CFD based modeling on chemical looping combustion in a packed bed reactor

Chemical looping combustion (CLC) with metal/metal-oxide oxygen carrier in a randomly packed bed reactor has been modeled and numerically simulated with a finite volume based CFD method with the help of the overset grid technique. The CLC reactor was modeled as a cylindrical fixed bed randomly packed with 450 porous spheres that represents the oxygen carrier particles. 3D transient incompressible Navier-Stokes equations and species transport equation were solved to obtain the flow, temperature and species fields in the interstitial spaces in the reactor. Inside the porous structure of particles, heterogenous reaction, species diffusion and heat conduction were modeled respectively with the changing grain size model (CGSM) and the effective parameter methods. The intra-particle transport processes were solved numerically and coupled through their surface flux with interstitial flow and scalar fields. As a numerical simulation of discrete particle methods, this CFD model provides very detailed fields of flow, temperature and species and their transient evolution in the interstitial void spaces of the reactor and inside the discrete particles. Internal diffusion resistance in large particles is the limiting factor to the overall reaction rate. Structured particles with egg-shell distribution of reactants were found to be helpful to improve the overall reaction rate for large particles. Sensitivity of the particle model to the prediction with the CFD model was also investigated and found to be a necessary concern for a successful CFD modeling for the packed bed CLC process. (C) 2015 Elsevier Ltd. All rights reserved.