Patent Description:
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: <NUM>) reducing the oxygen concentration, <NUM>) reducing the fuel concentration of the ullage to below the lower explosive limit (LEL), or <NUM>) 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, 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 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. 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 remove it from air.

<CIT> (describing all the features and steps of claims <NUM> and <NUM> respectively), discloses, according to its abstract, an inert gas generating system including an air source configured to provide an air stream that comprises at least one of ram air, external air, conditioned air, or compressed air. An electrochemical gas separator is configured to receive the air stream and to produce an oxygen-depleted air stream. A contained volume is configured to receive the oxygen-depleted air stream.

According to a first aspect of the present invention a system for providing inert gas to a protected space is defined in claim <NUM>. The system includes an electrochemical cell comprising a cathode and an anode separated by a separator comprising a proton transfer medium. Also in the system, a power source is arranged to provide a voltage differential between the anode and the cathode. 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 process water fluid flow path is in operative fluid communication with the anode fluid flow path inlet and the anode fluid flow path outlet, including a gas outlet that discharges gas from the process water fluid flow path. A gas discharge valve is in fluid communication with the gas outlet. The gas discharge valve is operative to allow fluid communication between the process water fluid flow path and a discharge side of the gas outlet in response to gas on the process water fluid flow path, and to block fluid communication between the process water fluid flow path and the discharge side of the gas outlet in response to a lack of gas on the process water fluid flow path.

According to a second aspect of the present invention, a method of inerting a protected space is defined in claim <NUM>. 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. A portion of the process water is electrolyzed at the anode to form protons and oxygen, and the protons are transferred across the separator to the cathode. Process water is directed through a process water fluid flow path including a gas outlet and a gas discharge valve in operative fluid communication with the gas outlet. The gas discharge valve opens in response to the presence of gas in the process water fluid flow path to remove the gas through the gas outlet and form a de-gassed process water, and the de-gassed process water is recycled to the anode. Air is delivered to the cathode and oxygen is reduced at the cathode to generate oxygen-depleted air, and the oxygen-depleted air is directed from the cathode of the electrochemical cell along an inerting gas flow path to the protected space.

In any one or combination of the foregoing aspects, the gas outlet can be located at a high point of the process water fluid flow path.

In any one or combination of the foregoing aspects, the the liquid-gas separator further includes said gas outlet.

In any one or combination of the foregoing aspects, the gas discharge valve can include a poppet valve that is buoyant with respect to process water on the process water fluid flow path or that is connected by a linkage to a float that is buoyant with respect to process water on the process water fluid flow path.

In any one or combination of the foregoing aspects, the gas discharge valve can include a closure connected by a pivotal lever linkage to a float that is buoyant with respect to process water on the process water fluid flow path.

In any one or combination of the foregoing aspects, the gas discharge valve can include a valve body including a lower inlet in fluid communication with the process water fluid flow path and an upper outlet, buoyant float, a pivotal lever linkage connected to the buoyant float, and a poppet valve including a lower poppet valve inlet, an upper poppet valve outlet, and a fluid passage between lower poppet valve inlet and the upper poppet valve outlet, wherein the gas discharge valve includes a first closure at the lower poppet valve inlet arranged to sealingly close against a valve seat on the pivotal lever linkage and a second closure at an upper end of the poppet valve arranged to sealingly close against a valve seat at the valve body upper outlet.

In any one or combination of the foregoing aspects, the gas discharge valve can include a closure responsive to different levels of force resulting from water on the process water fluid flow path and from gas on the process water fluid flow path.

In any one or combination of the foregoing aspects, the gas discharge valve can include a closure connected to an actuator comprising a hygroscopic material that swells in response to contact with process water on the process water fluid flow path.

In any one or combination of the foregoing aspects, the system can further include a heater or a first heat exchanger including a heat absorption side in operative fluid communication with the process water fluid flow path.

In any one or combination of the foregoing aspects, the system can further include a second heat exchanger including a heat rejection side in operative fluid communication with the process water fluid 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 gas outlet can receive process water discharged from the heater or first heat exchanger, and the heat rejection side inlet of the second heat exchanger receives process water from a process water fluid flow path side of the gas outlet.

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.

