基于GERG状态方程的杂质组分对CO_(2)减压波平台影响研究

Research of Impurity Components on the Decompression Plateau of CO_(2) Based on the GERG Equation of State

超临界CO_(2)特殊的热力学性质使其存在较长的减压波平台(饱和压力),导致裂纹尖端压力长时间维持在高水平,裂纹长程扩展,因此研究超临界CO_(2)的热力学性质变化规律具有重要意义。简述了目前常用的气体状态方程,并基于GERG-2008状态方程对N_(2)、Ar、H_(2)、CO、CH_(4)、O_(2)、H_(2)S与CO_(2)的混合物密度、气液平衡边界等性质进行计算,与试验数据进行对比以评估GERG-2008状态方程的适用性。分析了超临界CO_(2)流体主要杂质组分(摩尔比为0到10%)对超临界CO_(2)减压波平台压力的影响规律,并发现和纯CO_(2)相比,CO_(2)/N 2、CO_(2)/O_(2)、CO_(2)/CH 4、CO_(2)/Ar、CO_(2)/CO和CO_(2)/H_(2)使两相区向高压区移动,因此提高了气体减压过程的饱和压力,而H_(2)S和SO_(2)杂质降低CO_(2)的两相区的压力,从而降低饱和压力。研究表明通常情况下GERG-2008预测的减压波平台压力与试验结果具有较好的一致性,杂质气体对CO_(2)减压波的影响较大。研究结果可为超临界CO_(2)管道断裂控制设计和工程应用提供理论依据。

The special thermodynamic properties of supercritical CO_(2) 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 CO_(2).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 N_(2),Ar,H_(2),CO,CH_(4),O_(2),H_(2) S and CO_(2) 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 CO_(2) fluid on the pressure of the supercritical CO_(2) decompression plateau is summarized.Compared with pure CO_(2),the existence of CO_(2)/N_(2),CO_(2)/O_(2),CO_(2)/CH_(4),CO_(2)/Ar,CO_(2)/CO and CO_(2)/H_(2) moves the two-phase area to the high-pressure area,thus increasing the saturation pressure of the gas decompression process.However,H_(2)S and SO_(2) impurities reduce the pressure in the two-phase region of CO_(2),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 CO_(2) decompression wave.These results provide theoretical basis for the fracture control design and engineering application of supercritical CO_(2) pipelines.