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To study the similarities and differences in the macrocharacteristics of a coal seam during low-temperature oxidation at different regions of the same coal mine, six coal samples from the 13-1 seam were selected from Huainan, Anhui, China. The macroscopic spontaneous combustion characteristics, including the gaseous products and characteristic temperatures, during the low-temperature oxidation of samples from different regions of the same coal seam, were studied using a temperature-programmed test. The results revealed that the characteristic temperatures of the samples from the coal seam were close to each other, the critical temperature range was 70–80 °C, and the crack temperature range was 90–100 °C. The CO/O2 ratio varied considerably. Thus, the degree of incomplete oxidation reaction to release CO was different at different regions in the coal seam. Moreover, the variation in the CO/CO2 ratio of the samples from the coal seam was similar. A calorimeter (C80 Calvet, SETARAM, France) was adopted to explore the exothermic characteristics of the coal seam during low-temperature oxidation. The exothermic onset temperature of the samples from the coal seam was similar, with a range of 50.1–54.3 °C. Differences were observed in the total thermal energy released by oxidation at low temperature in the samples from the coal seam; however, the percentage of thermal energy release at low temperature and that during the entire oxidation process was similar. The changes in the apparent activation energy of coal specimens from the seam were similar. It was, and is, important to investigate the prediction and prevention technique of spontaneous combustion in regional coal seams.

Thermophysical properties govern the heat transfer during coal spontaneous combustion. Under different oxygen concentrations, the mass and heat intensity of three metamorphic levels of bituminous coal were investigated through synchronous thermal analysis, and their thermophysical parameters were tested using a laser-flash apparatus. The results indicated that as the oxygen concentration increased, the T3 (the temperature at maximum mass) and exothermic initial temperature slowly decreased. The changes in T1 (maximum adsorption temperature) and T2 (initial temperature at the oxygen-absorption and mass-gain stage) were nonsignificant. The effect of oxygen concentration on mass, heat intensity, and thermophysical parameters was primarily concentrated in high-temperature regions. As the temperature increased, the thermal diffusivity first decreased and then increased. The specific heat capacity gradually increased, then plateaued until it began to decrease; meanwhile, the thermal conductivity increased, first slowly and then quickly. A calculation model for different temperatures and oxygen concentrations was established through curve fitting.

Thermal properties of coal are crucial in the heat-transfer process of its spontaneous combustion. Thermophysical properties of four metamorphic-grade coal samples were investigated in air using a laser-flash apparatus. Their crystallinities were analyzed by X-ray diffractometry. The results indicated that the trend in thermal diffusivity was opposite to that of crystallinity. As the temperature increased, thermal diffusivity first decreased and then increased; specific heat first increased and then decreased. With the exception of the meager lean coal sample, the trend of thermal conductivity as a function of temperature agreed with that of specific heat. As the metamorphic grade of the samples increased, the thermal diffusivity minimum and specific heat maximum shifted toward higher temperatures; in contrast, the minimum thermal conductivity shifted toward lower temperatures. From these trends, it was possible to recognize different temperature ranges according to how different properties (thermal conductivity, thermal diffusivity, specific heat, and metamorphism grade) influenced each other.

To investigate the entire process of first and second coal spontaneous combustion, a 15-t experimental furnace for coal spontaneous combustion and synchronous thermal analyzer coupled with Fourier transform infrared spectroscopy were employed. The process of experimental tests was as follows: First, coal temperature was increased from 31.0 °C (room temperature) to 452.7 °C without intervention. Second, the coal sample was cooled to approximately 90.0 °C in an anaerobic atmosphere. Third, air was supplied until the sample reached 418.0 °C. Finally, the coal was cooled again to 100.0 °C in an anaerobic atmosphere. The variations of temperature, mass, heat energy intensity, and gaseous products were investigated. The results indicated that the temperature change rate first increased and then decreased during the first and second coal spontaneous combustion. Compared with the first coal spontaneous combustion, the rates of temperature and mass loss change with a heating rate of 2.5 °C/min were higher at the combustion stage of the second coal spontaneous combustion, but the variations of the exothermic reaction rate and mass loss with other heating rates (5.0, 10.0, and 15.0 °C/min) were lower. The differences among CO, CO2, alkanes, and alkenes during the first and second coal spontaneous combustions were insignificant until 300.0 °C. However, the emission of CO and CO2 during the second coal spontaneous combustion was significantly higher than during the first coal spontaneous combustion, whereas the release of alkanes and alkenes was substantially weaker when the temperature was higher than 300.0 °C. Moreover, the amount of H2O during the first coal spontaneous combustion was higher than that during the second coal spontaneous combustion.

