Background of the invention and prior art The construction and function of a typical turret is described in the international patent application publication PCT/NOOO/00447, which contains description of a system to supply cooling water to a cooling system on board a vessel for production of hydrocarbons, particularly a floating vessel with a LNG-plant on board. The turret according to said publication comprises a device for transferring seawater from an annulus arranged between the turret and the hull of the vessel and in connection with passage ways in the hull, wherein a device sealing against the seawater is arranged on each side of the annulus. The transfer of seawater takes place via a swivel unit located into an intake room in the hull of the vessel, such that the components of the device are more or less difficult to access for overhaul and replacement.

With the term turret in connection with the present invention it is meant any turning body that can be arranged within a vessel to receive risers, in that the turret and risers in substance are without rotation while the vessel can rotate freely around the turret, and an intake room for cooling water can be arranged with lowered water level within the turret.

In Norwegian patent application NO 2001 5345 an invention is described for which a device is provided for transfer of seawater from the turret to the rest of the vessel, wherein said transfer takes place at deck level, which inter alia results in easy access for replacement or maintenance of components. The device of NO 2001 5345 is distinguished in that it is comprising a toroide-shaped body which is stationary arranged on the deck of the vessel, concentric with the axis of rotation of the vessel, a number of outlets for the transfer of water from the turret to the toroide body, the outlets being coupled to means for transferring water supplied to the turret from the seawater hoses, a container body which communicates with the toroide body to receive water supplied thereto from the outlets, and a means which is coupled to the turret outlets and is provided with sealing means to prevent water leakage from the toroide body.

The toroide body or toroide is an annular volume used as transfer tank for cooling water.

The above mentioned device has turned out to result in disadvantages by being very demanding with respect to space, and problems occur in form of splashing at heavy sea, capsizing or listing of the vessel. It has turned out that the pumps have to be thoroughly adjusted mutually to avoid that the toroide body is emptied for water, such that the prior art device is very sensitive for operational disturbances, why an inappropriately large suckback tank is required.

An objective of the present invention is to provide a device resulting in that said disadvantages completely or partly are avoided.

Summary of the invention The objective of the invention has now surprisingly been met by providing a device for supply of cooling water to a process on board a vessel, said vessel containing a turret and laying in substance fixedly positioned on the surface by spread anchoring or dynamic positioning, such that the vessel can rotate freely around the turret that in substance is without rotation, in that cooling water in form of seawater by use of a riser system is brought to at least one upward open intake room in the turret, which intake room preferably has lowered water level compared to the sea surface, from which intake room cooling water can be brought further to the process. The device of the present invention is distinguished in that it is comprising: at least one pump lowered into the intake room in the turret, with fluid connection from the at least one pump to the process, to pump cooling water from the intake room to the process, wherein both the pump and the fluid connection are arranged stationary in relation to the deck of the vessel.

Thus rotation will take place between the at least one pump having fluid connection to the process and the intake room within the turret.

With the vessel laying in substance fixedly positioned it is meant a position that is fixed as achievable by use of anchoring or dynamic positioning, with the stiffness of the riser system and anchoring as a normal determining factor, which means maximum drift within a few degrees angular deviation for the risers.

With a turret in substance without rotation, it is meant a rotation within the limitations as determined by connected risers and anchoring, which normally means within about 360°.

With lowered water level it is meant that the surface of water within the turret is lower than the surface of the sea, for example 10-35 m lower than the surface of the sea.

A lowered water level within an intake room in the turret results in possibility for using a riser system without integrated pumps, however, this is not a limitation for the present invention.

The advantages with the device of the invention can be summarized as follows: There will be no water pipes on deck, which saves space and results in a smaller and less expensive turret.

There is no need for a swivel, cables and junction boxes for electric power, and the process swivel becomes simpler, less expensive and occupies less space.

There is no need for a swivel for control signals and cables to sensors for monitoring of the pumps within the turret, and the utility swivel becomes simpler and less expensive.

There is no need for crane and working space for servicing the pumps on the turret, which instead takes place from the vessel.

The lifting pumps are also booster pumps, thus the number of pumps is reduced by 30-50 % dependent on the total amount of water.

Reduced requirement for control valves and air shutters, the number reduced 30- 50%.

Increased operational regularity because fewer components may fail.

Simple start and shut down, independent for each pump, and without series connected pumps that must be coordinated.

No toroide, with sealing system, on deck.

