Patent Application
20060096185
The present invention relates to the production of sealed, thermally insulated tanks consisting of tank walls fixed to the load-bearing structure of a floating structure suitable for the production, storage, loading, ocean carriage and/or unloading of cold liquids such as liquefied gases, particularly those with a high methane content. The present invention also relates to a methane carrier provided with a tank of this type.
Ocean carriage of liquefied gas at very low temperature involves an evaporation rate per day's sailing that it would be advantageous to minimize, which means that the thermal insulation of the relevant tanks should be improved.
A sealed, thermally insulated tank consisting of tank walls fixed to the load-bearing structure of a ship has already been proposed, said tank walls having, in succession, in the direction of the thickness from the inside to the outside of said tank, a primary sealing barrier, a primary insulating barrier, a secondary sealing barrier and a secondary insulating barrier, at least one of said insulating barriers consisting essentially of juxtaposed non-conducting elements, each non-conducting element including a thermal insulation liner arranged in the form of a layer parallel to said tank wall, at least one panel extending parallel to said tank wall over at least one side of said thermal insulation liner and load-bearing partitions projecting from a face of said at least one panel facing said thermal insulation liner, said load-bearing partitions rising through the thickness of said thermal insulation liner in order to take up the compression forces.
For example, in FR-A-2 527 544 these insulating barriers consist of closed parallelepipedal caissons made from plywood and filled with perlite. On the inside, the caisson includes parallel load-bearing spacers interposed between a cover panel and a base panel in order to withstand the hydrostatic pressure exerted by the liquid contained in the tank. Non-load-bearing spacers made from plastic foam are placed between the load-bearing spacers in order to maintain their relative positioning. Manufacture of a caisson of this type, including the assembly of the outer walls made from plywood sections and the fitting of the spacers, requires a number of assembly operations, particularly stapling. Furthermore, the use of a powder such as perlite complicates the manufacture of the caissons because the powder produces dust. Thus, it is necessary to use high-quality and therefore expensive plywood so that the caisson is well sealed against dust, i.e. knot-free plywood. Furthermore, it is necessary to tamp down the powder with a specific pressure in the caisson, and it is necessary to circulate nitrogen inside each caisson in order to evacuate all the air present, for safety reasons. All these operations complicate manufacture and increase the cost of the caissons.
Moreover, if the thickness of the insulating caissons is increased with an insulating barrier, the risk of the walls of the caissons and the load-bearing spacers buckling increases considerably. If it is desired to increase the anti-buckling strength of the caissons and of their internal load-bearing spacers, the cross section of said spacers has to be increased, which increases the thermal bridges established between the liquefied gas and the load-bearing structure of the ship by the same amount. Furthermore, if the thickness of the caissons is increased it is observed that, inside the caissons, gas convection currents arise that are highly detrimental to good thermal insulation.
FR-A-2 798 902 describes other thermally insulated caissons designed for use in such a tank. Their method of manufacture consists in alternately stacking a plurality of low-density foam layers and a plurality of plywood panels, placing adhesive between each foam layer and each panel until the height of said stack corresponds to the length of said caissons, in cutting the above-mentioned stack into sections in the direction of the height, at regular intervals corresponding to the thickness of a caisson, and in adhesively bonding a base panel and a top panel made from plywood on either side of each stack section thus cut, said panels extending perpendicularly to said cut panels, which serve as spacers. Although the result of this is a good compromise in terms of anti-buckling strength and thermal insulation, it has to be admitted that this manufacturing process also requires numerous assembly stages. Furthermore, procurement of good-quality plywood could become problematic in the future.
An object of the invention is to propose a tank of this type while also improving at least one of the following characteristics without detriment to others of these characteristics: the tank's cost price, the ability of the walls to withstand pressure and the thermal insulation of the walls.
