Crewed Space missions require maintaining a safe environment that can both sustain a breathable atmosphere and remove airborne pollutants. Carbon dioxide (CO2), while not toxic in low concentrations, accumulates as crew members respire and can eventually affect the crew's health. Therefore, a system to constantly remove CO2 buildup is necessary for long-term missions. Currently, the prevailing method used to capture, transfer, and remove CO2 from air in submarines and industrial flue gas utilizes the liquid sorbent monoethanolamine. Diglycolamine (DGA) is an alternate primary amine that has similar performance with less volatility. DGA is currently being studied at Ames Research Center as the primary candidate for the operation of the sub-scale liquid amine CO2 removal test stand. The test stand is used to investigate liquid flow and liquid/gas interfaces for a system designed for both microgravity and surface applications. The test stand includes a wedge tray design that utilizes capillary action to contain DGA while allowing gas-liquid surface interaction for CO2 transfer. Trays using this wedge design are placed in a contactor unit to remove CO2 from the air stream as well as a degasser unit to regenerate the DGA. A capillary condensing heat exchanger to recapture water evaporated in the degasser unit is also incorporated. Nominal operating conditions for the contactor are an air flow rate of 26 SCFM enriched with pure CO2 to a concentration of 2600 ppm and a liquid mixture of 65/35vol% DGA/H2O flowing at a rate of 0.65 mL/min, while the degasser is operated at 100?C under slight vacuum. Integrated closed-loop operation yielded a final CO2 flux of 0.946 kg/m2/day and a total CO2 capture of 0.192 kg/day. All sub-assemblies in the system can be improved to increase the overall CO2 capture performance.
Cortez et al. (Sun,) studied this question.