Method for producing reduced iron

Abstract

Disclosed is a technique through which metallization rate can be increased by raising the internal pressure in a furnace when producing reduced iron by a direct hydrogen reduction process that uses a shaft furnace. A method for producing reduced iron according to the present disclosure includes reducing an iron oxide raw material with a reducing gas inside a shaft furnace. The method for producing reduced iron according to the present disclosure is characterized in that the reducing gas contains 80 vol% or more hydrogen gas, the output level V (Nm3 / t-DRI) of hydrogen gas supplied to the shaft furnace and the temperature T(°C) of the reducing gas supplied to the shaft furnace are controlled so as to satisfy the relationship V ≥ 0.0094 × T2 - 20.5 × T + 12,400, and the gauge pressure at the furnace top of the shaft furnace is controlled so as to exceed 0 MPa.

Description

Method for producing reduced iron

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

[0002] The HyL method is known as a method for producing reduced iron by directly reducing iron oxide using a shaft furnace (Non-Patent Document 1). In the HyL method, natural gas is mainly used as the raw material gas, and the furnace is operated with increased pressure. It is thought that increasing the furnace pressure promotes the reduction reaction inside the furnace, for example, and makes it easier to increase the metallization rate. Patent Document 1 also discloses a mathematical model for simulating the operating conditions of a shaft furnace.

[0003] International Publication No. 2021 / 241272

[0004] P. Duarte: “High-Carbon HBI and the Analysis of Formation of Iron Carbide and Behavior in the ENERGIRON ZR Process”, AISTech 2018 Proceedings., pp 633-647

[0005] In direct reduction using a shaft furnace, when hydrogen gas is used as the reducing gas, the endothermic effect of hydrogen reduction can lead to insufficient heat in the furnace, potentially reducing the metallization rate (MR: the proportion of metallic iron in total iron). While increasing the furnace pressure increases mass transfer, it does not significantly increase the heat transfer coefficient. In other words, in hydrogen reduction, the effect of increasing furnace pressure on improving the metallization rate is less pronounced compared to CO reduction, etc. In conventional technology, the operating conditions that allow for increasing furnace pressure to enhance the metallization rate when producing reduced iron by a direct hydrogen reduction process using a shaft furnace are unknown. Therefore, this application discloses operating conditions that allow for increasing furnace pressure to enhance the metallization rate when producing reduced iron by a direct hydrogen reduction process using a shaft furnace.

[0006] This application discloses the following multiple embodiments as means for solving the above problems. <Embodiment 1> A method for producing reduced iron, comprising: reducing an iron oxide raw material with a reducing gas inside a shaft furnace, wherein the reducing gas contains 80% by volume or more of hydrogen gas, and the hydrogen gas intensity V (Nm³) supplied to the shaft furnace. ３ The relationship between ( / t - DRI) and the temperature T (°C) of the reducing gas supplied to the shaft furnace is as follows: (1) V ≥ 0.0094 × T ２ A method for producing reduced iron, wherein the temperature is controlled to satisfy -20.5 × T + 12400 …(1), and the gauge pressure at the top of the shaft furnace is controlled to exceed 0 MPa. <Aspect 2> A method for producing reduced iron according to aspect 1, wherein the hydrogen gas intensity V and the temperature T have the following relationship (2): V ≥ 0.0103 × T ２ A method for producing reduced iron, controlled to satisfy -22.6 × T + 13749 …(2). <Aspect 3> A method for producing reduced iron according to aspect 1, wherein the hydrogen gas intensity V and the temperature T have the following relationship (3): V ≥ 0.0126 × T ２ A method for producing reduced iron, controlled to satisfy -27.2 × T + 16226 …(3). <Aspect 4> A method for producing reduced iron according to any of aspects 1 to 3, wherein the temperature T is 1100°C or higher and the gauge pressure at the top of the furnace is 0.4 MPa or less, or the temperature T is 1000°C or higher and less than 1100°C and the gauge pressure at the top of the furnace is 0.6 MPa or less, or the temperature T is 950°C or higher and less than 1000°C and the gauge pressure at the top of the furnace is 0.7 MPa or less. <Aspect 5> A method for producing reduced iron according to any of aspects 1 to 4, wherein the temperature T is 800°C or higher and 1150°C or lower.

[0007] According to the technology of this disclosure, in a hydrogen reduction process using a shaft furnace, the metallization rate tends to increase when the gauge pressure at the top of the furnace is greater than 0 MPa when a specific relationship (1) is satisfied.

