(364c) Multi-Scale Modeling of Reactive Dense Flows

Large-scale industrial processes involving coal/biomass gasification and combustion, reactive dense particulate flows coupled with mass, momentum, and heat transfer are frequently encountered. Both inter-phase and intra-particle interactions need to be considered, because these interactions govern the key features of dense particulate flows, such as solid mixing, cluster, and regime transitions. Therefore, these interactions prevail at different length scales and consequently a multi-scale approach is adopted to achieve a quantitative description of these complex flows. Specifically, the relevant details of particle-resolved direct numerical simulation (PR-DNS) and discrete element model (DEM) are used to develop closure laws to feed two-fluid model (TFM) which can be used to simulate dense flows on a much larger (industrial) scale. In recent years, such research has been rapidly developed worldwide. This talk will present an overview of the work in this direction at Zhejiang University. Parallel immersed boundary method has been developed and applied to explore a simplified experimental shallow fluidized bed and a laboratory bubbling fluidized bed coupled with a soft-sphere model. It is demonstrated that the present PR-DNS predicted results show a better agreement with experimental measurements compared with coarser approaches. Large-eddy simulation (LES)-discrete element model (DEM) approach with capability of high performance parallel computation has been developed and validated to explore the dense gas-particle flows in 3-D full-loop circulating fluidized beds (CFBs). Besides, this approach is extended to combine heat transfer and chemical reaction sub-models, used to simulate biomass pyrolysis and gasification in fluidized bed reactors. Moreover, the coarser approaches (coarse grained CFD-DEM, MPPIC, and TFM) are also developed to incorporate chemical reactions for industrial applications.