Development And Performance Evaluation Of Self-Boosting Energy Recovery Device In Seawater Desalination System

Energy recovery devices(ERDs)can reduce the energy consumption and permeating cost of seawater reverse osmosis(SWRO)system by recovering the pressure energy of the high-pressure(HP)brine.In this thesis,a self-boosting energy recovery device(SB-ERD)which followed the differential pressure principle and possessed the advantage of adjustable theoretical pressure-boosting ratio was designed based on the study of reciprocating-switcher energy recovery device(RS-ERD).The 1#SB-ERD with theoretical pressure-boosting ratio of 5.5%and the2#SB-ERD with theoretical pressure-boosting ratio of 3.4%were developed and coupled into the SWRO system for performance evaluation.The component performance tests of 1#SB-ERD were conducted firstly.Under the medium pressure of 6.0MPa,the average static leakage of the valve plate with the maximum leakage in the switcher was 0.0556m~3/h and the corresponding static leakage ratio was 0.37%.The piston starting pressure in the hydraulic cylinder from the seawater side to the brine side was nearly equal to that from the brine side to the seawater side,which was around 0.05MPa.The running experiment of 1#SB-ERD was conducted under the operating pressure of 6.0MPa and the capacity of 22m~3/h.The 1#SB-ERD could realize the pressure-boosting function with actual pressure-boosting amplitude of 0.09MPa and actual pressure-boosting ratio of 1.50%,which accounted for 15.6%of the theoretical pressure-boosting ratio.The 1#SB-ERD achieved the leakage ratio of 0.95%,which was lower than that of typical international ERD products.The energy recovery efficiency of 1#SB-ERD was92.41%,which was slightly lower than the efficiency of some international ERD with pressure-boosting function.The theoretical pressure-boosting ratio was optimized and the 2#SB-ERD was obtained and tested under different operating pressures.Under the pressure of 6.0MPa and the capacity of 15m~3/h,the pressure fluctuation amplitude of HP brine was0.65MPa and the flow fluctuation amplitude of HP brine was 0.26m~3/h.In the pressure range of 3.0~6.0MPa,the 2#SB-ERD achieved the leakage ratio of0.5%~1.2%,the pressurizing efficiency of 96.90%~97.55%and the energy recovery efficiency of 94.39%~94.68%.The energy consumption of RO system coupled with2#SB-ERD was analyzed and the specific energy consumption(SEC)was calculated as 2.63kWh/m~3.The 2#SB-ERD could reduce the SEC by 68.3%when compared with the conventional RO system without ERDs.The results above prove that the SB-ERD can achieve great energy-saving effect in the RO system and have a good prospect for widespread use.