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 Δ Tₛ ), 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 Δ Tₛ to avoid the convection-limited regime. Beyond Pe c , the CO₂ capture rate ( vc ) grows monotonically with Δ Tₛ , 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- Δ Tₛ 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 vc and η d , regime diagrams are proposed in Δ Tₛ – $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.