Pump system

Abstract

This pump system comprises: a tank in which liquefied gas can be stored; a plurality of pumps that are accommodated inside the tank and are immersed in the liquefied gas inside the tank; and series piping which connects the plurality of pumps in series, which directly connects, between two series-connected pumps, a discharge part of a low-pressure-side pump and a suction part of a high-pressure side-pump, and through which the liquefied gas can flow.

Description

Pump System

[0001] This application claims priority to Japanese Patent Application No. 2024-056623, filed on March 29, 2024, the contents of which are incorporated herein by reference.

[0002] For example, as disclosed in Patent Document 1, there is a method in which multiple pump devices are connected in series to pressurize liquefied gas to the pressure required on the demand side. In this method, the pressure of the liquefied gas is increased in stages by multiple pumps. The pump device has a tank that stores the liquefied gas and a pump that is immersed in the liquefied gas in the tank. The pump sucks the liquefied gas from the tank and discharges it into the tank of the subsequent pump device.

[0003] Japanese Patent Application Laid-Open No. 2023-173562

[0004] However, with the technology disclosed in Patent Document 1, pressurized liquefied gas is supplied to later tanks. As a result, the pressure inside the tank becomes higher the further the pump device is located in the later stage. For this reason, the later the tank, the higher the pressure-resistant design is required. Furthermore, the higher the pressure inside the tank, the more the evaporation of the liquefied gas inside the tank is suppressed. Therefore, the gas layer at the top of the tank becomes thinner in later tanks. As the gas layer becomes thinner, the top of the tank becomes colder, close to the temperature of the liquefied gas. As a result, the temperature difference between the flange at the top of the tank and the outside of the tank becomes larger, and thermal deformation of the top of the tank becomes greater. Furthermore, the thinner the gas layer, the greater the heat input into the tank.

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a pump system that can maintain a low pressure in a tank housing the pumps in a connection method in which multiple pumps are connected in series.

[0006] In order to solve the above problems, the pump system of the present disclosure comprises a tank capable of storing liquefied gas, a plurality of pumps housed within the tank and immersed in the liquefied gas in the tank, and a series pipe connecting the plurality of pumps in series, directly connecting the discharge portion of the low-pressure side pump to the suction portion of the high-pressure side pump for two of the series-connected pumps, and through which the liquefied gas can flow.

[0007] According to the pump system of the present disclosure, in a connection system in which a plurality of pumps are connected in series, the tank in which the pumps are housed can be maintained at a low pressure.

[0008] Fig. 1 is a schematic configuration diagram of a pump system according to an embodiment of the present disclosure; Fig. 2 is an enlarged view of a tank and a pump according to an embodiment of the present disclosure; Fig. 3 is an enlarged view of a suction side end of a series pipe according to an embodiment of the present disclosure; Fig. 4 is a schematic configuration diagram of a pump system according to another embodiment of the present disclosure; Fig. 5 is a schematic configuration diagram of a pump system according to another embodiment of the present disclosure; Fig. 6 is a schematic configuration diagram of a pump system according to another embodiment of the present disclosure;

[0009] (Configuration of Pump System) A pump system 1 according to an embodiment of the present disclosure will be described below with reference to FIGS. 1 to 3. The pump system 1 shown in FIG. 1 is an apparatus that supplies a pressurized fluid (hydrogen in this embodiment) to equipment or plant equipment that utilizes the pressurized fluid (not shown). The pump system 1 pressurizes a high-pressure gas to a target pressure and supplies the pressurized fluid (hydrogen in this embodiment) to the equipment or plant equipment that utilizes the pressurized fluid. In this embodiment, a case in which the pressurized fluid is liquefied hydrogen will be described as an example. Note that, hereinafter, "liquefied gas L" refers to a liquid gas, and "gas G" refers to a gaseous gas. As shown in FIGS. 1 and 2, the pump system 1 includes a tank 10, a pump 20, a supply source 2, a pump supply pipe 30, a serial pipe 31, a pump discharge pipe 32, a tank supply pipe 40, a gas vent pipe 50, a gas layer detection unit 3, and an alarm 4.

