An offshore fluid transfer system

Abstract

The present invention relates to an offshore fluid transfer system In particular the invention relates to such a system comprising a flexible pipeline connectable to a vessel manifold system with an emergency release coupling, and wherein the system is provided with a solution for combined fall-arrest and retrieval of a releasable end of the flexible pipeline upon decoupling.

Description

An offshore fluid transfer systemTechnical Field

[0001] The present invention relates to an offshore fluid transfer system. In particular the invention relates to such a system comprising a flexible pipeline connectable to a vessel manifold system with an emergency release coupling, and wherein the system is provided with a solution for combined fall-arrest and retrieval of a releasable end of the flexible pipeline upon decoupling.Background

[0002] As the world moves towards the use of cleaner and greener energy sources, there is an increased need for transportation of liquefied gases such as CO2, chemical gases, LNG or LPG. Typically, these products will be transported on large seagoing vessels. This form of transportation requires the establishment of import and export terminals to transfer the product on- or offshore. Such terminals are often located some distance from shore in order to accommodate the transportation vessels. At the terminal, a vessel can be moored in a conventional mooring system, alongside a quay, using mooring dolphins or kept stationary by other means such as dynamic positioning.

[0003] These import and export terminals may need to implement safety barriers for vessel drift-off scenarios or other scenarios where the vessel must rapidly leave its berth. It is known from the prior art to incorporate an emergency release coupling (ERG) connected between the terminal piping and a manifold system on the vessel. Typically, the emergency release coupling will be arranged on a balcony on a side of the vessel. The ERC is then mounted between hard piping on the vessel extending out to the balcony and a flexible pipeline, such that the flexible pipeline falls directly down and away from the vessel upon release.

[0004] W02023062206A1 discloses one such system. An issue with such systems is that the flexible pipeline may be damaged when it is released, potentially falling rapidly and uncontrollably towards the sea and sea floor. WO'206 describes that this can be mitigated by providing a fall-arrest system using pulleys and a lifting winch. The description discloses a large structure to accommodate the various components of the fall-arrest and retrieval system.

[0005] It is an object of the present invention to improve upon, mitigate or significantly alleviate the shortcomings of the prior art.Summary of the Invention

[0006] In a first aspect of the invention, there is provided an offshore fluid transfer system comprising: a floating vessel comprising a fluid manifold system; a flexible pipeline fluidly connectable to the fluid manifold system via an interface piping arranged at a side of the floating vessel, wherein the interface piping and flexible pipeline are configured to be connected via an emergency release coupling comprising a lower half arranged at an end of the flexible pipeline and an upper half arranged at an end of the interface piping; a harness connected to the lower half of the emergency release coupling; a spool for reeling the harness; and a drive unit connected to the spool, wherein the drive unit is configured to: impart rotation to the spool, thereby reeling the harness and consequently adjusting the vertical position of the lower half of the emergency release coupling when disconnected from the emergency release coupling; and braking rotation of the spool, thereby arresting the fall of the lower half of the emergency release coupling upon disconnection from the emergency release coupling.

[0007] Thus, by providing a drive unit that is configured to both impart rotation and brake rotation of the spool, a significant reduction in the amount of space and number of components is achieved in comparison to the prior art fall-arrest and retrieval systems. The reduction in space and components leads to a reduction in weight of the structural components supporting the fall-arrest and retrieval system and allows for smaller, more modular and pre-fabricated units to be employed.

[0008] The releasable end of the flexible pipeline may be the end of the flexible pipeline arranged for connection to the interface piping via the emergency release coupling. The lower half of the emergency release coupling may be arranged with shackles arranged on said coupling for connection to the harness. In certain embodiments, the harness may be connected to the releasable end of the flexible pipeline with a lug arranged on a flange at said end, or with a clamp to the flexible pipeline body.

[0009] The flexible pipeline may typically be a transfer pipeline such as a duct, pipe, hose, flexible pipe, flexible hose or conduit suitable for the medium to be transferred. Preferably, the flexibility of the pipeline is configured to transfer a liquefied gas between a floating vessel and a bottom-fixed structure, or between two floating units. Such flexible pipelines are known in the art and the skilled person will be familiar with the term flexible and its meaning within this context. A flexible flowline may be contrasted to a flowline that comprises stiff portions with a plurality of joints interconnecting the stiff portions. A flexible flowline may also be contrasted to a flowline that is arranged between two bottom-fixed structures that do not experience relative motion, or a flowline arranged along a sea floor.