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 involve 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 <FIG>, an aircraft includes an aircraft body <NUM>, which can include one or more bays <NUM> beneath a center wing box. The bay <NUM> can contain and/or support one or more components of the aircraft <NUM>. For example, in some configurations, the aircraft can include environmental control systems (ECS) and/or on-board inert gas generation systems (OBIGGS) within the bay <NUM>. As shown in <FIG>, the bay <NUM> includes bay doors <NUM> that enable installation and access to one or more components (e.g., OBIGGS, ECS, etc.). During operation of environmental control systems and/or fuel inerting systems of the aircraft, air that is external to the aircraft can flow into one or more ram air inlets <NUM>. The outside air may then be directed to various system components (e.g., environmental conditioning system (ECS) heat exchangers) within the aircraft. Some air may be exhausted through one or more ram air exhaust outlets <NUM>.

Also shown in <FIG>, the aircraft includes one or more engines <NUM>. The engines <NUM> are typically mounted on the wings <NUM> of the aircraft and are connected to fuel tanks (not shown) in the wings, but may be located at other locations depending on the specific aircraft configuration. In some aircraft configurations, air can be bled from the engines <NUM> and supplied to OBIGGS, ECS, and/or other systems, as will be appreciated by those of skill in the art.

Referring now to <FIG>, an electrochemical cell is schematically depicted. The electrochemical cell <NUM> comprises a separator <NUM> that includes an ion transfer medium. As shown in <FIG>, the separator <NUM> has a cathode <NUM> disposed on one side and an anode <NUM> disposed on the other side. Cathode <NUM> and anode <NUM> can be fabricated from catalytic materials suitable for performing the needed electrochemical reaction (e.g., the oxygen-reduction reaction at the cathode and an oxidation reaction at the anode). Exemplary catalytic materials include, but are not limited to, nickel, platinum, palladium, rhodium, carbon, gold, tantalum, titanium, tungsten, ruthenium, iridium, osmium, zirconium, alloys thereof, and the like, as well as combinations of the foregoing materials. Cathode <NUM> and anode <NUM>, including catalyst <NUM>' and catalyst <NUM>', are positioned adjacent to, and preferably in contact with the separator <NUM> and can be porous metal layers deposited (e.g., by vapor deposition) onto the separator <NUM>, or can have structures comprising discrete catalytic particles adsorbed onto a porous substrate that is attached to the separator <NUM>. Alternatively, the catalyst particles can be deposited on high surface area powder materials (e.g., graphite or porous carbons or metal-oxide particles) and then these supported catalysts may be deposited directly onto the separator <NUM> or onto a porous substrate that is attached to the separator <NUM>. Adhesion of the catalytic particles onto a substrate may be by any method including, but not limited to, spraying, dipping, painting, imbibing, vapor depositing, combinations of the foregoing methods, and the like. Alternately, the catalytic particles may be deposited directly onto opposing sides of the separator <NUM>. In either case, the cathode and anode layers <NUM> and <NUM> may also include a binder material, such as a polymer, especially one that also acts as an ionic conductor such as anion-conducting ionomers. In some embodiments, the cathode and anode layers <NUM> and <NUM> can be cast from an "ink," which is a suspension of supported (or unsupported) catalyst, binder (e.g., ionomer), and a solvent that can be in a solution (e.g., in water or a mixture of alcohol(s) and water) using printing processes such as screen printing or inkjet printing.

The cathode <NUM> and anode <NUM> can be controllably electrically connected by electrical circuit <NUM> to a controllable electric power system <NUM>, 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 <NUM>. In some embodiments, the electric power system <NUM> can optionally include a connection to the electric power sink <NUM> (e.g., one or more electricity-consuming systems or components onboard the vehicle) with appropriate switching (e.g., switches <NUM>), 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 <FIG>, a cathode supply fluid flow path <NUM> directs gas from an air source (not shown) into contact with the cathode <NUM>. Oxygen is electrochemically depleted from air along the cathode fluid flow path <NUM>, and can be exhausted to the atmosphere or discharged as nitrogen-enriched air (NEA) (i.e., oxygen-depleted air, ODA) to an cathode fluid flow path outlet <NUM> leading to an inert gas flow for delivery to an on-board fuel tank (not shown), or to a vehicle fire suppression system associated with an enclosed space (not shown), or controllably to either or both of a vehicle fuel tank or an on-board fire suppression system. An anode fluid flow path <NUM> is configured to controllably receive an anode supply fluid from an anode supply fluid flow path <NUM>'. The anode fluid flow path <NUM> includes water when the electrochemical cell is operated in an electrolytic mode to produce protons at the anode for proton transfer across the separator <NUM> (e.g., a proton transfer medium such as a proton exchange membrane (PEM) electrolyte or phosphoric acid electrolyte). If the system is configured for alternative operation in a fuel cell mode, the anode fluid flow path <NUM> can be configured to controllably also receive fuel (e.g., hydrogen). The protons formed at the anode are transported across the separator <NUM> to the cathode <NUM>, leaving oxygen on the anode fluid flow path, which is exhausted through an anode fluid flow path outlet <NUM>. The oxygen effluent may be entrained in process water in the form of bubbles or dissolved in the process water. Control of fluid flow along these flow paths can be provided through conduits and valves (not shown), which can be controlled by a controller <NUM> including a programmable or programmed microprocessor.

