Forced Convective Drying of Wastewater Sludge with Presentation of Exergy Analysis of the Dryer

摘要

The main objective is studying the fundamental aspect, by the mean of the drying kinetics, the application of forced convective drying of wastewater sludge with determination of the optimum drying conditions. The drying system is composed of two units; small samples of 2.5 g are dried in the first unit and bed of sludge weighting 250 g is dried the second unit. The experiments are performed under air temperatures varying between 80°C and 200°C. The range of the air velocity and its humidity is 1- 2 m/s and 0.005- 0.05 kgwater/kgdry air, respectively. The experiments are performed for two different sludges; activated sludge (AS) and thermalized and digested sludge (TDS). Usually, three main drying phases are observed during drying of bed of sludge. These phases are reduced to only two for small samples. Determination of the influent parameters shows that temperature of the drying air and sludge origin can profoundly influence the drying kinetic of the sludge. The exergy analysis of the two units of the drying system allows selecting 140 °C, 2 m/s, 0.05 kgwater/kgdry air as optimum drying condition with an exergy efficiency reaching 90\%.