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From: Coker Squirrel
Category: Safety
Date: 09 Jan 2005
Happy New Year to you too CAT! Our relief valves are redundant but a single relief valve will not handle 100% capacity at full rate. Our relief is to the Blowdown System and not to the Fractionator. We have contemplated adding a MOV on each drum relief line to isolate from the Blowdown System each time we open the Drum Vent. I know that some Cokers are doing this and are adding an interlock so that the relief line isolation valve will be opened if the vent is closed. The problem with this is that we would have to be dependant upon the mechanism of the gear operator on the MOV. If it breaks and does not open the isolation valve, we could coke a drum with no relief capability. Even with an interlock system, if the gear operator breaks it could show open and satisfy the interlock but the valve would actually be closed. We did do a risk analysis on a backflow through a drum relief valve and we are now looking for options. I noticed a previous post by Marius on June 25, 2002. He mentions something about Smithlocks. I didn’t realize that he was referring to a Velan valve. Thanks for clearing that up for CokerWP and me. Marius states in his posting to check the integrity of the relief valve after it has relieved. This is something that we do as well. It is extremely important to check the relief valves after a drum carry-over. Coke fines could cause the relief valve not to seat properly. This would allow for a backflow through the relief valve. I tend to agree with you on the monitoring. It should be stationary monitoring rather than Operators wearing it.