[0008] This is a schematic diagram illustrating a method for producing reduced iron according to one embodiment. This is a schematic diagram illustrating a method for producing reduced iron according to one embodiment. Fe ３ O ４ - This shows the concept of the state inside the furnace at FeO reduction equilibrium. In a hydrogen reduction process using a shaft furnace, it shows the region (heat surplus region) where the metallization rate is likely to improve due to an increase in furnace pressure. It shows the relationship between the gauge pressure at the top of the furnace, the reduction completion height, and the reduction gas supply temperature. For the case where the reduction gas supply temperature is 900°C, it shows the relationship between the gauge pressure at the top of the furnace, the reduction completion height (and hydrogen gas utilization rate), and the reduction gas temperature inside the furnace. For the case where the reduction gas supply temperature is 950°C, it shows the relationship between the gauge pressure at the top of the furnace, the reduction completion height (and hydrogen gas utilization rate), and the reduction gas temperature inside the furnace. For the case where the reduction gas supply temperature is 1000°C, it shows the relationship between the gauge pressure at the top of the furnace, the reduction completion height (and hydrogen gas utilization rate), and the reduction gas temperature inside the furnace.

[0009] The method for producing reduced iron according to the embodiments will be described below with reference to the drawings, but the technology of this disclosure is not limited to the following embodiments.

[0010] As shown in Figures 1 and 2, a method for producing reduced iron according to one embodiment includes reducing iron oxide raw material 10 with a reducing gas inside a shaft furnace 100. In this embodiment, the reducing gas contains 80% or more by volume of hydrogen gas and is supplied to the shaft furnace 100 with a hydrogen gas intensity V (Nm³). ３ The relationship between ( / t - DRI) and the temperature T (°C) of the reducing gas supplied to the shaft furnace 100 is as follows (1): V ≥ 0.0094 × T ２ The system is controlled to satisfy -20.5 × T + 12400 …(1), and the gauge pressure at the top of the shaft furnace 100 is controlled to be greater than 0 MPa.

[0011] 1. Iron Oxide Raw Material The iron oxide raw material 10 contains iron oxide. The iron oxide raw material 10 may be, for example, one or more selected from iron ore pellets, iron ore, and sintered ore. The iron oxide raw material 10 may contain impurities in addition to iron oxide. Examples of the impurities include one or both of silicon dioxide and aluminum oxide. The iron oxide raw material 10 may have a particle size distribution or may have a uniform particle diameter. The average particle diameter of the iron oxide raw material 10 may be, for example, 5.0 mm or more and 20.0 mm or less, or may be 10.0 mm or more and 15.0 mm or less.

[0012] In the present application, the "particle diameter" of the iron oxide raw material 10 is measured by the diameter (mesh opening) of the sieve when the iron oxide raw material 10 is sieved. When measuring the particle diameter of the iron oxide raw material 10, a plurality of sieves with different mesh openings are prepared. Specifically, a total of 5 types of sieves with mesh openings of <unk>20 mm, 16 mm, 12.5 mm, <unk>9.5 mm, and <unk>6.3 mm are prepared, and the iron oxide raw material 10 is sieved according to the dry sieving test described in JIS Z 8815: 1994. At this time, the particle diameter D of the iron oxide raw material that did not pass through the sieve with the largest mesh opening of <unk>20 mm １ is regarded as <unk>20 mm. Also, for the iron oxide raw material that passed through the sieve with a mesh opening of <unk>20 mm but did not pass through the sieve with a mesh opening of <unk>16 mm, the particle diameter D ２ is regarded as the average value of <unk>20 mm and <unk>16 mm, i.e., (20 + 16) / 2 mm. Similarly, for the iron oxide raw material that passed through the sieve with a mesh opening of <unk>16 mm but did not pass through the sieve with a mesh opening of <unk>12.5 mm, the particle diameter D ３ is regarded as (16 + 12.5) / 2 mm, and for the iron oxide raw material that passed through the sieve with a mesh opening of <unk>12.5 mm but did not pass through the sieve with a mesh opening of <unk>9.5 mm, the particle diameter D ４ is regarded as ( <unk>12.5 + <unk>9.5) / 2 mm, and for the iron oxide raw material that passed through the sieve with a mesh opening of <unk>9.5 mm but did not pass through the sieve with a mesh opening of <unk>6.3 mm, the particle diameter D ５ is regarded as ( <unk>9.5 + <unk>6.3) / 2 mm. Finally, for the iron oxide raw material that passed through the sieve with the smallest mesh opening of <unk>6.3 mm, the particle diameter D ６ It should be noted that there seem to be some missing values in the original text (the <unk> parts), which might affect the accuracy of the translation if not properly filled in the original context.It is assumed that this is (6.3 + 0) / 2 mm.

