Method for producing reduced iron briquettes

Abstract

The production method of reduced iron briquettes according to one aspect of the present invention is characterized by comprising: a reduced iron production step of producing reduced iron in a solid state; and a briquetting step of briquetting the reduced iron in a non-oxidizing and non-nitrogenous sealed gas atmosphere.

Description

Technical Field

[0001] This invention relates to a method for manufacturing reduced iron briquettes. This application claims priority based on 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 manufacturing solid reduced iron are known, such as those using a shaft furnace for reducing iron production (Patent Documents 1 and 2). In this technique, at least a portion of the manufactured reduced iron is thermally agglomerated (bulking) to form reduced iron briquettes (hot-pressed iron briquettes (HBI)). The agglomeration of the reduced iron is performed to prevent re-oxidation during transport. To prevent re-oxidation, the agglomeration of the reduced iron is carried out in a non-oxidizing gas atmosphere.

[0003] Existing technical documents Patent documents Patent Document 1: Japanese Utility Model Application Publication No. 63-167162 Patent Document 2: Japanese Patent Application Publication No. 2000-204419 Summary of the Invention

[0004] The problem that the invention aims to solve Patent Document 1 discloses nitrogen as a non-oxidizing gas, and Patent Document 2 discloses reduction furnace exhaust gas as a non-oxidizing gas. In both, nitrogen is commonly used primarily from a cost perspective. However, when using nitrogen as a non-oxidizing gas, there is a problem of reduced iron being nitrided. The nitrogen contained in the reduced iron becomes a problem, for example, in the smelting of high-grade steel.

[0005] Therefore, the present invention was made in view of the above-mentioned problems, and the object of the present invention is to provide a novel and improved method for manufacturing reduced iron agglomerates that can prevent the nitriding of reduced iron while agglomerating the reduced iron.

[0006] Methods for solving problems The main points of this invention are as follows.

[0007] (1) A method for manufacturing reduced iron agglomerates according to one aspect of the present invention is characterized in that it comprises: a reduced iron manufacturing step for manufacturing solid reduced iron; and an agglomeration step for agglomerating the reduced iron agglomerates under a non-oxidizing and non-nitrogenous sealed gas atmosphere.

[0008] (2) In the method for manufacturing reduced iron agglomerates described in (1) above, the sealing gas may also include any one or more of the group consisting of CO2 gas and hydrogen gas.

[0009] (3) In the method for manufacturing reduced iron agglomerates described in (1) or (2) above, a non-oxidizing and non-nitrogenous sealing gas may be supplied to the storage hopper for storing reduced iron or to the connection portion connecting the storage hopper to the housing of the molding machine equipped with the molding machine for forming the reduced iron agglomerates.

[0010] (4) In the method for manufacturing reduced iron lumps described in (3) above, a non-oxidizing and non-nitrogenous sealing gas may also be supplied to the housing of the molding machine.

[0011] Invention Effects According to the present invention, it is possible to prevent the nitriding of reduced iron while simultaneously agglomerating the reduced iron. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of an apparatus for manufacturing reduced iron lumps. Detailed Implementation

[0013] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0014] <1. Apparatus for manufacturing reduced iron lumps> Figure 1 This is a schematic diagram of an apparatus for manufacturing reduced iron briquettes. The apparatus for manufacturing reduced iron briquettes in this embodiment includes a reduction furnace 1, a sealing gas supply device 2, a storage hopper 3, a connecting part 4A, a feeder 4, a molding machine housing 5A, a molding machine 5, a separator 6, a sieve 7, an under-sieve circulation device 8, a conveyor belt 9, and a thermometer 10.

[0015] The reduction furnace 1 is an apparatus for reducing 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 following operations are performed in the shaft furnace, for example: First, iron oxide raw materials (e.g., iron oxide pellets) are charged into the shaft furnace from the top, and reducing gas is blown in from the bottom. Here, the reducing gas is heated to a specified temperature (e.g., around 900–950°C) before being blown into the shaft furnace. Then, the reducing gas blown into the shaft furnace reduces the iron oxide raw materials inside. Solid reduced iron is produced through this direct reduction process. The reduced iron is discharged from the bottom of the shaft furnace and cooled. From the top of the shaft furnace, top gas (exhaust gas) containing hydrogen, CO, water vapor, and CO2 is discharged. After removing water vapor from the top gas, the hydrogen and CO in the top gas are reused as part of the raw material gas. Alternatively, sometimes CO2 is removed after removing water vapor from the top gas.

