The Continuous Production of Alcohol in Tower Fermenters

Abstract

This research has been concerned with the continuous production of alcohol in tower fermenters and the development of equations to describe such systems. Initially the increasing market for both potable alcohol and ethanol as a fuel have been discussed. Detailed attention was also paid to the design of inlet/outlet ports for reactants/ products to ensure efficient operation of a pilot-scale tower fermenter. A number of batch fermentations, with flocculent yeasts later employed in the continuous fermenter, have been described. The kinetic data from these experiments were used to develop a mathematical model of the batch alcohol fermentation. The variables in the model are easily measured and although the model is empirical in nature it was found to be able to account for wide variations in results from fermentations. During continuous fermentations it was found that the tower consisted of three distinct reaction zones; (a) the base of the fermenter where a packed bed of yeast (20% of the tower height) existed. (b) the top zone of the fermenter (60% of the tower height) which could be considered as a continuous well mixed stirred reactor. q (c) a transition zone between the latter two zones. Sugar utilisation, nitrogen utilisation, and alcohol production rates were among the variables investigated during experimental work and some suggestions have been made for the stable operation of tower fermenters. Finally, a mathematical model of the continuous fermenter, which combined the batch kinetic model with the physical characteristics of continuous operation, was developed. Results predicted by the model have been compared with those obtained by experiment; the differences have been discussed although not fully explained.