottom of the shaft furnace 100. The gas discharge port 104 may be provided at a location different from the raw material supply port 101 at the top of the shaft furnace 100. By having the raw material supply port 101, the gas supply port 102, the reduced iron discharge port 103, and the gas discharge port 104 satisfy the above-mentioned positional relationship, (I) raw material 10 containing iron oxide can be supplied from the top of the shaft furnace 100 to the inside, and a packed layer 20 of raw material 10 can be formed inside the shaft furnace 100, (II) reducing gas containing hydrogen gas can be supplied from the side wall 100a of the shaft furnace 100 to the inside, and (III) reduced iron 30 can be obtained from the bottom of the shaft furnace 100 by reducing the iron oxide.

[0069] 2.2 Action Execution Device The shaft furnace 100 includes an action execution device 110. The action execution device 110 may be, for example, at least one of a cooling device 111, a mixing device 112, a gas supply device 113, and a raw material supply device 114. Here, the cooling device 111 is configured to cool at least the inner wall of the shaft furnace 100 at least between the raw material supply port 101 and the gas supply port 102. The mixing device 112 is configured to mix an inert gas with the reducing gas. The gas supply device 113 is configured to supply a first gas with a relatively low reducing power and a second gas with a relatively high reducing power from the gas supply port 102 into the shaft furnace 100, and is configured so that the supply position of the first gas is higher than the supply position of the second gas. The raw material supply device 114 is configured to supply the raw material 10 into the shaft furnace 100 through the raw material supply port 101 so that the average particle diameter of the raw material 10 supplied to the center of the shaft furnace 100 is larger than the average particle diameter of the raw material 10 supplied to the side wall of the shaft furnace 100. Details of the action performed by the action execution device 110 are as described above.

[0070] 2.2.1 Supplementary Information Regarding the Cooling Device The cooling device 111 may be configured to cool at least the inner wall 100ax of the shaft furnace 100 by water cooling, for example, at least between the raw material supply port 101 and the gas supply port 102. That is, the cooling device 111 may be a water-cooling device. More specifically, the cooling device 111 may have a mechanism for circulating cooling water inside the furnace wall of the shaft furnace 100 and at least between the raw material supply port 101 and the gas supply port 102. The cooling device 111 may be configured to cool the entire circumference of the inner wall of the shaft furnace 100. More specifically, the cooling device 111 may have a mechanism for circulating cooling water inside the furnace wall of the shaft furnace 100 and at least between the raw material supply port 101 and the gas supply port 102 around the entire circumference of the furnace wall of the shaft furnace 100. The cooling device 111 may have a configuration similar to that of a device for cooling the furnace wall of a blast furnace. The cooling device 111 is one of the specific means for performing the above-mentioned Action 1. The cooling conditions by the cooling device 111 may be the same as those in the above-mentioned Action 1.

[0071] 2.2.2 Supplementary Information Regarding the Mixing Device The mixing device 112 may be configured, for example, to connect an inert gas supply system to a reducing gas supply system as shown in FIG. 3 . More specifically, the mixing device 112 may be configured, for example, to connect a reducing gas supply system from a reducing gas source and an inert gas supply system from an inert gas source, so that the reducing gas and the inert gas are mixed in the mixing device 112. The mixing device 112 may include valves or the like that adjust the flow rate and pressure of the reducing gas from the reducing gas supply system to the mixing device 112, and the flow rate and pressure of the inert gas from the inert gas supply system to the mixing device 112. Examples of the mixing ratio of the reducing gas and the inert gas in the mixing device 112 are as described above. The mixing device 112 is one of the specific means for performing the above-mentioned Action 2. The mixing conditions and supply conditions of the reducing gas and the inert gas by the mixing device 112 may be the same as those in the above-mentioned Action 2.

