Modelling of an industrial fluidised bed dryer

Abstract

Although fluidised bed drying is often a vital operation in polymer production, it remains difficult to predict the dryer performance accurately as no general application models have been published. To investigate the coupled relationship between the operating parameters, fluidisation regimes and drying performance, the drying of industrial nylon-6.6 polymer particles (Geldart Type D) was studied both at laboratory and industrial-scale. At laboratory-scale, theoretical single-phase models using Chilton-Colburn analogy could predict the constant-rate drying period very well for the entire range of fluidisation conditions (from fixed bed to turbulent fluidisation). Beyond minimum fluidisation at industrial-scale, two-phase fluidisation theory is needed to improve the drying model for process optimisation. An iterative numerical solution strategy computes the results quickly and avoids the need to solve coupled heat and mass transport equations. In the falling-rate drying periods, a lumped mass transfer coefficient obtained from TGA experiments is used to describe the drying rate.