We optimized the operating conditions for maximizing power production by the pressure-retarded osmosis (PRO) process 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/m 3 , 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 the power production increased with increasing 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 increasing membrane permeability.
In this study, we developed a novel forward osmosis (FO) simulation method for a multicomponent system (water, NaCl, and thermoresponsive ethylene oxide−propylene oxide-based copolymer draw solute) targeted for direct seawater desalination using a hollow fiber (HF) membrane module. Box complex method was applied to numerically solve the FO simulation model of a three-component system. A good agreement between experimental and simulation results obtained in various operation conditions allowed us to estimate not only the effect of NaCl and draw solution (DS) concentration on the resulting water permeate flow rate but also the osmotic pressure inside and outside of the HF membranes. From the analysis, the HF modules were designed to decrease the dilution of the draw solution (DS) inside the module due to water permeation. We validated the suggestion by simulation of the increase of the water permeation rate in the modified HF modules, which were designed for the smooth flow of the DS to decrease the DS dilution. The simulation was further verified by reasonable results indicating that the decrease of NaCl concentration in the feed water is also effective in increasing the water permeation rate in the current HF module.
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