Search

Coal spontaneous combustion (CSC), as the central cause of coal fire disasters, gravely threatens the safety and efficiency of coalmine production. We take Huating long flame coal as an example and use simultaneous thermal analyzer to investigate how oxygen concentration and heating rate effects CSC characteristics. The reaction process, variation of characteristic temperature, and heat flow were studied. Besides, the kinetic model and parameters were calculated through Šatava and Ozawa methods. The results indicated that the curve peaks of TG and DSC moved to lower temperatures and the characteristic temperatures gradually decreased when the oxygen concentration changed from 3 to 21%. On the contrary, the curve peaks of TG and DSC moved to higher temperature region and the characteristic temperatures increased as the heating rate rose. The most probable mechanism function of Huating long flame is determined to be Avrami–Erofeev equation (n = 3) by calculation. When oxygen concentration is 3% or 21%, CSC showed larger tendency. The higher the heating rate, the larger the apparent activation energy, and harder to occur CSC. These findings provide a basis for discovering the formation and evolution mechanism of coal fires. [ABSTRACT FROM AUTHOR]

A large-scale experiment on coal spontaneous combustion (CSC) was conducted to investigate the experimental spontaneous combustion period (ESCP) and limit parameters. Coal samples were collected from the Wenjiapo coal mine in the Binchang mining area in Shaanxi Province, China. Specifically, the high-temperature point (HTP) migration of coal and the variations in the oxygen consumption rate, heat release intensity, lower limit oxygen concentration (LOC), maximum air leakage intensity (ALI), and minimum residual coal thickness (RCT) during CSC were investigated. The ESCP was discovered to be 35 days. During CSC, the HTP moved from the middle of the coal body to the bottom where air was supplied. Heat release intensity and oxygen consumption rate were directly proportional to coal temperature. Under the same conditions, minimum RCT increased with ALI, lower LOC decreased as RCT increased, and maximum ALI increased with RCT. [ABSTRACT FROM AUTHOR]

Coal-based activated carbon (CBAC) is widely used in several industrial processes and daily life, however, it is susceptible to spontaneous combustion during storage and transportation. Therefore, it is essential to probe the spontaneous combustion risk of CBAC. The oxidation process of briquetting material sample (BM), carbonized material sample (CM), and activated material sample (AM) was studied via thermogravimetric (TG–DTG) analysis. The oxidation mechanism of the samples was investigated via the proximate and ultimate analyses, Fourier transform Infrared (FTIR) spectroscopy, and nitrogen adsorption. Kinetic characteristics of the samples during the combustion were determined using the Kissinger–Akahira–Sunose (KAS) method. Five characteristic temperature points and the five stages of the samples during oxidation were obtained. With an increase in the heating rate, the hysteresis phenomenon was observed during thermal decomposition and combustion of AM in TG–DTG curves. The heating value of BM, CM, and AM were 6678, 6705, and 6776 cal g–1, respectively. AM has a developed pore structure that leads to enhanced oxygen adsorption and limited heat transfer, easy to induce spontaneous combustion. The main functional groups of AM were hydroxyl groups and aromatic hydrocarbons, especially hydroxyl groups that played a key role in the spontaneous combustion of AM. The apparent activation energy (Ea) during the combustion of BM, CM, and AM were 110.70, 85.90, and 111.80 kJ mol–1 from the KAS method, respectively. These results are expected to facilitate a better understanding of CBAC spontaneous combustion. [ABSTRACT FROM AUTHOR]

Coal fires are widespread in the coal–major producing countries, which causes serious environmental issues due to the high temperature and hazardous gases during coal combustion. Under oxygen–depleted atmospheres, the thermal behaviors and kinetic characteristics during coal combustion at high temperatures were paid more attention by the method of TG–DSC synchronous thermal analysis. The results indicate that the focused weightlessness and heat release processes became scattered under oxygen–depleted atmospheres, and the influence of oxygen concentration obviously increased when it was below 13 vol.%. The mass presented a linear correlation to the quantity of heat release, and the relationship between the mass and quantity of heat release showed stage characteristics with oxygen concentration. Moreover, the kinetic modes transformed from random nucleation and subsequent growth to contractive sphere, and the critical oxygen concentrations are consistent to these of thermal behaviors. These findings are significant for better understanding the characteristics of coal spontaneous combustion at high-temperature and under low-oxygen concentrations. [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]