[0013] Furthermore, in this application, the "average particle size" of the iron oxide raw material 10 means the weighted average value of the particle size of the iron oxide raw material 10, and is measured as follows. That is, as described above, a total of five types of sieves with mesh openings of 20 mm, 16 mm, 12.5 mm, 9.5 mm, and 6.3 mm are prepared, and the iron oxide raw material 10 is sieved according to the dry sieving test described in JIS Z 8815:1994. At this time, the iron oxide raw material that did not pass through the sieve with the largest mesh opening of 20 mm (particle size D １ The mass of 20 mm is X １ (g) is the iron oxide raw material (particle size D) that passed through a sieve with a mesh size of 20 mm and did not pass through a sieve with a mesh size of 16 mm. ２ The mass of (20 + 16) / 2 mm is X ２ (g) is the iron oxide raw material (particle size D) that passed through a sieve with a mesh size of 16 mm and did not pass through a sieve with a mesh size of 12.5 mm. ３ The mass of (16 + 12.5) / 2 mm is X ３ (g) represents iron oxide raw material (particle size D) that passed through a sieve with a mesh size of 12.5 mm and did not pass through a sieve with a mesh size of 9.5 mm. ４ The mass of (12.5 + 9.5) / 2 mm is X ４ (g) represents the iron oxide raw material (particle size D) that passed through a sieve with a mesh size of 9.5 mm and did not pass through a sieve with a mesh size of 6.3 mm. ５ The mass of (9.5 + 6.3) / 2 mm is X ５ (g) represents the iron oxide raw material that passed through the smallest sieve with a mesh size of 6.3 mm (particle size D ６ The mass of (6.3 + 0) / 2 mm is X ６ If (g), the average particle size of the iron oxide raw material (weighted average value of the particle size of the iron oxide raw material) D ａｖｅ It is calculated as follows: D ａｖｅ = [X １ ×D １ +X ２ ×D ２ +X ３ ×D ３ +X ４ ×D ４ +X ５×D ５ +X ６ ×D ６ ] / [X １ +X ２ +X ３ +X ４ +X ５ +X ６ ]

[0014] The iron oxide raw material 10 may be formed into pellets or the like, or it may be in the form of a lump or other shape.

[0015] The amount (feed rate) of iron oxide raw material 10 supplied to the shaft furnace 100 is not particularly limited. The iron oxide raw material 10 is supplied to the inside of the shaft furnace 100, for example, from a raw material supply port provided at the top of the shaft furnace 100, and a packed bed can be formed inside the shaft furnace 100. The packing rate of the packed bed is not particularly limited and may be the same as that of conventional methods for producing reduced iron using a shaft furnace. The packed bed moves downward inside the shaft furnace 100. That is, inside the shaft furnace 100, the iron oxide raw material 10 is substantially filled and moves gradually downward by falling or the like. When considering a single raw material particle in the packed bed, the raw material particle may move continuously downward at a constant speed, or it may move intermittently by repeatedly falling and stopping. When considering 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 amount (feed rate) of iron oxide raw material 10 supplied. When moving the packed bed downwards, a buried feeder or similar device may be used to prevent shelf tangling.

[0016] The temperature of the iron oxide raw material 10 supplied into the shaft furnace 100 (temperature at the raw material supply port) is not particularly limited and should be any temperature at which the reduction reaction by hydrogen gas can proceed inside the shaft furnace 100. The temperature of the iron oxide raw material 10 supplied into the shaft furnace 100 may be, for example, 0°C or more and 1000°C or less, or 600°C or more and 1000°C or less.

[0017] 2. Reducing Gas The technology of this disclosure can be said to solve problems that arise specifically when the reducing gas supplied to the shaft furnace 100 contains a large amount of hydrogen gas. In this embodiment, the reducing gas contains 80% or more by volume of hydrogen gas. The proportion of hydrogen gas in the reducing gas may be 85% or more by volume, 90% or more by volume, or 95% or more by volume. There is no particular upper limit to the proportion of hydrogen gas in the reducing gas; that is, the proportion of hydrogen gas in the reducing gas is 100% or less by volume. In addition to hydrogen gas, the reducing gas may also contain gases other than hydrogen gas. Examples of gases other than hydrogen gas include CO gas, hydrocarbon gases, and inert gases. Examples of inert gases include nitrogen gas, argon gas and other noble gases, and CO ２ The reducing gas may consist of one or more gases, water vapor, etc. The proportion of gases other than hydrogen gas in the reducing gas is 20% by volume or less, and may be 15% by volume or less, 10% by volume or less, or 5% by volume or less. As will be described later, when the reducing gas is produced using the exhaust gas from the shaft furnace 100, the reducing gas may contain, for example, water vapor. In addition, the reducing gas may be heated by oxygen combustion before being supplied to the shaft furnace 100. In this case as well, a portion of the reducing gas may be consumed by oxygen combustion, and water vapor may be generated. The amount of water vapor contained in the reducing gas should be as small as possible, and may be, for example, 5% by volume or less, 4% by volume or less, 3% by volume or less, or 2% by volume or less.

[0018] The reducing gas can be supplied to the interior of the shaft furnace 100, for example, from the side wall of the shaft furnace 100. The location from which the reducing gas is supplied is any location below the raw material supply port for the iron oxide raw material. The method of supplying the reducing gas from the side wall of the shaft furnace 100 is not particularly limited. For example, the reducing gas may be supplied to the packed bed inside the shaft furnace 100 via a reducing gas supply port provided in the side wall of the shaft furnace 100. The reducing gas supply port may be provided, for example, below the reduction zone of the shaft furnace 100. Piping or the like may be connected to the reducing gas supply port. In this case, the tip of the piping may or may not protrude inward from the inner wall of the shaft furnace 100. The reducing gas supplied to the interior of the shaft furnace 100 can rise to the top of the furnace while coming into contact with the iron oxide raw material and causing a reduction reaction, and can be discharged outside the system as exhaust gas through a gas outlet. The gas outlet may be provided at the same location as the raw material supply port, or at a different location. As will be described later, the exhaust gas from the shaft furnace 100 may be reused for the production of reducing gas.

