The objective of this research is to evaluate the average gas-to-char mass transfer coefficient predicted by a two-dimensional Eulerian multiphase CFD model in the conditions prevailing in a bench and a pilot scale bubbling and circulating fluidised bed combustors. It was found that the Eulerian multiphase CFD model is able to predict the same response of the bed Sherwood number to the fluidisation velocity as shown by the experimental results. The CFD simulations also suggest that the bed Sherwood number drops with increase of reactor width from the bench to the pilot scale. Research highlights that, in the combustion process, the bed Sherwood number is a function of Reynolds number, as well as phase mass transfer, char loading and chemical kinetics. (C) 2013 Elsevier Ltd. All rights reserved.