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Max. Viscosity in FCC MC Bottom

Max. Viscosity in FCC MC Bottom

Max. Viscosity in FCC MC Bottom


Does anyone have such experience with the viscosity limit in the FCC Main Column Bottom (MCB)? What is the recommended maximum viscosity of MCB (in cst @ 100 °C) in order to avoid fouling the bottom MCB exchangers?

The reason is we would like to maximize distillate makes by minimizing bottom product. We do monitor our bottom exchangers duties for fouling tendency .i.e watching the outlet temp. trends.

Thank you

RE: Max. Viscosity in FCC MC Bottom


I'm not sure if limiting the viscosity will be you most economic solution.  Most want to limit decant (MCB) production within the product specifications.

Have you looked at injecting one of the newer antifoulants designed for this service to keep your heat transfer equipment clean?  Talk to Petrolite and others...they can help you.



RE: Max. Viscosity in FCC MC Bottom

You are right Bob,

what we do here is to Maximize HLCO production up to its spec. (limit) (cut point 90% lv). but recently we did cut dipper in HLCO which has impacted on MCB spec. such as Viscosity. We don't have a spec. for MCB.

RE: Max. Viscosity in FCC MC Bottom

Fouling in MCB exchangers is a function of Time and temperature. So when you cut down the production of MCB, two things can happen (both or one). 1. The column bottom temperature goes up. 2. The residence time in column bottom as well the exchangers go up. You can possibly by maintaining a higher recycle flow control both. Try to maintain a Minimum velocity ( Normally specified by the Licensor) thru the exchangers. Best of luck.

RE: Max. Viscosity in FCC MC Bottom


 what we do is monitor the following :

  Ash, BSw, Viscosity( limit is 250 Seg, SSu a 99.8 °C)
  hexane insoluble,and °Api in the slurry oil.

  we inyected antifoulans in the bottom .



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