Simulation of gas-solids heat transfer in cyclone pyrolyzer using CFD-DEM model

Abstract

Fast heat transfer in the pyrolyzer can increase the yield of pyrolysis gas and tar, and improve the quality of tar. Compared with the downer pyrolyzer, the cyclone pyrolyzer can simultaneously achieve high solids holdup and violent turbulence, and correspondingly faster heat transfer. In this work, the heat transfer behavior in the cyclone pyrolyzer is specifically studied using the computational fluid dynamics-discrete element method. The simulation results reveal that the gas-solids heat convection contributes mainly to the heat transfer process, and the heat radiation and conduction are relatively small and almost negligible, respectively. Compared with the downer pyrolyzer under the same operating conditions, the heating rate is significantly increased in the cyclone pyrolyzer. By analyzing the flow characteristics in the cyclone pyrolyzer, it is found that the region of high convective heat transfer rate coincides with that of natural cyclone length. Additionally, the final coal temperature increases with the increase of gas velocity and exists a maximum value. These results can offer some qualitative understanding of the heat transfer behavior in the cyclone pyrolyzer.