1. Introduction
To design a distillation tray, combining empirical and related
theoretical findings is essential. An appropriate phase contact and an
improvement in a tray’s efficiency are achieved by a proper tray design.
It has been proved that the trays possess suitable flexibility for
operation in a satisfactory area of operation circumstances, which is
called the tray’s operation window or behavior diagram. This region is
stated by the liquid and vapor rates. By a low vapor rate, tray
efficiency declines by the liquid weeping; however, the force extends
toward the above tray and the entrainment phenomenon takes place at a
high vapor rate. Numerous distillation towers exist operating at a lower
capacity compared to their design capacity. Hence, by determining the
entrainment limits and liquid weeping of the trays, appropriate
information can be obtained for enhancing the performance in towers. The
weep fraction and dry tray pressure drop are two main hydraulic factors
determining the lower operation limit for a
tray[1-3]. The sieve trays are still
the normal mass transfer tools in petroleum industries with their
constant well features. The sieve tray’s simple geometry results in the
leakage of liquid within the deck holes at low vapor rates and decreases
its normal operation window. Furthermore, the weeping is regarded as a
usual reason for the trays’ mal-functions in chemicals, olefins,
refineries, and gas plants[4]. Lockett
et al. [5]computed the reduction of tray performance caused by
weeping. They attempted to prolong the former analyses’ applicability
[6-8] for industrial towers by
attending the point where the gas phase is not combined between the
trays. Fasesan [9] calculated the liquid weeping rate in absorption
trays by two equal trays. His study focused on an absorption column with
air-water system. The results were gained by two independent approaches
of dye trace and weep-age catch tray method. Additionally, this
researcher utilized a chimney tray for measuring the rate of weeping for
valve trays and sieve through a direct volumetric technique. The
findings illustrated that the liquid weeping is different between the
trays. The obtained results indicated that by increasing the liquid
load, the rate of weeping for a sieve tray working in the weeping trend
increases linearly.
To utilize sieve tray towers for industrial uses more effectively, it is
essential to have an enhanced theoretical understanding of the sieve
tray hydraulics. In this regard, understanding some measurable and
valuable parameters like pressure drop is essential but not enough.
Hence, comprehending the detailed performances of instant liquid and
vapor flows in the column is necessary. Previously, the mathematical
models were developed to predict the liquid weeping and its rate
[10-12] as alternative techniques to
interpret a tray performance over weeping circumstances. A model was
developed by Wijin [13] for lower
operation limits of absorption and distillation trays. This author
provided a novel technique to calculate the minimum gas flow rates of
valve trays and sieve operating in the churn, bubble, and turbulent flow
systems. Also, the researcher examined the association between tray
efficiency and weeping.
Mehta et al.[14] Used the numerical
method to investigate the hydrodynamic of perforated trays and presented
detailed information in this regard. Furthermore, Yu et al.
[15] and Liu et al.
[16] assessed the hydrodynamic of
tray by two- dimensional model through CFD. They presented models
focusing on the variations and ignored the liquid phase hydraulics along
with the gas flow in the direction of the dispersion height. A transient
three-dimensional CFD model was presented by Quarini and Fischer
[17] to investigate about the
hydrodynamic of perforated tray.in foresaid model, drag coefficient was
constant and equal to 0.44 . Moreover, the hydraulics of a sieve tray
was enhanced by Krishna et al. [18] and Krishna and Van Baten
[19] by approximating a novel drag coefficient for the large bubbles
swarm in terms of the association of Bennett et al.
[20]. A three-dimensional model was
presented by Gesit et al. [21] for
predicting the flow patterns and hydraulics of the sieve tray by CFD
device utilizing Colwell [22]
association for the liquid holdup working well in the force direction. A
three-dimensional CFD simulation was presented by Teleken et al. with
the mathematical homogeneous biphasic model [23-25] for evaluating
the effect of electrical resistance of heaters over the sieve tray
surfaces and its hydrodynamics. Moreover, Teleken et al. [24, 25]
assessed a falling liquid film’s flow via a distillation column via an
Eulerian-Eulerian CFD technique. They aimed to provide a better
interpretation of the feed distribution system. Patwardhan and Yadav
[26] and Ud Din et al.
[27] presented CFD models for
comprehending the sieve’s hydrodynamics and pulsed-sieve plate
extraction column utilizing Eulerian-Eulerian method and the standardk -ε turbulence model. Zarei et al.
[28] studied the weeping phenomena in
a circular sieve tray by experimental and CFD methods. The experiment
was performed in a pilot-scale column with a diameter of 1.22 m
including two chimney trays and two test trays. Some hydraulic
parameters and weeping rates were calculated in sieve trays with a hole
area of 7.04%. Overall, there was good consistency between the attained
CFD findings and the experimental data. A 3D and biphasic model was
presented by Yang et al [29] for the tray without a downcomer
(Ripple tray) using the CFD. The model was homogenous following
Euler-Euler interaction. They compared some elements like the clear
liquid’s height in the tray with the sieve tray and reported that the
Ripple tray without downcomer experiences a rather small pressure drop
compared to the sieve tray. Moreover, its operational flexibility was
enhanced in comparison to the sieve tray. In
[30], the hydraulics and flow
patterns of a valve tray were predicted utilizing computational fluid
dynamics simulation and experimental method. A three-dimensional CFD
model was presented in the Eulerian frame work. Experimental findings of
the average liquid holdup, froth height, clear liquid height, dry
pressure drop, and total pressure drop were investigated and compared
with the CFD results. The CFD results were in good consistency with
experimental results. CFD simulation and experimental study on bubble
cap tray were done in ref [31],
Simulations were performed in industrial range of gas and liquid rates.
Some hydrodynamic parameters were calculated and predicted. The gained
results were in agreement with experiment. Abbasnia et al.
[32] investigated the efficiency and
mass transfer for the Nye tray and sieve tray. The system in their
investigation was methanol-normal propanol. The distributions of
methanol compositions on the trays were obtained for four average
methanol compositions. The results revealed that the liquid composition
profile on the Nye tray is enhanced compared to the sieve tray and more
resembling the rectangular tray. Nye tray’s Murphree efficiency was
almost 10% higher than the sieve tray.