Piston pump

Abstract

A piston pump for pumping liquefied fluids, in particular a cryogenic fuel pump for pumping liquefied fuels such as liquid natural gas (LNG), hydrogen, methanol, ammonia or the like, comprising a pump housing (1) having a piston chamber (4) formed therein, an inlet flow valve (8) and a discharge check valve (6) provided in the pump housing, and a piston having a piston head (2) and a piston rod (3), the piston reciprocating along a longitudinal axis within the piston chamber to pump the liquid fuel within the chamber. The pump includes a piston provided for compressing a fluid to a high pressure, a first sealing means (21) provided on the piston head between the inner circumferential surface of the chamber and the piston head, and a second sealing means provided between the piston rod and a bore (10) of a pump housing, the second sealing means including a pressurized sealing means provided in the bore of the housing between at least two sealing rings (33, 34), the pressurized sealing means including an inlet (31) and an outlet (36) for pressurized lubricating fluid, and a pressurized fluid source for providing pressurized fluid in a fluid flow to the inlet.

Description

[Technical Field]

[0001] The present invention relates to a piston pump for pumping liquefied fluids, in particular to a cryogenic fuel pump for pumping liquefied fuels such as liquid natural gas (LNG), hydrogen, methanol, ammonia or the like, said pump comprising: a pump housing having a piston chamber formed therein, an inlet flow valve and a discharge check valve provided in the pump housing; a piston having a piston head and a piston rod, said piston being provided for reciprocating movement along a longitudinal axis in the piston chamber to compress a fluid in the chamber to a high pressure; and a first sealing means provided on the piston head between an inner circumferential surface of the chamber and the piston head. [Background technology]

[0002] Typically, a piston pump includes a high-pressure end where a piston head reciprocates within a piston chamber, pressurizing the incoming liquid before the liquid is expelled at high pressure. The other end of the piston pump is a low-pressure end. The piston is driven by a piston rod, which is sealed to a bore in the pump housing and through which it reciprocates.

[0003] US 2019 / 0293067A1 discloses a piston pump of the first-mentioned kind, in which the supply chamber is closed on the side opposite the piston by a cover including a first passage for allowing the supply of cryogenic liquid from the supply chamber and a second passage for allowing the discharge of the pumped liquid. The piston head is sealed to the piston bore to ensure that liquid does not escape from the supply chamber when pressurized by the piston head. The piston is driven in a reciprocating motion within the bore. A plurality of gas seals are provided within the bore that receives the piston passing through the pump body. Summary of the Invention [Problem to be solved by the invention]

[0004] The seal between the piston rod and the bore can be easily worn and in order to achieve an acceptable service life of the pump, the quantity of seal rings is increased. However, the object of the present invention is to provide an alternative, or at least a complement, to multiple seal rings so that the quantity of seal rings can be reduced in number. [Means for solving the problem]

[0005] In the present disclosure, several embodiments of a cryogenic piston pump are described. Accordingly, the present invention relates to a piston pump for pumping liquefied fluid, in particular a cryogenic fuel pump for pumping liquefied fuel such as liquid natural gas (LNG), hydrogen, methanol, or the like, the pump including: a pump housing having a piston chamber formed therein, an inlet flow valve and a discharge check valve provided in the pump housing; a piston having a piston head and a piston rod, the piston reciprocating along a longitudinal axis in the piston chamber to compress a fluid in the chamber to a high pressure; a first sealing means provided on the piston head between an inner peripheral surface of the chamber and the piston head; and a second sealing means provided between the piston rod and a bore of the pump housing, the second sealing means including a pressurized sealing device provided in the bore of the housing between at least two sealing rings, the pressurized sealing device including an inlet and an outlet for pressurized lubricating fluid, and a pressurized fluid source for providing the pressurized fluid in the fluid flow to the inlet.

[0006] By providing a pressurized seal around the piston rod, an active seal is provided to prevent liquid from escaping from the space behind the piston head into the bore, this solution is further advantageous as it provides additional lubrication of the piston rod.

