WO2025003763A1

WO2025003763A1 - Design and method to improve performance of cryogenic pump

Info

Publication number: WO2025003763A1
Application number: PCT/IB2024/000360
Authority: WO
Inventors: Joshua Light; Jerry Hayes
Original assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Current assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date: 2023-06-27
Filing date: 2024-06-27
Publication date: 2025-01-02
Anticipated expiration: 2025-12-27

Abstract

An apparatus and method for storage of a liquid cryogen, particularly liquid hydrogen, is provided. The apparatus may include: a cryogenic pump (20) positioned to receive the liquid cryogen from a liquid cryogen storage tank (10), wherein the cryogenic pump (20) comprises: a piston ring leak conduit (24) in fluid communication with a piston ring leak outlet (23) on the cryogenic pump (20) and the headspace (5) of the liquid cryogen storage tank (10); a piston ring leak check valve (17) disposed on the piston ring leak conduit (24); a piston ring leak vent valve (40) in fluid communication with the piston ring leak conduit (24); a pump discharge conduit (22) in fluid communication with the pump discharge outlet (21); and a pump discharge vent valve (19) in fluid communication with the pump discharge conduit (22).

Description

DESIGN AND METHOD TO IMPROVE PERFORMANCE OF CRYOGENIC PUMP

Cross Reference of Related Applications

This patent application claims priority to U.S. Provisional Patent Application Serial No. 63/523,528 filed on June T1 , 2024, which is hereby incorporated by reference in its entirety.

Technical Field of Invention

Embodiments of the invention relate to apparatuses and methods for cooling a pump during start-up, as well as improving pump efficiencies during operation. More particularly, the invention is particularly useful in handling a cryogenic fluid (e.g., liquid hydrogen, liquid oxygen, liquid nitrogen, liquid helium, etc.).

Background of the Invention

Before a cryogenic pump can transfer cryogenic liquid from a low-pressure storage tank to a high-pressure storage tank, the pump must be cooled to the appropriate cryogenic temperature to minimize liquid vaporization before reaching the internal cavities of the pump. This is because a cry ogenic pump generally does not function well with vapor or a mixture of liquid and vapor.

One method of addressing this issue is to submerge the pump in a low-temperature fluid to maintain it at liquid hydrogen temperature. Other ideas have included continuous delivery of cryogenic liquid through the pumping system in order to maintain the pump internals at cryogenic temperatures.

FIG. 1 provides an embodiment of a typical liquid hydrogen pumping system 2. During normal operation of liquid hydrogen pumps 20, liquid hydrogen 7 flows from the bottom of a storage tank 10 through a supply leg 12 of the suction piping to the pump 20. The return leg 14 of the suction piping allows vapor to flow to the gaseous headspace 5 of the hydrogen vessel. The liquid hydrogen then exits the pump 20 via the discharge outlet 21, and is ultimately discharged via the discharge line 22. Storage tank 10 preferably includes a double-walled enclosure with the interior portion 9 between the inner and outer walls being under a vacuum.

During cooldown procedure of the pump 20, the pump is not actively pumping. However, the supply leg 12 and return leg 14, as well as the internals of the pump need to be cooled down. In order to cool these components down, one option has been to initially open valve 13 and valve 15, in order to cool the supply and return legs (12, 14). Discharge vent valve 19 is then subsequently opened in order to allow liquid hydrogen to flow through the pump internals and out the discharge line 22. The driving force for this flow being simple pressure gradients since the tank is elevated and at higher pressure.

While this technique is somewhat effective, it still is not ideal for cooling all of the pump components. Namely, the areas behind the piston rings (area of the pump to the left of the discharge outlet 21). Therefore, it would be advantageous to provide for a method and apparatus that could improve upon this setup during a cooldown phase.

