Method for producing reduced iron and system for producing reduced iron

Abstract

Disclosed is a new technology capable of improving the average reduction rate of reduced iron when producing reduced iron using a shaft furnace. A method for producing reduced iron according to the present disclosure comprises feeding a raw material containing iron oxide into a shaft furnace, and feeding a reducing gas from each of a lateral wall and a central part of the shaft furnace, to reduce the iron oxide and obtain the reduced iron. The reducing gas mainly contains hydrogen gas. The temperature of the reducing gas fed from the central part of the shaft furnace is higher than the temperature of the reducing gas fed from the lateral wall of the shaft furnace.

Description

Reduced iron manufacturing method and reduced iron manufacturing system

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

[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 of a shaft furnace to the interior, and 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 includes, for example, hydrogen gas. When reducing gas containing hydrogen gas is supplied from the side wall of the shaft furnace to the interior, a portion of the hydrogen gas is consumed in the reduction reaction, resulting in an insufficient supply of hydrogen gas to the center of the shaft furnace, which can easily reduce the average reduction rate of the raw materials. To solve this problem, for example, a method for supplying reducing gas to the interior of the shaft furnace from both the side wall and the center of the shaft furnace has been disclosed (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 62-294127

[0004] Even if reducing gas is supplied from both the side wall and the center of the shaft furnace, there are cases in which the average reduction rate of reduced iron (the average rate of reduction of O (oxygen) bound to Fe in the raw materials) cannot be sufficiently improved. This problem is particularly likely to become apparent when the reducing gas contains hydrogen gas, causing the reduction reaction of iron oxide by the reducing gas to be an endothermic reaction. In this regard, when raw materials containing iron oxide and reducing gas are supplied into the shaft furnace to reduce the iron oxide and produce reduced iron, a new technology is needed that can improve the average reduction rate of reduced iron when the reducing gas contains hydrogen gas, causing the reduction reaction of iron oxide by the reducing gas to be an endothermic reaction.

[0005] The present application discloses the following multiple aspects as one means for solving the above-mentioned problems. <Aspect 1> A method for producing reduced iron, comprising: supplying a raw material containing iron oxide into a shaft furnace; and supplying a reducing gas from each of a side wall and a center of the shaft furnace to reduce the iron oxide to obtain the reduced iron, wherein the reducing gas contains 40 volume % to 100 volume % of hydrogen gas, and the temperature of the reducing gas supplied from the center of the shaft furnace is higher than the temperature of the reducing gas supplied from the side wall of the shaft furnace. <Aspect 2> The method for producing reduced iron according to Aspect 1, wherein the temperature of the reducing gas supplied from the center of the shaft furnace is higher by 50°C or more than the temperature of the reducing gas supplied from the side wall of the shaft furnace. <Aspect 3> The method for producing reduced iron according to Aspect 1 or 2, wherein the temperature of the reducing gas supplied from the side wall of the shaft furnace is 900°C or more and 1150°C or less. <Aspect 4> The method for producing reduced iron according to any one of Aspects 1 to 3, wherein the reducing gas contains 60 volume % or more and 100 volume % or less of the hydrogen gas. <Aspect 5> The method for producing reduced iron according to any one of Aspects 1 to 4, wherein in the reducing gas, the ratio of the volume of the hydrogen gas to the total volume of the hydrogen gas and the CO gas is 60 volume % or more and 100 volume % or less.<Aspect 6> A system for producing reduced iron, comprising: a shaft furnace, one or more gas supply devices, one or more first heating devices, and one or more second heating devices; the shaft furnace comprises one or more raw material supply ports, one or more first gas supply ports, one or more second gas supply ports, one or more reduced iron discharge ports, and one or more gas discharge ports; the raw material supply ports are provided in an upper portion of the shaft furnace; the first gas supply port is provided in a side wall of the shaft furnace below the raw material supply ports; the second gas supply port is provided in a center portion of the shaft furnace below the raw material supply ports; the reduced iron discharge port is provided below the first gas supply port and the second gas supply port; and the gas discharge port is provided above the first gas supply port and the second gas supply port; the gas supply device supplies a reducing gas containing 40 vol% to 100 vol% of hydrogen gas, A reduced iron manufacturing system, wherein a portion of the reducing gas supplied from the gas supply device is supplied to the first gas supply port via the first heating device, A portion of the reducing gas supplied from the gas supply device is supplied to the second gas supply port via the second heating device, The first heating device is provided upstream of the first gas supply port and heats the reducing gas on a path from the gas supply device to the first gas supply port, The second heating device is provided upstream of the second gas supply port and heats the reducing gas on a path from the gas supply device to the second gas supply port, The heating temperature of the second heating device is higher than the heating temperature of the first heating device. <Aspect 7> The reduced iron manufacturing system of Aspect 6, wherein the heating temperature of the second heating device is higher by 50°C or more than the heating temperature of the first heating device. <Aspect 8> The reduced iron production system according to aspect 6 or 7, wherein the first heating device heats the reducing gas supplied from the first gas supply port so that the temperature of the reducing gas is 900°C or higher and 1150°C or lower.<Aspect 9> The system for producing reduced iron according to any one of Aspects 6 to 8, wherein the reducing gas contains 60 volume % or more and 100 volume % or less of the hydrogen gas. <Aspect 10> The system for producing reduced iron according to any one of Aspects 6 to 9, wherein in the reducing gas, a ratio of the volume of the hydrogen gas to a total volume of the hydrogen gas and the CO gas is 60 volume % or more and 100 volume % or less.

