Process for preparing coal or binder material and process for manufacturing coke

Abstract

A method for preparing coal or binder material used alone or in combination with other coals as a raw material for coke making, before the coal or binder material enters the coking plant, while heating the coal or binder material contained in a container and rotating a stirrer, the content of particles with a particle size of 6 mm or more of the coal or binder material that satisfies at least one of the following: the bond strength (a - b) / a represented by the height b of the semi-coke formed on the inner side wall of the container and the height a of the semi-coke attached to the stirrer is 0.20 or more, and the height a is 30 mm or more, is adjusted to 30% by mass or less.

Description

Technical Field

[0001] The present invention relates to a preparation method for producing coke with high strength by adjusting the particle size of coal or binder using an evaluation method for evaluating the softening and melting characteristics of evaluation coal and binder, that is, a method for producing coal or binder with adjusted particle size. Background Art

[0002] In order to produce molten iron in a blast furnace, metallurgical coke used as a blast furnace raw material is preferably of high strength. If the strength of the coke is low, it will be pulverized in the blast furnace, hindering the air permeability of the blast furnace and making it impossible to produce molten iron stably. Therefore, from the viewpoint of not reducing the coke strength, it is necessary to evaluate the technology of coal as a raw material for metallurgical coke.

[0003] It is described in Patent Document 1 that during the coking process in a coke oven, coal in a softened and molten state has a great influence on the quality of coke. Thus, in the evaluation of coal, it is important to accurately evaluate the properties of the softened and molten state of coal. As described in Patent Document 1, as a method for performing this evaluation, it is known to measure the fluidity by the Gieseler plastometer method specified in JIS - M8801.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Patent Application Laid - Open No. 2000 - 304674

[0007] Non - Patent Document 1: Takashi Miyatsu et al., "Multiple Blending Plans and Evaluation of Raw Coal", Nippon Kokan Technical Report, vol. 67, 1975, pp. 125 - 137 Summary of the Invention

[0008] It is known that the fluidity measured by the Gieseler plastometer method has a problem that it cannot be said to simulate the phenomena occurring in an actual coke oven. Therefore, inferring the coke quality using the fluidity of coal measured by the Gieseler plastometer method is insufficient from the viewpoint of accuracy. Therefore, there is a need to seek a manufacturing technology for metallurgical coke and a manufacturing technology for coke using a parameter other than the fluidity of coal as an index. The present invention has been completed in view of such prior art, and its object is to provide a preparation method for coal or binder that can evaluate whether the target coal is likely to reduce the strength of coke and adjust the particle size of coal that is likely to reduce the coke strength.

[0009] The means for solving the above problems are as follows.

[0010] [1] A method for preparing coal or a binder material, which is a method for preparing coal or a binder material used alone or in combination with other coals as a raw material for coke production. Before the above-mentioned coal or binder material enters the coking plant, the content rate of particles with a particle size of 6 mm or more of the above-mentioned coal or binder material that satisfies at least one of the following conditions: the cohesiveness (a - b) / a represented by the height b of the semicoke formed on the inner side wall of the above-mentioned container and the height a of the above-mentioned semicoke attached to the above-mentioned stirrer is 0.20 or more, and the above-mentioned height a is 30 mm or more, is adjusted to 30% by mass or less.

[0011] [2] A method for preparing coal or a binder material, which is a method for preparing coal or a binder material used alone or in combination with other coals as a raw material for coke production. Before the above-mentioned coal or binder material enters the coking plant, particle size adjustment is performed so that the content rate of particles with a particle size of 6 mm or more of the above-mentioned coal or binder material that satisfies at least one of the following conditions: the cohesiveness (a - b) / a represented by the height b of the semicoke formed on the inner side wall of the above-mentioned container and the height a of the above-mentioned semicoke attached to the above-mentioned stirrer is 0.20 or more, and the above-mentioned height a is 30 mm or more, satisfies the following formula (1).

[0012] Content rate of particles with a particle size of 6 mm or more (mass%) ≤ 30 + 0.5 × (HGI - 60) ··· (1)

[0013] In the above formula (1), HGI is the Hardgrove grindability index of coal or a binder material.

[0014] [3] The method for preparing coal or a binder material according to [1] or [2], wherein the condition for rotating the stirrer while heating the above-mentioned container and the above-mentioned coal or binder material accommodated in the above-mentioned container is the measurement condition of the Gieseler fluidity.

[0015] [4] A method for preparing coal or a binder material, which is a method for preparing coal or a binder material used alone or in combination with other coals as a raw material for coke production. Before the above-mentioned coal or binder material enters the coking plant, for a variety of the above-mentioned coal or binder materials in advance, according to the relationship between the degree of cohesion (a - b) / a represented by the height b of the semi-coke formed on the inner side wall of the above-mentioned container and the height a of the semi-coke attached to the above-mentioned stirrer in the above-mentioned container by heating the above-mentioned coal or binder material contained in the container while rotating the stirrer, or the above-mentioned height a, and the strength of the coke obtained by mixing and coking a variety of the above-mentioned coal or binder materials with other coals, the range of the degree of cohesion (a - b) / a or the height a determined to be poor as the above-mentioned raw material for coke production is determined, and the content rate of particles with a particle size of 6 mm or more of the above-mentioned coal or binder material used as the above-mentioned raw material for coke production and having a degree of cohesion (a - b) / a or a height a within the range determined to be poor as the above-mentioned raw material for coke production is adjusted to 30% by mass or less.

