Structure provided with closed section and gas replacement method

Abstract

This structure provided with a closed section comprises: a wall member that forms a closed section; an air-permeable filler layer disposed in the closed section; and a gas sensor in which a gas sampling part is disposed in the filler layer. In a closed section gas replacement method, a filler layer is disposed, a second gas is introduced into a closed section in a first-gas atmosphere, a gas is sampled in the filler layer, and introduction of the second gas into the closed section is finished when the concentration of the first gas falls below a predetermined reference value.

Description

Structure with closed compartment and gas replacement method

[0001] The present disclosure relates to a structure having a closed compartment in which a packing material is disposed, and a method for gas replacement of said closed compartment.

[0002] There are various structures that include closed compartments in which filler materials are placed. For example, in tanks that store cryogenic liquefied gases such as liquefied hydrogen, a closed-compartment insulating layer is formed around the storage space to suppress evaporation of the liquefied gas. Patent Document 1 discloses a multi-shell tank that includes an inner tank that stores liquefied gas, an outer tank that surrounds the inner tank, and a closed compartment between the inner and outer tanks. An insulating material is placed in the closed compartment as a filler material.

[0003] The gas present in the closed compartment may be replaced with another gas. For example, the closed compartment may be replaced with an inert gas in an air environment, or with a flammable gas in an inert gas environment in a closed compartment, or vice versa. Whether the closed compartment has been replaced with the desired gas environment is determined by the detection results of a gas sensor. However, if a filler material is present in the closed compartment, the above method may not accurately determine whether the gas replacement is complete.

[0004] International Publication No. 2020 / 202578

[0005] An object of the present disclosure is to accurately evaluate the gas concentration in a closed compartment in which a breathable packing layer is present, and to determine in a timely manner whether gas replacement in the closed compartment has been completed.

[0006] A structure with a closed compartment according to one aspect of the present disclosure comprises a wall member that forms the closed compartment, a breathable filler layer that is placed in the closed compartment, and a gas sensor having a gas collection portion that is placed in the filler layer.

[0007] A gas replacement method for a closed compartment according to another aspect of the present disclosure includes introducing a second gas into a closed compartment in which a packing layer is disposed and which is under an atmosphere of a first gas, sampling the gas in the packing layer, and terminating the introduction of the second gas into the closed compartment when the concentration of the first gas falls below a predetermined reference value.

[0008] According to the present disclosure, in a structure having a closed compartment in which a breathable packing layer is present, it is possible to accurately evaluate the gas concentration in the closed compartment, and also to timely determine whether gas replacement in the closed compartment has been completed.

[0009] FIG. 1 is a schematic cross-sectional view of a multi-shell tank as an example of a structure with a closed compartment according to the present disclosure. FIGS. 2A and 2B are cross-sectional views showing another example of a multi-shell tank. FIGS. 3A and 3B are partial cross-sectional views of a multi-shell tank showing an example of the arrangement of a gas sampling unit of a gas concentration meter. FIG. 4 is a partial cross-sectional view of a multi-shell tank showing another example of the arrangement of a gas sampling unit. FIGS. 5A and 5B are cross-sectional views showing an example of the arrangement of a gas sampling unit of a gas concentration meter in a closed compartment formed by a tank wall and a gas barrier layer. FIG. 6 is a cross-sectional view of a multi-shell tank according to a modification of this embodiment. FIG. 7 is a cross-sectional view of a multi-shell tank according to a modification of this embodiment. FIGS. 8A and 8B are cross-sectional views of a multi-shell tank according to a modification of this embodiment. FIGS. 9A and 9B are cross-sectional views of a multi-shell tank according to a modification of this embodiment. FIG. 10 is a cross-sectional view of a multi-shell tank having a structure in a preliminary stage according to this embodiment.

[0010] Hereinafter, embodiments of a structure with closed compartments and a gas replacement method for a closed compartment according to the present disclosure will be described in detail with reference to the drawings.

[0011] [Overview of the Present Embodiment] The structure with a closed compartment of the present disclosure comprises a wall member forming the closed compartment, a breathable filler layer disposed in the closed compartment, and a gas sensor having a gas sampling portion disposed in the filler layer. The closed compartment includes a compartment enclosed by the wall member and sealed, as well as a compartment that can be treated as substantially sealed, although gas can enter and exit due to slight breathability of the wall member or slight gaps at joints between the wall members. The wall member forming the closed compartment can be a rigid metal plate such as iron or stainless steel, a flexible metal sheet such as aluminum foil, a plate or sheet made of rubber, resin, membrane, reinforcing resin, or a combination thereof.

[0012] The filler layer placed in the closed compartment may be a layer formed of a solid, semi-solid, foam, granular material, powder, thin leaf material, linear pieces, chips, etc., as long as it is breathable. The filler layer needs to be breathable, and the solid pieces or powder that form the filler layer do not need to be breathable. There is no limitation on the degree of breathability of the filler layer, as long as gas is present in the filler layer and the filler layer is breathable enough to allow the gas to be replaced by a replacement gas. For example, in Darcy's law, if the permeability is 1.0 x 10 －１４ [m ２ The gas sampling portion of the gas sensor is disposed in the filler layer. This will be described in detail later.

