Stability analysis and CFD validation of a new fluid-particle interaction force for mono-component gas-solid fluidized beds

A new closure relationship for the fluid-particle interaction force has been developed for the CFD modelling of gas fluidized beds. As a first step in verifying the applicability of the new closure, the mono-dimensional version of the equations of change for the fluid and solid phases has been examined analytically. Here, linear stability analysis theory has been applied to the continuity and momentum equations in the face of small fluctuations in the voidage or particle velocity. The effort leads to the development of a new stability criterion for homogenous gas fluidized beds with better predictive capability than the Foscolo and Gibilaro [P. Foscolo, L. Gibilaro, A fully predictive criterion for the transition between particulate and aggregate fluidisation, Chem. Eng. Sci. 39 (1984) 1667-1675.] criterion. This was attributed to the better predictive ability of the dynamic wave velocity developed in this work and which is expressed as a function of the local concentration of the particles. CFD validation of the drag force closure equation is also carried out. Here predictions of bed height and bed voidage obtained from the CFD simulation of a Geldart [D. Geldart, Types of gas fluidization, Powder Technol. 7 (1973) 285.] Group A material FCC catalyst (70 mu m) were used to validate the model. Results from simulations showed a very good agreement with predictions from the Richardson-Zaki [J. Richardson, W. Zaki, Sedimentation and fluidization, Trans. Inst. Chem. Eng. 32 (1954) 35.] equation. In the final part of the paper, CFD simulations of three Group B industrial powders are presented comparing the model predictions obtained for the case where the solid stress tensor is at first neglected and subsequently included in the model via the standard granular kinetic theory, results revealed that the collisional stresses do not dominate the macroscopic fluid bed predictions for bubbling dense gas-solid systems. (C) 2007 Elsevier B.V. All rights reserved.