Dry-up method, cool-down method, and heat-up method for pump device

Abstract

This dry-up method introduces a purge gas into a suction container (2A) of a pump device (100A), causes the purge gas to pass through a flow path switching device (5A) within the suction container (2A) while causing the purge gas to bypass a submerged pump (1A) within the suction container (2A), introduces, into a suction container (2B) of a pump device (100B), the purge gas that has been passed through the flow path switching device (5A), and causes the purge gas to pass through a flow path switching device (5B) within the suction container (2B) while causing the purge gas to bypass a submerged pump (1B) within the suction container (2B).

Description

Methods for drying up, cooling down, and heating up a pump device

[0001] The present invention relates to a method for drying up, a method for cooling down, and a method for hotting up a submersible pump used to transport liquefied gases such as liquefied hydrogen, liquid nitrogen, liquefied ammonia, liquefied natural gas, liquefied ethylene gas, and liquefied petroleum gas, and in particular to a technique for drying, cooling, and warming a submersible pump while preventing rotation of the impeller of the submersible pump when operation is stopped.

[0002] Natural gas is widely used in thermal power generation and as a chemical raw material. Hydrogen is also expected to be an energy source that does not produce carbon dioxide, a cause of global warming. Applications of hydrogen as an energy source include fuel cells and turbine power generation. Natural gas and hydrogen are in a gaseous state at room temperature, so they are cooled and liquefied for storage and transportation. Liquefied gases such as liquefied natural gas (LNG) and liquid hydrogen are first stored in liquefied gas storage tanks and then transported to power plants, factories, etc. by pumps.

[0003] FIG. 34 is a schematic diagram showing a conventional example of a pump device for pumping liquefied gas. Pump 500 is installed in a vertical suction vessel 505 connected to a liquefied gas storage tank (not shown) in which liquefied gas is stored. Liquefied gas is introduced into suction vessel 505 through suction port 501, and suction vessel 505 is filled with liquefied gas. Pump 500 is entirely immersed in liquefied gas. Therefore, pump 500 is a submersible pump that can operate in liquefied gas. When pump 500 is operating, liquefied gas is discharged by pump 500 through discharge port 502. During operation of pump 500, a portion of the liquefied gas in suction vessel 505 evaporates and becomes gas, which is discharged from suction vessel 505 through vent line 503.

[0004] 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.

[0005] 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.

[0006] 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 .

[0007] Japanese Utility Model Application Publication No. 59-159795 Japanese Utility Model Application Publication No. 62-031680

[0008] 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 35. The liquefied gas is sequentially pressurized by the pumps 500 of the multiple pumping devices.

[0009] 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.

[0010] SUMMARY OF THE INVENTION Accordingly, the present invention provides a method for performing drying-up, cooling-down, and hot-up on a submersible pump while preventing rotation of the impeller of the submersible pump during shutdown.

[0011] In one aspect, a drying-up method is provided for purging air from a plurality of pump devices including at least a first pump device and a second pump device connected in series, the method comprising: introducing a purge gas into a first suction container of the first pump device; passing the purge gas through a first flow path switching device in the first suction container while bypassing a first submersible pump in the first suction container; introducing the purge gas that has passed through the first flow path switching device into a second suction container of the second pump device; passing the purge gas through a second flow path switching device in the second suction container while bypassing a second submersible pump in the second suction container.

[0012] In one aspect, each of the first flow path switching device and the second 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 body disposed within the flow path structure that selectively connects 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 corresponding submersible pump, the container side flow path is connected to the interior of the corresponding suction container, and the outlet flow path is connected to the discharge port of the corresponding suction container.

[0013] In one aspect, a method for drying out air from a suction vessel containing a submersible pump is provided, the method comprising forming a vacuum within the suction vessel, then introducing a purge gas into the suction vessel, and passing the purge gas through a flow path switching device within the suction vessel while bypassing the submersible pump.

[0014] In one aspect, a cool-down method is provided for supplying liquefied gas to a plurality of pump devices including at least a first pump device and a second pump device connected in series, the cool-down method comprising: introducing the liquefied gas into a first suction container of the first pump device; passing the liquefied gas through a first flow path switching device in the first suction container while bypassing a first submersible pump in the first suction container; introducing the liquefied gas that has passed through the first flow path switching device into a second suction container of the second pump device; passing the liquefied gas through a second flow path switching device in the second suction container while bypassing a second submersible pump in the second suction container.

[0015] In one aspect, each of the first flow path switching device and the second 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 body disposed within the flow path structure that selectively connects 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 corresponding submersible pump, the container side flow path is connected to the interior of the corresponding suction container, and the outlet flow path is connected to the discharge port of the corresponding suction container.

[0016] In one aspect, a cool-down method for cooling a submersible pump housed in a suction container is provided, the cool-down method including introducing liquefied gas into the suction container, causing the liquefied gas to bypass the submersible pump, and passing the liquefied gas through a flow path switching device in the suction container.

[0017] In one aspect, there is provided a hot-up method for supplying heated gas to a plurality of pump devices including at least a first pump device and a second pump device connected in series, the hot-up method including: introducing heated gas into a first suction container of the first pump device; passing the heated gas through a first flow path switching device in the first suction container while bypassing a first submersible pump in the first suction container; introducing the heated gas that has passed through the first flow path switching device into a second suction container of the second pump device; and passing the heated gas through a second flow path switching device in the second suction container while bypassing a second submersible pump in the second suction container.

[0018] In one aspect, each of the first flow path switching device and the second 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 body disposed within the flow path structure that selectively connects 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 corresponding submersible pump, the container side flow path is connected to the interior of the corresponding suction container, and the outlet flow path is connected to the discharge port of the corresponding suction container.

[0019] In one aspect, a hot-up method for heating a submersible pump housed in a suction container is provided, which includes introducing a heated gas into the suction container, causing the heated gas to bypass the submersible pump, and passing the heated gas through a flow path switching device in the suction container.

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

[0021] 11 is a diagram showing an embodiment of a pump device for transferring liquefied gas. FIG. 12 is a cross-sectional view showing an embodiment of the detailed configuration of a flow path switching device. FIG. 13 shows the state of the flow path switching device when the submersible pump is operating. FIG. 14 is a diagram for explaining an embodiment of drying up. FIG. 15 is a diagram showing an embodiment of a process of forming a vacuum in a suction container. FIG. 16 is a diagram showing an embodiment of a process of introducing purge gas into the suction container. FIG. 16 is a diagram for explaining an embodiment of cool down. FIG. 17 is a diagram for explaining another embodiment of cool down. FIG. 18 is a diagram for explaining an embodiment of hot up. FIG. 19 is a diagram for explaining another embodiment of hot up of a submersible pump. FIG. 19 is a schematic diagram showing an embodiment of a pump system including a plurality of pump devices connected in series. FIG. 19 is a diagram for explaining how drying up is performed on the submersible pumps connected in series shown in FIG. 11. FIG. 19 is a diagram showing an embodiment of a process of forming a vacuum in a plurality of suction containers. FIG. 19 is a diagram showing an embodiment of a process of introducing purge gas into a plurality of suction containers. FIG. 19 is a diagram showing an embodiment of a cool down for cooling the submersible pumps connected in series shown in FIG. 11. FIG. 19 is a diagram showing another embodiment of a cool down for cooling the submersible pumps connected in series shown in FIG. FIG. 12 is a diagram showing an embodiment of a hot-up for heating submersible pumps connected in series shown in FIG. 11 . FIG. 13 is a diagram showing another embodiment of a hot-up for heating submersible pumps connected in series shown in FIG. 11 . FIG. 14 is a schematic diagram showing another embodiment of a pump system including a plurality of pump devices connected in series. FIG. 15 is a diagram showing a state in which a plurality of pump devices in the pump system shown in FIG. 19 are dried up. FIG. 16 is a diagram showing an embodiment of a process of forming a vacuum in a plurality of suction containers. FIG. 17 is a diagram showing an embodiment of a process of introducing a purge gas into a plurality of suction containers. FIG. 18 is a diagram explaining a state in which a submersible pump connected in series shown in FIG. 19 is cooled down. FIG. 19 is a diagram showing an embodiment of a cool-down for a plurality of submersible pumps in the pump system shown in FIG. 19 . FIG. 19 is a diagram showing an embodiment of a hot-up for a plurality of pump devices in the pump system shown in FIG. 19 . FIG. 19 is a diagram showing another embodiment of a hot-up for a plurality of pump devices in the pump system shown in FIG. 19FIG. 1 is a schematic diagram showing yet another embodiment of a pump system including a plurality of pump devices connected in series; FIG. 2 is a cross-sectional view showing another embodiment of a flow path switching device; FIG. 3 is a cross-sectional view showing yet another embodiment of a flow path switching device; FIG. 4 is a cross-sectional view showing another embodiment of a submersible pump; FIG. 5 is a cross-sectional view showing yet another embodiment of a submersible pump; FIG. 6 is a cross-sectional view showing an embodiment in which a gas vent valve is open; FIG. 7 is a cross-sectional view showing an embodiment in which a gas vent valve is closed; FIG. 8 is a schematic diagram showing a conventional example of a pump device for pumping up liquefied gas; FIG. 9 is a schematic diagram showing an example of a plurality of pump devices connected in series.

