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WO2025187535A1 - Procédé de production de fer réduit - Google Patents

Procédé de production de fer réduit

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Publication number
WO2025187535A1
WO2025187535A1 PCT/JP2025/006912 JP2025006912W WO2025187535A1 WO 2025187535 A1 WO2025187535 A1 WO 2025187535A1 JP 2025006912 W JP2025006912 W JP 2025006912W WO 2025187535 A1 WO2025187535 A1 WO 2025187535A1
Authority
WO
WIPO (PCT)
Prior art keywords
fluidized bed
reduction
raw material
reduced iron
material powder
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
PCT/JP2025/006912
Other languages
English (en)
Japanese (ja)
Other versions
WO2025187535A8 (fr
Inventor
昌史 牛尾
和也 藤野
孝 飯島
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nippon Steel Corp
Original Assignee
Nippon Steel Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nippon Steel Corp filed Critical Nippon Steel Corp
Publication of WO2025187535A1 publication Critical patent/WO2025187535A1/fr
Publication of WO2025187535A8 publication Critical patent/WO2025187535A8/fr
Pending legal-status Critical Current
Anticipated expiration legal-status Critical

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21B—MANUFACTURE OF IRON OR STEEL
    • C21B13/00—Making spongy iron or liquid steel, by direct processes
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21B—MANUFACTURE OF IRON OR STEEL
    • C21B13/00—Making spongy iron or liquid steel, by direct processes
    • C21B13/06—Making spongy iron or liquid steel, by direct processes in multi-storied furnaces
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21B—MANUFACTURE OF IRON OR STEEL
    • C21B13/00—Making spongy iron or liquid steel, by direct processes
    • C21B13/14—Multi-stage processes processes carried out in different vessels or furnaces

Definitions

  • the present invention relates to a method for producing reduced iron.
  • This application claims priority to Japanese Patent Application No. 2024-036243, filed March 8, 2024, and Japanese Patent Application No. 2024-053725, filed March 28, 2024, the contents of which are incorporated herein by reference.
  • Direct reduction has been known as one of the ironmaking methods for obtaining iron by reducing raw materials containing iron oxide. Compared to blast furnaces, direct reduction has advantages such as lower plant construction costs and easier operation. Direct reduction methods include those using shaft furnaces and fluidized beds. Shaft furnaces use raw materials agglomerated into pellets or other pellets. Fluidized beds are a processing method in which solid particles are blown upward with a fluid such as gas to create a suspended state, and the large contact area is utilized to efficiently promote chemical reactions and heat exchange. When using a fluidized bed in an ironmaking process to obtain reduced iron from fine iron ore, the costs and CO2 emissions associated with agglomeration are eliminated compared to shaft furnaces. Furthermore, these direct reduction methods can use hydrogen as a reducing agent. The use of hydrogen enables the reduction of CO2 emissions.
  • fluidized bed reduction When reducing iron ore powder using a fluidized bed (hereinafter, reduction of iron ore powder using a fluidized bed may be referred to as “fluidized bed reduction"), it is important to avoid the phenomenon of iron ore powder agglomerating together within the fluidized bed, known as sticking, and stagnation of the reduction reaction.
  • the gas flow rate is set according to the specific gravity and particle size of the powder, and a fluidized bed is created in the processing vessel at a flow rate equal to or greater than the minimum gas flow rate (minimum fluidization velocity) required for the powder to become fluidized.
  • minimum gas flow rate minimum fluidization velocity
  • processing is performed at the highest possible temperature to maximize the reduction rate within a range believed to achieve stable fluidity without sticking.
  • sticking is more likely to occur at higher temperatures and with higher iron concentrations in the raw iron ore powder. Therefore, in conventional processes, to avoid sticking and increase productivity, operation is often performed at a temperature range of approximately 600 to 750°C when using hydrogen gas.
  • Non-Patent Document 1 operates at 630 to 650°C. This is because, with iron ore for direct reduced iron production, which contains approximately 64% or more iron by mass and has been used in previous operations, sticking often occurs at temperatures above 750°C.
  • stagnation of the reduction reaction of iron ore powder (hereinafter, stagnation of the reduction reaction may be referred to as reduction stagnation), it is known that when metallic iron is formed on the surface of the iron ore powder during the reduction process, the progress of the reduction reaction may stagnate depending on the form of the metallic iron that covers the iron ore powder, and the more reduction progresses, the more difficult it may be to improve the reduction rate.
  • Non-Patent Document 2 describes that when a magnetite reagent is used, a significant reduction stagnation phenomenon occurs when dense iron is produced from a dense magnetite phase.
  • Non-Patent Document 2 also indicates that an effective method of avoiding the production of dense iron is to perform an oxidation treatment in advance to convert the magnetite phase to a hematite phase, and then refine the particle structure as the phase changes from the hematite phase.
  • the raw iron ore used in actual operations varies in chemical composition, particle size distribution, properties, etc. depending on the place of origin and mine. Therefore, when designing actual operational processes, it is necessary to consider different measures depending on the type of ore.
  • Non-Patent Document 3 discloses research into the reduction rate using actual iron ore.
  • Non-Patent Document 3 considers that the reduced iron produced on the periphery of the iron ore sinters at a temperature of around 700°C, which reduces the permeability of the water vapor generated during reduction, causing the unreduced material inside the iron ore to become difficult to reduce.
  • Patent Document 1 discloses a technology for suppressing reduction stagnation in a fluidized bed by adjusting the reduction conditions in the first preheated fluidized bed of a multi-stage fluidized bed, thereby suppressing the formation of dense, difficult-to-reduc magnetite from hematite within the preheated fluidized bed and increasing the metallization rate of the final reduced product.
  • Patent Document 2 describes a technology for suppressing the formation of high-density magnetite phases by setting the residence time at approximately 400 to 580°C as short as possible in order to suppress the formation of difficult-to-reduc magnetite in the first fluidized bed in a multi-stage fluidized bed reduction process.
  • Non-Patent Document 3 does not point out that the tendency for reduction stagnation itself differs depending on the ore type. According to the inventors' knowledge, the occurrence and degree of reduction stagnation in actual iron ore powder varies depending on the ore type. Therefore, for various ore types and their differences in specific components and properties, the tendency for reduction stagnation cannot be determined until reduction is actually carried out, making process design difficult. Furthermore, in actual plant operation, it is conceivable that multiple ore types will be mixed, and in this case, if ore types with different characteristics are mixed, it is difficult to design a process in terms of the reduction behavior of the ore powder after mixing.
  • the present invention has been developed in consideration of the above problems, and aims to provide a method for producing reduced iron that efficiently produces reduced iron with a high reduction rate while avoiding sticking and stagnation of the reduction reaction in a process for reducing iron ore powder using a fluidized bed, and that can reduce equipment costs.
  • a method for producing reduced iron according to one aspect of the present invention is a method for producing reduced iron by bringing a reducing gas into contact with a raw material powder containing iron oxide using a fluidized bed, and includes a fluidized bed reduction step of reducing the raw material powder, which has a crystal water content of 3.5 mass% or less, at a temperature of 400°C or higher and 590°C or lower.
  • the raw material powder may be raw material powder that has not been subjected to a step of removing water of crystallization by heat treatment at 105°C or higher.
  • the raw material powder may have a crystal water content of 3.0 mass % or less.
  • the raw material powder may have a crystal water content of 1.0 mass % or less.
  • the raw material powder may be a mixed raw material powder obtained by mixing a plurality of different iron ore powders each containing iron oxide, and at least one type of raw material powder among the plurality of different iron ore powders may have a crystal water content of 5.0 mass % or more.
  • the temperature may be 400°C or higher and 560°C or lower.
  • the temperature may be 500°C or higher and 530°C or lower.
  • the reducing gas may be hydrogen gas.
  • the raw material powder in the fluidized bed reduction step, the raw material powder may be reduced until a metallization rate reaches 70% or more.
  • the method for producing reduced iron according to any one of the above [1] to [9] may include an oxidation suppression step of suppressing oxidation of the reduced iron after the fluidized bed reduction step.
  • the oxidation suppression step may include a treatment for reducing a surface area of the reduced iron after the fluidized-bed reduction step before the raw material powder after the fluidized-bed reduction step is taken out into an oxidizing atmosphere.
  • the reduced iron in the treatment for reducing the surface area of the reduced iron, the reduced iron may be heat-treated at a temperature of 720°C or higher in an inert atmosphere.
  • the temperature in the fluidized bed in the fluidized bed heat treatment step may be set to 720°C or higher.
  • the fluidized bed in the fluidized bed heat treatment step may be a bubbling fluidized bed.
  • the non-oxidizing gas may be N2 gas or Ar gas.
  • the same fluidized bed may be used in the fluidized bed reduction step and the fluidized bed heat treatment step.
  • the present invention in a process for reducing iron ore powder using a fluidized bed, it is possible to efficiently obtain reduced iron with a high reduction rate while avoiding sticking and stagnation of the reduction reaction, and to reduce equipment costs.
  • FIG. 1 is a schematic diagram of a bubbling fluidized bed forming device.
  • FIG. 10 is a schematic diagram of another example of a bubbling fluidized bed forming apparatus.
  • FIG. 1 is a schematic diagram of a circulating fluidized bed forming apparatus.
  • FIG. 1 is a schematic diagram of a spouted fluidized bed forming device.
  • 1 is a schematic diagram showing an example of a reduced iron production facility equipped with one circulating fluidized bed forming device and three bubbling fluidized bed forming devices as reduction devices.
  • FIG. 1 is a graph showing the transition of the reduction rate during hydrogen reduction of each raw material powder in Example 1.
  • 2A is a graph showing the change in reduction rate during hydrogen reduction of powdered raw material B in Example 1
  • FIG. 2B is a graph showing the change in reduction rate.
  • 10 is a graph showing the transition of the reduction rate during hydrogen reduction of each raw material powder in Example 3.
