Studies On Characteristics And Application Of Energy Recovery Device For Seawater Reverse Osmosis Desalination System

Energy recovery device （ERDs） is one of the key parts of RO desalting system,which could transfer the pressure from the retentate brine to the raw seawater, andthefore reduce the energy consumption of product. Due to its high operating flexibility,high handing capacity and efficiency, ERDs of positive-displacement （PD） type isnow more and more applied. In this work, the focus is just put on PD type of ERDs,and the investigation is conducted in the following aspects: the fundamental displineof fluid switcher, experiment on single ERDs, hydraulic simulation system based onMatlab-Simulink and specific energy comupstion （SEC） of RO couped with ERDs.By finite elment method, the solid model of switcher was develped and thedeformation of switcher was obtained by applying pressure data of fluid channal tothe relevant solid surface. The results indicate that, the maximum deformation oftwo-position fluid switcher and four-position fluid switcher are0.0045mm and0.0052mm, respectively. In addition, the leakage rates of two-position fluid switcherand four-position fluid switcher are obtained by CFD method.Based on the new developed fluid switcher, the pilot scale of ERDs system wasestablished, and its performance of startup, running and close down were careffulystudied. The experimental conditions were: high pressure retentae brine flow rate of25m³/h,30m³/h and its pressure range of4.0MPa⁶.0MPa. The results show that, theERDs could conduct the pressurizing and depressurizing process in regular, withsmall flow rate and pressure fluctualtion, making it able to couple with the ROsystem.The hydraulic simulation system was developed by Matlab-Simulink, and thesimulation results show that，the hydraulic simulation system could provide therelevant variation curves of pump and each flow, which could be used as guidance tothe optimization of ERDs. By orthogonal design, the effects of revelant parameters onthe pressure fuluctualtion of pressurized seawater were studied, in specific, thedescending order is: check valve-openning pressure> cylinder-piston area> fluidswitcher-phase changing rate> cylinder-length.In this work, the SEC analyses of single-stage and two-stage RO desalting processwere conducted. The results show that, in the absence of ERDs, whetherY1is operating at its global optimized value, SECtwo stagenormis always more energy efficientthan SECsingle stagenormfor givenYt. While, in the presence of ERDs, if Y_t <50%,SECtwo stagenorm,ERDis higher thanSECsingle stagenorm,ERD. If Y_t>50%as well asY₁<Y_t <1-Y₁, thesingle stage process is more energy efficient than the two stage one. If Yt>50%aswell asY_t>1-Y₁, the two stage process is more energy efficient than the single one.