Method for producing reduced iron using a shaft furnace

Abstract

In a method for producing reduced iron using a shaft furnace, the heating amount of the reducing gas by an externally heated heater is suppressed to reduce the equipment load. The method for producing reduced iron using the shaft furnace of the present disclosure includes preheating an iron oxide raw material, subjecting a raw material gas containing 90% by volume or more of hydrogen gas to a predetermined treatment to obtain a reducing gas, and supplying the preheated iron oxide raw material into the shaft furnace, and blowing the reducing gas into the shaft furnace to reduce the iron oxide raw material to obtain reduced iron, and is characterized in that the relationship to be satisfied between the preheating temperature of the iron oxide raw material and the blowing temperature of the reducing gas is different depending on the predetermined treatment.

Description

Technical Field

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

Background Art

[0002] In the steel industry, as an alternative technology to the blast furnace method, reducing the amount of CO2 emissions by a direct reduction process using a reducing gas has been studied. For example, as a direct reduction process, a process using a shaft furnace has been studied. In the direct reduction process using a shaft furnace, a reducing gas is brought into contact with an iron oxide raw material to obtain direct reduced iron (DRI). As methods for producing reduced iron using a shaft furnace, the Midrex method and the HYL method are known. Here, the heat required for reduction in the shaft furnace is mainly compensated by heating the reducing gas to a desired temperature (for example, 800 to 1000 °C). The heating of the reducing gas can be carried out by (1) heat exchange with the exhaust gas of the shaft furnace, (2) heating with an externally heated heater, and (3) partial combustion of the reducing gas as necessary.

[0003] On the other hand, in a method for producing reduced iron using a shaft furnace, a technique for preheating an iron oxide raw material has been disclosed. For example, Patent Document 1 proposes a method of preheating an iron oxide raw material charged from the upper part of a reduction furnace to 100 °C or higher and 627 °C or lower in order to compensate for the endotherm due to the reaction between hydrogen gas and iron oxide. Thereby, when using a reducing gas mainly composed of hydrogen gas, excessive temperature rise and fusion at the lower part of the furnace are suppressed, the heat shortage at the upper part of the furnace is eliminated, and a high product reduction rate can be ensured. Further, Patent Document 2 discloses a method of directly charging a raw material into a reduction furnace while retaining the heat obtained during the production of the raw material.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0005] In the conventional method for producing reduced iron using a shaft furnace, there is room for improvement with respect to reducing the equipment load by suppressing the heating amount of the reducing gas by an external heating type heater.

MEANS FOR SOLVING THE PROBLEMS

[0006] This 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 iron oxide raw material; performing a first treatment, a second treatment, or a third treatment on a raw material gas containing 90% by volume or more of hydrogen gas to obtain a reducing gas; and feeding the preheated iron oxide raw material into the shaft furnace and blowing the reducing gas into the shaft furnace to reduce the iron oxide raw material to obtain reduced iron, wherein the first treatment includes heating the raw material gas by heat exchange with the exhaust gas of the shaft furnace and does not include partially burning the raw material gas with oxygen; the second treatment includes heating the raw material gas by heat exchange with the exhaust gas of the shaft furnace and, after the heat exchange, partially burning the raw material gas with oxygen to increase the temperature, and does not include heating the raw material gas by an external heating type heater after the heat exchange; the third treatment includes heating the raw material gas by heat exchange with the exhaust gas of the shaft furnace, heating the raw material gas by an external heating type heater after the heat exchange, and, after heating by the heater, partially burning the raw material gas with oxygen to increase the temperature; when the first treatment is performed on the raw material gas, the following relationships (1) and (2): Y≧0.0016X2 -0.8845X + 470.72 (1) X ≥ 600 (2) Y: Preheating temperature (°C) of the iron oxide raw material X: Blowing temperature (°C) of the reducing gas is satisfied, When the second treatment is performed on the raw material gas, the following relationships (3) and (4): Y ≥ 0.0016X 2 -1.3845X + 770.72 (3) X ≥ 600 (4) Y: Preheating temperature (°C) of the iron oxide raw material X: Blowing temperature (°C) of the reducing gas is satisfied, When the third treatment is performed on the raw material gas, 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 (°C) of the iron oxide raw material X: Blowing temperature (°C) of the reducing gas Z: Temperature (°C) of the raw material gas on the outlet side of the heater is satisfied, Method for producing reduced iron. <Aspect 2> The method for producing reduced iron according to Aspect 1, wherein the first treatment does not include heating the raw material gas by an externally heated heater. Method for producing reduced iron. <Aspect 3> The method for producing reduced iron according to Aspect 1 or 2, wherein the first treatment is performed on the raw material gas. Method for producing reduced iron. <Aspect 4> The method for producing reduced iron according to Aspect 1, wherein the second treatment is performed on the raw material gas. Method for producing reduced iron. <Aspect 5> The method for producing reduced iron according to Aspect 1, wherein the third treatment is performed on the raw material gas, Method for producing reduced iron. <Aspect 6> The method for producing reduced iron according to any one of Aspects 1 to 5, wherein X is 1100°C or lower, Method for producing reduced iron. <Aspect 7> The method for producing reduced iron according to any one of Aspects 1 to 6, wherein Y is 1000°C or lower, Method for producing reduced iron.

