Study On Structure And Classification Performance Of A Turbo Air Classifier

In the powder industry classification is one of the most important basic operation, which makes the particle size suit to the demand of powder product. As the third-generation dynamic air classification equipment, turbo air classifier has high classification precision and good classification performance. As we know, the key technology of turbo air classifier is as follows: dispersion and separation. In this study, mechanical dispersion of raw materials and the flow field characteristics in the turbo air classifier were investigated and analyzed.The mechanical pre-dispersion equipment was installed in a turbo air classifier before the raw materials were classified. Raw materials were suspended to disperse and conveyed into classifier by pressured airflow. The classification experiments of ground calcium carbonate and cement raw meal were made and the effect of mechanical pre-dispersion on classification performance was investigated under different operating parameters. The results show that on the high air flow rate condition the effect of different feeding manner on the classified particle cut size is unapparent and employing the dispersing equipment classification precision is improved enormously; the result that classification precision of cement raw meal is higher than that of ground calcium carbonate demonstrates that the dispersion equipment was suit to raw materials that are agglomerated largely because cement raw meal powder is prone to be agglomerated with contrast to ground calcium carbonate due to their particle size and difference nature of particles.Velocity measurement of the flow field in the passageway of two rotor blades in a turbo air classifier was performed by laser Doppler velocimeter (LDV). Three dimensional velocities of flow field under various operating parameters—inlet air velocity of the classifier volute and rotation speed of the rotor were measured. The effect of different operating parameters on the radial velocity distribution is more intense than that of the tangential velocity distribution. From two dimensional vectorgraphs of the tangential and radial velocity it is seen that intensity, position and rotational direction of a vortex is different under different operating parameters. By adjusting experimental operating parameters, intensity of vortex decreases. The classification results testify the measurement results of flow field.The axial velocity is in evidence because of the rotation of the rotor and the present of negative pressure. The axial velocity distribution is not uniform in the classification region of rotor blades and the value is in relation to the inlet air velocity and the rotation speed of the rotor. In the axial direction the axial velocity increases gradually. Because of the present of vortex the axial velocity distribution near different rotor blades is different. Horizontal boards are installed in the blades so that the axial velocity decreases in a certain extent. So flow field is optimized.