Parametric Study of Effects of Hills and Valleys on Onshore CO2 Pipeline Gas Dispersion Using CFD

Carbon capture and storage (CCUS) is an innovative approach to mitigate CO2 emissions, but there are risks associated with CCUS such as CO2 leaks. Flat terrain is commonly presumed for simplicity of dispersion modelling; however, this assumption could be extremely conservative in the case of hilly terrain. Therefore, this study performed parametric analysis on different terrain parameters to investigate the impact and complex interactions between topographical features specifically hills and valleys, on gas cloud dispersion. Many CO2 gas dispersion analyses are conducted with simplified two-dimensional tools which do not have the possibility to integrate the topography of the terrain for the gas dispersion analysis. For this study, a commercial three-dimensional multipurpose CFD software was used. Multi-component non-reacting gas was employed to simulate the CO2 gas dispersion. Drag, turbulent dispersion and gravity models were considered to account for the momentum exchange. The dispersion patterns and concentrations of the CO2 gas cloud were investigated based on varying parametric variables such as leak flowrates, and hills heights. These variables were also investigated under varying environmental conditions such as wind speeds to account for the environmental conditions on the CO2 gas cloud dispersion for hilly terrain. The aim was to provide valuable insights on CFD capabilities to perform complex analysis particularly involving complex terrains on the behavior of CO2 gas cloud dispersion. Correlation study with other published literature was conducted to validate the CFD model. The CO2 cloud dispersions under various wind velocities and CO2 leak flowrates were compared and analysed. Then, further investigations were performed to further analyze the dispersion patterns, concentrations and spreading rate of the CO2 gas cloud based on varying parametric variables such as hills heights, valley, and leak locations. These variables were also investigated under varying environmental conditions particularly on the wind speeds variation. Wind velocity of 2 m/s, 6 m/s and 15 m/s were specifically chosen to account for Malaysia’s wind velocities as the average wind velocity in Malaysia is around 1.8 to 2 m/s, during southwest monsoon it is often below 7 m/s and during the northeast monsoon, it could reach up to 15 m/s. The following observations and conclusions were derived based on the CFD analyses performed for the present study: Overall, terrain features such as hill heights, and slope angles have significant effects on the CO2 plume dispersion.As CO2 is heavier than air, it would likely accumulate in places like valleys generating localized pockets of CO2.At low wind velocity, the concentration of CO2 would be high in localized regions, close to hills/mountains while at higher velocity, the CO2 gas cloud would tend to disperse resulting in a wider exclusion zone.Complexity of terrains such as hills and valleys will significantly affect CO2 dispersion e.g. spreading rates and concentration levels.CFD is a good prediction tool to evaluate the CO2 dispersion zones with varying geometrical parameters and environmental conditions which would not be possible with the simplified two-dimensional model. The present study was able to demonstrate effectively the potential hazardous zone in complex topographic landscapes under different environmental conditions and offers critical insights for valuable safety protocol and emergency response planning for safe CCUS implementation. The CFD analysis demonstrated how topographical features significantly impact gas plume’s spread, concentration levels and help determine CO2 exclusion zone effectively. This study contributes to risk management for CCUS implementation particularly in complex landscapes and provides essential guidelines for environmental risk assessment and the development of mitigation strategies for onshore CO2 transport. Also, this study reviews the validity of flat terrain assumption in complex terrain such as hills and valleys.