Thermal insulation structure for cryogenic fluids

Abstract

To provide a heat insulation structure that has heat insulation performance sufficiently higher than that of a conventional technique, and can restrain the danger of occurrence of a fire by restraining the occurrence of liquid oxygen.SOLUTION: A heat insulation structure 1 is installed around a body 121 to be kept warm, and thermally insulates the body 121 to be kept warm. The heat insulation structure 1 comprises a foamed elastomer layer 12, a vacuum heat insulation material 14 comprising a metal deposition layer, and a foamed resin heat insulation layer 16, in this order toward an outside direction A from the side of the body 121 to be kept warm.SELECTED DRAWING: Figure 1B

Description

[Technical field]

[0001] The present invention relates to a thermal insulation structure for cryogenic fluids. [Background technology]

[0002] Tanks and piping for cryogenic fluids, such as liquid hydrogen (-253°C) and liquid nitrogen (-196°C), are generally provided with insulation around them.

[0003] For example, Patent Document 1 listed below discloses a composite vacuum insulation material in which a curved rigid foamed plastic is bonded to at least one of the upper and lower surfaces of a vacuum insulation material processed into a curved shape. Furthermore, the following Patent Document 2 discloses an insulating material that is placed around an object to be kept warm and insulates the object, the insulating material having a foamed polyurethane layer and a vacuum insulating material having a metal vapor deposition layer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2004-132438 A [Patent Document 2] Patent Publication No. 2021-50773 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the insulating cover disclosed in Patent Document 1 does not sufficiently insulate the object to be heated, for example, for extremely low-temperature fluids such as liquid hydrogen (-253°C), and there is a demand for insulating materials with even better insulating properties. The heat insulating material disclosed in the above-mentioned Patent Document 2 has a structure shown in FIG. 4, for example. FIG. 4 is a schematic cross-sectional view of one of the two-part covers that insulate the piping. In the heat insulating material 202 in FIG. 4, a vacuum heat insulating material 100 having a metal deposition layer, a first foamed polyurethane layer 21, and a second foamed polyurethane layer 23 are provided in this order on the heat-insulating object 121 (piping) from the heat-insulating object 121 side toward the outside. According to the study by the present inventors, this conventional heat insulating material has been found that, as shown in FIG. 5, the core material (vacuum heat insulating layer) sealed under reduced pressure inside the metal deposition layer of the vacuum heat insulating material 100 cannot follow the curved shape of the heat-insulating object 121, and an air layer P is formed between the heat-insulating object 121 and the vacuum heat insulating material 100, and the oxygen in the air layer P is cooled below the boiling point (below -183°C) to generate liquid oxygen. Liquid oxygen has a risk of causing a fire if it coexists with a flammable substance and a fire source. On the other hand, if the vacuum insulation material 100 comes into direct contact with the heat-insulating body 121, whose surface is extremely cold, the metal vapor deposition layer will be damaged, causing the internal filling material to leak out and making it impossible to maintain the vacuum state, which also poses problems in terms of workability.

[0006] Therefore, an object of the present invention is to provide an insulating structure that has sufficiently high insulating properties despite having a thinner total thickness of insulating material than the prior art, and that can suppress the generation of liquid oxygen and thereby reduce the risk of fire. [Means for solving the problem]

[0007] After extensive research, the inventors discovered that the above-mentioned problems could be solved by laminating a foamed elastomer layer, a vacuum insulation material having a metal vapor deposition layer, and a foamed resin insulation layer in that order to the object to be kept warm, and thus completed the present invention. That is, the present invention is as follows.