[0022] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a diagram showing one embodiment of a pump device for transporting liquefied gas. Examples of liquefied gas that can be transported by the pump device 100 shown in Fig. 1 include liquefied hydrogen, liquefied nitrogen, liquefied ammonia, liquefied natural gas, liquefied ethylene gas, and liquefied petroleum gas.

[0023] As shown in Figure 1, the pump device 100 includes a submersible pump 1 for transferring liquefied gas, a suction container 2 in which the submersible pump 1 is housed, and a flow path switching device 5 for preventing rotation of the impeller 15 of the submersible pump 1 when the pump is not in operation. The suction container 2 has a suction port 7 and a discharge port 8. Liquefied gas is introduced into the suction container 2 through the suction port 7, and the suction container 2 is filled with the liquefied gas. During operation of the submersible pump 1, the entire submersible pump 1 is immersed in the liquefied gas. Therefore, the submersible pump 1 is configured to be able to operate in liquefied gas.

[0024] The submersible pump 1 includes an electric motor 11 having a motor rotor 9 and a motor stator 10, a rotating shaft 12 connected to the electric motor 11, a plurality of bearings 14 that rotatably support the rotating shaft 12, an impeller 15 fixed to the rotating shaft 12, and a pump casing 16 that houses the impeller 15. The flow path switching device 5 is disposed within the suction vessel 2. More specifically, the flow path switching device 5 is connected to both the discharge port 4 of the submersible pump 1 and the discharge port 8 of the suction vessel 2. The specific configuration of the flow path switching device 5 will be described later.

[0025] The motor rotor 9 and motor stator 10 are disposed within a motor housing 13. When power is supplied to the electric motor 11 via a power cable (not shown), the electric motor 11 rotates the rotating shaft 12 and impeller 15 together. As the impeller 15 rotates, liquefied gas is sucked into the submersible pump 1 from the suction port 3 and discharged into the flow path switching device 5 through the discharge flow path 17 and the discharge port 4. The liquefied gas then passes through the flow path switching device 5 and is discharged through the discharge port 8 of the suction container 2.

[0026] A suction valve 22 is connected to the suction port 7, and a discharge valve 23 is connected to the discharge port 8. A drain line 25 is connected to the bottom of the suction container 2, and a drain valve 26 is connected to the drain line 25. The suction port 7 is provided on the side wall of the suction container 2 and is located higher than the bottom of the suction container 2. The discharge port 8 is provided on the top of the suction container 2 and is located higher than the suction port 7. When the submersible pump 1 is in operation, the suction valve 22 and the discharge valve 23 are open, and the drain valve 26 is closed.

[0027] A vent line 31 is connected to the top of the suction vessel 2. During operation of the submersible pump 1, part of the liquefied gas is vaporized into gas due to heat generated by the submersible pump 1, and this gas is discharged from the suction vessel 2 through the vent line 31. A vent valve 32 is connected to the vent line 31. In one embodiment, this gas may be led to a gas treatment device (not shown) through the vent line 31. The gas treatment device is a device that treats gas (e.g., natural gas or hydrogen gas) vaporized from the liquefied gas. Examples of gas treatment devices include a gas incineration device (flaring device), a chemical gas treatment device, and a gas adsorption device.

[0028] 2 is a cross-sectional view showing a detailed configuration of one embodiment of the flow path switching device 5. As shown in FIG. 2, the flow path switching device 5 includes a flow path structure 45 having a pump-side flow path 41, a container-side flow path 42, and an outflow flow path 43, and a valve body 47 disposed within the flow path structure 45. The pump-side flow path 41 communicates with the discharge port 4 of the submersible pump 1, the container-side flow path 42 communicates with the interior of the suction container 2, and the outflow flow path 43 communicates with the discharge port 8 of the suction container 2. The valve body 47 is disposed to selectively communicate the outflow flow path 43 with either the pump-side flow path 41 or the container-side flow path 42. The configuration of the flow path switching device 5 is not limited to the embodiment shown in FIG. 2 as long as it can perform its intended function.

[0029] 2 shows the state of the flow path switching device 5 when the submersible pump 1 is not operating. The valve element 47 is pressed against the flow path structure 45 by the spring 50 to close the pump-side flow path 41. More specifically, the flow path structure 45 has a valve seat 51 formed around the outlet of the pump-side flow path 41, and the valve element 47 is pressed against the valve seat 51 by the spring 50. Therefore, while the valve element 47 is pressed against the valve seat 51, the pump-side flow path 41 is closed, and the container-side flow path 42 and the outflow flow path 43 are in communication. The container-side flow path 42 opens inside the suction container 2 and is in communication with the suction port 7 through the interior of the suction container 2.

[0030] 3 shows the state of the flow path switching device 5 when the submersible pump 1 is operating. When the submersible pump 1 is operating, liquefied gas is discharged from the discharge port 4 of the submersible pump 1 and flows into the pump-side flow path 41 of the flow path switching device 5. The liquefied gas flowing through the pump-side flow path 41 moves the valve body 47 against the force of the spring 50, opening the pump-side flow path 41 and closing the container-side flow path 42 with the valve body 47. As a result, the pump-side flow path 41 and the outflow flow path 43 are connected to each other.

[0031] When the submersible pump 1 stops operating, the valve element 47 is pressed against the valve seat 51 by the spring 50. As a result, as shown in Figure 2, the pump-side flow path 41 is closed, and the container-side flow path 42 and the outflow flow path 43 are connected. In this way, the flow path switching device 5 of this embodiment operates only by the spring 50 and the flow of liquefied gas.

[0032] Before operating the submersible pump 1, a drying-up process is performed in which air is removed from the suction container 2 using a purge gas, and a cooling-down process is performed in which the submersible pump 1 is cooled with liquefied gas. The drying-up and cooling-down processes are performed when the operation of the submersible pump 1 is stopped. More specifically, as shown in Figure 2, the drying-up and cooling-down processes are performed in a state in which the pump-side flow path 41 is closed by the valve body 47 and the container-side flow path 42 and the outflow flow path 43 are connected to each other.

[0033] Drying-up is an operation in which room-temperature purge gas is introduced into the suction vessel 2 to dry the submersible pump 1. One embodiment of the drying-up is described below with reference to FIG. 4 . When the submersible pump 1 is not operating (i.e., the state shown in FIG. 2 ), purge gas is supplied into the suction vessel 2 through the suction port 7. The drain valve 26 and the vent valve 32 are closed, and the suction valve 22 and the discharge valve 23 are open. The vent valve 32 may be open. The purge gas pushes out air present in the suction vessel 2 and is discharged together with the air through the vessel-side flow path 42 and the outlet flow path 43 of the flow path switching device 5 and the discharge port 8. The suction vessel 2 is eventually filled with purge gas, thereby drying the submersible pump 1.

[0034] 4, the pump-side flow path 41 is closed by the valve body 47. Therefore, the purge gas introduced into the suction vessel 2 does not flow through the submersible pump 1. As a result, unintentional rotation of the impeller 15 of the submersible pump 1 is prevented, and damage to sliding parts such as the bearing 14 is prevented.

[0035] 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.

[0036] 5 and 6 are diagrams illustrating another embodiment of the dry-up method. The configuration and operation of this embodiment, which are not specifically described, are the same as those of the embodiment described above with reference to FIG. 4, and therefore, redundant description will be omitted.

[0037] 5 and 6, the pump device 100 includes a vacuum port 61 connected to the suction container 2 and a vacuum valve 63 connected to the vacuum port 61. The vacuum port 61 is in communication with the interior of the suction container 2 and is connected to a vacuum source (e.g., a vacuum pump) (not shown). In this embodiment, the drying-up process includes creating a vacuum in the suction container 2 and introducing a purge gas into the suction container 2. The steps of creating a vacuum in the suction container 2 and introducing a purge gas into the suction container 2 may be repeated multiple times until the amount of air in the suction container 2 is reduced to an acceptable level.

[0038] Figure 5 shows one embodiment of a process for creating a vacuum in the suction vessel 2. The suction valve 22, the discharge valve 23, the drain valve 26, and the vent valve 32 are closed. When the vacuum valve 63 is opened, a vacuum is created in the suction vessel 2. Figure 6 shows one embodiment of a process for introducing a purge gas into the suction vessel 2. When a vacuum is created in the suction vessel 2, the vacuum valve 63 is closed and the suction valve 22 is opened. The purge gas is supplied into the suction vessel 2 through the suction port 7. Thereafter, when the pressure in the suction vessel 2 becomes equal to or greater than atmospheric pressure, the discharge valve 23 is opened.

[0039] During the dry-up process, the submersible pump 1 is not in operation, and the flow path switching device 5 is in the state shown in Fig. 2. The purge gas bypasses the submersible pump 1 (i.e., the purge gas does not flow through the inside of the submersible pump 1) and passes through the flow path switching device 5.