[0007] In an embodiment of the invention, the pressurized sealing device includes an annular groove in the bore, which allows for the formation of an annular reservoir of lubricating fluid around the piston rod.

[0008] In some embodiments, the pressurized lubricating fluid can be a liquefied fuel for the pump, i.e., the pump's primary cargo fluid. In other currently preferred embodiments, the pressurized sealing device includes an inlet and an outlet for pressurized lubricating fluid, which is a lubricating oil that provides both a barrier and lubrication between the bore behind the piston head and the piston rod. The provision of pressurized fluid for sealing ensures that external fluids—gas or liquid—do not pass through the annular sealing area between the bore and the piston rod.

[0009] Preferably, a return fluid flow is provided between the outlet and the pressurized fluid source to form a closed fluid system. A closed, sealed fluid system may be provided. Advantageously, a filter is provided in the return fluid flow to remove any contaminants in the fluid, thereby protecting the sealing device.

[0010] Preferably, the source of pressurized fluid comprises a pressure booster, so that pressurized fluid is supplied to the inlet of the pressurized sealing device at a high pressure, advantageously 1 bar above the pressure of the cryogenic fluid, thereby ensuring a high pressure and therefore maintaining the seal.

[0011] In an embodiment of the high-pressure piston pump according to the invention, the pump housing comprises a sealing housing, and at least the pressurized sealing device of the second sealing means is provided within the sealing housing, which makes it possible to design the pump housing in a modular manner that is more efficient to produce and easier to service.

[0012] In a preferred embodiment, the sealed housing includes a heating system for providing a temperature to the sealing material that is higher than the temperature of the cryogenic fluid. The higher temperature can be in the range of 0°C to 45°C, and in a preferred embodiment, approximately 20°C. This is feasible because the higher viscosity of the sealing fluid allows for a better seal, and thermal insulation can be provided within the sealed housing so that this seal at temperatures higher than the low temperature range for which the pump is designed to operate does not affect the temperature of the primary cargo being pumped by the piston pump.

[0013] In a currently preferred embodiment, the second sealing device comprises at least two pressurized sealing devices mounted between at least two sealing rings, so that excess sealing fluid can be kept within the annular sealing area between the bore and the piston rod.

[0014] As mentioned above, the second sealing device may also provide lubrication for the piston rod.

[0015] From the above description of some preferred embodiments, it is noteworthy that the first sealing means includes a plurality of piston rings that seal the gap between the inner circumferential surface of the chamber and the piston head.

[0016] The invention will now be described with reference to the accompanying drawings. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a side cross-sectional view of a low-temperature, high-pressure piston pump according to an embodiment of the present invention. [Figure 2] FIG. 1 is a schematic cross-sectional detailed side view of the low pressure end of a piston pump having a second sealing means. [Figure 3] FIG. 1 is a cross-sectional detailed side view of the piston chamber end of a piston pump having an inlet valve. [Figure 4] FIG. 10 is a detailed cross-sectional view of an inlet that fills and discharges fluid in the piston chamber of the piston pump. [Figure 5]FIG. 10 is a detailed cross-sectional view of an inlet that fills and discharges fluid in the piston chamber of the piston pump. [Figure 6] FIG. 10 is a detailed cross-sectional view of an inlet that fills and discharges fluid in the piston chamber of the piston pump. DETAILED DESCRIPTION OF THE INVENTION

[0018] FIG. 1 shows an embodiment of a cryogenic piston pump for pumping liquefied fluids. The pump is a cryogenic fuel pump for pumping liquefied fuels, such as liquid natural gas (LNG), hydrogen, methanol, or the like. The pump includes a pump housing 1 having a piston chamber 4 formed therein, and an inlet flow valve 5 and a discharge check valve 6 disposed within the piston chamber 4. A piston, consisting of a piston head 2 and a piston rod 3, is provided inside the housing 1. A housing volume 7 is formed within the housing 1 behind the piston head 2, i.e., on the opposite side of the piston head 2 from the piston chamber 4. The piston head 2 is adapted to reciprocate within the piston chamber 4 along a longitudinal axis to compress the fluid within the chamber 4 to a high pressure.

