JP7680337B2 - Reciprocating Pump - Google Patents

Description

The present invention relates to reciprocating pumps such as plunger pumps and piston pumps, and in particular to reciprocating pumps suitable for transporting liquefied gas.

A reciprocating pump is configured to draw fluid into a cylinder by reciprocating a piston disposed within the cylinder, pressurize the fluid, and expel it from the cylinder. Such reciprocating pumps are sometimes used to transport liquefied gases such as liquid hydrogen, liquefied natural gas, liquefied ammonia, liquid nitrogen, liquefied ethylene gas, and liquefied petroleum gas.

Figure 6 is a schematic diagram showing a cross section of a conventional reciprocating pump. As shown in Figure 6, the reciprocating pump has a cylinder 500 and a piston 501 movably arranged within the cylinder 500. The piston 501 is connected to an actuator (not shown). A seal 503 is arranged between the inner surface of the cylinder 500 and the outer surface of the piston 501. Check valves 514 and 515 are connected to the suction port 510 and the discharge port 511 of the cylinder 500, respectively.

As the actuator reciprocates the piston 501 axially, fluid flows into the cylinder 500 through the check valve 514 and the suction port 510, is pressurized by the piston 501, and is discharged from the cylinder 500 through the discharge port 511 and the check valve 515.

U.S. Pat. No. 6,530,761

However, the conventional reciprocating pump shown in FIG. 6 has the following problems.
The first problem is that a part of the fluid pressurized by the piston 501 leaks out of the cylinder 500 through the seal 503. In particular, in a reciprocating pump for liquefied gas, a small leakage path is provided between the seal 503 and the cylinder 500 to reduce vaporization of the liquefied gas caused by the sliding heat of the seal 503, and a certain degree of leakage of the fluid is permitted. Therefore, as the piston 501 reciprocates, a part of the fluid pressurized by the piston 501 leaks out of the cylinder 500 through the seal 503.

The second problem is that when the piston 501 moves to suck in the fluid, the fluid remaining in the cylinder 500 expands, preventing a drop in pressure within the cylinder 500 and hindering the fluid from being sucked into the cylinder 500. In particular, in the case of liquefied gas, the fluid is likely to expand and vaporize as the piston 501 moves. When such expansion of the fluid occurs within the cylinder 500, it prevents a drop in pressure within the cylinder 500 and reduces the amount of fluid sucked into the cylinder 500. As a result, the efficiency of the reciprocating pump decreases.

Therefore, the present invention provides a reciprocating pump that can improve efficiency by reducing the amount of fluid leaking out of the cylinder and ensuring the amount of fluid flowing into the cylinder.

In one aspect, a reciprocating pump for transporting liquefied gas is provided, the reciprocating pump comprising: a cylinder having an inflow chamber, a reset chamber, an intermediate chamber, and a pressurizing chamber therein; a piston disposed in the cylinder; a first seal, a second seal, and a third seal disposed in a gap between the inner surface of the cylinder and the outer surface of the piston; a suction check valve connected to the suction port of the cylinder; an inflow check valve and an outflow check valve disposed in a piston flow path passing through the piston; a discharge check valve connected to the discharge port of the cylinder; and a leakage discharge check valve connected to a leakage discharge port of the cylinder, the leakage discharge port being connected to the reset chamber; the inflow chamber and the reset chamber are partitioned by the first seal, the reset chamber and the intermediate chamber are partitioned by the second seal, the intermediate chamber and the pressurizing chamber are partitioned by the third seal, and the piston has a communication flow path that communicates the piston flow path and the intermediate chamber.

In one embodiment, the reciprocating pump further includes a shaft seal device that seals a gap between the cylinder and a piston rod connected to the piston.
In one embodiment, the diameter of the inlet chamber is greater than the diameter of the pressurization chamber.
In one embodiment, the inflow chamber, the reset chamber, the intermediate chamber, and the pressurizing chamber are arranged in the order of the inflow chamber, the reset chamber, the intermediate chamber, and the pressurizing chamber along the longitudinal direction of the cylinder.

