Coke manufacturing method

Abstract

To provide a method for estimating coke strength that can estimate coke strength even when non-coking coal is included in molded coal.SOLUTION: A method for estimating coke strength estimates the coke strength of coke manufactured by carbonizing a coal blend containing molded coal in which non-coking coal is blended and powdered coal. The method estimates the coke strength of coke manufactured by carbonizing a coal blend in which the molded coal is partially pulverized, using the coke strength of coke produced by carbonizing a coal blend containing unpulverized molded coal and powdered coal, the blending ratio of molded coal in the coal blend, the strength of the molded coal, the blending ratio of non-coking coal in the molded coal, and the softening / melting characteristics of a mixture obtained by adding one or more compounds selected from primary and secondary amine compounds having an aromatic ring to the non-coking coal.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a method for estimating the coke strength of coke produced by carbonizing a coal blend containing powdered coal and molded coal blended with non- or slightly caking coal having low caking properties, and a method for producing coke. [Background technology]

[0002] Coke charged into a blast furnace is required to have high strength. Therefore, it is preferable to use coal with high caking properties that can produce high-strength coke as coke raw material. However, only coal with high caking properties is not mined; coal with low caking properties is also mined. Therefore, it is common to blend multiple types (brands) of coal with different properties to produce a coal blend, and use this blend as coke raw material. The caking property of coal is the property by which coal melts and solidifies during carbonization, and is an essential property for producing coke. Since caking property is determined by the properties of coal when it thermoplastically melts, it is effective to use values ​​(measured or estimated values) related to the thermoplastic properties of coal as an indicator when evaluating whether a certain brand of coal is suitable as coke raw material.

[0003] In addition, coal with high caking properties is often expensive, while coal with low caking properties is often cheap. For this reason, it is effective to actively use low-caking, so-called non- or slightly caking, coal as coke raw materials in order to reduce raw material costs.

[0004] Briquetting is a technique for effectively utilizing non- or slightly caking coal as a coke raw material. In coke production, the raw coal is pulverized so that the ratio of powder particles of 3 mm or less is, for example, 70 to 100% by mass, and the resulting powder is carbonized in a coke oven to produce coke. In the briquetting method, the powdered coal charged into the coke oven is partially briquetted to form briquettes, and the briquettes and the briquettes are mixed together to produce a blended coal, which is carbonized in a coke oven to produce coke.

[0005] Because molded coal is more compact than pulverized coal, the coal particles that make up the molded coal are closer together. This means that even coal with low caking properties can easily fuse and adhere to each other when heated, improving coke strength. Therefore, by using the molded coal blending method, coke strength can be maintained even if the amount of non- or slightly caking coal with poor caking properties is increased.

[0006] When carbonizing a coal blend in which briquettes are mixed with powdered coal, the blend of coal in the briquettes and powdered coal is often the same, and binders are added to the briquettes before molding. However, the blend of coal in the briquettes and powdered coal may be different.

[0007] It is empirically known that the coke strength of the coke produced varies depending on the brand of non- or slightly caking coal. One of the reasons for this is the low accuracy of evaluation of low-caking coal.

[0008] The Gieseler plastometer, specified in JIS M 8801:2008, is widely used to evaluate the caking properties of coal. In this method, coal is placed in a container with a stirrer and heated while a constant torque is applied to the stirrer. The thermoplasticity and melting properties of the coal are evaluated based on the maximum rotational speed of the stirrer (expressed as maximum fluidity (ddpm)). However, if the maximum fluidity of a non- or slightly caking coal is low, the superiority or inferiority of the non- or slightly caking coal cannot be evaluated with sufficient accuracy. This is partly because, although the measurable range of Gieseler maximum fluidity (MF) is 0 to approximately 50,000 ddpm, the evaluation is performed using a semi-logarithmic graph of the temperature versus the common logarithm of Gieseler maximum fluidity (logMF). Therefore, when the MF of coal, generally considered to be non- or slightly caking, is around 100 ddpm or less, it is difficult to evaluate the superiority or inferiority of the non- or slightly caking coal with sufficient accuracy. Furthermore, there are many non- or slightly caking coals with MF=0 (coals with MF=0 are sometimes called "non-caking coals"), and when these non-caking coals are used as coke raw materials, it becomes difficult to evaluate the differences in their caking properties.

