Packing Size Effect on the Mean Bubble Diameter in a Fixed Bed under Gas–Liquid Concurrent Upflow

Abstract

The influence of the packing size on the mean bubble diameter in a flooded bed reactor packed with glass spheres of three different diameters (1.9, 4.0, and 9.3 mm) was investigated. The gas saturation and interfacial area were respectively measured by electrical capacitance tomography and chemical absorption of oxygen. It is observed that the presence of packing has greatly reduced the bubble diameter and increased the gas saturation compared with a bubble column. To explore the underlying relationship between the bubble diameter and packing size, the packing size featured by the pore diameter was utilized as a reference. It shows that the bubble diameter is 2–3 times the pore for the 1.9 and 4.0 mm packings, while they are approached for the packing of 9.3 mm. An empirical correlation was proposed for the mean bubble diameter prediction with a discrepancy of less than 25% from the measurements.

Packing size effects on the liquid circulation property in an external‐loop packed bubble column

“…In the free fluid domain without packing, is set as zero, and can be written as where, is the bubble diameter, it is estimated by the empirical correlation proposed by Akita and Yoshida 43 for empty column without packing, and it is estimated by the empirical correlation proposed by Chen et al 8 for the packed column, is the drag coefficient, which follow the Ishii‐Zuber model 44 : is Eötvös number, defined by where, is gas–liquid surface tension. In addition, the RNG k ‐ ɛ model is used to account for the turbulence effect, the conservation equations are as follows: …”

“…In Equations ( 7), (8), and ( 10), E 1 and E 2 are assigned as 150 and 1.75, fitted by a large number of experiments, 42 ε s is the bed porosity, and d p is effective particle diameter.…”

“…It is due to a drop in the bubble rise velocity caused by the resistance of the packing, also, the presence of packing suppresses the growth of bubbles. The buoyancy force of bubble is reduced, 8 both factors make residence time of bubble in the column F I G U R E 5 Effects of packing size on the gas holdup under different superficial gas velocities and downcomer diameters longer and the gas holdup higher. It also can be observed that the gas holdup increases with the decrease of packing size.…”

“…On one hand, increasing superficial gas velocity increases the gas holdup, which provides more contact area for gas-liquid mass The presence of packing suppresses the growth of bubbles, a smaller bubble diameter can be obtained in the packed column compared to the empty column. 35 Chen et al 8 investigated that the effects of packing size on the bubble diameter and interfacial area with the packing of three different diameters, the results show that the finer packing is more effective in bubble breakup, and a smaller bubble diameter and higher interfacial area can be obtained. Deshpande et al 11 added that reducing the packing size is not always effective for gas-liquid mass transfer.…”

Local hydrodynamics investigation of industrial scaled‐down upflow moving‐bed hydrotreater reactor using a two‐tip optical probe

“…Collins et al [ 10 ] used MRI to study gas‐phase hydrodynamics on a two‐phase upflow packed bed (diameter 4.3 cm, height 80 cm). Electrical capacitance tomography (ECT) can be applied to slightly larger‐scale reactors, Hamidipour and Larachi [ 11 ] used ECT to study the liquid dynamics on a two‐phase upflow/downflow packed bed (diameter 5.3 cm, height 80 cm), and Chen et al [ 12 ] used ECT to study gas dynamics in a two‐phase upflow packed bed (diameter 14 cm, height 100 cm). The advantage of all these mentioned techniques is non‐invasiveness, while the major disadvantages is that implementation is limited by the size of the column, the operating conditions (low gas holdup), and the high operating costs, which makes it harder to implement in a pilot/industrial‐scale reactor as a flow monitoring/measurement device.…”