Experimental and numerical study of zero-gravity distillation units with infinite and finite reflux

Abstract

Zero-gravity distillation (ZGD) is a small-scale distillation process, which offers high separation efficiencies and can be used as a part of modular production plants. Instead of gravity, capillary forces are utilized to realise the fluid flow. In this study, two experimental ZGD setups with different dimensions and materials were built. Furthermore, a modified ZGD unit with dual side heating and cooling was developed. Experiments were carried out with ethanol/water mixtures, both in the infinite reflux mode and with feed and product streams, while the temperature and concentration profiles were recorded under varied feed concentrations and volumetric flow rates. The experimental data was used to validate the process model comprising coupled momentum, heat and mass transfer equations for the liquid and vapour phases as well as heat conduction equations for the unit walls. The fluid dynamics was described using the hydrodynamic analogy concept. A good agreement between simulated and measured ethanol concentrations and temperatures was found. With the validated model, sensitivity studies on the influence of the feed flow rate and the metal foam porosity on the ZGD process were performed. It was found that the separation efficiency decreases with increasing flow rate and increases with lower porosity.