Numerical modeling of char particle segregation in entrained-flow slagging gasifiers

This work illustrates how different numerical modeling approaches can be jointly used to understand segregation patterns of char particles in full-scale entrained-flow coal gasifiers operated in the slagging regime. A multi-level approach has been developed for this purpose. Firstly, a reduced compartmental model has been developed to give indications on the solids flow rates and flux transferred to the wall slag layer. Then, RANS-based simulations of the full-scale geometry with coal particle injection and tracking aimed to obtain the general behaviour of the flow field and particle trajectories. Simulations enabled to estimate the effect of swirl and tangential flow on the bulk-to-wall char particle deposition rate. Finally, RANS results were adopted in a more detailed numerical model based on the solution of the filtered Navier-Stokes equations. In this last model, a turbulence LES approach for the Eulerian gas phase was applied. Both RANS and LES simulations have been obtained with the aid of the OpenFOAM toolkit. The equations of particles motion were solved via a Lagrangian particle tracking algorithm with the TrackToFace method. Simulations were performed involving a number of particles from 10^5 to 10^6, a level of detail that allowed to obtain a clear picture of the multiphase flow behaviour responsible for char deposition phenomena. This multi-level approach enabled the assessment of the char particle deposition rates and the nature of char/slag interaction (segregation/entrapment) that are likely to occur in full-scale slagging gasifiers.