According to the present invention, the fluid leaking from the pressurizing chamber to the intermediate chamber through the third seal is mixed with the fluid in the piston flow passage through the communicating flow passage and is sent back to the pressurizing chamber as the piston moves. Therefore, the amount of fluid leaking outside the cylinder is reduced. Although a part of the fluid in the intermediate chamber leaks through the second seal to the reset chamber, the fluid in the reset chamber is discharged outside the cylinder through the leakage discharge port and the leakage discharge check valve. Therefore, the fluid in the reset chamber does not flow into the inlet chamber, and the pressure in the inlet chamber is maintained low. As a result, when the piston performs a suction operation, the intended amount of fluid is sucked into the inlet chamber. In this way, a sufficient amount of fluid is sucked in, pressurized, and transferred by the reciprocating motion of the piston, and the efficiency of the reciprocating pump is improved. Since the amount of fluid discharged from the reset chamber to the cylinder through the leakage discharge port and the leakage discharge check valve is small, the amount of fluid transferred by the reciprocating pump is not substantially reduced.

FIG. 1 is a schematic diagram illustrating one embodiment of a liquefied gas transfer system including a reciprocating pump. FIG. 1 is a cross-sectional view illustrating one embodiment of a reciprocating pump. FIG. 4 is a cross-sectional view showing a state in which the piston has moved to the bottom dead center. FIG. 4 is a cross-sectional view showing a state in which the piston has moved to the top dead center. FIG. 4 is a cross-sectional view showing another embodiment of a reciprocating pump. FIG. 1 is a schematic cross-sectional view of a conventional reciprocating pump.

Embodiments of the present invention will be described below with reference to the drawings. The reciprocating pump of the embodiment described below is suitable for transporting liquefied gases such as liquid hydrogen, liquefied natural gas, liquefied ammonia, liquid nitrogen, liquefied ethylene gas, and liquefied petroleum gas.

Figure 1 is a schematic diagram showing one embodiment of a liquefied gas transfer system equipped with a reciprocating pump. As shown in Figure 1, the liquefied gas transfer system includes a storage tank 1 for storing liquefied gas, a reciprocating pump 2 disposed in the storage tank 1, and an actuator 5 for driving the reciprocating pump 2. The liquefied gas is sent into the storage tank 1 through a liquefied gas inlet port 7 of the storage tank 1, and is stored in the storage tank 1.

Most of the liquefied gas in the storage tank 1 is in liquid form, but a small amount of heat from the surrounding atmosphere is transferred to the liquefied gas through the walls of the storage tank 1. As a result, part of the liquefied gas is gasified to form boil-off gas (BOG). Therefore, the storage tank 1 is provided with a boil-off gas discharge port 8 for discharging the boil-off gas. The boil-off gas in the storage tank 1 is discharged from the storage tank 1 through the boil-off gas discharge port 8.

The piston rod 10 of the reciprocating pump 2 is connected to the actuator 5 via a coupling device 12. The actuator 5 is fixed to the storage tank 1 via a bracket 9. Examples of the actuator 5 include a linear motor, a hydraulic cylinder, and a combination of a crank mechanism and an electric motor. The liquefied gas intake port of the reciprocating pump 2 is located lower than the liquid level of the storage tank 1, although it is not shown in FIG. 1. When the actuator 5 drives the reciprocating pump 2, the reciprocating pump 2 sucks in the liquefied gas in the storage tank 1, pressurizes it, and discharges it into the liquefied gas discharge line 14. The pressurized liquefied gas is transported to the outside of the storage tank 1 through the liquefied gas discharge line 14.

The liquefied gas transfer system further includes a leakage discharge line 15 connected to the reciprocating pump 2. As described below, this leakage discharge line 15 is provided to discharge from the reciprocating pump 2 a small amount of fluid that has leaked from the pressurizing chamber of the reciprocating pump 2.

Figure 2 is a cross-sectional view showing one embodiment of a reciprocating pump 2. The liquefied gas in the reciprocating pump 2 is in a liquid state, a vapor state, or a supercritical state, depending on its pressure and/or temperature. Therefore, in the following description, the liquefied gas is referred to as a "fluid," and the state of the "fluid" includes the liquid phase, the vapor phase, and the supercritical state.

The reciprocating pump 2 is a positive displacement pump for transporting liquefied gas. As shown in FIG. 2, the reciprocating pump 2 includes a cylinder 26 having an inlet chamber 21, a reset chamber 22, an intermediate chamber 23, and a pressurizing chamber 24 therein, a piston 30 disposed in the cylinder 26, and a first seal 31, a second seal 32, and a third seal 33 disposed in the gap between the inner surface of the cylinder 26 and the outer surface of the piston 30. The piston 30 is connected to a piston rod 10, which is connected to an actuator 5 shown in FIG. 1. The piston 30 is driven by the actuator 5 to reciprocate within the cylinder 26.

