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Copyright of Journal of Mine Automation is the property of Industry & Mine Automation Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to further study the influence of associated sulfur minerals on spontaneous combustion and ignition characteristics of coal, four coal samples with different sulfur contents were prepared by adding different sulfur minerals to raw coal, and through Thermogravimetric Analysis (TG) experiment, Differential Scanning Calorimeter (DSC) test and X-ray diffraction (XRD) analysis, the influence of associated sulfur minerals on spontaneous combustion and ignition characteristics of coal was studied. Experimental results show that with the increase of associated sulfur minerals, the characteristic temperature of coal decreases, while the oxygen absorption, flammability and incombustibility stability index increase gradually, indicating that the coal is more prone to spontaneous combustion after being mixed with the associated sulfur minerals. Based on Coats–Redfern method to calculate the activation energy of coal during combustion stage with different associated sulfur minerals in coal, the calculation shows that the activation energy of coal combustion stage decreases with the increase of the associated sulfur minerals in coal and makes it easily to burn. Through the XRD and DSC analysis of associated sulfur minerals, it is found that the main components of the associated sulfur minerals are melanterite and copiapite, which can react with water and oxygen at room temperature, and the exothermic reaction makes coal more prone to spontaneous combustion. The associated sulfur minerals are exothermic after 200°C and reach an exothermic peak at 565°C, which makes the activation energy of coal in combustion stage decrease and coal easily to burn. [ABSTRACT FROM AUTHOR]

The thermal decomposition of oxygen-containing functional groups produces CO, CO 2 and active sites that accelerate coal spontaneous combustion. Study on this process is of great significance for research on the mechanism of coal spontaneous combustion. In this paper, research was made on the dependency relationship between gas production and time under the condition of different coal samples, particle sizes and pyrolysis temperatures. Results reveal that the time-dependent generation rate of active sites follows an exponential compound function P = A + B e - t/ K 1 + C e - t/ K 2 during isothermal pyrolysis of coal. Besides, infrared spectrum experiments were also carried out to study changes in oxygen-containing functional groups of raw coal, pyrolyzed coal and room temperature oxidized coal after pyrolysis. The results prove that when coal reaches a certain temperature, oxygen-containing functional groups will adsorb heat and undergo decomposition to produce active sites and a few gas products. Then, active sites are oxidized, generating oxygen-containing functional groups and releasing both massive heat and gas products. Therefore, the whole reaction is a continuous cyclic process where combined effects of the two reactions cause rapid accumulation of heat, which triggers uncontrollable coal spontaneous combustion. The results from this research will be helpful to inhibit the occurrence of coal spontaneous combustion by reducing the generation and oxidation of active sites. • The isothermal pyrolysis experiments of coal samples were carried out. • Isothermal thermal decomposition of oxygen-containing functional groups was studied. • The law of CO and CO 2 gas generation during isothermal pyrolysis was obtained. • The generation law of active sites during isothermal pyrolysis was revealed. [ABSTRACT FROM AUTHOR]

Spontaneous combustion of oxidized coal occurs frequently in mining and utilization process, which is influenced by the first oxidation conditions significantly. With a focus on the influence of pre-oxidation temperature on spontaneous combustibility of oxidized coal, oxidized coal samples were prepared by heating at preset temperature of 50 °C, 70 °C, 90 °C, 110 °C and 130 °C. Programmed heating tests on oxidized coal and raw coal samples were carried out in air atmosphere of 120 mL min−1, with the heating rate of 0.3 °C min−1. The gaseous mixture of O2, CO and CO2 at the outlet was identified by gas chromatography to analyze oxidizability and exothermicity of experimental coal samples. The results showed that, with the increasing pre-oxidation temperature, the oxidizability and exothermicity of oxidized coals decreased first and increased later, which were related with change of oxygen consumption rate, emission rate of CO and CO2 gas. The spontaneous combustibility order by pre-oxidation temperatures was 130 °C, raw, 50 °C, 110 °C, 90 °C and 70 °C. Being oxidized at 130 °C could promote coal to self-heat, and being oxidized below 110 °C would inhibit coal self-heating. [ABSTRACT FROM AUTHOR]

Variations of gas products and reaction characteristics of main functional groups during low-temperature oxidation of coals with different metamorphic degrees were analyzed based on the gas chromatographic analysis of gas products and the FTIR determination of oxidized coal samples. Meanwhile, changes in the microcrystalline structure parameters during the low-temperature oxidation were determined with the aid of the XRD technology. Since gas product contents of coal with different metamorphic degrees grow continuously with the rise of oxidation temperature, a forecast system that adopted CO and C 2 H 4 as indicator gases in the low-temperature oxidation process was established. The content of CH 3 / CH 2 , the primary participant in the oxidation reaction, gradually falls with the rise of oxidation temperature. During the low-temperature oxidation of coal, the stacking height L c , ductility L a , stacking layer N and graphitization degree P of aromatic layers all increase with the rise of oxidation temperature. Finally, the critical temperature ranges (80–110 °C for RL coal, 110–140 °C for YL coal and 130–170 °C for WY coal) for drastic changes during low-temperature oxidation were proposed by comparatively analyzing the variation laws of gas products, main reaction functional groups and aromatic layers, as well as the corresponding temperature variations. [ABSTRACT FROM AUTHOR]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The gas and coal spontaneous combustion coexisting disasters have become a common mode of major and extraordinarily serious accident of coal mine, so it has important significance to predict the coexistence disaster for prevention and treatment. This study took the gas samples from gas drainage pipeline in the goaf of 1203 working face of Hongyang No. 2 Coal Mine, and then analyzed the chaotic characteristics of coal gas indexes from gas drainage pipeline by using the R/S analysis method. The results show that the Hurst index of time series of gas indicators related to coal spontaneous combustion shows stable statistical characteristics when the oxygen concentration fluctuates smoothly. However, when the oxidation of coal in goaf accelerates, the Hurst index will be smaller than 0.77025. The Hurst index of time series of gas indicators related to gas in the goaf of 1203 working face is greater than 0.5, which indicates that gas has persistent correlation. The Hurst index can quantitatively reflect the inherent tendency characteristics and persistent intensity of the gas concentration variation process. The Hurst index of time series of gas indicators related to coal spontaneous combustion at the monitoring point can be used to judge the time tendency of coal spontaneous combustion in goaf and further judge the spontaneous combustion state of coal. Therefore, methods for judging whether the coal in goaf is in the dangerous stage of spontaneous combustion and for determining the change trend of gas concentration in the goaf were proposed. On this basis, the coexisting disaster were forecasted, moreover, this kind of prediction method can reduce the misinformation of the coexisting disaster. The study provides a meaningful new idea and method for improving the theory of coexisting disaster prediction. [ABSTRACT FROM AUTHOR]

In order to uncover the effect of pyrite on the tendency of coal to spontaneously combust, thermal analysis was carried out to characterize the reaction process of coal with different pyrite contents at four heating rates of 5, 10, 15, and 20 K min−1 in air flow from 25 to 900 °C. The Flynn-Wall-Ozawa method was applied to calculate the activation energy of coal with different pyrite contents. The results show that the thermogravimetric (TG) curve of coal samples can be divided in four stages, being water evaporation, oxygen absorption, thermal decomposition and burnout. As the mass fraction of pyrite content increased, the ignition point of the coal samples decreased and the weight loss rate during the thermal decomposition phase diminished. Meanwhile, the exothermic peak and mass loss peak moved toward lower temperatures. The peak values in the derivative thermogravimetric (DTG) and differential scanning calorimetry (DSC) curves shifted to higher temperatures with higher ignition and burnout temperatures under faster heating rates, but the whole curve shape was not affected. The apparent activation energies of the coal samples declined with higher pyrite contents, so the spontaneous combustion of coal can be promoted by pyrite. [ABSTRACT FROM AUTHOR]

