Operation of the RO Kinetic® energy recovery system: Description and real experiences

Along with the older style centrifugal energy recovery devices (ERDs), there has been a recent proliferation of ERDs that employ positive displacement mechanisms. These “pressure-equalising” or isobaric ERDs transfer the energy from the membrane reject stream directly to the membrane feed stream. This direct, positive displacement approach results in a net transfer efficiency up to 97% [R.L. Stover, Seawater reverse osmosis with isobaric energy recovery devices. Desalination, 203 (2007) 168–175]. A number of devices have been developed to recover pressure energy from the brine reject stream. These ERDs fall into two general categories: centrifugal and isobaric devices.In order to avoid the efficiency losses associated with the energy-conversion steps inherent in centrifugal devices, in the 1980s engineers developed positive-displacement (PD) isobaric devices for seawater reverse osmosis (SWRO) plants. These devices place the SWRO reject and raw feed in contact in pressure-equalising or isobaric chambers. Current manufacturers of isobaric devices include Calder (DWEERTM) [2], KSB (SalTec DT) [3], ERI® (PX) [4] and RO Kinetic® (RO Kinetic® is a patent of the Canary Islands engineer Manuel Barreto).The RO Kinetic® is a novel energy savings system for RO desalination plants that implies an enormous advance in the specific energy consumption (SEC) reduction in this type of facilities. With this device, we are able to obtain a SEC of slightly higher than 2.20 kWh/m3, which approaches the theoretical minimum limit for energy consumption in seawater reverse osmosis processes [5].The physical principle that serves as the foundation for the RO Kinetic® system is the “incompressible property of liquids”, making it possible to submit a mass of water to a given pressure without expending any energy. Pressure exchangers are used to put this principle into practice.This article describes the state of the art of the RO Kinetic® energy recovery device; it explains the way it works and the advantages of using this type of ERD in SWRO plants. Furthermore it shows some operational data of different SWRO desalination plants with the RO Kinetic®.