JP2022179904A - Low-temperature liquid storage tank, manufacturing method therefor, and thermal shock reduction method - Google Patents

Abstract

To reduce thermal shock transmitted to a first foamed resin layer coated on an inside surface of an outer tank of a low-temperature liquid storage tank.SOLUTION: In a low-temperature liquid storage tank 100, an under-blown layer 12, a first foamed resin layer 13, and a second foamed resin layer 14 are laminated on the inner surface of an outer tank 30. Both the first foamed resin layer 13 and the second foamed resin layer 14 are hard urethane foam. The second foamed resin layer 14 has more cells Q having a continuous open cell structure than the first foamed resin layer 13 does. Most of the cells Q having an open cell structure in the second foamed resin layer 14 communicate in a plane direction.SELECTED DRAWING: Figure 4

Description

TECHNICAL FIELD The present invention relates to a low-temperature liquid storage tank in which low-temperature liquid of 0° C. or lower is stored, a manufacturing method thereof, and a thermal shock mitigation method for mitigating thermal shock to the low-temperature liquid storage tank.

As a conventional low-temperature liquid storage tank, it is equipped with an inner tank that stores the low-temperature liquid inside and an outer tank that covers the inner tank from the outside. It is known that a first foamed resin layer for the purpose is coated and a reinforcing sheet having a mesh structure is provided on the surface thereof (see, for example, Patent Document 1).

Patent No. 3044605 (paragraph [0002], Fig. 4)

In the above-described conventional low-temperature liquid storage tank, if the reinforcing sheet floats or peels off from the surface of the first foamed resin layer, the leaked low-temperature liquid may expose the first foamed resin layer to thermal shock and break it. Therefore, it is required to mitigate thermal shock transmitted to the first foamed resin layer.

The low-temperature liquid storage tank of the present disclosure includes an inner tank that stores a low-temperature liquid of 0 ° C or less, an outer tank that covers the outside, and a coating on the inner surface of the outer tank to suppress leakage of the low-temperature liquid and prevent thermal shock. A low-temperature liquid storage tank comprising: a first foamed resin layer for alleviating It is a cryogenic liquid storage tank.

1 is a cutaway front view of a cryogenic liquid storage tank according to an embodiment of the present disclosure; FIG. Enlarged sectional view of the tank Cross section of relief layer Schematic diagram showing the flow of liquefied natural gas entering the diffusion layer made of low-density rigid urethane foam. A diagram showing the state of construction of the relaxation layer on the inner surface of the outer tank Diagram showing the flow of construction method of relaxation layer

The cryogenic liquid reservoir 100 of the present disclosure will now be described with reference to FIGS. 1-4. As shown in FIG. 1, the cryogenic liquid storage tank 100 of this embodiment includes a hollow cylindrical tank portion 40 having an inner tank 20 and an outer tank 30, and a cylindrical liquid barrier surrounding the tank portion 40. 50. The tank part 40 stores the liquefied natural gas L inside the inner tank 20 . The capacity of the low-temperature liquid storage tank 100 is generally 140,000 to 230,000 kL, which is called a large one. The height is about 40m.

The inner tub 20 and the outer tub 30 are provided with ceiling portions 21 and 31, respectively, and have a structure in which the inside thereof is shut off from the outside. The ceiling portions 21 and 31 have a dome shape with a swollen central portion, and form a space filled with vaporized liquefied natural gas L. Both the inner tank 20 and the outer tank 30 are made of metal. For example, from the viewpoint of low temperature toughness, iron or steel is preferable. In particular, since the inner tank 20 is always exposed to extremely low temperatures, an alloy such as nickel having iron as a main component and having excellent low-temperature toughness is preferable.

The dike 50 is installed to prevent the diffusion of the liquefied natural gas L in the event of an accidental leakage of the liquefied natural gas L. In this embodiment, the inner surface of the dike 50 is superimposed on The dike 50 is made of prestressed concrete that is hard to crack.

In the tank part 40, the space formed between the inner tank 20 and the outer tank 30 is provided with a cold insulation layer 60 for keeping the liquefied natural gas L at about -160°C and reducing the vaporization of the liquefied natural gas L. It is The cold insulation layer 60 is composed of a ceiling cold insulation layer 61 , a side cold insulation layer 62 and a bottom cold insulation layer 63 .

Specifically, in the inner tank 20 and the outer tank 30, the space formed in the ceiling parts 21 and 31 and the space formed in the side parts 22 and 32 include the ceiling cold insulation layer 61 and the side cold insulation layer 61. The layer 62 is filled with granular perlite or the like having heat insulation performance. In addition, in the space formed in the bottoms 23 and 33 of the inner tank 20 and the outer tank 30, perlite concrete, lightweight cellular concrete, or the like having load-bearing performance and heat insulation performance is disposed as the bottom cold insulation layer 63. there is

In the cryogenic liquid storage tank 100, the inner surface 30S of the outer tank 30 is coated with the relaxation layer 10. As shown in FIG. The relaxation layer 10 is formed to prevent the thermal shock of the leaked liquefied natural gas L from being rapidly transmitted to the liquid barrier 50 .

