Pump device

Abstract

A pump device (7) comprises: a baffle structure (50) disposed in a suction container (9) and disposed above a pump (10); and a flow path switching device (5) coupled to an outlet (31) of the pump (10). The suction container (9) has a vacuum heat insulation container (18) and a vacuum heat insulation lid (19). A gas layer space (L) for forming a gas heat insulation layer composed of a boil-off gas is formed between the inner surface of the vacuum heat insulation container (18) and the outer surface of a sealing structure (25) of the vacuum heat insulation lid (19). The flow path switching device (5) is configured to selectively connect a liquefied gas discharge pipe (33) to either a pump chamber (30) or the outlet (31) of the pump (10).

Description

Pump equipment

[0001] The present invention relates to a pumping device for transporting liquefied gases such as liquefied hydrogen, liquid nitrogen, liquefied ammonia, liquefied natural gas, liquefied ethylene gas, and liquefied petroleum gas, and more particularly to a pumping device having a pump disposed in a suction vessel.

[0002] 28 is a schematic diagram showing a conventional example of a pump device for transferring liquefied gas. Pump 500 is installed in a vertical suction container 505 connected to a liquefied gas storage tank (not shown) in which liquefied gas is stored. Liquefied gas is introduced into suction container 505 through suction port 501, and pump 500 is entirely immersed in the liquefied gas. Therefore, pump 500 is a submersible pump that can operate in liquefied gas. When pump 500 is operated, liquefied gas is sucked into suction port 500a of pump 500 and discharged by pump 500 through discharge port 502.

[0003] Most of the liquefied gas in the suction vessel 505 is in a liquid state, but a small amount of heat from the surrounding atmosphere is transferred to the liquefied gas through the wall of the suction vessel 505. As a result, a part of the liquefied gas is gasified to form boil-off gas (BOG). Therefore, a boil-off gas discharge port 503 for discharging the boil-off gas is connected to the suction vessel 505. The boil-off gas in the suction vessel 505 is discharged from the suction vessel 505 through the boil-off gas discharge port 503.

[0004] Japanese Unexamined Patent Publication No. 64-36998

[0005] However, since the liquefied gas supplied into the suction vessel 505 vaporizes with even a slight change in the heat input into the suction vessel 505, bubbles are likely to form on the liquid surface of the liquefied gas. The generated bubbles cause the liquid surface of the liquefied gas to ripple, causing the liquid surface to fluctuate significantly up and down. When such ripples occur on the liquid surface, the amount of heat transferred from the room temperature region outside the suction vessel 505 through the wall of the suction vessel 505 to the liquefied gas fluctuates, making the liquefied gas supplied into the suction vessel 505 more likely to vaporize and generate bubbles. This results in an increase in boil-off gas in the suction vessel 505. Furthermore, when such ripples occur on the liquid surface, convection occurs in the gas layer, causing the liquefied gas to further vaporize and making bubbles more likely to form.

[0006] An increase in boil-off gas in the suction vessel 505 increases the loss of liquefied gas. Also, if air bubbles get into the pump 500, the head will not be increased, causing a loss in the discharge rate of the pump 500. Therefore, the operation of the pump 500 will become unstable.

[0007] In particular, liquid hydrogen vaporizes very easily because its boiling point at atmospheric pressure is −253° C. Therefore, it is required to improve the heat insulation of the suction vessel 505, reduce the amount of heat input into the suction vessel 505, stabilize fluctuations in the liquid level of the liquefied gas, and minimize the amount of boil-off gas in the suction vessel 505.

[0008] In a pump device that handles liquefied gas, before operating the pump 500, a drying-up process is performed in which air is removed from the suction container 505 using a purge gas, and a cooling-down process is performed in which the pump 500 is cooled with liquefied gas. When the air present in the suction container 505 comes into contact with the ultra-low temperature liquefied gas, the moisture in the air is cooled by the liquefied gas and solidifies, hindering the rotational operation of the pump 500. Furthermore, if the pump 500 is at room temperature when the pump 500 is started, the ultra-low temperature liquefied gas will vaporize when it comes into contact with the pump 500. To prevent such an event, the drying-up process and the cooling-down process are performed before operating the pump 500.

[0009] Drying up is performed by injecting a purge gas (e.g., nitrogen gas) into the suction vessel 505, and cooling down is performed by injecting a liquefied gas (e.g., liquefied natural gas) into the suction vessel 505. The purge gas or liquefied gas injected into the suction vessel 505 fills the suction vessel 505, flows into the pump 500 through the suction port 500a of the pump 500, and is then discharged through the discharge port 502.

[0010] Furthermore, for maintenance or replacement of the pump 500, before the ultra-low temperature pump 500 is removed from the suction vessel 505, a hot-up process is performed in which the pump 500 is warmed with a warm gas (e.g., an inert gas at room temperature). This hot-up process is performed before the pump 500 comes into contact with the ambient air, so that components in the air, such as nitrogen, do not liquefy on the surface of the pump 500. Hot-up is particularly effective when the liquefied gas is liquid hydrogen. That is, when the pump 500, which has been immersed in liquid hydrogen, is removed from the suction vessel 505, it is at an ultra-low temperature equivalent to that of liquid hydrogen. Because the boiling point of hydrogen (−253°C) is lower than the boiling point of oxygen (−183°C), if the pump 500 comes into contact with air immediately after being removed from the suction vessel 505, not only the nitrogen in the air but also the oxygen will liquefy and drip into the suction vessel 505. Therefore, a hot-up process is performed before the pump 500 is removed from the suction vessel 505, and the pump 500 is warmed with a warm gas. Therefore, when the air comes into contact with the pump 500 , the oxygen in the air is not liquefied, and the liquefied oxygen does not drip into the suction container 505 .

[0011] In order to pressurize the liquefied gas to the pressure required on the demand side, multiple pumping devices may be connected in series as shown in Figure 29. The liquefied gas is sequentially pressurized by the pumps 500 of the multiple pumping devices.

[0012] However, performing the above-described drying-up of pump devices connected in series poses the following problem. Specifically, when purge gas is flowed into the pump devices before they start operating, the purge gas flows through all of the pumps 500. This flow of purge gas forces the impellers of the pumps 500 to rotate while they are not operating. As a result, sliding parts such as bearings may be damaged. While it may be possible to flow purge gas at a low flow rate to prevent unintended rotation of the impellers of the pumps 500, in this case, it would take an extremely long time for all of the pump devices to complete the drying-up process. Similar problems can occur during cool-down and hot-up.

[0013] The present invention provides a pump device that can improve the thermal insulation of a suction vessel that houses a pump for transporting liquefied gas, and can prevent the rotation of the impeller of the pump when the pump is stopped while it is being dried up, cooled down, and heated up.

[0014] In one aspect, a pump device for transporting liquefied gas is provided, comprising: a suction container; a pump disposed within the suction container; a baffle structure disposed within the suction container and above the pump; a flow path switching device connected to the discharge port of the pump; and a liquefied gas discharge pipe connected to the flow path switching device. The suction container has a vacuum insulated container having a double-wall structure with a vacuum formed therein, and a vacuum insulated lid having a sealed structure with a vacuum formed therein. The pump is disposed in a pump chamber formed by the vacuum insulated container and the vacuum insulated lid. An air space for forming a gas insulation layer made of boil-off gas is formed between the inner surface of the vacuum insulated container and the outer surface of the sealed structure. The air space is connected to the pump chamber. The flow path switching device is configured to selectively connect the liquefied gas discharge pipe to either the discharge port of the pump or the pump chamber.

