Apparatus and method for producing reduced iron

Abstract

To provide a reduced iron production apparatus for producing reduced iron with a high carbon content that is easy to use in post-processing equipment of a reduction furnace. [Solution] A reduced iron production apparatus comprising: a reduction furnace consisting of a shaft-type reduction furnace that produces reduced iron by reducing iron oxide using a reducing gas; a first carburizing gas introduction section for introducing a first carburizing gas containing hydrocarbon gas into the reduction furnace; a reduced iron outlet for discharging the reduced iron inside the reduction furnace to the outside; a heating section located below the first carburizing gas introduction section and above the reduced iron outlet, for heating the reduced iron to a temperature at which a carburizing reaction occurs; and a second carburizing gas introduction section located below the first carburizing gas introduction section and above the reduced iron outlet, for introducing a second carburizing gas containing hydrocarbon gas into the reduction furnace, wherein the second carburizing gas introduction section is arranged so that at least a portion of the second carburizing gas passes through the heating section.

Description

Technical Field

[0001] The present invention relates to a reduced iron manufacturing apparatus and a reduced iron manufacturing method.

Background Art

[0002] Worldwide, the movement towards carbon neutrality is spreading. In the field of the steel industry, the direct reduced iron production method, which emits less CO2 than the blast furnace - converter process, has attracted attention.

[0003] As direct reduced iron production methods, for example, the Midrex (MIDREX (registered trademark)) process and the Energiron process are known. In the direct reduced iron production method using a shaft - type reduction furnace (shaft furnace) represented by the Midrex (MIDREX (registered trademark)) process and the Energiron process, for example, direct reduced iron (DRI) is produced as follows. Specifically, a reducing gas (CH4, H2, CO, etc.) is blown in from around the middle of the shaft furnace, and the iron oxide pellets are reduced by counter - current with the iron oxide pellets charged from the upper part of the shaft furnace, and reduced iron is produced. The reduced iron produced by the direct reduced iron production method is generally used as a raw material for an electric furnace together with scrap, but its use as a raw material for a blast furnace is also spreading.

[0004] In recent years, there has been a demand for increasing the carbon content in reduced iron. For example, when using reduced iron as a raw material in an electric furnace, increasing the carbon content of the reduced iron allows carbon to dissolve more easily into the molten metal bath than directly adding carbon to the furnace (external carburization), and is expected to improve the heat transfer efficiency due to carbon combustion. Furthermore, by introducing reduced iron with a higher carbon content into the electric furnace, CO gas is generated, allowing the slag to foam and expand sufficiently. This promotion of foaming in the electric furnace contributes to suppressing the nitrogen content of the molten steel, and consequently, avoids problems caused by high nitrogen content in the molten steel, such as cracking of cast slabs during continuous casting and deterioration of the ductility of steel during rolling. In addition, by performing arc heating in this foamed slag, the arc is covered with slag and the input power can be maximized, enabling efficient heating in the electric furnace. Furthermore, there are advantages such as improved carbon yield and reduced carbon cost per unit. Furthermore, especially in electric furnaces that use a large amount of low-carbon scrap, a high carbon content in the reduced iron raw material is sometimes required to compensate for the lack of carbon.

[0005] Furthermore, it is predicted that the raw materials used to produce reduced iron will be of lower grade (i.e., have a lower iron content) in the future. When low-grade reduced iron is used in an electric furnace, a large amount of slag is generated. To address this, a higher carbon content is required in the molten metal in order to reduce the amount of FeO dissolved in the slag, that is, to increase the iron yield. Therefore, a high carbon content is desired in the reduced iron fed into the electric furnace.

[0006] As a carburizing method to increase the carbon content in reduced iron, for example, Patent Documents 1 and 2 describe a method in which carburizing gas is blown into the lower part of a reduction furnace from the reducing gas inlet to increase the carbon content of reduced iron.

[0007] Furthermore, Patent Document 3 describes a method for increasing the carbon content of hot briquetted iron (HBI) to be fed into an electric furnace or reduced iron melter by compressing and molding char material together with reduced iron using a briquette machine after discharging reduced iron from a shaft furnace. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] U.S. Patent No. 4752329 [Patent Document 2] European Patent No. 2459755 [Patent Document 3] International Publication No. 2022 / 271576 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] In carburizing methods using carburizing gas as described in Patent Documents 1 and 2, the carburizing gas generally consists mainly of methane (CH4). By blowing in a gas mainly composed of methane, a cracking reaction (3Fe + CH4 → Fe3C + 2H2) occurs, which can increase the carbon content in reduced iron. However, the cracking reaction is an endothermic reaction, and the temperature of the reduced iron decreases as carburizing progresses. A problem arises in that the reaction efficiency of carburizing decreases as the temperature of the reduced iron decreases, and conventional techniques have limited the amount of carbon that can be added to the reduced iron.

[0010] Furthermore, when HBI is manufactured using reduced iron discharged from the reduction furnace, the decrease in the temperature of the reduced iron due to the carburizing reaction reduces its moldability and deteriorates the quality of the HBI, which presented a problem in that the amount of carburized iron could not be increased.

[0011] Furthermore, the carburizing gas blown into the reduction furnace from outside flows from the center of the furnace towards the top after the carburizing reaction. However, if the amount of carburizing gas is increased too much, the relatively low temperature of this gas causes a decrease in the temperature of the center of the furnace, which in turn inhibits the reduction reaction in the center of the furnace.

[0012] Here, the cracking reaction (carburizing reaction) is an endothermic reaction that proceeds in the temperature range of 500°C or higher, and proceeds particularly rapidly in the high temperature range of 700°C or higher. Therefore, in order to increase the reaction efficiency of carburizing, one could consider raising the temperature of the reduced iron by raising the temperature of the reducing gas, or using preheated carburizing gas. However, if the temperature of the reducing gas is raised too high, clustering occurs in the reduction furnace, where the reduced iron adheres to each other, obstructing the flow of reduced iron. Furthermore, there is a limit to the preheating temperature to prevent the cracking reaction from occurring when preheating the carburizing gas, and it is difficult to blow high-temperature carburizing gas into the reduction furnace. Specifically, if the temperature of the carburizing gas (methane gas) is raised too high in the preheating device, a cracking reaction occurs in the preheating device, causing carbon to accumulate, leading to problems such as clogging of pipes, overheating and short circuits in the heating section, and failure to obtain the required carburizing gas composition. Therefore, the preheating temperature for carburizing gas is limited to around 200-400°C, and it is difficult to preheat the carburizing gas to a temperature (700°C or higher) at which the cracking reaction proceeds rapidly.

[0013] Furthermore, in the method for increasing the carbon content described in Patent Document 3, the HBI is manufactured by briquetting solid DRI and carbon material, so the Fe and C in the HBI exist independently and do not form Fe3C (cementite). Therefore, when this HBI is added to the bath of an electric furnace, there is a problem that the carbon in the HBI does not easily dissolve into the bath, resulting in poor heat transfer efficiency due to carbon combustion. In addition, when such HBI is dissolved, unreacted carbon is discharged along with the exhaust gas and slag, leading to problems such as a decrease in carbon yield.