As shown in FIG. 2, the relieving layer 10 includes a side relieving layer 10S that covers the entire inner surface 30S of the outer tub 30, and an annular bottom surface that covers the entire periphery of the inner bottom surface 30T of the outer tub 30. and a relaxation layer 10T. The bottom relaxation layer 10T also covers the peripheral edge of the bottom cold insulation layer 63 .

FIG. 3 shows the cross-sectional structure of the relaxation layer 10 of this embodiment. The relaxation layer 10 is formed by laminating an under-blown layer 12, first foamed resin layers 13 (13A, 13B), and second foamed resin layers 14 on the inner surface (inner surface 30S and inner bottom surface 30T) of the outer tub 30. As shown in FIG.

The first foamed resin layer 13 is laminated on the underblown layer 12 and is made of rigid urethane foam formed by foaming and curing a urethane foam raw material. The first foamed resin layer 13 needs to mitigate the thermal shock of the liquefied natural gas L and suppress the impact of the thermal shock on the liquid barrier 50 . Therefore, it is preferable that the rigid urethane foam has excellent heat insulating performance and compressive strength, and that the thickness is thin from the viewpoint of efficient use of space. Specifically, it has a density of 40 to 80 kg/m ³ , air permeability of 1 ml/cm ² /s or less, thermal conductivity of 0.040 W/mK or less, and thermal resistance of 1.00 m ² K/W or more. is preferable, the compressive strength is preferably 360 kPa or more, and the thickness is preferably 40 mm or more and 60 mm or less.

Although the first foamed resin layer 13 is composed of two layers (13A, 13B) in the present embodiment, it may be composed of one layer, or may be composed of three or more layers. Here, the skin layer of the first foamed resin layer 13 is a high-density urethane layer, and the ratio of the urethane resin is increased compared to the core portion, so the thermal conductivity is increased and the heat insulation performance is lowered. Therefore, the number of layers constituting the heat insulating layer is preferably as small as possible, and it is more preferable that the heat insulating layer is composed of one or two layers.

The first foamed resin layer 13 of this embodiment has a density of 60 kg/m ³ , air permeability of 0.01 ml/cm ² /s or less, porosity of 95%, thermal conductivity of 0.022 W/mK, and thermal resistance of 2. 3m ² K/W compressive strength 520KPa, thickness 50mm (two layers of 25mm).

In addition, the compressive strength required for the first foamed resin layer 13 is based on the ``9.5.2.2 Calculation of load'' in the above-ground LNG storage tank guidelines of the Japan Gas Association. (Assuming a low-temperature liquid storage tank of 230,000 kL), and calculated with a safety factor of 2.0 from "8.4.4 Thermal resistance alleviating material", it is about 360 KPa. Therefore, the compressive strength required for the first foamed resin layer 13 is 360 KPa or more.

The underblown layer 12 is a layer directly laminated on the inner surface of the outer tank 30 and serves as a primer for ensuring the adhesiveness of the first foamed resin layer 13 . The under-blown layer 12 is made of the same hard urethane foam as the first foamed resin layer 13, and is formed by spraying the same urethane foam raw material as the first foamed resin layer 13 onto the inner surface of the outer tank 30 and curing or foaming. be done. The thickness of the underblown layer 12 is preferably 0.1 to 5 mm.

The second foamed resin layer 14 is laminated on the inner surface of the first foamed resin layer 13, constitutes the outermost surface of the relaxation layer 10, and serves as a protective layer that protects the first foamed resin layer 13 from thermal shock. Like the first foamed resin layer 13, the second foamed resin layer 14 is formed by foaming and curing a raw material of urethane foam, but is composed of a low-density hard urethane foam having a lower density than the first foamed resin layer 13. ing.

Next, the rigid urethane foam forming the second foamed resin layer 14 and the first foamed resin layer 13 will be described. As shown in FIG. 4, both rigid urethane foams are porous bodies having cells (cells) with a closed cell structure in which each cell P is independent, and the gas enclosed in the cells P is independent. This makes it difficult for the temperature change to be transmitted to the gas in the adjacent bubbles P, thereby exhibiting excellent heat insulating performance.

