Cool-down method for pump device

Abstract

In this cool-down method, liquefied gas is simultaneously introduced into suction containers (2A, 2B) through introduction lines (121, 122) extending from a liquefied gas storage tank (105), the liquefied gas is passed through a flow path switching device (5A) in the suction container (2A) while bypassing a submerged pump (1A) in the suction container (2A), the liquefied gas is passed through a flow path switching device (5B) in the suction container (2B) while bypassing a submerged pump (1B) in the suction container (2B), and the liquefied gas is discharged from the suction container (2A) and the suction container (2B) through the flow path switching device (5A) and the flow path switching device (5B).

Description

How to cool down a pump device

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

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

[0003] FIG. 41 is a schematic diagram showing a conventional pump device for pumping liquefied gas. Pump 500 is installed in a vertical suction vessel 505 connected to a liquefied gas storage tank (not shown) in which liquefied gas is stored. Liquefied gas is introduced into suction vessel 505 through suction port 501, and suction vessel 505 is filled with liquefied gas. Pump 500 is entirely immersed in liquefied gas. Therefore, pump 500 is a submersible pump that can operate in liquefied gas. When pump 500 is operating, liquefied gas is discharged by pump 500 through discharge port 502. During operation of pump 500, a portion of the liquefied gas in suction vessel 505 evaporates and becomes gas, which is discharged from suction vessel 505 through vent line 503.

[0004] If the pump 500 is at room temperature when the pump 500 is started, the ultra-low temperature liquefied gas will evaporate when it comes into contact with the pump 500. Therefore, in order to prevent the liquefied gas from evaporating, a cool-down process is performed in which the pump 500 is cooled with 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 then discharged through the discharge port 502.

[0006] Japanese Utility Model Application Publication No. 59-159795 Japanese Utility Model Application Publication No. 62-031680

[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, performing the above-described cool-down on pump devices connected in series poses the following problem. That is, when liquefied gas is flowed into pump devices before they start operating, the liquefied gas flows through all of the pumps 500. This flow of liquefied gas forces the impellers of the pumps 500 to rotate while they are not operating. As a result, sliding parts such as bearings may be damaged. While it may be possible to flow the liquefied gas at a low flow rate to prevent unintended rotation of the impellers of the pumps 500, in this case, it would take an extremely long time for 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.

[0010] 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 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 aspect, each of the first flow path switching device and the second flow path switching device includes a flow path structure having a pump-side flow path, a container-side flow path, and an outlet flow path, and a valve body disposed within the flow path structure and selectively connecting the outlet flow path to either the pump-side flow path or the container-side flow path, wherein the pump-side flow path is connected to a discharge port of the corresponding submersible pump, the container-side flow path is connected to the interior of the corresponding suction container, and the outlet flow path is connected to a discharge port of the corresponding suction container. In one aspect, 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 aspect, the liquefied gas is simultaneously introduced into the first suction receptacle and the second suction receptacle through the first inlet line and the second inlet line, and through a drain port of the first suction receptacle and a drain port of the second suction receptacle. In one aspect, the liquefied gas is simultaneously introduced into the first suction receptacle and the second suction receptacle through the first inlet line and the second inlet line, and through a suction port of the first suction receptacle and a suction port of the second suction receptacle. In one aspect, the first pump device and the second pump device are connected in series. In one aspect, 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 generated from 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; 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 bypassing the second submersible pump in the second suction container.

[0014] In one aspect, each of the first flow path switching device and the second flow path switching device includes a flow path structure having a pump-side flow path, a container-side flow path, and an outlet flow path, and a valve body disposed within the flow path structure and selectively connecting the outlet flow path to either the pump-side flow path or the container-side flow path, wherein the pump-side flow path is connected to a discharge port of the corresponding submersible pump, the container-side flow path is connected to the interior of the corresponding suction container, and the outlet flow path is connected to a discharge port of the corresponding suction container. In one aspect, 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 aspect, starting operation of the first submersible pump introduces the liquefied gas from the first suction container into the second suction container through a drain port of the second suction container. In one aspect, starting operation of the first submersible pump introduces 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 aspect, 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 aspect, the first pump device, the second pump device, and the third pump device are connected in series. In one aspect, the first pump device, the second pump device, and the third pump device are connected in parallel.

[0017] In one aspect, the plurality of pump devices further includes a third pump device connected to the first pump device and the second pump device, and 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 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 aspect, the first pump device, the second pump device, and the third pump device are connected in series. In another aspect, the first pump device, the second pump device, and the third pump device are connected in parallel.

[0018] In one aspect, the first pump device and the second pump device are connected in series. In one aspect, the first pump device and the second pump device are connected in parallel.

[0019] The flow path switching device can prevent 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 bearings and other sliding parts of the submersible pump can be prevented.

