JP7520199B2 - Low-temperature liquid storage tank, its manufacturing method, and side heat and cold resistance mitigation layer construction method - Google Patents

Description

This disclosure relates to a low-temperature liquid storage tank that stores low-temperature liquid below 0°C, a manufacturing method thereof, and a method for constructing a side thermal resistance mitigation layer that protects the liquid barrier of the low-temperature liquid storage tank from thermal shock.

A conventional cryogenic liquid storage tank is known that includes an inner tank that stores cryogenic liquid inside and an outer tank that covers the inner tank from the outside, and that includes a mesh-structured reinforcing sheet on the side heat and cold resistance mitigation layer formed on the inner surface of the outer tank (see, for example, Patent Document 1).

Patent No. 3044605 (paragraphs [0002], [0006], [0010], Figures 4 and 6)

In the conventional low-temperature liquid storage tank described above, the side cold-heat resistance mitigation layer is configured to have a reinforcing sheet on the surface of the heat insulation layer via an adhesive layer. In this configuration, in order to prevent the reinforcing sheet from floating off the surface of the heat insulation layer, large-scale equipment is required, or a process of cutting and flattening the surface of the heat insulation layer before applying the adhesive is required. In particular, in the latter case, the construction of the side cold-heat resistance mitigation layer is performed manually by workers riding on a gondola suspended on the inner surface of the outer tank. Such a cutting process and the work of removing dust caused by cutting required a huge amount of man-hours and costs. Furthermore, there was also the problem that dust not only worsened the working environment, but also posed a risk of dust explosion. For this reason, there was a demand for improving the workability of the construction of the side cold-heat resistance mitigation layer.

A first aspect of the invention made to solve the above problems is a low-temperature liquid storage tank in which an inner tank in which low-temperature liquid below 0°C is stored and an outer tank covering the outside of the inner tank are provided with a cold insulation layer, the outer surface of the outer tank is covered with a concrete liquid barrier, and the inner surface of the outer tank is coated with a side cold-heat resistance mitigating layer having a heat insulation layer containing rigid urethane foam as the cold insulation layer to prevent leakage of the low-temperature liquid and mitigate thermal shock, wherein the side cold-heat resistance mitigating layer is formed by applying a fixing layer made of rigid urethane foam to the inner surface of the heat insulation layer, and at least a portion of a mesh-structured reinforcing sheet arranged on the surface of the heat insulation layer is enclosed in the fixing layer.

A second aspect of the invention is the low-temperature liquid storage tank according to the first aspect, further comprising a plurality of temporary fasteners that hold the reinforcing sheet in a shape that matches the undulations of the inner surface of the heat insulation layer, the temporary fasteners being positioned in the recesses of the undulations of the heat insulation layer.

A third aspect of the present invention is the cryogenic liquid storage tank according to the second aspect , wherein the temporary fastener is made of resin.

A fourth aspect of the invention is a cryogenic liquid storage tank according to any one of the first to third aspects , in which the inner surface of the thermal insulation layer and the fixing layer are directly and physically bonded to each other by being in close contact with each other.

A fifth aspect of the present invention is the cryogenic liquid storage tank according to any one of the first to fourth aspects , wherein the fixed layer has a thickness of 5 to 30 mm.

A sixth aspect of the present invention is the cryogenic liquid storage tank according to any one of the first to fifth aspects , wherein the mesh size of the reinforcing sheet is 1.5 to 4 mm.

A seventh aspect of the invention is a construction method for coating a side cold resistance mitigating layer having a heat insulation layer including a rigid urethane foam as the cold insulation layer on the inner surface of the outer tank of a low-temperature liquid storage tank in which a low-temperature liquid of 0°C or less is stored and an outer tank covering the outer surface of the inner tank, in which an outer surface of the outer tank is covered with a concrete liquid barrier. The side cold resistance mitigating layer includes a first step of applying a urethane foam raw material to the inner surface of the outer tank and foaming and curing it to form a heat insulation layer, a second step of overlapping a mesh-structured reinforcing sheet on the inner surface of the heat insulation layer and temporarily fixing it with a plurality of temporary fasteners, and a third step of applying a urethane foam raw material that is the same as or different from the heat insulation layer from the inside of the reinforcing sheet and foaming and curing it to form a fixing layer that encapsulates at least a portion of the reinforcing sheet, thereby coating the side cold resistance mitigating layer including the heat insulation layer, the reinforcing sheet, and the fixing layer on the inner surface of the outer tank.

An eighth aspect of the invention is a method for manufacturing a cryogenic liquid storage tank using the method for applying a side cold resistance mitigating layer according to the seventh aspect .

According to the first, seventh and eighth aspects of the invention , the fixing layer is fixed to the thermal insulation layer with at least a part of the reinforcing sheet contained therein, so that the fixing layer can fix the reinforcing sheet to the thermal insulation layer in a state where it conforms to the surface shape of the thermal insulation layer. Here, as the principle of spray application, liquid particles are laminated while foaming, so the shape derived from the particles and, in some cases, the spraying pattern will appear on the surface, and it is difficult to avoid surface unevenness. In addition, steps may occur due to the shape of steps or grooves on the outer tank surface. Even if the surface of the thermal insulation layer has the above-mentioned unevenness or steps, according to the configuration of the present disclosure, the reinforcing sheet can be laminated to the thermal insulation layer without being limited by the shape. As a result, when laminating the reinforcing sheet, the process of cutting or polishing the surface of the thermal insulation layer to make it flat and the conventional process of fixing the reinforcing sheet to the thermal insulation layer with an adhesive can be omitted, and workability can be improved. Furthermore, by incorporating at least a portion of the reinforcing sheet inside the fixing layer, the fixing layer and the reinforcing sheet are bound together by an anchor effect, preventing the fixing layer from peeling off at the interface with the reinforcing sheet.

