Evaluating Seawater Energy Recovery Devices

There are several methods for reducing RO energy consumption in seawater membrane desalination (SWRO). They include advanced version of the Pelton Wheel, work and pressure exchangers and the hydraulic turbocharger. While these technologies are now being globally employed, the end-user and contracting and specification engineers are finding it difficult to differentiate which of these energy saving systems is most effective for their given project. The purpose of this paper is to examine each of the technologies as an aid to this selection process. With the cooperation of the energy recovery manufacturers, the top 3 installations for each technology were surveyed. There are five major commercial energy recovery devices (ERD): hydraulic turbocharger, pressure exchanger, work exchanger, Pelton wheel sometimes called impulse turbine and Francis turbine also called reverse running pump. This study includes a description of each system along with a picture or schematic of the unit as sold by its major proponent and the equations that can be employed to calculate the energy consumed. ERDs are associated in a fashion to the high pressure pump (HPP) and this couplet is the main contributor (about 80%) of the total energy utilized in a SWRO facility. Variable frequency drives (VFD) are currently being employed on most high energy consuming pumps.

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