Method for producing reduced iron using shaft furnace

Abstract

In this method for producing reduced iron using a shaft furnace, the burden on equipment is reduced by suppressing the amount that a reducing gas is heated by an external heater. The method for producing reduced iron using a shaft furnace according to the present disclosure is characterized by: including preheating an iron oxide starting material, obtaining a reducing gas by subjecting a starting material gas including at least 90 vol% hydrogen gas to prescribed processing, and reducing the iron oxide starting material and obtaining reduced iron by supplying the preheated iron oxide starting material into the shaft furnace and blowing the reducing gas into the shaft furnace; and the relationship to be satisfied by the preheating temperature of the iron oxide raw material and the temperature at which the reducing gas is blown in differs according to the prescribed processing.

Description

Method for producing reduced iron using a shaft furnace

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

[0002] In the steel industry, as an alternative to the blast furnace method, a direct reduction process using reducing gas is used to reduce CO ２ Studies are being conducted to reduce emissions. For example, a process using a shaft furnace is being considered as a direct reduction process. In a direct reduction process using a shaft furnace, direct reduced iron (DRI) is obtained by bringing a reducing gas into contact with an iron oxide raw material. Known methods for producing reduced iron using a shaft furnace include the Midrex process and the HYL process. Here, the heat required for reduction in the shaft furnace is compensated for mainly by heating the reducing gas to a desired temperature (e.g., 800 to 1000°C). Heating of the reducing gas is thought to be possible by (1) heat exchange with the exhaust gas from the shaft furnace, (2) heating with an external heater, and (3) partial combustion of the reducing gas as necessary.

[0003] Meanwhile, techniques for preheating oxidized iron raw materials have been disclosed in methods for producing reduced iron using a shaft furnace. For example, Patent Document 1 proposes a method of preheating oxidized iron raw materials charged from the top of a reducing furnace to 100°C or higher and 627°C or lower in order to compensate for the heat absorption caused by the reaction between hydrogen gas and iron oxide. This suppresses excessive temperature rise and fusion in the lower part of the furnace when using a reducing gas mainly composed of hydrogen gas, and eliminates heat shortage in the upper part of the furnace, thereby ensuring a high product reduction rate. Furthermore, Patent Document 2 discloses a method of directly charging raw materials into a reducing furnace while retaining the heat obtained during the production of the raw materials.

[0004] JP 2012-102371 A JP 2022-157631 A

[0005] Conventional methods for producing reduced iron using a shaft furnace have room for improvement in terms of reducing the amount of heating of the reducing gas by an external heater and thereby reducing the burden on the equipment.

[0006] The present application discloses the following multiple aspects as means for solving the above problems. <Aspect 1> A method for producing reduced iron using a shaft furnace, comprising: preheating an oxidized iron raw material; subjecting a raw material gas containing 90% by volume or more of hydrogen gas to a first treatment, a second treatment, or a third treatment to obtain a reducing gas; and supplying the preheated oxidized iron raw material into the shaft furnace and blowing the reducing gas into the shaft furnace to reduce the oxidized iron raw material to obtain reduced iron, wherein the first treatment comprises heating the raw material gas by heat exchange with exhaust gas from the shaft furnace, but does not comprise partially combusting the raw material gas with oxygen, and the second treatment comprises heating the raw material gas by heat exchange with exhaust gas from the shaft furnace, and partially combusting the raw material gas with oxygen after the heat exchange to raise the temperature, but does not comprise heating the raw material gas with an external heater after the heat exchange, the third treatment includes heating the raw material gas by heat exchange with exhaust gas from the shaft furnace, heating the raw material gas with an external heater after the heat exchange, and partially combusting the raw material gas with oxygen after heating with the heater to raise the temperature, and when the first treatment is performed on the raw material gas, the following relationships (1) and (2) are satisfied: Y≧0.0016X ２ −0.8845X+470.72 (1) X≧600 (2) Y: preheating temperature of the iron oxide raw material (° C.) X: blowing temperature of the reducing gas (° C.) is satisfied, and when the raw material gas is subjected to the second treatment, the following relationships (3) and (4) are satisfied: Y≧0.0016X ２ -1.3845X+770.72 (3) X≧600 (4) Y: preheating temperature of the iron oxide raw material (°C) X: blowing temperature of the reducing gas (°C) are satisfied, and when the raw material gas is subjected to the third treatment, the following relationships (5) to (7) are satisfied: Y≧(0.0016X ２-1.3845X+770.72)×600 / Z (5) X≧600 (6) Z≧600 (7) Y: preheating temperature of the oxidized iron raw material (°C) X: blowing temperature of the reducing gas (°C) Z: temperature of the raw material gas at the outlet side of the heater (°C) are satisfied. <Aspect 2> The method for producing reduced iron of Aspect 1, wherein the first treatment does not include heating the raw material gas with an externally heated heater. <Aspect 3> The method for producing reduced iron of Aspect 1 or 2, wherein the raw material gas is subjected to the first treatment. <Aspect 4> The method for producing reduced iron of Aspect 1, wherein the raw material gas is subjected to the second treatment. <Aspect 5> The method for producing reduced iron of Aspect 1, wherein the raw material gas is subjected to the third treatment. <Aspect 6> The method for producing reduced iron according to any one of Aspects 1 to 5, wherein X is 1100°C or less. <Aspect 7> The method for producing reduced iron according to any one of Aspects 1 to 6, wherein Y is 1000°C or less.

[0007] According to the technology of the present disclosure, in a method for producing reduced iron using a shaft furnace, the amount of heating of the reducing gas by an external heater can be reduced, thereby reducing the burden on the equipment.

