(FCC reactor / regernerator)
FCC overview
FCC units have three sections
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Reactor-regenerator section, cracking vacuum gasoil feed into a wide cut mixture
Our inferential model FCCS can be used for controlling the reactor
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Fractionator section, separating LCN (light cat naphtha) and lighter, HCN (heavy cat naphtha), LCO (light cycle oil) and slurry
Our fractionator GCC model can help control this separation
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Gas plant, separating fuel-gas (ethane and lighter), LPG (liquified butanes and propanes) and stabilized LCN. Some units further separate LPG into olefinic propane and butane
Our distillation GDS model can help control the gas plant
FCCS – reactor/regenerator inferences
Should FCC reactor APC rely on inferential models?
Many FCC units operate flat out, maximizing conversion to LPG and LCN. Such operation makes sense where gasoline demand is high
But some refineries hydrotreat LCO into diesel oil, and they find it economical to increase LCO production by limiting FCC conversion. Under those circumstances FCCS is a tool for controlling reactor conversion at target
Reactor severity model
Severity = f(Temperature) * f(Contact Time)
* (Cat to Oil Ratio)
IE, severity is calculated from reactor conditions only, without knowledge of the feed.
Crackability definition
Conv * (100 – Conv) = f(Feed, Catalyst) * Severity
f(Feed, Catalyst) = Unmeasured crackability
Function of feed and catalyst conditions
Catalytic coke model
% coke make = g(Feed, Catalyst) * Severity
g(Feed, Catalyst) = Unmeasured coking tendency,
Also a function of feed and catalyst conditions
FCC coke make example
FCC crackability example
Conversion definition
Volume reduction of gasoil
(100 – volume fraction boiling over 221°C)
Coke is a “converted material”
LCO is “not” a converted material
HCN is half and half.
This definition may be based on 1945 economics but it is more or less universal today
We use our fractionator GCC model to correctly calculate the conversion to a cutpoint of 221°C
Calculate conversion on the TBP curve
Crackability and coke make calculation
Crackability = [Conv / (100 – Conv)] / Severity
Calculate coke make from blower air flow and flue gas analyzer
Coking tendency = % coke make / Severity
Catalyst condition = Crackability * Coking tendency
Will that knowledge improve reactor control?
Cannot avoid disturbances during feedstock swings.
But can control conversion and reactor constraints during constant feed
Example FCC reactor trend – 1
Example FCC reactor trend – 2
FCC fractionator inferences via GCC model
TBP estimation
LCN 90% inference vs lab trend
LCO 90% inference vs lab trend
LCO cloud inference vs lab trend
FCC Gas Plant inferences via GDS models
C2 in C3 inference trend
RVP and C4 in LCN trend
C3 in C4 trend