The rigid urethane foam that constitutes the first resin foam layer 13 has more cells P having a closed cell structure than the low-density rigid urethane foam that constitutes the second resin foam layer 14. The low-density rigid urethane foam constituting the two-foamed resin layer 14 has more cells Q having an open-cell structure in which some cells Q communicate with each other than cells P having a closed-cell structure. Specifically, the closed cell ratio, which is the ratio of cells P having a closed cell structure in the cells Q and P, is 65 to 100% (preferably 80% or more) in the first foamed resin layer 13, while the The second foamed resin layer 14 is 0 to 35% (preferably 20% or less). Moreover, most of the cells Q having an open cell structure in the second foamed resin layer 14 communicate in the plane direction. Here, as a property of the spraying method, urethane foam has a low foaming efficiency and tends to be dense on the bonding surface and the surface, and the number of closed cells tends to increase. The core layer with the improved foaming efficiency spreads, that is, the open-cell portion spreads. As described above, "the cells Q having a continuous cell structure communicate in the surface direction" refers to a state in which the continuous cell portion spreads in the continuous surface direction.

In addition, when the closed cell ratio of the first foamed resin layer 13 is less than 65%, the thermal conductivity is lowered, and the necessary thickness for obtaining the necessary thermal resistance value is increased. If the thickness of the first foamed resin layer 13 increases, the cost increases and the work space becomes narrower, which may lead to a decrease in work efficiency, or may cause cracks due to accidental breakage.

Thereby, the second foamed resin layer 14 has a higher porosity and is more flexible than the first foamed resin layer 13 . Further, the second foamed resin layer 14 has higher air permeability than the first foamed resin layer 13 .

The density of the low-density rigid urethane foam as the second foamed resin layer 14 is 7 to 40 kg/m ³ , the air permeability in the thickness direction is 0.05 to 30 ml/cm ² /s, the compressive strength is 15 to 150 KPa, and the heat resistance. A value of 0.30 m ² K/W or more and a porosity of 97.5% or more are preferable. Moreover, the thickness is preferably 10 to 20 mm. Also, the thermal resistance value of the second foamed resin layer 14 is lower than the thermal resistance value of the first foamed resin layer 13 .

The second foamed resin layer 14 made of low-density rigid urethane foam used in this embodiment has a density of 11 kg/m ³ , a thermal conductivity of 0.036 W/mK, a porosity of 99.1%, and a thermal resistance of 0.42 m ^{2 .} K/W, air permeability 0.3 ml/cm ² /s, compressive strength 30 KPa, thickness 15 mm.

Now, when the liquefied natural gas L leaks from the inner tank 20 , the liquefied natural gas L contacts the second foamed resin layer 14 before the first foamed resin layer 13 . The surface (skin layer) of the second foamed resin layer 14 is locally exposed to rapid cooling, shrinks and breaks. At this time, since the second foamed resin layer 14 has a high proportion of cells Q having an open cell structure communicating in the plane direction, the thermal shock of the liquefied natural gas L spreads in the plane direction rather than in the thickness direction, and the first foamed resin layer 14 13 is slowly cooled, and thermal shock transmitted to the first foamed resin layer 13 is relieved.

In addition, since the second foamed resin layer 14 is more flexible than the first foamed resin layer 13, the surface (skin layer) is easily broken, but the break is less likely to spread to the back (the first foamed resin layer 13). . That is, since the portion of the second foamed resin layer 14 on the side of the first foamed resin layer 13 is difficult to break, the second foamed resin layer 13 is not exposed to local abrupt cooling. It is slowly cooled by the liquefied natural gas L inside 14, and the thermal shock transmitted to the first foamed resin layer 13 is alleviated. Moreover, since the breaking range of the second foamed resin layer 14 is shallow, the first foamed resin layer 13 is less susceptible to the energy of breaking occurring in the second foamed resin layer 14 .

Further, a temperature gradient is generated in the second foamed resin layer 14 such that the inner side near the liquefied natural gas L has a lower temperature and the outer side has a higher temperature. When the surface (skin layer) of the second foamed resin layer 14 breaks and the central portion of the second foamed resin layer 14 is exposed to the liquefied natural gas L, the temperature of the central portion is higher than that of the surface (skin layer). , the liquefied natural gas L is considered to boil. As a result, a gas layer is generated between the central portion of the second foamed resin layer 14 and the liquefied natural gas L until the central portion of the second foamed resin layer 14 is cooled. It is thought that this makes it difficult to enter the inside of the foamed resin layer 14 and provides a heat insulating effect. Since the first foamed resin layer 13 is gradually cooled during this time, it is considered that thermal shock transmitted to the first foamed resin layer 13 is alleviated.

Also, since the thermal conductivity of the second foamed resin layer 14 is slightly higher than the thermal conductivity of the first foamed resin layer 13 , the first foamed resin layer 13 is gradually cooled through the second foamed resin layer 14 . In addition, it is considered that the cooling rate of the first foamed resin layer 13 significantly increases when the thermal resistance value of the second foamed resin layer 14 becomes 0.30 m ² K/W or less.

