U.S. patent application number 11/265079 was filed with the patent office on 2006-05-11 for sealed, thermally insulated tank with compression-resistant non-conducting elements.
This patent application is currently assigned to GAZ TRANSPORT ET TECHNIGAZ. Invention is credited to Jacques Dhellemmes, Vincent Fargant, Pierre Michalski.
Application Number | 20060096235 11/265079 |
Document ID | / |
Family ID | 34951497 |
Filed Date | 2006-05-11 |
United States Patent
Application |
20060096235 |
Kind Code |
A1 |
Dhellemmes; Jacques ; et
al. |
May 11, 2006 |
Sealed, thermally insulated tank with compression-resistant
non-conducting elements
Abstract
Sealed, thermally insulated tank consisting of tank walls fixed
to the load-bearing structure (1) of a floating structure, 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 (8), a primary insulating barrier (6), a secondary sealing
barrier (5) and a secondary insulating barrier (2), at least one of
said insulating barriers consisting essentially of juxtaposed
non-conducting elements, each non-conducting element including a
thermal insulation liner (63) and load-bearing elements that rise
through the thickness of said thermal insulation liner in order to
take up the compression forces, characterized in that the
load-bearing elements of a non-conducting element include pillars
(65) of small transverse section as compared to the dimensions of
the non-conducting element in a plane parallel to said tank wall.
Sealed, thermally insulated tank has tank walls fixed to the
load-bearing structure (1) of a floating structure, the tank walls
having, in succession, in the direction of the thickness from the
inside to the outside of the tank, a primary sealing barrier (8), a
primary insulating barrier (6), a secondary sealing barrier (5) and
a secondary insulating barrier (2), at least one of the insulating
barriers includes juxtaposed non-conducting elements, each
non-conducting element including a thermal insulation liner (63)
and load-bearing elements that rise through the thickness of the
thermal insulation liner in order to take up the compression
forces, characterized in that the load-bearing elements of a
non-conducting element include pillars (65) of small transverse
section as compared to the dimensions of the non-conducting element
in a plane parallel to the tank wall.
Inventors: |
Dhellemmes; Jacques;
(Versailles, FR) ; Michalski; Pierre; (Le Havre,
FR) ; Fargant; Vincent; (Rochefort En Yvelines,
FR) |
Correspondence
Address: |
YOUNG & THOMPSON
745 SOUTH 23RD STREET
2ND FLOOR
ARLINGTON
VA
22202
US
|
Assignee: |
GAZ TRANSPORT ET TECHNIGAZ
SAINT-REMY-LES-CHEVREUSE
FR
|
Family ID: |
34951497 |
Appl. No.: |
11/265079 |
Filed: |
November 3, 2005 |
Current U.S.
Class: |
204/267 |
Current CPC
Class: |
F17C 3/027 20130101;
F17C 2203/0631 20130101; F17C 2203/0325 20130101; F17C 2223/0161
20130101; Y10S 220/901 20130101; F17C 2223/033 20130101; F17C
2221/033 20130101; F17C 2203/0358 20130101; B63B 25/16 20130101;
F17C 2270/0107 20130101 |
Class at
Publication: |
052/735.1 |
International
Class: |
E04C 3/30 20060101
E04C003/30 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 10, 2004 |
FR |
04 11968 |
Claims
1. Sealed, thermally insulated tank including at least one tank
wall fixed to the hull (1) 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 (8) a
primary insulating barrier (6), a secondary sealing barrier (5) and
a secondary insulating barrier (2), at least one of said insulating
barriers consisting essentially of juxtaposed non-conducting
elements (3, 7), each non-conducting element including a thermal
insulation liner (63) arranged in the form of a layer parallel to
said tank wall, and load-bearing elements that rise through the
thickness of said thermal insulation liner in order to take up the
compression forces, characterized in that the load-bearing elements
of a non-conducting element (60, 570, 670, 870) include pillars
(65, 575, 775, 875, 975, 1075, 1175, 1275) of small transverse
section as compared to the dimensions of the non-conducting element
in a plane parallel to said tank wall.
2. Sealed, thermally insulated tank according to claim 1,
characterized in that said pillars are regularly distributed over
the entire surface of the non-conducting element seen in a plane
parallel to the tank wall.
3. Sealed, thermally insulated tank according to claim 1,
characterized in that said pillars are identically spaced apart in
the length direction and in the width direction of the
non-conducting element.
4. Sealed, thermally insulated tank according to claim 1,
characterized in that said pillars have a closed hollow transverse
section.
5. Sealed, thermally insulated tank according to claim 4,
characterized in that said pillars are tubes of circular cross
section.
6. Sealed, thermally insulated tank according to claim 1,
characterized in that said pillars are produced from plastic or a
composite.
7. Sealed, thermally insulated tank according to claim 1,
characterized in that said insulation liner of the non-conducting
element includes a block of synthetic foam (63).
8. Sealed, thermally insulated tank according to claim 7,
characterized in that said block of synthetic foam is obtained by
pouring between said pillars so as to embed at least one height
portion of said pillars in said block of synthetic foam.