According to the second and seventh aspects of the invention , the reinforcing sheet is temporarily fixed in a shape that matches the undulations of the thermal insulation layer before the fixing layer is applied, so that the fixing layer can be applied in a state in which floating between the reinforcing sheet and the thermal insulation layer is suppressed. This allows the side cold resistance mitigation layer to be formed in a state in which the reinforcing sheet is disposed near the surface of the thermal insulation layer. In particular, by disposing the temporary fastener in the concave portion of the uneven shape formed on the surface of the thermal insulation layer, the reinforcing sheet can be effectively disposed near the surface of the thermal insulation layer ( second aspect of the invention ). In addition, by making the temporary fastener that temporarily fastens the reinforcing sheet to the thermal insulation layer from a resin instead of a metal, as in the third aspect of the invention , it is possible to make it difficult for the cold of the low-temperature liquid to be transmitted to the thermal insulation layer.

In conventional configurations, a rubber-based adhesive such as chloroprene or a plastic-based adhesive such as polyurethane or epoxy was applied between the reinforcing sheet and the heat insulation layer, and therefore the adhesive required raw materials and equipment in addition to the urethane foam raw material. In the present disclosure, the fixing layer plays the role of an adhesive that fixes the reinforcing sheet to the heat insulation layer. Furthermore, in the present disclosure, the fixing layer and the heat insulation layer are made of the same raw material and can be constructed using the same equipment, which makes it possible to shorten the construction period. Moreover, because the fixing layer and the heat insulation layer are made of the same urethane foam raw material, the affinity is higher than when an adhesive is applied to the heat insulation layer, and the adhesion is more stable.

Specifically, the surface (skin layer) of the thermal insulation layer and the fixing layer are directly attached to each other, forming a chemical and/or physical bond ( fourth aspect of the invention ). Examples of chemical bonds include urethane bonds and van der Waals forces (bonds), and examples of physical bonds include the anchor effect. This allows the fixing layer and the thermal insulation layer to be stably fixed to each other. The urethane bond is formed by reacting unreacted urethane foam raw material (e.g., polyol, polyisocyanate, etc.) remaining in the skin layer of the thermal insulation layer with the urethane foam raw material when the fixing layer is sprayed. The van der Waals bond is formed by attracting the urethane components (urethane bonds) with high polarity that the thermal insulation layer and the fixing layer have to each other by van der Waals forces. The anchor effect is formed by the urethane foam raw material when the fixing layer is sprayed into the recesses of the minute irregularities formed in the skin layer of the thermal insulation layer, and foaming and hardening, forming a physical bond. These bonds allow the fixing layer to be stably fixed to the thermal insulation layer.

In addition, it is easy to visually determine whether the reinforcing sheet is embedded in the fixing layer (specifically, near the surface of the heat insulation layer). In addition, because the reinforcing sheet is embedded in the fixing layer, there is less risk of it peeling off from the heat insulation layer compared to when the reinforcing sheet is fixed to the heat insulation layer with an adhesive.

The fixing layer is disposed on the surface of the side heat and cold resistance mitigation layer, enclosing at least a portion of the reinforcing sheet, so the reinforcing sheet is not disposed on the surface of the side heat and cold resistance mitigation layer, improving the appearance. Furthermore, the absence of adhesive between the fixing layer and the heat-insulating layer improves the insulation performance.

From the viewpoint of the permeability (passability) of the raw material for the urethane foam through the reinforcing sheet, it is preferable that the mesh size of the reinforcing sheet is 1.5 to 4 mm, as in the sixth aspect of the invention .

The thickness of the fixing layer is preferably 10 mm or more because the reinforcing sheet needs to be embedded in the fixing layer. If the thickness is too large, the binding force of the reinforcing sheet does not easily reach the surface of the fixing layer. For this reason, the surface of the fixing layer rapidly shrinks due to the thermal shock of the low-temperature liquid, making it easy for cracks to occur, so the thickness is preferably 30 mm or less ( fifth aspect of the invention ).

FIG. 1 is a cutaway front view of a cryogenic liquid tank according to an embodiment of the present invention; Enlarged cross-sectional view of the tank Cross-sectional view of the side heat and cold resistance mitigation layer Cross-sectional view of the reinforcing sheet temporarily attached to the heat insulating layer A diagram showing the construction of a side thermal resistance mitigation layer on the inside surface of the outer tank A diagram showing the flow of the construction method for the side thermal resistance mitigation layer Table showing the results of confirmatory experiment 2

An embodiment of the present disclosure will be described below with reference to Figs. 1 to 4. As shown in Fig. 1, the cryogenic liquid storage tank 100 of this embodiment comprises a hollow cylindrical tank section 40 equipped with an inner tank 20 and an outer tank 30, and a cylindrical liquid barrier 50 surrounding the tank section 40. The tank section 40 stores liquefied natural gas L inside the inner tank 20. The capacity of the cryogenic liquid storage tank 100 is generally 140,000 to 230,000 kL, and in the case of a 230,000 kL cryogenic liquid storage tank 100, the diameter of the liquid barrier 50 is approximately 90 m and its height is approximately 40 m.

The inner tank 20 and the outer tank 30 each have a ceiling 21, 31, and are structured so that their interiors are sealed off from the outside. The ceilings 21, 31 are dome-shaped with a bulging center, forming a space filled with vaporized liquefied natural gas L. Both the inner tank 20 and the outer tank 30 are made of metal, and from the standpoint of low-temperature toughness, for example, iron or steel is preferable. In particular, since the inner tank 20 is constantly exposed to extremely low temperatures, an alloy such as nickel, whose main component is iron and has excellent low-temperature toughness, is preferable.

The liquid barrier 50 is installed to prevent the diffusion of the liquefied natural gas L in the event of a leakage accident of the liquefied natural gas L, and in this embodiment, the inner surface of the liquid barrier 50 is overlapped with the outer surface of the outer tank 30. The liquid barrier 50 is made of prestressed concrete, which is resistant to cracking.

In the tank section 40, the space K 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 approximately -160°C and reducing the evaporation of the liquefied natural gas L. 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.

