Experimental investigation of ignition and combustion characteristics of single coal and biomass particles in O2/N2 and O2/H2O

Oxy-steam combustion is a potential new-generation option for CO2 capture and storage. The ignition and combustion characteristics of single coal and biomass particles were investigated in a flow tube reactor in O-2/N-2 and O-2/H2O at various oxygen concentrations. The ignition and combustion processes were recorded using a CCD camera, and the two-color pyrometry was used to estimate the volatile flame temperature and char combustion temperature. In O-2/N-2 and O-2/H2O, coal ignites heterogeneously at <O-2> = 21-50%. In O-2/N-2, biomass ignites homogeneously at <O-2> = 21-30%, while it ignites heterogeneously at <O-2> = 40-50%. In O-2/H2O, biomass ignites homogeneously at <O-2> = 21-50%. With increasing oxygen concentration, the ignition delay time, volatile burnout time and char burnout time are decreased, and the volatile flame temperature and char combustion temperature are increased. At a certain oxygen concentration in both atmospheres, the ignition delay time, volatile burnout time and char burnout time of biomass are shorter than those of coal. Moreover, biomass has a higher volatile flame temperature but a lower char combustion temperature than coal. The ignition delay time, volatile burnout time and char burnout time in O-2/H2O are lower than those in O-2/N-2 for coal and biomass. The presence of H2O can improve the combustion rates of coal and biomass. The volatile flame shows a lower temperature in O-2/H2O than in O-2/N-2 at <O-2> = 21-50%. The char combustion shows a lower temperature in O-2/H2O than in O-2/N-2 at <O-2> = 21-30%, while this behavior is switched at <O-2> = 40-50%. The results contribute to the understanding of the ignition and combustion characteristics of coal and biomass in oxy-steam combustion. (C) 2018 Energy Institute. Published by Elsevier Ltd. All rights reserved.