JP7833944B2 - Maintenance methods for liquefied gas tanks and pumps for liquefied gas tanks - Google Patents

Description

This disclosure relates to a liquefied gas tank for storing liquefied gas.

Liquefied gas tanks, which store liquefied gases such as liquefied hydrogen and liquefied natural gas, are equipped with pumps to discharge the liquefied gas from the tank. When discharging the liquefied gas through the tank roof, the pump is located inside the tank, and the liquefied gas is sent to the outside through a cylindrical pump barrel that penetrates the tank roof.

Here, as shown in Patent Document 1 below, for example, there are cases where the pump inside the tank needs to be removed from the tank for maintenance or other purposes. Specifically, in Patent Document 1, the pump is lifted using a winch installed on the tank roof and removed from the tank through the pump barrel.

Japanese Patent Publication No. 2017-132619

As mentioned above, when removing the pump from the tank, the upper end of the pump barrel is opened, which could lead to improper gas inflow or outflow. For example, there is a concern that gas corresponding to the liquefied gas in the tank may be dispersed into the atmosphere through the pump barrel, or that air or other substances may be mixed into the tank through the pump barrel. This can also occur when moving the pump into the tank.

This disclosure is made in view of the circumstances described above, and aims to provide a liquefied gas tank that can prevent improper gas inflow and outflow through the pump barrel during pump loading and unloading.

To solve the aforementioned problems, a liquefied gas tank according to one aspect of this disclosure comprises a tank body for storing liquefied gas, a pump disposed within the tank body for discharging the liquefied gas, a cylindrical pump barrel including a lower chamber housing the pump and extending upward from its housing position to the outside of the tank body, an intermediate chamber located above the lower chamber, and an upper chamber located above the intermediate chamber, a first on-off valve provided to be openable and closable between the upper chamber and the intermediate chamber, a second on-off valve provided to be openable and closable between the intermediate chamber and the lower chamber, and a gas replacement device capable of switching the gas in the intermediate chamber and the upper chamber between a gas corresponding to the liquefied gas and an inert gas.

The liquefied gas tank of this disclosure can prevent improper gas inflow and outflow through the pump barrel during pump loading and unloading.

This is a schematic diagram showing the structure of a liquefied gas tank according to one embodiment of the present disclosure. This is a partially enlarged view of Figure 1, showing details of the pump barrel and its surrounding structure. This is a diagram illustrating the procedure for removing the pump. This is a diagram illustrating the procedure for installing a pump.

The liquefied gas tank according to the embodiments of this disclosure will be described in detail below with reference to the drawings. The liquefied gas tank of this disclosure is a tank for storing low-temperature liquefied gases. The stored liquefied gases include, for example, liquefied hydrogen, liquid helium, liquid nitrogen, liquefied ammonia, liquefied natural gas, or liquefied petroleum gas. In particular, the liquefied gas tank according to this disclosure is suitable as a tank for storing liquefied hydrogen.

[Overall structure of the tank]
Figure 1 is a schematic diagram showing the structure of a liquefied gas tank 1 according to one embodiment of the present disclosure. The liquefied gas tank 1 is a tank for storing cryogenic liquefied hydrogen LH, and is a flat-bottomed tank with a multi-shell structure that is installed on the ground. The liquefied gas tank 1 comprises a tank body 10, a pump barrel 2, a pump 3, a lifting device 4, a valve device 5, and a gas replacement device 6. The tank body 10 is a dome-shaped container for storing liquefied hydrogen LH. The pump 3 is a submersible pump positioned inside the tank body 10 while immersed in liquefied hydrogen LH. The pump barrel 2 is a cylindrical body extending vertically through which the liquefied hydrogen LH discharged from the tank body 10 by the pump 3 flows. The lifting device 4 is a device for lifting the pump 3 through the pump barrel 2 when necessary for maintenance, etc. The valve device 5 is a device that can open and close the internal flow path of the pump barrel 2. The gas replacement device 6 is a device that replaces the gas in the upper part of the pump barrel 2 (the intermediate chamber 22 and upper chamber 23, which will be described later).

The tank body 10 is a sealed body that defines a space for storing liquefied hydrogen (LH) internally. While Figure 1 simplifies the tank body 10 to show a single-shell structure, the actual tank body 10 has a multi-shell structure, such as a double-shell or triple-shell structure. In the case of a double-shell structure, the tank body 10 consists of an outer tank erected on a foundation and an inner tank enclosed within the outer tank. The liquefied hydrogen (LH) is stored inside the inner tank. A thermal insulation layer is formed between the outer tank and the inner tank, and this thermal insulation layer is filled with a powdered insulating material, such as granular perlite, and a low-boiling-point gas. In the case of a triple-shell structure, the tank body 10 has an intermediate tank between the outer tank and the inner tank.

Figure 2 is a partially enlarged view of Figure 1, showing details of the pump barrel 2 and its surrounding structure. As shown in Figures 1 and 2, the pump barrel 2 penetrates the tank roof 11, connecting the inside and outside of the tank body 10. That is, the pump barrel 2 is formed to extend vertically, penetrating the tank roof 11, from a height near the bottom of the tank body 10 to a height above the tank roof 11. The pump barrel 2 functions as a discharge pipe for discharging liquefied hydrogen LH from the tank body 10 to the outside.

The valve device 5 comprises a first on-off valve 51, a second on-off valve 52, and a third on-off valve 53. Each of the first to third on-off valves 51 to 53 is a valve that can be switched between an open state, which opens the internal flow path of the pump barrel 2, and a closed state, which closes the internal flow path. The first to third on-off valves 51 to 53 are arranged in the middle of the pump barrel 2, from top to bottom, in the order of the first on-off valve 51, the third on-off valve 53, and the second on-off valve 52. That is, the third on-off valve 53 is positioned below the first on-off valve 51, and the second on-off valve 52 is positioned below the third on-off valve 53.

