A new empirical equation for minimum spouting/spout‐fluidization velocity in draft tube spout‐fluid beds at elevated temperature

Abstract

Draft tube spout‐fluid beds have been widely used in drying, coating, and granulation processes. In these processes, the spout‐fluid reactor is always operated at gas temperatures that exceed ambient conditions. Therefore, one objective of draft tube spout‐fluid bed research is to determine the critical factors that affect the minimum spouting velocity (Ums) and the minimum spout‐fluidization velocity (Umsf) at high temperatures. In this study, four types of particles were used to study the resulting pressure drops. Ums and Umsf were used in a conical draft tube spout‐fluid bed at temperatures of 293–500 K. In addition, a series of operating conditions and geometric configurations were investigated to systematically study the factors that affect Ums and Umsf. Overall, Ums and Umsf increased as the static bed height, entrainment zone height, draft tube diameter, and particle diameter increased. In contrast, Ums decreased as the superficial fluidizing gas velocity and spout nozzle diameter increased. In addition, Umsf increased as the superficial fluidizing gas velocity, spout nozzle diameter, and temperature increased. Furthermore, as the fluidizing gas flow increased, the minimum spouting velocity shifted from increasing to decreasing as the temperature gradually increased. Two general correlations between the Ums and Umsf values and the above factors were proposed. In addition, the influences of operating conditions and geometrical parameters on the minimum spouting velocity should be considered in the design and use of draft tube spout‐fluid beds.