In detail, the space K formed in the ceilings 21 and 31 of the inner tank 20 and the outer tank 30 is filled with granular perlite or the like having thermal insulation properties as the ceiling cold insulation layer 61. In the space K formed in the sides 22 and 32 of the inner tank 20 and the outer tank 30, the side cold resistance mitigation layer 10 is coated on the inner surface 30S of the outer tank 30 as the side cold insulation layer 62, and granular perlite or the like is filled between the side cold resistance mitigation layer 10 and the inner tank 20 in the same manner as the ceiling cold insulation layer 61. In addition, in the space K formed in the bottoms 23 and 33 of the inner tank 20 and the outer tank 30, perlite concrete, lightweight aerated concrete, or the like having load-bearing properties and thermal insulation properties is arranged as the bottom cold insulation layer 63. The side cold resistance mitigation layer 10 is formed to prevent the cold shock of the leaked liquefied natural gas L from being transmitted suddenly to the liquid barrier 50. Here, the side cold insulation layer 62 corresponds to the "cold insulation layer" in this disclosure.

As shown in FIG. 2, the side cold resistance mitigating layer 10 is composed of a side cold resistance mitigating layer 10S that covers the entire inner surface 30S of the outer tank 30, and an annular bottom cold resistance mitigating layer 10T that covers the entire periphery of the inner bottom surface 30T of the outer tank 30. The outer edge of the bottom cold resistance mitigating layer 10T is continuous with the lower end of the side cold resistance mitigating layer 10S, and the inner edge is bent upward and its end face is abutted against the end face of the bottom cold insulation layer 63 that covers the inner bottom surface 30T. Even if liquefied natural gas L flows into the inside of the outer tank 30, it is possible to suppress the sudden transfer of cold (cold shock) and to mitigate the cold shock inside the outer tank 30 before it reaches the surface of the liquid barrier 50. Here, if the thermal shock of the liquefied natural gas L is transmitted to the liquid barrier 50 slowly, for example, over 24 hours, the liquid barrier 50 will not be cooled rapidly, but will be cooled gradually. This means that the liquid barrier 50 will not be exposed to thermal shock, and problems such as cracks on its surface can be prevented.

Figure 3 shows the cross-sectional structure of the side cold resistance mitigating layer 10 of this embodiment. The side cold resistance mitigating layer 10 is formed by laminating a bottom layer 12, a heat insulating layer 13 (13A, 13B), a reinforcing sheet 14, and a fixing layer 15 on the inner surface (inner side surface 30S and inner bottom surface 30T) of the outer tank 30.

The under-blowing layer 12, the heat insulating layer 13, and the fixed layer 15 are all made of rigid urethane foam formed by foaming and hardening urethane foam raw material. Rigid urethane foam has excellent heat insulating properties despite its relatively thin thickness. This makes it possible to mitigate sudden temperature changes (thermal shock) caused by the cold heat of the liquefied natural gas L, and to prevent thermal shock from being applied to the liquid barrier 50.

The underspray layer 12 is a layer that is laminated directly on the inner surface of the outer tank 30 and acts as a primer to ensure the adhesion of the heat insulating layer 13. The thickness is preferably 0.1 to 5 mm.

The thermal barrier layer 13 is laminated on the under-blowing layer 12, and protects the dike 50 by suppressing and mitigating the rapid transfer of cold and heat from the liquefied natural gas L. For this reason, the thermal barrier layer 13 has excellent heat insulation performance and compressive strength, and is preferably thin in terms of efficient use of space. Specifically, the density is preferably 40 to 90 kg/m ³ , the thermal conductivity is preferably 0.040 W/mK or less, and the compressive strength is preferably 360 kPa or more. The thickness of the thermal barrier layer 13 is preferably 40 mm or more and 60 mm or less. By making the thickness this, it is possible to suppress a local temperature drop in the outer tank 30. In this embodiment, the thermal barrier layer 13 is composed of two layers (13A, 13B), but it may be composed of one layer or three or more layers. The skin layer of the thermal barrier layer 13 is a high-density urethane layer, and the ratio of urethane resin is increased compared to the core part, so that the thermal conductivity is increased and the thermal insulation performance is reduced. For this reason, it is preferable that the number of layers constituting the thermal barrier layer 13 is small, and it is more preferable that the thermal barrier layer 13 is composed of one or two layers.

The compressive strength required for the thermal barrier layer 13 is approximately 360 KPa, calculated from the Japan Gas Association's LNG aboveground storage tank guidelines (section 9.5.2.2 Load calculation), assuming a liquid barrier height of 40 m (assuming a 230,000 kL low-temperature liquid tank), and a safety factor of 2.0 (section 8.4.4 Cold and heat resistance mitigation material). Therefore, the compressive strength required for the thermal barrier layer 13 is 360 KPa or more.

The thermal barrier layer 13 of this embodiment has a density of 65 kg/m ³ , a thermal conductivity of 0.022 W/mK, and a compressive strength of 520 KPa. The measurement method and the method of preparing a measurement sample will be described later.

The fixing layer 15 constitutes the outermost surface of the side cold/heat resistance mitigation layer 10. The fixing layer 15 is laminated to the heat insulation layer 13, enclosing at least a portion of the mesh-structured reinforcing sheet 14 described below. Specifically, the fixing layer 15 is formed by applying urethane foam raw material from the inside (surface side) of the temporarily fixed reinforcing sheet 14. A portion of the applied urethane foam raw material passes through the mesh holes of the reinforcing sheet 14 and comes into direct contact with the surface of the heat insulation layer 13, thereby being laminated and fixed to the heat insulation layer 13. At that time, at least a portion of the reinforcing sheet 14 is embedded inside the fixing layer 15 by the urethane foam raw material.

The fixing layer 15 of this embodiment is made of the same urethane foam material as the heat insulating layer 13, so its properties such as density and compressive strength are the same as those of the heat insulating layer 13 described above. Here, the density was measured according to JIS K 7222:2005/ISO 845:1988, the thermal conductivity was measured according to JIS A 1412-2:1999/ISO 8301:1999, and the compressive strength was measured according to JIS K 7220:2006/ISO 844:2004.

