Application of Highly Accurate Phase-Equilibrium Models for CO2 Freezing Prediction of Natural Gas System

It is of great engineering significance to find an accurate model to predict CO2 freezing and avoid plugging in the light hydrocarbon separation process of natural gas. Research starts from CO2 freezing in simple CH4-CO2, binary systems. By use of a traditional model based on the Antoine equation, the calculated freezing temperature in liquid solid equilibrium (LSE) is not as accurate as that in vapor solid equilibrium (VSE). Then a new thermodynamic method of reference state of hypothetical fluid is used to replace LSE model based on the Antoine equation to calculate solid CO2 fugacity. The improved phase-equilibrium model based on GERG-2008 is proved to be the most accurate one to calculate CO2 freezing temperature, in which the Antoine equation is used in VSE model while reference state method is used in LSE model. Compared with experimental data, the calculated results also show a higher accuracy in complex natural gas system. Besides, the improved phase-equilibrium model is applied in the actual light hydrocarbon separation process to research the CO2 freezing phenomenon, which explains wide applicability of the new model.