Reciprocating pump device for liquefied gas

Abstract

The present invention relates to a reciprocating pump device for increasing the pressure of liquefied gas such as liquid hydrogen, liquefied natural gas, liquefied ammonia, liquid nitrogen, liquefied ethylene gas, and liquefied petroleum gas. The reciprocating pump device for liquefied gas is provided with: a cylinder (1); a piston (2) disposed in the cylinder (1); a pump shaft (41) coupled to the piston (2); a ball screw nut (42) fixed to the pump shaft (41); a screw shaft (45) screwed to the ball screw nut (42); and an electric motor (48) coupled to the screw shaft (45) and rotating the screw shaft (45).

Description

Reciprocating pump device for liquefied gas

[0001] The present invention relates to a reciprocating pump device for boosting liquefied gases such as liquid hydrogen, liquefied natural gas, liquefied ammonia, liquid nitrogen, liquefied ethylene gas, and liquefied petroleum gas.

[0002] Natural gas is widely used as a fuel for thermal power generation and as a chemical raw material. In addition, hydrogen is expected as an energy source that does not generate carbon dioxide, which causes global warming. Since natural gas and hydrogen are in a gaseous state at normal temperature, they are cooled and liquefied for storage and transportation. Liquefied gases such as liquefied natural gas (LNG) and liquid hydrogen are once stored in a liquefied gas storage tank and then transferred to the use point by a pump.

[0003] As a pump for liquefied natural gas, a reciprocating pump may be used (see, for example, Patent Document 1). The reciprocating pump has a piston disposed in a cylinder, a crankshaft connected to the piston, and an electric motor connected to the crankshaft. The crankshaft converts the rotation of the electric motor into a reciprocating motion and reciprocates the piston. When the piston reciprocates in the cylinder, the liquefied natural gas is sucked into the cylinder, pressurized by the piston in the cylinder, and then discharged from the cylinder.

[0004] Japanese Patent Publication No. 2015-501901

[0005] Recently, hydrogen is expected as a fuel for automobiles. Therefore, the demand for a small reciprocating pump that can be installed in an automobile is increasing. However, when the reciprocating pump is miniaturized, its capacity also becomes small, so there are cases where the reciprocating pump cannot sufficiently transfer the desired amount of liquid hydrogen depending on the output of the internal combustion engine.

[0006] Therefore, the present invention provides a reciprocating pump device for liquefied gas that can be miniaturized while ensuring pump performance.

[0007] In one embodiment, a reciprocating pump device for liquefied gas is provided, comprising a cylinder, a piston disposed within the cylinder, a pump shaft connected to the piston, a ball screw nut fixed to the pump shaft, a screw shaft screwed onto the ball screw nut, and an electric motor connected to the screw shaft for rotating the screw shaft.

[0008] In one embodiment, the reciprocating pump device further comprises a cylinder cover that surrounds the cylinder and forms a liquid chamber for the liquefied gas on the outside of the cylinder. In one embodiment, the reciprocating pump device further comprises a motor driver that rotates the electric motor alternately in one direction and in opposite directions. In one embodiment, the pump shaft is non-contact with the screw shaft. In one embodiment, the reciprocating pump device further comprises a pump casing that covers at least the cylinder and the cylinder cover, with a vacuum insulation layer between the cylinder cover and the pump casing. In one embodiment, the reciprocating pump device further comprises a guide rail that restricts the rotation of the ball screw nut while allowing the ball screw nut to move in the axial direction of the screw shaft, the ball screw nut having a groove into which the guide rail engages.

[0009] By rotating the screw shaft alternately in one and the opposite direction, the piston connected to the ball screw nut reciprocates. The combination of the ball screw nut and screw shaft eliminates the need for a crankshaft, allowing for a more compact reciprocating pump device. Furthermore, the amount of liquefied gas transferred per piston reciprocation can be adjusted by controlling the number of rotations of the screw shaft per piston stroke. Therefore, a reciprocating pump device can achieve a large transfer volume of liquid hydrogen while remaining compact.