[0020] FIG. 1 is a diagram illustrating an embodiment of a pump device for transferring liquefied gas. FIG. 2 is a cross-sectional view illustrating an embodiment of the detailed configuration of a flow path switching device. FIG. 3 shows the state of the flow path switching device when the submersible pump is operating. FIG. 4 is a diagram illustrating an embodiment of a cool-down. FIG. 5 is a diagram illustrating another embodiment of a cool-down. FIG. 6 is a schematic diagram illustrating an embodiment of a pump system including a plurality of pump devices connected in series. FIG. 7 is a diagram illustrating an embodiment of a cool-down for cooling the plurality of submersible pumps shown in FIG. 6. FIG. 8 is a schematic diagram illustrating another embodiment of a pump system including a plurality of pump devices connected in series. FIG. 9 is a diagram illustrating an embodiment of a cool-down for cooling the plurality of submersible pumps shown in FIG. 8. FIG. 10 is a schematic diagram illustrating an embodiment of a cool-down performed on a pump system including a plurality of pump devices connected in series and parallel. FIG. 11 is a schematic diagram illustrating another embodiment of a cool-down performed on a pump system including a plurality of pump devices connected in series and parallel. FIG. 12 is a schematic diagram illustrating yet another embodiment of a pump system including a plurality of pump devices connected in series. FIG. 13 is a schematic diagram illustrating an embodiment of a cool-down performed on the pump system shown in FIG. 12. Fig. 16 is a schematic diagram showing yet another embodiment of a pump system having a plurality of pump devices connected in series. Fig. 17 is a schematic diagram showing an embodiment of performing cool-down on the pump system shown in Fig. 15. Fig. 18 is a schematic diagram showing an embodiment of performing cool-down on the pump system shown in Fig. 18. Fig. 19 is a schematic diagram showing yet another embodiment of a pump system having a plurality of pump devices connected in series. Fig. 20 is a schematic diagram showing an embodiment of performing cool-down on the pump system shown in Fig. 21. Fig. 21 is a schematic diagram showing an embodiment of performing cool-down on the pump system shown in Fig. 21.FIG. 24 is a schematic diagram illustrating an embodiment of a pump system including a plurality of pump devices connected in series and in parallel. FIG. 25 is a schematic diagram illustrating an embodiment of performing a cool-down on the pump system shown in FIG. 24. FIG. 26 is a schematic diagram illustrating an embodiment of performing a cool-down on the pump system shown in FIG. 24. FIG. 27 is a schematic diagram illustrating an embodiment of a pump system including a plurality of pump devices connected in parallel. FIG. 28 is a schematic diagram illustrating an embodiment of performing a cool-down on the pump system shown in FIG. 27. FIG. 29 is a schematic diagram illustrating an embodiment of performing a cool-down on the pump system shown in FIG. 27. FIG. 30 is a schematic diagram illustrating an embodiment of performing a cool-down on the pump system shown in FIG. 30. FIG. 31 is a schematic diagram illustrating yet another embodiment of a pump system including a plurality of pump devices connected in parallel. FIG. 32 is a schematic diagram illustrating an embodiment of performing a cool-down on the pump system shown in FIG. 33. FIG. 33 is a schematic diagram illustrating yet another embodiment of a pump system including a plurality of pump devices connected in parallel. Fig. 37 is a schematic diagram showing an embodiment in which cool-down is performed on the pump system shown in Fig. 36. Fig. 38 is a schematic diagram showing an embodiment in which cool-down is performed on the pump system shown in Fig. 36. Fig. 39 is a cross-sectional view showing another embodiment of a flow path switching device. Fig. 40 is a cross-sectional view showing yet another embodiment of a flow path switching device. Fig. 41 is a schematic diagram showing a conventional example of a pump device for pumping up liquefied gas. Fig. 42 is a schematic diagram showing an example of a plurality of pump devices connected in series.

[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 transporting liquefied gas. Examples of liquefied gas that can be transported by the pump device 100 shown in Fig. 1 include liquefied hydrogen, liquefied nitrogen, liquefied ammonia, liquefied natural gas, liquefied ethylene gas, and liquefied petroleum gas.

[0022] As shown in Figure 1, the pump device 100 includes a submersible pump 1 for transferring liquefied gas, a suction container 2 in which the submersible pump 1 is housed, and a flow path switching device 5 for preventing rotation of the impeller 15 of the submersible pump 1 when the pump is not in operation. The suction container 2 has a suction port 7 and a discharge port 8. Liquefied gas is introduced into the suction container 2 through the suction port 7, and the suction container 2 is filled with the liquefied gas. During operation of the submersible pump 1, the entire submersible pump 1 is immersed in the liquefied gas. Therefore, the submersible pump 1 is configured to be able to operate in liquefied gas.

[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 that rotatably support the rotating shaft 12, an impeller 15 fixed to the rotating shaft 12, and a pump casing 16 that houses the impeller 15. The flow path switching device 5 is disposed within the suction vessel 2. More specifically, the flow path switching device 5 is connected to both the discharge port 4 of the submersible pump 1 and the discharge port 8 of the suction vessel 2. The specific configuration of the flow path switching device 5 will be described later.

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

[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 container 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 container 2 and is located higher than the bottom of the suction container 2. The discharge port 8 is provided on the top of the suction container 2 and is located higher than the suction port 7. When the submersible pump 1 is in operation, the suction valve 22 and the discharge valve 23 are open, and the drain valve 26 is closed.

[0026] A vent line 31 is connected to the top of the suction vessel 2. During operation of the submersible pump 1, part of the liquefied gas is vaporized into gas due to heat generated by the submersible pump 1, and this gas is discharged from the suction vessel 2 through the vent line 31. A vent valve 32 is connected to the vent line 31. In one embodiment, this gas may be led to a gas treatment device (not shown) through the vent line 31. The gas treatment device is a device that treats gas (e.g., natural gas or hydrogen gas) vaporized from the liquefied gas. Examples of gas treatment devices include a gas incineration device (flaring device), a chemical gas treatment device, and a gas adsorption device.

[0027] 2 is a cross-sectional view showing a detailed configuration of one embodiment of the flow path switching device 5. As shown in FIG. 2, the flow path switching device 5 includes a flow path structure 45 having a pump-side flow path 41, a container-side flow path 42, and an outflow flow path 43, and a valve body 47 disposed within the flow path structure 45. The pump-side flow path 41 communicates with the discharge port 4 of the submersible pump 1, the container-side flow path 42 communicates with the interior of the suction container 2, and the outflow flow path 43 communicates with the discharge port 8 of the suction container 2. The valve body 47 is disposed to selectively communicate the outflow flow path 43 with either the pump-side flow path 41 or the container-side flow path 42. The configuration of the flow path switching device 5 is not limited to the embodiment shown in FIG. 2 as long as it can perform its intended function.

[0028] 2 shows the state of the flow path switching device 5 when the submersible pump 1 is not operating. The valve element 47 is pressed against the flow path structure 45 by the spring 50 to close the pump-side flow path 41. More specifically, the flow path structure 45 has a valve seat 51 formed around the outlet of the pump-side flow path 41, and the valve element 47 is pressed against the valve seat 51 by the spring 50. Therefore, while the valve element 47 is pressed against the valve seat 51, the pump-side flow path 41 is closed, and the container-side flow path 42 and the outflow flow path 43 are in communication. The container-side flow path 42 opens inside the suction container 2 and is in communication with the suction port 7 through the interior of the suction container 2.

