Abstract:An accurate prediction of tray hydraulics is very important for large diameter trays design, and vapor cross-flow channeling is one of the key points that affect the hydraulics calculation.Therefore, in this article, a theoretical analysis was first conducted to reveal that the energy of gas-liquid on the tray was closely related to its flow state. Then, a model was obtained on the basis of the principle of the lowest energy, which can be used to calculate vapor cross-flow channeling.The model shows that the ratio of dry tray pressure drop to liquid height on a tray determines the gas distribution on the tray. Finally, the model was tested by comparisons with experimental results available in reference. The agreements are good. Furthermore, the effects of liquid load and fractional hole area on vapor cross-flow channeling were studied. The results are consistent with the field experience summarized in literatures.

Weeping is an important hydraulic parameter that needs to be considered for valve trays and for calculations in the distillation field. Therefore, the accurate prediction of weep rate is crucial for the optimal design of valve trays. First, the effects of gas and liquid loads and weir height on weep rate, tray pressure drop, and actual bubbling area were studied in a 1.5 m × 0.61 m cold simulator. Second, the weep modes on the valve tray were analyzed in detail. A theoretical model was then derived to calculate weeping. The model showed a clear relationship between the weep rate and the fractional bubbling area. The experimental data showed that the weir height substantially affected the orifice coefficient of the liquid passing through the valve. Finally, the relation between weir height and orifice coefficient was obtained by fitting the experimental data. The agreements were good, and the maximum deviations were approximately 25%.

An accurate prediction of gas-liquid interfacial area is very important for the design and optimization of column trays. However, the difference of the gas-liquid flow regimes operating at different scale trays significantly affect the interfacial area calculation. Therefore, in this study, an interfacial area model operating at small column was established using the Kolmogorov's isotropic turbulence hypothesis. According to the analyzes of the gas-liquid flow phenomena of different scale columns, an assumption that the similarity principle of flow characteristics of gas-liquid in full contact was proposed. Moreover, a new model that can be used to predict the gas-liquid interfacial area of a large column with exiting the nonideal flow was obtained through the extension of the small tray interfacial area model based on this principle. Finally, the new model was tested by comparisons with the experimental results of references. The prediction accuracy significantly improved with the maximum deviation of approximately 40%. V C 2015 American Institute of Chemical Engineers AIChE J, 62: 905-915, 2016 Keywords: distillation, different scales, valve tray, interfacial area, physical model IntroductionDistillation is the major process in present and future petroleum and/or chemical industries.1 Heat and mass transfers between gas and liquid phases occur in trays during distillation. Briefly, these transfer processes occur via phase interface. Hence, the interfacial area is an important field of investigation in chemical engineering research. Generally, studies on the interfacial area have mainly focused on two aspects: (1) increasing the contact interfacial area of the gasliquid interface by some means or the optimization of equipment structures to enhance the mass and heat transfer processes and (2) developing gas-liquid interfacial area models to predict the transfer of mass or heat. Valve trays grafted with some special structures are widely used as contactors for distillation/absorption columns because of their high tray efficiency, relatively low pressure drop, and large operation range (enhanced performance).2 However, previous research on hydrodynamics and mass transfer has mainly focused on sieve trays, [3][4][5][6][7][8][9][10] and little attention has been centered on valve trays.11-15 Therefore, high-accuracy models should be developed on the basis of theoretical research regarding the actual flow characteristics of gas-liquid in valve trays to calculate the hydraulic and mass transfer rates. These models will provide theoretical guidance for the reasonable design and optimization of trays.Column diameter and height are two main parameters involved in industrial column design. The column diameter is controlled by two-phase flow hydrodynamic behavior (weeping or flooding), whereas the total column height is controlled by mass transfer parameters. 15 To date, the actual trays of a column (cf. column height) are determined by two main methods: (1) tray efficiency based on equilibrium stage model [16][17][18] an...

Weeping is an important hydraulic parameter for the design and optimization of perforated plates because it determines the lower limit of the tray operation (vapor load). Therefore, an accurate prediction of the weep rate is very important. First, according to our theoretical analysis of the weeping phenomena of large-scale perforated trays, we proposed three weep modes on a perforated tray: (1) random weeping in the bubbling zone, (2) dumping in the nonbubbling zone, and (3) liquid fluctuation-induced weeping. Second, a weep rate model was developed, and the literature data were correlated to determine model parameters. Results showed the fractional hole area substantially affects the model parameters. We also examined the effects of the tray structure, flow parameter, and fluid physical properties on the weep rate. Finally, the developed model was used to predict the weep rate of different scale trays reported in references, and the prediction results showed good agreements.