Measuring the efficiency of the tumbling mill as a function of lifter configurations and operating parameters

Abstract

Grinding mills used in the mining industries are the most energy-intensive operation and also require a large number of wear resistant materials, which are utilized for mill liners and grinding media. In this research, the measuring method was successfully developed by custom-building the batch mill that facilitates changeable lifters and is equipped with a state-of-the art load cell for force measurements. The method was then used to study the effects of different lifter configurations and operating parameters on the mill efficiency and performance. The MillTraj software was also utilized to simulate the outermost charge trajectories in terms of lifter profiles and mill speeds. For the mill with higher mill load and lower speed, the power draw of the mill differed slightly for the different lifters with the same face angles of 20o. Rail lifter drew higher mill power and lower power for Hi-Lo lifter. The Hi-Lo lifter relatively indicated improvement in the energy efficiency of the mill approximately 22%. For the mill with lower mill load and higher speed, the power draw of the different lifters also showed a slight difference. The energy requirement of Hi lifter also varied slightly than the other lifters. In this case, the Hi lifter showed improvement in the energy efficiency of the mill approximately 6.7%. The product sizes of the different lifters become finer than at the higher load and lower speed. The breakage rates were found to closely fit the first-order and the Hi lifter demonstrated higher rate than the Rail and Hi-Lo lifters. The Hi lifter at the certain operating conditions would better improve both the mill efficiency and breakage rate. The trajectory simulations at the given operating conditions, particularly at higher mill speeds showed the actual mill charges of at least 31% should be applied to direct trajectories impacting on the toe of the charge for more effective milling and lower mill shell/liner wear as well. At 80% critical speed, the power draw of the different lifters decreased compared with lower mill speeds and size distributions were coarser than at 74% critical speed. In this case, the outer charge trajectories of each lifter could go down on the mill shell rather than on the toe of the mill charge, resulting reduced power draw and also ineffective grinding.