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

[0031] Before operating the submersible pump 1, a cool-down process is performed in which the submersible pump 1 is cooled with liquefied gas. The cool-down process is performed while the operation of the submersible pump 1 is stopped. More specifically, as shown in Figure 2, the cool-down process is performed with the pump-side flow path 41 closed by the valve body 47 and the container-side flow path 42 and the outflow flow path 43 in communication.

[0032] Figure 4 is a diagram illustrating one embodiment of cool-down of the submersible pump 1. When the submersible pump 1 is not operating (i.e., the state shown in Figure 2), liquefied gas is supplied into the suction container 2 through the suction port 7. The drain valve 26 and the vent valve 32 are closed, and the suction valve 22 and the discharge valve 23 are open. The vent valve 32 may be open. The liquefied gas comes into contact with the submersible pump 1 in the suction container 2 and is discharged through the container-side flow path 42 and the outlet flow path 43 of the flow path switching device 5 and the discharge port 8. The suction container 2 is eventually filled with liquefied gas, which cools the submersible pump 1.

[0033] During cool-down, the submersible pump 1 is in a stopped state. In Figure 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, unintentional rotation of the impeller 15 of the submersible pump 1 is prevented, and damage to sliding parts such as the bearing 14 is prevented.

[0034] FIG. 5 is a diagram illustrating another embodiment of the cool-down of the submersible pump 1. When the submersible pump 1 is not operating (i.e., the state shown in FIG. 2 ), liquefied gas is supplied into the suction container 2 through the drain port 25 connected to the bottom of the suction container 2. The suction valve 22 and vent valve 32 are closed, and the drain valve 26 and discharge valve 23 are open. The vent valve 32 may be open. As the liquefied gas is introduced from the bottom of the suction container 2, the liquid level of the liquefied gas in the suction container 2 gradually rises. The liquefied gas (and the vaporized gas from the liquefied gas) comes into contact with the submersible pump 1 in the suction container 2 and is discharged through the container-side flow path 42 and outlet flow path 43 of the flow path switching device 5 and the discharge port 8. The suction container 2 eventually fills with liquefied gas, thereby cooling the submersible pump 1.

[0035] During cool-down, the submersible pump 1 is in a stopped state. In Figure 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, unintentional rotation of the impeller 15 of the submersible pump 1 is prevented, and damage to sliding parts such as the bearing 14 is prevented.

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

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

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

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

[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 located 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 due to its own weight. In another example, the liquefied gas storage tank 105 may be located 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 container 2A, an inlet line 122 connected to the drain port 25B of the suction container 2B, and an inlet line 123 connected to the drain port 25C of the suction container 2C. The inlet lines 121, 122, and 123 are connected to the liquefied gas storage tank 105 and extend from the liquefied gas storage tank 105 to the suction containers 2A, 2B, and 2C. The suction containers 2A, 2B, and 2C are connected to the liquefied gas storage tank 105 via the inlet lines 121, 122, and 123.

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

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

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

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

[0046] Figure 7 shows an embodiment of a cool-down process for cooling submersible pumps 1A, 1B, and 1C. As shown in Figure 7, liquefied gas simultaneously (in parallel) flows into suction vessels 2A, 2B, and 2C of pump devices 100A, 100B, and 100C through drain ports 25A, 25B, and 25C of suction vessels 2A, 2B, and 2C. Suction valves 22A, 22B, and 22C and drain valves 26A, 26B, and 26C are closed, and inlet valves 125, 126, and 127 are open. Discharge valves 23A, 23B, and 23C are open, and outlet valves 132 and 134 are also open. Communication valves 114 and 115 are closed.

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

[0048] In this way, the flow path switching devices 5A, 5B, 5C can prevent the liquefied gas introduced into the suction vessels 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 operating, thereby preventing damage to the bearings and other sliding parts of the submersible pumps 1A, 1B, 1C. In particular, because the liquefied gas forms parallel flows within the suction vessels 2A, 2B, 2C, the submersible pumps 1A, 1B, 1C can be cooled simultaneously and in a short time.

[0049] 8 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, which are not specifically described, are the same as those of the embodiment described with reference to FIGS. 6 and 7, and therefore, redundant description will be omitted.

[0050] 8, inlet lines 122 and 123 are connected to suction ports 7B and 7C of suction containers 2B and 2C, respectively, instead of drain ports 25B and 25C. Inlet valves 126 and 127 are attached to inlet lines 122 and 123, respectively. Inlet line 121 and inlet valve 125 are not provided in this embodiment, but suction line 34 and inlet valve 22A correspond to inlet line 121 and inlet valve 125, respectively, in the above-described 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 a cool-down process for cooling the submersible pumps 1A, 1B, and 1C shown in FIG. 8 . During cool-down, as shown in FIG. 9 , inlet valves 126 and 127 are open. Liquefied gas simultaneously (in parallel) flows into suction vessels 2A, 2B, and 2C through suction ports 7A, 7B, and 7C of suction vessels 2A, 2B, and 2C of pump devices 100A, 100B, and 100C. Suction valves 22A, 22B, and 22C are open, drain valves 26A, 26B, and 26C are closed, and inlet valves 126 and 127 are open. Discharge valves 23A, 23B, and 23C are open, and outflow valves 132 and 134 are also open. Communication valves 114 and 115 are closed.

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

[0054] In this way, the flow path switching devices 5A, 5B, 5C can prevent the liquefied gas introduced into the suction vessels 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 operating, thereby preventing damage to the bearings and other sliding parts of the submersible pumps 1A, 1B, 1C. In particular, because the liquefied gas forms parallel flows within the suction vessels 2A, 2B, 2C, 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 of a cool-down process for a pump system including multiple pump devices connected in series and parallel. The configuration and operation of this embodiment are the same as those of the embodiment described with reference to FIGS. 6 and 7 , and therefore, redundant description will be omitted. The pump system of the embodiment shown in FIG. 10 further includes pump devices 100D, 100E, and 100F, each having the same configuration as pump devices 100A, 100B, and 100C described with reference to FIG. 7. Pump devices 100A, 100B, and 100C are connected in series, and pump devices 100D, 100E, and 100F are also connected in series. Pump devices 100D, 100E, and 100F are arranged in parallel with 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 storage tank 105 via a suction line 34, and the suction port 7D of the suction container 2D is connected to the liquefied gas storage tank 105 via 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 communication line 109, and a communication valve 152 is attached to communication line 110. When communication valve 151 is closed, communication between discharge port 8D of pump device 100D and suction port 7E of pump device 100E is blocked. When communication valve 152 is closed, communication between discharge port 8E of pump device 100E and suction port 7F of pump device 100F is blocked. When submersible pump 1D, submersible pump 1E, and submersible pump 1F are operating, 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 via the introduction lines 141, 142, and 143.

