Centrifugal force caused high-density rotating downward quasi-plug flow in cyclone reactors

Abstract

Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) model is used to simulate particle motions in the cyclone reactor, which reveals that the particles accumulate near the reactor wall due to the centrifugal effect, and with the increase in particle flux, their distribution pattern evolves from a uniform circumferential distribution to a local accumulation state and eventually develops into a particle belt pattern. No matter how the particles are distributed, they rotate downward in a form of “quasi-plug flow”. Most extant literatures report that the movement of particles always leads to the formation of an “accelerated quasi-plug” under the free-fall with the action of gravity. However, in this study, it is found that the rotating downflow exhibits “decelerated quasi-plug” or “constant velocity quasi-plug” behavior. Given similar particle flux and residence time in the reactor, the particle residence time distribution under the rotating downflow is narrower than that under the free-fall, and closer to an ideal plug flow. Meanwhile, centrifugal effects also significantly increase the solid holdup, permitting high-density operation of cyclone reactors even under the condition of lower inlet particle flux.