FR2887900A1 - Electricity generating system constructing and installing method, involves towing assembly of ballast, system and structure to site, maintaining descended structure on sea-bed and resetting cans in flotation after detaching, to be reused - Google Patents

Abstract

The method involves constructing a gravity structure formed of a column (5) fixed to a base (6). Removable floatation cans (131, 132) are attached to the structure. The structure is placed in flotation and alongside quay to load a ballast (9) and an electricity generating system on the structure. An assembly of the ballast, system and structure are towed to a final operation site, and the structure is descended on a sea-bed (7) by ballasting the cans. The structure is maintained on the sea-bed, and the cans are detached and reset in flotation by deballasting, for being recovered and reused. An independent claim is also included for a system for generating electricity in sea.

Description

The present invention relates to a method of constructing and

  in place of an offshore power plant including a wind turbine and gravity support structure of this wind turbine designed to rest on a seabed. The present invention also relates to such an installation adapted to

the implementation of this method.

  It has already been proposed to produce electricity using wind turbines installed at sea, particularly near a shore. According to the known proposals, the wind turbine is mounted on a tower, called "jacket", wire mesh for example, placed and fixed on a seabed, in the manner of a gravity platform.

  The installation of such an installation on a final site of operation then comprises two successive phases corresponding to the establishment of the tower and the wind turbine, respectively. These operations mobilize a large and therefore expensive fleet: special barges, derricks barges, etc .... They are also very dependent on weather conditions. These limitations currently affect the interest of the creation of farms or fields of wind turbines at sea whereas one wishes however to develop such farms at sea because it is there that the aesthetic nuisances or noise which are attached to them are the least sensitive .

  The present invention is specifically intended to overcome these limitations.

  This object of the invention is achieved, as well as others which will appear on reading the following description, with a method of constructing and setting up an offshore electricity production installation comprising a wind turbine. and a gravity support structure of this wind turbine designed to rest on a seabed, according to which: a) the dry structure is constructed by providing at least one space for receiving a ballast and attaching at least one flotation chamber; removable, b) the structure is floated and docked for the loading of the ballast and the installation of the wind turbine on the structure, from the wharf, c) the entire assembly thus formed is towed on its final operating site and the gravity structure is lowered on the seabed by ballasting the buoyancy chamber, and d) the said gravity structure is maintained on the said bottom under the effect of its own weight, the caisson is detached from the structure and it is returned in flotation by deballasting to be recovered and reused. 30

  As will be seen below in detail, the method according to the invention makes it possible to tow on site all the components of the installation in a single trip, which is very favorable from the economic point of view. This unique trip also makes the operation less dependent on weather conditions. The reuse of the buoyancy chamber (s) further reduces the cost of installation in the case of the construction of a wind farm.

  According to other features of the present invention: in step a), at least two buoyancy chambers are fixed on the gravity supporting structure, substantially symmetrically with respect to the axis of a support mast; an electricity generator forming part of the wind turbine, the box (es) are fixed in the vicinity of the periphery of the structure so as to ensure the stability of the assembly throughout its towing and its descent towards the bottom marine, - the removable box or boxes are dimensioned vertically so as to protrude from the surface of the water when the gravity structure comes to touch the seabed, - in step b), said structure is floated by shifting on a launching pad.

  The present invention also provides an offshore electricity production installation adapted to the implementation of this method, comprising a wind turbine and a gravity support structure of this wind turbine designed to rest on a seabed, remarkable in that it includes means for temporarily fixing at least one removable flotation box on the gravity structure, during the on-site towing of this assembly and during its controlled descent to the seabed, by ballasting the box.

  According to other characteristics of this installation: the fastening means are designed to temporarily retain at least two parallelepiped-shaped flotation chambers arranged in the vicinity of the periphery of the gravity support structure, substantially symmetrically with respect to the axis of a support pole of an electricity generator forming part of the wind turbine, the caissons are positioned and dimensioned to ensure the floatation and the stability of the wind turbine / support structure during the on-site towing of this assembly and the stability of the assembly during its controlled descent to the seabed, by ballasting of the caisson, the removable caissons are dimensioned vertically so as to overflow the surface of the water when the gravitational structure comes to touch the seabed - the gravity structure comprises a ballasted base with a solid ballast, - this base is also ballasted with water of m st.

  Other characteristics and advantages of the present invention will appear on reading the following description and on examining the appended drawing in which: FIG. 1 is an elevational view of the electricity generating installation in sea according to the invention, and - Figures 2A to 2G schematically illustrate successive steps of the construction and implementation of the installation shown in Figure 1.

  Referring to Figure 1 of the accompanying drawing which shows schematically a wind turbine 1 comprising a vertical mast 2 supporting a group 3 of electricity production consisting of an electric generator whose rotor is rotated by blades 4, at 43 set in motion by the wind, as is well known.