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. du Pont de Nemours and Company, Wilmington, Del. Alternatively, instead of an ion-exchange membrane, the separator <NUM> 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 at the anode undergoes an electrolysis reaction according to the formula:.

H<NUM>O → ½O<NUM> + <NUM>+ + 2e-     (1a).

<NUM><NUM>O → O<NUM> + <NUM>+ + 6e-     (1b).

By varying the voltage, the desired reaction 1a or 1b may be favored. For example, elevated cell voltage is known to promote ozone formation (reaction 1b). Since ozone is a form of oxygen, the term oxygen as used herein refers individually to either or collectively to both of diatomic oxygen and ozone.

The electrons produced by this reaction are drawn from electrical circuit <NUM> powered by electric power source <NUM> connecting the positively charged anode <NUM> with the cathode <NUM>. The hydrogen ions (i.e., protons) produced by this reaction migrate across the separator <NUM>, where they react at the cathode <NUM> with oxygen in the cathode flow path <NUM> to produce water according to the formula:.

½O<NUM> + <NUM>+ + 2e- → H<NUM>O     (<NUM>).

Removal of oxygen from cathode flow path <NUM> produces nitrogen-enriched air exiting the region of the cathode <NUM>. The oxygen and ozone evolved at the anode <NUM> by the reaction of formula (<NUM>) is discharged as anode fluid flow path outlet <NUM>.

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:.

The electrons produced by this reaction flow through electrical circuit <NUM> to provide electric power to the electric power sink <NUM>. The hydrogen ions (i.e., protons) produced by this reaction migrate across the separator <NUM>, where they react at the cathode <NUM> with oxygen in the cathode flow path <NUM> to produce water according to the formula (<NUM>): (½O<NUM> + <NUM>+ + 2e- → H<NUM>O,), in which removal of oxygen from cathode flow path <NUM> produces nitrogen-enriched air exiting the region of the cathode <NUM>.

As mentioned above, the electrolysis reaction occurring at the positively charged anode <NUM> 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 (<NUM>) and (<NUM>) 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 fluid flow path outlet <NUM> and/or the anode fluid flow path outlet <NUM> (either entrained or evaporated into the exiting gas streams). Accordingly, in some exemplary embodiments, water from a water source is circulated past the anode <NUM> along an anode fluid flow path (and optionally also past the cathode <NUM>). 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 <NUM> can be captured and recycled to anode <NUM> (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.

In some aspects, the gas outlet <NUM> can be disposed on a gas-liquid separator vessel such as a vessel <NUM> as shown in <FIG>. The gas-liquid separator <NUM> can include a tank with a liquid space and a vapor space inside, allowing for gas to separate and accumulate in the vapor space for discharge through the gas outlet <NUM>, and for liquid to be removed from the liquid space and transported back to the electrochemical cell <NUM>. In some aspects, a vessel for gas-liquid separation vessel is not necessary, and the gas outlet <NUM> can be disposed on a fluid flow conduit at a high point on the flow path <NUM>' where gas accumulates as shown in the example embodiment of <FIG>. It is noted here that <FIG> and <FIG> show different variations of fuel tank inerting systems, and use some of the same reference numbers as <FIG>. Such same numbers are used to describe the same components in <FIG> and <FIG> as in <FIG>, without the need for (or inclusion of) repeated descriptions of the components. For a description of the components identified by such same numbers, reference can be made to the description of <FIG> or other such previous Figure where the reference numbers were first introduced.

Removal of gas through the gas outlet <NUM> is promoted by gas discharge valve <NUM>. The gas discharge <NUM> is in fluid communication with the gas outlet. The gas discharge valve <NUM> is operative to allow fluid communication between the process water fluid flow path and a discharge side of the gas outlet in response to gas on the process water fluid flow path <NUM>', and to block fluid communication between the process water fluid flow path and the discharge side of the gas outlet in response to a lack of gas on the process water fluid flow path <NUM>'.