[0006] According to the technology disclosed herein, when raw materials containing iron oxide and a reducing gas are supplied into the interior of a shaft furnace and the iron oxide is reduced to produce reduced iron, the average reduction rate of the reduced iron can be increased even if the reducing gas contains hydrogen gas, causing the reduction reaction of the iron oxide by the reducing gas to be an endothermic reaction.

[0007] Fig. 1 is a schematic diagram illustrating an example of the configuration of a system for implementing a method for producing reduced iron. Fig. 2 is a schematic diagram for explaining the "center" of a shaft furnace. Fig. 3 shows the furnace body structure, the charging status of raw materials, and the gas injection status employed in calculations of the examples.

[0008] Hereinafter, a method for producing reduced iron according to an embodiment and a system for producing reduced iron according to an embodiment will be described with reference to the drawings, but the technology of the present disclosure is not limited thereto.

[0009] 1 and 2 , a method for producing reduced iron according to one embodiment includes supplying a raw material 10 containing iron oxide into a shaft furnace 100, and supplying a reducing gas from each of a side wall 100a and a center 100b of the shaft furnace 100 to reduce the iron oxide to obtain reduced iron 30. The reducing gas contains 40% by volume or more and 100% by volume or less of hydrogen gas. The temperature of the reducing gas supplied from the center 100b of the shaft furnace 100 is higher than the temperature of the reducing gas supplied from the side wall 100a of the shaft furnace 100.

[0010] 1.1 Raw Material Raw material 10 contains iron oxide. The raw material 10 containing iron oxide may be, for example, one or more selected from iron ore pellets, lump ore, and sintered ore. In addition to iron oxide, raw material 10 may also contain, 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 size. The average particle size of raw material 10 may be, for example, 5.0 mm or more and 30.0 mm or less, or 10.0 mm or more and 15.0 mm or less. Note that the "particle size of the raw material" refers to the sieve size of the raw material, and the "average particle size of the raw material" refers to the weighted average particle size of the raw material. Specifically, the average particle size of the raw material is measured as follows. That is, the average particle size of the raw material can be measured by obtaining a mass-based particle size distribution by a dry sieving test described in JIS Z 8815:1995, and then calculating the mass-weighted average of the maximum and minimum particle sizes of each sieve as the representative particle size. Raw material 10 may be formed into pellets or the like, or may be in the form of a powder, a lump, or any other shape.

[0011] The amount of raw material 10 supplied to the shaft furnace 100 may be selected optimally 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.

[0012] 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.

[0013] 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.

[0014] 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. In the packed bed 20, the raw material 10 may have a regular particle size distribution or an irregular particle size distribution. The temperature distribution in 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. In other words, the metallic iron obtained through the reduction zone can be cooled by a cooling gas below the reduction zone. The reducing gas supplied to the reduction zone and the cooling gas supplied below the reduction zone have different gas temperatures. The cooling gas may be, for example, one or more selected from an inert gas, natural gas, hydrogen gas, etc.

[0015] 1.2 Reducing Gas 1.2.1 Composition In this embodiment, the reducing gas contains 40% by volume or more and 100% by volume or less of hydrogen gas. The reducing gas may contain gases other than hydrogen gas in addition to hydrogen gas. Examples of gases other than hydrogen gas include CO gas, hydrocarbon gas, and inert gas. Examples of inert gases include rare gases such as nitrogen gas and argon gas, CO ２ It may be one or more selected from gas, water vapor, and the like.

[0016] The proportion of hydrogen gas in the reducing gas is 40% by volume or more, and may be 50% by volume or more, 55% by volume or more, 60% by volume or more, 65% by volume or more, 70% by volume or more, 75% by volume or more, 80% by volume or more, 85% by volume or more, 90% by volume or more, or 95% by volume or more. In particular, according to the inventor's new findings, a more significant effect is likely to be obtained when the reducing gas contains hydrogen gas at 60% by volume or more and 100% by volume or less.

[0017] The reducing gas may optionally contain CO gas in addition to hydrogen gas. According to the inventor's new findings, a more significant effect is likely to be obtained when the volume ratio of hydrogen gas to the total volume of hydrogen gas and CO gas in the reducing gas is 60% or more and 100% or less. The volume ratio of hydrogen gas to the total volume of hydrogen gas and CO gas in the reducing gas may be 65% or more, 70% or more, 75% or more, 80% or more, 85% or more, 90% or more, or 95% or more.

[0018] In this embodiment, reducing gas is supplied into the shaft furnace 100 from each of the side wall 100a and the center 100b of the shaft furnace 100. The composition of the reducing gas supplied from the side wall 100a of the shaft furnace 100 and the composition of the reducing gas supplied from the center 100b of the shaft furnace 100 may be the same as or different from each other.

