Manufacturing method for ferro-coke

Abstract

To provide a manufacturing method for ferro-coke, which is capable of producing ferro-coke that can maximize a drum strength even when using a coal blend with different maximum fluidity (MF).SOLUTION: There is provided a manufacturing method for ferro-coke, comprising: kneading a raw material for molding including coal, an iron source material and a binder; forming a resulting mixture into an agglomerate with a double roll molding machine; and carbonizing a resulting briquetting raw material to produce ferro-coke. The coal used as the material is sieved with a smaller mesh size in accordance with reduction in its maximum fluidity: MF (JIS M 8811), and oversized coal is used as ferro-coke. In a preferred embodiment, sieving is carried out in a range of 0.13×MF+10≤sieve mesh size≤0.22×MF+16. In addition, the coal to be blended into the molded coal is sieved within a range of maximum fluidity (MF) of 0 to 50.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing ferro-coke for metallurgy using an iron source material such as iron ore and coal as raw materials. [Background technology]

[0002] Ferro coke is produced by mixing raw materials, primarily composed of coal and iron ore, with a binder added for molding, in a kneader, molding the mixture into agglomerates of a target size, heating the resulting agglomerates, and carbonizing the coal in the agglomerates (see, for example, Patent Document 1).

[0003] Here, "mainly composed of coal and iron ore" means that the raw materials for ferrocoke are mainly coal and iron ore. Ferrocoke is produced using raw materials containing 70 mass% or more of coal and iron ore, but raw materials containing 80 mass% or more of coal and iron ore are usually used (see, for example, Patent Document 2). In addition, the raw materials discharged from the carbonization furnace are usually sieved, and the oversized material is transported to a blast furnace as a product. The undersized material contains iron and is used, for example, as an alternative heat source to the coagulating agent in the sintering process. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-277489 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-57005 Summary of the Invention [Problem to be solved by the invention]

[0005] As mentioned above, in the production of ferro-coke, it is necessary to sieve the coke before transporting it to the blast furnace. This is to prevent the under-sieved fines from being carried into the blast furnace and impairing the permeability. In addition, there are limitations on the sieved ferro-coke. For example, high strength is desirable from the viewpoint of ensuring the permeability of the blast furnace.

[0006] In order to prevent deterioration of permeability due to powdering during use in a blast furnace, ferro-coke is controlled, for example, so that its drum strength is 75% or more. Here, the drum strength in the present invention is the weight ratio of the ferro-coke remaining on a sieve obtained by placing 10 kg of a ferro-coke sample in a drum testing machine described in JIS K 2151, rotating it 150 times, and then separating the sample through a sieve with 6 mm mesh. Ferro-coke with a higher drum strength is more preferable because it is less likely to generate powder in a blast furnace.

[0007] When coal is heated, it softens at 350-400°C and becomes fluid. When heated further, it expands, and the coal solidifies between 450-500°C. This property is called "caking property," and to improve the drum strength of ferro-coke, it is necessary to control the maximum fluidity (MF) (JIS M 8811) of the coal that is the raw material for ferro-coke. MF is generally used as an indicator of caking property, and coal with a high MF melts well and has high drum strength. However, if melting proceeds excessively, volume expansion causes swelling and the development of coarse pores, reducing drum strength.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to propose a method for producing ferro-coke that can produce ferro-coke that can ensure maximum drum strength even when coal blends with different MFs are used. [Means for solving the problem]

[0009] The inventors have conceived a method for optimizing the drum strength of ferro-coke by optimizing the sieve opening size according to the maximum fluidity (MF) of coal, which is the raw material for ferro-coke, because the drum strength of ferro-coke has a strong influence on its fluidity and particle size.

[0010] The method for producing ferro-coke of the present invention is characterized in that, in the method for producing ferro-coke, a briquetting raw material containing coal, an iron source raw material, and a binder is mixed and kneaded, and the briquetting product is formed in a double-roll briquetting machine and carbonized to produce ferro-coke, the mesh size is made smaller as the maximum fluidity (MF) (JIS M 8811) of the coal used as the briquetting raw material is reduced, and the sieved coal is used as the ferro-coke.