Various types of valves can be used as the gas discharge valve <NUM> as shown in <FIG>, <FIG>, <FIG>. In each of these Figures, the lower end of the gas discharge valve is in operative fluid communication with the process water fluid flow path <NUM>' and the upper end is in operative fluid communication with a discharge space.

In some aspects, the gas discharge valve <NUM> can include a poppet valve that is buoyant with respect to process water on the process water fluid flow path or that is connected by a linkage to a float that is buoyant with respect to process water on the process water fluid flow path. <FIG> show schematic illustrations of a gas discharge valve 56a including a buoyant poppet valve. As shown in <FIG>, a poppet float <NUM> is disposed inside a valve body <NUM> that includes a discharge opening <NUM>. In <FIG>, the poppet float <NUM> is shown as buoyant, but the in the case of a non-buoyant poppet valve the bottom of the poppet float <NUM> can be connected via a vertical linkage (not shown) to a separate buoyant float (not shown). As shown in <FIG>, a relatively high water level <NUM> floats the poppet float <NUM> into a position in which it seats against discharge opening <NUM> so that the valve is closed. In <FIG>, gas accumulating in the upper portion of the interior of the valve body <NUM> causes the water level to drop to a lower water level <NUM>', which in turn causes poppet float <NUM> to drop along with the reduced water level <NUM>' so that the gas is discharged through the discharge opening <NUM> as represented by gas discharge arrow <NUM>. As gas is discharged through the discharge opening <NUM>, the water level can rise again and cause the gas discharge valve 56a to close.

In some aspects, the gas discharge valve <NUM> can include a closure connected by a pivotal lever linkage to a float that is buoyant with respect to process water on the process water fluid flow path. <FIG> show schematic illustrations of a gas discharge valve 56b including pivoted lever <NUM> linked to a buoyant float <NUM> in a valve body <NUM> with a discharge opening <NUM>. As shown in <FIG>, a relatively high water level <NUM> floats the buoyant float <NUM> into a position in which urges the pivoted lever <NUM> into a position in which it seats against discharge opening <NUM> so that the valve is closed. In <FIG>, gas accumulating in the upper portion of the interior of the valve body <NUM> causes the water level to drop to a lower water level <NUM>', which in turn causes buoyant float <NUM> to drop along with the reduced water level <NUM>'. As the buoyant float <NUM> drops, the pivoted lever <NUM> pivots around pivot mount <NUM> so that the pivoted lever <NUM> disengages from the discharge opening <NUM>, allowing the gas to be discharged through the discharge opening <NUM> as represented by gas discharge arrow <NUM>. As gas is discharged through the discharge opening <NUM>, the water level can rise again and cause the gas discharge valve 56b to close.

In some aspects, the gas discharge valve can include both pivoted lever closure and a poppet valve closure. As shown in <FIG>, a gas discharge valve 56c includes a buoyant float <NUM> disposed within a valve body <NUM> having a discharge opening <NUM>, along with a pivoted lever linkage <NUM> is disposed between a buoyant float <NUM> and a poppet valve <NUM> that includes a lower poppet valve inlet <NUM> and an upper poppet valve outlet <NUM> connected by a fluid passage. As shown in <FIG>, a relatively high water level <NUM> floats the buoyant float <NUM> into a position in which urges the pivoted lever <NUM> into a position in which it seats against the poppet valve inlet <NUM>, and the poppet valve <NUM> is also seated against the discharge opening <NUM> so that the valve is closed. In <FIG>, gas accumulating in the upper portion of the interior of the valve body <NUM> causes the water level to drop to a lower water level <NUM>', which in turn causes buoyant float <NUM> to drop along with the reduced water level <NUM>'. As the buoyant float <NUM> drops, the pivoted lever <NUM> pivots around pivot mount <NUM> so that the pivoted lever <NUM> disengages from the poppet valve inlet <NUM>, allowing the gas to enter the poppet valve inlet <NUM>, from which it flows through the poppet valve fluid passage and out of the poppet valve outlet <NUM> from which it discharged through the discharge opening <NUM> as represented by gas discharge arrow <NUM>. As gas is discharged through the discharge opening <NUM>, the water level can rise again and cause the valve to close. In the configuration shown in <FIG>, a pressure differential between the interior of the valve body <NUM> and the exterior keeps the poppet valve <NUM> sealed against the discharge opening <NUM>. However, in cases of a reduction in pressure on the process water fluid flow path <NUM>' such as from a leak that could draw a vacuum and potentially damage system components, the reverse pressure differential represented by gas flow arrow <NUM> will cause the poppet valve <NUM> to disengage from discharge opening <NUM>, providing a larger opening for gas flow as shown in <FIG>. In this configuration, the poppet valve <NUM> is supported by a poppet valve support <NUM> that includes openings for gas flow, so the poppet valve inlet <NUM> can remain engaged with or can be disengaged from the pivoted lever <NUM>.

