Fluidized-bed combustion of coal

Fluidized-bed combustion of coal has been investigated in a pilot-plant combustion facility. The test bed section has an internal diameter of 0.154 m and an overall height of 3.5 m. Sand with an average particle diameter of 1421 μm is used as inert bed material. The inert bed is heated to a temperature of about 1000 K by two propane burners installed in the preheater and calming sections. Experiments were conducted for coal-feed rates of 0.83 and 1.09 g/s with corresponding bed temperatures of 1220 ± 43 and 1259 ± 34 K for superficial air velocities in the range 0.63–1.07 m/s at ambient conditions. Concentrations of O2, CO, CO2, NOx, and SO2 were monitored in the flue gas, and their variations with operating parameters used to establish optimum combustion conditions. Material and energy balances were employed to compute carbon utilization and thermal combustion and combustion quality efficiencies. Optimum operating conditions were determined for efficient and environmentally friendly combustion. It is proposed that oxidation of coal nitrogen to NO is a first-order reaction with respect to O2 and a zero-order reaction with respect to coal nitrogen. Significant kinetic inferences are derived concerning oxidation of coal carbon and sulfur.