The subject matter disclosed herein generally relates to systems for generating and providing inert gas to protected spaces and optionally also providing oxygen and/or power. More specifically, the subject matter relates to thermal management of such systems.
It is recognized that fuel vapors within fuel tanks become combustible or explosive in the presence of oxygen. An inerting system decreases the probability of combustion or explosion of flammable materials in a fuel tank by maintaining a chemically non-reactive or inerting gas, such as nitrogen-enriched air, in the fuel tank vapor space, also known as ullage. Three elements are required to initiate combustion or an explosion: an ignition source (e.g., heat), fuel, and oxygen. The oxidation of fuel may be prevented by reducing any one of these three elements. If the presence of an ignition source cannot be prevented within a fuel tank, then the tank may be made inert by: 1) reducing the oxygen concentration, 2) reducing the fuel concentration of the ullage to below the lower explosive limit (LEL), or 3) increasing the fuel concentration to above the upper explosive limit (UEL). Many systems reduce the risk of oxidation of fuel by reducing the oxygen concentration by introducing an inerting gas such as nitrogen-enriched air (NEA) (i.e., oxygen-depleted air or ODA) to the ullage, thereby displacing oxygen with a mixture of nitrogen and oxygen at target thresholds for avoiding explosion or combustion.
It is known in the art to equip vehicles (e.g., aircraft, military vehicles, etc.) with onboard inerting gas generating systems, which supply nitrogen-enriched air to the vapor space (i.e., ullage) within the fuel tank. The nitrogen-enriched air has a substantially reduced oxygen content that reduces or eliminates oxidizing conditions within the fuel tank. Onboard inerting gas generating systems typically use membrane-based gas separators. Such separators contain a membrane that is permeable to oxygen and water molecules, but relatively impermeable to nitrogen molecules. A pressure differential across the membrane causes oxygen molecules from air on one side of the membrane to pass through the membrane, which forms oxygen-enriched air (OEA) on the low-pressure side of the membrane and nitrogen-enriched air (NEA) on the high-pressure side of the membrane. The requirement for a pressure differential necessitates a source of compressed or pressurized air. Another type of gas separator is based on an electrochemical cell such as a proton exchange membrane (PEM) electrochemical cell, which produces NEA by electrochemically generating protons for combination with oxygen to deplete air of combustible oxygen
A system is disclosed for providing inerting gas to a protected space. The system includes an electrochemical cell comprising a cathode and an anode separated by a separator comprising a proton transfer medium. A cathode fluid flow path is in operative fluid communication with the cathode between a cathode fluid flow path inlet and a cathode fluid flow path outlet. An anode fluid flow path is in operative fluid communication with the anode between an anode fluid flow path inlet and an anode fluid flow path outlet. A cathode supply fluid flow path is between an air source and the cathode fluid flow path inlet, and an inerting gas flow path in operative fluid communication with the cathode fluid flow path outlet and the protected space. An anode supply fluid flow path is between a supply of process water (i.e., a process water source) and the anode fluid flow path inlet.
The system for providing inerting gas includes thermal management. Thermal management includes a heat exchanger in operative fluid and thermal communication with the process water. A temperature sensor is in operative thermal communication with the cathode or the anode, or with both the cathode and the anode. A flow control device is arranged to control a flow of process water to a flow path in operative thermal communication with the cathode or anode, or with both the cathode and the anode. A controller is configured to provide a target temperature of the temperature sensor through control of a flow rate of process water or a temperature of process water, or both a flow rate and a temperature of process water, through a process water thermal management flow path in operative thermal communication with the cathode or the anode or with both the cathode and the anode.
In some aspects, the heat exchanger can include a heat rejection side in operative fluid communication with the process water thermal management flow path, and a heat absorption side in operative thermal communication with a heat sink.
In any one or combination of the foregoing aspects, the heat exchanger can include a heat absorption side in operative fluid communication with the process water thermal management flow path, and a heat rejection side in operative thermal communication with a heat source.
