FIELD OF THE INVENTION

The present invention relates to a piston pump for pumping liquidised fluids, in particular a cryogenic fuel pump for pumping liquidised fuel, such as liquid natural gas (LNG), hydrogen, methanol, ammonia or the like, said pump comprising a pump housing with a piston chamber formed inside and an inlet flow valve and a discharge check valve are provided in the pump housing; a piston having a piston head and a piston rod, said piston being provided to reciprocate along a longitudinal axis in the piston chamber to compress fluid in the chamber to an elevated pressure, and a first sealing means is provided on the piston head between an inner circumferential surface of said chamber and said piston head.

BACKGROUND OF THE INVENTION

Generally, a piston pump comprises a high pressure end where the piston head reciprocates in a piston chamber and pressurises the incoming liquid before the liquid is discharged at an elevated pressure. The other end of the piston pump is the low pressure end. The piston is driven by a piston rod, and the piston rod is sealed to the bore of the pump housing through which the piston rod reciprocates.

US2019/0293067A1 discloses a piston pump of the initially mentioned kind where the supply chamber is closed on the side opposite to the piston by a cover comprising a first passage to allow a supply of cryogenic liquid from the supply chamber and a second passage to allow discharge of pumped liquid. The piston head is sealed to the piston bore to ensure liquid does not escape the supply chamber as it is being pressurised by the piston head. The piston is driven in reciprocating motion in a bore. A plurality of gas seals are provided in the bore receiving the piston that passes through the pump body.

OBJECT OF THE INVENTION

The sealing between the piston rod and the bore may easily be worn and in order to achieve an acceptable service life of the pump, the amount of sealing rings are increased. However, it is an object of the present invention to provide an alternative to the plurality of sealing rings or at least a supplement so that the amount of sealing rings can be reduced in numbers.

SUMMARY OF THE INVENTION

In the present disclosure, there is described several embodiments of a cryogenic piston pump. Accordingly, the invention concerns a piston pump for pumping liquidised fluids, in particular a cryogenic fuel pump for pumping liquidised fuel, such as liquid natural gas (LNG), hydrogen, methanol or the like, said pump comprising a pump housing with a piston chamber formed inside and an inlet flow valve and a discharge check valve are provided in the pump housing; a piston having a piston head and a piston rod, said piston being provided to reciprocate along a longitudinal axis in the piston chamber to compress fluid in the chamber to an elevated pressure, a first sealing means is provided on the piston head between an inner circumferential surface of said chamber and said piston head; and a second sealing means is provided between the piston rod and a bore of the pump housing, wherein the second sealing means comprises a pressurised sealing arrangement provided in the bore of the housing between at least two sealing rings, and wherein the pressurised sealing arrangement comprises an inlet and an outlet for pressurised lubricating fluid, and a pressurised fluid source for the provision of pressurised fluid in a fluid flow to said inlet.

By providing a pressurised sealing arrangement around the piston rod, an active sealing is provided preventing liquid from escaping into the bore from the space behind the piston head. This solution is furthermore advantageous since additional lubrication of the piston rod is provided.

In an embodiment of the invention, the pressurised sealing arrangement comprises an annular groove in the bore. This allows to form a reservoir of lubrication fluid annularly around the piston rod.

In some embodiments, the pressurised lubrication fluid may be the liquidised fuel of the pump, i.e. the main cargo fluid of the pump. In other currently preferred embodiments, the pressurised sealing arrangement comprises an inlet and an outlet for pressurised lubricating fluid, which is a lubricating oil, which provides both a barrier and a lubrication between the bore behind the piston head and the piston rod. The provision of pressurised fluid for sealing ensures that no external fluids - gas or liquids - will pass the annular sealing region between the bore and the piston rod.

Preferably, there is provided a return fluid flow between the outlet and the pressurised fluid source to form a closed fluid system. Hereby, a closed sealing fluid system may be provided. Advantageously, a filter is provided in the return fluid flow. Hereby, any contaminants in the fluid may be removed thereby preserving the sealing arrangement.

Preferably, the pressurised fluid source comprises a pressure booster. Accordingly, the pressurised fluid is advantageously supplied to the inlet of the pressurised sealing arrangement at an elevated pressure, such as 1 bar above the pressure of the cryogenic fluid. Hereby, an elevated pressure is ensured so the sealing is maintained.

In an embodiment of the high pressure piston pump according to the invention, the pump housing comprises a sealing housing, and wherein at least the pressurised sealing arrangement of the second sealing means is provided in said sealing housing. This allows for designing the pump housing in a modular manner, which is more efficient in production and easier to service.

In a preferred embodiment, said sealing housing comprises a heating system for providing a higher temperature for the sealing material than the temperature of the cryogenic fluid. Said higher temperature may be in the range of between 0°C and 45°C, and in a preferred embodiment approx. 20°C. This allows for a better sealing due to the higher viscosity of the sealing fluid, and is feasible as thermal insulation may be provided in the sealing housing so that this sealing at a higher temperature than the cryogenic temperature range, in which the pump is designed for operating in, does not affect the temperature of the main cargo, which is being pumped by the piston pump. In the currently preferred embodiment, the second sealing arrangement comprises at least two pressurised sealing arrangements mounted between at least two sealing rings. Hereby, excess sealing fluid can be kept within the annular sealing region between the bore and the piston rod.

