JP2019164116A - Oxidation characteristic evaluation method of coal - Google Patents

Abstract

To provide an evaluation method of an oxidation characteristic of coal capable of evaluating the oxidation characteristic of coal flexibly, simply, and without restricting the measuring temperature, in a relatively low temperature region.SOLUTION: A coal oxidation characteristic evaluation method of the present invention includes: an oxidation process of oxidizing a coal sample in an atmosphere containingOgas; a spectrum acquiring process of acquiring aO nuclear magnetic resonance spectral spectrum by applying nuclear magnetic resonance spectral analysis to the coal sample after the oxidation; and an evaluation process of evaluating the oxidation characteristic of coal sample on the basis of the area of the peak in theO nuclear magnetic resonance spectral spectrum.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for evaluating oxidation characteristics of coal.

  The process of coal spontaneous ignition starts with the reaction of coal and oxygen at room temperature even under conditions where no external heat is applied to the coal. Therefore, it is necessary to investigate the reactivity between coal and oxygen at relatively low temperatures including near normal temperature, that is, the oxidation characteristics of coal, in order to understand the basic phenomenon and elucidate the mechanism leading to ignition.

  Several methods have been proposed to evaluate the oxidation characteristics of coal. For example, Patent Document 1 discloses a method of measuring the weight increase of coal with a thermobalance in a pure oxygen gas atmosphere of 60 ° C. or less and evaluating the pyrophoricity of coal based on the amount of weight increase. Patent Document 2 discloses a spontaneous ignition in which the temperature of a sample is increased and the sample temperature is stabilized, and then the sample is maintained at a set temperature in an oxygen-containing gas atmosphere and the time until the spontaneous ignition starts is measured. A test apparatus is disclosed.

Furthermore, Patent Document 3 discloses a method for elevating the low-grade coal in an air stream and evaluating the spontaneous ignition of the low-grade coal from changes in the amount of generated CO and CO ₂ . Patent Document 4 discloses a method of measuring the vitrinite average reflectance, the amount of active component and the amount of inactive component of a coal sample with a microscope, and evaluating the exothermic property of the coal sample from these.

JP 2017-68203 A Japanese Patent Laid-Open No. 9-304311 JP 2014-126541 A JP 2003-215079 A

  However, in the method disclosed in Patent Document 1, it is not possible to evaluate the oxidation characteristics of coal in an atmosphere exceeding 60 ° C. In particular, when coal contains water, weight increase due to oxidation and weight loss due to water evaporation proceed simultaneously, and the amount of oxidation cannot be measured correctly. Further, in the method disclosed in Patent Document 2, it is necessary to remove moisture from coal in order to stabilize the sample temperature, and the sample temperature is usually 100 ° C. or higher, for example, 130 ° C. or higher. is required.

In the method disclosed in Patent Document 3, since the generation amount of CO and CO ₂ is measured while raising the temperature, it is necessary to raise the temperature to a relatively high temperature, for example, 600 ° C. The identification of CO and CO ₂ is performed from the rising temperature of the low temperature side peak around 300 ° C. Furthermore, the method disclosed in Patent Document 4 requires observation with a microscope, and the work is complicated.

  As described above, in the conventional method, the oxidation characteristics of coal could not be easily evaluated in a relatively low temperature range, for example, in a temperature range from room temperature to 350 ° C. and without limitation of the measurement temperature.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to evaluate the oxidation characteristics of coal flexibly and easily without limitation of the measurement temperature in a relatively low temperature range. It is an object of the present invention to provide a new and improved method for evaluating the oxidation characteristics of coal.

As a result of intensive studies to solve the above-described problems, the inventors of the present invention oxidize coal in an atmosphere containing ¹⁷ O ₂ gas and perform ¹⁷ O nuclear magnetic resonance spectroscopy analysis on the oxidized coal. It was found that the oxidation characteristics of can be observed. Furthermore, as a result of further studies based on such knowledge, the inventors have arrived at the present invention shown below.