The pump barrel 2 comprises a lower chamber 21 located below the second on-off valve 52, an upper chamber 23 located above the first on-off valve 51, and an intermediate chamber 22 formed between the lower chamber 21 and the upper chamber 23 (in other words, between the first on-off valve 51 and the second on-off valve 52).

The lower chamber 21 is a straight cylindrical body with a substantially constant cross-section in the vertical direction. It extends upward from a position corresponding to the pump 3 inside the tank body 10 to the outside of the tank body 10 (above the tank roof 11). The lower chamber 21 has a lower end 21a that houses the pump 3 and an upper end 21b that protrudes above the tank roof 11. A discharge port 24 is provided protruding from the upper end 21b. The discharge port 24 is a port for discharging liquefied hydrogen L discharged when the pump 3 is operating to the outside.

The intermediate chamber 22 is a cylindrical body having the same diameter as the lower chamber 21 and is coaxially mounted between the lower chamber 21 and the upper chamber 23. In this embodiment, the intermediate chamber 22 is defined into two chambers by the first to third on-off valves 51 to 53. Specifically, the intermediate chamber 22 has a short cylindrical first intermediate chamber 221 formed between the first on-off valve 51 and the third on-off valve 53, and a short cylindrical second intermediate chamber 222 formed between the second on-off valve 52 and the third on-off valve 53.

The upper chamber 23 is a cylindrical body formed so that its cross-sectional area expands midway. Specifically, the upper chamber 23 has a small-diameter section 23a having the same diameter as the lower chamber 21 and the intermediate chamber 22, a large-diameter section 23b having a larger diameter than the small-diameter section 23a, and an intermediate section 23c connecting the small-diameter section 23a and the large-diameter section 23b. The small-diameter section 23a is coaxially connected to the first intermediate chamber 221 via the first on-off valve 51. The intermediate section 23c is formed so that its inner diameter increases towards the upper part closer to the large-diameter section 23b. The large-diameter section 23b is formed to extend upward from the upper end of the intermediate section 23c with the same diameter as that upper end.

A head plate 25 is detachably attached to the upper end of the upper chamber 23 (large-diameter section 23b). That is, the head plate 25 is a plate that can be opened and closed to close the upper opening of the upper chamber 23. A hanging handle 25a is provided protruding from the upper surface of the head plate 25.

Pump 3 is housed in the lower end 21a of the pump barrel 2 (lower chamber 21) and positioned within the tank body 10, immersed in liquefied hydrogen L. A foot valve 26 is attached to the lower end 21a of the pump barrel 2 to open and close the intake port, which is its lower opening. Pump 3 is mounted on the foot valve 26, and the weight of the pump 3 causes the foot valve 26 to descend, opening the intake port of the pump barrel 2. When the pump 3 is driven with the intake port open in this manner, it draws in liquefied hydrogen LH from the tank body 10 through the intake port, pumps it upward, and discharges the liquefied hydrogen LH to the outside through the pump barrel 2 (lower chamber 21).

The lifting device 4 is located inside the upper chamber 23 of the pump barrel 2. The lifting device 4 is a winch capable of lifting the pump 3, which is housed in the lower end 21a of the pump barrel 2 (lower chamber 21), up to the upper chamber 23. Specifically, the lifting device 4 comprises a drum 41 that is rotatable around a horizontal axis and a lifting wire 42 that connects the drum 41 and the pump 3. The lifting wire 42 is wound around the drum 41 and is routed to extend downward from the drum 41 to the pump 3. The drum 41 is a drum that can rotate in the forward direction to wind up the lifting wire 42 and in the reverse direction to pull out the lifting wire 42, and is supported by a support member 43 fixed to the lower surface of the head plate 25. That is, the drum 41 is rotatably supported inside the upper chamber 23 by being attached to the lower surface of the head plate 25 via the support member 43. Furthermore, the lifting device 4 may further include a drive source for rotating the drum 41 in both forward and reverse directions. As the drive source, an appropriate type may be used, such as a pneumatic type using gas or an electric type using electricity.

The first on-off valve 51 is positioned between the upper chamber 23 and the first intermediate chamber 221, and is switchable between an open state that connects the upper chamber 23 and the first intermediate chamber 221 and a closed state that blocks communication between them. The second on-off valve 52 is positioned between the second intermediate chamber 222 and the lower chamber 21, and is switchable between an open state that connects the second intermediate chamber 222 and the lower chamber 21 and a closed state that blocks communication between them. The third on-off valve 53 is positioned between the first intermediate chamber 221 and the second intermediate chamber 222, and is switchable between an open state that connects the first intermediate chamber 221 and the second intermediate chamber 222 and a closed state that blocks communication between them.

In the diagram, a symbol representing a valve being blacked out indicates that the valve is closed, while a symbol representing a valve not being blacked out indicates that the valve is open. As shown in Figures 1 and 2, during operation of the liquefied gas tank 1, the first to third on-off valves 51 to 53 are kept in the open state. The suspension wire 42 is routed to extend from the upper chamber 23 to the lower chamber 21, passing through each of the open on-off valves 51 to 53, and connects the pump 3 at the lower end 21a of the lower chamber 21 to the drum 41 in the upper chamber 23. On the other hand, when removing the pump 3 from the tank body 10 for maintenance or other purposes, the pump 3 is lifted from the lower chamber 21 to the upper chamber 23 by the lifting device 4. At this time, the first to third on-off valves 51 to 53 are kept in the open state until the pump 3 has moved to the upper chamber 23, and are switched to the closed state after the move is complete. To allow the pump 3 to move between the lower chamber 21 and the upper chamber 23, the first to third on-off valves 51 to 53 each have valve bodies that allow the pump 3 to pass through when open. Ball valves with hollow ball-shaped valve bodies are preferred as such on-off valves 51 to 53.

The gas replacement device 6 is a device that replaces the gas in the intermediate chamber 22 (first and second intermediate chambers 221, 222) and the upper chamber 23 when necessary, such as when the pump 3 is withdrawn. The gas replacement device 6 comprises a hydrogen gas supply source 60, a nitrogen gas supply source 61, a first hydrogen gas inlet pipe 62, a second hydrogen gas inlet pipe 63, a first nitrogen gas inlet pipe 64, a second nitrogen gas inlet pipe 65, first to fourth gas outlet pipes 66 to 69, and first to eighth valves 70A to 70H.

