Optimization of Pressure-Retarded Osmosis with Hollow-Fiber Membrane Modules by Numerical Simulation

We optimized the operating conditions for maximizing power production by pressure-retarded osmosis using seawater as the draw solution and river (pure) water as the feed solution using a simulation algorithm developed in our previous work combined with the Complex optimization method. The calculated results showed that the maximum power production was 104 W/module, i.e., 18.7 kW/m3, under the optimum conditions. The optimum hydraulic pressure applied to the draw solution was slightly higher than half the osmotic pressure difference between the draw solution and the feed solution, which was derived from the theoretical optimum pressure without concentration polarization and solute leakage. We also optimized the operating conditions of hypothetical modules that have improved membrane water permeability (2, 3, 4, and 5 times higher than the current membrane permeability coefficients). Although power production increased with an increase in water permeability, the relationship was not linear. The effects of internal and external polarization of the salt concentration and the solute permeability on the power production became significant with an increase in membrane permeability.