BETTER ECONOMICS OF DESALINATION THROUGH HYBRID SEAWATER – BRACKISH RO DESALINATION SYSTEMS

摘要

Seawater desalination is projected to be the major source of additional potable water in thefuture. The leading desalination technology for seawater desalination is reverse osmosis (RO).Although among seawater desalination methods the RO process has the lowest powerrequirement it is still quite high, in the range of 11 – 15 kwhr/kgallon (3 – 4 kwhr/m3). At theprevailing operating parameters of commercial seawater RO desalination systems, powerrequirement is mainly function of feed water salinity. The seawater salinity ranges from 3% -3.5% for Atlantic and Pacific Oceans, 3.8% - 4.2% for Mediterranean and 4% - 4.7% for theArabian Gulf area. By comparison, the salinity of brackish concentrate streams that aredischarged as waste from brackish RO desalination plants has salinity usually below 2%. Theconcentrate from brackish RO systems is saturated with sparingly soluble salts, conditionsdetermining the maximum recovery rate. However, if brackish RO concentrate is blended withhigher salinity seawater, the solubility of sparingly soluble salts increases due to increase of ionicstrength, allowing subsequent RO processing. At locations, where brackish RO and seawater ROplants are located adjacent to each other this phenomena opens possibility of utilizing thebrackish water concentrate stream to reduce salinity of seawater feed by blending feed toseawater RO with concentrate from brackish RO system. This approach will result in lowerpower requirement of seawater RO process, due to lower salinity of feed water and may alsosimplify discharge of brackish concentrate.The paper will evaluate the approach to optimizing RO seawater systems design through theutilization of a hybrid brackish – seawater process configuration. Projected process parametersand economic results for a number of selected sites will be presented. The rationale behind theselection of design parameters, economics benefits and the technical challenges associated withthe above hybrid configuration will be discussed.