Phase equilibrium analysis of CO2-N2 and thermodynamic optimization of a novel liquefied carbon capture system based on decarbonized flue gas expansion refrigeration

Liquefied carbon capture is essential for achieving global carbon neutrality, offering a direct pathway to liquid products that facilitates storage, transportation, and sequestration. However, refrigeration and compression stages impose substantial energy demands. This study proposes a novel liquefied carbon capture system integrating decarbonized flue gas expansion refrigeration (LCCS-DFER) to utilize cooling from high-pressure gas expansion. Considering the complexity of multiphase equilibrium in liquefied CO₂ from flue gas and the limited explicit analysis of capture performance, phase equilibrium behaviors are investigated for the CO₂-N₂ binary mixture, with particular attention to solid precipitation, a critical factor for operational safety and stability. Sensitivity analysis evaluates the impact of operating conditions on carbon capture rate and product purity. Thermodynamic optimization using a genetic algorithm identifies a minimum specific energy consumption of 287.6 kWh/t, with a compression energy demand of 21.20 MW and a power generation capacity of 8.06 MW, corresponding to operating conditions of 11 MPa and 250.2 K. Exergy analysis highlights turbines as the primary source of irreversible losses, contributing approximately 35.6 % of the total. These findings elucidate the phase equilibrium characteristics of CO₂-N₂ mixtures and provide a theoretical foundation for performance assessment and optimized design of liquefied carbon capture systems.