Advantages of the Invention

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

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

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

[0010] As shown in FIGS. 1 to 5, a method for producing reduced iron using a shaft furnace 11 according to an embodiment includes preheating the iron oxide raw material 1, subjecting a raw material gas 2 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 3, and feeding the preheated iron oxide raw material 1 into the shaft furnace 11 and blowing the reducing gas 3 into the shaft furnace 11 to reduce the iron oxide raw material 1 to obtain reduced iron 5. As shown in FIGS. 1 and 2, the first treatment includes heating the raw material gas 2 by heat exchange with the exhaust gas 4 of the shaft furnace 11 and does not include partially burning the raw material gas 2 with oxygen. As shown in FIG. 3, the second treatment includes heating the raw material gas 2 by heat exchange with the exhaust gas 4 of the shaft furnace 11, and after the heat exchange, partially burning the raw material gas 2 with oxygen to raise the temperature, and does not include heating the raw material gas 2 by an externally heated heater after the heat exchange. As shown in FIGS. 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 externally heated heater 15 after the heat exchange, and after heating by the heater 15, partially burning the raw material gas 2 with oxygen to raise the temperature. Here, When the first treatment is performed on the raw material gas 2, the following relationships (1) and (2): 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 are satisfied. When the second treatment is performed on the raw material gas 2, the following relationships (3) and (4): 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 (°C) of the iron oxide raw material 1 X: Blowing temperature (°C) of the reducing gas 3 Z: Temperature (°C) of the raw material gas at the outlet side of the heater are satisfied.

[0011] 1. Preheating of iron oxide raw material As shown in FIGS. 1 to 4, the iron oxide raw material 1 is preheated before being reduced by the reducing gas 3. The preheating of the iron oxide raw material 1 may be performed by a known heating device. The preheating temperature of the iron oxide raw material 1 can be appropriately adjusted so that a predetermined relationship is satisfied according to the first treatment to the third treatment applied to the raw material gas 2. Note that the "preheating temperature of the iron oxide raw material" refers to the average temperature in the furnace radius direction of the uppermost surface (raw material stock level) of the packed bed of the iron oxide raw material 1 inside the shaft furnace 11. The average temperature of the iron oxide raw material 1 in the radius direction of the shaft furnace can be specified, for example, by installing a rod-shaped member in the radius direction of the shaft furnace, providing a plurality of thermocouples on the member, and measuring a plurality of temperatures in the radius direction. For example, assuming that the temperature between the measured points is linearly distributed in the radius direction, the temperature distribution T(r) in the radius direction can be expressed as a combination of linear functions of r. At this time, 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 and is defined by the following formula. Note that r0 and r N+1 correspond to the center of the furnace (r0 = 0) and the position of the furnace wall (r N+1 = R), and the temperature at that point shall be obtained by extrapolation. According to such a method, even if there is a temperature distribution in the radius direction, it can be specified as the average temperature in the radius direction by averaging a plurality of measured temperatures. The number of thermocouples is not particularly limited, but for example, it is preferably arranged at 5 or more points.

