A method for determining coal spontaneous combustion tendency based on oxygen consumption rate integral

Abstract

This invention discloses a method for determining the spontaneous combustion tendency of coal based on the oxygen consumption rate integral. A new spontaneous combustion characteristic parameter, the oxygen consumption rate integral, is proposed. This integral comprehensively reflects the spontaneous combustion characteristics of coal during the latency period and the influence of low oxygen concentration (0-20.96%) on coal spontaneous combustion. A new coal spontaneous combustion tendency index, the aerobic rate integral, is proposed. The magnitude of the oxygen consumption rate integral can intuitively reflect the spontaneous combustion tendency of coal, thus quantifying it. The larger the oxygen consumption rate integral, the stronger the spontaneous combustion tendency of the coal.

Description

Technical Field

[0001] This invention relates to the field of prevention and control technology for spontaneous combustion of coal, and in particular to a method for determining the tendency of spontaneous combustion of coal based on the integral of oxygen consumption rate. Background Technology

[0002] For centuries, humanity has struggled against spontaneous combustion of coal, and the search for methods to differentiate its tendency to spontaneously combust has never ceased. In China, chromatographic oxygen uptake is used as a national standard to identify the tendency of coal to spontaneously combust. This method uses the amount of physical oxygen absorbed by 1g of dry coal at 30℃ and 101325Pa as an indicator. However, this method cannot reflect the amount of oxygen produced by chemical adsorption and chemical reaction, which plays a decisive role in spontaneous combustion. Therefore, it has been questioned by many scholars. Most other major coal-producing countries in the world differentiate the tendency of coal to spontaneously combust by studying the effect of coal-oxygen chemical reaction. The main method used is the oxidation experimental furnace method, in which coal samples are placed in the experimental furnace and oxygen is introduced. Parameters of the exothermic process of coal oxidation reaction (R70 index, SHT index, IRH, TTR, and CPT method) are measured using adiabatic, guided heating, or programmed heating methods. In addition, the oxygen consumption rate in this process is usually used as an important parameter of coal spontaneous combustion characteristics. This flow reactor oxygen consumption rate method is obtained by measuring the oxygen concentration at the inlet and outlet of the coal sample container. The macroscopic reason for spontaneous combustion of coal is that the heat generated by the reaction between coal and oxygen is greater than the heat dissipated; the calorific value of coal is directly proportional to the oxygen consumption. Therefore, the oxygen consumption rate is often used to distinguish the spontaneous combustion tendency of coal.

[0003] In fact, the spontaneous combustion process of coal involves three stages: the latency period (≤70℃), the self-heating period, and the combustion period. During the latency period, the reaction is slow, and heat gradually accumulates within the coal. During the self-heating period, the coal temperature rises rapidly. Then, spontaneous combustion becomes uncontrollable. Clearly, the spontaneous combustion characteristics of coal during the latency period best reflect its tendency to spontaneously combust. However, the cross-point temperature method cannot adequately reflect the spontaneous combustion characteristics of coal during the latency period due to excessively high temperatures. During the crucial latency period of coal spontaneous combustion, the experimental accuracy of methods such as the flow reactor oxygen consumption rate method and thermal analysis is difficult to guarantee. The R70 index is designed for the latency period, but it has drawbacks such as susceptibility to moisture and experimental equipment effects, long experimental cycles, and the risk of experimental failure. Furthermore, the R70 index cannot reflect the spontaneous combustion characteristics of coal at low oxygen concentrations (0-20%, 96%). Coal spontaneous combustion mainly occurs in goaf areas with oxygen concentrations ranging from 0-20% to 96%. Based on oxygen concentration, the goaf is divided into a "heat dissipation zone (15-20%, 96%)", an "oxidation zone (5-15%)", and a "suffocation zone (0-5%)". Oxygen concentration has a significant impact on coal spontaneous combustion. Although the tendency of coal to spontaneously combust is an inherent property of coal itself and is independent of the external environment, the oxidation characteristics of coal under different oxygen concentrations are an inherent property of coal. Currently, the reaction rate of coal with oxygen is usually assumed to be directly proportional to the oxygen concentration. However, the rationality and accuracy of assuming that the coal-oxygen reaction satisfies the first-order Arrhenius equation have been questioned. The low-temperature oxidation reaction of coal is characterized by multiple pathways and stages. It is clearly unreasonable to treat such a complex coal-oxygen reaction process as an elementary reaction.