The gist of the present invention completed based on the above findings is as follows.
(1) an oxidation step of oxidizing a coal sample in an atmosphere containing ¹⁷ O ₂ gas;
Performing a nuclear magnetic resonance spectroscopic analysis on the coal sample after oxidation to obtain a ¹⁷ O nuclear magnetic resonance spectroscopic spectrum;
An evaluation step of evaluating the oxidation characteristics of the coal sample based on the area of the peak in the ¹⁷ O nuclear magnetic resonance spectroscopy spectrum;
Method for evaluating oxidation characteristics of coal having
(2) In the evaluation step, the chemical shift of the ¹⁷ O nucleus in the ¹⁷ O nuclear magnetic resonance spectroscopy spectrum is based on the area of the peak having an apex in the range of −100 ppm to 80 ppm and / or 200 ppm to 400 ppm. The method for evaluating oxidation characteristics of coal according to (1), wherein the oxidation characteristics of the previous coal sample are evaluated.
(3) In the evaluation step, the oxidation characteristic of the previous coal sample is determined based on the area of the peak having a peak in the range where the chemical shift of ¹⁷ O nuclei in the ¹⁷ O nuclear magnetic resonance spectroscopy spectrum is 200 ppm or more and 400 ppm or less. The method for evaluating oxidation characteristics of coal according to (1), which is evaluated.
(4) In the evaluation step, the oxidation characteristics of the coal sample are evaluated on the premise that the area of the peak has a positive correlation with the oxidation characteristics of the coal. Any one of (1) to (3) The method for evaluating oxidation characteristics of coal according to item.
(5) In the said oxidation process, the temperature of the said coal sample and the said atmosphere is 350 degrees C or less, The oxidation characteristic evaluation method of the coal as described in any one of (1)-(4).
(6) Furthermore, it has a moisture adjustment step that is performed before the oxidation step and adjusts the moisture of the coal sample to a predetermined amount, and in the evaluation step, the oxidation of the coal sample containing the predetermined amount of the moisture The method for evaluating oxidation characteristics of coal according to any one of (1) to (5), wherein the characteristics are evaluated.

  As described above, according to the present invention, it is possible to provide a method for evaluating the oxidation characteristics of coal, which can flexibly and easily evaluate the oxidation characteristics of coal in a relatively low temperature range without limitation of the measurement temperature. It becomes possible.

2 is a ¹⁷ O NMR spectrum chart after oxidation of a coal sample obtained in Example 1. FIG. 2 is a graph comparing the peak areas around 300 ppm of the ¹⁷ O NMR spectrum in Example 1. FIG. 2 is a graph comparing the peak areas around 0 ppm of the ¹⁷ O NMR spectrum in Example 1. FIG. 2 is a graph comparing the areas of a peak near 300 ppm and a peak near 0 ppm of a ¹⁷ O NMR spectrum in Example 1. FIG. 4 is a ¹⁷ O NMR spectrum chart after oxidation of a coal sample obtained in Example 2. FIG. 4 is a graph comparing the areas of peaks near 300 ppm in a ¹⁷ O NMR spectrum in Example 2. FIG. 3 is a graph comparing the area of a peak near 300 ppm and a peak near 0 ppm in a ¹⁷ O NMR spectrum in Example 2. FIG. 6 is a graph comparing the area of a peak near 300 ppm and a peak near 0 ppm in a ¹⁷ O NMR spectrum in Example 3. FIG.

Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
<1. First Embodiment>
First, the oxidation characteristic evaluation method according to the first embodiment of the present invention will be described. The oxidation characteristic evaluation method according to the present embodiment includes an oxidation process in which a coal sample is oxidized in an atmosphere containing ¹⁷ O ₂ gas, and a nuclear magnetic resonance spectroscopy analysis of the oxidized coal sample, and a ¹⁷ O nuclear magnetic resonance spectroscopy spectrum. A spectrum acquisition step, and an evaluation step of evaluating the oxidation characteristics of the coal sample based on the peak area of the ¹⁷ O nuclear magnetic resonance spectrum.

(1.1. Preparation of sample)
First, prior to the oxidation step (oxidation of the coal sample), a coal sample is prepared.
A coal sample is obtained by adjusting a particle size about coal used as a raw material, for example. It does not specifically limit as coal used as the raw material of a coal sample, It can be used about any of anthracite, bituminous coal, subbituminous coal, lignite, and peat. Moreover, as needed, these 2 or more types of coal may be mixed and supplied to a coal sample as coal. Further, the coal sample may be a processed product of coal.

