About Vapor Recovery

Storage tanks are used to hold oil for periods of time stabilizing flow between production wells and transportation sites. During storage, light hydrocarbons dissolved in the crude oil "flash out" and collect in the space between the liquid and the fixed roof of the tank. As the liquid level in the tank changes, these vapors are often vented to atmosphere. The makeup of these vapors varies, but the largest component is methane (between 40 and 60 percent). Other components include more complex hydrocarbon compounds such as propane, butane, and ethane; natural inert gases such as nitrogen and carbon dioxide; and HAP like benzene, toluene, ethyl-benzene, and xylene (collectively these four HAP are referred to as BTEX).

VRUs (Vapor Recovery Units) are relatively simple systems that can capture about 95 percent of the Btu-rich vapors for sale or for use onsite as fuel. Recovered vapors contain natural gas liquids, that have a Btu content that is higher than that of pipeline quality natural gas (between 950 and 1,100 Btu per standard cubic foot [scf]). Depending on the volume of NGLs in the vapors, the Btu content can reach as high as 2,000 Btu per scf.

VRUs can provide significant environmental and economic benefits.

• Installing a VRU can be very profitable when the recovered vapors are sent to sale pipelines. Even using a conservative estimate of the value of recovered vapors of $3.00 per Mcf, the potential returns are attractive, particularly for the larger units. Average payback ranges from 3 months to 3 1/2 years
• Recovered vapors can be used onsite as fuel yields a value equivalent to the purchased fuel that is displaced—typically natural gas
• VRUs capture HAPs (hazardous air polutants) and can reduce emissions below actionable levels. By capturing methane, VRUs also reduce the emissions of a greenhouse gas.

• Identify possible locations for VRU installation
• Quantify the volume of vapor emissions
• Determine the value of the recovered emissions
• Determine the cost of a VRU project
• Evaluate VRU project economics

The Natural GasSTAR Partners published a twelve page "lessons Learned" article titled Installing Vapor Recovery Units on Crude Oil Storage Tanks. This Executive summary can be viewed and downloaded by clicking the following link

A critical component in assessing the economics of vapor recovery involves calculating crude tank vapor losses. To learn more about how to calculate losses, including formulas, software and a free Excel spreadsheet resulting from The Unversity of Tulsa research click on the following link.