Particle mixing behavior of fine coal in density control of gas–solid separation fluidized bed

Abstract

In a gas–solid separation fluidized bed, mixing of fine coal is necessary to achieve a suitable bed density to enable effective separation of low rank coal. On the basis of a variety of mixture models, a gas–solid separation fluidized bed was judged, where fine coal particles of 0.6–1.0mm were uniformly mixed with magnetite powder. High-speed dynamic camera technology was combined with a slump-sampling method to study the mixing process of the fine coal in the fluidized bed. These results showed that limitations of the fluidized bed structure cause the mixing process to be dominated by lateral diffusion and supplemented by axial diffusion. Axial diffusion was mainly achieved through the ascension of bubbles, whereas lateral diffusion was determined by the bursting action of the gas bubbles at the surface of the bed and the undulating characteristics of the bed. The effective lateral diffusion coefficient increased exponentially with gas velocity but had no strong relationship with the bed height. As the feed point moved toward the center, fine coal began to diffuse to both sides, which shortened the time for the bed density stabilization from 20 to 5min. The bed density of the layer was stabilized at approximately 1.75g/cm3. The separation efficiency of the gas–solid separation fluidized bed containing binary mixtures was more obvious for 6–50mm raw coal, with a probable error E of 0.16.