Method for Evaluating Spontaneous Combustibility of Coal

Abstract

To evaluate spontaneous heat buildup property of stored coals without pulverizing the stored coals.SOLUTION: Of stored coals, heat buildup rate (V_par) of coal having particle size equal to or below a predetermined particle size (Dth) is measured. According to the heat buildup rate (V_par) and a correction coefficient (k), heat buildup rate (V_all) for evaluating a spontaneous heat buildup property of the entire coal is obtained. The correction coefficient (k) is a ratio of the relative heat buildup rate (Vr_all) of a coal belonging to all particle size scales with respect to a relative heat buildup rate (Vr_par) of a coal belonging to the particle size scale equal to or below the predetermined particle size (Dth). The relative heat buildup rate (Vr_par) is value weighting and averaging relative heat buildup rate (Vrn) of each particle size scale equal to or below the predetermined particle size (Dth) by a mass ratio (Wn_par) of a coal of each particle size scale equal to or below the predetermined particle size (Dth). The relative heat buildup rate (Vr_all) is a weighted average value with a mass ratio (Wn_all) of a coal particle size scale of a relative heat buildup rate (Vrn) of each particle size scale of the all particle size scales.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a method for evaluating the spontaneous heating property of coal in a stored state.

Background Art

[0002] Patent Document 1 describes a method for evaluating the spontaneous heating property of coal in a short time using a small amount of coal sample. This evaluation method will be specifically described below.

[0003] A coal pulverized sample of 20 to 80 g is accommodated in an inner container, and this inner container is accommodated in a heating tank. By supplying oxygen gas into the heating tank, the coal pulverized sample in the heating tank is caused to spontaneously heat. The temperature of the coal pulverized sample is measured, and the temperature inside the heating tank is raised so as to follow the temperature rise of the coal pulverized sample accompanying the spontaneous heating. The time until the temperature of the coal pulverized sample rises from a predetermined initial temperature to a predetermined final temperature is measured, and the spontaneous heating property of the coal is evaluated based on this measured time. Here, it can be evaluated that the longer the measurement time, the less likely the coal is to undergo spontaneous heating.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In Patent Document 1, in order to prepare a coal pulverized sample, coal is pulverized to adjust coal having a particle size below a predetermined value. Here, the spontaneous heating property when using pulverized coal is more likely to be evaluated higher than the spontaneous heating property when using non-pulverized coal. This is because in pulverized coal, since the pulverized surface is exposed to the outside air, it becomes easier to spontaneously heat than non-pulverized coal.

[0006] Since the coal to be evaluated for spontaneous combustion is the coal stored in a yard or the like, if the spontaneous combustion property is evaluated using pulverized coal, the spontaneous combustion property will be overestimated compared to the stored coal. Therefore, in evaluating the spontaneous combustion property, it is preferable to evaluate the spontaneous combustion property of the coal in the stored state. On the other hand, if the coal is not pulverized, it is often difficult to measure for evaluating the spontaneous combustion property, and there is also a situation where the spontaneous combustion property of all coals cannot be measured.

[0007] Table 1 below shows the results of evaluating the spontaneous combustion property by the method of the following examples after dividing each of three types of coals A to C with different brands into coal with a particle size of 3 mm or less after pulverizing the coal and non-pulverized coal in the section with a particle size of 3 mm or less. Here, the heating rate [°C / day] is used as the evaluation value of the spontaneous combustion property.

[0008]

Table 1

[0009] According to Table 1 above, it can be seen that for any of coals A to C, the heating rate increases by pulverizing the coal compared to the non-pulverized coal. Therefore, as described above, if the spontaneous combustion property is evaluated using pulverized coal, the spontaneous combustion property will be overestimated compared to the stored coal (non-pulverized).

