Experimental investigation into the impact of sparger design on bubble columns at high superficial velocities

In this work we have quantified the impact of sparger design on the hydrodynamics of a pilot-scale bubble column (0.39 m in diameter and 2 m in height) at superficial velocities between 0.07 and 0.29 m/s. It was found that increasing the sparger orifice diameter from 0.5 mm to 3 mm led to different behaviour in the homogenous flow regime, this being attributed to the different bubble size distributions (BSDs) generated. At higher superficial velocities (i.e., in the heterogeneous flow regime), it was observed that the sparger orifice diameter had little impact on the column behaviour (as characterised by the BSD, overall hold-up, local hold-up profile, liquid velocity profile and mixing time). Changing from a symmetric to an asymmetric sparger design was observed to have a minimal impact on the BSD and overall hold-up, but a large impact on the flow behaviour (i.e., the local hold-up and liquid velocity profiles). The change in flow patterns caused by the asymmetric sparger generally led to a decrease in the mixing time for all measurement locations and tracer addition points. Results from this work are of clear interest in the design of bubble columns.