Ironmaking method and ironmaking system

Abstract

Disclosed is a new technique for producing granular iron by separating slag from reduced iron. An ironmaking method according to the present disclosure comprises: (1) obtaining an agglomerate containing a carbonaceous material and reduced iron obtained by reducing an iron oxide raw material containing iron ore; (2) heating the agglomerate in a rotary hearth furnace to produce carburized metallic iron and melt the metallic iron, followed by cooling in the rotary hearth furnace to obtain carburized granular iron and slag; and (3) separating the granular iron and the slag to recover the granular iron.

Description

Ironmaking methods and ironmaking systems

[0001] This application discloses a method and system for iron production.

[0002] In addition to methods that reduce iron oxide raw materials to produce molten iron, such as the blast furnace method, there is also the direct reduction ironmaking method, which reduces iron oxide raw materials in a solid state to produce reduced iron. Direct reduction ironmaking methods include the shaft furnace method, the rotary kiln method, and the fluidized bed furnace method. Shaft furnace methods include the MIDREX method and the HyL (ENERGIRON) method. The rotary kiln method is the SL / RN method. Fluidized bed furnace methods include the FINMET method disclosed in Non-Patent Document 1, the HYFOR method disclosed in Non-Patent Document 2, and the Circored method disclosed in Non-Patent Document 3.

[0003] Reduced iron produced by the direct reduction ironmaking method is melted and smelted in an electric furnace, for example, to become molten steel. Here, the reduced iron contains components derived from iron oxide raw materials such as gangue, which generate slag during melting. When considering the melting and smelting of reduced iron in an electric furnace, reduced iron with a low slag source is desirable.

[0004] One method for removing slag from reduced iron is to charge reduced iron together with carbon material into a melting furnace, and then melt the reduced iron, carburize it, and separate the slag within the furnace to produce molten iron (for example, Patent Documents 1 to 4). However, in this case, the melting furnace for producing molten iron and the steelmaking equipment for the next process must be adjacent to each other, which restricts the location of each piece of equipment.

[0005] International Publication No. 2023 / 054345, International Publication No. 2024 / 062742, Japanese Patent Publication No. 2016-145393, Japanese Patent Publication No. 2010-265485

[0006] Steel Handbook, 5th Edition, Vol. 1, Ironmaking and Steelmaking (2014), p. 212; Mitsubishi Heavy Industries Technical Report Vol. 59 No. 2 (2022), pp. 1-5; Steel Handbook, 5th Edition, Vol. 1, Ironmaking and Steelmaking (2014), p. 214

[0007] This invention discloses a novel technology for producing granular iron by separating slag from reduced iron.

[0008] This application discloses the following multiple embodiments as means for solving the above problems. <Embodiment 1> A method for making iron, comprising: obtaining an agglomerate containing reduced iron obtained by reducing an iron oxide raw material containing iron ore, and a carbon material; heating the agglomerate in a rotary hearth furnace to produce carburized metallic iron and melt the metallic iron, and then, after cooling in the rotary hearth furnace, obtaining carburized granular iron and slag; and separating the granular iron and the slag to recover the granular iron. <Embodiment 2> The method for making iron according to Embodiment 1, wherein the reduced iron is obtained by reducing an iron oxide raw material in a fluidized bed furnace. <Embodiment 3> The method for making iron according to Embodiment 1 or 2, wherein the agglomerate contains the reduced iron, the carbon material, and an iron-containing substance other than the reduced iron. <Aspect 4> A steelmaking method according to any of aspects 1 to 3, wherein γ, as defined by the following formula (1), is 14 or more, and the carbon concentration of the granular iron is 2.1% by mass or more: Steelmaking method: γ = α × β / 7.9 ... (1) α: Apparent density of the agglomerated material (g / cm³) ３) β: Iron content (mass%) of the agglomerated material <Aspect 5> A steelmaking method according to any one of aspects 1 to 4, comprising: dissolving and refining the recovered granular iron to obtain molten steel. <Aspect 6> A steelmaking method according to any one of aspects 1 to 5, wherein the reduced iron is obtained by reducing an iron oxide raw material with a reducing gas, and the reducing gas includes hydrogen gas. <Aspect 7> A steelmaking system comprising: an iron oxide raw material supply device; a reducing gas supply device; a reducing furnace connected to the iron oxide raw material supply device and the reducing gas supply device; a carbon material supply device; an agglomeration device provided downstream of the reducing furnace and the carbon material supply device; a rotary hearth furnace provided downstream of the agglomeration device; and a separation device provided downstream of the rotary hearth furnace. <Aspect 8> A steelmaking system according to aspect 7, wherein the reducing furnace is a fluidized bed furnace. <Aspect 9> A steelmaking system according to aspect 7 or 8, comprising a smelting furnace provided downstream of the separation device. <Aspect 10> A steelmaking system according to any one of aspects 7 to 9, wherein the reducing gas supply device supplies reducing gas containing hydrogen gas to the reducing furnace.

[0009] According to the ironmaking method and ironmaking system of this disclosure, granular iron can be produced by separating slag from reduced iron.

[0010] This is a diagram illustrating an example of the steelmaking method and steelmaking system of the present disclosure. This is a diagram illustrating the case where γ is small. This is a diagram illustrating the case where γ is small. This is a diagram illustrating the case where γ is large. This is a diagram illustrating another example of the steelmaking method and steelmaking system of the present disclosure.

[0011] The following description will refer to the drawings and explain the steelmaking method and steelmaking system according to the embodiments, but the technology of this disclosure is not limited to the following embodiments.