[0016] [5] A method for preparing coal or a binder material, which is a method for preparing coal or a binder material used alone or in combination with other coals as a raw material for coke production. Before the above-mentioned coal or binder material enters the coking plant, particle size adjustment is carried out so that for a variety of the above-mentioned coal or binder materials in advance, according to the relationship between the degree of cohesion (a - b) / a represented by the height b of the semi-coke formed on the inner side wall of the above-mentioned container and the height a of the semi-coke attached to the above-mentioned stirrer in the above-mentioned container by heating the above-mentioned coal or binder material contained in the container while rotating the stirrer, or the above-mentioned height a, and the strength of the coke obtained by mixing and coking a variety of the above-mentioned coal or binder materials with other coals, the range of the degree of cohesion (a - b) / a or the height a determined to be poor as the above-mentioned raw material for coke production is determined, and the content rate of particles with a particle size of 6 mm or more of the above-mentioned coal or binder material used as the above-mentioned raw material for coke production and having a degree of cohesion (a - b) / a or a height a within the range determined to be poor as the above-mentioned raw material for coke production satisfies the following formula (1).

[0017] Content rate of particles with a particle size of 6 mm or more (%) ≤ 30 + 0.5 × (HGI - 60) ··· (1)

[0018] HGI in the above formula (1) is the Hardgrove grindability index of coal or binder material.

[0019] [6] The method for preparing coal or a binder material according to any one of [1] to [5], wherein before charging into the coke oven, the content rate of particles with a particle size of 6 mm or more of the above-mentioned coal or binder material is adjusted to 5% by mass or less.

[0020] [7] The method for preparing coal or binder material according to any one of [1] to [6], wherein the particle size of the coal or binder material is adjusted before shipping from the site where the coal is produced or the site where the binder material is manufactured.

[0021] [8] A method for manufacturing coke, which manufactures coke by carbonizing the coal prepared by the method for preparing coal or binder material according to any one of [1] to [7].

[0022] [9] A method for manufacturing coke, which manufactures coke by carbonizing the coal and binder material prepared by the method for preparing coal or binder material according to any one of [1] to [7].

[0023] In the present invention, it is evaluated whether the coal is poor-quality coal that may reduce the coke strength, and the particle size of the coal evaluated as poor-quality is adjusted. Thus, even if coal that may reduce the coke strength is used, it is possible to suppress a decrease in the coke strength of the manufactured coke and achieve the manufacture of high-strength metallurgical coke. DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a vertical sectional view showing an example of the Gieseler plastometer 10 used in the method for evaluating the softening and melting characteristics of the coal in the present embodiment.

[0025] Figure 2 It is a schematic diagram showing the generation state of a defect structure when coking a blended coal obtained by mixing poor-quality coal particles 20 and non-poor-quality coal particles 22.

[0026] Figure 3 It is a schematic diagram showing the generation state of a defect structure when coking a blended coal containing only non-poor-quality coal particles 22.

[0027] Figure 4 It is a schematic diagram showing the generation state of a defect structure when coking a blended coal obtained by mixing coal particles 24 obtained by crushing and refining poor-quality coal particles 20 and non-poor-quality coal particles 22.

[0028] Figure 5 It is a graph showing the relationship between the maximum particle size and the drum strength of Coal A and Coal F.

[0029] Figure 6 It is a graph showing the relationship between the content rate of particles with a particle size of 6 mm or more in the blended coal and the coke strength. DETAILED DESCRIPTION OF THE INVENTION

[0030] In the present invention, the shape of semicoke formed by heating a device having a container for accommodating coal and a stirrer disposed within the container is used as an index to evaluate whether the coal is a coal that may reduce the coke strength. Further, it has been found that when the coal is evaluated as a coal that may reduce the coke strength, the particle size of the coal is adjusted in advance, and the coal is used alone or in combination with other coals as a raw material for coke production, whereby a reduction in the coke strength of the produced coke can be suppressed, and thus the present invention has been completed. Hereinafter, the present invention will be described by way of embodiments of the present invention.

[0031] Figure 1 FIG. 4 is a vertical sectional view showing an example of a Gieseler plastometer 10 used in the method for evaluating the softening and melting characteristics of coal in the present embodiment. The Gieseler plastometer 10 has a container 12 for accommodating the coal to be evaluated and a stirrer 14 disposed within the container 12. The Gieseler plastometer 10 further has a drive device (not shown), and the stirrer 14 is rotated by this drive device. When the stirrer 14 is rotated in a state where coal is accommodated in the container 12 and the container 12 is heated to raise its temperature, the heated coal becomes a softened and molten state. The softened and molten coal becomes a viscoelastic body and deforms, adheres to the rotating stirrer 14, but a force to maintain the shape acts on the coal, and a force to resist rotation acts on the stirrer 14.

[0032] In the Gieseler plastometer method, the rotational speed of the stirrer 14 is measured in a state where a predetermined torque is applied to the stirrer 14, and the maximum rotational speed during heating is obtained as the Gieseler maximum fluidity MF (ddpm). Sometimes, the measured value takes the common logarithm log of MF, and the Gieseler maximum fluidity is represented by logMF. The heating conditions of the coal, the measurement conditions such as the dimensions of the container 12, etc. in the Gieseler plastometer method are specified as follows in JIS M 8801.

[0033] (1) A stirrer having four cross bars (diameter 1.6 mm, length 6.4 mm, not shown in FIG. 4) perpendicularly mounted on a shaft with a diameter of 4.0 mm is inserted into a container with a depth of 35.0 mm and an inner diameter of 21.4 mm. Figure 1 not shown in FIG. 4)

[0034] (2) 5 g of coal is filled in the container.

[0035] (3) The container is immersed in a metal bath preheated to 300 °C or 350 °C, and after the temperature of the metal bath returns to the preheated temperature, heating is continued at a heating rate of 3 °C / min until the rotation of the stirrer stops.

[0036] It should be noted that the distance between the lowest cross bar and the bottom of the container is 1.6 mm, and the axial distance between the cross bars is 3.2 mm. The two central cross bars are located at positions 180 degrees apart from each other in the rotational direction, and the upper and lower cross bars are also located at positions 180 degrees apart from each other in the rotational direction. The two central cross bars and the two upper and lower cross bars are located at positions 90 degrees apart from each other in the rotational direction. The conditions specified in ASTM D2639 are the same as those of JIS M 8801, and the ASTM method can also be used. In addition, ISO 10329 or corresponding conditions can also be used. When not using a Gieseler plastometer, the container for accommodating coal is preferably cylindrical, and a stirrer with a diameter of 5 to 60% of its inner diameter is preferably used. The stirrer is preferably provided with cross bars, but even without cross bars, adhesion of the softened and molten coal to the stirrer occurs.