Copyright of China Sciencepaper is the property of China Sciencepaper and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Coal spontaneous combustion is characterized by high-temperature oxidation and microscopic mechanisms. These are essential aspects to understand when attempting to control or prevent spontaneous combustion. Three fresh bituminous coal samples were collected for experimentation from Huainan, China. X-ray diffraction and Fourier-transform infrared spectrometry were conducted to determine the microscopic characteristics of coal during high-temperature oxidation. The mineral structures and functional groups were ascertained to ensure that the original structural characteristics of the coals were obtained. Thermogravimetry–differential scanning calorimetry was used to divide the high-temperature oxidation into four substages and obtain detailed exothermic characteristics. The heat energy release exhibited a positive correlation with an increase in temperature. Moreover, to investigate the relationship between the functional groups and their exothermic characteristics, correlation analysis was conducted for describing the quantitative phenomena within the four oxidation stages. The results revealed that the oxygen-containing groups were initially the most active and reactive among the 14 types of functional groups. The most rapid stage of spontaneous combustion, in which should be the most cautious and aware of risks, was the oxygen adsorption and mass gain stage because the heat energy output increased rapidly and passed this stage, thus leading to dangerous and possibly unrecoverable situations. • TG-DSC was conducted to divide the high-temperature oxidation into four substages. • Fourteen types of functional groups were explored and elucidated in four substages. • Quantitative phenomena in four substages were described by correlation analysis. • Oxygen adsorption and mass gain stage were found as the critical stage. [ABSTRACT FROM AUTHOR]

• Mechanisms causing mass variation of combusting coal were separated and evaluated. • Contributions of different mechanisms to mass variation of coal were researched. • Transformation of the kinetic mode in spontaneous coal combustion was explored. • Kinetic compensation effect of variations in E a and A was investigated. Coal spontaneous combustion (CSC) is a severe threat to coal mining operations. Using thermogravimetric experiments, the contributions of different mechanisms to the mass variation during CSC were analysed. Furthermore, the kinetic mode and kinetic compensation processes were investigated. Among the different mechanisms of coal–oxygen reaction, solid-phase combustion contributes least to mass loss; for coals of high rank, gas-phase combustion makes the greatest contribution. Oxidative decomposition contributes most for coals of low rank. Furthermore, the kinetic mode governing CSC is three-dimensional diffusion in the mass gain stage and changes to random nucleation and subsequent growth in the mass loss stage. The apparent activation energy reaches its maximum near the ignition temperature and indicates a kinetic compensation effect with the pre-exponential factor in each stage. These findings are crucial for understanding the processes involved in CSC. [ABSTRACT FROM AUTHOR]

To explore the effects of methane on the characteristics of coal spontaneous combustion, coal low-temperature oxidation and Fourier transform infrared spectroscopy experiments were conducted. The tested airflows had an oxygen–nitrogen ratio of 0.266, and methane concentrations of 0−3% by volume. Moreover, the coal oxidation characteristics and the various types and quantities of functional groups were investigated. The results show that CO/CO2 production and oxygen consumption rates were higher for coal samples under airflow atmospheres containing methane than for airflow atmospheres without methane. However, the apparent activation energy of coal samples in airflows containing methane was lower than for airflow atmosphere without methane. It is speculated that airflows with 1−3% methane concentrations have a positive impact on coal spontaneous combustion. This study used OMNIC and PeakFit v4.12 programs to analyze the effect of airflows containing methane on the functional groups of coal spontaneous combustion. The Pearson correlation coefficient method was introduced to analyze the relationship between the key functional groups and apparent activation energies of coal samples. The results indicated that the key functional groups of the coal samples below the critical temperature were methyl (−CH3) and methylene (−CH2). Above the critical temperature, aromatic C−H, methyl (−CH3), and methylene (−CH2) were the key functional groups. After reaching the cracking temperature, aromatic C−H and alkyl ether C−O−C became the key functional groups. With increasing methane concentration, aromatic C–H makes a negative contribution to coal spontaneous combustion, while methyl (−CH3) and methylene (−CH2) make positive contributions. The inhibition of alkyl ether C−O−C to coal spontaneous combustion is weakened, and the inhibition of aromatic ring C=C to coal spontaneous combustion is enhanced. [ABSTRACT FROM AUTHOR]

Copyright of Rudarsko-Geolosko-Naftni Zbornik is the property of Faculty of Mining, Geology & Petroleum Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To understand the effects of water immersion on the spontaneous combustion of low-rank bituminous coal, and the underlying mechanism, the pore size distributions and active functional groups of water-immersed coal samples were studied. Characterization data were acquired by liquid nitrogen adsorption and Fourier transform infrared spectroscopy. The spontaneous combustion behaviors of the experimental coal samples were assessed based on oxidation kinetics obtained using a programmable temperature device. Water immersion promotes pore development and enhances the activity of functional groups, which in turn stimulates spontaneous combustion. A lower metamorphic degree of coal yields a more obvious effect. Water immersion causes existing pores to expand or forms new pores, such that the specific surface area and total pore volume of the coal increase. Pores with a radius value near 20 nm grew to the greatest extent. The activities of hydroxyl, ether and carbonyl functional groups and of multi-substituted aromatic hydrocarbons in the coal molecules increase, whereas the activities of methyl and methylene groups decrease. The expanded pores provide more space for the coal–oxygen reaction and enhance the functional group activities. These changes increase the risk for spontaneous combustion by increasing the oxygen consumption rate, decreasing the associated activation energy and increasing the pre-exponential factor. [ABSTRACT FROM AUTHOR]

Liquid N2 could be injected into goaf to decrease temperature and prevent spontaneous combustion during mining. A working face at Liangbaosi coal mine was adopted for study. Firstly, a mathematical model for calculating the temperature field in goaf was developed and field tests without injection of liquid N2 were conducted to validate the model. Comparable development trends and hot zones between the simulation and field measurements were found. The hot zones were located about 35-45 m behind the workface on the air-return and air-intake sides in the goaf. Then the model was employed to simulate the time development of temperature distribution in the goaf with injection of liquid N2 from different locations. It was observed that a low-temperature cooling zone (<300K) due to injection of liquid N2 gradually grew and became relatively stable 90 min after continuous injection. The size of the cooling zone depends on the injection location and flow rate. The cooling zone was smaller when the N2 was injected from the air-intake side than from the air-return side. The largest cooling zone was found when the N2 was injected 35m behind the workface from the air-return side. The cooling zone increases with increasing N2 perfusion rate. This study provides a quantitative assessment for preventing coal oxidation and Spontaneous combustion using the liquid N2 technology. [ABSTRACT FROM AUTHOR]