[0015] In one aspect, the flow path switching device includes a flow path structure having a pump-side flow path, a container-side flow path, and an outlet flow path, and a valve disposed within the flow path structure for selectively connecting the outlet flow path to either the pump-side flow path or the container-side flow path, wherein the pump-side flow path is connected to the discharge port of the pump, the container-side flow path is connected to the pump chamber, and the outlet flow path is connected to the liquefied gas discharge pipe. In one aspect, the baffle structure is disposed between the vacuum insulated lid and the flow path switching device. In one aspect, the baffle structure is a baffle plate. In one aspect, the baffle plate is fixed to the liquefied gas discharge pipe. In one aspect, the baffle plate is fixed to the inner surface of the vacuum insulated container. In one aspect, the baffle plate is located above the liquid level of the liquefied gas in the vacuum insulated container. In one aspect, the baffle plate is located below the liquid level of the liquefied gas in the vacuum insulated container. In one aspect, the baffle structure is fixed to the sealing structure. In one aspect, the baffle structure is a labyrinth flow path structure that forms a labyrinth flow path. In one aspect, the baffle structure is fixed to the flow path switching device.

[0016] In one aspect, a pump device for transferring liquefied gas is provided, the pump device comprising: a suction container having a suction port; a pump disposed in the suction container; a flow path switching device connected to the discharge port of the pump; a liquefied gas discharge pipe connected to the flow path switching device; and a boil-off gas discharge pipe connected to the suction container. The suction container has a vacuum insulated container having a double-wall structure with a vacuum formed therein, and a vacuum insulated lid having a sealed structure with a vacuum formed therein. The pump is disposed in a pump chamber formed by the vacuum insulated container and the vacuum insulated lid. An air space for forming a gas insulation layer made of boil-off gas is formed between the inner surface of the vacuum insulated container and the outer surface of the sealed structure. The air space is connected to the pump chamber. The inlet opening of the boil-off gas discharge pipe is located below the air space. The flow path switching device is configured to selectively connect the liquefied gas discharge pipe to either the discharge port of the pump or the pump chamber.

[0017] In one aspect, the flow path switching device includes a flow path structure having a pump-side flow path, a container-side flow path, and an outflow flow path, and a valve disposed within the flow path structure for selectively connecting the outflow flow path to either the pump-side flow path or the container-side flow path. The pump-side flow path is connected to the discharge port of the pump, the container-side flow path is connected to the pump chamber, and the outflow flow path is connected to the liquefied gas discharge pipe. In one aspect, the boil-off gas discharge pipe includes a first pipe connected to the side wall of the vacuum insulated container at a position between the suction port and the gas space, and a second pipe extending upward from the first pipe. In one aspect, the boil-off gas discharge pipe penetrates the vacuum insulated lid and protrudes downward from the vacuum insulated lid. In one aspect, the vacuum insulated lid seals the top opening of the vacuum insulated container, forming a dead-end space at the top of the vacuum insulated container that does not allow gas to escape. In one embodiment, the inlet opening of the boil-off gas discharge pipe is located above the inlet opening of the vessel-side flow path.

[0018] During pump operation, a portion of the liquefied gas in the suction vessel vaporizes to form boil-off gas. This boil-off gas accumulates in the gas space and functions as a gas insulation layer. This improves the thermal insulation of the suction vessel. Furthermore, the baffle structure disposed below the gas space can suppress the effects of turbulence on the liquid surface of the liquefied gas in the vacuum insulated vessel that occurs during pump operation, preventing fluidization or convection of the gas insulation layer made of boil-off gas. As a result, the baffle structure can maintain the insulating effect of the gas insulation layer made of boil-off gas.

[0019] When the liquid level of the liquefied gas rises during pump operation, the boil-off gas discharge pipe allows some of the liquefied gas to escape from the vacuum insulated container, preventing the liquid level of the liquefied gas from approaching the gas insulation layer made of boil-off gas. As a result, the boil-off gas discharge pipe can prevent fluidization or convection in the gas insulation layer, suppress the generation of bubbles, and maintain the insulating effect of the gas insulation layer made of boil-off gas. Furthermore, the dead-end space formed in the vacuum insulated container has a closed structure, making it difficult for the liquid level of the liquefied gas to rise.

[0020] The flow path switching device can prevent gas (purge gas, heated gas) or liquefied gas introduced into the suction vessel during dry-up, cool-down, and hot-up from being introduced into the pump. Therefore, the impeller of the pump does not rotate during shutdown, and as a result, damage to the sliding parts of the pump, such as bearings, can be prevented.

[0021] 13 is a schematic diagram showing an embodiment of a liquefied gas transfer system for transferring liquefied gas. FIG. 14 is a schematic diagram showing an embodiment of a pump device. FIG. 15 is an enlarged sectional view showing a portion of the pump device shown in FIG. 2. FIG. 16 is a diagram showing the state of a flow path switching device when the pump is not operating. FIG. 17 is a diagram explaining an embodiment of dry-up. FIG. 18 is an enlarged sectional view showing another embodiment of the pump device. FIG. 19 is an enlarged sectional view showing yet another embodiment of the pump device. FIG. 19 is an enlarged sectional view showing yet another embodiment of the pump device. FIG. 20 is an enlarged sectional view showing yet another embodiment of the pump device. FIG. 21 is an enlarged sectional view showing yet another embodiment of the pump device. FIG. 22 is an enlarged sectional view showing yet another embodiment of the pump device. FIG. 23 is an enlarged sectional view showing yet another embodiment of the pump device. FIG. 24 is an enlarged sectional view showing yet another embodiment of the pump device. FIG. 25 is an enlarged sectional view showing yet another embodiment of the pump device. FIG. 26 is an enlarged sectional view showing yet another embodiment of the pump device. FIG. 27 is an enlarged sectional view showing yet another embodiment of the pump device. FIG. 28 is a diagram explaining how a portion of the liquefied gas flows into a boil-off gas discharge pipe when the liquid level of the liquefied gas rises. FIG. 29 is a schematic diagram showing a modification of the embodiment described with reference to FIGS. 17 and 18. FIG. 29 is a schematic diagram showing another modification of the embodiment described with reference to FIGS. 17 and 18. Fig. 1 is an enlarged sectional view showing yet another embodiment of the pump device. Fig. 2 is a view explaining how a portion of liquefied gas flows into a boil-off gas discharge pipe when the liquid level of the liquefied gas rises. Fig. 3 is an enlarged sectional view showing yet another embodiment of the pump device. Fig. 4 is an enlarged sectional view showing yet another embodiment of the pump device. Fig. 5 is an enlarged sectional view showing yet another embodiment of the pump device. Fig. 6 is an enlarged sectional view showing yet another embodiment of the pump device. Fig. 7 is an enlarged sectional view showing yet another embodiment of the pump device. Fig. 8 is a schematic view showing a conventional example of a pump device for transferring liquefied gas. Fig. 9 is a schematic view showing a plurality of pump devices connected in series.

