Multi-shell tank

Abstract

This multi-hulled tank comprises: a first tank; a second tank surrounding the first tank; a heat insulating layer disposed between the first tank and the second tank and covering the outer wall of the first tank; and a first piping that is for air supply or expulsion, has a first opening disposed between the tanks in a first inter-tank region between the first tank and the heat insulating layer, passes between the tanks, and extends to outside of the tank.

Description

Technical Field

[0001] The present disclosure relates to the structure of a multi-shell tank for storing cryogenic liquefied gas.

Background Art

[0002] For example, in a tank for storing cryogenic liquefied gas such as liquid hydrogen, since the temperature difference between the liquefied gas and the outside is large, a heat-insulating layer with high heat-insulating performance is required to suppress the vaporization of the liquefied gas inside the tank. Therefore, as a tank for storing liquefied gas, a multi-shell tank is known that includes an inner tank for storing liquefied gas, an outer tank surrounding the inner tank, and a heat-insulating layer provided in the space between the inner and outer tanks. For example, Patent Document 1 discloses this type of multi-shell tank.

[0003] The multi-shell tank disclosed in Patent Document 1 includes an inner tank for storing liquefied gas, an outer tank that houses the inner tank inside, and a heat-insulating layer made of a heat-insulating material disposed in the space between the inner and outer tanks.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the multi-layered tanks described above, the space between the inner and outer tanks may be filled with the same gas as the vaporized gas of the liquefied gas contained in the inner tank, or with an inert gas. In such multi-layered tanks, during gas filling, gas replacement, cooling, and heating between the inner and outer tanks, a supply and exhaust treatment is performed to forcibly discharge the gas present between the inner and outer tanks and introduce new gas. Insulation materials, support materials, and strength members that constitute the heat-insulating layer are placed between the inner and outer tanks, and there are areas where gas flow is difficult. During the supply and exhaust treatment between the inner and outer tanks described above, gas flow tends to stagnate in areas where gas flow is difficult, which may reduce the efficiency of the supply and exhaust treatment.

[0006] This disclosure is made in view of the above circumstances, and its purpose is to provide a technology for improving the efficiency of supply and exhaust treatment between tanks in a multi-shell tank comprising a first tank, a second tank surrounding the first tank, and a heat-insulating layer disposed between the first and second tanks and covering the first tank. [Means for solving the problem]

[0007] To solve the above problems, a multi-shell tank according to one aspect of this disclosure is: Tank 1 and The second tank surrounds the first tank, It is positioned between the first tank and the second tank and covers the outer wall of the first tank. Includes insulation panels Heat-insulating layer, The system includes a first opening located in the inter-tank region between the first tank and the heat-insulating layer, and a first pipe for supplying or exhausting air that extends to the outside through the inter-tank space. [Effects of the Invention]

[0008] According to this disclosure, in a multi-shell tank comprising a first tank, a second tank surrounding the first tank, and a heat-insulating layer positioned between the first and second tanks and covering the first tank, a technology can be provided to improve the efficiency of supply and exhaust treatment between tanks. [Brief explanation of the drawing]

[0009] [Figure 1]Figure 1 is a vertical cross-sectional view showing a schematic configuration of a multi-shell tank according to one aspect of the present disclosure. [Figure 2] Figure 2 is a magnified view of the tip of the first pipe. [Figure 3] Figure 3 shows an example of the configuration of the first and second pipes that share a common section. [Figure 4] Figure 4 shows an example of the configuration of a first piping system having multiple first openings arranged in a ring shape. [Figure 5] Figure 5 shows an example of the configuration of the first piping having first openings both above and below the first tank. [Modes for carrying out the invention]

[0010] Next, embodiments of the present disclosure will be described with reference to the drawings. Figure 1 is a vertical cross-sectional view showing the schematic configuration of a multi-shell tank 1 according to one aspect of the present disclosure. The multi-shell tank 1 shown in Figure 1 is a tank for containing low-temperature liquefied gas L. Examples of liquefied gas L include liquid hydrogen and liquefied natural gas. The multi-shell tank 1 may be mounted on a floating structure such as a ship or offshore structure, or it may be installed at a land base. Furthermore, the multi-shell tank 1 may be a cargo tank for containing liquefied gas L as cargo, or a fuel tank for containing liquefied gas L as fuel.

