Experiments and modelling of two-phase transient flow during pipeline depressurization of CO2 with various N2 compositions

Abstract

Pressure-release experiments of CO2 with impurity contents of 10, 20 and 30 mol% nitrogen have been executed. The experimental investigations were performed in a 140 m long horizontal tube with an inner diameter of 10 mm. The initial conditions of the CO2-N2 mixtures were in the supercritical region at approximately 120 bar and 20 °C. The results, which showed a good repeatability, were then compared with numerical data from a homogeneous equilibrium model. The investigations have concentrated on the pressure wave at the start as well as the pressure and temperature development during the pressure release. The model, which has a certain complexity, but still contains several simplifications, gave relatively good results for all three gas mixtures. Although the absolute values for the temperature development showed to be consistently higher in the experimental results compared to the numerical results, the liquid dry-out points were predicted with good accuracy at all measurement points. The numerical results of the pressure development match the experimental results very well, both regarding the absolute and relative values. Regarding the speed of the pressure wave, the numerical results were consistently too high, which is believed to be caused by the EOS overpredicting the speed of sound for our cases. The good results, especially for the pressure, are promising, and further work is suggested to improve the model.