Page 62 - Fluid Catalytic Cracking Handbook

CHAPTER 2

FCC Feed

Characterization

Refiners process many different types of crude oil. As market
conditions and crude quality fluctuate, so does cat cracking feedstock.
Often the only constant in FCC operations is the continual change in
feedstock quality.
Feed characterization is the process of determining the physical and
chemical properties of the feed. Two feeds with similar boiling point
ranges may exhibit dramatic differences in cracking performance and
product yields.
FCC feed characterization is one of the most important activities
in monitoring cat cracking operation. Understanding feed properties
and knowing their impact on unit performance are essential. Trouble-
shooting, catalyst selection, unit optimization, and subsequent process
evaluation all depend on the feedstock.
Feed characterization relates product yields and qualities to feed
quality. Knowing the effects of a feedstock on unit yields, a refiner
can purchase the feedstock that maximizes profitability. It is not
uncommon for refiners to purchase raw crude oils or FCC feedstocks
without knowing their impact on unit operations. This lack of knowl-
edge can be expensive.
Sophisticated analytical techniques, such as mass spectrometry, are
not practical for determining complete composition of FCC feedstocks
on a routine basis. Simpler empirical correlations are more often used.
They require only routine tests commonly performed by the refinery
laboratory. They are excellent alternatives, but they have their limitations:
• They are usually intended for an olefin-free feed.
• They cannot distinguish among different paraffinic molecules.
• They cannot segregate an aromatic compound that may also
contain a paraffinic and naphthenic structure group.

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