Abstract:

Based on two groups of gaseous and supercritical CO₂ release experiments using an industrial scale CO₂ pipeline (258 m long, 233 mm i.d.) through a 100 mm diameter orifice, the dynamic pressure and visible cloud in the near field, and the temperature and concentration changes in the diffusion region were analyzed. The results show that the sharp drop in inventory pressure near the orifice produced a highly under-expanded jet and induced a sharp drop in temperature as a result of Joule-Thomson cooling. This effect led to the formation of solid CO₂ particles inside the under-expanded jet. The visible cloud remained a metastable state after the rapid expansion, and followed by a slow attenuation stage. The visible white cloud entraining the dry ice particles and condensed water rapidly expanded in the rapid expansion stage and dry ice particles have been sublimated into the ground before and did not form the ice bed. At the moment of the rupture, the temperature in the discharge area of gaseous and supercritical CO₂ releases dropped rapidly and then increased slowly, while the CO₂ concentrations increased quickly and then decreased. The dangerous distance of the 5% concentration of gaseous and supercritical CO₂ releases were at least 30 m and 50 m respectively.

Key words: carbon dioxide, pipeline release, diffusion, phase change, under-expanded jets

摘要：

通过气相和超临界状态的两组工业规模CO₂管道（长258 m、内径233 mm、泄放孔径100 mm）泄放实验，分析了近场动压、可见云以及扩散区域温度和浓度变化。研究表明：在大口径气相和超临界CO₂泄放中，泄漏口处会形成高度欠膨胀射流，在射流结构中会生成大量干冰颗粒；后者形成的欠膨胀射流结构范围较大，但马赫盘的位置都在0.4 m内。可见云在快速膨胀后，在一定时间内维持在亚稳定状态，随后缓慢衰减。可见云携带干冰颗粒和水雾快速扩散，干冰颗粒在降至地面前已全部升华，未形成干冰床。气相与超临界泄放中的扩散区域温度在迅速下降后缓慢上升，且超临界泄放中温降更大；CO₂浓度均升高后缓慢下降，预测二者5%浓度在泄漏方向上的危险距离至少为30和50 m。

关键词: 二氧化碳, 管道泄放, 扩散, 相变, 欠膨胀射流