During normal operation, heat is generated from several sources, and this heat will warm the liquid hydrogen. At localized points the amount of heat is enough to vaporize liquid hydrogen into gaseous hydrogen. The gaseous hydrogen must be removed from the suction of the pump so that the pump can draw liquid hydrogen. The suction return line 14 provides a path for the gaseous hydrogen to rise to the top of the storage tank due to the density difference between liquid hydrogen and the gaseous hydrogen. Unfortunately, as the pump continues to run, heat and pressure will continue to build up, thereby lowering the efficiency of the pump. Therefore, it would be advantageous to provide for a method and apparatus that could improve the pump’s efficiency, particularly during normal operation.

Summary of the Invention

The present invention is directed to an apparatus and method that satisfies at least one of these needs. In certain embodiments of the invention, a method for improving the operation of the pump is provided. For example, the pumping system may include the addition of a ring leak discharge line that is configured to allow any gases that get behind the piston rings to exit the internal area of the pump. By removing these otherwise trapped gases, the backpressure is lowered, which improves the overall efficiency of the pump, since the retract stroke (i.e., suction phase of the stroke) encounters less resistance due to the trapped gases.

In a preferred embodiment, an apparatus for storage of a liquid cryogen is provided, in which, the apparatus may include: a) a cryogenic pump positioned to receive the liquid cryogen from a liquid cryogen storage tank, wherein the cryogenic pump comprises: i. a pump discharge outlet for a pump discharge conduit through which liquid is passable out of the cryogenic pump; ii. piston rings positioned within the cryogenic pump, wherein the piston rings are configured to limit the flow of gaseous cryogen within the cryogenic pump from passing by the piston rings; iii. a piston ring leak outlet configured to allow for the gaseous cryogen that has moved past the piston rings to be withdrawn from the cryogenic pump; iv. a liquid cryogen inlet configured to receive liquid cryogen from the liquid cryogen storage tank; v. a gaseous return leg configured to transfer a portion of the gaseous cryogen within the cry ogenic pump to a headspace of the liquid cry ogen storage tank; b) a piston ring leak conduit in fluid communication with the piston ring leak outlet and the headspace of the liquid cryogen storage tank; c) a piston ring leak check valve disposed on the piston ring leak conduit, wherein the piston ring leak check valve is configured to prevent flow of gaseous cryogen from the liquid cryogen storage tank from flowing towards the piston ring leak outlet; d) a piston ring leak vent valve in fluid communication with the piston ring leak conduit; e) a pump discharge conduit in fluid communication with the pump discharge outlet; and f) a pump discharge vent valve in fluid communication with the pump discharge conduit.

In optional embodiments of the apparatus:

• the apparatus may also include a temperature sensor disposed on the pump discharge conduit configured to measure a temperature within the pump discharge conduit;

• the apparatus may also include a flow meter disposed on the pump discharge conduit configured to measure a flow rate within the pump discharge conduit;

• the apparatus may also include a piston ring leak temperature sensor disposed on the piston ring leak conduit configured to measure a temperature within the piston ring leak conduit;

• the apparatus may also include means for cooling down the cryogenic pump when the cryogenic pump is in a non-operational mode, wherein the means for cooling down the cryogenic pump comprise: a controller that includes a processor and memory coupled to the processor, the memory storing instructions that, when executed by the processor, cause the processor to perform operations comprising: setting the piston ring leak vent valve to an open position, comparing the temperature within the piston ring leak conduit to a predetermined set point, and closing the piston ring leak vent valve once the temperature within the piston ring leak conduit reaches or falls below the predetermined set point;

• the apparatus may also include means for monitoring a pump efficiency of the cryogenic pump;

• the means for monitoring the pump efficiency comprises a controller that includes a processor and memory coupled to the processor, the memory storing instructions that, when executed by the processor, cause the processor to perform operations comprising: determining whether the cry ogenic pump is operating within a targeted efficiency range, and adjusting the piston ring leak vent valve to an open or closed position based upon the determination whether the cr ogenic pump is operating within the targeted efficiency range;

• the step of determining whether the cry ogenic pump is operating within a targeted efficiency range includes: o receiving operational data from at least one of the following: a temperature sensor disposed on the pump discharge conduit configured to measure a temperature within the pump discharge conduit; a flow meter disposed on the pump discharge conduit configured to measure a flow rate within the pump discharge conduit; and/or a piston ring leak temperature sensor disposed on the piston ring leak conduit configured to measure a temperature within the pump discharge conduit; and o comparing the operational data to a predetermined range, wherein when the operational data is outside of the predetermined range, the processor proceeds to a secondary mode of operation in which the piston ring leak vent valve is set to an open position, wherein when the operational data is within the predetermined range, the processor proceeds to a primary mode of operation in which the piston ring leave vent valve is set to a closed position; and/or

• the liquid cryogen is liquid hydrogen.