[0010] Also, for the pulverized coal, the heating rate increases in the order of coal A, coal B, and coal C, but for the non-pulverized coal, the heating rates of coal A and coal C are the same, and the heating rate of coal B is the highest. Thus, since the relationship of the heating rate is different between the pulverized coal and the non-pulverized coal, it becomes difficult to determine the superiority or inferiority of the spontaneous combustion property for a plurality of types of stored coals even if the spontaneous combustion property of the pulverized coal is evaluated.

Means for Solving the Problem

[0011] The present invention is a method for evaluating the spontaneous heating property of coal, which includes a step of performing a heat generation test for measuring the heat generation rate on coal having a particle size equal to or less than a predetermined particle size among the stored coal, and a step of obtaining a heat generation rate for evaluating the spontaneous heating property of the entire stored coal based on the heat generation rate measured in the heat generation test and a correction coefficient obtained in advance. The correction coefficient is the ratio of the relative heat generation rate of the coal belonging to all particle size classifications to the relative heat generation rate of the coal belonging to the particle size classification having a particle size equal to or less than the predetermined particle size when the stored coal is divided into a plurality of particle size classifications.

[0012] The relative heat generation rate of the coal belonging to the particle size classification having a particle size equal to or less than the predetermined particle size is a value obtained by weighted-averaging the relative heat generation rates of each particle size classification having a particle size equal to or less than the predetermined particle size with the ratio of the mass of the coal of each particle size classification to the total mass of the coal having a particle size equal to or less than the predetermined particle size. The relative heat generation rate of the coal belonging to all particle size classifications is a value obtained by weighted-averaging the relative heat generation rates of each particle size classification of all particle size classifications with the ratio of the mass of the coal of each particle size classification to the total mass of the coal of all particle size classifications.

[0013] The predetermined particle size can be a particle size at which the heat generation rate can be measured in the heat generation test.

[0014] The above-described correction coefficient can be obtained as follows. First, the stored coal is classified into a plurality of particle size classifications, and the heat generation rate is measured for the coal belonging to each particle size classification by a heat generation test. Then, based on the measured heat generation rate, the relative heat generation rate of each particle size classification with respect to a predetermined heat generation rate is obtained, and the correction coefficient can be obtained based on the relative heat generation rate of each particle size classification and the mass ratio.

[0015] The coal used for obtaining the correction coefficient can be of the same brand as the coal for which the heat generation rate for evaluating the spontaneous heating property is obtained.

Advantages of the Invention

[0016] According to the present invention, for the stored coal, without pulverizing the coal, the heat generation rate for evaluating the spontaneous heating property can be appropriately grasped.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0018] In this embodiment, coal in a stored state is taken as the object of evaluation for natural exothermicity. Among this coal, the exothermic rate is measured for coal with a particle size below a predetermined value, and based on this exothermic rate and the correction coefficient k described later, the exothermic rate of the coal in the stored state (in other words, coal including all particle sizes) is obtained. Based on this exothermic rate, the natural exothermicity of the coal in the stored state can be evaluated. The following is a specific explanation.

[0019] The coal to be evaluated for natural exothermicity may be coal in a stored state, and the type of coal is not particularly limited. Here, when the coal stored in a yard or the like is coal that is likely to undergo natural exothermicity, management regarding natural exothermicity is necessary, so such coal can be taken as the object of evaluation for natural exothermicity. For example, coal with an oxygen content of 8 [mass%, dry basis] or more can be taken as the object of evaluation for natural exothermicity. Also, even for coal of the same brand, for coal with different lots, it is preferable to evaluate the natural exothermicity for each coal.

[0020] (Correction coefficient k) The above-mentioned correction coefficient k is obtained in advance. Hereinafter, the method for obtaining the correction coefficient k will be described using the flowchart shown in FIG. 1.

