Evaluation of osmotic energy extraction via FEM modeling and exploration of PRO operational parameter space

Power generation via pressure retarded osmosis (PRO) was explored based on a detailed two dimensional finite-element (2-D-FEM) PRO model. Using the numerical model, an approach is presented for determining the draw and feed crossflow velocities for maximizing peak power generation. The dependence of PRO power generation on channel dimensions, membrane transport parameters were then evaluated, followed by assessing the impact of frictional pressure losses and pumping and energy recovery device (ERD) efficiencies. Illustrative test cases are presented for three different draw/feed streams representing seawater/brackish water (SW/BW), seawater RO-brine/brackish water (SWB/BW), and Dead Sea water/Seawater RO-brine (DSW/SWB). The maximum peak power density attainable via PRO was for DSW/SWB (35.3 W/m2), followed by SWB/BW (7.29 W/m2) and SW/BW (3.53 W/m2) for the case of ideal pumps and ERD. For the optimistic Power generation from DSW/SWB PRO, high efficiency pumps (98%) and ERD (96%) would be required for peak power density to approach ~ 12 W/m2 and 1.6 W/m2 for the cases of DSW/SWB and SWB/BW, respectively, while net positive power generation is not expected for SW/BW. Higher permeability membranes could provide somewhat increased PRO performance; however, frictional pressure loses and less than ideal pumps and ERDs present a barrier for PRO as a viable approach for energy generation.