[0019] 1.2.2 Supply Position As described above, in this embodiment, the reducing gas is supplied to the packed bed 20 inside the shaft furnace 100 from each of the side wall 100a and the center 100b of the shaft furnace 100. In other words, in the shaft furnace 100 according to this embodiment, a first gas supply port 102ax for supplying the reducing gas from the side wall 100a of the shaft furnace 100 to the packed bed 20, and a second gas supply port 102bx for supplying the reducing gas from the center 100b of the shaft furnace 100 to the packed bed 20 are separately provided. The "center of the shaft furnace" refers to the portion of the shaft furnace 100 excluding the portion from the inner wall 100ax to (¼)D, where D is the inner diameter of the shaft furnace 100, as shown by the dashed line in FIG. 3 . That is, as shown in Figure 3, inside the shaft furnace 100, the part that is relatively closer to the furnace radial center 100bx is considered to be the "center of the shaft furnace," and the part that is relatively closer to the inner wall 100ax is considered to be the "part other than the center of the shaft furnace."

[0020] The method for supplying the reducing gas from the side wall 100a of the shaft furnace 100 is not particularly limited. For example, the reducing gas may be supplied to the packed bed 20 inside the shaft furnace 100 through a first opening 102a provided in the side wall 100a of the shaft furnace 100. The first opening 102a may be provided, for example, below a reduction zone 100ay of the shaft furnace 100 (a zone where a reduction reaction occurs above the gas supply ports 102ax and 102bx, i.e., a reduction zone). The first opening 102a may function as the first gas supply port 102ax. Alternatively, a pipe or the like may be connected to the first opening 102a, and the first gas supply port 102ax may be provided on the pipe. In this case, the tip of the pipe may or may not protrude inward from the inner wall 100ax inside the shaft furnace 100. When the tip of the pipe protrudes inward beyond the inner wall 100ax inside the shaft furnace 100 and the first gas supply port 102ax is provided at the tip of the pipe, the tip of the pipe is made not to protrude into the center 100b of the shaft furnace 100.

[0021] The method for supplying the reducing gas from the center 100b of the shaft furnace 100 is not particularly limited. For example, a pipe or the like can be inserted into the shaft furnace 100 through a second opening 102b provided in the side wall 100a of the shaft furnace 100, and the reducing gas can be supplied from the center 100b of the shaft furnace 100 to the packed bed 20 through the pipe or the like. The second opening 102b may be provided, for example, below the reduction zone 100ay of the shaft furnace 100. In this embodiment, the pipe inserted into the shaft furnace 100 through the second opening 102b is provided with the above-mentioned second gas supply port 102bx, and the second gas supply port 102bx is located at any position in the center 100b of the shaft furnace 100. 1 and 2 illustrate an example in which the second gas supply port 102bx is provided at the tip of the pipe inserted into the shaft furnace 100 through the second opening 102b, but the form of the second gas supply port 102bx is not limited to this. For example, the second gas supply port 102bx may be provided in the side wall of the pipe inserted into the shaft furnace 100 through the second opening 102b.

[0022] The height position at which the reducing gas is supplied from the side wall 100a of the shaft furnace 100 and the height position at which the reducing gas is supplied from the center 100b of the shaft furnace 100 may be the same as or different from each other. For example, the height position of the center of the first gas supply port 102ax for supplying the reducing gas from the side wall 100a of the shaft furnace 100 to the packed bed 20 inside the shaft furnace 100 may be higher or lower than the height position of the center of the second gas supply port 102bx for supplying the reducing gas from the center 100b of the shaft furnace 100 to the packed bed 20, or they may be at the same position.

[0023] The number of first gas supply ports 102ax for supplying reducing gas from the side wall 100a of the shaft furnace 100 to the packed bed 20 inside the shaft furnace 100 may be one or more, and may be two or more, three or more, or four or more. The shaft furnace 100 may have a plurality of first gas supply ports 102ax arranged in the circumferential direction of the shaft furnace 100. In other words, the shaft furnace 100 may have a plurality of first gas supply ports 102ax arranged circumferentially in a top view. The number of second gas supply ports 102bx for supplying reducing gas from the center 100b of the shaft furnace 100 to the packed bed 20 inside the shaft furnace 100 may be one or more, and may be two or more, three or more, or four or more.

[0024] 1.2.3 Temperature In this embodiment, it is important that the temperature of the reducing gas supplied from the center 100b of the shaft furnace 100 is higher than the temperature of the reducing gas supplied from the side wall 100a of the shaft furnace 100. According to the inventor's new findings, the reducing gas supplied from the side wall 100a of the shaft furnace 100 comes into contact with the iron oxide near the inner wall 100ax of the shaft furnace 100, causing a reduction reaction. In this embodiment, as described above, the reducing gas contains 40% to 100% by volume of hydrogen gas. The reduction reaction caused by hydrogen gas is an endothermic reaction. Therefore, in this embodiment, the temperature of the reducing gas supplied from the side wall 100a of the shaft furnace 100 tends to decrease as it approaches the center 100b of the shaft furnace 100. That is, the temperature of the reducing gas is insufficient in the center 100b of the shaft furnace 100, and the iron oxide tends to remain unreduced. In contrast, in the present embodiment, the reducing gas is supplied to the packed bed 20 inside the shaft furnace 100 from both the side wall 100a and the center 100b of the shaft furnace 100, and the temperature of the reducing gas supplied from the center 100b of the shaft furnace 100 is higher than the temperature of the reducing gas supplied from the side wall 100a of the shaft furnace 100. This suppresses a decrease in the temperature of the reducing gas in the center 100b of the shaft furnace 100, making it easier to properly reduce the iron oxide in the center 100b. As a result, a high average reduction rate is obtained.