[0021] In step S101, the stored coal is divided into a plurality of particle size categories. Here, the stored coal is used without being pulverized. Since the stored coal contains coals having various particle sizes, a plurality of particle size categories are set, and the coals belonging to each particle size category are sorted. For example, the coals belonging to each particle size category can be sorted by sieving. The total number of particle size categories and the range of particle sizes defining each particle size category can be determined as appropriate. After dividing the coal into a plurality of particle size categories, the mass of the coal belonging to each particle size category is measured, and for each particle size category, the ratio (mass percentage) [mass%] of the mass of the coal belonging to each particle size category to the total mass of the coal belonging to all particle size categories is obtained.

[0022] In step S102, for the coal belonging to each particle size category, the heat generation rate Vn [°C / day] is measured. The subscript n (n is a natural number) of the heat generation rate Vn means each particle size category. According to the examples described later, the larger the particle size of the coal, the smaller the heat generation rate Vn. The heat generation rate Vn can be measured, for example, by the heat generation property test described below.

[0023] FIG. 2 shows a schematic configuration of the measuring device used in the heat generation property test. The heat generation property test is to measure the temperature rise rate (heat generation rate V) by setting the internal temperature of the thermostatic and humidistatic chamber 1 so as to follow the temperature rise of the coal sample due to low-temperature oxidation heat generation in an air atmosphere, with the coal sample stored in the thermostatic and humidistatic chamber 1.

[0024] Inside a thermostatic and humidistatic chamber 1 having a predetermined internal volume (e.g., 225 [L]), a pale can 2, which is a cylindrical steel container (e.g., outer diameter 300 [mm], height 220 [mm]), is installed. The pale can 2 is filled with a coal sample. Here, an insulating material may be spread at the bottom of the pale can 2, and a coal sample layer having a predetermined height (e.g., about 100 [mm]) may be formed by filling the coal sample on the insulating material. As the insulating material, for example, a ceramic fiber board or the like can be used. As the container filled with the coal sample, instead of the pale can 2, a heat-insulating container (e.g., a vacuum heat-insulating container) can be used. By using a heat-insulating container, it is possible to suppress the heat transfer through the container from having an adverse effect on the exothermic test.

[0025] A temperature sensor 3a is arranged inside the coal sample layer, and the temperature of the coal sample can be measured by the temperature sensor 3a. For example, the temperature sensor 3a can be arranged at a depth position of 70 [mm] from the upper surface of the coal sample layer, and the temperature measured by this temperature sensor 3a can be used as the representative temperature of the coal sample. On the other hand, outside the pale can 2, a temperature sensor 3b for measuring the internal temperature of the thermostatic and humidistatic chamber 1 is arranged.

[0026] A water tank 4 is arranged inside the thermostatic and humidistatic chamber 1, and the water tank 4 is used to maintain the internal humidity of the thermostatic and humidistatic chamber 1 at a constant humidity (e.g., 50 [%]). Also, a gas is supplied to the thermostatic and humidistatic chamber 1 through a gas supply pipe, and this gas is heated by a heater 5. The internal temperature of the thermostatic and humidistatic chamber 1 can be adjusted by the temperature of the gas supplied to the thermostatic and humidistatic chamber 1. Specifically, the control unit 6 can adjust the internal temperature of the thermostatic and humidistatic chamber 1 by controlling the heating by the heater 5 based on the measurement results of the temperature sensors 3a and 3b to adjust the temperature of the gas supplied to the thermostatic and humidistatic chamber 1. The gas supplied to the thermostatic and humidistatic chamber 1 is discharged from the thermostatic and humidistatic chamber 1.

[0027] When conducting the heat generation test, first, in the constant temperature control mode, nitrogen gas is supplied to the thermo-hygrostat 1 at a predetermined flow rate (e.g., 30 [L / min]) so that the internal temperature of the thermo-hygrostat 1 and the temperature of the coal sample are maintained at the initial temperature (e.g., 60 [°C]). After the internal temperature of the thermo-hygrostat 1 and the temperature of the coal sample are maintained at the initial temperature, switch from the constant temperature control mode to the temperature tracking control mode.