[0013] The form of the structure is not particularly limited as long as it has the closed compartment described above. Examples include tanks and containers for storing fluids, piping equipment such as double-walled pipes for transporting fluids, mobile objects such as ships, aircraft, and vehicles equipped with closed compartments such as tanks and refrigerated rooms, above-ground or underground buildings and structures, and factory equipment. The tank may be a cargo tank or a fuel tank. Examples of the contents stored in the tank include low-temperature liquefied gases such as liquefied hydrogen and liquefied natural gas. In the following embodiments, a multi-shell tank for storing low-temperature liquefied gas will be described as an example of a structure with a closed compartment.

[0014] [Structure of Multi-shell Tank] Figure 1 is a schematic cross-sectional view of a multi-shell tank 1 according to this embodiment. The multi-shell tank 1 may be mounted on a ship, marine structure, or vehicle, or may be installed on land or underground. The multi-shell tank 1 is a spherical double-shell tank including an inner tank 2 for storing a fluid, an outer tank 3 surrounding the inner tank 2, and an insulating layer 4 disposed in a space 10 between the inner tank 2 and the outer tank 3. The multi-shell tank 1 may be a tank other than a spherical tank, such as an elliptical, cylindrical, or rectangular tank, and may have a multi-shell structure with three or more shells. The multi-shell tank 1 may also be either a Moss type or a membrane type.

[0015] The inner tank 2 includes a storage space 20 for liquefied gas. The storage space 20 contains liquefied gas such as the above-mentioned liquefied hydrogen, liquefied natural gas, liquefied nitrogen, or liquefied helium. The outer tank 3 surrounds the inner tank 2 at a predetermined distance from the outer peripheral surface of the inner tank 2. The inter-tank space 10 is a space defined by the tank wall of the inner tank 2 and the tank wall of the outer tank 3. In this embodiment, the inter-tank space 10 is a closed compartment, and the tank walls of the inner tank 2 and the outer tank 3 are wall members that define the closed compartment. The inter-tank space 10 is set to atmospheric pressure, but may also be set to a low vacuum of approximately 100 PaA to 100 kPaA. The inner tank 2 is supported by supports 11. The supports 11 extend vertically from the tank installation surface. The inner tank 2 is supported by a group of multiple supports 11 arranged in a cylindrical shape. Although not shown for the sake of simplicity, the outer tank 3 is also supported by a similar group of supports.

[0016] During operation of the multi-shell tank 1, the inter-tank space 10 is filled with inter-tank gas. The inter-tank gas is, for example, a vaporized liquefied gas stored in the inner tank 2, an inert gas, or the like. Piping for gas replacement between the inter-tank space 10 is attached to the outer tank 3. Specifically, a supply pipe 12 serving as a replacement gas supply port is attached to the top of the outer tank 3. An outlet pipe 13 serving as a replacement gas discharge port is attached to the bottom of the outer tank 3. This embodiment assumes a case in which the replacement gas has a higher specific gravity than the gas to be replaced. The replacement gas supplied from the supply pipe 12 to the inter-tank space 10 forms a replacement gas flow GF, which expels the gas to be replaced present in the inter-tank space 10 through the outlet pipe 13. The replacement gas discharge port does not necessarily have to be located at the bottom of the outer tank 3. For example, the outlet pipe 13 may be located at the top or side of the outer tank 3.

[0017] The insulating material layer 4 is attached to the outer peripheral wall of the inner tank 2 and serves to keep the liquefied gas in the storage space 20 cool. The insulating material layer 4 is made of a porous material and has breathability. The insulating material layer 4 can be formed using, for example, an insulating material with interconnected cells, such as glass wool, or an insulating material with closed cells, such as rigid urethane foam. In this embodiment, the insulating material layer 4 corresponds to a filler layer disposed in a closed compartment. The insulating material layer 4 is disposed in the radially inner region of the inter-tank space 10. The radially outer region of the inter-tank space 10 is the inter-tank flow path 101, which is an empty space. The replacement gas flow GF flows exclusively through the inter-tank flow path 101. Due to the difference in gas specific gravity, the gas to be replaced in the insulating material layer 4 is also pushed to the bottom of the tank, resulting in the replacement gas also entering the interior of the insulating material layer 4.

[0018] For example, assume that a flammable gas such as vaporized liquefied hydrogen gas is filled between the tanks 10 as the inter-tank gas. Before operation of the multi-shell tank 1, a first gas exchange is performed to replace the air present between the tanks 10 with an inert gas such as nitrogen gas. That is, an inert gas is supplied through the supply pipe 12, and the air and the inert gas are exhausted through the outlet pipe 13. Subsequently, a second gas exchange is performed to replace the inert gas filled between the tanks 10 with a flammable gas. During maintenance of the multi-shell tank 1 or at the end of operation, a gas exchange is performed to replace the flammable gas in the inter-tank spaces 10 with an inert gas.

