Characterization of two phase flows in chemical engineering reactors

Abstract

Most industrial processes like fermentation, hydrogenation, oxidation, water treatment, petrochemical, nuclear and aerospace involve intimate contact between continuous phase and dispersed phase. Bubble columns and external loop airlifts are commonly used in these operations. Although these reactors are widely used, and extensive research has been carried out there exists no perfect model to characterize the local hydrodynamics and mass transfer. Computational fluid dynamics has also evolved recently trying to model the flow and transfer within these reactors but a lot of results are conflicting. Besides, there is a need to validate these results with experimental work. This work is dedicated to the experimental methods of measuring the local parameters such as the gas hold-up, the bubble velocities, the liquid velocity, bubble sizes. Two intrusive methods are used in this study, hot film anemometry for measurements of liquid phase and bi-optic probe for the gas phase. Although intrusive methods may interfere with fluid flow, presently they are the most adapted for real industrial processes with opaque equipment walls and high gas hold-ups compared to non-intrusive methods such as imagery. In this study, an external loop airlift of 16.5 l capacity is used. Local variables are measured in the riser of an external loop airlift reactor in air/water medium. The results are presented in the form of the radial profiles of void fraction, bubble diameter, liquid velocities at superficial gas velocities ranging from 0.03 to 0.11 m/s. The axial variations of the same parameters are also investigated. The results suggest that the bi-optical probe and hot film anemometer can reliably predict flow characteristics in high gas hold up contactors.