[0037] Coal softens and melts upon heating to exhibit fluidity, and the melt solidifies again upon further heating. Therefore, after measuring the Gieseler fluidity, the coal heated at a temperature above the re-solidification temperature of the coal becomes semicoke 16 and is accommodated in the container 12. Since both the coal and the semicoke 16 are plastic bodies, after measuring the Gieseler fluidity, the semicoke 16 is pulled by the stirrer 14 while being in contact with the inner side wall of the container 12, and maintains a shape adhered to the stirrer 14 in a bonded manner. Therefore, for most varieties of coal, as Figure 1 shown, the height a of the semicoke 16 adhered to the stirrer 14 from the bottom surface of the container 12 is the highest, and the height b of the semicoke 16 in contact with the inner side wall of the container 12 from the bottom surface is the lowest. This behavior of the softened and molten coal is known as the Weissenberg effect.

[0038] The above-mentioned height a and height b can be measured by disassembling the container 12 after the measurement. In addition, after measuring the Gieseler fluidity, the container 12 can be scanned with a microfocus X-ray CT device to obtain an image of the shape of the semicoke 16, and the height a and height b can be measured from this image. Examples of the microfocus X-ray CT device include XTH320LC manufactured by Nikon Corporation, phoenix v|tome|x m300 manufactured by GE Sensing&Inspection Technologies Co., Ltd., etc. Since there is almost no difference in height a and height b caused by the position in the circumferential direction of the container, it is sufficient to measure the height of a specific cross section. Even when there is a height difference due to the position in the circumferential direction, the height can be measured at multiple cross sections and their average values can be used as the values of height a and height b.

[0039] The shape of the semicoke 16 after measuring the Gieseler fluidity varies depending on the properties of the coal. The inventors of the present invention believe that the shape of the semicoke 16 in the container 12 serves as an index indicating the influence on the strength of the coke, investigated the relationship between the cohesiveness (a - b) / a represented by the height a and height b of the semicoke 16 and the coke strength, and confirmed that the cohesiveness (a - b) / a serves as an index for evaluating whether the coal is likely to reduce the coke strength. Furthermore, the inventors of the present invention confirmed that even when using the height a of the semicoke 16 attached to the stirrer 14 instead of the cohesiveness, it can also serve as an index for evaluating whether the coal is likely to reduce the coke strength, similarly to the cohesiveness.

[0040] The investigation of the relationship between the cohesiveness (a - b) / a, the height a, and the coke strength was conducted as follows. To investigate the influence of the cohesiveness (a - b) / a and the height a on the coke strength, carbonization tests were performed using coals T to Y. The properties of the coals used are shown in Table 1. The carbonization test was carried out using an electric furnace capable of simulating the carbonization conditions of a coke oven, and the blended coal charged into the furnace at a bulk density of 750 kg / dry coal was carbonized at 1050°C for 6 hours to produce coke. The properties of the prepared coals, the cohesiveness (a - b) / a, and the height a are shown in Table 1.

[0041] [Table 1]

[0042]

[0043] The "ash content" and "volatile components" in Table 1 are the measured values based on the industrial analysis method of JIS M 8812 (mass % on a dry basis, respectively). "Ro" is the mean maximum reflectance of the vitrinite of the coal according to JIS M 8816, and "TI" is the amount of inert matter (volume %) in the coal tissue analysis calculated according to the Parr formula described in the method for measuring and explaining the fine tissue components of the coal in JIS M8816. "logMF" is the common logarithm log value of the maximum fluidity MF measured by the fluidity measurement method based on the Gieseler plastometer method specified in JIS M 8801. As shown in Table 1, the properties of coals T to Y are different.

[0044] The "cohesiveness" in Table 1 is the cohesiveness (a - b) / a value calculated using the height a and b in the evaluation method of the coal of the present embodiment measured by the Gieseler plastometer shown in Figure 1 . The height a and b are measured by actually measuring the cross-sectional shape image of the semicoke obtained by scanning the container 12 with the X-ray CT device XTH320LC manufactured by Nikon Corporation.

[0045] It should be noted in Table 1 that the height a of coals T and U is 30 mm or more, and the cohesiveness is 0.20 or more. In view of the properties of Ro and logMF shown in Table 1, coal Y is regarded as a standard coal in the technical field of manufacturing metallurgical coke from coal.

[0046] In this embodiment, coal T to X are further mixed with coal Y at a ratio of 2:8 to obtain two kinds of coal, and the mixed coal composed of these two kinds of coal is coked to produce coke. The strength of the obtained coke is shown in Table 2.

[0047] [Table 2]

[0048]

[0049] As the strength of the coke, based on the rotary strength test method of JIS K 2151, the mass ratio of coke with a particle size of 15 mm or more after the drum tester filled with a specified amount of coke rotates at 15 rpm for 150 revolutions is measured, and the drum strength "DI 150 / 15" is obtained by multiplying the mass ratio before rotation by 100. Table 2 shows the strength of the coke obtained from the mixed coal composed of two kinds of coal.

[0050] It can be seen from Table 2 that the coke obtained from the mixed coal composed of coal T or coal U and coal Y has a lower strength compared with the case of mixing coal V, W, and X with coal Y. Both coal T and U have a caking index (a - b) / a of 0.20 or more or a height a of 30 mm or more. Therefore, coal with a caking index (a - b) / a of 0.20 or more can be evaluated as poor as raw coal for coke production. Similarly, coal with a height a of 30 mm or more can also be evaluated as poor as raw coal for coke production.