[0028] In the temperature tracking control mode, the internal temperature of the thermo-hygrostat 1 is made to follow the temperature of the coal sample. Here, in order to ensure that the control target temperature of the thermo-hygrostat 1 (e.g., 60.0 [°C]) does not change, a bias value is set to the temperature of the coal sample to set the control temperature of the thermo-hygrostat 1, and nitrogen gas is supplied to the thermo-hygrostat 1 while waiting for a predetermined period (e.g., half a day or more). This predetermined period is set to make it easier to grasp the temperature rise of the coal sample due to the low-temperature oxidation reaction after switching the gas supplied to the thermo-hygrostat 1 from nitrogen gas to an oxygen-containing gas (e.g., air).

[0029] After the predetermined period has elapsed, switch the gas supplied to the thermo-hygrostat 1 from nitrogen gas to an oxygen-containing gas (e.g., air). By supplying the oxygen-containing gas to the thermo-hygrostat 1 at a predetermined flow rate (e.g., 30 [L / min]), the low-temperature oxidation reaction proceeds in the coal sample and the temperature of the coal sample rises. Here, in the temperature tracking control mode, since the internal temperature of the thermo-hygrostat 1 is made to follow the temperature of the coal sample, the internal temperature of the thermo-hygrostat 1 rises in response to the temperature rise of the coal sample.

[0030] While the temperature tracking control mode is set, record the change in the internal temperature of the thermo-hygrostat 1. This temperature change includes the temperature change while nitrogen gas is being supplied and the temperature rise while the oxygen-containing gas is being supplied. The temperature change rate is obtained from the temperature change while nitrogen gas is being supplied, and the temperature rise rate is obtained from the temperature rise while the oxygen-containing gas is being supplied. Here, the difference between the temperature change rate when nitrogen gas is supplied and the temperature rise rate when the oxygen-containing gas is supplied can be taken as the temperature rise rate due to the low-temperature oxidation reaction (i.e., the heat generation rate V).

[0031] In each particle size category set in the process of step S101, by measuring the heat generation rate Vn as described above, the relationship between each particle size category and the relative heat generation rate Vrn can be obtained. The relative heat generation rate Vrn is a relative value based on any one of the measured heat generation rates Vn among all the measured particle size categories. Specifically, it is a value obtained by dividing the heat generation rate Vn of each particle size category by the reference heat generation rate Vn. For example, as the reference heat generation rate Vn, the highest heat generation rate Vn or the lowest heat generation rate Vn can be used.

[0032] In addition, when obtaining the relative heat generation rate Vrn, in order to reduce the influence of the measurement variation of the heat generation rate Vn, the relationship between any particle size category and the relative heat generation rate Vrn can be obtained, and based on this relationship, the relative heat generation rate Vrn of a predetermined particle size category (which may be different from the measured particle size category) can be obtained. Also, for a particle size category where the heat generation rate Vn cannot be measured, the heat generation rate Vn can be obtained by extrapolating the above-described relationship.

[0033] Returning to FIG. 1, in step S103, for the coal belonging to the particle size category with a predetermined particle size Dth or less, the relative heat generation rate Vr_par described below is obtained. The particle size category with a predetermined particle size Dth or less is a part of all the particle size categories set in the process of step S101. The predetermined particle size Dth can be determined as appropriate, but it may be a particle size of coal that is easy to use in the measuring device described in FIG. 2. In other words, it may be a particle size of coal that is easy to fill into the bail can 2. For example, the predetermined particle size Dth can be 20 [mm], 15 [mm], 10 [mm], or 3 [mm].

[0034] The relative heat generation rate Vr_par is a value obtained by weighted-averaging the relative heat generation rates Vrn [-] of each of a plurality of particle size classifications divided within a range of a predetermined particle size Dth or less, using the mass ratio Wn_par [mass%] of each particle size classification of a predetermined particle size Dth or less, and is represented by the following formula (1). Here, the subscript n (n is a natural number) in the relative heat generation rate Vrn and the mass ratio Wn_par means each particle size classification of a predetermined particle size Dth or less.