[0008] 1A and 1B are schematic diagrams showing an example of a system for implementing a reduced iron production method in which a first treatment is performed on a raw material gas; FIG. 1A is a schematic diagram showing another example of a system for implementing a reduced iron production method in which a first treatment is performed on a raw material gas; FIG. 1B is a schematic diagram showing an example of a system for implementing a reduced iron production method in which a second treatment is performed on a raw material gas; FIG. 1C is a schematic diagram showing an example of a system for implementing a reduced iron production method in which a third treatment is performed on a raw material gas; FIG. 1D is a schematic diagram showing an example of a system for implementing a reduced iron production method in which a third treatment is performed on a raw material gas and dust contained in an exhaust gas is removed; and FIG. 1E shows the raw material preheating temperature required to omit heating of the raw material gas by an external heater when the reducing gas blowing temperature is variously changed when a reducing gas is produced by performing the first treatment or the second treatment on a raw material gas.

[0009] Hereinafter, an embodiment of the method for producing reduced iron according to the present disclosure will be described, although the method for producing reduced iron according to the present disclosure is not limited to the following embodiment.

[0010] 1 to 5 , a method for producing reduced iron using a shaft furnace 11 according to one embodiment includes: preheating an oxidized iron raw material 1; subjecting a raw material gas 2 containing 90% or more by volume of hydrogen gas to a first process, a second process, or a third process to obtain a reducing gas 3; and supplying the preheated oxidized iron raw material 1 into the shaft furnace 11 and injecting the reducing gas 3 into the shaft furnace 11 to reduce the oxidized iron raw material 1 to obtain reduced iron 5. As shown in FIGS. 1 and 2 , the first process includes heating the raw material gas 2 by heat exchange with an exhaust gas 4 from the shaft furnace 11, but does not include partially combusting the raw material gas 2 with oxygen. As shown in FIG. 3 , the second process includes heating the raw material gas 2 by heat exchange with an exhaust gas 4 from the shaft furnace 11, and partially combusting the raw material gas 2 with oxygen after the heat exchange to raise the temperature, but does not include heating the raw material gas 2 with an external heater after the heat exchange. 4 and 5, the third treatment includes heating the raw material gas 2 by heat exchange with the exhaust gas 4 of the shaft furnace 11, heating the raw material gas 2 by an external heater 15 after the heat exchange, and partially burning the raw material gas 2 with oxygen to raise the temperature after heating by the heater 15. Here, when the raw material gas 2 is subjected to the first treatment, the following relationships (1) and (2) are satisfied: Y≧0.0016X ２ -0.8845X+470.72 (1) X≧600 (2) Y: preheating temperature (°C) of the iron oxide raw material 1 X: blowing temperature (°C) of the reducing gas 3 When the second treatment is performed on the raw material gas 2, the following relationships (3) and (4) are satisfied: Y≧0.0016X ２ -1.3845X+770.72 (3) X≧600 (4) Y: preheating temperature (°C) of the iron oxide raw material 1 X: blowing temperature (°C) of the reducing gas 3 are satisfied. When the third treatment is performed on the raw material gas 2, the following relationships (5) to (7): Y≧(0.0016X ２-1.3845X+770.72)×600 / Z (5) X≧600 (6) Z≧600 (7) Y: preheating temperature of the iron oxide raw material 1 (°C) X: blowing temperature of the reducing gas 3 (°C) Z: temperature of the raw material gas at the outlet side of the heater (°C) is satisfied.

[0011] 1. Preheating of the Oxidized Iron Raw Material As shown in FIGS. 1 to 4, the oxidized iron raw material 1 is preheated before being reduced by the reducing gas 3. The preheating of the oxidized iron raw material 1 may be performed using a known heating device. The preheating temperature of the oxidized iron raw material 1 can be appropriately adjusted so as to satisfy a predetermined relationship depending on the first to third treatments performed on the raw material gas 2. Note that the "preheating temperature of the oxidized iron raw material" refers to the average temperature in the radial direction of the shaft furnace 11 at the top surface (raw material stock level) of the packed bed of the oxidized iron raw material 1. The average temperature of the oxidized iron raw material 1 in the radial direction of the shaft furnace can be determined, for example, by placing a rod-shaped member in the radial direction of the shaft furnace, attaching multiple thermocouples to the member, and measuring multiple temperatures in the radial direction. For example, assuming that the temperature between the measurement points is distributed linearly in the radial direction, the radial temperature distribution T(r) can be expressed as a combination of linear functions of r. In this case, the average temperature T ａｖｅ If the temperature is measured at N points, the radius of the measurement point i (i = 1 to N) is r ｉ is defined by the following formula: ０ , r Ｎ＋１ corresponds to the center of the furnace (r ０ = 0) and the furnace wall (r Ｎ＋１ = R), and the temperature at that point is determined by extrapolation. With this method, even if there is a temperature distribution in the radial direction, the average temperature in the radial direction can be determined by averaging multiple measured temperatures. The number of thermocouples is not particularly limited, but it is preferable to arrange five or more thermocouples, for example.

[0012] The oxidized iron raw material 1 contains iron oxide. The oxidized iron raw material 1 may be, for example, one or more materials selected from iron ore pellets, iron ore, and sintered ore. The oxidized iron raw material 1 may contain, in addition to iron oxide, for example, one or both of silicon dioxide and aluminum oxide. The oxidized iron raw material 1 may have a particle size distribution or may have a uniform particle diameter. The average particle diameter of the oxidized iron raw material 1 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. The "particle diameter" of the oxidized iron raw material 1 refers to the sieve diameter of the raw material. The "average particle diameter" of the oxidized iron raw material 1 refers to the weighted average value of the particle diameters of the raw material. The average particle diameter of the oxidized iron raw material 1 is measured as follows. That is, a mass-based particle size distribution is obtained by a dry sieving test described in JIS Z 8815:1995, and the average of the maximum and minimum particle sizes of each sieve is used as a representative particle size, and the mass-weighted average is calculated to measure the average particle size of the oxidized iron raw material 1. The oxidized iron raw material 1 may be formed into pellets or the like, may be in the form of powder, may be in the form of lumps, or may be in any other form.

