Effect Of Rotor Cage’s Structure Of Turbo Air Classifier On Classification Performance

Material classification is a very important unit operation of powder material production process. Turbo air classifier is a common classification equipment during this unit operation. With the development of the powder technology, higher demand for powder classification equipment has been raised. So the study on improvement of classifier is carried out all the time. The internal structure of classifier is an important factor for classification performance. In recent years, research on optimization of structure has made remarkable achievements, which will provide theoretical basis for the improvement of structure. In this paper, the rotor cage’s inner and outer radius and blades spacing of turbo air classifier have been improved. The inner flow field, before and after improvement of classifier, is simulated with FLUENT. The best rotor cage’s radius and blades spacing have been got, which make the flow field in the annular region and between blades stable. The material experiments with radius changed rotor cage verify the simulation results.In order to study the effect of rotor cage’s inner and outer radius on classification performance in turbo air classifier, with the same rotor cage’s blade width, the inner flow fields of different structures are simulated with FLUENT. The results indicate that:When the inner and outer radius both decrease 18 mm, the annular region width increases 18 mm, the tangential velocity in the annular region increases. It is advantageous to disperse materials. The changing rate of the tangential velocity in annular region decreases from 0.208 m·sr-1·mm-1 to 0.149 m·s-1·mm-1. That means the uniformity of flow field in the annular region is improved. The fluctuation of tangential velocity near the rotor cage’s entrance decreases from 2.7 m·s-1 to 0.8 m·s-1. It indicates that the tangential velocity distributes uniformly, so that the particle size distribution of fine powder product becomes narrow. The inertia counter rotating vortex between blades decreases because of the decreased blades spacing. Radial velocity in the blades channel distributes uniformly. Fine powder particles enter into the rotor cage rapidly, which reduces the possibility of the fine powder back-mixing the coarse powder. And the classification accuracy is improved. The CaCO3 experiments indicate that; When the inner and outer radius decrease 18 mm, the classification accuracy increases 3.3%-25.4%, and fine powder productivity increases 27.8%-76.2%. These experimental results are in good agreement with the simulation results.The blades spacing changed by changing of the number of rotor cage’s blades. With the same rotor cage’s inner and outer radius, there is a best blades spacing to make the flow field stable. By studying the different blades spacing of different rotor cages, it is found when the ratio between blades spacing and blades width is 0.23 that the radial velocity between blades FLUENT. The results indicate that:When the inner and outer radius both decrease 18 mm, the annular region width increases 18 mm, the tangential velocity in the annular region increases. It is advantageous to disperse materials. The changing rate of the tangential velocity in annular region decreases from 0.208 m·s-1·mm-1 to 0.149 m·s-1·mm-1. That means the uniformity of flow field in the annular region is improved. The fluctuation of tangential velocity near the rotor cage’s entrance decreases from 2.7 n·s- to 0.8 m·s-1. It indicates that the tangential velocity distributes uniformly, so that the particle size distribution of fine powder product becomes narrow. The inertia counter rotating vortex between blades decreases because of the decreased blades spacing. Radial velocity in the blades channel distributes uniformly. Fine powder particles enter into the rotor cage rapidly, which reduces the possibility of the fine powder back-mixing the coarse powder. And the classification accuracy is improved. The CaCO3 experiments indicate that: When the inner and outer radius decrease 18 mm, the classification accuracy increases 3.3%-25.4%, and fine powder productivity increases 27.8%-76.2%. These experimental results are in good agreement with the simulation results.The blades spacing changed by changing of the number of rotor cage’s blades. With the same rotor cage’s inner and outer radius, there is a best blades spacing to make the flow field stable. By studying the different blades spacing of different rotor cages, it is found when the ratio between blades spacing and blades width is 0.23 that the radial velocity between blades distributes most uniformly. The particle trajectories in blades passage are simulated when the ratio is 0.23. The the particle trajectories are simple between blades, and the particles can not collide with blades easily. Fine particles can pass into the rotor cage quickly, which can avoid the fine particles back-mixing to coarse particles. The classification accuracy is improved obviously.