Pore-scale study of CO₂ desublimation and sublimation in a packed bed during cryogenic carbon capture

Cryogenic carbon capture (CCC) is an innovative technology to desublimate CO₂ out of industrial flue gases. A comprehensive understanding of CO₂ desublimation and sublimation is essential for widespread application of CCC, which is highly challenging due to the complex physics behind. In this work, a lattice Boltzmann (LB) model is proposed to study CO₂ desublimation and sublimation for different operating conditions, including the bed temperature (subcooling degree ∆T_s), gas feed rate (Péclet number Pe) and bed porosity (ψ). The CO₂ desublimation and sublimation properties are reproduced. Interactions between convective CO₂ supply and desublimation/sublimation intensity are analysed. In the single-grain case, Pe is suggested to exceed a critical value Pe_c at each ∆T_s to avoid the convection-limited regime. Beyond Pe_c, the CO₂ capture rate (v_c) grows monotonically with ∆T_s, indicating a desublimation-limited regime. In the packed bed case, multiple grains render the convective CO₂ supply insufficient and make CCC operate under the convection-limited mechanism. Besides, in small-∆T_s and high-Pe tests, CO₂ desublimation becomes insufficient compared with convective CO₂ supply, thus introducing the desublimation-limited regime with severe CO₂ capture capacity loss (η_d). Moreover, large ψ enhances gas mobility while decreasing cold grain volume. A moderate porosity ψ_c is recommended for improving the CO₂ capture performance. By analysing v_c and η_d, regime diagrams are proposed in ∆T_s–Pe space to show distributions of convection-limited and desublimation-limited regimes, thus suggesting optimal conditions for efficient CO₂ capture. This work develops a viable LB model to examine CCC under extensive operating conditions, contributing to facilitating its application.