Tank system and gas replacement method

Abstract

To provide a tank system capable of improving maintainability.SOLUTION: A tank system comprises: a tank capable of storing gas; a first pipe having a plurality of openings arranged along an upper wall surface in the tank, and through which first gas flows in and out of the tank; and a second pipe having a plurality of openings arranged along a lower wall surface inside the tank, and through which second gas having a higher density than the first gas flows in and out of the tank. This allows the first gas to be easily replaced with the second gas in the tank using a simple facility.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a tank system and a gas replacement method.

Background Art

[0002] For example, Patent Document 1 discloses a tank structure capable of replacing gases with different densities. When the density of the replacement gas is smaller than the density of the gas to be replaced, this tank structure supplies the replacement gas upward from an upper nozzle ring disposed at the upper part inside the tank. Then, the gas to be replaced is discharged through a lower discharge pipe provided at the lower part of the tank. On the other hand, when the density of the replacement gas is larger than the density of the gas to be replaced, the replacement gas is supplied downward from a lower nozzle ring provided at the lower part inside the tank. Then, the gas to be replaced is discharged through an upper discharge pipe provided at the upper part of the tank.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in the tank structure described in Patent Document 1 above, in addition to the two nozzle rings for supplying the replacement gas into the tank, it is necessary to provide two discharge pipes for discharging the gas to be replaced inside the tank, one at the upper part and one at the lower part. Therefore, the piping structure has become complicated.

[0005] The present invention has been made in view of the above problems, and an object thereof is to provide a tank system and a gas replacement method capable of avoiding complication of the piping structure.

Means for Solving the Problems

[0006] To solve the above problems, the tank system according to the present disclosure includes a tank capable of storing gas, a first pipe having a plurality of openings provided along the upper wall surface in the tank, and through these openings, a first gas flows in and out between the inside of the tank, and a second pipe having a plurality of openings provided along the lower wall surface in the tank, and through these openings, a second gas having a density greater than that of the first gas flows in and out between the inside of the tank.

[0007] The gas replacement method according to the present disclosure is a gas replacement method using the above tank system, and includes a step of discharging the first gas in the tank through the opening of the first pipe while supplying the second gas through the opening of the second pipe into the tank in which the first gas is stored.

[0008] The gas replacement method according to the present disclosure is a gas replacement method using the above tank system, and includes a step of discharging the second gas in the tank through the opening of the second pipe while supplying the first gas through the opening of the first pipe into the tank in which the second gas is stored.

Advantages of the Invention

[0009] According to the tank system and the gas replacement method according to the present disclosure, maintainability can be improved.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

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Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0011] <First Embodiment> Next, the first embodiment of the tank system 1 according to the embodiment of the present disclosure will be described with reference to FIG. 1. <Tank System> As shown in FIG. 1, the tank system 1 includes a rectangular tank 10 as a tank, a first pipe 20, a second pipe 30, a first gas supply / discharge unit 40, a second gas supply / discharge unit 50, an inert gas supply unit 60, and a gas sensor 70.

[0012] <Rectangular Tank> The rectangular tank 10 is a tank having a rectangular parallelepiped shape and an internal gas storage space R. The top surface of the inner surface 11 of the rectangular tank 10 is the upper wall surface 12. The upper wall surface 12 extends horizontally and is flat. The bottom surface of the inner surface 11 of the rectangular tank 10 is the lower wall surface 13. The lower wall surface 13 extends horizontally and is flat. The upper wall surface 12 and the lower wall surface 13 are arranged parallel to each other and face each other in the vertical direction.

[0013] <First Pipe> The first pipe 20 is a pipe provided near the upper wall surface 12 at the upper part of the accommodation space R in the rectangular tank 10. The first pipe 20 has a first header 21 and a plurality of first branch pipes 22. The first header 21 extends horizontally along the upper wall surface 12 at a height position below the upper wall surface 12 close to the upper wall surface 12 in the accommodation space R. The first header 21 is fixed to the rectangular tank 10 via brackets (not shown), for example.

[0014] The first branch pipe 22 is a pipe communicating with the first header 21. A plurality of first branch pipes 22 are provided at intervals in the extending direction of the first header 21. The first branch pipe 22 extends upward from the base end, which is the connection point with the first header 21. A first opening 23 that opens upward is formed at the tip, which is the upper end of the first branch pipe 22. The first opening 23 allows the first gas to flow in and out between the inside of the first pipe 20 and the accommodation space R. The heights of the first openings 23 of the respective first branch pipes 22 are the same as each other. The first openings 23 of the respective first branch pipes 22 face the upper wall surface 12 of the rectangular tank 10 from below. The vertical interval between the first opening 23 and the upper wall surface 12 is set in the range of, for example, 30 mm to 200 mm, preferably in the range of 50 mm to 150 mm.

[0015] <Second Pipe> The second pipe 30 is a pipe provided near the lower wall surface 13 at the lower part of the accommodation space R in the rectangular tank 10. The second pipe 30 has a second header 31 and a plurality of second branch pipes 32. The second header 31 extends horizontally along the lower wall surface 13 at a height position above the lower wall surface 13 close to the lower wall surface 13 in the accommodation space R. The second header 31 is fixed to the rectangular tank 10 via brackets (not shown), for example.

[0016] The second branch pipe 32 is a pipe that communicates with the second header 31. A plurality of second branch pipes 32 are provided at intervals in the extending direction of the second header 31. The second branch pipe 32 extends downward from the proximal end which is the connection location with the second header 31. A second opening 33 that opens downward is formed at the distal end which is the lower end of the second branch pipe 32. The second opening 33 allows the second gas to flow in and out between the inside of the second pipe 30 and the accommodation space R. The heights of the second openings 33 of the respective second branch pipes 32 are the same as each other. The second openings 33 of the respective second branch pipes 32 face the lower wall surface 13 of the rectangular tank 10 from above. The vertical interval between the second opening 33 and the lower wall surface 13 is set in the range of, for example, 50 mm to 200 mm, and preferably in the range of 50 mm to 150 mm.

[0017] <First gas supply and discharge unit> The first gas supply and discharge unit 40 supplies the first gas to the first pipe 20 and discharges the first gas from the first pipe 20. The first supply and discharge unit has a first gas tank 41, a first gas pipe 42, a first supply and discharge pipe 43, a first gas valve 44, and a first exhaust valve 45.

