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To improve the accuracy of early warning on coal spontaneous combustion (CSC), this paper, on the basis of the principle of preferential selection of index gases in CSC process, carries out fitting analysis of the variation curve of index gas data with coal temperature by combining logistic fitting model, then establishes a CSC graded warning system based on positive pressure beam tube monitoring, and determines CO, O2, φ(CO)/φ(O2), C2H4, C2H6, φ(C2H4)/φ(C2H6) as the index gases for predicting and forecasting CSC, and accurately divides the CSC process into seven levels of early warning: safe, gray, blue, yellow, orange, red, and black. Applying the CSC positive pressure beam tube monitoring system to Dongtan coal mine and analyzing the error by manual sampling and sampling by positive pressure beam tube system, we find that the error is less than 0.1%. Monitoring of several working faces, we get that the CO and CH4 concentrations of 14,320 working face are higher than the normal level at the beginning of mining, and the 100 × CO/ΔO2 value is higher than the gray warning threshold of 0.1, and the warning level is gray warning. After taking timely preventive measures against coal oxidation and warming, the CO and CH4 concentrations return to the normal level and the warning level drops to the safe level. This paper improves the monitoring, identifying and early warning capabilities of underground CSC in its early stage. [ABSTRACT FROM AUTHOR]

Residual coal in mine goafs will be oxidized in the presence of air leakage, which can be well tracked through the radical reaction. This study aimed to explore the changes in radical parameters and the reactivity and persistence of newly produced radicals of coal at different temperature stages. To this end, an in situ electron spin resonance (ESR) spectrometer was adopted to measure changes in radical parameters at the heating, maintaining and cooling stages in real time. The following conclusions were drawn. At the heating stage, the radical concentration first rises slowly and then surges; the g factor remains small initially and increases rapidly later; the linewidth falls continuously. At the maintaining stage (230 °C), the radical concentration keeps increasing, while the g factor and the linewidth remain stable. At the cooling stage, the radical concentration first decreases and then stabilizes at a relatively high level, and both the g factor and the linewidth nearly return to the initial values. Based on the changes in radical parameters at different oxidation stages, the radicals in coal are divided into transient radicals and persistent radicals according to their survival times. Transient radicals, which are strongly reactive, are quickly consumed, while persistent radicals, which is of weak reactivity, can exist in the system for a long time. That is, the active radicals in coal are transient, while the stable ones are persistent. In addition, this paper gives insight into the changes in contents of active radicals and stable radicals at these stages. Finally, the changes in indicator gas and oxygen concentrations at these stages were analyzed. The research finding further explains the mechanism of radical reactions during coal spontaneous combustion. [ABSTRACT FROM AUTHOR]

To accomplish various and efficient inhibitions of coal spontaneous combustion (CSC) and solve the safety hazards of CSC encountered in the production and operation of coal mining enterprises, inhibitors play an important role in the prevention and management of CSC. Herein, we report quercetin, which is selection as an antioxidant to prepare a composite solid lipid inhibitor. The concentration of the composite solid lipid inhibitor with the best inhibition effect on the active groups is selected by Fourier pressure infrared experiments, the change pattern of gas content and characteristic temperature released from coal samples during an oxidation process warming process was tested by using a programmed warming test system and simultaneous thermal analysis experiments, and finally, the inhibitory rate and combustion characteristic index were calculated. The results of the research showed that 10 mass% of quercetin had the most impact on the various groups, the highest inhibitor rate of the composite solid lipid inhibitor is 80.67% in the coal low-temperature oxidation process, compared to the raw coal, the heat release of coal treated with the composite solid lipid inhibitor was decreased by 507.65 J g−1, the maximum amount of heat emitted was lowered by 60%, and the flammability index was reduced by 56.4. A composite solid lipid inhibitor containing quercetin developed in this paper indicated high effectiveness in inhibiting CSC, which is vital for coping with the safety management of coal mine production. [ABSTRACT FROM AUTHOR]

Spontaneous combustion of oxidized coal was one of the serious hazards during coal mining and utilization. However, spontaneous combustibility of oxidized coal affected by the first oxidation of coal was still unclear. In this paper, the influence of pre-heating with different oxygen concentrations on coal secondary spontaneous combustion behaviors was studied. Temperature-programmed heating experiments were carried out to prepare pre-heated coal samples by heating at the preset temperature of 80 °C in mixture atmosphere of N2 and O2 with different oxygen proportions of 0%, 5%, 10%, 15%, 20%. Pre-heated and raw coals were heated programmatically in an air atmosphere of 120 mL min−1 with a heating rate of 0.33 °C min−1. The gaseous compounds of O2, CO and CO2 were analyzed to identify spontaneous combustion behaviors of pre-heated and raw coals. The results showed that pre-heating at 80 °C promoted oxygen physisorption at low temperatures and lowered oxidability at high temperatures in the coal secondary oxidation process. Pre-heating at 80 °C with higher oxygen content reduced oxidability and exothermicity of coal secondary spontaneous combustion, but had no obvious effect on oxygen physisorption of coal low-temperature oxidation. [ABSTRACT FROM AUTHOR]