[0010] (Tank) The tank 10 is a container capable of storing liquefied gas L (liquefied hydrogen in this embodiment). An example of the tank 10 is a sump tank. The tank 10 is thermally insulated, for example, by being covered with a heat insulating material. The tank 10 has a tank body 11 and a flange 12. The tank body 11 opens upward. The flange 12 is provided at the top of the tank 10. The flange 12 closes the opening of the tank body 11. In this embodiment, multiple tanks 10 (three in this embodiment) are provided.

[0011] The tank 10 maintains the pump 20, which will be described later, at a low temperature by immersing the pump 20 in the liquefied gas L stored inside. Furthermore, a portion of the liquefied gas L vaporizes inside the tank 10, forming a gas layer GL in the upper part of the tank 10. The gas layer GL is formed over the entire lower surface of the flange 12. The gas layer GL insulates the liquefied gas L from the flange 12, preventing the flange 12 from being cooled by the liquefied gas L.

[0012] (Pump) A plurality of pumps 20 (three in this embodiment) are provided. In this embodiment, one pump 20 is housed in each tank 10. The pump 20 is suspended from the underside of the flange 12. The pump 20 is immersed in the liquefied gas L in the tank 10. The pump 20 has an inlet 21 that draws in the liquefied gas L and an outlet 22 that discharges the liquefied gas L. In this embodiment, the inlet 21 is provided at the lower end of the pump 20, and the outlet 22 is provided at the upper end of the pump 20. The pump 20 is a rotary (turbo) pump, and the liquefied gas L is sucked up and pressurized through the inlet 21 by the rotation of an impeller attached to a rotating shaft, and discharged from the outlet 22.

[0013] The pump system 1 employs a connection method in which multiple pumps 20 are connected in series. The pump system 1 uses the multiple pumps 20 to stepwise increase the pressure of the liquefied gas L. Of the multiple pumps 20, the pump 20 located on the lowest pressure side is referred to as the first stage, and the pumps 20 are referred to in order from the lowest pressure side as the first stage, second stage, and third stage. Similarly, the tanks 10 in which the pumps 20 are housed are referred to in order from the lowest pressure side as the first stage, second stage, and third stage.

[0014] In this embodiment, the inside of the pump 20 is completely separated from the inside of the tank 10. Therefore, the liquefied gas L in the pump 20 and the liquefied gas L in the tank 10 do not mix with each other inside the tank 10.

[0015] (Supply Source) The supply source 2 is a tank capable of storing the liquefied gas L. The supply source 2 stores the liquefied gas L to be supplied to the tank 10 and the pump 20.

[0016] (Pump supply piping) The pump supply piping 30 connects the supply source 2 and the suction portion 21 of the first-stage pump 20. The pump supply piping 30 supplies the low-pressure liquefied gas L stored in the supply source 2 to the first-stage pump 20.

[0017] (Series piping) The series piping 31 connects multiple pumps 20 in series. Liquefied gas L can flow through the series piping 31. In two pumps 20 connected in series, the discharge portion 22 of the low-pressure pump 20 and the suction portion 21 of the high-pressure pump 20 are directly connected by the series piping 31. In this embodiment, multiple series piping 31 are provided. The discharge portion 22 of the first-stage pump 20 and the suction portion 21 of the second-stage pump 20 are directly connected by the series piping 31. Furthermore, the discharge portion 22 of the second-stage pump 20 and the suction portion 21 of the third-stage pump 20 are directly connected by the series piping 31.

[0018] The series pipe 31 extends upward from the discharge portion 22 of the low-pressure side pump 20. The series pipe 31 penetrates the flange 12 of the low-pressure side tank 10 and is drawn out to the top of the tank 10. The series pipe 31 penetrates the flange 12 of the high-pressure side tank 10 and is introduced into the tank 10. The downstream end of the series pipe 31 is connected to the suction portion 21 of the high-pressure side pump 20.

[0019] As shown in Figure 3, the downstream end of the series pipe 31 connected to the suction section 21 is referred to as the suction side end 33. The suction side end 33 has a straight pipe section 34, a curved pipe section 35, a flange 36, and a flow straightening plate 37. The straight pipe section 34 is connected to the suction section 21 and extends in the direction of the liquefied gas L being sucked into the suction section 21. The curved pipe section 35 is located upstream of the straight pipe section 34 and is connected to the upstream end of the straight pipe section 34. The curved pipe section 35 is curved. The curved pipe section 35 changes the flow direction of the liquefied gas L to the suction direction of the suction section 21.

