To prevent air ingress into the riser two types of seals can be provided: a Molecular Seal bolted below the flare tip or an Air Lock Seal (Velocity type) within the flare tip.
The Molecular Seal works by relying on the density difference between the purge gas and air. In this way, only a very low continuous purge flow is necessary to maintain conditions within the seal.
The Molecular Seal maintains safe conditions in the upstream riser for several hours in the event of a loss of purge gas.
AIR LOCK SEALS
The Air Lock Seal (ALS) is a cone device located as an integral part of the flare tip. When a flare tip operates with very low flare gas flows, air will tend to enter the tip due to both wind action and by decantation and will slowly diffuse down the inside walls of the tip. The Air Lock Seal design locally increases the velocity of purge gas through the seal, thereby moving any air back out of the tip.
GBA install Air Lock Seals in all flare tips to minimise purge gas consumption and maximise flare tip operating life.