WO2003037703A1

WO2003037703A1 - An apparatus for supply of cooling water from the sea to a process aboard a turret-anchored vessel

Info

Publication number: WO2003037703A1
Application number: PCT/NO2002/000394
Authority: WO
Inventors: Knut Harry Fjell
Original assignee: Statoil Asa
Priority date: 2001-11-01
Filing date: 2002-10-31
Publication date: 2003-05-08
Also published as: NO20015345D0; NO20015345A; NO313584B1

Abstract

An apparatus for supply of cooling water from the sea to a process aboard a floating vessel for the production of hydrocarbons, where the vessel (1) is anchored by means of a turret (3) which is mounted in a receiving space (2) in the hull of the vessel allowing the vessel (1) to turn about an axis (X-X) of rotation, and which supports a swivel unit (12) for the transfer of hydrocarbons from risers (11) extending between the seabed and the turret (3). The apparatus comprises seawater hoses (18) depending from the turret (3) to a depth for intake of cooled seawater, and a pump means (34) for pumping of water from the seawater hoses to a place of use for the process. Further, the apparatus comprises a toroid-shaped body (28) which is stationarily arranged on the deck (5) of the vessel (1), concentric with the axis (X-X) of rotation of the vessel, a number of outlets (29) for the transfer of water from the turret (3) to the toroid body (28), the outlets being coupled to means (30, 31) for transferring water supplied to the turret (3) from the seawater hoses (18), a container body (32) which is communicates with the toroid body (28) to receive water supplied thereto from the outlets (29), and a means (35) which is coupled to the turret outlets (29) and is provided with sealing means (42, 43) to prevent water leakage from the toroid body.

Description

An apparatus for supply of cooling water from the sea to a process aboard a turret- anchored vessel

The invention relates to an apparatus for supply of cooling water from the sea to a process aboard a floating vessel for the production of hydrocarbons, where the vessel is anchored by means of a turret which is mounted in a receiving space in the hull of the vessel allowing the vessel and to turn about an axis of rotation, and which supports a swivel unit for the transfer of hydrocarbons from risers extending between the seabed and the turret, the apparatus comprising cooling water hoses depending from the turret to a depth for intake of cooled seawater, and a pumping means for pumping of water from the seawater hoses to a place of use for the process.

An apparatus of the above mentioned type is known from Norwegian patent application No. 1999 6449. This application shows a system for supply of cooling water from the sea to a vessel which is anchored by means of a rotating body which may be either a turret anchored to the seabed as stated above, or an underwater buoy of the bipartite Λype comprising a bottom-anchored central member and an outer member which is rotatably mounted on the central member.

The known apparatus distinguishes itself in that the rotating unit itself is designed as a swivel for the transfer of seawater, and the turret embodiment comprises a means for transferring seawater to an annulus which is arranged between the turret and the hull of the vessel and communicates with passages in the vessel hull, a seawater sealing means being arranged on each side of the annulus.

Thus, in the known apparatus the transfer of seawater takes place via a swivel unit which is situated in a receiving space in the vessel hull, so that the components of the apparatus partly are difficult to access for maintenance or replacement.

The object of the present invention is to provide an apparatus of the stated type where the transfer of seawater from the turret to the vessel takes place at deck level, something which, inter alia, results in an easy access for replacement or maintenance of components in the apparatus.

The above mentioned object is achieved with an apparatus of the introductorily stated type which, according to the invention, is characterised in that it comprises a toroid-shaped body which is stationarily 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 toroid 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 toroid 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 toroid body.

A preferred embodiment of the apparatus is characterised in that the outlets from the turret comprise of a number of pipe sockets extending downwards from an upper cantilever member of the turret, the means coupled to the outlets comprising an annular lid member for the toroid body, the pipe sockets being carried through the lid member in a sealing manner.

The invention will be further described below in connection with exemplary embodiments with references to the drawings, wherein

Fig. 1 shows a vertical cross-section through a turret and the surrounding part of a vessel hull, and shows schematically some of the main elements in an embodiment of an apparatus according to the invention;

Fig. 2 shows a schematic plan view of the lid member of the toroid body, with different associated devices shown schematically;

Fig. 3 shows an enlarged vertical cross-section along the line III-III in Fig.

Fig. 4 shows an enlarged vertical cross-section along the line IV-IV in

Fig.2;

Fig. 5 shows an enlarged vertical cross-section along the line V-V in Fig. 2; Fig. 6 shows an enlarged vertical cross-section along the line VI- VI in Fig.

2, and

Figs. 7 and 8 show a side view in a plane perpendicular to the sectional plane in Fig. 6, but for opposite rotational directions of the vessel relative to the turret.

