Oxygen transfer in two and three-phase internal-loop airlift reactor with riser diameter variation

The efficiency of the concentric tubes internal-loop airlift reactor depends on the hydrodynamic conditions that affect oxygen transfer to the biofilm. This work studied the effects of the relation between diameters of the tubes and of the carrier (sand) concentration on the global oxygen transfer coefficient (K(L)a). The tests - in 2,6 m high reactors with 250 mm external diameter and 100, 125, 150 and 200 mm internal diameters - were performed with air flow taxes up to 2,500 L.h(-1) and sand concentrations up to 150 g.L(-1). The K(L)a increased slightly for 30 g.L(-1) and decreased for higher concentrations, in accordance with related data for similar conditions. A model for K(L)a in biphasic medium was fitted embracing all the external/internal area relationships tested, based on the reduction of the liquid phase transfer coefficient and the bubble diameter ratio with increasing air flow rates.