Floating LNG plant

Abstract

The present invention relates to a floating LNG plant (1, 1, 100) comprising a converted LNG carrier with a hull and a plurality of LNG storage tanks (4, 104) wherein in that the floating LNG plant (1, 1, 100) comprises: at least one sponson (2, 2, 3, 3, 102, 103) on the side of the hull, for creating additional hull volume, process equipment (110) for LNG processing on the floating LNG plant (1, 1, 100), anda reservoir for storing fluids separated during the LNG processing, wherein said reservoir is formed by the ballast tank or in the space reserved for the ballast tank of the original LNG carrier.

Claims

1. A floating LNG plant comprising: a converted LNG carrier with a hull and a plurality of LNG storage tanks; at least a first sponson on one side of the hull for creating additional hull volume, wherein the at least first sponson is a double-walled sponson and is arranged to provide double hull protection; LNG process equipment for LNG processing on the floating LNG plant; a reservoir for storing fluids separated during the LNG processing, wherein a process equipment module for LNG processing on the floating LNG plant is installed on additional deck space created by adding of the at least first sponson on the one side of the hull, and a part of the process equipment module weight is supported by the hull of the converted LNG carrier with outboard module supports connected to the at least first sponson; and a new ballast tank in the additional hull volume created by the at least first sponson on the side of the hull, wherein a function of an original ballast tank that was present in an internal hull space of the converted LNG carrier is taken over by said new ballast tank and wherein the internal hull space for the original ballast tank is used for storing residual fluids which are produced in an LNG liquefaction process, wherein said residual fluids comprise at least one of oils and condensate.

2. The floating LNG plant according to claim 1, wherein the process equipment module for LNG processing on the floating LNG plant is installed on additional deck space created by the at least first sponson on the side of the hull.

3. The floating LNG plant according to claim 2, wherein the at least first sponson is used for supporting LNG transfer devices for at least one of loading or unloading LNG.

4. The floating LNG plant according to claim 3, wherein the converted LNG carrier is an LNG FPSO that is provided with the first sponson on the one side and a second sponson on another side of the converted LNG carrier, the first sponson is used for supporting the LNG transfer devices and the second sponson is used for supporting the LNG process equipment.

5. The floating LNG plant according to claim 3, wherein the at least first sponson is used for storage of a floating offloading hose.

6. The floating LNG plant, according to claim 1, wherein a power generation unit is placed within the at least first sponson.

7. The floating LNG plant according to claim 1, wherein the converted LNG carrier is an LNG FPSO that comprises a mooring system and a fluid transfer system, the fluid transfer system including a swivel and piping connecting the swivel to the LNG process equipment for LNG processing.

8. The floating LNG plant according to claim 7, comprising an external turret in order to allow the floating LNG plant to be weathervaning moored to a seabed via said external turret.

9. The floating LNG plant according to claim 7, comprising an offloading buoy in order to allow the floating LNG plant to be weathervaning moored to a seabed via said offloading buoy.

10. The floating LNG plant according to claim 1 wherein an outer shell of the at least first one sponson is provided with a collision protection.

11. The floating LNG plant according to claim 10, wherein the outer shell of the at least first sponson is protected against collision damage using SPS.

12. The floating LNG plant according to claim 1, wherein the space for the original ballast talk is used to partially house a newly constructed tank for said fluids wherein said tank extends for its remaining part into the space created by the adding of the at least one sponson.

13. The floating LNG plant according to claim 1, wherein the original ballast tank is used for storing said fluids.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention and the advantages thereof will be better understood, after the description below, which makes reference to the drawings, wherein:

(2) FIG. 1 shows a side and a top view of a possible embodiment of a floating LNG plant according to the present invention, which is moored via an external turret;

(3) FIG. 2 shows a cross section of the floating LNG plant according to FIG. 1;

(4) FIG. 3 shows a cross section of a alternative embodiment of the floating LNG plant according to the invention;

(5) FIG. 4 shows a plan view of a gas distribution system using a floating LNG plant according to the present invention;

(6) FIG. 5 shows an alternative offloading system for the LNG FPSO according to the present invention; and

(7) FIG. 6 shows a possible embodiment of the LNG FPSO according to the present invention which is adapted for side by side offloading.

(8) FIG. 1 shows a side and a top view of a possible embodiment of a floating LNG plant 1 according to the present invention. In FIGS. 1-6, reference is made to a floating LNG plant which has the form of an LNG FPSO. It should be understood that the advantages of the current invention can also be used in converting an existing LNG carrier into another floating LNG plant, such as an FSRU or an FPGU. The FPGU and FSRU are not shown in the figures.