[0012] 1. Ironmaking Method As shown in Figure 1, an ironmaking method according to one embodiment includes: obtaining an agglomerate containing reduced iron obtained by reducing an iron oxide raw material containing iron ore and a carbon material; heating the agglomerate in a rotary hearth furnace to produce carburized metallic iron and melt the metallic iron, and then, after cooling in the rotary hearth furnace, obtaining carburized granular iron and slag; and separating the granular iron and the slag to recover the granular iron.

[0013] 1.1 Reduction In the ironmaking method according to one embodiment, reduced iron is obtained by reducing iron oxide raw materials containing iron ore. An example of the production conditions for reduced iron is described below.

[0014] 1.1.1 Iron Oxide Raw Materials The iron oxide raw materials contain at least iron ore. Iron ore consists of iron oxide and impurities. The iron oxide raw materials may contain materials other than iron ore along with iron ore. That is, the iron oxide raw materials may contain iron oxide derived from iron ore, impurities derived from iron ore, and components derived from materials other than iron ore. It may also be a mixture of multiple iron oxide raw materials. The amount of iron ore contained in the iron oxide raw materials may be, for example, 50% by mass or more and 100% by mass or less, or 85% by mass or more and 100% by mass or less. The amount of iron oxide contained in the iron oxide raw materials may be, for example, 40% by mass or more and 100% by mass or less, or 70% by mass or more and 100% by mass or less. Examples of impurities contained in the iron oxide raw materials include gangue. For example, the iron oxide raw materials may contain oxides or hydroxides of elements such as silicon, aluminum, calcium, and magnesium, as well as compounds such as carbonates. Other materials that may be included in iron oxide raw materials include auxiliary raw materials consisting of oxides, hydroxides, carbonates, and other compounds of elements such as silicon, aluminum, calcium, and magnesium, as well as various recycled materials that contain iron as a constituent element.

[0015] The shape of the iron oxide raw material is not particularly limited, and a suitable shape can be selected depending on the reduction process. In one embodiment, the iron oxide raw material is granular. In this case, the iron oxide raw material may have a particle size distribution or a uniform particle size. The average particle size of the iron oxide raw material may be, for example, 44 μm or more and 30 mm or less, or 44 μm or more and 3 mm or less. Note that the "particle size" of the iron oxide raw material means the sieve diameter of the raw material, and the "average particle size" of the iron oxide raw material means the weighted average value of the particle sizes of the raw material. Specifically, the average particle size of the iron oxide raw material can be measured by obtaining a mass-based particle size distribution by the dry sieving test described in JIS Z 8815:1995, and then weighting the average of the maximum and minimum particle sizes of each sieve as the representative particle size by mass. Alternatively, the iron oxide raw material may be molded into pellets or the like, in lump form, or in any other shape.

[0016] 1.1.2 Reduction Conditions The conditions for producing reduced iron by reducing iron oxide raw materials are not particularly limited. As shown in Figure 1, the reduction of the iron oxide raw material may be carried out, for example, by bringing the iron oxide raw material into contact with a reducing gas in a reduction furnace 10. The reduction furnace 10 may be a fluidized bed furnace, a shaft furnace, or a rotary kiln furnace. In particular, when the reduction furnace 10 is a fluidized bed furnace, reduced iron suitable for agglomeration can be obtained, as will be described later. In other words, in the ironmaking method according to this embodiment, reduced iron may be obtained by reducing the iron oxide raw material in a fluidized bed furnace. The reducing gas may be any gas capable of reducing the iron oxide raw material. The reducing gas may contain one or more of the following: hydrogen gas, CO gas, hydrocarbon gas (e.g., hydrocarbon gas containing methane), and ammonia gas. The reducing gas may also contain other gases. Other gases may include inert gases and CO ２Examples include gases and water vapor. Examples of inert gases include nitrogen gas and argon gas. The reducing gas may be one or more of the following: blast furnace gas (BFG), coke oven gas (COG), converter gas (LDG), synthesis gas, natural gas, and liquefied ammonia, or a modified version thereof. In the ironmaking method according to one embodiment, a particularly high effect can be expected when the reduced iron is obtained by reducing an iron oxide raw material with a reducing gas, and the reducing gas contains hydrogen gas. When the reducing gas contains hydrogen gas, the hydrogen gas concentration of the reducing gas may be, for example, 40% to 100% by volume, 50% to 100% by volume, 60% to 100% by volume, 70% to 100% by volume, 75% to 100% by volume, or 80% to 100% by volume. Also, when the reducing gas contains hydrogen gas, the carbon-containing gas (CO gas, CO) contained in the reducing gas may be... ２ The concentration of the gas (a gas consisting of a compound containing carbon as a constituent element, such as a hydrocarbon gas) may be, for example, 0% to 60% by volume, 0% to 50% by volume, 0% to 30% by volume, or 0% to 25% by volume. The temperature of the reducing gas (temperature at the supply port of the reduction furnace 10) may be any temperature at which the reduction reaction with iron oxide occurs in the furnace, for example, 600°C to 1100°C. Preferably, the temperature of the reducing gas is 900°C to 1000°C.

[0017] (Fluided Bed Furnace Method) The fluidized bed furnace method is a known direct reduction ironmaking method that produces reduced iron by reducing granular (powdered) iron oxide raw materials with reducing gas. Examples of fluidized bed furnace methods include the FINMET method, HYFOR method, and Circored method. The reduced iron obtained by the fluidized bed furnace method is in the form of fine granules (powder) and can be used directly for agglomeration, as described later.

