多级配球降低半自磨中顽石积累及改善磨矿效果试验

Hard Rock Accumulation Decrease and Grinding Effect Improvement in Semi Autogenous Grinding by Multi-Stage Ball Distribution

针对新疆某铜镍矿半自磨机顽石积累严重、磨矿效果差的问题,采用离散元法(DEM)模拟仿真实验模拟分析不同级配钢球对顽石的碰撞能量分布及利用率,并在实验室进行半自磨机磨矿循环试验验证。研究结果表明:在此试验中,多级配球在能量利用率方面优于单一球径及偏大级配,多级配球可在提供与偏大级配相同冲击力的情况下增加碰撞次数,从而使能量分布更加合理,且改善磨矿效果的同时降低了衬板磨损;推荐级配钢球较现场级配及偏大级配切向碰撞能量利用率分别提高了8.88%和1.38%,法向碰撞能量利用率分别提高了3.66%和0.92%,推荐级配对衬板的碰撞能量较偏大级配降低了1061.84 J;验证试验中推荐级配顽石产率较现场级配及偏大级配分别降低了4.19%和3.36%,-74μm产率分别提高了4.80%和2.24%。从理论分析及试验验证多级配球可有效降低半自磨顽石积累并改善磨矿效果。

Autogenous mill,as one of the important equipment in grinding operation,has the characteristics of short process and small amount of equipment.The particle size of+100 mm plays a very important role as grinding medium in autogenous mill.The particle size of-80~+20 mm,as the critical particle size,does not participate in the grinding process of autogenous mill,and will block the discharge grid of autogenous mill,which belongs to"hard grinding particles",and is easy to produce hard rock accumulation.In this paper,the capacity ofФ5.5 m×1.8 m(D×L)semi autogenous mill was only 900~1000 t·d^(-1).The problem of hard rock accumulation seriously affected the capacity of the mill.Therefore,it was of great significance to explore the collision energy distribution between different grinding medium gradations of semi autogenous mill and ore,and improve the energy utilization rate of crushed ore for energy saving and consumption reduction of mine.Based on this,the energy utilization of the semi autogenous mill and the collision energy distribution of the grinding medium were analyzed by using the discrete element method(DEM),and the grinding cycle of the semi autogenous mill in the laboratory was analyzed,the reliability of the simulation was verified by experiments.DEM was a numerical technique used to predict the behavior of collision dominated particle flows.Each particle in the flow was tracked and all collisions between particles and between particles and boundaries were modelled.The particles were allowed to overlap and the extent of overlap was used in conjunction with a contact force law to give instantaneous forces from knowledge of the current positions,orientations,velocities and spins of the particles.The results showed that the energy utilization rate of multi-stage ball was better than that of single ball diameter and larger grading.Multi stage ball could increase the number of collisions under the condition of providing the same impact force as the larger grading,so as to make the energy distribution more reasonable,improve the grinding effect and reduce the liner wear.It was recommended that the tangential collision energy utilization rate of graded steel ball was higher than that of existing grading 88%,1.38%,3.66%and 0.92%,respectively.The maximum tangential collision energy of recommended grading was 690 J·kg^(-1),and the maximum tangential collision energy of large grading was 1040.9 J·kg^(-1).The results showed that the maximum energy of single tangential collision of plant grading was only 158.2 J·kg^(-1);the maximum energy of single normal collision of recommended grading was 418.5 J·kg^(-1),the maximum energy of single normal collision of larger grading was 471.7 J·kg^(-1) and the maximum energy of single normal collision of existing plant grading was 254.1 J·kg^(-1);the recommended grading could provide the same impact force as that of larger grading due to the existence ofΦ150 mm steel ball,and the increase of collision times made the grinding medium active and strong.The grinding and stripping effect of chemical grinding medium peeled off the edges and corners of the ore,making the ore nearly round to facilitate the subsequent ore crushing.Due to the larger size of steel balls,the number of steel balls was less under the condition of the same filling rate.In the energy spectrum,the number of collisions between steel balls and ore with self-grinding medium on hard rock was almost the same,which did not highlight the grinding effect of steel balls,although the impact force of steel balls was enough.However,the larger the size of the steel ball,the increase of porosity between the steel balls led to the decrease of the grinding area,and the irregular edges and corners of the ore could not be stripped.The ore could only be crushed by the grinding medium at one time when it was stripped to the appropriate particle size,which also showed that the larger the size of the steel ball was not the better,and the steel balls with the grading of 120 mm in the current plant,although the collision times were in three grades.This was also due to the lack of impact force,which could not effectively impact the crushed ore,so the grinding effect was poor and the problem of hard rock accumulation was serious.Therefore,the rationalization and accuracy of grinding medium was a direction to improve the grinding efficiency of semi autogenous mill in the future,and the collision energy of lining plate was relatively large,and the grading as reduced by 1061.84 J.In the verification test,the yield of hard rock in the recommended grading was 4.19%lower than that in the existing grading,3.36%lower than that in the larger grading,4.80%higher than that in the existing grading and 2.24%higher than that in the larger grading.Through theoretical analysis and experimental verification,multi-stage ball distribution could effectively reduce the accumulation of hard rock in semi autogenous mill and improve the grinding effect.That was to say,under the condition of ensuring enough impact force of grinding medium,increasing the number of collisions was the key to improve the accumulation of hard rock in semi autogenous mill.