Predicting the Decompression Characteristics of Carbon Dioxide Using Computational Fluid Dynamics

In a previous paper, we reported the development of CFD-DECOM, a Computational Fluid Dynamics (CFD) model based on the Arbitrary Lagrangian Eulerian (ALE) approach and the Homogeneous Equilibrium Method (HEM) for simulating multi-phase flows, to predict the transient flow following the rupture of pipelines conveying rich gas or pure carbon dioxide (CO₂). The use of CFD allows the effect of pipe wall heat transfer and friction to be quantified. Here, the former is considered through the implementation of a conjugate heat transfer model while the two-phase pipe wall friction is computed using established correlations. The model was previously validated for rich gas and to a limited extent dense phase CO₂ decompression against the available shock tube test data.

This paper describes the extension of the model to the decompression of both gaseous and dense phase CO₂ with impurities. The Peng-Robinson-Stryjek-Vera Equation Of State (EOS), which is capable of predicting the real gas thermodynamic behaviour of CO₂ with impurities, has been implemented in addition to the Peng-Robinson and Span and Wagner EOSs. The liquid-vapour phase equilibrium of a multi-component fluid is determined by flash calculations. The predictions are compared with the measurements of some of the recent gaseous and dense phase CO₂ shock tube tests commissioned by National Grid. The detailed comparison is presented showing reasonably good agreement with the experimental data. Further numerical study has also been carried out to investigate the effects of wall friction and heat transfer, different EOSs and impurities on the decompression behaviour.