Cooling water system

1. A system for supplying cooling water to a process on board a floating vessel for the production of hydrocarbons, wherein the vessel ( 1 ) is anchored by means of a bottom-anchored turning unit ( 20 ) mounted in a receiving space ( 7 ) in the hull ( 34 ) of the vessel and allowing turning of the vessel ( 1 ) about the turning unit, and wherein the turning unit ( 20 ) supports a swivel unit ( 24 ) for the transfer of hydrocarbons from production risers ( 28 ) extending between the seabed and the turning unit ( 20 ), the system comprising a conduit means ( 30 ) depending from the vessel ( 1 ) to a depth for taking in cooled sea water, and a pump means ( 44 ) for pumping of the sea water from the conduit to a place of use for the process, characterized in that the turning unit ( 20 ) is designed as a seawater swivel, the unit being provided with one or more passages ( 29 ) for receiving upper end portions of respective seawater risers ( 30 ) constituting the conduit means, and with a means for transferring sea water from the upper end portions of the risers ( 30 ) to an annulus ( 31 ) arranged at the boundary surface between mutually movable parts ( 21 , 22 ) of the turning unit ( 20 ) or between the turning unit ( 20 ) and the vessel hull ( 34 ), and communicating with one or more passages ( 41 ) arranged in the vessel hull and leading to said place of use, a seawater sealing means ( 37 , 39 ) being arranged on each side of the annulus ( 31 ).

2. A system according to claim 1 , wherein the turning unit is a two-part underwater buoy ( 20 ) comprising a bottom-anchored central member ( 21 ) and an outer buoyancy member ( 22 ) rotatably mounted on the central member, and wherein the receiving space ( 7 ) for the turning unit is arranged at the bottom of the vessel ( 1 ), characterized in that the passages for the risers ( 30 ) are arranged in the central member ( 21 ) of the buoy, and that the means for transferring sea water from the upper end portions of the risers ( 30 ) comprises said annulus ( 31 ) arranged between the central member ( 21 ) and the outer buoyancy member ( 22 ) of the buoy ( 20 ), and a number of radial passages ( 32 ) arranged in the buoyancy member between this annulus and an additional annulus ( 33 ) at the boundary surface between the turning unit ( 20 ) and the vessel hull ( 34 ).

3. A system according to claim 1 , wherein the turning unit is constituted by a turret ( 70 ) and the receiving space ( 90 ) for the turret ( 70 ) is arranged at the bottom of the vessel ( 1 ), characterized in that the means for transferring sea water from the upper end portions of the risers ( 30 ) comprises a number of radial passages ( 75 ) arranged in the turret ( 70 ) and communicating with said annulus ( 76 ) at the boundary surface between the turret ( 70 ) and the vessel hull.

4. A system according to claim 1 , characterized in that said passages ( 41 ) in the vessel hull debouch into a water intake ( 42 ) constituted by a wing tank on each side of the vessel ( 1 ).

5. A system according to claim 4 , characterized in that said pump means comprises one or more pumps ( 44 ) arranged at the bottom of each of the wing tanks ( 42 ) and which are connected to a respective conduit ( 45 ) for supplying water in the wing tank ( 42 ) to said place of use.

6. A system according to claim 5 , characterized in that each of the pumps ( 44 ) is arranged in a suction extension well ( 55 ) arranged at a level below the bottom of the wing tanks ( 42 ).

7. A system according to claim 1 , characterized in that the pump means comprises a number of pumps ( 56 ) arranged in respective ones of the sea water risers ( 30 ) at a location below the turning unit ( 20 ).

8. A system according to claim 1 , characterized in that the pump means comprises a number of pumps ( 61 ) arranged in a dry space ( 60 ) above the turning unit ( 20 ), each of the pumps ( 61 ) being connected to a respective one of said passages ( 64 ) in the vessel hull ( 34 ) and to a respective conduit ( 59 ) for supplying sea water from the risers ( 30 ) to said place of use.

9. A system according to claim 1 , wherein the turning unit is constituted by a turret ( 70 ) and the receiving space ( 71 ) is arranged at a level above the water surface ( 72 ), characterized in that the pump means comprises a number of pumps ( 80 ) arranged in respective ones of the seawater risers ( 30 ) at a chosen level below the water surface ( 72 ).

10. A system according to one claim 1 , characterized in that the seawater risers ( 9 ) extend between the turning unit ( 6 ) and the seabed ( 3 ) and with their lower end are connected to an anchoring means ( 10 ) on the seabed.

11. A system according to claim 9 , characterized in that the seawater risers ( 9 ) as well as the production risers ( 8 ) comprise an upper flexible part which, at its lower end, is connected to a submerged buoyancy unit ( 11 ), and a lower part extending between the buoyancy unit ( 11 ) and the seabed ( 3 ).

12. A system according to claim 8 , characterized in that the pump means is constituted by a pump station located on the seabed.