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.