Elaborate Classification of Fine Particles by Modified Type Cyclone and Its Optimization

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Experimental studies were conducted on the classification of fine particles by use of a modified cyclone with movable 50% cut size on a bench scale. The 50% cut size of cyclone changed from 1 to 10 , u m by the change of apex cone height and blow-up flow rate. When the height of apex cone was higher at a constant blow-up flow rate, the 50% cut size increased. The reason for this was due to the fact that a decrease in the effective cross-sectional area near the inlet of the dust box gave rise to the increased average upward fluid velocity.In the case of blow-down, two kinds of different-sized fine particle were obtained simultaneously. When the blow-down flow rate was 5%, collection efficiencies of 4 and 28% were obtained with mean particle diameters 2 and 6 mu m respectively. When both the blow-down method and a movable guide plate at the cyclone inlet were used, particles of average diameter of 1.5 mu m were collected. Although the cyclone diameter was 400 mm, elaborate classification of fine particles was achievable.In order to obtain the information of the high-performance cyclone classifier, three-dimensional numerical simulation and experimental studies were conducted on the fluid flow and particle trajectory in a cyclone classifier with and without blow-down. By use of blow-down method, the overall separation efficiency of a cyclone is higher than the case without blow-down. From the results of simulation, the reason for this is found to be the fact that downward velocity components near the conical wall are stronger in the case of blow-down compared to the case without blow-down.