SEALED AND THERMALLY INSULATING TANK

Abstract

The invention relates to a sealed and thermally insulating tank for storing fluid, comprising, from the outside to the inside of the tank, a secondary thermally insulating barrier and a secondary sealing membrane, the secondary sealing membrane being secured to the secondary thermally insulating barrier, a primary thermally insulating barrier resting against the secondary sealing membrane and a primary sealing membrane resting against the primary thermally insulating barrier, the tank comprising a duct that extends along a longitudinal direction, the duct being delimited on one hand by the secondary thermally insulating barrier and on the other hand by the secondary sealing membrane, a bottom of the duct being at least in part formed by the secondary thermally insulating barrier, the tank further comprising a pressure-drop stopper that is arranged in the duct and extends between the bottom of the duct and the sealing membrane.

Claims

1. A sealed and thermally-insulating fluid storage tank wherein a tank wall comprises from the exterior to the interior of the tank a secondary thermally-insulating barrier and a secondary sealed membrane, the secondary sealed membrane being anchored to the secondary thermally-insulating barrier, a primary thermally-insulating barrier resting against the secondary sealed membrane and a primary sealed membrane resting against the primary thermally-insulating barrier and being intended to be in contact with a fluid contained in the tank, wherein said secondary thermally-insulating barrier comprises a first plane portion and a second plane portion oriented at an angle to the first plane portion, a junction between the first secondary thermally-insulating barrier plane portion and the second secondary thermally-insulating barrier plane portion forming an edge, the first plane portion forming a first anchor zone for the secondary sealed membrane, the first anchor zone being at a distance from the edge, the second plane portion forming a second anchor zone for the secondary sealed membrane, the second anchor zone being at a distance from the edge, the secondary thermally-insulating barrier comprising a corner portion between the first anchor zone and the second anchor zone and comprising the edge, the secondary sealed membrane comprising a corner piece, said corner piece being sealed and comprising a first portion anchored to the first anchor zone and a second portion anchored to the second anchor zone, the corner piece further comprising a central portion between the first portion and the second portion, said central portion being free to deform relative to the secondary thermally-insulating barrier in line with the edge, the tank comprising a duct extending in a longitudinal direction parallel to the edge, said duct being delimited by the central portion of the secondary sealed membrane and the corner portion of the secondary thermally-insulating barrier, the corner portion of the secondary thermally-insulating barrier forming a bottom of the duct, the tank further comprising a pressure-drop obstacle arranged in the duct and extending between the bottom of the duct and the central portion of the secondary sealed membrane.

2. The sealed and thermally-insulating tank as claimed in claim 1 wherein the duct is parallel to the direction of terrestrial gravity or has a component perpendicular to the direction of terrestrial gravity.

3. The sealed and thermally-insulating tank as claimed in claim 1, wherein said pressure-drop obstacle includes comprises an anchor strip and a flexible portion, the anchor strip extending in a direction intersecting the longitudinal direction of the duct, the flexible portion comprising a plurality of flexible elements projecting from the anchor strip in the direction of the secondary sealed membrane, and a free end of the flexible elements opposite the anchor strip being in contact with the secondary sealed membrane so as to create a pressure drop for a flow circulating in the duct, said flexible elements being able to flex elastically in contact with the secondary sealed membrane.

4. The sealed and thermally-insulating tank as claimed in claim 3, wherein the anchor strip is fixed to the bottom of the duct.

5. The sealed and thermally-insulating tank as claimed in claim 3, wherein the pressure-drop obstacle comprises a textile layer covering flexible elements of the pressure-drop obstacle.

6. The sealed and thermally-insulating tank as claimed in claim 1, wherein said pressure-drop obstacle comprises a flexible film, said flexible film including comprising a first fixing zone and a second fixing zone, the first fixing zone extending transversely to the longitudinal direction of the duct, the first fixing zone of said flexible film being fixed to the bottom of the duct, the second fixing zone extending transversely to the longitudinal direction of the duct, the second fixing zone being fixed to the external face of the secondary sealed membrane delimiting the duct, the flexible film comprising an obstacle portion extending from the first fixing zone to the second fixing zone, said obstacle portion extending across the duct between the bottom and the duct and the secondary sealed membrane so as to create a pressure drop in the duct.

7. The sealed and thermally-insulating tank as claimed in claim 6, wherein the first fixing zone and the second fixing zone are situated at two opposite edges of the flexible film and are disposed at the same level in the longitudinal direction of the duct.

8. The sealed and thermally-insulating tank as claimed in claim 6, wherein the obstacle portion of the flexible film is a first obstacle portion, the flexible film comprises a third fixing zone extending transversely to the longitudinal direction of the duct, the third fixing zone being fixed to the bottom of the duct, the second fixing zone lying between the first fixing zone and the third fixing zone, the flexible film comprising a second obstacle portion extending from the second fixing zone to the third fixing zone, said second obstacle portion extending across the duct between the bottom of the duct and the secondary sealed membrane so as to create a pressure drop in the duct.

9. The sealed and thermally-insulating tank as claimed in claim 6, wherein the obstacle portion is deformable and comprises at least one fold along an axis transverse to the longitudinal direction of the duct.

10. The sealed and thermally-insulating tank as claimed in claim 9, wherein the obstacle portion comprises two folds spaced from one another in the longitudinal direction of the duct, each fold being produced along an axis transverse to the longitudinal direction of the duct.

