Q & A > Question Details
Pyrolysis gasoline from Ethylene unit is sent to a recovery unit to recover C7 minus components. These are recovered in two columns under vacuum. Maximum temperature is at the bottom of the second column which is ~ 145 deg C. Unrecovered stuff is sent to Utilities as liquid fuel.
Anti-oxidant injection is done in the Ethylene unit as Pygas contains precursors such as dienes which can lead to polymerisation.
Recovery unit was operating steady, without any problems, for 8 months. Now for some reason the frequency of choking of the strainer of bottoms pump of the last column has increased dramatically. Also, we are experiencing frequent choking of burner guns. Material found is coffee coloured granules which become powder when subjected to pressure.
Trying to understand root cause. Not much has changed in terms of operating conditions. Very few component analyses are done in the whole system and not much information is available.
Hope to get some inputs based on experience in similar units.
23/01/2011 A: Wim Bond, Licence to consult bv, wim.bond@zeggis.com
It is quite common that gum forms in fuel gas or fuel liquid streams, either by polymerisation, or by oxygen ingress, or both. Starting with a clean unit, it takes a while before the gum spreads over the whole unit until it finally reaches the vulnerable parts for blockage, the burner guns. Obviously, the strainer does not perform well enough to retain the gum particles. It is simply said a "stone catcher" and is not meant for collecting small particles below 1 mm size. In this case you need a self cleaning filter. However, most self cleaning filters suffer from the fact that the cleaning step does not reveal a completely clean filter, when the debris is more or less sticky. And the gum is really sticky in this case. From my 40 years of experience in Shell, and the last 15 years as "fouling mitigation" expert, with a special focus on filtration, I think I can guide you to the right filter choice. However, in order to be able to recommend the right filter type, we need to get in contact to collect more details on the process.
17/01/2011 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
This is really bad stuff to process in any manner. I expect that oxygen is entering the system during handling that maybe wasn't entering during the 8 months. Anti-oxidant may not be sufficient to control the situation.