An experimental study of the ignition and combustion characteristics of single coal gangue particles under oxy-fuel conditions

The ignition and combustion characteristics of single coal gangue particles under simulated oxy-fuel combustion conditions were experimentally studied. A coal gangue particle was suspended at the tip of a thin wire sample holder and introduced into an electrically heated furnace set at a desired temperature and in a predetermined atmosphere. A high-speed CCD camera was used to record the ignition phenomena and combustion process, which was examined to determine ignition mechanism, ignition delay time and volatile flame duration. The minimum ignition temperature (T-i,T-min) was also studied. The effect of furnace temperature (750-950 degrees C), particle size (3-9 mm), O-2 concentration (10-30% vol.) and steam addition was examined. Results indicate that the coal gangue ignition followed the homogeneous ignition mechanism under conventional combustion conditions (O-2/N-2). Under oxy-fuel conditions (O-2/CO2), however, the coal gangue particles ignited homogeneously at high temperature but heterogeneously at low temperature. Ignition mechanism changed from heterogeneous to homogeneous ignition with steam addition at low temperature. As the temperature or particle size increased, the volatile matter flames decreased in the brightness and size. Increasing O-2 concentration or steam addition resulted in larger and brighter volatile flames. The volatile flame duration became shorter as temperature and particle size increased but longer with increasing concentration of O-2 or steam. The T-i,T-min of particles in O-2/N-2 atmosphere was 662 degrees C but increased by 157 degrees C in O-2/CO2 atmosphere at the same O-2 concentration and decreased with increasing steam concentration.