[0040] By repeating the process of creating a vacuum in the suction vessel 2 shown in Fig. 5 and the process of introducing a purge gas into the suction vessel 2 shown in Fig. 6 multiple times, the amount of air in the suction vessel 2 can be reduced to an acceptable level. In the embodiment shown in Figs. 5 and 6, the vacuum port 61 is connected to the side wall of the suction vessel 2, but the location of the vacuum port 61 is not limited to this embodiment. In one embodiment, the vacuum port 61 may be connected to the top wall of the suction vessel 2.

[0041] Cooling down of the submersible pump 1 is performed after the drying-up is completed and before starting the submersible pump 1. FIG. 7 is a diagram for explaining one embodiment of cooling down of the submersible pump 1. When the submersible pump 1 is not operating (i.e., the state shown in FIG. 2 ), liquefied gas is supplied into the suction container 2 through the suction port 7. The drain valve 26 and the vent valve 32 are closed, and the suction valve 22 and the discharge valve 23 are open. The vent valve 32 may be open. The liquefied gas comes into contact with the submersible pump 1 in the suction container 2 and is discharged through the container-side flow path 42 and the outlet flow path 43 of the flow path switching device 5 and the discharge port 8. The suction container 2 is eventually filled with liquefied gas, which cools the submersible pump 1.

[0042] During cool-down, the submersible pump 1 is in a stopped state. In Figure 7, the pump-side flow path 41 is closed by the valve body 47. Therefore, the liquefied gas introduced into the suction container 2 does not flow through the submersible pump 1. In other words, the liquefied gas bypasses the submersible pump 1 and passes through the flow path switching device 5. As a result, unintentional rotation of the impeller 15 of the submersible pump 1 is prevented, and damage to sliding parts such as the bearing 14 is prevented.

[0043] FIG. 8 is a diagram illustrating another embodiment of the cool-down of the submersible pump 1. When the submersible pump 1 is not operating (i.e., the state shown in FIG. 2 ), liquefied gas is supplied into the suction container 2 through the drain line 25 connected to the bottom of the suction container 2. The suction valve 22 and vent valve 32 are closed, and the drain valve 26 and discharge valve 23 are open. The vent valve 32 may be open. As the liquefied gas is introduced from the bottom of the suction container 2, the liquid level of the liquefied gas in the suction container 2 gradually rises. The liquefied gas (and the vaporized gas from the liquefied gas) comes into contact with the submersible pump 1 in the suction container 2 and is discharged through the container-side flow path 42 and outlet flow path 43 of the flow path switching device 5 and the discharge port 8. The suction container 2 eventually fills with liquefied gas, thereby cooling the submersible pump 1.

[0044] During cool-down, the submersible pump 1 is in a stopped state. In Figure 8, the pump-side flow path 41 is closed by the valve body 47. Therefore, the liquefied gas introduced into the suction container 2 does not flow through the submersible pump 1. In other words, the liquefied gas bypasses the submersible pump 1 and passes through the flow path switching device 5. As a result, unintentional rotation of the impeller 15 of the submersible pump 1 is prevented, and damage to sliding parts such as the bearing 14 is prevented.

[0045] For maintenance or replacement of the submersible pump 1, before the submersible pump 1 is withdrawn from the suction vessel 2 at an extremely low temperature, a hot-up process is performed to warm the submersible pump 1 with a heating gas. This hot-up process is performed before the submersible pump 1 comes into contact with the ambient air, preventing components in the air, such as nitrogen, from liquefying on the surface of the submersible pump 1. Hot-up is particularly effective when the liquefied gas is liquid hydrogen. That is, when the submersible pump 1 is withdrawn from the suction vessel 2 after being immersed in liquid hydrogen, it is at the same extremely low temperature as liquid hydrogen. Because the boiling point of hydrogen (−253°C) is lower than the boiling point of oxygen (−183°C), if the submersible pump 1 comes into contact with air immediately after being withdrawn from the suction vessel 2, not only the nitrogen but also the oxygen in the air will liquefy and drip into the suction vessel 2. Therefore, a hot-up process is performed before the submersible pump 1 is withdrawn from the suction vessel 2, and the submersible pump 1 is heated with a heating gas. Therefore, when air comes into contact with the submersible pump 1, the oxygen in the air is not liquefied, and the liquefied oxygen does not drip into the suction vessel 2.

[0046] 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 that make up the liquefied gas. This is to prevent the heating gas from liquefying when it comes into contact with the cryogenic submersible pump 1. For example, if the liquefied gas is liquefied natural gas (LNG), the heating gas used is nitrogen gas. In another example, if the liquefied gas is liquefied hydrogen, the heating gas used is helium gas. In one embodiment, the heating gas may be vaporized liquefied gas (also known as boil-off gas (BOG)). For example, boil-off gas in a liquefied gas storage tank (not shown) for storing liquefied gas, located upstream of the submersible pump 1, may be used as the heating gas.

[0047] FIG. 9 is a diagram illustrating an embodiment of hot-up of the submersible pump 1. As shown in FIG. 9, when the submersible pump 1 is not operating (i.e., the state shown in FIG. 2), heated gas is supplied into the suction vessel 2 through the suction port 7. The drain valve 26 and the vent valve 32 are closed, and the suction valve 22 and the discharge valve 23 are open. The vent valve 32 may be open. The heated gas bypasses the submersible pump 1 (i.e., the heated gas does not flow through the submersible pump 1) and passes through the flow path switching device 5. The heated gas comes into contact with the submersible pump 1 in the suction vessel 2 and is discharged through the vessel-side flow path 42 and the outlet flow path 43 of the flow path switching device 5 and the discharge port 8. The suction vessel 2 is eventually filled with heated gas, thereby heating the submersible pump 1.

[0048] FIG. 10 is a diagram illustrating another embodiment of the hot-up of the submersible pump 1. When the submersible pump 1 is not operating (i.e., the state shown in FIG. 2 ), heated gas is supplied into the suction vessel 2 through the drain line 25 connected to the bottom of the suction vessel 2. The suction valve 22 and vent valve 32 are closed, and the drain valve 26 and discharge valve 23 are open. The vent valve 32 may be open. As the heated gas is introduced from the bottom of the suction vessel 2, it comes into contact with the submersible pump 1 inside the suction vessel 2 and is discharged through the vessel-side flow path 42 and the outlet flow path 43 of the flow path switching device 5 and the discharge port 8. Eventually, the suction vessel 2 is filled with heated gas, thereby heating the submersible pump 1.

[0049] During hot-up, the submersible pump 1 is in a stopped state. In Figure 10, the pump-side flow path 41 is closed by the valve body 47. Therefore, the heated gas introduced into the suction vessel 2 does not flow through the submersible pump 1. In other words, the heated gas bypasses the submersible pump 1 and passes through the flow path switching device 5. As a result, unintentional rotation of the impeller 15 of the submersible pump 1 is prevented, and damage to sliding parts such as the bearing 14 is prevented.

[0050] In order to pressurize liquefied gas to a pressure required on the demand side, multiple pump units 100 may be connected in series. FIG. 11 is a schematic diagram showing one embodiment of a pump system including multiple pump units 100A, 100B, and 100C connected in series. In FIG. 11, the multiple pump units 100A, 100B, and 100C have the same configuration as the pump unit 100 described with reference to FIGS. 1 to 10. In the following description, the submersible pump, suction container, and flow path switching device of pump unit 100A will be referred to as submersible pump 1A, suction container 2A, and flow path switching device 5A, respectively; the submersible pump, suction container, and flow path switching device of pump unit 100B will be referred to as submersible pump 1B, suction container 2B, and flow path switching device 5B, respectively; and the submersible pump, suction container, and flow path switching device of pump unit 100C will be referred to as submersible pump 1C, suction container 2C, and flow path switching device 5C, respectively.

[0051] Pump device 100A is disposed upstream of pump device 100B, which is disposed upstream of pump device 100C. Suction port 7 of pump device 100A is connected to liquefied gas storage tank 105, which stores liquefied gas therein. Pump device 100A is connected in series to pump device 100B via communication line 107, and pump device 100B is connected in series to pump device 100C via communication line 108. More specifically, discharge port 8 of pump device 100A is connected to suction port 7 of pump device 100B via communication line 107, and discharge port 8 of pump device 100B is connected to suction port 7 of pump device 100C via communication line 108.

[0052] Submersible pumps 1A, 1B, and 1C are connected in series in the order of submersible pump 1A, submersible pump 1B, and submersible pump 1C. Liquefied gas is sequentially pressurized by these submersible pumps 1A, 1B, and 1C. When submersible pumps 1A, 1B, and 1C are operating and transferring liquefied gas, flow path switching devices 5A, 5B, and 5C are in the state shown in Figure 3.

