Transient Model Of CO₂ Desublimation And Experimental Investigation Of Crystal Shape

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 system compactness.Solid CO₂ as an important industrial product is widely used in the fields of oil recovery,food and chemical industry,micro-nano processing,and electronic device cleaning.So far,there have been few research work on revealing the detailed desublimation characteristics of CO₂ associated with the flow as well as mass and energy conservation in the practical cryogenic CO₂capture process.It is beneficial to study the desublimation process and crystal growth morphology of CO₂ to capture CO₂ with high efficiency,control the growth of CO₂solid accurately,understand the properties of CO₂ solid,then develop CO₂desublimation capture technology and promote its application.Based on a set of CO₂low temperature desublimation capture visual experimental platform,some theoretical and experimental research on the desublimation process of CO₂ is carried out.The details are as follows:1)A one-dimensional transient numerical model for simulating CO₂desublimation in mixture under low temperature is proposed.The variation law of key parameters and the main factors affecting the capture rate and system energy consumption are revealed.The distribution of dynamic temperature,deposition rate and solid thickness during the desublimation process is systematically revealed.The effects of flow rate,concentration and time on the capture rate and energy consumption are analyzed.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 and high density there,and a low energy consumption will be obtained at high concentration and low flow velocity of CO₂supply.The theoretical method here provides better understanding of the CO₂desublimation features in annular tube,which will be helpful for conducting an efficient CO₂ capture process.2)According to the phase equilibrium theory and the crystal structure of CO₂,the two-dimensional nucleation of CO₂ crystals is analyzed.The low temperature visualization experiments are carried out to explore the nucleation rate and growth morphology of CO₂ crystal and reveal its thermodynamic mechanisms.The nucleation of CO₂ crystal under different working conditions is observed and analyzed through visual experiments,according to the classical nucleation theory and experiments,an empirical formula of CO₂ two-dimensional nucleation rate based on supersaturation,growth temperature and flow rate is established.The growth morphology of CO₂ crystal under different working conditions is observed and analyzed through visual experiments,the factors affecting crystal size and dendrite growth are analyzed,and the distribution pattern of CO₂ crystal growth is obtained.