(9) Typically, an FPGU would have power generation unit, equipment for gas treatment and power export facilities such as cables. If required, an FPGU could also be equipped with liquid export facilities.

(10) Typically, an FSRU would have equipment in order to transform LNG into gas. The floating LNG plant 1, according to the present invention, is moored via an external turret 10. The floating LNG plant 1 can weathervane around the turret 10. The floating LNG plant 1 is obtained by converting an existing LNG carrier vessel. The original LNG carrier vessel is for instance a Moss type tanker which has a steam boiler propulsion system.

(11) If the facility is to be used on a relatively rich gas field with a high condensate production rate the additional revenue it will generate will easily fund a separate condensate FSO (not shown), located nearby. This approach means that a relatively cheap standard LNG FPSO 1 can be built for both lean and rich gas fields, and can increase the potential opportunities for relocation.

(12) As can be seen in the top view in FIG. 1, the floating LNG plant 1 has a relatively wide sponson 2 on the larboard side of the hull. On the starboard side the floating LNG plant 1 is provided with a sponson 3 which is smaller then the sponson 2 on the larboard side.

(13) It has to be understood that the floating LNG plant 1 could also be equipped with similar sized sponsons on both sides of the vessel 1.

(14) According to FIG. 1 the original moss type tanker and therefore the floating LNG plant 1 is provided with 5 or 4 LNG tanks. The use of the moss type tanker has the advantage that the spherical moss type of LNG storage tanks provides ideal slosh tolerant storage for LNG and LPG.

(15) According to FIG. 1 the floating LNG plant 1 is provided with an external turret 10. In an alternative embodiment (not shown) the floating LNG plant 1 could be provided with an alternative mooring system with an internal turret mooring system (not shown), such as a disconnectable (submerged) offloading buoy. The construction of such a disconnectable offloading buoy is well known in the art and will not be described in detail. Another alternative mooring system (not shown) is a well known spread moored mooring arrangement that is non-weathervaning.

(16) In the embodiments shown in FIG. 1 the external turret 10 allows the floating LNG plant 1 to be designed with the ability to disconnect, for example for operation in cyclone areas, or for quick hook-up and/or ease of relocation on several very small gas fields in a campaign approach to gas monetization. Quick mooring line disconnection means also that major refits or maintenance can much more readily be carried out in a yard and returned quickly to service. The Riser Turret Mooring (RTM) would be ideal for this type of facility.

(17) Possible embodiments of the sponsons 2 and 3 are shown in FIGS. 2 and 3.

(18) As will be explained with reference to FIGS. 2 and 3, the additional sponsons 2 and 3 are fixed to the hull 5, 5 and offer all the required additional volume and space both above and below deck for the additional equipment which is required to provide the LNG carrier vessel to be operated as a LNG FPSO. The steam drive of the ship provides an installed boiler with which all of the electrical demand can be supplied through new steam turbine generators (not shown) which could be located in the sponsons 2, 3.

(19) The sponsons 2, 3 are designed to expand the width of the ship up to the maximum width that is still able to enter the majority of dry docks in the world. This means that the overall width is limited to about 59 m.

(20) According to FIG. 2 the sponson 3 at the starboard side of the floating LNG plant 1, 1 is provided with a space which serves as a ballast tank. That means that the original ballast tank that is present in the internal hull space indicated with reference number 11 can get a new function, the function of ballast is taken over by the space 31 in the sponson 3. The former ballast tank available in the space 11 can now be used for storing condensate or other residual fluids which are produced in the LNG liquefaction process.

(21) At the starboard side the floating LNG plant 1 has an improved collision protection by the presence of the sponson 3. The collision protection could be improved by using a double walled sponson 3. The collision protection could be even further improved against collision damage by using a polymer based plate structures such as SPS (Sandwich Plate System).

(22) According to FIG. 2 the sponson 2 at the starboard side of the floating LNG plant 1 is provided with a space 21 which serves as a ballast tank. The interior of the remaining part of the sponson 2 in combination with the space that was originally reserved for a ballast tank (see starboard side) is used to created a new storage space 22 used for storing condensate or other residual fluids which are produced in the LNG liquefaction process. That means that the original ballast tank on the larboard side has been removed or enlarged in order to create the relatively large storage space 22 on the larboard side of the floating LNG plant 1.

(23) In FIG. 3 an alternative arrangement for the sponsons 2 and 3 is shown. According to FIG. 3 the sponson 3 at the starboard side has a similar configuration as the sponson 3 according to FIG. 2 in order to allow the original space for the ballast tank 11 to be used for storing condensate or other residual fluids which are produced in the LNG liquefaction process. The space 31 is available to serve as ballast tank.