In another embodiment, a method for improving the operation of a cryogenic pump is provided, in which the method may include the steps of: providing any of the apparatuses as described herein; wherein the method includes a cool down mode of operation, a primary mode of operation, and a secondary mode of operation, wherein during the cool down mode of operation, the cry ogenic pump is in a non-operative state, and the piston ring leak vent valve is set to an open position thereby allowing gaseous cryogen to flow past the piston ring, through the piston ring leak conduit and then vented to the atmosphere, wherein during the primary mode of operation, the cry ogenic pump is in an operative state, and the piston ring leak vent valve is set to a closed position, wherein during the secondary mode of operation, the cryogenic pump is in the operative state, and the piston ring leak vent valve is set to the open position.

In optional embodiments of the method:

• the apparatus further comprises: a controller that includes a processor and memory coupled to the processor, the memory storing instructions that, when executed by the processor, cause the processor to perform operations comprising: switching between the cool down mode of operation, the primary' mode of operation, and the secondary mode of operation;

• the controller is configured to receive operational data from at least one of the following: a temperature sensor disposed on the pump discharge conduit configured to measure a temperature within the pump discharge conduit; a flow meter disposed on the pump discharge conduit configured to measure a flow rate within the pump discharge conduit; and/or a piston ring leak temperature sensor disposed on the piston ring leak conduit configured to measure a temperature w ithin the pump discharge conduit; • the controller is further configured to compare the operational data to a predetermined range, wherein when the operational data is outside of the predetermined range, the processor proceeds to the secondary mode of operation, wherein when the operational data is within the predetermined range, the processor proceeds to the primary mode of operation in which the piston ring leave vent valve is set to a closed position;

• the controller is configured to switch from the cool down mode of operation to the primary mode of operation upon a determination that the temperature within the piston ring leak conduit has reached or falls below a predetermined setpoint; and/or

• the liquid cryogen is liquid hydrogen.

Brief Description of the Drawings

These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments of the invention and are therefore not to be considered limiting of the invention’s scope as it can admit to other equally effective embodiments.

FIG. 1 provides an embodiment of a pumping system in accordance with an embodiment of the prior art.

FIG. 2 provides an embodiment of the present invention.

Detailed Description

While the invention will be described in connection with several embodiments, it will be understood that it is not intended to limit the invention to those embodiments. On the contrary, it is intended to cover all the alternatives, modifications and equivalence as may be included within the spirit and scope of the invention defined by the appended claims. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer’s specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary⁷ skill in the art having the benefit of this disclosure.

Piston ring leak:

The piston rings act as a restriction to retain hydrogen in the cylinder as the piston extends and forces the hydrogen to a high pressure. Although it is a restriction, the piston rings are not a perfect seal, and while the liquid hydrogen is pumped, some of the fluid pushes past the piston rings. Traditionally, this fluid is routed through chambers of the cold end back to the suction piping 14 where the vapor can rise through the return leg of the suction piping. However, this is not ideal since the added gaseous hydrogen sent to the storage tank 10 can have poor flow rates due to higher-pressures in the storage tank 10. As such, the flow of this gas will only proceed once the pressure of the leaked gas exceeds the pressure within the headspace 5 of the storage tank 10.

