Pore-scale study of CO2 desublimation in a contact liquid

Cryogenic carbon capture (CCC) designed to operate in a contact liquid is an innovative technology for capturing ${\text{CO}}_2$ from industrial flue gases, helping mitigate climate change. Understanding ${\text{CO}}_2$ desublimation properties in a contact liquid is crucial to optimizing CCC, but is challenging due to the complex physics involved. In this work, a multiphysics lattice Boltzmann (LB) model is developed to investigate ${\text{CO}}_2$ desublimation in a contact liquid for various operating conditions, with the multiple and fully-coupled physics being incorporated (i.e., two-phase flow, heat transfer across three phases, ${\text{CO}}_2$ transport between the gas and liquid, homogeneous and heterogeneous desublimation of ${\text{CO}}_2$, and solid ${\text{CO}}_2$ generation). The ${\text{CO}}_2$ desublimation process in a contact liquid is well reproduced. Moreover, parametric studies and quantitative analyses are set out to identify optimal conditions for CCC. The decreasing liquid temperature ($T_l$) and flue gas temperature ($T_0$) are found to accelerate the ${\text{CO}}_2$ desublimation rate and enhance the ${\text{CO}}_2$ capture velocity ($v_c$). However, excessively low $T_l$ and $T_0$ values should be avoided. These conditions increase the energy consumption of cooling while only marginally improving $v_c$, due to the limited ${\text{CO}}_2$ supply. The CCC system performs effectively when purifying flue gases with high ${\text{CO}}_2$ content ($Y_0$). This is because the large $Y_0$ accelerates the ${\text{CO}}_2$ desublimation rate and enhances the overall ${\text{CO}}_2$ capture efficiency. A high gas injection velocity (or $\text{Pe}$) is beneficial for amplifying $v_c$ by increasing the gas–liquid interfaces and enhancing the ${\text{CO}}_2$ supply. Nevertheless, too high a $\text{Pe}$ should be avoided, as it hinders the transport of ${\text{CO}}_2$ to the liquid or solid ${\text{CO}}_2$ surfaces, ultimately restricting the amount of ${\text{CO}}_2$ available for desublimation and inhibiting the enhancement of $v_c$. This study develops a viable LB methodology to investigate ${\text{CO}}_2$ desublimation in a contact liquid for varying conditions, which advances the knowledge base of CCC and facilitates its industrial applications.