[0010] In certain embodiments, the floating vessel may comprise a fluid manifold system for transporting and transferring liquefied gas, such as NH3, CO2, chemical gases, LNG or LPG.[Oil] A floating vessel may typically be a ship, but may also comprise a tanker vessel and / or a floating storage unit and / or carrier vessel.

[0012] In certain embodiments, the floating vessel may comprise a balcony arranged at a side of the vessel, and the interface piping, emergency release coupling, harness, spool and drive unit may be arranged on the balcony. The balcony may extend from the vessel and over a body of water to the side of the vessel. The interface piping, the emergency release coupling and the releasable end of the flexible pipeline may be arranged in a position on the balcony extending over the body of water, such that upon release the lower half of the emergency release coupling and the end of the flexible pipeline will fall down towards the body of water.

[0013] In certain embodiments of the invention, the balcony may be modular and configured to be retrofitted on the floating vessel. The floating vessel may compriseat least one balcony foundation at a side of the vessel, where a balcony supporting structure may be fixed. At least one of the balcony supporting structures may be arranged to extend from a deck of the vessel and out over a side of the ship's hull extending above a body of water. The balcony supporting structure may comprise a balcony beam, balcony tension rod and / or a combination such elements. The balcony may comprise a lattice structure.

[0014] The balcony foundation may comprise pre-arranged fixing means on a deck of the vessel, such as bolts, that are ready to engage with holes in the balcony supporting structure. Preferably at least two balcony foundations are arranged on the floating vessel. Preferably at least two balcony supporting structures, extending from different points on the balcony are connected to each balcony foundation. The balcony foundations may be arranged to take up tension and / or compression, depending on their configuration.

[0015] The balcony may comprise at least two levels, preferably three, where at least two of the following components may be arranged on two separate levels; an emergency release coupling comprising at least the upper half of the emergency release coupling, a drive unit and an interface piping with a connection to a pipe spool. The levels of the balcony may also herein be referred to as decks of the balcony. The interface piping may extend over several levels of the balcony, extending from an emergency release coupling at one level, to the connection to a pipe spool at another level.

[0016] Preferably, a drive unit and a spool may be arranged on a third level. In particular, a winch may be arranged on the third level, with a harness extending through the levels to the lower half of the emergency release coupling when it is in a coupled state. Thus it may be understood that the footprint of the balcony remains minimal, as the components of the invention are arranged vertically in relation to each other. This allows for easier pre-fabrication and installation of the balcony, such that it is modular and may be used for a variety of vessels.

[0017] Thus, for certain balcony arrangement embodiments there may be additional benefit in reducing the space, weight and number of components on the balcony. In particular because the structure of the balcony can be minimised, thereby reducing additional reinforcements that may be necessary on the deck of the ship. Prefabrication and modularisation of a balcony on which the elements are arranged may also be facilitated.

[0018] In certain embodiments, the spool may be directly connected to a shaft of the drive unit. Thus, these embodiments provide a gearless connection between the spool and the drive unit. The spool may be directly provided onto the shaft of the drive unit. The drive unit may therefore determine the speed of the spool's reeling without any intermediate mechanism such as gears or pulleys.

[0019] In certain embodiments, the drive unit may comprise a hydraulic power circuit and a shaft of the drive unit may be rotationally connected to an hydraulic rotary actuator which interacts with the fluid in the hydraulic power circuit. Thus, in these embodiments, the circulation of hydraulic fluid and its impact on the hydraulic rotary actuator in the circuit may directly determine the output of the drive unit shaft. The hydraulic rotary actuator may comprise an impeller, vane actuator, rack and pinion actuator, helical actuator , or any similar device converting hydraulic energy into rotational energy.

[0020] In certain embodiments, the hydraulic power circuit may comprise a hydraulic power unit arranged to provide hydraulic pressure to the hydraulic power circuit and wherein the hydraulic power circuit may comprise a flow restrictor arranged to restrict hydraulic pressure in the hydraulic power circuit. By circulating hydraulic fluid at a certain pressure and speed, the hydraulic power unit may therefore determine the rotation and power provided to the drive unit shaft. The hydraulic power unit may be arranged to circulate the hydraulic fluid in different directions, thereby determining the rotation of the spool and whether the harness is reeled in or out. By restricting the hydraulic pressure in the circuit, the flow restrictor impedes the speed of spool rotation thereby braking the falling speed of the flexible pipeline.