In any one or combination of the foregoing aspects, the process water thermal management flow path can include the anode fluid flow path, or the cathode fluid flow path, or a fluid flow path in operative thermal communication with the cathode or with the anode or with both the cathode and the anode and in fluid isolation from the cathode and fluid flow paths.
In any one or combination of the foregoing aspects, the process water thermal management flow path can include the anode fluid flow path.
In any one or combination of the foregoing aspects, the process water thermal management flow path can include the cathode fluid flow path.
In any one or combination of the foregoing aspects, the process water thermal management flow path can include the fluid flow path in operative thermal communication with the cathode or with the anode or with both the cathode and the anode and in fluid isolation from the cathode and fluid flow paths.
In any one or combination of the foregoing aspects, the fluid flow path in operative thermal communication with the cathode or with the anode or with both the cathode and the anode and in fluid isolation from the cathode and fluid flow paths can include a conduit disposed on the cathode fluid flow path or anode fluid flow path.
In any one or combination of the foregoing aspects, the system can include a plurality of said electrochemical cells in a stack separated by electrically-conductive fluid flow separators wherein the fluid flow path in operative thermal communication with the cathode or with the anode or with both the cathode and the anode and in fluid isolation from the cathode and fluid flow paths includes an internal passage through one or more of the electrically-conductive fluid flow separators.
In any one or combination of the foregoing aspects, the system can include a plurality of the electrochemical cells in a stack separated by electrically-conductive fluid flow separators.
Also disclosed is a system for providing inerting gas to a protected space. The system includes an electrochemical cell comprising a cathode and an anode separated by a separator comprising a proton transfer medium. A cathode fluid flow path is in operative fluid communication with the cathode between a cathode fluid flow path inlet and a cathode fluid flow path outlet. An anode fluid flow path is in operative fluid communication with the anode between an anode fluid flow path inlet and an anode fluid flow path outlet. A cathode supply fluid flow path is between an air source and the cathode fluid flow path inlet, and an inerting gas flow path in operative fluid communication with the cathode fluid flow path outlet and the protected space. An anode supply fluid flow path is between a process water source and the anode fluid flow path inlet. A cooling water fluid flow path is in operative fluid communication with the process water source, said cooling water fluid flow path in operative thermal communication with the cathode or with the anode or with both the anode and the cathode, and in fluid isolation from the cathode fluid flow path and the anode fluid flow path.
Also disclosed is a method of inerting a protected space. According to the method, process water is delivered to an anode of an electrochemical cell comprising the anode and a cathode separated by a separator comprising a proton transfer medium. Air is delivered to the cathode along with oxygen is reduced at the cathode to generate oxygen-depleted air. The oxygen-depleted air is directed from the cathode of the electrochemical cell along an inerting gas flow path to the protected space. A flow rate of process water or a temperature of process water is controlled, or both a flow rate and a temperature of process water are controlled, on a process water thermal management flow path in operative thermal communication with the cathode or the anode or with both the cathode and the anode, to provide a target temperature at the anode or at the cathode or at both the anode and the cathode.
In some aspects, the method can further include directing the process water through a heat rejection side of a heat exchanger comprising a heat absorption side in operative fluid communication with a heat sink.
In any one or combination of the foregoing aspects, the method can further include directing the process water through a heat absorption side of a heat exchanger comprising a heat rejection side in operative thermal communication with a heat source.
In any one or combination of the foregoing aspects, the process water thermal management flow path can include the anode fluid flow path, or the cathode fluid flow path, or a fluid flow path in operative thermal communication with the cathode or with the anode or with both the cathode and the anode and in fluid isolation from the cathode and fluid flow paths.
In any one or combination of the foregoing aspects, the process water thermal management flow path can include the anode fluid flow path.
In any one or combination of the foregoing aspects, the process water thermal management flow path can include the cathode fluid flow path.
In any one or combination of the foregoing aspects, the process water thermal management flow path can include the fluid flow path in operative thermal communication with the cathode or with the anode or with both the cathode and the anode and in fluid isolation from the cathode and fluid flow paths.
In any one or combination of the foregoing aspects, the fluid flow path in operative thermal communication with the cathode or with the anode or with both the cathode and the anode and in fluid isolation from the cathode and fluid flow paths can include a conduit disposed on the cathode fluid flow path or anode fluid flow path.