  • 10 is a graph showing the transition of the reduction rate during hydrogen reduction of each mixed powder in Example 3.
  • a method for producing reduced iron according to an embodiment of the present invention is a method for producing reduced iron by bringing a reducing gas into contact with a raw material powder containing iron oxide using a fluidized bed, and includes a fluidized bed reduction step of reducing raw material powder having a crystal water content of 3.5 mass% or less at a temperature of 400°C or higher and 590°C or lower.
  • the raw material powder having a crystal water content of 3.5 mass % or less is reduced at a temperature of 400°C or higher and 590°C or lower.
  • a fluidized bed is used for the reduction of the raw material powder.
  • the fluidized bed may be one or more bubbling fluidized beds (BFB), one or more circulating fluidized beds (CFB), one or more spouted fluidized beds, or a combination thereof.
  • BFB bubbling fluidized beds
  • CFB circulating fluidized beds
  • a bubbling fluidized bed is a fluidized bed in which gas bubbles are formed in the fluidized bed of raw material powder.
  • the shape of the bubbles varies depending on the fluidization state, and in some fluidization states, clear bubbles may not be formed.
  • a circulating fluidized bed is a fluidized bed in which the gas flow rate is increased to circulate the raw material powder while entraining it with the gas.
  • a spouted fluidized bed has a protrusion section (gas blow-through section) from which the raw material powder is protruded at a high gas flow rate, and a moving bed in which the raw material powder accumulates around the protrusion section and moves from the top to the bottom, repeating the behavior of being caught up in the high gas flow rate at the bottom of the moving bed and being protruded from the protrusion section.
  • a protrusion section gas blow-through section
  • a moving bed in which the raw material powder accumulates around the protrusion section and moves from the top to the bottom, repeating the behavior of being caught up in the high gas flow rate at the bottom of the moving bed and being protruded from the protrusion section.
  • the raw material powder is a powder containing iron.
  • the raw material powder may be a powder obtained by mixing multiple different iron ore powders containing iron oxide (hereinafter, this may be referred to as a mixed raw material powder or a mixed powder).
  • a mixed raw material powder or a mixed powder When reducing a raw material powder containing a mixture of iron ore powders with different components and properties, it is possible to estimate, from the average crystallization water content of the mixed raw material powder, whether reduction at a low temperature is advantageous depending on the crystallization water content under various mixing conditions.
  • the raw material powder may be, for example, iron ore powder mined from an iron ore mine, iron ore powder obtained by crushing and sieving such iron ore powder, or powder discharged and recovered from various steelmaking processes.
  • the raw material powder include sinter feed, which has traditionally been used as a raw material for sintered ore, pellet feed, which is used as a raw material for pellets, magnetite concentrate, and steelmaking dust.
  • dust includes converter dust, which is generated in converters, as well as fine particles of partially unreduced ore and fine particles of reduced iron that may be generated in direct reduced iron manufacturing plants, such as fluidized bed reducers and shaft furnace reducers.
  • the mixed powder is obtained by blending iron ore powders obtained from different supply sources. In particular, in iron-making processes, such as the blast furnace process, it is important to adjust the composition of the raw materials as much as possible in order to obtain the desired steel products.
  • Raw material powder used for iron production generally contains approximately 50 to 70 mass% Fe. From the viewpoint of reducing the energy required for the process of separating impurity components and suppressing the ore consumption rate, it is preferable to use raw material powder containing 55 to 68 mass% Fe. Therefore, it is preferable to use mixed powder containing 55 to 68 mass% Fe.
  • the crystal water content of the raw material powder is 3.5% by mass or less.
  • Raw material powder with a low crystal water content has a dense mineral structure of the particles constituting the raw material powder.
  • the metallic iron formed on the surface of the mixed powder is in a dense state and covers the mixed powder in a two-dimensional film shape. This makes reduction more likely to stagnate.
  • the crystal water content of the raw material powder is 3.5% by mass or less, reduction stagnation at low temperatures of 590°C or less can be suppressed, making it possible to efficiently obtain reduced iron with a high reduction rate.
  • the crystal water content is preferably 3.0% by mass or less, and more preferably 1.0% by mass or less.
  • the raw material powder used in this embodiment preferably has a crystal water content of 3.5% by mass or less when not subjected to heat treatment such as calcination above 105°C, except for drying treatment performed to remove attached moisture.
  • heat treatment such as calcination above 105°C
  • Examples of processes in which the heating temperature exceeds 105°C include ore preheating, granulation, and pre-oxidation. This is because, in the case of ores containing a large amount of crystal water, the crystal water is released during the heating process before the reduction process, causing cracks and pores to form in the particles that make up the raw material powder.
  • the drying process is a process that primarily removes adhering moisture, and is carried out in a dry air or inert gas environment at a temperature of 200°C or less, for example, in the range of 100-105°C.
  • the crystal water content of at least one of the iron ore powders be 5.0% by mass or more.
  • Iron ore powder with a high crystal water content is not suitable for low-temperature reduction on its own, but the inventors have discovered that by mixing it with iron ore powder with a low crystal water content, it is possible to effectively apply the reduction process in a low-temperature range. Even if the crystal water content of at least one iron ore powder is 5.0% by mass or more, as long as the crystal water content of the mixed powder is 3.5% by mass or less, reduction stagnation can be suppressed in a low temperature range of 590°C or less, and reduced iron with a high reduction rate can be efficiently obtained.
  • the content of water of crystallization is determined in accordance with JIS M 8211:2023 "Iron ore powder - Method for determining water of synthesis - Karl Fischer titration method.” In other words, it can be calculated as the weight ratio of water generated during heating of iron ore powder from 105°C to 950°C.
  • the median diameter of the raw material powder is less than 50 ⁇ m, it will exhibit poor fluidity during processing in a fluidized bed, so the median diameter of the raw material powder is 50 ⁇ m or greater.
  • the median diameter of the raw material powder is preferably 50 ⁇ m or greater and 8 mm or less.
  • a particle size of 8 mm or less is within the particle size range of iron ore powder used as normal sinter feed. In a fluidized bed, reduction is performed using gas.
  • the median diameter of the raw material powder is a small particle size within the above range, which results in a relatively large surface area.
  • the median diameter of the mixed powder is more preferably 50 ⁇ m or greater and 5 mm or less, and even more preferably 50 ⁇ m or greater and 2 mm or less.
  • the median diameter of the raw material powder can be measured by the following method. Specifically, the volume-based particle diameter d50 in the under-sieve cumulative distribution measured using a dry sieve and a wet laser diffraction particle size analyzer (Malvern Panalytical, Mastersizer 3000) is taken as the median diameter of the mixed powder.
  • the measurement conditions for the laser diffraction particle size analyzer are: dispersion medium: water, dispersion medium refractive index: 1.33, particle refractive index: 2.918 (refractive index of iron oxide Fe2O3 ).
  • the raw material powder is first sieved using dry sieves with nominal mesh sizes of 8.0 mm and 1.0 mm, and the mixed powder that falls on the 8.0 mm sieve is removed.
  • the mixed powder that falls on the 1.0 mm sieve is then sieved using a plurality of sieves with different mesh sizes, for example, 6.7 mm, 5.6 mm, 4.75 mm, 4.0 mm, 3.35 mm, 2.8 mm, 2.36 mm, 2.0 mm, 1.7 mm, 1.4 mm, and 1.18 mm, and the particle size distribution is measured.
  • a plurality of sieves with different mesh sizes, for example, 6.7 mm, 5.6 mm, 4.75 mm, 4.0 mm, 3.35 mm, 2.8 mm, 2.36 mm, 2.0 mm, 1.7 mm, 1.4 mm, and 1.18 mm
  • the particle size distribution is measured for the raw material powder that falls below the 1.0 mm sieve.
  • raw material powder is sampled from any five locations among the sample, and the particle size distribution is measured for each location using the laser diffraction particle size analyzer. The particle size distribution is then calculated by averaging the measurement results from the five locations.
  • the average particle size distribution over 1.0 mm measured by sieving and the particle size distribution of 1.0 mm or less measured by a laser diffraction particle size analyzer are combined to determine the overall particle size distribution of the raw material powder that sieved under the 8.0 mm sieve. Finally, using this overall particle size distribution, the smaller particle size distribution is integrated, and the particle diameter d50 at which the integrated value of the relative particle amount on a volume basis becomes 50% is defined as the median diameter.
  • multiple feeders may be provided in front of a mixed powder supply port that supplies mixed powder to a container that forms a fluidized bed inside, and different raw material powders may be supplied to each feeder, and mixed inside the container.
  • a mixing container may be provided between each feeder and the container, and the raw material powders may be mixed in the mixing container.
  • mixed powder which is a mixture of raw material powders mixed in advance, may be supplied to the container from the feeder through the mixed powder supply port.
  • the crystal water content and median diameter of the raw material powder may be quantified for each batch of that raw material powder.
  • the crystal water content and median diameter of the mixed powder may be quantified for the mixed powder, or may be quantified for each raw material powder before mixing, and calculated based on each quantified value and the mixing ratio.
  • Each raw material powder is divided into 100g portions using a divider capable of dividing the input powder into equal parts, and then 2g portions are removed using the cone quartering method. 3 random samples of powder from this are used for quantification.
  • the reducing gas may be any reducing gas.
  • the reducing gas include hydrogen gas, a mixed gas of hydrogen and nitrogen, a mixed gas of hydrogen and Ar, a mixed gas of hydrogen and water vapor, a mixed gas of hydrogen, water vapor, and nitrogen, CO gas, and a synthesis gas (a mixed gas of carbon monoxide and hydrogen).
  • the reducing gas may contain CH4 .
  • the reducing gas may also contain an inert gas.
  • the raw material powder is reduced by the reducing gas.