[0022] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Fig. 1 is a schematic diagram showing one embodiment of a liquefied gas transfer system for transferring liquefied gas. As shown in Fig. 1, the liquefied gas transfer system includes a storage tank 1 for storing liquefied gas, a pump column 2 arranged in the storage tank 1, an in-tank pump 3 arranged in the pump column 2, and a pump device 7 connected to the in-tank pump 3 via a liquefied gas transfer line 6. Examples of liquefied gas include liquefied hydrogen, liquefied natural gas, liquefied ammonia, liquid nitrogen, liquefied ethylene gas, and liquefied petroleum gas.

[0023] The pump device 7 includes a suction container 9, which is a fluid container, and a pump 10 disposed within the suction container 9. The liquefied gas sent through the liquefied gas transfer line 6 is introduced into the suction container 9. The pump 10 transfers the liquefied gas within the suction container 9 via a liquefied gas discharge pipe 33 to a point of use (not shown). In order to pressurize the liquefied gas to a target pressure, multiple pump devices 7 may be connected in series.

[0024] A small amount of heat from the ambient atmosphere of the pump device 7 is transferred to the liquefied gas in the suction vessel 9. As a result, a part of the liquefied gas is gasified to form boil-off gas (BOG) in the suction vessel 9. Therefore, the liquefied gas transfer system is provided with a boil-off gas return line 15 that returns the boil-off gas from the suction vessel 9 to the storage tank 1.

[0025] 2 is a schematic diagram showing one embodiment of the pump device 7. The pump device 7 includes a suction container 9 and a pump 10 disposed within the suction container 9. The suction container 9 includes a vacuum insulated container 18 having a double-wall structure with a vacuum formed therein, and a vacuum insulated lid 19 that closes the top opening of the vacuum insulated container 18. The side and bottom walls of the vacuum insulated container 18 have a double-wall structure including an inner wall 22A and an outer wall 22B. A vacuum is formed between the inner wall 22A and the outer wall 22B. In this embodiment, the vacuum insulated container 18 has a circular horizontal cross section, but in one embodiment, the vacuum insulated container 18 may have a horizontal cross section of another shape, such as a polygonal shape.

[0026] The vacuum insulated lid 19 has a sealed structure 25 in which a vacuum is formed and a flange 26 fixed to the outer surface of the sealed structure 25. The flange 26 is detachably fixed to the upper end of the vacuum insulated container 18 with fasteners (not shown) such as screws. The suction container 9 is composed of the vacuum insulated container 18 having a double-wall structure in which a vacuum is formed, and the vacuum insulated lid 19 equipped with the sealed structure 25 in which a vacuum is formed, so that the amount of heat input from the sides and bottom of the suction container 9 can be significantly reduced. Although a small amount of heat input occurs through the inner wall 22A of the vacuum insulated container 18, the heat input from the top of the suction container 9 is largely reduced by the sealed structure 25 in which a vacuum is formed inside the vacuum insulated lid 19.

[0027] The lower part of the sealing structure 25 is located inside the vacuum insulated container 18, and the upper part of the sealing structure 25 and the flange 26 are located outside the vacuum insulated container 18. The pump 10 is disposed in a pump chamber 30 formed by the vacuum insulated container 18 and the vacuum insulated lid 19. The pump chamber 30 is formed inside the suction container 9.

[0028] The pump device 7 further includes a liquefied gas discharge pipe 33 that penetrates the vacuum insulating lid 19 and extends to the outside of the pump chamber 30, and a boil-off gas discharge pipe 37 that penetrates the vacuum insulating lid 19 and extends to communicate between the inside and outside of the pump chamber 30. The liquefied gas discharge pipe 33 and the boil-off gas discharge pipe 37 are fixed to the sealed structure 25.

[0029] The suction vessel 9 has a suction port 40 connected to the side wall of the vacuum insulated vessel 18. The liquefied gas sent through the liquefied gas transfer line 6 shown in Figure 1 is introduced into the suction vessel 9 through the suction port 40. During operation of the pump 10, the entire pump 10 is immersed in the liquefied gas. Therefore, the pump 10 is a submersible pump that can operate in liquefied gas.

[0030] The pump device 7 further includes a baffle structure 50. The baffle structure 50 is disposed within the suction vessel 9 (more specifically, within the vacuum insulated vessel 18) and above the pump 10. The pump device 7 further includes a flow path switching device 5 disposed below the baffle structure 50. The flow path switching device 5 is connected to the discharge port 31 of the pump 10 and the liquefied gas discharge pipe 33. The flow path switching device 5 is in communication with the discharge port 31 of the pump 10, the liquefied gas discharge pipe 33, and the pump chamber 30. The discharge port 31 of the pump 10 is connected to the liquefied gas discharge pipe 33 via the flow path switching device 5. In one embodiment, as long as the flow path switching device 5 is in communication with the discharge port 31 of the pump 10, the liquefied gas discharge pipe 33, and the pump chamber 30, part or all of the flow path switching device 5 may be disposed within the pump 10 or the liquefied gas discharge pipe 33.

[0031] The flow path switching device 5 has a movable valve body 67 therein. The flow path switching device 5 is configured to selectively connect the liquefied gas discharge pipe 33 to either the discharge port 31 of the pump 10 or the pump chamber 30. The baffle structure 50 is disposed above the flow path switching device 5.

[0032] The pump 10 includes an electric motor 41 having a motor rotor 41A and a motor stator 41B, a rotating shaft 42 connected to the electric motor 41, a plurality of bearings 44 that rotatably support the rotating shaft 42, a plurality of impellers 45 fixed to the rotating shaft 42, and a pump casing 46 that houses the plurality of impellers 45. In one embodiment, the pump 10 may include a single impeller 45.

[0033] When power is supplied to the electric motor 41 through a power cable (not shown), the electric motor 41 rotates the rotary shaft 42 and the impeller 45 together. As the impeller 45 rotates, the liquefied gas is sucked into the pump 10 from the suction port 43 of the pump 10 and discharged into the flow path switching device 5 through the discharge port 31. The liquefied gas flows through the flow path switching device 5 and the liquefied gas discharge pipe 33 and is transported to the point of use.

[0034] Figure 3 is an enlarged cross-sectional view showing a portion of the pump device shown in Figure 2. As shown in Figure 3, a gas space L is formed between the inner surface of the vacuum insulated container 18 and the outer surface of the sealed structure 25. More specifically, the gas space L is surrounded by the inner surface of the inner wall 22A of the vacuum insulated container 18, the side surface of the sealed structure 25, and the underside of the flange 26. A gas insulation layer made of boil-off gas is formed within this gas space L. The gas space L is in communication with a pump chamber 30 in the vacuum insulated container 18. A portion of the boil-off gas generated in the pump chamber 30 is introduced into the gas space L.

