COMPUTATIONAL SIMULATION AND ANALYTICAL PREDICTION OF AMMONIA LEAKAGE FOR HAZARDOUS AREA CLASSIFICATION

Resumo

Ammonia is widely used in several chemical and food industries around the world,
nevertheless it is a toxic and flammable component which may cause accidents due to leakage and
dispersion. The international standard IEC 60079-10-1 regards flammable components leakage, it
accounts criteria and guidelines for explosive atmosphere formation and reducing the risk of explosion.
The standard claims, based on experiences, that a release of ammonia vapor will often dissipate rapidly
in the open air. This scenario will result in a negligible hazardous area extent in most cases. Hence, this
work aims to investigate ammonia leakage in open air under different leakage conditions. For this
purpose, the authors compared the extent of hazardous area, at the Lower Flammable Limit (LFL), using
analytical models with those obtained from a 2D Computational Fluid Dynamics model. The CFD model
was able to predict a characteristic barrel pattern at the exit of the leaking orifice, typical of choked flow.
The results obtained from analytical models show that the extent of hazardous area was overestimated
compared to the CFD model. Among the analytical models used in this study, Souza’s, Tommasini’s,
and Ewan and Moodie’s yielded results were closer to the CFD model. Furthermore, the extent of
hazardous area for ammonia release are small, just as the plume volume, when compared to definitions
presented at the international standard IEC 60079-10-1.