Drying of beans in a pulsed fluid bed dryer: Drying kinetics, fluid-dynamic study and comparisons with conventional fluidization

摘要

Fresh carioca beans (Phaseolus vulgaris) were submitted to convective drying in a pulsed fluidized bed (PFB) dryer. A full factorial design was developed in order to analyze the effects of the following process variables on the kinetic parameters of the Page's equation: inlet air temperature, airflow rate and frequency of pulsation. The only significant variable was the inlet temperature of air. At 60℃, drying was also performed under conventional fluidization. No difference was observed between the drying curves under pulsed and conventional fluidization: therefore, due to the lower pumping requirement, energy savings can be achieved with the pulsed fluidization technique without affecting the production yield. Complementary fluid-dynamic evaluation showed that the maximum pressure drop is approximately the same in both regimes. However, under pulsed fluidization that maximum value is affected by the initial bed height and slightly by the frequency of pulsation.