JP6988622B2 - How to determine the spontaneous combustion of char and how to determine the spontaneous combustion of coal - Google Patents

Description

The present invention relates to a method for determining the spontaneous combustion of char and a method for determining the spontaneous combustion of coal.

Since coal, especially coal with a low degree of coalification (brown coal, subbituminous coal, steam coal (highly volatile bituminous coal)) is highly pyrophoric, it is extremely important to ensure safety when transporting or storing these coals. be. In addition, it is known that the degree of spontaneous combustion differs depending on the coal type (brand) even if the coal has the same degree of coalification, and especially for brands that are rich in pyrophoricity, strict control is required. You will need it.

On the other hand, a technology has been proposed in which coal, which is rich in pyrophoricity, is carbonized (pyrolyzed) to make char. The volatile content of char is less than that of the original coal. Therefore, by using coal as char, it can be expected that the pyrophoricity of the original coal will be reduced.

However, the use of coal as char does not completely eliminate pyrophoricity. Therefore, as disclosed in Non-Patent Document 1 and Patent Document 1, for example, various studies have been made on the spontaneous combustion property of char.

Non-Patent Document 1 discloses that a char having a relatively large amount of volatile matter remaining is still pyrophoric. Patent Document 1 discloses findings on spontaneous combustion of treated coal in oil (dehydrated coal) treated at a relatively low temperature (100 to 350 ° C.). According to the findings disclosed in Patent Document 1, the BET specific surface area determined by the _{N 2} ^{gas adsorption method is 10 m 2} / g or more, and the BET specific surface area determined by the _{CO 2} ^{gas adsorption method is 160 m 2} / g or less. Some chars are not supposed to ignite spontaneously.

Japanese Unexamined Patent Publication No. 10-158666

Hiroyasu Fujitsuka, Ryuichi Ashida, Kouichi Miura al., "Upgrading and dewatering of low rank coals through solvent treatment at around 350 ℃ and low temperature oxygen reactivity of the treated coals" (Fuel 114 (2013) 16-20)

As mentioned above, the degree of pyrophoricity differs depending on the coal brand, but it is said that the chemical structure (type of functional group) of each coal brand is largely involved in the cause. On the other hand, when the present inventor evaluated the spontaneous combustion property of coal mined from different seams (coal layers) in a coal mine of the same brand using a commercially available evaluation test device, the degree of the spontaneous combustion property is significantly different. It turns out that there are cases. That is, in the past, it was considered that if the brands of coal were the same, the pyrophoricity of these coals would be about the same. However, when the present inventor analyzed the same brand of coal in detail, it was found that the spontaneous combustion properties of the coal may differ.

On the other hand, chars having a low volatile content of 5 to 10% by mass (hereinafter, such chars are also referred to as "low volatile content chars") have been considered to have no pyrophoricity. That is, conventionally, it has been considered that when the chars contain a small amount of volatile matter, the pyrophoric properties of these chars are about the same (that is, they are not pyrophoric). However, when the present inventor evaluated the spontaneous ignition of the low volatile content char using a commercially available evaluation test device, it was found that some of the low volatile content char still had the spontaneous ignition property. Hereinafter, coal and char are collectively referred to as "charcoal material".

As described above, the present inventor has analyzed in detail the charcoal materials that have been considered to have the same degree of spontaneous combustion, and found that the spontaneous combustion properties of these carbon materials may differ.

In addition, this evaluation test apparatus observes the temperature change due to the self-heating of the carbonaceous material to be evaluated after heating it in advance. That is, the evaluation test apparatus performs a so-called accelerated test to evaluate the spontaneous combustion property of the carbonaceous material.

However, low volatile content char, even if it is pyrophoric, has a very low content of volatile matter that causes temperature rise, so it takes a very long time to show signs of temperature rise. There was a problem. That is, when the conventional evaluation test apparatus was used, it took a very long time to determine whether or not the low volatile content char had spontaneous ignition. There is also a problem that an evaluation test device, which is a device dedicated to the evaluation test, is required. Further, there is a problem that it is necessary to prepare a relatively large amount of sample in order to reproduce the heat insulating state of the carbonaceous material. Here, the charcoal material is stored in a large amount (that is, as a pile) in a yard or the like. The charcoal material existing inside the pile is insulated from the outside air and easily generates heat. Therefore, in the evaluation test apparatus, it is necessary to reproduce such an environment in which heat is likely to be generated, so that a relatively large amount of sample is required.

