Abstract: Nowadays, reverse osmosis (RO) seawater desalination has already become a type of the widest application of all the desalination technologies. A RO desalination device usually consumes much energy, since in working mode it needs to retain a RO membrane work pressure of about 6 MPa at the seawater side to produce fresh water continuously; and after RO processing, a large amount of pressure energy still remains in the concentrated brine. Therefore, adding a turbo energy recovery device – that takes advantage of the pressure energy left in the concentrated brine to drive the pump side and boosts feed-seawater pressure – can greatly reduce energy consumption. This study focuses on an analysis of such a device running in the RO seawater desalination plant on Sansha Island. First, we develop a numerical model for the 3D steady flows in the entire channel of both its pump side and turbine side, using a SST model to account for turbulence effect. Then, we simulate its channel flows under different operating conditions, and analyze the hydraulic performances and flow behaviors of its turbine and pump sides based on numerical simulations. The results show that the calculated overall energy conversion efficiencies of this device agree well with measurements; under the present optimal operating condition, the hydraulic efficiency of its turbine or pump side has a large room for improvement. The turbine side features with a relatively wider range of high-efficiency operation. Under partial operating conditions, both the turbine and pump sides show a reduction in hydraulic efficiency and more complicated internal flow patterns.

Key words: energy recovery device, hydraulic performance, hydro-turbine, pump, CFD