A three-dimensional numerical analysis of the flow in a Gas-Solid Vortex Unit (GSVU) is carried out. The numerical model is first validated by comparing the bed pressure drop and solids velocity with experimental data. Next, the influence of gas flow rate, solids density, and particle diameter on the pressure drop, solids velocity, bed void fraction and slip velocity between the two phases is studied. A stable, solids bed is achieved for the entire range of gas flow rates tested (0.1-0.6 Nm(3)/s). No particle entrainment is observed when varying the solid density (180-0450 kg/m(3)) or the particle diameter (2-0.5 mm). A shift to bubbling fluidization regime is observed for small particle diameters (0.5 mm). The observed changes in the GSVU flow patterns are discussed by analyzing the changes in the cumulative centrifugal to drag force ratio over the bed. (C) 2016 The Authors. Published by Elsevier B.V.