Numerical Simulation Of Two Phase Turbulent Flows And Mass Transfer On Sieve Trays

During the past decade, catalytic distillation has received much attention from both industrial and academic communities due to its higher commercial profits. In the process, sieve tray tanks are always used as a reactor and separator. For the predictive design or performance intensification of such process, knowledge of hydrodynamics of two phase turbulent flows and mass transfer properties on sieve trays is inevitably needed.In this paper, hydrodynamics of two phase turbulent flows and mass transfer properties on sieve trays are investigated by using a numerical experiment method that is based on computational fluid dynamics (CFD) models. Firstly, a 2D quasi-single phase liquid turbulent flow model was developed. In this model, interactions between liquid and bubbling gas phase were taken account of, i.e., interphase drag force and the turbulent energy induced by the bubbling gas phase. Secondly, a 3D two fluid model was developed to model hydrodynamics of two phase turbulent flows on sieve trays. Finally, based on the two fluid model, a mass transfer model that describes composition distributions in the liquid phase was developed. The flow models and the mass transfer model were solved using the finite volume method and the CFX software. The main conclusions drawn from the simulation results are as the following:1. Simulation results of the qusai-single phase model showed that an overall agreement was obtained between model predicted values of local liquid velocities and the published data by Solari and Bell. It is shown that there exist five different zones exhibiting different flow patterns on a two dimensional tray. Typically, a circulating zone (large eddy) near to the elbow of tray changes its characteristic length scales with the operation conditions, i.e., superficial gas velocity and flow rate of liquid. The formation and variation of the large eddy were explained in terms of the liquid kinetic energy and its dissipation rate by using the turbulence model theory.2. The theoretical predictions by 3D two fluid model were in agreement with the published data by Solari and Bell.. The predicted gas phase volume fraction values of two fluid model were close to the well known Bennet formula values with an average relative error of 0.19%. The simulation results showed chaotic tray hydrodynamics and different liquid circulation patterns, which had a true three-dimensional character. The flow phenomenon was also explained in terms of the liquid kinetic energy and its dissipation rate by using the turbulence model theory.3. Simulation of the mass transfer model with the benzene-propylene two phase system showed that distribution of the liquid component in the top-view planes can be divided into two zones, i.e., a uniform zone with nearly uniform concentration distribution and back-mixing zone with concentration gradient, while characteristics of the two zones are highly dependent on the local turbulent conditions. In the vertical direction to the tray, there exist two different zones, i.e., a zone exhibiting characteristics of a concentration boundary layer and well-mixed zone.