[0025] In the present embodiment, the difference in temperature between the reducing gas supplied from the center 100b of the shaft furnace 100 and the reducing gas supplied from the side wall 100a of the shaft furnace 100 is not particularly limited. The temperature difference may be 10°C or more, 20°C or more, 30°C or more, 40°C or more, 50°C or more, 60°C or more, 70°C or more, 80°C or more, 90°C or more, or 100°C or more. The upper limit of the temperature difference is not particularly limited, and may be, for example, 250°C or less, 200°C or less, or 150°C or less. The temperature difference may be 10° C. to 250° C., 20° C. to 250° C., 30° C. to 250° C., 40° C. to 250° C., 50° C. to 250° C., 60° C. to 250° C., 70° C. to 250° C., 80° C. to 250° C., 90° C. to 250° C., 100° C. to 250° C., 10° C. to 200° C., or 10° C. to 150° C. According to the findings of the present inventors, a higher effect is likely to be obtained when the temperature of the reducing gas supplied from the center 100 b of the shaft furnace 100 is 50° C. or more higher than the temperature of the reducing gas supplied from the side wall 100 a of the shaft furnace 100.

[0026] The temperature of the reducing gas supplied from the side wall 100a of the shaft furnace 100 may be any temperature that can cause a reduction reaction of iron oxide. For example, the temperature of the reducing gas supplied from the side wall 100a of the shaft furnace 100 may be 900°C or higher and 1150°C or lower. On the other hand, the temperature of the reducing gas supplied from the center 100b of the shaft furnace 100 may be any temperature that can cause a reduction reaction of iron oxide and is higher than the temperature of the reducing gas supplied from the side wall 100a of the shaft furnace 100. Note that if the temperature of the reducing gas is too high, the reduced iron 30 may fuse, causing the packed bed 20 to clog, which may hinder diffusion of the reducing gas in the packed bed 20.

[0027] 1.2.4 Supply Amount and Supply Ratio The supply amounts of the reducing gas supplied from the side wall 100a of the shaft furnace 100 and the reducing gas supplied from the center 100b of the shaft furnace 100 are not particularly limited, and may be adjusted appropriately depending on the amount of raw material 10 to be processed, etc. The supply ratio of the reducing gas supplied from the side wall 100a of the shaft furnace 100 and the reducing gas supplied from the center 100b of the shaft furnace 100 is not particularly limited. For example, the proportion of the reducing gas supplied from the central portion 100b of the shaft furnace 100 to the total of the reducing gas supplied from the side wall 100a of the shaft furnace 100 and the reducing gas supplied from the central portion 100b of the shaft furnace 100 may be 1 vol% or more, 5 vol% or more, 10 vol% or more, 15 vol% or more, 20 vol% or more, or 25 vol% or more, or may be 50 vol% or less, 45 vol% or less, 40 vol% or less, 35 vol% or less, 30 vol% or less, 25 vol% or less, 20 vol% or less, 15 vol% or less, or 10 vol% or less. When this proportion is 1 vol% or more, the reduction rate at the central portion of the shaft furnace 100 is likely to be more significantly increased. Furthermore, when this proportion is 50 vol% or less, the balance between the reduction rate at the central portion of the shaft furnace 100 and the reduction rate on the side wall side is likely to be even better. The ratio may be 1% by volume or more and 50% by volume or less, 5% by volume or more and 50% by volume or less, 10% by volume or more and 50% by volume or less, 15% by volume or more and 50% by volume or less, 20% by volume or more and 50% by volume or less, or 25% by volume or more and 50% by volume or less, and may be 1% by volume or more and 45% by volume or less, 1% by volume or more and 40% by volume or less, 1% by volume or more and 35% by volume or less, 1% by volume or more and 30% by volume or less, 1% by volume or more and 25% by volume or less, or 1% by volume or more and 25% by volume or less. It may be 0 vol% or less, 1 vol% or more and 15 vol% or less, or 1 vol% or more and 10 vol% or less, or 5 vol% or more and 45 vol% or less, 5 vol% or more and 40 vol% or less, 5 vol% or more and 35 vol% or less, 5 vol% or more and 30 vol% or less, 5 vol% or more and 25 vol% or less, 5 vol% or more and 20 vol% or less, 5 vol% or more and 15 vol% or less, 5 vol% or more and 10 vol% or more and 15 vol% or less.In particular, a more significant effect is likely to be achieved when the proportion of reducing gas supplied from the center 100b of the shaft furnace 100 to the total of reducing gas supplied from the side wall 100a of the shaft furnace 100 and reducing gas supplied from the center 100b of the shaft furnace 100 is 5% by volume or more and 15% by volume or less.

