Coal spontaneous combustion grading early warning determination method based on characteristic gas and structure content

Abstract

The invention provides a coal spontaneous combustion grading early warning determination method based on characteristic gas and structure content, which comprises the following steps of: selecting temperature, symbolic gas and content of coal functional groups as indexes of coal spontaneous combustion grading early warning; the coal spontaneous combustion slow oxidation process is divided into six stages, namely a coal spontaneous combustion oxidation stage, a coal spontaneous combustion self-heating stage, a coal spontaneous combustion critical stage, a coal spontaneous combustion pyrolysis stage, a coal spontaneous combustion fission stage and a coal spontaneous combustion combustion stage, and the six stages correspond to gray early warning, blue early warning, yellow early warning, orange early warning, red early warning and black early warning in sequence. The concentration of O2, CO2, CO, C2H4 and C2H2 is collected through a gas sensor, the temperature of a goaf is collected through a temperature sensing probe, the type and metamorphism degree of coal are recognized through an intelligent camera, and data are transmitted to a ground monitoring computer in real time to be analyzed, judged and processed. The method is more refined and accurate, the timeliness, accuracy and reliability of coal spontaneous combustion danger early warning can be effectively improved, the using effect is good, and application and popularization are convenient.

Description

Technical Field

[0001] This invention relates to the field of coal mine safety early warning technology, specifically to a method for determining the classification and early warning of coal spontaneous combustion based on the content of characteristic gases and structures. Background Technology

[0002] Spontaneous combustion of coal leads to a large waste of resources and produces toxic and harmful gases, threatening the lives of underground workers. Furthermore, the high temperature and heat environment generated by spontaneous combustion of coal is one of the main factors that induce gas explosions, complicating the disaster and ultimately causing serious economic losses and casualties.

[0003] Temperature and gaseous products are key indicators for early warning of coal spontaneous combustion, and they have played a good role in practical applications. However, some problems exist. Early warning methods using CO, C2H4, and C2H2 as marker gases have a large temperature range, making it difficult to meet the development needs of precise early warning for coal spontaneous combustion. Furthermore, since a single gas is used as an indicator to monitor the oxidation and heating state of coal samples, it is easily affected by the external environment, especially since it does not consider the relationship between the degree of spontaneous combustion and oxygen concentration, lacking a comprehensive analysis of coal spontaneous combustion. Summary of the Invention

[0004] To address the aforementioned technical shortcomings, the purpose of this invention is to provide a method for classifying and predicting coal spontaneous combustion based on the content of characteristic gases and structures, thereby enabling accurate early prediction and proactive prevention of coal seam spontaneous combustion and preventing the occurrence of coal seam spontaneous combustion or secondary disasters.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for classifying and early warning of spontaneous combustion of coal based on the content of characteristic gases and structures includes the following steps:

[0007] S1. Temperature, marker gases, and the content of coal functional groups are selected as indicators for the classification and early warning of coal spontaneous combustion. The slow oxidation process of coal spontaneous combustion is divided into seven stages: latent stage, chain initiation stage, chemical oxygen uptake stage, critical temperature rise stage, olefin formation stage, cracking stage, and combustion stage. Each stage corresponds to a specific temperature range and indicator characteristics.

[0008] S2. The latent stage of coal spontaneous combustion corresponds to a white warning, the chain initiation stage corresponds to a gray warning, the chemical oxygen absorption stage corresponds to a blue warning, the critical temperature rise stage corresponds to a yellow warning, the olefin formation stage corresponds to an orange warning, the cracking stage corresponds to a red warning, and the combustion stage corresponds to a black warning.

[0009] S3. The concentrations of O2, CO2, CO, C2H4, and C2H2 are collected by gas sensors, the temperature sensing probe collects the temperature of the goaf, and the intelligent camera identifies the type of coal and its degree of metamorphism. The data is then transmitted in real time to the ground monitoring computer for analysis, judgment, and processing.