The density of the first foamed resin layer 13 and the second foamed resin layer 14 of the present embodiment is measured based on JIS K 7222:2005/ISO 845:1988, and the air permeability is measured according to JIS K 6400- 7 B method: Measured in accordance with 2012 / ISO 7231: 2010, thermal conductivity is measured in accordance with JIS A 1412-2: 1999 / ISO 8301: 1999, compressive strength is measured in accordance with JIS K 7220 :2006/ISO 844:2004, and the closed cell content was measured with reference to ASTM D 2856-87.

Specifically, the following measurement samples were prepared based on JIS A9526:2015 and measured. The sample for measurement is an aluminum plate of 900 mm square and 5 mm thick. Using the urethane foam raw material for the first foamed resin layer 13, an under-blown layer 12 of about 3 mm is sprayed, and then two heat insulating layers of about 25 mm are applied. By laminating, the first foamed resin layer 13 of about 50 mm was produced. For the second foamed resin layer 14 as well, similarly to the first foamed resin layer 13, the urethane foam raw material for the second foamed resin layer 14 was used to prepare a measurement sample.

The density was measured by cutting out a measurement sample into a 100 mm square×30 mm thickness (no skin layer on the entire surface) so as to include the skin layer of the outer first foamed resin layer 13A in the thickness direction. The thermal conductivity was measured by cutting a sample for measurement into a 200 mm square×25 mm thick (no skin layer on the entire surface) so as to include the skin layer of the outer first foamed resin layer 13A in the thickness direction. . Compressive strength was measured by cutting out a measurement sample into a 50 mm square×30 mm thickness (no skin layer on the entire surface) so as to include the skin layer of the outer first foamed resin layer 13A in the thickness direction. The air permeability was prepared by cutting out a 220 mm square×10 mm thick (no skin layer on the entire surface) from the first foamed resin layer 13B on the inner side of the sample for measurement. The air permeability was measured at the core without including the skin layers of the outer first foamed resin layer 13A and the inner first foamed resin layer 13B in the thickness direction. The closed cell ratio was measured by preparing the first foamed resin layer 13B and the second foamed resin layer 14 each having a size of 30 mm square and a thickness of 20 mm.

Next, a method for constructing the relaxation layer 10 will be described with reference to FIGS. The relaxation layer 10 is constructed in a state where the inner tank 20, the outer tank 30, and the dike 50 are almost completed, and before the granular perlite is filled between the side portions 22, 32 of the inner tank 20 and the outer tank 30. is performed on Therefore, as shown in FIG. 6, workers M, N, and O enter the narrow space between the side portion 22 of the inner tank 20 and the side portion 32 of the outer tank 30 to carry out construction. At this time, since the bottom cold insulation layer 63 is arranged on the outer tank 30 and the inner tank 20 is arranged thereon, the entrance is normally provided in the ceiling (not shown). The width of the side portion 22 of the inner bath 20 and the side portion 32 of the outer bath 30 is 1000 mm to 2000 mm, and the height is about 45 m.

Among the relief layers 10, the side relief layers 10S provided on the inner side surface 30S of the outer tank 30 are constructed, as shown in FIG. Construction is carried out by person M or N. The gondola 70 is suspended along the inner side surface 30S of the outer tank 30 in the space K so as to be vertically movable and horizontally movable.

Construction of the relaxation layer 10 is performed for each of a plurality of construction areas W obtained by dividing the inner surface 30S and the inner bottom surface 30T of the outer tank 30 at predetermined intervals in the vertical direction. In the construction of the side relief layer 10S, the worker M or N who got into the gondola 70 constructs the construction area W in order from the upper end or the lower end. When the construction of a certain construction area W is completed, it moves horizontally to the adjacent construction area W, and similarly construction is repeatedly performed from the upper end or the lower end. When the construction area W is constructed in order from the upper end or the lower end, an area that cannot be constructed from the gondola 70 is moved horizontally to the next construction area W without performing construction. Regarding the area of the side relief layer 10S that cannot be constructed from the gondola 70 and the bottom relief layer 10T, as shown in FIG. Worker O does it. Alternatively, M or N may get off the gondola 70 each time and work continuously.

FIG. 6 shows the construction flow of the relaxation layer 10 . As shown in the figure, in the construction of the relaxation layer 10, a first step S1 is first performed by an operator M. As shown in FIG. After that, the second step S2 is performed by the worker N so as to follow the worker M.

In the first step S<b>1 , a urethane foam raw material is sprayed onto the inner surface of the outer tank 30 by a spray method, and foamed and cured to form the first foamed resin layer 13 . At this time, before forming the first foamed resin layer 13, the under-blown layer 12 is formed by the same spray method.

Specifically, in the first step S1, the worker M sprays the urethane foam raw material toward the inner surface of the outer tank 30 with the spray gun 90 that he carries to form the under-blown layer 12, and then sprays it again, The first foamed resin layer 13 is formed to have a predetermined thickness. In this embodiment, the spraying is performed in two steps to form the two first foamed resin layers 13A and 13B. This is because even if it is attempted to form a predetermined thickness with a single spray, the sprayed urethane foam raw material drips, and there is a possibility that the predetermined thickness cannot be obtained. In this case, after the first spraying is completed, the second spraying is carried out after the hardening progresses and the tackiness (stickiness) of the surface disappears. The outer first foamed resin layer 13A and the inner first foamed resin layer 13B are formed so as to have substantially the same thickness.