[0014] Furthermore, in general, in HBI, metallic iron acts as a binder to maintain strength. However, HBI obtained by briquetting (compression molding) of carbon material and reduced iron has lower strength compared to HBI produced using only reduced iron because the carbon material acts as a release agent. Therefore, there were problems such as cracking and powder generation due to pulverization of HBI during transportation.

[0015] Furthermore, when using HBI obtained by briquetting carbon material and reduced iron as a raw material for downstream equipment of a briquette machine (for example, an electric furnace or a reduced iron melter), the temperature of the HBI decreases during the briquette process. This leads to a problem where the power consumption of the melting equipment increases compared to when hot direct reduced iron (HDRI) discharged at high temperature from the reduction furnace is used directly.

[0016] Furthermore, the method of increasing carbon content using briquettes presented problems in terms of equipment, including the need for additional equipment such as particle size adjustment equipment for reduced iron and carbon materials, carbon material addition equipment, and briquetting machines, as well as an increase in the height of the shaft furnace, resulting in a significant increase in equipment costs. In addition, maintenance costs for the briquetting machines were incurred, posing problems from an economic standpoint.

[0017] This invention has been made in view of the above problems, and aims to provide an apparatus and method for producing reduced iron, which has a high carbon content and is easy to use in equipment after the reduction furnace. [Means for solving the problem]

[0018] As a result of various studies, the inventors have found that the above objective can be achieved by the following invention.

[0019] A reduced iron production apparatus according to one aspect of the present invention comprises: a reduction furnace consisting of a shaft-type reduction furnace that produces reduced iron by reducing iron oxide with a reducing gas; a first carburizing gas introduction section for introducing a first carburizing gas containing hydrocarbon gas into the reduction furnace; a reduced iron outlet for discharging the reduced iron inside the reduction furnace to the outside; a heating section located below the first carburizing gas introduction section and above the reduced iron outlet, which heats the reduced iron to a temperature at which a carburizing reaction occurs; and a second carburizing gas introduction section located below the first carburizing gas introduction section and above the reduced iron outlet, which introduces a second carburizing gas containing hydrocarbon gas into the reduction furnace, wherein the second carburizing gas introduction section is arranged such that at least a portion of the second carburizing gas passes through the heating section.

[0020] This configuration allows for the production of reduced iron with a high carbon content, which is easily usable in downstream equipment of the reduction furnace. Furthermore, the carburizing reaction by the cracking reaction of hydrocarbon gas is generally an endothermic reaction, and the reaction proceeds more readily in the high-temperature range. This cracking reaction prevents overheating of the reduced iron that can occur due to heating, and also suppresses clustering, where reduced iron particles adhere to each other. In addition, the high-temperature H2 generated by the carburizing reaction with the second carburizing gas flows upward within the reduction furnace, and this high-temperature H2 can be used as a reducing gas. This improves the temperature drop in the center of the reduction furnace and promotes the reduction reaction.

[0021] Preferably, the reduced iron production apparatus includes a reducing gas introduction section for introducing the reducing gas into the reduction furnace, and a gas outlet located above the reducing gas introduction section for discharging the gas inside the reduction furnace to the outside of the reduction furnace. With such a configuration, the high-temperature H2 generated by the carburizing reaction with the second carburizing gas flows more reliably upward within the reduction furnace, and this high-temperature H2 is utilized as the reducing gas. This improves the temperature drop in the center of the reduction furnace and promotes the reduction reaction.

[0022] In the reduction iron manufacturing apparatus, it is preferable that the second carburizing gas introduction part is arranged below the heating part. According to such a configuration, the contact time between the second carburizing gas and the reduction iron becomes longer, and the carburizing amount can be increased. Therefore, reduction iron with a high carbon content can be manufactured more reliably.

[0023] In the reduction iron manufacturing apparatus, it is preferable that the heating part includes two or more heating devices, and the second carburizing gas introduction part is arranged between at least one heating device and the heating device adjacent to the heating device. According to such a configuration, since the reduction iron whose temperature has decreased due to the carburizing reaction can be reheated, it is easy to control the temperature of the obtained reduction iron.

[0024] In the reduction iron manufacturing apparatus, it is preferable that the heating part includes two or more heating devices, and one or more second carburizing gas introduction parts are arranged below the heating part and between at least one heating device and the heating device adjacent to the heating device, respectively. According to such a configuration, the contact time between the second carburizing gas and the reduction iron becomes longer, and the carburizing amount can be increased. Therefore, reduction iron with a high carbon content can be manufactured more reliably. Furthermore, since the reduction iron whose temperature has decreased due to the carburizing reaction can be reheated, it is also easy to control the temperature of the obtained reduction iron.

[0025] In the reduction iron manufacturing apparatus, it is preferable that the heating part includes an induction heating coil. By providing the heating part with an induction heating coil, the reduction iron can be heated evenly.

[0026] In the reduction iron manufacturing apparatus, it is preferable that the second carburizing gas contains 50% by volume or more of hydrocarbon gas with respect to the total amount of the gas. According to such a configuration, the carburizing reaction is likely to occur, and the carbon content of the reduction iron can be increased more reliably.

[0027] In the aforementioned reduced iron production apparatus, the temperature at which the carburizing reaction occurs is preferably 600°C or higher and 1000°C or lower. By setting the temperature at which the carburizing reaction occurs to 600°C or higher, the carburizing reaction can be carried out at a sufficient carburizing rate, thereby more reliably increasing the carbon content of the reduced iron. Furthermore, by setting the temperature at which the carburizing reaction occurs to 1000°C or lower, clustering, where reduced iron particles adhere to each other, can be suppressed.

[0028] A method for producing reduced iron according to another aspect of the present invention involves: introducing a raw material containing iron oxide into a reduction furnace consisting of a shaft-type reduction furnace for producing reduced iron; introducing a reducing gas into the reduction furnace and reducing the iron oxide with the reducing gas to produce reduced iron; discharging the reduced iron inside the reduction furnace to the outside through a reduced iron outlet; and introducing a first carburizing gas containing hydrocarbons into the reduction furnace below the introduction position of the reducing gas and above the reduced iron outlet, and performing carburizing by adding carbon to the reduced iron with at least a portion of the first carburizing gas. The method includes heating the reduced iron to a temperature at which a carburizing reaction occurs, below the introduction position of the reducing gas and the introduction position of the first carburizing gas, and above the reduced iron outlet; and introducing a second carburizing gas containing hydrocarbon gas into the reduction furnace at below the introduction position of the reducing gas and the introduction position of the first carburizing gas, and above the reduced iron outlet, so that at least a portion of the second carburizing gas is heated by contact with the heated reduced iron, and carburizing is performed by adding carbon to the heated reduced iron with at least a portion of the second carburizing gas.

[0029] This configuration allows for the production of reduced iron with a high carbon content, which is easily usable in downstream equipment of the reduction furnace. Furthermore, the carburizing reaction by the cracking reaction of hydrocarbon gas is generally an endothermic reaction, and the reaction proceeds more readily in the high-temperature range. This cracking reaction prevents the reduced iron from overheating due to heating, and also has the effect of suppressing clustering, where reduced iron particles adhere to each other. In addition, the high-temperature H2 generated by the carburizing reaction with the second carburizing gas flows upward within the reduction furnace, and this high-temperature H2 can be used as a reducing gas. This improves the temperature drop in the center of the reduction furnace and promotes the reduction reaction.

