Solid-State System Efficiently Generates Purified O2
Power Generation and Storage
Solid-State System Efficiently Generates Purified O2 (MSC-TOPS-148)
Uses waste heat to boost efficiency of oxygen generator
Overview
Innovators at NASA Johnson Space Center, in collaboration with inno-vators at American Oxygen, have developed a solid-state system and process that separates oxygen from ambient air and compresses the resulting purified oxygen – with a significant reduction in power con-sumption compared to prior state-of-the-art. It is based upon a proven solid oxide electrochemical oxygen separation and compression tech-nique that derives purified oxygen from ambient air and compresses it using an electrochemical pumping method.
This electrically driven technology relies upon the high operating tem-perature of electrochemical cell stacks for maximum efficiency. An inverse relationship exists between high temperature and electrical resistance; thus, a heated system requires less energy to drive oxide
ions across a cell membrane and compress the resulting purified oxy-gen. Ambient air that is fed and circulated for processing through the system also helps to stabilize high system operating temperatures.
To prevent the ambient air from overcooling the electrochemical pro-cess, the incoming air is preheated. However, in existing systems, this pre-heating incurs a large cost penalty in power consumption. The new solid-state system design performs electrochemical reactions to generate purified oxygen but uses an embedded heat exchanger to preheat the incoming air with system waste heat without the need for supplemental heaters, significantly boosting efficiency.
The Technology
This engineering system is essentially solid state. Other than an external circulation fan, there are no moving parts, rotating equip-ment, multistep distillation process, or selector valves like those required for pressure swing adsorption systems. Additionally, there are no concerns about hydrogen permeability, which can occur in classical membrane separation systems. The system design uses multiple electrochemical cell stacks in a segmented, serial configur-ation, and it can be connected into a single DC circuit. System sizing calculations project that the energy use for a moderate scale system, producing between 10-30 standard-liters-per-minute (slpm) of purified oxygen and compressing it to upwards of 300 psig, is less than 75 W/liter O2.
This system’s thermal tower design enables a fast sweep of “free-heated” process air, but it requires significantly less energy to do so over current systems that rely upon electrical preheating. At a 700-degree C system operating temperature, approximately 15% of the current performs electrochemical work, but 85% of the current results in waste heat. This system design incorporates a heat exchanger to transfer heat from the already-circulated and oxygen-depleted process air, to the fresh ambient process air feed. The waste heat generated by the lower, or first cell stack, preheats the second cell stack, and the temperature of the cell stack increases with each successive layer. With a sufficient number of layers, the temperature increase is substantial enough to enable the waste heat from the top cell stack to preheat the incoming air using the heat-exchanger, without the need of supplemental heaters.
This efficient oxygen separation and compression technology could have applications other than space systems, such as terrestrial life-support systems, cabin air-supply for confined environments, medical health and veterinarian clinics in remote locations where commercially produced bottled oxygen is not readily available, and remote pure oxygen production for oxy-fuel welding. This technology could replace pressure swing absorption methods for small-scale distributed oxygen generation due to its greater efficiency and higher purity oxygen output. Although this specific system design and process is for separating oxygen from an ambient air feed, at substantially higher voltages some solid oxide systems can disassociate CO2 into CO and oxide ions and electrochemically transport the oxide ions across a cell membrane.
The Solid State, Energy Efficient Method of Oxygen Separation and Compression technology has a technology readiness level (TRL) 4 (component and/or breadboard validation in laboratory environment), and it is now available for patent licensing. NASA does not manufac-ture products itself for commercial sale. Please note that the main image above shows a single cell stack technology demonstrator referred to as, “The Recirculator".
Benefits
- Significantly reduced power consumption over current state of the art
- Employs heat exchanger to “free-heat” fresh supply of ambient air/O2
- Requires no supplemental heaters during operation
- Uses proven solid oxide electrochemical O2 separation and compression technique
- Implements efficient one-step separation and compression process
- Process derives 99.999% purified O2 from ambient air
- Solid state methodology
- Scalable system design
- Potential to derive purified O2 from CO2
- Suitable for remote locations
Applications
- Space suit and terrestrial life support systems
- Cabin air supply for confined environments
- Medical health and veterinarian clinics in remote locations
- Home healthcare
- Oxy-fuel welding
Similar Results
Liquid Sorbent Carbon Dioxide Removal System
NASA's Liquid Sorbent Carbon Dioxide Removal System was designed as an alternative to the current CO2 removal technology used on the International Space Station (ISS), which uses solid zeolite media that is prone to dusting, has a low absorption capacity, and requires high regeneration temperatures and frequent maintenance. Motivated by CO2 removal systems on submarines, NASA innovators began investigating the use of liquid sorbents. Liquid sorbents have a capacity four times greater than solid zeolites, require low regeneration temperature, and need fewer unreliable moving mechanical parts than solid based systems. While submarine CO2 scrubbers spray an adsorbing chemical directly into the air stream and allow the liquid to settle, NASA's new system uses a capillary driven 3D printed microchannel direct air/liquid contactor in a closed loop system. The Liquid Sorbent Carbon Dioxide Removal System is robust and reliable, while being low in weight, volume, and power requirements. The system is capable of reaching equilibrium when the liquid sorbent surface is being regenerated at a rate equal to the rate of absorption into the liquid.
