Regeneration of zeotype catalysts for MTO

Abstract

Gas-solid fluidization technology has been commercialized in many industrial applications since its implementation in the fluid catalytic cracking process in the early 1940s, however, the understanding of the complex hydrodynamics of gas-solid flow inside fluidized beds is still far from satisfactory due to its dynamic and multiscale nature, especially, the critical role played by mesoscale structures. In recent decades, computational fluid dynamics (CFD) has become an important toolkit in understanding the physics of complex gas-solid flow and then for the scale-up, optimization and design of gas-solid fluidized bed reactors. This article presented a pedagogical and comprehensive review to the Navier-Stokes order continuum theory for CFD simulation of the hydrodynamics of gas-solid fluidization, without taking the effects of heat and mass transfer as well as chemical reactions into consideration. A concise introduction to the methods for multiscale CFD simulation of gas-solid fluidization was firstly provided, which include direct numerical simulation, (coarse-grained) discrete particle method, kinetic method, continuum method and mesoscale-structure-based multiscale method. The underlying postulates of homogeneous continuum theory that assume the structure inside each computational cell is (nearly) homogeneous were then examined, followed by an overview of the constitutive relationships available in literature, including the particle phase stress models, the interphase drag models and the models for particle-wall interactions. The importance of mesoscale structures that take the form of gas bubbles and/or particle clusters and streamers in the quantification of the hydrodynamics of gas-solid flows was then addressed, and the explicit resolution (or highly resolved) method and implicit modeling method for quantifying the effects of mesoscale structures in continuum modeling of gas-solid fluidization were highlighted. Coarse grid simulation of large scale fluidized beds with proper mesoscale, sub-grid scale or turbulent models for constitutive relationships were then reviewed, focusing on the filtered method, turbulence modelling and heterogeneity-based method where the energy-minimization multi-scale (EMMS) based method is a representative. Finally, the scope for the further research areas is described.