Vapor RecoveryStage One Vapor Recovery

July 4, 2011by tyrussum0

What is Stage One Vapor Recovery

Stage one vapor recovery is a way of controlling emissions during gasoline transfer from cargo tanks to storage tanks. During gasoline delivery to the storage tank, displaced gasoline vapor within the storage tank is diverted from the storage tank to the tanker delivering the gasoline. The collected vapor is then taken back to the terminal for recovery through condensation or adsorption or destruction via incineration.

What is its Purpose

This is an emissions control measure used to collect vapors resulting from the transfer of gasoline through the marketing and distribution process. Gasoline’s high volatility and tendency to evaporate causes vapors to form. These vapors can escape during fueling and refueling. When gasoline evaporates in a closed system, molecules within the vapor tend to condense on the liquid’s surface. Eventually, evaporation and condensation equal out and equilibrium is reached. In this state, vapor concentrations are highest near the liquid’s surface and decrease as distance from the liquid’s surface increases. Vapor pressure is the force exerted by vapor while in equilibrium with liquid.
The amount of hydrocarbons in gasoline vapor a well above the federal limit for emissions. Stage one vapor recovery must be in place on all storage tanks in order to meet federal emissions regulations. Vapor recovery technology reduces the amount of green house gas pollutants released into the air by several tons.

In stage one vapor recovery, vapors must be collected in the cargo tank as gasoline is supplied to the underground storage tank (UST) or above ground storage tank (AST). All tanks have fittings for gasoline delivery as well as vapor recovery.

Additionally, gasoline vapor recovery is a way of stretching the usefulness of gasoline further while allowing companies more profits. They hydrocarbons in the captured gasoline vapor can be separated from the vapor, condensed, and collected for reuse.

Stage One Vapor Recovery Methods

There are two main types of stage one vapor recovery methods. These methods are dual, or two-point systems, and coaxial, or one-point systems. The dual stage gasoline vapor recovery system is the most commonly used type of stage one vapor recovery.

Dual-Point Recovery

Dual-point stage one vapor recovery systems have separate points for gas delivery and the recovery of vapors. A delivery elbow and recovery elbow are fixed to each point during fuel delivery. Standard industry practice requires the vapor lid to be painted orange, allowing for easy identification.

Utilizing the dual-point stage one vapor recovery system, displaced gas vapor is recovered through two riser pipes while gas is being pumped into the storage tank. The gas is supplied via a drop tube, while vapors are forced up the riser pipes fro the ullage. Each riser pipe is equipped with a spill bucket and fitted with an adaptor and dust cap. Most spill buckets have a valve for draining accumulated gas back into the storage tank.

Coaxial Recovery

Coaxial stage one vapor recovery utilizes one pipe and elbow for both delivery of gasoline and gasoline vapor recovery. By using concentric tubing, gasoline may be pumped into the storage tank via one tube in the pipe while vapor is collected using another tube within the pipe. This limits the need for extra piping.

Coaxial stage one vapor recovery is an older form of recovery and is on the way to extinction. The use of one pipe for both delivery of gas and recovery of vapors  is both outdated and inefficient. The dual recovery method allows for more efficient collection of vapors by the tanker.

We’ve already covered industrial vapor recovery and stage one vapor recovery. Next time, we’ll talk about stage two vapor recovery and how it works.

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