11. The sealed and thermally-insulating tank as claimed in claim 6, wherein the flexible film is made of a material chosen in the group consisting of glass matting, polyethylene film and polyamide film.

12. The sealed and thermally-insulating tank as claimed in claim 6, wherein the first fixing zone and/or the second fixing zone extend(s) in a plane intersecting the longitudinal direction of the duct, preferably in a plane perpendicular to the longitudinal direction of the duct.

13. The sealed and thermally-insulating tank as claimed in claim 1, the tank comprising a plurality of pressure-drop obstacles arranged in the duct along the longitudinal direction of the duct.

14. The sealed and thermally-insulating tank as claimed in claim 13, wherein the pressure-drop obstacles of the plurality of pressure-drop obstacles are arranged in the duct at regular intervals along the longitudinal direction of the duct.

15. The sealed and thermally-insulating tank as claimed in claim 13, wherein the pressure-drop obstacles of the plurality of pressure-drop obstacles are arranged in the duct at irregular intervals along the longitudinal direction of the duct.

16. The sealed and thermally-insulating tank as claimed in claim 14, wherein the secondary thermally-insulating barrier forming the bottom of the duct comprises a plurality of spaced insulating panels and a plurality of junction zones situated between the insulating panels and the obstacles are arranged facing the insulating panels in such a manner that the junction zones at each edge of a panel are between the obstacles.

17. A ship for transporting a cold liquid product, the ship comprising a double hull and a tank as claimed in claim 1 disposed in the double hull.

18. A transfer system for a cold liquid product, the system comprising a ship as claimed in claim 17, insulated pipes arranged in such a manner as to connect the tank installed in the hull of the ship to a floating or terrestrial storage installation and a pump for driving a flow of cold liquid product through the insulated pipes from or to the floating or terrestrial storage installation to or from the tanker of the ship.

19. A method loading or offloading a ship as claimed in claim 17, wherein a cold liquid product is routed through insulated pipes from or to a floating or terrestrial storage installation to or from the tank of the ship.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0117] The invention will be better understood and other aims, details, features and advantages thereof will become more clearly apparent in the course of the following description with reference to the appended drawings of particular embodiments of the invention provided by way of non-limiting illustration only.

[0118] FIG. 1 is a schematic view in section and in perspective of a sealed and thermally-insulating tank portion arranged in a supporting structure;

[0119] FIG. 2 is a view in section of a corner of the sealed and thermally-insulating tank taken on the section plane Ill in FIG. 1;

[0120] FIG. 3 is a view to a larger scale of the detail 38 from FIG. 2 illustrating an edge of the secondary thermally-insulating barrier and the secondary sealed membrane;

[0121] FIG. 4 is a schematic perspective view of a pressure-drop obstacle including blades that can be used in the corner of the tank from FIG. 2;

[0122] FIG. 5 is a schematic perspective view of a pressure-drop obstacle in accordance with one embodiment including blades and a woven fabric;

[0123] FIG. 6 is a schematic perspective view of a corner structure that can be used in the tank illustrated in FIG. 1;

[0124] FIG. 7 is an enlarged detail view of the corner structure in FIG. 6 at the level of an edge of the secondary thermally-insulating barrier;

[0125] FIG. 8 is a schematic representation in section illustrating the secondary sealed membrane and the secondary thermally-insulating barrier at the level of the corner of the sealed and thermally-insulating tank at ambient temperature;

[0126] FIG. 9 is a view analogous to FIG. 8 in the tank containing a cryogenic liquid;

[0127] FIG. 10 is a schematic representation in perspective illustrating a pressure-drop obstacle fixed to the secondary thermally-insulating barrier at the level of the edge formed by said secondary thermally-insulating barrier;

[0128] FIG. 11 is a view analogous to FIG. 9 representing a variant of the corner of the sealed and thermally-insulating tank;

[0129] FIG. 12 is a schematic view in perspective illustrating the corner of the sealed and thermally-insulating tank provided with a pressure-drop obstacle in accordance with a further embodiment;

[0130] FIG. 13 is a lateral view of the pressure-drop obstacle in the direction of the arrow XIII in FIG. 12;

[0131] FIG. 14 is a view analogous to FIG. 13 of a pressure-drop obstacle in accordance with another embodiment;

[0132] FIG. 15 is a schematic cutaway representation of a methane tanker tank including a sealed and thermally-insulating tank, and of a terminal for loading/offloading that tank.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0133] By convention, the terms “external” and “internal” are used to define the relative position of one element with respect to another with reference to the interior and to the exterior of the tank.

[0134] A sealed and thermally-insulating tank for storing and transporting a cryogenic fluid, for example liquefied natural gas (LNG), includes a plurality of tank walls each having a multilayer structure.

[0135] A tank wall of this kind includes, from the exterior to the interior of the tank, a secondary thermally-insulating barrier 1 anchored to a supporting structure 2 by secondary retaining members, a secondary sealed membrane 3 carried by the secondary thermally-insulating barrier 1, a primary thermally-insulating barrier 4 resting on the secondary sealed membrane 3, and a primary sealed membrane 5 carried by the primary thermally-insulating barrier 4 and intended to be in contact with the cryogenic fluid contained in the tank.