Therefore, the present invention has been made in view of the above problems, and the object of the present invention is a coal material which has been considered to have the same degree of spontaneous combustion, that is, low volatile content chars or each other. To provide a new and improved method for determining the spontaneous combustion of char and a method for determining the spontaneous combustion of coal, which can more easily and quickly determine the spontaneous combustion of coals of the same brand. be.

In order to solve the above problems, according to a certain viewpoint of the present invention, it is a method for determining the pyrophoricity of a char containing 5 to 10% by mass of volatile matter, and the BET specific surface area of the char is measured by the _{N 2 adsorption method.} A method for determining the pyrophoricity of char is provided, which comprises a step of determining that the char has spontaneous ignition when the BET specific surface area is 80 m ^{2 / g or more.} ..

According to another aspect of the present invention, there is provided a pyrophoric determination method of coal of the same brand, measuring a BET specific surface area of the coal by N ₂ adsorption method, conventional evaluation ignition start of the coal The process of measuring with the test equipment, the process of identifying the correlation between the BET specific surface area and the time of ignition start, and the process of setting the BET threshold for determining the spontaneous ignition of coal based on the correlation, and the BET. If the specific surface area is greater than or equal to the BET threshold, the coal is classified as the first category with high spontaneous ignition , and if the specific surface area is less than the BET threshold, the coal is spontaneously ignited as compared to the first category. Provided is a method for determining spontaneous ignition of coal, which comprises a step of classifying into a second category having low sex properties.

The BET specific surface area by N ₂ adsorption method, there is a high correlation whether pyrophoric. Furthermore, the BET specific surface area can be measured in a short time using a general-purpose device. Moreover, it does not require many samples for measurement. According to the present invention, since the pyrophoricity is evaluated using such a BET specific surface area, it is possible to more easily and quickly determine the pyrophoricity of low volatile content char or the pyrophoricity of coal of the same brand. It will be possible.

It is a graph which shows the correspondence relationship between the temperature of a char (sample temperature) and the elapsed time from the start of an evaluation test for each char. It is a graph which shows the correspondence relationship between the temperature (sample temperature) of the coal mined from the different seams of the same coal mine (that is, the brand) and the elapsed time from the start of the evaluation test for each coal.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present specification and the drawings, components having substantially the same functional configuration are designated by the same reference numerals, and duplicate description will be omitted.

<1. Examination by the present inventor>
First, the study by the present inventor will be described. The present inventor evaluates the spontaneous combustion property of the same brand of coal (that is, mined from the same coal mine) and the spontaneous combustion property of the low volatile content char using a conventional evaluation test device, and thereby the same brand of coal. However, it was found that the degree of spontaneous combustion may differ, and that some low-volatile coals have spontaneous combustion. However, the evaluation method using the conventional evaluation test apparatus has a problem that it takes a very long time to determine whether or not the same brand of coal and low volatile content char has spontaneous ignition.

Therefore, the present inventor has diligently studied a technique capable of more easily and quickly discriminating the spontaneous combustion property of coal of the same brand and low volatile content char. Therefore, the present inventor first focused on the BET specific surface area. This is because it is considered that the larger the BET specific surface area, the more oxygen is adsorbed and the easier it is to ignite.

