Study On The "Fish-Hook Effect" And Dispersion Of The Powder In Turbo Air Classifier

Turbo air classifier is widely used to prepare powders in the fields of cement, mineral processing, chemical industry, food processing and medical industry. With the development of modern science and technology, all these industries have put forward more and more strict demand on classification efficiency and classifying precision. So how to improve the classification efficiency and classifying precision is the heated research focus currently. But up to now, researches on the flow field are still limited, and the theoretical analysis is not very clear either. So the study on the classification principle, the "fish-hook" effect and the dispersion of powder in this paper has great scientific meaning and practical value and will give a new way for the improvement of classification efficiency and classifying precision of turbo air classifier. From the micrographs of the powders and the observation of the settling out of particles in water medium, a conclusion can be drawn that the finer the particles, the worse the dispersion result is. Contrarily, the bigger the particles, the better the dispersion result is.The superfine of particles during the process of classification will make "fish-hook effect" happened on Tromp curve worse and lead to the decrease of classification efficiency. This paper studies the "Fish-hook effect" in Turbo air classifier. In terms of the experimental results, the factors that influenced on the "Fish-hook effect" during the process of classification, such as rotating speeds of rotor, velocity of air inlet, feed rate and dimension of the particle of raw material are analyzed. The result showed that with the increasing rotating speed of rotor,Tromp curve moves left, which makes particles agglomeration easier and the tail of hook drive up; Enhancing feed rate makes the solid concentration in classification room increased, followed more often by particles colliding and more seriously agglomerating; Increasing velocity of air inlet can make material dispersed better, less fine powder entered into coarse, fish-hook effect weakened and classification efficiency increased; particles fined further are easier to agglomerate, which makes fish-hook effect more serious, classification efficiency lower and classification precision higher.By analyzing the dispersion principle and mode of air-turbo classifier, we point out that the classifying precision and the dispersion property of turbo air classifier can be improved by changing the structure of carrying dish and the distribution of frequency. According to the analysis of the experiment results, conclusions can be drawn as following: Enhancing velocity of air can highly improve the dispersion of powder and the classification precision. The improvement of dispersion of fine powder caused by increasing velocity of air is more than that of coarse powder in the classifier. Although the increasing of rotating speed made powder dispersion worsen and classification precision reduced, it has greater influence on the dispersion of coarse powder than finer powder in the interior of the classifier. So in order to get higher classification precision in practical production, rotating speed and velocity of air should been changed together.