[0019] The gas concentration meter 5 measures the concentration of the target gas at a measurement point. In this embodiment, the gas concentration meter 5 measures the concentration of the gas to be replaced present in the inter-tank 10 or the concentration of the replacement gas supplied to the inter-tank 10. The gas concentration meter 5 corresponds to the gas sensor of the present disclosure. The gas concentration meter 5 includes a main body 51, a sampling tube 52, and a gas collection unit 5P. The main body 51 includes a gas detection unit for detecting the gas concentration and a pump for introducing the target gas into the gas detection unit. The gas detection unit may be a detection unit employing a known detection method, such as catalytic combustion, semiconductor, thermal conduction, or infrared. The sampling tube 52 is a long tube extending from the main body 51. The tip opening of the sampling tube 52 is the gas collection unit 5P.

[0020] The gas sampling unit 5P is disposed inside the insulating material layer 4 between the tanks 10. Although the insulating material layer 4 is breathable, its airflow resistance is considerably greater than that of the inter-tank flow path 101, which is an open space. For this reason, the progress of gas replacement in the insulating material layer 4 is slower than that in the inter-tank flow path 101. In particular, the tank bottom, which is farthest from the supply pipe 12 into which the replacement gas is introduced, is the part of the insulating material layer 4 where gas replacement progresses most slowly. In consideration of this, the gas sampling unit 5P is disposed at a point located at the tank bottom of the insulating material layer 4, and sucks in gas from this position and sends it to the main body 51. By sampling gas from a point where the progress of gas replacement is slow, the gas replacement status between the tanks 10, such as whether the gas replacement is complete or not, can be accurately determined.

[0021] The gas sampling unit 5P is preferably located at a specific portion that is identified as a portion where, when a replacement gas is introduced between the tanks 10, replacement with the replacement gas is delayed compared to other portions between the tanks 10. The specific portion is basically located inside the insulation layer 4. A portion of the insulation layer 4 where gas replacement is expected to be delayed based on the structure of the multi-shell tank 1 can be set as the specific portion. The insulation layer 4 at the tank bottom in FIG. 1 is an example of the specific portion. The specific portion may also be a portion derived as a portion where gas replacement is delayed from a computer-based analysis of gas replacement between the tanks 10.

[0022] 2A and 2B are cross-sectional views showing other examples of multi-shell tanks in which the gas sampling unit 5P of the gas concentration meter 5 is arranged at a different position. In these figures, parts with the same reference numerals as in FIG. 1 have the same structure as the multi-shell tank 1 in FIG. 1. The multi-shell tank 1A in FIG. 2A is an example in which the gas sampling unit 5P is arranged within the insulation layer 4 located in the narrow portion NA. The narrow portion NA is the area below the portion where the upper end of the support 11 is connected to the inner tank 2. In the narrow portion NA, the structure of the support 11 is close to the inner tank 2, narrowing the space, and the flow of replacement gas is particularly hindered. By arranging the gas sampling unit 5P in such a narrow portion NA, erroneous determination of the completion of gas replacement can be suppressed.

[0023] The multi-shell tank 1B in FIG. 2(B) is an example in which the gas sampling unit 5P is located within the thick-walled portion 4T of the thermal insulation layer 4. The thermal insulation layer 4 may be installed so that its radial thickness varies in parts due to factors such as insulation design and tank assembly. The thermal insulation layer 4 in FIG. 2(B) has a thick-walled portion 4T near the equator of the inner tank 2, where the radial thickness is thick. In the thick-walled portion 4T, the flow of replacement gas is often impeded compared to thinner portions. By locating the gas sampling unit 5P in such a thick-walled portion 4T, erroneous determination of the completion of gas replacement can be suppressed.

[0024] [Advantages of the Multi-shell Tank of the Present Disclosure] The advantages of the multi-shell tank 1 of this embodiment will be described in comparison with the multi-shell tank of the previous stage of this disclosure. Figure 10 is a cross-sectional view of a multi-shell tank 100 having a structure of the previous stage of this embodiment. In the multi-shell tank 100, parts that are assigned the same reference numerals as in Figure 1 are the same as those in the multi-shell tank 1 of this embodiment, and therefore their description will be omitted. The difference from the multi-shell tank 1 is that the multi-shell tank 100 does not have a thermal insulation layer 4 between the tanks 10. In other words, the entire area between the tanks 10 is open space.

[0025] In the multi-shell tank 100, the gas sampling unit 5P of the gas concentration meter 5 is disposed in a delay location where gas replacement is structurally difficult to progress. For example, the delay location is a narrow portion NA, such as near the support position of the inner tank 2 by the support column 11 or near the intersection of the support column 11 and the outer tank 3. For example, a sampling pipe 52 is extended from the main body 51 toward the narrow portion NA, and gas sampling units 5P1 and 5P2 are disposed in the narrow portion NA. The inter-tank 10 at the bottom of the tank, which is farthest from the supply pipe 12, can also be considered a structural delay location. By disposing the gas sampling unit 5P3 in the outlet pipe 13, which serves as the exhaust path for the replacement gas, the gas replacement status in the inter-tank 10 at the bottom of the tank can be grasped.

