Thermophysical evolution during different decompression of N2-containing S-CO2 pipelines

Pipelines transporting impure supercritical carbon dioxide in the carbon capture, utilization, and storage (CCUS) chain exhibit varying decompression characteristics due to engineered emissions or accidental leakage, resulting in diverse temperature drops and heat transfer mechanisms in the media and pipe walls. Therefore, studying heat transfer characteristics during slow and instantaneous decompression is crucial to investigating pipeline operational risks. In this work, supercritical CO₂ pipeline valve release and rupture disc release experiments were performed with a 1.5% molar ratio of N₂ content in an experimental pipeline (16 m long, 100 mm inner diameter). The evolution of the medium and pipe wall's physical properties was measured and discussed. Two methods of depressurization were employed to analyze the phase changes and heat transfer processes in the pipe. The instantaneous decompression process has a shorter decompression time and undergoes fluctuating and stable decompression stages. The slow decompression process has a slower temperature drop rate, but the wall during the process can reach a lower minimum temperature. Both release methods cause a larger temperature drop and Nusselt number at the bottom of the pipe wall due to evaporation heat transfer compared to the middle and top. The slow decompression process demonstrates a higher peak Nusselt number at the bottom, resulting in superior heat transfer efficiency compared to the instantaneous decompression process. © 2023 Society of Chemical Industry and John Wiley & Sons, Ltd.