Enhanced numerical stability in transient flow modeling of CCUS pipelines: A finite volume method with application to water hammer analysis

Supercritical/dense-phase CO 2 pipeline transportation is a critical link in carbon capture, utilization, and storage technology, which is a major approach to reducing emissions. The thermo-hydraulic simulation of CO 2 pipelines usually applies numerical methods developed for oil and gas pipelines. However, the CO 2 properties are highly sensitive to temperature and pressure, compared to natural gas, which may lead to numerical instability. This study improves finite volume method (FVM) with staggered grids and an explicit discretization method of convective terms. The results show that under conditions with rapid flow state changes, the improved FVM enhances the computational stability. Additionally, an adaptive time-step adjustment algorithm is introduced to dynamically adjust the time step based on the rate of flow state changes, ensuring both computational accuracy and efficiency. The proposed algorithm is validated with a pipeline shutdown scenario, where the fluid state along the pipeline undergoes relatively intense changes, demonstrating the stability of the numerical solutions proposed. Furthermore, a comparative analysis of water hammer pressure during shutdown is conducted with theoretical equations and simulations, showing that in addition to direct compression pressure, the pipeline endpoint is also subjected to fluid packing pressure, which should be considered in water hammer control.