In any one or combination of the foregoing aspects, the method can further include a plurality of said electrochemical cells in a stack separated by electrically-conductive fluid flow separators wherein the fluid flow path in operative thermal communication with the cathode or with the anode or with both the cathode and the anode and in fluid isolation from the cathode and fluid flow paths includes an internal passage through one or more of the electrically-conductive fluid flow separators.
The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike:
A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures.
Although shown and described above and below with respect to an aircraft, embodiments of the present disclosure are applicable to on-board systems for any type of vehicle or for on-site installation in fixed systems. For example, military vehicles, heavy machinery vehicles, sea craft, ships, submarines, etc., may benefit from implementation of embodiments of the present disclosure. For example, aircraft and other vehicles having fire suppression systems, emergency power systems, and other systems that may electrochemical systems as described herein may include the redundant systems described herein. As such, the present disclosure is not limited to application to aircraft, but rather aircraft are illustrated and described as example and explanatory embodiments for implementation of embodiments of the present disclosure.
As shown in
Also shown in
Referring now to
The cathode 14 and anode 16 can be controllably electrically connected by electrical circuit 18 to a controllable electric power system 20, which can include a power source (e.g., DC power rectified from AC power produced by a generator powered by a gas turbine engine used for propulsion or by an auxiliary power unit) and optionally a power sink 21. In some embodiments, the electric power system 20 can optionally include a connection to the electric power sink 21 (e.g., one or more electricity-consuming systems or components onboard the vehicle) with appropriate switching (e.g., switches 19), power conditioning, or power bus(es) for such on-board electricity-consuming systems or components, for optional operation in an alternative fuel cell mode.
With continued reference to
Exemplary materials from which the electrochemical proton transfer medium can be fabricated include proton-conducting ionomers and ion-exchange resins. Ion-exchange resins useful as proton conducting materials include hydrocarbon- and fluorocarbon-type resins. Fluorocarbon-type resins typically exhibit excellent resistance to oxidation by halogen, strong acids, and bases. One family of fluorocarbon-type resins having sulfonic acid group functionality is NAFION™ resins (commercially available from E. I. du Pont de Nemours and Company, Wilmington, Del.). Alternatively, instead of an ion-exchange membrane, the separator 12 can be comprised of a liquid electrolyte, such as sulfuric or phosphoric acid, which may preferentially be absorbed in a porous-solid matrix material such as a layer of silicon carbide or a polymer than can absorb the liquid electrolyte, such as poly(benzoxazole). These types of alternative “membrane electrolytes” are well known and have been used in other electrochemical cells, such as phosphoric-acid fuel cells.
During operation of a proton transfer electrochemical cell in the electrolytic mode, water at the anode undergoes an electrolysis reaction according to the formulae:
H2O→½O2+2H++2e− (1)
The electrons produced by this reaction are drawn from electrical circuit 18 powered by electric power source 20 connecting the positively charged anode 16 with the cathode 14. The hydrogen ions (i.e., protons) produced by this reaction migrate across the separator 12, where they react at the cathode 14 with oxygen in the cathode flow path 23 to produce water according to the formula
½O2+2H++2e−→H2O (2)
Removal of oxygen from cathode flow path 23 produces nitrogen-enriched air exiting the region of the cathode 14. The oxygen evolved at the anode 16 by the reaction of formula (1) is discharged as anode exhaust 26.
During operation of a proton transfer electrochemical cell in a fuel cell mode, fuel (e.g., hydrogen) at the anode undergoes an electrochemical oxidation according to the formula
H2→2H++2e− (3)
The electrons produced by this reaction flow through electrical circuit 18 to provide electric power to the electric power sink 21. The hydrogen ions (i.e., protons) produced by this reaction migrate across the separator 12, where they react at the cathode 14 with oxygen in the cathode flow path 23 to produce water according to the formula (2).
½O2+2H++2e−→H2O (2)
Removal of oxygen from cathode flow path 23 produces nitrogen-enriched air exiting the region of the cathode 14.