[0072] 2.2.3 Supplementary Information Regarding the Gas Supply Device The gas supply device 113 may have, for example, two gas supply systems (upper and lower) as shown in FIG. 4 , or three or more gas supply systems (upper, middle, and lower), and may be configured to supply a first gas from at least one upper system and a second gas from at least one lower system. More specifically, the gas supply device 113 may have, for example, two or more gas supply systems, at least one of which is a first gas supply system from a first gas source, and at least one other gas supply system is a second gas supply system from a second gas source, and the first and second gas supply systems are connected to the sidewall of the shaft furnace 100, and the connection position between the first gas supply system and the sidewall of the shaft furnace 100 is higher than the connection position between the second gas supply system and the sidewall of the shaft furnace 100. The type of first gas in the first gas supply system and the type of second gas in the second gas supply system are as described above. For example, the gas supply device 113 may be configured so that the first gas and the second gas satisfy one or both of the following conditions A and B. The gas supply device 113 is one of the specific means for performing the above-mentioned action 3. The gas supply conditions by the gas supply device 113 may be the same as those in the above-mentioned action 3. Condition A: The temperature of the first gas is lower than the temperature of the second gas. Condition B: The hydrogen gas concentration of the first gas is lower than the hydrogen gas concentration of the second gas.

[0073] 2.2.4 Supplementary Information Regarding the Raw Material Supply Device The raw material supply device 114 may be configured to supply the raw materials 10 to the side wall side of the shaft furnace 100. The raw material supply device 114 may be, for example, a rotating chute as shown in FIG. 6 or multiple hoppers arranged in the furnace radial direction as shown in FIG. 7. More specifically, the raw material supply device 114 may be, for example, a rotating chute that supplies the raw materials 10 into the shaft furnace 100 so that the top 20x of the packed bed 20 is formed on the side wall side of the shaft furnace 100. Alternatively, the raw material supply device 114 may be, for example, a device including multiple first and second hoppers arranged in the furnace radial direction of the shaft furnace 100, in which fine-grained raw materials are supplied from the first hopper arranged on the side wall side of the shaft furnace 100 and coarse-grained raw materials are supplied from the second hopper arranged on the central side of the shaft furnace 100. Here, the first hopper may be connected to, for example, a first raw material supply source, and the second hopper may be connected to, for example, a second raw material supply source different from the first raw material supply source, such that raw material having a fine particle size is supplied from the first raw material supply source to the first hopper, and raw material having a coarse particle size is supplied from the second raw material supply source to the second hopper. The raw material supply device 114 is one of the specific means for performing the above-mentioned action 4. The raw material supply conditions by the raw material supply device 114 may be the same as those in the above-mentioned action 4.

[0074] 2.3 Estimation Device and Control Device The shaft furnace 100 may include estimation devices 105, 107 and control devices 106, 108. For example, the estimation devices 105, 107 may be configured to estimate information related to the reduction rate of the raw materials 10 inside the shaft furnace 100, and the control devices 106, 108 may control the action execution device 110 so that the action is performed based on the estimated information. More specifically, the information estimated by the estimation device 105 may be the reduction rate R of the raw materials 10 on the side wall side inside the shaft furnace 100 or an index I representative of the reduction rate R. In this case, the control device 106 may control the action execution device 110 so that the action is performed when the estimated reduction rate R or the index I representative of the reduction rate R is greater than a first threshold. Alternatively, the information estimated by the estimation device 107 may be the deviation D in the furnace radial direction for the reduction rate R of the raw material 10 inside the shaft furnace 100 or the index I representing the reduction rate R, and in this case, the control device 108 may control the action execution device 110 so that the above action is taken when the estimated deviation D is greater than a second threshold value.

[0075] 2.3.1 Supplementary Information Regarding the Estimation Device (First Form) As described above, the estimation device 105 may be configured to estimate the reduction degree R of the raw material 10 at the furnace inner wall or the index I representing the reduction degree R. The method for estimating the reduction degree R and the index I has been described above. As described above, the reduction degree R and the index I can be estimated, for example, based on a numerical simulation of the operating conditions in the shaft furnace 100. That is, the estimation device 105 may be a numerical simulation device. Alternatively, the estimation device 105 may sample raw material from a predetermined position on the furnace inner wall of the shaft furnace 100 and estimate the reduction degree R of the raw material based on the analysis results of the raw material. Alternatively, the estimation device 105 may estimate the index I representing the reduction degree R of the raw material from the analysis results of the sampled gas. The index I representing the reduction degree R can be, for example, a hydrogen gas concentration or a hydrogen utilization rate. The estimation device 105 has a configuration necessary for making such an estimation. For example, the estimation device 105 may include a known computing device.