[0051] In this way, by mixing multiple kinds of coal with different caking indices (a - b) / a or heights a with other coal, and investigating the relationship between the strength of the coke obtained by coking the mixed coal and the caking index (a - b) / a or height a, it is possible to determine the range of the caking index (a - b) / a or height a that is evaluated as poor as raw coal for coke production. In this example, the coals T to X to be evaluated are added to the same coal Y in such a way that the mixing amounts of coals T to X are constant, and coking is carried out under the same conditions to produce coke. As a method for evaluating the coking test of coal, this method is not limited. For example, the addition amount of the coal to be evaluated can be set to be constant, and the type and mixing amount of the remaining coal can be adjusted to make the average grade of the mixed coal containing the coal to be evaluated constant for testing. In this case, as the average grade, it is preferable to make the weighted average reflectance Ro and the weighted average logMF (common logarithm of the Gieseler maximum fluidity) constant.

[0052] Based on the relationship between coke strength and cohesiveness (a - b) / a or height a, the range of cohesiveness (a - b) / a or height a evaluated as poor for the raw coal used in coke production can be determined, for example, based on the following method. In the operation of a blast furnace, if the strength of the coke is low, the blast furnace cannot be stably operated. Therefore, the strength of the coke that enables stable operation of the blast furnace is determined based on the actual operating conditions of the blast furnace, and the cohesiveness (a - b) / a or height a corresponding to the coke strength that enables stable operation of the blast furnace is determined based on the relationship between coke strength and cohesiveness (a - b) / a or height a. If the cohesiveness (a - b) / a or height a is below the value thus determined, the blast furnace can be stably operated, but if it exceeds the determined value, the stable operation of the blast furnace is likely to become difficult. Therefore, the range of cohesiveness (a - b) / a or height a that exceeds the determined value can be defined as the range of cohesiveness (a - b) / a or height a evaluated as poor for the raw material for coke production.

[0053] Here, the properties of coal evaluated as poor for coke raw materials are determined based on the strength test specified by JIS, but strength indicators other than this can also be used. As a rotational strength test method similar to the JIS method, Micum strength, drum strength, type I drum strength, etc. are known, and these strengths can be obtained according to the standards of ISO and ASTM. In addition, mechanical strengths such as the compressive strength of coke can be used to determine the range of cohesiveness and height evaluated as poor for coke raw materials.

[0054] It is speculated that coal with high cohesiveness and coal with a large height a of the semicoke 16 attached to the stirrer 14 have excessive expansibility in the softened and molten state, and are likely to produce defective structures in the heated coke, which has an adverse effect on coke strength. Therefore, in the present embodiment, when the cohesiveness of the coal or the height a is above a specified value, the coal is evaluated as poor coal that may reduce coke strength. Specifically, among the measurement conditions of the fluidity of coal based on the Gieseler plastometer method specified by JIS or the like, coal that satisfies at least one of a cohesiveness of 0.20 or more and a height a of 30 mm or more is evaluated as poor for the coal for metallurgical coke. It should be noted that the greater the cohesiveness and the height a, the greater the expansibility, and it can be judged that there is an adverse effect on coke strength. Therefore, an upper limit value for the cohesiveness and the height a may not be set. However, the measured values of both the cohesiveness and the height a are restricted by the size of the container 12 that houses the coal sample. Therefore, it is preferable to use a container that can measure values of cohesiveness of 0.20 or more and a height a of 30 mm or more for measurement.

[0055] Depending on the type of coal, sometimes all of the semicoke 16 is pulled by the stirrer 14 and the semicoke 16 does not come into contact with the inner wall of the container 12 at all. Even in this case, the coal is speculated to have excessive expansibility. Therefore, it does not prevent the calculation of cohesiveness to evaluate the coal, and it is only necessary to substitute 0 for b and calculate the cohesiveness as 1.

[0056] If coal evaluated as poor is used as the raw coal (raw coal for coke), large defects remain during coking, and a tissue structure with thin pore walls is formed. Therefore, the coke strength of the produced coke decreases. However, the present inventors have found that even when coal evaluated as poor is used as the raw coal for coke, by adjusting the particle size of the coal evaluated as poor, a decrease in strength can be suppressed.

[0057] Figure 2 It is a schematic diagram showing the generation state of the defect structure during coking of a blended coal obtained by mixing coal particles 20 evaluated as poor and coal particles 22 not evaluated as poor. Figure 2 (a) shows the state before coking, Figure 2 (b) shows the state after coking. The coal particles 20 evaluated as poor expand during coking and penetrate into the voids between the packed particles and large defects 26 in large quantities. Therefore, thin pore walls are formed, and large defects 26 are generated where the coal particles 20 originally existed. Due to the formation of these thin pore walls and large defects 26, a decrease in coke strength occurs in the coke produced using the blended coal containing the coal particles 20 evaluated as poor. Even when the coal evaluated as poor is carbonized alone (without being mixed with other coal), such large defects 26 are generated. This is because the entire layer of the coal evaluated as poor expands, and defects are generated due to this phenomenon, resulting in a decrease in coke strength. The inventors have found the correlation between the ease of generation of such defects and the cohesiveness (a - b) / a or the height a.

[0058] Figure 3 It is a schematic diagram showing the generation state of the defect structure during coking of a blended coal containing only coal particles 22 not evaluated as poor. Figure 3 (a) shows the state before coking, Figure 3 (b) shows the state after coking. The coal particles 22 not evaluated as poor are less likely to penetrate into the voids between the packed particles and large defects during coking. Therefore, thick pore walls are formed, and no large defects remain where the coal particles 22 originally existed. Therefore, no decrease in coke strength occurs in the coke produced using only the coal particles 22 not evaluated as poor.

[0059] Figure 4 It is a schematic diagram showing the generation state of the defect structure during coking of a blended coal obtained by mixing coal particles 24 obtained by pulverizing and refining the coal particles 20 evaluated as poor and coal particles 22 not evaluated as poor. Figure 4 (a) shows the state before coking, Figure 4(b) represents the coked state. The coal evaluated as poor penetrates into the gaps between the packed particles and large defects during coking. However, since the defects formed at the original locations of the particles become smaller, thus, even when using blended coal containing the coal evaluated as poor, by using coal particles 24 obtained by pulverizing and refining this coal, it is possible to suppress the reduction in the coke strength of the produced coke.

