CFD modeling of continuous CO₂ capture in a full-loop circulating fluidized bed reactor using sodium carbonate sorbents

This study investigates the hydrodynamics, heat transfer, and reaction kinetics in a three-dimensional (3D) full-loop circulating fluidized bed reactor (CFBR) used for continuous carbon dioxide (CO₂) capture with a sodium carbonate (Na 2 CO 3 ) based sorbent. Gas–solid flow dynamics, heat transfer, and adsorption–regeneration reactions were simulated using a two-fluid modeling (TFM) approach. The influence of three different superficial gas velocities (U g = 1.25, 1.50, and 2.00 m/s) on the adsorption and desorption performance of the full-loop CFBR was systematically evaluated. The predicted hydrodynamic results exhibit typical CFBR characteristics, such as a dense-to-dilute axial transition and a core–annulus structure in the riser, while the downer shows a spouted-bed-like flow pattern. The temperature distribution shows a clear thermal difference between the riser and downer sections. In the riser, the predicted average sorbent temperature remains approximately 335–337 K, which favors the adsorption reaction, while the downer operates at a higher temperature of approximately 394–400 K, suitable for sorbent regeneration. Moreover, increasing U g enhances solids circulation but reduces the gas–solid residence time; consequently, CO ₂ capture performance decreases. The highest adsorption and desorption efficiencies predicted in this work are 92.2% and 88.8%, respectively, at U g = 1.25 m/s.