[0026] However, when a thermal insulation layer 4 is disposed between tanks 10, as in the multi-shell tank 1 shown in Figure 1, it is not possible to identify delay locations where gas replacement is difficult to progress simply due to the degree of spatial narrowness or distance from the supply pipe 12. For example, even if a gas sampling unit 5P is disposed in a narrow portion around the support 11 in the inter-tank flow path 101 or near the tank bottom in the inter-tank flow path 101, it is not possible to accurately determine the completion of gas replacement. This is because the thermal insulation layer 4 is the delay location compared to the inter-tank flow path 101. In other words, even if gas is sampled from the inter-tank flow path 101, where gas replacement progresses more quickly, it is not possible to accurately evaluate the gas replacement status of the entire inter-tank 10, including the thermal insulation layer 4.

[0027] If inter-tank gas is introduced when gas replacement between the tanks 10 is insufficient, a reaction may occur between the remaining gas and the inter-tank gas. For example, if flammable gas is introduced when replacement of the air environment with nitrogen gas between the tanks 10 is insufficient, that is, when air remains between the tanks 10, a fire reaction may occur. On the other hand, if the gas replacement operation is performed excessively in anticipation of the presence of the thermal insulation layer 4, unnecessary consumption of replacement gas may occur.

[0028] In contrast, in the multi-shell tank 1 of this embodiment, the gas sampling part 5P of the gas concentration meter 5 is disposed in the breathable insulation layer 4. Moreover, the gas sampling part 5P is disposed in a specific part of the insulation layer 4 where gas replacement is expected to be delayed, that is, in the insulation layer 4 at the bottom of the tank in the example of Figure 1. Therefore, the gas replacement status between the tanks 10 can be accurately grasped based on the detection results of the gas concentration meter 5.

[0029] An example of a gas replacement method for the inter-vessel space 10 in a multi-shell tank 1 is shown. The gas replacement method comprises the following steps (1) to (3) that are performed in sequence. (1) A second gas for replacement is introduced from a supply pipe 12 into the inter-vessel space 10, which is provided with a thermal insulation layer 4 and is under an atmosphere of a first gas. Exhaust is performed from an outlet pipe 13. (2) While continuing the introduction and exhaust of the second gas, gas is sampled from a gas sampling section 5P arranged in the thermal insulation layer 4, and the concentration of the first gas (or second gas) is monitored with a gas concentration meter 5. (3) When the concentration of the first gas falls below a predetermined reference value, the introduction of the second gas into the inter-vessel space 10 is terminated.

[0030] In the above gas replacement method, for example, the first gas is air, and the second gas is nitrogen gas as a replacement gas. The gas concentration meter 5 detects, for example, the oxygen concentration. Of course, the gas concentration meter 5 may also detect the nitrogen gas concentration. Alternatively, the first gas is a combustible gas, and the second gas is nitrogen gas. The gas concentration meter 5 detects, for example, the concentration of the combustible gas. According to the above gas replacement method, gas is sampled in the insulation layer 4, where the progress of gas replacement is slow, and the concentration of the first gas or the second gas is determined. Therefore, the completion of gas replacement between the tanks 10 where the insulation layer 4 is arranged can be determined in a timely manner. Therefore, the gas replacement work time can be appropriately managed, which contributes to ensuring safety and suppressing unnecessary consumption of replacement gas.

[0031] [Various Arrangements of Gas Sampling Section in Thermal Insulation Layer] Figures 3(A) and (B) are partial cross-sectional views of a multi-shell tank, showing specific arrangement examples of the gas sampling section 5P of the gas concentration meter 5. Figure 3(A) shows an arrangement example of the gas sampling section 5P in the thermal insulation layer 4 when the internal structure of the inter-vessel 10 is the same as that of the multi-shell tank 1 shown in Figure 1. The thermal insulation layer 4 is composed of a panel-shaped thermal insulation material attached to the tank wall of the inner vessel 2. An inter-vessel flow path 101 is formed between the outer vessel 3 and the surface layer 401 of the thermal insulation layer 4. During the gas replacement operation between the vessels 10, a replacement gas flow is generated in the inter-vessel flow path 101 as shown by arrow A1.

[0032] The gas sampling unit 5P is disposed inside the thermal insulation layer 4 near the inner tank 2. The replacement gas in the intertank flow path 101 permeates from the surface layer 401 into the interior of the thermal insulation layer 4, eventually reaching a deep portion of the thermal insulation layer 4, i.e., the joint surface 402 with the inner tank 2. Therefore, the region near the joint surface 402, which is farthest from the intertank flow path 101, is the region in the thermal insulation layer 4 where gas replacement progresses the slowest. In view of this, the gas sampling unit 5P is disposed near the joint surface 402 of the thermal insulation layer 4. The gas sampled from the gas sampling unit 5P disposed in this manner is sent to the main body 51 through the sampling tube 52 and subjected to gas sensing, thereby enabling accurate determination of the completion of gas replacement between the tanks 10, etc.