[0010] Preferably, in step S1, the temperature range and index characteristics of each stage are as follows:

[0011] Latent stage: T<30℃, coal and oxygen mainly react through physical adsorption with little exothermic reaction;

[0012] Chain initiation stage: T < 40℃, ΔCO% / [C=O] > ΔCO2% / [COOH], side chains are activated and oxygen-containing groups produce gas for the first time;

[0013] Chemical oxygen uptake stage: T<85℃, ΔCO% / [C=O]<ΔCO2% / [COOH], aldehyde group is oxidized to carboxyl group and the first maximum value of Graham coefficients R2 and R3 appears at 80-90℃;

[0014] Critical temperature rise stage: T < 105℃, ΔCO% > ΔCO2%, oxygen molecules react with carboxyl groups on the side chain of benzene ring to form a chain cycle;

[0015] Olefin formation stage: T < 155℃, C2H4 > 0 exists, and the side chain of aliphatic hydrocarbons breaks;

[0016] During the cracking stage: when T < 210℃, the C2H4 / C2H6 ratio reaches its maximum and ΔC2H4% > ΔC2H6%, leading to an intensified coal-oxygen complex reaction.

[0017] Combustion stage: T>210℃, C2H2>0 exists, and the stage is divided by the initial appearance temperature of C2H2.

[0018] Preferably, the concentration data of O2, CO2, CO, C2H4 and C2H2 collected by the gas sensor in step S3 need to be transmitted in real time, the temperature data of the goaf collected by the temperature sensing probe also need to be transmitted in real time, and the information on coal type and metamorphism degree identified by the smart camera also needs to be transmitted to the ground monitoring computer in real time.

[0019] Preferably, the Graham coefficient R2 is ΔCO / ΔO2, which is the ratio between the increase in CO concentration and the decrease in O2, and the Graham coefficient R3 is ΔCO / ΔCO2, which is the ratio between the increase in CO concentration and the increase in CO2 concentration.

[0020] Preferably, ΔCO2% / [COOH] is the ratio between the percentage increment of CO2 and the molar amount of the oxygen-containing functional group carboxyl COOH, ΔCO% / [C=O] is the ratio between the percentage increment of CO and the molar amount of the oxygen-containing functional group carbonyl C=O, [C=O] is quantitatively determined by the peak area method using an infrared spectrometer, and [COOH] is the content of COOH in the coal sample.

[0021] Preferably, when the ground monitoring computer analyzes and judges:

[0022] First, judge whether it exists. If M0 does not exist, no alarm is issued. If M0 exists, enter the next-level judgment.

[0023] Preferably, after M0 exists, enter the next-level judgment:

[0024] Judge whether it exists. If M0 exists and M1 does not exist, it is the normal state and no alarm is issued. If M1 exists, enter the next-level judgment.

[0025] Preferably, after M1 exists, enter the next-level judgment:

[0026] Judge whether M2={(ΔCO% / [C=O]) / (ΔCO2% / [COOH])<1}∩{0.36~0.41<R3<1.2} exists. If M1 exists and M2 does not exist, a gray alarm is issued. If M2 exists, enter the next-level judgment.

[0027] Preferably, after M2 exists, enter the next-level judgment:

[0028] Judge whether M3={0.49<(ΔCO% / ΔCO2%)<1} exists. If M2 exists and M3 does not exist, a blue alarm is issued. If M3 exists, enter the next-level judgment.

[0029] Preferably, after M3 exists, successively conduct the judgment. When M3 exists and M4 does not exist, a yellow alarm is issued. When M4 exists and M5 does not exist, an orange alarm is issued. When M5 exists and M6 does not exist, a red alarm is issued. When M6 exists, a black alarm is issued, where is the oxygen consumption, is the gas concentration content, ΔCO% is the percentage increment of CO concentration, and ΔCO% / ΔCO2% is the ratio of the percentage increments of CO and CO2.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] (1) This invention uses multiple early warning methods such as the ratio of active functional groups to gaseous products, marker gases, and auxiliary indicators to conduct graded early warning, which effectively overcomes the shortcomings of the existing technologies that only use the indicator gas analysis method and the temperature method.

[0032] (2) Based on the reaction characteristics of the initial stage of coal spontaneous combustion, this invention comprehensively considers the increase in gaseous products and the changes in the precursor structure of coal, studies the ratio of the increase in gaseous products to functional groups at different temperature stages, and uses new graded early warning indicators and methods to solve the problem that the graded early warning of gas indicators is easily affected by the environment, and increases the comprehensive analysis of the influence of coal self-desorption and desorption.