The hydrogen gas supply source 60 is a supply source that supplies the gas corresponding to the liquefied gas (in this case, liquefied hydrogen LH) stored in the tank body 10, i.e., hydrogen gas, and includes, for example, a gas pump capable of pumping hydrogen gas. The nitrogen gas supply source 61 is a supply source that supplies nitrogen gas as an inert gas, and includes, for example, a gas pump capable of pumping nitrogen gas. Note that the hydrogen gas supply source 60 corresponds to the first supply source in this disclosure, and the nitrogen gas supply source 61 corresponds to the second supply source in this disclosure.

The first hydrogen gas inlet pipe 62 is a pipe connecting the hydrogen gas supply source 60 and the upper chamber 23. The second hydrogen gas inlet pipe 63 is a pipe connecting the hydrogen gas supply source 60 and the second intermediate chamber 222. The first nitrogen gas inlet pipe 64 is a pipe connecting the nitrogen gas supply source 61 and the upper chamber 23. The second nitrogen gas inlet pipe 65 is a pipe connecting the nitrogen gas supply source 61 and the first intermediate chamber 221. The first gas outlet pipe 66 and the second gas outlet pipe 67 are pipes connected to the upper chamber 23 for discharging the replaced gas. The third gas outlet pipe 68 is a pipe connected to the first intermediate chamber 221 for discharging the replaced gas. The fourth gas outlet pipe 69 is a pipe connected to the second intermediate chamber 222 for discharging the replaced gas. The first and second hydrogen gas inlet pipes 62, 63 and the first and second nitrogen gas inlet pipes 64, 65 correspond to the inlet section in this disclosure. In particular, the first and second hydrogen gas inlet pipes 62 and 63 correspond to the first gas inlet pipe in this disclosure, and the first and second nitrogen gas inlet pipes 64 and 65 correspond to the second gas inlet pipe in this disclosure. Furthermore, the first to fourth gas outlet pipes 66 to 69 correspond to the outlet sections in this disclosure.

The first valve 70A is a valve that can be opened and closed on the first hydrogen gas inlet pipe 62. The second valve 70B is a valve that can be opened and closed on the first nitrogen gas inlet pipe 64. The third valve 70C is a valve that can be opened and closed on the second nitrogen gas inlet pipe 65. The fourth valve 70D is a valve that can be opened and closed on the second hydrogen gas inlet pipe 63. The fifth valve 70E is a valve that can be opened and closed on the first gas outlet pipe 66. The sixth valve 70F is a valve that can be opened and closed on the second gas outlet pipe 67. The seventh valve 70G is a valve that can be opened and closed on the third gas outlet pipe 68. The eighth valve 70H is a valve that can be opened and closed on the fourth gas outlet pipe 69.

The gas replacement device 6 is capable of performing gas replacement by switching the gas in the intermediate chambers 22 (first and second intermediate chambers 221, 222) and the upper chamber 23 between hydrogen gas supplied from the hydrogen gas supply source 60 and nitrogen gas supplied from the nitrogen gas supply source 61. During this gas replacement, the first to eighth valves 70A to 70H are opened as needed. On the other hand, during operation of the liquefied gas tank 1, as shown in Figures 1 and 2, the first to eighth valves 70A to 70H are all kept closed.

[Pump removal work]
As mentioned above, the pump 3 may be removed from the tank body 10, for example, for maintenance. The details of this procedure will be explained using Figure 3.

Prior to the removal of pump 3 (Figure 3), the first step is to push the liquefied hydrogen LH in the pump barrel 2 into the tank body 10. During operation of the liquefied gas tank 1, liquefied hydrogen LH is present inside the pump barrel 2. Generally, except when discharging liquefied hydrogen LH, the liquefied hydrogen LH in the pump barrel 2 is present up to the same height as the liquid level in the tank body 10. From the viewpoint of reducing the lifting resistance of pump 3 or suppressing liquid entrapment, it is desirable that there is no liquid in the pump barrel 2 when pump 3 is removed. Therefore, in this embodiment, as preparation before removing pump 3, a gas corresponding to the stored liquefied gas (in this case, liquefied hydrogen LH), i.e., hydrogen gas, is supplied to the pump barrel 2 from the discharge port 24. At this time, the first to eighth valves 70A to 70H are all kept closed. Then, the liquefied hydrogen LH in the pump barrel 2 is pushed back into the tank body 10 by the hydrogen gas supplied from the discharge port 24. This results in the pump barrel 2 being completely filled with hydrogen gas. Note that this extrusion of liquefied hydrogen (LH) can be performed only as needed and can be omitted.

Next, as shown in step 1-1 of Figure 3, the pump 3 is lifted to the upper chamber 23 using the lifting device 4. During this lifting, the first to third on-off valves 51 to 53 are kept open, just as they are during operation of the liquefied gas tank 1. The lifted pump 3 moves from the lower chamber 21 to the upper chamber 23 of the pump barrel 2, passing through the open on-off valves 51 to 53. Furthermore, the first to eighth valves 70A to 70H are all kept closed until the pump 3 has completed its movement to the upper chamber 23. This ensures that the upper chamber 23, the first intermediate chamber 221, and the second intermediate chamber 222 remain filled with hydrogen gas until the pump 3 has completed its movement (lifting).

Next, as shown in step 1-2 of Figure 3, the gas in the upper chamber 23 and the first intermediate chamber 221 is replaced from hydrogen gas to nitrogen gas. Specifically, while keeping the first on-off valve 51 in the open state, the second and third on-off valves 52 and 53 are switched from the open state to the closed state. Also, while keeping the first, second, and sixth valves 70A, 70B, and 70F in the closed state, the third, fourth, fifth, seventh, and eighth valves 70C, 70D, 70E, 70G, and 70H are switched from the closed state to the open state. As a result, with the communication between the first intermediate chamber 221 and the second intermediate chamber 222, and the communication between the second intermediate chamber 222 and the lower chamber 21 respectively blocked, nitrogen gas is introduced into the first intermediate chamber 221 from the second nitrogen gas introduction pipe 65, and hydrogen gas is introduced into the second intermediate chamber 222 from the second hydrogen gas introduction pipe 63. This results in the replacement of the gas in the upper chamber 23 and the first intermediate chamber 221.

