EnviroPro Combustion & Waste Heat Recovery Solutions

Keeping oxygen out of the flare system is a critical safety concern. At low waste gas flow rates, air can enter the flare tip through the top and travel down the inside wall of the tip. To prevent this, purge or sweep gas is used. Purge gas can be any gas that will not condense. Natural gas and nitrogen are the two most commonly used. Purge reduction devices are used to reduce the amount of purge gas required to keep the oxygen level below 8% and minimize utility costs. There are two types of purge reduction devices commonly in use:

  • Molecular Seals, also known as a buoyancy seals, are installed just below the flare tip flange. The seals internals force the waste and purge gas travelling up the stack to make a 180 degree turn down and then it must turn again to go up to the flare tip. The light gases will collect at the top of the seal creating a barrier to any oxygen that may have come down the flare stack. This design provides a greater reduction in required purge gas but are considerably larger and more expensive than velocity seals. Molecular Seals can also collect liquids which can freeze in cold environments.
  • Velocity Seal: A velocity seal is simply a cone or chevron that is located inside the flare tip just above the flare tip flange. The cone shaped design breaks the flow of air into the system by disrupting the flow attachment of the air to the wall and creates a velocity differential barrier in the purge gas. A velocity seal doesn’t collect liquids or require draining making it suitable for cold weather environments. They are less expensive but do not reduce the amount of purge gas as much as a molecular seal.

Contact EnviroPro to discuss your flare system projects.

Contact EnviroPro to discuss your flare applications!