[0033] (3) Based on the traditional three early warning stages of coal spontaneous combustion, this invention further refines the classification of each interval, overcomes the problem of the large temperature range of the early warning method for coal spontaneous combustion, and further refines the early warning stages of coal spontaneous combustion.

[0034] (4) This invention takes into account the relationship between the degree of spontaneous combustion of coal and oxygen concentration, thereby improving the accuracy of coal spontaneous combustion early warning.

[0035] (5) The early warning classification method of the present invention is more refined and accurate, which can effectively improve the timeliness, accuracy and reliability of early warning of coal spontaneous combustion danger. It has good use effect and is easy to promote and use. Attached Figure Description

[0036] Figure 1 The oxygen consumption curves for four coal samples are shown in this invention.

[0037] Figure 2 The figures show the CO variation curves of four coal samples as a function of temperature according to the present invention.

[0038] Figure 3 The figures show the CO2 variation curves of four coal samples as a function of temperature according to the present invention.

[0039] Figure 4 The curves showing the change of ΔCO as a function of temperature for four coal samples according to the present invention are shown.

[0040] Figure 5 This is a graph showing the generation and variation of CXHY from northern lignite, as described in this invention.

[0041] Figure 6 This is a graph showing the generation and variation of Yima long-flame coal CXHY according to the present invention.

[0042] Figure 7 This is a graph showing the generation and variation of Jiaxiang gas coal CXHY according to the present invention.

[0043] Figure 8 This is a graph showing the generation and variation of the new bridge anthracite CXHY according to the present invention.

[0044] Figure 9 This is a comparison chart showing the variation of the Graham coefficient R2 (ΔCO / ΔO2) of various coal samples in this invention with temperature.

[0045] Figure 10 This is a comparison graph showing the variation of the Graham coefficient R3 (ΔCO / ΔCO2) with temperature for four coal samples of this invention.

[0046] Figure 11 The bar chart shows the functional group content of four coal samples according to the present invention.

[0047] Figure 12 This is a spline diagram showing the percentage increase ratio of CO to CO2 in this invention;

[0048] Figure 13 This is a spline diagram showing the changes in ΔCO2% / carboxyl group / ΔCO% / carbonyl group as a function of temperature for four coal samples according to the present invention;

[0049] Figure 14 The curve showing the relationship between the Graham coefficient R2 and coal temperature at the Baiguan Gou 2506 working face;

[0050] Figure 15 The curve showing the relationship between the Graham coefficient R3 and coal temperature at the Baiguan Gou 2506 working face is shown. Detailed Implementation

[0051] The present invention will be further described in detail below with reference to specific embodiments.

[0052] In the following examples, four coal samples with different metamorphic degrees from different coal-forming periods in major coal-forming areas of my country were selected as experimental materials: Shandong Beizao Mine (BZ), Henan Yima Mine (YM), Shandong Jiaxiang Mine (JX), and Henan Xinqiao Mine (XQ).

[0053] A method for determining the classification and early warning of spontaneous combustion of coal, comprising the following steps:

[0054] 1. Determination of early warning indicators for spontaneous combustion of coal

[0055] (1) Remove the oxidized surface layer of each coal sample, then take the central part of the coal sample and crush it. After crushing, carefully sieve out the coal powder with a particle size range of 40 to 80 mesh. Place the sieved coal sample under vacuum drying at 40°C for 48 hours to completely remove external moisture.

[0056] (2) Weigh 50g of coal sample using an electronic balance, put all the weighed sample into the coal sample reaction vessel, and lay a thin layer of asbestos at the mouth of the coal sample reaction vessel to prevent the pipeline from being blocked.

[0057] Air was introduced into the coal sample reaction vessel at a flow rate of 50 mL / min. The system was set to programmed temperature rise mode with a heating rate of 0.1 °C / min. Data collection began when the system temperature stabilized at 40 °C. Oxygen consumption data and other gaseous product data were collected every 10 °C. Data collection was stopped at 190 °C, and the data was exported.

