Cool-down method for pump devices

Abstract

To provide a method for cooling down submerged pumps while preventing rotation of impellers of the submerged pumps during a shutdown.SOLUTION: A cool-down method simultaneously introduces liquefied gas into suction containers 2A and 2B through introduction lines 121 and 122 extending from a liquefied gas storage tank 105, passes the liquefied gas through a flow passage switching device 5A in the suction container 2A while making the liquefied gas bypass a submerged pump 1A in the suction container 2A, passes the liquefied gas through a flow passage switching device 5B in the suction container 2B while making the liquefied gas bypass a submerged pump 1B in the suction container 2B, and discharges the liquefied gas from the suction container 2A and the suction container 2B through the flow passage switching device 5A and the flow passage switching device 5B.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a method for cooling down a submersible pump used for transporting 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 cooling a submersible pump while preventing rotation of the impeller of the submersible pump when operation is stopped. [Background technology]

[0002] Natural gas is widely used for thermal power generation and as a chemical raw material. Hydrogen is also expected to be an energy source that does not emit carbon dioxide, which causes 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 in order to be stored and transported. Liquefied gases such as liquefied natural gas (LNG) and liquid hydrogen are temporarily stored in liquefied gas tanks and then transported to power plants, factories, etc. by pumps.

[0003] FIG. 41 is a schematic diagram showing a conventional example of a pump device for pumping up liquefied gas. The pump 500 is installed in a vertical suction vessel 505 connected to a liquefied gas tank (not shown) in which liquefied gas is stored. The liquefied gas is introduced into the suction vessel 505 through a suction port 501, and the suction vessel 505 is filled with the liquefied gas. The entire pump 500 is immersed in the liquefied gas. Therefore, the pump 500 is a submerged pump that can be operated in the liquefied gas. When the pump 500 is operated, the liquefied gas is discharged by the pump 500 through the discharge port 502. During the operation of the pump 500, a part of the liquefied gas in the suction vessel 505 is vaporized into gas, and this gas is discharged from the suction vessel 505 through a vent line 503.

[0004] If the pump 500 is at room temperature when the pump 500 is started, the liquefied gas at ultra-low temperature will vaporize when it comes into contact with the pump 500. Therefore, in order to prevent the liquefied gas from vaporizing, a cool-down process is performed in which the pump 500 is cooled with the liquefied gas before the pump 500 is operated.

[0005] Cooling down is performed by injecting liquefied gas (e.g., liquefied natural gas) into the suction vessel 505. The 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 discharged through the discharge port 502. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Utility Model Application Publication No. 59-159795 [Patent Document 2] Japanese Utility Model Publication No. 62-031680 Summary of the Invention [Problem to be solved by the invention]

[0007] 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 42. The liquefied gas is sequentially pressurized by the pumps 500 of the multiple pumping devices.

[0008] However, when the above-mentioned cool-down is performed on pump devices connected in series, the following problem occurs. That is, when liquefied gas is flowed into the pump devices before they start operating, the liquefied gas flows through all of the pumps 500. This flow of liquefied gas forcibly rotates the impellers of the pumps 500 that are not operating. As a result, sliding parts such as bearings are damaged. In order to prevent unintended rotation of the impellers of the pumps 500, it is possible to flow the liquefied gas at a low flow rate, but in this case, it takes a very long time for the cool-down to be completed in all of the pump devices.

[0009] Therefore, the present invention provides a method for performing a cool-down on a submersible pump while preventing rotation of the impeller of the submersible pump during shutdown. [Means for solving the problem]

[0010] In one aspect, there is provided a cool-down method for cooling multiple submersible pumps of multiple pump devices including at least a first pump device and a second pump device connected to each other with liquefied gas, the cool-down method comprising: simultaneously introducing liquefied gas into a first suction container of the first pump device and a second suction container of the second pump device through a first inlet line and a second inlet line extending from a liquefied gas storage tank; passing the liquefied gas through a first flow path switching device in the first suction container while bypassing the first submersible pump in the first suction container, and passing the liquefied gas through a second flow path switching device in the second suction container while bypassing the second submersible pump in the second suction container; and discharging the liquefied gas from the first suction container and the second suction container through the first flow path switching device and the second flow path switching device.

[0011] In one embodiment, 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 outflow flow path, and a valve body 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, 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 outflow flow path is connected to the discharge port of the corresponding suction container. In one embodiment, each of the first flow path switching device and the second flow path switching device further includes a spring that presses the valve body against the flow path structure to close the pump side flow path.

[0012] In one embodiment, the liquefied gas is simultaneously introduced into the first suction container and the second suction container through the first inlet line and the second inlet line, and through a drain port of the first suction container and a drain port of the second suction container. In one embodiment, the liquefied gas is simultaneously introduced into the first suction container and the second suction container through the first inlet line and the second inlet line, through the suction port of the first suction container and the suction port of the second suction container. In one embodiment, the first pump device and the second pump device are connected in series. In one embodiment, the first pump device and the second pump device are connected in parallel.

[0013] In one aspect, there is provided a cool-down method for cooling a plurality of submersible pumps of a plurality of pump devices including at least a first pump device and a second pump device connected to each other with liquefied gas, the cool-down method including: introducing liquefied gas into a first suction container of the first pump device; passing the boil-off gas through a first flow path switching device in the first suction container while causing boil-off gas generated from the liquefied gas to bypass the first submersible pump in the first suction container; introducing the boil-off gas from the first suction container into a second suction container of the second pump device; starting operation of the first submersible pump; introducing the liquefied gas from the first suction container into the second suction container; and passing the liquefied gas through a second flow path switching device in the second suction container while causing the liquefied gas to bypass the second submersible pump in the second suction container.

[0014] In one embodiment, 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 outflow flow path, and a valve body 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, 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 outflow flow path is connected to the discharge port of the corresponding suction container. In one embodiment, each of the first flow path switching device and the second flow path switching device further includes a spring that presses the valve body against the flow path structure to close the pump side flow path.

[0015] In one embodiment, the first submersible pump is started to operate, thereby introducing the liquefied gas from the first suction container into the second suction container through a drain port of the second suction container. In one embodiment, the first submersible pump is started to introduce the liquefied gas from the first suction container into the second suction container through a suction port of the second suction container.

[0016] In one embodiment, the plurality of pump devices further includes a third pump device connected to the first pump device and the second pump device, the third pump device having the same configuration as the first pump device and the second pump device, and the method further includes introducing the boil-off gas from the second suction container into a third suction container of the third pump device, and after starting operation of the first submersible pump, introducing the liquefied gas from the second suction container into the third suction container, and passing the liquefied gas through a third flow path switching device in the third suction container while bypassing the third submersible pump in the third suction container. In one embodiment, the first pump device, the second pump device, and the third pump device are connected in series. In one embodiment, the first pump device, the second pump device, and the third pump device are connected in parallel.

[0017] In one embodiment, the plurality of pump devices further includes a third pump device connected to the first pump device and the second pump device, the third pump device having the same configuration as the first pump device and the second pump device, and the method further includes simultaneously introducing the boil-off gas from the first suction container into the second suction container of the second pump device and the third suction container of the third pump device, starting operation of the first submersible pump to simultaneously introduce liquefied gas from the first suction container into the second suction container and the third suction container, passing the liquefied gas through the second flow path switching device while bypassing the second submersible pump, and passing the liquefied gas through the third flow path switching device in the third suction container while bypassing the third submersible pump in the third suction container, and simultaneously discharging the liquefied gas from the second suction container and the third suction container through the second flow path switching device and the third flow path switching device. In one embodiment, the first pump device, the second pump device, and the third pump device are connected in series. In one embodiment, the first pump device, the second pump device, and the third pump device are connected in parallel.

[0018] In one embodiment, the first pump device and the second pump device are connected in series. In one embodiment, the first pump device and the second pump device are connected in parallel. Effect of the Invention

[0019] The flow path switching device can prevent the liquefied gas introduced into the suction vessel during cool-down from passing through 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. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 illustrates an embodiment of a pumping device for transferring liquefied gas. [Diagram 2] FIG. 2 is a cross-sectional view showing a detailed configuration of a flow path switching device according to an embodiment. [Diagram 3] 1 shows the state of the flow path switching device when the submersible pump is operating. [Figure 4] FIG. 13 is a diagram for explaining an embodiment of a cool-down process. [Diagram 5] FIG. 11 is a diagram for explaining another embodiment of the cool-down. [Figure 6] FIG. 1 is a schematic diagram illustrating an embodiment of a pump system including multiple pump devices connected in series. [Figure 7] FIG. 7 illustrates an embodiment of a cooldown for cooling the multiple submersible pumps shown in FIG. [Figure 8] FIG. 13 is a schematic diagram illustrating another embodiment of a pump system including multiple pump devices connected in series. [Figure 9] FIG. 9 illustrates an embodiment of a cooldown for cooling the multiple submersible pumps shown in FIG. [Figure 10] FIG. 1 is a schematic diagram illustrating an embodiment of performing a cool-down for a pump system having multiple pump devices connected in series and parallel. [Figure 11] FIG. 13 is a schematic diagram showing another embodiment of performing cool-down for a pump system having multiple pump devices connected in series and parallel. [Figure 12] FIG. 13 is a schematic diagram illustrating yet another embodiment of a pump system including multiple pump devices connected in series. [Figure 13] FIG. 13 is a schematic diagram illustrating an embodiment of performing a cool-down on the pump system shown in FIG. 12. [Figure 14] FIG. 13 is a schematic diagram illustrating an embodiment of performing a cool-down on the pump system shown in FIG. 12. [Figure 15]FIG. 13 is a schematic diagram illustrating yet another embodiment of a pump system including multiple pump devices connected in series. [Figure 16] FIG. 16 is a schematic diagram illustrating an embodiment of performing a cool-down on the pump system shown in FIG. 15. [Figure 17] FIG. 16 is a schematic diagram illustrating an embodiment of performing a cool-down on the pump system shown in FIG. 15. [Figure 18] FIG. 13 is a schematic diagram illustrating yet another embodiment of a pump system including multiple pump devices connected in series. [Figure 19] FIG. 19 is a schematic diagram illustrating an embodiment of performing a cool-down on the pump system shown in FIG. 18. [Figure 20] FIG. 19 is a schematic diagram illustrating an embodiment of performing a cool-down on the pump system shown in FIG. 18. [Figure 21] FIG. 13 is a schematic diagram illustrating yet another embodiment of a pump system including multiple pump devices connected in series. [Figure 22] FIG. 22 is a schematic diagram illustrating an embodiment for performing a cool-down on the pump system shown in FIG. 21. [Diagram 23] FIG. 22 is a schematic diagram illustrating an embodiment for performing a cool-down on the pump system shown in FIG. 21. [Figure 24] FIG. 1 is a schematic diagram illustrating an embodiment of a pump system including multiple pump devices connected in series and parallel. [Diagram 25] FIG. 25 is a schematic diagram illustrating an embodiment for performing a cool-down on the pump system shown in FIG. 24. [Figure 26] FIG. 25 is a schematic diagram illustrating an embodiment for performing a cool-down on the pump system shown in FIG. 24. [Figure 27] FIG. 1 is a schematic diagram illustrating an embodiment of a pump system including multiple pump devices connected in parallel. [Figure 28] FIG. 28 is a schematic diagram illustrating an embodiment for performing a cool-down on the pump system shown in FIG. 27. [Figure 29]FIG. 28 is a schematic diagram illustrating an embodiment for performing a cool-down on the pump system shown in FIG. 27. [Diagram 30] FIG. 13 is a schematic diagram illustrating another embodiment of a pump system including multiple pump devices connected in parallel. [Diagram 31] FIG. 31 is a schematic diagram illustrating an embodiment for performing a cool-down on the pump system shown in FIG. 30. [Diagram 32] FIG. 31 is a schematic diagram illustrating an embodiment for performing a cool-down on the pump system shown in FIG. 30. [Diagram 33] FIG. 13 is a schematic diagram illustrating yet another embodiment of a pump system including multiple pump devices connected in parallel. [Diagram 34] FIG. 34 is a schematic diagram illustrating an embodiment for performing a cool-down on the pump system shown in FIG. 33. [Diagram 35] FIG. 34 is a schematic diagram illustrating an embodiment for performing a cool-down on the pump system shown in FIG. 33. [Diagram 36] FIG. 13 is a schematic diagram illustrating yet another embodiment of a pump system including multiple pump devices connected in parallel. [Figure 37] FIG. 37 is a schematic diagram illustrating an embodiment for performing a cool-down on the pump system shown in FIG. 36. [Figure 38] FIG. 37 is a schematic diagram illustrating an embodiment for performing a cool-down on the pump system shown in FIG. 36. [Figure 39] FIG. 11 is a cross-sectional view showing another embodiment of the flow path switching device. [Diagram 40] FIG. 11 is a cross-sectional view showing still another embodiment of the flow path switching device. [Diagram 41] FIG. 1 is a schematic diagram showing a conventional example of a pump device for pumping up liquefied gas. [Diagram 42] FIG. 2 is a schematic diagram illustrating an example of multiple pump devices connected in series. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] 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 transferring liquefied gas. Examples of liquefied gas transferred 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.