However, the BET specific surface area varies greatly depending on the type of gas used for the measurement. The present inventor measured the BET specific surface area of coal and low volatile content char using _{N 2} gas and CO _{2 gas, respectively.} As a result, _{no correlation was found between the BET specific surface area measured using CO 2} gas and the pyrophoricity of coal and low volatile content char, but the BET ratio measured using _{N 2 gas.} It was revealed that there is a strong correlation between the surface area and the pyrophoricity of coal and low volatility char. Specifically, it was clarified that the low volatile content char having a BET specific surface area of 80 m ² _{/ g or more measured using N 2 gas has pyrophoricity.} Furthermore, it was clarified that the pyrophoricity of the same brand of coal can also be discriminated by the BET specific surface area. Specifically, it was clarified that the presence or absence of pyrophoricity can be determined by the threshold value of the BET specific surface area (that is, the BET threshold value). The BET threshold can vary from stock to stock. Here, since _{the particles of N 2} gas are relatively large, it is difficult for them to enter the so-called micropores (pores having a diameter of 2 nm or less). Therefore, the _{BET specific surface area measured by the N 2} gas is the specific surface area due to the relatively large pores (that is, the pores larger than the micropores). Therefore, coal and low volatile content char having a large number of relatively large pores will have relatively large pyrophoricity. Based on such findings, the present inventor has come up with a method for determining the spontaneous combustion property of coal and low volatile content char of the same brand according to the present embodiment. Hereinafter, the method for determining the spontaneous combustion of char and the method for determining the spontaneous combustion of coal according to the present embodiment will be described in detail.

<2. First Embodiment (Method for determining the spontaneous combustion of char)>
First, the first embodiment will be described. In the first embodiment, the pyrophoricity of the low volatile content char is determined. The method for determining the pyrophoricity of the char according to the present embodiment is _{a step of measuring the BET specific surface area of the low volatile content char by the N 2} adsorption method, and a low volatile content when the BET specific surface area is 80 m ^{2 / g or more.} Includes a step of determining that the char is pyrophoric.

Here, the type of coal used as a raw material for the low volatile content char is not particularly limited. For example, the low volatile content char may be produced by carbonizing brown coal, subbituminous coal, or steam coal (highly volatile bituminous coal). Further, the low volatile content char is a char containing 5 to 10% by mass of volatile content, as described above. Here, the mass% of the volatile matter is the mass% with respect to the total mass of the char. The _{device for measuring the BET specific surface area by the N 2} adsorption method is not particularly limited, and any general-purpose device may be used.

As described above, according to the present embodiment, since the pyrophoricity of the low volatile content char can be discriminated based on the BET specific surface area measured by _{the N 2 adsorption method, the discrimination can be performed in a short time.} .. Further, the BET specific surface area may be measured by a general-purpose device. Further, a small amount of sample is required for measuring the BET specific surface area. Therefore, it becomes possible to more easily and quickly determine the pyrophoricity of the low volatile content char.

<3. Application example of this embodiment>
Regarding the low volatile content char determined to have pyrophoricity according to the present embodiment, the period from the time when it is manufactured in a manufacturing facility such as a rotary kiln to the time when it is consumed in a char-using facility such as a sintering machine (yard or coal storage). It is desirable to keep the storage period in the tank as short as possible. also. Even during storage in the yard, it is important to measure the pile temperature (particularly the internal temperature) on a regular basis and take necessary measures such as watering when a tendency for temperature rise is confirmed.

<4. Second embodiment (method for determining spontaneous combustion of coal)>
Next, the second embodiment will be described. In the second embodiment, the BET specific surface area of the coal of the same brand and specific and measuring the N ₂ adsorption method, the correlation between the pyrophoric BET specific surface area and coal, based on the correlation, coal In the process of setting the BET threshold value for determining the pyrophoricity of coal, and when the BET specific surface area is equal to or higher than the BET threshold value, coal is classified into the first category and the BET specific surface area is the BET threshold value. If it is less than, the step of classifying the coal into a second category having a lower pyrophoricity than the first category is included.

First, the BET specific surface area of the coal of the same brand by N ₂ adsorption method. The target coal here is not particularly limited as long as it is the same brand of coal. However, coal with a low degree of coalification is likely to have pyrophoricity. Therefore, the target coal is preferably coal having a low degree of coalification (for example, lignite, subbituminous coal, steam coal (highly volatile bituminous coal), etc.). Here, the brand of coal is given to each coal mine, for example. That is, the brand of coal indicates, for example, the coal mine from which the coal was mined. Therefore, coal of the same brand is, for example, coal mined in the same coal mine. These coals were mined from the same coal mine, but may have been mined from different seams. Coal mined from different seams may have different pyrophoricities. In the second embodiment, the spontaneous combustion property of these coals can be determined. The _{device for measuring the BET specific surface area by the N 2} adsorption method is not particularly limited, and any general-purpose device may be used.