  The particle size of coal can be adjusted, for example, by pulverization or classification. The pulverization can be performed using various pulverizers such as a ball mill, a bead mill, a mortar, and a hammer mill. The classification can be performed by a dry classifier such as a classification sieve, a gravity classifier, an inertia classifier, or a centrifugal classifier.

  Although the particle size of a coal sample is not specifically limited, For example, it is 250 micrometers or less, Preferably it can be 150 micrometers or less. In this step, in order to carry out the oxidation reaction in a short time, it is preferable to promote the oxidation reaction by making the particle size relatively small. In order to unify the oxidation conditions of the coal sample in this step, it is preferable that the plurality of coal samples to be compared have a particle size within a certain range, for example, within the above-described range.

  Moreover, you may remove the water | moisture content adhering about a coal sample as needed. In general, moisture is attached to the raw material coal according to the type of coal and the environment in which it is stored. Since the energy generated by oxidation during the oxidation process can be used not only to increase the temperature of the moisture but also contribute to the promotion of the oxidation reaction, the moisture adhering to such coal is responsible for the oxidation characteristics of the coal. May affect the evaluation results. Therefore, when the objective is to evaluate the oxidation characteristics of a coal sample by eliminating the influence of moisture, it is preferable to remove the moisture from the coal sample.

  For example, the moisture present in the coal sample can be removed by heating the coal sample in a reduced-pressure atmosphere. The heating conditions can be, for example, 80 ° C. or higher and 120 ° C. or lower and 12 hours or longer and 24 hours or shorter in a reduced pressure atmosphere of 10 hPa or lower.

  It is not necessary to remove moisture from the coal sample. For example, it can be said that the oxidation characteristics of coal in a state where moisture adheres in accordance with the environment to be stored more accurately indicate the oxidation characteristics of coal stored in the environment. Therefore, the oxidation characteristics of the obtained coal can be an important indicator in examining the storage method of coal in the environment. As described above, the method for evaluating the oxidation characteristics of coal according to the present embodiment can be implemented without removing the water present in the coal sample. Therefore, compared with the conventional method of evaluating the oxidation characteristics of coal after removing moisture, the evaluation method for the oxidation characteristics of coal according to the present embodiment allows flexible condition setting.

(1.2. Oxidation process)
In the oxidation step, the coal sample is oxidized in an atmosphere containing ¹⁷ O ₂ gas. In nature, there is no level of ¹⁷ O detectable in nuclear magnetic resonance spectroscopy. Therefore, almost all of ¹⁷ O detected in nuclear magnetic resonance spectrum measurement of a treated coal sample is in this step. It is thought to be derived from a ¹⁷ O-containing functional group generated by the reaction between the ¹⁷ O ₂ gas and the coal sample. Therefore, in this step, oxidation treatment is performed in an atmosphere containing ¹⁷ O ₂ gas, and by analyzing ¹⁷ O detected in the coal sample, the evaluation of the oxidation characteristics of the coal sample under the treatment conditions in this step can be performed. It becomes possible.

The treatment atmosphere of coal is not particularly limited as long as it contains ¹⁷ O ₂ gas. For example, ¹⁷ O ₂ gas may be mixed with an inert gas such as air, nitrogen gas, or argon gas, and this may be used as a processing atmosphere. Alternatively, an oxygen gas containing ¹⁷ O ₂ gas may be used as a treatment atmosphere. In particular, it is preferable to use oxygen gas as the treatment atmosphere because the time of this step can be shortened. In this case, the content of the ¹⁷ O ₂ gas in the oxygen gas is preferably as high as possible, for example, 90% by volume or more, and preferably 95% by volume or more.

  In addition, the treatment of the coal sample may be performed while continuously circulating the gas constituting the treatment atmosphere in the system in which the coal sample is arranged, or the atmosphere in the system in which the coal sample is arranged is generated by the gas. The replacement may be performed after sealing and shielding from other atmospheres.