In some aspects, the gas discharge valve <NUM> can include a closure responsive to different levels of force resulting from water on the process water fluid flow path and from gas on the process water fluid flow path. <FIG> show schematic illustrations of a gas discharge valve 56d including a valve member <NUM> biased in a downward direction by a bias member <NUM> such as a spring in a valve body <NUM> with a discharge opening <NUM> and an intake opening <NUM> in operative fluid communication with the process water fluid flow path <NUM>'. As shown in <FIG>, a relatively high force is exerted against the valve member <NUM> by water flowing on the process water fluid flow path <NUM>'. The force is sufficient to overcome the bias from bias member <NUM>, causing the valve member <NUM> to seat against discharge opening <NUM> so that the valve is closed. In <FIG>, reduced a presence of air on the process water fluid flow path <NUM>' reduces the mass of the fluid and thus the momentum and force applied against the valve member <NUM>, which allows the bias member <NUM> to urge the valve member <NUM> to disengage from the discharge opening <NUM>, allowing the gas to be discharged through the discharge opening <NUM> as represented by gas discharge arrow <NUM>. As gas is discharged through the discharge opening <NUM>, valve configuration can revert to the configuration shown in <FIG> with the valve closed. <FIG> shows a valve configuration in a system shut-down mode, in which a lack of force from process water flowing on the process water fluid flow path <NUM>' allows the bias member <NUM> to urge the valve member <NUM> into engagement with the intake opening <NUM> so that the gas discharge valve 56d is closed.

In some aspects, the gas discharge valve <NUM> can include a closure connected to an actuator comprising a hygroscopic material that swells in response to contact with process water on the process water fluid flow path <NUM>'. As shown in <FIG>, a gas discharge valve 56e includes a valve member <NUM> disposed inside a valve body <NUM> that includes a discharge opening <NUM>. The valve member <NUM> is engaged with an actuator <NUM> that includes a hygroscopic material <NUM>. Examples of hygroscopic materials include but are not limited to neoprene, cellulose, polyacrylamide gel, polyether block amide copolymer, bentonite, and hydrogels based on hydrophilic polymers such as poly(N-isopropylacrylamide), poly-(<NUM>-hydroxyethyl methacrylate), and poly(acrylic acid)-poly(allylamine hydrochloride) that expand in response to contact with water. As shown in <FIG>, a relatively high water level <NUM> keeps the hygroscopic material in an expanded state in which it urges the actuator into a position to in which the valve member <NUM> is seated against discharge opening <NUM> so that the valve is closed. In <FIG>, gas accumulating in the upper portion of the interior of the valve body <NUM> causes the water level to drop to a lower water level <NUM>' below that of the actuator <NUM> including hygroscopic material <NUM>, which in turn causes the hygroscopic material <NUM> to contract so that the valve member <NUM> disengages from the discharge opening so that the gas is discharged through the discharge opening <NUM> as represented by gas discharge arrow <NUM>. As gas is discharged through the discharge opening <NUM>, the water level can rise again and cause the gas discharge valve 56e to close.

With continuing reference to <FIG>, and also <FIG> discussed below, oxygen from the gas outlet <NUM> can be exhausted to atmosphere or can be used for other applications such as an oxygen stream directed to aircraft occupant areas, occupant breathing devices, an oxygen storage tank, or an emergency aircraft oxygen breathing system. Ozone from the gas outlet <NUM> can be exhausted to atmosphere or can be used for other onboard applications such as for water purification or as a biocide for biofilms such as can form in tanks such as fuel tanks and water tanks. Additional components promoting the separation of gas from liquid on the flow path <NUM>' such as coalescing filters, vortex gas-liquid separators, membrane separators, heaters, heat exchangers, etc. can also be utilized, as described in further detail below as described in further detail below or in <CIT>. Other components and functions can also be incorporated with the flow path <NUM>', including but not limited to water purifiers such as disclosed <CIT>.

