We apply a recently developed two-fluid continuum model (TFM) based on kinetic theory of granular flow (KTGF) in three dimensional cylindrical coordinates, to investigate bubble formation through a single central orifice in a gas-solid fluidized bed. A comprehensive study for Geldart D type particles, revealing the influence of particle diameter, jet injection flow rate, and bed size on bubble characteristics have been investigated. At a given gas injection flow rate, the bubble diameter continuously increases while gas leakage from the bubble to the emulsion phase decreases with time. With increasing particle diameter, leakage fraction increases and hence a smaller bubble diameter is predicted. These results are consistent with DPM simulations, experimental results and approximate bubble formation models reported previously in the literature. (C) 2014 Elsevier B.V. All rights reserved.