[0030] In the method for producing reduced iron described above, it is preferable to include discharging the gas inside the reduction furnace to the outside of the reduction furnace at a point above the introduction position of the reducing gas. With this configuration, the high-temperature H2 generated by the carburizing reaction with the second carburizing gas flows more reliably upward within the reduction furnace, and this high-temperature H2 is utilized as the reducing gas. This improves the temperature drop in the center of the reduction furnace and promotes the reduction reaction.

[0031] In the aforementioned method for producing reduced iron, it is preferable to introduce the second carburizing gas below the position where the heating is performed. With this configuration, the contact time between the second carburizing gas and the reduced iron is increased, and the amount of carburization can be increased. Therefore, reduced iron with a high carbon content can be produced more reliably.

[0032] In the method for producing reduced iron described above, it is preferable to perform the heating using two or more heating devices, and to introduce the second carburizing gas between at least one heating device and a heating device adjacent to it. With such a configuration, the reduced iron whose temperature has decreased due to the carburizing reaction can be reheated, making it easy to control the temperature of the resulting reduced iron.

[0033] It is preferable to perform the heating using two or more heating devices, and to introduce the second carburizing gas at positions below the heating location and at least one heating device and a heating device adjacent to it. With this configuration, the contact time between the second carburizing gas and the reduced iron is increased, and the amount of carburization can be increased. As a result, reduced iron with a high carbon content can be produced more reliably. Furthermore, since the reduced iron whose temperature has decreased due to the carburizing reaction can be reheated, it is easy to control the temperature of the resulting reduced iron.

[0034] In the above-mentioned method for producing reduced iron, it is preferable that the heating method is induction heating. By using induction heating, the reduced iron can be heated uniformly.

[0035] In the method for producing reduced iron described above, it is preferable that the second carburizing gas contains 50% or more by volume of hydrocarbon gas relative to the total amount of gas. With such a configuration, the carburizing reaction is more likely to occur, and the carbon content of the reduced iron can be increased more reliably.

[0036] In the above-mentioned method for producing reduced iron, it is preferable that the temperature at which the carburizing reaction occurs is between 600°C and 1000°C. By setting the temperature at which the carburizing reaction occurs to 600°C or higher, the carburizing reaction can be carried out at a sufficient carburizing rate, thereby more reliably increasing the carbon content of the reduced iron. Furthermore, by setting the temperature at which the carburizing reaction occurs to 1000°C or lower, it is possible to suppress the occurrence of clustering, where reduced iron particles adhere to each other. [Effects of the Invention]

[0037] According to the present invention, it is possible to provide an apparatus and method for producing reduced iron, which has a high carbon content and is easy to use in equipment for post-processing of a reduction furnace. [Brief explanation of the drawing]

[0038] [Figure 1]Figure 1 is a schematic diagram showing an example of a reduced iron production apparatus according to an embodiment of the present invention. [Figure 2] Figure 2 is a schematic cross-sectional view showing the duct structure at the bottom of the reduction furnace in the reduced iron production apparatus shown in Figure 1. [Figure 3] Figure 3 is a schematic diagram showing another example of a reduced iron production apparatus according to an embodiment of the present invention. [Figure 4] Figure 4 is a schematic diagram showing another example of a reduced iron production apparatus according to an embodiment of the present invention. [Modes for carrying out the invention]

[0039] Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited thereto.

[0040] [Iron reduction production equipment] An embodiment of the present invention provides a reduced iron production apparatus comprising: a reduction furnace consisting of a shaft-type reduction furnace that produces reduced iron by reducing iron oxide using a reducing gas; a first carburizing gas introduction section for introducing a first carburizing gas containing hydrocarbon gas into the reduction furnace; a reduced iron outlet for discharging the reduced iron inside the reduction furnace to the outside; a heating section located below the first carburizing gas introduction section and above the reduced iron outlet, which heats the reduced iron, whose temperature has decreased due to a carburizing reaction (cracking reaction) by the first carburizing gas, to a temperature at which a carburizing reaction occurs; and a second carburizing gas introduction section located below the first carburizing gas introduction section and above the reduced iron outlet, which introduces a second carburizing gas containing hydrocarbon gas into the reduction furnace, wherein the second carburizing gas introduction section is arranged such that at least a portion of the second carburizing gas passes through the heating section.

[0041] This configuration makes it possible to produce reduced iron with a high carbon content that is easy to use in equipment downstream of the reduction furnace. More specifically, reduced iron reduced by a reducing gas is first carburized by a first carburizing gas. However, since the carburizing reaction by cracking hydrocarbon gases is generally an endothermic reaction, the temperature of the reduced iron decreases as carburizing progresses. When the temperature of the reduced iron decreases, the reaction efficiency of the carburizing reaction decreases. Therefore, in this invention, after carburizing the reduced iron with the first carburizing gas, the reduced iron is heated to a temperature at which the carburizing reaction occurs by a heating section located below the introduction section of the first carburizing gas. Then, a second carburizing gas is introduced into the reduction furnace so that at least a portion of the second carburizing gas passes through the heating section. The reduced iron is carburized again by at least a portion of the introduced second carburizing gas. This allows for an efficient carburizing reaction and makes it possible to obtain reduced iron with a high carbon content.

[0042] Furthermore, as mentioned above, it is conceivable to use preheated carburizing gas to increase the reaction efficiency of carburizing, but there is an upper limit to the preheating temperature of the carburizing gas, making it difficult to raise the carburizing gas to a temperature at which the carburizing reaction proceeds rapidly. As an alternative, increasing the amount of carburizing gas introduced is conceivable, but if the reaction temperature is low, it is difficult to increase the amount of reduced iron carburized even if the amount of carburizing gas introduced is increased. However, in the present invention, reduced iron is heated in a heating section, and then a second carburizing gas is introduced into the reduction furnace so that at least a portion of the second carburizing gas passes through the heating section. Then, at least a portion of the introduced second carburizing gas carburizes the heated reduced iron. This makes it possible to efficiently generate a carburizing reaction. Therefore, the carbon content of reduced iron can be efficiently increased simply by adjusting the energy for heating and the amount of second carburizing gas introduced.

[0043] It is known that reduced iron undergoes clustering at high temperatures, where the reduced iron particles adhere to each other. However, by heating the reduced iron in the heating section and allowing at least a portion of the second carburizing gas to pass through the heating section, an endothermic carburizing reaction occurs in the heating section. This self-regulating reaction prevents overheating of the reduced iron and suppresses clustering.

[0044] Furthermore, with the above configuration, the high-temperature H2 generated by the carburizing reaction with the second carburizing gas (hereinafter also referred to as the second carburizing reaction) flows upward within the reduction furnace and can be utilized as a reducing gas. This improves the temperature reduction in the center of the reduction furnace and promotes the reduction reaction.

