AU2008361718A1

AU2008361718A1 - Floating unit for storage of gas

Info

Publication number: AU2008361718A1
Application number: AU2008361718A
Authority: AU
Inventors: Kare Syvertsen
Original assignee: Sevan Marine ASA
Current assignee: Sevan Marine ASA
Priority date: 2008-09-11
Filing date: 2008-09-11
Publication date: 2010-03-18
Also published as: BRPI0823079A2; KR20110050671A; CN102149598A; WO2010030187A1

Description

WO 2010/030187 PCT/N02008/000323 1 Floating unit for storage of gas 5 The present invention relates to a floating unit for storing of liquefied gas comprising a platform body having a shape for storing of cooled gas (LNG, LPG and such). NO 319 971 discloses a circular floating platform for production of and drilling for oil. This type of platform has large storing capacity for oil and ballast in segregated 10 tanks in the hull, large capacity for deck cargo, may be anchored in a fixed orientation using conventional mooring equipment, i.e. it need not to rotate with the weather, avoids transfer of gas, liquid, current, etc. through a swivel, and a large number of risers may be connected to a fixed point. Today's technology for storing of liquefied gas mainly is based on storing of 15 liquefied gas in tanks on shore. Only lately, solutions have been presented where units comprising tanks for liquefied gas have been placed off shore. Some of the suggested solutions are placed on the bottom of the sea, whereas some are arranged in floating units (barges of ship hulls). Common for these is that they comprise a number of tanks in the same way as ships built for transportation of liquefied gas. For ship hulls there 20 are used the following three different types of tanks - ball tanks in aluminum. The tanks are self supporting and supported in the hull on a "stomach girdle". - membrane tanks comprising thin plates of stainless steel abutting the insulation. The steel plates in this structure do not contribute a strengthening element, merely as a seal 25 towards the gas. The thin steel plates are arranged with a certain corrugation to absorb deformations due to temperature variations. In membrane tanks usually two membrane layers are used as there exists a certain risk for puncturing the thin membrane plates. - self-supporting "conventional" tanks. These are tanks which may have been built in stainless steel or aluminum. The concept is based on building of free standing tanks 30 arranged in rooms/tanks in the ship hull. All tanks are insulated on the exterior side of the plates and the insulation must be sufficient to maintain gas stored at temperatures down to -170 *C. It is therefore important to have as small surface as possible. Typical divisions of the tank volume in a ship hull are division in 4-8 tanks depending on the arrangement, the size of the ship 35 etc. The purpose of the present patent application is to further develop the cylindrical shape of the platform described in NO 319 971 for the use of liquefied storing for cooled gas (LNG and LPG). This is achieved with the platform according to the present invention as defined by the features stated in the claims.

