Membrane scaling in Vacuum Membrane Distillation - Part 2: Crystallization kinetics and process performance

In order to advance the applicability of Membrane Distillation for the treatment of salt solutions near saturation, this paper investigates scaling phenomena in flat sheet Vacuum Membrane Distillation channels. Membrane scaling plays a crucial role in Membrane Distillation, since it can impact the product quantity as well as its quality and the membrane integrity. Scaling kinetics and the interaction of scale formation with the process were experimentally investigated under process conditions typical for Vacuum Membrane Distillation. We directly observed scales forming on the membrane with light microscopy extended by Digitally Simulated Dark Field Illumination. This allowed us to automatically evaluate the images and quantitatively track the crystal growth process. The results show the influence of process conditions on the kinetics of scale formation and the resulting feedback on the process performance. Thus, the findings support the design process of Vacuum Membrane Distillation plants and can be used to control the range of operation to avoid critical conditions.