[0010] This is a cross-sectional view showing one embodiment of a reciprocating pump device for liquefied gas. This is a view of the groove of a ball screw nut and the guide rail that engages with the groove, as seen from the axial direction. This is a diagram illustrating the movement of the piston when liquid hydrogen is drawn into the cylinder through the liquid inlet. This is a diagram illustrating the movement of the piston when liquid hydrogen is discharged from the cylinder through the discharge channel.

[0011] Embodiments of the present invention will be described below with reference to the drawings. Figure 1 is a cross-sectional view showing one embodiment of a reciprocating pump device for liquefied gases. The reciprocating pump devices of the embodiments described below are used for pressurizing and transporting liquefied gases such as liquid hydrogen, liquefied natural gas, liquefied ammonia, liquid nitrogen, liquefied ethylene gas, and liquefied petroleum gas. Below, an embodiment of a reciprocating pump device for pressurizing liquid hydrogen as a liquefied gas will be described.

[0012] As shown in Figure 1, the reciprocating pump device comprises a cylinder 1 and a piston 2 disposed within the cylinder 1. The installation direction of the reciprocating pump device is not limited to the embodiment shown in Figure 1, and can be horizontal, vertical, or diagonal. The piston 2 is arranged to reciprocate within the cylinder 1, as indicated by the arrow. Multiple seal rings 3 are arranged on the outer circumference of the piston 2 to minimize the gap between the outer surface of the piston 2 and the inner surface of the cylinder 1. These seal rings 3 reciprocate together with the piston 2. The number of seal rings 3 is not limited to the embodiment shown in Figure 1. In one embodiment, the seal rings 3 may be arranged on the inner surface of the cylinder 1 instead of the piston 2. These seal rings 3 can be classified into piston rings, rider rings, etc. The function of the piston ring is mainly sealing the liquefied gas, and the function of the rider ring is mainly coaxial fixing of the piston 2 and the cylinder 1. Depending on the type of seal ring 3, it is also possible to give the function of the seal ring 3 to the piston 2 itself, resulting in a seal ring-less structure.

[0013] The reciprocating pump device is equipped with a suction check valve 7 located at the liquid inlet 6 of the cylinder 1. The suction check valve 7 allows liquid hydrogen as a liquefied gas to flow into the cylinder 1 through the liquid inlet 6, while preventing liquid hydrogen from being discharged from the cylinder 1 through the liquid inlet 6. More specifically, when the piston 2 moves away from the liquid inlet 6 of the cylinder 1, the suction check valve 7 opens, and liquid hydrogen is drawn into the cylinder 1 through the liquid inlet 6. When the piston 2 moves toward the liquid inlet 6 of the cylinder 1, the suction check valve 7 closes, and the liquid hydrogen is pressurized within the cylinder 1. The shape of the suction check valve 7 is not particularly limited, and round, flat, or other shapes can be used.

[0014] The reciprocating pump device further includes a cylinder cover 9 surrounding the cylinder 1. The cylinder cover 9 is configured to form a liquid chamber 12 for liquid hydrogen on the outside of the cylinder 1. The cylinder cover 9 in this embodiment has a cylindrical shape. The cylinder cover 9 is positioned radially outward of the cylinder 1 and piston 2 and covers the outer circumferential surface 1a of the cylinder 1 and the liquid inlet 6. The liquid inlet 6 is formed on the suction-side end face 1b of the cylinder 1 and communicates with the liquid chamber 12 and the inside of the cylinder 1. One opening of the cylinder cover 9 is covered by an inlet end wall 15, and the opposite opening of the cylinder cover 9 is closed by a partition wall 16. The partition wall 16 is fixed to the outer circumferential surface 1a of the cylinder 1. The cylinder cover 9 and the partition wall 16 may be an integral structure.

[0015] The liquid chamber 12 is formed between the outer circumferential surface 1a of the cylinder 1 and the inner circumferential surface of the cylinder cover 9, and between the suction-side end face 1b of the cylinder 1 and the inlet end wall 15. The inlet end wall 15 has a suction port 20. This suction port 20 communicates with the liquid chamber 12 and further communicates with the liquid inlet 6 of the cylinder 1. The suction port 20 communicates with a liquid hydrogen source (liquefied gas source) not shown. As the piston 2 moves, liquid hydrogen flows from the suction port 20 into the liquid chamber 12 and fills the liquid chamber 12. The outer circumferential surface 1a and the suction-side end face 1b of the cylinder 1 are in contact with the cryogenic liquid hydrogen, and the cylinder 1 and piston 2 are cooled. The liquid hydrogen flows from the liquid chamber 12 into the cylinder 1 through the liquid inlet 6.

