This paper presents the development of a reduced-order model (ROM) for dynamics of non-reactive, isothermal fluidized beds, based on the proper orthogonal decomposition (POD) method. Several implementations of this ROM were developed for a two-dimensional bubbling fluidized bed using numerical results from a full computational fluid dynamics (CFD) simulation of the bed. The solutions of the ROM were used to investigate the influence of the size of the particles on the motion of the bed. The solutions of the ROM were compared with the full model solutions for different particle diameters. The differences between the ROM and the full order solutions (the CFD results) were less than 3% within the range of diameters used for POD generation. The computational time of the ROM varied between 25 and 33% of the computational time of the full CFD solution. The computational speed-up depended on the complexity of the transport phenomena, the ROM methodology and the reconstruction error. (c) 2005 Elsevier Ltd. All right reserved.