A calculation method for the numerical simulation of oil products evaporation and vapor diffusion in an internal floating-roof tank under the unsteady operating state

Abstract

A calculation method was established for numerically simulating the evaporation of oil products and vapor diffusion from the annular rim gap of the floating deck in an internal floating-roof tank (IFRT) under the unsteady operating state. The proposed method is based on the “thin film” theory, Stefan diffusion, and the realizable k-ε turbulence model. The accuracy of the calculation method was verified by wind tunnel experiments. Considering various operating conditions, the oil evaporation and vapor diffusion were investigated, and the mass transfer mechanism in the gas space was revealed. The results show that the vapor concentration isosurface in the gas space exhibits a “wave-shaped” distribution, and the vapor concentration can easily accumulate in the windward side of the gas space under the influence of a wind speed. In addition, the evaporation rate is closely related to the type of oil product, and the evaporation rate increases with increasing wind speed or floating deck height. The evaporation rate was initially in a fluctuating state and stabilized soon. Furthermore, when the width of the annular leaking rim gap was 0.2 m in a gasoline IFRT with a volume of 1000 m3, the vapor concentration in the most of the gas space was higher than the lower explosive limit; the region with a high vapor concentration will further expand with increasing wind speed. The calculation method and the numerical simulation results in this study can provide important theoretical support for reducing oil evaporation loss, controlling air pollution, and ensuring safe operation of IFRTs.