Desublimation based separation of CO2 inside a cryogenic packed bed: Performance mapping with the spatiotemporal evolution of CO2 frost

Abstract

Preferential desublimation of carbon dioxide from vapour phase onto cooled packing at low pressure (1–5 atm) shows great promise to separate carbon dioxide in pure from flue/natural gas. A new transport phenomena model that takes into account the interfacial heterogeneous nucleation of solid CO2 on the packing and on the bed wall and also incorporates the interstitial homogeneous nucleation, is used to simulate the performance of desublimation based separation of CO2 in a cryogenic packed bed. The spatiotemporal evolution of CO2 frost layer inside the bed is simulated for different operating conditions namely inlet flow rates, initial bed temperature profiles, flow configurations. The extent of separation of CO2 and the resulting void fraction is mapped over the space-time domain. Bed saturation and bed critical times are simulated and validated with experimental data. Non-dimensional numbers are derived for simultaneous heat and mass transfer process with phase change and their effects on the extent of separation and optimum process conditions are simulated. Apart from evaluating the extent of separation, the model additionally helps in identifying the different operative zones and operational problems namely choking. The significance of the study is in the model based inferential prediction of frost layer thickness and its application in the choice of operating and bed switching conditions of cryogenic packed bed for separation of carbon dioxide from flue gas and natural gas.