  Moreover, the temperature of the coal sample and the processing atmosphere at the time of processing the coal sample is not particularly limited, but can be appropriately set in a temperature range of 350 ° C. or less, for example. In the conventional method, the measurement temperature is limited in such a relatively low temperature region, but in the method for evaluating the oxidation characteristics of coal according to the present embodiment, there is no such limitation. The processing temperature can be appropriately set according to the target condition.

  The temperature of the coal sample and the treatment atmosphere during the treatment of the coal sample is preferably from 25 (room temperature) ° C. to 140 ° C., more preferably from the viewpoint of improving the rate of the oxidation reaction and avoiding oxygen shortage in the system. It is 40 degreeC or more and 100 degrees C or less. Note that during the processing of the coal sample, the temperature of the coal sample and the processing atmosphere may be changed over time. Moreover, the temperature of a coal sample and process atmosphere is the same normally at the time of the process of a coal sample. Therefore, only one of the temperatures may be measured.

  The treatment time of the coal sample is not particularly limited, but may be, for example, 1 hour to 168 hours, preferably 24 hours to 72 hours.

As described above, the coal sample can be oxidized in an atmosphere containing ¹⁷ O ₂ gas. In addition, although the processing conditions of a coal sample are not specifically limited, It is possible to select the above-mentioned conditions suitably, It is preferable to make it the same about the several coal sample used as a comparison object.

(1.3. Spectrum acquisition process)
Next, nuclear magnetic resonance ( ¹⁷ O NMR) spectral analysis is performed on the oxidized coal sample to obtain a ¹⁷ O nuclear magnetic resonance spectral spectrum (hereinafter also simply referred to as “ ¹⁷ O NMR spectrum”). Since the coal sample is a solid sample, the analysis performed in this step is usually solid nuclear magnetic resonance spectroscopy. In this step, based on a conventionally known method, a solid nuclear magnetic resonance spectroscopic analysis is performed on a coal sample, and a ¹⁷ O nuclear magnetic resonance spectroscopic spectrum having a chemical shift as a horizontal axis and a signal intensity as a vertical axis can be obtained. .

(1.4. Evaluation process)
Finally, the oxidation characteristics of the coal sample are evaluated based on the peak area of the ¹⁷ O nuclear magnetic resonance spectroscopy spectrum.

In this step, first, the peak area of the ¹⁷ O nuclear magnetic resonance spectrum is calculated by integrating the peak intensities. As described above, the peaks of the ¹⁷ O nuclear magnetic resonance spectrum detected from the coal sample are almost entirely derived from ¹⁷ O-containing functional groups generated by the reaction of the ¹⁷ O ₂ gas with the coal sample in the oxidation step. Conceivable. Therefore, in this step, the area may be calculated for an arbitrary peak in the measured range.

For example, in this step, the area may be calculated for an arbitrary peak in all measured ranges. Alternatively, the area may be calculated for a peak in which the chemical shift of the ¹⁷ O nucleus in the ¹⁷ O nuclear magnetic resonance spectroscopy spectrum has an apex in a specific range. For example, according to the study by the present inventors, the peak having a peak near 0 ppm of the obtained ¹⁷ O NMR spectrum is derived from the chemical shift of the ¹⁷ O nucleus of a hydroxyl group (—OH group), and has a peak near 300 ppm. It is presumed that the peak having is derived from the chemical shift of the ¹⁷ O nucleus of the carboxy group (—COOH group). Therefore, the area may be calculated for a peak having a peak in the vicinity of 0 ppm, that is, −100 ppm to 80 ppm, and / or a peak having a peak in the vicinity of 300 ppm, that is, 200 ppm to 400 ppm.

  In particular, when the heat of reaction is estimated from the reaction mechanism for generating oxygen-containing functional groups due to the oxidation of coal, it can be said that the generation reaction of carboxyl groups accounts for the majority of the calorific value and is the dominant reaction of the spontaneous exothermic phenomenon. For this reason, it is preferable to calculate an area about the peak which has a peak in 200 ppm or more and 400 ppm or less estimated to originate in a carboxy group (-COOH group). Moreover, in the Example mentioned later, it was suggested that it is appropriate to evaluate an oxidation characteristic based on the area of the same peak.