Next, the correlation between the BET specific surface area and the pyrophoricity of coal is identified. For example, the correlation between the BET specific surface area and the ignition start time of coal is specified. The starting point of ignition of coal can be specified by using a conventional evaluation test device. The details will be described in Examples, but the temperature of the sample is raised by using a conventional evaluation test device. Then, when the temperature of the sample reaches 230 to 250 ° C. or the measurement time reaches 2900 minutes, the measurement is terminated. Then, when the temperature of the sample reaches 230 to 250 ° C., it is determined that the sample, that is, coal has pyrophoricity. Then, the intersection of the tangents at the measurement start time and the measurement end time of the temperature rise curve obtained as a result of the measurement is set as the ignition start time. Details will be described in Examples, but the larger the BET specific surface area, the shorter the time from the start of measurement to the start of ignition.

Then, based on the correlation, a BET threshold value for determining the spontaneous combustion property of coal is set. For example, the BET specific surface area when the time from the measurement start time to the ignition start time becomes a predetermined time (this predetermined time may be adjusted according to the storage performance required for coal) is set as the BET threshold value. ..

When the BET specific surface area is equal to or higher than the BET threshold value, the coal is classified into the first category, and when the BET specific surface area is less than the BET threshold value, the coal is more spontaneously ignited than the first category. Is classified into the second category with low. Therefore, it can be said that the coal belonging to the first category has higher pyrophoricity than the coal belonging to the second category. The process for setting the BET threshold requires some time because it requires testing using conventional evaluation test equipment (still, coal tends to ignite faster than char, so the more char Often does not take time). However, once the BET threshold is set, the spontaneous combustion property of coal can be determined based on the BET threshold.

Thus, according to this embodiment, it is possible to determine the pyrophoric coal based on the measured BET specific surface area by N ₂ adsorption method, it is possible to perform the determination in a short time. Further, the BET specific surface area may be measured by a general-purpose device. Further, a small amount of sample is required for measuring the BET specific surface area. Therefore, it becomes possible to determine the spontaneous combustion property of coal more easily and quickly.

<5. Application example of this embodiment>
For coal (coal belonging to the first category) judged to have particularly high pyrophoricity by this embodiment, the period until consumption (storage period in a yard or a coal storage tank) shall be as short as possible. Is desirable. also. Even during storage in the yard, it is important to measure the pile temperature (particularly the internal temperature) on a regular basis and take necessary measures such as watering when a tendency for temperature rise is confirmed.

<1. Example 1 (Example corresponding to the first embodiment>
<1-1. Coal preparation ＞
The present inventor conducted the experiment described below in order to confirm the effect of the first embodiment of the present invention. First, coals A and B shown in Table 1 were prepared as coal as a raw material for char. The industrial analysis value is a value measured according to JIS M8812, and the elemental analysis value is a value measured according to JIS M8819 and JIS M8813. In addition, each value is mass% at the time of drying, and is mass% with respect to the total mass of coal.

<1-2. Char making>
Next, coals A and B were carbonized in a rotary kiln or a batch-type carbonization furnace to produce char. Here, a plurality of types of chars were produced by carbonizing coals A and B while arbitrarily changing the type of equipment for carbonization and the temperature conditions during carbonization. Then, the composition of each char (specifically, volatile matter and the like) was measured by performing the same industrial analysis and elemental analysis as in Table 1. Then, chars having a volatile mass% of 10% by mass or less were arbitrarily picked up, and these chars were used as the chars to be measured. Table 2 shows the physical property values of the char to be measured. The method for measuring each physical property value is the same as in Table 1.

<1-3. Evaluation of pyrophoricity using conventional evaluation test equipment>
Next, the spontaneous combustion property of chars A-1 to B-8 was evaluated using a conventional evaluation test device (SIT-2 manufactured by Shimadzu Corporation). The test conditions are as follows.
・ Measurement start temperature: 130 ° C
-Measurement end condition: The measurement was terminated when the temperature of the sample reached 230 to 250 ° C. or the measurement time was 2900 minutes.
-Atmospheric gas: When the temperature rises (normal temperature → 130 ° C) / Nitrogen, when measuring / Air-Sample particle size: 1 mm or more and less than 1.7 mm-Sample mass: 1-2 g
-Ignition start time point: The intersection of the tangents at the measurement start time point and the measurement end time point of the temperature rise curve obtained as a result of the measurement is defined as the ignition start time point.