Fig. 1 shows a vertical section through a part of the hull of a vessel 1 which is provided with a through-going receiving space 2 in which there is rotatably mounted a circular cylindrical turret 3. The turret is provided with an upper cantilever member 4 and is mounted on the deck 5 of the vessel by means of a combined axial and radial bearing means 6, so that the vessel under the influence of wind and weather can turn about the turret about an essentially vertical axis of rotation X-X. An annular opening 7 is present between the wall of the receiving space and the outer surface of the turret.

The turret 3 is anchored by means of a number of anchor chains 8 (only one shown) which are carried vertically through the turret 3 and are connected through respective anchor winches 9. Further, the turret is supplied with a number of vertical passages 10 for risers 11 for produced hydrocarbons and for injection. The risers are in a usual manner connected to a swivel stack 12 which is mounted on top of the turret and which is coupled to a pipe system (not shown) on the vessel for the transfer of hydrocarbons, etc.

A gantry structure 13 is mounted on the deck of the vessel above the turret. This structure supports a winch 8 for pull-in of risers and seawater hoses. The gantry structure, and also a superstructure 15 on the turret 3, further are shown to be provided with respective openings 16 and 17, respectively, for pull-in of risers, seawater hoses and seawater lift pumps (described below).

The seawater which is to be used as cooling water on the vessel, is taken in at the bottom of the turret 3 through a number of seawater hoses 18 (only one is shown). These are suspended at the bottom of the turret via bending stiffeners 19.

The seawater hoses in principle can hang freely down from the turret or be arranged via a catenary configuration to a riser tower. In the latter case one will take in the seawater via the tower and guide it into the hoses via for instance a manifold device. This solution is especially suited in regions where the surface water has a high temperature, and where one has to get down to a large depth to get hold of cold seawater. The solution to hang the seawater hoses from the turret, either freely or via a catenary configuration to a riser tower, is advantageous for a turret-anchored vessel, as the seawater hoses do not get in conflict with the anchoring lines, specially if these are equipped with buoyancy buoys which are normally used in deep water. By arranging the seawater hoses from the turret one can take in seawater at such a large depth as desired without getting in conflict with the anchoring lines, something which will happen if the seawater hoses are arranged from the hull itself.

The lower part of the turret 3 is arranged as a reservoir 20 into which the seawater can flow through the seawater hoses. In the reservoir there are placed lift pumps 21 lifting the seawater up to a level causing it to flow freely over to the deck level on the vessel. The inflow to the reservoir 20 in the turret is initiated and maintained in that the seawater in the reservoir 20 in the turret is pumped down to a level which is below the seawater level outside. The level to which the water in the reservoir can be pumped without the lift pumps 21 taking in air, is dimensioned based on the flow resistance existing from the inlet of the seawater hoses 18 and into the reservoir in the turret, and further dimensioned based on possible effects of salinity and temperature of the seawater from the relevant depth.

As shown in Fig. 1, in connection with the lift pumps 21 there are arranged vertical guide pipes 22 in the turret, for lowering and pulling-up of the pumps. Further, there are arranged a number of guide pipes 23 for pull-in and replacement of seawater hoses 18.

An embodiment of the apparatus for transferring cooling water from the sea to the relevant process on the vessel will be described below. As appears from Fig. 1, a ring-shaped or toroid-shaped body (hereinafter called toroid body) is 28 stationarily arranged on the deck 5 of the vessel 1, concentric with the axis of rotation X-X of the vessel 1. The toroid body is arranged below the cantilever member 4 of the turret, at a radius inside of the bearing means 6 of the turret. The turret 3 is provided with a number of outlets 29 for transfer of water to the toroid body, the outlets being coupled to transfer pipes 30, 31 which are coupled to the lift pumps 21.

Below the toroid body 28 there is arranged a container body 32 which communicates with the toroid body, to receive water which is supplied to the toroid body from the outlets 29. Thus, the container body 32 constitutes a seawater reservoir from which the seawater is pumped further for use as a cooling medium in the processing plant on the vessel, or for cooling of gas to liquid form (LNG). The reservoir for this purpose is provided with a number of outlets to cooling water pipes 33 in which there are connected pumps 34 for increasing the water pressure towards the processing plant on the vessel.

As suggested in Fig. 1, the apparatus also comprises a means 35 which is connected to the turret outlets 29 and which is provided with sealing means to prevent water leakage from the toroid body 28. In the present embodiment, which is shown in more detail in Figs. 2-6, the means 35 comprises an annular lid member

36 for the toroid body 28, and different elements associated with the lid member.

A schematic plan view of the lid member 36 with associated elements is shown in Fig. 2. In the figure there are shown four sectional views III-III, IV-IV, V- V and VI- VI, and the arrangements according to these views will be further described below.

