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From: Coker Squirrel
Category: Safety
Date: 06 Jan 2005
With a top head open, there is a potential of H2S exposure due to the possibility of a reverse flow through coke drum relief valves. This issue has been previously discussed earlier in this forum but I thought that I would bring it up again because we also have contemplated installing a MOV on a downstream isolation valve on the relief line from each coke drum with an interlock tied to the drum vent MOV. We would like to do this but we see a draw back. What if the MOV actuator on the isolation valve goes bad and does not open the valve or the gate breaks loose from the stem? The relief header from that drum would still be isolated during the next coking cycle. A coke drum without a relief capacity could be just as dangerous as H2S exposure. We have purge steam on the downstream side of the relief valves to mitigate a reverse flow problem. We also have auto top head removal on one coker but not on the other. We have considered having the Operators wear personal H2S monitors for an early warning indication but we don’t want them to think that this is a protection devise so we are reluctant to do that because this may give them a false sense of security. What other solutions or alternatives are there?