Measurement of phase equilibrium characteristics and optimization of state equation for N2-CO2 binary system
XIE Naiya1,YAN Feng2,ZHU Jianlu1,CHEN Junwen3,CHENG Lei2,WANG Qihang1

1.College of Pipeline and Civil Engineering, China University of Petroleum (East China)//Shandong Key Laboratory of Oil & Gas Storage and Transportation Safety; 2.PipeChina Institute of Science and Technology; 3.Southwest Branch of China Petroleum Engineering & Construction Corporation

CO2, phase equilibrium, experimental measurement, state equation

DOI: 10.6047/j.issn.1000-8241.2024.05.007


【目的】杂质的存在会影响CO2的相平衡性质,进而影响CO2管道输送安全。随着CCUS(Carbon Capture, Utilization and Storage)技术的进一步应用,含杂质CO2体系相平衡研究对推广CCUS技术至关重要。【方法】自主设计了一套基于气体、液体可压缩性差异的含杂质CO2体系相特性测量实验装置,可以在-30~50℃范围内测量并计算含杂质CO2体系的泡点压力、露点压力。将实验结果与PR方程、GERG-2008方程、BWRS方程、SRK方程、PRSV方程模拟结果进行对比,分析各方程预测精度。【结果】针对不同比例的N2-CO2二元体系,随N2含量增加,各状态方程对于泡点压力、露点压力的预测精度下降。不同温度区间各状态方程预测精度不同,PR方程在0℃以下的泡点压力、露点压力预测精度较高,在0℃及以上,预测精度下降;GERG-2008方程在0℃以下的泡点压力、露点压力预测精度较低,在0℃及以上,预测精度较高;BWRS方程无明显规律性,但对各体系总体预测精度较低;SRK方程在0℃及以下预测精度较低,在0℃以上预测精度较高;PRSV方程在0℃以下预测精度较低,在0℃及以上预测精度较高。【结论】除BWRS方程无明显规律性外,其他方程在不同温度区间表现出不同的预测精度。状态方程优选建议:针对纯CO2,在0℃以下推荐使用PR方程,在0℃及以上推荐使用PRSV方程;对于99.5%CO2+0.5%N2的体系,在-20~20℃范围内,推荐使用PR方程;对于96%CO2+4%N2的体系,在-30~20℃范围内,推荐使用PR方程、PRSV方程。(图 10,参[21]
[Objective] The presence of impurities impacts the phase equilibrium of CO2, potentially compromising the safety of CO2 pipeline transmission. As efforts intensify towards advancing the application of Carbon Capture, Utilization and Storage (CCUS) technology, examining the phase equilibrium of impurity-containing CO2 systems is essential for the broader adoption of this technology. [Methods] An experimental setup was independently developed to measure the phase characteristics of impurity-containing CO2 systems, utilizing the compressibility difference between gas and liquid phases. This setup allows for the measurement and calculation of pressure at the bubbling and dew points for impurity-containing CO2 systems over the temperature range of -30 ℃ to 50 ℃. The experimental results were compared with simulations generated by the PR equation, GERG-2008 equation, BWRS equation, SRK equation, and PRSV equation to assess their predictive accuracy. [Results] For N2-CO2 binary systems with varying ratios, the predictive accuracy of all these state equations for pressure at the bubbling and dew points diminished as the N2 content increased. Additionally, the predictive accuracy varied across temperature intervals for these equations. Specifically, the PR equation demonstrated enhanced accuracy in pressure prediction at both the bubbling and dew points below 0 ℃, compared to predictions above 0 ℃. Conversely, the GERG-2008, SRK, and PRSV equations displayed an opposite trend. Furthermore, the BWRS equation consistently exhibited low predictive accuracy for this system across all ratios, without any identifiable pattern. [Conclusion] Taking into account the predictive accuracy trends of equations across different temperature intervals, excluding the BWRS equation which lacks any discernible pattern, optimization recommendations are suggested for these state equations. For pure CO2, it is advisable to utilize the PR equation below 0 °C and the PRSV equation above 0 °C. In the case of a mixture comprising 99.5% CO2 and 0.5% N2, the PR equation is recommended for use within the temperature range of -20 ℃ to 20 ℃. Similarly, for a mixture of 96% CO2 and 4% N2, both the PR equation and PRSV equation are recommended for use within the temperature range of -30 ℃ to 20 ℃. (10 Figures, 21 References)