新疆油田超临界CO2管道安全停输工艺边界范围确定

1.中国石油大学(北京)克拉玛依校区工学院·新疆多介质管道安全输送重点实验室;2.国家管网集团科学技术研究总院分公司;3.中国石油新疆油田分公司开发公司

超临界CO2;管道输送;停输过程;瞬变特性;相变;安全运行工艺边界

Establishing boundaries of safe shutdown process for supercritical CO2 pipeline of Xinjiang Oilfield Branch
LI Xinze1,SUN Chen1,ZHANG Xueqin2,ZOU Weijie1,YUAN Liang3,XIONG Xiaoqin1,XING Xiaokai1,XU Ning1

1.Engineering School, China University of Petroleum-Beijing at Karamay//Xinjiang Key Laboratory for Transportation Safety of Multi-Medium Pipelines; 2.PipeChina Institute of Science and Technology; 3.Development Company of PetroChina Xinjiang Oilfield Branch

supercritical CO2, pipeline transportation, shutdown process, transient characteristics, phase transition, safe operational process boundary

DOI: 10.6047/j.issn.1000-8241.2024.05.011

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【目的】超临界CO2管道不同于原油、天然气管道,其在停输的瞬态过程中存在相特性变化问题。为保障超临界CO2管道停输后的安全,确定其停输前的安全运行工艺(输送压力、输送温度)边界具有重要意义。【方法】为准确描述管道停输后的瞬态过程,以新疆油田超临界CO2管道示范工程为例,采用OLGA软件建立了水力热力计算模型。同时基于管流连续性方程、运动方程、能量方程、PR状态方程及热力学关系式,采用Matlab编程计算的方式对商业软件模型的准确性进行了验证。根据获得的管道停输过程中管内温度、压力、密度及相态协同变化波动规律,提出在压力和温度协同作用下,以CO2密度发生阶跃变化来确定管道安全停输时间的原则,从而将安全停输时间问题转化为避免输送体系中超临界CO2转变为气相的问题。【结果】基于该示范工程的压力和温度运行参数范围,分别确定了夏季和冬季工况下高压低温、高压高温、低压低温、低压高温共8种典型工艺运行边界。同时对比分析了不同季节、不同边界条件下的停输过程管内参数波动变化特征、温压协同变化关系、相态转变路径及规律等。【结论】高压低温边界最安全,低压高温边界最危险;冬季相比夏季,管道安全停输时间大幅缩短。为指导工程实际,分别给出了夏季和冬季示范工程安全停输工艺边界范围及函数表达式。研究结果可为超临界CO2管道安全运行提供理论支持和技术保障。(图8表4,参[24]
[Objective] Unlike crude oil and natural gas pipelines, supercritical CO2 pipelines encounter phase characteristic changes during the transient shutdown process. To ensure post-shutdown safety of a supercritical CO2 pipeline, it is crucial to establish the safe operational process (transport pressure and temperature) boundaries prior to shutdown. [Methods] A hydrothermodynamic calculation model was developed using OLGA to accurately depict the transient process of a post-shutdown pipeline, with the supercritical CO2 pipeline demonstration project of Xinjiang Oilfield Branch serving as a case study. At the same time, the accuracy of the commercial software model was validated through Matlab programming calculations utilizing the equation of flow continuity, equation of motion, energy equation, PR equation of state, and thermodynamic relations. Based on the observed fluctuation law from the coordinated variations of temperature, pressure, density, and phase state in the pipeline during shutdown, it was proposed that the safe shutdown time for the pipeline should be determined by the step change of CO2 density under the synergic action of pressure and temperature. This approach reframes the concern of safe shutdown time to preventing the transition of supercritical CO2 into the gas phase in the transportation system. [Results] Based on the operating pressure and temperature parameters in this demonstration project, eight typical operational process boundaries were identified for summer and winter scenarios, including high-pressure & low-temperature, high-pressure & high-temperature, low-pressure & low-temperature, and low-pressure & high-temperature process boundaries. Furthermore, an analysis was conducted to compare and study the fluctuation characteristics of parameters in the pipeline, the coordinated variation between temperature and pressure, as well as the phase transition path and behavior during shutdown processes under various seasonal and boundary conditions. [Conclusion] The findings revealed that the high-pressure & low-temperature boundary is the safest, while the low-pressure & high-temperature boundary poses the highest risk. Additionally, the safe shutdown time for the pipeline in winter was significantly reduced compared to summer. To guide engineering practices, process boundary ranges and functional expressions for the safe shutdown of the demonstration project were provided for summer and winter scenarios. The research results can offer theoretical support and technical assurance for the safe operation of supercritical CO2 pipelines. (8 Figures, 4 Tables, 24 References)
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