Coal spontaneous combustion has always been a worldwide problem, which causes waste of coal resources, greenhouse gas emissions and other atmospheric environmental pollution problems. Although coal temperature monitoring is the most direct and accurate means of predicting the spontaneous combustion of coal, the coal temperature often cannot be directly measured owing to various physical restrictions. As an alternative, the present study assessed the qualitative and quantitative analysis of the CO and C2H4 formation rates, as well as various gas ratios such as the CO/CO2 ratio and fire coefficient R2 (R2 = 100 × ΔCO/ΔO2), to predict spontaneous combustion. This method was established based on the temperature-programmed experiments of three different coal rank (including lignite, bituminous coal and anthracite), and was verified using data obtained from on-site monitoring at an actual mine. The results show that the method accuracy is as high as 97% when predicting the coal temperature to within 15 °C (allowable error range of the predicted value). This degree of accuracy should be sufficient for on-site fire prevention and control. This new technique is not only accurate and reliable but also has theoretical significance with regard to the identification of coal spontaneous combustion in goaf and for the development of fire prevention and suppression technologies. [ABSTRACT FROM AUTHOR]

• A novel evaluating method was proposed to determinate the spontaneous combustion of coal. • Variations of the indexes of spontaneous combustion from three rank coal were obtained. • The prediction accuracy of this method can be set according to the actual requirements of coal mine site. • The evaluating method is simple and applicable to the coal of different ranks. Coal spontaneous combustion has always been a worldwide problem, which causes waste of coal resources, greenhouse gas emissions and other atmospheric environmental pollution problems. Although coal temperature monitoring is the most direct and accurate means of predicting the spontaneous combustion of coal, the coal temperature often cannot be directly measured owing to various physical restrictions. As an alternative, the present study assessed the qualitative and quantitative analysis of the CO and C 2 H 4 formation rates, as well as various gas ratios such as the CO/CO 2 ratio and fire coefficient R 2 (R 2 = 100×ΔCO/ΔO 2), to predict spontaneous combustion. This method was established based on the temperature-programmed experiments of three different coal rank (including lignite, bituminous coal and anthracite), and was verified using data obtained from on-site monitoring at an actual mine. The results show that the method accuracy is as high as 97% when predicting the coal temperature to within 15 °C (allowable error range of the predicted value). This degree of accuracy should be sufficient for on-site fire prevention and control. This new technique is not only accurate and reliable but also has theoretical significance with regard to the identification of coal spontaneous combustion in goaf and for the development of fire prevention and suppression technologies. [ABSTRACT FROM AUTHOR]

• Both field test and simulation show occurrence of coal oxidation in workface #3418. • Injection of liquid N 2 forms a cooling zone suppressing coal oxidation. • Injection of N 2 reduces maximum goaf temperature preventing spontaneous combustion. • Cooling zone and effectiveness are strongly affected by injection location and rate. Liquid N 2 could be injected into goaf to decrease temperature and prevent spontaneous combustion during mining. A working face at Liangbaosi coal mine was adopted for study. Firstly, a mathematical model for calculating the temperature field in goaf was developed and field tests without injection of liquid N 2 were conducted to validate the model. Comparable development trends and hot zones between the simulation and field measurements were found. The hot zones were located about 35–45 m behind the workface on the air-return and air-intake sides in the goaf. Then the model was employed to simulate the time development of temperature distribution in the goaf with injection of liquid N 2 from different locations. It was observed that a low-temperature cooling zone (<300K) due to injection of liquid N 2 gradually grew and became relatively stable 90 min after continuous injection. The size of the cooling zone depends on the injection location and flow rate. The cooling zone was smaller when the N 2 was injected from the air-intake side than from the air-return side. The largest cooling zone was found when the N 2 was injected 35m behind the workface from the air-return side. The cooling zone increases with increasing N 2 perfusion rate. This study provides a quantitative assessment for preventing coal oxidation and spontaneous combustion using the liquid N 2 technology. [ABSTRACT FROM AUTHOR]

The technology of preventing and controlling coal spontaneous combustion by paralysant is one of the most important technologies in coal spontaneous combustion prevention and control system, especially the layered double hydroxide (LDHs) developed in recent years is a new type of coal spontaneous combustion inhibitor. In order to study the inhibition effect of LDHs on coal spontaneous combustion and the best ratio (the most economical and efficient addition), this paper uses self-made LDHs inhibitor preparation device to successfully make the LDHs in a variety of metal ion ratios by coprecipitation method. And then, the paper uses the thermal gravimetric analysis to obtain the TD-DTG curves of coal samples at 3 %, 5 %, 10 % and 15 %by 5 kinds of LDHs additive amounts, and then, the inhibition effect of various inhibitors under different adding conditions is investigated. The results show that when the LDHs physical mixing amount is 15 %, it can effectively prevent the spontaneous combustion of coal samples; finally, according to the test results, the hypothesis of LDHs inhibiting coal spontaneous combustion mechanism is put forward, that is, on the one hand, the La3+ in LDHs will have complexation effect with active groups in coal to prevent the reaction of coal and oxygen; on the other hand, the intermediate bound water between rare earth layered double hydroxides will increase with the adding of La3+, so as to restrain the spontaneous combustion of coal by self-heating. The research findings will have better theoretical guidance and reference significance for the study on LDHs new type self-ignition inhibitor and its on-site economical and efficient use. [ABSTRACT FROM AUTHOR]

During coal oxidation and temperature rise, a significantly large amount of electromagnetic radiation (EMR) signals are generated as a result of thermal deformation and thermal cracking. The generation of EMR signal is the comprehensive embodiment of the physical and chemical changes in coal during its oxidation and subsequent heating. Therefore, the generated signals contain complex and rich messages that can reflect the changes in the internal structure of coal. In this work, the characteristics of EMR signal were analyzed by multifractal theory. Multifractal analysis was used to deconstruct EMR signals. Our preliminary study indicated that the multifractal spectrum of the EMR signal had a feature of small probability event. Further analysis demonstrated that the characteristic parameters of EMR signal are quite different at the later heating stage from those at the early heating stage. At the initial stage of coal spontaneous combustion, the multifractal spectrum of the signal is wider, but when coal combustion is reached, the scale range of EMR signal increases significantly, and its structure changes at different temperature ranges. The research results presented provide a basis for monitoring and presenting an early warning of coal spontaneous combustion risk. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Mine Automation is the property of Industry & Mine Automation Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Mine Automation is the property of Industry & Mine Automation Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The coal spontaneous combustion has obvious mesoscale characteristics. The application of the mesoscale science and theory to correlate the microscopic reaction mechanism with the macroscopic properties of coal spontaneous combustion contributes to the in depth study in the field of coal spontaneous combustion. Firstly, the physical process and the mathematical concept of the coal pile gradation in which the mesoscale II exists are made clear. The differences and interrelationships among the three scales of single coal particle, particle cluster and coal pile are explained in detail. Specifically, multi scale simulation depends on the reasonable information transfer among scales, which is mainly realized by upscaling method in the study of coal spontaneous combustion. From the point of view of mathematical modeling, it is pointed out that the essence of coal particle cluster is the representative elementary volume (REV) of the coal pile. The REV scale simulation, whose minimum unit is REV, is based on macro model, which ignores the structural changes in the cluster. Correspondingly, the pore scale simulation, which considers the interaction of individual coal particles inside the REV, is based on micro model. Secondly, based on the definition of the REV scale, the governing equations, including continuity, momentum, energy and concentration equations, which consider the effects of the transient porosity and high temperature radiation, are built and the corresponding solving method is briefly described. Besides, it is pointed out that the parameters including porosity, permeability and heat transfer coefficient, etc. should be obtained from the pore scale simulation. Thirdly, the Lattice Boltzmann equations of pore scale simulation are discussed. A sample is employed to illustrate the procedures for the 3D digital reconstruction and the extraction of the REV. Finally, based on the constitutive relation of parameters between different scales, the upscaling method for obtaining parameters, such as porosity, permeability, inertia coefficient and convective heat transfer coefficient in macro control equation, from the pore scale is proposed, which realizes the information transmission from the pore scale simulation with micro model to the REV scale simulation with macro model mathematically. Consequently, the multi scale physical and mathematical modeling from pore scale to REV scale is completed. [ABSTRACT FROM AUTHOR]

