The sorption enhanced steam methane reforming (SE-SMR) in a laboratory scale fluidized bed reactor is investigated using a three-fluid model. The binary sorbent and catalyst particles segregate due to the density difference between them. The light sorbent particles tend to rise and the heavy catalyst particles tend to sink initially. As the process proceeds, the sorbent particles adsorb more CO2 and become heavier, and the density difference between the binary particles will become smaller, thus they tend to be well-mixed. As the sorbent particles are either at the upper sections of the bed or well-mixed with the catalysts, the adsorption of CO2 can always play the role of sorption enhancement, the hydrogen purity at the outlet is between 98-99% before the breakthrough, which is much higher than that (73-74%) of steam methane reforming (SMR) process. Due to the exothermic CO2 adsorption reaction and the mixing of the gas particle flows, a homogeneous gas/particle temperature distribution is found in the whole bed. In general, the hydrogen purity obtained in the simulations agrees fairly well with the experimental data from Johnsen et al. . Copyright © 2012 Published by Elsevier Ltd.