A multistage NOx reduction process for a FCC regenerator

NOx emission from a fluid catalytic cracking (FCC) regenerator is of environmental concern. A new NOx reduction technology that comprised only a simple change in the configuration and operating condition of a commercial FCC regeneration process was proposed. NO reduction by CO in a lab scale fluidized bed reactor under simulated FCC regeneration conditions was investigated. The results indicated that a multistage regenerator would give a higher efficiency for NO reduction than a single stage regenerator. The conversion of NO was increased to 90% in a multistage regenerator as compared to 50% in a single stage regenerator under the same operation conditions. The carbon content of the regenerated catalyst was less than 0.02 wt%. In the range of 400–700 °C, a higher temperature gave more NO conversion to N2. The O2 and CO concentrations were crucial factors that affected the conversion of NO. The catalyst in the FCC process limits the use of the regeneration temperature to less than 700 °C and mole ratio of O2/CO to less than 0.25% in the reduction stage of the regenerator. A phase diagram of the NO + O2 + CO reaction was obtained that was divided into a slow reaction zone and a rapid reaction zone. The regenerator can also be used as a flue gas denitrification facility located downstream of the catalyst regenerator or a coal-burning boiler to reduce the NO concentration in the flue gas to under 20 ppm.