Mixing in gas-liquid contactors agitated by multiple turbines

Abstract

Liquid hydrodynamics in multiple-turbine aerated tanks was modelled in the loading regime by the compartments-in-series model with back flow streams. Back flows between compartments were assumed to be the sum of two components, which derive from mechanical and pneumatical mechanisms of flow generation. Liquid flows due to these mechanisms were correlated in terms of the operating variables N and Q G . Correct simulation of gassed and ungassed mixing of a pulse input of tracer was achieved in all cases under study. The mixing model is robust to changes in geometrical parameters and operating conditions with tanks of 0.3 and 0.5 m diameter T, double- and triple-turbine agitators and turbine sizes T 3 and T 2 . A dimensionless mixing time correlation was deduced from mixing simulation by the model. The dimensionless gassed mixing time θ is obtained from θ 0 in the ungassed situation through θ = θ 0/∏ − KFl ef (K > 0) where Π is the gassed-to-ungassed power ratio, Fl ef = Fl Π is the effective gas flow number and K is a configurational constant. The correlation is general and it is found to represent the interactive combination of the mechanical and pneumatical mixing mechanisms. It was successfully tested not only in the same situations as the mixing model, but also with single-turbine agitators.