Fuel cell performance enhancement through O2 enrichment from LH2 cooling interface

Abstract

An air feed conditioning system for a hydrogen (h2) fuel cell (FC) powered vehicle, such as an aircraft, in which H2 from a vehicle onboard liquid hydrogen (LH2) fuel store 142 is reacted with oxygen

Description

[0001] The present disclosure relates to hydrogen-fueled proton exchange membrane fuel cell-(PEMFC)-powered transport vehicles. The disclosure has particular utility in connection with PEMFC-powered aircraft and will be described in connection with such utility, although other utilities are contemplated. Background and Summary

[0002] This section provides background information related to the present disclosure which is not necessarily prior art. This section provides a general summary of the disclosure and is not a comprehensive disclosure of its full scope or all its features.

[0003] Exhaust emissions from transport vehicles are a significant contributor to climate change. Conventional fossil-fuel-powered aircraft engines release CO2 emissions. Also, fossil-fuel-powered aircraft emissions include non-CO2 effects due to nitrogen oxide (NOx), vapor trails, and cloud formation triggered by the altitude at which aircraft operate. These non-CO2 effects are believed to contribute twice as much to global warming as aircraft CO2 and are estimated to be responsible for two-thirds of aviation’s climate impact. Additionally, the high-speed exhaust gasses of conventional fossil-fuel-powered aircraft engines contribute significantly to the extremely large noise footprint of commercial and military aircraft, particularly in densely populated areas.

[0004] Rechargeable battery-powered terrestrial vehicles, i.e., “EVs”, are slowly replacing conventional fossil-fuel-powered terrestrial vehicles. However, the weight of batteries and limited energy storage of batteries makes rechargeable battery-powered aircraft generally impractical.

[0005] PEMFCs or hydrogen (H2) fuel cells (FCs), for short, offer an attractive alternative to fossil-fuel-burning engines. H2 fuel tanks may quickly be filled and store significant energy, and other than the relatively small amount of unreacted H2 gas, the reaction output exhausted from H2 FCs comprises essentially only water.

[0006] H2 FCs are electrochemical cells that convert chemical energy into electrical energy by spontaneous electrochemical reduction-oxidation (redox) reactions. Referring to Fig. 1, a typical H2 FC 10 comprises a housing 12 containing an anode 14 and a cathode 16 separated by a proton exchange membrane (PEM) 18 that permits only protons to pass between the anode 14 and cathode 16. During operation, a fuel (e.g., H2) is supplied via an H2 fuel inlet 20 and is distributed via a gas diffusion layer 24 onto the anode 14, and an oxidant (e.g., 02 or air) is supplied via an 02 inlet 22 and is distributed via a gas diffuser layer 26 onto the cathode 16. The H2 fuel is oxidized at the anode 14, producing positively charged ions (i.e., H2 protons) and electrons. The positively charged protons travel through the PEM 18 from the anode 14 to the cathode 16, while the electrons simultaneously travel from the anode 14 to the cathode 16 outside the H2 FC 10 via an external circuit 28, which produces an electric current. The oxidant supplied to the cathode is reduced by the electrons arriving from the external circuit and combines with the positively charged ions to form water (H2O).

[0007] Also included in the H2 FC 10 are an H2 recycling outlet 30 and an 02 and H2O outlet 32.

[0008] Conventional vehicle-mounted H2 FCs typically use air from the surrounding environment to eliminate the requirement for onboard liquid oxygen (LOX) storage, the weight of which would decrease overall system efficiency. However, the cathode reaction of a H2 FC is rate limited by available 02 (partial pressure of 02), which is about 21.3 kPa at sea level but falls to 14.63 kPa at 10,000 ft. Thus, in the case of H2 FC-powered aircraft, which typically are designed to cruise at 30,000-42,000 ft, the decrease in overall system efficiency is particularly acute.

