Drying Kinetics of Extruded Pellets in Fixed Beds

To study the drying behavior of extruded feed pellets in a fixed bed, the drying kinetics were investigated in a laboratory-scale dryer. The effect of types of aeration, air temperature, and bed depth on drying curves and moisture nonuniformity was analyzed. The results showed that drying was mainly affected by the air flow direction, air temperature, and bed depth. The moisture nonuniformity was 2% for an alternating air flow direction drying, where as it was 7% for one-way drying at a bed depth of 15 cm at 33 min. Alternating direction drying improved moisture uniformity, but the drying rate was decreased at a bed depth of 20 cm. A constant drying stage was observed at a critical bed depth, where as an increasing drying rate stage was observed for a deeper bed. The pressure drop (Delta P/L) was studied by ventilation experiments considering the effect of air flow rate, moisture content, bed type, and bed depth. The result showed that pressure drop in a double bed was greater than that in a single bed with the same bed depth. The pressure drop increased with air flow rate and decreased with moisture content and bed depth.