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Fluctuations In Delayed Coker Unit

refining delayed coker unit hydrotreater control

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#1 franchescamarie

franchescamarie

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Posted 30 March 2015 - 10:21 PM

Hi! I would like to ask especially those people who have an expertise in operating Delayed Coker Unit. We are currently experiencing high fluctuations in the product flows especially during their backwarming activity. The problem is that the downstream units experienced high feed fluctuations which will affect the operation of their unit and the feed quality. In our plant, most of the downstream units of Delayed Coker Units were hydrotreaters. But because of the feed fluctuations, we are forced to use recirculation lines in the hydrotreaters but this would result also to variations in feed quality, not constant hydrogen flow and unstable operation. With this, what is the recommended control in the Delayed Coker Unit in order to avoid such problems and have a constant product flows?

 

Thank you so much!



#2 eph0909

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Posted 03 April 2015 - 11:25 AM

Hello 

 

1. How many drums do you have? Swings are more severe in 2 drum units vs 6 drum units. 

2. Are you operators making proactive moves on the fractionator before backwarming? How fast are you attempting to backwarm? A lighter hand can help. 

3. Do you have a coke condensate drum?

4. Do you have total draw trays in the frac for light and heavy gas oil?

5. APC systems can help but you will always have swings. It is just a matter of severity. 

6. Does it happen all the time or just some of the time? The coker's cyclic nature means that a lot is in the control of the board operator.  Small details can have a big impact. Outside operators too. 

 

- Evan Hyde



#3 franchescamarie

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Posted 06 April 2015 - 09:25 PM

Hi, regarding your questions:

 

1. How many drums do you have? Swings are more severe in 2 drum units vs 6 drum units.  We have 4 coke drums

2. Are you operators making proactive moves on the fractionator before backwarming? How fast are you attempting to backwarm? A lighter hand can help. Yes we are doing a proactive move by increasing level in drawoff trays before backwarming. How fast: 3-4 hours

3. Do you have a coke condensate drum? Yes

4. Do you have total draw trays in the frac for light and heavy gas oil? Partial draw tray for light gas oil, total draw for Heavy gas oil

5. APC systems can help but you will always have swings. It is just a matter of severity. Noted

6. Does it happen all the time or just some of the time? The coker's cyclic nature means that a lot is in the control of the board operator.  Small details can have a big impact. Outside operators too. The swing in temperature and flows happened every cycle during start of preheating and during coke drum switching. But the dips in the level reading of stripper, happens all the time but no pattern observed. 



#4 eph0909

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Posted 07 April 2015 - 08:13 AM

With 4 drums, the swings should be managable to the other units.  Flows will dip about ~10-15% only if done right.  Recovery in ~1hr. 

 

Beyond the tray levels, you can adjust pumparound, wash oil rate and reflux to keep the tower hotter during backwarm.  Also, you must consider how fast you are swinging into the cold drum.  It have be only slightly lower pressure than the online drum and be done over a period of minutes to no rock the tower. 

 

The condensate drum should stay to the b/d for the first hour (maybe >300F or so) when it is cold to now disturb the tower.  Then line up to tower. 

 

It's hard to say more without looking at trends, CV, OP, etc. 



#5 eph0909

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Posted 17 April 2015 - 01:43 PM

1 final idea.... we will be holding a best practices panel discussion at this conference.  I'm not sure where in the world you are but it will be a good opportunity to get more information about solving this issue from a variety of experts. 

 

http://coking.com/galveston2015/

 

- Evan






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