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

[0061] The pump system further includes an outflow line 161 connected to the discharge port 8D of the suction container 2D, an outflow valve 162 attached to the outflow line 161, an outflow line 163 connected to the discharge port 8E of the suction container 2E, and an outflow valve 164 attached to the outflow line 163. The outflow valve 162 is disposed downstream of the discharge valve 23D, and the communication valve 151 is located between the discharge valve 23D and the outflow valve 162. The outflow valve 164 is disposed downstream of the discharge valve 23E, and the communication valve 152 is located between the discharge valve 23E and the outflow 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, and therefore a duplicated description thereof will be omitted. Corresponding components in the pump devices 100A, 100B, 100C, 100D, 100E, and 100F are designated by the same reference numerals and suffixes A, B, C, D, E, and F, respectively.

[0063] The liquefied gas flows into the suction vessels 2A, 2B, 2C, 2D, 2E, and 2F simultaneously (in parallel) 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 Figure 10, during 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 Figure 2. Therefore, the liquefied gas bypasses the submersible pumps 1A, 1B, 1C, 1D, 1E, and 1F (i.e., the liquefied gas does not flow inside the submersible pumps 1A, 1B, 1C, 1D, 1E, and 1F) and passes through the flow path switching devices 5A, 5B, 5C, 5D, 5E, and 5F. The liquefied gas forms a parallel flow in the suction vessels 2A, 2B, 2C, 2D, 2E, and 2F, cooling the submersible pumps 1A, 1B, 1C, 1D, 1E, and 1F. The liquefied gas flows out of the suction vessels 2A, 2B, 2C, 2D, 2E and 2F simultaneously through the discharge ports 8A, 8B, 8C, 8D, 8E and 8F.

[0065] In this way, flow path switching devices 5A, 5B, 5C, 5D, 5E, 5F can prevent liquefied gas introduced into suction containers 2A, 2B, 2C, 2D, 2E, 2F from passing through submersible pumps 1A, 1B, 1C, 1D, 1E, 1F during cool-down. Therefore, the impellers of submersible pumps 1A, 1B, 1C, 1D, 1E, 1F do not rotate during shutdown, preventing damage to sliding parts such as bearings of submersible pumps 1A, 1B, 1C, 1D, 1E, 1F. In particular, because the liquefied gas forms parallel flows within suction containers 2A, 2B, 2C, 2D, 2E, 2F, 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 of a pump system that performs cool-down on a pump system including multiple pump devices connected in series and parallel. The configuration and operation of this embodiment, unless otherwise specified, are the same as those of the embodiment described with reference to FIGS. 8 to 10 , and therefore, redundant description will be omitted. The pump system of the embodiment shown in FIG. 11 further includes pump devices 100D, 100E, and 100F, each having the same configuration as pump devices 100A, 100B, and 100C described with reference to FIG. 8 . Pump devices 100A, 100B, and 100C are connected in series, and pump devices 100D, 100E, and 100F are also connected in series. Pump devices 100D, 100E, and 100F are arranged in parallel with pump devices 100A, 100B, and 100C.

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

[0068] During cool-down, liquefied gas simultaneously (in parallel) flows into 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 Figure 11, during 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 Figure 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 simultaneously flows out of the suction vessels 2A, 2B, 2C, 2D, 2E, 2F through the discharge ports 8A, 8B, 8C, 8D, 8E, 8F.

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

[0070] Figure 12 is a schematic diagram showing another embodiment of a pump system including multiple pump devices 100A, 100B, and 100C connected in series. The configuration and operation of this embodiment, unless otherwise specified, are the same as those of the embodiment described with reference to Figure 6, and therefore redundant description will be omitted. The pump system shown in Figure 12 differs from the embodiment shown in Figure 6 in that it does not include the communication valves 114 and 115, the inlet lines 121 and 122, the inlet lines 123, the inlet valves 125 and 126, the inlet valves 127, the outlet lines 131 and 133, the outlet valves 132, and the outlet valves 134 shown in Figure 6, but the other configurations are the same.

[0071] 13 and 14 are schematic diagrams illustrating an embodiment of a cool-down process for the pump system shown in FIG. 12. As shown in FIG. 13, the suction valves 22A, 22B, and 22C are open, the drain valves 26A, 26B, and 26C are closed, and the discharge valves 23A, 23B, and 23C are open. 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. 13, the flow of the boil-off gas is indicated by a dotted line.

[0072] More specifically, liquefied gas is first introduced into suction vessel 2A of pump device 100A through suction port 7A. The liquefied gas evaporates in suction vessel 2A, forming boil-off gas. The boil-off gas passes through flow path switching device 5A while bypassing submersible pump 1A. After passing through flow path switching device 5A, the boil-off gas is introduced into suction vessel 2B through communication line 107 and suction port 7B of pump device 100B. After bypassing submersible pump 1B, the boil-off gas passes through flow path switching device 5B. After passing through flow path switching device 5B, the boil-off gas is introduced into suction vessel 2C through communication line 108 and suction port 7C of pump device 100C. After bypassing submersible pump 1C, the boil-off gas passes through flow path switching device 5C. The boil-off gas is discharged through the discharge port 8C of the pump device 100C.

[0073] Next, as shown in FIG. 14 , submersible pump 1A is started. Submersible pumps 1B and 1C remain stopped. As submersible pump 1A operates, liquefied gas flows into suction container 2A through suction port 7A. Submersible pump 1A sequentially sends the liquefied gas to suction containers 2B and 2C. More specifically, the liquefied gas is pressurized by operation of submersible pump 1A and passes through flow path switching device 5A. The liquefied gas that has passed through flow path switching device 5A is introduced into suction container 2B through communication line 107 and suction port 7B of pump device 100B. The liquefied gas bypasses submersible pump 1B while passing through flow path switching device 5B. Furthermore, the liquefied gas that has passed through flow path switching device 5B is introduced into suction container 2C through communication line 108 and suction port 7C of pump device 100C. The liquefied gas passes through the flow path switching device 5C while bypassing the submersible pump 1C, and is discharged through the discharge port 8C of the pump device 100C.

