Multiscale analysis and modeling of multiphase chemical reactors

Abstract

Abstract Multiphase gas–solids fluidized bed reactors are of multiscale structure, i.e. single particles, particle clusters/bubbles and reactor vessel, and of multiple physics, i.e. hydrodynamics, heat and mass transfer, and reaction kinetics. The formation of complex structures/patterns in each regime is a result of a compromise between dominant mechanisms at multiple scales. Coupling of hydrodynamics, heat and mass transfer, and reaction kinetics takes place at molecular and particle levels where conductive and convective transfer and diffusion within the internal pores of the catalyst are accompanied by the adsorption, surface reaction and desorption of reactant and product on the surface. This work first presents an overview of the general multiscale approaches, including the sequential approach, iterative/concurrent approach and the variational multiscale approach, applicable to multiphase flow and reaction systems, followed by a review on multiscale modeling of gas–solids fluidized bed reactors including bubbling/turbulent and fast fluidized bed reactors. Finally, a multiscale circulating fluidized bed reactor model is outlined in which hydrodynamics are modeled by the combined energy-minimization multiscale/two-fluid computational fluid dynamics coupled with multiscale heat and mass transfer sub-models and reaction kinetics. The interaction and compromise among dominant mechanisms are represented by the variational criterion.