The first seal 31, the second seal 32, and the third seal 33 are held by the piston 30 and move back and forth with the piston 30. Therefore, the seals 31, 32, and 33 are movable seals. The structure of the seals 31, 32, and 33 is not particularly limited as long as they are configured to seal the gap between the inner surface of the cylinder 26 and the outer surface of the piston 30. For example, the first seal 31, the second seal 32, and the third seal 33 are seal rings made of resin or metal.

The reciprocating pump 2 further includes a shaft seal device 35 that seals the gap between the piston rod 10 and the cylinder 26. The shaft seal device 35 is a stationary seal device held in the cylinder 26. The shaft seal device 35 faces the inflow chamber 21 in the cylinder 26 and has the function of separating the inflow chamber 21 from the outside of the cylinder 26 (i.e., the atmospheric portion above the storage tank 1 shown in FIG. 1). An example of the shaft seal device 35 is a gland packing. In one embodiment, the shaft seal device 35 may be a movable seal that is held by the piston rod 10 and can move together with the piston rod 10.

The inflow chamber 21, the reset chamber 22, the intermediate chamber 23, and the pressurizing chamber 24 are formed between the piston 30 and the cylinder 26. The inflow chamber 21, the reset chamber 22, the intermediate chamber 23, and the pressurizing chamber 24 are arranged in the order of the inflow chamber 21, the reset chamber 22, the intermediate chamber 23, and the pressurizing chamber 24 along the longitudinal direction of the cylinder 26. That is, the inflow chamber 21 is adjacent to the reset chamber 22, the reset chamber 22 is adjacent to the intermediate chamber 23, and the intermediate chamber 23 is adjacent to the pressurizing chamber 24. The inflow chamber 21 and the reset chamber 22 are partitioned by a first seal 31, the reset chamber 22 and the intermediate chamber 23 are partitioned by a second seal 32, and the intermediate chamber 23 and the pressurizing chamber 24 are partitioned by a third seal 33. The reset chamber 22 is located between the first seal 31 and the second seal 32, and the intermediate chamber 23 is located between the second seal 32 and the third seal 33.

The cylinder 26 has a fluid suction port 26A and a fluid discharge port 26B. The suction port 26A is connected to the inflow chamber 21, and the discharge port 26B is connected to the pressurizing chamber 24. The piston 30 has a piston flow path 40 that extends through its interior. The piston flow path 40 extends from the inflow chamber 21 to the pressurizing chamber 24. That is, the inlet of the piston flow path 40 opens at the inflow chamber 21, and the outlet of the piston flow path 40 opens at the pressurizing chamber 24. The piston 30 further has a communication flow path 41 that communicates the piston flow path 40 and the intermediate chamber 23. One end of the communication flow path 41 is connected to the piston flow path 40, and the other end of the communication flow path 41 is connected to the intermediate chamber 23.

The cylinder 26 has a leakage discharge port 45 that communicates with the reset chamber 22. The reciprocating pump 2 is equipped with a suction check valve 51 connected to the suction port 26A of the cylinder 26, an inlet check valve 52 and an outlet check valve 53 arranged in the piston flow path 40, a discharge check valve 54 connected to the discharge port 26B of the cylinder 26, and a leakage discharge check valve 55 connected to the leakage discharge port 45 of the cylinder 26.

The inlet of the suction check valve 51 is located in the storage tank 1 shown in FIG. 1 and is located lower than the liquid level in the storage tank 1. The suction check valve 51 is configured to allow the fluid (liquefied gas) in the storage tank 1 to flow into the inlet chamber 21 in the cylinder 26, but not to allow the fluid to flow in the reverse direction.

The inlet check valve 52 is disposed on the inlet side of the piston flow passage 40, and the outlet check valve 53 is disposed on the outlet side of the piston flow passage 40. The inlet check valve 52 and the outlet check valve 53 are configured to allow fluid to flow from the inlet chamber 21 to the pressurizing chamber 24, but not to allow flow in the reverse direction. The inlet check valve 52 and the outlet check valve 53 are fixed to the piston 30, and move back and forth together with the piston 30. The communication flow passage 41 is connected to the piston flow passage 40 at a position between the inlet check valve 52 and the outlet check valve 53.