In detail, the following measurement samples were prepared and measured based on JIS A9526:2015. The measurement samples were prepared by spraying an approximately 3 mm underlayer 12 onto an aluminum plate measuring 900 mm square and 5 mm thick using urethane foam raw material for the heat insulation layer 13, and then laminating two heat insulation layers of approximately 25 mm each to produce a heat insulation layer 13 of approximately 50 mm. Note that the fixing layer 15 is made from the same urethane foam raw material as the heat insulation layer 13, so no measurement samples were prepared or measured.

The density was measured by cutting out a measurement sample to a size of 100 mm square by 30 mm thick (no skin layer on the entire surface) so that the skin layer of the first heat insulation layer 13A was included in the thickness direction. The thermal conductivity was measured by cutting out a measurement sample to a size of 200 mm square by 25 mm thick (no skin layer on the entire surface) so that the skin layer of the first heat insulation layer 13A was included in the thickness direction. The compressive strength was measured by cutting out a measurement sample to a size of 50 mm square by 30 mm thick (no skin layer on the entire surface) so that the skin layer of the first heat insulation layer 13A was included in the thickness direction.

The reinforcing sheet 14 is laminated near the surface of the heat insulating layer 13 so that at least a portion of it is enclosed within the fixing layer 15. The reinforcing sheet 14 has a mesh structure, and in this embodiment is a glass mesh. The reinforcing sheet 14 may be a mesh structure made of carbon fiber or nylon reinforcing material other than glass.

The reinforcing sheet 14 prevents the thermal insulation layer 13 from locally shrinking and cracking due to the thermal shock of the liquefied natural gas L. In this embodiment, the reinforcing sheet 14 is disposed near the surface of the thermal insulation layer 13 with at least a portion of the reinforcing sheet 14 enclosed within the fixing layer 15, so that even if the thermal insulation layer 13 is subjected to the thermal shock of the liquefied natural gas L, the reinforcing sheet 14 prevents cracks from occurring. From the viewpoint of the permeability of the urethane foam raw material, the size of the mesh holes in the reinforcing sheet 14 is preferably 1.5 to 4 mm.

The fixing layer 15 is laminated on the heat insulating layer 13 with at least a part of the reinforcing sheet 14 of a mesh structure enclosed therein. Here, the reinforcing sheet 14 does not protrude from the surface of the fixing layer 15 toward the inner tank 20 side, but is arranged inside the surface of the fixing layer 15. Therefore, the thickness of the fixing layer 15 is preferably 5 mm or more, more preferably 10 mm or more. On the other hand, if the thickness is too large (for example, 30 mm or more), the binding force of the reinforcing sheet 14 does not reach the surface of the fixing layer 15, and there is a risk that cracks will occur in the fixing layer 15 itself due to thermal shock. The cracks that occur in the fixing layer 15 are stopped by the reinforcing sheet 14 embedded in the fixing layer 15, and the heat insulating layer 13 can be protected. However, from an economical point of view, in order to have the function of enclosing the reinforcing sheet 14 inside the fixing layer 15, the thickness is preferably 30 mm or less. In addition, the thickness of the fixing layer 15 in this embodiment is 10 mm. If the thickness is 10 mm, the binding force of the reinforcing sheet 14 on the fixing layer 15 extends to its surface, preventing cracks from occurring in the fixing layer 15 itself.

As shown in FIG. 4, the reinforcing sheet 14 is fixed to the heat insulating layer 13 by a temporary fastener 16. In this embodiment, a tacker is used as the temporary fastener 16. Here, the material of the staples of the tacker is not particularly limited, but it is more preferable to use resin needles with a lower thermal conductivity than metal needles. The temporary fastener 16 holds the reinforcing sheet 14 in a shape that matches the undulations of the heat insulating layer 13 and fixes (temporarily fixes) it. The temporary fastener 16 fixes the reinforcing sheet 14 superimposed on the heat insulating layer 13 at the recesses of the undulations of the heat insulating layer 13. Fixing at the recesses allows the reinforcing sheet 14 to follow the undulations of the heat insulating layer 13, and it is possible to suppress the occurrence of floating (gaps) between the reinforcing sheet 14 and the heat insulating layer 13. Note that the reinforcing sheet 14 does not need to completely follow the undulations of the heat insulating layer 13, and there may be a gap between the reinforcing sheet 14 and the heat insulating layer 13. This gap is filled by the fixing layer 15 when the fixing layer 15 is laminated.

Next, the construction method of the side cold resistance mitigation layer 10 will be explained with reference to Figures 5 and 6. The construction of the side cold resistance mitigation layer 10 is performed when the inner tank 20, the outer tank 30, and the liquid barrier 50 are almost completed, and before filling the granular perlite as the side cold insulation layer 62 to be placed on the sides 22, 32 of the inner tank 20 and the outer tank 30 in the space K. Therefore, as shown in Figure 6, a worker enters the narrow space K between the side 22 of the inner tank 20 and the side 32 of the outer tank 30 to perform construction. At this time, since the bottom cold resistance mitigation layer 11 is arranged on the outer tank 30 at the bottom, and the inner tank 20 is arranged on top of it, workers usually enter and exit through an entrance provided in the ceiling (not shown). The width between the side 22 of the inner tank 20 and the side 32 of the outer tank 30 is 1000 mm to 2000 mm, and the height is about 45 m.

The construction of the side cold resistance mitigating layer 10S provided on the inner surface 30S of the outer tank 30 is performed by a worker who boards a gondola 70 attached to a trolley beam installed on the ceiling (not shown), as shown in FIG. 5. The gondola 70 is suspended within the annular space K so that it can move up and down and horizontally along the inner surface 30S of the outer tank 30.

