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, e G , large bubble diameter, d Lb , and large bubble rise velocity, V Lb , in a 0.1 m wide, 0.02 m deep and 0.95 m high rectangular slurry bubble column operated at ambient temperature and pressure conditions. The superficial gas velocity U was varied in the range of 0±0.2 m/s, spanning both the homogeneous and heterogeneous flow regimes. Air was used as the gas phase. The liquid phase used was C 9 -C 11 paraffin oil containing varying volume fractions (e S = 0, 0.05, 0.10, 0.15, 0.20 and 0.25) of porous catalyst (alumina catalyst support, 10 % < 10 lm; 50 % < 16 lm; 90 % < 39 lm). With increasing slurry concentrations, e G is significantly reduced due to enhanced bubble coalescence and for high slurry concentrations the ªsmallº 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 e S > 0.05 and U > 0.1 m/s. The measured large bubble rise velocity V Lb agrees with the predictions of a modified Davis-Taylor relationship.

Bubble dynamics investigation in a slurry bubble column

“…This phenomenon is consistent with other reported results. 5,9,12,21 It is believed that an increase in solids loading increases the apparent viscosity of the pseudo-slurry phase and then enhances the bubble coalescence rate. 3 These effects tend to increase the mean bubble size, and the fast effusion of these large bubbles reduces gas holdup.…”

“…The advantage of the video imaging technique [6][7][8][9] is that it does not disturb the flow inside the column during the experiments. However, the video imaging technique requires a transparent wall and liquid, and it is only able to capture the bubble characteristics at low gas holdup conditions in a 2D column and close to the wall in a 3D bubble column.…”

Regime transition in viscous and pseudo viscous systems: A comparative study

“…1,2 The main influence of the solid concentration in a SBC reactor lies in an increase of the pseudo slurry viscosity of the slurry phase, which suppresses the bubble breakup in the column and attributes to the formation of large and fast moving bubbles, thus, decreases the gas holdup. [3][4][5] The properties of the liquid-solid suspension can be influenced by size, concentration, and wettability of the particles, as well as by the superficial gas velocity; which in turn increases the shear rate in the liquid and interaction between solid and liquid phase. The suspension behavior of the solid particles in a stationary liquid in terms of the pseudo slurry viscosity was first addressed theoretically by Einstein 6 (l sL / l L 5 1 1 2.5a s ) for small isolated spheres.…”

“…[3][4][5] However, the qualitative similarity between the systems was found only based on the average gas holdup, which does not signify the local distribution of the gas phase and the mixing inside the column. 40 No attempt was yet made to compare quantitatively the effect of liquid viscosity in twophase (gas-liquid) systems and pseudo slurry viscosity in three-phase (gas-liquid-particles) systems on the hydrodynamics under similar operating conditions.…”

“…The gas holdup decreases with increasing solid concentration due to the increase of the pseudo slurry viscosity of the slurry phase, which is believed to enhance the bubble coalescence. 3,33,[36][37][38][39][40] In our recent articles, 1,2 the "dual effect" of the influence of the particle concentration on the gas holdup at different superficial gas velocities in an SBC was quantitatively studied. An increase in the gas holdup was found for solid concentration up to 0.03.…”