[0009] Patent Document 1 discloses a method for evaluating the caking properties of such low-caking, non- or slightly caking coals by adding a primary or secondary amine compound with an aromatic ring to the coal and measuring its Gieseler fluidity. Adding a primary or secondary amine compound with an aromatic ring to the coal improves its fluidity, and even for non- or slightly caking coals with a Gieseler maximum fluidity (MF) of 0 ddpm measured with the coal alone, the Gieseler maximum fluidity (MF) measured with the amine added differs. Furthermore, Patent Document 1 discloses that the coke strength obtained by adding non- or slightly caking coal to powdered coal shows a good correlation with the Gieseler maximum fluidity (MF) measured with the addition of a primary or secondary amine compound with an aromatic ring. In other words, Patent Document 1 claims that the fluidity measured with the addition of this amine can be used as an indicator for evaluating the superiority of non- or slightly caking coals as coke feedstocks. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] International Publication No. 2016 / 136191 Summary of the Invention [Problem to be solved by the invention]

[0011] However, when non- or slightly caking coal is blended with molded coal and coke is produced using the molded coal, there is a problem that coke with the target coke strength cannot be produced even when coal evaluated as usable using the method of Patent Document 1 is used. The present invention has been made in consideration of this problem, and its object is to provide a coke strength estimation method that can estimate coke strength even when non- or slightly caking coal is blended with molded coal. Another object of the present invention is to provide a coke production method that uses the coke strength estimation method. [Means for solving the problem]

[0012] The means for solving the above problems are as follows. [1] A method for estimating coke strength of a coke produced by carbonizing a coal blend containing powdered coal and molded coal blended with non- or slightly caking coal, the method comprising: estimating the coke strength of a coke produced by carbonizing a coal blend containing powdered coal and molded coal blended with non- or slightly caking coal, the coke strength of the coke produced by carbonizing a coal blend containing the molded coal in an unpowdered state and the powdered coal, the blending ratio of the molded coal blended in the coal blend, the strength of the molded coal, the blending ratio of the non- or slightly caking coal blended in the molded coal, and the thermoplasticity and melting properties of a mixture of the non- or slightly caking coal and one or more selected from a primary amine compound and a secondary amine compound having an aromatic ring. [2] A coke manufacturing method for producing coke by carbonizing a coal blend containing powdered coal and molded coal blended with non- or slightly caking coal, the method comprising: adjusting one or more of the following to prepare molded coal and / or a coal blend: the coke strength of the coke produced by carbonizing a coal blend containing the unpowdered molded coal and the powdered coal; the blending ratio of the molded coal to be blended in the coal blend; the strength of the molded coal; the blending ratio of the non- or slightly caking coal to be blended in the molded coal; and the thermoplasticity and melting properties of a mixture of the non- or slightly caking coal and one or more selected from a primary amine compound and a secondary amine compound having an aromatic ring; and carbonizing the prepared coal blend to produce coke, so that the coke strength estimated by the coke strength estimation method described in [1] is equal to or greater than a predetermined coke strength. [3] A method for producing coke by carbonizing a coal blend containing molded coal blended with non- or slightly caking coal and powdered coal, comprising: adding 1 part by mass of N,N'-di-2-naphthyl-p-phenylenediamine to 10 parts by mass of the non- or slightly caking coal, measuring the Gieseler maximum fluidity (MF); preparing a coal blend so that the blending ratio of non- or slightly caking coal in the molded coal having a common logarithm of the measured Gieseler maximum fluidity (MF) of 3.0 or less is higher than the blending ratio of non- or slightly caking coal in the powdered coal having a common logarithm of the measured Gieseler maximum fluidity (MF) of 3.0 or less; and carbonizing the prepared coal blend to produce coke. [Effects of the Invention]

[0013] By using the method for estimating coke strength according to the present invention, it is possible to estimate with high accuracy the coke strength of coke produced using a coal blend containing non- or slightly caking coal, partially pulverized molded coal, and powdered coal. By producing coke using this method for estimating coke strength, it is possible to produce coke with a target coke strength. Furthermore, since it is possible to increase the amount of inexpensive non- or slightly caking coal with low caking properties used while still achieving the target coke strength, it is also possible to reduce the cost of coke production. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a graph showing the relationship between the log CATMF of non- or slightly caking coal contained in molded coal and the coke strength of coke produced using a coal blend in which the molded coal is blended with powder coal. [Figure 2] FIG. 2 is a graph showing the relationship between the logCATMF of the non- or slightly caking coal contained in the pulverized coal and the coke strength of the coke produced using the pulverized coal. [Figure 3] FIG. 3 is a graph showing the relationship between the powdering rate of briquettes and the strength of coke produced by blending the briquettes with powdered coal. [Figure 4] FIG. 4 is a graph showing the relationship between the log CATMF of non- or slightly caking coal blended in molded coal and the decrease in coke strength per 1 mass % of powdering rate. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will be described below through embodiments of the present invention. In the method for estimating coke strength according to the present embodiment, the coke strength of a coke produced by carbonizing a coal blend containing molded coal (including molded coal in a partially powdered state) blended with non- or slightly caking coal and powdered coal (hereinafter, sometimes referred to as "powdered coal") is estimated using the following five parameters: 1. Coke strength (DI base) of coke produced by carbonizing blended coal containing unpulverized briquettes and powdered coal 2. Blending ratio of molded coal to be blended into the coal blend (Wbq) 3. Strength of molded charcoal (Sbq) 4. Blending ratio of non- or slightly caking coal to be blended into molded coal (Wncc) 5. Thermoplasticity and Melting Properties of Mixtures of Non- or Slightly Caking Coal with Addition of Primary or Secondary Amine Compounds Having Aromatic Rings (CATP) First, the background to the idea of ​​the method for estimating coke strength according to this embodiment will be described.

