Prediction of gas–liquid interfacial area in valve trays

Abstract

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...

Experimental study and modeling of weeping rate in rectangular large‐scale valve trays

“…The correlation proposed by Wang is used to calculate the liquid holdup of the bubbling area, which can eliminate the iteration in the calculation of h cl with , where u s is the superficial gas velocity.…”