Seawater intakes for desalination plants

The seawater intake has to ensure sufficient seawater in terms of quantity and quality independently from the type of desalination plant (RO, MED, MSF) installed downstream. The best seawater quality can be reached by beach wells, but in these cases the amount of water which can be extracted from each well is limited by the earth formation, and therefore the amount of water available by beach wells is very often far below the demand of the desalination plant. In these cases the developer has the choice between (I) an intake from deep seawater with the advantage to have less polluted seawater and the disadvantage of high investment cost which normally limits this type of seawater intake to 20,000 m(3)/h; (2) open seawater intakes with the advantage of low investment cost but the disadvantage of biologically more active water which requires more efforts to treat the seawater. Offshore seawater intakes require a submerged pre-screening device minimizing the amount of sand sucked into the pipeline and ensuring that no particles able to damage or block the pump can enter. A description with pros and cons of the different available pre-screening devices will be given in the presentation, with special consideration of how the different types influence the total project cost. Open seawater intakes have to handle much higher amounts of coarse debris as well as micro organisms. The different kinds of available open seawater intakes will be presented in the presentation as well, demonstrating how efficiently and economically the different intake types fulfil this requirement.