[0011] The multi-shell tank 1 is a double-shell tank comprising a first tank 21 for containing liquefied gas L and a second tank 22 surrounding the first tank 21. The first tank 21 and the second tank 22 are spaced apart radially from each other in the multi-shell tank 1. However, the multi-shell tank 1 according to this disclosure is not limited to a double-shell tank and may have three or more shells (i.e., tanks) with further tanks outside the second tank 22. By reinterpreting the relationship between the first tank 21 and the second tank 22 in this disclosure as the relationship between two adjacent tanks inside and outside, this disclosure can be applied to multi-shell tanks with three or more layers.

[0012] A heat-insulating layer 24 is placed between the first tank 21 and the second tank 22, in a space 23. The heat-insulating layer 24 covers the outer wall of the first tank 21 in the space 23, suppressing heat input to the first tank 21. The heat-insulating layer 24 is made of, for example, an insulating panel.

[0013] The multi-hull tank 1 is supported by a tank foundation 10 via supports 71 and 72. The tank foundation 10 is, for example, the hull of a floating structure such as a ship or offshore structure, or the concrete foundation of a land base. The supports 71 and 72 are cylindrical bodies extending substantially vertically and mainly include a first skirt 71 that supports the first tank 21 and a second skirt 72 that supports the second tank 22. The first skirt 71 is surrounded by the second skirt 72. The upper end of the second skirt 72 is joined to the second tank 22, and the lower end of the second skirt 72 is fixed to the tank foundation 10. The upper end of the first skirt 71 is joined to the first tank 21 in the tank-to-tank space 23. The first skirt 71 passes through the tank-to-tank space 23, and the lower end of the first skirt 71 is fixed to the tank foundation 10. At the intersection of the first tank 21 and the first skirt 71, there is a narrow space between the first tank 21 and the first skirt 71 where gas flow is stagnant. Also, at the intersection of the heat-insulating layer 24 covering the first tank 21 and the first skirt 71, there is a narrow space surrounded by the heat-insulating layer 24 and the first skirt 71 where gas flow is stagnant.

[0014] Here, the space between the first tank 21 and the heat insulation layer 24 is referred to as the "first inter-tank region 25", and the space between the heat insulation layer 24 and the second tank 22 is referred to as the "second inter-tank region 26". That is, in the inter-tank 23, a first inter-tank region 25 surrounding the first tank 21 and a second inter-tank region 26 surrounding the first inter-tank region 25 are formed. The first inter-tank region 25 and the second inter-tank region 26 may be a connected space or may be independent spaces from each other. The first inter-tank region 25 may be formed in a gap provided between the outer wall of the first tank 21 and the heat insulation layer 24, or may be formed by voids or pores formed on the surface of the heat insulation layer 24 facing the outer wall of the first tank 21. Further, as shown in FIG. 2, when a recess 25a recessed from the outer wall of the first tank 21 more than other portions is formed on the surface of the heat insulation layer 24, the space in this recess 25a is also included in the first inter-tank region 25.

[0015] Returning to FIG. 1, each of the first inter-tank region 25 and the second inter-tank region 26 in the inter-tank 23 is filled with an inter-tank gas G. The inter-tank gas G is a gas of the same kind as the vaporized gas of the liquefied gas L or an inert gas. For example, when the liquefied gas L is liquid hydrogen, hydrogen gas is adopted as the inter-tank gas G. Further, for example, when the liquefied gas L is liquefied natural gas, nitrogen gas is adopted as the inter-tank gas G.

[0016] The multi-layered tank 1 includes a first pipe 3 and a second pipe 4 for supplying gas to the inter-tank 23 and exhausting gas from the inter-tank 23. The first pipe 3 and the second pipe 4 may be widely used for supply and exhaust gas treatment involving exhaust from the inter-tank 23 and supply of gas to the inter-tank 23, such as filling, gas replacement, cooling, and temperature rise of the inter-tank gas G in the inter-tank 23.

[0017] The first pipe 3 has a first opening 31 that opens into the first inter-tank region 25. The first pipe 3 is mainly used for supplying gas to and / or exhausting gas from the first inter-tank region 25. In the example shown in FIG. 1, one system of the first pipe 3 is used for both gas supply and exhaust, but a gas supply system first pipe 3 having the first opening 31 as a gas supply port and an exhaust system first pipe 3 having the first opening 31 as an exhaust port may be provided respectively.