WO 2010/030187 PCT/N02008/000323 2 The invention will be described further in the following in connection with embodiments disclosed in the drawing where figure 1 discloses a platform according to the invention, seen from the side, figure 2 discloses a platform of figure 1 seen from above, figure 3 discloses a section C-C in figure 2, figure 4 discloses a section A-A in 5 figure 3, figure 5 discloses a section B-B in figure 3, figures 6 and 7 disclose a ship anchored to a quay arrangement on the platform and figure 8 discloses a ship anchored to the platform without a quay arrangement. It is referred to figures 1-8. A floating gas storage 1 as disclosed above, comprises a circular hull 2 having a large tank 3 in the centre. On top of the hull 2 and 10 partly integrated in the upper part of the hull, is arranged living quarters 4, equipment modules 5, plant 6 for re-gasification, cooling plant for gas etc. The hull 2 comprises a bottom section 7 (double bottom), a cylindrical side section 8 and an upper equipment section 9. The bottom section 7 is designed as a conventional double bottom, however 15 with a height sufficient to carry all loads coming from exterior sea loads and internal tank pressure. The bottom structure is divided into tank sections 10. The tank sections from the lower part of the ballast tanks. In the centre portion 11 of the bottom section 7 is arranged a centre section comprising pumping room where all ballast pipes, ballast valves and ballast pumps are arranged. Admission to the centre section preferably will 20 be down through the side section and further through an access shaft into the centre. Admission also may be through a vertical section (not disclosed) in case it is chosen to arrange such a section in the gas tank. The side section 8 of the hull is shaped as double hull having an exterior hull side 13 and internal bulkheads 14. The external plates 13 are dimensioned to bear loads 25 from the sea etc. whereas the internal plates 14 are dimensioned to receive forces transferred from local tanks in the side and loads transferred from the tanks comprising liquefied gas. The lower part 15 of the side section 8 is used as ballast tanks 10. The ballast tanks 10 in the side are shaped as a continuation of the ballast tanks in the bottom. 30 Filling and emptying of these tanks may be performed from the centre section in the bottom. In the upper part 17 of the side section 8 spaces may be made for tanks, storing, equipment and machinery, living quarters, etc. The bottom section 7 and the side section 8 is such designed that they can withstand loads from the outer water 35 pressure, from loads transferred from the tanks in the centre section and loads from different tanks and equipment arranged in or on the hull sections. The main store for liquefied gas comprises a large, cylindrical tank or a division into several tanks 23, 25. The tanks must be constructed of a material able to withstand low temperatures, such as stainless steel or aluminum of suitable quality. The WO 2010/030187 PCT/N02008/000323 3 tanks will be constructed in such a way that they rest on the bottom section 7. All vertical loads are transferred as pressure to the insulation box 27 (shaded area between the internal tank and the bottom section) under the tank 3 and further to the bottom section 7. The sides in the tanks may be self-supporting, partly self-supporting or being 5 such shaped that all load is transferred to the insulation blocks and further to the side bulkhead 14 in the hull 2. This will depend on which detail design is used to build the tank skin 3'. It also may be adequate to arrange an additional barrier to intercept gas in case of a leakage in the other tank skin. The volume in the hull which the tanks occupy can vary between 50 and 90 % of the volume of the platform and most usual will be io between 85 and 90 % of the volume of the platform. In the centre of the tank 3 it will be arranged a vertical support structure 16 where piping system, pumps etc., which is used for handling the gas, will be arranged. As an alternative a vertical section (not disclosed) can be arranged in the centre giving excess to the pumping room in the centre of the bottom section 7. is The tank section also can be divided into more than one section 22, 23, 24, 25. By a division into several sections 22, 23, 24, 25 the tanks individually can be self supporting, or there may be arranged bulkheads between the sections. By division into several sections the same structure with the double bottom and the load bearing sides may be maintained. The division normally will have one of two alternatives, a first 20 embodiment where a cylindrical section 22 with sections 23 are arranged around in sectors out from the core and a second embodiment where a hexagonal section 24 is arranged in the centre of the tank with the rest of the section 25 in sectors outwardly from each corner 26 of the hexagon 24. Equipment on the floating unit may be arranged in the upper part of the side 25 hull 17 on deck or in individual modules 9, 18 arranged on deck. In the upper part 17 of the hull sides there is a relatively large volume which can be utilized for equipment. Here it also is possible to store what will be needed of water and fuel tanks etc. The living quarters 4 may be arranged in this part of the hull or as a section 9 on deck. 30 The equipment modules 5, 6 for which space has to be reserved, are equipment for generating of power, receiving arrangement for import of liquefied gas, re gasification plant for export of dry gas through pipe lines, cooling plant for boiled gas, helicopter deck 19 with corresponding arrangement, etc. The receiving plant for gas may be through flexible hoses 20 from a gas tanker 35 being anchored or there may be arranged "quay structures" 21 along one of the sides of the gas storage 1. A gas tanker then may be moored conventionally and loading may be performed by standard equipment. The gas unit may be ballasted during the loading operation, such that it maintains approximately constant draught.

WO 2010/030187 PCT/N02008/000323 4 Export of the gas may be performed through flexible hoses (risers). The hose may be withdrawn into a protection pipe in the hull thereby reducing the risk for damage from the ship or from external waves. Alternatively the export hose may be secured to a connection point on the side of the unit.

Claims

1. Floating unit for storing of liquefied cooled gas, comprising a semi 5 submersible platform body (2) supporting such equipment and living quarter arranged in the upper part of the unit and storing tanks for gas in the centre part, whereby the platform body (2) being shaped as a vertical cylinder having a substantially flat bottom, and that the diameter of the platform body being substantially larger than the draft, where the buoyancy centre for the submerged part of the platform (1) is arranged lower 10 than the centre of gravity of the platform, characterized in that it comprises an outer cylindrical hull having integrated tanks for ballast, fuel, water, etc., equipment room having strength enough to carry internal and external loads and an individual tank for storing liquefied gas arranged in the centre of the hull.

2. Platform according to claim 1, characterized in the tank in the centre of the 15 hull having between 80 and 90 % of the diameter of the platform.

3. Platform according to claim 1, characterized in that the tank in the centre of the hull being protected by a double bottom and double sides.

4. Platform according to claim 1, characterized in that the tank in the centre of the hull may be divided into several tank sections. 20

5. Platform according to claim 1, characterized in the platform being anchored with mooring lines making it possible to anchor independently of the water depth.

6. Platform according to claim 1, characterized in that it may be loaded directly from the ship with liquefied gas directly into the platform through a 25 conventional loading system for liquefied cooled gas with the ship moored to a quay arrangement on the hull.

7. Platform according to claim 1, characterized in that it may be loaded directly from a ship with liquefied gas and into the platform through a flexible hose of suitable quality, said ship may be suspended in an anchoring system. 30

8. Platform according to claim 1, characterized in there may be installed plants on the platform being able to regas liquefied gas in such a way that it may be exported as dry gas.

9. Platform according to claim 1, characterized in that dry gas may be exported from the platform through one or several flexible hoses (riser) being 35 connected to gas pipes or a gas pipe net on the seabed.

10. Platform according to claim 1, characterized in that there may be installed equipment and arrangements covering all needs for operation on the platform.