Cryogenic Fluid Dispensing System and Method

Abstract

A system for dispensing a cryogenic fluid includes a bulk tank configured to contain a supply of a cryogenic liquid, a first sump and a first liquid feed valve configured to direct liquid from the bulk tank to the first sump when in an open condition and to prevent transfer of liquid from the bulk tank to the first sump when in a closed condition. A first positive displacement pump is positioned within the first sump and configured to pump and be submerged in cryogenic liquid when the first sump contains cryogenic liquid above a predetermined liquid level within the first sump. A delivery line is in fluid communication with an outlet of the first positive displacement pump and is configured to direct cryogenic fluid from the first positive displacement pump to a use device when the first positive displacement pump is activated.

Claims

1. A system for dispensing a cryogenic fluid comprising: a. a bulk tank configured to contain a supply of a cryogenic liquid; b. a first sump; c. a first liquid feed valve configured to direct liquid from the bulk tank to the first sump when in an open condition and to prevent transfer of liquid from the bulk tank to the first sump when in a closed condition; d. a first positive displacement pump positioned within the first sump and configured to pump and be submerged in cryogenic liquid when the first sump contains cryogenic liquid above a predetermined liquid level within the first sump; e. a delivery line in fluid communication with an outlet of the first positive displacement pump, said delivery line configured to direct cryogenic fluid from the first positive displacement pump to a use device when the first positive displacement pump is activated.

2. The system of claim 1 further comprising a first vapor return valve configured to direct vapor from the first sump to the bulk tank when in an open condition and to prevent transfer of vapor from the first sump to the bulk tank when in a closed condition.

3. The system of claim 1 further comprising: f. a second sump; g. a second liquid feed valve configured to direct liquid from the bulk tank to the second sump when in an open condition and to prevent transfer of liquid from the bulk tank to the second sump when in a closed condition; h. a second positive displacement pump positioned within the second sump and configured to pump and be submerged in cryogenic liquid when the second sump contains cryogenic liquid above a predetermined liquid level within the second sump; and wherein the delivery line is in fluid communication with an outlet of the second positive displacement pump, said delivery line configured to direct cryogenic fluid from the second positive displacement pump to a use device when the second positive displacement pump is activated.

4. The system of claim 3 further comprising a second vapor return valve configured to direct vapor from the second sump to the bulk tank when in an open condition and to prevent transfer of vapor from the second sump to the bulk tank when in a closed condition.

5. The system of claim 3 wherein the first and second positive displacement pumps are two-stage positive displacement pumps configured to deliver vapor.

6. The system of claim 3 wherein the first and second positive displacement pumps are single stage positive displacement pumps and wherein the delivery line includes a vaporizer.

7. The system of claim 1 wherein the delivery line includes a vaporizer.

8. The system of claim 7 further comprising a buffer tank configured to selectively receive and store vapor from the vaporizer and to selectively deliver pressurized vapor to a headspace of the first sump.

9. The system of claim 1 wherein the first positive displacement pump is a single stage positive displacement pump.

10. The system of claim 9 wherein the deliver line includes a vaporizer.

11. The system of any of the preceding claims wherein the bulk tank includes an inner vessel and an outer jacket with vacuum insulation therebetween.

12. The system of claim 1 further comprising a liquid level sensor configured to determine a liquid level within the first sump.

13. The system of claim 1 further comprising a pressure sensor configured to determine a pressure within a top portion of the first sump.

14. The system of claim 13 further comprising a temperature sensor configured to determine a temperature of cryogenic liquid within the first sump.

15. The system of claim 1 further comprising a sump pressure building circuitry including a pressure building heat exchanger configured to selectively receive and vaporize liquid from the first sump and deliver vapor to a headspace of the first sump.

16. A method for dispensing cryogenic fluid comprising the steps of: a. transferring cryogenic liquid from a bulk tank to a first sump so that a first positive displacement pump within the first sump is submerged in the cryogenic liquid; b. isolating liquid in the first sump from liquid in the bulk tank; c. activating the first positive displacement pump; d. building pressure within the first sump using heat from the first positive displacement pump so that cryogenic liquid within the sump is subcooled; e. pumping cryogenic fluid from the first sump using the first positive displacement pump.

17. The method of claim 16 wherein the cryogenic fluid includes hydrogen.

18. The method of claim 16 wherein the pumped cryogenic fluid is subcooled cryogenic liquid and further comprising the step of vaporizing the pumped subcooled cryogenic liquid.

19. The method of claim 16 further comprising the steps of: f. transferring cryogenic liquid from the bulk tank to a second sump so that a second positive displacement pump within the second sump is submerged in the cryogenic liquid during step e.; g. isolating liquid in the second sump from liquid in the bulk tank.