[0016] The inventors confirmed the coke strength of coke produced using molded coal containing non- or slightly caking coal and the coke strength of coke produced using pulverized coal containing non- or slightly caking coal. As a result, they found that although the caking property of non- or slightly caking coal can be evaluated by measuring the Gieseler fluidity with the addition of an amine, the presence of non- or slightly caking coal in molded coal and the presence of non- or slightly caking coal in pulverized coal have different effects on the strength of the coke produced using the non- or slightly caking coal, and thus came up with the method for estimating coke strength according to the present embodiment.

[0017] The following describes a cokemaking test that confirmed the effect of non- or slightly caking coal on coke strength. The properties of the eight types of non- or slightly caking coal (T1 to T8) used in the cokemaking test are shown in Table 1 below.

[0018] [Table 1]

[0019] In Table 1 above, MF is the Gieseler maximum fluidity MF (ddpm) determined according to the method specified in JIS M 8801:2008. Ro is the average maximum vitrinite reflectance (%) of the coal determined according to the method specified in JIS M 8816:1992. TI is the total inert (volume %) calculated using the following equation (1), which is based on the amount of fine grain components of the coal determined according to the method specified in JIS M 8816:1992 and the Parr equation described in the accompanying commentary.

[0020] TI (volume %) = Fujinit (volume %) + Miklinite (volume %) + (2 / 3) × Semifuginite (volume %) + Minerals (volume %) (1)

[0021] The CATMF in Table 1 is the maximum fluidity (ddpm) measured in accordance with the method described in Patent Document 1, using a mixture prepared by adding 1 part by mass (0.5 g) of N,N'-di-2-naphthyl-p-phenylenediamine to 10 parts by mass (5 g) of coal, based on the measurement method specified in JIS M 8801:2008. In this embodiment, the maximum fluidity measured under these conditions is referred to as CATMF. For reference, the logCATMF, which is the common logarithm of CATMF, is also shown in the column to the right of CATMF. This CATMF is an example of the thermoplastic thermoplastic property (CATP) of a mixture prepared by adding a primary amine compound or a secondary amine compound having an aromatic ring to the non- or slightly caking coal described above.

[0022] The non- or slightly caking coals (T1 to T8) shown in Table 1 all have an MF of 0 ddpm, and are coals that do not exhibit fluidity according to the measurement method specified in JIS M 8801:2008. However, when a mixture of non- or slightly caking coal with N,N'-di-2-naphthyl-p-phenylenediamine was measured, even these non- or slightly caking coals exhibited fluidity, indicating that the fluidity CATMF when amine was added varies depending on the brand of non- or slightly caking coal. The CATMF values ​​in Table 1 indicate that, among the non- or slightly caking coals (T1 to T8), T7 and T1 are coals with high caking properties, while T4 and T5 are coals with low caking properties.

[0023] In the above test, N,N'-di-2-naphthyl-p-phenylenediamine was used as the amine for improving coal fluidity, but this is not limited to this. Other amines may be used as long as they are primary or secondary amine compounds having an aromatic ring and can be added to coal to improve the fluidity of the coal. Furthermore, the amine is not limited to one type, and multiple types may be used in combination. Specifically, phenothiazine, carbazole, N-phenyl-1-naphthylamine, etc. may be used. The fluidity of non- or slightly caking coal may also be evaluated by changing the addition ratio of the above amines.

[0024] Next, we will explain the coke strength of coke produced by producing molded coal blended with non- or slightly caking coal, and then carbonizing the molded coal blended with pulverized coal that does not contain non- or slightly caking coal. The blending composition of the molded coal used to produce the coke is shown in Table 2 below. All of the coal used in the molded coal was pulverized so that the total amount was 3 mm or less (under a sieve with 3 mm openings). In this embodiment, the blending ratio is expressed as mass % on a dry basis.

[0025] [Table 2]

[0026] B1 to B4 shown in Table 2 above are coals with caking properties, and TARP is a heavy pitch obtained from coal tar added as a caking agent. The properties of coals B1 to B4 are shown in Table 3 below.

[0027] [Table 3]

[0028] The logMF in Table 3 is the common logarithm of the maximum fluidity MF (log [ddpm]) measured using the measurement method specified in JIS M 8801:2008. Ro and TI are the same as in Table 1.

[0029] To the total mass of each coal blended in the ratios shown in Table 2, 0.5% by mass of soft tar pitch (SOP) and 6% by mass of coal tar were added as a binder, and the mixture was kneaded for 1.5 minutes while being heated and steam was blown in. Under this condition, the raw material temperature reached approximately 95°C, and the moisture content was 12-15% by mass. The mixture was then molded in a double-roll molding machine with a cup measuring 44 mm x 44 mm x 13 mm (one side) at a roll gap of 2 mm to produce MASEC-type molded coal. The density of the molded coal was 1120 kg / m 3 It was.