As mentioned above, the electrolysis reaction occurring at the positively charged anode 16 requires water, and the ionic polymers used for a PEM electrolyte perform more effectively in the presence of water. Accordingly, in some embodiments, a PEM membrane electrolyte is saturated with water or water vapor. Although the reactions (1) and (2) are stoichiometrically balanced with respect to water so that there is no net consumption of water, in practice some amount of moisture will be removed through the cathode exhaust 24 and/or the anode exhaust 26 (either entrained or evaporated into the exiting gas streams). Accordingly, in some exemplary embodiments, water from a water source is circulated past the anode 16 along an anode fluid flow path (and optionally also past the cathode 14). Such water circulation can also provide cooling for the electrochemical cells. In some exemplary embodiments, water can be provided at the anode from humidity in air along an anode fluid flow path in fluid communication with the anode. In other embodiments, the water produced at cathode 14 can be captured and recycled to anode 16 (e.g., through a water circulation loop, not shown). It should also be noted that, although the embodiments are contemplated where a single electrochemical cell is employed, in practice multiple electrochemical cells will be electrically connected in series with fluid flow to the multiple cathode and anode flow paths routed through manifold assemblies.
An example embodiment of an inerting system that can be used as an on-board aircraft inerting system with an electrochemical cell 10 (or cell stack) is schematically shown in
As further shown in
In some embodiments, the electrochemical cell can be used in an alternate mode to provide electric power for on-board power-consuming systems, as disclosed in the aforementioned US Patent Application Publication No. 2017/0331131A1. In this mode, fuel (e.g., hydrogen) is directed from a fuel source to the anode 16 where hydrogen molecules are split to form protons that are transported across the separator 12 to combine with oxygen at the cathode. Simultaneously, reduction and oxidation reactions exchange electrons at the electrodes, thereby producing electricity in an external circuit (18, 21
With reference now to
In some embodiments, the controller 36 can be configured/programmed to control either the flow rate of process water and/or the temperature of the process water fluid flowing through the electrochemical stack 10′. A temperature sensor 31 is shown in
Flow rate of the process water through the electrochemical cell can be regulated by controlling the speed of the pump 34 or with a control valve (not shown) along the process water flow path (e.g., 22′). Control of process water temperature based on output from a temperature sensor (not shown) along the anode fluid flow path 25 (and/or a temperature sensor along the cathode fluid flow path 23) can be accomplished, for example, by controlling the flow of process water through the heat exchanger 38 (e.g., by controlling the speed of the pump 34 or by diverting a controllable portion of the output flow of the pump 34 through a bypass around the heat exchanger 38 with control valves (not shown)) or by controlling the flow of a heat transfer fluid through the heat exchanger 38 along the flow path represented by 40.
In some embodiments, process water for thermal management can be directed along a flow path that is in thermal communication with the anode 16 or with the cathode 14 or with both the anode 16 and the cathode 14, but is in fluid isolation from the cathode fluid flow path 23 and the anode fluid flow path 25. This can provide a beneficial technical effect of allowing for optimum water flow to the anode 16 for electrolysis to produce protons that remove oxygen at the cathode 14while allowing for separate control of cooling water to achieve optimum temperatures. Additionally, the design of separate flow paths for thermal management can provide for opposite-direction or cross-direction flows, and for multiple passes of thermal control water through anode or cathode fluid flow paths. Moreover, flows of water for thermal control on flow paths that are separate from the cathode and anode fluid flow paths allows for thermal management to be optimized without regard for impact on hydrodynamic effects on the electrochemical reactions occurring at the electrodes.
An example embodiment of a system with segregated thermal management fluid flow paths is schematically shown in
Of course, routing of the thermal control process water through passages in the bipolar plates is one example embodiment of a thermal control flow path isolated from the cathode and anode fluid flow paths 23/25, and thermal control can be implemented with other example embodiments. One such example embodiment is shown in
The term “about” is intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms “a”, “an”, “the”, or “any” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof.
While the present disclosure has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this present disclosure, but that the present disclosure will include all embodiments falling within the scope of the claims.