No need to dump cold seawater in the surface.

The turret/annular volume contains much water, which results in inertia in the system and stability.

Self regulating adjustment of the lowering of the water level within the turret is possible, since increased pumping results in lowered water level and increased differential pressure and thereby increased inflow of cold seawater through the risers.

A suckback tank between the process plant and the turret is not required.

Drawings The invention is illustrated with one sheet of drawing having two figures, wherein Fig. 1 illustrates a cut of a turret, with a device according to the present invention.

Fig. 2 illustrates a sketch seen from above of a turret having a device according to the present invention.

Detailed description The device according to the invention preferably comprises at least two pumps, having pipe connection from each pump to the process plant, to achieve sufficient operational stability, such that production can be maintained at shut down of one pump.

Usually it is most preferred with more than two pumps, for example 4,6, 8 or 10 pumps, which should be considered in each case. For example it appears to be most preferable technical and economical to use 8 pumps in a specific embodiment with a LNG-plant on the vessel.

The pumps and pipe connections are preferably free hanging from a support frame fastened to the deck of the vessel or they are built into a supporting frame.

Alternatively the pumps and lines for fluid connection are preferably suspended with rollers or sliding bearings towards the turret and is fixedly fastened to the vessel hull/deck.

In a preferred embodiment of the device according to the invention the pumps and pipes for fluid connection are suspended with roller bearings to the turret and are axially displaceable fastened to the vessel hull by being fastened with roller bearings to a rail that is arranged perpendicular and radial to the rotation of the turret surface. Thereby it is possible with a construction giving easy deployment and retrieval of pumps and lines. The lines can preferably be flexible hoses. The lowest parts of the rails can be free hanging down into the intake room, while the upper part is fastened to the hull and deck of the vessel. The orientation of the rail is parallel with the rotational axis of the turret, and with a slope from the parallel axis radially outwards or inwards, or in other words, the rails are perpendicular to the rotational tangent of the turret surface. If the rail is to be brought further out over the deck of the vessel, the orientation thereon can be chosen freely.

Preferably at least one swivel device is arranged in the turret, where two further risers, lines or cables are connected, to handle rotation between the further connections and the vessel.

Preferably a maximum flow rate from the pumps by the lowest acceptable water level within the intake room in the turret corresponds to the flow rate that can be delivered through the riser system at said water level, without pumps in the riser system, such that a self regulating adjustment of the water level within the turret can be achieved.

If desired a valve can be arranged in the turret to regulate the water level and thereby the flow rate of water from the riser system to the intake room, and a suckback tank can be arranged upstream of the process plant, however, none of said devices are required or obligatory.

The device according to the invention is preferably part of a riser system that provides about 50000 m3/h cold seawater to an intake room with lowered water level within the turret, for further transport to a LNG-plant arranged on the vessel, by using eight submerged pumps having fluid communication to said LNG-plant.

The further description is made with reference to the figures. On Figure 1 a typical device according to the present invention is illustrated, the illustrated cut showing two pumps 1 deployed in an intake room 2 having lowered water level 3. The pumps are freely hanging down into the intake room, in a framework 4, such that the lower part of the framework 4, with pumps 1 and the lower part of pipe 5 for fluid communication, hang stationary and freely down into the intake room. The upper part 6 of the framework is fastened to the hull of the vessel and deck construction. Openings upwards from the intake room are not required to be larger than achieving sufficient venting and space for retrieval and deployment of equipment, and access for personnel. The process plant is connected to point 7. A swivel device 8 is placed on a swivel deck 9 to handle rotation of further risers (not illustrated) and cables than the cooling water riser system delivering water to the intake room.

On Figure 2 the same device as illustrated on Fig. 1 is illustrated, but viewed from above. The embodiment has arranged in total eight pumps 1, of which three are indicated on Figure 2. Further, the interior of the turret 10 and outer part 11, which also can be seen on Figure 1, are illustrated. An access route 12 to the pumps is indicated on the figure, likewise the storage devices 13.

Start and shut down can be undertaken relatively simple since the pumps can be operated independently, without series connected pumps that must be coordinated. By start-up the intake room within the turret can be filled with water corresponding to the sea level, such that the water level is lowered slowly as water is pumped to the process, and the inflow through the riser system commences slowly. With a valve device in the inlet from the riser system the start-up can preferably be undertaken with lowered water level in the intake room of the turret, such that cold seawater can be provided more quickly.