Development of a transient numerical simulation model and analysis of shutdown conditions for a supercritical CO₂ pipeline

Objective Phase transitions of supercritical CO₂ fluid may happen in the transient process of pipeline transportation, posing higher flow safety risks than those in natural gas pipelines. Therefore, it is essential to precisely simulate the transient process of supercritical CO₂ pipelines to ensure operational safety.

Method Utilizing the GERG-2008 equation, which currently offers the highest computational accuracy, a physical property calculation module was developed, and a pipeline thermohydraulic transient numerical simulation model was established. The physical property calculation module generated a fluid property table within the operating discrete temperature and pressure ranges. During the simulation, fluid properties were obtained through linear interpolation, which significantly enhanced simulation speed compared to directly invoking the physical property calculation module within the thermohydraulic simulation iteration process. For the shutdown conditions of a supercritical CO₂ pipeline, the model governing equations and boundary conditions of the model were improved. Such as considering the potential for reverse flow during transient processes in the pipeline, the velocity variable in the transient equations was specifically adjusted. Additionally, more realistic post-shutdown heat transfer boundary conditions were set, replacing the commonly used isothermal boundary condition.

Result The model was validated based on shutdown conditions, and compared with OLGA simulation results, the temperature and pressure errors were not more than 0.05% and 0.80%, respectively.

Conclusion This model can be used for thermohydraulic simulations and water hammer pressure analysis under shutdown conditions, serving as an important tool for flow safety analysis. It can also be applied to calculations for general transient conditions involving fluctuations in pressure, temperature, and flow rate. The proposed physical property model and thermohydraulic simulation technology can contribute to the development and intelligent construction of carbon capture, utilization, and storage (CCUS) projects.