Continuously sweeping a stack with purge gas can result in exorbitant operating expenses over time; especially for large diameter stacks. The Molecular Seal is a purge reduction device which allows the flare system operator to use 98% less purge gas while continually sweeping the system. The savings in daily purge gas consumption over the long run makes for a short payback period on the initial capital investment of the molecular seal, which can also be referred to as labyrinth or density seal.
Whenever a process requires that entrained droplets be removed from a vapor stream, a knockout drum should be integrated into the system. Condensation can occur when hot process gases cool considerably in the flare gas header and riser, and some gases also go to dew point at ambient temperatures and pressures and can therefore generate liquids. These droplets must be removed in order to avoid the phenomenon known as flaming rain, which occurs when liquid droplets are blown out the top of a flare stack along with ignited process gases. These vessels can be either horizontal or vertical.