[0076] 2.3.2 Supplementary Note on Estimation Device (Second Form) Alternatively, the estimation device 107 may be configured to estimate the deviation D in the furnace radial direction of the reduction degree R of the raw materials 10 or the index I representing the reduction degree R. The method for estimating the deviation D is as described above. As described above, the deviation D can be estimated, for example, based on a numerical simulation of the operating conditions in the shaft furnace 100. That is, the estimation device 107 may be a numerical simulation device. Alternatively, the estimation device 107 may obtain the hydrogen utilization rate on the furnace wall side and the hydrogen utilization rate on the furnace center side by obtaining the hydrogen distribution in the furnace radial direction of the exhaust gas at the furnace top from the analysis results of the exhaust gas components in the furnace radial direction at the furnace top, and estimate the deviation D in the furnace radial direction of the reduction degree R of the raw materials 10 based on, for example, the difference between the hydrogen utilization rate on the furnace wall side and the hydrogen utilization rate on the furnace center side. Alternatively, the estimation device 107 may estimate the deviation D in the furnace radial direction of the reduction degree R of the raw materials 10 based on the deviation of the gas flow rate in the furnace radial direction from the measurement result of the gas flow rate in the furnace radial direction of the exhaust gas at the furnace top. Alternatively, the estimation device 107 may estimate the deviation D in the furnace radial direction of the reduction degree R of the raw materials 10 based on the reduction degrees of the reduced material at the furnace wall and the reduced material at the furnace center. The estimation device 107 has a configuration necessary for making such an estimation. For example, the estimation device 107 may include a known calculation device or the like.

[0077] 2.3.3 Supplementary Information Regarding the Control Device (First Form) The control device 106 may control the action execution device 110 so that the action described above is performed when the return rate R or the index I representing the return rate R estimated by the estimation device 105 is greater than a first threshold. The control device 106 has a configuration necessary for controlling the execution of an action based on the estimation result by the estimation device 105. For example, the control device 108 may include a CPU, RAM, ROM, etc.

[0078] 2.3.4 Supplementary Information Regarding the Control Device (Second Form) The control device 108 may control the action execution device 110 so that the above action is performed when the deviation D estimated by the estimation device 107 is greater than a second threshold. The control device 108 has a configuration necessary for controlling the execution of an action based on the estimation result of the deviation D by the estimation device 107. For example, the control device 108 may have a CPU, RAM, ROM, etc.

[0079] 2.4 Other Configurations The shape of the shaft furnace 100 may be similar to that of known shaft furnaces. For example, as shown in FIGS. 1 to 9 , the shaft furnace 100 may have a furnace top, a furnace bottom, and a cylindrical portion (cylindrical portion) forming a sidewall between the furnace top and the furnace bottom. The cylindrical portion may have a barrel portion and a tapered portion located below the barrel portion, and the inner diameter of the furnace may decrease from top to bottom at the tapered portion. The shaft furnace 100 may also be equipped with a burden feeder or the like to prevent the packed bed 20 from hanging when moving downward inside the shaft furnace 100. The shaft furnace 100 may also be equipped with a cooling gas supply port for supplying cooling gas and a cooling gas outlet for discharging cooling gas below the gas supply port 102. The cooling gas supply port may be located inside the sidewall of the furnace, and the cooling gas outlet may be located on the sidewall of the furnace below the gas supply port 102. The burden feeder, the cooling gas supply port, and the cooling gas discharge port provided in the shaft furnace 100 are known.

