Fluidized bed spray agglomeration is a common process of particle size enlargement in process engineering. The objective of this study is to derive a general fluidized bed model, which takes the particle size enlargement by agglomeration and the simultaneous drying of particles into account. Therefore, a population balance approach is used to predict the size distribution, the moisture content and the temperature of the particles. The interaction of solid and gas phases is described by means of a heterogeneous fluidization model with active bypass. Selected simulation results are presented and discussed. The model is validated by various comparisons of simulations and batch agglomeration experiments. (c) 2006 Elsevier Ltd. All rights reserved.