  • the reducing gas is preferably a gas containing hydrogen gas, and more preferably hydrogen gas. Hydrogen gas has a higher reduction rate than CO gas and does not generate carbon dioxide, which is generated when CO gas or synthesis gas is used, so that the environmental load is small.
  • the reducing gas preferably contains 30 vol% or more of hydrogen gas, and more preferably contains 50 vol% or more of hydrogen gas. From the viewpoint of CO2 reduction, a higher hydrogen gas content is preferable, and the reducing gas preferably contains 70 vol% or more of hydrogen gas.
  • the flow velocity of the reducing gas is equal to or greater than the minimum fluidization velocity of the fluidized bed.
  • the minimum fluidization velocity is the minimum gas flow velocity at which the pressure loss in the fluidized bed remains constant as the gas flow velocity increases, and iron ore powder will not fluidize below the minimum fluidization velocity.
  • the flow velocity of the reducing gas is, for example, 0.02 m/s or more and 20 m/s or less.
  • the flow velocity of the reducing gas is preferably 0.03 m/s or more and 10 m/s or less. From the perspective of stably fluidizing raw material powder with a large particle size, the flow velocity of the reducing gas is preferably at least approximately 1.2 times the minimum fluidization velocity of the raw material powder.
  • the flow velocity of the reducing gas is preferably 0.2 m/s or more and less than 1.0 m/s.
  • the flow velocity of the reducing gas for forming the bubbling fluidized bed is lower than the flow velocity of the reducing gas for forming the circulating fluidized bed, and very little raw material powder escapes from the bubbling fluidized bed.
  • the flow velocity of the reducing gas for forming the bubbling fluidized bed is more preferably 0.3 m/s or more and 0.8 m/s or less.
  • the flow velocity of the reducing gas is, for example, 1.0 m/s or more and 20 m/s or less. From the perspective of improving the reaction efficiency with the gas, which is one of the advantages of circulating fluidized beds, it is preferable to set the flow velocity of the reducing gas so that the difference between the average gas velocity and the average particle velocity (slip velocity) is large.
  • the flow velocity of the reducing gas is preferably 3.0 m/s or more and 10 m/s or less.
  • the flow rate of the reducing gas is the superficial velocity at which a fluidized bed is formed, and is the gas flow rate per unit time supplied divided by the cross-sectional area of the fluidized bed.
  • the flow rate of the reducing gas can be measured using a flow meter attached to the gas supply piping.
  • the minimum fluidization velocity can be experimentally measured using the following method.
  • the pressure drop in a fluidized bed can be determined by measuring the pressure difference between above and below the bed where the raw material powder is present (the difference in pressure between the gas reservoir below the distributor plate and the open space above the bed, as described below), and subtracting the pressure difference when no raw material powder is charged (the pressure drop through the distributor plate alone).
  • the pressure drop in the fluidized bed is plotted against the gas superficial velocity to determine the minimum gas flow rate at which the pressure drop stabilizes.
  • the gas flow rate is gradually reduced from a level sufficient for fluidization, and the minimum fluidization velocity is determined as the point at which the pressure drop begins to decrease from a constant range.
  • the pressure measurement locations do not need to be limited to the gas reservoir below the distributor plate and the open space above the bed. Pressure measurement locations can also be, for example, inside the fluidized bed and the open space above the bed, as long as they are pressure measurement locations at which the pressure drop in the fluidized bed can be measured.
  • the terminal velocity ut (m/s) of the raw material powder can be expressed by the following equation (1) when the raw material powder is approximated to a spherical shape to the first order:
  • g (m/s 2 ) is the acceleration of gravity
  • ⁇ p (kg/m 3 ) is the particle density of the raw material powder
  • ⁇ f (kg/m 3 ) is the density of the reducing gas
  • D p (m) is the median diameter of the raw material powder
  • C d ( ⁇ ) is the drag coefficient, which is arranged in terms of the Reynolds number Re and is expressed below using the Brown and Lawler approximation formula (formula (2)):
  • the temperature during reduction in the fluidized bed (reduction temperature) is between 400°C and 590°C.
  • a fluidized bed temperature of between 400°C and 590°C promotes the reduction reaction while avoiding reduction stagnation for the raw material powder with a low content of crystal water, enabling efficient production of reduced iron with a high reduction rate. While the reason why reduction stagnation is avoided at temperatures below 590°C is not entirely clear, the inventors speculate, based on the Fe-O phase diagram, that the wüstite phase, which is thermodynamically stable at temperatures above 570°C, may contribute to the densification of the iron. The inventors speculate that a temperature below 590°C reduces the likelihood of the wüstite phase forming during the reduction process, thereby avoiding reduction stagnation.
  • the temperature of the fluidization zone is between 400°C and 590°C.
  • the reduction temperature is preferably above 500°C.
  • the reduction temperature is preferably below 560°C, more preferably below 530°C.
  • a characteristic of fluidized beds is that if the raw material powder is sufficiently fluidized, the gas and material mix extremely well and the temperature within the fluidized bed is uniform, making temperature control in a fluidized bed easier than other reaction control methods.
  • One heating method is to surround the reaction vessel containing the fluidized bed with insulating material, and supply and mix particles and gas that have been preheated to a predetermined temperature. It is also possible to adjust the temperature within the fluidized bed to a predetermined temperature by heating the reaction vessel from the outside and exchanging heat with the vessel wall.
  • Temperature inside the fluidized bed is measured using a thermocouple whose tip is positioned in the fluidized part of the raw material powder.
  • the average residence time of the raw material powder in the reaction vessel may be determined taking into consideration the type of fluidized bed, the time required to achieve a desired reduction rate depending on the reducing gas components and temperature, etc.
  • the average residence time of the raw material powder retained in the bubbling fluidized bed is preferably 3 minutes or more and 180 minutes or less.
  • An average residence time of 3 minutes or more produces reduced iron with a high reduction rate.
  • an average residence time of 180 minutes or less maintains high processing efficiency as a reduction device.
  • an average residence time of 180 minutes or less prevents a decrease in the strength of the raw material powder due to excessive reduction, or the raw material powder being pulverized due to collisions between the raw material powder particles or between the raw material powder and the device during circulation, resulting in a decrease in the recovery efficiency of reduced iron. Therefore, an average residence time of 180 minutes or less is preferable.
  • the average residence time of the raw material powder retained in the bubbling fluidized bed is more preferably 5 minutes or more and 60 minutes or less.
  • the average residence time can be controlled by changing the reduction gas velocity, the amount of particles retained in the reaction vessel, the particle withdrawal rate, etc.
  • the average residence time of the iron ore powder in the circulating fluidized bed depends on the temperature of the reduction reaction, but is preferably 3 minutes or more and 180 minutes or less.
  • the average residence time for the raw material powder in the circulating fluidized bed is more preferably 5 minutes or more and 60 minutes or less. The reasons why the above average residence times are preferable are the same as when the fluidized bed is a bubbling fluidized bed.
  • the average residence time of the raw material powder in the spouted fluidized bed depends on the temperature of the reduction reaction, but is preferably 3 minutes or more and 180 minutes or less.
  • the average residence time of the raw material powder in the spouted fluidized bed is more preferably 5 minutes or more and 60 minutes or less. The reasons why the above average residence times are preferable are the same as when the fluidized bed is a bubbling fluidized bed.
  • the average residence time of the raw material powder can be calculated using the following method. That is, a fixed amount of ore powder with the same median diameter but different gangue components is added as tracer particles, and the change in the gangue component content of the discharged reduced iron powder is examined. The peak time period obtained, during which the content of the gangue components that characterize the added tracer ore powder is highest, is taken as the average residence time of the raw material powder. Using the above method, it is possible to experimentally measure the average residence time.
  • the reduction rate is preferably 70% or higher and 100% or lower.
  • the proportion of metallic iron on the surface of the raw material powder increases.
  • the metallic iron covers the surface of the raw material powder in a two-dimensional film, causing reduction to stagnate at temperatures between 600 and 800°C.
  • temperatures below 590°C the surface of the raw material powder is prevented from being covered in a two-dimensional film by metallic iron, allowing a high surface area to be maintained. If the reduction rate is low, the amount of metallic iron produced is small, and these differences due to reduction temperature do not occur, and the advantages of reduction at low temperatures are not realized.
  • a reduction rate of 70% or higher is preferable.
  • a reduction rate of 80% or higher is more preferable.
  • improvement in the reduction rate may stagnate even when reduced at low temperatures, reducing the significant difference due to the reduction temperature. Therefore, a reduction rate of 95% or lower is more preferable.
  • the reduction rate is set according to the purpose.
  • the reduction rate achieved is 90% or higher. If the reduction rate is 90% or higher, the final reduced iron product can be provided to users who, for example, refining in an electric furnace.
  • the reduced iron is fed as raw material into a blast furnace for the purpose of reducing the usage rate of reducing agents such as coke in the blast furnace, or for use in an electric furnace for producing molten iron, the reduction rate does not need to exceed 90%; for example, the reduction rate may be around 70-80%.
  • the reduction rate can be calculated, for example, by the following method. That is, approximately 0.1 g of raw material powder is weighed into a quartz cell in a glove box with a nitrogen atmosphere, and the raw material powder is immersed in benzene to prevent contact with the air. The quartz cell is placed in a thermobalance (TGD7000, manufactured by Shinku Riko Co., Ltd.), and the system is evacuated to a vacuum. Nitrogen is then introduced at a rate of 2.00 ⁇ 10 ⁇ 4 m 3 /min, and the temperature is increased to 200°C at a heating rate of 20°C/min to evaporate the benzene.
  • TGD7000 thermobalance
  • the temperature is then increased to 700°C at a heating rate of 20°C/min, and after the temperature and the balance have stabilized, oxygen is introduced into the system, and the system is maintained until no weight increase occurs.
  • the system is then cooled to below 100°C, evacuated, purged with nitrogen, and heated again to 700°C at a heating rate of 20°C/min.