[0008] 1. A thermal insulation structure that is installed around an object to be insulated and insulates the object, The heat insulating structure has, in this order from the heat-insulating body side toward the outside, a foamed elastomer layer, a vacuum heat insulating material having a metal vapor deposition layer, and a foamed resin heat insulating layer. A thermal insulation structure characterized by: 2. The heat insulating structure described in 1 above, wherein the foamed elastomer layer has a closed cell structure. 3. The heat insulating structure according to claim 1 or 2, further comprising a metal foil layer between the foamed elastomer layer and the vacuum insulation material. 4. The heat insulating structure described in any one of 1 to 3 above, characterized in that the foamed resin insulation layer provided on the outside of the vacuum insulation material is a foamed phenolic resin layer or a sprayed urethane foam layer having a closed cell structure. 5. The heat insulating structure according to 4 above, further comprising a metal foil layer provided as an outermost layer on the foamed phenolic resin layer or the sprayed urethane foam layer. 6. The heat insulating structure according to any one of 1 to 5 above, wherein the metal vapor deposition layer in the vacuum insulation material is an aluminum vapor deposition layer. 7. The heat insulating structure described in any one of 1 to 6, characterized in that the object to be kept warm is one or more selected from the group consisting of liquid hydrogen piping, liquid hydrogen tanks, liquid nitrogen piping and liquid nitrogen tanks. 8. The heat insulating structure according to item 7, wherein the object to be kept warm is one or more selected from a pipe for liquid hydrogen and a tank for liquid hydrogen. Effect of the Invention

[0009] The thermal insulation structure of the present invention is characterized by having, in this order from the side of the object to be kept warm toward the outside, a foamed elastomer layer, a vacuum insulation material having a metal vapor deposition layer, and a foamed resin insulation layer. The foamed elastomer layer is flexible and adheres closely to the curved object to be kept warm, and is itself difficult to permeate air, so that no air layer is formed at the interface between the object to be kept warm and the foamed elastomer layer, and liquid oxygen is not generated. In addition, the vacuum insulation material sandwiched between the two insulation materials is air-impermeable because a metal deposition layer 108 is provided on the surface of the bag body 104 as described below, and contact between the object to be kept warm and oxygen is prevented. Furthermore, in a preferred embodiment, when a metal foil layer is further provided on the outside of the foamed resin insulation layer, the permeation of air to the object to be kept warm is further suppressed. From the above, the heat insulation structure of the present invention can suppress the generation of liquid oxygen and suppress the risk of fire. In addition, since the object to be kept warm and the vacuum insulation material are not in direct contact, damage to the vacuum insulation material is prevented. On the other hand, since the vacuum insulation material used in the present invention has an extremely low thermal conductivity (high thermal insulation), it is possible to provide a heat insulation structure with a thinner total thickness of the insulation material than in the prior art. [Brief description of the drawings]

[0010] [Figure 1A] FIG. 2 is a schematic cross-sectional view for explaining the heat insulating structure of the present invention. [Figure 1B] FIG. 2 is a schematic cross-sectional view for explaining the heat insulating structure of the present invention. [Diagram 2] FIG. 2 is a schematic cross-sectional view for explaining a vacuum insulation material used in the present invention. [Diagram 3] 1 is a cross-sectional view of a thermal insulation structure of the present invention in a preferred form. [Figure 4] FIG. 1 is a cross-sectional view for explaining a heat insulating structure of the prior art. [Diagram 5] FIG. 1 is a cross-sectional view for explaining the mechanism of liquid oxygen generation in a thermal insulation structure of the prior art. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, embodiments of the present invention will be described in more detail with reference to the drawings.

[0012] FIG. 1A is a schematic cross-sectional view for explaining a thermal insulation structure of the present invention, and is a schematic cross-sectional view of one of two separate covers that insulate a pipe as one embodiment. FIG. 1B is a schematic cross-sectional view for explaining a thermal insulation structure similar to FIG. 1A, but each layer is represented as a rectangle to facilitate understanding of the structure. 1A and 1B, the thermal insulation structure 1 of the present invention has, on an object to be heated 121 (piping), a foamed elastomer layer 12, a vacuum insulation material 14 having a metal vapor deposition layer, and a foamed resin insulation layer 16, in this order, from the side of the object to be heated 121 toward the outside (the direction of arrow A in FIG. 1B). As shown in FIG. 1A, a cryogenic internal fluid 122 (e.g., liquid nitrogen, liquid hydrogen) flows inside the object to be heated 121.

