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What is the best practice regarding the coker main fractionator bottom liquid holdup and surge times? Woud it depend upon the availability of a coker feed surge tk or there is a minimum value for all cases?
Thanks,
Lucky
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Lucky reviewing the 4 of coker Fractionator , I can tell you that in all this design the HLL were between 13 and 12 feet and the LLL between 8-12 inch (from the TL) . The capacities for these units are approximately between 28000 and 66000 BPSD, and the time between HLL-LLL were around 13 to 16 minutes
Also the liquid surge requeriments for a chimneys trays (wash section)are determined as the greater of the following three
Circulating pumparound 1 minute
Product to storage 2 minute
wash oil (pumped induced reflux) 5 minute
All this number is a normal capacity (nominal)
I hope that help you -
It really helps; I’m getting about 12-15 min (LLL-HLL) as well.
Thanks, -
Having a lower temperature (~400 F) external coker feed day tank is essential for reliable operations. High surge volume in the fractionator bottom section increases the residence time for undesirable condensation (coking) reactions.
Similarly, the upstream vacuum distillation tower benefits from low bottom liquid residence time. In the bottom of the coker fractionator, the process objective is good mixing of coker feed and condensed natural recycle. Nominal (5 minutes) residence time (based on fresh feed) is more than adequate. Without an upstream coker feed storage tank (typically 12 hrs holdup at 50% liquid level), the coker fractionator must provide surge volume for charge pump protection. Not a good situation.
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10-15mins for liquid hold-up for feed surge..
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