In other words, nitrogen gas from the second nitrogen gas inlet pipe 65 is not only introduced into the first intermediate chamber 221, but also into the upper chamber 23 through the first on-off valve 51, which is in an open state. This introduction of nitrogen gas fills the first intermediate chamber 221 and the upper chamber 23 with nitrogen gas, while the hydrogen gas present in the first intermediate chamber 221 and the upper chamber 23 is pushed out to the first gas outlet pipe 66 and the third gas outlet pipe 68. In other words, the state in which the first intermediate chamber 221 and the upper chamber 23 are filled is switched from a state where they are filled with hydrogen gas to a state where they are filled with nitrogen gas. Meanwhile, hydrogen gas from the second hydrogen gas inlet pipe 63 is discharged through the second intermediate chamber 222 to the fourth gas outlet pipe 69. This maintains the second intermediate chamber 222 in a state where it is filled with hydrogen gas. While details are omitted here, if gas is discharged from outlet pipes 66-69 (especially hydrogen gas), it is desirable to recover this exhaust gas. Therefore, it is desirable to connect recovery devices to outlet pipes 66-69 as appropriate.

Next, as shown in step 1-3 of Figure 3, the head plate 25 is removed from the upper chamber 23, and the lifting device 4 and pump 3 are transported out together with the head plate 25. Specifically, the fixing means such as bolts securing the head plate 25 are released, and the head plate 25 is transported out using a pre-prepared external transport device such as a winch. For example, with the wire W extending from the external transport device attached to the lifting handle 25a of the head plate 25, the external transport device is operated to transport the head plate 25 to a predetermined destination. Once the head plate 25 is removed through this transport, the upper surface of the upper chamber 23 is opened, and the gas (nitrogen gas) inside the upper chamber 23 is replaced with air as appropriate. Here, the lifting device 4 is fixed to the head plate 25, and the lifting device 4 holds the pump 3 by a lifting wire 42. Therefore, when the head plate 25 is transported out, the lifting device 4 and pump 3 are also transported out together with the head plate 25.

The removal of the pump 3 (removal of the head plate 25) described above is performed with the first to third on-off valves 51 to 53 all closed. That is, after step 1-2, the operation is performed to switch the first on-off valve 51 from the open state to the closed state while maintaining the second on-off valve 52 and the third on-off valve 53 in the closed state, and the pump 3 is removed in that state. Also, before the removal of the pump 3, the fifth valve 70E is switched from the open state to the closed state. On the other hand, the other valves other than the fifth valve 70E, namely the first to fourth valves 70A to 70D and the sixth to eighth valves 70F to 70H, remain unchanged from the state in step 1-2. As a result, from step 1-2 to step 1-3, the supply of nitrogen gas from the second nitrogen gas inlet pipe 65 and the supply of hydrogen gas from the second hydrogen gas inlet pipe 63 are both continued. This gas supply ensures that the first intermediate chamber 221 is filled with nitrogen gas and the second intermediate chamber 222 is filled with hydrogen gas during the discharge of pump 3.

With the above steps completed, the process of removing the pump 3 from the tank body 10 is finished. The removed pump 3 will be subjected to maintenance and other prescribed procedures at the destination. In the pump removal process described above (Figure 3), step 1-1, which involves lifting the pump 3 from the lower chamber 21 to the upper chamber 23, corresponds to the first step in this disclosure; step 1-2, which involves replacing the gas in the upper chamber 23 and the first intermediate chamber 221 from hydrogen gas to nitrogen gas and filling the second intermediate chamber 222 with hydrogen gas, corresponds to the second step in this disclosure; and step 1-3, which involves opening the upper chamber 23 and removing the pump 3 from the upper chamber 23, corresponds to the third step in this disclosure.

[Pump installation work]
Next, the process of installing the pump 3 onto the tank body 10 will be explained using Figure 4.

First, the head plate 25 is fixed to the upper surface of the upper chamber 23, and the lifting device 4 and pump 3 are inserted into the upper chamber 23. This operation is the reverse of steps 1-3 in Figure 3, and is achieved by fixing the head plate 25, along with the lifting device 4 and pump 3, to the upper surface of the upper chamber 23. The fixing of the head plate 25 traps air inside the upper chamber 23.

Next, as shown in step 2-1 of Figure 4, the gas in the upper chamber 23 is replaced from air to nitrogen gas. Specifically, the first to third on-off valves 51 to 53 and the first and sixth valves 70A and 70F are kept closed, and the third, fourth, seventh, and eighth valves 70C, 70D, 70G, and 70H are kept open, while the second and fifth valves 70B and 70E are switched from closed to open. As a result, nitrogen gas is introduced into the upper chamber 23 from the first nitrogen gas inlet pipe 64, and air is discharged from the upper chamber 23 through the first gas outlet pipe 66. In other words, the inside of the upper chamber 23 is switched from a state filled with air to a state filled with nitrogen gas. During this gas replacement of the upper chamber 23, the supply of gas (nitrogen gas or hydrogen gas) continues from the second nitrogen gas inlet pipe 65 and the second hydrogen gas inlet pipe 63, respectively. This ensures that the first intermediate chamber 221 is filled with nitrogen gas, while the second intermediate chamber 222 is filled with hydrogen gas.

