Achieving sustainable operation for hypersaline membrane distillation applications: A novel strategy based on the critical Reynolds number

Membrane distillation is emerging as a promising alternative in zero liquid discharge and brine mining. However, the MD operation with hypersaline solutions is often interrupted by severe scaling formation on the membrane surface. This study aimed to establish a thermodynamic framework to achieve sustainable MD performance in hypersaline processing, enabling the prediction of an operational threshold, above which membrane scaling would not occur. With sodium chloride as the model solute, 2-dimensional temperature and concentration profiles were obtained in CFD to calculate the distribution of supersaturation ratio S in the DCMD flow channel. Through a comprehensive investigation on the effects of temperature and flow dynamics, a preliminary and conservative hydrodynamic threshold represented by a critical Reynolds number Re* at S = 1 was identified, below which scaling formation was inevitable. The relationship between Re* and dimensionless membrane flux (JM/rho vF1) collapsed into one decreasing line, resulting in a semi-empirical correlation and indicating that the operational window can be widened at an elevated feed temperature. Another empirical correlation of Re* was derived based on temperature inputs, providing fast and simple approaches to predict scaling-free operation zone. The hydrodynamic criterion proposed are essential towards establishing the general guideline for achieving sustainable operation in MD hypersaline processing.

Automated summary

Membrane distillation (MD) is a promising alternative for zero liquid discharge and brine mining, but scaling formation on the membrane surface with hypersaline solutions can interrupt operations. This study aimed to establish a thermodynamic framework to predict an operational threshold for sustainable MD performance in hypersaline processing, identifying a critical Reynolds number below which scaling formation is inevitable. Various correlations and empirical approaches were derived to widen the operational window and predict scaling-free operation, essential for sustainable operation in MD hypersaline processing.