[0016] The reciprocating pump device comprises a cylinder 1, a cylinder cover 9, and a pump casing 22 surrounding an inlet end wall 15. The inlet end wall 15 is fixed to the pump casing 22 and covers the open end of the pump casing 22. The cylinder 1 has a flange 1c at its end, and the outer circumferential surface of the flange 1c is fixed to the inner circumferential surface of the pump casing 22.

[0017] The reciprocating pump device includes a vacuum insulation layer 25 surrounding the cylinder 1 and the cylinder cover 9. This vacuum insulation layer 25 is located between the cylinder cover 9 and the pump casing 22. The vacuum insulation layer 25 is formed by the cylinder 1, the cylinder cover 9, the pump casing 22, and the inlet end wall 15. More specifically, the vacuum insulation layer 25 is formed by the flange 1c of the cylinder 1, the outer circumferential surface 1a of the cylinder 1, the partition wall 16, the outer circumferential surface of the cylinder cover 9, the inner circumferential surface of the pump casing 22, and the inlet end wall 15.

[0018] The vacuum insulation layer 25 surrounds the liquid chamber 12. That is, the liquid chamber 12 filled with liquid hydrogen exists outside the cylinder 1, and the vacuum insulation layer 25 exists outside the liquid chamber 12. The vacuum insulation layer 25 can prevent heat from the surroundings of the reciprocating pump device from being transferred to the liquid hydrogen in the liquid chamber 12. Furthermore, the double structure of the liquid chamber 12 and the vacuum insulation layer 25 can prevent heat from the surroundings of the reciprocating pump device from being transferred into the cylinder 1. The flange 1c of the cylinder 1 is separated from the partition wall 16, and the vacuum insulation layer 25 exists between the partition wall 16 and the flange 1c of the cylinder 1. This vacuum insulation layer 25 can prevent heat transfer from the flange 1c to the partition wall 16. Furthermore, the double structure of the liquid chamber 12 and the vacuum insulation layer 25 also has the effect of preventing noise, dust, and shock from the surroundings of the reciprocating pump device and reducing the noise of the reciprocating pump device itself.

[0019] The reciprocating pump device further includes a discharge port 31 having a discharge passage 30 that communicates with the inside of the cylinder 1. The discharge port 31 is fixed to the outer circumferential surface 1a of the cylinder 1 and extends through the liquid chamber 12, the cylinder cover 9, the vacuum insulation layer 25, and the pump casing 22. The discharge port 31 has a discharge check valve 33 inside. This discharge check valve 33 is configured to allow liquid hydrogen to flow out of the cylinder 1 through the discharge passage 30 to the outside of the reciprocating pump device, while preventing liquid hydrogen from flowing into the cylinder 1 from the outside of the reciprocating pump device through the discharge passage 30. The liquid hydrogen pressurized by the piston 2 is discharged through the discharge passage 30. The shape of the discharge check valve 33 is not particularly limited, and round, flat, etc., can be used.

[0020] A portion of the liquid hydrogen in the liquid chamber 12 may vaporize due to heat from outside the reciprocating pump device. To discharge the vaporized hydrogen, i.e., hydrogen gas, from the liquid chamber 12, a gas relief hole 35 communicating with the liquid chamber 12 is provided. One end of the gas relief hole 35 communicates with the liquid chamber 12, and the other end of the gas relief hole 35 opens on the outer surface of the pump casing 22. In one embodiment, the gas relief hole 35 extends from the liquid chamber 12 through the inlet end wall 15 and the pump casing 22 to the outside of the reciprocating pump device.