[0035] During operation of the pump 10, a small amount of heat input from outside the suction vessel 9 and / or heat generated by the electric motor 41 of the pump 10 causes a portion of the liquefied gas to vaporize and form boil-off gas. The gas space L is surrounded by the inner surface of the inner wall 22A of the vacuum insulated vessel 18, the side surface of the sealed structure 25, and the underside of the flange 26, forming a dead-end space structure that does not allow gas to escape to the outside. Therefore, the boil-off gas accumulates in the gas space L and forms a gas insulation layer. The gas insulation layer in the gas space L is located between the vacuum insulated vessel 18 and the vacuum insulated lid 19 and can prevent heat input from the outside at the position between the vacuum insulated vessel 18 and the vacuum insulated lid 19, particularly heat input from the flange 26 of the vacuum insulated lid 19 at the top of the suction vessel 9 through the inner wall 22A of the vacuum insulated vessel 18. Therefore, the gas insulation layer made of boil-off gas can improve the thermal insulation of the suction vessel 9. Excess boil-off gas is discharged from the suction vessel 9 through a boil-off gas discharge pipe 37 communicating with the pump chamber 30 and returned to the storage tank 1 through the boil-off gas return line 15 shown in FIG.

[0036] The baffle structure 50 is located below the gas space L. The baffle structure 50 of this embodiment is a baffle plate disposed between the pump 10 and the sealing structure 25. That is, the baffle structure 50 is located above the pump 10 and the suction port 40, and below the sealing structure 25. The baffle structure (baffle plate) 50 is fixed to the liquefied gas discharge pipe 33. The baffle structure 50 of this embodiment has a disk shape.

[0037] The baffle structure (baffle plate) 50 is located above the liquid level of the liquefied gas in the vacuum insulated container 18. The outer edge of the baffle structure 50 is separated from the inner surface of the vacuum insulated container 18 (i.e., it is not in contact with the inner surface of the vacuum insulated container 18). Therefore, the boil-off gas generated in the pump chamber 30 moves through the gap between the baffle structure 50 and the inner surface of the vacuum insulated container 18 into the gas space L, forming a gas insulation layer in the gas space L. In one embodiment, as long as communication between the gas space L and the pump chamber 30 is established, part of the outer edge of the baffle structure 50 may be in contact with the inner surface of the vacuum insulated container 18.

[0038] During operation of the pump 10, the liquefied gas in the suction vessel 9 flows at a fairly high speed. Therefore, the liquid surface of the liquefied gas in the suction vessel 9 may undulate (wave). In particular, when transferring a large amount of liquefied gas, the liquefied gas may splash within the suction vessel 9. The baffle structure 50, located below the gas space L, prevents turbulence of the liquefied gas surface from causing a fluid flow in the space filled with boil-off gas above the liquefied gas surface. This in turn reduces the impact on the gas insulation layer made of boil-off gas in the gas space L, preventing fluidization or convection of the gas insulation layer. It is desirable that the gas insulation layer made of boil-off gas in the gas space L be as still as possible. This is to prevent heat from outside the suction vessel 9 from being carried to the liquefied gas by convection of the boil-off gas in the gas space L.

[0039] The baffle structure 50 can suppress fluidization or convection of the gas insulation layer caused by disturbances in the liquid surface of the liquefied gas that occur when the pump 10 is operating, and as a result, the insulating effect of the gas insulation layer made of boil-off gas can be maintained.

[0040] The flow path switching device 5 includes a flow path structure 65 having a pump-side flow path 61, a container-side flow path 62, and an outlet flow path 63, and a valve body 67 disposed within the flow path structure 65. The pump-side flow path 61 communicates with the discharge port 31 of the pump 10, the container-side flow path 62 communicates with the pump chamber 30 in the suction container 9, and the outlet flow path 63 communicates with the liquefied gas discharge pipe 33 of the suction container 9. The container-side flow path 62 may protrude from the outer surface of the flow path structure 65, as described below. For example, the container-side flow path 62 may protrude from the outer surface of the flow path structure 65 and extend downward, as described below.

[0041] The valve element 67 is arranged to selectively connect the outflow passage 63 to either the pump-side passage 61 or the container-side passage 62. In other words, the passage switching device 5 is configured to selectively connect the liquefied gas discharge pipe 33 to either the discharge port 31 of the pump 10 or the pump chamber 30. The configuration of the passage switching device 5 is not limited to the embodiment shown in Figure 3 as long as it can perform its intended function.

[0042] FIG. 3 shows the state of the flow path switching device 5 when the pump 10 is operating, and FIG. 4 shows the state of the flow path switching device 5 when the pump 10 is not operating. The baffle structure 50 is located above the inlet opening 62a of the container-side flow path 62. As shown in FIG. 4, when the pump 10 is not operating, the valve element 67 is pressed against the flow path structure 65 by a spring 70 to close the pump-side flow path 61. More specifically, the flow path structure 65 has a valve seat 71 formed around the outlet of the pump-side flow path 61, and the valve element 67 is pressed against the valve seat 71 by the spring 70. Therefore, while the valve element 67 is pressed against the valve seat 71, the pump-side flow path 61 is closed, and the container-side flow path 62 and the outflow flow path 63 are in communication. The container-side flow path 62 opens in the pump chamber 30 of the suction container 9 and is in communication with the suction port 40 through the pump chamber 30.

[0043] 3, when the pump 10 is operating, liquefied gas is discharged from the discharge port 31 of the pump 10 and flows into the pump-side flow path 61 of the flow path switching device 5. The liquefied gas flowing through the pump-side flow path 61 moves the valve element 67 against the force of the spring 70, opening the pump-side flow path 61 and closing the container-side flow path 62 with the valve element 67. As a result, the pump-side flow path 61 and the outflow flow path 63 are connected to each other. The inlet opening 62a of the container-side flow path 62 is located below the liquid level of the liquefied gas in the suction container 9.

[0044] When the operation of the pump 10 stops, the valve element 67 is pressed against the valve seat 71 by the spring 70. As a result, as shown in Figure 4, the pump-side flow path 61 is closed, and the container-side flow path 62 and the outflow flow path 63 are connected. In this way, the flow path switching device 5 of this embodiment operates only by the spring 70 and the flow of liquefied gas.

[0045] Before operating the pump 10, a drying-up process is performed in which air is removed from the suction container 9 using a purge gas, and a cooling-down process is performed in which the pump 10 is cooled with liquefied gas. The drying-up and cooling-down processes are performed when the operation of the pump 10 is stopped. More specifically, as shown in Figure 4, the drying-up and cooling-down processes are performed in a state in which the pump-side flow path 61 is closed by the valve body 67 and the container-side flow path 62 and the outflow flow path 63 are in communication.

[0046] During drying-up, cool-down, and hot-up, fluids such as purge gas, liquefied gas, and heated gas bypass the pump 10 and flow through the flow path switching device 5 and the liquefied gas discharge pipe 33, as shown by the arrows in FIG. 4 . The baffle structure 50 is positioned above the inlet opening 62 a of the container-side flow path 62 of the flow path switching device 5. This is to prevent the baffle structure 50 from obstructing the flow of fluid toward the inlet opening 62 a of the container-side flow path 62 during drying-up, cool-down, and hot-up. Because the baffle structure 50 does not obstruct the flow of fluid (purge gas, liquefied gas, and heated gas), it is possible to reliably prevent the pump 10 from running idly during operation shutdowns during drying-up, cool-down, and hot-up. In the embodiment shown in FIG. 4 , the inlet opening 62 a of the container-side flow path 62 is located within the outer surface of the flow path structure 65. However, in one embodiment, the inlet opening 62 a of the container-side flow path 62 may protrude from the outer surface of the flow path structure 65.

