Operating the fluid catalytic cracking unit (FCCU) in afterburning conditions
can increase the regenerator temperatures above the metallurgical design
leading to mechanical failures of the cyclones and plenum chamber. This
paper presents the methodology applied in a commercial FCCU to investigate
the afterburning causes and the technical solutions that can be implemented
to reduce the afterburning. Thus, by evaluating the regenerator temperature
profile, regenerator as-build design and the internals mechanical status, it
was concluded that the main cause of afterburning was the non-uniform
distribution and mixing of air and catalyst. The industrial results showed
that optimizing the catalyst bed level, stripping steam, reaction
temperature and equilibrium catalyst (e-cat) activity reduced the
afterburning by 39%. Other process parameters such as feed preheat
temperature, slurry recycling and excess oxygen did not have a significant
influence on afterburning because of air and catalyst maldistribution.
Revamping the regenerator to assure a symmetrical layout of cyclones reduced
the afterburning by 86%, increased the fines retention in FCCU inventory and
provided a better regeneration of the spent e-cat. The reduction of
operating temperatures at around 701?C removed the risk of catalyst thermal
deactivation and therefore the e-cat activity was increased by 10.2 wt.%.