[0033] 3(B) shows an example of the arrangement of the gas sampling section 5P when a gas barrier layer 6 that blocks gas is attached to the thermal insulation layer 4 between the tanks 10. The gas barrier layer 6 is adjacent to the outer surface 403 of the thermal insulation layer 4. The gas barrier layer 6 is an adhesive layer of metal foil or metal sheet, such as aluminum foil, and has the function of preventing gas from passing in the radial direction. A first inter-tank flow path 102, which is a circulation space for the replacement gas, is formed between the gas barrier layer 6 and the outer tank 3. A second inter-tank flow path 103, which is a circulation space for the replacement gas, is also formed between the inner surface 404 of the thermal insulation layer 4 and the inner tank 2.

[0034] During the gas replacement operation between the tanks 10, a replacement gas flow is generated in the first inter-tank flow path 102 as indicated by arrow A2 and in the second inter-tank flow path 103 as indicated by arrow A3. The replacement gas accompanying the gas flow indicated by arrow A2 is blocked by the gas barrier layer 6 and does not permeate into the thermal insulation layer 4. On the other hand, the replacement gas accompanying the gas flow indicated by arrow A3 permeates from the inner surface 404 into the thermal insulation layer 4. For this reason, the gas sampling part 5P is disposed near the gas barrier layer 6, that is, near the outer surface 403 of the thermal insulation layer 4 which is farthest from the second inter-tank flow path 103.

[0035] In the example of Figure 3(A), the space between the tanks 10 separated by the tank walls of the inner tank 2 and the outer tank 3 is a closed compartment. On the other hand, in the example of Figure 3(B), the area separated by the tank wall of the inner tank 2 and the gas barrier layer 6, which are arranged to sandwich the insulating material layer 4, is a closed compartment. Note that the area sandwiched between the outer tank 3 and the gas barrier layer 6 with the insulating material layer 4 in between may also be a closed compartment. In other words, the area separated by the gas barrier layer 6 and either the tank wall of the inner tank 2 or the tank wall of the outer tank 3 may also be treated as a closed compartment. In either example, the area near the gas barrier layer 6 is a specific portion in the insulating material layer 4 where gas replacement is delayed, so the gas sampling part 5P may be located in this nearby area.

[0036] FIG. 4 is a partial cross-sectional view of a multi-shell tank showing another example of the arrangement of the gas sampling unit. The configuration of the tank chamber 10 shown in FIG. 4 is the same as that shown in FIG. 3(B). The difference from the example shown in FIG. 3(B) is that the gas sampling unit 5P is arranged in a gas-permeable portion 41 provided in the insulating material layer 4. The gas-permeable portion 41 is a small region with excellent breathability and is arranged in a specific portion of the insulating material layer 4 where gas replacement is expected to be delayed. In this embodiment, the gas-permeable portion 41 is arranged in an area adjacent to the gas barrier layer 6. The gas-permeable portion 41 is formed of a material with higher breathability than the insulating material layer 4, such as sponge. Alternatively, the gas-permeable portion 41 may simply be a space large enough to accommodate the gas sampling unit 5P. For example, if the breathability of the insulating material layer 4 is 1.0×10 in terms of permeability according to Darcy's law, the gas-permeable portion 41 may be arranged in a specific portion of the insulating material layer 4 where gas replacement is expected to be delayed. －１２ [m ２ ] to 1.0 × 10 －１３ [m ２ ], it is desirable that the breathable portion 41 has an air permeability that is at least one order of magnitude higher than the above-mentioned air permeability.

[0037] The gas concentration meter 5 draws gas from the gas sampling portion 5P at the tip of the sampling tube 52 by operating a pump built into the main body 51 or an external pump. The porous material that makes up the insulation layer 4 has a certain degree of breathability, but there are cases where the pressure loss is large. In this case, the suction force of the pump is not sufficient to draw in the gas, and the gas concentration cannot be detected. In consideration of this problem, a gas-permeable portion 41 is provided in the specific portion of the insulation layer 4, and the gas sampling portion 5P is located in the gas-permeable portion 41. This makes it easier to draw gas from the gas sampling portion 5P and to send gas to the main body 51.

[0038] 5A and 5B are cross-sectional views showing an example of the arrangement of a gas sampling section 5P of a gas concentration meter 5 in a tank with a single-shell structure. In the above-described embodiment, a multi-shell tank 1 including an inner tank 2 and an outer tank 3 is exemplified as an example of a structure with a closed compartment. The present disclosure is also applicable to a closed compartment 10A provided in a tank with a single-shell structure.

[0039] The closed compartment 10A shown in FIG. 5(A) is a closed compartment formed by the tank wall 7 and gas barrier layer 6 of a single-shell tank. The radially inner side of the tank wall 7 is a fluid storage space 200. The radially outer side of the tank wall 7 is surrounded by an insulating material layer 4 for cold insulation. The gas barrier layer 6 is attached to the radially outer surface 405 of the insulating material layer 4. A gas flow path 104, which is a circulation space for replacement gas, is formed between the inner surface 406 of the insulating material layer 4 and the tank wall 7. The replacement gas, which forms the gas flow indicated by arrow A4 flowing through the gas flow path 104, permeates from the inner surface 406 into the insulating material layer 4. For this reason, the gas sampling unit 5P is located near the gas barrier layer 6, i.e., near the outer surface 405 of the insulating material layer 4, which is farthest from the gas flow path 104.

