Product vapor control with floating roof tanks

Internal floating roofs have been used in tanks as small as 15 ft in diameter to minimize product losses. Increased emphasis on the control of evaporative emissions from storage tanks might change the roll of floating-roof tanks in the future with the increased use in smaller tanks. In general, floating-roof tanks have been used only at terminal or refinery locations where larger storage capacities are needed. Product losses increase whenever the roof is not in complete contact with the liquid surface. Landing the floating roof during normal tank operations should be avoided. A floating roof should be landed only if the tank is to be removed from service for routine inspection or maintenance activities. The tank working capacity is obtained by operating a floating-roof tank between the maximum high gauge and recommended low landing position for the specific floating-roof tank design. 1 shows a typical internal floating-roof tank. The tank vapor space located above the floating roof and below the fixed-roof includes circulation vents to allow natural ventilation of the vapor space reducing the accumulation of product vapors and possible formation of a combustible mixture. The internal floating roof tank (IFRT) was developed in the mid-1950s to provide protection of the floating roof from the elements, including lightning strikes to the floating roof. The external floating roof floats on the surface of the liquid product and rises or falls as product is added or withdrawn from the tank. The goal with all floating-roof tanks is to provide safe, efficient storage of volatile products with minimum vapor loss to the environment.ĭesign requirements for external floating roofs are provided in Appendix C of the API Standard 650.

In general, they are not suitable for applications in which the products have not been stabilized (vapors removed). Floating-roof tanks are not intended for all products. Environmental Protection Agency permits the use of a floating-roof as the primary means of vapor control from the storage tank. When product vapor pressure is greater than 0.5 psia (more in some states) but less than 11.1 psia, the U.S. 6 Product vapor control with floating roof tanks.5 Floating roof tank networking capacity.

Atmosferic tanks standards