Method for producing reduced iron briquettes

Abstract

A method for producing reduced iron briquettes according to one embodiment of the present invention is characterized by comprising a reduced iron production step for producing a solid reduced iron, and a briquette step for briquetting the reduced iron in a non-oxidizing and a non-nitrogenous seal gas atmosphere.

Description

Manufacturing method of reduced iron briquettes

[0001] The present invention relates to a method for producing reduced iron briquettes. This application claims priority to Japanese Patent Application No. 2024-059687, filed on April 2, 2024, the contents of which are incorporated herein by reference.

[0002] For example, techniques for producing solid reduced iron, such as a method for producing reduced iron using a shaft furnace, are known (Patent Documents 1 and 2). In these techniques, at least a portion of the produced reduced iron is hot briquette-formed (agglomerated) to produce reduced iron briquettes (hot briquette iron (HBI)). The briquetting of reduced iron is performed to prevent the reduced iron from being reoxidized during transportation. The briquetting of reduced iron is performed in a non-oxidizing gas atmosphere to prevent the reoxidation of the reduced iron.

[0003] Japanese Utility Model Application Publication No. 63-167162 Japanese Patent Application Publication No. 2000-204419

[0004] Patent Document 1 discloses nitrogen gas as a non-oxidizing gas, and Patent Document 2 discloses reducing furnace exhaust gas as a non-oxidizing gas. Of these, nitrogen gas is widely used mainly from the viewpoint of cost. However, when nitrogen gas is used as a non-oxidizing gas, there is a problem that reduced iron is nitrided. Nitrogen contained in reduced iron is a problem, for example, in the production of high-grade steel.

[0005] Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a new and improved method for producing reduced iron briquettes, which is capable of briquetting reduced iron while preventing nitridation of the reduced iron.

[0006] The gist of the present invention is as follows: (1) A method for producing reduced iron briquettes according to one aspect of the present invention includes a reduced iron production step of producing solid reduced iron, and a briquetting step of briquetting the reduced iron in a non-oxidizing and non-nitrogenous seal gas atmosphere. (2) In the method for producing reduced iron briquettes described above in (1), the seal gas is a CO ２(3) In the method for producing reduced iron briquettes described in (1) or (2) above, a non-oxidizing and non-nitrogenous seal gas may be supplied to a storage hopper that stores reduced iron or to a connecting portion that connects the storage hopper to a molding machine casing that includes a molding machine that briquettes the reduced iron. (4) In the method for producing reduced iron briquettes described in (3) above, a non-oxidizing and non-nitrogenous seal gas may be supplied to the molding machine casing.

[0007] According to the present invention, reduced iron can be briquetted while preventing nitridation of the reduced iron.

[0008] FIG. 1 is a schematic diagram showing a manufacturing apparatus for reduced iron briquettes.

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0010] 1 is a schematic diagram showing an apparatus for manufacturing reduced iron briquettes. The apparatus for manufacturing reduced iron briquettes according to this embodiment includes a reduction furnace 1, a seal gas supply device 2, a storage hopper 3, a connecting portion 4A, a feeder 4, a molding machine casing 5A, a molding machine 5, a separator 6, a sieve 7, an under-sieve circulating device 8, a transport conveyor 9, and a thermometer 10.

[0011] The reduction furnace 1 is a device that reduces iron oxide raw materials to produce solid reduced iron. The reduction furnace 1 is, for example, a shaft furnace or a rotary hearth furnace. In a shaft furnace, for example, the following operation is performed. First, iron oxide raw materials (e.g., iron oxide pellets) are charged from the top of the shaft furnace, and reducing gas is blown into the shaft furnace from the bottom. Here, the reducing gas is heated to a predetermined temperature (e.g., about 900 to 950°C) and then blown into the shaft furnace. The reducing gas blown into the shaft furnace then reduces the iron oxide raw materials in the shaft furnace. Solid reduced iron is produced by this direct reduction process. The reduced iron is discharged from the bottom of the shaft furnace and cooled. Hydrogen gas, CO gas, water vapor, and CO are blown into the shaft furnace from the top of the shaft furnace. ２After steam is removed from the furnace top gas, the hydrogen gas and CO gas in the furnace top gas are reused as part of the raw material gas. ２ In some cases, gas may be removed.

[0012] The reducing gas used in the shaft furnace is a carbon-containing raw gas (e.g., natural gas, coke oven gas, etc.) mixed with steam or CO ２ It can be obtained by reforming the raw material gas using gas such as nitrogen or oxygen. Alternatively, the raw material gas can be used as a reducing gas in the shaft furnace without reforming it. The main component of the reducing gas is hydrogen gas (H ２ ), CO gas (CO), CH ４ It's gas.