[0053] FIG. 12 is a diagram illustrating an embodiment of drying up the submersible pumps 1A, 1B, and 1C connected in series as shown in FIG. 11 . As shown in FIG. 12 , purge gas sequentially flows into the suction vessels 2A, 2B, and 2C of the pump devices 100A, 100B, and 100C through their respective suction ports 7. During dry-up, the submersible pumps 1A, 1B, and 1C are stopped. Therefore, the flow path switching devices 5A, 5B, and 5C are in the state shown in FIG. 2 . Therefore, the purge gas bypasses the submersible pumps 1A, 1B, and 1C (i.e., the purge gas does not flow through the submersible pumps 1A, 1B, and 1C) and passes through the flow path switching devices 5A, 5B, and 5C.

[0054] More specifically, the purge gas is first introduced into the suction vessel 2A of the pump device 100A through the suction port 7. The purge gas is passed through the flow path switching device 5A while bypassing the submersible pump 1A. The purge gas that has passed through the flow path switching device 5A is introduced into the suction vessel 2B through the communication line 107 and the suction port 7 of the pump device 100B. The purge gas is passed through the flow path switching device 5B while bypassing the submersible pump 1B. Furthermore, the purge gas that has passed through the flow path switching device 5B is introduced into the suction vessel 2C through the communication line 108 and the suction port 7 of the pump device 100C. The purge gas is passed through the flow path switching device 5C while bypassing the submersible pump 1C. The purge gas is discharged through the discharge port 8 of the pump device 100C.

[0055] In this way, flow path switching devices 5A, 5B, 5C can prevent purge gas introduced into suction vessels 2A, 2B, 2C during dry-up from being introduced into submersible pumps 1A, 1B, 1C. Therefore, the impellers of submersible pumps 1A, 1B, 1C do not rotate when the pumps are not operating, and as a result, damage to the bearings and other sliding parts of submersible pumps 1A, 1B, 1C can be prevented.

[0056] 13 and 14 are diagrams illustrating an embodiment in which drying-up is performed on a plurality of pump devices 100A, 100B, and 100C according to the embodiment described with reference to Fig. 5 and Fig. 6. The configuration and operation of this embodiment, which are not specifically described, are the same as those of the embodiment described with reference to Fig. 12, and therefore, redundant description will be omitted. The vacuum ports 61 and vacuum valves 63 of the pump devices 100A, 100B, and 100C are connected to vacuum lines 121, 122, and 123, respectively.

[0057] Figure 13 illustrates one embodiment of a process for creating a vacuum in suction vessels 2A, 2B, and 2C of pumping devices 100A, 100B, and 100C. As shown in Figure 13, suction valve 22, discharge valve 23, drain valve 26, and vent valve 32 of pumping devices 100A, 100B, and 100C are closed, and vacuum valve 63 is opened. This creates a vacuum in suction vessels 2A, 2B, and 2C.

[0058] FIG. 14 illustrates one embodiment of a process for introducing purge gas into the suction vessels 2A, 2B, and 2C. When a vacuum is created in the suction vessels 2A, 2B, and 2C, the vacuum valves 63 of the pumping devices 100A, 100B, and 100C are closed and the suction valves 22 are opened. The purge gas flows sequentially into the suction vessels 2A, 2B, and 2C of the pumping devices 100A, 100B, and 100C through their respective suction ports 7. Then, when the pressure in the suction vessels 2A, 2B, and 2C reaches or exceeds atmospheric pressure, the discharge valves 23 of the pumping devices 100A, 100B, and 100C are opened. During dry-up, the submersible pumps 1A, 1B, and 1C are in a stopped state. Therefore, the flow path switching devices 5A, 5B, and 5C are in the state shown in FIG. 2. The purge gas bypasses the submersible pumps 1A, 1B, and 1C (i.e., the purge gas does not flow inside the submersible pumps 1A, 1B, and 1C) and passes through the flow path switching devices 5A, 5B, and 5C.

[0059] The steps of forming a vacuum in the suction vessels 2A, 2B, 2C shown in Figure 13 and introducing purge gas into the suction vessels 2A, 2B, 2C shown in Figure 14 may be repeated multiple times until the amount of air in the suction vessels 2A, 2B, 2C is reduced to an acceptable level.

[0060] FIG. 15 is a diagram showing one embodiment of a cool-down process for cooling submersible pumps 1A, 1B, and 1C. As shown in FIG. 15, liquefied gas sequentially flows into suction vessels 2A, 2B, and 2C of pump devices 100A, 100B, and 100C through their respective suction ports 7. During cool-down, submersible pumps 1A, 1B, and 1C are in a stopped state. Therefore, flow path switching devices 5A, 5B, and 5C are in the state shown in FIG. 2. Therefore, liquefied gas bypasses submersible pumps 1A, 1B, and 1C (i.e., liquefied gas does not flow through the submersible pumps 1A, 1B, and 1C) and passes through the flow path switching devices 5A, 5B, and 5C.

[0061] More specifically, liquefied gas is first introduced into suction container 2A of pump device 100A through suction port 7. The liquefied gas is passed through flow path switching device 5A while bypassing submersible pump 1A. The liquefied gas that has passed through flow path switching device 5A is introduced into suction container 2B through communication line 107 and suction port 7 of pump device 100B. The liquefied gas is passed through flow path switching device 5B while bypassing submersible pump 1B. Furthermore, the liquefied gas that has passed through flow path switching device 5B is introduced into suction container 2C through communication line 108 and suction port 7 of pump device 100C. The liquefied gas is passed through flow path switching device 5C while bypassing submersible pump 1C. The liquefied gas is discharged through discharge port 8 of pump device 100C.

[0062] In this way, flow path switching devices 5A, 5B, 5C can prevent liquefied gas introduced into suction vessels 2A, 2B, 2C during cool down from being introduced into submersible pumps 1A, 1B, 1C. Therefore, the impellers of submersible pumps 1A, 1B, 1C do not rotate when the pumps are not operating, and as a result, damage to the bearings and other sliding parts of submersible pumps 1A, 1B, 1C can be prevented.

[0063] Fig. 16 is a diagram showing another embodiment of the cool-down system for cooling the submersible pumps 1A, 1B, and 1C. As shown in Fig. 16, the drain line 25 and the drain valve 26 of the pump device 100A are connected to a liquefied gas storage tank 105 in which liquefied gas is stored.

[0064] The drain line 25 and drain valve 26 of the pump device 100B are connected to the discharge port 8 of the pump device 100A through a communication line 131. A portion of the communication line 107 connecting the suction port 7 of the pump device 100B and the discharge port 8 of the pump device 100A may form part of the communication line 131. The drain line 25 and drain valve 26 of the pump device 100C are connected to the discharge port 8 of the pump device 100B through a communication line 132. A portion of the communication line 108 connecting the suction port 7 of the pump device 100C and the discharge port 8 of the pump device 100B may form part of the communication line 132.

[0065] During the cool-down, liquefied gas is sequentially supplied into the suction vessels 2A, 2B, and 2C through the drain line 25 connected to the bottom of the suction vessels 2A, 2B, and 2C. The suction valve 22 and the vent valve 32 are closed, and the drain valve 26 and the discharge valve 23 are open. As the liquefied gas is introduced from the bottom of the suction vessels 2A, 2B, and 2C, the liquid levels of the liquefied gas in the suction vessels 2A, 2B, and 2C gradually rise.

[0066] During the cool-down period, the submersible pumps 1A, 1B, and 1C are not in operation, and the flow path switching devices 5A, 5B, and 5C are in the state shown in Figure 2. Therefore, the liquefied gas bypasses the submersible pumps 1A, 1B, and 1C (i.e., the liquefied gas does not flow through the submersible pumps 1A, 1B, and 1C) and passes through the flow path switching devices 5A, 5B, and 5C.

[0067] More specifically, liquefied gas is first introduced into suction container 2A of pump device 100A through drain line 25. The liquefied gas is passed through flow path switching device 5A while bypassing submersible pump 1A. The liquefied gas that has passed through flow path switching device 5A is introduced into suction container 2B through communication line 131 and drain line 25 of pump device 100B. The liquefied gas is passed through flow path switching device 5B while bypassing submersible pump 1B. Furthermore, the liquefied gas that has passed through flow path switching device 5B is introduced into suction container 2C through communication line 132 and drain line 25 of pump device 100C. The liquefied gas is passed through flow path switching device 5C while bypassing submersible pump 1C. The liquefied gas is discharged through discharge port 8 of pump device 100C.

[0068] FIG. 17 is a diagram showing one embodiment of a hot-up system for heating submersible pumps 1A, 1B, and 1C. As shown in FIG. 17, heated gas flows sequentially into suction vessels 2A, 2B, and 2C of pump devices 100A, 100B, and 100C through their respective suction ports 7. During hot-up, submersible pumps 1A, 1B, and 1C are in a stopped state. Therefore, flow path switching devices 5A, 5B, and 5C are in the state shown in FIG. 2. Therefore, the heated gas bypasses submersible pumps 1A, 1B, and 1C (i.e., the heated gas does not flow through the submersible pumps 1A, 1B, and 1C) and passes through the flow path switching devices 5A, 5B, and 5C.