[0040] The closed compartment 10B shown in Figure 5(B) is also a closed compartment formed by the tank wall 7 of a single-shell tank and a gas barrier layer 6. The closed compartment 10B differs from the closed compartment 10A in that it has a two-layer structure, an insulating material layer 4A. The insulating material layer 4A is formed by laminating a radially inner open-cell insulating material layer 42 and a radially outer closed-cell insulating material layer 43. The gas barrier layer 6 is attached to the outer surface of the closed-cell insulating material layer 43. The open-cell insulating material layer 42 is formed of an insulating material with open cells, and therefore has relatively high breathability. On the other hand, the closed-cell insulating material layer 43 is formed of an insulating material with closed cells, and therefore has low breathability.

[0041] The gas sampling unit 5P is located in the open-cell insulation layer 42 near the boundary 407 between the open-cell insulation layer 42 and the closed-cell insulation layer 43. The replacement gas in the gas flow path 104 permeates into the insulation layer 4A from the inner surface 406. The replacement gas easily penetrates the open-cell insulation layer 42 but has difficulty penetrating the closed-cell insulation layer 43, which has low breathability. If the gas sampling unit 5P is located in the closed-cell insulation layer 43, gas detection by the gas concentration meter 5 may not be possible. Therefore, the gas sampling unit 5P is located in the open-cell insulation layer 42, which has relatively high breathability, near the boundary 407, which is the farthest position from the gas flow path 104. A similar arrangement of the gas sampling unit 5P can also be applied when the two-layer insulation layer 4A is applied to, for example, the multi-shell tank shown in FIG. 3(B).

[0042] [Modification] Figure 6 is a cross-sectional view showing a multi-shell tank 1C according to a modification of this embodiment. The structure of the multi-shell tank 1C itself is the same as that of the multi-shell tank 1 shown in Figure 1. The difference is that in the multi-shell tank 1C, granular insulation material 44 is filled between the tanks 10. In addition to attaching solid insulation material to the tank wall of the inner tank 2 as shown in Figure 1, other ways of providing thermal insulation to the tank include filling the entire volume of the tank space 10 or nearly so with fluid insulation material. The granular insulation material 44 is, for example, perlite granules or glass bubbles.

[0043] In this type of multi-shell tank 1C, the gas sampling part 5P of the gas concentration meter 5 is also placed at a delay point in the inter-tank space 10 where gas replacement is expected to be slowest. The replacement gas flow GF flows through the granular insulation material 44. The delay point is again near the bottom of the tank between the tanks 10. Therefore, the gas sampling part 5P is placed inside the granular insulation material 44 near the bottom of the inter-tank space 10.

[0044] FIG. 7 is a cross-sectional view showing a multi-shell tank 1D according to another modification of this embodiment. The structure of the multi-shell tank 1D itself is the same as that of the multi-shell tank 1 shown in FIG. 1 . The difference is that in the multi-shell tank 1D, instead of the gas concentration meter 5 using a sampling pipe 52, a gas concentration sensor 50 is embedded directly in the insulating material layer 4 between the tanks 10. The gas concentration sensor 50 has a probe portion that serves as a gas sampling unit and is capable of detecting gas concentration. The gas concentration sensor 50 is disposed inside the insulating material layer 4 near the bottom of the tank 10, which is a delay location. In this way, a sensor with gas detection function may be embedded directly in the delay location within the insulating material layer 4 to determine the gas replacement status.

[0045] 8A and 8B are cross-sectional views showing multi-shell tanks 1E and 1F, which are other variations of the spherical tank. The multi-shell tank 1E shown in Fig. 8A is configured to supply replacement gas to the tank space 10 from the bottom of the outer tank 3 and discharge the replacement gas from the top of the outer tank 3. In the multi-shell tank 1E, the tank top, which is farthest from the tank bottom where the replacement gas is introduced, is the delay point in the insulation layer 4 where gas replacement progresses most slowly. Therefore, the gas sampling section 5P of the gas concentration meter 5 is located at a point on the insulation layer 4 that is located at the tank top.

[0046] The multi-shell tank 1F shown in Figure 8(B) is provided with ring structures 21 that reinforce the inner tank 2 near the equator and in the lower hemisphere of the inner tank 2. The ring structures 21 are made of plates that protrude from the outer surface of the inner tank 2 into the space between tanks 10. The flow of replacement gas is hindered in the portion of the thermal insulation layer 4 where the ring structures 21 are present. Therefore, in the multi-shell tank 1F, a gas sampling section 5P is located in the thermal insulation layer 4 near the ring structures 21.