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

[0075] 15 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, which will not be specifically described, are the same as those of the embodiment described with reference to FIG. 6, and therefore, redundant description will be omitted.

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

[0077] An inlet line 171 extends from the liquefied gas storage tank 105 to the drain port 25A of the suction container 2A. When an inlet valve 176 is opened, the drain port 25A of the suction container 2A is connected to the liquefied gas storage tank 105 via the inlet line 171. An inlet line 172 extends from the discharge port 8A of the suction container 2A to the drain port 25B of the suction container 2B. When an inlet valve 177 is opened, the drain port 25B of the suction container 2B is connected to the discharge port 8A of the suction container 2A via the inlet line 172. An inlet line 173 extends from the discharge port 8B of the suction container 2B to the drain port 25C of the suction container 2C. When an inlet valve 178 is opened, the drain port 25C of the suction container 2C is connected to the discharge port 8B of the suction container 2B via the inlet line 173. As shown in FIG. 15, during operation of the submersible pumps 1A, 1B, and 1C, the inlet valves 176, 177, and 178 are closed.

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

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

[0080] More specifically, liquefied gas is first introduced into suction vessel 2A of pump device 100A through drain port 25A. The liquefied gas evaporates in suction vessel 2A, forming boil-off gas. The boil-off gas bypasses submersible pump 1A and passes through flow path switching device 5A. After passing through flow path switching device 5A, the boil-off gas is introduced into suction vessel 2B through inlet line 172 and drain port 25B of pump device 100B. After bypassing submersible pump 1B, the boil-off gas passes through flow path switching device 5B. After passing through flow path switching device 5B, the boil-off gas is introduced into suction vessel 2C through inlet line 173 and drain port 25C of pump device 100C. After bypassing submersible pump 1C, the boil-off gas passes through flow path switching device 5C. 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. As the submersible pump 1A operates, the liquefied gas flows into the suction container 2A through the suction port 7A.

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

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

[0084] Figure 18 is a schematic diagram showing another embodiment of a pump system including multiple pump devices 100A, 100B, and 100C connected in series. The configuration and operation of this embodiment, unless otherwise specified, are the same as those of the embodiment described with reference to Figure 15, and therefore redundant description will be omitted. The pump system of this embodiment shown in Figure 18 includes an introduction line 181 connected to the discharge port 8A of the suction container 2A and the drain port 25C of the suction container 2C, and an introduction valve 182 attached to the introduction line 181. The discharge port 8A of the suction container 2A is connected to both the drain port 25B of the suction container 2B and the drain port 25C of the suction container 2C via the introduction line 172 and the introduction line 181.

[0085] When inlet valve 176 is opened, drain port 25A of suction container 2A is connected to liquefied gas storage tank 105 through inlet line 171. When inlet valve 177 is opened, drain port 25B of suction container 2B is connected to discharge port 8A of suction container 2A through inlet line 172. Inlet line 181 bypasses pump device 100B and extends from discharge port 8A of suction container 2A to drain port 25C of suction container 2C. When inlet valve 182 is opened, drain port 25C of suction container 2C is connected to discharge port 8A of suction container 2A through inlet 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 Figure 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 one embodiment of performing a cool-down on the pump system shown in Figure 18. As shown in Figure 19, inlet 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 valves 176, 177, and 182 are open, and outlet valve 134 is open.

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

[0089] More specifically, 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, forming boil-off gas. The boil-off gas passes through the flow path switching device 5A while bypassing the submersible 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 inlet line 172 and the drain port 25B of the pump device 100B, and simultaneously introduced into the suction vessel 2C through the inlet line 181 and the drain port 25C of the pump device 100C. The inlet line 172 and the inlet 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 submersible 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 and passes 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. As the submersible pump 1A operates, the liquefied gas flows into the suction container 2A through the suction port 7A.

[0091] Submersible pump 1A simultaneously (i.e., in parallel) sends liquefied gas to suction containers 2B and 2C. More specifically, the liquefied gas is pressurized by operation of submersible pump 1A and passes through flow path switching device 5A. The liquefied gas that has passed through flow path switching device 5A is introduced into suction container 2B through inlet line 172 and drain port 25B of pump device 100B, and simultaneously introduced into suction container 2C through inlet line 181 and drain port 25C of pump device 100C. While bypassing submersible pump 1B, the liquefied gas passes through flow path switching device 5B. After passing through flow path switching device 5B, the liquefied gas is discharged from suction container 2B through discharge port 8B and outflow line 133. Similarly, the liquefied gas passes through flow path switching device 5C while bypassing 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, flow path switching devices 5A, 5B, 5C can prevent liquefied gas and boil-off gas from passing through submersible pumps 1A, 1B, 1C that are out of operation during cool down. Therefore, the impellers of submersible pumps 1A, 1B, 1C that are out of operation do not rotate, and as a result, damage to sliding parts such as bearings of submersible pumps 1A, 1B, 1C can be prevented.

[0093] Figure 21 is a schematic diagram showing yet another embodiment of a pump system including multiple pump devices 100A, 100B, and 100C connected in series. The configuration and operation of this embodiment, unless otherwise specified, are the same as those of the embodiment described with reference to Figure 12, and therefore redundant description will be omitted. The pump system shown in Figure 21 further includes an inlet line 191 connected to the discharge port 8A of the suction container 2A of the pump device 100A and the suction port 7C of the suction container 2C of the pump device 100C, an inlet valve 192 attached to the inlet line 191, an outlet line 133 connected to the discharge port 8B of the suction container 2B of the pump device 100B, an outlet valve 134 attached to the outlet line 133, and a communication valve 115 attached to the communication line 108.

[0094] An inlet line 191 bypasses the pump device 100B and extends from the discharge port 8A of the suction vessel 2A to the suction port 7C of the suction vessel 2C. 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 are communicated 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, and 1C, the inlet valve 192 and the outlet valve 134 are closed, and the communication valve 115 is open.

