Numerical study on gas-solid flow characteristics of ultra-light particles in a cyclone separator

Abstract

Cyclone separator is a widely used mechanical equipment that removes solid materials from transport gas, and the separation characteristics depends heavily on material properties. Most separation objects commonly studied are micron-sized powders or particles of high density with the magnitude ranging from 102 to 103kg/m3. While the particle density of expanded graphite (EG), a new type of material that is widely used in industry, is only a few tenths of conventional materials. However, the cyclone separation of such ultra-light particle has not been studied so far. This paper, based on the computational fluid dynamics and discrete element (CFD-DEM) coupling method, performs simulation experiments of the ultra-light particle cyclone separation at different inlet velocities. The pressure and velocity distribution of the continuous phase in the separator are studied. The effects of ultra-light particles on the flow field are revealed. The particle flow patterns are obtained and the force characteristics of the ultra-light particle are analyzed. Simulation results are verified experimentally. The results show that the separation characteristics of ultra-light particles are different from that of conventional materials: a) the appearance of ultra-light particles has negligible effect on the flow field in the separator; b) the ultra-light particles can be completely separated even if the inlet velocity is low; c) when the inlet velocity is higher than 7.5m/s, "top ash ring" composed of ultra-light particles appears under the roof of the cyclone, and multi-helical particle stream is observed in the cylinder region; besides,some "stagnant" particles rotate horizontally in the cone separation zone; d) particle turbulent diffusions in the upper part of the cyclone become stronger first and then weaker as the inlet velocity increases; e) the gas-particle coupling force and collision force are much larger than the particle gravity, and collisions of particles with different sizes are the main cause of secondary particle breakage.