Freight tank

Abstract

To provide a freight tank that is suitable for replacement between two kinds of liquid gas differing in temperature to be controlled.SOLUTION: A freight tank 1 comprises: an outer shell 11 which contains two kinds of liquid gas differing in temperature to be controlled by replacement, and includes an inner wall in a curved surface shape having a perpendicular center part formed to swell most in a horizontal direction; a first filling line which is provided so as to inject at least one liquid gas between the two kinds of liquid gas into the outer shell 11, and is provided with a first spout hole at a height larger than the middle height between the height of the center part in the inside space of the outer shell 11 and the height of the deepest part so that a spouted liquid gas flows along the curved surface shape of the inner wall; and a second filling line which is provided so as to inject the at least one liquid gas between the two kinds of liquid gas into the outer shell 11, and also provided with a second spout hole so that the liquid gas is spouted to the bottom surface of the outer shell 11.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a cargo tank for storing cargo.

Background Art

[0002] Generally, ships are known that load liquefied gases such as LNG (liquefied natural gas) into cargo tanks and transport them. For example, an LNG ship that can suppress the heel amount and efficiently cool the cargo tank is disclosed (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the temperature to be controlled varies depending on the type of liquefied gas. Therefore, if the contents of the cargo tank are replaced with another substance having a different temperature to be controlled, problems may occur. For example, when replacing from LNG with a low temperature to be controlled to liquefied carbon dioxide (carbon dioxide) with a high temperature to be controlled, if the injection of liquefied carbon dioxide into the cargo tank is too fast, the liquefied carbon dioxide will solidify (become dry ice). In order to avoid this problem, it is necessary to warm the cargo tank before replacing the cargo. However, since the heat capacity of the tank body is large, it takes time to warm it.

[0005] An object of an embodiment of the present invention is to provide a cargo tank suitable for replacing two types of liquefied gases having different temperatures to be controlled in a shorter time.

Means for Solving the Problems

[0006] The cargo tank according to the aspect of the present invention includes an outer shell that contains and exchanges two types of liquefied gases with different temperatures to be managed, and has an inner wall with a curved surface shape formed such that the central portion in the vertical direction bulges the most in the horizontal direction, and at least one of the two types of liquefied gases is provided for injecting into the inside of the outer shell. A first filling line provided with a first ejection hole at a height equal to or higher than the intermediate height between the height of the central portion and the deepest portion of the internal space of the outer shell so that the ejected liquefied gas flows along the curved surface shape of the inner wall, and at least one of the two types of liquefied gases is provided for injecting into the inside of the outer shell. A second filling line provided with a second ejection hole so that liquefied gas is ejected onto the bottom surface of the outer shell.

Advantages of the Invention

[0007] According to an embodiment of the present invention, it is possible to provide a cargo tank suitable for exchanging two types of liquefied gases with different temperatures to be managed.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0009] (Embodiment) FIG. 1 is a configuration diagram showing the configuration of a cargo tank 1 according to an embodiment of the present invention. In the drawings, the same parts are denoted by the same reference numerals, and redundant descriptions are omitted as appropriate.

[0010] The cargo tank 1 is a tank mounted on a ship for loading cargo. At least two types of liquefied gases with different controlled temperatures are alternately stored in the cargo tank 1. Therefore, the temperature to be controlled inside the cargo tank 1 is changed according to the type of liquefied gas stored.

[0011] The cargo tank 1 is a type C bi-lobe tank. In FIG. 1, one side of the bi-lobe tank is shown with the inside visible. The other side of the bi-lobe tank is also configured symmetrically with respect to the left and right of FIG. 1. Therefore, the same configuration as in FIG. 1 is also provided on the opposite side of the cargo tank 1 that is not shown. Note that the configuration shown in FIG. 1 may be configured only on one side of the cargo tank 1, and for any equipment or the like, only one may be provided in the cargo tank 1.