Coal spontaneous combustion is a major disaster in underground mine. CO as a common indicator gas due to its good correlation with coal selfheating temperature. However, abnormal high concentration of CO was detected without coal fire during production process of some underground mines that not only impact production but also threat the safety of miners. To investigate the sources appointment of abnormal CO without coal spontaneous combustion, quantitative analysis of primordial and oxidation product were conducted with self-designed vacuum desorption and coal/gas interaction testing apparatus. The results indicated that CO as a gaseous product generated from coal oxidation under ambient temperature (18-22°C) was the main source in underground mine. Coal oxidation ability under ambient temperature was too partial to completely demonstrate coal spontaneous combustion propensity. Infrared spectra and ESR indicated the mechanism of coal oxidation under ambient temperature. It showed that oxygencontaining functional groups were prone to oxidation under ambient temperature. The results of the research could be improve the accuracy of early detection with CO for coal spontaneous combustion. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Random forest (RF) model was developed to predict coal spontaneous combustion. • RF and SVM models were optimized using particle swarm optimization (PSO). • In-situ data were employed to establish and compare the proposed RF and SVM models. • The prediction of the RF model was less affected by its hyper-parameters. • The PSO method can significantly improve the prediction accuracy of the SVM. Abstract The accurate prediction of coal temperature plays a vital role in preventing and controlling the spontaneous combustion of coal in coal mines. In this study, a long-term in-situ observation experiment was conducted in a fully mechanized caving face of the Dafosi Coal Mine, where the in-situ data of gases and temperature were obtained. Two machine learning approaches, random forest (RF) and support vector machine (SVM) were introduced and compared for predicting coal spontaneous combustion based on the in-situ monitoring data. The particle swarm optimization (PSO) was employed to optimize the RF and SVM by finding their optimal hyper-parameters. Principal component analysis (PCA) was used to transform the original input data into a new dataset of uncorrelated variables, reducing dimension for input variables. The results indicated that regardless of whether the models with or without PCA, the RF model was more robust than the SVM model and less affected by its own parameters, while the SVM model was highly sensitive to its parameters. Although the PSO could find the optimal hyper-parameters of the RF model, the RF model with default parameters could also accurately predict coal spontaneous combustion and possess satisfactory generalization. However, the predictive performance of the SVM model was dramatically improved in predicting after the PSO optimization. Moreover, the models with PCA also showed the above characteristics. These results suggest that both the RF and SVM methods can be used to predict coal spontaneous combustion, while the RF method can obtain accurate predictions without special parameter settings, it is more suitable for practical applications and can potentially be further employed as a reliable method for the determination of complicated relationships. [ABSTRACT FROM AUTHOR]

The disaster of coal spontaneous combustion mainly occurs in a concealed oxygen-poor environment in the underground coal mine. The formation law of hydrocarbon index gases can accurately reflect the degree of coal spontaneous combustion. In this paper, the influence of oxygen-poor degree on the formation law of hydrocarbon index gases was investigated by the program heating experiment of coal spontaneous combustion in different oxygen-poor environments. The results reveal that the rising tendency of the alkane index gas volume fraction can be reduced by the increase in oxygen-poor degree. Olefin index gases can predict the disaster of coal spontaneous combustion more reliably than alkane index gases in the oxygen-poor environment. As the optimal predictive index of coal spontaneous combustion in the oxygen-poor environment, the volume fraction ratios of olefins to alkanes can be used which increase steadily with the oxygen-poor degree. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Mine Automation is the property of Industry & Mine Automation Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract Air leakage to the gob is an indispensable factor in spontaneous combustion in underground coal mine. Foam cement is used as an effective means to overcome this problem. To obtain high-quality foam, a novel foaming device was designed. The performance of the device was tested under different working conditions. The test results demonstrate that reasonable operating conditions of the device are: a gas pressure of 0.4–0.6 MPa, foaming agent flow rate of 0.006–0.012 m3/h, and gas-water flow ratio of 14–17. Comparing the filling effect of the foam cement produced by the novel foaming device to a traditional filling material, loess, it is found that the oxygen and carbon monoxide concentrations in the gob are greatly reduced; in other words, the foam cement showed an outstanding effect of plugging air leakage. The proposed novel foaming device could greatly promote the large-scale application of foam cement filling technology used to suppress air leakage in underground coal mines to prevent spontaneous combustion. Graphical abstract Unlabelled Image Highlights • A novel foaming device was designed. • The foaming device has the advantages of safe, simple structure, small-sized, light-weight, and easy to operate. • The foam what is produced by the foaming device which is designed in this paper has excellent performance. [ABSTRACT FROM AUTHOR]

Granularity is one of the primary extrinsic factors that can influence the process of coal spontaneous combustion. Lignite was selected for studying the influence of granularity. A self-developed temperature-programmed oil bath experimental system was adopted to capture the changes in the spontaneous combustion characteristic parameters for different particle sizes. Moreover, the microcrystalline structure and functional group distribution of different granularities were obtained using an X-ray diffractometer and Fourier transform infrared spectrometer. The results show that the microcrystalline structure, the types of functional groups and the release order of gases of different granularities have equal influence during the process of coal spontaneous combustion. A smaller granularity has a lower aromatic group content and a higher content of high-activity hydroxyl groups, aliphatic hydrocarbons and oxygen-containing functional groups. Moreover, a smaller particle size results in a lower critical temperature. The distributions of coal granularity also affect the characteristic of coal spontaneous combustion. A wide particle size distribution produces a larger surface area for contact between coal and oxygen than a narrow distribution, which results in a coal with a stronger spontaneous combustion tendency. [ABSTRACT FROM AUTHOR]

Copyright of China Sciencepaper is the property of China Sciencepaper and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The influence of mudstone on the spontaneous combustion of coal was investigated in this study. The effects of different proportions of mudstone on the characteristic temperature, thermal effect, thermal physical parameters, and combustion characteristic index of coal were analyzed by TG-DSC experiments and thermal physical parameter test experiments. The catalytic mechanism of mudstone on the active structure of coal oxidation was obtained by Fourier transform infrared spectroscopy. The results showed that an interaction exists between coal and mudstone, and different stages had different effects. The combustion characteristic index showed a trend of an initial increase followed by a decrease. The thermal conductivity and thermal diffusivity of MY-1 samples were larger than those of raw coal samples, indicating that a small amount of mudstone had the most obvious effect on coal combustion and played a promoting role in the heat transfer of coal samples. The carbon content of mudstone was much lower than that of coal, and the content of metals and their oxides and sulfides was higher. The content of aliphatic hydrocarbons and hydroxyl groups in the samples mixed with mudstone decreased. When coal coexists with a small amount of mudstone, the risk of spontaneous combustion of coal increases. • The interaction between coal and mudstone in the process of spontaneous combustion • The influence of mudstone on coal spontaneous combustion process is demonstrated is reflected by physical parameters • The effect of mudstone on coal is analyzed by microscopic mechanism [ABSTRACT FROM AUTHOR]