[0013] 2. Production of Reducing Gas In this embodiment, the reducing gas 3 is produced by subjecting the raw material gas 2 containing 90% by volume or more of hydrogen gas to the first treatment, the second treatment, or the third treatment.

[0014] 2.1 Source Gas The source gas 2 contains 90% by volume or more of hydrogen gas. The source gas 2 may contain 95% by volume or more, 97% by volume or more, or 99% by volume or more of hydrogen gas. The source gas 2 may contain, in addition to hydrogen gas, a gas other than hydrogen. Examples of gas other than hydrogen include CO gas, CH ４ Gas, C ２ H ６ Gas, inert gas, CO ２ Examples of the inert gas include nitrogen gas and argon gas.

[0015] 2.2 Heating of Source Gas In this embodiment, the source gas 2 is heated to obtain the reducing gas 3. The source gas 2 is heated by any one of the following first to third processes.

[0016] 2.2.1 First Process As shown in FIG. 1 or 2 , the first process includes heating the raw material gas 2 by heat exchange with the exhaust gas 4 of the shaft furnace 11. As described above, in this embodiment, the iron oxide raw material 1 is preheated. As a result, the sensible heat carried into the shaft furnace 11 increases, and the exhaust gas 4 discharged to the outside of the system may become hot. By utilizing such high-temperature exhaust gas 4, the raw material gas 2 can be heated by heat exchange. The heat exchange between the exhaust gas 4 and the raw material gas 2 may be performed, for example, by a heat exchanger 13. The temperature of the exhaust gas 4 before the heat exchange may be, for example, 400° C. or higher and 1200° C. or lower. The temperature of the raw material gas 2 after the heat exchange may be, for example, 300° C. or higher and 1150° C. or lower.

[0017] 1 or 2 , the first treatment does not include partial combustion of the raw material gas 2 with oxygen. The partial combustion of the raw material gas 2 will be described later. In this embodiment, in a system in which the raw material gas 2 passes through a combustion device 16, the first treatment may be performed on the raw material gas 2 while the combustion device 16 is stopped. In other words, when the first treatment is performed, the presence of the combustion device 16 is not necessarily excluded from the production facility for the reducing gas 3.

[0018] As shown in FIG. 1 , the first process may not include heating the source gas 2 with an external heater 15. Alternatively, as shown in FIG. 2 , the first process may include heating the source gas 2 with an external heater 15. When the first process does not include heating the source gas 2 with an external heater 15, as shown in FIG. 1 , the burden on the equipment can be further reduced. Note that in this embodiment, in a system in which the source gas 2 can be heated with an external heater 15, the first process may be performed on the source gas 2 with heating by the heater 15 stopped. In other words, even if the source gas 2 is not heated by the heater 15 when the first process is performed, the heater 15 is not necessarily excluded from the equipment for producing the reducing gas 3.

[0019] 2 , when the first treatment includes heating the raw material gas 2 by an external heater 15 after heat exchange, the external heater 15 may be any heater capable of heating the raw material gas 2, and any known heater may be employed. In this embodiment, as described above, the iron oxide raw material 1 is preheated, so that the sensible heat carried into the shaft furnace 11 increases and the raw material gas 2 can be heated by heat exchange with the exhaust gas 4, thereby reducing the amount of heating of the raw material gas 2 by the heater 15. The temperature of the gas on the outlet side of the heater 15 may be, for example, 500° C. or higher and 1200° C. or lower, or 500° C. or higher and 1000° C. or lower.

[0020] As described above, in the first process, the temperature of the raw material gas 2 is increased by heat exchange with the exhaust gas 4, and then the raw material gas 2 is optionally heated by the external heater 15, thereby obtaining the reducing gas 3. The reducing gas 3 is blown into the shaft furnace 11.

[0021] 3, the second process includes heating the raw material gas 2 by heat exchange with the exhaust gas 4 of the shaft furnace 11. The heat exchange between the exhaust gas 4 and the raw material gas 2 is as described above.

[0022] As shown in FIG. 3 , the second process includes partially combusting the raw material gas 2 with oxygen after the heat exchange to raise the temperature. The partial combustion with oxygen may be performed, for example, in the combustion device 16. Specifically, the raw material gas 2 and oxygen gas are each supplied to the inside of the combustion device 16 and heated, and a portion of the hydrogen contained in the raw material gas 2 is reacted with the oxygen and combusted, thereby raising the temperature of the raw material gas 2. The temperature of the raw material gas 2 after the partial combustion may be, for example, 700°C or higher and 1200°C or lower. The temperature rise of the raw material gas 2 due to the partial combustion (the difference between the temperature of the raw material gas 2 after the partial combustion and the temperature of the raw material gas 2 before the partial combustion) may be, for example, 0°C or higher and 350°C or lower, higher than 0°C and 350°C or lower, 100°C or higher and 350°C or lower, or 100°C or higher and 300°C or lower. Setting the temperature rise within such a range facilitates more stable operation.

[0023] 3 , the second treatment does not include heating the source gas 2 by the external heater 15 after the heat exchange. In this embodiment, in a system in which the source gas 2 can be heated by the external heater 15, the second treatment may be performed on the source gas 2 while heating by the heater 15 is stopped. In other words, when the second treatment is performed, the heater 15 is not necessarily excluded from the production equipment for the reducing gas 3.

[0024] As described above, in the second treatment, the temperature of the raw material gas 2 is increased by heat exchange with the exhaust gas 4, and then the temperature of the raw material gas 2 is increased by partial combustion, thereby obtaining the reducing gas 3. The reducing gas 3 is blown into the shaft furnace 11.