[0018] (Shaft furnace method, rotary kiln method) The shaft furnace method and rotary kiln method are also known as direct reduction ironmaking methods that produce reduced iron by reducing iron oxide raw materials with reducing gas. These methods produce reduced iron by bringing lump raw materials such as pellets or lump ore into contact with reducing gas. The reduced iron obtained by the shaft furnace method and rotary kiln method is in lump form and should be crushed into powder or granules that can be used for agglomeration as described later.

[0019] 1.1.3 Reduced Iron In this embodiment, the particle size of the reduced iron obtained as described above may be, for example, 44 μm or more and 30 mm or less, or 44 μm or more and 3 mm or less. Also, the average particle size of the reduced iron may be, for example, 44 μm or more and 30 mm or less, or 44 μm or more and 3 mm or less. Furthermore, in order to facilitate agglomeration, the reduced iron may have its particle size reduced by crushing or the like before agglomeration, as described later. In other words, the ironmaking method according to one embodiment may include reducing the particle size of the reduced iron obtained as described above before agglomeration. Note that "particle size" of reduced iron means the sieve diameter of the reduced iron, and "average particle size" of reduced iron means the weighted average value of the particle sizes of the reduced iron. Specifically, the average particle size of reduced iron can be measured by obtaining a mass-based particle size distribution using the dry sieving test described in JIS Z 8815:1995, and then taking the average value of the maximum and minimum particle sizes from each sieve as the representative particle size and weighting it by mass.

[0020] In this embodiment, the metallization rate of reduced iron may be high or low. For example, the metallization rate of reduced iron may be 50% or more and 100% or less, or 90% or more and 100% or less. The metallization rate refers to the proportion of iron that constitutes metallic iron out of the total iron contained in the reduced iron (metallization rate (%) = 100 × [amount of metallic iron contained in hot reduced iron (mass%)] / [amount of all iron contained in hot reduced iron (mass%)]). In this application, the metallization rate of reduced iron is determined by determining the proportion of metallic iron (M.Fe) contained in the reduced iron by the bromine methanol dissolution / EDTA method (JIS M 8213) and the proportion of all iron (T.Fe) contained in the reduced iron by the titanium(III) chloride reduced potassium dichromate titration method (JIS M 8212).

[0021] In this embodiment, reduced iron includes unreduced iron oxide and impurities derived from iron ore. For example, reduced iron includes gangue. Reduced iron may also contain oxides, hydroxides, carbonates, and other compounds of elements such as silicon, aluminum, calcium, and magnesium. The amount of gangue contained in reduced iron may be, for example, greater than 0% by mass and 5% by mass or less, or greater than 0% by mass and 20% by mass or less. The total amount of Si and Al contained in reduced iron is SiO ２ and Al ２ O ３ The equivalent value may be, for example, greater than 0% by mass and 15% by mass or less, 0.4% by mass and 15% by mass or less, 0.7% by mass and 15% by mass or less, or 1.0% by mass and 15% by mass or less.

[0022] 1.2 Agglomeration As shown in Figure 1, in the ironmaking method according to one embodiment, an agglomerated product containing the reduced iron and carbon material is produced. That is, at least the reduced iron and carbon material are mixed, and the reduced iron and carbon material are made to adhere to each other to obtain a lump-shaped agglomerated product. Agglomeration may be carried out in an agglomeration apparatus 20.

[0023] 1.2.1 Carbon material The carbon material contains carbon (elemental carbon or compounds). The carbon content of the carbon material may be, for example, 70% by mass or more and 100% by mass or less. The carbon content of the carbon material may be 85% by mass or more and 100% by mass or less, 90% by mass or more and 100% by mass or less, or 95% by mass or more and 100% by mass or less. The carbon material may contain various impurities such as elements such as silicon, aluminum, calcium, magnesium, iron, potassium, and sulfur, and their oxides.

[0024] There are no particular restrictions on the type of char material; it is acceptable as long as it can form agglomerated material together with the reduced iron mentioned above, and can reduce at least a portion of the iron oxide remaining in the reduced iron by heating in the rotary hearth furnace described later, and can also be carburized. The char material is a substance containing carbon, as described above, and may be a substance obtained by heat treatment such as dry distillation. For example, it may contain one or both of coke and biomass charcoal. Biomass charcoal refers to charcoal obtained from biological resources (biomass) other than fossil fuels. Specific examples of biomass include thinned wood, pruned branches, waste wood, bark chips, other wood, bamboo, grass, coconut shells, palm oil residue, vegetables, fruits, food waste, sludge, etc. The biomass may also be woody biomass such as thinned wood, pruned branches, waste wood, bark chips, and other wood. Biomass charcoal may be obtained, for example, by dry distillation of biomass to carbonize part or all of the biomass.

[0025] The carbon material has a size that can be used for agglomeration. In this embodiment, the particle size of the carbon material may be, for example, 44 μm to 500 μm, or 44 μm to 3 mm. The average particle size of the carbon material may also be, for example, 44 μm to 500 μm, or 44 μm to 3 mm. Note that "particle size" of the carbon material means the sieve diameter of the carbon material, and "average particle size" of the carbon material means the weighted average value of the particle sizes of the carbon material. Specifically, the average particle size of the carbon material can be measured by obtaining a mass-based particle size distribution by the dry sieving test described in JIS Z 8815:1995, and then weighting the average of the maximum and minimum particle sizes of each sieve as the representative particle size by mass.