(24) The sponson 2 at the larboard side of the floating LNG plant 1 according to FIG. 3 is provided with a space 22 which comprises the interior of the sponson 22 in combination with the space that was originally reserved for a ballast tank (see starboard side) to created a relatively large storage space 22 for storing condensate or other residual fluids which are produced in the LNG liquefaction process.

(25) In order to improve the collision protection of the floating LNG plant 1 according to FIG. 3 the exterior of the sponson 2 is provided with an adapted collision protection 40. This collision protection 40 is adapted to absorb energy during an impact in order to avoid or limit damage to the part of the floating LNG plant 1 that comprise either equipment for the LNG liquefaction process or that comprise storage space either for gas or for the condensate or other residual fluids which are produced in the LNG liquefaction process.

(26) As shown in FIGS. 1, 2 and 3 the sponsons 2 and 3 provide a large amount of additional deck space for several uses. This will make the concept feasible without removing any of the existing LNG tanks 4.

(27) The length of the sponson 2, 2, 3, 3 can be used for lengthwise storage of a floating LNG offloading hose. This could for instance be in a gutter on the spoon deck or within the sponsons 2, 2, 3, 3. The LNG offloading hose would be used for a known tandem offloading configuration of two vessels. In case the floating LNG offloading hose would be stored in this way, no hose real is needed on the haft of the floating LNG plant 1. It should be noted that a hose real normally takes a lot of deck space.

(28) A standard LNG moss type carrier has either four or five tanks 4. The tanker according to FIGS. 1-4 has 5 tanks. Retaining all tanks 4 means that with one taken out of service temporarily for inspection or maintenance the remaining tanks 4 will be able to be used to provide an effective ongoing operation with one tank for LPG and two or three tanks used for LNG.

(29) It is envisaged that a floating LNG plant 1 with sponsons 2, 2, 3, 3 of say less than 4-5 m breadth, oil/condensate would be stored in tanks that had previously been used for ballast. Broader sponsons 2, 2, 3, 3 would allow the combined storage of both hydrocarbons and tanks for dynamic ballast systems within the new structure.

(30) The top side of the sponsons 2, 2, 3, 3 does not need to be flat and does not need to be flush with the tanker's main deck. The sponsons 2, 2, 3, 3 may be connected (horizontally, upper) below the main deck which is preferable both for constructability and for reducing stress concentrations at the connection. A substantial part of the module weight will be supported by the existing vessel with the outboard module supports (legs) connected to the sponson 2, 2, 3, 3. As the upper part of the sponson 2, 2, 3, 3 may be lower than the main deck then the outboard module legs will be longer than those inboard supports which are connected to the existing deck.

(31) A possible arrangement for the liquefaction process comprises, among other elements: steam Turbine electrical Generators (STG) and associated vacuum condenser exchangers, Seawater lift pumps, storage space 11, 11, 22, 22 for a quantity of stabilised condensate, condensate export pumps, sea water lift deep-well electric pumps mounted in caissons, sea water used for cooling of topside equipment, cooling Medium/Seawater (CM/SW) plate exchangers for main process cooling located below sea level to reduce power demand on the sea water lift pumps, additional ballasteither active SW or passive permanent inhibited water, local Equipment Room (LER) that contains electrical/motor switchgear and some local control equipment can be built long and thin, or divided into two rooms (one for electrical and one for instruments), storage of any potential single mixed refrigerant make up refrigerants, if applicable (typically ethane, propane and butanes), air compressors, driers, nitrogen generation, fresh water makers (some or all of these may be fitted within the engine room depending on the tanker design), fore-to-aft escape tunnel (this may be above deck, or not installed at all), fore to aft cable ways and fire water piping headers (these may also be above deck), gas turbine driven compressor modules for the LNG refrigeration system, end flash and boil off gas compressors (if required), LNG export system equipment for side-by-side offloading (hose or rigid arm system possible), inlet conditioning (separation, heating and/or cooling) facility, condensate stabilisation facility, mol sieve dehydration facility, amine CO2 removal facility, mercury removal facility, LPG extraction (distillation) facility, fuel Gas system, flare drums and stack/vent masts, lay-down module and cranes.

(32) The LNG FPSO will also comprise a refrigeration facility, including a main LNG refrigeration plant, which is to be powered by direct mechanical drive. Ideally such a LNG refrigeration plant uses two 50% gas turbines and is located on the top of one of the sponsons 2, 2, 3, 3.

