BALLAST CONTROL SYSTEM (FPSO)

 BALLAST CONTROL SYSTEM (FPSO)

A Ballast tank is a compartment within a boat, ship or other floating structure that holds water.

The ballast system keeps the offshore unit in a stable condition and at a suitable draught, heel and trim in all relevant states of operation.

In order to provide adequate stability to vessels at sea, ballast is used to weight the ship down and lower its centre of gravity.

The segregated ballast system is designed in floating production storage and offloading (FPSO) to comply with International Convention for the Prevention of Pollution from Ships (MARPOL) regulations. It has ballasting/ de-ballasting and transfer functions from one tank to any other ballast tanks. Ballast filling is via ballast main pipes which run to the ballast seawater from topside seawater lift pumps or topside utility pumps using gravity filling.

In previous FPSO projects, the ballast pumps were located in pump room, but recently projects have installed the hydraulic operated, submersible centrifugal type pumps in the central wing ballast tanks. In semi-submersible type projects, ballast pumps had functions of ballasting/ de-ballasting and located at the machinery space in pontoon areas. However, in the recent projects, the ballasting is operated by topside seawater lift pumps and electric motor driven, centrifugal type, de-ballasting to overboard above the deepest waterline. To size ballast pumps, cargo loading/ offloading capacity is to be considered in ships shape projects and restoring units from damage conditions in semi-submersible projects.

The Ballast system performs the following functions:

  • Compensation  of  the  heel  induced  on  the  FPSO  by  permanent  riser  asymmetric hang-off or Topsides CoG eccentricity (permanent ballast).
  • Ensure sufficient draft of the FPSO during tow and during on-site operation when little cargo is stored.
  • Adjust heel and trim of the FPSO (for lifting of settled water in cargo tank before offloading, tank stripping or during tank inspection and maintenance).
  • Minimize stresses in the Hull due to still water shear forces and bending moments induced during FPSO towing phase and during on-site operation, especially due to tank inspection/maintenance cases.
  • Transfer contaminated ballast water to the slop tanks for settling and treatment.
  • Strip ballast tanks, cofferdams and void Spaces (bilge function).
  • Emergency pumping of pump room in case of flooding.

The Ballast system consists of the following:

  • Manifolds
  • Ballast pumps
  • Ballast tanks
  • Void spaces and cofferdam
  • Oil discharge monitoring system
  • Air vent and sounding
  • Ballast system in connection with other systems
 BALLAST TANK IN HULL



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