Eulerian gas-solid CFD simulations are applied to derive interphase mass transfer coefficients for the Geldart B and D solids in a bench and a pilot size fluidized bed combustion reactor. The interphase mass transfer coefficients obtained from the bubbling and turbulent churning fluidized bed CFD simulations are compared to the empirical data and correlations, which are primarily available only for the Geldart A solids. Particularly, the effect of fluidization velocity, particle diameter and bubble size on the interphase mass transfer coefficients is evaluated. (C) 2013 Elsevier Ltd. All rights reserved.