Insight into the chemical reaction process of coal during the spontaneous combustion latency

The oxidation reaction intensity of coal is quite weak during the spontaneous combustion latency. A thermopile sensor suitable for an isothermal flow reactor was developed to monitor the temperature of coal during the spontaneous combustion latency. The role of oxidation temperature and particle size were discussed. The element and oxygen-containing functional group changes of coal samples after oxidation were measured by X-ray photoelectron spectroscopy (XPS). The results show that the coal temperature has remarkable laws which conforms to a quadratic polynomial T = T0+A t-B t2+C t3-D t4. In the temperature range 20–70 °C, a temperature dependence of reaction rate which does not conform to the Arrhenius equation. The laws accord with a third order polynomial function ln(Dt/dt) = A(1/T)3+B(1/T)2+C(1/T)+D. The decrease of particle size can effectively increase the oxidation heat released by coal during the spontaneous combustion latency. Singly bonded C–O groups, phenol, alcohol or ether, dominate at all temperatures over other oxygen-containing functional groups. The contents of C–O groups and hydroperoxide continue to increase during the spontaneous combustion latency. The results will be helpful to further reveal the oxidation mechanism of coal during the spontaneous combustion latency.