Experimental And Numerical Studies On CO₂ Leakage And Diffusion From Pipelines

As the intermediate link of the carbon capture and storage technology,the high pressure pipeline exist a high risk of CO₂ leakage during the transportation process.When a long-distance CO₂ pipeline leaks,a high-speed jet is formed,resulting in a large amount of dry ice particles.The high concentrations of CO₂ formed during CO₂ diffusion and dry ice sublimation endanger the health of nearby residents and the safety of equipment.However,there isn't a theoretical model to describe the high-pressure CO₂ leakage and diffusion characteristics accurately and completely.The relevant industrial scale experiments have not been carried out.In view of the present research situation,based on the industrial scale and the small-scale CO₂ release experiments,numerical simulation and theoretical analysis,the law of diffusion during high-pressure CO₂ leakage was studied.The main contents and conclusions of this paper are as follows:?1?A small scale and an industrial scale CO₂ release experiment device were designed.Based on these devices,the release experiments with different orifices and different phases have been carried out.The temperature developmentnear the leakage,the evolution of the jet cloud,the generation and disappearance of the dry ice and the change of the far-field temperature and concentration in the diffusion area were analyzed.?2?Small-scale CO₂ release experiments were carried out.The results show that: Under the same initial phase,the temperature drop amplitude near the orifice became greater as the release orifice size increased.Under the same orifice,the temperature drop amplitude near the orifice during the supercritical CO₂ release was larger than that during the gaseous CO₂ release.In the case of gas phase test,when the orifice size was less than 1.6 mm,the dry ice particles wasn't formed.When the orifice size was larger than 5.4 mm,the stable dry ice wasn't formed.The dry ice particles were generatedin all supercritical experiments.When the orifice size was 1.6 mm,there was a stable dry ice bank.When the orifice size was larger than 5.4 mm,the dry ice particles accumulated didn't form a stable dry ice bank.?3?Industrial scale CO₂ release experiments were carried out.The results show that: After the release,the evolution of jet cloud can be divided into three stages.The jet cloud entraining the dry ice particles and condensing water rapidly expanded in the rapid expansion stage and the dry ice particles have been sublimated before falling to the ground and did not form a ice bed.At the moment of the rupture,the temperature in the discharge area dropped rapidly and then increased slowly,while the CO₂ concentrations increased quickly and then decreased.The low temperature region and the dangerous area of dense phase test were larger than that of gas phase test.When the release orifice was 50 mm,the critical region length of dense phase,supercritical phase and gas phase were estimated to be 45 m,35 m and 25 m.?4?Based on the actual pipeline leakage,a numerical model for predicting gas phase CO₂ leakage behaviourwas established.The research showed that: The velocity field in the diffusion region appeared as an irregular ellipse.The velocity gradient became larger with increasing distance from the orifice.Under the same initial pressure,the horizontal diffusion range of CO₂ increased as the orifice size increased,while the vertical diffusion range increased linearly as the orifice size increased.Under the same orifice size,the horizontal and vertical diffusion distance increased linearly as the initial pressure increased.As the diffusion distance increased,the axis temperature dropped rapidly.The leakage pressure and the orifice size had a significant influence on the temperature drop amplitude and the low temperature range in the discharge area.?5?In this paper,the applicability of the diffusion model for predicting supercritical and dense phase CO₂ leakage behaviour was evaluated.The model was suitable for the simulation of the CO₂ concentration field during the supercritical CO₂ leakage.The simulation value of the CO₂ concentration during the dense phase CO₂ leakage was lower than the experimental value of the CO₂ concentration about 5%.The simulation values of the CO₂ temperature in the supercritical and dense phase CO₂ tests were higher than the experimental value about 10²0?.