• Gas action inhibits initial coal oxidation, but promotes pyrolysis and combustion. • Significant differences in the effect of particle size on oxidation and pyrolysis. • The mechanism of gas transport on the process of coal spontaneous combustion was analyzed. • Gas has a stage-specific effect on the derivation of oxidized gas from the coal body. Heat release and gas derivation can reflect the degree of coal spontaneous combustion (CSC) as important indicators. Meanwhile, both physical and chemical properties of gas-containing coal and methane molecules are important factors for CSC. The C600 high-precision microcalorimeter was coupled with a gas chromatograph to conduct oxidation and pyrolysis experiments on gas-containing coal. The thermal effects and gas derivation rules in the process were analyzed. The influence of the physicochemical properties of gas-containing coal on the spontaneous combustion process was clarified. The quantitative relationship between particle size and heat release coal was discussed. The experimental results show that compared with raw coal, the unique characteristics of gas-containing coal are as follows: (1) The oxidation process is slowed down, while high temperature combustion is more adequate, and pyrolysis is more likely to occur and more intense; (2) The heat absorption and release intensity increased to different degrees, and the characteristic temperature shifted forward; (3) With the decrease of oxygen consumption and generation of CO 2 , CO release increases significantly; (4) As the particle size of gas-containing coal decreases, the oxidation is more likely to occur, while pyrolysis is slowed down. The research results provide an important theoretical basis for the prevention and control of spontaneous combustion of gas-containing coal. [ABSTRACT FROM AUTHOR]

• Inflatable temperature–sensitive hydrogel (HPMC–CS–EM) was prepared to prevent coal spontaneous combustion. • The HPMC–CS–EM (A 50 , B 50) prepared with Hydroxypropyl Methyl Cellulose viscosity of 50 mPa∙s and Expanded Microsphere content of 0 %, 0.5 %, had good stability, expansibility and fluidity. • The inhibition effect of B 50 gel was obvious in the initial mass loss stage of coal, and the inhibition effect of A 50 gel was mainly manifested in the slow oxidation stage. A serious of inflatable temperature–sensitive hydrogel (HPMC–CS–EM) were prepared to prevent coal spontaneous combustion (CSC). Through performance tests, it was found that gel of 50 mPa∙s HPMC had good fluidity, the addition of EM can increase the water loss in the early pyrolysis stage. A 50 , B 50 prepared by 50 mPa∙s HPMC and 0 %, 0.5 % EM had good performance which were suitable for the prevention of CSC. The inhibition of A 50 , B 50 on CSC was tested by means of paramagnetic resonance spectroscopy and thermogravimetry. Inhibition experiments revealed that more water and hydrocarbon gas were released from B 50 gel, thereby significantly reducing the concentration and amount of free radicals, the maximum water loss rate temperature and the dry crack temperature. The more carbon residue of A 50 gel made it have better inhibition effect in the slow oxidation stage. The average apparent activation energy was obtained by the combination of universal integral and differential at multiple heating rates, indicating that these two gels remarkably reduced the tendency of CSC. [ABSTRACT FROM AUTHOR]

• RES can effectively inhibit the formation of functional groups. • The mechanisms involving RES on CSC have been probed. • RES increased the activation energy of the coal to inhibit the CSC. • The effects of different concentrations of RES on inhibiting CSC were compared. The inhibitory effect of antioxidants on the prevention of coal spontaneous combustion (CSC) has been tremendously studied. In this paper, we investigated the inhibitory effect of Resveratrol (RES) on CSC. The oxidation properties of coal were revealed by a temperature-programmed test. Mass changes and heat flow effects of coal oxidation was investigated by TG-DSC. Fourier-transform infrared spectroscopy was conducted to confirm the variations in reactive groups in coal. Furthermore, combining the above results, the reaction mechanism of RES was analyzed by the Quantum chemical theory. The results show that different concentration of RES (5 wt%, 10 wt% and 15 wt%) exhibits an extraordinary ability to prevent CSC. After the 10 wt% RES treated, the apparent activation energy of treated coal obtained an 11.85 kJ/mol increase. The RES-treated coal achieved a maximum inhibition rate of 79 %, a lower mass loss rate than that of the raw coal, and a 20 % reduction in the maximum heat flow. In addition to carboxylic groups, the content of other active groups decreases after RES-treated. RES provides protonated hydrogen, which consumes oxygen-containing radicals and inhibits the formation of new hydrocarbon radicals. The proposed RES is water-soluble antioxidant which can be dispersed evenly on the coal surface and has been convinced as an effective antioxidant in preventing CSC. [ABSTRACT FROM AUTHOR]

Polymer gel foam shows excellent development potential and application prospects in the prevention of coal spontaneous combustion. To reveal the relationship between the characteristics of gel foam and the prevention of coal spontaneous combustion, XG/GG/HPAM gel foam consisting of polymer xanthan gum (XG), guar gum (GG), and polyacrylamide (HPAM) is prepared. The characteristics of gel foam are investigated in terms of microstructure, viscosity, thermal stability, and film-forming. The effects of gel foam on gas products, characteristic temperature, combustion characteristics parameters, and functional groups during coal oxidation are studied. The results show that polymer delays the foam coarsening and improves the foam stability. XG/GG/HPAM gel foam exhibits a slow foam coarsening process, concentrated bubble diameter distribution, shear-thinning behavior, excellent thermal stability, and film-forming properties. Moreover, the inhibition rate of XG/GG/HPAM gel foam on coal is 43.63% higher than that of ordinary foam. XG/GG/HPAM gel foam effectively improves the apparent activation energy of coal, the maximum weight loss rate of the coal is decreased by 7.55%, and the combustibility, combustion stability, and comprehensive combustion index are diminished by 8.50%, 7.64%, and 10.17%, respectively. Simultaneously, XG/GG/HPAM gel foam reduces the oxidation activity of aliphatic hydrocarbons and oxygen-containing functional groups in coal, blocks the chain reaction, and thus inhibits coal spontaneous combustion. The results provide support for achieving efficient fire prevention performance of gel foam. [Display omitted] • The stability of gel foam was characterized by microstructure and water loss rate. • The effects of gel foam on combustion characteristics and oxidation kinetics of coal were discussed. • XG/GG/HPAM gel foam reduces oxidation activity of coal aliphatic hydrocarbon. [ABSTRACT FROM AUTHOR]

