Contribuições para a classificação de áreas devido a liberação bifásica de inflamáveis via fluidodinâmica computacional.

Abstract

Industrially, flammable gases are stored and transported in the form of pressurized liquid. The occurrence of leaks from pressurized flammable liquids in vessels or pipes may cause a two-phase release containing a mixture of liquid droplets and vapour of flammable substances, therefore the study of this type of release of fundamental importance for the hazardous areas classification. The most important standard used for classification of areas does not address cases where the release of liquefied gases is two-phase nature but recommends the use of computational fluid dynamics (CFD) for these situations. In the present work, a CFD model was defined to hazardous areas classification where possible releases of liquefied gases can occur, for which the commercial software Ansys® CFX 16.1 was used. A detailed study of the release of the flammable two-phase jet was conducted using propane and liquefied petroleum gas (LPG). The results showed that on average for most simulated cases the extensions of the classified areas presented in the standards are larger than those obtained by the model, resulting in oversizing of the hazardous area for most of the cases analyzed. The influence of the wind was analyzed, where it was verified that a gradual increase of the wind intensity in the same direction of the release contributes to an increase in the extension and a reduction in the volume of the explosive atmosphere. For low wind velocity and opposite direction to the leak, an increase in the extent and volume of the explosive atmosphere was observed. The simulations conducted in CFD with inert confirmed the effectiveness of the process of inertization to reduce the hazardous area. Using the fluid dynamics model it was possible to propose an equation to determine the extent of the explosive atmosphere, providing a fast and accurate response, thus eliminating the high computational cost required by the CFD. The numerical model results agree with available experimental results.