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Har Adar, Israel

Pressure retarded osmosis (PRO) for hydroelectric power generation from worldwide widespread salinity gradient sources is of growing interest for large-scale clean energy generation. This approach requires membranes of specific characteristic and the evaluation of peak power density of such membranes at present time proceeds by extrapolation from theoretical curves with limited experimental data support mostly in a region far removed from the actual applied pressure of peak power generation. This study describes the use of actual/ideal flux ratio term (β) derived from PRO flux measurement at zero applied pressure (forward osmosis flux conditions) in a distinct salinity gradient for a defined membrane of known permeability coefficient (A) for the flux and power density projections of said membrane. The β-A approach for PRO flux, power density, and peak power projections is illustrated in the context of some recently reported theoretical and experimental results of several advanced Thin Film Composite-PRO membranes. © 2015 Balaban Desalination Publications. All rights reserved.

The present status and future prospects of pressure related osmosis (PRO) for hydroelectric power generation from the most widespread salinity gradients of seawater and river water systems (SW–RW) are analyzed by a theoretical model in terms of the membrane, module, and method. The selected membrane in the model analysis comprises MP # 1 of the highest presently known permeability coefficient (5.81 Lmh/bar) with a projected peak power density of 10 W/m2 at 13 bar. The performance of the referred MP # 1 membrane was ascertained in the context of the closed circuit PRO (CC-PRO) and conventional PRO methods at different HSF (high salinity feed or “draw” solution) to permeate flow ratio (δ), and percent permeate (α) in HSDF (high salinity diluted feed or diluted “draw” solution) with emphasis of the membrane power density (PD) and the net electric power density (NEPD) which takes into account the fraction of power consumed by the auxiliary pumps. The theoretical CC-PRO simulation of a typical SW–RW salinity gradient using MP # 1 with actual/ideal flux ratio (β) of 0.374 shows maximum membrane PD as function of flow ratio (δ) and hydraulic pressure difference in the declined order of 10.00 W/m2 at 13 bar (δ > 40); 8.52 W/m2 at 12 bar (δ = 5.0); 7.45 W/m2 at 11 bar (δ = 2.5); 6.13 W/m2 at 10 bar (δ = 1.25); 5.69 W/m2 at 10 bar (δ = 1.00); and 5.16 W/m2 at 9 bar (δ = 0.75). The simulated NEPD availability of this system reveals the declined order of 4.2 W/m2 at 13 bar (δ = 2.5) 4.1 W/m2 at 12 bar (δ = 1.25); 3.9 W/m2 at 11 bar (δ = 1.00); and 3.6 W/m2 at 10 bar (δ = 0.75). Compared with the CC-PRO technology of near absolute energy conversion efficiency, the PD and NEPD of the conventional PRO technique with MP # 1 show lower values since they depend on the efficiency of the energy recovery device. A further decline of PD and NEPD availability also takes place for membrane having A < 5.81 Lmh/bar and/or β < 0.374, suggesting the low feasibility of the SW–RW gradient systems for economic PRO hydroelectric power generation in the near future. © 2015 Balaban Desalination Publications. All rights reserved.

This study explores the prospects for clean energy generation in coastal regions from salinity gradient made of seawater (SW) and its concentrates (SWC) by the CC-PRO technology of near absolute energy efficiency without energy recovery device and semi-permeable membranes such as HTI-TFC (A = 2.49 lmh/bar, B = 0.39 lmh, and S = 564 μm) of 48.3 bar maximum applied pressure and alike. This power generation process is fueled by SW as low salinity feed and SWC as high salinity feed (HSF) and the regeneration of HSF from the produced high salinity diluted feed achieved through evaporation ponds of the types extensively used by the sea salt manufacturing industry. Large-scale harvesting of clean energy from the sea could be found particularly attractive along coastlines of arid zones where climate conditions (e.g. solar radiation, temperature, wind, humidity, etc.) favor effective evaporation from reservoirs of SWC. The simulated CC-PRO process of the SW (4.2%)–SWC (25%) salinity gradient with the HTI-TFC membrane revealed maximum membrane power density of 55.6 W/m2 and net electric power density after accounting for the auxiliary pumps of 39.3 W/m2 at the hydraulic pressure difference of 48.3 bar under draw/permeation flow ratio of 5.0 and membrane actual/ideal flux ratio of 0.2 estimated from available forward osmosis data of the same membrane in the 1.0–3.0 NaCl salinity gradients range. HTI-TFC membrane surface area of 1,000 m2 should provide 943 kWh electric energy per day enough to desalinate 377 m3/d of SW (4.2%) with 50% recovery by means of the closed circuit desalination (CCD) technology (RO: 2.5 kWh/m3). The results of this study reveal that the CC-PRO technology opens the door for large-scale commercial clean power generation from SW–SWC salinity gradients already with existing PRO membranes and improved economic feasibility when PRO membrane of higher actual/ideal flux ratio and burst pressure shall become available in the near future. © 2015 Balaban Desalination Publications. All rights reserved.

