EP1562823B1 - Liquefied gas transfer installation and use thereof - Google Patents

Abstract

The installation is designed to transfer liquefied gas from a first surface reservoir (8) to a second surface reservoir (6) using a transfer line (28) designed to be connected to the reservoirs. The two reservoirs are spaced apart during the transfer and the transfer line is immersed in the water The first and second reservoirs are more than 300 m apart, and preferably more than 1 marine mile, during the transfer. A first terminal (8) carries the first reservoir and a second terminal (22), in particular a loading buoy, is spaced from the first terminal so the transfer line extends between the two terminals. The second terminal is designed to connect the transfer line to a loading pipe (24) with connectors (25) to the second reservoir carried by a vessel. The transfer line has a main rigid section (32) which is horizontal in the layer of water where dynamic movements are reduced and flexible sections (40, 42) which are vertical and which connect the ends of the main section to the terminals and ensure continuity of liquid gas transport and absorb the dynamic movements. The main rigid section is in a layer of water where the maximum speed of the current is less than 1 m/s, preferably less than 0.5 m/s. The main section and the flexible sections of the transfer line have an internal transfer line and an external casing defining an annular space which extends the whole length of the transfer line and which is thermally insulated. The annular space is connected to means of evacuation so the space is held at a pressure below atmosphere, preferably below 100 mbar, more preferably below 30 mbar. The annular space is also placed under inert gas, in particular nitrogen. The installation includes means of verifying that the envelope and/or the pipe are leakproof. This is done using a detector of pressure variation in the annular space and delivers an alarm signal when the pressure variation is above a set value. Alternatively, a sensor detects the presence of one of the components of the liquefied gas in the annular space, in particular CH4, or detecting a drop in the amount of inert gas in the annular space. The internal pipe in the main section has a compensator (76, 78) at at least one end and the variation in length allowed by the compensator is at least the variation in length of the rigid part subject to the variation between the water temperature and the temperature of the liquefied gas. The main rigid section is suspended from a balancing body (94) which is designed to give it floatability or ballast. The main rigid section is suspended from the two terminals or anchored to the seabed by an anchor line. The main rigid section is a bundle of parallel pipes which include a pipe for returning the liquefied gas to the gaseous state, which passes from the second to the first reservoir.

Description

The present invention relates to an offshore transfer installation of a liquefied gas, especially liquefied natural gas, as described in the preamble of claim 1. Such an installation is described in the document US Pat. No. 3,984,059.

It applies in particular to processes for filling transport boats with liquefied gas or liquefied natural gas (LNG tanker).

Processes for filling transport boats with natural gas and liquefied natural gas are known.

Known gas transport vessels comprise liquid gas transport tanks and, in some cases (liquefied petroleum gas), a gas liquefaction plant.

In order to fill these vessels with liquefied gas, the liquefaction plant is connected to a transfer line which is connected to a source of liquefied gas, for example a storage tank on land or at sea.

Processes for loading a vessel with liquefied gas are also known in which the gas is liquefied and stored in a temporary storage tank located for example on a production platform. Then, the liquefied gas is transferred to the boat via a transfer facility.

Such a transfer installation is described in the document FR-A-2 793 235. This transfer installation is composed of a plurality of articulated pipe segments in the form of deformable lozenges, the ends of which are connected on the one hand to a connection system of the ship, and secondly to a pipe arranged along a crane.

This installation must meet important mechanical constraints. It is placed near the production platform and must be able to adapt to the movements of the production platform (six degrees of freedom including rolling, pitching, heave, cavally). In addition, the installation has many rotating joints that are constantly in motion. Its maintenance is therefore relatively expensive. This type of installation is used for the loading and unloading of LNG carriers in the ports of liquefied natural gas production or reception terminals, along sheltered jetties.

Other liquefied gas transfer facilities are known. These facilities are used to transfer liquefied gas or liquefied natural gas (LNG) between two vessels. They imply that the two boats are positioned one behind the other or side by side.

