463 / 2018-09-05 14:35:08

Modeling of Biomass Pyrolysis In a Downer Reactor: Characteristics of Flow Behavior and Heat Transfer

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The present work focuses on the modeling of hydrodynamics and heat transfer of solid mixture in a downer reactor. Two approaches, two-fluid model (TFM) and computational fluid dynamics-discrete element method (CFD-DEM) are employed to study the gas-solid flow and interphase heat transfer in the downer reactor. According to the comparison of simulation results, it is found that TFM can generally capture the mixing and dispersion of solid mixture in the reactor meanwhile simulations by CFD-DEM can deliver better results in accordance with the experiments. The mixing status of hot and cold particles in the reactor is also studied by varying the size of heat carrier from 1 to 3mm. the simulation results indicate that the smallest size of heat carrier is benefit to the heating up of cold particles. Meanwhile the wall of constant temperature can heat the cold particles more efficiently. The effect of different structures on the heating up of cold particles is also investigated by establishing the inclined, V-shaped and Z-shaped tubes. With the increasing residence time, the temperature of cold particles will climb up higher in the Z-shaped tube than that in the V-shaped tube but the additional corner does not give the obvious shift up of temperature as the first corner does.