[0026] 1.2.2 Other Materials In this embodiment, the reduced iron and carbon material described above may be mixed with other materials to produce an agglomerate. For example, the agglomerate may contain the reduced iron, the carbon material, and iron-containing substances other than the reduced iron. Examples of iron-containing substances other than reduced iron include iron-containing dust (e.g., shaft furnace dust), scale, and iron ore.

[0027] 1.2.2 Conditions for Agglomeration The conditions for agglomeration are not particularly limited, as long as an agglomerated product containing reduced iron and carbon material can be obtained. For example, an agglomerated product may be obtained by granulating reduced iron, carbon material, and any other material by mixing reduced iron, carbon material, and any other material with water and a suitable binder. That is, the agglomeration apparatus 20 may be a mixing apparatus that mixes reduced iron, etc., together with water and a binder. Alternatively, an agglomerated product may be obtained by mixing reduced iron with carbon material while maintaining a suitable temperature and briquetting it. That is, the agglomeration apparatus 20 may be a molding apparatus that molds reduced iron, etc. The latter is particularly preferred from the viewpoint of ease of adjusting the density of the agglomerated product and the elimination of the need for water. The molding temperature and molding pressure in briquetting are not particularly limited.

[0028] 1.2.3 Agglomerated Compounds As described above, agglomerated compounds contain reduced iron, carbon material, and optionally other materials. In this embodiment, "agglomerated compound" refers to a mass formed when multiple particles (powder) of reduced iron and multiple particles (powder) of carbon material adhere to and aggregate with each other. In this embodiment, the amount of reduced iron in the agglomerated compound may be, for example, 2% by mass or more and 98% by mass or less, or 8% by mass or more and 95% by mass or less. The amount of carbon material in the agglomerated compound may be, for example, 2% by mass or more and 30% by mass or less, or 5% by mass or more and 20% by mass or less. The amount of other materials in the agglomerated compound may be, for example, 0% by mass or more and 80% by mass or less, or 0% by mass or more and 75% by mass or less.

[0029] In one embodiment, the amount of reduced iron and carbon material in the agglomerated product may be such that the carbon concentration in the carburized metallic iron or carburized granular iron described later is 2.1% by mass or more. This corresponds to the amount by which the melting point (liquid phase formation temperature) of metallic iron is reduced to 1150°C or below by reduction and carburization during heating and cooling in the rotary hearth furnace described later. This makes it possible to lower the required heating temperature in the rotary hearth furnace, thereby reducing manufacturing costs, etc. However, if it exceeds 4.3% by mass, the carbon material will remain unreacted and become slag or dust, reducing productivity. In this regard, it is preferable that the amount of reduced iron and carbon material in the agglomerated product is such that the carbon concentration in the carburized metallic iron or carburized granular iron described later is 2.1% by mass or more and 4.3% by mass or less.

[0030] Furthermore, it is easy to determine the amount of carbon material added to agglomerated materials from the mass balance. As a simple method, if the carbon content of the carbon material constituting the agglomerated material is C (mass%), and the content of total iron, iron oxide, and metallic iron other than carbon material are T. Fe (mass%), FeO (mass%), and M. Fe (mass%), then when it is assumed that the carbon material is added as an additional w (mass%) to the raw materials other than carbon material, the w may be calculated using the following formula. Here, the carbon content is measured according to JIS G1211-1:2011, and the FeO and metallic iron content is measured according to JIS M8213:1995. w = ((T.Fe / 55.85-FeO / (55.85+16)-M.Fe / 55.85)*1.5+FeO / (55.85+16))*12+c*T.Fe / (100-c))*100 / C

[0031] The diameter of the agglomerate depends on factors such as the means of transporting it to the rotary hearth furnace described later and the impact associated with heating in the rotary hearth furnace, but may be, for example, 5 mm to 50 mm, or 10 mm to 20 mm. Note that "diameter of the agglomerate" refers to the diameter of a sphere having the same volume as the agglomerate (equivalent diameter of the volume sphere).

[0032] 1.3 Heating and Cooling in a Rotary Hearth Furnace As shown in Figure 1, in the ironmaking method according to one embodiment, the above-mentioned agglomerate is heated in the rotary hearth furnace 30 to produce carburized metallic iron, which is then melted. After subsequent cooling in the rotary hearth furnace 30, carburized granular iron and slag are produced. The above-mentioned agglomerate may be preheated before being charged into the rotary hearth furnace 30.

[0033] 1.3.1 Heating Conditions in a Rotary Hearth Furnace Any known rotary hearth furnace 30 may be used (for example, Non-Patent Documents 4-6 below). By charging the agglomerate into the rotary hearth furnace 30 and heating it, the carburization of the metallic iron contained in the agglomerate proceeds. In addition, the iron oxide remaining in the reduced iron is reduced by the carbon material to produce metallic iron, and carburization also proceeds for this newly produced metallic iron. This reaction results in a high metallization rate and a fast reaction rate. Non-Patent Document 4: Iron and Steel Handbook, 5th Edition, Vol. 1, Ironmaking and Steelmaking (2014), p. 218 Non-Patent Document 5: Kobe Steel Technical Report Vol. 60 No. 1 (April 2010), pp. 29-35 Non-Patent Document 6: JFE Technical Report No. 22 (November 2008), pp. 73-78