[0021] In certain embodiments, wherein the hydraulic power circuit may comprise a first subcircuit, wherein the flow restrictor is arranged, a second subcircuit, wherein the hydraulic pressure unit is arranged, wherein the first subcircuit and the second subcircuit are arranged in parallel and connected by flow control devices.

[0022] Thus, the first subsection may have a braking function which is used in a fall-arrest mode and the second subsection may have a power providing functionwhich is used in a winch mode. The flow control devices may therefore direct flow such that either function is activated. Typically, the flow control devices may comprise three-way valves, but other know flow control devices within the art may also be employed.

[0023] When the emergency release coupling is connecting the releasable end of the flexible pipeline to the interface piping, the hydraulic circuit may be in a fallarrest mode by default. However, when the lower half of the emergency release coupling and the flexible pipeline have been decoupled and it is desirable to recouple the connection, the hydraulic circuit may be switched to a retrieval / winch mode.

[0024] In certain embodiments of the invention, a positioning sensor may be arranged on the floating vessel configured to detect the position of the vessel. The positioning sensor may be a global positioning sensor. Other embodiments of positioning sensors may include; a wire linked to a control unit issuing a signal when the wire is pulled, a laser or any other sensors capable of measure the relative position of the vessel compared to a permitted motion envelope. The positioning sensor may be signally connected to a control unit, wherein the control unit may be arranged on the vessel or the balcony. The control unit may be configured to determine whether the floating vessel is drifting off, or will drift off from its moored position and thereby require an activation of the emergency release coupling. The control unit may be signally connected to the emergency release coupling in order to activate a release of the coupling. The control unit may be configured to verify that the drive unit is in a fall-arrest mode, and if not, signal to actuators of the fluid control devices to switch to a fall-arrest mode before decoupling of the emergency release coupling is activated. Preferably, the system may stay in a fall-arrest mode, unless maintenance is ongoing or after a decoupling of the emergency release coupling.

[0025] In certain embodiments, the first hydraulic power circuit may comprise a hydraulic fluid cooler. The temperature of the hydraulic fluid may rise as it is passed through a flow restrictor. The hydraulic fluid cooler may prevent excessive temperature of the hydraulic fluid, which can change the viscosity of the fluid and which may negatively affect performance of the hydraulic power circuit.

[0026] In certain embodiments, the hydraulic fluid cooler may be arranged in the first subcircuit. Thus, the fluid may be cooled after passing through a flow restrictor.

[0027] In certain embodiments, the first subcircuit may comprise a second flow restrictor, arranged in a parallel sub-subcircuit to the flow restrictor. Thus, the second flow restrictor may provide redundancy should the flow restrictor fail and excessively restrict the flow of hydraulic fluid. The sub-subcircuit may therefore be provided with a pressure sensitive valve which opens the parallel sub-subcircuit upon experiencing pressure of a predetermined limit.

[0028] In certain embodiments, a sensor may be arranged to measure the reeling speed of the harness and / or the length of harness reeled out from the spool.

[0029] In certain embodiments, the sensor may be an RPM sensor arranged to measure rotations per minute on the shaft of the drive unit.

[0030] In certain embodiments, the RPM sensor may be an induction sensor.

[0031] In certain embodiments, the flow restrictor may be adjustable. Thus the flow restrictor may be configured to vary the restriction of hydraulic pressure in the circuit. Thus, the flow restrictor may vary the braking speed of the flexible pipeline according to certain predetermined values. These values may be predetermined based on the specifications of the transfer system, such as the height above water of the emergency release coupling, the weight of the flexible pipeline, the strength of materials in the transfer system and other considerations that will affect the desired braking speed. An adjustable flow restrictor may comprise any of the following: an adjustable orifice, a manual or actuated throttle valve, a control valve or any similar device typically used to restrict flow.

[0032] In certain embodiments, the second flow restrictor may be a pressure relief valve by passing the flow restrictor in the parallel sub-subcircuit. The pressure relief valve may have a set pressure marginally higher than the largest expected operating pressure of the first subcircuit during the reeling out of the spool. The orifice of the pressure relief valve is such that the velocity of the falling lower half of the emergency release coupling and releasable end of the flexible pipeline is within a given range. Thus, should the first flow restrictor fail, either mechanically or due to a failure of a control system, the pressure relief valve will be activated.