[0018] The first gas tank 41 is a tank that is arranged outside the rectangular tank 10 independently of the rectangular tank 10, and the first gas is stored in a compressed state. The first gas pipe 42 is a pipe connected to the first gas tank 41. That is, one end of the first gas tank 41 is connected to the first gas tank 41 in a communicating state. The other end of the first gas tank 41 is connected to the outside of the system.

[0019] The first supply and discharge pipe 43 is a pipe that extends through the rectangular tank 10 so as to connect the first gas pipe 42 and the first pipe 20. One end of the first supply and discharge pipe 43 is arranged in communication with the first gas pipe 42. The other end of the first supply and discharge pipe 43 is connected in communication with the first header 21 of the first pipe 20.

[0020] The first gas valve 44 is an on-off valve provided on the first gas pipe 42. The first gas valve 44 is provided at a position closer to the first gas tank 41 than the connection point of the first gas pipe 42 with the first supply and discharge pipe 43. The first exhaust valve 45 is an on-off valve provided on the first gas pipe 42. The first exhaust valve 45 is provided at a position on the side opposite to the first gas tank 41 with respect to the connection point of the first gas pipe 42 with the first supply and discharge pipe 43. That is, the connection point of the first gas pipe 42 and the first supply and discharge pipe 43 is located between the first gas valve 44 and the first exhaust valve 45.

[0021] <Second gas supply and discharge section> The second gas supply and discharge section 50 supplies the second gas to the second pipe 30 and discharges the second gas from the second pipe 30. The second gas supply and discharge section 50 includes a second gas tank 51, a second gas pipe 52, a second supply and discharge pipe 53, a second gas valve 54, and a second exhaust valve 55.

[0022] The second gas tank 51 is a tank provided outside the rectangular tank 10 and independent of the rectangular tank 10, and the second gas is stored in a compressed state.

[0023] Here, the density of the second gas under the atmosphere is greater than the density of the first gas. The first gas and the second gas can adopt various gases as long as there is the above density difference. On the premise that there is the above density difference, for example, ammonia gas or the like can be adopted as the first gas, and carbon dioxide gas, LNG gas, LPG gas or the like can be adopted as the second gas. Specific combinations of the first gas and the second gas include ammonia · dry air, dry air · carbon dioxide, methane · carbon dioxide, propane · nitrogen, and the like.

[0024] The second gas pipe 52 is a pipe connected to the second gas tank 51. That is, one end of the second gas tank 51 is connected to the gas tank in a communicating state. The other end of the second gas tank 51 is connected to the outside of the system.

[0025] The second supply and discharge pipe 53 is a pipe that penetrates through the rectangular tank 10 so as to connect the second gas pipe 52 and the second pipe 30. Both ends of the second supply and discharge pipe 53 are arranged in communication with the second gas pipe 52. The other end of the second supply and discharge pipe 53 is connected in communication with the second header 31 of the second pipe 30.

[0026] The second gas valve 54 is an on-off valve provided on the second gas pipe 52. The second gas valve 54 is provided at a position closer to the second gas tank 51 side than the connection point of the second gas pipe 52 with the second supply and discharge pipe 53. The second exhaust valve 55 is an on-off valve provided on the second gas pipe 52. The second exhaust valve 55 is provided at a position on the side opposite to the second gas tank 51 than the connection point of the second gas pipe 52 with the second supply and discharge pipe 53. That is, the connection point of the second gas pipe 52 and the second supply and discharge pipe 53 is located between the second gas valve 54 and the second exhaust valve 55.

[0027] <Inert gas supply section> The inert gas supply section 60 is capable of supplying inert gas into the rectangular tank 10. The inert gas supply section 60 includes an inert gas source 61, a first inert pipe 62, a first inert valve 63, a second inert pipe 64, and a second inert valve 65.

[0028] The inert gas source 61 is a device capable of generating inert gas. The density of the inert gas under the atmosphere is greater than the density of the first gas and less than the density of the second gas. The inert gas is a gas interposed during the replacement of the first gas and the second gas. In this embodiment, it is defined that in addition to an inert gas such as nitrogen, air is also included as the inert gas. As long as it does not react with each of the first gas and the second gas, air can also be used as the inert gas.

[0029] The first inert gas pipe 62 connects the inert gas source 61 and the first pipe 20. One end of the first inert gas pipe 62 is communicatively connected to the inert gas source 61. The other end of the first inert gas pipe 62 is communicatively connected to the first gas pipe 42. That is, in the present embodiment, the first inert gas pipe 62 is connected to the first pipe 20 via the first gas pipe 42.

[0030] The first inert gas valve 63 is an on-off valve provided on the first inert gas pipe 62. By opening and closing the first inert gas valve 63, the supply of inert gas to the first pipe 20 is permitted and regulated.

[0031] The second inert gas pipe 64 connects the inert gas source 61 and the second pipe 30. One end of the second inert gas pipe 64 is communicatively connected to the inert gas source 61. The other end of the second inert gas pipe 64 is communicatively connected to the second gas pipe 52. That is, in the present embodiment, the second inert gas pipe 64 is connected to the second pipe 30 via the second gas pipe 52.

[0032] The second inert gas valve 65 is an on-off valve provided on the second inert gas pipe 64. By opening and closing the second inert gas valve 65, the supply of inert gas to the second pipe 30 is permitted and regulated.

[0033] <Gas sensor> The gas sensor 70 is a sensor capable of detecting the components of the gas inside the rectangular tank 10. The gas sensor 70 is capable of detecting the components of the gas it contacts. The gas sensor 70 of the present embodiment can detect the components of the first gas, the second gas, and the inert gas respectively. Note that the gas sensor 70 may be configured to detect the presence of the first gas, the second gas, and the inert gas by detecting the concentration of a specific gas component such as oxygen.

[0034] A plurality of gas sensors 70 are provided at intervals in the vertical direction inside the rectangular tank 10. Note that the position of the gas sensor 70 shown in the figure indicates the gas detection position by the gas sensor 70. Among the plurality of gas sensors 70, the gas sensor 70 located at the uppermost position is installed at the same height position as the first opening 23 of the first pipe 20, or at a height position in contact with the upper wall surface 12, or at a height position between the first opening 23 of the first pipe 20 and the upper wall surface 12. Among the plurality of gas sensors 70, the gas sensor 70 located at the lowermost position is installed at the same height position as the second opening 33 of the second pipe 30, or at a height position in contact with the lower wall surface 13, or at a height position between the second opening 33 of the second pipe 30 and the lower wall surface 13. Note that not only a plurality of gas sensors 70 are provided only in the vertical direction, but also a plurality of gas sensors 70 may be provided in the horizontal direction.