[0022] As shown in Fig. 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 an impeller 15 of the submersible pump 1 when the submersible pump 1 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.

[0023] 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 for rotatably supporting the rotating shaft 12, an impeller 15 fixed to the rotating shaft 12, and a pump casing 16 for housing the impeller 15. The flow path switching device 5 is disposed in 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. A specific configuration of the flow path switching device 5 will be described later.

[0024] The motor rotor 9 and the motor stator 10 are disposed within a motor housing 13. When power is supplied to the electric motor 11 through a power cable (not shown), the electric motor 11 rotates the rotating shaft 12 and the impeller 15 together. As the impeller 15 rotates, the liquefied gas is sucked into the submersible pump 1 from the suction port 3, and is discharged into the flow path switching device 5 through the discharge flow path 17 and the discharge port 4. The liquefied gas further passes through the flow path switching device 5 and is discharged through the discharge port 8 of the suction container 2.

[0025] A suction valve 22 is connected to the suction port 7, and a discharge valve 23 is connected to the discharge port 8. The suction vessel 2 has a drain port 25 connected to its bottom. A drain valve 26 is connected to the drain port 25. The suction port 7 is provided on the side wall of the suction vessel 2 and is located higher than the bottom of the suction vessel 2. The discharge port 8 is provided on the top of the suction vessel 2 and is located higher than the suction port 7. During operation of the submersible pump 1, the suction valve 22 and the discharge valve 23 are open, and the drain valve 26 is closed.

[0026] A vent line 31 is connected to the top of the suction vessel 2. During operation of the submersible pump 1, a part of the liquefied gas is vaporized into gas due to heat generation 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 the gas treatment device include a gas incineration device (flaring device), a chemical gas treatment device, and a gas adsorption device.

[0027] FIG. 2 is a cross-sectional view showing an embodiment of the detailed configuration 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 arranged in 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 inside 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 arranged 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.

[0028] 2 shows the state of the flow path switching device 5 when the submersible pump 1 is not operating. The valve body 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 body 47 is pressed against the valve seat 51 by the spring 50. Therefore, while the valve body 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 in the suction container 2 and is in communication with the suction port 7 through the inside of the suction container 2.

[0029] 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.

[0030] When the operation of the submersible pump 1 stops, the valve body 47 is pressed against the valve seat 51 by the spring 50. As a result, as shown in Fig. 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 manner, the flow path switching device 5 of this embodiment is operated only by the spring 50 and the flow of liquefied gas.

[0031] Before operating the submersible pump 1, a cool-down is performed in which the submersible pump 1 is cooled with liquefied gas. The cool-down is performed when the operation of the submersible pump 1 is stopped. More specifically, as shown in Fig. 2, the cool-down is 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 in communication.

[0032] 4 is a diagram for explaining one embodiment of the cool-down of the submersible pump 1. When the operation of the submersible pump 1 is stopped (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 opened. 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 outflow flow path 43 of the flow path switching device 5, and the discharge port 8. The inside of the suction container 2 is soon filled with liquefied gas, which cools the submersible pump 1.

[0033] During the cool-down, the submersible pump 1 is not in operation. In FIG. 4, 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, unintended rotation of the impeller 15 of the submersible pump 1 is prevented, and damage to sliding parts such as the bearing 14 is prevented.

[0034] FIG. 5 is a diagram for explaining another embodiment of the cool-down of the submersible pump 1. In a state where the operation of the submersible pump 1 is stopped (i.e., the state shown in FIG. 2), the liquefied gas is supplied into the suction container 2 through the drain port 25 connected to the bottom of the suction container 2. The suction valve 22 and the vent valve 32 are closed, and the drain valve 26 and the discharge valve 23 are open. The vent valve 32 may be opened. While 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 gas evaporated 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 the outflow flow path 43 of the flow path switching device 5, and the discharge port 8. The inside of the suction container 2 is soon filled with the liquefied gas, which cools the submersible pump 1.

[0035] During the cool-down, the submersible pump 1 is not in operation. In FIG. 5, 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, unintended rotation of the impeller 15 of the submersible pump 1 is prevented, and damage to sliding parts such as the bearing 14 is prevented.

[0036] In order to pressurize the liquefied gas to a pressure required by the demand side, a plurality of pump devices 100 may be connected together. FIG. 6 is a schematic diagram showing an embodiment of a pump system including a plurality of pump devices 100A, 100B, and 100C connected in series. In FIG. 6, the plurality of pump devices 100A, 100B, and 100C have the same configuration as the pump device 100 described with reference to FIGS. 1 to 5. In the following description, the submersible pump, suction vessel, and flow path switching device of the pump device 100A are referred to as the submersible pump 1A, the suction vessel 2A, and the flow path switching device 5A, respectively, the submersible pump, suction vessel, and flow path switching device of the pump device 100B are referred to as the submersible pump 1B, the suction vessel 2B, and the flow path switching device 5B, respectively, and the submersible pump, suction vessel, and flow path switching device of the pump device 100C are referred to as the submersible pump 1C, the suction vessel 2C, and the flow path switching device 5C, respectively.

[0037] The pump device 100A is disposed upstream of the pump device 100B, which is disposed upstream of the pump device 100C. The suction port 7A of the pump device 100A is connected to a liquefied gas storage tank 105 in which liquefied gas is stored by a suction line 34. The pump device 100A is connected in series to the pump device 100B by a communication line 107, and the pump device 100B is connected in series to the pump device 100C by a communication line 108. More specifically, the discharge port 8A of the pump device 100A is connected to the suction port 7B of the pump device 100B by the communication line 107, and the discharge port 8B of the pump device 100B is connected to the suction port 7C of the pump device 100C by the communication line 108.

[0038] A communication valve 114 is attached to the communication line 107, and a communication valve 115 is attached to the communication line 108. When the communication valve 114 is closed, communication between the discharge port 8A of the pump device 100A and the suction port 7B of the pump device 100B is blocked. When the communication valve 115 is closed, communication between the discharge port 8B of the pump device 100B and the suction port 7C of the pump device 100C is blocked. When the submersible pumps 1A, 1B, and 1C are operating, the communication valves 114 and 115 are open.

[0039] The submersible pumps 1A, 1B, and 1C are connected in series in the order of submersible pump 1A, submersible pump 1B, and submersible pump 1C. The liquefied gas is successively pressurized by these submersible pumps 1A, 1B, and 1C. When the submersible pumps 1A, 1B, and 1C are in operation and transferring the liquefied gas, the flow path switching devices 5A, 5B, and 5C are in the state shown in Figure 3.

[0040] The relative position of the liquefied gas storage tank 105 with respect to the pump devices 100A, 100B, and 100C is not particularly limited. For example, the liquefied gas storage tank 105 may be disposed at a higher position than the pump devices 100A, 100B, and 100C, and the liquefied gas in the liquefied gas storage tank 105 may reach the pump devices 100A, 100B, and 100C by its own weight. In another example, the liquefied gas storage tank 105 may be disposed at the same height as the pump devices 100A, 100B, and 100C or at a lower position than the pump devices 100A, 100B, and 100C, and the liquefied gas in the liquefied gas storage tank 105 may be sent to the pump devices 100A, 100B, and 100C by a pump (not shown).

[0041] The pump system includes an inlet line 121 connected to the drain port 25A of the suction vessel 2A, an inlet line 122 connected to the drain port 25B of the suction vessel 2B, and an inlet line 123 connected to the drain port 25C of the suction vessel 2C. The inlet lines 121, 122, and 123 are connected to the liquefied gas tank 105 and extend from the liquefied gas tank 105 to the suction vessels 2A, 2B, and 2C. The suction vessels 2A, 2B, and 2C are connected to the liquefied gas tank 105 through the inlet lines 121, 122, and 123.

[0042] The pump system further includes an introduction valve 125 attached to the introduction line 121, an introduction valve 126 attached to the introduction line 122, and an introduction valve 127 attached to the introduction line 123. When the introduction valves 125, 126, and 127 are opened, the drain port 25A of the suction vessel 2A, the drain port 25B of the suction vessel 2B, and the drain port 25C of the suction vessel 2C communicate with the liquefied gas storage tank 105. During operation of the submersible pump 1A, the submersible pump 1B, and the submersible pump 1C, the introduction valves 125, 126, and 127 are closed, as shown in FIG.

[0043] The drain valves 26A, 26B, and 26C are connected to the drain ports 25A, 25B, and 25C, respectively. During operation of the submersible pump 1A, the submersible pump 1B, and the submersible pump 1C, the drain valves 26A, 26B, and 26C are closed as shown in FIG.

[0044] 6, during operation of the submersible pump 1A, the submersible pump 1B, and the submersible pump 1C, the suction valve 22A connected to the suction port 7A of the suction vessel 2A, the suction valve 22B connected to the suction port 7B of the suction vessel 2B, and the suction valve 22C connected to the suction port 7C of the suction vessel 2C are open. Similarly, during operation of the submersible pump 1A, the submersible pump 1B, and the submersible pump 1C, the discharge valve 23A connected to the discharge port 8A of the suction vessel 2A, the discharge valve 23B connected to the discharge port 8B of the suction vessel 2B, and the discharge valve 23C connected to the discharge port 8C of the suction vessel 2C are open.

