Simulation of Full-Scale Pressure Retarded Osmosis Processes

The pressure-retarded osmosis (PRO) concept can be used to generate power when solutions of different salinities are separated by a semi-permeable membrane. This work presents the development of a PRO process simulator for a bench scale and plant scale simulation. For bench scale simulation, this work takes into account the effect of internal concentration polarization (ICP), external concentration polarization (ECP) and reverse solute flux that occurs in the membrane. The bench scale model is simulated and the model is verified with experimental data. For plant scale simulation, membrane discretization (finite difference method) is employed to model concentration polarization (variation in concentration) along the membrane. This leads to the development of co and counter current process flow configurations within the simulator. For an accurate representation of a plant scale simulation, equation of state is used to determine physical properties resulting in the evaluation of accurate driving force across the membrane based on changing concentration and flowrates along the membrane. Rigorous equipment models for pumps, turbines and pressure exchangers were implemented by utilizing energy and entropy balances. The development of the simulator is done in a modular fashion such that any process configuration, may it be either single stage membrane, multi-stage membrane or a parallel configuration, can be simulated by manipulating the input files of the simulator. A Nelder-Mead based routine is adapted for the process simulator as an optimization tool. The optimizer can optimize single stage and multi-stage pressures to find the optimum power densities. All this has culminated into the development of a simulator for plant-scale PRO simulation which can reliably be used as a tool to evaluate the viability of membranes and processes