Experimental and numerical investigation on near-field temperature and surface CO2 concentrations of buried dense phase CO2 pipeline leakage

Abstract

Once the CO₂ fluid in the buried long-distance dense-phase pipeline leaks, it poses a significant threat to the surrounding environment and the safety of personnel. A large-scale field leakage diffusion test was conducted based on the CCUS million-ton buried dense phase long-distance CO₂ pipeline project in this study. The impact of the leakage's size (2 mm, 3 mm, 4 mm) and direction (horizontal, upward, and downward) on the soil morphology, temperature change, and surface CO₂ concentration around the leakage hole was studied. The velocity, CO₂ concentrations, and temperature field near the leakage port during the leakage process are simulated to supplement the experiments. The findings indicate that soil fissuring occurs when the leakage aperture exceeds 3 mm. The diameter of the frozen soil generated when the diameter of the vertical leakage is 4 mm is approximately twice that of the leakage diameter of 2 mm. Downward leakage has the most significant impact on low-temperature areas and the largest dry ice area under the condition of the same leakage port. The temperature drop rate increased directly to the size of the leakage hole, especially in the region 20–30 cm away from the leakage port. The surface CO₂ concentrations at the monitoring point at a height of 0.4 m above the leakage point for 2 mm leakage are predominantly influenced by wind. A height of 0.8–1.2 m can be selected as the appropriate monitoring height for leakage detection of the buried dense phase CO₂ pipeline. The surface CO₂ concentrations initially increase, subsequently decline and then experience a sudden surge due to the rupture and refreezing of the dry ice layer for leakage with an aperture larger than 3 mm. The horizontal and vertical diffusion distances of CO₂ concentrations up to 5 vol% were 1.5 m and 0.8 m for different direction tests after the rupture of soils. The research findings can provide valuable insights for improving leakage detection systems and performing risk assessments.