CFD ANALYSIS OF FLOW REGIMES IN AIRLIFT REACTOR USING EULERIAN-LAGRANGIAN APPROACH

The hydrodynamic aspects of the concentric tube airlift reactor have been studied using two-phase CFD simulations with a Eulerian-Lagrangian approach. The three-dimensional CFD simulations are carried out with the experimental geometry of airlift reactor (H/D=12) reported in the published literature. The standard k-E turbulence model is used with additional consideration of production and dissipation of buoyancy-induced turbulence. Two different bubble size distributions (BSDs) and their Sauter mean diameters have been considered to represent the gas distribution at sparger in the reactor. This study shows that the BSD1 (1-5-10mm) containing a high fraction of small bubbles (5mm) represents the hydrodynamics of flows appropriately as compared to the BSD2 (5-10-15mm) containing a high fraction of large bubbles (10mm) or the single size bubble diameters (5.25mm and 10mm). Further, three regimes of operation such as no gas bubbles in the downcomer (regime I), stationary gas bubbles in the downcomer (regime II), and gas bubble recirculation from the downcomer section to the riser section (regime III), are verified using CFD simulations with Lagrangian particle tracking. Satisfactory agreement (within 15% deviation) with the experimental data was observed for parameters such as the gas holdups in the riser and downcomer and the liquid circulation velocity in the flow regimes I and II for BSD1.