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2013|14 Annual Report Fraunhofer IGB

121 Dr. Thomas Schiestel Phone +49 711 970-4164 thomas.schiestel@igb.fraunhofer.de References [1] Loeb, S. J. (1998) Energy production at the Dead Sea by pressure-retarded osmosis: challenge or chimera?, Desalination 120: 247 – ​262 [2] Touati, K.; Schiestel, T. (2013) Evaluation of the potential of osmotic energy as renewable energy source in realistic condi- tions, Energy Procedia 42: 261 – ​269 Funding We would like to thank the European Union for funding the project H2OCEAN within the scope of the Seventh Framework Research Programme (FP7 / 2007 – 2013), grant agreement no. 288145. Project partner Prof. Fernando Tadeo, University of Valladolid, Valladolid, Spain Further information www.h2ocean-project.eu Increased power density The membranes developed at the IGB have a special open-po- rous carrier structure with a thin separating layer. The power densities are therefore substantially higher. Besides the mem- brane structure, process parameters also play a decisive role in the overall performance of the process. Increased flow veloci- ties (Fig. 3) reduce the external concentration polarization at the membrane boundary and result in higher power densities. With realistic flow velocities for technical PRO processes, we currently achieve power densities of 3 W / ​m2 . Tests also show the strong influence of the temperature. With a rise in tem- perature, the power density increases significantly (Fig. 4). The reason for this is the temperature dependence of the diffusion coefficient, which rises with the increase in temperature. As a result, more water can be transported through the membrane at higher temperatures. Outlook An economically viable implementation of osmotic power sta- tions assumes a power density of approx. 5 W / ​m2 . We can achieve this objective in the near future by further developing the material and structure of the membrane as well as opti- mizing the process parameters. The principle is also ideally suited for energy recovery from the retentate of seawater desalination plants or using (warm) sa- line process wastewater from the chemical industry. 1 Measuring cell to determine the performance of the membranes. 2 During the filtration process a boundary layer forms on the membrane which results in a concentration difference, the concentration polarization. 3 Comparison of the power density at different flow velocities and ambient temperatures. 4 Comparison of the power density at different tem- peratures and a flow velocity of 0.017 m / ​s. 3 4 feed: VE water draw solution: 0.55 M NaCl Contact powerdensity[W / ​m2 ] counter pressure [bar] 3 2 1 0 2 4 6 80 10 5 4 6 IGB membrane @ 25°C IGB membrane @ 60°C IGB membrane @ 40°C feed: 8.6 mM NaCl draw solution: 1 M NaCl powerdensity[W / ​m2 ] counter pressure [bar] 3 2 1 0 2 4 86 10 100 14 5 4 6 IGB membrane @ 0.008 m / ​s IGB membrane @ 0.017 m / ​s IGB membrane @ 0.050 m / ​sIGB membrane @ 0.033 m / ​s

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