Vaporization of Drum when by-passing the unit

[Maximiliano Barchiesi]

How much vapor do you recommend to get into a drum that is in warming-up process, in order to eliminate the HC vapors, if you decide to by-pass your DC unit?
I know its recommended at least 3 drum volumes when eliminating the air before warming-up, would you follow the same criteria?

[Mike Kimbrell]

Using an inert gas to remove the hydrocarbons from the coke drum to make it safe from an explosive mixture standpoint, a purge volume of 3 times the drum volume will get the hydrocarbon concentration down to 1% of what it was when the purge was started assuming perfect mixing. A purge volume of 4 to 5 times the drum volume should be adequate to account for any incomplete mixing an make the drum safe to vent to the atmosphere.

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