[0058] (3) Currently, the commonly used indicators of coal spontaneous combustion gases are mainly divided into oxidizing gases and pyrolysis gases. Oxidizing gases are mainly CO and CO2, both of which are related to coal oxygen complexation and coal temperature; pyrolysis gases include CH4, C2H6, C3H8, C2H4 and C2H2. The ratio of gas products is greatly affected by the original gases (CO2, CH4, C2H6 and C3H8, etc.) in coal. Therefore, through experimental detection and screening, CO was determined as the indicator gas, and C2H4 and C2H2 were determined as auxiliary indicator gases.

[0059] Determine the oxygen consumption change curves of coal samples from Shandong Beizao Mine, Henan Yima Mine, Shandong Jiaxiang Mine, and Henan Xinqiao Mine obtained in step (2) during the heating process, as follows: Figure 1 As shown; determine the CO variation curves of four coal samples with temperature, as follows. Figure 2 As shown; determine the CO2 variation curves of four coal samples with temperature, as follows. Figure 3 As shown; determine the ΔCO variation curves of four coal samples with temperature, as follows. Figure 4 As shown; the variation curves of hydrocarbon gaseous products (CH4, C2H6, C3H8, C2H4) for the four coal samples were determined respectively, as shown in the figure. Figure 5 , Figure 6 , Figure 7 , Figure 8 As shown.

[0060] (4) By Figure 2 , Figure 3 , Figure 5 , Figure 6 , Figure 7 , Figure 8 It can be seen that among the gaseous products generated by the combination of coal samples and oxygen, CO is produced in the largest quantity at temperatures between 50℃ and 70℃, with a CO production exceeding 1.21 ppm / g. However, due to differences in the metamorphic degree of the coal samples, the amount and rate of production also vary. Besides CH4, C2H6, and C3H8, the temperatures at which C2H4 and C2H2 were detected were relatively high, suggesting that CO can be used as an indicator gas for the slow oxidation stage.

[0061] Apart from Xinqiao anthracite, the temperatures at which C2H4 was detected were all relatively high, ranging from 110℃ to 120℃, with the temperature of rapid increase being approximately 140℃ to 150℃. These temperatures showed a distinct interval and can be used as auxiliary marker gases for the rapid oxidation stage.

[0062] The absence of C2H2 at temperatures between 30℃ and 190℃ indicates that its occurrence temperature is above 190℃. The presence of C2H2 indicates that the coal has undergone a violent chemical reaction, and due to its special properties, it serves as an auxiliary marker gas for the violent oxidation stage.

[0063] Based on the initial temperatures at which CO, C2H4, and C2H2 appear, coal spontaneous combustion is divided into three major warning stages: slow oxidation (CO-C2H4), rapid oxidation (C2H4-C2H2), and violent oxidation (after C2H2 is produced).

[0064] (5) A single gas is easily affected by environmental factors such as wind flow, so other composite indicators, namely the Graham coefficient, are used as auxiliary indicators.

[0065] Calculate the Graham coefficients for the four coal samples based on the oxygen consumption and gaseous product data obtained in steps (1) and (2). Determine the value of R²(ΔCO / ΔO₂), which is the ratio of the increase in CO concentration to the decrease in O₂ concentration. Figure 9 As shown; R3(ΔCO / ΔCO2), that is, the increase in CO2 concentration compared to the increase in CO concentration, as... Figure 10 As shown. Observation Figure 9 , Figure 10 It was found that the curves of R2 and R3 both showed their first maximum value at around 90℃.

[0066] In the slow oxidation stage of coal spontaneous combustion in step (4), the critical stage of coal spontaneous combustion is determined, with a temperature of 70-90℃, and R2 and R3 reach their first maximum values.

[0067] In the slow oxidation stage of coal spontaneous combustion in step (4), the coal spontaneous combustion pyrolysis stage is determined, with a temperature of 90-120℃, and C2H4 gas appears.

[0068] (6) Based on the temperature change curves of the four coal samples measured in step (1), it can be seen that except for anthracite, the other coal samples all have a significant maximum value of CO increase at around 160℃.

[0069] In the rapid oxidation stage of coal spontaneous combustion in step (4), the coal spontaneous combustion fission stage is determined, with a temperature of 120-160℃, where a significant maximum value of CO increment appears.

[0070] In the intense oxidation stage of coal spontaneous combustion in step (4), the coal spontaneous combustion stage is determined to be at a temperature greater than 190°C. At this time, not only does a large amount of C2H2 appear, but the coal also rises to a higher temperature range.