In these two configurations, the distance separating the boats is relatively small. Both boats are large and comparable in size and subject to swell and currents. Thus, each of them moves with six degrees of freedom and relatively independently of the other. The transfer facility is designed to take into account these relative movements of the two vessels that are otherwise weather dependent

Another transfer installation, known for example from the patent application FR-A-2,815,025, comprises a flexible catenary transfer line connecting the storage facility to the transport vessel. At rest, the flexible pipe is stored on a gantry linked to a production and storage facility. The connection of the flexible pipe to the ship is effected by means of a connection module integral or independent of this flexible pipe.

In the patent application WO 01/87 703 is proposed a transfer facility of a production site to a LNG carrier. This installation consists of an arm placed on the production site and extending over a length of 30 to 60% of the safety distance between the two vessels. A flexible pipe is wound on a wheel at the end of the arm. This pipe is connected to the LNG carrier during the transfer.

In WO 01/34460 is proposed an aerial transfer facility liquefied natural gas between two ships with a connection system mounted at the end of a flexible pipe that connects to the installation of the second vessel.

In most of these known devices, the pipes used for the transfer of the gas have a relatively short length (less than 100 meters) and extend above the sea surface. the boat can only be done when it is near the platform or the dispatcher, which creates the risk of collision and makes the transfer device very dependent on weather conditions.

The present invention aims to overcome the disadvantages mentioned, and to provide a liquefied gas transfer facility that is economical and safe.

For this purpose the invention relates to an installation of the aforementioned type, characterized by the features of claim 1.

According to other embodiments, the installation comprises one or more of the features of the dependent claims 2 to 13.

The invention furthermore relates to the use of an installation as defined above for transferring a liquefied gas from a first tank to a second tank.

The invention will be better understood on reading the description which follows, given solely by way of example and with reference to the appended drawing, in which FIG. 1 is a diagrammatic view of an embodiment of a transfer installation according to the invention, in partial section.

In Figure 1 is shown a filling plant of a boat 2 of liquefied gas or liquefied natural gas, designated by the general reference 4.

In what follows the expression "gas" will be used for any product or compound which, under ambient conditions (1013 hPa, 20 ° C) is in the gaseous state. The term "liquid gas" will be used for such a product which is at least partially in the liquid state, and the expression "gas in the gaseous state" will be used for any product in the gaseous state.

The boat 2 is a tanker, known per se, on which is installed a transport tank 6 of liquid gas.

In general, the boat 2 is a vessel adapted to carry liquefied gas, and in particular a tanker.

The installation 4 comprises a production facility (linked to or including a drilling installation comprising the gas producing wells) constituted, for example, by a production barge 9 or a platform anchored or fixed on the seabed 10 The production plant is connected to a natural gas pocket 14 in the gaseous state by a riser 15. This feeds a liquefaction device 16 of the gas in the gaseous state supported by the Barge 9. An output of the liquefaction device 16 opens into a tank 18 for temporary storage of liquefied gas.

The installation 4 further comprises means 20 for transferring liquid gas from the storage tank 18 into the transport tank 6.

The gas transfer means 20 in the transport tank 6 comprise a loading buoy 22 on which the tanker comes to connect for loading. According to the invention, this loading buoy 22 is spaced apart distally from the barge 9 of production. This configuration allows the tanker or LNG carrier to move and dock independently of the barge 9 without risk of collision.

On the other hand, the connection between the loading buoy 22 and the transport tank 6 of the boat 2 is effected by a loading line 24.

The loading pipe 24 extends entirely above the surface M of the sea. It has means for temporarily connecting the tank 6.

The tank 6 is filled with liquefied gas or liquefied natural gas (LNG) from the loading buoy 22 to transport this gas to the ground.

The charging line 24 is known per se. It may be constituted by rigid pipe sections, interconnected by rotating joints, or by a flexible pipe. The loading line 24 is supported by a suitable support structure, such as a crane (not shown) or floating and designed accordingly.

The loading buoy 22 is anchored to the seabed 10 by cables and / or chains 26 and is spaced distally from the production barge 9. The distance A between the loading buoy 22 and the production barge is greater than 300 m, and will preferably be of the order of one nautical mile (1.852km).

The loading buoy 22 is small in relation to the boat 2. The boat 2 is subject to swell, currents and weather conditions. It can rotate freely around the loading buoy 22 when loading liquefied gas or liquefied natural gas.

The transfer means 20 further comprise a transfer line 28 immersed in water, which connects the storage tank 18 to the loading buoy 22.

