Circulating fluidized bed reactor (CFBR) has been widely used for combustion, gasification and cracking. Each reaction has its own characteristics and requires different reactor responses. In this work, novel designs of the riser geometries were studied using a 2D transient Eulerian approach with kinetic theory of granular flow in a commercial simulation package. The new designs were based on the improvement of main factors that have an effect on reaction characteristics. It was found that the tapered-out riser improves the turbulence or mixing while the tapered-in riser enhances particle residence time and gives uniform temperature distribution in the system. (C) 2008 Elsevier B.V. All rights reserved.