[0034] In the agglomerated material heated by the rotary hearth furnace 30, at least (1) carburized metallic iron, (2) slag, and (3) voids are present, and in some cases (4) unreduced iron oxide and (5) unreacted carbon material are also present. When the agglomerated material is sufficiently heated, the metallic iron particles assimilate through sintering and melting to form agglomerated iron masses, which, after cooling as described later, produce granular iron also called nuggets. Here, the parts where metallic iron particles that are in contact with each other (or not separated by other particles or sufficiently large voids) are connected are called "clusters." Since the assimilation of metallic iron proceeds in cluster units, the size of the resulting agglomerated iron masses depends on the size of the clusters. Also, when the agglomerated material is sufficiently heated, the slag particles also assimilate, but they are glassy and brittle, and the assimilated material obtained after cooling has lower strength compared to granular iron. Unreacted carbon material does not assimilate. If the carbon material is burned away by reduction or carburizing, that part becomes a void and inhibits assimilation. Furthermore, when unreduced iron oxide is in contact with carbon material, direct reduction proceeds to produce metallic iron, while unreduced iron oxide that is not in contact with carbon material assimilates, for example, with slag.

[0035] In the agglomerated material charged into the rotary hearth furnace 30, if the proportion (volume fraction) of metallic iron (reduced iron raw material) is low, as schematically shown in Figure 2A, after melting and cooling in the rotary hearth furnace 30, it becomes a large number of small iron particles of a finite size, or, as schematically shown in Figure 2B, it becomes agglomerated iron particles in which small iron particles are weakly bound together by simple contact or slag. Here, metallic iron that has been melted from reduced iron and separated from the slag, and which has undergone assimilation and integration with other reduced iron particles depending on the circumstances, is called "iron particles," while metallic iron that has been melted from reduced iron and separated from the slag, but has not undergone assimilation and integration with other metallic iron particles, and has become agglomerated by surface sintering, fusion, or adhesion with slag is called "agglomerated iron particles." In the form shown in Figure 2A, although the size of the iron particles obtained after melting and cooling is small, the density of the iron particles is high, and the strength is also high. On the other hand, as schematically shown in Figure 3, when the proportion of metallic iron (reduced iron raw material) is high in the agglomerate charged into the rotary hearth furnace 30, the clusters that are formed also become larger. When the proportion of metallic iron exceeds a certain threshold, the clusters rapidly grow to enormous sizes. Also, because metallic iron has high surface tension, densification of the metallic iron particles progresses at this time. As the metallic iron particles densify, the density of the iron particles increases, the strength of the iron particles increases, and their size also increases. This is because the linkage of clusters expands from a localized finite structure to the entire agglomerate. In percolation theory, this is called the critical point, and the volume fraction of metallic iron at that point is called the critical permeation volume fraction. Beyond this point, the clusters can grow infinitely large. This is determined solely by the dimension, except for extremely rod-shaped or flattened particles. In addition, while Figures 2A, 2B, and 3 illustrate the case where the carbon material disappears after the agglomerate is melted and cooled in a rotary hearth furnace, it is also possible for unconsumed carbon material to remain after melting and cooling.

[0036] As described above, since the ratio of metallic iron in the agglomerate charged into the rotary hearth furnace 30 is high, the carburized granular iron obtained after heating and cooling in the rotary hearth furnace has high strength and a large size. According to the findings of the present inventors, when γ defined by the following formula (1) is 14 or more, in the carburized granular iron obtained after heating and cooling in the rotary hearth furnace 30, the connection of metallic iron increases, and the hot strength is further improved. That is, the granular iron tends to have higher strength and a larger size. γ defined by the following formula (1) may be 16 or more, or 18 or more.

[0037] γ=α×β / 7.9 ・・・(1) α: Apparent density of the agglomerate (g / cm ３ ) β: Iron content of the agglomerate (mass%)

[0038] In the above formula (1), "apparent density α of the agglomerate (g / cm ３ )" is measured in accordance with JIS M8716:1990 and JIS M8715:2009 Annex B-4 for volume measurement. In addition, in the above formula (1), "iron content β of the agglomerate (mass%) (that is, total iron content)" is measured in accordance with JIS M8212:2005. Furthermore, in the above formula (1), the numerical value "7.9" corresponds to the density of metallic iron (7.9 g / cm ３ ).

[0039] The heating temperature and heating time in the rotary hearth furnace 30 may be any temperature as long as the aforementioned carburized metallic iron is generated and melted, and granular iron and slag can be obtained after cooling described later. In one embodiment, the heating temperature in the rotary hearth furnace 30 may be, for example, 1200°C to 1450°C, or 1300°C to 1400°C, and the heating time may be, for example, 5 minutes to 25 minutes, or 10 minutes to 15 minutes. Alternatively, when ITmk3 is used as the rotary hearth furnace, it is preferable that the melting temperature in ITmk3 is 1500°C or lower. This is because if the melting temperature exceeds 1500°C, the powder generated by the bursting of the agglomerate may fuse into a plate shape, and there is a risk that separability will deteriorate. There are also no particular limitations on the heating atmosphere in the rotary hearth furnace 30, and for example, it may be an inert gas atmosphere such as nitrogen gas or argon gas.

[0040] 1.3.2 Cooling in the rotary hearth furnace In this embodiment, after the heating in the aforementioned rotary hearth furnace 30, cooling is also performed in the same rotary hearth furnace 30, whereby carburized granular iron and slag are obtained. There are no particular limitations on the cooling conditions (cooling rate, cooling stop temperature, cooling atmosphere, etc.) in the rotary hearth furnace 30.