[0060] In this way, even for coal evaluated as poor, by pre-refining the particle size of this coal, it is possible to suppress the generation of large defects during coking. Thus, even when using coal evaluated as poor, it is possible to suppress the reduction in the coke strength of the coke after carbonization.

[0061] In addition, the binder added to the blended coal can also be the cause of reducing the coke strength by the same mechanism. Therefore, it is preferable to adjust the particle size of the binder to the same particle size as the coal evaluated as poor before the binder enters the coking plant.

[0062] It was confirmed to what extent the coal evaluated as poor should be refined before carbonization for blending to suppress the reduction in coke strength. As a result, it was confirmed that if the content rate of particles of 6 mm or more in the coal before carbonization, that is, the coal charged into the coke oven, is 5% by mass or less, it is possible to suppress the reduction in coke strength. The detailed content will be described later, but by making the content rate of particles of 6 mm or more in the coal 5% by mass or less, the coke strength of the coke produced using blended coal in which the coal evaluated as poor is blended in the range of 8% by mass or more and less than 12% by mass is equal to the coke strength of the coke produced using blended coal in which the coal evaluated as poor is blended at 2% by mass or less. This result means that if the content rate of particles of 6 mm or more in the coal is 5% by mass or less, even if the blending rate of the coal evaluated as poor is 8% by mass or more and less than 12% by mass, and even if the blending rate of this coal is 2% by mass or less, the coke strength remains unchanged. From this, it can be known that it is possible to suppress the reduction in coke strength caused by blending the coal evaluated as poor.

[0063] Usually, coke is produced using blended coal containing 10 to 15 varieties of coal. At this time, the coal and binder entering the coking plant are pulverized more finely to a particle size suitable for coke production. However, in the coking plant for producing coke, adjusting only the particle size of a specific variety of coal to a specific particle size will complicate the operation, so it is not preferable. Therefore, it is preferable to pre-adjust the particle size of the coal evaluated as poor before entering the coke production plant. In this way, it is pulverized more finely in the pulverization process before charging into the coke oven. Thus, without complicating the particle size adjustment in the coke production plant, it is possible to suppress the reduction in the coke strength of the produced coke.

[0064] The content rate of particles larger than 6 mm in coal can be calculated based on the mass ratio of the particles on the sieve or under the sieve to the total sample by screening with a sieve of a specified mesh size in a state where the moisture content of the coal is dried to 6% by mass or less. If the moisture content rate of the coal is 6% by mass or less, the coal particles do not aggregate with each other to form pseudo-particles or fine powder does not adhere to the coarse particles, so there is no error in the measured value of the particle size. Therefore, it is preferable to measure the content rate of particles larger than 6 mm in coal with the moisture content rate of the coal being 6% by mass or less.

[0065] The coal entering the coking plant is further pulverized in the coking plant and then charged into the coke oven. Therefore, the content rate of particles larger than 6 mm in the coal before entering the coking plant is not necessarily 5% by mass or less. Therefore, the particle size of the coal with a content rate of particles larger than 6 mm in the coal being 5% by mass or less after being pulverized under the standard pulverization conditions of the coking plant was confirmed. As a result, it can be known that if the content rate of particles larger than 6 mm in the coal is 30% by mass or less, the content rate of particles larger than 6 mm after pulverization under the standard coal pulverization conditions is 5% by mass or less. Therefore, for the coal evaluated as poor, it is only necessary to adjust the particle size so that the content rate of particles larger than 6 mm in the coal is 30% by mass or less before entering the coking plant. Through pulverization in the coking plant, the content rate of particles larger than 6 mm in the coal is adjusted to 5% by mass or less before being charged into the coke oven.

[0066] Here, as a method for adjusting the particle size of coal, for example, when making the particle size of coal finer, it can be adjusted by mining in a way that makes the particle size finer at the coal mining stage, or by performing pulverization, classification, and screening in the coal preparation process and blending process from after mining to shipment. In a coal mine, since the grade of the coal produced from each coal seam is measured in advance, the caking index is also measured, and the particle size can be adjusted according to the measured value. Pulverization of coal can be performed using known crushers such as impact crushers and hammer crushers. In addition, by using these crushers in combination with a sieve, only the coarse particle part of the coal that causes a decrease in coke strength can be taken out and pulverized, so the particle size can be adjusted more effectively. It should be noted that since the particle size of coal inevitably varies depending on various conditions such as the mining location, time, equipment, transportation, and storage after mining, it is different for each batch. Therefore, the particle size of coal can also be adjusted by blending batches with different particle sizes.

[0067] Furthermore, the hardness of coal can also be considered to adjust the particle size of coal. If the crushing conditions are the same, the softer the coal, the finer it will be crushed. Therefore, if the target value of the content rate of particles with a particle size of more than 6 mm after crushing in a coking plant is constantly 5% by mass or less, it is considered that even if the content rate of particles with a particle size of more than 6 mm before the coal is supplied to the crusher in the coking plant is large, the specified target value can be satisfied. As an index of the hardness of coal, HGI (Hardgrove Grindability Index) is usually used. Therefore, the HGI of coal with a content rate of particles with a particle size of more than 6 mm of 30% by mass in the coal is measured. The coal is crushed under standard coal crushing conditions and the content rate of particles with a particle size of more than 6 mm in the coal is 5% by mass or less. As a result, the HGI of this coal is 60. It should be noted that HGI is an index obtained by the crushing test method described in JIS M 8801.

