The subject matter disclosed herein generally relates to systems for generating and providing inert gas, oxygen, and/or power on vehicles, and more specifically to fluid flow operation 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 inert 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 vapor 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 inert gas such as nitrogen-enriched air (NEA) (i.e., oxygen-depleted air or ODA) to the ullage. The introduction of NEA or ODA to the ullage displaces 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 inert gas generating systems, which supply nitrogen-enriched air to the vapor space (i.e., ullage) within the fuel tank. It is also known to store inert gas such as Halon onboard for fire suppression systems. In the case of nitrogen-enriched air, the nitrogen-enriched air has a substantially reduced oxygen content that reduces or eliminates oxidizing conditions within the fuel tank. Onboard inert 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. Other types of inert gas generators rely on reactions in which oxygen is reacted with a reactant to incorporate the oxygen into an inert compound. Examples of such inert gas generators include catalytic oxidation reactors or electrochemical cell reactors.
Inert gas generators that react oxygen with a reactant can use air as a source of oxygen; however, ambient air may not always be available at specified conditions for operation (e.g., pressure and temperature). Accordingly, there is a need for alternative arrangements to provide oxygen to inert gas generator reactors.
A system is disclosed for providing inerting gas to a protected space. The system includes an oxygen source, a reactant source, and a reactor configured to chemically react the oxygen with the reactant and incorporate the oxygen into a non-combustible compound. The reactor includes an inlet in operative fluid communication with the reactant source, and an outlet in operative fluid communication with the protected space. The system also includes an ejector including a motive fluid port in operative fluid communication with the oxygen source, a suction port in operative fluid communication with an air source, and an outlet port in operative fluid communication with the reactor inlet.
In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the reactor can include an electrochemical cell including a cathode and an anode separated by an electrolyte, a cathode-side inlet in operative fluid communication with the ejector outlet port, a cathode-side outlet in operative fluid communication with the protected space, and an anode-side inlet in operative fluid communication with the reactant source.
In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the electrochemical cell can be configured as a proton transfer electrochemical cell reactor including a proton transfer medium as said electrolyte.
In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the electrochemical cell can be configured as an oxygen ion transfer electrochemical cell reactor including an oxygen ion transfer medium as said electrolyte.
In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the system can include an electrical connection in controllable communication between the electrochemical cell and a power sink, and between the electrochemical cell and a power source, and a controller configured to alternatively operate the system in alternate modes of operation selected from a plurality of modes, including: a first mode in which electric power is directed from the power source to the electrochemical cell to provide a voltage difference between the anode and the cathode, and an inerting gas is directed from the cathode-side outlet to the protected space, and a second mode in which reactant from the reactant source is directed to the anode, electric power is directed from the electrochemical cell to the power sink, and the inerting gas is directed from the cathode-side outlet to the protected space
In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the reactor can include a catalytic oxidation reactor configured to react oxygen with reactant from the reactant source in an oxidation reaction in the presence of a catalyst.
In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the system can further include a controller configured to alternatively operate the system in alternate modes of operation selected from a plurality of modes, including: a first mode in which the oxygen source and ejector are isolated from the reactor, and the reactor receives compressed air as an alternate source of oxygen; and a second mode in which compressed air is not used, and the reactor receives oxygen and air from the ejector outlet port.
In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the oxygen source can include stored compressed oxygen gas.
In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the system can further include a heater or heat exchanger arranged to heat or cool the oxygen from the oxygen source.
In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the system can further include a pressure regulator disposed on an oxygen flow path between the oxygen source and the ejector.
Also disclosed is a method for providing inerting gas to a protected space. According to the method, oxygen is directed from an oxygen source to a motive port of an ejector, and air is introduced to a suction port of the ejector. A gas mixture of oxygen and air is directed from an outlet port of the ejector to a reactor, and a reactant is directed from a reactant source to the reactor. Oxygen in the gas mixture is reacted with the reactant to incorporate the oxygen into a non-combustible compound, and an inerting gas comprising the non-combustible compound is directed to the protected space.
