Drying Kinetics of Paddy in a Reduced Pressure Superheated Steam Fluidized Bed

Abstract

Drying kinetics of paddy are experimentally studied in a superheated steam fluidized bed operating at reduced pressure. During the experiments, different operating pressures (40–67 kPa), operating temperatures (98–118°C), superficial steam velocities (2.9–4.0 m/s), and mass flow rates (0.0061–0.0103 kg/s) were employed. The condensation problem, typically observed in the initial part of the process, was eliminated in the majority of the experiments through some additional heat supplied into the column by electrical resistances.

The experiments demonstrated that drying rates increase by increasing operating temperature. Nevertheless, the operating pressure and the superficial steam velocity showed only limited influences over the process. The degree of superheating was identified as the principal parameter controlling the phenomenon. It was also observed that higher degrees of superheating generate lower equilibrium moisture contents and a superheating steam fluidized bed operating at reduced pressure can achieve drying processes at relatively lower temperatures.

Keywords:

• Fluidized bed drying
• Superheated steam drying
• Vacuum drying