[0028] 1.3 Reduced Iron When part or all of the iron oxide contained in the raw material 10 is reduced by the reduction reaction described above, reduced iron 30, which is a solid reactant containing metallic iron, is obtained. In addition to metallic iron, the reduced iron 30 may also contain iron oxide, silicon dioxide, aluminum oxide, and the like that remain unreduced. The reduced iron 30 containing metallic iron can be recovered from a reduced iron discharge port 103 at the bottom of the shaft furnace 100 (below the position where the reducing gas is supplied).

[0029] 2. Reduced Iron Manufacturing System The technology disclosed herein includes a reduced iron manufacturing system in addition to the above-described reduced iron manufacturing method. As shown in FIGS. 1 and 2 , a reduced iron manufacturing system 1000 according to one embodiment includes a shaft furnace 100, one or more gas supply devices 200, one or more first heating devices 301, and one or more second heating devices 302. The shaft furnace 100 includes one or more raw material supply ports 101, one or more first gas supply ports 102ax, one or more second gas supply ports 102bx, one or more reduced iron discharge ports 103, and one or more gas discharge ports 104. The raw material supply port 101 is provided in an upper portion of the shaft furnace 100. The first gas supply port 102ax is provided in a side wall 100a of the shaft furnace 100 below the raw material supply port 101. The second gas supply port 102bx is provided in the center 100b of the shaft furnace 100 below the raw material supply port 101. The reduced iron discharge port 103 is provided below the first gas supply port 102ax and the second gas supply port 102bx. The gas discharge port 104 is provided above the first gas supply port 102ax and the second gas supply port 102bx. The gas supply device 200 supplies a reducing gas containing 40% by volume or more and 100% by volume or less of hydrogen gas. A portion of the reducing gas supplied from the gas supply device 200 is supplied to the first gas supply port 102ax via a first heating device 301. A portion of the reducing gas supplied from the gas supply device 200 is supplied to the second gas supply port 102bx via a second heating device 302. The first heating device 301 is provided upstream of the first gas supply port 102ax and heats the reducing gas from the gas supply device 200 to the first gas supply port 102ax. The second heating device 302 is provided upstream of the second gas supply port 102bx and heats the reducing gas from the gas supply device 200 to the second gas supply port 102bx. In this embodiment, the heating temperature of the second heating device 302 is higher than the heating temperature of the first heating device 301.

[0030] The reduced iron manufacturing system 1000 according to this embodiment has the above-described configuration, and thereby: (1) a raw material 10 containing iron oxide is supplied from the raw material supply port 101 into the interior of the shaft furnace 100; (2) a reducing gas containing 40% by volume or more and 100% by volume or less of hydrogen gas is supplied from each of the first gas supply port 102ax and the second gas supply port 102bx into the interior of the shaft furnace 100; and (3) the temperature of the reducing gas supplied from the second gas supply port 102bx is higher than the temperature of the reducing gas supplied from the first gas supply port 102ax.

[0031] 2.1 Raw Material Supply Port, First Gas Supply Port, Second Gas Supply Port, Reduced Iron Discharge Port, and Gas Discharge Port In the shaft furnace 100, the raw material supply port 101, the first gas supply port 102ax, the second gas supply port 102bx, the reduced iron discharge port 103, and the 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. Alternatively, each of the first gas supply port 102ax and the second gas supply port 102bx may be provided, for example, below the position of the reduction zone 100ay of the shaft furnace 100. Alternatively, the reduced iron discharge port 103 may be provided at the bottom of the shaft furnace 100. Alternatively, 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. When the raw material supply port 101, the first gas supply port 102ax, the second gas supply port 102bx, 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 bed 20 of the raw material 10 can be formed inside the shaft furnace 100, (II) a reducing gas containing 40 vol% to 100 vol% hydrogen gas can be supplied from each of the side wall 100a and the center 100b of the shaft furnace 100, and (III) iron oxide contained in the raw material 10 can be reduced to obtain reduced iron 30 from the lower part of the shaft furnace 100.

