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Hydrodynamic Characteristics of a Pilot-Scale Screw Conveyor Dryer

This article presents results of an experimental study on the flow characteristics of a pilot-size screw conveyor dryer (SCD). In particular, the effects of granular solids flow rate (15.2–206 kg/h) and screw speed (10.8–28 rpm) on the residence time distribution (RTD) were studied using sand as the model material. The RTD was measured using a dynamic step change in the solids flow rate. Parameters such as solids holdup, degree of fullness, mean residence time, and uniformity of the discharge flow were studied. The solids holdup and hence the degree of fullness was found to decrease with increase in the screw speed and decrease with the solids flow rate. The mean residence time was found to decrease with an increase in the screw speed, as expected. The screw speed and the solids flow rate strongly affected the discharge uniformity. An optimum value of the degree of fullness was observed with regard to the solids flow rate. Over the operating range examined, the solids flow pattern was close to plug flow, as indicated by high values of N and Pe number.