Simulation of vibrated bulk density of anode-grade coke particles using discrete element method

Packing density is an important quality parameter of calcined cokes used in aluminum industry to produce carbon anodes. Vibrated bulk density (VBD) test is a well established method to measure the packing density of coke samples. In the present work, Discrete Element Method (DEM) is coupled with a three-dimensional imaging technique to investigate the possibility of using DEM to simulate the packing behavior of calcined cokes. As the method verified, effects of shape, friction coefficient, size and size distribution of the particles on the VBD of cokes are also investigated. DEM simulations, in accordance with the experiments, show that vibrated bulk density of coke samples decreases as the content of coarse particles in the mixture increases. Moreover, it is shown that friction coefficient has a negative effect on the VBD value and this effect is more pronounced for the samples with lower sphericity. High friction coefficient restricts the movement and rearrangements of the particles and thus vibrational forces cannot effectively rearrange the particles and fill the porosities. Lower sphericity of coke samples not only induces a higher initial porosity level in the samples but it also increases the chance of formation of locks and particle bridges which result in lower VBD. Results also show that sphericity and friction coefficient have a synergic effect on the VBD of coke so that, for the samples with lower average sphericity the rate of decrease in VBD is higher with increasing the friction coefficient.