Gasification and combustion of porous char particles occurs in many industrial applications. Reactor-scale outputs of importance depend critically on processes that occur at the particle-scale. Because char particles often possess a wide range of pore sizes and react under varying operating conditions, predictive models which can account for the numerous physical and chemical processes and time-dependent boundary conditions to which a particle is subjected are necessary. A comprehensive, transient, spherically symmetric model of a reacting, porous char particle entrained in the surrounding flow has been developed. The model incorporates the adaptive random pore model and consistent flux relations to account for an evolving, multi-modal pore structure. The model has been validated against zone II reaction data with good agreement. The framework allows for concurrent annealing, particle size reduction and the possibility of ash adherence to the particle surface, although the latter two submodels require the specification of several parameters. The ability of the model to calculate the evolution of temperature, species and porosity profiles for char, ash and the surrounding boundary layer has been demonstrated. The importance of accounting for multiple reactions and for different pore sizes separately has been illustrated through their effect on overall particle conversion. (C) 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.