0011-9164/09/$– See front matter © 2008 Elsevier B.V. All rights reserved Desalination 238 (2009) 233–245 Behaviour of energy recovery devices in unsteady flow conditions and application in the modelling of the Hamma desalination plant S. Mambretti a* , E. Orsi a , S. Gagliardi b , R. Stover c a DIIAR, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano, Italy Tel. +39 (02) 2399 6245; email: stefano.mambretti@polimi.it b GE Water and Process Technologies, Via Antonelli 9, 20100 Milano, Italy c Energy Recovery Inc., San Leandro, CA, USA Received 15 October 2007; Accepted 18 February 2008 Abstract The Hamma (Algeria) desalination plant, briefly described in the paper, was mathematically modelled in order to check its behaviour in an advanced phase of its design. The plant will employ 288 ERI’s PX units to recover the pressure of the brine discarded from the RO membranes. This way of recovering energy is one of the most advanced and efficient now available, and its functioning is also briefly described in the paper. The devices’ behaviour in unsteady flow conditions was checked by tests carried out in the hydraulics laboratory of the Politecnico di Milano, Italy. The paper reports on the experimental plant and the results obtained. On the basis of the experimental results, which showed an almost perfect hydraulic disconnection between the high and low pressure lines, the mathematical model of the Hamma plant was built using the momentum and continuity equations integrated by means of the characteristic method. The paper describes the mathematical model and sets out the results, which evidence of the plant’s safety even under the worst conditions likely to occur. Keywords: Seawater reverse osmosis (SWRO); Pressure exchanger; Water hammer; Hydraulic model 1. Introduction In a reverse osmosis (RO) water desalination system, a high percentage of water (brine) has to be discarded, consuming a great deal of energy *Corresponding author. used to obtain the high pressure necessary in these plants. As a consequence, many systems have been developed in order to recover this energy. One of the most advanced devices is implemented in the ERI PX (registered trade- marks of Energy Recovery, Inc.) energy recovery doi:10.1016/j.desal.200 .0 .0 8 2 15 .