[0035] <Function and effect> Next, the function and effect of this embodiment will be described. By using the tank system 1, it is possible to replace the first gas and the second gas via the inert gas.

[0036] <Replacement from a gas with a low density to a gas with a high density> First, the procedure for replacing the first gas filled in the rectangular tank 10 with an inert gas will be described. Starting from a state where all valves are closed, the second inert valve 65 and the first exhaust valve 45 are opened. As a result, the inert gas stored in the inert gas source 61 is guided to the second pipe 30 via the second inert pipe 64, the second gas pipe 52, and the second supply / discharge pipe 53. The inert gas passes through the second header 31 of the second pipe 30, reaches each second branch pipe 32, and reaches the inside of the rectangular tank 10 through the second opening 33 of the second pipe 30.

[0037] Since the inert gas has a higher density than the first gas, it accumulates in the lower part of the accommodation space R of the rectangular tank 10. As the pressure inside the rectangular tank 10 increases accordingly, the first gas, which is lighter than the inert gas, loses its place inside the rectangular tank 10 and thus enters each first branch pipe 22 through each first opening 23 of the first pipe 20 and circulates inside the first pipe 20. The first gas circulating inside the first pipe 20 in this way flows through the first supply and discharge pipe 43, the first gas pipe 42, and the first exhaust valve 45 and is led to the outside of the system where the pressure is lower than the internal pressure of the rectangular tank 10. Thereby, the gas replacement inside the rectangular tank 10 proceeds.

[0038] As the gas replacement proceeds, the inert gas occupies the lower region of the accommodation space R, and the first gas is forced into the upper part of the accommodation space R. That is, the interface between the inert gas and the first gas sequentially migrates upward in the accommodation space R. Such migration of the interface can be confirmed by the detection components of the plurality of gas sensors 70.

[0039] Then, the first gas concentrated near the upper wall surface 12 of the accommodation space R is discharged from the inside of the accommodation space R through the first opening 23 of the first pipe 20. As a result, the entire region inside the accommodation space R will be occupied by the inert gas. Thereby, the replacement from the first gas to the inert gas is completed. The completion of the replacement can be confirmed by the detection results of the gas sensor 70.

[0040] Next, after once closing all the valves, the second gas valve 54 and the first exhaust valve 45 are opened. Thereby, similar to the above, the replacement from the inert gas to the second gas proceeds from the lower part to the upper part inside the accommodation space R of the rectangular tank 10, and the inert gas or the mixed gas of the inert gas and the second gas is discharged to the outside of the system of the rectangular tank 10.

[0041] In addition, when replacing the inert gas with the second gas in this way, it is necessary to make the supply pressure of the second gas higher than the internal pressure of the rectangular tank 10. Therefore, a blower for pumping the second gas may be provided.

[0042] <Replacement from a gas with a high density to a gas with a low density> Next, a procedure for replacing the second gas with an inert gas in the rectangular tank 10 will be described. Starting from a state where all valves are closed, the first inert gas valve 63 and the second exhaust valve 55 are opened. As a result, the inert gas supplied from the inert gas source 61 is guided to the first pipe 20 via the first inert gas pipe 62, the first gas pipe 42, and the first supply / drain pipe 43. The inert gas passes through the first header 21 of the first pipe 20, reaches each first branch pipe 22, and reaches the inside of the rectangular tank 10 via the second opening 33 of the first pipe 20.

[0043] Since the inert gas has a lower density than the second gas, it accumulates in the upper part of the accommodation space R of the rectangular tank 10. As the pressure inside the rectangular tank 10 increases accordingly, the second gas, which is heavier than the inert gas, loses its place inside the rectangular tank 10 and thus enters each second branch pipe 32 via each second opening 33 of the second pipe 30 and circulates inside the second pipe 30. The second gas circulating inside the second pipe 30 in this way flows through the second supply / drain pipe 53, the second gas pipe 52, and the second exhaust valve 55 and is guided to the outside of the system where the pressure is lower than the internal pressure of the rectangular tank 10. As a result, the gas replacement inside the rectangular tank 10 proceeds.

[0044] As the gas replacement proceeds, the inert gas occupies the upper region of the accommodation space R, and the second gas is pushed into the lower part of the accommodation space R. That is, the interface between the inert gas and the second gas sequentially migrates downward in the accommodation space R. Similar to the above, the migration of the interface can be confirmed by a plurality of gas sensors 70.

[0045] Then, the second gas concentrated near the lower wall surface 13 of the accommodation space R is discharged from the inside of the accommodation space R via the second opening 33 of the second pipe 30. As a result, the entire region inside the accommodation space R will be occupied by the inert gas. Thus, the replacement from the second gas to the inert gas is completed. Note that when replacing the inert gas inside the rectangular tank 10 with the first gas, it can also be made to proceed by appropriately operating the valves in the same manner as above. Further, the replacement of the first gas and the second gas may be performed directly without passing through an inert gas.

[0046] As described above, in this embodiment, when replacing the gas in the rectangular tank 10, both the first pipe 20 and the second pipe 30 are used for both gas supply and discharge. Therefore, for example, it is not necessary to separately provide the supply pipes and discharge pipes for the first gas and the second gas, respectively, and the piping configuration can be simplified. As a result, the material cost and labor cost during manufacturing can be reduced, and various advantages such as simplification of equipment, reduction in the number of monitoring points during operation, reduction in the number of operation targets, reduction in the number of inspection targets during maintenance, and reduction in the number of repair targets can be obtained.

[0047] In addition, the first opening 23 of the first pipe 20 is arranged close to and along the upper wall surface 12, and the second opening 33 of the second pipe 30 is arranged close to and along the lower wall surface 13, so that the gas accumulated in the upper or lower part of the accommodation space R can be smoothly discharged. Thereby, gas replacement using the specific gravity difference can be performed promptly, and the remaining replaced gas in the rectangular tank 10 can be minimized as much as possible. Therefore, the working efficiency can be improved, and the amount of gas exhausted until the replacement is completed can be reduced.

