CFD study of distillation sieve tray flow regimes using the droplet size distribution technique

A good understanding on the characteristics of sieve tray flow regimes is one of the keys to achieve an efficient distillation operation. A 3-D computational fluid dynamics (CFD) model based on the volume-of-fluid (VOF) and the large eddy simulation (LES) has been developed to simulate the complex flow phenomena in a sieve tray. The analysis of droplet size distribution (DSD), which was made possible by the use of VOF model, was then carried out to characterize the prevailing flow regime. The obtained results are in good agreement with the experimental data available in the literature in terms of the prediction of clear liquid height. The results obtained from the DSD analysis reveal that the sphere equivalent droplet diameter, ddrop,eq, is inversely proportional to the gas superficial velocity, and is directly proportional to the liquid volumetric flow rate, QLo. Approaching the froth-to-spray transition regime, ddrop,eq was found to range from 0.008 m to 0.0114 m. These findings may serve as valuable information in assisting tray designers and process engineers to decide on ranges of operating conditions which allows the attainment of high efficiency distillation operation, and also providing some insights into future development of sieve tray technology.