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I am looking after delayed coker unit. We are operating 4 drum coker with 1kg pressure, 496 COT. We are frequently facing problems during coke cutting, in terms of Hot spots, bed collapse, lot of stem comes out at cutting deck during intial drilling operation.. When ever we tried to increase cot , coke drum cone portion cutting becomes very difficult. Can anybody tell me what are the reason's for this, how to avoid?
 
Answers
05/02/2016 A: Satyalal Chakravorty, Sr Consultant, satya1354@yahoo.co.in
Steam stripping procedure (including the duration) for the coke chambers should be reviewed: Steam must be flowing before the switch and immediately after the switch; otherwise, the yet unconverted liquid feed on top of the coke bed will run down the channels which will coke or solidify and plug the channels resulting in hot spot.
03/02/2016 A: Prabhakar Reddy, Suncor Energy, Inc., preddy@suncor.com
So your drums are operating at ~ 14 psig with COT 925 F. Coke morphology is mainly effected by your MCR / CCR content in feed. Higher the MCR or CCR content in the feed leads to shot coke formation, which can cause few of the issues you have listed above.
What is your CCR /MCR content in the feed ? Are you forming shot coke or sponge coke ? Your cycle time and the approximate water quench time ? Are you using a ramp fuction in your water quench - i.e start with small flow ~ 200 gpm and then after 30-45 min start a ramp in WQ step to completion. What is the drum outlet temperature - i.e before you add the quench oil ?
One thing you can do is do to prevent hot drum - are increase the water soak time after the final fill of the drum. You can also do a double water quench - ie fill the drum to the top K-ray and drain the drum to the third K-ray from the top and refill the drum again. I would check the way you coker operators are cutting the coke - if you cut too fast you could collapse the coke bed. Ideal you would cut 5 ft every 5-10 min - total drum cut should be around ~1 hr.