[0136] The supporting structure 2 may in particular be a self-supporting metal plate or, more generally, any type of rigid partition having appropriate mechanical properties. The supporting structure 2 may in particular be formed by the hull or the double hull of a ship, as illustrated in FIG. 1. The supporting structure 2 includes a plurality of walls defining the general shape of the tank, usually a polyhedral shape. Some tanks may include only one thermally-insulating barrier and one sealed membrane, for example for storing LPG.

[0137] As illustrated in FIG. 1 the tank, here of polyhedral shape, includes lateral tank walls 6 and transverse walls 7 (only one transverse wall being illustrated in FIG. 1) that have a vertical component, that is to say a component parallel to the direction of terrestrial gravity. In tank walls 6, 7 of this kind having a vertical component the presence of ducts extending over all the height of the tank wall 6, 7 is likely to favour phenomena of natural convection. In fact, in tank walls 6, 7 of this kind thermosyphon phenomena may occur which leads to deterioration of the insulating performance of the thermally-insulating barriers 1, 4. One aspect of the invention starts from the idea of limiting or even eliminating these natural convection phenomena.

[0138] As illustrated in FIG. 2, the secondary thermally-insulating barrier 201 includes a first corner insulating panel 35 forming one edge of the secondary thermally-insulating barrier 201 of the first tank wall 33. Likewise, the secondary thermally-insulating barrier 201 includes a second corner insulating panel 36 forming an edge of the secondary thermally-insulating barrier 201 of the second tank wall 34. The first corner insulating panel 35 and the second corner insulating panel 36 form an edge 37 of the secondary thermally-insulating barrier 201 at the level of a corner of the secondary thermally-insulating barrier 201 formed by the junction of the first tank wall 33 and the second tank wall 34.

[0139] The term “edge” denotes the junction zone between the two tank walls, which may have different shapes with greater or lesser curvature. It therefore encompasses a sharp edge, a rounded edge and a fillet.

[0140] As illustrated in FIGS. 2 and 3 the secondary thermally-insulating barrier 201 includes a first corner insulating panel 35 forming one edge of the secondary thermally-insulating barrier 201 of the first tank wall 33. Likewise, the secondary thermally-insulating barrier 201 includes a second corner insulating panel 36 forming an edge of the secondary thermally-insulating barrier 201 of the second tank wall 34. The first corner insulating panel 35 and the second corner insulating panel 36 form an edge 37 of the secondary thermally-insulating barrier 201 at the level of a corner of the secondary thermally-insulating barrier 201 formed by the junction of the first tank wall 33 and the second tank wall 34.

[0141] An internal face of the first corner insulating panel 35 forms a first anchor zone 39 and an internal face of the second corner insulating panel 36 forms a second anchor zone 40. The first anchor zone 39 is on the internal face of the first corner insulating panel 35 at a distance from the edge 37 and, likewise, the second anchor zone 40 is on the internal face of the second corner insulating panel 36 at a distance from the edge 37. These first and second anchor zones 39 and 40 include a metal plate (not illustrated) analogous to the plates 13 described hereinabove extending parallel to the edge 37.

[0142] In order to assure the continuity of the secondary sealed membrane 203 between the first tank wall 33 and the second tank wall 34 the secondary sealed membrane 203 includes a corner piece. A corner piece of this kind is, for example, a metal angle-iron 41. This angle-iron 41 enables connection in sealed manner of a portion of the secondary sealed membrane 203 that is part of the first tank wall 33 and a portion of the secondary sealed membrane 203 that is part of the second tank wall 34.

[0143] A first portion 42 of the angle-iron 41 is anchored in sealed manner to the first anchor zone 39 and a second portion 43 of the angle-iron 41 opposite the first portion 42 is anchored in sealed manner to the second anchor zone 40. The anchoring of the first and second portions 42 and 43 of the angle-iron 41 to the metal plate forming the first and second anchor zones 39 and 40 may be direct, for example by direct welding to said metal plate, or indirect, for example by overlap welding to a portion of the secondary sealed membrane 203 carried by the corresponding tank wall that is between the portion 42 or 43 of the angle-iron 41 and the corresponding anchor zone 39 or 40.

[0144] In order to absorb loads in the secondary sealed membrane 203 at the level of the corner, in particular at the level of the edge 37, a central portion 44 of the angle-iron 41 between the first portion 42 and the second portion 43 is left free relative to the secondary thermally-insulating barrier 201. Accordingly, when the tank is cooled, the first and second anchor portions 42, 43 of the angle-iron 41 remain anchored to the anchor zones 39 and 40 of the secondary thermally-insulating barrier 201 and the loads, such as the loads stemming from contraction of the secondary sealed membrane 203 or the secondary thermally-insulating barrier 201 distancing the anchor zones 39, 40 from one another, at the level of the corner, are absorbed by deformation of the central portion 44 of the angle-iron 41. In particular, the central portion 44 extends between the first and second portions 42 and 43 of said angle-iron 41 so that said central portion 44 moves away from the edge 37 on deforming. This separation between the central portion 44 of the angle-iron 41 and the edge 37 produces or enlarges a duct between the secondary thermally-insulating barrier 201 and the angle-iron 41 of the secondary sealed membrane 203. This duct extends over all the length of the edge 37, parallel to the vertical direction of the tank and therefore, as explained hereinabove, liable to favour natural convection and to degrade the insulating performance of the tank.

