Computational fluid dynamics study of flow around floating-roof oil storage tanks

Volatile organic compounds (VOCs) emitted from petrochemical plants and storage facilities play a key role in forming ground-level ozone, which causes breathing problems for humans and damages plants. External floating-roof oil storage tanks are a major source of VOC emissions. Wind passing over the fittings that penetrate the tank roof cause product to evaporate from the surface of the tank. This paper presents the results of a detailed CFD study of the wind speeds and flow structures observed above and around the tanks. The model was developed using AEA Technologyʹs CFX4, and validated from a series of known 2-d cases and then from extensive field measurements, on small- and full-scale tanks. Two distinct flow regimes have been observed above the roof: at large roof depressions (empty tank), the flow recirculates within the tank cavity; at small roof depression (full tank), the flow reattaches within the cavity. Implications for tank design and emissions measurement are presented.