Pump performance is heavily dependent on the conditions of the fluid entering the pump and on the pump’s design, running hours, and the initial temperature of the pump cold end at the beginning of the pump run. The pump design and running hours of the pump are variables that cannot be manipulated. In order for the pump to perform as well as possible, the startup sequence, which sets the initial temperature of the pump cold end, and the fluid conditions, which is measured as the net positive suction head (NPSH), should be optimized. When the pump is operating near the minimum NPSH required or the initial temperature of the cold end is not properly established, the pump performs poorly. Performance of the pump may be observ ed by the pump flow rate and the yield of the pump. The pump flow rate can be measured by calculating the amount of mass filled into the destination container, or by employing a flowmeter along the discharge line 22. The yield of the pump may be measured by taking a mass balance on the system. By knowing the amount of hydrogen filled into the final container and the total amount of hydrogen used from the storage tank 10, the yield and the amount of vented hydrogen are determined as shown below.

Total mass used

= mount of hydrogen filled into container + amount of hydrogen vented

Due to the long period of the pump runs (4 to 8+ hours) in a trailer filling process, a significant amount of vapor can reintroduced to the liquid storage tank 10 from the suction return line 14. As vapor is supplied to the storage tank 10, the pressure rises, and the storage tank 10 reaches the setpoint of the economizer valve (spring operated backpressure regulator). When the setpoint of the economizer is reached, the economizer valve opens to maintain a constant pressure in the storage tank 10. All additional gaseous hydrogen that is introduced to the tank from the pump’s suction return line is vented in order to keep the pressure at the economizer’s setpoint pressure. The economizer setpoint pressure generally cannot be raised because it is based on the vessel’s maximum allowable working pressure, which cannot be exceeded for safety purposes. The vented mass represents the amount of hydrogen that is vaporized by the pump, and the amount of hydrogen that is not usable because of running the pump.

In liquid hydrogen pumping, the NPSH is significantly dependent on the pressure in the vessel (HA) and the vapor pressure of the liquid (HVP). Due to the extremely low density of liquid hydrogen, the vertical height of liquid does not contribute materially to the NPSH, and the friction losses and velocity head are also non-material. Because the vapor pressure of the liquid (HVP) and the pressure in the vessel (HA) are often expressed in units of psi, the NPSH for liquid hydrogen will be expressed in units of psi.

As liquid hydrogen absorbs heat, the temperature of the liquid and the associated vapor pressure of the liquid increase. The NPSH is a very important factor impacting the pump performance because it relates to the amount of heat that the hydrogen can absorb before vaporizing. Heat is produced in several ways during the pumping process, and it must be minimized to effectively pump liquid hydrogen.

The sources of heat in liquid hydrogen pumping are (1) initial heat in the pump, (2) heat leak from the cold end and suction piping, (3) friction from the piston rings along the cylinder wall, (4) compression of gaseous hydrogen, (5) warm gaseous hydrogen from the piston ring leak mixing with the liquid at the suction of the pump, and (6) other sources (compressibility of liquid hydrogen, ). Sources 2, 3, 5, and 6 are defined by the pump design and the running hours, and they cannot be manipulated. Source 3 (the amount of gas being compressed in the cylinder during the pumping stroke) can be controlled by operating the pump at the appropriate NPSH and removing heat prior to startup.

In the traditional startup sequence, the internals of the pump are mostly cooled during the unloaded pumping period (3 min) during which liquid hydrogen is pushed through the pump cylinder to the vent 19. Performance of the pump suggests that this cooling period is not sufficient because the pump performs much better when provided with additional cooling. Due to the drastic temperature difference between the initial pump temperature and liquid hydrogen, the pump must remain at liquid hydrogen temperatures for a period longer than 3 minutes to allow the thermal gradient to reach equilibrium; otherwise, much of the heat initially in the pump is not removed. If the heat is not removed, it will be absorbed by hydrogen in the midst of the pumping process, which increases the heat gain of the hydrogen and equally increases the NPSH required.

Adhering to the NPSH requirement for the liquid hydrogen pump is important to ensure that gaseous hydrogen is not present in the pumping process. Once the pump begins operating with NPSH available (NPSHA) below the NPSH requirement (NPSHR), an increased amount of gaseous hydrogen is present in the pump cylinder. The excess gas creates heat by the additional heat of compression, and the excess gas increases the amount of flow past the piston rings. The heat of compression warms the pump cylinder and the remnant hydrogen and increases the amount of heat that the incoming liquid hydrogen needs to absorb in the next stroke (increases the NPSH required for the next stroke).

