Numerical investigation of cold flow hydrodynamics in an internally circulating dual fluidized bed for coal gasification

Cold flow hydrodynamic study of a full loop, three-dimensional internally circulating dual fluidized bed (ICDFB) for coal gasification has been carried out using a Eulerian-Eulerian approach. The ICDFB system consists of a central riser and an annular bubbling fluidized bed (BFB) placed concentrically and interconnected by a solids separator and a loop seal. The compact design and simple geometric configuration are novel features of the proposed ICDFB system. All components of the ICDFB system are interconnected in such a manner that when air is injected through different aeration ports, a stable internal loop of solids circulation is established. A sensitivity study of various operating parameters that potentially influence solids distribution and recirculation rate has been conducted. Numerical results reveal that the highest pressure region is formed at the bottom of the loop-seal when a statistically steady solids circulation is reached. The riser gas superficial velocity and loop-seal aeration rate are found to be the major controlling factors of solids recirculation rate. Further, the performance of the gravity-based solids separator, specifically designed to capture Geldart B particles, is found to be suitable for the given range of riser superficial velocity and loop-seal aeration rate.