[0016] The reducing gas used in vertical shaft furnaces is obtained by modifying carbon-containing feed gases (such as natural gas, coke oven gas, etc.) using steam, CO2, oxygen, etc. Alternatively, the feed gases can be used directly as reducing gases in the vertical shaft furnace without modification. The main components of the reducing gas are hydrogen (H2), CO (CO), and CH4.

[0017] 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 the molding machine housing 5A via a connecting part 4A. Therefore, the internal spaces of the storage hopper 3, the connecting part 4A, and the molding machine housing 5A are interconnected. A feeder 4 is provided in the connecting part 4A. The feeder 4 supplies the reduced iron stored in the storage hopper 3 into the molding machine housing 5A at a certain speed.

[0018] A forming machine 5 and a separator 6 are installed inside the forming machine housing 5A. The forming machine 5, for example, consists of a pair of rollers, which agglomerate the reduced iron supplied from the feeder 4 at a certain speed. Here, the manufactured reduced iron agglomerates are connected to each other by connecting ribs. The separator 6 separates the reduced iron agglomerates connected by the connecting ribs into individual agglomerates. The separated reduced iron agglomerates are then fed to a sieve 7.

[0019] The sieve 7 removes the fine powder mixed between the reduced iron lumps and passes it through the sieve. Afterwards, the reduced iron lumps are cooled by water and gas, and then conveyed to the next process via the conveyor belt 9. The fine powder passing through the sieve is returned to the storage hopper 3 via the undersize recycling device 8.

[0020] The sealing gas supply device 2 is connected to the molding machine housing 5A via connecting pipe a and to the storage hopper 3 via connecting pipe b. The sealing gas supply device 2 supplies sealing gas to the storage hopper 3 via connecting pipe b. This seals the internal space of the storage hopper 3 and the connecting portion 4A with the sealing gas. Because the reduced iron in the storage hopper 3 and the connecting portion 4A is at a high temperature for thermoforming, it is prone to nitriding. Therefore, a non-oxidizing and non-nitrogenous sealing gas atmosphere is set inside the storage hopper 3 and the connecting portion 4A. Preferably, the sealing gas supply device 2 supplies sealing gas to the molding machine housing 5A via connecting pipe a, sealing the internal space of the molding machine housing 5A with the sealing gas. Since the residence time of the reduced iron in the internal space of the molding machine housing 5A is short, nitriding of the reduced iron is not easily generated; however, by sealing the internal space of the molding machine housing 5A with sealing gas, nitriding can be further suppressed. Therefore, in this embodiment, it is preferable to maintain the solid reduced iron produced in the reduced iron manufacturing process under a sealed gas atmosphere and supply the reduced iron to the molding machine housing 5A, which is equipped with a molding machine 5 for agglomerating reduced iron. The sealed gas is discharged to the outside through a drain pipe c provided at the upper end of the storage hopper 3.

[0021] The sealing gas is non-oxidizing and non-nitrogenous. That is, the sealing gas essentially contains neither oxygen nor nitrogen. Therefore, it can prevent not only the oxidation of reduced iron but also nitriding. It should be noted that the sealing gas may also contain these gases as long as it does not impair the effects of this embodiment. For example, these gases may unavoidably be included in the manufacturing process of the sealing gas.

[0022] The sealing gas may be composed of, for example, any one or more gases selected from the group consisting of CO2 and hydrogen. More specifically, the sealing gas may be composed of CO2 or hydrogen, or a mixture of these gases. Other types of gases may also be included in the sealing gas without impairing the effectiveness of this embodiment.

[0023] When the sealing gas contains hydrogen, the hydrogen reacts with the nitrogen contained in the reduced iron to produce ammonia, and the nitrogen contained in the reduced iron can be expected to be removed by the hydrogen. As a result, the manufacture of high-grade steel becomes easier. It should be noted that when using hydrogen for denitrification, it is preferable to maintain the temperature of the reduced iron in the storage hopper 3 at around 700°C. This allows for efficient denitrification using hydrogen. It should be noted that, as described above, the temperature of the reduced iron in the storage hopper 3 is measured by thermometer 10. Furthermore, the temperature of the reduced iron in the storage hopper 3 can be adjusted, for example, by the flow rate of the sealing gas supplied to the storage hopper 3. When the sealing gas contains hydrogen, the hydrogen concentration in the sealing gas can 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 sealing gas can be, for example, less than 100% by volume, less than 100% by volume, or less than 98% by volume. When the sealing gas is pure hydrogen, the hydrogen concentration in the sealing gas is 98% by volume or more and less than 100% by volume. In addition, for example, the gas obtained by modifying the gas discharged from the top of the shaft furnace after reducing iron ore by blowing natural gas into it sometimes contains more than 50% by volume hydrogen.