[0048] It is preferable that the vertical distance between the first opening 23 and the upper wall surface 12 and the vertical distance between the second opening 33 and the lower wall surface 13 are appropriately set according to the outflow velocity of the gas discharged during gas replacement. For example, when the average flow velocity is 20 m / s, it is preferable that the above distance is in the range of 150 mm or less. On the other hand, if the above distance is too small, due to the difference in thermal expansion between the first pipe 20, the second pipe 30, and the rectangular tank 10, they may come into contact with each other. Therefore, it is preferable to set the above distance to, for example, 30 mm or more, more preferably 50 mm or more.

[0049] <Second Embodiment> Next, a second embodiment of the present disclosure will be described with reference to FIG. 2. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. The tank of the second embodiment is a spherical tank 110, and accordingly, the configurations of the first pipe 20 and the second pipe 30 are different from those of the first embodiment. Further, in the second embodiment, in addition to the configuration of the first embodiment, a first internal valve 24 and a second internal valve 34 are provided.

[0050] The spherical tank 110 is a spherical tank, and a gas storage space R is formed inside. The upper part of the inner surface 111 of the spherical tank 110 is an upper wall surface 112, and the lower part is a lower wall surface 113.

[0051] The upper wall surface 112 constitutes the upper part of the inner surface 111 of the spherical tank 110. The upper wall surface 112 is in the range above the center of the vertical height of the inner surface 111 of the spherical tank 110, preferably in the upper one-third range including the upper end of the inner surface 111, more preferably in the one-fourth range, and even more preferably in the one-fifth range. The upper wall surface 112 has a concave curved surface shape that is concave upward.

[0052] The lower wall surface 113 constitutes the lower part of the inner surface 111 of the spherical tank 110. The lower wall surface 113 is in the range below the center of the vertical height of the inner surface 111 of the spherical tank 110, preferably in the upper one-third range including the lower end of the inner surface 111, more preferably in the one-fourth range, and even more preferably in the one-fifth range. The lower wall surface 113 has a concave curved surface shape that is concave downward.

[0053] The first header 21 of the first pipe 20 is arranged to curve along the concave curved surface-shaped upper wall surface 112. The first header 21 has a top corresponding to the top of the upper wall surface 112, and has a shape that curves downward as it extends horizontally from both sides of the top. A first supply / discharge pipe 43 is connected near the top of the first header 21.

[0054] The first branch pipe 22 of the first pipe 20 extends upward from the first header 21, and each first opening 23 faces the upper wall surface 112 having a concave curved surface shape. The vertical interval between each first branch pipe 22 and the upper wall surface 112 is constant. The vertical dimensions of each first branch pipe 22 are the same. One of the first branch pipes 22 is arranged at the center which is the top of the first header 21. The first opening 23 of the central first branch pipe 22 is located at the highest position, and the height of the first opening 23 of the first branch pipe 22 decreases as it moves away from the center in the horizontal direction on both sides of the first branch pipe 22. Accordingly, the heights of the first openings 23 of adjacent first branch pipes 22 are different from each other. In the present embodiment, one first branch pipe 22 is provided at the center of the first header 21, and two first branch pipes 22 are arranged on each of the horizontal sides of the first branch pipe 22 at the top, that is, a total of five first branch pipes 22 are provided. Note that the number of the first branch pipes 22 is not limited to this and can be changed as appropriate.

[0055] The second header 31 of the second pipe 30 is arranged to curve along the lower wall surface 113 having a concave curved surface shape. The second header 31 has a bottom corresponding to the bottom of the lower wall surface 113, and has a shape that curves upward as it goes from the bottom toward both sides in the horizontal direction. A second supply and discharge pipe 53 is connected near the bottom of the second header 31.

[0056] The second branch pipe 32 of the second pipe 30 extends downward from the following second header 31, and each second opening 33 faces the lower wall surface 113 having a concave curved surface shape. The vertical interval between each second branch pipe 32 and the lower wall surface 113 is constant. The vertical dimensions of each second branch pipe 32 are the same. One of the second branch pipes 32 is arranged at the center which is the bottom of the second header 31. The second opening 33 of the central second branch pipe 32 is located at the lowest position, and as it moves away from both sides in the horizontal direction from the second branch pipe 32, the height of the second opening 33 of the second branch pipe 32 increases. Thereby, the heights of the second openings 33 of adjacent second branch pipes 32 are made different from each other. In the present embodiment, in the present embodiment, one second branch pipe 32 is provided at the center of the second header 31, and two second branch pipes 32 are arranged on both sides in the horizontal direction of the first branch pipe 22 at the bottom, that is, a total of five second branch pipes 32 are provided. Note that the number of second branch pipes 32 is not limited to this and can be changed as appropriate.

[0057] The first internal valve 24 is an on-off valve provided in a pair on the first header 21 in the first pipe 20. The first internal valve 24 is provided between adjacent first branch pipes 22 in the first header 21. That is, the first internal valve 24 is provided between adjacent first openings 23. In the present embodiment, among a total of five first branch pipes 22, the first internal valves 24 are respectively provided at positions between the two first branch pipes 22 at both ends that are farthest from the center and the first branch pipes 22 near the top adjacent to these first branch pipes 22.

[0058] The second internal valve 34 is an on-off valve provided in a pair on the second header 31 in the second pipe 30. The second internal valve 34 is provided between adjacent second branch pipes 32 in the second header 31. That is, the second internal valve 34 is provided between adjacent second openings 33. In the present embodiment, among a total of five second branch pipes 32, the second internal valves 34 are respectively provided at positions between the two second branch pipes 32 at both ends that are farthest from the center and the second branch pipes 32 near the top adjacent to these second branch pipes 32.

[0059] Also in the second embodiment, as in the first embodiment, a plurality of gas sensors 70 are provided at intervals in the vertical direction.

[0060] One gas sensor 70 (referred to as the upper specific gas sensor 70) disposed above the accommodation space R among the plurality of gas sensors 70 is provided at a height position between a pair of adjacent first openings 23 disposed so as to sandwich the first internal valve 24 from above and below. That is, the upper specific gas sensor 70 is provided at a height position between the first openings 23 of the first branch pipes 22 at both ends farthest from the center of the first header 21 and the first openings 23 of the first branch pipes 22 at one center from both ends.

