Cryogenic fuel tank venting system and method

Abstract

The cryogenic fuel tank system includes a fuel tank configured to contain a cryogenic liquid such that a headspace above the cryogenic liquid contains cryogenic vapor. A fuel cell converts the cryogenic vapor from the headspace into electricity and water vapor. A vent valve directs excess cryogenic vapor from the headspace to the fuel cell when pressure in the fuel tank exceeds a predetermined pressure level.

Description

[Technical field]

[0001]

[0001] This application claims priority to U.S. Provisional Application No. 63 / 287,690, filed December 9, 2021, the contents of which are incorporated herein by reference.

[0002]

[0002] This disclosure relates generally to tanks of cryogenic liquids, and more particularly to a cryogenic fuel tank venting system and method. [Background technology]

[0003]

[0003] In recent years, concerns about the environment and reducing harmful vehicle emissions have led to a push towards vehicles using fuels other than gasoline, diesel, and / or other petroleum-based fuels. Fuel cells have been identified as a promising alternative fuel technology.

[0004]

[0004] Fuel cells generally convert fuel into electricity that can be used to power vehicles or other devices that utilize batteries and / or motors for operation. Hydrogen fuel cells are becoming increasingly popular because, during operation, hydrogen fuel is mixed with oxygen to produce water, heat, and electricity without emitting other chemicals that are harmful to the environment.

[0005]

[0005] Fuel cells typically consume gaseous hydrogen at high pressure. However, industrial gases such as hydrogen are advantageously stored or transported in a liquid state so that they occupy a much smaller volume. However, storing liquid hydrogen is challenging because it is extremely cold and has a low density. Heat dissipation from the environment into the storage vessel or tank causes evaporation and a resulting increase in pressure therein. The problem is amplified for small vessels such as vehicle tanks. Venting hydrogen gas to the atmosphere is undesirable, especially when the vehicle is in an enclosed space where hydrogen gas can accumulate. It is desirable to be able to extend the time before the necessary venting of hydrogen vapor from the tank to the atmosphere, or to avoid such venting altogether. Summary of the Invention [Means for solving the problem]

[0006]

[0006] There are several aspects of the present subject matter that may be embodied separately or together in the methods, apparatus, and systems described and claimed below. These aspects may be employed alone or in combination with other aspects of the present subject matter described herein, and describing these aspects together does not exclude the use of these aspects separately or the claiming of such aspects separately or in different combinations than those recited in the claims appended hereto.

[0007]

[0007] In one aspect, a cryogenic fuel tank system includes a fuel tank configured to contain a cryogenic liquid, where a headspace above the cryogenic liquid contains cryogenic vapor, a fuel cell configured to convert the cryogenic vapor into electricity and water vapor, and a vent valve configured to direct excess cryogenic vapor from the headspace to the fuel cell when pressure in the fuel tank exceeds a predetermined pressure level.

[0008]

[0008] In another aspect, a system for powering a vehicle includes a fuel tank configured to contain a cryogenic liquid, where a headspace above the cryogenic liquid contains cryogenic vapor, a battery, a vehicle motor, a fuel cell configured to convert cryogenic fluid from the fuel tank into electricity to power the vehicle motor and charge the battery, and a vent valve configured to direct excess cryogenic vapor from the headspace to the fuel cell when pressure in the fuel tank exceeds a predetermined pressure level so that the battery is charged.

[0009]

[0009] In another aspect, a system for powering a vehicle includes a fuel tank configured to contain a cryogenic liquid, where a headspace above the cryogenic liquid contains cryogenic vapor, a battery, a vehicle motor, a fuel cell configured to convert cryogenic fluid from the fuel tank into electricity to power the vehicle motor and charge the battery, a second fuel cell, and a vent valve configured to direct excess cryogenic vapor from the headspace to the second fuel cell when pressure in the fuel tank exceeds a predetermined pressure level.