To that end, a subject of the invention is a sealed, thermally insulated tank including at least one tank wall fixed to the load-bearing structure of a floating structure, said tank wall having, in succession, in the direction of the thickness from the inside to the outside of said tank, a primary sealing barrier, a primary insulating barrier, a secondary sealing barrier and a secondary insulating barrier, at least one of said insulating barriers consisting essentially of juxtaposed non-conducting elements. Each non-conducting element includes a thermal insulation liner arranged in the form of a layer parallel to said tank wall, at least one panel extending parallel to said tank wall over at least one side of said thermal insulation liner and load-bearing partitions projecting from a face of said at least one panel facing said thermal insulation liner, said load-bearing partitions rising through the thickness of said thermal insulation liner in order to take up the compression forces. This tank is characterized in that said load-bearing partitions include at least one anti-buckle partition that, seen in cross section in a plane parallel to said at least one panel, has a general longitudinal direction and includes a plurality of anti-buckle wall elements that have a respective orientation forming an angle relative to said general longitudinal direction of the anti-buckle partition.
The basic idea here is to create one or more partitions, called anti-buckle partitions, having a respective general longitudinal direction and including wall elements, called anti-buckle wall elements, that are not oriented parallel to this general direction so as to increase the partition's moment of inertia in the transverse direction of the partition. Thus, even produced with a thin wall, the partition has good resistance to the compression forces in the direction perpendicular to the base and/or cover panel(s). It is thus possible to obtain a spacing partition that combines different qualities in terms of mechanical strength, economy of materials, light weight and effective cross section for the conduction of heat.
An anti-buckle partition of this type may have various structures. Preferably, an anti-buckle partition of this type has a substantially continuous wall extending in the general longitudinal direction. This may be a single wall or an unlined wall with a transverse gap or, alternately, a wall in which certain portions are single and others unlined. It is also possible for the anti-buckle partition to have, at least locally, more than two walls spaced apart in the transverse direction.
According to a particular embodiment, suitable, in particular, for a single-wall anti-buckle partition—although not exclusively—the anti-buckle partition includes a wall, called anti-buckle wall, that includes anti-buckle wall elements linked together directly or indirectly and that, seen in cross section in a plane parallel to said base and/or cover panel(s), extends in said general longitudinal direction of said anti-buckle partition with a profile deviating laterally on either side of a longitudinal median line of said anti-buckle partition. In this embodiment, the anti-buckle wall elements form an integral part of the anti-buckle wall. They are connected as a single piece, either directly or by means of other portions of the anti-buckle wall, i.e. by somewhat longitudinal portions.
The profile of the anti-buckle wall thus formed may have a regular form, i.e. devoid of angles, for example a form with alternate half-circles or a substantially sinusoidal wave. In such a case, the anti-buckle wall may have an orientation that varies continuously.
Alternately, or in combination, the profile of the anti-buckle wall may also have, at least locally, an angular form. For example, anti-buckle wall elements may be connected directly together, forming mutual angles in the manner of triangular teeth or of a more complicated polygonal line. Somewhat longitudinal wall elements may also be intercalated, at least locally, with anti-buckle wall elements, for example in order to form a profile in the form of rectangular or trapezoidal crenelations. Other profile forms are also possible, for example by alternating different motifs and by using straight or curved anti-buckle wall elements.
According to a further particular embodiment, suitable, in particular, for a single-wall or multiple-wall anti-buckle partition, said anti-buckle partition includes at least one wall extending in said general longitudinal direction to which anti-buckle wall elements projecting from said wall are linked. In such a case, the anti-buckle wall elements act as buttresses of a wall in order to increase the latter's moment of inertia in the transverse direction and thus to increase its resistance to compression and buckling forces. This is, for example, a straight planar wall or an anti-buckle wall of the above-mentioned type. The wall elements acting as buttress may have all kinds of forms in cross section in a plane parallel to the panel, for example a straight form, an open or closed curved form, an open or closed polygonal form, etc.
In the above embodiments, it is possible to make provision for anti-buckle wall elements to be arranged in such a manner as to longitudinally delimit a plurality of successive cells that, seen in a plane parallel to said at least one panel, have an open cross section.
According to a particular embodiment, said anti-buckle partition includes a second wall extending in said general longitudinal direction and spaced apart from the first wall in the transverse direction of the partition, said two walls being connected by a plurality of anti-buckle wall elements arranged between them. Such anti-buckle wall elements may be planar or curved. There may be any angle, for example a right angle, between the anti-buckle wall elements and each of the two walls.