[0020] (Flange) The flange 36 is provided at the downstream end of the straight pipe portion 34. The flange 36 protrudes radially outward from the outer circumferential surface of the straight pipe portion 34. The straight pipe portion 34 is connected to the suction portion 21 of the pump 20 by the flange 36 without any gap.

[0021] (Straightening Plate) One or more straightening plates 37 are provided in the curved pipe section 35. In the illustrated example, a plurality of straightening plates 37 are provided. However, only one straightening plate 37 may be provided. These one or more straightening plates 37 are arranged at equal intervals in a direction perpendicular to the flow direction of the liquefied gas L. However, these one or more straightening plates 37 do not have to be arranged at equal intervals. The intervals between the straightening plates 37 can be changed as appropriate. Furthermore, these one or more straightening plates 37 are all curved with a curvature having the same center. Furthermore, each straightening plate 37 is curved with a curvature having the same center as the curved pipe section 35. The straightening plate 37 straightens the flow of the liquefied gas L flowing through the curved pipe section 35.

[0022] (Pump discharge piping) The pump discharge piping 32 extends from the discharge portion 22 of the pump 20 on the highest pressure side (the third-stage pump 20 in this embodiment) among the plurality of pumps 20. The pump discharge piping 32 guides the liquefied gas L pressurized by the plurality of pumps 20 to equipment or plant equipment (not shown) that utilizes the pressurized fluid (hydrogen in this embodiment).

[0023] (Tank supply piping) The tank supply piping 40 supplies liquefied gas L from the supply source 2 to the tanks 10. In this embodiment, the tank supply piping 40 supplies liquefied gas L from the supply source 2 to each of the multiple tanks 10. The tank supply piping 40 supplies liquefied gas L to one of the multiple tanks 10. The tank supply piping 40 includes a main piping 41 and branch piping 42. One main piping 41 extends from the supply source 2. The branch piping 42 is provided in the same number as the tanks 10. Each branch piping 42 branches off from the main piping 41 and is connected to each tank 10.

[0024] (Gas vent piping) The gas vent piping 50 is a piping that vents the gas G from the tank 10. In this embodiment, the gas vent piping 50 connects the supply source 2 to each of the multiple tanks 10. The gas vent piping 50 includes a main piping 51 and branch piping 52. One main piping 51 extends from the supply source 2. The same number of branch piping 52 as the number of tanks 10 is provided. Each branch piping 52 branches off from the main piping 51 and is connected to each tank 10. The branch piping 52 is installed below the upper end of the tank 10.

[0025] The gas layer GL formed inside the tank 10 has a minimum thickness required for thermal insulation between the flange 12 and the liquefied gas L. Hereinafter, the height of the liquid level S of the liquefied gas L when the gas layer GL has this minimum thickness is referred to as the reference height H. In this embodiment, the branch pipe 52 of the gas vent pipe 50 is attached to the reference height H of the tank 10.

[0026] The gas G vented from each tank 10 through the gas vent pipe 50 is temporarily stored in the supply source 2 and then utilized as gaseous hydrogen in a gas compression device (not shown). Alternatively, the gas G is temporarily stored in the supply source 2 and then liquefied in a re-liquefaction device (not shown). Alternatively, the gas G is temporarily stored in the supply source 2 and then discharged.

[0027] 2, the gas layer detection unit 3 detects the gas layer GL in the tank 10. The gas layer detection unit 3 is provided in each tank 10. In this embodiment, the gas layer detection unit 3 includes a liquid level detection unit 3a and a pressure sensor 3b.

[0028] (Liquid Level Detector) The liquid level detector 3a is provided in the tank 10. The liquid level detector 3a detects the height of the liquid level S of the liquefied gas L stored in the tank 10.

[0029] In this embodiment, the liquid level detection unit 3a includes a plurality of temperature sensors 3c. The plurality of temperature sensors 3c are attached to the side surface of the tank 10 at intervals in the vertical direction. The liquefied gas L is stored in the tank 10 from the bottom up. Therefore, the plurality of temperature sensors 3c come into contact with the liquefied gas L starting from the lower temperature sensor 3c and detect the temperature of the liquefied gas L. The liquid level detection unit 3a utilizes this to detect the height of the highest temperature sensor 3c among the temperature sensors 3c that have detected the temperature of the liquefied gas L as the height of the liquid level S of the liquefied gas L.

