The Effect of Carbon Dioxide on Ammonia-Removal Efficiency During Pressure-Swing Trace Contaminant Control in Exploration Portable Life Support System (xPLSS)

The Trace Contaminant (TC) removal system in the Exploration Portable Life Support System (xPLSS) is a limiting factor for long-term Extravehicular Activities (EVAs), and making it regenerable will remove a major roadblock to suit advancement. The TC control system (TCCS) operates in the pressure-swing fashion, alternating between adsorption and desorption steps, the latter ones taking place under vacuum. The TC-removal efficiency depends on the TC-sorption capacity, which is important in the adsorption step, and also on the degree to which the sorbent is regenerated in the desorption step. The TC-removal efficiency should be as high as possible, even though it does not have to be 100 percent. Thus, it is advantageous to use TC sorbents with high TC-sorption capacities and to operate the regeneration step under conditions that favor efficient TC desorption from the sorbent. This paper concerns the latter factor, (i.e. improved ammonia desorption from the TC sorbent). During the desorption step, sorbent regeneration may be limited by the system configuration, vacuum level, and/or half-cycle period. This, in turn, may limit the amount of ammonia that can be adsorbed in the subsequent adsorption step. The current TCCS/RCA integration geometry involves TC sorbents that are located downstream of the Rapid-Cycle Amine (RCA) swing beds. This configuration may provide an increased overall ammonia-removal efficiency, presumably due to the presence of carbon dioxide released from the RCA bed during the desorption/regeneration step. In this paper, findings are presented on the enhancement of vacuum-regeneration of ammonia sorbents caused by the presence of CO2 during desorption. 1/6-scale experiments showed that the ammonia-removal efficiency was improved from about 40 percent for the case with no CO2 to 65 percent in the presence of CO2.