20. The method of claim 19 wherein the cryogenic fluid includes hydrogen.

21. The method of claim 19 wherein step f includes transferring vapor from the second sump to the bulk tank.

22. The method of claim 16 wherein step a. includes transferring vapor from the first sump to the bulk tank.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 is a schematic of a first embodiment of the cryogenic fluid dispensing system of the disclosure;

[0016] FIG. 2 is a schematic of a second embodiment of the cryogenic fluid dispensing system of the disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

[0017] A first embodiment of the cryogenic fluid dispensing system of the disclosure is indicated in general at 4 in FIG. 1. While the embodiments of the disclosure are presented below as hydrogen refueling stations for fuel cell vehicles, it is to be understood that the technology may be used to dispense alternative cryogenic fluids, either as gases or liquids, in alternative applications.

[0018] A bulk liquid storage tank, indicated in general at 6, includes an inner tank or vessel 8 surrounded by an outer jacket 10. The inner vessel 8 contains a supply of liquid hydrogen 12. The space 14 between the inner vessel and outer jacket 10 is preferably vacuum insulated, and while not shown, the bulk liquid storage tank 6 includes a refilling port so that the tank may be refilled with liquid hydrogen. A liquid feed line 16 includes a liquid feed valve 18 having an inlet that is in fluid communication with the bottom portion or liquid side of the bulk tank 12. A vapor return line 22 includes a vapor return valve 24 having an outlet that is in fluid communication with the top portion or head space 26 of the bulk tank. Alternatively, the return line 22 may be configured to the wall area of the bottom head of the inner vessel 8 such that a thermo-siphon style feed to the sump is established.

[0019] A sump, indicated in general at 30, includes a liquid inlet port 32 that is in fluid communication with the outlet of the liquid feed valve 18 and a vapor outlet port 34 that is in fluid communication with the inlet of the vapor return valve 24. A liquid level sensor 36 is configured to determine the level of liquid hydrogen in the sump so as to provide an indication when the sump needs to be refilled. As examples only, the liquid level sensor may include a differential pressure gauge of the type illustrated in commonly owned U.S. Pat. Nos. 6,542,848; 6,782,339 and/or 6,944,570 to Neeser et al., the contents of each of which are hereby incorporated by reference.

[0020] The sump may also be provided with a pressure sensor 38 that detects and indicates the pressure in the headspace of the sump 30 and a temperature sensor 42 that detects and indicates the temperature of the liquid in the bottom portion of the sump.

[0021] A positive-displacement pump 44, which may be a single stage pump or a two-stage pump (or a pump with any number of stages), is positioned within the sump and is submerged within liquid hydrogen 46 that is supplied by the bulk tank 6, as will be described below. An inlet of the pump receives the liquid within the sump for pumping. A motor 48, which is typically positioned outside of the sump, drives the pump 44 via a drive rod or shaft 52.

[0022] A fluid delivery line 54 receives hydrogen fluid from the outlet of the pump 44 for dispensing to a vehicle via dispensing connection 56. As will be explained below, the fluid delivery line 54 may be provided with an optional vaporizer 58 that is configured to vaporize hydrogen liquid or to warm cold hydrogen gas. In alternative embodiments, prior to, or instead of, entering the vaporizer, the fluid flow may pass a mixing valve (which may also receive fluid from a buffer tank or other source) or a carbon dioxide heat capacitor.

[0023] The system 4 of FIG. 1 provides a pumping system which generates significant subcool for either a single stage or two-stage pump 44 (or a pump with a greater number of stages) while not adding excessive heat to the main bulk tank 6.

[0024] In operation, vapor return valve 24 and liquid feed valve 18 are opened, and liquid hydrogen flows through liquid feed line 16 to the sump. Vapor within the sump interior is either condensed by the entering hydrogen liquid or displaced so as to travel back to the bulk tank head space via vapor return line 22. When the desired level of liquid hydrogen 46 in the sump is reached, as indicated by liquid level indicator 36, valves 18 and 24 are closed so that the liquid within the sump 30 is isolated from the liquid within the bulk tank 6.

[0025] Heat from the pump motor 48 is transmitted by the drive rod 52 into the sump 30. In addition, pump friction and blowby result in substantial heat gains within the sump 30. Rather than sending that heat to the liquid in the bulk tank 6, all pump heat losses are retained within the sump so as to cause an increase in pressure within the sump above the liquid. This increase in pressure is above the saturation pressure corresponding to the temperature of the liquid hydrogen in the sump, and thus causes the liquid hydrogen in the sump to be subcooled. As a result, the system of FIG. 1 uses the pump heat itself to guarantee significant subcool above the liquid within the sump.