In addition, detection of a peak in a ¹⁷ O NMR spectrum and separation of the peak can be performed by a conventionally known method. The peak detection / separation method is preferably the same for a plurality of coal samples to be compared.

Subsequently, the oxidation characteristics of the coal sample are evaluated based on the calculated peak area of the coal sample. In addition, since the peak area of the calculated coal sample increases in proportion to the amount of the coal sample subjected to ¹⁷ O NMR spectroscopy, the comparison is performed after the amount of the coal sample, for example, the mass is subtracted from the peak area.

  The oxidation characteristics of the coal sample can be evaluated, for example, on the assumption that the peak area has a positive correlation with the oxidation characteristics of the coal sample. That is, when the peak area is large, it is estimated that the coal sample is more oxidized in the oxidation step. For this reason, when a peak area is large, it can be evaluated that a coal sample and by extension, coal which is a raw material of a coal sample are easily oxidized.

  The coal oxidation characteristics evaluation method according to the present embodiment has been described above. According to the method for evaluating oxidation characteristics of coal according to this embodiment, unlike the conventional method, there is no limitation on the measurement temperature in the low temperature range. Therefore, it is possible to evaluate the oxidation characteristics of coal in an arbitrary temperature range. In addition, since the conventional method has a limit on the measurement temperature, it is difficult to evaluate the oxidation characteristics of coal under different temperature conditions including a temperature outside the limit. On the other hand, the oxidation characteristic evaluation method for coal according to the present embodiment can evaluate the oxidation characteristic by the same method for different temperature conditions. For this reason, it contributes to the elucidation of the phenomenon generation and reaction mechanism about the spontaneous heat generation and spontaneous ignition of coal.

  Moreover, compared with the conventional method which evaluates the oxidation characteristic of coal after removing water | moisture content, the flexible condition setting is possible for the evaluation method of the oxidation characteristic of coal which concerns on this embodiment. Specifically, the method for evaluating oxidation characteristics of coal according to the present embodiment can evaluate the oxidation characteristics including the influence of moisture in the coal. In this case, the oxidation characteristics of the obtained coal can be an important index in examining the coal storage environment.

<2. Second Embodiment>
Next, an oxidation characteristic evaluation method according to the second embodiment of the present invention will be described. Moisture adjustment step of adjusting the moisture of the coal sample according to the present embodiment to a predetermined amount, an oxidation step of oxidizing the coal sample in an atmosphere containing ¹⁷ O ₂ gas, and nuclear magnetic resonance spectroscopy for the oxidized coal sample analyzed, obtaining ^{17 O} nuclear magnetic resonance spectrum, the spectrum acquisition step, based on the area of the peak of the ^{17 O} nuclear magnetic resonance in the spectrum, the oxidation properties of the coal sample containing the predetermined amount of water An evaluation step.

  That is, the oxidation characteristic evaluation method according to the present embodiment further includes a moisture adjustment step of adjusting the moisture of the coal sample to a predetermined amount, and evaluates the oxidation property of the coal sample containing the predetermined amount of moisture in the evaluation step. This is different from the oxidation characteristic evaluation method according to the first embodiment. Hereinafter, differences between the first embodiment and the present embodiment will be mainly described, and description of similar matters will be omitted.

  In the moisture adjustment step, the moisture of the coal sample is adjusted to a predetermined amount, that is, a target amount. As described above, in the present embodiment, the water content in the coal sample is dared to be adjusted, and the oxidation characteristics of the coal sample at a predetermined water content are evaluated. This is different from the first embodiment in which evaluation is performed in a state where moisture is completely removed.

  The water content of the coal sample can be adjusted by, for example, adding water to the coal sample and mixing it, or removing water from the coal sample, or adding predetermined water after completely removing water from the coal sample. This can be done by mixing.

  When adding water to a coal sample and mixing, well-known equipment for mixing, such as a mortar, a stirrer (mixer), and a kneader, can be used, for example. In addition, as the removal of water, water may be evaporated by heating, decompression or the like, or a centrifuge or a spray dryer may be used. After the removal of water, water addition, stirring, kneading, or the like may be performed in order to adjust the moisture content or improve the uniformity of the moisture content in the coal sample.