[0033] In certain embodiments, a control unit may be signally connected to an actuator coupled to the flow restrictor. The control unit may comprise predetermined values for the flow restrictor, which determine the flow restriction as a function of time. Thus, the braking speed of the flexible pipeline may be controlled by the control unit in order to ensure customisable fall speed and avoiding high shock loads.

[0034] In certain embodiments, the sensor may be signally connected to the control unit. Thus, the sensor may provide data on the reeling speed of the harness and / or the length of harness reeled out from the spool. The control unit may therefore use this data to control the actuator coupled to the flow restrictor.

[0035] In certain embodiments, the control unit may be configured to: process the signals from the sensor to calculate a reeling speed of the harness; compare the reeling speed with predetermined speed values; determine an adjustment to the flow restrictor in order to minimise the deviation between the actual speed and the predetermined values; transmit signals to the flow restrictor actuator thereby adjusting the pressure in the hydraulic circuit.

[0036] Thus, the fall speed of the flexible pipeline may be customisable according to the specifications of the transfer system and the forces acting on the harness may be dampened by the sytstem. Additional precision of the fall speed may also be achieved where a balance is struck between avoiding high shock loads and the flexible pipeline hitting the surface of the water, or the bottom of the sea floor.

[0037] In the following description, numerous specific details are introduced by way of example only to provide a thorough understanding of embodiments of the claimed system. One skilled in the relevant art, however, will recognize that these embodiments can be practiced without one or more of the specific details, or with other components, systems, etc. In other instances, well-known structures or operations are not shown, or are not described in detail, to avoid obscuring aspects of the disclosed embodiments.Brief Description of the Figures

[0038] The following drawings are appended to facilitate the understanding of the invention. The drawings show embodiments of the invention, which will now be described by way of example only, where:

[0039] Fig. 1 is a schematic illustration of an exemplary embodiment of the invention, illustrating components of the offshore fluid and transfer system.

[0040] Fig. 2 is a schematic illustration of an exemplary embodiment illustrating details of the balcony where a dual-function fall-arrest and retrieval system is arranged.

[0041] Fig. 3 is a schematic illustration of the drive unit comprising the hydraulic power circuit and its components.Detailed Description of the Figures

[0042] In the following, general embodiments as well as particular exemplary embodiments of the invention will be described. References will be made to the accompanying drawings. It shall be noted, however, that the drawings are exemplary embodiments only, and that other features and embodiments may well be within the scope of the invention as claimed. Further, the mentioning of references such as "a" or "an" etc. should not be construed as excluding a plurality.

[0043] Unless otherwise defined, all terms of art, notations and other scientific terms or terminology used herein are intended to have the meanings commonly understood by those of skill in the art to which this invention pertains. Certain terms of art, notations, and other scientific terms or terminology may, however, be defined specifically as indicated below.

[0044] In Fig. 1, an exemplary embodiment is illustrated showing the system extending from a subsea pipeline end manifold to the balcony of a floating vessel. Furthermore, Fig. 1 illustrates the flexible pipeline 30 in two different states, coupled 30 and decoupled 30'.

[0045] A cross-section of a portion of a floating vessel 20 is shown in the body of water 1. The vessel comprises a balcony 22 arranged at a side of the vessel 20, thebalcony 22 extending out from a side of the vessel 20. Fig. 1 does not illustrate all the components or details of the balcony 22, but it can be seen that the emergency release coupling 50, interface piping 40, harness 23b, winch 23a and spool 25 are all arranged on the balcony 22. In particular, the components are exemplified as being arranged such that the majority are arranged on the part of the balcony 22 extending past the side of the vessel 20.

[0046] In particular, the emergency release coupling 50 is arranged on the part of the balcony 22 extending past the side of the vessel 20 such that the lower half 53 of the emergency release coupling 50 releasable end 31 of the flexible pipeline 30, when decoupled, will fall down towards the body of water 1. An embodiment of the balcony 22 and its components will be described in further detail with reference to Fig. 2.

[0047] The floating vessel 20 is supported against a spacer element 122 to a side of the vessel 20. The spacer element 122 forms part of a hang-off support structure 120 and ensures that the floating vessel 20 is kept at a distance to said structure 120. This distance ensures that when the emergency release coupling 50 is activated, the lower half 53 of the emergency release coupling 50 and the releasable end 31 of the flexible pipeline 30 will fall towards the body of water 1 and is unlikely to come into contact with the vessel 20 or hang-off support structure 120 as it falls.