[0030] In this embodiment, four temperature sensors 3c are provided. One of the temperature sensors 3c is provided at the same height as the gas vent pipe 50. Another temperature sensor 3c is provided above the gas vent pipe 50 and below the flange 12. The other two temperature sensors 3c are provided below the gas vent pipe 50. When the temperature sensor 3c located higher than the gas vent pipe 50 detects the temperature of the liquefied gas L, this means that the height of the liquid level S of the liquefied gas L is higher than the reference height H, and the gas layer GL is thinner than expected. Conversely, when the temperature sensor 3c located lower than the gas vent pipe 50 detects the temperature of the liquefied gas L, this means that the height of the liquid level S of the liquefied gas L is lower than the reference height H, and the gas layer GL is thicker than expected.

[0031] (Pressure Sensor) The pressure sensor 3b is provided inside the tank 10. The pressure sensor 3b is provided at an upper part inside the tank 10. The pressure sensor 3b detects the pressure of the gas layer GL inside the tank 10. The thicker the gas layer GL, the higher the pressure of the gas layer GL tends to be. Therefore, the operator can estimate the thickness of the gas layer GL from the pressure detected by the pressure sensor 3b. The pressure sensor 3b can also be used to detect abnormal pressure conditions inside the tank 10.

[0032] (Alarm) The alarm 4 notifies the surrounding area when a gas layer GL of the minimum thickness required for thermal insulation between the flange 12 and the liquefied gas L is not formed inside the tank 10. An alarm 4 is provided for each tank 10.

[0033] (Control Device) The control device 5 manages the thickness of the gas layer GL in the tank 10 and the height of the liquid level S in the tank 10 based on information acquired from the gas layer detection unit 3. For example, if the height of the liquid level S of the liquefied gas L in the tank 10 is higher than the reference height H, the control device 5 lowers the height of the liquid level S of the liquefied gas L by, for example, reducing the amount of gas G vented from the tank 10. Conversely, if the height of the liquid level S of the liquefied gas L in the tank 10 is lower than the reference height H, the control device 5 raises the height of the liquid level S of the liquefied gas L by, for example, increasing the amount of gas G vented from the tank 10. Furthermore, for example, the control device 5 increases the amount of gas G vented from the tank 10 in accordance with the pressure of the gas layer GL.

[0034] Furthermore, the control device 5 activates the alarm 4 based on the information acquired from the gas layer detection unit 3. For example, if the height of the liquid level S of the liquefied gas L in the tank 10 is higher than the reference height H, the control device 5 activates the alarm 4 to notify those around that a gas layer GL of sufficient thickness has not formed in the tank 10.

[0035] The control device 5 may perform the above-mentioned control automatically based on information obtained from the gas layer detection unit 3, or may perform the above-mentioned control by being operated by an operator.

[0036] (Operations and Effects) The pump system 1 of this embodiment can achieve the following operations and effects.

[0037] In this embodiment, the pump system 1 includes a tank 10, a plurality of pumps 20, and a series pipe 31. The tank 10 can store liquefied gas L. The pumps 20 are housed in the tank 10 and are immersed in the liquefied gas L in the tank 10. The series pipe 31 connects the plurality of pumps 20 in series. The series pipe 31 directly connects the discharge portion 22 of the pump 20 on the low-pressure side to the suction portion 21 of the pump 20 on the high-pressure side of two pumps 20 connected in series. The liquefied gas L can flow through the series pipe 31.

[0038] According to the above configuration, the liquefied gas L pressurized by the low-pressure pump 20 is directly supplied to the high-pressure pump 20. Therefore, the liquefied gas L pressurized by the low-pressure pump 20 is not supplied to the tank 10 housing the high-pressure pump 20. Therefore, the pump system 1 can maintain the tank 10 housing the high-pressure pump 20 at low pressure (normal pressure). This eliminates the need for a pressure-resistant design for the tank 10 housing the high-pressure pump 20 located downstream. Furthermore, because all tanks 10 are maintained at low pressure, the liquefied gas L in the tanks 10 is appropriately vaporized, forming a gas layer GL in the upper part of the tank 10. The gas layer GL insulates the liquefied gas L from the upper part of the tank 10, maintaining the upper part of the tank 10 at a high temperature. This reduces the temperature difference between the temperature of the upper part of the tank 10 and the ambient temperature. This suppresses thermal deformation of the upper part of the tank 10. In addition, since the heat input into the tank 10 is suppressed, the pump system 1 of this embodiment can reduce the amount of liquefied gas L vaporized in the tank 10 (boil off gas (BOG) amount).

