CFD Simulation of an Industrial High-Efficiency FCC Regenerator

A  three-dimensional  simulation  of  the  gas-particle  flow  behavior,  heat transfer,  and  coke  combustion  inside  commercial high-efficiency FCC  regenerator that includes  a combustor and  a regenerator vessel was carried  out. The  simulation  has  several  goals:  to  evaluate  the  behavior  under present conditions  of  operation, identify  and  propose  solutions  to  operating troubles. The  kinetic  for  coke  combustion  was  simulated  in  MATLAB  to understand  its  performance. The CFD simulation based on the Eulerian-Eulerian model for  coke combustion was conducted using  a  commercial  CFD  package  Fluent  15.0,  that  uses  the  finite   volume method to solve the partial differential equations of  continuity,  momentum, energy and  species transport  by discretizing the equations  over finite volumes.  The  Phase  Coupled  SIMPLE  algorithm  was  used  to  adjust  the  pressure  and  velocities after each iteration when solve the gas-solid momentum equations. For  simulate  the  combustor,  a  CFD  simulation  of  the  gas  distributor  was needed in order to define boundary conditions of the gas inlet for the combustor. The results obtained  of  the CFD  simulation  of  the  combustor shows lower  concertation  of the  solid  particles  in  this  zone  of  the  regenerator.  Homogeneous  mixture between solid particle and gas in the regeneration process is critical since most of the catalyst in the  bed has very little coke on it, about 1 %w. At the same time, the CO content in the  flue gases is high due inefficient  mix between  the  air  and  the particles.  Afterburning results when  the CO content in the flue gases mix with the high oxygen content gases  in the  regenerator  vessel.  Afterburning  causes thermal  deactivation  of  the  catalyst  FCC and damage on cyclons due to  hot spots.  To  correct  these  problems,  different  designs  of  the  spent  catalyst distributor  was  evaluated.  The  results  obtained  with the new designs of the distributor showed decreased of the afterburning  phenomenon  in  the regenerator vessel.