[0035]

Number

[0036] In the above formula (1), the relative heat generation rate Vrn is obtained from the heat generation rate Vn of each particle size classification measured in the process of step S102, as described above. The mass ratio Wn_par is the ratio [mass%] of the mass of coal belonging to each particle size classification of a predetermined particle size Dth or less to the total mass of coal of a predetermined particle size Dth or less. The mass ratio Wn_par can be obtained from the mass of coal belonging to each particle size classification measured in the process of step S101.

[0037] In step S104, for all particle size classifications, the relative heat generation rate Vr_all described below is obtained. All particle size classifications refer to all particle size classifications set in the process of step S101. The relative heat generation rate Vr_all is a value obtained by weighted-averaging the relative heat generation rates Vrn [-] of each of all particle size classifications, using the mass ratio Wn_all [mass%] of each of all particle size classifications, and is represented by the following formula (2). Here, the subscript n (n is a natural number) in the relative heat generation rate Vrn and the mass ratio Wn_all means each particle size classification.

[0038]

Number

[0039] In the above formula (2), the relative heat generation rate Vrn is obtained from the heat generation rate Vn of each particle size fraction measured in the process of step S102, as described above. The mass ratio Wn_all is the ratio [mass%] of the mass of the coal belonging to each particle size fraction to the total mass of the coal belonging to all particle size fractions. The relative heat generation rate Vr_all targets all particle size fractions, while the relative heat generation rate Vr_par described above targets the particle size fractions with a predetermined particle size Dth or less. That is, the denominator of the mass ratio Wn_all (the total mass of the coal belonging to all particle size fractions) used for calculating the relative heat generation rate Vr_all is different from the denominator of the mass ratio Wn_par (the total mass of the coal with a particle size of Dth or less) used for calculating the relative heat generation rate Vr_par.

[0040] In step S105, a correction coefficient k [-] is obtained based on the relative heat generation rate Vr_par obtained in the process of step S103 and the relative heat generation rate Vr_all obtained in the process of step S104. The correction coefficient k is the value of the relative heat generation rate Vr_all with respect to the relative heat generation rate Vr_par and is represented by the following formula (3). As will be described later, the correction coefficient k is used when obtaining the heat generation rate of the coal to be evaluated for spontaneous heating.

[0041] [Number]

[0042] (Evaluation of Spontaneous Combustibility of Coal) Next, a method for evaluating the spontaneous combustibility of coal will be described. In the evaluation of spontaneous combustibility, as will be described below, the heat generation rate V_all of the coal to be evaluated is obtained. Then, based on this heat generation rate V_all, it is possible to evaluate whether the coal to be evaluated is likely to spontaneously combust, or to evaluate the order of ease of spontaneous combustion or the order of difficulty of spontaneous combustion for multiple types of coal. Figure 3 is a flowchart for explaining the process of obtaining the heat generation rate V_all of the coal to be evaluated.

[0043] In step S201, coal with a particle size of not more than a predetermined particle size Dth is selected from the coal to be evaluated. The coal to be evaluated is coal stored in a yard or the like and has not been subjected to a pulverization process. Here, the predetermined particle size Dth is the same as the predetermined particle size Dth described in the process of step S103 above. For example, by screening the coal to be evaluated, coal with a particle size of not more than the predetermined particle size Dth can be selected.

[0044] In step S202, for the coal (coal with a particle size of not more than the predetermined particle size Dth) selected in step S201, the heat generation rate V_par is measured by performing the above-described heat generation test. In step S203, based on the heat generation rate V_par measured in the process of step S202 and the correction coefficient k obtained in advance in the process shown in FIG. 1, the heat generation rate V_all of the coal to be evaluated for spontaneous combustion property, which includes all particle sizes, is obtained. The heat generation rate V_all is a value obtained by multiplying the heat generation rate V_par by the correction coefficient k and is represented by the following formula (4). Based on this heat generation rate V_all, the spontaneous combustion property of the coal stored in a yard or the like can be evaluated.

