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 the future. The leading desalination-technology for seawater desalination is reverse osmosis (RO). Although among seawater desalination methods the RO process has the lowest power requirement it is still quite high, in the range of 11 - 15 kwhr/kgallon (3 - 4 kwhr/m3). At the, prevailing operating parameters of commercial seawater RO desalination systems, power requirement 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 the Arabian Gulf area. By comparison, the salinity of brackish concentrate streams that are discharged as waste from brackish RO desalination plants has salinity usually below 2%. The concentrate from brackish RO systems is saturated with sparingly soluble salts, conditions determining the maximum recovery rate. However, if brackish RO concentrate is blended with higher salinity seawater, the solubility of sparingly soluble salts increases due to increase of ionic strength, allowing subsequent RO processing. At locations, where brackish RO and seawater RO plants are located adjacent to each other this phenomena opens possibility of utilizing the brackish water concentrate stream to reduce salinity of seawater feed by blending feed to seawater RO with concentrate from brackish RO system. This approach will result in lower power requirement of seawater RO process, due to lower salinity of feed water and may also simplify discharge of brackish concentrate. The paper will evaluate the-approach to optimizing RO seawater systems design through the utilization of a hybrid brackish - seawater process configuration. Projected process parameters and economic results for a number of selected sites will be presented. The rationale behind the selection of design parameters, economics benefits and the technical challenges associated with the above hybrid configuration will be discussed.