Page 105 - Fluid Catalytic Cracking Handbook

82 Fluid Catalytic Cracking Handbook

The nitrogen compounds in the FCC feed deactivate the FCC
catalyst activity resulting in an increase in coke and dry gas. Hydro-
denitrogenation reduces nitrogen compounds in FCC feeds. In the
regenerator, the nitrogen and the attached heterocyclic compounds add
unwanted heat to the regenerator causing a low unit conversion.
Hydrodemetallization reduces the amount of nickel and, to a lesser
extent, vanadium in FCC feeds. Nickel dehydrogenates feed to molecular
hydrogen and aromatics. Removing these metals allows heavier gas
oil cut points.
Polynuclear aromatics (PNA) do not react in the FCC and tend to
remain in coke. Adding hydrogen to the outer ring clusters makes them
more crackable and less likely to form coke on the catalyst.
Hydroprocessing reduces the Conradson carbon residue of heavy
oils, Conradson carbon residue becomes coke in the FCC reactor. This
excess coke must be burned in the regenerator, increasing regenerator
air requirements.

It is important to characterize FCC feeds as to their molecular
structure. Once the molecular configuration is known, kinetic models
can be developed to predict product yields. The simplified correlations
above do a reasonable job of defining hydrocarbon type and distribu-
tion in FCC feeds. Each correlation provides satisfactory results within
the range for which it was developed. Whichever correlation is used,
the results should be trended and compared with unit operation.
A clear understanding of feed physical properties is essential to
successful work in the areas of troubleshooting, catalyst selection, unit
optimization, and any planned revamp.

REFERENCES

1. Dhulesia, H., "New Correlations Predict FCC Feed Characterizing Param-
eters," Oil & Gas Journal, January 13, 1986, pp. 51-54
2. ASTM, "Standard Test Method for Calculation of Carbon Distribution
and Structural Group Analysis of Petroleum Oils by the n-d-M Method,"
ASTM Standard D-3238-85, 1985.
3. Riazi, M. R., and Daubert, T. E., "Prediction of the Composition of
Petroleum Fractions," Ind. Eng. Chem. Process Dev., Vol. 19, No. 2,
1982, pp. 289-294.