Characterising gas behaviour during gas–liquid co-current up-flow in packed beds using magnetic resonance imaging

Abstract

Magnetic resonance (MR) imaging techniques have been used to study gas phase dynamics during co-current up-flow in a column of inner diameter 43 mm, packed with spherical nonporous elements of diameters of 1.8, 3 and 5 mm. MR measurements of gas holdup , bubblesize distribution, and bubble-rise velocities were made as a function of flow rate and packing size. Gas and liquid flow rates were studied in the range of 20-250 cm 3 s-1 and 0-200 cm 3 min-1 , respectively. The gas holdup within the beds was found to increase with gas flow rate, while decreasing with increasing packing size and to a lesser extent with increasing liquid flow rate. The gas holdup can be separated into a dynamic gas holdup , only weakly dependent on packing size and associated with bubbles rising up the bed, and a 'static' holdup which refers to locations within the bed associated with temporally-invariant gas holdup , over the measurement times of 512 s, associated either with gas trapped within the void structure of the bed or with gas channels within the bed. This 'static' gas holdup is strongly dependent on packing size, showing an increase with decreasing packing size. The dynamic gas holdup is comprised of small bubbles-of order of the packing size-which have rise velocities of 10-40 mm s-1 and which move between the packing elements within the bed, along with much larger bubbles, or agglomerates of bubbles, which move with higher rise velocities (100-300 mm s-1). These 'larger' bubbles, which may exist as streams of smaller bubbles or 'amoeboid' bubbles, behave as a single large bubble in terms of the observed high rise velocity. Elongation of the bubbles in the direction of flow was observed for all packings.

Gas hold‐up and bubble behavior in an upflow packed bed column in the limit of low flow rate

“…They also reported a reduction in the liquid hold‐up by increasing the reactor pressure and gas velocity. Collins et al measured liquid and gas hold‐up during cocurrent gas–liquid upflow in a packed bed by magnetic resonance imaging technique. Gas hold‐up within the bed was found to increase with gas flow rate and decrease with increasing packing size, and to a lesser extent with increasing liquid flow rate.…”

Towards Tomography-Based Real-Time Control of Multiphase Flows: A Proof of Concept in Inline Fluid Separation

“…For instance, wire-mesh sensors (WMSs) have been used to measure the cross-sectional profiles of the volumetric fraction in gas-liquid [12,13], liquid-liquid [14,15] and three-phase [16,17] flows. In the field of industrial tomography, soft-field techniques such as electrical resistance [18,19], electrical capacitance [20,21], and electrical impedance tomography [22] have been applied in the study of the distribution of the phases and volumetric fractions of multiphase flows, and more sophisticated (hardfield) techniques such as MRI [23][24][25] and ultrasound [26,27] have been applied in the measurement of both the volumetric fraction and flow velocity. However, until recently, these techniques were still limited to slow processes or offline applications, and the realtime control of multiphase flows was limited to flow variables that are faster to measure, but are only indirectly connected to performance, such as pressure [28,29], density, or flow rate [30].…”

“…Figure25. Controlled core size in the presence of a square wave disturbance in the air flow rate of the experimental facility.…”

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

“…Sankey et al [ 8 ] and Mantle et al [ 9 ] used MRI in a two‐phase upflow packed bed (diameter 4 cm, height 50 cm). 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).…”