[0068] Since the higher the HGI of coal means the softer it is, it is found that even if the HGI of coal increases by 1 (becomes softer), the content rate of particles with a particle size of more than 6 mm before the coal is supplied to the crusher in the coking plant increases by 0.5% by mass, and the content rate of particles with a particle size of more than 6 mm in the crushed coal can be 5% by mass or less. From this finding, it is preferable to adjust the particle size so that the content rate of particles with a particle size of more than 6 mm before the coal judged to be poor enters the coking plant or before the coal is shipped from the place where the coal is produced satisfies the following formula (1).

[0069] Content rate of particles with a particle size of more than 6 mm (% by mass) ≤ 30 + 0.5 × (HGI - 60) ··· (1)

[0070] The HGI of coal usually distributes in the range of 40 to 100, but the HGI of the coal evaluated as poor is measured, and the result is about 60 to 80. Therefore, it can be said that the coal with the above HGI of 60 is the hardest coal among the coals evaluated as poor, and it can be said that at least when the content rate of particles with a particle size of more than 6 mm in the coal evaluated as poor is 30% by mass or less, the content rate of particles with a particle size of more than 6 mm in the coal after crushing under standard coal crushing conditions in the coking plant is 5% by mass or less. It should be noted that considering the variation of the HGI of coal, it is more preferable that the content rate of particles with a particle size of more than 6 mm in the coal evaluated as poor is 20% by mass or less.

[0071] The coal whose particle size is adjusted by the preparation method of coal or binder material according to this embodiment is raw coal of individual varieties, which is defined as the unit of raw coal managed as a single batch when entering a coke manufacturing plant or when shipped from the coal production location. Here, managing as a single batch includes cases where the characteristics of the entire batch are represented by representative analysis values based on sampling from the batch, cases where it is stacked in a coal yard as a single batch, cases where it is put into the same coal bin, and cases where it is traded as a single batch or a single variety name in a procurement contract, etc. Therefore, in this embodiment, when the particle size is adjusted at a stage before the coal enters the coke manufacturing plant, the coal is defined as raw coal of a single variety.

[0072] Entering the coking plant means receiving at the coal yard or coal hopper attached to the coking plant in order to be crushed into a particle size suitable for coke manufacturing in the coking plant or to be blended with other varieties of coal. For example, in the case of an ironworks located in a coastal area, after receiving coal at the raw material wharf, it is transported into the coal yard attached to the coking plant. In this case, the receiving time at the raw material wharf is regarded as entering the coking plant.

[0073] In addition, shipping from the coal production site means sending out as individual varieties of coal from a mine or a shipping base by means of transportation such as ships, trucks, lorries or conveyors. In this embodiment, as long as it is shipped as individual varieties of coal from a mine, a shipping base, etc., the shipping method (ships, trucks, etc.) and the shipping stage (when shipping by truck and then changing to shipping by ship) are not questioned. This is because once it is identified as individual varieties of coal, except for inevitable cases, the composition and particle size will not change thereafter.

[0074] Example 1

[0075] Hereinafter, a method for determining the optimal particle size of coal evaluated as defective will be described. First, the influence of the shape difference of semicoke after heating and stirring on the coke strength was confirmed. For 18 kinds of coal (Coal A - Coal R) and 1 kind of binder material (Binder Material S), the shape of the semicoke was measured after measuring the Gieseler fluidity. The characteristics of the coal and binder material used are shown in Table 3. Ro in Table 3 is the mean maximum reflectance of the vitrinite of the coal according to JIS M 8816, and logMF is the common logarithm of the maximum fluidity (Maximum Fluidity: MF) measured by the Gieseler plastometer method. In addition, the volatile component (VM) and ash are the measured values based on the industrial analysis method of JISM 8812.

[0076] [Table 3]

[0077]

[0078] Use Figure 1The Gieseler plastometer 10 shown in the figure measures the height a and height b based on the shape of the semicoke formed after heating and stirring, and calculates the caking index (a - b) / a. The values shown in the column "Caking index" in Table 3 are the values of the caking index (a - b) / a, and the values shown in the column "Height a" are the values of the height a of the semicoke adhering to the stirrer. The height a and height b of the semicoke are measured using the image of the semicoke 16 obtained by scanning the container 12 with the XTH320LC manufactured by Nikon Corporation after heating and stirring.

[0079] Among the coals shown in Table 3, the values of the caking index (a - b) / a of Coal C, Coal F, and Coal G are 0.20 or more. Therefore, Coal C, Coal F, and Coal G are evaluated as poor coals that may reduce the coke strength. It should be noted that, as can be seen from Table 3, it is also possible to judge whether it is a poor coal by whether the value of the height a is 30 mm or more.

[0080] In the existing coal blending theory for predicting coke strength, it is considered that the coke strength is mainly determined by the mean maximum reflectance (Ro) and logMF of the vitrinite of the coal (for example, refer to Non-Patent Document 1). Therefore, blended coals of various coals are prepared in such a way that the weighted average Ro and weighted average logMF of the whole blended coal are equal (Ro = 0.99, logMF = 2.2). For Coal A and Coal F, magnesium with a content rate of 100% by mass of particles with a particle size less than 1 mm, a content rate of 100% by mass of particles with a particle size less than 3 mm, or a content rate of 100% by mass of particles with a particle size less than 6 mm is prepared, and for the other coals, the content rate of particles with a particle size less than 3 mm is 100% by mass, and 6 grades of blended coals (A1 - 3 and F1 - 3) are prepared using these coals. The blending ratios, etc. of these blended coals are shown in Table 4. It should be noted that [%] of the blending ratios in Table 4 are all by mass.

[0081] [Table 4]

[0082]

[0083] Here, the value of the caking index (a - b) / a of Coal A is 0.17, so it is evaluated as a non-poor coal. On the other hand, as described above, the value of the caking index (a - b) / a of Coal F is 0.24, so it is evaluated as a poor coal.