The discharge check valve 54 is configured to allow fluid to flow out of the pressurized chamber 24 and not allow flow in the reverse direction. The outlet of the discharge check valve 54 is connected to the liquefied gas discharge line 14. The leakage discharge check valve 55 is configured to allow fluid to flow out of the reset chamber 22 and not allow flow in the reverse direction. The outlet of the leakage discharge check valve 55 is connected to the leakage discharge line 15.

As shown in FIG. 2, the diameter W1 of the inflow chamber 21 is larger than the diameter W2 of the pressurizing chamber 24. As can be seen from FIG. 2, the piston rod 10 is present in the inflow chamber 21, so the volume of the inflow chamber 21 is smaller by the volume of the piston rod 10. Therefore, by making the diameter W1 of the inflow chamber 21 larger than the diameter W2 of the pressurizing chamber 24, it is possible to make the volume of the inflow chamber 21 the same as the volume of the pressurizing chamber 24, or to adjust the volume ratio. In addition, since the surface area of the cylinder 26 that forms the small-diameter pressurizing chamber 24 is small, there is also the advantage that the compression heat of the fluid in the pressurizing chamber 24 is less likely to be transmitted to the outside of the cylinder 26.

Next, the operation of the reciprocating pump 2 will be described. As shown in FIG. 3, when the piston 30 moves toward the discharge port 26B (toward bottom dead center), the inflow chamber 21 expands, and the fluid flows into the inflow chamber 21 through the suction check valve 51 and the suction port 26A. Next, as shown in FIG. 4, when the piston 30 moves toward the suction port 26A (toward top dead center), the fluid in the inflow chamber 21 flows through the inflow side check valve 52, the piston flow path 40, and the outflow side check valve 53, and flows into the pressurizing chamber 24.

Furthermore, as shown in FIG. 3, when the piston 30 moves toward the discharge port 26B, the fluid in the pressurizing chamber 24 is pressurized and discharged from the pressurizing chamber 24 through the discharge port 26B and the discharge check valve 54. At the same time, the inflow chamber 21 expands, and the fluid flows into the inflow chamber 21 through the suction check valve 51 and the suction port 26A. The pressurized fluid flows through the liquefied gas discharge line 14 and is transferred to the outside of the storage tank 1 shown in FIG. 1. In this way, when the piston 30 moves in one direction, the fluid is sucked into the inflow chamber 21 and the fluid is pressurized in the pressurizing chamber 24, and when the piston 30 moves in the opposite direction, the fluid moves from the inflow chamber 21 to the pressurizing chamber 24.

The first seal 31, the second seal 32, and the third seal 33 have small leakage paths between the seals 31, 32, and 33 and the cylinder 26 to prevent evaporation of the fluid due to sliding heat, and allow a certain amount of fluid leakage. Therefore, when the piston 30 moves as shown in FIG. 3, some of the fluid leaks from the pressurized chamber 24 through the third seal 33 into the intermediate chamber 23. Similarly, when the piston 30 moves as shown in FIG. 4, some of the fluid in the inlet chamber 21 leaks into the reset chamber 22 through the first seal 31.

The fluid leaking from the pressurized chamber 24 to the intermediate chamber 23 through the third seal 33 is a high-enthalpy fluid. This high-enthalpy fluid mixes with the relatively large amount of low-enthalpy fluid present in the intermediate chamber 23 to become a low-enthalpy fluid. Furthermore, the low-enthalpy fluid in the intermediate chamber 23 is sent to the pressurized chamber 24 through the communication flow path 41 and the piston flow path 40. In this way, the fluid leaking from the pressurized chamber 24 to the intermediate chamber 23 through the third seal 33 flows back to the pressurized chamber 24 through the communication flow path 41 and the piston flow path 40, reducing the amount of fluid leaking outside the cylinder 26.

