Development of semi-parallel reaction model of devolatilization and heterogeneous reaction for pulverized coal particles

A semi-parallel reaction model for the devolatilization and heterogeneous reaction of coal particles during pulverized coal combustion was developed. The quasi-steady mass transfer around a single coal particle with devolatilization and the oxidation of char were analyzed to investigate the effect of the convective flow generated by devolatilization on the mass transfer of the oxidant to the particle surface at various reaction temperatures and particle diameters. The oxidation rates of char with devolatilization were lower than those without devolatilization. This tendency became pronounced with increasing reaction temperature and particle diameter. This indicated that the convective flow generated by devolatilization inhibits the mass transfer of the oxidant to the particle surface and that the influence of the devolatilization depends on the reaction temperature and particle diameter. In addition, the oxidation rates estimated by the semi-parallel reaction model were compared with those obtained from the conventional sequential reaction model and parallel reaction model. In contrast to the other models, the semi-parallel reaction model more accurately represented the decrease in char oxidation rates with increasing devolatilization rate.