[0045] The pump system further comprises an outlet line 131 connected to the discharge port 8A of the suction vessel 2A, an outlet valve 132 attached to the outlet line 131, an outlet line 133 connected to the discharge port 8B of the suction vessel 2B, and an outlet valve 134 attached to the outlet line 133. The outlet valve 132 is disposed downstream of the discharge valve 23A, and the communication valve 114 is disposed between the discharge valve 23A and the outlet valve 132. The outlet valve 134 is disposed downstream of the discharge valve 23B, and the communication valve 115 is disposed between the discharge valve 23B and the outlet valve 134.

[0046] Fig. 7 is a diagram showing an embodiment of a cool-down for cooling the submersible pumps 1A, 1B, 1C. As shown in Fig. 7, liquefied gas flows into the suction vessels 2A, 2B, 2C simultaneously (in parallel) through the drain ports 25A, 25B, 25C of the suction vessels 2A, 2B, 2C of the pump devices 100A, 100B, 100C. The suction valves 22A, 22B, 22C and the drain valves 26A, 26B, 26C are closed, and the introduction valves 125, 126, and 127 are opened. The discharge valves 23A, 23B, 23C are opened, and the outflow valves 132 and 134 are also opened. The communication valves 114 and 115 are closed.

[0047] During the cool-down, the submersible pumps 1A, 1B, 1C are not in operation. Therefore, the flow path switching devices 5A, 5B, 5C are in the state shown in FIG. 2. Therefore, the liquefied gas bypasses the submersible pumps 1A, 1B, 1C (i.e., the liquefied gas does not flow inside the submersible pumps 1A, 1B, 1C) and passes through the flow path switching devices 5A, 5B, 5C. The liquefied gas forms parallel flows in the suction vessels 2A, 2B, 2C and cools the submersible pumps 1A, 1B, 1C. The liquefied gas flows out of the suction vessels 2A, 2B, 2C simultaneously (in parallel) through the discharge ports 8A, 8B, 8C.

[0048] In this way, the flow path switching devices 5A, 5B, 5C can prevent the liquefied gas introduced into the suction containers 2A, 2B, 2C during cool-down from passing through the submersible pumps 1A, 1B, 1C. Therefore, the impellers of the submersible pumps 1A, 1B, 1C do not rotate when the pumps are not in operation, and as a result, damage to the sliding parts of the submersible pumps 1A, 1B, 1C, such as the bearings, can be prevented. In particular, the liquefied gas forms parallel flows in the suction containers 2A, 2B, 2C, so that the submersible pumps 1A, 1B, 1C can be cooled simultaneously and in a short time.

[0049] Fig. 8 is a schematic diagram showing another embodiment of a pump system including a plurality of pump devices 100A, 100B, 100C connected in series. The configuration and operation of this embodiment, which are not specifically described, are the same as those of the embodiment described with reference to Figs. 6 and 7, and therefore repeated description will be omitted.

[0050] 8, the introduction line 122 and the introduction line 123 are connected to the suction ports 7B and 7C of the suction containers 2B and 2C, respectively, instead of the drain ports 25B and 25C. The introduction valves 126 and 127 are attached to the introduction line 122 and the introduction line 123, respectively. The introduction line 121 and the introduction valve 125 are not provided in this embodiment, but the suction line 34 and the suction valve 22A correspond to the introduction line 121 and the introduction valve 125, respectively, of the above-mentioned embodiment.

[0051] The suction line 34, the introduction line 122, and the introduction line 123 are connected to the liquefied gas storage tank 105 and extend from the liquefied gas storage tank 105 to the suction vessels 2A, 2B, and 2C. When the submersible pumps 1A, 1B, and 1C are in operation, the introduction valves 126 and 127 are closed.

[0052] FIG. 9 is a diagram showing an embodiment of the cool-down for cooling the submersible pumps 1A, 1B, and 1C shown in FIG. 8. During the cool-down, as shown in FIG. 9, the introduction valves 126 and 127 are opened. Liquefied gas flows into the suction vessels 2A, 2B, and 2C simultaneously (in parallel) through the suction ports 7A, 7B, and 7C of the suction vessels 2A, 2B, and 2C of the pump devices 100A, 100B, and 100C. The suction valves 22A, 22B, and 22C are opened, the drain valves 26A, 26B, and 26C are closed, and the introduction valves 126 and 127 are opened. The discharge valves 23A, 23B, and 23C are opened, and the outflow valves 132 and 134 are also opened. The communication valves 114 and 115 are closed.

[0053] During the cool-down, the submersible pumps 1A, 1B, 1C are not in operation. Therefore, the flow path switching devices 5A, 5B, 5C are in the state shown in FIG. 2. Therefore, the liquefied gas bypasses the submersible pumps 1A, 1B, 1C (i.e., the liquefied gas does not flow inside the submersible pumps 1A, 1B, 1C) and passes through the flow path switching devices 5A, 5B, 5C. The liquefied gas forms parallel flows in the suction vessels 2A, 2B, 2C and cools the submersible pumps 1A, 1B, 1C. The liquefied gas flows out of the suction vessels 2A, 2B, 2C simultaneously (in parallel) through the discharge ports 8A, 8B, 8C.

[0054] In this way, the flow path switching devices 5A, 5B, 5C can prevent the liquefied gas introduced into the suction containers 2A, 2B, 2C during cool-down from passing through the submersible pumps 1A, 1B, 1C. Therefore, the impellers of the submersible pumps 1A, 1B, 1C do not rotate when the pumps are not in operation, and as a result, damage to the sliding parts of the submersible pumps 1A, 1B, 1C, such as the bearings, can be prevented. In particular, the liquefied gas forms parallel flows in the suction containers 2A, 2B, 2C, so that the submersible pumps 1A, 1B, 1C can be cooled simultaneously and in a short time.

[0055] FIG. 10 is a schematic diagram showing an embodiment in which a cool-down is performed on a pump system including a plurality of pump devices connected in series and in parallel. The configuration and operation of this embodiment that are not particularly described are the same as those of the embodiment described with reference to FIG. 6 and FIG. 7, so that the overlapping description will be omitted. The pump system of the embodiment shown in FIG. 10 further includes pump devices 100D, 100E, and 100F having the same configuration as the pump devices 100A, 100B, and 100C described with reference to FIG. 7. The pump devices 100A, 100B, and 100C are connected in series, and the pump devices 100D, 100E, and 100F are also connected in series. The pump devices 100D, 100E, and 100F are arranged in parallel with the pump devices 100A, 100B, and 100C.

[0056] The pump device 100D includes a suction container 2D, a submersible pump 1D disposed in the suction container 2D, and a flow path switching device 5D, the pump device 100E includes a suction container 2E, a submersible pump 1E disposed in the suction container 2E, and a flow path switching device 5E, and the pump device 100F includes a suction container 2F, a submersible pump 1F disposed in the suction container 2F, and a flow path switching device 5F. The suction port 7A of the suction container 2A is connected to the liquefied gas tank 105 through a suction line 34, and the suction port 7D of the suction container 2D is connected to the liquefied gas tank 105 through a suction line 35.

[0057] 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 8D of pump device 100D is connected to suction port 7E of pump device 100E by communication line 109, and discharge port 8E of pump device 100E is connected to suction port 7F of pump device 100F by communication line 110.

[0058] A communication valve 151 is attached to the communication line 109, and a communication valve 152 is attached to the communication line 110. When the communication valve 151 is closed, communication between the discharge port 8D of the pump device 100D and the suction port 7E of the pump device 100E is blocked. When the communication valve 152 is closed, communication between the discharge port 8E of the pump device 100E and the suction port 7F of the pump device 100F is blocked. When the submersible pump 1D, the submersible pump 1E, and the submersible pump 1F are operating, the communication valves 151 and 152 are open.

[0059] The pump system includes an introduction line 141 connected to the drain port 25D of the suction container 2D, an introduction line 142 connected to the drain port 25E of the suction container 2E, and an introduction line 143 connected to the drain port 25F of the suction container 2F. The introduction lines 141, 142, and 143 are connected to the liquefied gas storage tank 105 and extend from the liquefied gas storage tank 105 to the suction containers 2D, 2E, and 2F. That is, the suction containers 2D, 2E, and 2F are connected to the liquefied gas storage tank 105 through the introduction lines 141, 142, and 143.

[0060] The pump system further includes an introduction valve 145 attached to the introduction line 141, an introduction valve 146 attached to the introduction line 142, and an introduction valve 147 attached to the introduction line 143. When the introduction valves 145, 146, and 147 are opened, the drain port 25D of the suction vessel 2D, the drain port 25E of the suction vessel 2E, and the drain port 25F of the suction vessel 2F communicate with the liquefied gas storage tank 105. During the operation of the submersible pump 1D, the submersible pump 1E, and the submersible pump 1F, the introduction valves 145, 146, and 147 are closed.

[0061] The pump system further comprises an outlet line 161 connected to the discharge port 8D of the suction vessel 2D, an outlet valve 162 attached to the outlet line 161, an outlet line 163 connected to the discharge port 8E of the suction vessel 2E, and an outlet valve 164 attached to the outlet line 163. The outlet valve 162 is disposed downstream of the discharge valve 23D, and the communication valve 151 is disposed between the discharge valve 23D and the outlet valve 162. The outlet valve 164 is disposed downstream of the discharge valve 23E, and the communication valve 152 is disposed between the discharge valve 23E and the outlet valve 164.

[0062] The pump devices 100A, 100B, 100C, 100D, 100E, and 100F have the same configuration as the pump device 100 described with reference to Figures 1 to 3, so duplicated descriptions thereof will be omitted. In the pump devices 100A, 100B, 100C, 100D, 100E, and 100F, corresponding components are designated by the same reference numerals and suffixes A, B, C, D, E, and F.

[0063] The liquefied gas flows simultaneously (in parallel) into the suction vessels 2A, 2B, 2C, 2D, 2E, and 2F through the drain ports 25A, 25B, 25C, 25D, 25E, and 25F of the suction vessels 2A, 2B, 2C, 2D, 2E, and 2F.

[0064] As shown in FIG. 10, during the cool-down, the submersible pumps 1A, 1B, 1C, 1D, 1E, 1F are in a stopped state. Therefore, the flow path switching devices 5A, 5B, 5C, 5D, 5E, 5F are in a state shown in FIG. 2. Therefore, the liquefied gas bypasses the submersible pumps 1A, 1B, 1C, 1D, 1E, 1F (i.e., the liquefied gas does not flow inside the submersible pumps 1A, 1B, 1C, 1D, 1E, 1F) and passes through the flow path switching devices 5A, 5B, 5C, 5D, 5E, 5F. The liquefied gas forms a parallel flow in the suction containers 2A, 2B, 2C, 2D, 2E, 2F and cools the submersible pumps 1A, 1B, 1C, 1D, 1E, 1F. Liquefied gas flows out of the suction vessels 2A, 2B, 2C, 2D, 2E, 2F simultaneously through the discharge ports 8A, 8B, 8C, 8D, 8E, 8F.

