Effects of alkali and alkaline earth metallic species on pyrolysis characteristics and kinetics of Zhundong coal

The pyrolysis process of raw (R-form) and acid-washed (H-form) Zhundong coal was investigated by temperature-programmed thermogravimetry, and the kinetic parameters were calculated using distributed activation energy model (DAEM). The results show that the pore structures of Zhundong coal keep abundant in pyrolysis. The presence of alkali and alkaline earth metals (AAEM) has no significant influence on the macromolecular network structure of Zhundong coal, but raises its equilibrium moisture content and release rate of volatiles during the secondary degasification stage. AAEM lowers release rate of volatiles during the main pyrolysis stage and final weight loss. The pyrolysis behavior of Zhundong coal could be described by the DAEM accurately within a wide range of temperature. The pyrolysis activation energy of R-form and H-form coal increases with increasing conversion. The activation energy of R-form coal is higher than that of H-form coal at the same conversion. The maximum value of activation energy distribution function of R-form and H-form coal is 261.85 and 264.51 kJ/mol, respectively. AAEM elevates the pyrolysis activation energy, makes its distribution more concentrated, and reduces the pyrolysis reactivity. The relationship between frequency factor and activation energy presents obvious kinetic compensation effect.