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Energy conservation is becoming an increasingly important issue in waterpurification. Owners and engineers alike are looking for new methods to cut downon operating costs without increasing operation and maintenance requirements.Energy consumption has always been one of the largest operating costs in membranewater treatment plants. Energy consumption has been dramatically reduced in thepast several years through the introduction of new low-pressure membraneelements. Additional energy savings may be realized through the incorporation ofenergy recovery devices (ERDs). These devices transfer some of the residualpressure from the system concentrate to boost another flow stream. The units havehistorically been used on seawater systems to increase the feed pressure at thehead of the membrane system. There are new innovative applications of ERDs oninterstage applications in brackish water and even membrane softening systems.Additional benefits are obtained from using boosters on interstage applicationssuch as improving hydraulic balance, increasing permeate quality, and potentiallyextending membrane life by balancing flux rates and loading. There are severaldifferent types of energy recovery devices commercially available. The focus ofthis paper will be to present information on several main types and evaluatetheir advantages and disadvantages from an objective, non-commercial perspective.The types of ERDs that will be compared are: reverse turbine (i.e. HydraulicTurbocharger); Pelton Wheel; Pressure Exchanger; and, electric motor drive (EMD)incorporating energy recovery. The reverse turbine-type Hydraulic Turbochargeruses a turbine that is rotated by the high-pressure brine. The energy is thentransferred to a forward turning turbine that adds pressure to the feed orinterstage stream. This process boasts a hydraulic recovery of 92-97%. The Peltonwheel is another high efficiency mechanism, recovering up to 90% of the brineenergy. The high-pressure brine is aimed by a nozzle to hit a paddlewheel, whichthen turns a turbine to pressurize the incoming feed. The pressure exchanger usesa cylindrical rotor, which rotates in between the two flows (brine and feed).Energy is transferred through the rotor, from the brine to the feed, with anobserved efficiency near 95%. The final ERD, the electric motor drive, iscommonly used on SWRO systems, and has displayed energy savings of 20-35%, inrecent pilot studies. This system also uses the high-pressure brine stream topower the feed pump using hydraulic mechanisms. How each manufacturer evaluatesand promotes their efficiency will be carefully reviewed and explained. Herein,data on capital costs and energy savings and recovery, of each of the ERDs, willbe discussed and evaluated. Several brief case studies will be includedpresenting specific data on the performance of the ERDs. Includes 6 references, figure.

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Edition: Vol. - No. Published: 05/01/2001 Number of Pages: 9File Size: 1 file , 170 KB