[0065] In this way, the flow path switching devices 5A, 5B, 5C, 5D, 5E, 5F can prevent the liquefied gas introduced into the suction containers 2A, 2B, 2C, 2D, 2E, 2F from passing through the submersible pumps 1A, 1B, 1C, 1D, 1E, 1F during cool-down. Therefore, the impellers of the submersible pumps 1A, 1B, 1C, 1D, 1E, 1F do not rotate during operation, and as a result, damage to the sliding parts of the submersible pumps 1A, 1B, 1C, 1D, 1E, 1F, such as the bearings, can be prevented. In particular, the liquefied gas forms parallel flows in the suction containers 2A, 2B, 2C, 2D, 2E, 2F, so that the submersible pumps 1A, 1B, 1C, 1D, 1E, 1F can be cooled simultaneously and in a short time.

[0066] FIG. 11 is a schematic diagram showing another embodiment in which a cool-down is performed on a pump system including a plurality of pump devices connected in series and in parallel. The configuration and operation of this embodiment that are not particularly described are the same as those of the embodiment described with reference to FIG. 8 to FIG. 10, so that the overlapping description will be omitted. The pump system of the embodiment shown in FIG. 11 further includes pump devices 100D, 100E, and 100F having the same configuration as the pump devices 100A, 100B, and 100C described with reference to FIG. 8. The pump devices 100A, 100B, and 100C are connected in series, and the pump devices 100D, 100E, and 100F are also connected in series. The pump devices 100D, 100E, and 100F are arranged in parallel with the pump devices 100A, 100B, and 100C.

[0067] The inlet line 142 and the inlet line 143 are connected to the suction ports 7E and 7F of the suction vessels 2E and 2F, respectively. The inlet valves 146 and 147 are attached to the inlet line 142 and the inlet line 143, respectively. The suction line 35 and the suction valve 22D constitute the inlet line and the inlet valve for introducing liquefied gas into the suction vessel 2D for cooling down. The suction line 35, the inlet line 142, and the inlet line 143 are connected to the liquefied gas tank 105 and extend from the liquefied gas tank 105 to the suction vessels 2D, 2E, and 2F, and from the liquefied gas tank 105 to the suction vessels 2D, 2E, and 2F. During the operation of the submersible pumps 1D, 1E, and 1F, the inlet valves 146 and 147 are closed. During the cool down period, as shown in FIG. 11, the inlet valve 146 and the inlet valve 147 are opened.

[0068] During the cool-down, the liquefied gas flows in simultaneously (in parallel) through the suction ports 7A, 7B, 7C, 7D, 7E, and 7F of the suction containers 2A, 2B, 2C, 2D, 2E, and 2F of the pump devices 100A, 100B, 100C, 100D, 100E, and 100F. As shown in Fig. 11, during the cool-down, the submersible pumps 1A, 1B, 1C, 1D, 1E, and 1F are in a stopped state. Therefore, the flow path switching devices 5A, 5B, 5C, 5D, 5E, and 5F are in the state shown in Fig. 2. Therefore, the liquefied gas bypasses the submersible pumps 1A, 1B, 1C, 1D, 1E, 1F (i.e., the liquefied gas does not flow inside the submersible pumps 1A, 1B, 1C, 1D, 1E, 1F) and passes through the flow path switching devices 5A, 5B, 5C, 5D, 5E, 5F. The liquefied gas forms parallel flows in the suction vessels 2A, 2B, 2C, 2D, 2E, 2F and cools the submersible pumps 1A, 1B, 1C, 1D, 1E, 1F. The liquefied gas flows out of the suction vessels 2A, 2B, 2C, 2D, 2E, 2F simultaneously through the discharge ports 8A, 8B, 8C, 8D, 8E, 8F.

[0069] In this way, the flow path switching devices 5A, 5B, 5C, 5D, 5E, 5F can prevent the liquefied gas introduced into the suction containers 2A, 2B, 2C, 2D, 2E, 2F from passing through the submersible pumps 1A, 1B, 1C, 1D, 1E, 1F during cool-down. Therefore, the impellers of the submersible pumps 1A, 1B, 1C, 1D, 1E, 1F do not rotate during operation, and as a result, damage to the sliding parts of the submersible pumps 1A, 1B, 1C, 1D, 1E, 1F, such as the bearings, can be prevented. In particular, the liquefied gas forms parallel flows in the suction containers 2A, 2B, 2C, 2D, 2E, 2F, so that the submersible pumps 1A, 1B, 1C, 1D, 1E, 1F can be cooled simultaneously and in a short time.

[0070] Fig. 12 is a schematic diagram showing another embodiment of a pump system including a plurality of pump devices 100A, 100B, and 100C connected in series. The configuration and operation of this embodiment that are not particularly described are the same as those of the embodiment described with reference to Fig. 6, so that the duplicated description will be omitted. The pump system shown in Fig. 12 differs from the embodiment shown in Fig. 6 in that it does not include the communication valve 114, the communication valve 115, the inlet line 121, the inlet line 122, the inlet line 123, the inlet valve 125, the inlet valve 126, the inlet valve 127, the outflow line 131, the outflow line 133, the outflow valve 132, and the outflow valve 134 shown in Fig. 6, but the other configurations are the same.

[0071] 13 and 14 are schematic diagrams showing an embodiment of performing a cool-down for the pump system shown in FIG. 12. As shown in FIG. 13, the suction valves 22A, 22B, and 22C are opened, the drain valves 26A, 26B, and 26C are closed, and the discharge valves 23A, 23B, and 23C are opened. First, with all the submersible pumps 1A, 1B, and 1C stopped, liquefied gas flows into the suction vessel 2A of the pump device 100A through the suction port 7A of the suction vessel 2A. The liquefied gas evaporates in contact with the suction vessel 2A and the submersible pump 1A, which are at room temperature, to form boil-off gas. In FIG. 13, the flow of the boil-off gas is indicated by a dotted line.

[0072] More specifically, the liquefied gas is first introduced into the suction vessel 2A of the pump device 100A through the suction port 7A. The liquefied gas evaporates in the suction vessel 2A to form boil-off gas. The boil-off gas passes through the flow path switching device 5A while bypassing the submerged pump 1A. The boil-off 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 7B of the pump device 100B. The boil-off gas passes through the flow path switching device 5B while bypassing the submerged pump 1B. Furthermore, the boil-off 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 7C of the pump device 100C. The boil-off gas passes through the flow path switching device 5C while bypassing the submerged pump 1C. The boil-off gas is discharged through the discharge port 8C of the pump device 100C.

[0073] Next, as shown in FIG. 14, the submersible pump 1A is started. The submersible pumps 1B and 1C are kept stopped. The operation of the submersible pump 1A causes the liquefied gas to flow into the suction vessel 2A through the suction port 7A. The submersible pump 1A sequentially sends the liquefied gas to the suction vessels 2B and 2C. More specifically, the liquefied gas is pressurized by the operation of the submersible pump 1A and passes through the flow path switching device 5A. The liquefied 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 7B of the pump device 100B. The liquefied gas passes through the flow path switching device 5B while bypassing the submersible pump 1B. Furthermore, the liquefied 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 7C of the pump device 100C. The liquefied gas passes through the flow path switching device 5C while bypassing the submersible pump 1C. The liquefied gas is discharged through the discharge port 8C of the pump device 100C.

[0074] In this way, the flow path switching devices 5A, 5B, 5C can prevent the liquefied gas and boil-off gas from passing through the submersible pumps 1A, 1B, 1C that are out of operation during cool down. Therefore, the impellers of the submersible pumps 1A, 1B, 1C that are out of operation do not rotate, and as a result, damage to the sliding parts such as the bearings of the submersible pumps 1A, 1B, 1C can be prevented.

[0075] Fig. 15 is a schematic diagram showing another embodiment of a pump system including a plurality of pump devices 100A, 100B, 100C connected in series. 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. 6, and therefore repeated description will be omitted.

[0076] 15, the pump system of this embodiment includes an introduction line 171 connected to the liquefied gas storage tank 105 and the drain port 25A of the suction container 2A, an introduction line 172 connected to the discharge port 8A of the suction container 2A and the drain port 25B of the suction container 2B, and an introduction line 173 connected to the discharge port 8B of the suction container 2B and the drain port 25C of the suction container 2C. The pump system further includes an introduction valve 176 attached to the introduction line 171, an introduction valve 177 attached to the introduction line 172, and an introduction valve 178 attached to the introduction line 173.

[0077] The introduction line 171 extends from the liquefied gas tank 105 to the drain port 25A of the suction vessel 2A. When the introduction valve 176 is opened, the drain port 25A of the suction vessel 2A communicates with the liquefied gas tank 105 through the introduction line 171. The introduction line 172 extends from the discharge port 8A of the suction vessel 2A to the drain port 25B of the suction vessel 2B. When the introduction valve 177 is opened, the drain port 25B of the suction vessel 2B communicates with the discharge port 8A of the suction vessel 2A through the introduction line 172. The introduction line 173 extends from the discharge port 8B of the suction vessel 2B to the drain port 25C of the suction vessel 2C. When the introduction valve 178 is opened, the drain port 25C of the suction vessel 2C communicates with the discharge port 8B of the suction vessel 2B through the introduction line 173. As shown in FIG. 15, during operation of the submersible pumps 1A, 1B, and 1C, the introduction valves 176, 177, and 178 are closed.

[0078] Figures 16 and 17 are schematic diagrams showing an embodiment for performing a cool-down on the pump system shown in Figure 15. As shown in Figure 16, the intake valves 22A, 22B, and 22C are closed, the drain valves 26A, 26B, and 26C are closed, the discharge valves 23A, 23B, and 23C are open, and the inlet valves 176, 177, and 178 are open.

[0079] First, with all of the submersible pumps 1A, 1B, and 1C stopped, liquefied gas flows into the suction vessel 2A through the inlet line 171 and the drain port 25A of the suction vessel 2A. The liquefied gas evaporates when it comes into contact with the suction vessel 2A and the submersible pump 1A, which are at room temperature, to form boil-off gas. In Figure 16, the flow of the boil-off gas is indicated by a dotted line.

[0080] More specifically, the liquefied gas is first introduced into the suction vessel 2A of the pump device 100A through the drain port 25A. The liquefied gas evaporates in the suction vessel 2A to form boil-off gas. The boil-off gas passes through the flow path switching device 5A while bypassing the submerged pump 1A. The boil-off gas that has passed through the flow path switching device 5A is introduced into the suction vessel 2B through the introduction line 172 and the drain port 25B of the pump device 100B. The boil-off gas passes through the flow path switching device 5B while bypassing the submerged pump 1B. Furthermore, the boil-off gas that has passed through the flow path switching device 5B is introduced into the suction vessel 2C through the introduction line 173 and the drain port 25C of the pump device 100C. The boil-off gas passes through the flow path switching device 5C while bypassing the submerged pump 1C. The boil-off gas is discharged through the discharge port 8C of the pump device 100C.

[0081] Next, as shown in Figure 17, the suction valve 22A is opened and the introduction valve 176 is closed. Then, the submersible pump 1A is started. The submersible pumps 1B and 1C remain stopped. By the operation of the submersible pump 1A, the liquefied gas flows into the suction vessel 2A through the suction port 7A.