[0061] One gas sensor 70 (referred to as the lower specific gas sensor 70) disposed below the accommodation space R among the plurality of gas sensors 70 is provided at a height position between a pair of adjacent second openings 33 disposed so as to sandwich the second internal valve 34 from above and below. That is, the lower specific gas sensor 70 is provided at a height position between the second openings 33 of the second branch pipes 32 at both ends farthest from the center of the second header 31 and the second openings 33 of the second branch pipes 32 at one center from both ends.

[0062] <Operational Effect> In this embodiment as well, gas replacement is performed in the same procedure as in the first embodiment. On the other hand, since the height positions of the plurality of first openings 23 and the height positions of the plurality of second openings 33 are different, the following procedure is added to avoid accidental gas outflow.

[0063] <Replacement from a Gas with a Smaller Density to a Gas with a Larger Density> When replacing the first gas in the spherical tank 110 with the second gas, the interface between these first gas and second gas gradually rises in the accommodation space R. When the interface exceeds the height of the lowermost first opening 23 in the first pipe 20, the second gas that should not be discharged is discharged through the first opening 23.

[0064] Therefore, in the present embodiment, when the height position of the first opening 23 where the gas interface is the lowest is exceeded, the upper specific gas sensor 70 detects a change in the gas component. Thereby, the operator performs an operation to change the first internal valve 24 from the open state to the closed state. Here, if the open state of the first internal valve 24 is maintained, when the gas interface exceeds the height of the first opening 23 where it is the lowest, the discharge of the second gas, which is the replacement gas, starts. On the other hand, by closing the first internal valve 24 as in the present embodiment, the discharge of the second gas can be avoided. In addition, when replacing the first gas with an inert gas, inadvertent discharge of the inert gas can be avoided by the same procedure as above.

[0065] <Replacement from a gas with a high density to a gas with a low density> On the other hand, when replacing the second gas in the spherical tank 110 with the first gas, the interface between the first gas and the second gas gradually descends within the accommodation space R. When the interface falls below the height of the uppermost second opening 33 in the second pipe 30, the first gas that should not be discharged is discharged through the second opening 33.

[0066] Therefore, similarly to the above, when the gas interface falls below the height position of the uppermost second opening 33, the lower specific gas sensor 70 detects a change in the gas component. Thereby, the operator performs an operation to change the second internal valve 34 from the open state to the closed state. Here, if the open state of the second internal valve 34 is maintained, when the gas interface falls below the height of the uppermost second opening 33, the discharge of the first gas, which is the replacement gas, starts. On the other hand, by closing the second internal valve 34 as in the present embodiment, the discharge of the first gas can be avoided. In addition, when replacing the second gas with an inert gas, inadvertent discharge of the inert gas can be avoided by the same procedure as above.

[0067] For example, as shown in FIG. 3, as a modification of the second embodiment, the first header 21 and the second header 31 may be straight tubular and extend in the horizontal direction. In this case, the vertical dimensions of the plurality of first branch pipes 22 are different from each other, and the vertical dimensions of the plurality of second branch pipes 32 are different from each other. That is, the vertical dimensions of the first branch pipe 22 and the second branch pipe 32 increase as they approach the center. Also by this, the same operational effects as those of the second embodiment can be achieved.

[0068] Further, the arrangement position of the first internal valve 24 in the first header 21 is not limited to the above. For example, it may be provided between the central first branch pipe 22 in the first header 21 and the first branch pipe 22 adjacent to the central first branch pipe 22. Also in this case, by providing the upper specific gas sensor 70 at the height position between the first opening 23 of the central first branch pipe 22 and the second opening 33 of the first branch pipe 22 adjacent to the central first branch pipe 22, the discharge of gas that should not be discharged can be suppressed as described above. Further, the first internal valve 24 may be provided between all adjacent first branch pipes 22 in the first header 21.

[0069] Similarly, the arrangement position of the second internal valve 34 in the second header 31 is not limited to the above. For example, it may be provided between the central second branch pipe 32 in the second header 31 and the second branch pipe 32 adjacent to the central second branch pipe 32. Also in this case, by providing the lower specific gas sensor 70 at the height position between the second opening 33 of the central second branch pipe 32 and the second opening 33 of the second branch pipe 32 adjacent to the central second branch pipe 32, the discharge of gas that should not be discharged can be suppressed as described above.

[0070] <Third Embodiment> Next, the third embodiment of the present disclosure will be described with reference to FIG. 4. In the third embodiment, the same components as those in other embodiments are denoted by the same reference numerals, and detailed description thereof is omitted. The first pipe 20 of the third embodiment does not have the first branch pipe 22, and the first opening 23 is formed in the first header 21. That is, in the first header 21, a plurality of first openings 23 penetrating the inside and outside of the first header 21 are formed at intervals in the extending direction of the first header 21. Each first opening 23 opens upward at the upper part of the first header 21.

[0071] The first header 21 of the third embodiment is arranged closer to the upper wall surface 12 than in the first and second embodiments. That is, in order to bring the first opening 23 closer to the upper wall surface 12, the first header 21 itself is located at the height of the tip of the first branch pipe 22 in the first and second embodiments. Also by this, similar to the first and second embodiments, the gas staying near the upper wall surface 12 can be discharged smoothly.

[0072] Note that a similar configuration is also applicable to the second pipe 30. That is, the second opening 33 may be directly formed in the second header 31 without providing the second branch pipe 32 in the second pipe 30. Further, the third embodiment may be applied to the second embodiment, and a configuration in which the first internal valve 24 and the second internal valve 34 are provided may be adopted.

[0073] <Fourth Embodiment> Next, a fourth embodiment of the present disclosure will be described with reference to FIG. 5. In the fourth embodiment, the same reference numerals are given to the same components as in the other embodiments, and detailed descriptions thereof are omitted. The first branch pipe 22 of the fourth embodiment has a tapered tubular shape in which the inner peripheral surface and the outer peripheral surface expand in diameter from the base end to the tip end. As a result, the opening area of the first opening 23 is larger than that in the first and second embodiments.

[0074] By the expansion of the first opening 23, the flow velocity sucked into the first opening 23 becomes slower. Thereby, it is possible to prevent the gas at a location away from the upper wall surface 12 downward from being inadvertently sucked in. Further, by increasing the contact area of the first opening 23 with respect to the gas staying near the upper wall surface 12, a wider range of gas can be recovered.