The critical temperature is a key parameter in coal spontaneous combustion. To acquire variation of the critical temperature and the corresponding relationship between the index gases and critical temperature, we gleaned the coal samples from No. 3 seam in Yanzhou coalfield, Shandong Province, China. Thermogravimetry (TG) was used to analyze the effects of particle size, heating rate, and oxygen concentration on critical temperature. The index gases were determined by 15-t experimental furnace of coal spontaneous combustion. The results showed that the critical temperature measured by TG experiment indicates a trend that is augmented with the increase in particle size. When the heating rate was set up with 5 °C min and the oxygen concentration was 14.9 mass% (13 vol%), the critical temperatures of coal samples with different particle sizes reached the maximal values. When the heating rate rose to 20 °C min and the oxygen concentration was 14.9 mass% (13 vol%), the critical temperatures of coal samples with particle sizes <0.105 mm reached maximums, while they reached minimums when the particle size was >0.105 mm. As the particle was smaller than 0.098 mm, the difference in critical temperatures during two kinds of heating rate tended to first increase, then decrease, and reached a maximum under the condition that the oxygen concentration was 14.9 mass% (13 vol%), while it reached a minimum when the particle size was larger than 0.098 mm and presented a style of 'M.' The critical temperature as measured by TG experiment was in the range of 45.4-103.2 °C. The critical temperature is, respectively, achieved in coal spontaneous combustion by the 15-t experimental furnace, in which the concentrations of CO and CO increased obviously and the value of CO/CO reached its maximum. [ABSTRACT FROM AUTHOR]

Coal spontaneous combustion (CSC) is a major concern in the exploitation and utilisation processes of coal. Various technologies for inhibiting CSC have been developed, promoting industrial safety. With consideration of the complexity of the processes involved, efficient fire prevention and control techniques should be developed. Commonly used retardants for CSC prevention were reviewed. Based upon the necessary conditions required for CSC and coal − oxygen reaction mechanism, various materials used in CSC inhibition are analysed in detail and classified into physical-based, chemical-based, as well as composite retardants. The novel composite retardants combine both physical and chemical-based mechanisms in controlling CSC. The advantages and disadvantages of each CSC retardant are discussed and inter-compared. This review can promote research in the most needed areas to develop more efficient and affordable materials for CSC prevention. [ABSTRACT FROM AUTHOR]

• Variation of atomic ratio and microcrystalline structure with temperature under nitrogen atmosphere were explored. • Abrupts of H/C and O/C occured as rising the temperature of coal samples. • Correlation was established by thermal property with atomic ratio and microcrystalline structure. To explore the main influencing factors of atomic ratio (O/C, N/C, and H/C) as well as microcrystalline structure (d 002 , L a , L c , and M c) on thermal properties (specific heat capacity, thermal conductivity, and thermal diffusivity) at certain temperatures within 30.0–300.0 °C, three coal samples were collected from coal mines of Dafosi, Yangjiaping, and Hujiahe in Binchang coalfield, Shaanxi Province, PR China. Thermal properties of coal samples were determined by laser-flash apparatus in nitrogen atmosphere. After temperature treated at 30.0, 60.0, 90.0, ..., 300.0 °C in nitrogen atmosphere, the atomic ratio and microcrystalline structure of samples were measured by proximate analyser and X-ray diffractometer. The results indicated that with an increment in the temperature, the value of H/C for three coal samples diminished slightly and then promptly, whereas O/C diminished slightly and then increased before 120.0 °C, as well as finally increasing, and the N/C had no obvious change. Concurrently, the microcrystalline structure of coal samples became more orderly and complete. Furthermore, the TD decreased with temperature, the SHC and TC showed an opposite trend with TD. Based upon grey correlation analysis, the major influencing factors of atomic ratio and microcrystalline structure on thermal property were approached. The results provided insight into the physicochemical properties of the coal of interest for predicting the progress of coal spontaneous combustion. [ABSTRACT FROM AUTHOR]

• Analytical method combining thermal analysis with thermal property was adopted. • Effect of oxygen concentration on the thermal property of coal was investigated. • Model of thermal diffusivity and thermal conductivity was established. • Macroscopic variations of mass and heat intensity were revealed by microcosmic. 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 T 3 (the temperature at maximum mass) and exothermic initial temperature slowly decreased. The changes in T 1 (maximum adsorption temperature) and T 2 (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. [ABSTRACT FROM AUTHOR]