In this embodiment, the underblown layer 12 is formed by applying the same urethane foam raw material as the first foamed resin layer 13 . The presence of the under-blown layer 12 can improve the adhesion of the outer first foamed resin layer 13A to the inner surface 30S of the outer tank 30 . In this case as well, after the under-blown layer 12 has been sprayed, it is sprayed after the hardening progresses and the tackiness of the surface disappears. When the first foamed resin layer 13 is formed directly on the inner surface of the outer tank 30 without providing the under-blown layer 12, heat is taken from the portion adhering to the inner surface of the outer tank 30 which is made of metal and has high thermal conductivity. As a result, the degree of foaming may become insufficient, or the adhesive force between the outer tub 30 and the first foamed resin layer 13 may decrease, causing the first foamed resin layer 13 to peel off from the outer tub 30 .

In the second step S2, the operator N sprays the urethane foam raw material on the first foamed resin layer 13 with a spray gun 90 carried by him/her to form the second foamed resin layer 14 made of low-density hard urethane foam. formed to a thickness of At this time, a urethane foam raw material that forms a rigid urethane foam having a density lower than that of the first foamed resin layer 13 is sprayed. Specifically, the polyol (corresponding to an “active hydrogen compound”) in the urethane foam raw material of the second foamed resin layer 14 has a higher molecular weight (weight average Some of them have a large molecular weight (Mw) (that is, have a high molecular weight). For example, the polyol in the urethane foam raw material of the first foamed resin layer 13 mainly has an average molecular weight of 1000 or less, and the polyol in the urethane foam raw material of the second foamed resin layer 14 has an average molecular weight of 1500 or more. It contains 5 wt% or more.

The configuration of the relaxation layer 10 of the present embodiment and the construction method thereof have been described above. Next, the effects of the relaxation layer 10 and its construction method will be described.

In the relaxation layer 10 of the present embodiment, the first foamed resin layer 13 is covered with the second foamed resin layer 14, and the liquefied natural gas L leaked from the inner tank 20 is released before the first foamed resin layer 13. It contacts the second foamed resin layer 14 . Then, the surface (skin layer) of the second foamed resin layer 14 is locally exposed to rapid cooling, shrinks and breaks. At this time, since the second foamed resin layer 14 has a high proportion of cells Q having an open cell structure communicating in the plane direction, the thermal shock of the liquefied natural gas L spreads in the plane direction rather than in the thickness direction, and the first foamed resin layer 14 13 is slowly cooled, and thermal shock transmitted to the first foamed resin layer 13 is relieved. In addition, since the second foamed resin layer 14 is softer than the first foamed resin layer 13 and has a smaller compressive strength than the first foamed resin layer 13, the surface (skin layer) of the second foamed resin layer 14 is easily broken, but the breakage extends to the back (the first foamed resin layer 13). It is becoming difficult to spread. That is, since the portion of the second foamed resin layer 14 on the side of the first foamed resin layer 13 is difficult to break, the second foamed resin layer 13 is not exposed to local abrupt cooling. It is slowly cooled by the liquefied natural gas L on the inner side of 14 (inside the fractured portion), and the thermal shock transmitted to the first foamed resin layer 13 is alleviated. Moreover, since the breaking range of the second foamed resin layer 14 is shallow, the first foamed resin layer 13 is less susceptible to the energy of breaking occurring in the second foamed resin layer 14 .

Moreover, since the first foamed resin layer 13 can be protected from the thermal shock of the liquefied natural gas L by providing the second foamed resin layer 14, the surface of the first foamed resin layer 13 can be reinforced as in the conventional art. It is not necessary to provide the reinforcing sheet of the mesh structure.

Specifically, in the configuration in which the reinforcing sheet is laminated on the surface of the first foamed resin layer 13, the reinforcing sheet is attached to the surface of the first foamed resin layer 13 with an adhesive or the like after the first step S1. At this time, the reinforcing sheet may float or come off from the surface of the first foamed resin layer 13 due to its rigidity. Therefore, a step of cutting and flattening the surface of the first foamed resin layer 13 is required. This process must be performed manually for all the construction areas W, and requires a huge amount of man-hours and costs. Moreover, man-hours and costs for removing the dust are required. Furthermore, dust from cutting chips generated during cutting not only worsens the work environment, but also poses the risk of dust explosion. On the other hand, in the present embodiment, since this step is not required, such problems do not arise and workability can be improved.

