Aplicação de técnicas de Fluidodinâmica Computacional (CFD) na avaliação da hidrodinâmica e da transferência de massa em estágio de coluna de destilação

Abstract

Distillation is one of the most important industrial separation techniques. It requires high quantity of energy, corresponding to around 40% of the total energy consumption of chemical industries. As such, the optimization of a distillation column is indispensable, and it is only possible from the knowledge of the fluid dynamics phenomena occurring within the column. Some of models used for this, such as the models based on equilibrium and non-equilibrium stage concepts, usually provide useful results, but consider empirically many of the fluid dynamics phenomena by assuming a perfect mixture in each phase. In recent years, the advent of the high-speed computers combined with the development of accurate numerical methods for solving physical problems has revolutionized the way we deal with fluid dynamics phenomena. Computational fluid dynamics (CFD) techniques allow a microscopic description of the physical characteristics of the fluid motion. The main purpose of this study was develop a computational fluid dynamics model for gas-liquid flows that was able to predict the hydrodynamics and mass transfer on a sieve tray. A two-phase, three-dimensional and transient model, in an Eulerian-Eulerian framework was proposed for air/water (25°C) and ethanol/water systems at 1 atm. The continuity, momentum and mass equations were used to describe the gas and liquid phases. The sieve tray geometry simulated was based on experimental work of Solari e Bell (1986). The variables predicted were the velocity profiles, volume fraction of each phase, clear liquid height, recirculation areas, mass fraction and efficiency. The hydrodynamic and mass transfer model predictions were compared with experimental and numerical data from some authors and presented good agreement. This study shows that CFD can be used as a powerful tool for sieve tray simulation.