Equation

[0012] The oxidized iron raw material 1 includes iron oxide. The oxidized iron raw material 1 may be, for example, one or more selected from iron ore pellets, iron ore, and sintered ore. The oxidized iron raw material 1 may include, 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 taken as a representative particle size, and a weighted average is calculated by the mass 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, second treatment, or third treatment.

[0014] 2.1 Raw material gas The source gas 2 contains 90% or more by volume of hydrogen gas. The source gas 2 may contain 95% or more by volume, 97% or more by volume, or 99% or more by volume of hydrogen gas. The source gas 2 may contain a gas other than hydrogen in addition to hydrogen gas. Examples of the gas other than hydrogen include CO gas, CH4 gas, C2H6 gas, inert gas, CO2 gas, and water vapor. Examples of the inert gas include nitrogen gas and argon gas.

[0015] 2.2 Heating of raw gas In this embodiment, the raw material gas 2 is heated to obtain the reducing gas 3. The heating of the raw material gas 2 is carried out 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, and accordingly, the enthalpy brought into the shaft furnace 11 increases, and the exhaust gas 4 discharged to the outside of the system can be at a high temperature. By using 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 by, for example, a heat exchanger 13. The temperature of the exhaust gas 4 before heat exchange may be, for example, 400°C or higher and 1200°C or lower. Also, the temperature of the raw material gas 2 after heat exchange may be, for example, 300°C or higher and 1150°C or lower.

[0017] As shown in FIG. 1 or 2, the first process does not include partially burning 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 the combustion device 16, the first process may be performed on the raw material gas 2 while the combustion device 16 is in a stopped state. That is, when performing the first process, the presence of the combustion device 16 is not necessarily excluded from the manufacturing facility of the reducing gas 3.

[0018] As shown in FIG. 1, the first process may not include heating the raw material gas 2 by the externally heated heater 15. Alternatively, as shown in FIG. 2, the first process may include heating the raw material gas 2 by the externally heated heater 15. As shown in FIG. 1, when the first process does not include heating the raw material gas 2 by the externally heated heater 15, the equipment burden can be further reduced. In the present embodiment, in a system in which the raw material gas 2 can be heated by the externally heated heater 15, the first process may be performed on the raw material gas 2 with the heating by the heater 15 stopped. That is, when performing the first process, when the raw material gas 2 is not heated by the heater 15, the presence of the heater 15 is not necessarily excluded from the production equipment of the reducing gas 3.

[0019] As shown in FIG. 2, when the first process includes heating the raw material gas 2 by the externally heated heater 15 after heat exchange, the externally heated heater 15 may be any heater as long as it can heat the raw material gas 2, and any known heater can be adopted. In the present embodiment, as described above, by preheating the iron oxide raw material 1, the sensible heat brought into the shaft furnace 11 increases, and the raw material gas 2 can be heated by heat exchange with the exhaust gas 4, and the heating amount of the raw material gas 2 by the heater 15 can be reduced. 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, after the temperature of the raw material gas 2 is increased by heat exchange with the exhaust gas 4, the reducing gas 3 is obtained through optional heating of the raw material gas 2 by the externally heated heater 15. The reducing gas 3 is blown into the interior of the shaft furnace 11.

[0021] 2.2.2 Second Process As shown in FIG. 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 treatment includes subjecting the raw material gas 2 to partial combustion with oxygen to increase the temperature after the above heat exchange. The partial combustion with oxygen may be performed, for example, in the combustion device 16. Specifically, each of the raw material gas 2 and the oxygen gas is supplied into the combustion device 16 and heated, and a part of the hydrogen contained in the raw material gas 2 is reacted with oxygen and burned to increase the temperature of the raw material gas 2. The temperature of the raw material gas 2 after partial combustion may be, for example, 700°C or higher and 1200°C or lower. The amount of temperature increase 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, more 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. By setting the amount of temperature increase within such a range, the operation is more likely to be stabilized.

