Q & A > Question Details
We have FCC (DCC) commissioned last year, full combustion regenerator. We are facing following problems:
a. Both DFAH and torch oil were in line to satisfy heat balance requirement of Rx-Reg. Torch oil firing results in high afterburning in regenerator ovhd line. Also slurry recycle (feed recycle to MF, not slurry generation) injected at reactor stripper section. Is there any possibility of increase in coke make if we stop fresh feed preheater and inject feed at low temperatures? what are other solutions?
b. Even after stopping DFAH and torch oil, we are facing problems of afterburning in regenerator. Is the afterburning due to slurry injection at rx stripper section (afterburning temp comes down when reducing slurry recycle), or any maldistribution in combustion air distribution?
c. Regenerator Flue gas stack SPM is high when doing soot blowing of Flue gas cooler tubes. Is this due to inefficient working of TSS-FSS or more fines in the circulating catalyst?
 
Answers
30/03/2015 A: Eric Hennings, Technip Stone & Webster, EHennings@technip.com
a) Heat balance is severely challenged at low throughput (~35% of design). Heat loss through Rx-Regen remains constant and a larger percentage of abbreviated feed. Lower feed preheat is counter-productive in that the higher C/O will convert more slurry, thus reducing the quantity available for recycle. Heat balance can be improved by adding coke precursors to the feed.
b) Heat balance (and regen performance) will be improved by adding coke precursors to the feed. If the operation is longer term, consider catalyst additive to promote more coke.
c) Fines in regenerator flue gas are generally a strong function of high velocity. Check all gas injection points for excessive flow.
28/03/2015 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
e-mail e-technology@sinopec.com. with your question.