The gaseous hydrogen in the cylinder creates more flow through the piston rings because the gaseous hydrogen is less viscous than liquid hydrogen, which allows it flow through the piston rings at a greater rate. Depending on the design of the pump, the additional piston ring leak (1, traditional design) sends more warm gaseous hydrogen to the the suction of the pump where is mixes with the liquid hydrogen and raises the temperature / vapor pressure of the liquid hydrogen at the pump suction (e.g, where lines 12 and 14 meet the pump 20). which decreases the NPSH available, and then the warm gaseous hydrogen introduces heat to the bulk liquid hydrogen in the vessel by flowing back to the vessel through the suction return line 14.

Alternately (third port design 23), the additional warm gaseous hydrogen from the piston ring leak flows directly back to the storage tank 10 via line 24 and introduces heat into the vessel where it raises the temperature / vapor pressure of the bulk liquid hydrogen. In order to prevent continually worsening performance, the pump should be stopped when the NPSH available is less than the NPSH required, and the liquid hydrogen should be conditioned to decrease the temperature I vapor pressure of the liquid. Operating with proper NPSH (NPSHA > NPSHR) will increase the longevity of the cold end and maximize yield.

Test data using this embodiment has shown to the pump to have a yield between 90% and 50% depending on the hours of service (0 hours -90% yield; -700 hours -50% yield) and the average flow rate for was 33 kg/hr.

Fig. 2 provides an embodiment of the present invention. In this embodiment, the pump 20 may include a piston ring leak outlet 23 that is disposed behind the piston rings. Further, a piston ring leak conduit 24 can be attached to the piston ring leak outlet 23 in order to route the leaked gas to the headspace of the storage tank.

In another embodiment, the addition of the piston ring leak vent valve 40 allows the piston ring leak to be vented. In order to prevent hydrogen from the tank from being vented, a piston ring leak check valve 17 can be implemented on piston ring leak conduit 24 at a location disposed after the vent valve 40. Operation of this piston ring leak vent valve 40 releases hydrogen behind the piston rings to the vent to the atmosphere, thereby creating an area of low pressure behind the piston rings. The piston rings are a severe restriction to flow, as designed, so the area behind the piston rings stays at a low- pressure as long as the piston ring vent valve 40 is open. This is a new flow path that has not been utilized in prior art such as FIG. 1, and utilization of this feature during cool dow n and pump operation improves performance of the pump.

Cooldown The piston ring vent valve should be opened during the cool down period of the pump startup sequence. The effect is that a pressure differential is created between the suction piping and the area behind the piston rings, which drives a small flow of hydrogen through the flow path. Liquid hydrogen is drawn into the pump cylinder for a significant period of time, which allows the internals of the pump to reach thermal gradient equilibrium with the liquid hydrogen, unlike the 3-minute period that is typically used to cool down the pump internals. As the liquid hydrogen absorbs heat, it is vaporized and the gaseous hydrogen can flow to the low-pressure area through the piston rings.

Although the flow is small, the cold hydrogen allows the pump’s internal components to soak, which gives appropriate time for the thermal gradient to reach equilibrium. The thermal gradient at equilibrium with liquid hydrogen minimizes heat input from the pump and minimizes flashing of the liquid during pumping, thereby reducing NPSHR. Under otherwise stable conditions, pump internals that are sufficiently cooled have shown a significant impact on flow' rate of the pump, which relates directly to a positive impact on the yield of the pump.

