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This work presents the thermodynamic design and performance assessment of an integrated process line for the separation, liquefaction, storage, and valorization of carbon dioxide (CO2) and nitrogen (N2) from flue gas streams. The proposed system aims to combine carbon capture with cryogenic energy storage by exploiting the thermophysical properties of the main flue gas constituents. A representative flue gas derived from complete methane combustion (9.5% CO2, 71.5% N2, and 19% H2O by volume) is considered as the feed stream. The process is developed and simulated in DWSIM v9.0.5, adopting a steady-state mass and energy balance framework coupled with rigorous thermodynamic modeling of phase equilibria and unit operations. The plant configuration is based on sequential cooling, compression, and expansion stages, enabling the selective condensation of H2O, CO2, and N2 at different temperature levels. The system integrates heat exchangers, compressors, pumps, turboexpanders, phase separators, and cryogenic storage tanks, while a portion of the liquefied CO2 is reused as an energy carrier through vaporization and expansion in a dedicated turbine. The results demonstrate that the process achieves a CO2 capture ratio of 81.7%, with a specific electric consumption (SEC) of 10.44 kWh/kgCO2 and 1.71 kWh/kgN2. The overall net electric demand is 1.29 kWh/kg of treated flue gas, while the round-trip efficiency (ηRT,CO2) is 18.6%. A significant amount of energy can further be recovered from the “waste” exhaust water stream (12.94 kgL-H2O/kgflue-gas, at 91 °C and 1.2 bar) up to 800 Wh/kgflue-gas, improving the performance of the entire process (SECCO2: 3.86 kWh/kgCO2, ηRT,CO2: 69.8%). The study confirms the thermodynamic feasibility of the proposed configuration and identifies nitrogen liquefaction as the dominant energy-intensive step. Future optimization efforts should therefore focus on reducing exergy destruction in the deep cryogenic section through improved heat integration, enhanced cold-energy recovery, optimized compression–expansion staging, and reduced pressure losses.
Corigliano et al. (Tue,) studied this question.