Modeling two-phase multicomponent CO2 mixtures in offshore pipelines under hydraulic shock

Abstract

Carbon capture and storage is crucial for reducing emissions from fossil fuel power plants and industries with significant CO${}_2$ production. To ensure safe pipeline design, integrated emergency shutdown systems are implemented, which can induce rapid changes in flow conditions, potentially causing critical pressure spikes and phase transitions, accelerating cavitation and material fatigue. In this work, we used a homogeneous two-phase flow model to evaluate the risk of two-phase flow during a hydraulic shock. The heat transfer between the CO${}_2$-rich stream and its surroundings is modeled using a heat transfer model with steady-periodic thermal boundary conditions. We considered pure CO${}_2$ and CO${}_2$ mixtures containing impurities obtained from pre-combustion and post-combustion carbon capture technologies. We investigated the influence of impurities, the choice of equation of state, pipeline inclination, and flow closure characteristics. The flow model is approximated using a weighted essentially non-oscillatory scheme coupled with the Harten–Lax–van Leer Contact flux. The model was benchmarked against a Riemann problem, a depressurization scenario, and decompression wave speed measurements, and further validated using pressure pulse data from cavity collapse experiments caused by rapid valve closure in water. The model’s applicability is demonstrated through a case study of an offshore pipeline, utilizing parameters from the Porthos project. Results indicated that CO${}_2$-rich streams initially in the liquid phase and near the saturation line can trigger vapor formation, but it depends on the impurity content. The results showed to be sensitive for the selected equation of state.