FI81545B - Cryogenic vessel - Google Patents

Abstract

A vessel (10) with a curved surface (13) is insulated with the first layer of insulation (14) formed of a plurality of closed loops (15) joined to each other. A second layer of insulating material (17) is disposed over the first layer (14) and is comprised of a plurality of closed loops (18) of insulating material with adjacent portions of the loops (18) being affixed to each other. Such arrangement allows thicker insulation without the requirement of increased space and heavier equipment.

Description

81 545

Cryogenic vessel

The invention relates to an isolated cryogenic vessel. More specifically, the invention relates to a cryogenic container having a curved outer surface insulated by a first foam insulating layer insulated by heat-sealing a layered strip-like composite material in which the laminated strip-like material defines a plurality of longitudinal slits opening toward the outer container. a reinforcing mesh attached to the first foam layer. When transporting cryogenic liquids, such as liquefied natural gas, the containers used must have relatively effective thermal insulation in order to prevent the loss of liquefied cargo during transport. Various ships have been designed to carry liquefied natural gas. One of the most desirable structures for such vessels uses spherical tanks supported equatorially. Ships usually use a plurality of spherical tanks with an equatorial flange supported by a generally cylindrical wall attached to the hull of the ship. When spherical tanks are used, the surface to volume ratio is as small as possible, which minimizes the surface that must be provided with suitable thermal insulation to prevent undesired evaporation of the liquefied cargo. Such spherical tanks are useful not only for ship use but also for onshore storage. For cryogenic liquids, various shapes of containers have been used, such as rectangular, cylindrical, and the like. Cryogenic tanks have been insulated by many different methods. One method that has gained some popularity is the so-called a panel insulation method in which a plurality of insulating panels are attached to a cryogenic tank and the transported panels are joined together by means of a suitable adhesive, for example with wage foamed urethane foam. Panel insulation technology is labor intensive and therefore undesirable for many applications. When the panel system is used in rectangular tanks, the attachment 5 is very easy. When a panel system is used for non-rectangular containers, such as cylindrical or spherical, it is generally considered that cutting and fitting the panels to the containers takes too much time. As-10 discs in the form of a rotating body, such as a cylinder or a sphere, can advantageously be isolated using a so-called The spiral generation process. The term "helix formation" refers to the formation of structures by progressively depositing insulating foam or similar building material with a material layering device that travels along a predetermined path to deposit successive loops or turns of insulating material on a cylindrical or spherical vessel. In fact, when the helical forming technique is used, 20 strips of insulating material are wrapped around the container to be insulated, and adjacent turns of the strip are effectively secured together. The helical forming technique and modifications thereof are disclosed in U.S. Patents 3,206,899; 3,337,384; 3,507,735; 3,874,983; 3,879,254; 3,902,943; 3,919,034; 25 3 923 573; 3,924,039; 4,017,346; 4,050,607; 4,098,635 and 4,175,998.

U.S. Patent 4,017,346 discloses an apparatus and method for attaching a thermoplastic foam insulation to a cryogenic vessel in the form of a rotating body. Attached to the container is a connected strip having a vapor barrier layer spaced apart from the container, which is usually a flexible aluminum sheet. The strip of thermoplastic foam is attached to the adjacent loops by heat, as well as the adjacent turns of the aluminum shell are joined together by heat seal-35 rack, corrugated or the like. The isolation of the container according to the present invention can be easily performed using the method and apparatus disclosed in U.S. Patent 4,017,346.

In a typical method of attaching the thermal insulation to a container in the form of a rotating body 5, a strip with a cross-sectional area of about 20 cm 2 can be used. Attaching the insulation by the helix reinforcement technique generally becomes easier as the cross-sectional area of the insulation strip decreases. As the cross-sectional size of the strip increases, the weight of the equipment required to layer such a strip generally also increases. In most cases, it is highly desirable to keep the device used to layer the strip in the helix formation process as small as possible. This is particularly the case in ship installations, where a tank, such as a spherical tank, is installed at least partially inside the hull of the ship and the tank is insulated after said installation. Weather protection is often used for such a tank if the tank extends above the hull of the ship. It is preferable to keep the weight and size of the coil forming apparatus used to attach the insulation as small as possible. Ideally, the size and weight of the helical forming equipment are relatively small, which facilitates their transfer from one location to another and requires as little space as possible around the container when attaching the insulating material.

