CFD-DEM study on fluidization characteristics of gas-solid fluidized bed reactor containing ternary mixture

Abstract

Coupled computational fluid dynamics - discrete element method (CFD-DEM) simulations are carried out to investigate the fluidization characteristics of gas-solid fluidized bed reactor (FBR) containing ternary particles (spheres, ideal and elongated cylinders, the latter two are rod-like particles). The mixing efficiency, velocity distribution, orientation distribution and height change of different particles during the mixing process are fully investigated and discussed. Numerical results show that when the superficial gas velocity is low, the mixing efficiency would decrease with the increase of the volume fraction of elongated cylinders due to the inter-locking. However, the discrepancy of mixing degree induced by particle shape can be weakened by increasing the superficial gas velocity. Elongated cylinders become quite active when the inter-locking is broken with more uncertainty in their motion. Ideal cylinders prefer to be horizontal at all the superficial gas velocities considered but elongated ones only show similar behavior at low superficial gas velocities. When the superficial gas velocity is high, the time-averaged orientation of elongated cylinders becomes quite uniform. The inclined angle of both ideal and elongated cylinders decreases with the increase of height and large inclined angles are found at the two lower corners of the reactor. The ideal cylinders turn to be more vertical when the position moves to the central line of the FBR. In the lower half of the bed material, the elongated cylinders prefer to be horizontal in the near-wall region but more vertical in the center of the upper half. Within the range of currently considered superficial gas velocities, the overall mixing degree of the ternary mixture can be enhanced by increasing the superficial gas velocity both in efficiency and stable mixing degree. The findings can be very useful to guide the improvement of existing reactors and the design of novel ones.Numerical simulation; Fluidization; Ternary granular mixture; Mixing behavior; Rod-like particles.