[0048] The hang-off support structure 120 is exemplified as a pillar construction, fixedly installed to the sea floor 2 and in the form of a free-standing structure, i.e. it does not have any physical supporting structures connecting it to the shore. Although not illustrated, there may be a plurality of pillar structures, interconnected by railings or other structures, in order to provide a plurality of intermittently arranged spacers to keep the vessel in a position with clearance to the hang-off support structure 120.

[0049] The hang-off support structure 120 is illustrated in Fig. 1 as comprising a hang-off support arm 123 at its top end. In this exemplary embodiment, the hang- off support arm 123 extends a distance above the top of the hang-off support structure 120 and provides clearance from the structure 120 to a sling 121 connected at the end of the hang-off support arm 123. The hang-off support structure 120 and sling 121, combined with their connection point on the releasable end 31 of the flexible pipeline 30 form a fall-restraint system. The fall restraintsystem is configured to hinder the lower half 53 of the emergency release coupling 50from falling into the body of water 1. However, the fall-restraint system may not provide any arresting or damping function on the falling velocity of the flexible pipeline 30.

[0050] Although not disclosed from the angle shown in Fig. 3, the hang-off support arm 123 may be arranged on a beam, railing or truss structure interconnecting the top of at least two hang-off support structures 120. Thus, the lower half 53 of the emergency release coupling 50 and the releasable end 31 of the flexible pipeline 30 will hang between two pillars 120 when it is in the decoupled state 121'.

[0051] The sling 121 at the end of the hang-off support arm 123 is shown connected at the lower half 53 of the emergency release coupling 50in two different states, coupled 121 and decoupled 121'. In the coupled state, the sling 121 extends towards the lower half 53 of the emergency release coupling 50when it is coupled together with the on the balcony 22. Upon activation of the emergency release coupling 50, the lower half 53 of the emergency release coupling 50 and the releasable end 31 of the flexible pipeline 30 falls towards the body of water 1 but is prevented from being submerged by the restraining action of the sling 121'.

[0052] Fig. 1 also illustrates the lower half 53 of the emergency release coupling 50 and the releasable end 31 of the flexible pipeline 30 in the decoupled state 31'. Here, the sling 121' is shown extending vertically downwards from the end of the hang-off support arm 123. The lower half 53 of the emergency release coupling 50 and the releasable end 31 of the flexible pipeline 30 is thus hanging between the balcony 22 and the body of water 1, and between two pillars of the hang-off support structure 120. The harness 23b is shown extending from the lower half 53 of the emergency release coupling 50 in the decoupled state. The harness extends up through the emergency release coupling 50, through the vertical extent of the balcony 22 and to the top level of the balcony where a winch 23a is arranged for reeling the harness 23b.

[0053] For the coupled and decoupled states of the flexible pipeline 30,30', Fig. 1 illustrates the different positions as it extends towards a subsea pipeline end manifold 73. A subsea flowline 60 is not shown in Fig. 1, but it will be understood that it extends from the subsea pipeline end manifold 73 towards a subsea pipeline end terminal 61, also not shown. The subsea pipeline end manifold 73 isfurthermore illustrated as being supported on a supporting structure 71 resting on the sea floor 2. Such supporting structures will be familiar to the skilled person.

[0054] Turning to Fig. 2, an exemplary embodiment of a balcony 22 is illustrated at the side of a floating vessel 20. The balcony 22 comprises three decks26a, 26b, 26c each having a similar footprint and arranged at three vertically spaced apart levels. A balcony beam is shown extending from the first lower deck 26a of the balcony 22 and to a first deck 28 of the floating vessel 20. The balcony beam 27 is shown reinforced with a triangular truss structure extending along the height of the first deck 26a of the balcony 22. On the first deck 28 of the floating vessel 20, the balcony beam 27 is connected to a balcony beam foundation 27a. The balcony beam foundation 27a is typically installed to the vessel 20 in a drydock as it may require reinforcement of the vessel 20 structure. Preferably, the balcony beam foundation 27a is arranged with means for providing rapid connection between the balcony beam 27 and balcony beam foundation 27a such as bolts that connect into bolt holes on the beam 27.