[0030] A coal blend was prepared by blending 20 parts by mass of the produced coal briquettes with 80 parts by mass of powder coal that had been crushed and adjusted for particle size. The powder coal was crushed to adjust its particle size so that the total amount was 3 mm or less (under a 3 mm mesh sieve). The blending composition of the powder coal blended into the coal briquettes is shown in Table 4 below, and the properties of coals C1 to C7 used as the powder coal are shown in Table 5 below.

[0031] [Table 4]

[0032] [Table 5]

[0033] Eight types of briquettes produced using eight types of non- or slightly caking coal (T1 to T8) were blended with the above powder coal to produce eight types of blended coals, which were then carbonized. The carbonization of the blended coals was carried out until the bulk density of the blended coals reached 844 kg / m 3 The bulk density was 1120 kg / m 3 20% by mass of briquettes and a bulk density of 775 kg / m 3 This is the weighted average bulk density of 80 mass% of fine coal.

[0034] A 10 kg weight was placed on the coal in the carbonization vessel, and the coal was carbonized for 6 hours in an electric furnace at a furnace temperature of 1050°C. The coal was then removed from the electric furnace and cooled under a nitrogen atmosphere to produce coke. For each coke, the mass of coke with a particle size of 15 mm or more was measured after 150 rotations at a rotation speed of 15 rpm based on the rotation strength test method specified in JIS K 2151:2004. The ratio of this mass to the total mass of the coke used in the test was multiplied by 100 to determine the drum strength index DI (150 / 15). In this embodiment, this drum strength index DI (150 / 15) was used as the coke strength.

[0035] The coke strength of the coke produced by carbonizing the briquettes, which were prepared by blending the non- or slightly caking coals (T1 to T8) shown in Table 1 with coals in the blending ratios shown in Table 2, and the blended coals were blended with the powder coals shown in Table 4 in a ratio of briquettes mass:powder coal mass = 20:80, is shown in Table 6 below.

[0036] [Table 6]

[0037] Figure 1 is a graph showing the relationship between the logCATMF of non- or slightly caking coal contained in molded coal and the coke strength of coke produced using a coal blend in which the molded coal is blended with powder coal. The horizontal axis of Figure 1 is the logCATMF (log [ddpm]) of non- or slightly caking coal, and the vertical axis is the coke strength DI (150 / 15)(-). Note that (-) means that the graph is dimensionless. For convenience, data for MF = 0 ddpm are plotted at the position of logMF = 0.

[0038] As shown in Figure 1, coke strength was almost constant regardless of the CATMF of the non- or slightly caking coal. This result confirmed that, as long as non- or slightly caking coal is blended into molded coal, the caking properties of the non- or slightly caking coal do not affect the coke strength of the produced coke.

[0039] Next, we will explain the coke strength of coke produced by blending non- or slightly caking coal with powder coal and carbonizing the blended coal containing the powder coal. The blending composition of the powder coal is shown in Table 7 below.

[0040] [Table 7]

[0041] The properties of coals A1 to A5 used as powder coals other than the non- or slightly caking coals are shown in Table 8 below.

[0042] [Table 8]

[0043] Each coal was crushed to adjust the particle size so that the total amount was 3 mm or less (under a 3 mm sieve). Eight types of blended coals, each containing 20 mass% of non- or slightly caking coal (T1 to T8), were prepared, and the bulk density was 775 kg / m 3 The mixture was packed into a carbonization vessel so that the weight of the coal blend containing the molded coal was 100g, and the mixture was carbonized under the same conditions as those for the carbonization of the above-mentioned molded coal blend to produce coke. The coke strength of the produced coke is shown in Table 9 below.

[0044] [Table 9]

[0045] Figure 2 is a graph showing the relationship between the logCATMF of non- or slightly caking coal contained in pulverized coal and the coke strength of coke produced from that pulverized coal. The horizontal axis of Figure 2 is the logCATMF (log [ddpm]) of non- or slightly caking coal, and the vertical axis is the coke strength DI (150 / 15)(-). For convenience, data for MF = 0 ddpm is plotted at the position of logMF = 0.

[0046] As shown in Figure 2, when non- or slightly caking coal was blended with powdered coal, a correlation was observed between the CATMF of the non- or slightly caking binder and coke strength; the lower the CATMF of the non- or slightly caking binder, the lower the coke strength. Figures 1 and 2 show that the coke strength difference for cokes produced using molded coal containing non- or slightly caking coals (T1 to T8) was 0.1, whereas the coke strength difference for cokes produced using powdered coal containing the same non- or slightly caking coals (T1 to T8) increased to 12.4. The coke strength difference is the difference in strength between the coke with the highest strength and the coke with the lowest strength in the same graph.

[0047] When non- or slightly caking coal is added to the molded coal, the proportion of non- or slightly caking coal in the blend is 4% by mass (20% by mass of non- or slightly caking coal in the molded coal × 20% by mass of molded coal in the blend). Therefore, it is thought that the strength reduction effect of blending 20% ​​by mass of non- or slightly caking coal in powdered coal is about five times that of blending it in molded coal. Even taking this into consideration, the reduction in coke strength when non- or slightly caking coal is blended in molded coal is significantly smaller. These results confirm that when non- or slightly caking coal is blended in powdered coal, coke strength is significantly reduced for coals with low CATMF, whereas when the same non- or slightly caking coal is added to molded coal, there is almost no reduction in coke strength.

