Extension of the EFFECTS dispersion model for buoyant plume rise including lift-off

Abstract

Alternative energy carriers such as hydrogen and ammonia play an important role for the energy transition to reduce global CO2 emissions substantially. These substances will be produced and used in much larger amounts in the near future to replace hydrocarbons that are widely used nowadays. Therefore, consequences and risks of bulk storage, handling and transport of these materials must be addressed accurately. Because these substances have a low molecular weight, pressurised or liquefied gases released by accident may undergo a transition from heavy gas to rising plume behaviour during dispersion depending on the storage, release and atmospheric conditions, as well as surface effects such as heat transfer. The plume lift-off, plume rise, and the entrainment of ambient air play a significant role in the effect distances and the volume of a flammable or toxic cloud. The consequence modelling software tool EFFECTS contains different dispersion models for neutral and heavy gas dispersion, which are based on a 1-D discretisation method. Since the code for these dispersion models was developed in the past with the focus on heavy or neutral gas conditions, the simulation of buoyant plumes so far was limited. The aim of the present research was to improve the accuracy of the EFFECTS dispersion model for strongly buoyant plumes and predict the transition from the momentum dominated to the buoyant regime correctly. The paper describes the theoretical background of the extensions implemented in the dispersion model in EFFECTS. These extensions are aimed at improving the modelling approach for lighter than air plumes. The validation of the models incorporating these improvements has been performed and is based on results compared against experimental data including instantaneous and continuous releases, jets and low momentum releases from the ground for different materials including helium and hydrogen.