Abstract:

CO₂ pipelines is a key link of CCUS technology, when it encounters leakage, corrosion and other damage, it is necessary to vent the pipeline first to carry out subsequent repair work. In order to ensure the safety of the venting operation, it is necessary to evaluate the potential danger of dry ice generation and the risk of valve freezing during the venting process. In this paper, based on the industrial-scale CO₂ pipeline throttling experimental device, two groups of supercritical phase venting experiments with different throttle valve openings were performed. The results showed that during the direct venting process, a dry ice zone (length shorter than 149.2 m, height lower than 58.3 mm) appeared at the injection end of the main pipeline at the later stage of the venting, and that the generated dry ice particles had migration phenomena. The minimum temperature of the vent pipe drops to -23.2℃, and the subzero low temperature continues for 600.4 s. Although the throttling effect can improve the minimum temperature of the dry ice area at the injection end, but dry ice accumulation occurs at the discharge end (the length of the accumulation is shorter than 10.4 m, and the height is lower than 116.5 mm). The throttling effect can reduce the pressure filling level of the vent pipe (pressure reduction of 40%), but will also reduce the temperature drop of the vent pipe (the lowest temperature down to -35.4℃) and increase the potential danger of valve freezing.

Key words: safety, carbon dioxide, experimental validation, throttle, dry ice freezing blockage, valve low temperature

摘要：

CO₂输送管道作为碳捕集、利用与封存（CCUS）技术的关键环节，当遇到泄漏、腐蚀等损伤时需要先对管道放空来开展后续修复工作。为确保放空操作的安全性，需对放空过程中的干冰冻堵隐患与冻阀危险进行评估。故基于工业规模CO₂管道节流实验装置，开展了2组不同节流阀开度的超临界相放空实验。结果表明，直接放空过程中，放空后期主管道的注入端出现干冰区（长度小于149.2 m，高度小于58.3 mm），并且生成的干冰颗粒存在迁移现象。放空管最低温度降至-23.2℃，零下低温持续600.4 s。节流放空虽能提升注入端干冰区最低温度，但在泄放端会出现干冰堆积（堆积长度小于10.4 m，高度小于116.5 mm）。节流作用可以降低放空管充压水平（降压幅度为40%），但同时也会降低放空管的温降幅度（最低温度降至-35.4℃）从而增加冻阀隐患。

关键词: 安全, 二氧化碳, 实验验证, 节流, 干冰冻堵, 阀门低温