Coal-fueled chemical looping gasification: A CFD-DEM study

Abstract

Chemical looping gasification (CLG) is an emerging technology for reducing greenhouse gas emissions, yet the complex physical-thermal-chemical behaviour in the CLG unit has not been well understood. This work developed a high-fidelity computational fluid dynamics-discrete element method (CFD-DEM) reactive model considering four heat transfer modes (e.g., conduction, convection, radiation, and reaction heat) and complex heterogeneous and homogeneous reactions. The hydrodynamics and thermochemical characteristics in a CLG unit operating under several key operating parameters are numerically studied. The contribution from each heat transfer mode is quantified and the relationship between particle-scale behaviour and mesoscale bubble structures is quantitatively illuminated. The results show that the solids vertical dispersion coefficient is one order of magnitude larger than the horizontal one. At a low solid holdup, the interphase drag force plays a dominant role and particles in the bubble phase have higher vertical slip velocities. The ratio of particle-averaged heating rates for char particles through conduction, convection, radiation, and reaction take 5.41%, 14.91%, 14.39%, and 65.29%, and that for oxygen carriers take 7.77%, 23.46%, 20.33%, and 48.44%, respectively. For char particle and oxygen carriers, the reaction heat dominates the heat transfer process. Increasing gas inlet velocity promotes particle mixing, alleviates dead zone, and finally increases gas products while increasing the char to oxygen carrier mass ratio decreases gas products. The present work provides a cost-effective tool for the in-depth understanding of heat and mass transfer mechanisms in the CLG process.