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.
LPG (liquid petroleum gas) sweetening is a very important refining process in which mercaptans are extracted from LPG by caustic solution, resulting in mercaptide salts. Subsequently, these mercaptides are oxidized in the presence of air and catalyst to disulphides involving gas liquid (G‐L) reactions in an oxidizer. This review discusses design and operational aspects of a laboratory G‐L oxidizer which are essential for determination of intrinsic kinetic parameters of the mercaptide oxidation step. These kinetic parameters are subsequently used for scale‐up and design of grass root industrial scale oxidizers. The sweetening is categorized as a slow reaction. Hence, reaction takes place both in the film and the bulk. Transport of oxygen across the air to the aqueous alkaline phase in the oxidizer is critical and controlled by the liquid film mass transport term. Thus, oxygen transportation limitations need to be overcome and ensured before conducting kinetic studies. This paper fills the gap between laboratory reactor design and operational aspects by presenting a detailed review on chemical engineering analysis for maximization of the volumetric mass transfer coefficient using operational aspects of an agitated sparged G‐L reactor.
Gas–liquid
(G-L) reaction kinetics studies need ideally
to be carried out (a) in the total recirculation regime, signifying
maximum mass transfer rates (K
L
S) and (b) in contactors, which geometrically support higher K
L
S. G-L mixing enhancement
by agitation and gas sparging is generally practiced to enhance K
L
S. The agitated and sparged
tank contactor (ASTC) consisting of baffles, stirrers, and spargers
is the preferred mode of contacting. It is essential to understand
how the impeller–sparger geometry affects K
L
S in a standard ASTC while operating
in the total recirculation regime. A film theory-based approach shows
that K
L
S may be approximated
by the gas holdup (εg) in the total recirculation
regime. Combinations of standard radial and axial impellers with ring
spargers of different sizes are used in an ASTC of 0.25 m diameter
containing 1 × 10–2 m3 water. The
oxygen flow rate (Q
g) is varied from (6.26
to 25.02 × 10–5) m3 s–1, and agitation intensity (N
0) is varied
from (1.67 to 16.67) rps at the temperature (θ) = 313 K under
atmospheric pressure to understand the effects of geometry on εg while operating in the total recirculation regime. Results
of our investigations show how an ASTC with an impeller of high-power
number (N
P) and a ring sparger of near
impeller diameter (D) form an ideal combination and
will result in maximum εg (indirectly optimum K
L
S), making it suitable for
kinetics studies.
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