[0013] The foamed elastomer layer 12 is flexible and conforms to the shape of the heat-insulating body 121, which prevents the formation of the air layer P as shown in FIG. 5 and prevents the generation of liquid oxygen. The foamed elastomer layer 12 preferably has flame retardancy equivalent to UL94 V-0. There are no particular limitations on the material of the foamed elastomer layer 12, but examples include foamed EPDM, which preferably has a closed cell structure from the viewpoint of air impermeability and flexibility. The foamed elastomer layer 12 can be a commercially available product, such as Aeroflex (foamed EPDM) by AEROFLEX.

[0014] The thickness of the foamed elastomer layer 12 is, for example, 3 mm to 50 mm, and preferably 10 mm to 39 mm. The density of the foamed elastomer layer 12 is, for example, 30 kg / m 3 ~100kg / m 3 and preferably 40 kg / m 3 ~80kg / m 3 The density is measured according to JIS K 7222 "Foam plastics and rubber - Determination of apparent density". The thermal conductivity of the foamed elastomer layer 12 is, for example, 0.030 W / (m·K) to 0.040 W / (m·K), and preferably 0.034 W / (m·K) to 0.038 W / (m·K). The thermal conductivity is measured at 23° C. according to JIS A 1412.

[0015] FIG. 2 is a schematic cross-sectional view illustrating a vacuum heat insulating material 14 having a metal vapor deposition layer used in the present invention. The vacuum insulation material 14 can be made by housing the core material 102 in a bag 104 made of a gas barrier film, and joining the ends of the bag 104 with a heat seal 106. The inside of the bag 104 is depressurized and hermetically sealed. A metal deposition layer 108 is provided on the surface of the bag 104.

[0016] The metal deposition layer 108 is a deposition film formed of a metal, such as aluminum, copper, silver, or a mixture of these, and among these, aluminum is preferred from the viewpoint of heat insulation. The metal deposition layer 108 forms a discontinuous surface of metal atoms, and is therefore presumed to suppress heat conduction, prevent the heat bridge phenomenon, and have excellent heat insulation properties.

[0017] The thickness of the metal deposition layer 108 may be appropriately determined depending on the type of metal and the application of the heat insulating material, but is usually within the range of 1 nm to 1000 nm. The metal deposition layer 108 can be formed by a known method, such as a vacuum deposition method.

[0018] The core material 102 may be an organic material such as open-cell rigid urethane foam or open-cell polystyrene foam, or an inorganic fiber such as glass wool, or an inorganic powder such as silica. The size of the vacuum insulation material 100 may be determined appropriately taking into consideration the shape of the object to be insulated. For example, the planar area is 90 cm. 2 ~10,000cm 2 The thickness is approximately 10mm to 35mm.

[0019] In addition, the vacuum insulation material 14 having a metal vapor deposition layer used in the present invention can be further laminated with known protective layers or other gas barrier films as necessary, in addition to the materials exemplified above.

[0020] The foamed resin insulation layer 16 preferably has flame retardancy equivalent to UL94 V-1. The material of the foamed resin insulation layer 16 is not particularly limited, but examples include foamed phenolic resin and sprayed urethane foam. Foamed phenolic resin is a foaming mixture made by mixing resol resin, which is made by polymerizing phenol and formalin with an alkaline catalyst, with a foaming agent, a curing catalyst, and other additives, and then foaming and curing the mixture. From the viewpoint of air impermeability and flexibility, it is preferable that the foamed resin insulation layer 16 has a closed cell structure. Note that the foamed resin insulation layer 16 can be a commercially available product, and for example, when the foamed resin insulation layer 16 is a foamed phenolic resin, an example of the product is Neoma Foam manufactured by Asahi Kasei Construction Materials Corporation.

[0021] The thickness of the foamed resin insulation layer 16 is, for example, 10 mm to 450 mm, and preferably 10 mm to 400 mm. The density of the foamed resin insulation layer 16 is, for example, 25 kg / m 3 ~60kg / m 3 and preferably 27 kg / m 3 ~40kg / m 3 It is. The thermal conductivity of the foamed resin insulation layer 16 is, for example, 0.010 W / (m·K) to 0.035 W / (m·K), and preferably 0.018 W / (m·K) to 0.024 W / (m·K). The moisture permeability coefficient of the foamed resin insulation layer 16 is, for example, 10 to 60 ng / m 2 s Pa, preferably 25 to 50 ng / m 2 ·s·Pa. The moisture permeability coefficient is measured at a thickness of 25 mm based on JIS K9521. In addition, in tanks for storage purposes, it is possible to use sprayed urethane foam having a closed cell structure as the foamed resin insulation layer 16, and to provide an outer layer of polyurea, FRP, metal foil, etc., to further suppress air permeation.