(33) The simplest refrigeration system that is best suited to this concept is one of the dual refrigerant loop nitrogen and methane based systems because there is no need to produce or store refrigerants. An alternative providing slightly higher production capacity (assuming the same installed drivers) is to use a single mixed refrigerant. In this case make up refrigerants would be stored in up to four very slim type-C tanks mounted very close to the refrigeration equipment. In this case refrigerants should ideally be imported, not made on board to minimize weight, congestion, manning requirements and hence minimize CAPEX.

(34) The floating LNG plant 1 according is adapted to allow LNG transfer between the floating LNG plant 1 and a LNG carrier. This LNG transfer is schematically indicated in FIG. 4.

(35) The gas is being transferred from the riser via the turret 10 to the process equipment on board of the floating LNG plant 1 where the gas is liquefied into LNG. Thereafter the LNG is stored within the LNG storage tanks 4. In order to offload the LNG a LNG tanker 50 is connected to the floating LNG plant 1. Then the stored LNG is being offloaded to the LNG carrier 50 via a transfer LNG hose that can be of any type (floating, aerial, submarine).

(36) In FIG. 4, the offloading configuration shown between the floating LNG plant 1 and the LNG carrier 50 is a tandem offloading configuration where hawsers 18 are used to connect the LNG carrier to the LNG FPSO, the transfer LNG hose is for instance a flexible floating cryogenic hose 19.

(37) FIG. 4 shows a plan view of a gas distribution system 60 using a floating LNG plant 1 according to the present invention. The gas distribution system 60 shown in FIG. 4 includes a floating LNG plant 1 that stores large amounts (in the order of at least 50 million standard cubic feet) of LNG produced from gas extracted from a distant LNG source 61. A mass of LNG is offloaded from the floating LNG plant 1 through the hose 19 to a LNG barge or shuttle tanker 50, which is provided with insulated tanks 51 where the very cold LNG is stored. The shuttle tanker 50 carry LNG from the floating LNG plant 1 to at least one of the local coastal station 70 that lies at the coast or near shore; for instance, in the vicinity of a community that consumes natural gas (either directly or by consuming electricity produced using natural gas as fuel). At intervals, the shuttle tanker 50 sails to the floating LNG plant 1, where insulated tanks 51 on the shuttle tanker receive LNG that has been temporary stored in the floating LNG plant 1. The shuttle tanker 50 then sails away to one of the local coastal stations such as 70.

(38) At the local coastal station 70, the LNG is transferred through an conduit 80 to an onshore regas storage facility 22 of the coastal station 70 (which may comprise a network of pipelines) where it is heated to into gaseous hydrocarbons and pumped into a gas distribution grid

(39) According to an alternative offloading system, shown in FIG. 5, the local coastal station includes a floating structure 85 such as an FSRU or a converted FSRU that is moored to the sea floor as by a gas discharge buoy or any type of receiving facility 25 moored by catenary lines, to allow the structure to weathervane, or that is spread moored. In the embodiment of a gas distribution system using a floating LNG plant 1 shown in FIG. 5, shuttle tankers 50 carry LNG from the floating LNG plant 1 to an offloading region where a LNG FSRU 85 has also been sailed. At this location, the FSRU 85 is designed to receive LNG from the LNG carrier 50 by lightering LNG, i.e. transferring the cryogenic liquid from ship to ship while sailing together at a safe location in calm waters away from the gas discharge buoy 25. After transfer of LNG, the FSRU sails to the coastal receiving facility and the shuttle tankers 50 returns to the floating LNG plant 1.

(40) FIG. 6 shows an alternative floating LNG plant adapted for a side by side offloading configuration. The floating LNG plant 100 comprises sponsons 102 and 103 each provided with a double hull protection by providing internal spaces 121 and 131 which provide either void or ballast space. These spaces 121 and 131 would typically be in the order of two meters in width.

(41) According to FIG. 6, the top of the sponson 103 is typically used in order to support part of the process equipment 110 in the side by side configuration shown in FIG. 6. The sponson 103 which is not used to moor a LNG carrier in a side by side offloading situation could be used for support of the most hazardous process modules. That means that those potentially dangerous process modules are not placed between the two vessels 150. The vessel 50 could be any type of known LNG tanker (or LNG Carrier). Offloading according to FIG. 6 is possible via an arrangement 11 comprising rigid loading arms which are mounted on the upper deck of sponson 102, or via short LNG transfer hoses or combinations of rigid arms and LNG hoses (both not shown)

(42) In order to improve safety of the arrangement according to FIG. 6, blast walls 115 can be placed between the potentially hazardous process modules on the sponson 103 and the spherical LNG storage tanks 104 or the LNG FPSO 100.