[0047] Drying-up is an operation in which room-temperature purge gas is introduced into the suction container 9 to dry the pump 10. One embodiment of drying-up will be described below with reference to FIG. 5. Drying-up is performed when no liquefied gas is present in the suction container 9. When the operation of the pump 10 is stopped (i.e., the state shown in FIG. 4), purge gas is supplied into the pump chamber 30 of the suction container 9 through the suction port 40. The purge gas pushes out air present in the pump chamber 30 and is discharged together with the air through the flow path switching device 5 and the liquefied gas discharge pipe 33. Eventually, the pump chamber 30 is filled with purge gas, thereby drying the pump 10.

[0048] 5, the pump-side flow path 61 communicating with the discharge port 31 of the pump 10 is closed by a valve body 67. Therefore, the purge gas introduced into the suction vessel 9 does not flow through the pump 10. As a result, unintentional rotation of the impeller 45 of the pump 10 is prevented, and damage to sliding parts such as the bearing 44 is prevented.

[0049] The purge gas used for the dry-up is an inert gas composed of elements having a boiling point lower than that of the elements constituting the liquefied gas. This is to prevent the purge gas from liquefying when it comes into contact with the cryogenic liquefied gas introduced after the dry-up. For example, when the liquefied gas is liquefied natural gas (LNG), the purge gas used is nitrogen gas. In another example, when the liquefied gas is liquid hydrogen, the purge gas used is helium gas.

[0050] Cool-down, in which the pump 10 is cooled with liquefied gas, is performed after dry-up and before the start of operation of the pump 10. During cool-down, liquefied gas is supplied into the pump chamber 30 of the suction container 9 through the suction port 40 instead of purge gas. The operation of each component of the pump device 7 (including the flow path switching device 5) during cool-down is the same as the operation during dry-up described with reference to FIG. 5 , so a duplicated description will be omitted.

[0051] For maintenance or replacement of the pump 10, before the pump 10 is withdrawn from the suction vessel 9 at a cryogenic temperature, the pump 10 is heated with a heating gas (hot-up). This hot-up is performed before the pump 10 comes into contact with the ambient air, so that components in the air, such as nitrogen, do not liquefy on the surface of the pump 10. Hot-up is particularly effective when the liquefied gas is liquid hydrogen. That is, the pump 10 immersed in liquid hydrogen is at the same cryogenic temperature as liquid hydrogen when withdrawn from the suction vessel 9. Because the boiling point of hydrogen (−253°C) is lower than the boiling point of oxygen (−183°C), if the pump 10 comes into contact with air immediately after being withdrawn from the suction vessel 9, not only the nitrogen in the air but also the oxygen will liquefy and drip into the suction vessel 9. Therefore, before withdrawing the pump 10 from the suction vessel 9, hot-up is performed, and the pump 10 is heated with a heating gas. Therefore, when the air comes into contact with the pump 10, the oxygen in the air is not liquefied, and the liquefied oxygen does not drip into the suction vessel 9.

[0052] An example of the heating gas is a room-temperature inert gas composed of elements having a boiling point lower than the boiling points of the elements constituting the liquefied gas. This is to prevent the heating gas from liquefying when it comes into contact with the cryogenic pump 10. For example, when the liquefied gas is liquefied natural gas (LNG), the heating gas used is nitrogen gas. In another example, when the liquefied gas is liquefied hydrogen, the heating gas used is helium gas. In one embodiment, the heating gas may be vaporized liquefied gas (boil-off gas). For example, boil-off gas in a liquefied gas storage tank 1 (see FIG. 1) for storing liquefied gas, which is located upstream of the pump 10, may be used as the heating gas.

[0053] Like the dry-up and cool-down, the hot-up is performed when the operation of the pump 10 is stopped. During the hot-up, the heated gas described above is supplied into the pump chamber 30 of the suction container 9 through the suction port 40. The operation of each component of the pump device 7 (including the flow path switching device 5) during the hot-up is the same as the operation during the dry-up described with reference to FIG. 5 , so a duplicated description will be omitted.

[0054] 6 is an enlarged cross-sectional view showing another embodiment of the pump device 7. The configuration and operation of this embodiment, which will not be specifically described, are the same as those of the embodiment described with reference to FIGS.

[0055] 6, the baffle structure 50 is a baffle plate fixed to the inner surface of the vacuum insulated container 18. In this embodiment, the vacuum insulated container 18 has a circular horizontal cross section, and the baffle structure (baffle plate) 50 is annular. The baffle structure (baffle plate) 50 is disposed between the vacuum insulated lid 19 and the pump 10. More specifically, the baffle structure (baffle plate) 50 is disposed above the inlet opening 62a of the flow path switching device 5 and below the vacuum insulated lid 19.

[0056] The inner edge of the baffle structure 50 is separated from the outer surface of the liquefied gas discharge pipe 33 (i.e., not in contact with the liquefied gas discharge pipe 33). Therefore, the gas layer space L is in communication with the pump chamber 30. In this embodiment, the baffle structure 50 can also protect the gas insulation layer from turbulent liquefied gas flows that occur during operation of the pump 10, and as a result, the insulating effect of the gas insulation layer made of boil-off gas can be maintained. In one embodiment, as long as communication between the gas layer space L and the pump chamber 30 is established, part of the inner edge of the baffle structure 50 may be in contact with the outer surface of the liquefied gas discharge pipe 33.

[0057] 7 is an enlarged cross-sectional view showing yet another embodiment of the pump device 7. The configuration and operation of this embodiment, which will not be specifically described, are the same as those of the embodiment described with reference to FIGS.

[0058] In the embodiment shown in FIG. 7 , the baffle structure 50 is a labyrinth flow path structure that forms a labyrinth flow path 53. In this example, the baffle structure 50 has a first labyrinth structure 51 fixed to the inner surface of the vacuum insulation container 18 and a second labyrinth structure 52 fixed to the sealing structure 25, and the labyrinth flow path 53 is formed between the first labyrinth structure 51 and the second labyrinth structure 52. The gas layer space L and the pump chamber 30 are connected through the labyrinth flow path 53. The baffle structure (labyrinth flow path structure) 50 is disposed between the vacuum insulation lid 19 and the pump 10. The baffle structure (labyrinth flow path structure) 50 is disposed above the flow path switching device 5. The baffle structure 50, which constitutes the labyrinth flow path structure, can protect the gas insulation layer from turbulent flow of liquefied gas that occurs during operation of the pump 10, and as a result, the insulating effect of the gas insulation layer made of boil-off gas can be maintained.

[0059] 8 is an enlarged cross-sectional view showing yet another embodiment of the pump device 7. The configuration and operation of this embodiment, which will not be specifically described, are the same as those of the embodiment described with reference to FIGS.

[0060] In the embodiment shown in Figure 8, the baffle structure 50 is fixed to the sealing structure 25. The baffle structure 50 protrudes from the sealing structure 25 toward the inner surface of the vacuum insulated container 18. The outer edge of the baffle structure 50 is separated from the inner surface of the vacuum insulated container 18 (i.e., it is not in contact with the inner surface of the vacuum insulated container 18). Therefore, the boil-off gas generated in the pump chamber 30 moves through the gap between the baffle structure 50 and the inner surface of the vacuum insulated container 18 to the gas space L, forming a gas insulation layer in the gas space L. In one embodiment, as long as communication between the gas space L and the pump chamber 30 is established, part of the outer edge of the baffle structure 50 may be in contact with the inner surface of the vacuum insulated container 18.

