Global hydrodynamic of hybrid external loop airlift reactor: Experiments and CFD modelling

Abstract

In this study, the mixing and mass transfer of air-water system were characterized in hybrid external loop airlift reactor using the computational fluid dynamics (CFD). This hybrid configuration involves the advantages of both airlift and torus reactors. To predict the flow in hybrid geometry, an Eulerian-Eulerian approach has been adopted with per-phase interaction of the standard k–ε turbulence model. To simplify the solution, the bubbles were considered to have approximately the same size. The global flow characteristics were experimentally determined by a conductimetric method. Gassing-out method was applied to determine gas-liquid mass transfer coefficients. The findings highlighted a uniform gas flow distribution in the riser tube, despite the riser included two different sections. It was noticed that beyond the superficial gas velocity, 0.0253 m/s, the fine rotational bubbles were dragged away by the liquid recirculation in the downcomer section. The STD k–ε turbulence model with per-phase effect, estimated correctly the hydrodynamic of homogenous and transition regimes except for high superficial gas velocity, Ug = 0.0703 m/s. For superficial gas velocities ranging from 0.0253 to 0.0703 m/s, there was a good agreement between simulated and experimental values; the error was less than 6%. Optimal conception of this hybrid geometry and its industrial scale use need further research and testing.