[0012] Note that the cargo tank 1 may be of any type and any shape. For example, the cargo tank 1 may be a mono-lobe type (cylinder type). In this case, the cargo tank 1 is configured symmetrically, but only one piece of equipment or the like provided near the center of the cargo tank 1 may be sufficient. For example, one second filling line 14 may be provided at the deepest part of the bottom surface, and one third filling line 15 may be provided at the topmost part.

[0013] For example, the cargoes are LNG and liquefied carbon dioxide (carbon dioxide). The temperature for controlling LNG is, for example, -162°C, and the temperature for controlling liquefied carbon dioxide is, for example, -50°C. The cargo may be liquefied petroleum gas (LPG) or any other liquefied gas. Also, three or more types of liquefied gases including two or more types of liquefied gases with the same controlled temperature may be alternately stored in the cargo tank 1.

[0014] The cargo tank 1 includes an outer shell 11, a frame member 12, a first filling line 13, a second filling line 14, a third filling line 15, three valves 16a, 16b, 16c, and a hatch portion 17. Note that the cargo tank 1 may include any components or devices not described herein. For example, the cargo tank 1 may be provided with a handling pump or a temperature sensor for managing the temperature inside the cargo tank 1.

[0015] The outer shell 11 is a portion that serves as a shell covering the outside of the cargo tank 1. The internal space of the outer shell 11 is a space for storing the liquefied gas, which is the cargo of the cargo tank 1. The outer shell 11 has a shape suitable for storing the liquefied gas compressed at high pressure. For example, the outer shell 11 has a curved surface shape formed such that the central portion in the vertical direction bulges most in the horizontal direction. For example, the cross-sectional shape of the outer shell 11 is a circle, an ellipse, or a shape combining these shapes. Specifically, the outer shell 11 has a bi-lobe shape or a mono-lobe shape.

[0016] The frame member 12 is a member that supports the outer shell 11 to reinforce it. The frame member 12 is provided on the inner wall of the outer shell 11 at regular intervals in the longitudinal direction of the outer shell 11. Each frame member 12 is provided so as to go around the inner circumference in a direction perpendicular to the longitudinal direction of the outer shell 11.

[0017] The first filling line 13 is a pipe for injecting the liquefied gas (including the gas in its gaseous state), which is the cargo, into the cargo tank 1. The first filling line 13 is used when replacing the liquefied gas with a lower density (e.g., LNG) with the liquefied gas with a higher density (e.g., liquefied carbon dioxide gas).

[0018] The first filling line 13 includes a pipe 131 extending vertically so as to be inserted into the cargo tank 1 from the hatch portion 17 of the cargo tank 1, and a plurality of ejection holes H13 for ejecting liquefied gas. The first filling line 13 is provided on both sides (left and right sides) located in a direction perpendicular to the longitudinal direction of the outer shell 11, and includes a pipe 132 extending horizontally near the equator of the inner wall of the outer shell 11. Here, the equator is the most bulging portion of the outer shell 11 in the horizontal direction. The ejection holes H13 are provided in the pipe 132 at regular intervals in the longitudinal direction of the outer shell 11. The ejection holes H13 are provided such that the liquefied gas to be ejected flows from near the equator along the inner wall of the outer shell 11 to the bottom surface. Thereby, the liquefied gas ejected from the ejection holes H13 flows while warming the inner wall of the outer shell 11 from near the equator to the bottom surface. Note that all the pipes 132 provided with the ejection holes H13 may be connected to one another. For example, the pipes 132 are provided symmetrically on the left and right side surfaces of the inner wall of the outer shell 11, but the pipes 132 provided on the left and right may be connected to each other, or the pipes 132 may be configured to go around the inner wall.

[0019] For example, the first filling line 13 is fixed to the bone member 12. Note that the first filling line 13 may be fixed to the inner wall of the outer shell 11 in any manner, or may be fixed to a portion other than the bone member 12. For example, the first filling line 13 may be directly fixed to the outer shell 11, or a new member for fixing the first filling line 13 may be provided.