9. Sealed, thermally insulated tank according to claim 7,
characterized in that said pillars (65) are inserted in holes (64)
machined in said block of synthetic foam.
10. Sealed, thermally insulated tank according to claim 1,
characterized in that said non-conducting element includes a planar
positioning element (69) arranged parallel to said tank wall in the
thickness of the insulation liner and having openings traversed by
said pillars (65) in order to define their mutual positioning.
11. Sealed, thermally insulated tank according to claim 1,
characterized in that said non-conducting element includes at least
one panel (61, 62, 571, 572, 711, 872) extending parallel to said
tank wall over at least one side of said non-conducting
element.
12. Sealed, thermally insulated tank according to claim 11,
characterized in that the inner face of one said panel (572) has
recesses (573) arranged in such a manner as to interact by
flush-fitting with said pillars (575).
13. Sealed, thermally insulated tank according to claim 12,
characterized in that said panel (572) has a thermal expansion
coefficient that is different from that of said pillars (575) so as
to give rise to gripping between said panel and said pillars
flush-fitted in it when the tank is cooled.
14. Sealed, thermally insulated tank according to claim 11,
characterized in that said non-conducting element has the form of a
closed box with a base panel (571), a cover panel (572) and
peripheral walls (601) extending between said panels along the
edges of the latter.
15. Floating structure, characterized in that it comprises a
sealed, thermally insulated tank according to claim 1.
16. Floating structure according to claim 15, characterized in that
it consists of a methane carrier.
17. Sealed, thermally insulated tank according to claim 2,
characterized in that said pillars are identically spaced apart in
the length direction and in the width direction of the
non-conducting element.
Description
[0001] 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.
[0002] 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.
[0003] 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, and load-bearing elements that rise through the
thickness of said thermal insulation liner in order to take up the
compression forces.
[0004] 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.
[0005] 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.
[0006] 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. A further object of the invention
is to propose a tank of this type in which the non-conducting
elements are easily adaptable in terms of their dimensions, without
compromising the ability of the walls to withstand pressure and the
thermal insulation of the walls.
[0007] To that end, a subject of the invention is a sealed,
thermally insulated tank including at least one tank wall fixed to
the hull 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 including a thermal insulation liner
arranged in the form of a layer parallel to said tank wall, and
load-bearing elements that rise through the thickness of said
thermal insulation liner in order to take up the compression
forces, characterized in that said load-bearing elements of a
non-conducting element include pillars of small transverse section
as compared with the dimensions of the non-conducting element in a
plane parallel to said tank wall.
[0008] Small-cross section pillars of this type have the advantage
that they can be distributed in the non-conducting element as a
function of local requirements. By adapting the number and the
distribution of the load-bearing pillars, the non-conducting
element's compression strength can, in particular, be made more
uniform than with prior-art spacers. It is also possible to prevent
localized depression or pinching of a cover panel. Advantageously,
said pillars are regularly distributed over the entire surface of
the non-conducting element seen in a plane parallel to the tank
wall. A further advantage of the non-conducting element with
small-cross section pillars is that it allows the manufacture of a
non-conducting element of any desired dimensions without loss of
compression strength, at least insofar as these dimensions remain
greater than or equal to the spacing between the pillars. A
non-conducting element of small surface area may, in particular, be
obtained by cutting an element of larger surface area.
[0009] According to a particular embodiment, said pillars are
identically spaced apart in the length direction and in the width
direction of the non-conducting element.
[0010] Pillars of this type may have a hollow or solid cross
section, for which a number of shapes are possible. Preferably,
said pillars have a closed hollow transverse section. Such hollow
pillars with a closed transverse section, in particular tubes with
a circular cross section, make it possible to obtain very good
anti-buckling resistance while at the same time minimizing the
effective thermal conduction cross section.
[0011] Advantageously, said pillars are produced from plastic or a
composite.
[0012] Preferably, said insulation liner of the non-conducting
element includes a block of synthetic foam.
[0013] According to one embodiment, said pillars are inserted in
holes machined in said block of synthetic foam.
[0014] According to a further embodiment, said block of synthetic
foam is obtained by pouring between said pillars so as to embed at
least one height portion of said pillars, for example half or all
their height, in said block of synthetic foam.
[0015] Advantageously, said non-conducting element includes a
planar positioning element arranged parallel to said tank wall in
the thickness of the insulation liner and having openings traversed
by said pillars in order to define their mutual positioning.
[0016] Preferably, said non-conducting element includes at least
one panel extending parallel to said tank wall on a side of said
non-conducting element. In other words, in such a case, the
non-conducting element comprises a base panel or a cover panel. By
convention, "cover" is the name given to a panel on that side of
the non-conducting element that faces toward the inside of the tank
and "base" is the name given to a panel on the side of the
non-conducting element that faces toward the load-bearing
structure. The non-conducting element may also include both a base
panel and a cover panel. Any fixing means may be used for fixing a
panel of this type to the non-conducting element.