[0023] As shown in FIG. 3, the second treatment does not include heating the raw material gas 2 by the externally heated heater 15 after the above heat exchange. In the present embodiment, in a system in which the raw material gas 2 can be heated by the externally heated heater 15, the second treatment may be performed on the raw material gas 2 in a state where the heating by the heater 15 is stopped. That is, when performing the second treatment, the presence of the heater 15 is not necessarily excluded from the production facility of the reducing gas 3.

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

[0025] 2.2.3 Third treatment As shown in Fig. 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 the externally heated heater 15 after the heat exchange, and partially burning the raw material gas 2 with oxygen to raise 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 temperature rise of the raw material gas 2 by partial combustion are as described above.

[0026] 3. Production of Reduced Iron In this embodiment, the iron oxide 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, so that the iron oxide raw material 1 is reduced in the shaft furnace 11 to obtain reduced iron 5. Specifically, inside the shaft furnace 11, the reducing gas 3 having a temperature of a certain level or higher is brought into contact with the iron oxide raw material 1 having a temperature of a certain level or higher. Thereby, a reduction reaction between iron oxide and hydrogen occurs, and reduced iron 5 containing metallic iron is obtained. The reduced iron 5 may contain, in addition to metallic iron, unreacted remaining iron oxide, silicon dioxide, aluminum oxide, etc. Further, the reduced iron 5 may be one in which the carbon concentration is 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 well-known. For example, the furnace body of the shaft furnace 11 may have a top part, a bottom part, and a cylindrical part (circular cylindrical part) constituting the side wall between the top part and the bottom part. In this case, the cylindrical part may have a body part and a reduced-diameter part provided below the body part, and the inner diameter of the furnace may decrease from top to bottom in the reduced-diameter part.

[0028] The iron oxide raw material 1 can be supplied into the shaft furnace 11, for example, through a raw material supply port provided at the top of the shaft furnace 11. Further, the iron oxide raw material 1 can form a packed bed in the shaft furnace 11. The packing ratio of the packed bed is not particularly limited and may be the same as that in the 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 iron oxide raw material 1 is in a substantially filled state and gradually moves downward by dropping or the like. When focusing on a single raw material particle in the packed bed, the raw material particle may continuously move downward at a constant speed or may intermittently move by repeating dropping 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 can be adjusted according to the supply amount (supply speed) of the iron oxide raw material 1. The shaft furnace 11 may be provided with a burden feeder or the like for preventing the packed bed from hanging up when moving the packed bed of the iron oxide raw material 1 downward inside.

[0029] The reducing gas 3 can be supplied, for example, from the side wall of the shaft furnace 11 into the furnace interior. The position for supplying the reducing gas 3 is an arbitrary position below the raw material supply port of the iron oxide raw material 1. The method for supplying the reducing gas 3 is not particularly limited. For example, a pipe or the like can be connected to a 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 into the interior of the shaft furnace 11 through the pipe or the like. The reducing gas 3 supplied into the interior of the shaft furnace 11 can contact the iron oxide raw material 1 to cause a reduction reaction, rise to the upper part of the furnace, and be discharged out of the system as exhaust gas 4 through the gas discharge port. The gas discharge port may be provided at the same position as the raw material supply port or at another position.

[0030] Furthermore, the shaft furnace 11 may be provided with a cooling gas supply port for supplying cooling gas and a cooling gas discharge port for discharging cooling gas below the reduction gas supply port. The cooling gas supply port may be provided on the side wall of the furnace or may be provided inside the side wall of the furnace. The cooling gas discharge port may be provided on the side wall of the furnace.