[0021] The reciprocating pump device further comprises a pump shaft 41 connected to a piston 2, a ball screw nut 42 fixed to the pump shaft 41, a screw shaft 45 screwed onto the ball screw nut 42, and an electric motor 48 connected to the screw shaft 45 for rotating the screw shaft 45. The pump shaft 41, ball screw nut 42, screw shaft 45, and electric motor 48 are arranged inside a pump casing 22. The pump shaft 41 is fixed to the piston 2 and reciprocates together with the piston 2. In one embodiment, the pump shaft 41 and the piston 2 may be a single integrated structure. The ball screw nut 42 also reciprocates together with the pump shaft 41 and the piston 2.

[0022] The screw shaft 45 may be connected to the electric motor 48 via a coupling (not shown). In one embodiment, the screw shaft 45 may be rotatably supported by a bearing (not shown) located within the pump casing 22. The electric motor 48 is configured to rotate the screw shaft 45 in one direction and in opposite directions. The ball screw nut 42 and the pump shaft 41 may be connected by a housing (not shown) or a bracket (not shown). In one embodiment, the ball screw nut 42 and the screw shaft 45 may be in the form of a roller screw.

[0023] The reciprocating pump device includes a motor driver 49 that controls the rotational speed and direction of the electric motor 48. An inverter is a specific example of the motor driver 49. The motor driver 49 is configured to supply a variable frequency current to the electric motor 48 and rotate the electric motor 48 alternately in one direction and opposite directions at a predetermined rotational speed. In one example, the motor driver 49 rotates the electric motor 48 alternately in one direction and opposite directions with a period of 1 to several seconds.

[0024] The ball screw nut 42 has a plurality of balls 51 arranged along the helical thread groove of the screw shaft 45. Ball screw nuts 42 with such a configuration are available on the market. The reciprocating pump device further includes a guide rail 53 that restricts the rotation of the ball screw nut 42 while allowing it to move axially along the screw shaft 45. The guide rail 53 is fixed to the inner surface of the pump casing 22 and extends parallel to the screw shaft 45. The ball screw nut 42 has a groove 55 into which the guide rail 53 engages. As the electric motor 48 rotates the screw shaft 45, the ball screw nut 42 moves axially along the screw shaft 45.

[0025] Figure 2 is a view from the axial direction of the groove 55 of the ball screw nut 42 and the guide rail 53 that engages with the groove 55. The guide rail 53 is loosely engaged with the groove 55 and does not hinder the axial movement of the ball screw nut 42. When torque from the screw shaft 45 is applied to the ball screw nut 42, the engagement between the groove 55 of the ball screw nut 42 and the guide rail 53 prevents the rotation of the ball screw nut 42. Since the function of the guide rail 53 is to prevent the rotation of the ball screw nut 42, the shape of the guide rail 53 and groove 55 is not limited to the embodiment shown in Figure 2, as long as it can perform that function. For example, the shape of the guide rail 53 and groove 55 may be cylindrical or the like. In addition to fixing the guide rail 53 to the pump casing 22, the guide rail 53 and groove 55 may be passed through the inside of the ball screw nut 42, and only both ends of the guide rail 53 may be fixed to the pump casing 22.

[0026] As shown in Figure 3, when the electric motor 48 rotates the screw shaft 45 in one direction, the piston 2 moves toward the screw shaft 45, causing liquid hydrogen to flow from the suction port 20 into the liquid chamber 12, and the liquid hydrogen in the liquid chamber 12 is then drawn into the cylinder 1 through the liquid inlet 6. At this time, the suction check valve 7 is open and the discharge check valve 33 is closed. Next, as shown in Figure 4, when the electric motor 48 rotates the screw shaft 45 in the opposite direction, the piston 2 moves toward the discharge passage 30, causing the liquid hydrogen to be discharged through the discharge passage 30 while being pressurized within the cylinder 1. At this time, the suction check valve 7 is closed and the discharge check valve 33 is open.

[0027] Thus, the combination of the ball screw nut 42 and the screw shaft 45 can convert the rotation of the electric motor 48 into the reciprocating motion of the piston 2. Therefore, the crankshaft that is provided in conventional reciprocating pump devices can be eliminated. As a result, the reciprocating pump device of this embodiment can be made compact. Furthermore, the amount of reciprocating movement of the piston 2, that is, the amount of liquid hydrogen transferred per reciprocating motion of the piston 2, can be adjusted by the number of rotations of the screw shaft 45 per stroke of the piston 2. In other words, the reciprocating pump device of this embodiment can achieve a large amount of liquid hydrogen transfer while being small. The number of rotations of the screw shaft 45 per stroke of the piston 2 can be adjusted by the motor driver 49.