[0047] 9A and 9B are cross-sectional views showing modified multi-shell tanks 1G and 1H for irregular-shaped tanks. In the multi-shell tank 1G shown in FIG. 9A, the inner tank 2 is provided with a protruding structure 22. The protruding structure 22 is a portion near the top of the inner tank 2 that protrudes outward from the outer tank 3 through the tank gap 10. The portion of the insulating material layer 4 where the protruding structure 22 exists becomes a delay point where the flow of the replacement gas is impeded. Therefore, in the multi-shell tank 1G, a gas sampling section 5P is located within the insulating material layer 4 near the protruding structure 22.

[0048] The multi-shell tank 1H shown in Figure 9(B) includes an inner tank 2S and an outer tank 3S each having a rectangular cross section, and a thermal insulation layer 4S disposed between the tanks 10. The outer diameter of the inner tank 2S is a rectangular parallelepiped or cylindrical shape. The inner tank 2S is supported by support legs 24. The flow of the replacement gas in the thermal insulation layer 4 is impeded near edge portions 23, such as corners and ridges, of the inner tank 2S, and near the support legs 24. Therefore, in the multi-shell tank 1H, a gas sampling section 5P is disposed in the thermal insulation layer 4 near the edge portions 23 and the support legs 24.

[0049] [Summary of the Disclosure] The specific embodiments described above include disclosures having the following configurations.

[0050] A structure with a closed compartment according to a first aspect of the present disclosure comprises a wall member that forms the closed compartment, a breathable filler layer that is placed in the closed compartment, and a gas sensor having a gas collection portion that is placed in the filler layer.

[0051] According to the first aspect, the gas sampling unit of the gas sensor is disposed in the breathable filler layer, enabling accurate monitoring of the gas situation within the closed compartment. For example, consider a case in which the closed compartment is occupied by a filler layer and a space where no filler is present, and the existing gas in the closed compartment is replaced with another gas. In this case, gas replacement in the filler layer progresses more slowly than in the space, so detecting the gas concentration in the space does not accurately evaluate the gas replacement status of the closed space. However, in the first aspect, the gas sampling unit is disposed in the filler layer and the gas concentration in the filler layer is detected, allowing accurate evaluation of the gas replacement status of the closed space. This prevents problems such as insufficient gas replacement in the closed compartment, which can lead to reactions with a gas introduced later, or excessive gas replacement, which can waste replacement gas.

[0052] A structure with a closed compartment according to a second aspect is the structure with a closed compartment according to the first aspect, wherein the structure is a tank that stores a fluid, and the wall member includes a tank wall.

[0053] According to the second aspect, for a tank in which at least a portion of the wall member of the closed compartment is constituted by a tank wall, the gas replacement status of the closed space can be accurately evaluated.

[0054] A structure with a closed compartment according to a third aspect is a structure with a closed compartment according to the first or second aspect, wherein the structure is a multi-shell tank including an inner tank for storing a fluid and an outer tank surrounding the inner tank, the closed compartment is formed between the inner tank and the outer tank, and the wall member includes at least one of the tank wall of the inner tank and the tank wall of the outer tank.

[0055] According to the third aspect, the gas replacement status of the closed space formed between the inner and outer vessels of a multi-shell tank can be accurately evaluated. The space between the inner and outer vessels of a multi-shell tank is generally an airtight space and may be provided with various filler layers. Therefore, this space is suitable for application of the ideas of the present disclosure.

[0056] A structure with closed compartments according to a fourth aspect is the structure with closed compartments according to the third aspect, wherein the wall members are tank walls of the inner tank and the outer tank.

[0057] In many cases, the space between the inner and outer tanks of a multi-shell tank is filled with vaporized liquefied gas stored in the inner tank or an inert gas. In other words, the space between the tanks is a space where gas exchange is essential. According to the fourth aspect, the gas exchange status of the closed space directly separated by the tank walls of the inner and outer tanks can be accurately evaluated.

[0058] A structure with a closed compartment according to a fifth aspect is the structure with a closed compartment according to the third aspect, wherein the wall member comprises either the tank wall of the inner tank or the tank wall of the outer tank, arranged so as to sandwich the filler layer, and a gas barrier layer that blocks gas.

[0059] In a multi-shell tank, a closed space may be formed between the tanks by the tank wall of the inner or outer tank and the gas barrier layer, and a filler may be placed in the closed space. According to the fifth aspect, the gas replacement status in the closed space defined by the tank wall and the gas barrier layer can be accurately evaluated.

[0060] A structure with closed compartments according to a sixth aspect is the structure with closed compartments according to any one of the first to fifth aspects, wherein the filler layer is a layer formed of a porous member.

[0061] When the porous member is arranged in a closed compartment, the flow of gas tends to be stagnant in the area of ​​the porous member. According to the sixth aspect, the gas sampling section is arranged in the packing layer made of the porous member, so that the gas replacement status in the area of ​​the porous member can be accurately grasped.

[0062] A structure with closed compartments according to a seventh aspect is the structure with closed compartments according to any one of the first to sixth aspects, wherein the filler layer is a heat insulating material attached to the wall member.

[0063] According to the seventh aspect, since the gas sampling section is disposed in the heat insulating layer, the gas replacement status in the closed compartment including the heat insulating layer can be accurately grasped.

