I know that injecting antifoam into the feed has been tried. I think most of the experience has been that this injection point will work, but the response time to a foaming event is much longer.
The antifoam molecules start to decompose into smaller fragments as they are heated. These smaller fragments exit the coke drum as they have a lower boiling point than the longer chain polymer of the original antifoam. Injecting the antifoam into the unit feed will cause the antifoam to see higher temperatures for a longer time before it gets to the coke drum which will cause more of the antifoam to be decomposed as it reaches the boiling liquid layer on top of the coke pile.
There have also been reports of antifoam being injected into the crude oil as it is produced in the upstream facilities. Those crudes have resulted in Coker feed that has been high in silicon and has caused the Coker heater to lay down deposits that cause the heater tube metal temperatures to increase in the upper radiant section of the heater. Typically, Coker heaters foul in the lower radiant section due to asphaltenes becoming destabilized and then polymerizing. Those are the same reactions that occur in the coke drum.
I think injecting the antifoam into the top of the coke drum using a LCGO carrier and using a 600,000 cSt antifoam version is a very effective way to manage the normal foam front in a Delayed Coker.