[0019] The temperature T of the reducing gas supplied to the shaft furnace 100 (the temperature of the reducing gas at the reducing gas supply port) is not particularly limited and should be any temperature at which the reduction reaction by hydrogen gas can proceed. The temperature T of the reducing gas supplied into the shaft furnace 100 may be, for example, 800°C to 1150°C, or 900°C to 1100°C. The temperature T of the reducing gas supplied to the shaft furnace 100 can be appropriately changed and controlled by adjusting the amount of heating of the reducing gas before it is supplied to the shaft furnace 100.

[0020] The amount of reducing gas supplied to the shaft furnace 100 is not particularly limited, and any amount that allows the reduction reaction by hydrogen gas to proceed is acceptable. Here, the hydrogen gas intensity V can be said to be determined based on the amount of reducing gas supplied to the shaft furnace 100. That is, the hydrogen gas intensity V can be appropriately changed and controlled by adjusting the amount of reducing gas supplied to the shaft furnace 100. In this embodiment, the hydrogen gas intensity V is controlled to satisfy a predetermined relationship (1) with the temperature T described above, and the gauge pressure at the top of the shaft furnace 100 is controlled to exceed 0 MPa, thereby efficiently reducing the iron oxide raw material in the furnace and significantly increasing the metallization rate of reduced iron.

[0021] 3. Relationship between hydrogen gas intensity V and reducing gas temperature T In this embodiment, the hydrogen gas intensity V (Nm³) supplied to the shaft furnace 100 is ３ The ratio of ( / t - DRI) and the temperature T (°C) of the reducing gas supplied to the shaft furnace 100 are such that V ≥ 0.0094 × T ２ The system is characterized by being controlled to satisfy the relationship (1) -20.5 × T + 12400, and by being controlled so that the gauge pressure at the top of the shaft furnace 100 exceeds 0 MPa. Here, the unit of hydrogen gas intensity V is "Nm ３ In " / t-DRI", "DRI" means reduced iron, and "t-DRI" means 1 ton of reduced iron, or "Nm ３ " / t-DRI" refers to the amount of hydrogen gas supplied per ton of reduced iron (Nm³). ３ This means that, in this embodiment, by controlling the gauge pressure at the top of the shaft furnace 100 to exceed 0 MPa, the absolute pressure inside the shaft furnace 100 is naturally controlled to exceed atmospheric pressure.

[0022] According to the inventors' findings, V ≥ 0.0094 × T ２When the equation is -20.5 × T + 12400, the metallization rate of reduced iron increases sufficiently, and in the region where V is greater than or equal to this equation, sufficient heat is likely to be generated inside the shaft furnace 100. When the heat inside the furnace is sufficient, the hydrogen reduction reaction can be promoted by increasing the pressure inside the furnace, and a higher metallization rate can be ensured inside the shaft furnace 100 compared to when the pressure inside the furnace is not increased. That is, V ≥ 0.0094 × T ２ When the relationship (1) -20.5 × T + 12400 is satisfied, and the gauge pressure at the top of the shaft furnace 100 is controlled to exceed 0 MPa, it is considered that the pressure inside the furnace is increased when sufficient heat is secured inside the furnace, the hydrogen reduction reaction is promoted, and the metallization rate can be improved. The relationship between the hydrogen gas intensity V and the temperature T will be explained in more detail in the examples described later.

[0023] According to the inventors' findings, a higher metallization rate can be secured inside the shaft furnace 100 when the hydrogen gas intensity V and temperature T are controlled to satisfy the following relationship (2), and the gauge pressure at the top of the shaft furnace 100 is controlled to exceed 0 MPa. Furthermore, an even higher metallization rate can be secured inside the shaft furnace 100 when the hydrogen gas intensity V and temperature T are controlled to satisfy the following relationship (3), and the gauge pressure at the top of the shaft furnace 100 is controlled to exceed 0 MPa. Relationships (2) and (3) will be explained in more detail in the embodiments described later. V ≥ 0.0103 × T ２ -22.6 × T + 13749 …(2) V ≥ 0.0126 × T ２ -27.2 × T + 16226 …(3)

[0024] In this embodiment, when the above relationship (1) is satisfied, the gauge pressure at the top of the shaft furnace 100 should be controlled to exceed 0 MPa, and the upper limit of the gauge pressure is not particularly limited. However, even if the gauge pressure is excessively increased, the effect of improving the metallization rate will saturate. According to the inventors' findings, the higher the temperature T of the reducing gas supplied to the shaft furnace 100, the lower the gauge pressure at which the effect of improving the metallization rate saturates. From this viewpoint, in this embodiment, (1) the temperature T may be 1100°C or higher and the gauge pressure at the top of the furnace may be 0.4 MPa or less, (2) the temperature T may be 1000°C or higher and less than 1100°C and the gauge pressure at the top of the furnace may be 0.6 MPa or less, and (3) the temperature T may be 950°C or higher and less than 1000°C and the gauge pressure at the top of the furnace may be 0.7 MPa or less. The relationship between temperature T and required gauge pressure will be explained in more detail in the embodiments described later.