[0010]

[0010] In another aspect, a method for reducing emissions of cryogenic fuel vapor to the atmosphere from a fuel tank of a vehicle powered by a cryogenic fuel, the vehicle having a battery and a motor, the method including the steps of directing fluid from the fuel tank to a fuel cell, converting the fluid into electricity using the fuel cell, powering the motor and partially charging the vehicle battery using the electricity, directing excess vapor from the tank to the fuel cell when pressure in the tank exceeds a predetermined level, converting the excess vapor into additional electricity using the fuel cell, and using the additional electricity to further charge the battery.

[0011]

[0011] In another aspect, a method for reducing emissions of cryogenic fuel vapor to the atmosphere from a fuel tank of a vehicle powered by cryogenic fuel, the vehicle having a battery and a motor, the method including the steps of directing fluid from the fuel tank to a first fuel cell, converting the fluid into electricity using the first fuel cell, powering the motor and partially charging the vehicle battery using the electricity, directing excess vapor from the tank to a second fuel cell when pressure in the tank exceeds a predetermined level, converting the excess vapor into additional electricity using the second fuel cell, and using the additional electricity to further charge the battery. [Brief description of the drawings]

[0012] [Figure 1]1 is a schematic diagram of a first embodiment of a cryogenic fuel tank venting system and method of the present disclosure. [Diagram 2]

[0013] FIG. 2 is a schematic diagram of a second embodiment of the cryogenic fuel tank venting system and method of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013]

[0014] Embodiments of the cryogenic fuel tank venting system and method of the present disclosure are described below as being incorporated into a fuel cell system for powering a vehicle. However, the systems and methods of the present disclosure may be utilized in any device or process that consumes liquid hydrogen (or any cryogenic liquid). Additionally, although the cryogenic fuel is described below as being hydrogen, the techniques of the present disclosure may be used in the storage of any cryogenic fluid.

[0014]

[0015] A fuel cell system incorporating an embodiment of the tank venting system of the present disclosure is generally shown at 10 in Figure 1. The fuel cell system 1 has a cryogenic fuel tank 12, which preferably contains liquid hydrogen. Although not shown in the figure, the cryogenic fuel tank may have an inlet port for refilling the tank with liquid hydrogen fuel. In alternative embodiments, the cryogenic tank may store a variety of cryogenic liquids.

[0015]

[0016] The cryogenic fuel tank 12 may be jacketed to reduce heat transfer to the tank interior and may have insulation between the inner and outer walls (or shell) of the jacketed tank. The space between the inner and outer walls may also or alternatively be vacuum insulated.

[0016]

[0017] The fuel cell system 10 also includes a fuel cell 14. The fuel cell 14 may be any type of fuel cell known in the art. The fuel cell 14 may be a solid oxide, molten carbonate, phosphoric acid, proton exchange membrane, or alkaline fuel cell.

[0017]

[0018] As known in the art, the fuel cell system 10 may also include a heat exchanger 20 for converting liquid hydrogen from the cryogenic fuel tank 12 to vapor for consumption in the fuel cell 14. Alternatively, the heat exchanger 20 may be used to warm vapor from the headspace of the tank 12 before directing the vapor to the fuel cell. The heat exchanger 20 may be a multi-pass heat exchanger, but may also be any heat exchanger known in the art, including, but not limited to, a single pass heat exchanger or a heat exchanger coil. Although one heat exchanger is shown, two or more heat exchangers may be utilized in the fuel cell system 10. The fuel cell system 10 may utilize ambient heat or an alternative heat source, such as a trim heater or vaporizer.

[0018]

[0019] During operation, liquid or vaporized hydrogen from the fuel tank 12 is warmed in heat exchanger 20 and then directed to fuel cell 14 which converts the warmed vapor into electrical energy that is used to power vehicle motor 16 and / or charge vehicle battery 18 under the direction of circuitry 26 and controller 28. By way of example only, the system may feature a battery charge sensor 30 which determines the charge level of battery 18 and provides corresponding data to controller 28. This data may be used by the controller to determine when charging of battery 18 with electricity from fuel cell 14 should be initiated and / or terminated by the controller configuring the circuitry accordingly.