[0071] (7) Start the Fourier transform infrared spectrometer. After the preheating is complete, set the parameters as shown in Table 1.

[0072] Table 1 Spectrometer Parameter Settings

[0073]

[0074]

[0075] Next, fill the in-situ reaction cell with KBr powder and collect KBr background basis vectors. After the collection is completed, pour out the powder and clean the in-situ reaction cell. Take the prepared coal powder that is stored for later use, grind it carefully with an agate grinding mortar, fill the in-situ reaction cell with the ground coal powder, level the reaction cell, and cover it with the pre-prepared KBr window.

[0076] (8) Open the pure oxygen cylinder and introduce pure oxygen into the in-situ reaction tank, setting the flow rate to 10 mL / min; start the temperature control device and set the temperature rise rate to 1℃ / min. In order to avoid overheating and damage to the in-situ reaction tank, the water cooling system also needs to be started; observe and wait for the temperature of the experimental sample to rise to 30℃, and collect data according to the set time interval to obtain the infrared spectrum data of the coal sample during the heating process.

[0077] (9) The infrared spectral data obtained in step (5) are analyzed and processed. The content of major functional groups in four different coal samples—Shandong Beizao Mine, Henan Yima Mine, Shandong Jiaxiang Mine, and Henan Xinqiao Mine—can be obtained using the peak area method. A columnar content chart is plotted as follows. Figure 11 As shown.

[0078] During the oxidation reaction between coal and oxygen, the generated CO mainly comes from the C=O group, while the generated CO2 mainly comes from the COOH group. Further processing of the experimental data resulted in spline plots of the percentage increase ratios of CO and CO2 and spline plots of ΔCO2% / carboxyl group / ΔCO% / carbonyl group as a function of temperature. (See...) Figure 12 , Figure 13 .

[0079] (10) Analysis Figure 12 It can be seen that, in the temperature range of 55–90℃, the percentage increase of CO is less than the percentage increase of CO2, while in the high-temperature range, the percentage increase of CO is greater than the percentage increase of CO2; in the temperature ranges of 55–80℃ and 95–110℃, the percentage increase of CO is less than the percentage increase of CO2, while in other temperatures, the percentage increase of CO is greater than the percentage increase of CO2; in the temperature ranges of 70–85℃, 155–165℃ and 175–185℃, the percentage increase of CO is less than the percentage increase of CO2; and in the temperature range of 165–180℃, the percentage increase of CO is less than the percentage increase of CO2.

[0080] The above observations show that below 50℃, the ΔCO2% / ΔCO% ratio of all four coal samples is less than 1, indicating that the percentage increase in CO is greater than the percentage increase in CO2 for all four coal samples. However, as the temperature rises, in the 50–110℃ range, the percentage increase in CO2 for lower-rank coals with lower metamorphic grades, such as Beizao lignite and Yima long-flame coal, begins to exceed the percentage increase in CO. When the temperature rises to the 110–150℃ range, all four coal samples again uniformly show a greater percentage increase in CO than in CO2. Above 150℃, however, higher-rank coals, such as Jiaxiang gas coal and Xinqiao anthracite, exhibit a greater percentage increase in CO2 than in CO. This demonstrates that the value of this ratio being greater than 1 gradually increases with coal rank.

[0081] (11) Corrected based on the group ratio coefficient Figure 13 The data shows that, except for the abnormally low value at 90℃, after 50℃, the ΔCO2% / carboxyl group ratio in the coal samples from Beizao, Yima, and Jiaxiang is greater than the ΔCO% / carbonyl group ratio. This means that, after functional group coefficient correction, the percentage increase in CO2 after 50℃ is greater than the percentage increase in CO. This can be used as a standard for stage division.

[0082] In the slow oxidation stage of coal spontaneous combustion in step (4), the temperature is determined to be less than 50°C, and ΔCO2% / carboxyl group is greater than ΔCO% / carbonyl group.

[0083] In the slow oxidation stage of coal spontaneous combustion in step (4), the coal spontaneous combustion and self-heating stage is determined to be at a temperature of 50-70℃, and the amount of CO produced is the highest, with a concentration greater than 1.21ppm / g.

