Ignition behavior of single coal particle in a fluidized bed under O2/CO2 and O2/N2 atmospheres: A combination of visual image and particle temperature

Single coal particle ignition behavior was studied in a two-dimensional (200 mm × 20 mm × 400 mm) fluidized bed under O2/N2 and O2/CO2 atmosphere with O2 volume concentration in the range of 0-40%, by a combination of visual observation of the volatile flame and measurement of the particle center temperature. A piece of transparent quartz glass was used as the front wall of the fluidized bed to allow visual observation. The investigated fuel particles were spherical sub-bituminous coal particles with diameter in a range of 6-13 mm, which were artificially carved from selected original coal particles. The volatile combustion flame was recorded by a color video camera to analyze its ignition time delay and extinction behavior. The temperature in the particle center was measured by a very thin thermocouple to follow the particle heating process. Results indicate that under O2/CO2 atmosphere the ignition delay time is much longer than in O2/N2 atmosphere. The devolatilization process is controlled by internal and external heat transfer but it is almost unaffected by atmosphere at the same O2 concentration. The effect of volatile combustion on heating and extinction delay time can be neglected for larger coal particles.