Further, since the purpose of the cutting process is to flatten the surface, it is necessary to perform the cutting process after the foam hardening of the first foamed resin layer 13 progresses and sufficient strength is exhibited. If processing such as cutting or grounding is performed before sufficient strength is developed, there is a risk that the material may not be cut flat or may be torn. As a guideline, it takes about 24 hours (1 day) until sufficient strength is developed, which requires an extra number of days, resulting in an increase in cost. On the other hand, in the present embodiment, the second step S2 can be performed after the hardening in the first step S1 has progressed and the tack on the surface has disappeared. This eliminates the time required to wait for the foaming and curing of the first foamed resin layer 13 in the first step S1. Therefore, the above problem does not occur, and workability can be improved.

[Confirmation experiment]
Regarding the relaxation layer 10 of the above embodiment, by protecting the first foamed resin layer 13 made of rigid urethane foam with the second foamed resin layer 14 made of low-density rigid urethane foam, when a thermal shock is received, the thermal shock is reduced. It was confirmed by experiment that it can be alleviated. In this experiment, a relaxation layer 10 was prepared in a metal mold, liquid nitrogen was poured over it, and it was confirmed whether cracks would occur in the first foamed resin layer 13 made of rigid urethane foam. The temperature of liquid nitrogen is -196.degree. Nitrogen is an inert gas and has no fire risk, so it was used as an alternative liquid for experiments.

Specifically, a dismantleable metal mold having internal dimensions of 1600 mm length×700 mm width×100 mm thickness and having an open upper side is prepared. A metal mold is erected (with the length direction and the thickness direction as the bottom surface), the bottom surface of the metal mold (the side opposite to the open surface) is regarded as the outer tank 30, and the urethane foam raw material for the first foamed resin layer 13 is sprayed to form approximately After forming the under-blown layer 12 with a thickness of 3 mm, a first foamed resin layer 13 made of rigid urethane foam with a thickness of 50 mm (a two-layer structure, each layer having a thickness of 25 mm) was formed. Furthermore, a urethane foam raw material for the second foamed resin layer 14 was sprayed thereon to form a second foamed resin layer 14 made of low-density rigid urethane foam with a thickness of 15 mm (single-layer structure) to prepare a test piece. . Then, the prepared test piece is laid down (the length direction and the width direction are the bottom surface), liquid nitrogen is poured from above (the second foamed resin layer 14 side), and the liquid surface of the liquid nitrogen is the second foamed resin It was made to be 20-30 mm high from the layer 14 . Thereafter, the liquid nitrogen was replenished at any time so that the liquid level of the liquid nitrogen became 20 to 30 mm, and the liquid nitrogen was allowed to pass for 2 hours. After 2 hours had passed, the liquid nitrogen was removed from the metal mold, and the presence or absence of cracks was visually confirmed. When cracks were generated, a solvent-diluted dye was dripped from the surface of the cracks with a dropper and allowed to stand for about 1 hour to color the cracks. After that, the metal mold was dismantled, a test piece was taken out, the test piece was cut, and the cross section of the cut was visually observed to confirm the presence or absence of cracks in the first foamed resin layer 13 made of rigid urethane foam. For comparison, Comparative Sample 1 having only the first foamed resin layer (50 mm thick (two-layer structure, each layer has a thickness of 25 mm)) without the second foamed resin layer 14 made of low-density rigid urethane foam; Comparative sample 2 in which a urethane foam raw material for the first foamed resin layer is sprayed on one foamed resin layer (50 mm thick (two-layer structure, each layer has a thickness of 25 mm) to laminate a rigid urethane foam with a thickness of 15 mm, and for reference , and a reference sample (conventional configuration) fixed to the surface of the first foamed resin layer (50 mm thick (two-layer structure, each layer having a thickness of 25 mm)) with a reinforcing sheet adhesive.

As a result, the heat insulating layer of a conventional relaxation layer having a reinforcing sheet on the surface of the first foamed resin layer 13 of the relaxing layer 10 having the second foamed resin layer 14 made of low-density rigid urethane foam and the first foamed resin layer , no cracks occurred. On the other hand, the first foamed resin layers of Comparative Samples 1 and 2 had many cracks. From this experiment, it was found that by protecting the first foamed resin layer 13 made of rigid urethane foam with the second foamed resin layer 14 made of low-density rigid urethane foam, the hardness of the first foamed resin layer 13 was reduced when subjected to a thermal shock. It was confirmed that the occurrence of cracks in urethane foam could be suppressed. In addition, it was confirmed that the relaxation layer of the present disclosure mitigates thermal shock in the same manner as a conventional relaxation layer having a reinforcing sheet on the surface of the first foamed resin layer.

[Other embodiments]
(1) In the above embodiment, the low-temperature liquid storage tank 100 stores liquefied natural gas L, but other low-temperature liquid such as liquefied propane gas may be used.

(2) In the above embodiment, the tank part 40 has the ceiling parts 21 and 31, but it may have a structure in which a lid is provided and the top is open.

