Effect of Temperature and Suspended Solids on Local Void Fraction in a Sparged Reactor with a Multi-Impeller Agitator

Abstract

The void fraction distribution in the vertical direction in a tall, sparged, gas–liquid reactor of 0.48 m diameter is measured at various temperatures with and without glass beads in the suspension. The agitator comprises two up-pumping wide-blade hydrofoils positioned above a hollow-blade dispersing turbine. Operating temperatures range from 24 to 81°C with solid concentrations of up to 21 vol%. Detailed comparisons of the void distributions at 24 and 81°C in the presence of 9 and 15 vol% solids are presented. All the experiments reported here are performed at a constant agitator speed of N = 6 s–1.Temperature affects the overall and integrated local void distributions in a similar manner. At all temperatures, the local gas fraction is the maximum in the region just above the levels of the top and bottom impellers. At fixed agitator speeds and superficial gas flow rates the overall and local gas holdup values are always less at high temperature in the absence of solids. At ambient temperature, the local gas fraction is reduced at high solid concentrations. At 81°C, on the other hand, the effect of solid concentration on the void fraction is almost nil although the local extremes in the void distribution are somewhat high. The measured local void fractions show a less uniform gas distribution in the presence of solids and at high temperatures.The results of this study help improve our understanding of the differences between two- and three-phase reactors operating under cold- and hot-sparged conditions.