[0041] 1.3.3 Carburized granular iron The granular iron obtained through the above process has an increased carbon concentration due to carburization. As described above, when heating in the rotary hearth furnace 30, from the perspective of sufficiently lowering the melting point of metallic iron through carburization, if the addition amount of carbonaceous material in the agglomerate is set to a predetermined value or more, the carbon concentration of the finally obtained granular iron will also be a predetermined value or more. For example, the carbon concentration of granular iron may be 2.1 mass% or more, or may be 2.1 mass% to 4.3 mass%.

[0042] The size of the granular iron is not particularly limited. However, larger granular iron makes separation from slag (described later) easier. In this regard, the diameter of the granular iron may be, for example, 5 mm to 50 mm, or 10 mm to 20 mm. Note that the "diameter of granular iron" refers to the diameter of a sphere having the same volume as the volume of the granular iron (volume-equivalent sphere diameter).

[0043] 1.3.4 Slag The slag obtained as described above may be in a state of adhering to the aforementioned granular iron. The composition and amount of the slag vary depending on the amount of gangue in the reduced iron described above and the like. In the present embodiment, regardless of the composition and amount of the slag, granular iron and slag can be easily separated as described later.

[0044] 1.4 Separation As shown in FIG. 1, in the iron-making method according to one embodiment, the granular iron and the slag are separated, and the granular iron is recovered. Granular iron (metallic iron) and slag are melt-separated from each other and aggregated respectively. Therefore, for example, by applying an appropriate impact through a repeated dropping operation called a shutter as the separation device 40, or a rotating operation using a cylindrical drum called a tumbler, granular iron and slag can be easily separated, and granular iron can be recovered.

[0045] 1.5 Other Steps As shown in FIG. 4, the iron-making method according to one embodiment may include melting and refining the recovered granular iron to obtain molten steel. That is, the granular iron recovered from the separation device 40 may be charged into a smelting furnace 50, and melting and refining of the granular iron may be performed in the smelting furnace 50. Examples of the smelting furnace 50 include an electric arc furnace. As described above, the granular iron according to the present embodiment has a small slag content, so the load on the electric arc furnace is easily reduced. Further, as described above, the carbon concentration of the granular iron according to the present embodiment has been increased by carburization, so it can be easily melted at a low temperature. In addition, the carbon contained in the granular iron can also function as a heat source during refining.

[0046] 2. Iron-Making System The technology of the present disclosure includes an embodiment as an iron-making system in addition to the embodiment as the above-described iron-making method. As shown in FIG. 1, the iron-making system 100 according to one embodiment comprises: an iron oxide raw material feeding device 1, a reducing gas feeding device 2, a reduction furnace 10 connected to the iron oxide raw material feeding device 1 and the reducing gas feeding device 2, a carbonaceous material feeding device 3, a agglomeration device 20 provided on the downstream side of the reduction furnace 10 and the carbonaceous material feeding device 3, a rotary hearth furnace 30 provided on the downstream side of the agglomeration device 20, a separation device 40 provided on the downstream side of the rotary hearth furnace 30.

[0047] Furthermore, as shown in Figure 4, the ironmaking system 100 according to one embodiment may include a smelting furnace 50 located downstream of the separation device 40.

[0048] 2.1 Iron Oxide Raw Material Supply Device The iron oxide raw material supply device 1 supplies iron oxide raw materials to the reduction furnace 10. The iron oxide raw material supply device 1 may be configured to supply iron oxide raw materials into the interior of the reduction furnace 10 by means of, for example, a conveyor, a chute, or a hopper. Details of the iron oxide raw materials are as described above.

[0049] 2.2 Reducing Gas Supply Device The reducing gas supply device 2 supplies reducing gas to the reducing furnace 10. The reducing gas supply device 2 may be configured to supply reducing gas from a reducing gas source to the reducing furnace 10 via piping, for example. For example, the reducing gas supply device 2 may supply reducing gas containing hydrogen gas to the reducing furnace 10. Details of the reducing gas are as described above.

[0050] 2.3 Charcoal Material Supply Device The charcoal material supply device 3 supplies charcoal material to the agglomeration device 20. The charcoal material supply device 3 may be configured to supply charcoal material into the agglomeration device 20 by means of, for example, a conveyor, a chute, or a hopper. Details of the charcoal material are as described above.

[0051] 2.4 Details of the reduction furnace 10 for reducing other iron oxide raw materials to obtain reduced iron, the agglomeration device 20 for agglomerating the reduced iron obtained in the reduction furnace 10 and carbon material to obtain agglomerated material, the rotary hearth furnace 30 for heating and cooling the agglomerated material obtained in the agglomeration device 20 to obtain carburized granular iron and slag, the separation device 40 for separating the granular iron and slag obtained in the rotary hearth furnace 30 to recover the granular iron, and the smelting furnace 50 for refining using the granular iron are as described above and will not be explained here. As mentioned above, the reduction furnace 10 is preferably a fluidized bed furnace.

[0052] 3. Effects According to the steelmaking method and steelmaking system of this embodiment, slag can be separated from reduced iron to produce, for example, high-density, i.e., high-strength granular iron. In this embodiment, in the rotary hearth furnace 30, the reduction rate is improved by reducing the unreduced iron oxide contained in the reduced iron with carbon material, and the slag is separated. This makes it possible to produce easily transportable granular iron using low-grade (high slag content) iron ore, which has a low metallization rate (reduction rate) and was previously difficult to use, as a raw material for reduced iron. Furthermore, this eliminates location constraints with downstream processes after steelmaking. In addition, by appropriately reducing the unreduced iron oxide in the rotary hearth furnace 30, the constraints on the reduction rate that must be achieved in the reduction furnace 10 can be eased. At the same time, concerns about troubles associated with operational actions aimed at improving the reduction rate in the reduction furnace 10, such as sticking and clustering, are also eliminated. In particular, when a fluidized bed furnace is adopted as the reduction furnace 10, the constraints on the appropriate gas flow rate due to the particle size distribution of the iron oxide raw material, and the resulting constraints on the reduction rate, are also eased.

