LES of atmospheric dispersion of ammonia from storage tank ullage space under real meandering wind currents in 800 m domain.

This study aims to develop and validate a CFD model for large eddy simulations of gaseous ammonia released from the ullage space of a storage tank through the piping system to the atmosphere under realistic wind conditions measured experimentally. The simulations are validated against Test No.1 conducted by INERIS (Bouet et al., 2005) of 460 s release duration with ammonia concentration decay measured up to 800 m downwind of the release nozzle. The computational domain was designed to represent a large-scale atmospheric dispersion scenario in conditions of meandering wind currents. The atmospheric turbulence is simulated by incorporating real-time meteorological data on wind direction and speed oscillations. The proposed methodology accounts for meandering wind currents. This methodology, combined with sub-grid scale Smagorinsky-Lilly turbulence modelling, enables accurate simulations of ammonia dispersion observed in the experiment. The simulations reproduced measured in the near-field (20 m from the release nozzle) transient ammonia concentration with high accuracy. The simulations also accurately captured the average concentration decay up to 800 m downwind of the release location. The hazard distance defined by the flammability of the ammonia-air mixture is estimated as 13.2 m from the release. The maximum toxicity cloud envelope extends to 205 m downwind, 9.5 m vertically, and 21.3 m laterally for the fatality threshold and increasing to 837 m, 18 m, and 53 m, respectively, for the injury limit. The study highlights the importance of proper modelling and simulations of real wind meandering currents for predicting realistic hazard distances.