The transfer line 28 is adapted to transfer liquid gas from the production barge 9 to the loading buoy 22, while being immersed in the water during the transfer of the liquefied gas. The barge 9 forms a first terminal of the transfer line 28 and the loading buoy 22 forms a second terminal of the transfer line 28.

The terminals, in this case the loading buoy 22 and the production barge 9, can move independently of each other in all directions over a distance of up to 10% of the water depth. at great depth and more for depths less than 150m. The amplitude of the relative movement between the two terminals can thus reach more than 20% of the depth of water.

The submerged transfer line 28 will therefore be able to absorb these variations in distance between the two floating terminals 9 and 22.

Dynamic bending and vibration forces are generated on the immersed part of the transfer line 28 by the wave movements, the marine currents and the relative displacements of the terminals 9, 22.

The combination of these dynamic forces and vibrations causes significant fatigue of the submerged portion of the transfer line 28, which significantly reduces its life.

Rigid pipes are very sensitive to these dynamic forces and vibrations. This is why it is usually necessary to connect the rigid pipe to the terminals by a kind of spherical joint / joint (flexjoint in English) so as to follow the movements of the terminals and absorb more or less dynamic stresses. In addition, areas subject to significant vibration must generally be equipped with additional specific means, such as anti-vibration helical fins.

Flexible pipes are known for their high strength and their ability to absorb these dynamic stresses, but their cost is high.

These dynamic stresses are especially present in the so-called turbulence zone. The turbulence zone is a layer of water in which the effects of waves and currents are important. This zone is defined as the zone in which the maximum velocity of the water flow is above a determined threshold. Generally, this threshold is 1 m / s or even 0.5 m / s.

For example, in the case of Brazil (area where the speed of the currents is important), the turbulent zone can descend to a depth of 300 m, or even 500 m (15% to 25% of the depth of water) in some fields. On the contrary, in West Africa (zone where the turbulences are rather weak), this zone of turbulence can have a maximum depth of the order of 50 m (5% of the depth of water).

The transfer line 28 according to the invention is a flexible and rigid hybrid line combining the advantages of flexible pipes in the area subjected to high dynamic loads and the low cost of rigid pipes in areas where these dynamic stresses are limited.

The transfer line 28 thus comprises a substantially horizontal rigid main section 32 extending over a distance close to the distance A and situated in an area of the water layer where the dynamic stresses are reduced, and flexible sections 30 and 34. substantially vertical which connect the ends of the main section 32 to the terminals 8, 22 and ensure the continuity of the transport of liquid gas and the recovery of dynamic stresses.

The rigid main section 32 extends at a depth P with respect to the surface of the sea. This depth P is greater than the depth of the previously defined turbulence zone, preferably greater than 50 m.

The sections 30 and 34 are substantially identical and consist of a flexible outer casing 36, 38 with a circular cross section of diameter D and a flexible inner pipe 40, 42 with a circular cross section of diameter d. The envelopes 36, 38 and the conduits 40, 42 are relatively flexible to bending. Each of the conduits 40, 42 is arranged coaxially in the corresponding casing 36, 38, forming an annular space 44, 46 of radial width 1r. The cryogenic flexible pipes 40, 42 are known per se and comprise radially from inside to outside a wavy, reinforcing armor fiberglass spiral, for example at 55 °, and one or more layers of thermal insulation separated by watertight layers.

The flexible outer casing may consist of a conventional flexible pipe known per se or an undulating one.

The double-shell configuration protects the inner pipe and confines liquefied gas or liquefied natural gas in case of leakage.

Each of the sections 30 and 34 terminates at its lower end by a double connecting flange 52, 54, at the central section 32.

The lateral section 30 is fixed at its upper end to the production barge 9, while the section 34 is fixed at its upper end to the loading buoy 22. The lateral sections 30, 34 are thermally insulated.

The upper end of the pipe 40 is connected to the storage tank 18, by a pipe system 58 known per se.

The pipe 42 of the section 34 is connected to the loading pipe 24 by known connecting means 59. These connecting means 59 are adapted to allow a displacement of the boat 2 ° around the loading buoy 22.

The horizontal central section 32 consists of a cylindrical outer jacket 66 of horizontal axis diameter D , in which a rigid internal pipe 68 of diameter d is placed leaving an annular space 69.

