Patent Publication Number: US-11638900-B2

Title: Process water gas management of electrochemical inert gas generating system

Description:
BACKGROUND 
     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 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 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 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, 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. 
     BRIEF DESCRIPTION 
     A system is disclosed for providing inert 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. 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 disposed between an air source and the cathode fluid flow path inlet, and an inert gas flow path is 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. A baffle is disposed on the process water fluid flow path, and a gas outlet from the process water fluid flow path is in operative fluid communication with the baffle. 
     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. 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 to a baffle to form 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. The oxygen-depleted air is directed from the cathode of the electrochemical cell along an inert gas flow path to the protected space. 
     In some aspects, the method further includes controlling a flow rate of process water or a temperature of process water, or both a flow rate and a temperature of process water, to provide a target level of dissolved oxygen in the process water. 
     In some aspects, the gas outlet can be located at a high point of the process water fluid flow path. 
     In some aspects, the system can further include 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 wherein the liquid-gas separator further includes said gas outlet. 
     In some aspects, the baffle can be disposed in the liquid-gas separator. 
     In some aspects, the baffle can be disposed in a fluid flow conduit along the process water fluid flow path. 
     In any one or combination of the foregoing aspects, the baffle can include a solid plate, a perforated plate, a solid sheet, a perforated sheet, a fin, a mesh, a strainer, a screen, a chain, a rope, chord, a ring, a turbulator, a vane, or an aggregate material in a packed bed. 
     In any one or combination of the foregoing aspects, the system can further include a heater in operative thermal communication with the process water fluid flow path, or a first heat exchanger including a heat absorption side in operative fluid communication with the process water fluid 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 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 baffle can be in operative fluid communication to receive process water discharged from the heater or first heat exchanger, and the baffle is in operative fluid communication to direct process water to a heat rejection side inlet of the second heat exchanger. 
     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 system can include a plurality of said electrochemical cells in a stack separated by electrically-conductive fluid flow separators. 
     In any one or combination of the foregoing aspects, the system can include a sensor configured to directly or indirectly measure dissolved oxygen content of process water received by the baffle, and a controller configured to provide a target response of the 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. 
     In any one or combination of the foregoing aspects, the sensor can include a temperature sensor, and the controller is configured to provide a target temperature response of the temperature sensor. 
     In any one or combination of the foregoing aspects including a sensor and a controller, the sensor can further include an oxygen sensor, and the controller is configured to provide a target temperature response of the temperature sensor in response to output of the oxygen sensor. 
     In any one or combination of the foregoing aspects including a controller, the controller is configured to provide a target response of the measurement device through control of a flow rate of process water on the anode fluid flow path and/or the cathode fluid flow path. 
     In any one or combination of the foregoing aspects including a controller, the controller can be configured to provide a target response of the measurement device through control of a flow rate through control of a voltage differential applied between the anode and the cathode. 
     In any one or combination of the foregoing aspects including a controller, the controller can be configured to provide a target response of the sensor through control of a flow of process water through a heat transfer device or through a control of a temperature of a heat transfer device. 
     In any one or combination of the foregoing aspects including a controller, the controller can be configured to operate the inerting system in a mode selected from a plurality of modes including a first mode under normal operating conditions and in an oxygen removal mode in response to a high oxygen level signal from the sensor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike: 
         FIG.  1 A  is a schematic illustration of an aircraft that can incorporate various embodiments of the present disclosure; 
         FIG.  1 B  is a schematic illustration of a bay section of the aircraft of  FIG.  1 A ; 
         FIG.  2    is a schematic depiction an example embodiment of an electrochemical cell; 
         FIG.  3    is a schematic illustration of an example embodiment of an electrochemical inert gas generating system with a baffle in a liquid-gas separator vessel; 
         FIGS.  4 A and  4 B  are each a schematic illustration of baffles; 
         FIG.  5    is a schematic illustration of an example embodiment of an electrochemical inert gas generating system with a baffle and a liquid-gas separator vessel; 
         FIG.  6    is a schematic illustration of an example embodiment of an electrochemical inert gas generating system with a baffle and a gas outlet; 
         FIG.  7    is a schematic illustration of another example embodiment of another electrochemical inert gas generating system; and 
         FIG.  8    is a schematic illustration of an example embodiment of yet another electrochemical inert gas generating system. 
     
