soft coke formation in the coke drum

[ruslannwaxMember]

Hi,
 
Alls,  a problem about  soft coke formation in the coke drum had confused me recently.
Now let us assume the situation that for a pair of coke drums for a two drums coker, when we had switched the coker feed from the full drum to the empty drum,  and two or three hours later(all in all, less than six hours),  there occured some emergy situation inside the DCU, such as the electricity failure or coker heater tube failure( fracture). And in this situation, we had to shutdown the heater feed and the coke drum feed, and also the unit. So there are concerns for the soft coke formation(very difficult to be hydraulically decoked) in the coke drum since the coking time is too short(less than six hours)? what should we do to avoid it? and what about your experence and consideration?
I had discussed with some DCU operators and all of them told me that they did not experience it.
Wish to hear your voice.
Thanks.

[antonio saura CebrianParticipant]

Partially filled coke drums especially those of a few hours or less will contain only partially coked contents even though heater outlet temperatures are above 935aF. This is due to the lack of sufficient coke mass in the drum which normally provides a thermal source for the continuation of the coking reactions after charge has been discontinued. Such drums need to be steamed stripped for longer periods of time, up to four to five hours, versus 1-1/2 hours for a normal drum in order to help solidify the contents. However, partially charged drums of several hours, generally four hours or less, that also have residuum in them from emergency steaming of the heater will have a tendency to have soft asphalt like properties due to partial polymerization, and will have a plastic like deformable nature. This material, although allowing steam and water flow into the drum, can prevent water draining by plugging drum channels much the same as a check valve prevents backflow in a line.

you can found some point about that in coke drum /tarry drum

espana2005

[Lucibar DavalilloParticipant]

Here is my 2 cents on this…
That kind of failure is typical in cokers, but it becomes part of the most difficult decission as well.. what would i do? here are my rule of thombs: 1) if you were not more than 20 minutes with  cold material (less than 750 DegF) and still far away (less than 2/3 of coking cycle) before switching, i’d go back into the coke drum and cook it as hard i can; 2) if you were over 20 min with cold feed, but less than 1 hr, now you need to be very early in coking cycle (less than 1/3 of coking cycle), before you attemp a crazy comeback to that drum.  3) if you already passed 2/3 of coking cycle, do not even try going back and get prepared for the worst.

[james jonesParticipant]

‘he s’tuat’on you refer to ‘s a short run drum. there are several schools of thought on how to handle th’s s’tuat’on. ‘he key var’able ‘s how long you were ‘n the drum at cok’ng temperature pr’or to feed loss. We feel that ‘n s’x hours at cok’ng temperature (I go by a drum overhead temperature of 800*F as cok’ng temp.)that the drum at that po’nt can be quenched as normal. Less than 6 hours at cok’ng temp. ‘t becomes tr’cky. In all cases at the loss of feed try to get steam go’ng ‘nto the drum. If steam flow can be establ’shed then you have a couple of cho’ces. If you can put steam through your heater and you can put on some burners to super heat the steam to a temperature that w’ll cook the res’d ‘n the drum. If putt’ng the steam through the furnaces ‘s not an opt’on then extend your steam’ng of the drum for up to 24 hours, and extend your water quench.We would try to dra’n to the p’t, but ‘f o’l ‘s present we would dra’n to our coke condensate drum then rewater quench. If you can’t get steam ‘n the drum, then top water quench’ng may be your only opt’on. In any case get your techn’cal people ‘nvolved when deal’ng w’th a short run drum.

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