Liquid Sorbent Carbon Dioxide Removal System

The NASA life support system uses a regenerable vacuum swing adsorption process, known as Sorbent-Based Air Revitalization (SBAR), to separate water and carbon dioxide for disposal. The SBAR system is an adsorbent-based swing bed system that has been optimized to provide both humidity and carbon dioxide control for a spacecraft cabin atmosphere. The system comprises composite silica gel and zeolite-packed beds for adsorption and a bypass system for flow control. Under normal operating conditions, the disposal system would require a high-quality vacuum environment to operate. Improvements to the SBAR system include an enhanced inherent capacitance that extends the operation time within a non-vacuum environment for up to 4.5 hours. Flight time can be further expanded with multiple SBAR systems to allow for system regeneration. By scheduling periodic thermal regenerations&#151nominally during sleep periods&#151the SBAR technology may be suitable for missions of unlimited duration.

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.

Storage and transfer of fluid commodities such as oxygen, hydrogen, natural gas, nitrogen, argon, etc. is an absolute necessity in virtually every industry on Earth. These fluids are typically contained in one of two ways; as low pressure, cryogenic liquids, or as a high pressure gases. Energy storage is not useful unless the energy can be practically obtained ("un-stored") as needed. Here the goal is to store as many fluid molecules as possible in the smallest, lightest weight volume possible; and to supply ("un-store") those molecules on demand as needed in the end-use application. The CFC concept addresses this dual storage/usage problem with an elegant charging/discharging design approach. The CFC's packaging is ingeniously designed, tightly packing aerogel composite materials within a container allows for a greater amount of storage media to be packed densely and strategically. An integrated conductive membrane also acts as a highly effective heat exchanger that easily distributes heat through the entire container to discharge the CFC quickly, it can also be interfaced to a cooling source for convenient system charging; this feature also allows the fluid to easily saturate the container for fast charging. Additionally, the unit can be charged either with cryogenic liquid or from an ambient temperature gas supply, depending on the desired manner of refrigeration. Finally, the heater integration system offers two promising methods, both of which have been fabricated and tested, to evenly distribute heat throughout the entire core, both axially and radially. NASA engineers also applied the CFC to a Cryogenic Oxygen Storage Module to store oxygen in solid-state form and deliver it as a gas to an end-use environmental control and/or life support system. The Module can scrub out nuisance or containment gases such as carbon dioxide and/or water vapor in conjunction with supplying oxygen, forming a synergistic system when used in a closed-loop application. The combination of these capabilities to work simultaneously may allow for reduced system volume, mass, complexity, and cost of a breathing device.

This water filtration innovation is an acoustically driven molecular sieve embedded with small-diameter carbon nanotubes. First, water enters the device and contacts the filter matrix, which can be made of polymer, ceramic, or metallic compounds. Carbon nanotubes within the matrix allow only water molecules to pass through, leaving behind any larger molecules and contaminants. The unique aspect of the technology is its use of acoustics to help drive water through the filter. An oscillator circuit attached to the filter matrix propagates acoustic vibration, further causing water molecules to de-bond and move through the filter. This use of acoustics also eliminates dependence on gravity (and thus filter orientation) to move water through the device. When water exiting the system diminishes to a pre-determined set point, a cleaning cycle is triggered to clear the sediment from the inlet of the filter, reestablishing the standard system flow rate. Unlike other filtration systems, flushing of the filter system is not required. The combination of acoustics and small-diameter carbon nanotubes in this innovation make it an effective and efficient means of producing contaminant-free, clean water.

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".