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

Abstract

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.

Graphene Oxide Incorporated Polysulfone Substrate for Flat Sheet Thin Film Nanocomposite Pressure Retarded Osmosis Membrane

“…With the addition of GO into the membrane substrates, the S values decline sharply with TFN-0.25GO exhibiting the smallest S value, 726 μm. Generally, membranes incorporating GO have high A values and have lower S values, which is due to the improved hydrophilicity and reduced ICP effect [ 3 ].…”

“…It was hypothesised that, when the applied pressure was increased, the flux decreased and the external concentration polarization (ECP) became less severe on the draw side of the membrane, resulting in the increase of salt crossover to the FS as the concentration of the DS against the membrane surface is higher. The salt crossover will also increase when membranes start to deform due to increased pressure [ 3 ]. Nevertheless, the J s /J w shows good stability for TFN-0.1GO and TFN-0.25GO, explaining how good performance could be maintained despite the increasing J s value.…”

“…It has been found that maximum W production is obtained when Δ P = Δ π/2 . W max can be obtained by [ 3 , 4 , 5 ]: W max = A (Δ π 2 /4) …”

The Need for Accurate Osmotic Pressure and Mass Transfer Resistances in Modeling Osmotically Driven Membrane Processes

“…Known theoretical expressions, i.e., Equations (13) and (15), for cases of kd→∞ and kf→∞, and the presented ones, Equations (16) and (17), were applied for prediction of the values of the structural parameter, S. These were conducted using the measured water flux data under the previously specified operating conditions. There has been no direct, acceptable measurement's method for the determination of the structural parameter until now.…”

“…Equations (13) and (15) define the value of the structural parameter as a function of more easily determinable intrinsic parameters. These include A and B as well as the water flux rate, Jw without external transfer resistances, and the diffusion coefficient in the bulk fluid phase, D. This procedure does not involve any external mass transport resistances.…”