Fluidizing Behaviors Of Ultra-fine Powders In A Spouted Bed With A Draft Tube

Ultra-fine powders, particles of the group C according to the Geldart classification, are very adhesive and hard to fluidize by conventional methods, hence they were rarely used as fluidization materials in the past. However, following the rapidly growing application of the ultra-fine particles in industry, fluidization of the ultra-fine powders has become a significant emerging field in recent years. And how to improve fluidization quality is a key point for further investigation.Fluidized behaviors of ultra-fine powder CaCO3 of mean diameter 5 um in a spouted bed with a draft tube were investigated, studying the effects of geometry and operating parameters on the two-phase fluidized characters such as the initial spouted behavior, the solid circulation rate, the gas flow distribution in the spout and the annulus, and the solid flow in the annulus. It was found that the ultra-fine powder can flow smoothly in a spouted bed with a draft tube under some sorts of design parameter and operating condition, thus a new effective method to improve fluidization quality of the ultra-fine powders is obtained; at higher supplied gas velocity, an increase in the solid circulation rate is observed; the extent of thedistance between the nozzle and the draft tube inlet result in the promotion of the solid circulation rate; the solid circulation rate increase with increasing the draft tube diameter or the bed mass; the gas bypassing is nearly zero in the present work; and the solid flow in the annulus is observed as a moving bed.On the base of large numbers of experiments, a theoretical model to describe the hydrodynamics is established by the aid of the theory of two-phase flow and soil mechanics. From the model, the effective factors are acquired. By non-dimensional analysis of the model, a series of non-dimensional parameters are deduced. The solid circulation rate is obtained by regressing experimental data, which can predict the solid circulation rate within deviation of + 29%.From this work, a new way to improve the fluidization quality of the ultra-fine powders is found, and the studying result can supply as a basis of further investigation and be able to be used in the design of a spouted bed with a draft tube for the ultra-fine powders.