What follows is not accurate!
The model I have built does not have valid kinetic parameters. I have arbitrarily assigned values to the rate constants and the activation energies because I don't currently have access to values determined by a kinetic study. I adjusted the parameter values to achieve a dry flue gas analysis that appears to be reasonable: 2% O2, 3% CO, and 10+% CO2. These are the values at the lowest air flow rate in the Flue Gas (Dry) plot below.
In spite of the warning, I believe that some of the trends to be discussed will still be valid. In other words, the slope sign of a curve will be correct if not the actual slope value. This is just an exercise to show what a model can provide.
The assumed system
I have assumed the following parameter values were obtained from a tracer study:
Effect of air rate on temperatures
Increasing the air flow rate has almost no effect on the dense bed temperature for this reactor. That is due to the constant air flow rate to the emulsion phase. With a nearly fixed amount of oxygen to the emulsion phase, and a constant catalyst flow rate, the amount of coke burn remains constant.
The flue gas temperature increases for two reasons. First, catalyst entrainment increases with air rate. Second, higher air rates bring more oxygen to the freeboard zone for more coke burn.
Some validation of the assumed model?
The difference between the flue gas and bed temperatures appears to be common for this reactor. A plug flow model is not likely to show this size of temperature difference because it wouldn't have bypass gas with higher oxygen content for the freeboard region.
Effect of air rate on coke levels
This plot shows that increasing the air rate does lower the coke on the regenerated catalyst, even though I said above that the coke burn rate in the bed is constant. The reduction comes from the extra burnoff in the freeboard region. The freeboard catalyst goes through the cyclones and is returned to the bed, thereby lowering the overall coke level.
I will wait until the integrated reactor model is built to study the effects of catalyst flow rate and the coke on the spent catalyst. At that time, we may also see that the air flow rate does affect the bed temperature via the secondary effect of lower carbon on the regenerated catalyst and increased reaction rate in the riser reactor.
In the next post, I will study how changes in the system parameters (f, f2, etc.) affect the performance of the reactor.