[0069] More specifically, heated gas is first introduced into suction vessel 2A of pump device 100A through suction port 7. The heated gas is passed through flow path switching device 5A while bypassing submersible pump 1A. The heated gas that has passed through flow path switching device 5A is introduced into suction vessel 2B through communication line 107 and suction port 7 of pump device 100B. The heated gas is passed through flow path switching device 5B while bypassing submersible pump 1B. Furthermore, the heated gas that has passed through flow path switching device 5B is introduced into suction vessel 2C through communication line 108 and suction port 7 of pump device 100C. The heated gas is passed through flow path switching device 5C while bypassing submersible pump 1C. The heated gas is discharged through discharge port 8 of pump device 100C.

[0070] In this way, flow path switching devices 5A, 5B, 5C can prevent heated gas introduced into suction vessels 2A, 2B, 2C during hot-up from being introduced into submersible pumps 1A, 1B, 1C. Therefore, the impellers of submersible pumps 1A, 1B, 1C do not rotate when the pumps are not operating, and as a result, damage to the bearings and other sliding parts of submersible pumps 1A, 1B, 1C can be prevented.

[0071] 18 is a diagram showing another embodiment of a hot-up system for heating submersible pumps 1A, 1B, and 1C. The drain line 25 and drain valve 26 of pump device 100B are connected to the discharge port 8 of pump device 100A via a communication line 131. A portion of communication line 107 connecting the suction port 7 of pump device 100B to the discharge port 8 of pump device 100A may form part of communication line 131. The drain line 25 and drain valve 26 of pump device 100C are connected to the discharge port 8 of pump device 100B via a communication line 132. A portion of communication line 108 connecting the suction port 7 of pump device 100C to the discharge port 8 of pump device 100B may form part of communication line 132.

[0072] In the hot-up mode, heated gas is sequentially supplied into the suction vessels 2A, 2B, and 2C through the drain line 25 connected to the bottom of the suction vessels 2A, 2B, and 2C. The suction valve 22 and the vent valve 32 are closed, and the drain valve 26 and the discharge valve 23 are open. As the heated gas is introduced from the bottom of the suction vessels 2A, 2B, and 2C, it comes into contact with the submersible pumps 1A, 1B, and 1C in the suction vessels 2A, 2B, and 2C.

[0073] During hot-up, the submersible pumps 1A, 1B, and 1C are not in operation. Therefore, the flow path switching devices 5A, 5B, and 5C are in the state shown in Figure 2. Therefore, the heated gas bypasses the submersible pumps 1A, 1B, and 1C (i.e., the heated gas does not flow through the submersible pumps 1A, 1B, and 1C) and passes through the flow path switching devices 5A, 5B, and 5C.

[0074] More specifically, heated gas is first introduced into suction vessel 2A of pump device 100A through drain line 25. The heated gas is passed through flow path switching device 5A while bypassing submersible pump 1A. The heated gas that has passed through flow path switching device 5A is introduced into suction vessel 2B through communication line 131 and drain line 25 of pump device 100B. The heated gas is passed through flow path switching device 5B while bypassing submersible pump 1B. Furthermore, the heated gas that has passed through flow path switching device 5B is introduced into suction vessel 2C through communication line 132 and drain line 25 of pump device 100C. The heated gas is passed through flow path switching device 5C while bypassing submersible pump 1C. The heated gas is discharged through discharge port 8 of pump device 100C.

[0075] 11-18 includes three pump devices 100A, 100B, and 100C connected in series, the number of pump devices is not limited to this embodiment. In one embodiment, the pump system may include only two pump devices connected in series, or may include four or more pump devices connected in series.

[0076] Fig. 19 is a schematic diagram showing another embodiment of a pump system including a plurality of pump devices connected in series. The configuration and operation of this embodiment, unless otherwise specified, are the same as those of the embodiment described with reference to Fig. 11 , and therefore redundant description will be omitted. The pump system of the embodiment shown in Fig. 19 further includes pump devices 100D, 100E, and 100F connected in series, in addition to pump devices 100A, 100B, and 100C connected in series.

[0077] The pump device 100D comprises a suction container 2D, a submersible pump 1D arranged in the suction container 2D, and a flow path switching device 5D; the pump device 100E comprises a suction container 2E, a submersible pump 1E arranged in the suction container 2E, and a flow path switching device 5E; and the pump device 100F comprises a suction container 2F, a submersible pump 1F arranged in the suction container 2F, and a flow path switching device 5F.

[0078] Pump device 100D is connected in series to pump device 100E by communication line 109, and pump device 100E is connected in series to pump device 100F by communication line 110. More specifically, discharge port 23 of pump device 100D is connected to suction port 7 of pump device 100E by communication line 109, and discharge port 23 of pump device 100E is connected to suction port 7 of pump device 100F by communication line 110.

[0079] Pump devices 100D, 100E, and 100F are arranged in parallel with pump devices 100A, 100B, and 100C. The multiple pump devices 100A, 100B, 100C, 100D, 100E, and 100F have the same configuration as pump device 100 described with reference to Figures 1 to 3, so redundant description thereof will be omitted. Pump device 100A and pump device 100D are connected to a liquefied gas storage tank 105 in which liquefied gas is stored. According to the embodiment shown in Figure 19, liquefied gas is pumped by submersible pumps 1A to 1C of pump devices 100A to 100C and submersible pumps 1D to 1F of pump devices 100D to 100F, which are arranged in parallel.

[0080] FIG. 20 is a diagram showing a drying-up process for the plurality of pump devices 100A-100F of the pump system shown in FIG. 19. As shown in FIG. 20, the suction valves 22 and discharge valves 23 of the pump devices 100A-100F are open, and the drain valves 26 and vent valves 32 are closed. Purge gas flows in parallel through the pump devices 100A-100C and the pump devices 100D-100F. More specifically, the purge gas is introduced into the suction containers 2A, 2B, 2C, 2D, 2E, and 2F through their respective suction ports 7. Furthermore, as described with reference to FIG. 4, the purge gas flows through the flow path switching devices 5A-5F while bypassing the submersible pumps 1A-1F (without flowing through the submersible pumps 1A-1F).

[0081] Figures 21 and 22 are diagrams showing an embodiment in which drying up is performed on a plurality of pump devices 100A to 100F in the embodiment described with reference to Figures 5 and 6. The arrangement of pump devices 100A to 100F not specifically described is the same as in the embodiment described with reference to Figure 19, so duplicated explanations will be omitted.

[0082] The vacuum ports 61 and vacuum valves 63 of the pumping devices 100A, 100B, and 100C are connected to vacuum lines 121, 122, and 123, respectively, and the vacuum ports 61 and vacuum valves 63 of the pumping devices 100D, 100E, and 100F are connected to vacuum lines 124, 125, and 126, respectively. The vacuum lines 121, 122, 123, 124, 125, and 126 are connected to a vacuum source (e.g., a vacuum pump) not shown.

[0083] Figure 21 illustrates one embodiment of a process for creating a vacuum within suction vessels 2A-2F of pumping devices 100A-100F. As shown in Figure 21, suction valve 22, discharge valve 23, drain valve 26, and vent valve 32 of pumping devices 100A-100F are closed, and vacuum valve 63 is opened. This creates a vacuum within suction vessels 2A-2F.

[0084] FIG. 22 illustrates one embodiment of a process for introducing purge gas into the suction vessels 2A-2F. When a vacuum is created in the suction vessels 2A-2F, the vacuum valves 63 of the pumping devices 100A-100F are closed and the suction valves 22 are opened. The purge gas sequentially flows into the suction vessels 2A-2F of the pumping devices 100A-100F through their respective suction ports 7. Then, when the pressure in the suction vessels 2A-2F reaches or exceeds atmospheric pressure, the discharge valves 23 of the pumping devices 100A-100F are opened. During dry-up, the submersible pumps 1A-1F are in a stopped state. Therefore, the flow path switching devices 5A-5F are in the state shown in FIG. 2. The purge gas bypasses the submersible pumps 1A-1F (i.e., the purge gas does not flow through the submersible pumps 1A-1F) and passes through the flow path switching devices 5A-5F.

[0085] The steps of forming a vacuum in the suction vessels 2A-2F shown in FIG. 21 and introducing purge gas into the suction vessels 2A-2F shown in FIG. 22 may be repeated multiple times until the amount of air in the suction vessels 2A-2F is reduced to an acceptable level.

[0086] FIG. 23 illustrates an embodiment of cool-down for multiple pump units 100A-100F of the pump system shown in FIG. 19 . As shown in FIG. 23 , the suction valves 22 and discharge valves 23 of pump units 100A-100F are open, and the drain valves 26 and vent valves 32 are closed. Liquefied gas flows in parallel through pump units 100A-100C and pump units 100D-100F. More specifically, the liquefied gas is introduced into suction containers 2A, 2B, 2C, 2D, 2E, and 2F through their respective suction ports 7. Furthermore, as described with reference to FIG. 7 , the liquefied gas flows through flow path switching devices 5A-5F while bypassing submersible pumps 1A-1F (without flowing through the submersible pumps 1A-1F).