[0020] The second filling line 14 is a pipe for injecting liquefied gas (including its gaseous state gas) as cargo into the cargo tank 1. The second filling line 14 is used both when replacing from a liquefied gas with a low density (e.g., LNG) to a liquefied gas with a high density (e.g., liquefied carbon dioxide gas), and when replacing from a liquefied gas with a high density (e.g., liquefied carbon dioxide gas) to a liquefied gas with a low density (e.g., LNG). The second filling line 14 is used to perform gas replacement in the cargo tank 1 in layers to improve the replacement efficiency. Specifically, the two gases to be replaced form layers respectively, and while injecting one gas into the cargo tank 1 with the two layers separated vertically, the other gas is withdrawn from the cargo tank 1. Also, the second filling line 14 is used when discharging the liquefied gas (including its gaseous state gas) accumulated at the bottom from the cargo tank 1.

[0021] The second filling line 14 includes a pipe 141 extending in the vertical direction so as to be inserted into the interior of the cargo tank 1 from the hatch portion 17, and a pipe 142 provided with a plurality of ejection holes H14 for ejecting liquefied gas and extending in the longitudinal direction of the outer shell 11 near the deepest part of the bottom surface. The ejection holes H14 are provided in the pipe 142 at regular intervals in the longitudinal direction of the outer shell 11. The ejection holes H14 are provided so that liquefied gas ejects toward the deepest part of the outer shell 11. The liquefied gas ejected from the ejection holes H14 gradually starts to accumulate from the deepest part of the bottom surface of the outer shell 11.

[0022] The pipe 141 extending in the vertical direction of the second filling line 14 is joined to the pipe 131 extending in the vertical direction of the first filling line 13 to form one pipe in the vicinity of the hatch portion 17 inside the outer shell 11. Note that the two pipes 131 and 141 extending in the vertical direction may be joined outside the outer shell 11, or may remain separate without being joined.

[0023] For example, the second filling line 14 is fixed to the bone member 12. Note that the second filling line 14 may be fixed in any manner near the bottom surface of the outer shell 11, or may be fixed to a portion other than the bone member 12. For example, the second filling line 14 may be directly fixed to the bottom surface of the outer shell 11, or a new member for fixing the second filling line 14 may be provided. Further, the second filling line 14 may be configured in the same manner as the filling line provided in a known cargo tank (for example, an LNG tank) that stores liquefied gas.

[0024] The third filling line 15 is used to spray liquid for cooling the cargo tank 1 and the cargo. For example, the third filling line 15 is used when replacing from a liquefied gas with a high density (for example, liquefied carbon dioxide gas) to a liquefied gas with a low density (for example, LNG). Also, similar to the second filling line 14, the third filling line 15 may be used to perform the gas replacement of the cargo tank 1 in a layered manner to improve the replacement efficiency.

[0025] The third filling line 15 is inserted into the cargo tank 1 from the hatch portion 17 and includes a pipe that extends in the longitudinal direction of the outer shell 11 near the topmost part. Injection holes are provided at regular intervals in the longitudinal direction of the outer shell 11 in the pipe. The injection holes are provided so that liquefied gas jets downward from the upper part of the outer shell 11. The pipe of the third filling line 15 inserted into the cargo tank 1 from the hatch portion 17 is provided separately from the first filling line 13 and the second filling line 14, but may be configured to be coupled to at least one of the first filling line 13 and the second filling line 14.

[0026] For example, the third filling line 15 is fixed to the bone member 12. Note that the third filling line 15 may be fixed in any manner near the upper surface of the outer shell 11, or may be fixed to a portion other than the bone member 12. For example, the third filling line 15 may be directly fixed to the upper surface of the outer shell 11, or a new member for fixing the third filling line 15 may be provided. Further, the third filling line 15 may be configured in the same manner as a filling line provided at the upper part of a known cargo tank (e.g., an LNG tank) for storing liquefied gas. Note that the third filling line 15 may not be provided in the cargo tank 1.