[0017] The non-conducting elements may be open or closed.
Advantageously, the presence of a cover panel provides uniform
support for the adjacent sealing barrier. However, a panel of this
type is not mandatory because sufficient support of this type may
also be obtained from the pillars alone. Advantageously, the
presence of a base panel provides well distributed transmission of
compression forces from the primary insulating barrier toward the
secondary insulating barrier or from the secondary insulating
barrier toward the hull. However, a panel of this type is not
mandatory because this transmission may also be sufficiently
guaranteed by the pillars alone. Panels of this type may be formed
in several ways. One possibility is to form a load-bearing
structure incorporating, as a single piece, a panel with the
pillars. A further possibility is to fix a separate panel on a side
of the non-conducting element.
[0018] Advantageously, the inner face of a said panel has recesses
arranged in such a manner as to interact by flush-fitting with said
pillars. This results in a particularly robust link. In such a
case, the panel may have a thermal expansion coefficient that is
different from that of said pillars so as to give rise to gripping
between said panel and said pillars flush-fitted in the latter when
the tank is cooled.
[0019] According to a particular embodiment, said non-conducting
element has the form of a closed box with a base panel, a cover
panel and peripheral walls extending between said panels along the
edges of the latter. A design of this type allows the fitting of an
insulation liner in the form of granular material. However,
depending on the construction of the insulation liner, it is
possible, also, to use non-conducting elements that do not have
peripheral walls.
[0020] According to a further particular embodiment, said
load-bearing elements of a non-conducting element are produced in
the form of at least one load-bearing structure formed as a single
piece including, on each occasion, linking means that rigidly link
said load-bearing elements together and at least one height portion
of said pillars.
[0021] A load-bearing structure of this type formed as a single
piece combines very advantageous mechanical properties both in
terms of stiffness and in terms of anti-buckling resistance in the
direction of the thickness of the hollow elements, of ease of
forming, of thermal insulation and of cost price. Indeed, for a
given geometry of the pillars, their anti-buckling resistance is
increased by the rigid integral links as compared to separate
pillars. Furthermore, manufacture of the links between the pillars
and pillars, i.e. at least one portion of their height, in the form
of a single piece makes it possible to dispense with certain
assembly operations, makes it possible to obtain a relatively rigid
load-bearing structure without excessively increasing the cross
section of the pillars and/or their thickness, and thus the thermal
bridges, and simplifies fitting of the thermal insulation liner in
the non-conducting element.
[0022] According to a further embodiment of the linking means, said
linking means include arms extending between said pillars.
Advantageously, said arms extend parallel to said tank wall along
at least one side of said insulation liner. Positioned in this way,
the arms offer a supplementary surface, in addition to that of the
pillars, for the fixing of a possible base panel and/or cover panel
formed independently of the load-bearing structure.
[0023] According to a preferred embodiment of the linking means,
said linking means of a load-bearing structure include a panel
extending parallel to said tank wall on a side of said
non-conducting element, said pillars projecting from an inner face
of said panel.
[0024] According to one embodiment of the non-conducting element,
it has two load-bearing structures arranged in such a manner that
their respective panels have said inner faces turned toward one
another, the pillars projecting from said inner faces being
assembled in pairs in the region of their ends located opposite
said panels in order to form, on each occasion, a pillar of said
non-conducting element. In other words, in such a case, the pillars
of each of the two load-bearing structures are placed end to end in
order to form, on each occasion, a pillar having two parts
extending, respectively, through a portion of the thickness of the
non-conducting element. In particular, it is possible to use two
completely symmetrical load-bearing structures.
[0025] Advantageously, an insulation piece having a thermal
conductivity that is lower than that of said pillars is interposed,
on each occasion, between the two assembled pillars. This makes it
possible to improve the thermal insulation obtained by means of the
non-conducting element.
[0026] The two load-bearing structures may be assembled by any
means. Preferably, the pillars of the two load-bearing structures
are assembled in pairs, on each occasion, by means of a linking
piece having a thermal expansion coefficient that is different from
that of said pillars so as to give rise to gripping between said
linking piece and said pillars when the tank is cooled. As a
variant embodiment, or in combination, the linking piece may also
be flush fitted, adhesively bonded, snap-fitted, etc.
[0027] Preferably, the load-bearing structure or structures of a
non-conducting element is (or are) manufactured using a process of
molding, extrusion, pultrusion, thermoforming, blow-molding,
injection-molding or rotational molding. The load-bearing
structures may be manufactured from any material suitable for the
above-mentioned processes, particularly plastics such as PC, PBT,
PA, PVC, PE, PS, PU and other resins. Advantageously, the
load-bearing structures are produced from a composite material. The
use of this type of materials brings together the conditions
necessary for obtaining load-bearing elements with a thinner wall
thickness than with plywood, while at the same time offering better
or equivalent thermal conductivity and a lower expansion
coefficient. For example, said load-bearing structures may be
produced from a polymer-resin-based composite material, for example
polyester resin or another resin. Within the meaning of the
invention, 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 also be employed to reduce the material's
density and/or improve its thermal properties, particularly
reducing its thermal conductivity and/or its expansion coefficient.