[0032] 2.2 Gas Supply Device and Heating Device In the reduced iron production system 1000, the reducing gas supplied from the gas supply device 200 is heated by the first heating device 301 and the second heating device 302. Here, the heating temperature of the second heating device 302 is higher than the heating temperature of the first heating device 301. As a result, the temperature of the reducing gas supplied from the second gas supply port 102bx is higher than the temperature of the reducing gas supplied from the first gas supply port 102ax. As shown in FIGS. 1 and 2 , the gas supply device 200 supplies the reducing gas to the shaft furnace 100. Specifically, a portion of the reducing gas supplied from the gas supply device 200 can be supplied to the first gas supply port 102ax via the first heating device 301, and a portion of the reducing gas supplied from the gas supply device 200 can be supplied to the second gas supply port 102bx via the second heating device 302. The first heating device 301 is provided upstream of the first gas supply port 102ax and heats the reducing gas on the way from the gas supply device 200 to the first gas supply port 102ax. The second heating device 302 is provided upstream of the second gas supply port 102bx and heats the reducing gas on the way from the gas supply device 200 to the second gas supply port 102bx. Here, as shown in FIG. 1 , the reducing gas may be supplied from the gas supply device 200 to each of the first heating device 301 and the second heating device 302, the reducing gas heated by the first heating device 301 may be supplied to the first gas supply port 102ax, and the reducing gas heated by the second heating device 302 may be supplied to the second gas supply port 102bx. 2, the reducing gas may be supplied from the gas supply device 200 to the first heating device 301, the reducing gas heated by the first heating device 301 may be supplied to each of the first gas supply port 102ax and the second heating device 302, and the reducing gas heated by the second heating device 302 may be supplied to the second gas supply port 102bx. Alternatively, the reducing gas may be supplied from the gas supply device 200 to the inside of the shaft furnace 100 in a form different from the form shown in FIGS.As long as the temperature of the reducing gas supplied from the first gas supply port 102ax to the inside of the shaft furnace 100 (i.e., the temperature of the reducing gas supplied from the side wall 100a of the shaft furnace 100) and the temperature of the reducing gas supplied from the second gas supply port 102bx to the inside of the shaft furnace 100 (i.e., the temperature of the reducing gas supplied from the center 100b of the shaft furnace 100) satisfy the above-mentioned magnitude relationship, the supply form of the reducing gas from the gas supply device 200 to the first gas supply port 102ax and the second gas supply port 102bx can be configured in various ways.

[0033] The gas supply method of the gas supply device 200 is not particularly limited, and any known method may be adopted. For example, the gas supply device 200 may be equipped with a reducing gas source and piping, and may supply reducing gas from the reducing gas source to the heating device via the piping. The number of gas supply devices 200 may be one or more, and may be two or more. The heating method of the first heating device 301 and the second heating device 302 is not particularly limited. For example, various heating methods such as an electric heating method, an electric arc heating method, and a radiant tube method may be adopted. Alternatively, the first heating device 301 and the second heating device 302 may be equipped with a mechanism for introducing oxygen gas together with the reducing gas and heating the reducing gas by burning a portion of the reducing gas. For example, the first heating device 301 and the second heating device 302 may be equipped with a mechanism for partially burning hydrogen gas contained in the reducing gas (O ２ Supply H ２ The heating method of the first heating device 301 and the heating method of the second heating device 302 may be the same or different. The number of first heating devices 301 may be one or more, or may be two or more. The number of second heating devices 302 may also be one or more, or may be two or more.

[0034] 2.3 Supplementary Notes The reduced iron production system 1000 having such a configuration can implement the reduced iron production method of the present disclosure. The supply mode of the reducing gas in the reduced iron production system 1000 is as described above. For example, in one embodiment, the heating temperature of the second heating device 302 may be higher by 50°C or more than the heating temperature of the first heating device 301 in the reduced iron production system 1000. As a result, the temperature of the reducing gas supplied from the second gas supply port 102bx is higher by 50°C or more than the temperature of the reducing gas supplied from the first gas supply port 102ax. In the reduced iron production system 1000 according to the embodiment, the first heating device 301 may heat the reducing gas supplied from the first gas supply port 102ax so that the temperature of the reducing gas is 900°C or more and 1150°C or less. In the reduced iron production system 1000 according to the embodiment, the reducing gas may contain hydrogen gas at 60% by volume or more and 100% by volume or less. Furthermore, in the reduced iron production system 1000 according to one embodiment, the ratio of the volume of hydrogen gas to the total volume of hydrogen gas and CO gas in the reducing gas may be 60% or more and 100% or less.

[0035] 3. Effects As described above, it is believed that multiple heating devices are necessary to increase the temperature of the reducing gas supplied from the center of the shaft furnace. In this regard, in the prior art, intentionally increasing the temperature of the gas supplied from the center of the shaft furnace by varying the temperature of the reducing gas blown in from the side wall of the shaft furnace and the temperature of the reducing gas blown in from the center of the shaft furnace was not anticipated due to equipment limitations. Furthermore, in the prior art, supplying a reducing gas with a high temperature tends to be avoided in order to prevent clustering, and intentionally increasing the temperature of the reducing gas supplied to the center of the shaft furnace was not anticipated from this perspective either. Furthermore, in the prior art method for producing reduced iron by CO reduction, increasing the temperature of CO gas used as the reducing gas makes it difficult for the reduction reaction to proceed. Therefore, from this perspective as well, there was no thought of increasing the gas temperature. In contrast, the technology disclosed herein solves the specific problems that arise when the reducing gas contains hydrogen gas (hydrogen reduction). According to the technology disclosed herein, when raw material 10 containing iron oxide and a reducing gas are supplied into the interior of a shaft furnace 100 to reduce the iron oxide and produce reduced iron 30, if the reducing gas contains hydrogen gas, a decrease in the temperature of the reducing gas in the center 100b of the shaft furnace 100 can be suppressed, and the iron oxide can be appropriately reduced in the center 100b, which makes it easier to improve the average reduction rate of the reduced iron 30 that is ultimately produced.

[0036] 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.

