Converting AG to SAG mills: The Gol-E-Gohar Iron Ore Company case

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  • hmic

    f thiny an(5

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    ease inimporreasonbrokentheir e

    gle lifte, especall on lakage.

    ment towards the use of larger diameter steel grinding balls in

    height have been incorporated in shell lifter design. Increasing shell

    ling (DEM) computer programs that model charge ow in mills. DEM

    Powder Technology 217 (2012) 100106

    Contents lists available at SciVerse ScienceDirect

    Powder Te

    e lsorder to increase grinding efciency. A traditional top ball size wasaround 104 mm. Currently, 125 mm balls are in common use withsome mills using 140 and 152 mm balls (165 mm balls are nowbeing proposed). These developments have required a new approachto liner design through consideration of charge motion, especially themotion of the steel media in the mill. Aims of new designs are to im-prove the effective grinding through changes in shell lifter face angles

    helps to understand chargemotion in SAGmills for given liner designsand lifters, ball and rock properties and mill operating conditions.Based on the success of the 2-D model of the SAG mill the 3-D modelin DEM was developed. The model could help to study charge motionand energy draft more accurately and also could provide informationregarding the effect of shell liner spacing as well as lifter face angleon charge motion. [3,8,9,11,15,21,22].and the spacing of the lifters [13,20,23,26].It has been known for many years that a

    on SAG mill shell lifters results in a change

    Corresponding author. Tel.: +98 341 2515901; fax:E-mail address: banisi@uk.ac.ir (S. Banisi).

    0032-5910/$ see front matter 2011 Elsevier B.V. Alldoi:10.1016/j.powtec.2011.10.014g to improved mill per-en the parallel develop-

    The availability of large-scale cost-effective computing power inrecent years has allowed the development of Discrete ElementModel-and improved ball-on-charge impacts, leadinformance [23,25]. Furthermore, there has beThe availability of these mills plays anics of the operation. One of the mainthe time required to change worn orble advantage of SAG over AG mills ising feed hardness variations.

    The use of liners with large face aner spacing has grown in recent yearsThe claimed benets were reduced bincreased liner lives and less ball bretant role in the econom-s for mills down time isliners [1,27,28]. A nota-xibility in accommodat-

    rs along with wider lift-ially in large SAG mills.iner impacts, leading toThese reduced packing

    Charge trajectory modelling has been used to present and interpretaggregate motion of a number of balls critical to the performance ofthe mill [24,25].

    Lifters are essential elements in the tumbling action of a grindingmill, whose purpose is to prevent slippage of the mill charge. Suchslippage consumes energy without substantial breakage, and themill may not lift the charge sufciently high to promote impactbreakage. Hence, the size, shape and number of lifters have a strongimpact on the tumbling action of the media [4,18].the mineral industry has been on risein capital and operating costs and incro a signicant reductionthe plants throughputs.

    lifter face angles (for the same mill speed) does reduce the impactpoint of thrown balls and can reduce shell liner damage [19,23,29].The use of large AG (autogenous)/SAG (semiautogenous) mills indue tConverting AG to SAG mills: The Gol-E-Go

    M. Maleki-Moghaddam, M. Yahyaei, S. Banisi Shahid Bahonar University of Kerman, Mining Engineering Group, Engineering Faculty, Isla

    a b s t r a c ta r t i c l e i n f o

    Article history:Received 30 June 2011Received in revised form 11 September 2011Accepted 10 October 2011Available online 14 October 2011

    Keywords:SAG millMill llingLifter face angleBall trajectory

    At the concentration plant omills (xed speed) are usedthe target value indicated b515 m and low power drawangle from 7 to 30 while ketrajectory. When the propos5% (v/v balls were added t501 m.