[0011] In the method for producing ferro-coke of the present invention configured as described above, (1) Sifting is performed in the range of 0.14 × MF + 10 ≦ sieve size ≦ 0.21 × MF + 16; (2) The maximum fluidity of the coal to be blended into the molded coal: MF is sieved within the range of 0 to 50. This is considered to be a more preferable solution. [Effects of the Invention]

[0012] According to the method for producing ferro-coke of the present invention, by sieving the ferro-coke with a smaller mesh size in accordance with the reduction in the maximum fluidity (MF) of the coal used as a briquetting raw material, it is possible to produce ferro-coke that can ensure maximum drum strength even when using coal blends with different MFs. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram showing an embodiment of the method for producing ferro coke of the present invention. [Figure 2] 1 is a graph showing an embodiment of the particle size distribution of ferro-coke in the present invention. [Figure 3] 1 is a graph showing the relationship between the drum strength of ferro-coke and the mesh size of a sieve in the present invention. [Figure 4] 1 is a graph showing the optimum sieve size and drum strength of ferro-coke produced by changing the MF of coal in the present invention. [Figure 5] 1 shows the relationship between the MF of coal and the sieve opening when the drum strength of ferro-coke is 75% or more in the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] The following describes in detail the embodiments of the present invention. Note that the following embodiments are intended to exemplify devices and methods for embodying the technical concept of the present invention, and are not intended to limit the configuration to that described below. In other words, the technical concept of the present invention can be modified in various ways within the technical scope defined in the claims.

[0015] <One embodiment of the method for producing ferro-coke of the present invention> FIG. 1 is a schematic diagram showing one embodiment of the method for producing ferro-coke of the present invention. In the example shown in FIG. 1, coal 1 and iron source raw material 2 are pulverized to a predetermined particle size or less in a pulverizer (not shown) and then blended in a predetermined ratio. For example, the coal is pulverized to 3 mm or less, and the iron source raw material is pulverized to 0.5 mm or less. Then, for example, the coal and iron source raw material are blended in a ratio of 60 to 90 mass % and 10 to 40 mass %. Iron ore is mainly used as the iron source raw material 2, but iron source raw materials by-produced in steelworks, such as blast furnace dust, converter dust, and rolling sludge, may be used instead of iron ore. Furthermore, multiple brands of iron ore and coal may be combined. In this embodiment, iron ore is used as the iron source raw material 2.

[0016] The blended coal 1 and iron ore 2 are fed into the kneader 3. A binder is added to the kneader 3 from a binder tank 4. Commonly used binders include SOP (soft pitch), ASP (asphalt pitch), and ferrotar (a by-product produced during the carbonization process of ferro-coke), and one or more types can be used in combination. The binder is added from the binder tank 4 at the same time as the coal 1 and iron ore 2 are fed into the kneader 3, or during kneading. Through the above process, a mixed raw material for molding can be obtained.

[0017] The mixed raw materials for molding are molded under high pressure in a double-roll molding machine 5, which is a high-pressure molding machine. The molded products (molded coal) molded in the double-roll molding machine 5 are heated in a carbonization furnace 6, which is a vertical shaft furnace, and discharged from the bottom. The discharged molded products are separated into oversize fraction 7 and undersize fraction 8 through a sieve, and the molded products separated as oversize fraction 7 are supplied to a blast furnace 9 as ferro-coke, while the molded products separated as undersize fraction 8 are reused as sintering raw material in a sintering plant 10.

[0018] Fig. 2 is a graph showing one embodiment of the particle size distribution of ferro-coke in the present invention. In the example shown in Fig. 2, the particle size of the ferro-coke is mostly comprised of 16 to 22 mm. [Example]

[0019] Briquettes were produced using the ferro-coke raw materials (high MF, medium MF-1, medium MF-2, and low MF) with the blending ratios shown in Table 1 below, according to the flow chart of the ferro-coke production method shown in Figure 1. Coals with different maximum fluidity (MF) were blended as the ferro-coke raw materials to control the MF. The resulting briquettes were then sieved, and the remaining sieve was used as the ferro-coke product. The sieve mesh size was varied to determine the drum strength. A perfect screen (PS) was used to increase sieving efficiency and enable accurate evaluation. Figure 3 shows the relationship between the mesh size of the sieve used and the drum strength. The drum strength was calculated by placing 10 kg of a sample sampled from the ferro-coke product into a drum testing machine specified in JIS K 2151, rotating it 150 times, and then separating the sample through a 6 mm mesh sieve.

