Gas Hold Up and Mixing in the Liquid Phase of Bubble Columns Used in Continuous Fermentation

Abstract

The bubble column has recently received a great deal of attention since its applications are increasing. Recent work has shown that there is a viable possibility of utilising bubble columns in aerobic systems such as fermentation. At present there is a considerable amount of knowledge available on the various parameters affecting the operation of systems. Unfortunately the majority of the research work carried out has been with simple two phase systems such as air/water. Consequently there is virtually no working design-data for complex two-phase and three-phase systems. The object of this research programme was to attempt to apply present two-phase knowledge to three-phase systems and to endeavour to determine the effects of various parameters, if they act differently. The initial experimental work was concerned with obtaining a reliable and reproducible means of determining bubble diameters and a preliminary study of the factors affecting the size of bubbles generated from single orifices in yeast suspensions. The work then progressed to some small-scale studies of two-phase systems in an effort to relate the initial single bubble data to bubble swarm systems. The physical size of the apparatus was then increased to simulate industrial type equipment. Extensive studies were carried out with this equipment to measure the effects of gas and liquid flow-rates and column diameter on gas hold-up in yeast suspensions of varying concentrations, in comparison to air/water systems, Finally, a study of the liquid-phase mixing was made, using the same parameters. The overall object of this thesis is to put forward preliminary data on two and three-phase systems which, it is hoped, will enable more extensive studies to be carried out on various aspects of the work.