[0080] 2.5 Supplementary Information The shaft furnace 100 may have both the configuration according to the first embodiment and the configuration according to the second embodiment. In this case, the estimation device 105 and the estimation device 107 may be the same device or different devices. For example, one estimation device provided in the shaft furnace 100 may function as both the estimation device 105 and the estimation device 107. Furthermore, the control device 106 and the control device 108 may be the same device or different devices. For example, one control device provided in the shaft furnace 100 may function as both the control device 106 and the control device 108. Furthermore, the estimation devices 105 and 107 and the control devices 106 and 108 may be the same device or different devices. For example, one device provided in the shaft furnace may function as both the estimation devices 105 and 107 and the control devices 106 and 108. Specifically, for example, in the shaft furnace 100, the estimation device may be configured to estimate at least one of the reduction rate R of the raw materials 10 on the furnace inner wall or an index I representative of the reduction rate R, and a deviation D of the reduction rate R of the raw materials 10 or the index I representative of the reduction rate R in the furnace radial direction, and the control device may control the action execution device 110 to perform the action when the estimated reduction rate R, the index I, and / or the deviation D are greater than a threshold value. The control device may also control the action execution device 110 to suspend or stop the action.

[0081] 3. Effects As described above, according to the technique of the present disclosure, when reduced iron is produced using the shaft furnace 100, the average reduction rate of the reduced iron 30 is likely to be improved.

[0082] The effects of the technology of the present disclosure will be described in more detail below with reference to examples, but the technology of the present disclosure is not limited to the following examples.

[0083] 1. Furnace structure and boundary conditions When raw materials containing iron oxide are reduced with reducing gas (hydrogen gas) in a shaft furnace to obtain reduced iron, the behavior of the reducing gas inside the furnace (hydrogen concentration distribution, pressure distribution, flow velocity distribution), the reduction rate distribution of iron oxide inside the furnace, and the average reduction rate were analyzed by numerical simulation using the following furnace structure and boundary conditions.

[0084] The furnace body structure shown in Figure 10 was adopted. The structure shown in Figure 10 is the left half structure when the furnace internal structure in a cross section passing through and along the central axis of the furnace is divided into right and left halves with the central axis as the boundary. The reducing gas flow rate was 6300 (Nm ３ The reducing gas was pure hydrogen, and the temperature was 950° C. A cooling gas was supplied below the reducing gas supply position. ４ The flow rate of the cooling gas was set to 1400 (Nm) so that the average product temperature was approximately 80°C. ３ The cooling gas extraction flow rate was set to 1260 (Nm / min) so that it was 90% of the input amount. ３ / min).

[0085] 2. Calculation conditions Based on the conditions described above, calculations were performed for cases where the reducing gas injection conditions, raw material conditions, pressure conditions, and wall surface thermal boundary conditions were changed, and the average reduction rates were compared. A list of the calculation conditions is shown in Table 1 below.

[0086]

[0087] 3. Calculation results The calculation results are shown in Table 2.

[0088]

[0089] 3.1 Base As shown in Table 2, the average reduction rate in the base was 94.7%.

[0090] 3.2 Furnace Wall Cooling (Action 1) The effect of cooling the furnace wall was investigated. Calculations were performed using the same boundary conditions as those of a blast furnace (water cooling at 25°C) as the wall boundary conditions. As shown in Action 1 in Table 2, the average reduction rate after Action 1 was performed improved by 1.4% compared to the base. It is believed that the effect of lowering the reduction completion point exceeded the effect of reducing the heat amount.

[0091] 3.3 Part of the reducing gas: N ２ Substitution (Action 2) Part of the reducing gas is replaced with N ２As shown in Action 2 in Table 2, the average reduction rate after Action 2 was improved by 1.1% compared to the base. When the hydrogen concentration distribution was checked, it was found that the hydrogen-rich region near the wall had decreased and the pressure had increased. It is believed that the weakened reducing power lowered the reduction completion point near the wall, making it easier for gas to flow toward the center of the furnace, and this effect outweighed the effect of the weakened reducing power of the gas.

[0092] 3.4 Divided injection of reducing gas (Action 3) As a means of lowering the reduction completion point, we considered a method of providing multiple inlets for the reducing gas and injecting a gas with low reducing power from above. Here, another inlet was added 1 m above the injection position under the base conditions, and a gas with the same composition but 150°C lower temperature was injected into the reactor at a total volume of 6300 (Nm ３ As shown in Action 3 in Table 2, the average return rate after taking Action 3 increased by +2.0% compared to the base rate.

