Testing VOC Evaporation Losses from Floating Roof Tank Turnovers
Air emissions from floating roof tanks have been well characterized and documented by the U.S. Environmental Protection Agency (EPA). The estimation methods have been revised and updated throughout the years. However, an unusual aspect of air emissions from tanks with a floating roof during a tank turnover has not been addressed. Petroleum storage tank floating roofs are landed on tank legs and re-floated during a change of product service or certain tank maintenance operations. When the tank roof is landed on its legs, a vapor space is created between the floating roof, floor, and tank shell. This volume of vapor will be expelled into the atmosphere when the tank is refilled with liquid. A study was performed to address the quantification methods used to estimate emissions from floating roof tanks during a period between emptying and refilling. As part of the study, field tests were conducted at various pipeline breakout stations to determine the percentage concentration of petroleum vapors in the space under the floating roof with respect to time (vapor saturation rate). This paper focuses on the testing methods applied by the study group.