Numerical Simulation of Hydrodynamic Behaviours in a Novel Gas-Solids Moving Bed Reactor Under a Downer

The downer can be used in the circulating fluidized bed as a pyrolyzer of coal and/or biomass because of its characteristics of gas-solids contact in a short time, uniform distribution, and so on. In a practical process, some escaping particles of coal or biomass which are not pyrolyzed completely and produced tar could get in the char gasification unit and hinder the gasification of char. To solve this problem, a gas-solids moving bed rector is considered to be added at the bottom of downer which can let coal/biomass pyrolyzed completely and simultaneously tar cracked effectively on the char. In this study, FLUENT 19.0 commercial software, a 3D grid, and the Eulerian–Eulerian two-fluid model were applied to simulate the hydrodynamic behaviours in this gas-solids moving bed reactor. The results of numerical simulation showed that this moving bed could increase solids holdup extremely, reaching a value of above 0.35. There was a peak of solids holdup near the wall while many particles concentrated at the center of the moving bed. This phenomenon should be caused by the radial velocity of particles. In addition, the axial velocity distribution was the similar as that in the downer, where the first acceleration section, the second acceleration section and the constant velocity section were observed.

[Acknowledgements] This is supported by the JSPS KAKENHI Grant-in-Aid for Scientific Research B (Kiban B, 17H03451), Japan and the National Natural Science Foundation of China (U1710101)