[0025] 4 , the third process includes heating the raw material gas 2 by heat exchange with the exhaust gas 4 of the shaft furnace 11, heating the raw material gas 2 by an external heater 15 after the heat exchange, and partially combusting the raw material gas 2 with oxygen to increase its temperature after heating by the heater 15. The heat exchange between the exhaust gas 4 and the raw material gas 2, the heating of the raw material gas 2 by the heater 15, and the increase in temperature of the raw material gas 2 by partial combustion are each as described above.

[0026] 3. Production of Reduced Iron In this embodiment, the oxidized iron raw material 1 preheated as described above is supplied into the shaft furnace 11, and the reducing gas 3 produced as described above is blown into the shaft furnace 11. This reduces the oxidized iron raw material 1 in the shaft furnace 11, thereby producing reduced iron 5. Specifically, inside the shaft furnace 11, the reducing gas 3 having a temperature equal to or higher than a certain level is brought into contact with the oxidized iron raw material 1 having a temperature equal to or higher than a certain level. This causes a reduction reaction between the iron oxide and hydrogen, producing reduced iron 5 containing metallic iron. In addition to metallic iron, the reduced iron 5 may contain unreduced iron oxide, silicon dioxide, aluminum oxide, and the like. Furthermore, the carbon concentration of the reduced iron 5 may be increased by carburization or the like after hydrogen reduction. That is, the reduced iron 5 may contain carbon in addition to metallic iron.

[0027] The configuration of the shaft furnace 11 and the reduction reaction in the shaft furnace 11 are publicly known. For example, the furnace body of the shaft furnace 11 may have a furnace top, a furnace bottom, and a tubular portion (cylindrical portion) that forms a side wall between the furnace top and the furnace bottom. In this case, the tubular portion may have a body portion and a reduced diameter portion provided below the body portion, and the inner diameter of the furnace may decrease from top to bottom in the reduced diameter portion.

[0028] The oxidized iron raw material 1 may be supplied into the shaft furnace 11, for example, through a raw material supply port provided at the top of the shaft furnace 11. The oxidized iron raw material 1 may form a packed bed in the shaft furnace 11. The packing rate of the packed bed is not particularly limited and may be the same as that in a conventional method for producing reduced iron using a shaft furnace. The packed bed moves downward inside the shaft furnace 11. That is, inside the shaft furnace 11, the oxidized iron raw material 1 is substantially filled and gradually moves downward by falling or the like. When focusing on a single raw material particle in the packed bed, the raw material particle may move continuously downward 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, the average downward movement speed of the raw material particle is not particularly limited. For example, the average movement speed may be adjusted depending on the supply amount (supply speed) of the oxidized iron raw material 1. The shaft furnace 11 may be provided with a burden feeder or the like for preventing the packed bed of the oxidized iron raw material 1 from hanging when the packed bed is moved downward inside the shaft furnace 11.

[0029] The reducing gas 3 can be supplied into the interior of the shaft furnace 11, for example, from the side wall of the shaft furnace 11. The position at which the reducing gas 3 is supplied is any position below the raw material supply port for the oxidized iron raw materials 1. The method for supplying the reducing gas 3 is not particularly limited. For example, a pipe or the like can be connected to the reducing gas supply port provided on the side wall of the shaft furnace 11, and the reducing gas 3 can be supplied from the outside to the interior of the shaft furnace 11 via the pipe or the like. The reducing gas 3 supplied into the interior of the shaft furnace 11 rises to the top of the furnace while coming into contact with the oxidized iron raw materials 1 to cause a reduction reaction, and can be discharged to the outside of the system as exhaust gas 4 through the gas exhaust port. The gas exhaust port may be provided at the same position as the raw material supply port or at a different position.

[0030] The shaft furnace 11 may be provided with a cooling gas supply port for supplying a cooling gas and a cooling gas exhaust port for exhausting the cooling gas below the reducing gas supply port. The cooling gas supply port may be provided in a side wall of the furnace, or may be provided inside the side wall of the furnace. The cooling gas exhaust port may be provided in the side wall of the furnace.

[0031] 4. Relationship between Preheating Temperature of Oxidized Iron Raw Material and Injection Temperature of Reducing Gas In this embodiment, as described above, the oxidized iron raw material 1 is preheated, and the raw material gas 2 is heated by any one of the first to third processes. Here, by preheating the oxidized iron raw material 1 to perform thermal compensation required for hydrogen reduction, it is believed that the reduction reaction can proceed appropriately even if the sensible heat from the reducing gas 3 is reduced. Specifically, by raising the temperature of the oxidized iron raw material 1 to a certain level or higher by preheating, the amount of heat required for the raw material gas 2 can be reduced, and of the heat exchange with the exhaust gas 4, heating by the external heater 15, and partial combustion with oxygen, for example, heating by the heater 15, which imposes a heavy equipment burden, can be omitted or reduced.

[0032] According to the new findings of the present inventors, the preheating temperature of the iron oxide raw material 1 required to omit or reduce the heating of the raw material gas 2 by the heater 15 can be changed depending on which of the first to third treatments is applied to the raw material gas 2.

[0033] 4.1 When the First Treatment is Performed on the Source Gas When the first treatment is performed on the source gas 2, the following relationships (1) and (2) are satisfied, so that heating of the source gas 2 by the heater 15 can be omitted or reduced. When the first treatment is performed on the source gas 2, for example, the preheating temperature Y of the oxidized iron raw material 1 may be controlled in accordance with the blowing temperature X of the reducing gas 3 so that the following relationships (1) and (2) are satisfied, or the blowing temperature X of the reducing gas 3 may be controlled in accordance with the preheating temperature Y of the oxidized iron raw material 1 so that the following relationships (1) and (2) are satisfied, or both the blowing temperature X of the reducing gas 3 and the preheating temperature Y of the oxidized iron raw material may be controlled in accordance with the following relationships (1) and (2). Furthermore, a method for producing reduced iron according to an embodiment may include, when the first treatment is performed on the source gas 2, determining one or both of the blowing temperature X of the reducing gas 3 and the preheating temperature Y of the oxidized iron raw material so that the following relationships (1) and (2) are satisfied.

