Study of sparger design effects on the hydrodynamic and mass transfer characteristics of a D-shape hybrid airlift reactor

This study investigated the effect of sparger designs on a D-shape hybrid airlift reactor (DHALR) performances. The designs of airlift and torus reactors were combined to get the hybrid configuration. Experiments were carried out over a range of superficial gas velocities from 0.86 to 5.10 × 10-2 m/s, using three different spargers: single orifice (S-SO), multiple orifices (S-MO) and flexible membrane (S-FM). The findings highlighted that the S-FM sparger performed much better than the other spargers. An improvement in the gas holdup, ?G, volumetric mass transfer coefficient, kLa, liquid circulation velocity, UL, and mixing time, tm, was observed and was attributed to the bubble size distribution enhancement. The S-FM sparger generates smaller and evenly distributed bubbles. However, it increases the axial dispersion coefficient and therefore the backmixing extent. It was demonstrated that even if S-FM leads to more pressure drop at the sparger level, it remains the most efficient in terms of power saving for a given mass transfer rate. The results demonstrated that the sparger has less effect at high superficial gas velocities in the DHALR. The flow inside the DHALR was modelled by the Axial Dispersion and the Tank in Series Models. The results show that the DHALR has a plug-flow-like behaviour.