[0019] Liquefied fluid is drawn from fluid chamber 9 through inlet fluid channel 5 and inlet valve 8 into piston chamber 4 when piston 2 is retracted in, the liquid in piston chamber 4 is then pressurized when piston head 2 is advanced, and the pressurized liquid is then discharged through discharge valve 6. To ensure that liquid does not escape from piston chamber 4 into housing volume 7 when pressure is building up in piston chamber 4 (and thus the pressure difference between piston chamber 4 and housing volume 7 increases), first sealing means 21 are provided on piston head 2, between the inner circumferential surface of piston chamber 4 and said piston head 2. These first sealing means 21 may be piston rings arranged annularly around piston head 2.

[0020] At the low pressure end of the pump, within the housing 1 opposite the piston chamber 4, a second sealing means 30 is provided between the piston rod 3 and the bore 10 of the pump housing 1. The second sealing arrangement 30 comprises a pressurized sealing arrangement 31 provided within the bore 10 of the housing 1 between at least two sealing rings 33, 34.

[0021] FIG. 2 shows a more detailed view of the low-pressure end of the second sealing means according to an embodiment of the present invention. As shown in FIG. 2, the housing is provided with two pressurized sealing devices 30, each including an annular groove 35 in the bore 10. Each of the pressurized sealing devices 30 further includes an inlet 31 and an outlet 32 ​​for a pressurized fluid, such as oil, and a pressurized fluid source 36 for providing the pressurized fluid in a fluid flow to the inlet 31 via a fluid line 38. From the outlet 32, a return fluid flow line 39 is provided between the outlet 32 ​​and the pressurized fluid source 36 to form a closed fluid system. The return fluid line 39 is joined, and a filter 37 is provided in the return fluid flow to remove any contaminants from the fluid. The pressurized fluid source includes a pressure booster 36, which provides pressurized fluid to the inlet 31 of the pressurized sealing device 30 at a high pressure, such as 1 bar above the supply pressure of the cryogenic fluid (P+1 bar). The pressure booster 36 is also connected to the housing volume 7 via a fluid line 40, whereby fluid is supplied at the cryogenic fluid pressure Pgas.

[0022] The section of the pump housing 1 that houses the second sealing means 30 is provided as a sealed housing 1A. This sealed housing 1A may be provided with a heating system 12 for providing the sealed fluid with a temperature higher than that of the cryogenic fluid. The heating system may be any suitable heating system, such as a heating chamber through which the fluid flows, or any other type of heating system.

[0023] In the embodiment shown in FIGS. 1 and 2, the second sealing device includes at least two pressure sealing devices 30 that are mounted between sealing rings 33 and 34 on either side of the pressure sealing device 30 .

[0024] The second sealing device may provide an additional pressurized fluid conduit 35 for not only sealing but also lubricating the piston rod 3 reciprocating within the bore 10 of the housing 1. The fluid conduits 35 are provided annularly within the bore 10 of the seal housing 1A. Each of the conduits 35 is provided with a fluid inlet 31 and a fluid outlet 32. Sealing rings 33 and 34 are provided on each side of the pressurized seal 30 to restrict oil flow within the sealing device 30. The fluid inlet 31 is supplied with pressurized fluid, such as oil, through a one-way valve 31A within the inlet 31. The outlet 32 ​​is preferably located opposite the inlet 31 and is also provided with a one-way valve 32A, thereby regulating fluid flow. In the embodiment shown in FIGS. 1 and 2, two sealing devices 30 are provided, and the two inlets 31 receive pressurized fluid from a pressure booster 36 via a fluid line 38. Pressure is increased to ensure an oil seal is maintained between the piston rod 3 and the bore 10.

