Abstract:
A structure ( 20 ) for loading and unloading at least one fluid transport ship ( 1 ): a ship ( 1 ) mooring platform ( 21 ), comprising at least one concrete caisson ( 22 ) having an opening and closing device for moving the caisson by filling water, between a flotation position for transporting the platform, and a position anchored at the bottom of the sea. The platform comprises a submerged lower anchoring portion and an upper portion, partially outside of the water, for berthing the ship.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a 35 U.S.C. §371 National Phase conversion of PCT/FR2009/050754, filed Apr. 23, 2009, which claims benefit of French Application No. 08 52814, filed Apr. 25, 2008, the disclosure of which is incorporated herein by reference. The PCT International Application was published in the French language. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a structure for loading and unloading at least one ship for transporting a fluid, such as for example hydrocarbons, liquefied natural gas (LNG), liquefied petroleum gas (LPG) or any other liquefied gas. 
     The present invention applies in particular to the transfer of this type of product between a ship and a fixed structure consisting for example of a liquefaction unit or a regasification terminal when loading the ship, or a fluid reservoir when unloading the ship. 
     In view of certain constraints relating to safety and the movement of ships, it is preferable to carry out the fluid transfer operations while keeping the ship out of a port, in deeper waters, for example a few hundred meters away from the coast. 
     For carrying out such operations in open water, ship loading and unloading stations are known in particular which comprise a fluid transfer platform attached to the seabed by an attachment structure consisting of a set of piles driven into the seabed. 
     The platform supports articulated fluid transfer arms which are intended to be connected to pipe systems of the ship known as “manifolds” on the ship. 
     The known loading stations additionally comprise a set of mooring dolphins for absorbing the energy of berthing of the ship and the tide after berthing. The mooring dolphins are also attached to the seabed by rigid metal piles. 
     The fluid transfer platform is connected to a reservoir located on the coast or on a fixed platform at sea by a flexible conduit or pipeline that is partially or fully submerged. 
     This type of transfer platform requires a very large number of piles and is expensive and requires the use of heavy equipment for installation purposes. 
     Furthermore, due to their distance from the coast, this type of transfer platform is subject to the swell of the open sea and it is therefore necessary to orient them in such a way that, when the ship is moored at said platform, the ship faces towards the dominant swell. The “wind” factor must also be taken into account in the same way as the swell. 
     One aim of the invention is to propose a structure for loading and unloading at least one ship, which can be easily transported from a manufacturing site to the site of loading or unloading of the ship and can also be easily installed at this site, while withstanding waves of great height in extreme conditions. 
     SUMMARY OF THE INVENTION 
     The invention therefore relates to a structure for loading and unloading at least one fluid transport ship, characterised in that the structure is formed by a quay for mooring the ship, said quay comprising at least one concrete caisson equipped with closing and opening means for moving said caisson, by filling it with water, between a floating position for transporting the quay and a position anchored in the seabed, in which this caisson comprises a submerged lower part of said caisson for anchoring purposes and an upper part of said caisson, partially out of the water, for the berthing of said ship. 
     According to other features of the invention:
         the quay comprises a plurality of caissons placed end to end and connected to one another by complementary joining means,   the lower part of said at least one caisson comprises at least one compartment equipped with closing and opening means,   the lower part of said at least one caisson comprises a plurality of compartments, each equipped with closing and opening means,   each closing and opening means is formed by a bottom plate of the compartment connected to means for displacing said bottom plate between a position of closing the corresponding compartment and a position of opening this compartment,   the displacement means are formed by means for the step-by-step or continuous displacement of the bottom plate,   said at least one compartment of the caisson comprises at least one member for locking the bottom plate in the closed position so as to keep said compartment sealed,   the lower edge of the lower part of said at least one caisson comprises means for embedding the caisson in the seabed, and   the embedding means are formed by orifices for spraying a pressurised fluid into the seabed.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood on reading the following description, given solely by way of example and with reference to the appended drawings, in which: 
         FIG. 1  is a schematic plan view of a loading and unloading structure according to the invention, after the mooring of a fluid transport ship, 
         FIG. 2  is a schematic plan view of a concrete caisson of the loading and unloading structure according to the invention, 
         FIG. 3  is a schematic view in vertical section of the caisson of  FIG. 2 , in the floating position, 
         FIG. 4  is a schematic view of the caisson of  FIG. 2 , in the position anchored in the seabed, and 
         FIG. 5  is a schematic perspective view, partially cut-away, of the means for opening and closing a compartment of the caisson of the structure, according to the invention. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  schematically shows a structure denoted by the general reference  20  for loading and unloading at least one ship  1  for transporting a fluid, such as for example liquefied hydrocarbons, in particular liquefied gas, such as liquefied natural gas (LNG), liquefied petroleum gas (LPG), or any other type of liquefied gas. 
     In a conventional manner, the ship  1  comprises a floating hull  2  delimiting a lateral mooring edge  3  and at least one reservoir  2   a  for storing the liquefied fluid. The ship  1  additionally comprises, along its mooring edge  3 , mooring lines  4  attached respectively at the front, at the rear and in the middle part of the ship  1 . 