[0048] The difference in the effect on coke strength between using non- or slightly caking coal as molded coal and using powdered coal as is was first discovered by conducting coke production tests using non- or slightly caking coal with different CATMFs as molded coal and powdered coal as is. Patent Document 1 suggests that adding coal with a low CATMF to powdered coal may reduce coke strength. However, the fact that the CATMF of non- or slightly caking coal does not affect the coke strength of the coke produced when non- or slightly caking coal is used as molded coal was first discovered by this coke production test.

[0049] Next, we will explain the effect of briquette powder on coke strength. In coke production processes involving carbonization of a blend of briquette and powdered coal, using non- or slightly caking coal as powdered coal can potentially reduce coke strength. However, using non- or slightly caking coal as briquette does not reduce coke strength. This finding is important for practical operation. The reason is that in practical operation, briquette coal inevitably undergoes some degree of powdering during transportation and handling. Therefore, even if the briquette is the same, if the briquette is weak and prone to powdering, powdered non- or slightly caking coal will be released due to the briquette's powdering. If the released powdered coal has a low CATMF, coke will be produced using a coal blend containing non- or slightly caking powdered coal with a low CATMF, which could significantly reduce the coke strength of the resulting coke. It has been thought that powdering of molded coal has a negative effect on coke strength, and that higher molded coal strength is preferable. However, it was not known that the impact of powdering differs depending on the CATMF of the non- or slightly caking coal used.

[0050] In other words, the reason why it was difficult to estimate coke strength when using molded coal containing non- or slightly caking coal is thought to be because it was not correctly understood that the decrease in coke strength due to powdering of molded coal varies depending on the CATMF of non- or slightly caking coal. Therefore, the inventors confirmed the extent to which coke strength decreases due to powdering of molded coal containing non- or slightly caking coal.

[0051] First, we prepared molded coal containing non- or slightly caking coals with different CATMFs. Each molded coal was then impacted to pulverize it into crushed molded coals. The molded coals were produced using the following procedure. First, 20% by mass of one of the non- or slightly caking coals T1, T5, or T8 listed in Table 1 was blended with the other coals O17 to O20 and a caking agent pitch (TARP) in the blending ratios listed in Table 10 below. To this mixture, 0.5% by mass of soft pitch (SOP) and 6% by mass of tar (tar slag) containing solid fines recovered from a tar decanter were added, and the mixture was mixed for 1.5 minutes while heating and injecting steam. The mixture was molded using a double-roll molding machine with a 44mm x 44mm x 13mm (one side) cup at a roll gap of 2mm to produce MASEC-type molded coals. The blending composition of the briquettes is shown in Table 10 below, and the properties of the coals O17 to O20 used to produce the briquettes are shown in Table 11 below.

[0052] [Table 10]

[0053] [Table 11]

[0054] Each of the three types of briquettes produced was pulverized by impact. The briquettes were placed in a cylindrical drum and impacted by rotating the drum. By varying the rotation time of the drum, two types of briquettes with different pulverization rates were prepared for each briquette. 13% by mass of the briquettes thus prepared (a mixture of the briquettes that remained unpulverized and the powder generated by pulverization) was mixed with 87% by mass of separately prepared powdered coal, and carbonized to confirm the effect of briquette powdering on coke strength. The carbonization conditions were the same as those in the coke production test described above, but the bulk density of the combined powder generated by briquette powdering and the powdered coal was 775 kg / m 3The mixture of powder coals C21 to C27 blended into the molded coal (or powdered molded coal) is shown in Table 12 below. The properties of the coals C21 to C27 used as the powdered coal are shown in Table 13 below.

[0055] [Table 12]

[0056] [Table 13]

[0057] Table 14 shows the strength of the coke produced from each of the three types of molded coal, including non- or slightly caking coal T1, T5, or T8, when it was not pulverized and when the pulverization rate was changed to two levels.

[0058] [Table 14]

[0059] The powdering rate (mass%) of the briquette coal is a value calculated by the following formula (2). A powdering rate of 0.0 mass% indicates a test level where the coal was carbonized without being powdered.

[0060] Pulverization rate = (mass of generated powder) × 100 / (mass of molded coal charged into the test machine) (2)

[0061] Fig. 3 is a graph showing the relationship between the powdering rate of briquettes and the strength of coke produced by blending the briquettes with powdered coal. The horizontal axis of Fig. 3 represents the powdering rate (mass%) of the briquettes, and the vertical axis represents the coke strength DI (150 / 15)(-).

[0062] As shown in Figure 3, for all three types of non- or slightly caking coal, coke strength decreased as the powdering rate of the briquettes increased, but the amount of decrease in coke strength varied depending on the type of non- or slightly caking coal. The decrease in coke strength per 1% by mass of powdering rate for each brand of non- or slightly caking coal was calculated from the slope of the regression line and is shown in Table 15 below. Table 15 also shows the logCATMF measurement results for the non- or slightly caking coals shown in Table 1.