Here, when the temperature of the sample reaches 230 to 250 ° C., it is determined that the sample has spontaneous ignition. The sample particle size is a value measured by sieves having different openings. That is, the sample was sieved to have an opening of X mm, the particle size of the sample remaining on the sieve was set to X mm or more, and the particle size of the sample dropped from the sieve was set to less than X mm. The measurement start time is the time when the temperature of the sample reaches 130 ° C., and the measurement end time is the time when the measurement end condition is satisfied. The time of ignition start was measured when the sample had pyrophoricity.

Specifically, the following tests were conducted. First, the sample was set in an evaluation test device, and the sample was heated in a nitrogen atmosphere until the temperature of the sample reached 130 ° C. The measurement start time was set when the temperature of the sample reached 130 ° C., and the heating of the sample was completed. Then, the time change of the temperature of the sample was measured. The atmosphere at the time of measurement was air. The measurement was terminated when the temperature of the sample reached 230 to 250 ° C. or the elapsed time from the start of the measurement reached 2900 minutes. The time when the measurement was completed was defined as the time when the measurement was completed. Then, when the temperature of the sample reaches 230 to 250 ° C., it is determined that the sample has spontaneous combustion, and when the temperature of the sample does not reach 230 to 250 ° C. and 2900 minutes have passed, the sample is sampled. Was determined not to be pyrophoric. When the sample is pyrophoric, the intersection of the tangents at the start and end of the measurement of the temperature rise curve obtained as a result of the measurement is defined as the start of ignition. FIG. 1 shows a temperature rise curve obtained as a result of the measurement. As is clear from FIG. 1, chars A-2 and B-4 to B-6 were pyrophoric. However, it took more than 500 minutes for the temperatures of these chars A-2 and B-4 to B-6 to reach 230 to 250 ° C.

<1-4. Evaluation of BET specific surface area by N _{2 adsorption method>}
To confirm the correlation between BET specific surface area by the pyrophoric and N ₂ adsorption method of char was calculated BET specific surface area by N ₂ adsorption method. Specifically, a sample (grain size 0) that has been pretreated (heated at 150 ° C. for 4 hours while exhausting the vacuum) in advance using a commercially available constant volume method adsorption amount measuring device (constant volume method specific surface area measuring device). _{By adsorbing N 2} as an adsorption gas to .25 mm or more and less than 0.5 mm at -196 ° C, the relative pressure (ratio of adsorption equilibrium pressure to saturated vapor pressure) 0.02 to 0.1 (in 0.01 increments) ), The adsorption amount _{of N 2 was measured.} Then, the specific surface area (BET specific surface area) was calculated based on the relationship between the gas adsorption amount and the relative pressure obtained above and the BET formula. The evaluation of the BET specific surface area could be performed in a very short time as compared with the evaluation test of spontaneous ignition using the evaluation test device.

<1-5. Evaluation of BET specific surface area by CO _{2 adsorption method>}
For comparison, the BET specific surface area was calculated by _{the CO 2 adsorption method.} Specifically, a carbonaceous material sample that has been pretreated (heated at 150 ° C. for 4 hours while exhausting the vacuum) using a commercially available constant volume adsorption amount measuring device (constant volume specific surface area measuring device) (a carbonaceous material sample). Relative pressure (ratio of adsorption equilibrium pressure to saturated vapor pressure) 0.012-0.03 (0.002) by adsorbing _{CO 2} as an adsorption gas to a particle size of 0.25 mm or more and less than 0.5 mm at 0 ° C. _{The amount of CO 2} adsorbed in the range of ticks) was measured. Then, the specific surface area (BET specific surface area) was calculated based on the relationship between the gas adsorption amount and the relative pressure obtained above and the BET formula.

<1-6. Comparison of pyrophoricity and BET specific surface area>
Table 3 shows the pyrophoricity and the BET specific surface area in comparison.

