100 Most asked questions by Chemical Engineers

download the ASKNORMLIEBERMAN APP http://h.fanapp.mobi/asknormlieberman1

Wednesday, October 7, 2015


Delayed Coker

My coker fractionation tower top pressure surges higher by 5 psi for a few hours. Tower top temperature jumps by 20°F - 40°F. The level in light gas oil pan drops. This occurs every few days. What’s happening?


You’re salting-up the top few trays. The top reflux can’t cool off the upper trays. They get hot, and sublime off the salts. A simple way to prevent the problem, is to periodically heat up the top of the tower, maybe for 30 minutes by 30°F, every few days. I’m not too sure about time and temperature factors. Periodic water washing is also possible, but a lot more complicated.


  1. The DCU furnace tube radiation delta pressure is increasing slowly but the skin temperature is not increasing. What could be the possible cause of this?

  2. It could be that you have only coke formation in a localized area where you are not monitoring skin temperature?
    Perhaps composition of feed has gotten slightly lighter with time and % vaporization is increasing and causing higher delta P?
    Best to be guided by tube color, rather than skin temperature, as coking may be occurring with no skin TI.