The electrochemical cell or cell stack <NUM> generates an inert gas on the cathode fluid flow path <NUM> by depleting oxygen to produce oxygen-depleted air (ODA), also known as nitrogen-enriched air (NEA) at the cathode <NUM> that can be directed to a protected space <NUM> (e.g., a fuel tank ullage space, a cargo hold, or an equipment bay). An air source <NUM> (e.g., ram air, compressor bleed, blower) is directed to the cathode fluid flow path <NUM> where oxygen is depleted by electrochemical reactions with protons that have crossed the separator <NUM> as well as electrons from an external circuit (not shown) to form water at the cathode <NUM>. The ODA thereby produced can be directed to a protected space <NUM> such as an ullage space in in the aircraft fuel tanks as disclosed or other protected space <NUM>. The inert gas flow path (cathode fluid flow path outlet <NUM>) can include additional components (not shown) such as flow control valve(s), a pressure regulator or other pressure control device, and water removal device(s) such as a heat exchanger condenser, a membrane drier or other water removal device(s), or a filter or other particulate or contaminant removal devices. Additional information regarding the electrochemical production of ODA can be found in <CIT>, <CIT>, and <CIT>.

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 above-referenced <CIT>. In this mode, fuel (e.g., hydrogen) is directed from a fuel source to the anode <NUM> where hydrogen molecules are split to form protons that are transported across the separator <NUM> to combine with oxygen at the cathode. Simultaneously, reduction and oxidation reactions exchange electrons at the electrodes, thereby producing electricity in an external circuit. Embodiments in which these alternate modes of operation can be utilized include, for example, operating the system in alternate modes selected from a plurality of modes including a first mode of water electrolysis (either continuously or at intervals) under normal aircraft operating conditions (e.g., in which an engine-mounted generator provides electrical power) and a second mode of electrochemical electricity production (e.g., in response to a demand for emergency electrical power such as due to failure of an engine-mounted generator). ODA can be produced at the cathode <NUM> in each of these alternate modes of operation.

In some aspects, the gas inerting system can promote gas(es) dissolved in the process water (e.g., oxygen) to evolve gas in the gas phase that can be removed from the process water fluid flow path <NUM>' through the gas outlet <NUM>. The solubility of gases such as oxygen in water varies inversely with temperature and varies directly with pressure. Accordingly, higher temperatures can provide lower solubility of oxygen (or ozone) in water, and lower temperatures provide greater solubility of oxygen (or ozone) in water. Similarly, reduced pressures provide lower solubility of oxygen in water. In some embodiments, the systems described herein can be configured to promote evolution of gas(es) from dissolved gas(es) in the process water through thermal control and/or pressure control for removal from the process water fluid flow path. Thermal and pressure management can be provided as discussed in more detail further below.

With reference now to <FIG>, example embodiments are shown of a gas inerting system utilizing an electrochemical cell or stack <NUM> and thermal and/or pressure management. As shown in <FIG>, the cathode side of the electrochemical cell or stack <NUM> produces ODA on the cathode fluid flow path <NUM> as inert gas for a protected space in the same manner as discussed above with respect to <FIG>. Also, for ease of illustration, the separator <NUM>, cathode <NUM>, and anode <NUM> are shown as a single membrane electrode assembly (MEA) <NUM>. It is noted that <FIG> show counter-flow between the anode and cathode sides of the MEA <NUM>, whereas <FIG> show co-flow; however, many configurations can utilize cross-flow configurations that are not shown in the Figures herein for ease of illustration. It is further noted that, although not shown in <FIG>, process water for thermal management can also be in fluid and thermal communication with the cathode side of the electrochemical cell <NUM> as will be understood by the skilled person. On the anode side of the electrochemical cell <NUM>, process water from the water source (e.g. a water reservoir <NUM>' equipped with a process make-up water feed line <NUM>) is directed along the anode supply fluid flow path <NUM>' by a pump <NUM>. The pump <NUM> provides a motive force to move the process water along the anode fluid flow path <NUM>, from which it is directed through flow control valve <NUM> to a gas-liquid separator <NUM>. Oxygen or other gases on the process water fluid flow path can be removed through a gas outlet <NUM> from the vessel <NUM> to gas discharge space <NUM>, or the water reservoir <NUM>' can itself serve as a gas-liquid separator by providing a sufficiently large volume for reduced flow velocity and a vapor space for gas-liquid separation and a gas outlet (not shown) to the gas discharge space <NUM>.

