Process Availability

[murthy ns]

Request from experts in Coker operation to list the top 5 issues in Coker which cause either slow down the unit intake and or interrupt the operation and result in both planned and unplanned shutdowns. Also, indicate the overall experiences of refiners who have pushed the coking cycle from design 21 hours to say 14 hours.

best regards

[evan]

Hello

There are as many answers to this question as there are stars in the sky but a common list includes

+ Delay in cycle step causing temporary slow down
+ Decoking or coke handling equipment failure
+ Structure valve issues
+ Heater Fouling and subsequent decoking

RE cycle time reduction, the lowest cycle time I’m aware of was 9 hours between switches. There are many sites which operate on a 12 hour cycle while 16 hours is a typical design basis. It would be impossible to document all the scenarios of debottlenecking to achieve shorter cycle time but the obvious ones include:

+ Fractionator loading
+ Heater duty and fouling
+ Drum cycle step reduction
+ Compressor loading
+ Heat integration (preheat, P/A, cooling, etc)

[murthy ns]

Thanks Evan & Paul for your valuable responses. If I go by the four issues that you have mentioned viz. + Delay in cycle step causing temporary slow down; + Decoking or coke handling equipment failure; + Structure valve issues; and + Heater Fouling and subsequent decoking, can we say that in any calendar year roughly 90%+ downtime can be attributed to the last issue i.e. heater fouling and subsequent decoking.

As regards, attending RefComm® Mumbai. I will leave a word with my management and take further. Thanks once again for the information.

[Paul R Orlowski]

If heater fouling is an issue for you Murthy, I’d suggest attending RefComm® Mumbai. There’s going to be a section on fired heaters.
http://refiningcommunity.local/refcomm-mumbai-2016/fired-heaters-mumbai/

[onuraka]

Hi,

-Coke Cutting Nozzle issues (due to Decoking Control Valve seal failure and/or coke fines)
-Online spalling requirement
-Coke drum vapor line coking (hydroblasting requirement)
-Hotspots problems in some specific feeds
-Downstream Hydrocracking/Hydroprocessing unit upsets or shutdowns

Can anyone suggest any exit for HCGO when the downstream Hydrocracker is shutdown? In our case FCC is not an option since it is relatively a very little unit with coke burning constraints. Does anyone know any market for HCGO? We also considered downgrading it into Fuel Oil pool but it is also limited since we are almost a zero fuel oil refinery.

Best regards.

[murthy ns]

I have seen refiners cutting back crude intake when major secondary processing units like HCU or FCC or Coker goes for TA. We do store HCGO with suitable addition of anti-oxidants so that there is no gum formation during storage. I am aware of sale of VGO fractions in international market. Perhaps buyers can accept HCGO in such blends within fixed Bromine number. Other alt could be making bitumen out of Coker feed with corresponding cut back on Coker thru put inter-alia HCGO make. Other options for HCGO will be to produce bunker fuel or use HCGO as fertilizer feed stock. Best of luck in managing HCGO.

[evan]

Murthy – no, not all downtime is heater related. In some sites, online spalling is the only decoking method between TAR so there is no downtime for those plants associated with the heater. It is all site specific.

RE HCGO uses…. one can increase unit recycle to try to convert more of the material. Only ~50% may react away from HCGO on the 2nd trip to the drum but it could help. You may also consider greatly increasing your wash oil rate to “clean up” the HCGO so the FCC can take a bit more. Lastly, sales as the other comments indicated.

[murthy ns]

Thanks Evan for the update. I understand a few refiners On line spalling two to three times followed by one time pigging. Further it is reported that online spalling does not completely restore the Tube skin temp.

[Author]

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