[0145] Moreover, the sealed membrane illustrated in FIGS. 2 and 3 may be produced by a composite sheet that is stuck on instead of a metal membrane that is welded on. In this case the metal angle-iron 41 may be replaced by a flexible composite sheet 41, for example a laminated sealed film including a metal foil between two layers of fiber such as glass fiber, for example. A corner piece in the form a flexible composite sheet 41 may for example have a first portion stuck to the first anchor zone of the thermally-insulating barrier and a second portion glued to the second anchor zone of the thermally-insulating barrier. The central portion of a flexible composite sheet 41 of this kind is then left free relative to the corner portion of the thermally-insulating barrier and the pressure-drop obstacle would be arranged in an analogous manner between said central portion of the flexible composite sheet and the thermally-insulating barrier. A secondary sealed membrane including this kind of flexible composite sheet at the level of a corner of the tank is for example described in the document WO2014167214.

[0146] In this case also, contraction of the flexible composite sheet 41 in line with the edge 37 produces or enlarges a duct between the secondary thermally-insulating barrier 201 and the secondary sealed membrane 203.

[0147] In order to prevent this a pressure-drop obstacle 217 is disposed in the duct, as illustrated in FIG. 3. The pressure-drop obstacle 217 is illustrated in FIG. 4.

[0148] The pressure-drop obstacle 217 takes the form of a sheet 132 that includes a continuous lower portion forming the anchor strip 224 and regularly spaced blades 229 over all its width. The blades 229 are flexible and in the same plane when at rest. Each blade 229 has a first end 330 continuous with the anchor strip 224 and a free second end 331.

[0149] The anchor strip 224 is fixed to a corner portion of the secondary thermally-insulating barrier formed by the internal face of the first corner insulating panel 35 between the first anchor zone 39 and the edge 37 and the internal face of the second corner insulating panel 36 between the second anchor zone 40 and the edge 37. This corner portion typically forms the bottom 220 of the duct.

[0150] The first corner insulating panel 35 and the second corner insulating panel 36 include a slot (not illustrated) extending in the thickness of the internal plate of said corner insulating panels 35, 36 from the first anchor zone 39 or the second anchor zone 40 as far as a plane 45 of contact between said corner insulating panels 35, 36. In other words, slots of this kind are advantageously contiguous at the level of the junction plane 45 between the corner insulating panels 35, 36 in order together to form a housing for the pressure-drop obstacle 217, a pressure-drop obstacle 217 of this kind in the form of a sheet having a shape that is simple to manufacture and that is simple to insert in said housing.

[0151] Pressure-drop obstacles 217 of this kind are preferably installed by prefabrication during the fabrication of a corner insulating block formed of the first corner insulating panel 35 and the second corner insulating panel 36. When installing the corner angle-iron 41, the blades 229 are deformed by the angle-iron 41 or the flexible composite sheet 41 bearing on said blades 229. Moreover, during cooling of the tank causing an increase in the section of the duct, the load exerted by the angle-iron 41 or the flexible composite sheet 41 on the blades 229 is reduced and the elasticity and the length of the blades 229 allow said blades 229 to accompany the increase in the section of the duct by maintaining contact with the external surface of the angle-iron 41 or the flexible composite sheet 41 in order to obstruct said duct.

[0152] FIG. 5 shows another embodiment of a pressure-drop obstacle 317 further including a woven fabric. In this embodiment the pressure-drop obstacle 317 takes the form of a sheet 132 covered in part by a woven fabric 50. The sheet 132 includes a continuous lower portion forming the anchor strip 324. Each blade 329 has a first end 330 contiguous with the anchor strip 324 and a free second end 331. The blades 329 are regularly spaced from one another over all the width of the sheet 132. The woven fabric 50 of the pressure-drop obstacle 317 overlaps and is stuck to the anchor strip 324 and the blades 329. The woven fabric 50 has an excess length so as to form expansion bellows 82 in line with the separations between the blades 329. The blades 329 therefore remain relatively uncoupled from one another in bending.

[0153] Referring to FIGS. 6 to 9 there will now be described another embodiment of the corner of the tank in which a convection duct may appear in a similar manner.

[0154] At the level of the junction between a first wall 8 of the tank, for example a lateral wall 6, and a second wall 9 of the tank, for example a transverse wall 7, the tank includes a corner structure 51 illustrated in FIG. 6. This corner structure 51 is advantageously prefabricated.

[0155] The corner structure 51 illustrated in FIG. 6 includes a first corner secondary insulating panel 52 and a second corner secondary insulating panel 53. The corner secondary insulating panels have, from the exterior of the tank to the interior of the tank, a rigid external plate 54, an insulating packing 55 and a rigid internal plate 15. The first corner secondary insulating panel 52 and the second corner secondary insulating panel 53 also have a bevelled face, the bevelled faces of said two corner secondary insulating panels 52, 53 being contiguous. Accordingly, as illustrated in detail in FIG. 7, the corner secondary insulating panels form an edge 16 of the secondary thermally-insulating barrier 1.