    
    
     DETAILED DESCRIPTION 
     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 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  FIGS.  1 A- 1 B , an aircraft includes an aircraft body  101 , which can include one or more bays  103  beneath a center wing box. The bay  103  can contain and/or support one or more components of the aircraft  101 . 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  103 . As shown in  FIG.  1 B , the bay  103  includes bay doors  105  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  107 . 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  109 . 
     Also shown in  FIG.  1 A , the aircraft includes one or more engines  111 . The engines  111  are typically mounted on the wings  112  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  111  and supplied to OBIGGS, ECS, and/or other systems, as will be appreciated by those of skill in the art. 
     Referring now to  FIG.  2   , an electrochemical cell is schematically depicted. The electrochemical cell  10  comprises a separator  12  that includes an ion transfer medium. As shown in  FIG.  2   , the separator  12  has a cathode  14  disposed on one side and an anode  16  disposed on the other side. Cathode  14  and anode  16  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  14  and anode  16 , including catalyst  14 ′ and catalyst  16 ′, are positioned adjacent to, and preferably in contact with the separator  12  and can be porous metal layers deposited (e.g., by vapor deposition) onto the separator  12 , or can have structures comprising discrete catalytic particles adsorbed onto a porous substrate that is attached to the separator  12 . 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  12  or onto a porous substrate that is attached to the separator  12 . 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  12 . In either case, the cathode and anode layers  14  and  16  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  14  and  16  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 ink jet printing. 
     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  FIG.  2   , a cathode supply fluid flow path  22  directs gas from an air source (not shown) into contact with the cathode  14 . Oxygen is electrochemically depleted from air along the cathode fluid flow path  23 , and can be exhausted to the atmosphere or discharged as nitrogen-enriched air (NEA) (i.e., oxygen-depleted air, ODA) to a cathode fluid flow path outlet  24  leading to an inert gas flow path 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  25  is configured to controllably receive an anode supply fluid from an anode supply fluid flow path  22 ′. The anode fluid flow path  25  includes water when the electrochemical cell is operated in an electrolytic mode to produce protons at the anode for proton transfer across the separator  12  (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  25  can be configured to controllably also receive fuel (e.g., hydrogen). The protons formed at the anode are transported across the separator  12  to the cathode  14 , leaving oxygen on the anode fluid flow path, which is exhausted through an anode fluid flow path outlet  26 . 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  36  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. 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 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 2 O→½O 2 +2H + +2 e   −   (1a)
 
3H 2 O→O 3 +6H + +6 e   −   (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  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:
 
½O 2 +2H + +2 e   − →H 2 O  (2)
 
     Removal of oxygen from cathode flow path  23  produces nitrogen-enriched air exiting the region of the cathode  14 . The oxygen and ozone evolved at the anode  16  by the reaction of formula (1) is discharged as anode fluid flow path outlet  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:
 
