Carbon Capture and Storage (CCS) is widely seen as an effective technique to reduce what is perceived as excessive CO₂ concentration in the atmosphere. This technique includes transporting CO₂ from source point to the storage site, usually through high-pressure pipelines. In order to ensure safe transport (i.e. to prevent the contents from being released into the atmosphere), it is important to estimate the required pipe toughness in the design stage. This requires an accurate prediction of the speed of the ‘decompression wave’ in the fluid, which is created when the high-pressure fluid escapes into the ambient. In this paper, a multi-phase Computational Fluid Dynamics (CFD) model is presented to simulate the decompression of high-pressure pipelines carrying CO₂ mixtures. A ‘real gas’ Equation of State (EOS), the GERG-2008 EOS, is incorporated into the CFD code to model the thermodynamic properties of the fluid in both liquid and vapour states. The non-equilibrium liquid/vapour transition is modelled by introducing ‘source terms’ for mass transfer and latent heat. The model is validated through simulation of a ‘shock tube’ test. A ‘time relaxation factor’ is used to control the inter-phase mass transfer rate. The measured decompression wave speed is compared with that predicted using different values of the time relaxation factor. It is found that the non-equilibrium phase transition has a significant influence on the decompression wave speed. Also, the effects of delayed bubble formation and of various impurities on the decompression wave speed are investigated.

碳捕集与封存（CCS）被广泛认为是减少大气中过量的CO ₂浓度的有效技术。该技术包括通常通过高压管道将CO ₂从源头传输到存储位置。为了确保安全运输（即防止内容物释放到大气中），重要的是在设计阶段估算所需的管道韧性。这需要准确预测流体中“减压波”的速度，这是在高压流体逸入环境时产生的。本文提出了一种多相计算流体动力学（CFD）模型来模拟载有CO ₂的高压管道的减压。混合物。CFD代码中包含了一种“真实气体”状态方程（EOS），即GERG-2008 EOS，可对液体在液态和气态下的热力学性质进行建模。通过引入传质和潜热的“源项”来模拟非平衡液体/蒸气的转变。该模型通过模拟“冲击管”测试进行了验证。“时间弛豫因子”用于控制相间传质速率。将测得的减压波速与使用不同时间松弛因子值预测的减压波速进行比较。发现非平衡相变对减压波速有重要影响。另外，研究了气泡的延迟形成和各种杂质对减压波速的影响。