[0093] 3.5 Imparting particle size segregation (Action 4) In the above, we considered lowering the reduction completion point near the wall as a measure to promote gas introduction to the center. Here, we considered a more direct approach, manipulating particle size, which is a condition on the solid side, to promote gas introduction to the center. Specifically, large particles were placed in the center and small particles were placed on the wall side so that the overall harmonic mean diameter was 13.5 mm. A particle size segregation was imposed, with the particle size changing linearly from the center to the wall side, so that the difference between the minimum and maximum particle sizes was 1 mm. As a result, the hydrogen region near the wall was reduced, and the average reduction rate improved by +1.5% compared to the base.

[0094] 4. Summary From the above results, it can be seen that in the method for producing reduced iron using a shaft furnace, the average reduction rate of the raw materials is improved by performing an action (for example, the above-mentioned actions 1 to 4) that shifts the flow of reducing gas inside the shaft furnace from the side wall side of the shaft furnace to the center side of the shaft furnace.

[0095] That is, it can be said that the average reduction degree of raw materials can be increased in the production of reduced iron using a shaft furnace according to the following (1). In particular, it can be said that the effect of improving the average reduction degree of raw materials is particularly remarkable according to the following (2).

[0096] (1) A method for producing reduced iron, comprising: supplying a raw material containing iron oxide from an upper portion of a shaft furnace to an interior thereof; and supplying a reducing gas containing hydrogen gas from a side wall of the shaft furnace to an interior thereof; and reducing the iron oxide to obtain reduced iron from a lower portion of the shaft furnace, the method comprising: performing an action to change the flow of the reducing gas inside the shaft furnace from a side wall side of the shaft furnace to a center side of the shaft furnace. (2) A method for producing reduced iron, wherein the action is at least one of the following actions 1 to 4: Action 1: Cooling at least the inner wall of the shaft furnace at least between the supply position of the raw materials and the supply position of the reducing gas; Action 2: Mixing an inert gas with the reducing gas; Action 3: Dividing the reducing gas to be supplied into the shaft furnace into a first gas having a relatively low reducing power and a second gas having a relatively high reducing power, and supplying the first gas from above the second gas; Action 4: Making the average particle diameter of the raw materials supplied to the center side of the shaft furnace larger than the average particle diameter of the raw materials supplied to the side wall side of the shaft furnace.

[0097] REFERENCE SIGNS LIST 10 Raw material 20 Packed bed 30 Reduced iron 100 Shaft furnace 100a Side wall 100ax Inner wall 101 Raw material supply port 102 Gas supply port 103 Reduced iron discharge port 104 Gas discharge port 105, 107 Estimation device 106, 108 Control device 110 Action execution device 111 Cooling device 112 Mixing device 113 Gas supply device 114 Raw material supply device

Claims

1. A method for producing reduced iron, comprising: supplying a raw material containing iron oxide from the upper part to the inside of a shaft furnace, supplying a reducing gas containing hydrogen gas from the side wall to the inside of the shaft furnace, and reducing the iron oxide to obtain reduced iron from the lower part of the shaft furnace, and performing an action of changing the flow of the reducing gas inside the shaft furnace from the side wall side of the shaft furnace to the central side of the shaft furnace.

2. The method for producing reduced iron according to claim 1, wherein the action is at least one of the following Actions 1 to 4: Action 1: Cooling at least the inner wall of the shaft furnace at least between the supply position of the raw material and the supply position of the reducing gas; Action 2: Mixing an inert gas with the reducing gas; Action 3: Dividing the reducing gas supplied into the shaft furnace into a first gas having a relatively low reducing power and a second gas having a relatively high reducing power, and supplying the first gas from above the second gas; Action 4: Making the average particle diameter of the raw material supplied to the central side of the shaft furnace larger than the average particle diameter of the raw material supplied to the side wall side of the shaft furnace.

3. The method for producing reduced iron according to claim 2, wherein the Action 1 is the following Action 1A: Action 1A: Cooling at least the inner wall of the shaft furnace by water cooling at least between the supply position of the raw material and the supply position of the reducing gas.

