Thermodynamic Analysis of a Reverse Osmosis Desalination Unit with Energy Recovery System

A thermodynamic study is performed on a Reverse Osmosis (RO) desalination unit with and without energy recovery device. Such a study is based on the application of mass and energy balances on each subsystem as well as on the whole unit and using the properties of saltwater modelled as ideal solution. Three configurations of the desalination unit are considered. The first configuration includes a throttling valve in the rejection of concentrated brine side while the two others incorporate a hydraulic turbine and a pressure exchanger system (PES) respectively. The results show the variation of several performance indicators with several variables such as the feed salinity and temperature and the applied pressure. Examples of these indicators are the specific energy consumption (expressed in kWh/m3 of fresh water produced) and the recovery ratio. The results show the importance of incorporating an energy recovery device when the feed salinity is high. Besides, a theoretical minimum specific energy consumption was obtained and presented for the cases with and without pressure exchanger system.