Circulating fluidized bed steam reformers (CFBSR) represent an important alternative for hydrogen production, a promising energy carrier. Although the reactor hydrodynamics play crucial role, modeling efforts to date are limited to one-dimensional models, thus ignoring many of the flow characteristics of fluidized beds that have strong effects on the reactor efficiency. The flow inside the riser is inherently complex and requires at least two-dimensional modeling to capture its details. In the present work, the computational fluid dynamics (CFD) simulations of the hydrodynamics of the riser part of a novel CFBSR were carried out using two-phase Eulerian-Eulerian approach coupled with kinetic theory of granular flow and K-ε model. Cold flow simulations were carried under different fluidization regimes. It was found that catalyst of Geldart's type “A” particle is more efficient for flow inside the catalytic reactor and dense suspension upflow (DSU) fluidization regime yields the best homogeneous catalyst distribution in the riser and thus best reactor performance. The optimum range for catalyst flux was found to be higher than 1150？kg/m2·s for a gas flux of 6.78？kg/m2·s. It was also noted that the value of 500？Kg/m2·s for catalyst flux represents the critical value below which the riser will operate under pneumatic transport regime. 1. Introduction Hydrogen has many uses in chemical and energy industries; it is an essential raw material and component for ammonia production and in all hydrocracking plants. It is gaining much attention as the second important energy carrier after electricity [1]. The continuous and fast development in fuel cells technology increased the importance of hydrogen as it is the most efficient feed for fuel cells since it produces only water when utilized [2]. Steam reforming of hydrocarbons is the main production method of hydrogen, especially from methane [3], although the use of higher hydrocarbons [4] and biodiesel [5, 6] is gaining more attention. Typically, the process involves a fixed bed reactor with special focus on heat transfer efficiency of the system. New reformer designs are investigated to attempt to overcome the process mass transfer, equilibrium limitations, and catalyst deactivation hurdle. A comparison between different reformers generations is presented in Table 1. The fundamental structure of the circulating fluidized bed membrane reactor (CFBMR), the most recent design, is shown schematically in Figure 1. Table 1: Comparison between fixed bed steam reformers, bubbling fluidized bed steam reformers (BFBMSR),
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