[0039] In this embodiment, a plurality of tanks 10 are provided. Each tank 10 accommodates one pump 20.

[0040] In the above configuration, for example, when a worker performs maintenance on one pump 20, the worker only needs to discharge the liquefied gas L from the tank 10 in which the pump 20 is housed, and does not need to discharge the liquefied gas L from the other tanks 10. Furthermore, when multiple pumps 20 are housed in one tank 10, the weight of the flange 12 increases because multiple pumps 20 are attached to one flange 12. On the other hand, in this embodiment, only one pump 20 is required to be attached to the flange 12. Therefore, the weight of the flange 12 can be reduced compared to when multiple pumps 20 are housed in one tank 10. Therefore, the flange 12 can be easily opened and closed during maintenance of the pump 20, eliminating the need for large lifting equipment. This improves maintainability.

[0041] In this embodiment, the system further includes a supply source 2 of liquefied gas L, and a tank supply pipe 40 that supplies the liquefied gas L from the supply source 2 to each of the multiple tanks 10.

[0042] As a result, the liquefied gas L is supplied individually to the multiple tanks 10. This allows the operator to separate the multiple tanks 10 and manage them individually, thereby improving maintainability.

[0043] In this embodiment, the pump system 1 further includes a gas vent pipe 50 that vents the gas G from the tank 10. The gas vent pipe 50 is installed below the upper end of the tank 10.

[0044] This prevents the gas G generated by vaporization of the liquefied gas L in the tank 10 from being immediately discharged from the upper end of the tank 10. Therefore, the pump system 1 of this embodiment can form a gas layer GL of a predetermined thickness in the upper space inside the tank 10.

[0045] In this embodiment, the pump system 1 further includes a gas layer detection unit 3 that detects the gas layer GL in the tank 10 .

[0046] This allows the pump system 1 to detect the presence or absence of the gas layer GL using the gas layer detection unit 3. Therefore, the operator can prevent the pump system 1 from operating in a state where the gas layer GL is not formed.

[0047] In this embodiment, the series pipe 31 has a downstream suction-side end portion 33 connected to the suction portion 21. The suction-side end portion 33 has a flange 36 that protrudes radially outward from the outer circumferential surface. The suction-side end portion 33 is connected to the suction portion 21 without any gaps by the flange 36.

[0048] This prevents the liquefied gas L in the tank 10 from flowing into the suction portion 21 of the pump 20.

[0049] In this embodiment, the series pipe 31 has a straight pipe section 34, a curved pipe section 35, and a flow rectifying plate 37. The straight pipe section 34 is connected to the suction section 21 and extends in the direction of the liquefied gas L being sucked into the suction section 21. The curved pipe section 35 is located upstream of the straight pipe section 34 and is connected to the upstream end of the straight pipe section 34. One or more flow rectifying plates 37 are provided within the curved pipe section 35. The one or more flow rectifying plates 37 are arranged at intervals in a direction perpendicular to the flow direction. Furthermore, all of these one or more flow rectifying plates 37 are curved with a curvature having the same center. Furthermore, each flow rectifying plate 37 is curved with a curvature having the same center as the curved pipe section 35.

[0050] The liquefied gas L flowing through the curved pipe section 35 passes between the plurality of straightening plates 37, thereby suppressing the occurrence of drift when the flow direction of the liquefied gas L is changed to the suction direction of the suction section 21. Drift here refers to a flow of the liquefied gas L that does not follow the flow of the curved pipe section 35. This allows the suction section 21 to smoothly suck in the liquefied gas L.

[0051] In this embodiment, the pump system 1 includes an alarm 4. The alarm 4 notifies those around that the gas layer GL has not been formed to a minimum thickness required for thermal insulation between the flange 12 and the liquefied gas L.

[0052] This prevents the pump system 1 from operating in a state where the gas layer GL is not formed in the tank 10.