[0025] In this embodiment, for example, pressure adjustment chambers 201 and 202 are connected to the top side and the reduced iron discharge side of the shaft furnace 100, respectively, thereby controlling the pressure inside the shaft furnace 100, and the gauge pressure at the top of the shaft furnace 100 can exceed 0 MPa. That is, the gauge pressure at the top of the shaft furnace 100 can be appropriately changed and controlled by the pressure adjustment chambers 201, 202, etc., provided in the shaft furnace. The specific form of the pressure adjustment chambers 201 and 202 is not particularly limited, and any chamber capable of controlling the pressure inside the furnace and at the top of the furnace is acceptable.

[0026] In this embodiment, the hydrogen gas intensity V (Nm³) supplied to the shaft furnace is also present. ３ / t-DRI) is the amount of hydrogen gas supplied to the shaft reactor per unit time F (Nm³). ３ From the hydrogen gas production rate per unit time P(t-DRI / h) and the production rate of reduced iron per unit time P(t-DRI / h), the hydrogen gas intensity V = F / P(Nm³ / h) ３It can be determined as ( / t - DRI). The "amount of hydrogen gas supplied to the shaft furnace per unit time F" can be determined from the amount of reducing gas supplied to the shaft furnace per unit time and the hydrogen gas concentration of the reducing gas. The "amount of reducing gas supplied to the shaft furnace" can be directly determined, for example, by a flow meter installed between the outlet of the reducing gas supply device and the reducing gas supply port of the shaft furnace. The "amount of reduced iron produced per unit time" can be determined, for example, by directly measuring the weight of reduced iron produced per unit time. The "temperature T (°C) of the reducing gas supplied to the shaft furnace" can be determined, for example, by measuring the temperature of the reducing gas with a thermometer installed at the reducing gas supply port of the shaft furnace. The "gauge pressure at the top of the shaft furnace" can be said to be substantially the same as the pressure on the upper surface of the packed bed inside the shaft furnace. That is, the "gauge pressure at the top of the shaft furnace" can be determined, for example, by measuring the pressure in the space inside the shaft furnace that is above the packed bed with a pressure gauge. In this application, "gauge pressure" refers to the value calculated as "gauge pressure = absolute pressure - atmospheric pressure (0.1 MPa)". In other words, in this embodiment, "gauge pressure at the top of the furnace is greater than 0 MPa" means "absolute pressure at the top of the furnace is greater than 0.1 MPa". "gauge pressure at the top of the furnace is 0.4 MPa or less" means "absolute pressure at the top of the furnace is 0.5 MPa or less", "gauge pressure at the top of the furnace is 0.6 MPa or less" means "absolute pressure at the top of the furnace is 0.7 MPa or less", and "gauge pressure at the top of the furnace is 0.7 MPa or less" means "absolute pressure at the top of the furnace is 0.8 MPa or less".

[0027] 4. Other Matters 4.1 Reuse of Exhaust Gas As shown in Figure 2, in this embodiment, exhaust gas from the shaft furnace 100 may be reused for the production of reducing gas. The exhaust gas from the shaft furnace 100 may contain hydrogen gas, water vapor, etc. At least a portion of the gases other than hydrogen gas (water vapor, etc.) contained in the exhaust gas may be removed in the reducing gas production device 300. In addition, raw material gas may be supplied to the reducing gas production device 300 via a separate system from the exhaust gas. The raw material gas may be, for example, hydrogen gas. In the reducing gas production device 300, the exhaust gas from which water vapor, etc. has been removed and the raw material gas are mixed and heated to produce reducing gas.

[0028] 4.2 Cooling Process In this embodiment, the reduction process of the iron oxide raw material 10 in the shaft furnace 100 has been described in detail, but in addition to the reduction process, a cooling process and a carburizing process may be performed downstream of the reduction process in the shaft furnace 100. That is, the shaft furnace 100 may be provided with a cooling gas supply port for supplying cooling gas and a cooling gas outlet 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 on the inside of the side wall of the furnace. The cooling gas outlet may be provided on the side wall of the furnace.

[0029] 4.3 Reduced Iron In this embodiment, at least a portion of the iron oxide contained in the iron oxide raw material 10 is reduced by the above reduction reaction to obtain reduced iron 20, which is a solid reactant containing at least metallic iron. In addition to metallic iron, the reduced iron 20 may also contain unreduced iron oxide, silicon dioxide, aluminum oxide, etc. The reduced iron 20 containing metallic iron can be recovered from the lower part of the shaft furnace 100 (below the reducing gas supply position).

