Experimental study of leakage characteristics and risk prediction of N2-containing dense-phase CO2 pipelines in real transportation conditions

Abstract

In the background of pipelines being widely used as a critical transportation chain for the carbon capture, utilization and storage (CCUS) process, studying the leak diffusion characteristics and risks of high-pressure impure CO2 pipelines in real transportation conditions is critical for process safety. Due to the limitations of the capture process and economic cost, the CO2 used for sequestration contains impurities in the range of 3% molar ratio, mainly N2. In this paper, the first leakage experiments involving dense-phase CO2 with a 3% molar ratio of N2 impurity were conducted on a large CO2 pipeline (258m long and 233mm inner diameter) using initial leakage orifices of 50mm and 100mm. Data concerning the thermodynamic properties of the impurity-containing leakage source were gathered for the analysis of phase transitions and flow alterations within the pipeline, as well as near-field temperature and the progression of the far-field concentration. The pressure-temperature curve in the pipe shifted along the dew line and then slowly shifted to the saturation line of pure CO2 with the influence of N2 impurities during the multiphase leakage phase. In the near-field region, cryogenic diffusion was governed by the boundary of the jet, with the control distance decreasing as the leakage orifice increased. In addition, an accurate prediction model of CO2 concentration on the leak axis was established based on the virtual source theory and the concentration decay law, and the predicted locations of CO2 concentrations at the 5% were 169m and 210m. As the leak orifice increases, the risk of low temperatures and high concentrations escalates, albeit with a sharp decrease in duration. These data provide accurate leakage characteristics and risk assessment for safely operating high-pressure CO2 processes under real conditions with impurities.