[0013] The storage hopper 3 temporarily stores the reduced iron discharged from the reduction furnace 1. The temperature of the reduced iron in the storage hopper 3 is measured by a thermometer 10. The thermometer 10 is, for example, a thermocouple or a radiation thermometer. The lower end of the storage hopper 3 is connected to a molding machine casing 5A via a connecting portion 4A. Therefore, the internal spaces of the storage hopper 3, the connecting portion 4A, and the molding machine casing 5A are in communication. A feeder 4 is provided within the connecting portion 4A. The feeder 4 supplies the reduced iron stored in the storage hopper 3 into the molding machine casing 5A at a constant speed.

[0014] A molding machine 5 and a separator 6 are provided inside the molding machine casing 5A. The molding machine 5 is composed of, for example, a pair of rolls, and briquettes the reduced iron supplied at a constant speed from the feeder 4. The produced reduced iron briquettes are connected to each other by ribs. The separator 6 separates the ribbed reduced iron briquettes into individual pieces. The separated reduced iron briquettes are supplied to a sieve 7.

[0015] The sieve 7 removes fine particles mixed between the reduced iron briquettes. The reduced iron briquettes are then cooled by water spray or gas, and transported to the next process by a transport conveyor 9. The fine particles that fall below the sieve are returned to the storage hopper 3 by an under-sieve circulation device 8.

[0016] The seal gas supply device 2 is connected to the molding machine casing 5A via a connecting pipe a and to the storage hopper 3 via a connecting pipe b. The seal gas supply device 2 supplies seal gas to the storage hopper 3 via the connecting pipe b. This seals the internal space of the storage hopper 3 and the connecting portion 4A with the seal gas. Because briquettes are produced by hot molding, the reduced iron in the storage hopper 3 and the connecting portion 4A is at a high temperature and therefore prone to nitriding. Therefore, a non-oxidizing, non-nitrogenous seal gas atmosphere is created inside the storage hopper 3 and the connecting portion 4A. The seal gas supply device 2 preferably supplies seal gas into the molding machine casing 5A via the connecting pipe a to seal the internal space of the molding machine casing 5A with the seal gas. Because the residence time of reduced iron in the internal space of the molding machine casing 5A is short, nitriding of the reduced iron is unlikely to occur. However, sealing the internal space of the molding machine casing 5A with the seal gas can further suppress nitriding. Therefore, in this embodiment, it is preferable to hold the solid reduced iron produced in the reduced iron production process in a seal gas atmosphere and supply the reduced iron to a molding machine casing 5A equipped with a molding machine 5 that briquettes the reduced iron. The seal gas is discharged to the outside through a discharge pipe c provided at the upper end of the storage hopper 3.

[0017] The seal gas is non-oxidizing and non-nitrogenous. That is, the seal gas does not substantially contain oxygen gas or nitrogen gas. This prevents not only oxidation but also nitridation of the reduced iron. The seal gas may contain these gases as long as the effects of this embodiment are not impaired. For example, the seal gas may contain these gases unavoidably during the production of the seal gas.

[0018] The seal gas is, for example, CO ２ The seal gas is composed of a gas containing at least one selected from the group consisting of CO gas and hydrogen gas. ２ The seal gas may be composed of a gas such as nitrogen or hydrogen gas, or a mixture of these gases. The seal gas may further contain other types of gases as long as the effects of this embodiment are not impaired.

[0019] When hydrogen gas is contained in the seal gas, the hydrogen gas reacts with nitrogen contained in the reduced iron to generate ammonia, and the hydrogen gas is expected to remove the nitrogen contained in the reduced iron. As a result, high-quality steel can be produced more easily. When denitrification using hydrogen gas is performed, it is preferable to maintain the temperature of the reduced iron in the storage hopper 3 at approximately 700°C. This allows denitrification using hydrogen gas to proceed efficiently. As described above, the temperature of the reduced iron in the storage hopper 3 is measured by the thermometer 10. The temperature of the reduced iron in the storage hopper 3 can be adjusted, for example, by the flow rate of the seal gas supplied into the storage hopper 3. When hydrogen gas is contained in the seal gas, the hydrogen concentration in the seal gas may be, for example, 50 vol% or more, 90 vol% or more, 98 vol% or more, or 100 vol%. The hydrogen concentration in the seal gas may be, for example, 100 vol% or less, less than 100 vol%, or less than 98 vol%. When the seal gas is pure hydrogen, the hydrogen concentration in the seal gas is 98 vol% or more and 100 vol% or less. Furthermore, for example, after natural gas is blown into a shaft furnace to reduce iron ore, the gas discharged from the top of the shaft furnace is reformed and the reformed gas may contain 50% or more by volume of hydrogen.