[0084] (12) Based on the characteristic temperature and other indicators of coal sample producing specific hydrocarbon gases, the temperature and characteristic point of CO gas increment, the ratio of coal sample functional groups to gas product increment as the dividing standard, and the Graham coefficients R2 and R3, the coal spontaneous combustion process in the temperature range of this experiment is divided into six stages. The specific division is shown in Table 2.

[0085] Table 2. Classification of Coal Spontaneous Combustion Status and Early Warning Levels Based on Indicator Status

[0086]

[0087] 2. Field application of No. 5 coal seam in Baiguangou 2506 working face

[0088] (1) Overview: Baiguangou Coal Mine is located in Chongxin County, Gansu Province. The mine is a single-level inclined shaft development, divided into four mining areas. The minefield is 6.3km long, 1.7km wide, and covers an area of ​​7.5707km², with a total resource volume of 7624.0km² and a designed production capacity of 0.60Mt / a. Basic parameters of the 2506 working face: The 2506 working face is the second tunneling working face arranged in the second mining area of ​​Baiguangou Coal Mine. Currently, 2506 is in the early stage of mining, and the working face is 18 meters away from the opening.

[0089] (2) Real-time monitoring and analysis of the No. 5 coal seam in the Baiguangou 2506 working face was conducted using an underground coal spontaneous combustion early warning platform. Multiple environmental data acquisition devices were placed in the No. 5 coal seam of the Baiguangou 2506 working face to collect underground environmental data in real time. The environmental data acquisition devices uploaded the underground environmental data to the surface via wired or wireless communication. The environmental data acquisition devices included oxygen concentration acquisition devices, carbon monoxide concentration acquisition devices, carbon dioxide concentration acquisition devices, acetylene concentration acquisition devices, ethylene concentration acquisition devices, propane concentration acquisition devices, ethane concentration acquisition devices, methane concentration acquisition devices, and temperature acquisition devices.

[0090] (3) Dynamic monitoring and early warning of temperature and coal spontaneous combustion indicator gas concentrations are conducted, i.e., real-time monitoring of temperature change rate and coal spontaneous combustion indicator gas concentrations and their change rates, which serve as reference values ​​for determining the degree of coal spontaneous combustion hazard. Based on the indicator gas measurement results of the Baiguan Gou No. 5 coal seam, the indicator gases mainly include CO, CO2, CH4, C2H2, and C2H4. As the working face advances, the indicator gas concentrations and ambient temperatures of the No. 5 coal seam in April are shown in Table 3.

[0091] Table 3. Index gas concentrations and ambient temperatures in the No. 5 coal seam of the Baiguan Gou 2506 working face.

[0092]

[0093] (4) Analysis of the environmental data test results from the Baiguangou 2506 working face revealed that no acetylene gas was detected in the data collected in April, and the working face temperature was far below 190℃. It should be noted that no ethylene gas was also detected, and the temperature was below 120℃. These phenomena indicate that the coal temperature had not reached the pyrolysis temperature. The normal concentrations of acetylene and ethylene are both 0 ppm, confirming that the Baiguangou 2506 working face had not reached the stage of spontaneous combustion pyrolysis of the coal.

[0094] (5) The Graham coefficient is calculated according to the formula. After substituting the changes in CO and O2 content into the formula, the change characteristics of R2 with temperature increase in different periods of coal seam can be calculated. After substituting the changes in CO and CO2 content into the formula, the change characteristics of R3 with temperature increase in different periods of coal seam can be calculated.

[0095] (6) The relationship curve between the Graham coefficient R2 of the working face and the coal temperature is as follows: Figure 14 As shown in the curves for early and mid-April, R² decreases significantly with rising temperature, and after reaching a certain temperature, the ratio tends to increase rapidly without reaching a maximum value. The curve for late April shows that R² gradually decreases with rising temperature, and when it reaches the maximum temperature of 82℃, it shows an upward trend, indicating that R² did not reach a maximum value in April.

[0096] The relationship curve between the working face Graham coefficient R3 and coal temperature is as follows: Figure 15 As shown in the curves from early April, R3 first increases and then decreases with rising temperature, reaching a maximum value. However, since only R3 reaches a maximum value, and R2 does not, and the maximum value corresponds to a temperature of around 60℃, which is less than 70℃, it does not meet the judgment criteria. From the curves from mid-April and late April, it can be seen that R3 decreases significantly with rising temperature, reaches a minimum value, and then rises again, without reaching a maximum value. Based on the maximum values ​​of the Graham coefficients R2 and R3, it can be determined that the Baiguan Gou 2506 working face did not reach the critical stage for coal spontaneous combustion during the monitoring phase.

