Study On The Numerical Simulation Of The Double Chamber Vertical Stirred Mill Based On EDEM

With the continuous reduction of high quality coal resources in China,the rational and highly efficient use of scarce coking coal resources,represented by coking coal and fat coal,has received increasing attention.As an intermediate product in the coal washing process,the middle coal still contains a certain amount of clean coal that has not been effectively released and recycled,resulting in a waste of coking coal resources.For the fine-grained middle coal,coal grinding operations can achieve effective dissociation of the coal cohesive connecting bodies at fine scale.However,current coal washing processes rarely involve grinding operations.Therefore,in order to achieve a better dissociation effect,an in-depth study of the coal grinding process is required.The preliminary test of this topic has verified that the vertical stirred mill has better coal grinding effect,and designed a laboratory-type double chamber vertical stirred mill.However,due to the complex grinding process,it is difficult to directly obtain the medium movement law and energy distribution during the grinding process by the test method.Therefore,this paper simulates and analyzes the grinding process of single chamber and double chamber vertical stirred mills based on the discrete element method,and then the relevant parameters of the double chamber vertical stirred mill are optimized,the main contents are as follows:(1)The grinding mechanism of laboratory single chamber and double chamber vertical stirred mill were analyzed,the relevant parameter values required for subsequent simulation tests are determined through the calculation of key parameters such as media filling rate,spiral angle,stirrer rotation speed,stirrer diameter,medium size and medium ratio,etc.that affect the grinding effect of the mill.(2)Using EDEM software,a single chamber and double chamber vertical stirred mill as the research object,a vertical stirred mill media movement process numerical model was established.According to the results of the simulation test,the stability of the media particles during the operation of the mill was determined,and the energy consumption of the two kinds of mills and the movement laws of the media balls inside the mill were compared.The mill performance was comprehensively compared.The results show that the linear velocity of the media ball reaches the maximum at the edge of the stirring spiral blade,and there is a clear velocity gradient in the cylinder.The velocity gradient of the media ball in the double chamber vertical stirred mill is larger.When the unit energy consumption is lower than that of the single chamber vertical stirred mill,the energy conversion rate is 6.38 % higher than the single chamber mill.(3)Based on the above studies,the operating parameters of the double chamber vertical stirred mill have been further optimized.The four key parameters of the media filling rate,spiral angle,stirrer rotation speed and stirrer diameter were selected,and a four-factor three-level simulation test was designed based on the orthogonal test method.The results show that when the contact force is used as the test index,the influence of the stirrer rotation speed is the greatest,followed by the stirrer diameter,and then the media filling rate,the spiral angle is the least affected.When the unit mass power is used as the test index,the influence of the stirrer rotation speed is the greatest,followed by the stirrer diameter,and then the media filling rate,the spiral angle is the least affected.Through comprehensive analysis,the optimal parameter combination of the double chamber vertical stirred mill is obtained,that is,when the media filling rate is 70%,the spiral angle is 22°,stirrer rotation speed is 210 rpm,and stirrer diameter is 140 mm,a better grinding effect can be achieved.