More than 30% energy saving seawater desalination system by combining with sewage reclamation

Abstract

Although seawater reverse osmosis (RO) system has been applied commonly in the world, there are still remaining two key issues for further expansion; (1) High energy consumption and (2) Marine environmental impact attributing to high salt concentration of brine water. Herein, new seawater RO system that enables us to overcome the issues has been proposed. The key feature of this system is to reduce salt concentration of seawater by dilution using the water derived from wastewater treatment or reclamation system to achieve the extreme energy reduction of high pressure pump and to make salt concentration of brine water to the same level as the seawater. In order to demonstrate this system, a demo plant designed “water plaza” was built up and operated in Kitakyushu, Japan, where 1,500 m3/d of sewage and 500 m3/d of seawater are used as raw water, and product water is supplied and used as a boiler feed raw water in the Shin-Kokura Thermal Power Plant of Kyushu Electric Co., Inc. During the plant operation, the pressure of high pressure pump for seawater desalination, which is normally 5–6 MPa, has been kept at approximately 3.5–4.0 MPa. It shows that the proposed system can realize more than 30% of energy saving for seawater desalination.