Mathematical Modeling of Batch Fluidized Bed Drying of Alumina

Fluidized bed drying is an efficient and widely used method for drying wet powders and granular products. To optimize this drying process, several approaches for modeling, including empirical, semi-empirical, or more complex computational fluid dynamics models are used. This work aims to simulate batch fluidized bed drying processes of alumina using the multi-phase model equation. Firstly, a thermodynamic characterization of alumina was carried out using the static gravimetric method to determine sorption isotherms, enthalpy and entropy. Than, drying kinetics at different operating conditions (temperature and air flow) are investigated. Finaly, A three-phase mathematical model describing the fluidized bed dryer has been provided based on a numerical method. The system of equations (heat and mass transfer) is solved numerically by the finite element method using "COMSOL multiphasic" software. Results show that, for the sorption isothermes, the increase in temperature inducing the decrease in the equilibrium water content, and that the GAB model can describe correctly experimental isotherms. The high sorption enthalpy value (8000 kJ/mol) is an indication of the strong water-solid surface interaction in the product. The desorption entropy has a high dependence on the water content, particularly for low water contents. The maximum desorption entropy value reaches 200 kJ/mol. K at low equilibrium water contents values. Temperature is the major factor influencing drying kinetics. According to the fluidized bed drying simulation, results show the capacity of the three-phase Kunii-Levenspiel model to describe and predect the spacio-temporal distribution of water content of alumina and temperature in the fluized bed during drying The model was validated on distinct operating conditions.