Plant Equipment and Hire February 2020 | Page 24

INDUSTRY EQUIPMENT: MINING it is not that economical to mine with a surface miner,” Fennell adds. Frequent questions are about fuel consumption and maintenance, especially replacing tips on the milling drum. “It all depends on how hard the material is that you are mining, how fast you are driving the machine and how deep you are milling. There is a lot of variation. You cannot say that because you change one or two tips at 200+ hours in Botswana harvesting salt, which is a very soft material (although very corrosive) the same would apply to an iron ore mine in Australia, for example. In a coal mining operation, you will have to change tips more often than in the salt mines for example, but less than in an iron ore operation,” Fennell explains. “If compared to the cost of a traditional surface mining operation, and all the steps in the process that the surface miner eliminates, the machine is more fuel efficient per ton,” he adds. Coal mining’s potential The biggest potential for the surface miners lies in the coal mining industry. It is ideal for the way Australian and India mines their coal deposits, however, South African coal mines seems to be battling in breaking the traditional way of mining,” says Fennell. Fennell says that surface miners offer significant advantages in the reduction of contamination experienced in normal open cast mining methods. In the coal mining industry, the breakage of coal occurs throughout production, from extraction at the face to end use. While some of this breakage is intentional, such as during extraction and crushing, breakage occurring during transportation, stockpiling, sizing or washing Lingering questions The surface miners are ideal for large coal mining operations. is not desired. Generally speaking, breakage behaviour depends heavily on geology, but mining technology of today offers the option to reduce the amount of fines generated during production to maximise coal recovery for optimised operation as well as minimising contamination of mined coal to increase yields. Most coal mines measure the particle size distribution (PSD) of their plant feed to obtain information about the suitability of the feed for their processes, especially with regards to fines content. However, few mines know precisely where these fines come from and even fewer measure the fines content at the face to compare it with the plant feed data and to optimise the connecting processes. “There are a number of challenges associated with failing to optimise this connecting process. The cost of washing coal fines is higher because of the intensive processes used and the product losses that occur, all resulting in a lower rate of recovery. With increased losses, more tailings must be suitably disposed of and coal that does not meet the customer’s size requirements cannot be sold. Furthermore, coal mines have the tendency to retain moisture, which can cause problems in the downstream process,” says Fennell. “On the other hand, optimising fines content and reducing contamination of the run-of-mine (ROM) coal offers numerous savings and benefits, such as a lower level of respirable and airborne dust, increasing workplace safety, reducing the risk of coal dust explosions and improving yields,” adds Fennell. PSD field tests The material can be loaded directly from the conveyor into the haul truck. 22 JANUARY/FEBRUARY 2020 In Wirtgen’s many field tests over the years on PSD and material degradation, coal and sedimentary ore from eight different pits were analysed to obtain their PSD. Close to 8 000 tons of material was screened to compare the material produced by surface miners versus conventional mining methods. In one coal mine, Wirtgen surface miners operated alongside dozers that employed the conventional rip-and-stack method and in view of the coal prices at the time, the mine was optimising every step of the operation. This included www.equipmentandhire.co.za