In other words, this section 32 forms a double-jacketed pipe.

The density of the liquefied natural gas being 0.45, the export transfer line 28 may therefore have, depending on its diameter, a positive or negative buoyancy.

The main section 32 may then be associated with a balancing body 94, in order to maintain this section 32 at the required water depth and to ensure that it will extend substantially horizontally.

If the buoyancy of the main section 32 is positive, the balancing body 94 can be a body of ballast. If this is negative, the balancing body 94 can provide the main section 32 of buoyancy.

The main section 32 has a length L which is at least 50% of the distance A between the two terminals 8, 22, and which is preferably at least 90% of this distance.

The section 32 ends at its two ends by two double-flanges 70, 72 complementary to those of the two double-flanges 52, 54.

It should be noted that all the double-flanges 52, 54, 70, 72, are adapted to connect the pipes 40, 42, 38 and the envelopes 36, 38, 66, in a liquid and gas-tight manner.

Furthermore, each of the double-flanges 52, 54, 70, 72 comprises through-openings which connect the annular spaces 44, 46, 69, in order to ensure a continuity of the thermal insulation in the annular space, all the way through. of the transfer line 28.

The pipe 68 comprises a cylindrical rigid central portion 74 having a diameter d which is integral on both sides with an axially deformable bellows 76, 78. Each bellows 76, 78 is integral with one of the double-flanges 70, 72.

The bellows 76, 78 each have a length l which is sufficient to compensate for thermal contraction in the axial direction of the central portion 74 of the pipe 68, in a temperature range between the water temperature and the gas temperature. liquid to be transferred. The temperature of the water is generally between 4 ° C and 20 ° C. In the case of a loading of the transport tank 6 of liquefied natural gas, the temperature of the liquid gas is between -150 ° C and -180 ° C. The bellows 76, 78 then have a length sufficient to compensate for a dilation of the part central 74 over a temperature range of the order of 200 ° C.

The central pipe 68 is made of a metal having a low coefficient of thermal expansion. The coefficient of expansion α is less than 16x10 ^-6 m / m ° C, and preferably less than 2x10 ^-6 m / m ° C. The central pipe 68 is for example a material marketed under the trade name INVAR (R) by IMPHY and CREUSOT-LOIRE. This material has an expansion coefficient α of 1.6x10 ^-6 m / m ° C 'at temperatures below -150 ° C.

For a distance A of 1 nautical mile between the production barge 9 and the loading buoy 22 the length l of contraction is approximately 2.5 m, and preferably between 2 and 3 m.

The envelope 66 is made of standard steel, for example carbon steel for underwater application.

Furthermore, the central portion 74 is centered radially with respect to the central envelope 66 by centering discs 84 or spacers disposed in the annular space 69. These discs 84 are made of a material of low thermal conductivity, for example polyurethane , made of polypropylene or polyamide.

Section 32 should be thermally insulated. To do this, the annular space 69 present between the casing 66 and the duct 68 will comprise a thermal insulation having a thermal conductivity lower than the thermal conductivity of the air at atmospheric pressure.

• des mousses de matière plastique (résine polystyrénique, polyvinylique, palyuréthane) ;
• de la mousse de verre ;
• des poudres (perlite, alumine) ;
• de superisolants qui présentent le meilleur compromis pour réduire les principaux flux de chaleur. Ils sont composés d'une succession d'écrans réflecteurs (en aluminium) entre lesquels sont interposés des feuilles intercalaires peu conductrices thermiques (films en matière plastique, fibres de verre) ; ou
• d'autres matériaux microporeux.

The annular spaces 44, 46, 69 may be filled with thermal insulation material, such as:

• plastic foams (polystyrene, polyvinyl, palyurethane resin);
• glass foam;
• powders (perlite, alumina);
• super-insoles that offer the best compromise for reducing the main heat flows. They consist of a series of reflector screens (aluminum) between which are interposed interlayers low thermal conductive films (plastic films, glass fibers); or
• other microporous materials.

Moreover, to further improve the thermal insulation, the thermal insulation material can be partially evacuated.