  • hydrogen gas is passed through at 2.00 ⁇ 10 ⁇ 4 m 3 /min and maintained at this rate until no weight change is observed.
  • the reduction rate is calculated from the weight change as described above using the following formula (3).
  • X ⁇ (m Fe2O3 ⁇ m sample ) ⁇ 0.329 ⁇ (m Fe2O3 ⁇ m Fe ) ⁇ / ⁇ 0.671 ⁇ ((m Fe2O3 ⁇ m Fe ) ⁇ ...Formula (3) where X is the reduction rate (%), mFe2O3 is the weight of the raw material powder after oxidation (the weight of the raw material powder when there is no more weight increase after oxygen is introduced), msample is the mass of the raw material powder, and mFe is the weight of the raw material powder after reduction (the weight of the raw material powder when there is no more weight increase after hydrogen gas is introduced). Note that the chemical forms of the raw material powder after oxidation and reduction using a thermobalance can be confirmed to be Fe2O3 and Fe, respectively, by X-ray diffraction.
  • the reduced iron after the fluidized bed reduction process has a high specific surface area and may be oxidized by oxygen in the atmosphere, resulting in a decrease in the reduction rate. To suppress oxidation, it is preferable to carry out an oxidation suppression process after the fluidized bed reduction process.
  • the oxidation suppression process is not particularly limited as long as it is a process that suppresses oxidation of the reduced iron after the fluidized bed reduction process.
  • a surface area reduction process and a heat treatment process will be described.
  • the reduced iron after the fluidized bed reduction process may be simply referred to as reduced iron.
  • the reduced iron is hot-briquetted in an inert atmosphere.
  • HBI hot briquette iron
  • a known hot briquetting method can be used to obtain HBI, such as the method described in JP 2009-79292 A.
  • the briquetting method described in JP 2009-79292 A involves sandwiching a powdered or granular raw material containing a large amount of reduced iron between a pair of rollers with a concave mold at a relatively high temperature of 1000°C or less, for example, 500 to 800°C, to produce HBI.
  • the HBI is then cooled to room temperature using a water-cooling device.
  • the reduced iron is pressed into a mold. Therefore, to sufficiently reduce the oxidizability of the reduced iron obtained by fluidized bed reduction, it is desirable to obtain a high-density molded product that minimizes voids between the reduced iron particles.
  • the atmosphere in the surface area reduction step is preferably an inert atmosphere.
  • the molding temperature is preferably 720°C or higher.
  • the heat treatment step is a step of heat treating the reduced iron after the fluidized-bed reduction step with a non-oxidizing gas.
  • a fluidized-bed heat treatment step using a fluidized bed will be described.
  • the fluidized-bed heat treatment step is a step of heat treating the reduced iron after the fluidized-bed reduction step with a non-oxidizing gas using a fluidized bed that is the same as or different from the fluidized bed used in the fluidized-bed reduction step.
  • a fluidized bed is used for the heat treatment of the reduced iron.
  • the fluidized bed may be one or more bubbling fluidized beds, one or more circulating fluidized beds, one or more spouted fluidized beds, or a combination thereof.
  • the fluidized bed used in this step may be formed in the same vessel as that used in the fluidized-bed reduction step.
  • the reduced iron does not need to be transferred to another vessel, allowing for efficient treatment of the reduced iron.
  • the reduced iron after the fluidized-bed reduction step is not exposed to the atmosphere, further suppressing oxidation of the reduced iron.
  • the non-oxidizing gas is, for example, a gas that does not oxidize the reduced iron after the fluidized bed reduction process, such as N2 , He, Ne, Ar, Kr, or Xe.
  • the reduced iron is heat-treated in a non-oxidizing gas environment, and its specific surface area is reduced.
  • the non-oxidizing gas is preferably N2 gas or Ar gas.
  • the gas flow velocity of the non-oxidizing gas is preferably at least 1.5 times greater than the gas flow velocity of the reducing gas in the fluidized bed in the fluidized bed reduction process, or at least four times the minimum fluidization velocity of the fluidized bed in the fluidized bed heat treatment process. Essentially, the latter applies when the gas flow velocity of the reducing gas in the fluidized bed reduction process is high, and the former applies when it is low. If the fluidized bed in the fluidized bed reduction process is a circulating fluidized bed, the latter applies, i.e., the gas flow velocity of the non-oxidizing gas is at least four times the minimum fluidization velocity of the fluidized bed in the fluidized bed heat treatment process.
  • the flow velocity of the non-oxidizing gas used to form the bubbling fluidized bed is lower than the flow velocity of the non-oxidizing gas used to form the circulating fluidized bed, and very little raw material powder escapes from the bubbling fluidized bed. Therefore, if the fluidized bed is a bubbling fluidized bed, the gas flow velocity of the non-oxidizing gas may be greater than the minimum fluidization velocity and less than the terminal velocity.
  • the flow rate of the non-oxidizing gas is the superficial velocity at which a fluidized bed is formed, and is calculated by dividing the gas flow rate per unit time supplied by the cross-sectional area of the fluidized bed.
  • the flow rate of the non-oxidizing gas can be measured using a flow meter attached to the gas supply piping.
  • the temperature in the fluidized bed in the fluidized bed heat treatment process is preferably higher than the temperature in the fluidized bed in the fluidized bed reduction process.
  • the temperature in the fluidized bed in the fluidized bed heat treatment process can be set to a higher temperature than the temperature in the fluidized bed in the fluidized bed reduction process, for example, 700°C or higher and 900°C or lower.
  • the temperature in the fluidized bed in the fluidized bed heat treatment process is preferably 720°C or higher, and more preferably 750°C or higher. Furthermore, to suppress agglomeration of the reduced iron, the temperature in the fluidized bed in the fluidized bed heat treatment process is 850°C or lower. Therefore, the temperature in the fluidized bed in the fluidized bed heat treatment process is preferably 720°C or higher and 850°C or lower, and more preferably 750°C or higher and 850°C or lower.
  • the reduced iron can be heat-treated at a high temperature, thereby reducing the specific surface area and suppressing oxidation of the reduced iron after heat treatment. Furthermore, a reducing gas is not used in the fluidized-bed heat treatment process. If a reducing gas containing hydrogen gas were used in the fluidized-bed heat treatment process, a large amount of hydrogen gas would be required to maintain the fluidized state. On the other hand, in the fluidized-bed heat treatment process, only a small amount of hydrogen is consumed in the reduction of the raw material powder, and a large amount of hydrogen gas containing H 2 O produced by the reduction of the raw material powder is discharged outside the vessel. To reuse the discharged hydrogen gas, the temperature of the hydrogen gas must be lowered for dehydration and then raised again.
  • the energy load can be reduced by performing heat treatment using a non-oxidizing gas that does not contribute to the reaction and is inexpensive to use. Furthermore, if a reducing gas is used, further reduction may occur during heat treatment at a higher temperature than in the reduction treatment process, resulting in the formation of new active metallic iron on the surface, which may cause sticking.
  • the heat treatment is carried out under conditions such that the ratio of the total sieved mass of the post-heat treatment raw material powder on the sieve with the specified mesh openings when the total sieved mass of the pre-heat treatment raw material powder reaches 20 mass% or more is 1.0 to 1.2 times. If the ratio is 1.0 to 1.2, it can be said that aggregation of the raw material powder is suppressed and the heat treatment process is carried out stably.
  • the reduction apparatus may be, for example, one or more circulating fluidized bed forming apparatuses that form a circulating fluidized bed, one or more bubbling fluidized bed forming apparatuses that form a bubbling fluidized bed, one or more spouting fluidized bed forming apparatuses that form a spouting fluidized bed, or a combination thereof.
  • Fig. 1 is a schematic diagram of an apparatus capable of forming a bubbling fluidized bed.
  • Fig. 2 is a schematic diagram of another example of a container in an apparatus capable of forming a bubbling fluidized bed.
  • Fig. 3 is a schematic diagram of an apparatus capable of forming a circulating fluidized bed.
  • Fig. 4 is a schematic diagram of an apparatus capable of forming a spouting fluidized bed.
  • the bubbling fluidized bed forming apparatus 10 includes a container 11 and a dry dust collector 12 .
  • the vessel 11 has, for example, a gas supply port 111 located at the bottom through which reducing gas is supplied into the interior of the vessel 11, a raw material powder supply port 112 through which raw material powder is supplied, and a dispersion plate 113 located above the gas supply port 111.
  • the bubbling fluidized bed is formed by fluidizing the raw material powder with gas supplied from the gas supply port 111 and rectified through multiple vent holes in the dispersion plate 113.
  • the gas ventilation method and form for forming the bubbling fluidized bed are not limited to specific forms, as long as it is possible to supply reducing gas into the vessel 11, blow up the raw material powder, and form a fluidized bed, using a flat dispersion plate 113 such as a porous plate or slit plate, as well as a simple nozzle type, a cap type with a nozzle tip equipped with a cap with various types of blowing holes, or a pipe type with a grid tube with multiple holes on the side of the tube.
  • the reduced iron after reduction or after heat treatment is discharged through an openable and closable reduced iron powder outlet (not shown).
  • the bubbling fluidized bed forming device may also have a container that forms multiple bubbling fluidized beds inside.
  • Figure 2 is a schematic diagram of another example of a container in an apparatus capable of forming a bubbling fluidized bed.
  • the container 11A may include, for example, a raw material powder supply port 112A provided on one longitudinal side, an outlet 114 provided on the other longitudinal side, multiple gas supply ports 111A arranged in parallel in the longitudinal direction, a dispersion plate 113A provided above each gas supply port 111A, and a partition plate 115 provided between adjacent gas supply ports 111A.
  • the space between the inner wall of the container 11A and the partition plate 115, and the space between adjacent partition plates 115 form the space where the fluidized bed is formed.