According to a particular embodiment, said anti-buckle partition includes double-wall longitudinal portions that include, on each occasion, two laterally spaced wall elements and, in the region of the longitudinal ends of said portion, anti-buckle wall elements connecting said laterally spaced wall elements.
Seen in a plane parallel to the panel(s) of the non-conducting element, the double-wall portions thus formed may have any cross section—polygonal, rectangular, circular, ellipsoidal or the like, open or closed. The double-wall portions thus formed may be arranged adjacent to one another or spaced apart in the general longitudinal direction, the anti-buckle partition including single-wall longitudinal portions inserted between double-wall longitudinal portions.
For example, the anti-buckle wall elements and the laterally spaced wall portions may be connected, forming an angle. Alternately, the anti-buckle wall elements and the laterally spaced wall portions may be connected as a single piece in order to form a wall whose orientation varies continuously so as to enclose a cell of rounded cross section. However, when cells are formed in the anti-buckle partition, at least one ventilation hole is always left in order to avoid trapping air that might form an explosive mixture with the cargo in the event of an incident.
Preferably, apart from in the region of its ends, said anti-buckle partition has a periodic structure in the general longitudinal direction. A structure of this type guarantees good uniformity of the resistance to compression. Conversely, the structure of the anti-buckle partition may also be non-periodic, for example with a view to meeting certain localized mechanical requirements.
An anti-buckle partition may have a height direction substantially perpendicular to said base and/or cover panel(s), which is an optimum arrangement for taking up the compression forces, or, otherwise, be inclined relative to the said panels, which is an appropriate arrangement to counter shear and overturning forces received by the non-conducting element. In this regard, provision may be made for two anti-buckle partitions having opposite inclinations.
An anti-buckle partition and a base or cover panel may be assembled together by any means, such as adhesive bonding, welding, stapling, flush-fitting, etc., and combinations thereof. According to a particular embodiment, said or each anti-buckle partition is flush fitted in at least one base and/or cover panel of the non-conducting element. A method of assembly of this type is particularly robust, for example against the forces of shear and overturning.
According to a particular embodiment, said or each anti-buckle partition includes at least one load-distribution sole plate in the region of an edge of said anti-buckle partition facing a base or cover panel of the non-conducting element, said load-distribution sole plate extending in the direction of the length of said anti-buckle partition and having a planar surface fixed against said panel. For example, the load-distribution sole plate has a width greater than or equal to the lateral extent of the anti-buckle wall elements of the anti-buckle partition. This load-distribution sole plate, which may be provided on a side or on the two edges of the anti-buckle partition, stiffens the latter and prevents a concentration of stresses in a particular zone of the anti-buckle partition, which prevents localized pinching of the panel and offers a larger surface area for the link between the partition and the panel.
Alternately, or in combination, the anti-buckle partition may include at least one load-distribution sole plate in the region of an edge of said or each anti-buckle partition opposite said panel of the non-conducting element, said load-distribution sole plate extending in the direction of the length of said anti-buckle partition and having a planar surface bearing against the adjacent sealing barrier. In this embodiment, a face of the non-conducting element parallel to the tank wall is formed by a base or cover panel and its opposite face has no panel. Planar sole plates extending along the edge of the anti-buckle partitions opposite the panel fulfill the function of supporting a sealing barrier when they face toward the inside of the tank, or, when they face toward the load-bearing structure, the function of transmitting the pressure force of the non-conducting element onto the underlying sealing barrier.
An anti-buckle partition may be produced from any material that can be formed by molding, blow-molding, injection-molding, rotational molding, thermoforming, extrusion or pultrusion, particularly plastics and composite materials having at least two heterogeneous constituents. For example, the anti-buckle partitions may be produced from a polyester-resin-based composite, for example polyester resin or another resin. Within the meaning of the invention, the polymer-resin-based composite materials include polymers or mixtures of polymers with all kinds of fillers, additives, reinforcements or fibers, for example glass fibers or other fibers, providing sufficient rupture strength and rigidity and other properties. Additives may be employed to reduce the material's density and/or improve its thermal properties, particularly reducing its thermal conductivity and/or its expansion coefficient.
