Experimental study on gas-heat characteristic scales during the entire coal spontaneous combustion-extinction-reignition process in sealed fire zones

Sealed fire zones in coal mines present severe reignition risks during unsealing. This issue stems primarily from the overlapping and coupling of multiple parameters during the coal spontaneous combustion-extinction-reignition process (CERP), making it difficult to distinguish key characteristic information and accurately guide on-site disposal. Spontaneous combustion tendency theoretical calculations and a self-developed similarity simulation test system were used to systematically investigate the gas-thermal characteristics and spatiotemporal evolution laws throughout the CERP. The results show that the heat propagation rate in the vertical direction is higher than that in the horizontal direction. High-temperature zones (>30 °C) are distributed approximately in a “flat elliptical” shape centered on heating rods D2 and D3, while the high-temperature zone centered on heating rod D1 presents an “inverted conical” distribution. The area of the high-temperature zone gradually expands from bottom to top, with the top layer having the largest area. Convective heat transfer of high-temperature flue gas dominates the heating/cooling process of loose coal. When reheated after cooling under a pure N₂ atmosphere, the coal reaches a higher maximum temperature than that of the first heating process, corresponding to the shortest heating time. This is followed by cooling under 10% O₂ and 21% O₂ atmospheres and finally under 3% O₂ and 5% O₂ atmospheres. Coal samples cooled under different atmospheres show higher concentrations of CO, CO₂, CH₄, and C₂H₄ compared to raw coal. Meanwhile, when the coal samples cooled under different atmospheres are reheated for reignition, each gas concentration at the same stage is generated earlier than raw coal, and the order of gas concentrations (from highest to lowest) is pure N₂ > 10% O₂, 21% O₂ > 3% O₂, 5% O₂ > raw coal. The findings provide technical support for “medium-large” scale tests of sealed fire zones as well as a theoretical basis for guiding the on-site management of fire zones. © 2026 Elsevier Ltd.