[0097] (7) The production of hydrocarbon gases is much smaller than that of CO and CO2. Methane gas appears earlier, while C3H8 and C2H6 begin to appear at 50℃. Ethylene and acetylene gases appear in relatively high temperature ranges, roughly between 140 and 150℃. Based on the actual field conditions, and through the collection and analysis of observation data, a comprehensive analysis of various characteristics during normal mining is presented. Table 4 shows a comparison of the gas parameters of the goaf in normal mining.

[0098] Table 4 Comparison of Indicator Gas Parameters in Goaf Areas During Normal Mining

[0099]

[0100] Table 4 confirms that CO was present in April, indicating the start of coal oxidation. The average CO concentration in early April was 2.68 ppm, and the average CH4 concentration was 2.305 ppm; in mid-April, the average CO concentration was 3.61 ppm, and the average CH4 concentration was 2.278 ppm; in late April, the average CO concentration was 4.92 ppm, and the average CH4 concentration was 2.317 ppm. C2H6 and C3H8 were present in very small quantities because these alkane gas components desorb one by one according to their carbon atom sequence (i.e., their boiling points increase from low to high) as the coal temperature rises. CO production was the highest compared to alkane gas production, with the working face ambient temperature generally between 50℃ and 70℃. The average temperature in April was 74℃, higher than 70℃, because as the working face advanced, the quality of residual coal increased, air leakage channels increased, the rate of coal spontaneous combustion and oxidation accelerated, the temperature inside the goaf increased, and the production of various gases increased.

[0101] (8) According to the spontaneous combustion characterization parameters of the coal spontaneous combustion experiment: when the temperature is 50-70℃ and the CO production is the highest, with a concentration greater than 1.21 ppm / g, it is determined to be the coal spontaneous combustion and self-heating stage. Comparing with the field observation data, the ambient temperature of the working face is roughly between 50℃ and 70℃, and the CO production is the highest compared to the alkane gas production, with a CO concentration greater than 1.21 ppm / g. It can be determined that the Baiguangou 2506 working face has a self-heating reaction in the low-temperature stage, but no spontaneous combustion phenomenon has occurred, and it is in the coal spontaneous combustion pyrolysis stage.

Claims

1. A method for classifying and early warning of spontaneous combustion of coal based on the content of characteristic gases and structures, characterized in that, Includes the following steps: S1. Temperature, marker gases, and the content of coal functional groups are selected as indicators for the classification and early warning of coal spontaneous combustion. The slow oxidation process of coal spontaneous combustion is divided into seven stages: latent stage, chain initiation stage, chemical oxygen uptake stage, critical temperature rise stage, olefin formation stage, cracking stage, and combustion stage. Each stage corresponds to a specific temperature range and indicator characteristics. S2. The latent stage of coal spontaneous combustion corresponds to a white warning, the chain initiation stage corresponds to a gray warning, the chemical oxygen absorption stage corresponds to a blue warning, the critical temperature rise stage corresponds to a yellow warning, the olefin formation stage corresponds to an orange warning, the cracking stage corresponds to a red warning, and the combustion stage corresponds to a black warning. S3. The concentrations of O2, CO2, CO, C2H4, and C2H2 are collected by gas sensors, the temperature sensing probe collects the temperature of the goaf, and the intelligent camera identifies the type of coal and its degree of metamorphism. The data is then transmitted in real time to the ground monitoring computer for analysis, judgment, and processing.