The construction of the side cold resistance mitigating 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 a predetermined interval in the vertical direction. In the construction of the side cold resistance mitigating layer 10S, the worker M, N, or O who boards the gondola 70 works on 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, the worker moves horizontally to the adjacent construction area W and repeats the construction from the upper end or the lower end in the same manner. When the construction of the construction area W is performed in order from the upper end or the lower end, the area that cannot be constructed from the gondola 70 is not constructed and the worker moves horizontally to the adjacent construction area W. The above-mentioned areas of the side cold resistance mitigating layer 10S that cannot be constructed from the gondola 70 and the bottom cold resistance mitigating layer 10T are performed by the worker O after the construction of the side cold resistance mitigating layer 10S is completed, as shown in FIG. Alternatively, M or N may get off the gondola 70 each time and carry out the work continuously.

Figure 6 shows the flow of construction of the side cold-heat resistance mitigating layer 10. As shown in the figure, in construction of the side cold-heat resistance mitigating layer 10, the first step S1 is first performed by worker M. Then, the second step S2 is performed by worker N, following worker M. Furthermore, after that, the third step S3 is performed by worker O, following worker N.

In the first step S1, the urethane foam raw material is sprayed onto the inner surface of the outer tank 30 by a spraying method, and is foamed and cured to form the heat insulating layer 13. Before forming the heat insulating layer 13, the under-blow layer 12 is formed by the same spraying method.

In detail, in the first step S1, the worker M sprays the spray gun 90 carried by him/her against the inner surface of the outer tank 30 to form the underspray layer 12, and then sprays again to form the heat insulating layer 13 to a predetermined thickness. In this embodiment, spraying is performed twice to form two heat insulating layers 13A and 13B. This is because, even if a predetermined thickness is to be formed with one spray, the foaming and curing of the sprayed urethane foam raw material progresses to a certain extent, and the layer drips before it can exert its shape retention, making it difficult to ensure a uniform predetermined thickness. In this case, after the first spraying is completed, the second spraying is performed after the curing progresses and the tack (stickiness) of the surface disappears. The first heat insulating layer 13A and the second heat insulating layer 13B are formed to have approximately the same thickness.

In this embodiment, the under-blow layer 12 is formed by applying the same urethane foam raw material as the thermal insulation layer 13. The presence of the under-blow layer 12 can improve the adhesion of the first thermal insulation layer 13A to the inner surface 30S of the outer tank 30. In this case, the under-blow layer 12 is sprayed after the curing has progressed and the tackiness of the surface has disappeared. If the under-blow layer 12 is not provided and the thermal insulation layer 13 is formed directly on the inner surface of the outer tank 30, heat is taken away from the part attached to the inner surface of the outer tank 30, which is made of metal and has high thermal conductivity, and the degree of foaming may become insufficient or the adhesive strength between the outer tank 30 and the thermal insulation layer 13 may decrease, causing the thermal insulation layer 13 to peel off from the outer tank 30.

In the second step S2, the reinforcing sheet 14 is temporarily fixed to the surface of the heat insulation layer 13 with a tacker. The worker N unrolls the required length of the rolled reinforcing sheet 14 loaded into the gondola 70, places it on the surface of the heat insulation layer 13, and fixes it with a tacker while maintaining the shape of the reinforcing sheet 14 to match the unevenness of the heat insulation layer 13. At this time, if the reinforcing sheet 14 is temporarily fixed at the concave part of the unevenness of the heat insulation layer 13, the reinforcing sheet 14 can be made to follow the unevenness of the heat insulation layer 13. Here, the reinforcing sheet 14 applied to the heat insulation layer 13 is temporarily fixed so that it overlaps the adjacent construction area W. The overlap between adjacent reinforcing sheets 14 is not particularly limited, but may be about 50 mm.

In the third step S3, the reinforcing sheet 14 temporarily fixed to the heat insulating layer 13 is sprayed to form a fixed layer 15 of a predetermined thickness. At this time, the urethane foam raw material is sprayed from the inside (inner tank 20 side) of the reinforcing sheet 14 temporarily fixed to the surface of the heat insulating layer 13. For example, the worker O can spray the urethane foam raw material vertically from a distance of 20 to 70 cm against the mesh holes of the reinforcing sheet 14 with the spray gun 90, making it easier for the urethane foam raw material to enter the mesh holes. In this way, the reinforcing sheet 14 is fixed to the heat insulating layer 13 with the fixed layer 15 encased within it. This allows the reinforcing sheet 14 temporarily fixed to the heat insulating layer 13 by the tacker in the second step S2 to be placed near the surface of the heat insulating layer 13 via the fixed layer 15.

At this time, if the foaming and hardening speed of the urethane foam raw material is too fast, the passage becomes poor, and the fixing layer 15 is formed before the urethane foam raw material has sufficiently passed through the mesh holes of the reinforcing sheet 14. In this case, gaps are likely to occur between the heat insulation layer 13 and the fixing layer 15 (reinforcing sheet 14), and the fixing layer 15 and the heat insulation layer 13 are not sufficiently bonded, and there is a risk that the fixing layer 15 will peel off entirely from the heat insulation layer 13. On the other hand, if the foaming and hardening speed of the urethane foam raw material is too slow, dripping will cause poor workability, and it will be difficult to control the uniformity of the thickness.

The urethane foam raw material is composed of liquid A, which is made up of components other than isocyanate such as polyol, and liquid B, which is made up of isocyanate. The speed at which the urethane foam raw material foams and hardens can be evaluated by the time it takes for the raw material to begin to expand after mixing and stirring liquids A and B (cream time). From the standpoint of permeability and workability, it is preferable that the cream time be 0.1 to 1 second when liquids A and B are sprayed with a spray machine with the temperature adjusted to 40°C.

Here, the fixing layer 15 is fixed to the heat insulating layer 13 by direct adhesion between the surface (skin layer) of the heat insulating layer 13 and the fixing layer 15, forming a chemical and/or physical bond with each other, and is stable. In detail, active hydrogen groups derived from isocyanate groups and polyols remain in an unreacted state in the skin layer of the heat insulating layer 13. It is considered that by applying the urethane foam raw material for laminating the fixing layer 15 to the heat insulating layer 13, a urethane bond, which is a chemical bond, is formed with the unreacted isocyanate groups and active hydrogen groups present in the heat insulating layer 13. For this reason, the fixing layer 15 can be stably fixed to the heat insulating layer 13.