[0055] Towards the upper end of the balcony's 22 second deck 26b, Fig. 2 illustrates a balcony tension rod 29 extending towards the floating vessel 20. The tension rod 29 is exemplified as being connected to a tension rod foundation 29a on a side plating above the first deck 28. It will be understood that the tension rod foundation 29a may be arranged on any superstructure or other suitable structure above the first deck 28. The tension rod foundation 29a is typically installed during drydocking of the vessel 20, in order to fix it with the necessary reinforcements to the underlying structure on the vessel 20.

[0056] Together, the balcony tension rod 29 and balcony beam 27 support the balcony's 22 weight and moment, whilst allowing for rapid connection to the floating vessel 20. The construction of the balcony 22 can therefore be modular, allowing pre-fabrication with the necessary components before installation to the floating vessel 20 in diverse locations thereby avoiding costly downtime at drydock. Additional structures for allowing ease of access to personnel may be arranged on the balcony 22 and from the floating vessel to the balcony, such as stairs, protection- and handrails, which are illustrated in Fig. 2.

[0057] The exemplary embodiment of Fig. 2 furthermore illustrates three different components arranged at each of the three decks 26a, 26b, 26c. On the third upper deck 26c, a winch 23a is illustrated. The winch 23a has a harness 23b extendingdown toward a lower half 53 of the emergency release coupling 50, shown hanging below the balcony 22. Thus, the winch 23a may ensure that the falling velocity of the lower half 53 of the emergency release coupling 50 and releasable end 31' of the flexible pipeline 30' is restrained upon activation of the emergency release coupling 50. The winch 23a is also capable of reeling in the lower half 53 of the emergency release coupling 50 and flexible pipeline 30' after it has decoupled in order to recouple the emergency release coupling 50. This is due to the drive unit 80 of the winch 23a, which has a dual function fall-arrest and retrieval system 23.34. The drive unit 80 may be configured according to the embodiment described in relation to Fig. 3 and it may form an integral part of the winch 23a.

[0058] On the first lower deck 26a of the balcony 22, the emergency release coupling 50 is illustrated in decoupled state. The emergency release coupling 50 has thus been activated in order to release the lower half 53 of the emergency release coupling 50 and releasable end 31' of the flexible pipeline 30. Hanging below the first lower deck 26a of the balcony 22, attached to the harness 23b of the winch 23a, the lower half 53 of the emergency release coupling 50 and releasable end 31' of the flexible pipeline 30' are shown. In a coupled state, the lower half 53 of the emergency release coupling 5033 will engage with the upper half 52 of the emergency release coupling 50 ensuring a fluid tight connection.

[0059] The emergency release coupling 50 may comprise a hydraulically or mechanically activated solution. One solution, illustrated in the exemplary embodiment of Fig. 2 comprises hydraulically activated clamps 51 arranged to hold the lower half 53 of the emergency release coupling 50in a coupled position such that it is engaged with the upper half 52 of the emergency release coupling 50. Upon activation of the emergency release coupling 50, a hydraulic actuator is arranged to rotate a ring which acts on a hinge of the clamps 51 which releases the upper 52 and lower 53 halves from a coupled position. Other solutions known in the art include providing a mechanically activated collar as an emergency release coupling 50, which holds halves 52,53 together.

[0060] Interface piping 40 is shown extending from the emergency release coupling 50, where the first end 42 of the interface piping 40 fluidly connects to said coupling 50. The interface piping 40 extends up towards and through the second middle deck 26b of the balcony 22. At the second middle deck 26b, the interface piping 40 makes a junction and connects to a pipe spool 43 extending out towards the floating vessel 20and over the side of the balcony decks 26. The pipespool 43 ends at a position above the first deck 28 of the vessel 20, where it will be connected to a fluid manifold system 21 of the vessel 20.

[0061] Thus, it can be seen in the embodiment of Fig. 2 that the footprint of the balcony 22 remains minimal, as the interface piping 40, emergency release coupling 50 and dual function fall-arrest and retrieval system 23,24, comprising the winch 23a, harness 23b and spool 25, are all arranged vertically in relation to each other. This allows for easier pre-fabrication and installation of the balcony 22, such that it may be modular and may be used for a variety of vessels 20.

[0062] Turning to Fig. 3, an exemplary embodiment is illustrated where the drive unit 80 comprises a hydraulic power circuit 82. The shaft 81 of the drive unit 80 is shown connected to a hydraulic rotary actuator exemplified as an impeller 83 that is arranged in the hydraulic power circuit 82. The impeller 83 interacts with the hydraulic fluid in the power circuit 82.

