MechChem Africa May 2018

The payback from efficient mill liners

According to Sam Hearn, global sales and business development manager at Multotec Rubber, there is a misconception that mill liners are expensive purchases. In this article he explains that the liners only cost between 10 to 20% of the operating cost of a mill, and that the cost of power is far greater. In addition, the efficiency of the mill liner relates directly to recovery efficiency of the downstream equipment.

One of the major costs associated with operating a minerals processing plant is the specific cost of power in kWh/t and this is significant becausewhen the efficiency of the closed-circuit mill is reduced, the material is essentiallybeing treatedmore thanonce. This is amajor additional cost factor, but oftenone that is not apparent. Sam Hearn, global sales and business development manager at Multotec Rubber says that a hurdle that needs to be jumped is the misconception that the mill liner is an expensive purchase. “Once we have engaged with the plant engineers and drawn to their attention that the liners only cost between 10 to 20% of the operating cost of a mill, and that the cost of power is far greater, we then have their attention,” Hearn says.” Power is a monthly expenditure for a plant and in most cases is not directly allocated to the mill’s operating costs, yet power accounts for about 60% of the total operating cost for that mill.” He says that if it is accepted that thepower cost is 60%and the liner cost is 10%, then the balance of the mill’s operating costs can be attributed to the grinding media. “This is an area which can be adversely affected by liner profile and charge trajectory, so Multotec takes special care to ensure the design is cor- rect,” he explains. Worn liners allow more slippage of the charge and this results in an acceleration of

“ T he correct time to change mill liners is when the efficiency of the mill drops and not when the lining is completelyworn.” This is according to Spike Taylor, managing director of Multotec Rubber, who goes on to explain that the efficiency of the mill liner relates directly to recovery efficiency of the down- stream equipment, and that plant operators need to adopt a far more proactive approach in this regard. “A further ramification of waiting too long to change out the mill lining is that the fresh feedratewilldecreasesignificantlybecauseof thehigherrecirculatingload,and thiswill have an obvious impact on production throughput of the plant,” Taylor says. Spike Taylor, managing director of Multotec Rubber, and Samuel Hearn, the company’s business development manager.

The correct time to change mill liners is when the efficiency of the mill drops and not when one thinks the lining is completely worn. lifespanof the liner and the point atwhich the mill will become inefficient. The automatic measurement and display of the charge level is valuable in confirming that the operation of themill is correct and this value is essential in calculating the trajectory. Highly skilled technicians take thedata ac- quiredbyMultoScan and leverageMultotec’s Hawkeyeproprietaryprogramme to interpret and analyse the data. Significantly there is no time lag on the information analysis, which makes the level of responsiveness possible unprecedented, and allows customers imme- diate feedback on the condition of the liners and any immediate issues can be addressed on the spot. Multotec Rubber has a sound reputa- tion with its customers where the use of its MultoScan system has been implemented. Using the MultoScan measurements and the SCADA data that the company receives from customers, it is possible to generate an accurate report on the performance of the mill. This enables Multotec’s technical team to engage with the mill operator directly in terms of mill performance and costs. “In many instances, it is possible to make recommendationsbasedon thisdatamotivat- ing for an earlier mill liner change out as this can dramatically reduce operating costs and increase overall plant efficiency,” Hearn ex- plains.What ismost important in this scenario isMultotec’s ability touse the data generated to accurately determine the actual payback period for the new lining. q

the wear rate, which can lead to the pre- dicted life not being achieved. Sudden re- placement require- ments mean that more frequent liner measurements need to be taken as the lin- ers near the end of their lives. The introduction of MultoScan several years agomade it pos- sible for plants to ac- curatelymeasuremill liner profiles. Using this information, end users can easily and accuratelypredict the

Highly skilled technicians take the data acquired by MultoScan and leverage Multotec’s Hawkeye propriety programme to interpret and analyse the data.

12 ¦ MechChem Africa • May 2018