[0045]

Equation

[0046] In this embodiment, the coal when obtaining the correction coefficient k and the coal when evaluating the spontaneous combustion property may be coal of the same brand or coal of different brands. Also, as the coal of the same brand, it may be coal of the same lot or coal of different lots. If it is coal of the same brand or coal of the same brand and lot, the accuracy of evaluating the spontaneous combustion property can be improved.

[0047] On the other hand, even if the coals have different brands, the spontaneous heating property can be evaluated based on the heat generation rate V_all obtained from the above formula (4). Here, the correction coefficient k for obtaining the heat generation rate V_all is determined from the relative heat generation rate Vr_par of the coal belonging to the particle size classification of a predetermined particle size Dth or less and the relative heat generation rate Vr_all of the coal belonging to all particle size classifications, as described above. Even if the coals have different brands, the maximum particle size of the coal stored in a yard or the like is the same (for example, about 50 [mm]), and the particle size ranges are common to each other. Therefore, the particle size ranges defining the relative heat generation rates Vr_par and Vr_all are common even for coals with different brands. Thus, even for coals with different brands, the heat generation rate V_all can be obtained using the common correction coefficient k, and the spontaneous heating property can be evaluated based on this heat generation rate V_all.

[0048] If the spontaneous heating property of coal is evaluated based on the heat generation rate V_all, countermeasures against heat generation for the coal stored in a yard or the like can be considered. For example, for coal evaluated to have a relatively high spontaneous heating property, the period of storing the coal in a yard or the like can be shortened, watering for heat extraction from the coal can be enhanced, the coal can be compacted so that air intrusion is difficult, or a chemical for suppressing excessive heat generation can be sprayed on the coal.

Example

[0049] Hereinafter, examples will be described, but the present invention is not limited to these examples.

[0050] (Specification of correction coefficient k) Five coals A to D(2) with different oxygen contents were prepared. These coals were stored in the yard and were not crushed coals. Table 2 below shows the oxygen contents of the five coals. Coals D(1) and D(2) shown in Table 2 below are of the same brand but different lots. As shown in Table 2 below, when the lots of coals D(1) and D(2) are different, the oxygen contents are also different. Note that coals A, B, and C shown in Table 2 below are the same as coals A, B, and C shown in Table 1 above.

[0051]

Table 2

[0052] Coal D(1) was classified into a plurality of particle size ranges, and for the coal D(1) belonging to each particle size range, the heat generation rate Vn was measured using the above-described measuring device (see Figure 2).

[0053] The method for measuring the heat generation rate Vn is as described above. Figure 4 schematically shows an example of the change over time in the internal temperature of the constant temperature and humidity chamber 1 and the temperature of the coal in the measurement of the heat generation rate Vn. In Figure 4, the left vertical axis is the internal temperature [°C] of the constant temperature and humidity chamber 1, the right vertical axis is the temperature [°C] of the coal, and the horizontal axis is time [days]. Note that in Figure 4, the temperatures on the left and right vertical axes are shifted to make it easier to distinguish the temperature change of the constant temperature and humidity chamber 1 and the temperature change of the coal.

[0054] As shown in Figure 4, from the start of measurement at time t0 to time t1, control is performed in the constant temperature control mode, and after time t1, control is performed in the temperature tracking control mode. Here, from time t0 to time t2, nitrogen gas was supplied to the constant temperature and humidity chamber 1, and after time t2, an oxygen-containing gas (air gas) was supplied to the constant temperature and humidity chamber 1.

