Study of cyclic operation of RO desalination process

Abstract

The performance of a tubular reverse osmosis (RO) process for water desalination was investigated when the unit was periodically forced. The study was performed using a dynamic model that was developed and validated in a previous work of the authors [Al-haj Ali et al., Desalination 245, 194-204 (2009)]. The forcing was carried out through feed pressure using both symmetric and asymmetric rectangular pulses. For a symmetric pulse, it was found that the permeate flow rate increased monotonically with the forcing amplitude. The improvement in the permeate flow rate was limited by the constraints on the operating pressure. For an asymmetric pressure pulse, the permeate flow rate reached a clear maximum for some values of ratio of pulse width to the period. For both pulses, the model predicted that the enhancement in the permeate flow rate was attributed to the reduction in the effect of concentration polarisation. Moreover, the trends obtained with both symmetric and asymmetric shapes were consistent with the experimental results reported in the literature.On a analysé le rendement d'une osmose inverse (OI) tubulaire pour le dessalement de l'eau lorsque l'unitéétait forcée de façon périodique. L'étude aété réalisée en utilisant un modèle dynamique créé et validé dans un travail antérieur des auteurs [Al-haj Ali et al., Desalination 245, 194-204 (2009)]. Le forçage aété réalisé par une pression d'alimentation en utilisantà la fois des impulsions rectangulaires symétriques et asymétriques. Pour une impulsion symétrique, on a trouvé que le débit de perméation augmentait monotonement avec l'amplitude de forçage. L'amélioration du débit de perméationétait limitée par les contraintes de la pression de fonctionnement. Pour une impulsion de pression asymétrique, le débit de perméation a atteint un maximum clair pour certaines valeurs de ratio de largeur d'impulsion pour la période. Pour les deux impulsions, le modèle a prédit que l'accroissement du débit de perméationétait attribuéà la réduction de l'effet de la polarisation de concentration. De plus, les tendances obtenuesà la fois pour les formes symétriques et asymétriques correspondaient aux résultats expérimentaux de la littérature.Keywords: reverse osmosis, cyclic operation, symmetric forcing function, asymmetric forcing function INTRODUCTION R everse osmosis (RO) is an important filtration process used extensively for the desalination of sea and brackish water all over the world. Concentration polarisation and membrane fouling are major concerns in the operation of RO process, since they reduce the permeate flux and result in loss of productivity. Fouling is characterised by an irreversible decrease in flux while concentration polarisation results in a reversible decline in water flux through the membrane. Fouling could be eliminated by cleaning the membrane using various chemical or physical methods (Cheryan, 1986). Concentration polarisation, on the other hand, can be controlled using two main methods: changes in the characteristics of the membrane or modification...

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