[0025] FIG. 3 shows a detailed view of the high-pressure end of the piston pump of FIG. 1, with piston chamber 4, inlet flow valve 8, and discharge valve 6 provided. Pump housing 1 is provided with a fluid chamber 9 arranged annularly around piston chamber 4. Inlet flow valve 8 and discharge check valve 6 are provided within housing 1 for supplying fluid from fluid chamber 9 through inlet valve 8 to piston chamber 4, and for discharging said fluid at increased pressure from piston chamber 4 through discharge check valve 6. As shown in connection with FIG. 1, a piston has piston head 2 and piston rod 3, with piston head 2 provided for reciprocating movement along a longitudinal axis within piston chamber 4 to compress fluid in chamber 4 to a high pressure.

[0026] Fluid in the annular fluid chamber 9 is under a specific pressure and flows through equally annularly spaced inlet flow channels 5 toward openings in these channels 5. The inlet flow valve device 8 includes an annular inlet space 51 concentric with the fluid chamber 9 and having a shared wall 52 with said fluid chamber 9, in which fluid channels 5 are provided so that fluid communication between the fluid chamber 9 and the annular inlet space 51 can be established through a plurality of fluid openings provided by the fluid channels 5 in the shared wall 52 between said fluid chamber 9 and said inlet space 51. A valve plate 81 is provided in the inlet space 51 and is spring-loaded so that the valve plate 81 is biased by the spring force toward the shared wall 52, thereby blocking flow in the fluid channels 5 by blocking the fluid openings on the inlet space side of the shared wall 52.

[0027] The valve plate 81 is ring-shaped. The common wall 52 is also ring-shaped and is provided concentrically with the longitudinal axis. The spring load of the valve plate 81 is provided by a plurality of springs 82 (see FIG. 3 ) that provide a spring force axially relative to the flow direction in the fluid channel 51 as shown in FIG. 3 . In some preferred embodiments, the springs 82 are coil springs. Within the housing 1, an annular inlet space 51 is formed integrally with the piston chamber 4, and fluid flow within the inlet space 51 is radially inward into the piston chamber 4.

[0028] This spring force is such that the valve plate 81 is biased towards closing fluid flow through the fluid channel 5, but when the piston head 2 is retracted within the piston chamber 4 so that pressure drops within the chamber 4, pressure from the fluid in the fluid chamber 9 forces the valve plate 81 backward, loading the spring 82 and thereby opening the inlet valve device 8.

[0029] When the piston head 2 is again advanced within the piston chamber 4, the pressure in the chamber 4 increases and the valve plate 81 is then immediately forced back to the closed position, preventing any fluid flow back into the fluid chamber 9. Instead, the discharge check valve 6 opens. The discharge valve 6 is provided coaxially on the longitudinal axis of the pistons 2, 3.

[0030] Discharge check valve 6 includes a valve head 61 that is biased toward a valve seat 62 formed within housing 1. Valve head 61 is subjected to a spring force axially toward piston chamber 4. When the pressure within piston chamber 4 exceeds a certain threshold, the spring force urging valve head 61 toward valve seat 62 is overcome and valve head 61 is moved rearward from a closed position to an open position, thereby discharging fluid from piston chamber 4 through discharge check valve 6 at high pressure relative to the pressure within fluid chamber 9.

[0031] The steps in the cycle of the piston pump are shown step by step in FIGS.

[0032] 4 illustrates the step of drawing fluid into the piston chamber 4. The inlet valve 8 is opened when the valve plate 81 is forced forward and fluid flows into the piston chamber 4 as illustrated by the arrows Fi.

[0033] This causes the piston head 2 to move rearward, creating a lower pressure in the piston chamber 4. This lower pressure causes the inlet valve plate 81 to open, moving against the spring 82, and liquid flows into the piston chamber 4 until the piston head 2 reaches its lower, or most retracted, position.

