Research of Impurity Components on the Decompression Plateau of CO2 Based on the GERG Equation of State
The special thermodynamic properties of supercritical CO2 result in the existence of a long decompression wave plateau(saturation pressure),which leads to the long-term maintenance of crack tip pressure at a high level and long-range crack propagation.Therefore,it is of great significance to study the change law of thermodynamic properties of supercritical CO2.Firstly,a brief introduction to the common gas equation of state is provided.Based on the GERG-2008 equation of state,the mixture density and gas-liquid equilibrium boundary of N2,Ar,H2,CO,CH4,O2,H2S and CO2 are calculated with comparison to experimental data to evaluate its applicability.The influence of the main impurity components with molar ratio from 0 to 10％in supercritical CO2 fluid on the pressure of the supercritical CO2 decompression plateau is summarized.Compared with pure CO2,the existence of CO2/N2,CO2/O2,CO2/CH4,CO2/Ar,CO2/CO and CO2/H2 moves the two-phase area to the high-pressure area,thus increasing the saturation pressure of the gas decompression process.However,H2 S and SO2 impurities reduce the pressure in the two-phase region of CO2,thereby reducing the saturation pressure.The results show that under normal circumstances,the plateau pressure predicted by GERG-2008 is in good agreement with the test results,and impurity gas shows few impacts on the curve of CO2 decompression wave.These results provide theoretical basis for the fracture control design and engineering ap-plication of supercritical CO2 pipelines.
CO2 pipeline transportationsupercritical CO2equations of state(EOS)saturation pressuredecompression plateau
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