Numerical Modelling of the FCC Regenerator Reactor Based on Shrinkage Reaction Rate Model

Fluid catalytic cracking (FCC) reactors are applied to convert gas oils and residues to lighter, higher-value products. Circulating fluidized bed technologies are used in modern FCC units, where cracking reactions take place in the riser with co-current upflow of the vaporized gasoil feed and the catalyst. After the disengagement from the product gas, the catalyst needs to be regenerated to compensate the deactivation due to coke deposition. The deactivation of the FCC catalyst can occur already in a few seconds and regeneration of the deactivated catalyst plays an important role for the yield of the FCC unit. For an effective regeneration, burning of deposited coke in the fluidized bed solves the early decay time of the catalysts. During the process the heavy hydrocarbons deposit on the catalyst, which subsequently block the active sites. To restore the activity, deposited hydrocarbons are oxidized with air in the regenerator reactor. The performance of the regenerator as well as its coupling with the cracking reactor are important to reach a high overall yield in the FCC unit. Usually, Geldart-A particles are used as catalyst in the FCC reactors. As the aeration rate of the FCC catalyst is low and the particles are cohesive, big bubbles are formed, channeling occurs and fluidization is often nonhomogeneous, which makes the hydrodynamic modeling a challenge. The clustering behavior of the fluidizing gas also increases the complexity of the reactor design. The complicated hydrodynamic behavior of gas phase and solid particles is a critical point to model coupled heat and mass transfer phenomena inside the fluidized reactors. The aim of the work is to develop an Eulerian-Eulerian numerical model for the FCC regenerator reactor operated as a fluidized bed based on the kinetic theory of granular flows to consider the clustering effect of the FCC catalysts in the regeneration process. In addition, the model shall consider the impact of the shrinkage of the deposited coke on FCC catalyst regeneration time, product yield, and temperature history of the regenerator reactor.