[0018] The first pipe 3 penetrates through the second tank 22, passes through the second tank space region 26 in the inter-tank space 23, and the first opening 31 provided at the tip portion 3a is disposed within the first tank space region 25.

[0019] FIG. 2 is an enlarged view of the tip portion 3a of the first pipe 3. As shown in FIG. 2, a first opening 31 that opens into the first tank space region 25 is provided at the tip portion 3a of the first pipe 3. The tip portion 3a of the first pipe 3 is supported by the first tank 21 by a first support member 36 fixed to the first tank 21. The intermediate portion 3b of the first pipe 3 is disposed along the inner wall of the second tank 22 in the second tank space region 26 and is supported by the second tank 22 by a second support member 37 fixed to the second tank 22.

[0020] The first pipe 3 has an expansion / contraction portion 38 between the tip portion 3a supported by the first support member 36 and the intermediate portion 3b supported by the second support member 37. The expansion / contraction portion 38 is constituted by, for example, a flexible hose. When the liquefied gas L is stored in the first tank 21, in the first pipe 3, the relative positions of the tip portion 3a supported by the first tank 21 and the intermediate portion 3b supported by the first tank 21 change due to the cold heat of the liquefied gas L. The change in the relative positions of the tip portion 3a and the intermediate portion 3b of the first pipe 3 is absorbed by the expansion or contraction of the expansion / contraction portion 38, and the stress generated in the first pipe 3, the stress generated at the joint between the first support member 36 and the first tank 21, and the stress generated at the joint between the second support member 37 and the second tank 22 are reduced.

[0021] Returning to FIG. 1, the second pipe 4 has a second opening 41 that opens into the second tank space region 26. The second pipe 4 is mainly used for the supply and exhaust treatment of the second tank space region 26. In the multi-shell tank 1 illustrated in FIG. 1, the second pipe 4 is used for both air supply and exhaust, but it may be provided with a second pipe 4 of the air supply system having the second opening 41 as the air supply port and a second pipe 4 of the exhaust system having the second opening 41 as the exhaust port, respectively.

[0022] The second pipe 4 penetrates the second tank 22 and passes through the second inter-tank region 26 of the inter-tank space 23, with a second opening 41 at its tip located within the second inter-tank region 26. The first pipe 3 and the second pipe 4 are independent pipes in the inter-tank space 23 of the multi-shell tank 1. However, the first pipe 3 and the second pipe 4 may share a portion of their piping. Figure 3 shows an example of the configuration of the first pipe 3 and the second pipe 4 having a shared portion. The multi-shell tank 1 illustrated in Figure 3 includes a common pipe 30 that penetrates the second tank 22 and passes through the second inter-tank region 26 of the inter-tank space 23, a first branch pipe 35 connected to the common pipe 30 and having a first opening 31 at its tip, and a second branch pipe 45 connected to the common pipe 30 and having a second opening 41 at its tip. Here, the combination of the common pipe 30 and the first branch pipe 35 functions as the first pipe 3, and the combination of the common pipe 30 and the second branch pipe 45 functions as the second pipe 4.

[0023] Returning to Figure 1, the first pipe 3 has at least one first opening 31 that opens in the height range where the first tank 21 and the second tank 22 overlap in the vertical direction. The second pipe 4 also has at least one second opening 41 that opens in the height range where the first tank 21 and the second tank 22 overlap in the vertical direction. In the space between the tanks 23, in particular, in the height range where the first tank 21 and the second tank 22 overlap in the vertical direction, the heat insulating material, support material, and strength members that constitute the heat insulating layer 24 are concentrated, and there are places where gas does not flow easily. It is preferable that the openings 31 and 41 be located in such places where gas does not flow easily.

[0024] For example, the first pipe 3 preferably has at least one first opening 31 located in the narrow space between the first tank 21 and the first skirt 71 at the intersection of the first tank 21 and the first skirt 71. For example, the second pipe 4 preferably has a second opening 41 located in the narrow space between the heat-insulating layer 24 and the first skirt 71 at the intersection of the heat-insulating layer 24 and the first skirt 71. As mentioned above, gas flow tends to stagnate in narrow spaces compared to other areas, but by supplying and / or exhausting air through the openings 31, 41 located in the narrow spaces, gas flow in the narrow spaces is promoted, improving the efficiency of the supply and exhaust treatment.