In addition, the highly polar urethane components (urethane bonds) that make up the thermal barrier layer 13 and the fixing layer 15 attract each other through van der Waals forces, forming chemical bonds. This also ensures stable adhesion between the fixing layer 15 and the thermal barrier layer 13.

The physical bond is called the anchor effect, which is formed when the urethane foam raw material is sprayed onto the fixing layer 15 and penetrates into the minute irregularities, particularly the recesses, that form on the skin layer of the heat insulating layer 13, and foams and hardens. This also ensures stable adhesion between the fixing layer 15 and the heat insulating layer 13.

This concludes the explanation of the configuration of the side heat resistance mitigating layer 10 and its construction method in this embodiment. Next, we will explain the effects of the side heat resistance mitigating layer 10 and its construction method.

In the side cold-heat resistance mitigation layer 10 of this embodiment, the fixing layer 15 is fixed to the heat insulation layer 13 with at least a part of the reinforcing sheet 14 embedded therein. Therefore, the fixing layer 15 can fix the reinforcing sheet 14 in a state that conforms to the surface shape of the heat insulation layer 13. Here, as the principle of spray application, liquid particles are foamed while being layered, so the shape derived from the particles and, in some cases, the spray pattern will appear on the surface, and it is difficult to avoid surface unevenness. In addition, steps may occur due to the shape of steps or grooves on the surface of the outer tank 30. Even if the surface of the heat insulation layer 13 has the above-mentioned unevenness or steps, according to the configuration of this embodiment, the reinforcing sheet 14 can be layered on the heat insulation layer 13 without being limited by the surface shape. As a result, it is possible to omit the conventional process of cutting or polishing the surface of the heat insulation layer 13 to make it flat, or of bonding the reinforcing sheet 14 with an adhesive before laminating the reinforcing sheet 14 on the heat insulation layer 13, thereby improving workability.

Specifically, as described above, when the reinforcing sheet 14 is attached to the surface of the heat insulating layer 13 with an adhesive, there is a risk that the stiffness of the reinforcing sheet 14 will cause it to float and peel off from the surface of the heat insulating layer 13. Therefore, in order to adhere the reinforcing sheet 14 to the heat insulating layer 13, a process of cutting the surface of the heat insulating layer 13 to make it flat is required. This cutting process not only worsens the working environment due to the dust from the cutting debris generated during cutting, but also creates a risk of dust explosions. In contrast, since the cutting process is not required in this embodiment, such problems do not occur and workability can be improved.

Furthermore, since the cutting process is intended to flatten the surface, it must be carried out after the foaming and hardening of the heat insulating layer 13 has progressed and sufficient strength has been achieved. If cutting or grinding is performed before sufficient strength is achieved, there is a risk that the surface will not be cut flat or may tear. In contrast, in this embodiment, the second process is carried out after the hardening of the first process S1 has progressed and the tack on the surface has disappeared, and the third process is carried out after the second process is completed. This does not cause the above-mentioned problems, and improves workability.

The fixing layer 15 also functions as an adhesive for the reinforcing sheet 14 to the heat insulation layer 13 by incorporating at least a portion of the reinforcing sheet 14 inside. In the conventional configuration, as described above, a rubber-based or plastic-based adhesive was applied between the reinforcing sheet and the heat insulation layer, which required procurement of raw materials and equipment for the adhesive in addition to the urethane foam raw materials, and there was a risk of management becoming complicated. In this embodiment, the fixing layer 15 can be applied using the same raw materials and the same equipment as the heat insulation layer 13 and the underblow layer 12, simplifying management and shortening the construction period. Moreover, since the fixing layer 15 is made of the same raw materials as the heat insulation layer 13, it has a higher affinity and is more stable than when an adhesive is applied to the heat insulation layer 13.

Specifically, the thermal insulation layer 13 and the fixing layer 15 are directly bonded to each other, so that they are chemically bonded to each other through urethane bonding, or physically bonded to each other through the anchor effect. This ensures stable adhesion between the fixing layer 15 and the thermal insulation layer 13. In addition, the urethane components (urethane bonds) that make up the thermal insulation layer 13 and the fixing layer 15 attract each other due to van der Waals forces, so that the fixing layer 15 can be stably bonded to the thermal insulation layer 13.

In addition, in the conventional configuration, since an adhesive layer is provided between the heat insulating layer 13 and the reinforcing sheet 14, it is not easy to inspect the adhesion by visual inspection. In this embodiment, the fixing layer 15, which corresponds to the adhesive, is on the outermost surface, and it is easy to visually determine whether or not the reinforcing sheet 14 is contained. Therefore, it is easy to inspect whether or not the fixing layer 15 (reinforcing sheet 14) is in close contact with the heat insulating layer 13. In addition, since the heat insulating layer 13 and the fixing layer 15 are chemically and/or physically bonded, the risk of the fixing layer 15 peeling off from the heat insulating layer 13 can be reduced, and since at least a portion of the reinforcing sheet 14 is embedded in the fixing layer 15, the risk of peeling off from the heat insulating layer 13 can also be reduced.

Furthermore, the fixing layer 15 has better insulating properties than adhesives, and can also improve the insulating properties of the side thermal resistance mitigation layer 10.

In addition, in this embodiment, in the second step S2, the reinforcing sheet 14 is temporarily fixed in advance in a state where it matches and follows the undulations of the heat insulating layer 13. Therefore, when the fixing layer 15 is applied in the third step S3, it is possible to suppress the occurrence of floating between the fixing layer 15 and the heat insulating layer 13. Moreover, since the fixing layer 15 has the reinforcing sheet 14 embedded inside, the reinforcing sheet 14 is not placed on the outermost surface of the side cold and heat resistance mitigation layer 10, and the appearance is improved. Furthermore, compared to when the reinforcing sheet 14 is fixed to the heat insulating layer 13 with an adhesive, the insulation performance can be improved. Here, if the reinforcing sheet 14 sags or is distorted diagonally, the reinforcing sheet 14 can be cut and placed again so that it becomes straight. At that time, the reinforcing sheet 14 is placed so that it overlaps by more than a predetermined width so that there are no areas where the reinforcing sheet 14 is not placed.