Alternatively, the space 69 is put under a pressure below atmospheric pressure, which may represent a vacuum of the order of 30 mbar abs. For this purpose, the installation 4 comprises a vacuum pump 86 situated on the loading buoy 22 or on the production barge 9 and connected with its suction side to the annular space 46 of the section 34 or to the annular space 44 of the section 30.

One of the interests of the transfer line 28 according to the invention is that it has a continuous annular space over its entire length. This annular space makes it possible to confine any leaks inside the outer casing and increases the security of the transfer line.

In addition, this continuous annular space makes it possible to ensure the continuity of the thermal insulation, for example by keeping this annular space under reduced pressure or under vacuum. Finally, it allows to control the integrity of the export line (leakage, etc.). To do this, the installation 4 may therefore include means 88 for detecting a gas leak in the lines 40, 42, 68 or a leakage of one of the envelopes 36, 38, 66.

These detection means 88 consist of a pressure and / or pressure variation sensor 90 and / or of natural gas, in particular CH ₄ , arranged in the space 46 or 44 and connected to a display device 92.

When the pressure or the variation of the pressure exceeds predetermined values, the sensor 90 delivers an alert signal to the display device 92.

Thus, a change of pressure in the space 46 will make it possible to detect a leakage of the lines 40, 42, 68 or envelopes 36, 38, 66.

Alternatively, the annular spaces 44, 46, 69 may be filled with an inert gas, for example nitrogen, as a thermal insulator (preferably at a pressure below atmospheric pressure). This gas makes it possible to control the atmosphere of the annular space and to make sure that there will be no oxygen, which will limit the risks of corrosion. In addition, a gas leak or leakage can then be detected by measuring the pressure in the gap 46 or by measuring the rate of the inert gas.

The installation according to the invention operates as follows.

The production plant 8 produces gas in the "gaseous" state which is liquefied by the liquefying device 16 and which is stored in the storage tank 18.

The boat 2 with the empty transport tank 6 approaches the loading buoy 22, and the transport tank 6 is connected to the pipe 42 of the section 34 via the loading pipe 24.

The liquefied gas is conveyed from the storage tank 18 through lines 24, 40, 42, 68 to the transport tank 6.

Since the gas flows through the pipes in the liquid state, a large mass flow of gas in the liquid state is obtained, for a pressure and a cross-section of the pipe data. The filling of the transport tank 6 is then carried out quickly. The order of magnitude of the filling time according to this method is about 12 hours.

The fact that the transfer line 28 is immersed in the water makes it possible to connect the loading buoy 22 to the production barge 9 over great distances. The loading of the tanker 2 is therefore carried out at a great distance A without risk of collision of the tanker or the LNG carrier and the barge 9 of production.

The transfer line 28 according to the invention also makes it possible to quickly discharge the liquid gas from the transport tank 6 to a storage tank (not shown).

Alternatively, the transfer line 28 may comprise a bundle of pipes arranged parallel to each other (bundle). In particular, this bundle of pipes may comprise one or more pipes for the return of gas in the gaseous state, which will pass from the transport tank 6 to the storage tank 18 and one or more conduits for the transport of liquid gas, and a balancing body for the main section 32.

In another variant, each of the ends of the main section 32 can be connected to the corresponding terminal 8, 22 by means of a mooring line (not shown) connected in parallel with the lateral sections 30, 34.

Each mooring line has a length less than the length of the lateral sections 30, 34, so that the lateral sections 30, 34 are not subjected to the traction force generated by the main section 32. The mooring line is consisting of a chain, a carbon fiber cable, a steel cable or a polypropylene rope. In this case, the section 32 will be slightly heavy or the Mooring lines will be tensioned by counterweights at the ends of the main section 32.

In another alternative, the main section 32 may be anchored directly to the seabed by mooring lines. In this case, the main section 32 will be slightly floating or the mooring lines will be energized by buoys located at the ends of the main section 32.

According to another variant, the sections 30, 34 each comprise an inner duct of the corrugated type and an outer casing of the corrugated type. The pipe and casing are made of stainless steel or INVAR (R). In addition, reinforcing armor is wrapped around the inner pipe, preferably over its entire length.

The thermal insulation layer of these sections is composed, according to the length of the sections, a succession of rigid centering discs, consisting of two assembled half-shells, and flexible rings.