[0004] Therefore, the determination of coal spontaneous combustion tendency should fully consider two key factors: the spontaneous combustion characteristics during the incubation period and the influence of low oxygen concentration (0-20%, 96%) on coal spontaneous combustion. A method for determining coal spontaneous combustion tendency based on the integral of oxygen consumption rate is proposed. Summary of the Invention

[0005] To address the technical problems existing in the background art, this invention proposes a method for determining the spontaneous combustion tendency of coal based on the integral of oxygen consumption rate.

[0006] The present invention proposes a method for determining the spontaneous combustion tendency of coal based on the integral of oxygen consumption rate, comprising the following steps:

[0007] S1: The coal sample was crushed in a ball mill under nitrogen protection;

[0008] S2: Place the coal sample in the coal sample container and replace the gas in the system with nitrogen;

[0009] S3: Removes the original adsorbed gas from the coal sample;

[0010] S4: Under nitrogen atmosphere, the coal sample is heated to 70°C, and after vacuuming, a nitrogen-oxygen mixture with an oxygen concentration of C1 is introduced using a soap film flow meter. The value of C1 is between 19.5% and 23.5%.

[0011] S5: Conduct an isothermal gas circulation closed oxidation experiment under the air pump;

[0012] S6: Based on the experimental results, obtain the change of oxygen concentration over time, and substitute the experimental results of the change of oxygen concentration over time into the following formula to calculate the change of oxygen consumption rate over time:

[0013]

[0014] In the formula: R is the oxygen consumption rate, with the unit being mol / (kg·s);

[0015] C represents the oxygen concentration;

[0016] V m The value is the molar volume of the gas, taken as 22.4 L / mol;

[0017] m represents the mass of the coal, in kg.

[0018] t represents time, measured in seconds (s).

[0019] V is the volume of gas inside the reaction apparatus, in L;

[0020] S7: By fitting the functional relationship between oxygen consumption rate and oxygen concentration, the empirical formula is obtained: R = AC 2 +BC, where A and B are coefficients;

[0021] S8: Integrating the empirical formula yields the oxygen consumption rate integral (OCRI):

[0022]

[0023] In the formula: R -1 (0) is the oxygen concentration when the oxygen consumption rate is 0, and C1 is the oxygen concentration of the mixed gas introduced in step S4.

[0024] The larger the integral of the oxygen consumption rate, the stronger the spontaneous combustion tendency of coal.

[0025] This invention proposes a new index for coal spontaneous combustion tendency based on the integral of oxygen consumption rate. The magnitude of the integral of oxygen consumption rate can intuitively reflect the spontaneous combustion tendency of coal. The spontaneous combustion tendency of coal can be quantified. The larger the integral of oxygen consumption rate, the stronger the spontaneous combustion tendency of coal.

[0026] Specifically, the particle size of the coal sample is 0.12-0.38 mm after being crushed by the crusher.

[0027] Preferably, the original adsorbed gas in the coal sample is removed by vacuum desorption.

[0028] Preferably, the coal sample is dried after being crushed by the crusher before being placed into the coal sample container.

[0029] Preferably, the coal sample drying process is as follows: the coal sample is vacuum dried at 40℃ for 24 hours.

[0030] Preferably, C1 is set to 20.96%.

[0031] This invention proposes a method for determining the spontaneous combustion tendency of coal based on the integral of oxygen consumption rate. The spontaneous combustion tendency index of this invention comprehensively reflects the spontaneous combustion characteristics of coal during the latency period and the influence of low oxygen concentration (0-C1) on coal spontaneous combustion. It not only solves the problem of insufficient experimental accuracy in the traditional flow reactor oxygen consumption rate method, but also considers the influence of low oxygen concentration (0-C1) on coal spontaneous combustion, without simply assuming that the reaction between coal and oxygen follows the first-order Arrhenius equation. The integral of oxygen consumption rate can more reasonably and accurately reflect the ease or difficulty of coal spontaneous combustion.

[0032] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the device structure used in this invention;

[0034] Figure 2 This is a graph showing the change of oxygen concentration over time in an embodiment of the present invention;

[0035] Figure 3 This is a graph formed by fitting the functional relationship between oxygen consumption rate and oxygen concentration in an embodiment of the present invention;

[0036] Figure 4 This is an integral graph showing the oxygen consumption rate of different coal types in an embodiment of the present invention.

