Combustion behaviors of various coals and chars: From covalent bonds’ and radicals’ perspective

Abstract The combustion behaviors of chars under reaction control are important for utilization, correlating work from bonds’ and radicals’ perspective are needed for further quantitative works. In this work, the effects of minerals, and mass and heat transfer were eliminated using deashed samples and temperature-programed combustion with low heating rate. The combustion of 15 coals and 45 chars prepared under different temperatures were studied. Using differential thermal analysis, nuclear magnetic resonance, electron spin resonance data coupled with model compounds, the combustion behaviors of coals and chars can be divided into three regions, with temperature lower than 325 °C, higher than 325 °C and lower than 430 °C, higher than 430 °C, and the eight covalent bonds with or without effect of radicals can be sorted into three steps corresponding to the three regions. The initial step rely highly on aliphatic carbon bonds and the last step are mainly determined by the aromatic bonds in poly-aromatic rings. Therefore, pyrolysis processes with less volatile-char interaction or sufficient bonds’ dissociation with less emission of volatiles are preferred to prepare chars as alternative feeds, and the three-region division can help to build generic kinetic networks on combustion of complex hydrocarbons.