Effect of Initial Pyrolysis on Radical Reaction During Coal Spontaneous Combustion

Abstract

ABSTRACT Coal in high-temperature deep mines or igneous intrusion mines is prone to complicated spontaneous combustion in the mining process, because it has occurred in a pyrolysis state for a long time. In order to investigate the effect of initial pyrolysis on coal oxidation, in this study, the coal samples were first pyrolyzed to different temperatures in the nitrogen atmosphere and then oxidized in the dry air atmosphere. Meanwhile, the changes in radical parameters (linewidth of ESR spectra, g factor and radical concentration), CO release and O2 content in the process of changing the states of coal samples from pyrolysis to oxidation at 70°C, 110°C, 150°C and 190°C were determined through experiments. The following conclusions were drawn: When the coal samples change from the pyrolysis state to the oxidation state, their linewidths of ESR spectra increase suddenly, and such an increase is more obvious when the change is made at a lower temperature. The linewidth increases by more than 0.066 mT after the change at a temperature lower than 110°C. Initial pyrolysis promotes the turning point temperature of g factor, and the turning point temperatures of g factor of coal after the gas atmosphere is changed from nitrogen to dry air at 70°C, 110°C, 150°C and 190°C are 160°C, 180°C, 190°C and 200°C, respectively. The growth rate of radical concentration surges after the change from the pyrolysis state to the oxidation state, and the radical concentrations of the coal samples whose states are changed after 150°C grow faster than that of the coal sample oxidized in dry air. When the temperature is lower than 110°C, the CO release under the pyrolysis and oxidation conditions is low, the maximum value being only 105 ppm. At the final temperature of 230°C, when the gas atmosphere is changed from nitrogen to dry air at 70°C, 110°C, 150°C and 190°C, the CO produced by coal is 14,386 ppm, 13220 ppm, 11836 ppm and 10,287 ppm, respectively. The mode of the effect of initial pyrolysis on coal spontaneous combustion was discussed in the end, and the conclusions are of guiding significance for coal spontaneous combustion control.