[0020] [Table 1]

[0021] Figure 3 shows that even for ferro-coke produced from the same raw material blend, the drum strength varied with the size of the sieve mesh used to sieve the briquettes, reaching a maximum value. Furthermore, it was found that the optimum sieve mesh at which the drum strength reached a maximum value shifted when the blending MF differed. This is presumably because, in the case of ferro-coke produced from low-MF coal as a raw material for ferro-coke, the sample particle size itself was small due to insufficient melting, resulting in a smaller optimum sieve mesh. Conversely, in the case of ferro-coke produced from high-MF coal as a raw material for ferro-coke, the average particle size itself increased due to expansion, presumably resulting in a larger optimum sieve mesh.

[0022] Based on the above findings, we investigated the optimal sieve mesh size for achieving maximum drum strength. Figure 4 is a graph showing the optimal sieve mesh size and drum strength for ferro-coke produced by varying the MF of coal. In the example shown in Figure 4, the optimal sieve mesh sizes, in descending order of MF, were 20 mm (high MF), 16 mm (medium MF-1), 16 mm (medium MF-2), and 12 mm (low MF). While a higher MF is preferable from the perspective of drum strength, coal with an MF exceeding 50 can melt in the carbonization furnace, hindering operation. Furthermore, from the perspective of economic rationality, it is necessary to actively utilize coal with an MF of 0. This method allows for flexible use within the range of MF = 50 or less.

[0023] From the above, it has been found that in the present invention, ferro-coke with high drum strength can be produced by sieving ferro-coke using sieves with different mesh sizes depending on the maximum fluidity (MF) of the coal used as a briquetting raw material.

[0024] Figure 5 shows the relationship between the MF of coal and the sieve mesh size at which the drum strength of ferro-coke is 75% or more. It can be seen from Figure 5 that the appropriate sieve mesh size increases as the MF increases. Furthermore, in Figure 5, the range between two sieve meshes at the same MF is the appropriate region at which the drum strength of 75% or more can be achieved. It can be seen from Figure 5 that, in the present invention, it is preferable to operate within the range shown below. 0.13×MF+10≦sieve size≦0.22×MF+16 [Industrial Applicability]

[0025] According to the present invention, the drum strength of the produced ferro-coke can be optimized by sieving the ferro-coke with a smaller mesh size in accordance with the reduction in the maximum fluidity (MF) of the coal used as the briquetting material, which results in ensuring good gas permeability in the blast furnace, reducing the reducing agent rate, and reducing production costs and CO2 emissions. [Explanation of symbols]

[0026] 1. Coal 2. Iron ore 3. Mixing machine 4 binder tank 5 Double roll molding machine 6. Dry distillation furnace 7 Sieve top 8 Under the sieve 9 blast furnace 10 Sintering Plant

Claims

1. A method for producing ferro coke, comprising mixing and kneading a molding raw material containing coal, an iron source raw material, and a binder, forming the agglomerates in a double roll molding machine, and carbonizing the resulting molded products to produce ferro coke, characterized in that the mesh size of the sieve is reduced in accordance with a reduction in the maximum fluidity (MF) (JIS M 8811) of the coal used as the molding raw material, and the sieved coal is used as the ferro coke.

2. The method for producing ferro-coke according to claim 1, characterized in that sieving is carried out in the range of 0.13×MF+10≦sieve mesh size≦0.22×MF+16.

3. 2. The method for producing ferro-coke according to claim 1, wherein the sieving is carried out when the maximum fluidity (MF) of the coal to be blended into the molded coal is in the range of 0 to 50.

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