Study on propagation characteristics of decompression wave of supercritical CO2 pipeline based on isochoric thermodynamics.

Predicting the decompression behavior and controlling the fracture of CO₂ pipelines are crucial research areas for the safe transport of CO₂. Existing decompression wave prediction models have problems such as large errors in calculating the sound speed of the gas-liquid two-phase flow and difficulties in convergence near the critical point. The local sound speed calculation method based on isochoric thermodynamics was improved and a new decompression wave prediction model was established. The effects of gas compositions, initial phase state, initial pressure, and initial temperature on decompression wave curves and pressure drop curves were calculated and analyzed. Additionally, the decompression behavior of CO₂ pipeline leaks in practical engineering scenarios was predicted. The results show that compared to post-combustion capture or pre-combustion capture, the initial decompression wave speed under gas by oxy-fuel combustion capture is reduced by approximately 26%, and the decompression plateau pressure increases by 22%. During the decompression process, the temperature and pressure operating point of medium inside the pipeline no longer move along the gas-liquid equilibrium line but directly enter the gas-liquid two-phase region. Compared to the dense phase state, the saturation pressure corresponding to the intersection of the pressure drop curve and the CO₂ bubble point line is about 26% higher in the supercritical state, and the decompression plateau pressure is higher. Lower operating temperatures and higher operating pressures can effectively reduce the decompression plateau pressure. Due to the differences in operating parameters along the pipeline, the risk of pipeline fracture decreases sequentially from the starting point of the pipeline, with the front section of the pipeline being the high-risk section. This study provides a theoretical basis for CO₂ pipeline design and engineering applications. [ABSTRACT FROM AUTHOR]