The additional benefits of using this method are that the cool down time may be reduced, and the unloaded pumping time may be reduced. In certain embodiments, a fifteen-minute period for cool down was established to allow for sufficient thermal gradient. In the traditional step, the pump w as not directly cooled, and the cooling only occurred indirectly through conduction. This took an extremely long time and was not effective. With the flow of hydrogen through the pump, all components are in direct contact with liquid hydrogen, so the distance for conductive heat transfer is much smaller. Because of this, much less time is required to reach a thermal gradient equilibrium. Next, the period of running the pump unloaded is reduced. Traditionally, the period of running the pump unloaded is when the internal components of the pump first interact with liquid hydrogen and are cooled dramatically. The liquid hydrogen used in the unloading period is vented directly and the flow rate is at 100% volumetric efficiency of the pump. As an example, existing pumps might typically vent 4.5 kg of hydrogen per pump start. With the aforementioned process of using the piston ring vent valve 40 during cool down, there is very little benefit to the three minute unloading period. This unloaded period could be reduced to ~15 seconds, which is sufficient time for the motor to come up to speed before putting the load of discharge pressure on the pump motor.

There are a couple of different ways to use the piston ring vent valve for cool down:

(1) The piston ring vent valve 40 can be used to minimize the amount of liquid hydrogen vaporized during cool down. The valve 40 may be opened in conjunction with the suction return line valve 15 in order to allow cold gaseous hydrogen to flow from the top of the tank through the return line and into the pump. This process will remove the majority of heat in the suction piping 14, and heat that is absorbed by the cold gas is vented out of the system through the piston ring vent valve 40. The heat does not vaporize liquid hydrogen and it does not stay in the system. Once the system is sufficiently cooled, the liquid valve 13 can be opened to continue with the normal cool down process.

There are several scenarios when the pump 20 will need to be ready to run at a moment’s notice. Keeping liquid hydrogen on the pump can cause significant ice formation on the pump and add significant heat and pressure rise to the system. The piston ring vent valve 40 can be used to keep the pump 20 cold without these side effects. The heat that leaks into the pump system is absorbed by the cold gaseous hydrogen and flows out of the piston ring vent valve 40. The gaseous hydrogen will not exchange as much heat as liquid due to the lower heat transfer coefficient, which will prevent severe ice buildup on the cold end.

Impact of invention during pump operation

While the pump is running, the piston ring leak vent valve 40 can be opened. The impact of opening the piston ring leak vent valve 40 is that the area behind the piston rings is vented to a low pressure instead of the tank pressure (-100 psig). The lower pressure creates a larger pressure differential across the piston rings. The pressure differential will impact each portion of the stroke.

Extend:

The pressure in the cylinder is building quickly until the pressure reaches the destination pressure at which point the pressure in the cylinder pushes the discharge valve open and hydrogen begins flowing out of the pump cylinder through the discharge outlet 21 . The suction valve is held shut by the high pressure in the cylinder throughout the extend stroke. During this portion of the stroke, the lower pressure behind the piston rings will create a larger pressure differential across the piston rings. The larger pressure difference increases the flow rate across the piston rings, and this is especially relevant to gaseous hydrogen that flows across the piston rings.

Top dead center:

As the pump approaches top dead center, the flow out of the discharge valve slows to a stop. The fluid in the pump cylinder is at the destination pressure (e.g., -6,000 psig). At top dead center, the piston changes direction to begin to retract. Through the process of changing directions the piston rings have a brief period when they are no longer sealing because the face pushing the piston rings changes. When the piston rings are not sealing, some of the remnant fluid (which is warm compared to liquid hydrogen) flows past the piston rings with a very large pressure difference of -6,000 psig. Because the pressure behind the piston rings is minimal (slightly more than 0 psig), the flow rate past the piston rings increases as compared to the area behind the piston rings being routed to the liquid hydrogen vessel. The removal of the remnant fluid from the pump cylinder decreases the amount of heat in the cylinder and equally decreases the amount of NPSHR by the pump.

Retract:

The piston begins retracting creating a pressure lower than the pressure at the suction of the pump. The pressure differential causes the liquid hydrogen at the suction of the pump to push the suction valve open and flow into the pump cylinder. The discharge valve is held closed by the high pressure on the discharge of the pump.