2. The method for determining the classification and early warning of coal spontaneous combustion based on the content of characteristic gases and structures as described in claim 1, characterized in that, In step S1, the temperature range and index characteristics of each stage are as follows: Latent stage: T<30℃, coal and oxygen mainly react through physical adsorption with little exothermic reaction; Chain initiation stage: T < 40℃, ΔCO% / [C=O] > ΔCO2% / [COOH], side chains are activated and oxygen-containing groups produce gas for the first time; Chemical oxygen uptake stage: T<85℃, ΔCO% / [C=O]<ΔCO2% / [COOH], aldehyde group is oxidized to carboxyl group and the first maximum value of Graham coefficients R2 and R3 appears at 80-90℃; Critical temperature rise stage: T < 105℃, ΔCO% > ΔCO2%, oxygen molecules react with carboxyl groups on the side chain of benzene ring to form a chain cycle; Olefin formation stage: T < 155℃, C2H4 > 0 exists, and the side chain of aliphatic hydrocarbons breaks; During the cracking stage: when T < 210℃, the C2H4 / C2H6 ratio reaches its maximum and ΔC2H4% > ΔC2H6%, leading to an intensified coal-oxygen complex reaction. Combustion stage: T>210℃, C2H2>0 exists, and the stage is divided by the initial appearance temperature of C2H2.

3. The method for determining the classification and early warning of coal spontaneous combustion based on the content of characteristic gases and structures as described in claim 1, characterized in that, In step S3, the concentration data of O2, CO2, CO, C2H4, and C2H2 collected by the gas sensor need to be transmitted in real time. The temperature data of the goaf collected by the temperature sensing probe also need to be transmitted in real time. The information on coal type and metamorphism degree identified by the smart camera also needs to be transmitted to the ground monitoring computer in real time.

4. The method for determining the classification and early warning of coal spontaneous combustion based on the content of characteristic gases and structures as described in claim 2, characterized in that, The Graham coefficient R2 is ΔCO / ΔO2, which is the ratio between the increase in CO concentration and the decrease in O2 concentration. The Graham coefficient R3 is ΔCO / ΔCO2, which is the ratio between the increase in CO concentration and the increase in CO2 concentration.

5. The method for classifying and early warning of coal spontaneous combustion based on the content of characteristic gases and structures as described in claim 2, characterized in that, ΔCO2% / [COOH] is the ratio between the percentage increase of CO2 and the molar amount of COOH in the oxygen-containing functional group carboxyl group; ΔCO% / [C=O] is the ratio between the percentage increase of CO and the molar amount of C=O in the oxygen-containing functional group carbonyl group; [C=O] is quantitatively determined by the peak area method using an infrared spectrometer; and [COOH] is the COOH content in the coal sample.

6. The method for determining the classification and early warning of coal spontaneous combustion based on the content of characteristic gases and structures as described in claim 1, characterized in that, When the ground monitoring computer analyzes and judges: First, determine If M0 does not exist, no alarm will be issued; if M0 exists, proceed to the next level of judgment.

7. The method for determining the classification and early warning of coal spontaneous combustion based on the content of characteristic gases and structures as described in claim 6, characterized in that, If M0 exists, proceed to the next level of judgment: judge If M0 exists but M1 does not, then it is the normalization phase and no alarm is issued. If M1 exists, proceed to the next level of judgment.

8. The method for determining the classification and early warning of spontaneous combustion of coal based on the content of characteristic gases and structures as described in claim 7, characterized in that, If M1 exists, proceed to the next level of judgment: Determine whether M2 = {(ΔCO% / [C=O]) / (ΔCO2% / [COOH]) < 1} ∩ {0.36~0.41 < R3 < 1.2} exists. If M1 exists but M2 does not, a gray alert is issued. If M2 exists, proceed to the next level of judgment.

9. The method for determining the classification and early warning of coal spontaneous combustion based on the content of characteristic gases and structures as described in claim 8, characterized in that, After M2 exists, proceed to the next level of judgment: Determine whether M3 = {0.49 < (ΔCO% / ΔCO2%) < 1} exists. If M2 exists but M3 does not, a blue alert is issued. If M3 exists, proceed to the next level of judgment.

10. The method for determining the classification and early warning of coal spontaneous combustion based on the content of characteristic gases and structures as described in claim 9, characterized in that, After M3 exists, proceed sequentially. The system determines the presence and absence of M4, issuing a yellow alert when M3 exists and M4 does not, an orange alert when M4 exists and M5 does not, a red alert when M5 exists and M6 does not, and a black alert when M6 exists. This refers to oxygen consumption. ΔCO% represents the gas concentration content, ΔCO% is the percentage increase in CO concentration, and ΔCO% / ΔCO2% is the ratio of the percentage increases in CO and CO2.

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