[0034] This position is shown in Figure 5, with the piston head 2 in the lower position and fluid entering the piston chamber 4. The piston 2 now begins to move forward again as the piston chamber 4 now fills, closing the inlet valve plate 81 and high pressure builds up in the piston chamber during piston travel.

[0035] The discharge step is shown in Figure 6. The piston 2 moves forward, creating high pressure in the cylinder 4. This causes the outlet valve 6 to open and move against the spring 63. Fluid flows out of the piston chamber 4 until the piston 2 reaches its upper position. This discharge flow is illustrated by the arrow Fo. The outlet valve 6 closes again as soon as the piston head 2 starts to retract again.

[0036] In this disclosure, the term "discharge check valve" is generally used for a non-return valve that allows fluid to flow therethrough in only one direction, i.e., a one-way valve.

[0037] Although the present invention has been described in connection with specific embodiments, it should not be construed as being limited in any way to the examples presented. The scope of the present invention is defined by the appended claim set. In the context of the claims, the terms "comprising" or "comprises" do not exclude other potential elements or steps. Also, the use of references such as "a" or "an" should not be construed as excluding a plurality. The use of reference signs in the claims for elements shown in the figures should also not be construed as limiting the scope of the invention. Furthermore, individual features recited in different claims can possibly be advantageously combined, and the recitation of these features in different claims does not exclude that combinations of features are not possible and advantageous.

[0038] The present invention is described above in connection with presently preferred embodiments. However, it is recognized that the present invention allows other embodiments and variations to be provided without departing from the scope of the invention as defined in the appended claims.

Claims

1. A piston pump for pumping liquefied fluids, in particular a cryogenic fuel pump for pumping liquefied fuels such as liquid natural gas (LNG), hydrogen, methanol, ammonia or the like, comprising: a pump housing having a piston chamber formed therein, wherein an inlet flow valve and a discharge check valve are provided within the pump housing; a piston having a piston head and a piston rod, the piston being adapted for reciprocating movement along a longitudinal axis within the piston chamber to compress a fluid within the chamber to a high pressure; a first sealing means provided on the piston head between the inner circumferential surface of the chamber and the piston head; and second sealing means provided between the piston rod and the bore of the pump housing, the second sealing means including a pressurized sealing device provided in the bore of the housing between at least two sealing rings, the pressurized sealing device including an inlet and an outlet for pressurized lubricating fluid and a pressurized fluid source for providing pressurized fluid into a fluid flow to the inlet.

2. The pump of claim 1 , wherein the pressurized sealing device includes an annular groove within the bore.

3. 3. A pump as claimed in claim 1 or 2, wherein the pressurised lubricating fluid is a lubricating oil that provides both a barrier and lubrication between the bore behind the piston head and the piston rod.

4. A pump according to any preceding claim, wherein a return fluid flow is provided between the outlet and the source of pressurised fluid to form a closed fluid system.

5. The pump of claim 4 wherein a filter is provided in the return fluid stream.

6. A pump according to any preceding claim, wherein the source of pressurised fluid comprises a pressure booster.

7. A pump according to any preceding claim, wherein the pressurised fluid is supplied to the inlet of the pressurised sealing device at a high pressure, such as 1 bar above the supply pressure of the cryogenic fluid.

8. A pump according to any one of the preceding claims, wherein the pump housing comprises a sealed housing, and wherein at least the pressurized sealing device of the second sealing means is provided within the sealed housing.

9. 9. The pump of claim 8, wherein the sealed housing includes a heating system for providing a sealing material with a temperature greater than a temperature of the cryogenic fluid.

10. A pump according to any one of the preceding claims, wherein the second sealing device comprises at least two pressurized sealing devices mounted between at least two sealing rings.

11. A pump according to any one of claims 1 to 10, wherein the second sealing device provides lubrication for the piston rod.

12. A pump according to any preceding claim, wherein the first sealing means comprises a plurality of piston rings sealing a gap between the inner circumferential surface of the chamber and the piston head.

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