Use may also be made of a composite that includes a high
proportional of sawdust with a synthetic binder. In certain
embodiments, the load-bearing structure may also be made from
laminated wood or plywood molded by hot compression.
[0028] According to a particular embodiment, said at least one
insulating barrier consisting of said non-conducting elements is
covered, on each occasion, by one of said sealed 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 having
cover panels carrying parallel grooves spaced 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
face of the cover panel and on whose two faces the raised edges of
two adjacent plate strakes are welded in a leaktight manner. 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.
[0029] 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.
[0030] 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/m.sup.3, for example around 40 to
50 kg/m.sup.3, 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.times.10.sup.-3
W.m.sup.-1.K.sup.-1, preferably less than 16.times.10.sup.-3
W.m.sup.-1.K.sup.-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.
[0031] 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.
[0032] 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
particular embodiment of the invention that is given solely by way
of non-limiting illustrative example with reference to the appended
drawings, in which:
[0033] FIG. 1 is a stripped-back perspective view of a tank wall
according to a general embodiment that is useful for understanding
the invention;
[0034] FIGS. 2 and 3 show a primary retention member of the tank
wall of FIG. 1 seen in two perpendicular directions;
[0035] FIG. 4 is a transverse sectional view of a tank wall
according to one embodiment of the invention;
[0036] FIG. 5 is an expanded perspective view of a non-conducting
element of the tank wall shown in FIG. 4;
[0037] FIG. 6 is a perspective view of a molding step for obtaining
a non-conducting element according to the first embodiment of the
invention;
[0038] FIG. 7 shows, in perspective, a load-bearing structure
molded as a single piece;
[0039] FIG. 8 is a partial sectional view showing a variant
embodiment of the load-bearing structure of FIG. 7;
[0040] FIG. 9 is an expanded perspective view of two types of
non-conducting element produced with the aid of the load-bearing
structure of FIG. 7;
[0041] FIG. 10 is a partial, sectional view showing the assembly of
a non-conducting element of FIG. 9;
[0042] FIGS. 11 and 12 are views similar to FIG. 7, showing other
variant embodiments of the load-bearing structure;
[0043] FIG. 13 is a partial, sectional view of a non-conducting
element according to a further embodiment of the invention;
[0044] FIG. 14 is a plan view of the load-bearing structure of the
non-conducting element of FIG. 13;
[0045] FIGS. 15 to 18 show further embodiments of load-bearing
elements in the form of pillars, seen in transverse section;
[0046] FIG. 19 is a view similar to FIG. 6, showing an alternate
molding method;
[0047] FIG. 20 is an expanded perspective view of a non-conducting
element according to a further embodiment of the invention;
[0048] FIG. 21 shows, in perspective, a load-bearing structure
thermoformed from a single piece; and
[0049] FIGS. 22 and 23 show in plan view and in sectional view on
line XXIII a non-conducting element according to a further
embodiment.
[0050] 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.
[0051] A description is now given of a general embodiment that is
useful for understanding the invention, with reference to FIGS. 1
to 3. FIG. 1 shows a zone of the double hull of the ship, denoted
by 1. The tank wall is composed, in succession, in its thickness,
of a secondary insulating barrier 2 formed from caissons 3
juxtaposed on the double hull 1 and anchored to the latter by means
of secondary retention members 4, then a secondary sealing barrier
5 carried by the caissons 3, then a primary insulating barrier 6
formed from juxtaposed caissons 7 anchored to the secondary sealing
barrier 5 by primary retention members 48, and finally a primary
sealing barrier 8 carried by the caissons 7.
[0052] The caissons 3 and 7 are parallelepipedal non-conducting
elements with a mutually identical or different structure and
mutually identical or different dimensions.
[0053] Secondary retention members 4 are fixed on pins 31 welded to
the double hull 1 in a regular rectangular grid arrangement so that
these retention members 4 can, on each occasion, hold four caissons
3, whose corners meet. Also provided are two secondary retention
members 4 in the central zone of each caisson 3. However, depending
on the size of the caisson, more or fewer than six anchoring points
per caisson 3 may be necessary.
[0054] 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
FIG. 3, the cover panels 11 of the caissons 3 have longitudinal
grooves, with an inverted-T-shaped cross section, denoted by 41. A
weld support 42 in the form of a strip of Invar folded in the form
of an L, is inserted slideably in each groove 41. Each plate strake
40 extends between two weld supports 42 and has two raised edges 43
welded, on each occasion, continuously by a weld bead 44 to the
corresponding weld support 42, as may be seen in FIGS. 2 and 3. The
primary sealing barrier 8 is produced in the same manner.
