A comprehensive physical model describing the agglomeration behavior present during fluidization of fine powders is still missing in literature. A model of balance of farces acting on a single solid particle is introduced, aiming at predicting and locally estimating the size of the agglomerates created in the bed. Computational fluid dynamics (CFD) have been used to investigate the hydrodynamics of a gas-solid fluidized bed operated with particles belonging to group A of Geldart classification.(1) The key issue is that, in the gas and particle flow field, both hydrodynamic and interparticle forces are of importance. The model is incorporated into simulations based oil an Eulerian approach and using the kinetic theory of granular flow. In the simulations, the closure models describing the hydrodynamics of the solids phase are directly affected by the behavior of the agglomerates. No empirical data or parameters were used to close the model. The simulations are compared with experiments of an independent research group, through the time-averaged solids volume fraction in a fluidized bed operated at different gas velocities. The agreement obtained between the simulation results and data from the literature is very good. Also, it is shown that, under flow conditions treated in this work, agglomerates of size of several single particle diameters are present in the fluidized bed. (C) 2007 American Institute of Chemical Engineers.