As mentioned above, the second sealing arrangement may also be providing lubrication of the piston rod.

By the above description of some preferred embodiments, it is noticeable that the first sealing means comprises a plurality of piston rings sealing the gap between the inner circumferential surface of the chamber and the piston head.

DETAILED DESCRIPTION

The invention is described in the following with reference to the accompanying drawings, in which:

Figure 1 is a cross-sectional side view of a cryogenic high-pressure piston pump according to an embodiment of the invention;

Figure 2 is a schematic cross-sectional detailed side view of the low-pressure end of the piston pump with the second sealing means;

Figure 3 is a cross-sectional detailed side view of the piston chamber end of the piston pump with the inlet valve; and

Figures 4 to 6 are detailed cross-sectional views of the inlet, filling and discharging of fluid in the piston chamber of the piston pump.

In figure 1 an embodiment of a cryogenic piston pump for pumping liquidised fluids is shown. The pump is a cryogenic fuel pump for pumping liquidised fuel, such as liquid natural gas (LNG), hydrogen, methanol or the like. The pump comprises a pump housing 1 with a piston chamber 4 formed inside and an inlet flow valve 5 and a discharge check valve 6 installed in the piston chamber 4.

Inside the housing 1, there is provided a piston which is made up by a piston head 2 and a piston rod 3. In the housing 1 there is also formed a housing volume 7 behind the piston head 2, i.e. the housing volume 7 on the opposite side of the piston head 2 than the piston chamber 4. The piston head 2 is provided to reciprocate along a longitudinal axis in the piston chamber 4 to compress fluid in the chamber 4 to an elevated pressure.

Liquidised fluid is drawn from a fluid chamber 9 into the piston chamber 4 through the inlet fluid channels 5 and the inlet valve 8 as the piston 2 is retracted therein and the liquid in the piston chamber 4 is then pressurised as the piston head 2 is advanced and the pressurised liquid is then discharged through the discharge valve 6. In order to ensure that the liquid does not escape from the piston chamber 4 into the housing volume 7 as the pressure is building up in the piston chamber 4 (and thereby the pressure difference between the piston chamber 4 and the housing volume 7 increases), first sealing means 21 are provided on the piston head 2 between an inner circumferential surface of the piston chamber 4 and said piston head 2. These first sealing means 21 may be piston rings annularly disposed around the piston head 2.

At the low pressure end of pump, in the housing 1 opposite of the piston chamber 4 there are provided second sealing means 30 between the piston rod 3 and a bore 10 of the pump housing 1. The second sealing arrangement 30 comprises a pressurised sealing arrangement 31 provided in the bore 10 of the housing 1 between at least two sealing rings 33, 34.

In fig. 2 a more detailed view of the low pressure end is shown of the second sealing means according to an embodiment of the invention. As shown in fig. 2, the housing is provided with two pressurised sealing arrangements 30 that each comprise an annular groove 35 in the bore 10. Each of the pressurised sealing arrangements 30 further comprise an inlet 31 and an outlet 32 for pressurised fluid, such as oil, and a pressurised fluid source 36 for the provision of pressurised fluid in a fluid flow to the inlets 31 via fluid lines 38. From the outlets 32, return fluid flow lines 39 are provided between the outlet 32 and the pressurised fluid source 36 to form a closed fluid system. The return fluid lines 39 are joined and a filter 37 is provided in the return fluid flow to remove any contaminants from the fluid. The pressurised fluid source includes a pressure booster 36, whereby the pressurised fluid is supplied to the inlet 31 of the pressurised sealing arrangements 30 at an elevated pressure, such as 1 bar above the supply pressure of the cryogenic fluid (P _g as + 1 bar). The pressure booster 36 is also connected to the housing volume 7 via the fluid line 40, and thereby the fluid is supplied at the pressure Pgas of the cryogenic fluid.

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

In the embodiment shown in figures 1 and 2, the second sealing arrangement comprises at least two pressurised sealing arrangements 30 mounted between sealing rings 33 and 34 on both sides of the pressurised sealing arrangements 30.

By the second sealing arrangement further pressurised fluid canals 35 may be provided not only for sealing, but also for lubrication of the piston rod 3, which is reciprocating in the bore 10 of the housing 1. The fluid canals 35 are provided annularly in the bore 10 of the sealing housing 1A. Each of the canals 35 are provided with a fluid inlet 31 and a fluid outlet 32. On each side of the pressurised sealing 30 sealing rings 33 and 34 are provided in order to constrain the oil in the sealing arrangement 30. The fluid inlet 31 is fed with pressurised fluid, such as oil, through a one-way valve 31A in the inlet 31. The outlet 32 is preferably positioned opposite the inlet 31 and is also provide with a one-way valve 32A. Hereby, the fluid flow is regulated. In the embodiment shown in figure 1 and 2, the two sealing arrangements 30 are provided and the two inlets 31 receive pressurised fluid from a pressure booster 36 via fluid lines 38. The pressure is elevated to ensure that the oil seal is maintained between the piston rod 3 and the bore 10.