[0075] Note that a similar configuration may be applied to the second branch pipe 32 of the second pipe 30. That is, the second branch pipe 32 may have a tapered tubular shape that expands in diameter from the base end toward the tip end.

[0076] <Fifth Embodiment> Next, a fifth embodiment of the present disclosure will be described with reference to FIG. 6. In the fifth embodiment, the same reference numerals are given to the same components as in the other embodiments, and the detailed description thereof will be omitted. In the fifth embodiment, in addition to the configuration of the fourth embodiment, the inner peripheral surface of the first branch pipe 22 has a spiral structure 22a. The spiral structure 22a is a protrusion that protrudes from the inner peripheral surface of the first branch pipe 22 and is formed so as to twist around the axis as it extends in the axial direction of the first branch pipe 22.

[0077] As a result, inside the first branch pipe 22, the sucked gas flows in a swirling manner along the spiral structure 22a. Therefore, decompression inside the first branch pipe 22 can be achieved, and the flow in the direction of sucking the gas around the first opening 23 can be induced. Thus, it becomes possible to collect the gas more smoothly.

[0078] Note that the spiral structure 22a may be not only a protrusion but also, for example, a groove that is recessed from the inner peripheral surface of the first branch pipe 22 and twists around the axis as it extends in the axial direction of the first branch pipe 22. By this as well, the same operational effects can be obtained. Also, a similar configuration may be applied to the second branch pipe 32 of the second pipe 30. That is, the spiral structure 22a may be provided on the inner peripheral surface of the second branch pipe 32. Furthermore, the spiral structure 22a may be adopted for the first branch pipe 22 and the second branch pipe 32 having a straight tubular shape as in the first and second embodiments.

[0079] <Sixth Embodiment> Next, a sixth embodiment of the present disclosure will be described with reference to FIG. 7. In the sixth embodiment, the same reference numerals are given to the same components as in the other embodiments, and the detailed description thereof will be omitted. In the sixth embodiment, in addition to the first configuration, a flange 22b is provided on the first branch pipe 22. The flange 22b is formed so as to project radially outward from the axis of the first branch pipe 22 over the entire circumferential direction of the first branch pipe 22 from the tip of the first branch pipe 22. The flange 22b has a plate shape extending in the horizontal direction. The opposing surface of the flange 22b that faces the upper wall surface 12 is arranged at a distance from the upper wall surface 12 and along the upper wall surface 12.

[0080] Thereby, it is possible to avoid suction of gas from a location spaced downward from the upper wall surface 12. Therefore, it is possible to suppress the discharge of gas that should not be discharged. When this embodiment is applied to the second embodiment, the flange 22b is arranged along the upper wall surface 12 having a concave curved surface shape. That is, the opposing surface of the flange 22b is opposed along the curved surface of the upper wall surface 12. Thereby, inadvertent gas discharge can be avoided. Also, a similar configuration may be applied to the second branch pipe 32 of the second pipe 30. That is, a flange 22b may be provided at the tip of the second branch pipe 32.

[0081] <Seventh Embodiment> Next, the seventh embodiment of the present disclosure will be described with reference to FIG. 8. In the seventh embodiment, the same reference numerals are given to the same components as in the other embodiments, and detailed description thereof is omitted. In the sixth embodiment, in addition to the other embodiments, a convex portion 22c facing the first opening 23 is provided on the upper wall surface 12. The convex portion 22c is formed so as to project from the upper wall surface 12 toward the first opening 23 of the first branch pipe 22. The convex portion 22c has a tapered shape whose diameter decreases toward the first opening 23 at the tip of the first branch pipe 22. The tip of the convex portion 22c is arranged at a vertical interval from the first branch pipe 22. The tip of the convex portion 22c is provided at a position overlapping the first opening 23 in plan view. The diameter of the base end of the convex portion 22c is set larger than the diameter of the first opening 23.

[0082] Accordingly, when sucking gas from the first opening 23, a flow along the outer peripheral surface of the convex portion 22c can be induced. Therefore, the suction flow rate of the gas staying on the upper wall surface 12 can be increased, and the gas can be discharged smoothly. Note that the convex portion 22c may be provided so as to face the second opening 33 of the second branch pipe 32 of the second pipe 30.

[0083] <Eighth Embodiment> Next, a description will be given of an eighth embodiment of the present disclosure with reference to FIG. 9. In the eighth embodiment, the same reference numerals are given to the same components as those in the other embodiments, and the detailed description thereof will be omitted. The eighth embodiment is configured such that an elastic tube 22d is provided at the tip of the first branch pipe 22. The elastic tube 22d is made of an elastic material such as rubber. The proximal end of the elastic tube 22d is attached to the tip of the first branch pipe 22 so as to cover it from the outer peripheral side. The elastic tube 22d extends upward from the tip of the first branch pipe 22 and is bent horizontally by contacting the upper wall surface 12. As a result, the opening at the tip of the elastic tube 22d faces horizontally. In the present embodiment, the opening of the elastic tube 22d is the first opening 23 in the first pipe 20.

[0084] Accordingly, the first opening 23 can be brought as close as possible to the upper wall surface 12. Therefore, the gas staying on the upper wall surface 12 can be efficiently and reliably recovered. Further, even when thermal expansion of the first branch pipe 22 occurs, it is possible to avoid the first branch pipe 22 and the upper wall surface 12 from coming into contact with each other.

[0085] <Other Embodiments> As described above, the embodiments of the present disclosure have been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and design changes and the like within a range not departing from the gist of the present disclosure are also included. For example, the third to eighth embodiments may be applied to the spherical tank 110 of the second embodiment. Further, a cylindrical tank may be employed instead of the rectangular tank or the spherical tank. In this case, the first pipe 20 is provided along the top of the upper wall surface, and the second pipe 30 is provided along the bottom of the lower wall surface.

[0086] <Supplementary Note> The tank system 1 and the gas replacement method according to this embodiment are understood as follows. (1) The tank system 1 includes a tank capable of storing gas, a plurality of openings provided along the upper wall surfaces 12 and 112 in the tank, and a first pipe 20 that allows a first gas to flow in and out between the inside of the tank through these openings, and a plurality of openings provided along the lower wall surfaces 13 and 113 in the tank, and a second pipe 30 that allows a second gas having a density greater than that of the first gas to flow in and out between the inside of the tank through these openings.