H 2 →2H + +2 e   −   (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): (½O 2 +2H + +2e − →H 2 O), in which 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 fluid flow path outlet  24  and/or the anode fluid flow path outlet  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 a protected space inerting system that can be used as an on-board aircraft inerting system with an electrochemical cell  10  is schematically shown in  FIG.  3   . As shown in  FIG.  3   , water from a process water source  28  is directed (e.g., by a pump, not shown) along the anode supply fluid flow path  22 ′ to the anode fluid flow path  25 , where it is electrolyzed at the anode  16  to form protons and oxygen. The protons are transported across the separator  12  to the cathode  14 , where they combine with oxygen from airflow along the cathode fluid flow path  23  to form water. Removal of the protons from the anode fluid flow path  25  leaves oxygen gas on the anode fluid flow path, which is discharged as anode fluid flow path outlet  26  to a fluid flow path  26 ′. As further shown in  FIG.  3   , the fluid flow path  26 ′ includes a baffle or a plurality of baffles  56 . The baffles  56  are shown in a vessel  58 , but can be disposed anywhere along the fluid flow path  26 ′ such as in a pipe, duct, or other fluid flow conduit. Although water is consumed at the anode by electrolysis, the fluid exiting as anode fluid flow path outlet  26  can include unreacted liquid water and gases such as oxygen formed at the anode  16  and water vapor, and also dissolved gases such as oxygen dissolved in the water. The baffles  56  can provide a beneficial technical effect of promoting coalescing of gas entrained in the liquid water as well as evolution of a gaseous phase gas from dissolved gases, which can then be removed from the fluid flow path  26 ′ such as through a gas outlet  60 , while degassed water is returned to the electrochemical cell  10  through water return flow path  32 , which is a part of the flow path  26 ′. Without removal, such gas(es) could accumulate in the system, and excess levels of gas(es) (including both gases dissolved in the liquid water and also in a gas phase) can cause problems such as pump cavitation or an equilibrium-based shift contrary to the electrolysis reaction(s) at the anode (see Le Chatelier&#39;s Principle). 
     As used herein, the term “baffle” means a surface disposed in an otherwise open fluid flow area on a flow path that redirects or partially obstructs fluid flow without preventing fluid flow altogether. Baffles can take various forms, including but not limited to solid plates, perforated plates, solid sheets, perforated sheets, fins, mesh, strainers, screens, chains, ropes or chords, rings, turbulators, mixing veins, metal wool, or aggregate material in a packed bed of various geometries (e.g. spheres, rods, cylinders, coils, nuts, bolts, washers), and any other form of a surface that redirects or partially obstructs fluid flow. The baffles can be configured in multiple stages (e.g., cascading plates) or single stages, and can be formed from various materials including but not limited to metal (e.g., steel, stainless steel, aluminum), plastic, wood, composite materials, and the like. Example embodiments of baffle configurations are shown in  FIGS.  4 A and  4 B , which carry over numbering from  FIG.  3    without the need or inclusion of language to repeat the description of same-numbered components.  FIG.  4 A  shows baffles configured as cascaded baffle plates  56 ′, and  FIG.  4 B  shows baffles configured as a mesh or screen  56 ″. 
     With reference again to  FIG.  3   , the electrochemical cell or cell stack  10  generates an inert gas on the cathode fluid flow path  23  by depleting oxygen to produce oxygen-depleted air (ODA), also known as nitrogen-enriched air (NEA) at the cathode  14  that can be directed to a protected space  54  (e.g., a fuel tank ullage space, a cargo hold, or an equipment bay). As shown in  FIG.  3   , an air source  52  (e.g., ram air, compressor bleed, blower) is directed to the cathode fluid flow path  23  where oxygen is depleted by electrochemical reactions with protons that have crossed the separator  12  as well as electrons from an external circuit (not shown) to form water at the cathode  14 . The ODA thereby produced can be directed to a protected space  54  such as an ullage space in in the aircraft fuel tanks as disclosed or other protected space  54 . The inert gas flow path (cathode fluid flow path outlet  24 ) 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 U.S. Pat. Nos. 9,963,792, 10,312,536, and U.S. patent application Ser. No. 16/029,024, the disclosures of each of which are incorporated herein by reference in their entirety. 
     The oxygen from the gas outlet  60  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  60  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 fuel tanks. Additional components promoting the separation of gas from liquid on the flow path  26 ′ such as coalescing filters, vortex gas-liquid separators, membrane separators, heaters, heat exchangers, etc. can also be utilized, as described in further detail below or in U.S. patent application Ser. No. 16/375,659, the disclosure of which is incorporated herein by reference in its entirety. 
     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 U.S. Pat. No. 10,312,536. 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. 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  14  in each of these alternate modes of operation. 
