(21b) Valve Tray Efficiency Models for Binary Distillation – A Review of the State-of-the-Art

Tray efficiency models can be classified as empirical or theoretical. The empirical models are data-driven and developed to best describe the experimental efficiency data in terms of the physical properties, tray geometry, and operating conditions. The empirical models express efficiency either as a functional relationship or as relationships of dimensionless groups. The theoretical models are based on phenomenological relationships developed from the analysis of the two-phase characteristics, mass-transfer, and the cross-flow hydraulic effects on the tray. This paper addresses the developments in theoretical valve tray efficiency modeling for binary distillation applications.

There have been no reviews of valve tray efficiency models in the published literature. Vital et al. (1984) compiled a list of valve tray efficiency data, but it had not been updated in 25 years. Although valve tray efficiencies were studied experimentally, there have been no theoretical models for valve tray efficiency after the Todd and Van Winkle (1972) model. Therefore, there is clearly a need for a fundamental study of valve tray efficiency.

Despite the lack of valve tray efficiency model work, much of the hydraulic and mass-transfer studies on sieve trays are applicable to valve trays. The last sieve tray efficiency model was proposed in 2007 by Syeda et al. Among others, Chan and Fair (1984), Lockett (1986), Kister (1992), and Bennett et al. (1997) provide excellent reviews of the sieve tray efficiency models. The developments in the sieve tray efficiency models, however, have not been applied or considered from a valve tray point of view.

This work not only presents a critical review but also a unique comparison of the valve and sieve tray efficiency models in terms of the three fundamental measures required for efficiency modeling ? two-phase characteristics, mass-transfer, and cross-flow hydraulic effects. The goal of this work is to identify the similarities, differences, and gaps among valve and sieve tray efficiency models. The gaps in literature and the opportunities for improved valve tray efficiency predictions are highlighted with directions towards future research.

This work serves as the basis for the current work at Oklahoma State University on enhancing existing models or developing new models for predicting valve tray efficiency in binary distillation applications.