Modelling Dry Ice Formation Following Rapid Decompression of CO2 Pipelines

A fundamentally important issue regarding the safety assessment of CO2 pipelines is the possibility of solid or ‘dry ice’ discharge during an accidental release. This is particularly relevant given the near-adaibatic decompression process and the unusually high Joule Thomson coefficient of expansion of CO2. Solids discharge will affect many aspects of the ensuing hazard spanning the erosion of surrounding equipment, modification of the toxic dose duration, atmospheric dispersion and possibly, the pipeline’s propensity to fracture propagation. This paper describes the development of a Cubic Equation of State capable handling solid CO2 as a third phase. Pipeline rupture outflow data are reported based on the coupling of this new equation of state into a rigorous transient outflow model in order to investigate the impact of the pipeline design and operating conditions as well as the presence of the typical impurities on solid CO2 discharge