[0037] 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 in the furnace (hydrogen concentration distribution, temperature distribution), the reduction rate distribution of the iron oxide in the furnace, and the average reduction rate were analyzed by a numerical simulation employing the following furnace structure and boundary conditions. The numerical simulation in this example was performed using a shaft furnace mathematical model developed by applying the blast furnace mathematical model described in Non-Patent Document 1 below. Non-Patent Document 1: Nishioka et al., "Development of Mathematical Models for Blast Furnaces," Nippon Steel & Sumitomo Metal Technical Report No. 120 (2018).

[0038] The furnace body structure, the state of charging raw materials, and the state of gas injection are as shown in Figure 4. The structure shown in Figure 4 is the left half of the furnace structure when the furnace internal structure in a cross section passing through and along the central axis of the shaft furnace is divided into right and left halves with the central axis as the boundary. The total flow rate of reducing gas supplied into the furnace was 1633 Nm ３ / t-DRI (Nm ３ / t-DRI: Flow rate of reducing gas per ton of direct reduced iron (DRI) Nm ３ ) and pure hydrogen was used as the reducing gas. The reducing gas supply conditions were as follows:

[0039] 1.1 Comparative Example 1 Reducing gas at 950° C. was supplied only from the side wall of the shaft furnace.

[0040] 1.2 Comparative Example 2 A reducing gas at 950°C was blown from the side wall of the shaft furnace at a rate of 1508 Nm ３ / t-DRI, and reducing gas at 950°C was supplied from the center of the shaft furnace at a flow rate of 125 Nm ３ The gas was supplied at a flow rate of 1 / t-DRI.

[0041] 1.3 Example 1 A reducing gas at 950°C was blown from the side wall of the shaft furnace at a rate of 1508 Nm ３ / t-DRI, and reducing gas at 1000°C was supplied from the center of the shaft furnace at a flow rate of 125 Nm３ The gas was supplied at a flow rate of 1 / t-DRI.

[0042] 1.4 Example 2 A reducing gas at 950°C was blown from the side wall of the shaft furnace at a rate of 1508 Nm ３ / t-DRI, and reducing gas at 1050°C was supplied from the center of the shaft furnace at a flow rate of 125 Nm ３ The gas was supplied at a flow rate of 1 / t-DRI.

[0043] 1.5 Example 3 A reducing gas at 950°C was blown from the side wall of the shaft furnace at a rate of 1508 Nm ３ / t-DRI, and reducing gas at 1100°C was supplied from the center of the shaft furnace at a flow rate of 125 Nm ３ The gas was supplied at a flow rate of 1 / t-DRI.

[0044] 1.6 Example 4 A reducing gas at 950°C was blown from the side wall of the shaft furnace at a rate of 1508 Nm ３ / t-DRI, and reducing gas at 1150°C was supplied from the center of the shaft furnace at a flow rate of 125 Nm ３ The gas was supplied at a flow rate of 1 / t-DRI.

[0045] 1.7 Example 5 A reducing gas at 950°C was blown from the side wall of the shaft furnace at a rate of 1584 Nm ３ / t-DRI, and reducing gas at 1000°C was supplied from the center of the shaft furnace at a flow rate of 49 Nm ３ The gas was supplied at a flow rate of 1 / t-DRI.

[0046] 1.8 Example 6 A reducing gas at 950°C was blown from the side wall of the shaft furnace at a rate of 1306 Nm ３ / t-DRI, and reducing gas at 1000°C was supplied from the center of the shaft furnace at a flow rate of 327 Nm ３ The gas was supplied at a flow rate of 1 / t-DRI.

[0047] 1.9 Example 7 A reducing gas at 950°C was blown from the side wall of the shaft furnace at a rate of 817 Nm ３ / t-DRI, and reducing gas at 1000°C was supplied from the center of the shaft furnace at a flow rate of 817 Nm ３ The gas was supplied at a flow rate of 1 / t-DRI.

[0048] 2. Calculation results Calculations were performed under the above conditions, and the average reduction rates of the product reduced iron were compared. The calculation results are shown in Table 1 below.

[0049]

[0050] As is clear from the results shown in Table 1, when reducing iron oxide in a shaft furnace to obtain reduced iron, the average reduction rate of the product reduced iron is improved by supplying reducing gas from both the side walls and the center of the shaft furnace and by making the temperature of the reducing gas supplied from the center higher than that of the reducing gas supplied from the side walls. In particular, a more significant effect can be obtained when the temperature of the reducing gas supplied from the center of the shaft furnace is 50°C or more higher than that of the reducing gas supplied from the side walls of the shaft furnace.

[0051] 3. When the hydrogen concentration was changed (1) Reducing gas containing 100% CO gas by volume (Comparative Examples A and B) (2) Reducing gas containing 30% hydrogen gas by volume and 70% CO gas by volume (Comparative Examples C and D) (3) Reducing gas containing 40% hydrogen gas by volume and 60% CO gas by volume (Comparative Example E, Examples E1 and E2) (4) Reducing gas containing 50% hydrogen gas by volume and 50% CO gas by volume (Comparative Example F and Example F) (5) Reducing gas containing 60% hydrogen gas by volume and 40% CO gas by volume (Comparative Example G and Example G) (6) Reducing gas containing 100% hydrogen gas by volume (Comparative Example H and Example H) The same calculations as above were performed for each of the following cases, and the average reduction rates of the product reduced iron were compared. The calculation results are shown in Table 2 below.