  • the height of the partition plate 115 is lower than the height of the bubbling fluidized bed.
  • a container 11A configured in this manner can increase the average residence time of the raw material powder and increase the achieved reduction rate. It goes without saying that the locations and number of raw material powder supply ports, the locations and number of outlets, and the locations and number of partition plates are not limited to the embodiment shown in Figure 2 and may be changed as appropriate.
  • the circulating fluidized bed forming apparatus 20 includes a riser section 21 which is a container in which the raw material powder forms a fluidized bed, a cyclone 22 connected to an outlet 214 provided at the top of the riser section 21, and a circulation line 23 which extends downward from the bottom of the cyclone 22 and is connected to the bottom of the riser section 21.
  • the circulating fluidized bed forming apparatus 20 can include a dry dust collector 24 connected to the cyclone 22 for collecting pulverized iron ore powder and reduced iron (dust) contained in the off-gas.
  • the riser section 21 has a gas supply port 211, a raw material powder supply port 212, and a dispersion plate 213 arranged above the gas supply port 211.
  • the riser section 21 is basically the same as the vessel 11 in the bubbling fluidized bed forming apparatus 10.
  • the cyclone 22 captures particles that are dispersed along with the exhaust gas.
  • the captured particles are returned to the riser section 21 through the circulation line 23, and the exhaust gas is discharged outside the circulating fluidized bed forming device 20 via the dry dust collector 24.
  • the circulation line 23 is connected to the bottom of the cyclone 22 and has a downcomer 231, which serves as a flow path for the raw material powder separated from the gas in the cyclone 22, and a loop seal section 232, one end of which is connected to the bottom of the downcomer 231 and the other end of which is connected above the distribution plate 213 of the riser section 21.
  • the loop seal section 232 provides a sealing effect by using the raw material powder that is temporarily stored therein.
  • the gas ventilation method and form for forming the circulating fluidized bed are not limited to specific forms, as long as it is possible to supply reducing gas into the riser section 21, blow up the raw material powder, and form a fluidized bed, using a flat distribution plate 113 such as a porous plate or slit plate, as well as a simple nozzle type, a cap type with a cap with various types of blowing holes at the tip of the nozzle, or a pipe type with a grid tube with multiple holes on the side of the tube.
  • a flat distribution plate 113 such as a porous plate or slit plate, as well as a simple nozzle type, a cap type with a cap with various types of blowing holes at the tip of the nozzle, or a pipe type with a grid tube with multiple holes on the side of the tube.
  • the exhaust gas may contain dust. Therefore, a dry dust collector 24 can be used to capture the dust contained in the off-gas.
  • the dry dust collector 24 may be, for example, a cyclone, multiclone, or ceramic filter.
  • a cyclone smaller than the cyclone 22 may be installed in series as the dry dust collector 24 after the cyclone 22.
  • the raw material powder supplied from the raw material powder supply port 212 is fluidized by the reducing gas supplied from the gas supply port 211 and rectified through multiple vents in the dispersion plate 213. Specifically, the raw material powder is transported from bottom to top within the riser section 21, passes through the cyclone 22 and circulation line 23, and circulates within the circulating fluidized bed forming apparatus 20. Therefore, the interior of the circulating fluidized bed forming apparatus 20 forms a circulating fluidized bed. The raw material powder remains in the loop seal section 232 for a while.
  • the reduced or heat treatment using the circulating fluidized bed forming apparatus 20 is a batch process
  • the processed powder is extracted, for example, from an openable outlet (not shown) located at the bottom of the cyclone 22 (midway through the downcomer 231).
  • the valve of the openable outlet located in the riser section 21 is opened at regular intervals or continuously, and the processed powder is extracted, while raw material powder is replenished from the raw material powder supply port 212.
  • the spout-fluidized-bed forming apparatus 30 basically has the same configuration as the bubbling fluidized-bed forming apparatus 10. However, the spout-fluidized-bed forming apparatus 30 differs from the bubbling fluidized-bed forming apparatus 10 in that it does not uniformly stir the entire mixture. For example, as shown in FIG. 4 , a protruding section 311 (gas blow-through section) from which the raw material powder is protruding at a high gas flow rate above the gas supply port 111 and a moving layer 312 in which the raw material powder accumulates around the protruding section and moves from top to bottom are formed.
  • a protruding section 311 gas blow-through section
  • the raw material powder at the bottom of the moving layer 312 is entrained in the reducing gas flowing at a high gas flow rate through the protruding section 311, and the raw material powder is repeatedly protruding from the protruding section 311.
  • the fluidized bed composed of the protruding section 311 and the moving layer 312 is the spout-fluidized bed 310.
  • Each of the fluidized bed for reducing the raw material powder and the fluidized bed for heat-treating the reduced iron may be one circulating fluidized bed, one bubbling fluidized bed, or one spouting fluidized bed, or may be a plurality of circulating fluidized beds, a plurality of bubbling fluidized beds, or a plurality of spouting fluidized beds, or may be a combination of one or more circulating fluidized beds, one or more bubbling fluidized beds, or one or more spouting fluidized beds.
  • the difference between the average flow velocity of the reducing gas and the average movement velocity of the raw material powder is large, so the gas in contact with the raw material powder is exchanged frequently, and during reduction, the surroundings of the raw material powder approach an equilibrium state, preventing the reduction reaction from stagnating, and the raw material powder is reduced efficiently.
  • the average movement velocity of the raw material powder itself is high, mechanical wear and destruction occur due to collisions between raw material powder particles, and dust is easily generated.
  • a bubbling fluidized bed In a bubbling fluidized bed, the difference between the average flow velocity of the reducing gas and the average movement velocity of the raw material powder (slip velocity) is smaller than in a circulating fluidized bed, so the reduction efficiency of the raw material powder in a bubbling fluidized bed is inferior to that in a circulating fluidized bed.
  • dust generation tends to be suppressed more than in a circulating fluidized bed, and by reducing the gas flow velocity, it is possible to reduce the energy cost for gas supply.
  • a spouted fluidized bed larger particle sizes of raw material powder can be used compared to a circulating fluidized bed.
  • a spouted fluidized bed is advantageous when it is desired to shorten the residence time of the raw material powder. It is preferable to determine the configuration of the fluidized bed taking into consideration the characteristics of the circulating fluidized bed, bubbling fluidized bed and spouted fluidized bed, as well as the median diameter and Fe content of the raw material powder.
  • FIG. 5 is a schematic diagram showing an example of a reduced iron production facility equipped with one circulating fluidized bed forming device 20 and three bubbling fluidized bed forming devices 10 as reduction devices.
  • solid arrows indicate the flow of powder
  • dashed arrows indicate the flow of gas.
  • the reduced iron production equipment 1 shown in Figure 5 includes one circulating fluidized bed forming device 20 and three bubbling fluidized bed forming devices 10 as reduction devices 2.
  • reduced iron 41 is produced as follows.
  • Raw material powder 40 is supplied to the riser section 21 of the circulating fluidized bed forming device 20.
  • the raw material powder 40 supplied to the riser section 21 is reduced by a reducing gas 42 in the circulating fluidized bed.
  • the partially reduced raw material powder 40 is sent to the first-stage vessel 11 of the bubbling fluidized bed forming device 10, where reduction of the raw material powder 40 progresses in the bubbling fluidized bed formed by the raw material powder 40 and the reducing gas 42.
  • the raw material powder 40 in the vessel 11 is sequentially supplied to the second-stage vessel 11 and the third-stage vessel 11 and reduced there.
  • the raw material powder 40 is finally reduced in the bubbling fluidized bed in the third-stage vessel 11 to produce reduced iron 41.
  • a dry dust collector 12 connected to each of the containers 11 recovers raw material powder 40 that may be contained in the off-gas, and the recovered raw material powder 40 is re-fed into each container 11.
  • the dust-containing off-gas separated by the cyclone 22 of the circulating fluidized bed forming device 20 and the dry dust collector 12 of the bubbling fluidized bed forming device 10 is sent to the dry dust collector 24.
  • the dust is separated from the off-gas in the dry dust collector 24 and recovered.
  • reduced iron can be produced, for example, by a reduced iron production facility equipped with one circulating fluidized bed former 20 and three bubbling fluidized bed formers 10 as reduction devices.
  • a reduction device 1 in which a bubbling fluidized bed former 10 is installed downstream of the circulating fluidized bed former 20 can shorten the reduction time in the early stages of reduction, where the reduction reaction tends to progress rapidly due to the supply rate of the reducing gas reaching the surface of the raw material powder, and can avoid excessive use of reducing gas in the later stages of reduction, where the reduction rate tends to stagnate due to the rate of material diffusion within the ore.
  • multiple bubbling fluidized bed formers 10 the average residence time of the raw material powder can be ensured and residence time variation can be suppressed, making it possible to obtain reduced iron with the desired reduction rate and little variation in quality.
  • the pressure loss in the fluidized bed may be constantly monitored. If excessive agglomeration occurs or if gas bypass (channeling) occurs in areas where the raw material powder has segregated, abnormalities may occur, such as pressure loss becoming excessively large beyond the weight of the fluidized bed due to clogging of the entire fluidized bed, or pressure loss approaching zero due to gas blowing through the fluidized bed and not contributing to fluidization. In this case, large-scale maintenance of the manufacturing equipment may be required. However, if pressure loss is constantly monitored, it becomes possible to shut down the equipment at the appropriate time before clogging or segregation progresses and the maintenance burden becomes too great. This type of configuration is achieved using a pressure measurement device.
  • the reduced iron production method according to this embodiment can efficiently produce reduced iron from raw material powder containing iron, even when iron ore powder of different ore types is mixed, which has a low content of crystallized water and exhibits significant reduction stagnation in conventional reduction processes. Furthermore, the reduced iron production method according to this embodiment deliberately selects a low temperature range of 590°C or less, which is lower than the process temperatures conventionally employed. This reduces equipment costs by addressing equipment issues associated with using reducing gas at high temperatures, particularly the deterioration of furnace materials due to high-temperature hydrogen, eliminating heat-resistant measures for mechanical drives, and downgrading furnace material. Furthermore, lower reduction temperatures also lead to reduced operating costs.
