Reverse Electrodialysis for Sustainable Electricity Production by Coupling Thermal and Salinity Gradients

Reverse Electrodialysis for Sustainable Electricity Production by Coupling Thermal and Salinity Gradients

Rahul Patil¹, Jiuqing Liu² and Glenn Lipscomb¹

1 Department of Chemical and Environmental Engineering, University of Toledo, Toledo, Ohio, USA,43606, rahul.patil2@utoledo.edu

2 College of Metallurgical Science and Engineering, Central South University, Changsha, Hunan 410083, China, jiuqing_liu@163.com

The constantly growing world population leads to increased energy demand and is stretching available energy supplies. Consequently, new energy sources must be identified and developed. Economic, environmental, and social impact must be considered when evaluating alternative energy sources. An ideal source would be locally distributed and renewable with minimal economic and environmental impact on our current lifestyle.

Sun is the source of most energy consumed by civilizations in the form of fossil fuels, wind energy, photovoltaic or thermal solar, and hydroelectric. Significant interest exists in using the salinity difference between fresh water and sea water to produce power from mixing the two streams. Membrane processes such as Reverse Electrodialysis (RED) and Pressure Retarded Osmosis (PRO) can be used to produce electricity using salinity gradients [1, 2].

The Nernst equation indicates that a temperature gradient between the salt solutions will increase the driving force for ion exchange in RED and also increase the conductance of the salt solutions. We have investigated the effect of superimposition of temperature and concentration gradients on RED performance. For a temperature difference of 15 ^oC, the power increases by 20%.  The effects of varying temperature and concentration differences are reported.

We also report a theoretical and experimental study of spacer design on performance. The computational fluid dynamics package COMSOL was used to evaluate flow distribution within the RED flow channels for a standard spacer and designs that improve flow uniformity. The modified designs are evaluated experimentally to determine the actual effect on performance. The results indicate that improvements in flow distribution can improve overall RED performance.

Keywords: Reverse Electrodialysis, renewable energy, energy sustainability, salinity gradient energy, temperature gradient, electricity, computational fluid dynamics, spacer design

 

References:

1. Post, J. et al., Salinity-gradient power: Evaluation of pressure-retarded osmosis and reverse electrodialysis, Journal of Membrane Science 288 (2007) 218–230.

 

1. Dlugolecki, P. et al., Practical Potential of Reverse Electrodialysis as Process for Sustainable Energy Generation, Environmental Science and Technology 43 (2009) 6888–6894.