  The amount of water contained in the coal sample after moisture content adjustment is not particularly limited, and can be, for example, 100% by mass or less, 50% by mass or less, or 30% by mass or less based on the dry weight of the coal sample. .

In this step, one or more coal samples whose water content is adjusted to a predetermined amount may be prepared, and a plurality of samples may be prepared. In this case, by preparing a plurality of coal samples having the same conditions except for the water content, it becomes easy to grasp the influence of the water content on the oxidation characteristics. In addition, when preparing a plurality of coal samples, you may prepare the coal sample which does not contain water, ie, a moisture content is 0 mass%.
In addition, the coal sample before adjustment of a moisture content can be prepared similarly to 1st Embodiment mentioned above.

  Next, as in the first embodiment, an oxidation process and a spectrum acquisition process are performed. Since these are the same as those in the first embodiment, description thereof will be omitted.

  Finally, in the evaluation step, the oxidation characteristics of the coal sample containing a predetermined amount of moisture are evaluated. The calculation of the peak area and the evaluation of the oxidation characteristics in this step can be the same as in the first embodiment described above.

  In this embodiment, it is possible to evaluate the oxidation characteristics of a coal sample containing a known amount of moisture. Therefore, it is possible to evaluate the influence of moisture contained in the coal sample. Specifically, by comparing with the oxidation characteristics of a dried coal sample or a coal sample having a different moisture content, it is possible to evaluate a change in the oxidation characteristics associated with moisture fluctuations in the coal sample. It is considered that the oxidation characteristics evaluated in this way can be used, for example, to determine an appropriate amount of water for suppressing spontaneous ignition in the preservation and storage of coal.

  Hereinafter, the method for evaluating the oxidation characteristics of coal according to the present invention will be specifically described with reference to examples. In addition, the Example shown below is an example of the oxidation characteristic evaluation method of the coal which concerns on this invention to the last, Comprising: This invention is not limited to the following example.

<Example 1>
Coals A to D shown in Table 1 below were prepared, and the oxidation characteristics (pyrophoric properties) of each of the coals A to D were evaluated. Coal A is a low calorific value coal (brown coal), coal B is a high calorific value coal (brown coal), coal C is lignite, and coal D is bituminous coal. Moreover, the elemental analysis values of coals A to D are as shown in Table 1 below. Elemental analysis was performed based on JIS M 8812: 2004.

  Coals A to D were prepared in an amount of 500 mg each. Moreover, as coal A-D, the water | moisture content was removed by drying the thing in the range whose particle size is 150-250 micrometers in 80 degreeC and 12 hours in the pressure-reduced atmosphere of 10 hPa or less, and prepared.

[Oxidation process]
Using a glass container having an internal volume of 16 mL, coals A to D were filled, respectively. Furthermore, the space in the glass container was replaced with ¹⁷ O ₂ gas ( ¹⁷ O ₂ content: 94% by volume), and the glass container was sealed. Thereafter, the glass container was placed in an oven to raise the ambient temperature from room temperature to 40 ° C. and allowed to stand for 6 days.

[Spectrum acquisition step: ¹⁷ O NMR measurement]
Next, ¹⁷ O NMR measurement was performed on the coals A to D after the oxidation treatment. ^For the measurement of ¹⁷ O NMR, JNM-ECA700 (manufactured by JEOL RESONANCE Inc.) was used. A silicon nitride sample tube (4 mmφ) was filled with each of the coals A to D after the above-described oxidation treatment, and the amount of filling was measured in advance. The measurement was performed using an Oldfield Echo sequence to reduce ringing and rotating at 18 kHz with a magic angle. FIG. 1 shows the obtained ¹⁷ O NMR spectrum.

  As shown in FIG. 1, in coal A and B, two different peaks were observed around 300 ppm and around 0 ppm, respectively. In Coal C, a peak around 0 ppm was observed, and the peak intensity around 300 ppm was slight. In Coal D, the peak intensity around 0 ppm was slight, and the peak around 300 ppm was hardly observed. Since the peak near 300 ppm is derived from a carboxy group, and the peak near 0 ppm is estimated to be derived from a hydroxyl group, the above-described oxidation treatment produces a carboxy group and a hydroxyl group in coals A and B, and a hydroxyl group in coal C. It is thought that it was mainly produced and almost no oxygen-containing functional groups were produced in coal D.

