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 O₂/N₂ and O₂/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 O₂/N₂ and O₂/H₂O, coal ignites heterogeneously at <O₂> = 21–50%. In O₂/N₂, biomass ignites homogeneously at <O₂> = 21–30%, while it ignites heterogeneously at <O₂> = 40–50%. In O₂/H₂O, biomass ignites homogeneously at <O₂> = 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 O₂/H₂O are lower than those in O₂/N₂ 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 O₂/H₂O than in O₂/N₂ at <O₂> = 21–50%. The char combustion shows a lower temperature in O₂/H₂O than in O₂/N₂ at <O₂> = 21–30%, while this behavior is switched at <O₂> = 40–50%. The results contribute to the understanding of the ignition and combustion characteristics of coal and biomass in oxy-steam combustion.