This study aims at the assessment of a combined heat and power (CHP) biomass bubbling fluidized bed gasification unit coupled with an internal combustion engine (ICE) by using a comprehensive mathematical model based on the Aspen Plus process simulator. The model is based on a combination of modules that Aspen Plus simulator provides representing the 3 steps of gasification process (drying, pyrolysis, and oxidation), gas cleaning and ICE. The model is based on mass and energy balances and reaction kinetics. The model was validated by using data obtained by operating a pilot atmospheric bubbling fluidized bed gasifier at Aristotle University of Thessaloniki, fed with olive kernel with a capacity of 1 kg/h and an energy output of 5 kW(th), and has showed very good agreement. A sensitivity analysis was further conducted for the investigation of the system's behavior under different temperatures and air equivalence ratios. The proposed model is capable of dealing with a wide variety of biomasses (olive kernel, corn cob/stalks, rapeseed and sunflower stalks) using air as the fluidization agent and to predict the system's performance in terms of cold gas and thermal efficiency. (C) 2011 Elsevier B.V. All rights reserved.