Simulation Study on the Effects of Impurities on the Phase Behavior, Transport Characteristics, and Compression Performance of CO ₂

ABSTRACT CO 2 compression and liquefaction are critical process in carbon capture, utilization, and storage (CCUS) systems. However, CO 2 streams obtained from capture sources often contain impurities such as N 2 , O 2 , and H 2 O, which significantly alter the thermophysical properties of pure CO 2 and pose considerable challenges for system design and operation. In this study, the Peng–Robinson equation of state was employed within the Aspen HYSYS process simulation platform to systematically investigate the effects and mechanisms of these typical impurities on CO 2 throughout the processes of compression, liquefaction, and pipeline transportation. The results reveal the quantitative influence of impurities on the thermodynamic properties, pipeline characteristics, and compression performance of CO 2 . N 2 and O 2 decrease the critical temperature and increase the critical pressure of the CO 2 mixture, whereas H 2 O exhibits the opposite effect. In terms of thermodynamic properties, the density of CO 2 is more sensitive to pressure variation, whereas viscosity and thermal conductivity are more sensitive to impurity concentration. N 2 and O 2 exhibit similar effects, whereas the influence of H 2 O on viscosity and thermal conductivity is negligible. During pipeline transportation, the presence of impurities intensifies pressure loss and pressure drop, with H 2 O exerting the most significant influence, whereas temperature distribution is only slightly affected. In the compression process, N 2 and O 2 increase the compressibility factor of CO 2 and shift the compression path to the right on the pressure–enthalpy ( p – H ) diagram, leading to a considerable rise in compression energy consumption. The total energy consumption increases with impurity concentration. This study provides a solid theoretical basis and valuable data support for the optimized design, safe operation, and economic performance of industrial processes involving CO 2 mixtures containing impurities.