Papers by Keyword: Turbo Air Classifier

Abstract: The classification performance of a dry classifier depends on cut size, classification accuracy, classification efficiency, classifier process capability, and yield of fine powders, which should meet the required particle-size distribution. Consequently, the classification performance indices limit each other and only a comprehensive assessment of these classification performance indices can evaluate the classification performance truly and synthetically. In the present paper, the Analytic Hierarchy Process is used to calculate the weights of the classification performance indices after determining the hierarchical model. The dimensionless transformation eliminates the effect of the different dimensions. Then, the comprehensive assessed value of the classification performance for each experiment is obtained using the linear weighted method. The maximum value corresponds to the best classification performance among these assessed values. In the present study, a turbo air classifier was used as the classification system and talc powders were used as materials. The best classification performance indices were a cut size of 21 μm, a classification precision index of 0.6, a Newton classification efficiency of 61%, and a yield of fine powders of 57%. The corresponding optimal operational parameter combination consists of a feeding speed of 1.1 kg/min, a wind speed of 8 m/s, and the rotary speed of its rotor cage is 1200 rpm. This assessment method avoids the limitation of evaluating a single classification performance index and the incomplete information derived from single factor experiments. Furthermore, the method also provides quantitative evaluation criteria for the classification performance of a dry classifier. In the proposed method, the classification performance indices can be selected and the comparison matrix can be set flexibly according to production requirements.

Abstract: Talc powder is widely used in building engineering, especially preparation for coating, waterproof material and ceramics. With increasing demands for building material quality, the requirement for the particle fineness and particle-size distribution of talc power becomes higher than ever. A new method of process parameters analysis on turbo air classifier for talc powder is put forward in this paper. The effect of the two process parameters on a classification performance index is reflected visually through the 3-D drawing based on Matlab, so the one-dimensional process parameter analysis method is expanded to the two-dimensional process parameters analysis method. In the present study, a turbo air classifier is used as the classification system and fine talc powder is used as materials. The sample data is gathered through setting different process parameters. The experiment results show that process parameters analysis can be implemented quickly and visually. In actual production applications of turbo air classifier system, the user can select the suitable process parameters flexibly considering the production requirements according to the 3-D meshes based on Matlab. This method is also applicable for classification of other powder.

Abstract: The turbo air classifier is one of the most widely used equipment in powder classification. The complex flow behaviour inside it, however, prevents material experiments from providing information about its internal separation mechanisms. A study of the interaction of structural variables is therefore undertaken examining air flow behaviour, specifically the air flow between the blades of the rotor cage. The investigation of these flow field characteristics made use of the computational fluid dynamics (CFD) to simulate the air flow in the classifier. It was found that the inlet velocity of the turbo air classifier and the rotary speed of the rotor cage are two of the dominating, non-structural factors that affect velocity distributions in the region between the rotor cage blades. Once the inlet velocity settles, a critical rotary speed must be present to smoothen the flow field between the blades, resulting in an excellent classification performance. Three-dimensional velocity measurements of the region between the blades by laser Doppler velocimeter (LDV) were performed to test the results of the flow field simulation. This revealed that when inlet velocity is invariable, the velocity distributions in the region between the blades are at its most symmetric with the critical rotary speed of the rotor cage making it more favourable for classification. The velocity measurement results are likewise in good agreement with the results of the flow field simulation. Newly structured rotor cages are also simulated and compared with a conventional turbo air classifier, air flow in the newly structured model is smoother. The distributions of radial and tangential velocities are more symmetric and the trend of the rotating vortex between the blades attenuates, particularly when the rotary speed is high. The newly structured rotor cages can therefore achieve higher classification performances.