[0087] Fig. 24 is a diagram showing another embodiment of cool-down for the plurality of pump devices 100A to 100F of the pump system shown in Fig. 19. As shown in Fig. 24, the drain lines 25 and drain valves 26 of the pump devices 100A and 100D are connected to a liquefied gas storage tank 105 in which liquefied gas is stored.

[0088] The drain line 25 and drain valve 26 of pump device 100B are connected to the discharge port 8 of pump device 100A via a communication line 131. The drain line 25 and drain valve 26 of pump device 100C are connected to the discharge port 8 of pump device 100B via a communication line 132. The drain line 25 and drain valve 26 of pump device 100E are connected to the discharge port 8 of pump device 100D via a communication line 133. The drain line 25 and drain valve 26 of pump device 100F are connected to the discharge port 8 of pump device 100E via a communication line 134.

[0089] During cool-down, the suction valves 22 and vent valves 32 of the pump units 100A-100F are closed, and the drain valves 26 and discharge valves 23 are open. Liquefied gas flows in parallel through the pump units 100A-100C and the pump units 100D-100F. More specifically, the liquefied gas is introduced into the suction containers 2A, 2B, 2C, 2D, 2E, and 2F through their respective drain lines 25. As the liquefied gas is introduced from the bottoms of the suction containers 2A-2F, the liquid levels of the liquefied gas in the suction containers 2A-2F gradually rise.

[0090] During the cool-down period, the submersible pumps 1A to 1F are not in operation. Therefore, the flow path switching devices 5A to 5F are in the state shown in Fig. 2. As described with reference to Fig. 8, the liquefied gas flows through the flow path switching devices 5A to 5F while bypassing the submersible pumps 1A to 1F (without flowing through the interiors of the submersible pumps 1A to 1F).

[0091] FIG. 25 is a diagram illustrating the process of hot-up of the multiple pump devices 100A-100F of the pump system shown in FIG. 19. As shown in FIG. 25, the suction valves 22 and discharge valves 23 of the pump devices 100A-100F are open, and the drain valves 26 and vent valves 32 are closed. Heated gas flows in parallel through the pump devices 100A-100C and the pump devices 100D-100F. More specifically, the heated gas is introduced into the suction containers 2A, 2B, 2C, 2D, 2E, and 2F through their respective suction ports 7. Furthermore, as described with reference to FIG. 9, the heated gas flows through the flow path switching devices 5A-5F while bypassing the submersible pumps 1A-1F (without flowing through the submersible pumps 1A-1F).

[0092] Figure 26 is a diagram showing another embodiment in which hot-up is performed on multiple pump devices 100A to 100F of the pump system shown in Figure 19. As shown in Figure 26, the drain line 25 and drain valve 26 of pump device 100B are connected to the discharge port 8 of pump device 100A via a communication line 131. The drain line 25 and drain valve 26 of pump device 100C are connected to the discharge port 8 of pump device 100B via a communication line 132. The drain line 25 and drain valve 26 of pump device 100E are connected to the discharge port 8 of pump device 100D via a communication line 133. The drain line 25 and drain valve 26 of pump device 100F are connected to the discharge port 8 of pump device 100E via a communication line 134.

[0093] During hot-up, the suction valves 22 and vent valves 32 of the pump units 100A-100F are closed, and the drain valves 26 and discharge valves 23 are open. The heated gas flows in parallel through the pump units 100A-100C and the pump units 100D-100F. More specifically, the heated gas is introduced into the suction vessels 2A, 2B, 2C, 2D, 2E, and 2F through their respective drain lines 25. As the heated gas is introduced from the bottom of the suction vessels 2A-2F, it comes into contact with the submersible pumps 1A-1F inside the suction vessels 2A-2F.

[0094] During the hot-up period, the submersible pumps 1A to 1F are not in operation. Therefore, the flow path switching devices 5A to 5F are in the state shown in Fig. 2. As described with reference to Fig. 10, the heated gas flows through the flow path switching devices 5A to 5F while bypassing the submersible pumps 1A to 1F (without flowing through the interiors of the submersible pumps 1A to 1F).

[0095] Figure 27 is a schematic diagram showing yet another embodiment of a pump system including a plurality of pump devices connected in series. The configuration and operation of this embodiment, unless otherwise specified, are the same as those of the embodiment described with reference to Figure 19 , and therefore redundant description will be omitted. In the embodiment shown in Figure 27 , communication line 107 connecting pump device 100A and pump device 100B is connected to communication line 109 connecting pump device 100D and pump device 100E by intermediate header 111. Furthermore, communication line 108 connecting pump device 100B and pump device 100C is connected to communication line 110 connecting pump device 100E and pump device 100F by intermediate header 112.

[0096] The pump units 100A-100C are also connected in series to the pump units 100D-100F via the intermediate headers 111 and 112. As a result, various flows of liquefied gas are formed, enabling various operations of the pump units 100A-100C and the pump units 100D-100F. For example, it is possible to stop the operation of the pump unit 100C or the pump unit 100F for maintenance or in response to a pressure demand on the demand side.

[0097] Drying up, cooling down, and heating up of the pump system shown in Figure 27 are performed in a similar manner to the embodiment described with reference to Figures 20 to 26. Purge gas, liquefied gas, and warmed gas can flow through the intermediate headers 111, 112 in a variety of ways.

[0098] In the pump systems shown in Figures 19 and 27, two rows of pump devices 100A to 100C and pump devices 100D to 100F are provided in parallel, but three or more rows of pump devices may also be provided in parallel.

[0099] FIG. 28 is a cross-sectional view showing another embodiment of the flow path switching device 5. The configuration and operation of this embodiment, unless otherwise specifically described, are the same as those of the embodiment described with reference to FIGS. 2 and 3 , and therefore redundant description will be omitted. As shown in FIG. 28 , the flow path structure 45 includes a bypass flow path 55 that connects the pump-side flow path 41 and the outflow flow path 43. The cross-sectional area of ​​the bypass flow path 55 is smaller than the cross-sectional area of ​​the pump-side flow path 41. More specifically, the cross-sectional area of ​​the bypass flow path 55 is such that, when the valve element 47 closes the pump-side flow path 41 and a fluid (purge gas, liquefied gas, or heated gas) flows through the submersible pump 1 and the bypass flow path 55, the impeller 15 of the submersible pump 1 does not rotate due to the flow of the fluid.

[0100] The bypass flow path 55 may be a through hole as shown in FIG. 28 or a groove formed in the valve seat 51. Multiple bypass flow paths 55 may be provided as long as the fluid does not rotate the impeller 15. According to this embodiment, fluids such as purge gas, liquefied gas, or heated gas can be smoothly introduced into the submersible pump 1 during drying-up, cool-down, and hot-up. As a result, the drying-up, cool-down, and hot-up of the submersible pump 1 can be completed in a shorter time. In particular, the bypass flow path 55 eliminates the liquid level difference between the inside and outside of the submersible pump 1 when liquefied gas is introduced into the suction vessel 2 during cool-down, thereby reducing stress generated in the submersible pump 1 due to the temperature difference between the inside and outside of the submersible pump 1.

[0101] The flow path switching device 5 described with reference to FIG. 28 may be applied to the flow path switching devices 5, 5A to 5F in the embodiments described with reference to FIGS.

[0102] FIG. 29 is a cross-sectional view showing yet another embodiment of the flow path switching device 5. The configuration and operation of this embodiment, unless otherwise specified, are the same as those of the embodiment described with reference to FIGS. 2 and 3 , and therefore redundant description will be omitted. As shown in FIG. 29 , the valve element 47 has a through hole 57 that connects the pump-side flow path 41 and the outflow flow path 43. The through hole 57 extends from the pump side of the valve element 47 to the opposite side of the pump. The cross-sectional area of ​​the through hole 57 is smaller than the cross-sectional area of ​​the pump-side flow path 41. More specifically, when the valve element 47 closes the pump-side flow path 41 and a fluid (purge gas, liquefied gas, or heated gas) flows through the submersible pump 1 and the through hole 57, the cross-sectional area of ​​the through hole 57 is such that the impeller 15 of the submersible pump 1 does not rotate due to the flow of the fluid.

[0103] A plurality of through holes 57 may be provided in the valve body 47 as long as the fluid does not rotate the impeller 15. According to this embodiment, fluid such as purge gas, liquefied gas, or heated gas can be smoothly introduced into the interior of the submersible pump 1 during drying-up, cooling-down, and hot-up. As a result, the drying-up, cooling-down, and hot-up of the submersible pump 1 can be completed in a shorter time. In particular, when liquefied gas is introduced into the suction vessel 2 during cool-down, the through holes 57 eliminate the liquid level difference between the inside and outside of the submersible pump 1, and reduce stress generated in the submersible pump 1 due to the temperature difference between the inside and outside of the submersible pump 1.

[0104] The flow path switching device 5 described with reference to FIG. 29 may be applied to the flow path switching devices 5, 5A to 5F in the embodiments described with reference to FIGS.