[0025] The first pipe 3 and the second pipe 4 merge at a junction 50 located in an exposed area outside the multi-shell tank 1. A supply air system or an exhaust air system is connected to this junction 50 via a filter 34. The filter 34 collects dust from the gas flowing through the first pipe 3 and the second pipe 4. The supply air system includes a blower for supplying air and gas sources such as a cooling gas source, a heating gas source, a displacement gas source, or an inter-tank gas source. The exhaust air system includes, for example, an exhaust blower, a discharge tower for releasing inter-tank gas G into the atmosphere outside the multi-shell tank 1 (i.e., in an exposed area), and fuel-using equipment that uses inter-tank gas G as fuel. While either the supply air system or the exhaust air system is connected to the junction 50, the connected system may be switchable via a switching valve.

[0026] The confluence of the first pipe 3 and the second pipe 4 at the confluence 50 allows for the supply and / or exhaust of gas between tanks 23 to be performed by a single system, reducing the number of filters 34 and blowers. Furthermore, the connection of the first pipe 3 and the second pipe 4 at the confluence 50 equalizes the pressure in the first inter-tank region 25 and the second inter-tank region 26, preventing the heat-insulating layer 24 from floating or being damaged. However, each of the first pipe 3 and the second pipe 4 may be equipped with a filter 34 and a blower. In this case, the temperature, pressure, or supply amount of gas supplied to each of the first inter-tank region 25 and the second inter-tank region 26 can be adjusted independently, and the discharge amount from each of the first inter-tank region 25 and the second inter-tank region 26 can be adjusted independently.

[0027] At the junction 50 of the first pipe 3 and the second pipe 4, valves for operating the first pipe 3 and the second pipe 4, such as flow path switching valves and flow control valves, may be concentrated in one area. This allows the operator to centrally operate the valves of the first pipe 3 and the second pipe 4.

[0028] The first pipe 3 and the second pipe 4 have a sampling device 51 in an exposed location outside the multi-shell tank 1. The sampling device 51, for example, collects gas discharged from the tank junction 23 or gas supplied to the tank junction 23 and detects the concentration of the gas. The sampling device 51 may be located at the junction 50 of the first pipe 3 and the second pipe 4. By providing the sampling device 51 in the first pipe 3 and the second pipe 4 in this way, the concentration of gas supplied to the tank junction 23 or gas exhausted from the tank junction 23 can be detected, and the supply air flow rate or exhaust air flow rate can be adjusted.

[0029] The first pipe 3 illustrated in Figure 1 has first openings 31 located at the bottom and in the narrow section of the inter-tank region 23, but preferably the first pipe 3 has a plurality of first openings 31. More preferably the plurality of first openings 31 are distributed in the first inter-tank region 25 on a substantially horizontal circumference surrounding the first tank 21. The gas supplied from the plurality of annularly arranged first openings 31 diffuses substantially evenly in the first inter-tank region 25.

[0030] Figure 4 shows an example of the configuration of a first piping system 3 having a plurality of first openings 31 arranged in an annular shape. The first piping system 3 illustrated in Figure 4 comprises a ring-shaped header pipe 32 and a plurality of nozzles 33 connected to the header pipe 32, each having a first opening 31 at its tip. In addition, the combination of the header pipe 32 and the plurality of nozzles 33 may be arranged in multiple stages in the vertical direction.

[0031] Furthermore, similar to the first pipe 3, the second pipe 4 may have a plurality of second openings 41, which may be distributed on a substantially horizontal circumference surrounding the first tank 21 in the second inter-tank region 26. However, the configuration of the first pipe 3 having a plurality of first openings 31 and the configuration of the second pipe 4 having a plurality of second openings 41 are not limited to the example in Figure 4.

