A new two-stage vertical grinder is designed,which can effectively reduce the middling coal crushing rate and improve the yield of clean coal. To better understand the performance of the grinder,working process of the grinder is simulated using discrete element software EDEM. The material crushing effect is evaluated based on the number of broken bonding in middling coal,and the influence of different coarse crushing speed on broken bonding is obtained. Then,an optimal coarse crushing speed is selected, and...