[0031] 4. Relationship between preheating temperature of iron oxide raw material and blowing temperature of reduction gas In this embodiment, as described above, the iron oxide raw material 1 is preheated and the raw material gas 2 is heated by any one of the first to third processes. Here, it is considered that by preheating the iron oxide raw material 1 to perform heat compensation required for hydrogen reduction, even if the sensible heat from the reduction gas 3 is reduced, the reduction reaction can proceed appropriately. Specifically, by raising the temperature of the iron oxide raw material 1 to a certain level or higher by preheating, the required heating amount of the raw material gas 2 can be reduced, and among heat exchange with the exhaust gas 4, heating by the external heat type heater 15, and partial combustion with oxygen, for example, heating by the heater 15 with a heavy equipment burden can be omitted or reduced.

[0032] According to the new findings of the present inventor, 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 may vary depending on which of the first to third processes is performed on the raw material gas 2.

[0033] 4.1 When the first process is performed on the raw material gas When the first treatment is performed on the raw material gas 2, the following relationships (1) and (2) are satisfied, so that the heating of the raw material gas 2 by the heater 15 can be omitted or reduced. When the first treatment is performed on the raw material gas 2, for example, the preheating temperature Y of the iron oxide raw material 1 may be controlled according to 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 according to the preheating temperature Y of the iron oxide 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 iron oxide raw material may be controlled so that the following relationships (1) and (2) are satisfied. Further, the method for producing reduced iron according to an embodiment includes determining one or both of the blowing temperature X of the reducing gas 3 and the preheating temperature Y of the iron oxide raw material so that the following relationships (1) and (2) are satisfied when the first treatment is performed on the raw material gas 2.

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

[0035] In the above relationship (1), the upper limit of the preheating temperature Y of the iron oxide raw material 1 is not particularly limited. The preheating temperature Y may be, for example, 1200°C or lower, 1150°C or lower, 1100°C or lower, 1050°C or lower, or 1000°C or lower. In particular, when the preheating temperature Y is 1000°C or lower, a higher effect according to the technology of the present disclosure can be expected. Also, 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 lower, 1200°C or lower, 1150°C or lower, 1100°C or lower, 1050°C or lower, or 1000°C or lower. In particular, when the blowing temperature X is 1100°C or lower, a higher effect according to the technology of the present disclosure can be expected.

[0036] 4.2 When the second treatment is performed on the raw material gas When a second treatment is performed on the raw material gas 2, the heating of the raw material gas 2 by the heater 15 can be omitted by satisfying the following relationships (3) and (4). When a second treatment is performed on the raw material gas 2, for example, the preheating temperature Y of the iron oxide raw material 1 may be controlled according to 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 according to the preheating temperature Y of the iron oxide 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 iron oxide raw material may be controlled so that the following relationships (3) and (4) are satisfied. Further, the method for producing reduced iron according to an embodiment includes determining one or both of the blowing temperature X of the reducing gas 3 and the preheating temperature Y of the iron oxide raw material so that the following relationships (3) and (4) are satisfied when a second treatment is performed on the raw material gas 2.

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

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

[0039] 4.3 When a third treatment is performed on the raw material gas When a third treatment is performed on the raw material gas 2, the following relationships (5) to (7) are satisfied, so that the heating of the raw material gas 2 by the heater 15 can be reduced. When a third treatment is performed on the raw material gas 2, for example, the preheating temperature Y of the iron oxide raw material 1 may be controlled according to the blowing temperature X of the reducing gas 3 so that the following relationships (5) to (7) are satisfied, or the blowing temperature X of the reducing gas 3 may be controlled according to the preheating temperature Y of the iron oxide 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 iron oxide raw material may be controlled so that the following relationships (5) to (7) are satisfied. Further, the method for producing reduced iron according to an embodiment includes determining one or both of the blowing temperature X of the reducing gas 3 and the preheating temperature Y of the iron oxide raw material so that the following relationships (5) to (7) are satisfied when a third treatment is performed on the raw material gas 2.