(3) In the above embodiment, the second foamed resin layer 14 made of low-density rigid urethane foam is one layer, but multiple layers may be laminated.

(4) In the above embodiment, a reinforcing sheet having a mesh structure may be laminated between the first foamed resin layer 13 and the second foamed resin layer 14 .

At this time, a step S12 of laminating a reinforcing sheet on the first foamed resin layer 13 is performed between the first step S1 and the second step S2. In step S12, the reinforcing sheet is superimposed on the first foamed resin layer 13 and temporarily fixed with a tucker or the like, and then the second step S2 is performed, whereby the reinforcing sheet becomes a low-density rigid urethane foam as the second foamed resin layer 14. You may make it adhere to the 1st foaming resin layer 13 so that it may include. This eliminates the need for an adhesive for attaching the reinforcing sheet to the first foamed resin layer 13, and also eliminates the step of flattening the first foamed resin layer 13. FIG.

(5) In the above embodiment, the second foamed resin layer 14 is made of low-density rigid urethane foam, but may be made of other foamed resin such as soft urethane foam. Also, the first foamed resin layer 13 may be made of another foamed resin.

(6) In the above embodiment, the second foamed resin layer 14 was formed by spraying the urethane foam raw material onto the first foamed resin layer 13 and foaming and hardening it. may be formed by fixing the panel to the first foamed resin layer 13 .

Although specific examples of the technology included in the claims are disclosed in the specification and drawings, the technology described in the claims is not limited to these specific examples. Various modifications and changes of the examples are included, and a part of specific examples is also included.

<Appendix>
Hereinafter, the first to eleventh aspects of the invention extracted from the above-described embodiments will be described while showing effects and the like as necessary.

[First aspect]
An inner tank in which a low-temperature liquid of 0° C. or less is stored, an outer tank that covers the outside thereof, and a first foam that is laminated on the inner surface of the outer tank and suppresses leakage of the low-temperature liquid and mitigates thermal shock. A cryogenic liquid storage tank comprising a resin layer,
A low-temperature liquid storage tank having a second foamed resin layer having a cell structure communicating in a plane direction on the inner tank side surface of the first foamed resin layer.

According to the first aspect of the invention, since the second foamed resin layer has a cell structure that communicates in the plane direction, the thermal shock of the low-temperature liquid spreads in the plane direction rather than the thickness direction, and the first foamed resin layer is cooled slowly. and the thermal shock transmitted to the first foamed resin layer is alleviated.

[Second aspect]
The low-temperature liquid storage tank according to the first aspect, wherein the second foamed resin layer has a higher porosity than the first foamed resin layer.

[Third aspect]
The cryogenic liquid storage tank according to the first aspect or the second aspect, wherein the porosity of the second foamed resin layer is 97.5% or more.

According to the second aspect of the invention, since the second foamed resin layer has a higher porosity and is more flexible than the first foamed resin layer 13, the fracture range of the second foamed resin layer is shallow, and the first foamed resin layer is It becomes difficult to receive the energy of fracture occurring in the second foamed resin layer. Moreover, the porosity of the second foamed resin layer is preferably 97.5% or more (third aspect).

[Fourth aspect]
The low-temperature liquid storage tank according to any one of the first to third aspects, wherein the second foamed resin layer has a lower thermal resistance value than the first foamed resin layer.

[Fifth aspect]
The low-temperature liquid storage tank according to the fourth aspect, wherein the thermal resistance value of the second foamed resin layer is 0.30 m ² ·K/W or more.

According to the fourth aspect of the invention, the second foamed resin layer transfers coldness to the first foamed resin layer, and the first foamed resin layer is gradually cooled. It is considered that the cooling rate of the first foamed resin layer is appropriate when the heat resistance value of the second foamed resin layer is 0.30 m ² ·K/W or more (fifth aspect).

[Sixth aspect]
The aspect of any one of the first aspect to the fifth aspect, wherein the closed cell rate of the first foamed resin layer is 65% to 100%, and the closed cell rate of the second foamed resin layer is 0 to 35%. Cryogenic liquid reservoir according to .

According to the sixth aspect of the invention, since the cells of the second foamed resin layer are more continuous than the first foamed resin layer, the thermal shock of the low-temperature liquid spreads in the second foamed resin layer, and the first foamed resin layer The resin layer is slowly cooled, and thermal shock transmitted to the first foamed resin layer is alleviated.

[Seventh aspect]
8. The cryogenic liquid storage tank according to claim 1, wherein the first foamed resin layer and the second foamed resin layer are made of urethane foam.