[0032] Figure 5 shows an example configuration of a first piping system 3 having first openings 31 both above and below the first tank 21. The first piping system 3 illustrated in Figure 5 includes a lower first piping system 3B having a first opening 31 located in the first inter-tank region 25 below the first tank 21, and an upper first piping system 3U having a first opening 31 located in the first inter-tank region 25 above the first tank 21. The lower first piping system 3B and the upper first piping system 3U may be used simultaneously as an air supply pipe. Alternatively, the lower first piping system 3B and the upper first piping system 3U may be used simultaneously as an exhaust pipe. Or, one of the lower first piping system 3B and the upper first piping system 3U may be used as an air supply pipe and the other as an exhaust pipe. The first piping system 3 used as an exhaust pipe is connected to an exhaust system outside the multi-shell tank 1. The first piping system 3 used as an air supply pipe is connected to an air supply system outside the multi-shell tank 1. By switching between supplying and exhausting air through the lower first pipe 3B and the upper first pipe 3U according to the purpose of the air supply and exhaust treatment between tanks 23 and the characteristics of the gas, efficient air supply and exhaust treatment becomes possible.

[0033] Furthermore, similar to the first piping 3, the second piping 4 includes a lower second piping 4B having a second opening 41 located in the second inter-tank region 26 below the first tank 21, and an upper second piping 4U having a second opening 41 located in the second inter-tank region 26 above the first tank 21. The lower second piping 4B and the upper second piping 4U may be used simultaneously as an air supply pipe. Alternatively, the lower second piping 4B and the upper second piping 4U may be used simultaneously as an exhaust pipe. Or, one of the lower second piping 4B and the upper second piping 4U may be used as an air supply pipe and the other as an exhaust pipe.

[0034] [Summary] The multi-shell tank 1 relating to this disclosure is Tank 1, 21, The second tank 22 surrounds the first tank 21, A heat-insulating layer 24 is placed between the first tank 21 and the second tank 22, and covers the outer wall of the first tank 21. The system includes a first opening 31 located in the first inter-tank region 25 between the first tank 21 and the heat-insulating layer 24 in the inter-tank region 23, and a first pipe 3 for supplying or exhausting air that extends to the outside through the inter-tank region 23.

[0035] In the multi-shell tank 1 with the above configuration, at least one of supplying air and exhausting air to the first inter-tank region 25 can be performed using the first piping 3. By actively supplying and exhausting air to the first inter-tank region 25 between the first tank 21 and the heat-insulating layer 24 in this way, the supply and exhaust treatment between tanks 23 can be made more efficient.

[0036] The multi-shell tank 1 according to the second item of this disclosure further comprises a support 71 joined to the outer wall of the first tank 21 in the space between the tanks 23, and the first opening 31 is located in the narrow space between the first tank 21 and the support 71.

[0037] The narrow space between the first tank 21 and the support 71 is prone to gas stagnation, but the placement of the first opening 31 in this narrow space promotes gas flow. As a result, the supply and exhaust treatment between the tanks 23 can be made more efficient.

[0038] The multi-shell tank 1 according to the third item of this disclosure is a multi-shell tank 1 according to the first or second item, wherein the first piping 3 has a plurality of first openings 31 arranged circumferentially around the first tank 21.

[0039] By arranging multiple first openings 31 in a distributed manner, the flow of supply or exhaust air around the first tank 21 can be made uniform.

[0040] The multi-shell tank 1 according to item 4 of this disclosure is a multi-shell tank 1 according to any of items 1 to 3, wherein the tip portion 3a of the first pipe 3, including the first opening 31, is supported by a first support member 36 fixed to the outer wall of the first tank 21.

[0041] In this way, the tip portion 3a of the first pipe 3 is supported by the outer wall of the first tank 21, which suppresses the change in the relative position between the first tank 21 and the first opening 31 when the first tank 21 undergoes thermal contraction.

[0042] The multi-shell tank 1 relating to item 5 of this disclosure is a multi-shell tank 1 relating to item 4, wherein the first piping 3 has an expandable section 38 between the tanks 23.

[0043] As a result, when a relative displacement occurs between the tip portion 3a supported by the first portion 21 and the other portion of the first pipe 3 due to the difference in the amount of thermal contraction between the first portion 21 and the second portion 22, the expansion and contraction of the expansion / contraction portion 38 reduces the stress generated in the first pipe 3.

[0044] The multi-shell tank 1 relating to item 6 of this disclosure is a multi-shell tank 1 relating to any of items 1 to 5, wherein the first piping 3 is supported by a second support member 37 fixed to the inner wall of the second tank 22.

