Abstract

The development, testing and validation of a two-fluid transient flow model for simulating outflow following the failure of high pressure CO 2 pipelines is presented. Thermal and mechanical non-equilibrium effects during depressurisation are accounted for by utilising simple constitutive relations describing inter-phase mass, heat and momentum transfer in terms of relaxation to equilibrium. Pipe wall/fluid heat exchange on the other hand is modelled by coupling the fluid model with a finite difference transient heat conduction model. The two-fluid transient flow model's performance is tested by comparison of the predicted transient pressure and temperature profiles along the pipeline against those based on the simplified homogeneous equilibrium model (HEM) as well as real data captured during the full bore rupture of a 260 m long, 233 mm internal diameter pipeline containing CO 2 at 36 bara and 273 °C. The two-fluid model is found to produce a reasonably good degree of agreement with the experimental data throughout the depressurisation process. The HEM based flow model on the other hand performs well only near the rupture plane and during the early stages of the depressurisation process. Document type: Article

Abstract

International audience; The development of an homogeneous relaxation flow model for simulating the discharge behaviour following the full bore rupture of dense phase CO2 pipelines is presented. Delayed liquid-vapour transition during the decompression process is accounted for using an empirically derived equation for the relaxation time to thermodynamic equilibrium. The flow model's robustness is successfully demonstrated based on a series of hypothetical shock tube tests. Model validation on the other hand is performed by comparison of the predictions against experimental data obtained for the full bore rupture of realistic scale CO2 pipelines. Within the ranges investigated, it is found that although delayed phase transition effects have negligible impact on the pipeline decompression rate, ignoring such phenomena results in underestimating the transient discharge rate. This is important since the latter governs the minimum safety distances to CO2 pipelines and emergency response planning in the unlikely event of pipeline failure.