Chars A-1 to B-6 are so-called low volatile content chars because they contain 5 to 10% by mass of volatile matter (see Table 2). As is apparent from Table 3, it was confirmed that there is a high correlation between the BET specific surface area by the pyrophoric and N ₂ adsorption method of low-volatile char. That is, the BET specific surface area of the low volatile content char having spontaneous ignition is 80 m ² / g or more, but the BET specific surface area of the low volatile content char having no pyrophoricity is ^{less than 80 m 2} / g. became. Therefore, when the BET specific surface area is 80 m ² / g or more, it can be determined that the low volatile content char has spontaneous ignition.

On the other hand, no correlation was found between the pyrophoricity of the low volatile content char and the BET specific surface area by the _{CO 2 adsorption method.} Therefore, the type of gas used for the measurement of the BET specific surface area is very important, and, in the case of using N ₂ gas, it was confirmed that it was possible the BET specific surface area correlated with pyrophoric. The BET specific surface area of char B-7 by the N ₂ ^{adsorption method was 80 m 2} / g or more, but char B-7 did not have pyrophoricity. Since the volatile content of char B-7 is 1.9% by mass, which is even smaller than the volatile content of low volatile content char, it can be understood that it is difficult to ignite even if the BET specific surface area is large.

<2. Example 2 (Example corresponding to the second embodiment)>
<2-1. Coal preparation ＞
The present inventor conducted the experiment described below in order to confirm the effect of the second embodiment of the present invention. First, the coals A1 to A3 and B1 to B3 shown in Table 4 were prepared as the target coals. Coals A1 to A3 and coals B1 to B3 are coals mined from different seams of coal mine A and coal mine B, respectively. That is, coals A1 to A3 are coals of the same brand, and coals B1 to B3 are coals of the same brand. The industrial analysis value is a value measured according to JIS M8812, and the elemental analysis value is a value measured according to JIS M8819 and JIS M8813. In addition, each value is mass% at the time of drying, and is mass% with respect to the total mass of coal.

<2-2. Evaluation of pyrophoricity using conventional evaluation test equipment>
Next, the spontaneous combustion properties of coals A1 to A3 and B1 to B3 were evaluated using a conventional evaluation test device (SIT-2 manufactured by Shimadzu Corporation). The test conditions are the same as in Example 1, and the specifics are as follows.
・ Measurement start temperature: 130 ° C
-Measurement end condition: The measurement was terminated when the temperature of the sample reached 230 to 250 ° C. or the measurement time was 2900 minutes.
-Atmospheric gas: When the temperature rises (normal temperature → 130 ° C) / Nitrogen, when measuring / Air-Sample particle size: 1 mm or more and less than 1.7 mm-Sample mass: 1-2 g
-Ignition start time point: The intersection of the tangents at the measurement start time point and the measurement end time point of the temperature rise curve obtained as a result of the measurement is defined as the ignition start time point.

Here, when the temperature of the sample reaches 230 to 250 ° C., it is determined that the sample has spontaneous ignition. The sample particle size is a value measured by sieves having different openings. The measurement start time is the time when the temperature of the sample reaches 130 ° C., and the measurement end time is the time when the measurement end condition is satisfied. The time of ignition start was measured when the sample had pyrophoricity.

Specifically, the following tests were performed in the same manner as in Example 1. First, the sample was set in an evaluation test device, and the sample was heated in a nitrogen atmosphere until the temperature of the sample reached 130 ° C. The measurement start time was set when the temperature of the sample reached 130 ° C., and the heating of the sample was completed. Then, the time change of the temperature of the sample was measured. The atmosphere at the time of measurement was air. The measurement was terminated when the temperature of the sample reached 230 to 250 ° C. or the elapsed time from the start of the measurement reached 2900 minutes. The time when the measurement was completed was defined as the time when the measurement was completed. Then, when the temperature of the sample reaches 230 to 250 ° C., it is determined that the sample has spontaneous combustion, and when the temperature of the sample does not reach 230 to 250 ° C. and 2900 minutes have passed, the sample is sampled. Was determined not to be pyrophoric. When the sample is pyrophoric, the intersection of the tangents at the start and end of the measurement of the temperature rise curve obtained as a result of the measurement is defined as the start of ignition.

