Waste energy recovery in seawater reverse osmosis desalination plants. Part 1: Review

Abstract

The reduction of energy consumption constitutes one of the major thrust areas of research in seawater reverse osmosis (SWRO) desalination plants. The cost of energy in the SWRO process is usually about 30–50% of the total production cost of water and can be as much as 75% of the operating cost, depending on the cost of electricity. Thus, energy forms the major contributing factor in determining the water production cost. Hence reducing the energy consumption, which is mainly due to wastage of energy in high-pressure brine, is a major goal of desalination industries.Energy recovery devices are employed in seawater reverse osmosis (SWRO) desalination plants to recover the high pressure energy from the membrane exhaust stream (60:80 bar) and return it back to the process. Because of this high exhaust (concentrate) pressures at high flow rates, the membrane exhaust stream contains a considerable amount of energy to be recovered. Recently, isobaric energy recovery devices and turbochargers have been used for SWRO performance improvement. These devices are intended to provide greater energy-savings and greater capacity than was previously achievable.This paper gives a comprehensive overview of the available energy recovery devices (ERDs) that can be used in seawater reverse osmosis (SWRO) systems, with emphasis on technologies and economics. A comparative study between different ERDs technologies as well as performance and economics has been done. These include turbines, turbochargers and isobaric devices at different design configurations. Special attention is given to the use of ERDs in seawater RO desalination. Finally, some general guidelines are given for selection of ERDs and parameters that need to be considered (specific power consumption kW h/m3, energy saving%, and the corresponding cost saving).