[0009] To address this latter problem the art as proposed using compressor-based purification, i.e., (pressure swing absorption) to increase partial pressure of 02 at altitude. See Introduction to Hydrogen Technology - Science Direct https: / / www.sciencedirect.com / science / articWpii / S03787753230Q1787. However, the use of compression-based purification can consume up to 20% of the power output of the FCs. See Banaszkiewicz, T.; Chorowski, M. Energy Consumption of Air-Separation Adsorption Methods. Entropy 2018, 20, 232. https: / / doi.org / 10.3390 / e2004Q232

[0010] Existing literature has demonstrated that enriching air to 40-50% 02 provides a near 10% improvement in H2 FC efficiency, which not only increases efficiency at sea level, but also increases efficiency during climb and at cruise levels. See Figs. 2A and 2B and Butori et al “The effect of oxygen partial pressure and humidification in proton exchange membrane fuel cells at intermediate temperature (80-120°C)”, Journal of Power Sources 563 (2023) 232803.

[0011] In accordance with the present disclosure, the 02 content of an H2 FC cathode input gas is enriched by employing a low temperature rectification or cryogenic 02 enrichment process to remove nitrogen, carbon dioxide, water vapor, and other elemental gases from the incoming ambient air, resulting in a “rich liquid” with substantially increased 02 content (as compared to ambient air) which approaches 50 volume %. A feature and advantage of the instant disclosure is that we are able to perform an 02 enrichment operation with minimal added weight, using existing onboard liquid hydrogen (LH2) from the onboard H2 fuel tank to provide a cold source for the rectification or cryogenic 02 enrichment process of the air.

[0012] The utilization of existing LH2 infrastructure to perform cryogenic enrichment reduces added weight and refrigeration energy requirements, while also vaporizing and conditioning the LH2 prior to reaching the anode. Additionally, the cryogenic process of the present disclosure avoids the use of compressor-based purification (i.e. pressure swing adsorption) which, as previously mentioned, is infeasible for vehicle-mounted systems such as disclosed in US 2009 / 0291338 due to its consumption of up to 20% of the power output of an FC.

[0013] To perform cryogenic 02 enrichment in accordance with the present disclosure, air must first be freed of components with high solidification points, notably water vapor (H2O) and carbon dioxide (CO2). After this is achieved, the remaining air stream can be cooled to cryogenic temperature to liquify the 02. The temperature and pressure at which the cryogenic process is conducted is chosen to preferentially liquefy 02, which separates the incoming stream into a 40-50% 02 content liquid phase and a nitrogen (N2) rich gas phase. The temperature should fall between the boiling points of 02 and N2, reference values for which are provided in Figure 3. In an alternative embodiment, the 02 may be separated from the N2 and collected as a vapor via a cyclonic or membrane-based separation process.

[0014] H2O and CO2 must be removed from the input stream prior to exposure to cryogenic temperatures. H2O vapor content will of course be highly variable with weather conditions and with vehicle altitude, and may be, by way of example, 5ppm if the vehicle is undergoing stratospheric flight (30-42k ft) (assuming -50°C outside air) and may increase to 300 ppm at 15k ft. On the other hand, CO2 content is relatively invariant with altitude, with a reported concentration of ~400ppm throughout an altitude range of 5-9 mi. Accordingly, a drying process is necessary to prevent the buildup of water ice and dry ice on the cryogenic temperature heat exchanger.

[0015] In accordance with one embodiment of the disclosure we employ a molecular sieve for separating solid droplets of H2O and CO2 from the air stream. In practice, two molecular sieves are employed, one in use in the separation process, and one for recharging the sieve, to separate solidifying droplets of H2O and CO2 from the air stream. As intake air is cooled to -79°C, H2O and CO2 ice particulates form but are unable to flow through the microporous material used (e.g. zeolites) in the sieves. Cooling to -79°C can be achieved via an expansion turbine found in a conventional air cycle machine (ACM), or by harnessing a waste stream from a later cryogenic enrichment process step in which low temperature N2-rich air is discarded as will be described below. The ACM approach becomes further energy efficient when used at altitude, where the input air is expected to be close to -50°C. In some embodiments, the recharging molecular sieve also may be used to humidify air prior to introduction into the FC stack.