To identify effects of the pre-oxidation process on the spontaneous combustion characteristics of Shendong low-rank long-flame coal, the microstructure and oxidation reactivity of coal samples pre-oxidized at different temperature including 70 °C, 100 °C, 200 °C, 300 °C, and 400 °C were studied and compared with those of raw coal. The surface morphology, pore features, functional groups, and microcrystalline structure of coal were studied using SEM, N 2 adsorption, XPS, and XRD analyses. Moreover, TG-DSC experiments were conducted to investigate the changes in the spontaneous combustion characteristics of coal. The results indicated that low-temperature pre-oxidation at 70 °C and 100 °C does not alter the physical and chemical structure significantly, so the pore parameters, functional group contents, and microcrystalline structure of these two samples were very similar to those of raw coal. When the pre-oxidation temperature reached and exceeded 200 °C, the specific surface area and total pore volume of coal samples exhibited a significant decrease due to extensive thermal decomposition and consumption of coal components via oxidation. Moreover, high-temperature pre-oxidation treatment above 200 °C sharply reduced the aromatic and aliphatic carbon C–C/C–H content, and this is ascribed to the substantial consumption of primordial organic matter, this made coal macromolecules more tightly packed with an increase in carbon crystal size and carbon matrix order. In addition, with increasing temperature from 200 °C to 400 °C, the C–C/C–H contents decreased and aromaticity of coal increased, which revealed the weak oxidative activity. The heat release △ H 1 from 30 °C to 300 °C of coal samples after pre-oxidation at 200–400 °C was significantly lower than that of raw coal, while the △ H 1 values of coal samples treated at 70 °C and 100 °C were close to that of raw coal. Notably, that oxidation treatment at 70 °C resulted in an increase in the amount of heat released, because of the largest specific surface area that increases the risk of spontaneous combustion. Thus, the pre-oxidation treatment increases the risk of spontaneous combustion of coal when the pre-oxidation temperature is lower than a critical temperature. • Using pore structure parameters could estimate coal spontaneous combustion. • Microcrystalline structure analysis of pre-oxidized coal and raw coal. • Chemical group transformation law of Shendong coal during pre-oxidation process. • Oxidized coal below critical temperature was more easily to spontaneous combustion. [ABSTRACT FROM AUTHOR]

The current technologies employed to prevent the spontaneous combustion of coal, such as grouting, inert gas, retardants, gels and foams have the disadvantages of high pollution, easy failure at high temperature, and high cost. In this study, in order to develop an environmentally friendly, efficient and low-cost composite gel material to inhibit coal spontaneous combustion, tea polyphenols were added to the gel for grafting, while nanomaterial halloysite nanotubes were introduced for intercalation reaction. Finally, sodium bicarbonate and acetic acid were used as foaming agents to produce tea polyphenol nanofoaming gels. The microscopic characterization of the composite gel was studied using X-ray diffraction experiments and scanning electron microscopy. Experiments on physical properties such as fluidity, thermal stability and adhesion were also carried out. In addition, fire performance studies such as thermogravimetric experiments, oxidation kinetic analysis, infrared spectroscopy of gas products, analysis of the change law of active functional groups and crossing-point temperature analysis were completed. The results show that composite gel renders the activity of active functional groups inert, which inhibits coal spontaneous combustion, while it can cover the surface of coal and plug the fissures efficiently. Therefore, it is an ideal material to inhibit the spontaneous combustion of coal. • A tea polyphenol nanofoamed gel was synthesized as a new inhibitor. • Microscopic characterization was studied by SEM and X-ray diffraction experiments. • Fluidity, thermal stability and adhesion of the gel were studied. • The fire performance of the gel was studied by TGA and other experiments. [ABSTRACT FROM AUTHOR]

• The effect of sodium on coal spontaneous combustion can be divided into two stages: slow oxidation and rapid combustion. • Sodium promotes coal combustion in the slow oxidation stage and inhibits it in the rapid combustion stage. • Organic sodium inhibits the oxidation of ether bonds and inorganic sodium promotes the oxidation of hydroxyl groups. • Organic sodium combines with peroxy radicals and inhibit the oxidation process of ether bonds; inorganic sodium replaces the hydrogen in hydroxyl groups and promote the oxidation reaction of coal. In order to investigate the effect of sodium in coal spontaneous combustion, different types of inorganic and organic sodium were added to the raw coal to analyze the changes of spontaneous combustion characteristics of coal samples. The combustion characteristics parameters of each group of coal samples were calculated by simulating the spontaneous combustion reaction process of coal through programmed warming thermogravimetric experiments, and the results showed that the combustibility index of coal samples loaded with various types of sodium-containing reagents increased by 8.32 %–45.37 %, and the combustion characteristics index decreased by 13.82 %–39.15 %. It indicates that inorganic sodium salts and organic sodium salts promote the combustion of coal in the low temperature stage and inhibit it in the high temperature stage. Subsequently, the changes of characteristic functional groups in coal during combustion after loading sodium were analyzed by using in-situ infrared spectroscopy experiments, and it was concluded that sodium in organic salts would combine with peroxyl radicals and thus inhibit the oxidation process of oxygen-containing functional groups in coal; sodium in inorganic salts would replace hydrogen in carboxyl and hydroxyl groups and thus promote the oxidation reaction of coal. The results of the study can provide some theoretical basis for the development of new coal spontaneous combustion inhibitors with specific functions. [ABSTRACT FROM AUTHOR]

• The particle size distribution law of broken coal bodies was calculated. • A random pore network development method for broken coal bodies is proposed. • The pore network was adjusted using permeability and the conductivity adjustment factor η i was verified to be general. Coal spontaneous combustion (CSC) in the gob areas is considered to be an important safety issue in the coal industries. Numerical simulation is a reasonable tool for predicting and preventing this problem. The commonly applied finite-volume and finite-element techniques are computationally expensive when they must account for pore-scale phenomena. A pore-network model (PNM) has the advantage of lower computational cost while also simulating heat and mass transfers in porous media at scale with reasonable accuracy. This study provides a method for extending pore networks to packed coal particles with a wide spectrum of size distributions, and to generate pore networks of arbitrary size within a range. This method was developed based on the Voronoi and Delaunay tessellations theories. Statistical data on the size distribution, porosity, and permeability of packed coal particles were collected experimentally. This method requires a relatively low network generation cost for the preservation of the voids that are formed among larger particles and characterize the effect of fine particles filling in throat channels by reference to a conductivity adjustment factor η i , which depends on axial stress. The average relative error of predicted and experimental permeability does not exceed 5% when this new pore-network construction procedure is used. The predicted result holds until the volume upscaling ratio reaches 58. [ABSTRACT FROM AUTHOR]

• An interaction order between anions and cations with coal molecules was obtained. • Types of interaction forces between IL and coal molecules were determined. • Order of the reactivity of IL with coal molecules was revealed. • Mechanism of IL inhibiting the oxidation of functional groups was revealed. The interaction between ionic liquid and coal (IL-coal) plays a theoretically pivotal role in revealing the internal mechanism of ILs inhibiting coal spontaneous combustion (CSC). This can determine the degree of reaction or inhibitory ability between IL-coal molecules. First, the activity characteristics of FTIR structural parameters from molecular surfaces affected by [BMIM][BF 4 ] were obtained. In addition, the optimal structures of [BMIM][BF 4 ] with methyl, hydroxyl, ether bond, methylene, and carboxyl groups were determined based upon Density Functional Theory. The activity characteristics of the IL-coal complexes were investigated from the aspects of charge population and transfer, bond length change, and electrostatic potential distribution. Finally, the types and relationships of the forces between the five structures of the IL-coal complexes and the stability and activity order were explored. The results demonstrated that [BMIM][BF4] could possibly reduce the structural abundance, side chain length, and oxygen-containing groups of aliphatic hydrocarbons. The interaction between anion [BF 4 ]− and active groups was more stable than that between cation [BMIM]+ and active groups. Meanwhile, the dissolution and destruction of coal active groups by ILs were not completely determined by the number of hydrogen bonds formed between ILs and coal active groups, but by the strength of hydrogen bonds formed between anions and coal active groups, and the effect of anions was stronger than that of cations. The order of oxidation capacity of the IL-coal complexes was: [BMIM][BF 4 ]–CH 2 – > [BMIM][BF 4 ]–O– > [BMIM][BF 4 ]–COOH > [BMIM][BF 4 ]–CH 3 > [BMIM][BF 4 ]–OH. The van der Waals effect mainly presented complexes. Despite this, there were hydrogen bonds between the complexes formed by hydroxyl groups, but the hydrogen bond force showed exceptionally slight effects. [ABSTRACT FROM AUTHOR]

