Development and fluid fluctuation analysis of a novel valve-controlled energy recovery device for small-scale reverse osmosis desalination systems

Energy recovery devices (ERD) are vital for improving the energy efficiency of reverse osmosis (RO). Nevertheless, small-scale seawater RO systems are rarely equipped with ERDs, mainly because of the associated high capital and maintenance costs. Herein, we propose a new type of reciprocating switcher (RS)-ERD with dual selfboost hydraulic cylinders that can pre-pressurize the low-pressure hydraulic cylinder during stroke switching. The structure and working process of the pre-pressurization reciprocating switcher (PPRS)-ERD are presented, and mathematical models of the entire system are established. Based on these models, a detailed performance analysis is performed. Compared to the conventional RS-ERD, both the high pressure (HP) check valve cores and hydraulic cylinders move smoothly, which suggests that the vibrations of the check valves and cylinders can be neglected. The maximum pressure fluctuation amplitudes of HP seawater (HPS) at the outlet and HP brine (HPB) at the inlet are 0.015 MPa and 0.016 MPa, which represent decreases of 98.91 % and 98.87 %, respectively. The flow fluctuation amplitudes of HPS and HPB do not exceed 0.17 m3/h and 0.07 m3/h, which represent improvements of 95.34 % and 96.59 %, respectively.