Hydrodynamics, mixing and mass transfer in a pilot-scale bubble column with dense internals

Abstract

Bubble column reactors with exothermic reactions are often equipped with dense tube bundle heat exchangers. While there is some knowledge about the impact of such internals on hydrodynamics and mass transfer for narrow columns, its role in pilot-scale columns is less clear. In this paper we report on a study of hydrodynamics and mass transfer in a BCR of 4.2 m height and 0.392 m diameter. We investigated different tube arrangements with triangular and square pitch and tube diameters of 32 × 10−3 m and 45 × 10−3 m at the same cross-sectional coverage (∼25%). The column was operated at homogeneous and heterogeneous flow conditions. A customized three-layer wire-mesh sensor was utilized to visualize gas phase dynamics and liquid mixing characteristics in the column’s cross-section. We found that sub-channel size is the most crucial geometric design parameter. Tracer mixing experiments revealed that internals reduce the mixing time due to the induction of large-scale liquid circulation. Mass transfer was studied with the oxygen stripping method. Here we found, that the effect of the internals on the gas-liquid mass transfer is almost negligible. Eventually, correlations for gas holdup, axial liquid dispersion and the volumetric gas-liquid mass transfer coefficient are given, which take the internals’ geometry into account.