     The reservoir  2   a  comprises a plurality of manifolds  5  which open transversely relative to the hull  2 . Each manifold  5  is equipped at its outer end with a removable connector  6  for connecting it to a conduit  10  for transferring fluids to a terminal (not shown) which is arranged for example on the coast, or at sea, away from the structure  20 , and which comprises reservoirs for storing liquefied hydrocarbons. The conduit  10 , shown in dashed line in  FIG. 1 , is in this case a cryogenic conduit submerged in the expanse of water. 
     The structure  20  for loading and unloading the ship  1  will now be described with reference more particularly to  FIGS. 1 to 3 . 
     This structure  20  comprises a quay  21  for receiving and mooring the ship  1 . This quay  21  comprises at least one concrete caisson  22  and, in the example of embodiment shown in  FIG. 1 , a plurality of caissons  22  placed end to end. 
     To this end, and as shown in  FIG. 2 , the end walls of each caisson  22  comprise complementary joining means which consist, on one of the end walls, of projecting elements  23  and, on the other opposite end wall, of a recessed part  24  intended to receive the projecting elements  23  of the adjacent caisson  22  when the caissons are placed one next to the other. 
     Each concrete caisson  22  can be installed, by filling it with water, at an installation site in the open water, where each caisson  22  is anchored in the seabed A, as shown in  FIG. 4 , after transporting each caisson  22  in a floating position, as shown in  FIG. 3 , between a manufacturing site and the installation site. 
     Each caisson  22  comprises a lower part  22   a  making it possible to fill the caisson  22  with water, as will be seen below, and an upper part  22   b  forming technical sleeves for the passage for example of the conduits for connection (not shown) to the ship  1  or for the passage of any other member. The passage of the connecting conduits in the upper parts  22   b  of the caissons  22  thus makes it possible to protect these conduits from the swell and from any impact. 
     In the floating position shown in  FIG. 3  the lower part  22   a  of the caisson  22  is sealed and is partially submerged and the upper part  22   b  is located above the water level B, and in the position anchored in the seabed A the lower part  22   a  of the caisson  22  is submerged and is partially embedded in the seabed A and the upper part  22   b  is partially out of the water for the purpose of berthing the ship  1 . 
     The lower part  22   a  of the caisson  22  comprises at least one compartment  25  and, in the example shown in the figures, this lower part  22   a  comprises four compartments. 
     Each compartment  25  is equipped with closing and opening means  30  for moving the caisson  22 , by filling it with water, between its floating position and its position anchored in the seabed A. 
     The means  30  for closing and opening each compartment  25  consists of a bottom plate  31  which is movable and which is connected to means  35  for displacing this bottom plate  31  between a position in which it closes the corresponding compartment  25  in a sealed manner and a position in which said compartment  25  is open. In the position in which it closes the compartment  25 , the bottom plate  31  bears against a rim  26   a  formed on the lower edge  26  of the lower part  22   a  of the caisson  21 , as shown in  FIG. 3 . 
     One means of displacing a bottom plate  31  will now be described with reference to  FIGS. 3 to 5 , each displacement means being identical and one bottom plate  31  being able to be associated with a plurality of displacement means  35 . 
     Each displacement means  35  is formed by a rod  36  having a lower end  36   a , connected to the corresponding bottom plate  31  by an articulation axle  37 , and a free upper end  36   b . The rod  36  passes through the lower part  22   a  and the upper part  22   b  of the caisson  22 . The rod  36  carrying the bottom plate  31  can be displaced by step-by-step or continuous means. 
     In the case of step-by-step displacement means, these means consist of two assemblies  38 , a first assembly  38  being placed above the lower part  22   a  and a second assembly  38  being placed above the upper part  22   b  of the caisson  22 . 
     One assembly  38  will now be described with reference to  FIG. 5 , the other assemblies being identical. 
     As shown schematically in  FIG. 5 , each assembly  38  comprises a plurality of jaws  39  which can be displaced transversely and perpendicular to the corresponding rod  36  between a position moved away from this rod  36  and a position clamped against said rod  36 . Each assembly  38  also comprises cylinders  40  for displacing the jaws  39  vertically. 
     In the case of means for continuously displacing the rod  36  carrying a corresponding bottom plate  31 , the displacement means consist for example of a rack-and-pinion assembly of the known type (not shown). 
     The displacement of each rod  36  may be carried out by any other suitable system. 
     As shown more particularly in  FIG. 3 , each bottom plate  31  is associated with at least one locking member  41  for locking this bottom plate  31  in the sealed closed position of the corresponding compartment  25 . Each locking member consists for example of a screw-and-nut mechanism of the known type or of any other suitable mechanism. 
     In order to make it easier to anchor the caisson  22  in the seabed A, in addition to the intrinsic weight of the caisson, the lower edge  26  of the lower part of this caisson  22  comprises means for embedding the caisson  22  in the seabed A. 