[0156] The first corner secondary insulating panel 52 carries a first secondary sealed membrane portion 56 and the second corner secondary insulating panel 53 carries a second secondary sealed membrane portion 18. These first and second secondary sealed membrane portions 56, 18 may be produced in numerous ways. In one embodiment the first and second secondary sealed membrane portions 56, 18 are made of laminated sealed film. Laminated sealed film of this kind includes a metal, for example aluminium, sheet between two layers of fibers coated with resin. Secondary sealed membrane portions 56, 18 made of laminated sealed film of this kind are for example stuck to the internal face of the corner secondary insulating panels 52, 53. In another embodiment the first and second secondary sealed membrane portions 56, 18 are metal plates anchored on the corner secondary insulating panels 52, 53.

[0157] As illustrated in FIG. 7 the secondary sealed membrane portions 56, 18 have a longitudinal edge extending parallel to the edge 16 of the secondary thermally-insulating barrier 1, said edge being at a distance from the edge 16. The first secondary sealed membrane portion 56 typically forms an edge of the secondary sealed membrane 3 of the first wall 8 and the second secondary sealed membrane portion 18 typically forms an edge of the secondary sealed membrane 3 of the second wall 9.

[0158] In order to seal the secondary sealed membrane 3 in the corner of the tank the corner structure 51 includes a corner secondary sealed membrane portion 19. This corner secondary sealed membrane portion 19 connects in sealed manner the first secondary sealed membrane portion 56 and the second secondary sealed membrane portion 18. This corner secondary sealed membrane portion may be produced in numerous ways. In one embodiment the corner secondary sealed membrane portion 19 is made of laminated sealed film, for example including a metal foil between two layers of fibers not coated with resin. A corner secondary sealed membrane portion 19 made of laminated sealed film of this kind is for example glued to the first and second secondary sealed membrane portions 56, 18.

[0159] In accordance with another embodiment the corner secondary sealed membrane portion 19 is formed by a metal angle-iron anchored in sealed manner to the first and second secondary sealed membrane portions 56, 18.

[0160] As illustrated in detail in FIG. 7 the corner secondary sealed membrane portion 19 extends along the edge 16. The corner secondary sealed membrane portion 19 has longitudinal edges parallel to the edge 16. A first longitudinal edge of the corner secondary sealed membrane portion 19 forms a first anchor zone 20, illustrated in dashed line in FIG. 7, which is fixed in sealed manner to the first secondary sealed membrane portion 56. Likewise, a second longitudinal edge of the corner secondary sealed membrane portion 19 forms a second anchor zone 21, illustrated in dashed line in FIG. 7 that is fixed in sealed manner to the second secondary sealed membrane portion 18.

[0161] The fixing in sealed manner of the anchor zones 20, 21 of the corner secondary sealed membrane portion 19 to the secondary sealed membrane portions 56, 18 may be obtained in numerous ways, for example by gluing in the case of a corner secondary sealed membrane portion 19 in the form of a laminated sealed film or by welding in the case of a corner secondary sealed membrane portion 19 in the form of a metal angle-iron. The internal rigid plate 15 of the corner secondary insulating panels 52, 53 may include a thermal protection band accommodated in a recess in order to protect said corner secondary insulating panels 52, 53 when carrying out such welding.

[0162] The corner structure 51 further includes a plurality of primary insulating elements 22 juxtaposed along the edge 16 of the secondary thermally-insulating barrier 1. Each primary insulating element 22 includes a first primary insulating block 23 resting on the first secondary sealed membrane portion 56 and a second primary insulating block 24 resting on the second secondary sealed membrane portion 18. The plurality of primary insulating elements 22 forms the primary thermally-insulating barrier 4.

[0163] The primary sealed membrane 5 includes a plurality of metal corner angle-irons 25 each resting on a respective primary insulating block 23, 24. Accordingly, each metal angle-iron includes a first flange 26 resting on the first primary insulating block 23 of a primary insulating element 22 and a second flange 27 resting on the second primary insulating block 24 of said primary insulating element 22.

[0164] The corner secondary sealed membrane portion 19 includes a central zone 28 between the first anchor zone 20 and the second anchor zone 21. This central zone 28 is arranged in line with the edge 16 and extends along the edge 16. This central zone 28 is not fixed to the secondary thermally-insulating barrier 1. In other words, the central zone 28 is free relative to the secondary thermally-insulating barrier 1 and more particularly relative to the edge 16. Other details and features of a corner structure of this kind are described for example in the document WO2014167214A2.

[0165] The absence of fixing of the central zone 28 of the corner second sealed membrane portion 19 to the secondary thermally-insulating barrier 1 makes it possible to absorb the loads to which the second sealed membrane 3 is subjected in line with the edge 16. In fact, as illustrated in FIG. 8, when the tank is constructed the corner secondary sealed membrane portion 19 is arranged so that the central zone 28 is as close as possible to edge 16. This arrangement makes it possible to limit the presence of an empty space favouring convection between the secondary sealed membrane 3 and the secondary thermally-insulating barrier 1.

[0166] However, during cooling of the tank, the secondary sealed membrane 3 and therefore the corner secondary sealed membrane portion 19 contract, which causes deformation of said corner secondary sealed membrane portion 19 as illustrated in FIG. 9. Likewise, the corner secondary insulating panels 52, 53 contract, which moves the anchor zones 20, 21 of the corner secondary sealed membrane portion 19 away from one another and therefore also bring about deformation of said corner secondary sealed membrane portion 19.