[0034] Y≧0.0016X ２−0.8845X+470.72 (1) X≧600 (2) Y: Preheating temperature of iron oxide raw material 1 (°C) X: Injection temperature of reducing gas 3 (°C)

[0035] In the above relationship (1), the upper limit of the preheating temperature Y of the oxidized iron raw material 1 is not particularly limited. The preheating temperature Y may be, for example, 1200°C or less, 1150°C or less, 1100°C or less, 1050°C or less, or 1000°C or less. In particular, when the preheating temperature Y is 1000°C or less, the technology of the present disclosure can be expected to have a higher effect. Furthermore, in the above relationship (2), the upper limit of the blowing temperature X of the reducing gas 3 is not particularly limited. The blowing temperature X may be, for example, 1250°C or less, 1200°C or less, 1150°C or less, 1100°C or less, 1050°C or less, or 1000°C or less. In particular, when the blowing temperature X is 1100°C or less, the technology of the present disclosure can be expected to have a higher effect.

[0036] 4.2 When the Second Treatment is Performed on the Source Gas When the second treatment is performed on the source gas 2, the following relationships (3) and (4) are satisfied, and therefore heating of the source gas 2 by the heater 15 can be omitted. When the second treatment is performed on the source gas 2, for example, the preheating temperature Y of the oxidized iron raw material 1 may be controlled in accordance with the blowing temperature X of the reducing gas 3 so that the following relationships (3) and (4) are satisfied, or the blowing temperature X of the reducing gas 3 may be controlled in accordance with the preheating temperature Y of the oxidized iron raw material 1 so that the following relationships (3) and (4) are satisfied, or both the blowing temperature X of the reducing gas 3 and the preheating temperature Y of the oxidized iron raw material may be controlled in accordance with the following relationships (3) and (4). Furthermore, a method for producing reduced iron according to an embodiment may include, when the second treatment is performed on the source gas 2, determining one or both of the blowing temperature X of the reducing gas 3 and the preheating temperature Y of the oxidized iron raw material so that the following relationships (3) and (4) are satisfied.

[0037] Y≧0.0016X ２ −1.3845X+770.72 (3) X≧600 (4) Y: Preheating temperature of iron oxide raw material 1 (°C) X: Injection temperature of reducing gas 3 (°C)

[0038] In the above relationship (3), the upper limit of the preheating temperature Y of the oxidized iron raw material 1 is not particularly limited. The preheating temperature Y may be, for example, 1200°C or less, 1150°C or less, 1100°C or less, 1050°C or less, or 1000°C or less. In particular, when the preheating temperature Y is 1000°C or less, the technology of the present disclosure can be expected to have a higher effect. Furthermore, in the above relationship (4), the upper limit of the blowing temperature X of the reducing gas 3 is not particularly limited. The blowing temperature X may be, for example, 1250°C or less, 1200°C or less, 1150°C or less, 1100°C or less, 1050°C or less, or 1000°C or less. In particular, when the blowing temperature X is 1100°C or less, the technology of the present disclosure can be expected to have a higher effect.

[0039] 4.3 When the Source Gas is Subjected to the Third Treatment When the source gas 2 is subjected to the third treatment, the heating of the source gas 2 by the heater 15 can be reduced by satisfying the following relationships (5) to (7). When the source gas 2 is subjected to the third treatment, for example, the preheating temperature Y of the oxidized iron raw material 1 may be controlled in accordance with the blowing temperature X of the reducing gas 3 so that the following relationships (5) to (7) are satisfied; alternatively, the blowing temperature X of the reducing gas 3 may be controlled in accordance with the preheating temperature Y of the oxidized iron raw material 1 so that the following relationships (5) to (7) are satisfied; or both the blowing temperature X of the reducing gas 3 and the preheating temperature Y of the oxidized iron raw material may be controlled in accordance with the following relationships (5) to (7). Furthermore, a method for producing reduced iron according to an embodiment may include, when the source gas 2 is subjected to the third treatment, determining one or both of the blowing temperature X of the reducing gas 3 and the preheating temperature Y of the oxidized iron raw material so that the following relationships (5) to (7) are satisfied.

[0040] Y≧(0.0016X ２ −1.3845X+770.72)×600 / Z (5) X≧600 (6) Z≧600 (7) Y: Preheating temperature of iron oxide raw material 1 (°C) X: Blowing temperature of reducing gas 3 (°C) Z: Temperature of raw material gas 2 at the outlet side of heater 15 (°C)