  • Example 1 For the raw material powders A to H shown in Table 1, in order to estimate the transition of the hydrogen reduction rate in the fluidized bed reduction vessel, the transition of the reduction rate during hydrogen reduction in a stationary state was measured by thermogravimetry (TG).
  • Table 1 shows the iron content (T.Fe), water of crystallization (CW), and gangue component SiO 2 , Al 2 O 3 , CaO, and MgO of each raw material powder.
  • Components other than those shown in Table 1 are impurities such as MnO, P, and S, and the contents of each were in the range of 0.001 to 0.3 mass%.
  • the impurities are components that have little effect on reduction using a fluidized bed.
  • Raw material powders A to C are hematite-based concentrates mainly composed of hematite (Fe 2 O 3 ).
  • Raw material powders D and E are hematite-based fine ores.
  • Raw material powders F to H are goethite-based (FeO(OH)) fine ores.
  • Raw material powders A to C are fine ores that have undergone ore dressing processing to increase their iron content and have a relatively sharp particle size distribution.
  • Raw material powders D to H were dry-classified to 0.
  • Thermogravimetric analysis was performed using a high-temperature differential thermobalance TG-DTA/H (Rigaku Corporation, Thermo plus EVO2). 15 mg of raw material powder was placed in an alumina sample container, and the sample was heated to the following set temperature at a heating rate of 10°C/min under a nitrogen gas flow (214 cc/min). The nitrogen gas flow rate was set so that the internal space of the apparatus was replaced with gas sufficiently quickly, without the sample being carried away by the airflow. The reduction temperature was set at six levels between 500°C and 1000°C in 100°C intervals.
  • Figure 6 shows graphs of the reduction rate transition for each raw powder shown in Table 1, arranged in order of crystal water content.
  • reduction at 500°C reached a reduction rate of over 90% faster than reduction in the 600-700°C range, as indicated by the dashed line in Figure 6.
  • reduction stagnation in the 600-700°C range was significant.
  • the inventors speculate that the reason for this is as follows: A high crystal water content causes a transformation from the goethite phase to the hematite phase due to dehydration during the heating process before reduction, forming cracks and pores in the raw powder during this process.
  • Example 2 Fluidized bed reduction was performed on raw material powders B, D, and E in Example 1. Specifically, a dispersion plate made of fired glass beads was installed inside a vessel with an inner diameter of 35 mm, and the raw material powder was packed onto the dispersion plate. The thickness of the raw material powder layer was 35 mm. The tip of a thermocouple was positioned inside the raw material powder layer. A heating mechanism was installed on the outer periphery of the vessel so that the inside of the vessel could be heated. N2 gas was supplied into the vessel from below, and the temperature was increased while fluidizing the iron ore powder. After the fluidized bed reached the temperature shown in Table 2, a mixed gas of 90 vol% H2 gas and 10 vol% N2 gas was supplied.
  • the gas flow rate of this mixed gas was set under the conditions shown in Table 2.
  • the minimum fluidization velocity of raw material powders B, D, and E was 0.02 m/s, and the terminal velocity was 0.3 m/s.
  • the reduction time was 2 hours from the start of the reaction.
  • using a pressure probe with its tip positioned inside the iron ore powder layer and a pressure probe with its tip positioned above the iron ore powder layer the pressure in the iron ore powder layer (fluidized bed) during gas flow and the pressure in the space above the iron ore powder layer were continuously measured to determine whether the fluidized bed was stable.
  • the time required for the reduction rate to reach 90% was measured and compared to the time required for the reduction rate to reach 90% when the reduction process was performed at 600°C. If the time required for the reduction rate to reach 90% was shorter than when the reduction process was performed at 600°C, the reduction efficiency was rated A; if it was about the same, it was rated B; and if the reduction rate did not reach 90%, it was rated C. A rating of A was considered a pass, and a rating of B or C was considered a fail.
  • the time required to reach a 90% reduction rate was measured using the following method. Specifically, the residual hydrogen concentration in the exhaust gas passing through the fluidized bed was measured using gas chromatography, and the amount of hydrogen gas consumed by the reduction reaction as it passed through the fluidized bed was calculated from the difference with the supplied hydrogen gas concentration. The percentage of iron oxide reduced out of the estimated hematite-equivalent weight of iron oxide based on the amount fed in and chemical analysis component values was then calculated, and the time elapsed from the start of hydrogen gas flow until a 90% reduction rate was measured.
  • Example No. 8 in Table 2 hot-molded reduced iron was produced using reduced iron without contact with an oxidizing atmosphere, and then removed into the atmosphere.
  • reduced iron was heat-treated using a fluidized bed without contact with an oxidizing atmosphere, and then removed into the atmosphere.
  • the atmosphere (“gas" in Table 2) used in these treatments was the gas flow rate and treatment temperature shown in Table 2.
  • the temperature of the reduced iron was lowered to less than 40°C after reduction and then removed into the atmosphere. If the maximum surface temperature of the reduced iron measured with a radiation thermometer within 1 minute after removal into the atmosphere was 50°C or less, the oxidizing property was evaluated as A. If the maximum surface temperature of the reduced iron was 200°C or higher, the oxidizing property was evaluated as B. An evaluation of A was considered pass, and an evaluation of B was considered fail.
  • Example No. 1 the reduction temperature was too low at 300°C, so the reduction rate did not reach 90%. Furthermore, since Example No. 1 did not reach a reduction rate of 90%, it was excluded from the evaluation of oxidation properties.
  • Example No. 2 the content of water of crystallization was 3.5% by mass or less, the temperature during reduction was 400° C., and the evaluation result of the reduction rate was acceptable.
  • Example No. 2 the cooled reduced iron was taken out directly into the air after reduction, so oxidation occurred and heat was generated at a high temperature, resulting in a failure in the evaluation of oxidation resistance.
  • Example No. 3 the content of water of crystallization was 3.5 mass % or less, the temperature during reduction was 500° C., and the evaluation result of the reduction rate was acceptable.
  • the cooled reduced iron was taken out directly into the air after reduction, which caused oxidation and generated heat at a high temperature, resulting in a failure in the evaluation of oxidation resistance.
  • Example No. 4 the temperature during reduction was 600° C., and the evaluation result of the reduction rate was unacceptable.
  • Example No. 4 the cooled reduced iron was taken out directly into the air after reduction, which caused oxidation and generated heat at a high temperature, resulting in a failure in the evaluation of oxidation resistance.
  • Example No. 5 the temperature during reduction was 700° C., and the evaluation result of the reduction rate was unacceptable.
  • Example No. 5 the cooled reduced iron was taken out directly into the air after reduction, and oxidation occurred, generating heat at a high temperature, resulting in a failure in the evaluation of oxidation resistance.
  • Example No. 6 the reduction temperature was 800°C, and the reduction rate evaluation result was acceptable. However, excessive aggregation occurred due to reduction at a high temperature.
  • Example No. 7 the reduction temperature was 900°C, and the reduction rate evaluation result was acceptable. However, excessive agglomeration occurred due to reduction at a high temperature.
  • Example No. 8 the content of water of crystallization was 3.5% by mass or less, the temperature during reduction was 400° C., and the evaluation result of the reduction rate was acceptable.
  • Example No. 8 HBI was produced to reduce the surface area and then taken out into the atmosphere, so the evaluation of oxidation resistance was passed.
  • Example No. 9 the content of water of crystallization was 3.5% by mass or less, the temperature during reduction was 500° C., and the evaluation result of the reduction rate was acceptable.
  • heat treatment was performed at 750°C in an N2 gas atmosphere using BFB, and the surface area of the reduced iron was reduced, so the evaluation of oxidation resistance was acceptable.
  • Example No. 10 the content of water of crystallization was 3.5 mass % or less, the temperature during reduction was 525° C., and the evaluation result of the reduction rate was acceptable.
  • heat treatment was performed at 750°C in an N2 gas atmosphere using BFB, and the surface area of the reduced iron was reduced, so the evaluation of oxidation resistance was passed.
  • Example No. 11 the content of water of crystallization was 3.5 mass % or less, the temperature during reduction was 550° C., and the evaluation result of the reduction rate was acceptable.
  • heat treatment was performed at 750°C in an N2 gas atmosphere using BFB, and the surface area of the reduced iron was reduced, so the evaluation of oxidation resistance was acceptable.
  • Example No. 12 the content of water of crystallization was 3.5 mass % or less, the temperature during reduction was 575° C., and the evaluation result of the reduction rate was acceptable.
  • heat treatment was performed at 750°C in an N2 gas atmosphere using BFB, and the surface area of the reduced iron was reduced, so the evaluation of oxidation resistance was passed.
  • Example No. 13 the content of water of crystallization was 3.5 mass % or less, the temperature during reduction was 550° C., and the evaluation result of the reduction rate was acceptable.
  • heat treatment was performed at 750° C. in an Ar gas atmosphere using BFB, and the surface area of the reduced iron was reduced, so the evaluation of oxidation resistance was acceptable.
  • Example No. 14 the content of water of crystallization was 3.5 mass % or less, the temperature during reduction was 550° C., and the evaluation result of the reduction rate was acceptable.
  • heat treatment was performed at 750°C in an N2 gas atmosphere using CFB, and the surface area of the reduced iron was reduced, so the evaluation of oxidation resistance was passed.
  • Example No. 15 the content of water of crystallization was 3.5 mass % or less, the temperature during reduction was 550° C., and the evaluation result of the reduction rate was acceptable.
  • heat treatment was performed in a N gas atmosphere using BFB, but because the heat treatment temperature was as low as 550°C, the surface area of the reduced iron was not reduced sufficiently, and the sample failed the evaluation of oxidation resistance.