    1. Introduction

    j ourna l homepage: www.change in the face anglein the trajectory of the

    +98 341 2112764.

    rights reserved.ar Iron Ore Company case

    Republic Blvd., Kerman, P.O. Box 761175-133, I.R. Iran

    e Gol-E-Gohar Iron Ore Company (Iran) three 9 m2.05 m AG (autogenous)parallel in a dry operation. The performance of AG mills has been lower thanincrease in the product size (P80; 80% passing size) from 450 m (target) to0% of nominal). By simulation it was found that increasing the liner lifter faceng the original lifter height (i.e., 22.5 cm) could provide an appropriate chargeliners installed in one of the AG mills, the throughput increased by 27%; whenthroughput increased by 40%. The product size also decreased from 515 to

    2011 Elsevier B.V. All rights reserved.

    thrown grinding balls. With the development of trajectory generat-ing computer programs, the effects of face angle, packing and lifter

    chnology

    ev ie r .com/ locate /powtecYahyaei and Banisi [29] used 3-D liner wear modeling to showthat the liner wear along the mill length is not uniform and providedindustrial data from a SAG mill used at the Sarcheshmeh copper com-plex [28,29]. They developed a spreadsheet-based software to modelcharge trajectory in tumbling mills using Powell's [17] analytical ap-proach and investigated charge trajectory change during the lifetime of a liner set. According to Powell if the grinding media is posi-tioned at the tip of lifter it will start its free ight after the point of

  • conversion on a smaller scale, which resulted in higher grinding per-formance [12]. A methodology is proposed beginning with nding an

    number of lifters are entered. In parameter section, static and dynamicfrictions and mill speed for each liner design are entered.

    2.2. The model mill

    In order to determine ball trajectories at different operating condi-tions and liner proles, a 100 cm3.6 cm mill was designed and con-structed. The transparent end of the mill made possible accuratetrajectory determination by image analysis. A 2.5 kW motor with avariable speed drive was used to provide sufcient exibility to testvarious operating speed conditions. A diameter scale down ratio of9 to 1 was used to construct the model mill using the plant mill di-mensions. The mill served as a 2-D model, but there is the possibilityof changing it to a 3-D model mill.

    In order to exactly duplicate the plant liners arrangement in themill, a polyurethane ring was accurately machined to create 36 liftersin a row (Fig. 1). By this method any number of liners in a row withdifferent designs could be tested. Between the lifters 36 plates werealso included consistent with the plant liner design. Only one of thethree sections of the liners along the mill length was built andinstalled in the 2D model mill.

    101M. Maleki-Moghaddam et al. / Powder Technology 217 (2012) 100106appropriate charge trajectory by mathematical modelling consideringvarious liner proles, testing physical models of the selected linerproles in a laboratory mill and nally arriving at a liner design forlarge-scale industrial mills. It is believed for the rst time the trajecto-ry obtained for a single ball is corrected with the introduction of asafe operating window concept. In fact, the effects of charge andliner prole which impose extra forces on balls are taken indirectlyinto account on the charge trajectory calculation through using thesafe operating window.

    2. Materials and methods

    2.1. Charge trajectory predication software

    In order to determine charge trajectory, a software called GMT(Grinding Media Trajectory) was used [29]. The approach taken byPowell [17] was used as a base to determine charge trajectory. GMTin comparison with other software packages has the advantages ofusing all MS Excel readily available functions and capabilities. Themain feature of GMT is the ability to show the kidney-type shape ofthe charge along with the trajectory which has not been incorporatedin similar software packages. Morrell's [16] approach was applied todetermine shape of the charge in which he used a laboratory millwith one transparent end and photographed the load under variousoperating conditions. The variation of the toe and shoulder positionsfor three different liner proles at various mill speeds and llingswere studied in his work. Then he proposed various empirical equa-tions to relate the positions of toe and shoulder and inner load radiusto mill speed and lling. Because of the differences in the calculationof charge trajectory for rods and balls an option in GMT has been pro-vided which enables the user to choose the media type. The dataentry section of the software includes ve parts to be completed bythe user: general information, mill, grinding media and liner data,and parameters. In the mill section, the values indicating the effectivediameter, speed and lling are entered. In the grinding media section,the media type (i.e., ball or rod), diameter and density are recorded.equilibrium. Otherwise, it will start to role or to slide on the lifter sur-face until it reaches the edge of the lifter. Then it will fall into freeight. When the grinding media reaches the edge of liner, the refer-ence frame should change to a Cartesian coordination which its originis positioned at the mill center to simplify the calculations. The speedof the particle composed of its linear velocity parallel with the lifterface and angular speed resulted from mill rotation. These two typesof speeds should resolve into components parallel with Cartesianaxes for calculating the charge trajectory. The free ight of chargewill end when it encounter the mill shell. Yahyaei and Banisi [29]showed that the largest difference in the angles of charge impactpoints along the mill length due to non uniform wear was 34which occurred after 3000 h of operation.

    As the charge volume increases, the greater f