Botom dead center:

As the pump approaches botom dead center, the flow into the suction valve decreases to a stop. The fluid in the pump cylinder is at the vessel pressure (-100 psig). At botom dead center, the piston changes direction to begin the extend stroke. Through the process of changing directions the piston rings have a brief period when they are no longer sealing because the face pushing the piston rings changes. While the piston rings are not sealing, some of the liquid hydrogen flows past the piston rings. When the pump is running well and fluid conditions are suitable, there is no need to utilize the piston ring vent valve 40 while pumping, and due to the losses of hydrogen through the vent, it will not be used unless needed.

However, as the running hours of the pump increase or the NPSH decreases below the NPSHR, the flow rate decreases. The piston ring vent valve 40 can be opened to increase the flow rate of the pump. There will be losses from venting hydrogen, but the increased flow rate and volumetric efficiency may subsequently improve the yield to effectively discount the venting losses. This embodiment provides a significant improvement in flow rate and reduced wear and tear on the pump.

In certain embodiments, the invention may include the use of a controller that is configured to receive operational data from at least one of the following: a temperature sensor (51 ) disposed on the pump discharge conduit (22) configured to measure a temperature within the pump discharge conduit (22); a flow meter (53) disposed on the pump discharge conduit (22) configured to measure a flow rate within the pump discharge conduit (22); and/or a piston ring leak temperature sensor (55) disposed on the piston ring leak conduit (24) configured to measure a temperature within the pump discharge conduit (22).

While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations that fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, language referring to order, such as first and second, should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps or devices can be combined into a single step/device.

The singular forms "a", "an", and "the" include plural referents, unless the context clearly dictates otherwise. The terms about/approximately a particular value include that particular value plus or minus 10%, unless the context clearly dictates otherwise.

Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.

Claims

CLAIMS We claim:

1 . An apparatus for storage of a liquid cryogen, the apparatus comprising: a) a cryogenic pump (20) positioned to receive the liquid cryogen from a liquid cryogen storage tank (10), wherein the cryogenic pump (20) comprises: i. a pump discharge outlet (21) for a pump discharge conduit (22) through which liquid is passable out of the cryogenic pump (20); ii. piston rings positioned within the cryogenic pump (20). wherein the piston rings are configured to limit die flow of gaseous cryogen within the cryogenic pump (20) from passing by the piston rings; iii. a piston ring leak outlet (23) configured to allow for the gaseous cryogen that has moved past the piston rings io be withdrawn from the cryogenic pump (20); iv. a liquid ctyogen inlet configured to receive liquid cryogen from the liquid cryogen storage tank ( 10); v. a gaseous return leg (14) configured to transfer a portion of the gaseous cryogen within the cryogenic pump (20) to a headspace (5) of the liquid cryogen storage tank (10): b) a piston ring leak conduit (24) in fluid communication with the piston ring leak outlet (23) and the headspace (5) of the liquid cryogen storage tank (10); c) a piston ring leak check valve (17) disposed on the piston ring leak conduit (24), wherein the piston ring leak check valve (17) is configured to prevent flow of gaseous cry ogen from the liquid cryogen storage tank (10) from flowing towards the piston ring leak outlet (23); d) a piston ring leak vent valve (40) in fluid communication with the piston ring leak conduit (24); e) a pump discharge conduit (22) in fluid communication with the pump discharge outlet (21); and f) a pump discharge vent valve (19) in fluid communication with the pump discharge conduit (22).

2. The apparatus as claimed in Claim 1, further comprising a temperature sensor (51) disposed on the pump discharge conduit (22) configured to measure a temperature within the pump discharge conduit (22).

3. The apparatus as claimed in Claim 1, further comprising a flow meter (53) disposed on the pump discharge conduit (22) configured to measure a flow rate within the pump discharge conduit (22).

4. The apparatus as claimed in Claim 1 , further comprising a piston ring leak temperature sensor (55) disposed on the piston ring leak conduit (24) configured to measure a temperature within the piston ring leak conduit (24).

5. The apparatus as claimed in Claim 4, further comprising means for cooling down the cryogenic pump (20) when the cryogenic pump (20) is in a non-operational mode, wherein the means for cooling down the cryogenic pump (20) comprise: a controller that includes a processor and memory coupled to the processor, the memory storing instructions that, when executed by the processor, cause the processor to perform operations comprising: setting the piston ring leak vent valve (40) to an open position, comparing the temperature within the piston ring leak conduit (24) to a predetermined set point, and closing the piston ring leak vent valve (40) once the temperature within the piston ring leak conduit (24) reaches or falls below the predetermined set point.