Next, as shown in step 2-2 of Figure 4, the gas in the upper chamber 23 is replaced from nitrogen gas to hydrogen gas. Specifically, the first to third on-off valves 51 to 53 are kept closed, and the third, fourth, seventh, and eighth valves 70C, 70D, 70G, and 70H are kept open, while the first valve 70A and the sixth valve 70F are switched from closed to open, and the second and fifth valves 70B and 70E are switched from open to closed. As a result, hydrogen gas is introduced into the upper chamber 23 from the first hydrogen gas inlet pipe 62, and nitrogen gas is discharged from the upper chamber 23 through the second gas outlet pipe 67. In other words, the state in which the upper chamber 23 is filled with nitrogen gas is switched to a state in which it is filled with hydrogen gas. During this gas replacement of the upper chamber 23, the supply of gas (nitrogen gas or hydrogen gas) continues from the second nitrogen gas inlet pipe 65 and the second hydrogen gas inlet pipe 63, respectively. This ensures that the first intermediate chamber 221 is filled with nitrogen gas, while the second intermediate chamber 222 is filled with hydrogen gas.

Next, as shown in step 2-3 of Figure 4, the gas in the first intermediate chamber 221 is replaced from nitrogen gas to hydrogen gas. Specifically, while keeping the second and third on-off valves 52 and 53 and the second and fifth valves 70B and 70E in a closed state and keeping the first, fourth, seventh and eighth valves 70A, 70D, 70G and 70H in an open state, the first on-off valve 51 is switched from a closed state to an open state, and the third and sixth valves 70C and 70F are switched from an open state to a closed state. As a result, hydrogen gas is introduced into the first intermediate chamber 221 from the first hydrogen gas introduction pipe 62 through the first on-off valve 51, which is in an open state, and nitrogen gas is discharged from the first intermediate chamber 221 through the third gas outlet pipe 68. In other words, the state in which the inside of the first intermediate chamber 221 is filled with hydrogen gas is switched from a state in which it is filled with nitrogen gas. Furthermore, the second intermediate chamber 222 is maintained in a state of being filled with hydrogen gas by the continuous supply of hydrogen gas from the second hydrogen gas introduction pipe 63.

Next, the pump 3 is lowered from the upper chamber 23 to the lower end 21a of the lower chamber 21 using the lifting device 4. Before this lowering, the first to eighth valves 70A to 70H are all closed, and the first to third on-off valves 51 to 53 are all opened (see Figures 1 and 2). The pump 3 moves from the upper chamber 23 to the lower end 21a of the lower chamber 21, passing through the open on-off valves 51 to 53.

As a result, the pump 3 is returned to its proper storage position within the pump barrel 2 (the lower end 21a of the lower chamber 21), and the installation of the pump 3 into the tank body 10 is completed. In the pump 3 installation process described above (Figure 4), the operation of inserting the pump 3 into the upper chamber 23 (the operation preceding step 2-1) corresponds to step 4 in this disclosure; the operation of step 2-1, which replaces the gas in the upper chamber 23 from air to nitrogen gas, corresponds to step 5 in this disclosure; the operations of steps 2-2 and 2-3, which replace the gas in the upper chamber 23 and the first intermediate chamber 221 from nitrogen gas to hydrogen gas and fill the second intermediate chamber 222 with hydrogen gas, correspond to step 6 in this disclosure; and the operation of lowering the pump 3 from the upper chamber 23 to the lower chamber 21 (the operation following step 2-3) corresponds to step 7 in this disclosure.

[Effects and Effects]
As described above, in this embodiment, a first intermediate chamber 221 and a second intermediate chamber 222 are formed between the lower chamber 21 and the upper chamber 23 of the pump barrel 2, separated by first to third on-off valves 51 to 53. A gas replacement device 6 capable of filling the interiors of each intermediate chamber 221, 222 and the upper chamber 23 with hydrogen gas or nitrogen gas is applied to the pump barrel 2. This configuration has the advantage of preventing improper gas inflow and outflow through the pump barrel 2 when the pump 3 is being loaded or unloaded.

For example, when removing the pump 3 from the tank body 10 for maintenance or other purposes, the pump 3 is lifted from the lower chamber 21 to the upper chamber 23, and the gas in the first intermediate chamber 221 and the upper chamber 23 is replaced with nitrogen gas, an inert gas, using the gas replacement device 6. In this state, the pump 3 is then removed from the upper chamber 23 (see Figure 3). This prevents the gas corresponding to the stored liquefied gas (liquefied hydrogen LH), i.e., hydrogen gas, from being released into the atmosphere. On the other hand, when installing the pump 3 in the lower chamber 21 of the pump barrel 2, the gas in the first and second intermediate chambers 221, 222, and the upper chamber 23 is replaced with hydrogen gas using the gas replacement device 6. In this state, the pump 3 is then lowered from the upper chamber 23 to the lower chamber 21 (see Figure 4). This prevents gases other than hydrogen gas from entering the tank body 10.

Specifically, the gas replacement device 6 used in this embodiment comprises a hydrogen gas supply source 60 and a nitrogen gas supply source 61, a plurality of inlet pipes 62 to 65 for selectively introducing hydrogen and nitrogen gas supplied from each source into the intermediate chambers 221, 222 or the upper chamber 23, and a plurality of outlet pipes 66 to 69 for discharging gas from the intermediate chambers 221, 222 and the upper chamber 23. By using such a gas replacement device 6, the aforementioned gas replacement required during the loading and unloading of the pump 3 can be appropriately performed in this embodiment.

For example, when replacing the contents of the first intermediate chamber 221 and the upper chamber 23 with nitrogen gas before removing the pump 3, the nitrogen gas can be properly replaced by opening the first on-off valve 51 and closing the third on-off valve 53, introducing nitrogen gas into the first intermediate chamber 221 and the upper chamber 23 from, for example, the second nitrogen gas inlet pipe 65, and then discharging the introduced nitrogen gas from the first and third gas outlet pipes 66 and 68 (see step 1-2 in Figure 3). Then, by removing the pump 3 from the upper chamber 23 after the gas replacement (see step 1-3 in Figure 3), it is possible to prevent hydrogen gas from being released into the atmosphere from the upper chamber 23.