[0045] Furthermore, according to the above configuration, the reduced iron is carburized by the carburizing gas, and Fe3C (cementite) is formed in the reduced iron. Therefore, when the obtained reduced iron is used as a raw material for an electric furnace, the heat transfer efficiency due to carbon combustion is improved, and the carbon yield is improved. In addition, HBI formed using reduced iron carburized with carburizing gas has higher strength compared to HBI formed by briquetting carbon material and reduced iron, and cracking and powder generation due to powdering of HBI during transportation are reduced.

[0046] Furthermore, with the above configuration, there is no need to use a briquette machine in the process of increasing the carbon content of reduced iron, so there is no temperature drop of reduced iron due to briquetting. Therefore, when using reduced iron as a raw material for downstream equipment of an adjacent reduction furnace (e.g., electric furnace, melter, etc.), the HDRI discharged at high temperature from the reduction furnace can be used directly, thus reducing the power consumption of the melting equipment. In addition, the equipment required when increasing the carbon content of reduced iron using a briquette machine (briquette machine, equipment for adjusting the particle size of reduced iron and carbon material, equipment for adding carbon material, etc.) is not required, reducing equipment costs and maintenance costs. Also, because these pieces of equipment are not required, the height of the reduction furnace can be reduced, further reducing equipment costs.

[0047] An example of a reduced iron production apparatus according to an embodiment of the present invention is specifically the reduced iron production apparatus 1 shown in Figure 1. The reduced iron production apparatus 1 shown in Figure 1 comprises a shaft-type reduction furnace 2 that produces reduced iron by reducing iron oxide using a reducing gas, a raw material supply port 3 that receives the raw material for reduced iron, a reduced iron discharge port 4 that discharges the reduced iron produced inside the reduction furnace 2, a reduction gas introduction unit 5 for introducing the reducing gas into the reduction furnace 2, a first carburizing gas introduction unit 6 for introducing a first carburizing gas containing hydrocarbon gas into the reduction furnace 2, a heating unit 7 that heats the reduced iron to a temperature at which a carburizing reaction occurs, a second carburizing gas introduction unit 8 for introducing a second carburizing gas containing hydrocarbon gas into the reduction furnace 2, and a gas discharge port 9 that discharges the gas inside the reduction furnace 2 to the outside of the reduction furnace 2.

[0048] The reduction furnace 2 is a furnace that produces reduced iron by reducing iron oxide using a reducing gas. The reduction furnace 2 is a vertically elongated shaft-type reduction furnace with a cylindrical shape that is long in the vertical direction. The reduction furnace 2 continuously supplies the raw material for reduced iron and continuously discharges the reduced iron while maintaining the temperature and pressure under predetermined conditions. An example of the reduction furnace 2 is a shaft furnace used in the MIDREX® process.

[0049] The raw material supply port 3 is located at the upper end of the reduction furnace 2. The raw material supply port 3 connects the external space and the internal space of the reduction furnace 2 so that raw materials for reducing iron can be supplied from the external space to the internal space through the supply port 3. The raw materials contain iron oxide and include, for example, iron ore, iron oxide pellets, CBQ (Cold Bond Briquette), and sintered ore. Examples of iron ore include stones containing iron oxide in their natural state. Examples of iron oxide pellets include those made by mixing iron ore, a binder, and water and firing them. Examples of sintered ore include those made by mixing iron ore powder, carbon, and lime and firing them.

[0050] The reduced iron outlet 4 is located at the lower end of the reduction furnace 2. The reduced iron outlet 4 connects the internal space and the external space of the reduction furnace 2 so that reduced iron can be discharged from the internal space to the external space through the outlet 4.

[0051] The reducing gas introduction section 5 is for introducing reducing gas into the reduction furnace 2. The reducing gas introduction section 5 connects the external space and the internal space of the reduction furnace 2 so that reducing gas can be introduced from the external space to the internal space through the reducing gas introduction section 5. The reducing gas introduction section 5 is located below the raw material supply port 3. For example, at least one reducing gas introduction section 5 may be arranged on the side wall (outer surface) of the reduction furnace 2, specifically, at multiple locations at equal intervals along the side wall, left and right and / or top and bottom. A compressor for introducing reducing gas (not shown) is connected to the reducing gas introduction section 5, and the amount of reducing gas introduced into the interior of the reduction furnace 2 can be adjusted.

[0052] In the reduction furnace 2, raw materials for reduced iron are supplied through the raw material supply port 3, and these raw materials remain in the internal space of the reduction furnace 2. In this state, reducing gas is introduced into the reduction furnace 2 from the reducing gas introduction port 5. The reducing gas is not particularly limited as long as it is a gas capable of reducing iron oxide, and examples include hydrogen, COG (Coke Oven Gas), Syngas, Biogas, and natural gas. Inside the reduction furnace 2, as the raw materials descend, the iron oxide contained in the raw materials is reduced by the reducing gas to become iron (hereinafter referred to as reduced iron). Most of the gas generated inside the reduction furnace 2 by the reduction reaction is discharged from the gas outlet 9 at the top of the reduction furnace 2. The discharged gas may be dedusted and cooled by a wet dust remover (not shown), then compressed again by a compressor and mixed with a hydrocarbon gas such as methane, and reformed by a reformer to be used as a reducing gas. Alternatively, oxidizing gases such as CO2 and H2O may be removed from the discharged gas and used as a reducing gas.

[0053] The first carburizing gas introduction section 6 is for introducing a first carburizing gas containing hydrocarbon gas into the reduction furnace 2. The first carburizing gas introduction section 6 connects the external space and the internal space of the reduction furnace 2 so that the first carburizing gas can be introduced from the external space to the internal space of the reduction furnace 2 through the first carburizing gas introduction section 6, and the amount of first carburizing gas introduced into the interior of the reduction furnace 2 can be adjusted. The first carburizing gas introduction section 6 is located below the reduction gas introduction section 5. The first carburizing gas introduction section 6, like the reduction gas introduction section 5, may be arranged at least once on the side wall (outer surface) of the reduction furnace 2, specifically, at multiple locations at equal intervals along the side wall, left and right and / or up and down.

[0054] A first carburizing gas is introduced into the reduction furnace 2 from the first carburizing gas introduction section 6. Inside the reduction furnace 2, the carbon content of the iron reduced by the reducing gas (reduced iron) increases due to a carburizing reaction by the first carburizing gas (hereinafter also referred to as the first carburizing reaction). The first carburizing gas is a gas used for carburizing treatment that adds carbon to the reduced iron, and contains hydrocarbon gases. Examples of the hydrocarbon gases include CH4, C2H6, C3H8, etc. The composition of the first carburizing gas can be described in the same way as the composition of the second carburizing gas, which will be described later. Most of the gas generated inside the reduction furnace 2 by the first carburizing reaction is discharged from the gas outlet 9 at the top of the reduction furnace 2.

[0055] The heating section 7 is for heating the reduced iron, which has been carburized by the first carburizing gas and whose temperature has decreased, to a temperature at which the carburizing reaction occurs. The heating section 7 is equipped with at least one heating device. Examples of such heating devices include heating devices that use heating methods such as induction heating, resistance heating, high-temperature gas injection, and microwave heating. Preferably, the heating section 7 is equipped with an induction heating coil for heating the reduced iron by electromagnetic induction heating. By using an induction heating device (induction heating coil) as the heating section 7, the reduced iron can be heated uniformly.