[0020] The temperature and flow rate of the seal gas are not particularly limited and may be adjusted as appropriate as long as the effects of this embodiment are not impaired. The supply amount of seal gas is set to an amount that prevents air from entering the apparatus through gaps in the joints of the apparatus, the exhaust pipe c provided at the top end of the storage hopper 3, and the briquette discharge portion, and the pressure inside the storage hopper 3, the connecting portion 4A, and the molding machine casing 5A is set to be equal to or greater than the external pressure.

[0021] Also, the connecting pipe a may be omitted. In this case, the inside of the molding machine casing 5A is not sealed with a seal gas. However, since the reduced iron is briquetted inside the molding machine casing 5A, the porosity decreases and the reduced iron is less likely to react with the surrounding gas. In other words, the reduced iron is less likely to be oxidized and nitrided. Therefore, the quality of the reduced iron briquettes is ensured even if the inside of the molding machine casing 5A is not sealed.

[0022] 2. Manufacturing Method of Reduced Iron Briquettes Next, a manufacturing method of reduced iron briquettes using a manufacturing apparatus for reduced iron briquettes will be described. The manufacturing method of reduced iron briquettes according to this embodiment includes a reduced iron manufacturing step of manufacturing solid reduced iron, and a briquetting step of briquetting the reduced iron in a non-oxidizing and non-nitrogenous seal gas atmosphere.

[0023] More specifically, solid reduced iron is first produced in a reduction furnace 1 (reduced iron production process). Then, the produced reduced iron is temporarily stored in a storage hopper 3. The temperature of the reduced iron in the storage hopper 3 is measured by a thermometer 10.

[0024] Next, the feeder 4 supplies the reduced iron stored in the storage hopper 3 into a molding machine casing 5A at a constant speed. Next, the molding machine 5 briquettes the reduced iron supplied at a constant speed from the feeder 4. The produced reduced iron briquettes are connected to each other by ribs. A separator 6 separates the connected reduced iron briquettes into individual pieces. The separated reduced iron briquettes are supplied to a sieve 7.

[0025] On the other hand, the seal gas supply device 2 supplies a seal gas to the storage hopper 3 via the connecting pipe b. This seals the internal space of the storage hopper 3 and the connecting portion 4A with the seal gas. It is preferable that the seal gas supply device 2 supplies the seal gas into the molding machine casing 5A via the connecting pipe a and seals the internal space of the molding machine casing 5A with the seal gas.

[0026] The seal gas is non-oxidizing and non-nitrogenous. That is, the seal gas does not substantially contain oxygen gas or nitrogen gas. This prevents not only oxidation but also nitridation of the reduced iron. Therefore, the molding machine 5 briquettes the reduced iron in a non-oxidizing and non-nitrogenous seal gas atmosphere (briquetting process).

[0027] The sieve 7 removes fine particles mixed between the reduced iron briquettes. The reduced iron briquettes are then transported to the next process by a transport conveyor 9. The fine particles that fall below the sieve are returned to the storage hopper 3 by an under-sieve circulation device 8.

[0028] As described above, according to the method for manufacturing reduced iron briquettes of this embodiment, the reduced iron is briquetted in a non-oxidizing and non-nitrogenous seal gas atmosphere, so that the reduced iron can be briquetted while preventing nitridation of the reduced iron.

[0029] Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to these examples. It is clear that a person skilled in the art to which the present invention pertains can conceive of various modifications and alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

[0030] REFERENCE SIGNS LIST 1 Reduction furnace 2 Seal gas supply device 3 Storage hopper 4 Feeder 4A Connecting portion 5 Molding machine 5A Molding machine casing 6 Separator 7 Sieve 8 Under-sieve circulation device 9 Transport conveyor 10 Thermometer

Claims

1. A method for producing reduced iron briquettes, comprising: a reduced iron production step of producing solid reduced iron; and a briquetting step of briquetting the reduced iron in a non-oxidizing and non-nitrogenous seal gas atmosphere.

2. The seal gas is CO ２ 2. The method for producing reduced iron briquettes according to claim 1, wherein the gas contains at least one selected from the group consisting of a gas and a hydrogen gas.

3. A method for producing reduced iron briquettes as described in claim 1 or 2, in which a non-oxidizing and non-nitrogenous seal gas is supplied to a storage hopper that stores reduced iron or to a connecting portion that connects the storage hopper to a molding machine casing that includes a molding machine that briquettes the reduced iron.

4. The method for producing reduced iron briquettes according to claim 3, wherein a non-oxidizing and non-nitrogenous seal gas is supplied to the molding machine casing.

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