Coarse grid simulation of heterogeneous gas–solid flow in a CFB riser with EMMS drag model: Effect of inputting drag correlations

Abstract

Two-fluid model combined with Energy-Minimization Multi-Scale (EMMS) drag model has been accepted as an effective method to simulate the hydrodynamics of heterogeneous gas–solid flow in circulating fluidized beds. In the EMMS drag model, a drag correlation obtained from homogeneous fluidization and/or packed bed, denoted as traditional drag correlation, is necessary to describe the homogeneous gas–solid interactions within three (dilute-phase, dense-phase and inter-phase) sub-systems. In this article we study the effects of different traditional drag correlations on the effective inter-phase drag force of clustered gas–solid flow within the framework of EMMS drag model, and their consequent effects on CFD results. It was shown that due to the proper consideration of meso-scale structural effect, CFD results using the EMMS drag model are in a reasonable agreement with experimental data (including radial and axial solid concentration profiles and root mean square of local solid concentration), and are slightly affected by different inputting traditional drag correlations. Present conclusion is quite different from the one obtained in previous studies, where coarse grid simulation with traditional drag correlation failed to predict the hydrodynamics of CFB risers and was sensitive to the traditional drag correlation used. Therefore, the EMMS drag model appears as an advantage over traditional drag correlations, since it is not only insensitive to the empirical input, but also gives much better agreement with experiments.