A one-dimensional mathematical model of the fluid dynamics and combustion process in a bubbling fluidized bed was developed. In the bubble phase, the model includes the throughflow and bypass flow, which crosses the bed without taking part in combustion because of the preferential bubble paths expected in large fluidized-bed systems. Unlike in the classic approach, the emulsion phase was considered not to remain under minimum fluidization conditions, and the influence of downward particles was considered. A correction factor for the equation of the mass transfer coefficient previously described by other authors was therefore proposed to take into account the bypass flow expected in large systems. The main results provided by the model are the velocities and volumetric flows of the gases in the bed (emulsion, visible bubble and throughflow gases), the mass transfer between bed phases and the oxygen profile in the bed. (C) 2018 Elsevier Ltd. All rights reserved.