[0037] In the diagram: 1. First valve; 2. Second valve; 3. Third valve; 4. Fourth valve; 5. Fifth valve; 6. Sixth valve; 7. Seventh valve; 8. Experimental gas cylinder; 9. Nitrogen cylinder; 10. Soap film flow meter; 11. Air pump; 12. Flow meter; 13. Oil bath; 14. Temperature sensor; 15. Pressure sensor; 16. Heat transfer oil; 17. Heating copper wire; 18. Drain outlet; 19. Coal sample container; 20. Vacuum pump; 21. Condenser; 22. Water collector; 23. Oxygen sensor. Detailed Implementation

[0038] Embodiments of the present invention are described in detail below. Examples of these embodiments are illustrated in the accompanying drawings, wherein the same or similar symbols denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0039] like Figure 1 The experimental apparatus used in the method of this invention is a coal spontaneous combustion tendency determination device based on the integral of oxygen consumption rate (this device has been published in "ScienceDirect" in "Study on oxidation kinetics of low-rank coal during the spontaneous combustion"). The device, disclosed in "Study on Oxidation Kinetics of Spontaneous Combustion Latency in Low-Rank Coal," includes an oil bath 13 containing heat-conducting oil 16 and heating copper wire 17. The oil bath 13 has a drain outlet 18 and a coal sample container 19 placed within it. Temperature sensors 14 and pressure sensors 15 are also included to detect the temperature and pressure of the coal sample container 19. The device also includes an experimental gas cylinder 8 and a nitrogen cylinder 9. The experimental gas cylinder 8 has an eighth valve, and the nitrogen cylinder 9 has a ninth valve. The experimental gas cylinder 8 is connected to a soap film flow meter 12 via a pipeline, and a seventh valve 7 is located on the pipeline connecting the experimental gas cylinder 8 and the soap film flow meter 12. The soap film flow meter 12 and the nitrogen cylinder 9 are connected to a gas pump 11 via a main pipeline, and a first valve 1 is located on the main pipeline. The gas pump 11 discharges gas... The end is connected to the coal sample tank 19 through a pipeline, and the pipeline connecting the air pump 11 to the coal sample tank 19 is equipped with a flow meter 12 and a second valve 2. A vacuum pump 20 is also provided. The vacuum pump 20 is connected to a three-way pipe through a pipeline. A third valve 3 is provided on the pipeline connecting the three-way pipe to the vacuum pump 20. One end of the three-way pipe is directly connected to the coal sample tank 19, and the other end of the three-way pipe is connected to a condenser 21 through a fourth valve 4. The condenser 21 is connected to a discharge pipe. The discharge pipe is connected to the main pipeline through a pipeline, and the position where the discharge pipe is connected to the main pipeline is between the first valve 1 and the air pump 11. A sixth valve 6 is provided on the pipeline connecting the discharge pipe to the main pipeline. A fifth valve 5 is provided on the discharge pipe. The fifth valve 5 is far away from the condenser 21 relative to the pipeline connecting the discharge pipe to the main pipeline. An oxygen sensor 23 and a water collector 22 are provided on the discharge pipe.

[0040] It should be noted that the nitrogen cylinder contains nitrogen (99.999%), while the experimental gas cylinder 8 contains a 20.96% oxygen-nitrogen mixture, meaning that the experimental gas cylinder contains a mixture of nitrogen and oxygen, with oxygen accounting for 20.96%.

[0041] Coal Sample Preparation: Fresh coal samples obtained by the mining team were immediately sealed in vacuum bags. After removing the outer layer, the coal samples were crushed in a planetary ball mill under inert gas (nitrogen). The particle size range of the coal samples was 0.12-0.38 mm, and the mass was 270 g. The coal samples were vacuum dried at 40℃ for 24 h. The processed coal samples were used as experimental coal; six types of coal samples were used, ranging from lignite to anthracite. The coal samples were lignite from Baorixile Coal Mine in Inner Mongolia, long-flame coal from Selian Coal Mine, non-caking coal from Yangchangwan Coal Mine in Ningxia, lean coal from Ezhuang Coal Mine in Shandong, and coking coal from Xinhu Coal Mine and anthracite from Hengyuan Coal Mine in Anhui. They were labeled as BR, SL, YC, EZ, XH, and HY, respectively.