[0105] Figure 30 is a cross-sectional view showing another embodiment of the submersible pump 1. The configuration and operation of this embodiment, which are not specifically described, are the same as those of the embodiment described with reference to Figures 1 to 3 , and therefore, redundant description will be omitted. As shown in Figure 30 , the motor housing 13 of the electric motor 11 has a through hole 70. The motor rotor 9 and motor stator 10 are disposed within the motor housing 13. The through hole 70 is formed in the upper part of the submersible pump 1 (in this embodiment, the upper wall of the motor housing 13) and is located above the impeller 15, motor rotor 9, and motor stator 10. The through hole 70 connects the interior and exterior of the submersible pump 1.

[0106] The cross-sectional area of ​​the through hole 70 is smaller than the cross-sectional area of ​​the pump-side flow path 41 of the flow path switching device 5. More specifically, the cross-sectional area of ​​the through hole 70 is such that when the valve body 47 closes the pump-side flow path 41 and a fluid (purge gas, liquefied gas, or heated gas) flows through the submersible pump 1 and the through hole 70, the impeller 15 of the submersible pump 1 does not rotate due to the flow of the fluid.

[0107] When a fluid such as purge gas, liquefied gas, or heated gas is introduced into the suction container 2 during drying-up, cooling-down, or heating-up, part of the fluid flows into the submersible pump 1 through the suction port 3. Part of the fluid also flows into the motor housing 13 of the electric motor 11. Gas present in the submersible pump 1 is expelled from the submersible pump 1 by the inflowing fluid through the through-hole 70.

[0108] According to this embodiment, fluid such as purge gas, liquefied gas, or heated gas can be smoothly introduced into the submersible pump 1 during drying-up, cool-down, and hot-up. As a result, drying-up, cool-down, and hot-up of the submersible pump 1 can be completed in a shorter time. In particular, when liquefied gas is introduced into the suction container 2 during cool-down, the through hole 70 eliminates the liquid level difference between the inside and outside of the submersible pump 1 and reduces stress generated in the submersible pump 1 due to the temperature difference between the inside and outside of the submersible pump 1. Multiple through holes 70 may be provided in the motor housing 13 as long as the fluid does not rotate the impeller 15.

[0109] 31 , the submersible pump 1 may further include a gas vent valve 75 connected to the through hole 70. The gas vent valve 75 is fixed to the motor housing 13. The gas vent valve 75 is configured to close when the submersible pump 1 is operating and to open when the submersible pump 1 is not operating.

[0110] 32 is a cross-sectional view showing one embodiment of the gas vent valve 75. The gas vent valve 75 includes a seal valve element 78, a valve rod 79 connected to the seal valve element 78, a valve seat 82 having a flow path 81 that allows the passage of a fluid such as a purge gas, a liquefied gas, or a heated gas, a rod support structure 85 that supports the valve rod 79 so that it can move in the axial direction, a spring 88 as a biasing member that biases the seal valve element 78 and the valve rod 79 in a direction away from the valve seat 82, and a valve housing 90 that accommodates the seal valve element 78, the valve rod 79, and the valve seat 82 inside.

[0111] The valve housing 90 has a relief hole 91 that communicates with the flow path 81 in the valve seat 82. The relief hole 91 communicates between the interior and exterior of the valve housing 90. Furthermore, the interior of the valve housing 90 communicates with the through hole 70 in the motor housing 13, and the valve housing 90 covers the outlet of the through hole 70. A spring 88 is disposed between the rod support structure 85 and the seal valve body 78. More specifically, one end of the spring 88 contacts the rod support structure 85, and the other end of the spring 88 contacts the valve rod 79. The spring 88 presses the valve rod 79 and the seal valve body 78 downward together, separating the seal valve body 78 from the flow path 81 in the valve seat 82. Therefore, as shown in FIG. 32 , the flow path 81 communicates with the through hole 70 in the motor housing 13.

[0112] Axial movement of the valve rod 79 and the sealing valve body 78 caused by the spring 88 is limited by a rod movement limiting member 93 fixed to the valve rod 79. The position and structure of the rod movement limiting member 93 are not limited to the embodiment shown in Figure 32. In one embodiment, the rod movement limiting member 93 may be provided on the valve housing 90 or the motor housing 13.

[0113] The gas vent valve 75 shown in Figure 32 is in a state when the submersible pump 1 is not operating. In other words, when the submersible pump 1 is not operating, the gas vent valve 75 is in an open state. The interior of the motor housing 13 communicates with the interior of the suction container 2 (see Figure 31) through the through hole 70 and the gas vent valve 75 (i.e., the flow path 81 and the relief hole 91 of the gas vent valve 75).

[0114] Figure 33 shows the state of the gas vent valve 75 when the submersible pump 1 is operating. As shown in Figure 33, when the submersible pump 1 is operating, some of the liquefied gas pressurized by the rotation of the impeller 15 flows through the bearing 14 into the motor housing 13. The interior of the motor housing 13 is filled with pressurized liquefied gas. The liquefied gas flows into the valve housing 90 through the through-hole 70 and pushes the valve rod 79 and seal valve element 78 up against the force of the spring 88. The seal valve element 78 is pressed against the valve seat 82 by the pressure of the liquefied gas, closing the flow path 81 in the valve seat 82. This blocks communication between the flow path 81 in the valve seat 82 and the through-hole 70 in the motor housing 13. In other words, the gas vent valve 75 is closed.

[0115] In this way, when the submersible pump 1 is operating, the gas vent valve 75 is closed by the pressure of the liquefied gas, and the liquefied gas inside the motor housing 13 is not discharged to the outside of the motor housing 13. Therefore, a decrease in the discharge pressure of the submersible pump 1 is prevented.

[0116] When the submersible pump 1 is not operating, the vent valve 75 is open, as shown in Figure 32. Therefore, during drying up, cooling down, and hot up, fluids such as purge gas, liquefied gas, or heated gas flow into the motor housing 13 and are discharged from the motor housing 13 through the through hole 70 and the vent valve 75 (i.e., the flow path 81 and the relief hole 91 of the vent valve 75). As a result, the fluids can be smoothly introduced into the submersible pump 1.

[0117] The embodiment described with reference to FIGS. 30 to 32 may be applied as appropriate to the embodiment described with reference to FIGS.

[0118] 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.

[0119] The present invention can be used in methods for drying up, cooling down, and hotting up submersible pumps used to transport liquefied gases such as liquefied hydrogen, liquid nitrogen, liquefied ammonia, liquefied natural gas, liquefied ethylene gas, and liquefied petroleum gas.

[0120] 1, 1A, 1B, 1C, 1D, 1E, 1F Submersible pump 2, 2A, 2B, 2C, 2D, 2E, 2F Suction vessel 3 Suction port 4 Discharge port 5, 5A, 5B, 5C, 5D, 5E, 5F Flow path switching device 7 Suction port 8 Discharge port 9 Motor rotor 10 Motor stator 11 Electric motor 12 Rotating shaft 13 Motor housing 14 Bearing 15 Impeller 16 Pump casing 17 Discharge flow path 22 Suction valve 23 Discharge valve 25 Drain line 26 Drain valve 31 Vent line 32 Vent valve 41 Pump side flow path 42 Vessel side flow path 43 Outlet flow path 45 Flow path structure 47 Valve body 50 Spring 51 Valve seat 55 Bypass flow path 57 Through hole 61 Vacuum port 63 Vacuum valve 70 Through hole 75 Gas vent valve 78 Seal valve body 79 Valve rod 81 Flow path 82 Valve seat 85 Rod support structure 88 Spring 90 Valve housing 91 Relief hole 93 Rod movement limiting member 100, 100A, 100B, 100C, 100D, 100E, 100F Pump device 105 Liquefied gas storage tank 107, 108, 109, 110, 131, 132, 133, 134 Communication line 111, 112 Intermediate header 121, 122, 123, 124, 125, 126 Vacuum line

Claims

1. A method for drying out a pump device to remove air, The purge gas is introduced into the suction container of the pump device. A drying method comprising passing the purge gas through a flow path switching device in the suction container while bypassing a submersible pump in the suction container.

2. The flow path switching device is A flow channel structure having a pump-side flow channel, a container-side flow channel, and an outlet flow channel, The flow path structure is provided with a valve body that is arranged within the flow path structure and selectively connects 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 submersible pump, The container-side flow path communicates with the inside of the suction container, The drying method according to claim 1, wherein the outflow channel is connected to the discharge port of the suction container.

3. The dry-up method according to claim 2, wherein the flow path switching device further comprises a spring that presses the valve body against the flow path structure to close the pump-side flow path.

4. The dry-up method according to claim 2, wherein the flow path switching device further comprises a bypass flow path that connects the pump-side flow path and the outflow flow path, and the cross-sectional area of ​​the bypass flow path is smaller than the cross-sectional area of ​​the pump-side flow path.

5. The dry-up method according to claim 2, wherein the valve body is provided with a through hole that connects the pump-side passage and the outflow passage, and the cross-sectional area of ​​the through hole is smaller than the cross-sectional area of ​​the pump-side passage.

6. The dry-up method according to claim 1, wherein the purge gas is introduced into the first suction container, a portion of the purge gas is introduced into the submersible pump, and the gas present in the submersible pump is discharged from the submersible pump through a through hole provided at the top of the submersible pump.

