The characteristics of particle flow and mixing have a considerable influence on the mass and heat transfer, as well as the product quality. In order to further enhance the particle mixing in the internally circulating fluidized bed (ICFB), especially along the radial direction, a new-type particle mixer with slots on the draft tube (as shown in Fig.1) was proposed in the present work. The hydrodynamics of the mixer was investigated by using a multi-scale computational fluid dynamics (CFD) with the EMMS drag. The prediction in terms of cross-sectionally averaged solid holdup and solid velocity were compared to experimental data for validation. In draft tube, a low pressure region can be observed near the slots, smaller than the pressure in the region between the adjacent slots. This pressure drop forced particles inside the draft tube to move towards the slots and pass through them, which significantly facilitates the mixing of the particles along the radial direction. In the annulus the pressure in the vicinity of the slots seems larger than that in the region between the adjacent slots, inducing horizontal particle immigration and mixing. Nearly 25.4% to 29.7% of gas in the draft tube bypassed and flowed through the slots into the annulus. Gas bypassing into the annulus was finally brought out of the annulus by the circulating particles, and the ratio of the mass flux of the tracer gas bypassing into the annulus to that of total tracer gas is approximately equal to 0, much smaller than that in a conventional ICFB (usually within 15%). With increasing the superficial gas velocity in the draft tube from 0.3 m/s to 0.45 m/s, the total solid mass flux increased from 4.87 kg/s to 10.86 kg/s, while the mass flux through slots decreased from 2.69 kg/s to 0.52 kg/s.
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Fig. 1 Schematic diagram of the new-type particle mixer
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