Marshall Space Flight Center, Alabama
Conventional air revitalization technology for removal of CO2, moisture, and trace organic contaminants usually involves a packed bed of sorbent pellets that can be regenerated using a concept similar to that of pressure swing adsorption (PSA). Additional heat input for thermal regeneration is preferred during the adsorption-desorption process to increase the regeneration efficiency. Typically, a pair of adsorber modules consisting of the same sorbent material with identical loading capacity is placed in parallel and work in tandem, where one module adsorbs the contaminants from the process air while the other is in regeneration mode. The two adsorber modules have separate housings and may be placed in separate locations.
Recently, the concept of an efficient thermally-linked bed for removing moisture or CO2 from air was developed via collaboration between Marshall Space Flight Center (MSFC) and Precision Combustion, Inc. (PCI). In this process, two or more repeating chambers (or modules) are tailored so the adsorbing chamber/module and the regenerating chamber/module were located adjacent to each other. The amount of heat released by the adsorbing chamber was then used to provide the heat required by the adjacent desorbing/regenerating chamber, providing a self-sustaining adsorption-desorption system, maintaining minimal temperature changes within the bed, and eliminating the need for an external heat source. This concept can lead to improved reliability and process efficiency over typical two-module packed beds of sorbent pellets.
In order to optimize the benefit of highly conductive metal strands for efficient heat transfer within the thermally-linked chambers, an effective coating technique was developed by PCI that enables application of sorbent materials directly on the lattice structures with high sorbent loading, good adhesion, high uniformity, and long-term durability. The lattice structures for the coating development were fabricated by MSFC via a laser sintering method and were supplied to PCI. The lattice structures can also be produced using other fabrication methods, such as Electron Beam Melting (EBM); however, for some metals such as aluminum (desirable due to its high thermal conductivity), the laser sintering method offers better dimensional control. Coating the sorbent materials directly on the surface of the metal strands allows better surface-to-sorbent contact and less resistance for a more efficient heat transfer from the adsorbing chambers to the regenerating chambers. A lower thermal resistance results in higher heat flux between the two adjacent chambers.
Direct contact of the sorbent with the heat transfer media is especially advantageous during vacuum desorption, since in this case, the usually dominant convective heat transfer mode is not active. Other heat transfer modes are gas conduction and radiation, and conduction in the metallic substrate. This invention creates intimate contact between the sorbent and the metallic support substrate to more effectively transfer the heat released by the adsorbing chambers to the regenerating chambers and thus keeping the temperature changes minimal within the thermally-linked beds.