7. The drying method according to claim 6, wherein the through hole is connected to a gas vent valve, the gas vent valve is closed when the submersible pump is in operation and open when the operation of the first submersible pump is stopped.

8. The drying method according to claim 1, further comprising creating a vacuum in the suction vessel of the pump device before introducing the purge gas into the suction vessel of the pump device.

9. A drying method for removing air from a suction container housing a submersible pump, A vacuum is formed in the aforementioned suction container, and then, The purge gas is introduced into the suction container. A drying method comprising passing the purge gas through a flow path switching device in the suction container while bypassing the submersible pump.

10. The aforementioned flow path switching device is A flow channel structure having a pump-side flow channel, a container-side flow channel, and an outlet flow channel, The flow path structure is provided with a valve body that is arranged within the flow path structure and selectively connects 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 submersible pump, The container-side flow path communicates with the inside of the suction container, The drying method according to claim 9, wherein the outflow channel is connected to the discharge port of the suction container.

11. The dry-up method according to claim 10, wherein the flow path switching device further comprises a spring that presses the valve body against the flow path structure to close the pump-side flow path.

12. The dry-up method according to claim 10, wherein the flow path switching device further comprises a bypass flow path that connects the pump-side flow path and the outflow flow path, and the cross-sectional area of ​​the bypass flow path is smaller than the cross-sectional area of ​​the pump-side flow path.

13. The dry-up method according to claim 10, wherein the valve body is provided with a through hole that connects the pump-side passage and the outflow passage, and the cross-sectional area of ​​the through hole is smaller than the cross-sectional area of ​​the pump-side passage.

14. The dry-up method according to claim 9, wherein the purge gas is introduced into the suction container, a portion of the purge gas is introduced into the submersible pump, and the gas present in the submersible pump is discharged from the submersible pump through a through hole provided at the top of the submersible pump.

15. The drying method according to claim 14, wherein the through hole is connected to a gas vent valve, the gas vent valve is closed when the submersible pump is in operation, and is open when the submersible pump is stopped.

16. A method for supplying liquefied gas to a pump device, The liquefied gas is introduced into the suction container of the pump device, A cooling method comprising passing the liquefied gas through a flow path switching device in the suction container while bypassing the submersible pump in the suction container.

17. The flow path switching device is A flow channel structure having a pump-side flow channel, a container-side flow channel, and an outlet flow channel, The flow path structure is provided with a valve body that is arranged within the flow path structure and selectively connects 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 submersible pump, The container-side flow path communicates with the inside of the suction container, The cool-down method according to claim 16, wherein the outflow channel is connected to the discharge port of the suction container.

18. The cool-down method according to claim 17, wherein the flow path switching device further comprises a spring that presses the valve body against the flow path structure to close the pump-side flow path.

19. The cool-down method according to claim 17, wherein the flow path switching device further comprises a bypass flow path that connects the pump-side flow path and the outflow flow path, and the cross-sectional area of ​​the bypass flow path is smaller than the cross-sectional area of ​​the pump-side flow path.

20. The cool-down method according to claim 17, wherein the valve body is provided with a through hole that connects the pump-side passage and the outflow passage, and the cross-sectional area of ​​the through hole is smaller than the cross-sectional area of ​​the pump-side passage.

21. The cool-down method according to claim 16, wherein the liquefied gas is introduced into the suction container, a portion of the liquefied gas is introduced into the submersible pump, and the gas present in the submersible pump is discharged from the submersible pump through a through hole provided at the top of the submersible pump.

22. The cool-down method according to claim 21, wherein the through hole is connected to a gas vent valve, the gas vent valve is closed when the submersible pump is in operation, and is open when the submersible pump is stopped.

23. The cool-down method according to claim 16, wherein the liquefied gas is introduced into the suction container from a first drain line connected to the bottom of the suction container.

24. A method for cooling down a submersible pump housed in a suction container, The liquefied gas is introduced into the suction container, A cooling method comprising passing the liquefied gas through a flow path switching device in the suction container while bypassing the submersible pump.

25. The cool-down method according to claim 24, wherein the liquefied gas is introduced into the suction container from a drain line connected to the bottom of the suction container.

26. The aforementioned flow path switching device is A flow channel structure having a pump-side flow channel, a container-side flow channel, and an outlet flow channel, The flow path structure is provided with a valve body that is arranged within the flow path structure and selectively connects 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 submersible pump, The container-side flow path communicates with the inside of the suction container, The cool-down method according to claim 24, wherein the outflow channel is connected to the discharge port of the suction container.

27. The cool-down method according to claim 26, wherein the flow path switching device further comprises a spring that presses the valve body against the flow path structure to close the pump-side flow path.

28. The cool-down method according to claim 26, wherein the flow path switching device further comprises a bypass flow path that connects the pump-side flow path and the outflow flow path, and the cross-sectional area of ​​the bypass flow path is smaller than the cross-sectional area of ​​the pump-side flow path.

29. The cool-down method according to claim 26, wherein the valve body is provided with a through hole that connects the pump-side passage and the outflow passage, and the cross-sectional area of ​​the through hole is smaller than the cross-sectional area of ​​the pump-side passage.

30. The cool-down method according to claim 24, wherein the liquefied gas is introduced into the suction container, a portion of the liquefied gas is introduced into the submersible pump, and the gas present in the submersible pump is discharged from the submersible pump through a through hole provided at the top of the submersible pump.

31. The cool-down method according to claim 30, wherein the through hole is connected to a gas vent valve, the gas vent valve is closed when the submersible pump is in operation, and is open when the submersible pump is stopped.

32. A method for supplying heated gas to a pump device, The heated gas is introduced into the suction container of the pump device, A hot-up method comprising passing the heated gas through a flow path switching device in the suction container while bypassing a submersible pump in the suction container.

33. The flow path switching device is A flow channel structure having a pump-side flow channel, a container-side flow channel, and an outlet flow channel, The flow path structure is provided with a valve body that is arranged within the flow path structure and selectively connects 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 submersible pump, The container-side flow path communicates with the inside of the suction container, The hot-up method according to claim 32, wherein the outflow channel is connected to the discharge port of the suction container.

34. The hot-up method according to claim 33, wherein the flow path switching device further comprises a spring that presses the valve body against the flow path structure to close the pump-side flow path.

35. The hot-up method according to claim 33, wherein the flow path switching device further comprises a bypass flow path that connects the pump-side flow path and the outflow flow path, and the cross-sectional area of ​​the bypass flow path is smaller than the cross-sectional area of ​​the pump-side flow path.

36. The hot-up method according to claim 33, wherein the valve body is provided with a through hole that connects the pump-side passage and the outflow passage, and the cross-sectional area of ​​the through hole is smaller than the cross-sectional area of ​​the pump-side passage.

37. The hot-up method according to claim 32, wherein the heating gas is introduced into the suction container, a portion of the heating gas is introduced into the submersible pump, and the gas present in the submersible pump is discharged from the submersible pump through a through hole provided at the top of the submersible pump.

38. The hot-up method according to claim 37, wherein the through hole is connected to a gas vent valve, the gas vent valve is closed when the submersible pump is in operation, and is open when the submersible pump is stopped.

39. The hot-up method according to claim 32, wherein the heating gas is introduced into the suction container from a first drain line connected to the bottom of the suction container.

40. A method for heating a submersible pump housed in a suction container, A heating gas is introduced into the suction container, A hot-up method comprising passing the heated gas through a flow path switching device in the suction container while bypassing the submersible pump.

41. The hot-up method according to claim 40, wherein the heating gas is introduced into the suction container from a drain line connected to the bottom of the suction container.

42. The aforementioned flow path switching device is A flow channel structure having a pump-side flow channel, a container-side flow channel, and an outlet flow channel, The flow path structure is provided with a valve body that is arranged within the flow path structure and selectively connects 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 submersible pump, The container-side flow path communicates with the inside of the suction container, The hot-up method according to claim 40, wherein the outflow channel is connected to the discharge port of the suction container.

43. The hot-up method according to claim 42, wherein the flow path switching device further comprises a spring that presses the valve body against the flow path structure to close the pump-side flow path.

44. The hot-up method according to claim 42, wherein the flow path switching device further comprises a bypass flow path that connects the pump-side flow path and the outflow flow path, and the cross-sectional area of ​​the bypass flow path is smaller than the cross-sectional area of ​​the pump-side flow path.

45. The hot-up method according to claim 42, wherein the valve body is provided with a through hole that connects the pump-side passage and the outflow passage, and the cross-sectional area of ​​the through hole is smaller than the cross-sectional area of ​​the pump-side passage.

46. The hot-up method according to claim 40, wherein the heating gas is introduced into the suction container, a portion of the heating gas is introduced into the submersible pump, and the gas present in the submersible pump is discharged from the submersible pump through a through hole provided at the top of the submersible pump.

47. The hot-up method according to claim 46, wherein the through hole is connected to a gas vent valve, the gas vent valve is closed when the submersible pump is in operation, and is open when the submersible pump is stopped.