[0041] In the above relationship (5), the upper limit of the preheating temperature Y of the oxidized iron raw material 1 is not particularly limited. The preheating temperature Y may be, for example, 1200°C or less, 1150°C or less, 1100°C or less, 1050°C or less, or 1000°C or less. In particular, when the preheating temperature Y is 1000°C or less, the technology of the present disclosure can be expected to have a higher effect. In one embodiment, the preheating temperature Y may be 900°C or more and 1100°C or less, or 900°C or more and 1000°C or less. Furthermore, in the above relationship (6), the upper limit of the blowing temperature X of the reducing gas 3 is not particularly limited. The blowing temperature X may be, for example, 1250°C or less, 1200°C or less, 1150°C or less, 1100°C or less, 1050°C or less, or 1000°C or less. In particular, when the blowing temperature X is 1100°C or less, the technology of the present disclosure can be expected to have a higher effect. In one embodiment, the blowing temperature X may be 600°C or higher and 1250°C or lower, 650°C or higher and 1200°C or lower, 700°C or higher and 1150°C or lower, 750°C or higher and 1100°C or lower, or 800°C or higher and 1100°C or lower. Furthermore, in the above relationship (7), the upper limit of the temperature Z of the raw material gas 2 at the outlet side of the heater 15 is not particularly limited. The outlet temperature Z may be, for example, 1200°C or lower, 1150°C or lower, 1100°C or lower, 1050°C or lower, or 1100°C or lower. In one embodiment, the temperature Z of the raw material gas 2 at the outlet side of the heater 15 may be 600°C or higher and 1200°C or lower, 600°C or higher and 1100°C or lower, 600°C or higher and 1000°C or lower, 600°C or higher and 900°C or lower, or 600°C or higher and 800°C or lower. In the third process, the raw material gas 2 is heated by the external heater 15 to raise the temperature of the raw material gas 2 to temperature Z, and then the temperature of the raw material gas 2 is maintained or further raised by partial combustion, thereby obtaining a reducing gas 3 at temperature X. That is, in the third process, temperature X naturally becomes equal to or higher than temperature Z. The amount of temperature rise of the raw material gas 2 due to partial combustion (the difference between the temperature of the raw material gas 2 after partial combustion and the temperature of the raw material gas 2 before partial combustion) may be, for example, 0°C or higher and 350°C or lower, higher than 0°C and 350°C or lower, 100°C or higher and 350°C or lower, or 100°C or higher and 300°C or lower. Setting the amount of temperature rise within such a range makes it easier to stabilize operation.

[0042] As described above, in the third process, the raw material gas 2 is heated by the external heater 15 to raise the temperature of the raw material gas 2 to temperature Z, and then the temperature of the raw material gas 2 is further raised by partial combustion, thereby obtaining a reducing gas 3 at temperature X. When the raw material gas 2 is heated by the external heater 15 in this way to raise the temperature of the raw material gas 2 to temperature Z in advance, the amount of partial combustion required to raise the temperature of the raw material gas 2 to temperature X is smaller than when the raw material gas 2 is not heated by the heater 15. In other words, the composition (particularly the moisture content) of the reducing gas 3 blown into the shaft furnace differs between (A) the case where, after heat exchange, the temperature of the raw material gas 2 is raised to temperature X only by partial combustion without heating the raw material gas 2 by the external heater 15, and (B) the case where, after heat exchange, the raw material gas 2 is heated by the external heater 15, the temperature of the raw material gas 2 at the outlet side of the heater 15 reaches temperature Z, and then the temperature of the raw material gas 2 is further raised to temperature X by partial combustion. Specifically, the moisture content of the reducing gas in case (A) is greater than the moisture content of the reducing gas in case (B). The above relationship (5) can be said to take into account the effect of the composition (particularly the moisture content) of the reducing gas 3 on the temperature inside the shaft furnace by taking into account the temperature Z on the outlet side of the heater 15. As a result of various experiments and calculations, the present inventors have found that the minimum required temperature for the preheating temperature Y can be determined by multiplying the right-hand side of the above relationship (3) by 600 / Z as a coefficient, as shown in the above relationship (5). That is, when the temperature Z is 600°C or higher, the higher the temperature Z, the lower the minimum required temperature for the preheating temperature Y.

[0043] 5. Other Matters In the production method of the present disclosure, the preheating temperature Y of the oxidized iron raw material 1 and the blowing temperature X of the reducing gas 3 (as well as the temperature Z of the raw material gas 2 at the outlet side of the heater 15) only need to satisfy the above-mentioned predetermined relationship, and other conditions are not particularly limited. For example, the supply amount of the oxidized iron raw material 1 and the blowing amount of the reducing gas 3 can be controlled within a range in which a desired reduction rate of reduced iron can be achieved. In one embodiment, the blowing amount of the reducing gas 3 may be changed depending on the blowing temperature of the reducing gas 3. In the production method of reduced iron according to one embodiment, for example, the following relationship (8) may be satisfied. When the following relationship (8) is satisfied, the reduction rate of reduced iron can be more significantly improved.

[0044] R≧0.0068X ２ −16.074X+10875 (8) R: Amount of reducing gas 3 blown in (Nm ３ / t-DRI) X: blowing temperature of reducing gas 3 (°C)

[0045] In the manufacturing method of the present disclosure, a portion of the exhaust gas 4 from the shaft furnace 11 may be reused as part of the raw material gas 2 or the reducing gas 3. As shown in FIG. 5 , a manufacturing method according to an embodiment may include, for example, removing dust contained in the exhaust gas 4 using a dust removal device 12, removing moisture contained in the exhaust gas 4 using a dehydration device 14, or adding the exhaust gas 4 after dust removal and dehydration to one or both of the raw material gas 2 and the reducing gas 3. Known devices may be used as the dust removal device 12 and the dehydration device 14. The timing of dust removal and dehydration is not particularly limited, and may be before or after heat exchange between the exhaust gas 4 and the raw material gas 2. Furthermore, the timing of adding the exhaust gas 4 to the raw material gas 2 or the reducing gas 3 is also not particularly limited.

[0046] 5 illustrates an example of the manufacturing method of the present disclosure in which the third treatment is performed, and also includes dust removal from the flue gas 4 by the dust remover 12, dehydration of the flue gas 4 by the dehydrator 14, and addition of the flue gas to the raw material gas 2 and the reducing gas 3. However, the manufacturing method of the present disclosure is not limited to this example. In the manufacturing method of the present disclosure, the embodiments shown in FIGS. 1 to 5 may be combined. For example, in any of the manufacturing methods shown in FIGS. 1 to 4, dust removal from the flue gas 4 by the dust remover 12 as shown in FIG. 5 may be performed, dehydration of the flue gas 4 by the dehydrator 14 may be performed, or the flue gas 4 may be added to the raw material gas 2 and the reducing gas 3.

