Co-pyrolysis characteristics and kinetics of low metamorphic coal and pine sawdust

Co-pyrolysis experiments with low metamorphic coal (LC) and pine sawdust (PS) were carried out in a fixed-bed pyrolysis reactor. The effect of biomass addition on the yield distribution and composition of the coal pyrolysis products was investigated. The pyrolysis behavior was studied by thermogravimetric analysis. The Coats–Redfern integral and Achar differential methods were used to study the mechanism functions and the kinetic parameters of the pyrolysis process of each sample. The results show that there is a synergistic effect on the co-pyrolysis and it is most pronounced at a PS mixing ratio of 30%, and it results in improved tar and gas yields. Part of the polycyclic aromatic hydrocarbons (PAHs) in the co-pyrolysis tar are converted into phenolic substances with a simple structure, which improves the quality of the tar. At the same time, the alcohols and acids in the PS and LC react to generate a large number of esters. The addition of PS shifted the LC pyrolysis process towards the low temperature region, lowering the pyrolysis temperature of the coal sample and increasing the pyrolysis rate of the sample. The main pyrolysis process of LC conforms to the second-order chemical reaction law with an activation energy of 35.93 kJ mol(−1), and the main pyrolysis process of PS conforms to the one-dimensional diffusion parabolic law with an activation energy of 63.84 kJ mol(−1), and the main pyrolysis process of LC and PS co-pyrolysis conforms to a second-order chemical reaction law with an activation energy of 86.19 kJ mol(−1).