Date of Award
Open Access Dissertation
James A. Ritter
Pressure Swing Adsorption (PSA) and Temperature Swing Adsorption (TSA) are some of the most used cyclic adsorption technologies that is used for separating gas components from its mixture. Carbon Dioxide Removal Assembly (CDRA) in the International Space Station (ISS) facilitates the continuous removal of CO2 by the cyclic adsorption process. The use of structured adsorbents has drawn attention due its several advantages over traditional beaded adsorbents. This work evaluates the role of different design variables on the effective thermal conductivity of a structured adsorbent bed for its possible application in a temperature swing adsorption (TVSA) process for space applications. The objective of this work is to perform a parametric study on the Cu MFEC structured adsorbent bed by carrying out a TVSA cyclic process on the various parameters such as feed flowrate, Counter current Depressurization (CnD) pressure, bed temperature and Air Save (AS) step time etc., and test the superior thermal conductivity of the bed, and its process performance.
The lab-scale bed is 21” high, with 18” of loaded length and 1.61” internal diameter. The highly porous sorbents such as zeolite 13X (17.7 vol%) of about 137g are immobilized in the bed of 6-20 μm Copper fibers (7 vol%). The lab-scale experiment consists of 1-bed 4-step cycle schedule process having average feed concentration of CO2 of about 2700 ppm in N2. The base case scenario consists of 2 minutes of AS step, 18 minutes of CnD step, 2 seconds of FP and the remainder 1198 seconds of F step, with the pressure at the end AS step being 5 Torr and pressure at the end of CnD step being 2 Torr. The parametric study is carried out at different Feed times of 35, 40, 45 and 50 SLPM, different CnD pressures of 2, 4, 6, and 8 Torr, different Regeneration temperatures of 140, 155, 170, 180, and 200 oC, and different AS step times of 2, 3, and 5 Torr. Three Process Langmuir (TPL) model has been used to correlate the single gas equilibrium adsorption isotherms of N2 and CO2 on zeolite 13X. The experimental results obtained from the lab-scale experimental setup has been modelled by COMSOL Multiphysics, and the process thermal parameters are obtained. The design and scale-up of the IM bed is studied using in-house built FORTRAN code, DAPS, and the parametric study has been carried out.
Finally, in the last chapter a kinetically limited linear driving force (KLLDF) model was employed and compared against the linear driving force (LDF) model to predict the separation of methane and Nitrogen via kinetic separation via pressure swing adsorption (PSA) using the carbon molecular sieve (CMS) 172K. The PSA cycle was carried out in a single 1 Lt bed and consisted of a feed pressurization, feed, three equalization down, counter current depressurization, light reflux, three equalization up and idle steps. Three tanks of 3.8 liter each were used to temporarily store the gas during the equalization steps. The PSA cycles were carried out with mixtures 85/15 methane/nitrogen at room temperature with the pressures oscillating between 28 and 606 kPa. 4 different cycle times of 144, 300, 900 and 1800 s were used with feed flowrates varying between 1.67 and 15 SLPM. The results show that the KLLDF consistently displayed a superior predictive ability than the LDF model in all conditions.
Charles Antony Amalraj, P. B.(2023). Design of a TVSA Cycle for CO2 Removal From Spacecraft Cabins Using a Structured Adsorbent. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/7146
Available for download on Thursday, May 15, 2025