The centering discs are attached to the inner pipe and are made of rigid microporous airgel material. The flexible rings consist of several layers of flexible microporous airgel material.

Claims (14)

1. An installation for transferring a liquefied gas at sea, notably liquefied natural gas, of the type including a first tank (18) and being adapted to transfer liquefied gas from the first tank (18) to a second tank, which is a surface tank (6), further including a transfer line (28) adapted to be coupled to said tanks (6, 18), the two tanks being spaced apart in a distal manner during the transfer of the liquefied gas, the transfer line (28) being immersed in the water, the installation including a first terminal (8) bearing the first tank (18) and a second terminal (22), notably a loading buoy, which is spaced apart from said first terminal (8) in a distal manner, the transfer line (28) extending between the two terminals (8, 22), characterised in that the first tank is a surface tank (18), in that the transfer line (28) includes a substantially horizontal rigid main section (32) located in a water layer area where the dynamic loads are reduced and flexible and substantially vertical sections (30, 34) which link the ends of the main section (32) to the terminals (18, 22) and ensure the continuity of the transport of the liquid gas and the recovery of the dynamic loads, in that the main section (32) and the flexible sections (30, 34) include an internal pipeline (40, 42, 68) and an external casing (36, 38, 66) defining an annular space (44, 46, 49), in that the annular space (44, 46, 69) extends over the entire length of the transfer line (28), in that the annular space (44, 46, 69) is thermally insulated by thermal insulation means, and in that it further includes means to fill the annular space (44, 46, 69) with inert gas, notably with nitrogen.
2. The installation according to Claim 1, characterised in that the rigid main section (32) includes a bundle of flowlines arranged parallel to one another.
3. The installation according to Claim 2, characterised in that the bundle of flowlines includes a flowline for returning the gas to the gaseous state, which gas will migrate from said second tank (6) towards said first tank (18).
4. The installation according to one of Claims 1 to 3, characterised in that it includes verification means (90, 92) adapted to verify the impermeability of the casing (36, 38, 66) and/or of the flowline (40, 42, 68).
5. The installation according to Claim 4, characterised in that the verification means include a sensor (90) adapted to detect the pressure variation established in the annular space (44, 46, 69) and able to deliver an alarm signal when the pressure variation is above a predetermined value.
6. The installation according to Claim 4 or 5, characterised in that the verification means include a sensor adapted to detect the presence, in the annular space (44, 46, 69), of at least one of the components of the liquefied gas to be routed via the flowline (40, 42, 68), notably CH₄, or adapted to detect the level of inert gas in the annular space (44, 46, 69).
7. The installation according to any of Claims 1 to 6, characterised in that the rigid main section (32) is located in a water layer area in which the maximum speed of the water current is below 1 m/s, preferably below 0.5m/s.
8. The installation according to one of Claims 1 to 7, characterised in that said first and said second tanks (6,18) are spaced apart by a distance of over 300 metres, and preferably in the region of 1 nautical mile, during the transfer of the liquefied gas.
9. The installation according to one of the preceding claims, characterised in that said second terminal (22) is adapted to link the transfer line (28) to a loading flowline (24) provided with means (25) for connecting to the second tank (6) which is borne by a ship.
10. The installation according to any one of the preceding claims, characterised in that the annular space (44, 46, 69) is linked to evacuation means (86) adapted to keep this space (44, 46, 69) at a pressure lower than atmospheric pressure, notably at a pressure lower than 100 mbars, and in particular at a pressure of substantially 30 mbars.
11. The installation according to one of the preceding claims, characterised in that the internal flowline (68) of the main section (32) includes a metal rigid part (74), including, at at least one of its ends, a compensation bellows (76, 78), and in that the variation in length permitted by the bellows (76, 78) is at least the variation in length of the rigid part (74) under a variation in temperature between the temperature of the water and the temperature of the liquefied gas.
12. The installation according to any one of the preceding claims, characterised in that the rigid main section (32) is suspended from a balancing body (94) which is adapted to provide it with buoyancy or ballast.
13. The installation according to any one of the preceding claims, characterised in that the rigid main section (32) is suspended from two terminals (8, 22) or anchored to the sea-bed by a mooring line.
14. Use of an installation according to any one of the preceding claims to transfer liquefied gas from a first tank (18) to a second tank (6).

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