[0045] In this way, the first pipe 3 is stably supported by laying it in the space between the tanks 23 using the inner wall of the second tank 22, which has less thermal contraction compared to the first tank 21.

[0046] The multi-shell tank 1 according to item 7 of this disclosure is a multi-shell tank 1 according to any of items 1 to 6, wherein the first piping 3 has a plurality of first openings 31, and the plurality of first openings 31 include first openings 31 located above the first tank 21 and first openings 31 located below the first tank 21.

[0047] By designating one of the first openings 31 located above the first tank 21 and the other located below the first tank 21 as an air intake and the other as an exhaust port, the supply and exhaust treatment between the tanks 23 can be efficiently performed. Furthermore, if the supply and exhaust of air can be switched at each of the first openings 31 located above the first tank 21 and the first opening 31 located below the first tank 21, depending on the type of gas supplied to or discharged between the tanks 23, even more efficient supply and exhaust treatment can be achieved.

[0048] The multi-shell tank 1 according to item 8 of this disclosure is a multi-shell tank 1 according to any one of items 1 to 7, further comprising a second opening 41 located in the second inter-tank region 26 between the heat-insulating layer 24 and the second tank 22 in the inter-tank region 23, and a second pipe 4 for supplying or exhausting air that extends to the outside through the inter-tank region 23.

[0049] By supplying and / or exhausting air in the first inter-tank region 25 and the second inter-tank region 26 of the inter-tank space 23, the supply and exhaust treatment of air between the tanks 23 can be efficiently carried out.

[0050] The multi-shell tank 1 relating to item 9 of this disclosure is a multi-shell tank 1 relating to item 8 in which the first pipe 3 and the second pipe 4 have a junction 50 located on the outside.

[0051] In this way, the connection between the first pipe 3 and the second pipe 4 at the junction 50 allows for equalization of the pressure in the first inter-tank region 25 and the second inter-tank region 26. Furthermore, the connection between the first pipe 3 and the second pipe 4 at the junction 50 allows for the supply and / or exhaust of gas between the tanks 23 to be performed through a single system.

[0052] The discussions of this disclosure described above are presented for illustrative and explanatory purposes only and are not intended to limit the disclosure to the forms disclosed herein. For example, in the detailed description above, various features of the disclosure are grouped into a single embodiment for the purpose of streamlining the disclosure, but some of the features may be combined. Also, some of the features included in this disclosure may be combined into alternative embodiments, configurations, or aspects other than those discussed above.

Claims

1. The first tank and The second tank surrounds the first tank, A heat-insulating layer, which includes an insulating panel that is placed between the first tank and the second tank and covers the outer wall of the first tank, The system comprises a first opening located in the first inter-tank region between the first tank and the heat-insulating layer, and a first pipe for supplying or exhausting air that extends to the outside through the inter-tank space, Multi-shell tank.

2. The tanks further include a support joined to the outer wall of the first tank, The first opening is located in a narrow space sandwiched between the first tank and the support. A multi-shell tank according to claim 1.

3. The first piping has a plurality of first openings arranged circumferentially around the first tank, A multi-shell tank according to claim 1 or 2.

4. The tip portion of the first pipe, including the first opening, is supported by a first support member fixed to the outer wall of the first tank. A multi-shell tank according to claim 1 or 2.

5. The first piping has an expandable section between the tanks, The multi-shell tank according to claim 4.

6. The first piping is supported by a second support member fixed to the inner wall of the second tank. A multi-shell tank according to claim 1 or 2.

7. The first piping has a plurality of first openings, the plurality of first openings including first openings located above the first tank and first openings located below the first tank, one of the upper first openings and the lower first opening being an air intake and the other being an exhaust port. A multi-shell tank according to claim 1 or 2.

8. The system further includes a second opening located in the second inter-tank region between the heat-insulating layer and the second tank, and a second pipe for supplying or exhausting air that extends to the outside through the inter-tank space. A multi-shell tank according to claim 1 or 2.

9. A first tank, The second tank surrounds the first tank, A heat-insulating layer is placed between the first tank and the second tank, Between the tanks, a support is joined to the outer wall of the first tank, In the first inter-tank region between the first tank and the heat-insulating layer, there is a first opening located in the narrow space between the first tank and the support, and a first pipe for supplying or exhausting air extends to the outside through the inter-tank region, Multi-shell tank.

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