Fig. 3 shows an enlarged sectional view along the line III-III in Fig. 2. As appears, the turret outlets 29 in this embodiment comprise a number of pipe sockets

37 projecting downwards from the cantilever member 4 of the turret, and the pipe sockets are carried through the lid member in a sealing manner. The pipe sockets 37 are carried with a clearance through a central flanged opening 38 in the lid member 36, and the lid member is sealingly connected with the pipe sockets via respective bellows elements 39 allowing a relative movement between the lid member and the pipe sockets.

As shown, the toroid body comprises inner and outer walls 40 and 41, respectively, which, on their mutually confronting sides, are provided with peripherally extending flanges 42 and 43, respectively, forming gasket holders for receipt of a respective annular gasket 44 and 45, respectively, forming a seal against the upper surface of the lid member 36. By means of this sealing arrangement, water leakage from the interior of the toroid body 28 is prevented. As further shown, the lid member 36 is dimensioned such that there is a clearance "L" between the outer and inner walls, 40 and 41, respectively, of the toroid body and the adjacent circumferential edges of the lid member.

The container body 32 which is arranged below the toroid body 28 as mentioned above, here consists of an annular reservoir member having walls which are formed integrally with the walls of the toroid body. The toroid body communicates with the reservoir member via a diffuser means 46 providing for a controlled and as much as possible stationary course of flow into the reservoir member 32.

Further, the toroid body 28 is provided with an outlet pipe 47 for discharge of excess water from the toroid body. This allows for the lift pumps 21 in the turret reservoir 20 to be dimensioned so that they pump a constant and lager volume of seawater into the toroid body/reservoir member than that used in the process. The excess water runs into the annular space 37 between the turret and the vessel. A valve 48 is arranged in the outlet pipe 47, for control of the discharge. This arrangement will require only a simple form of control loop between the lift pumps 21 in the turret reservoir and the pumps 34 pumping seawater into the process on the vessel.

Fig. 4 shows an enlarged sectional view along the line IV-IV in Fig. 2. The figure shows one of a number of hydraulic cylinders 49 which are mounted between the cantilever member 4 of the turret and the lid member 36. These have the purpose to maintain a desired constant pull on the lid member, to thereby achieve a controlled surface pressure on the gaskets 44, 45. The hydraulic cylinders are coupled to a reservoir of nitrogen and oil, with an arrangement of valves allowing relative, vertical displacement between the turret and the vessel without the surface pressure of the gaskets 44, 45 being significantly changed, allowing the loads which are transferred to the lid member and thereby to the toroid body, to be controlled.

Fig. 5 shows an enlarged sectional view along the line V-V in Fig. 2. As appears, the lid member 36 of the toriod body has an opening 50 which is connected to an outlet pipe 51 for possible discharge of water, for providing an overpressure protection in case the outlet pipes 47 of the toriod body should not manage to take off all the excess water. The outlet pipe 51 has a downwardly extending outlet pipe which is adapted so that discharging water runs into the annular space 7 between the turret and the vessel. As appears from Fig. 2, there are arranged four such outlet pipes from the lid member. The overpressure protection is to see to it that the toroid body, the lid member and the gaskets are not overloaded if the outlet pipes 47 become too small for discharging the excess water.

Fig. 6 shows an enlarged view along the line VI- VI in Fig. 2. The figure shows one of a number of carrier members 52 projecting downwards from the cantilever member 4 of the turret and being arranged to cooperate with a carrier means on the lid member 36, to hold the lid member against the turret in case of turning of the vessel about the turret. The carrier means on the lid member consists of a pair of brackets 53, 54 which, as shown in Figs. 7 and 8, are mutually spaced in the circumferential direction of the lid member, to allow a certain turning of the vessel before the appurtenant carrier member 52 on the turret 3 comes into engagement.

The lid member 36 further is provided with a circumferentially extending centering rail 55 which cooperates with the carrier members 52 of the turret, to centre the lid member 36 with a clearance against the walls 40, 41 of the toroid body.

The lid carrier and centring units thus have two functions, viz.

• to see to it that the lid member is held fixedly to the geostationary turret when the hull of the vessel turns to keep the bow up against the dominating wind and wave direction, and

• to centre the lid member with a clearance against the walls of the toroid body, so that horizontal, relative displacement between the turret and the vessel can be accepted at any time.

The carrier brackets 53, 54 on the lid member 36 are arranged to take a respective turning direction of the vessel hull. This is illustrated on Figs. 7 and 8 where the arrows Al and A2 show the direction of rotation of the vessel.

As mentioned, the distance between the brackets 53, 54 allows a certain turning of the vessel hull before the turret carriers get into engagement. This reduces the number of times one gets a movement of the lid member in relation to the toroid body, something which gives reduced wear of the gaskets. The distance between the carrier brackets is adapted to the clearance between lid member and pipe sockets, so that constraining forces are not applied to the pipe sockets.

