Energy recovery considerations in brackish water desalination

In brackish water reverse osmosis (RO) desalination, the low total dissolved solids (TDS) in the feed water and relatively low brine flow make the use of energy recovery devices (ERDs) ambiguous. The decision to implement energy recovery devices must always be based on the life cycle cost estimation of the plant.

This article discusses the design considerations concerning energy recovery device selection and field experience in the Lahat brackish water desalination plant (40 000 m3/day) in Israel.

Two types of energy recovery device are generally considered in brackish water RO desalination: turbocharger and isobaric energy recovery devices. Taking into consideration the simplicity of the turbocharger, it was selected for the first phase of the Lahat brackish water desalination plant with a design recovery range of 80–88%.

The turbocharger was designed for maximum recovery, and an external bypass line was added to operate the plant at low recoveries. For such a wide recovery range, an overall turbocharger efficiency range of 30–40% was achieved.

However, the turbocharger is unable to operate efficiently over a broad recovery range. Thus, given the life cycle cost benefits of the isobaric energy recovery device, the latter was selected for the second phase of the Lahat brackish water desalination plant.

Desalination, Volume 339, 15 April 2014, Pages 34–39.