[0087] Thereby, the replacement between the first gas and the second gas in the tank can be easily performed with simple equipment.

[0088] (2) In the tank system 1 of (2), the first pipe 20 has a header extending horizontally in the tank, and a plurality of branches provided at intervals in the extending direction of the header of the first pipe 20, extending from the base end communicating with the header of the first pipe 20 toward the upper wall surfaces 12 and 112, and having an opening of the first pipe 20 formed at the tip. The second pipe 30 has a header extending horizontally in the tank, and a plurality of branches provided at intervals in the extending direction of the header of the second pipe 30, extending from the base end communicating with the header of the second pipe 30 toward the lower wall surfaces 13 and 113, and having an opening of the second pipe 30 formed at the tip. It is the tank system 1 of (1).

[0089] Thereby, the supply and discharge of the first gas and the second gas can be smoothly performed.

[0090] (3) The tank system 1 of (3) is the tank system 1 of (2) in which the inner peripheral surface of the branch pipe expands in diameter from the base end toward the tip.

[0091] As a result, the opening area of the opening portion expands, so that the gas staying on the upper wall surfaces 12 and 112 and the lower wall surfaces 13 and 113 of the tank can be smoothly sucked in.

[0092] (4) The tank system 1 is the tank system 1 of (2) or (3) having a spiral structure 22a that protrudes from the inner peripheral surface of the branch pipe and is twisted in the extending direction of the branch pipe.

[0093] As a result, a spiral gas flow is induced in the branch pipe, thereby reducing the pressure in the branch pipe. Therefore, the gas can be smoothly sucked in.

[0094] (5) The tank system 1 is the tank system 1 of (2) to (4) provided at the tip of the branch pipe and having a flange 22b that protrudes in the radial direction of the branch pipe.

[0095] As a result, the gas staying on the upper wall surfaces 12 and 112 and the lower wall surfaces 13 and 113 of the tank can be smoothly sucked in.

[0096] (6) The tank system 1 is any one of the tank systems 1 of (2) to (5) provided on the inner surfaces 11 and 111 of the tank and having a convex portion 22c that protrudes toward the tip of the branch pipe and whose diameter decreases toward the tip.

[0097] As a result, a gas flow toward the opening of the branch pipe can be formed.

[0098] (7) The tank system 1 is any one of the tank systems 1 of (2) to (6) connected to the tip of the branch pipe and having an elastic tube 22d formed of an elastic body and extending in a direction away from the tip of the branch pipe.

[0099] As a result, an opening can be brought into contact with the upper wall surfaces 12 and 112 or the lower wall surfaces 13 and 113.

[0100] The tank system 1 of (8) has a header in which the first pipe 20 extends horizontally in the tank and a plurality of openings of the first pipe 20 are formed at intervals in the extending direction, and the second pipe 30 extends horizontally in the tank and has a header in which a plurality of openings of the second pipe 30 are formed at intervals in the extending direction. It is the tank system 1 of (1).

[0101] Also by this, the supply and discharge of the first gas and the second gas can be smoothly performed.

[0102] The tank system 1 of (9) has a concave curved surface that is recessed upward in the upper wall surface 112, and the plurality of openings of the first pipe 20 are arranged along the concave curved upper wall surfaces 12 and 112 so that the heights of adjacent first openings 23 are different from each other. It is the tank system 1 of any one of (1) to (8).

[0103] Thereby, for example, the replacement of the second gas with the first gas in a spherical tank can be easily performed with simple equipment.

[0104] The tank system 1 of (10) has a concave curved surface that is recessed downward in the lower wall surface 113, and the plurality of second openings 33 are arranged along the concave curved lower wall surfaces 13 and 113 so that the heights of adjacent second openings 33 are different from each other. It is the tank system 1 of any one of (1) to (9).

[0105] Also by this, for example, the replacement of the first gas with the second gas in a spherical tank can be easily performed with simple equipment.

[0106] The tank system 1 of (11) further includes an internal valve provided between adjacent openings in the header having different heights from each other. It is the tank system 1 of (9) or (10).

[0107] By closing the internal valve from the open state at an appropriate timing, unintended gas suction can be avoided.

[0108] The tank system 1 of (12) is the tank system 1 of any one of (1) to (11), further comprising a gas sensor 70 provided at a plurality of vertically spaced positions within the tank and capable of detecting the components of the gas within the tank.

[0109] Thereby, the progress of gas replacement can be confirmed.

[0110] The tank system 1 of (13) is the tank system 1 of (11), further comprising a gas sensor 70 provided at a plurality of vertically spaced positions within the tank and capable of detecting the components of the gas within the tank, and at least one of the plurality of gas sensors 70 is provided at a height position between a pair of adjacent openings arranged so as to sandwich the internal valve from above and below.

[0111] Thereby, unintended gas suction can be avoided.

[0112] The tank system 1 of (14) is the tank system 1 of any one of (1) to (13), comprising a first gas supply / discharge unit 40 capable of supplying the first gas to the first pipe 20 and discharging the gas within the tank through the first pipe 20, and a second gas supply / discharge unit 50 capable of supplying the second gas to the second pipe 30 and discharging the gas within the tank through the second pipe 30.

[0113] Thereby, the replacement between the first gas and the second gas can be appropriately performed.

[0114] The tank system 1 of (15) is the tank system 1 of (14), further comprising an inert gas supply unit 60 capable of supplying an inert gas as the first gas to the first pipe 20 and supplying an inert gas as the second gas to the second pipe 30.

[0115] Accordingly, replacement of the first gas with the inert gas or replacement of the second gas with the inert gas can be performed.

[0116] The gas replacement method of (16) is a gas replacement method using any one of the tank systems 1 of (1) to (15), and includes a step of discharging the first gas in the tank through the opening of the first pipe 20 while supplying the second gas into the tank through the opening of the second pipe 30 in the tank in which the first gas is stored.

[0117] The gas replacement method of (17) is a gas replacement method using any one of the tank systems 1 of (1) to (15), and includes a step of discharging the second gas in the tank through the opening of the second pipe while supplying the first gas into the tank through the opening of the first pipe 20 in the tank in which the second gas is stored.

