Coal combustion characteristic in a circulating fludidzed bed

Abstract

In the bubbling and the circulating fluidized bed (7.79 cm I.D. × 260 cm high) combustion, combustion efficiency, temperature profiles and flue gas composition of coal-air system have been determined. Bituminous coal having heating value of 6900 Kcal/kg was employed. Coal particle size of 0.725 and 1.03 mm, excess air of 0, 15, 30 and 45%, bed temperature of 750, 800, 850 and 900℃, feeding rate of 1, 2 and 3 kg/hr, recycle rate of 20 and 40 kg/hr were employed for combustion studies. In the bubbling and the circulating fluidized bed combustion, combustion efficiency for the circulating fluidized bed combustion is higher than for the bubbling fluidized bed, and temperature profile is relatively uniform through the whole bed in the circulating fluidized bed combustion. Combustion efficiency increases with increasing excess air and bed temperature, decreases with increasing particle size in the bubbling and the circulating fluidized bed combustion. Combustion efficiency relatively increases with increasing recycle rate of unburn coal in the circulating fluidized bed combustion. The ratio of $CO/CO_2$ decreases with increasing bed temperature and excess air, and the ratio of $O_2/(CO + CO_2)$ decreases with increasing bed temperature in the bubbling and the circulating fluidized bed combustion.