Aluminum dome roof tanks (ADRTs) are used globally today. The origin of ADRTs dates back 60 years, but the reasons for their use on petroleum tanks evolved over the past 40 years. Aluminum geodesic domes originated in 1956 with a hotel bar cover in Honolulu. Many stressed skin design aluminum domes were installed. A famous installation is the American National Exhibition in Moscow, site of the 1959 Nixon/Khrushchev “kitchen debate.” In 1971, the Amundsen-Scott South Pole Station in Antarctica installed a structurally supported aluminum dome.
Large clear span geodesic roofs are for architectural and bulk materials. A modified geodesic dome (minimized material) is for covering wastewater treatment, water and petroleum storage tanks. In 1977, the first aboveground storage tank (AST) was covered for petroleum. In 1989, API produced API 650 Annex G: “Structurally-Supported Aluminum Dome Roofs.”
Early petroleum ADRTs were used in the northern U.S as weather covers to keep snow and ice off the decks of external floating roofs (EFRs). By 1980, some owners began to cover tanks, replacing EFRs with lower-profile internal floating roofs (IFRs). This maximized working capacity, reduced emissions, and avoided the wind-induced emissions associated with an EFR. The covered tank was recognized to improve fire safety, and over 70 percent of large AST fires occur with EFRs. Aluminum construction avoids column penetrations, corrosion and coating cost associated with steel. AST operators reported temperature reduction with ADRTs. By 1982, ADRT installations spread south to Brownsville, Texas. By 1985, gasoline additives and water disposal drove further conversion of EFRTs to ADRTs.
The API Committee on Evaporation Loss Estimation (CELE) sponsors research to produce the Manual of Petroleum Measurement Standards (MPMS) Chapter 19. This has emission factors for various AST configurations/components. Early 1980s research identified emission-loss factors for floating roofs, various seal types, and deck fittings and variables such as temperature. Wind drives emission loss for EFRs. MPMS 19.2 covers emission factors for floating roof ASTs, and domed external floating roof tanks is a special category. It includes reduced emission factors for deeper rim seals of an EFRT, combined with elimination of wind-driven losses. Sample emission calculations in MPMS Chapter 19.2, Section 5 — using a 100-foot-diameter EFR as a baseline — indicate emissions are reduced to 35 percent for an IFR and to 10 percent for a domed EFR. In 2006, API CELE research collected thermal data on ADRTs and EFRTs located in Dammam, Saudi Arabia and Edmonton, Alberta. EFRTs had slightly lower “average bulk temperature” — EFRs lose heat rap-idly at night, whereas ADRTs do not — but diurnal daylight surface liquid temperature peaks resulted in lower overall reduced emissions for a domed EFRT. API MPMS 19.4 includes thermal research information in Annex I and a table comparing superior reflective properties for mill-finish aluminum versus steel-painted white (or other colors). EPA monitors the API CELE work to produce AP42 Chapter 7 as a means to calculate emissions inventory from ASTs. Section 7.1.1.3 covers emission factors for IFRTs, and a full-contact-type design with cable supports (avoid penetration emissions) is an effective means to further minimize emissions. Section 7.1.1.4 covers domed external floating roof tanks.
State and local jurisdictions issue air permits. In regions that do not attain clean air standards, the goal is to further reduce emissions. Considering wind reduction factors alone — prior to thermal benefits from high reflectivity/low emissivity of aluminum — to reduce emissions inventory, the South Coast Air Quality District of Southern California in 2001 issued SCAMD Rule 1178, requiring the conversion of EFRTs to ADRTs. In Harris County, the Texas Commission on Environmental Quality issues permits for domed external floating roof tanks to minimize emission inventory.
The original objective for aluminum domes to cover tanks remains as an efficient, cost-effective means to reduce maintenance and operating cost, but recent motivation is to further reduce the emissions associated with petroleum storage tanks.
For more information, email George.Morovich@TankEnv.com or call (979) 247-4812.