[0118] The gas replacement method of (18) is a gas replacement method using the tank system 1 of (13), and includes a step of discharging the second gas in the tank through the opening of the second pipe while supplying the first gas into the tank through the opening of the first pipe 20 in the tank in which the second gas is stored, and a step of closing the internal valve provided in the second pipe 30 when the component of the gas detected by the gas sensor 70 changes from the second gas to the first gas.

[0119] The gas replacement method of (19) is a gas replacement method using the tank system 1 of (13), and includes a step of discharging the first gas in the tank through the opening of the first pipe 20 while supplying the second gas into the tank through the opening of the second pipe 30 in the tank in which the first gas is stored, and a step of closing the internal valve provided in the second pipe 30 when the component of the gas detected by the gas sensor 70 provided at the height position between a pair of adjacent openings arranged so as to sandwich the internal valve from above and below changes from the first gas to the first gas.

Explanation of Reference Numerals

[0120] 1 Tank system 10 Square tank 11 Inner surface 12 Upper wall surface 13 Lower wall surface 20 First pipe 21 First header 22 First branch pipe 22a Spiral structure 22b Flange 22c Protrusion 22d Elastic tube 23 First opening 24 First internal valve 30 Second pipe 31 Second header 32 Second branch pipe 33 Second opening 34 Second internal valve 40 First gas supply / discharge section 41 First gas tank 42 First gas pipe 43 First supply / discharge pipe 44 First gas valve 45 First exhaust valve 50 Second gas supply / discharge section 51 Second gas tank 52 Second gas pipe 53 Second supply / discharge pipe 54 Second gas valve 55 Second exhaust valve 60 Inert gas supply section 61 Inert gas source 62 First inert pipe 63 First inert valve 64 Second inert pipe 65 Second inert valve 70 Gas sensor 110 Spherical tank 111 Inner surface 112 Upper wall surface 113 Lower wall surface R Accommodation space

Claims

1. A tank capable of storing gas, A first pipe having a plurality of openings provided along the upper wall surface in the tank, and through which a first gas flows in and out between the inside of the tank, A second pipe having a plurality of openings provided along the lower wall surface in the tank, and through which a second gas having a density greater than that of the first gas flows in and out between the inside of the tank, A tank system comprising:

2. The first pipe is A header extending horizontally in the tank, A plurality of branch pipes provided at intervals in the extending direction of the header of the first pipe, extending from the base end communicating with the header of the first pipe toward the upper wall surface, and having the opening of the first pipe formed at the tip, And having The second pipe is A header extending horizontally in the tank, A plurality of branch pipes provided at intervals in the extending direction of the header of the second pipe, extending from the base end communicating with the header of the second pipe toward the lower wall surface, and having the opening of the second pipe formed at the tip, The tank system according to claim 1, having

3. The tank system according to claim 2, wherein the inner peripheral surface of the branch pipe expands in diameter from the base end toward the tip.

4. The tank system according to claim 3, having a spiral structure that protrudes or recesses from the inner peripheral surface of the branch pipe and twists in the extending direction of the branch pipe.

5. The tank system according to claim 2, having a flange provided at the tip of the branch pipe and protruding in the radial direction of the branch pipe.

6. The tank system according to claim 2, having a convex portion provided on the inner surface of the tank, protruding toward the tip of the branch pipe and having a reduced diameter toward the tip.

7. The tank system according to claim 2, having an elastic tube connected to the tip of the branch pipe, extending in a direction away from the tip of the branch pipe, and formed of an elastic body.

8. The first pipe is Extending horizontally in the tank and having a header with a plurality of the openings of the first pipe formed at intervals in the extending direction, The second pipe is Extending horizontally in the tank and having a header with a plurality of the openings of the second pipe formed at intervals in the extending direction, the tank system according to claim 1.

9. The upper wall surface has a concave curved surface shape that is concave upward, The tank system according to claim 2, wherein the plurality of openings of the first pipe are arranged such that the heights of adjacent ones of the openings are different from each other along the concave curved upper wall surface.

10. The lower wall surface has a concave curved shape that is concave downward, The tank system according to claim 2, wherein the plurality of openings of the second pipe are arranged such that the heights of adjacent ones of the openings are different from each other along the concave curved lower wall surface.

11. The tank system according to claim 9 or 10, further comprising an internal valve provided between the openings in the header.

12. The tank system according to any one of claims 1 to 10, further comprising a gas sensor provided at a plurality of vertically spaced positions within the tank and capable of detecting the components of the gas in the tank.

13. The tank system further comprises a gas sensor provided at a plurality of vertically spaced positions within the tank and capable of detecting the components of the gas in the tank, The tank system according to claim 11, wherein at least one of the plurality of gas sensors is provided at a height position between a pair of the openings arranged so as to sandwich the internal valve from above and below.

14. A first gas supply / discharge unit capable of supplying the first gas to the first pipe and discharging the gas in the tank through the first pipe, A second gas supply / discharge unit capable of supplying the second gas to the second pipe and discharging the gas in the tank through the second pipe, The tank system according to claim 1.

15. The tank system according to claim 14, further comprising an inert gas supply unit capable of supplying an inert gas as the first gas to the first pipe and capable of supplying an inert gas as the second gas to the second pipe.

16. A gas replacement method using the tank system according to any one of claims 1 to 10, comprising: A step of discharging the first gas in the tank through the opening of the first pipe while supplying the second gas through the opening of the second pipe into the tank in which the first gas is stored.

17. A gas replacement method using the tank system according to any one of claims 1 to 10, A gas replacement method including a step of discharging the second gas in the tank through the opening of the second pipe while supplying the first gas into the tank storing the second gas through the opening of the first pipe.

18. A gas replacement method using the tank system according to claim 13, a step of discharging the first gas in the tank through the opening of the first pipe while supplying the second gas into the tank storing the first gas through the opening of the second pipe; a step of closing the internal valve provided in the first pipe when the component of the gas detected by the gas sensor at the height position between a pair of adjacent openings arranged to sandwich the internal valve provided in the first pipe from above and below changes from the first gas to the first gas; A gas replacement method including the above.

19. A gas replacement method using the tank system according to claim 13, a step of discharging the second gas in the tank through the opening of the second pipe while supplying the first gas into the tank storing the second gas through the opening of the first pipe; a step of closing the internal valve provided in the second pipe when the component of the gas detected by the gas sensor at the height position between a pair of adjacent openings arranged to sandwich the internal valve provided in the second pipe from above and below changes from the second gas to the second gas; A gas replacement method including the above.

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