CO2 transportation is an indispensable intermediate link in the CCUS industry chain. When transporting large capacity and long-distance CO2 with impurities, pipeline transportation is more safe and more efficient. In the event of accidental CO2 pipeline leakage or engineering venting process, the sudden phase change and expansion of CO2 in the pipeline will lead to a sudden drop in the temperature of the pipeline, which will increase the risk of pipeline rupture. The research on the change of temperature on the wall of the pipeline during the venting process and the heat transfer properties of phase change has essential significance in avoiding the cracking of cracks and reducing the risk of crack expansion. In order to conduct small-scale pipeline safety research, a 16m long, 100mm inner diameter pipeline test device is set up. The distribution of temperature in the pipeline, the temperature on the pipe wall and the change of pressure in the pipeline in the process of slow valve opening and instantaneous full-diameter venting of nitrogen-containing supercritical phase CO2 were measured by venting experiment with inner diameter of 25mm. The influence of different venting modes on the depressurization of the pipeline, the temperature change inside and outside the pipeline, and the influence of phase change on the heat transfer in the pipeline were analyzed. The pressure, temperature and wall temperature values at the front, middle and rear sections of the pipeline were measured. It can be seen from the results that at the same elevation, the wall temperature drop at the vent end is smaller than that at the medium injection end, and the trend is the same as that of the temperature change in the pipeline. On the same section, the wall temperature drop at the bottom of the pipeline is the largest, and it is much larger than the wall temperature drop at the top and middle of the pipeline. At the injection end of the pipeline, the wall temperature is lower than the bottom temperature of the pipeline due to the continuous phase change and heat absorption of the medium. Compared with instantaneous full-diameter venting, valve opening venting has a longer phase change heat transfer time, larger wall temperature drop, and greater brittle fracture risk.
Keywords Pipeline transportation, Pressure drop, Temperature inside the pipe, Temperature on the pipe wall