FLUIDIZED-BED COMBUSTION OF COAL

Fluidized-bed combustion of coal has been investigated in a pilot-plan t combustion facility. The test bed section has an internal diameter o f 0.154 m and an overall height of 3.5 m. Sand with an average particl e diameter of 1421 mu m is used as inert bed material. The inert bed i s heated to a temperature of about 1000 K by two propane burners insta lled in the preheater and calming sections. Experiments were conducted for coal-feed rates of 0.83 and 1.09 g/s with corresponding bed tempe ratures of 1220 +/- 43 and 1259 +/- 34 K for superficial air velocitie s in the range 0.63-1.07 m/s at ambient conditions. Concentrations of O-2, CO, CO2, NOx, and SO2 were monitored in the flue gas, and their v ariations with operating parameters used to establish optimum combusti on conditions. Material and energy balances were employed to compute c arbon utilization and thermal combustion and combustion quality effici encies. 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 O-2 and a zero-order reaction with respect to coal nitrogen. Significant kine tic inferences are derived concerning oxidation of coal carbon and sul fur. (C) 1997 Elsevier Science Ltd.