A Thermally-Regenerated Solid Amine CO2 Removal System Incorporating Water Vapor Recovery and Ullage Air Recovery
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The Thermal Amine Scrubber (TAS) flight experiment was developed under contract with NASA/JSC with the goal to demonstrate a TRL5 prototype advanced carbon dioxide (CO2) removal system based on a thermally-regenerated solid amine adsorbent. The TAS was designed to fit within two double lockers within an ISS Express Rack, consisting of a Water Save Subsystem (WSS), a CO2 Removal Subsystem (CRS), and an ISIS drawer for the system controller. The WSS incorporates a passive water save desiccant canister technology capable of recovering ~90% of the incoming humidity present in the process air stream. A supplemental desiccant wheel boosts the overall water recovery to ~97%. The CRS receives dry air from the WSS and splits flow between two pairs of CO2 removal beds containing the solid amine. Each pair of beds is restricted to 1 adsorbing bed and 1 desorbing bed, the latter of which is isolated from the process air and exposed to vacuum during thermal regeneration. A valve assembly redirects flow back to the regenerated bed at a regular interval, but first ~96% of the ullage air from the previous adsorbing bed is evacuated using a scroll compressor in an intermediary valve state. This design allows for a removal rate of ~3.7 kg/day of CO2 at 2 mmHg partial pressure CO2 in the process air, which corresponds to approximately a 4 crewmember equivalent. The TAS will provide an additional means of removing CO2 from the ISS, potentially providing additional capacity for time periods with increased crew size. Addition of a vacuum compressor, residual water separator, and accumulator downstream of TAS will enable integration with a CO2 reduction system and is directly applicable to exploration missions requiring oxygen recovery.