DEM Investigations Of Power Draw For Material Movement In Rotary Drums

Rotary drum is an important process equipment for mixing and heat treatment of granular materials.It is usually driven by a DC motor,and the choice of motor driving ability is very important to the design of the rotary drum.The power draw of material movement in rotary drum accounts for 70%-75% of the total power consumption of motor drive,and is thus the focus of the design of motor drive system.In addition,the change of the power draw of material movement directly affects the electrical current of the motor,and is thus usually monitored as an important process variable in practice.Therefore,much efforts have been devoted to the research work on the mechanism of material movement in rotary drums,and several empirical equations have been given to calculate the power draw for material movement.However,most of these empirical equations assume that the particles are mono-sized and distributed homogenously in the drum,and the velocity of the material mass center is representative for velocities of all the particles,which are not in accordance with the actual situation.Moreover,these empirical equations cannot predict the change of the power draw with time.In addition,the influence of the axis offset on the power draw for material movement,which occurs during installation and operation of the drum,is not considered by these empirical equations.With the rapid development of high performance computing technology,the discrete element method(DEM)has become an efficient simulation tool to study the material transport process in rotary drums.With DEM,the velocity information of the material can be obtained on particle level and the results can be visualized.According to the current research on material movement power draw,a DEM model for material movement process in rotary drum is constructed in the present work,based on which the power draw for multi-dispersed material movement and its influence parameters are studied deeply by simulation.The research results provide a theoretical basis for the design and safety monitoring of the motor drive system of the rotary drum process equipment,which is of theoretical and practical importance.The main work of the paper and the results achieved are as follows:(1)Based on PFC3 D software platform,different sizes of particles were used to simulate the uneven distribution of material in the rotary drum,and DEM models were constructed to simulate the material movement in the drum.(2)In order to verify the accuracy of the DEM model,an experimental platform of rotary drum was built and several sets of physical experiments were carried out.The effectiveness of the DEM simulation model was verified by comparing the actual and simulated images of the material,and the measured and simulated characteristic parameters(repose angle,contact number between particles)and the simulated characteristic parameters of the material.(3)The method for calculating the power draw for material movement was studied,and 18 sets of DEM simulation experiments were carried out with varying parameters of drum axis offset,rotational speed and filling degree.The time evolutions of the power draw under different conditions are given.(4)The fluctuation of the power draw profile was studied using Discrete Fourier Analysis Method.It is found that the periodicity of the power draw profile is caused by the axis offset of the rotary drum,and its frequency is the same as the rotational frequency of the drum.The quantitative relationship between peak value,mean value,overshoot of the power draw profile and the axis offset,rotational speed and filling degree of rotary drum was studied by linear fitting method.The results show that the peak value increases linearly with the axial offset,rotational speed and filling degree.However,the average value of power draw is only related to rotational speed and material filling degree,and is less influenced by the axis offset.In addition,the overshoot is only affected by the axis offset.When the axis shift remains constant,the overshoot remains approximately unchanged.