Transient model of carbon dioxide desublimation from nitrogen-carbon dioxide gas mixture

Carbon dioxide (CO2) cryogenic desublimation separation has become an emerging carbon capture method in recent years due to its advantages of a contamination-free process and compactness. So far, there have been few research works on revealing the detailed desublimation characteristics of CO2 associated with the flow as well as mass and energy conservation in the practical cryogenic CO2 capture process. In this study, a transient model for analyzing the CO2 cryogenic desublimating in mixture gas is proposed. The model contains a tube-in-tube counter-flow heat exchanger including three control volumes, the nitrogen (or helium) coolant, the wall with the solid CO2 layer and the mixture. The deposition distribution, capture rate and energy consumption of the dynamic desublimation process under different operation conditions are investigated. The model is verified by some experiment results. Results show that an improved modeling accuracy is obtained by taking the solid CO2 layer into consideration. During the dynamic desublimation process, the deposition rate is the highest near the inlet of gas mixture due to the high mass diffusion there, and a low energy consumption will be obtained at high concentration and low flow velocity of CO2 supply. The theoretical method here provides better understanding of the CO2 desublimation features in annular tube, which will be helpful for conducting an efficient CO2 capture process.