[0022] The insulating structure of the present invention preferably has a configuration in which a metal foil layer is further provided between the foamed elastomer layer 12 and the vacuum insulation material 14, and / or a metal foil layer is further provided on the foamed resin insulation layer 16 as the outermost layer. Figure 3 is a cross-sectional view of the insulation structure of the present invention to explain the above-mentioned form, and this insulation structure 11 has, on an object to be insulated 121 (piping), in the order from the side of the object to be insulated 121 toward the outside (the direction of arrow A in Figure 3), a foamed elastomer layer 12, a first metal foil layer 13, a vacuum insulation material 14 having a metal vapor deposition layer, a foamed resin insulation layer 16, and a second metal foil layer 18. Providing the first metal foil layer 13 and / or the second metal foil layer 18 can further suppress contact of air (oxygen) with the object to be kept warm 121. In addition, the vacuum insulation material 14 having a metal vapor deposition layer suppresses air permeation, and can suppress the generation of liquid oxygen by the object to be kept warm between each member. The material for the first metal foil layer 13 and the second metal foil layer 18 is not particularly limited, but examples thereof include aluminum foil, copper foil, and the like. In a more preferred form of the invention, the first metal foil layer 13 and the second metal foil layer 18 are applied simultaneously.

[0023] The heat insulating structure of the present invention can be formed by laminating the foamed elastomer layer 12, the vacuum insulation material 14, and the foamed resin insulation layer 16 in this order. Here, it is preferable to fill the spaces between the layers with an adhesive such as a urethane-based or phenol-based adhesive to further prevent air permeation. As described above, in the present invention, it is preferable to further provide a first metal foil layer 13 between the foamed elastomer layer 12 and the vacuum insulation material 14, and / or to further provide a second metal foil layer 18 as the outermost layer on the foamed resin insulation layer 16. In addition, when the heat insulating structure of the present invention is, for example, a multi-split cover, it is preferable to fill the joints with the above-mentioned adhesive and / or to attach a metal tape such as an aluminum tape to further prevent air permeation.

[0024] The insulating structure of the present invention has significantly higher insulating properties than conventional technology and can suppress the generation of liquid oxygen and reduce the risk of fire, making it useful as an insulating material for liquid hydrogen piping, liquid hydrogen tanks, liquid nitrogen piping, and liquid nitrogen tanks, and is particularly useful as an insulating material for liquid hydrogen piping and liquid hydrogen tanks. EXAMPLES

[0025] The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0026] Example 1 A thermal insulation structure as shown in FIG. 1A and FIG. 1B was fabricated. On liquid hydrogen piping 121, from the piping 121 side toward the outside (the direction of arrow A in FIG. 1B), a foamed elastomer layer 12, a vacuum insulation material 14 having a metal deposition layer, and a foamed resin insulation layer 16 were laminated in this order. The above-mentioned adhesive was filled between each layer to further prevent air permeation, and the joints between the two-piece cover were filled with the above-mentioned adhesive and aluminum tape was attached. Aeroflex, a product name of AEROFLEX, was used as the foamed elastomer layer 12. The foamed elastomer layer 12 had a thickness of 13 mm and a density of 60 kg / m 3Its thermal conductivity is 0.0356 W / (m K) and its flame retardancy is equivalent to UL94 V-0. The vacuum insulation material 14 having a metal vapor deposition layer was prepared by storing a core material 102 made of open-cell rigid urethane foam in a bag 104 made of a gas barrier film, joining the ends of the bag 104 with a heat seal 106, and providing an aluminum vapor deposition layer 108 on the surface of the bag 104. The size of the vacuum insulation material 14 was determined to be suitable for insulating the piping 121. Neoma Foam, a product name of Asahi Kasei Building Materials Co., Ltd., was used as the foamed resin insulation layer 16. The foamed resin insulation layer 16 had a thickness of 60 mm and a density of 27 kg / m 3 It has a thermal conductivity of 0.020 W / (m K) and flame retardancy equivalent to UL94 V-1. Next, liquid hydrogen was flowed into the pipe 121, and the temperature between the foamed elastomer layer 12 and the vacuum insulation material 14 was measured. The temperature was found to be -170°C, which was above the boiling point of liquid oxygen, eliminating the possibility of liquid oxygen being generated. Next, the created insulation structure was disassembled, and the area between the piping 121 and the foamed elastomer layer 12 was observed, but no air layer P was found. Although an air layer P was found between the vacuum insulation material 14 and the foamed resin insulation layer 16, the actual measured interface temperature between the vacuum insulation material 14 and the foamed resin insulation layer 16 was -80°C, which is higher than the boiling point of liquid oxygen, which is -183°C, so liquid oxygen is not generated at this interface and this does not pose a problem.

