Applying the direct quadrature method of moments to improve multiphase FCC riser reactor simulation

The hydrodynamic behavior of dispersed gas-solid flow is simulated for an industrial-scale Fluid Catalytic Cracking (FCC) riser using the multi-fluid approach, with complementary information from the Kinetic Theory of Granular Flow (KTGF) for the transport coefficients of the solid phase. A continuous Particle Diameter Distribution (PDD) is considered for the solid phase catalyst. The three-dimensional gas-solid flow is considered to be non-isothermal and turbulent. The hydrodynamics of the riser reactor is coupled to a 12-lump FCC kinetic model to predict the influence of a polydisperse distribution on gas-solid reactive flow. The kinetic model involves lumped species consisting of paraffins, naphthenes, aromatic rings, and aromatic substituent groups in medium and heavy fuel oil fractions and includes the effect of aromatic ring adsorption and catalyst deactivation due to coke formation. In this study, a Computational Fluid Dynamics (CFD) model using the Eulerian-Eulerian multi-fluid approach and a Population Balance Model (PBM) are coupled. The hydrodynamic equations are solved by means of a finite volume method, while the population balance equations are solved using the Direct Quadrature Method of Moments (DQMOM). The moments of the solids phase velocity are modeled using classical kinetic theory, while the moments of the PDD are described using quadrature weights and abscissas. To account for the catalyst PDD, three different approaches namely simple, surface-averaged and volume-averaged coupling have been attempted. The latter two approaches, assuming surface and volumetric reaction kinetics respectively, predict with a good precision the yields of the different product families obtained in an industrial FCC unit showing a slight improvement from a conventional heterogeneous reactor model with a monodispersed distribution. (C) 2012 Elsevier Ltd. All rights reserved.