[0082] The submersible pump 1A sequentially sends liquefied gas to the suction vessels 2B and 2C. More specifically, the liquefied gas is pressurized by the operation of the submersible pump 1A and passes through the flow path switching device 5A. The liquefied gas that has passed through the flow path switching device 5A is introduced into the suction vessel 2B through the introduction line 172 and the drain port 25B of the pump device 100B. The liquefied gas passes through the flow path switching device 5B while bypassing the submersible pump 1B. Furthermore, the liquefied gas that has passed through the flow path switching device 5B is introduced into the suction vessel 2C through the introduction line 173 and the drain port 25C of the pump device 100C. The liquefied gas passes through the flow path switching device 5C while bypassing the submersible pump 1C. The liquefied gas is discharged through the discharge port 8C of the pump device 100C.

[0083] In this way, the flow path switching devices 5A, 5B, 5C can prevent the liquefied gas and boil-off gas from passing through the submersible pumps 1A, 1B, 1C that are out of operation during cool down. Therefore, the impellers of the submersible pumps 1A, 1B, 1C that are out of operation do not rotate, and as a result, damage to the sliding parts such as the bearings of the submersible pumps 1A, 1B, 1C can be prevented.

[0084] Fig. 18 is a schematic diagram showing another embodiment of a pump system including a plurality of pump devices 100A, 100B, and 100C connected in series. The configuration and operation of this embodiment not specifically described are the same as those of the embodiment described with reference to Fig. 15, and therefore the overlapping description will be omitted. The pump system of this embodiment shown in Fig. 18 includes an introduction line 181 connected to the discharge port 8A of the suction vessel 2A and the drain port 25C of the suction vessel 2C, and an introduction valve 182 attached to the introduction line 181. The discharge port 8A of the suction vessel 2A is connected to both the drain port 25B of the suction vessel 2B and the drain port 25C of the suction vessel 2C through the introduction line 172 and the introduction line 181.

[0085] When the introduction valve 176 is opened, the drain port 25A of the suction vessel 2A is connected to the liquefied gas storage tank 105 through the introduction line 171. When the introduction valve 177 is opened, the drain port 25B of the suction vessel 2B is connected to the discharge port 8A of the suction vessel 2A through the introduction line 172. The introduction line 181 bypasses the pump device 100B and extends from the discharge port 8A of the suction vessel 2A to the drain port 25C of the suction vessel 2C. When the introduction valve 182 is opened, the drain port 25C of the suction vessel 2C is connected to the discharge port 8A of the suction vessel 2A through the introduction line 181.

[0086] The pump system of this embodiment further includes an outflow line 133 connected to the discharge port 8B of the suction vessel 2B, and an outflow valve 134 attached to the outflow line 133. The outflow valve 134 is disposed downstream of the discharge valve 23B. As shown in Fig. 18, during operation of the submersible pumps 1A, 1B, and 1C, the inlet valves 176, 177, and 182 are closed, and the outflow valve 134 is also closed.

[0087] Figures 19 and 20 are schematic diagrams illustrating an embodiment for performing a cool down on the pump system shown in Figure 18. As shown in Figure 19, intake valves 22A, 22B, and 22C are closed, drain valves 26A, 26B, and 26C are closed, and discharge valves 23A, 23B, and 23C are open. Inlet valve 176, inlet valve 177, and inlet valve 182 are open, and outlet valve 134 is open.

[0088] First, with all of the submersible pumps 1A, 1B, and 1C stopped, liquefied gas flows into the suction vessel 2A through the inlet line 171 and the drain port 25A of the suction vessel 2A. The liquefied gas evaporates when it comes into contact with the suction vessel 2A and the submersible pump 1A, which are at room temperature, to form boil-off gas. In Figure 19, the flow of the boil-off gas is indicated by a dotted line.

[0089] More specifically, the liquefied gas is first introduced into the suction vessel 2A of the pump device 100A through the drain port 25A. The liquefied gas evaporates in the suction vessel 2A to form boil-off gas. The boil-off gas passes through the flow path switching device 5A while bypassing the submerged pump 1A. The boil-off gas that has passed through the flow path switching device 5A is introduced into the suction vessel 2B through the introduction line 172 and the drain port 25B of the pump device 100B, and is simultaneously introduced into the suction vessel 2C through the introduction line 181 and the drain port 25C of the pump device 100C. The introduction line 172 and the introduction line 181 are pre-cooled by the boil-off gas. The boil-off gas passes through the flow path switching device 5B while bypassing the submerged pump 1B. The boil-off gas that has passed through the flow path switching device 5B is discharged from the suction vessel 2B through the discharge port 8B and the outflow line 133. Similarly, the boil-off gas bypasses the submersible pump 1C while passing through the flow path switching device 5C. The boil-off gas that has passed through the flow path switching device 5C is discharged from the suction vessel 2C through the discharge port 8C.

[0090] Next, as shown in Figure 20, the suction valve 22A is opened and the introduction valve 176 is closed. Then, the submersible pump 1A is started. The submersible pumps 1B and 1C remain stopped. By the operation of the submersible pump 1A, the liquefied gas flows into the suction vessel 2A through the suction port 7A.

[0091] The submersible pump 1A sends liquefied gas to the suction vessels 2B and 2C simultaneously (i.e., in parallel). More specifically, the liquefied gas is pressurized by the operation of the submersible pump 1A and passes through the flow path switching device 5A. The liquefied gas that has passed through the flow path switching device 5A is introduced into the suction vessel 2B through the inlet line 172 and the drain port 25B of the pump device 100B, and is simultaneously introduced into the suction vessel 2C through the inlet line 181 and the drain port 25C of the pump device 100C. The liquefied gas passes through the flow path switching device 5B while bypassing the submersible pump 1B. The liquefied gas that has passed through the flow path switching device 5B is discharged from the suction vessel 2B through the discharge port 8B and the outflow line 133. Similarly, the liquefied gas passes through the flow path switching device 5C while bypassing the submersible pump 1C. The liquefied gas that has passed through the flow path switching device 5C is discharged from the suction container 2C through the discharge port 8C.

[0092] In this way, the flow path switching devices 5A, 5B, 5C can prevent the liquefied gas and boil-off gas from passing through the submersible pumps 1A, 1B, 1C that are out of operation during cool down. Therefore, the impellers of the submersible pumps 1A, 1B, 1C that are out of operation do not rotate, and as a result, damage to the sliding parts such as the bearings of the submersible pumps 1A, 1B, 1C can be prevented.

[0093] Fig. 21 is a schematic diagram showing yet another embodiment of a pump system including a plurality of pump devices 100A, 100B, and 100C connected in series. The configuration and operation of this embodiment that are not particularly described are the same as those of the embodiment described with reference to Fig. 12, so that the overlapping description will be omitted. The pump system shown in Fig. 21 further includes an introduction line 191 connected to the discharge port 8A of the suction vessel 2A of the pump device 100A and the suction port 7C of the suction vessel 2C of the pump device 100C, an introduction valve 192 attached to the introduction line 191, an outflow line 133 connected to the discharge port 8B of the suction vessel 2B of the pump device 100B, an outflow valve 134 attached to the outflow line 133, and a communication valve 115 attached to the communication line 108.

[0094] The inlet line 191 extends from the discharge port 8A of the suction vessel 2A to the suction port 7C of the suction vessel 2C, bypassing the pump device 100B. When the inlet valve 192 is opened, the discharge port 8A of the suction vessel 2A and the suction port 7C of the suction vessel 2C communicate with each other through the inlet line 191. The communication valve 115 is located between the discharge valve 23B and the outlet valve 134. As shown in Figure 21, during operation of the submersible pumps 1A, 1B, 1C, the inlet valve 192 and the outlet valve 134 are closed, and the communication valve 115 is opened.

[0095] Figures 22 and 23 are schematic diagrams showing an embodiment of performing a cool-down on the pump system shown in Figure 21. As shown in Figure 22, the suction valves 22A, 22B, and 22C are opened, the drain valves 26A, 26B, and 26C are closed, and the discharge valves 23A, 23B, and 23C are opened. The communication valve 115 is closed, and the inlet valve 192 and the outlet valve 134 are opened.

[0096] First, with all of the submersible pumps 1A, 1B, and 1C stopped, liquefied gas flows into the suction vessel 2A of the pump device 100A through the suction port 7A of the suction vessel 2A. The liquefied gas evaporates upon contact with the suction vessel 2A and the submersible pump 1A, which are at room temperature, to form boil-off gas. In FIG. 22, the flow of the boil-off gas is indicated by a dotted line.

[0097] More specifically, the liquefied gas is first introduced into the suction vessel 2A of the pump device 100A through the suction port 7A. The liquefied gas evaporates in the suction vessel 2A to form boil-off gas. The boil-off gas passes through the flow path switching device 5A while bypassing the submerged pump 1A. The boil-off 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 7B of the pump device 100B, and is simultaneously introduced into the suction vessel 2C through the introduction line 191 and the suction port 7C of the pump device 100C. The communication line 107 and the introduction line 191 are pre-cooled by the boil-off gas. The boil-off gas passes through the flow path switching device 5B while bypassing the submerged pump 1B. The boil-off gas that has passed through the flow path switching device 5B is discharged from the suction vessel 2B through the discharge port 8B and the outflow line 133. Similarly, the boil-off gas bypasses the submersible pump 1C while passing through the flow path switching device 5C. The boil-off gas that has passed through the flow path switching device 5C is discharged from the suction vessel 2C through the discharge port 8C.

[0098] Next, as shown in Fig. 23, the submersible pump 1A is started. The submersible pumps 1B and 1C remain stopped. By operating the submersible pump 1A, the liquefied gas flows into the suction vessel 2A through the suction port 7A.

[0099] The submersible pump 1A sends liquefied gas to the suction vessels 2B and 2C simultaneously (i.e., in parallel). More specifically, the liquefied gas is pressurized by the operation of the submersible pump 1A and passes through the flow path switching device 5A. The liquefied 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 7B of the pump device 100B, and is simultaneously introduced into the suction vessel 2C through the introduction line 191 and the suction port 7C of the pump device 100C. The liquefied gas passes through the flow path switching device 5B while bypassing the submersible pump 1B. The liquefied gas that has passed through the flow path switching device 5B is discharged from the suction vessel 2B through the discharge port 8B and the outflow line 133. Similarly, the liquefied gas passes through the flow path switching device 5C while bypassing the submersible pump 1C. The liquefied gas that has passed through the flow path switching device 5C is discharged from the suction container 2C through the discharge port 8C.

[0100] In this way, the flow path switching devices 5A, 5B, 5C can prevent the liquefied gas and boil-off gas from passing through the submersible pumps 1A, 1B, 1C that are out of operation during cool down. Therefore, the impellers of the submersible pumps 1A, 1B, 1C that are out of operation do not rotate, and as a result, damage to the sliding parts such as the bearings of the submersible pumps 1A, 1B, 1C can be prevented.

[0101] The embodiment described with reference to Fig. 12 to Fig. 23 can also be applied to a pump system in which a plurality of pump devices are arranged in series and in parallel. For example, the pump system of the embodiment shown in Fig. 24 includes pump devices 100A, 100B, and 100C described with reference to Fig. 12, and pump devices 100D, 100E, and 100F having the same configuration as these pump devices. The pump devices 100A, 100B, and 100C are connected in series, and the pump devices 100D, 100E, and 100F are also connected in series. The pump devices 100D, 100E, and 100F are arranged in parallel with the pump devices 100A, 100B, and 100C.

