Numerical calculation model for decompression waves in CO2 pipeline leakage and effect of initial temperature and pressure
YAN Feng1,YIN Buze2,OUYANG Xin1,HU Qihui2,ZHI Shujie1,LI Yuxing2,GONG Jiyu2

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

CO2 pipeline, CO2 leakage, calculation of decompression waves, propagation behavior of decompression waves, experiment

DOI: 10.6047/j.issn.1000-8241.2024.05.010


【目的】超临界/密相CO2管道是目前长距离运输CO2的主要方式,由于超临界/密相CO2管道维持高压运行,对其管材止裂韧性的计算评估极其重要。减压波特性是评估管材止裂韧性的重要依据,然而CO2泄漏涉及跨相态减压过程,导致其减压波传递规律复杂,预测难度增加,影响管材止裂评估。【方法】为研究CO2管道泄漏时减压波的传递规律,搭建了CO2泄漏减压波实验平台,以均相流模型为框架,结合气体状态方程、声速模型及出流速度模型建立了减压波数值计算模型,通过将模型计算结果与实验数据进行对比,验证了模型的准确性,并以此为基础,开展了不同初始温度、压力下的数值计算。【结果】不同相态CO2减压波平台的起始点波速均随压力的升高而升高,随温度的升高而降低。与气态CO2不同,密相和超临界CO2减压波平台的高度均随压力的升高而降低,随温度的升高而升高。温度和压力对减压波平台影响的本质为对初始熵值和密度的影响。减压平台的高度取决于初始熵值,对于气相,初始熵值越低,减压波平台越高;对于密相和超临界相,初始熵值越高,减压波平台越高。无论何种相态,初始密度越高,平台长度越长。【结论】实际工程中应重点关注起点高温高压位置的管道止裂,该实验方法和减压波计算模型可为CO2管道止裂韧性计算评估和管道设计提供理论支撑。(图 11表1,参[21]
[Objective] Supercritical/dense-phase CO2 pipelines serve as the primary mode for long-distance CO2 transportation. Given their high-pressure operation, it is crucial to calculate and evaluate the crack arrest toughness of pipe materials. Understanding the characteristics of decompression waves is vital for evaluating the crack arrest toughness of pipe materials. However, CO2 leakage involves a multi-phase decompression process that complicates the propagation behavior of decompression waves, posing challenges for accurate prediction of decompression wave and evaluation of crack arrest toughness. [Methods] To investigate the propagation behavior of decompression waves in CO2 pipeline leakage, an experimental setup was constructed specifically for this purpose. A numerical calculation model for decompression waves was then developed using the homogeneous flow model as the framework, integrating the state equation of gas, sound velocity model, and outflow velocity model. The accuracy of the model was verified through a comparison of calculated outcomes with experimental data. On this basis, numerical calculations were conducted at different initial temperatures and pressure levels. [Results] According to the experimental results, the wave velocities at the initial point of CO2 decompression wave plateau varied directly with pressure and inversely with temperature across different phase states. In contrast to gaseous CO2, the plateau height of decompression waves for dense-phase and supercritical CO2 decreased with rising pressure and increased with rising temperature. The effect of temperature and pressure on the decompression wave plateau is essentially the effect of initial entropy and density. The height of the decompression plateau depends on the initial entropy. Specifically, a lower initial entropy value in the gas phase results in a higher plateau, while higher initial entropy values lead to higher plateaus in dense-phase and supercritical states. Furthermore, higher initial density prolongs the plateau duration across all phase states. [Conclusion] In practical engineering, close attention should be paid to pipe crack arrest at the onset of high temperature and high pressure. The experimental method and calculation model for decompression waves can offer theoretical support for evaluating CO2 pipeline crack arrest toughness and informing pipeline design. (11 Figures, 1 Table, 21 References)