[0019]

[0020] During normal operation, such as when the vehicle is being driven, instead of charging the battery 100% fully, the battery is only partially charged. By way of example only, the battery may be charged to about 80%-90% of a fully charged battery state. In alternative embodiments, the battery may only be partially charged to less than about 80% of a fully charged battery state, or to any percentage amount less than a fully charged battery state.

[0020]

[0021] By charging the battery 18 to less than full charge, the liquid hydrogen tank 12 can be vented to the fuel cell 14 rather than to atmosphere and used to charge the battery. More specifically, when the vehicle is idle and no liquid or vaporized hydrogen is being drawn from the tank, the liquid hydrogen in the tank 12 will vaporize and increase the tank pressure. When the pressure in the tank 12 reaches a predetermined vent pressure, a vent valve 22 in the vent circuit opens to allow vapor to escape from the headspace of the tank. This reduces the pressure in the tank and automatically cools the liquid hydrogen therein.

[0021]

[0022] However, instead of venting the vapor to atmosphere, the original headspace vapor from the open vent valve 22 is directed through line 24, through heat exchanger 20, and to fuel cell 14, where the warmed vapor is converted to electricity and directed by circuit 26 and controller 28 to charge battery 18 the remainder (or partial remainder) of the way to 100% full charge. As shown by dashed line 32 in FIG. 1, the vapor can alternatively be directed to fuel cell 14 without passing through heat exchanger 20. In either case, the hydrogen used cannot collect in the enclosed space, since the hydrogen is converted to harmless water vapor. If the battery is fully charged, but the pressure in the tank still needs to be vented, the electricity generated by the fuel cell using the vapor vented from the tank headspace can simply be lost.

[0022]

[0023] The vent valve 22 closes when the tank pressure drops below a predetermined vent pressure.

[0024] Tank 12 features an emergency vent valve 34 that vents to atmosphere if pressure within tank 12 rises to an emergency vent level that is higher than the predetermined vent pressure of vent valve 22 .

[0023]

[0025] A fuel cell system incorporating an alternative embodiment of the tank venting system of the present disclosure is shown generally at 100 in Figure 2. Fuel cell system 100 can include components (having the same functions) of fuel cell system 10, and like components are similarly numbered. Components of Figure 1 that are not shown in Figure 2 can also be optionally included in the system of Figure 2.

[0024]

[0026] The fuel cell system 100 further includes, among other things, a second fuel cell 210. In the embodiment of FIG. 2, the second fuel cell 210 is independently configured as a vent gas converter. The energy potential of the fuel cell 210 is omitted for convenience and simplicity, and the fuel cell 210 serves only to reduce the pressure in the tank while preventing hydrogen gas from potentially accumulating outside the fuel tank. When the pressure in the tank 120 reaches a predetermined vent pressure, a vent valve 220 in the vent circuit opens to allow vapor to escape from the headspace of the tank 120. This reduces the pressure in the tank and automatically cools the liquid hydrogen therein.

[0025]

[0027] However, instead of venting the vapor to the atmosphere, the original headspace vapor from the open vent valve 220 is directed to the fuel cell 210, which then converts the gas to release water and heat. As previously indicated, the electricity generated by the fuel cell 210 can simply be lost, or in an alternative embodiment, it can be directed by line 140 to the partially charged vehicle battery 180 for further charging (as disclosed in the embodiment of FIG. 1) under the control of the control circuit 142 and controller 280, which determines the charge level of the battery 180 using sensor 300.

[0026]

[0028] It should be noted that an alternative embodiment of the present disclosure omits the heat exchanger 200, fuel cell 140, motor 160, and battery 180 of FIG. 2, but retains the tank 120, fuel cell 210, and vent valve 220 for tank pressure reduction, using the hydrogen in the tank 120 primarily for alternative purposes.

