Mass transfer coefficient prediction method for CFD modeling of riser reactors

In gas-solid reactors, particularly circulating fluidized beds (CFB) and riser it is becoming 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 are necessary for most processes today. These models need to take into account the interphase mass transfer. Unless equipped with specific experimentally based empirical correlations for the reactor system under consideration, the modeler is required to go to the open literature to obtain correlations for the mass transfer coefficient between the solid and gas phases. This is a difficult task at present since these literature values differ by up to 7 orders of magnitude as found in the literature dating back to 1949. The wide variation in the prediction of mass transfer coefficients in the existing literature is credited to flow regime differences that can be identified in the cited literature upon careful inspection.Applying a new theory developed by Breault and Guenther [1] that takes into account the local hydrodynamics, a predictive methodology is presented that allows the local mass transfer coefficient to be calculated based upon local properties in a CFD simulation. A sample calculation is presented and compared with the data used in developing the theory as well as correlation for the literature.