[0055] The measurement results of the heat generation rate described above are shown in FIG. 5 and Table 3 below. In FIG. 5, the vertical axis on the left side represents the heat generation rate Vn [°C / day] which is the measurement result, the vertical axis on the right side represents the relative heat generation rate Vrn [-], and the horizontal axis represents the particle size [mm] of coal D(1). Note that the particle size on the horizontal axis is the geometric mean diameter of the particle size classification. In this example, the relative heat generation rate Vrn is the ratio (Vn / Vn_max) of the heat generation rate Vn of each particle size classification to the highest heat generation rate Vn_max among the heat generation rates Vn of all particle size classifications. Here, the relative heat generation rate Vrn of the heat generation rate Vn_max is 1.0, and the relative heat generation rate Vrn can take values within the range of 0 or more and 1.0 or less.

[0056] Table 3 below shows the relative heat generation rate Vrn [-] of each particle size classification. As can be seen from Table 3 below, the larger the particle size of coal D(1), the lower the relative heat generation rate Vrn (in other words, the heat generation rate Vn). Note that for the particle size classification with a particle size of 25 [mm] or more, the heat generation rate Vn could not be measured and the relative heat generation rate Vrn could not be obtained, so the relative heat generation rate Vrn was obtained by the extrapolation method based on the relationship shown in FIG. 5.

[0057]

Table 3

[0058] Next, based on the relative heat generation rate Vrn of each particle size classification shown in Table 3 above and the mass ratios Wn_par and Wn_all of coal D(1) belonging to each particle size classification, the relative heat generation rate Vr_par and the relative heat generation rate Vr_all were obtained respectively. The relative heat generation rate Vr_par is obtained from the above formula (1), and the relative heat generation rate Vr_all is obtained from the above formula (2).

[0059] Table 4 below shows, for coal D(1), the mass fraction Wn_all of each particle size fraction when all particle size fractions are targeted, and the mass fraction Wn_par of each particle size fraction when the particle size fractions with a predetermined particle size Dth or less are targeted. In this example, the predetermined particle size Dth was set to 3 [mm]. Figure 6 shows the relationship (particle size distribution) between the particle size [mm] and the cumulative undersize mass (mass%) for coals A to D(2).

[0060]

Table 4

[0061] The mass fraction Wn_all is the ratio of the mass of coal D(1) belonging to each particle size fraction to the total mass of coal D(1) in all particle size fractions, and as shown in the above formula (2), it is used to obtain the relative heating rate Vr_all. The mass fraction Wn_par is the ratio of the mass of coal D(1) belonging to each particle size fraction with a predetermined particle size Dth (3 [mm]) or less to the total mass of coal D(1) with a predetermined particle size Dth (3 [mm]) or less, and as shown in the above formula (1), it is used to obtain the relative heating rate Vr_par. The mass fraction Wn_par can be obtained from the mass fraction Wn_all of each particle size fraction.

[0062] For coal D(1), the relative heating rate Vr_par, the relative heating rate Vr_all, and the correction coefficient k obtained from the above formula (3) are shown in Table 5 below. Also, for each of coals A to C and D(2), the relative heating rate Vr_par and the relative heating rate Vr_all were obtained in the same manner as coal D(1) described above, and the correction coefficient k was obtained. This result is also shown in Table 5 below.

[0063]

Table 5

[0064] (Evaluation of Spontaneous Combustibility) For each of coals A to D(2), coal with a particle size of 3 mm or less was separated by sieving. For this separated coal, the heat generation rate V_par was measured using the above-described measuring device (see Fig. 2). Further, based on the measured heat generation rate V_par and the correction coefficient k shown in Table 5 above, the heat generation rate V_all as an evaluation value was obtained. The heat generation rate (evaluation value) V_all is the value obtained by multiplying the measured heat generation rate V_par by the correction coefficient k, and is the heat generation rate (estimated value) of each of coals A to D(2) including all particle sizes. The results are shown in Table 6 below.

[0065] On the other hand, Table 6 below also shows the heat generation rate (measured value) V_all measured by the above-described measuring device (see Fig. 2) using coal including all particle sizes for each of coals A to D(2). Here, for coals B, D(1), and D(2), since they could not be uniformly filled in the pellet can 2 (see Fig. 2) and the temperature sensor 3a could not be appropriately arranged inside the coal sample layer, the heat generation rate (measured value) V_all could not be measured.

