Structural Optimization And Performance Evaluation On The Isobaric Energy Recovery Device For Seawater Desalination

The isobaric energy recovery device(ERD),as one of the key energy-saving equipments,recovers the pressure energy in high pressure(HP)brine through the direct contact pattern,which achieves the reduction of energy consumption for the membrane seawater desalination.There exists the issue of the higher driving energy consumption,the larger fluid fluctuations and the difficulties in performance prediction for parallel schemes in the operation of reciprocating-switcher energy recovery device(RS-ERD).To solve the issues above,the structural optimization and performance evaluation for RS-ERD are studied in this thesis.And a new roatating-plate energy recovery device(RP-ERD)is developed on the basis of RS-ERD.Firstly,there exists the higher starting pressure,the larger energy consumption at switching,and the imperfect sealing performance in the operation of RS-ERD.A new RS-ERD is developed which employs the pilot-operated switching and self-energized sealing functions.The new RS-ERD is experimentally tested at the flowrate of30 m~3/h and pressure of 6.00 MPa.The results indicate that the starting pressure decreases from 0.50 MPa to 0.25 MPa,and the shunt volume reduces by 72.16%for the new RS-ERD.The sealing force realizes the self-adaptation dynamically.The leakage ratio of pilot-operated RS-ERD is about 1.00%and the energy recovery efficiency is as high as 98.50%.Secondly,the HP fluid fluctuates during the stroke switching process,which is resulted from the discontinuous alternation of opening and closing for valve plates.To solve the issue,a new driving structure of valve plates is developed which achieves the overlapping function in the two high pressure valves.And three overlapping distances,0 mm,6 mm and 12 mm,are realized in the stroke distance of two high pressure valves.The experimantal tests indicate that compared to 0 mm overlapping distance,the fluctuation amplitude of flowrate and pressure loss has decreased by26.92%and 62.82%for HP fluid,and the corresponding fluctuations decline by 90.77%and 98.72%in 12mm overlapping distance,respectively.Thirdly,parallel operation is one of the key methods to realize the capacity expansion.To investigate the operating characteristics,the pressure loss and internal leakage are associated with the operating conditions through the parameterization methods,and the universalized performance parameters are obtained for RS-ERD.The variation characteristics of performance parameters are investigated through the CFD simulation and verifying experiments for single-operation,two-parallel operation and three-parallel operation.The results indicate that the pressure loss parameter decreases with the 1/N~2 rate while the leakage parameter increases with the N rate when the parallel number N increases for RS-ERD.The flowrate range with high efficiency broadens linearly when the number increases for parallel RS-ERD.The flow continuity of high and low pressure can be realized in the parallel operating schemes with asynchronous switching strategy.Finally,RP-ERD is developed from the advantage combination of the RS-ERD and rotary energy recovery device,which adopts the structure of"rotating plate-pressure exchanging cylinders-sliding valve nest".The continuous pressure exchanging process is achieved by the rotating plate and reciprocating slide valves in RP-ERD.The operating performance of RP-ERD is investigated through the CFD simulation approach.In the operating flowrate of 35 m~3/h and pressure of 6.00 MPa,the balanced rotational speed is 690 rpm for the rotating plate.The pressure exchanging fluids have a stable flow states,and the pressure loss at high pressure and low pressure fluids are0.25 MPa and 0.13 MPa.The salinity mixing between seawater and brine is 1.52%in stable operation.