Analysis of the Dynamic Behavior of Supercritical CO2 Pipeline Based on the Nonisothermal Transient Flow Model

Abstract

In supercritical CO₂ pipeline transport, the operation of pumps and valves often causes the pipeline to enter a transient state. Accurately describing the dynamic response in this state is crucial for making safety control decisions. This paper proposes a nonisothermal one-dimensional transient flow model for supercritical CO₂ pipelines based on one-dimensional transient flow equations and equipment characteristic equations. By comparison with experimental data, the GERG-2008 equation, known for its high accuracy, is chosen to calculate the physical property parameters of CO₂. By comparing with several sets of literature data, the results show that the errors are all within the acceptable range, which verifies the high accuracy of the model. The study investigates the hydraulic and thermal changes in the pipeline under transient operating conditions, including valve closure, slow startup, and sudden shutdown of the centrifugal pump. The results showed that the water-strike intensity of a supercritical CO₂ pipeline is one-third that of a water pipeline but 12 times that of a methane pipeline, which requires sufficient attention. The effect of impurity composition on water strike is significant, particularly when the N₂ content reaches 5%, at which point the maximum pressure decreases by 15.1%. In addition, the timing and method of valve shutoff significantly impact water strikes. It is recommended to prioritize the calculation of piping cycles, determine the maximum valve closing time in conjunction with industry standards, and use a linear valve closing method to reduce the water strike pressure. Studies have shown that the startup or sudden shutdown of centrifugal pumps at the inlet can cause sharp fluctuations in the pressure and flow rate, but the new equilibrium state will be established quickly. In addition, doping reduces the magnitude and rate of pressure changes in the pipeline. This study provides an essential foundation for the safe and stable operation of supercritical CO₂ pipelines.