[0026] The pressure increase in the sump above the liquid, and thus the amount of subcool of the liquid hydrogen within the sump 30, can be determined and controlled by using the temperature sensor 42 to determine the saturation temperature (Tsat) of the hydrogen liquid in the sump. As is known in the art, the corresponding saturation pressure of the liquid hydrogen (Psat) at that temperature may be determined. The pressure (Psump) within the sump over the liquid hydrogen may be determined using pressure sensor 38. As a result, Subcool=Psump−Psat gives the pressure increase, and thus the subcool, of the liquid hydrogen within the sump.

[0027] With reference to FIG. 1, the system may optionally include provisions to apply additional pressure to the vapor phase/headspace of the sump to increase the subcool of the liquid in the sump. Such pressure building typically would only be needed when the liquid within the sump is hot and the pump 44 is idled. Normal heat generated by the pump will typically ensure adequate subcool. As an example only, an optional high pressure hydrogen gas storage buffer tank 102 may receive gas from the system via line 104 when valve 106 is opened. High pressure gas from the buffer tank 102 may be provided to the headspace to the sump for pressure building via line 108 by opening valve 112 (while valve 106 is closed). As another example, an optional pressure building circuit 122 may be provided. The pressure building circuit 122 includes a pressure building heat exchanger 124 with an inlet valve 126 and an outlet valve 128. When the valves 126 and 128 are opened, and valves 18 and 24 are closed, liquid from the bottom of the sump is vaporized in the pressure building heat exchanger 124 with the resulting vapor introduced into the sump headspace. Dedicated pressure building inlet an outlet ports may alternatively be provided for the sump in place of sharing liquid inlet and vapor outlet ports 32 and 34 with valves 18 and 24.

[0028] If the pressure within the headspace of sump 30 becomes too great, valve 24 may be opened for venting or pressure safety valves (not shown) may be provided and opened to relieve pressure within the sump.

[0029] With the pump activated and the hydrogen liquid in the sump 30 in a subcooled state, when the positive displacement pump 44 is a single stage pump, subcooled liquid hydrogen 46 from the sump is directed through the delivery line 54 to the vaporizer 58, where it is vaporized. The resulting vapor is then delivered to a fuel tank onboard of a fuel cell vehicle via dispensing connection 56. When the positive displacement pump 44 is a two-stage pump whereby hydrogen gas is provided, hydrogen gas travels through delivery line 54 to the dispensing connection 56 for refueling of the vehicle (the vaporizer 58 is not required unless warming of the gas is desired).

[0030] The sump is designed such that the liquid capacity of the sump provides a reasonable duty cycle for delivery. Once the sump 30 is near empty of liquid hydrogen, pumping is terminated so that the sump is offline. The sump 30 may then be re-equilibrated with the main tank and refilled by opening valves 18 and 24.

[0031] An embodiment of the system of the disclosure wherein continuous, or nearly continuous, dispensing of hydrogen is indicated in general at 60 in FIG. 2. This system is similar to the system of FIG. 1 with the exception that two sumps, indicated in general at 62a and 62b, are provided. The construction of each of the sumps 62a and 62, and the corresponding components, matches sump 30 of FIG. 1.

[0032] In one mode of operation, sump 62a is filled with liquid hydrogen from bulk tank 6 by opening liquid feed valve 64a and vapor return valve 66a that are in fluid communication with lines 16 and 22. As for the sump of FIG. 1, the valves are closed to terminate the fill. The pump 68a is then activated so that subcool is created in the sump and subcooled liquid hydrogen (if the pump is a single stage pump) is directed to vaporizer 72 via delivery line 74. As a result, hydrogen gas is dispensed to a vehicle through dispensing connection 76. If pump 68a is a two-stage pump whereby hydrogen gas is created, the vaporizer 72 may be omitted unless warming of the gas is desired.

[0033] After the liquid feed and vapor return valves 64a and 66a for sump 62a are closed, corresponding valves 64b and 66b are opened so that sump 62b is filled with liquid hydrogen from bulk tank 6. The valves are closed when the liquid within the sump 62b reaches the desired level. As a result, when sump 62a requires refilling, pump 68b may be activated to pump subcooled liquid hydrogen or hydrogen gas from sump 62b so that dispensing of hydrogen by the refueling station is not interrupted as sump 62a is refilled. Sump 62a may be refilled as dispensing of hydrogen from sump 62b occurs.

[0034] The systems of the disclosure may include the benefits of reduced heat load to the main bulk tank, and consequently less heat venting by the system, as well as the generation of higher subcool with a positive displacement pump, where the pump benefits by the higher subcool. There may also be benefits in volumetric efficiency and system venting even for two-stage positive displacement pumps. System analysis of embodiments shows overall thermodynamic advantages where more heat is delivered to the customer and system venting is minimized. Furthermore, the main tank pressures may be at low pressures without the need for venting, assuming sufficient station utilization.

[0035] While the preferred embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made therein without departing from the spirit of the invention.