Simulation and validation of a model for a batch wall heated fluidized bed dryer

Abstract

Drying of wet particulate solids is carried out in a novel way in a wall heated fluidized bed dryer. The experimental data shows that drying occurs effectively. The temperature variation with respect to time reveals that there is evaporative cooling occurring in the solids. Initially, there is lowering of temperature, then an increase is noticed and finally it reaches steady state. This phenomenon of wall heated drying is modelled first by percolation model by taking radial average of temperature of air, temperature of solids and moisture content of solids but accounting for axial variation along the height of the cylindrical fluidized bed. The drying rate is considered to depend on the local temperature of the solids in the fluidized bed. This procedure produced three coupled partial differential equations: one for temperature of air, second for temperature of solids and third for moisture content of solids. The axial convective heat transport equation and drying rate equation are solved using an explicit Euler numerical method. Well-mixed (CSTR) model and CSTRs-in-series model are also presented to account for recirculations in the bubbling regime of fluidization. The simulation results of CSTRs-in-series model show a good agreement with experimental data for temperature and moisture variation. Especially, the evaporative cooling phenomenon is captured successfully through simulation.