A very critical factor in cryogenic insulation is the vapor barrier, which, as disclosed in U.S. Patent 4,017,346, comprises an aluminum outer shell surrounding 30 vessels and an insulating material. In the event that water vapor easily enters the insulation area of the cryogenic vessel, ice may form, resulting in a substantial and significant deterioration in the insulation capacity. The insulation system disclosed in U.S. Patent 4,017,346 was highly satisfactory when transporting liquefied natural gas, provided that the amount of liquefied natural gas was relatively small. A single layer of insulation and a gas barrier provided adequate insulation and protection for the cryogenic vessel even when vaporized liquefied natural gas was led from the cryo-5 gene tank to ship fuel. As the amount of liquefied natural gas increased relative to heavy fuel oil, such as Bunker C, better thermal insulation was needed in vessels used to transport and / or store liquefied natural gas.

The present invention provides an improved cryogenic as Tian around which the gas barrier properties of the thermal insulation placed are improved. The container according to the invention is characterized in that it comprises a second foam insulating layer placed on the outside of the first foam insulating layer without attachment at a distance from a uniform gas barrier layer connected to the first insulating layer, the second insulating layer consisting of several turns of strip-like material adjacent turns are heat sealed to each other, the first foam insulation layer comprising a second reinforcing mesh disposed within the layered strip material, the layered strip material having a plurality of longitudinal slits opening toward the outer surface of the container and terminating at a proximity to the second reinforcing mesh. Preferred embodiments of the container according to the invention are set out in the appended claims 2-5.

Other features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings, in which: Figure 1 is a fragmentary view of a container insulated in accordance with the present invention;

81 545 5

Figure 1 shows a fragmentary view of a container 10 insulated in accordance with the present invention. The generally spherical container 10 has an outer surface 13. Adjacent the outer surface 13 of the container 10 is a first insulating layer 14 formed by a plurality of closed insulating loops 15 connected to each other. A second insulating material layer 17 is placed outside the insulating material layer 14. The layer 17 comprises a plurality of closed insulating material loops 18, the adjacent parts of which are attached to each other. The helical forming device 20 comprises a curved rod 21 having an upper or axial end 22 and a lower or equatorial end 23. The wheels 24 and 25 support the ends 22 and 23, respectively. The upper end 22 of the rod 21 is rotatably attached to an axial bearing pin 27 attached to the steam dome 12 of the container 11. The rod 21 supports an insulation lay-up end 28 which can move along the rod 21 between the ends 22 and 23. A layer of insulating material 31 is associated with the layering end 28, which is effectively wound around the container 11 to form a second insulating layer 17. The layering device 20 provides both layers 20 and 17 of insulation 20 as they rotate around the container 11 during the layering of the insulation.

Figure 2 schematically shows a cross-sectional view of a portion of an insulation 40 in accordance with the present invention. The insulation 40 has a first or inner 41 and a second or 25 outer 42. The insulation 40 comprises a first or inner layer 43 and a second or outer layer 44. The inner layer 43 comprises a plurality of loops or turns 45, each comprising a first or inner strip portion 46 and a second or 30 outer strip portion 47. Adjacent portions of the turns 45 are joined together at joints 48. Such joints 48 between adjacent turns are preferably formed by heating the thermoplastic foam of the sheet members 46 and 47 to a sufficiently high temperature so that the foam melts and adjacent layers heat seal 81 815 6 together. A reinforcing mesh 49 is disposed on and secured to the inner surface 41 of the insulation. It is preferred that the reinforcing mesh 49 be of a coarse glass fabric that mechanically reinforces the strip portions 46. Each of the turns 45 forms slits 51 extending from the inner surface 41 in a partially inward direction. 46. A reinforced mesh 53 is interposed and heat-sealed between the strip portions 46 and 47. It is preferred that the mesh 53 be of coarse glass fabric and mechanically reinforce the helical wire racks 45. An optional reinforced glass mesh 54 is attached to the strip portions 47 remote from the inner surface 41. or a gas barrier layer 55, which is preferably aluminum. The vapor barrier layer 55 is wider than the turns 45 and is heat sealed with suitable hot melt adhesives to adjacent portions of the vapor barrier material 55 on adjacent turns 45. Each of the turns 45 forms a recess 57 associated with the cold or inside near its edges and recesses 58 associated with the vapor barrier layer 55. It is preferred that the recessed recesses 57 form a groove on the inner surface 41 to provide a free gap for the heat seal plate when forming the joints or fused parts. The grooves 58 facilitate the closure of adjacent portions of the gas barrier layer 55 as well as the folding of the closed portions so that the closed portions 25 are generally parallel to the main portions of the gas barrier layer 55. The outer insulating layer 44 comprises a plurality of loops or turns 61. Each turn 61 has a body 62 formed of a synthetic resin-containing foam insulation and an inner surface 63 to which a reinforcing mesh 64, such as a coarse glass fabric, is optionally attached. The body portion 62 has an outer surface 65 to which a reinforcing mesh 66 is glued, to which a gas barrier layer 67 is in turn glued, which generally corresponds to a gas barrier layer 55. The body portion 62 has a first or inner recess 35 68. Adjacent recesses 68 form grooves 68 545 open toward the inner surface 63. Similar recesses 69 engage the outer surface 65 and form outwardly opening grooves against the gas barrier layer 67.