[0084] Adjustment is made so that the moisture content of the whole blended coal is 8% by mass, so that the bulk density of 16 kg of this blended coal is 750 kg / m 3It is filled into the retort in such a way that, with a 10-kg heavy object placed thereon, it is carbonized in an electric furnace with a furnace wall temperature of 1050 °C for 6 hours. Then, the retort is taken out of the electric furnace and nitrogen-cooled to obtain coke. The coke strength is determined by the rotating strength test method based on JIS K 2151 using the obtained coke. The mass ratio of coke with a particle size of 15 mm or more after 150 rotations at 15 rpm is measured, and the ratio to the mass before rotation is calculated as the drum strength DI150 / 15. Furthermore, CSR (strength after thermal CO 2 reaction, determined according to the ISO18894 method) and microscopic strength (MSI+65) are also measured. These measurement results are shown together in Table 4.

[0085] Figure 5 It is a graph showing the relationship between the maximum particle size of Coal A and Coal F and the drum strength. It was confirmed that at any particle size, the strength of coke produced from blended coal containing Coal F, which was evaluated as poor, was lower than that of coke produced from blended coal containing Coal A, which was evaluated as non-poor. Although the experiment was conducted under the condition that there was no significant difference in the Ro and logMF values of Coal A and Coal F and the weighted average values of Ro and logMF of the blended coal were also the same, there was a difference in coke strength. Therefore, it was confirmed that the cohesiveness and the value of height a measured in this embodiment were factors affecting coke strength and were factors that could not be explained by the conventionally used Ro and logMF.

[0086] From the test results, it can be seen that when Coal A with a cohesiveness of 0.17 and a height a of 28 mm is added to the blended coal, it is not easy to cause a decrease in coke strength, while when Coal F with a cohesiveness of 0.24 and a height a of 31 mm is added to the blended coal, it is easy to cause a decrease in coke strength. Therefore, it is appropriate to evaluate coal that satisfies at least one of a cohesiveness of 0.20 or more and a height a of 30 mm or more as poor for use in manufacturing metallurgical coke. In the case where it is desired to more reliably prevent a decrease in coke strength, the criteria for evaluation as poor can also be made stricter, and coal that satisfies at least one of a cohesiveness exceeding 0.17 and a height a exceeding 28 mm can be evaluated as poor for use in manufacturing metallurgical coke. In addition, it was confirmed that in either case of the blended coal containing Coal A, which was evaluated as non-poor, and the blended coal containing Coal F, which was evaluated as poor, the coke strength of the coke produced by refining the coal particle size was increased. In particular, in the case of the blended coal containing Coal F, which was evaluated as poor, the increase in coke strength accompanying the refinement of the particle size of this coal was remarkable.

[0087] Next, an actual coke oven was used to study to what extent the coal evaluated as poor should be refined. Usually, in the normal operation of an actual coke oven, individual coal varieties are mixed at a prescribed blending ratio and then crushed. At this time, the particle size of the blended coal is managed by the ratio of the mass of the oversize or undersize when the blended coal passes through a certain prescribed sieve mesh to the total mass.

[0088] Two kinds of blended coals (two kinds: blended coal with the blending ratio of poor-quality coal ≤ 2% by mass and blended coal with 8% ≤ blending ratio of poor-quality coal < 12% by mass) prepared by variously changing the content rate of particles with a particle size of less than 6 mm in the coal evaluated as poor-quality were coked in an actual coke oven, and the drum strength DI150 / 15 was measured respectively as the strength of the coke after coking. The average properties of the blended coals used (weighted average of the characteristic values of each coal in the blended coal based on the blending ratio of each coal), the coking temperature (combustion chamber temperature), and the temperature in the coal after coking (temperature of the coke at the center of the height and width directions of the carbonization chamber) are shown in Table 5 below. It should be noted that the blended coals were prepared to reduce the variation range of the average properties, coking temperature, and temperature in the coal after coking, and the influence of these factors on the coke strength was excluded. Based on the measurement results, the relationship between the content rate of particles with a particle size of more than 6 mm in the blended coal and the coke strength was confirmed, and to what extent the coal evaluated as poor-quality was pulverized was confirmed. It should be noted that the conditions in Table 5 are an example of the conditions used in the experiment. Generally, under the conditions where Ro is in the range of 0.9 - 1.3% in the average properties of the blended coal, logMF is in the range of 2.3 - 3.0, the moisture content is in the range of 3 - 12% by mass, and the temperature of the coke after coking is in the range of 900 - 1200 °C, good coke can be produced.

[0089] [Table 5]

[0090]

[0091] Figure 6 is a chart showing the relationship between the content rate of particles with a particle size of more than 6 mm in the blended coal and the coke strength. As Figure 6 shown, when the blending ratio of the coal evaluated as poor-quality is more than 8% and less than 12% by mass, if the content rate of particles with a particle size of more than 6 mm increases and the overall coal particle size becomes coarser, the coke strength of the produced coke is greatly reduced. In contrast, in the case of the blended coal with the blending ratio of the coal evaluated as poor-quality being 2% by mass or less, the decrease in coke strength due to the coarsening of the coal particle size is smaller. This indicates that even for blended coals with the same overall particle size, if they contain the coal evaluated as poor-quality, the coke strength of the coke produced from such blended coals is reduced.

[0092] On the other hand, if the content rate of particles with a particle size of more than 6 mm in the blended coal is about 5% by mass, even if the blended coal contains the coal evaluated as poor-quality with more than 8% and less than 12% by mass, the strength of the produced coke is the same as that in the case where the coal evaluated as poor-quality (2% by mass or less) is not contained. From this result, it is speculated that if the pulverization is carried out until the content rate of particles with a particle size of more than 6 mm is 5% by mass or less, the reduction in coke strength caused by blending the coal evaluated as poor-quality can be suppressed. Since the coal with high caking property is likely to form asFigure 2 The large defects shown, so it is considered that by reducing the content of coal particles with large particle sizes, the generation of large defects can be suppressed, and the reduction of coke strength can be significantly suppressed.

