A numerical study of ammonia dispersion in an industrial area with the CFD tool FLACS

Abstract

As the use of ammonia increases, knowledge about dispersion patterns and dispersion tendencies is of enhanced importance. Due to its toxic nature, very few realistic experiments of ammonia dispersion in complex situations have been completed, and one has to rely on numerical models instead. Many of these models are traditional, simplified dispersion models, which are not valid in complex situations. Therefore, CFD (Computational Fluid Dynamics) codes, such as FLACS, are essential. The codes are in constant development, and new models that comprehend new scenarios are regularly added. In this thesis, release and dispersion of ammonia in a complex industrial area is studied. By varying wind speed and wind direction, different scenarios are produced and examined. The varying wind conditions are found to result in a range of dispersion patterns, where the distance covered on land vary from 72 m to 1660 m. Due to the extensive dispersion in some scenarios, and accompanied enlarging of the considered domain, the grid cells had to be adjusted to maintain an acceptable computational time. This seemingly brings by an overestimation of the extent due the implementation of larger cells. The effects of changing the temperature or adding a Pasquill class is not remarkable, while elevating the leak or removing the obstacles result in a completely different dispersion.