On the other hand, when replacing the contents of the first and second intermediate chambers 221, 222 and the upper chamber 23 with hydrogen gas before bringing in the pump 3, the first on-off valve 51 is opened and the second and third on-off valves 52, 53 are closed. For example, hydrogen gas is introduced into the upper chamber 23 and the first and second intermediate chambers 221, 222 from the first and second hydrogen gas introduction pipes 62, 63, and the introduced nitrogen gas is discharged from the third and fourth gas outlet pipes 68, 69 (see step 2-3 in Figure 4). This allows for proper replacement with hydrogen gas. Then, by moving the pump 3 from the upper chamber 23 to the lower chamber 21 after the gas replacement, it is possible to prevent other gases from entering the tank body 10.

Furthermore, in this embodiment, since a second intermediate chamber 222 is formed below the first intermediate chamber 221, filling the second intermediate chamber 222 with hydrogen gas during the loading and unloading of the pump 3 further reduces the possibility of improper gas inflow and outflow through the pump barrel 2.

For example, by closing both the second valve 52 and the third valve 53, introducing hydrogen gas from the second hydrogen gas inlet pipe 63 into the second intermediate chamber 222, and then discharging the introduced hydrogen gas from the fourth gas outlet pipe 69, the inside of the second intermediate chamber 222 can be kept filled with hydrogen gas. In this embodiment, since the pump 3 can be moved in and out while continuously filling the second intermediate chamber 222, located directly above the lower chamber 21, with hydrogen gas, it is possible to effectively prevent hydrogen gas from scattering into the atmosphere from the upper chamber 23, and to prevent other gases (such as nitrogen gas) from mixing into the tank body 10 through the lower chamber 21.

Specifically, when pump 3 is brought in, the second intermediate chamber 222 is filled with hydrogen gas, and the gas in the upper chamber 23 and the first intermediate chamber 221 is replaced from nitrogen gas to hydrogen gas (see Figure 4). By lowering pump 3 from the upper chamber 23 to the lower chamber 21 in this state, it is possible to effectively prevent nitrogen gas from mixing into the tank body 10. In this case, if the sealing performance of the closed third on-off valve 53 separating the first intermediate chamber 221 and the second intermediate chamber 222 is not perfect, it is expected that a small amount of nitrogen gas will leak from the first intermediate chamber 221 to the second intermediate chamber 222 through the third on-off valve 53. However, the leaked nitrogen gas will be diluted in the hydrogen gas filling the second intermediate chamber 222. This reduces the possibility of further nitrogen gas leakage from the second intermediate chamber 221 to the lower chamber 21 as much as possible, thus effectively preventing nitrogen gas from mixing into the tank body 10 through the lower chamber 21.

On the other hand, when removing the pump 3, the gas in the upper chamber 23 and the first intermediate chamber 221 is replaced from hydrogen gas to nitrogen gas while the second intermediate chamber 222 is filled with hydrogen gas (see step 1-2 in Figure 3). By removing the pump 3 from the upper chamber 23 in this state, it is possible to effectively prevent hydrogen gas from being released into the atmosphere from the upper chamber 23. In this case, if the sealing performance of the closed third on-off valve 53 separating the first intermediate chamber 221 and the second intermediate chamber 222 is not perfect, it is expected that a small amount of hydrogen gas will leak from the second intermediate chamber 222 to the first intermediate chamber 221 through the third on-off valve 53. However, the leaked hydrogen gas will be diluted in the nitrogen gas filling the first intermediate chamber 221. This reduces the possibility of further hydrogen gas leakage from the first intermediate chamber 221 to the upper chamber 23 as much as possible, thus effectively preventing hydrogen gas from being released into the atmosphere from the upper chamber 23.

As described above, in this embodiment, an intermediate chamber 22, consisting of a first intermediate chamber 221 and a second intermediate chamber 222, is formed between the lower chamber 21 and the upper chamber 23. By selectively filling the intermediate chamber 22 with nitrogen gas or hydrogen gas, the intermediate chamber 22 can be effectively utilized as a buffer to prevent the direct exchange of different gases between the lower chamber 21 and the upper chamber 23. This effectively prevents the dispersion of hydrogen gas into the atmosphere and the mixing of gases other than hydrogen gas into the tank body 10.

Furthermore, in this embodiment, a lifting device 4 capable of lifting the pump 3 from the lower chamber 21 to the upper chamber 23 of the pump barrel 2 is positioned in the upper chamber 23, making it relatively easy to remove the pump 3 from inside the tank body 10.

For example, when removing the pump 3 from the tank body 10, the pump 3 can be lifted by the lifting device 4 with all three valves 51-53 open, allowing the pump 3 to move from the lower chamber 21 to the upper chamber 23 of the pump barrel 2, and then the pump 3 can be removed from the upper chamber 23. Furthermore, after lifting the pump 3 to the upper chamber 23, the communication between the upper chamber 23 and the lower chamber 21 can be blocked by switching the first to third valves 51-53 from the open to the closed state. This prevents air from flowing from the upper chamber 23 to the lower chamber 21, while allowing the head plate 25 to be removed from the upper chamber 23, opening the upper chamber 23 and allowing the pump 3 to be easily removed from the upper chamber 23.

[Variations]
While preferred embodiments of the present disclosure have been described above, the disclosure is not limited thereto, and variations such as the following are possible.

In the above embodiment, in step 1-2 of Figure 3, where the gas in the upper chamber 23 and the first intermediate chamber 221 is replaced from hydrogen gas to nitrogen gas, the seventh valve 70G is switched from a closed state to an open state. However, the seventh valve 70G may remain in a closed state. In this case, the hydrogen gas from the first intermediate chamber 221 is discharged through the first gas outlet pipe 66 instead of the third gas outlet pipe 68. That is, the hydrogen gas in the first intermediate chamber 221 is pushed by the nitrogen gas introduced from the second nitrogen gas introduction pipe 65, moving from the first intermediate chamber 221 to the upper chamber 23 through the first on-off valve 51, which is in an open state, and then discharged to the outside from the upper chamber 23 through the first gas outlet pipe 66. Since nitrogen gas is heavier than hydrogen gas, such discharge of hydrogen gas can be carried out without any problems.

