Drying of a porous material in a pulsed fluid bed dryer: The influences of temperature, frequency of pulsation, and air flow rate

Abstract

In this work, a four-section pulsed fluid bed apparatus with a 0.18 m2 cross-section area was used to investigate the influence of pulsed-fluidization variables on the drying process of molecular sieves, a test material that was chosen because it presents an initial constant drying rate period. A two-level factorial design was developed to evaluate the influences of the inlet gas temperature - 40 and 70°C - the frequency of pulsation - 250 and 900 rpm-and the air flow rate-500 and 600 m3(STP)/h - on the drying rate. In addition, a comparison was made between the drying rates achieved with conventional and pulsed fluidization. Results showed that all the investigated variables affect the drying rate. Moreover, drying rates with conventional fluidization are considerably higher, which shows that one must expect a lower drying rate when pulsation is used in a drying process controlled by the external evaporation. Concerning fluid dynamics, this work also analyzed the influence of the frequency of pulsation on the pressure drop across the bed. The higher the frequency, the higher the pressure drop. That result can be explained by the reduction of channeling.