INFRACORP WATER

Seawater intake and Outfall

Seawater intake

We don’t just take water from the ocean.We partner with it, designing intakes that protect ecosystems, optimize energy, and future-proof coastal infrastructure.

At InfraCorp, we engineer intake systems that respect marine ecosystems, secure long-term reliability, and set the foundation for high-efficiency desalination performance.

Engineering the future of desalination starts at the shoreline

Intake Types

Selecting the most feasible type of intake structure will mainly depend on the following:

  • The required feedwater volume and quality;
  • Site-specific coastal and physical processes;
  • The seabed bathymetry;
  • Geophysical conditions;
  • Environmental considerations;
  • Cost of construction; and
  • Future maintenance costs.

A direct seawater intake refers to an intake structures which extracts seawater directly from theocean. This type of structure can either be constructed below the surface (sub-surface) at an offshorelocation, or as an open channel (surface intake) protected from waves by groynes or in a natural bay .

Physical characteristics of the intake

  • Intake type
  • Required water depth
  • Required flow
  • Water quality
  • Meteorological conditions
  • Oceanographic conditions (i.e. seabed slope, bathymetry)

Environmental processes

Waves (i.e. construction constrains, intake structure stability, turbidity at intake works)

Currents (i.e. construction constrains, intake structure stability)

Sediment processes

Environmental impacts

  • Pollution
  • Fouling
  • Aesthetic considerations (i.e could change character and appearance of beaches)
  • Marine biology (i.e. Impact on shore and benthic marine organisms in the area of the intake,
  • Entrainment issues (area rich in marine species))

Environmental design considerations

The most significant environmental concern of open seawater intake facilities is the impingement andentrainment of marine life.

The impacts of impingement and entrainment effects depend upon a number of factors, including theextraction flow rate, locations of intake and local ocean conditions. The following technologicalmeasures as well as design considerations can reduce impingement and entrainment associated with

direct intake systems :

  • Intake location
  • Intake velocity
  • Velocity cap
  • Screening methods
  • Physical barriers
  • Behavioural systems

Hydraulic design

The following design guidelines, which  should be taken into account to ensure the optimum hydraulic performance of aseawater intake structure:

  • The water flow path between the inlet openings in the intake structure and the flow pipe/ductto shore should be streamlined to obtain water velocities increasing gradually;
  • Abrupt changes in flow cross section areas should be avoided in order to minimize turbulenceand consequent power loss;
  • The flow section between a rectangular intake opening and a round duct (pipe or tunnel) isparticularly important: The transition should be made over a flow distance equal to one ormore conduit diameters, and
  • Model tests are of great value in determining the direction of the flow path between the intakeopening and the duct.

Marine Pipelines

If feedwater is extracted from an offshore intake structure, the feedwater is transferred via a tunnel or

pipeline from the seawater intake to land. The brine waste stream is transported from the headworks(or brine holding tank pump station) through the main outfall pipe out to the diffuser. The following

section summarizes the general considerations which have to be taken into account when designing a

sea pipeline.

Structural design

  • Bathymetry: A bathymetry survey provides water depth contours, the slope of the seafloor,protruding reefs and offshore sandbars.
  • Seabed physiography determines the method therefore also affects the cost of constructionand a side scan sonar survey can be used for this purpose.
  • Sub-seabed conditions: If a pipe is buried in a trench.
  • Further geotechnical investigations required in detail design include soil analysis, rockanalysis and seismic stability.
  • Sediment movement: Large seasonal changes in sand depth can occur in the surf zone due towave-induced turbulence and currents, especially during storms .
  • Waves: Wave data are crucial for detailed structural design of the pipeline .
  • Tides: Tidal variations also have to be taken into account for the hydraulic design withrespect to the available head (pressure or gravity).
  • Pipe stability :The stability of a pipeline resting on the seafloor is affected by the forces caused by waves andcurrents, the resistance from the seafloor and the physical characteristics such as outside diameter,weight, length, etc. of the pipeline.

BRINE DISCHARGE

 A desalination plant will consist of a feedwater stream, a product water stream, and a waste stream of concentrated reject solution .

Brine can kill organisms in the short terms, but may also cause more subtle changes in the community assembly over longer time periods.

The composition of the brine effluent is very critical, since the type of constituents and their concentrations will directly affect the required dilutions which have to be achieved and subsequently

Pigging Cleaning System

Piging systems are designed as “One way” open systems which mean that the pig will have to be removed from the pipeline at the end of each run. Subsequently this could lead to problems with both safety and process interruption since the pipeline need to be opened at the pig receiving end and the pig removed and replaced at the other end of the pipe. Therefore, it is necessary to ensure that marine fouling is minimized as much as possible by mans of other mitigation measures such as chlorine dosing, maintaining high flow velocities and coating the inside of the pipes with anti-foul paints.