[0056] The heating section 7 is located below the first carburizing gas introduction section 6 and above the reduced iron outlet 4. Figure 2 is a cross-sectional view of the plane A of the reduction furnace 2 in Figure 1, viewed from the axial direction. As shown in Figures 1 and 2, the lower part of the reduction furnace 2 (the part below the first carburizing gas introduction section 6) is provided with two or more duct pipes (two visible in Figure 1, eight in Figure 2) branching in the direction of the reduced iron flow, forming a duct structure in which the reduced iron rejoins before passing through the reduced iron outlet 4. Preferably, the two or more duct pipes are arranged symmetrically with respect to the axis P of the reduction furnace 2 and at equal intervals (distances). In Figure 2, the eight duct pipes are arranged so as to make one full circle around the axis P of the reduction furnace 2 in the circumferential direction. At least one heating device is provided on the side wall (outer surface) of each duct pipe. Note that the structure of the lower part of the reduction furnace 2 does not have to be a duct structure as shown in Figures 1 and 2. In that case, at least one heating device may be placed on the side wall (outer surface) of the reduction furnace 2, specifically, for example, at multiple locations at equal intervals along the side wall. From the viewpoint of efficiently heating the reduced iron, it is preferable that two or more heating devices are placed on the side of each duct pipe, as shown in Figure 1.

[0057] The lower structure of the reduction furnace 2 may be, for example, a structure in which a cone 10 is provided below the duct pipe, as shown in the reduced iron production apparatus 11 in Figure 3. Figure 3 is a schematic diagram showing another example of a reduced iron production apparatus according to an embodiment of the present invention, and components with the same reference numerals as in Figure 1 are the same components. As shown in Figure 3, by providing a cone 10 below the duct pipe, the contact time between the second carburizing gas and the reduced iron can be extended, ensuring sufficient time for the second carburizing reaction to occur. Specifically, since the cross-sectional area of ​​the cone 10 is larger than the cross-sectional area of ​​the duct pipe, when the amount of reduced iron discharged from the reduction furnace per unit time is constant, the speed at which the reduced iron passes through the cone 10 is slower than the speed at which the reduced iron passes through the duct pipe when the cone 10 is not provided and the reduced iron is discharged directly from the duct pipe. Therefore, by providing a cone 10 between the reduced iron outlet and the duct pipe, the second carburizing gas and the reduced iron can be in contact for a longer period, ensuring sufficient time for the second carburizing reaction to occur.

[0058] The temperature at which the carburizing reaction occurs is typically between 600°C and 1000°C. That is, it is preferable that the temperature of the reduced iron (solid) inside the heating section be between 600°C and 1000°C. By setting the temperature of the reduced iron to 600°C or higher, the carburizing reaction can be carried out at a sufficient carburizing rate, thereby more reliably increasing the carbon content of the reduced iron. Furthermore, by setting the temperature of the reduced iron to 1000°C or lower, it is possible to suppress the occurrence of clustering, where the reduced iron particles adhere to each other. It is more preferable that the temperature of the reduced iron (solid) inside the heating section be between 650°C and 950°C, and even more preferable that be between 700°C and 900°C. The heating section 7 has a heating section control unit (not shown), and the temperature of the reduced iron inside the heating section can be adjusted by this heating section control unit.

[0059] The second carburizing gas introduction section 8 is for introducing a second carburizing gas containing hydrocarbon gas into the reduction furnace 2. The second carburizing gas introduction section 8 connects the external space and the internal space of the reduction furnace 2 so that the second carburizing gas can be introduced from the external space to the internal space through the second carburizing gas introduction section 8, and the amount of second carburizing gas introduced into the heating section 7 can be adjusted.

[0060] The second carburizing gas introduction section 8 is located below the first carburizing gas introduction section 6 and above the reduced iron outlet 4. Furthermore, the second carburizing gas introduction section 8 is positioned so that at least a portion of the second carburizing gas passes through the heating section 7.

[0061] The second carburizing gas introduction section 8 is located, for example, below the heating section 7. Specifically, for example, in Figure 1, the second carburizing gas introduction section 8 is located on the side wall (outer surface) of the duct pipe between the heating section 7 and the reduced iron outlet 4. Also, for example, if the lower structure of the reduction furnace 2 is not a duct structure as shown in Figure 1, at least one second carburizing gas introduction section 8 may be located on the side wall (outer surface) of the reduction furnace 2 between the heating section 7 and the reduced iron outlet 4, specifically, for example, at multiple locations at equal intervals along the side wall. Furthermore, in Figure 3, the second carburizing gas introduction section 8 is located on the side wall (outer surface) of the cone 10 between the heating section 7 and the reduced iron outlet 4, but it is not limited to that, and may be located on the side wall (outer surface) of the duct pipe below the heating section 7.

[0062] The second carburizing gas introduction section 8 may be located between at least one heating device and a heating device adjacent to that heating device. Specifically, for example, the reduced iron production apparatus 21 shown in Figure 4 has two second carburizing gas introduction sections 8, and the heating section 7 has six heating devices (7a to 7f). The two second carburizing gas introduction sections 8 are located on the side walls (outer surfaces) of the duct pipe between heating device 7b and heating device 7c, or on the side walls (outer surfaces) of the duct pipe between heating device 7e and heating device 7f. In Figure 4, for example, the two second carburizing gas introduction sections may be located on the side walls (outer surfaces) of the duct pipe between heating device 7a and heating device 7b, or on the side walls (outer surfaces) of the duct pipe between heating device 7d and heating device 7e. Furthermore, for example, even if the lower part of the reduction furnace 2 has a structure in which a cone 10 is provided on the lower side of the duct pipe, as shown in Figure 3, the second carburizing gas introduction section 8 may be located on the side wall (outer surface) of the duct pipe between at least one heating device and a heating device adjacent to the said heating device. Also, for example, if a duct structure as shown in Figure 4 is not provided at the lower part of the reduction furnace 2, at least one second carburizing gas introduction section 8 may be located on the side wall (outer surface) of the reduction furnace 2 between at least one heating device and a heating device adjacent to the said heating device, specifically, for example, multiple sections may be located at equal intervals along the side wall.

[0063] Alternatively, although not shown in the figures, the second carburizing gas introduction section 8 may be located below the heating section 7 and at least one may be positioned between at least one heating device and a heating device adjacent to that heating device.

[0064] While specific examples have been given to describe the location of the second carburizing gas introduction section 8, the design is not limited to these. The second carburizing gas introduction section 8 only needs to be located at a position where the second carburizing gas can be introduced so that at least a portion of the second carburizing gas passes through the heating section 7. For example, it may be located in multiple locations. Furthermore, having two or more second carburizing gas introduction sections 8 located at positions where the second carburizing gas can be introduced so that at least a portion of the second carburizing gas passes through the heating section 7 has the advantage of making the second carburizing reaction more efficient.

[0065] Figure 4 is a schematic diagram showing another example of a reduced iron production apparatus according to an embodiment of the present invention. The reduced iron production apparatus 21 shown in Figure 4 differs from the reduced iron production apparatus 1 shown in Figure 1 in that the second carburizing gas introduction section 8 is located between at least one heating device and a heating device adjacent to the said heating device.