[0102] The suction port 7A of the suction container 2A is connected to the liquefied gas tank 105 through the suction line 34, and the suction port 7D of the suction container 2D is connected to the liquefied gas tank 105 through the suction line 35. The discharge port 8D of the pump device 100D is connected to the suction port 7E of the pump device 100E through a communication line 109, and the discharge port 8E of the pump device 100E is connected to the suction port 7F of the pump device 100F through a communication line 110.

[0103] The cool-down of the submersible pumps 1A, 1B, 1C, 1D, 1E, 1F is performed in the same manner as in the embodiment described with reference to Figs. 13 and 14. That is, as shown in Fig. 25, when all the submersible pumps 1A, 1B, 1C, 1D, 1E, 1F are stopped, the liquefied gas flows into the suction vessels 2A, 2D. The liquefied gas evaporates upon contact with the suction vessels 2A, 2D and the submersible pumps 1A, 1D, which are at room temperature, to form boil-off gas. In Fig. 25, the flow of the boil-off gas is indicated by dotted lines. The boil-off gas flows from the suction vessel 2A to the suction vessel 2B and the suction vessel 2C, and at the same time, the boil-off gas flows from the suction vessel 2D to the suction vessel 2E and the suction vessel 2F. The submersible pumps 1A, 1D in the suction vessels 2A, 2D are cooled by liquefied gas, and the submersible pumps 1B, 1C, 1E, 1F in the suction vessels 2B, 2C, 2E, 2F are pre-cooled by boil-off gas.

[0104] Next, as shown in FIG. 26, the submersible pumps 1A and 1D are started. The submersible pumps 1B, 1C, 1E, and 1F remain stopped. The operation of the submersible pump 1A causes the liquefied gas to flow into the suction vessel 2A through the suction port 7A. The submersible pump 1A sends the liquefied gas to the suction vessels 2B and 2C in sequence. The operation of the submersible pump 1D causes the liquefied gas to flow into the suction vessel 2D through the suction port 7D. The submersible pump 1D sends the liquefied gas to the suction vessels 2E and 2F in sequence. The submersible pumps 1A, 1B, 1C, 1D, 1E, and 1F are cooled by the liquefied gas.

[0105] Although not shown, a similar cool-down can be performed for a pump system in which a plurality of pump devices having the same configuration as the embodiment described with reference to FIGS. 15 to 23 are arranged in series and in parallel.

[0106] Fig. 27 is a schematic diagram showing an embodiment of a pump system including a plurality of pump devices 100A, 100B, and 100C connected in parallel. The configurations of the pump devices 100A, 100B, and 100C are the same as those of the embodiment described with reference to Figs. 1 to 5, and therefore, redundant description will be omitted.

[0107] In this embodiment, the suction port 7A of the suction container 2A is connected to the liquefied gas tank 105 through the suction line 34, the suction port 7B of the suction container 2B is connected to the liquefied gas tank 105 through the suction line 35, and the suction port 7C of the suction container 2C is connected to the liquefied gas tank 105 through the suction line 36. The suction line 36 extends from the liquefied gas tank 105 to the suction port 7C of the suction container 2C. The discharge port 8A of the suction container 2A is connected to a discharge line 201, and an outlet valve 202 is attached to the discharge line 201. The discharge port 8B of the suction container 2B is connected to a discharge line 203, and an outlet valve 204 is attached to the discharge line 203.

[0108] The pump system of this embodiment includes an introduction line 211 connected to the liquefied gas storage tank 105 and the drain port 25A of the suction vessel 2A, an introduction line 212 connected to the discharge port 8A of the suction vessel 2A and the drain port 25B of the suction vessel 2B, and an introduction line 213 connected to the discharge port 8B of the suction vessel 2B and the drain port 25C of the suction vessel 2C. The pump system further includes an introduction valve 215 attached to the introduction line 211, an introduction valve 216 attached to the introduction line 212, and an introduction valve 217 attached to the introduction line 213.

[0109] The introduction line 211 extends from the liquefied gas tank 105 to the drain port 25A of the suction vessel 2A. When the introduction valve 215 is opened, the drain port 25A of the suction vessel 2A communicates with the liquefied gas tank 105 through the introduction line 211. The introduction line 212 extends from the discharge port 8A of the suction vessel 2A to the drain port 25B of the suction vessel 2B. When the introduction valve 216 is opened, the drain port 25B of the suction vessel 2B communicates with the discharge port 8A of the suction vessel 2A through the introduction line 212. The introduction line 213 extends from the discharge port 8B of the suction vessel 2B to the drain port 25C of the suction vessel 2C. When the introduction valve 217 is opened, the drain port 25C of the suction vessel 2C communicates with the discharge port 8B of the suction vessel 2B through the introduction line 213. As shown in FIG. 27, during operation of the submersible pumps 1A, 1B, and 1C, the inlet valves 215, 216, and 217 are closed, and the outlet valves 202 and 204 are open.

[0110] Figures 28 and 29 are schematic diagrams illustrating an embodiment of performing a cool down for the pump system shown in Figure 27. As shown in Figure 28, the intake valves 22A, 22B, and 22C are closed, the drain valves 26A, 26B, and 26C are closed, and the discharge valves 23A, 23B, and 23C are open. The inlet valves 215, 216, and 217 are open, and the outlet valves 202 and 204 are closed.

[0111] First, with all of the submersible pumps 1A, 1B, and 1C stopped, liquefied gas flows into the suction vessel 2A through the inlet line 211 and the drain port 25A of the suction vessel 2A. The liquefied gas evaporates when it comes into contact with the suction vessel 2A and the submersible pump 1A, which are at room temperature, to form boil-off gas. In Figure 28, the flow of the boil-off gas is indicated by a dotted line.

[0112] More specifically, the liquefied gas is first introduced into the suction vessel 2A of the pump device 100A through the drain port 25A. The liquefied gas evaporates in the suction vessel 2A to form boil-off gas. The boil-off gas passes through the flow path switching device 5A while bypassing the submerged pump 1A. The boil-off gas that has passed through the flow path switching device 5A is introduced into the suction vessel 2B through the introduction line 212 and the drain port 25B of the pump device 100B. The boil-off gas passes through the flow path switching device 5B while bypassing the submerged pump 1B. Furthermore, the boil-off gas that has passed through the flow path switching device 5B is introduced into the suction vessel 2C through the introduction line 213 and the drain port 25C of the pump device 100C. The boil-off gas passes through the flow path switching device 5C while bypassing the submerged pump 1C. The boil-off gas is discharged through the discharge port 8C of the pump device 100C.

[0113] Next, as shown in Figure 29, the suction valve 22A is opened and the introduction valve 215 is closed. Then, the submersible pump 1A is started. The submersible pumps 1B and 1C remain stopped. By the operation of the submersible pump 1A, the liquefied gas flows into the suction container 2A through the suction port 7A.

[0114] The submersible pump 1A sequentially sends the liquefied gas to the suction vessels 2B and 2C. More specifically, the liquefied gas is pressurized by the operation of the submersible pump 1A and passes through the flow path switching device 5A. The liquefied gas that has passed through the flow path switching device 5A is introduced into the suction vessel 2B through the introduction line 212 and the drain port 25B of the pump device 100B. The liquefied gas passes through the flow path switching device 5B while bypassing the submersible pump 1B. Furthermore, the liquefied gas that has passed through the flow path switching device 5B is introduced into the suction vessel 2C through the introduction line 213 and the drain port 25C of the pump device 100C. The liquefied gas passes through the flow path switching device 5C while bypassing the submersible pump 1C. The liquefied gas is discharged through the discharge port 8C of the pump device 100C.

[0115] In this way, the flow path switching devices 5A, 5B, 5C can prevent the liquefied gas and boil-off gas from passing through the submersible pumps 1A, 1B, 1C that are out of operation during cool down. Therefore, the impellers of the submersible pumps 1A, 1B, 1C that are out of operation do not rotate, and as a result, damage to the sliding parts such as the bearings of the submersible pumps 1A, 1B, 1C can be prevented.

[0116] Fig. 30 is a schematic diagram showing another embodiment of a pump system including a plurality of pump devices 100A, 100B, 100C connected in parallel. The configuration and operation of this embodiment, which are not specifically described, are the same as those of the embodiment described with reference to Figs. 27 to 29, and therefore duplicated descriptions will be omitted.

[0117] The pump system of this embodiment includes an inlet line 221 connected to the discharge port 8A of the suction vessel 2A and the suction port 7B of the suction vessel 2B, an inlet line 222 connected to the discharge port 8B of the suction vessel 2B and the suction port 7C of the suction vessel 2C, an inlet valve 224 attached to the inlet line 221, and an inlet valve 225 attached to the inlet line 222. The pump system further includes an inlet valve 227 attached to the suction line 35 and an inlet valve 228 attached to the suction line 36. The inlet valve 227 is disposed upstream of the suction valve 22B, and the inlet valve 224 is disposed between the inlet valve 227 and the suction valve 22B. The inlet valve 228 is disposed upstream of the suction valve 22C, and the inlet valve 225 is disposed between the inlet valve 228 and the suction valve 22C.

[0118] The introduction line 221 extends from the discharge port 8A of the suction vessel 2A to the suction port 7B of the suction vessel 2B. When the introduction valve 224 is opened, the discharge port 8A of the suction vessel 2A communicates with the suction port 7B of the suction vessel 2B through the introduction line 221. The introduction line 222 extends from the discharge port 8B of the suction vessel 2B to the suction port 7C of the suction vessel 2C. When the introduction valve 225 is opened, the discharge port 8B of the suction vessel 2B communicates with the suction port 7C of the suction vessel 2C through the introduction line 222. As shown in FIG. 30, during the operation of the submersible pumps 1A, 1B, 1C, the introduction valves 224 and 225 are closed, the outlet valves 202 and 204 are opened, and the inlet valves 227 and 228 are opened.

[0119] Figures 31 and 32 are schematic diagrams illustrating an embodiment for performing a cool-down on the pump system shown in Figure 30. As shown in Figure 30, the intake valves 22A, 22B, and 22C are opened, the drain valves 26A, 26B, and 26C are closed, and the discharge valves 23A, 23B, and 23C are opened. The inlet valves 224 and 225 are opened, and the outlet valves 202 and 204 are closed. The inlet valves 227 and 228 are closed.

[0120] First, with all of the submersible pumps 1A, 1B, and 1C stopped, liquefied gas flows into the suction vessel 2A of the pump device 100A through the suction port 7A of the suction vessel 2A. The liquefied gas evaporates upon contact with the suction vessel 2A and the submersible pump 1A, which are at room temperature, to form boil-off gas. In FIG. 31, the flow of the boil-off gas is indicated by a dotted line.

[0121] More specifically, the liquefied gas is first introduced into the suction vessel 2A of the pump device 100A through the suction port 7A. The liquefied gas evaporates in the suction vessel 2A to form boil-off gas. The boil-off gas passes through the flow path switching device 5A while bypassing the submerged pump 1A. The boil-off gas that has passed through the flow path switching device 5A is introduced into the suction vessel 2B through the introduction line 221 and the suction port 7B of the pump device 100B. The boil-off gas passes through the flow path switching device 5B while bypassing the submerged pump 1B. Furthermore, the boil-off gas that has passed through the flow path switching device 5B is introduced into the suction vessel 2C through the introduction line 222 and the suction port 7C of the pump device 100C. The boil-off gas passes through the flow path switching device 5C while bypassing the submerged pump 1C. The boil-off gas is discharged through the discharge port 8C of the pump device 100C.