  • Example No. 16 the content of water of crystallization was 3.5 mass % or less, the temperature during reduction was 550° C., and the evaluation result of the reduction rate was acceptable.
  • heat treatment was performed at 800°C in an N2 gas atmosphere using BFB, and the surface area of the reduced iron was reduced, so the evaluation of oxidation resistance was acceptable.
  • Example No. 17 the content of water of crystallization was 3.5 mass % or less, the temperature during reduction was 550° C., and the evaluation result of the reduction rate was acceptable. In addition, in Example No. 17, the cooled reduced iron was taken out directly into the air after reduction, so oxidation occurred, generating heat at a high temperature, and the evaluation of oxidation resistance was unacceptable.
  • Example No. 18 the content of water of crystallization was 3.5 mass % or less, the temperature during reduction was 550° C., and the evaluation result of the reduction rate was acceptable.
  • heat treatment was performed in a N gas atmosphere using BFB, but because the heat treatment temperature was as low as 650°C, the surface area of the reduced iron was not reduced sufficiently, and the sample failed the evaluation of oxidation resistance.
  • Example No. 19 the content of water of crystallization was 3.5 mass % or less, the temperature during reduction was 550° C., and the evaluation result of the reduction rate was acceptable.
  • heat treatment was performed at 800°C in an N2 gas atmosphere using BFB, and the surface area of the reduced iron was reduced, so the evaluation of oxidation resistance was acceptable.
  • Example No. 20 the content of water of crystallization was 3.5 mass % or less, the temperature during reduction was 550° C., and the evaluation result of the reduction rate was acceptable. In addition, in Example No. 20, the cooled reduced iron was taken out directly into the air after reduction, so oxidation occurred and heat was generated at a high temperature, and the evaluation of oxidation resistance was unacceptable.
  • Example No. 21 the content of water of crystallization was 3.5 mass % or less, the temperature during reduction was 550° C., and the evaluation result of the reduction rate was acceptable.
  • heat treatment was performed in a N gas atmosphere using BFB, but because the heat treatment temperature was as low as 650°C, the surface area of the reduced iron was not reduced sufficiently, and the sample failed the evaluation of oxidation resistance.
  • Example No. 22 the content of water of crystallization was 3.5 mass % or less, the temperature during reduction was 550° C., and the evaluation result of the reduction rate was acceptable.
  • heat treatment was performed at 800°C in an N2 gas atmosphere using BFB, and the surface area of the reduced iron was reduced, so the evaluation of oxidation resistance was passed.
  • Example No. 23 a raw material powder having a crystal water content of 3.5% by mass or less was used, a two-stage fluidized bed using CFB and BFB was used, and the temperature during reduction was set to 550°C, and the evaluation result of the reduction rate was acceptable.
  • heat treatment was performed at 750°C in an N2 gas atmosphere using BFB, and the surface area of the reduced iron was reduced, so the evaluation of oxidation resistance was acceptable.
  • Example No. 24 a raw material powder having a crystal water content of 3.5% by mass or less was used, a two-stage BFB was used, and the reduction temperature was 550°C, and the evaluation result of the reduction rate was acceptable.
  • heat treatment was performed at 750°C in an N2 gas atmosphere using BFB, and the surface area of the reduced iron was reduced, so the evaluation of oxidation resistance was passed.
  • Example No. 25 a raw material powder having a crystal water content of 3.5% by mass or less was used, a two-stage CFB was used, and the reduction temperature was set to 550°C, and the evaluation result of the reduction rate was acceptable. In addition, in Example No. 25, heat treatment was performed at 750°C in an N2 gas atmosphere using BFB, and the surface area of the reduced iron was reduced, so the evaluation of oxidation resistance was passed.
  • Example 3 In order to estimate the transition of the hydrogen reduction rate in the fluidized bed reduction vessel for iron ore powders A to C shown in Table 3, the transition of the reduction rate during hydrogen reduction in a stationary state was measured by thermogravimetry (TG).
  • Table 3 shows the iron content (T.Fe), water of crystallization (CW), and gangue component SiO 2 , Al 2 O 3 , CaO, and MgO (mass %) of each iron ore powder.
  • Components other than those listed in Table 3 are impurities such as MnO, P, and S, and the contents of each were in the range of 0.001 to 0.3 mass %. The impurities have little effect on reduction using a fluidized bed.
  • Iron ore powder A is a hematite-based concentrate mainly composed of hematite (Fe 2 O 3 ).
  • Iron ore powder B is a hematite-based ore powder, and iron ore powder C is a goethite-based ore powder.
  • Iron ore powder A is a fine ore that has undergone ore dressing processing to increase its iron content and has a relatively sharp particle size distribution. Iron ore powders B and C are dry-classified to 0.25 mm or less.
  • Iron ore powders A to C were mixed in the proportions shown in Table 4, and the crystal water content, gangue content, and iron content of the resulting mixed powder are shown in Table 4.
  • Thermogravimetric analysis was performed using a high-temperature differential thermobalance TG-DTA/H (Rigaku Corporation, Thermo plus EVO2). 15 mg of raw material powder was placed in an alumina sample container, and the sample was heated to the following set temperature at a heating rate of 10°C/min under a nitrogen gas flow (214 cc/min). The nitrogen gas flow rate was set so that the internal space of the apparatus was replaced with gas sufficiently quickly, without the sample being carried away by the airflow. The reduction temperature was set at six levels between 500°C and 1000°C in 100°C intervals.
  • Figure 8 shows graphs of the reduction rate transition for each iron ore powder shown in Table 3, arranged in order of crystal water content.
  • the reduction rate was measured for each iron ore powder at different reduction temperatures. Reduction stagnation was noticeable for iron ore powder A, which has a high iron content, but no reduction stagnation was observed around 700°C for iron ore powder C, which has a high crystal water content.
  • iron ore powder B whose crystal water content is between that of iron ore powder A and that of iron ore powder C, the reduction behavior showed an intermediate trend between that of raw material powder A and that of raw material powder B.
  • Figure 9 shows graphs of the reduction rate transition for raw material powders (cases) b-f and h-l shown in Table 4, arranged in order of crystal water content.
  • Raw material powders (cases) a, g, and m in Table 4 correspond to iron ore powders A, C, and B, respectively. Therefore, the graphs for raw material powders (cases) a, g, and m are shown in Figure 8.
  • graphs with the legend "500” in each graph show the reduction rate transition when the reduction temperature was 400-590°C
  • graphs with the legend "700” show the reduction rate transition when the reduction temperature was 600-700°C.
  • reduction stagnation depends on the crystal water content of the raw material powder, with ores with lower crystal water content showing a stronger tendency for reduction stagnation.
  • Reduction stagnation was more pronounced for raw material powders with low crystal water content, particularly those with less than 3.5% by mass, and reduction at 400-590°C was found to reach a reduction rate of over 90% faster than reduction at 600-700°C. This is presumably because a high crystal water content causes dehydration during the heating process before reduction, resulting in a transformation from the goethite phase to the hematite phase. This process forms pores in the ore, which inhibit the formation of a dense wustite phase that causes reduction stagnation in the production of metallic iron. Furthermore, when the crystal water content is 2.0% by mass or less, reduction at 400-590°C was advantageous, reaching a reduction rate of 90% even more quickly than reduction at 600-700°C.
  • Example 4 Fluidized bed reduction was performed on raw material powders (cases b and c) in Example 3. Specifically, a dispersion plate made of fired glass beads was placed inside a vessel with an inner diameter of 35 mm, and the raw material powder was packed onto the dispersion plate. The thickness of the raw material powder layer was 35 mm. The tip of a thermocouple was positioned inside the raw material powder layer. A heating mechanism was installed on the outer periphery of the vessel so that the inside of the vessel could be heated. N2 gas was supplied into the vessel from below, and the raw material powder was heated while fluidizing it. After the fluidized bed reached the temperature shown in Table 5, H2 gas was supplied. The gas flow rate was as shown in Table 5.
  • the minimum fluidization velocity of raw material powders (cases b and c) was 0.03 m/s, and the terminal velocity was 1.4 m/s.
  • the reduction time was 2 hours from the start of the reaction. Furthermore, using a pressure probe with its tip positioned inside the raw material powder layer and a pressure probe with its tip positioned above the raw material powder layer, the pressure in the raw material powder layer (fluidized bed) during gas flow and the pressure in the space above the raw material powder layer were continuously measured to determine whether the fluidized bed was stable.
  • the time required for the reduction rate to reach 90% was measured and compared to the time required for the reduction rate to reach 90% when the reduction process was performed at 600°C. If the time required for the reduction rate to reach 90% was shorter than when the reduction process was performed at 600°C, the reduction efficiency was rated A; if it was about the same, it was rated B; and if the reduction rate did not reach 90%, it was rated C. A rating of A was considered a pass, and a rating of B or C was considered a fail.
  • the time required to reach a 90% reduction rate was measured using the following method. Specifically, the residual hydrogen concentration in the exhaust gas passing through the fluidized bed was measured using gas chromatography, and the amount of hydrogen gas consumed by the reduction reaction as it passed through the fluidized bed was calculated from the difference with the supplied hydrogen gas concentration. The percentage of iron oxide reduced out of the estimated hematite-equivalent weight of iron oxide based on the amount fed in and chemical analysis component values was then calculated, and the time elapsed from the start of hydrogen gas flow until a 90% reduction rate was measured.
  • Example No. 33 in Table 5 hot-molded reduced iron was produced using reduced iron without contact with an oxidizing atmosphere, and then removed from the atmosphere.
  • the reduced iron was heat-treated using a fluidized bed without contact with an oxidizing atmosphere, and then removed from the atmosphere.
  • the atmosphere (“Gas Type" in Table 5), gas flow rate, and treatment temperature used in these treatments were as shown in Table 5.