[0167] As illustrated in FIG. 9, this deformation of the corner secondary sealed membrane portion 19 moves the central zone 28 away from the edge 16, which significantly increases the volume of empty space between the corner secondary sealed membrane portion 19 and the secondary thermally-insulating barrier 1 at the level of the edge 16. A duct 29 therefore appears or increases in size between the secondary sealed membrane 3 and the secondary thermally-insulating barrier 1. This duct 29 extends over all the length of the edge 16 present in a longitudinal direction parallel to the edge 16. This duct is typically delimited by an external face of the central portion 28 of the corner secondary sealed membrane portion 19 and by a portion of the internal faces of the rigid plates 15 of the corner secondary insulating panels 52, 53 between the edge 16 and the first and second secondary sealed membrane portions 56 and 18, said portion of the internal faces of the rigid plates 15 forming a bottom 60 of the duct 29.

[0168] To prevent convection in the duct 29 the tank includes a pressure-drop obstacle. A pressure-drop obstacle of this kind is arranged in the duct 29 between an internal face of the secondary thermally-insulating barrier 1 and an external face of the secondary sealed membrane 3. It may be produced in various ways.

[0169] FIG. 10 illustrates one embodiment of a pressure-drop obstacle of this kind. This pressure-drop obstacle is produced in the form of a flexible film 30.

[0170] The flexible film 30 may be made of numerous materials, for example thermoplastic materials including polyethylene (PE), polyethylene terephthalate (PET), polyamide, polyimide, polyetherimide, polypropylene in the form of a textile or other film or any other material or textile having flexibility at low temperature. The pressure-drop obstacle may equally be made of woven textile, possibly coated. The woven textile may be based on different types of fibers, for example mineral fibers, such as glass fibers, basalt fibers, or natural fibers, for example based on hemp, flax or wool or a thermoplastic (PE, PET, PP, PI, PEI, . . . ).

[0171] The flexible film 30 illustrated in FIG. 10 includes a first fixing zone 31, a second fixing zone 32 and a third fixing zone 57. The first fixing zone 31 and the third fixing zone 57 are formed at the level of two opposite edges of the flexible film 30. These first and third fixing zones 31, 57 are for example formed by opposite transverse edges of the flexible film 30.

[0172] The second fixing zone 32 lies between the first fixing zone 31 and the third fixing zone 57, for example at substantially equal distances from the first and third fixing zones 31 and 57.

[0173] The flexible film 30 also includes a first obstacle portion 58 between the first fixing zone 31 and the second fixing zone 32 and a second obstacle portion 59 between the second fixing zone 32 and the third fixing zone 57.

[0174] The first fixing zone 31 and the third fixing zone 57 are fixed to the secondary thermally-insulating barrier 1. To be more specific, the first fixing zone 31 and the third fixing zone 57 are fixed to the bottom 60 of the duct 29 in such a manner as to extend transversely, preferably perpendicularly, to the longitudinal direction of the duct 29.

[0175] This fixing of the first and third fixing zones 31 and 57 to the bottom 60 of the duct 29 may be effected in numerous ways. This fixing is for example effected by gluing or by means of a double-sided adhesive tape, for example containing polytetrafluoroethylene (PTFE), lying between each of said first and third fixing zones 31 and 57 and the bottom 60 of the duct 29.

[0176] The second fixing zone 32 is fixed to the external face of the central portion 28 of the corner secondary sealed membrane portion 19. In an analogous manner to the fixing of the first and third fixing zones 31 and 57, the second fixing zone 32 may be fixed in numerous ways, for example by gluing or by means of a double-sided adhesive tape between the second fixing zone 32 and the external face of the central zone 28 of the corner secondary sealed membrane portion 19.

[0177] In accordance with one embodiment, installing the flexible film 30 in the tank includes first fixing the first and third fixing zones 31 and 57 to the bottom 60 of the duct 29 by gluing or by means of an adhesive tape. Moreover, a double-sided adhesive tape is applied to the external face of the central portion 28 of the corner second sealed membrane portion 19 at the location where the second fixing zone 32 must be fixed. The corner secondary sealed membrane portion 19 with said double-sided adhesive tape on it is then anchored to the first and second secondary sealed membrane portions 56 and 18. Anchoring the corner secondary sealed membrane portion to said secondary sealed membrane portions 56 and 18 brings the double-sided adhesive tape against the second fixing zone 32 and therefore fixes said second fixing zone 32 to the corner secondary sealed membrane portion 19. In the context of a laminated sealed film corner secondary sealed membrane portion, pressure exerted on an internal face of said laminated sealed film in line with the double-sided adhesive tape can improve the fixing of the second fixing zone 32 to said laminated sealed film.

[0178] The first obstacle portion 58 and the second obstacle portion 59 are free relative to the secondary thermally-insulating barrier 1 and the secondary sealed membrane 3. In other words, said first and second obstacle portions 58 and 59 are not fixed either to the secondary thermally-insulating barrier 1 or to the secondary sealed membrane 3. The longitudinal edges 61 of the obstacle portions 58 and 59 are therefore loose and enable on the one hand reduced circulation of gas in the duct 29, that is to say with a pressure drop linked to the arrangement of said obstacle portions 58 and 59 in the duct 29, and, on the other hand, deformation of the flexible film 30 to accompany the deformation of the corner secondary sealed membrane portion 19.

