Impurities in CO₂ - Rich Mixtures Impact CO₂ Pipeline Design: Implications for Calculating CO₂ Transport Capacity

Existing carbon dioxide (CO₂) pipelines commonly contain over 90% of CO₂ mixed with major impurities such as methane (CH₄), hydrogen sulfide (H₂S), and nitrogen (N₂). Other minor impurities are carbon monoxide (CO), oxygen (O₂), C₂+ hydrocarbons, and H₂O. CO₂ is transported in the gas phase, liquid phase, or as a supercritical fluid. Phase behaviors of CO₂ mixtures are based on the Vapor Liquid Equilibrium (VLE) and critical points of mixtures. The predictions of VLE are essential to the design and operation of CO₂ mixture pipelines. The VLE and critical points for binary or ternary CO₂ mixtures are predicted by Equations of State (EOS). This study illustrates how major impurities impact transport capacities of CO₂-rich mixture pipelines. The calculations indicate that the flow capacity in the liquid phase is approximately twice as high as in the gas phase.