Claims

P a t e n t c l a i m s

1. An apparatus for supply of cooling water from the sea to a process aboard a floating vessel for the production of hydrocarbons, where the vessel (1) is anchored by means of a turret (3) which is mounted in a receiving space (2) in the hull of the vessel allowing the vessel (1) to turn about an axis (X-X) of rotation, and which supports a swivel unit (12) for the transfer of hydrocarbons from risers (11) extending between the seabed and the turret (3), the apparatus comprising seawater hoses (18) depending from the turret (3) to a depth for intake of cooled seawater, and a pump means (34) for pumping of water from the seawater hoses to a place of use for the process, characterised in that it comprises a toroid-shaped body (28) which is stationarily arranged on the deck (5) of the vessel (1), concentric with the axis (X-X) of rotation of the vessel, a number of outlets (29) for the transfer of water from the turret (3) to the toroid body (28), the outlets being coupled to means (30, 31) for transferring water supplied to the turret from the seawater hoses (18), a container body (32) which communicates with the toroid body (28) to receive water supplied thereto from the outlets (29), and a means (35) which is coupled to the turret outlets (29) and is provided with sealing means (42, 43) to prevent water leakage from the toroid body.

2. An apparatus according to claim 1, characterised in that the outlets (29) from the turret (3) comprise a number of pipe sockets (37) extending downwards from an upper cantilever member (4) of the turret (3), the means (35) coupled to the outlets comprising an annular lid member (36) for the toroid body (28), the pipe sockets (37) being carried through the lid member (36) in a sealing manner.

3. An apparatus according to claim 2, characterised in that the pipe sockets (37) are provided with a clearance through the lid member (36), and that the lid member (36) is sealingly connected to the pipe sockets (37) via respective bellows elements (39) allowing relative movement between the lid member and the pipe sockets.

4. An apparatus according to claim 2 or 3, characterised in that the toroid body (28) has outer and inner walls (40, 41) which on their mutually confronting sides above the lid member (36) are provided with peripherally extending flanges (42 resp. 43) forming gasket holders to receive annular gaskets (44 resp. 45) forming a seal against the upper surface of the lid member (36).

5. An apparatus according to claim 4, characterised in that a number of hydraulic cylinders (49) are mounted between the lid member (36) and the cantilever member (4) of the turret (3), to maintain a constant pull on the lid member.

6. An apparatus according to claim 4 or 5, characterised in that the lid member (36) is dimensioned so as to give a clearance (L) between the outer and the inner walls (40 resp. 41) of the toroid body (28) and the adjacent circumferential edges of the lid member (36).

7. An apparatus according to one of the claims 2-6, characterised in that the cantilever member (4) of the turret (3) is provided with a number of downwards projecting carrier members (52) cooperating with a carrier means (53, 54) on the lid member (36), to hold the lid member against the turret (3) when the vessel (1) turns about the turret.

8. An apparatus according to claim 7, characterised in that the carrier means on the lid member (36) consists of two brackets (53, 54) which are mutually separated in the circumferential direction of the lid member, to allow a certain turning of the vessel (1) before the appurtenant carrier member (52) on the turret (3) comes into engagement.

9. An apparatus according to claims 7 or 8, characterised in that the lid member (36) is provided with a circumferentially extending centering rail (55) which cooperates with the carrier members (52) of the turret (3) to centre the lid member (36) with a clearance towards the walls (40, 41) of the toroid body (28).

10. An apparatus according to one of the previous claims, characterised in that the lower part of the turret (3) contains a water reservoir (20) for seawater supplied from the seawater hoses (18).

11. An apparatus according to claim 10, characterised in that the water reservoir (20) of the turret (3) is connected with the turret outlets (29) via respective pipelines (30, 31) which, at their lower end, are provided with a lift pump (21) for pumping the seawater to the turret outlets (29).

12. An apparatus according to claim 11, characterised in that the lift pumps (21) are dimensioned to supply a larger volume of seawater to the toroid body (28) than that used in the process on the vessel (1), and that the toroid body (28) in its upper part is provided with an outlet pipe (47) for discharge of excess water to the annular space (7) between the turret (3) and the vessel hull.

13. An apparatus according to claim 12, characterised in that the lid member (36) of the toroid body (28) is connected with a number of outlet pipes (51) for discharge of water via respective openings (50) in the lid member (36) to the annular space (7) between the turret (3) and the vessel hull, for providing pressure protection in case the outlet pipes (47) for the excess water do not manage to take off all the excess water.

14. An apparatus according to one of the preceding claims, characterised in that the container body (32) consists of an annular reservoir member which is arranged below the toroid body (28) and is connected to this via a diffuser device (46).

15. An apparatus according to claim 14, characterised in that the reservoir member (32) is provided with a number of transfer lines (33) in which there are connected pumps (34) for increasing the seawater pressure towards the processing plant on the vessel (1).