Time scale analysis of a fluidized-bed catalytic reactor based on a generalized dynamic model

Abstract

A fluidized-bed reactor model is implemented to simulate a Maleic Anhydride (MA) reactor with special emphasis on its dynamic behaviour. The dynamic model is general enough that it can treat a wide range of catalytic systems, subject to mass and energy balances within the phases. The model represents multiple phases and regions (low-density phase, high-density phase, freeboard region) and can account for heat and mass axial and radial anisotropic dispersion, change in molar/volumetric flow due to reaction, temperature and pressure profiles, hydrodynamic regime variation, catalyst deactivation, energy options, and multiple membranes of various geometries for introduction/extraction of any compound. The model reduces, as special cases, to most fluidized bed reactor models reported in the literature, allowing the influence of simplifying assumptions to be investigated. Introduction of different assumptions for a MA fluidized-bed reactor of industrial scale reveal quite different predicted time scales for key dynamic phenomena inherent to the process. A mass transfer/reaction time scale was found to be close to the residence time of the gas molecules in the reactor. The heat transfer time scale is several orders of magnitude larger for the current system. This type of timescale analysis may be a useful tool to identify the appropriate degree of sophistication to predict the dynamics of complex reacting systems.