The conventional RO processes in water desalination and purification predominantly employ long pressure vessels in which 6-8 membrane elements of 1 meter long are connected in series.  Such pressure vessels can achieve an overall recovery (the ratio of permeate flow rate to feed flow rate) of 40-60% while the recovery of individual element is maintained below 10% for seawater or 15% for brackish water, which are required by the manufacturers for satisfactory performance.  However, only a fraction of energy in a conventional RO process with long pressure vessels is used for permeate production while a large amount of energy is wasted either with the retentate discharge or on associated concentration polarization. A thorough understanding and quantitative assessment of the energy consumption in the RO systems is essential for further improvement of energy efficiency of the technology.  This talk will present a quantitative method to detail the energy spent in an RO process as the minimal energy requirement, the fraction to maintain the required permeate flux, and the fraction spent to overcome concentration polarization. The energy spending patterns (relative magnitudes of various energy components) at low, medium, and high salinities were simulated and discussed.  The impact of reduced membrane resistance on all energy components particularly elaborated.  Interesting findings were that the flux energy component decreases with decreasing membrane resistance while all other energy components increase and that permeate flux of membrane desalination process could not be significantly increases by further reduction of membrane resistance.

Energy spending patterns analysis in RO desalination processes

246th National Meeting (2013)

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