CCD series no-19: The lowest energy prospects for SWRO through single-element modules under plug-flow and closed-circuit desalination conditions

Abstract

The future targets of the SWRO desalination industry to reduce significantly energy consumption are realized already today by the newly emerging closed-circuit desalination (CCD) technology with demonstrated energy consumption of 2.12 kWh/m³ for Mediterranean water (4.0%) and 1.72 kWh/m³ for ocean (3.5%) water without the need for energy recovery with energy saving greater than 35%. The fundamental differences between CCD and the conventional plug flow desalination (PFD) techniques are evaluated in the present study by rigorous theoretical model simulations of CCD compared with multi-stage PFD of the same single-element modules under the same conditions in the flux range of 13.0–0.1 lmh. The results of this study reveal that CCD under fixed flow and variable pressure conditions behaves as near-perfect multi-stage PFD with energy dependence on recovery also manifesting increased frequency of CCD cycles and residence time. The origin of energy savings by CCD and multi-stage PFD compared with conventional single-pass through multi-element module is revealed and explained. While multi-stage SWRO designs are economically prohibited by high fabrication costs, CCD designs are simple and inexpensive and should play a major role in future design of SWRO desalination plants of low energy consumption and high energy conversion efficiency without the need of ERD.

Keywords:

• Seawater desalination energy
• Low-energy SWRO desalination
• Closed-circuit desalination (CCD)
• SWRO-CCD of low energy
• Entropy efficiency of SWRO desalination
• Entropy efficiency of SWRO-CCD

Acknowledgments

Funds to Desalitech Ltd. by AQUAGRO FUND L.P. (Israel) and by Liberation Capital LLC (USA) and Spring Creek Investments (USA) are gratefully acknowledged.