Study Of Fluidization Of Ultrafine Particles And Agglomerate Size Model

Ultrafine particles are widely used in various fields due to their small size and specific surface area.Fluidization technology can effectively carry out the mixing,transportation and modification of solid particles.There are more and more reports on the fluidization of ultrafine particles.Due to the small particle size of ultrafine particles,there is a strong viscous force between the primary particles.The fluidization process is different from that of conventional particles.The fluidization behavior of three ultrafine particles,SiO2,Al2O3 and TiO2,was investigated experimentally in the traditional fluidized bed.And through introducing the vibration field,the ultrafine particle flow behavior of vibration was researched.At the same time,according to the binding force and separation force of the agglomerate particle in the fluidization,we established a model based on force equilibrium.The study found that the traditional flow of the ultrafine SiO2 particles flow with the superficial gas velocity increases,the proportion is divided into segments,yield,bubbling,turbulent flow zone and splash period of five stages,stable fluidization showed similar particulate fluidization state.In contrast,Al2O3 and TiO2 keep bubbling fluidization and steady flow.With the increase of the primary particle size,the fluidization ability of the particles decreases firstly and then increases,and the particle size of the original particle size of 5?m is the weakest.Shallow bed ultrafine particles upward gas flow rate is higher than the deep bed,and the bed expansion ratio is high,but the downward gas flow rate is almost the same.In this paper,the experiment of "positive-negative-positive" is used to prove that the initial bed structure and cohesive force are the causes of the hysteresis.In the vibration fluidization experiment,we found that by introducing vibration energy in lower speed appears suddenly the bed expansion,the phenomenon of violent flow.At the same time,the introduction of vibrational energy weakens the fluidization hysteresis of ultrafine particles.Under the constant vibration frequency,the higher the amplitude,the better the fluidization effect.Under constant amplitude,the influence of vibration frequency on the fluidization behavior of ultrafine particles has two sides.With the increase of vibration frequency,the fluidization effect is better under the lower frequency.When more than a critical value,the effect of increasing the frequency of ultrafine particles is worse.According to the particle agglomerate fluidization force balance,this paper established agglomerate breaking-polymerization dynamic model used to predict the size distribution of ultrafine particles in the fluidized bed,and compared with the data in the literature,most of the error is less than 20%.The size of SiO2,Al2O3 and TiO2 three kinds of ultrafine particles were predicted by using the model at different initial particle size and different static bed height.The results show that the average size of agglomerates increases first and then decreases with the primary particle size,and the average size of agglomerates is 5 ?m.With the increase of the static bed height,the average size of agglomerates increases slightly.