Evaluation of the validity of tray and point efficiency correlations at elevated liquid viscosities and proposal of an improved point efficiency correlation

Abstract

The accuracy of the distillation efficiency correlations plays a critical role in cost-effectively designing distillation columns. Liquid viscosity is considered to be a major factor that influences distillation efficiency through its contribution to the liquid-phase mass transfer coefficient, interfacial area of mass transfer, and vapor and liquid phase residence times. Nearly all of the distillation efficiency correlations in the literature were developed or validated on the basis of efficiency data at liquid viscosities less than 1.5mPas. However, distillation at liquid viscosities greater than 1.5mPas is encountered in several cases in the chemical process industry. In this paper, the evaluation of three different tray and point efficiency correlations using Oldershaw column data at liquid viscosities from 0.2 to 4.2mPas is presented. In addition, we propose an improved point efficiency correlation, based on the Duss and Taylor correlation, with a modified liquid viscosity exponent for the liquid-phase mass transfer coefficient. The proposed correlation was validated with commercial sieve tray efficiency data and Oldershaw column data. This proposed correlation will aid in the cost-effective design of distillation columns, especially at elevated liquid viscosities.