[0063] [Table 15]

[0064] Fig. 4 is a graph showing the relationship between the logCATMF of non- or slightly caking coal blended in the molded coal and the decrease in coke strength per 1% by mass of powdering rate. The horizontal axis of Fig. 4 is logCATMF (log[ddpm]), and the vertical axis is the decrease in coke strength (-).

[0065] As shown in Figure 4, for non- or slightly caking coals T1 and T8, whose logCATMF exceeds 3.0, coke strength hardly decreased even when the briquettes were broken down. On the other hand, for non- or slightly caking coal T5, whose logCATMF is 3.0 or less, coke strength decreased when the briquettes were broken down. These results suggest that non- or slightly caking coals with logCATMF exceeding 3.0 are non- or slightly caking coals that do not experience a decrease in coke strength even when the briquettes are broken down. Based on the results in Figure 2, a linear correlation is observed between coke strength and the logCATMF of non- or slightly caking coals. Therefore, a linear correlation is also observed between the decrease in coke strength and logCATMF shown in Figure 4. In other words, non- or slightly caking coals with logCATMF below 3.0 are non- or slightly caking coals that experience a decrease in coke strength when the briquettes are broken down.

[0066] The degree of powdering of molded coal varies depending on the strength of the molded coal, but it is difficult to completely prevent powdering of the produced molded coal. Therefore, when blending non- or slightly caking coal with a logCATMF of 3.0 or less into molded coal, it is preferable to increase the strength of the molded coal to suppress powdering. To increase the strength of molded coal, for example, the amount of binder added to the molded coal may be increased, or a binder with higher adhesive strength may be used.

[0067] Non- or slightly caking coal suitable for use in the coke strength estimation method according to this embodiment is coal with a Gieseler fluidity of 0 ddpm, which means that fluidity is not observed using conventional measurement methods. Some coals with a log CATMF of 3.0 or less have a Gieseler maximum fluidity (MF) specified in JIS M 8801:2008 of more than 0 ddpm. Furthermore, as shown in Figure 4, it is estimated that coal with a log CATMF of more than 4.0 experiences almost no reduction in coke strength due to powdering of the briquettes. Therefore, non- or slightly caking coal suitable for use in the coke strength estimation method according to this embodiment can be defined as coal with a log CATMF of 4.0 or less. A simpler definition, taking advantage of the correlation between CATMF and Gieseler fluidity, may define non- or slightly caking coal as coal with a Gieseler maximum fluidity (MF) specified in JIS M 8801:2008 of 20 ddpm or less.

[0068] By utilizing the above-mentioned findings revealed by the inventors, it is possible to estimate with higher accuracy than conventional methods the coke strength of coke produced by carbonizing a blended coal containing molded coal and powdered coal, to which non- or slightly caking coal has been added and which has been partially pulverized by impacts such as logistics.

[0069] In the method for estimating coke strength according to this embodiment, first, the coke strength DIbase is calculated assuming no breakage of the briquettes. Coke strength also depends on the properties of coal other than the non-slightly caking coal in the briquettes and the properties of the powdered coal mixed with the briquettes. Therefore, the coke strength DIbase is calculated assuming no breakage of the briquettes, and the coke strength is estimated by subtracting the strength reduction due to breakage from this coke strength.

[0070] The coke strength DIbase assuming no briquette disintegration can be determined, for example, by a coke production test. Specifically, a blend of briquette and powdered coal expected to be used in a commercial coke oven is determined, and briquette is experimentally produced using this blend. The coke strength of the coke produced in the commercial coke oven is measured to determine the coke strength assuming no briquette disintegration. Producing coke in a commercial coke oven allows coke to be produced without briquette disintegration during handling. The coke strength in the commercial oven can be estimated by considering the correlation between the coke strength produced in the commercial coke oven and the coke strength produced in the commercial coke oven. It is preferable to confirm the correlation between the coke strength in the commercial coke oven and that in the commercial coke oven in advance through a test using briquette that does not contain non- or slightly caking coal, which would cause a decrease in coke strength. Alternatively, a coke strength estimation formula obtained by a known method can be used without conducting a carbonization test.

[0071] An example of a method for estimating the decrease in coke strength due to briquette breakage is shown below. The decrease in coke strength occurs when powdered non- or slightly caking coal is released into the pulverized coal due to briquette breakage. Therefore, it is first necessary to estimate the amount of released non- or slightly caking coal.

