Modeling the Relationship Between Power Density and Energy Recovery in Large – Scale Application of Salinity Gradient Energy Technologies

Most published research on salinity gradient energy (SGE) technologies has focused on the maximum power density extractable from pressure retarded osmosis (PRO) and reverse electrodialysis (RED). However, in addition to power density considerations, energy recovery is also an important driver of process economics. Recent theoretical work has shown that there are considerable differences in the energy recovery profiles for the two processes. While in RED most of the energy is recovered at lower extents of mixing, in PRO energy extraction progresses practically linearly with mixing. Here, we apply simplified thermodynamic and process models in order to gauge the scale-up of both processes. We observe how energy recovery and power density relate to large-scale operations, specifically with respect to the required membrane area (a proxy for capital expenditure). Variation in flow rates and concentrations, as well as membrane properties, impact the shape of the power density and energy recovery profiles, and thus, process optimization.