  In FIG. 1 it also appears that the mast 2, of axis X, is mounted and fixed coaxially on a column 5 itself secured to a base 6 resting on a seabed 7, the column projecting from the surface 8 of the water.

  The upper end 5a of the column 5, on which the mast 2, also establishes an inspection platform, located at a height such that it is never reached by the water during storms. It is at this platform that connections are established between the electrical cables (not shown) delivering the energy produced by the wind turbine and those driving this energy to the land use locations.

  The base 6 takes the form of a flat box of square, rectangular, polygonal or circular vertical section, for example, ballasted with a solid ballast 9 completed, in the embodiment shown by way of illustrative and nonlimiting example only, by a volume of seawater.

  The base 6 can be anchored in the seabed 7 by spades such as those referenced 111 and 112 arranged around the periphery of its lower face.

  The column 5 and the base 6 and ballasted together constitute a gravity support structure of the wind turbine 1 on the seabed 7. The mast 2 and this structure are of course dimensioned vertically so that the blades 41 to 43 of the wind turbine can turn widely above the surface 8 of the water. Such a structure 5, 6 may be made of steel or concrete, for example.

  The base 6 of the structure 5, 6 makes it possible to transmit to the seabed the environmental efforts, such as those due to waves, wind, ocean currents, earthquakes, ... suffered by the sea. wind turbine and this structure.

  For reasons that will become apparent in the following description, the base 6 carries means for temporarily fixing at least one buoyancy chamber on its upper face. These means, schematized in 121 and 122 in Figure 1, may take various forms well known in the art of offshore construction.

  Referring now to Figures 2A-2G to describe in detail the method according to the invention for the construction and implementation of the power generation plant described above in connection with Figure 1.

  As shown diagrammatically in FIG. 2A, the column 5 and the base 6 are constructed and assembled dry, in dry dock or, as shown, docked, steel or concrete as mentioned above.

  According to an important feature of the present invention, at the stage of construction shown in Figure 2A, is further attached to the base 6 at least one buoyancy chamber, removably. In the embodiment shown, it is actually attached to this base 6 two buoyancy chambers 131 and 132, with the fixing means 121 and 122 respectively, provided for this purpose on this basis as seen more high in connection with Figure 1.

  As will be seen below this or these water boxes are positioned and sized to ensure the floatation and stability of the wind turbine / support structure during the towing of this assembly on the final site of operation of the electricity generation installation according to the invention. They also ensure the stability of this set during its descent to the seabed.

  Boxes 131 and 132 shown are of parallelepipedal shape and are arranged in the vicinity of the periphery of the base 6 of the gravity structure 5, 6, symmetrically with respect to the axis X of the column 5 and the mast 2, so as to optimize their effectiveness in the stabilization function assigned to them.

  At the stage of the process according to the invention illustrated by FIG. 2B, the structure of FIG. 2A is launched by shifting on a launching ramp 14, with the aid of a tug, not shown. The floatation of the structure is ensured by the volume of air contained in the base 6, then empty of all ballast, with a suitable sizing of this base.

  The floating structure is then towed to the dock to receive its solid ballast 9, loaded in the base 6 (see Figure 2C) and the wind itself (Figure 2D). Under the weight of the ballast and the wind turbine, the structure sinks into the water without ceasing to float thanks to the floatation caissons then also partially sunk into the water.

  The assembly thus formed is then towed again (Figure 2E) to its final operating site where the support structure is submerged to rest on the seabed, by a gradual ballast and controlled seawater, floatation caissons 13 and 132 (FIG. 2F).

  The gravity support structure now rests on the seabed under the effect of its own weight and that of the solid ballast 9, possibly supplemented by a complementary ballast 10 in seawater of this base.

  This gravity structure is possibly fixed on the seabed fixed by the spades provided on the base 6 (see Figure 1).

  According to the present invention, divers will then disconnect the buoyancy chambers from the base 6 by deactivation of the fastening means 121 and 122. The caissons are finally emptied of the water they contain by pumping and thus floated back (FIG. 2G) to be retrieved for the installation of another installation.

  It is understood that this recovery, added to the on-site transport of all the elements of the installation in a single trip, makes the process according to the invention particularly economical and safe, especially when it comes to installing large fields of wind turbines, this in accordance with the purpose of the invention announced in

  preamble of the present description.

  It is furthermore understood that by reversing the steps of the method illustrated by FIGS. 2A to 2G, it is possible to bring a plant back to shore for maintenance or repair operations. These operations can then be performed under much better conditions than at sea. This inverted process also makes it possible to move installations from one field to another, as needed.