[0016] In one embodiment of the disclosure, we employ a cyclonic separation process to remove both H2O and CO2 particles. In such embodiment, the ACM or cold waste N2 gas is used to achieve cooling to -79°C. The gas stream is then flowed through a cyclonic separation unit to remove both H2O and CO2 particles. The higher mass of the H2O and CO2 solidifying particles causes collisions with the cyclone walls and leads to the particles falling into a collection hopper / waste tube. The remaining gas (now dry air) flows through unimpeded. To achieve high removal efficiency, multi-channel cyclones may be deployed. In some embodiments, the hopper waste stream may be recirculated into the inlet air stream to humidify the FC inlet air stream prior to exposure to the FC stack.

[0017] Once the air is dried, it is cooled to cryogenic temperatures to generate a fraction that is O2-rich. While conventional industrial techniques employ adiabatic processes that require significant pressure changes (and energy consumption) to achieve cooling, in accordance with the present disclosure the LH2 fuel source onboard the vehicle provides an energy and weight efficient cold source alternative. In construction the LH2 tank is a cryogenic storage dewar utilizing a vacuum flask design to limit heat conduction and LH2 evaporation. When LH2 is needed to operate the FC stack, the LH2 is exposed to the ambient environment causing vaporization. Incorporated into the onboard LH2 vaporizer is a heat exchanger which harvests the cold source LH2 at -250°C.

[0018] Input air is then run through a tube / channel and into contact with the heat exchanger. The temperature of the cold source of the heat exchanger (-250°C) is sufficiently low to liquefy components of the input air. Contact time is controlled to achieve cooling that liquefies the 02 content but not the N2 content of the input air. The resulting liquefied fraction of the input air contains 02, with a purity of between 40-50%. In some embodiments, the 02 also may be extracted from the gas phase as a vapor using a cyclonic separation technique. The remaining gas fraction is N2-rich and is discarded as a waste stream. In some embodiments, the waste stream may be used to cool input air to perform the drying steps above mentioned before being discarded. A significant benefit of using the N2 waste gas to cool the input air is that it avoids wasting the latent heat energy from the LH2 or N2-rich gas, the former which can better be used for cryogenic enrichment and the latter which would otherwise be lost when ejected from the system. Finally, the 02-rich fraction is evaporated and humidified and directed to the FC cathode, where it is reduced by electrons arriving from the external circuit and combines with the positively charged ions to form H2O.

[0019] According to Aspect A there is provided an air feed conditioning system for an H2 FC-powered vehicle in which H2 from a vehicle onboard LH2 fuel store is reacted with 02 in the air feed to produce electricity, wherein an 02 content of the air feed is enriched by cryogenic rectification of the air feed using the onboard LH2 fuel store as a cold source for said cryogenic rectification.

[0020] In another embodiment the H2O and / or the CO2 are frozen and are removed from the air feed as solid particles of H2O and CO2 prior to said cryogenic rectification.

[0021] In a further embodiment the solid particles of H2O and CO2 are removed via cyclonic separation, or by sieving.

[0022] In yet another embodiment the system comprises first and second molecular sieves which sieves are operated sequentially so that when the first molecular sieve is being used to remove the solid particles of H2O and CO2, the second molecular sieve is being recharged, and vice versa.

[0023] In another embodiment particles of H2O and CO2 are solidified via a turboexpander in the onboard ACM, or particles of H2O and CO2 are solidified via a heat exchanger with a cryogenic gas stream.

[0024] In a further embodiment the waste gas stream comprises a cryogenic gas stream.

