With CO combustion promoters

the role of combustion air flow rate for concerns of economics and control is important. The combustion air is conceptually divided to three parts: the air consumed by coke burning

the air consumed by CO combustion and the air unreacted. A mathematical model of a fluid catalytic cracking (FCC) unit

which includes a quantitative correlation of CO heterogeneous combustion and the amount of CO combustion promoters

is introduced to investigate the effects of promoters on the three parts of combustion air. The results show that the air consumed by coke burning is almost linear to combustion air flow rate

while the air consumed by CO combustion promoters tends to saturate as combustion air flow rate increases

indicating that higher air flow rate can only be used as a manipulated variable to control the oxygen content for an economic concern.