Mixing in mechanically agitated gas-liquid contactors, bubble columns and modified bubble columns

Abstract

Mixing time measurements were made in 300 and 1000 mm i.d. mechanically agitated contactors with different types of impellers, located at different heights from the bottom of the vessel. Mixing time measurements were also made in 150, 200, 385 and 1000 mm i.d. bubble columns with varying liquid heights. Transient pH measurement and conductivity measurement were used to measure the mixing times. Impeller speed was varied in the range of 3.33-20 r/sec in the case of mechanically agitated contactors and gas superficial velocity was varied in the range of 10-250 mm/sec in bubble columns. Effect of physical properties of the fluid (surface tension, ionic strength, liquid viscosity) and that of the non-Newtonian behavior on mixing time was studied. Mixing time in the presence of drag reducing agents was also investigated. • In the range of variables covered in this work mixing time in mechanically agitated contactors and bubble columns was found to be in the range of 4-6. • Mixing time predictions based on the longest loop length and circulation velocity are made in the presence and absence of a gas for mechanically agitat. • A procedure is given for the prediction of the critical impeller speed for gas phase dispersion in mechanically agitated contactors.