Spontaneous combustion of coal leading to mine fire is a major problem in most of the coal mining countries in the world. It causes major loss to the Indian economy. The liability of coal to spontaneous combustion varies from place to place and mainly depends on the coal intrinsic properties and other geo-mining factors. Hence, the prediction of spontaneous combustion susceptibility of coal is of utmost importance for preventing the risk of fire in coal mines and utility sectors. Machine learning tools are pivotal in system improvements in relation to the statistical analysis of experimental results. Wet oxidation potential (WOP) of coal determined in the laboratory is one of the most relied indices used for assessing the spontaneous combustion susceptibility of coal. In this study, multiple linear regression (MLR) and five different machine learning (ML) techniques, such as Support Vector Regression (SVR), Artificial Neural Network (ANN), Random Forest (RF), Gradient Boosting (GB) and Extreme Gradient Boost (XGB) algorithms, were used to predict the spontaneous combustion susceptibility (WOP) of coal seams based on the coal intrinsic properties. The results derived from the models were compared with the experimental data. The results indicated excellent prediction accuracy and ease of interpretation of tree-based ensemble algorithms, like Random Forest, Gradient Boosting and Extreme Gradient Boosting. The MLR exhibited the least while XGB demonstrated the highest predictive performance. The developed XGB achieved R2 of 0.9879, RMSE of 4.364 and VAF of 84.28%. In addition, the results of sensitivity analysis showed that the volatile matter is most sensitive to the changes in WOP of coal samples considered in the study. Thus, during spontaneous combustion modelling and simulation, volatile matter can be used as the most influential parameter for assessing the fire risk of the coal samples considered in the study. Further, the partial dependence analysis was done to interpret the complex relationships between the WOP and intrinsic properties of coal. [ABSTRACT FROM AUTHOR]

Coal spontaneous combustion (CSC) has been endangering the safety of the coal industry. Spontaneous combustion of coal may lead to coal seam combustion and gas explosions in coal mines, causing a lot of damage. At the same time, CSC will produce a large amount of carbon dioxide, which seriously endangers the ecological environment. Therefore, what reduces the spontaneous combustion of coal is necessary. Ionic liquid (IL) is a new kind of green organic solvent. It has the characteristics of good stability and can be used as a flame retardant for CSC. In this study, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (Bmim[Ntf2]) was selected as the flame retardant of bituminous coal spontaneous combustion, where thermal stability of bituminous coal treated by Bmim[Ntf2] and raw bituminous coal was studied by the simultaneous thermogravimetric analyzer. The apparent activation energy was calculated by the FWO method. The decomposition gas products of bituminous coal and bituminous coal treated with Bmim[Ntf2] were analyzed by Fourier-transformed infrared spectrometer to investigate the effect of intramolecular hydrogen bond on bituminous coal spontaneous combustion. The results show that Bmim[Ntf2] inhibits the spontaneous combustion of bituminous coal. The addition of Bmim[Ntf2] increases the decomposition temperature of bituminous coal, where the apparent activation energy is increased. The results of Fourier-transformed infrared spectrometry show that the reduction in hydrogen bonds reduces the risk of spontaneous combustion of bituminous coal. [ABSTRACT FROM AUTHOR]

There is a high potential for coal spontaneous combustion (CSC) above the roof beams of supports during the mining-stopped period. Early detection of temperature abnormal zones and corresponding measures are necessary to prevent CSC. In this work, a top-coal temperature measurement method was proposed, combining the coal surface temperature detection and the drilling temperature observation. Furthermore, an apparatus was developed that dramatically increases the rate of dry ice sublimation, resulting in the rapid release of cryogenic carbon dioxide gas. The device utilizes water from firefighting pipes in underground coal mines as a heat source for dry ice sublimation without electrical energy and has been applied and validated taking Silaogou Coal Mine in China as a field test site. Specifically, we found that during the stoppage period, the coal above the supports near the air inlet tunnel is more likely to appear hot spots; the carbon dioxide gas generated by the dry ice phase change device can quickly reduce the hot spots temperature, and the coal temperature does not rebound after the gas injection is stopped. Based on the above analysis, this work can effectively prevent the early top-coal spontaneous combustion during the stop mining period. [ABSTRACT FROM AUTHOR]