Development and operational stability evaluation of new three-cylinder energy recovery device for SWRO desalination system

The energy recovery device (ERD) plays an important role in reducing energy consumption of seawater reverse osmosis (SWRO) system. However, for reciprocating-switcher energy recovery device (RS-ERD), stroke switching will cause flowrate and pressure pulsations of high and low pressure fluids, which will affect the operation stability of SWRO system. In this paper, we develop a three-cylinder energy recovery device (TC-ERD) and a matching control strategy with instantaneous overlap function to simultaneously reduce the flowrate and pressure pulsations of high and low pressure fluids. Under design capacity (30 m(3)/h) and 5.0 MPa operating pressure, the pressure pulsation amplitude of HP brine is only 0.0675 MPa, which is 86.5% lower than that of RSERD. The flowrate pulsation amplitude (0.954 m(3)/h) of LP seawater decreases by 68.2% compared with RS-ERD, while that (1.336 m(3)/h) of HP brine is approximately doubled. The doubling of HP brine flowrate pulsation arises from the fact that the actual operating point of the boost pump is much lower than its rated operating point, which can be improved by optimizing pump selection in future work. The energy recovery efficiency of the TC-ERD is as high as 97.1% at design capacity and 5.0 MPa operating pressure.