[0040] 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 2 on the outlet side of the heater 15 (°C)

[0041] In the above relationship (5), the upper limit of the preheating temperature Y of the iron oxide raw material 1 is not particularly limited. The preheating temperature Y may be, for example, 1200°C or lower, 1150°C or lower, 1100°C or lower, 1050°C or lower, or 1000°C or lower. Particularly when the preheating temperature Y is 1000°C or lower, a higher effect by the technology of the present disclosure can be expected. In one embodiment, the preheating temperature Y may be 900°C or higher and 1100°C or lower, or 900°C or higher and 1000°C or lower. Also, 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 lower, 1200°C or lower, 1150°C or lower, 1100°C or lower, 1050°C or lower, or 1000°C or lower. Particularly when the blowing temperature X is 1100°C or lower, a higher effect by the technology of the present disclosure can be expected. 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. Also, in the above relationship (7), the upper limit of the temperature Z of the raw material gas 2 on 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 on 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 treatment, the raw material gas 2 is heated by the externally heated heater 15 and the temperature of the raw material gas 2 is raised to the temperature Z, and then, through the temperature of the raw material gas 2 being maintained or further raised by partial combustion, the reducing gas 3 at the temperature X is obtained. That is, in the third treatment, the temperature X naturally becomes equal to or higher than the temperature Z. The amount of temperature increase of the raw material gas 2 by 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, more 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. By setting the amount of temperature increase within such a range, the operation is more likely to be stabilized.

[0042] As described above, in the third process, the raw material gas 2 is heated by the externally heated heater 15 so that the temperature of the raw material gas 2 rises to the temperature Z, and then, through further temperature rise of the raw material gas 2 by partial combustion, the reducing gas 3 at the temperature X is obtained. When the raw material gas 2 is heated by the externally heated heater 15 in this way to pre-elevate the temperature of the raw material gas 2 to the temperature Z in advance, compared with the case where the heating of the raw material gas 2 by the heater 15 is not performed, the amount of partial combustion required to elevate the temperature of the raw material gas 2 to the temperature X decreases. In other words, after heat exchange, when the temperature of the raw material gas 2 is elevated to the temperature X only by partial combustion without heating the raw material gas 2 by the externally heated heater 15 (case A), and after heat exchange, when the raw material gas 2 is heated by the externally heated heater 15 and the temperature of the raw material gas 2 on the outlet side of the heater 15 becomes the temperature Z, and then the temperature of the raw material gas 2 is further elevated to the temperature X by partial combustion (case B), the composition of the reducing gas 3 (especially the moisture content) blown into the shaft furnace is different. Specifically, the moisture content of the reducing gas in case (A) is higher than the moisture content of the reducing gas in case (B). It can be said that the above relationship (5) takes into account the influence of the composition of the above-mentioned reducing gas 3 (especially the moisture content) on the temperature in the shaft furnace by considering the temperature Z on the outlet side of the heater 15. As a result of various experiments and calculations, the inventor has found that, as in the above relationship (5), by multiplying the right side of the above relationship (3) by 600 / Z as a coefficient, the required minimum temperature of the preheating temperature Y is determined. That is, when the temperature Z is 600°C or higher, the higher the temperature Z, the lower the required minimum temperature of the preheating temperature Y.

[0043] 5. Other matters In the manufacturing method of the present disclosure, it is only necessary that the preheating temperature Y of the iron oxide raw material 1 and the blowing temperature X of the reducing gas 3 (and the temperature Z of the raw material gas 2 on the outlet side of the heater 15) satisfy the above-described predetermined relationship, and other conditions are not particularly limited. For example, within the range where a desired reduction rate as reduced iron can be achieved, the supply amount of the iron oxide raw material 1 and the blowing amount of the reducing gas 3 can be controlled. In one embodiment, the blowing amount of the reducing gas 3 may be changed according to the blowing temperature of the reducing gas 3. In the manufacturing 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: Blowing amount of the reducing gas 3 (Nm 3 / t-DRI) X: Blowing temperature of the reducing gas 3 (°C)

