Critical Impeller Speed (NSG) for Solid Suspension in Sparged Stirred Vessels Fitted with Helical Coils

An attempt has been made to investigate the effect of the presence of a helical coil, used in specific cases to increase the heattransfer rate, on the critical impeller speed (NSG) for a solid suspension in a sparged stirred tank reactor. It has been observed that the coil disturbs the flow pattern generated by the impeller, consequently affecting the critical impeller speed. The critical impeller speed increases with an increase in the superficial gas velocity (investigated in the range of 0.52-9.74 mm s^-1). For the small-size solids (<150 (mu)m), typical of the industrial catalyst size and the range of solid loading investigated (0.5-2 wt %), the six-bladed downflow-pitched (45 (degree)) turbine was found to be the most efficient impeller in terms of power required for a solid suspension.