In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the reactor can include an electrochemical cell including a cathode and an anode separated by an electrolyte, a cathode-side inlet in operative fluid communication with the ejector outlet port, a cathode-side outlet in operative fluid communication with the protected space, and an anode-side inlet in operative fluid communication with the reactant source.
In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the electrochemical cell can be configured as an oxygen ion transfer electrochemical cell reactor including an oxygen ion transfer medium as the electrolyte, and the method includes directing reformate or hydrogen reactant to the anode-side inlet.
In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the electrochemical cell can be configured as a proton transfer electrochemical cell reactor including a proton transfer medium as the electrolyte, and the method includes directing hydrogen reactant to the anode-side inlet.
In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the method can further include alternatively operating the system in alternate modes of operation selected from a plurality of modes including: a first mode in which electric power is directed from a power source to the electrochemical cell to provide a voltage difference between the anode and the cathode, and an inerting gas is directed from the cathode-side outlet to the protected space; and a second mode in which reactant from the reactant source is directed to the anode, electric power is directed from the electrochemical cell to a power sink, and the inerting gas is directed from the cathode-side outlet to the protected space.
In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the reactor can include a catalytic oxidation reactor configured to react oxygen with the reactant in an oxidation reaction in the presence of a catalyst.
In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the method can further include alternatively operating the system in alternate modes of operation selected from a plurality of modes including: a first mode in which the oxygen source and ejector are isolated from the reactor, and the reactor receives compressed air as an alternate source of oxygen; and a second mode in which compressed air is not used, and the reactor receives oxygen and air from the ejector outlet port.
In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the oxygen source can include stored compressed oxygen gas.
In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the method can further include heating or cooling the oxygen from the oxygen source.
In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the method can further include regulating a pressure of oxygen on an oxygen flow path between the oxygen source and the ejector.
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 stationary 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 involve inert gas-generating systems as described herein may include the 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
With reference now to
An example embodiment of an ejector 18 is shown in
In the example embodiment of
With reference now to
Electrochemical cell reactors and their deployment and operation in an inert gas-generating system are described in further detail below. Referring now to
In some aspects, the electrochemical cell can be arranged and configured to operate exclusively as a fuel cell for providing electrical power and inerting gas. In some aspects, as shown in
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 212 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 electrolyzers and fuel cells.
During operation of a proton transfer electrochemical cell in the electrolytic mode, water is directed to the anode as a reactant source. The water at the anode undergoes an electrolysis reaction according to the formula:
H2O→½O2+2H++2e− (1a)
Ozone can also be produced at the anode by a reaction according to the formula:
3H2O→O3+6H++6e− (1b)
The electrons produced by these reactions are drawn from electrical circuit 218 powered by electric power source 220 connecting the positively charged anode 216 with the cathode 214. The hydrogen ion reactant (i.e., protons) produced by this reaction migrate across the separator 212, where they react at the cathode 214 with oxygen in the cathode flow path 223 to produce water according to the formula:
½O2+2H++2e−→H2O (2)
Removal of oxygen from cathode flow path 223 produces nitrogen-enriched air exiting the region of the cathode 214. The oxygen evolved at the anode 216 by the reaction of formula (1) is discharged as anode exhaust 226.
During operation of a proton transfer electrochemical cell in a fuel cell mode, fuel (e.g., hydrogen) is directly supplied to the anode as a reactant. The 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 218 to provide electric power to the electric power sink 221. The hydrogen ions (i.e., protons) produced by this reaction migrate across the separator 212, where they react at the cathode 214 with oxygen in the cathode flow path 223 to produce water according to the formula (2):
½O2+2H++2e−→H2O (2)
Removal of oxygen from cathode flow path 223 produces nitrogen-enriched air exiting the region of the cathode 214.