[0095] Figures 22 and 23 are schematic diagrams showing an embodiment for 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 open, the drain valves 26A, 26B, and 26C are closed, and the discharge valves 23A, 23B, and 23C are open. The communication valve 115 is closed, and the inlet valve 192 and the outlet valve 134 are open.

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

[0097] More specifically, 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, forming boil-off gas. The boil-off gas passes through the flow path switching device 5A while bypassing the submersible 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 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 submersible 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 and passes 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 Figure 23, the submersible pump 1A is started. The submersible pumps 1B and 1C remain stopped. As the submersible pump 1A starts, the liquefied gas flows into the suction container 2A through the suction port 7A.

[0099] Submersible pump 1A simultaneously (i.e., in parallel) sends liquefied gas to suction containers 2B and 2C. More specifically, the liquefied gas is pressurized by operation of submersible pump 1A and passes through flow path switching device 5A. The liquefied gas that has passed through flow path switching device 5A is introduced into suction container 2B through communication line 107 and suction port 7B of pump device 100B, and simultaneously introduced into suction container 2C through introduction line 191 and suction port 7C of pump device 100C. While bypassing submersible pump 1B, the liquefied gas passes through flow path switching device 5B. After passing through flow path switching device 5B, the liquefied gas is discharged from suction container 2B through discharge port 8B and outflow line 133. Similarly, the liquefied gas passes through flow path switching device 5C while bypassing 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, flow path switching devices 5A, 5B, 5C can prevent liquefied gas and boil-off gas from passing through submersible pumps 1A, 1B, 1C that are out of operation during cool down. Therefore, the impellers of submersible pumps 1A, 1B, 1C that are out of operation do not rotate, and as a result, damage to sliding parts such as bearings of submersible pumps 1A, 1B, 1C can be prevented.

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

[0102] The suction port 7A of the suction container 2A is connected to the liquefied gas storage tank 105 via the suction line 34, and the suction port 7D of the suction container 2D is connected to the liquefied gas storage tank 105 via 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 via the 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 via the communication line 110.

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

[0104] Next, as shown in Figure 26, submersible pumps 1A and 1D are started. Submersible pumps 1B, 1C, 1E, and 1F remain stopped. When submersible pump 1A is operated, liquefied gas flows into suction container 2A through suction port 7A. Submersible pump 1A sequentially sends liquefied gas to suction containers 2B and 2C. When submersible pump 1D is operated, liquefied gas flows into suction container 2D through suction port 7D. Submersible pump 1D sequentially sends liquefied gas to suction containers 2E and 2F. 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 parallel.

[0106] 27 is a schematic diagram showing one 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 thereof will be omitted.

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

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

[0109] An inlet line 211 extends from the liquefied gas storage tank 105 to the drain port 25A of the suction container 2A. When the inlet valve 215 is opened, the drain port 25A of the suction container 2A is connected to the liquefied gas storage tank 105 via the inlet line 211. An inlet line 212 extends from the discharge port 8A of the suction container 2A to the drain port 25B of the suction container 2B. When the inlet valve 216 is opened, the drain port 25B of the suction container 2B is connected to the discharge port 8A of the suction container 2A via the inlet line 212. An inlet line 213 extends from the discharge port 8B of the suction container 2B to the drain port 25C of the suction container 2C. When the inlet valve 217 is opened, the drain port 25C of the suction container 2C is connected to the discharge port 8B of the suction container 2B via the inlet 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 one embodiment of performing a cool-down on the pump system shown in Figure 27. As shown in Figure 28, inlet 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 valves 215, 216, and 217 are open, and outlet valves 202 and 204 are closed.

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

[0112] More specifically, liquefied gas is first introduced into suction vessel 2A of pump device 100A through drain port 25A. The liquefied gas evaporates in suction vessel 2A, forming boil-off gas. The boil-off gas bypasses submersible pump 1A and passes through flow path switching device 5A. After passing through flow path switching device 5A, the boil-off gas is introduced into suction vessel 2B through inlet line 212 and drain port 25B of pump device 100B. After bypassing submersible pump 1B, the boil-off gas passes through flow path switching device 5B. After passing through flow path switching device 5B, the boil-off gas is introduced into suction vessel 2C through inlet line 213 and drain port 25C of pump device 100C. After bypassing submersible pump 1C, the boil-off gas passes through flow path switching device 5C. 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. As the submersible pump 1A operates, the liquefied gas flows into the suction container 2A through the suction port 7A.

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

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

[0116] 30 is a schematic diagram showing another embodiment of a pump system including multiple pump devices 100A, 100B, and 100C connected in parallel. The configuration and operation of this embodiment, which will not be specifically described, are the same as those of the embodiment described with reference to FIGS. 27 to 29, and therefore, redundant description 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 located upstream of the suction valve 22B, and the inlet valve 224 is located between the inlet valve 227 and the suction valve 22B. The inlet valve 228 is located upstream of the suction valve 22C, and the inlet valve 225 is located between the inlet valve 228 and the suction valve 22C.

[0118] An inlet 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 inlet 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 inlet line 221. An inlet 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 inlet 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 inlet line 222. As shown in Figure 30, during operation of the submersible pumps 1A, 1B, and 1C, the inlet valves 224 and 225 are closed, the outlet valves 202 and 204 are open, and the inlet valves 227 and 228 are open.

[0119] Figures 31 and 32 are schematic diagrams showing one embodiment of performing a cool-down on the pump system shown in Figure 30. As shown in Figure 30, suction 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 valves 224 and 225 are open, and outlet valves 202 and 204 are closed. Inlet valves 227 and 228 are closed.

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

[0121] More specifically, liquefied gas is first introduced into suction vessel 2A of pumping device 100A through suction port 7A. The liquefied gas evaporates in suction vessel 2A, forming boil-off gas. The boil-off gas bypasses submersible pump 1A while passing through flow path switching device 5A. After passing through flow path switching device 5A, the boil-off gas is introduced into suction vessel 2B through inlet line 221 and suction port 7B of pumping device 100B. After bypassing submersible pump 1B, the boil-off gas passes through flow path switching device 5B. After passing through flow path switching device 5B, the boil-off gas is introduced into suction vessel 2C through inlet line 222 and suction port 7C of pumping device 100C. After bypassing submersible pump 1C, the boil-off gas passes through flow path switching device 5C. The boil-off gas is discharged through the discharge port 8C of the pump device 100C.

