Spatiotemporal Distributions of the Temperature and Index Gases during the Dynamic Evolution of Coal Spontaneous Combustion

To study the migration of the high-temperature region and the dynamic changes in the index gas concentration during spontaneous coal combustion and oxidation, we established spatiotemporal distributions of the temperature and index gases during the dynamic evolution of spontaneous coal combustion. The XK-VI coal spontaneous combustion experimental system was used to investigate the migration law of the high-temperature region of loose coal in an air leakage field environment, and gas was then collected and analyzed. The results indicated that the coal temperature showed a stepwise change during the whole heating process. The general trend of the migration changes of the high-temperature points in the test furnace was to move toward the air inlet side and move from the low-oxygen concentration area toward the high-oxygen concentration area. Before the critical temperature, the high-temperature points were approximately 65 cm away from the air inlet. After the critical temperature, the high-temperature points gradually appeared at a distance of 45 cm from the air inlet. When the coal temperature exceeded the dry cracking temperature, the high-temperature points moved down to approximately 8 cm from the air inlet and finally moved to the air supply surface. Through analysis of the gas concentration in the furnace, the gas content varied with the migration of the high-temperature points in the furnace. The oxygen consumption rate and CO and CO2 production rates increased slowly before the dry cracking temperature and increased rapidly after the dry cracking temperature. The gas ratios of CO/CO2, CH4/C2H6, and C2H4/C2H6 changed near the critical temperature, and CO/CO2 and CH4/C2H6 changed from decreasing to rapidly increasing, and C2H4/C2H6 sharply increased from zero.

Automated summary

The study found that during spontaneous coal combustion, the migration distance of the high-temperature region changes with time and temperature, while the oxygen consumption rate and gas production rates increase slowly before the dry cracking temperature and rapidly after. Gas ratios also change near the critical temperature.