[0061] 8, the baffle structure 50 is an annular member fixed to the bottom surface of the sealing structure 25. In one embodiment, the baffle structure 50 may be an annular member fixed to the side surface of the sealing structure 25.

[0062] 9 is an enlarged cross-sectional view showing yet another embodiment of the pump device 7. The configuration and operation of this embodiment, which will not be specifically described, are the same as those of the embodiment described with reference to FIGS.

[0063] 9, the baffle structure 50 is a baffle plate located below the liquid level of the liquefied gas in the vacuum insulated container 18. That is, the baffle structure (baffle plate) 50 is fixed to the liquefied gas discharge pipe 33 and is disposed in the liquefied gas in the vacuum insulated container 18. This baffle structure (baffle plate) 50 can calm the liquid level of the liquefied gas in the vacuum insulated container 18. As a result, the insulating effect of the gas insulating layer made of boil-off gas can be maintained.

[0064] Fig. 10 is an enlarged cross-sectional view showing yet another embodiment of the pump device 7. The configuration and operation of this embodiment, which will not be specifically described, are the same as those of the embodiment described with reference to Fig. 6, and therefore, redundant description thereof will be omitted.

[0065] 10 , the baffle structure 50 is a baffle plate located below the liquid level of the liquefied gas in the vacuum insulated container 18. That is, the baffle structure (baffle plate) 50 is fixed to the inner surface of the vacuum insulated container 18 and is disposed in the liquefied gas in the vacuum insulated container 18. This baffle structure (baffle plate) 50 can calm the liquid level of the liquefied gas in the vacuum insulated container 18. As a result, the insulating effect of the gas insulating layer made of boil-off gas can be maintained.

[0066] Fig. 11 is an enlarged cross-sectional view showing yet another embodiment of the pump device 7. The configuration and operation of this embodiment, which will not be specifically described, are the same as those of the embodiment described with reference to Fig. 3, and therefore, redundant description thereof will be omitted.

[0067] In the embodiment shown in FIG. 11 , a vacuum is formed inside the sealing structure 25 by the side wall 81, the top wall 82, and the raised bottom wall 80 of the sealing structure 25. The raised bottom wall 80 is located higher than the lower end of the side wall 81. More specifically, the raised bottom wall 80 is located at the same height as the flange 26. The side wall 81 has a portion 81a extending downward from the raised bottom wall 80, and a gas phase space L is formed between the outer surface of this downwardly extending portion 81a and the inner surface of the inner wall 22A of the vacuum insulated container 18. A boil-off gas discharge pipe 37 communicating with the pump chamber 30 extends through the vacuum insulated lid 19. An inlet opening 37c of the boil-off gas discharge pipe 37 is located lower than the gas phase space L and higher than the suction port 40, the flow path switching device 5, and the baffle structure 50.

[0068] Fig. 12 is a diagram showing a modification of the embodiment shown in Fig. 11. In this modification, the raised bottom wall 80 of the sealing structure 25 is located lower than the flange 26 and higher than the lower end of the side wall 81. The other configurations are the same as those of the embodiment shown in Fig. 11. The sealing structure 25 of the embodiment shown in Figs. 11 and 12 can also be applied to the embodiments described with reference to Figs. 6 to 10.

[0069] Fig. 13 is an enlarged cross-sectional view showing yet another embodiment of the pump device 7. The configuration and operation of this embodiment, which will not be specifically described, are the same as those of the embodiment described with reference to Fig. 3, and therefore, redundant description thereof will be omitted.

[0070] 13 , the baffle structure 50 is a baffle plate fixed to the flow path switching device 5. That is, the baffle structure (baffle plate) 50 is fixed to a side surface of the flow path structure 65 of the flow path switching device 5. In one embodiment, the baffle structure (baffle plate) 50 may be fixed to the upper surface of the flow path structure 65. The baffle structure 50 is disposed in the liquefied gas in the vacuum insulated container 18. The baffle structure 50 is positioned above the inlet opening 62 a of the container-side flow path 62 of the flow path switching device 5. This is to prevent the baffle structure 50 from obstructing the flow of fluid toward the inlet opening 62 a of the container-side flow path 62 during drying-up, cooling-down, and hot-up.

[0071] The structure of the pump device 7 including the flow path switching device 5 and the pump 10 is not limited to the embodiments shown in Figures 1 to 13. In one embodiment, the flow path switching device 5 may be fixed to the bottom of the vacuum insulated lid 19 as shown in Figure 14. In another embodiment, the flow path switching device 5 may be configured integrally with the pump 10 as shown in Figure 15. In yet another embodiment, the flow path switching device 5 may be configured integrally with the pump 10 and fixed to the bottom of the vacuum insulated lid 19 as shown in Figure 16. The embodiments shown in Figures 14 to 16 can be appropriately applied to the embodiments described with reference to Figures 3 to 13 as long as the intended purpose can be achieved.

[0072] 17 is an enlarged cross-sectional view showing yet another embodiment of the pump device 7. The configuration and operation of this embodiment, which will not be specifically described, are the same as those of the embodiment described with reference to FIGS.

[0073] In this embodiment, the baffle structure 50 of the above-described embodiments is not provided. Instead, the boil-off gas discharge pipe 37 penetrates the side wall of the vacuum insulated container 18 and is connected to the vacuum insulated container 18. The suction port 40 is connected to the side wall of the vacuum insulated container 18 at a position lower than the boil-off gas discharge pipe 37. The connection position between the boil-off gas discharge pipe 37 and the side wall of the vacuum insulated container 18 is below the gas layer space L. Note that the baffle structure 50 of the above-described embodiments may be disposed above or below the liquid level of the liquefied gas. The object of this embodiment can also be achieved by combining the boil-off gas discharge pipe 37 of this embodiment with the baffle structure 50.

[0074] The boil-off gas discharge pipe 37 is not provided on the vacuum insulated lid 19. The vacuum insulated lid 19 seals the top opening of the vacuum insulated container 18, forming a dead-end space D at the top of the vacuum insulated container 18 that does not allow gas to escape. The dead-end space D is surrounded by the inner surface of the inner wall 22A of the vacuum insulated container 18, the side surface 25a and bottom surface 25b of the sealed structure 25, and the underside of the flange 26. Therefore, the gas layer space L forms part of the dead-end space D. The boil-off gas in the dead-end space D also functions as a gas insulation layer.

[0075] The boil-off gas discharge pipe 37 includes a first pipe 37A connected to the side wall of the vacuum insulated container 18 and a second pipe 37B extending upward from the first pipe 37A. The first pipe 37A extends horizontally, and the second pipe 37B extends vertically. The inlet opening 37c of the boil-off gas discharge pipe 37 is located below the gas space L and above the inlet opening 62a of the container-side flow path 62 of the flow path switching device 5 and the suction port 40. In other words, the connection position between the first pipe 37A and the side wall of the vacuum insulated container 18 is located between the suction port 40 and the gas space L. The boil-off gas discharge pipe 37 is connected to the boil-off gas return line 15 shown in FIG. 1 .

