Engineering & Mining Journal

JUN 2018

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Page 52 of 115

VENTILATION JUNE 2018 • E&MJ 51 can offer additional advantages in some applications. A recent paper* highlighted benefits identified by a Codelco engineering team that was tasked with choosing a sin- gle door type to be used for ventilation and fire control throughout the company's huge Chuquicamata underground mine project. Having used "barn door" units — com- prising two panels hinged vertically on the outside edges and opening from the center in one direction — exclusively in its oper- ations in the past, the Codelco engineers analyzed the drawbacks of this door type and decided to take a look at other designs including overhead models as well as the swing-type or "Z" doors. They determined that the swing doors offered a number of benefits for this particular application: • Because barn doors must be configured, for safety reasons, to open in the direc- tion opposite airflow, a certain number of these doors, once installed, would have to be reinstalled — a two-weeklong operation — to work in the other direction as the mine's ventilation plan changed throughout the long construction phase. This could adversely impact construc- tion/production schedules. Swing doors, on the other hand, operate independent- ly of air flow direction. • Although the swing door models evalu- ated by the Codelco team could only withstand about half the maximum pres- sure drop encountered in some areas of the mine, the use of multiple swing doors in an airlock configuration, where need- ed, could overcome this problem. Sup- ply, installation and maintenance costs for the swing doors were estimated to be about 36% lower than barn doors — sig- nificant savings for a project that calls for installation of about 100 ventilation and fire control doors. • The swing doors required minimal or no additional rock removal for installation, the concrete foundations were smaller than those required for barn doors, and workers could be quickly trained in in- stallation and maintenance procedures. The Electric Avenue Workplace mobility, mechanical famil- iarity and lack of viable alternative prod- ucts have kept diesel-powered equipment ubiquitous in underground hardrock op- erations for decades, but the presence of diesels in deep mines always comes at a price: i.e., the need for, and high cost of providing sufficient ventilation to han- dle the combustion emissions, heat and moisture generated by conventional hy- drocarbon fuel-powered equipment. However, battery and drive technology has advanced to the point at which under- ground equipment suppliers are predict- ing that diesel-powered LHDs, drills and trucks will eventually disappear like dino- saurs over the next decade or two as mine operators gravitate toward battery-pow- ered underground fleets wherever possi- ble. It's a highly likely scenario, if only because the numbers are so persuasive. For example, Goldcorp's Borden Lake project, billed as the world's first all-elec- tric underground gold mine, is expected to reach full production in the second half of 2019 using an all-electric under- ground fleet of tethered and battery-elec- tric units. According to equipment sup- plier Sandvik, by eliminating diesels underground and fully electrifying Borden Lake, Goldcorp expects a 70% reduction in greenhouse gases and annual savings of 2 million liters of diesel fuel and 1 mil- lion liters of propane. The company also expects to save 35,000 megawatt hours of electricity yearly, due in large part to drastically reduced ventilation needs. The mine reportedly was able to eliminate a return air raise from its layout and re- duce the diameter of its intake raise from 5 meters (m) to 4 m, saving additional money in the process. Illustrative of the kind of equipment employed at Borden Lake are two Sandvik DD422iE electric development jumbos currently in service at the mine, locat- ed in Ontario, Canada. These drills use power from an onboard battery during tramming, then tap into the mine's exist- ing electric infrastructure when drilling. Sandvik's driveline technology enables the battery to recharge during the drilling cycle, and it will even recharge while the jumbos are tramming downhill, using en- ergy generated by the braking system. Maclean Engineering, another mobile equipment supplier to Borden Lake, has be- gun offering battery-powered underground road graders, one of which — based on a Caterpillar 12M platform — was delivered to the mine in April. The grader, modified under a partnership with Ontario-based en- gineering firm Medatech, features an on- board charging system that travels with the machine, eliminating a need for multiple fixed-location charging stations. In a recent blog post, Maclean Engi- neering's Stuart Lister presented an anal- ysis of the potential savings that could accrue from operating a fleet of its electric underground equipment including a scis- sor bolter, scissor lift, two cassette trucks and a boom truck. The total annual savings in ventilation costs compared with a simi- Despite higher initial capital expense, battery-powered underground equipment such as this Maclean Engineering grader are regarded as a vital part of the solution to control rising mine ventilation costs. * Enrique I. Acuña, Ventilation and Fire Door Coverage Solution at the Chuquicamata Underground Mine Pro- ject, 1 st International Conference on Underground Mining Technology, October 2017, Sudbury, Ontario, Canada.

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