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

[0046] Further, in FIG. 5, in the manufacturing method of the present disclosure, while the third treatment is performed, the form in which the exhaust gas 4 is dust-removed by the dust removal device 12, the exhaust gas 4 is dehydrated by the dehydration device 14, and the exhaust gas is added to the raw material gas 2 or the reducing gas 3 is illustrated. However, the manufacturing method of the present disclosure is not limited thereto. In the manufacturing method of the present disclosure, the forms shown in FIGS. 1 to 5 may be combined. For example, in any of the manufacturing methods shown in FIGS. 1 to 4, the exhaust gas 4 may be dust-removed by the dust removal device 12 as shown in FIG. 5, the exhaust gas 4 may be dehydrated by the dehydration device 14, or the exhaust gas 4 may be added to the raw material gas 2 or the reducing gas 3.

[0047] 6. Effects In the method for producing reduced iron 5 using the shaft furnace 11, when the preheating temperature Y of the iron oxide 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. When 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 the externally heated heater 15 is required to raise the temperature to the blowing temperature X, resulting in an increase in equipment load. On the other hand, in the present embodiment, it has been found that when the relationships (1) and (2), the relationships (3) and (4), or the relationships (5) to (7) are satisfied in view of the overall heat balance of the system, heating by the externally heated heater can be reduced or omitted. As described above, according to the present embodiment, in the method for producing reduced iron 5 using the shaft furnace 11, the heating amount of the reducing gas 3 by the externally heated heater 15 can be suppressed, and the equipment burden can be reduced.

Examples

[0048] Hereinafter, the present invention will be further described while showing examples, but the present invention is not limited to the following examples. The present invention can adopt various conditions as long as it does not deviate from the gist and can achieve the object.

[0049] 1. Regarding the first treatment or the second treatment 1.1 Calculation conditions The iron oxide raw material is preheated, and the raw material gas (hydrogen gas: 100% by volume) is subjected to the first treatment or the second treatment to produce a reducing gas. While the preheated iron oxide raw material is supplied into the shaft furnace, the produced reducing gas is blown into the shaft furnace to obtain reduced iron having a predetermined reduction rate. In this case, while variously changing the blowing temperature X (°C) of the reducing gas, the preheating temperature Y (°C) of the iron oxide raw material required to omit the external heat type gas heating was determined. Here, as the first treatment, a treatment of heating the raw material gas by heat exchange with the exhaust gas of the shaft furnace, and not heating the raw material gas by an external heat type heater after the heat exchange was adopted. Further, as the second treatment, a treatment of heating the raw material gas by heat exchange with the exhaust gas of the shaft furnace, and then partially burning the raw material gas with oxygen to raise the temperature, and not heating the raw material gas by an external heat type heater after the heat exchange was adopted. The calculation conditions (simulation conditions) are as follows.

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

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

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

[0053] Finally, under each condition, the heat balance of the entire system including the exhaust gas system was calculated. At that time, the required heat (reaction heat, sensible heat of reduced iron, sensible heat of exhaust gas) was set under the same standard conditions. Also, regarding the heat exchange between the exhaust gas and the raw material gas, it was assumed that the introduction temperature of the exhaust gas into the heat exchanger was approximately the same as the top gas temperature, and the heat exchange efficiency was set at 85%. Furthermore, calculations were performed assuming that the raw material gas would increase in temperature by 50°C to 200°C (for example, 750°C → 800°C, 800°C → 900°C, 800°C → 1000°C) due to partial combustion of the raw material gas by oxygen from the temperature on the outlet side of the heat exchanger.

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

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

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

[0057] In the above embodiments, in the first process, the calculation was performed on the assumption that the raw material gas was not heated by an externally heated heater after heat exchange. However, the form of the first process is not limited to this. In the first process, the raw material gas may be heated by an externally heated heater after heat exchange. Even when the raw material gas is heated by an externally heated heater after heat exchange in the case where the first process is performed on the raw material gas, if the above relationships (1) and (2) are satisfied, the heating by the heater can be reduced.