[0053] As described above, the ironmaking method and ironmaking system according to this embodiment allow the use of low-grade iron sources (iron ore, etc.) in the direct reduction ironmaking method. Furthermore, the metallization rate of the reduced iron produced by the direct reduction ironmaking method can be reduced, thereby improving the productivity of the direct reduction ironmaking process and solving the aforementioned operational problems. In addition, slag sources such as gangue contained in the reduced iron can be separated as slag, improving density and strength, and increasing the density of granular iron obtained through the rotary hearth furnace 30. In other words, density constraints for overseas transport can be alleviated. Moreover, since residual iron oxide in the reduced iron is reduced by the carbon material in the rotary hearth furnace 30, the reduction rate of granular iron obtained through the rotary hearth furnace 30 can be improved. In other words, the impact of the limits and constraints on the reduction rate in the direct reduction ironmaking method can be mitigated.

[0054] 4. Supplementary Information In the steelmaking method according to this embodiment, as described above, an agglomerate containing reduced iron and carbon material is heated in a rotary hearth furnace 30 to produce carburized metallic iron, which is then melted. After subsequent cooling in the rotary hearth furnace 30, carburized granular iron and slag are produced. When the agglomerate contains reduced iron, for example, the bulk density is higher than when the agglomerate contains iron ore. In other words, according to this embodiment, the production yield is more easily improved than when an agglomerate mainly containing iron ore is used as the solid iron source. Furthermore, according to the steelmaking method according to this embodiment, reduced iron (granular iron) with a high metallization rate, which was difficult to produce in processes using shaft furnaces or fluidized bed furnaces due to the significantly increased reduction time, can be produced with high productivity. In addition, when molten steel is obtained by melting and refining the granular iron obtained by the steelmaking method according to this embodiment in an electric furnace, the amount of iron oxide charged into the electric furnace can be suppressed, enabling cost reduction and improvement of molten steel quality by using a large amount of reduced iron (suppression of tramp elements).

[0055] Furthermore, while ITmk3 is a process for reducing and carburizing agglomerates containing iron oxide and carbon in a rotary hearth furnace, ITmk3 is a process aimed at producing metallic iron from iron oxide with high productivity, so there was no advantage in actively using reduced iron as a raw material from a cost perspective. Moreover, since the principle of the process assumes that FeO in the molten slag generated by heating and reduction plays an important role in various behaviors such as carburization, the active use of reduced iron that does not contain or contains little iron oxide was not envisioned or considered. In addition, rotary hearth furnace processes such as FASTMET (registered trademark) and RHF are generally used to reduce iron ore and to treat dust to reduce and metallize low-reduction-rate components, and are not used for processing reduced iron that has already undergone metallization, especially for separating metallic iron from slag. In contrast, in the ironmaking method according to this embodiment, as described above, by heating the agglomerated material containing reduced iron and carbon material in a rotary hearth furnace 30, the unprecedented effects described above can be obtained, and the desired granular iron can be produced with high productivity.

[0056] The effects of the technology of this disclosure will be further explained below with reference to examples. The following examples are simulations for the purpose of illustrating the effects of the technology of this disclosure, and the technology of this disclosure is not limited to these examples.

[0057] 1. Test Method 1.1 Samples were prepared by sieving the raw material coke, iron ore, and reduced iron produced by fluidizing and reducing the iron ore in a hydrogen atmosphere at 700°C, using a sieve of 250 to 500 μm. The composition of each is as follows. The content of iron oxides other than FeO in the iron ore and reduced iron can be determined from the T. Fe content, FeO content, and metallization rate. Coke Carbon content: 85.7 mass% Slag: 10.6 mass% Iron ore T. Fe: 61.7 mass% FeO: 0.2 mass% Slag: 5.8 mass% Metallization rate: 0% Reduced iron material T. Fe: 88.0 mass% M. Fe: 74.8 mass% FeO: 17.0 mass% Slag: 8.3 mass% Metallization rate: 85%

[0058] 1.2 Molding The above raw materials were mixed and compressed to obtain agglomerated products (tablets) with a diameter of 1.5 cm and a height of 0.8 cm. During compression molding, a load was applied so that the porosity of the tablets was 20%. The value γ, shown in the following formula (1), was determined from the obtained tablets. Twenty tablets were obtained for each condition. γ = α × β / 7.9 ... (1) α: Apparent density of the tablet (g / cm³) ３ ) β: Iron content of the tablet (mass %)

[0059] 1.3 Simulation of a Rotary Hearth Furnace (1) In order to simulate heating and cooling in a reductive carburizing melting rotary hearth furnace, in this embodiment, a tablet was placed in an electric furnace, and a simple reductive carburizing melting test was performed by heating in the electric furnace. The heating conditions were as follows: Heating conditions Temperature: 1350°C Time: 10 minutes Atmosphere: Nitrogen atmosphere

[0060] (2) In order to simulate cooling in a cooled rotary hearth furnace, in this embodiment, (1) the tablet sample after the reductive carburizing melting test was cooled to room temperature in an electric furnace under a nitrogen atmosphere.

