Influence of internals on counter-current bubble column hydrodynamics: Holdup, flow regime transition and local flow properties

Abstract

However, in most industrial applications, internal devices are often added to control heat transfer, to foster bubble break-up or to limit liquid phase back mixing. These elements can have significant effects on the multiphase flow inside the bubble column reactor and the prediction of these effects is still hardly possible without experimentation. In this paper, we study experimentally a counter-current gas-liquid bubble column in the open tube and annular gap configurations. In the annular gap bubble column, two vertical internal tubes are considered. The column has an inner diameter of 0.24 m, and the global and local hydrodynamic properties are studied using gas holdup measurements and a double-fiber optical probe. The gas holdup measurements are compared with the literature and used to investigate the flow regime transition. A double-fiber optical probe is used to acquire midpoint data and radial profiles of the local properties to study the flow properties and to further investigate the flow regime transition. The counter-current mode is found to increase the holdup, decrease the bubble velocity and cause regime transition at lower superficial gas velocity. The holdup curves in the annular gap and open tube configurations are similar in shape and values, suggesting that the presence of internals has a limited influence on the global hydrodynamic. In addition, it is found that the presence of the internals stabilizes the homogeneous regime in terms of transition gas velocity and holdup.

Comprehensive experimental investigation of counter-current bubble column hydrodynamics: Holdup, flow regime transition, bubble size distributions and local flow properties

“…Otake et al (1981) observed an earlier regime transition increasing the liquid flowrate in the counter-current mode (U L up to À 0.15 m/s). Similar conclusions were drawn by Yamaguchi and Yamazaki (1982a) (d c ¼0.04 m and 0.08 m), Besagni et al (2014 and Besagni and Inzoli (2016a). It is worth noting that the hydrodynamic properties of bubble columns are determined by the momentum exchange between the liquid and gas phases.…”

“…Their analysis covered gas superficial velocities up to 0.26 m/s and liquid superficial velocities up to À 0.11 m/s. It appears that the influence of the operation mode is lower at high holdup (Besagni and Inzoli, 2016a;Besagni et al, 2014Jin et al, 2010). With regard to the regime transition, Jin et al (2010) reported that the transition point is the same among the three working modes if U L is lower than 0.04 m/s, whereas for higher U L (in co-current and counter-current modes), the transition velocity decreases with increasing superficial liquid velocity.…”

“…The appearance of the first large bubble is responsible for this sudden increase in swarm velocity and is an indication of flow regime transition. This method has previously been employed by Krishna et al (1991), Letzel et al, (1997), Gourich et al, (2006), Ribeiro and Mewes (2007), Besagni et al (2014 and , 2016a, 2016b. In this study, the quantitative evaluation of U trans is determined by the intersection between the trends of U swarm in the two regimes.…”

“…Similar trends were found by Otake et al (1981) (d c ¼0.05 m, H c ¼1.5 m). Besagni et al (2014 (d c ¼ 0.24 m, H c ¼5.3 m), (Besagni and Inzoli, 2016a) found that the counter-current mode influences the column hydrodynamics affecting both the holdup and the local flow properties in annular gap and open tube (with a "pipe-sparger") bubble columns. Their analysis covered gas superficial velocities up to 0.26 m/s and liquid superficial velocities up to À 0.11 m/s.…”

“…For example, Akita and Yoshida (1973) (d c ¼0.152 m, H c ¼2.5 m) observed a negligible effect of U L (up to 0.04 m/s) in both co-current and countercurrent operations. At higher liquid velocities, the column operation influences the holdup: the co-current mode reduces the holdup (Biń et al, 2001;Chaumat et al, 2005b;Jin et al, 2007;Kumar et al, 2012;Otake et al, 1981;Pjontek et al, 2014;Shah et al, 2012;Simonnet et al, 2007), and the counter-current mode increases the holdup (Besagni and Inzoli, 2016a;Besagni et al, 2014Biń et al, 2001;Jin et al, 2010;Otake et al, 1981) as bubbles are either accelerated or decelerated by liquid motion (Leonard et al, 2015;Rollbusch et al, 2015a). Baawain et al (2007) showed that the counter-current or cocurrent operation modes influenced the holdup by approximately 5% in weight, and less than 1% in bubble size, showing that the effect observed is mainly caused by the bubble rise velocity and not only the bubble size.…”