Estimation of Liner Design in a Tube Mill by Discrete Element Method

Abstract

１．IntroductionMany industries have large-scale ball mills in grinding processes because the ball milling is one of the easiest methods for producing powder, and size reduction is, of course, one of the most important unit operations. For example, in a cement production process, the grinding is taken in initial and final stages. The raw materials of limestone, hematite and silica solids are ground in a tube mill at the initial stage, and cement clinker, which is produced by calcinations in a rotary kiln, is also ground with gypsum to produce the final product. It has been reported that about 100 kWh of electricity must be needed to produce 1.0 ton of cement, and more than 60% of total electricity is consumed in the grinding process 1) . The wear of balls is another serious problem; e.g. it was reported that the consumption of balls is 850 g/day 2) . Therefore, it is important to g rind materials with high g rinding eff iciency, and optimisation of ball milling is necessary.Most of tube mills have liner on the inner mill wall as lifter in order to increase the grinding efficiency, and ball charge motion is sensitive to the shape of liner 3) . There are several investigations into the tube milling [4][5][6] , and analysis of tumbling ball milling by using a computational simulation based on the Discrete Element Method (DEM) 7-10) had been developed. The ball charge motion with considering presence of powder was simulated by Authors 11) . The effect of presence of powder in a ball mill was considered by frictional coefficient, which was obtained by an angle of repose of powder sample. The authors had proposed the impact energy which was calculated from the relative velocity on the collision, and the correlation between the grinding rate in the experimental work and the specific impact energy of balls was found out 12) . This relationship was given by a straight line, regardless of grinding conditions; e.g. mill scale 13) , ball-filling 14) , ball size 15) or ground materials 16) . The specific impact energy is also useful for the designing of the planetary ball mill. The pot rotational direction and speed ratio between pot and disk rotations were optimised by the impact energy, 17) and the scale-up method of the planetary ball mill was proposed 18) . Therefore, this impact energy has a high potential to estimate the grinding performance in an industryscale tube mill. The tube mill in cement industry has liner on the inner mill wall, and there are several liner designs. People want to know the effect of the liner shape on the grinding performance, however each mill has some compartment with different liner shape, and the type of classifier is also different. Thus, it is quite difficult to evaluate the effect of the liner design on the grinding performance.In this paper, the modelling of the liner in the tube mill was conducted by DEM. Ball charge motions in five tube mills having different shapes of liner design; i.e. MODEL I (duolift), II (steps), III (step wave) and IV (lifter liner), and O (without liner) are simu...

Investigation of Part Detachment Process from Printed Circuit Boards for Effective Recycling Using Particle-Based Simulation

“…To estimate parts detachment and board breakage indirectly, collision energy at each collision between a particle and another particle, or a wall was calculated. Various models are available to calculate collision energy 14,[16][17][18] . In this study, the collision energy was de ned as…”

Fundamental Study of Parts Detachment Mechanism from Wasted Printed Circuit Boards in Agitation Mill

“…In this simulation, collision energy between particles or particle and wall was calculated from kinetic energy at the instant of impact, as follows [22][23][24] .…”

Speed-up of computing time for numerical analysis of particle charging process by using discrete element method

“…Discrete Element Method (DEM) (Cundall and Strack, 1979) is one of the most famous and reliable simulation methods for the numerical analysis of solid particle behavior, and many researches on the particulate processes; such as hopper (Cleary and Sawley, 2002;Zhu et al, 2006;Ketterhangen et al, 2008), rotating drum (Yang et al, 2003;Taberlet et al, 2006), blast furnace (Yuu et al, 2005;Zhou et al, 2005;Mio et al, 2007a), particle breakage (Moreno et al, 2003;Thornton and Liu, 2004), mixing (Bertrand et al, 2005;Arratia et al, 2006), electrophotographic system (Severens et al, 2006;Mio et al, 2006a), ball milling (Rajamani et al, 2000;Gudin et al, 2006;Mio et al, 2007b), fluidized bed (Kaneko et al, 1999;Kawaguchi et al, 2000;Kafui et al, 2002) and so on, have been modeled by using DEM. They have given many significant results and useful information, however there is still important issue on DEM work; i.e.…”