Such anti-buckle partitions made from plastic or a composite combine very advantageous properties in terms of mechanics, of ease of forming, of thermal insulation and of cost price. The use of plastics or composites based on polymer resin, in particular with reinforcement fibers, provides the conditions necessary to obtain load-bearing partitions whose manufacture in the form of partitions of any profile, for example a corrugated profile, is fairly easy, while offering a thermal conductivity that is the same as or better than plywood and a lower expansion coefficient. For example, such anti-buckle partitions may be obtained by molding, extrusion or pultrusion of the composite material. It is possible, in particular, to obtain anti-buckle partitions in the form of profiled elements that are cut to the desired height, such that the size of the corresponding non-conducting elements can easily be modified.
Injection-molding is also an appropriate manufacturing process, for example using plastics such as PVC, PC, PBT, PU, PE, PA, PS and other polymer resins.
According to a particular embodiment, said load-bearing partitions of a non-conducting element are formed as a single piece with one said panel of the non-conducting element. A structural piece of this type including a base or cover panel and load-bearing partitions projecting from the latter may be injection-molded. It is also possible to form the load-bearing partitions of a non-conducting element as a single molded piece with arms extending between them in order to link them and to add a base panel and/or a cover panel independent of a piece of this type.
Anti-buckle partitions may also be produced from laminated wood or plywood produced using sheets of wood, for example beech, pine, birch, poplar or the like and mixtures thereof, superposed on and adhesively bonded to one another. A material of this type may be hot-compression-molded, for example with a corrugated profile. It is also possible to use a composite that includes a high proportion of sawdust with a synthetic binder.
Preferably, the non-conducting element includes a base panel on that side of the thermal insulation liner that faces said load-bearing structure, said load-bearing partitions including peripheral partitions projecting from said base panel along its edges in order to form a box. In particular, said load-bearing partitions may delimit a closed space between said base panel and a cover panel. Non-conducting elements of this type in the form of a box, in particular a closed box, make it possible to use all kinds of insulation liner, in particular granular or pulverulent materials. According to a particular embodiment, the non-conducting element includes a plurality of anti-buckle partitions arranged in such a manner as to compartmentalize the inner space of said box, the longitudinal ends of said anti-buckle partitions being fixed to said peripheral partitions.
This fixing may be achieved by any means. Advantageously, said longitudinal ends of the parallel anti-buckle partitions can be flush fitted into said peripheral partitions. Flush-fitting load-bearing partitions of this type offer a very good mechanical link.
According to a particular embodiment, said anti-buckle partitions are arranged in parallel at a distance from one another and have assembly tabs in the region of their two longitudinal ends, said peripheral partitions comprising end partitions arranged perpendicularly to said anti-buckle partitions in the region of the two longitudinal ends of the latter and having, on the face facing said anti-buckle partitions, a plurality of spaced-apart parallel grooves capable of receiving and retaining an assembly tab of a respective anti-buckle partition. The number and spacing of the anti-buckle partitions in a non-conducting element may thus be easily modified by adapting the position and spacing of the grooves.
Advantageously, each of the said end partitions includes a plurality of spaced-apart parallel ribs projecting from the face facing said anti-buckle partitions, said grooves being provided, on each occasion, in a respective rib. The production of the end partition in the form of a thin continuous wall with ribs makes it possible to obtain the desired anti-buckling strength while limiting the thermal bridges in the region of the end partition and maximizing the volume available for the thermal insulation liner in the hollow element.
Preferably, said end partition carries at least one load-distribution sole plate interposed between said thin continuous wall and said base or cover panel of the non-conducting element, said load-distribution sole plate extending in the direction of the length of said end partition and having a width substantially equal to the projection of said ribs. A load-distribution sole plate of this type provided on the upper and/or lower side of the partition stiffens the partition and prevents a concentration of stresses on a particular zone of the partition, which prevents localized pinching of the panel and offers a larger surface area for the link between the partition and the panel.
The peripheral partitions may be rectilinear. According to a particular embodiment, at least some of the peripheral partitions are anti-buckle partitions. In this regard, all the structures provided for the anti-buckle partitions can be applied to the peripheral partitions.