[0027]

[0029] While preferred embodiments of the present disclosure have been shown and described, it will be apparent to those skilled in the art that changes and modifications can be made in the preferred embodiments without departing from the spirit of the disclosure, the scope of which is defined by the following claims.

Claims

1. 1. A cryogenic fuel tank system, comprising: a fuel tank configured to contain a cryogenic liquid, wherein a headspace above the cryogenic liquid contains a cryogenic vapor; and a fuel cell configured to convert the cryogenic vapor into electricity and water vapor; a vent valve configured to direct excess cryogenic vapor from the headspace to the fuel cell when pressure within the fuel tank exceeds a predetermined pressure level; A cryogenic fuel tank system comprising:

2. 1. A system for powering a vehicle, comprising: a fuel tank configured to contain a cryogenic liquid, wherein a headspace above the cryogenic liquid contains a cryogenic vapor; and Batteries and A vehicle motor; a fuel cell configured to convert cryogenic fluid from the fuel tank into electricity to power the vehicle motor and charge the battery; a vent valve configured to direct excess cryogenic vapor from the headspace to the fuel cell so that the cell may be charged when pressure within the fuel tank exceeds a predetermined pressure level; A system comprising:

3. 3. The system of claim 2, The system further comprises a heat exchanger configured to receive a cryogenic fluid from the fuel tank and to direct a warmed cryogenic fluid to the fuel cell.

4. 3. The system of claim 2, The system further comprises a controller and circuitry configured to only partially charge the battery while the vehicle is in operation, and to more fully charge the battery when the vehicle is idling using excess cryogenic steam from the vent valve and electricity generated by the fuel cell.

5. A system according to any one of claims 1 to 4, comprising: The system wherein the cryogenic liquid is liquid hydrogen.

6. 1. A system for powering a vehicle, comprising: a fuel tank configured to contain a cryogenic liquid, wherein a headspace above the cryogenic liquid contains a cryogenic vapor; and Batteries and A vehicle motor; a fuel cell configured to convert cryogenic fluid from the fuel tank into electricity to power the vehicle motor and charge the battery; a second fuel cell; and a vent valve configured to direct excess cryogenic vapor from the headspace to the second fuel cell when pressure in the fuel tank exceeds a predetermined pressure level; A system comprising:

7. 7. The system of claim 6, The system wherein the cryogenic liquid is liquid hydrogen.

8. 1. A method for reducing atmospheric emissions of cryogenic fuel vapors from a fuel tank of a vehicle powered by a cryogenic fuel, the vehicle having a battery and a motor, the method comprising: directing fluid from the fuel tank to a fuel cell; converting the fluid into electricity using the fuel cell; powering the motor and using the electricity to partially charge the vehicle battery; directing excess vapor from the tank to the fuel cell when pressure within the tank exceeds a predetermined level; converting the excess steam into additional electricity using the fuel cell; further charging the battery with the additional electricity; A method comprising:

9. 9. The method of claim 8, The method, wherein partially charging the battery comprises charging the battery to less than 90%.

10. 10. The method of claim 9, The method, wherein partially charging the battery comprises charging the battery to between 80-90%.

11. 9. The method of claim 8, The method further comprising the step of warming the fluid as it is passed from the fuel tank to the fuel cell.

12. 1. A method for reducing atmospheric emissions of cryogenic fuel vapors from a fuel tank of a vehicle powered by a cryogenic fuel, the vehicle having a battery and a motor, the method comprising: directing fluid from the fuel tank to a first fuel cell; converting the fluid into electricity using the first fuel cell; powering the motor and using the electricity to partially charge the vehicle battery; directing excess vapor from the tank to a second fuel cell when pressure within the tank exceeds a predetermined level; converting the excess steam into additional electricity using the second fuel cell; further charging the battery with the additional electricity; A method comprising:

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