[0025] In yet another embodiment the waste stream comprises an N2-rich waste gas stream from rectification or an O2-rich gas stream undergoing vaporization.

[0026] In still yet another embodiment H2O, CO2, N2 and argon (Ar) are removed within the same distillation column via single stage fractional distillation.

[0027] In a further embodiment the 02 is enriched as a vapor via a cyclonic or a membrane-based cryogenic rectification separation process.

[0028] In yet another embodiment cold N2 gas is separated from the air feed during said cryogenic rectification.

[0029] In a further embodiment the air feed is cooled by said cryogenic rectification to a temperature between a boiling point of 02 and a boiling point of N2.

[0030] In another embodiment a sensor and / or a metering device is used to control the oxygen content of the air stream provided to the FC cathode.

[0031] In yet another embodiment of Aspect A, the vehicle comprises an H2 FC-powered aircraft.

[0032] According to Aspect B there is provided a method of enhancing an efficiency of an H2 FC-powered vehicle having an onboard LH2 fuel store, which comprises enriching an 02 content of the FC cathode air input by subjecting the air input to a cryogenic rectification process using the onboard LH2 store as a cold source to perform said cryogenic rectification.

[0033] In one embodiment H2O and / or CO2 are removed from the input air as solid particles prior to the cryogenic rectification process.

[0034] In a further embodiment the solid particles of H2O and CO2 are removed by a sieving process or by a cyclonic separation process prior to said cryogenic rectification process.

[0035] In another embodiment the 02 in the air input is liquified at least in part during the cryogenic rectification process, and optionally including the steps of evaporating the liquid 02 before delivering the 02 to the cathode input.

[0036] In still yet another embodiment the 02 is enriched in vapor form.

[0037] In another embodiment the enriched 02 is collected via a cyclonic or a membrane-based separator process.

[0038] In another embodiment cooled N2 gas is removed from the air feed during the cryogenic rectification process, and the cooled N2 gas is passed in heat exchange with fresh input air to cool the fresh input air to precipitate solid particles of H2O and CO2.

[0039] In still yet another embodiment, the solid particles of H2O and CO2 are separated from the air input upstream of said cryogenic rectification.

[0040] According to a first aspect of the present invention there is provided an air feed conditioning system for a hydrogen (H2) fuel cell (FC)-powered vehicle in which H2 from a vehicle onboard liquid hydrogen (LH2) fuel store is reacted with oxygen (02) in the air feed to produce electricity, wherein an 02 content of the air feed is enriched by cryogenic rectification of the air feed using the onboard LH2 fuel store as a cold source for said cryogenic rectification.

[0041] Preferably the H2O and / or the CO2 are removed from the air feed as solid particles of H2O and CO2 prior to said cryogenic rectification.

[0042] Preferably the solid particles of H2O and CO2 are removed via cyclonic separation or by sieving.

[0043] Preferably the system comprises first and second molecular sieves which sieves are operated sequentially so that when the first molecular sieve is being used to remove the solid particles of H2O and CO2, the second molecular sieve is being recharged, and vice versa.

[0044] Preferably particles of H2O and CO2 are solidified via a turboexpander in the onboard ACM, or wherein particles of H2O and CO2 are solidified via heat exchange with a cryogenic gas stream.

[0045] Preferably the waste gas stream comprises an N2-rich waste gas from rectification or an O2-rich gas stream undergoing vaporization.

[0046] Preferably H2O, CO2, nitrogen, and argon are removed within the same distillation column via single stage fractional distillation.

[0047] Preferably the 02 is enriched as a vapor via a cyclonic or a membrane-based cryogenic rectification separation process.

[0048] Preferably cold nitrogen (N2) gas is separated from the air feed during said cryogenic rectification.

[0049] Preferably the air feed is cooled by said cryogenic rectification to a temperature between a boiling point of 02 and a boiling point of N2.

[0050] Preferably a sensor and / or a metering device is used to control the oxygen content of the air stream provided to the FC cathode.