[0030] 4.4 Shaft Furnace In the shaft furnace 100, the raw material supply port is provided, for example, at the top of the shaft furnace 100 (for example, the top), the reducing gas supply port is provided, for example, on the side wall of the shaft furnace 100 below the raw material supply port (particularly below the position that becomes the reduction zone of the shaft furnace 100), the reduced iron discharge port is provided, for example, below the reducing gas supply port (for example, at the bottom of the shaft furnace 100), and the gas discharge port is provided, for example, above the reducing gas supply port (for example, at the top of the shaft furnace 100, in a part different from the raw material supply port). Furthermore, as described above, the shaft furnace 100 may be equipped with pressure adjustment chambers 201 and 202 on the top side and the reduced iron discharge side.

[0031] 5. Effects As described above, when producing reduced iron 20 by a hydrogen reduction process using a shaft furnace 100, the hydrogen gas intensity V (Nm³) is as described above. ３ The metallization rate of reduced iron 20 is easily increased when the (t-DRI) and the above temperature T (°C) are controlled to satisfy any of the above relationships (1) to (3), and the gauge pressure at the top of the furnace is controlled to exceed 0 MPa.

[0032] The effects of the technology of this disclosure will be explained in more detail below with reference to examples, but the technology of this disclosure is not limited to the following examples. In the following examples, the influence of the furnace pressure during hydrogen reduction in a shaft furnace on the reduction completion time (furnace height position) was investigated by simulation using a one-dimensional mathematical model.

[0033] 1. Range in which the effect of increased furnace pressure occurs: In a direct reduction process using a shaft furnace, when hydrogen gas is used as the reducing gas, the endothermic effect of hydrogen reduction causes a heat deficiency inside the furnace, and Fe ３ O ４ -FeO reduction equilibrium is easily reached. ３ O ４ - The state inside the furnace at FeO reduction equilibrium is schematically shown, for example, as in Figure 3. In Figure 3, the dotted outline indicates the reduction zone inside the shaft furnace. In the reduction zone, as indicated by the black arrows, the iron oxide raw material (Fe) supplied from the top of the furnace... ２ O ３While the iron oxide raw material moves downward, hydrogen gas, supplied from the furnace bottom at a unit consumption V and temperature T, moves upward, as indicated by the white arrow. In this way, the iron oxide raw material supplied from above and the hydrogen gas supplied from below come into contact, reducing the iron oxide raw material (Fe ２ O ３ →Fe ３ O ４ The reaction (→FeO→Fe) proceeds, and ultimately reduced iron with a metallization rate of R% is obtained. For example, 1 mol of Fe ３ O ４ If all of it is reduced to metallic iron (Fe) and reduced iron with a 100% metallization rate is obtained, the amount of metallic iron (Fe) produced will be 3 mol.

[0034] The present inventors, assuming the furnace conditions shown in Figure 3 when the reducing gas supplied to the shaft furnace 100 contains 100% by volume of hydrogen gas, calculate the heat balance from the reaction stagnation region to the reducing gas supply port, and determine the hydrogen gas intensity V (Nm³) supplied to the shaft furnace when the metallization rate of reduced iron is R%. ３ The relationship between ( / t-DRI) and the supply temperature T (°C) of the reducing gas was determined. Here, the reduction reaction: Fe ３ O ４ +H ２ = 3FeO + H ２ The equilibrium temperature at O ​​was set to 570°C, the equilibrium constant to K, and the equilibrium composition to 1 / (1+K). Then, assuming that the metallization rate of reduced iron is 90%, the heat-matter balance was calculated, and the vertical axis was plotted on the hydrogen gas intensity V (Nm). ３ When the relationship between V and T was plotted and graphed with the supply temperature T (°C) of the reducing gas as the x-axis (where T is the x-axis), as shown in Figure 4, V = 0.0094 × T ２The relationship -20.5 × T + 12400 was obtained. This means that when this equation is satisfied, the inside of the shaft furnace is in equilibrium. In the direction in which the furnace heat decreases from the direction of this equation, that is, in the region where V is below the boundary of this equation (the lower region of the graph in Figure 4), the furnace heat will be insufficient, and the equilibrium state will not change. On the other hand, in the direction in which the furnace heat increases from the direction of this equation, that is, in the region where V is above the boundary of this equation (the upper region of the graph in Figure 4), the furnace heat will be sufficient, and the equilibrium state will be broken. Thus, when the heat inside the furnace is sufficient, the hydrogen reduction reaction can be promoted by increasing the pressure inside the furnace, and it is thought that a higher metallization rate can be secured inside the shaft furnace compared to when the pressure inside the furnace is not increased. That is, hydrogen gas intensity V (Nm ３ The ratio of ( / t - DRI) to the supply temperature T (°C) of the reducing gas is such that V ≥ 0.0094 × T ２ It is believed that by controlling the furnace to satisfy the relationship -20.5 × T + 12400, and by controlling the gauge pressure at the top of the shaft furnace to exceed 0 MPa, the pressure inside the furnace increases when sufficient heat is secured inside the furnace, promoting the hydrogen reduction reaction and significantly improving the metallization rate.

