This study provides new insights into fluid catalytic cracking (FCC) riser reactor from multi-scale viewpoint. The problem of simultaneous intraparticle molecule transfer and reaction, particle kinetics, and gas-solid Row in polydisperse FCC riser reactors was considered. A multi-scale CFD method was developed for constructing a multi-scale model to solve this problem. The multi-scale model consisted of a two-phase CFD model incorporating a single-particle model and a population balance model. The main flow field distribution parameters within the catalyst particles and reactors as well as the solid particle size distribution (PSD) could be calculated simultaneously based on intraparticle transfer and reaction using these models. The single-particle and multi-scale models were first verified and evaluated. Based on the validated models, intraparticle transfer limitations and/or flow fields in two size-scale FCC riser reactors were predicted. The simulations demonstrated three different reaction zones in FCC risers, and more elaborate mass, heat, and momentum transfer behaviors could be obtained. The simulations also demonstrated that particle kinetics (ie., breakage and aggregation) have obvious influences on the FCC flow field in FCC risers; these effects have not been observed in conventional CFD models. (c) 2014 Elsevier Ltd. All rights reserved