Analysis of specific energy consumption in reverse osmosis desalination processes

This paper aims to quantify the contribution of the various factors to energy consumption in reverse osmosis (RO) desalination processes and to identify those with the greatest potential for reduction. Specific energy consumption (SEC), in kWh per m3 of permeate production, is due to the retentate osmotic pressure, the resistance to fluid permeation through the membrane, the friction losses in the retentate and permeate channels of the spiral wound membrane (SWM) modules and the non-ideal operation of high pressure pumps and energy recovery devices (ERD). Taking advantage of a recently developed SWM-module performance simulator, the aforementioned individual contributions to SEC are determined for two case studies, typical of seawater and brackish water desalination processes, for steady state operation. Detailed results are obtained with SEC itemized per SWM element in a typical 7-element pressure vessel. Comparative assessment of the results is enlightening, showing that the greatest margin for the desirable SEC reduction is related to improvements of membrane permeability and efficiency of pumps and ERD. The indirect, yet significant, effect of other key design and operating process parameters is also discussed.