A review of gas-solid dispersion and mass transfer coefficient correlations in circulating fluidized beds

It is increasingly more important to be able to predict the conversion and yield of reactant species given the ever rising cost of the reactants and the ever decreasing acceptable level of effluent contaminants. As such, the development and use of predictive models for the reactors is necessary for most processes today. These models all take into account in some manner the relative movement of the gas and of the solid species as well as the interphase mass transfer. The model developer, unless equipped with specific experimentally based empirical correlations for the reactor system under consideration, is required to go to the open literature to obtain correlations for the axial and radial gas dispersion coefficients, the solids axial and radial dispersion coefficients and the interphase mass transfer coefficient between the solid phase and the gas phase. This is a difficult task at present since these values differ by up to 7 orders of magnitude for the mass transfer coefficient and up to 5 orders of magnitude for dispersion coefficients. This paper presents a summary of the work in these areas as found in the literature dating back to 1949 and provides a critical review to guide the selection of the best correlation (s) in circulating fluidized bed reactors. The driver for this paper is the uncertainties due to hydrodynamics that effect conversion in CFBs and as such only reviews the mass transfer coefficient and the gas and solids dispersion coefficients. A comparison of heat transfer coefficients is therefore not included. (C) 2006 Elsevier B.V. All rights reserved.