[0122] Next, as shown in FIG. 32 , submersible pump 1A is started. Submersible pumps 1B and 1C remain stopped. As submersible pump 1A operates, liquefied gas flows into suction container 2A through suction port 7A. Submersible pump 1A sequentially sends the liquefied gas to suction containers 2B and 2C. More specifically, the liquefied gas is pressurized by operation of submersible pump 1A and passes through flow path switching device 5A. After passing through flow path switching device 5A, the liquefied gas is introduced into suction container 2B through inlet line 221 and suction port 7B of pump device 100B. While bypassing submersible pump 1B, the liquefied gas passes through flow path switching device 5B. Furthermore, after passing through flow path switching device 5B, the liquefied gas is introduced into suction container 2C through inlet line 222 and suction port 7C of pump device 100C. The liquefied gas passes through the flow path switching device 5C while bypassing the submersible pump 1C, and is discharged through the discharge port 8C of the pump device 100C.

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

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

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

[0126] When the inlet valve 215 is opened, the drain port 25A of the suction vessel 2A is connected to the liquefied gas storage tank 105 through the inlet line 211. When the inlet 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 inlet line 212. The inlet line 231 bypasses the pump apparatus 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 inlet 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 inlet line 231. As shown in Figure 33, during operation of the submersible pumps 1A, 1B, and 1C, the inlet 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 one embodiment of performing a cool-down on the pump system shown in Figure 33. As shown in Figure 34, inlet 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 submersible pumps 1A, 1B, and 1C stopped, liquefied gas flows into suction vessel 2A through inlet line 211 and drain port 25A of suction vessel 2A. The liquefied gas evaporates upon contact with suction vessel 2A and submersible pump 1A, which are at room temperature, to form boil-off gas. In Figure 34, the flow of boil-off gas is indicated by a dotted line.

[0129] More specifically, liquefied gas is first introduced into suction vessel 2A of pump device 100A through drain port 25A. The liquefied gas evaporates in suction vessel 2A, forming boil-off gas. The boil-off gas passes through flow path switching device 5A while bypassing submersible pump 1A. The boil-off gas that has passed through flow path switching device 5A is introduced into suction vessel 2B through inlet line 212 and drain port 25B of pump device 100B, and simultaneously introduced into suction vessel 2C through inlet line 231 and drain port 25C of pump device 100C. The boil-off gas passes through flow path switching device 5B while bypassing submersible pump 1B. The boil-off gas that has passed through flow path switching device 5B is discharged from suction vessel 2B through discharge port 8B and discharge line 203. Similarly, the boil-off gas bypasses the submersible pump 1C and passes 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. As the submersible pump 1A operates, the liquefied gas flows into the suction container 2A through the suction port 7A.

[0131] Submersible pump 1A simultaneously (i.e., in parallel) sends liquefied gas to suction containers 2B and 2C. More specifically, the liquefied gas is pressurized by operation of submersible pump 1A and passes through flow path switching device 5A. The liquefied gas that has passed through flow path switching device 5A is introduced into suction container 2B through inlet line 212 and drain port 25B of pump device 100B, and simultaneously introduced into suction container 2C through inlet line 231 and drain port 25C of pump device 100C. While bypassing submersible pump 1B, the liquefied gas passes through flow path switching device 5B. After passing through flow path switching device 5B, the liquefied gas is discharged from suction container 2B through discharge port 8B and discharge line 203. Similarly, the liquefied gas passes through flow path switching device 5C while bypassing 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, flow path switching devices 5A, 5B, 5C can prevent liquefied gas and boil-off gas from passing through submersible pumps 1A, 1B, 1C that are out of operation during cool down. Therefore, the impellers of submersible pumps 1A, 1B, 1C that are out of operation do not rotate, and as a result, damage to sliding parts such as bearings of submersible pumps 1A, 1B, 1C can be prevented.

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

[0134] The pump system of this embodiment includes an introduction line 221 connected to the discharge port 8A of suction vessel 2A and the suction port 7B of suction vessel 2B, an introduction line 241 connected to the discharge port 8A of suction vessel 2A and the suction port 7C of 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 inlet valve 224 is opened, discharge port 8A of suction vessel 2A communicates with suction port 7B of suction vessel 2B through inlet line 221. Inlet line 241 bypasses pump apparatus 100B and extends from discharge port 8A of suction vessel 2A to suction port 7C of suction vessel 2C. When inlet valve 242 is opened, discharge port 8A of suction vessel 2A communicates with suction port 7C of suction vessel 2C through inlet line 241. As shown in Figure 36, during operation of submersible pumps 1A, 1B, 1C, inlet valves 224 and 242 are closed, outlet valves 202 and 204 are open, and inlet valves 227 and 228 are open.

[0136] Figures 37 and 38 are schematic diagrams illustrating one 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 submersible pumps 1A, 1B, and 1C stopped, liquefied gas flows into suction vessel 2A of pump device 100A through suction port 7A of suction vessel 2A. The liquefied gas evaporates upon contact with suction vessel 2A and submersible pump 1A, which are at room temperature, to form boil-off gas. In Figure 37, the flow of boil-off gas is indicated by a dotted line.

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

[0140] Submersible pump 1A simultaneously (i.e., in parallel) sends liquefied gas to suction containers 2B and 2C. More specifically, the liquefied gas is pressurized by operation of submersible pump 1A and passes through flow path switching device 5A. The liquefied gas that has passed through flow path switching device 5A is introduced into suction container 2B through inlet line 221 and suction port 7B of pump device 100B, and simultaneously introduced into suction container 2C through inlet line 241 and suction port 7C of pump device 100C. While bypassing submersible pump 1B, the liquefied gas passes through flow path switching device 5B. After passing through flow path switching device 5B, the liquefied gas is discharged from suction container 2B through discharge port 8B and discharge line 203. Similarly, the liquefied gas passes through flow path switching device 5C while bypassing 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, flow path switching devices 5A, 5B, 5C can prevent liquefied gas and boil-off gas from passing through submersible pumps 1A, 1B, 1C that are out of operation during cool down. Therefore, the impellers of submersible pumps 1A, 1B, 1C that are out of operation do not rotate, and as a result, damage to sliding parts such as bearings of submersible pumps 1A, 1B, 1C can be prevented.

