CO combustion promoter have been used extensively for several decades now.
Historically the CO combustion promoter has been Platinum (Pt) based.
The rule of thumb is 1 ppm of Pt in the circulating inventory for continuous control.
Also, the rule of thumb has been to maintain the delta temperature between the
regenerator bed to the cyclone inlets at less than 35 to 40 deg F. However, that
control strategy has changed somewhat over the last few years to “just keep
the cyclones under 1400 deg F.”
The problem or issue with utilizing Pt based CO combustion promoters has been
a significant increase in NOx emissions.
Therefore, there has been the development and utilization of a non-Pt based CO
combustion promoter, usually Pallidium (Pd) based. The issue of increased
NOx emissions has been retarded with the Pd based promoters.
However, Pd based promoters have been more expensive and have been
less effective (agressive) at controlling immediate high levels of after-burn.
Pd CO combustion promoters have proven to be more effective as a
long-term control modulator. Then the Pt based additive would be
used/employed for “emergency” situations.