As mentioned above,the controller <NUM> controls system operating parameters to provide a target dissolved gas content (e.g., a dissolved oxygen content) in the process water during operation. Dissolved oxygen concentration in the process water can be measured directly. Examples of oxygen sensors include (i.e., an oxygen sensor calibrated to determine dissolved oxygen content), but are not limited to sensors that utilize the measurement of variables such as impedance, spectral transmittance/absorbance of light, chemical reactivity of analytes with dissolved oxygen, electrochemical sensors (including the anode and cathode of the electrochemical cell/stack <NUM> and spot measurements thereon), chemical interactions, or combinations (e.g., chemiluminescent sensors). Dissolved oxygen levels can also be determined without a sensor calibrated directly for dissolved oxygen. For example, this can be accomplished by measuring one or more of other process parameters including but not limited to process water temperature, electrode temperatures, electrode voltages, electrode current densities, water pressure, vapor pressure (e.g., in a vapor phase in the vessel <NUM>), cumulative readings and values determined over time for any of the above or other measured system parameters, elapsed time of operation, and comparing such parameters against empirical oxygen content data (e.g., a look-up table) to determine an inferred dissolved oxygen concentration. A sensor <NUM> is shown in <FIG> disposed in the flow path <NUM>', and can represent one or more sensors at the location shown or elsewhere in the system to measure any one or more of the above-mentioned or other parameters. For the sake of discussion below, the sensor <NUM> may be referred to as measuring for a concentration of dissolved oxygen in the process water, process water temperature, gas temperature, and pressure including gas pressure or liquid pressure. The sensors represented by sensor <NUM> can be located as shown in <FIG> at or immediately upstream of the vessel <NUM>. Other sensor locations can be utilized. For example, a dissolved oxygen sensor and/or temperature sensor could be disposed in the liquid space in reservoir <NUM>'. Process water temperature and pressure can be measured at any of a number of potential locations such as at the anode flow path outlet, or upstream and/or downstream of the pump <NUM>, or upstream and/or downstream of the flow control valve <NUM>, or anywhere along either or both of the cathode fluid flow path <NUM> or the anode fluid flow path <NUM>.

As mentioned above, the solubility of oxygen in water varies inversely with temperature, and in some embodiments the system can be controlled to add heat to the process water to promote dissolution and evolution of gas phase oxygen so that it can be separated and removed. In some embodiments, the process water can be contacted with a heat source upstream of a liquid-gas separator. A separate heat source can be used, such as a heater or a heat exchanger with a heat rejection side in fluid and/or thermal communication with a heat source. The heat source can also be the electrochemical cell/stack <NUM> itself. The enthalpy of the chemical reactions resulting from electrolytic generation of inert gas occurring on each side of the separator <NUM> are balanced, with water molecules being split on the anode side and atoms combined to form water on the cathode side. Accordingly, the electrical energy entered into the system results in generation of heat. Disposition of the gas outlet <NUM> in the flow path <NUM>' downstream of the cell/stack <NUM> allows for heat generated by the cell/stack <NUM> to promote evolution of oxygen for separation and removal from the process water. Continual addition of heat into the system to promote oxygen removal could cause heat to accumulate in the system, and thermal management of the system can be accomplished with various protocols. For example, in some embodiments, heat can be dissipated into a volume of water such as the reservoir <NUM>' without increasing process water temperatures outside of normal parameters during a projected duration of system operation. However, in situations where the reservoir <NUM>' cannot absorb process heat within tolerances, a heat exchanger can be included in the system as shown in <FIG> with heat exchanger <NUM>. The heat exchanger <NUM> can provide cooling from a heat sink along the heat transfer flow path <NUM> (e.g., RAM air, a refrigerant from a cooling system such as a vapor compression cooling system). Multiple heat exchangers can also be used.