Similarly, the caissons 7 of the primary insulating barrier 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
FIGS. 2 and 3. The primary retention member 48 has a lower sleeve
49 integral with a lug 50 welded at several, for example three,
points 51 of a weld support 42 above the raised edges 43 of the
plate strakes 40. A rod 52 made from Permali, a composite material
based on resin-impregnated beech wood, has a lower end fixed in the
lower sleeve 49 and an upper end fixed in a sleeve 54 integral with
a support washer 53 that bears on the cover panels 11 of the
caissons 7, being accommodated in countersinks 28 at the corners of
the caissons 7 and at the central shafts 30. The sleeve 54 is
threaded and is screwed onto a corresponding threaded end of the
rod 52. When the washer 53 has been thus positioned, immobilizing
screws 56 are engaged through holes 55 provided in the washer 53
and screwed into the panel 11 in order thus to prevent any
subsequent rotation of the washer 53. In each insulating barrier,
the caissons 3 and 7 are juxtaposed with a small intermediate space
of the order of 5 mm.
[0055] 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.
[0056] 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
CO.sub.2 or alcohol, to displace the gel solvent. Aerogels'
properties may be modified by using a variety of doping and
reinforcement agents.
[0057] 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, by
using an aerogel bed in textile form in the caissons 3 and 7. The
tank wall then has a total thickness of 310 mm. As a variant
embodiment, it is possible to conceive of a tank wall having a
total thickness of 400 mm by using, on each occasion, a layer of
aerogel particles, particularly aerogel beads, in the caissons 3
and 7.
[0058] With reference to FIGS. 4 and 5, a description will now be
given of a first embodiment of a sealed, thermally insulated tank
according to the invention. In the first embodiment, the primary
and secondary insulating barriers are formed from non-conducting
elements in the form of parallelepipedal caissons 60 whose
structure is shown in FIG. 5 and that are arranged and anchored in
a similar manner to the caissons 3 and 7 of FIG. 1, so a further
description is unnecessary in this regard.
[0059] The caisson 60 includes a block of low-density synthetic
foam 63, for example low-density polyurethane foam, optionally
reinforced with fibers, sandwiched between a base panel 61 and a
cover panel 62 that are fixed to its larger faces, for example by
means of adhesive bonding.
[0060] Between the panels 61 and 62, load-bearing pillars 65 in the
form of hollow tubes with a circular cross section extend in holes
64 provided in the thickness of the block 63. In the example shown,
the pillars 65 are distributed in the form of a square-mesh grid,
but other forms of distribution are possible. In the case of a
non-conducting element with a 1.5-m-sided square cross section,
provision is made, for example, for sixty-four pillars 65. However,
the density of the pillars may be modified, particularly as a
function of the forces to be taken up and of the cross section of
the pillars. The inside of the pillars 65 is filled with
insulation, which is, for example, the same foam as that forming
the block 63 between the pillars 65, or another material, for
example a material of higher density, in order to take up more
compression forces.
[0061] In the embodiment of FIG. 5, the caisson 60 may be
manufactured by means of the following steps: cutting a block of
foam 63 from a bed of continuously-poured foam, machining holes 64
through the block 63, inserting pillars 65 in the holes 64,
inserting plugs of insulation 66 in the pillars 65, and adhesive
bonding of the panels 61 and 62.
[0062] An alternate manufacturing method corresponds to FIG. 6, in
which the block of foam is omitted. In such a case, pillars 65 are
placed in the cavity 68 of a mold 67 and then foam is poured
between the pillars 65 so as to obtain a block of foam in which the
pillars 65 are embedded. The pillars 65 may also be filled during
the same pouring step if their diameter is fairly large, for
example greater than 100 mm. In order to guarantee the positioning
and holding of the pillars 65 in the cavity of the mold, a planar
positioning element is used, in this case in the form of a grid or
of a glass mat 69, through which the pillars 65 are tightly fitted.
The grid or glass mat 69 is also embedded in the thickness of the
block of foam after molding, which makes it possible to reduce the
expansion coefficient of the foam in this zone and thus to reduce
the shear stresses between the panels 61 and 62 and the foam.
Lastly, the panels 61 and 62 are adhesively bonded. Alternately, or
in combination with this adhesive bonding, it is possible to fit
the panels and the ends of pillars 65 together, which ends should,
in such a case, extend beyond the block 63.
[0063] It would also be possible to commence by fixing the pillars
65 on the panel 61 and placing this assembly in the mold 67 in
order to pour the foam directly over the panel 61, with or without
the grid 69.
[0064] FIG. 19 illustrates, using the same reference numerals as in
FIG. 6, a further variant embodiment of the process in which the
block of foam 63 is molded between the panels 61 and 62, which
panels are placed with the pillars 65 (and, as appropriate, the
grid or glass mat 69) in the mold 67, which is closed by a cover
59. This results in a caisson 60 that is finished in a single
operation.
[0065] The pillars 65 may be manufactured in a number of materials.
Plastics such as PVC, PC, PA, ABS, PU, PE and the like are
particularly suited to the molding of pillars of any form and have
an advantageous cost price. Other possible materials are
composites, wood, plywood or synthetic foams. The panels 61 and 62
may be produced from plywood, plastic resin or a composite
material. For example, their thicknesses are 6.5 mm for the base
and 12 mm for the cover.