[0066] The reduced iron carburized by the first carburizing gas described above experiences a decrease in temperature due to the carburizing reaction, as the carburizing reaction is endothermic. Since a lower temperature of the reduced iron reduces the efficiency of the carburizing reaction, it is difficult to increase the carbon content of the reduced iron even if the amount of carburizing gas introduced is increased. On the other hand, by heating the reduced iron in the heating unit 7 and then bringing at least a portion of the second carburizing gas into contact with the reduced iron heated by the heating unit 7, the carburizing reaction can be efficiently generated, and the carbon content of the resulting reduced iron can be increased.

[0067] The second carburizing gas is a gas used for carburizing treatment, which adds carbon to reduced iron, and contains hydrocarbon gas. Examples of the hydrocarbon gas include CH4, C2H6, C3H8, etc., and these include those derived from natural gas and biomass. Preferably, the second carburizing gas contains 50% or more by volume of hydrocarbon gas relative to the total amount. When the reduced iron heated in the heating section 7 comes into contact with the second carburizing gas containing 50% or more by volume of hydrocarbon gas relative to the total amount of gas, a cracking reaction is easily generated, and the carbon content of the reduced iron can be increased more efficiently. Furthermore, since the cracking reaction is an endothermic reaction, the occurrence of the cracking reaction also has the effect of preventing overheating of the reduced iron. It is also possible to increase the reaction rate by increasing the amount of the second carburizing gas introduced while keeping the concentration of hydrocarbon gas relative to the total amount of gas low, but by setting the hydrocarbon gas content to 50% or more by volume relative to the total amount of gas, the utilization efficiency of the carburizing gas is improved.

[0068] The second carburizing gas may contain gases other than hydrocarbon gases, but specifically, it is preferable to have less of gases such as N2, H2, CO, H2O, and CO2. If the second carburizing gas contains inert gases such as N2, the inert gas will accumulate in the process flow, and it will be necessary to discharge a certain amount of it, but at the same time unused and reusable gases will also be discharged, which may reduce energy efficiency. Also, if the second carburizing gas contains H2, the reverse reaction of the carburizing reaction will proceed more easily, which may reduce the carburizing rate. Furthermore, if a carburizing gas other than hydrocarbon gases (such as CO) is used as the second carburizing gas, the carburizing reaction will be an exothermic reaction, which may cause the temperature of the reduced iron to rise and lead to clustering. In addition, if the second carburizing gas contains oxidizing gases such as H2O or CO2, it will consume carbon and inhibit carburizing, which may reduce the reaction efficiency of the carburizing reaction. Therefore, by setting the hydrocarbon gas content to 50% or more by volume relative to the total gas volume, it is possible to suppress the content of other gases mentioned above, which has the advantage of improving the utilization efficiency and energy efficiency of the carburized gas.

[0069] The second carburizing gas more preferably contains 80% or more by volume of hydrocarbon gas, and even more preferably 90% or more by volume. There is no particular upper limit to the hydrocarbon gas content relative to the total amount of the second carburizing gas, and the higher the hydrocarbon gas content, the better.

[0070] Most of the gas generated by the second carburizing reaction flows towards the top of the reduction furnace 2 and is discharged from the gas outlet 9 at the top of the reduction furnace 2. The high-temperature H2 produced by the carburizing reaction with the second carburizing gas flows towards the top of the reduction furnace 2, and this high-temperature H2 can be used as a reducing gas. This improves the temperature drop in the center of the reduction furnace and promotes the reduction reaction. Specifically, in the conventional carburizing method using carburizing gas, relatively low-temperature H2 is generated by the carburizing reaction that occurs below the reduction gas introduction section, and this H2 passes near the center of the reduction furnace and is discharged from the top of the reduction furnace. As a result, the temperature near the center of the reduction furnace is relatively low, which may lead to an insufficient reduction reaction. If the reduction reaction is insufficient, the efficiency of the subsequent carburizing reaction decreases. On the other hand, the H2 produced by the carburizing reaction of the second carburizing gas is heated in the heating section 7 and flows into the center of the reduction furnace 2 at a relatively high temperature, which raises the temperature in the center of the reduction furnace 2 and allows the reduction reaction in the center of the reduction furnace 2 to proceed efficiently. Furthermore, the generated H2 is effectively used as a reducing gas. Therefore, as the reduction reaction proceeds efficiently, the carburizing reactions by the first and second carburizing gases also proceed efficiently, and the carbon content of the reduced iron can be increased.

[0071] The gas outlet 9 is for discharging the gas inside the reduction furnace 2 to the outside of the reduction furnace 2. The gas outlet 9 is also located above the reduction gas introduction section 5. The gas outlet 9 connects the internal space and the external space of the reduction furnace 2 so that the gas inside the reduction furnace 2 can be discharged from the internal space to the external space through the outlet 9. The type of gas inside the reduction furnace 2 is not particularly limited and examples include the reduction gas, the gas generated by the reduction reaction, the first carburizing gas, the gas generated by the first carburizing reaction, and the second carburizing gas, the gas generated by the second carburizing reaction, etc.

[0072] The reduced iron produced by the reduced iron production apparatus in this embodiment preferably has a carbon content of 2% by mass or more, more preferably 2.5% by mass or more, and even more preferably 3% by mass, relative to the total amount of reduced iron.

[0073] The reduced iron produced by the reduced iron production apparatus in this embodiment has a high carbon content and suppresses temperature drop, making it easy to use in equipment downstream of the reduction furnace. The reduced iron can be suitably used as a raw material in equipment downstream of the reduction furnace, and production efficiency (improvement of energy intensity and productivity) can be improved, including the steelmaking process downstream of the reduction furnace. Specific examples of equipment downstream of the reduction furnace include electric furnaces, melters, briquetting machines, and other types of equipment.

[0074] [Method for producing reduced iron] Next, the method for producing reduced iron in this embodiment will be described in detail.

[0075] The method for producing reduced iron in this embodiment involves: introducing a raw material containing iron oxide into a reduction furnace consisting of a shaft-type reduction furnace for producing reduced iron; introducing a reducing gas into the reduction furnace and using the reducing gas to reduce the iron oxide and produce reduced iron; discharging the reduced iron inside the reduction furnace to the outside through a reduced iron outlet; introducing a first carburizing gas containing hydrocarbons into the reduction furnace below the introduction position of the reducing gas and above the reduced iron outlet, and performing carburizing by adding carbon to the reduced iron with at least a portion of the first carburizing gas; The method includes heating the reduced iron to a temperature at which a carburizing reaction occurs, below the introduction position of the reducing gas and the introduction position of the first carburizing gas, and above the reduced iron outlet; and introducing a second carburizing gas containing hydrocarbon gas into the reduction furnace at the introduction position of the reducing gas and the introduction position of the first carburizing gas, and above the reduced iron outlet, so that at least a portion of the second carburizing gas is heated by contact with the heated reduced iron, and at least a portion of the second carburizing gas adds carbon to the heated reduced iron to perform carburizing. By this method, reduced iron with a high carbon content that is easy to use in equipment downstream of the reduction furnace can be produced.

