The Effect of Impeller–Sparger Geometry on the Gas Holdup in an Oxygen–Water System Using an Agitated and Sparged Tank Contactor

Gas–liquid (G-L) reaction kinetics studies need ideally to be carried out (a) in the total recirculation regime, signifying maximum mass transfer rates ( K L S ) and (b) in contactors, which geometrically support higher K L S . G-L mixing enhancement by agitation and gas sparging is generally practiced to enhance K L S . The agitated and sparged tank contactor (ASTC) consisting of baffles, stirrers, and spargers is the preferred mode of contacting. It is essential to understand how the impeller–sparger geometry affects K L S in a standard ASTC while operating in the total recirculation regime. A film theory-based approach shows that K L S may be approximated by the gas holdup (ε g ) in the total recirculation regime. Combinations of standard radial and axial impellers with ring spargers of different sizes are used in an ASTC of 0.25 m diameter containing 1 × 10 –2 m 3 water. The oxygen flow rate ( Q g ) is varied from (6.26 to 25.02 × 10 –5 ) m 3 s –1, and agitation intensity ( N 0 ) is varied from (1.67 to 16.67) rps at the temperature (θ) = 313 K under atmospheric pressure to understand the effects of geometry on ε g while operating in the total recirculation regime. Results of our investigations show how an ASTC with an impeller of high-power number ( N P ) and a ring sparger of near impeller diameter ( D ) form an ideal combination and will result in maximum ε g (indirectly optimum K L S ), making it suitable for kinetics studies.