4. The method for producing reduced iron according to claim 2, wherein the Action 4 is the following Action 4A: Action 4A: Supplying the raw material to the side wall side of the shaft furnace so that the average particle diameter of the raw material supplied to the central side of the shaft furnace is larger than the average particle diameter of the raw material supplied to the side wall side of the shaft furnace.

5. The method for producing reduced iron according to claim 2, wherein the first gas and the second gas in the action 3 satisfy one or both of the following conditions A and B: The method for producing reduced iron: Condition A: The temperature of the first gas is lower than the temperature of the second gas; Condition B: The hydrogen gas concentration of the first gas is lower than the hydrogen gas concentration of the second gas.

6. The method for producing reduced iron according to any one of claims 1 to 5, comprising estimating information regarding the reduction rate of the raw material inside the shaft furnace and performing the action based on the estimated information.

7. The method for producing reduced iron according to claim 6, wherein the information is the reduction rate of the raw material on the side wall side inside the shaft furnace or an index representing the reduction rate, and the action is performed when the estimated reduction rate or the index representing the reduction rate is greater than a first threshold value.

8. The method for producing reduced iron according to claim 6, wherein the information is the deviation in the furnace diameter direction regarding the reduction rate of the raw material inside the shaft furnace or an index representing the reduction rate, and the action is performed when the estimated deviation is greater than a second threshold value.

9. A shaft furnace comprising a raw material supply port, a gas supply port, a reduced iron discharge port, a gas discharge port, and an action execution device, wherein the raw material supply port is provided at the upper part of the shaft furnace, the gas supply port is provided on the side wall of the shaft furnace below the raw material supply port, the reduced iron discharge port is provided below the gas supply port, the gas discharge port is provided above the gas supply port, and the action execution device is configured to perform an action of changing the flow of the reducing gas inside the shaft furnace from the side wall side of the shaft furnace to the central side of the shaft furnace.

10. The shaft furnace according to claim 9, wherein the action execution device is at least one of a cooling device, a mixing device, a gas supply device, and a raw material supply device; the cooling device is configured to cool at least the inner wall of the shaft furnace between at least the raw material supply port and the gas supply port; the mixing device is configured to mix an inert gas with the reducing gas; the gas supply device is configured to supply a first gas with a relatively low reducing power and a second gas with a relatively high reducing power from the gas supply port into the interior of the shaft furnace, and the supply position of the first gas is configured to be above the supply position of the second gas; and the raw material supply device is configured to supply the raw material into the interior of the shaft furnace through the raw material supply port such that the average particle diameter of the raw material supplied to the central side of the shaft furnace is larger than the average particle diameter of the raw material supplied to the side wall side of the shaft furnace.

11. The shaft furnace according to claim 10, wherein the cooling device is configured to cool at least the inner wall of the shaft furnace by water cooling between at least the raw material supply port and the gas supply port.

12. The shaft furnace according to claim 10, wherein the raw material supply device is configured to supply the raw material to the side wall side of the shaft furnace.

13. The shaft furnace according to claim 10, wherein the gas supply device is configured such that the first gas and the second gas satisfy one or both of the following conditions A and B: Condition A: The temperature of the first gas is lower than the temperature of the second gas; Condition B: The hydrogen gas concentration of the first gas is lower than the hydrogen gas concentration of the second gas.

14. The shaft furnace according to any one of claims 9 to 13, comprising an estimation device and a control device, wherein the estimation device is configured to estimate information regarding the reduction rate of the raw material inside the shaft furnace, and the control device controls the action execution device such that the action is performed based on the estimated information.

15. The shaft furnace according to claim 14, wherein the information is a reduction rate of the raw material on the side wall side inside the shaft furnace or an index representing the reduction rate, and the control device controls the action execution device so that the action is performed when the estimated reduction rate or the index representing the reduction rate is greater than a first threshold value. Shaft furnace.

16. The shaft furnace according to claim 14, wherein the information is a deviation in the furnace diameter direction with respect to the reduction rate of the raw material on the side wall side inside the shaft furnace or an index representing the reduction rate, and the control device controls the action execution device so that the action is performed when the estimated deviation is greater than a second threshold value. Shaft furnace.

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