In fig. 3, a detailed view of the high-pressure end of the piston pump of fig. 1 is shown, where the piston chamber 4, the inlet flow valve 8 and the discharge valve 6 are provided. The pump housing 1 is provided with a fluid chamber 9 annularly arranged around the piston chamber 4. The inlet flow valve 8 and the discharge check valve 6 are provided in the housing 1 for supplying fluid from the fluid chamber 9 to the piston chamber 4 through the inlet valve 8 and discharging said fluid at an increased pressure from the piston chamber 4 through the discharge check valve 6. As explained in relation to fig. 1, the piston has a piston head 2 and a piston rod 3 and the piston head 2 is provided to reciprocate along a longitudinal axis in the piston chamber 4 to compress fluid in the chamber 4 to an elevated pressure.

The fluid in the annular fluid chamber 9 is under a certain pressure and flows through evenly angularly space apart inlet flow channels 5 towards openings in these channels 5. The inlet flow valve arrangement 8 comprises an annular inflow space 51 concentrically with the fluid chamber 9 and having a shared wall 52 with said fluid chamber 9 and in which shared wall 52 the fluid channels 5 are provided so that fluid communication between the fluid chamber 9 and the annular inflow 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 inflow space 51. A valve plate 81 is provided in the inflow space 51 and spring- loaded so that said valve plate 81 is biased towards the shared wall 52 by the spring force and thereby blocking the flow in the fluid channels 5 by blocking the fluid openings on the inflow space side of the shared wall 52.

The valve plate 81 is ring-shaped. The shared wall 52 is also ring-shaped and provided concentrically with the longitudinal axis. The spring-loading of the valve plate 81 is provided by a plurality of springs 82 (see fig. 3) providing a spring force in the axial direction against the flow direction in the fluid channels 51 as shown in fig. 3. In some preferred embodiments, the springs 82 are coil springs. In the housing 1, the annular inflow space 51 is formed integrated with the piston chamber 4 and the fluid flow in the inflow space 51 will be a radially inwardly flow into the piston chamber 4.

This spring force is such that the valve plate 81 is biased towards closing the fluid flow through the fluid channels 5, but when the piston head 2 is retracted in the piston chamber 4 and the pressure thereby drops in the chamber 4, the pressure from the fluid in the fluid chamber 9 forces the valve plate 81 backwards and loading the springs 82 whereby the inlet valve arrangement 8 opens. When the piston head 2 is advanced again in the piston chamber, the pressure in the chamber 4 increased and the valve plate 81 is then immediately forced back in the closing 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 piston 2, 3.

The discharge check valve 6 comprises a valve head 61, which is biased towards a valve seat 62 formed in the housing 1. The valve head 61 is subjected to a spring force in the axial direction towards the piston chamber 4. When the pressure in the piston chamber 4 exceeds a certain threshold, the spring force forcing the valve head 61 towards the valve seat 62 is overcome and the valve head 61 is moved backwards from the closed position to an open position whereby the fluid from the piston chamber 4 is discharges through the discharge check valve 6 at an elevated pressure relative to the pressure in the fluid chamber 9.

The steps in the cycle of the piston pump are shown step by step in the figures 4 to 6.

In fig. 4 the step of suction of fluid into the piston chamber 4 is illustrated. The inlet valve 8 is opened as the valve plate 81 is forced forward and fluid flows into the piston chamber 4 as illustrated by the arrows Fi.

This is due to the piston head 2 travelling backward and creates a lower pressure in the piston chamber 4. This lower pressure causes the inlet valve plate 81 to open and move against the springs 82 and the liquid will flow into the piston chamber 4 until the piston head 2 reaches the bottom position, i.e. the most retracted position.

In fig. 5, this position is shown where the piston head 2 is at the bottom position and fluid has entered the piston chamber 4. The piston 2 will now start to move forward again as piston chamber 4 is now charged. This causes the inlet valve plate 81 to close and a high pressure will be built up in the piston chamber during piston travel. In fig. 6, the step of discharging is shown. The piston 2 travels forward and makes a high pressure in the cylinder 4. This causes the outlet valve 6 to open and move against the springs 63. The fluid will flow out of the piston chamber 4 until the piston 2 reached top position. This discharge flow is illustrated by the arrows F _o . The outlet valve 6 will close again as soon as the piston head 2 starts to retract again.

In the present disclosure, the term "discharge check valve" is used for a nonreturn valve, i.e. a one-way valve that normally allows fluid to flow through it in only one direction.

Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms "comprising" or "comprises" do not exclude other possible elements or steps. Also, the mentioning of references such as "a" or "an" etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.

Above, the invention is described with reference to some currently preferred embodiments. However, by the invention it is realised that other embodiments and variants may be provided without departing from the scope of the invention as defined in the accompanying claims.