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

Abstract

Drying of wetparticulate solidsiscarriedout ina novel wayinawallheatedfluidizedbeddryer.Theexperimental data shows thatdrying occurseffectively. The temperature variation with respect to timereveals that there is evaporative cooling occurring in the solids. Initially, there is lowering of temperature, then an increase is noticed andfinallyitreachessteadystate. Thisphenomenon ofwallheateddryingismodelledfirstbypercolationmodel by taking radial average of temperature of air, temperature of solids and moisture content of solids but accounting for axial variation along the height ofthecylindrical fluidized bed. The dryingrate isconsideredtodepend on thelocaltemperatureofthesolidsinthefluidizedbed.Thisprocedureproducedthreecoupledpartialdifferential 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.