Abstract
Based on computational fluid dynamics (CFD) and Realizable k-ε turbulence model, we established a numerical simulation method for wind and vapor-concentration fields of various external floating-roof tanks (EFRTs) (single, two, and four) and verified its feasibility using wind-tunnel experiments. Subsequently, we analysed superposition effects of wind speed and concentration fields for different types of EFRTs. The results show that high concentrations of vapor are found near the rim gap of the floating deck and above the floating deck surface. At different ambient wind speeds, interference between tanks is different. When the ambient wind speed is greater than 2 m/s, vapor concentration in leeward area of the rear tank is greater than that between two tanks, which makes it easy to reach explosion limit. It is suggested that more monitoring should be conducted near the bottom area of the rear tank and upper area on the left of the floating deck. Superposition in a downwind direction from the EFRTs becomes more obvious with an increase in the number of EFRTs; vapor superposition occurs behind two leeward tanks after leakage from four large EFRTs. Considering safety, environmental protection, and personnel health, appropriate measures should be taken at these positions for timely monitoring, and control.
Highlights
External floating-roof tanks (EFRTs) are widely used for crude oil storage [1]
As the elasticity of the rim seal gradually decreases with long-term usage, the rim gap widens
The results showed that when there is a rim leakage between the floating deck and tank wall, oil vapor diffuses along the tank wall to the upper space of the floating deck
Summary
External floating-roof tanks (EFRTs) are widely used for crude oil storage [1]. With the development of petroleum reserve strategies, different types of EFRTs have been developed. The floating deck in an EFRT cannot seal a tank wall absolutely as it needs to float up and down freely [2]. There is an annular rim gap between the floating deck and tank wall. As the elasticity of the rim seal gradually decreases with long-term usage, the rim gap widens. Improper operation or poor maintenance will aggravate the attrition of the sealing device. Under such conditions, oil evaporation from the rim gap and oil vapor diffusion into the atmosphere increase simultaneously
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