[0051] Preferably the vehicle comprises an H2 FC- powered aircraft.

[0052] According to a second aspect of the present invention there is provided a method of enhancing an efficiency of a hydrogen (H2) fuel cell (FC)-powered vehicle having an onboard liquid hydrogen (LH2) fuel store, which comprises enriching an oxygen (02) content of the FC cathode air input by subjecting the air input to a cryogenic rectification process using the onboard LH2 fuel store as a cold source to perform said cryogenic rectification.

[0053] Preferably n water (H2O) and / or carbon dioxide (CO2) are removed as solid particles from the input air prior to the cryogenic rectification process.

[0054] Preferably the H2O and CO2 are removed as solid particles by a sieving process or by a cyclone separator process.

[0055] Preferably the 02 in the air input is liquified at least in part during the cryogenic rectification process, and optionally including the steps of evaporating the liquid 02 before delivering the 02 to the cathode.

[0056] Preferably vthe 02 is enriched in vapor form.

[0057] Preferably the enriched 02 is collected via cyclonic or a membrane-based separation process.

[0058] Preferably cooled nitrogen (N2) gas is removed from the FC cathode air input during the rectification process, and the cooled N2 gas is passed in heat exchange with fresh input air to cool the fresh input air to precipitate solid particles of H2O and CO2.

[0059] Preferably the method includes the step of separating the solid particles of H2O and CO2 from the air input upstream of said cryogenic rectification.

[0060] Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. Brief Description of the Drawings

[0061] Further features and advantages of the disclosure will be seen in the following detailed description, taken in conjunction with the accompanying drawings, wherein like numerals depict like parts. The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations and are not intended to limit the scope of the present disclosure. In the drawings: Fig. 1 is a cross-sectional view of a conventional H2 FC; Fig. 2A is a graph plotting cell voltage and current density showing the effective gas pressures for a non-pressurized and pressurized FC in accordance with the prior art; Fig. 2B is a graph plotting voltage vs. current for an FC fed with various increased 02 content in accordance with the prior art; Fig. 3 is a table of the boiling point of various components of air at ambient pressure and at elevated pressure in accordance with the prior art; Fig. 4 is a schematic illustration of an 02 enrichment system for use with an FC in accordance with the present disclosure; Fig. 5A is a cross-sectional diagram illustrating a cyclonic separation system useful in the practice of the present disclosure; Fig. 5B is a perspective view, in partial cross section of a multi-clone cyclonic separator system useful in the practice of the present disclosure; Fig. 6 illustrates an alternative embodiment of an 02 enrichment system for use with an FC in accordance with the present disclosure; Fig. 7 illustrates an additional alternative embodiment of an 02 enrichment system for use with an FC in accordance with the present disclosure; and Fig. 8 is a schematic depiction of an H2 FC-powered aircraft incorporating an 02 enhancement system in accordance with the present disclosure. Detailed Description

[0062] Example embodiments will now be described more fully with reference to the accompanying drawings. Example embodiments are provided so that this disclosure will be thorough and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms, and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.

[0063] The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, components, and / or groups, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.

[0064] When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0065] Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers, and / or sections, these elements, components, regions, layers, and / or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another element, component, region, layer, or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer, or section discussed below could be termed a second element, component, region, layer, or section without departing from the teachings of the example embodiments.

[0066] Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

[0067] As used herein PEMFC and H2 FC are used interchangeably.

[0068] As used herein the term “cryogenic process” or “cryogenic rectification” encompass distillation purification processes via both heating or cooling.

