5 replies to this topic

[bam88]

What is the purpose of relieving to a blowdown drum first before being vent to the flare stack?

From what I have read, blowdown drum is used to prevent vented chemicals, possibly toxic, from being released into the atmosphere.

[mbeychok]

The purpose of a flare stack is to burn unwanted waste gas or gas released by safety relief valves. The purpose of a blow-down drum ahead of the flare stack is to remove any large amounts of liquid that may accompany the gas before that liquid reaches the flare:

You may find it informative to read these two articles in the online encyclopedia Citizendium:

Flare stack

Vapor-liquid separator

[bam88]

What is the purpose of relieving to a blowdown drum first before being vent to the flare stack?

From what I have read, blowdown drum is used to prevent vented chemicals, possibly toxic, from being released into the atmosphere.

Dear mbeychok,

Thanks for your reply.

Let me clarify my question. In my company, relief is sent to the blowdown drum, and then to a KO drum, before sending it to the flare.

My question is why do they need 2 vapor-liquid separators one after another? Is there a safety issue involved here?

[fallah]

My question is why do they need 2 vapor-liquid separators one after another? Is there a safety issue involved here?

The purpose of second KO drum which installed as close the flare stack as possible,is eliminating any liquid accompany the gas may be formed due to condensation of gaseous hydroicarbons moving along usual considerable distance between first KO drum inside the plant and second KO drum outside plant's battery limit.

[mbeychok]

Another reason may be that the blowdown drum is there to remove any large quantities or "slugs" of liquid which might overload the following vapor-liquid knockout drum.

[VikingUK]

Another reason may be that the blowdown drum is there to remove any large quantities or "slugs" of liquid which might overload the following vapor-liquid knockout drum.

Also if the flare stack is high and especially if vertical the 2nd vessel catches any condensed liquids that flow back from mid way between flare tip/base