Estimation of Gas Holdup Using the Gassed to Ungassed Power Ratio of an Oxygen–Water System in a Stirred and Sparged Tank Contactor

Abstract

Gas holdup (εg) and power correlations in gas–liquid (G–L) systems, apart from the physicochemical properties of the liquid phase, are dependent on impeller–sparger–vessel geometry. To date, reported correlations do not specifically address this issue, and it must be investigated with a unified approach. Here, we propose a correlation via the use of a normalized εg that involves the impeller–sparger system geometry for a vessel of standard geometry expressed as a function of an easily measurable and independent operational parameter, that is, (1 – P g/P l), where P g/P l is the gassed to ungassed power ratio. Furthermore, our work demonstrates that P g/P l can be used as a tool for the identification of hydrodynamic regimes. Radial and axial impellers with ring spargers were used in a stirred and sparged contactor (SSTC) of 0.25 m diameter containing 1 × 10–2 m3 water. The oxygen flowrate (Q g) was varied from 2.5 to 40 LPM or (4.17 to 66.7) × 10–5 m3 s–1, and the agitation intensity (N 0) was varied from 1.67 to 50 rps at the temperature (θ) = 313 K under atmospheric pressure. This novel correlation is easy to use, offers reasonable precision, and can serve as a valuable alternative to more complex correlation models.

The Effect of Impeller–Sparger Geometry on the Gas Holdup in an Oxygen–Water System Using an Agitated and Sparged Tank Contactor

“…2 In an ASTC, gas is introduced from a sparger beneath the impeller, and sparged bubbles are broken up by impeller action and uniformly dispersed throughout the system. 2,3 It may be shown by film theory that the overall K L S is linearly dependent on ε g , 4 which provides a more straightforward alternate technique indicative of mass transfer rates. Experimental K L S determination can be tedious; therefore, an easily measurable parameter such as ε g is desirable.…”

“…15−17 To date, reported ε g correlations do not specifically address the issue of geometrical dependence, so we developed a unified approach in our recent work. 4 Our novel correlation is impellerring sparger geometry-based for a vessel of standard geometry and yet simple to use. The generic form of the correlation, shown in eq 2, exhibits a better root-mean-square deviation (rmsd) fit with the experimental data 4 than other published correlations due to the incorporation of the impeller-sparger geometrical parameter in the correlation.…”

“…Previously Published Work. Five distinctive hydrodynamic regimes 1,4,6,7,11,12,18,19 in G-L systems have been characterized (Figure 1), and their descriptions are listed:…”

“…Therefore, operation in this regime needs to be purposely avoided during G-L kinetic studies. 4 Many experimental techniques and correlation-based approaches for the identification of hydrodynamic regime transitions have been reported. Van't Riet (1973), 5 Warmoeskerken et al (1984), 6 Warmoeskerken and Smith (1985), 7 and Bombac et al (1997) 9 discuss the relationship between cavity structures (e.g., vortex, clinging, "3−3", large, and ragged) and hydrodynamic regimes.…”

“…However, to date, reported ε g correlations do not specifically address the geometrical dependence issue; thus, we investigated this aspect with a unified approach. Accordingly, in our recent work, 4 we developed a novel ε g correlation, 4 which is impeller-ring sparger geometry-based for a vessel of standard geometry and yet simple to use.…”