[0072] The amount of non- or slightly caking coal released by the powdering of briquettes (its proportion in the blended coal) can be calculated by multiplying the blending ratio of briquettes by the powdering ratio of briquettes and the blending ratio of non- or slightly caking coal in the briquettes. The powdering ratio of briquettes is determined by the strength of the briquettes and the impact force applied to the briquettes. Here, if the rate of powder generation due to impacts received from the briquettes during the period from their production to their charging into the coke oven is used as an index of strength, the powdering ratio and strength have the same meaning. In other words, the strength of the briquettes in this case can be expressed as the rate of powder generation due to impacts received from the briquettes during their production to their charging into the coke oven (the powdering ratio). This strength (the powdering ratio) can be determined, for example, by estimating the impacts received from the briquettes during their production to their charging into the coke oven, for example, by a cumulative drop height, and then measuring the amount of powder generated when the briquettes are subjected to the impacts. Furthermore, the powdering ratio may be estimated based on the correlation between other strength indices and the powdering ratio.

[0073] As mentioned above, coke strength decreases when non- or slightly caking coal fines generated by the break down of briquettes are mixed into the powdered coal. The decrease in coke strength due to an increase in the blending ratio of non- or slightly caking coal in powdered coal depends on the logCATMF of the non- or slightly caking coal, as shown in Figure 2. It also depends on the break down rate of the briquettes (the amount of fines generated), as shown in Figure 3.

[0074] From the slope of the graph in Figure 2, it can be seen that when the blending ratio of non- or slightly caking coal is 20 mass%, a decrease in logCATMF of 1 results in a decrease in coke strength of 3.07. Therefore, the decrease in coke strength per 1 mass% blending ratio of non- or slightly caking coal in pulverized coal is calculated by dividing 3.07 by 20, which is 0.1535.

[0075] In the example shown in Figure 4, it is estimated that the strength reduction is almost zero when logCATMF is 4.0 or more. Therefore, the reduction in coke strength per 1 mass% of non- or slightly caking coal in pulverized coal due to a reduction in logCATMF of 1 can be calculated as (4.0 - logCATMF) x 0.1535. Therefore, if the method for estimating coke strength based on the example shown in Figure 4 is expressed in the form of an equation, it can be seen that coke strength can be estimated using the following equation (3).

[0076] DI(150 / 15)=DIbase-K×(a-logCATMF)×R...(3)

[0077] In the above equation (3), a is the minimum logCATMF threshold at which coke strength does not decrease even when briquettes containing non- or slightly caking coal are pulverized. In the example shown in Figure 4, a is 4.0. logCATMF is the common logarithm of the CATMF measurement value of non- or slightly caking coal and is an example of the thermoplastic thermoplastic property (CATP) of a mixture of non- or slightly caking coal and a primary or secondary amine compound having an aromatic ring. K is a constant that represents the decrease in coke strength per unit of logCATMF and per unit of non- or slightly caking coal content in the briquettes. In the example shown in Figure 4, K is 0.1535.

[0078] R is the increase in the non- or slightly caking coal content in the powdered coal due to powdering of the briquettes. The increase in the non- or slightly caking coal content in the powdered coal due to powdering of the briquettes, R, can be calculated as follows: The proportion of powder generated in the total coal blend is calculated from the blending ratio of the briquettes, Wbq, the blending ratio of the non- or slightly caking coal in the briquettes, Wncc, and the powdering rate when the briquettes are subjected to an impact equivalent to the impact they receive before being charged into the coke oven. If the powdering rate when the briquettes are subjected to the impact they receive before being charged into the coke oven is defined as the strength of the briquettes, Sbq, and the proportion of powder generated in the total coal blend, Wp, then Wp = Wbq × Wncc × Sbq.

[0079] Due to this generated fines, the ratio of fine coal in the coal blend increases by Wp from the fine coal ratio before pulverization (1-Wbq), so the increase ratio R of non-slightly caking coal fines in the fine coal is R=Wp / (1-Wbq+Wp).

[0080] Therefore, if the constants a and K are determined in advance by experiments or the like, DIbase is determined by carbonization tests or the like, the thermoplasticity and melting characteristic CATP of non- or slightly caking coal (logCATMF in the above example) is measured, and R is calculated from Wbq, Wncc, and Sbq, then coke strength can be estimated using the above equation (3) taking into account the powdering of the molded coal.

[0081] As described above, the coke strength estimation method according to this embodiment is a method for estimating the coke strength of a coke produced by carbonizing a coal blend containing powdered coal and molded coal blended with non- or slightly caking coal, using the following five parameters: 1. Coke strength (DI base) of coke produced by carbonizing blended coal containing unpulverized briquettes and powdered coal 2. Blending ratio of molded coal to be blended into the coal blend (Wbq) 3. Strength of molded charcoal (Sbq) 4. Blending ratio of non- or slightly caking coal to be blended into molded coal (Wncc) 5. Thermoplasticity and melting properties (CATP) of mixtures of non- or slightly caking coal with one or more primary amine compounds and secondary amine compounds having aromatic rings added

[0082] By estimating coke strength using the above five parameters, it is possible to estimate coke strength while taking into account the decrease in coke strength due to the powdering of some of the briquettes contained in the coal blend. This makes it possible to estimate the coke strength of coke produced from a coal blend containing briquettes containing non- or slightly caking coal and powdered coal with higher accuracy than conventional methods.