Although a portion of the low-enthalpy fluid in the intermediate chamber 23 leaks through the second seal 32 into the reset chamber 22, the fluid in the reset chamber 22 is discharged to the outside of the cylinder 26 through the leakage discharge port 45 and the leakage discharge check valve 55. Therefore, the fluid in the reset chamber 22 does not flow into the inflow chamber 21, and the pressure in the inflow chamber 21 is maintained low. As a result, when the piston 30 performs a suction operation, the intended amount of fluid is sucked into the inflow chamber 21. In this way, a sufficient amount of fluid is sucked, pressurized, and transferred by the reciprocating action of the piston 30, thereby improving the efficiency of the reciprocating pump 2. Since the amount of fluid discharged from the reset chamber 22 to the outside of the cylinder 26 through the leakage discharge port 45 and the leakage discharge check valve 55 is small, the amount of fluid transferred by the reciprocating pump 2 is not substantially reduced.

As shown in FIG. 1, the leakage discharge line 15 extends outside the storage tank 1 and is either open to the atmosphere or connected to a gas treatment device (not shown). Examples of gas treatment devices include a gas incineration device (flaring device), a chemical gas treatment device, a gas adsorption device, and the like. In one embodiment, the outlet of the leakage discharge line 15 may be located within the storage tank 1 shown in FIG. 1. In this case, the fluid that flows through the leakage discharge line 15 is returned to the storage tank 1.

Figure 5 is a cross-sectional view showing another embodiment of the reciprocating pump 2. The configuration and operation of this embodiment, which are not specifically described, are the same as those of the embodiment described with reference to Figures 1 to 4, and therefore will not be described again.

As shown in FIG. 5, the first seal 31, the second seal 32, and the third seal 33 are stationary seals fixed to the inner surface of the cylinder 26. Therefore, these seals do not move with the reciprocating movement of the piston 30. In the embodiment shown in FIG. 5, as in the embodiment described above, the amount of fluid leaking outside the cylinder 26 is reduced and the efficiency of the reciprocating pump 2 is improved.

The above-described embodiments have been described for the purpose of enabling a person having ordinary knowledge in the technical field to which the present invention pertains to practice the present invention. Various modifications of the above-described embodiments would naturally be possible for a person skilled in the art, and the technical ideas of the present invention may also 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 ideas defined by the scope of the claims.

REFERENCE SIGNS LIST 1 Storage tank 2 Reciprocating pump 5 Actuator 7 Liquefied gas inlet port 8 Boil-off gas discharge port 9 Bracket 10 Piston rod 12 Joint device 14 Liquefied gas discharge line 15 Leakage discharge line 21 Inflow chamber 22 Reset chamber 23 Intermediate chamber 24 Pressurizing chamber 26 Cylinder 26A Suction port 26B Discharge port 30 Piston 31 First seal 32 Second seal 33 Third seal 35 Shaft seal device 40 Piston flow path 41 Communication flow path 45 Leakage discharge port 51 Suction check valve 52 Inflow side check valve 53 Outflow side check valve 54 Discharge check valve 55 Leakage discharge check valve

Claims (4)

1. A reciprocating pump for transporting liquefied gas, comprising:
a cylinder having an inflow chamber, a reset chamber, an intermediate chamber, and a pressurizing chamber therein;
A piston disposed within the cylinder;
a first seal, a second seal, and a third seal disposed in a gap between an inner surface of the cylinder and an outer surface of the piston;
a suction check valve connected to the suction port of the cylinder;
an inlet check valve and an outlet check valve disposed in a piston flow passage passing through the piston;
a discharge check valve connected to the discharge port of the cylinder;
a leakage discharge check valve connected to the leakage discharge port of the cylinder;
The leakage discharge port is in communication with the reset chamber,
the inlet chamber and the reset chamber are partitioned by the first seal,
the reset chamber and the intermediate chamber are partitioned by the second seal,
the intermediate chamber and the pressurizing chamber are partitioned by the third seal,
The piston has a communication passage that communicates the piston passage with the intermediate chamber. The reciprocating pump according to claim 1, further comprising a shaft seal device that seals the gap between the piston rod connected to the piston and the cylinder. The reciprocating pump according to claim 1 or 2, wherein the diameter of the inlet chamber is greater than the diameter of the pressurizing chamber. The reciprocating pump according to any one of claims 1 to 3, wherein the inflow chamber, the reset chamber, the intermediate chamber, and the pressurizing chamber are arranged in the order of the inflow chamber, the reset chamber, the intermediate chamber, and the pressurizing chamber along the longitudinal direction of the cylinder.

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