     These embedding means, shown in  FIG. 5 , consist of orifices  45  for spraying a pressurised fluid into the seabed A. These orifices  45  are distributed along the length of the lower edge  26  of the caisson  22 . 
     One of the side faces of the upper part  22   b  comprises a framework  50  formed of a trellis of beams on which the ship  1  is moored by means of mooring ropes  4 , as shown in  FIG. 1 . On the side face opposite to the one carrying the framework  50 , the upper part  22   b  of the caisson  22  comprises breakwaters  51 . 
     The caissons  22  intended to form the quay  21  are installed at sea as follows. Each caisson  22  is brought in the floating state to the installation site. To this end, the bottom plate  31  of each compartment  25  is kept pressed against the rim  26   a  of the lower edge  26  so as to seal each compartment  25  of the caisson  22 . The bottom plate  31  of each compartment  25  is kept in this position by at least one locking member  41 , as shown in  FIG. 3 . 
     At the ship mooring site, two methods for anchoring the caissons  22  intended to form the quay  21  are possible. 
     First of all, the caissons  22  are oriented in such a way that the breakwaters  51  arranged on one side of the upper part  22   b  of the caisson  22  are oriented on the dominant swell side so as to break this swell and protect the ship  1  when it is moored at the quay  21 . 
     The first method of submerging the caissons  22  consists of submerging each caisson  22  separately. 
     The locking member  41  for locking each bottom plate  31  is retracted in order to release this bottom plate  31 . 
     The bottom plate  31  of each compartment  25  is then displaced from the position in which it closes the corresponding compartment  25  to the position in which it opens this compartment  25 . To this end, the jaws  39  of the lower displacement assembly  38  are locked so as to lock the rod  36  carrying the bottom plate  31  that is to be opened. The jaws  39  of the upper displacement assembly  38  are unlocked on the corresponding rod  36  and the cylinders  40  of the upper displacement assembly  38  are actuated, which has the effect of displacing the rod  36  vertically upwards and of raising the bottom plate  31  of the corresponding compartment  25 . 
     The water starts to penetrate into the compartment  25  and, after this first displacement of the rod  36  and of the bottom plate  31 , the jaws  39  of the upper displacement assembly  38  are locked onto the rod  36 . The jaws  39  of the lower displacement assembly  38  are unlocked and returned to their initial position by the cylinders  40 . 
     The cylinders  40  of the upper displacement assembly  38  are then actuated so as to displace the rod  36  and the bottom plate  31  by a further step. A larger quantity of water thus penetrates into the compartment  25  of the lower part  22   a  of the caisson  22 . The displacement of the rod  36  and of the corresponding bottom plate  31  thus takes place in successive steps. 
     The bottom plates  31  of the compartments  25  of the caisson  22  may be displaced in a synchronised manner or separately so that the caisson  22  gradually sinks and comes to lie on the seabed B. The caissons  22  intended to form the entire quay  21  are thus submerged one another the other and are placed on the seabed B. 
     The bringing-together and joining of the caissons one next to the other can be carried out by a system of cables and winches of the known type (not shown). To this end, a cable passes longitudinally through each caisson  22  via a longitudinal passage  47  ( FIG. 5 ) formed between the parts, lower  22   a  and upper  22   b  respectively, of the caisson  22 . 
     A second method of submerging the caissons  22  intended to form the quay  21  consists of assembling these caissons  22  one next to the other in the floating state. 
     The set of caissons  22  thus assembled is submerged, as above, by successively or simultaneously raising the bottom plates  31  of all the compartments  25  of the caissons  22 . 
     As the caisson  22  is placed on the seabed A, this caisson  22  gradually becomes embedded in the seabed A under the effect of its own weight and this embedding is facilitated by spraying a pressurised fluid into the seabed A through the orifices  45 . The bottom plates  31  of the compartments  25  are kept in the open position of each compartment  25 , as shown in  FIG. 4 . 
     When the caissons  22  forming the quay  21  are thus anchored in the seabed A with the breakwaters  51  directed towards the dominant swell side, the conduits (not shown) provided in the upper part  22   b  of the caissons  22  of the quay  21  and intended for unloading a ship  1  after the latter has berthed are connected to the underwater conduit  10  so as to be able to transfer the fluid unloaded from the ship  1  towards the coast and towards a storage site. 
     The number of caissons  22  makes it possible to control and manage the descent of the quay as it is placed onto the seabed. This is because the greater the number of caissons  22 , the more it is possible to open and/or close caissons in order to stabilise the descent of the quay as a whole. 
     According to one variant, the lower part  22   a  of the caissons  22  may be a cylindrical section and, in this case, the bottom plate  31  of each compartment  25  is curved. 
     The loading and unloading structure according to the invention has the advantage of being able to be brought to the loading or unloading site by floating and also of enabling a ship to berth in difficult conditions. 
     The structure according to the invention can be easily anchored at sea without it being necessary to drive in a multitude of piles and without any need to use heavy equipment in order to install it. A simple tug is sufficient for bringing the quay to the ship mooring site.