[0069] Fig. 4 illustrates an air feed conditioning system for an H2 FC-powered vehicle in accordance with the present disclosure. The air feed conditioning system 100 comprises an expansion turbine 102 or so-called turboexpander. A turboexpander is a centrifugal or axial-flow turbine, through which a high-pressure gas is expanded to produce work. Because work is extracted from the expanding high-pressure gas, the expansion is approximated by an isentropic process (i.e., a constant-enthopy process), producing a low-pressure exhaust gas at a very low temperature (e.g. -150°C), resulting in freezing of H2O (freezing point 0°C) and CO2 (freezing point -79°C) in the air and precipitation of the frozen H2O and CO2 as particulates of frozen H2O (H2O ice) and frozen CO2 (so-called “dry-ice”). The resulting H2O and CO2 particulates are then flowed with the chilled air under pressure to a particulate filtration system 106, wherein the frozen H2O and CO2 particulates are removed from the chilled air stream via conduit 118.

[0070] Referring also to Fig. 5A particulate filtration system 106 may comprise a cyclonic separator 108 in which a high-speed rotating (air)flow 154 is established within a cylindrical or conical container 152. Air flows in a helical pattern, beginning at the top (wide end) 156 of the cyclone and ending at the bottom 158 (narrow) end before exiting the cyclone in a straight stream though the top center outlet 160 of the cyclone. Particulates 162 of frozen H2O and CO2 in the rotating stream 154 have too much inertia to follow the tight curve of the stream, and thus strike the inside wall of the conical container and fall to the bottom 158 of the conical container where they are removed under an influence of gravity, while the dry chilled air is passed from the top center outlet 160 via conduit 120 (shown in Fig. 4) to cryogenic rectification column 130.

[0071] Referring to Fig. 5B, the particulate filtration system 106 may comprise a multi-cyclone or so-called “Multiclone” separator 180 consisting of a plurality of small diameter cyclones 182 having a common inlet 184 and a common outlet 186. Multiclone apparatuses operate on the same principle as simple cyclone separators creating an outer downward vortex and an ascending inner vortex. As in the case of cyclone separator 108 described in Fig. 5A, particulates of frozen H2O and CO2 are separated out and fall to the bottom 188 of the multiclone where they are removed, while the chilled dry air is passed from outlet 186 via conduit 120 to the cryogenic rectification column 130 (shown in Fig. 4).

[0072] Removal of CO2 and H2O vapor is essential to the process since the lower temperatures encountered in the cryogenic rectification process would otherwise cause any CO2 and H2O present in the air feed to freeze and clog the downstream cryogenic rectification equipment.

[0073] Referring again to Fig. 4, cryogenic rectification column 130 comprises a distillation column having an inlet 132 for the dry chilled air from filtration system 106, an intermediate outlet 134 for an N2 rich waste stream and a concentrated 02 outlet 136 from which liquid 02 or an 02 rich vapor stream is withdrawn. Rectification column 130 is cooled by heat exchange 138 with LH2 from LH2 fuel tank 142 in LH2 vaporizer 140. The LH2 from LH2 fuel tank 142 is vaporized in vaporizer 140, giving up heat to cool rectification column 130, and the vaporized H2 is passed via conduit 144. Both the O2-rich stream 136 and vaporized H2 stream 144 may then be separately exposed to a pre-FC heat exchanger 146 to condition the streams to a temperature appropriate for exposure to the FC stack. After conditioning, the O2-rich stream passes to the cathode inlet 22 and the H2 passes to the anode inlet 20 of the FC 10.

[0074] The N2-rich waste stream 134 from rectification column 130 may be vented (see Fig. 7), or alternatively passed via conduit 200 to a heat exchanger 202 (see Fig. 6) for cooling the input air prior to introduction into filtration system 106.

