Modeling of CO2 Decompression across the Triple Point

The formation of significant quantities of solid CO 2 as a result of surpassing its triple point during rapid decompression of CO 2 pipelines employed as part of the carbon capture and sequestration (CCS) chain can present serious operational and safety challenges. In this paper, the development, testing and validation of a rigorous computational fluid dynamics (CFD) flow model for predicting solid CO 2 formation during decompression is presented. Multiphase flow is modeled by assuming homogeneous equilibrium, and the pertinent thermodynamic data are computed using real-fluid equations of state. The flow model is validated against pressure and temperature data recorded during the decompression of an extensively instrumented 144 m long, 150 mm i.d. CO 2 pipe initially at 5.25 °C and 153.3 bar. For the conditions tested, the simulated results indicate CO 2 solid mass fractions as high as 35% at the rupture plane, whose magnitude gradually decreases with distance toward the pipe's intact end