Advantageously, the two insulating barriers consist essentially of non-conducting elements that include, on each occasion, a plurality of mutually parallel anti-buckle partitions, said non-conducting elements being arranged in such a manner that, in any zone of said at least one tank wall, the parallel anti-buckle partitions of the non-conducting elements of an insulating barrier are oriented substantially perpendicularly to the parallel anti-buckle partitions of the non-conducting elements of the other insulating barrier. Such an arrangement of the non-conducting elements of the two insulating barriers reduces the surface area of the zones of the tank wall in which the anti-buckle partitions of the two insulating barriers are superposed, which limits the corresponding thermal bridges. Any other mutual orientation of the elements of the two barriers is also possible, particularly by making all the anti-buckle partitions of the non-conducting elements superposed in the region of a zone of the tank wall parallel.
Preferably, said at least one insulating barrier consisting of said non-conducting elements is covered, on each occasion, by one of said sealing barriers that is formed from thin metal plate strakes with a low expansion coefficient, the edges of which are raised toward the outside of said non-conducting elements, said non-conducting elements including cover panels carrying parallel grooves spaced apart by the width of a plate strake in which weld supports are slideably retained, each weld support having a continuous wing projecting from the outer surface of the cover panel and on whose two faces the raised edges of two adjacent plate strakes are welded in a leaktight manner. This structure and this method of fixing the sealing barrier are preferably used for the two sealing barriers of the tank. The sliding weld supports form gliding joints allowing different barriers to move relative to one another through the effect of differences in thermal contraction and movements of the liquid contained in the tank.
Advantageously, secondary retention members integral with the load-bearing structure of the ship fix the non-conducting elements forming the secondary insulating barrier against said load-bearing structure, and primary retention members linked to said weld supports of the secondary sealing barrier retain said primary insulating barrier against the secondary sealing barrier, said weld supports retaining said secondary sealing barrier against the cover panels of the non-conducting elements of the secondary insulating barrier. Thus, the primary insulating barrier is anchored on the secondary insulating barrier, with no effect on the continuity of the secondary sealing barrier interposed between them.
According to a preferred embodiment, said thermal insulation liner includes reinforced or unreinforced, rigid or flexible foam of low density, i.e. under 60 kg/m3, for example around 40 to 50 kg/m3, which has very good thermal properties. It is also possible to use a material of nanoscale porosity of the aerogel type. A material of the aerogel type is a low-density solid material with an extremely fine and highly porous structure, possibly with a porosity up to 99%. The pore size of these materials is typically in the range between 10 and 20 nanometers. The nanoscale structure of these materials greatly limits the mean free path of the gas molecules, and therefore also convective heat and mass transfer. Aerogels are thus very good thermal insulators, with a thermal conductivity, for example, below 20×10−3 W.m−1.K−1, preferably less than 16×10−3 W.m−1.K−1. They typically have a thermal conductivity 2 to 4 times as low as that of other, conventional insulators, such as foams. Aerogels may be in different forms, for example in the form of powder, beads, nonwoven fibers, fabric, etc. The very good insulating properties of these materials make it possible to reduce the thickness of the insulating barriers in which they are used, which increases the useful volume of the tank.
The invention also provides a floating structure, in particular a methane carrier, characterized in that it comprises a sealed, thermally insulated tank according to the subject of the above invention. A tank of this type may, in particular, be employed in an FPSO (floating, production, storage and offloading)
facility, used to store the liquefied gas with a view to exporting it from the production site, or an FSRU (floating storage and regasification unit) used to unload a methane carrier with a view to supplying a gas transportation system.
The invention will be better understood and further objects, details, characteristics and advantages thereof will become more clearly apparent in the course of the following description of a plurality of particular embodiments of the invention that are given solely by way of non-limiting illustrative example with reference to the appended drawings, in which:
FIGS. 13 to 19 are views similar to
A description will be given below of several embodiments of a sealed, thermally insulated tank incorporated in and anchored to the double hull of a structure of the FPSO or FSRU type or of a methane-type carrier. The general structure of such a tank is well known per se and has a polyhedral form. Therefore, a description will be given only of a wall zone of the tank, it being understood that all the walls of the tank have a similar structure.
