In a paper1presented at the IDA World Congress in Bahrain in 2002，an evaluation was undertaken of the commercial，major energy recovery devices(ERD)．These units included the impulse turbine(Pelton wheel)，hydraulic turbo charger，work exchanger，pressure exchanger and reverse running ump(Francis turbine)．It was found the most energy efficient systems were the two exchangers；the least plausible device was the reverse running pump．The Francis turbine is installed in a number of older membrane desalination plants，for it was the first such unitoffered tO the trade．A detailed examination of the cases depicted in the paper indicated that，for large plants，the impulse turbine was now closely approximating its highest practical，operational efficiency，90﹪．The two exchangers，with pressure transfer efficiencies of 92﹪-94﹪，have little room for further improvement except for reducing the level of fluid being．bypassed from the brine to feed streams．Bypassing now amounts tO about 3﹪to 6﹪．Demonstration of equipment life，and scale-up of the pressure exchanger beyond small and medium size plants is required．The work exchanger has favorable economic value，basically，in plants whose train sizes are in excess of about 6,000m3/d(1.6MGD)．
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