[0042] The industrial and elemental analyses of the coal samples are shown in Table 1:

[0043] Table 1

[0044]

[0045]

[0046] Place the coal sample into the coal sample container 19, close the third valve 3, the sixth valve 6 and the seventh valve 7, open the first valve 1, the second valve 2, the fourth valve 4 and the fifth valve 5, and immediately introduce 99.999% nitrogen gas until the oxygen volume fraction is 0;

[0047] To check the airtightness of coal sample container 19, connect the third valve 3 to the U-shaped water column gauge, open the first valve 1, the second valve 2, the third valve 3, the fourth valve 4 and the sixth valve 6, and close the fifth valve 5 and the seventh valve 7. Introduce nitrogen gas through valve 1 to create a pressure difference in the U-shaped water column gauge. If there is no significant change in the pressure difference after closing valve 1 for 30 minutes, the airtightness is good.

[0048] After confirming that the coal sample container 19 is airtight, the original adsorbed gas in the coal sample is removed by vacuum desorption at 30℃. Specifically, the second valve 2 and the fourth valve 4 are closed, the third valve 3 is opened, and vacuum pump 20 is used for desorption for 4 hours.

[0049] Under nitrogen atmosphere, the coal sample was heated to 70°C. Valve 1 (first valve), 5 (fifth valve), and 7 (seventh valve) were closed, while the remaining valves were opened and a vacuum was created. A flow rate of 15-20 cm³ was then introduced using a soap film flow meter. 3 The nitrogen-oxygen mixture in experimental gas bottle 8.

[0050] Close valves 1, 3, 5, and 7, and open valves 2, 4, and 6. Conduct an isothermal gas circulation closed oxidation experiment under the influence of gas pump 11. The experiment terminates when the oxygen concentration reaches 0 or the reaction time is 24 hours.

[0051] The change in oxygen concentration over time was obtained based on the experimental results. For example... Figure 2 As shown.

[0052] Substitute the experimental results of oxygen concentration changes over time into the following formula to calculate the change in oxygen consumption rate over time;

[0053]

[0054] In the formula: R is the oxygen consumption rate, with the unit being mol / (kg·s);

[0055] C represents the oxygen concentration, in percent.

[0056] V m The value is the molar volume of the gas, taken as 22.4 L / mol;

[0057] m is the mass of the coal, which is taken as 0.27 kg;

[0058] t represents time, measured in seconds (s).

[0059] V is the volume of the gas inside the reaction apparatus, which is taken as 1.52L.

[0060] By fitting the functional relationship between oxygen consumption rate and oxygen concentration, the empirical formula is obtained: R = AC 2 +BC (A and B are coefficients). For example... Figure 3 The fitting relationship is shown in Table 2.

[0061] Table 2

[0062]

[0063] Integrating the empirical formula yields a new parameter for coal spontaneous combustion characteristics: the integral of oxygen consumption rate (OCRI).

[0064] In the formula: R -1 (0) represents the oxygen concentration when the oxygen consumption rate is 0.

[0065] The physical meaning of the oxygen consumption rate integral is the sum of oxygen consumption rates under different oxygen concentrations, expressed as mol / (kg·s). The oxygen consumption rate integrals for different coal types are shown below. Figure 4 The area of ​​the shaded region is shown.

[0066] The classification of coal spontaneous combustion tendency levels based on oxygen consumption rate integral, as determined by experiments, is shown in Table 3:

[0067] Table 3

[0068]

[0069] Table 4 shows the results of the chromatographic oxygen absorption method and the actual ignition situation in the coal mine.

