Optimizing Convective Drying for Efficient Reduction of Phosphate Sludge Moisture: Experimental Investigations and Mathematical Modeling

Abstract

Abstract Phosphate extraction process produces large amounts of waste sludge, that is disposed of in the environment. Phosphate sludge (PS) is characterized by high moisture content (70–80%) which is a major handicap for any further disposal. To overcome this issue, the drying of this waste could be an appropriate solution to minimize its volume. The present work is focused on the convective drying behavior of PS and its mathematical modeling to optimize the drying processes. Drying experiments were conducted using thicknesses of 1, 2 and 4 cm. Drying air temperature and velocity ranged respectively in 50–70°C and 1–2 m/s. The findings showed that improving drying air temperature and velocity, and decreasing sample thickness enhance considerably the drying rate. Furthermore, the drying curves showed the presence of two main drying periods corresponding to constant drying rate and falling drying rate periods. Moreover, a model considering heat and mass transfer equations for each phase in wet sludge was used to fit the experimental results. Based on the analytical solutions and according to the statistical criteria R2 and RMSE ranged from 0.9957–0.9996 and 0.0157–0.0276, respectively, it was concluded that the model describes the drying behavior of washing PS in all tested convective drying conditions.