An experimental study of ignition and combustion of single biomass pellets in air and oxy-fuel

This study presents an experimental investigation of the ignition and combustion characteristics of single biomass pellets in air and O-2/CO2 atmospheres containing 21%, 30%, 40%, 50% and 100% oxygen mole fractions. In this experiment, the temperature of the gas surrounding the biomass pellets was set respectively at 873 K, 973 K and 1073 K. The rate of co-flow gas was set at 10 L/min, 15 L/min and 20 L/min. Single pellets of Pinus bungeana and rice husk were fixed on a thermocouple and burned in a vertical heating tube furnace. High-speed photography was used to record images of the combustion process of biomass pellets. The resulting images exhibit two ignition behaviors: (1) homogeneous ignition of volatile, and (2) heterogeneous ignition on the particles' surface. After ignition, the combustion was no longer a homogeneous combustion of volatile. When the oxygen concentration exceeded 50%, the biomass showed a hetero-homogeneous combustion. Similarly, when the concentration of O-2 increased, the flame became shorter and more stable. With the same oxygen concentration, and once the N-2 was replaced by CO2, the ignition delay, internal ignition temperature and the volatile combustion time increased. Inversely, when the oxygen concentration exceeded 21% (i.e. under the conditions of oxy-fuel), these parameters were correspondingly reduced. In other words, the ignition and combustion intensity were increased. The effects of oxygen concentration and co-flow temperature on ignition and combustion of biomass pellets were greater than that of co-flow velocity. The study's results show that the biomass pellets did not break during combustion. (C) 2016 Elsevier Ltd. All rights reserved.