Numerial Simulation Of Separation Character For Mill Separator Of Medium Speed Coal Pulverizer

With the development of national economy, energy source comes to be the chief issue. Saving and a reasonable use of the energy source is a main part of scientific development concept. Electric power should develop first in the development of economy; thus, many scholars pay their attention to research how to save the energy when developing electric power.Mill separator is the main equipment in power station and other pulverized-coal systems of burning coal set, it has a huge influence on contribute and function of the mill. Classify efficiency and the size of coal powder at the export of the mill separator have an directly influence on the security, the stabilization and economy of the combustion in the hearth. It's difficult to analyze the interior flow through experiment because of a complex equipment structure, a large energy consumption when operate, an actual larger interior size and high temperature of the boiler. So research flow and velocity character of mill separator through CFD simulation is feasible in this thesis.In the past few decades,with the development of the calculation technique and the advance of the computer, computational fluid dynamics (CFD) has become more and more as a modern alternative for reducing the use of wind tunnels in automotive engineering. Now CFD is widely applied to various stages of aerodynamic design of automobiles. By contrast to the tunnel test, CFD is cheaper and takes less time to complete. However,the present CFD technology has still many problems to be solved for turbulence ,and it seems to be difficult to find an appropriate turbulence model to universal situations.FlUENT software is used in this thesis to simulate several work conditions of classify character and flow character of the mill separator. The main work done as follows:1 Analyzed the principium of radial classifier and read lots of literature on gas and liquid flow, chose a reasonable model, established a three-dimension model by CATIA software, plotted girding by guiding GAMBIT, researched the performance of radial classifier by single gas flow and gas-liquid double phrases flow separately. A k-epsilon onflow model was used in single gas flow research and a disperse model was used in gas-liquid double phrases flow research.2 The result of single gas flow research for radial mill separator shows, gas has different velocity and angle when flowing different parts of radial tailing where the volume and the shape changes. The flow character and the swirl flow shape of axial interface and radial interface are clear to see. High flow velocity of integer flow field is come out in seldom areas. And high quality is needed in these areas, especially the damper where the velocity and press change acutely and get damaged easily. So maintenance is needed to guarantee the efficiency of mill separator.3 The result of gas-liquid double phrases flow research for radial mill separator shows;Choose different degree of damper 35, 45, 55, the drag force of the gas is crucial when the particle is small in mill separator, the gravity and the resistance have little influence. The particle can go out of the exit of the mill separator easily with airflow. The gravity get strengthen when the diameter of the particle grows, and the drag force, the separation force, the gravity and the resistance act on the particle together, so it's difficult to analyze the condition of the particle. One part of the particle flow with airflow, the other goes back to the exit of the mill separator. When the diameter of the particle keeps on grows, the drag force of the particle can't generate separation force. The main force acted on the particle is the gravity and the resistance. Most of the particle is selected back to the pipe. A conclusion would make that with the diameter of the particle grows, the effect of drag force grows with a square multiple, and effect of the gravity grows with a cubic multiple. When the effect of drag force and effect of the gravity get close, the condition of the particle is most complex and the track of the particle is most difficult to analyze.Choose the degree of damper is 50, the particle will be random classified by Rosin-Rammler. When the velocity of the airflow is slow, the efficiency of mill separator is lower, and a high velocity of the airflow will confuse the track of the particle, which will reduce the separation efficiency and make it difficult to analyze movement law of the particle.4 Reconstruct radial mill separator to be axial mill separator rationally. Change the radial 16 leaves damper to 32 axial dampers. The result shows: The performance of mill separator improved, axial mill separator has a simple configuration, without centrum and the resistance are smaller, the unnecessary turn round coal powder reduced. So the separation performance of the coal powder is improved and the energy gets saved. The exit area of the mill separator is smaller than the entrance area, it's useful to enhance the flow velocity, and strengthen the following force of the airflow under the same condition. The velocity of the airflow is slower and the fray is smaller in axial mill separator, so axial mill separator gets a longer life.