A comprehensive CFD model has been developed to simulate the gasification process within an air-blown updraft coal gasifier. Updraft fixed bed gasification processes are characterized by complex behavior, since they involve different space- and time-dependent sub-processes where coal preheating, drying, de-volatilization and char reactions take place. Simplified models, such as non-dimensional ones, useful for preliminary gross mass and energy balance, are unable to correctly simulate the overall gasification phenomena and more sophisticated approaches are required. In particular, CFD models could be used to describe in a detailed way the complex time- and space-dependent phenomena involved in the gasification process. Considering the high volume fraction of the solid phase, close to the packing condition, the Euler-Euler approach is required to model this multiphase flow. The solid phase is considered as a continua according to the kinetic and plastic theory of granular flows. The operation of a Wellman-Galusha gasifier is investigated, considering a non-continuous loading of coal and extraction of the ash, with the aim of characterizing the space- and time-dependent behavior of the process. (C) 2011 Elsevier Ltd. All rights reserved.