MODELING OF FLOW AND VENTILATION WITHIN PETROLEUM PROCESS PLANTS

Adequate natural ventilation in petroleum process plants is of crucial importance when classification of hazardous areas is considered. The term ''adequate'' is most often referring to either the number of air changes in a given area or to the frequency of occurence of wind speed s less than a given value, typically 0.5 m/s or 2 m/s. In an attempt t o specify these parameters accurately, and to aid in the assessment of area classification, CFD can be used to simulate the wind flow field and gas dispersion around and within process plants. A case study from a hydrocarbon production platform in the North Sea is presented. For this installation, a computer model comprising 50.000 grid elements we re used. Wind simulations were carried out for three different wind sp eeds and eight wind directions, using a 'finite volume' solution of th e governing equations with the standard k-epsilon model of turbulence applied. Combined with information from the wind rose for the actual s ite, the simulations yielded the frequency of occurence of number of a ir changes on all area of the installation considered, as well as air velocity distributions. The results obtained this way were used in the area classification considerations, to establish whether the requirem ents for adequate natural ventilation were met. Given the wind flow fi eld, gas dispersion simulations were also carried out to consider the likelihood of having ignitable gas-air concentrations into non-hazardo us areas of the plant in the case of a gas release. An ''ample is give n on a calculated gas concentration profile around the platform.