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From: atc/nc cat
Category: Safety
Date: 10 Dec 2004
We are optimizing the Coke Drum venting/steam test cycle as part of the DCU Safety upgrades. After the completion of coke cutting, we isolate the coke drum for oxygen venting & CD pressure boundary steam test. I have separated this cycle into 2 steps operations in forming the control logic scheme. During the venting cycle the program timer is set at 2 minutes. This timer will start as soon as the CD pressure reach ~ 2 psig and alert the operator to close the vent valves MOVs in order to proceed with CD steam pressure test. The question are as follow: (1) How long do you guys normally vent the coke drum? Is 2 minutes adequate enough to get rid of the oxygen to minimize if not entirely eliminate oxygen gas going into the fractionator or is this too long. (2) Have you ocassionally by-pass the venting operation thinking that the next step is Warm to BDC anyway before Warm to fractionator. (3) Any concerns on polymers formation in the fractionator due to not having enough time for venting cycle? The goal is to get rid of oxygen in the CD and minimize steam consumption. The coke drum we have is 26'-0" dia. X 68'-0" height. The steam pressure is ~ 180 psig and steam line size is 6" in diameter. Appreciate sharing what you have done and thought on this subject.