[0058] 2. Regarding the third process 2.1 Calculation conditions The same calculations as above were performed, except that the third process was performed on the raw material gas (hydrogen gas: 100% by volume) to produce a reducing gas. Here, the third process is a process of heating the raw material gas by heat exchange with the exhaust gas of the shaft furnace, heating the raw material gas by an externally heated heater after heat exchange, and partially burning the raw material gas with oxygen to raise the temperature after heating by the heater.

[0059] 2.2 Calculation results The calculation results are shown in Table 1 below. In Table 1 below, X is the blowing temperature (°C) of the reducing gas, Y is the preheating temperature (°C) of the iron oxide raw material, and Z is the temperature (°C) of the raw material gas on the outlet side of the heater. In Table 1 below, while reducing the heating by the externally heated heater (specifically, keeping the difference Z - Z between the temperature Z of the raw material gas on the inlet side of the externally heated heater and the temperature Z of the raw material gas on the outlet side of the heater at 400°C or less), the case where it is possible to produce reduced iron with a desired reduction rate (92% or more) was evaluated as "A: Pass". Also, when it was not possible to produce reduced iron with a desired reduction rate (92% or more) (the heating amount by the externally heated heater was insufficient, and in order to produce reduced iron with a desired reduction rate (92% or more), it was necessary to increase the difference Z - Z between the temperature Z of the raw material gas on the inlet side of the heater and the temperature Z of the raw material gas on the outlet side of the heater to more than 400°C), it was evaluated as "B: Fail". in between the temperature Z of the raw material gas on the inlet side of the externally heated heater and the temperature Z of the raw material gas on the outlet side of the heater in while reducing the heating by the externally heated heater (specifically, keeping the difference Z - Z between the temperature Z of the raw material gas on the inlet side of the externally heated heater and the temperature Z of the raw material gas on the outlet side of the heater at 400°C or less), the case where it is possible to produce reduced iron with a desired reduction rate (92% or more) was evaluated as "A: Pass". Also, when it was not possible to produce reduced iron with a desired reduction rate (92% or more) (the heating amount by the externally heated heater was insufficient, and in order to produce reduced iron with a desired reduction rate (92% or more), it was necessary to increase the difference Z - Z between the temperature Z of the raw material gas on the inlet side of the heater and the temperature Z of the raw material gas on the outlet side of the heater to more than 400°C), it was evaluated as "B: Fail". in between the temperature Z of the raw material gas on the inlet side of the heater and the temperature Z of the raw material gas on the outlet side of the heater in while reducing the heating by the externally heated heater (specifically, keeping the difference Z - Z between the temperature Z of the raw material gas on the inlet side of the externally heated heater and the temperature Z of the raw material gas on the outlet side of the heater at 400°C or less), the case where it is possible to produce reduced iron with a desired reduction rate (92% or more) was evaluated as "A: Pass". Also, when it was not possible to produce reduced iron with a desired reduction rate (92% or more) (the heating amount by the externally heated heater was insufficient, and in order to produce reduced iron with a desired reduction rate (92% or more), it was necessary to increase the difference Z - Z between the temperature Z of the raw material gas on the inlet side of the heater and the temperature Z of the raw material gas on the outlet side of the heater to more than 400°C), it was evaluated as "B: Fail".

[0060]

Table 1

[0061] As a result of calculations, it was found that when the third treatment is performed on the raw material gas, reduced iron can be appropriately produced when 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 on the outlet side of the heater (°C)

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

Explanation of Symbols

[0064] Iron oxide raw material Raw material gas Reducing gas Exhaust gas Reduced iron Shaft furnace Dust removal device Heat exchanger Dehydration device Heater Combustion device

Claims

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

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

3. The method for producing reduced iron according to claim 1, wherein the first treatment is performed on the raw material gas. A method for producing reduced iron.

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

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

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

7. The method for producing reduced iron according to any one of claims 1 to 5, wherein Y is 1000 °C or lower, A method for producing reduced iron.

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