[0066] It will be noted that the caisson 60 may be manufactured,
or, above all, easily cut out, in any form whatsoever in order to
achieve precise connections when the tank is constructed or to take
up tolerances. Indeed, it is easy to cut the panels 61 and 62 and
the block 63 between the pillars 65 without compromising the
cohesion and compression strength of each caisson part thus
separated. As appropriate, it is also possible to cut hollow
pillars 65 vertically.
[0067] The tank wall produced with the aid of the caissons 60 is
shown in section in FIG. 4. In this example, thicker caissons are
used for the secondary insulating barrier 2 than for the primary
insulating barrier 6. The detail of the primary 4 and secondary 48
anchoring members and of the sealing barriers 5 and 8 is not shown.
Reference may be made to FIGS. 1 to 3 in this regard.
[0068] As the geometry of the double hull 1 is irregular, provision
is made for shims around the threaded pins 31. The thickness of
each shim is calculated by computer on the basis of a topographical
survey of the inner surface of the double hull 1. Thus, the base
panels 61 of the secondary barrier 2 are positioned along a
theoretical regular surface. Between the base panels 61 and the
double hull 1, provision is conventionally made for beads of mastic
70 that are adhesively bonded to the base panels 61 and are crushed
against the double hull when the caissons 60 are fitted, so as to
provide their support. To avoid this mastic adhering to the double
hull, a sheet of Kraft paper (not shown) is provided between them.
Preferably, the beads 70 are placed in line with the pillars 65 in
order to prevent flexing of the panel 61 on account of the
compression force, which is transmitted predominantly in the region
of the pillars 65. Furthermore, it would be possible to dispense
with base panels and to rest the pillars 65 directly on the beads
70.
[0069] According to a variant embodiment (not shown), provision is
made for peripheral walls extending to the periphery of the caisson
60 between the panels 61 and 62 so as to form a closed box capable
of containing granular insulation. These walls may be fixed to the
panels by means of adhesive bonding, stapling, flush-fitting and
other fixing means. The caisson 60 may also be assembled in
monobloc fashion, for example by means of blow-molding or
rotational molding.
[0070] According to a further variant embodiment, the panels 61
and/or 62 are replaced by panel portions that cover only zones of
the block 63 at the end of the pillars 65, not the entire surface
of the block 63. The weld supports 42 will then be housed in the
cover-panel portions.
[0071] Provision may be made for oblique pillars 65, i.e. pillars
whose axis is not perpendicular to the base 61 and cover 62 panels.
An inclination of this type makes it possible to take up not only
shear forces but also overturning forces applied to the caisson 60.
With reference to FIGS. 7 to 12, a description is given of further
embodiments of non-conducting caissons or elements that can be used
to form the insulating barriers of the tank wall, the general
structure of which was described for FIGS. 1 to 3. The production
of the sealing barriers and the attachment of the various barriers
is similar to the preceding embodiments, there will be no point in
describing them again here.
[0072] FIG. 9 shows, in expanded perspective view, a caisson 570
and a caisson 670 that are, respectively, manufactured with the aid
of molded load-bearing structures 500, a description of which will
now be given with reference to FIG. 7.
[0073] The load-bearing structure 500 is an injection-molded piece
made from any appropriate material. It has a flat plate 571 with
chamfered corners, for example in the form of a 1.5-m-sided square
or of a rectangular, from one face of which sixteen hollow circular
cylindrical pillars 575 project, arranged in the form of a regular
square grid, plus two tubes 581 of smaller cross section in the
region of a central zone of the plate, and also four triangular
cylindrical pillars 580 in the region of the four corners of the
plate. The plate 571 is continuous in the region of the base of the
pillars 575 and 580, but pierced in the region of the base of the
tubes 581 in order to allow the passage of a coupler rod.
Furthermore, in the case of a caisson of the primary barrier 6, the
plate 571 is slit in order to allow through the weld supports 42
and the raised edges 43 of plate strakes of the secondary sealing
barrier. The pillars 580 serve to receive the bearing forces of the
coupling members used at each corner of the non-conducting
elements. The cross section of the pillars 575 is, for example, 300
mm for a 1.5 m square plate. As for the insulating liner, the
load-bearing structure 500 may be covered with a layer of
low-density foam, which is poured between and into the pillars
575.
[0074] The cross section of the pillars may be reasonably large,
the important thing being to always make provision for several
pillars per caisson. Thus, the dimensions of the pillars in terms
of cross section may be 1/3 or even 1/2 of the corresponding
dimensions of the caisson.
[0075] In order to form the caisson 570, an independent panel 572
with the same dimensions as the plate 571 is fixed on the end of
the pillars 575 opposite this plate. This panel may be fixed by any
means (adhesive bonding, stapling, flush fitting, etc.). In FIG. 9,
provision has been made for circular grooves 573 on the inner face
of the panel 572, for receiving the end of each pillar 575
tightly.