[0093] Next, the effect of improving coke strength caused by adjusting the particle size of individual varieties will be described. Among the production areas of G coal shown in Table 3, the content rate of particles above 6 mm in G coal shipped after normal mining and coal preparation is 39% by mass. However, the G coal after coal preparation is crushed by an impact crusher, and the content rate of particles above 6 mm in G coal is adjusted to 30% by mass. This coal is designated as G' coal. After G coal and G' coal enter the coking plant, the blending ratio of G coal or G' coal is 10% by mass, and it is blended with A coal, B coal, H coal, J coal, L coal, N coal, O coal, and R coal to prepare blended coal with a weighted average reflectance = 1.01% and a weighted average logMF = 2.4. At this time, the cohesiveness of G coal and G' coal is measured by the same method as described in Table 1. The cohesiveness of G coal and G' coal is 0.34. Therefore, G coal is evaluated as poor.

[0094] The blended coal g containing G coal and the blended coal g' containing G' coal are respectively crushed by an impact crusher installed in the coking plant until the content rate of particles below 3 mm is 78% by mass. The content rate of particles above 6 mm in the crushed blended coal g or g' is 5.5% by mass. This blended coal is coked in a coke oven under the condition of an operating rate of 125%, and the produced coke is dry-extinguished, and then the JIS drum strength DI150 / 15 index is measured. As a result, the drum strength of the coke produced from the blended coal g is 82.9, while the drum strength of the coke obtained from the blended coal g' is 83.1. From this result, it was confirmed that by adjusting the content rate of particles above 6 mm in the coal of individual varieties before entering the coking plant to 30% by mass, even if the coal evaluated as poor is used, the reduction of the coke strength of the produced coke can be suppressed, and the production of high-strength metallurgical coke can be achieved.

[0095] The same test was conducted using K coal (the content rate of particles of 6 mm or more at the time of shipment from the production area was 37% by mass) instead of G coal. As a result, in the case where the content rate of particles of 6 mm or more in K coal was adjusted to 30% by mass and in the case where no particle size adjustment was made, the coke strength was 83.0, and no improvement effect of the coke strength with respect to the particle size adjustment of the coal was confirmed. The degree of cohesion of the semicoke of K coal was 0.16 and less than 0.20, and the height of the semicoke adhering to the stirrer was 27 mm and less than 30 mm. Therefore, it was confirmed that K coal was evaluated as non-defective coal, and even if the particle size of this coal was adjusted in advance, the coke strength of the produced coke did not increase. From this result, it was confirmed that in the method for preparing coal or binder material of the present embodiment, by evaluating whether the coal is defective and adjusting the particle size of the coal evaluated as defective, it is possible to suppress a decrease in the coke strength of the produced coke, and thus it is possible to achieve the production of high-strength metallurgical coke. In addition, by evaluating whether the coal is defective and selecting the coal evaluated as defective for particle size adjustment, the amount of coal to be particle size-adjusted becomes smaller, so it is also possible to contribute to reducing the load required for coke production and energy saving.

[0096] Symbol Explanation

[0097] 10 Gieseler plastometer

[0098] 12 Container

[0099] 14 Stirrer

[0100] 16 Semicoke

[0101] 20 Coal particles evaluated as defective

[0102] 22 Coal particles not evaluated as defective

[0103] 24 Micronized coal particles

[0104] 26 Coarse defect

Claims

1. A method for preparing coal or binder material, which is a method for preparing coal or binder material used alone or in combination with other coals as a raw material for coke production, before the coal or binder material enters a coking plant, preferably for a variety of the coal or binder material, while heating the coal or binder material contained in a container specified in JIS M 8801 under the coal fluidity measurement conditions in the Gieseler plastometer method specified in JIS M 8801 and rotating a stirrer, a variety of the coal or binder material satisfying at least one of the following conditions: the cohesiveness (a - b) / a represented by the height b of the semicoke formed on the inner side wall of the container in the container and the height a of the semicoke attached to the stirrer is 0.20 or more, and the height a is 30 mm or more, is judged to be poor as the raw material for coke production, and particle size adjustment is performed so that the content rate of particles with a particle size of 6 mm or more in the coal or binder material judged to be poor as the raw material for coke production is 30% by mass or less.

2. A method for preparing coal or binder material, which is a method for preparing coal or binder material used alone or in combination with other coals as a raw material for coke production, before the coal or binder material enters a coking plant, preferably for a variety of the coal or binder material, while heating the coal or binder material contained in a container specified in JIS M 8801 under the coal fluidity measurement conditions in the Gieseler plastometer method specified in JIS M 8801 and rotating a stirrer, a variety of the coal or binder material satisfying at least one of the following conditions: the cohesiveness (a - b) / a represented by the height b of the semicoke formed on the inner side wall of the container in the container and the height a of the semicoke attached to the stirrer is 0.20 or more, and the height a is 30 mm or more, is judged to be poor as the raw material for coke production, and particle size adjustment is performed so that the content rate of particles with a particle size of 6 mm or more in the coal or binder material judged to be poor as the raw material for coke production satisfies the following formula (1), Content rate of particles with a particle size of 6 mm or more ≤ 30 + 0.5 × (HGI - 60) ··· (1) In the formula (1), HGI is the Hardgrove grindability index of the coal or binder material, and the unit of the content rate is % by mass.

3. The method for preparing coal or binder material according to claim 1 or 2, wherein, before charging into a coke oven, particle size adjustment is performed so that the content rate of particles with a particle size of 6 mm or more in the coal or binder material judged to be poor as the raw material for coke production is 5% by mass or less.

4. The method for preparing coal or binder material according to any one of claims 1 to 3, wherein, particle size adjustment is performed on the coal or binder material before shipping from the place where the coal is produced or the place where the binder material is manufactured.

5. A method for manufacturing coke, which manufactures coke by carbonizing the coal prepared by the method for preparing coal or binder material according to any one of claims 1 to 4.

6. A method for manufacturing coke, which comprises carbonizing coal and a binder prepared by the method for preparing coal or a binder according to any one of claims 1 to 4 to produce coke.

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