Furthermore, if the seventh valve 70G is kept closed in step 1-2 of Figure 3 as described above, then in the subsequent step 1-3, the seventh valve 70G is switched from the closed state to the open state. This allows the upper chamber 23 to be opened to the atmosphere while the first intermediate chamber 221 is kept filled with nitrogen gas.

In the above embodiment, the process of replacing the gas in the upper chamber 23 from nitrogen gas to hydrogen gas (step 2-2 in Figure 4) and the process of replacing the gas in the first intermediate chamber 221 from nitrogen gas to hydrogen gas (step 2-3 in Figure 4) were performed in this order. However, these gas replacements for the upper chamber 23 and the first intermediate chamber 221 may be performed simultaneously. That is, after step 2-1, in which the gas in the upper chamber 23 is replaced from air to nitrogen gas, the first on-off valve 51 and the first valve 70A are switched from the closed state to the open state, and the second, third, and fifth valves 70B, 70C, and 70E are switched from the open state to the closed state, thereby proceeding directly to step 2-3 without going through step 2-2. In this way, the replacement of nitrogen gas with hydrogen gas in the upper chamber 23 and the first intermediate chamber 221 can be performed simultaneously.

In the above embodiment, assuming that the liquefied gas stored in the liquefied gas tank 1 is liquefied hydrogen LH, a gas replacement device 6 capable of replacing the gas in the intermediate chambers 22 (first and second intermediate chambers 221, 222) and the upper chamber 23 of the pump barrel 2 with hydrogen gas or nitrogen gas was applied to the pump barrel 2. However, the gas replacement device only needs to be capable of replacing the gas in the intermediate chambers and upper chambers with a gas corresponding to the liquefied gas or an inert gas, and to that extent, the type of replacement gas can be changed as appropriate.

In the above embodiment, a lifting device 4 capable of lifting the pump 3 from the lower chamber 21 to the upper chamber 23 of the pump barrel 2 was attached to the lower surface of the head plate 25 that constitutes the ceiling of the upper chamber 23. Alternatively, the lifting device 4 may be detachably attached to the inner wall of the upper chamber 23. Furthermore, the placement of the lifting device 4 in the upper chamber 23 may be omitted altogether. For example, when loading or unloading the pump 3, an external lifting device, such as a winch, may be installed outside the pump barrel 2, and the pump 3 may be loaded or unloaded using this external lifting device.

In the above embodiment, an intermediate chamber 22 consisting of two chambers (first intermediate chamber 221 and second intermediate chamber 222) separated by first to third on-off valves 51 to 53 is provided between the lower chamber 21 and the upper chamber 23. However, an intermediate chamber consisting of three or more chambers may be provided. Conversely, the intermediate chamber may consist of a single chamber. In other words, the pump barrel may include an upper chamber, a single intermediate chamber positioned below the upper chamber with the first on-off valve in between, and a lower chamber positioned below the intermediate chamber with the second on-off valve in between. Even in this case, by using a gas replacement device to replace the gas in the intermediate chamber and upper chamber with nitrogen gas when the pump is removed, and to replace the gas in the intermediate chamber and upper chamber with hydrogen gas when the pump is brought in, it is possible to prevent inappropriate gas inflow and outflow through the pump barrel during pump removal and installation.

[summary]
The embodiments and their modifications include the following disclosures.

A liquefied gas tank according to one aspect of this disclosure comprises a tank body for storing liquefied gas, a pump disposed within the tank body for discharging the liquefied gas, a cylindrical pump barrel including a lower chamber housing the pump and extending upward from its housing position to the outside of the tank body, an intermediate chamber located above the lower chamber, and an upper chamber located above the intermediate chamber, a first on-off valve provided to be openable and closable between the upper chamber and the intermediate chamber, a second on-off valve provided to be openable and closable between the intermediate chamber and the lower chamber, and a gas replacement device capable of switching the gas in the intermediate chamber and the upper chamber between a gas corresponding to the liquefied gas and an inert gas.

This liquefied gas tank prevents improper gas inflow and outflow through the pump barrel during pump loading and unloading.

For example, when removing a pump from the tank body for maintenance, the pump is lifted from the lower chamber to the upper chamber, and the gas inside the intermediate and upper chambers is replaced with an inert gas using a gas replacement device. By removing the pump from the upper chamber under these conditions, it is possible to prevent the gas corresponding to the stored liquefied gas from being released into the atmosphere. Conversely, when installing the pump into the lower chamber of the pump barrel, the gas inside the intermediate and upper chambers is replaced with a gas corresponding to the liquefied gas using a gas replacement device. By lowering the pump from the upper chamber to the lower chamber under these conditions, it is possible to prevent a gas other than the one corresponding to the liquefied gas from entering the tank body.

In particular, according to this embodiment, in which an intermediate chamber is formed between the lower chamber and the upper chamber, the intermediate chamber can be used as a buffer to prevent the direct exchange of different gases between the lower and upper chambers by selectively filling it with a gas corresponding to the liquefied gas or an inert gas, thereby effectively preventing the inappropriate exchange of gases described above.

Preferably, the liquefied gas tank further comprises a third on-off valve positioned between the first on-off valve and the second on-off valve, and the intermediate chamber includes a first intermediate chamber defined between the first on-off valve and the third on-off valve, and a second intermediate chamber defined between the second on-off valve and the third on-off valve.

Thus, by providing two intermediate chambers (the first intermediate chamber and the second intermediate chamber) separated by an on-off valve, the buffer function expected of the intermediate chambers can be enhanced, and the inappropriate entry and exit of gas through the pump barrel can be prevented with a high probability.

Preferably, the gas replacement device includes a first supply source for supplying a gas corresponding to the liquefied gas, a second supply source for supplying the inert gas, an introduction section for selectively introducing the gases supplied from the first and second supply sources into the first and second intermediate chambers and the upper chamber, and an outlet section for discharging the gas from the first and second intermediate chambers and the upper chamber.

