Abstract:

Based on an industrial-scale CO₂ pipeline venting experimental platform, throttling and venting experiments were conducted for both dense-phase and supercritical CO₂. Through the analysis and comparison of the experimental results, this study reveals the evolution patterns and differences in pressure, temperature, and phase state of CO₂ within the venting pipeline during the release process under different initial phase conditions. The findings provide direct data support, valuable insights, and practical recommendations for CO₂ pipeline venting operations in industrial applications. The results show that during both subcritical and supercritical CO₂ venting, the pressure at the upstream and downstream sections of the valve undergoes distinct phases: a rapid depressurization stage followed by a pressurization stage at the upstream and downstream sections, respectively. The downstream pressure then decreases as the main pipeline pressure drops. The temperature evolution at each section follows a two-stage process of cooling and heating, corresponding to the initial valve opening and the subsequent throttling phase. After the valve is fully opened, the temperature drop is more pronounced during dense-phase CO₂ venting, with the minimum temperatures inside the pipeline being -35.75℃ for dense-phase CO₂ and -28.63℃ for supercritical CO₂. This indicates that dense-phase CO₂ undergoes a greater temperature drop during venting. Furthermore, the pressure differential across the valve is greater during supercritical CO₂ venting than during dense-phase CO₂ venting, which could result in more significant valve shock. However, despite the above problems, the CO₂ in the supercritical CO₂ venting pipe can leave the gas-liquid saturation phase earlier than that in the dense-phase CO₂ venting pipe. Overall, the study provides valuable insights into the behavior of CO₂ under different phases during venting and offers practical guidance for optimizing CO₂ pipeline venting operations to enhance safety, performance, and operational efficiency.

Key words: safety, carbon dioxide, experimental verification, CO₂ pipeline, venting characteristics, CO₂ phase state

摘要：

基于工业规模CO₂管道放空实验平台，开展了密相和超临界相CO₂节流放空实验。通过对放空实验的结果进行分析和对比，揭示了不同初始相态CO₂放空过程中，放空管管内CO₂的压力、温度和相态的演变规律和差异，为实际工业CO₂管道放空操作提供直接的数据支持和参考建议。结果表明，密相和超临界相CO₂放空过程阀门上游截面和下游截面压力会分别经历快速降压阶段和充压阶段。各截面温度演变过程均会经历两段温降和温升过程。相较密相CO₂放空，超临界相CO₂放空阀门前后截面的压差更大，这可能会对阀门造成更为强烈的冲击。然而，尽管可能存在上述问题，超临界相CO₂放空相较密相CO₂放空管内CO₂可以更早脱离气液饱和相。因此，超临界CO₂放空时管内发生干冰冻堵的风险也相对较低。

关键词: 安全, 二氧化碳, 实验验证, CO₂管道, 放空特性, CO₂相态