[0028] As shown in Figures 3 and 4, during operation of the reciprocating pump device, the pump shaft 41 is separated from the screw shaft 45 and is not in contact with the screw shaft 45. Therefore, heat from the electric motor 48 is not easily transferred from the screw shaft 45 to the pump shaft 41. The pump shaft 41 can also be made hollow to improve heat insulation. As a result, the temperature rise of the liquid hydrogen in the cylinder 1 is prevented, and vaporization of the liquid hydrogen is prevented.

[0029] Cylinder 1 has a leak recovery hole 60 that penetrates radially through the flange 1c. One end of the leak recovery hole 60 opens on the inner circumferential surface of cylinder 1, and the other end of the leak recovery hole 60 opens on the outer circumferential surface of pump casing 22. When piston 2 pressurizes the liquid hydrogen in cylinder 1, a small portion of the liquid hydrogen leaks through seal ring 3. The leaked liquid hydrogen reaches the leak recovery hole 60 and is discharged from the reciprocating pump device through the leak recovery hole 60. Furthermore, the leaked liquid hydrogen is returned to a liquid hydrogen source (liquefied gas source) connected to the suction port 20 of the reciprocating pump device. The liquid hydrogen source (liquefied gas source) is not limited to a separate container such as a tank. It is also possible to immerse part or all of the reciprocating pump device in the liquid hydrogen source (liquefied gas source) to simplify the flow path, improve cooling performance, and improve suction performance. It is also possible to use an electric motor 48 that can be immersed in the liquid hydrogen source (liquefied gas source).

[0030] The embodiments described above are intended to enable persons with ordinary skill in the art to carry out the present invention. Various modifications of the above embodiments can be made naturally by those skilled in the art, and the technical idea of ​​the present invention can be applied to other embodiments as well. Therefore, the present invention is not limited to the embodiments described, but is to be interpreted in the broadest sense according to the technical idea defined by the claims.

[0031] The present invention can be used in reciprocating pump devices for pressurizing liquefied gases such as liquid hydrogen, liquefied natural gas, liquefied ammonia, liquid nitrogen, liquefied ethylene gas, and liquefied petroleum gas.

[0032] 1 Cylinder 2 Piston 3 Seal ring 6 Liquid inlet 7 Suction check valve 9 Cylinder cover 12 Liquid chamber 15 Inlet end wall 16 Partition 20 Suction port 22 Pump casing 25 Vacuum insulation layer 30 Discharge path 31 Discharge port 33 Discharge check valve 35 Gas relief hole 41 Pump shaft 42 Ball screw nut 45 Screw shaft 48 Electric motor 49 Motor driver 51 Ball 53 Guide rail 55 Groove 60 Leak recovery hole

Claims

1. A reciprocating pump device for liquefied gas, comprising: a cylinder; a piston disposed within the cylinder; a pump shaft connected to the piston; a ball screw nut fixed to the pump shaft; a screw shaft screwed onto the ball screw nut; and an electric motor connected to the screw shaft for rotating the screw shaft.

2. The reciprocating pump device according to claim 1, further comprising a cylinder cover that surrounds the cylinder and forms a liquid chamber for the liquefied gas on the outside of the cylinder.

3. The reciprocating pump device according to claim 1, further comprising a motor driver that rotates the electric motor alternately in one direction and in opposite directions.

4. The reciprocating pump device according to claim 1, wherein the pump shaft is not in contact with the screw shaft.

5. The reciprocating pump device according to claim 1, further comprising a pump casing that at least covers the cylinder and the cylinder cover, wherein there is a vacuum insulation layer between the cylinder cover and the pump casing.

6. The reciprocating pump device according to claim 1, further comprising a guide rail that restricts the rotation of the ball screw nut while allowing the ball screw nut to move in the axial direction of the screw shaft, wherein the ball screw nut has a groove into which the guide rail engages.

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