[0066]

Table 6

[0067] According to Table 6 above, for each of coals A and C, no significant deviation was observed between the heat generation rate (evaluation value) V_all and the heat generation rate (measured value) V_all. Therefore, it was found that by obtaining the correction coefficient k in advance and measuring the heat generation rate V_par of coal (non-ground coal) with a particle size of 3 mm or less, the heat generation rate V_all of coal including all particle sizes can be grasped. In particular, for coals B, D(1), and D(2), as described above, the heat generation rate (measured value) V_all for all particle size ranges could not be measured, but the heat generation rate for all particle size ranges could be evaluated.

[0068] If the heat generation rate (evaluation value) V_all is determined as in this embodiment, the high and low relationship of the heat generation rate (spontaneous combustibility) can be grasped. Specifically, it was found that coal D(2) has a higher spontaneous combustibility than coal D(1), and coal D(1) has a higher spontaneous combustibility than coals A to C. Also, it was found that coals A to C have comparable spontaneous combustibilities.

[0069] Focusing on the heat generation rate V_par of coal with a particle size of 3 mm or less, the heat generation rate of coal A is lower than that of coal B. However, according to the particle size distribution shown in Fig. 6, since coal A has a relatively smaller particle size than coal B, it was found that for the heat generation rate (evaluation value) V_all, coals A and B are comparable. Also, although coals D(1) and D(2) only differ in lot, since the heat generation rate (evaluation value) V_all is significantly different, it was found that it is necessary to evaluate the spontaneous combustibility for each lot.

Explanation of Signs

[0070] 1: Constant temperature and humidity chamber, 2: Pail can, 3a, 3b: Temperature sensors, 4: Water tank, 5: Heater, 6: Control unit

Claims

1. A step of performing a calorific value test for measuring the calorific value generation rate on coal having a particle size equal to or smaller than a predetermined particle size among the stored coal; A step of obtaining a calorific value generation rate for evaluating the self-heating property of the entire stored coal based on the calorific value generation rate measured in the calorific value test and a correction coefficient obtained in advance; The correction coefficient is a ratio of the relative calorific value generation rate of the coal belonging to all particle size categories to the relative calorific value generation rate of the coal belonging to the particle size category equal to or smaller than the predetermined particle size when the stored coal is divided into a plurality of particle size categories; The relative calorific value generation rate of the coal belonging to the particle size category equal to or smaller than the predetermined particle size is a value obtained by weighted-averaging the relative calorific value generation rates of the respective particle size categories equal to or smaller than the predetermined particle size with the ratio of the mass of the coal in each particle size category to the total mass of the coal equal to or smaller than the predetermined particle size; A method for evaluating the self-heating property of coal, characterized in that the relative calorific value generation rate of the coal belonging to all particle size categories is a value obtained by weighted-averaging the relative calorific value generation rates of the respective particle size categories of all particle size categories with the ratio of the mass of the coal in each particle size category to the total mass of the coal of all particle size categories.

2. The method for evaluating the self-heating property of coal according to claim 1, characterized in that the predetermined particle size is a particle size at which the calorific value generation rate can be measured in the calorific value test.

3. Classifying the stored coal into a plurality of particle size categories; Measuring the calorific value generation rate by the calorific value test for the coal belonging to each particle size category; Obtaining the relative calorific value generation rate of each particle size category based on the measured calorific value generation rate with reference to a predetermined calorific value generation rate; The method for evaluating the self-heating property of coal according to claim 1 or 2, characterized in that the correction coefficient is obtained based on the relative calorific value generation rate of each particle size category and the ratio of the masses.

4. The method for evaluating the self-heating property of coal according to any one of claims 1 to 3, characterized in that the coal used for obtaining the correction coefficient is of the same brand as the coal for which the calorific value generation rate for evaluating the self-heating property is obtained.

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