[Eighth aspect]
A method for manufacturing a cryogenic liquid storage tank according to any one of the first to seventh aspects,
The foamed resin raw material used for the second foamed resin layer contains an active hydrogen compound (mainly polyol) having a higher molecular weight than the active hydrogen compound (mainly polyol) in the foamed resin raw material used for the first foamed resin layer. A method of manufacturing a cryogenic liquid storage tank comprising:

[Ninth aspect]
A method for manufacturing a cryogenic liquid storage tank according to any one of the first to seventh aspects,
A first step of applying a raw material to the inner surface of the outer tank and foaming and curing to form the first foamed resin layer;
A second step of applying a raw material to the inner tank side surface of the first foamed resin layer and foaming and curing to form the second foamed resin layer;
A method for manufacturing a cryogenic liquid storage tank.

[Tenth Aspect]
A method for manufacturing a cryogenic liquid storage tank according to any one of the first to seventh aspects,
A method for manufacturing a cryogenic liquid storage tank, comprising a panel installation step of installing a resin panel in which the first foamed resin layer and the second foamed resin layer are laminated on the inner surface of the outer tank.

[11th aspect]
An inner tank in which a low-temperature liquid of 0° C. or less is stored, an outer tank that covers the outside thereof, and a first foam that is laminated on the inner surface of the outer tank and suppresses leakage of the low-temperature liquid and mitigates thermal shock. A thermal shock mitigation method for a cryogenic liquid storage tank comprising a resin layer,
A low temperature for disposing a second foamed resin layer on the inner tank side surface of the first foamed resin layer, which has a cell structure communicating in the plane direction and boils the low temperature liquid leaked from the inner tank to generate a gas layer. A thermal shock mitigation method for a liquid storage tank.

According to the eleventh aspect of the invention, a gas layer is generated between the central portion of the second foamed resin layer and the low-temperature liquid until the central portion of the second foamed resin layer is cooled. The foamed resin layer is gradually cooled, making it difficult for the first foamed resin layer to break.

10 relaxation layer 13 first foamed resin layer 14 second foamed resin layer 20 inner tank 30 outer tank 50 liquid barrier 100 low temperature liquid storage tank L liquefied natural gas (low temperature liquid)

Claims (11)

An inner tank in which a low-temperature liquid of 0° C. or less is stored, an outer tank that covers the outside thereof, and a first foam that is laminated on the inner surface of the outer tank and suppresses leakage of the low-temperature liquid and mitigates thermal shock. A cryogenic liquid storage tank comprising a resin layer,
A low-temperature liquid storage tank having a second foamed resin layer having a cell structure communicating in a plane direction on the inner tank side surface of the first foamed resin layer. The low-temperature liquid storage tank according to claim 1, wherein the second foamed resin layer has a higher porosity than the first foamed resin layer. 3. The low-temperature liquid storage tank according to claim 1, wherein the second foamed resin layer has a porosity of 97.5% or more. The low-temperature liquid storage tank according to any one of claims 1 to 3, wherein the second foamed resin layer has a lower thermal resistance value than the first foamed resin layer. 5. The low-temperature liquid storage tank according to claim 4, wherein the second foamed resin layer has a thermal resistance value of 0.30 m ^<2> ·K/W or more. 6. The method according to any one of claims 1 to 5, wherein the closed cell rate of the first foamed resin layer is 65% to 100%, and the closed cell rate of the second foamed resin layer is 0 to 35%. A cryogenic liquid reservoir as described. 8. The low-temperature liquid storage tank according to claim 6, wherein the first foamed resin layer and the second foamed resin layer are made of urethane foam. A method for manufacturing a cryogenic liquid storage tank according to any one of claims 1 to 7,
A method for producing a low-temperature liquid storage tank, wherein the foamed resin raw material used for the second foamed resin layer comprises an active hydrogen compound having a higher molecular weight than the active hydrogen compound in the foamed resin raw material used for the first foamed resin layer. A method for manufacturing a cryogenic liquid storage tank according to any one of claims 1 to 7,
A first step of applying a raw material to the inner surface of the outer tank and foaming and curing to form the first foamed resin layer;
A second step of applying a raw material to the inner tank side surface of the first foamed resin layer and foaming and curing to form the second foamed resin layer;
A method for manufacturing a cryogenic liquid storage tank. A method for manufacturing a cryogenic liquid storage tank according to any one of claims 1 to 7,
A method for manufacturing a low-temperature liquid storage tank, comprising a panel installation step of installing a resin panel in which the first foamed resin layer and the second foamed resin layer are laminated on the inner surface of the outer tank. An inner tank in which a low-temperature liquid of 0° C. or less is stored, an outer tank that covers the outside thereof, and a first foam that is laminated on the inner surface of the outer tank and suppresses leakage of the low-temperature liquid and mitigates thermal shock. A thermal shock mitigation method for a cryogenic liquid storage tank comprising a resin layer,
A low temperature for disposing a second foamed resin layer on the inner tank side surface of the first foamed resin layer, which has a cell structure communicating in the plane direction and boils the low temperature liquid leaked from the inner tank to generate a gas layer. A thermal shock mitigation method for a liquid storage tank.

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