In some embodiments, the electrochemical cell stack <NUM>' can be controlled to operate at parameters that provide a temperature at or upstream of a liquid-gas separator that is sufficient to produce a target dissolved oxygen level (as used herein, the terms upstream and downstream are defined as a position in a single iteration of the flow loop that begins and ends with the electrochemical cell stack <NUM>'). In some embodiments, however, it may be desirable to operate the electrochemical cell stack at temperatures below that at which sufficient levels of dissolved oxygen are desolubilized. In such cases, a separate heater or heat exchanger can be included in the system, such as heater/exchanger <NUM> as shown in <FIG>. The configuration of <FIG> can provide added heat from heater/exchanger <NUM> upstream of the vessel <NUM>, and the added heat can be dissipated into a heat sink such as reservoir <NUM>' or can be removed with a heat exchanger such as heat exchanger <NUM>. Alternatively, or in addition to the use of a heater/exchanger <NUM> to add heat to the system, in some embodiments the electrochemical cell stack can be operated temporarily at a higher temperature during an oxygen-removal cycle, and then returned to operate at a lower temperature after completion of the oxygen-removal cycle.

Pressure management can also be utilized for promotion of evolution of gaseous oxygen from dissolved oxygen. For example, the placement of the control valve <NUM> upstream of the liquid-gas-separator can provide a reduction in pressure that can promote evolving of oxygen for removal from the process water. Output pressure of the pump <NUM> can also modify pressure to promote oxygen evolution.

In some embodiments, the process water can be heated using the pump and a pressure regulator. The pump performs mechanical work on the process water to actively heat it. In this way, the pump and pressure regulator serve as a heating element. Those skilled in the art will readily appreciate that in accordance with the First Law of Thermodynamics, the work performed on the process water elevates the internal energy of said fluid. In addition, in some embodiments the process water may also remove waste heat from the pump (e.g. bearings, motor drive, etc.). Those skilled in the art will readily appreciate that the work imparted to a fluid results from the change in the pressure and the change in volume of the fluid.

A flow rate of the process water through the electrochemical cell can be regulated by controlling the speed of the pump <NUM> or with a pressure regulator (not shown) along the process water flow path (e.g., <NUM>'). Control of process water temperature based on output from a temperature sensor (not shown) along the anode fluid flow path <NUM> (and/or a temperature sensor along the cathode fluid flow path <NUM>) can be accomplished, for example, by controlling the flow of process water through the heat exchanger <NUM> (e.g., by controlling the speed of the pump <NUM> or by diverting a controllable portion of the output flow of the pump <NUM> through a bypass around the heat exchanger <NUM> with control valves (not shown)) or by controlling the flow of a heat transfer fluid through the heat exchanger <NUM> along the flow path represented by <NUM>.

It should be noted that system configurations shown in <FIG> represent example embodiments, and that changes and modifications are contemplated. For example, in some embodiments a heat source (including the electrochemical cell or stack ("stack"), or a separate heat source) can be disposed upstream of a gas outlet with a gas discharge valve <NUM> ("outlet"), which can be disposed upstream of a heat-absorbing heat exchanger ("HX") in thermal communication with a heat sink. Such embodiments can provide a technical benefit of adding heat to promote evolution of gas from gas dissolved in the process water, and subsequent removal of such added heat from the process water. Examples of configurations of components include but are not limited to stack→heat source-> outlet→HX, heat source->stack->outlet->HX, stack->outlet->HX. A pressure regulator can also be included to provide a lower pressure at the separator to promote evolution of gas, for example with an order of components of pump->stack/heat source->pressure regulator->outlet->HX.

Claim 1:
A system for providing inerting gas to a protected space, such as a fuel tank ullage space, a cargo hold, or an equipment bay, the system comprising:
an electrochemical cell (<NUM>) comprising a cathode (<NUM>) and an anode (<NUM>) separated by a separator comprising a proton transfer medium;
a power source arranged to provide a voltage differential between the anode and the cathode;
a cathode fluid flow path 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 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 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 between a process water source and the anode fluid flow path inlet;
a process water fluid flow path in operative fluid communication with the anode fluid flow path inlet and the anode fluid flow path outlet, including a gas outlet that discharges gas from the process water fluid flow path;
a liquid-gas separator on the process water fluid flow path, wherein the liquid-gas separator includes an inlet and a liquid outlet each in operative fluid communication with the process water fluid flow path; and
a gas discharge valve (<NUM>) in fluid communication with the gas outlet, said gas discharge valve operative to allow fluid communication between the process water fluid flow path and a discharge side of the gas outlet in response to gas on the process water fluid flow path, and to block fluid communication between the process water fluid flow path and the discharge side of the gas outlet in response to a lack of gas on the process water fluid flow path; and characterized by
a sensor configured to directly or indirectly measure dissolved oxygen content of process water that enters the gas-liquid separator;
a controller configured to provide a target response of the sensor through control of a pressure differential between the process water fluid flow path and the discharge side of the gas outlet.