Residence time distribution in spouted bed drying of maltodextrin solutions on a bed of inert particles

Residence time distributions (RTD) for aqueous maltodextrin solutions were determined in two kinds of spouted bed dryers: (1) conventional spouted bed (CSB) 0.305 m diameter with a bed of polypropylene beads and (2) spout‐fluid bed 0.143 m diameter with draft tube submerged in a bed of FEP® pellets (S‐FBDT). RTD, mean residence time t m , and spread of the distribution σ 2 , were determined at different drying temperatures, spouting velocities, bed depths, spraying pressures, and feed concentrations. Average values of t m and σ 2 were 6.5 min and 26.6 min 2 for the CSB and 6.9 min and 36 min 2 for the S‐FBDT, respectively, for all operating conditions except spraying pressure. RTD curves were well represented by the response of an ideal stirred tank with a superimposed bypass of 15% on average for the CSB and 7% on average for the S‐FBDT dryer for all operating conditions. Increase in spraying pressure produced a reduction of t m and an increase in the bypass fraction of the product in both dryers. © 2011 Canadian Society for Chemical Engineering