Adsorbents and adsorption models for capture of Kr and Xe gas mixtures in fixed-bed columns

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Switzerland : 1996), 2019-11, Vol.375 (C), p.122073, Article 122073
• Main Authors: Ladshaw, Austin P., Wiechert, Alexander I., Welty, Amy K., Lyon, Kevin L., Law, Jack D., Jubin, Robert T., Tsouris, Costas, Yiacoumi, Sotira
• Format: Article
• Language: English
• Subjects: Adsorption; Finite elements; Modeling; Noble gases; Nuclear fuel recycling; Separations
• ISSN: 1385-8947; 1873-3212
• DOI: 10.1016/j.cej.2019.122073

•Off-gases from nuclear fuel reprocessing contain mixtures of Kr and Xe.•Engineered adsorbents are developed for separation of Kr and Xe in gas streams.•Operating packed columns in series can effectively separate Kr from Xe.•A model to simulate Kr and Xe gas adsorption in columns was developed and validated. Off-gases produced during the reprocessing of used nuclear fuel (UNF) include 129I2, 3HHO, 14CO2, 85Kr, and 135Xe, which are volatilized out into the off-gas. In order to meet regulatory requirements for reprocessing plant emissions, these gases must be captured and removed from the off-gas stream prior to off-gas emission. Of particular interest are the noble gases, Kr and Xe, which can be fairly difficult to remove from the off-gas due to their low chemical reactivity. Thus, this work is focused on utilizing engineered adsorbents, AgZ-PAN and HZ-PAN, to capture Kr and Xe from a mixed-gas stream at relatively low temperatures (191–295 K) and various flow rates (50–2000 mL/min). Isothermal data for Kr and Xe on each adsorbent are analyzed to produce the Langmuir parameters needed to model the mixture adsorption capacities at relevant temperatures using the Extended Langmuir model. Those parameters are then incorporated into a fixed-bed adsorption model developed in this work using the Mulitphysics Object-Oriented Simulation Environment (MOOSE). That model is used to simulate breakthrough times for Kr and Xe in packed columns of AgZ-PAN and HZ-PAN, ranging in length from 6 to 20 in., at relevant temperatures and flow rates. Breakthrough times varied from nearly instantaneous for Kr in AgZ-PAN to 30 h for Xe in HZ-PAN. After the developed model was validated by comparisons with experimental breakthrough data, the model framework was used to simulate the performance of multiple fixed-bed columns connected in series.