The effect of gas‐liquid counter‐current operation on gas hold‐up in bubble columns using electrical resistance tomography

Abstract

BACKGROUND: In order to improve the performance of a counter-current bubble column, radial variations of the gas hold-ups and mean hold-ups were investigated in a 0.160 m i.d. bubble column using electrical resistance tomography with two axial locations (Plane 1 and Plane 2). In all experiments the liquid phase was tap water and the gas phase air. The superficial gas velocity was varied from 0.02 to 0.25 m s −1 , and the liquid velocity varied from 0 to 0.01 m s −1 . The effect of liquid velocity on the distribution of mean hold-ups and radial gas hold-ups is discussed.

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

“…This change is explained by the effect of the liquid flow, which slows down the rise of the bubbles, leading to higher holdup: the more compact arrangement of the bubbles leads to an earlier flow regime transition (Sections 3.2 and 3.4). Our results prove that U L (countercurrent mode) has an influence on the holdup, which agrees with the findings of Otake et al (1981), Baawain et al (2007), Biń et al (2001), Jin et al (2010), Besagni et al (2014 and Besagni and Inzoli (2016a) but disagrees with Akita and Yoshida (1973). Our results are probably due to the comparable order of magnitude of the liquid and gas velocities.…”

“…The effect is more pronounced at high gas velocities, and the difference in the holdup between co-current and counter-current mode is approximately 10%. The same trends were observed by Jin et al (2010) (d c ¼0.160 m, H c ¼2.5 m), who reported a maximum difference of 2% between counter-counter and co-current modes. Similar trends were found by Otake et al (1981) (d c ¼0.05 m, H c ¼1.5 m).…”

“…The main difference between the present bubble column and the "AG" bubble column is the value of the holdup for which U L has no more influence. In the literature, Jin et al (2010) observed that the influence of working mode is lower at high holdup. The discrepancy of the holdup in the transition regime between the batch and counter-current modes is hardly justified.…”

“…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. 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).…”

“…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.…”