[Confirmation Experiment 1]
It was confirmed by an experiment that the side heat resistance mitigating layer 10 of the above embodiment can suppress the occurrence of cracks in the heat insulation layer 13 when subjected to a heat shock by fixing the fixing layer 15 made of a hard urethane foam containing the reinforcing sheet 14 to the heat insulation layer 13 made of a hard urethane foam. In this experiment, the side heat resistance mitigating layer 10 was made in a metal mold, liquid nitrogen was poured on top of it, and it was confirmed whether or not cracks occurred in the heat insulation layer 13. The temperature of liquid nitrogen is -196°C, which is a more severe condition than liquefied natural gas L, which is about -160°C. In addition, nitrogen is an inert gas and does not pose a risk of fire, etc., so it was used as a substitute liquid for the experiment.

Specifically, a dismantled metal mold with inner dimensions of 1600 mm length x 700 mm width x 100 mm thickness and open top is prepared. The metal mold is set upright (the bottom is in the length direction and thickness direction), and the bottom surface of the metal mold (opposite the open surface) is treated as the outer tank 30. The urethane foam raw material for the heat insulating layer 13 is sprayed to form a bottom blown layer 12 of about 3 mm, and then a 50 mm thick (two-layer structure with each layer being 25 mm thick) heat insulating layer 13 is formed. On top of that, a reinforcing sheet 14 is temporarily fixed with a tacker (a resin needle), and further, a 10 mm thick (single-layer structure) fixing layer 15 is formed by spraying the urethane foam raw material from above the reinforcing sheet 14 to form a test piece. At this time, the same urethane foam raw material is used for the heat insulating layer 13 and the fixing layer 15. For the reinforcing sheet 14, a glass mesh with a mesh hole size of 2.5 mm is used.

Then, the test piece was turned over (the length direction and width direction were the bottom surface), and liquid nitrogen was poured in from above (the fixing layer 15 side) until the liquid nitrogen level was 20 to 30 mm above the fixing layer 15. After that, liquid nitrogen was added as needed so that the liquid nitrogen level was 20 to 30 mm, and two hours were allowed to pass. After two hours, the liquid nitrogen was removed from the metal mold, and the presence or absence of cracks was visually confirmed. If cracks were present, a dye diluted with a solvent was dripped onto the surface of the crack with a dropper, and the crack was colored by leaving it for about one hour. The metal mold was then disassembled, the test piece was removed, the test piece was cut, and the cut cross section was visually observed to confirm the presence or absence of cracks in the heat insulating layer 13. For reference, a reference sample (conventional configuration) was prepared in which a reinforcing sheet was fixed with adhesive to the surface of the heat insulating layer (50 mm thick (two-layer structure with each layer being 25 mm thick)).

As a result, no cracks were generated in the heat insulation layer 13 of the side heat resistance mitigating layer 10 having a fixing layer 15 with a thickness of 10 mm (single layer structure) and in the heat insulation layer of a conventional side heat resistance mitigating layer having a reinforcing sheet on the surface of the heat insulation layer. From this experiment, it was confirmed that by adhering the fixing layer 15 made of a rigid urethane foam containing at least a part of the reinforcing sheet 14 to the heat insulation layer 13 made of a rigid urethane foam, it is possible to suppress the occurrence of cracks in the rigid urethane foam of the heat insulation layer 13 when subjected to a thermal shock. It was confirmed that the side heat resistance mitigating layer of the present disclosure can mitigate thermal shock to the same extent as a side heat resistance mitigating layer having a reinforcing sheet on the surface of a conventional heat insulation layer.

[Confirmation Experiment 2]
As confirmation experiment 2, the size of the mesh hole of the reinforcing sheet 14 in confirmation experiment 1 was changed to prepare a test piece, and a similar experiment was performed. The size of the mesh hole was 1.0 mm, 1.5 mm, 3.1 mm, 4.0 mm, 6.0 mm, and 8.0 mm in addition to 2.5 mm (confirmation experiment 1). The results are shown in FIG. 7. Here, the handleability is the ease of handling (workability) when preparing the test piece, and the presence or absence of defects such as the end being easily loosened or the mesh hole being distorted due to tension during construction. If there were no such defects, it was marked as "○", and if there were defects, it was marked as "×". The impregnation was confirmed by checking whether or not the urethane foam raw material passed through the mesh hole when applied. If the urethane foam raw material passed through the mesh hole, it was marked as "○", and if it did not pass through, it was marked as "×". If both the handleability and the impregnation were "○", the judgment was marked as "○", and if either one was "×", the judgment was marked as "×". From the table shown in FIG. 7, it was confirmed that the mesh holes of the reinforcing sheet 14 are preferably set to 1.5 mm to 4.0 mm.

[Confirmation Experiment 3]
For the urethane foam raw material forming the fixing layer 15 in the side cold-heat resistance mitigating layer 10 of the above embodiment, multiple urethane foam raw materials with different foaming and hardening speeds (cream times) were prepared, and a confirmation experiment was conducted on the permeability and workability of each urethane foam raw material to the reinforcing sheet 14 temporarily fixed to the thermal insulation layer 13. In this experiment, the urethane foam raw material forming the fixing layer 15 was sprayed onto the reinforcing sheet 14 temporarily fixed to the thermal insulation layer 13, and the permeability and workability were evaluated visually. The test pieces were prepared in the same manner as in Confirmation Experiment 1.