[0076] Specifically, first, a raw material containing iron oxide is introduced into the reduction furnace for producing reduced iron. More specifically, the raw material is introduced into the internal space of the reduction furnace from the raw material inlet. As a result, the inside of the reduction furnace is filled with the raw material containing iron oxide. The raw material is the same as that exemplified in the [reduced iron production apparatus] described above. In the reduction furnace, the raw material, while filling the inside of the reduction furnace, gradually descends through the inside of the reduction furnace as reduced iron is discharged from the reduced iron discharge port at the lower end of the reduction furnace.

[0077] Next, with the raw materials containing iron oxide filling the reduction furnace, a reducing gas is introduced into the reduction furnace, and the iron oxide is reduced by the reducing gas to produce reduced iron. Examples of the reducing gas include hydrogen, COG (Coke Oven Gas), Syngas, Biogas, and natural gas. The reducing gas is introduced into the reduction furnace filled with raw materials at a temperature above the temperature at which the reduction reaction of iron oxide can occur (for example, 700 to 1000 degrees Celsius) under pressure (for example, about 0.3 to 0.9 MPa) using a compressor or the like. The iron oxide (specifically Fe2O3, Fe3O4, etc.) is reduced by the reducing gas to produce reduced iron (for example, iron with a weight ratio of 80% or more Fe).

[0078] Next, below the introduction position of the reducing gas, a first carburizing gas containing hydrocarbons is introduced into the reduction furnace, and carburizing (first carburizing reaction) is carried out by adding carbon to the reduced iron with at least a portion of the first carburizing gas. The first carburizing gas is a gas containing hydrocarbons, for example, methane (CH4) can be used as the carburizing gas. More specifically, the first carburizing gas can be the same as those exemplified in the [reduced iron production apparatus] above. The first carburizing gas is introduced into the reduction furnace at a temperature lower than the temperature of the reducing gas (for example, about 200 to 400 degrees Celsius) and under pressure (for example, about 0.3 to 0.9 MPa).

[0079] Subsequently, the reduced iron is heated to a temperature at which the carburizing reaction occurs, below the introduction point of the reducing gas and the introduction point of the first carburizing gas. The method of heating the reduced iron is not particularly limited, and various heating methods such as resistance heating, induction heating, high-temperature gas blowing, and microwave heating can be cited. Among these, induction heating is preferred. By using induction heating, the reduced iron can be heated uniformly.

[0080] The temperature at which the carburizing reaction occurs is usually between 600°C and 1000°C. That is, it is preferable to heat the reduced iron (solid) so that its temperature is between 600°C and 1000°C. By raising the temperature of the reduced iron to 600°C or higher, the carburizing reaction can be carried out at a sufficient carburizing rate, thereby more reliably increasing the carbon content of the reduced iron. Furthermore, by raising the temperature of the reduced iron to 1000°C or lower, it is possible to suppress clustering, where the reduced iron particles adhere to each other. The temperature is more preferably between 650°C and 950°C, and even more preferably between 700°C and 900°C.

[0081] Next, a second carburizing gas containing hydrocarbons is introduced into the reduction furnace at a position lower than the introduction position of the reducing gas and the introduction position of the first carburizing gas, so that at least a portion of the second carburizing gas is heated by contact with the heated reduced iron, and carburizing (second carburizing reaction) is carried out by adding carbon to the heated reduced iron with at least a portion of the second carburizing gas. The position where the second carburizing gas is introduced is lower than the introduction position of the reducing gas and the introduction position of the first carburizing gas, and is not particularly limited as long as it is a position in which the second carburizing reaction can be carried out. Specifically, for example, the second carburizing gas may be introduced at a position lower than the position in which the heating is performed, or the heating may be performed using two or more heating devices, and the second carburizing gas may be introduced between at least one heating device and a heating device adjacent to that heating device. Furthermore, the heating may be performed using two or more heating devices, and the second carburizing gas may be introduced at positions lower than the position in which the heating is performed and at at least one heating device and a heating device adjacent to that heating device.

[0082] The second carburizing gas is a gas containing hydrocarbons, such as CH4, C2H6, C3H8, etc., and these include natural gas and bio-derived gases. Preferably, the second carburizing gas contains 50% or more by volume of hydrocarbon gas relative to the total amount. When the reduced iron heated by the heating process comes into contact with the second carburizing gas containing 50% or more by volume of hydrocarbon gas relative to the total amount of gas, a cracking reaction is easily generated, and the carbon content of the reduced iron can be increased more efficiently. Furthermore, since the cracking reaction is an endothermic reaction, the occurrence of the cracking reaction also has the effect of preventing the reduced iron from overheating, which can occur due to heating. It is also possible to increase the reaction rate by increasing the amount of the second carburizing gas introduced while keeping the concentration of hydrocarbon gas relative to the total amount of gas low, but the utilization efficiency of the carburizing gas is improved by making the hydrocarbon gas content 50% or more by volume relative to the total amount of gas. More specifically, the second carburizing gas is the same as that exemplified in the [reduced iron production apparatus] described above. The second carburizing gas is introduced into the reduction furnace at a temperature of approximately 25 to 400°C, under pressure (for example, approximately 0.1 to 0.9 MPa).

[0083] Most of the gas generated by the second carburizing reaction flows towards the top of the reduction furnace. For example, the H2 produced by the second carburizing reaction is heated in the reduction furnace and flows into the center of the furnace at a relatively high temperature. This raises the temperature in the center of the reduction furnace, allowing the reduction reaction to proceed efficiently. Furthermore, the generated H2 is effectively used as a reducing gas. Note that the H2 produced by the carburizing reaction with the first carburizing gas is at a relatively low temperature, and its flow into the center of the reduction furnace results in a relatively low temperature in the center. On the other hand, the H2 produced by the second carburizing reaction is at a relatively high temperature, and its flow into the center of the reduction furnace raises the temperature in the center, promoting reduction. As the reduction reaction proceeds efficiently, the carburizing reactions with the first and second carburizing gases also proceed efficiently, increasing the carbon content of the reduced iron.

[0084] The method for producing reduced iron in this embodiment may include discharging the gas inside the reduction furnace to the outside of the reduction furnace above the reducing gas introduction position. The type of gas inside the reduction furnace is not particularly limited and may include, for example, the reducing gas, the gas generated by the reduction reaction, the first carburizing gas, the gas generated by the first carburizing reaction, the second carburizing gas, and the gas generated by the second carburizing reaction. By discharging the gas inside the reduction furnace to the outside of the reduction furnace above the reducing gas introduction position, the high-temperature H2 produced by the carburizing reaction by the second carburizing gas flows more reliably upward within the reduction furnace and is utilized as a reducing gas. This improves the temperature drop in the center of the reduction furnace and promotes the reduction reaction.

[0085] The reduced iron inside the reduction furnace is sequentially discharged to the outside through the reduced iron outlet.

[0086] The aforementioned method for producing reduced iron can be carried out, for example, using the reduced iron production apparatus shown in Figures 1, 3, and 4.

[0087] The reduced iron obtained by the reduced iron production method of this embodiment preferably has a carbon content of 2% by mass or more, more preferably 2.5% by mass or more, and even more preferably 3% by mass, relative to the total amount of reduced iron.