[0070] Table 4

[0071]

[0072] As is well known, coal spontaneous combustion begins at room temperature. After a long latency period, the coal temperature rises rapidly. Subsequently, spontaneous combustion becomes uncontrollable, resulting in a fire. The oxygen consumption rate of coal during the latency period effectively reflects its oxidation characteristics. Furthermore, coal spontaneous combustion occurs in goaf areas with low oxygen concentrations (0-20.96%). The integral of the oxygen consumption rate can effectively reflect both the latent spontaneous combustion characteristics and the impact of low oxygen concentrations (0-20.96%) on coal spontaneous combustion. Compared to chromatographic oxygen absorption, the integral of the oxygen consumption rate provides a more reasonable and accurate assessment of the risk of coal spontaneous combustion. According to chromatographic oxygen absorption, both XH and YC coals belong to Class I easily spontaneously combustible coals. However, the ignition period of XH coal is 2.78 times that of YC, as shown in Table 4. Meanwhile, the integral of the oxygen consumption rate of YC coal is 71.23 times that of XH coal. Clearly, it is unreasonable to classify the spontaneous combustion tendency of these two coals into the same category. Chromatographic oxygen uptake uses multiple indicators to determine the spontaneous combustion tendency of coal. Therefore, the amount of oxygen absorbed physically does not reflect the spontaneous combustion tendency of coal. BR, SL, and YC coals all have a spontaneous combustion tendency level of I. However, the oxygen consumption rate integral of YC coal is 5.75 times that of BR coal. YC coal has a stronger spontaneous combustion tendency. More stringent measures to prevent coal spontaneous combustion should be implemented.

[0073] The magnitude of the coal spontaneous combustion tendency index in this invention can intuitively reflect the spontaneous combustion tendency of coal. The larger the oxygen consumption rate integral, the stronger the spontaneous combustion tendency of coal.

[0074] The coal spontaneous combustion tendency index of this invention comprehensively reflects the spontaneous combustion characteristics of coal during the incubation period and the influence of low oxygen concentration (0-20.96%) on coal spontaneous combustion. It not only solves the problem of insufficient experimental accuracy in the traditional flow reactor oxygen consumption rate method, but also considers the impact of low oxygen concentration (0-20.96%) on coal spontaneous combustion, without simply assuming that the reaction between coal and oxygen follows the first-order Arrhenius equation. The integral of the oxygen consumption rate can more reasonably and accurately reflect the ease or difficulty of coal spontaneous combustion.

[0075] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for determining the spontaneous combustion tendency of coal based on the integral of the oxygen consumption rate, characterized in that, The method comprises the following steps: S1: crushing the coal sample by a ball mill under nitrogen protection; S2: placing the coal sample in a coal sample tank and replacing the gas in the system with nitrogen; S3: removing the original adsorbed gas of the coal sample; S4: The coal sample is raised to 70°C under nitrogen, vacuumed and then oxygen is introduced at a concentration of 19.5% to 23.5% using a soap film flowmeter. C 1 C 1 S5: performing isothermal gas circulation closed oxidation experiment under a gas pump; S6: obtaining the change of oxygen concentration with time according to the experimental results, and substituting the experimental results of the change of oxygen concentration with time into the following formula to calculate the change of oxygen consumption rate with time: ； wherein: R is the oxygen consumption rate in mol / (kg-s). C Oxygen concentration; V m Molar volume of the gas, taken as 22.4 L / mol; m Qcoal is the quality of the coal, in kg; t t is time, in s; V V is the volume of the gas in the reaction device, in L; S7: The function relationship between oxygen consumption rate and oxygen concentration is fitted to obtain an empirical formula: , wherein A and B are coefficients. S8: The integral of the oxygen consumption rate is obtained by integrating the empirical equation OCRI : ； In the formula: C0is the oxygen concentration at which the oxygen consumption rate is 0; C 1 is the oxygen concentration of the mixed gas introduced in step S4; The greater the integral of the oxygen consumption rate, the stronger the spontaneous combustion tendency of the coal.

2. The coal spontaneous combustion propensity determination method based on oxygen consumption rate integration according to claim 1, characterized by, The particle size of the coal sample crushed by the crusher is 0.12-0.38 mm.

3. The coal spontaneous combustion liability determination method based on the oxygen consumption rate integration according to claim 1, characterized in that, The original adsorbed gas of the coal sample is removed by a vacuum desorption method.

4. The coal spontaneous combustion liability determination method based on the oxygen consumption rate integration according to claim 1, characterized in that, The coal sample crushed by the crusher is dried before being placed into the coal sample tank.

5. The coal spontaneous combustion propensity determination method based on the integral of the oxygen consumption rate according to claim 4, characterized by, The drying process of the coal sample is: vacuum drying the coal sample at 40°C for 24h.

6. The coal spontaneous combustion liability determination method based on oxygen consumption rate integration according to claim 1, characterized in that, C 1Value is 20.96%.

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