Modelling and experimental studies on oxy-fuel combustion of coarse size coal char

Oxy-fuel combustion of single coarse sub-bituminous coal char particle is investigated in an isothermal mass loss apparatus. Experimental studies are performed at the reactor temperature of 1100 K and in varying O2 concentrations of 42-60% in both O2-CO2 and O2-N2 environments. A fully transient model is developed for the combustion and gasification reactions including the transport of heat and mass in the porous char particle and the gas film. The model is validated with experimental findings of the present authors as well as that reported in literature over a wide range of O2 concentrations. Simulation study is carried out to assess the effect of the particle size, the reactor temperature and the gas composition. The simulation shows that low diffusivity of O2 within the reactor in CO2 environment and the endothermic gasification reaction are mainly responsible for lowering the peak temperature and the rate of combustion of char than that in O2-N2 environment. It is also observed that though the effect of CO2 on the combustion rate at low temperatures is insignificant, it is considerable at the reactor temperature of 1273 K and above in O2-CO2 environment. The model is expected to provide vital information for reactor design under oxy-fuel combustion and its integration with CFD analysis for identifying the optimum particle size, reactor temperature and oxygen concentration.