An Experimental Study of the Thermal Performance of a Screw Conveyor Dryer

Abstract

ABSTRACT In the present study drying of fine crystalline solid was carried out in a non-insulated jacketed screw conveyor dryer SCD of 3 m length and 0.072 m screw diameter. It is nitrogen-swept to carry off the evaporated moisture. Dryer performance was evaluated in terms of the final moisture content, heat-transfer coefficient, thermal efficiency and power consumption. From the experimental results it was observed that drying under low pressure gives 92% moisture removal compared to 30–40% using low flow rates of nitrogen. The initial moisture content was in the range of 5 to 6%. Over the parameter range studied, the overall heat transfer coefficient was found to be in the range of 46–102 W/m2K. The average rise in the temperature of the product was 40 to 50°C. Thermal efficiency (based on sensible and latent heat) of the dryer obtained was found to be in the range of 25–62%, typical values obtained in falling rate drying period. Power consumption per metric ton of dried material was found to be a strong function of screw speed and material feed rate, material properties, and drive efficiency.