  It is clear that the stability of the installations or plant parts transported by the method according to the invention has remained good throughout the implementation of this method. To do this the boxes must be sized to give them the buoyancy to compensate for the weight supported by these boxes, and this at all times of transport and immersion. It will therefore be ensured that at all times the expression (p - a) remains positive, p being the metacentric radius of the floating body and at the height of the center of gravity of this body above the hull.

  In this respect we will notice an advantageous arrangement of the water boxes, illustrated in Figure 2F. In this figure it appears in fact that these boxes are dimensioned vertically so as to slightly exceed the surface 8 of the water when the gravity structure 5, 6 rests on the seabed. This maximizes the inertia of the section of the entire structure / caissons throughout the immersion of this structure and therefore the value of p which is directly proportional to this inertia.

  It will also be noted that the stability in place is due to the effort exerted by the ballast on the bottom, this stability to withstand the torque reversal due to current and wind forces.

  It will again be noted that the reuse of the water boxes, and therefore their removal from the final installation, reduces the environmental efforts suffered by this installation, by reducing the grip offered to such efforts.

  By way of illustrative and non-limiting example, the invention makes it possible to produce an offshore power generation installation with a power of 3 MW delivered by a generator installed at about 70 m above sea level. The total weight of such an installation, including a gravity steel structure, is about 6000 tons during its transport, including about 450 tons of buoyancy tanks with an overall volume of 4700 m3. We understand that the reuse of these is generating a substantial saving.

  Of course, the invention is not limited to the embodiment shown which has been given only as an example. Thus, the shape, number and arrangement of the water boxes may differ widely from those described above, at the choice of the designer and / or according to specific needs, provided that they meet the constraints. buoyancy and stability posed above.

Claims (11)

  1. A method for constructing and setting up an offshore electricity generating installation comprising a wind turbine (1) and a gravity structure (5, 6) for supporting this wind turbine designed to rest on a seabed (7). ), characterized by the following steps: a) said structure (5, 6) is dryly constructed by providing a space for receiving a ballast (9) and attaching thereon at least one removable flotation box (131, 132) (b) placing said float and dock structure (5, 6) for loading said ballast (9) and installing said wind turbine (1) on said structure (5, 6) from said platform, c) the assembly thus formed is towed on its final operating site and said gravity structure (5, 6) is lowered onto said seabed (7) by ballasting said buoyancy chamber (131, 132), and d) maintained said gravity structure (5, 6) on said bottom (7) under the effect of its own weight, said box (131, 132) being detached of said structure (5, 6) and is floated by deballasting to be recovered and reused.   2. Method according to claim 1, characterized in that, in step a), at least two buoyancy chambers (131, 132) are fixed on said support gravity structure (5, 6), substantially symmetrically relative to to the axis (X) of a mast (2) for supporting an electricity generator (3) forming part of the wind turbine (1).   3. Method according to any one of claims 1 and 2, characterized in that the fixed or said boxes (131,132) in the vicinity of the periphery of said structure (5, 6) so as to ensure the stability of said assembly throughout its towing and descent to the seabed (7).   4. Method according to claim 3, characterized in that the or said removable boxes (131, 132) are dimensioned vertically so as to overflow the surface (8) of the water when said gravity structure (5, 6) comes touching the seabed (7).   5. Method according to any one of claims 1 to 4, characterized in that, in step b), said structure (5, 6) is placed in flotation by shifting on a launching ramp.   6. Offshore electricity production installation adapted to the implementation of the method according to any one of claims 1 to 5, comprising a wind turbine (1) and a gravity structure (5, 6) for supporting this wind turbine. (1) designed to rest on a seabed (7), characterized in that it comprises means (121, 122) for temporarily fixing at least one removable flotation chamber (121, 12: z) on said structure gravity (5, 6), during the on-site towing of this assembly and during its controlled descent to the seabed (7), by ballasting said box (131, 132).   7. Installation according to claim 6, characterized in that said fixing means (121, 122) are designed to temporarily retain at least two flotation compartments (121, 122) of parallelepipedal shape disposed in the vicinity of the periphery of said structure gravity carrier (5, 6), substantially symmetrically with respect to the axis (X) of a mast (2) for supporting an electricity generator forming part of the wind turbine (1).   8. Installation according to any one of claims 6 and 7, characterized in that the or said caissons (121, 122) are positioned and sized to ensure the floatation and stability of the wind turbine / support structure during the on-site towing of this assembly and the stability of said assembly during its controlled descent to the seabed (7), by ballasting said caisson.   9. Installation according to any one of claims 6 to 8, characterized in that said removable boxes (121, 122) are dimensioned vertically so as to overflow the surface (8) of the water when said gravity structure (5). , 6) touches the seabed (7).   10. Installation according to any one of claims 6 to 9, characterized in that said gravity structure comprises a base (6) ballasted with a solid ballast (9).   11. Installation according to claim 10, characterized in that said base (6) is also ballasted with sea water.