Abstract

In a pressure retarded osmosis (PRO) power plant, osmosis is used to generate electric power in a 2-channel system through a semipermeable membrane. Such system can be operated in the co- or in the counter-current mode, depending on relative flow direction of the fresh and the salt (draw) water along the membrane. In order to study and compare these two cases, models which describe the variations of the various quantities across the membrane are needed. The variations across the membrane have become relevant, particularly in transition from lab-scale PRO systems to real scale PRO systems. Based on a recently developed model, we simulate and optimize the co- and the counter-current case, compare the two cases and compare the results to other available examples from the literature. We optimize the power and the power per volume ratio with respect to both operational parameters such as applied pressures and with respect to geometric and membrane parameters. The results predict an advantage.

Key words: Pressure retarded osmosis (PRO), co and counter-current mode, semi-permeable membrane, mass flow rate, power density, specific energy.