Large bubble sizes and rise velocities in a bubble column slurry reactor

Abstract

The results are reported of an experimental study of the gas holdup, ϑ_G, large bubble diameter, d_Lb, and large bubble rise velocity, V_Lb, in a 0.1m wide, 0.02m deep and 0.95m high rectangular slurry bubble column operated at ambient temperature and pressure conditions. The superficial gas velocity U was varied in the range of 0-0.2m/s, spanning both the homogeneous and heterogeneous flow regimes. Air was used as the gas phase. The liquid phase used was C₉-C₁₁ paraffin oil containing varying volume fractions (ϑ_S = 0, 0.05, 0.10, 0.15, 0.20 and 0.25) of porous catalyst (alumina catalyst support, 10% < 10μm; 50% < 16μm; 90% < 39μm). With increasing slurry concentrations, ϑ_G is significantly reduced due to enhanced bubble coalescence and for high slurry concentrations the "small" bubbles are significantly reduced in number. By the use of video imaging techniques, it was shown that the large bubble diameter is practically independent of the gas velocity for ϑ_S > 0.05 and U > 0.1m/s. The measured large bubble rise velocity V_Lb agrees with the predictions of a modified Davis-Taylor relationship.