Exploring high-density spiral particles belt built in a vortical-type downer pyrolyzer via CFD-DEM simulation

The solids flow behaviors in a specially designed vortical-type downer are systematically investigated using the CFD-DEM simulation. Different from conventional cylindrical-type downer, this novel structure converts the vertical solids feeding direction into a horizontally tangential feeding. By utilizing the movement characteristics of the particles spirally moving downward along the reactor wall, it is expected to build a mesoscale spiral particles belt, in which high-density particles can be accumulated to strengthen the binary particles heat transfer efficiency. Simulation results confirm the successful formation of the spiral particles belt, with a significant increase in solids holdup (0.3–0.4). Further analysis reveals that higher solids flux, lower gas velocity, larger particles size and density are beneficial for the construction of spiral particles belt. Based on the discussion above, the advantages of high-density operation in the vortical-type downer are also discussed compared with the conventional cylindrical-type downer. These results offer a theoretical basis for the R&D and industrial application of the next-generation pyrolysis device.