This work focuses upon the 3D full loop CFD isothermal simulation of a transparent plexi - glass CFB carbonator. This unit is a scaled cold model of IFK’s (USTUTT) carbonator and was particularly built by IFK for the hydrodynamic investigation of this novel reactor. The state – of – the - art TFM approach is adopted coupled with the advanced EMMS scheme. Moreover, in this work, the re - circulation system of the unit i.e. cyclone, down - comer and a pneumatic valve (Loop Seal, working as flow regulator), is included in the simulation. In depth investigation with CFD techniques of Loop – Seal hydrodynamics is for the first time performed. The Pitman - Schaffer - Gray - Stiles yield criterion is used in the pneumatic valve, for the formulation of the granular material stress tensor, to address the modeling of high frictional forces within the Loop - Seal. The CFB loop was discretized by 286,753 elements. Particles (Geldart B) mean diameter is 146 ìm and their density 5700 kg/m3. Simulation results are averaged over a time period of 120 seconds and pressure profile and re - circulation flux are compared with the corresponding experimental data. Moreover, predicted flow patterns are compared with visual observations. Simulation results converge very well with the experimental data, regarding the pressure profile and the re – circulation flux. Indeed, the error in the re – circulation rate is less than 2%. Such level of accuracy is hard to achieved, verifying the development of a sophisticated model. Moreover, pressure profile of the CFB loop agrees well with five pressure measurements along the riser and three in the returning system. The predicted multiphase flow patterns agree well with visual observations especially for the riser bottom and exit region and for the Loop – Seal weir, slit and supply chamber.

Keywords: EMMS, TFM, Loop-Seal, full-loop, CFD