[0179] In fact, as explained hereinabove with reference to the figures, during cooling of the tank the corner secondary sealed membrane portion 19 is stretched. During this stretching of the corner secondary sealed membrane portion 19 the second fixing zone 32 of the flexible film 30 fixed to the central zone 28 of the corner secondary sealed membrane portion 19 accompanies the variation of the position of said central zone 28 linked to the deformation of the corner secondary sealed membrane portion 19. The first and third fixing zones 31 and 57 of the flexible film 30 are fixed to the secondary thermally-insulating barrier 1, the obstacle portions 58 and 59 of the flexible film 30 are in tension between said fixing zones 31, 32 and 57 and extend in the duct 29 between the secondary thermally-insulating barrier 1 and the secondary sealed membrane 3. The duct 29 is therefore obstructed by the first obstacle portion 58 and the second obstacle portion 59 between the central zone 28 of the corner secondary sealed membrane portion 19 and the secondary thermally-insulating barrier 1 whilst enabling a circulation of gas with a pressure drop in the flow.

[0180] The accompanying of the variation of position of a corner secondary sealed membrane portion 19 by the second fixing zone 32 is facilitated if the flexible film 30 has good flexibility at low temperature. Accordingly, as represented in FIG. 10, when the tank is cooled the obstacle portions 58 and 59 can deform slightly and take on a conical shape.

[0181] Pressure-drop obstacles of this kind are advantageously arranged in the tank at the level of corners of the tank the edge 16 of which has a component parallel to terrestrial gravity, typically between the lateral walls 6 and the transverse walls 7 of the tank. Pressure-drop obstacles of this kind may equally be arranged in a tank at the level of corners of the tank the edge 16 of which is perpendicular to terrestrial gravity. Moreover, a plurality of pressure-drop obstacles may be arranged, for example at regular intervals, along the duct 29, thus controlling the pressure drop along the duct 29.

[0182] FIG. 11 illustrates an embodiment in which the corner secondary sealed membrane portion 19 is formed by a laminated sealed film stuck to the first and second secondary sealed membrane portions 56 and 18 and in which the tank further includes a stop 62 for positioning the corner secondary sealed membrane portion 19.

[0183] A stop 62 of this kind is arranged on the bottom 60 of the duct 29, along the edge 16, and has a first face 63 resting on the internal rigid plate 15 of a corner secondary insulating panel and a second face 64 resting on the internal rigid plate 15 of a corner secondary insulating panel. This stop 62 further includes an internal face 65 connecting the first and second faces 63 and 64 of the stop 62. This internal face 65 has a concave shape the cavity of which faces toward the interior of the tank.

[0184] During installation of the corner secondary sealed membrane portion 19 the central zone 28 of said corner secondary sealed membrane portion 19 is arranged in such a manner as to rest on the internal face 65 of the stop 62. The corner secondary sealed membrane portion 19 is therefore easily positioned for gluing the first and second fixing zones 20 and 21 to the first and second secondary sealed membrane portions 56 and 18, respectively.

[0185] A stop 62 of this kind therefore makes it possible to control the radius of curvature of the central zone 28 of the corner secondary sealed membrane portion 19 when gluing said corner secondary sealed membrane portion 19, typically during fabrication of the tank. A stop 62 of this kind further enables reduction of the dimensions of the duct 29, but is not able to prevent enlargement of said duct 29 during cooling of the tank, as illustrated by the corner secondary sealed membrane portion 19 illustrated in this FIG. 11 under tension linked to thermal contraction, as explained hereinabove. In a duct 29 of this kind the internal face 65 then forms the bottom 60 of said duct 29.

[0186] In the presence of a stop 62 of this kind the first fixing zone 31 and the third fixing zone 57 of the pressure-drop obstacle can be fixed directly to the internal face 65 of the stop 62.

[0187] In one embodiment a first end of one or more of the fixing zones 31, 32 and/or 57 of the flexible film 30 lies between the first sealed membrane portion 56 and the first anchor zone 20 of the corner secondary sealed membrane portion 19. Likewise, a second edge of one or more fixing zones 31, 32 and/or 57 lie(s) between the second secondary sealed membrane portion 18 and the second anchor zone 21 of the corner secondary sealed membrane portion 19. These edges of said fixing zones 31, 32 and/or 57 are therefore and typically pinched between the first and second secondary sealed membrane portions 56 or 18 and the corner secondary sealed membrane portion 19, thus providing a simple way of fixing the fixing zones 31, 32 and/or 57.

[0188] In an embodiment illustrated in FIGS. 12 and 13 the pressure-drop obstacle takes the form of a flexible film 130 that includes a first fixing zone 69 and a second fixing zone 332. The first fixing zone 69 and the second fixing zone 332 are formed at the level of two opposite edges of the flexible film. The first fixing zone 69 is fixed to a bottom 236 of the duct 68. The second fixing zone 332 is fixed to an external face of the secondary sealed membrane 203. The first fixing zone 69 and the second fixing zone 332 are offset in the longitudinal direction of the duct 68. In other words, the first fixing zone and the second fixing zone are not face to face, with the result that the obstacle portion 235 extends with a component parallel to the longitudinal direction of the duct 68. The obstacle portion 235 includes two spaced folds and therefore has a Z shape.