[0088] The reduced iron obtained by the reduced iron production method in this embodiment has a high carbon content and suppresses the temperature drop of the reduced iron, making it easy to use in equipment downstream of the reduction furnace. The reduced iron can be suitably used as a raw material in equipment downstream of the reduction furnace, and it is possible to improve production efficiency (improvement of energy intensity and productivity) including the ironmaking and steelmaking processes downstream of the reduction furnace. Specifically, examples of equipment downstream of the reduction furnace include electric furnaces, melters, briquetting machines, and other types of equipment.

[0089] The present invention will be described in more detail below with reference to examples, but the scope of the present invention is not limited thereto. [Examples]

[0090] As shown below, reduced iron was adjusted to desired temperatures (700°C, 750°C, and 800°C), and a carburizing reaction was carried out by adding carbon to the reduced iron adjusted to each temperature. The carbon content of each reduced iron after the carburizing reaction was then confirmed.

[0091] Approximately 50 g of raw material containing iron oxide was placed in a reduction laboratory test furnace. Specifically, high-quality pellets with a composition of T.Fe > 67% were used as the raw material. A reducing gas (a mixed gas of H2, CO, and oxidizing gases (CO2 and H2O gas) simulating the actual equipment) was introduced into the reduction laboratory test furnace at approximately 10 NLM. The reducing gas and the raw material were reacted for about 180 minutes. In this way, the iron oxide was reduced to produce reduced iron.

[0092] Next, while flowing N2 gas into the reduction laboratory test furnace, the temperature of the reduced iron was adjusted to 700°C. Then, while maintaining the temperature, the N2 gas was switched to a carburizing gas (CH4: 20% by volume, H2: 80% by volume) and introduced into the reduction laboratory test furnace. The carburizing gas and the reduced iron were allowed to react for about 15 minutes. As a result, a carburizing reaction occurred, adding carbon to the reduced iron. The carbon content of this reduced iron was 1.08% by mass.

[0093] Furthermore, except that the temperature of the reduced iron was adjusted to 800°C instead of 700°C, the carbon content of the reduced iron after carburization was 3.74% by mass, using the same procedure as described above.

[0094] Furthermore, except that the temperature of the reduced iron was adjusted to 850°C instead of 700°C, the carbon content of the reduced iron that underwent the carburizing reaction was 5.13% by mass, in the same manner as described above.

[0095] From these results, it was found that by increasing the temperature of the reduced iron to induce a carburizing reaction, reduced iron with a high carbon content can be produced. [Explanation of Symbols]

[0096] 1, 11, 21 Reduced Iron Production Equipment 2. Reduction furnace 3 Raw material supply port 4. Reduced iron outlet 5. Reducing gas introduction section 6. First Carburizing Gas Inlet 7 Heating section 7a, 7b, 7c, 7d, 7e, 7f heating device 8. Second Carburizing Gas Inlet 9 Gas outlet 10 Corn

Claims

1. A reduction furnace consisting of a shaft-type reduction furnace that produces reduced iron by reducing iron oxide using a reducing gas, A first carburizing gas introduction unit for introducing a first carburizing gas containing hydrocarbon gas into the reduction furnace, A reduced iron outlet for discharging the reduced iron inside the reduction furnace to the outside, A heating section is located below the first carburizing gas introduction section and above the reduced iron outlet, and heats the reduced iron to a temperature at which the carburizing reaction occurs. The apparatus includes a second carburizing gas inlet, which is located below the first carburizing gas inlet and above the reduced iron outlet, for introducing a second carburizing gas containing hydrocarbon gas into the reduction furnace, The second carburizing gas introduction section is arranged such that at least a portion of the second carburizing gas passes through the heating section, in a reduced iron production apparatus.

2. A reducing gas introduction unit for introducing the reducing gas into the reducing furnace, The reduced iron production apparatus according to claim 1, further comprising a gas outlet positioned above the reducing gas introduction section for discharging gas from inside the reducing furnace to the outside of the reducing furnace.

3. The reduced iron production apparatus according to claim 1, wherein the second carburizing gas introduction section is located below the heating section.

4. The heating unit comprises two or more heating devices, The reduced iron production apparatus according to claim 1, wherein the second carburizing gas introduction section is arranged between at least one heating device and a heating device adjacent to the heating device.

5. The heating unit comprises two or more heating devices, The reduced iron production apparatus according to claim 1, wherein the second carburizing gas introduction section is located below the heating section and one or more are arranged between at least one heating device and a heating device adjacent to the heating device.

6. The reduced iron production apparatus according to claim 1, wherein the heating section comprises an induction heating coil.

7. The reduced iron production apparatus according to claim 1, wherein the second carburizing gas contains 50% or more by volume of hydrocarbon gas relative to the total amount of gas.

8. The reduced iron production apparatus according to claim 1, wherein the temperature at which the carburizing reaction occurs is 600°C or higher and 1000°C or lower.

9. The process involves introducing raw materials containing iron oxide into a reduction furnace consisting of a shaft-type reduction furnace for producing reduced iron. A reducing gas is introduced into the reduction furnace, and the iron oxide is reduced by the reducing gas to produce reduced iron. Discharging the reduced iron inside the reduction furnace to the outside through the reduced iron outlet, Below the introduction position of the reducing gas and above the discharge port of the reduced iron, a first carburizing gas containing hydrocarbons is introduced into the reducing furnace, and carburizing is performed by adding carbon to the reduced iron with at least a portion of the first carburizing gas. The reduced iron is heated to a temperature at which a carburizing reaction occurs, below the introduction position of the reducing gas and the introduction position of the first carburizing gas, and above the reduced iron outlet, and A method for producing reduced iron, comprising introducing a second carburizing gas containing hydrocarbon gas into the reduction furnace at a location below the introduction position of the reducing gas and the introduction position of the first carburizing gas, and above the reduced iron outlet, so that at least a portion of the second carburizing gas is heated by contact with the heated reduced iron, and performing carburizing by adding carbon to the heated reduced iron with at least a portion of the second carburizing gas.

10. The method for producing reduced iron according to claim 9, further comprising discharging the gas inside the reduction furnace to the outside of the reduction furnace at a position above the introduction point of the reducing gas.

11. The method for producing reduced iron according to claim 9, wherein the second carburizing gas is introduced below the position where the heating is performed.

12. The heating is performed using two or more heating devices. The method for producing reduced iron according to claim 9, wherein the second carburizing gas is introduced between at least one heating device and a heating device adjacent to the heating device.

13. The heating is performed using two or more heating devices. The method for producing reduced iron according to claim 9, wherein the second carburizing gas is introduced at a position below the heating position and at a position between at least one heating device and a heating device adjacent to the heating device.

14. The method for producing reduced iron according to claim 9, wherein the heating method is an induction heating method.

15. The method for producing reduced iron according to claim 9, wherein the second carburizing gas contains 50% by volume or more of hydrocarbon gas with respect to the total amount of gas.

16. The method for producing reduced iron according to claim 9, wherein the temperature at which the carburizing reaction occurs is 600°C or higher and 1000°C or lower.

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