[Evaluation process]
Next, the peak area was calculated from the obtained ¹⁷ O NMR spectrum. The peak area is calculated by (1) the peak area having a peak near 300 ppm, (2) the peak area having a peak near 0 ppm, and (3) the area of all peaks in the measurement range (the peak near 300 ppm). The sum of the area of the peak having the peak and the area of the peak having the apex in the vicinity of 0 ppm was calculated. In the case of (1), the peak area is integrated for the range of 80 to 1000 ppm, in the case of (2), the peak is integrated for the range of -400 to 80 ppm, and in the case of (3), the range of -400 to 1000 ppm Peak accumulation was performed for. The results are shown in FIGS.

  In addition, as a reference index for examining the validity of the method of the present invention, the time required for coal A to D to reach 200 ° C. using the spontaneous combustion test apparatus SIT-2 (Shimadzu Corporation). Was measured and the natural heat generation properties of coals A to D were evaluated.

(1) Area of peak having apex around 300 ppm FIG. 2 shows the area of the peak having apex around 300 ppm for coals A to D. FIG. It was suggested that the peak areas were larger in the order of coals A, B, C, and D, and that oxidation was easy in this order, that is, oxidation characteristics were large.

Next, for coals A to D, the peak area having a peak near 300 ppm calculated in the present example was compared with the spontaneous heat generation evaluation by a spontaneous ignition test apparatus (SIT). The results are shown in Table 2. In Table 2, the peak area is a value obtained by dividing the above-described peak area near 300 ppm by the weight of the sample used for ¹⁷ O NMR measurement.

As shown in Table 2, it can be seen that the peak area around 300 ppm in the ¹⁷ O NMR spectra of coals A to D is roughly correlated with the time required to reach 200 ° C. by SIT as a reference example. . This result also suggests that the peak area has a positive correlation with the oxidation characteristics of coal.

That ^is, the larger the peak area in the vicinity of 300ppm of 17 O NMR spectrum, short time required to reach 200 ° ^C., the smaller the peak area in the vicinity of 300ppm of 17 O NMR spectra were taken to reach 200 ° C. You can see that the time is long. Therefore, it can be seen that the larger the peak area near 300 ppm in the ¹⁷ O NMR spectrum, the greater the oxidation characteristics, that is, the higher the spontaneous exothermicity. The smaller the peak area near 300 ppm in the ¹⁷ O NMR spectrum, the smaller the oxidation characteristics. That is, it turns out that spontaneous exothermic property is low.

(2) Area of peak having apex near 0 ppm FIG. 3 shows areas of peaks having apexes near 0 ppm for coals A to D. FIG. When comparing the areas of peaks having apexes near 0 ppm, the peak areas are larger in the order of coal B, A, C, and D. Therefore, the results did not agree with the spontaneous exothermic evaluation obtained as a reference example. On the other hand, it was found that the larger the peak area having a peak near 0 ppm, the easier it is to oxidize, that is, the greater the tendency of oxidation characteristics.

(3) Areas of all peaks in the measurement range FIG. 4 shows the areas of all peaks in the measurement range for coals A to D. When the areas of all peaks in the measurement range are compared, the peak areas are larger in the order of coals B, A, C, and D. Therefore, the results did not agree with the spontaneous exothermic evaluation obtained as a reference example. On the other hand, it was found that the larger the peak area having a peak near 0 ppm, the easier it is to oxidize, that is, the greater the tendency of oxidation characteristics.

<Example 2>
Each 500 mg of coals A to D were prepared, and the particle size was in the range of 150 to 250 μm. The above-mentioned glass containers were filled with coals A to D, respectively, and filled with ¹⁷ O ₂ gas, whereby the atmosphere gas of coals A to D was changed to ¹⁷ O ₂ gas. In this state, the ambient temperature was raised from room temperature to 100 ° C., and left to stand for 6 days. The ¹⁷ O NMR measurement of coal and the evaluation of oxidation characteristics were the same as described above. FIG. 5 shows the obtained ¹⁷ O NMR spectrum.