[0052]

[0053] As is clear from the results shown in Table 2, when reducing iron oxide in a shaft furnace to obtain reduced iron, the effect of supplying reducing gas from both the sidewall and the center of the shaft furnace and raising the temperature of the reducing gas supplied from the center higher than that of the reducing gas supplied from the sidewall can be achieved when the reducing gas contains 40% by mass or more and 100% by mass or less of hydrogen gas. In particular, this effect can be more pronounced when the reducing gas contains 60% by volume or more and 100% by volume or less of hydrogen gas. Furthermore, this effect can be more pronounced when the ratio of the volume of hydrogen gas to the total volume of hydrogen gas and CO gas in the reducing gas is 60% by volume or more and 100% or less.

[0054] In the above example, the case where reducing gas is supplied from both the side wall and the center of the shaft furnace and the temperature of the reducing gas supplied from the center is increased has been described. However, the same effect can be achieved even when reducing gas is supplied from both the side wall and near the center of the shaft furnace (the "center" that is relatively closer to the center than the side wall) and the temperature of the reducing gas supplied from the center is increased. In other words, the supply position of the reducing gas is not limited to the exact center of the shaft furnace, but may be in the vicinity thereof. Specifically, as shown by the dashed line in Figure 3, when the inner diameter of the shaft furnace is D, the area excluding the part from the inner wall of the shaft furnace to (¼)D is considered to be the "center" of the shaft furnace.

[0055] REFERENCE SIGNS LIST 10 raw material 20 packed bed 30 reduced iron 100 shaft furnace 100a side wall 100ax inner wall 100b center 100bx center 101 raw material supply port 102a first opening 102ax first gas supply port 102b second opening 102bx second gas supply port 103 reduced iron discharge port 104 gas discharge port 200 gas supply device 301 first heating device 302 second heating device 1000 reduced iron production system

Claims

1. A method for producing reduced iron, comprising: supplying a raw material containing iron oxide into the interior of a shaft furnace; and supplying a reducing gas from each of a side wall and a center of the shaft furnace to reduce the iron oxide to obtain the reduced iron, wherein the reducing gas contains 40% by volume or more and 100% by volume or less of hydrogen gas, and the temperature of the reducing gas supplied from the center of the shaft furnace is higher than the temperature of the reducing gas supplied from the side wall of the shaft furnace.

2. A method for producing reduced iron according to claim 1, wherein the temperature of the reducing gas supplied from the center of the shaft furnace is at least 50°C higher than the temperature of the reducing gas supplied from the side wall of the shaft furnace.

3. A method for producing reduced iron according to claim 1, wherein the temperature of the reducing gas supplied from the side wall of the shaft furnace is 900°C or higher and 1150°C or lower.

4. A method for producing reduced iron according to any one of claims 1 to 3, wherein the reducing gas contains 60% by volume or more and 100% by volume or less of the hydrogen gas.

5. A method for producing reduced iron according to any one of claims 1 to 3, wherein in the reducing gas, the ratio of the volume of the hydrogen gas to the total volume of the hydrogen gas and the CO gas is 60% or more and 100% or less.

6. A reduced iron manufacturing system comprising a shaft furnace, one or more gas supply devices, one or more first heating devices, and one or more second heating devices, wherein the shaft furnace comprises one or more raw material supply ports, one or more first gas supply ports, one or more second gas supply ports, one or more reduced iron discharge ports, and one or more gas discharge ports, wherein the raw material supply ports are provided in an upper portion of the shaft furnace, the first gas supply port is provided in a side wall of the shaft furnace below the raw material supply ports, the second gas supply port is provided in a center portion of the shaft furnace below the raw material supply ports, the reduced iron discharge port is provided below the first gas supply port and the second gas supply port, and the gas discharge port is provided above the first gas supply port and the second gas supply port, and the gas supply device supplies a reducing gas containing 40 volume % to 100 volume % of hydrogen gas, a portion of the reducing gas supplied from the gas supply device is supplied to the first gas supply port via the first heating device; a portion of the reducing gas supplied from the gas supply device is supplied to the second gas supply port via the second heating device; the first heating device is provided upstream of the first gas supply port and heats the reducing gas between the gas supply device and the first gas supply port; the second heating device is provided upstream of the second gas supply port and heats the reducing gas between the gas supply device and the second gas supply port; and a heating temperature of the second heating device is higher than a heating temperature of the first heating device.

7. A reduced iron manufacturing system according to claim 6, wherein the heating temperature of the second heating device is higher than the heating temperature of the first heating device by 50°C or more.

8. A reduced iron production system according to claim 6, wherein the first heating device heats the reducing gas supplied from the first gas supply port so that the temperature of the reducing gas is 900°C or higher and 1150°C or lower.

9. A reduced iron production system according to any one of claims 6 to 8, wherein the reducing gas contains 60% by volume or more and 100% by volume or less of the hydrogen gas.

10. A reduced iron production system according to any one of claims 6 to 8, wherein the ratio of the volume of the hydrogen gas to the total volume of the hydrogen gas and the CO gas in the reducing gas is 60% or more and 100% or less.

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