[0075] In other embodiments, the oxygen enrichment process may be achieved via a single stage fractional distillation device, as illustrated in Fig. 7. Liquid hydrogen from LH2 fuel tank 142 is used as the single coolant to both (1) separate H2O and CO2 and then (2) cool the air down to its boiling point. Within the distillation chamber 190, heat exchange with LH2 initially cools the incoming air to -79°C, whereupon H2O and CO2 are removed via particle conduits 118A and 118B, respectively. Additional LH2 heat exchange lowers the air stream to cryogenic temperature, at which point nitrogen and argon can be distilled and ejected at one or more intermediate outlets 134 and 135, respectively. Oxygen is distilled and sent to a pre-FC heat exchanger 146 where it is fully evaporated and conditioned. The fully conditioned oxygen may flow through a metering device 192 that meters the appropriate amount of oxygen into the cathode inlet air stream of the FC. The pre-FC heat exchanger 146, which is used to condition the oxygen, may have a separate compartment to condition the gaseous hydrogen that exits from the fractional distillation device. Both gas streams are then conditioned appropriately for use in the FC 10. Waste heat from the FC 10 is used in the heat exchanger 146 for conditioning of the oxygen and the hydrogen.

[0076] Fig. 8 illustrates an aircraft 250 including an air feed conditioning system 252 for enriching the 02 air feed to onboard fuel cells 254 in accordance with the present disclosure.

[0077] The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. By way of example, referring again to Fig. 4, filtration system 106 may comprise first and second molecular sieves, shown in phantom at 260, 262. Molecular sieves 260, 262 comprise beds of microporous, primarily uniform size particulate material formed of, for example, aluminosilicate zeolites. Molecular sieves 260, 262 are configured so that one of the molecular sieves, e.g., molecular sieve 262 is in use in separating solidifying droplets or particles of H2O and CO2 from the gas stream, while the other molecular sieve 260 is being recharged. As the intake air is cooled to -79°C, small H2O and CO2 ice particles form but are unable to flow through the microporous material. As the one molecular sieve 262 becomes loaded with captured H2O and CO2 ice particles, it is then taken off live and recharged, while the other molecular sieve 260 is used in the separator process, and vice versa. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure. Various changes and advantages may be made in the above disclosure without departing from the spirit and scope thereof. List of References: 10 H2 FC 12 housing 14 anode 16 cathode 18 PEM 20 H2 fuel inlet 22 02 inlet 24, 26 gas diffusion layer 28 external circuit 30 H2 recycling outlet 32 02 and H2O outlet 100 air feed conditioning system expansion turbine particulate filtration system cyclonic separator conduit H2O particle conduit CO2 particle conduit conduit rectification column inlet N2 waste stream Argon waste stream 02 outlet heat exchange vaporizer LH2 fuel tank conduit pre-FC heat exchanger container rotating airflow top bottom top center particulates separator cyclones inlet outlet bottom single stage distillation chamber metering device conduit heat exchanger aircraft air feed conditioning system onboard fuel cells 262 molecular sieves

Claims

1. An air feed conditioning system for a hydrogen (H2) fuel cell (FC)-powered vehicle in which H2 from a vehicle onboard liquid hydrogen (LH2) fuel store is reacted with oxygen (02) in the air feed to produce electricity, wherein an 02 content of the air feed is enriched by cryogenic rectification of the air feed using the onboard LH2 fuel store as a cold source for said cryogenic rectification.

2. The air feed conditioning system of claim 1, wherein the H20 and / or the C02 are removed from the air feed as solid particles of H20 and C02 prior to said cryogenic rectification.

3. The air feed conditioning system of claim 2, wherein the solid particles of H20 and C02 are removed via cyclonic separation or by sieving.

4. The air feed conditioning system of claim 3, wherein the system comprises first and second molecular sieves which sieves are operated sequentially so that when the first molecular sieve is being used to remove the solid particles of H20 and C02, the second molecular sieve is being recharged, and vice versa.

5. The air feed conditioning system of claim 2, wherein particles of H20 and C02 are solidified via a turboexpander in the onboard ACM, or wherein particles of H20 and C02 are solidified via heat exchange with a cryogenic gas stream.

6. The system of claim 5, wherein the waste gas stream comprises an N2-rich waste gas from rectification or an 02-rich gas stream undergoing vaporization.