FIG. 6 shows values obtained by dividing the peak area near 300 ppm by the mass of the sample used for measurement in the obtained ¹⁷ O NMR spectrum. As shown in FIG. 6, the peak area in the vicinity of 300 ppm in the ¹⁷ O NMR spectrum was found to be larger in the order of coals A, B, C, and D. This result is the same as that in the case of the oxidation treatment at 40 ° C. in Example 1, and the usefulness of this method could be confirmed regardless of the oxidation temperature.

FIG. 7 shows values obtained by dividing the areas of all peaks in the measurement range by the sample mass used for measurement in the obtained ¹⁷ O NMR spectrum. As shown in FIG. 7, the areas of all peaks in the measurement range in the ¹⁷ O NMR spectrum were found to be larger in the order of coal B, A, C, and D. This result was the same as in Example 1 when the oxidation treatment was performed at 40 ° C.

<Example 3>
Using a sample obtained by adding and kneading 10% by mass of water to coal A to D shown in Example 1 (dry mass of coal A to D) and a sample obtained by adding and kneading 20% by mass of water to coal A, Similarly, oxidation treatment of coal (at 40 ° C. for 6 days) and ¹⁷ O NMR measurement of coal were performed.
FIG. 8 shows the peak area per unit mass of 300 ppm in the ¹⁷ O NMR spectrum together with that of each dry coal.

  From this result, it was found that, for example, when any of coals A to D is contained at a moisture content of 10% by mass with respect to the dry state, the oxidizability is lowered. Further, it was found that the oxidation characteristics of coal A and coal B, which have high spontaneous heat generation, are reduced to about 80%. Moreover, even if it increased the moisture content from 10 mass% to 20 mass% about coal A, the fall of the oxidation characteristic was not seen.

  The above knowledge is considered to be useful, for example, in determining an appropriate amount of water for suppressing spontaneous ignition in the preservation and storage of coal. For example, it can be seen that coal A needs to be added at a ratio of 10 to 20% by mass in order to suppress the spontaneous exothermicity to the same level or less as that of dry coal B.

The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

Claims (6)

An oxidation step of oxidizing the coal sample in an atmosphere containing ¹⁷ O ₂ gas;
Performing a nuclear magnetic resonance spectroscopic analysis on the coal sample after oxidation to obtain a ¹⁷ O nuclear magnetic resonance spectroscopic spectrum;
An evaluation step of evaluating the oxidation characteristics of the coal sample based on the area of the peak in the ¹⁷ O nuclear magnetic resonance spectroscopy spectrum;
Method for evaluating oxidation characteristics of coal having In the evaluation step, a chemical shift of ¹⁷ O nuclei in the ¹⁷ O nuclear magnetic resonance spectroscopy spectrum is based on the area of the peak having an apex in the range of −100 ppm to 80 ppm and / or 200 ppm to 400 ppm. The method for evaluating oxidation characteristics of coal according to claim 1, wherein the oxidation characteristics of the sample are evaluated. In the evaluation step, the oxidation characteristic of the previous coal sample is evaluated based on the area of the peak having a peak in the range where the chemical shift of ¹⁷ O nuclei in the ¹⁷ O nuclear magnetic resonance spectroscopy spectrum is 200 ppm or more and 400 ppm or less. The method for evaluating oxidation characteristics of coal according to claim 1.   The coal according to any one of claims 1 to 3, wherein in the evaluation step, the oxidation characteristics of the coal sample are evaluated on the assumption that the area of the peak has a positive correlation with the oxidation characteristics of the coal. Evaluation method of oxidation characteristics.   In the said oxidation process, the temperature of the said coal sample and the said atmosphere is 350 degrees C or less, The oxidation characteristic evaluation method of the coal as described in any one of Claims 1-4. Furthermore, it is performed before the oxidation step, and has a moisture adjustment step of adjusting the moisture of the coal sample to a predetermined amount,
The method for evaluating oxidation characteristics of coal according to any one of claims 1 to 5, wherein, in the evaluation step, the oxidation characteristics of the coal sample containing the predetermined amount of the moisture are evaluated.

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