Application of γ-ray Attenuation for Measurement of Gas Holdups and Flow Regime Transitions in Bubble Columns

Abstract

In this study a γ-ray densitometry was used to measure radial and axial volume fraction distributions in a 0.21 m diameter bubble column, and flow regime transitions in a 0.05 m and 0.21 m diameter bubble columns. Experiments were conducted with two- and three-phase systems (nitrogen−Fischer−Tropsch derived waxes−iron oxide or silica particles) in both batch and continuous modes of operation at 265 °C and ambient pressure. Average radial gas holdups in the large diameter column showed the existence of a maximum at the center of the column, in both two- and three-phase systems. The maximum was more pronounced at higher superficial gas velocities (churn-turbulent flow regime). The axial and average gas holdup measurements in two-phase systems were in good agreement with results obtained by a conventional method (pressure measurements along the column height). An independent treatment of all three phases did not yield satisfactory results, due to large impact of small experimental errors on calculated holdups. Alternative methods based on measured values of solids concentration in the slurry yielded satisfactory results. Instantaneous signals from the nuclear density gauges were used successfully to determine transitions from homogeneous flow regime to slug flow (small diameter column) or churn-turbulent flow regime (large diameter column) in two-phase systems.

Quantitative measurement of gas hold-up distribution in a stirred chemical reactor using X-ray cone-beam computed tomography

“…Thus, Veera et al [17] reported on the use of a ␥-ray attenuation technique to measure time-averaged radial gas distribution profiles in an aerated stirred tank from sets of chordal attenuation measurements obtained at different horizontal cross-sections. Bukur et al [18] used this technique in bubble columns. Kumar et al [19], Kemoun et al.…”

Population balance modeling of bubbly flows considering the hydrodynamics and thermomechanical processes

“…However, these results were found to clearly contradict the measurements performed by Hibiki et al 48 as well as some experimental observations. 67,68 One plausible explanation for this discrepancy could possibly be the error embedded in the turbulent dissipation rate prediction 69 as a consequence of the turbulence model being applied contributing in turn to excessively high coalescence rates in the MUSIG model. As reported in Chen et al, 39 similar observations also confirmed the high coalescence rates that were experienced in their bubble column study.…”

An algorithm for estimating radial gas holdup profiles in bubble columns from chordal densitometry measurements

“…either gas phase or liquid phase , as follows (as shown in Figure ): Combining Equations we get expression (6):­ where is intensity measured at two‐phase operating conditions, is intensity measured with pure gas phase (unity gas holdup), is intensity measured with liquid phase (zero gas holdup), and denotes the discrete chordal holdup of the gas phase at different x i . For extracting chordal‐averaged gas holdup at any x i , three measurements are required: column filled with liquid phase, column filled with gas phase (empty column), and column operating at two‐phase conditions …”