The cream time of foaming by hand mixing was measured as follows. First, the raw materials for urethane foam, liquid A (components other than isocyanate such as polyol) and liquid B (isocyanate), were weighed and the temperature of each was adjusted to 10°C. Next, liquid B was poured into the container of liquid A, and after stirring for 3 seconds with a stirring blade adjusted to 3600 rpm, the stirring blade was removed from the container. The time when the liquid level began to rise was measured using a stopwatch. Here, when applying with a spray foaming machine, the temperatures of liquid A and B are high and the reaction is too fast, making it difficult to measure the difference in cream time. Therefore, by setting the temperatures of liquid A and B low and foaming by hand mixing, it becomes possible to clearly measure the difference in cream time.

As a result, in the case of a urethane foam raw material with a cream time of 1 to 3 seconds by hand mixing, the foam hardening speed of the urethane foam raw material was too fast, and when applied by a spray foaming machine, the fixing layer 15 was formed without passing through the mesh holes of the reinforcing sheet 14 sufficiently. In addition, in the case of a urethane foam raw material with a cream time of more than 10 seconds by hand mixing, the foam hardening speed of the urethane foam raw material was too slow when applied by a spray foaming machine, causing dripping and deteriorating the workability. From this experiment, it was confirmed that when the cream time of foaming by hand mixing is 4 to 10 seconds when the temperature of the urethane foam raw material is 10°C, when application is performed by a spray foaming machine, the permeability and workability to the reinforcing sheet 14 are good. Note that when applying the side heat resistance mitigating layer 10 of the above embodiment, the temperature of liquid A and liquid B are adjusted to 40°C. When foaming by hand mixing at 10°C, the cream time of the urethane foam raw material with a cream time of 4 to 10 seconds is 0.1 to 1 second when foaming by a spray foaming machine at 40°C.

[Other embodiments]
(1) In the above embodiment, the cryogenic liquid storage tank 100 stores liquefied natural gas L. However, the cryogenic liquid storage tank 100 may store other cryogenic liquids, such as liquefied propane gas.

(2) In the above embodiment, the tank portion 40 has ceiling portions 21, 31, but it may also have a lid and be open at the top.

(3) In the above embodiment, the fixing layer 15 is a single layer, but it may be a laminate of multiple layers.

(4) In the above embodiment, the fixing layer 15 encases the reinforcing sheet 14 and is fixed to the heat insulating layer 13. However, the reinforcing sheet 14 may be placed on the heat insulating layer 13 and a conventional adhesive such as a rubber-based or plastic-based adhesive may be applied thereon. In this case, the reinforcing sheet 14 may be temporarily fixed to the heat insulating layer 13 in advance with the temporary fastener 16.

(5) In the above embodiment, the temporary fasteners 16 fixed the reinforcing sheet 14 overlaid on the heat insulating layer 13 at the recesses of the undulations of the heat insulating layer 13, but the temporary fasteners 16 may also fix the reinforcing sheet 14 at the protrusions in addition to the recesses of the undulations of the heat insulating layer 13. This allows the reinforcing sheet 14 to further conform to the undulations of the heat insulating layer 13, and prevents the reinforcing sheet 14 and the heat insulating layer 13 from floating.

(6) In the above embodiment, a roll-shaped reinforcing sheet 14 is used, but it may be cut into a specified shape and used. This is particularly effective in places where there are steps or grooves on the surface of the outer tank 30. In this case, the reinforcing sheets 14 are arranged so that they overlap each other, so that there are no places where the reinforcing sheets 14 are not placed.

REFERENCE SIGNS LIST 10 Side cold/heat resistance mitigating layer 13 Heat-insulating layer 14 Reinforcing sheet 15 Fixing layer 20 Inner tank 30 Outer tank 62 Side cold-insulating layer (cold-insulating layer)
50 Liquid barrier 100 Low-temperature liquid storage tank L Liquefied natural gas (low-temperature liquid)

Claims (8)

A low-temperature liquid storage tank including an inner tank for storing a low-temperature liquid below 0°C, an outer tank covering the outer tank, and a side cold resistance mitigation layer having a heat insulating layer including a urethane foam coated on the inner surface of the outer tank ,
The side heat resistance reducing layer is formed by applying a fixing layer made of urethane foam or adhesive to the inner surface of the heat insulating layer,
A low-temperature liquid storage tank, wherein at least a portion of a mesh-structured reinforcing sheet disposed on a surface of the thermal insulation layer is enclosed within the fixing layer. a plurality of temporary fasteners for holding the reinforcing sheet in a shape that matches the contours of the inner surface of the heat insulating layer;
The cryogenic liquid storage tank according to claim 1 , wherein the temporary fasteners are disposed in recesses of the undulations of the thermal insulation layer. The low-temperature liquid storage tank according to claim 2, wherein the temporary fastener is made of resin. The low-temperature liquid storage tank according to any one of claims 1 to 3, wherein the inner surface of the thermal barrier layer and the fixing layer are directly attached to each other, thereby chemically and/or physically bonding them together. The low-temperature liquid storage tank according to any one of claims 1 to 4, wherein the thickness of the fixed layer is 5 to 30 mm. The low-temperature liquid storage tank according to any one of claims 1 to 5, wherein the mesh size of the reinforcing sheet is 1.5 to 4 mm. A method for coating a side cold resistance mitigating layer having a heat insulating layer including a urethane foam on an inner surface of an outer tank of a low-temperature liquid storage tank including an inner tank for storing a low-temperature liquid below 0°C and an outer tank covering the outer surface of the inner tank, comprising:
A first step of applying a urethane foam raw material to the inner surface of the outer tank and foaming and curing the raw material to form a heat insulating layer;
A second step of overlapping a mesh-structured reinforcing sheet on the inner surface of the heat insulating layer;
A third step of applying an adhesive or a urethane foam raw material from the inside of the reinforcing sheet and foaming and curing the adhesive or urethane foam raw material to form a fixing layer that encapsulates at least a portion of the reinforcing sheet,
A method for applying a side cold/heat resistance mitigating layer, comprising coating the side cold/heat resistance mitigating layer, including the heat insulating layer, the reinforcing sheet, and the fixing layer, on the inner surface of the outer tank. A method for manufacturing a low-temperature liquid storage tank using the method for constructing a side heat resistance mitigation layer described in claim 7.

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