Document Type

Article

Publication Date

3-13-2024

Abstract

Most chemical process simulators in widespread use today allow users to apply some type of efficiency correction to individual equilibrium stages or to equilibrium stage sections in order to align the stage or section separation performance more closely to actual tray performance in the field. Some simulators even allow for the use of component efficiencies on individual stages or in stage sections. It is our contention, however, that two of the more commonly available efficiency models, the vaporization efficiency and Murphree vapor phase efficiency, have generally been implemented incorrectly. The three major conceptual inconsistencies are (1) the assumption that the liquid and vapor exit a stage at the same temperature even in the presence of stage or component efficiencies, (2) specification of all “C” component efficiencies when only “C-1” are independent, and (3) in the case of the vaporization efficiency, the assumption that there can be equal component efficiencies for all components. All three assumptions can lead to impossible column composition and temperature profiles, coupled with violations of some of the most fundamental thermodynamic principles. To correct these mathematical and thermodynamic issues, we suggest: (1) the liquid and vapor streams exiting a stage always be treated as bubble point liquids and dew point vapors, (2) specification of only “C-1” component efficiencies, and, perhaps most importantly, (3) an improved understanding of solution thermodynamics on the part of programmers and a reevaluation of the quality assurance function at organizations producing chemical process simulation software.

Publication Source (Journal or Book title)

Industrial and Engineering Chemistry Research

First Page

4519

Last Page

4532

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