[0076] The materials of the structure 500 and of the panel 572 may
be chosen so as to produce heat-shrinking of the pillars 575 in the
panel. For example, with a piece 500 made from PVC and a panel 572
made from plywood, which exhibits less heat shrinkage, the end of
the pillars 575 is made to grip the circular core delimited by the
groove 573 when the tank is cooled. Conversely, gripping of the
pillars 575 could also be obtained with a panel 572 that contracts
more than the piece 500.
[0077] The panel 572 has holes 574 opposite the tubes 581 of the
molded structure 500.
[0078] In the caisson 670, two identical molded structures 500 are
arranged symmetrically and assembled together by causing their
respective pillars 575 to bear against one another. This assembly
may be produced by any means (adhesive bonding, welding, flush
fitting, etc.). In FIG. 9, it is achieved with the aid of a linking
ring 680 interposed, on each occasion, between two aligned pillars
575 and flush fitted over them. This assembly can be seen better in
FIG. 10, where it will be observed that the linking ring 680 has an
outer annulus 682 and an inner annulus 681 that are connected by
means of a radial tongue 683. The pillars 575 flush fit between the
two annuli 681 and 682 and abut on either side of the tongue 683.
The material of the ring 680 may be chosen to have lower
conductivity than that of the pillars 575, in order to fulfill a
thermal insulation function. They may also, alternately or in
combination, be chosen to have an expansion coefficient that is
different from that of the pillars 575 in order to fulfill a
thermal assembly function. In a variant embodiment, two molded
structures having pillars with complementary cross sections may be
fixed together by means of direct nesting of the pillars
together.
[0079] The foam-filled piece 500 may also be used alone without a
supplementary panel by rotating the plate 571 toward the inside of
the tank in order to support the adjacent sealing barrier. The
non-conducting element thus formed rests via the pillars 575 on the
secondary sealing barrier or on the strips of resin fixed to the
hull.
[0080] FIGS. 11 and 12 show molded load-bearing structures 600 and
700 that make it possible to produce non-conducting elements in a
manner similar to the structure 500 described previously.
[0081] In FIG. 11, identical reference numerals to those in FIG. 7
denote identical elements. The structure 600 includes planar
peripheral walls 601 extending continuously along the four edges of
the plate 571, forming a box capable of containing insulation in
the form of powder, beads or the like. For example, a structure 600
containing aerogel beads may be combined with a structure 600
containing low-density foam to form a caisson 670 as shown in FIG.
9.
[0082] In FIG. 12, the planar plate 771 carries thirty-six hollow
tubular pillars 775 of smaller cross section (for example 100 mm)
than the above-mentioned pillars 575, four hollow tubular pillars
780 with an even smaller cross section (for example 50 to 60 mm) in
the region of its corners, and two tubular pillars 781, similar to
the pillars 780, in the region of a central zone of the plate 771
in order to allow the coupling members serving to attach the
insulating barrier to pass through.
[0083] The structures 500, 600 and 700 may be injection-molded. A
similar structure may also be obtained by thermoforming from a
plastic plate. This possibility is illustrated in FIG. 8. In such a
case, the initially planar plate 571 is heated and deformed to
match the impression of a female mold 560. This results in
load-bearing pillars 575 whose plate-side end is open and whose
opposite end is closed by a wall 583. In such a case, the space 582
located inside the pillars 575 is filled with, for example, foam
from the face of the plate 571 opposite these pillars.
[0084] The walls 601 may also obtained by thermoforming.
[0085] FIG. 21 shows, in perspective, a thermoformed load-bearing
structure 1300 that includes a plate 1371 that can act as base
panel or cover panel for a caisson, and load-bearing pillars 1375
obtained in a similar way to the pillars 575 in FIG. 8. In the
example shown, the pillars 1375 have a frustoconical shape, which
facilitates their forming. For example, provision may be made for a
pillar diameter that varies from 160 mm at the base to 120 mm at
the top, over a height of approximately 100 mm.
[0086] In order to serve as base panel of a caisson of the primary
insulating barrier, the plate 1371 is provided with two
longitudinal ribs 1384 extending over the entire length of the
plate 1371. Each rib 1384 is obtained during the thermoforming
operation by pushing the material in the same direction as the
pillars 1375, so as to form a V-shaped fold that is open on the
planar face of the plate 1371, the inner space 1385 of which allows
the weld supports 42 and the raised edges 43 of the secondary
sealing barrier to pass through. In the case of the secondary
insulating barrier, the ribs 1384 are unnecessary.
[0087] A description was given previously of the load-bearing
structures that include a plate acting as cover or base panel. A
description is now given of a further embodiment of a
non-conducting element 870 with reference to FIG. 13, in which the
molded load-bearing structure 800 includes load-bearing elements
875 of small cross section connected by arms 890. This load-bearing
structure is in plan view in FIG. 14. The load-bearing elements 875
are hollow circular cylindrical pillars arranged in a regular grid
and connected by arms 890 that are arranged in the form of a
square-mesh grid. A cover panel 872 and a base panel 871, for
example made from plywood, plastic, composite or another material,
are adhesively bonded on the two faces opposite the load-bearing
structure 800. The arms 890 are located at the end of the
load-bearing elements 875 adjacent to the panel 872 and have a
planar upper face, which may serve for adhesive bonding of the
panel 872.
