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.

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