A description is now given of an embodiment with reference to FIGS. 1 to 12.
The caissons 3 and 7 may have identical or different structures and identical or different dimensions. With reference to FIGS. 2 to 8, a description is now given of a caisson 3 of the secondary insulating barrier. As may be seen in
The end partitions 13 are shown in FIGS. 4 to 6. The end partition 13 has a rectilinear continuous wall 16, for example with a thickness of approximately 2 mm, with a lower sole plate 18 and an upper sole plate 17 extending over its entire length and projecting from the inner side of the wall 16. On this inner side, between the sole plates 17 and 18, the wall 16 carries a series of vertical ribs 19 of triangular cross section that are parallel and spaced apart at regular intervals, which serve as flush-fitting members for the corrugated partitions 14. As may be better seen in
A corrugated partition 14 is shown in
The caisson 3 has cut corners that are formed by a corresponding cutoff of the sole plates 17 and 18 of the end partitions 13 and by an inclined end border of the continuous wall 16, denoted by 27. In the region of the corners of the caisson 3, the cover panel 11 has countersinkings 28 for receiving a washer of the secondary retention member 4. The caisson 3 also has two central shafts 30 traversing the panels 10 and 11 and the insulating liner housed between them and forming supplementary anchor points for the caisson 3.
By virtue of their form, the corrugated partitions 14 have a high anti-buckling resistance without it being necessary to provide the wall 25 with any great thickness. Thus, the free space 12 in the caissons 3 is maximized. This free space receives a thermal insulation liner that may be made from any appropriate material, for example low-density polyurethane foam, for example with a density of approximately 40 kg/m3, phenolic foam, flexible PE, PVC or other foams, nanoporous materials of the aerogel type, pearlite, glass wool or the like. This liner is preferably also inserted in the open cells 65 that are formed on either side of the corrugated wall 25.
The end partitions 13 and the corrugated partitions 14 are manufactured from a polymer-resin-based composite material, for example polyester resin or epoxy resin reinforced with glass or carbon fibers. Preferably, the end partitions 13 and the corrugated partitions 14 are obtained by injection-molding.
A number of modifications are possible to the caisson 3 described above. For example, the base panel 10 may be dispensed with, at least when the insulation liner of the caisson is a foam or a rigid material that can be adhesively bonded to the inner face of the cover panel 11 and to the partitions 13 and 14. In a variant embodiment, it is possible to dispense with the cover panel 11. In such a case, the sealing barrier supported by the caisson 3 will rest on the sole plates 24 of the partitions 14, which could be widened for this purpose, and optionally on the masses of insulating material placed in the compartments 12. In such a case, the members ensuring attachment of the caisson may bear on the inner face of the base panel 10 or on the outer face of the sole plates 24.
According to a variant embodiment shown in
According to yet a further variant embodiment (not shown), a piece that includes not only the base panel 10 but also the partitions 13 and 14 projecting from it could be injection-molded. Thus, the assembly of the caisson is particularly simplified.
The form of the profile of the anti-buckle partitions is not limited to the form of alternate half-circles visible in
The partition 114 shown in
The partition 214 shown in
The partition 314 shown in
FIGS. 13 to 15 also show sketches of the end partitions 13 whose means of flush-fitting with the ends of the anti-buckle partitions are not shown. Means of this type are not, however, necessary when inter-partition assembly is achieved by other means (adhesive bonding, stapling, etc.)
FIGS. 16 to 18 show yet further embodiments of the anti-buckle partitions that can be used in the caissons 3 and 7 and have cells with a closed cross section. These cells may be left empty or be lined with thermal insulation that may or may not be identical to the insulation liner placed between the partitions, or alternatively receive mechanical reinforcement elements made from wood, plastic or the like.
The partition 414 shown in
The partition 514 shown in
The partition 614 shown in
As shown in
With reference to
As may be seen in
As the geometry of the double hull 1 is irregular, provision is made for shims 36 around threaded pins 31. The thickness of each shim 36 is calculated by computer on the basis of a topographical survey of the inner surface of the double hull 1. Thus, the base panels 10 are positioned along a theoretical regular surface. Between the base panels 10 and the double hull 1, provision is conventionally made for beads of polymerizable resin 29 that are adhesively bonded to the base panels 10 and are crushed against the double hull when the caissons 3 are fitted, so as to provide their support. To avoid this resin adhering to the double hull, a sheet of Kraft paper (not shown) is provided between them.
