Numerical Stimulation Study On Optimization Of Ring Nozzle Structure

The operation condition of medium speed mill has a great effect on the normal operaton of the boiler.Improving the performance of medium speed mill is an important way to enhance the stability and to promote the energy utilization efficiency of the boiler system.There is few research conducted on mills by means of numerical stimulation.And there is few research on the structural optimization of nozzle rings.Researches on flow structure,gangues discharge and pulverized coal separation properties was carried out in this essay,and the influence of ring nozzle blade inclination on the flow structure and properties of the medium speed mill was studied.Firstly,the numerical stimulation on the flow structure inside the mill was conducted.And an analysis on the influence of ring nozzle blade inclination on the flow structure was based on this.When ring nozzle blade inclination is 40°,45° and 50°,the average axial speed of the flow at the exit of the ring nozzle is separately 52.07m/s,45.32m/s,36.37m/s,the tangential speed is separately 52.07m/s,45.32m/s,36.37m/s.The difference in average tangential and axial speed will lead to the difference in the flow's structure in the whole mill.As for flow resistance,the ring nozzle and the four outlets of the mill are positions where the flow resistance reaches the maximum.An analysis on the coal particle coupling flow field was conducted based on the stimulation results of the non-coupling flow field,and the velocity,pressure and pulverized coal distribution inside the mill was obtained.The results showed that the injection of pulverized coal affects the flow structure mainly by decreasing the flow speed,and it has little affect on the velocity,pressure and pulverized coal distribution inside the mill.As for pulverized coal concentration distribution,the areas where pulverized coal concentration is high coincides with that of high speed.The influence of ring nozzle blade inclination on the gangues discharge and pulverized coal separation performance of the mill was studied by numerical simulation based on the pulverized coal coupling flow field obtained beforehand.The results showed that when blade inclination is 45°,the ratio of low-density gangues deposition is 3.65%,the ratio of high-density gangues deposition is 13.19%,the mill has the best gangues discharge performance.The mill also has the best small coal particle transportation performance when blade inclination is 45°.Comprehensively,the medium speed mill has the best performance when nozzle ring blade inclination is 45°.Basing on all these researches on the flow structure and performance of the mill,the structure of the ring nozzle that optimizes the performance of the mill was determined.