  • the temperature of the reduced iron was lowered to 40°C after reduction and then removed from the atmosphere. If the maximum surface temperature of the reduced iron, measured with a radiation thermometer within 1 minute after removal from the atmosphere, was 50°C or less, the oxidizing property was evaluated as A. If the maximum surface temperature of the reduced iron was 200°C or higher, the oxidizing property was evaluated as B. A rating of A was considered a pass, and a rating of B was considered a fail.
  • Example No. 26 the reduction temperature was too low at 300°C, so the reduction rate did not reach 90%. Note that Example No. 26 was excluded from the evaluation of oxidation potential because the reduction rate did not reach 90%.
  • Example No. 27 the content of water of crystallization was 3.5% by mass or less, the temperature during reduction was 400° C., and the evaluation result of the reduction rate (reduction efficiency) was acceptable.
  • the cooled reduced iron was taken out directly into the air after reduction, so oxidation occurred and heat was generated at a high temperature, resulting in a failure in the evaluation of oxidation resistance.
  • Example No. 28 the content of water of crystallization was 3.5% by mass or less, the temperature during reduction was 500° C., and the evaluation result of the reduction rate was acceptable.
  • the cooled reduced iron was taken out directly into the air after reduction, and oxidation occurred, generating heat at a high temperature, resulting in a failure in the evaluation of oxidation resistance.
  • Example No. 29 the temperature during reduction was 600° C., and the evaluation result of the reduction rate was unacceptable.
  • the cooled reduced iron was taken out directly into the air after reduction, which caused oxidation and generated heat at a high temperature, resulting in a failure in the evaluation of oxidation resistance.
  • Example No. 30 the temperature during reduction was 700° C., and the evaluation result of the reduction rate was unacceptable.
  • Example No. 30 the cooled reduced iron was taken out directly into the air after reduction, and oxidation occurred, generating heat at a high temperature, resulting in a failure in the evaluation of oxidation resistance.
  • Example No. 31 the reduction temperature was 800°C, and the reduction rate evaluation result was acceptable. However, excessive aggregation occurred due to reduction at a high temperature.
  • Example No. 32 the reduction temperature was 900°C, and the reduction rate evaluation result was acceptable. However, excessive aggregation occurred due to reduction at a high temperature.
  • Example No. 33 the content of water of crystallization was 3.5% by mass or less, the temperature during reduction was 400° C., and the evaluation result of the reduction rate was acceptable.
  • HBI was produced to reduce the surface area and then taken out into the atmosphere, so the evaluation of oxidation resistance was passed.
  • Example No. 34 the content of water of crystallization was 3.5% by mass or less, the temperature during reduction was 500° C., and the evaluation result of the reduction rate was acceptable.
  • heat treatment was performed at 750°C in an N2 gas atmosphere using BFB, and the surface area of the reduced iron was reduced, so the evaluation of oxidation resistance was passed.
  • Example No. 35 the content of water of crystallization was 3.5 mass % or less, the temperature during reduction was 525° C., and the evaluation result of the reduction rate was acceptable.
  • heat treatment was performed at 750°C in an N2 gas atmosphere using BFB, and the surface area of the reduced iron was reduced, so the evaluation of oxidation resistance was passed.
  • Example No. 36 the content of water of crystallization was 3.5 mass % or less, the temperature during reduction was 550° C., and the evaluation result of the reduction rate was acceptable.
  • heat treatment was performed at 750°C in an N2 gas atmosphere using BFB, and the surface area of the reduced iron was reduced, so the evaluation of oxidation resistance was passed.
  • Example No. 37 the content of water of crystallization was 3.5 mass % or less, the temperature during reduction was 575° C., and the evaluation result of the reduction rate was acceptable.
  • heat treatment was performed at 750°C in an N2 gas atmosphere using BFB, and the surface area of the reduced iron was reduced, so the evaluation of oxidation resistance was passed.
  • Example No. 38 the content of water of crystallization was 3.5 mass % or less, the temperature during reduction was 550° C., and the evaluation result of the reduction rate was acceptable.
  • heat treatment was performed at 750° C. in an Ar gas atmosphere using BFB, and the surface area of the reduced iron was reduced, so the evaluation of oxidation resistance was passed.
  • Example No. 39 the content of water of crystallization was 3.5 mass % or less, the temperature during reduction was 550° C., and the evaluation result of the reduction rate was acceptable.
  • heat treatment was performed at 750°C in an N2 gas atmosphere using CFB, and the surface area of the reduced iron was reduced, so the evaluation of oxidation resistance was passed.
  • Example No. 40 the content of water of crystallization was 3.5 mass % or less, the temperature during reduction was 550° C., and the evaluation result of the reduction rate was acceptable.
  • heat treatment was performed in a N gas atmosphere using BFB, but because the heat treatment temperature was as low as 550°C, the surface area of the reduced iron was not reduced sufficiently, and the sample failed the evaluation of oxidation resistance.
  • Example No. 41 the content of water of crystallization was 3.5 mass % or less, the temperature during reduction was 550° C., and the evaluation result of the reduction rate was acceptable.
  • heat treatment was performed at 800°C in an N2 gas atmosphere using BFB, and the surface area of the reduced iron was reduced, so the evaluation of oxidation resistance was passed.
  • Example No. 42 the content of water of crystallization was 3.5 mass % or less, the temperature during reduction was 550° C., and the evaluation result of the reduction rate was acceptable.
  • Example No. 42 the cooled reduced iron was taken out directly into the air after reduction, so oxidation occurred, generating heat at a high temperature, and the evaluation of oxidation resistance was unacceptable.
  • Example No. 43 the content of water of crystallization was 3.5 mass % or less, the temperature during reduction was 550° C., and the evaluation result of the reduction rate was acceptable.
  • heat treatment was performed in a N gas atmosphere using BFB, but because the heat treatment temperature was as low as 650°C, the surface area of the reduced iron was not reduced sufficiently, and the sample failed the evaluation of oxidation resistance.
  • Example No. 44 the content of water of crystallization was 3.5 mass % or less, the temperature during reduction was 550° C., and the evaluation result of the reduction rate was acceptable.
  • heat treatment was performed at 800°C in an N2 gas atmosphere using BFB, and the surface area of the reduced iron was reduced, so the evaluation of oxidation resistance was passed.
  • Example No. 45 a raw material powder having a crystal water content of 3.5% by mass or less was used, a two-stage fluidized bed using CFB and BFB was used, and the temperature during reduction was set to 550°C, and the evaluation result of the reduction rate was acceptable.
  • heat treatment was performed at 750°C in an N2 gas atmosphere using BFB, and the surface area of the reduced iron was reduced, so the evaluation of oxidation resistance was passed.
  • Example No. 46 a raw material powder having a crystal water content of 3.5% by mass or less was used, a two-stage BFB was used, and the reduction temperature was 550°C, and the evaluation result of the reduction rate was acceptable.
  • heat treatment was performed at 750°C in an N2 gas atmosphere using BFB, and the surface area of the reduced iron was reduced, so the evaluation of oxidation resistance was passed.
  • Example No. 47 a raw material powder having a crystal water content of 3.5% by mass or less was used, a two-stage CFB was used, and the reduction temperature was set to 550°C, and the evaluation result of the reduction rate was acceptable.
  • heat treatment was performed at 750°C in an N2 gas atmosphere using BFB, and the surface area of the reduced iron was reduced, so the evaluation of oxidation resistance was passed.
  • Example 5 For the examples of raw material powders A to H in Example 1 and mixed powders (cases) c, k, and l in Example 3, the time required to reach a reduction rate of 90% when the reduction temperature was 400 to 590°C or 600 to 700°C is shown in Table 6.
  • Table 6 the reduction temperature "500” indicates that the reduction temperature was 400 to 590°C, and "700” indicates that the reduction temperature was 600 to 700°C.

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Abstract

Ce procédé de production de fer réduit utilise un lit fluidisé et produit du fer réduit par mise en contact d'un gaz réducteur avec une poudre de matière première contenant de l'oxyde de fer. Le procédé comprend une étape de réduction de lit fluidisé dans laquelle la poudre de matière première, qui a une teneur en eau de cristallisation de 3,5% en masse ou moins, est réduite à une température de 400°C à 590° C.
PCT/JP2025/006912 2024-03-08 2025-02-27 Procédé de production de fer réduit Pending WO2025187535A1 (fr)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH08260172A (ja) * 1995-03-23 1996-10-08 Kobe Steel Ltd 表面被覆還元鉄および還元鉄の酸化防止法
JPH11100607A (ja) * 1997-09-26 1999-04-13 Nippon Steel Corp 高結晶水粉鉄鉱石の流動還元方法
JP2013147718A (ja) * 2012-01-20 2013-08-01 Nippon Steel & Sumitomo Metal Corp 焼結鉱の製造方法
JP2021188093A (ja) * 2020-05-29 2021-12-13 日本製鉄株式会社 還元鉄の製造設備および還元鉄の製造方法
JP7315125B1 (ja) * 2022-02-24 2023-07-26 Ｊｆｅスチール株式会社 粉鉄鉱石の還元方法

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH08260172A (ja) * 1995-03-23 1996-10-08 Kobe Steel Ltd 表面被覆還元鉄および還元鉄の酸化防止法
JPH11100607A (ja) * 1997-09-26 1999-04-13 Nippon Steel Corp 高結晶水粉鉄鉱石の流動還元方法
JP2013147718A (ja) * 2012-01-20 2013-08-01 Nippon Steel & Sumitomo Metal Corp 焼結鉱の製造方法
JP2021188093A (ja) * 2020-05-29 2021-12-13 日本製鉄株式会社 還元鉄の製造設備および還元鉄の製造方法
JP7315125B1 (ja) * 2022-02-24 2023-07-26 Ｊｆｅスチール株式会社 粉鉄鉱石の還元方法

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