The secondary sealing barrier 5 is produced in accordance with the known technique in the form of a membrane consisting of Invar plate strakes 40 with raised edges. As may be seen better in
As was stated, the caissons 7 of the primary insulating barrier may have a structure similar to the caissons 3. Similarly, in such a case, the caissons 7 are anchored, on each occasion, to the four corners and at two points in the central zone of the caisson 7. To that end, use is made, on each occasion, of a primary retention member 48 shown in detail in
It will be appreciated that the weld supports 42 retaining the secondary sealing barrier 5 pass either between the caissons 7 of the primary insulating barrier or in the middle of these caissons. In such a case, the base panel 10 of the caisson 7 has a corresponding longitudinal notch for the passage of the weld support 42, which longitudinal notch is shown by 60 in
The caissons 3 and 7 are self-supporting caissons capable of withstanding the pressure of the liquid in the tank, such that the sealing barriers 5 and 8 supported by them have no need themselves to support this pressure and are advantageously produced in the form of very thin membranes with a thickness, for example, of 0.7 mm of Invar. Preferably, the caissons 3 and 7 are arranged in such a manner that their respective anti-buckle partitions 14 (or 114, 214, etc.) are perpendicular.
Advantageously, a layer of nanoporous materials of the aerogel type, which are very good thermal insulators, is included as insulation liner in the caissons 3 and/or 7. Aerogels also have the advantage of being hydrophobic, so absorption of the moisture from the boat into the insulating barriers is thus prevented. An insulation layer may be produced with aerogels, possibly pocketed, in textile form or in the form of beads. Of course, the insulation liner of a non-conducting element may include several layers of material.
Generally speaking, aerogels may be made from a number of materials, including silica, alumina, hafnium carbide and also varieties of polymers. Furthermore, in accordance with the manufacturing process, aerogels may be produced in powder, bead, monolithic sheet and reinforced flexible fabric form. Aerogels are generally manufactured by extracting or displacing the liquid of a gel of micronic structure. The gel is typically manufactured by means of chemical conversion and reaction of one or more dilute precursors. This results in a gel structure in which a solvent is present. Use is generally made of hypercritical fluids such as CO2 or alcohol, to displace the gel solvent. Aerogels' properties may be modified by using a variety of doping and reinforcement agents.
The use of aerogels as insulation liners significantly reduces the thickness of the primary and secondary insulating barriers. It is, for example, possible to conceive of barriers 2 and 6 having a thickness of 200 mm and 100 mm, respectively, with a woven aerogel bed in the caissons 3 and 7, the tank wall then having a total thickness of 310 mm. It is possible to conceive of a tank wall having a total thickness of 400 mm by making provision for a layer of aerogel particles in the caissons 3 and 7.
An anti-buckle partition may have any orientation relative to the edges of the base and/or or cover panels, i.e. parallel or non-parallel. The anti-buckle partitions of a non-conducting element are not necessarily mutually parallel. Although a description has been given of essentially parallelepipedal, right-angled non-conducting elements, other forms of cross section are possible, notably any polygonal form capable of rendering a planar surface discrete. When the hull serving as support for the tank wall is not planar, the tank wall may be produced using non-conducting elements that are also non-planar.
When one of the primary and secondary insulating barriers is produced with the aid of the non-conducting elements described above, it is possible, but not necessary, to produce the other insulating barrier in an identical manner. Non-conducting elements of two different types may be used in the two barriers. One of the barriers may consist of prior-art non-conducting elements.
The caissons of the secondary insulating barrier and of the primary insulating barrier may be anchored to the ship's hull in a different way from the example shown in the figures, for example with the aid of retention members engaged on the base panel of the caissons.
Although the invention has been described in connection with a number of particular embodiments, it is obviously not limited to these in any way and includes all technical equivalents of the means described and also combinations thereof if they fall within the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0411967 | Nov 2004 | FR | national |
