Catalytic cracking process

DETAILED DESCRIPTION OF THE INVENTION The improved process and method of control of this invention applies particularly to FCC, i.
e.
fluid catalytic cracking.
It relies on the use of a model of the cracking process including regeneration of catalyst contaminated by coke.
In the improved process and method, it is preferred to use a kinetic predictive model such as that described in copending patent applications Ser.
No.
529,055 filed Dec.
3, 1974 and Ser.
No.
472,525 filed May 23, 1974, the entire contents of which are incorporated herein by reference.
The model is used, as illustrated hereinafter, with no constraint of the CO.
sub.
2 /CO ratio, i.
e.
the CO.
sub.
2 /CO ratio is allowed to vary from about 1.
5, which usually obtains in the absence of the CO combustion promoter, to about 100, corresponding to substantially complete combustion of CO.
Alternatively, the value of the ratio may be subjected to limited contstraint, i.
e.
restricted to within the range of from about 1.
5 to about 10, as when it is desirable to operate a CO boiler, for example.
Either of these constraint conditions represent a novel departure in the use of the model since, ordinarily, wide variation of the CO.
sub.
2 /CO ratio would not be contemplated.
It is a feature of the process and method of control of this invention that it is readily adaptable to change of feedstock, change in optimal product slate, or both.
The type of operation may rapidly be changed from conventional, where the normal unpromoted CO combustional occurs with CO.
sub.
2 /CO ratios of about 1.
5, to a partial CO burning mode where improved regenerator performance is observed as the CO.
sub.
2 /CO ratio increases to a range of 1.
5-100, preferably in a region of 1.
5-10, to complete CO burning where the CO in the effluent is completely combusted so that the effluent concentration is below 0.
2%.
As will become evident hereinbelow, there is usually a preferred method of operation that depends on the charge stock being used, the catalyst activity in the unit, certain metallurgical constraints, as well as the specific characteristics of the particular FCC unit that this invention is practiced on