With an aim to conduct performance rating and optimization of an industrial-scale fluidized bed dryer, a decision tree has been devised to aid selection of the most appropriate mathematical model. The operating fluidization regime is first identified and a theoretical criterion using a cross flow factor is used to decide between using the Class I model based on plug flow or the Class 3 model based on the Davidson bubble. In this case-study, this approach is applied on an existing multi-stage dryer for large Geldart Type D nylon particles. The optimization study was carried out using the Class 3 model, which applies the two-phase fluidization theory to determine the transport of moisture between the dense and the bubble phases. An iterative numerical solution has been used to reduce computational time by avoiding the need to solve complex coupled heat and mass balance equations. Changes in bubble size and wall effects along the bed height are taken into account to improve model accuracy. The sensitivity of operating conditions (temperature, weir height, fluidization velocity) and recommendations for optimal operation are presented. (c) 2007 Elsevier B.V. All rights reserved.