[0047] 6. Effects In a method for producing reduced iron 5 using a shaft furnace 11, if the preheating temperature Y of the oxidized iron raw material 1 or the blowing temperature X of the reducing gas 3 changes, the temperature of the exhaust gas 4 from the shaft furnace 11 also changes. If the temperature of the exhaust gas 4 changes, the temperature X' of the raw material gas 2 after heat exchange with the exhaust gas 4 also changes. If the temperature X' of the raw material gas 2 after heat exchange is too low, heating by an external heater 15 is required to raise the temperature to the blowing temperature X, which increases the equipment load. In contrast, in this embodiment, it has been found that, by considering the heat balance of the entire system, heating by an external heater can be reduced or omitted when relationships (1) and (2), relationships (3) and (4), or relationships (5) to (7) are satisfied. As described above, according to this embodiment, in a method for producing reduced iron 5 using a shaft furnace 11, the amount of heating of the reducing gas 3 by the external heater 15 can be reduced, thereby reducing the equipment load.

[0048] The present invention will be further described below with reference to examples, but the present invention is not limited to the following examples. The present invention allows various conditions to be adopted as long as the object is achieved without departing from the gist of the present invention.

[0049] 1. First Process or Second Process 1.1 Calculation Conditions In a case where reduced iron with a predetermined reduction rate is obtained by preheating an oxidized iron raw material, subjecting a raw material gas (100% hydrogen gas by volume) to the first process or the second process to produce a reducing gas, supplying the preheated oxidized iron raw material to a shaft furnace, and injecting the produced reducing gas into the shaft furnace, the preheating temperature Y (°C) of the oxidized iron raw material required to omit external gas heating was determined while varying the reducing gas injection temperature X (°C). Here, the first process employed was a process in which the raw material gas was heated by heat exchange with exhaust gas from the shaft furnace, without heating the raw material gas with an external heater after the heat exchange. The second process employed was a process in which the raw material gas was heated by heat exchange with exhaust gas from the shaft furnace, and then partially combusted with oxygen after the heat exchange to raise the temperature of the raw material gas, without heating the raw material gas with an external heater after the heat exchange. The calculation conditions (simulation conditions) were as follows:

[0050] First, a required amount of reducing gas corresponding to each reducing gas temperature was calculated using a one-dimensional model. That is, in this example, the amount of reducing gas injected into the shaft furnace was changed depending on the reducing gas injection temperature so that the reduction rate of the ultimately produced reduced iron would be the same. Specifically, the calculation was performed while the amount of reducing gas injected and the reducing gas injection temperature satisfied the following relationship (A):

[0051] R = 0.0068X ２ -16.074X+10875 (A) R: Amount of reducing gas blown in (Nm ３ / t-DRI) X: reducing gas blowing temperature (°C)

[0052] Next, the reaction heat, the sensible heat of reduced iron, and the sensible heat of exhaust gas were calculated.

[0053] Finally, the heat balance of the entire system, including the exhaust gas system, was calculated under each set of conditions. The required heat (heat of reaction, sensible heat of reduced iron, and sensible heat of exhaust gas) was calculated under the same standard conditions. Regarding the heat exchange between the exhaust gas and the raw material gas, the temperature of the exhaust gas entering the heat exchanger was assumed to be approximately the same as the furnace gas temperature, and the heat exchange efficiency was set to 85%. Furthermore, the calculations were performed assuming that the temperature of the raw material gas would rise by 50 to 200°C from the outlet of the heat exchanger due to partial combustion of the raw material gas by oxygen (e.g., 750°C → 800°C, 800°C → 900°C, 800°C → 1000°C).

[0054] 1.2 Calculation Results The calculation results are shown in Figure 6. As shown in Figure 6, it was found that when the first treatment is performed on the raw material gas, reduced iron can be appropriately produced while omitting external gas heating if the following relationships (1) and (2) are satisfied. It was also found that when the second treatment is performed on the raw material gas, reduced iron can be appropriately produced while omitting external gas heating if the following relationships (3) and (4) are satisfied. It was also found that when the first treatment is performed on the raw material gas, the reduction rate of reduced iron is likely to be increased if the following relationships (1) and (2) are satisfied, and when the second treatment is performed on the raw material gas, the reduction rate of reduced iron is likely to be increased if the following relationships (3) and (4) are satisfied.

[0055] Y≧0.0016X ２ −0.8845X+470.72 (1) X≧600 (2) Y: preheating temperature of the iron oxide raw material (°C) X: blowing temperature of the reducing gas (°C)

[0056] Y≧0.0016X ２ −1.3845X+770.72 (3) X≧600 (4) Y: preheating temperature of the iron oxide raw material (°C) X: blowing temperature of the reducing gas (°C)

[0057] In the above examples, calculations were performed assuming that the source gas was not heated by an external heater after heat exchange in the first process, but the form of the first process is not limited to this. In the first process, the source gas may be heated by an external heater after heat exchange. When the source gas is subjected to the first process, even if the source gas is heated by an external heater after heat exchange, heating by the heater can be reduced as long as the above relationships (1) and (2) are satisfied.

[0058] 2. Regarding the third process 2.1 Calculation conditions The same calculations as above were performed, except that the reducing gas was produced by subjecting the raw material gas (100% by volume of hydrogen gas) to the third process. Here, the third process involves heating the raw material gas by heat exchange with the exhaust gas from the shaft furnace, heating the raw material gas using an external heater after the heat exchange, and then partially combusting the raw material gas with oxygen after heating using the heater to raise the temperature.