Abstract: The Red Sea (RS) to Dead Sea (DS) water transfer project in Jordan under the sponsorship of the World Bank is intended to stop the sea-level decline of the DS as well as for the desalination of RS water and for hydroelectric power generation. Red Sea Brine (RSB ~7.13%) disposal to the DS (~34%) creates a salinity gradient of interest for PRO hydroelectric power generation and the prospects of such an application are explored in the present study with the most advanced existing tools including a new Closed Circuit PRO technology (CC-PRO) of near absolute energy efficiency without need of ERD and a recent PRO membrane (HTI-TFC) of the highest reported strength to withstand applied pressure up to 48.3 bar. Power generation prospects from RSB–DS using CC-PRO with HTI-TFC are assessed in the actual/ideal flux ratio (β) range 0.123–0.400 and High Salinity Feed (DS as draw solution) to permeation flow ratio (δ) range 1–25. The minimum β = 0.123 for said process is established from available PRO experimental data with HTI-TFC for 0.6–3.0 M NaCl salinity gradients accounting for the presence of considerable concentrations of divalent cations such as Ca and Mg in DS water. The Net Electric Power (NEP) generation prospects from the RSB–DS Jordanian project using CC-PRO and HTI-TFC are assessed on the basis of 120 Mm3/year RSB availability for mixing with DS water. The results of this study accounting for the pressure limitation of HTI-TFC reveal NEP generation prospects of 7,753 kW under the conditions of δ = 1.0 and β = 0.123-0.200 from the RSB–DS gradient, or a supplement of 56.6% more power on top of the conventional hydroelectric power generation facility of the project (~13,698 kW). If the HTI-TFC membrane, or alike, could be made to operate at maximum PRO pressures of 60 and 86 bar, the CC-PRO NEP availability from RSB–DS is expected to rise to 9,767 kW (71.3%) and 13,219 kW (96.5%), respectively, with added power to the project indicated in parenthesis. In simple terms, the current state of the art revealed in this study suggest the immediate availability of the CC-PRO technology with HTI-TFC membranes for economical NEP generation from the RSB–DS gradient in the context of the Jordanian project with future improvements of membranes to withstand higher applied pressures expected to improve the economic feasibility. © 2014 Balaban Desalination Publications. All rights reserved.

Power generation from salinity gradients by means of Pressure Retarded Osmosis (PRO) is currently preformed by conventional methods, wherein Energy Recovery (ER) is an essential feature without which such a process is impossible. The newly conceived Closed Circuit (CC) Pressure Retarded Osmosis technology (CC-PRO) described herein is based on a continuous consecutive sequential batch process; wherein, pressurized high salinity feed (HSF) is continuously supplied to the inlets of PRO modules and pressurized effluent removed from their outlets through internal circulation means by the alternating engagement/disengagement of two side conduits (SC). This process proceeds with high energy conservation without need of ER means. The new CC-PRO technology enables high operational flexibility achieved by set point selection of the permeation flux; the circulation flow; the applied pressure of power generation; and the flow ratio circulation/permeation which defines the salinity and osmotic pressure gradients inside the PRO modules. The high flexibility is manifested by the availability of an infinite number of set point combinations for the optimization of the process with respect to maximum power production under lower membrane detrimental effects and reduced fouling factors. © 2013 © 2013 Balaban Desalination Publications.

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