[0053] (Other Embodiments) Although the embodiments of the present disclosure have been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and design changes and the like within the scope that does not deviate from the gist of the present disclosure are also included.

[0054] For example, as shown in Fig. 4, the suction section 21 of the first-stage pump 20, which is located on the lowest pressure side among the plurality of pumps 20, may be installed so as to suck in the liquefied gas L in the tank 10. In this case, the first-stage pump 20 may have the same configuration as a conventional pump. This makes it easy to introduce the pump system 1 of this embodiment into an existing system.

[0055] 5, the tank supply pipe 40 may supply the liquefied gas L from the supply source 2 to one of the multiple tanks 10 (in the illustrated example, the first tank 10). The pump system 1 includes a connection pipe 43. A plurality of connection pipes 43 are provided. The connection pipes 43 connect the first tank 10 to the second tank 10, and connect the second tank 10 to the third tank 10. The liquefied gas L can flow through the connection pipes 43. The multiple tanks 10 are connected by the connection pipes 43 so that the liquefied gas L can flow. In this case, since the liquefied gas L can flow between the multiple tanks 10, it is easy to uniform the height of the liquid level S of the liquefied gas L and the temperature of the liquefied gas L among the multiple tanks 10. This makes it easy to manage the liquefied gas L stored in the multiple tanks 10.

[0056] 6, multiple pumps 20 may be accommodated in one tank 10. All of the multiple pumps 20 are suspended from the flange 12. The discharge portions 22 of the pumps 20 are located in the vertical center of the pumps 20. The series pipe 31 connecting the discharge portion 22 of the low-pressure pump 20 to the suction portion 21 of the high-pressure pump 20 is accommodated in the tank 10 without being pulled out from the flange 12. In this case, the number of tanks 10 and the number of gas layer detectors 3, alarms 4, etc. installed in each tank 10 can be reduced, thereby reducing costs. Furthermore, the pump system 1 can be prevented from becoming too large.

[0057] In the above embodiment, the liquefied gas L is liquid hydrogen, but this is not limiting. For example, the liquefied gas L may be liquefied natural gas or liquid helium.

[0058] Furthermore, in the above embodiment, a case where three pumps 20 are provided has been described, but this is not limitative. The number of pumps 20 can be changed as appropriate. The number of pumps 20 may be two. It is preferable that the number of pumps 20 connected in series is up to three.

[0059] In addition, in the above embodiment, the same type of liquefied gas L is supplied to the tank 10 and the pump 20, but this is not limited to this. If the inside of the pump 20 and the inside of the tank 10 are completely separated, different types of liquefied gas L may be supplied to the tank 10 and the pump 20.

[0060] <Additional Notes> The pump system 1 described in each embodiment can be understood, for example, as follows.

[0061] (1) The pump system 1 according to the first aspect comprises a tank 10 capable of storing liquefied gas L, a plurality of pumps 20 housed within the tank 10 and immersed in the liquefied gas L in the tank 10, and a series pipe 31 connecting the plurality of pumps 20 in series, directly connecting the discharge portion 22 of the pump 20 on the low-pressure side to the suction portion 21 of the pump 20 on the high-pressure side for two of the pumps 20 connected in series, and through which the liquefied gas L can flow.

[0062] According to the above configuration, the liquefied gas L pressurized by the low-pressure pump 20 is directly supplied to the high-pressure pump 20. Therefore, the liquefied gas L pressurized by the low-pressure pump 20 is not supplied to the tank 10 housing the high-pressure pump 20. Therefore, the pump system 1 can maintain the tank 10 housing the high-pressure pump 20 at a low pressure. This maintains all of the tanks 10 at a low pressure. Therefore, the liquefied gas L in the tank 10 is vaporized appropriately, and a gas layer GL is formed in the upper part of the tank 10.

[0063] (2) The pump system 1 of the second aspect is the pump system 1 of (1), in which a plurality of the tanks 10 are provided, and one pump 20 is housed in each of the tanks 10.

[0064] In this embodiment, for example, when an operator performs maintenance on one pump 20, the operator only needs to discharge the liquefied gas L from one tank 10 in which the pump 20 is housed, and does not need to discharge the liquefied gas L from other tanks 10.

