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From: atc/nc cat
Category: Safety
Date: 07 Jan 2005
There are many ways to skin a cat but before I attempt to give you some alternative approach, I would like to pose to you the following (1) Are your PRV redundant and 100% capacity? I am assuming you have 2 ea. 100% PRV vented to blowdown contactor vessel and 2 ea. 100% PRV vented to fractionator vessel. (2) I am assuming you are adding motor actuator on a direct manual isolation valve or replacing it with a new MOV assembly on all of them. (3) What is the rationale of operator wearing H2S monitor? Don’t you have H2S area monitor in the work area being visited by the operator outside of the enclosed local control shelter at the top deck? I believe area monitor is a prudent approach than having H2S monitor attached to the operator. (4) Why have an interlock with drum vent MOV? Bear in mind that coke drum vent MOV shall be opened during coke drum steam purging and at this time the PRV must be in service & its discharge isolation MOV must be opened. Why not use the position LS of the top and bottom heading valve when they are open and Decoking cycle mode is on “Coke Cutting Mode”. PRV discharge isolation valve must be open before coke drum oxygen gas purge. (5) I am also assuming you are doing the MOV installation on the coke drum wherein top & bottom heading can be controlled remotely and DCU liquid and gas process power operated valves (AOV & MOV) related to Decoking cycle are in placed otherwise it is meaningless. (6) Are you planning to monitor the PRV outlet motorized gate valve using actuator position limit switch as well as gate valve disc sliding plate travel? (7) Are you installing your isolation gate valve(s) with motor actuator on the horizontal position. (8) Are you guys entertaining the idea of remote control operation of the coke drum top heading and coke cutting operation? This means no operator on the DCU top structure. If you have completed your risk analysis, Hazop analysis, safety egress at the DCU structure, and have officially obtained ASME Pressure Vessel code variance in having isolation valve at the PRV escape pipe and you have addressed all the above, you could sort your solution(s). Hope this helps. Atc/nc cat