Thermogravimetric and infrared spectroscopic study of bituminous coal spontaneous combustion to analyze combustion reaction kinetics

Abstract

Thermogravimetry and in-situ Fourier transform infrared spectroscopy were used to study spontaneous combustion in bituminous coal. The results show that the coal’s spontaneous combustion can be divided into five stages, Stages I–V. Qualitative analysis of changes in the molecular functional groups allowed the chemical reactions in each stage to be deduced. Through semi-quantitative calculations of alkyl side bond length, and the degrees of aromatic condensation and oxygen enrichment degree, the critical temperature T1, mass maximum temperature T2 and ignition temperature T3 were identified as important characteristic temperature points for spontaneous combustion which shows that coal spontaneous combustion is produced by multi-stage reactions. Isoconversional calculations found that the apparent activation energies of the oxygen absorption and weight gain and slow chemical reaction stages gradually increased as the temperature increased but the apparent activation energy decreased after T3. Calculations also show that different stages have different reaction mechanism functions. Recognizing that these stages exist is important for deepening our understanding of coal oxidation reactions.