[0035] Furthermore, assuming that the metallization rate of reduced iron is 95%, the heat and mass balance is taken, and the vertical axis is plotted on the hydrogen gas intensity V (Nm³). ３ When the relationship between V and T was plotted and graphed with the supply temperature T (°C) of the reducing gas as the x-axis (where T is the x-axis), as shown in Figure 4, V = 0.0103 × T ２ The relationship -22.6 × T + 13749 is obtained, and assuming that the metallization rate of reduced iron is 100%, the heat and mass balance is taken, and the vertical axis is set to hydrogen gas intensity V (Nm). ３ When the relationship between V and T was plotted and graphed with the supply temperature T (°C) of the reducing gas as the x-axis (where T is the x-axis), as shown in Figure 4, V = 0.0126 × T ２The relationship of -27.2×T + 16226 was obtained. In the region where V is greater than or equal to these equations as the boundary line (the upper region of the graph in FIG. 4), the heat inside the shaft furnace is more sufficient. In such a case, by increasing the pressure inside the furnace, it is considered that the hydrogen reduction reaction can be further promoted. That is, the hydrogen gas unit V (Nm ３ / (t - DRI)) and the supply temperature T (°C) of the reducing gas are such that V ≥ 0.0103×T ２ -22.6×T + 13749, and by controlling so that the gauge pressure at the furnace top exceeds zero MPa, it is easier to ensure a more significant effect of improving the metallization rate. The hydrogen gas unit V (Nm ３ / (t - DRI)) and the supply temperature T (°C) of the reducing gas are such that V ≥ 0.0126×T ２ -27.2×T + 16226, and by controlling so that the gauge pressure at the top of the shaft furnace exceeds zero MPa, it is easier to ensure an even more significant effect of improving the metallization rate.

[0036] 2. Relationship between the supply temperature of the reducing gas and the effect of increasing the furnace pressure Hydrogen gas (100% by volume) was adopted as the reducing gas. With the hydrogen gas unit V: 1900 Nm ３ / (t - DRI), the supply temperature of the hydrogen gas was set at 900 - 1100 °C, and the effect of increasing the furnace pressure was examined. For the examination, numerical simulation was performed using the one-dimensional model described in paragraph 0012 of Patent Document 1 (International Publication No. 2021 / 241272). The calculation conditions are as follows. ・Furnace shape Furnace height: 5 m, ２ Furnace diameter: 6 m・Reducing gas ３ H ２ / CO: 100 / 0・Supply temperature of the reducing gas ３ 900 - 1100 °C・Hydrogen gas unit ３ ３ ・Residence time in the furnace 70 minutes (raw material descent speed: 4.3 m / h)​​

[0037] The calculation results are shown in Figures 5 and 6A-C. In Figure 5, the vertical axis represents the height at which the reduction of iron oxide raw material is completed (the height at which the metallization rate reaches 100%; reduction completion height), with the height of the raw material level (stock line) at the top of the shaft furnace set to 0 and the height of the reducing gas supply port (lower end of the reduction zone) at the bottom of the furnace set to 1. The horizontal axis in Figure 5 represents the top pressure (gauge pressure) (MPa). In Figures 6A-C, the vertical axis represents the relative height (relative height) with the height of the raw material level (stock line) at the top of the furnace set to 0 and the height of the reducing gas supply port (lower end of the reduction zone) at the bottom of the furnace set to 1. The upper horizontal axis represents the metallization rate (%) and hydrogen utilization rate (%) of the iron oxide raw material, and the lower horizontal axis represents the temperature of the reducing gas inside the shaft furnace (°C). From the calculation results shown in Figures 5 and 6A-C, the following can be said.

[0038] As shown in Figure 5, when the reducing gas supply temperature is 900°C, the height at which the metallization rate reaches 100% does not substantially change even when the furnace top pressure is increased, indicating that the reduction-promoting effect due to the pressure increase is small. As shown in Figure 5, when the reducing gas supply temperature is 950°C, the height at which the metallization rate reaches 100% rises with increasing furnace top pressure, and the reduction rate improves significantly up to a furnace top pressure of 0.7 MPa (gauge pressure). Also, as shown in Figure 5, when the reducing gas supply temperature is 1000°C, the height at which the metallization rate reaches 100% rises with increasing furnace top pressure, and the reduction rate improves significantly up to a furnace top pressure of 0.6 MPa (gauge pressure). Also, as shown in Figure 5, when the reducing gas supply temperature is 1100°C, the height at which the metallization rate reaches 100% rises with increasing furnace top pressure, and the reduction rate improves significantly up to a furnace top pressure of 0.4 MPa (gauge pressure). Furthermore, as shown in Figure 6A, when the reducing gas supply temperature is 900°C, increasing the pressure does not significantly increase the reduction completion height. However, as shown in Figures 6B and 6C, when the reducing gas supply temperature is 950°C and 1000°C, increasing the pressure does increase the reduction completion height. Therefore, it is possible to enjoy the advantages of reducing equipment costs by lowering the furnace height, or increasing the production speed without changing the furnace height.