FIG. 2 shows the temperature rise curve obtained as a result of the measurement. Of the three types of coal mined from the A coal mine, coal A1 and coal A3 had high pyrophoricity, but the pyrophoricity of coal A2 was slightly suppressed. Of the three types of coal mined from the B coal mine, coal B1 had a high pyrophoricity, but the pyrophoricity of coal B2 and coal B3 was considerably suppressed.

<2-3. Evaluation of BET specific surface area by N _{2 adsorption method>}
To confirm the correlation between BET specific surface area by the pyrophoric and N ₂ adsorption method of coal was calculated BET specific surface area by N ₂ adsorption method. Specifically, a sample (grain size 0) that has been pretreated (heated at 150 ° C. for 4 hours while exhausting the vacuum) in advance using a commercially available constant volume method adsorption amount measuring device (constant volume method specific surface area measuring device). _{By adsorbing N 2} as an adsorption gas to .25 mm or more and less than 0.5 mm at -196 ° C, the relative pressure (ratio of adsorption equilibrium pressure to saturated vapor pressure) 0.02 to 0.1 (in 0.01 increments) ), The adsorption amount _{of N 2 was measured.} Then, the specific surface area (BET specific surface area) was calculated based on the relationship between the gas adsorption amount and the relative pressure obtained above and the BET formula. The evaluation of the BET specific surface area could be performed in a very short time as compared with the evaluation test of spontaneous ignition using the evaluation test device.

<2-4. Evaluation of BET specific surface area by CO _{2 adsorption method>}
For comparison, the BET specific surface area was calculated by _{the CO 2 adsorption method.} The specific processing is the same as that of the first embodiment.

<2-5. Comparison of pyrophoricity and BET specific surface area>
Table 5 shows the pyrophoricity and the BET specific surface area in comparison.

As apparent from Table 5, it was confirmed that there is a high correlation between the BET specific surface area by the pyrophoric and N ₂ adsorption method of coal. That is, with respect to coal mined from the same coal mine, the spontaneous ignition of coal having a larger specific surface area tended to be higher. Regarding coals A1 to A3, it was clarified that the pyrophoricity changed significantly at the BET specific surface area = 10.0 m ^{2 / g.} Therefore, for the brands to which coals A1 to A3 belong, the BET threshold value may be 10.0 m ² / g. Then, the coals A1 and A3 having a BET specific surface area of 10.0 m ² / g or more are classified into the first category, and the coal A2 having ^{a BET specific surface area of less than 10 m 2 / g is classified.} It may be classified into the second category. Regarding coals B1 to B3, it was clarified that the pyrophoricity changed significantly at the BET specific surface area = 4.0 m ^{2 / g.} Therefore, for the brand to which coals B1 to B3 belong, the BET threshold value may be 4.0 m ² / g. Then, the coal B1 having a BET specific surface area of 4.0 m ² / g or more is classified into the first category, and the coal B2 ^{having a BET specific surface area of less than 4.0 m 2 / g.} B3 may be classified into the second category.
On the other hand, no correlation was found between the pyrophoricity of the low volatile content char and the BET specific surface area by the _{CO 2 adsorption method.}

Although the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person having ordinary knowledge in the field of technology to which the present invention belongs can come up with various modifications or modifications within the scope of the technical ideas described in the claims. , These are also naturally understood to belong to the technical scope of the present invention.

Claims (2)

It is a method for determining the pyrophoricity of char containing 5 to 10% by mass of volatile matter.
The step of measuring the BET specific surface area of the _{char by the N 2 adsorption method and}
A method for determining the spontaneous combustion of char, which comprises a step of determining that the char has spontaneous combustion when the BET specific surface area is 80 m ^{2 / g or more.} It is a method for determining the spontaneous combustion of coal of the same brand.
The step of measuring the BET specific surface area of the _{coal by the N 2 adsorption method and}
The process of measuring the ignition start time of the coal with a conventional evaluation test device, and
A step of specifying a correlation between the BET specific surface area and the ignition start time point, and setting a BET threshold value for determining the spontaneous combustion property of the coal based on the correlation.
When the BET specific surface area is equal to or greater than the BET threshold, the coal is classified into the first category having high pyrophoricity , and when the BET specific surface area is less than the BET threshold, the coal is classified into the first category. A method for determining spontaneous combustion of coal, which comprises a step of classifying into a second category having a lower spontaneous combustion property than the first category.

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