(54cd) CFD Modeling of Liquefied Gases Discharging through a Pipeline Full Bore Rupture

Large amounts of substances are transported in pipelines worldwide. This activity represents a hazard that needs to be quantitatively assessed through discharge models that are capable of accurately predict the outflow when a pipeline ruptures. The calculation of the discharge rate of pipelines transporting gases or liquids is well understood and accurate models exist for this purpose; less well understood is the discharge of flashing liquids. When a pipeline transporting a liquefied gas ruptures (e.g., CO₂, LNG or LPG pipelines), the expansion generates a phase transition which results in a two-phase release.

In general, there are two different scenarios when a pipeline ruptures: the full bore rupture, and the puncture case. A full bore rupture is a complete rupture of the pipeline, so the substance flows out through the pipeline cross-sectional area. On the other hand, a puncture is represented by the substance flowing through an orifice or crack in the pipeline walls. A full bore rupture is associated with a quicker depressurization of the system in comparison to the puncture case. Even though a full bore rupture is usually more catastrophic, a puncture is more common in a real scenario.

Numerous researchers have used one-dimensional conservation equations to describe the discharge of liquefied gases when a pipeline full bore rupture occurs. However, a systematic study on how the accuracy of different equations of state affects the depressurization prediction is lacking for this case. The main objective of this research is to propose a two-dimensional discharge model using Computational Fluid Dynamic (CFD) tools in order to predict the pressure and temperature profiles along the pipeline, as well as the discharge rate and phase transition; while investigating the effect of different equations of state on the predictions for the full bore rupture case. In order to validate the 2-D discharge model, full bore rupture experiments with dense-phase CO₂ pipelines have been used. The validation step evaluates the assumptions that have been implemented to model the physics of the transient phenomenon. This study will help to improve the formulation of current discharge models for liquefied gases. Once the full bore rupture study is completed, the subsequent step will be to propose a three-dimensional model to predict the behavior of liquefied gases discharging through a puncture. The previous scenario will complete the picture for predicting the discharge of flashing liquids when a pipelines ruptures, especially for the puncture case, where the physics is less well understood than for the full bore rupture scenario.

Keywords: Consequence Modeling, Source Term, Pipelines, Carbon Dioxide, Computational Fluid Dynamics (CFD)