Benchmarking CO2 and methane dispersion from high-pressure pipelines

The rapid development of carbon capture and storage (CCS) projects has increased the need for robust process safety guidance for the transport of carbon dioxide (CO2) in high-pressure pipelines. While the dispersion behaviour of natural gas releases is supported by extensive industry experience, equivalent understanding for CO2 – particularly under high-pressure pipeline release conditions – remains limited. This study benchmarks the dispersion behaviour of CO2 and methane following high-pressure pipeline releases using computational fluid dynamics. A systematic simulation matrix is developed to evaluate the influence of operating pressure, temperature, release orientation (horizontal, upward, and downward), and atmospheric conditions on dispersion characteristics. Representative high-pressure pipeline conditions are considered using a fixed 50 mm release diameter in unobstructed benchmark scenarios. The results demonstrate clear differences between dense-phase CO2 and buoyant methane across all release orientations. CO2 consistently forms broader, ground-attached clouds, whereas methane produces narrower plumes with greater vertical development. Atmospheric stability is identified as the dominant factor controlling the hazard footprint, with stable conditions leading to the largest near-ground CO2 extents. Release pressure influences near-field momentum and plume development, while differences in operating temperature are secondary and do not change the overall dispersion behaviour. This study complements previous work by providing unobstructed benchmark cases that highlight orientation-dependent dispersion behaviour under high-pressure conditions, supporting consequence assessment and CCS process safety guidance. Given the lack of experimental validation data for dense-phase CO2 pipeline releases, the flame acceleration simulator (FLACS) simulations are intended as indicative model predictions for relative benchmarking between CO2 and methane.