[0039] 3. Supplementary Information: In the above embodiment, the case in which hydrogen gas (100% by volume) is used as the reducing gas was illustrated. However, even when the reducing gas includes other gases along with hydrogen gas, V ≥ 0.0094 × T ２ It is believed that when the relationship -20.5 × T + 12400 is satisfied, the gauge pressure at the top of the shaft furnace exceeds 0 MPa, thereby promoting the hydrogen reduction reaction and improving the metallization rate. This is because gases other than hydrogen gas do not undergo an endothermic reaction with iron oxide (they contribute to the temperature rise or temperature maintenance inside the furnace), so the more gases other than hydrogen gas contained in the reducing gas increase, the more likely it is that there will be a heat surplus inside the furnace. However, if the proportion of gases other than hydrogen gas contained in the reducing gas is too high, the endothermic reaction by hydrogen gas and the associated problem of insufficient heat inside the furnace are unlikely to occur in the first place. The technology of this disclosure is considered to solve the problems that specifically arise when the reducing gas supplied to the shaft furnace contains a large amount of hydrogen gas. As far as the inventors have confirmed, when the reducing gas contains 80% or more by volume of hydrogen gas, the above problem of insufficient heat tends to become apparent, or in other words, the advantageous effects of the technology of this disclosure tend to be enjoyed.

[0040] 4. Summary From the above results, it was found that when reduced iron is produced by reducing iron oxide raw materials with reducing gas inside a shaft furnace, a significant effect due to the increase in furnace pressure can be obtained when the following requirements (A), one of requirements (B1) to (B3), and requirement (C) are met. (A) The reducing gas contains 80% or more by volume of hydrogen gas. (B1) The hydrogen gas intensity V (Nm³) supplied to the shaft furnace. ３ The relationship between ( / t - DRI) and the temperature T (°C) of the reducing gas supplied to the shaft furnace is as follows (1): V ≥ 0.0094 × T ２ -20.5 × T + 12400 …(1) is controlled to satisfy this condition. (B2) The hydrogen gas intensity V and the temperature T have the following relationship (2): V ≥ 0.0103 × T ２-22.6 × T + 13749 …(2) is controlled to satisfy this condition. (B3) The relationship between the hydrogen gas intensity V and the temperature T is as follows (3): V ≥ 0.0126 × T ２ (3) The following is controlled: (c) The gauge pressure at the top of the shaft furnace is controlled to be greater than 0 MPa.

[0041] Furthermore, it has been found that the effect of increased furnace pressure becomes even more pronounced when the following requirements (D) to (F) are met: (D) When the temperature T is 1100°C or higher, the gauge pressure at the top of the furnace is 0.4 MPa or less (absolute pressure at the top of the furnace is 0.5 MPa or less). (E) When the temperature T is 1000°C or higher and less than 1100°C, the gauge pressure at the top of the furnace is 0.6 MPa or less (absolute pressure at the top of the furnace is 0.7 MPa or less). (F) When the temperature T is 950°C or higher and less than 1000°C, the gauge pressure at the top of the furnace is 0.7 MPa or less (absolute pressure at the top of the furnace is 0.8 MPa or less).

[0042] 10 Iron oxide raw material 20 Reduced iron 100 Shaft furnace 201, 202 Pressure adjustment chamber 300 Reduced gas production equipment

Claims

1. A method for producing reduced iron, comprising reducing an iron oxide raw material with a reducing gas inside a shaft furnace, wherein the reducing gas contains 80% or more by volume of hydrogen gas, and the hydrogen gas intensity V (Nm³) supplied to the shaft furnace. ３ The relationship between ( / t - DRI) and the temperature T (°C) of the reducing gas supplied to the shaft furnace is as follows (1): V ≥ 0.0094 × T ２ A method for producing reduced iron, wherein the process is controlled to satisfy -20.5 × T + 12400 …(1), and the gauge pressure at the top of the shaft furnace is controlled to exceed 0 MPa.

2. A method for producing reduced iron according to claim 1, wherein the hydrogen gas intensity V and the temperature T have the following relationship (2): V ≥ 0.0103 × T ２ A method for producing reduced iron, controlled to satisfy -22.6 × T + 13749 …(2).

3. A method for producing reduced iron according to claim 1, wherein the hydrogen gas intensity V and the temperature T have the following relationship (3): V ≥ 0.0126 × T ２ A method for producing reduced iron, controlled to satisfy -27.2 × T + 16226 …(3).

4. A method for producing reduced iron according to any one of claims 1 to 3, wherein the temperature T is 1100°C or higher and the gauge pressure at the top of the furnace is 0.4 MPa or less, or the temperature T is 1000°C or higher and less than 1100°C and the gauge pressure at the top of the furnace is 0.6 MPa or less, or the temperature T is 950°C or higher and less than 1000°C and the gauge pressure at the top of the furnace is 0.7 MPa or less.

5. A method for producing reduced iron according to any one of claims 1 to 4, wherein the temperature T is 800°C or higher and 1150°C or lower.

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