Manufacturing method of reduced iron briquettes

Abstract

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.

Description

[Technical Field]

[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. [Background technology]

[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 carried out to prevent the reduced iron from being reoxidized during transportation. The briquetting of reduced iron is carried out in a non-oxidizing gas atmosphere to prevent the reoxidation of the reduced iron. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japan Utility Model Publication No. 63-167162 [Patent Document 2] Japanese Patent Publication No. 2000-204419 Summary of the Invention [Problem to be solved by the invention]

[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. The 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. [Means for solving the problem]

[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; a step of supplying a non-oxidizing and non-nitrogenous seal gas into a molding machine casing in which a molding machine is installed, and creating a non-oxidizing and non-nitrogenous seal gas atmosphere inside the molding machine casing; 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 in (1) above, the seal gas may contain at least one gas selected from the group consisting of CO 2 gas and hydrogen gas. (3) In the method for producing reduced iron briquettes according to the above (1) or (2), a storage hopper for storing reduced iron, or a combination of the storage hopper and The aforementioned A non-oxidizing and non-nitrogenous seal gas may be supplied to the connecting portion that connects to the molding machine casing. 。 [Effects of the Invention]

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

[0008] [Figure 1] FIG. 1 is a schematic diagram showing a manufacturing apparatus for reduced iron briquettes. DETAILED DESCRIPTION OF THE INVENTION

[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. Reduced iron briquette manufacturing equipment> 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. The shaft furnace, for example, operates as follows: First, iron oxide raw materials (e.g., iron oxide pellets) are charged from the top of the shaft furnace, and reducing gas is injected into the shaft furnace from the bottom. The reducing gas is heated to a predetermined temperature (e.g., approximately 900 to 950°C) and then injected into the shaft furnace. The reducing gas injected into the shaft furnace then reduces the iron oxide raw materials in the shaft furnace. This direct reduction process produces solid reduced iron. The reduced iron is discharged from the bottom of the shaft furnace and cooled. A top gas (exhaust gas) containing hydrogen gas, CO gas, water vapor, and CO2 gas is discharged from the top of the shaft furnace. After water vapor is removed from the top gas, the hydrogen gas and CO2 gas in the top gas are reused as part of the raw material gas. Alternatively, CO2 gas may be removed from the top gas after water vapor is removed.

[0012] The reducing gas used in shaft furnaces is obtained by reforming raw gas containing carbon (such as natural gas or coke oven gas) with steam, CO2 gas, oxygen gas, etc. Alternatively, the raw gas can be used as the reducing gas in the shaft furnace without reforming it. The main components of reducing gas are hydrogen gas (H2), CO gas (CO), and CH4 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 further suppresses 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 from 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 sealing gas may be, for example, a gas containing at least one selected from the group consisting of CO2 gas and hydrogen gas. More specifically, the sealing gas may be CO2 gas or hydrogen gas, or a mixture of these gases. The sealing 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 from 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% by volume or more, 90% by volume or more, 98% by volume or more, or 100% by volume. The hydrogen concentration in the seal gas may be, for example, 100% by volume or less, less than 100% by volume, or less than 98% by volume. When the seal gas is pure hydrogen, the hydrogen concentration in the seal gas is 98% by volume or more and 100% by volume 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 may be reformed and 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 should be such that air does not flow into 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 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 it becomes less likely to react with the surrounding gas. In other words, it becomes less likely to be oxidized or 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 method for manufacturing reduced iron briquettes using the apparatus for manufacturing reduced iron briquettes will be described. The method for manufacturing 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 the 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 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 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. [Explanation of symbols]

[0030] 1. Reduction furnace 2. Seal gas supply device 3 Storage hopper 4 Feeder 4A Connecting part 5 Molding machine 5A molding machine casing 6 Separator 7 Sieve 8 Under-sieve circulation device 9 Transport Conveyor 10 Thermometer

Claims

1. a reduced iron production process for producing solid reduced iron; supplying a non-oxidizing and non-nitrogenous seal gas into a molding machine casing in which a molding machine is installed, thereby creating a non-oxidizing and non-nitrogenous seal gas atmosphere inside the molding machine casing; a briquetting step of briquetting the reduced iron in the molding machine under 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. 3. The method for producing reduced iron briquettes according to claim 1, wherein 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 and the molding machine casing.

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