Abstract: Ultra-fine powders are difficult to be fluidized due to the strong particle to particle cohesiveness.However,the authors’experiments showed that the ultra-fine powder CaCO₃ could be stably fluidized in a spouted bed with a draft tube.The effects of geometric and operating parameters on solid circulation rate of ultra-fine powder CaCO₃ were investigated in a 120 mm diameter transparent semicircular spouted bed with a draft tube.Three draft tubes with different sizes were used in this study.It was found that the solids circulation rate was mainly dependent on the drawing rate of the gas jet from the nozzle, then on the gas transport capacity in the draft tube.With increasing gas feed rate, distance between the nozzle and the draft tube inlet and draft tube diameter,the solids circulation rate could be increased.Based on the jet theory,a quantitative correlation was proposed for predicting the solid circulation rate of ultra-fine powders in a spouted bed with a draft tube by taking into account the gas transport capacity in the draft tube.