Drying of water treatment process sludge in a fluidized bed dryer

The drying characteristics of water treatment process (WTP) sludge were inv estigated with a fluidized bed. The equilibrium moisture ratio of WTP sludg e increased with relative humidity and decreased with temperature of drying air. However, equilibrium moisture ratio of WTP sludge was mon sensitively dependent on relative humidity than temperature of drying air. When the sl udge was dried in a batch fluidized bed, the drying rate of sludge decrease d as the moisture ratio of sludge in the bed decreased. The periods of cons tant drying rates were apparently nor observed on the drying rate curves. I n addition, the maximum drying rates were increased with bed temperature an d superficial air velocity. As the fluidized bed was operated continuously, the degree of drying of WTP sludge increased with bed temperature but was weakly dependent on superficial air velocity. However, the drying efficienc y was decreased with bed temperature and relatively insensitive to superfic ial air velocity and increased with feed rate of sludge.