In this embodiment, during pump loading and unloading, the second intermediate chamber near the lower chamber is filled with a gas corresponding to the liquefied gas, while the gas in the first intermediate chamber near the upper chamber can be appropriately exchanged between the gas corresponding to the liquefied gas and an inert gas. This effectively prevents the gas corresponding to the liquefied gas from being dispersed into the atmosphere and prevents other gases from mixing into the tank body, thus preventing improper gas entry and exit through the pump barrel with a high probability.

Specifically, the introduction section may include a first gas introduction pipe for introducing a gas corresponding to the liquefied gas into the upper chamber and the second intermediate chamber, and a second gas introduction pipe for introducing the inert gas into the upper chamber and the first intermediate chamber.

In this embodiment, the gas replacement described above can be appropriately performed using the first and second gas introduction pipes.

A maintenance method for a pump for a liquefied gas tank, relating to another aspect of this disclosure, is a method for maintaining the pump in the liquefied gas tank described above, comprising: a first step of lifting the pump from the lower chamber to the upper chamber with the first to third on-off valves open; a second step of using the gas replacement device to replace the gas in the upper chamber and the first intermediate chamber from the gas corresponding to the liquefied gas to the inert gas, and filling the second intermediate chamber with the gas corresponding to the liquefied gas, with the second and third on-off valves closed; and a third step of opening the upper chamber with the first to third on-off valves closed and removing the pump from the upper chamber.

Furthermore, the maintenance method may further include, after the third step, a fourth step of inserting the pump into the upper chamber; a fifth step of replacing the gas in the upper chamber from air to the inert gas using the gas replacement device with the first on-off valve closed; a sixth step of replacing the gas in the upper chamber and the first intermediate chamber from the inert gas to the gas corresponding to the liquefied gas using the gas replacement device with the second and third on-off valves closed, and filling the second intermediate chamber with the gas corresponding to the liquefied gas; and a seventh step of lowering the pump from the upper chamber to the lower chamber with the first to third on-off valves open.

This method allows for proper transport of the pump into and out of the tank while preventing improper gas inflow and outflow through the pump barrel.

LH: Liquefied Hydrogen (Liquefied Gas)
1. Liquefied gas tank 2. Pump barrel 3. Pump 6. Gas replacement device 10. Tank body 21. Lower chamber 22. Middle chamber 23. Upper chamber 51. First shut-off valve 52. Second shut-off valve 53. Third shut-off valve 60. Hydrogen gas supply source (first supply source)
61. Nitrogen gas supply source (second supply source)
62. First hydrogen gas inlet pipe (first gas inlet pipe; inlet section)
63. Second hydrogen gas inlet pipe (first gas inlet pipe; inlet section)
64. First nitrogen gas inlet pipe (second gas inlet pipe; inlet section)
65. Second nitrogen gas inlet pipe (second gas inlet pipe; inlet section)
66. First gas outlet pipe (outlet section)
67. Second gas outlet pipe (outlet section)
68. Third gas outlet pipe (outlet section)
69. Fourth gas outlet pipe (outlet section)
221 First Intermediate Room 222 Second Intermediate Room

Claims (6)

The tank body for storing liquefied gas,
A pump is placed inside the tank body to discharge the liquefied gas,
A cylindrical pump barrel including a lower chamber that houses the pump and extends upward from the pump's housing position to the outside of the tank body, an intermediate chamber located above the lower chamber, and an upper chamber located above the intermediate chamber,
A first on/off valve is provided between the upper chamber and the intermediate chamber so as to be openable and closable,
A second on/off valve is provided between the intermediate chamber and the lower chamber so as to be openable and closable,
A liquefied gas tank comprising a gas replacement device capable of switching the gas in the intermediate chamber and the upper chamber between a gas corresponding to the liquefied gas and an inert gas. In the liquefied gas tank according to claim 1,
The system further comprises a third on-off valve positioned between the first on-off valve and the second on-off valve,
The intermediate chamber includes a first intermediate chamber defined between the first on-off valve and the third on-off valve, and a second intermediate chamber defined between the second on-off valve and the third on-off valve, in a liquefied gas tank. In the liquefied gas tank according to claim 2,
The gas replacement device is a liquefied gas tank comprising: a first supply source for supplying a gas corresponding to the liquefied gas; a second supply source for supplying the inert gas; an introduction section for selectively introducing the gases supplied from the first and second supply sources into the first and second intermediate chambers and the upper chamber; and an outlet section for discharging the gas from the first and second intermediate chambers and the upper chamber. In the liquefied gas tank according to claim 3,
The introduction section is a liquefied gas tank having a first gas introduction pipe for introducing a gas corresponding to the liquefied gas into the upper chamber and the second intermediate chamber, and a second gas introduction pipe for introducing the inert gas into the upper chamber and the first intermediate chamber. A method for maintaining the pump in a liquefied gas tank according to any one of claims 2 to 4,
The first step is to lift the pump from the lower chamber to the upper chamber with the first to third on-off valves open,
With the second and third on-off valves closed, the second step involves using the gas replacement device to replace the gas in the upper chamber and the first intermediate chamber from the gas corresponding to the liquefied gas to the inert gas, and filling the second intermediate chamber with the gas corresponding to the liquefied gas.
A method for maintaining a pump for a liquefied gas tank, comprising a third step of opening the upper chamber with the first to third on-off valves closed and removing the pump from the upper chamber. In the maintenance method for a liquefied gas tank pump according to claim 5,
After the third step, the fourth step is to insert the pump into the upper chamber,
A fifth step in which, with the first on/off valve closed, the gas in the upper chamber is replaced from air to the inert gas using the gas replacement device,
A sixth step in which, with the second and third on-off valves closed, the gas replacement device is used to replace the gas in the upper chamber and the first intermediate chamber from the inert gas to a gas corresponding to the liquefied gas, and the second intermediate chamber is filled with the gas corresponding to the liquefied gas,
A method for maintaining a pump for a liquefied gas tank, further comprising a seventh step of lowering the pump from the upper chamber to the lower chamber while the first to third on-off valves are open.