[0076] In Figure 17, the liquid level of the liquefied gas in the vacuum insulated container 18 is lower than the connection point between the boil-off gas discharge pipe 37 and the side wall of the vacuum insulated container 18. During operation of the pump 10, the liquid level of the liquefied gas may rise suddenly. As shown in Figure 18, when the liquid level of the liquefied gas rises, the boil-off gas discharge pipe 37 releases some of the liquefied gas from the vacuum insulated container 18. On the other hand, since the dead end space D above the connection point between the suction container 9 and the boil-off gas discharge pipe 37 is blocked by the vacuum insulated lid 19 and the vacuum insulated container 18, the pressure in the dead end space D increases as the liquid level of the liquefied gas rises, and the liquid level of the liquefied gas is repelled by the pressure in the dead end space D and prevented from rising. Therefore, the liquid level of the liquefied gas does not rise above the connection point of the boil-off gas discharge pipe 37 in the suction container 9. Therefore, it is possible to prevent the liquid surface of the liquefied gas from approaching the gas insulation layer made of boil-off gas present in the gas space L. As a result, it is possible to prevent fluidization or convection of the gas insulation layer in the gas space L, and it is possible to maintain the insulating effect of the gas insulation layer made of boil-off gas.

[0077] Furthermore, the amount of heat input to the liquid surface due to heat conduction from the room-temperature region above the wall surface of the inner wall 22A of the suction vessel 9 with a vacuum double insulation structure to the liquid surface can be kept constant. This is because the liquid surface does not rise from the position of the first pipe 37A and the thickness of the gas insulation layer in the dead end space D does not change, so the heat transfer distance from the room-temperature region above to the liquid surface can be kept constant. Therefore, the amount of heat transfer is kept constant, and an increase in the amount of heat transfer can be suppressed.

[0078] 18, the liquefied gas rises to a certain height in the vertically extending second pipe 37B but does not flow any further. The dead end space D formed in the vacuum insulated container 18 makes it difficult for the liquid level of the liquefied gas to rise within the vacuum insulated container 18.

[0079] FIG. 19 is a schematic diagram illustrating a modification of the embodiment described with reference to FIGS. 17 and 18 . As shown in FIG. 19 , the flow path switching device 5 includes a fluid guide portion 90 protruding from the outer surface of the flow path structure 65. The container-side flow path 62 is formed by the flow path structure 65 and the fluid guide portion 90. More specifically, the container-side flow path 62 is formed within the flow path structure 65 and the fluid guide portion 90. The fluid guide portion 90 in this embodiment is a flow path pipe extending downward from the outer surface of the flow path structure 65. The inlet opening 62a of the container-side flow path 62 is formed by the lower end opening of the fluid guide portion 90. The fluid guide portion 90 may be fixed to the flow path structure 65 or may be formed integrally with the flow path structure 65. During drying-up, cooling-down, and hot-up, fluids such as purge gas, liquefied gas, and heated gas flow into the container-side flow path 62 formed within the fluid guide portion 90 and the flow path structure 65. The inlet opening 37 c of the boil-off gas discharge pipe 37 is located at a higher position than the inlet opening 62 a of the vessel-side flow path 62 .

[0080] FIG. 20 is a schematic diagram showing another modified example of the embodiment described with reference to FIGS. 17 and 18 . As shown in FIG. 20 , the fluid guide portion 90 of this embodiment is configured with a wall that protrudes from the outer surface of the flow path structure 65 and extends downward. In one embodiment, the fluid guide portion 90 may be configured with a wall that surrounds the outer surface of the flow path structure 65. The upper end of the fluid guide portion 90 is fixed to the flow path structure 65. There is no gap between the upper end of the fluid guide portion 90 and the flow path structure 65, and the upper part of the fluid guide portion 90 is sealed. The container-side flow path 62 is formed by the flow path structure 65 and the fluid guide portion 90. More specifically, the container-side flow path 62 is formed within the flow path structure 65 and the fluid guide portion 90. The lower part of the fluid guide portion 90 is open, forming an inlet opening 62a of the container-side flow path 62. The inlet opening 37c of the boil-off gas discharge pipe 37 is located higher than the inlet opening 62a of the container-side flow path 62. During drying up, cooling down, and heating up, fluids such as purge gas, liquefied gas, and heated gas flow into the container-side flow path 62 formed inside the fluid guide portion 90 and in the flow path structure 65.

[0081] 19 and 20 are merely examples, and the specific structure of the fluid guide portion 90 is not particularly limited as long as the fluid guide portion 90 forms the container-side flow path 62 and its inlet opening 62a. The fluid guide portion 90 described with reference to Figures 19 and 20 may be applied to the embodiments described with reference to Figures 2 to 12.

[0082] Figure 21 is an enlarged cross-sectional view showing yet another embodiment of the pump device 7. The configuration and operation of this embodiment, unless otherwise specified, are the same as those of the embodiment described with reference to Figures 17 and 18, and therefore redundant description will be omitted. The boil-off gas discharge pipe 37 extends through the vacuum insulated lid 19 and protrudes downward from the vacuum insulated lid 19. More specifically, the boil-off gas discharge pipe 37 penetrates the sealed structure 25, inside which a vacuum is formed, and protrudes downward from the bottom surface 25b of the sealed structure 25. The inlet opening 37c of the boil-off gas discharge pipe 37 is located below the gas layer space L and above the inlet opening 62a of the container-side flow path 62 of the flow path switching device 5 and the suction port 40.

[0083] As shown in Figure 22, when the liquid level of the liquefied gas rises, the boil-off gas discharge pipe 37 releases a portion of the liquefied gas from the vacuum insulated container 18. Meanwhile, the dead-end space D above the inlet opening 37c of the boil-off gas discharge pipe 37 is blocked by the vacuum insulated lid 19 and the vacuum insulated container 18. Therefore, as the liquid level of the liquefied gas rises, the pressure in the dead-end space D increases. The liquid level of the liquefied gas is repelled by the pressure in the dead-end space D and prevented from rising. Therefore, the liquid level of the liquefied gas does not rise above the inlet opening 37c of the boil-off gas discharge pipe 37. This prevents the liquid level of the liquefied gas from approaching the gas insulation layer made of boil-off gas present in the gas space L. As a result, fluidization or convection of the gas insulation layer in the gas space L can be prevented, and the insulating effect of the gas insulation layer made of boil-off gas can be maintained.

[0084] 23 is a diagram showing an embodiment of a combination of the embodiment of the boil-off gas discharge pipe 37 described with reference to FIGS. 21 and 22 and the embodiment of the fluid guide unit 90 described with reference to FIG. 19. The fluid guide unit 90 of this embodiment is a flow path pipe extending downward from the outer surface of the flow path structure 65. During drying-up, cooling-down, and hot-up, fluids such as purge gas, liquefied gas, and heated gas flow into the fluid guide unit 90 and the container-side flow path 62 formed in the flow path structure 65. The inlet opening 37c of the boil-off gas discharge pipe 37 is located higher than the inlet opening 62a of the container-side flow path 62.

