Empty Spray Sections of Vacuum Towers: Heat and Mass Transfer with a CFD approach

Abstract

Distillation columns are the core of a refining process. An understanding of their heat and mass transfer is essential to propose modifications of the equipment. A multiphase model is applied to the vacuum tower with the vapor-liquid flow being modeled with an Eulerian-Lagrangian approach. An ideal multicomponent equilibrium model is adopted to represent the thermodynamics in the heat and mass transfer processes. The characteristic time scales are used in the classification and the understanding of the dominant mechanisms in gas-liquid suspensions. This methodology is general, and therefore can be applied to any turbulent gas-liquid flow. The present work applies a simplified multicomponent Fick's law and gamma-phi approach to liquid-vapor equilibrium in an Eulerian-Lagrangian multiphase flow model in order to get multicomponent heat and mass transfer. The simplification proposed here is that the diffusive flux is independent of the other fluxes. This implies that each flux can be calculated without information on the other fluxes. On the other hand, thermodynamic equilibrium takes all components into account. Thus, it is rigorously calculated. The main target of this work is to gather information on vacuum tower fluid dynamics using an Eulerian-Lagrangian model with computational fluid dynamics (CFD) techniques, which is a powerful tool for better understanding the physical phenomena involved in vacuum towers.