[0064] The structure with closed compartments according to the eighth aspect is a structure with closed compartments according to any one of the first to seventh aspects, wherein the packing layer includes a specific part that is specified to delay replacement with the replacement gas when the replacement gas is introduced into the closed compartment compared to other parts of the packing layer, and the gas sampling part is arranged in the specific part.

[0065] The degree of progress of gas replacement may vary even within the packing layer. According to the eighth aspect, a location in the packing layer where gas replacement is delayed is identified, and the gas sampling unit is disposed at the identified location. Therefore, it is possible to accurately determine the completion of gas replacement in the closed compartment including the packing layer.

[0066] A structure with closed compartments according to a ninth aspect is the structure with closed compartments according to the eighth aspect, wherein the filler layer has a predetermined air permeability, the specific portion has an easily breathable portion having an air permeability higher than the predetermined air permeability, and the gas collection portion is arranged in the easily breathable portion.

[0067] If the specific portion has low air permeability, a situation may arise in which gas cannot be sent from the gas sampling portion to the main body of the gas sensor due to the influence of pressure loss. According to the ninth aspect, since the gas sampling portion is disposed in the easily breathable portion, it is possible to easily extract gas from the specific portion.

[0068] A structure with a closed compartment according to a tenth aspect is the structure with a closed compartment according to the fifth aspect, wherein the filler layer is adjacent to the gas barrier layer, a replacement gas flow space is formed between the tank wall and the filler layer, and the gas sampling section is arranged near the gas barrier layer.

[0069] According to the tenth aspect, the replacement gas permeates from the flow space into the filler layer. Therefore, the area near the gas barrier layer is the area where gas replacement is slowest. By locating the gas sampling unit in such an area, it is possible to accurately determine the completion of gas replacement in the closed compartment defined by the tank wall and the gas barrier layer.

[0070] A gas replacement method for a closed compartment according to an eleventh aspect includes introducing a second gas into a closed compartment in which a packing layer is placed and which is under an atmosphere of a first gas, sampling the gas in the packing layer, and terminating the introduction of the second gas into the closed compartment when the concentration of the first gas falls below a predetermined reference value.

[0071] According to the eleventh aspect, the gas is sampled in the packing layer where the progress of gas replacement is slow, and the concentration of the first gas is determined. This allows the completion of gas replacement in the closed compartment to be determined in a timely manner. This prevents problems such as insufficient gas replacement in the closed compartment, which causes a reaction with a gas introduced later, or excessive gas replacement, which unnecessarily consumes replacement gas.

Claims

1. A structure with a closed compartment, comprising: a wall member that forms a closed compartment; a breathable filler layer disposed in the closed compartment; and a gas sensor in which a gas sampling portion is disposed in the filler layer.

2. The structure with a closed compartment according to claim 1, wherein the structure is a tank that stores a fluid, and the wall member includes a tank wall, and the structure is a structure with a closed compartment.

3. The structure with a closed compartment according to claim 1, wherein the structure is a multi-shell tank including an inner tank that stores a fluid and an outer tank that surrounds the inner tank, the closed compartment is formed between the inner tank and the outer tank, and the wall member includes at least one of the tank wall of the inner tank and the tank wall of the outer tank, and the structure is a structure with a closed compartment.

4. The structure with a closed compartment according to claim 3, wherein the wall member is the tank wall of the inner tank and the tank wall of the outer tank, and the structure is a structure with a closed compartment.

5. The structure with a closed compartment according to claim 3, wherein the wall member is composed of either one of the tank wall of the inner tank or the tank wall of the outer tank disposed so as to sandwich the filler layer and a gas barrier layer that shields gas, and the structure is a structure with a closed compartment.

6. The structure with a closed compartment according to any one of claims 1 to 5, wherein the filler layer is a layer formed of a porous member, and the structure is a structure with a closed compartment.

7. The structure with a closed compartment according to any one of claims 1 to 5, wherein the filler layer is a heat insulating material attached to the wall member, and the structure is a structure with a closed compartment.

8. The structure with a closed compartment according to any one of claims 1 to 5, wherein the filler layer includes a specific portion identified as having a delay in substitution into the replacement gas compared to other locations of the filler layer when a replacement gas is introduced into the closed compartment, and the gas sampling portion is disposed in the specific portion, and the structure is a structure with a closed compartment.

9. The structure with a closed compartment according to claim 8, wherein the filler layer has a predetermined air permeability, the specific portion has an easily breathable portion with an air permeability higher than the predetermined air permeability, and the gas sampling portion is disposed in the easily breathable portion, and the structure is a structure with a closed compartment.

10. The structure with a closed compartment according to claim 5, wherein the filler layer is adjacent to the gas barrier layer, a flow space for the replacement gas is formed between the tank wall and the filler layer, and the gas sampling portion is disposed in the vicinity of the gas barrier layer, and the structure is a structure with a closed compartment.

11. A method for gas replacement in a closed compartment, comprising: introducing a second gas into a closed compartment in which a filler layer is disposed and which is under an atmosphere of a first gas; sampling the gas in the filler layer; and terminating the introduction of the second gas into the closed compartment when the concentration of the first gas falls below a predetermined reference value.

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