(326d) Development of Pressure Swing Adsorption Technology for Spaceflight Oxygen Concentrators

A source of medical oxygen will certainly be needed at some point to keep an astronaut alive during a spaceflight or space mission, on the space station, or at a Lunar or Martian outpost. To meet these needs, the ideal oxygen source would be a light, compact unit that uses minimal electricity or battery power in all of these settings, and can supply oxygen continuously for many hours or even days at a time. No current technology truly meets these requirements. Traditional compressed-oxygen cylinders provide a limited amount of oxygen in a heavy, inconvenient package and are not ideally suited for space mission applications. A D-sized cylinder weighing 14 pounds only lasts 2.5 hours at 4 liters per minute (LPM). The need to refill and replace the cylinders continually makes logistics difficult. In addition, with oxygen stored at pressures approaching 3000 psi, the cylinders can cause fires, explode or turn into missiles if dropped, mishandled, or damaged.

Oxygen concentrators, which extract oxygen from air using electricity, can eliminate these problems. They avoid the hazards of storing oxygen under pressure. They can supply oxygen continuously, for as long as energy is available from batteries, generators or other power sources. These kinds of medical oxygen concentrators are already used in residential and military applications. However, existing systems are too big, use too much power, and are too heavy to be carried into space. The NSBRI Smart Medical Systems and Technology Team has identified a need for the development of oxygen concentrators with specific requirements and technologies that minimize volume, mass and power draw, making them more suitable for spaceflight. The objective of this project is to meet their needs.

Compared with the most advanced oxygen concentrators now in production by SeQual, a unit that can produce oxygen continuously at 4 LPM, weigh less than 7 pounds and use less than 100 Watts of electric power requires a two-fold reduction in weight and power consumption. Nevertheless, this requirement may be met by combining new air compressor designs with advances in Pressure Swing Adsorption (PSA) technology. SeQual and the proposed team of researchers from the University of South Carolina, Vanderbilt University and the Marshall Space Flight Center are uniquely positioned to achieve this next level of performance.

SeQual has been the technology leader in small oxygen concentrators for over 13 years. They recently released the first fully portable, battery powered, continuous-flow medical oxygen concentrator. This system is 2 to 3 times lighter and uses 2 to 3 times less power than other existing oxygen concentrators with similar flow rates. However, the proposed team, which has ready been working together for a number of years, believes there is significant room for improvement in both the PSA module, which enables oxygen enrichment, and the air compressor that supplies the pressurized air and partial vacuum used by the PSA module.

To determine whether this significant, revolutionary, improvement is possible, this team is carrying out an extensive mathematical modeling study of the physical system using computer simulation, coupled with breadboard system design and testing.  Computer simulations are being carried out by Professor Ritter and his team at USC. Sorely needed physical property data for the adsorption process simulator, such as adsorption thermodynamic and mass transfer data, are being measured by Professor LeVan and his team at Vanderbilt.  SeQual and their team will build breadboard systems based on the simulation results. Jim Knox at the MSFC, along with SeQual, will test these new systems to ensure that they meet all the requirements of space mission applications.

It is anticipated that this program will identify approaches to improve the efficiency of the PSA separation. As the PSA module is the primary component of the separation, improving its efficiency will carry through to all other system components including the air compressor. Coupled with compressor advancements already identified and being worked on, it is anticipated that this effort will culminate in a revolutionary breadboard system that will supply 4 LPM of oxygen, weigh 7.2 pounds and require 106 Watts of electric power. This effort will begin at technology readiness level (TRL) 3 and end at a high TRL 4 over a four year period.