Application of directional freezing for seawater desalination: Parametric analysis using experimental and computational methods

Abstract

Directional freezing is valuable due to their capability to provide excellent relocation of impurities away from ice crystals and thus produce higher desalination efficiency. In this work, desalination of surrogate seawater using directional freezing in radial and vertical directions of a cylindrical crystallizer was assessed experimentally and numerically. Experiments on the effect of different brine concentration and freezing direction on the salinity at various spatial locations was conducted. Moreover, a transient computational fluid dynamics model of multispecies flow which allows for solidification and melting was developed in order to simulate the experimental set-up. Subsequently, a modified model was developed to investigate the role of stirring on the solutes distribution during the directional ice growth. The developed model showed good agreement with the experimental results. The model also showed a successful directional freezing by obtaining the anticipated salinity gradient due to salt diffusion away from the ice growth layer. Performance metrics such as effective partition coefficient, removal efficiency and energy consumption of the desalination process were evaluated. Results showed that better partition and removal efficiency were achieved under lower salinity brine, top freezing instead of bottom or radial freezing, and with stirred flow versus stagnant configurations. Freeze desalination (FD) consumed less energy as compared to multi-stage flash distillation (MSH), humidification-dehumidification (HDH). The FD consumed 11.34 kWh/m3 as compared to MSH and HDH which require 24.6kWh/m3 and 123kWh/m3, respectively. Although the energy consumed in FD (11.34 kWh/m3) was more that of reverse osmosis (RO) (8.2 kWh/m3), it was relatively close.