[0027] Comparative Example 1 The heat insulating material 202 shown in FIG. 4 and disclosed in Patent Document 2 (JP Patent Publication No. 2021-50773) was produced. That is, on the liquid hydrogen pipe 121, a vacuum insulation material 100 having a metal vapor deposition layer, a first foamed polyurethane layer 21, and a second foamed polyurethane layer 23 were laminated in this order from the pipe 121 side toward the outside. The above-mentioned adhesive was filled between each layer to further prevent air permeation, and the joints of the two-piece cover were filled with the above-mentioned adhesive and aluminum tape was attached. The vacuum insulation material 100 used was the same as that used in the first embodiment. Next, liquid hydrogen was flowed into the pipe 121, and the temperature of the air layer P was measured, which was found to be −190° C., which is below the boiling point of liquid oxygen, suggesting the production of liquid oxygen. Next, the prepared heat insulating material was disassembled, and the space between the pipe 121 and the vacuum heat insulating material 14 was observed, whereby an air layer P as shown in FIG. 5 was confirmed. [Explanation of symbols]

[0028] 1,11,202 Thermal insulation structure 12 Foam elastomer layer 13 First metal foil layer 14,100 Vacuum insulation material 16 Foamed resin insulation layer 18 Second metal foil layer 21 First foamed polyurethane layer 23 Second foamed polyurethane layer 102 Core material 104 Bag body 106 Heat seal 108 Metal evaporated layer 121 Insulated body 122 Cryogenic internal fluids (e.g. liquid nitrogen, liquid hydrogen) P Air layer

Claims

1. A thermal insulation structure that is installed around a heat-insulating object and insulates the heat-insulating object, The thermal insulation structure has, in this order from the heat-insulating body side toward the outside, a foamed elastomer layer, a vacuum insulation material having a metal vapor deposition layer, and a foamed resin insulation layer, The foamed elastomer layer has a closed cell structure, The object to be kept warm is at least one selected from the group consisting of a liquid hydrogen pipe, a liquid hydrogen tank, a liquid nitrogen pipe, and a liquid nitrogen tank. A thermal insulation structure characterized by:

2. 2. The heat insulating structure according to claim 1, further comprising a metal foil layer provided between the foamed elastomer layer and the vacuum insulation material.

3. 3. The heat insulating structure according to claim 1, wherein the foamed resin insulation layer provided on the outside of the vacuum insulation material is a foamed phenolic resin layer or a sprayed urethane foam layer having a closed cell structure.

4. 4. The heat insulating structure according to claim 3, further comprising a metal foil layer provided as an outermost layer on said foamed phenolic resin layer or said sprayed urethane foam layer.

5. 5. The heat insulating structure according to claim 1, wherein the metal vapor deposition layer in the vacuum insulation material is an aluminum vapor deposition layer.

6. 2. The heat insulating structure according to claim 1, wherein the object to be kept warm is at least one selected from a liquid hydrogen pipe and a liquid hydrogen tank.

Images