[0027] The hatch portion 17 is a portion that serves as the entrance and exit of the cargo tank 1. The first filling line 13, the second filling line 14, and the third filling line 15 are connected to pipes outside the cargo tank 1 via the hatch portion 17.

[0028] The first valve 16a and the second valve 16b are provided at positions immediately after the first filling line 13 and the second filling line 14 branch into two pipes 131 and 141 from the portion where they are joined together. The first valve 16a is provided in the first filling line 13. The second valve 16b is provided in the second filling line 14. The third valve 16c is provided in the pipe immediately before the third filling line 15 branches after being inserted from the hatch portion 17.

[0029] By opening each of the valves 16a, 16b, and 16c, each of the filling lines 13, 14, and 15 can be used individually. Also, by closing each of the valves 16a, 16b, and 16c, each of the filling lines 13, 14, and 15 can be made unusable individually.

[0030] Note that the valves 16a, 16b, and 16c may be opened and closed by remote control, by a computer, or manually by an operator. Also, if each filling line 13, 14, 15 is configured to be individually usable, the valves 16a, 16b, and 16c may not be provided in the cargo tank 1.

[0031] FIG. 2 is a cross-sectional view simply showing the position of the pipe 132 of the first filling line 13 according to the present embodiment. With reference to FIG. 2, the position of the ejection hole H13 provided in the pipe 132 of the first filling line 13 will be described. Note that the ejection hole H13 may be provided in any manner as long as the liquefied gas to be ejected flows along the inner wall to the bottom surface, not limited to the configuration described here.

[0032] The ejection hole H13 is provided on the surface of the cylindrical pipe 132. For example, when the direction of the inner wall is set as 0 degrees in the horizontal direction and the vertically downward direction is set as 90 degrees, the ejection hole H13 is provided so that the liquefied gas is ejected in a direction within the range of 0 degrees to 90 degrees. By providing the ejection hole H13 in this way, the liquefied gas ejected from the ejection hole H13 flows along the inner wall to the bottom surface.

[0033] Next, the height of the ejection hole H13 will be described. Here, in the internal space of the outer shell 11, the height of the uppermost part is set as 100%, the height of the equator is set as 0%, and the height of the deepest part is set as -100%. Note that the internal space of the outer shell 11 has a cross-sectional shape that occupies most of the outer shell 11 as shown in FIG. 2, and does not include the space with a special cross-sectional shape of a part of the outer shell 11 such as the hatch part 17.

[0034] The height of the ejection hole H13 is preferably set within a range of -20% to 20% of the height, and more preferably set at a height of 0% (the height of the equator) or more. By having the ejection hole H13 at a height of 0% or more, the liquefied gas ejected can warm the inner wall on the lower side from near the equator. By having the ejection hole H13 at a height of 20% or less, the liquefied gas ejected can easily flow along the inner wall to the bottom surface. By setting the height of the ejection hole H13 to -20% or more, it is possible to sufficiently secure the area through which the ejected liquefied gas flows in order to obtain the effect of warming the inner wall with the liquefied gas. Further, when the height of the ejection hole H13 is less than -50% (when the height of the ejection hole H13 is less than the intermediate height between the height of the equator and the deepest part), the effect of warming the inner wall with the liquefied gas may not be obtained.

[0035] Next, a method for replacing the contents of the cargo tank 1 from LNG to liquefied carbon dioxide gas will be described. In the case of replacing from a liquefied gas with a low density (i.e., a liquefied gas with a low temperature to be managed) to a liquefied gas with a high density (i.e., a liquefied gas with a high temperature to be managed), it can be replaced in the same manner as the method described below. Also, the replacement method described here is an example, and the contents of the cargo tank 1 can be replaced in any way.

[0036] When replacing the contents of the cargo tank 1 from a liquefied gas with a low temperature to be managed (e.g., LNG) to a liquefied gas with a high temperature to be managed (e.g., liquefied carbon dioxide gas), the first filling line 13 is used.

[0037] First, all the LNG in the cargo tank 1 is discharged (unloaded). However, even if all the LNG is discharged, the cargo tank 1 is filled with methane gas.

