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.