Prediction model of decompression wave velocity in supercritical CO₂ pipelines containing impurities

Once a supercritical CO₂ pipeline fractures, decompression wave will appear at both end of the crack. Hence, the calculation of the decompression wave velocity during the pipeline fracturing is critical for the prediction and control of pipeline fracture. Based on the GERG-2008 equation of state, a decompression wave velocity prediction model for the supercritical CO₂ pipelines containing impurities was established with reference to the homogeneous flow model and the sound velocity calculation model for gas-liquid two-phase flow, and a calculation procedure thereof was developed. In addition, the effects of single-component non-polar impurities, single-component polar impurities and multi-component mixed impurities on the decompression wave curve of the supercritical CO₂ pipelines were studied. The results show that the addition of non-polar impurities increases the plateau pressure of the decompression wave curve, and thus the decompression wave is more likely to intersect with the pipeline fracture curve, increasing the risk of pipeline fracture. However, the presence of polar impurities can slightly reduce the plateau pressure of the decompression wave curve of the supercritical CO₂ pipelines, further reducing the risk of pipeline fracture. Therefore, this model could provide a theoretical basis for pipeline crack arrest and impurity composition control.