7. The air feed conditioning system of any one of claims 1 to 6, wherein H20, C02, nitrogen, and argon are removed within the same distillation column via single stage fractional distillation.

8. The air feed conditioning system of any one of claims 1 to 7, wherein the 02 is enriched as a vapor via a cyclonic or a membrane-based cryogenic rectification separation process.

9. The air feed conditioning system of any one of claims 1 to 8, wherein cold nitrogen (N2) gas is separated from the air feed during said cryogenic rectification.

10. The air feed conditioning system of any one of claims 1 to 9, wherein the air feed is cooled by said cryogenic rectification to a temperature between a boiling point of 02 and a boiling point of N2.

11. The air feed conditioning system of any one of claims 1 to 10, wherein a sensor and / or a metering device is used to control the oxygen content of the air stream provided to the FC cathode.

12. The air feed conditioning system of any one of claims 1 to 11, wherein the vehicle comprises an H2 FC- powered aircraft.

13. A method of enhancing an efficiency of a hydrogen (H2) fuel cell (FC)-powered vehicle having an onboard liquid hydrogen (LH2) fuel store, which comprises enriching an oxygen (02) content of the FC cathode air input by subjecting the air input to a cryogenic rectification process using the onboard LH2 fuel store as a cold source to perform said cryogenic rectification.

14. The method of claim 13, wherein water (H2O) and / or carbon dioxide (CO2) are removed as solid particles from the input air prior to the cryogenic rectification process.

15. The method of claim 14, wherein the H2O and CO2 are removed as solid particles by a sieving process or by a cyclone separator process.

16. The method of any one of claims 13 to 15, wherein the 02 in the air input is liquified at least in part during the cryogenic rectification process, and optionally including the steps of evaporating the liquid 02 before delivering the 02 to the cathode.

17. The method of any one of claims 13 to 16, wherein the 02 is enriched in vapor form.

18. The method of claim 17, wherein the enriched 02 is collected via cyclonic or a membrane-based separation process.

19. The method of any one of claims 13 to 18, wherein cooled nitrogen (N2) gas is removed from the FC cathode air input during the rectification process, and the cooled N2 gas is passed in heat exchange with fresh input air to cool the fresh input air to precipitate solid particles of H20 and C02.

20. The method of claim 19, including the step of separating the solid particles of H20 and C02 from the air input upstream of said cryogenic rectification.Application No: GB2415238.1Examiner: Mr Michael ShawClaims searched: 1-20Date of search: 24 March 2025Patents Act 1977: Search Report under Section 17Documents considered to be relevant:Category Relevant to claims Identity of document and passage or figure of particular relevance X,E 1,9-13, 16, 17 GB 2632288 A (BADGERWORKS LTD), see figure 2, abstract X 1-4, 8-18, CN 117039050 A (BEIJING INST AEROSPACE TESTING TECH) see figures, EPODOC abstract X 1,8-13, 16-18 CN 217589016 U (BEIJING SINOHYTEC CO LTD) see figures, EPODOC abstract X 1,8-13, 16-18 US 5106035 A (LANGFORD) see figures, column 4, lines 28-45Categories:X Document indicating lack of novelty or inventive step A Document indicating technological background and / or state of the art. Y Document indicating lack of inventive step if combined with one or more other documents of same category. P Document published on or after the declared priority date but before the filing date of this invention. & Member of the same patent family E Patent document published on or after, but with priority date earlier than, the filing date of this application.Field of Search:Search of GB, EP, WO &US patent documents classified in the following areas of the UKCX :International Classification:Subclass Subgroup Valid From F25J 0003 / 04 01 / 01 / 2006 B64D 0027 / 355 01 / 01 / 2024 B64D 0037 / 00 01 / 01 / 2006 B64D 0041 / 00 01 / 01 / 2006 F17C 0013 / 08 01 / 01 / 2006

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