[0085] 24 is a diagram showing an embodiment in which the embodiment of the boil-off gas discharge pipe 37 described with reference to FIGS. 21 and 22 is combined with the embodiment of the fluid guide unit 90 described with reference to FIG. 20. The fluid guide unit 90 of this embodiment is configured with a wall that protrudes from the outer surface of the flow path structure 65 and extends downward. The container-side flow path 62 is formed inside the flow path structure 65 and the fluid guide unit 90. The inlet opening 37c of the boil-off gas discharge pipe 37 is located higher than the inlet opening 62a of the container-side flow path 62. During drying-up, cooling-down, and hot-up, fluids such as purge gas, liquefied gas, and heated gas flow into the inside of the fluid guide unit 90 and the container-side flow path 62 formed in the flow path structure 65.

[0086] The embodiments shown in Figures 14 to 16 can be appropriately applied to the embodiments described with reference to Figures 17 to 24 as long as the intended purpose can be achieved. For example, as shown in Figure 25, the flow path switching device 5 may be fixed to the bottom of the vacuum insulated lid 19. In another embodiment, as shown in Figure 26, the flow path switching device 5 may be configured integrally with the pump 10. In yet another embodiment, as shown in Figure 27, the flow path switching device 5 may be configured integrally with the pump 10 and fixed to the bottom of the vacuum insulated lid 19. Although not shown, the embodiments of the flow path switching device 5 and the pump 10 shown in Figures 25 to 27 can be applied to the embodiments described with reference to Figures 21 to 24.

[0087] The above-described embodiments have been described for the purpose of enabling a person of ordinary skill in the art to practice the present invention. Various modifications of the above-described embodiments would be obvious to a person skilled in the art, and the technical concept of the present invention may be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but is to be interpreted in the broadest scope in accordance with the technical concept defined by the claims.

[0088] The present invention can be used in a pump device for transporting liquefied gases such as liquefied hydrogen, liquid nitrogen, liquefied ammonia, liquefied natural gas, liquefied ethylene gas, and liquefied petroleum gas.

[0089] REFERENCE SIGNS LIST 1 Storage tank 2 Pump column 3 In-tank pump 5 Flow path switching device 6 Liquefied gas transfer line 7 Pump device 9 Suction container 10 Pump 15 Boil-off gas return line 18 Vacuum insulated container 19 Vacuum insulated lid 22A Inner wall 22B Outer wall 25 Sealing structure 26 Flange 30 Pump chamber 31 Discharge port 33 Liquefied gas discharge pipe 37 Boil-off gas discharge pipe 37A First pipe 37B Second pipe 40 Suction port 41 Electric motor 41A Motor rotor 41B Motor stator 42 Rotating shaft 44 Bearing 45 Impeller 46 Pump casing 50 Baffle structure 51 First labyrinth structure 52 Second labyrinth structure 53 Labyrinth flow path 61 Pump-side flow path 62 Container-side flow path 63 Outlet flow path 65 Flow path structure 67 Valve body 70 Spring 71 Valve seat 80 Raised bottom wall 81 Side wall 82 Upper wall 90 Fluid guide portion L Air layer space D Dead end space

Claims

1. A pump device for transferring liquefied gas, comprising: a suction container; a pump disposed within the suction container; a baffle structure disposed within the suction container and above the pump; a flow path switching device connected to the discharge port of the pump; and a liquefied gas discharge pipe connected to the flow path switching device, wherein the suction container has a vacuum insulated container with a double-wall structure inside which a vacuum is formed, and a vacuum insulated lid having a sealed structure inside which a vacuum is formed, the pump is disposed in a pump chamber formed by the vacuum insulated container and the vacuum insulated lid, an air layer space for forming a gas insulation layer made of boil-off gas is formed between the inner surface of the vacuum insulated container and the outer surface of the sealed structure, the air layer space is connected to the pump chamber, and the flow path switching device is configured to selectively communicate the liquefied gas discharge pipe with either the discharge port of the pump or the pump chamber.

2. The pump device according to claim 1, wherein the flow path switching device comprises: a flow path structure having a pump-side flow path, a container-side flow path, and an outlet flow path; and a valve body disposed within the flow path structure for selectively connecting the outlet flow path to either the pump-side flow path or the container-side flow path, wherein the pump-side flow path is connected to the discharge port of the pump, the container-side flow path is connected to the pump chamber, and the outlet flow path is connected to the liquefied gas discharge pipe.

3. The pump device according to claim 1, wherein the baffle structure is disposed between the vacuum insulating lid and the flow path switching device.

4. The pump apparatus of claim 1, wherein the baffle structure is a baffle plate.

5. The pump device according to claim 4, wherein the baffle plate is fixed to the liquefied gas discharge pipe.

6. The pump device according to claim 4, wherein the baffle plate is fixed to the inner surface of the vacuum insulated container.

7. The pump device according to claim 4, wherein the baffle plate is positioned above the liquid level of the liquefied gas in the vacuum insulated container.

8. The pump device according to claim 4, wherein the baffle plate is located below the liquid level of the liquefied gas in the vacuum insulated container.

9. The pumping apparatus of claim 1, wherein said baffle structure is fixed to said sealing structure.

10. The pump device according to claim 1, wherein the baffle structure is a labyrinth flow path structure that forms a labyrinth flow path.

11. The pump device according to claim 1, wherein the baffle structure is fixed to the flow path switching device.

12. A pump device for transferring liquefied gas, comprising: a suction container having a suction port; a pump disposed in the suction container; a flow path switching device connected to the discharge port of the pump; a liquefied gas discharge pipe connected to the flow path switching device; and a boil-off gas discharge pipe connected to the suction container, wherein the suction container has a vacuum insulated container having a double-wall structure with a vacuum formed therein, and a vacuum insulated lid having a sealed structure with a vacuum formed therein, the pump is disposed in a pump chamber formed by the vacuum insulated container and the vacuum insulated lid, an air space for forming a gas insulation layer made of boil-off gas is formed between the inner surface of the vacuum insulated container and the outer surface of the sealed structure, the air space is connected to the pump chamber, the inlet opening of the boil-off gas discharge pipe is located below the air space, and the flow path switching device is configured to selectively connect the liquefied gas discharge pipe to either the discharge port of the pump or the pump chamber.

13. The pump device according to claim 12, wherein the flow path switching device comprises: a flow path structure having a pump-side flow path, a container-side flow path, and an outlet flow path; and a valve body disposed within the flow path structure for selectively connecting the outlet flow path to either the pump-side flow path or the container-side flow path, wherein the pump-side flow path is connected to the discharge port of the pump, the container-side flow path is connected to the pump chamber, and the outlet flow path is connected to the liquefied gas discharge pipe.

14. The pump device according to claim 12, wherein the boil-off gas discharge pipe has a first pipe connected to the side wall of the vacuum insulated container at a position between the suction port and the gas space, and a second pipe extending upward from the first pipe.

15. The pump device according to claim 12, wherein the boil-off gas discharge pipe passes through the vacuum insulated lid and protrudes downward from the vacuum insulated lid.

16. The pump device according to claim 12, wherein the vacuum insulated lid seals the top opening of the vacuum insulated container, forming a dead-end space at the top of the vacuum insulated container that does not allow gas to escape.

17. The pump device according to claim 13, wherein the inlet opening of the boil-off gas discharge pipe is located above the inlet opening of the vessel-side flow path.

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