[0122] Next, as shown in FIG. 32, the submersible pump 1A is started. The submersible pumps 1B and 1C are kept stopped. The operation of the submersible pump 1A causes the liquefied gas to flow into the suction vessel 2A through the suction port 7A. The submersible pump 1A sequentially sends the liquefied gas to the suction vessels 2B and 2C. More specifically, the liquefied gas is pressurized by the operation of the submersible pump 1A and passes through the flow path switching device 5A. The liquefied gas that has passed through the flow path switching device 5A is introduced into the suction vessel 2B through the introduction line 221 and the suction port 7B of the pump device 100B. The liquefied gas passes through the flow path switching device 5B while bypassing the submersible pump 1B. Furthermore, the liquefied gas that has passed through the flow path switching device 5B is introduced into the suction vessel 2C through the introduction line 222 and the suction port 7C of the pump device 100C. The liquefied gas passes through the flow path switching device 5C while bypassing the submersible pump 1C. The liquefied gas is discharged through the discharge port 8C of the pump device 100C.

[0123] In this way, the flow path switching devices 5A, 5B, 5C can prevent the liquefied gas and boil-off gas from passing through the submersible pumps 1A, 1B, 1C that are out of operation during cool down. Therefore, the impellers of the submersible pumps 1A, 1B, 1C that are out of operation do not rotate, and as a result, damage to the sliding parts such as the bearings of the submersible pumps 1A, 1B, 1C can be prevented.

[0124] Fig. 33 is a schematic diagram showing yet another embodiment of a pump system including a plurality of pump devices 100A, 100B, 100C connected in parallel. The configuration and operation of this embodiment, which are not specifically described, are the same as those of the embodiment described with reference to Figs. 27 to 29, and therefore duplicated descriptions will be omitted.

[0125] The pump system of this embodiment includes an introduction line 211 connected to the liquefied gas storage tank 105 and the drain port 25A of the suction container 2A, an introduction line 212 connected to the discharge port 8A of the suction container 2A and the drain port 25B of the suction container 2B, and an introduction line 231 connected to the discharge port 8A of the suction container 2A and the drain port 25C of the suction container 2C. The pump system further includes an introduction valve 215 attached to the introduction line 211, an introduction valve 216 attached to the introduction line 212, and an introduction valve 232 attached to the introduction line 231.

[0126] When the introduction valve 215 is opened, the drain port 25A of the suction vessel 2A is connected to the liquefied gas tank 105 through the introduction line 211. When the introduction valve 216 is opened, the drain port 25B of the suction vessel 2B is connected to the discharge port 8A of the suction vessel 2A through the introduction line 212. The introduction line 231 extends from the discharge port 8A of the suction vessel 2A to the drain port 25C of the suction vessel 2C, bypassing the pump device 100B. When the introduction valve 232 is opened, the drain port 25C of the suction vessel 2C is connected to the discharge port 8A of the suction vessel 2A through the introduction line 231. As shown in FIG. 33, during the operation of the submersible pumps 1A, 1B, and 1C, the introduction valves 215, 216, and 232 are closed, and the outlet valves 202 and 204 are opened.

[0127] Figures 34 and 35 are schematic diagrams illustrating an embodiment of performing a cool down on the pump system shown in Figure 33. As shown in Figure 34, intake valves 22A, 22B, and 22C are closed, drain valves 26A, 26B, and 26C are closed, and discharge valves 23A, 23B, and 23C are open. Inlet valve 215, inlet valve 216, and inlet valve 232 are open, outlet valve 202 is closed, and outlet valve 204 is open.

[0128] First, with all of the submersible pumps 1A, 1B, and 1C stopped, liquefied gas flows into the suction vessel 2A through the inlet line 211 and the drain port 25A of the suction vessel 2A. The liquefied gas evaporates when it comes into contact with the suction vessel 2A and the submersible pump 1A, which are at room temperature, to form boil-off gas. In Figure 34, the flow of the boil-off gas is indicated by a dotted line.

[0129] More specifically, the liquefied gas is first introduced into the suction vessel 2A of the pump device 100A through the drain port 25A. The liquefied gas evaporates in the suction vessel 2A to form boil-off gas. The boil-off gas passes through the flow path switching device 5A while bypassing the submerged pump 1A. The boil-off gas that has passed through the flow path switching device 5A is introduced into the suction vessel 2B through the introduction line 212 and the drain port 25B of the pump device 100B, and is simultaneously introduced into the suction vessel 2C through the introduction line 231 and the drain port 25C of the pump device 100C. The boil-off gas passes through the flow path switching device 5B while bypassing the submerged pump 1B. The boil-off gas that has passed through the flow path switching device 5B is discharged from the suction vessel 2B through the discharge port 8B and the discharge line 203. Similarly, the boil-off gas bypasses the submersible pump 1C while passing through the flow path switching device 5C. The boil-off gas that has passed through the flow path switching device 5C is discharged from the suction vessel 2C through the discharge port 8C.

[0130] Next, as shown in Figure 35, the suction valve 22A is opened and the introduction valve 215 is closed. Then, the submersible pump 1A is started. The submersible pumps 1B and 1C remain stopped. By the operation of the submersible pump 1A, the liquefied gas flows into the suction container 2A through the suction port 7A.

[0131] The submersible pump 1A sends liquefied gas to the suction vessels 2B and 2C simultaneously (i.e., in parallel). More specifically, the liquefied gas is pressurized by the operation of the submersible pump 1A and passes through the flow path switching device 5A. The liquefied gas that has passed through the flow path switching device 5A is introduced into the suction vessel 2B through the inlet line 212 and the drain port 25B of the pump device 100B, and is simultaneously introduced into the suction vessel 2C through the inlet line 231 and the drain port 25C of the pump device 100C. The liquefied gas passes through the flow path switching device 5B while bypassing the submersible pump 1B. The liquefied gas that has passed through the flow path switching device 5B is discharged from the suction vessel 2B through the discharge port 8B and the discharge line 203. Similarly, the liquefied gas passes through the flow path switching device 5C while bypassing the submersible pump 1C. The liquefied gas that has passed through the flow path switching device 5C is discharged from the suction container 2C through the discharge port 8C.

[0132] In this way, the flow path switching devices 5A, 5B, 5C can prevent the liquefied gas and boil-off gas from passing through the submersible pumps 1A, 1B, 1C that are out of operation during cool down. Therefore, the impellers of the submersible pumps 1A, 1B, 1C that are out of operation do not rotate, and as a result, damage to the sliding parts such as the bearings of the submersible pumps 1A, 1B, 1C can be prevented.

[0133] Fig. 36 is a schematic diagram showing yet another embodiment of a pump system including a plurality of pump devices 100A, 100B, 100C connected in parallel. The configuration and operation of this embodiment, which are not specifically described, are the same as those of the embodiment described with reference to Figs. 30 to 32, and therefore duplicated descriptions will be omitted.

[0134] The pump system of this embodiment includes an introduction line 221 connected to the discharge port 8A of the suction vessel 2A and the suction port 7B of the suction vessel 2B, an introduction line 241 connected to the discharge port 8A of the suction vessel 2A and the suction port 7C of the suction vessel 2C, an introduction valve 224 attached to the introduction line 221, and an introduction valve 242 attached to the introduction line 241. The introduction valve 242 is located between the inlet valve 228 and the suction valve 22C.

[0135] When the introduction valve 224 is opened, the discharge port 8A of the suction vessel 2A communicates with the suction port 7B of the suction vessel 2B through the introduction line 221. The introduction line 241 extends from the discharge port 8A of the suction vessel 2A to the suction port 7C of the suction vessel 2C, bypassing the pump device 100B. When the introduction valve 242 is opened, the discharge port 8A of the suction vessel 2A communicates with the suction port 7C of the suction vessel 2C through the introduction line 241. As shown in Figure 36, during the operation of the submersible pumps 1A, 1B, 1C, the introduction valves 224 and 242 are closed, the outlet valves 202 and 204 are opened, and the inlet valves 227 and 228 are opened.

[0136] Figures 37 and 38 are schematic diagrams illustrating an embodiment for performing a cool down on the pump system shown in Figure 36. As shown in Figure 37, intake valves 22A, 22B, and 22C are open, drain valves 26A, 26B, and 26C are closed, and discharge valves 23A, 23B, and 23C are open. Inlet valve 224, inlet valve 242, and outlet valve 204 are open, and inlet valve 227, inlet valve 228, and outlet valve 202 are closed.

[0137] First, with all of the submersible pumps 1A, 1B, and 1C stopped, liquefied gas flows into the suction vessel 2A of the pump device 100A through the suction port 7A of the suction vessel 2A. The liquefied gas evaporates upon contact with the suction vessel 2A and the submersible pump 1A, which are at room temperature, to form boil-off gas. In FIG. 37, the flow of the boil-off gas is indicated by a dotted line.

[0138] More specifically, the liquefied gas is first introduced into the suction vessel 2A of the pump device 100A through the suction port 7A. The liquefied gas evaporates in the suction vessel 2A to form boil-off gas. The boil-off gas passes through the flow path switching device 5A while bypassing the submerged pump 1A. The boil-off gas that has passed through the flow path switching device 5A is introduced into the suction vessel 2B through the introduction line 221 and the suction port 7B of the pump device 100B, and is simultaneously introduced into the suction vessel 2C through the introduction line 241 and the suction port 7C of the pump device 100C. The boil-off gas passes through the flow path switching device 5B while bypassing the submerged pump 1B. The boil-off gas that has passed through the flow path switching device 5B is discharged from the suction vessel 2B through the discharge port 8B and the discharge line 203. Similarly, the boil-off gas bypasses the submersible pump 1C while passing through the flow path switching device 5C. The boil-off gas that has passed through the flow path switching device 5C is discharged from the suction vessel 2C through the discharge port 8C.

[0139] Next, as shown in Figure 38, the submersible pump 1A is started. The submersible pumps 1B and 1C remain stopped. By operating the submersible pump 1A, the liquefied gas flows into the suction vessel 2A through the suction port 7A.

[0140] The submersible pump 1A sends liquefied gas to the suction vessels 2B and 2C simultaneously (i.e., in parallel). More specifically, the liquefied gas is pressurized by the operation of the submersible pump 1A and passes through the flow path switching device 5A. The liquefied gas that has passed through the flow path switching device 5A is introduced into the suction vessel 2B through the introduction line 221 and the suction port 7B of the pump device 100B, and is simultaneously introduced into the suction vessel 2C through the introduction line 241 and the suction port 7C of the pump device 100C. The liquefied gas passes through the flow path switching device 5B while bypassing the submersible pump 1B. The liquefied gas that has passed through the flow path switching device 5B is discharged from the suction vessel 2B through the discharge port 8B and the discharge line 203. Similarly, the liquefied gas passes through the flow path switching device 5C while bypassing the submersible pump 1C. The liquefied gas that has passed through the flow path switching device 5C is discharged from the suction container 2C through the discharge port 8C.

