Investigation Of The Classification And Grinding Performance Of Opposed Fluidized Bed Milling Process

Supersonic speed airflow grinding process is a rapid development ultrafine grinding technology in recent years. Because it has a higher grinding intensity, thermosensitive resistance,its powder production has ultrafine size, narrow distribution, less contamination and can use of inert gas in the grinding process. It has widely applied to the preparation of pharmaceutical, chemical material and specialty powder refinement industries.Firstly this paper uses the aerodynamic foundation theory to calculate the flow condition of the supersonic laval nozzle related to the grinding and calssification performance of airflow grinding milling,including the different work conditions of nozzle, kinetic energy and velocity on the outlet of nozzle and particle motion in the the opposed jet flow.In order to investigate the influence of different condition about grinding gas pressure, back pressure and classifier rotational speed on the performance of air grinding and particle classification. It establish a three dimensional model of a fluidized bed jet milling and then simulate the flow field of the grinding zone, fluidized zone and classification zone in the airflow grinding milling using computational fluid dynamic software. Then use the gas-solid model to simulate the separation diameter and classification efficiency of the inner classifier and investigates the effects of different classifier rotational speed and inlet pressure on the separation diameter. The result show that, low rotational speed and grinding gas pressure less then0.4MPa can cause airflow flow out of the impeller, which would cause the classification efficiency decreased. The lower rotational speed the more total number of particles larger than the separation diameter leaving the classifier, but it’s beneficial to particles circulation in the conditions of low grinding gas pressure. The influence of classifier rotational speed on separation diameter is greater than pressure on the nozzle inlet, and the higher height of the classifier, the more non-uniform distribution of separation diameter along the height of classifier.A fluidized bed jet milling system was established, which includes jet grinding, classification and dust collecting unit. It completed the experiment of ultrafine grinding coal powder at room temperature under the condition of low air grinding pressure using this system, simply investigate the influence of classifier rotational speed and nozzle grinding gas pressure on the number-average diameter, distribution uniformity, and sphericity degree in the grinding process. The results show that, At low rotational speed less then1200r/min, the system back pressure have a greater effect on the grinding particle number-average size, particle size distribution and sphericity, but the effect is small at high rotational speed. While as meeting the size requirements of the grinding demand well as possible to increase the back pressure to improve the grinding efficiency.Finally, experimental research of grinding coarse particles of waste rubber use of liquid nitrogen is processed by the fluidized bed jet milling system, it investigate the influence of freezing temperature, grinding gas pressure and classifier rotational speed on the number-average diameter, distribution uniformity and sphericity degree, it’s also studied the morphology of particles under different operating parameters. The result show that, air grinding pressure has little influence on the number average particle diameter, maximum number-average diameter value variation only change28.9%at same rotational speed. Particles are mostly lamellar structure when the nozzle inlet pressure is0.75MPa, the getting production is most coarse in the lower rotational speed. Particle fracture surface are more regular and smooth with the rotational speed increased. Cryogenic condition increases the rate of brittle fracture for such ductile materials like rubber material. The crack of lamellar particles sectional obtained under cryogenic conditions significantly reduced, and the lower the freezing temperature, the more smooth the sectional surface.