[0038] Next, the first valve 16a provided in the first filling line 13 is opened, and at the same time, the second valve 16b provided in the second filling line 14 is opened. Thereby, the first filling line 13 and the second filling line 14 can be used.

[0039] Using the first filling line 13, pre-warmed carbon dioxide gas (for example, carbon dioxide at about 40°C) is injected into the cargo tank 1. The injected carbon dioxide gas jets out from the ejection holes H13 provided near the equator of the inner wall. The carbon dioxide gas jetting out from the ejection holes H13 flows along the inner wall from near the equator towards the deepest part of the bottom surface. As a result, the inner wall is warmed and the methane gas that filled the cargo tank 1 is discharged. By continuing the injection of carbon dioxide gas, all the methane gas is discharged from the cargo tank 1, and the inside of the cargo tank 1 is filled with carbon dioxide gas.

[0040] Also, the internal temperature of the cargo tank 1 is warmed to a temperature at which liquefied carbon dioxide gas can be injected. At the same time, the internal pressure of the cargo tank 1 is increased to a pressure at which liquefied carbon dioxide gas can be injected. For example, the temperature and pressure at which liquefied carbon dioxide gas can be injected are the temperature and pressure at which no problems occur when injecting liquefied carbon dioxide gas. Specifically, they are the temperature and pressure at which the injected liquefied carbon dioxide gas does not solidify (the temperature and pressure at which it does not become dry ice).

[0041] When all the methane gas has been discharged from the cargo tank 1 and the internal temperature and pressure of the cargo tank 1 have reached a predetermined temperature and pressure at which it is determined that liquefied carbon dioxide gas can be injected, the injection of liquefied carbon dioxide gas is started. Liquefied carbon dioxide gas is injected until the cargo tank is full of liquefied carbon dioxide gas. In this way, the contents of the cargo tank 1 are replaced from LNG to liquefied carbon dioxide gas.

[0042] Next, a method for replacing the contents of the cargo tank 1 from liquefied carbon dioxide gas to LNG will be described. Note that when replacing from a liquefied gas with a high density (i.e., a liquefied gas with a high temperature to be controlled) to a liquefied gas with a low density (i.e., a liquefied gas with a low temperature to be controlled), it can be replaced in the same manner as the method described below. Also, the replacement method described here is an example, and the contents of the cargo tank 1 can be replaced in any way.

[0043] First, all the liquefied carbon dioxide gas in the cargo tank 1 is discharged (unloading). However, even if all the liquefied carbon dioxide gas is discharged, carbon dioxide gas remains.

[0044] Next, the second valve 16b provided on the second filling line 14 is opened. At this time, the first valve 16a provided on the first filling line 13 is closed. Thereby, the second filling line 14 can be used.

[0045] Using the second filling line 14, methane gas is injected. The injected methane gas jets out from the jet hole H14 provided near the deepest part of the bottom surface. The methane gas jetting out from the jet hole H14 starts to accumulate from the deepest part. By injecting the methane gas, all the carbon dioxide gas remaining on the bottom surface is discharged from the upper part of the cargo tank 1 (for example, the hatch part 17). Thereby, the inside of the cargo tank 1 is filled with methane gas.

[0046] When all the carbon dioxide gas has been discharged from the cargo tank 1, the injection of LNG is started. LNG is injected until the cargo tank is full of LNG. In this way, the contents of the cargo tank 1 are replaced from liquefied carbon dioxide gas to LNG.

[0047] FIG. 3 is a configuration diagram showing the configuration of a ship 20 to which the cargo tank 1 according to the present embodiment is applied.

[0048] For example, the ship 20 is a tanker that transports by swapping LNG and liquefied carbon dioxide gas. The ship 20 transports LNG on the way to the destination and transports liquefied carbon dioxide gas on the way back from the destination. Thereby, LNG can be transported from the production place of LNG to the destination, and the carbon dioxide discharged by the use of LNG can be returned to the production place of LNG.