[0141] In this way, the flow path switching devices 5A, 5B, 5C can prevent the liquefied gas and boil-off gas from passing through the submersible pumps 1A, 1B, 1C that are out of operation during cool down. Therefore, the impellers of the submersible pumps 1A, 1B, 1C that are out of operation do not rotate, and as a result, damage to the sliding parts such as the bearings of the submersible pumps 1A, 1B, 1C can be prevented.

[0142] The above-mentioned embodiments may be appropriately combined. For example, during the cool-down, the liquefied gas may be introduced into each suction vessel through either the suction port or the drain port of each suction vessel. For example, the liquefied gas may be introduced into the suction vessel 2A through the suction port 7A, into the suction vessel 2B through the drain port 25B, and into the suction vessel 2C through the suction port 7C. In another example, the liquefied gas may be introduced into the suction vessel 2A through the drain port 25A, into the suction vessel 2B through the suction port 7B, and into the suction vessel 2C through the suction port 7C.

[0143] FIG. 39 is a cross-sectional view showing another embodiment of the flow path switching device 5. The configuration and operation of this embodiment not specifically described are the same as those of the embodiment described with reference to FIG. 2 and FIG. 3, and therefore the overlapping description will be omitted. As shown in FIG. 39, the flow path structure 45 includes a bypass flow path 55 that communicates 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 a cross-sectional area in which, when the valve body 47 closes the pump side flow path 41 and a fluid (liquefied gas or boil-off gas) flows through the submerged pump 1 and the bypass flow path 55, the impeller 15 (see FIG. 1) of the submerged pump 1 does not rotate due to the flow of the fluid.

[0144] The bypass flow passage 55 may be a through hole as shown in FIG. 39 or a groove formed in the valve seat 51. A plurality of bypass flow passages 55 may be provided as long as the fluid does not rotate the impeller 15. According to this embodiment, the liquefied gas can be smoothly introduced into the inside of the submersible pump 1 during the cool-down. As a result, the cool-down of the submersible pump 1 can be completed in a shorter time. In particular, the bypass flow passage 55 can eliminate the liquid level difference between the inside and outside of the submersible pump 1 when the liquefied gas is introduced into the suction vessel 2 during the cool-down, and can reduce the stress generated in the submersible pump 1 due to the temperature difference between the inside and outside of the submersible pump 1.

[0145] The flow path switching device 5 described with reference to FIG. 39 may be applied to the flow path switching devices 5, 5A to 5F in the embodiments described with reference to FIGS.

[0146] FIG. 40 is a cross-sectional view showing yet another embodiment of the flow path switching device 5. The configuration and operation of this embodiment not specifically described are the same as those of the embodiment described with reference to FIG. 2 and FIG. 3, and therefore the overlapping description will be omitted. As shown in FIG. 40, the valve body 47 has a through hole 57 that communicates the pump side flow path 41 and the outflow flow path 43. The through hole 57 extends from the pump side to the opposite side of the valve body 47. 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, the cross-sectional area of ​​the through hole 57 is a cross-sectional area in which, when the valve body 47 closes the pump side flow path 41 and a fluid (liquefied gas or boil-off gas) flows through the submerged pump 1 and the through hole 57, the impeller 15 (see FIG. 1) of the submerged pump 1 does not rotate due to the flow of the fluid.

[0147] 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, the liquefied gas can be smoothly introduced into the inside of the submersible pump 1 during cool-down. As a result, the cool-down of the submersible pump 1 can be completed in a shorter time. In particular, when the liquefied gas is introduced into the suction container 2 during cool-down, the through holes 57 can eliminate the liquid level difference between the inside and outside of the submersible pump 1, and can reduce the stress generated in the submersible pump 1 due to the temperature difference between the inside and outside of the submersible pump 1.

[0148] The flow path switching device 5 described with reference to FIG. 40 may be applied to the flow path switching devices 5, 5A to 5F in the embodiments described with reference to FIGS.

[0149] The above-described embodiments have been described for the purpose of enabling a person having ordinary skill in the art to practice the present invention. Various modifications of the above-described embodiments are naturally possible for a person skilled in the art, and the technical idea of ​​the present invention can 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 according to the technical idea defined by the claims. [Explanation of symbols]

[0150] 1,1A,1B,1C,1D,1E,1F Submersible pump 2, 2A, 2B, 2C, 2D, 2E, 2F Suction vessel 3 Intake port 4 Discharge port 5,5A,5B,5C,5D,5E,5F Flow path switching device 7,7A,7B,7C,7D,7E,7F Suction port 8,8A,8B,8C,8D,8E,8F Discharge port 9 Motor rotor 10 Motor stator 11 Electric motor 12 Rotation axis 13 Motor housing 14 Bearings 15 Impeller 16 Pump casing 17 Discharge channel 22, 22A, 22B, 22C, 22D, 22E, 22F Suction valve 23, 23A, 23B, 23C, 23D, 23E, 23F Discharge valve 25, 25A, 25B, 25C, 25D, 25E, 25F drain port 26, 26A, 26B, 26C, 26D, 26E, 26F Drain valve 31 Vent Line 32 Vent valve 34, 35, 36 Suction lines 41 Pump side flow path 42 Container side flow path 43 Outlet Channel 45 Flow path structure 47 Valve body 50 Spring 51 Valve seat 55 Bypass flow path 57 Through hole 100, 100A, 100B, 100C, 100D, 100E, 100F Pump equipment 105 Liquefied gas storage tank 107, 108, 109, 110 Connecting lines 114,115 Connecting valve 121,122,123 Introduction Line 125,126,127 Inlet valve 131,133 Outflow line 132,134 Outlet valve 141,142,143 Introduction Line 145,146,147 Inlet valve 151,152 Connecting valve 161,163 Outflow line 162,164 Outlet valve 171,172,173 Introduction Line 176,177,178 Inlet valve 181 Introduction Line 182 Inlet valve 191 Introduction Line 192 Inlet valve 201,203 Discharge line 202,204 Outlet valve 211, 212, 213 Introduction Line 215,216,217 Inlet valve 221,222 Introduction Line 224,225 Inlet valve 227,228 Inlet valve 231 Introduction Line 232 Inlet valve 241 Introduction Line 242 Inlet valve

Claims

1. A cool-down method for cooling a plurality of submersible pumps of a plurality of pump devices including at least a first pump device and a second pump device connected to each other with a liquefied gas, comprising: Simultaneously introducing liquefied gas into a first suction container of the first pump device and a second suction container of the second pump device through a first introduction line and a second introduction line extending from a liquefied gas storage tank; 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, and 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; A cool-down method comprising discharging the liquefied gas from the first suction container and the second suction container through the first flow path switching device and the second flow path switching device.

2. Each of the first flow path switching device and the second flow path switching device is a flow path structure having a pump side flow path, a container side flow path, and an outflow flow path; a valve body disposed in the flow path structure and selectively connecting the outflow path to either the pump side flow path or the container side flow path; The pump side flow path communicates with the discharge port of the corresponding submersible pump, The container-side flow path communicates with the interior of the corresponding suction container, The method of claim 1 , wherein the outlet passage communicates with a discharge port of the corresponding suction container.

3. The cool-down method according to claim 2 , wherein each of the first flow path switching device and the second flow path switching device further includes a spring that presses the valve body against the flow path structure to close the pump side flow path.

4. 2. The cool-down method according to claim 1, wherein the liquefied gas is simultaneously introduced into the first suction container and the second suction container through the first inlet line and the second inlet line, and through a drain port of the first suction container and a drain port of the second suction container.

5. 2. The cool-down method according to claim 1, wherein the liquefied gas is simultaneously introduced into the first suction container and the second suction container through the first introduction line and the second introduction line, and through the suction port of the first suction container and the suction port of the second suction container.

6. The cool-down method of claim 1 , wherein the first pump device and the second pump device are connected in series.

7. The method of claim 1 , wherein the first pump device and the second pump device are connected in parallel.

8. A cool-down method for cooling a plurality of submersible pumps of a plurality of pump devices including at least a first pump device and a second pump device connected to each other with a liquefied gas, comprising: Introducing liquefied gas into a first suction vessel of the first pump device; The boil-off gas generated from the liquefied gas is passed through a first flow path switching device in the first suction vessel while bypassing a first submerged pump in the first suction vessel; Introducing the boil-off gas from the first suction vessel into a second suction vessel of the second pump device; Starting the operation of the first submersible pump to introduce liquefied gas from the first suction container into the second suction container; A method for cooling down, comprising passing the liquefied gas through a second flow path switching device in the second suction vessel while bypassing a second submersible pump in the second suction vessel.

9. Each of the first flow path switching device and the second flow path switching device is a flow path structure having a pump side flow path, a container side flow path, and an outflow flow path; a valve body disposed in the flow path structure and selectively connecting the outflow path to either the pump side flow path or the container side flow path; The pump side flow path communicates with the discharge port of the corresponding submersible pump, The container-side flow path communicates with the interior of the corresponding suction container, The method of claim 8 , wherein the outlet passage communicates with a discharge port of the corresponding suction container.

10. The cool-down method according to claim 9 , wherein each of the first flow path switching device and the second flow path switching device further includes a spring that presses the valve body against the flow path structure to close the pump side flow path.

11. 9. The cool-down method according to claim 8, further comprising the step of starting operation of the first submersible pump to introduce the liquefied gas from the first suction container into the second suction container through a drain port of the second suction container.

12. 9. The cool-down method according to claim 8, further comprising the step of starting operation of the first submersible pump to introduce the liquefied gas from the first suction container into the second suction container through a suction port of the second suction container.

13. the plurality of pump devices further includes a third pump device coupled to the first pump device and the second pump device; the third pump device has the same configuration as the first pump device and the second pump device, The method comprises: Introducing the boil-off gas from the second suction vessel into a third suction vessel of the third pump device; After the first submersible pump starts operating, the liquefied gas is introduced from the second suction container into the third suction container; 9. The method of claim 8, further comprising passing the liquefied gas through a third flow path switching device in the third suction receptacle while bypassing a third submersible pump in the third suction receptacle.

14. The cool-down method of claim 13 , wherein the first pump device, the second pump device, and the third pump device are connected in series.

15. 14. The cool-down method of claim 13, wherein the first pump device, the second pump device, and the third pump device are connected in parallel.

16. the plurality of pump devices further includes a third pump device coupled to the first pump device and the second pump device; the third pump device has the same configuration as the first pump device and the second pump device, The method further includes simultaneously introducing the boil-off gas from the first suction receptacle into the second suction receptacle of the second pump device and into a third suction receptacle of the third pump device; Starting the operation of the first submersible pump to simultaneously introduce liquefied gas from the first suction container into the second suction container and the third suction container; passing the liquefied gas through the second flow path switching device while bypassing the second submersible pump, and passing the liquefied gas through a third flow path switching device in the third suction container while bypassing a third submersible pump in the third suction container; The cool-down method according to claim 8 , wherein the liquefied gas is simultaneously discharged from the second suction container and the third suction container through the second flow path switching device and the third flow path switching device.

17. 17. The cool down method of claim 16, wherein the first pump device, the second pump device, and the third pump device are connected in series.

18. 17. The cool down method of claim 16, wherein the first pump device, the second pump device, and the third pump device are connected in parallel.

19. The cool-down method of claim 8 , wherein the first pump device and the second pump device are connected in series.

20. The method of claim 8 , wherein the first pump device and the second pump device are connected in parallel.

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