If you had a nickel for every time a vapor recovery unit did not work because it was incorrectly plumbed in, you would have…well, a pile of nickels I bet.
The proper way to plumb a VRU or combustor is to follow one of the diagrams below. The first diagram shows the proper way when using a vapor recovery tower in conjunction with a vapor recovery unit. The second shows a standard setup using a compressor to pull straight off of the production tanks.
The key thing to remember here is to never let the piping get below the suction side of the unit you are trying to install. You can angle the pipe down at a 45 degree angle or you can run straight down to a 90 degree angle that is level with the scrubber and plumb into the suction side of the scrubber. All of OTA’s units have the suction inlet height set at about four feet. Our combustor suction inlet is about the same height as well.
Why does all of this matter so much? Well, tank vapors and or flash vapors from a vapor recovery tower are much higher in BTU value than vapors directly from the wellhead, which means wetter gas. When trying to move wet gas at the low pressures we are using on the suction side of the unit, liquid can and will accumulate in the low sections of pipe. Many think that they can justify laying pipe on the ground or even burry it because you should be able to move “x” amount of liquid in “x” amount of pipe at “x” pressure. While these calculations are obviously true you have to realize that vapor recovery units do not run at a constant pressure. Often you will see that a vapor recovery unit only runs for small portions of the day. The amount of time the unit will run is based on how much gas we have coming to us. When a separator dumps you often have large amounts of liquid coming to the tanks and in turn the wet gas that is flashing off and coming to the unit can clog the piping in the incorrectly piped portions and essentially render a vapor recovery unit inoperable.