• The software COMBUSS-Dimensionless was developed to simulate the dimensionless solid temperature field. • The dimensionless prejudgment criteria of the CSC in gobs were proposed. • A series of Nomograms was established to prejudge the possibility of the CSC in gobs. Coal spontaneous combustion (CSC) in longwall gobs is the result of the coupling of multiple physical fields, making its development difficult to predict, so the prejudgment indicators need to be refined. In this work, the dimensionless model of CSC in the gob was established, and three prejudgment indicators such as air leakage intensity indicator, longwall advance rate indicator and exothermic intensity indicator were proposed to consist of the dimensionless prejudgment criteria of CSC in gobs. Numerical simulations were performed to obtain the relationship curves between each indicator and the dimensionless maximum excess temperature in the gob. These curves had formed a series of nomograms that can be used to prejudge the CSC. It shows that the risk of the CSC in gobs is positively correlated with the air leakage intensity indicator and the exothermic intensity indicator, but inversely proportional to the longwall advance rate indicator. The field application indicates that the prejudgment criteria and its Nomogram can be used to accurately predict whether the CSC could occur in the gob, and has good prospects for application. [ABSTRACT FROM AUTHOR]

The surface isotope radon measurement method (SIRMM) is widely used in fire source detection in abandoned mines. However, studies on the long-distance migration of radon during coal spontaneous combustion are lacking, which hinders the further popularization of this technology in coal fire prevention and control. For this reason, the migration law of radon in overlying strata in fire areas was studied through experiments and numerical simulation. The radon exhalation concentration of coal was found to increase at first and then decrease in the range of 30–350 °C through experiments. The radon concentration reaches the maximum value (557.1 Bq/m3) at 150 °C, which is 6.3 times higher than that at 30 °C. Based on the radon source term obtained by fitting the experimental data, the radon migration model of coal spontaneous combustion in abandoned goaf was constructed, and the dynamic distribution characteristics of the airflow, temperature, and radon concentration fields in the overlying strata area were analyzed. The internal relationship between surface radon and underground fire source was discussed. The simulation results revealed the sharp change in the porosity of the overlying rock causes radon concentration at the interface between the caving and fissure zones to increase continually with the process of spontaneous combustion, providing material and energy support for the long-distance radon migration. When the maximum temperature of the coal pile reaches 70 °C, the concentration of radon released from the coal pile increases rapidly to 13696 Bq/m3, and the radon from the underground space appears on the surface at this temperature. In the range of 70–150 °C, with rapid increase in radon released from coal piles, the surface concentration of radon also increased rapidly to 225 Bq/m3. At the high-temperature stage exceeding 150 °C, the concentration of radon released from coal piles exhibited a downward trend, resulting in a decrease in the rate of increase of radon concentration on the surface. A close relationship between the surface radon concentration and underground fire source temperature in the process of coal spontaneous combustion was observed. In the spatial position, the peak position of radon on the surface was highly consistent with that of the fire source longitudinally, which ensures the accuracy of the SIRMM to determine the location of the hidden fire source. This suggests that the SIRMM can accurately evaluate the fire source's temperature and fire area's development trend. •Get the functional relationship between radon concentration and coal temperature. •Build a multi-physical field coupling model of radon migration in fire areas. •Radon accumulates at the junction of the caving zone and fissure zone. • The surface radon and fire sources are closely related in time and space [ABSTRACT FROM AUTHOR]

To investigate the reaction pathways of key reactive groups in coal when coal undergoes oxidation at low temperatures, the start-up stage of the reaction pathways, and the evolution of free radicals and functional groups. Firstly, according to the similarity in the types of groups, this paper classifies many reactive groups in coal and uses GaussView 6.0 to construct molecular models of primary (-CH 3 , –OH, –CHO, –COOH) and secondary (-R∙, –C(O)∙, –COO∙, ∙OOH) groups. Then the reaction channels of primary and secondary groups were built and verified based on the similarity of the reaction forms of the groups. The results show that both primary and secondary groups have "dual channel reactions" when coal undergoes oxidation. Channel A of the primary group reacts with O 2 with a start-up stage of 70∼200 °C, and channel B reacts with ∙OH with a start-up stage of 30∼70 °C; channel C of the secondary group reacts with O 2 at about 30 °C and channel D reacts with self-decomposition with a start-up stage of 70∼200 °C. The results show that oxygen insulation and cooling can be adopted according to channels A and C. Channels B, C, and D eliminate R∙ and ∙OH to efficiently prevent and control coal spontaneous combustion(CSC). • The model of primary and secondary groups in coal was constructed. • The reaction channels of each key group were simulated and validated at the atomic and molecular levels. • A two-channel reaction model exists for both primary and secondary groups. • Delineated the initiation phase of each reaction channel. [ABSTRACT FROM AUTHOR]

• Studied the auto-oxidation characteristics of coal at different stages. • Studied the correlation between radical reactions and temperature changes. • Analyzed the relationship between the self-oxidation of micro radicals and macro heat release. The spontaneous combustion in the mining gob are often caused by the low-temperature oxidation of coal, and the low-temperature oxidation process has a long process leading to different characteristics in each stage, which brings great difficulties to the prevention and control of coal spontaneous combustion in the underground mining gob. Therefore, this article investigated the oxidation characteristics of coal at different stages of the low-temperature oxidation, mainly including: analyzing the changes in radical concentration and g factor based on electron spin resonance (ESR) experiments, studying the variations in coal temperature by using the programmed temperature controller and analyzing the characteristics of gas products and oxygen consumption by using the gas chromatograph. And the degree of auto-oxidation of coal was characterized by the difference between dry air and nitrogen conditions during the constant temperature period. The results showed that when the constant temperature reached 130 ℃, the coal began to exhibit auto-oxidation characteristics, while when the constant temperature reached 180 ℃, the auto-oxidation phenomenon of the coal significantly intensified, the types and content of radicals rapidly grew, the coal temperature significantly rose, and the oxygen consumption rapidly increased, while releasing a large amount of CO and CO 2. And the relationship between the spontaneous oxidation ability of coal radicals and the temperature change of coal during constant temperature was obtained. The conclusions obtained provide theoretical guidance for the safety and clean production of coal resources in mines, as well as the prevention and control of coal spontaneous combustion fires. [ABSTRACT FROM AUTHOR]

