Study On The Mechaism Of Backflow Undersift Of Three-product Cyclone Classification Screen

Three-product cyclone classification screen, a new efficiency classification equipment for fine coal, is of research significance and applied prospects. Taking inner flow field of three-product cyclone classification screen as investigating subject,this work mainly analyzes the forming cause and influence factor of backflow, which offer fundamental supports for further research.In this work, inner flow field of three-product cyclone classification screen is theoretical analyzed to better determine the calculation model and boundary conditions. In order to improve computation accuracy and computation speed, as well as facilitating post-processing, the structure of three-product cyclone classification screen is simplified, which highlight the research focus. By establishing model in Solidworks, extracting flow field in Workbench, pre-processing in ICEM and simulating in FLUENT, the flow field information in three-product cyclone classification screen is obtained.Based on the results of flow field analysis, the existence of backflow is identified.Furthermore, radical velocity and flow rate are analyzed, which verified the reliability of backflow. According to previous liquid phase screening theory of three-product cyclone classification screen, this work arguments that differential pressure between internal and external side of screen directly causes the backflow. Combing with the Bernoulli equation and the pressure of the FLUENT software, the further analysis shows that the differential pressure between internal and external side of screen is the main cause for backflow. In the undersizd of screen, the external pressure is higher than internal pressure, which causes the backflow phenomenon.Finally, the structural parameters and process parameters influencing backflow is analyzed. When the discharge outlet is located on the bottom of screen, backflow phenomenon will disappear, and the reasonable amplification of discharge outlet diameter can reduce the backflow scale and flow rate. When the discharge outlet is above interface of columns and taper, the backflow rate will decrease as the increase of inserting depth of center pipe; when the discharge outlet is under interface of columns and taper, the backflow rate has no change as the increase of inserting depth of center pipe. In addition, the increase of column height will cause the increase of backflow rate. When the flow rate in entrance is less, the scale of backflow will decrease as the increase of flow rate in entrance; when the flow rate in entrance is beyond a certain range, the scale of backflow will keep stable.In this paper, the research results offer a new view to furtherly study the inner flow field of three-product cyclone classification screen, which provide theoretical direction for structure optimization and process adjustment of three-product cyclone classification screen, as well as promote the equipment’s industrial application.