6. The apparatus as claimed in Claim 1, further comprising means for monitoring a pump efficiency of the cry ogenic pump (20).

7. The apparatus as claimed in Claim 6, wherein the means for monitoring the pump efficiency comprises a controller that includes a processor and memory' coupled to the processor, the memory' storing instructions that, when executed by the processor, cause the processor to perform operations comprising: determining whether the cryogenic pump (20) is operating within a targeted efficiency range, and adjusting the piston ring leak vent valve (40) to an open or closed position based upon the determination whether the cryogenic pump (20) is operating within the targeted efficiency range.

8. The apparatus as claimed in Claim 7, wherein the step of determining whether the cryogenic pump (20) is operating within a targeted efficiency range includes: receiving operational data from at least one of the following: a temperature sensor (51) disposed on the pump discharge conduit (22) configured to measure a temperature within the pump discharge conduit (22); a flow meter (53) disposed on the pump discharge conduit (22) configured to measure a flow' rate within the pump discharge conduit (22); and/or a piston ring leak temperature sensor (55) disposed on the piston ring leak conduit (24) configured to measure a temperature within the pump discharge conduit (22); and comparing the operational data to a predetermined range, wherein w hen the operational data is outside of the predetermined range, the processor proceeds to a secondary mode of operation in which the piston ring leak vent valve (40) is set to an open position, wherein w'hen the operational data is within the predetermined range, the processor proceeds to a primary mode of operation in which the piston ring leave vent valve is set to a closed position.

9. The apparatus as claimed in Claim 1, wherein the liquid cryogen is liquid hydrogen.

10. A method for improving the operation of a cryogenic pump (20), the method comprising the steps of: providing the apparatus as claimed in Claim 1 ; wherein the method includes a cool down mode of operation, a primary⁷ mode of operation, and a secondary⁷ mode of operation, wherein during the cool down mode of operation, the cryogenic pump (20) is in a nonoperative state, and the piston ring leak vent valve (40) is set to an open position thereby allowing gaseous cry ogen to flow past the piston ring, through the piston ring leak conduit (24) and then vented to the atmosphere, wherein during the primary⁷ mode of operation, the cryogenic pump (20) is in an operative state, and the piston ring leak vent valve (40) is set to a closed position, wherein during the secondary mode of operation, the cryogenic pump (20) is in the operative state, and the piston ring leak vent valve (40) is set to the open position.:

1 1. The method as claimed in Claim 10, wherein the apparatus further comprises: a controller that includes a processor and memory' coupled to the processor, the memory storing instructions that, w hen executed by the processor, cause the processor to perform operations comprising: switching between the cool down mode of operation, the primary mode of operation, and the secondary mode of operation.

12. The method as claimed in Claim 11, wherein the controller is configured to receive operational data from at least one of the following: a temperature sensor (51) disposed on the pump discharge conduit (22) configured to measure a temperature within the pump discharge conduit (22); a flow meter (53) disposed on the pump discharge conduit (22) configured to measure a flow rate within the pump discharge conduit (22); and/or a piston ring leak temperature sensor (55) disposed on the piston ring leak conduit (24) configured to measure a temperature within the pump discharge conduit (22).

13. The method as claimed in Claim 12, wherein the controller is further configured to compare the operational data to a predetermined range, wherein when the operational data is outside of the predetermined range, the processor proceeds to the secondary mode of operation, wherein when the operational data is within the predetermined range, the processor proceeds to the primary mode of operation in which the piston ring leave vent valve is set to a closed position.

14. The method as claimed in Claim 12, wherein the controller is configured to switch from the cool down mode of operation to the primary mode of operation upon a determination that the temperature within the piston ring leak conduit (24) has reached or falls below a predetermined setpoint.

15. The method as claimed in Claim 10, wherein the liquid cryogen is liquid hydrogen.