Combustion of single char particles from Victorian brown coal under oxy-fuel fluidized bed conditions

Abstract

Combustion performance of individual and large spherical single char particles of 5–6mm diameter during oxy-fuel fluidized bed (Oxy-FB) combustion is investigated. These char particles were prepared from briquetted Victorian brown coal. In these experiments, a thin thermocouple was inserted inside each char particle to monitor the particle temperature during the experiment. Particle temperature was observed to be higher compared to the bed temperature which varied between 880°C and 925°C. Up to 48°C difference was noticed between the char particle temperature and the bed temperature using 15% steam in oxy-fuel combustion atmosphere. A kinetic model on char combustion was developed to calculate the combustion time, carbon consumption rate and the particle diameter as a function of time in an atmosphere consisting of O2, CO2 and steam. It was evident that boundary-layer oxygen diffusion controlled the carbon combustion rate during oxy-fuel fluidized bed combustion of these brown coal char particles. The gasification reactions were almost negligible for the feed gases and temperature range applicable for Oxy-FB combustion.