CFD Modelling of Hydrodynamics in a Dual Circulating Fluidized Bed: Effect of Drag Models

Chemical looping combustion (CLC) is an alternative to conventional oxy-combustion technologies, and a dual circulating fluidized bed (composed of two risers, two pot-seals, two cyclones and two downcomers) is one promising CLC process. In this work, a CFD model is developed to describe the complex behaviour in an interconnected dual fluidized bed based on the Eulerian–Eulerian two-fluid model. In particular, the effect of various drag model on simulations results is investigated in aspects of pressure, particle distribution, and oxygen carrier recirculation rate. The drag laws used in this study are Gidaspow (1994), EMMS (1994), Rong et al. (2013), Tang et al. (2016). Both qualitative and quantitative results indicated that the drag model had a significant effect on internal flow behaviour. The results showed the EMMS drag model was found to achieve comparable predictions compare to the measurements in dual circulating fluidized bed, while other drag models can only predict certain fluidization regimes reliably. This work provides a guideline for choosing appropriate drag models for simulating oxygen carrier in dual circulating fluidized bed CLC system.