[0059] 2.2 Calculation Results The calculation results are shown in Table 1 below. In Table 1 below, X is the blowing temperature of the reducing gas (°C), Y is the preheating temperature of the iron oxide raw material (°C), and Z is the temperature of the raw material gas at the outlet side of the heater (°C). In Table 1 below, while reducing the heating by the external heater (specifically, the temperature Z of the raw material gas at the inlet side of the external heater), ｉｎ and the temperature Z of the raw material gas at the outlet side of the heater, Z-Z ｉｎ The case where reduced iron with the desired reduction rate (92% or more) could be produced (while keeping the temperature Z of the raw material gas at the inlet side of the heater at 400°C or less) was evaluated as "A: Pass." In addition, the case where reduced iron with the desired reduction rate (92% or more) could not be produced (because the amount of heat generated by the external heater was insufficient and the temperature Z of the raw material gas at the inlet side of the heater was too low to produce reduced iron with the desired reduction rate (92% or more) was evaluated as "A: Pass." ｉｎ and the temperature Z of the raw material gas at the outlet side of the heater, Z-Z ｉｎ The test results were evaluated as "B: Fail" when the test temperature was too high and the test temperature had to be increased to more than 400°C.

[0060]

[0061] As a result of the calculation, it was found that when the third treatment is performed on the raw material gas, reduced iron can be appropriately produced if the following relationships (5) to (7) are satisfied.

[0062] Y≧(0.0016X ２ −1.3845X+770.72)×600 / Z (5) X≧600 (6) Z≧600 (7) Y: preheating temperature of the iron oxide raw material (°C) X: blowing temperature of the reducing gas (°C) Z: temperature of the raw material gas at the outlet side of the heater (°C)

[0063] 3. Supplementary Note: In the above examples, results were shown for the case where a source gas containing 100% hydrogen gas by volume was used. Here, when the amount of hydrogen gas in the source gas is 100% by volume, the preheating temperature needs to be increased compared to when the amount of hydrogen gas in the source gas is less than 100% by volume. In other words, when the amount of hydrogen gas in the source gas is 100% by volume, heating by a heater or the like is required more than when the amount of hydrogen gas in the source gas is less than 100% by volume. In other words, even if the calculation results when the amount of hydrogen gas in the source gas is 100% by volume are applied to a case where the amount of hydrogen gas in the source gas is less than 100% by volume (for example, 90% by volume), it can be said that the same effect as when the amount of hydrogen gas in the source gas is 100% by volume can be obtained. That is, when a raw material gas containing 90% by volume or more of hydrogen gas is subjected to the first treatment, the second treatment, or the third treatment to obtain a reducing gas, when the raw material gas is subjected to the first treatment, the above relationships (1) and (2) are satisfied, when the raw material gas is subjected to the second treatment, the above relationships (3) and (4) are satisfied, and when the raw material gas is subjected to the third treatment, the above relationships (5) to (7) are satisfied. As a result, it can be said that reduced iron can be appropriately produced while omitting or reducing external gas heating.

[0064] REFERENCE SIGNS LIST 1 Iron oxide raw material 2 Raw material gas 3 Reducing gas 4 Exhaust gas 5 Reduced iron 11 Shaft furnace 12 Dust removal device 13 Heat exchanger 14 Dehydration device 15 Heater 16 Combustion device

Claims

1. A method for producing reduced iron using a shaft furnace, comprising: preheating an oxidized iron raw material; subjecting a raw material gas containing 90% by volume or more of hydrogen gas to a first treatment, a second treatment, or a third treatment to obtain a reducing gas; and supplying the preheated oxidized iron raw material into the shaft furnace and injecting the reducing gas into the shaft furnace to reduce the oxidized iron raw material to obtain reduced iron; wherein the first treatment comprises heating the raw material gas by heat exchange with exhaust gas from the shaft furnace, but does not comprise partially burning the raw material gas with oxygen; and wherein the second treatment comprises heating the raw material gas by heat exchange with exhaust gas from the shaft furnace, and partially burning the raw material gas with oxygen after the heat exchange to raise the temperature, but does not comprise heating the raw material gas with an external heater after the heat exchange; the third treatment includes heating the raw material gas by heat exchange with exhaust gas from the shaft furnace, heating the raw material gas with an external heater after the heat exchange, and partially combusting the raw material gas with oxygen after heating with the heater to raise the temperature, and when the first treatment is performed on the raw material gas, the following relationships (1) and (2) are satisfied: Y≧0.0016X ２ −0.8845X+470.72 (1) X≧600 (2) Y: preheating temperature of the iron oxide raw material (° C.) X: blowing temperature of the reducing gas (° C.) is satisfied, and when the raw material gas is subjected to the second treatment, the following relationships (3) and (4) are satisfied: Y≧0.0016X ２ -1.3845X+770.72 (3) X≧600 (4) Y: preheating temperature of the iron oxide raw material (°C) X: blowing temperature of the reducing gas (°C) are satisfied, and when the raw material gas is subjected to the third treatment, the following relationships (5) to (7) are satisfied: Y≧(0.0016X ２ -1.3845X+770.72)×600 / Z (5) X≧600 (6) Z≧600 (7) Y: preheating temperature of the iron oxide raw material (°C), X: blowing temperature of the reducing gas (°C), and Z: temperature of the raw material gas at the outlet side of the heater (°C).

2. The method for producing reduced iron according to claim 1, wherein the first treatment does not include heating the raw material gas with an external heater.

3. The method for producing reduced iron according to claim 1 or 2, wherein the raw material gas is subjected to the first treatment.

4. The method for producing reduced iron according to claim 1, wherein the raw material gas is subjected to the second treatment.

5. The method for producing reduced iron according to claim 1, wherein the raw material gas is subjected to the third treatment.

6. A method for producing reduced iron according to any one of claims 1 to 5, wherein X is 1100°C or less.

7. A method for producing reduced iron according to any one of claims 1 to 6, wherein the Y is 1000°C or less.

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