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Maximising recovery from sea water RO desalination plants

posted Mar 31, 2012, 3:36 AM by Sanjay Ganguly   [ updated Mar 31, 2012, 3:47 AM ]
As the power plants are set across coastal locations the need for more reliable and cost effective desalination is pertinent. Traditionally desalination plants have been associated with not more than 30 to 35% efficiency, but higher efficiency in SWRO with recoveries of 40 to 45% is achieved since 1999. 


To obtain 40% permeate with fluctuating TDS content varying from 38,000 Mg/lit. to 46,000 Mg/lit. with a feed water temperature variation of 25 degrees to 35 degrees C,  with stringent treated water quality of less than 450 mg/lit. TDS level at the outlet of SWRO!!!!!!!!!!!!!!!!!!!! 

Can be achieved?

Yes to achieve that consistently, a reliable pretreatment system and a comprehensive operation and controls mandate was required. The robust pretreatment system consisting of a 2*6160 GPM (2*1400 cubic meters/hr) pretreatment plant followed by a two stage filtration using dual media and pressure sand filters ensures fine and consistant pretreated water quality at the inlet of the Membrane system.

The membrane system consists of four streams of SWRO trains, each with its dedicated energy recovery device, to optimize the energy consumption per unit volume of permeate produced. The energy recovery device used is the advanced pressure exchanger system. The permeate water is mainly used as service water for complete power plant facility.

A part of the desalinated water is further treated through a BWRO system to produce 660 GPM (3600 cubic meters/day) of permeate for feeding the downstream mixed beds demineralization plant for boiler feed application. TDS levels at the outlet of the brakish water reverse osmosis system are in the range of 5-7 Mg/lit. This ensures consistent performance of the downstream mixed bed polisher.