Depressurization of CO₂ in a pipe:High-resolution pressure and temperature data and comparison with model predictions

The design of safe and cost-efficient CO₂-transportation systems is an integral part of CO₂ capture and storage (CCS) deployment. To achieve this, accurate transient flow models capturing the occurrence of gas, liquid and solid CO₂ are needed. These in turn rely on experimental validation. In this work, we present a new experimental facility designed to capture pressure and temperature during the depressurization of CO₂ and CO₂-rich mixtures in a tube at high spatial and temporal resolution. Experiments with pure CO₂ starting from both gaseous and dense (liquid) states are presented, and a reference experiment with N2 is included. The experimental results for both pressure and temperature are analysed by comparison with predictions by a homogeneous equilibrium model. Emphasis is put on the decompression-wave speed, of particular relevance for running-ductile fracture in CO₂-transportation pipelines. We observe good agreement with predicted decompression-wave speeds in the single-phase region, and fair agreement for two-phase flows when the calculations are based on the assumption of equilibrium. However, the observed ‘pressure plateau’, a key factor in the prediction of running-ductile fracture, can be significantly lower than that calculated assuming equilibrium.