Heating seawater: the solution or the pipe dream of reverse osmosis electrical consumption

Abstract

The desalination market based on reverse osmosis is a growing market thanks to much lower energy consumption compared to thermal desalination. This leading position implies that a lot of efforts should be done to improve both its acceptability and cost to thwart its detractors. For those reasons, the further improvement of the energy consumption is a key factor and one of the main objectives of the desalination community. It is well known that temperature has an impact on membranes’ feed pressure. For equivalent feed water quality and operational conditions, high temperature water will require less pressure to produce the same amount of permeate. Based on this reality, some projects are considering the opportunity to recover cooling waters from cooling towers or MSF/MED cooling system as seawater feed to RO plants to reduce electrical consumption, in particular on hybrid, IWPP, or co-location projects. But temperature has also an adverse effect on the permeate water quality that could result in increasing the 2nd Pass flow requirement or the use of tighter membranes. The present paper analyses the impact on electrical consumption and design of the complete RO plant using a heated seawater source. Through case studies based on typical middle east seawaters, 41 g/l and 45 g/l and two different permeate water quality targets, 200 mg/l and 500 mg/l TDS, it attempts to conclude if overall benefits can be identified in such conditions.