In this study, a numerical model has been developed by the combined approach of computational fluid dynamics (CFD) and discrete element method (DEM) collisional model to study the particle-fluid flow of the fluidized bed reactor for solar beam-down concentrating system. The contact forces between the particles have been calculated by the spring-dashpot model, based on the soft-sphere method. An experimental visualization of particles circulation pattern and mixing of two-tower fluidized bed system has been presented. A good agreement has been found between the experimental measurements and numerical predictions. To investigate the influence of fluid flow rate and particle size on the flow pattern of the reactor, simulations have been performed for various conditions. The results indicate that the large size particles induce three-dimensional effects as they are accumulated at the central axis region. The average bed height of the left tower increased by 23.4% when increasing the flow rate about 70%. (C) 2017 Elsevier B.V. All rights reserved.