Engineering & Mining Journal

JUL 2013

Engineering and Mining Journal - Whether the market is copper, gold, nickel, iron ore, lead/zinc, PGM, diamonds or other commodities, E&MJ takes the lead in projecting trends, following development and reporting on the most efficient operating pr

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PLANT DESIGN The Case for Going Gearless Gearless drive systems for conveyors or mills can simplify installation, increase machine efficiency and reduce maintenance costs, according to a company that's been a pioneer in the technology In recent years a trend can be discerned—particularly in newer South American mines—toward higher and higher volumes of throughput of raw materials, which requires faster belt speeds and wider belts, plus the capability to cope with large variations in elevation along the conveyor route. In these types of applications, conventional drive configurations for large belt conveyors with gearboxes meet their physical limits. For example, a belt conveyor with a drive power demand of 20,000 kW would require eight conventional drive systems, each equipped with 2,500-kW motors. The high number of mechanical and electrical components alone decreases availability. With a gearless drive system, the drive power demand can be attained with just three drive systems. An Attractive Alternative A Siemens gearless drive system powers a 6.5-km-long overland conveyor belt at the Antapaccay copper project in Peru. With gearless drive systems, a low-speed synchronous motor replaces the high-speed asynchronous motor, gearboxes and couplings required in conventional gearbox-based systems. Earlier this year, Siemens AG's Drive Technology Division hosted an online press conference at which it presented the technical specifications of its gearless drive conveyor installation at the new Antapaccay copper mine in Peru—a 5,260-mt/h-capacity overland belt that was commissioned in 2012 and has been operating at production levels since October. It also provided background information on why its gearless drive systems for low-speed mine equipment such as conveyors and mills offer an attractive alternative to traditional gearbox-driven systems for these types of applications. Although not directly related to plant design technology, the issues that Siemens said its gearless systems are designed to overcome play an important role in plant efficiency: After all, if the desired speed, availability and power performance demanded from a main overland conveyor system feeding a plant isn't consistently achieved, even the most well-designed plant will have a hard time meeting its throughput target. 36 E&MJ; • JULY 2013 The Siemens presenters noted that raw materials are nearly always excavated in harsh environments—but new mines are increasingly located in inhospitable environments: at high altitude, in deserts or arctic cold. Underground mines are getting deeper and more complex. Infrastructure costs for energy and water supply are climbing. Meanwhile, higher tonnages of lower grade ore are being excavated and transported over longer distances. To deal with these challenges and to meet increasingly stringent requirements for equipment availability, new technologies are needed for conveyor and transport systems, according to Siemens. Belt conveyors have traditionally been designed with conventional drive systems consisting of highspeed motors, gearboxes and couplings. A rating of approximately 2,500 kW is the upper limit for a single, large conventional gearbox used in belt conveyor applications. If higher performance is required, a second drive system is installed on the opposite side of the drive pulley, or an additional drive pulley with drive units is added. As the need to reduce energy consumption and increase reliability continues to grow among mineral producers, gearless drives for conveyors would seem to be an attractive alternative. According to Siemens, system capital costs for a gearless system are similar or less than a conventional geared solution. Furthermore, the company maintains, a gearless drive solution offers several advantages compared with a traditional arrangement using high-speed motors and gear reducers: • The drive size is no longer limited by the available gearbox size, so for the required drive power demand only one drive per drive pulley is necessary. This, in turn, decreases the number of drive pulleys. • The number of ancillary components also can be reduced. For example, if a gearless drive system were to be used in place of a conventional drive system with two drives per drive pulley, 20 fewer bearings and four less couplings per drive pulley would be required. • The necessary drive power can be made available with only one drive per pulley. As a result, electrical components such as converters and switchgears are not needed and the "e-house" can have smaller dimensions. www.e-mj.com

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