Energy recovery consideration in brackish water desalination

Abstract

In brackish water RO desalination, the low feed water TDS and relatively low brine flow make the use of energy recovery devices ambiguous. The decision to implement energy recovery device must always be based on the Life Cycle Cost estimation of the plant. Design considerations concerning the energy recovery device selection and field experience in Lahat brackish water desalination plant (40,000m3/day) are presented in this article.Two types of energy recovery device are generally considered in the brackish water RO desalination, turbocharger and isobaric energy recovery devices. Taking into consideration the simplicity of the turbocharger, it was selected for the 1st phase of the Lahat brackish water desalination plant with the design recovery range of 80%–88%. The turbocharger was designed for max recovery and external bypass line was added to operate the plant at low recoveries. For such wide recovery range the turbocharger entire efficiency range of 30%–40% was achieved.Due to the limitation of the turbocharger to operate efficiently at the broad recovery range and Life Cycle Cost benefits of isobaric energy recovery device, the isobaric energy recovery device was selected for the 2nd phase of the Lahat brackish water desalination plant.