Room temperature oxygen sensors
NASA Ames has developed very small-sized oxygen sensors made of a graphene and titanium dioxide (TiO2) hybrid material. With ultraviolet (UV) illumination, these sensors are capable of detecting oxygen (O2) gas at room temperature and at ambient pressure. The sensors are able to detect oxygen at concentrations ranging from about 0.2% to about 10% by volume under 365nm UV light, and at concentrations ranging from 0.4% to 20% by volume under short wave 254nm UV light. These sensors have fast response and recovery times and can also be used to detect ozone.
This unique room temperature O2 sensor provides significant advantages in O2 sensing applications, especially those applications where high operating temperature requirements cannot be met, or would result in inefficient manufacturing processes. Since graphene is not intrinsically responsive to O2, and TiO2 is not responsive to oxygen at room temperature, the materials are first synthesized as a hybrid material. The synthesized graphene- TiO2 hybrid material is then ultrasonicated and then drop-casted onto a series of Interdigitated Electrodes (IDE) to form the sensors.
Ultrasonication ensures effective charge transfer at the graphene- TiO2 interphase. The graphene and the titanium dioxide may be present in the composite material in different ratios to ensure optimal oxygen detection. It is the combination of graphene with TiO2 that yields a semiconducting material capable of O2 sensing at room-temperature operation.
Cryogenic Oxygen Storage Modules COSM
The COSM employs NASA's Cryogenic Flux Capacitor core to store liquid oxygen (at 90 K) in silica aerogel material at ambient pressure, and then discharges cold oxygen gas into an in-line flow loop in response to heat input. If the composition of the incoming effluent stream contains gases with condensation or freezing points above the 90 K oxygen storage temperature--such as carbon dioxide or water vapor--these gasses can be removed from the stream as it moves through the COSM. The current COSM is sized to be wearable on the person but can be easily scaled to much larger sizes and various geometries.
COSM is designed with a long "cold path" which provides for greater residence times which increase the probability that condensable/freezable gases will be trapped in the COSM. Also, the longer the cold path, the longer the time a COSM can be used prior to the oxygen being depleted and the scrubbed gasses liberated. Two COSM geometries have been designed, built, and tested-a round spiral and a prismatic serpentine--to achieve long cold paths, and intrinsic vapor cooling to manage heat loads.
Coil-On-Plug Igniter for Reliable Engine Starts
Spark-ignition devices have proven to be a high-reliability option for LOX/LCH4 ignition during development of the Integrated Cryogenic Propulsion Test Article (ICPTA) main and reaction control engines (RCEs); however, issues including spark plug durability (ceramic cracking) and corona discharge during simulated altitude testing have been observed, contributing to degraded spark output and no-light engine-start conditions. Innovators discovered that ignition system reliability could be improved and weight reduced by eliminating the traditional coil and spark plug wire. To achieve this result, engineers made the innovation by modifying an automotive coil-on-plug igniter to provide new high sparking energies at the point of combustion using low supply voltages. The coil was modified by vacuum-potting it into a threaded interface that mounts into existing spark plug ports on the ICPTA main engine and the RCEs. Engineers fabricated custom electrode tips that were thread-mounted into the potted coil body. Epoxy insulation was chosen with high dielectric strength to maintain insulation between the electrode and threaded adapter. Vacuum potting successfully prevented pressure or vacuum leakage into the coil body and maintained spark energy and location at the electrode tip. Successful hot-fire ignition was observed at sea-level, altitude, and thermal-vacuum for both ICPTA RCE and main engine igniters down to 10^-3 torr, which approaches the vacuum of cislunar space.
This technology is at technology readiness level (TRL) 7 (system prototype demonstration in an operational environment), and the related patent is now available to license. Please note that NASA does not manufacture products itself for commercial sale.
Modular Container System Preserves Sample Integrity
The Astromaterials Acquisition and Curation Office (AACO) at NASA Johnson Space Center currently curates 500 milligrams of the regolith sample from the Asteroid Ryugu that was collected by the Japan Aerospace and Exploration Agency’s Hayabusa II spacecraft and returned to Earth in 2021. In September 2023, NASA’s OSIRIS-REx spacecraft returned 70 grams of regolith collected from the surface of Asteroid Bennu. These astromaterial sample collections are stored and handled in gloveboxes and desiccators that are continuously purged with ultrapure nitrogen in order to minimize contamination and alteration of extraterrestrial samples from terrestrial environments.
For collaborative astromaterial sample research conducted outside of the AACO, a need emerged for a sample container system suitable for global transport, capable of maintaining the same low-oxygen envi-ronment as laboratory gloveboxes. Thus, the MCS was developed. MSC’s of different sizes (2, 4, and 8-inch sample container models) have been developed to store contact pads and bulk samples from NASA missions, including the OSIRIS-REx Asteroid Bennu mission.
MCS’s are designed with seal profiles to prevent oxygen from seeping into the sample container. Additionally, the MCS uses a sample container form-factor that optimizes favorable nitrogen to oxygen gas ratios. The final prototypes were tested and verified using optochemical sensors to measure trace oxygen levels within the sealed containers.
The Modular Container System (MCS) could fill a critical gap in the existing high-purity logistics and storage market in its ability to provide a passively maintained, verifiable, multi-year, glovebox-level low-oxygen environment in a portable robust form-factor. Although this technology was originally developed for astromaterial transport and storage, commercial applications may also exist in biopharmaceutical/ bio-banking, microelectronics/ semiconductor, and other industries.
