In this work, a detailed grid refinement study was carried out for two well-documented circulating fluidized bed (CFB) systems with the focus on grid convergence of 2D numerical simulations. It is demonstrated that the grid convergence of numerical simulations depends on the flow field variable chosen for verification. For axial pressure gradient, this study shows that no general rule for grid size is available to guarantee the grid-independent results. In addition, the inlet and outlet configuration used in the 2D simulations shows a significant impact on the grid convergence. A 3D grid study is also presented with the intent to probe the differences between 2D and 3D numerical simulations with respect to the grid convergence. For the case considered in this study, the 3D simulation demonstrates better grid convergent behavior than the 2D simulation with comparable grid sizes. (C) 2014 Elsevier B.V. All rights reserved.