[0063] The example in Fig. 3 illustrates that the hydraulic power circuit 82 divides into two parallel subcircuits 86,87 on either side of the impeller 83. In the first subcircuit 86, a flow restrictor 85 is arranged in series with a hydraulic fluid cooler 89. In the second subcircuit 87, a hydraulic power unit 84 is arranged.

[0064] At the two divides, flow control devices 88 are exemplified in the form of three-way valves 88. However, the skilled person will understand that other devices known in the art may be used for directing the flow in the circuit 82. The three-way valves 88 can direct the hydraulic fluid to either of the two subcircuits 86,87, thereby changing between a retrieval / winch mode and a fall-arrest mode of the drive unit 80. The flow control devices 88 may be controlled by a control unit 100, which is signally connected to actuators of the devices. The control unit 100 may be configured to send signals changing mode of the drive unit 80 upon, or immediately before activation of the emergency release coupling 50.

[0065] In a winch mode, the three-way valves 88 only allow hydraulic fluid to circulate between the impeller 83 and the hydraulic power unit 84, i.e. the flow is directed to the second subcircuit 87. In this winch mode, the circulation of the fluid is caused by a pumping action of the hydraulic power unit 84. The impeller 83 is therefore rotated by the circulation of the hydraulic fluid. The rotation of the impeller 83 drives the rotation of the drive unit shaft 81, and thereby the reeling of the spool 25. As disclosed in Fig. 3, the hydraulic power unit 84 can circulate thefluid in either direction of the circuit 86, thereby causing the harness 24 to be reeled either in or out. As will be understood, the winch mode is used for lifting, lowering or holding the flexible pipeline 30 when it is decoupled from the emergency release coupling 50.

[0066] In a fall-arrest mode, the three-way valves only allow hydraulic fluid to circulate between the impeller 83, the flow restrictor 85 and the hydraulic fluid cooler 89, i.e. the flow is directed to the first subcircuit 86. In this fall-arrest mode, the circulation of the fluid is caused by rotation of the impeller 83. However, the impeller 83 is only rotated once the flexible pipeline 30 has been decoupled from the emergency release coupling 50 and starts falling towards the body of water 1. The harness 24 connected to the releasable end 31 of the flexible pipeline 30 starts reeling out from the spool 25 once the falling motion occurs, which causes a rotation of the drive unit shaft 81 and thereby the impeller 83.

[0067] The hydraulic fluid is thus circulated through the flow restrictor 85 where there is a smaller cross-section than the rest of the hydraulic circuit 82. The flow restrictor 85 is exemplified as a fixed orifice flow restrictor in Fig. 3, but it will be understood that variable restrictors can be implemented. The smaller cross section allows less fluid to flow per unit of time. The reduction in fluid flow thereby affects the speed at which the impeller 83 can rotate causing a braking effect on the drive unit shaft 81 and thereby braking the falling speed of the flexible pipeline 30 when it is decoupled by the activation of the emergency release coupling 50.

[0068] However, the pressure differential caused by the flow restrictor 85 can increase the temperature of the hydraulic fluid. To avoid an unwanted change in viscosity, which may affect the operation of the hydraulic circuit 82, a hydraulic fluid cooler 89 is therefore provided downstream of the flow restrictor 85. Such hydraulic fluid coolers 89 are known in the art, and may for example take the form of a simple air cooler in the form of a radiator.

[0069] Although not illustrated in Fig. 3, the flow restrictor 85 may be coupled to an actuator. The actuator can adjust the cross-section of the restrictor thereby also adjust the rotational speed of the drive unit 80. The actuator may be manually adjusted, or it may be signally connected to a control unit 100. The control unit 100 may be configured to send signals to the actuator that cause it to adjust the crosssection of the flow restrictor 85 as a function of time. For example, certain predetermined values may be programmed into the control unit 100 ensuring thatit regulates the falling speed of the flexible pipeline 30 over time, starting from activation of the emergency release coupling 50, to avoid high shock loads.

