Three-dimensional CFD simulation of tapered gas-solid risers by coupling the improved EMMS drag

Tapered gas-solid risers have been used in some industrial processes in order to adapt to the requirements of various reactions, but little attention was paid to these reactors in previous investigation. In this work, three-dimensional gas-solid flow in tapered-out and tapered-in risers was simulated by the two-fluid model using an improved structure-dependent drag based on the EMMS model. The EMMS model was solved at different axial levels to determine different correlations of heterogeneity index with voidage, which were then interpolated between these levels to improve the prediction of varying interphase drag in the tapered risers. Considering the axial variation of the EMMS drag, the simulation predicts much more reasonable flow dynamics in the tapered risers than those coupled with an average EMMS drag or homogeneous drag laws. The axial and radial heterogeneities as well as the parametric effects on the flow dynamics in the tapered risers were discussed in detail, so as to provide reference for the proper design of tapered gas-solid riser reactors. (C) 2019 Elsevier B.V. All rights reserved.