Mathematical Simulation of the Sorbent-Based Atmosphere Revitalization System for the Crew Exploration Vehicle

A cyclic adsorption process simulator was used to determine preliminary bed size and characteristics for a sorbent-based atmosphere revitalization (SBAR) system being designed by NASA for the Crew Exploration Vehicle. An initial study of a 2-bed 3-step 3-layer, vacuum swing adsorption cycle, utilizing 50% silica gel, 17% 13X zeolite, and 33% 5A zeolite revealed that a 10 L bed could easily meet the CO₂ and H₂ O removal criteria for a 3 person crew. A parametric study showed that the cycle time, layering percentage of silica gel, and H₂ O-silica gel mass transfer coefficient were important parameters in the SBAR design. Increasing the cycle time diminished the CO₂ and H₂ O removal performances but resulted in less O₂ lost to space. The CO₂ and H₂ O removal performances increased considerably when a silica gel layer was added to the bed, with the above layering percentages being close to optimum. As more silica gel was added to the bed slightly more O₂ was lost. Larger values of the H₂ O-silica gel mass transfer coefficient improved the CO₂ and H₂ O removal performances but at the expense of slightly more O₂ lost.