[0049] On the ship 20, a plurality of cargo tanks 1 are installed inside the hull. For example, three cargo tanks 1 are arranged side by side in the longitudinal direction of the hull. The filling lines 13, 14, and 15 provided in each cargo tank 1 are all connected to a manifold 21 by a pipe 22 provided in the hull. The manifold 21 is a connection part for connecting to an external pipe such as on land. For example, the manifold 21 is connected to a pipeline provided on land during cargo handling. The ship 20 may be provided with several manifolds 21.

[0050] The pipe 22 connecting each filling line 13, 14, 15 to the manifold 21 may form any path. For example, the pipe 22 may branch or join at any location. Also, various valves or pumps etc. may be provided in the pipe 22.

[0051] According to this embodiment, in the cargo tank 1, by providing the first filling line 13 provided with the ejection hole H13 near the equator of the inner wall and the second filling line 14 provided with the ejection hole H14 near the bottom surface, two types of liquefied gases with different temperatures to be managed can be efficiently replaced.

[0052] Specifically, the injected liquefied gas or its gaseous state gas (such as liquefied carbon dioxide gas) ejects from the ejection hole H13 of the first filling line 13, so that the inner wall of the cargo tank 1 can be heated from near the equator to the bottom surface. Thereby, the inside of the cargo tank 1 can be efficiently heated.

[0053] In addition, additional advantages and modifications may easily occur to those skilled in the art. Therefore, the present invention in its broader aspect is not limited to the specific details and representative embodiments shown and described in this specification. Therefore, various modifications can be made without departing from the spirit or scope of the general inventive concept defined by the appended claims and their equivalents.

Explanation of Reference Numerals

[0054] 1…Cargo tank, 11…Outer shell, 12…Bone member, 13…First filling line, 14…Second filling line, 15…Third filling line, 16a, 16b, 16c…Valve, 17…Hatch part.

Claims

1. An outer shell that houses two types of liquefied gas with different temperatures to be managed by replacing them, and includes an inner wall with a curved surface shape formed such that the central portion in the vertical direction bulges most in the horizontal direction, A first filling line provided for injecting at least one of the two types of liquefied gas into the interior of the outer shell, and having a first ejection hole provided at a height equal to or higher than the intermediate height between the height of the central portion and the height of the deepest portion in the interior space of the outer shell so that the ejected liquefied gas flows along the curved surface shape of the inner wall, A second filling line provided for injecting at least one of the two types of liquefied gas into the interior of the outer shell, and having a second ejection hole provided so that liquefied gas ejects from the bottom surface of the outer shell A cargo tank, characterized by comprising the same.

2. The first ejection hole is provided at a height in the range of -20% to 20% when the height of the uppermost portion is 100%, the height of the central portion is 0%, and the height of the deepest portion is -100% in the interior space of the outer shell. The cargo tank according to claim 1, characterized by the same.

3. A third filling line having a third ejection hole provided so as to spray at least one of the two types of liquefied gas downward from the upper part of the outer shell The cargo tank according to claim 1, characterized by comprising the same.

4. Valves provided respectively in the first filling line, the second filling line, and the third filling line The cargo tank according to claim 3, characterized by comprising the same.

5. A hull, A cargo tank provided on the hull, The cargo tank An outer shell that houses two types of liquefied gas with different temperatures to be managed by replacing them, and includes an inner wall with a curved surface shape formed such that the central portion in the vertical direction bulges most in the horizontal direction, A first filling line provided for injecting at least one of the two types of liquefied gas into the interior of the outer shell, the first ejection hole being provided at a height equal to or greater than the intermediate height between the height of the central portion and the depth of the interior space of the outer shell so that the ejected liquefied gas flows along the curved surface shape of the inner wall, A second filling line provided for injecting at least one of the two types of liquefied gas into the interior of the outer shell, the second ejection hole being provided so that the liquefied gas ejects onto the bottom surface of the outer shell, A ship characterized by the above.

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