The potential for power production from salinity gradients by pressure retarded osmosis

Thorsen, T.; Holt, Torleif

doi:10.1016/j.memsci.2009.03.003

Cited by 351 publications

(234 citation statements)

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“…Studies of the power production possible with PRO systems have often been based on the zero-dimensional approximation model [1][2][3][4][5][6][7][8][9][10]. Under that model, the power produced by the system, comprised of an exchanger, a pump, and a turbine, is linearly proportional to the membrane area.…”

Section: Introductionmentioning

confidence: 99%

Limits of power production due to finite membrane area in pressure retarded osmosis

Banchik

Sharqawy

Lienhard

2014

Journal of Membrane Science

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Dimensionless analytical expressions for the power attainable from an ideal counterflow pressure retarded osmosis (PRO) system model are developed using a one-dimensional model that accounts for streamwise variations in concentration. This ideal PRO system has no salt permeation or concentration polarization. The expressions show that the optimal hydraulic pressure difference, for which the maximum power is produced, deviates significantly from the classical solution of one-half of the trans-membrane osmotic pressure difference, Δπ/2, as the dimensionless membrane area (MTU π ) increases and the ratio of draw to feed mass flow rates (MR) varies. The overall maximum power attainable from a PRO membrane is found to occur in the limit of infinitely large MTU π (an effectiveness of unity) and infinite MR. For an ideal PRO system which mixes seawater (35 g/kg) and river water (1.5 g/kg), the overall maximum power of 1.57 kJ per kilogram of feed can be attained at roughly MTU π of 15, an MR of 10, and a pressure of 0.83Δ . Due to economic considerations, a PRO system in practice will have limited membrane area and will operate at an effectiveness of less than unity.The present work can be used to estimate the operating conditions and area required for a PRO system of given performance. The effect of concentration polarization on optimal hydraulic pressure difference and maximum power performance is also investigated using a numerical model.

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Section: Introductionmentioning

confidence: 99%

Limits of power production due to finite membrane area in pressure retarded osmosis

Banchik

Sharqawy

Lienhard

2014

Journal of Membrane Science

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“…If the number of cells connected is large enough, the total voltage will be larger than the electrode reaction potential, and energy can be extracted. Although considerable advances have been produced in both techniques [8,9,10,11,12,13], they are mostly at the laboratory scale. In addition, they present clear drawbacks which must be dealt with, concerning mainly membrane selectivity, fouling and cost, and the necessity of using additional converters such as turbines for effectively producing electricity.…”

Section: Introductionmentioning

confidence: 99%

Predictions of the maximum energy extracted from salinity exchange inside porous electrodes

Jiménez

Fernández

Ahualli

et al. 2013

Journal of Colloid and Interface Science

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Capacitive energy extraction based on double layer expansion (CDLE) is the name of a new method devised for extracting energy from the exchange of fresh and salty water in porous electrodes. It is based on the change of the capacitance of electrical double layers (EDLs) at the electrode/solution interface when the concentration of the bulk electrolyte solution is modified. The use of porous electrodes provides huge amounts of surface area, but given the typically small pore size, the curvature of the interface and EDL overlap should affect the final result. This is the first aspect dealt with in this contribution: we envisage the electrode as a swarm of spherical particles, and from the knowledge of their EDL structure, we evaluate the stored charge, the differential capacitance and the extracted energy per CDLE cycle. In all cases, different pore radii and particle sizes and possible EDL overlap are taken into account. The second aspect is the consideration of finite ion size instead of the usual point-like ion model: given the size of the pores and the relatively high potentials that can be applied to the electrode, excluded volume effects can have a significant role. We find an extremely strong effect: the double layer capacitance is maximum for a certain value of the surface potential. This is a consequence of the limited ionic concentration at the particle-solution interface imposed by the finite size of ions, and leads to the presence of two potential ranges: for low electric potentials the capacitance increases with the ionic strength, while for large potentials we find the opposite trend. The consequences of these facts on the possibility of net energy extraction from porous electrodes, upon changing the solution in contact with them, are evaluated.

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“…If the number of cells connected is large enough, the total voltage will be larger than the electrode reaction potential, and energy can be extracted. Although considerable advances have been produced in both techniques, [4][5][6][7]9,15 they are mostly at the laboratory scale. However, a recent analysis has shown that, at least for the river and sea water availabilities in the Dutch coast, a 1 MW RED plant could be competitive in the near future.…”

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confidence: 99%

Polyelectrolyte-coated carbons used in the generation of blue energy from salinity differences

Ahualli

Jiménez

Fernández

et al. 2014

Phys. Chem. Chem. Phys.

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In this work we present a method for the production of clean, renewable electrical energy from the exchange of solutions with different salinities. Activated carbon films are coated with negatively or positively charged polyelectrolytes by well-established adsorption methods. When two oppositely charged coated films are placed in contact with an ionic solution, the potential difference between them will be equal to the difference between their Donnan potentials, and hence, energy can be extracted by building an electrochemical cell with such electrodes. A model is elaborated on the operation of the cell, based on the electrokinetic theory of soft particles. All the features of the model are experimentally reproduced, although a small quantitative difference concerning the maximum opencircuit voltage is found, suggesting that the coating is the key point to improve the efficiency. In the used experimental conditions, we obtain a power of 12.1 mW/m 2 . Overall, the method proves to be a fruitful and simple approach to salinity-gradient energy production.Obtaining energy from salinity differences as those existing in river mouths 1,2 is a challenging task involving various complications. Although several attempts have been reported, 3-10 no one appears to prevail over the others, and a final choice has not been made. This applies as well to the recent proposals of the capmix group, 11 based on the change in the capacitance of the electrical double layer (EDL) at the interface between a conducting electrode and an ionic solution, when the salinity of the latter is modified.The capmix methods are not the only ones devised to harvest salinity difference energy. Desalination techniques operated in reverse are good candidates, in particular, pressureretarded osmosis (PRO), 8,12,13 and reverse electrodyalisis (RED). 3,14 In the former, fresh water is allowed to flow through a semipermeable membrane into a pressurized sea a Department of Applied Physics, School of Sciences, University of Granada, 18071, Granada, Spain. b Dipartimento di Scienze della Salute, Universit degli Studi di MilanoBicocca, Via Cadore 48, Monza (MB) 20900, Italy. * Corresponding author, E-mail: sahualli@ugr.es water chamber; this high-pressure solution is used to obtain electrical energy by depressurizing it through a turbine. In RED, concentrated salt solutions and fresh water flow through alternating cells which are separated by ion exchange membranes; the cells will be alternatively enriched in cations and anions, thus producing, respectively, negative and positive potentials at the corresponding electrodes. If the number of cells connected is large enough, the total voltage will be larger than the electrode reaction potential, and energy can be extracted. Although considerable advances have been produced in both techniques, [4][5][6][7]9,15 they are mostly at the laboratory scale. However, a recent analysis has shown that, at least for the river and sea water availabilities in the Dutch coast, a 1 MW RED plant could be competitive in the near f...

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The potential for power production from salinity gradients by pressure retarded osmosis

Cited by 351 publications

References 10 publications

Limits of power production due to finite membrane area in pressure retarded osmosis

Limits of power production due to finite membrane area in pressure retarded osmosis

Predictions of the maximum energy extracted from salinity exchange inside porous electrodes

Polyelectrolyte-coated carbons used in the generation of blue energy from salinity differences

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