Solid oxide electrochemical gas separator inerting system (united technologies) electricity transmission vs distribution


Fuel tanks can contain potentially combustible combinations of fuel vapors, oxygen, and ignition sources. To prevent combustion, inert gas, such as nitrogen-enriched air (NEA) or oxygen-depleted air (ODA), is introduced into the ullage of a fuel tank, in order to keep the oxygen concentration in the ullage below 12%. A variety of membrane-based technologies have conventionally been used to inert fuel tank air. Similarly, fire suppression systems, such as fire suppression systems deployed in aircraft cargo holds, can function with inert gas. SUMMARY

In one embodiment, a gas inerting system includes a solid oxide electrochemical gas separator system, a dilution air source configured to selectively add dilution air to the incoming process air or the oxygen-enriched air, a controller configured to control the dilution air source, and an outlet configured to direct the oxygen-depleted air to a location requiring inerting. The solid oxide electrochemical gas separator system includes a cathode configured to receive incoming process air and produce oxygen-depleted air, and an anode configured to evolve oxygen.

In another embodiment, a gas inerting method includes separating incoming process air into oxygen-enriched air and oxygen-depleted air in a solid oxide electrochemical gas separator system, selectively temperature controlling the solid oxide electrochemical gas separator system with dilution air, selectively diluting the oxygen-enriched air with dilution air, and inerting a space with the oxygen-depleted air. BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure describes a system and method to generate inert gas for use in combustion prevention and fire suppression. In particular, the system can be applied to fuel tank inerting or to fire suppression for aircraft cargo areas, dry bays, and other areas that require fire protection. The system uses solid oxide electrochemical gas separators (SOEGS) cells configured to transport oxygen out of incoming process air, resulting in inert oxygen-depleted air. The use of SOEGS cells is beneficial for purposes of energy efficiency and lower system weight. In addition, the replacement of ozone-depleting organic halides such as Halon that are used as fire extinguishing agents on aircraft with an inert gas generation system is more environmentally benign.

Ceramic solid oxide fuel cells have been leveraged in a variety of systems. Generally, past uses configure the system as a fuel cell for producing electrical current. In this configuration, both fuel and air are fed into the cells, resulting in a voltage difference across the cell that can be used to generate an electric current. In this traditional configuration, the cathode of the fuel cell is positive, while the anode of the fuel cell is negative. In similar configurations, solid oxide systems have been used to accomplish electrolysis of water or carbon dioxide, splitting the water or carbon dioxide into separated components. However, solid oxide technology has scarcely been used in a “gas separator” configuration.

Rarely have ceramic solid oxide cells been used as solid oxide electrochemical gas separators (SOEGS). In a gas separator configuration, the polarity of the cell changes sign in comparison to a fuel cell according to convention. The cathode is negative, and the anode is positive (higher potential). Nonetheless, the anode is the site of oxidation and the cathode is the site of reduction reactions. When a solid oxide cell is used in such a configuration, instead of generating a current, the SOEGS generates oxygen-depleted air. In the SOEGS configuration, an applied DC voltage induces a current that causes incoming oxygen to reduce in the cathode and be transported through the oxygen-conducting electrolyte to the anode.

The use of SOEGS has several benefits. First, the use of an SOEGS is more energy efficient in operation than the use of other types of electrochemical gas separators, such as those containing a proton exchange membrane. Second, the use of SOEGS has the potential to decrease the weight of the inert gas and fire suppression systems. Finally, the proposed SOEGS gas separation system exhaust comes out dry with no need to remove humidity from the system, as compared to proton exchange membrane gas separator systems.

FIG. 1 is a schematic diagram of solid oxide electrochemical gas separator (SOEGS) cell 2. The diagram of SOEGS cell 2 includes cathode 4, anode 6, electrolyte 8, bias voltage 10, heated process air (HPA), anode process air (APA), oxygen-depleted air (ODA), oxygen-enriched air (OEA), oxygen molecules (O2), oxygen ions (O═), and electrons (e−). Cathode 4 and anode 6 are separated by electrolyte 8, which may be a film. Cathode 4 and anode 6 are thus separated from each other, but bias voltage 10 is run across SOEGS cell 2 from anode 6 to cathode 4, electrically connecting anode 6 and cathode 4.

Cathode 4 and anode 6 are generally made of ceramic material such as lanthanum strontium manganite, lanthanum strontium cobaltite, and lanthanum strontium cobalt ferrite; or composite material such as noble metal supported on a ceramic substrate. Electrolyte 8 is an oxygen ion conductor, such as yttrium-stabilized zirconia or ceria doped with rare earth metals. Electrolyte 8 can be a thin film between anode 6 and cathode 4, while anode 6 and cathode 4 may consist of porous ceramic materials that can support the electrolyte. When SOEGS cell 2 is running, a bias voltage 10 of about 1 V per SOEGS cell is applied across SOEGS cell 2 from anode 6 to cathode 4. Incoming heated process air (HPA) is heated outside the SOEGS (see FIG. 4A-4E), and is run through cathode 4. Oxygen molecules (O2) in heated process air are reduced in cathode 4. Resulting oxygen ions (O═) are conducted through electrolyte 8 to anode 6. Heated process air becomes oxygen-depleted air (ODA) as oxygen ions are conducted to anode 6. Thus, oxygen-depleted air exits cathode 4. Oxygen-depleted air has less than 12% oxygen content by volume, and is used to inert a commercial aircraft fuel tank or in a fire suppression system. The oxygen content in the inert product gas can be varied for different applications by changing the cathode flow rate. For fire suppression in which live subjects are present, a higher oxygen content may be preferred (e.g. 15%). In contrast, inert gas on a military aircraft may call for a lower oxygen content (e.g. 9%).

While SOEGS cell 2 is running, anode process air is flowed through anode 6 to reject waste heat from SOEGS cell 2 and to dilute the evolved oxygen. The difference in temperature between the sides of the SOEGS should be no more than approximately 200 degrees Celsius to prevent mechanical failure due to thermally induced stresses. Temperature control air exits anode 6 along with oxygen that is evolved at anode 6; this flow stream contains oxygen previously removed from the incoming heated process air in cathode 4.