[0088] FIG. 20 shows the non-conducting element 870 in expanded
perspective view, in a version that its slightly modified in terms
of the arrangement of the linking arms 890.
[0089] Other arms may be provided in the region of the lower end of
the pillars 875. The arms may also be placed in another region of
the load-bearing pillars (for example half way up).
[0090] The inner space of the caisson 870, i.e. the inner space 880
of the pillars 875, and the space 876 between the pillars is filled
with one or more types of insulation. When low-density foam is
used, the caisson may be manufactured by placing a structure 800 of
rectangular form in plan view in a mold, pouring the foam into the
mold so as to embed the structure 800 in a parallelepipedal block
of foam, then fixing the panels 872 and 871 to this block. The base
panel 871 is not always necessary. One of the panels may also be
molded as a single piece with the structure 800.
[0091] Although a description has been given of hollow load-bearing
pillars of circular cross section in the caisson 60 and the
load-bearing structures 500, 600, 700 and 800, the load-bearing
pillars may have any other form in terms of cross section and any
type of regular or irregular spatial distribution. For example FIG.
15 shows a load-bearing pillar 975 consisting of a plurality of
concentric cylindrical walls 976. In the pillar 1075 of FIG. 16,
the cylindrical walls 1076 have a square cross section.
[0092] FIG. 17 shows pillars 1175 distributed in lines in the form
of a regular figure and with a hollow, square cross section with
chamfered corners. In FIG. 18, pillars 1275, for example solid
circular cylinders, are distributed in a staggered arrangement.
Other cross sections are also achievable, i.e. rectangular,
polygonal, I-shaped, solid or hollow, dihedral, etc. cross
sections. The load-bearing pillars may also have a cross section
that varies over their height, for example frustoconical
pillars.
[0093] In all cases, such pillars may be molded so as to project
from a plate and/or be linked by arms and/or by any linking means.
When use is made of low-density foam as thermal insulation liner
layer, it is particularly advantageous to pour this foam in a
single step over the entire surface area of the linking plate,
between and possibly into the load-bearing pillars. Another
possibility is to machine wells in a block of foam formed in
advance and to insert the load-bearing pillars into the wells
formed for that purpose.
[0094] In the case of a granular insulation, it is necessary to use
a non-conducting element with peripheral walls that are preferably
formed as a single piece with the load-bearing structure, as in
FIG. 11. By virtue of the form of the load-bearing elements of
small cross section, the inner space of the box between them is not
compartmentalized, and therefore the granular material is easier to
distribute over the entire surface area of the non-conducting
element. The granular material may also be inserted into hollow
pillars. Load-bearing pillars of very small cross section, for
example smaller than 40 mm, may be left empty without detriment to
the thermal insulation. Hollow pillars of small cross section may
also be filled with a flexible-PE foam cone or with glass wool.
[0095] In the load-bearing structures 500, 600, 700 and 800
described previously, some pillars may also be replaced by
partitions creating compartments inside the load-bearing
structure.
[0096] With reference to FIGS. 22 and 23, a description is now
given of an embodiment of a non-conducting element that comprises a
monobloc hollow caisson 1470 produced by rotational molding or by
injection blow-molding. This caisson has the form of a closed
hollow envelope 1477 that includes eight frustoconical pillars 1475
formed so as to project from the base wall 1471 of the envelope and
each having a top wall 1483 capable of bearing against the top wall
1472 of the envelope in order to take up the compression
forces.
[0097] To fix the caisson, six frustoconical shafts 1480 are
provided, arranged at the periphery of the envelope and open
through the top wall 1472. These shafts each have a base wall
capable of bearing against the base wall 1471 in order take up the
compression forces- and capable of being pierced in order to
receive a fixing rod, shown diagrammatically at 1431, which is, for
example, a pin welded to the hull or a coupling device fixed to an
underlying sealing barrier.
[0098] The inner space 1476 of the caisson and the inner space 1482
of the pillars 1475 may be filled with any suitable insulation, for
example by injection of foam.
[0099] Similarly, the shafts 1480 may be filled with insulation,
for example PE foam or glass wool, after the caisson is fixed.
[0100] To mold the caisson 1470, use may be made, for example, of
high-density PE, polycarbonate, PBT or another plastic. The shafts
1480 may also be dispensed with if use is made of another method of
attaching the caissons, for example coupling members passing
between the caissons to be attached and bearing on the top wall
1472 in the manner of the retention members 48 of FIGS. 2 and 3.
Base and/or cover panels may also be fixed to the walls of the
envelope in order to reinforce it.
[0101] 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.
[0102] Of course, the insulation liner of a non-conducting element
may include an number of layers of material.
[0103] 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.
[0104] 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.
[0105] 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.
* * * * *