[0083] Next, we will explain an embodiment of a coke manufacturing method in which coke strength is estimated based on the softening and melting characteristics of the non-slightly caking coal to be blended into the molded coal, and the blending ratio of the non-slightly caking coal to be blended into the molded coal is determined based on the estimated coke strength.

[0084] In the coke manufacturing method according to this embodiment, coal having a Gieseler maximum fluidity (MF) of 20 ddpm or less as specified in JIS M 8801: 2008 was selected as the non- or slightly caking coal to be blended into the molded coal. First, the Gieseler maximum fluidity (CATMF) of the selected non- or slightly caking coal was measured by adding 1 part by mass of N,N'-di-2-naphthyl-p-phenylenediamine to 10 parts by mass of the non- or slightly caking coal.

[0085] Next, the type and blending ratio of coal other than non- or slightly caking coal to be used in the briquettes, as well as the type and blending ratio of coal in the powder coal to be blended in the briquettes, are determined, and briquettes containing non- or slightly caking coal at the determined blending ratio (Wncc) are produced. The briquettes produced are blended with the powder coal at a predetermined blending ratio (Wbq) without being pulverized, and the coke strength (DIbase) of the coke produced is determined by a carbonization test or the like.

[0086] Furthermore, if the strength (Sbq) of the produced molded coal is calculated as the rate of powdering due to impact forces during the process from the production of the molded coal to its charging into the coke oven, the coke strength of the coke produced under those conditions can be estimated using the above formula (3). Then, the above five parameters are adjusted so that the estimated coke strength is equal to or greater than the target coke strength. For example, if the estimated coke strength is lower than the target coke strength, the molded coal strength (Sbq) can be increased by, for example, increasing the amount of binder in the molded coal. This can improve the coke strength of the produced coke. The target coke strength is an example of a predetermined coke strength.

[0087] In addition, the blending ratio of non- or slightly caking coal in the molded coal may be adjusted to adjust the coke strength of the produced coke. If the estimated coke strength is higher than the target coke strength, the blending ratio of inexpensive non- or slightly caking coal can be increased to reduce the cost of coke production while maintaining the target coke strength. If the estimated coke strength is lower than the target coke strength, the blending ratio of non- or slightly caking coal may be decreased.

[0088] Changing the blending ratio of selected non- or slightly caking coal in the briquettes may change the coke strength (DI base) produced by carbonizing a coal blend containing unpulverized briquettes and pulverized coal. In this case, by conducting a cokemaking test using a coal blend with a different blending ratio of non- or slightly caking coal and understanding the correlation between the coke strength (DI base) and the blending ratio (Wncc) of non- or slightly caking coal in the briquettes in advance, it becomes possible to estimate the coke strength while taking into account changes in coke strength (DI base). This allows the use of inferior non- or slightly caking coal with low caking properties to be maximized while achieving the target coke strength, contributing to cost reductions and the effective use of coal resources.

[0089] In addition, it is preferable to prepare a coal blend so that the blending ratio of non- or slightly caking coal having a logCATMF of 3.0 or less in the molded coal is higher than the blending ratio of non- or slightly caking coal having a logCATMF of 3.0 or less in the powdered coal, and to produce coke by carbonizing the prepared coal blend. The logCATMF of non- or slightly caking coal is the common logarithm of the Gieseler maximum fluidity MF specified in JIS M 8801:2008, measured by adding 1 part by mass of N,N'-di-2-naphthyl-p-phenylenediamine to 10 parts by mass of non- or slightly caking coal.

[0090] As shown in Figures 1 and 4, non- or slightly caking coal with a log CATMF of 3.0 or less does not reduce coke strength when it is included in molded coal, but does reduce coke strength when it is included in powdered coal. For this reason, it is preferable to blend as much non- or slightly caking coal with a log CATMF of 3.0 or less as possible into molded coal, and it is preferable to increase the blending ratio of this non- or slightly caking coal in the molded coal compared to the blending ratio in the powdered coal. This makes it possible to produce coke with higher strength.

[0091] In the above explanation, the influence of the properties of non- or slightly caking coal and the powdering of molded coal on the strength reduction was estimated based on a linear relationship from experimental results, but a non-linear correlation may also be used. Furthermore, if necessary, some variables may be approximated, variables with little influence may be omitted, or the form of the equation may be modified.

Claims

[Claim 1] A coke manufacturing method for manufacturing coke by carbonizing a coal blend containing molded coal blended with non- or slightly caking coal and powdered coal, 1 part by mass of N,N′-di-2-naphthyl-p-phenylenediamine was added to 10 parts by mass of the non- or slightly caking coal, and the Gieseler maximum fluidity MF was measured. A method for producing coke, comprising: preparing a coal blend so that the blending ratio of non- or slightly caking coal in molded coal, the common logarithm of which measured Gieseler maximum fluidity factor (MF) is 3.0 or less, is higher than the blending ratio of non- or slightly caking coal in powdered coal, the common logarithm of which measured Gieseler maximum fluidity factor (MF) is 3.0 or less; and carbonizing the prepared coal blend to produce coke.

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