[0070] Although not illustrated in Fig. 3, a sensor 90 may be arranged on the drive unit shaft 81, in order to, for example measure rotations per minute. The sensor 90 can be signally connected to the control unit 100 in order to transmit the RPM numbers, which the control unit 100 may process to calculate a falling speed of the flexible pipeline 30, and thereby adjust the flow restrictor 85 in order to bring the falling speed closer to certain predetermined values that are set to dampen the fall and avoid high shock loads. In the preceding description, various aspects of the system 10 according to the invention have been described with reference to the illustrative embodiments. For purposes of explanation, specific numbers, systems and configurations were set forth in order to provide a thorough understanding of the system and its workings. However, this description is not intended to be construed in a limiting sense. Various modifications and variations of the illustrative embodiment, as well as other embodiments of the system, which are apparent to persons skilled in the art to which the disclosed subject matter pertains, are deemed to lie within the scope of the present invention.List of Reference Numbers

Claims

Claims1. An offshore fluid transfer system (10) comprising: a floating vessel (20) comprising a fluid manifold system (21); a flexible pipeline (30) fluidly connectable to the fluid manifold system (21) via an interface piping (40) arranged at a side of the floating vessel (20), wherein the interface piping (40) and flexible pipeline (30) are configured to be connected via an emergency release coupling (50) comprising a lower half (53) arranged at an end of the flexible pipeline (3) and an upper half (52) arranged at an end of the interface piping (40); a harness (24) connected to lower half (53) of the emergency release coupling (50); a spool (25) for reeling the harness (24); and a drive unit (80) connected to the spool (25), wherein the drive unit (80) is configured to: impart rotation to the spool (25), thereby reeling the harness (24) and consequently adjusting the vertical position of the lower half (53) of the emergency release coupling (50) when disconnected from the emergency release coupling (50); and braking rotation of the spool (25), thereby arresting the fall of the lower half (53) of the emergency release coupling (50) upon disconnection from the emergency release coupling (50).

2. The offshore fluid transfer system (10) according to claim 1, wherein the floating vessel (20) comprises a fluid manifold system (21) for transporting and transferring liquefied gas, such as NH3, CO2, chemical gases, LNG or LPG.

3. The offshore fluid transfer system (10) according to claim 1 or 2, wherein the floating vessel (20) comprises a balcony (22) arranged at a side of the floating vessel (20), and the interface piping (40), emergency release coupling (50), harness (24), spool (25) and drive unit (80) are arranged onthe balcony (22).

4. The offshore fluid transfer system (10) according to any of the preceding claims, wherein the drive unit (80) comprises a hydraulic power circuit (82) and a shaft of the drive unit (81) is rotationally connected to a hydraulic rotary actuator (83) which interacts with a fluid in the hydraulic power circuit (82).

5. The offshore fluid transfer system (10) according to claim 4, wherein the hydraulic power circuit (82) comprises a hydraulic power unit (84) arranged to provide hydraulic pressure to the hydraulic power circuit (82) and wherein the hydraulic power circuit (82) comprises a flow restrictor (85) arranged to restrict hydraulic pressure in the hydraulic power circuit (82).

6. The offshore fluid transfer system according to claim 5, wherein the hydraulic power circuit (82) comprises a hydraulic fluid cooler (89).

7. The offshore fluid transfer system (10) according to any of claims 4 or 5, wherein the hydraulic power circuit (82) comprises a first subcircuit (86), wherein the flow restrictor (85) is arranged, a second subcircuit (87), wherein the hydraulic power unit (84) is arranged, wherein the first subcircuit (86) and the second subcircuit (87) are arranged in parallel and connected by flow control devices (88).

8. The offshore fluid transfer system according to claim 7, wherein the hydraulic fluid cooler (89) is arranged in the first subcircuit (86).

9. The offshore fluid transfer system (10) according to any of claims 5-8, wherein the flow restrictor (85) is adjustable.

10. The offshore fluid transfer system (10) according to any of the preceding claims, wherein a sensor (90) is arranged to measure the reeling speed of the harness (24) and / or the length of harness (24) reeled out from the spool (25).

11. The offshore fluid transfer system (10) according to claim 10, comprising a control unit (100) signally connected to an actuator (110) coupled to the flow restrictor (85).

12. The offshore fluid transfer system (10) according to claim 11, wherein the sensor (90) is signally connected to the control unit (100).

13. The offshore fluid transfer system according to claim 12, wherein the control unit (100) is configured to: process signals from the first sensor (90) to calculate a reeling speed of the harness (24); compare the reeling speed with predetermined speed values; determine an adjustment to the flow restrictor (85) in order to minimise the deviation between the actual speed and the predetermined values; transmit signals to the flow restrictor actuator (110) to adjust the pressure in the hydraulic power circuit.

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