       FIG.  3    shows baffles  56  disposed in a vessel  58  that can also function as a gas-liquid separator for accumulation of separated gas at an upper portion of the vessel  58  for discharge through the gas outlet  60 . However, other configurations can be utilized such as a configuration with gas-liquid separator that is separate from the baffles as shown in the example embodiment of  FIG.  5   . In  FIG.  5   , a gas-liquid separator  27  is disposed on the flow path  26 ′ downstream from the baffles  56 . The gas-liquid separator  27  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  60 , and for liquid to be removed from the liquid space and transported back to the electrochemical cell  10 . In some aspects, a vessel for gas-liquid separation is not necessary, and the gas outlet  60  can simply be disposed on a fluid flow conduit at a high point on the flow path  26 ′ as shown in the example embodiment of  FIG.  6   . 
     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  26 ′ through the gas outlet  60 . 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 is provided as discussed in more detail below. 
     With reference now to  FIG.  7   , an example embodiment is shown of a gas inerting system utilizing an electrochemical cell or stack  10  and thermal and/or pressure management. As shown in  FIG.  7   , the cathode side of the electrochemical cell or stack  10  produces ODA on the cathode fluid flow path  23  as inert gas for a protected space in the same manner as discussed above with respect to  FIGS.  3 ,  5 , and  6   . Also, for ease of illustration, the separator  12 , cathode  14 , and anode  16  are shown as a single membrane electrode assembly (MEA)  15 . It is noted that  FIG.  7    shows counter-flow between the anode and cathode sides of the MEA  15 , whereas  FIGS.  3 ,  5 , and  6    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.  7   , process water for thermal management can also be in fluid and thermal communication with the cathode side of the electrochemical cell  10  as will be understood by the skilled person. On the anode side of the electrochemical cell  10 , process water from the water source (e.g. a water reservoir  28 ′ equipped with a process make-up water feed line  33 ) is directed along the anode supply fluid flow path  22 ′ by a pump  34 . The pump  34  provides a motive force to move the process water along the anode fluid flow path  25 . Oxygen or other gases on the process water fluid flow path can be removed through a gas outlet  60  from the vessel  58  with baffles  56 , or the water reservoir  28 ′ 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 through a gas outlet (not shown). 
     As mentioned above, in some embodiments the controller  36  can control 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  10  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  58  or gas-liquid separator  27 ), 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  31  is shown in  FIG.  7    disposed in the flow path  26 ′, 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  31  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  31  can be located as shown in  FIG.  7    at or immediately upstream of the vessel  58 . 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  28 ′. 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  34 , or upstream and/or downstream of the flow control valve  30 , or anywhere along either or both of the cathode fluid flow path  23  or the anode fluid flow path  25 . 
     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  10  itself. The enthalpy of the chemical reactions resulting from electrolytic generation of inert gas occurring on each side of the separator  12  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 baffles  56  and gas outlet  60  in the flow path  26 ′ downstream of the cell/stack  10  allows for heat generated by the cell/stack  10  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  28 ′ without increasing process water temperatures outside of normal parameters during a projected duration of system operation. However, in situations where the reservoir  28 ′ cannot absorb process heat within tolerances, a heat exchanger can be included in the system as shown in  FIG.  7    with heat exchanger  38 . The heat exchanger  38  can provide cooling from a heat sink along the heat transfer flow path  40  (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  10 ′ 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  10 ′). 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  35  as shown in  FIG.  8   . The configuration of  FIG.  8    can provide added heat from heater/exchanger  35  upstream of the vessel  58  with baffles  56 , and the added heat can be dissipated into a heat sink such as reservoir  28 ′ or can be removed with a heat exchanger such as heat exchanger  38 . Alternatively, or in addition to the use of a heater/exchanger  35  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  30  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  34  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  34  or with a pressure regulator (not shown) along the process water flow path (e.g.,  26 ′). 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 . 
     It should be noted that system configurations shown in  FIGS.  7 - 8    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 baffle or baffles (“baffles”), 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→baffles→HX, heat source→stack→baffles→HX, stack→baffles→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→baffles→HX. 
     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.