Avaliação fluidodinâmica de liberações bifásicas para classificação de áreas em atmosfera explosiva: modelagem e simulação.

Abstract

The scenarios generated by two-phase releases of flammable substances are pointed out as one of the most dangerous scenarios given the extent and high volumes formed by the sometimes dense gas clouds. The attention given to these scenarios is of great relevance for industries that deal with the transport and storage of flammable substances, with each piece of equipment involved in the process being a possible ignition source on the verge of forming an explosive gas atmosphere. The application of area classification methodology is a necessary measure for industries to mitigate or reduce hazardous releases likely to form an explosive atmosphere, providing process safety. The international standard IEC 60079-10-1 is one of the regulatory standards for the classification of areas of explosive gas atmospheres and recommends the application of the CFD technique for area classification and evaluation of complex scenarios, in addition to serving as a basis for the graphics generation presented in the standard. It is important for area classification and, consequently, for industries, to deepen the understanding of two-phase fugitive emissions scenarios, as well as to understand the influence of parameters that interfere in the release steps. In this sense, the present work aims to investigate and understand, through CFD simulations, the scenarios of two-phase fugitive releases of liquefied propane gas under pressure, aiming to contribute to the area classification studies and application. For this, two flow conditions that result in two-phase releases were analyzed: the flow in thermodynamic equilibrium and the flow in nonthermodynamic equilibrium, simulated in an open environment. A sensitivity analysis was performed for each flow condition by varying the storage pressure, orifice diameter, wind speed, and the height of the release source relative to the ground. As a result, values of extent and volume of the plume formed in each case were obtained and evaluated at the concentrations of interest around the substance LEL. From the profiles traced of plume extension and volume, it was noticed that the pressure is the parameter with the least influence on the plume extent and volume. Since with the height variation, there was an increase of 99.8% in the extent when compared to the free jet condition. A non monotonic behavior in the extent and volume profile was noticed with the variation of the wind speed in favor and against the release flow, where in some cases a lateral scattering of the plume occurred with the greatest reach detected not in the symmetry plane, but along the domain. In most cases, the classification was Zone 2 type, considering the secondary release degree used. The extent results using the IEC 60079-10-1 standard were, in most cases, higher than those obtained in CFD, corresponding to a general average of 1.6 times the CFD extent for equilibrium flow cases, and 1.9 times for nonequilibrium flow.