As mentioned above, the electrolysis reaction occurring at the positively charged anode 216 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 224 and/or the anode exhaust 226 (either entrained or evaporated into the exiting gas streams). Accordingly, in some exemplary embodiments, water from a water source 228 is directed along a water flow path 230 past the anode 216 along an anode fluid flow path (and optionally also past the cathode 214). Such water, which can be recirculated in a flow loop, 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 214 can be captured and recycled to anode 216 (e.g., through a water circulation loop, not shown). It should also be noted that, although aspects of this disclosure are contemplated where a single electrochemical cell is employed, in practice multiple electrochemical cells can be electrically connected in series with fluid flow along multiple cathode and anode flow paths routed through manifold assemblies.
In some embodiments, the electrochemical cell 210 can operate utilizing the transfer of oxygen anions across the separator 212. Exemplary materials from which the electrochemical oxygen anion-transporting electrolytes can be fabricated include solid oxides such as yttria-stabilized zirconia and/or ceria doped with rare earth metals. These types of materials are well known and have been used in solid oxide fuel cells (SOFC).
During operation of an oxygen anion transfer electrochemical cell in a power consuming (e.g., electrolyzer) mode, oxygen at the cathode undergoes an electrochemical reduction reaction according to the formula:
½O2+2e−→O═ (4).
The electrons consumed by this reaction are drawn from electrical circuit 218 powered by electric power source 220 connecting the positively charged anode 216 with the cathode 214. The oxygen anions produced by this reaction migrate across the separator 212, where they undergo an electrochemical oxidation reaction at the anode 214 according to the formula:
O=→½O2+2e− (5)
Removal of oxygen from cathode flow path 224 produces nitrogen-enriched air exiting the region of the cathode 214. The oxygen produced at the anode 216 by the reaction of formula (5) is discharged as oxygen or an oxygen-enriched air stream as anode exhaust 26.
During operation of an oxygen ion transfer electrochemical cell in a fuel cell mode, oxygen at the cathode undergoes an electrochemical reduction reaction according to the formula (4), and the electrons consumed by this reaction are drawn from electrons liberated at the anode, which flow through electrical circuit 218 to provide electric power to electric power sink (not shown). The oxygen anions produced by this reaction migrate across the separator 212, where they react with fuel such as hydrogen (i.e., reactant) at the anode according to the formula:
½O2+2e→O═ (4)
and
H2+O═→H2O+2e− (6)
Carbon monoxide (e.g., contained in fuel reformate) can also serve as fuel in solid oxide electrochemical cells. In this case, the oxygen anions produced at the cathode according to formula (4) migrate across the separator 212 where they react with carbon monoxide at the anode according to the formula:
CO+O═→CO2+2e− (7)
Removal of oxygen from cathode flow path 224 produces nitrogen-enriched air exiting the region of the cathode 214. The steam and carbon dioxide produced at the anode 216 by the reactions of formulas (6) and (7) respectively is discharged along with unreacted fuel as anode exhaust 226. Any unreacted fuel that exits anode 216 via anode exhaust flow path 226 can be recycled to fuel flow path 432 using an ejector or blower (not shown), or can be fed to a fuel processing unit wherein the steam and carbon dioxide contribute to reforming.
As mentioned above, in some embodiments the reactor can be a catalytic oxidation reactor that reacts a fuel (e.g., a hydrocarbon fuel) with oxygen in a controlled oxidation in the presence of a catalyst. This reaction proceeds according to the formula:
CnH2n+2+(1.5n+0.5)O2→nCO2+(n+1)H2O (8)
With reference now to
As further shown in the Figures, the systems disclosed herein can include a controller 48. The controller 48 can be in operative communication with the components shown in the Figures, as well as additional components (not shown) that may be utilized by the skilled person in implementing this disclosure, including but not limited to the ejector 18, reactors, reactant sources, and any associated valves, pumps, compressors, conduits, ejectors, pressure regulators, or other fluid flow components, and with switches, sensors, and other electrical system components, and any other system components to operate the inerting gas system. These control connections can be through wired electrical signal connections (not shown) or through wireless connections. In some embodiments, the controller 48 can be configured to operate the system according to specified parameters, as discussed in greater detail further above. The controller can be an independent controller dedicated to controlling the inert gas generating system, or can interact with other onboard system controllers or with a master controller. In some embodiments, data provided by or to the controller 48 can come directly from a master controller.
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.