[0024] It should be noted that there are no particular restrictions on the temperature and flow rate of the sealing gas. As long as the effect of this embodiment is not impaired, appropriate adjustments can be made. The supply of sealing gas is such that atmospheric air does not flow into the device from the gap of the joint of the device, the pipe c at the upper end of the storage hopper 3, or the discharge part of the lumps. The pressure in the storage hopper 3, the connecting part 4A, and the molding machine housing 5A only needs to be greater than or equal to the external pressure.

[0025] Furthermore, the connecting pipe a can be omitted. In this case, the inside of the molding machine housing 5A is no longer sealed by the sealing gas. However, since the reduced iron is agglomerated inside the molding machine housing 5A, the porosity decreases, making it less likely to react with the surrounding gas. That is, it becomes less susceptible to oxidation and nitriding. Therefore, even if the inside of the molding machine housing 5A is not sealed, the quality of the reduced iron agglomerates can be ensured.

[0026] <2. Method for manufacturing reduced iron lumps> Next, a method for manufacturing reduced iron lumps using an apparatus for manufacturing reduced iron lumps will be described. The method for manufacturing reduced iron lumps in this embodiment includes: a reduced iron manufacturing step for manufacturing solid reduced iron; and a lumping step for lumping reduced iron lumps under a non-oxidizing and non-nitrogenous sealed gas atmosphere.

[0027] More specifically, firstly, solid reduced iron is produced using a reduction furnace 1 (reduced iron manufacturing process). Next, 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 using a thermometer 10.

[0028] Next, the feeder 4 supplies the reduced iron accumulated in the storage hopper 3 into the molding machine housing 5A at a certain speed. Then, the molding machine 5 clumps the reduced iron supplied from the feeder 4 at a certain speed. Here, the manufactured reduced iron clumps are connected to each other by connecting ribs. The separator 6 separates the reduced iron clumps connected by the connecting ribs into individual pieces. The separated reduced iron clumps are then fed to the sieve 7.

[0029] On the other hand, the sealing gas supply device 2 supplies sealing 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 sealing gas. Preferably, the sealing gas supply device 2 supplies sealing gas to the molding machine housing 5A via the connecting pipe a, and seals the internal space of the molding machine housing 5A with the sealing gas.

[0030] The sealing gas is non-oxidizing and non-nitrogenous. That is, the sealing gas essentially contains no oxygen or nitrogen. Therefore, it not only prevents the oxidation of reduced iron but also prevents nitriding. Thus, the forming machine 5 agglomerates the aforementioned reduced iron in a non-oxidizing and non-nitrogenous sealing gas atmosphere (agglomeration process).

[0031] The sieve 7 removes the fine powder mixed between the reduced iron lumps and passes it through the sieve. The reduced iron lumps are then conveyed to the next process via the conveyor belt 9. The fine powder passing through the sieve is returned to the storage hopper 3 via the undersize recycling device 8.

[0032] Based on the above, the method for manufacturing reduced iron lumps according to this embodiment can prevent the nitridation of reduced iron while lumping the reduced iron because the reduced iron is lumped in a non-oxidizing and non-nitrogenous sealed gas atmosphere.

[0033] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the examples described. Those skilled in the art will readily conceive of various modifications or alterations within the scope of the technical concept described in the claims, and these modifications are, of course, also understood to fall within the technical scope of the present invention.

[0034] Explanation of symbols 1. Reduction Furnace 2 Sealing gas supply device 3. Storage hopper 4. Feeder 4A Connection Section 5 Molding Machine 5A Molding Machine Housing 6. Separator 7 sieves 8. Screening underflow circulation device 9. Conveyor belt 10. Thermometer

Claims

1. A method for manufacturing reduced iron briquettes, characterized in that, Include: The process of manufacturing reduced iron in solid form; and The agglomeration process of reducing iron in a sealed gas atmosphere that is neither oxidizing nor nitrogenous.

2. The method for manufacturing reduced iron briquettes according to claim 1, characterized in that, The sealing gas comprises one or more gases selected from the group consisting of CO2 and hydrogen.

3. The method for manufacturing reduced iron briquettes according to claim 1 or 2, wherein, A non-oxidizing and non-nitrogenous sealing gas is supplied to the hopper storing reduced iron, or to the connection portion connecting the hopper to the housing of a molding machine equipped with a molding machine for agglomerating the reduced iron.

4. The method for manufacturing reduced iron briquettes according to claim 3, wherein, A non-oxidizing and non-nitrogenous sealing gas is supplied to the housing of the molding machine.

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