Vapor Recovery & Liquefied Gas Transfer

What is a vapor recovery unit (VRU)?

A VRU system is primarily composed of a scrubber, reciprocating compressor, motor, and switchgear. Its main purpose is to recover vapors that normally would be discarded by releasing to the atmosphere or flaring off. The pressure switch detects pressure variations inside the tanks and turns the compressor on and off. The vapors are sucked through a scrubber, where the liquid trapped is returned to the liquid pipeline system or to the tanks, and the vapor recovered is pumped into gas lines.

Corken reciprocating compressors mounted on engineered skid packages are used to boost pressure on pipeline applications as well as to scavenge vapors from well sites and tank farms (click on the Vapor Recovery illustration to the right for more details).

Typical reciprocating compressor applications include…

Candidates for vapor recovery units includes propane bottle filling stations, petroleum tank farms, pipelines, well sites where fugitive emissions are an issue, refineries, chemical processing plants, recycling plants, and gas utilities.

The through the use of a four-way valve, a vapor recovery unit can also be used for a liquefied gas transfer application. A common example of liquefied gas transfer is tank car unloading. The principles of the liquefied gas transfer are fairly simple. Through the use of a vapor return line, a reciprocating compressor reduces the pressure in the stationary tank and increases the pressure in the tank car. The increased pressure in the tank car forces the liquid through liquid return line at the top of tank car and through the liquid line at the bottom of the stationary storage tank (click on the Liquid Transfer illustration below for details).

Recommended reciprocating compressors…

Corken single-stage reciprocating compressors work well in low pressure recovery, our two stage compressors are for the high pressure applications up to 600 psig max working pressure. For the high flow area like scavenging from several well sites or a large storage tank, Corken’s horizontal reciprocating compressors are a great choice.

Materials of construction…

The compressor’s materials of construction vary as to what the gas being recovered is.Natural gas would primarily use Buna-N o-rings and aluminum gaskets. Process gases may need more exotic O-rings like Kalrez® (Kalrez is a registered trademark of DuPont) or PTFE, and Iron-lead gaskets. Corken can also add a corrosion resistant nickel and PTFE coating to the gas wetted components when compressing a corrosive gas. If there is no electrical power on site to run an electric motor for the compressor, the units can be driven by a diesel fired engine.