[0065] (3) The pump system 1 of the third aspect may be the pump system 1 of (2), further comprising a supply source 2 of liquefied gas L and a tank supply pipe 40 that supplies liquefied gas L from the supply source 2 to each of the plurality of tanks 10.

[0066] As a result, the liquefied gas L is supplied individually to the multiple tanks 10. Therefore, the worker can separate the multiple tanks 10 and manage them individually.

[0067] (4) A fourth aspect of the pump system 1 is the pump system 1 of (2), further comprising a supply source 2 of liquefied gas L and a tank supply pipe 40 for supplying liquefied gas L from the supply source 2 to one of the plurality of tanks 10, and the plurality of tanks 10 may be connected in series to allow the liquefied gas L to flow through them.

[0068] This allows the liquefied gas L to flow between multiple tanks 10, making it easy to make the height of the liquid surface S of the liquefied gas L and the temperature of the liquefied gas L uniform among multiple tanks 10.

[0069] (5) The pump system 1 of the fifth aspect may be any one of the pump systems 1 of (1) to (4), and may further include a gas vent pipe 50 that is installed below the upper end of the tank 10 and that vents gas G from the tank 10.

[0070] This prevents the gas G generated by vaporization of the liquefied gas L in the tank 10 from being immediately discharged from the upper end of the tank 10. Therefore, the pump system 1 of this embodiment can form a gas layer GL of a predetermined thickness in the upper space inside the tank 10.

[0071] (6) The pump system 1 of the sixth aspect may be any one of the pump systems 1 of (1) to (5) and further include a gas layer detection unit 3 that detects the gas layer GL in the tank 10.

[0072] This allows the pump system 1 to detect the presence or absence of the gas layer GL using the gas layer detection unit 3.

[0073] (7) The pump system 1 of the seventh aspect is any one of the pump systems 1 of (1) to (6), and the suction section 21 of the first stage pump 20, which is located on the lowest pressure side among the multiple pumps 20, may be installed to suck in the liquefied gas L in the tank 10.

[0074] As a result, the first-stage pump 20 can have the same configuration as the conventional pump, which makes it easy to introduce the pump system 1 of this embodiment into an existing system.

[0075] According to the pump system of the present disclosure, in a connection system in which a plurality of pumps are connected in series, the tank in which the pumps are housed can be maintained at a low pressure.

[0076] REFERENCE SIGNS LIST 1 Pump system 2 Supply source 3 Gas layer detection section 3a Liquid level detection section 3b Pressure sensor 3c Temperature sensor 4 Alarm 5 Control device 10 Tank 11 Tank body 12 Flange 20 Pump 21 Suction section 22 Discharge section 30 Pump supply piping 31 Series piping 32 Pump discharge piping 33 Suction side end 34 Straight pipe section 35 Curved pipe section 36 Flange 37 Flow straightener 40 Tank supply piping 41 Main piping 42 Branch piping 43 Connection piping 50 Gas vent piping 51 Main piping 52 Branch piping G Gas GL Gas layer H Reference height L Liquefied gas S Liquid level

Claims

1. A pump system comprising: a tank capable of storing liquefied gas; a plurality of pumps housed within said tank and immersed in the liquefied gas within said tank; and a series pipe connecting said plurality of pumps in series, wherein for each of said two pumps connected in series, the discharge portion of said low-pressure pump is directly connected to the suction portion of said high-pressure pump, and through which the liquefied gas can flow.

2. The pump system according to claim 1, wherein a plurality of the tanks are provided, and each of the tanks accommodates one pump.

3. The pump system according to claim 2, further comprising: a liquefied gas supply source; and tank supply piping for supplying liquefied gas from said supply source to each of said plurality of tanks.

4. The pump system according to claim 2, further comprising: a liquefied gas supply source; and a tank supply pipe for supplying the liquefied gas from the supply source to one of the plurality of tanks, wherein the plurality of tanks are connected in series to allow the liquefied gas to flow therethrough.

5. The pump system according to any one of claims 1 to 4, further comprising a gas vent pipe installed below the upper end of the tank for venting gas from the tank.

6. The pump system according to any one of claims 1 to 4, further comprising a gas layer detector that detects a gas layer in the tank.

7. A pump system as claimed in any one of claims 1 to 4, wherein the suction section of the first stage pump, which is located on the lowest pressure side among the plurality of pumps, is installed so as to suck in the liquefied gas in the tank.

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