As shown in Figure 2, the slits 51 5 reduce tension as the inner surface 41 cools to cryogenic temperature. The reinforcing mesh 53 provides an effective means of limiting any cracks that may be caused by the shrinkage of the surface 41 associated with the strip portion 46 and of minimizing the tendency for vertical cracks to form, i.e. in the Plane-10. The network 54 associated with the gas barrier layer 55 increases the mechanical strength to resist thermal stresses as the inner surface 41 of the strip portion 46 cools to cryogenic temperatures. The outer insulating layer 44 increases the thermal insulation of the gas barrier layer 55 and the mechanical protection. Accordingly, the insulation 40 forms two effective concentric vapor barriers which are highly reliable as protective structures if liquefied gas leaks from the tank and if water vapor penetrates from outside the tank. The grooves 20 formed by the recesses 57, 58, 68 and 69 serve as appropriate paths for the purge gas flow, if desired.

The thermoplastic foam used in the practice of this invention may be any of a number of foams. However, styrene-25 polymer foams, such as polystyrene foam, which generally has a density of the order of 24-40 kg / m 3, are particularly desirable, and for many cryogenic applications it is preferred to make the foam flexible. This is done by crushing the foam in a controlled manner so that it bends more easily. Making such foams or wood is well known and disclosed in U.S. Patents 3,159,700 and 3,191,224. Making the foam used for the insulation of this invention flexible generally facilitates handling of the foam as it is fed to the foam deposition head. Making the foam flexible also increases its elongation at break and reduces the tendency of such foam to crack at cryogenic temperatures.

Figure 3 schematically shows a cross-sectional view of an insulation according to the present invention, generally designated 70. The insulation 70 comprises a first insulating layer 71 and a second insulating layer 72. The insulating layer 71 is associated with the insulating vessel and has the same structure as the insulating layer 43 of Figure 2. has a cold inner side 73 and a warm outer side 74. The structure of the second layer 72 is the same as that of the first layer 71 except that an optional mesh is omitted below the vapor barrier layer 75 of the outer layer 72 and the gas barrier layer is attached directly to the foam body. to the part forming the layers 15 forming the turns 72 thereof. The arrangement shown in Figure 3, which uses two layers of generally equal thickness, provides the desired insulation in mechanical terms and minimizes the modification of equipment in the manufacture of the laminate material that forms the loops of each layer. After the insulating strips forming the turns of the layer 71 have been made, the laminates for the second layer 72 can be easily made by omitting the network associated with the gas barrier. Thus, materials for layers 71 and 72 can be fabricated and layered without undesired modification or adjustment of devices 25. In general, in preparing the insulation of this invention, it is often desirable to step, i.e., move to the side, the joints between the turns forming successive layers. Such offset or staggering minimizes the possibility of cracks propagating from layer to layer in the fusion between adjacent turns.