[0061] (3) Tumbler Separation In this embodiment, impact was applied using a cylindrical tumbler container to simulate the separation of granular iron and slag in the separation apparatus. The separation conditions were as follows: Tumbler dimensions: inner diameter 130 mm x length 200 mm Rotation speed: 30 rpm Number of rotations: 100 rpm

[0062] After tumbler treatment, granular iron was separated from the sample by visual inspection and magnetic separation.

[0063] This series of simulated operations allows for the simulation of the heating of agglomerate ore by radiative heat transfer in a rotary hearth furnace, the reduction, carburization, and melting of the carbonaceous material and iron oxide contained in the agglomerate ore by supplied heat, cooling within the furnace, and the separation of granular iron and slag by impact in the separation device.

[0064] 1.4 Evaluation After reduction carburizing and melting, the arithmetic mean values ​​of the tablet composition and density were calculated for each condition, and the arithmetic mean value of the density of the granular iron recovered from the tablets was also calculated. Furthermore, the granular iron recovered from the tablets was classified by sieving, and the mass percentage of granular iron with a size of 1 mm or less was determined.

[0065] 2. Test Results The test results are shown in Table 1 below. Example 1 involved the above tests and evaluations on a mixture of reduced iron and coke formed into augmented masses in a predetermined ratio. Examples 2 to 5 involved the above tests and evaluations on a mixture of reduced iron, coke, and iron ore formed into augmented masses in a predetermined ratio. Comparative Example 1 involved the above tests and evaluations on a mixture of iron ore and coke formed into augmented masses in a predetermined ratio. Comparative Example 2 involved the above tests and evaluations on an augmented mass of reduced iron alone.

[0066] In all of Examples 1 to 5, reduction and carburizing proceeded well, and subsequent tumbler separation allowed for the separation of granular iron from slag, enabling the recovery of granular iron. In all of Examples 1 to 5, the density of the granular iron after tumbler separation was high, meaning it had high strength. However, as the proportion of reduced iron decreased, γ as defined in formula (1) above decreased, and consequently the granular iron became porous, resulting in decreased density and strength, and there was a tendency for a large number of small granular iron particles with a size of 1 mm or less to be produced. On the other hand, Comparative Example 1 involved agglomeration of only iron ore and coke, but in this case, the density of the granular iron ultimately obtained was lower than that of Examples 1 to 5. Furthermore, in Comparative Example 1, although the carbon material necessary for carburizing was guaranteed and separation of slag metal was possible by carburizing melt, the contact between the molten metallic iron particles was insufficient, resulting in a large number of small granular iron particles with a size of 1 mm or less. Furthermore, in Comparative Example 2, only reduced iron was agglomerated, but after melting and cooling the agglomerated material, the tablets maintained their shape due to sintering of metallic iron and slag, and granular iron could not be obtained even after tumbler separation. In addition, the metallization rate of the finished product remained low, raising concerns that the load on the electric furnace in the next process would increase. It should be noted that in Comparative Example 2, powder with a size of 1 mm or less was obtained after tumbler separation, but this was merely due to the low-strength parts of the sintered body of metallic iron and slag being partially turned into powder.

[0067] Although the above example illustrates the use of reduced iron powder produced in a fluidized bed, it is clear from the principle that similar results can be obtained by crushing reduced iron produced in a shaft furnace or the like.

[0068] 1. Iron oxide raw material supply device 2. Reducing gas supply device 3. Charcoal material supply device 10. Reducing furnace 20. Agglomeration device 30. Rotary hearth furnace 40. Separation device 50. Smelting furnace 100. Steelmaking system

Claims

1. A method for making iron, comprising: obtaining an agglomerate containing reduced iron obtained by reducing an iron oxide raw material containing iron ore and a carbon material; heating the agglomerate in a rotary hearth furnace to produce carburized metallic iron and melt the metallic iron, and subsequently cooling in the rotary hearth furnace to obtain carburized granular iron and slag; and separating the granular iron and the slag to recover the granular iron.

2. A method for making iron according to claim 1, wherein the reduced iron is obtained by reducing the iron oxide raw material in a fluidized bed furnace.

3. A method for ironmaking according to claim 1 or 2, wherein the agglomerated product comprises the reduced iron, the carbon material, and an iron-containing substance other than the reduced iron.

4. A method for ironmaking according to any one of claims 1 to 3, wherein γ, as defined by the following formula (1), is 14 or more, and the carbon concentration of the granular iron is 2.1% by mass or more: γ = α × β / 7.9 ... (1) α: apparent density of the agglomerated material (g / cm³) ３ ) β: Iron content of the agglomerated material (mass%) 5. A method for making iron according to any one of claims 1 to 4, comprising: dissolving and refining the recovered granular iron to obtain molten steel.

6. A method for ironmaking according to any one of claims 1 to 5, wherein the reduced iron is obtained by reducing an iron oxide raw material with a reducing gas, and the reducing gas includes hydrogen gas.

7. A steelmaking system comprising: an iron oxide raw material supply device; a reducing gas supply device; a reducing furnace connected to the iron oxide raw material supply device and the reducing gas supply device; a carbon material supply device; an agglomeration device provided downstream of the reducing furnace and the carbon material supply device; a rotary hearth furnace provided downstream of the agglomeration device; and a separation device provided downstream of the rotary hearth furnace.

8. The steelmaking system according to claim 7, wherein the reducing furnace is a fluidized bed furnace.

9. A steelmaking system according to claim 7 or 8, comprising a smelting furnace provided downstream of the separation device.

10. A steelmaking system according to any one of claims 7 to 9, wherein the reducing gas supply device supplies a reducing gas containing hydrogen gas to the reducing furnace.

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