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link. The low temperature oxidation of coal is a contradictory and unified dynamic process of coexisting mass and heat transfer. The thermophysical properties are crucial during coal spontaneous combustion. In the current paper, the variations of moisture, ash, volatiles, fixed carbon and thermophysical properties (thermal diffusivity, specific heat and thermal conductivity) of three coal samples from 30 °C to 300 °C were studied, and their grey correlation was analyzed. The results indicated that with the increase of temperature, the free moisture of Coals A and B decreased first but then increased, while the free moisture of Coal C kept decreasing without a later increase. The variation of surface moisture was consistent with that of free moisture. The trend of volatiles and fixed carbon was completely the opposite, showing a significant negative correlation. Ash was less affected by temperature. Along with the rise of temperature, the thermal diffusivity of three coal samples decreased first but later increased, and the specific heat was always in a state of increasing. The change in thermal conductivity was mainly affected by specific heat. By calculating the gray correlation degree, the major factors affecting the thermophysical properties were obtained.

The properties of coal and rock mass in coalfield fire areas require investigation because both coal and rock can become deformed by impact or under high temperatures. Thermo-mechanical coupling forms interconnected channels in the air and can produce a combustion center along a coal seam which can further promote unwanted spontaneous combustion. This paper uses a MTS880/25T electro-hydraulic servo material test system to conduct uniaxial compression experimental tests on coal and rock samples from Huojitu coal mine located in Yulin City, Shaanxi Province, China. Various mechanical parameters were recorded for the samples at different temperatures. Results indicate that temperature has a significant effect on the strength of coal and rock mass. As temperature increased, peak strain, elastic modulus, and peak stress of coal and rock mass decreased at first, then rose, and eventually decreased. From 25 to 200 °C, the elastic modulus and peak stress of the rock samples gradually decreased with an increase in temperature, showing a decrease of 31.45% and 34.07%, respectively. Above 200 °C, they gradually rose to their maximum and promptly dropped until the temperature exceeded 400 °C. Peak strain of the rock samples was slightly different from the elastic modulus and peak stress in the same temperature stage. At 300 °C, peak strain increased to its maximum value. Above 300 °C, peak strain began to drop. The peak strain, elastic modulus, and peak stress of the coal sample were less affected by temperatures below 100 °C. They gradually increased until temperatures exceeded 100 °C. The maximal values for peak strain, elastic modulus, and peak stress corresponded to temperatures of 140, 200, and 200 °C, respectively. After the temperatures corresponding to the maximal values were exceeded, the peak strain, elastic modulus, and peak stress of the coal samples decreased.

Belt conveyor has played an essential role in underground coal transportation. However, due to long-distance transport, it facilely confused ventilation system. Furthermore, once belt fires occurred, the accident would be spread to other areas rapidly. Numerous toxic and harmful flue gases would flow along the roadway, which posed a significant threat to the safety of underground miners. In this research, the ventilation system in Wangjialing coal mine, Hejin City, Shanxi Province, China which was taken as the object to investigate how to control the spread of flue gases by the disaster-relief dampers, when the fire happened in belt conveying roadway. The air-quantity could be achieved before and after the adjustment of local ventilation system by the ventilation network calculation. Furthermore, airflow velocities markedly impacted on the belt fire in the roadway in the 20102 face, conducted by the FDS software. The results indicated that an effective method to control the spread of flue gases was install11 disaster-relief dampers in the underground connecting roadways which located among belt-conveying roadway, main return airway, and auxiliary-transport roadway. When the wind speed was about 2.5 m/s, the effect of exhaust smoke was better in the roadway of 20102 working face. The direction of flue gases changed observably after adjusting local ventilation as the disaster relief dampers. Most flue gases went into the main return airway, the quantity of flue gases significantly decreased flowing to the working areas. Therefore, the short circuit and the open circuit for air flow achieved by governing ventilation system as disaster relief dampers was significant for the control of areas flue gases spreading.