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

[0143] Figure 39 is a cross-sectional view showing another embodiment of the flow path switching device 5. The configuration and operation of this embodiment, unless otherwise specifically described, are the same as those of the embodiment described with reference to Figures 2 and 3 , and therefore redundant description will be omitted. As shown in Figure 39 , the flow path structure 45 includes a bypass flow path 55 that connects the pump-side flow path 41 and the outflow flow path 43. The cross-sectional area of ​​the bypass flow path 55 is smaller than the cross-sectional area of ​​the pump-side flow path 41. More specifically, the cross-sectional area of ​​the bypass flow path 55 is such that, when the valve element 47 closes the pump-side flow path 41 and a fluid (liquefied gas or boil-off gas) flows through the submersible pump 1 and the bypass flow path 55, the impeller 15 (see Figure 1 ) of the submersible pump 1 does not rotate due to the flow of the fluid.

[0144] The bypass flow path 55 may be a through hole as shown in FIG. 39 or a groove formed in the valve seat 51. Multiple bypass flow paths 55 may be provided as long as the fluid does not rotate the impeller 15. According to this embodiment, liquefied gas can be smoothly introduced into the interior 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, the bypass flow path 55 eliminates the liquid level difference between the inside and outside of the submersible pump 1 when liquefied gas is introduced into the suction container 2 during cool-down, thereby reducing stress generated in the submersible pump 1 due to the temperature difference between the inside and outside of the submersible pump 1.

[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, unless otherwise specified, are the same as those of the embodiment described with reference to FIGS. 2 and 3 , and therefore redundant description will be omitted. As shown in FIG. 40 , the valve element 47 has a through hole 57 that connects the pump-side flow path 41 and the outflow flow path 43. The through hole 57 extends from the pump side to the opposite side of the valve element 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, when the valve element 47 closes the pump-side flow path 41 and a fluid (liquefied gas or boil-off gas) flows through the submersible pump 1 and the through hole 57, the cross-sectional area of ​​the through hole 57 is such that the impeller 15 (see FIG. 1 ) of the submersible 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, liquefied gas can be smoothly introduced into the interior 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 liquefied gas is introduced into the suction container 2 during cool-down, the through holes 57 eliminate the liquid level difference between the inside and outside of the submersible pump 1, and can reduce 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 of ordinary skill in the art to practice the present invention. Various modifications of the above-described embodiments would be obvious to a person skilled in the art, and the technical concept of the present invention may be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but is to be interpreted in the broadest scope in accordance with the technical concept defined by the claims.

[0150] The present invention relates to a method for cooling down a submersible pump used to transport liquefied gases such as liquefied hydrogen, liquid nitrogen, liquefied ammonia, liquefied natural gas, liquefied ethylene gas, and liquefied petroleum gas.

[0151] 1, 1A, 1B, 1C, 1D, 1E, 1F Submersible pump 2, 2A, 2B, 2C, 2D, 2E, 2F Suction vessel 3 Suction port 4 Discharge port 5, 5A, 5B, 5C, 5D, 5E, 5F Flow path switching device 7, 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 Rotating shaft 13 Motor housing 14 Bearing 15 Impeller 16 Pump casing 17 Discharge flow path 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 line 41 Pump side flow path 42 Container side flow path 43 Outlet flow path 45 Flow path structure 47 Valve body 50 Spring 51 Valve seat 55 Bypass flow path 57 Through hole 100, 100A, 100B, 100C, 100D, 100E, 100F Pump device 105 Liquefied gas storage tank 107, 108, 109, 110 Communication line 114, 115 Communication valves 121, 122, 123 Inlet lines 125, 126, 127 Inlet valves 131, 133 Outlet lines 132, 134 Outlet valves 141, 142, 143 Inlet lines 145, 146, 147 Inlet valves 151, 152 Communication valves 161, 163 Outlet lines 162, 164 Outlet valves 171, 172, 173 Inlet lines 176, 177, 178 Inlet valves 181 Inlet line 182 Inlet valve 191 Inlet line 192 Inlet valve 201, 203 Discharge lines 202, 204 Outlet valves 211, 212, 213 Inlet lines 215, 216, 217 Inlet valves 221, 222 Introduction lines 224, 225 Introduction valves 227, 228 Inlet valves 231 Introduction line 232 Introduction valve 241 Introduction line 242 Introduction valve

Claims

1. 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, comprising the steps of: 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.

2. A cool-down method as described in claim 1, wherein each of the first flow path switching device and the second flow path switching device comprises: a flow path structure having a pump side flow path, a container side flow path, and an outlet flow path; and a valve body disposed within the flow path structure for selectively connecting the outlet flow path to either the pump side flow path or the container side flow path, wherein the pump side flow path is connected to the discharge port of the corresponding submersible pump, the container side flow path is connected to the interior of the corresponding suction container, and the outlet flow path is connected to the discharge port of the corresponding suction container.

3. A cooling down method as described in 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. A cooling down method as described in 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. A cooling down method as described in 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 cool-down 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 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, comprising the steps of: introducing liquefied gas into a first suction container of the first pump device; passing the boil-off gas generated from 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; 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 to introduce 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 bypassing the second submersible pump in the second suction container.

9. A cool-down method as described in claim 8, wherein each of the first flow path switching device and the second flow path switching device comprises: 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.

10. A cooling down method as described in 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. A cooling down method as described in claim 8, wherein the liquefied gas is introduced from the first suction container into the second suction container through a drain port of the second suction container by starting operation of the first submersible pump.

12. A cooling down method as described in claim 8, wherein the liquefied gas is introduced from the first suction container into the second suction container through a suction port of the second suction container by starting operation of the first submersible pump.

13. The cool-down method according to claim 8, wherein 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; introducing the liquefied gas from the second suction container into the third suction container after the first submersible pump starts operating; 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.

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. 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 cool-down method according to claim 8, wherein 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.

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

Images