[0189] In order to facilitate integration of the obstacle in the tank a prefabricated pressure-drop obstacle 130 may be installed in the corner structure 51 before placing the corner structure 51 in the sealed and thermally-insulated tank. The structure of the obstacle 130 is simpler to fit during prefabrication in the factory of the panels with a portion of the sealed membrane covering them.

[0190] In an embodiment illustrated in FIG. 14 the pressure-drop obstacle also takes the form of a flexible film 230 substantially in the shape of a U that is folded about an axis transverse to the longitudinal direction of the duct. The obstacle 230 includes a first fixing zone 231, a second fixing zone 232 and an obstacle portion folded on itself. The first fixing zone 231 and the second fixing zone 232 are formed at the level of two opposite edges of the flexible film. The first fixing zone 231 is fixed to a bottom 236 of the duct. The second fixing zone 232 is fixed to an external face of the sealed membrane 203. The first fixing zone 231 and the second fixing zone 232 are face to face. When the obstacle portion is arranged in a plane, the flexible film has a length greater than the distance between a fixing surface of the first fixing zone 231 to the bottom of the duct 229 and a fixing surface of the second fixing zone 232 to the sealed membrane.

[0191] In accordance with one embodiment, the flexible film forms a fold in which is accommodated a compressible element 99, for example made of wadding, felt, glass wool, rock wool, polymer foam. The compressible element 99 is compressed between the first and second fixing zones 231, 232 and therefore exerts a reaction force that facilitates the fixing by gluing of the first fixing zone 231 and the second fixing zone 232 to the bottom of the duct and to the external face of the sealed membrane, respectively. The obstacle 230 is inserted in the sealed and thermally-insulating tank in the interstice between the bottom of the duct 236 and the sealed membrane.

[0192] In accordance with one embodiment, a non-stick film (not represented) that prevents the two parts of the flexible film folded relative to one another sticking together is inserted in the fold of the flexible film in place of or in combination with the compressible element 99.

[0193] For the installation of the obstacle 230 in the duct 236 a tool in the form of a blade may be used, where appropriate a curved blade the curvature of which corresponds to the shape of the bottom of the duct, for example the curvature of the stop 62. The non-stick film and the flexible film are successively folded around the edge at the end of the blade in order to push them into the duct 236, for example between the stop 62 and the corner secondary sealed membrane portion 19.

[0194] The technique described hereinabove for producing a sealed and thermally-insulating tank may be used in different types of reservoirs, for example in an LNG reservoir in a terrestrial installation or in a floating structure such as a methane tanker or other ship.

[0195] In a manner known in itself loading/offloading pipes 73 disposed on the top deck of the ship may be connected by means of appropriate connectors to a maritime or harbour terminal to transfer a cargo of LNG from or to the tank 71.

[0196] FIG. 15 shows an example of a maritime terminal including a loading and offloading station 75, an underwater pipe 76 and a terrestrial installation 77. The loading and offloading station 75 is a fixed off-shore installation including a mobile arm 74 and a tower 78 that supports the mobile arm 74. The mobile arm 74 carries a bundle of insulated flexible tubes 79 that can be connected to the loading/offloading pipes 73. The orientable mobile arm 74 adapts to all methane tanker loading gauges. A connecting pipe that is not shown extends inside the tower 78. The loading and offloading station 75 enables loading and offloading of the methane tanker 70 from or to the terrestrial installation 77. The latter includes liquefied gas storage tanks 80 and connecting pipes 81 connected via the underwater pipe 76 to the loading or offloading station 75. The underwater pipe 76 enables transfer of the liquefied gas between the loading or offloading station 75 and the terrestrial installation 77 over a great distance, for example 5 km, which enables the methane tanker ship 70 to remain at a great distance from the coast during loading and offloading operations.

[0197] Pumps onboard the ship 70 and/or pumps equipping the terrestrial installation 77 and/or pumps equipping the loading and offloading station 75 are used to generate the pressure necessary to transfer the liquefied gas.

[0198] Although the invention has been described in connection with a plurality of particular embodiments, it is obvious that it is in no way limited to them and that it encompasses all technical equivalents and combinations of the means described if the latter fall within the scope of the invention.

[0199] Likewise, the embodiment illustrated in the figures represents a pressure-drop obstacle including one or two fixing zones cooperating with the thermally-insulating barrier and a fixing zone cooperating with the secondary sealed membrane, but the number of fixing zones able to cooperate with the sealed membrane and the number of fixing zones able to cooperate with the thermally-insulating barrier may be different. A pressure-drop obstacle can thus include a plurality of fixing zones intended to cooperate with the thermally-insulating barrier alternately with a plurality of fixing zones intended to cooperate with the sealed membrane so that the obstacle portions between a fixing zone on the thermally-insulating barrier and a fixing zone on the sealed membrane extend in a duct to obstruct said duct.

[0200] Generally speaking, pressure-drop obstacles of this kind can therefore be installed in any interstice linked to a positioning or production clearance liable to form or to generate in use of a tank a duct favouring convection phenomena.

[0201] Although the invention has been described in connection with a plurality of particular embodiments, it is obvious that it is in no way limited to them and that it encompasses all technical equivalents and combinations of the means described if the latter fall within the scope of the invention.

[0202] The use of the verb “to have”, “to include” or “to comprise” and conjugate forms thereof does not exclude the presence of elements or steps other than those stated in a claim.

[0203] In the claims, any reference sign between parentheses should not be interpreted as a limitation of the claim.