CFD Simulation Of The Spinning Band Distillation Column

Recently, spinning band distillation has been widely used to separate liquid mixtures with approached boiling point or thermo sensitive substances. Both high vacuum and high numbers of theoretical plates could be achieved within this new device. When it worked, the spinning band rotated in the column with high speeds, which made the condensate flowing down the top of the column into jet flow. And the jet flow transferred mass and heat with the rising gas. This specific working mechanism resulted in effective gas/liquid contact and increased surface renewal frequency to achieve higher separating efficiency. In addition, the spinning band distillation had other advantages such as low HETP value (height equivalent theoretical plate), low liquid holdup, and low pressure drop. However, reports on the theoretical research of this device have not been available so far. So taking the lead in studying this apparatus would help us to know about this advanced technique.The hydrodynamics capabilities of spinning band column were simulated with software Fluent6.2. This study referred to the measurement of the RTD (residence time distribution), the distribution of the tracer concentration and the velocity field, and the formation of liquid film under different operating conditions. Moreover, the effects of the liquid's physical properties on the hydrodynamics capabilities of the spinning band column were analyzed, and all of the conclusions proved credible to their experimental counterparts.Single phase flow in the column under different operating conditions was simulated using realizable turbulent model. The results showed that the distribution of the tracer concentration was more homogenous with lower feed rate, and the residence time was longer and the velocity plot of the liquid was smoother with higher rotating speed. The mean residence time and the distribution of the tracer concentration accorded to the experimental data.Eulerian multiphase model was also applied to study gas-liquid flowing field. Increasing liquid phase feed rate, the tangential velocity, the liquid holdup and the pressure drop all increased, and the liquid film was more uniform. The tangential velocity, the liquid holdup and the pressure drop all increased and the liquid film became thicker as gas phase feed rate increased. However, the liquid was blown back when the gas velocity arrive a certain value. The simulation results were acceptable compared with the experiment.The influences of the surface tension and viscosity on the flowing field were studied by VOF model. The surface tension mainly affected the tangential velocity of liquid. And viscosity has more influence on the velocity field. The liquid of higher viscosity had lower tangential and axial velocity. Further more, the liquid assembled within the column which influenced the contact of gas and liquid. But the situation can be promoted by increasing rotating speeds.