An Assessment Capability for LNG Leaks in Complex Environments

Pollutants may be introduced into urban or marine settings by various means and could result in an adverse impact to public safety and the environment. Therefore, it is important for emergency management personnel to understand the potential risks and physical extents of a leaked substance, whether it is toxic, flammable or explosive. Traditional tools for predicting the atmospheric dispersion of leaked substances are quick and simple to use, but may not adequately consider the effects of the built environment that includes complex urban and terrain geometries. Alternatively, CFD methods have been increasing in application;although, their superior accuracy is met with commensurate manual effort. The All Hazards Planner is a fast, accurate gas dispersion modelling tool for city and port environments, which employs a full-physics CFD approach but automates the intensive manual effort. In this work, a credible LNG leak from a 12-mm-diameter hole is modelled for two hypothetical case studies: adjacent to an LNG tanker and between a cruise ship and pier during bunkering. The LNG vapour flammability extents are compared to an empirical model in the absence of geometry effects and are contrasted with geometry effects to highlight the importance of the real environment. The free-field extents are invariant, whereas the inclusion of geometry is shown to reduce the flammability extents by spreading at the ground-level and forcing the plume upwards.

Experimental and numerical investigation of gas diffusion under an urban underground construction

Rapid increase of urban underground constructions has a great consideration of underground environment safety and how to expel toxic gasses out of tunnels effectively.The utility tunnel is a typical urban tunnel construction with multiple underground pipelines including gas pipelines,and it is necessary to investigate characteristic of gas diffusion and monitor gas leakage to ensure tunnel safety.In this study,the experimental measurements of airflow and gas distributions were conducted in a 10 m full-scaled utility tunnel mockup,and gas diffusion characteristic was also investigated.Numerical simulation of utility tunnel leakage was also conducted by computational fluid dynamics(CFD).Different turbulence models and different air supply diffuser models were compared via the experimental results based on visualization and the relative root-mean-square error(RRMSE)index,which quan-titated the difference between the numerical and experimental results.The results showed that the standard k−εturbulence model and random air opening model could provide better results than other models.According to the experimental data analysis,it was necessary to consider the optimization of monitoring detector arrangements in actual utility tunnels.This study provided basic experimental data and the validated numerical model for the leakage source identification and underground tunnels simulation research.