January 29, 2014 at 8:21 am #11561
Quick question for the experts. Is there a valid relief case when you lose feed due to the residual feed/hot catalyst in the riser?
Posted on behalf of Bart Carpenter
Technology Director at URS Corporation
January 31, 2014 at 1:42 pm #11627
Bart, I’m not sure I understand what you are looking for when you say ‘valid relief case’. Are you asking about installing pressure relief valves or PSVs or are you looking for shutdown procedures, or what’s a quick way to regain feed? Would this also be a question relating to a refinery overall flare relief system study? Could you clarify that for us?” Thanks -Chris
February 6, 2014 at 9:28 am #11646
Can you please clarify your question/query? Once the feed is removed from the reactor riser, the reactor pressure begins to decrease, unless steps are akin to bolster pressure. Currently, your question implies a pressure build or rise that requires corrective actions in order to avoid an over-pressure situation??
Scenario: This is a power failure scenario but the air blow remains online via steam turbine. Wet gas compressor down. All Main Frac pumparounds down so there is little equipment left to remove any heat.
Here is what typically happens during a power failure:
1. Feed is automatically diverted from the reactor riser to the main fractionator bottom. (procedure-operations to immediately hard-block feed to riser)
2.Emergency steam to the reactor riser kicks-in / opens.
3.Feed rate flow to the main fractionator bottom (MFB) is reduced.
4.The electric pumps obviously stop & the steam back-up pumps auto-start.
5.The catalyst (regenerated & spent) slide-valves close, stopping catalyst circulation.
6.The reactor pressure decreases / sags due to the loss of volume expansion of cracking feed.
7.The heat input into the main fractionator decreases significantly (there is no reboiler to the MF- the heat is supplied by reactor outlet product flow).
8.There typically is no need for corrective action for pressure relief on a power failure case.
9.Our biggest relief scenario is a fire in the area.
10.Upon loss of WGC, the flare valves open and the flow from the top of the main fractionator is routed to the flare-stack.
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