Simultaneous Momentum, Mass, and Energy Transfer Analysis of a Distillation Sieve Tray Using CFD Techniques: Prediction of Efficiencies

Abstract

Conventional models for distillation columns are based on equilibrium and nonequilibrium stage concepts. Although equilibrium and nonequilibrium stage models provide useful results, they neglect the fluid dynamics phenomena by assuming a perfect mixture on the plates in each phase. However, the flow pattern on a distillation tray is of great importance in terms of the mass and energy transfer mechanisms, and this influence can only be analyzed by carrying out a fluid dynamics study. The main objective of this study is to obtain experimental data of clear liquid height in a distillation sieve tray apparatus operating with air and water, and to apply a computational fluid dynamics (CFD) model in a Eulerian−Eulerian framework for gas−liquid flows that is able to predict the momentum, mass, and thermal phenomena of multiphase flows. A two-phase, three-dimensional and transient model with chemical species, energy, and momentum conservation balances was applied to predict the volume fraction, velocity, pressure, temperature, and concentration fields of two-phase flows on distillation sieve trays. The mathematical model was applied in the CFD commercial code for numerical studies, with the construction of a particular numerical grid and with its own subroutines in Fortran language for the closure equations of the model. The hydrodynamic model was compared with experimental data and presented good agreement. The results of the model show the volume fraction, velocity, temperature, and concentration profiles as a function of time and the position on the distillation sieve tray. The model implemented in this study allows direct application to predict efficiencies in distillation plates, more specifically point, plate, component, and global efficiencies.

Estudo Da Transferência De Massa De Um Prato Perfurado Industrial Na Destilação Do Etanol Através De CFD

“…Acredita-se que esta discrepância dos resultados obtidos numericamente dê-se por dois motivos: primeiro e principalmente pelo tamanho e características do prato avaliado e segundo pelas difusividades estipuladas. O menor diâmetro do prato avaliado por Noriler et al(2010) e um vertedor mais alto, provavelmente permitem um tempo menor de contato entre as fases e aumenta as chances de recirculação. Somados a isso, as difusividades estipuladas diferiram-se nos valores, o que provavelmente acarretou taxas diferentes de transferência de espécies químicas.…”

“…Neste contexto, podese citar os principais trabalhos como de Rahimiet al (2006), Noriler et al(2010) e Rahimi et al (2012), os quais predisseram a eficiência de separação no estágio de destilação e os campos de fração mássica dos componentes distribuídos ao longo do prato perfurado.…”

CFD analysis of laboratory scale phase equilibrium cell operation

“…Laakkonen et al (2006a;2006b) have investigated mass transfer in agitated fermenter vessels considering local population balance distribution. In separation process analysis for liquidliquid extraction in micro and macroscale (Buffo et al, 2016;Tsaoulidis and Panagiota, 2015;Xu et al, 2013;Chasanis et al, 2010;and Jildeh et al, 2012) or distillation process (Jiang et al, 2013;Sun et al, 2007;Rahimi et al, 2012;Wang et al, 2004;Rahimi et al, 2006;and Noriler et al, 2010), CFD is used to predict flow field, mass transfer, concentration profiles, and finally efficiencies. Importantly, all these studies a) Author to whom correspondence should be addressed: mohamed.jama@ aalto.fi.…”

Simultaneous Momentum and Energy Transfer Analysis in a Distillation Column Sieve Tray Using CFD Techniques: Study of Influence of the Inlet Downcomer

“…Thus, the continuity equations and the energy and momentum conservation balances were applied for both chemical species, for predictions of volume fractions and velocities, temperatures and pressure fields. NORILER et al (2010) analyzed the mass and energy transfers along the sieve tray simultaneously. The authors proposed a transient, 3-D, multiphase, and multicomponent flow, in an Eulerian-Eulerian approach.…”