[Display omitted] • The first application of Glutathione in the field of CSC inhibition was studied. • The inhibition effect and mechanism of Glutathione were explored by combining experiment and calculation. • Comparing with the physical inhibitor, the Glutathione inhibitor solution has excellent inhibition effects. • The anti-oxidation mechanism of Glutathione was it reacts with the active free radicals produced in the CSC process. Inhibitors play an important role in preventing and controlling coal spontaneous combustion (CSC). In this study, the inhibitory effects of antioxidant-reduced glutathione (G-SH) on CSC were examined. Thermogravimetric-differential scanning calorimetry (TG-DSC), cross-point temperature (CPT), and oxidation product tests were used to examine the effect of G-SH on the tendency of CSC and compare the discrepancy in the inhibition effect of G-SH and the halogen inhibitor. The changes in the free radical type, concentration, and surface functional groups in coal before and after the addition of G-SH were analyzed using electron spin resonance spectroscopy (ESR) and Fourier transform infrared spectroscopy (FT-IR). Six common active radical models were constructed, and the thermodynamic parameters of the reaction were calculated using density functional theory (DFT). The results revealed that G-SH inhibits the spontaneous combustion of coal. The inhibitory effect of G-SH was significantly stronger than that of the halogen salt inhibitors CaCl 2 and MgCl 2 , and the higher the concentration of G-SH, the stronger is the inhibitory effect. The characteristic temperature points in the thermogravimetric experiment of coal samples with G-SH shifted to a higher temperature zone, and the CO concentration and oxygen consumption were lower than those of raw coal. After G-SH treatment, the type and relative concentration of free radicals in coal were lower than those in raw coal, the content of aliphatic hydrocarbon functional groups and oxygen-containing functional groups decreased, and the content of sulfur-containing functional groups increased. According to the calculation of Gibbs free energy and reaction enthalpy, G-SH can effectively neutralize the active free radicals in the process of coal oxidation, and the reaction activity with the free radicals in the process of coal oxidation is ·OOH > ·OH > ·CH 3 > RO· > R· > ROO·. According to the experimental results, it is inferred that G-SH continuously supplies a large number of hydrogen donors (·H) for the reaction during the oxidation process and simultaneously neutralizes carbon free radicals and carbon oxygen free radicals, thereby reducing the concentration and reactivity of free radicals in the whole chain reaction process and blocking the occurrence of coal-oxygen composite reaction. [ABSTRACT FROM AUTHOR]

A stable and highly efficient 1, 1, 3, 3, 3-hexamethyldisilazane (HMDS) terminated m-Cresol inhibitor was synthesized based on the protection-deprotection strategy. The inhibitory effect of HMDS terminated m-Cresol inhibitor on spontaneous combustion of lignite was explored through temperature-programmed oxidation tests, in-situ infrared analysis and thermogravimetric analysis. Results show that, the oxidation of active phenolic hydroxyl groups in the m-Cresol inhibitor can be hindered by the protection of HMDS. After encountering coal, the HMDS terminated inhibitor can be gradually deprotected to regenerate the m-Cresol inhibitor that contains massive active phenolic hydroxyl groups, thus improving the chemical inhibition efficiency of coal spontaneous combustion. For the coal sample inhibited with HMDS terminated m-Cresol inhibitor, the initial contents of the active functional groups are lower and more stable during heating, and the inhibition rate reaches 70% at 130 °C. Moreover, the crossing-point temperature rises by 32.4 °C–181.2 °C. The activation energy increases by 11 kJ/mol and 18 kJ/mol at below and above 130 °C respectively. The peak temperature at maximum weight loss rate rises by 65 °C–431.2 °C, and the corresponding residual carbon rate increased by 31.3%–61.6%. The inhibition mechanism of the HMDS terminated m-Cresol inhibitor on coal spontaneous combustion was deduced. • A stable and highly efficient HMDS terminated m-Cresol inhibitor is synthesized. • The inhibition effect of HMDS terminated m-Cresol inhibitor is studied. • The protection-deprotection process remarkably enhance the inhibition efficiency. • Inhibition mechanism of the HMDS terminated m-Cresol inhibitor is proposed. [ABSTRACT FROM AUTHOR]

The frequent occurrence of coal spontaneous combustion (CSC) disasters poses a serious threat to green and safe coal production. Currently, inhibitor application is a crucial method for preventing CSC. In this study, layered double hydroxides (LDHs) were modified using the rare-earth element La3+ to prepare inhibitors (La/LDHs) with varying La3+ content. The prepared La/LDHs were characterized through X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Through a temperature-programmed method and thermogravimetry–differential scanning calorimetry, the effect of the prepared La/LDHs on the low-temperature (30–170 °C) oxidation characteristics and thermodynamic properties of coal were investigated, and the CSC inhibition mechanism of La/LDHs was determined. The results indicated that five La/LDH inhibitors were successfully prepared. The CO concentration, CO generation rate, and oxygen absorption rate of coal samples decreased after the addition of La/LDHs. Moreover, the CSC inhibition effect of the La/LDHs was the strongest at oxidation temperatures of 110–130 °C. The composite coal samples containing La/LDHs exhibited higher adsorption temperature (T 0), critical temperature (T 1), stagnation temperature (T 2), growth-rate temperature (T 3), and burnout temperature (T 7) but lower mass-maxima temperature (T 4), kindling-point temperature (T 5), and maximum-weight-loss-rate temperature (T 6). The La/LDHs shortened the heat release process of coal and considerably reduced the quantity of heat released, with a maximum reduction of 474 J/g. Moreover, the apparent activation energy increased in the mass gain stage and the thermal decomposition stage, with the highest increases of 148.7 and 233.2 kJ/mol, respectively. Among the prepared samples, La/LDH-3 and La/LDH-5 exhibited the strongest CSC inhibition effects. These research results have important practical implications for the prevention and control of CSC during coal production and storage, and for improving environmental protection and safety in coal production. [Display omitted] • Layered double hydroxides (LDHs) containing rare-earth La3+ were successfully prepared. • La/LDHs exhibited the strongest inhibition at 110–130 °C. • La/LDHs increased the apparent activation energy and decreased the heat release. • The inhibition mechanism of coal spontaneous combustion by La/LDHs was determined. [ABSTRACT FROM AUTHOR]

From the perspective of airflow rate adjustment for disaster prevention, controlling methane concentration and reducing spontaneous combustion zone in the goaf naturally contradict. Generally, an increased airflow rate is beneficial in reducing methane concentration but also increases the risk of coal spontaneous combustion. Coal pillars on both sides of an isolated mining face are broken to form air leakage passages, which connect its goaf and the two sides of the goafs to form triple goafs. Especially for triple goafs of the isolated mining faces with high methane concentration and coal spontaneous combustion tendencies, the lack of air leakage law and knowledge of the distribution of methane and oxygen concentrations makes disaster prevention and control difficult. To solve the above problem, this study adopts a computational fluid dynamics (CFD) modeling method to construct a physical model containing triple goafs and investigate the optimal airflow rates for safe production, with an isolated mining face in a mine in Guizhou taken as an object. Results show that the air leakage paths in the triple goafs of the isolated mining face mainly consist of "U–shaped" and "semi–U–shaped". The optimal airflow rates to maintain methane concentration at safety limits and to minimize the spontaneous combustion zone in the triple goafs are 1800 m3/min to 2000 m3/min. In consideration of economic efficiency and workload, the optimal installation spacing of the dynamic barriers is determined as 15.0 m–20.0 m. The study results provide scientific concepts and practical guidance for the prevention and control of methane and coal spontaneous combustion hazards in triple goafs of isolated working faces. [ABSTRACT FROM AUTHOR]