CFD modeling can play a very significant role in the design optimization of CFB reactors. Such reactors are used for combustion, gasification, carbonation / calcination and other technological applications. This paper presents novel numerical features that should be taken into consideration, when a Circulating Fluidized Bed is simulated via a Two Fluid Model approach. Particles clustering, which is neglected when conventional drag models are applied, can be properly addressed by the advanced Energy Minimization Multi-Scale (EMMS) drag schemes that incorporate the effect of clusters through sub grid calculations. Moreover, the full loop numerical approach, models not only the CFB riser, but also its recirculation system (cyclone downcomer pneumatic valve). A proper stress model is necessary for the calculation of viscous stresses experienced by the granular phase in the dense regions of the recirculation system. Such a stress model is proposed, based on the yield criterion Pitman - Schaeffer - Gray Stiles and its implementation is essential for properly addressing the dominant inter - particle friction forces in the returning system. Moreover, the paper presents the effect of grid density distribution on the numerical results, where a uniform one is found to be the most efficient choice in terms of balance between computational cost and numerical accuracy. Concluding, a straightforward Two Fluid - Model (TFM) numerical approach is developed for the efficient and accurate simulation of the flow inside industrial CFBs, including: a) the EMMS drag scheme; b) full loop simulation; c) the Pitman - Schaeffer - Gray Stiles yield criterion for the formulation of the stress tensor of granulates inside the recirculation system

Keywords: advanced energy technologies, energy systems for power generation, circulating fluidized beds (CFB), EMMS, CFD