Figure 4 schematically shows a partial cross-sectional view of an alternative embodiment of an insulation according to the present invention. The insulation 80 comprises, in combination, a first or inner insulating layer 81, a second or intermediate insulating layer 82 and a third or outer insulating layer 83. The inner insulating layer 81 comprises a plurality of loops or turns 85 connected to each other at their edges. Each of the turns 85 comprises a first or inner body portion 86 and a second or outer body portion 87. The body portions 86 and 87 are laminated together with a reinforcing mesh 88, such as a coarse glass fabric, therebetween. Attached to the surface of the inner body portion 86, remote from the outer body portion 87, is a generally similar mesh 89. The inner body portion 86 is provided with stress reducing slots 91 extending a portion of the distance inwardly to the body 86 from the surface having the net 89. The body portion 87 is provided with stress-reducing recesses, grooves or slots 92 extending inwardly from the surface provided with the gas barrier layer 94. The intermediate layer 82 is similar in structure to the inner layer 81 and comprises a plurality of loops or turns 85a. Each of the turns 85a comprises a first or inner foam body 101 having adjacent turns 85 to which a reinforcing mesh 102 is attached. The body 101 forms a pair of stress reducing slits 103 and 104 extending inwardly from the net 102. A second, generally rectangular, foam body is laminated to the body 101. Attached to the frames 106 and 106 is a reinforcing mesh 107. Attached to the frame 106 is an external reinforcing mesh 108 that is generally parallel to and spaced from the nets 107 and 102. A vapor barrier 109 is attached to the body 106, immediately associated with the mesh 108. The vapor barrier 109 is attached and glued to an adjacent vapor barrier 109a of loops or turns 85a. 110. The groove 110 generally extends inwardly from the mesh 102. Generally similar grooves 112 are formed between adjacent turns 35a, adjacent the mesh 108 and the vapor barrier 109. The third or outer layer 83 comprises a plurality of loops or turns 115 of insulating material. Each of the turns 115 comprises a foam body 116 having a generally rectangular cross-section. Attached to the rounds 115 is a reinforced mesh 117 generally near the intermediate insulation layer 81.

At a distance from the reinforcing mesh 117, a parallel vapor barrier layer 118 is attached. The vapor barriers 118 are attached to the body 116 by means of an air layer 119. Adjacent portions of the vapor barriers 118 of the turns 115 are glued together and folded so that they are generally parallel to the net 117. Adjacent turns 115 form first grooves 121 inwardly which extend inwardly and exit inwardly from the mesh 117. Adjacent turns 115 also form outwardly providing grooves 122 which exit inwardly from the vapor barrier 118 toward the grooves 121.

The insulation of the present invention allows considerable flexibility in the choice of materials. In general, the inner layer of the insulating material may consist of a foam with relatively high elongation and insulation values, while going towards the outermost layer of the insulation, 20 foams with a lower elongation may be used depending on the specific requirements of the insulation installation. The use of multiple vapor or gas barriers is an essential advantage because it is difficult to guarantee the integrity of a simple vapor barrier. The use of multiple vapor barriers makes it possible to use a lower atmospheric pressure near the insulated tank 25, which can be maintained near the vessel by using a pump of minimal power.

As will be apparent from the foregoing description, various modifications and variations can be made in the present invention which may differ specifically from those described in the foregoing description. It is therefore to be understood that all of the foregoing is intended to be illustrative only and is not to be construed as limiting or limiting the invention, except as set forth and defined in the appended claims.

Claims (5)

A cryogenic vessel having a curved outer surface (13) insulated with a first foam insulation layer (43) insulated by heat-sealing layers of a strip-like composite material (45), wherein the vessel (10) defines a plurality of longitudinal slits (45). 51) which open towards the outer surface (11) of the container and terminate near a second reinforcing mesh (53) attached to the first foam insulation layer (43), characterized in that it comprises a second foam insulation layer (44) disposed on the first foam insulation layer ( 43) on the outside without attachment at a distance from a continuous gas barrier layer (55) connected to the first insulating layer (43), the second insulating layer (44) being formed by a plurality of turns (61) of strip-like material so that its adjacent turns are massed together so that the first layer of foam insulation 20 (4 3) comprises a second reinforcing mesh (53) disposed within the layered strip material (45), the layered strip material having a plurality of longitudinal slits (51) opening towards the outer surface of the container (11) and terminating at a point substantially adjacent to the second reinforcing mesh. (53) in the vicinity. An insulated cryogenic vessel according to claim 1, characterized in that a second vapor barrier (67) is connected to the second insulating layer (44) at a distance from the gas barrier layer (55). An insulated cryogenic vessel according to claim 2, characterized in that a third reinforcing mesh (54) is connected to the first insulating layer (43) adjacent to the curved outer surface (13) of the container and that adjacent turns (45) of strip-like material define inward the grooves „81545 12 (57) next to the curved outer surface (13) of the container and outwards the grooves (58) away from the container (11). An insulated cryogenic vessel according to claim 1, characterized in that the second longitudinal slits (92) extend from the second reinforcing mesh (88) towards the gas barrier (94). An insulated cryogenic vessel according to claim 1, characterized in that the foam insulation (43) of the first foam insulation layer is a flexible thermoplastic foam having a density of about 24-40 kg / m 3. li 13 81 545